Iranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Impacts of variation of river geometry on flowing water quality (Case Study: Ghezel Ozan River)Impacts of variation of river geometry on flowing water quality (Case Study: Ghezel Ozan River)1179924510.30482/jhyd.2019.190869.1398FAZohre EmamgholiDepartment of Irrigation and Reclamation Engineering, University of Tehran, IranMehdi YasiAssociate Professor, Department of Irrigation &amp; Reclamation Engineering,
University of Tehran, IRAN0000-0002-2512-2317Journal Article20190704Introduction: Rivers are generally receiving wastewater from agriculture, industrial and urban areas. Population growth, urban development and human activities have always been a threat to the quantity and quality of river water flows. In general the purer the water, the more valuable and useful it is for riverine ecology and for abstractions to meet human demands such as irrigation, drinking and industry. Conversely, the more polluted the water, the more expensive it is to treat to satisfactory levels. This leads to disruption of natural food chains and the loss of riverine lives. Protecting and improving the quality of river flows is a priority. <br /> The changing hydrological regime associated with the developing water demand schemes may alter the capacity of the environment to assimilate water soluble pollution. In particular, reductions in low flows result in increased pollutant concentrations already discharged into the water course either from point sources, such as industry, irrigation drains and urban areas, or from non-point sources, such as agrochemicals leaking into groundwater and soil erosion. Reduced flood flows may remove beneficial flushing, and reservoirs may cause further concentration of pollutants. Monitoring of water quality in different reaches of rivers depends on the purposes of water uses and requires a long-time and high-cost planning. Numerical simulator models are useful tools for a rapid and low-cost assessment and prediction of water quality in the present and in the future conditions of the rivers reaches. Different scenarios can be tested for determining and evaluating the effects of point and non-points sources of pollutants discharging into the river, and for predicting the effectiveness of alternative restoration plans in the management of water-based lives instream and in riverine riparian areas. In the present study, the effects of discharging pollutants on water quality in a long river reach have been investigated under the present condition and in different scenarios of river training schemes. <br /> Methodology: In this study, the 51-km Diwandra-Bijar Reach of the Ghezel Ozan River was selected. Modeling of the existing conditions of river quality was performed using existing geometric-hydraulic and river water quality data. Two mathematical models QUAL2KW and WASP were used to simulate the water quality. Simulation of different parameters (such as: DO, BOD, COD, Norg, NH3, Q, h, V, T and pH) were considered. In order to calibrate these models, RMSE and MAPE statistical indices were used. Using the QUAL2KW model, five river training schemes (variation of 1- river width, 2- side slope, 3- longitudinal slope, 4-coefficient of roughness; and 5- width and longitudinal slope of the river) were considered.<br /> Results and discussion: Comparison of river conditions simulation with two models of QUAL2KW and WASP with observational data showed that both models have the proper ability to simulate water quality. The study of river conditions showed that the river flow increased during the study area due to the entry of the sub branch. Due to changes in geometry and river flow, depth and flow velocity are changing along the path. Changes in river water temperature to 35 km are decreasing and then rising. The concentration of dissolved oxygen from the upstream to downstream of the river is decreasing. BOD concentration is rising from kilometer 19. The concentration of nitrate in kilometer 32 has increased due to the arrival of the Cham Zard River. The concentration of Norg has increased from Kilometer 19. This is due to changes in the river section and a decrease in sedimentation due to the increase of flow and entry of pollutants into the river. Ammonia concentration also increased at Kilometer 19 with the arrival of the Cham Zard River, and finally decreased by the arrival of the Yol Gashti river. Investigating scenarios showed that, in decreasing river width, flow velocity increased, resulting in an increase in the concentration of dissolved oxygen that increased the amount of river self-purification capacity. The concentration of NO3, BOD and COD parameters also increased slightly in high Discharge. The effect of the scenario of the Side slope on the water quality and hydraulic performance of the river is very small and has the least impact on the water quality of the river. By reducing the slope of the river bed, the flow rate is reduced, so the dissolved oxygen decreases. And the concentration of BOD and COD parameters has increased and the concentration of nitrate has decreased. This scenario is appropriate for the condition where the river needs to reduce the BOD. By the roughness increases, the flow velocity decreases. Consequently, the concentration of quality parameters (such as: BOD, DO and COD) are decreased. <br /> Conclusion: The results indicated that both models are capable of simulating the qualitative status of the river reach. The results of the five river training scenarios prove that wherever the dissolved oxygen (DO) is insufficient in the flowing water, the decrease in the channel width has the greatest effect. Implementation of both the decrease in channel slope and the increase in the channel width is effective in the reduction of BOD and COD, while does not result in a significant reduction in DO. Nitrate variations are almost negligible in all scenarios, indicating a low susceptibility of this parameter to the changes the channel geometry. However, wherever the concentration of Nitrate is a major treat, the increase in the channel width together with the decrease in the channel slope would be an alternative training solution.<br /> Keywords: River training, Water quality, QUAL2KW model, WASP model, Ghezel Ozan River.Introduction: Rivers are generally receiving wastewater from agriculture, industrial and urban areas. Population growth, urban development and human activities have always been a threat to the quantity and quality of river water flows. In general the purer the water, the more valuable and useful it is for riverine ecology and for abstractions to meet human demands such as irrigation, drinking and industry. Conversely, the more polluted the water, the more expensive it is to treat to satisfactory levels. This leads to disruption of natural food chains and the loss of riverine lives. Protecting and improving the quality of river flows is a priority. <br /> The changing hydrological regime associated with the developing water demand schemes may alter the capacity of the environment to assimilate water soluble pollution. In particular, reductions in low flows result in increased pollutant concentrations already discharged into the water course either from point sources, such as industry, irrigation drains and urban areas, or from non-point sources, such as agrochemicals leaking into groundwater and soil erosion. Reduced flood flows may remove beneficial flushing, and reservoirs may cause further concentration of pollutants. Monitoring of water quality in different reaches of rivers depends on the purposes of water uses and requires a long-time and high-cost planning. Numerical simulator models are useful tools for a rapid and low-cost assessment and prediction of water quality in the present and in the future conditions of the rivers reaches. Different scenarios can be tested for determining and evaluating the effects of point and non-points sources of pollutants discharging into the river, and for predicting the effectiveness of alternative restoration plans in the management of water-based lives instream and in riverine riparian areas. In the present study, the effects of discharging pollutants on water quality in a long river reach have been investigated under the present condition and in different scenarios of river training schemes. <br /> Methodology: In this study, the 51-km Diwandra-Bijar Reach of the Ghezel Ozan River was selected. Modeling of the existing conditions of river quality was performed using existing geometric-hydraulic and river water quality data. Two mathematical models QUAL2KW and WASP were used to simulate the water quality. Simulation of different parameters (such as: DO, BOD, COD, Norg, NH3, Q, h, V, T and pH) were considered. In order to calibrate these models, RMSE and MAPE statistical indices were used. Using the QUAL2KW model, five river training schemes (variation of 1- river width, 2- side slope, 3- longitudinal slope, 4-coefficient of roughness; and 5- width and longitudinal slope of the river) were considered.<br /> Results and discussion: Comparison of river conditions simulation with two models of QUAL2KW and WASP with observational data showed that both models have the proper ability to simulate water quality. The study of river conditions showed that the river flow increased during the study area due to the entry of the sub branch. Due to changes in geometry and river flow, depth and flow velocity are changing along the path. Changes in river water temperature to 35 km are decreasing and then rising. The concentration of dissolved oxygen from the upstream to downstream of the river is decreasing. BOD concentration is rising from kilometer 19. The concentration of nitrate in kilometer 32 has increased due to the arrival of the Cham Zard River. The concentration of Norg has increased from Kilometer 19. This is due to changes in the river section and a decrease in sedimentation due to the increase of flow and entry of pollutants into the river. Ammonia concentration also increased at Kilometer 19 with the arrival of the Cham Zard River, and finally decreased by the arrival of the Yol Gashti river. Investigating scenarios showed that, in decreasing river width, flow velocity increased, resulting in an increase in the concentration of dissolved oxygen that increased the amount of river self-purification capacity. The concentration of NO3, BOD and COD parameters also increased slightly in high Discharge. The effect of the scenario of the Side slope on the water quality and hydraulic performance of the river is very small and has the least impact on the water quality of the river. By reducing the slope of the river bed, the flow rate is reduced, so the dissolved oxygen decreases. And the concentration of BOD and COD parameters has increased and the concentration of nitrate has decreased. This scenario is appropriate for the condition where the river needs to reduce the BOD. By the roughness increases, the flow velocity decreases. Consequently, the concentration of quality parameters (such as: BOD, DO and COD) are decreased. <br /> Conclusion: The results indicated that both models are capable of simulating the qualitative status of the river reach. The results of the five river training scenarios prove that wherever the dissolved oxygen (DO) is insufficient in the flowing water, the decrease in the channel width has the greatest effect. Implementation of both the decrease in channel slope and the increase in the channel width is effective in the reduction of BOD and COD, while does not result in a significant reduction in DO. Nitrate variations are almost negligible in all scenarios, indicating a low susceptibility of this parameter to the changes the channel geometry. However, wherever the concentration of Nitrate is a major treat, the increase in the channel width together with the decrease in the channel slope would be an alternative training solution.<br /> Keywords: River training, Water quality, QUAL2KW model, WASP model, Ghezel Ozan River.https://jhyd.iha.ir/article_99245_f96251bd88393a4de85900b187821e6d.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Single Bridge Pier Scour in Uniform and Non-uniform Sediment Beds Under Steady and Unsteady FlowSingle Bridge Pier Scour in Uniform and Non-uniform Sediment Beds Under Steady and Unsteady Flow19339924610.30482/jhyd.2019.198223.1405FAMahin Eshaghianدانش آموخته کارشناسی ارشدSaeed GohariDepartment of Water Engineering, College of Agriculture, Bu-Ali Sina University, 3869565178, Hamadan, Iran.0000-0001-6599-7161Seyyed Saeid OkhraviDepartment Water Science Engineering Faculty of Agriculture BU-Ali Sina University- Hamedan-Iran.Journal Article20190820Introduction:<br /> Bridge scour is one of the most important challenges in river engineering. Research into local scour has primarily focused on investigating the impact of different hydrodynamic conditions on scour in a bed of uniformly graded material. However, local scour investigations in a bed of uniformly well-graded material provided knowledge of the underlying processes, field sediment beds are much more complex consisting of non-uniform sediment mixtures ("σ" _"g" ">1.4" ). In the case of complex sediment beds, selective transport of the finer particles due to unequal mobility can make the bed surface to be armored. There have been relatively few studies reported in the literature relating to scour in complex sediment beds, and most of these relate to quite specific situations. With regards to natural river materials (non-uniform sediments) and its great effects on the dimension and the time evolution of scour hole, the interaction of flow-structures with non-uniform sediments is very crucial due to armor layer development. The aim of this study is to improve understanding of scour development and armoring evolution in non-uniform sediment beds for estimating the scour depth in more realistic field conditions. Therefore, the rate of variation of erosion over time around single cylindrical pier is investigated in different bed sediment types.<br /> Methodology: <br /> The armored layer due to selective transport of the finer particles in non-uniform sediments causes complexity for predicting equilibrium scour depth. The present experiments on local bridge scour were conducted in hydraulic laboratory of the Bu-Ali Sina University (Hamadan, Iran). The pier model with a diameter of 4 cm was put inside a 0.5 m wide, 10.5 m long and 0.5 m depth rectangular tilting flume. In this study, the number of 15 experiments were organized at five different sediment beds, uniform and non-uniform in two steady flow condition (20 and 35 l/s with the same flow intensity of u/uc~0.9) along with an unsteady flow. The duration of tests was fixed at 8 hours in all runs based on the empirical method given by Ettema (1980).<br /> Results and Discussion:<br /> The experimental results revealed that with increasing flow rate from 20 to 35 l/s (increasing follow shallowness, h/b) at the same sediment bed, not only larger scour depths were recorded, but also the armor layer became coarser. The comparison between the bed configurations with uniform and non-uniform sediments represented dramatical reduction of the scour depth regards with increasing sediment non-uniformity. The effect of non-uniform sediments on scour in a current clear water conditions showed that maximum scour depth was less than scour depth in a uniform sand with the same d50 value. The comparison between these two mentioned bed configurations showed that the change in geometric standard deviation ("σ" _"g" ) from 1.4 to 2 (altering the uniform bed to non-uniform), decreased the maximum depth of scour by 70% and 60% in two corresponding experiments. As the armor layer coarser grains remains at upstream flow bed and at the vicinity of scour hole in the same flow intensity, the scour depth was decreased. Otherwise, there was not remarkable decrease on the scour depth by increasing non-uniformity index, since two sediment beds types were non-uniform. Also, a slight increase on scour depth has been observed by reduction of median grain size in the beds with non-uniform sediments at the same geometric standard deviation. By taking into account of the grain size of the armor layer and ice cover roughness, Wu et al. (2014) analyzed the dimensionless maximum scour depth and they found out that with an increase in grain size of the armor layer, the dimensionless maximum scour depth decreases. Singh et al. (2018) investigated the incipient motion for gravel particles in cohesionless sediment mixtures having silt and sand. The visual observations of the channel bed after the end of incipient motion indicated appearance of gravel particles at the top surface of the sediment bed. The critical shear stress for the gravel particles was found to be lower in the presence of silt. Presence of silt in the mixture affects the critical shear stress for gravel particles. They concluded from the present study that high silt content in the mixture leads to the higher deviation of critical shear stress from the revised Shields curve. They proposed an equation for the determination of critical shear stress of gravel particles in the non-uniform sediment mixture. <br /> Conclusion:<br /> The results showed that scour depths were reduced dramatically as sediment non-uniformity index ("σ" _"g" ) increase in clear water conditions. The larger particles form an armor layer protecting the bed from eroding. Also, the observation indicated that with increasing flow depth, the armor layer coarsens, and larger scour depths were recorded. However, scour depth increase rate was very different for the various bed sediment types.Introduction:<br /> Bridge scour is one of the most important challenges in river engineering. Research into local scour has primarily focused on investigating the impact of different hydrodynamic conditions on scour in a bed of uniformly graded material. However, local scour investigations in a bed of uniformly well-graded material provided knowledge of the underlying processes, field sediment beds are much more complex consisting of non-uniform sediment mixtures ("σ" _"g" ">1.4" ). In the case of complex sediment beds, selective transport of the finer particles due to unequal mobility can make the bed surface to be armored. There have been relatively few studies reported in the literature relating to scour in complex sediment beds, and most of these relate to quite specific situations. With regards to natural river materials (non-uniform sediments) and its great effects on the dimension and the time evolution of scour hole, the interaction of flow-structures with non-uniform sediments is very crucial due to armor layer development. The aim of this study is to improve understanding of scour development and armoring evolution in non-uniform sediment beds for estimating the scour depth in more realistic field conditions. Therefore, the rate of variation of erosion over time around single cylindrical pier is investigated in different bed sediment types.<br /> Methodology: <br /> The armored layer due to selective transport of the finer particles in non-uniform sediments causes complexity for predicting equilibrium scour depth. The present experiments on local bridge scour were conducted in hydraulic laboratory of the Bu-Ali Sina University (Hamadan, Iran). The pier model with a diameter of 4 cm was put inside a 0.5 m wide, 10.5 m long and 0.5 m depth rectangular tilting flume. In this study, the number of 15 experiments were organized at five different sediment beds, uniform and non-uniform in two steady flow condition (20 and 35 l/s with the same flow intensity of u/uc~0.9) along with an unsteady flow. The duration of tests was fixed at 8 hours in all runs based on the empirical method given by Ettema (1980).<br /> Results and Discussion:<br /> The experimental results revealed that with increasing flow rate from 20 to 35 l/s (increasing follow shallowness, h/b) at the same sediment bed, not only larger scour depths were recorded, but also the armor layer became coarser. The comparison between the bed configurations with uniform and non-uniform sediments represented dramatical reduction of the scour depth regards with increasing sediment non-uniformity. The effect of non-uniform sediments on scour in a current clear water conditions showed that maximum scour depth was less than scour depth in a uniform sand with the same d50 value. The comparison between these two mentioned bed configurations showed that the change in geometric standard deviation ("σ" _"g" ) from 1.4 to 2 (altering the uniform bed to non-uniform), decreased the maximum depth of scour by 70% and 60% in two corresponding experiments. As the armor layer coarser grains remains at upstream flow bed and at the vicinity of scour hole in the same flow intensity, the scour depth was decreased. Otherwise, there was not remarkable decrease on the scour depth by increasing non-uniformity index, since two sediment beds types were non-uniform. Also, a slight increase on scour depth has been observed by reduction of median grain size in the beds with non-uniform sediments at the same geometric standard deviation. By taking into account of the grain size of the armor layer and ice cover roughness, Wu et al. (2014) analyzed the dimensionless maximum scour depth and they found out that with an increase in grain size of the armor layer, the dimensionless maximum scour depth decreases. Singh et al. (2018) investigated the incipient motion for gravel particles in cohesionless sediment mixtures having silt and sand. The visual observations of the channel bed after the end of incipient motion indicated appearance of gravel particles at the top surface of the sediment bed. The critical shear stress for the gravel particles was found to be lower in the presence of silt. Presence of silt in the mixture affects the critical shear stress for gravel particles. They concluded from the present study that high silt content in the mixture leads to the higher deviation of critical shear stress from the revised Shields curve. They proposed an equation for the determination of critical shear stress of gravel particles in the non-uniform sediment mixture. <br /> Conclusion:<br /> The results showed that scour depths were reduced dramatically as sediment non-uniformity index ("σ" _"g" ) increase in clear water conditions. The larger particles form an armor layer protecting the bed from eroding. Also, the observation indicated that with increasing flow depth, the armor layer coarsens, and larger scour depths were recorded. However, scour depth increase rate was very different for the various bed sediment types.https://jhyd.iha.ir/article_99246_0a1126a8078c02bec9df6dfcedb264d6.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220The role of urban wastewater on the rate of cohesive sediment erosion in water transfer channelsThe role of urban wastewater on the rate of cohesive sediment erosion in water transfer channels354910549610.30482/jhyd.2020.105496FAZahra TaheriFerdosi Mashhad UniversityKazem Esmailiwater and science engineering Dept.
Ferdowsi university of mashhadHosein Samadishahrekord universitySaeed Reza KHODASHENASProfessorJournal Article20190401در حال حاضر به دلیل پیچیدگی رفتار رسوبات چسبنده، پروسه انتقال این رسوبات به طور کامل شناخته شده و قابل درک نیست. به طور کلی انتقال رسوبات چسبنده را میتوان شامل فرآیندهای فرسایش، رسوبگذاری و تحکیم داست (Krishnappan 2006). رفتار رسوبات چسبنده تحت تأثیر پیوندهای بین ذرهای است که این پیوندها به شدت به تعامل بین پارامترهای فیزیکی، شیمیایی، مکانیکی و بیولوژیکی وابسته است. به دلیل وجود جاذبه بین ذرهای در رسوبات چسبنده که تحت تاثیر عوامل محیطی نظیر میزان موارد ارگانیک، pH، شوری، میزان رطوبت و حتی بیوفیلمها قرار دارد؛ پیشبینی رفتار این نوع رسوبات همچون فرآیند فرسایشپذیری، با مشکل مواجه شده است (Black et al.2002; winterwerp and Van Kestern.2004; Grobowski.2011).<br /> از طرفی در سالهای اخیر که استفاده از منابع آب تجدیدپذیر نظیر پسابهای تصفیه شده شهری رواج یافته است لذا استفاده از پساب در زمینه کشاورزی نیز گسترش یافته که منجر به جریان آن در کانالهای انتقال آب گردیده و لذا به خاطر دارا بودن خصوصیات شیمیایی بر پروسه رسوبگذاری در کانالها نیز تاثیرگذار بوده است. <br /> رسوبات چسبنده به دلیل ویژگیهای فیزیکی-شیمیایی و وجود یونهای قوی در سطح ذرات تمایل به تشکیل تودههای بزرگتری به نام فلوکها دارند که این پدیده تحت عنوان هماوریشدن شناخته میشود. فلوکها سریعتر از اجزای تشکیل دهنده خودشان سقوط میکنند و به واسطه اینکه دارای میزانی رطوبت میباشند لذا پس از تهنشینی یک بستر نرم را ایجاد مینمایند. قابل ذکر است که میزان رطوبت فلوکها به طور مستقیم با اندازه آنها در ارتباط است (winterwerp and Van Kestern. 2004). در بستر تازه تشکیل شده که فرآیند تحکیم در آن آغاز شده است مشخصاتی مانند، دانسیته، چسبندگی و مقاومتبرشی تهنشینی افزایش مییابد که مقاومت ذرات بستر در برابر فرسایش را به همراه دارد (Chein et al.1999). مطالعات آزمایشگاهی مختلفی برای تعیین نرخ فرسایش رسوبات چسبنده توسط جریان با استفاده از کانالهای دایرهای (Parchure and Mehta 1985; Kuijper et al 1989; Amos et al 1992) و کانالهای مستقیم (Orvain et al 2003; Robert et al 1998; Le Hir 2008; Abrele 2003; Parteniades 2003) صورت گرفته است. مهمترین نتیجه حاصل از این آزمایشها وجود یک تنشبرشی آستانه فرسایش است که تنش برشی بحرانی بستر برای فرسایش ( ) نامیده شد که در تنشهای جریان فراتر از آن، رسوبات فرسایش مییابند. تنشبرشی آستانه فرسایش یکی از پارامترهای مهم در مدلهای انتقال رسوبات چسبنده است. برای رسوبات چسبنده مقدار تنش-برشی بحرانی برای فرسایش بزرگتر از تنشبرشی بحرانی تهنشینی است (Huang et al. 2006). بر اساس نظر محققان فرسایش رسوبات چسبنده را میتوان در سه حالت فرسایش فلوک، فرسایش سطحی و فرسایش جرمی در نظر گرفت. فرسایش فلوک در شرایطی که تنش برشی بستر بیشتر از چسبندگی بین فلوکها و بستر باشد به صورت جدا شدن فلوک به صورت مجزا از بستر رخ میدهد. فرسایش سطحی به شرایطی گفته میشود که ذرات منفرد بهصورت آشکار شروع به حرکت از سطح بستر رسوبات چسبنده میکنند. Jacobs (2011) فرسایش فلوک را یک خصوصیت تصادفی از شرایط جریان و مقاومت سطح رسوبات است در حالیکه فرسایش سطحی با شاخص خمیری در ارتباط است. فرسایش تودهای در مقادیر بزرگتر تنش برشی (سرعت) رخ میدهد و مشخصه آن جدا شدن تودههای بزرگ رسوب از بستر میباشد و جدا شدن تودهای از ذرات، فرسایش جرمی معرفی شد (winterwerp and Van Kestern. 2004). <br /> در حال حاضر دو دیدگاه مختلف فکری در مورد آستانه فرسایش رسوبات چسبنده وجود دارد. اولین دیدگاه، بر عدم وجود آستانه فرسایش رسوبات چسبنده معتقد است چرا که برخی از ذرات در هر مقدار از تنشبرشی بستر دچار فرسایش میشوند (به عنوان مثال Lovelle et al. 1984 and Parchure et al. 1985). Lovelle et al (1984) میزان نرخ فرسایش (ε) را با استفاده از مفهوم عدم وجود آستانه فرسایش به صورت زیر ارائه کردند:<br /> (1) <br /> <br /> در این رابطه α و β ضرائب تجربی هستند.<br /> Mehta and Partheniades (1982) یک تابع نمایی برای فرسایش بسترهای تازه تهنشین شده ارائه نمودند: <br /> (2) <br /> <br /> که در آن ، و ضریب هستند . رابطه اخیر توسط سایر محققان به یک معادله توانی به صورت زیر توسعه یافت. <br /> (3) <br /> <br /> که در آن : تنش برشی بحرانی بستر برای فرسایش، : تنش برشی بستر و : یک تابع توانی از ترکیب رسوبات : پارامتر رسوب . Baptiste et al (2017)ضریب n را تابعی توانی از ترکیببندی رسوبات معرفی کرده و مقدار آن را برای رسوبات چسبنده یک و برای رسوبات غیر چسبنده 5/1 در نظر گرفتند. در شرایطی که خواص بستر نسبتاً یکنواخت باشد معادله زیر برای پروسه فرسایش رسوبات چسبنده ارائه گردید (Mitchener 1996; Mei 1997) <br /> (4) E=M(τ_b-τ_c )^a <br /> Bui (2000) فرسایش رسوبات از بستر به عنوان جرم رسوبات جابهجا شده توسط تنشبرشی بستر در نظر گرفت و رابطه زیر را ارائه داد:<br /> (5) E=ε(τ_b-τ_s ) <br /> در این معادله E نرخ فرسایش، ε ضریب فرسایش،τ_b تنشبرشی بستر وτ_s تنش مقاومتی بستر است.Zhu (2006) با تقسیم معادله (4) بر دانسیته رسوبات و قرار دادان نمایه 1a= فرمول زیر را پیشنهاد کرد:<br /> (6) E=M_e (τ_b-τ_c )<br /> E نرخ فرسایش در طول بر واحد زمان (m/s) ، M_e=M⁄ρ_s ضریب توصیف قابلیت فرسایش رسوبات. عبارات M_e یا M و τ_c پارامترهای رسوب هستند در حالیکه τ_b یک پارامتر هیدرولیکی است. Parchure and Mehta (1985) برای بسترهای چسبندهای که دارای روند افزایش دانسیته با عمق هستند، رابطهای را برای نرخ فرسایش پیشنهاد کردند:<br /> (7) <br /> <br /> E_0 و K_3 از طریق آزمایشات تعیین شدند و به خصوصیات رسوبات بسیار حساس هستنددر حال حاضر به دلیل پیچیدگی رفتار رسوبات چسبنده، پروسه انتقال این رسوبات به طور کامل شناخته شده و قابل درک نیست. به طور کلی انتقال رسوبات چسبنده را میتوان شامل فرآیندهای فرسایش، رسوبگذاری و تحکیم داست (Krishnappan 2006). رفتار رسوبات چسبنده تحت تأثیر پیوندهای بین ذرهای است که این پیوندها به شدت به تعامل بین پارامترهای فیزیکی، شیمیایی، مکانیکی و بیولوژیکی وابسته است. به دلیل وجود جاذبه بین ذرهای در رسوبات چسبنده که تحت تاثیر عوامل محیطی نظیر میزان موارد ارگانیک، pH، شوری، میزان رطوبت و حتی بیوفیلمها قرار دارد؛ پیشبینی رفتار این نوع رسوبات همچون فرآیند فرسایشپذیری، با مشکل مواجه شده است (Black et al.2002; winterwerp and Van Kestern.2004; Grobowski.2011).<br /> از طرفی در سالهای اخیر که استفاده از منابع آب تجدیدپذیر نظیر پسابهای تصفیه شده شهری رواج یافته است لذا استفاده از پساب در زمینه کشاورزی نیز گسترش یافته که منجر به جریان آن در کانالهای انتقال آب گردیده و لذا به خاطر دارا بودن خصوصیات شیمیایی بر پروسه رسوبگذاری در کانالها نیز تاثیرگذار بوده است. <br /> رسوبات چسبنده به دلیل ویژگیهای فیزیکی-شیمیایی و وجود یونهای قوی در سطح ذرات تمایل به تشکیل تودههای بزرگتری به نام فلوکها دارند که این پدیده تحت عنوان هماوریشدن شناخته میشود. فلوکها سریعتر از اجزای تشکیل دهنده خودشان سقوط میکنند و به واسطه اینکه دارای میزانی رطوبت میباشند لذا پس از تهنشینی یک بستر نرم را ایجاد مینمایند. قابل ذکر است که میزان رطوبت فلوکها به طور مستقیم با اندازه آنها در ارتباط است (winterwerp and Van Kestern. 2004). در بستر تازه تشکیل شده که فرآیند تحکیم در آن آغاز شده است مشخصاتی مانند، دانسیته، چسبندگی و مقاومتبرشی تهنشینی افزایش مییابد که مقاومت ذرات بستر در برابر فرسایش را به همراه دارد (Chein et al.1999). مطالعات آزمایشگاهی مختلفی برای تعیین نرخ فرسایش رسوبات چسبنده توسط جریان با استفاده از کانالهای دایرهای (Parchure and Mehta 1985; Kuijper et al 1989; Amos et al 1992) و کانالهای مستقیم (Orvain et al 2003; Robert et al 1998; Le Hir 2008; Abrele 2003; Parteniades 2003) صورت گرفته است. مهمترین نتیجه حاصل از این آزمایشها وجود یک تنشبرشی آستانه فرسایش است که تنش برشی بحرانی بستر برای فرسایش ( ) نامیده شد که در تنشهای جریان فراتر از آن، رسوبات فرسایش مییابند. تنشبرشی آستانه فرسایش یکی از پارامترهای مهم در مدلهای انتقال رسوبات چسبنده است. برای رسوبات چسبنده مقدار تنش-برشی بحرانی برای فرسایش بزرگتر از تنشبرشی بحرانی تهنشینی است (Huang et al. 2006). بر اساس نظر محققان فرسایش رسوبات چسبنده را میتوان در سه حالت فرسایش فلوک، فرسایش سطحی و فرسایش جرمی در نظر گرفت. فرسایش فلوک در شرایطی که تنش برشی بستر بیشتر از چسبندگی بین فلوکها و بستر باشد به صورت جدا شدن فلوک به صورت مجزا از بستر رخ میدهد. فرسایش سطحی به شرایطی گفته میشود که ذرات منفرد بهصورت آشکار شروع به حرکت از سطح بستر رسوبات چسبنده میکنند. Jacobs (2011) فرسایش فلوک را یک خصوصیت تصادفی از شرایط جریان و مقاومت سطح رسوبات است در حالیکه فرسایش سطحی با شاخص خمیری در ارتباط است. فرسایش تودهای در مقادیر بزرگتر تنش برشی (سرعت) رخ میدهد و مشخصه آن جدا شدن تودههای بزرگ رسوب از بستر میباشد و جدا شدن تودهای از ذرات، فرسایش جرمی معرفی شد (winterwerp and Van Kestern. 2004). <br /> در حال حاضر دو دیدگاه مختلف فکری در مورد آستانه فرسایش رسوبات چسبنده وجود دارد. اولین دیدگاه، بر عدم وجود آستانه فرسایش رسوبات چسبنده معتقد است چرا که برخی از ذرات در هر مقدار از تنشبرشی بستر دچار فرسایش میشوند (به عنوان مثال Lovelle et al. 1984 and Parchure et al. 1985). Lovelle et al (1984) میزان نرخ فرسایش (ε) را با استفاده از مفهوم عدم وجود آستانه فرسایش به صورت زیر ارائه کردند:<br /> (1) <br /> <br /> در این رابطه α و β ضرائب تجربی هستند.<br /> Mehta and Partheniades (1982) یک تابع نمایی برای فرسایش بسترهای تازه تهنشین شده ارائه نمودند: <br /> (2) <br /> <br /> که در آن ، و ضریب هستند . رابطه اخیر توسط سایر محققان به یک معادله توانی به صورت زیر توسعه یافت. <br /> (3) <br /> <br /> که در آن : تنش برشی بحرانی بستر برای فرسایش، : تنش برشی بستر و : یک تابع توانی از ترکیب رسوبات : پارامتر رسوب . Baptiste et al (2017)ضریب n را تابعی توانی از ترکیببندی رسوبات معرفی کرده و مقدار آن را برای رسوبات چسبنده یک و برای رسوبات غیر چسبنده 5/1 در نظر گرفتند. در شرایطی که خواص بستر نسبتاً یکنواخت باشد معادله زیر برای پروسه فرسایش رسوبات چسبنده ارائه گردید (Mitchener 1996; Mei 1997) <br /> (4) E=M(τ_b-τ_c )^a <br /> Bui (2000) فرسایش رسوبات از بستر به عنوان جرم رسوبات جابهجا شده توسط تنشبرشی بستر در نظر گرفت و رابطه زیر را ارائه داد:<br /> (5) E=ε(τ_b-τ_s ) <br /> در این معادله E نرخ فرسایش، ε ضریب فرسایش،τ_b تنشبرشی بستر وτ_s تنش مقاومتی بستر است.Zhu (2006) با تقسیم معادله (4) بر دانسیته رسوبات و قرار دادان نمایه 1a= فرمول زیر را پیشنهاد کرد:<br /> (6) E=M_e (τ_b-τ_c )<br /> E نرخ فرسایش در طول بر واحد زمان (m/s) ، M_e=M⁄ρ_s ضریب توصیف قابلیت فرسایش رسوبات. عبارات M_e یا M و τ_c پارامترهای رسوب هستند در حالیکه τ_b یک پارامتر هیدرولیکی است. Parchure and Mehta (1985) برای بسترهای چسبندهای که دارای روند افزایش دانسیته با عمق هستند، رابطهای را برای نرخ فرسایش پیشنهاد کردند:<br /> (7) <br /> <br /> E_0 و K_3 از طریق آزمایشات تعیین شدند و به خصوصیات رسوبات بسیار حساس هستندhttps://jhyd.iha.ir/article_105496_c66717d1effe8695a1a5a77f4702df28.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Study on stability and sensitivity analysis of protective riprap layer placed around bridge pier by using reliability analysis theoryStudy on stability and sensitivity analysis of protective riprap layer placed around bridge pier by using reliability analysis theory516810549810.30482/jhyd.2020.105498FAMojtaba Karimaei TabarestaniAssistant Professor of Hydraulic Engineering in Shahid Rajaee Teacher Training University0000-0001-9673-1315Journal Article20190831Introduction - The formation of scour hole around bridge pier is recognized as the number one cause of bridge failure. This phenomenon results from a complex flow field with large-scale turbulence structures generated by flow around the pier. On the other hand, predicting the stability of scour countermeasure around bridge pier such as riprap layer is one of the main challenges in hydraulic engineering. However, the damage mechanism of riprap layer is a very complicated phenomena and many uncertainties affect the exact estimation of different effective parameters in riprap stone design. Therefore, quantifying these uncertainties by using reliability analysis to ensure the stability of the bridge is necessary. Recently, reliability analysis methods have been highly considered due to their high ability to optimize engineering designs and improve project exploitation. Reliability analysis provides a systematic and organized framework to minimize model uncertainties. In addition, it allows the designer to determine the role of each of the effective parameters in the uncertainty of model output. This is essential for identifying important parameters in order to pay more attention to them to achieve their exact value and effect, and ultimately reduce the uncertainty of the model output. <br /> Methodology - In the present study, the stability of riprap layer was investigated by using a reliability-based framework. Monte Carlo Simulation Technique (MCST) and First Order Reliability Method (FORM) were established to determine the stability of riprap layer against shear failure. In FORM, the reliability is measured in terms of a reliability index, β, and it is related to the probability of failure or probability of limit state violation for any limit state. In addition, MCST consists of drawing samples of the basic variables according to their probabilistic characteristics and then feeding them into the limit state function and therefore the probability of failure, Pf, can be found. MCST is considered in principle an exact method, and, FORM as an approximate method. However, FORM is computationally fast and inexpensive as compared to MCST. The first stage in reliability analysis or evaluation of the probability of a system failure is to determine a limit state or performance function between the basic random variables. In the present study, the equation presented by Karimaee and Zarrati, (2013) and Karimaee et al. (2015) is used here as limit state equation. The advantage of this equation is that it can be used for unprotected and protected piers with a collar and circular as well as rectangular piers, and aligned or skewed piers corresponding to the flow direction. The application of the present method was illustrated in an applied example which is a bridge with two piers located in the main channel and flood plain. The data for this case studies was extracted from different previous studies.<br /> Results and discussion - At first, results showed that β values and Pf obtained using FORM are having close proximity with MCST results. Therefore, it is also appropriate to use FORM for reliability assessment of riprap layer around bridge pier. In addition, it was found that due to existing uncertainties, the stability of designed riprap size which was calculated from deterministic method was low and equal to 44% for the pier placed in the main channel and 28% for the pier in the flood plain. In addition, two equations between safety factor and reliability index was determined for riprap size design placed around bridge pier in the main channel or flood plain. Results showed that by increasing the reliability index parameter, the safety factor should be increased. Using these equations one can find out an appropriate value of safety factor for desired riprap layer reliability. For example, these equations give the safety factor corresponding to target reliability index (βT) = 3 as 2.93 and 1.46 for the riprap layer size placed around bridge pier located in the main and flood channels, respectively. Next, sensitivity analysis was performed to examine the impact of each random variable on the probability of riprap layer stability in the reliability method. Results showed that the most critical parameter affecting the reliability of riprap size was the mean flow velocity, so that by decreasing the amount of this parameter for about 75% form the Mean value, the amount of parameter β increased for more than 16 times. Therefore, this parameter needs to be determined more accurately in riprap design to decrease the failure probability of riprap layer, efficiently. Finally, the effect of parameters’ uncertainties on reliability analysis of riprap layer was investigated. Results showed that for all of the effective parameters by increasing the parameters’ uncertainties, the stability of riprap layer decreases.<br /> Conclusion – Present reliability assessment methodology showed that due to existing uncertainties, the stability of designed riprap size which was calculated from deterministic method was not reliable as desired. In addition, an overall influence of various random variables on riprap layer’s reliability was assessed through sensitivity analysis. It was shown that if through better quality control; regular maintenance and proper care uncertainties can be minimized, reliability of riprap layer could be improved.Introduction - The formation of scour hole around bridge pier is recognized as the number one cause of bridge failure. This phenomenon results from a complex flow field with large-scale turbulence structures generated by flow around the pier. On the other hand, predicting the stability of scour countermeasure around bridge pier such as riprap layer is one of the main challenges in hydraulic engineering. However, the damage mechanism of riprap layer is a very complicated phenomena and many uncertainties affect the exact estimation of different effective parameters in riprap stone design. Therefore, quantifying these uncertainties by using reliability analysis to ensure the stability of the bridge is necessary. Recently, reliability analysis methods have been highly considered due to their high ability to optimize engineering designs and improve project exploitation. Reliability analysis provides a systematic and organized framework to minimize model uncertainties. In addition, it allows the designer to determine the role of each of the effective parameters in the uncertainty of model output. This is essential for identifying important parameters in order to pay more attention to them to achieve their exact value and effect, and ultimately reduce the uncertainty of the model output. <br /> Methodology - In the present study, the stability of riprap layer was investigated by using a reliability-based framework. Monte Carlo Simulation Technique (MCST) and First Order Reliability Method (FORM) were established to determine the stability of riprap layer against shear failure. In FORM, the reliability is measured in terms of a reliability index, β, and it is related to the probability of failure or probability of limit state violation for any limit state. In addition, MCST consists of drawing samples of the basic variables according to their probabilistic characteristics and then feeding them into the limit state function and therefore the probability of failure, Pf, can be found. MCST is considered in principle an exact method, and, FORM as an approximate method. However, FORM is computationally fast and inexpensive as compared to MCST. The first stage in reliability analysis or evaluation of the probability of a system failure is to determine a limit state or performance function between the basic random variables. In the present study, the equation presented by Karimaee and Zarrati, (2013) and Karimaee et al. (2015) is used here as limit state equation. The advantage of this equation is that it can be used for unprotected and protected piers with a collar and circular as well as rectangular piers, and aligned or skewed piers corresponding to the flow direction. The application of the present method was illustrated in an applied example which is a bridge with two piers located in the main channel and flood plain. The data for this case studies was extracted from different previous studies.<br /> Results and discussion - At first, results showed that β values and Pf obtained using FORM are having close proximity with MCST results. Therefore, it is also appropriate to use FORM for reliability assessment of riprap layer around bridge pier. In addition, it was found that due to existing uncertainties, the stability of designed riprap size which was calculated from deterministic method was low and equal to 44% for the pier placed in the main channel and 28% for the pier in the flood plain. In addition, two equations between safety factor and reliability index was determined for riprap size design placed around bridge pier in the main channel or flood plain. Results showed that by increasing the reliability index parameter, the safety factor should be increased. Using these equations one can find out an appropriate value of safety factor for desired riprap layer reliability. For example, these equations give the safety factor corresponding to target reliability index (βT) = 3 as 2.93 and 1.46 for the riprap layer size placed around bridge pier located in the main and flood channels, respectively. Next, sensitivity analysis was performed to examine the impact of each random variable on the probability of riprap layer stability in the reliability method. Results showed that the most critical parameter affecting the reliability of riprap size was the mean flow velocity, so that by decreasing the amount of this parameter for about 75% form the Mean value, the amount of parameter β increased for more than 16 times. Therefore, this parameter needs to be determined more accurately in riprap design to decrease the failure probability of riprap layer, efficiently. Finally, the effect of parameters’ uncertainties on reliability analysis of riprap layer was investigated. Results showed that for all of the effective parameters by increasing the parameters’ uncertainties, the stability of riprap layer decreases.<br /> Conclusion – Present reliability assessment methodology showed that due to existing uncertainties, the stability of designed riprap size which was calculated from deterministic method was not reliable as desired. In addition, an overall influence of various random variables on riprap layer’s reliability was assessed through sensitivity analysis. It was shown that if through better quality control; regular maintenance and proper care uncertainties can be minimized, reliability of riprap layer could be improved.https://jhyd.iha.ir/article_105498_1c56f33c8bd2c25355ef210936d01893.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Three Dimensional Laser Scanning System for Illumination of Fluorescent flow for the Environmental Hydraulic investigationsThree Dimensional Laser Scanning System for Illumination of Fluorescent flow for the Environmental Hydraulic investigations698110549910.30482/jhyd.2020.105499FAOzeair AbessiBabol Noshirvani University of Technology0000-0002-8329-8556Ali Rahmani FiroozjaeeFaculty member, school of Civil Eng, Babol Noshirvani University of TechnologyMehdi HamidiFaculty of Civil Engineering, Babol Noshirvani University of technology, babol, Iran0000-0002-7376-3303Mohammad Amin BassamPower and Electronic institute, Malek Ashtar UniversityZahra KhodabakshiShahrood University of TechnologyJournal Article20190913Introduction<br /> The experimental modeling and laboratory observation is probably the first step in the recognition of the flow complicated behavior in fluid mechanics. Since long time ago, various methods have developed for the measurement of the flow parameters. These methods are based on the illumination and inscription of flow variables in different conditions. Facilities and equipment were temperature and conductivity probes for scalar quantities and Hot-wire anemometers and Acoustic Doppler Velocimeters for velocity measurement as a vector variable in each point. Such equipment will cause disturbances in the flow as they are intrusive into the body of the ambient water. The measurements are point-based and data sampling needs too many probes for each test. Therefore, these probes do not appropriate for data sampling in many applications of the experimental fluid mechanics, especially in small scales. With recent progress in digital technologies, there are various methods have newly developed for the inspection of concentration and velocity field that are non-intrusive. These methods are more based on flow simulation in the transparent chamber, flow illumination with laser and fluorescent or small particles and filming the flow with high accuracy for later visual processing.<br /> <br /> Methodology <br /> In this paper, the capabilities of the three-dimensional laser scanning system are exhibited which is developed for first time in Iran at Babol Noshirvani University of Technology (BNUT). It includes a water tank, pomp, the three-dimensional laser scanning system, high-speed camera, and data processing apparatus that all located in the darkroom. The optical system consists of two fast scanning mirrors that drive the beam from an argon-ion laser through the flow in a programmed pattern. The system is controlled by a computer for overall timing control, and image capture. Having added an infinitesimal quantity of a fluorescent dye (Rhodamine 6G, Sigma-Aldrich, St. Louis, Missouri), the discharged effluent would be fluoresced under the impression of the laser. So due to the function of laser beam, the jet of fluorescent illuminated and recorded in the wavelength of orange light. The orange filter is used to filter out all the scattered lights of the green laser to increase the contrast, and accordingly quality of the images. The apparatus is set in a glass-made tank with length, width, and height, respectively. A charge-coupled device (CCD) camera with the resolution of x pixels was successively capturing the reflected light in the separated illustrations, at approximately 100 frames per second. Each captured illustration had to be modified for laser attenuation and sensor response at each pixel by using clear and dyed water. Having used image processing techniques in a software coded in C#, subsequently, the stream of images for unsteady flow and also time-averaged results were obtained. So the images are processed by a specially written computer program NITLIF, which is a new version of TFLOOK that previously was developed by Tian and Roberts (2003) at Georgia Institute of Technology. This software through lengthy computational procedures that explained by Tian and Roberts (2003) computes concentration pixel-by-pixel after a complicated calibration process. The images then turn into a real scale of position, time and concentration for every single frame in Tecplot. The program eventually can time-averaged the frames and placed them next to each other to form a two dimensional or three-dimensional configuration of flow dynamic. The accuracy of the dilution measurements is computed . It should be noticed that this system had been originally incepted by Tian and Roberts (2003) and the one that developed here is the new version of it that upgraded for temporal analysis and space-time evolution of the concentration field.<br /> <br /> Results and discussion<br /> The system is designed in a way that can record and visualize the three-dimensional configuration of the flow. Due to fast recording of the experiments with our high-speed camera with the frequency of 100 Hz, this apparatus is appropriately able to physically analyze the turbulence of the flow, turbulence energy spectrum and intensity and strength profile of the flow. The turbulence is a fluid motion that characterized by chaotic changes in flow variables. Getting 100 Hz data from each point in this system makes us be able for the frequency analysis of flow turbulent properties. <br /> <br /> Conclusion<br /> As a demonstration, the results of our observation for an inclined dense jet are exhibited. Th temporally-averaged intensity along vertical cut and energy spectrum are plotted at jet maximum height together with the instantaneous and time-averaged 2D and 3D configurations of the flow. Turbulence kinetic energy spectrums are well fitted with the power law of Kolmogorov theory for the inertial subrange. The time-averaged intensity distribution shows that for the location of maximum high, eddies are always present in centerline which shows the dominance of jet-like behavior in this point.Introduction<br /> The experimental modeling and laboratory observation is probably the first step in the recognition of the flow complicated behavior in fluid mechanics. Since long time ago, various methods have developed for the measurement of the flow parameters. These methods are based on the illumination and inscription of flow variables in different conditions. Facilities and equipment were temperature and conductivity probes for scalar quantities and Hot-wire anemometers and Acoustic Doppler Velocimeters for velocity measurement as a vector variable in each point. Such equipment will cause disturbances in the flow as they are intrusive into the body of the ambient water. The measurements are point-based and data sampling needs too many probes for each test. Therefore, these probes do not appropriate for data sampling in many applications of the experimental fluid mechanics, especially in small scales. With recent progress in digital technologies, there are various methods have newly developed for the inspection of concentration and velocity field that are non-intrusive. These methods are more based on flow simulation in the transparent chamber, flow illumination with laser and fluorescent or small particles and filming the flow with high accuracy for later visual processing.<br /> <br /> Methodology <br /> In this paper, the capabilities of the three-dimensional laser scanning system are exhibited which is developed for first time in Iran at Babol Noshirvani University of Technology (BNUT). It includes a water tank, pomp, the three-dimensional laser scanning system, high-speed camera, and data processing apparatus that all located in the darkroom. The optical system consists of two fast scanning mirrors that drive the beam from an argon-ion laser through the flow in a programmed pattern. The system is controlled by a computer for overall timing control, and image capture. Having added an infinitesimal quantity of a fluorescent dye (Rhodamine 6G, Sigma-Aldrich, St. Louis, Missouri), the discharged effluent would be fluoresced under the impression of the laser. So due to the function of laser beam, the jet of fluorescent illuminated and recorded in the wavelength of orange light. The orange filter is used to filter out all the scattered lights of the green laser to increase the contrast, and accordingly quality of the images. The apparatus is set in a glass-made tank with length, width, and height, respectively. A charge-coupled device (CCD) camera with the resolution of x pixels was successively capturing the reflected light in the separated illustrations, at approximately 100 frames per second. Each captured illustration had to be modified for laser attenuation and sensor response at each pixel by using clear and dyed water. Having used image processing techniques in a software coded in C#, subsequently, the stream of images for unsteady flow and also time-averaged results were obtained. So the images are processed by a specially written computer program NITLIF, which is a new version of TFLOOK that previously was developed by Tian and Roberts (2003) at Georgia Institute of Technology. This software through lengthy computational procedures that explained by Tian and Roberts (2003) computes concentration pixel-by-pixel after a complicated calibration process. The images then turn into a real scale of position, time and concentration for every single frame in Tecplot. The program eventually can time-averaged the frames and placed them next to each other to form a two dimensional or three-dimensional configuration of flow dynamic. The accuracy of the dilution measurements is computed . It should be noticed that this system had been originally incepted by Tian and Roberts (2003) and the one that developed here is the new version of it that upgraded for temporal analysis and space-time evolution of the concentration field.<br /> <br /> Results and discussion<br /> The system is designed in a way that can record and visualize the three-dimensional configuration of the flow. Due to fast recording of the experiments with our high-speed camera with the frequency of 100 Hz, this apparatus is appropriately able to physically analyze the turbulence of the flow, turbulence energy spectrum and intensity and strength profile of the flow. The turbulence is a fluid motion that characterized by chaotic changes in flow variables. Getting 100 Hz data from each point in this system makes us be able for the frequency analysis of flow turbulent properties. <br /> <br /> Conclusion<br /> As a demonstration, the results of our observation for an inclined dense jet are exhibited. Th temporally-averaged intensity along vertical cut and energy spectrum are plotted at jet maximum height together with the instantaneous and time-averaged 2D and 3D configurations of the flow. Turbulence kinetic energy spectrums are well fitted with the power law of Kolmogorov theory for the inertial subrange. The time-averaged intensity distribution shows that for the location of maximum high, eddies are always present in centerline which shows the dominance of jet-like behavior in this point.https://jhyd.iha.ir/article_105499_9f44eaf9e0e3ee6bb3ba0a75bf8a58e1.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Development of multiquadric method for solving dam break problemDevelopment of multiquadric method for solving dam break problem839810550010.30482/jhyd.2020.105500FAHanieh Kahid BasiriGhadir Boulvard
University of QomReza BabaeeGhadir Boulvard
University of Qom0000-0002-3068-3602Alireza FallahGhadir Boulvard
University of Qom0000-0002-6245-8567Ehsan JabbariUniversity of Qom
Ghadir Boulvard0000-0002-6345-8567Journal Article20191015Introduction:<br /> In order to avoid meshing and its difficulties and costs, Multiquadric Radial Basis Function (MQ-RBF) method has been developed (Kansa 1990) and has been examined for different types of physical phenomena. In this regard, the present study develops this meshless method for analysis of dam break problem. MQ is more convenient and accurate than other RBF methods for solving partial differential equations (Fallah et al. 2019). This meshless method have advantages such as; 1) creating a continuous response function all over the computational domain, 2) no need to discretize the entire domain with optimal usability in large-scale problems, 3) high capability in modelling irregular and complex geometries, 4) high ability to simulate discontinuities of responses, 5) easy generalization to 3D problems, and etc. Both the accuracy and the convergence rate of MQ depend strongly on its shape parameter (Koushki et al. 2019). So far, researchers have been working on many methods for determining the optimal shape parameter but a comprehensive method has not been developed yet (Babaee et al. 2019). In this study, the commonly previous methods have been investigated for determining the optimal shape parameter and a novel idea has been presented for analyzing the flood flow caused by dam break. The efficiency and accuracy of the present approach compared to other solutions have been shown through three examples.<br /> Methodology:<br /> The governing PDEs of dam break problem consist of the continuity equation and two momentum equations in two dimensions. MQ approximates solution of 2D equations system using an estimation function in which the unknown coefficients have to be determined for each unknown variable of the PDE, i.e. the velocities in two directions and the pressure. In one hand, for definition of the estimation function, the RBF methods need N center points inside the domain or on the boundaries which leads to N unknown coefficients. On the other hand, the governing PDEs and their boundary conditions again have to be satisfied on N collocation points which leads to N algebraic equations to be solved for the mentioned unknown coefficients. A critical parameter, namely, the shape parameter strongly affects the precision of the estimation function which may be considered constant or variable from point to point for each estimation function. Determining the optimal value of the shape parameter has always been a challenge in using MQ and other RBF methods. In this study it has been shown that the shape parameter in all time steps can be equal and a new high-speed idea is proposed to determine its optimal value. In this approach, the initial conditions of the problem will be estimated using MQ function and it has been shown that the optimal value of the shape parameter in the initial conditions is also the optimal value of the shape parameter for the next time steps and there is no need to be optimized for every next time steps. Therefore the computational cost will be considerably reduced. Also for discretizing the time dependent terms, the forward finite difference method is used and it was shown that for discretizing the local terms, the implicit method must be used by substituting MQ function. Consequently, the presented approach becomes unconditionally stable.<br /> In order to verify and validate the proposed approach, three 2D numerical examples are presented. In two of the examples with 1D and 2D behaviors, discontinuities in initial conditions and run times are different. Sharp discontinuities highlight the capabilities of the approach while in long run time shows stability. Besides, results of the proposed approach have been compared with those of other numerical and analytical methods. Also, in this research, inefficiency of previously common methods for determining the optimal shape parameter in solving the dam-break problem was shown (Golbabai et al. 2015). In verification, the RMSE error criterion has been considered which results in errors less than 5 percent. In the third example capability of the numerical model has been demonstrated by a two dimensional dam break flow.<br /> Conclusion: <br /> Using the MQ-RBF, the disadvantages of mesh-based method including; high cost of meshing, need to fundamental solution dependence on the conditions of each problem, singularity, continuous discretization of domain and need to a regular mesh will be eliminated.<br /> The benefits of the proposed idea for the optimal value of the shape parameter respect to existing methods include 1) independency of a secondary solution of the problem, 2) solving problem using just one set of computational centers, 3) independency of the geometry and physics of the problems, 4) needless to optimize the shape parameter at every time step, 5) low computational cost and 6) convenient to use. Finally result of several different examples compared to other numerical and analytical methods showed acceptable accuracy of the present approach.Introduction:<br /> In order to avoid meshing and its difficulties and costs, Multiquadric Radial Basis Function (MQ-RBF) method has been developed (Kansa 1990) and has been examined for different types of physical phenomena. In this regard, the present study develops this meshless method for analysis of dam break problem. MQ is more convenient and accurate than other RBF methods for solving partial differential equations (Fallah et al. 2019). This meshless method have advantages such as; 1) creating a continuous response function all over the computational domain, 2) no need to discretize the entire domain with optimal usability in large-scale problems, 3) high capability in modelling irregular and complex geometries, 4) high ability to simulate discontinuities of responses, 5) easy generalization to 3D problems, and etc. Both the accuracy and the convergence rate of MQ depend strongly on its shape parameter (Koushki et al. 2019). So far, researchers have been working on many methods for determining the optimal shape parameter but a comprehensive method has not been developed yet (Babaee et al. 2019). In this study, the commonly previous methods have been investigated for determining the optimal shape parameter and a novel idea has been presented for analyzing the flood flow caused by dam break. The efficiency and accuracy of the present approach compared to other solutions have been shown through three examples.<br /> Methodology:<br /> The governing PDEs of dam break problem consist of the continuity equation and two momentum equations in two dimensions. MQ approximates solution of 2D equations system using an estimation function in which the unknown coefficients have to be determined for each unknown variable of the PDE, i.e. the velocities in two directions and the pressure. In one hand, for definition of the estimation function, the RBF methods need N center points inside the domain or on the boundaries which leads to N unknown coefficients. On the other hand, the governing PDEs and their boundary conditions again have to be satisfied on N collocation points which leads to N algebraic equations to be solved for the mentioned unknown coefficients. A critical parameter, namely, the shape parameter strongly affects the precision of the estimation function which may be considered constant or variable from point to point for each estimation function. Determining the optimal value of the shape parameter has always been a challenge in using MQ and other RBF methods. In this study it has been shown that the shape parameter in all time steps can be equal and a new high-speed idea is proposed to determine its optimal value. In this approach, the initial conditions of the problem will be estimated using MQ function and it has been shown that the optimal value of the shape parameter in the initial conditions is also the optimal value of the shape parameter for the next time steps and there is no need to be optimized for every next time steps. Therefore the computational cost will be considerably reduced. Also for discretizing the time dependent terms, the forward finite difference method is used and it was shown that for discretizing the local terms, the implicit method must be used by substituting MQ function. Consequently, the presented approach becomes unconditionally stable.<br /> In order to verify and validate the proposed approach, three 2D numerical examples are presented. In two of the examples with 1D and 2D behaviors, discontinuities in initial conditions and run times are different. Sharp discontinuities highlight the capabilities of the approach while in long run time shows stability. Besides, results of the proposed approach have been compared with those of other numerical and analytical methods. Also, in this research, inefficiency of previously common methods for determining the optimal shape parameter in solving the dam-break problem was shown (Golbabai et al. 2015). In verification, the RMSE error criterion has been considered which results in errors less than 5 percent. In the third example capability of the numerical model has been demonstrated by a two dimensional dam break flow.<br /> Conclusion: <br /> Using the MQ-RBF, the disadvantages of mesh-based method including; high cost of meshing, need to fundamental solution dependence on the conditions of each problem, singularity, continuous discretization of domain and need to a regular mesh will be eliminated.<br /> The benefits of the proposed idea for the optimal value of the shape parameter respect to existing methods include 1) independency of a secondary solution of the problem, 2) solving problem using just one set of computational centers, 3) independency of the geometry and physics of the problems, 4) needless to optimize the shape parameter at every time step, 5) low computational cost and 6) convenient to use. Finally result of several different examples compared to other numerical and analytical methods showed acceptable accuracy of the present approach.https://jhyd.iha.ir/article_105500_f619146fad48fbb0fbd3f465fcf051ca.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Effect of Floating Debris and Slot on Scour around a Bridge PierEffect of Floating Debris and Slot on Scour around a Bridge Pier9911010550110.30482/jhyd.2020.105501FADamoon Mohamad Ali NezhadianShiraz UniversityHossein HamidifarWater Engineering Department, Shiraz UniversityJournal Article20191227Introduction <br /> One of the significant issues in bridge hydraulics and river engineering is the phenomenon of bridge pier scouring. Scour is a phenomenon caused by the flow of water in rivers and channels. Determining the maximum depth of scouring is essential because it indicates the amount of potential degradation of the flow around the structure and also plays a decisive role in estimating the dimensions and size of structures. In hydraulic structures, this phenomenon can damage the stability of hydraulic structures because water can wash sediments beneath and around hydraulic structures and carry them in the flow direction. Over time, this phenomenon drains around the bridge pier and, eventually leading to the destruction of the bridge. Generally, two fundamental procedures may reduce scour around bridge piers. First includes changing the flow pattern by using a slot through the pier, for example. The second method includes enhancing the ability of the bed material to withstand erosion by placing riprap in front of the pier, for example. In recent years, piercing a slot through the pier is a new method to control the depth of scouring. The mechanism of operation of the slot is reducing the strength of the horseshoe vortex due to the reduction of the effective diameter of the pier. Although many studies have been carried out on the scouring of bridge piers so far, the study on the effect of floating debris on the effectiveness of a slot in protecting the pier against this phenomenon has not been investigated so far. The purpose of this study is to investigate the simultaneous effect of slot and debris on the scour around bridge piers. So the results of different bridge-pier tests in clear water conditions are presented.<br /> <br /> Methodology<br /> The experiments were performed in Sediment Hydraulics Laboratory, Water Engineering Department, Shiraz University in a glass-walled flume with a rectangular cross-section of 0.4 m wide and 9 m long with a slope of 0.002. At the downstream end of the flume, a tailgate was installed to adjust the flow depth. Uniformly graded sediment particles with a median diameter of 0.8 mm were used. In each experiment, the discharge rate was determined to maintain the clear water scour conditions according to the ratio of the average velocity to critical velocity (Uc/U=1). The diameter of the bridge pier model used in this study was 40 mm. The width of the slot used was 10 mm corresponds to ¼ of the pier diameter. Also, a 200 mm long and 12 mm diameter cylinder installed on the pier at the water surface was used to simulate the accumulated debris. The first experiment was performed with a bridge pier without slot and debris accumulation (control experiment), and each other test was a combination of the presence or absence of slot and debris.<br /> <br /> Results and discussion<br /> The results showed that although the presence of the slot reduces the maximum scour depth, the accumulated debris neutralized this effect considerably. It was found that using the slot alone can reduce the scour depth upto 20%, but the debris accumulation reduces this value to 15%. In the control case, with the code NS-ND-130, the ds/b ratio is 0.85, where ds and b are the maximum scour depth and pier diameter, respectively. It was also observed that in NS-D12-130, i.e., the simple pier with accumulated debris and flow depth of 130 mm, this ratio is 1, which is 17.6% greater compared to the control test. The reason for this increase is the presence of debris. The slot guides the flow in a straight line and prevents the flow separation. Hence, in the S-D12-130 experiment, i.e., a slotted pier with accumulated floating debris, the maximum scour depth decreased by 11% compared to the control, and the ratio (ds/b) indicating maximum scour depth it reached 0.775, indicating the effect of the slot in reducing scour. Besides, it was observed that with increasing the flow depth, the effect of debris would decrease. Since no relationship has been provided so far to calculate the maximum depth of scour around the bridge piers in the presence of slot and floating debris, the ds values in the present study are compared with the results of other researchers with no slots and no floating debris conditions.<br /> <br /> Conclusion<br /> Various methods have been proposed by researchers to reduce scour and protect the bridge pier against scour, for example, a vertical slot through the pier. In this study, the effect of accumulated floating debris during floods on the effectiveness of a slot in reducing the scour around a cylindrical bridge pier was investigated. The results showed that although the presence of the slot reduces the scour depth, the accumulated debris neutralized this effect considerably. Finally, although using the slot can reduce the scour depth to 20%, but the debris accumulation reduces this value to 15%.Introduction <br /> One of the significant issues in bridge hydraulics and river engineering is the phenomenon of bridge pier scouring. Scour is a phenomenon caused by the flow of water in rivers and channels. Determining the maximum depth of scouring is essential because it indicates the amount of potential degradation of the flow around the structure and also plays a decisive role in estimating the dimensions and size of structures. In hydraulic structures, this phenomenon can damage the stability of hydraulic structures because water can wash sediments beneath and around hydraulic structures and carry them in the flow direction. Over time, this phenomenon drains around the bridge pier and, eventually leading to the destruction of the bridge. Generally, two fundamental procedures may reduce scour around bridge piers. First includes changing the flow pattern by using a slot through the pier, for example. The second method includes enhancing the ability of the bed material to withstand erosion by placing riprap in front of the pier, for example. In recent years, piercing a slot through the pier is a new method to control the depth of scouring. The mechanism of operation of the slot is reducing the strength of the horseshoe vortex due to the reduction of the effective diameter of the pier. Although many studies have been carried out on the scouring of bridge piers so far, the study on the effect of floating debris on the effectiveness of a slot in protecting the pier against this phenomenon has not been investigated so far. The purpose of this study is to investigate the simultaneous effect of slot and debris on the scour around bridge piers. So the results of different bridge-pier tests in clear water conditions are presented.<br /> <br /> Methodology<br /> The experiments were performed in Sediment Hydraulics Laboratory, Water Engineering Department, Shiraz University in a glass-walled flume with a rectangular cross-section of 0.4 m wide and 9 m long with a slope of 0.002. At the downstream end of the flume, a tailgate was installed to adjust the flow depth. Uniformly graded sediment particles with a median diameter of 0.8 mm were used. In each experiment, the discharge rate was determined to maintain the clear water scour conditions according to the ratio of the average velocity to critical velocity (Uc/U=1). The diameter of the bridge pier model used in this study was 40 mm. The width of the slot used was 10 mm corresponds to ¼ of the pier diameter. Also, a 200 mm long and 12 mm diameter cylinder installed on the pier at the water surface was used to simulate the accumulated debris. The first experiment was performed with a bridge pier without slot and debris accumulation (control experiment), and each other test was a combination of the presence or absence of slot and debris.<br /> <br /> Results and discussion<br /> The results showed that although the presence of the slot reduces the maximum scour depth, the accumulated debris neutralized this effect considerably. It was found that using the slot alone can reduce the scour depth upto 20%, but the debris accumulation reduces this value to 15%. In the control case, with the code NS-ND-130, the ds/b ratio is 0.85, where ds and b are the maximum scour depth and pier diameter, respectively. It was also observed that in NS-D12-130, i.e., the simple pier with accumulated debris and flow depth of 130 mm, this ratio is 1, which is 17.6% greater compared to the control test. The reason for this increase is the presence of debris. The slot guides the flow in a straight line and prevents the flow separation. Hence, in the S-D12-130 experiment, i.e., a slotted pier with accumulated floating debris, the maximum scour depth decreased by 11% compared to the control, and the ratio (ds/b) indicating maximum scour depth it reached 0.775, indicating the effect of the slot in reducing scour. Besides, it was observed that with increasing the flow depth, the effect of debris would decrease. Since no relationship has been provided so far to calculate the maximum depth of scour around the bridge piers in the presence of slot and floating debris, the ds values in the present study are compared with the results of other researchers with no slots and no floating debris conditions.<br /> <br /> Conclusion<br /> Various methods have been proposed by researchers to reduce scour and protect the bridge pier against scour, for example, a vertical slot through the pier. In this study, the effect of accumulated floating debris during floods on the effectiveness of a slot in reducing the scour around a cylindrical bridge pier was investigated. The results showed that although the presence of the slot reduces the scour depth, the accumulated debris neutralized this effect considerably. Finally, although using the slot can reduce the scour depth to 20%, but the debris accumulation reduces this value to 15%.https://jhyd.iha.ir/article_105501_ad0b01cbfcff9de69f8e533e29b99191.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Experimental study of the effect of floor roughness on wave characteristics resulting from dam break in indirect pathwayExperimental study of the effect of floor roughness on wave characteristics resulting from dam break in indirect pathway11112210550210.30482/jhyd.2020.215555.1434FARazieh KavandMS.c Student, Department of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.Mehdi GhomeshiProfessor, Department of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.0000-0002-8361-1645Mehdi DaryaeeAssistant Professor, Faculty of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran0000-0003-4304-0240Journal Article20200115Introduction<br /> Considering the comparison between the number of dams constructed around the globe and the number of dam failures, the estimated probability of occurrence of failure in each dam is 10-4 dams a year. Although this probability is seemingly low, the experiences of these accidents through the history indicate that it is irrational and unreasonable to overlook the importance of this issue. Despite the extremely high accuracy of calculations and studies conducted for the construction of reservoir dams as well as the comprehensive, complete, and highly accurate research, the probability of dam failure and the need for preparedness for crisis management and floods caused by dam failures cannot be overlooked due to some limitations such as the lack of accurate statistics on the hydrology and flood characteristics on dam construction sites, the complicated geological problems and issues, foundation construction and full waterproofing challenges, flaws in dam construction, and unpredicted problems in the construction or the operation phase. The construction of most reservoir dams in meanders and rocky river beds explains the rational for this research, which was carried out in a flume with a tangent path.<br /> Methodology<br /> The present study was conducted at the physical and hydraulic models laboratory of Water Sciences and Engineering Faculty of Shahid Chamran University of Ahvaz. The rectangular flume used in this research consisted of three 90-degree bends including an acute angle bend, a normal angle bend, and a mild angle bend. A gate was installed and the flood wave created by the dam failure was simulated in the flume. The gate installed divided the flume into an upstream section (the dam reservoir) and a downstream section (the river path). A pneumatic jack was installed on the gate. The jack suddenly sent a wave to the flume downstream using a pressure compressor, thereby simulating the wave caused by the dam failure. The experiments in this study were conducted in the normal-angle bend in this flume. The wave speed and the wave front height of the wave originating from the dam failure were calculated with high accuracy using a fast-switching camera. <br /> Results and Discussion<br /> In the dry downstream, there was no opportunity for the formation of the wave body after it flowed beneath the gate due to the considerable depth height difference between the upstream and downstream sections and the enormous energy. Besides, the wave and the wave failed mass formed at the beginning when the wave passed by the gate before it entered the curved path. The wave continued traveling without showing any fungal or dive state. Moreover, the wave height at the bend inlet was at its peak and it continued towards the end of the canal with a considerably decreasing slope. On the water surface with an upstream of 25 cm, the downstream was dry and the bed was smooth. Besides, the wave speed difference from the angle of 0 to the angle of 45 degrees and the angle of 45 to the angle of 90 degrees showed a 30% increase and a 7% decrease as compared to the beginning of the bend, respectively. This trend showed a 29% increase and an 11% decrease with the 10-mm roughness. It also showed a 25% increase and a 5% decrease with the 16-mm roughness and a 13% increase and a 4% decrease with the 20-mm roughness as compared to the beginning of the bend. The aforesaid trend decreased with an increase in the upstream height because the volume of water released from behind the gate increased, the wave did not hit the flume bed, and the wave continued moving.<br /> Moreover, the wave height at the bend inlet was at its peak and it continued moving towards the end of the canal with a considerably decreasing slope. On the water surface with an upstream of 45 cm, the downstream was dry and the bed was smooth. Besides, the wave speed difference from the angle of 0 to 45 degrees and the angle of 45 to 90 degrees showed a 23% and a 15% decrease as compared to the beginning of the bend, respectively. This trend showed a 21% and a 23% decrease with the 10-mm roughness. It also showed a 23% and a 13% decrease with the 16-mm roughness, and a 23% and an 8% decrease with the 20-mm roughness as compared to the beginning of the bend. <br /> Conclusions<br /> Since the speed increased at the apex of the bend, the speed was higher at the distances following the apex as compared to a direct path, and the construction of pumping stations or recharge points in the second half of the meander was feasible, it is recommended to take protective measures or cut the meander and turn it into a direct path to control and reduce the loss caused by the failure-induced flood.Introduction<br /> Considering the comparison between the number of dams constructed around the globe and the number of dam failures, the estimated probability of occurrence of failure in each dam is 10-4 dams a year. Although this probability is seemingly low, the experiences of these accidents through the history indicate that it is irrational and unreasonable to overlook the importance of this issue. Despite the extremely high accuracy of calculations and studies conducted for the construction of reservoir dams as well as the comprehensive, complete, and highly accurate research, the probability of dam failure and the need for preparedness for crisis management and floods caused by dam failures cannot be overlooked due to some limitations such as the lack of accurate statistics on the hydrology and flood characteristics on dam construction sites, the complicated geological problems and issues, foundation construction and full waterproofing challenges, flaws in dam construction, and unpredicted problems in the construction or the operation phase. The construction of most reservoir dams in meanders and rocky river beds explains the rational for this research, which was carried out in a flume with a tangent path.<br /> Methodology<br /> The present study was conducted at the physical and hydraulic models laboratory of Water Sciences and Engineering Faculty of Shahid Chamran University of Ahvaz. The rectangular flume used in this research consisted of three 90-degree bends including an acute angle bend, a normal angle bend, and a mild angle bend. A gate was installed and the flood wave created by the dam failure was simulated in the flume. The gate installed divided the flume into an upstream section (the dam reservoir) and a downstream section (the river path). A pneumatic jack was installed on the gate. The jack suddenly sent a wave to the flume downstream using a pressure compressor, thereby simulating the wave caused by the dam failure. The experiments in this study were conducted in the normal-angle bend in this flume. The wave speed and the wave front height of the wave originating from the dam failure were calculated with high accuracy using a fast-switching camera. <br /> Results and Discussion<br /> In the dry downstream, there was no opportunity for the formation of the wave body after it flowed beneath the gate due to the considerable depth height difference between the upstream and downstream sections and the enormous energy. Besides, the wave and the wave failed mass formed at the beginning when the wave passed by the gate before it entered the curved path. The wave continued traveling without showing any fungal or dive state. Moreover, the wave height at the bend inlet was at its peak and it continued towards the end of the canal with a considerably decreasing slope. On the water surface with an upstream of 25 cm, the downstream was dry and the bed was smooth. Besides, the wave speed difference from the angle of 0 to the angle of 45 degrees and the angle of 45 to the angle of 90 degrees showed a 30% increase and a 7% decrease as compared to the beginning of the bend, respectively. This trend showed a 29% increase and an 11% decrease with the 10-mm roughness. It also showed a 25% increase and a 5% decrease with the 16-mm roughness and a 13% increase and a 4% decrease with the 20-mm roughness as compared to the beginning of the bend. The aforesaid trend decreased with an increase in the upstream height because the volume of water released from behind the gate increased, the wave did not hit the flume bed, and the wave continued moving.<br /> Moreover, the wave height at the bend inlet was at its peak and it continued moving towards the end of the canal with a considerably decreasing slope. On the water surface with an upstream of 45 cm, the downstream was dry and the bed was smooth. Besides, the wave speed difference from the angle of 0 to 45 degrees and the angle of 45 to 90 degrees showed a 23% and a 15% decrease as compared to the beginning of the bend, respectively. This trend showed a 21% and a 23% decrease with the 10-mm roughness. It also showed a 23% and a 13% decrease with the 16-mm roughness, and a 23% and an 8% decrease with the 20-mm roughness as compared to the beginning of the bend. <br /> Conclusions<br /> Since the speed increased at the apex of the bend, the speed was higher at the distances following the apex as compared to a direct path, and the construction of pumping stations or recharge points in the second half of the meander was feasible, it is recommended to take protective measures or cut the meander and turn it into a direct path to control and reduce the loss caused by the failure-induced flood.https://jhyd.iha.ir/article_105502_d5ae087c0d18d97f0184a41f7d16b538.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Hydraulic characteristics of flow over the asymmetric hydrofoil weirsHydraulic characteristics of flow over the asymmetric hydrofoil weirs12313610550310.30482/jhyd.2020.105503FAElham Bahmanelhambahman69@gmail.comAbdorreza Kabiri-SamaniAssociate Professor, Department of Civil Engineering, Isfahan University of Technology0000-0002-5984-3892Mohammad Navid MoghimDepartment of Civil Engineering, Isfahan University of Technology0000-0002-8765-882XJournal Article20191005Introduction<br /> Weirs are one of the most common hydraulic structures and are used to regulate the upstream approach flow depth, measure the flow discharge, and evacuate the excess flow discharge in dams, irrigation and drainage networks. Based on the ratio of the total head of the upstream approach flow to the length of the weir, weirs of finite crest length are categorized into four main groups, namely sharp-crested, short-crested, broad-crested, and long-crested type weirs. The thickness of the crest results in different velocity and pressure profiles over the weir crest and consequently tends to various flow behaviors. The short-crested weirs are categorized as three different types, including ogee, circular-crested, and hydrofoil weirs. The hydrofoil weirs are a type of short-crested weirs that are designed on the basis of airfoil theory. This kind of weirs has some merits compared to the other types, such as high discharge coefficient, stability and submergence limit, and low fluctuations of pressure and water free-surface profile. Despite the extensive studies have been carried out on the hydraulic characteristics of the ogee and circular-crested weirs, there is a lack of comprehensive studies on the hydrofoil weirs, and therefore the flow characteristics over the hydrofoil weirs are still unknown. <br /> <br /> Methodology<br /> A hydrofoil weir is designed, on the basis of the Joukowsky transformation function to the equation of a reference circle on the source coordinate plane. The weir pattern generated on the destination coordinate plane is a function of the radius and the coordinate of the center of the circle on the source coordinate plane. If the center of a circle in the source coordinate plane is offset just on the horizontal axis, the Joukowsky transformation yields a symmetric hydrofoil. In this situation, if the center of a circle in the source coordinate plane is offset as large as the radius of the reference circle, the Joukowsky transformation yields a circular-crested weir. On the other hand, if the center of the circle in the source coordinate plane is offset on both the horizontal- and vertical axis, the Joukowsky transformation yields an asymmetric hydrofoil. So far, only three published studies have investigated the flow characteristics over symmetrical hydrofoil weirs. In symmetric hydrofoil weirs, the height of the weir is small, therefore these weirs have received less attention by the researchers till now. Whereas, by applying the asymmetric hydrofoil weirs instead of the symmetric ones, the weir height increases to be used for practical purposes. The present research subjects to study the flow behavior over the asymmetric hydrofoil weirs using experimental and numerical models. An experimental and numerical investigation was conducted, applying three and five models of the asymmetric hydrofoil weirs, respectively, designed on the basis of the Joukowsky transform function. Numerical simulations were performed using open source, OpenFoam v.4.0.1, CFD software. The interFoam solver and the VOF (volume of fluid) method is used to achieve the water free surface profiles and the other hydrodynamic characteristics of the flow field. The PIMPLE (pressure implicit method for pressure linked equations) algorithm was applied to couple the pressure and velocity equations in two-phase flows. In the present study, structured meshes with hexahedral elements were created by the blockMesh utility of OpenFOAM software. To generate a finer grid mesh close to the weir body and along the water free surface, snappyHexMesh utility was applied. To validate the numerical results, former experimental results and the present experimental data of different hydrofoil weirs were applied. Based on the recommendations of former studies, the k-ω SST turbulence model was used for the determination of flow characteristics over the hydrofoil weirs.<br /> <br /> Results and discussion<br /> The results of the numerical simulations including different geometrical characteristics, showed that the asymmetric hydrofoil weirs decrease the possibility of cavitation and the range of positive pressure downstream of the weir compared to those of circular-crested weirs, without decreasing the weir height. Also, in the asymmetric hydrofoil weirs, the results demonstrated that the greatest bed shear stresses and the compressive forces occur at the downstream end of the hydrofoil weir with a more camber, therefore, the downstream zone of these weirs is responsible for large values of bed erosion. Furthermore, the possibility of the downstream bed erosion is the same for the circular-crested weirs and the asymmetric hydrofoil weirs, having equal height. <br /> Conclusion<br /> Finally, by applying asymmetric hydrofoil weirs instead of circular-crested weirs, unfavorable flow conditions would be removed, leading to a more safe and economic hydraulic structures, without decreasing the weir structural height.<br /> Keywords: Bed shear stress, Joukowsky transform function, OpenFoam software, Pressure distribution, Velocity profile.Introduction<br /> Weirs are one of the most common hydraulic structures and are used to regulate the upstream approach flow depth, measure the flow discharge, and evacuate the excess flow discharge in dams, irrigation and drainage networks. Based on the ratio of the total head of the upstream approach flow to the length of the weir, weirs of finite crest length are categorized into four main groups, namely sharp-crested, short-crested, broad-crested, and long-crested type weirs. The thickness of the crest results in different velocity and pressure profiles over the weir crest and consequently tends to various flow behaviors. The short-crested weirs are categorized as three different types, including ogee, circular-crested, and hydrofoil weirs. The hydrofoil weirs are a type of short-crested weirs that are designed on the basis of airfoil theory. This kind of weirs has some merits compared to the other types, such as high discharge coefficient, stability and submergence limit, and low fluctuations of pressure and water free-surface profile. Despite the extensive studies have been carried out on the hydraulic characteristics of the ogee and circular-crested weirs, there is a lack of comprehensive studies on the hydrofoil weirs, and therefore the flow characteristics over the hydrofoil weirs are still unknown. <br /> <br /> Methodology<br /> A hydrofoil weir is designed, on the basis of the Joukowsky transformation function to the equation of a reference circle on the source coordinate plane. The weir pattern generated on the destination coordinate plane is a function of the radius and the coordinate of the center of the circle on the source coordinate plane. If the center of a circle in the source coordinate plane is offset just on the horizontal axis, the Joukowsky transformation yields a symmetric hydrofoil. In this situation, if the center of a circle in the source coordinate plane is offset as large as the radius of the reference circle, the Joukowsky transformation yields a circular-crested weir. On the other hand, if the center of the circle in the source coordinate plane is offset on both the horizontal- and vertical axis, the Joukowsky transformation yields an asymmetric hydrofoil. So far, only three published studies have investigated the flow characteristics over symmetrical hydrofoil weirs. In symmetric hydrofoil weirs, the height of the weir is small, therefore these weirs have received less attention by the researchers till now. Whereas, by applying the asymmetric hydrofoil weirs instead of the symmetric ones, the weir height increases to be used for practical purposes. The present research subjects to study the flow behavior over the asymmetric hydrofoil weirs using experimental and numerical models. An experimental and numerical investigation was conducted, applying three and five models of the asymmetric hydrofoil weirs, respectively, designed on the basis of the Joukowsky transform function. Numerical simulations were performed using open source, OpenFoam v.4.0.1, CFD software. The interFoam solver and the VOF (volume of fluid) method is used to achieve the water free surface profiles and the other hydrodynamic characteristics of the flow field. The PIMPLE (pressure implicit method for pressure linked equations) algorithm was applied to couple the pressure and velocity equations in two-phase flows. In the present study, structured meshes with hexahedral elements were created by the blockMesh utility of OpenFOAM software. To generate a finer grid mesh close to the weir body and along the water free surface, snappyHexMesh utility was applied. To validate the numerical results, former experimental results and the present experimental data of different hydrofoil weirs were applied. Based on the recommendations of former studies, the k-ω SST turbulence model was used for the determination of flow characteristics over the hydrofoil weirs.<br /> <br /> Results and discussion<br /> The results of the numerical simulations including different geometrical characteristics, showed that the asymmetric hydrofoil weirs decrease the possibility of cavitation and the range of positive pressure downstream of the weir compared to those of circular-crested weirs, without decreasing the weir height. Also, in the asymmetric hydrofoil weirs, the results demonstrated that the greatest bed shear stresses and the compressive forces occur at the downstream end of the hydrofoil weir with a more camber, therefore, the downstream zone of these weirs is responsible for large values of bed erosion. Furthermore, the possibility of the downstream bed erosion is the same for the circular-crested weirs and the asymmetric hydrofoil weirs, having equal height. <br /> Conclusion<br /> Finally, by applying asymmetric hydrofoil weirs instead of circular-crested weirs, unfavorable flow conditions would be removed, leading to a more safe and economic hydraulic structures, without decreasing the weir structural height.<br /> Keywords: Bed shear stress, Joukowsky transform function, OpenFoam software, Pressure distribution, Velocity profile.https://jhyd.iha.ir/article_105503_df2689166697ad43427eb1086299972b.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-423714420200220Experimental investigation downstream of USBRVI stilling basin with steeped end sillExperimental investigation downstream of USBRVI stilling basin with steeped end sill13714810557310.30482/jhyd.2020.105573FAMilad SaberFaculty of civil and environmental eng. Tarbiat modares uinversity- Tehran - IranMassoud GhodsianTarbiat Modarres UniversityJournal Article20191015Experimental investigation on scour downstream of USBRIV stilling basins<br /> <br /> M. Saber1, M. Ghodsian 2*<br /> 1- Ex.MSc student of Hydraulic Structures, Faculty of Civil Engineering, Tarbiat Modares University, Tehran, Iran<br /> 2- Prof. of Hydraulics, Faculty of Civil and Environmental Engineering and Water Engineering Research Institute,, Tarbiat Modares University, Tehran, Iran<br /> <br /> * ghods@modares.ac.ir <br /> <br /> Introduction<br /> Energy dissipaters are usually installed at the outlets of canals, outlets of chutes and outlets of culverts and other hydraulic structures. They are used to dissipate the excess energy of the outlet flow from the hydraulic structures. For dissipation of excess energy at the outlets, usually stilling basins are used. There are different types of stilling basins introduced and used in different parts of word. The USBR type VI stilling basin was first introduced by Bradely and Peterka (1995) and later on modified by Biechley (1978). In this paper results of experiments on the scour at the downstream of the USBR type VI stilling basin are reported. <br /> <br /> Experiments<br /> Experiments were conducted in a 0.8 m wide, 0.6 m height, and 0.58 m length rectangular channel. The bed and sides of the channel were made of still and glass respectively, and supported by metal frames. Uniform sediment with mean diameter of 1.64 mm were used as the bed material. The sediment layer with thickness of 0.4 m and length of 2.75 m were prepared at the downstream of stilling basin. <br /> Experiments were conducted for duration of six hours, at which almost equilibrium scour was reached. The bed topography and depth of scour were measured by a digital point gauge with the accuracy of ± 0.01 mm. The dimensions of different parts of stilling basing was selected following the method introduced by Biechley (1978). Total of 32 experiments were conducted for different Froude number (1.99, 3.03, 4.06, 4.07, 5.97, 8.11, 9.27 and 13.91) and four different stepped end sills (with one step, with two steps, with three steps, with four steps and with five steps). The width, height and length of all the end sills were kept equal in all the experiments. <br /> <br /> Results<br /> It was found that by increasing the Froude number, the length of scour hole increases for all the experiments. By increasing the Froude number from 2 to 4, the relative depth of scour initially increases, reach to a maximum value at Froude number equal to about 3 and then after decreases. The variations of the relative depth of scour for the range of Froude number from 4 t 6 is marginal. But the amount of the relative depth of scour for Froude number greater that about 6 significantly decreases. <br /> By increasing the Froude number (from 1.99 to 3.03), the scouring potential of the outflow from the stilling basin increase. As a result relative depth of scour increases. But for higher values of the Froude number, the weep out of the flow from the stilling basin occurs. In this case dissipating potential of the out flow jet from the stilling basin reduces, as a result the relative depth of scour reduces. This decreasing trend is more significant at Froude number greater than about 6.<br /> By increasing the Froude number, scour index (2ds/Lt) increases and enhances the performance of the stilling basin. Here ds is maximum depth of scour and Lt is distance of location of maximum scour depth from the stilling basin. The performance of the end sill with four steps was better for the Froude number in the range of 1.99 to 4.07. The amount of scour depth at the downstream of the end sill with four steps was minimum for the Froude numbers in the ranges of 9.27 to 13.91. The volume of scour hole at the downstream of the end sill with four steps was less than that due to other end sills. An asymmetry index was defined to see the symmetry/asymmetry of the bed topography after the experiments. The values of asymmetry indices for the end sills with five steps under Froude number in the range of 1 to 4, and for the end sills with four steps under Froude number in the range of 4 to 13.9 were minimum. Time variations of the scour showed that about 65 to 70 percent of the scour occurs during 60 minutes from onset of experiments. An equation was obtained for the dimensionless longitudinal profile of scour profile. Time variations of the scour showed that about 65 to 70 percent of the scour occurs during 60 minutes from onset of experiments. An equation was obtained for the dimensionless longitudinal profile of scour profile.Experimental investigation on scour downstream of USBRIV stilling basins<br /> <br /> M. Saber1, M. Ghodsian 2*<br /> 1- Ex.MSc student of Hydraulic Structures, Faculty of Civil Engineering, Tarbiat Modares University, Tehran, Iran<br /> 2- Prof. of Hydraulics, Faculty of Civil and Environmental Engineering and Water Engineering Research Institute,, Tarbiat Modares University, Tehran, Iran<br /> <br /> * ghods@modares.ac.ir <br /> <br /> Introduction<br /> Energy dissipaters are usually installed at the outlets of canals, outlets of chutes and outlets of culverts and other hydraulic structures. They are used to dissipate the excess energy of the outlet flow from the hydraulic structures. For dissipation of excess energy at the outlets, usually stilling basins are used. There are different types of stilling basins introduced and used in different parts of word. The USBR type VI stilling basin was first introduced by Bradely and Peterka (1995) and later on modified by Biechley (1978). In this paper results of experiments on the scour at the downstream of the USBR type VI stilling basin are reported. <br /> <br /> Experiments<br /> Experiments were conducted in a 0.8 m wide, 0.6 m height, and 0.58 m length rectangular channel. The bed and sides of the channel were made of still and glass respectively, and supported by metal frames. Uniform sediment with mean diameter of 1.64 mm were used as the bed material. The sediment layer with thickness of 0.4 m and length of 2.75 m were prepared at the downstream of stilling basin. <br /> Experiments were conducted for duration of six hours, at which almost equilibrium scour was reached. The bed topography and depth of scour were measured by a digital point gauge with the accuracy of ± 0.01 mm. The dimensions of different parts of stilling basing was selected following the method introduced by Biechley (1978). Total of 32 experiments were conducted for different Froude number (1.99, 3.03, 4.06, 4.07, 5.97, 8.11, 9.27 and 13.91) and four different stepped end sills (with one step, with two steps, with three steps, with four steps and with five steps). The width, height and length of all the end sills were kept equal in all the experiments. <br /> <br /> Results<br /> It was found that by increasing the Froude number, the length of scour hole increases for all the experiments. By increasing the Froude number from 2 to 4, the relative depth of scour initially increases, reach to a maximum value at Froude number equal to about 3 and then after decreases. The variations of the relative depth of scour for the range of Froude number from 4 t 6 is marginal. But the amount of the relative depth of scour for Froude number greater that about 6 significantly decreases. <br /> By increasing the Froude number (from 1.99 to 3.03), the scouring potential of the outflow from the stilling basin increase. As a result relative depth of scour increases. But for higher values of the Froude number, the weep out of the flow from the stilling basin occurs. In this case dissipating potential of the out flow jet from the stilling basin reduces, as a result the relative depth of scour reduces. This decreasing trend is more significant at Froude number greater than about 6.<br /> By increasing the Froude number, scour index (2ds/Lt) increases and enhances the performance of the stilling basin. Here ds is maximum depth of scour and Lt is distance of location of maximum scour depth from the stilling basin. The performance of the end sill with four steps was better for the Froude number in the range of 1.99 to 4.07. The amount of scour depth at the downstream of the end sill with four steps was minimum for the Froude numbers in the ranges of 9.27 to 13.91. The volume of scour hole at the downstream of the end sill with four steps was less than that due to other end sills. An asymmetry index was defined to see the symmetry/asymmetry of the bed topography after the experiments. The values of asymmetry indices for the end sills with five steps under Froude number in the range of 1 to 4, and for the end sills with four steps under Froude number in the range of 4 to 13.9 were minimum. Time variations of the scour showed that about 65 to 70 percent of the scour occurs during 60 minutes from onset of experiments. An equation was obtained for the dimensionless longitudinal profile of scour profile. Time variations of the scour showed that about 65 to 70 percent of the scour occurs during 60 minutes from onset of experiments. An equation was obtained for the dimensionless longitudinal profile of scour profile.https://jhyd.iha.ir/article_105573_b52dca70a59cd81a831866490e045c71.pdf