فهرست مطالب

هیدرولیک - سال شانزدهم شماره 2 (تابستان 1400)

مجله هیدرولیک
سال شانزدهم شماره 2 (تابستان 1400)

  • تاریخ انتشار: 1400/07/06
  • تعداد عناوین: 8
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  • وحید بابایی نژاد، بابک خورسندی* صفحات 1-13

    باتوجه به کاهش منابع طبیعی آب شیرین، استفاده از کارخانه های آب شیرینکن افزایش چشمگیری داشته است. پساب تولیدی توسط کارخانه های آب شیرینکن درصورت تخلیه نامناسب در محیط آبی، به دلیل دارا بودن غلظت بالای پساب خسارات جبران ناپذیری به محیط زیست وارد می کنند. استفاده از تخلیه کننده های چند مجرایی باعث کاهش شار مومنتوم جت خروجی می شود و به همین دلیل ارتفاع صعود ماکزیمم جت کاهش پیدا می کند و استفاده از این نوع تخلیه کننده ها در عمق کم ساحل را امکان پذیر می سازد. در این پژوهش با استفاده از روابط تجربی به اعتبار سنجی مدلهای CORMIX و CorJet برای تخمین پارامترهای پساب شور تخلیه شده به صورت چند مجرایی در محیط ساکن و پویا پرداخته می شود. در صورت ادغام پساب ها (فاصله افقی تخلیه کننده ها کم باشد)، به دلیل اثر پدیده کواندا و هماوری جت ها، پارامترهای پساب چگال در محیط ساکن و پویا (میزان رقیق سازی، فاصله افقی نقطه برخورد پساب به زمین و ارتفاع صعود ماکزیمم جت)، با خطای زیادی توسط مدلها دست بالا تخمین زده می شود. اما درصورتیکه فاصله افقی تخلیه کننده ها افزایش یابد احتمال ادغام پساب ها در پایین دست کاهش می یابد و در این صورت مدلها با اختلاف کمتری نسبت به روابط تجربی ، پارامترهای پساب چگال تخلیه شده را تخمین می زنند. مدل CorJet محل ادغام پساب ها در محیط ساکن را در مقایسه با روابط تجربی با اختلافی کمتر از 10 درصد به خوبی پیش بینی می کند. طبق نتایج این پژوهش، مدل CorJet رفتار پساب چگال تخلیه شده از تخلیه کننده های چند مجرایی در محیط ساکن و پویا را در مقایسه با مدل CORMIX با خطای کمتری تخمین می زند.

    کلیدواژگان: CorJet، CORMIX، کارخانه آب شیرین کن، پساب، پلوم، جت
  • مرتضی زنگانه* صفحات 15-30

    این مقاله به مطالعه آبگرفتگی شهرک صنعتی آق قلا و مناطق اطراف آن می پردازد و همچنین به ارایه راهکار جهت حفاظت این زیرساخت در برابر سیلاب می پردازد. به همین منظور، در این مقاله سناریوهای گوناگون سیلاب با دوره بازگشت مختلف اطراف شهرک صنعتی آق قلا مورد بررسی قرار می گیرد در حالی که به منظور مدل سازی پخش سیلاب در منطقه مذکور با توجه به رفتار دو بعدی آن از نرم افزار MIKE- HD، استفاده می شود. همچنین با استفاده از سیلاب به وقوع پیوسته در منطقه طرح در اسفند ماه سال 1397 و فروردین سال 1398 مدل مذکور کالیبره گردید. پس از کالیبراسیون مدل موردنظر تمامی سیلاب های محتمل با دوره بازگشت مختلف 2، 5، 10، 25، 50، 100، 200 و 500 ساله در منطقه طرح مورد ارزیابی قرار می گیرد. نتایج نشان می دهد که سیلاب مورد نظر همانطور که پیش بینی می شود دارای رفتار دو بعدی بوده و بیشتر به صورت آبگرفتگی در منطقه طرح خود را نمایان می کند. همچنین مشخص گردید بهترین گزینه جهت حفاظت منطقه مورد نظر در برابر سیلاب دیوار حفاظتی می باشد که در طراحی آن باید بالاترین تراز آب موجود را برای طراحی با دوره بازگشت طرح مورد نظر در نظر گرفت. به طور مثال حداکثر تراز آب برابر 94/15- متر برای سیلاب 500 ساله بدست آمد که تقریبا معادل حداکثر تراز آب در سیلاب اسفند 1397 و فرودین 98 بوده است.

    کلیدواژگان: آبگرفتگی، شهرک صنعتی آق قلا، MIKE- HD، حفاظت، سیل
  • علیرضا جوادی*، ابراهیم اسدی صفحات 31-42

    وقوع پدیده پرش هیدرولیکی در کانال های روباز باعث کاهش سطح انرژی و تبدیل جریان فوق بحرانی به زیر بحرانی می گردد. تعبیه موانع با هندسه های مختلف بر مسیر جریان تاثیر مهمی بر کنترل محل پرش، کاهش طول پرش هیدرولیکی و افزایش افت انرژی جریان در طی پرش دارد. در این تحقیق اثر تغییرات ارتفاع و فاصله میان بلوک های مستطیلی، که به صورت زیگزاگی در کف کانال روباز ذوزنقه ای نصب شده بود، بر مشخصات پرش هیدرولیکی بررسی شد. مجموعا 60 آزمایش در بازه اعداد فرود 1.8 تا 18.8 انجام پذیرفت . نتایج بدست آمده نشان می دهد که در صورت استفاده از بلوک های مستطیلی به طور میانگین شاهد کاهش عمق ثانویه به مقدار 3.69 درصد، کاهش طول پرش هیدرولیکی به میزان 49.5 درصد و افزایش افت انرژی پرش هیدرولیکی به میزان 46.34 درصدی نسبت به بستر صاف می باشد. مشاهدات بیانگر تاثیر بیشتر بلوک های مستطیلی زیگزاگی بر مشخصات پرش نسبت به بسترهای زبر علیرغم تراکم کمتر و همچنین اثر کمتر نسبت به بلوک های با طرح بدون زاویه می باشد. افزایش ارتفاع بلوک ها بر مشخصات پرش هیدرولیکی، نسبت به فاصله میان بلوک ها بوده است.

    کلیدواژگان: افت انرژی، پرش هیدرولیکی، بلوک زیگزاگی، عمق مزدوج، مدل فیزیکی
  • مسعود قدسیان*، چنور عبدی، آرام غفوری صفحات 43-58
    در این تحقیق مشخصات حفره آبشستگی و تغییرپذیری های آن در پایین دست سرریز کلیدپیانویی ذوزنقه ای و سرریز کلیدپیانویی مثلثی مورد بررسی آزمایشگاهی قرار گرفت. بدین منظور سرریزهای کلیدپیانویی ذوزنقه ای و مثلثی در فلوم آزمایشگاهی به طول 10 متر و عرض و ارتفاع 75 و 80 سانتی متر با دو میزان دبی (35 و 45 لیتر بر ثانیه) و عمق پایاب های مختلف (8 الی 18 سانتی متر) مورد آزمایش قرار گرفت. جنس بستر پایین دست سرریز، مصالح ماسه ای با دانه بندی یکنواخت، قطر متوسط 64/1 میلی متر، با انحراف معیار هندسی 24/1 و به ضخامت 5/42 سانتی متر و طول 2 متر بود. نتایج حاصله نشان می دهد که در اعداد فرود ذره رسوب کم، بیشینه عمق حفره آبشستگی پایین دست سرریز کلیدپیانویی مثلثی نسبت به سرریز کلیدپیانویی ذوزنقه ای در فاصله ای نزدیک تری از سرریز رخ داده است. اما با افزایش عدد فرود ذره رسوب، این روند تغییر یافته و بیشینه عمق حفره آبشستگی و موقعیت آن در سرریز کلیدپیانویی ذوزنقه ای کمتر و در فاصله ی نزدیکتری نسبت به سرریز کلیدپیانویی مثلثی رخ داده است. به طور کلی با افزایش عدد فرود ذره، فراسنجه های بیشینه عمق حفره آبشستگی، موقعیت مکانی آن، طول و حجم حفره آبشستگی پایین دست هر دو شکل سرریز افزایش می یابند. معادله هایی با دقت مناسب برای پیش بینی بیشینه عمق حفره آبشستگی، موقعیت مکانی آن، طول حفره آبشستگی، عمق آبشستگی پای دیوار پایین دست سرریز و حجم حفره آبشستگی برای دو شکل سرریز به دست آمد.
    کلیدواژگان: مطالعه آزمایشگاهی، آبشستگی، شرایط هیدرولیکی جریان، سریز کلیدپیانویی، سریز کلیدپیانویی مثلثی، سریز کلیدپیانویی مستطیلی
  • مهدی ماجدی اصل*، مهدی فولادی پناه، رعنا ذیفر، زهرا قسمی صفحات 59-72

    جریان مستغرق به دلیل افزایش تراز سطح آب پایین دست سرریز نسبت به تاج سرریز روی می دهد. هدف این پژوهش، بررسی معادله دبی-اشل برای سرریز غیرخطی کلیدپیانویی استاندارد (PK-S) و اصلاح شده (PK-M) تحت شرایط جریان مستغرق به کمک الگوریتم های هوشمند شامل ماشین بردار پشتیبان (SVM) و برنامه ریزی بیان ژن (GEP) براساس داده های آزمایشگاهی است. با استفاده از تحلیل ابعادی چهار پارامتر بی بعد H_d/H_o ، 〖Fr〗_d، 〖Fr〗_u و H_o/P به دست آمدند. با استفاده از آماره های مجذور میانگین مربعات خطا، RMSE، ضریب تبیین، 2R، میانگین خطای نرمال، MNE، آماره ی نسبت تفاوت توسعه داده شده، DDR، عملکرد مدل ها مقایسه شدند. همچنین از یک معادله ی تجربی برای مقایسه قدرت پیش بینی شبیه سازها استفاده شد. نتایج نشان داد که پارامترهای موثر در الگوریتم SVM برای سرریزهای PK-S و PK-M برابر با H_o/P و H_d/H_o و در الگوریتم GEP مشتمل بر H_d/H_o ، Frd، Fru و H_o/P بودند. همچنین مقدار بهینه ی ضرایب ارزیابی عملکرد برای الگوریتم SVM در هر دو نوع سرریز PK-S و PK-M از دو شبیه ساز دیگر بهتر بود که نشان از برتری الگوریتم SVM دارد.

    کلیدواژگان: الگوریتم ماشین بردار پشتیبان، الگوریتم برنامه ریزی بیان ژن، سرریز کلید پیانویی، جریان مستغرق
  • شیما ابوالفتحی*، سید محمود کاشفی پور، محمود شفاعی بجستان، دیوید آر فوهرمن صفحات 73-90

    گروه پایه های پل احداث شده در رودخانه، از جمله سازه های مهمی هستند که آبشستگی اطراف آن ها نه تنها توسط خصوصیات جریان، بلکه به واسطه تعداد و آرایششان نیز تحت تاثیر قرار می گیرد. این پژوهش به صورت آزمایشگاهی تاثیر خصوصیات هیدروگراف شامل سه دبی حداکثر و سه زمان تداوم هیدروگراف را برای سه فاصله نسبی متفاوت در یک گروه پایه متشکل از سه پایه استوانه ای هم اندازه را در طول زمان بررسی می کند. همچنین به مطالعه تغییرات زمانی حفره آبشستگی در جریان ماندگار متناظر با سه دبی حداکثر هیدروگراف و سه فاصله نسبی متفاوت می پردازد. در بررسی تغییرات زمانی حفره آبشستگی در جریان غیر ماندگار، نتایج نشان داد که در صورت وجود شرایط خاص در روند هیدروگراف، حفره آبشستگی پایه دوم و سوم می تواند پس از فروکش کردن دبی جریان، توسط رسوبات فرسایش یافته از حفره قبلی، مجددا پر شود؛ که این پدیده، بازپر شدگی حفره آبشستگی نامیده شد و حداکثر مقدار آن در آزمایش ها، به اندازه 24 درصد قطر پایه مشاهده گردید.

    کلیدواژگان: جریان غیرماندگار، آبشستگی، گروه پایه پل، هیدروگراف سیل، تغییرات زمانی
  • مجید فضلی*، هدی نبوی صفحات 91-105
    یکی از روش های متداول برای استهلاک انرژی جنبشی جریان در پاییندست سازه های آبی در حوضچه های آرامش، پرش هیدرولیکی میباشد‎ .‎زبری کف ‏حوضچه عامل مهمی در کنترل، کاهش طول و عمق ثانویه و نیز افزایش افت انرژی توسط پرش هیدرولیکی می باشد. جهت کاهش ابعاد حوضچه آرامش اقداماتی ‏مانند ساخت بلوک های میانی، پله های مثبت و منفی و آستانه انتهایی به منظور اتلاف بیشتر انرژی جنبشی جریان در محدوده پرش هیدرولیکی و کاهش ‏مشخصه های آن مورد استفاده قرار می گیرد. در این تحقیق تلاش گردیده است که پرش هیدرولیکی در حوضچه آرامش به همراه بلوک های میانی و آستانه انتهایی ‏طبق استاندارد ابعاد حوضچه آرامش‎ USBR III ‎به صورت آزمایشگاهی مورد بررسی قرار گیرد. با این تفاوت که در این پژوهش بلوک های میانی و آستانه انتهایی ‏و نیز کف بستر، علاوه بر حالت صلب، در حالت توری سنگی با درصد تخلخل های مختلف نیز ساخته شده و مورد بررسی و آزمایش قرار گرفتند نتایج نشان می دهد ‏که افزایش میزان تخلخل بلوک های میانی و آستانه انتهایی و همچنین کف بستر با عث کاهش طول پرش هیدرولیکی و عمق ثانویه می گردد. همچنین مشاهده ‏می شود که اتلاف انرژی نسبی پرش هیدرولیکی در هر نوع کف بستر اعم از متخلخل و صلب، با افزایش درصد تخلخل بلوک و آستانه روند افزایشی را طی می کند. ‏طول پرش هیدرولیکی و عمق ثانویه بر روی بستر با مانع نسبت به بستر بدون مانع بسیار کاهش می یابد و درنهایت مشاهده شد که اتلاف انرژی نسبی بر روی بستر ‏با مانع نسبت به بستر بدون مانع افزایش می یابد.‏
    کلیدواژگان: پرش هیدرولیکی، بلوک های میانی، آستانه انتهایی، توری سنگی، درصد تخلخل، طول پرش
  • آیدا شبانی، حسین خزیمه نژاد*، محسن پوررضا بیلندی، یوسف رمضانی صفحات 107-121

    تنداب سرریز به دلیل انرژی بالا و سرعت زیاد آب روی آن در معرض خطر ناشی از پدیده کاویتاسیون قرار می گیرد. کارهای مختلفی در جهت شناخت و رفع پدیده کاویتاسیون انجام شده است، هدف از انجام پژوهش حاضر، دستیابی به درکی بهتر از عملکرد زبری، با تغییر در آرایش زبری (ردیفی، واگرا و همگرا)، تعداد زبری (9، 12، 15 و 18) و ارتفاع موثر زبری (008/0، 017/0 و 026/0) بر شاخص کاویتاسیون در بدنه پایین دست سرریز اوجی با استفاده از یک مدل آزمایشگاهی است. نتایج نشان داد، نصب زبری روی سرریز، با آرایش ها ، تعداد و ارتفاع های موثر مختلف، باعث افزایش شاخص کاویتاسیون نسبت به حالت شاهد شده است. وجود زبری باعث کاهش سرعت جریان و افزایش فشار بر روی سرریز می شود. این مساله در رفع یا تخفیف پدیده کاویتاسیون بر روی سرریز، نقش بسزایی دارد. نتایج نشان داد، متوسط شاخص کاویتاسیون در آرایش همگرا 17/15، در آرایش واگرا 8/11 و در آرایش ردیفی 11/16 درصد نسبت به حالت شاهد افزایش یافته است. همچنین نتایج نشان داد بیشترین تغییر در آرایش ردیفی و ارتفاع موثر 017/0 و تعداد 18 صفحه زبری نسبت به آزمایش های شاهد اتفاق افتاد.

    کلیدواژگان: سرریز اوجی، مدل آزمایشگاهی، شاخص کاویتاسیون، زبری
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  • Vahid Babaiynejad, Babak Khorsandi * Pages 1-13
    Introduction

    In today's world, fresh water is known as a limited resource that all economic and social activities of human beings and more importantly human life and other organisms depend on this limited resource and this limited resource is decreasing day by day. At present, in most countries, desalination of the seas and oceans is the most important source of water supply near the coast. One of the products of desalination plants is saline effluent that is discharged into the sea environment. Improper discharge of this effluent causes damage to the environment and can cause irreparable damage to human life and other organisms. Due to the fact that the use of multichannel dischargers has increased in recent decades, it is necessary to conduct numerical and laboratory studies on these types of dischargers. Many studies have been performed to validate CORMIX and CorJet models for effluent discharge using single-channel dischargers, but so far the accuracy of these models for dense effluent discharge using multi-channel dischargers has not been investigated. For this reason, in this research, the validation of CORMIX and CorJet models is investigated to investigate the flow of saline effluent discharged from multi-channel dischargers in a static and dynamic environment.

    Methodology

    CORMIX is a hydrodynamic model that uses flow classification to investigate the behavior of effluents with positive, negative and neutral buoyancy in the aquatic environment. Predicting the behavior of the effluent in the distant field, considering the wind flow, roughness and slope of the bed are among the features of this model. CORMIX consists of three sub-models: CORMIX1 (discharge using single-channel discharge), CORMIX2 (discharge using multi-duct discharge) and CORMIX3 (surface discharge) .Corjet is an accurate, three-dimensional integration model for analyzing the concentration and flow path of discharged effluents in the aqueous medium. This model is a subset of the CORMIX model and can be run directly or independently of the CORMIX system. This model solves the equations and predicts the dilution of effluents with positive, neutral and negative densities based on the Eulerian integral method.CorJet is used for single-channel and multi-channel dischargers. A feature of this model is the integration of jets in multichannel unloaders. This model does not consider any boundaries and only applies to near field and does not predict dilution in far field.

    Results and Discussion

    As the discharge distance from each other increases, the dilution of the effluent at the point of impact with the ground increases almost linearly. The results of the CorJet model are in good agreement with the results of the laboratory study. In contrast, the results of the CORMIX model for diluting the effluent from multi-channel dischargers in the residential environment are 62% more erroneous than the results of the experimental study and are not reliable. The CorJet model estimates the value of Xi well with an average error of 11%, and as the horizontal distance between the dischargers increases, the error rate between the model results and the experimental study decreases. But the CORMIX model predicts the horizontal distance of the point of impact of the effluent to the ground with a high error. CORMIX and CorJet overestimate the maximum jet climb height if the horizontal discharge distances are close to each other. The results of CORMIX and CorJet models for predicting effluent dilution at the point of impact in dynamic environments differ by 48 and 18%, respectively, for different discharge distances from each other. In this case, the CorJet model estimates the amount of effluent dilution at the point of impact with less error than the CORMIX model. Comparing the results of CorJet and the laboratory study, it can be seen that CorJet predicts the height of the jet ascent in direct and non-direct current with an error of about 33% and 20%, respectively. CORMIX also estimates the maximum ascent height of the jet in direct and non-direct flow mode with a difference of about 13 and 7%, respectively. According to the results, the CORMIX model predicts the maximum ascent height of the jet in dynamic environments with less difference than the CorJet model.

    Conclusion

    In this research, multichannel dischargers were simulated in static and dynamic environment using CORMIX and CorJet models and the results were compared with the results of laboratory studies. According to the results, the CorJet model estimates all the parameters of the discharged condensed effluent (Si, Xi and Z) from the multi-channel dischargers in the static and dynamic environment with acceptable error. But the CORMIX model only estimates the maximum ascent height of the effluent jet in the dynamic environment well and estimates the other parameters of the discharged effluent with a high difference.

    Keywords: CorJet, CORMIX, Desalination Plant, Effluent, Plume, Jet
  • Morteza Zanganeh * Pages 15-30
    Introduction

    Aq Qala industrial state is one of the most important infrastructure in Golestan province. The layout of this area in the vicinity of Gorganrood and Gharesoo rivers connected by Shurhayat channel has increased its vulnerability against medium and large floods. March 2018 flood in Golestan province has just revealed many weak points of this area versus any upcoming floods. Therefore, in this paper the author tries to deal with the problem in order to remedy Aq Qala industrial state resilience against future possible flood. In addition, it is attempted to find a reliable solution to protect this area. Various numerical models have been developed for simulation of flood inundation to delineate the floodplain zones bordering the rivers and calculate the associated risk considering various return periods. Numerical models to simulate floods are categorized into (a) one-dimensional (1D) models, (b) two dimensional (2D) models, and (c) one-dimensional river flow models coupled with two-dimensional floodplain flow (1D-2D) models. In this paper, due to two-dimensional behavior of flood flow around the state MIKE-HD model widly used by many resarcher is used to simulate flood around the region. To achieve this, initially the MIKE-HD model was calibrated and validated for the rivers an flood pain at the studty area and subsequently, the flood inundation is simulated using MIKE-HD for various return periods. The simulated flood inundation is validated using March 2018 flood. This flood was one of the biggest flood in previous 500-year by which many houses were evacuated for 3 weeks intensifiing by snowmelt for another 2 weeks. Several cities and villages in Golestan Province in Iran were engaged by this flood in more than 200 km area at Gorganrood river neighborhood.

    Methodology

    In order to simulate flood inundation around the industrial state many factors and parameters must be considered. The first requirement is topographical data which are important to clear the flood flow direction. In this study, three datasets are used while the first one goes back to data gathered by photogrammetric operation. In this data set more than 6799 hectares are surveyed by drone with an accuracy abour 20m to 50m. The second one goes back to the ground survey around the industrial state while the last one is related to the Gorganrod bathymetrical data provided by Golestan province Regional Water Organization. After gathering topographical data sets together an event is considered to calibrate flood model in the MIKE-HD software with two parameters including water levels and flood inundation area. To achieve this, the flood occurred in March 2018 is chosen as the event. In this flood many parameters such as the observed flood plain by aerial images and water levels are considered as calibration parameters. In the model the bridge laid on Aq Qala-Gogran road over Gharehsoo river was taken in to th accout to make the more accurate. Finally, the model is developed and evaluated versus various flood with different return periods. Results show that the maximum water level for 500-year return period is -15.94m CD. Also results show that the behavior of flood flow in the area has a two dimensional behavior with low speed. This show that protection alternatives like river dikes haven’t got any problem to be collapsed by scouring. Also, it is concluded that the obtained water levels for diferent return periods converge to each other in the highest value of return periods.

    Results and Discussion

    Obtained results show that the flood flow has a two dimensional behavior in the study area for all return periods so floods showing themselves by water level changing and inundation. This confirms two options for the industrial state protection against future possible flood. The first one is construction of walls to protect the area while increasing the levels of foundation for the structures can be the second alternative. However, changing level of foundation for the client is too difficult because most of the buildings are constructed now and any movement or changing in this way is not cost-effective. In addition, to protect the industrial area from runoff inundation construction some pump stations can be recommended specially for flood times. The pump station are remedies to convey produced runoff by the area at rainig time on the back of protection wall especially in inundation time. Also results show that a level about -15.94 CD can be a fair level to construct the protection wall as the ulimate level. Not that wave and wind-setup freebords must be added to this level because of inundation enduring.

    Conclusion

    In this study flood flow around Aq Qala industrial state was studied. Result show that the best option for protection of the study area is flood wall along with 9 pump stations at the lower level areas. Highlights about the study can be categorized as follows:1- Simulation of March 2018 flood at the study area 2- Finding final options for the protection of the industrial state against future possible flood3- Flood levels for various return periods and its ultimate values4- Flood behavior for the flat area like Aq Qala industrial state is showing itself as level fluctuation rather than a high velocity fluid flow5- In order to remedy flood inundation at the study area considring wave and wind setup as a free board to design the protection wall is essential.Keywords: Inundation, Aq Qala Industrial State, MIKE-HD, Protection, Flood

    Keywords: Inundation, Aq Qala Industrial State, MIKE-HD, Protection, flood
  • Alireza Javadi *, Ebrahim Asadi Pages 31-42

    Hydraulic jump is a phenomenon in which the flow regime changes from supercritical to subcritical. The characteristics of hydraulic jump are rapid expansion of the flow with turbulence, high local energy loss and increase in the height of the free surface of the water. Due to the nature of the flow, the specific force remains constant before and after the hydraulic jump.In this phenomenon, the water depth increases in a short distance and consequently the flow velocity decreases. This increase in depth and decrease in velocity, together with a noticeable decrease in energy, causes turbulence in the flow and converts the kinetic energy of water into heat energy. The turbulence created in the stream decreases as it approaches the end of the jump. Installing obstacles with different geometries on the path of flow have an important effect on controlling the jump location, reducing the length of the hydraulic jump and increasing the energy dissipation of flow during the hydraulic jump.The research flume is 6 meters in length and 60 centimeters in height.The flume is trapezoidal with a floor width of 16 cm and the side of the trapezoid has a slope of 75 degrees and in the length has a slope of zero degrees. Water is pumped from a storage tank to the reservoir at the beginning of the flume (Figure 1). To provide the water load required to achieve higher froude numbers, a sediment tank at the beginning of the flume, which is cylindrical in shape, has been used. This tank is measured by a gauge with an accuracy of 1 mm to read the height of the water inside the tank. In order for the flow to be developed at the beginning of the channel, a part called the jet box is used. By controlling the opening of this part and the pump flow, the desired head in the tank can be reached as well as certain froude numbers (Figure 2). A total of 60 experiments were performed. The blocks have three heights and the distance between the rows of blocks in three modes, so the arrangement of the blocks is divided into nine types. The height of the stream is considered in six different cases. To draw the jump curve, water depth was measured at three points including the end of the blocks, the point equal to the middle of the jump length, and the water depth at the end of the jump.The ratio of the secondary depth of the hydraulic jump to the primary depth is one of the most important parameters used in the design of relaxation ponds. According to Figure 9, the ratio of hydraulic jump conjugate numbers related to the experiments of this research can be defined by the mean curve of the relation 5. Comparing this formula with the experiences of previous researchers shows a good agreement. The results of previous studies by other researchers also show a decrease in the ratio of conjugate depths to smooth surface if obstacles in the waterway are used. with the diagram of figure 10, it can be said that the secondary depth of hydraulic jump is reduced if rectangular blocks are used. Also, to reduce this depth, increasing the height of the block has a greater effect than increasing the distance between the blocks. Also by shortening the length of the hydraulic jump, the length of the required pond will be shortened and it will be more economical. According to Figure 12 and 13 the length of the hydraulic jump compared to the flat bed decreased by an average of 49.5%. In a hydraulic jump, when the flow lines collide with each other, the perturbation created in the flow path, the kinetic energy related to velocity, is converted into heat energy and causes the kinetic energy of the flow to be depleted and its regime to change from supercritical to subcritical. Therefore, calculating the amount of kinetic energy consumption and jump assessment is one of the important topics in this discussion. Figure 14 shows the ratio of energy drop to initial flow energy versus initial froude number in all experiments. According to the graph, with increasing the froude number, the value of this ratio also increases, which in the maximum value is approximately equal to 85.5% energy loss. To determine the effect of rectangular blocks on changes in this energy loss ratio, parameter G is defined as Equation 19. According to Figure 15, the maximum value of this parameter is 84.8% and the minimum value is 0.8%.A diagram related to the dimensionless profile of the water surface shows that the profiles related to all experiments can be defined by a regression curve with a good approximation. The ratio of sequent depths of hydraulic jump with rectangular blocks to smooth bed decreases. This decrease is more noticeable within higher froude numbers. The maximum value of parameter D of the hydraulic jump in this study is equal to 9.4%, which indicates the effect of increasing the height and the distance between the blocks on the secondary depth of the jump. The maximum drop of flow energy on rectangular blocks is equal to 85.5%. Increasing the height of the blocks has a more effective role in reducing the flow energy than increasing the distance between the blocks.

    Keywords: Dissipate of flow energy, Hydraulic jump, Physical Model, Sequent depth, Zigzag block
  • Massoud Ghodsian *, Chonoor Abdi, Aram Ghafouri Pages 43-58
    Introduction
    With the increasing demand for water storage in recent years, the need to build structures such as dams has increased, which increases the likelihood of flooding with larger volumes (Anderson et al., 2013). Therefore, in order to increase the safety of dams, the need to build weirs with higher efficiency is felt more (Gonzalez and Chanson, 1995). Labyrinth weirs are hydraulic structures that are used to regulate the water level and control the flow in dam reservoirs. The crown axis of this type of weir is indirect and consists of walls attached to each other. The geometric shape of this type of weir is repeated in a triangular, trapezoidal, rectangular and bended plane with alternating widths. The main hypothesis in the design of this type of weir is to increase the weir capacity of the weir by increasing their crown length in a constant width and for a certain height of the water surface upstream of the weir (Lux and Hinchcliff, 1985). The piano key weir is a type of Labyrinth weir and is used as a suitable option to correct weirs that have difficulty in passing the maximum flow (Lempérière and Ouamane, 2003). In piano key weirs, unlike Labyrinth weirs, the openings are sloping inwards and outwards. Execution of this type of weirs requires less space than Labyrinth weirs, and therefore the foundation of this type of weirs can have smaller dimensions. This advantage has made it possible to use this type of weir on the canopy of concrete dams (Lempérière, 2017). Scour downstream of the weir can have a direct impact on the stability of the structure. For this reason, predicting the shape and dimensions of the scour hole at the downstream of these structures has been of interest to researchers. Therefore, in this paper, we compare scouring downstream of triangular and trapezoidal piano key weirs with changes in discharge and tailwater.
    Methodology
    Every experiment was conducted in a rectangular channel with a width of 75 cm, metal bed, glass walls and a height of 80 cm in the hydraulic laboratory of water and hydraulic structural engineering department of Tarbiat Modares University in Tehran. The intended PKW was set up and sealed at a distance of 1 m from the beginning of the channel bend. All experiments on the weir were conducted under free flow conditions. A layer of uniform sediments with an average diameter of 1.64 mm, a geometric standard deviation of 1.24, a height of 42.5 cm, and a length of 2 m was placed downstream of the weir. A Type-A triangular and trapezoidal piano key weir made of thermoplastic (common PLA Filament) with a thickness of 1.2 cm was utilized in this study. Each weir has 6 keys (3 inlet keys and 3 outlet keys), a width of 75 cm (the same as the channel), and the crest length and a height of respectively 50 and 20 cm. The experiments were conducted with two discharge values of 35 and 45 Lit/s and five tailwater depths from 8 to 18 cm a long 5 hours.
    Results and discussion
    Experimental observations show that there are two dominant currents in piano switch weirs: the inlet switch draws the approaching currents to itself and the current is discharged downward from the inlet crown. The second pattern is formed on the output keys. In this section, the current flowing through the outlet crown, like a jet, is discharged downstream of the sloping section of the switch. Also, the output current from the inlet switch hits the surface of the bed downstream and, due to the existing tailwater depth, appears as surface rotation (at low tailwater depth) and surface turbulence (at high tailwater depth). Part of the flow also deflects downstream and after colliding with the sediment bed surface, creates a weak rotational zone under the inlet switch. The flow pattern on the output switch is much more complex than the input switch. In this part of the weir, due to the intersection of the flow caused by the falling jets from the side crowns with the upstream outflow, the water level rises and when the outflow enters the downstream area as a falling jet, the rotating area It forms strongly in front of the output key. For this reason, sediments from the bed in front of the outlet switch are washed more often. Downstream of the weir, the flow passing through the sediment bed causes the bed to be washed away. The scouring site begins immediately after the weir wall. Over time, the dimensions of the hole become larger, and the jet passing through the hole becomes a rotational flow that helps to transport some of the sediment down to the downstream.
    Conclusions
    The results showed that at low particle Froude number, the maximum depth of the lower downstream scour hole of the triangular weir occurred closer to the weir than the trapezoidal model. However, with increasing the number of Froude, this trend has changed and the maximum depth of the scour hole and its position has occurred in less trapezoidal weir and at a closer distance to the triangular weir. In general, as the particle particle Froude number increases, the maximum parameters of the scour hole depth, its location, and the length of the downstream scour hole opening of both weir models increase. Equations with appropriate accuracy were obtained to predict the maximum depth of the scour hole, its location, the length of the scour hole and the scour of the lower wall of the weir wall for the two weir forms used. It was also observed that in all discharges and for each tailwater depth, the maximum distance between the hole depth to the weir foot and the length of the scour hole opening in the triangular model is on average 37% less and 15.5% more than the trapezoidal model. The data show that the geometric parameters of the downstream scour hole of the piano key weirs depend on the characteristics of the sediments, the discharge and tailwater.
    Keywords: experimental study, Scouring, Hydraulic flow conditions, piano key weir
  • Mahdi Majedi Asl *, Mehdi Fuladipanah, Rana Zifar, Zahra Gasami Pages 59-72
    Introduction

    Weirs are commonly used to measure flow, divert flow, and/or control flow water conduits. Although weirs are generally designed to run under free-flow conditions, they can become submerged under certain conditions. Weir submergence occurs when the downstream water level exceeds the crest elevation. Relative to traditional linear weirs (e.g., ogee crest), the use of nonlinear weirs to increase the flow capacity in discharge channels of limited width without much increasing the required Ho is becoming more common. Typical nonlinear weirs include labyrinth and piano key (PK) weirs which the second one has been considered in this paper. When deciding between a labyrinth and a PK weir for a channel application, the potential influence of submergence, along with the free-flow discharge capacity of both weirs, must be considered. Little works have been conducted on the submergence effects of PK weirs. This paper aims to describe an intelligent method to extract the head-discharge relationship in standard and modified Piano key weirs under submerged conditions. Support vector machine and gene expression programming intelligent algorithms were utilized to predict submerged head-discharge relationship using Dabling et al. (2014) experimental data. In the end, a comparison has been performed among SVM, GEP, and experimental based predictors using assessment criteria.

    Methodology

    Gathered data were from a laboratory flume measuring 0.93 m wide, 0.61 m deep, and 7.4 m long. A stilling well with a point gauge (readable to ±0.15 mm) was hydraulically connected to the flume sidewall at a distance of 4P times the weir height, (approximately 0.8 m) upstream of the weir for measuring the piezometric head level (ho and h*). A second stilling well with a point gauge connected to the flume 10P (approximately 2.0 m) downstream of the weir was used to measure the downstream piezometric head (hd). Both Ho and Hd were calculated by adding the velocity head (U2/2g) corresponding to the average cross-sectional velocity at the respective measurement locations. For the submergence investigation, variations in tailwater elevation were produced using an adjustable gate located 15P (approximately 3.0 m) downstream of the weir. A calibrated orifice meter located in the 305 mm diameter supply piping was used to accurately measure the weir discharge (± 0.2%). Repeating variables were opted as upstream flow velocity, Uu, downstream flow velocity, Ud, upstream flow depth relative to weir peak under free condition, ho, upstream flow depth relative to weir peak under submerged condition, h*, downstream flow depth relative to weir peak under submerged condition, hd, total free flow head relative to the weir crest, Ho, total submerged flow head relative to the weir crest, H*, weir height, P, gravity acceleration, g, specific mass of flow, ρ, water viscosity, µ, and water surface tension, σ. The dimensionless linear independent parameters were extracted as follow with omitting the viscosity and surface tension effects (Eq. 12)Where Frd and Fru are downstream and upstream Froud numbers, respectively. Various combination of dimensionless parameters were examined to check the best performance of the SVM and the GEP algorithms to predict H^*/H_o using root mean square error, RMSE, determination coefficient, R2, mean normalized error, MNE, and Developed Discrepancy Ratio, DDR.

    Results and Discussion

    Two intelligent algorithms, i.e. SVM and GEP, were trained and tested using laboratory data from Dabling et al. (2014). The share of training and testing percent od measured data for the SVM were 60% and 40% and those of the GEP were 70% and 30%, respectively. Superior combination for the SVM to predict H^*/H_o included H_d/H_o andH_o/P for both PK-S and PK-M. The values of (RMSE, R2, MNE) for the train and the test phases for PK-S and PK-M were (0.008, 0.9996, 0.234), (0.002, 0.9989, 0.237), (0.098, 0.9833, 0.308) and (0.0918, 0.9899, 0.282), respectively. The opted dimensionless parameters for the GEP predictor included all four mentioned parameters in equation (1). The corresponding values of above mentioned criteria for train and test phases were calculated (0.0070, 0.9999, 0.3284), (0.0180, 0.9991, 0.3127), (0.0099, 0.9984, 0.2433) and (0.0097, 0.9998, 0.1825) respectively. A comparison was done between intelligent predictors and experimental equation extracted by Dabling et al., (2014). Their analogy was performed using standardized DDR values for every three predictors, i.e. ZDDR. The amount of the maximum values of ZDDR was obtained 8.517, 6.582, and 4.098 for the SVM, the GEP, and the experimental predictor, respectively. The results showed that the SVM intelligent algorithm has superiority than to the others.

    Conclusion

    Dispite the high values of experimental studies, the results showed that using artificial and intelligent algorithm is more practical to extract the hidden relationship among dependent and independent variables (Three-dimensional and complex flow over these weirs) for achieving high accuracy prediction. The results showed that the SVM and GEP as intelligent algorithms leads to very accurate results.

    Keywords: Support Vector Machine Algorithm, Gene Expression Programming Algorithm, Submerged flow, Piano-Key Weir
  • Shima Abolfathi *, Seyed Mahmood Kashefipour, Mahmood Shafai Bejestan, David R. Fohrman Pages 73-90
    Introduction

    The pier group is one of the important hydraulic structures that the scouring around them is affected not only by the flow characteristics, but also by their number and arrangement. Each pile in a group has an individual scouring mechanism that can influence the other piles in the group. The following are mechanisms that make pier group scouring more complicated than a single pile: 1) sheltering, 2) reinforcement, and 3) horse-shoe vortex compression (Nazariha, 1996).More recent attention has focused on the arrangement and geometric variables and their effects on the scouring size and process in steady flow. Several reviews of the angle of attack, spacing, numbers, and pier diameter have been undertaken (Hannah, 1978; Nouh, 1986; Vittal et al., 1994).As seen, most studies in the field of scouring around pier groups have only focused on steady current, and there is a relatively small body of literature that is concerned with scouring in pier groups in unsteady flow, while floods, waves and unsteady flows are the most destructive phenomena in rivers and coastal environments. This paper uses the experimental investigation of three piers in the tandem arrangement as a pier group and analyses the impact of hydrograph unsteadiness on scouring with different pier spacing in the clear-water regime and investigate the time variation of the scouring depth to understand the scouring process around pier groups in unsteady flow.

    Methodology

    The experiments were conducted in a flume 10 m in length, 0.74 m in width and 0.6 m in depth at the Hydraulic Laboratory of Shahid Chamran University. In the flume a pump was used to drive the water from an underground reservoir to a head tank. A false bed was built at the bottom of the flume with 0.15 m height, with a 1.7 m length sand bed located 2.8 m from the inlet. The sediment part of the bed was filled with d50=0.7 mm uniform sand (Geometric standard deviation of the sand size(σ)=1.3) and the other parts were covered with the materials as rough as the sand.In this study, 36 experiments were done to evaluate the pier group scouring, which included 9 tests of steady flow in different discharge and pier spacing, and 27 tests of unsteady flow in different peak discharge, time duration and pier spacing. It is worth mentioning that all experiments were performed in the clear water regime.During the experiments, four cameras (Full High Definition (FHD) resolution) recorded the scouring process from four different angles to investigate the temporal changes (Fig. 4). All piles were scaled to extract the scouring depth from the videos and remove the light deflection effect in the water.

    Results and Discussion

    Steady flow

    results

    What stands out from the steady flow experiments investigation is that the scour depth around the first pier was more than the next one due to the flow attack. In other piers, because of the previous pier's protection, the scour depth was less than the first one. As shown in Figure 4, the scour depth changing rate decreased earlier at lower discharges, which may be due to the lower flow intensity to continue the scouring process. Early in the second and third pier scouring process, the scouring depth remains constant for a while, which is due to the eroded sediments from the previous pier into the next pier's scouring hole and the equal amount of deposited and eroded sediment. This issue is also seen in figures of Mahjoub et al.'s (2014) research.
    Unsteady flow

    results

    The scouring depth around each pier gradually increases with increasing flow discharge during the hydrograph's rising limb. This increase occurred at the beginning of the process slower than the steady flow due to a gradual increase in flow discharge and, consequently, a gradual increase in flow intensity and shear stress to erode sediments around the pier (fig 5-8).In the unsteady flow experiments, the first pier's scouring process was gradually stopped after the peak discharge and during the falling limb due to the decrease in flow discharge. However, evaluating the recorded videos from the scouring process angles and the extracted data showed that the process proceeded differently for the second and third pier in some experiments. In these cases, four conditions around the pier were occurring by reducing the flow discharge in the falling limb. These conditions caused new phenomena called backfilling in this study..ufficient height of deposition region resulting from previous pier scouring.Sufficient flow intensity for erosion and moving the sediment Short distance for sediment to reach the next pier scouring hole. weak vortex of the next pier to re-erode the entered sediments into the hole

    Conclusion

    Evaluating the scouring hole's temporal variation during the unsteady flow shows that the scouring process around the pier group in unsteady flow can differed from steady flow around rear piers and caused a new phenomenon, which is called backfilling. This difference is due to the extra mechanisms in the pier group scouring process, and the flow changes during the hydrograph and changed with changing the pier spacing.

    Keywords: Unsteady flow, Scouring, Bridge pier group, flood hydrograph, Time variation
  • Hoda Nabavi Pages 91-105
    Introduction
    Hydraulic jump occurred widely in most of hydraulic structures, such as spillways in high dams, downstream ‎weirs and sluice gates, where is high velocity, the condition of occurrence of a hydraulic jump is to change flow suddenly from ‎supper critical flow (low depth with high velocity) to subcritical flow (high depth with a low velocity). Stilling basin must be designed perfectly to ensure efficient operating over a wide range of flow. Additional devices may be used to ‎stabilize the jump, reduce the length and height of the jump and increase the energy dissipation. ‎‎ Baffle blocks one of these devices which used to stabilize the jump and dissipate energy as a result of impact action. Baffle block ‎used with different shapes such as cubic and trapezoidal (trapezoidal shape in section), the cubic shape is effective when the best ‎dimensions of height, width, spacing, and the best location in the basin were used. United States Department of the Interior Bureau ‎of Reclamation (USBR) recommended that the corners of baffle block must be not be rounded because the corners are effective in ‎producing of eddies which help in energy dissipation. Previous studies showed that, the model of baffle blocks which have an ‎ability to circulate the jet of water in the vertical transverse direction behave best than others for dissipation of energy, also the ‎rotation in jet of water prevents the jump action to the extent, in this case there is a complete energy dissipation and reduction in the ‎stilling basin length.‎However, an insufficient number of studies on gabion baffle blocks and gabion end sill have been developed more recently ‎compared with ‎studies on fixed baffle blocks and fixed end sill.‎ Also, another insecurity that exists for the baffle blocks of stilling ‎basin is cavitation around them, which can be reduced if gabion baffles are used due to changes in the flow pattern conditions.‎In this research a hydraulic jump stilling basin equipped with baffle blocks and end sill in two condition was to be tested in ‎laboratory to determine the dissipation and other characteristics of hydraulic jump for various type of baffle blocks and end sill. In ‎one condition the bed and baffle blocks and end sill of stilling basin were rigid and in the other condition the bed was rigid but the ‎baffle blocks and end sill were permeable and were constructed with gabion by different porosity.‎
    Methodology
    Experiments were carried out at the Hydraulic Laboratory of the Faculty of Engineering, Bu-Ali Sina ‎University of Hamedan in a flume 15 m long and 0.6 m wide and 0.6 m deep. In this research a hydraulic jump stilling basin ‎equipped with baffle blocks and end sill in different conditions. The bed of stilling basin was rigid but various type of baffle blocks ‎and end sills with different permeability were used. The concrete was used for constructing rigid baffle blocks and rigid end sill and ‎gabion was used for constructing baffle blocks and end sill by 30, 45 and 60 percent permeability. Sand and gravel were used to ‎make permeable baffle blocks and end sills. A sluice gate was used for creating of flow by high velocity and low depth to create ‎high Froude Number. The sluice gate was placed in 8 meters from beginning of flume. The tailwater depth was adjusted by a ‎butterfly gate at the end of flume.‎The Baffle blocks and end sill dimension and positions were according to USBR III recommendations. All experiments were done ‎in three Froude numbers of 3.8, 4.3 and 5.1. The flow depth was measured on a grid 5 cm5 cm using a depth gauge with an ‎accuracy of 0.1 mm. ‎
    Results and discussion
    After measuring the flow depth, the parameters of conjugate depth ratio, relative depth, relative ‎length, relative energy loss and water surface profile for hydraulic jumps formed in the stilling basin with rigid floor and baffle ‎blocks and end sill with different porosities 0, 30, 45% and 60% were calculated. Then the changes of these parameters were ‎investigated according to the Froude number of the inlet flow to the stilling basin. Advantages shows that by increasing the porosity ‎of baffle blocks and end sill. The results show that by increasing the porosity of the baffle blocks and end sill, the ratio of conjugate ‎depths decreases and the amount of this decrease increases with increasing the Froude number of the inlet flow to the stilling basin. ‎So that for Froude number equal to 5 and porosity 60% of baffle blocks and end sill, this reduction reaches about 40%. The change ‎in the relative depth and relative length of the hydraulic jump has a similar trend to the conjugate depth due to the increased porosity ‎of the baffle blocks and the end sill. For the Froude number equal to 5 and the porosity to 60% of the baffle blocks and the end sill, ‎the relative length and relative depth of the hydraulic jump are reduced by about 77% and 22%, respectively. While the relative ‎energy loss increases with increasing the porosity of the baffle blocks and the end sill and reaches about 45% for Froude number ‎equal to 5 and porosity 60%. ‎
    Conclusion
    In this study, in addition to rigid baffle blocks and rigid end sill, the permeable baffle blocks and permeable end ‎sill with porosities of 30 45 and 60 percent were used in the USBR type III stilling basin. Then the important parameters of ‎hydraulic jumps in stilling basin were computed and compared for different Froude number. The results show that the permeable ‎baffle blocks and permeable end sill by changing the flow pattern in the stilling basin reduces the relative depth and relative length of ‎the hydraulic jump, while increasing the relative energy losses. The results also show which increasing the permeability of ‎baffle ‎blocks and end sill increases the relative energy losses and decreases relative depth and relative length of hydraulic jumps.‎
    Keywords: Hydraulic jump, Stilling basin, porosity, Baffle blocks, End sill
  • Aida Shabani, Hossein Khozeymehnezhad *, Mohsen Pourreza Bilondi, Y. Ramezani Pages 107-121
    Introduction

    Due to the height of the dams, water behind dams have high energy and velocity on the spillway is high. Downstream of the spillway as a result of high energy and velocity of water on the spillway, is at the risk of cavitation and damage. The study of cavitation is crucial in this respect, and indicates the amount of flow degradation in the structure. Various works have been conducted on how to eliminate cavitation. Given the nature of cavitation, caused by high speed and pressure reduction, the use of roughness in parts of the spillway can help reduce or eliminate this phenomenon. This study aimed at investigating the effect of roughness under different conditions on changes in cavitation index in the downstream peak body.

    Methodology

    To achieve a better understanding of how roughness functions, this research was carried out by changing its arrangement, number and different heights on the cavitation index using a laboratory model. In order to achieve a more real-life simulation, a spillway was installed at a distance of 5.5 m from the opening of the canal to ensure the flow is expanded and that the turbulence of incoming current is minimized. Peak spillway was considered in the study, designed and constructed according to USBR standards. Eight holes were installed on the spillway which were connected to 8 piezometers located in the channel body through flexible pipes to read the amount of pressure static. Effective parameters were identified with dimensional analysis, and three parameters (roughness arrangement, number of roughnesses, effective height of roughness) were tested. The roughness used in this research is made of PVC. After installing the spillway in the canal, the roughness was installed on the spillway. The piezometers were ventilated before each experiment. The channel slope was adjusted. Then, the pump was turned on, and after adjusting the flow rate, the test began. The depth gauge was calibrated for each aperture to measure and correct the height on the apertures. The equivalent pressure height inside the piezometer tubes was read and adjusted for the piezometer base and channel slope. Finally, according to the data, the roughness performance was evaluated using the cavitation index.

    Results and Discussion

    The experiments of the present study were performed with different Froude numbers and slopes. After the control experiments, the experiments were evaluated in three modes: the effect of arrangement, number and effective height.• Evaluation of cavitation index changes in control experiments:Observations show that cavitation index decreases as water falls on the spillway. The minimum cavitation index in the control experiment occurs at point 8. Moreover, the average cavitation index increases compared to the control mode by placing the roughness.• Investigation of roughness arrangement on the cavitation index:Observations show that the placement of roughness with convergent, divergent and row arrangement increase the cavitation index compared to the control. In the Froude number of 1.08, the changes in the cavitation index range from 1 to 8, 3.7, 4, 4.2, 4.4, 4, 3.7, 3.8 and 3.5%, respectively, compared to the case. • The number of roughnesses on the cavitation index:By placing 9, 12, 15 and 18 roughnesses in the row arrangement, the observations showed that in all graphs, the cavitation index increased compared to the control. Moreover, with the number of roughness, the cavitation index has a slight increasing trend. With 18 roughnesses in the flow rate of 1.08, the increase in the percentage of cavitation index (compared to the control) was piezometric points 1 to 8, 11.1, 4.03, 12.3, 17.6, 4.4, 4, 3.7 and 7.1.• Investigation of effective roughness height on the cavitation index:Considering the three effective heights of roughness, the observations showed that in all three cases, there is an increase in the cavitation index compared to the control mode, and the most evident change in the effective height has occurred at 0.017. With 1.08% increase in the flow rate of cavitation index compared to the control condition, 1 to 8, 7.5, 4, 12.7, 26.9, 4.1, 3.8, 7.3 and 6, respectively were obtained.

    Conclusion

    In general, it can be concluded that the installation of roughness on the spillway, the effective height of roughness, the number of roughnesses and its various arrangements, increase the cavitation index compared to the control. The presence of roughness reduces the flow velocity and increases the pressure on the spillway. This issue has a key role to play in eliminating or mitigating the cavitation phenomenon on the spillway. Compared to the control, the average cavitation index increased by 15.17% in the convergent arrangement, 11.8% in the divergent arrangement and 16.11% in the row arrangement. The results show that the greatest change in row arrangement and effective height occurs at 0.017 and n = 18.

    Keywords: Cavitation Index, Laboratory model, Ogee-Spillway, Roughness