فهرست مطالب

مهندسی عمران و محیط زیست دانشگاه تبریز - سال چهل و پنجم شماره 1 (پیاپی 78، بهار 1394)

نشریه مهندسی عمران و محیط زیست دانشگاه تبریز
سال چهل و پنجم شماره 1 (پیاپی 78، بهار 1394)

  • تاریخ انتشار: 1394/04/05
  • تعداد عناوین: 6
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  • بهمن ارشد شب خانه*، حبیب حکیم زاده صفحات 1-13
    وجود خطوط لوله در محیط بستر دریا سبب تغییر الگوی جریان در مجاورت آن ها شده و نیز موجب به وجود آمدن گردابه هایی در قسمت های جلو و پشت لوله گردیده که همراه با افزایش شدت آشفتگی است. این تغییرات می توانند منجر به خستگی سازه و یا آبشستگی در اطراف آن گردند و نهایتا پایداری سازه را تهدید نمایند. در این مقاله، به منظور بررسی کنش لوله روی جریان، تغییرات به وجود آمده در الگوی جریان اطراف خطوط لوله فراساحلی نیمه مدفون به صورت آزمایشگاهی و عددی در حالت جریان دائمی مورد بررسی قرار گرفته اند. جهت مدل سازی تجربی، آزمایش هایی در آزمایشگاه تحقیقاتی هیدرولیک انجام شده است. آزمایش ها در یک کانال آزمایشگاهی و با استفاده از یک لوله PVC برای نسبت های متفاوت عمق دفن شدگی به قطر لوله انجام گرفته است. جهت مشاهده الگوی جریان از ذرات پلی استایرن استفاده شده و نیز به منظور کمک به درک فیزیکی پدیده از کلیه مراحل انجام آزمایش ها به وسیله دوربین دیجیتال، فیلم برداری شده است. در بخش شبیه سازی عددی نیز از روش حجم محدود استفاده شده و میدان جریان با استفاده از نرم افزار دینامیک سیالات محاسباتی FLUENT تحلیل شده است. ایجاد هندسه و شبکه بندی مدل نیز به وسیله پیش پردازنده GAMBIT صورت گرفته است. سرانجام نتایج عددی به دست آمده با نتایج تجربی این پژوهش و سایر پژوهشگران مقایسه شده اند که تطابق نسبتا خوبی حاصل شده است. نتایج تجربی و عددی نشان دادند که با افزایش نسبت عمق دفن شدگی به قطر لوله، مقادیر طول نواحی جدایی در بالادست و پایین دست خطوط لوله در حالت منفرد و تاندوم کاهش می یابد. همچنین با افزایش عمق دفن شدگی، از مقدار سرعت های بیشینه مثبت در بالای خط لوله و نیز از سرعت های بیشینه منفی در محل تشکیل گردابه ها کاسته می شود که نتیجه امر کاهش تنش برشی بستر را در پی خواهد داشت. بنابر این می توان پیش بینی نمود که با افزایش عمق دفن شدگی مشکلات ناشی از فرسایش و آبشستگی کاهش خواهند یافت.
    کلیدواژگان: الگوی جریان، خطوط لوله فراساحلی، شرایط تاندوم، مدل آزمایشگاهی، شبیه سازی عددی، روش حجم محدود
  • بابک لشکرآرا*، علی لشکرآرا، منوچهر فتحی مقدم صفحات 41-50
    جریان خروجی از سیستم های تخلیه سیلاب اغلب به صورت جت می باشد. بسته به عمق پایاب، جت می تواند به صورت آزاد یا مستغرق عمل نماید. هرگاه مقدار تراز پایاب از تراز جت بیش تر باشد، جت به صورت مستغرق عمل می نماید. ابعاد و مشخصات حفره آبشستگی متاثر از متغیرهای متعددی از قبیل پارامترهای جریان، مشخصات بستر آبرفتی، زمان و هندسه آبراهه و همچنین ارتفاع ریزش می باشد. در این تحقیق به بررسی ابعاد حفره آبشستگی تحت اثر جت های قائم دایره ای مستغرق پرداخته شده است. در پژوهش حاضر از مصالح شن ریز یکنواخت با قطر متوسط 1/ 11 میلیمتر استفاده شده است. جهت انجام آزمایش ها، سناریوهای مختلفی با تغییر در ارتفاع ریزش جت مستغرق نسبت به بستر اولیه رسوبات و همچنین تغییر در سرعت جریان خروجی از جت تدوین گردید. از بررسی روند تغییرات عمق و طول نسبی متعادل شده آبشستگی در مقابل عدد فرود جت در حوضچه استغراق ملاحظه می گردد که با افزایش عدد فرود جت، میزان عمق و طول نسبی متعادل شده حفره آبشستگی افزایش می یابد. از طرفی نتایج نشان می دهند که افزایش یک درصدی ارتفاع نصب جت منجر به کاهش 33/ 0درصدی تفاضل نسبی عمق آبشستگی دینامیکی و استاتیکی خواهد شد.
    کلیدواژگان: آبشستگی دینامیکی، آبشستگی استاتیکی، جت قائم، نازل، فرود جت
  • مجید منتصری *، بابک امیرعطایی صفحات 51-63
    توابع توزیع عمومی (Generalized distribution functions) برای پیش بینی احتمالاتی خصوصیات مختلف خشکسالی در شمال غرب ایران با استفاده از روش شبیه سازی مونت کارلو، تئوری ران و شاخص بارش استاندارد (SPI) توسعه داده شده اند. چنین هدفی صرفا بر اساس داده های تاریخی یا ثبت شده بارندگی کاملا غیر ممکن به نظر می رسد، چرا که داده های تاریخی، بدون در نظر گرفتن طول دوره آماری آن ها، تنها یک سری یا نمونه ای از هزاران سری ممکن جامعه آماری داده ها محسوب می شوند. بنابر این، یک روش استوکستیکی به طور وسیع برای تولید 1000 سری زمانی بارندگی در دوازده ایستگاه سینوپتیک در شمال غرب ایران استفاده شده است. داده های مصنوعی تولید شده، به عنوان پایه ای برای پایش خشکسالی جهت مشخص کردن مجموعه ای از ویژگی های خشکسالی ممکن از قبیل مدت، شدت، بزرگی و فواصل بین دو خشکسالی متوالی، به کار گرفته شده و توزیع احتمالی ویژگی های مختلف خشکسالی بر اساس شاخص SPI و ماتریس احتمال انتقال رخداد های خشکسالی توسعه یافته است. نتایج نشان داد که انتظار خشکسالی هایی با تداوم پنج سال یا بیشتر در منطقه مطالعاتی تقریبا نزدیک به صفر بوده است. همچنین بررسی همگرایی خشکی سالیانه با ماه های مختلف سال نشان داد که ماه های پر باران سال نقش اصلی در تعیین موقعیت خشکی سال ایفا نموده و بقیه ماه های سال که به عنوان ماه های کم باران مطرح هستند، تقریبا نقش بسیار ناچیزی دارند. همچنین نتایج مطالعه موید محدودیت اساسی داده های تاریخی در مطالعات پایش خشکسالی و ضرورت به کارگیری روش مونت کارلو برای استنتاج های دقیق و واقعی از پدیده خشکسالی هستند.
    کلیدواژگان: خشکسالی، روش مونت کارلو، ماتریس احتمال انتقال، شاخص بارش استاندارد
  • سیدروح الله موسوی *، محمدرضا اصفهانی، مهر الله رخشانی مهر، سیدحجت الله موسوی، بنیامین قربان زاده صفحات 65-77
    خسارت در سازه موجب کاهش سختی آن می شود. در تیرهای مسلح شده با میلگردهای GFRP به دلیل مدول الاستیسیته کم این میلگردها، کاهش سختی پس از ترک خوردگی شدیدتر خواهد بود. برای ارزیابی وضعیت سازه های موجود پس از ایجاد خسارت باید مدل اجزای محدود آن ها به هنگام شود. از تحلیل مدل به هنگام شده بر اساس پارامترهای ارتعاشی، مقاومت سازه خسارت دیده در مقابل بارهای موجود بررسی و نقاط ضعف آن برای تقویت مشخص می شوند. در این مقاله، یک روش عملی شناسایی خسارت معرفی می شود. با استفاده از الگوریتم ژنتیک، توزیع سختی تیر به گونه ای تخمین زده می شود که فرکانس ها و شکل های مود به دست آمده از مدل تحلیلی کمترین خطا را در مقایسه با مقادیر آزمایشگاهی به دست آمده از آزمایش مودال داشته باشد. برای این منظور 10 نمونه آزمایشگاهی از تیرهای مسلح شده با میلگردهای GFRP ساخته شده است. نمونه های مذکور شامل دو گروه با وصله و بدون وصله می باشند که در آن ها میلگرد عرضی در طول وصله، مقاومت بتن و نسبت میلگرد طولی به عنوان متغیر در نظر گرفته شده اند. آزمایش استاتیکی، با هدف ایجاد خسارت صورت می گیرد. در بین هر گام بارگذاری استاتیکی، آزمایش مودال انجام می گیرد. با استفاده از این آزمایش تغییرات پارامترهای ارتعاشی در گام های مختلف خسارت ارزیابی می شود. همچنین، مقادیر تجربی فرکانس ها و شکل های مود برای استفاده در تابع هدف بهینه سازی و به هنگام سازی سختی تیر خسارت خورده برداشت می شوند. نتایج نشان می دهند که مقادیر ممان اینرسی تخمین زده شده با وضعیت ترک خوردگی نمونه های آزمایشگاهی در همان سطح بارگذاری هم خوانی دارند.
    کلیدواژگان: آزمایش مودال، الگوریتم ژنتیک، انحنای مودال، بهینه سازی، شکل مود، فرکانس، میلگردهای GFRP
  • سهراب کریمی*، حسین بنکداری، امیرحسین زاجی صفحات 93-102
    آبگیر های جانبی برای انحراف و انتقال جریان در سیستم های هیدرولیکی استفاده می شوند. نصب فلومتر ها یکی از رایج ترین روش های اندازه گیری سرعت و یا دبی در کانال های روباز می باشد. فلومتر ها به کمک اندازه گیری سرعت متوسط در حجم محدودی از جریان با استفاده از یک ضریب کالیبراسیون، سرعت متوسط مقطع را محاسبه می کنند. در نزدیکی محل آبگیر به دلیل ماهیت سه بعدی و پیچیده جریان و وجود جریان های ثانویه قوی در مقطع عرضی، سرعت اندازه گیری شده توسط فلومتر در ناحیه محدود مورد اندازه گیری توسط سنسور، با سرعت متوسط واقعی کانال اختلاف دارد. اما با وجود این اختلاف، میانگین سرعت های اندازه گیری شده توسط فلومتر مطابقت نسبتا خوبی با سرعت متوسط واقعی کانال دارد. سرعت جریان های عبوری و ابعاد هندسی کانال های فرعی و اصلی بر روی اختلاف بین سرعت اندازه گیری شده توسط فلومتر و سرعت متوسط واقعی جریان موثر هستند. در این مطالعه، مدل آزمایشگاهی آبگیر جانبی به صورت سه بعدی با استفاده از نرم افزارANSYS-CFX، شبیه سازی شده است. بعد از صحت سنجی با استفاده از مدل عددی و نتایج مدل آزمایشگاهی، دقت اندازه گیری فلومتر در نسبت عرض های مختلف کانال اصلی به کانال فرعی مورد بررسی قرار گرفت. نتایج نشان می دهند که با افزایش نسبت عرض کانال فرعی به کانال اصلی از 6/ 0 تا 1، حداکثر خطای اندازه گیری فلومتر از 18 درصد تا 139 درصد افزایش می یابد. با افزایش بیشتر عرض در کانال فرعی به دلیل کاهش سرعت، میزان خطای فلومتر کاهش می یابد، به طوری که در نسبت عرضی 4/ 1 این خطا به 47 درصد می رسد.
    کلیدواژگان: آبگیر های جانبی، فلومتر، سرعت متوسط جریان، نسبت عرض ها، ANSYS، CFX
  • عباس یگانه بختیاری *، علی پورزنگبار، فاطمه حاجی ولیئی صفحات 115-122
    آبشستگی در پای سازه های ساحلی یکی از عوامل اصلی آسیب یا خرابی این سازه ها می باشد. بنابر این، تخمین دقیق عمق بیشینه آبشستگی در پای سازه های ساحلی از اهمیت زیادی برخوردار است. در این مطالعه، از روش روش برنامه ریزی ژنتیک برای تخمین عمق بیشینه آبشستگی استفاده شده است. برای آموزش و آزمایش مدل های ایجاد شده به وسیله شبکه عصبی و برنامه ریزی ژنتیک از 45 مجموعه داده که از مقالات منتشر شده استخراج شده اند استفاده شده است. برای مقایسه عملکرد مدل های ایجاد شده و روابط موجود از شاخص های آماری مانند ضریب همبستگی، جذر میانگین مربعات خطا و ضریب پراکندگی استفاده شده است. نتایج نشان می دهند که روش برنامه ریزی ژنتیک مدل های به مراتب دقیق تری نسبت به روابط تجربی ارائه می دهد. علاوه بر این، از آن جائی که برنامه ریزی ژنتیک رابطه ای صریح بین متغیرها ارائه می کند می تواند به عنوان یک معیار برای تخمین عمق آبشستگی استفاده شود.
    کلیدواژگان: برنامه ریزی ژنتیک، روابط تجربی، سازه ساحلی، عمق آبشستگی
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  • Bahman Arshad Shabkhaneh*, Habib Hakimzadeh Pages 1-13
    1.
    Introduction
    he ever-increasing need to fossilized fuel has caused a rapid development in offshore industries. One of the most important offshore structures that have extensively been used for transporting oil and gas products is pipeline. On the other hand, fatigue of these structures mainly causes huge evil economic and environmental consequences. The pipelines lying at sea bed normally cause variations in flow pattern around them and also create eddies in the front- and backward of pipeline which is along with an increasing in turbulence intensity 1]. These variations can lead to the fatigue in structure or scour around it and eventually threaten structural stability [2]. In this paper, in order to consider the action of pipe on flow, the caused variations on flow pattern around the semi-buried offshore pipelines due to steady current have experimentally and numerically been investigated.2.
    Methodology
    2.1. Experimental studyGenerally, the main aim of doing the laboratory tests was to find out the separation lengths at the upstream and downstream of the pipelines in tandem positions for different burial depth-diameter ratios (i.e., G/D). The experiments have been conducted in the Hydraulic Research Laboratory. For the experimental section, a number of tests have been carried out in a flume with 10 meters length, 0.3 meters width and 0.5 meters depth using P.V.C pipes with 6.35 centimeters in diameter at steady state flow condition and for different burial depth-diameter ratios (i.e., G/D) and for the single and double pipelines. To visualize the flow patterns, the polystyrene particles with 1.05 gr/cm3 in density have been used (Fig. 1). In order to help to physical understanding of the phenomenon, the whole processes of tests have been recorded using a digital camera.2.2. Numerical modeling For the numerical modeling, the flow field has been analyzed using a computational fluid dynamics software, called FLUENT. For this software, the governing equations have been discretized using the finite volume method. The algebraic equations have then been solved using simple pressure-velocity coupling method. For the turbulence model, the two-equations k-ε RNG model has been deployed to calculate the Reynolds stresses. Geometry and mesh generation processes have also been done using a preprocessor software, called GAMBIT. The used discritized methods and under relaxation coefficients are shown in Tables 1 and 2, respectively.3.
    Results And Discussion
    The numerical model results were first verified against the experimental and numerical model results of the other researches and it was found that the simulation model results of the current study were in good agreements with the experimental data of the other researchers. Then, the results of numerical models were compared with the test data of the current study and some relatively good agreements were achieved (Table 3). In this regard, it was found that the maximum discrepancy between the experimental and numerical model results for the reattachment length was generally less than 17% and only in two cases for single pipeline it increased up to 25%.4.
    Conclusions
    The main results of this research study may be summarized as: 1. Three separation zones (one at upstream and two at downstream) around a single pipeline were generally observed.
    Keywords: Flow pattern, Offshore pipelines, Experimental model, Numerical simulation, Finite volume method
  • Babak Lashkar‐Ara*, Ali Lashkar‐Ara, Manoochehr Fathi‐Moghadam Pages 41-50
    1.
    Introduction
    In the field of hydraulic research, bed erosion is of considerable importance because it is necessary to estimate and control erosion near hydraulic structures [1]. The cause of erosion in many conditions could be flow concentration as in a high velocity jet. The structures involved in hydraulic science are subjected to scour around their foundations. If the depth of scour becomes significant, the stability is endangered 2]. Therefore, study of maximum scour depth is required for the safe and economic design of hydraulic structures and their foundations. Research on erosion by jets has been mainly empirical because of the complex nature of the flow and its interaction with the sediment bed. Because of three dimensional intrinsic characteristics of turbulent flows in energy dissipation studies, and also problematic aspects of mathematic governing equations of the study, researchers have to focus on physical model. The model generally has an ability to respond the complexities of the subject. Not to mention that it needs expert people to be involved including its relative high costs. The effects of the variation of hydraulic condition on the scour hole in the plunge pool are investigated in present study using a physical model.2.
    Methodology
    The purpose of this study is the investigation of the variation of hydraulic condition and tailwater depth on the scour hole in the plunge pool by a submerged circular vertical jet. Therefore, a physical model was prepared. The model had an electromagnetic flow meter and pressure transducers. A slice gate was used for regulating tailwater depth. Experiments were conducted in a pool with 2m length, 1m width and m depth. Fig. 1 shows the experimental system of this research. Discharge was transported to the nozzle by a circular pipe with 4 inch diameter. For simulating a vertical jet, a roller for the nozzle was fixed at 90º. Tailwater depths were regulated at 0.325m, 0.385m and 0.435m [3]. The equilibrium time of scouring was determined for five times. For data acquisition of bed profile, a laser meter was used. Buckingham π theorem is used for determining effective parameters of scour hole as shown in Fig. 1. 3. Experimental: Results The experimental conditions were regulated to evaluate the effect of jet depth on the jet Froude number. After the equilibrium time, scouring dynamic depth was measured using a point gage. Scour profile was recorded using a laser meter after stopping the jet and filling the pool out. 4.
    Discussion
    The results of the experimental study on scour under submerged circular vertical jet were presented. It is noticeable that by variation of jet Froude number between 4 to 7, the relative scour hole length and depth are changed between 0.5 to 0.7, and 0.2 to 0.4, respectively. The present study extends the range of existing experimental data by involving jet diameters, different sediment size (gravel), and jet distance to bed resulting in much more complete conclusion than in all previous experimental studies.
    Keywords: Dynamic scouring, Static scouring, Vertical jet, Nozzle, Jet froude number
  • Majid Montaseri *, Babak Amirataee Pages 51-63
    1.
    Introduction
    In recent years, droughts have been occurring more frequently, and their impacts are being aggravated by the rise in water demand and the variability in hydro-meteorological variables due to climate change. As a result, probabilities of different characteristics of drought have a great importance in planning and managing water resource systems to cope with the effects of droughts [1]. A lot of researchers have focused to investigate drought frequency analysis, and most of them are based on historical data record or Markov chain model. But the Markov first order model cannot reproduce the observed persistence of annual rainfalls and the correlation structure among rainfalls in different months, although the correlation between any two consecutive months is reproduced. Therefore, both short and long timescale drought behavior investigation must be accomplished using a stochastic procedure such as Valencia-Schaake disaggregation model that is able to reproduce both characteristics of annual rainfalls and all correlations among monthly rainfalls in the same year [2].2. Methodology2.1. Study area and data analysis:In this study, the monthly and annual time series of rainfall of twelve synoptic stations were used as base stations geographically located in the northwest of Iran. The rainfall data series had a 50-year statistical period (1961-2010). First, the rainfall data records were checked using a number of initial statistical tests. Then, the Pearson type III is found the most appropriate distribution of monthly and annual rainfalls at all stations using the PPCC test.2.2. Stochastic data generation procedure:In this study, annual and monthly rainfall data are required to investigate drought characteristics at both annual and monthly levels. However, efforts must be made to ensure that annual and within year statistical characteristics are equally preserved in the generated sequences; hence rather than generating monthly rainfalls directly, annual rainfalls were first generated based on AR (1) model and later disaggregated to monthly rainfalls using the Valencia- Schaake approach. For each of the twelve synoptic stations, 1000 possible sequences of annual and monthly rainfalls were generated. Then, the probabilities of different characteristics of drought, including duration, intensity, interarrival time, transition probability matrix and convergence of annual and monthly drought events were estimated and predicted by using of Standardized Precipitation Index (SPI).3. Results and discussion3.1. Probability of nonexceedance:drought Probability of non-exceedance of various drought durations derived from the generated and historical time series shown in Fig. 1 for Urmia station. Fig. 1 shows that the non-exceedance drought probability increases with increasing drought duration, so that, for drought duration of more than 5-years, it approaches to unity (100%). Also, according to Fig. 1, expected probabilities from historical data have a significant deviation from the generated data and this irregular behavior has also been obtained for other stations. Fig. 2 compares the probability density function of SPI drought classes between historical and generated data for Urmia station. The figure shows that the probability density function of SPI drought classes according to the generated data adapts more closely to the normal distribution. Considering the drought as a natural phenomenon, it is justified that the longer data series would result in the more fitness of drought probabilities to the normal distribution.3.2. Drought intensity:According to RUN theory, drought intensity is determined by dividing deficiency of a drought parameter below the critical level to duration. Fig. 3 show the absolute values of drought intensities for periods of 1-10 year by SPI values for all stations. It is observed that, the 1-year drought intensity values for all sites are very close to 1.59, but these values for the 2-years period are very significantly for different sites. We found that the 2-year drought intensity highly correlates with serial correlation lag-1 of annual data and with increasing the serial correlation lag-1 of annual data, the 2-year drought intensity increases.3.3. Probability of drought interarrival time:Fig. 4 shows the probability of drought interarrival time between any two continuous droughts for all stations. It is observed that the probability function of drought interarrival time is nonlinear and the probability of 2-years interarrival time between two continuous droughts has the maximum value for all sites. This value decreases as the drought interarrival time increases. 3.4. Joint probability of drought duration severity:Drought duration and severity are both random in nature, and are significantly correlated. The relationship between these two parameters is an important feature of the drought characteristics investigations. Fig. 4 as an example, shows the joint probability distribution of drought duration and severity for Urmia station. According to Fig. 4, joint probabilities distribution of drought duration and severity are follow a bivariate exponential function. Values of expected drought probabilities with less duration and intensity are more and rapidly decrease with increasing duration and intensity.3.5. Transition probability matrix: Transition probabilities can be determined for short and long-term planning, and for the probabilistic characterization of the progression and recession of droughts. Table 1 shows the probability matrix values based on the distinction between generated and historical data in three drought classes for Urmia station (i.e. dry (D), normal (N) and wet (W) periods). It is seen that, probability of “normal” state after all different drought states for generated and historical data are equal and quite similar results have also been obtained for other stations. However, the results for the historical data for all stations have complete disagreement with each other and very different results from generated data. 3.4. Convergence of annual, season and monthly drought events: Annual drought is generally affected by the deficits of rainfall in the different months. The effect of each month and season on the annual drought is presented in Figure 13 for all sites within the study area. The results indicate that the dryness of the year is mostly affected by the rainy month (wet periods) rather than the dry periods. In other words, rainy months like November to May play a major role in determining drought status and the rest of the months of the year known as low rainfall months are considered as almost to have a negligible role.4.
    Conclusions
    -The results suggest that there are serious doubts to cite the results of historical data and using stochastic simulation approach in the more accurate analysis of drought seems necessary and according to the results of historical data in such analyzes would be highly unreliable and with high error. -Non-exceedance drought probabilities increase with increasing drought duration and its value for more than 5- years drought duration is unity.-Change in drought intensities follows an urceolate asymmetric relationship, so that, maximum drought intensity is related to 2-year drought in most sites of study area. Nevertheless, significant difference between drought intensities in all sites and has a very high affinity with serial correlation Lag-1.-Joint probabilities distribution of drought duration and severity are follow a bivariate exponential function and values of expected drought probabilities with less duration and intensity are more and rapidly decrease with increasing duration and intensity.-According to the transition probability matrix, there is a high chance that a ‘normal’ state would follow an extreme ‘dry’ or ‘wet’ period in the study area and not spatial.- Results show that rainy month played a major role in determining the drought status and the rest of the months of the year known as low rainfall months are considered as almost to have a negligible role.
    Keywords: Drought probability, Monte Carlo simulation, SPI Index, Transition probability matrix
  • Seyed Roohollah Mousavi*, Mohammad Reza Esfahani, Mehrollah Rakhshani Mehr, Seyed Hojjatollah Mousavi, Benyamin Ghorbanzadeh Pages 65-77
    1.
    Introduction
    Damage in reinforced concrete beams causes a reduction in stiffness. Since the elastic modulus of Glass Fiber Reinforced Polymer (GFRP) bars is lower than that of steel bars, concrete beams reinforced with GFRP bars have a lower stiffness after cracking. The finite element model should be updated for analyzing the structure after being damaged. Experimental dynamic measurement can be used for damage assessment of structures. Flexural stiffness reduction due to cracking of reinforced concrete beams is simulated by reducing the elastic modulus [1].This paper presents a practical and user-friendly damage identification technique for estimating the stiffness of FRP reinforced concrete beams using the genetic algorithm and vibration test results. The identification is based on the finite element model updating involving an optimization process in which the objective function is defined as the difference between the analytical and corresponding experimental modal data.2. Methodology2.1. Experimental study:A total of 10 RC beam specimens with the length of 2.3 m (the distance between two supports was 2 m) strengthened with GFRP bars, were manufactured. Width and height of the beam cross section were 150 mm and 200 mm, respectively. Three concrete mixtures with cylindrical compressive strength of 20, 38 and 64 MPa were used in this study. Three specimens had lap-spliced bars. Splice length and the amount of transverse reinforcement in splice zone had been designed based on the equation represented by Esfahani and Kianoush [2].3.
    Results And Discussion
    In Fig. 3, it is observed that with increasing load and more severe damage, the peak of the FRF curve takes place in lower frequency and the structural natural frequencies decrease. In Fig. 4, with increasing in load level, relative variations of frequency are raised. The greatest loss in frequency is caused mainly by the load step L1 and the intensity of frequency drops is reduced in L2 and L3 steps. Variation of the modal curvature has been used as a damage index [4]. According to Fig., it is illustrated that after damage, the slope of mode shapes grows. Fig.6 compares the values of moment of inertia predicted by the genetic algorithm in specimens B-1 and B-7. Specimen B-1 with concrete compressive strength of 20 MPa reinforced with two 10 mm diameter GFRP tension reinforcement has degradation in the moment of inertia far greater than specimen B-7 with concrete strength of 64 MPa and three GFRP bars with a diameter of 16 mm and one 10 mm.4.
    Conclusions
    By comparing the values of moment of inertia estimated by the genetic algorithm with cracking status of the beam specimens, it is concluded that the aforementioned program predicts the stiffness distribution of damaged beams with good accuracy. The program evaluates the moment of inertia in specimens with lower concrete strength and longitudinal reinforcement ratio as being less than the values related to the specimens with higher concrete strength and reinforcement ratio. These results indicate that the process of stiffness updating is logical.
    Keywords: Modal test, Genetic algorithm, Modal curvature, Optimization, Mode shapes, Frequency, GFRP bars
  • Sohrab Karimi *, Hossein Bonakdari, Amir Hossein Zaji Pages 93-102
    1.
    Introduction
    One of the ways of controlling floods and deviating a part of the flow in open channels is to use intakes. Identifying the flow model and calculating the passing discharge are amongst the crucial issues of hydraulics engineering. Using flow meters is one of the most popular methods of measuring the velocity or the discharge in open channels. Flowmeters rely on measuring the velocity and they calculate the discharge through the continuity equation as the multiplication of the mean velocity by the wet cross section (Q = A(h ×Umean). The A (h) cross section is computed through measuring the height of the free surface (h) and using precise geometrical information. Determining the mean velocity passing through the cross section requires special knowledge. It should be noted that due to the three-dimensional and complex nature of the flow near the intake location and the presence of strong secondary flows in the transverse cross section, the velocity measured by the sensors located on the flowmeter in the intended area is different from the actual mean velocity of the channel. However, despite this difference, the mean velocities measured by the flowmeter are fairly consistent with the actual mean velocity area of the channel. The velocity of the passing flows and the geometrical size of the main and branch channels affect the difference between the velocity measured by the flowmeter and the actual mean velocity of the flow [1-6].2.
    Methodology
    The experimental model [7] of a 90-degree intake with a rectangular cross section has been three dimensionally simulated by the ANSYS- CFX software in this study. The k-ω turbulence model has been used to solve the turbulence equations in this simulation. The results of the numerical model have been compared with that of the experimental model in order to examine the accuracy of the numerical model. The flowmeter measurement accuracy was examined in different width ratios wr= 1.4, 1.2, 1.0, 0.8, 0.6 (the branch channel width to the main channel width) through using the numerical model and the results of the experimental model after verification. With regard to the fact that the discharge passing through the branch channel is constant in all the wr states, the effective ratio for fluid movement increases in the branch channel as the width ratio increases as the result of an increase in the branch channel width from wr= 0.6 to wr= 1.4. This causes the width of the separation zone and the contraction degree of the compression zone to increase and the longitudinal velocity to get close to v*max equal to -0.6. Therefore wr= 1.4 width ratio is considered the critical width ratio among all the presented wrs regarding the vastness and density of the separation zone and the compression zone. An increase in the width ratio of the channels increase the difference between the read velocities and the mean velocity of the branch channel which means as the width ratio increases from wr= 0.6 to wr=1.0, the difference between the read velocity and the branch channel mean velocity increases from 18 percent to 139 percent at the peak point. The reason behind this error percentage increase is that as wr= 0.6 increases to wr= 1.0, the size of the separation zone increases and the density of the contraction zone increases as well however this increasing process continues to wr= 1.0, width ratio and after the width ratio of 1 as the width ratio of the channels increase from wr= 1.0 to wr= 1.4, the difference between the read velocities and the actual mean velocity decreases in the branch channel which means as the width ratio increases from wr= 1.0 to wr= 1.4, the difference between the read velocity and the branch channel mean velocity drops from 139 percent to 47 percent because as the width ratio increases from wr= 1.0 to wr= 1.4, the effective ratio of fluid movement increases in the channel and the difference between the read velocity and the branch channel mean velocity increases. This is because when the channels’ width ratios become excessively large, the branch channel’s cross section excessively increases and as a result the flow velocity significantly drops and this decreases in the velocity leads to lesser volume of flow entering the separation zone and the value of vmax decreases in the compression zone and so the difference between the read longitudinal velocity and the branch channel mean velocity decreases.4.
    Conclusions
    With regard to the results, the flowmeter measurement accuracy is fairly desirable in the middle of the channel in specific longitudinal distances except for the rotating areas. In case the flowmeters are installed exactly in the complex rotation areas and the deviation location their measurement accuracy decreases and the maximum error is equal to 139 percent in some cross sections and this error percentage occurs in wr= 1.0 width ratio (Fig. 1). In other words when the branch channel width is equal to the main channel width, the difference between the velocity read by the flowmeter and the branch channel mean velocity reaches its maximum level.
    Keywords: Intakes, Channel width, Velocity distribution, Flowmeter, ANSYS, CFX software
  • Abbas Yeganeh‐Bakhtiary*, Ali Pourzangbar, Fatemeh Hajivalie Pages 115-122
    1.
    Introduction
    Scour could cause significant structural instability in front of the coastal structures, which can lead to their failure [1]; hence, prediction of scour depth at coastal structures is of great importance in coastal engineering discipline. Extensive experimental studies carried out to predict the maximum scour depth and resulted in some empirical formulas [2-4]. However, these empirical formulas have not been capable of predicting the maximum scour depth. Another drawback of the empirical formulas is their shortage in considering all of the effective parameters in scour processes; therefore, a comprehensible model for scour depth prediction at the coastal structures is very essential. The main objective of the current study is to present an alternative model in the form of genetic programming (GP) to the present empirical formulas. We utilized around forty eight data set to train and test the evolved GP models. To evaluate the accuracy of developed GP model the statistical parameters were determined, e.g. root mean square error (RMSE) and correlation coefficient (R2) and scatter index (SI). To verify the developed models, the predicted results were compared with those of the measurements and empirical relations. Moreover, a simplified analytic form of the GP proposed model also presented in this study.2.
    Methodology
    GP (genetic programming) is a branch of the genetic algorithm belonging to the family of evolutionary algorithms used to evolve models. In the first place, the capability of GP in developing accuarate equations compared with those of empirical investigations. In order to have a logical comparison, firstly the same input and output parameters and also the same data set were utilized to evolve models with GP. To develop the best model, GP employs some operations that can affect strongly on the accurate of developed model. These operations depending on the weights relate the input parameters to each other and evolve the GP model. Since with the variation of operations, the evolved model and its accuracy changes, four types of operations considered to evolve GP models. Table. 1 shows these different operation sets.3.
    Results And Discussion
    Results of different models including GP and empirical ones showed that the trend of prediction is similar in both GP and empirical models. However, the discrepancy of the measured and predicted scour depth in empirical formulas are very larger in comparison with those of GP. Furthermore, the empirical formulas are not able to have an acceptable prediction for the other experiments’ data set and this can be one of the most important shortage of these formulas. In most cases, the experimental investigations studied the effect of one or two important parameters on the scour at coastal structures. However, considering all of the experimental studies, various parameters can affect mainly on the scour process.4.
    Conclusions
    Results of the evolved models with GP showed that in almost all of the models, GP evolved equation significantly perform better than the empirical ones with the same input and output parameters and same data set. Furthermore, GP is capable to develop a comprehensive model includes all of the effective parameters on the scour at the coastal structures. The comprehensive model of GP showed acceptable accuracy and can be utilized for predicting the maximum scour depth.
    Keywords: Coastal structures, Genetic programming, Scour depth, Regression, based equations