بررسی آزمایشگاهی تاثیر تغییرات ارتفاع بر خصوصیات هیدرولیکی سرریزهای تاج دایره ای مورب تحت شرایط جریان غیردائمی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 مرکز تحقیقاتی مطالعات آب، واحد اصفهان (خوراسگان)، دانشگاه آزاد اسلامی، اصفهان، ایران

2 دانشجوی کارشناسی ارشد مهندسی آب و سازه های هیدرولیکی، گروه مهندسی عمران، دانشکده فنی مهندسی، واحد اصفهان (خوراسگان)، دانشگاه آزاد

3 استادیار، دانشکده فنی و مهندسی، گروه مهندسی عمران، دانشگاه شهید اشرفی اصفهانی، اصفهان، ایران

چکیده

سرریز‌های تاج دایره‌ای از سرریزهای مطمئن جهت استفاده در کانال‌ها می‌باشند که به صورت عمود بر جریان یا به صورت زاویه دار(مورب) نسبت به راستای جریان احداث می‌شوند. سرریزهای زاویه دار جهت افزایش طول مؤثر سرریز و افزایش ظرفیت آبگذری استفاده میشوند. در این مقاله به کالیبراسیون ضریب دبی سرریز تاج دایره‌ای مورب تحت تغییر پارمتر ارتفاع سرریز تحت شرایط جریان غیردائمی پرداخته شده است. برای این منظور سه سرریز تاج دایره‌ای مورب به ارتفاع 15،10و20 سانتی‌متر تحت الگوهای مختلف تغییر دبی در فلوم تحقیقاتی به طول 10 متر و عرض 6/0 متر مورد بررسی قرار گرفته اند. این فلوم دارای دستگاه پی ال سی برای تنظیم دبی و ثبت داده های دبی و عمق جریان می‌باشد. نتایج با استفاده از الگوریتم ژنتیک تحلیل شده و مقادیر ضریب دبی کالیبره شده در شرایط جریان آزاد غیردائمی تحت الگوهای مختلف تغییر دبی محاسبه شده است. نتایج تحلیل داده های آزمایشگاهی حاکی از آن بوده که با افزایش ارتفاع سرریز و همچنین نسبت ارتفاع آب بالادست سرریز به ارتفاع سرریز، ضریب دبی جریان غیردائمی کاهش می‌یابد. همچنین مقدار ضریب دبی جریان غیردائمی تحت شرایط مختلف ارتفاع جریان بالادست و ارتفاع سرریز و الگوی تغییر دبی بین 5/٠ تا 5/1 متغیر بوده است..

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Experimental study of the effect of weir height on hydraulic characteristics of the oblique circular-crested weir under unsteady flow condition

نویسندگان [English]

  • Ali Khoshfetrat 1
  • Mehdi Afiounizadeh Esfahani 2
  • Elham Izadinia 3
1 Water Studies Research Center, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
2 Department of Civil Engineering, Faculty of Engineering. Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
3 Assistant Professor, Engineering College, Department of Civil Engineering, Shahid Ashrafi Esfahani University, Isfahan, Iran
چکیده [English]

Introduction:

Weirs are a type of water structures that are used to pass floods, control water levels and measure flow rates. The accurate and appropriate design of the weir is of particular importance, and the existence of weirs with inappropriate discharge capacity is one of the most important factors of channel inefficiency. Circular crest weirs are reliable weirs for use in channels that are built perpendicular to the flow or at an angle (oblique) to the direction of the flow. Oblique weirs are used to increase the effective length of the weir and increase the water-passing capacity and hydraulic parameters such as the discharge coefficient. On the other hand, the study of the flow in the unsteady state, in which the flow variables in the channel vary with time, is of special importance in hydraulic science. In this research, the calibration of the discharge coefficient of the oblique circular crest weir under unsteady flow condition has been discussed. Also, the effect of changing the height of the weir and changing the flow pattern on the discharge coefficient of the unsteady flow in this type of weir has been investigated.



Methods:

In this research, three oblique circular crest weirs with a height of 15, 10 and 20 cm and other identical geometric parameters under free and unsteady flow conditions in the flow range of 25 to 51 liters per second under the range of flow rate changes of 1, 3 and 5 liters per second and the range of time changes of 5, 10 and 15 seconds have been tested. Therefore, the total number of tests was equal to 27. Experiments were carried out in the research flume of Islamic Azad University, Isfahan (Khorasgan) branch with a rectangular cross-section of 10 meters in length and 0.6 meters in width, and weirs were installed at 2.5 meters from the entrance of the channel The flume has no slope of the floor and the height of the flume is the same without change and its walls are made of tempered glass and completely sealed. The mentioned flume is equipped with a closed water circulation system and can provide a maximum flow rate of up to 55 liters per second. The tank of this flume is made of fiberglass and has a cylindrical shape with a volume of 10 cubic meters and is placed underground at a height of about 2 meters. Flow can be regulated by PLC device. The depth gauge of the device without contacting the free surface of the flow, by sending and receiving ultrasonic waves, measures the distance with very high speed and accuracy, and in this way the depth of the flow is recorded in the PLC device. In fact, the most important part of this test set is the PLC device connected to the flume, which controls all flow settings, including the flow rate, maximum flow rate, relevant hydrographs, and records the flow depth data. In this study, the governing relations were first extracted and then the genetic algorithm was used for optimization. The optimization process in the genetic algorithm is based on a guided random process. This method is based on the theory of gradual evolution and Darwin's fundamental ideas. Genetic Algorithm is a non-algebraic optimization method that is suitable for functions whose optimization with algebraic methods is exhausting. This algorithm and other evolutionary algorithms examine the response space in parallel and cluster by cluster and not member by member and for this reason, the possibility of occurrence of local maxima or minima is eliminated. Also, these methods do not need information about the derivatives of the target function and only the main form of the function is required. In this research, the solver available in Excel software was used for optimization with evolutionary algorithm method. After specifying the target variable, which is the discharge coefficient in this research, the evolutionary algorithm option is selected, and the software performs its analysis to calculate the best discharge coefficient with the lowest value for total errors.



Results:

The results obtained in this research show that in all patterns of flow changes, increasing the ratio of water height relative to the weir crest to the weir height (H/P) causes a decrease in the discharge coefficient of unsteady flow. Also, in all patterns of flow rate change, increasing the height of the weir causes a decrease in the discharge coefficient of the unsteady flow, that is, the discharge coefficient of the unsteady flow in the oblique circular crest weir is a function of the upstream flow conditions and the height of the weir. Also, the unsteady flow rate coefficient in this type of weir is a function of the flow rate change pattern. As can be seen from the graphs obtained in this research, the flow rate change pattern does not have much effect on the slope of the flow coefficient changes compared to the H/P changes, but it is effective on the degree of influence of the weir height changes for a fixed H/P value. On the other hand, the graphs show that the discharge coefficient of unsteady flow for oblique circular crest weir varies between 0.5 and 1.5, which previous researchers had also concluded that the discharge coefficient of unsteady flow for other weirs is not constant and is a function of the geometry of the weir and the pattern of changes in flow rate.

کلیدواژه‌ها [English]

  • Unsteady flow
  • Inclined circular-crested spillway
  • Discharge coefficient
  • Genetic algorithm