جريان عبوري درون گذري و روگذري در سرريز گابيوني در شرايط آزاد در بستر ماسه يي

Overflow and underflow within the broad-crested gabion weir in free flow with sand bed conditions

در پژوهش حاضر، به بررسي هيدروليك جريان عبوري درون‌گذري و روگذري در سرريز گابيوني لبه‌پهن پرداخته شده است؛ لذا از مدل آزمايشگاهي در جهت برآورد پارامترهاي هيدروليكي، از جمله: عمق آب‌شستگي پايين‌دست، ضريب دبي و ميزان دبي درون‌گذري و روگذري استفاده شده است. تخمين ضريب دبي و بيشينه‌ي عمق آب‌شستگي از روش رگرسيون غيرخطي بر پايه‌ي داده‌هاي آزمايشگاهي صورت پذيرفته است. در روش اخير، با به كارگيري پارامترهاي هندسي و هيدروليكي دبي جريان درون‌گذري و روگذري از سرريز گابيوني، تأثير پارامترهايي از جمله قطر متوسط ذرات گابيون در عمق آب‌شستگي بررسي شده و نتايج نشان داده است كه با افزايش اندازه‌ي ذرات درون گابيون، ميزان عمق آب‌شستگي در پايين‌دست افزايش يافته است. همچنين مقايسه‌ي بيشينه‌ي عمق آب‌شستگي با مطالعه‌هاي پيشين نشان داد كه استفاده از سرريز گابيوني به دليل داشتن جريان درون‌گذر، ميزان عمق آب‌شستگي در پايين‌دست كاهش پيدا كرده است. اين امر به دليل وجود جريان درون‌گذري در گابيون است، كه باعث كاهش قدرت جت روگذر مي‌شود. همچنين نتايج نشان داد كه روابط ارائه شده با خطاي حدود 17\٪ مي‌توانند در برآورد جريان درون‌گذر و روگذر از گابيون كاربرد داشته باشند.

In order to calculate and predict the discharge flow through and over the gabion weir, 33 experimental broad-crested gabion models were carried out through the sand bed condition. The flow conditions through and over the gabion were presented as three classifications which involved partial flow conditions through a gabion, fully gabion flow through a gabion weir, and overflow on a gabion weir. These classifications were considered due to the free flow conditions. Based on the partial and fully gabion flows, an equation was proposed to calculate the gabion flow. Moreover, the flow discharge over the gabion was considered based on the broad-crested weir formula and then, the coefficient discharge of broad-crested gabion weir was proposed based on experimental measurements. Comparison between the proposed values and experimental measurements illustrates that good agreement is between the proposed and experimental flow discharges. Also, the investigation of flow variations through the gabion showed that the error of gabion equation increased significantly due to overflowing on gabion weir. In order to raise the accuracy of the calculation process of flow discharge through the gabion an equation was proposed based on the geometry and Darcy Wisbech’s parameters. The porosity, length, and particle size were defined based on Darcy Wisbech equations. Some math indexes were considered for this equation and by employing the Mathematical software, these parameters were presented based on the non-liner technique. The error was measured based on the experimental and proposed values and the result of the comparison pointed to the suitable agreement between the two groups of values. Finally, the maximum scour hole was measured by point-gauge along the longitudinal section. Based on threshold velocity and geometrical and hydraulic parameters, an equation was proposed to predict the maximum scour hole depth at the downstream of the broad-crested gabion weir.