بررسي عددي تاثير سازه حفاظتي در آبشستگي ناشي از شكست سد با استفاده از مدل لاگرانژي دو فازي

Numerical Study on the Effect of Protective Structures on Scouring due to Dam Break Using a Two-phase Lagrangian Model

مقدمه: جريان هاي سريع بعد از شكست سد و آبشستگي متناظر با آن از مسائل مهمي است كه براي شبيه سازي مناسب آن بايد از مدل هاي چند فازي استفاده كرد. در سال هاي اخير روش جديد لاگرانژي هيدروديناميك ذرات هموار بعنوان روش بدون شبكه ايده آل براي اين كاربرد معرفي شده است. روش­: در مقاله حاضر با استفاده از اين روش عددي و اصلاح آن براي جريانات چندفازي، آبشستگي رسوب كف بعد از شكست سد مدل‌سازي شده است. در ابتدا، نتايج روش عددي حاضر با مطالعات آزمايشگاهي مرتبط مقايسه و صحت سنجي شده و سپس تاثير شرايط هندسي سازه محافظ در ميزان آبشستگي مورد مطالعه قرار گرفته است. در اين راستا، چندين مدل سازي براي شرايط مختلف طول كف صلب و همچنين ارتفاع مانع انتهايي به عنوان پارامترهاي اصلي، انجام شد. يافته ­ها: بر اساس نتايج به دست آمده، مدل مورد استفاده توانمدي مدل سازي شرايط پيچيده آبشستگي ناشي از جريانات متلاطم را دارد و به عنوان نتيجه كاربردي، مشاهده گرديد كه تاثير افزايش طول سازه حفاظتي، كم تر از تاثير افزايش ارتفاع آن است. همچنين ارتفاع بهينه اي براي عملكرد مطلوب سازه حفاظتي وجود دارد بگونه اي كه افزايش بيش از حد ارتفاع حتي مي تواند منجر به افزايش آبشستگي نسبت به شرايط اوليه گردد. نتيجه­ گيري: اگرچه استفاده از سازه حفاظتي مي تواند علاوه بر جلوگيري از خوردگي پاي كف صلب، عمق آبشستگي را نيز كاهش دهد، تعيين ارتفاع بهينه آن اهميت شاياني در عملكرد مطلوب اين نوع سازه ها دارد.

Introduction: Scouring depth due to dam break flows as one of the important engineering problems can be investigated numerically by means of an appropriate multiphase model. Smoothed Particle Hydrodynamic (SPH) model is a Lagrangian Mesh-free based method that has been introduced to solve such complicated flows. Methods: A Multiphase version of this model is modified in this study to predict scouring depth after dam break flows. At first, the introduced model is validated via comparing the results with experimental data and it is confirmed that the model can well predict turbulent multiphase flows. Then, the performance of a scour protection structure with different length and heights is simulated against dam break flow to find an optimum geometry for this structure. Findings: Based on the results, it is concluded that the effect of structure height on scour reduction is more sensible than the effect of structure length. In contrast to the structure length, a small edge at the end of the protective structure can efficiently decrease the final scoured depth. However, there exists an optimum height with the best performance. A too high scour protection structure can even result in a higher scouring depth than an unprotected case. Therefore, it is necessary to use a protection structure with an appropriate height and the introduced model can be utilized as a helpful tool to check the required performance of this structure.Introduction: Scouring depth due to dam break flows as one of the important engineering problems can be investigated numerically by means of an appropriate multiphase model. Smoothed Particle Hydrodynamic (SPH) model is a Lagrangian Mesh-free based method that has been introduced to solve such complicated flows. Methods: A Multiphase version of this model is modified in this study to predict scouring depth after dam break flows. At first, the introduced model is validated via comparing the results with experimental data and it is confirmed that the model can well predict turbulent multiphase flows. Then, the performance of a scour protection structure with different length and heights is simulated against dam break flow to find an optimum geometry for this structure. Findings: Based on the results, it is concluded that the effect of structure height on scour reduction is more sensible than the effect of structure length. In contrast to the structure length, a small edge at the end of the protective structure can efficiently decrease the final scoured depth. However, there exists an optimum height with the best performance. A too high scour protection structure can even result in a higher scouring depth than an unprotected case. Therefore, it is necessary to use a protection structure with an appropriate height and the introduced model can be utilized as a helpful tool to check the required performance of this structure.