برآورد فشار موج تنهاي در حال شكست بر موج‌شكن صندوقي شناور مهار‌شده، با استفاده از روش كسر حجمي سيال

ESTIMATION OF BREAKING SOLITARY WAVE PRESSURE ON MOORED PONTOON FLOATING BREAKWATERS USING VOF METHOD

جريان‌هاي تراكم‌ناپذير لزج با سطح آزاد متحرك از پديده‌هاي مهم در طبيعت‌اند كه در مسايل مهندسي نيز كاربرد فراوان دارند. در بررسي اين جريان‌ها، يكي از پيچيده‌ترين كارها تعيين موقعيت سطح آزاد متحرك در هر لحظه از زمان و در هر نقطه از مكان است. در اين تحقيق مدلي دو‌بعدي براساس روش VOF براي تعيين مشخصه‌ي سطح آب تهيه شده است. ابتدا، از مقايسه‌ي نتايج اين مدل با نتايج آزمايشگاهي درخصوص يك مثال كلاسيك صحت مدل اثبات شده است. سپس ميدان سرعت و فشار ناشي از برخورد يك موج تنها به يك موج‌شكن شناور مهار‌شده با استفاده از اين مدل به دست آمده است. نتايج حاصله نشان مي‌دهد كه امواج در حال شكست قادرند نيروهاي بسيار بيشتري در مقايسه با امواج نشكسته به موج‌شكن شناور وارد ‌كنند.

Incompressible viscous flow with moving free surface is an important phenomenon in nature which has broad application in engineering. For these flows, determination of temporal and spatial position of this moving free surface in unsteady or non-uniform conditions is very difficult. One of the most complicated phenomenons in coastal zone is wave breaking. The study of these waves is of importance in many applications, such as destructive impact forces on marine structures and cross-shore and long-shore sediment transport. Being highly nonlinear, transient and complex, a theoretical analysis of wave impact would be impossible without numerical simulations. In this study fluid is considered as viscous and incompressible. Therefore, Navier-Stokes and continuity are considered as governing equations. To solve these equations, a finite volume method based on the PISO algorithm is used. The effect of turbulence was considered using standard k-? model. Two dimensional VOF model using Donor-Acceptor algorithm as a simple line interface construction method was developed for free surface modeling. A piston-type wave maker and Goring formula is used in the left lateral boundary condition to generate shallow water solitary wave. A sloped beach is considered as right lateral boundary condition to simulate breaking wave. A pontoon floating breakwater is exposed to incident wave. Euler equation is used to estimate pressure exerted on pontoon floating breakwater. To validate the present model, dam break test is adopted as a benchmark. The results are compared with available data and show the accuracy of the developed model. Then the velocity and pressure field due to interaction of a solitary wave and moored floating breakwater was obtained using coupled VOF and N-S solver. To compare the effect of wave breaking force on the structure, the pontoon floating breakwater is located in and out of the breaking wave zone. The results showed that the breaking solitary wave implies much greater force than non-breaking wave on the floating breakwater.