مدل‌سازي تاثير سكان در شبيه‌سازي عددي شناور‌هاي تندرو

Rudder Influence Modeling In Numerical Simulation Of High Speed Craft

در اين تحقيق اثر سكان بر حركات يك شناور، در يك كد ديناميك سيالات محاسباتي بررسي شده است. روش معمول در مدل‌سازي سكان استفاده از شبكه‌بندي هم براي سكان و هم براي بدنه است. اما استفاده از اين روش، به‌دليل افزايش تعداد سلول‌هاي محاسباتي به كاهش سرعت حل مي‌انجامد. افزون بر اين، با توجه به پيچيدگي فرايند ايجاد شبكه در حالتي كه سكان وجود دارد، در شبكه‌بندي فقط بدنه‌ي شناور مد نظر قرار مي‌گيرد و نيروهاي سكان به‌صورت روابط تجربي به آن اضافه و در حل معادلات حركت از آن استفاده مي‌شود. در اين پژوهش ابتدا روش‌هايي براي تخمين نيروهاي سكان در شرايطي كه جريان با سرعت يكنواخت به آن برخورد مي‌كند ارايه مي‌شود. سپس در حالتي كه بدنه و پروانه بر جريان ورودي به سكان اثر مي‌گذارند، روش اصلاح نيروها بيان مي‌شود.

Maneuvering capability is one of the most important aspects of a ship. The rudder is often used for maneuvering, and its dimensions, type and location must be designed correctly. In the first steps of design, similar boats can be used, but, in the final steps of design, exact dimensions must be assigned. A method for achieving this is a model test, which is precise but very costly. The use of numerical simulations, such as CFD, is another method. Its precision is high and it is not costly, but it does, however, have weaknesses in complicated geometries. Rudder simulation using meshing is a time consuming and more complex procedure. Consequently, we use meshing only for the hull, but rudder forces are added by experimental and numerical equations. Software created and developed by the CFD group of Sharif University of Technology Marine Laboratory, NUMELS, is used to solve the fluid domain. It is based on the finite volume method. After the solution process, cell velocity, body orientation and body linear velocity are used to compute rudder lift and drag. Finally, rudder forces and moments are added to the pressure, viscous forces and moments. After a six degree of freedom equation solution, angular and linear accelerations are achieved, and after computation of angular and linear velocities and body motions and orientations, simulation for the current time step finishes. This method of boat and rudder simulation is fast. Compared to simulation of boats without rudders, speed loss in the solution does not exist, because time consumption for computation of rudder forces and moments relative to time consumption for boat simulation is negligible. The only problem when using this method is the accuracy of the rudder forces. The accuracy of equations used for rudder force calculations in the current research is investigated and the certainty of precision is gained.