Prediction of ship rudder-propeller interaction using parallel computations and wind tunnel measurements.
University of Southampton, Ship Science,
A theoretical method has been developed to predict the forces developed due to the interaction between a ship rudder and propeller. A parallel lifting suface panel program (PALISUPAN) ha sbeen written in Occam2 which is designed to run across variable sized square arrays of transputers. thsi program forms teh basis of the theoretical method. The rudder and propeller are modelled separately. Their interaction is accounted for through an iterative process whereby their respective inflow velocity fields are modified using a circumferential average of the disturbance velcoity due to the other body. Prior to writing PALISUPAN, software techniques for the implementation of computational fluid dynamics algorithms across arrays of transputers were developed. The approach used is based on a geometric parallelism. At the outermost level on each transputer the particular CFD algorithm runs in parallel with a harness process. The harness controls teh communication across teh transputer array. to prove thsi concept an explicit finite volume solver for the two-dimensional Euler equations has been implemented. PALISUPAN itself uses a perturbation potential formulation and an explicit zero pressure loading condition is enforced at the trailing edge. Use of the communications harness greatky reduces code development time and although an implicit solver PALISUPAN gives good parallel performance. Wind tunnel tests were undertaken to derive experimental data for validation of the prediction method. These used a 3.5m x 2.5m low speed widn tunnel and a range of flow an dgeometrical parameters were tested. Total rudder forces and moments, propeller thrust and torque and quasi-steady rudder surface pressures were measured. Empirical relationships for teh prediction of rudder lift, drag and stall for use in ship manoeuvring studeis were also derived. The validated theoretical prediction for rudder-propeller interaction using PALISUPAN allows the detailed design of sjip rudder-propeller systems to be enhanced. The parallel performance of the pALISUPAN demonstrates the practicality of using transputer arrays to solve CFD problems.
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