Applying Steady and Unsteady Body Force Methods to the Simulation of Ship Self-Propulsion
- Yu-Wen Hsieh (National Taiwan Ocean University) | Suz-Kuan Huang (National Taiwan Ocean University) | Sin-An Lai (National Taiwan Ocean University) | Ching-Yeh Hsin (National Taiwan Ocean University)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- body force method, self-propulsion, effective wake, boundary element method, RANS
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- 18 since 2007
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In this paper, an unsteady body force method developed for marine propellers is presented. The body force method is defined as using computed forces to represent the effects of propellers instead of using the real geometries, and the Navier-Stokes equation is solved by introducing these forces as body force terms. The unsteady body force method presented is that propeller blade forces varying with angular positions, and an actuator sector model is adopted. Both steady and unsteady propeller body force methods are used to simulate the self-propulsions and to compute a single propeller, and results are compared and verified to each other.
Propellers operate in the thick boundary layer of ships with the effect of the propeller/hull interactions. This leads to the “nominal wake” and the “effective wake” problems, and some experiments show that the forces on propellers can be differed by 20% in the nominal inflow and effective inflow. This difference is due to coupling of the propeller to the vorticity in the incoming flow - namely, the ship wake. The simulation of effective wake has been done by various numerical methods. Huang and Groves (1976) developed a method to calculate the effective inflow for axisymmetric bodies. This method is very efficient; however, it is unable to predict the separated flow due to neglecting the effect of viscosity, and the flow has to be assumed axisymmetric. Schetzar and Favin (1977) developed a theory to treat the propeller forces as the body force terms in the Navier-Stokes equation, and the propeller flow field was simulated using the actuator disk theory. Stern and his colleagues (Stern, 1988a, 1988b, 1994) further extended the “body-force” concept, and solved the effective inflow by coupling the viscous flow solver and the potential flow lifting surface method. Korpus (1992) also used a similar approach to calculate the effective inflow. Kerwin and his colleagues (1994) developed the “equivalent body force” concept, and have proved that to accurately couple the viscous flow solver and the potential flow solver, the circulation distribution on the propeller has to be the same in both solvers, not the propeller forces. The body force method presented in this paper is originated from Kerwin, and modified by using the boundary element method to calculate the propeller forces. From previous research at NTOU (Hsin, 2000, 2008, 2014; Wei, 2012), we have successfully validated that the current body force method can provide very accurate results to simulate the interactions between the ship hull, rudder and the propeller.
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