A numerical solution for potential flows including the effects of vortex shedding
01 May 1993-Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 115, Iss: 2, pp 111-115
TL;DR: In this article, a discrete vortex method was incorporated into a time domain boundary element algorithm for the numerical simulation of oscillating flow past a normal flat plate, where separation from a sharp edge results in the formation of a vortex sheet issuing from the edge.
Abstract: This paper reports on an attempt to include vortex shedding effects into potential flow calculations using the boundary element method. Significant computational advantages results because of the relatively simple approach to handling separation at the sharp edges while working only with the boundary values. A discrete vortex method was incorporated into a time domain boundary element algorithm for the numerical simulation of oscillating flow past a normal flat plate. Separation from a sharp edge results in the formation of a vortex sheet issuing from the edge. This vortex sheet is modelled by a series of discrete vortices introduced one at a time into the flow field at regular intervals. The motion of each vortex is traced over time using its convection velocity. As long as the Keulegan-Carpenter number is small enough, vortex shedding takes place close to the edge. The discrete vortex method can, in such cases, be looked upon as the inner region solution to the problem of normal oscillating flow past the flat plate. The inner region solution has to be matched with the outer potential flow solution. The combination of boundary element and discrete vortex methods provides this matching and at the same time do not require calculations inside the domain.
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01 Jan 1994
TL;DR: In this article, a simple numerical cross-flow algorithm based on slender body theory was developed to convert the three dimensional problem into a series of two dimensional wavemaker problems in the plane of transverse sections, marching in small steps from the bow section towards the stem.
Abstract: The accurate determination of hydrodynamic loads on moving ships is important for hull form design and optimization and structural design purposes. This is especially true at the preliminary design stage during which time quick predictions of the forces and moments acting on a ship advancing steadily with, and without, yaw would be extremely useful. hi view of this, simple numerical cross-flow algorithms has been developed. The numerical procedures are based on slender body theory, which is used to convert the three dimensional problem into a series of two dimensional wavemaker problems in the plane of transverse sections, marching in small steps from the bow section towards the stem. Fluid density stratification, vortex shedding, finite water depth and nonlinear free surface effects can be allowed for in the algorithms. A procedure for handling density stratified flow has been developed and successfully used for the calculation of surface and interfacial waves created by a prolate spheroid. Vortex shedding is modelled using the discrete vortex method. A hybridization of the discrete vortex and boundary element methods is achieved and illustrated in a test case of predicting the forces acting on an oscillating flat plate. The wavemaker, with the fully nonlinear free surface conditions, is used for calculating the generated wave pattern and wavemaking resistance of a Wigley hull. The effects of finite water depth on wavemaking resistance are calculated. The hybrid boundary element-discrete vortex method is used for determining the hydrodynamic forces and moments acting on a yawed Wigley hull.
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