Calculation of Deep-Water Wash Waves Using a Combined Rankine/Kelvin Source Method

2003 ◽  
Vol 47 (04) ◽  
pp. 313-326
Author(s):  
Carl-Erik Janson ◽  
Michael Leer-Andersen ◽  
Lars Larsson
Keyword(s):  
Boundary Condition ◽  
Deep Water ◽  
Outer Edge ◽  
Source Distribution ◽  
Far Field ◽  
Source Method ◽  
Rankine Source ◽  
Rankine Source Method ◽  
Outer Domain ◽  
Wigley Hull

This paper presents a method for computation of far-field wash waves in deep water. The method combines a nonlinear Rankine source method in an inner domain with a Kelvin source method for the far-field waves in an outer domain. Kelvin sources are distributed on a vertical matching wall, positioned at the outer edge of the inner domain. These sources are used to specify a boundary condition for the disturbance velocity potential on the matching wall. The boundary condition is used in the Rankine source solution of the inner domain. The size of the inner domain can be reduced in the transverse direction compared to a method using Rankine sources only, as the wave reflections at the edge of the inner domain are eliminated. Further, the far-field waves can be computed using the solution on the matching wall together with the Kelvin source distribution. The verification of the present method includes a comparison for a single Kelvin point source and a comparison to a Rankine source method at intermediate distances for the Wigley hull and for a catamaran. A grid dependence study for the position, size, and panel density on the matching wall is included for the Wigley hull. Computed and measured longitudinal wave cuts are compared for a catamaran both in the inner and the outer domain. Good agreement is obtained.

Rankine Source Method for Seakeeping Predictions

2012 ◽  
Author(s):  
Heinrich Söding ◽  
Alexander von Graefe ◽  
Ould el Moctar ◽  
Vladimir Shigunov
Keyword(s):  
Steady Flow ◽  
Potential Flow ◽  
Transfer Functions ◽  
Stokes Equations ◽  
Computational Time ◽  
Ship Motions ◽  
Periodic Flow ◽  
Source Method ◽  
Rankine Source ◽  
Rankine Source Method

Model tests are usually used for the traditional seakeeping predictions (transfer functions of ship motions and loads in regular waves). Experience shows that numerical solution of Reynolds-averaged Navier-Stokes equations (RANSE) can provide accurate results for this task, however, such computations require too much computational time for the required large number of the loading conditions, ship speeds and wave directions and periods. Traditionally, potential flow methods are used for such computations at early design stages. Although potential flow methods can produce results very quickly for large number of conditions, viscosity effects (most important for the roll motion) have to be taken into account using measurements or RANSE computations. Rankine source method, applied to seakeeping problems perhaps for the first time by Yeung [1] to oscillating ship sections, is increasingly used in practical seakeeping analysis. This paper presents a three-dimensional Rankine source code GL Rankine. Patch method is used instead of the usual collocation method to satisfy boundary conditions on the solid body surface. Periodic flow due to waves is linearized with respect to wave and motion amplitude, taking into account interactions between the nonlinear steady flow and periodic flow due to waves and ship motions. The steady flow solution accounts for the nonlinear free-surface conditions, ship wave and dynamic squat. The paper shows results of the method for ship motions in waves in comparison with model measurements and RANSE simulations.

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