Fast Calculation Method Of Near-field Perturbation Velocity Potential And Far-field Wave Of Ship

The theory of steady ship waves is the fundamental problem of ship hydrodynamics.Steady waves under linear free surface condition have been studied for over one hundred years.With the concept of green ship getting more and more attention,how to calculate the wave resistance and waveform as accurately as possible and provide the basis for energy-saving and ship-type optimization has been widespread concern.In this paper,three aspects of the work have been carried out.Compared with constant panel method or high-order boundary element method,the Taylor expansion boundary element method can achieve higher numerical precision especially in the non-smooth boundary and corners.In present study,the Taylor expansion boundary element method has been used to calculate the wave-making resistant and ship-generated wave.Double-body stream is chosen as the basic flow,and using upstream finite difference operator to handle the free-surface condition.By calculating the wave resistance of Wigley and S60 ship model and comparing with other methods and experimental values,it is shown that TEBEM can accurately calculate the wave resistance and wave height,and has wide applicability.And the TEBEM is applied to the prediction of wave-making resistance and hull gesture.It is indicated that this method is robust and suitable to the calculation of sinkage,trim and wave-making resistance with different hull type at various speed.It is very important for the design and optimization of the high speed craft.However,when consider the far-field ship wave,the basic difficulty is that the Green function satisfying the linear free-surface condition with forward speed is considerably more complicated than other kind of Green function.Noblesse put forward a simplified Green function for diffraction-radiation of time-harmonic waves with forward speed in 2004.It describes point source generated waves accurately in the far field.The present study is to give the practical numerical algorithm of the steady ship wave Green function and its gradient.The parameter analysis of the integral limit,the division of integral interval,the depth of the source and the Froude number is implemented.In addition,the velocity potential and wave height of the far-field free surface can be obtained according to the velocity potential in the hull calculated from the TEBEM by the simplified Green function and the Green's third for-mula,which overcomes the huge computational burden of TEBEM for it only require a distribution of singularities over a near field portion of the free surface.So this method can be used for fast calculation of large area wave in the far field.