| Ships have been affected by the role of waves for long time,seakeeping for its safety and reliability has a significant impact.For high-speed ships,the seakeeping of high speed is the important performance indicators which designer must consider.For high-speed problem,the calculated results of current wave load theory are so different from the experimental value or actual value that it can not predict the ship movement accurately.Therefore,this paper aims to study the motion prediction method of high speed ship.At present,the two most important methods in the theory of potential flow are Rankine source Green function method and Kelvin source Green function method.Both methods have advantages and disadvantages.Rankine source has simple form,but it can not meet the free surface conditions,so there need a large number mesh at free surface and a damping area in the border.Kelvin source method meet the free surface conditions,but when both the field point and the source point on the free surface,it will appear singularity and high oscillation,so there must be a lot of mesh within a wavelength.The idea of this paper is to combine these two methods together,let they learn from each other.Therefore,this paper research the problems as follows:Firstly,an infinite cylindrical shape control surface is arranged in the entire flow field,and the fluid domain is divided into two subdomains,inner and outer domains.The Rankine source Green function is used in the inner domain,and the Kelvin source Green function is used in the outer domain.The integration method and matching method of two Green functions on the control surface is the focus and difficulty of this paper.In order to improve the accuracy,the meshless method is used on the control surface in this paper,carrying out the series expansion of the Green function on the control surface.Fourier series is used in the horizontal direction considering the cyclical of volatility,and Laguerre series is used in the vertical direction considering the attenuation.Then,the expansion coefficient of the series is analyzed and researched in this paper.Secondly,according to the results of Green’s function in the control surface of the series,this paper research the zero-speed problem as basement and verification.This paper studies the formula derivation and numerical solution of the outer domain problem under zero speed,and verifies the outer domain method by comparing with the analytical solution by the infinite cylindrical circumference problem.The matching problem of the inner and outer domains under zero-speed is studied.Since the introduction of the control surface makes the original flow field integral equation not closed,it is necessary to find the supplementary equation on the control surface,which is the relationship between the velocity potential and its normal derivative on the control surface,and the new flow field linear integral equations under the matching method are given in this paper.The hydrodynamic coefficients of the hemisphere are calculated by the new flow field integral equations and analyzed and compared with the numerical solutions of the current methods.Then,the influence of the size of the control surface radius on the calculation accuracy and the computational efficiency is studied,which lays the foundation for the subsequent calculation of the forward speed problem.Finally,according to the previous work,this paper studies the problem of frequency domain matching at forward speed.According to the definite condition of the speed problem and the result of series expansion of Kelvin source Green function on the control surface,this paper research the formula of the outer domain and the matching formula between the inner and outer domain of the forward speed problem.Then the hydrodynamic coefficient of the hemisphere is calculated at the forward speed. |
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