Calculation And Analysis Of The Steady Wave Drag And Free Surface Waves Induced By Ships

Steady ship wave problem,which mainly considers wave drag and free-surface waves generated by a ship that advances along straight path at a constant speed in calm water,is a key point to the speedability of ships.As is well known to all that the speedability of a ship includes resistance,of which the wave drag is a significant part,and propulsion.So it is necessary and meaningful to have a deep understanding of steady ship wave problem.On the other hand,an accurate and efficient wave drag solver can be widely useful for routine applications to preliminary ship design and hull-form optimization.In addition,analysis of the free-surface waves induced by a ship may give us a more profound thinking of the mechanism of wave-making resistance and interference effects of ship waves.The thesis developes a steady ship wave solver based on the Neumann-Michell theory combined with the practical method to evaluate the near-field and far-field ship waves which is also put forward in this thesis.For illustration and validation purpose,the solver is applied to five hulls,specifically Wigley,Series 60,KCS,DTMB 5415 and Delft,with both monohull ship and catamaran included.Comparisons between experimental measurements and numerical predictions are also considered here.Furthermore,the thesis gives an analysis of the apparent wave angle where the largest waves created by a ship are found based on the interference model between divergent waves created by the ship hull.The numerical validations of the narrow ship wake are also reported in the thesis.The Neumann-Michell(NM)theory was first proposed by Noblesse in 2013.The theory is within the framework of linear potential flow and the expression given in NM theory is a consistent linear approximation compared with the Neumann-Kelvin(NK)theory.Thus,the waterline integral of the NK flow representation is eliminated in the NM flow representation.Meanwhile,the numerical inaccuracies associated with the evaluation of the waterline integral are then moot issues in the NM theory.Additionally,the iterative approximations in the NM theory make it more efficient than the Hess-Smith method used in the NK theory.The Fourier integral is a major and critical element of the computation of ship waves.The integrand of the Fourier integral is a trigonometric function and oscillates rapidly in the far-field.Accurate numerical integration of the Fourier integral in the far-field therefore requires a huge number of integration points and is not practical.Based on the Kelvin’s Stationary phase theory,a modification,which eliminates the rapidly oscillatory part in the far-field,to the integrand of the Fourier integral is made in the thesis.The modification is also applied in the solver based on the NM theory to calculate near-field and far-field ship waves.The solver is applied to five hulls,specifically Wigley,Series 60,KCS,DTMB 5415 and Delft,with both monohull ship and catamaran included for validation and verification purpose.And comparisons between experimental measurements and numerical predictions of wave drag,sinkage,trim,wave profile,wave cuts are also reported in the thesis.In addition,the thesis analyzes the interference effects on the Kelvin wake of fast ships.The apparent wake angle expression,with regard to Froude number,of a ship is also given in the thesis.And numerical predictions of free-surface waves created by a series of monohull ships and catamarans are illustrated and compared with the largest wave angle expression derived from the analysis based on the divergent wave interference model.It also validates the divergent wave interference theory.