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The shape of the ship’s forebody has a greater impact on the ship’s resistance, and a reasonable optimization of the forebody can play a role in reducing the propulsion power and optimizing the resistance performance. Under the premise of Rankine source method of potential flow wave theory as the theoretical basis, SHIPFLOW software is used as the calculation tool, and CAESES software is used as the optimization tool to study the optimal design of the ship with minimum wave resistance. In the optimization process, a real ship is taken as the object, and the optimal solution of the rising wave resistance coefficient is calculated with the rising wave resistance coefficient as the objective function and the ship speed and displacement as the constraints. The real ship is selected as the mother ship, the parameters of the hull shape are taken as the design variables, and the shape of the forebody is optimized by the Lackenby shift method, so as to obtain a ship shape with less wave resistance at the same speed and within the displacement limit. The results show that the improved ship shape has obvious effect of reducing the wave resistance, which verifies the effectiveness and feasibility of this method for ship shape optimization

The wave loads and motion responses of an Unmanned Surface Vehicle (USV) in water will directly influence the powering requirement, energy supply design and function of the installed sensors. In the present article, to investigate the wave loads and motions response characteristics of a USV advancing on the free surface, a Higher-Order Rankine Source (HORS) method is proposed. During the discretization of the boundary elements, bi-quadratic B-splines are applied to distribute the velocity potentials on the body surface and free surface. Based on the proposed HORS method, steady state simulation and time-domain simulation approaches are both used for predicting the wave loads and motion responses of a novel Small Waterplane Area (SWA) USV in calm water and regular waves, respectively. The predicted wave loads in calm water and the predicted heave and pitch in heading wave are compared with corresponding model test data. The good agreement found indicates the validity of the proposed HORS method. Finally, the heave and pitch motion responses and the wave components of the USV including diffraction and radiation forces and Froude−Krylov forces are investigated when the SWA USV is running against heading wave under different conditions of wavelength, wave steepness and advancing velocity.

Yin, X.; Lu, Q.; Lu, Y.; Zou, J., and Wan, L., 2021. Hydrodynamic optimization of foreship hull-form using contrastive optimization algorithms. Journal of Coastal Research, 37(5), 1063–1078. Coconut Creek (Florida), ISSN 0749-0208. In this study, a hydrodynamic optimization design of the foreship hull-form for the Series 60 ship is presented in terms of minimum wave-making resistance by using contrastive optimization algorithms. The partially parametric approach was developed to modify the original foreship hull-form. The wave-making resistance as an objective function was obtained by the Rankine source panel method with nonlinear free-surface boundary conditions in which the numerical computation results were validated against available experimental data and found to be in good agreement with the test. Different optimal design methods were proposed based on the minimum wave-making resistance: the nonlinear programming method (NLP), the nondominated sorting genetic algorithm (NSGA-II), and particle swarm optimization (PSO). Through the implementation and integration of the hull-form deformation module, the hydrodynamic module, and the optimization module the hydrodynamic optimization framework can be established subsequently. This module realizes the full automation of ship-shape optimization design and searches for the most efficient target through intelligent optimization algorithm. The hydrodynamic optimization applications for the Series 60 ship indicate that the wave-making resistance is reduced distinctly at various Froude numbers by the contrastive optimization algorithms and each optimized foreship hull-form is smoothing. The present study demonstrates an effective and robust integrated approach for the hydrodynamic optimization of ship design.

A novel numerical method combining Eigenfunction matching method (EMM) and 3D Rankine source method is developed to investigate wave-body interaction over a sloping bottom. The extended EMM is proposed to create an incident wave model over the sloping bottom, thereby obtaining the Froude-Krylov force and Neumann data on wet surfaces of the floating body for the diffraction problem. A 3D Rankine source method concerning the sloping bottom is developed, in which the free surface and seabed are both divided into the inner domain and outer domain. Source panels are placed in an exponential manner in the latter domain, by which the far field radiation condition is well satisfied. To verify the proposed method, comparisons with other mathematical models involving added mass and damping coefficients, wave exciting forces and motion RAOs by a floating hemisphere and a LNG carrier are carried out.

This work presents a comparison of two analytical methods on the components of resistance, transverse and divergent waves, and the profile and contour of the waves. Michell’s thin linearization theory is applied to estimate the wave resistance and analysis of the method compared to the solution of the wave resistance coefficient based on the Rankine source method. The hull of series 60 is utilized as the initial hull, and varying the shape of the bow to the mid-ship with the hull offset variable. Computation of the wave resistance coefficient at low Froude number (Fr<0.3) shows the results of the wave resistance from the thin ship theory are higher, but it gives a graphical agreement with the Rankine source method. The wave profile provides a very similar profile line for both of them. However, the thin ship theory does not establish a significant difference in the wave profile from the initial hull of the improved hull variation. Comparison of contour displays is presented in different versions of the wave contour. Still, it affords a good contour match on the initial hull and the results of hull variations from both methods. At high Froude number (Fr>0.7), the initial hull and variations in the hull have minimal effects with small differences in wave resistance, profile and contour.

This paper presents a frequency-domain Rankine source method based on a biquadratic B-spline scheme with an improved radiation mechanism. The improved radiation mechanism, based on the introduction of spatially varying Rayleigh artificial damping in addition to the simplified Seto’s radiation boundary conditions, is considered for modeling radiation of generated waves at various τ conditions, where τ=ωU/g including the undercritical condition (τ<0.25); this condition is present when a ship undergoes slow translation or low oscillatory frequency. In evaluations, the proposed method yields accurate solutions for unsteady flows produced by an oscillating, translationally moving submerged singularity. The radiation problem induced by a RIOS bulker is solved to have the resultant added mass and damping coefficients for further comparisons with the experimental data and the public numerical prediction by a simplified combined method at a wide τ region.

There is plenty of energy contained in the ocean waves, and great efforts have been made over recent decades to make full use of these sustainable energy resources. As a novel device to utilize ocean wave energy, the authors propose in this paper a whipping energy converter, which utilizes a linear generator extracting power from ship’s whipping and springing (hull girder 2-node vibration) responses. The device is designed resonant to the hull girder 2-node vibration frequency. Numerical simulation of the responses of the whipping energy converter was carried out under irregular head sea condition, using time domain ship motion analysis by Rankine source method and subsequent three-dimensional whole ship FE analysis, and the main parameters of the whipping energy converter was studied. A 14,000 TEU large container ship was utilized in this study, because large container ship is prone to constant whipping and springing responses in real seas. As a result, it was found that the whipping energy converter can effectively generate power from the whipping and springing responses, and at the same time, the whipping energy converter functions as a dynamic damper. With the piston weight of 5–10 tons, the whipping vibration is visibly reduced, while if the piston weight is about 100 tons, the spectral peak is reduced to less than one-third. This implies that the whipping energy converter contributes to the prevention of fatigue damage due to whipping and springing, which is an imminent concern in the design of large container ships. It was also found that larger power generation can be expected as the piston weight is heavier, and the bow is the most effective location for this device.

Finite water depth effect for wave-body problems are studied by continuous Rankine source method and non- desingularized technique. Free surface and seabed surface profiles are represented by continuous panels rather than a discretization by isolated points. These panels are positioned exactly on the fluid boundary surfaces and therefore no desingularization technique is required.Space increment method is applied for both free surface source and seabed source arrangements to reduce computational cost and improve numerical efficiency. Fourth order Runge-Kutta iteration scheme is adopted on the free surface updating at every time step. The finite water depth effect is studied quantitatively for a series of cylinders with different B/T ratios. The accuracy and efficiency of the proposed model are validated by comparison with published numerical results and experimental data. Numerical results show that hydrodynamic coefficients vary for cylinder bodies with different ratios of B/T. For certain set of B/T ratios the effect of finite water depth increases quickly with the increase of motion frequency and becomes stable when frequency is relatively large. It also shows that water depths have larger hydrodynamic effects on cylinder with larger breadth to draft ratios. Both the heave added mass and damping coefficients increase across the frequency range with the water depths decrease for forced heave motion. The water depths have smaller effects on sway motion response than on heave motion response.

The main objective of this article is to describe an innovative methodology for the hydrodynamic optimization of a ship bulbous bow which considers multiple operating conditions. The proposed method is more practical and effective than the traditional optimization process, which is only based on contractually specified design condition. Parametric form approaches are adopted by employing an F-spline curve in order to generate variants of the hull bulbous bow forms using form design parameters modified, resulting in an optimization system based on improved genetic algorithms. The Rankine source panel method is used for the hydrodynamic evaluation, wherein non-linear free surface conditions and the trim and sinkage of the ship are taken into consideration. The validity and effectiveness of the proposed methodology for a large container ship is investigated by comparing the computational results with experimental data, which demonstrates that the proposed methodology can engage well in the automation process and improve hydrodynamic performance during actual ship design practices.