Experimental and Numerical Study on Holding Power of Rectangular-Shaped Anchors

This paper discusses the experimental and numerical investigations for the holding power of rectangular-shaped anchors. As the offshore developments are promoted, the mooring systems are often used as the station keeping systems of the marine floating structures. From a viewpoint of the energy consumption, the mechanical mooring systems with anchors are better than the dynamic mooring systems with thrusters. Up to now, however, the research and development regarding the mooring systems with the high holding anchors in the deep sea area, especially more than 500 m in depth, have hardly been carried out in Japan. In most cases, the conventional anchor shapes have experimentally and/or empirically been decided. In addition, only a few studies which relate the numerical analysis to the experimental test have been performed for the holding power. In order to obtain the optimal shape of anchors theoretically, therefore, the purpose of this study is to develop the estimation method for the holding power and to clarify the penetration mechanism of anchors in soil. In this paper, a series of experiments utilizing the small-sized anchor model is conducted. Here, the fluke shape of specimen is modeled by the rectangular flat plate for simplicity. From several experiments varying the geometric characteristics of the anchor model, the experimental results, e.g., the history of the holding power, the penetration depth, and the fluke surface angle at the maximum holding power, are obtained. Furthermore, the numerical simulation to evaluate the holding power is also carried out using the dynamic explicit non-linear finite element analysis (NLFEA) code, LS-DYNA, as well as the in-house distinct element method (DEM) code. From the comparison between the numerical results and the experimental results, the calculation accuracy is verified.

Understanding Regular Waves Effect on Ship by Numerical Wave Tank Simulation

This study establishes three-dimensional numerical wave tank based on the theory of viscous flow to simulate the unsteady motion response of a Wigley advancing in regular heading waves. The governing equations, Reynolds Averaged Navier-Stokes and continuity equations are discretized by finite volume method, a Reynolds-averaged NavierStokes solver is employed to predict the motions of ship, and volume of fluid method is adopted to capture the nonlinear free surface by writing user-defined functions. The outgoing waves are dissipated inside an artificial damping zone located at the rear part (about 1-2 wave lengths) of the wave tank. The numerical simulation results are compared with theoretical and experimental data from Delft University of Technology, and show good agreement with them. This research can be used to further analyze and predict hydrodynamic performance of ship and marine floating structures in waves and help to extend the applications of numerical wave tank.