Rapid 3-dimensional Hydroelastic Analysis Of Large Offshore Structures

This paper lays emphasis on the method which can improve the calculating efficiency of 3-D hydroelastic analysis, and provides a good environment for the wide application of this analysis in ocean engineering. Firstly, the method of determining the restarted number of GMRES by using Arnoldi process is put forward, the stop criterion of GMRES is given by the backward error analysis. The hydroelastic response and the second-order mean force (and moment) of large offshore structure are solved by GMRES. Numerical tests show that the computational efficiency of GMRES is higher than that of conventional method and this method can exert tremendous effect in engineering application.Secondly, the precorrected-FFT method is expanded to the hydroelastic analysis from the rigid body hydrodynamic analysis, and a grid singularity collocation method is presented which can make the precorrected-FFT method use less calculating time and occupy less memory. The hydroelastic analysis of single and multiple elastic floating bodies is carried out by the precorrected-FFT method. Due to the high computational efficiency of the precorrected-FFT method, the naval architects now can use this method on personal computers to solve the hydroelastic response of large offshore structures that could be computed only on workstations or parallel computers many years ago, which means that the precorrected-FFT method has met the demand of engineering application.Because of the difference of the hydrodynamic pressure on the wet surface of marine structures, it is the naval architects' concern for a long time that after the hydrodynamic or hydroelastic analysis how to add the hydrodynamic pressureonto numerous finite elements so as to analyze the structure strength of marine architecture. In this paper we propose a method based on the Patran Command Language which can automatically load the hydrodynamic pressure for the FEM analysis of marine structures in frequency domain. The elements on waterline and below waterline are treated separately. The pressures acting on elements below waterline are added onto the panels directly using PCL. The quadrilateral elements on the waterline are translated into triangle elements. The distributed pressure on the triangle elements are translated into concentrated force and added onto the nodes using PCL. This method thoroughly solves the difficult problem that has puzzled the naval architects for many years.