Development of dynamic simulation method for floating bridges subjected to wind and wave loadings

本研究的目的是开发一种方法来预测风和波浪载荷作用下的浮桥的动态响应，其中可以同时考虑以下三个项目：1）上部结构的弹性变形，2）水动力的频率依赖性，和3）系泊系统的非线性恢复力特性。为了实现这一方法，本文进行了以下工作：1）对浮桥上部结构进行有限元建模（FEM; NASTRAN），并通过定义在浮基端点处的附加质量和阻尼特性来模拟包括频率依赖性在内的水动力特性; 2）在模态坐标中，用Newmark-β法求解了频率相关的水动力和非线性恢复力特性的记忆效应函数，编制了在时域内预报浮桥在不规则波作用下动力响应的计算机程序。本研究以分离式浮体基础之浮桥为研究对象。浮式基础采用六自由度刚体模型，上部结构采用线弹性体模型。系泊系统被建模为具有非线性恢复力特性的弹簧。由于辐射波浪力的频率依赖性，在时域中考虑了记忆效应。开发程序的方法与几个典型的分离型浮式基础浮桥的数值算例。

The objective of this research is to develop a method for prediction of dynamic response of a floating bride subjected to wind and wave loadings where the following three items can be considered at the same time 1) elastic deformation of the superstructure, 2) frequency dependence of the hydrodynamic forces, and 3) nonlinear restoring force characteristics of the mooring system. In order to realize such a methodology, the following procedure has been implemented: 1) the super-structure of the floating bridge is modeled by Finite Element Method (FEM; NASTRAN is actually used) and the hydrodynamic force characteristics including frequency dependency is modeled by added-mass and damping characteristics defined at the nodal-points of the floating foundations, 2) in the modal-coordinates, the memory-effect function of the frequency-dependent hydrodynamic force and the nonlinear restoring force characteristics is solved by Newmark-β method.Then, the development of a computer program for prediction of dynamic response of a floating bridge subjected to irregular waves in the time domain has been made. In this research, the floating bridge with separate-type floating foundations is considered. The floating foundations are modeled as rigid-bodies, each of which having six degree of freedoms, and the super-structure, which connects the floating foundations, is modeled as linear elastic-body. The mooring systems are modeled as springs having nonlinear restoring force characteristics. Because of the frequency-dependence of the radiation wave forces, the memory effect has been taken into account in the time domain. The methodology of the developed program is presented with several numerical examples for a typical floating bridge with separate-type floating foundations.