【摘要】 桩基式海洋平台的组成,是由平台及其上部设备搁置在钢导管架的顶部,并用桩通过导管架的桩腿打入海洋土壤中,将导管架固定到海底,在动力分析中总是必须要考虑流体-结构-桩-土的相互作用。作用于这一系统上的动载荷包括波灌、风载、流、设备载荷、地震等。其中波浪载荷是基本重要而且在本质上是非线性的。桩土的相互作用可由分布的弹簧表征,其刚度的非线性变化由p-y曲线定出。由于这一大型复杂系统的求解方程,无论是线性或是非线性的,其自由度都太高,采用通常的有限单元法进行动力分析是困难的其至是不可能的。 本文首先采用一种模态综合技术,即部件模态综合法,进行模态分析;而后将模态综合和模态叠加法推广到研究在规则波浪载荷作用下系统的非线性动力响应。按照特定的波浪理论,由给定的设计波可以计算出波浪力。由模态综合和模态叠加获得减缩的系统非线性动力方程,采用直接积分法(Newmark-B)进行求解,在每一步长或迭代过程中,非线性波浪力和非线性土壤反力将移置到方程右端作为伪力矢量。这样可以节省计算机的存贮和机时,其成功的关键是由于能够显著地降低系统的自由度而又不改变问题的物理本质。采用两次成功的减缩方法,系统自由度可以下降两个量级,例如1000自由度系统可以降为100自由度进行模态分析,?更多还原

【Abstract】 The interaction of fluid-structure-pile-soil always has to be considered in the dynamic analysis of fixed offshore platform, which consits of a deck and some equipments on it, resting on the tap of s steel jacket, and this is fixed to the seabed by a set of piles, which generally pass through the legs of jacket and then penetrated into the soil.The dynamic forces applied on such system include loads due to waves,-winds, currents, operations, earthquakes, etc. Among these, the wave loads are of fundamental importance and have a nonlinear nature. The pile-soil interaction can’be represented by distributed springs, whose stiffness vary rionlinearly acconding to P-Y curves.The dynamic analysis of such a large complex structural system is difficult or impossible by means of the usual finite element method, because the number of DOF of linear or nonlinear equations to be solved is too large.In this paper, at first, a kind of modal synthesis technique, component mode synthesis, is applied in the study of modal analysis; and then the modal synthesis as well as modal superposition are extended to the study of nonlinear dynamic response of such system, which are subjected to regular wave loads. Considering aparticular wave theory, the wave forces.are computed for a given design ware. The direct integration method (Newmark-β method) is adoped for the solution of the reduced nonlinear dynamic equations, which are performed by modal synthesis and mode superposition. In the approach, the nonlinear wave forces and nonlinear soil reactcon forces are transfered from the left hand of the equations to the .right as pseudo force vectors in each steps or iterations. Thus considerable saving in computer storage and execution time can be expected. The key to success is due to the significant reduction in the number of DOF. without distorting the physical essence of the problems. Using two successive reduction techniques, the number of DOF of system can be reduced by two orders, for example,the number over than 1000 DOF can be reduced to 100 DOF for modal analysis. Further truncated to 10 DOF, the nonlinear dynamic response can be analyzed easily.Up to now, the reduction methods to problems in nonlinear dynamic analysis have been limited, but this kind of work is of particular importance for large complex systems, whose predicted nonlinear response are costly and time-consuming. Using the final computer program DAPOS, the examples showing the advan-ages and success of the presented method are given.更多还原