Reliability estimation on dynamic responses of offshore structures

大甲板面积的海洋平台为开发海洋空间提供了很大的可能性，可作为居住区、机场、发电站等。由于这些结构具有非常大的自重，基础上的反作用力变得非常大，需要非常牢固的基础体系。如果可以通过浮力式大直径构件等方法减小这些反作用力，那么浮力式大直径构件大型海洋平台的概念可能会在海洋工业中流行起来。在本研究中，重点研究了这种结构在海浪、海流和地震作用下的动力响应。结果表明：(1)靠近海底的浮力型结构的波浪力和相应的响应较小。另一方面，水流对具有浮力构件的海上结构的响应评估有重要影响，对这些影响的评估具有重要意义。(2)近海结构的动力响应受波浪力评估和结构特性相关参数变化的影响。由于这些随机参数也会影响响应值，因此有必要研究它们对响应和可靠性评估的影响。(3)海洋结构在波浪力和地震力作用下的可靠度评估有必要制定合理的方法，因为波浪力和地震力在激发时间上具有完全不同的特征。其中一种方法可能是先计算地震反应，然后将其与等效波反应和波荷载条件相关联。

Offshore platform with large deck area may provide great possibilities to develop ocean spaces which may be used as resident areas, airport, power stations, etc.. Since these structures have very heavy dead loads, reaction forces on the base foundation become severe and necessitate very firm foundation system. If thses reaction forces can be reduced by some method such as large diameter members of buoyancy-type, the concept of large offshore platforms with the buoyancy type large diameter member may become popular in the offshore industry. In this study, emphasis is placed on examining the dynamic response of such a structure under the action of sea waves, currents and earthquakes. The main results are summarized as follows :(1)The wave forces and the corresponding responses are amaller for the structure which has the buoyancy type member near the sea bottom. On the other hand, the current force gives significant effects on the response evaluations for the offshore structure with buoyancytype member and it is important to evaluate these effects.(2)The dynamic responses of the offshore structure are influenced by the variation of parameters which are related to the wave force evaluation and structural characteristics. Since these random parameters also influence the response values, it is necessary to examine their effects on the responses and the reliability evaluation.(3)It is necessary to develop rational methods to evaluate the reliability of offshore structures subjected to wave and earthquake forces which have entirely different characteristics in terms of excitation duration. One of the methods may be to compute the earthquake response first and then correlate it to the equivalent wave response and the wave loading conditions.