Reliability estimation on dynamic responses of offshore structures

具有大甲板面积的海上平台可以提供开发海洋空间的巨大可能性，这些海洋空间可以用作居民区、机场、电站等。由于这些结构具有非常重的恒载，基础上的反作用力变得严重，需要非常坚固的基础系统。如果这些反作用力可以通过某种方法来减小，例如浮力型大直径构件，则具有浮力型大直径构件的大型海上平台的概念可能在海上工业中流行。在这项研究中，重点放在检查下的海浪，海流和地震的作用下，这样的结构的动力响应。主要研究结果如下：（1）在近海底设置浮力型构件的结构，其波浪力和相应的响应较小。另一方面，海流力对具有浮式构件的海洋结构物的响应评估具有重要影响，因此评估海流力对浮式构件海洋结构物的响应评估具有重要意义。（2）结构的动力响应受波浪力计算参数和结构特性参数的影响。由于这些随机参数也影响响应值，因此有必要研究它们对响应和可靠性评估的影响。(3)It在波浪力和地震力作用下，海洋结构物在激振持续时间方面具有完全不同的特性，因此有必要开发合理的方法来评估其可靠性。其中一种方法是先计算地震响应，然后将其与等效波浪响应和波浪荷载条件相关联。

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.