Safety evaluations of an large offshore structure subjected to dynamic forces

在对海上结构进行波浪动力响应评估时，必须考虑结构特性和波浪力的不确定性。在可靠性评估中，评估不确定参数对最大响应评估的影响是非常重要的。蒙特卡罗模拟（MCS）提供了一种评估不确定性的有效方法。本文应用MCS方法对海上结构的不确定性进行了评价。研究表明，由于不确定性参数在最大响应评估中起着重要作用，因此考虑不确定性参数对响应的影响对于海洋结构的可靠设计至关重要。主要研究结果如下：(1)由于波浪力计算的不确定性对结构的响应特性有重要影响，因此明确波浪力计算的不确定性对结构的可靠设计至关重要。为了提高海上结构在强波浪力作用下的安全性，必须考虑不确定参数的影响。(2)在目前情况下，阻力系数、惯性系数等不确定性对可靠性指标的影响相对较小。另一方面，由于平均波高和平均波周期的变化对最大响应评价有重要影响，因此考虑结构可靠度指标的不确定参数贡献对于结构的可靠设计很重要。

Performing the dynamic response evaluations for the offshore structure subjected to wave forces, uncertainties on the characteristics of the structure and wave forces have to take into accounts for the response evaluations. It is very important to evaluate the uncertain parameter effects on the maximum response evaluation for the reliability evaluation. The Monte Carlo simulation (MCS) gives an effective method on the evaluations of the uncertainties. The MCS approach is applied to evaluate effects of the uncertainties on the offshore structure in the present study. It is shown that since the uncertain parameters play the important roles on the maximum response evaluations, it is important for the reliable design of the offshore structure to account for the effects on uncertainty with respect to the response. The main results are summarized as follows :(1)Since the uncertainties with respect to the wave force evaluations play important contributions on the response properties, it is essential for the reliable design of the structure to make it clear the response properties due to uncertainties. For enhancing the safety of the offshore structure subjected to severe wave forces, it is important to account for the uncertain parameter effects.(2)The uncertainties such as the drag coefficient and the inertia coefficient play relatively small effects on the reliability index in the present situation. The other hand, since the variations of the mean wave height ant and mean wave period give important effects on the maximum response evaluation, it is important for the reliable design of the structure to account for the uncertain parameter contributions with respect to reliability index.