Second-lrder Changes in Mean Surface Level and Long Period Motious of an Offshore Structure in Shallow Water

在本项目期间，对浅水海洋结构物的平均表面水平和长周期运动的二阶变化进行了研究，得到了以下结果：1)研究了二维双色辐射波在实验水槽中引起的局部平均表面水平的二阶变化。从数值算例中发现，自由波分量在局地平均表面能级的计算中起着重要作用。2)考虑造波者产生的二阶自由波的影响，精确求解了双色波中固定体的二阶绕射问题，发现：a)浅水中二阶速度势对二阶长周期波力的影响是不可忽略的。B)二阶长波力的合理预测。

The research on the second-order changes in mean surface level and long period motions of an offshore structs in shallow water have been done during the term of this project and the fellowing reslts have been obtained : 1)The second-order changes in local mean surface level induced by two-dimensional bichromatic radiation waves in an experimental flume with a paddel thpe wave maker have been investigated. From the numerical examples, it has been found that the free-wave vomponent plays an important roll in the evaluation of the local mean surface level. 2)The second-order diffraction problem for a fixed body in bichromatic waves has been solved exactly including the effects of second-order free wanes generated by a wave maker and it has been found that : a)The effects of the second-order velocity potential on the second-order long period wabe forces cannot ve neglected in shallow water. b)The reasonable prediction of second-order long wave forces.