多色波绕射的低频作用问题研究

Study on Low-Frequency Effects of Multicolored Wave Diffraction

海洋的层化将导致流域中表面波与内波共存现象的出现,从而引起对大尺度离岸结构的多色波绕射作用,其中就包括了可能引起结构共振的二阶低频作用.基于层化海波浪理论,对二层海洋中垂直圆柱可能承受的低频力即二阶水平漂移力和二阶差频力给予了分析.给出了多色波绕射二阶低频力的一般算式,并对直柱的二阶平均漂移力和最大二阶差频力进行了实算.结果表明:海况条件以及结构参数的变化对于低频波浪力存在一定影响,而最大二阶差频力可能与二阶平均漂移力具有相同量级.

Ocean stratification may cause surface wave and inner waves concurring in flow region, which will lead to multicolored wave diffraction effects, including second order low-frequency forces possibly resulting in body resonance, on large scale offshore structures. Based on stratified ocean wave theory, second order drift forces and second order difference-frequency forces on vertical circular cylinders in two layer ocean had been analyzed. The formulas of second-order low-frequency force of multicolored wave diffraction were derived, and the second-order drift force and difference-frequency force on a single vertical circular cylinder were evaluated. The result shows that the variation of ocean condition and structure parameter have some effects on low-frequency forces and in some case the magnitude of difference-frequency force is close to that of second-order drift forces.