柱壳和锥壳结构自由振动特征的数值计算与校验

为了评估柱壳和锥壳结构自由振动特征数值计算的精度,分析不同边界条件、环肋、纵肋以及流体载荷对自由振动特征的影响,计算并校验了典型壳体结构在空气中、浸没以及浸没并充满水情况下的自由振动特征。结果表明,空气中干模态分析在2 kHz内、单面及双面接触水情况下的流固耦合湿模态分析在500 Hz内的计算精度能够控制在10%以内。壳体流固耦合自由振动分析时可以采用实体单元离散也可以采用壳单元离散的方法,前者精度略高,能够有效保证求解收敛的频带范围更宽,但工作量更大。径长比大于0.2时,浸没于水中的自由振动分析可以转换为内部填充水时的自由振动分析,转换时应保证两者流固耦合湿表面积相等,如半浸水和半充满水,能够有效减小计算量;环肋和流体载荷对壳体自由振动特征的影响明显,环肋使柱壳同阶自振频率增加,流体载荷使柱壳同阶自振频率减小且影响幅度更大,两者均会使得柱壳模态振型呈现错序排列;流固耦合效应对无肋柱壳和环肋柱壳自振频率的影响效果相当;柱壳内外有水相对于单面接触水而言,同阶自振频率进一步减小,模态振型基本不变;流体载荷对环肋锥壳的自振频率和模态振型的影响幅度较对环肋柱壳小。 

Numerical prediction and validation of natural vibration characteristics of cylinder shell and conical shell

Numerical prediction of the natural vibration characteristics of ring-stiffened and axial stiffened cylindrical shells and conical shell with different boundary conditions and being immersed in air and water and filled with water were conducted. Within this process, numerical precision of calculations were validated. Results show that numerical precision of dry modal analysis over the frequency range of 2 kHz and wet modal calculations with one or two-side added water in the range of 500 Hz is limited with a maximum difference less than 10%. Natural vibration of cylindrical shell coupled with fluid-solid interaction (FSI) can be processed by solid or shell mesh element, wherein the solid element discretization method qualifying a little higher precision and a winder efficient frequency range compared with that of shell element method with the cost of a lot more work. The natural vibration analysis of shell structure with diameter- to-length ratio bigger than 0.2 immersed in water is able to be switched into the case of filled with water with equal wetted surface area to decrease the computational load including partial FSI interface. The ring ribs and static fluid load significantly affect the natural vibration of cylindrical shell including both the natural frequency and modal shape, exactly speaking, the ring ribs inducing an increase of natural frequency whilein a contrary direction for the fluid load with a bigger rate. The phenomenon of different order of modal shape exists for both of the two affecting factors. The effect of FSI on natural frequency of cylindrical shell with or without ring ribs is considerable. Compared to the case of being contacted with one side water, the cylindrical shell contacted with two-side water shows a further reduction of natural frequency but the modal shape basically unchangeable. The effect of fluid load on natural frequency and modal shape for conical shell is smaller than that for cylindrical shell.