利用大型通用有限元分析软件MSC.patran/Nastran,以某船用柴油机机座结构为算例,并且结合类似研究中对约束条件的讨论,进行初步的线性无阻尼模态分析.在船用柴油机机座的模态分析中常存在的局部模态无法辨识,整体模态振型无法提取的实际应用问题,因而本文分别提出模态有效质量系数以及"虚拟梁"2种技巧.通过有效质量系数来进行模态结果的筛选得出具有主要影响作用的主模态,从而剔除了局部模态.通过虚拟梁的方法提取由于局部变形而无法观察到的结构整体振型.在此基础上以期能够更加深入的进行有限元模态分析,有效地将计算数据提取并加以利用.该算例得出的计算结果以及计算方法还能扩展为同类型的机座结构进行针对性的动力学优化计算.%A basement structure of a marine diesel engine is taken as a simulation example, through the MSC.Patran/Nastran, a common FEM software, to perform a basic non-damping linear modal analysis, in which the con-straint condition are compared with other similar articles. However, in modal analysis of a main engine basement structure in a vessel, there are problems that local modals can't be identified and whole modal vector can't be showed. Therefore, two skills named as modal effective mass fraction and"fake beam"are proposed. The modal effective mass fraction are used to filter all modal results to get the main modal which imposes major influence on whole structure's response, meanwhile the local modal can be removed. The"fake beam"are used to extract the whole structure's deformation which is usually invis-ible due to the local modal's deformation. Subsequently, more detailed analysis can be performed, while the calculating data and methods in this case can be utilized efficiently to optimize the dynamic character of the structure which is similar as the main engine basement.
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