The literature about the mass associated with a certain mode, usually denoted as the modal mass, is sparse. Moreover, the units of the modal mass depend on the technique which is used to normalize the mode shapes, and its magnitude depends on the number of degrees of freedom (DOFs) which is used to discretize the model. This has led to a situation where the meaning of the modal mass and the length of the associated mode shape is not well understood. As a result, normally, both the modal mass and the length measure have no meaning as individual quantities but only when they are combined in the frequency response function. In this paper, the problems of defining the modal mass and mode shape length are discussed, and solutions are found to define the quantities in such a way that they have individual physical meaning and can be estimated in an objective way.

中文翻译：

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结构动力学中的模态质量和模态形状的长度

关于与某种模式有关的质量（通常称为模式质量）的文献很少。此外，模态质量的单位取决于用于标准化模态形状的技术，其大小取决于用于离散化模型的自由度（DOF）数。这导致了这样一种情况：模态质量的含义和相关的模态形状的长度未被很好地理解。结果，通常，模态质量和长度量度都没有意义作为单独的数量，而仅当它们组合在频率响应函数中时才有意义。本文讨论了定义模态质量和模态形状长度的问题，