多体动力分析出现这个问题，请问有大神能看一看么，谢...

Huy

用abaqus做多体动力分析，提交作业后报错
Global mass matrix is singular. Please specify proper material densities, concentrated masses and rotary inertias, or nonstructural mass to fix the mass matrix. As a workaround, *dynamic, singular mass=warning can be used.

Abaqus/Standard Analysis exited with an error - Please see the  message file for possible error messages if the file exists.

请问有大神了解么？谢谢！