modify world in gazebo [closed]

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I want to create a new world file in gazebo, but failed every time. after i added my model and save it as, the terminal show the errors below and cannot save it succussfully.

Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration] Error [Param.cc:363] Unable to set value [-nan -nan -nan -nan -nan -nan] for key[acceleration]

anyone who can help me ? thank you in advance～