Using the Drop Test Module, (DTM), I made a simple four element beam model and "dropped" it as follows:
gravity = 0 and plenty of initial height so that the model can spin without interference
translational velocity = 0
rotational velocity = -6.28 (rad/sec)
With a solution time of 1 second, I expected the beam's final position to be 6.28 radians (1 revolution) from the starting position. But the solution shows that the beam only gets to 2.47 radians after 1 second. Can you please explain why?
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To define an initial angular velocity, you must simultaneously define an angular velocity AND spatially varying (proportional to radial coordinate) translational velocities. The initial rotational velocity specification applies only to elements having rotational degrees of freedom. For example, SOLID164 elements will be completely unaffected by an initial angular velocity since they have no rotational DOFs. The way in which the initial angular velocity feature is presented in the GUI is misleading. In general, it does NOT cause an entire body to rotate about its axis at the specified value of angular velocity. Additional notes: In conclusion, there are 2 ways to define initial angular velocity: 1) Use VGEN option, specify ONLY angular velocities 2) Use VELO option and specify initial translational velocities equivalent to desired initial angular velocities PLUS initial angular velocities (if nodes have rotational DOFS which they do for beams and shells). |
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