i have a plate which is fixed at one end. I need to calculate normal modes of the plate at each at various rpms about x-axis like 0, 10000, 15000 and so on.
i have defined the entire plate as a rotor region and run a SOL 107. when i open the f06 file, the modal frequency at each rpm is not accurate. what could be the issue? i need to calculate first modes at each rpm, how do i extract this data ? thanks.
Your description is too vague to provide a meaningful answer. A plate fixed at one end does not sound like a realistic rotor. Is the end it is fixed at the axis of rotation? Perpindicular to the axis of rotation, something else?
Are you really looking for gyroscopic effects, or do you just want to account for the stress stiffening caused by the rotation?
If it's just the differential stiffness you want (i.e. similar to calculating modes of a guitar string as you increase the tension), you can do this with a standard SOL 103 analysis. Include a static subcase containing an RFORCE load, followed by a modal subcase containing a STATSUB pointing to the previous static subcase. Nastran will add the differential stiffness due to the rotational force to the structural stiffness when calculating the modes.
Thank you for your reply Jim. i have observed that the problem is about centrifugal stiffening. the plate is offset 0.64in from the x-axis and rotating about x-axis. so i ran a SOL 103 frequency response with a different rpm for each subcase. the results are kind of close. so i need to check further.