Centrifugal Forces in Dynamic Non-Linear 3D

protontim

I would like to model rotor flapping on a fixed pitch multirotor gyrocopter (see aergility.com). In "real life" the rotor experiences a time variant (position dependent) load as it rotates on its axis. I would like to replicate this loading condition and measure the tip deflection which can be quite large (several inches tip deflection on a 9' diameter rotor) and which is influenced by inertial forces. It appears that I can use the dynamic non-linear 3D solver and apply a time variant load to the blade but it does not look like a centrifugal load is available in that mode. Is there a way to emulate the centrifugal forces besides doing a "hand calculation" and applying the centrifugal loads piecewise to sections of the rotor? I can do that if I have to, but I was hoping for a better way if there is one.

Also, if anyone can suggest some reference documentation that would show me how to add a time variant load to the dynamic simulation (I would like to read data out of a file and apply it to the model over time), that would be appreciated.

protontim

Well looks like I asked a similar question a couple years ago. I am investigating that answer. Sorry for the redundancy. Still would appreciate any documentation on applying a time variant load in dynamic non-linear 3D

Victor

I think you can still use centrifugal force with nonlinear dynamic response but I haven't tested it so it's disabled. Add the centrifugal force by changing analysis type to something else that does support it, like static, then change back again afterwards. It'll appear in red with an error message but it still solves.

protontim

Excellent, thank you. I tried non linear dynamic using a ccx CENTRIF card and it seemed to work. I also verified that MECWAY centrifugal load appears to work (even though it is red). That makes things easy as far as configuration goes.

JohnM

For your time variant load, you can actually cut and paste fairly large files (time, value) directly into the table definition in Mecway. Another way to do this is to define a dummy unit load, write your CCX input file, then clip the load step into the custom load step definition. replace your dummy load with an "amplitude definition that suits your needs. what I like about this method is you can use a *include file that has this amplitude definition so if you have many load sets to try this might be the best choice.