Learning Forum

[Allen Sirkin]

I am trying to make a model of fan blades rotating however no matter how I try to set up the dynamic relaxation I end up with different kinds of errors resulting in the failure of the model and many elements being deleted. The model uses a rigid element to rotate the bottom of the shaft which should in turn cause the fan blades attached to the shaft to spin as well. When run without dynamic relaxation I set the curve for the angular velocity to slowly ramp up and then maintain the peek velocity to. Now I would like to run it using dynamic relaxation so that it can start at full speed however trying to run it both by ramoping up the angular velocity and starting it at the maximum in the dynamic relaxation stage has resulted in errors in oveer a dozen ways I have tested it. Any advice on how I should set it up would be greatly apreciated. 

[Reno Genest]

Hello Allen,

Is the fan blade rotating in the the dynamic relaxation phase? Dynamic relaxation us used to find the static equilibrium of a system under preload. For example, a car under gravity, bolt pretension, etc. So, if the fan blade is rotating, you won't be able to find the static equilibrium. 

The way to do this is to apply rotational centrifugal preload (without rotation) in the dynamic relaxation phase using *LOAD_BODY_RX and then apply the real rotation as an initial condition at time 0 of the explicit phase using *INITIAL_VELOCITY_GENERATION. See the following example from the Aerospace Working Group:

https://awg.ansys.com/AWG+ERIF+Test+Example+12

The Aerospace Working Group is a great resouce with example models and documents:

https://awg.ansys.com/tiki-index.php

https://awg.ansys.com/Resources

https://awg.ansys.com/MGD

 

Let me know how it goes.

 

Reno.

 

[Allen Sirkin]

Thank you for your help. I was able to get my model to work correctly.

[Reno Genest]

Hello Allen,

Great! Thank you for the update.

Have a great day!

 

Reno.