Learning Forum

[Kuba]

Hi, nI have built my model (axisymmetric), constrained it and solved in Static Structural. The solution looks quite satisfying, but I want to use it as a pre-stress condition for a modal analysis, because the part is rotating with velocity of about 30 000 RPM, so stress stiffening can affect the modal solution. The problem is that when I turn The Coriolis Effect On in Static Structural, I get stress equal to 0 in a whole model. Could someone tell me what should I do? nThanks in advancen

[peteroznewman]

nTo pre-stress an axisymmetric model of a rotor, apply a Rotational Velocity load. That way, you enter the rotor speed in Rad/Sec and the axis. The stress from that load will be computed.n

[Kuba]

Thank You for reply,. nThe problem is that I did that. If You have a while, please take a look at screenshots below.nThis is my geometry:nThe method of constraining is Yours, Mr. Peter, I've found it in some other topic. The rings and lumped masses simulate centrifugal and inertial load from blades. Mass points are connected to outer rings surfaces:nRotational velocity is given as a tabular data and stress results of static calculations with Coriolis Effect OFF for the highest velocity are (Coarse mesh only for demonstration):nNow, the problem is that when I turn The Coriolis Effect in Static Structural on, I get zero stress:nPre-stressed Modal needs Coriolis Effect to be turned on in Static Structural, so my question is: What should I do to properly include Coriolis Effect, so I can proceed with pre-stressed Modal?

[hari.sh]

Hi, 

Can you please explain how you constraint the lump mass to simulate centrifugal and inertial load?

[Kuba]

Are there any differences between principles of modeling structures in stationary and rotating reference frame? By default, model is solved in rotating reference frame and the results seem okay. The only thing I changed in order to conduct further investigations on pre-stresed structure was turning on the Coriolis Effect, which changes reference frame to stationary. If you know why do I get zero stress in such conditions, Please let me know. nKind Regards n

[Rahul Kumbhar]

nWhen omega is applied in Static Structural analysis, the effect due to centrifugal load is already calculated. Now, if we turn on coriolis in SRF then gyroscopic effect is introduced as a load vector again.nYou can follow this APDL example. You can see coriolis effect is off in static analysis here.nhttps://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v202/en/ans_rot/Hlp_G_ROTEXCAMPPRES.htmln

[Kuba]

The point was, that turning on Coriolis didn't work. By trial and error I found that adding APDL command PSTRES,ON was what I expected, however I am not sure why this commad works such way. nAnyway, as I was expected, another obstacles occured in modal analysis:nDo you know what these errors mean? I already tried to find the answer on the Internet, but I found nothing and I don't want to waste another 2 weeks on searching.n

[Rahul Kumbhar]

Hi @Kuba,nLooks like it is giving error because coriolis effect is ON in both static and modal. Please check the previous APDL example link and try setup similarly. In the example, coriolis effect is turned off and in modal analysis it is on.n

[Kuba]

that is correct, because when Coriolis is turned off in static, there is an error in modal saying ?Coriolis effect is off in the base analysis(...)?n

[sbo]

nRotating frame and stationary frame are used to make rotordynamic analysis in ansys. Ansys default option is rotating refererence frame without coriolis effect. (coriolis,on,,,off). When you open the coriolis effect in workbench, you change your frame from rotating to stationary with gyroscopic moment (Coriolis force in rotating frame). Centrifugal force does not have any effect in SRF. Please read how to derive equation of motion in stationary frame in any rotordynamic book, Therefore, when you open coriolis effect, it blocks centrifugal forces which is correct. So make you analysis without adding pres-stress due to centrifugal forces in SRF. n