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no gyroscopic effect is detected

Experimenter
Experimenter

Dear all,

During the study of Rotor dynamic I have encountered problem that gyroscopic effect is not detected. The related example is “6.2.3 Rotating Cylinder Modeled with Solid Elements” (Page 107, NX Nastran 9 Rotor Dynamics User’s Guide). After read the example, I have read excises

After I read this example, I’d like to make an excise with a simple Jeffcott rotor.

 

The Difference between the example and my excises:

  1. In the excise 2D mesh (shell elements) is not created;
  2. The shaft and the plate are through “face gluing” connected;
  3. Density of the whole shaft is defined. In the example is the density at the middle part defined. In other words the density in both end parts of the shaft is 0.

 

The results are following:

  1. First I analyze with SOL 103, to check whether the modals OK are. Please see the 1. Picture.

caculation result SOL103.JPG2. Then in the SOL110 simulation run in NX 9.1 the whirl directions for all solutions are linear. Theoretically the 4. and 5. solution (by 22.7 Hz) are tilting modes. There should be forward and backward whirl. But it seems no gyroscopic effects are detected. I have upload the input .dat data of my excise.

 

Detection of whirls in SOL110.JPG

 

Could someone kindly explain why the gyroscopic effect is not detected? 

 

Best Regards

TEX

09.01.2015

3 REPLIES

Re: no gyroscopic effect is detected

Siemens Phenom Siemens Phenom
Siemens Phenom

The gyroscopic terms are 0 because of difference #1. Grids attached to solid elements have no rotational terms so no gyroscopic forces can be calculated from them in the fixed system. The solid faces need to be coated with thin shells to give the grids rotational terms.

Re: no gyroscopic effect is detected

Experimenter
Experimenter

Many thanks, Jim. With your hint I have solved this problem. I have also found, when man create surface coat elements, it is also to select “net in solver export” in “Grid settings”, otherwise the gyroscopic effects cannot be detected.

 

surface coat.JPG

 

Thank you again for the explanation.

 

Best regards

TEX

19.01.2015

Re: no gyroscopic effect is detected

Experimenter
Experimenter

Hi, 

 

I'am trying to make a campbell diagram for a sepcified model by SOL 110. 

My output-campbell diagram have to be something like this: 

 

Afb2.JPG

 

My settings(rotordynamic output) and model is like this: 

 

Afb1.JPG

The thin piece is from steel 

The cilinder is from aluminium. 

I've created two different meshes en conncect the two pieces with an mesh mating condition. 

 

As explained in this topic i created a surface coat. One for the cilinder and one for the thin piece (is this correct). 

 

I don't have created 1D-mesh, because i think this is not needed for this model because there is no bearing. (ok?)

 

when a post process a campbell diagram, the solution for my eingenfrequencys are like this:

 

Afb3.JPG

 

 

As you see this is not similair from my expections. I don't see any gyroscopic effects i guess. 

 

Also  i'm not capable to install the range of the x-axis. it is always from 0 to 450 rpm, unless i change the starting speed, step size, en numer of steps in my ROTORD card. (have anyone a solution for this.) 

 

If there is anyone who can explain me my questions? 

 

 

Greets

Dries