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Resonance frequency of component with SOL103 in NX 8.5

Creator
Creator

Dear Community,

 

I am having problems with simulating the resonance frequency of a component in NX 8.5 with Advanced Simulation. I am using the SOL103 Flexible Body. The result of the simulation, the .rfi file, will be used in a Motion Simulation. The component is for a test setup. The test is used to check if we can use a linear motor to put the component in its own resonance. The test setup looks like bellow.

Test.PNG

If the motor change direction 15 times per second then it shouldn't be that the components will be in his own resonance.

 

The component is 60 mm in height, 90 mm wide and 50 mm in length. The flextures are 0.8 mm thick. The two solid blocks are 5 mm thick and the distance between the flextures is 28.4 mm.

Component.PNG

The component is fixed by 4 bolts of the size m4. Around the the holes of the bolts I sketched a circle and divided the face so I can simulate a bolt connection with a 1D connector.

 

I started with Advanced Simulation and created a new FEM and SIM, with the following aspects. See the image bellow.

New_FEM_and_SIM.PNG

Following the creation of the new FEM and SIM I made a new SOL 103 Flexible solution. I left everything untouched. Case control looks like follows.

Case_Control.PNG

 

Then I mashed the component via 3D Tetrahedal Mesh. The mesh setup looks liks:

3D_Mesh.PNG

Then I added a material to the mesh. The material I added is ABS. The material properties are down below.

nformation listing created by : 446041
Date : 04/12/2018 14:46:54
Current work part : D:\Test_0001\test_0002\test_0003\Test_Flextures_0001_fem2.fem
Node name : czc517399x
============================================================

------------------------------------------------------------

MATERIAL INFORMATION

------------------------------------------------------------

Library Material : ABS
Category PLASTIC
SubCategory ABS Polymer
Library Reference physicalmateriallibrary.xml
Category : PLASTIC
Sub-Category : ABS Polymer
Material Type : IsotropicMaterial
Version : 3.0
Mass Density (RHO) : 1.05e-006kg/mm^3

======== Mechanical
Young's Modulus (E) : 2000000mN/mm^2(kPa)
Poisson's Ratio (NU) : 0.4
Type of Nonlinearity (TYPE) : 1
Yield Function Criterion (YF) : 1
Hardening Rule (HR) : 1

======== Strength
Yield Strength : 40000mN/mm^2(kPa)

======== Thermal/Electrical
Thermal Expansion Coefficient (A) : 7e-0051/C
Thermal Conductivity (K) : 170microW/mm-C
Specific Heat (CP) : 1800000000microJ/kg-K

 

After assignen in the material I added 4 1D connector to simulate the bolt connection. The connection looks like:

1DConnection.PNG

 

Then I added the fixed degree of freedom constraints with all the DOFs fixed.


Constreint.PNGI did this to all the 1D connections.

 

Finally I solved the solutions. I do get results but the results seem way off. The following results were created.

Resultaten.PNG

I The component seems to got lose from the constraints. Also the frequencies are way to high for such small and light product. 130 Hertz, while my college using other software got around 36 hertz. 

 

Sorry for the long post, but I spend quite a bit of time trying to solve this to no avail. Can anybody please help me?

 

20 REPLIES 20

Re: Resonance frequency of component with SOL103 in NX 8.5

Phenom
Phenom

what does the hand calc give you? see blevins  Table 6.2, case 24 for example

Production: NX.CAE 10.0.2.6
Development: VB.NET (amateur level !)

Re: Resonance frequency of component with SOL103 in NX 8.5

Creator
Creator

At the moment I don't have access to Blevins. But the person in charge of the test already did the test in the past. And according to him the resonance frequency should be around 36 hertz. 

 

 

Re: Resonance frequency of component with SOL103 in NX 8.5

Gears Phenom Gears Phenom
Gears Phenom

Try to reduce element size. Use 3 elements per thickness, especialy here.

large.png

Also try to change your constraints. Your model should not have rigid body modes.

Can you share geometry in neutral format, like .x_t?

Model on screenshoots dont look like 60x90x50 mm.

Re: Resonance frequency of component with SOL103 in NX 8.5

Gears Phenom Gears Phenom
Gears Phenom

Make plate model, give simple constraints (fixed on edge) and get first frequency 26,5 Hz.

Model have dimensions 60x90x50 but dont look like your model for some reasons.

Change dimensions to 90x60x50 - get 16 Hz.

1.png

Re: Resonance frequency of component with SOL103 in NX 8.5

Creator
Creator

You didn't use any 1D connectors and just went straight to fixed degree of freedom constraints? 

Re: Resonance frequency of component with SOL103 in NX 8.5

Phenom
Phenom
I'd brick mesh (or shell) this thing and you'll get much better results... Elongated structures with TET mesh like this is no good (good enough for SolidWorks people, but we don't care about them :-) ).

Would you happen to have a CAD model handy? Even x_t would do...

Re: Resonance frequency of component with SOL103 in NX 8.5

Creator
Creator

I will try to add a x_t file tomorrow. At the moment I don't have acces to my workstation.

Re: Resonance frequency of component with SOL103 in NX 8.5

Phenom
Phenom

40Hz, first try with brick elements with MSC Nastran and NX Nastran, built from your dimensions.  I eyeballed the fillets at 2mm radius...  All holes fixed (connected to a center node by RBE2, no different)

 

MODE.pngFirst Mode at 40Hz

 

Apart from TET elements, your mesh is very coarse in the fillet region, I'd refine that at a minimum...  But 136Hz given your dimensions is more than off, it is plain wrong.  If I use your element size, I end up with 48Hz, 30% off, not 3000%, something elese is going on... 

 

MODE tet.pngTET mesh mode

From the picture you posted, looks like your rigids are extending to the fillets, and there might be some other issues too...

Re: Resonance frequency of component with SOL103 in NX 8.5

Phenom
Phenom

There should be a note about back to basic: Is tet element (even tet10) really appropriate for such model!

 

PS: @TENTECHLLC: Is that MSc. Apex used?

Production: NX.CAE 10.0.2.6
Development: VB.NET (amateur level !)