Learning Forum

[tumulpurwar]

Hello all

Question1 )

I want apply stiffeness whose value I know to a cuboid geometry.

Is it possible to apply stiffeness in Ansys mechanical?

How?

Question 2)

If say I know modal frequency of my complex geometry(Car engine) , say (between 6 to 7 Hz), how I can calculate stiffeness of that geometry?

Will I just need use that simple formula " In which we can calculate natural frequency? But I guess that formula, is suitable only for simple geometry? (Photo attached)/

Question 3)

Statement below from Internet :

"Six-order frequency means that exciting frequency in six times more than shaft rotation. If the speed range of m/s engine is 80-110 rpm then six-order frequency is 8-11 Hz"

How they calculated frequency, I didnt understand?

[Ashish Khemka]

Please see if the following course helps you:

Modal Analysis | Ansys Innovation Courses
Regards Ashish Khemka

[peteroznewman]

1) A block has a length L and a cross-sectional area A and is made from a material with a Young's Modulus E has a stiffness AE/L.

[tumulpurwar]

Thankyou Peter.. Right ­ƒÖÅ

[tumulpurwar]

Dear Peter
Just please if you can answer :
I want do vibration analysis, where I want know how engine vibration affects car body, and if there is chance of resonance.
As I can't model detailed engine, I would like apply correct Siffeness and CG to my simplified engine geometry.
I will get frequency range from engine manufacturer of engine.
I want know how to calculate engine stiffeness from given frequency range?
Can you please tell.. Not every time engine manufacturer provide engine stiffeness on asking.

Thanks

[peteroznewman]

Frequency alone is not a sufficient definition of the load the engine puts on the car. You also need to know the force amplitude.
If you know the force and the frequency that the engine applies to the frame, you may not need the engine stiffness.
Resonance occurs when the forcing frequency is equal to the natural frequency of the structure. There are many examples of structures where this happens. The important feature of structures where the forcing frequency stays near the natural frequency is that the damping is large enough to limit the response of the structure. In lightly damped structures, one strategy to limit the response is to move quickly past the natural frequency, such as a turbine.

[tumulpurwar]

Thanks for answer.
I hope , force amplitude you mean to say Engine excitation force.To apply this engine excitation force in model, i need geometry of engine i guess?
The photo below shows applied engine excitaton forces...if i dont have engine modeled,where i will apply the excitation forces?..Thanks
I want to see especially engine foundation structure..how it get affected also

[tumulpurwar]

 

Hi Peter

 

Can you please read these paragraph and if you can let me know how i calculate equivalent stiffeness value of engine dummy geometry?

Please, thankyou

 

Regards

Tumul