Modal Analysis-target Frequency

Altair Forum User

How do we decide target frequency for modal analysis?

 

gopal_rathore

Hi,

 

For a fixture design, it depends on the operating frequency range on which the system is tested. You can for keeping the natural frequency around 1.5- 2 times of the operating frequency.

If you are going for a component or system level design, understand the range of frequencies to which it is subjected to.

For understanding local frequency effect, try running the frequency response analysis.

Altair Forum User

you are right it depends on the operating frequency range but what about the assemblies which are not directly mounted on exciattion source like any assembly on chasis of vehicle say tail lamp

 

Altair Forum User

Altair Forum User said:

you are right it depends on the operating frequency range but what about the assemblies which are not directly mounted on exciattion source like any assembly on chasis of vehicle say tail lamp

Sumit, I think it again narrows down to component level.

 

Road loads to tyre, to control arms, etc....

Altair Forum User

Thanks Prakesh,

yes it narrows down but how to target that. if some has to design his assembly then there must be certain criteria and how to determine? 

Altair Forum User

Sumit,

 

I agree, and this criteria is the ride comfort or ride quailty which is affected by lot of factors like bump, roll, pitch etc...

 

Maybe from a MBD analysis for different ride conditions one can get the loads and verify the strurtural integrity and fine tune at the same time.

 

 

Altair Forum User

Altair Forum User said:

Sumit,

 

I agree, and this criteria is the ride comfort or ride quailty which is affected by lot of factors like bump, roll, pitch etc...

 

Maybe from a MBD analysis for different ride conditions one can get the loads and verify the strurtural integrity and fine tune at the same time.

 

 

Thanks Prakash,

Do you have any example or ppt which it explain me in a detail?

and what i know MBD is used to simulate motion and extract forces. will it also tell us about natural frequency to be set as target? i am in doubt.

Altair Forum User

Altair Forum User said:

Do you have any example or ppt which it explain me in a detail?

and what i know MBD is used to simulate motion and extract forces. will it also tell us about natural frequency to be set as target? i am in doubt.

I dont but you can refer books like Race Car Vehicle Dynamics, by William F. Milliken and Douglas L. Milliken

gopal_rathore

Hi,

To understand vehicle dynamics you need to refer these books mentioned above and also fundamentals of vehicle dynamics by Thomas Gillespie.

If you need the soft copies of these book, I can send you over email if you can provide me.

Also I think if you can clarify your problem statement as mentioned earlier it is about  tail lamp assembly natural frequency, this might not be directly related to the ride and handling from vehicle dynamics point of view. Thus more clarity can be obtained regarding the same.

Altair Forum User

Altair Forum User said:

Hi,

To understand vehicle dynamics you need to refer these books mentioned above and also fundamentals of vehicle dynamics by Thomas Gillespie.

If you need the soft copies of these book, I can send you over email if you can provide me.

Also I think if you can clarify your problem statement as mentioned earlier it is about  tail lamp assembly natural frequency, this might not be directly related to the ride and handling from vehicle dynamics point of view. Thus more clarity can be obtained regarding the same.

Thanks Gopal. My email id is ersumitnitk@gmail.com

 

In general I want to know how to determine target frequency. For engine mounted components I know it depend upon the RPM of engine but I want to know how to determine target frequency for components or assemblies which are mounted away from engine for example tail lamp at the end of chasis or spare tyre carrier assembly(mid of chasis) or battery box etc. What factor decide target frequency and how?

Altair Forum User

Altair Forum User said:

Hi,

 

For a fixture design, it depends on the operating frequency range on which the system is tested. You can for keeping the natural frequency around 1.5- 2 times of the operating frequency.

If you are going for a component or system level design, understand the range of frequencies to which it is subjected to.

For understanding local frequency effect, try running the frequency response analysis.

Hi gopal_rathore,

According to the theory of vibration isolation, the excitation frequency should be 1.414 times of the natural frequency. Why did you said the natural frequency around 1.5-2 times of the operating frequency?

 

Best Wishes

Roy