Frequency response analysis

gopal_rathore

Hi,

I am working on a FRA where the load is acting at a constant frequency of 3 Hz. I have to further use the results to perform a fatigue analysis.There are two queries I have:

 

1) How to make the run only for one frequency and not for range of frequencies. TABLE D1 requires two values, both cannot be same.

2) As the frequency is constant, can this be more better understood with transient analysis to understand fatigue life of the component.

 

Thank you.

Altair Forum User

Hi Gopal,

 

Can you define a frequency of 2.999 and 3hz and check if this helps?

gopal_rathore

Hi,

Can I get results in .op2 format for only one frequency even if I give a range of frequencies. This is the main objective.

 

As the load is acting at constant frequency , I want to make a transient run with force as function of frequency and time i.e F=fsin wt. How shall I define this load in transient run using this expression instead of plotting values

Altair Forum User

Hi Gopal,

 

I will run a test case to check if we can get .op2 as you need.

 

 

gopal_rathore

Hi Prakash,

Thank you for your support.

The objective is to do a fatigue run on the component with loading condition as force acting at constant frequency and for some thousands cycles. For the same, as I need a base result , I was thinking since the frequency is constant, the analysis can can be more accurately studied in time domain rather than frequency response where generally response due to range of frequency is a study and here I have constant frequency.

Kindly let me know your view over it.

Thank you.

gopal_rathore

Hi Prakash, 
Any update?

Altair Forum User

Hi Gopal,

 

So far no success at my end...

gopal_rathore

Altair Forum User said:

Hi Prakash,

Thank you for your support.

The objective is to do a fatigue run on the component with loading condition as force acting at constant frequency and for some thousands cycles. For the same, as I need a base result , I was thinking since the frequency is constant, the analysis can can be more accurately studied in time domain rather than frequency response where generally response due to range of frequency is a study and here I have constant frequency.

Kindly let me know your view over it.

Thank you.

Hi,

What are your views on the second point regarding the fatigue analysis?

 

Thank you.

Altair Forum User

Hi Gopal,

 

Generally time domain will provide accurate and faster results as converting the frequency domain output to time domain is again a time eating process. 

Altair Forum User

Gopal,

 

Here is a transient fatigue setup example. 

Unable to find an attachment - read this blog

gopal_rathore

Hi,

In the above file, in FATLOAD load collector TID is not provided. This throw an error that TID is not defined. however in the help file it is written that if  sub loadcase is transient, TID needs to be left blank as it can directly take the values form the transient load data.

Kindly let me know about this.

gopal_rathore

Hi @Prakash
Kindly let me know about it.

Altair Forum User

Hi Gopal,

 

Did you provide the LCID (Transient Subcase) in the FATLOAD card?

 

I ran the model which I shared with you as it is and it works without any error. 

gopal_rathore

Hi Prakash,

I have assigned the LCID as transient loadstep subcase. But it throws error.

Altair Forum User

Gopal,

 

Can you share the model file and .out file?

gopal_rathore

Hi Prakash,

Sorry it was an version issue. I was running it in 12 .0 version. I ran it in 13.0 and it runs fine.

Altair Forum User

Gopal,

 

OK, thanks for the update /emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20'>