Questions about frequency response analysis

Altair Forum User

Dear all

     I have some questions about frequency response analysis which motivated force is on the bases.

1.  When I use DAREA for force, the dof on the force direction should be released. Is that right?  For the result shows at 0Hz, the displacement response is very high. Is that right?

2. When I use SPCD for DIS, VEL and ACC. The constraints should not be released. Is that right?

Thanks!

 

Rahul Rajan_21763

Hi,

DAREA is used when load is in the form of Force.using Tabled1 card you can apply dynamic load.For 0 hz displacement should  be 0.

 

Yes when you have load in the form of DIS,VEL & ACC one should use SPCD card.Refer SPCD userguide.

 

Regards

Rahul R

 

Altair Forum User

Altair Forum User said:

Hi,

DAREA is used when load is in the form of Force.using Tabled1 card you can apply dynamic load.For 0 hz displacement should  be 0.

 

Yes when you have load in the form of DIS,VEL & ACC one should use SPCD card.Refer SPCD userguide.

 

Regards

Rahul R

 

Thanks for your answering. But my question is when the dynamic force applied on the constrained base. I need to release the dof of the force direction.  The result shows that at 0 Hz, the displacement response is very high. Why?

Rahul Rajan_21763

Could you share us input deck along with out file?

 

Regards

Rahul R

Altair Forum User

Altair Forum User said:

Could you share us input deck along with out file?

 

Regards

Rahul R

yes, thanks!

Unable to find an attachment - read this blog

Rahul Rajan_21763

I checked your files.Boundary condition seems to be incorrect.That is the reason you get high displacement at 0 hz.

 

Regards

Rahul R

Altair Forum User

Altair Forum User said:

I checked your files.Boundary condition seems to be incorrect.That is the reason you get high displacement at 0 hz.

 

Regards

Rahul R

How to correct them? If I constraint the dof of force direction, the result is always 0 at all frequencies.

Rahul Rajan_21763

I see your load is in the form of Force ( DAREA ).What is the actual scenario for flat plate.How it is fixed & what type of load is acting?

 

Regards

Rahul R

Altair Forum User

Altair Forum User said:

I see your load is in the form of Force ( DAREA ).What is the actual scenario for flat plate.How it is fixed & what type of load is acting?

 

Regards

Rahul R

Thanks for your patience. I want to analyse base vibration. The exciting force is applied on the base constrained. Just like a building in the earthquake. The exciting foce is from the base. Is it clearly?

Altair Forum User

Altair Forum User said:

I see your load is in the form of Force ( DAREA ).What is the actual scenario for flat plate.How it is fixed & what type of load is acting?

 

Regards

Rahul R

Thanks for your patience. I want to analyse base vibration. The exciting force is applied on the base constrained. Just like a building in the earthquake. The exciting foce is from the base. Is it clearly?

Altair Forum User

Altair Forum User said:

I see your load is in the form of Force ( DAREA ).What is the actual scenario for flat plate.How it is fixed & what type of load is acting?

 

Regards

Rahul R

Thanks for your patience. I want to analyse base vibration. The exciting force is applied on the base constrained. Just like a building in the earthquake. The exciting foce is from the base. Is it clearly?

Altair Forum User

Thanks for your patience. I want to analyse base vibration. The exciting force is applied on the base constrained. Just like a building in the earthquake. The exciting foce is from the base. Is it clearly?

Altair Forum User

Thanks for your patience. I want to analyse the vibration when excited forces are applied on the constrained base. It is a little like the building on the earthquake.  

The force will be applied on the place where is constrianed. Am I clearly?

Altair Forum User

Thanks for your patience. I want to analyse the vibration when excited forces are applied on the constrained base. It is a little like the building on the earthquake.  

The force will be applied on the place where is constrianed. Am I clearly?

Altair Forum User

Thanks for your patience. I want to analyse the vibration when excited forces are applied on the constrained base. It is a little like the building on the earthquake.  

The force will be applied on the place where is constrianed. Am I clearly?

Altair Forum User

Thanks for your patience.

I want to analyse the vibration when excited forces are applied on the constrained base. It is a little like the building on the earthquake. 

The force will be applied on the place where is constrianed. Am I clearly?

Altair Forum User

Thanks for your patience.

I want to analyse the vibration when excited forces are applied on the constrained base. It is a little like the building on the earthquake. 

The force will be applied on the place where is constrianed. Am I clearly?

Rahul Rajan_21763

Hi,

For any base motions excitation (ACC / DISP /VEL) you need to constrain the same node.

 

Create an SPC, SPCD pair, with the SPC constraining the dof that is to have the enforced displacement and the SPCD defining the magnitude and dof of the enforced displacement. Both must be referenced in the subcase (loadstep) definition.

Will check if I have any runnable deck to share.

 

Regards

Rahul R

Rahul Rajan_21763

Just replied to your query.

 

Regards

Rahul R

Altair Forum User

Altair Forum User said:

Hi,

For any base motions excitation (ACC / DISP /VEL) you need to constrain the same node.

 

 

 

 

 

Create an SPC, SPCD pair, with the SPC constraining the dof that is to have the enforced displacement and the SPCD defining the magnitude and dof of the enforced displacement. Both must be referenced in the subcase (loadstep) definition.

 

 

Will check if I have any runnable deck to share.

 

Regards

Rahul R

Thanks for your answering, I have done as you said. In my example, I use SPC constrain 5 dofs and DAREA for the last dof. But the results shows that at 0Hz, the displacement response is extremely high. I don't know the reason.

Altair Forum User

If you are looking to apply an excitation at the base, you must use load type of SPCD instead of DAREA.  if you chance your card to SPCD, it will(should) be correct.