Frequency response analysis

Altair Forum User

In frequency response analysis, if we say that X Newton's of force is applied on a structure at say 1000Hz.

What does it mean?

Pranav Hari

Hi Mayurd67

 

Frequency Response Analysis is used to calculate the response of a structure subject to steady state oscillatory excitation. The loading is sinusoidal. The loads can be forces, displacements, velocity and acceleration. The response occurs at the same frequency and damping would lead to a phase shift. The outputs from a frequency response analysis are displacements, velocities, accelerations, forces, stresses and strains. The responses are usually complex numbers that are either given as magnitude and phase angle or as real and imaginary part

 

 So if  X Newton's of force is applied on a structure at say 1000Hz, then the system will give corresponding frequency response outputs as displacements, velocities, accelerations, forces, stresses and strains.

 

Refer this forum post and OptiStruct tutorial OS-T 1300 also for better understanding.

 

https://community.altair.com/community?id=community_question&sys_id=4886483a1b2bd0908017dc61ec4bcbf3

 

Altair Forum User

@Pranav Hari

So does it mean when we apply X N force, it will cause the structure to complete 1000 cycles per second?

Pranav Hari

Altair Forum User said:

@Pranav Hari

So does it mean when we apply X N force, it will cause the structure to complete 1000 cycles per second?

 

Hi,

 

It means that for X newton of force and given excitation frequency ranges, it will give you necessary response outputs

It will give you results on how the system behaves under a particular load (X) with a given excitation frequencies (1000 Hz)

 

Altair Forum User

@Mayurd67

 

To understand better, try an FRF analysis with zero frequency. This result will be close to your static analysis result.

 

This means the frequency applied is the loading frequency and is zero which is a case of static loading.

 

Now there could be loads which acts on the component at different frequencies. To understand the response of the component at these frequencies, we use FRF analysis. 

Altair Forum User

@Prakash Pagadala

@Pranav Hari

Take example of a motor,

Motor is running at 3000rpm and 8Nm,

So running frequency 3000/60= 50Hz.

And now the loading frequencies, i.e loads applied at different frequencies.

What's the difference between two frequencies?

Pranav Hari

Hi Mayurd67

 

The running frequency is the applied frequency (50 Hz) for the motor. The frequency response analysis will give you outputs or response on how the motor behaves for the mentioned (50Hz) frequency.