## General Mechanical

#### How to Run harmonic response with forces of different frequencies and different amplitudes

• seki
Subscriber

Hello sir,

I have a question about harmonic analysis with 2 forces of different frequencies and different amplitudes,

but I am confusing how to apply forces at once, for examples, Force1 (10Hz, 100N) and Force2 (30Hz, 200N).

how can run the problem in ansys workbench?

Thank you in advance.

Seki

• Eric_Eric
Subscriber

Just simply apply the sum of the two harmonic forces F(t)=100sin(2Pi*10*t)+200sin(2Pi*30*t).

• peteroznewman
Subscriber

Eric, that would work in a Transient Structural simulation, but a Harmonic Response does not have time in the equation. All forces in a Harmonic Response must be at the same frequency, though they can have different Phase relationships and different Amplitudes. The solver sweeps through a range of frequencies to produce results.

• seki
Subscriber

Hi Eric, thank you for your reply.

Yes, As answer from peteroznewman, all forces in a Harmonic Response must be at the same frequency.

• seki
Subscriber

Hi peteroznewman, Thank you for your reply.

Would you please tell me the way to run harmonic response analysis with two different frequencies.

By the way,  Is it possible to run it as below:

step1: run harmonic response analysis with Force1 and Force2 separately.

step2:sum up the two results, as the system is linear.

Thanks a lot.

• peteroznewman
Subscriber

Yes, it is a linear system, so you can combine load cases, but...

the problem is you want Force1 at one frequency and Force2 at a different frequency.

That means that the phase relationship between the two forces is continuously changing over time.

You could compute 24 sets of results for Force2 at 15 degree Phase Angle increments. Then combine each one with the Force1 results.  Sort through the 24 combined cases to find the one with the maximum response.

Or you could simulate in the Time Domain and run a Transient Structural as Eric suggested.

• seki
Subscriber
Hi peteroznewman, Thank you for your reply.nI'm sorry to reply you later.nThere are somethings to ask.nQestion1 : In harmonic response analysis with pre-stress, It is possible to define the force on nodes or surface Using GUI(not APDL)?.Qestion2 : In harmonic response analysis with pre-stress, It is possible to define the force on vertex Using GUI(not APDL)?.Qestion3 : As shown in the picture below, the force on vertex can be defined as Tabular data with different magnitude and phase angle with different frequency.nI do not know the meaning of this setting, Is it the answer for this topic?.Thank you inadvance.nSekinnn
• peteroznewman
Subscriber
Workbench allows you to create a Nodal Named Selection. Then you can use the Named Selection to define loads.nYou can define a Force on a Vertex.nHere is the ANSYS Help description for Force loadingnYou can have frequency dependent force. I have never used this. I assume that it will linearly interpolate the force for all the frequencies between the values in the table, but I don't know that for sure. I would make sure the Frequency upper and lower limit in Analysis Settings matches the largest and smallest values in the load table.n
• Cpwtub
Subscriber
Hi Guys,nWhat if we have a frequency domain earthquake load. Would that be possible to bring different Amplitudes for different frequencies within the frequency range of interest in harmonic?. May be as tabular data?nThank you very muchn