I am performing Acousitc Analysis on an object. I have my domain and bounday conditions defined. How do I apply 1N force to a node or face of my element?

An Acoustic analysis is solving for unknown pressure at each node. Every load can be translated into an incident pressure. In Harmonic Acoustic analysis the following different types of loads can be applied on the system:

• Mass Source

• Surface Velocity

• Diffuse Sound Field

• Incident Wave Source

• Port In Duct

If you have a force applied to a face, you can divide the force by the area of the face and that is a pressure.

Harmonic Acoustics is a frequency analysis, so the input is the amplitude of a sinusiodal variation of pressure over time at a range of frequencies that are input into the Analysis Settings.

So let's say I have obtained the pressure for face I want to apply the load to, which type of load do I define now? I thought about mass source, but it has unit of kg/m^2 * s which doesn't seem right for pascals

If you choose Incident Wave Source, Planar Wave, you can define a pressure to send a Planar Wave into your domain.

But maybe a Monopole is more appropriate, which will send a Spherical Wave into your domain.

You can also choose Loudspeaker.

If you say more about how that load is known, what created that pressure, how was it measured? What is the shape of the domain, what are the boundary conditions on that domain?

This is a kind of rattle with pebbles inside - if you shake it, they hit the walls and generate the sound.

What I want to do was to apply 1N force on one face of the inner wall, like you do in harmonic analysis, in order to obtain pressure generated at some point by the excitation in spectrum of 10Hz to 10kHz

The domain is a sphere. I applied radiation boundary on the external face of the sphere. I also defind physics and acoustics region, as well as fluid-solid interface. I also applied fixed support to the bottom of this object.

I tried to play around with mass source, but somehow the results are wrong - I have done spectrum analysis of real sound gen erated by this rattle, as well as modal analysis of this exact model and both resulted in frequences around 9.2kHz and 9.5kHz, meanwhile the results I got from this analysis are presented below

How was the rattle supported and how was it excited when the recording was made? How was the support included in the model?

Review this discussion, which shows how to link a Modal to a Harmonic Response to a Harmonic Acoustic analysis to predict the sound generated in the air by a vibrating tuning fork.

A tuning fork is in a quasi steady state of vibration, with very small damping, so the sound lasts a long time.

A rattle has a housing, which when struck by a pebble, will have much higher damping so the sound lasts a very short time. The above analysis cannot estimate the duration of the sound, but it should be adequate to estimate the tone and harmonics of the sound.

A Transient Structural analysis could predict the waveform decay of the sound of one pebble striking the housing in one place. You would not want to attempt a simulation of tens of pebbles hitting each other and the walls of the housing as it was shaken in a Transient Structural analysis. Other types of software, such as Explicit Dynamics or LS-Dyna could attempt such a model.

How was the rattle supported and how was it excited when the recording was made? - It was held by fingers and shaken

How was the support included in the model? - I wasn't sure what to do, I just played around. I tried to do fixed support on the bottom of the object, but in modal analysis resulting frequencies were wrong. When I didn't do any support, I got 6 frequencies around ~0 and the next 2 were right.

I have managed to link a Modal to a Harmonic Response to a Harmonic Acoustic analysis, but I have problem with importing velocities. I've tried doing it on simpler examples like fork lift or even simple bar and the velocities are always 0

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## Answers

11,073An Acoustic analysis is solving for unknown pressure at each node. Every load can be translated into an incident pressure. In Harmonic Acoustic analysis the following different types of loads can be applied on the system:

• Mass Source

• Surface Velocity

• Diffuse Sound Field

• Incident Wave Source

• Port In Duct

If you have a force applied to a face, you can divide the force by the area of the face and that is a pressure.

Harmonic Acoustics is a frequency analysis, so the input is the amplitude of a sinusiodal variation of pressure over time at a range of frequencies that are input into the Analysis Settings.

12Thank you kindly for your response.

So let's say I have obtained the pressure for face I want to apply the load to, which type of load do I define now? I thought about mass source, but it has unit of kg/m^2 * s which doesn't seem right for pascals

11,073If you choose Incident Wave Source, Planar Wave, you can define a pressure to send a Planar Wave into your domain.

But maybe a Monopole is more appropriate, which will send a Spherical Wave into your domain.

You can also choose Loudspeaker.

If you say more about how that load is known, what created that pressure, how was it measured? What is the shape of the domain, what are the boundary conditions on that domain?

12This is a kind of rattle with pebbles inside - if you shake it, they hit the walls and generate the sound.

What I want to do was to apply 1N force on one face of the inner wall, like you do in harmonic analysis, in order to obtain pressure generated at some point by the excitation in spectrum of 10Hz to 10kHz

The domain is a sphere. I applied radiation boundary on the external face of the sphere. I also defind physics and acoustics region, as well as fluid-solid interface. I also applied fixed support to the bottom of this object.

I tried to play around with mass source, but somehow the results are wrong - I have done spectrum analysis of real sound gen erated by this rattle, as well as modal analysis of this exact model and both resulted in frequences around 9.2kHz and 9.5kHz, meanwhile the results I got from this analysis are presented below

I'd appreciate any help

11,073How was the rattle supported and how was it excited when the recording was made? How was the support included in the model?

Review this discussion, which shows how to link a Modal to a Harmonic Response to a Harmonic Acoustic analysis to predict the sound generated in the air by a vibrating tuning fork.

A tuning fork is in a quasi steady state of vibration, with very small damping, so the sound lasts a long time.

A rattle has a housing, which when struck by a pebble, will have much higher damping so the sound lasts a very short time. The above analysis cannot estimate the duration of the sound, but it should be adequate to estimate the tone and harmonics of the sound.

A Transient Structural analysis could predict the waveform decay of the sound of one pebble striking the housing in one place. You would not want to attempt a simulation of tens of pebbles hitting each other and the walls of the housing as it was shaken in a Transient Structural analysis. Other types of software, such as Explicit Dynamics or LS-Dyna could attempt such a model.

12How was the rattle supported and how was it excited when the recording was made? - It was held by fingers and shaken

How was the support included in the model? - I wasn't sure what to do, I just played around. I tried to do fixed support on the bottom of the object, but in modal analysis resulting frequencies were wrong. When I didn't do any support, I got 6 frequencies around ~0 and the next 2 were right.

I have managed to link a Modal to a Harmonic Response to a Harmonic Acoustic analysis, but I have problem with importing velocities. I've tried doing it on simpler examples like fork lift or even simple bar and the velocities are always 0

1sir,

can you please provide me a tutorial for a monopole simulation. I am struck in ansys for the past 15 days not finding any substantial help on youtube.