Learning Forum

[YH]

I would like to calculate sound induced by pipe flow and propagating in the steel pipe and sorunding cement structure. So I wanna do DAVA analysis which combins ANSYS Fluent and Harmonic Response in Mechanocal like this https://www.youtube.com/watch?v=xpdLQYqBCAk&t=160s. My questions are 

1) How can I import cgns file generated in Fluent to Mechanical. The user help mentions we can import from Environment => Loads => Imported CFD Pressure. But I couldn't use (figure1). Some previous sleds mentioned using External Data. But it also doesn't work. Would you tell me how we can import the Fluent data to Harmonic Response? 

2) I found a youtube cannel that combining Fluent and Harmonic Acoustics https://www.youtube.com/watch?v=jPjBltKfAkQ. What's the difference between Harmonic Acoustics and Harmonic Response?

[Erik Kostson]

Hi

Imported CFD Pressure can only be used with Harmonic Acoustics (not with Harmonic Response).

The difference between these two is that Harmonic response is for pure structural analysis, while Harmonic acoustics is for pure acoustic or for coupled structural-acoustic (vibro-acoustic) analysis like they have in the DAVA videos (structure+air/acoustic domain present).

All the best

Erik

[YH]

[YH]

Hi Erik, thank you for replying my questions. Based on your answers, still I have several questions.

1) I don't perfectly understand what the structural analysis is. Is the sound wave propagating inside solid called the structural analysis? And is the one propagating inside flluid media called the acoustic analysis?

2) I want to calculate the acoustic propagation like the figure. The sound is generated inside  the water domain using Fluent. And the sound propagates in steel pipe and cement and is measured by microphone. In this case, which tools do I have to use Harmonic Response and Harmonic Acoustics?

3) The DAVA youtube video (https://www.youtube.com/embed/xpdLQYqBCAk) seems to use Hrmonic Response, do you know how to import CFD data without 'Imported CFD Pressure'?

Thank you. 

 

[Erik Kostson]

 

 

My final answers to this (as you can not carry out what you want using this approach – DAVA is made for the type of situations as shown in the video (exterior aerodynamics and interactions with structure)

1) I don’t perfectly understand what the structural analysis is. Is the sound wave propagating inside solid called the structural analysis? And is the one propagating inside flluid media called the acoustic analysis?

So Structural harmonic response is done on a solid elastic structure say made of an isotropic elastic material say like steel, and has translation degrees of freedom (UX,UY,UZ). We have a free course on that which I suggest to look at.

Thus it supports both long./compression and shear elastic wave propagation.

Acoustic (Harmonic acoustic) is for pure acoustics (so only pressure degree of freedom and acoustic equations and acoustic/long./compression waves propagate) or for coupled structural-acoustic (vibro-acoustic in this case we have both UX,UY,UZ on the structural region and pressure on the acoustic domain) analysis like they have in the DAVA videos (structure+air/acoustic domain present).

Please see the help manual for this type of analysis and theory used behind them.

2) I want to calculate the acoustic propagation like the figure. The sound is generated inside  the water domain using Fluent. And the sound propagates in steel pipe and cement and is measured by microphone. In this case, which tools do I have to use Harmonic Response and Harmonic Acoustics?

The sound also propagates mainly in the water, and due to its interaction with the pipe, some goes into the pipe and the surroundings. Hence DAVA cannot capture the most important part which is the acoustic wave propagation in water and the interaction with the pipe. It just adds some pressures to the wall which is not enough for your analysis so you cannot do what you want. As said DAVA is for exterior aerodynamics and interactions with structure.

3) The DAVA youtube video (https://www.youtube.com/embed/xpdLQYqBCAk) seems to use Hrmonic Response, do you know how to import CFD data without ‘Imported CFD Pressure’?

This is an old video I assume – as you show in your image and checked now the ‘Imported CFD Pressure’ can only be used with a Harmonic acoustic system.

For you I would suggest to look at a 2 way FSI analysis (search the internet, there are many examples on this), but again I am not sure if it can perhaps capture this.

Thank you. 

 

 

[YH]

 

 

Erik, 

Thank you so much for the clarifications. 

They are very helpful information for me and I could import CFD data to Harmonic Acoustics. 

However I don’t understand your second answer much. The figure is my image for the DAVA calulation. Fluent calculate the acoustic source information on the surface between fluid and steel pipe. Do we calculate all the wave propagation including water, pipe and cement region, if we set the water as acoustic region and the pipe and cement as structural region, even if it is 1 way FSI (Ignoring the fluid convenction effect)?

I have not completed the prelimianary calculation yet and I just started such an acoustic study, so I’m sorry if this question is weired.

 

 

 

 

[Erik Kostson]

Hi

Thats is great to hear.

Yes this is a good question and tricky to explain.

As we said the DAVA is for exterior aerodyn. say around bodies. It calculates both the static/turbulent field and the sound generated by flow (aeroacoustic sound, that will propagate away from a region unlike the turbulent field that will stop at some point especially due to viscosity). Assuming we run a full comprssible CFD analysis.

In your case the sound will propagate also in the water, and due to its interaction with the pipe, some goes into the pipe and the surroundings. Hence DAVA cannot capture this part which is the acoustic wave propagation in the fluid/water and the interaction with the pipe. It just adds some pressures (static/turbulent field + the sound generated by flow) to the pipe wall but that is not enough as it does not transfer the hydroacoustic sources on the fluid region (we can not do that yet) which is really what you need for your analysis so you cannot do what you want.

So in short it only captures one part of the physics, which is the flow and possibly some sound interacting with pipe wall, it does not capture the hydroacoustic sources that exist also inside the fluid and that propagate in the fluid (as sound) and interact downstream with the pipe wall.

What you want to do is quite tricky and nothing we can do at the moment, using the DAVA workflow.

[YH]

 

Hi Erik, Thank you so much. 

Based on your answer I updated the figure. So the Harmonic Acoustics can calculate the sound propagating to So we can calcuate the sound propagation inside the steel pipe region and the cement region (exterior region) but cannot calcuate the sound propagation inside the water region and its incidence to the exterior region.

 

• Honestly I still couldn’t why the sound propagation inside the water cannot be calculated (Sorry for being so persistent). If my understanding is corrct, the sound source data is transfer to face. If we apply the imported CFD Pressure to the face between water and the pipe, isn’t it impossible to treat the water region as an exterior region? 
• Can we transfer the part of acoustic data? We think that a small leakage on a pipe wall makes significantly loud sound (like the figure below). If we apply the Imported CFD Pressure to the wall only around the leakage, the rest of the water region becomes exterior region. 
• If you have any recomended other way including adding user defined function or somthing, wound you please let me know?

 

 

[Erik Kostson]

 

 

 

 

Hi

As I said you can not do what you want – sorry for repeating that is the bottom line. I know it is hard to understand the complex physics here.

Again the reason is that there is a lot of sound (acoustic waves inisde the fluid line) that is generated by the leakage as seen in the image below, and that leakage “sound” (not sure how you would calculate it with Fluent, but that is another question), consists of hydrodynamic acoustic sources, which would need to come in/be transfered into the acoustic FE mesh in harmonic acoustics, and so we can propagate them (acoustic sound sources due to leak) along the fluid (of course they will interact with the pipe wall also), and that can not be done as we can not obtain them (sound sources), and finally more importantly transfer those into harmonic acoustics (so there is no way of coupling these). DAVA is very different (imported cfd pressure) and as I said only for exterior flow problems like the side car window video we refer to for DAVA. 

See here and look on the slide (aeroacoustics – methods) with coupling (not possible to transfer to Ansys, but some other tools are mentioned were the coupling exists ). Also even if we could which we can not as you see there, it is only valid for aerodynamic acoustic sources (aeroacoustics), not hydroacoustics.

https://www.finiteelementanalysis.com.au/featured/take-your-acoustics-simulations-next-level-with-vrx-sound-rendering/

In anyway I will close this discussion with this explanation as it might be useful to others.

Of course this is my feedback and limitation here, but of course one can apply the imported cfd pressures and calculate something.

All the best

Erik