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[fares abbara]

Hello Everyone,

 

I am working on an FSI model for fluid flow in an elastic tube. The aim is to study the effect of a vibrational force applied on the outer surface of the elastic tube. My question is as follows:

I used the system coupling feature where I created my structural and fluid domains and completed the necessary constraints and boundary conditions for each, then i connected the domains to the system coupling block. For the vibrational force, i used tabulated pressure vs. time data at one frequency. The process was somewhat tedious and seemed impractical, which led me to think there could be a better way to input the vibration. I have access to tabulated pressure data in the time and frequency domains. Moreover, i would like to study the vibrations at specific frequencies as well as the full range of frequencies recorded.

[Erik Kostson]

Hi

When you do FSI (CFD+Structural analysis) it will be in time domain, so the force will be vs time of course.

 

Also perhaps we can offer some help if you provide more info (aim of the study, what type of device is this, etc., what is important and what are you trying to get out of this study).

 

All the best

 

Erik

 

[fares abbara]

Hello Erik,

My model is aimed to resemble a section of a carotid artery. I am trying to understand the power transmission of mechanical vibrations induced by snoring originating from the pharyngeal walls. Ultimately, my main focus is to study the stress distrubution along the arterial wall to locate possible Damage areas. In the beginning, i tried Harmonic reponse and modal analysis, however, i was not able to pair those responses with the fluid field. I do have raw time data taken from the pressure transducer and i do have the power spectrum. 

regards,

Fares.

[Claudio Pedrazzi]

Could you elaborate on what do you mean with "For the vibrational force, i used tabulated pressure vs. time data at one frequency.".  Do you mean you used a so called time history, with a given sampling frequency? because to me it is unclear what does "at one frequency" mean.  The time history, if sufficiently sampled, will contain all frequencies up to the Nyquist frequency.  With time history I mean a long list of couples of data points: for example t=0, p=p0; t=0.001, p=p1, and so on...

 

I am not familiar wiht FSI. But for simply mechanical analysis the input of a PSD as vibration excitation is certainly possible.  Differently from a time history, a PSD is a statistical approach, though.  

[fares abbara]

Hello,

I just generated a sine function on matlab. I specified the frequency to bo 60Hz and sampling frequency of 200. I evaluated the function at time steps 1/Fs and tabulated this data. so i just inputted arbitrary pressure vs. time data as an input to the pressure on transient structural. To give you a better insight, my model aims to study the effect of snoring induced vibrations on the carotid artery. Two pressure transducers picked up pressure readings inside and outside the artery. Then the data were used to produce the power spectrum. Now my aim is to apply those pressure readings. I want to study the full snoring segment as well as the higher and lower frequency vibrations on their own. I have already tried to filter the power spectrum and do a reverse fourier transform, but i am getting complex numbers.  

[Erik Kostson]

 

 

 

That is very good information.

One important question here is, the excitation source, I assume it first of all is external vibration/pressures on the exterior artery walls (so coming from the outside of the artery and not from the inside of the artery)?

 

All the best

Erik

 

 

 

[fares abbara]

Correct,

It was found from the power spectrums of the innner and outer vibrations that 90.5 percent of the power was transferred to the inner side of the arterial wall. 

Regards,

Fares.

[Erik Kostson]

 

 

 

So in that case, instead of 2 way FSI analysis in time domain, you can try and use harmonic acoustic analysis in frequency domain – the arteries are the structural regions, and the fluid inside them is the acoustic region, and you apply a Pressure load on the walls which is Pressure (Pa) vs. frequency instead (use radiation boundary to avoid any reflections from the end of the model in the acoustic regions). See the internet for tutorials and search this forum:

See this video – in this case you do not need cfd since you know the external wall pressures which you can just apply onto the wall using the Pressure load (tabular vs freq.), so no need to use the Imported CFD press. as in the video.

https://www.youtube.com/watch?v=jPjBltKfAkQ

 

Hope this helps

 

Erik