Notifications
Clear all

Need Advice  

 

snipesc
(@snipesc)
New Member
Joined: 1 week ago
Posts: 1
July 30, 2020 5:51 pm  

I'm a biology student and new to FEA. I am trying to model a vibration through the hyoid apparatus of an echolocating bat. It's believed that when the bat sends out a call, it registers that call by sending a vibration from the larynx > hyoid body > stylohyal bone > tympanic bone. The stylohyal wrapping around the tympanic bone is unique to echolocators. To form a picture in the brain, we think the bat compares this vibration with the returning echo. However, this has never been tested. 

 

Some information:

The loudness of a call is 120 decibels. The frequency is how often the force gets applied per second. The vocal chords are vibrating at 50khz, causing the larynx to vibrate at the same frequency which pushes on the hyoid at that frequency. With a force of 120 db which is 1N, I'm assuming that half the hyoid would recieve 0.5N. I am only modeling half of the hyoid, although I am open to adding the entire thing if necessary.

 

My question: which analysis would be best for my goal, which is to test and confirm that this is the functionality of this system ? I have attached a photo with named parts. I can send a file if needed  Using ANSYS. 

 

 

1596127912-model2.png

Quote
manual_surtax
(@manual_surtax)
New Member
Joined: 6 days ago
Posts: 4
July 31, 2020 5:44 pm  

So first big thing you need to do is make sure you have your material properties correct. A popular saying in the analysis community is garbage in = garbage out. From my limited bio knowledge it seems you have two bones and two fleshy bodies. For the bones you can probably treat them as perfectly elastic to start then later move to a visco elastic model or add some artificial dampening for more accuracy. You will need good density data and good young's modulus data for the elastic mode. For the visco-elastic/ dampening properties what you will need will depend on the specific material model.

The fleshy bodies are more difficult. They are softer, and will have larger amounts of dampening. I would look for similar literature (FEA of biological parts) to best model these parts. In fact, that goes for all of the parts. Look for literature modeling bones, and fleshy bodies but make sure they are looking for acoustic/vibration responses as opposed to only structural responses.

You are also going to have to think real hard about your constraints/contact. How is everything being held in place? What all is touching each part? The contact between each part matters as well. How does each part interface with the next? Do they directly touch? Is there intermediate connective tissue? Is there some sort of fluid interface? Each one of these will lead to different modeling assumptions.

Another big question is what results are you trying to get? This is going to effect the analysis type. Do you want stress in the bones? Required energy to excite the resonance? You are not going to be able to tell if the bat forms a picture in its brain from this analysis. It would be possible to tell though if the system responds to some distorted version of the 50khz wave.

In terms of analysis type, I would start with a modal analysis, see where the resonant frequencies for each part are. This is a relatively cheap analysis so you can iterate quickly. For more advice I would need to know more about the problem.


ReplyQuote
manual_surtax
(@manual_surtax)
New Member
Joined: 6 days ago
Posts: 4
July 31, 2020 6:06 pm  

In addition to all of that the file you posted looks like a .stl file (laser scan data?) So ANSYS may or may not accept that as geometry. If it does, be wary because ANSYS can create some really bad meshes without proper control. (bad mesh -> bad equations -> bad results). So check the element quality metrics like Jacobian, skew, warpage etc. If it does not take it, make it into a solid body like a .iges, solidpart, etc. then bring it in. I would mesh with solid elements, using a tet4 to get it to work, then remesh to a tet10 for accuracy. 

I have linked a enterfea blog post that might be handy and there are likely many more. These are an easy read with lots of pictures and little jargon to help you understand some of these topics. If you are brand new to FE, this is a difficult problem to start with so dont get discouraged. Feel free to ask more questions below. Good Luck!

Fundamentals of Finite Element Analysis: Complete Beginners Guide

This post was modified 5 days ago by Negative Volume

ReplyQuote
geardyn.1
(@geardyn-1)
Active Member
Joined: 9 months ago
Posts: 14
August 2, 2020 11:37 am  

ALE modeling with frequency response  of the model  might help. 


ReplyQuote
Negative Volume
(@negativevolume)
Estimable Member Admin
Joined: 2 years ago
Posts: 246
August 2, 2020 2:36 pm  

@manual_surtax

Helpful advice! Try to limit any links that you post to be directly relevant to the topic, otherwise it comes across as spammy 🙂


ReplyQuote
Negative Volume
(@negativevolume)
Estimable Member Admin
Joined: 2 years ago
Posts: 246
August 2, 2020 2:49 pm  

Hi @snipesc

Sounds like an interesting project! Looks like you've already gotten some good advice. I would start off by looking at it from the big picture and thinking about what you want to accomplish with this study specifically, then make design decisions from there. Things like: Do you need a 2D or 3D model? Do you have access to surface files for these structures? Do you have access to material properties for these parts and know what FEA material model to use? How will you connect all of these parts together to accurately represent the anatomy of a bat? And then how will you simulate the vibration and how will you measure the echo? 

Since you are interested in the echo mainly, then I would focus on that aspect of the problem and make assumptions regarding the materials and vibration transmission. FEA gets infinitely more complicated when you start to cross between things like solids and fluids (FSI - fluid solid interaction). So maybe do a simplified 2D analysis to start where you just study the sound wave created from the vibration and the resulting echo?

I would also make sure to triple check all units and hand calculations as you go (120 db does not equal 1N). 

Does your school have an engineering department? I would highly suggest partnering up with someone within engineering who has experience within FEA. Otherwise, this will be quite difficult for somebody to pick up and model something with meaningful results. 


ReplyQuote
Share: