Two things you can try.

1. Use isotropic material to be sure that your unit system is consistent.

2. Check the step width Abaqus calculates for your problem. It might be larger than the impuls time of your signal. If it is so, you can pre define a fixed step width. In that case you have to check if your chosen step width is smaller or equal the one calculated by Abaqus.

Thanks a bunch for your answer Christian.

Isotropic material is used for this simulation.

I couldn't get what you mean by the second part. would you please take a look at this picture and tell me about the point

Based on your figure my second guess does not hold. Do you have a local deformation, where your force is applied? If not I assume you have an error in the load definition. If there is a deformation I assume there is an error in the material defintion. Try linear elastic material. For that the unit system is easier to check.

I had a local deformation, but could not see wave propagation.

"Try linear elastic material. For that the unit system is easier to check." do you mean I simply model it as a metal with an E and Nu, and check if there is any inconsistencies?

I wonder if it has anything to do with defining an acoustic medium for this material or any other consideration?

Did you see any weird or wrong values among my input data?

Once again thanks a lot for your time and detailed answers.

Do you use an Abaqus Standard (implicit) or Explicit? Based on your figure you defined a fixed step width of 1e-9s?!? An automatic time-step control with an explicit solver would be the better choice. Furthermore, it would be helpful if you could post a picture of your result. Just a few snapshots of different time steps would be enough.

Cheers,

Sascha

Hi Sascha,

I used a dynamic-explicit step. I will change the time-step control as you suggested and will let you know what happened.

Just the point (for concentrated force load) or elements (for pressure load) go up and down during applying excitation and then everything remains as it is till the job becomes complete.

Should you have got any FE simulations about ultrasound propagation in soft tissue using ABAQUS or any kind of loading on soft tissue in ABAQUS, please let me know.

Any kind of information about this matter is highly appreciated.

I only did some simulations in alu, steel or cfrp. What do you mean by defining an acoustic medium? Don't you juat do a structiral dynamics analysis?

By applying a concentrated load to a node (or a set of nodes), the deformation at that point will be significantly greater (O(um)) than the amplitude of the ultrasonic waves which will propagate (O(nm) or O(pm)).  

Have you sampled the time-history of displacement (magnitude or component) at a node "far" away from where you are applying the load?  Remember, the displacements will be comparatively small away from the source.

If your answer to the above is affirmative, and you are simply trying to visualize the wave field propagate, you will have to set the max/min scales to a much tighter window due to the large amount of deformation which occurs at the load application site.

Dear Sascha,

I unfortunately have not worked on Hyper elastic materials previously and have done only 2 sound propagation problems on metals. Now modeling this propagation in a hyper elastic material seems a bit confusing to me. So, any links, documents or previously done simulations on this issue would be quite helpful.

As I was not familiar with material required inputs for this problem, I thought the problem might lay in material properties, like defining acoustic medium. I have no idea about applications of acoustic medium.

I just want to see the wave propagation at least in a spherical model with 5mm diameter. The wave length is 0.15mm.

Thanks a lot for your time.

Hi Brian,

1-What is this statement applicable for: " By applying .... O(pm))."

I applied both concentrated force and distributed pressure, but had the same results. Just a local movement of nodes and no propagations.

2- yes. I defined two sensor points for time history output, in 0.5 and 5.0 mm distance from excitation point and the wave length is supposed to be 0.15 mm. Please see my input data at top of the page, for possible inconsistencies! I could not see any displacements due to wave propagation by the way.

3- Do you mean I should narrow down the Max/Min values shown by color spectrum? for example -0.05 to +0.05 instead of -0.5 to +0.5 for displacement?

Also, if you had a sample of impact or wave propagation in hyper elastic material, or at least input data for a specific hyper elastic material properties, please let me know.

Thanks a lot for your assistance.

Hey,

to get it straight. I thought you wanted to simulate the propagation of elastic waves in the ultrsonic frequency regime in an kidney?!? The kidney should be modelled by an hyper-elastic material model in your case, right?

So why do you need an acoustic medium? Do you want to compute the sound pressure in the surrounding of the kidney? Otherwise, I am not sure I understand to need for an acoustic medium?

Best, Sascha

Hi Sascha,

You are quite right.

I simply do not know if using an acoustic medium property for my case will make my simulations better or not. My project is developing a FEM for simulation of wave propagation in a soft tissue like kidney. The results would be used for prediction of young's modulus and further cancer diagnosis.

Thanks,

In this case, at least from my point of view, you only have wave propagation in an elastic medium.

Ahmad,

It sounds like there are several things going on here.

1. From what I understand from your original post, you are prescribing a force/pressure over a finite amount of time. A concentrated force prescribed over a finite amount of time is a broadband source (think Fourier analysis on the time history of your load application).  Thus, you don't have a single frequency (wavelength) propagating but rather a spectrum of frequencies/wavelengths.

2. The acoustic medium formulation is really only valid for fluids modelling, where viscosity is not of primary concern.  It will only support dilatational wave propagation, not dilatational and shear wave propagation as is what happens with ultrasound in soft tissue.  As previously recommended, start with a simple *ELASTIC material definition to narrow down the problem.  If that simulation provides expected results, progress to the *HYPERELASTIC material card.

If you post your actual input deck (leave out the element and connectivity information), folks may be able to help you troubleshoot.

Brian