vTAWSS - vOSI - vshear_pulse

[Michela Garau]

Hi guys,

I have some question on the "average_result.vtp" file.

What is the difference between vTAWSS, vOSI, vshear_pulse and the version of each of these parameters with the "_wss" (like vTAWSS_wss)?
Maybe the difference is represented by the unit of measurement? In this case, which one are they?

Moreover, can you suggest me some link or paper for the related mathematical equations?

Thank you so much in advance

Regards

Michela

[David Parker]

Hi Michela,

vTAWSS and vOSI are computed from inplane tractions, the _wss results are compute using wall shear stresses.

I don't know of a paper where the equations are defined. You can look online or in a book on CFD or biomechanics I think.

Cheers,
Dave

[Michela Garau]

Perfect, thank you David.

So, I can imagine that all the quantities are expressed in cgs system measure (for example TAWSS [dyne/cm2]).

Cheers,
Michela

[David Parker]

Hi Michela,

Quantities are expressed in units consistent with those used in your simulation. If you used CGS units in your simulation then TAWSS will have units dyne/cm2.

The SV documentation needs to have a description of the results output by svSolver. There is a Github Issue open for that.

I often find it useful to look at the svSsolver source code https://github.com/SimVascular/svSolver ... solver.cxx to better understand how the results are computed. However, it is sometimes not easy to figure out what is going on!

Cheers,
Dave

[Charlie Bright]

Hi Dave,

Sorry to bring up an old thread.
I've got a simulation in mm-units and when I load the converted-results into ParaView the 'as-is' value of WSS seems reasonable if the unit for the results was the CGS dyne/cm^2 (0-15 TAWSS).

If the value is actually in dyne/mm^2 however, then they'd be huge in comparison. Unfortunately I don't have a known dataset to compare against.

I've had a quick check of the source code you linked & I couldn't find any reference to the 'sim_units_mm' or 'RequestedUnitsCm' tags when going through the sections detailing 'vWSS'.
Is there any chance the units could be different to what is expected when converting results for MGS sims?

Thanks,
Charlie

[David Parker]

Hi Charlie,

The solver does not have units, your simulation input (mesh, BCs, etc.) just needs to be consistent.

The only results that seem to be scaled are pressure_avg_mmHg values which are written to the average_result.vtp file (see https://github.com/SimVascular/svSolver ... solver.cxx).

Cheers,
Dave

[Charlie Bright]

Hi Dave,

Cheers for the info, it helped me solve my issue.
Seems I got muddled up when figuring out units - mmgs stress should be in Pa which makes a lot more sense!

Thanks again,
Charlie