Velocity timescale separation cannot divide this interior viscosity timescale separation

[mojtabaAmiraslanpour]

Hi,

This is my first time running a simulation in V 2.6, when I start running I get this error:

(HemoCell) Error, Velocity timescale separation cannot divide this interior viscosity timescale separation, exiting ...

Can anybody help me with it?

[gzavo]

Hi @mojtabaAmiraslanpour ,

This should not be the effect of the version change. This is the triggered error message:

HemoCell/core/hemoCell.cpp

Lines 613 to 619 in ccccc63

	if (global.enableInteriorViscosity) {
	if (cellfields->interiorViscosityEntireGridTimescale%cellfields->particleVelocityUpdateTimescale!=0 ||
	cellfields->interiorViscosityTimescale%cellfields->particleVelocityUpdateTimescale!=0) {
	hlog << "(HemoCell) Error, Velocity timescale separation cannot divide this interior viscosity timescale separation, exiting ..." <<endl;
	exit(1);
	}
	}

The error means you have internal viscosity enabled, and the steps where you update the internal cells don't coincide with the steps when the cell model is updated (which is a problem).
The time scales are updated through the functions from (and the subsequent functions below this in the same file):

HemoCell/core/hemoCell.cpp

Line 384 in ccccc63

void HemoCell::setMaterialTimeScaleSeparation(string name, unsigned int separation){

In most examples these are set from the config.xml.

[mojtabaAmiraslanpour]

Thanks @gzavo
Well, this is strange because I think I have everything right in the config.xml but still, the two numbers are not dividable. This is how my config file is set:

<ibm>
    <stepMaterialEvery> 5 </stepMaterialEvery> <!-- Update particle material model after this many fluid time steps. -->
    <stepParticleEvery> 5 </stepParticleEvery> <!-- Update particles position after this many fluid time steps. -->
</ibm>

<domain>
	...
</domain>

<sim>
    <tmax> 20000000 </tmax> <!-- total number of iterations -->
    <tmeas>  10000 </tmeas> <!-- interval after which data is written -->
    <tlog>  1000 </tlog> <!-- interval after which data is logged on the screen -->
    <tcsv>  10000 </tcsv> <!-- interval after which simple mean cell values are written to a CSV file -->
    <tcheckpoint> 100000 </tcheckpoint>
    <interiorViscosity>5</interiorViscosity>
    <interiorViscosityEntireGrid>1000</interiorViscosityEntireGrid>
</sim>

[mojtabaAmiraslanpour]

I found the solution. So in order to add interior viscosity one needs to add the following line into the main code to set Interior Viscosity Timescale Separation:

hemocell.setInteriorViscosityTimeScaleSeperation((*cfg)["sim"]["interiorViscosity"].read<int>(),(*cfg)["sim"]["interiorViscosityEntireGrid"].read<int>());

This is better to be mentioned here in the user guide for less future confusion:
https://www.hemocell.eu/user_guide/Case.html#compiling-examples-with-special-features

Have a nice day!