strain rate magnitude

Kanarya · September 1, 2014, 07:45

Hi,
I am using tensors in udf so my question is:
should I initialize the tensors?or there is no need for it?
for example

PHP Code:


			
 for(j=0;j<ND_ND;j++)

{

for(i=0;i<ND_ND;i++)

{

  S12[i][j]=0.0;

}

}

and then 

for(j=0;j<ND_ND;j++)

{

for(i=0;i<ND_ND;i++)

{

  S12[i][j]=....calculate;

}

}

is it ok?
thanks in advance!

m zahid · November 19, 2014, 11:01

hi, anybody know the difference in equation of vorticity and strain rate in CFD fluent. i want to write the UDF of vorticity in 3D.
if anybody know about this, please share this .
thanks

prasa · July 10, 2018, 09:12

Hi,
I know this conversation is very old, but the information here is very important.

I would like to know, shear stress for the incomprehensible fluid is given as following equation, by just removing the linear expansion terms?

$s=\sqrt{(u_{z}+w_{x})^{2}+(u_{y}+v_{x})^{2}+(w_{y}+v_{z})^{2}}$

Is it correct ?

arashfluid · July 17, 2018, 04:51

Hi friends,
How can I write gradient of strain rate (∇γ ̇) in udf?
Can anyone help me?
Thanks,

mdmtramper · February 9, 2021, 10:07

Hi, thanks for this

Does anyone has a good reference for the derivation? Thanks!

mcanoenen · September 23, 2021, 03:33

Could you please help about this as well. And could you possibly suggest me a tensor book for a beginner?

Quote:

Originally Posted by rembe

Hi,

I'm not a expert in fluid mechanics. Can you tell me the difference between the strain rate magnitude:

and the mean strain rate:

Sij=1/2*(dUi/Dxj+dUj/dxi)

I need th correct formulation in the SMAGORINSKY-model.

Thank you very much
Michael

Regards,

mcanoenen

September 1, 2014, 07:45		#21
Kanarya Senior Member Join Date: May 2011 Posts: 231 Rep Power: 16	Hi, I am using tensors in udf so my question is: should I initialize the tensors?or there is no need for it? for example PHP Code: `for(j=0;j<ND_ND;j++) { for(i=0;i<ND_ND;i++) { S12[i][j]=0.0; } } and then for(j=0;j<ND_ND;j++) { for(i=0;i<ND_ND;i++) { S12[i][j]=....calculate; } }` is it ok? thanks in advance!

November 19, 2014, 11:01	vorticity vs strain rate	#22
m zahid Member Qureshi M Z I Join Date: Sep 2013 Posts: 81 Rep Power: 13	hi, anybody know the difference in equation of vorticity and strain rate in CFD fluent. i want to write the UDF of vorticity in 3D. if anybody know about this, please share this . thanks

July 17, 2018, 04:51	Gradient of strain rate	#24
arashfluid Member Arash Mahboubidoust Join Date: Jun 2013 Location: Iran Posts: 58 Rep Power: 13	Hi friends, How can I write gradient of strain rate (∇γ ̇) in udf? Can anyone help me? Thanks,

LinkBacks (?) LinkBack to this Thread: https://www.cfd-online.com/Forums/fluent-udf/90818-strain-rate-magnitude.html
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what is strain rate_Baby's home	This thread	Refback	May 8, 2015 16:37

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July 10, 2018, 09:12		#23
prasa New Member Prasanna Welahettige Join Date: Jan 2016 Location: Norway Posts: 28 Rep Power: 10	Hi, I know this conversation is very old, but the information here is very important. I would like to know, shear stress for the incomprehensible fluid is given as following equation, by just removing the linear expansion terms? $s=\sqrt{(u_{z}+w_{x})^{2}+(u_{y}+v_{x})^{2}+(w_{y}+v_{z})^{2}}$ Is it correct ?

February 9, 2021, 10:07		#25
mdmtramper New Member Nederland Join Date: Sep 2020 Posts: 9 Rep Power: 6	Hi, thanks for this Does anyone has a good reference for the derivation? Thanks!