Force and Pressure

IADInocencio · December 23, 2021, 02:54

Hi all, it's been a while. I just wanted to ask if there is a paper/reference on how the force computation if I use the force box or how the pressure is computed? I am trying to validate the hydrodynamic forces on a stepped outfall with some baffles that our structural team has to consider. I have attached a snippet of the results; on the left is a slice just above the first step showing the Pressure, while the image on the right just shows the velocities.

Felix_Sp · December 23, 2021, 06:19

Hey,

This here helps me all the time: https://doi.org/10.1016/j.compfluid.2016.09.012
Maybe the official team has something even better.

It is stated the force

is calculated by:

$F = \int_\Omega \left(-\textbf{n}p + \textbf{n} \cdot \tau \right)d\Omega$

with:
$\Omega$ : surface
$\textbf{n}$ : unit normal vector

: pressure
$\tau$ : viscous stress tensor

The exact paragraph reads:

"The pressure

and the normal component of viscous stress tensor $\tau$ are integrated over the surface $\Omega$ of the structure. The integration is performed in a discrete manner, by using

and $\tau$ for each cell surface of the structure:"; then the forumla
"here $\textbf{n}$ is the unit normal vector to the surface, pointing into the fluid. The Navier-Stokes equations in Eq. (2) are solved including the gravity term. Then the pressure obtained from the projection method includes the hydrostatic part in addition to the dynamic part. Consequently, it is the total force acting on a structure that is determined by Eq. (28)."

Happy holidays!

IADInocencio · January 20, 2022, 01:07

Thanks Felix, apologies for the late reply. I will look into this paper; it looks like they have also published it on the Reef3D main website. https://reef3d.files.wordpress.com/2...wt_cf-2016.pdf

kamath · January 20, 2022, 02:31

The postscript versions of all our publications are/will/should be available on the REEF3D homepage.

January 20, 2022, 01:07		#3
IADInocencio Member Ismael Incoencio Join Date: Sep 2021 Posts: 45 Rep Power: 6	Thanks Felix, apologies for the late reply. I will look into this paper; it looks like they have also published it on the Reef3D main website. https://reef3d.files.wordpress.com/2...wt_cf-2016.pdf __________________ Still learning

January 20, 2022, 02:31		#4
kamath Senior Member Arun Kamath Join Date: Nov 2014 Location: Trondheim, Norway Posts: 265 Rep Power: 13	The postscript versions of all our publications are/will/should be available on the REEF3D homepage. __________________ Arun X years with REEF3D

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December 23, 2021, 06:19		#2
Felix_Sp Member Felix S. Join Date: Feb 2021 Location: Germany, Braunschweig Posts: 85 Rep Power: 6	Hey, This here helps me all the time: https://doi.org/10.1016/j.compfluid.2016.09.012 Maybe the official team has something even better. It is stated the force is calculated by: $F = \int_\Omega \left(-\textbf{n}p + \textbf{n} \cdot \tau \right)d\Omega$ with: $\Omega$ : surface $\textbf{n}$ : unit normal vector : pressure $\tau$ : viscous stress tensor The exact paragraph reads: "The pressure and the normal component of viscous stress tensor $\tau$ are integrated over the surface $\Omega$ of the structure. The integration is performed in a discrete manner, by using and $\tau$ for each cell surface of the structure:"; then the forumla "here $\textbf{n}$ is the unit normal vector to the surface, pointing into the fluid. The Navier-Stokes equations in Eq. (2) are solved including the gravity term. Then the pressure obtained from the projection method includes the hydrostatic part in addition to the dynamic part. Consequently, it is the total force acting on a structure that is determined by Eq. (28)." Happy holidays!