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subdomain and boundary integration

Posted 19.10.2011, 04:30 GMT-4 3 Replies

Leman Güler
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Hello,

I working on design of microejector with Comsol. The conditions I use, are stated below;

Space Diemension : 3D
COMSOL Application Modes
Fluid Dynamics
Incompressible Navier Stokes
Steady State Analysis

I would like to use subdomain integration and boundary integration properties of post processing. Bıt I couldn't understand the formula of these integration. For example, the unit of subdomain integration of velocity field m^4/s, I could find how this unit is calculated and where can I use this result.
I will be very pleased if somebody could explain the aim of these integrations and the answer of my questions.

Thanks in advance

Leman Güler
3 Replies Last Post 12.07.2012, 13:56 GMT-4
Lasse Murtomäki
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Posted: 1 decade ago 19.10.2011, 07:52 GMT-4
The dimension is m^4/s because it is the product of linear velocity v (m/s) and volume element dV (m^3). It is naturally not a very meaningful quantity, but if you do boundary integration of the velocity field, you'll get the volume flow rate across that boundary, which is meaningful.

dV/dt = int(v*dA)

In electrochemistry, current distribution across an electrode quite often is uneven. Then you have to integrate over the electrode to obtain the total current, which is the measured quantity.
The dimension is m^4/s because it is the product of linear velocity v (m/s) and volume element dV (m^3). It is naturally not a very meaningful quantity, but if you do boundary integration of the velocity field, you'll get the volume flow rate across that boundary, which is meaningful. dV/dt = int(v*dA) In electrochemistry, current distribution across an electrode quite often is uneven. Then you have to integrate over the electrode to obtain the total current, which is the measured quantity.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 19.10.2011, 08:57 GMT-4
Hi

indeed do not forget the dimension of the dx*dy*dz (or dx*dy in 2D) think it over if it is the (weighted) average or the integration value you need, the first one is already divided by the total volume / respective area

--
Good luck
Ivar
Hi indeed do not forget the dimension of the dx*dy*dz (or dx*dy in 2D) think it over if it is the (weighted) average or the integration value you need, the first one is already divided by the total volume / respective area -- Good luck Ivar
Urmi Roy
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Posted: 1 decade ago 12.07.2012, 13:56 GMT-4
If all the velocity field vectors point in the negative direction in a region, will the subdomain integration of the velocity field in that region be negative?
Also, could I use subdomain integration of the velocity field to calculate the net fluid flux passing through the region at a given instant of time?
If all the velocity field vectors point in the negative direction in a region, will the subdomain integration of the velocity field in that region be negative? Also, could I use subdomain integration of the velocity field to calculate the net fluid flux passing through the region at a given instant of time?

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