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pressure load in minus z-direct
Posted 14.04.2010, 08:18 GMT-4 1 Reply
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Hello,
My general problem is:
I have a thin layer in the middle of package and want to apply a pressure load on each of the two boundaries of the layer, one in z-direct. and one in minus z-direct.
The usual case in Comsol is that the pressure load is applied in z-direction.
To apply it in minus z-direction I tried to put a minus in front of the expression, but than the pressure gets negative, but not the direction.
How can I express the negative direction?
Thanks for all hints to solve it!
Best regards,
Christoph Mannal
My general problem is:
I have a thin layer in the middle of package and want to apply a pressure load on each of the two boundaries of the layer, one in z-direct. and one in minus z-direct.
The usual case in Comsol is that the pressure load is applied in z-direction.
To apply it in minus z-direction I tried to put a minus in front of the expression, but than the pressure gets negative, but not the direction.
How can I express the negative direction?
Thanks for all hints to solve it!
Best regards,
Christoph Mannal
1 Reply Last Post 14.04.2010, 16:25 GMT-4
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Posted:
1 decade ago
Hi
I'm not sure I fully catch your model, but when applying pressure defined w.r.t a boundary its defined by default w.r.t the external "up" side, compressing the internal volume, so if you want to compress a simple rectangle (in 2D) from both top and bottom sides you should apply a POSITIVE pressure on BOTH edges (note that an edge in 2D is an area with a default depth in z of 1[m] if you hav'nt changed the "thickness" material variable, if you have changed the thickness along z, you must correct the"pressure" to ensure coherent units and values). So here the sign is defined by convention "+" is compressing the volume.
What becomes more trickier is if you apply a pressure on an internal boundry, as the definition of "up and down" might be turned around. Therefore I prefer then to apply force loads, even if these are expressed as pressures, they are just forces normalised or spread over the boundary area, and the boundary areas (or the volume of a subdomain or the length of an edge) are quickly calculated by an appropriate Integration Coupling Variable
By the way have you turned on the "symbols" to see your boundary conditions "Options - Preferences - visualization tab - symbols tick" or just click on the icon to the left of your graphical screen border, the one just bove the "thermometer"
Have fun Comsoling
Ivar
I'm not sure I fully catch your model, but when applying pressure defined w.r.t a boundary its defined by default w.r.t the external "up" side, compressing the internal volume, so if you want to compress a simple rectangle (in 2D) from both top and bottom sides you should apply a POSITIVE pressure on BOTH edges (note that an edge in 2D is an area with a default depth in z of 1[m] if you hav'nt changed the "thickness" material variable, if you have changed the thickness along z, you must correct the"pressure" to ensure coherent units and values). So here the sign is defined by convention "+" is compressing the volume.
What becomes more trickier is if you apply a pressure on an internal boundry, as the definition of "up and down" might be turned around. Therefore I prefer then to apply force loads, even if these are expressed as pressures, they are just forces normalised or spread over the boundary area, and the boundary areas (or the volume of a subdomain or the length of an edge) are quickly calculated by an appropriate Integration Coupling Variable
By the way have you turned on the "symbols" to see your boundary conditions "Options - Preferences - visualization tab - symbols tick" or just click on the icon to the left of your graphical screen border, the one just bove the "thermometer"
Have fun Comsoling
Ivar