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Addition of gravity effect and initial purturbation
Posted Sep 15, 2009, 3:03 p.m. EDT 1 Reply
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I have to include the gravity effect in my model, which is axial water flow over a flexible cylinder inside a channel. Kindly guide how can I do this. The other thing I want is to impose an initial purturbation to the cylinder. I think it is not possible to do the initial purturbation in a steady prblem. But I will be going to transient case eventually. So kindly describe the procedure to do so.
Thank you.
Thank you.
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1 Reply Last Post Sep 19, 2009, 9:18 a.m. EDT
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Posted:
2 decades ago
Hi
for gravity forces, the easiest is to define the gravity acceleration as a constant, let's say:
G0 9.81[m/s^2] but you can also say
G0 1[lbf/lb] then COMSOL uses directly its internally stored G0 value, its more precise
"lbf" are the imperial units for pound-force, and "lb" of a pound
then in 3D you go to the physics menus of the solids whre you want to apply your gravity field and you set the force, let us say :
Fy -G0*rho_smpn or Fy -G0*rho_ns or both, depending on what you apply your gravity field
the rho_ns is just reading back the density rho, of the specific application mode you are using, such that you do not need to reenter its value, you can also use your externally defined density variable.
In 2D, or with Euler beams in 3D you must carefully check the units as you might need to multiply by the beam area A or "A_smeulip" or the by the thickness_... or even by 2*pi*r in ayxisymmtry mode, in later version there is a tick box to automatically include the thickness or axisymmetry 2*pi*r for physics, BUT NOT in the integration variables when you define your own values
Good luck
Ivar
for gravity forces, the easiest is to define the gravity acceleration as a constant, let's say:
G0 9.81[m/s^2] but you can also say
G0 1[lbf/lb] then COMSOL uses directly its internally stored G0 value, its more precise
"lbf" are the imperial units for pound-force, and "lb" of a pound
then in 3D you go to the physics menus of the solids whre you want to apply your gravity field and you set the force, let us say :
Fy -G0*rho_smpn or Fy -G0*rho_ns or both, depending on what you apply your gravity field
the rho_ns is just reading back the density rho, of the specific application mode you are using, such that you do not need to reenter its value, you can also use your externally defined density variable.
In 2D, or with Euler beams in 3D you must carefully check the units as you might need to multiply by the beam area A or "A_smeulip" or the by the thickness_... or even by 2*pi*r in ayxisymmtry mode, in later version there is a tick box to automatically include the thickness or axisymmetry 2*pi*r for physics, BUT NOT in the integration variables when you define your own values
Good luck
Ivar