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Modelling gravity
Posted 21 oct. 2015, 11:09 UTC−4 2 Replies
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Hi All,
I am trying to model water exiting a hose at a given velocity. I want to model the water trajectory and find out how far it travels before hitting the ground. Can anyone tell me where to start in Comsol? I am familiar with CFD, just not with the gravity part.
Thanks
I am trying to model water exiting a hose at a given velocity. I want to model the water trajectory and find out how far it travels before hitting the ground. Can anyone tell me where to start in Comsol? I am familiar with CFD, just not with the gravity part.
Thanks
2 Replies Last Post 22 oct. 2015, 01:59 UTC−4
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Posted:
9 years ago
Hi
In the flow node, add Volume force and define the y component as -g*rho (gravity acceleration*fluid density). Assuming that y axis is vertical.
Lasse
In the flow node, add Volume force and define the y component as -g*rho (gravity acceleration*fluid density). Assuming that y axis is vertical.
Lasse
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Posted:
9 years ago
Hi
Lasse gave you the correct way.
To easier remember it you should think over the units.
Gravity is a "domain load" (or Volume load) hence it applies to each element of volume dx*dy*dz (this dx*dy*dz element is not mentioned in the COMSOL GUI entries, but is always there in an implicit way).
In macroscopic physics we always say force is mass time acceleration
F[N]=m[kg]*a[m/s^2]
But in the microscopic continuum way one says:
F[N]= integral_over_volume(rho[kg/m^3]*a[m/s^2]*dx[m]*dy[m]*dz[m])
This is the default entry method of all GUI fields in COMSOL but COMSOL omits (implicitely) the "integral_over_volume(" and the ending "*dx*dy*dz)" and keep only the "rho_density*acceleration"
--
Good luck
Ivar
Lasse gave you the correct way.
To easier remember it you should think over the units.
Gravity is a "domain load" (or Volume load) hence it applies to each element of volume dx*dy*dz (this dx*dy*dz element is not mentioned in the COMSOL GUI entries, but is always there in an implicit way).
In macroscopic physics we always say force is mass time acceleration
F[N]=m[kg]*a[m/s^2]
But in the microscopic continuum way one says:
F[N]= integral_over_volume(rho[kg/m^3]*a[m/s^2]*dx[m]*dy[m]*dz[m])
This is the default entry method of all GUI fields in COMSOL but COMSOL omits (implicitely) the "integral_over_volume(" and the ending "*dx*dy*dz)" and keep only the "rho_density*acceleration"
--
Good luck
Ivar