Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Modelling gravity
Posted Oct 21, 2015, 11:09 a.m. EDT 2 Replies
Please login with a confirmed email address before reporting spam
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 Oct 22, 2015, 1:59 a.m. EDT
Please login with a confirmed email address before reporting spam
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
Please login with a confirmed email address before reporting spam
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