Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.
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.
Terminal Falling Velocity of a sand garin (tutorial)
Posted 2012年2月23日 GMT-5 02:41 Fluid & Heat, Parameters, Variables, & Functions Version 4.2 1 Reply
Please login with a confirmed email address before reporting spam
Could someone please explain me why you add the GLOBAL VARIABLE X : X t - Xdo t. ?
The physics of the problem only state the necesity to establish the equation
Xdo t: Xdo tt-(F_z+F_g)/m_grain.,
which corresponds to the Ordinary Differential Equation:
(m_grain) * (Xdo tt) = (F_g+ F_z)
or
(F_g+ F_z)/(m_grain) - (Xdo tt) = 0 ; as is supossed to be entered in the software
The systems uses cylindrical coordinates so there is no conflict in x,y,z,t or X,Y,Z,T.
Thanks for your help on beforehand
Kind regards
Hello Clotario Tapia
Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.
If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.
Please login with a confirmed email address before reporting spam
The ODE below can be removed from the model without affecting the solution.
falling_sand.mph > Model 1 > Laminar flow > Global Equations
Xt - Xdot = 0
However, if you * do * include the ODE for "X" in the Global Equations, then you have the opportunity to plot the position of the grain particle in the z direction (denoted by the variable "X"). For example, you can plot "X" vs. time to see the position of the grain as a function of time.
See also the related link below
www.comsol.com/community/forums/general/thread/46937
-DW