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Terminal Falling Velocity of a sand garin (tutorial)
Posted 23 feb 2012, 02:41 GMT-5 Fluid & Heat, Parameters, Variables, & Functions Version 4.2 1 Reply
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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
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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