User Field Function - Velocity Vector

Vitor_Manuel · May 3, 2017, 18:49

Hello,

I want to create a velocity function for some boundary surfaces walls (with morph mesh). It's a damper, with the main piston moving at a certain constant velocity which will "push" the piston separating the oil from the gas at the gas Chamber, as the oil is incompressible fluid, the difference in velocity is just the ratio between the area of the rod entering the Oil chamber and the area of the piston of the gas chamber multiplied by the velocity of the moving rod.

I am having a hard time trying to get the syntax correct, at this moment I am using the value introduced by hand but it's neither practical or accurate because it's not an exact number.

Thank you in advance for any response!

PS: If there is a way (and perhaps more accurate) of simply giving a velocity to the rod and have the piston in the gas chamber moving freely from the reaction force generated by the moving fluid (pushed or the opposite if the rod is exiting the oil chamber instead of entering).

me3840 · May 7, 2017, 13:02

Is the output a vector or just a magnitude?

Is the moving rod velocity a constant imposed on the simulation or is this a DFBI problem?

What have you tried so far?

Vitor_Manuel · May 7, 2017, 19:03

First of all, thank you for your response and time,

So far I have defined Motion as Morphing and applied it to the region motion specification.
As initial conditions I have a perfectly still fluid, and defined a constant grid velocity (only in the direction of the rod) which will impose flow through existing hole in the moving piston. Every moving Wall I give the same Grid Velocity (Morpher specification>Displacement>Grid velocity) value as [0.0 , 0.025 , 0.0] (for example), the extending walls I define as Floating (as the Morpher specification)

As it is incompressible flow the decrease of the volume as to be compensated by the other end, The gas chamber wall. I have defined it the same way I defined the piston but with the oposite velocity multiplied by the area ratio (it's a rounded number not exact which is a problem).

For now I am using a constant velocity, but I have interest in defining a field function because I want to apply a Sinusoidal Velocity profile.

May 3, 2017, 18:49	User Field Function - Velocity Vector	#1
Vitor_Manuel New Member Vítor M.B.M. Santos Join Date: Dec 2016 Posts: 2 Rep Power: 0	Hello, I want to create a velocity function for some boundary surfaces walls (with morph mesh). It's a damper, with the main piston moving at a certain constant velocity which will "push" the piston separating the oil from the gas at the gas Chamber, as the oil is incompressible fluid, the difference in velocity is just the ratio between the area of the rod entering the Oil chamber and the area of the piston of the gas chamber multiplied by the velocity of the moving rod. I am having a hard time trying to get the syntax correct, at this moment I am using the value introduced by hand but it's neither practical or accurate because it's not an exact number. Thank you in advance for any response! PS: If there is a way (and perhaps more accurate) of simply giving a velocity to the rod and have the piston in the gas chamber moving freely from the reaction force generated by the moving fluid (pushed or the opposite if the rod is exiting the oil chamber instead of entering).

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May 7, 2017, 13:02		#2
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	Is the output a vector or just a magnitude? Is the moving rod velocity a constant imposed on the simulation or is this a DFBI problem? What have you tried so far?

May 7, 2017, 19:03		#3
Vitor_Manuel New Member Vítor M.B.M. Santos Join Date: Dec 2016 Posts: 2 Rep Power: 0	First of all, thank you for your response and time, So far I have defined Motion as Morphing and applied it to the region motion specification. As initial conditions I have a perfectly still fluid, and defined a constant grid velocity (only in the direction of the rod) which will impose flow through existing hole in the moving piston. Every moving Wall I give the same Grid Velocity (Morpher specification>Displacement>Grid velocity) value as [0.0 , 0.025 , 0.0] (for example), the extending walls I define as Floating (as the Morpher specification) As it is incompressible flow the decrease of the volume as to be compensated by the other end, The gas chamber wall. I have defined it the same way I defined the piston but with the oposite velocity multiplied by the area ratio (it's a rounded number not exact which is a problem). For now I am using a constant velocity, but I have interest in defining a field function because I want to apply a Sinusoidal Velocity profile.