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-   -   Moving Mesh Velocity Issue: Mesh velocity does not equal displacement (http://www.cfd-online.com/Forums/cfx/92276-moving-mesh-velocity-issue-mesh-velocity-does-not-equal-displacement.html)

Doginal September 8, 2011 10:44

Moving Mesh Velocity Issue: Mesh velocity does not equal displacement
 
Hello everyone

I'm modeling a blade moving through a liquid by using a subdomain that surrounds a blade within a large domain and applying a moving mesh to the subdomain.

I want the blade to start at a stand still and accelerate linearly to 2 m/s over 1s in the x direction.

These are the CEL functions I use to define the moving mesh.

Specified mesh location X is: X Still + X New Tran

X Still = (x-X0) - Total Mesh Displacement X
X New Tran = X Vel * t
X Vel = 2 [m s^-2] * t

Total time of simulation = 1s
Time steps = Total time/500

The issue i have is very odd. After running the simulation, the velocity which the blade/inner subdomain moves is twice what it should. What is strange is that the distance that the blade moves is normal.
example to explain
at t=1
Blade mesh velocity should be 2m/s but it actual is 4m/s
Mesh Displacement at the blade is 4/500
however Total mesh Displacement at the blade is 2m.

The total displacement of the blade does not equal the mesh velocity or the sum of the timestep displacements, throughout the entire simulation, the mesh velocity is double compared to the mesh displacement at that timestep

I'm really confused as to why or how this is happening so any help would be great.

Thank You,

DM

singer1812 September 8, 2011 11:42

For constant accel:

v=at
s=integral(at)dt=1/2*a*t^2

you have

s=a*t^2

Doginal September 8, 2011 12:02

Quote:

Originally Posted by singer1812 (Post 323441)
For constant accel:

v=at
s=integral(at)dt=1/2*a*t^2

you have

s=a*t^2

Wow. I'm an idiot for missing that one. Thanks


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