CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

Moving Mesh Velocity Issue: Mesh velocity does not equal displacement

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   September 8, 2011, 10:44
Default Moving Mesh Velocity Issue: Mesh velocity does not equal displacement
  #1
Member
 
anonymous
Join Date: Jun 2011
Posts: 55
Rep Power: 6
Doginal is on a distinguished road
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
Doginal is offline   Reply With Quote

Old   September 8, 2011, 11:42
Default
  #2
Senior Member
 
Edmund Singer P.E.
Join Date: Aug 2010
Location: Minneapolis, MN
Posts: 494
Rep Power: 11
singer1812 is on a distinguished road
For constant accel:

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

you have

s=a*t^2
singer1812 is offline   Reply With Quote

Old   September 8, 2011, 12:02
Default
  #3
Member
 
anonymous
Join Date: Jun 2011
Posts: 55
Rep Power: 6
Doginal is on a distinguished road
Quote:
Originally Posted by singer1812 View Post
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
Doginal is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
SnappyHexMesh for internal Flow vishwa OpenFOAM Native Meshers: snappyHexMesh and Others 23 August 6, 2014 03:50
how to set periodic boundary conditions Ganesh FLUENT 13 January 22, 2014 05:11
external flow with snappyHexMesh chelvistero OpenFOAM 11 January 15, 2010 20:43
Moving Mesh Run problem - Scientific Linux G. SE CD-adapco 2 May 7, 2008 07:15
How to control Minximum mesh space? hung FLUENT 7 April 18, 2005 09:38


All times are GMT -4. The time now is 02:34.