CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > Siemens > STAR-CCM+

Different calc for lift between: force coefficient report and 6-DOF body force report

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 15, 2020, 09:16
Default Different calc for lift between: force coefficient report and 6-DOF body force report
  #1
New Member
 
Norge
Join Date: Nov 2017
Location: Norway
Posts: 20
Rep Power: 4
hxax is on a distinguished road
This is for a hydrofoil vessel. Lift coeff force report say 80 tons, 6-DOF body force report 90. About 10 ton difference. What is this?
hxax is offline   Reply With Quote

Old   January 15, 2020, 09:35
Default
  #2
Senior Member
 
Matt
Join Date: Aug 2014
Posts: 809
Rep Power: 14
fluid23 is on a distinguished road
A lift coefficient report will not have units of tons. You will have to provide more info about your report setups if you want any useful feedback.
fluid23 is offline   Reply With Quote

Old   January 15, 2020, 19:21
Default
  #3
New Member
 
Norge
Join Date: Nov 2017
Location: Norway
Posts: 20
Rep Power: 4
hxax is on a distinguished road
well, the body mass lifted in DFBI is about ten tons higher than the lift capability predicted by the standard force coefficient reports.

Is the pressure somehow accounted for is some additional manner?

ton= N*E3/(9,81).
hxax is offline   Reply With Quote

Old   January 16, 2020, 10:08
Default
  #4
Senior Member
 
Matt
Join Date: Aug 2014
Posts: 809
Rep Power: 14
fluid23 is on a distinguished road
Since a force coefficient report doesn't directly indicate lift capability on its own, you have to make sure that your nondimensionalization parameters are appropriate. The coefficient report properties include reference values for pressure, density, velocity and area. If these aren't defined correctly then the force report and coefficient report will not agree. Likewise, if you are taking a coefficient and redimensionalizing it from a coefficient into a scalar value with units (i.e. N or lbf) then you need to make sure that the reference values used correspond to the coefficient assumptions. For that matter, also make sure that both reports include all the same surfaces/regions... it seems trivial but its easy to overlook the small stuff.

Now your second question is much more specific and probably a little easier to answer. I am not very familiar with 6DOF, but a quick read of the software documentation reveals a difference in the calculation of a force report and a 6DOF force report. Namely, it is the inclusion of user forces and gravity in 6DOF. A standard force report will only include pressure and shear forces.

That being said, it does sound like something is off. One wouldn't expect the inclusion of gravity to increase the net lift force.

I would suggest double checking your DFBI and report setups. Its impossible to troubleshoot without more info.
fluid23 is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
CFD Force Coefficient Report Error Urodele STAR-CCM+ 1 January 29, 2018 11:17
Question about heat transfer coefficient setting for CFX Anna Tian CFX 1 June 16, 2013 06:28
Viscous force and coefficient viscous force tobino Main CFD Forum 0 February 20, 2011 21:06


All times are GMT -4. The time now is 02:30.