×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

(OP)
What is the degree of freedom in both sliding boundary condition and ball-joint boundary condition?

RE: FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

"ball joint" sounds like pinned (in three directions)

"sliding" sounds like pinned in one or two directions (does the point slide along a line or free to translate on a plane).
you'll need to consider rigid body motion to correctly restrain your model.

RE: FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

(OP)
Thanks for the reply.

The rear wheel of bicycle is sliding in the x-axis only. So, i should let x-axis free to move (TX uncheck), and check the y and z translational, as well as the 3 rotational?

RE: FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

i'd constrain MX only (for rigid body motion)

RE: FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

(OP)
sorry, i'm a bit slow.

From the ball-joint boundary conditions, you said it should constraint the 3 translational motion, and uncheck the rotational motion because it is free to rotate in the 3 axes(x, y and z). There's no translational motion.

But sliding boundary conditions, the rear wheel can only move in the x-direction, so shouldn't i should uncheck x-axis, and constraint all the others?

RE: FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

yes you are (being a bit slow) ...

sliding doesn't require moment fixity. in particular in your case you're looking at the rear axle of a bike, clearly one axis has no moment stiffness.

ask around. it is better to constraint the model either minimally (reacting the 6 degrees of rigid body motion) or as realistically as possible (which in my mind says avoid rotational fixity as much as possible ... what is truly "fixed" in reality ?). adding redundant constraints to your model will at least mess with the loadpaths, at worse mess with all your results.

if you want try it either way and see the effect. which answer is right (or righter) ?

RE: FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

(OP)
your answer don't convince me much

but thanks..

RE: FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

'k ... get a 2nd opinion

RE: FEMAP: Constraint in sliding boundary condition and ball-joint boundary condition?

Dear Steve,
The following picture can help you to understand how to setup the FE problem correctly using FEMAP & NX NASTRAN:



Prescribe different beam cross section properties to every member of the frame and play with them to reach the best design that fits the prescribed requirements of both weight & stress -- good luck!.

Best regards,
Blas.

PD
Here you are a real life model of a mountain-bike meshed with FEMAP & NX NASTRAN at http://iberisa.wordpress.com/2012/05/24/ejemplos-d...:



~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog de FEMAP & NX Nastran: http://iberisa.wordpress.com/

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources