Learning Forum

[jccubisino]

Dear Fellows:

I would appreciate any help on how to constrain the long edges of the plate shown bellow in order to get straigth line between vertices as shown in the next picture. Thanks

[peteroznewman]

Mesh the rectangle with a single linear element and you will get straight edges.

[jccubisino]

Thank you Peter for your quick reply. I am afraid that if I proceed in the way suggested above, the precision of the results would be affected since the plate is in fact a 1500 x 500 mm stiffened plate. Could you please give me any other idea? Thank you. 

[peteroznewman]

What are the true boundary conditions and loads applied to it.

How is it possible that those loads and boundary conditions result in straight edges?

If the true deformation results in non-straight edges, why would you want to enforce a non-physical boundary condition?

[jccubisino]

Dear Peter, boundary conditions and loads are shown in pictures below (they are referred to the 2nd picture above). Boundary conditions are established by a regulatory body in ship structrural certification therefore I am not sure about the background to require straight edges but usually is because the panel is sorrounded by many other panels, therefore edges are assumed ideally straight.

I tried using simetric conditions in edges B3 a B4 but, in this case, edges can not be loaded. I hope this helps. Thank you in advance.

[peteroznewman]

Use Constraint Equations.

First in geometry, split the surface to create a vertex where you need to control the side of the shape.

In Mechanical, create Remote Points at all the corners and sides that need to be controlled. Mesh with one linear element per body.

Next create Constraint Equations to force the mid point to stay halfway between the corners in the X and Y directions. For example, this equation forces B2 to be halfway between C2 and C3 in the X direction. I used a total of seven Constraint Equations.

Apply other loads and boundary conditions that are needed to deform the part.

The result is the sides remain straight and parallel.

Note that Constraint Equations add stiffness to the part compared with having no constraint equations. Observe below how much larger the deformation is under the same loads without the constraint equations.

Good luck!

[jccubisino]

Thank you Peter for your help and your time. Your ideas are allways really appreciated.

Best Regards