Selecting multiple surfaces within FEMAP

[adnanh]

Hi,

Is it possible to select multiple surfaces at once within FEMAP? For example, when I want to apply a pressure load within a cylinder which has some other faetures on the inside, which means that there are multiple surface of the interior of the cylinder. You can always select the surfaces one by one nut that's not always very practical.

And how can change an already existing load set or constrain set, for example changing the force or prescribed displacement or simply adding more nodes or surfaces to which the load/constraint is applied. I do this by deleting the whole load/constraint set and then defining a new one. I believe this is not really theintention of the program.

Kind regards.

 

[ThomasH]

I'm not sure that I understand your problem correct. You can apply loads to multiple surfaces by Model-Load-On Surface and then select multiple surfaces.

As for change it can be a bit more complicated. You can use Modify-Edit-Load individual and select for example pressures associated with surfaces.

But if you add nodes to a surface after you have expanded the loads from the geometry (surface) to the model (nodes/elements) that might be a problem. As far as I know there is no "Unexpand" command.

What I would do is to copy the original load set. Say that you have geometry based loads in set 1. Copy the entire set to set 2 and expand the loads. It there is a change you simply delete set 2 and again copy set 1 to set 2.

Not perfect but it might do the job.

Good Luck

Thomas

 

[adnanh]

Hi Thomas,

What I mean by selecting multiple surfaces is the following. Rather than selecting surfaces one by one (thus individual surfaces), in many CAD programs you are often given the option to select more than one surface. In Pro/Engineer for example it is possible to select surfaces by the socalled "Seed and Boundary" method. Here, you specify the seed surface and a boundary surface and all other surfaces surrounded by these two, are selected automatically. This is very handy for exampl when the surface region you need to select exists from many individual surfaces. Thus rather than selecting all individual surfaces separatively you can apply this trick and select them all in a blink of an eye.

Now suppose you have some pressure vessel internally loaded. The interior of this vessel is consists of features like enforcing ribs and stuff like that. This means that the interior is not represented one single surface, but from many smaller surafaces. In order to apply the pressure you will need to select them all. Selecting surfaces one by one often leads to frustration.

Regards,

Adnan

 

[rb1957]

can't you (i don't have FeMap in fornt of me now, but i was using it recently) select surfaces by surface number ? ... so that if you're careful setting up your model all the internal surfaces will be sequential.

 

[rb1957]

thinking aboutthe question for a second longer ... i'd be careful about applying the pressure to the surfaces of the internal stiffeners ... either
1) you've modelled the stiffeners as a single surface, so the pressure acts on both sides, negating itself; or
2) you've modelled both sides of the stiffener (maybe they're big and chunky and you're doing 3D elements, maybe they're webs enclosing a space that isn't pressurised), in which case applying pressure to the surface would be correct.

 

[adnanh]

Hi rb1957,

The effect of the pressure on the internal stiffeners is partially compensated indeed. However, there are some parts of the stiffeners on which the pressure acts only from one side, however these have relatively small surface area. Excluding these when applying pressure would probably not make big difference (if at all). However, it should be possible to select surfaces in some kind of a more systematic manner. This, I would like to know how it is done.

Further, I am using MSC Marc/Mentat sometimes too. I have an even bigger problem with MSC Mentat. In Mentat I can not figure out how to select one single surface at all. Pressure loads are applied to element faces, and I am not able to select faces by surface. I can only select faces by elements, thus one by one...
If I try to select faces by some other method provided by Mentat, also faces of elements in the interior of the mesh are selected. These, I obviusly don't need as I am trying to apply a pressure load. However, I will post this in the MARC/Mentat part of the forum.

Regards,

Adnan

 

[rb1957]

in FeMap you can make a group of surfaces, which shouldn't be too hard to pick out. be careful about the surface normals ... i think the pressure is defined with repsect to the normal, which can flip depending on how you specified the surface. you can flip elemnt normals (under modify element, i think), and you can renumber surfaces if that makes it easier.

good luck

 

[ThomasH]

Ok, now I understand the problem. The easiest solution might be what rb1957 suggests. Create a group and use that group. You can also use surface numbers, colours och layers. Basically, anything that makes the surfaces unique compared to the other surfaces in the model.

But to select a sufface and automatically get all that surround that surface. Might be possible but I don't know how.

I hope things work out anyway.

Thomas

 

[adnanh]

Thanks all you!

Selecting surfaces by groups is most appropriate indeed.

Adnan