Import loads by global coordinates?

[tlemonds]

Hey guys,

I have some general FEA experience using ANSYS during my undergrad. Mech Eng education but I am now trying out NX NASTRAN for the first time. Is there a quick and easy way to import a set of loads by global coordinates? I was imagining basically a text file with 4 columns and as many rows as loads. Three of those columns would obviously be coordinates and the fourth the magnitude of the load. However, I'm thinking I would also need to include something to indicate the direction that these loads should be applied in. They are all purely Z-directional loads if that makes it easier. Maybe there's a way to have global coordinates and unit vector info along with the loads? The only reason I ask is because I have to import 30+ loads maybe 20 or 30 times and they will be different every time. Was hoping for some sort of even halfway efficient method to do this...

Thanks,
Tyler

 

[dwallace1971]

You can write out your "load cards" in excel and export them as a delimited file to a text editor which NASTRAN can read. In order to do this, though, you'll need to read up on NASTRAN syntax. If you really want to get fancy, you write a control deck that calls all of your other cards (material, property, loads, etc.) then you can mix and match at will. It's not hard, but you'll need a good understanding of the NASTRAN .bdf file format and the NASTRAN format. A good reference is MSC.Nastran Primer.

"On the human scale, the laws of Newtonian Physics are non-negotiable"

 

[tlemonds]

For now, I think going with the "load cards" method would be best from a learning curve standpoint (at least from how you described it). The coordinates where these loads are located already being generated in order to create certain geometry within the CAD model and they will always occur at these locations, at most I'll go through 3 or 4 material changes. You suggested this "MSC.Nastran Primer" as a reference. I only have access to an NX NASTRAN license, can I use this suggested tool for free? If not, any suggestions of some kind of free reference material or something related to my NX license I could use? Thanks for the quick response!

 

[dwallace1971]

The MSC.Nastran Primer for Linear Analysis is a book. NX Nastran started out as MSC Nastran 2001, so most of the info is relevant to both products. At the very least the book will get you up to speed on how the NASTRAN input files are formatted and how to write input decks.

"On the human scale, the laws of Newtonian Physics are non-negotiable"

 

[nlgyro]

What you're essentially trying to do can be easily achieved by using the nastran FORCE card.

Get a hold of the nastran quick reference guide and have a look at the format of the force card.

 

[tlemonds]

I figured it out the other day but you guys would probably consider it a "work-around". I imported the coordinates where I wanted to apply the loads as points into the idealized part file which then showed up in the FEM file. Selected each point and made it a mesh point. Then used the force card and its spatial field option to import the .csv file that contained the global coordinates and magnitude of the load in the Z direction. I was under the impression that I would need to apply the load on a node/mesh point and so this is why I took the step to make the coordinates mesh points. Is this not necessary? If it is, I don't see how I could accomplish this in the force card without messing with the FEM file unless of course the coordinates I was interested in happened to already be the EXACT locations of node points.

 

[nlgyro]

Having nodes exactly at location where you have point loads is desirable, but cannot be achieved always.

One option when the loading coordinates are not at EXACT locations of node points is to use RBE3 elements which typically "beam" the applied loads onto your mesh.