Questions about HW use and Optistruct

Rahul_P1

1. For unit consistency, if I'm using U.S. customary units, should I define all units based on lbm and inches? For example, for a downward force, would units of force be mg = lbm*386in/s^2? Or is lbf automatically interpreted in entering loads without the extra factor of 386 manually entered? I'm also concerned about this for entering stress values.

2. Is there a straightforward way to apply a GRAV card and point forces/moments to one loadstep? I've tried using a LOAD card but when the optimization is run an error states that no loads are referenced.

3. When applying forces to multiple nodes, is the value of force entered spread equally among the nodes selected? Or does is apply that force value to each node individually?

4. With a force constraint on multiple nodes, does the constraint apply to the sum of the forces on the nodes or does is just check the force on each individual node?

5. When multiple load cases are defined, how does OptiStruct compromise the different load cases to come up with a design that satisfies them all? (qualitative answer would be great!)

6. What would be the best way to set up a load case that extracts natural frequencies so that I may place a constraint on them?

Rahul_P1

For unit consistency, you have to enter the converted values manually. in your example units of force should be mg = lbm*386in/s^2.

 

To combine forces and gravity load, You will need to create another loadcollector, with LOAD card image.

Choose LOAD_Num_Set =2. Select the two load collectors (and assign the corresponding scale factors for the loads).
Use this load collector in the loadstep.
Since LOAD is a Static Load Combination card, you can combine loads here.
Create another load collector with the LOAD card image, then set load_num_set at the bottom of this card to 2, you can find this when you card edit your newly created load collector.
Now select your older load collector with the LOAD card image and the load collector with the grav card image as L1(1) and L1(2).

 

When applying forces to multiple nodes, this force is applied individually to a node, it is not spread out. 

 

Please also refer to other queries in the forum and the Optistruct help documentation,