being curious of how to determine what boundary will be fixed as a constraint

[S3067834]

As I attached pictures that I have drawn myself, I want to understand a principle of how to determine what boundary will be fixed at each
structure. As shown in picture 1, there is a simple wing structure comprised of 4 ribs, 3 spars and 2 skins. And a load is applied at wingtip.
And a wing root are all fixed in translation and rotation directions. After its being statically analyzed by Nastran and extracted internal loads at each component. Here I want to use the internal load at each component to get optimized structure by sol 200 later on.
In picture 2, I import one of the spars (spar 2) and also import the relevant internal load into this spar 2.

But I am so confused of how to set the boundary condition to separated components because this is a structure jointed structurally with ribs and skins itself. So, anyone can help me understand this in order to determine correct boundary condition on each component and is there any source like books, examples or tutorials covering this????

 

[rb1957]

if you're trying to look at the spar in isolation, you need to remember that the spar is supported by the skins and ribs. i think you need to apply the displacements from the full model (this Might be the same as applying the interface loads) and constrain at the root (fully fixed).

mind you, you can't optimise the spar in isolation (changing the stiffness of the spar will change the internal loadpaths), so i'm not really sure why you'd do this ...

Quando Omni Flunkus Moritati

 

[S3067834]

So, I wonder that how to optimize the spar 2 in isolation. but here setting constraint is a problem. The optimization can mean thickness changes and shape changes and topology etc. what I understood, we basically analyze a full assembled model first and get the internal loads at each component after the static analysis. By using this load, I believe it conducts an optimization process for each component.

There is an example done by Radioss and Hyperworks (but I am still mixed up of setting constrains into a part in isolation)