Volume of a Box = LWH

[UGDAVE]

I know this is simple, but I have been in Shanghai for two weeks and I am burnt out.

If it is given that a box size is 25 liters and I need to control the L,W, & H what is the best way to set up the expresions.

I want to be able to change any one of the 3 and the other two would update.

Sorry for the simple question.

 

[JohnRBaker]

I'm not sure that you could create 3 independent expressions in such as a way that changing ANY one of them would cause the others to update. The NX expression system solves the equations simultaneously and thus there is no way to do what you described above, at least not without some 'outside' help. Now it could be done using an optimization routine, created as a KF routine. Another approach would be to just write a progrsm, in GRIP or UFUNC. Of course, part of the problem is when you change one value, BOTH of the others could change and therefore, what rules do you wish to apply as to how to 'distribute' the change in values between the other two values?

For example, if you start out with all sides being equal, a 25 liter 'block' would have each side equal to 29.24 mm. Now if I change the size of one side, which one of the others sides do I change? Or do I change them both?

So you see, it've not a trivial, nor even a straightforward problem to solve.


John R. Baker, P.E.
Product 'Evangelist'
UGS NX Product Line
SIEMENS
UGS PLM Software
Cypress, CA

http://www.siemens.com/ugs

http://www.plmworld.org/museum/

 

[mjcole]

You can use Excel to do a goal seek by telling it what you want the volume to be and giving it the parameters you want it to change and ranges for each of them to bound your solution. But it seems like simple arithmatic would be more worth your while.

Once before I had to base the weight of a block used in a toque gage based on a supplied value so a wrote a relation for the Xsec Area and used that to drive the block thickness base on the supplied Parameter for it's weight.

Michael

 

[cbrn]

Hi,
using the Expression system of NX, couldn't you subordinate the update to a "switch" which indicates which dimension has to drive the others?
Example:
switch=1 (1 = length and width are independent; 2 = width and height are independent; 3 = height and width are independent)
IF switch =1 then ...
IF switch = 2 then...
IF switch =3 then...

Regards