Hose Modeling

[butelja]

Any tips on how to do the following?

Given: Hose endpoints X,Y,Z coordinates, endpoint tangent vectors, and hose length.

How to construct spline that has minimum strain energy for the constraints given above.

 

[Shadowspawn]

Sounds like a good use for 'bridge curve'... connecting two lines representing the vectors. Assumming a little bit of a straight line at each end point of the hose (and being defined by the x,y,z and vectors, you can use <insert> <curve from curve> <bridge curve> to create the missing spline for the hose. A little bit of playing with it should provide you with what you need...

Hope this helps...

Regards,
SS
CAD should pay for itself, shouldn't it?

 

[cowski]

An interesting problem, and bridge curve is a good start. The problem you will have is keeping a specified length.

If this is a common problem, you may want to look into the 'routing' application.

 

[Shadowspawn]

Cowski,
Good point! I wasn't sure what Butelja meant by 'strain energy' so I just "assummed" simplicity would be the best place to start (that, and I've no experience with the routing application, other than to know that it exists)... but ya know what that means!

Regards,
SS
CAD should pay for itself, shouldn't it?

 

[butelja]

In this particular instance, the detailed free shape needs to be accurately modeled, as there are potential interference points along the hose routing that must be avoided.

The true free shape (absent gravity and hydraulic loads) should be a path that meets the boundary conditions (position, slope, and overall length) while minimizing the strain energy (think energy stored in a spring) of the total hose assembly.

This is really as much a solid mechanics / strength question as it is a modeling question.

 

[TCMartist]

Hi butelja, Shadowspawn and Cowski,

I'm not quite sure of understanding the solid mechanics/strength issue of your problem, but from what I understood of the geometric constraints you have (both end positions of hose - G0-, both end tangancy - G1 -, and hose length), bridge curve can effectively help you. As Cowski said, the remaining problem is the length. I can't tell you anything about routing as I know as much as Shadowspawn about it, however, a spreadsheet may help you:

- make a bridge curve fulfilling the position and tangancy constraints.
- in the expressions, make the second shape control value equal to the expression of the first one (the default valueis 1) (this is a constraint you may not want though)
- name the bridge curve: Edit/properties (!! do not name the feature only, it won't work!!)
- go to Tools/Spreadsheet...
- extract expressions
- enter the ARCLEN formula in one cell (see the "MASS3D" help file of NX for how the ARCLEN works)
- then, still in excel, make a Tool/Goalseek with the length of the core of the hose as "target value" and all your geometric constraints will be satisfied.

hope that'll help
EVALCURV function in the MASS3D functions may also interest you for your strain problem.

TP

 

[TCMartist]

just forgot to specified, in the goalseek, the variable cell is the one refering to the value of the first tangency control of the bridge curve

TP

 

[Xwheelguy]

I'd recommend using an Associative Studio Spline over the Bridge Curve since you need to avoid other objects along the path of the curve.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[cowski]

I have had to route wires/hoses of a specified length through an obstacle course (aka 'assembly'). Usually what I do is make short lines for the ends and make a bridge curve between them, check to see what I interfere with, delete the bridge curve, add a line or arc as "control points" and make new bridge curves. After I get it to avoid other parts, then I tweak for length. I have never had to worry about minimizing strain energy, though. I only do it for an assembly pictoral view, as long as I don't interfere and the length is 'close' I call it good.

As a disclaimer, I also know nothing about the routing application except that it exists.