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# Bending of a Tube with restaints at mid-height

Hi all,

I want to analyse the behaviour of a sailboat mast. To begin with, I designed a tube, and added 2 little surfaces on Y face to be able to add limited restraints at the base of the mast and at the shrouds/stay (for now at mid-height of the mast).

• Base is restraint in X,Y,Z.
• Mid is just restraint in X.
• Force is X on the upper face of the tube.

But bending simulation do not meet my expectations. Upper part is OK, but lower part of the tube should bend slightly in the opposite direction of the force.

Is there something wrong about my restraints ?

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### Replies to This Discussion

Some details :

William,

What is happening is the small restraint in X mid-mast also prevents bending of the mast beyond this point. This occurs because restraining this face in X also prevents its rotation (and thus bending) about the Y-axis in this neighborhood.

In the current version (1.3), you could instead apply a vector load (direction= {-1,0,0}) mid-mast where you currently restrain in X.  This will not impose any restrictions on the bending of the mast at the mid-point.  You will have to do a few back-of-the-envelope beam calculations to determine the proper load magnitude or experiment with a few different loads until the X-displacement mid-mast is zero.

Does this help?

~Michael

Thanks Michael,

I even tried to put the small restraint on the _side_ of mid-mast - as to put a possible rotation point. But effectively no success ;-)

The counter vector should be possible on simple cases of study. In the real world - and futur analysises - I'd put some "wires" (stays, shrouds) to maintain the mid-mast.

So i'am on hot coals waiting for the next version with multi-body parts interconnected or multi-materials ;-)

The best, William

Some results ...

I still have to do some improvements to "free" the base of the mast a bit (for now bottom is XYZ constraint), as for the bridge example.

Hi William

I am working on a similar problem:  a 20m prototype wing mast for a catamaran I am building.  I tilted the mast back 1.189 degrees so that a vertical line from the shroud attachment point (a single bracket on the front of the mast 17 m up) goes through the centre of the base plate.

There is a lot of huffing and puffing from my laptop, will let you know when I get a nice picture.

Michael

William,

With Version 1.4, you might try inserting a linear edge (edge of a small block unioned with the mast) mid-mast and restrain this edge in X.  The restrained edge will allow rotation about its length as you were trying to do with the small face.

~Michael