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# (Simplified) Sail physics

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Hi, i am trying to model the physical behaviour of a (windsurf) sail (just the sail, not buoyancy of board and other "water-related" stuff). Up to now i just incorporated lift force and aerodynamic drag and the sail is attached to a fixed up-axis (just left/right rotation is possible). Are there any approx. for finding the center of pressure on sail (assuming a simple triangular shape), it doesn''t have to be accurate i just need a point to apply the lift force to the sail and not to the board where it is attached to (thats what i''ve done up to now). Thank you very much in advance. regards, Stephan
eisscholle.de

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quote:
Original post by stephanh
Are there any approx. for finding the center of pressure on sail (assuming a simple triangular shape)

Pressure of what?
If it is wind,You can take the center of mass of triangle as its center.

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quote:
Original post by XELON
quote:
Original post by stephanh
Are there any approx. for finding the center of pressure on sail (assuming a simple triangular shape)

Pressure of what?
If it is wind,You can take the center of mass of triangle as its center.

Sorry, yes, i ment wind.
I`ll try it with the center of mass then, thank you very much.
I also thought about some displacementfactor to give the shape some influence.

regards,
Stephan

eisscholle.de

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The triangle center might work as an approximation, but it depends on how accurate you want to be. Should your sail be able to deform in the wind (ie. bulge out), or is it a mostly fixed planar construction (ie. more like a wing) ?

I developed a wind pressure simulator for realworld sail construction some time ago. I also tried various kinds of approximations, but got stuck due to lack of accuracy. I ended up using particle flow dynamics for the wind, and a spring-mass model for the sail. The individual force components, drag, friction, turbulences, etc, were computed on per-particle base, using micro-collisions on the sail surface. The model turned out to be pretty realistic, but also pretty slow (not realtime).

Depends on how accurate you want it to be. Using a too approximative model might get you into trouble later on (ie. mathematical instabilities -> simulation blows up).

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quote:
Original post by Yann L
The triangle center might work as an approximation, but it depends on how accurate you want to be. Should your sail be able to deform in the wind (ie. bulge out), or is it a mostly fixed planar construction (ie. more like a wing) ?

Yes, my plan was to treat it as a fixed planar triangle. Accuracy isn''t that important here i am just trying to mimic the behaviour of a skateboard-longboard mounted windsurf sail.

quote:

I developed a wind pressure simulator for realworld sail construction some time ago. I also tried various kinds of approximations, but got stuck due to lack of accuracy. I ended up using particle flow dynamics for the wind, and a spring-mass model for the sail. The individual force components, drag, friction, turbulences, etc, were computed on per-particle base, using micro-collisions on the sail surface. The model turned out to be pretty realistic, but also pretty slow (not realtime).

Sounds pretty interesting but is way over my head.

Thank you very much.

regards,
Stephan

eisscholle.de

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