search

weymouth / lily-pad

Real-time two-dimensional fluid dynamics simulations in Processing. Initiated by Dr G D Weymouth:
https://github.com/weymouth/
MIT License
161 stars 78 forks source link

Meaning of NACA Variable "ma" #20

Closed jwethan closed 1 year ago

jwethan commented 1 year ago

I'm working on a new adaptation of the code to simulate heaving and passive pitching foils. I'm trying to implement code to treat the pitching about the leading edge as a torsional spring in response to the moment imposed by the fluid. I am using the NACA geometry as the body and I was wondering what the variable "ma" is holding in the NACA file. It's used in the Body "react" function in computing the dynamics, what does it represent? Seems like it has something to due with the shape inertias but I'm not sure.

All help is appreciated, thanks.

weymouth commented 1 year ago

It is the body's added mass.

jwethan commented 1 year ago

I may be confused, but why does it have 3 different components? The z-component of the PVector is used to calculate the new ddotphi in the rotational dynamics, what is that accounting for?

ddotphi = M + ma.z*ddotphi/(I0 + ma.z);

I don't see the need for it in my equations, so I'm wondering if I am missing something.

Why are both the moment of inertia calculated from Body getArea() and ma.z needed?

Thanks for the help.

weymouth commented 1 year ago

Apologies. It is the added mass. The linear inertia due to accelerating the surrounding water from translation in x or y or rotation around z.