# What is a lifting function ?

1. Jul 9, 2009

### Hoplite

What is a "lifting function"?

Hi,

I was reading a journal article and they mentioned something called a "lifting function". It was apparently used with the Navier-Stokes equation to translate the boundary conditions (which were complicated, and NOT non-slip), into a body force.

It looks like think technique could be useful, so I wanted to find out what it was. The problem is that they reference given in the article was some lecture series from the 1950s, which I can't get a hold of.

So, could anyone here explain what a lifting function is, or hopefully point me to a good explanation?

(I notice that there is something called a lifting function used in topology, but I assume it's unrelated.)

2. Jul 9, 2009

### HallsofIvy

Staff Emeritus
Re: What is a "lifting function"?

I don't recognize the term "lifting function" itself but such things as "Stoke's theorem":
$$\int_C \vec{f}\cdot \vec{ds}= \int\int_S \nabla\times\vec{f}\cdot\vec{dS}$$
Where C is the one-dimensional boundary of the two-dimensional surface S
and the "divergence theorem"
[tex]\int\int_S \vec{F}\cdot\vec{dS}= \int\int\int_V \nabla\cdot\vec{F} dV[/itex]
Where S is the two-dimensional surface of the three-dimensional region V seem to be what you are talking about.

3. Jul 10, 2009

### Hoplite

Re: What is a "lifting function"?

Thanks, HoI. The divergence theorem could well be what they meant.