# Mass calculus

1. May 22, 2006

### Miro

Hi everybody,
didn't really know where to put this thread since it's physics using math, so I'm sorry if it's not in its appropriate place.

My problem is:
I need to compute the mass of oil in a cylindrical core put into a core holder.it's partially filled of oil. I didn't know how to numerically calculate it knowing that the porosity of the core is different of the outside annular's one.

I'd be so thankful if u could help.

PS: it's none of HW, but I need it in a project I'm working on.

2. May 22, 2006

### dav2008

Well if you know the density of oil (mass per volume) you can just multiply the density by the volume that you need to fill to find the mass needed.

3. May 22, 2006

### Miro

It wasn't really my question,

it's some kind of discreet summation over the volume which contains two different media (porous medium & fracture: 2 different porosities).

hope it's clear..

4. May 23, 2006

### benorin

You want to find the center of mass of the system then? If so, just compute the center of mass of each component and compute the weighted average of them as though they were point-masses.

5. May 27, 2006

### Miro

Not really, thx anyway, I found out how to do it:
sum(2*3.14*porosity(i,j,k)*r(i)*dr(i)*dz(k)*density)

where (i,j,k) are the coordinates of a point,