Originally Posted By: CraigB
Oh, come on Boise Nick. Think.

All forces and moments acting on any point in the univers can be translated to forces and moments acting on any other point in the universe, using relatively simple algebra. And if a set of forces and moments act at the resolution point, then they are simply summed "as is." There is no requirement in NEMA SM-23 to create nonexistent moments from forces acting on a line passing through the resolution point.

I agree with Dave Diehl - if the centerline of the exhaust and the turbine rotor intersect, use that point.

If they do not intersect, I have always simply resolved the forces and moments to the point on the centerline of the exhaust nozzle nearest the turbine rotor centerline.


Sigh...I believe CraigB is missing the point. Yes I know all about the parallel axis therom and summation of components. I will try to make this simple by using an example: Pick 3 points in 3D space, A,B,and C. All points have x,y,z forces and mx,my,mz moments. So we have a total of...

Point A-> Fxa,Fya,Fza & Mxa,Mya,Mza.
Point B-> Fxb,Fyb,Fzb & Mxb,Myb,Mzb.
Point C-> Fxc,Fyc,Fzc & Mxc,Myc,Mzc.

So the following are true...

Total forces
X->Fxa+Fxb+Fxc
Y->Fya+Fyb+Fyc
Z->Fza+Fzb+Fzc

Total moments
MX->Mxa+Mxb+Mxc
MY->Mya+Myb+Myc
MZ->Mza+Mzb+Mzc

This is what the example says to do and what some of you would agree with. NOW, this is where I see a difference if you are going to resolve them around a point, I think it should be this...

Total forces
X->Fxa+Fxb+Fxc
Y->Fya+Fyb+Fyc
Z->Fza+Fzb+Fzc

Total moments
MX->Mxa+Mxb+Mxc+Fya(L)+Fyb(L)+Fyc(L)+Fza(L)+Fzb(L)+Fzc(L)
MY->Mya+Myb+Myc+Fxa(L)+Fxb(L)+Fxc(L)+Fza(L)+Fzb(L)+Fzc(L)
MZ->Mza+Mzb+Mzc+Fxa(L)+Fxb(L)+Fxc(L)+Fya(L)+Fyb(L)+Fyc(L)

Where 'L' is the distance to whatever axis the force is perp. to.
^This should be the correct way and is how every freebody diagram is set up.

I am arguing that the code implies an incorrect way of doing this.

Also, I called NEMA and was told that NEMA SM-23 is getting dropped because there is no product group to support it anymore. The person who took my call mentioned there were others with the same inqury.