Mass Moment of Inertia
Mass Moment of Inertia
(OP)
Dear friends
I am trying to find a mass moment of inertia of an wind turbine on its rotor.
No of blades = 3
Weight of blade = 11.5T
COG = 15m
If i use mass x radius 2
i get 2587.5 x 3 = 7762.5 Tm2
i want to find an equivalent box section with provides me same mass moment of inertia in the same vertical axis.
for a box section = (M/12) x (b2 + h2)
If i keep the mass constant 11.5*3= 34.5 T
b=51m and h=14.5m
can anyone advice me how to best represent a 3 blade rotor to a rectangular box.
Thanks in advance.
Regards
I am trying to find a mass moment of inertia of an wind turbine on its rotor.
No of blades = 3
Weight of blade = 11.5T
COG = 15m
If i use mass x radius 2
i get 2587.5 x 3 = 7762.5 Tm2
i want to find an equivalent box section with provides me same mass moment of inertia in the same vertical axis.
for a box section = (M/12) x (b2 + h2)
If i keep the mass constant 11.5*3= 34.5 T
b=51m and h=14.5m
can anyone advice me how to best represent a 3 blade rotor to a rectangular box.
Thanks in advance.
Regards






RE: Mass Moment of Inertia
m*r^2 is the inertia of a point mass at a distance r, but you have a rotating blade. to use an analogy, when calculating the moment of inertia of a section you have Ax^2+Io, the 2nd term being the self moment of inertia of the area.
i think you need to divide the blade up into a bunch of small segments so that the self moment term is small enough to be negligible.
RE: Mass Moment of Inertia
Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis
http://www.engissol.com/cross-section-analysis-des...
RE: Mass Moment of Inertia
For rotors, Ip = M(15)2 = 225M
For box section, Ip = M(b2 +h2)/12
So (b2 + h2) = 12*225 = 2700
For a square, b = h = 36.7m
For a rectangle with b = 51m, h = 9.95m (say 10m)
BA
RE: Mass Moment of Inertia
In any case, you need to perform the integral from 0 to R of mass(r)*r^2 to get the moment of inertia.
TTFN
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RE: Mass Moment of Inertia
BA
RE: Mass Moment of Inertia
TTFN
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RE: Mass Moment of Inertia
are you guys sure it's imply m*cg^2 ? particularly with the rectangle solution. i mean the cg^2 for a rectangle will be (b^2+h^2)/4 ... no?
RE: Mass Moment of Inertia
For a rectangle, Ip = Ix + Iy = bh3/12 +hb3/12 = bh(b2 + h2)/12
Polar Mass Moment of Inertia is Ip*ρ = M(b2 + h2)/12 where ρ is density per unit area.
BA
RE: Mass Moment of Inertia
it seems to me that we're talking about a blade (maybe it can be simplified to a rectangle) rotating about it's base. so that'd change "/12" to /3 ... ?
RE: Mass Moment of Inertia
TTFN
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RE: Mass Moment of Inertia
I have no idea why he wants to find this, but that is my understanding of the problem. If that is not what the OP is asking, perhaps he could clarify.
BA
RE: Mass Moment of Inertia
TTFN
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RE: Mass Moment of Inertia
though a round plate, or better yet three concentrated weights, would be "better".
RE: Mass Moment of Inertia
RE: Mass Moment of Inertia
BA