APPENDIX G – Pumps and Turbines
Surge Analysis and the Wave Plan Method
Supplementary Material: Example Problems and Solutions
Appendix G – Problem 13
G.13 Compute weight moment of inertia (WR2) of an irregular shaped object (with respect to certain axis s) with a total mass of 2109.248 N and a radius of gyration of 0.375m about the same s-axis. Convert the computed weight moment of inertia (in the form of WR2) into GD2 format commonly expressed by many European hydro-machinery manufacturers.
Solution:
Weight moment of inertia Isw = W Rs2, where W is weight of the object in N and Rsw is its radius of gyration about s-axis.
Isw =2109.248 * 0.3752 = 296.6 N-m2
While the R in WR2 represents the radius of gyration, the D in GD2 represents the diameter of gyration. Also, while WR2 is expressed in N-m2, GD2 is expressed in kgf-m2. As one kgf is 9.81N, the value in WR2 should be first divided by 9.81 (or the appropriate gravitational acceleration value in m/s2) to convert kgf into N and the resulting value should be multiplied by 4 to convert R2 into D2. That is, GD2 = (WR2) * (4 / 9.81)
Isw expressed in GD2=2109.248 * (4/9.81) = 860.04 kgf-m2
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