Effect of shape factor, operating stresses, and electrical conductors on the energy density of rotating machines

The ability to store as much energy as possible for the least weight, defined by the rotor´s energy density (U/m~J/g), is of paramount importance to the pulsed power supply of electromagnetic guns. This paper extends the work presented in a complementary paper in which the shape factors, F_s, for a representative number of rotating machines were derived and compared. The effects of shape factor, maximum allowable operational stress σ_θmax, and effective rotor density ρ_eff (determined by the addition of electrical conductors to the rotor for power extraction) on rotor energy density and tip speed are presented in this paper. A comparison between two candidate composite designs for electromagnetic pulsed power generation-a laminated disk (LD) and a rim rotor (RR)-is performed. Our analyses have determined that the true discriminator between the LD and the RR designs is the allowable stress each can operate at since they both have the same shape factor and about the same composite density. The LD design is limited by the interlaminar shear strength of the epoxy bond to hoop stresses in the range of 150 ksi(1.0·10⁹ N/m²), while the RR design is able to take full advantage of the strength limit of the composite fiber and operate at hoop stresses as high as 350 ksi (3.1·10⁹ N/m²)