Publications Details
Projectile transverse motion and stability in electromagnetic induction launchers
The transverse motion of a projectile in an electromagnetic induction launcher is considered. The equations of motion for translation and rotation are derived assuming a rigid projectile and a flyway restoring force per unit length that is proportional to the local displacement. Transverse forces and torques due to energized coils are derived for displaced or tilted projectile elements based on a first order perturbation method. The resulting equations of motion for a rigid projectile composed of multiple elements in a multi-coil launcher are analyzed as a coupled oscillator system of equations and a simple stability condition is derived. The equations of motion are incorporated into the 2-D Slingshot code and numerical solutions for the transverse motion are obtained. For the 20 meter navy launcher parameters we find that stability is achieved with a flyway spring constant of k {approx} 1{times} 10{sup 8} N/m{sup 2}. For k {approx} 1.5 {times} 10{sup 8} N/m{sup 2} and sample coil misalignment modeled as a sine wave of I mm amplitude at wavelengths of one or two meters, the projectile displacement grows to a maximum of 4 mm. This growth is due to resonance between the natural frequency of the Projectile transverse motion and the coil displacement wavelength. This resonance does not persist because of the changing axial velocity. Random coil displacement is also found to cause roughly the same projectile displacement. For the maximum displacement a rough estimate of the transverse pressure is 50 bars.