CCDC AC, WSEC, FCDD-ACM-FI Picatinny Arsenal United States
A projectile body is modeled as a hollow thick shell infinite cylinder subject to a rotating transverse B-field, in order to study the effects of soft-iron and eddy-current distortion on the geomagnetic field as the projectile spins during flight to predict magnetometer reading error. An analytical two-dimensional 2D model is derived using modified Bessel functions, which capture the effects of material permeability and conductivity on the field distortion. Two example cylinders are studied aluminum and steel, each 155 mm in diameter. The derivation results show that induced magnetic dipole moments are formed on the exterior of the cylinders, while an attenuated and rotated uniform field is formed on the interior of the cylinders. The complex moments, attenuation factors, and rotation angles are plotted against spin rate. Variation with material temperature is explored. The results are compared against 2D finite element analysis simulations using ANSYS Electronics Desktop. A three-dimensional finite cylinder is also modeled to explore the effects of length against the validity of the 2D thick shell model. Methods of distortion correction are discussed, along with optimum placement of magnetometers.