PROGRAM 3DFEEM - A MULTIDIMENSIONAL ELECTROMAGNETIC FINITE-ELEMENT MODEL

A suite of programs collectively referred to as 3Dfeem (3-D finite ele ment electromagnetic model) has been developed to simulate the respons e of a given assemblage of conductors to a plane-wave or electric-dipo le source. This application of the finite element method is based on t he principle of minimization of energy; solution electric or magnetic vector fields are sought that minimize an expression giving the energy in the field and their sources at discrete points within the modelled volume. Solution fields are considered to be a superposition of 'prim ary' fields, the response of a 1-D earth in the presence of specified source(s), and 'anomalous' fields resulting from heterogeneities withi n the 1-D model. Results from 2- and 3-D conductivity configurations a re seen to be in favourable agreement with those from other computer s imulators. Additionally, a comparison of solution fields from 3Dfeem a nd a 2-D analytic solution indicates that, with appropriate mesh spaci ng, 3Dfeem gives field estimates that are accurate to within about 8 p er cent. An automesher program ensures that the error criteria are met . The method chosen to solve the set of finite element equations allow s rapid estimation of the responses for perturbations in the conductiv ity structure of the starting model. The theory with which to allow di scontinuous behaviour of the electric fields and the curls of the magn etic fields is discussed.