Computation of electromagnetic modes at low frequencies
Résumé
The study of electromagnetic (EM) wave propagation is essential for investigating the impact of electromagnetic activities on the environment. Oshore wind power, for example, is transported by dynamic twisted cables, whose armouring prevents the propagation of a signicant proportion of the waves. Nevertheless, what remains eventually escape from the cable, and we aim to study how EM elds diuse in the vast expanse of seawater in which the cable is immersed. We focus on the computation of EM modes in a three-dimensional cable, at low or very low frequencies. Due to the large kernel of the operator curl curl in the Maxwell equations, the linear modal problem with transverse elds happens to give inaccurate results when the frequency is small. We then propose another modal problem which considers only the longitudinal elds Ez and Hz as unknowns. First, we present the model and show how it can be validated using the example of coaxial cables. We then move on to more general cases of tri-conductor cables, considering modes obtained by numerical simulation. Finally, to consider more realistic helicoïdal cables, we discuss wave behavior when conductors are twisted inside the cable and present numerical results, calculated with MONTJOIE
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