ANSYS workbench OpenACC (open accelerators) Technology: general issues analytical formula artificial thunderstorm cell corona corona discharge distribution lines electromagnetic field electromagnetic pulse electromagnetic radiation spectrum finite difference time domain (FDTD) graphics processing unit (GPU) grounding modeling lightning lightning magnetic fields lightning protection lightning protection system lightning surge lightning-induced overvoltages lightning-induced voltages model element numerical codes overhead line simulation soil resistivity transient calculation transmission line monitoring system upward streamer discharges wavelet