inline double get_sim_time_sec () const { return sim_time_sec; }
inline void inc_sim_time_sec (double dt) { sim_time_sec += dt; }
inline void set_sim_time_sec (double t) { sim_time_sec = t; }
inline double get_sim_time_sec () const { return sim_time_sec; }
inline void inc_sim_time_sec (double dt) { sim_time_sec += dt; }
inline void set_sim_time_sec (double t) { sim_time_sec = t; }