Transversely finite sound beams traveling in fluid media with negligible viscous damping and scattering have seven quantities constant along the length of the beam. The simplest of these is the cycle-averaged momentum per unit length of the beam. The seven constant quantities are proved to be invariants from conservation laws. An angular momentum flux density tensor is introduced, in the formul...

It has been observed in laboratory experiments that when nonlinear dispersive waves are forced periodically from one end of undisturbed stretch of the medium of propagation, the signal eventually becomes temporally periodic at each spatial point. The observation has been confirmed mathematically in the context of the damped Korteweg-de Vries (KdV) equation and the damped Benjamin-Bona-Mahony (B...