  We propose a self-adaptive absorbing technique for quasilinear ultrasound
waves in two- and three-dimensional computational domains. As a model for the
nonlinear ultrasound propagation in thermoviscous fluids, we employ
Westervelt's wave equation solved for the acoustic velocity potential. The
angle of incidence of the wave is computed based on the information provided by
the wave-field gradient which is readily available in the finite element
framework. The absorbing boundary conditions are then updated with the angle
values in real time. Numerical experiments illustrate the accuracy and
efficiency of the proposed method.
