Abstract:  Shock and ultrasonic waves in water often induce the growth and collapse of cavitation bubbles, or clusters of bubbles, which, in turn, can lead to erosion and other types of damage to nearby materials and structures. In traditional applications like marine propellors, cavitation erosion is unambiguously undesirable, but in medical procedures such as lithotripsy and histotripsy, cavitation can amplify shock energy and thereby mediate stone erosion and tissue ablation, respectively, but it can also lead to collateral damage and other bioeffects. We pose a series of model problems aimed at understanding the mechanisms at play during shock-induced collapse of cavitation bubbles near surfaces. Numerical simulations of one or a few bubbles allow us to quantify the stresses induced in nearby surfaces and understand the role played by secondary shocks emitted during bubble collapse. Under repeated shocks or continuous irradiation, clusters or clouds containing many bubbles are formed, and the complex, collective behavior of the cloud can lead to even greater focussing of energy or, at sufficiently high void fractions, to undesirable scattering and dispersion of energy. Continuum bubbly flow models have been employed to qualitatively describe these effects, but quantitative predictions, especially at relatively high void fractions, require both better models and less computationally intensive ways to represent a poly-disperse cloud of bubbles. We close by describing recent a recent effort aimed at achieving these goals.  For more information on Dr. Colonius & his work please visit his website at http://colonius.caltech.edu/ Host:  Eckart Meiburg