(2023-08-15) Simon, Blake Elliott; Hamilton, Mark F.; Haberman, Michael R; Wilson, Preston S; Ling, Hao; Gunderson, Aaron M

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This dissertation is a study of the acoustic radiation force and torque on a sphere or spheroid in an inviscid fluid near a planar boundary. First, a linear analytical solution for the acoustic scattering by the object and boundary is derived. The solution is based on expansion of the pressure field in spherical or spheroidal wave functions. The condition at the boundary is satisfied using the method of images, which is exact for rigid and pressure release boundaries. The analytical solution imposes no restriction on the structure of the incident field or size of the object. An approximation is introduced that extends the analytical solution to other types of boundaries, including a fluid-fluid interface. Next, the expansion coefficients in the linear solution are substituted into a known analytical expression for the acoustic radiation force and torque on the sphere or spheroid that follows from integration of the radiation stress tensor. The radiation force and torque are also modeled numerically using the finite element method, which is used to validate results from the analytical model. The finite element model is less computationally efficient than the analytical model, but it can be used for objects of any shape. Calculations based on both models illustrate the influence of multiple scattering effects between the object and the boundary on the radiation force and torque acting on the object. Radiation force on a polypropylene sphere in water was measured as a function of distance from a reflecting surface in the presence of an incident sound beam. The force was measured by forming a pendulum with the sphere and tracking its displacement. Measurements of the radiation force on the sphere are compared with the analytical model.