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SUMMARYA numerical method based on a hybrid meshfree-Cartesian grid is developed for solving three-dimensional fluid-solid interaction (FSI) problems involving solid bodies undergoing large motion. The body is discretized and enveloped by a cloud of meshfree nodes. The motion of the body is tracked by convecting the meshfree nodes against a background of Cartesian grid points. Spatial discretization of secondorder accuracy is accomplished by the combination of a generalized finite difference (GFD) method and conventional finite difference (FD) method, which are applied to the meshfree and Cartesian nodes, respectively. Error minimization in GFD is carried out by singular value decomposition. The discretized equations are integrated in time via a second-order fractional step projection method. A time-implicit iterative procedure is employed to compute the new/evolving position of the immersed bodies together with the dynamically coupled solution of the flow field. The present method is applied on problems of free falling spheres and tori in quiescent flow and freely rotating spheres in simple shear flow. Good agreement with published results shows the ability of the present hybrid meshfree-Cartesian grid scheme to achieve good accuracy. An application of the method to the self-induced propulsion of a deforming fish-like swimmer further demonstrates the capability and potential of the present approach for solving complex FSI problems in 3D.

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