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Highlights: [•] We suggest a node refill method for application to the lattice Boltzmann model in FSI problems. [•] We apply fluid-particle and fluid–flexible plate problems with a refill scheme. [•] No loss of accuracy compared to the standard Lattice Bhatnagar–Gross–Krook (LBGK) model. [•] Our methods showed enhanced stability with unit density refill. [Copyright &y& Elsevier]

Abstract: This paper presents computational analysis of a fluid–structure interaction for a flapping flexible plate moved with propulsive velocity in quiescent fluid to investigate the effect of flexibility on propulsive velocity, which is critical for fish, birds, insects, and micro air vehicles with flapping wings. This study found that the mechanism of the flapping plate moved with propulsive velocity differs from that of the plate fixed in the propulsive direction, and the flexibility of the plate improves the propulsive velocity to create an optimal propulsion. The lattice Boltzmann method with an immersed boundary technique using a direct forcing scheme is used to simulate the fluid, while the finite element method with Euler beam elements is used to model structural deformation of the flexible plate. We developed the moving domain scheme to reversely move the domain at the velocity of the plate to simulate the moving plate. [Copyright &y& Elsevier]

Abstract: This paper presents the computational analysis of a fluid–structure interaction for a flapping flexible plate in quiescent fluid to investigate the effect of flexibility on the generation of propulsion that is critical for birds, insects, and micro-air vehicles with flapping wings. It is known that rotation of the flapping rigid plate or wing near the end of a translational stroke enhances propulsion. This study found that flexibility improves the efficiency of propulsion during the rotation process and creates an optimal point in the propulsion. The lattice Boltzmann method with an immersed boundary technique using a direct forcing scheme is used to simulate the fluid, while the finite element method with Euler beam elements is used to model structural deformation of the flexible plate. The direct forcing scheme of the lattice Boltzmann method was improved by introducing a participation ratio, which represents the ratio of fluid lattice points to effective interpolated points and modifies the force term for the zero-thickness plate. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a new boundary treatment with almost second-order accuracy that does not require neighboring lattice information. In order to achieve improved accuracy for the boundary lattices, we used adaptive relaxation times reflecting boundary length scales that were unequal to the length scale of the internal fluid region lattices. Since the boundary treatment using adaptive relaxation times at the boundaries was formulated without information about the neighboring lattices, it could be easily applied to complex geometries. Numerical results using the proposed boundary treatment showed almost second-order accuracy for two-dimensional and three-dimensional problems without using information from neighboring lattices, unlike interpolation or extrapolation methods. [Copyright &y& Elsevier]