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In this work, the authors utilize a lattice-Boltzmann lattice-spring method to simulate the deformation of blockages and fluid properties in an elastic blood vessel for the first time. Precisely, in this method, the lattice Boltzmann method is used to capture fluid behavior, and the lattice spring model is employed to mimic the deformation of the blood vessel and blockages while the immersed boundary method is applied to deal with the fluid-solid interaction. A validation of the present method is carried out by comparing the simulation results with a theoretical prediction of deformation of a pulmonary blood vessel in a steady flow. Subsequently, the method is applied to study the relationship between the fluid properties and the deformation of blockages. It is found that the blockages are rotated and expanded to the vessel central area so that a narrow gap or opening is formed in the blood vessel. The opening and flow rates decrease and the pressure drop increases as the thickness and deformation of the blockages increase. [ABSTRACT FROM AUTHOR]

A lattice-Boltzmann lattice-spring method is employed to simulate cruise dynamic behaviors of self-propelled flexible swimming bodies at finite Reynolds numbers in a three-dimensional space. In simulations, the leading edge of the swimmer plunges in the vertical direction and generates a thrust force, which drives the swimmer to move in the horizontal direction freely. To investigate the effect of rigidity and inertia on cruising speed, power coefficient, propulsive efficiency, and deformation are computed while the rigid and inertia are varied at different levels. It is demonstrated that at a given Reynolds number, the cruising forward speed increases as the rigidity decreases from a high level. The forward speed increases continuously and arrives at a maximum as the rigidity reduces to an intermediate level. However, the forward cruise speed decreases when the rigidity continuously decreases. When the rigidity further reduces to a level lower than a critical value, the cruise reverses its direction and the swimmer moves backward. In this study, it is revealed that a snake-shaped two-curved swimming body due to large deformation induces two vortices and their “sucking” effect is responsible for the backward cruise while the reaction force of sweeping motion of one-curved swimming body causes the forward cruise. It is also found that the forward cruise may become backward as the inertia exceeds a critical level, suggesting that the inertia has a significant impact on the cruising direction reversal. It is revealed that two swimmers in a tandem configuration have one equilibrium separating distance, associated with the reverse Karman vortex street, which is independent of initial distances. [ABSTRACT FROM AUTHOR]

Dynamic motion of two flexible fibers settling in an infinitely long fluid column at moderate Reynolds numbers is numerically simulated in a three-dimensional space by using a lattice-Boltzmann lattice-spring method. In the simulations, rectangular and cylindrical flexible fibers are used. The fiber rigidity, density, shape, initial distance, and aspect ratio are varied at different levels and their effects on drafting, kissing, and tumbling (DKT) behavior are studied. It is demonstrated that the fiber rigidity has a profound impact on settling velocity, fluid structures, and DKT phenomenon. [ABSTRACT FROM AUTHOR]