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In this paper, we describe a three-dimensional simulation of the fluid–structure interaction (FSI) of the aortic valve using a direct-forcing immersed-boundary method. The geometry of the valve is taken from a bioprosthetic valve, and the computational framework is based on a previous partitioned approach that is versatile for handling a range of biological FSI problems involving large deformations. When applying the approach in the heart valve simulation, we implemented an efficient parallel algorithm based on domain decomposition to handle the costly flow simulation. As compared with previous simulations of the aortic valve, our simulation was able to capture both realistic deformation of the leaflets and vortex structures in the flow, thus providing a balanced modeling approach for the flow and the valve. The results show that the pressure distribution on the leaflet surface is highly nonuniform and the jet flow contains a sequence of vortices during the opening process. After the valve is fully opened, both the three leaflets and the jet still experience significant oscillations. The drag resistance of the valve is also characterized, and it is found that the resistance is approximately equivalent to the inertial force of accelerating the fluid column of three diameter length. These details could be potentially used to characterize FSI of the aortic valve. [ABSTRACT FROM AUTHOR]

Abstract: Small elements of circular, square, triangular and thin-strip cross-sections are used to suppress vortex shedding from a rectangular cylinder of stream-wise to transverse scale ratio L/B=3.0 at Reynolds numbers in the range of Re=V ∞ B/ν=75–130, where V ∞ is the on-coming velocity of the stream, and ν is the kinematic viscosity. The relative transverse dimension of the small element b/B is fixed at 0.2. The results of numerical simulation and visualization experiment show that, vortex shedding from both sides of the cylinder can be suppressed and the fluctuating drag and lift of the cylinder can be greatly reduced, if the element is placed in a certain region referred to as the effective zone. Comparisons at a specific Reynolds number indicate that the square element produces the largest size of the effective zone, whereas the triangular element yields the smallest. Results also show that the effective zone for the square element shrinks with increasing Re and disappears at Re>130. Independent of element cross-section shape and Reynolds number, the center of the effective zone is always at X/B=2.5–3.0 and Y/B≈1.0. The mechanism of the suppression is discussed from the view points of velocity profile stability and stress distribution. [Copyright &y& Elsevier]

We present a reduced-order model for fluid–structure interaction (FSI) simulation of vocal fold vibration during phonation. This model couples the three-dimensional (3D) tissue mechanics and a one-dimensional (1D) flow model that is derived from the momentum and mass conservation equations for the glottal airflow. The effects of glottal entrance and pressure loss in the glottis are incorporated in the flow model. We consider both idealized vocal fold geometries and subject-specific anatomical geometries segmented from the MRI images of rabbits. For the idealized vocal fold geometries, we compare the simulation results from the 1D/3D hybrid FSI model with those from the full 3D FSI simulation based on an immersed-boundary method. For the subject-specific geometries, we incorporate previously estimated tissue properties for individual samples and compare the results with those from the high-speed imaging experiment of in vivo phonation. In both setups, the comparison shows good agreement in the vibration frequency, amplitude, phase delay, and deformation pattern of the vocal fold, which suggests potential application of the present approach for future patient-specific modeling. • A novel 1D flow model was used to simulate the pulsatile glottal airflow. • The 1D flow model was used in FSI of vocal fold vibration. • Both idealized 3D vocal fold and anatomical geometries are considered. • The new model is validated against the full 3D FSI model or in vivo experiment. [ABSTRACT FROM AUTHOR]