The effects of chordwise deformation and the half-amplitude asymmetry on the hydrodynamic performance and vortex dynamics of batoid fish have been numerically investigated, in which the two parameters were represented by the wavenumber (
$W$
) and the ratio of the half-amplitude above the longitudinal axis to that below (
$HAR$
). Fin kinematics were prescribed based on biological data. Simulations were conducted using the immersed boundary method. It was found that moderate chordwise deformation enhances the thrust, saves the power and increases the efficiency. A large
$HAR$
can also increase thrust performance. By using the derivative-moment transformation theory at several subdomains to capture the local vortical structures and a force decomposition, it was shown that, at high Strouhal numbers (
$St$
), the tip vortex is the main source of thrust, whereas the leading-edge vortex (LEV) and trailing-edge vortex weaken the thrust generation. However, at lower
$St$
, the LEV would enhance the thrust. The least deformation (
$W=0$
) leads to the largest effective angle of attack, and thus the strongest vortices. However, moderate deformation (
$W=0.4$
) has an optimal balance between the performance enhancement and the opposite effect of different local structures. The performance enhancement of
$HAR$
was also due to the increase of the vortical contributions. This work provides a new insight into the role of vortices and the force enhancement mechanism in aquatic swimming.
In this study, numerical simulations are employed to investigate the hydrodynamic performance and wake topology of a swimming Rhinoptera javanica. The study is motivated by the quest to understand the hydrodynamics of median and paired fin(MPF) mode with both spanwise and chordwise flexibility. The simulations employ an immersed boundary(IB)-simplified sphere function-based gas kinetic scheme(SGKS) method that allows us to simulate flows with complex moving boundaries on fixed Cartesian grids. A computational model is constructed based on biological data. The evolution of the hydrodynamic force and 3D vortex structures are presented. Besides, the effect of frequency and amplitude are also discussed to explain some behaviors of the actual Rhinoptera javanica. This work can provide a baseline for the design of a bio-inspired underwater vehicle. INDEX TERMS MPF, flexibility, swimming/flying, bio-inspired, biological fluid dynamics.
Compared with conventional well, herringbone-like laterals wells can increase the area of oil release, and can reduce the number of wellhead slots of platforms, and also can greatly improve the development efficiency. Based on threshold pressure gradient in heavy oil reservoir, and the applied principle of mirror reflection and superposition, the pressure distribution equation of herringbone-like laterals wells is obtained in heavy oil reservoir. Productivity model of herringbone-like laterals wells is proposed by reservoir-wellbore steady seepage. The example shows that the productivity model is great accuracy to predict the productivity of herringbone-like laterals wells. The model is used to analyze the branching length, branching angle, branching symmetry, branching position and spacing and their effects on productivity of herringbone-like laterals wells. The principle of optimizing the well shape of herringbone-like laterals wells is proposed.
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