附加质量泵吸消除阻力
Drag cancellation by added-mass pumping
摘要：
由于附加质量能量的变化，水下物体在突然变形时会受到很大的力。虽然这种现象已被研究为单一的驱动事件，应用于持续推进需要研究\textit{periodic}形状变化。我们这样做，在这项工作中，通过调查的弹簧质量振荡器淹没在静态流体受到周期性变化的体积。我们开发了一个分析模型来研究附加质量变化和粘性阻尼之间的关系，并在大Stokes数下用完全耦合的流固Navier-Stokes模拟来证明其应用范围。我们的研究结果表明，附加质量动能的恢复可以用来完全取消流体的粘性阻尼，驱动持续振荡的振幅高达四倍的平均身体半径$r_0$的发病。一个准线性关系被发现链接的终端振幅的振荡$X$，大小变化$a$的程度，与$X/a$峰值在值从4到4.75取决于形状变化运动学的细节。此外，它被发现，泵浦的频率范围内的$1-\frac{a}{2r_0}<ω^2/ω_n^2<1+\frac{a}{2r_0}$是需要持续振荡。该分析的结果揭示了形状变化机构和生物启发的水下航行器的背景下的附加质量恢复的作用。
英文摘要：
A submerged body subject to a sudden shape-change experiences large forces due to the variation of added-mass energy. While this phenomenon has been studied for single actuation events, application to sustained propulsion requires studying \textit{periodic} shape-change. We do so in this work by investigating a spring-mass oscillator submerged in quiescent fluid subject to periodic changes in its volume. We develop an analytical model to investigate the relationship between added-mass variation and viscous damping and demonstrate its range of application with fully coupled fluid-solid Navier-Stokes simulations at large Stokes number. Our results demonstrate that the recovery of added-mass kinetic energy can be used to completely cancel the viscous damping of the fluid, driving the onset of sustained oscillations with amplitudes as large as four times the average body radius $r_0$. A quasi-linear relationship is found to link the terminal amplitude of the oscillations $X$, to the extent of size change $a$, with $X/a$ peaking at values from 4 to 4.75 depending on the details of the shape-change kinematics. In addition, it is found that pumping in the frequency range of $1-\frac{a}{2r_0}<ω^2/ω_n^2<1+\frac{a}{2r_0}$ is required for sustained oscillations. The results of this analysis shed light on the role of added-mass recovery in the context of shape-changing bodies and biologically-inspired underwater vehicles.
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