Dynamics of Bluff Bodies with Internal Nonlinear Oscillators: Vortex-Induced Vibration Suppression, Partial Wake Stabilization, and Drag Reduction

流固耦合在一系列工程应用中无处不在，从空气动力学中的颤振和散度，到核动力反应堆中燃料棒的振动，海上平台的张力腿，风力涡轮机塔和水动力能量收集。这项工作的一个主要目的是证明，在钝体内部故意设计非线性振荡器，可以被动抑制涡激振动-涡激振动，部分稳定经过体的尾迹，并减少周围流体施加的阻力，而无需任何外部修改。这项研究可以在不同的领域产生广泛而重大的影响。例如，通过内部非线性振荡器的作用来减小钝体上的阻力，可能会对未来的飞行器和船只的设计产生重大影响，从而提高它们的性能，扩大它们的运行范围和降低燃料消耗。此外，通过对振动体内部非线性振子的合理设计和优化，可以实现高效、经济的水动力振动能量收集。在本研究中，将研究强非线性有限维振荡器与无限维流体流动的动力学相互作用。这不仅对理解流固相互作用在各种情况下的重要性，而且在更广泛的意义上，因为它可以作为理解涉及耦合有限维和无限维部件的非线性相互作用的各种其他机械（和非机械）系统的非线性动力学行为的试验台。处理中高雷诺数范围Re的根本重要性在于，我们的初步结果表明，二维层流情况下吸引子的维数小于4，而在湍流情况下，吸引子的维数预计会随着Re的9/4次方而增长。因此，该系统为理解流固相互作用的动力学提供了一个独特的机会，其中吸引子的维度从1（周期响应）变化到更大的值。我们还将研究迄今为止尚未探索的角动量在涡激振动中的作用。最后，将探讨强非线性内振荡元件在中高Re下大幅改变钝体尾迹并降低其阻力系数的能力。该研究将使用慢/快动态分解、不变慢流形考虑、非线性系统识别和降阶建模技术进行。高保真的流固相互作用计算将在层流、过渡和湍流状态下进行。

Fluid-structure interaction is ubiquitous across a range of engineering applications, from flutter and divergence in aerodynamics, to vibration of fuel rods in nuclear power reactors, tension legs in offshore platforms, wind turbine towers, and hydrokinetic energy harvesting. A major aim of this work is to demonstrate that using intentionally designed nonlinear oscillators inside a bluff body it is possible to passively suppress vortex induced vibrations - VIVs, partially stabilize the wake past the body, and reduce the drag force exerted by the surrounding fluid without any external modification. This research can have broad and significant impact in diverse fields. For example, the reduction of the drag forces on a bluff body through the action of internal nonlinear oscillators might significantly affect the design of future air vehicles and boats by enhancing their performance, enlarging their range of operation and decreasing fuel consumption. Also, enhanced and economical hydrodynamic vibration energy harvesting could be achieved by appropriate design and optimization of internal nonlinear oscillators inside a body undergoing VIVs.In this research, the dynamic interactions of a strongly nonlinear finite-dimensional oscillator with an infinite-dimensional fluid flow will be studied. This is important in understanding not only fluid-structure interaction in a variety of contexts, but also, in a broader sense, because it serves as a testbed for understanding the nonlinear dynamical behavior of a variety of other mechanical (and nonmechanical) systems involving nonlinear interactions of coupled finite- and infinite-dimensional parts. The fundamental importance of dealing with an intermediate-to-high range of Reynolds number -- Re -- lies in the fact that our preliminary results show that the dimension of the attractor in the two-dimensional laminar case is less than four, while in the turbulent case, it is expected to grow as Re to the 9/4 power. This system thus provides a unique opportunity to understand the dynamics of fluid-structure interaction, where the dimension of the attractor varies from one (for periodic response) to much larger values. We will also study the heretofore unexplored role of angular momentum in VIV. Finally, the capacity of strongly nonlinear internal oscillating elements to drastically modify the wake of a bluff body and reduce its drag coefficient at both intermediate and higher Re will be explored. The research will be performed using slow/fast dynamical decompositions, invariant slow manifold considerations, nonlinear system identification, and reduced-order modeling techniques. High-fidelity fluid-structure interaction computations will be performed in the laminar, transition, and turbulent regimes.