Numerical study on hydrodynamic effect of flexibility in a self-propelled plunging foil

Zhu, Xiaojue; He, Guowei; Zhang, Xing

doi:10.1016/j.compfluid.2014.03.031

Cited by 87 publications

(50 citation statements)

References 54 publications

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“…We performed direct numerical simulations (DNS) using the immersed boundary method. The solver uses the discrete stream-function formulation for the incompressible Navier-Stokes equations [24] with a virtual force implementation [25], which enables us to deal with both light and heavy particles. A rectangular computational domain of the size 100D × 16D is used, with a grid width of 0.01L near the cylinder, where D is the cylinder diameter.…”

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confidence: 99%

Mass and Moment of Inertia Govern the Transition in the Dynamics and Wakes of Freely Rising and Falling Cylinders

et al. 2017

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In this Letter, we study the motion and wake-patterns of freely rising and falling cylinders in quiescent fluid. We show that the amplitude of oscillation and the overall system-dynamics are intricately linked to two parameters: the particle's mass-density relative to the fluid m * ≡ ρp/ρ f and its relative moment-of-inertia I * ≡ Ip/I f . This supersedes the current understanding that a critical mass density (m * ≈ 0.54) alone triggers the sudden onset of vigorous vibrations. Using over 144 combinations of m * and I * , we comprehensively map out the parameter space covering very heavy (m * > 10) to very buoyant (m * < 0.1) particles. The entire data collapses into two scaling regimes demarcated by a transitional Strouhal number, Stt ≈ 0.17. Stt separates a mass-dominated regime from a regime dominated by the particle's moment of inertia. A shift from one regime to the other also marks a gradual transition in the wake-shedding pattern: from the classical 2S (2-Single) vortex mode to a 2P (2-Pairs) vortex mode. Thus, auto-rotation can have a significant influence on the trajectories and wakes of freely rising isotropic bodies.Path-instabilities are a common observation in the dynamics of buoyant and heavy particles. Common examples are the fluttering of falling leaves and disks, and the cork-screw and spiral trajectories of air-bubbles rising in water [1,2,3]. The oscillatory dynamics of such particles can vary a lot depending on the particle's size, shape and its inertia, and the surrounding flow properties. This can be important in a variety of fields ranging from sediment transport and fluidization to multiphase particleand bubble-column reactors [4,5,6].Examples of organisms that exploit path-instabilities are plants and aquatic animals. These often make use of passive appendages attached to their bodies (plumed seeds, barbs, tails, and protrusions) to generate locomotion [7,8,9]. Recently, Lācis et al. [7] demonstrated that the interaction between the wake of a falling bluff body and a protrusion clamped to its rear end can generate a sidewards drift by means of a symmetry-breaking instability similar to that of an inverted pendulum. Such kinds of passive interactions are advantageous to locomotion, since no energy needs to be spent by the animal. Instead, the energy can be extracted through fluid-structure interaction.

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Mass and Moment of Inertia Govern the Transition in the Dynamics and Wakes of Freely Rising and Falling Cylinders

et al. 2017

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“…In this work, we use the first natural frequency of a passive elastic sheet in axial flow as a better approximation to that of the current system. An inviscid "vortex sheet" representation of the wake is then used to compute the natural frequency ω 1 of the system [12]. The evolution of the normalized efficiency with increasing reduced forcing frequency is shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…First, we define the first frequency ratio, ω = ω f /ω 1 = 2π f /ω 1 , where ω f is the driving angular frequency at the leading edge and ω 1 is the first natural angular frequency of the system. For the cases of large mass ratios (where the influence of outside fluid can be neglected), the natural frequencies of the system are approximated by those of a clamped-free elastic sheet in vacuum [12]. For such cases (e.g.…”

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“…The inextensibility condition of the filament is enforced by solving a Poisson equation for ζ [11][12][13]. Extensive validations of the immersed boundary solver can be found in Ref.…”

Section: Numerical Methods For Fsi Simulationmentioning

confidence: 99%

“…The motions of the fluid and the filament are governed by the Navier-Stokes equations coupled with a geometrically nonlinear structural equation [11][12][13] …”

Section: Governing Equationsmentioning

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Underlying principle of efficient propulsion in flexible plunging foils

Zhu

Zhang

2014

Acta Mech Sin

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Passive flexibility was found to enhance propulsive efficiency in swimming animals. In this study, we numerically investigate the roles of structural resonance and hydrodynamic wake resonance in optimizing efficiency of a flexible plunging foil. The results indicates that (1) optimal efficiency is not necessarily achieved when the driving frequency matches the structural eigenfrequency; (2) optimal efficiency always occurs when the driving frequency matches the wake resonant frequency of the time averaged velocity profile. Thus, the underlying principle of efficient propulsion in flexible plunging foil is the hydrodynamic wake resonance, rather than the structural resonance. In addition, we also found that whether the efficiency can be optimized at the structural resonant point depends on the strength of the leading edge vortex relative to that of the trailing edge vortex. The result of this work provides new insights into the role of passive flexibility in flapping-based propulsion.

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(Bio)manufactured Solutions for Treatment of Bone Defects with an Emphasis on US‐FDA Regulatory Science Perspective

Ghelich

Kazemzadeh-Narbat²,

Najafabadi

et al. 2022

Advanced NanoBiomed Research

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With a global prevalence of more than 2 million graft procedures per year, bone grafts are one of the most common transplants. [1][2][3][4][5] Small bone defects can be restored naturally, while large defects created by severe trauma, accidents, or tissue resection are unable to heal on their own. [6] As a rigid organ in humans and live animals, bone supports and protects different organs, tissues, and facilitates the mobility of the body. [7,8] These unique applications of bone are mainly attributed to the hierarchical architecture of bone, which mainly consists of the soft collagen protein and stiffer apatite mineral. [9] The overall stiffness of bone is primarily controlled by the natural mineral content as well as collagen to mineral ratio. [7,10] The mechanism of bone regeneration can be categorized as direct or indirect healing. [11] The size of fracture is one of the important factors that affects the bone healing mechanism. Direct bone healing mainly starts when a small and narrow (≤0.1 mm) fracture occurs, and the site of a fracture is rigidly stabilized. During direct bone healing, the small gap is covered directly by continuous ossification, following Haversian remodeling in a serial order. [12] Larger defects mostly heal by the indirect bone healing via various parallel events, such as blood clotting, inflammatory response, fibrocartilage callus formation, intramembranous and endochondral ossification, and results in bone remodeling. [11,12] A critical size defect is defined as the minimum defect dimension which is incapable of repairing without intervention. Per Food and Drug Administration (FDA) recognized standard ASTM F2721, in a critical size defect, the length of defect is at least 1.5-2 times the diameter of the selected bone. Critically sized defects can overwhelm the tissue regeneration capacity and lead to permanent disabilities. [13,14] Thus, surgical interventions are needed for the treatment of critically sized defects (Figure 1).Bone mimetic grafts, with hierarchical structure, and effective functionality could be engineered by merging suitable biomaterials, [7] cells, [15] and bioactive agents. [16] To design biomimetic bone scaffolds, a combination of nano-/microtechnologies with macrotechnologies is required. [17] Although many technologies have been developed for bone tissue engineering incorporating

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Numerical study on hydrodynamic effect of flexibility in a self-propelled plunging foil

Cited by 87 publications

References 54 publications

Mass and Moment of Inertia Govern the Transition in the Dynamics and Wakes of Freely Rising and Falling Cylinders

Mass and Moment of Inertia Govern the Transition in the Dynamics and Wakes of Freely Rising and Falling Cylinders

Underlying principle of efficient propulsion in flexible plunging foils

(Bio)manufactured Solutions for Treatment of Bone Defects with an Emphasis on US‐FDA Regulatory Science Perspective

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