Keith W. Moored

Lehigh University · Department of Mechanical Engineering and Mechanics

The interaction between a pair of tandem in-line oscillating hydrofoils is presented. The hydrofoils undergo sinusoidal pitching about their leading edges with a fixed Strouhal number of [Formula: see text] and a Reynolds number of 10,000. The streamwise spacing, spanwise spacing, and phase offset between the hydrofoils are varied. Force measuremen...

A transient two-dimensional acoustic boundary element solver is coupled to a potential flow boundary element solver via Powell's acoustic analogy to determine the acoustic emission of isolated hydrofoils performing biologically-inspired motions. The flow-acoustic boundary element framework is validated against experimental and asymptotic solutions...

A classic lift decomposition (von K\'arm\'an & Sears 1938) is conducted on potential flow simulations of a near-ground pitching hydrofoil. It is discovered that previously observed stable and unstable equilibrium altitudes are generated by a balance between positive wake-induced lift and negative quasi-steady lift while the added mass lift doesn't...

When swimming near a solid planar boundary, bio-inspired propulsors can naturally equilibrate to certain distances from that boundary. How these equilibria are affected by asymmetric swimming kinematics is unknown. We present here a study of near-boundary pitching hydrofoils based on water channel experiments and potential flow simulations. We foun...

We present new measurements of non-uniformly flexible pitching foils fabricated with a rigid leading section joined to a flexible trailing section. This construction enables us to vary the bending pattern and resonance condition of the foils independently. A novel effective flexibility, defined as the ratio of added mass forces to elastic forces, i...

We present three-dimensional scaling relations for the thrust production and power consumption of combined heaving and pitching hydrofoils by extending the three-dimensional pitching scaling laws introduced by Ayancik et al. (“Scaling Laws for the Propulsive Performance of Three-Dimensional Pitching Propulsors,” Journal of Fluid Mechanics, Vol. 871...

View Video Presentation: https://doi.org/10.2514/6.2022-0330.vid Schooling interactions in fish have long fascinated scientists and engineers. One unresolved issue is the effect of vertical changes in swimmer relative positions in modulating hydrodynamic interactions. In this paper the spanwise relative position is tested experimentally using simpl...

Scaling laws for the thrust production and power consumption of a purely pitching hydrofoil in ground effect are presented. For the first time, ground-effect scaling laws based on physical insights capture the propulsive performance over a wide range of biologically relevant Strouhal numbers, dimensionless amplitudes and dimensionless ground distan...

New experiments examine the interactions between a pair of three-dimensional (AR = 2) non-uniformly flexible pitching hydrofoils through force and efficiency measurements. It is discovered that the collective efficiency is improved when the follower foil has a nearly out-of-phase synchronization with the leader and is located directly downstream wi...

Animals and bio-inspired robots can swim/fly faster near solid surfaces, with little to no loss in efficiency. How these benefits change with propulsor aspect ratio is unknown. Here we show that lowering the aspect ratio weakens unsteady ground effect, thrust enhancements become less noticeable, stable equilibrium altitudes shift lower and become w...

Inviscid computations are presented of a self-propelled virtual body connected to a combined heaving and pitching foil that uses continuous and intermittent motions. It is determined that intermittent swimming can improve efficiency when the dimensionless heave ratio is h*<0.7 while it degrades efficiency for h*≥0.7. This is a consequence of the ph...

The propulsive performance and acoustic emission of undulatory swimmers are investigated using an integrated unsteady potential flow and acoustic boundary element solver. Anguilliform and carangiform swimming gaits are modeled by a deforming NACA 0012 airfoil section for various reduced frequencies and dimensionless wave numbers based on the body l...

We present new experiments and free-swimming simulations of a pair of pitching hydrofoils interacting in a simple school. The hydrofoils have an out-of-phase synchronization and their arrangement is varied from in-line to side-by-side arrangements through a series of staggered arrangements representing the two-dimensional interaction plane. It is d...

A transient two-dimensional acoustic boundary element solver is coupled to a potential flow boundary element solver via Powell's acoustic analogy to determine the acoustic emission of isolated hydrofoils performing biologically-inspired motions. The flow-acoustic boundary element framework is validated against experimental and asymptotic solutions...

Scaling laws for the thrust production and power consumption of a purely pitching hydrofoil in ground effect are presented. For the first time, ground effect scaling laws based on physical insights capture the propulsive performance over a wide range of biologically-relevant Strouhal numbers, dimensionless amplitudes, and dimensionless ground dista...

Inviscid computations are presented of a self-propelled virtual body connected to a combined heaving and pitching foil that uses continuous and intermittent motions. It is determined that intermittent swimming can improve efficiency when the dimensionless heave ratio is $h^* < 0.7$ while it degrades efficiency for $h^* \geq 0.7$. This is a conseque...

We present new scaling laws for the thrust production and power consumption of three-dimensional combined heaving and pitching hydrofoils by extending the three-dimensional pitching scaling laws introduced by Ayancik et al. (2019). New self-propelled inviscid simulations and previously published experimental data are used to validate the scaling la...

Exact solutions for ground effect - Volume 891 - Peter J. Baddoo, Melike Kurt, Lorna J. Ayton, Keith W. Moored

Many species of fish gather in dense collectives or schools where there are significant flow interactions from their shed wakes. Commonly, these swimmers shed a classic reverse von Kármán wake, however, schooling eels produce a bifurcated wake topology with two vortex rings shed per oscillation cycle. To examine the schooling interactions of a hydr...

Cetaceans convert dorsoventral body oscillations into forward velocity with a complex interplay between their morphological and kinematic features and the fluid environment. However, it is unknown to what extent morpho-kinematic features of cetaceans are intertwined to maximize their efficiency. By interchanging the shape and kinematic variables of...

"Ground effect" refers to the enhanced performance enjoyed by fliers or swimmers operating close to the ground. We derive a number of exact solutions for this phenomenon, thereby elucidating the underlying physical mechanisms involved in ground effect. Unlike previous analytic studies, our solutions are not restricted to particular parameter regime...

Scaling laws for the propulsive performance of three-dimensional pitching propulsors – ADDENDUM - Volume 873 - Fatma Ayancik, Qiang Zhong, Daniel B. Quinn, Aaron Brandes, Hilary Bart-Smith, Keith W. Moored

Experiments and computations are presented for a foil pitching about its leading edge near a planar, solid boundary. The foil is examined when it is constrained in space and when it is unconstrained or freely swimming in the cross-stream direction. It was found that the foil has stable equilibrium altitudes: the time-averaged lift is zero at certai...

Scaling laws for the thrust production and energetics of self-propelled or fixed-velocity three-dimensional rigid propulsors undergoing pitching motions are presented. The scaling relations extend the two-dimensional scaling laws presented in Moored & Quinn ( AIAA J. , 2018, pp. 1–15) by accounting for the added mass of a finite-span propulsor, the...

Recently, it was demonstrated in an inviscid flow that burst-and-coast or intermittent swimming can save energy when compared with continuous swimming and that the energy savings are maximized for large-amplitude pitching motions where flow separation is likely to occur. This paper examines the effects of flow separation on altering inviscid flow p...

A transient, two-dimensional acoustic boundary element solver is developed using double-layer potentials accelerated by the fast multiple method for application to multibody, external field problems. The formulation is validated numerically against canonical radiation and scattering configurations of single and multiple bodies, and special attentio...

Many aquatic animals propel themselves efficiently through the water by oscillating flexible fins. These fins are, however, not homogeneously flexible, but instead their flexural stiffness varies along their chord and span. Here, we develop a simple model of these functionally graded materials where the chordwise flexibility of the foil is modeled...

Scaling laws for the thrust production and energetics of self-propelled or fixed-velocity three-dimensional rigid propulsors undergoing pitching motions are presented. The scaling relations extend the two-dimensional scaling laws presented in Moored & Quinn (2018) by accounting for the added mass of a finite-span propulsor, the downwash/upwash effe...

Scaling laws for the thrust production and energetics of self-propelled or fixed-velocity three-dimensional rigid propulsors undergoing pitching motions are presented. The scaling relations extend the two-dimensional scaling laws presented in Moored & Quinn (2018) by accounting for the added mass of a finite-span propulsor, the downwash/upwash effe...

Cetaceans have evolved a broad range of morphological characteristics and swimming gaits associated with enhanced thrust production, high propulsive efficiency, and reduced drag. These variations in their fluke shape and swimming gait influence their force pro- duction and energy requirements for swimming. The present study aims to disentangle the...

Experimental measurements are presented on the performance of two finite-span pitching wings with an aspect ratio of AR = 2 interacting in a side-by-side arrangement. Experiments are conducted for various synchronies and cross-stream spacings. The thrust, power and lift coefficients as well as the efficiency are reported for both the individual win...

We present experiments that examine the modes of interaction, the collective performance and the role of three-dimensionality in two pitching propulsors in an in-line arrangement. Both two-dimensional foils and three-dimensional rectangular wings of $AR = 2$ are examined. \kwm{In contrast to previous work, two interaction modes distinguished as the...

For aquatic animals, turning maneuvers represent a locomotor activity that may not be confined to a single coordinate plane, making analysis difficult particularly in the field. To measure turning performance in a three-dimensional space for the manta ray (Mobula birostris), a large open-water swimmer, scaled stereo video recordings were collected....

Many aquatic animals propel themselves eeciently through water by oscillating exible ns. ese ns are, however, not homogeneously exible, but instead their exural stiiness varies along their chord and span. Here, we developed a low order model of these functionally-graded materials where the chordwise exibility of the foil is modeled by one or two to...

In nature, many fish aggregate into large groups or schools for protection against predators, for social interactions and to save energy during migrations. Regardless of their prime motivation, fish experience three-dimensional flow interactions amongst themselves that can improve or hamper swimming performance and give rise to fluid-mediated force...

An unsteady three-dimensional boundary element method is developed to provide fast calculations of biological and bio-inspired self-propelled locomotion. The approach uniquely combines an unsteady three-dimensional boundary element method, a boundary layer solver and self-propelled equations of motion. This novel implementation allows for the self-...

Inviscid computational results are presented on a self-propelled virtual body combined with an airfoil undergoing pitch oscillations about its leading-edge. The scaling trends of the time-averaged thrust forces are shown to be predicted accurately by Garrick's theory. However, the scaling of the time-averaged power for finite amplitude motions is s...

Computational results are presented on comparison of intermittently and continuously pitching two dimensional airfoils. In literature, a viscous mechanism proposed by Lighthill (1971) where skin friction of an undulating body can be around 3 - 5 times greater than a rigidly-held coasting body, has been the well adopted explanation of energetic adva...

Proper selection of kinematics and bending pattern of the propulsive surfaces are the key elements for utilizing fast and efficient propulsion. St number is one of the most important kinematic input parameters to a flapping system and it has been both experimentally studied and observed in nature that 0.2 < St < 0.4 is the most efficient propulsion...

Many aquatic animals propel themselves efficiently through water by oscillating flexible fins. These fins are, however, not homogeneously flexible, but instead their flexural rigidity varies along their chord and span. To detail the flow structures and propulsive performance of these functionally-graded propulsors a simple model of an unsteady pitc...

The manta is the largest marine organism to swim by dorsoventral oscillation (flapping) of the pectoral fins. The manta has been considered to swim with a high efficiency stroke, but this assertion has not been previously examined. The oscillatory swimming strokes of the manta were examined by detailing the kinematics of the pectoral fin movements...

From an engineering perspective, biological swimmers are a composite material system with varying material properties across their propulsors. These material properties govern how the swimmer's structure interacts with its surrounding fluid. A two dimensional boundary element fluid solver is strongly coupled to a direct, implicit, geometrically non...

Dolphins and whales, known as cetaceans, have morphological characteristics associated with enhanced thrust production, high propulsive efficiency and reduced drag. These animals oscillate their moderate aspect ratio flukes in a heaving and pitching motion to propel themselves through the water. Surprisingly, these animals display a large variation...

Dolphins and whales, known as cetaceans, have morphological characteristics associated with enhanced thrust production, high propulsive efficiency and reduced drag. These animals oscillate their moderate aspect ratio flukes in a heaving and pitching motion to propel themselves through the water. Surprisingly, these animals display a large variation...

We present the linear stability analysis of experimental measurements obtained from unsteady flexible pitching panels. The analysis establishes the connections among the wake dynamics, propulsor dynamics, and Froude efficiency in flexible unsteady propulsion systems. Efficiency is calculated from direct thrust and power measurements and wake flowfi...

Experimental and computational results are presented on an aerofoil undergoing pitch oscillations in ground effect, that is, close to a solid boundary. The time-averaged thrust is found to increase monotonically as the mean position of the aerofoil approaches the boundary while the propulsive efficiency stays relatively constant, showing that groun...

We present experimental results on the role of flexibility and aspect ratio in bio-inspired aquatic propulsion. Direct thrust and power measurements are used to determine the propulsive efficiency of flexible panels undergoing a leading-edge pitching motion. We find that flexible panels can give a significant amplification of thrust production of $...

Aquatic animals propel themselves using a wide variety of mechanisms. In manta rays, propulsion is achieved by combining oscillating and undulating motions of flexible surfaces. We describe two principal sets of experiments to study the effects of excitation and flexibility on the wake flowfield: undulating and flapping three-dimensional fins of el...

Here we report an experimental study of the flow field and axial thrust generated by a single rigid helix rotating around its axis at Reynolds numbers based on the tangential velocity and the helix diameter between 0.045 and 0.18. Particle image velocimetry measurements are carried out on helices with pitch angles of 30°, 45° and 60°, at three diff...

For millions of years, aquatic species have utilized the principles of unsteady hydrodynamics to perform efficient, highly maneuverable and silent swimming motions. The manta ray, Manta birostris, has been identified as one such high performance species due to their ...

Swimming and flying animals generate thrust by creating an unsteady vortex wake through the oscillation of their appendages. To determine the vortex spacing that maximizes propulsive efficiency, a finite core vortex array model was developed to compute the unsteady velocity field generated by vortex streets representative of bio- inspired propulsio...

In this study, three dimensional wake structures are generated by an actively flexible robotic elliptical fin. Particle image velocimetry is used to characterize and quantify the wake and to extract time averaged velocity profiles. A linear spatial stability analysis is performed on the velocity profiles to find the frequency of maximum spatial gro...

The benefits of flying and swimming near the ground have been well-documented for fixed-wing vehicles, and have led to 'wing-in-ground' craft (WIG) with higher efficiencies than their conventional counterparts. Here it is examined whether unsteady propulsion techniques experience these same enhancements. Experimental particle image velocimetry was...

A pair of pitching panels arranged in a side-by-side configuration are experimentally examined under free swimming conditions. The panels were pitched about their leading edges by shafts located just behind the trailing edge of a NACA 0012-64 airfoil to suppress the formation of leading edge vortices. A recirculating water channel is set with a flo...

For millions of years, aquatic species have utilized the principles of unsteady hydrodynamics for propulsion and maneuvering. They have evolved high-endurance swimming that can outperform current underwater vehicle technology in the areas of stealth, maneuverability and control authority. Batoid fishes, including the manta ray, Manta birostris, the...

Mobuliform swimmers are inspiring novel approaches to the design of underwater vehicles. These swimmers, exemplified by manta rays, present a model for new classes of efficient, highly maneuverable, autonomous undersea vehicles. To improve our understanding of the unsteady propulsion mechanisms used by these swimmers, we report detailed studies of...

As tensegrity research is moving away from static structures toward active structures it is becoming critical that new actuation strategies and comprehensive active structures theories are developed to fully exploit the properties of tensegrity structures. In this paper a new general tensegrity paradigm is presented that incorporates a concept refe...

Myliobatidae is a family of large pelagic rays including cownose, eagle and manta rays. They are extremely efficient swimmers, can cruise at high speeds and can perform turn-on-a-dime maneuvering, making these fishes excellent inspiration for an autonomous underwater vehicle. Myliobatoids have been studied extensively from a biological perspective;...

Myliobatidae is a family of large pelagic rays including cownose, eagle and manta rays. They are extremely efficient swimmers, can cruise at high speeds and can perform turn-on-a-dime maneuvering, making these fishes excellent inspiration for an autonomous underwater vehicle. Myliobatoids have been studied extensively from a biological perspective;...

Tensegrity structures have become of engineering interest in recent years, but very few have found practical use. This lack of integration is attributed to the lack of a well formulated design procedure. In this paper, a preliminary procedure is presented for developing morphing tensegrity structures that include actuating elements. To do this, the...

Current attempts to build fast, efficient, and maneuverable underwater vehicles have looked to nature for inspiration. However, they have all been based on traditional propulsive techniques, i.e. rotary motors. In the current study a promising and potentially revolutionary approach is taken that overcomes the limitations of these traditional method...

Current attempts to build fast, efficient, and maneuverable underwater vehicles have looked to nature for inspiration. However, they have all been based on traditional propulsive techniques, i.e. rotary motors. In the current study a promising and potentially revolutionary approach is taken that overcomes the limitations of these traditional method...

An Orion sounding rocket will be launched from NASA's Wallops Flight Facility and will carry a University of Virginia payload to an altitude of 65.7 km to measure the distribution of methane in the Earth's upper atmosphere and record images and quantitative measurements of the distribution of chlorophyll in the Metompkin Inlet, Virginia. This will...