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J. M. Anderson

Bio: J. M. Anderson is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Randomized controlled trial & Vorticity. The author has an hindex of 2, co-authored 2 publications receiving 1393 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the phase angle between transverse oscillation and angular motion is the critical parameter affecting the interaction of leading-edge and trailing-edge vorticity, as well as the efficiency of propulsion.
Abstract: Thrust-producing harmonically oscillating foils are studied through force and power measurements, as well as visualization data, to classify the principal characteristics of the flow around and in the wake of the foil. Visualization data are obtained using digital particle image velocimetry at Reynolds number 1100, and force and power data are measured at Reynolds number 40 000. The experimental results are compared with theoretical predictions of linear and nonlinear inviscid theory and it is found that agreement between theory and experiment is good over a certain parametric range, when the wake consists of an array of alternating vortices and either very weak or no leading-edge vortices form. High propulsive efficiency, as high as 87%, is measured experimentally under conditions of optimal wake formation. Visualization results elucidate the basic mechanisms involved and show that conditions of high efficiency are associated with the formation on alternating sides of the foil of a moderately strong leading-edge vortex per half-cycle, which is convected downstream and interacts with trailing-edge vorticity, resulting eventually in the formation of a reverse Karman street. The phase angle between transverse oscillation and angular motion is the critical parameter affecting the interaction of leading-edge and trailing-edge vorticity, as well as the efficiency of propulsion.

1,209 citations

Journal ArticleDOI
TL;DR: The fish benefits from smooth near-body flow patterns and the generation of controlled body-bound vorticity, which is propagated towards the tail, shed prior to the peduncle region and then manipulated by the caudal fin to form large-scale vortical structures with minimum wasted energy.
Abstract: We consider the motions and associated flow patterns of a swimming giant danio (Danio malabaricus). Experimental flow-visualization techniques have been employed to obtain the unsteady two-dimensional velocity fields around the straight-line swimming motions and a 60 degrees turn of the fish in the centerline plane of the fish depth. A three-dimensional numerical method is also employed to predict the total velocity field through simulation. Comparison of the experimental and numerical velocity and vorticity fields shows good agreement. The fish morphology, with its narrow peduncle region, allows for smooth flow into the articulated tail, which is able to sustain a large load for thrust generation. Streamlines of the flow detail complex processes that enhance the efficiency of flow actuation by the tail. The fish benefits from smooth near-body flow patterns and the generation of controlled body-bound vorticity, which is propagated towards the tail, shed prior to the peduncle region and then manipulated by the caudal fin to form large-scale vortical structures with minimum wasted energy. This manipulation of body-generated vorticity and its interaction with the vorticity generated by the oscillating caudal fin are fundamental to the propulsion and maneuvering capabilities of fish.

317 citations

Journal ArticleDOI
TL;DR: In this paper , an analysis of 142 upper and lower extremity fracture RCTs demonstrated one-half failed to reach publication and two-fifths were discontinued prior to trial completion.
Abstract: Abstract Purpose To our knowledge, no study has quantified the rate of discontinuation and nonpublication of randomized controlled trials (RCTs) regarding upper and lower extremity fractures. Methods We searched ClinicalTrials.gov on September 9th, 2020, for phase 3 and 4 RCTs pertaining to upper and lower extremity fractures. Trial completion status was determined using records available on ClinicalTrials.gov. Publication status was determined using records on ClinicalTrials.gov and by searching PubMed (MEDLINE), Embase, and Google Scholar. We queried corresponding authors on trial status if a peer-reviewed publication was not identified. Results Our final analysis included 142 RCTs, of which 57 (40.1%) were discontinued and 71 (50%) were unpublished. Thirty-six (of 57, 63.2%) discontinued trials failed to provide a reason for discontinuation, the most commonly identified reason for discontinuation was due to inadequate recruitment (13/21, 61.9%). Completed trials were more likely to reach publication (59/85; 69.4%; X 2 = 32.92; P ≤ 0.001) than discontinued trials. Trials with more than 80 participants were less likely not to reach publication (AOR: 0.12; 95% CI 0.15–0.66). Conclusion Our analysis of 142 upper and lower extremity fracture RCTs demonstrated one-half failed to reach publication and two-fifths were discontinued prior to trial completion. These findings indicate the need for increased guidance in developing, completing, and publishing RCTs in upper and lower extremity fractures. Discontinuation and nonpublication of orthopaedic RCTs hinder the public’s access to collected data and negate the valued contribution from study participants. Discontinuation and non-publication of clinical trials may subject participants to potentially harmful interventions, limit the advancement of clinical research, and contribute to research waste. Level of Evidence : III.

1 citations


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Journal ArticleDOI
TL;DR: In this article, an overview of the swimming mechanisms employed by fish is presented, with a relevant and useful introduction to the existing literature for engineers with an interest in the emerging area of aquatic biomechanisms.
Abstract: Several physico-mechanical designs evolved in fish are currently inspiring robotic devices for propulsion and maneuvering purposes in underwater vehicles. Considering the potential benefits involved, this paper presents an overview of the swimming mechanisms employed by fish. The motivation is to provide a relevant and useful introduction to the existing literature for engineers with an interest in the emerging area of aquatic biomechanisms. The fish swimming types are presented, following the well-established classification scheme and nomenclature originally proposed by Breder. Fish swim either by body and/or caudal fin (BCF) movements or using median and/or paired fin (MPF) propulsion. The latter is generally employed at slow speeds, offering greater maneuverability and better propulsive efficiency, while BCF movements can achieve greater thrust and accelerations. For both BCF and MPF locomotion, specific swimming modes are identified, based on the propulsor and the type of movements (oscillatory or undulatory) employed for thrust generation. Along with general descriptions and kinematic data, the analytical approaches developed to study each swimming mode are also introduced. Particular reference is made to lunate tail propulsion, undulating fins, and labriform (oscillatory pectoral fin) swimming mechanisms, identified as having the greatest potential for exploitation in artificial systems.

1,512 citations

Journal ArticleDOI
TL;DR: In this article, a review of the recent progress in flapping wing aerodynamics and aeroelasticity is presented, where it is realized that a variation of the Reynolds number (wing sizing, flapping frequency, etc.) leads to a change in the leading edge vortex (LEV) and spanwise flow structures, which impacts the aerodynamic force generation.

877 citations

Journal ArticleDOI
16 Oct 2003-Nature
TL;DR: Tuning cruise kinematics to optimize St seems to be a general principle of oscillatory lift-based propulsion of swimming and flying animals.
Abstract: Dimensionless numbers are important in biomechanics because their constancy can imply dynamic similarity between systems, despite possible differences in medium or scale. A dimensionless parameter that describes the tail or wing kinematics of swimming and flying animals is the Strouhal number, St = fA/U, which divides stroke frequency (f) and amplitude (A) by forward speed (U). St is known to govern a well-defined series of vortex growth and shedding regimes for airfoils undergoing pitching and heaving motions. Propulsive efficiency is high over a narrow range of St and usually peaks within the interval 0.2 < St < 0.4 (refs 3-8). Because natural selection is likely to tune animals for high propulsive efficiency, we expect it to constrain the range of St that animals use. This seems to be true for dolphins, sharks and bony fish, which swim at 0.2 < St < 0.4. Here we show that birds, bats and insects also converge on the same narrow range of St, but only when cruising. Tuning cruise kinematics to optimize St therefore seems to be a general principle of oscillatory lift-based propulsion.

865 citations

Journal ArticleDOI
TL;DR: In this article, the principal mechanism for producing propulsive and transient forces in oscillating flexible bodies and fins in water, the formation and control of large-scale vortices, was identified.
Abstract: Interest in novel forms of marine propulsion and maneuvering has sparked a number of studies on unsteadily operating propulsors. We review recent experimental and theoretical work identifying the principal mechanism for producing propulsive and transient forces in oscillating flexible bodies and fins in water, the formation and control of large-scale vortices. Connection with studies on live fish is made, explaining the observed outstanding fish agility.

816 citations

Journal ArticleDOI
TL;DR: The vortex wake shed by the tail differs between eel-like fishes and fishes with a discrete narrowing of the body in front of the tail, and three-dimensional effects may play a major role in determining wake structure in most fishes.
Abstract: What mechanisms of flow control do animals use to enhance hydrodynamic performance? Animals are capable of manipulating flow around the body and appendages both passively and actively. Passive mechanisms rely on structural and morphological components of the body (i.e., humpback whale tubercles, riblets). Active flow control mechanisms use appendage or body musculature to directly generate wake flow structures or stiffen fins against external hydrodynamic loads. Fish can actively control fin curvature, displacement, and area. The vortex wake shed by the tail differs between eel-like fishes and fishes with a discrete narrowing of the body in front of the tail, and three-dimensional effects may play a major role in determining wake structure in most fishes.

684 citations