scholarly journals Unsteady propulsion by an intermittent swimming gait

2017 ◽  
Vol 834 ◽  
pp. 149-172 ◽  
Author(s):  
Emre Akoz ◽  
Keith W. Moored
Keyword(s):  
Scaling Laws ◽  
Energy Savings ◽  
Leading Edge ◽  
Added Mass ◽  
Energetic Cost ◽  
Scaling Relations ◽  
Power Scaling ◽  
Cost Of Transport ◽  
The Mean ◽  
Jet Structure

Inviscid computational results are presented on a self-propelled swimmer modelled as a virtual body combined with a two-dimensional hydrofoil pitching intermittently about its leading edge. Lighthill (Proc. R. Soc. Lond. B, vol. 179, 1971, pp. 125–138) originally proposed that this burst-and-coast behaviour can save fish energy during swimming by taking advantage of the viscous Bone–Lighthill boundary layer thinning mechanism. Here, an additional inviscid Garrick mechanism is discovered that allows swimmers to control the ratio of their added-mass thrust-producing forces to their circulatory drag-inducing forces by decreasing their duty cycle, $DC$, of locomotion. This mechanism can save intermittent swimmers as much as 60 % of the energy it takes to swim continuously at the same speed. The inviscid energy savings are shown to increase with increasing amplitude of motion, increase with decreasing Lighthill number, $Li$, and switch to an energetic cost above continuous swimming for sufficiently low $DC$. Intermittent swimmers are observed to shed four vortices per cycle that give rise to an asymmetric time-averaged jet structure with both momentum surplus and deficit branches. In addition, previous thrust and power scaling laws of continuous self-propelled swimming are further generalized to include intermittent swimming. The key is that by averaging the thrust and power coefficients over only the bursting period then the intermittent problem can be transformed into a continuous one. Furthermore, the intermittent thrust and power scaling relations are extended to predict the mean speed and cost of transport of swimmers. By tuning a few coefficients with a handful of simulations these self-propelled relations can become predictive. In the current study, the mean speed and cost of transport are predicted to within 3 % and 18 % of their full-scale values by using these relations.

scholarly journals A Rotating Respirometer to Monitor Voluntary Activity and Associated Exchange of Respiratory Gases in the Land Hermit Crab (Coenobita Compressus)

1985 ◽  
Vol 119 (1) ◽  
pp. 85-101
Author(s):  
MICHÉLE G. WHEATLY ◽  
BRIAN R. MCMAHON ◽  
WARREN W. BURGGREN ◽  
ALAN W. PINDER
Keyword(s):  
Gas Exchange ◽  
Hermit Crab ◽  
Activity Patterns ◽  
Energetic Cost ◽  
Voluntary Activity ◽  
Good Correspondence ◽  
Cost Of Transport ◽  
Comparable Activity ◽  
The Mean ◽  
Respiratory Gases

A rotating respirometer was designed which enabled respiratory gas exchange in the land hermit crab Coenobita compressus to be correlated with voluntary submaximal sustained pedestrian activity. In the laboratory, crabs remained spontaneously active for up to 150 min, maintaining velocities of 0.6cm s−1. Comparable activity patterns were observed in the field. Quiescent O2 uptake (MOO2) increased logarithmically as a function of load rating of the adopted molluscan shell. Steady-state MOO2 and MCOCO2 were measured after 30 min of spontaneous activity and both increased linearly with velocity. There was good correspondence between Y-intercept values and those measured in inactive crabs. At the mean locomotory speed, MOO2 and MCOCO2 were increased 3.4-fold and 2.6-fold respectively above settled rates. Minimum and gross energetic cost of transport were estimated and compared with values in the literature. MOO2 and MCOCO2 returned to settled levels within the first hour of recovery. The activity profile and concomitant changes in gas exchange are discussed in the context of acquisition of the shell-dwelling habit.

scholarly journals LOCOMOTOR PERFORMANCE AND ENERGETIC COST OF SIDEWINDING BY THE SNAKE CROTALUS CERASTES

1992 ◽  
Vol 163 (1) ◽  
pp. 1-14 ◽  
Author(s):  
STEPHEN M. SECOR ◽  
BRUCE C. JAYNE ◽  
ALBERT F. BENNETT
Keyword(s):  
Oxygen Consumption ◽  
Energetic Cost ◽  
Linear Scaling ◽  
Locomotor Performance ◽  
Forward Speed ◽  
Cost Of Transport ◽  
Lateral Undulation ◽  
Crotalus Cerastes ◽  
The Mean ◽  
The Cost

We measured the performance (burst speed and endurance) and the energetic cost of sidewinding locomotion for the viperid snake Crotalus cerastes. The linear scaling regressions relating log mass to log burst speed and log endurance have slopes of 0.29 and 1.01, respectively. Maximal burst speed observed for an individual snake (SVL=41.9cm, SVL is snout-vent length) was3.7kmh−1. Adult snakes were able to match a tread speed of 0.5 km h−1 for times ranging from 33 to more than 180 min, and at 0.7kmh−1 endurance times ranged from 9 to 52 min. Rates of oxygen consumption increased linearly over a range of aerobically sustainable speeds (0.28–0.50kmh−1), with a resulting net cost of transport (NCT) of 0.408mlO2g−1km−1 for eight snakes with a mean mass of 110g. Sidewinding of C.cerastes involves periodic movements with a frequency that increases linearly with mean forward speed. At 0.50 km h−1, the mean (N=8) mass-specific energetic cost per cycle of movement was 0.28 JulO2g−1 cycle−1 for sidewinding. The NCT and the cost per cycle of movement of C. cerastes sidewinding are significantly less than those of similar mass snakes (Coluber constrictor) performing either terrestrial lateral undulation or concertina locomotion. The NCT of C. cerastes sidewinding is also significantly less than that predicted for the terrestrial limbed locomotion of lizards of similar mass. Mean VOO2max of C. cerastes (0.405 ml O2g−1h−1) is only about half that reported for C. constrictor; however, the mean endurance at 0.60 km h−1 (73 min) for sidewinding C. cerastes does not differ significantly from that reported for C. constrictor laterally undulating.

scholarly journals Scaling laws for parametrizations of subgrid interactions in simulations of oceanic circulations

2014 ◽  
Vol 372 (2018) ◽  
pp. 20130285 ◽  
Author(s):  
V. Kitsios ◽  
J. S. Frederiksen ◽  
M. J. Zidikheri
Keyword(s):  
Antarctic Circumpolar Current ◽  
Scaling Laws ◽  
Regression Method ◽  
Energy Spectra ◽  
Least Squares Regression ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Circumpolar Current ◽  
Jet Structure

Parametrizations of the subgrid eddy–eddy and eddy–meanfield interactions are developed for the simulation of baroclinic ocean circulations representative of an idealized Antarctic Circumpolar Current. Benchmark simulations are generated using a spectral spherical harmonic quasi-geostrophic model with maximum truncation wavenumber of T =504, which is equivalent to a resolution of 0.24 ° globally. A stochastic parametrization is used for the eddy–eddy interactions, and a linear deterministic parametrization for the eddy–meanfield interactions. The parametrization coefficients are determined from the statistics of benchmark simulations truncated back to the large eddy simulation (LES) truncation wavenumber, T R < T . A stochastic technique is used to determine the eddy–eddy coefficients, and a new least-squares regression method for the eddy–meanfield terms. Truncations are repeated for various T R , and the resolution dependence of the subgrid coefficients is identified. The mean jet structure and the kinetic and potential energy spectra resulting from the LESs closely agree with those from the benchmark simulations.

scholarly journals Scaling laws for the propulsive performance of three-dimensional pitching propulsors

2019 ◽  
Vol 871 ◽  
pp. 1117-1138 ◽  
Author(s):  
Fatma Ayancik ◽  
Qiang Zhong ◽  
Daniel B. Quinn ◽  
Aaron Brandes ◽  
Hilary Bart-Smith ◽  
...  
Keyword(s):  
Scaling Laws ◽  
Three Dimensional ◽  
Added Mass ◽  
Scaling Relations ◽  
The Novel ◽  
Vortex System ◽  
Propulsive Performance ◽  
Dimensional Scaling ◽  
Aspect Ratios ◽  
Thrust Production

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 downwash/upwash effects from the trailing vortex system of a propulsor and the elliptical topology of shedding trailing-edge vortices. The novel three-dimensional scaling laws are validated with self-propelled inviscid simulations and fixed-velocity experiments over a range of reduced frequencies, Strouhal numbers and aspect ratios relevant to bio-inspired propulsion. The scaling laws elucidate the dominant flow physics behind the thrust production and energetics of pitching bio-propulsors, and they provide guidance for the design of bio-inspired propulsive systems.

scholarly journals Virtual Energy Management for Physical Energy Savings in a Legged Robot Hopping on Granular Media

2021 ◽  
Vol 8 ◽  
Author(s):  
Sonia F. Roberts ◽  
Daniel E. Koditschek
Keyword(s):  
Granular Media ◽  
Energy Savings ◽  
Single Step ◽  
Active Damping ◽  
Energetic Cost ◽  
Direct Drive ◽  
Cost Of Transport ◽  
Physical Experiments ◽  
Physical Energy ◽  
Damping Controller

We discuss an active damping controller to reduce the energetic cost of a single step or jump of dynamic locomotion without changing the morphology of the robot. The active damping controller adds virtual damping to a virtual leg spring created by direct-drive motors through the robot’s leg linkage. The virtual damping added is proportional to the intrusion velocity of the robot’s foot, slowing the foot’s intrusion, and thus the rate at which energy is transferred to and dissipated by the ground. In this work, we use a combination of simulations and physical experiments in a controlled granular media bed with a single-leg robot to show that the active damping controller reduces the cost of transport compared with a naive compression-extension controller under various conditions.

The effects of metabolic inhibitors on the contraction of creatine-depleted muscle

1982 ◽  
Vol 60 (2) ◽  
pp. 114-119 ◽  
Author(s):  
G. W. Mainwood ◽  
M. Alward ◽  
B. Eiselt
Keyword(s):  
Creatine Phosphate ◽  
Diaphragm Muscle ◽  
Metabolic Inhibitors ◽  
Energetic Cost ◽  
Energy Reserves ◽  
Similar Extent ◽  
Additional Energy ◽  
Energy Stores ◽  
Wet Weight ◽  
The Mean

Rats were fed on a diet containing 1% β-guanidinopropionate (Gp) to deplete their muscles of creatine. The apparent energy reserves (creatine phosphate (CrP) + ATP) of rested state diaphragm muscle strips were found to be 79% depleted by this treatment. To determine if the effective energy reserves for contraction were depleted to a similar extent, the response to direct electrical stimulation (0.2-s tetani) was measured in the presence of inhibitors of respiration (NaCN) and glycolysis (iodoacetate). Only 4 ± 1 contractions could be elicited from strips from Gp-fed animals. Normal strips gave 15 ± 2 contractions under the same conditions. For both sets of diaphragms the energetic cost of contraction in terms of ~P was approximately 1 μmol/g wet weight. The mean level of Pi generated following stimulation to exhaustion was 10.1 μmol/g more in normal than in depleted strips. It is concluded that no significant additional energy stores such as phosphorylated Gp are readily available for contraction in muscles depleted of creatine by Gp treatment.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1999 ◽  
Vol 121 (3) ◽  
pp. 558-568 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

scholarly journals Review of Icing Effects on Wind Turbine in Cold Regions

2018 ◽  
Vol 72 ◽  
pp. 01007 ◽  
Author(s):  
Faizan Afzal ◽  
Muhammad S. Virk
Keyword(s):  
Wind Turbine ◽  
Structural Integrity ◽  
Turbine Blades ◽  
Leading Edge ◽  
Added Mass ◽  
Cold Climate ◽  
Ice Accretion ◽  
Wind Turbine Blades ◽  
Turbine Performance ◽  
Ice Shedding

This paper describes a brief overview of main issues related to atmospheric ice accretion on wind turbines installed in cold climate region. Icing has significant effects on wind turbine performance particularly from aerodynamic and structural integrity perspective, as ice accumulates mainly on the leading edge of the blades that change its aerodynamic profile shape and effects its structural dynamics due to added mass effects of ice. This research aims to provide an overview and develop further understanding of the effects of atmospheric ice accretion on wind turbine blades. One of the operational challenges of the wind turbine blade operation in icing condition is also to overcome the process of ice shedding, which may happen due to vibrations or bending of the blades. Ice shedding is dangerous phenomenon, hazardous for equipment and personnel in the immediate area.

Viscous boundary layers in reversing flow

1976 ◽  
Vol 74 (1) ◽  
pp. 59-79 ◽  
Author(s):  
T. J. Pedley
Keyword(s):  
Boundary Layer ◽  
Shear Rate ◽  
Leading Edge ◽  
Wall Shear Rate ◽  
Viscous Boundary Layer ◽  
Large Molecules ◽  
Displacement Thickness ◽  
The Mean ◽  
Wall Shear ◽  
Viscous Boundary

The viscous boundary layer on a finite flat plate in a stream which reverses its direction once (at t = 0) is analysed using an improved version of the approximate method described earlier (Pedley 1975). Long before reversal (t < −t1), the flow at a point on the plate will be quasi-steady; long after reversal (t > t2), the flow will again be quasi-steady, but with the leading edge at the other end of the plate. In between (−t1 < t < t2) the flow is governed approximately by the diffusion equation, and we choose a simple solution of that equation which ensures that the displacement thickness of the boundary layer remains constant at t = −t1. The results of the theory, in the form of the wall shear rate at a point as a function of time, are given both for a uniformly decelerating stream, and for a sinusoidally oscillating stream which reverses its direction twice every cycle. The theory is further modified to cover streams which do not reverse, but for which the quasi-steady solution breaks down because the velocity becomes very small. The analysis is also applied to predict the wall shear rate at the entrance to a straight pipe when the core velocity varies with time as in a dog's aorta. The results show positive and negative peak values of shear very much larger than the mean. They suggest that, if wall shear is implicated in the generation of atherosclerosis because it alters the permeability of the wall to large molecules, then an appropriate index of wall shear at a point is more likely to be the r.m.s. value than the mean.

scholarly journals Aeroacoustic Optimization of the Bionic Leading Edge of a Typical Blade for Performance Improvement

Machines ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 175
Author(s):  
Haoran Liu ◽  
Yeming Lu ◽  
Jinguang Yang ◽  
Xiaofang Wang ◽  
Jinjun Ju ◽  
...  
Keyword(s):  
Performance Improvement ◽  
Sound Pressure ◽  
Leading Edge ◽  
Wave Structure ◽  
Mechanism Analysis ◽  
Optimization Strategy ◽  
Flow Mechanism ◽  
Adjustment Factor ◽  
Bionic Blade ◽  
The Mean

New, innovative optimization approaches to improve turbomachine performance and reduce turbomachine noise are significant in engineering. In this paper, based on the bionic concept, a wave structure is used to shape the leading edge of the blade. Using an NACA0018 blade as the basic blade, a united parametric approach controlled by three parameters is proposed to configure the wavy leading edge. Then, a new optimization strategy boosting design efficiency is established to output the optimal design results. Finally, the corresponding performance and flow mechanism are analyzed. Taking into account the existence of the hub wall and the shroud wall from the closed impeller, a near-wall adjustment factor is added, the significance of which is herein demonstrated. An optimal bionic blade is successfully obtained by the optimization strategy, which can reduce the mean drag coefficient by about 6% and the overall sound pressure level by about 3 dB, in relative to the original blade. Mechanism analysis revealed that the wave structure can induce spanwise velocity at the leading edge and cause a further delay in flow separation in the downstream region, synchronously reducing drag and noise.

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