scholarly journals Wave-Slope Soaring of the Brown Pelican

2021 ◽  
Author(s):  
Ian Stokes ◽  
Andrew Lucas
Keyword(s):  
Gravity Waves ◽  
Ground Effect ◽  
Ocean Surface ◽  
The Body ◽  
Surface Gravity ◽  
Cost Of Transport ◽  
Surface Gravity Waves ◽  
Wave Slope ◽  
Ocean Conditions ◽  
Wave Induced

Abstract Background: From the laboratory at Scripps Institution of Oceanography, it is common to see the brown pelican (Pelecanus occidentalis) traveling along the crests of ocean waves just offshore of the surf zone. When flying in this manner, the birds can travel long distances without flapping, centimeters above the ocean's surface. Here we derive a theoretical framework for assessing the energetic savings related to this behavior, `wave-slope soaring,' in which an organism in flight takes advantage of localized updrafts caused by traveling ocean surface gravity waves. Methods: The energy cost of steady, constant altitude flight in and out of ground effect are analyzed as controls. Potential flow theory is used to quantify the ocean wave-induced wind associated with near-shoaling, weakly nonlinear, shallow water ocean surface gravity waves moving through an atmosphere initially at rest. Using perturbation theory and the Green's function for Laplace's equation in 2D with Dirichlet boundary conditions, we obtain integrals for the horizontal and vertical components of the wave-induced wind in a frame of reference moving with the wave. Wave-slope soaring flight is then analyzed using an energetics-based approach for waves under a range of ocean conditions and the body plan of P. occidentalis . Results: For ground effect flight, we calculate a ~ 15 - 25% reduction in cost of transport as compared with steady, level flight out of ground effect. When wave-slope soaring is employed at flight heights ≤ 2m in typical ocean conditions (2m wave height, 15s period), we calculate 60-70% reduction in cost of transport as compared with flight in ground effect. A relatively small increase in swell amplitude or decrease in flight height allows up to 100% of the cost of transport to be offset by wave-slope soaring behavior. Conclusions: The theoretical development presented here suggests there are energy savings associated with wave-slope soaring. Individual brown pelicans may significantly decrease their cost of transport utilizing this mode of flight under typical ocean conditions. Thus wave-slope soaring may provide fitness benefit to these highly mobile organisms that depend on patchy prey distribution over large home ranges.

scholarly journals Wave-slope soaring of the brown pelican

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Ian A. Stokes ◽  
Andrew J. Lucas
Keyword(s):  
Gravity Waves ◽  
Ground Effect ◽  
Ocean Surface ◽  
The Body ◽  
Surface Gravity ◽  
Cost Of Transport ◽  
Surface Gravity Waves ◽  
Wave Slope ◽  
Ocean Conditions ◽  
Wave Induced

Abstract Background From the laboratory at Scripps Institution of Oceanography, it is common to see the brown pelican (Pelecanus occidentalis) traveling along the crests of ocean waves just offshore of the surf-zone. When flying in this manner, the birds can travel long distances without flapping, centimeters above the ocean’s surface. Here we derive a theoretical framework for assessing the energetic savings related to this behavior, ‘wave-slope soaring,’ in which an organism in flight takes advantage of localized updrafts caused by traveling ocean surface gravity waves. Methods The energy cost of steady, constant altitude flight in and out of ground effect are analyzed as controls. Potential flow theory is used to quantify the ocean wave-induced wind associated with near-shoaling, weakly nonlinear, shallow water ocean surface gravity waves moving through an atmosphere initially at rest. Using perturbation theory and the Green’s function for Laplace’s equation in 2D with Dirichlet boundary conditions, we obtain integrals for the horizontal and vertical components of the wave-induced wind in a frame of reference moving with the wave. Wave-slope soaring flight is then analyzed using an energetics-based approach for waves under a range of ocean conditions and the body plan of P. occidentalis. Results For ground effect flight, we calculate a ∼15 - 25% reduction in cost of transport as compared with steady, level flight out of ground effect. When wave-slope soaring is employed at flight heights ∼2m in typical ocean conditions (2m wave height, 15s period), we calculate 60-70% reduction in cost of transport as compared with flight in ground effect. A relatively small increase in swell amplitude or decrease in flight height allows up to 100% of the cost of transport to be offset by wave-slope soaring behavior. Conclusions The theoretical development presented here suggests there are energy savings associated with wave-slope soaring. Individual brown pelicans may significantly decrease their cost of transport utilizing this mode of flight under typical ocean conditions. Thus wave-slope soaring may provide fitness benefit to these highly mobile organisms that depend on patchy prey distribution over large home ranges.

scholarly journals Wave-Slope Soaring of the Brown Pelican

2020 ◽  
Author(s):  
Ian Stokes ◽  
Andrew Lucas
Keyword(s):  
Gravity Waves ◽  
Upper Bound ◽  
Ground Effect ◽  
Ocean Surface ◽  
Mechanical Advantage ◽  
Surface Gravity Waves ◽  
Level Flight ◽  
Steady Level ◽  
Wave Slope ◽  
Wave Induced

Abstract Background: From the laboratory at Scripps Institution of Oceanography, one can observe the brown pelican (Pelecanus occidentalis) traveling along the crests of near-shoaling waves just outside the surf zone. In this manner, the birds travel great distances without flapping, all the while a scant ~ 30 cm off the ocean's surface. Here we derive a theoretical framework for assessing the energetic benefit of this behavior, "wave-slope soaring,'' in which an organism in flight takes advantage of updrafts caused by traveling ocean surface gravity waves. Methods: The energy cost of steady, constant altitude flight is analyzed as a control. Potential flow theory is used to quantify the ocean wave-induced wind associated with near-shoaling, weakly nonlinear, shallow water ocean surface gravity waves. Using a regular expansion of the Stokes stream function and the Green's function for Laplace's equation in 2D with Dirichlet boundary conditions, we obtain integral expressions for the horizontal and vertical components of the wave-induced wind. The development of these relationships produces expressions for the components of the wave-induced wind in a frame of reference moving with the wave. Wave-slope soaring flight is then analyzed using an energetics-based approach for waves of typical ocean conditions (wave height of 1m, period of 10s) and the body plan of P. occidentalis . Results: For pure ground effect flight, we calculate an upper bound mechanical advantage of ~ 20 - 25\% as compared with steady, level flight without ground effect. When wave-slope soaring is employed, we calculate an upper bound mechanical advantage of ~ 50 - 60\% as compared with steady, level flight without ground effect. Conclusions: The theoretical development presented here suggests there are energy savings associated with wave-slope soaring. Individual brown pelicans may gain upwards of 50\% mechanical advantage utilizing this mode of flight under typical ocean conditions, as compared to steady, level flight out of ground effect. Thus wave-slope soaring appears to provide a significant benefit to these highly mobile organisms that depend on patchy prey distribution over large home ranges.

Measurements of Wave-Induced Pressure over Surface Gravity Waves

1986 ◽  
pp. 353-368 ◽  
Author(s):  
D. Hasselmann ◽  
J. Bösenberg ◽  
M. Dunckel ◽  
K. Richter ◽  
M. Grünewald ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Surface Gravity ◽  
Surface Gravity Waves ◽  
Wave Induced

Surface Gravity Waves

2017 ◽  
Author(s):  
John A. Adam
Keyword(s):  
Gravity Waves ◽  
Water Waves ◽  
Water Surface ◽  
Wave Pattern ◽  
The Body ◽  
Surface Gravity ◽  
Shallow Water Waves ◽  
Ship Waves ◽  
Surface Gravity Waves ◽  
Basic Fluid

This chapter deals with the underlying mathematics of surface gravity waves, defined as gravity waves observed on an air–sea interface of the ocean. Surface gravity waves, or surface waves, differ from internal waves, gravity waves that occur within the body of the water (such as between parts of different densities). Examples of gravity waves are wind-generated waves on the water surface, as well tsunamis and ocean tides. Wind-generated gravity waves on the free surface of the Earth's seas, oceans, ponds, and lakes have a period of between 0.3 and 30 seconds. The chapter first describes the basic fluid equations before discussing the dispersion relations, with a particular focus on deep water waves, shallow water waves, and wavepackets. It also considers ship waves and how dispersion affects the wave pattern produced by a moving object, along with long and short waves.

scholarly journals VISIR-1.b: ocean surface gravity waves and currents for energy-efficient navigation

2019 ◽  
Vol 12 (8) ◽  
pp. 3449-3480 ◽  
Author(s):  
Gianandrea Mannarini ◽  
Lorenzo Carelli
Keyword(s):  
Energy Efficiency ◽  
Gravity Waves ◽  
Ocean Surface ◽  
Surface Gravity ◽  
Ocean Current ◽  
Ship Routing ◽  
Surface Gravity Waves ◽  
Waves And Currents ◽  
The Impact

Abstract. The latest development of the ship-routing model published in Mannarini et al. (2016a) is VISIR-1.b, which is presented here. The new version of the model targets large ocean-going vessels by considering both ocean surface gravity waves and currents. To effectively analyse currents in a graph-search method, new equations are derived and validated against an analytical benchmark. A case study in the Atlantic Ocean is presented, focussing on a route from the Chesapeake Bay to the Mediterranean Sea and vice versa. Ocean analysis fields from data-assimilative models (for both ocean state and hydrodynamics) are used. The impact of waves and currents on transatlantic crossings is assessed through mapping of the spatial variability in the tracks, an analysis of their kinematics, and their impact on the Energy Efficiency Operational Indicator (EEOI) of the International Maritime Organization. Sailing with or against the main ocean current is distinguished. The seasonal dependence of the EEOI savings is evaluated, and greater savings with a higher intra-monthly variability during winter crossings are indicated in the case study. The total monthly mean savings are between 2 % and 12 %, while the contribution of ocean currents is between 1 % and 4 %. Several other ocean routes are also considered, providing a pan-Atlantic scenario assessment of the potential gains in energy efficiency from optimal tracks, linking them to regional meteo-oceanographic features.

What happens to the ocean surface gravity waves when ENSO and MJO phases combine during the extended boreal winter?

2019 ◽  
Vol 54 (3-4) ◽  
pp. 1407-1424 ◽  
Author(s):  
Victor A. Godoi ◽  
Felipe M. de Andrade ◽  
Tom H. Durrant ◽  
Audalio R. Torres Júnior
Keyword(s):  
Gravity Waves ◽  
Ocean Surface ◽  
Surface Gravity ◽  
Boreal Winter ◽  
Surface Gravity Waves

Inertial-Convective Subrange Estimates of Thermal Variance Dissipation Rate from Moored Temperature Measurements

2010 ◽  
Vol 27 (11) ◽  
pp. 1950-1959 ◽  
Author(s):  
Yanwei Zhang ◽  
James N. Moum
Keyword(s):  
Temperature Gradient ◽  
Gravity Waves ◽  
Dissipation Rate ◽  
Vertical Motion ◽  
Unknown Origin ◽  
Surface Gravity ◽  
Measured Signal ◽  
Vertical Temperature ◽  
Surface Gravity Waves ◽  
Wave Induced

Abstract A procedure for estimating thermal variance dissipation rate χT by scaling the inertial-convective subrange of temperature gradient spectra from thermistor measurements on a Tropical Atmosphere Ocean (TAO) equatorial mooring, maintained by NOAA’s National Data Buoy Center, is demonstrated. The inertial-convective subrange of wavenumbers/frequencies is contaminated by the vertical motion induced by the pumping of the surface float by surface gravity waves through the local vertical temperature gradient. The uncontaminated signal can be retrieved by removing the part of the measured signal that is coherent with the signal induced by surface gravity waves, which must be measured independently. An estimate of χT is then obtained by fitting corrected spectra to theoretical temperature gradient spectra over the inertial-convective subrange (0.05 < f < 0.5 Hz); this estimate is referred to as χTIC. Here χTIC was calculated over 120-min intervals and compared with estimates of χTo determined by scaling temperature gradient spectra at high wavenumbers (viscous-convective and viscous-diffusive subranges). Large differences up to a factor of 20 and of unknown origin occur infrequently, especially when both background currents and vertical temperature gradients are weak, but the results herein indicate that 75% of the data pairs are within a factor of 3 of each other. Tests on 15-, 30-, 60-, 120-min intervals demonstrate that differences between the two methods are nearly random, unbiased, and less than estimates of natural variability determined from unrelated experiments at the same location. Because the inertial-convective subrange occupies a lower-frequency range than is typically used for turbulence measurements, the potential for more routine measurements of χT exists. The evaluation of degraded signals (resampled from original measurements) indicates that a particularly important component of such a measurement is the independent resolution of the surface wave–induced signal.

Array measurements of atmospheric pressure fluctuations above surface gravity waves

1981 ◽  
Vol 102 ◽  
pp. 1-59 ◽  
Author(s):  
R. L. Snyder ◽  
F. W. Dobson ◽  
J. A. Elliott ◽  
R. B. Long
Keyword(s):  
Gravity Waves ◽  
Atmospheric Pressure ◽  
Pressure Sensors ◽  
Phase Speed ◽  
Limited Range ◽  
Surface Gravity ◽  
Wave Number ◽  
Surface Gravity Waves ◽  
Array Measurements ◽  
Wave Induced

A joint experiment to study microscale fluctuations of atmospheric pressure above surface gravity waves was conducted in the Bight of Abaco, Bahamas, during November and December 1974. Field hardware included a three-dimensional array of six wave sensors and seven air-pressure sensors, one of which was mounted on a wave follower. The primary objectives of the study were to resolve differences in previous field measurements by Dobson (1971), Elliott (1972b) and Snyder (1974), and to estimate the vertical profile of wave-induced pressure and the corresponding input of energy and momentum to the wave field.Analysis of a pre-experiment intercalibration of instruments and of 30 h of field data partially removes the discrepancy between the previous measurements of the wave-induced component of the pressure and gives a consistent picture of the profile of this pressure over a limited range of dimensionless height and wind speed. Over this range the pressure decays approximately exponentially without change of phase; the decay is slightly less steep than predicted by potential theory. The corresponding momentum transfer is positive for wind speeds exceeding the phase speed. Extrapolation of present results to higher frequencies suggests that the total transfer is a significant fraction of the wind stress (0·1 to 1·0, depending on dimensionless fetch).Analysis of the turbulent component of the atmospheric pressure shows that the ‘intrinsic’ downwind coherence scale is typically an order-of-magnitude greater than the crosswind scale, consistent with a ‘frozen’ turbulence hypothesis. These and earlier data of Priestley (1965) and Elliott (1972c) suggest a horizontally isotropic ‘intrinsic’ turbulent pressure spectrum which decays ask−νwherekis the (horizontal) wave-number and ν is typically −2 to −3; estimates of this spectrum are computed for the present data. The implications of these findings for Phillips’ (1957) theory of wave growth are examined.

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