Estimates Of Energy Dissipation Research Articles

The correlation between ocean wave energy dissipation and ambient noise

An experiment that measured the NSL between 2 to 25 kHz, the wind speed U, and the directional wave spectrum was conducted off the coast of Oregon to examine the correlation between the ambient noise spectrum level (NSL) and surface wave parameters. These measurements show that although the correlation between the ambient NSL and the rms wave height is poor, the NSL and wave height spectrum energy levels at frequencies somewhat higher than the spectral peak give correlation coefficients that are comparable to that between the well-known correlation between U and NSL. Estimates of wave energy dissipation due to breaking waves using models proposed by Komen etal. [J. Phys. Ocean. 14, 1271–1285 (1984)] and Phillips [J. Fluid Mech. 156, 505–531 (1985)] likewise give comparable correlation coefficients. These results are consistent with the laboratory experiments [M. R. Loewen and W. K. Melville, J. Fluid Mech. 224, 601–623 (1991)] which show that the energy dissipated by wave breaking scales with the acoustic energy radiated. The implications of these results for acoustic remote sensing of breaking waves and associated processes of air–sea interaction are discussed.

Modelling of global ocean tides with allowance for island effects

Parameterization schemes for single islands, island chains and archipelagos are described. It is shown that their utilization within the framework of a global tidal model leads not only to local peculiarities in the spatial structure of tidal characteristics, but also to cardinal restructuring of the tidal pattern far beyond the islands and an appreciable increase (about 0.5·1012W) of the global tidal energy dissipation. The latter is commensurable by the order of magnitude with the imbalance between estimates of tidal energy dissipation in the World Ocean as a whole and on the continental shelf.

Energy Dissipation in Determinate Steel Beams

The aim of this study is to predict the amount of energy dissipated in a statically determinate steel beam due to material hysteresis. The case considered is that of a simply supported beam with a centrally applied point load. For any given central‐deflection limit history, an analysis is made to determine the load‐deformation response. The structural response is built up from the sectional response, which, in turn, is built up from the material response, i.e., a discrete element approach is implemented. This approach allows an in‐depth assessment of the stress and strain distributions at sections in the critical regions. Numerical integration is used to determine the cumulative area within the load‐deflection hysteresis curves, i.e., the energy dissipated. A full‐scale beam test is performed to provide a comparison with theoretical estimates of energy dissipation. These theoretical predictions are derived using a variety of cyclic stress‐strain models as input.

A Semigeostrophic Eady-Wave Frontal Model Incorporating Momentum Diffusion. Part II: Kinetic Energy and Enstrophy Dissipation

Abstract Momentum diffusion has been introduced into a semigeostrophic Eady-wave frontal model by Blumen (Part I). This model is used to determine the kinetic energy and enstrophy dissipations within a frontal zone that extends from the ground to a midtropospheric level. The largest amount of kinetic energy dissipation occurs when a relatively small nondimensional eddy viscosity coefficient is used, and the front attains an equilibrated state—a balance between unstable growth and momentum diffusion. The magnitude of kinetic energy dissipation ranges from about 50 to 250 W m−2 for parameter values that characterize surface-based fronts. These values are comparable to the 75 W m−2 determined by Kennedy and Shapiro from observations in an upper-level front, but are about one to two orders of magnitude larger than previous estimates of kinetic energy dissipated locally in clear-air turbulence zones and in the planetary boundary layer. An estimate of global kinetic energy dissipation in the planetary boundary ...

Tidal progression in a near-resonant system—A case study from South Australia

Detailed observations of the tide in a shallow southern-hemisphere gulf are described. The gulf is close to quarter-wave resonance with the semi-diurnal tide, but the nature of the tide changes with distance from the head of the gulf. Near the head, the tide behaves as a standing wave: the phase is almost constant in this region and the tidal currents lead elevations by 90°. Near the entrance to the gulf, the semi-diurnal tide behaves more as a progressive wave: there is a regular change in phase of elevation with distance and the phase difference between current and elevation is reduced. It is shown here that this behaviour can be understood in terms of a simple conceptual model proposed by Redfield (1950, Papers in Physical Oceanography and Meteorology 11, 1–36). In this model friction causes the amplitude of the tidal wave to diminish exponentially with distance travelled. Near the gulf head, the incident and reflected waves are of similar amplitude, and a standing wave is produced. Further from the head, the incident wave is considerably larger than the reflected wave and the resulting wave is predominantly progressive. The observations presented here are in good agreement with this model if the tidal wave amplitude is allowed to fall by 1 e for every wavelength travelled. This decay in wave amplitude implies a rate of energy loss in the region (for the M 2 tide) of 135 MW, a figure which is consistent with an independent estimate of energy dissipation.

New estimates of oceanic tidal energy dissipation from satellite altimetry

As a novel approach to computing the flux of tidal power into shelf areas, tidal maps of an oceanic area near the Patagonian Shelf are derived from 11 months of altimetry records from the GEOSAT satellite. Power fluxes are computed from the maps through Laplace's tidal equations. Flux vectors for M2 clearly show a convergence on to the southern portion of the shelf sea and their total is nearly twice the loss computed by Miller for that area. A decrease of ‘quality factor' with frequency from M2 to S2 is in keeping with Webb's hypothesis of shelf resonances at frequencies a little higher than the tidal band.

Some Constraints on Chromospheric Modelling for Solar-Type Stars with High S:N Spectra

High signal to noise spectra are required in chromospheric modelling because chromospheric emission lines are formed in a boundary layer under conditions of NLTE and in non-hydrostatic equilibrium, as well as in multiple magnetically-controlled streams, with horizontal structure on several scales, and vertical velocity fields. To obtain useable estimates of energy dissipation with height we have obtained sequences of spectra from F8 to K5 and for stars of different activity levels. These comprise Call H and K, the IR triplet, and MgII h and k obtained with the ESO CAT+CES or IUE. We outline the constraints such observations place on models and indicate theoretical and observational difficulties.

Convectively driven superfluid turbulence in dilute solutions of 3He in superfluid 4He

A dilute solution of 3He in superfluid 4He usually behaves as a single-component classical fluid in the context of thermal convection. However, certain convective states can be excited that do not seem to exist in classical convection. These states are characterized by noisy temperature fluctuations and a pronounced decrease in heat transport relative to the classical convecting states. Critical convective-flow fields are observed analogous to critical velocities for superfluid turbulence in pipes. The magnitudes of the average critical velocities for these two types of superfluid turbulence are in good agreement. Also, a quantitative estimate of energy dissipation due to the interaction of normal fluid and quantized vortex lines is consistent with the large decrease in heat transport for the turbulent states. These states are identified as states of convectively driven superfluid turbulence.

An active nutation control system for spin stabilised satellites

A familiar problem associated with the design of spin stabilised satellites is the requirement to constrain the satellite to spin about an axis of greatest moment of inertia. This paper is concerned with the design of a nutation control system using a nutation sensor linked to a gas jet system which removes this constraint. The choice of nutation sensor is discussed and the effects of sensor misalignment are investigated. Stability criteria are examined which derive from the sensor/thruster system, energy dissipation and incorrect estimates of the nutation frequency. The results from theoretical analysis are supported by analogue simulation.

An Active Nutation Control System for Spin Stabilised Satellites

A familiar problem associated with the design of spin stabilised satellites is the requirement to constrain the satellite to spin about an axis of greatest moment of inertia. This paper is concerned with the design of a nutation control system using a nutation sensor linked to a gas jet system which removes this constraint. The choice of nutation sensor is discussed and the effects of sensor misalignment are investigated. Stability criteria are examined which derive from the sensor/thruster system, energy dissipation and incorrect estimates of the nutation frequency. The results from theoretical analysis are supported by analogue simulation.

Tidal Patterns and Energy Balance in the Gulf of California

Roden and Groves1 wrote: “The oceanographic aspects of the Gulf of California, one of the least known marginal seas of the North Pacific, are both interesting and complex”. Tidal processes certainly justify the statement. With a reported spring range of 10 m as well as currents exceeding 6 knots (ref. 2) the tides in the Gulf of California are among the most spectacular and dangerous in the world. Nevertheless, because of the rarity and inadequacy of observations, no consistent picture could be drawn until recently. Many quantitative studies of this area must thus be regarded as provisional; there is, for example, an eight-fold range in estimates of energy dissipation for the semidiurnal lunar tide, namely, Heiskanen3,4: 2.5×1017 erg s−1; Miller5: 4×1017 erg s−1; Hendershott6: 1 to 2×1017 erg s−1; and my proposed values: 4.35×1016 erg s−1 for M2 alone, 4.65×1016 erg s−1 for all semidiurnal lunar constituents and 4.85×1016 erg s−1 for all lunar constituents.

The Evaporation-Precipitation Cycle of the Trades

The area distribution of surface wind strengths between 30° S and 30° N is expressed as a function of the median velocity, on the basis of climatological data. This is used to obtain estimates of evaporation and energy dissipation over the same area.
 The main energy supply of the trade circulation is due to condensation in the equatorial trough. It depends partly on evaporation into the trade winds at some earlier time. A study of the energy balance shows that this may lead to oscillations with a period of about 3 weeks; corresponding to the mode of the time which elapses between the evaporation and the precipitation of the same vapour molecules.
 Disturbances or fluctuations in the direct meridional circulation of the sub-tropics may be initiated by changes in the infra-red cooling rate and by changes in the height of the tropopause. It is suggested tentatively that this could be caused by changes in the ozone distribution above the tropical tropopause.