Wave Energy Transport Research Articles

Simulated envelopes of non-isotropically scattered body waves as compared to observed ones: another manifestation of fractal heterogeneity

Envelopes of scalar waves are simulated at various distances from an instant point source embedded in a random uniformly scattering medium by means of direct Monte-Carlo modelling of wave-energy transport. Three types of scattering radiation pattern ('indicatrix') are studied, for media specified by (1) a Gaussian autocorrelation function of inhomogeneities, (2) a power-law ('fractal', k−α) inhomogeneity spectrum and (3) the mix of case (1) and the isotropic indicatrix (very small + large inhomogeneities). We look for a model that can qualitatively reproduce the two most characteristic features of real S-wave envelopes of near earthquakes, namely (1) the broadening of the ‘direct’ wave group with distance and (2) the monotonously decaying shape of the coda envelope that does not deviate strongly from that expected in the isotropic scattering case. Both properties are observed for any band over a wide frequency range (1–40 Hz). The well-studied isotropic scattering model realistically predicts the appearance of codas but fails to predict pulse broadening. The model of large-scale inhomogeneity realistically predicts the mode of pulse broadening but fails to predict codas. We have found that, for a particular frequency band, within each class of inhomogeneity studied, both requirements can be qualitatively satisfied by a certain choice of parameters. In the Gaussian-ACF case, however, this match can be obtained only for a narrow frequency range. In contrast, the fractal case (with a value of exponent a of about 3.5–4) reproduces qualitatively the observed wide-band behaviour, and we consider it a reasonable representation of the gross properties of the earth medium.

Comparison of the wave energy transport at comets p/Halley and p/Giacobini-Zinner

Using magnetic field, plasma density and flow observations from spacecraft flybys of two comets, Elsässer variables are determined in order to study wave propagation directions. The inbound path of the Giotto spacecraft flyby of comet p/Halley is investigated outside the bow shock (between 10:36 and 19:11 UT on March 13, 1986, corresponding to distances from 3.3 × 10 6 to 1.2 × 10 6 km from the nucleus) and the inbound and outbound path of the ICE spacecraft flyby of comet p/Giacobini-Zinner is investigated outside of the bow wave (between 00:00 and 9:24 UT and between 12:25 and 23:30 UT on September 11, 1985, corresponding to distances from 8.5 × 10 5 to 1.2 × 10 5 km from the nucleus and from 1.0 × 10 5 to 9.3 × 10 5 km from the nucleus, respectively). The interaction of cometary pick-up ions and the solar wind is expected to generate waves which are assumed to be dominated by field-aligned propagating Alfvén waves. This predicted wave propagation combined with observed wave modes generated by the ion cyclotron resonance instability are compared with observed wave properties. Three mhd-modes are possible: right-hand polarized waves propagating toward the Sun ( RH −) and left-hand polarized waves propagating toward ( LH −) and away from the Sun ( LH +). Plasma conditions dictate that the RH − mode is the most unstable mode and satisfactory agreement is found between observed and predicted energy flow directions in regions outside the bow shock at Halley and the bow wave at Giacobini-Zinner, where local cometary ion pick-up conditions dominate.

Localization, Scaling, and Diffuse Transport of Wave Energy in Disordered Media

The Anderson localization literature in structural acoustics has to date been concerned largely with applications to the vibrations of one dimensional structures, whether mono-coupled or multi-coupled, and to steady state responses in such systems. This paper presents a brief tutorial on the theory of wave localization in one and higher dimensions with an emphasis on the scaling theory of localization. It then reviews the acoustic and optical literature on wave localization with an emphasis on diffuse time domain responses to transient loads. Numerical and laboratory experiments demonstrating localization in higher dimensions and investigating the time-domain behavior of such systems are discussed. Scaling theory is shown to provide predictions for localization lengths in weakly disordered multi-coupled systems, and for localization lengths in weakly disordered two-dimensional systems as well. Theoretical arguments for rates of diffuse transport are contrasted with the experimental evidence. The paper concludes with a discussion of wave energy confinement in non-localizing disordered systems.

Utilización del modelo Nedwam para el cálculo y pronóstico del oleaje en el Mar Caribe

Paper describes one of the NedWAM model versions, which was adapted in the CIOH 10 forecast wind-wave and swell parameters. Some numerical schemes for the discretization of the wave energy transport equation are studied and the results of the model for the wave fields. calculated with bases on climatological data from the Pilot Charts are introduced.

Energy properties and shoaling of higher-order stokes waves on a current

The energy density, the energy flux, the set-down, the radiation stress, and some wave energy velocities have been derived correct to fourth order in wave steepness for waves on a vorticity-free current. The energy flux and the set-down have been used for shoaling predictions for finite amplitude waves with and without a net volume flux. The results with a zero volume flux are compared with more accurate shoaling predictions showing rather good accordance, except for large steepnesses. This also applies to the deep water wave energy transport velocity. The results with a net volume flux show that the steepness of the waves reduces the influence of this flux on the wave evolution. Some problems in connection with the orders in Stokes waves are discussed, among others concerning the dispersion relation and the orders of integral properties. Bed shear and accompanying dissipation is neglected.

Diffuse wave energy transport in multicoupled, one-dimensional Anderson localizing systems

The spatial and time domain evolution of energy density in a multicoupled, one-dimensional disordered system is investigated. Scaling theory predictions are presented for both localization lengths and rates of diffuse transport. Scaling arguments suggest that localization lengths equal πρDo, where ρ is the modal density per unit length and Do is the bare diffusivity. Additionally, the rate of diffuse energy transport over a distance L is found to scale as ρL. These predictions are compared with the behavior of a numerical model for an Anderson localizing system. The system modeled is a cylindrical membrane disordered by the introduction of a random foundation of springs. [Work supported by ONR.]

Canterbury Plains, New Zealand--Implications for Sequence Stratigraphic Models

The Canterbury Plains, New Zealand, bounded by the Southern Alps and the Pacific Ocean, are traversed by four large gravel rivers. The coastline is wave dominated and microtidal (<2 m) with high rates of longshore sediment transport. The Canterbury coast is subdivided into southern and northern portions separated by the Banks Peninsula. The southern coastline, which is subjected to large oceanic swell originating as far away as 2000 km, is retrogradational and has wave-cut cliffs up to 25 m high. Coastal erosion at about 1 m/yr steepens the gradient, causing the rivers to incise 1.5-4.2 mm/yr during the present sea level highstand and accompanying transgression. Coastal erosion is caused by the extreme wave energy and efficient longshore sediment transport. River mouth are incising into the regional flood plain, with the amount of incision decreasing inland from the coast. The fluvial headwaters in the Southern Alps are rising tectonically and isostatically, causing incision that decreases seaward. Thus, fluvial incision takes place in the west due to mountain uplift and in the east, along the coast, due to a retreating shoreline during marine transgression. A zone of minimal valley incision occurs 8-15 km from the coast. In contrast to this observation, sequence stratigraphic models suggest that downcutting should occur during falling sea level, not during transgression. The northern coastline progrades about 1 m/yr and is largely sandy in its southern reaches. Thus, the Canterbury coastline is at one locale progradational and elsewhere retrogradational. The thickness of material being removed by erosional shoreface retreat during the present transgression is about 40 m. Although sea level plays a role, more important controls on progradation, retrogradation, and valley incision on the Canterbury Plains are the extreme wave energy and longshore drift.

FD-TD modeling of digital signal propagation in 3-D circuits with passive and active loads

Most existing computer-aided circuit design tools are limited when digital clock speeds exceed several hundred MHz. These tools may not deal effectively with the physics of UHF and microwave electromagnetic wave energy transport along metal surfaces such as ground planes or in the air away from metal paths that are common at or above this frequency range. In this paper, we discuss full-wave modeling of electronic circuits in three dimensions using the finite-difference time-domain (FD-TD) solution of Maxwell's equations. Parameters such as stripline complex line impedance, propagation constant, capacitance per unit length and inductance per unit length can be easily computed as a function of frequency. We also discuss FD-TD Maxwell's equations computational modeling of lumped-circuit loads and sources in 3-D, including resistors and resistive voltage sources, capacitors, inductors, diodes, and transistors. We believe that this approach will be useful in simulating the large-signal behavior of very high-speed nonlinear analog and digital devices in the context of the full-wave time-dependent electromagnetic field. >

Wind driven seas: Optimal parameter choice for the wind input term

The JONSWAP experiment provided the wave modelling community with much needed wave data and led to the determination of growth curves for parameters describing the evolution of the wave energy spectrum with fetch such as the total energy and the peak frequency. On the other hand mathematical models have been developed to solve the wave energy transport equation. The interest here is to find out if it is possible to “tune” certain parameters in the wind input and in the dissipation term automatically so that the solution of the energy transport equation for fetch limited conditions fits the measurements as closely as possible. Use is made of standard mathematical optimization routines to minimize a sum of squares cost function. Numerical experiments were done with the energy transport equation in deep water. The Snyder-type wind input term with a linear dependency on the friction velocity gives for the proposed growth curve and the current numerical scheme slightly better results compared to the Stewart-type wind input term with a quadratic dependency onthe friction velocity. However, the optimization routine proposes for both expressions physically unrealistic negative damping values. It is felt that the wave steepness could influence the wind input. Although over steeper waves the drag coefficient is larger than over waves near full development, this should not necessarily translate into a greater wind input. The Miles' mechanism for wave generation is probably more effective and better coordinated near full development than when the waves are rough and generate larger turbulence levels in the air. Therefore the wind input was made dependent on the wave steepness. A substantial improvement in the fits to the JONSWAP growth curves is noticed.

Acoustic Bloch wave energy transport and group velocity

The relationship between the steady‐state rate of energy transport and the group velocity is investigated for acoustic Bloch waves in a periodic waveguide. A time‐average energy flux relation is derived and used to find the energy transport velocity for an arbitrary periodic waveguide. An apparent disparity between the energy transport velocity and the power delivery is discussed. The group velocity is derived using a Bloch wave generalization of the usual Fourier transform method and is shown to be equal to the rate of energy transport. The integral transform method works well for the boundary value problem as the associated Bloch wave transform is relatively straightforward. The initial value problem, however, involves the inverse Bloch wave transform, the problems associated with which are discussed. [Work supported by the Office of Naval Research.]

A comparison of ULF fluctuations in the solar wind, magnetosheath, and dayside magnetosphere: 2. Field and plasma conditions in the magnetosheath

Data from three spacecraft (AMPTE IRM, AMPTE CCE, and ISEE 1 or 2) are used to study the correlation among the field and plasma conditions in the subsolar magnetosheath region, ULF wave activity in the magnetosphere, and the cone angle of the IMF. A disturbance parameter, R, which is the magnitude of the normalized resultant of unit vectors (calculated from measurements of the magnetic field or the plasma bulk velocity in a time interval), is used to describe the disturbance of the magnetosheath region. A “quiet” state has R values close to unity. We have studied five time intervals and found that when the R values of the magnetosheath magnetic field were below 0.8, indicative of a disturbed magnetosheath near local noon, transverse harmonic oscillations of magnetic field lines in the Pc 3, 4 range were observed in the magnetosphere and small cone angles were observed in the solar wind. We have also investigated the variation of other magnetosheath parameters (such as the magnetic pressure, the thermal pressure, the dynamic pressure, and the perturbation energy, etc.) under various magnetosheath conditions by comparing them with the disturbance parameter. It is found that the thermal beta (the ratio of the thermal pressure to the magnetic pressure) and the perturbation energy increase greatly as R decreases (i.e., as the magnetosheath region becomes more disturbed). The total pressure, which is the sum of the magnetic, thermal, and dynamic pressure of the subsolar magnetosheath region, decreases as the region becomes more disturbed. The dynamic pressure and the dynamic beta (the ratio of the dynamic pressure to the magnetic pressure) measured in the magnetosheath are poorly correlated with R, indicating that the changes in magnitude of the plasma bulk velocity in the subsolar magnetosheath have little effect on the occurrence of Pc 3‐4 waves in the outer magnetosphere. All magnetosheath parameters we examined became more variable during disturbed periods than during quiet ones. The implication of the above results to the transport of wave energy from the solar wind to the magnetosphere is discussed.

A note on specific variability of long surface gravity waves and drag coefficient in coastal upwelling zone

In this paper we solve analytically wave kinematic equations and the wave energy transport equation, for basic long surface gravity wave in the coastal upwelling zone. UsingGent andTaylor's (1978) parameterization of drag coefficient (which includes interaction between long surface waves and the air flow) we find variability of this coefficient due to wave amplification and refraction caused by specific surface water current in the region. The drag coefficient grows towards the shore. The growth is faster for stronger current. When the angle between waves and the current is less than 90° the growth is mainly connected with the waves steepness, but when the angle is larger, it is caused by relative growth of the wave phase velocity.

Effects of wave energy, topographic relief and sediment transport on the distribution of shallow-water gorgonians of Puerto Rico

Environmental factors controlling the distribution of shallow-water gorgonians of Puerto Rico were inferred from a Reciprocal Averaging ordination analysis. The data set included several samples taken before and after the passage of Hurricane David and the mass mortality of the sea urchin Diadema antillarum. We could infer only a single environmental gradient associated with the distribution of gorgonians. Stations at opposite extremes of this gradient were characterized by combinations of high wave action with low topographic relief, or low wave action with high topographic relief. This gradient was also associated with sediment transport across the bottom (bedload). A detailed examination of ordination results in relation to Hurricane David and the Diadema mortality indicated that sediment transport, rather than water movement and topographic relief, is more directly related to the distribution of shallow-water gorgonians.

STUDY OF SHELF WAVES VS SAND DRIFT IN NW COAST OF TAIWAN

For the planning and design of harbor and coastal Engineering, most important affected factors are waves and Littoral drift. This research deals with analysis of the measured waves and the budget of the beach material whether it is deposited or scoured in the North-western coast of Taiwan; and the relationship between wave energy and littoral transport rate. For processing this research the field Survey wave measurement, sand sampling, and echo sounding is necessitated. The objective of this research is to establish the model of waves and littoral transport budget. Therefore, the results of this research are planned to submit to the planning and design of harbor and coastal engineering works of the Taiwan west sandy coast. The main contains of this research are consisted of (1) Analysis, observations and investigations of the field oceanographic data, winds, waves, coastal geomorphology and littoral drift of the North-western coast of Taiwan. (2) Analysis of the shelf waves from the actual measured wave records. (3) Research of the wave decaying process of the continental shelf waves. (4) Statistical research of the measured waves and establishment of the practical model of the relationship between the shelf wave energy and the littoral transport rate in the north-west coast of Taiwan.

Morphological variations and sediment transport in crenulate-bay beaches, Kodiak Island, Alaska

Grain size, sorting, beachface slope variability, and sediment transport directions were examined at five mixed sand, granule, and pebble crenulate-bay beaches located at Kodiak Island, Alaska. Fitted log-spiral curves were used to differentiate zones of erosion and deposition and to determine the equilibrium morphology of each beach. Convergence and divergence of wave orthogonals from a computer-generated wave refraction diagram provided wave energy and sediment transport direction patterns. Delineation of this information combined with ground truth data permits the development of a crenulate-bay beach model. Crenulate bays are divided into three distinct shore segments based upon beach position. The shadow zone at the hooked end of the bay exhibits low wave energy, small grain size, relatively well-sorted sediment, gentle beachface slope, and an eroding shoreface relative to the remainder of the shoreline. The converse is true for the center of the beach which is subject to high wave energies and is characterized by large grain size, poor sorting, a moderate beachface slope, and a shoreline which is transitional between erosion and deposition. The characteristics of the tangential end are similar to those of the shadow zone except that the beachface slope is steep and the shoreline is depositional. Sediment transport is predominantly toward the tangential end. A headland, natural or artificial may result in the formation of a downdrift crenulate bay which eventually develops a stable equilibrium morphology, resulting in wave crests breaking simultaneously along the entire bay shoreline and a zero net longshore transport rate. Wave regime, grain size, sorting, beachface slope, erosion, deposition, and sediment transport all interact to determine the morphology of a crenulate-bay beach. The model of this study is partially based upon crenulate-bay theory which assesses the future morphology of a beach. Additionally, much of the previous work on crenulate bays is synthesized, with beach processes intergrated into the description of such bays.

COMPUTATIONAL HYDRAULICS: AN ALTERNATIVE VIEW

In almost all classical hydraulics, problems are posed in terms of determining what happens at given places and times. It is possible, however, to pose these problems "the other way around", so to speak, by asking at which place a given event occurs at a given time. In quantitative terms, the problem is posed of determining those values of the independent variables at which given values of the dependent variables occur at given times. This alternative view has certain advantages over that traditionally used, and also disadvantages. The traditional approach can be used most efficiently when, roughly speaking, the same order of variation occurs in the dependent variables over most of the domain during most of the time. In a large number of real-life situations, however, nothing much happens in most of the domain during most of the time but the areas of interest are concentrated in small regions that may move across the domain in time. Examples are the spillage, transport and dispersion of pollutants in watercourses, the propagation of Tsunamis waves, halocline and thermocline decay, bio-chemical process at air-water and bed-water interfaces and haloclines and also the transport of short wave energy. The alternative methods provide a generally superior resolution in these situations, as compared with the traditional ones, but this advantage is bought at the cost of an increased complexity of the numerical scheme or code. Applications are shown to the transport processes, dispersion process and conservation (propagation) processes of hydraulics, so covering most common applications. The transport applications are shown to be related to an existing method, which is then generalised, the dispersion applications appear to be new in hydraulics while the conservation applications generalise on the one side to a method so far only outlined in gas dynamics and on the other side to the method of characteristics. The study concludes with an outline of the problem of best descriptions.

A study of the occurrence of singly ionized calcium emission in late-type spectroscopic binary stars

view Abstract Citations (86) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A study of the occurrence of singly ionized calcium emission in late-type spectroscopic binary stars. Young, A. ; Koniges, A. Abstract A sample of spectroscopic binaries with published orbits is studied spectroscopically at high dispersion for the occurrence and properties of emission in the Ca II H and K lines. The sample contained 68 binaries with periods between 1 day and 40 years, and spectral types from F8 to K5, including main sequence, subgiant, and giant components. Eighteen systems were found to exhibit such emission, and all but two have periods under 100 days. However, there are 12 systems within the same period domain that are devoid of emission. Based upon radial velocity measurements, we demonstrate that the emission is chromospheric in origin, and we suggest that tidal-coupling effects have altered the 'acoustic' and the 'mechanical' wave energy transport mechanisms which are thought to heat the chromosphere. Publication: The Astrophysical Journal Pub Date: February 1977 DOI: 10.1086/154992 Bibcode: 1977ApJ...211..836Y Keywords: Binary Stars; Emission Spectra; Late Stars; Stellar Spectra; Atmospheric Tides; Calcium; Chromosphere; Giant Stars; Main Sequence Stars; Tables (Data); Wave Propagation; Astronomy full text sources ADS | data products SIMBAD (63)

Enhanced scattering inherent to ’’loss-cone’’ ion distributions— General geometry

The ion scattering rate due to the Post–Rosenbluth convective loss‐cone instability is calculated for general geometry. Noise generated by particle discreteness is amplified by the instability, the details of which are sensitively dependent upon the spatial variation of plasma parameters. Ray equations are developed for the transport and amplification of wave energy.

Effect of Artificial Sea Grass on Wave Energy and Nearshore Sand Transport: ABSTRACT

The emplacement of offshore, artificial sea-grass beds directly influences nearshore sand transport. Artificial sea grass will decrease wave energy because of bending of the fronds, increased bottom drag, internal deformation, and refraction. The latter three effects change as a result of the increased bottom slope caused by the sea grass beds. In turn, the mean longshore current and longshore component of wave power are reduced. Total wave power and incident angle to the beach specifies the longshore component of wave power (PL) which is equated to the quantity of sand moved per unit distance (dq/dx). The average bending moment per individual frond was calculated to be approximately 2.0 lb-in. A dense bed of sea grass has the potential to reduce wave energy by 20 percent, on the basis solely of energy lost to bending. The reduction of wave height, corresponding to the energy loss, results in decreased wave power per unit distance expended at the breaker zone. Ginsburg and Lowenstam reported that Thallassia testudinum offers a suitable substrate for many benthic communities. Algae, foraminifers, bryozoans, etc., attach to the fronds, whereas mollusks, echinoderms, and crustaceans use the network of baffles for protection and food gathering. These organisms add substantially to the binding ability of the grass, and sediment will be accumulated readily within the bed. Variations in the type of community present will depend on wave energy (turbulence), temperature of the water, tidal range, and salinity. In areas of low-wave energy, embankments may grow forming a series of offshore bars which further will influence approaching orthogonals. End_of_Article - Last_Page 2214------------

LONGSHORE TRANSPORT OF SUSPENDED SEDIMENT

In excess of 800 suspended sediment samples were collected from stations along the City Pier, Ventnor, New Jersey and Jennettes Pier, Nags Head, North Carolina using a tractor-mounted pump sampler. Most samples were collected within the surf zone at the Ventnor site. At the Nags Head site, sample collections included the surf zone, but generally extended over a wider range of the nearshore zone. Average sampling time was 3 minutes. Nozzle elevation varied from 3 inches above the bottom up to a maximum about mid-depth, generally not greater than 2.5 feet above bottom. Maximum concentrations at Ventnor ranged up to 2.6 ppt by weight and at Nags Head were about 4.0 ppt. Median size at Ventnor ranged from 0.12 to 0.15 mm and averaged about 0.20 mm in depths of 4 feet and less at Nags Head. Results are summarized in a series of scatter plots which relate suspended sediment concentration to nozzle height, wave height, water depth and sampling distance from an observed wave-breaker-line. Results are compared to CERC laboratory data, to two excerpted concentrations from unidirectional flow tests and to the CERC TR-4 design curve of longshore wave energy versus longshore transport.