Wave Zone Research Articles

Numerical analysis of an Uppsala University WEC deployment by a barge for different sea states

Wave energy converters (WECs) have been deployed onshore, nearshore, and offshore to convert ocean wave movement into electricity. The exploitation of renewable energy sources has restrictions; in the case of wave energy, high installation, maintenance, and decommissioning costs have limited their commercial use. Moreover, these offshore operations can be compromised by safety issues. This paper draws attention to offshore operation safety of a WEC developed by Uppsala University. Specifically, this paper investigates what sea states are suitable for the safe deployment of a WEC from a barge. This study follows recommendations in DNV-RP-H103 for analysis of offshore operations, namely lifting through the wave zone. ANSYS Aqwa is used to find hydrodynamic forces acting on a typical barge, using frequency domain analysis. Based on these hydrodynamic simulation results and methodology given in DNV-RP-H103, tables are created to show the sea states that would allow for the safe installation of a WEC using a typical barge. Considered sea states have significant wave heights varying between 0 m and 3 m and the wave zero crossing periods varying between 3 s and 13 s. The WEC submersions are considered between 0 m and 7 m, i.e. when the WEC is in the air until it is fully submerged.

Mechanism of the ultrasound influence on combustion and structure formation at SHS in titanium-base systems

Using the developed experimental setup, the effect of ultrasonic oscillations (USO) on the temperature and combustion velocity during self-propagating high-temperature synthesis (SHS) in the Ti–C, Ti–C–Ni–Mo and Ti–B systems is studied. Basing on the analysis of data known in literature and our own measurements, theoretical explanation to the observed results is proposed. The effect of the intensity of ultrasonic oscillations on the composition and structure of the final synthesis products is established. It was found that along with changes in the parameters of the combustion wave, the completeness of the interaction increases, and changes in the microstructure and phase composition of the reaction products occur. The concept of separation of the effect of USO on SHS into thermal, or macroscopic, and non-thermal, or microscopic is proposed. The former is associated with forced convection of gas around an oscillating specimen and leads to a decrease in temperature and combustion velocity. The latter is connected with a change in the melt spreading conditions, the progress of heterogeneous reactions and mass transfer in the liquid phase in the high-temperature zone of the SHS wave, which lead to a change in the phase composition and structure of the final product.

Electric and Magnetic Dipole Fields in the Wave Zone Allowing for Ground Effects

We derive asymptotic Green’s functions for the Helmholtz equations describing the radiation from electric and magnetic dipoles located at an interface. The directional diagram of a distributed magnetic antenna is analyzed, formulas are derived for the phase shifts between different radiators intended for controlling the peak direction, an approximate formula is obtained for the angular width of the antenna main lobes.

Analysis of wave climate and trends in a semi-enclosed basin (Persian Gulf) using a validated SWAN model

Results from a spectral wave model of the Persian Gulf for a long-term period (32-year) are used to describe and quantify the seasonal wave climate and trends. The model is forced by a wind reanalysis dataset and validated against a set of field measurements and altimeter data from various satellite missions. The results revealed the existence of a more energetic wave (higher Hm0 and larger TP) zone located at the southern regions of the Gulf that is linked to the predominant and stronger north-westerly winds. The wave heights and periods are intensified in winter (Hm0>2.7m and TP > 8s for the 99th percentile) followed by spring. The waves conditions are milder in autumn. The analysis of wave climate trends throughout the region clearly show an overall slight positive trend (0–0.2%/year) in mean Hm0, which is associated with long-term positive trends in wind speed. There is generally a positive trend in the mean significant wave height during winter (0–0.8%/year), spring (0–0.6%/year) and autumn (0–1.0%/year), and negative during summer (0–0.8%/year). The results indicate that the more statistically significant results are at the areas with larger magnitude of trends.

STUDY OF EFFECTS OF LUNAR TIDAL WAVE PASSAGE IN UPPER ATMOSPHERE OF EARTH ACCORDING TO MONITORING DATA AT RADIO TELESCOPE «URAN-4» RI NANU

The paper examines data on the effects of the lunar tidal wave in the Earth 's upper atmosphere on the observed flux of radio sources. Monitoring of the fluxes of powerful galactic and extragalactic radio sources is carried out at the URAN-4 radio telescope of the Odessa Observa- tory of the Institute of Radio Astronomy of the NAS of Ukraine since 1987 till now. The monitoring program in- cludes radio galaxies 3C274, 3C405 and supernova rem- nants 3C144, 3C461. Changes of fluxes of radiation sources at decameter waves are determined by the condi- tion of an ionosphere resulted due to space weather varia- tion and tidal events. When radio sources are observed through a tidal wave, a plasma lens effect is realized in the ionosphere. Depending on the position of the radio source relative to the tidal wave, the radiation wave front is sought. As a result, various effects are realized: strong fo- cusing, intense flickering or blurred recording of the ra- dio source. According to the data of radiation monitoring of powerful radio sources, the dimensions and structure of the tidal wave zone in the upper atmosphere producing the effect of plasma lensing have been determined. The total size of this zone according to observations on frequent 20 and 25 MHz is on the order of 30-60 angular degrees in right ascension and declination.

Interior of a Binary Black Hole Merger.

We find strong numerical evidence for a new phenomenon in a binary black hole spacetime, namely, the merger of marginally outer trapped surfaces (MOTSs). By simulating the head-on collision of two nonspinning unequal mass black holes, we observe that the MOTS associated with the final black hole merges with the two initially disjoint surfaces corresponding to the two initial black holes. This yields a connected sequence of MOTSs interpolating between the initial and final state all the way through the nonlinear binary black hole merger process. In addition, we show the existence of a MOTS with self-intersections formed immediately after the merger. This scenario now allows us to track physical quantities (such as mass, angular momentum, higher multipoles, and fluxes) across the merger, which can be potentially compared with the gravitational wave signal in the wave zone, and with observations by gravitational wave detectors. This also suggests a possibility of proving the Penrose inequality mathematically for generic astrophysical binary back hole configurations.

Estimate of Coastal Water Depth Based on Aerial Photographs Using a Low-Altitude Remote Sensing System

Observing coastal water depths is very important to understand physical processes of the coastal environment and manage coastal resources. In this study, a low-altitude remote sensing system, Helikite, with an optic sensor was used to measure shallow water depths. This system not only enables us to observe the highresolution water depths in the coastal waters in a very short time, but also allow us to estimate water depths of the breaking wave zone where erosion is most active. The “Anmok Beach” study area has undergone severe coastal erosion from typhoons in summer and abnormally high waves in winter. Therefore, aerial photographs were taken and a field water depth survey was carried out at Anmok Beach to estimate water depths. In order to convert aerial orthomosaic images to water depths, the following three steps were undertaken. First, georeferencing was performed via the Oceanic Ground Control Point based on a ground reference point available on the sea surface. Second, error values generated from the aeolian current and sunglint were filtered out from the orthomosaic images. Third, the relationships between in-situ water depth data and brightness values of the orthomosaic image were calculated using the second polynomial regression equation. The obtained regression coefficients (R2) values were 0.90, 0.95, and 0.91 for the R, G, and B-bands, respectively and the corresponding RMSE values were 0.45 m, 0.30 m, and 0.44 m for the R, G, and B-bands, respectively. The accuracy of the G-band based water depth was highest. Using this result, we could estimate the submarine topography of the crescent bar produced by complex coastal currents in the study area.

Spatio-temporal trend in heat waves over India and its impact assessment on wheat crop

This study presents two aspects of heat waves over India. Firstly, we have analysed the gridded daily temperature data (1° × 1°) for six decades (1951–2015) to understand the changes in heat waves using the heat wave magnitude index daily (HWMId). Secondly, we have post-facto assessed the impact of the March 2010 heat wave on the growth and yield of wheat crop over north India. The study clearly showed the effectiveness of HWMId to capture the heat waves over India. The most-intense heat waves have significantly increased over 56% area of the country, and over the past three decades, it also started occurring in non-conventional heat wave regions of the southern peninsula and northeastern India. Among different categories of HWMId, the rate of spatial spread was highest for the very extreme category. The auto-regressive integrated moving average (ARIMA) intervention technique showed negative impact of the March 2010 extreme heat on yield of wheat over north India. The yield decreased by 4.9%, 4.1% and 3.5% over Punjab, Haryana and Uttar Pradesh, respectively, which were statistically significant (p < 0.1). Though the total production decreased, it was non-significant due to the slight increase in harvested area. Satellite-derived crop phenology parameters also captured the event. The rate of browning increased significantly over the study area. There were inter-district variations in the heat-wave impacts. The results may be used for identification of potential heat wave zones. It may also be used for devising zone-specific adaptation strategies for shielding wheat crop from such events.

The lifetime of shoreface nourishments in fields with nearshore sandbar migration

Migration of nearshore sandbars results from nonlinear interacting hydro- and morphodynamic processes in the surf zone of wave dominated sandy shorelines. To gain new insights in the largely varying temporal effects of shoreface nourishments within these areas, the principle component analysis is applied to sixteen data sets with i) natural sandbar migration on different timescales and ii) interfering shoreface nourishments. The statistical methodology is able to separate the non-stationary effects of shoreface nourishments from the natural stationary migration of the sandbars. Depending on other long-term morphodynamic changes and nourishment interactions in the data, the duration of these interferences (the nourishment lifetimes) can be quantified. Relating these nourishment lifetimes (Ln) with respect to the bar cycle return periods (Tr) of these areas (e.g. the relative nourishment lifetime) of twenty-one shoreface nourishments with several design parameters, and parameters of the sandbar system in which they were placed, remained inconclusive. A negative exponential fit with the bar cycle return period itself was the most significant (r2 = 0.41). Assuming a linear system of the parameters increases the predictive capability (r2 = 0.67). The most influential parameters in this relation are the nourishment concentration (+), the nourishment depth (+), the concentration of the migrating sandbars (−) and the bar cycle return period (−), thereby indicating the prominent roles of both nourishment design and natural sandbar system in the inter-site variability of shoreface nourishment lifetimes.

High performance computing simulations of spall phenomenon in a submicron thick nanocrystalline aluminum

The spall failure phenomenon is investigated at nano-scale in a plate-on-plate impact configuration using large-scale molecular dynamics (MD) high performance computing (HPC) simulationson three multi-billion 0.5 μm thick nanocrystalline aluminum (nc-Al) systems, each with an average grain size in the range of 18–100 nm and each under impact velocities in the range of 0.7–1.5 km s−1. Using a material conserving atom section-averaging process, distributions of several mechanical responses were obtained and the extremely transient spall failure phenomena were located in the interaction zones of the stress release waves released from the impacted and free ends of the atom systems. The spall zones’ thicknesses were estimated along with the spall strengths. For the nc-Al atom systems, the spall strength was observed to increase as the impact velocity increased from 0.7 to 1.5 km s−1, but only showed a slight decrease as the grain size increased from 18 to 100 nm. The spall strengths thus estimated from the stress release waves’ interaction zones were found to be conservative when compared to the traditional estimates obtained from the pullback velocity signatures in the free-end velocity evolutions. The MD results were further analyzed using a crystal analysis algorithm and a twin dislocation identification method to obtain the densities of the atomistic microstructures evolving under the interaction of the stress release waves. High-fidelity large-scale HPC simulation results showed that certain dislocation partials strongly influenced the spall response. The Stair-rod type dislocation partials increased by more than a factor of 10 during the interaction of the stress release waves as the spall failure commenced.

Nonequilibrium radiation behind shock waves in oxygen at speeds up to 10 km/s

In this work, the radiation characteristics of shock-heated oxygen in the spectral range of 190-700 nm are investigated. The presence of radiation from the Schumann-Runge bands from the nonequilibrium zone of the shock wave for velocities of 5–10 km/s is shown. The magnitude of the emission of oxygen from a nonequilibrium zone was measured. The results of comparison of pure oxygen and air radiations are presented. These data gives the possibility to estimate the contribution of this spectrum region emission to the nonequilibrium emission of air. The emission of some atomic oxygen lines was investigated also in experiment for these conditions.

Analytical model of resonant electromagnetic dipole-quadrupole coupling in nanoparticle arrays

An analytical model for investigations of multipole coupling effects in the finite and infinite nanoparticle arrays supporting electromagnetic resonances is presented and discussed. This model considers the contributions of both electric and magnetic modes excited in the nanoparticles, including electric and magnetic dipoles and electric and magnetic quadrupoles. The magnetic quadrupole propagator (Green's tensor) that describes the electromagnetic field generated by a point magnetic quadrupole source in all wave zones is derived. As an example, we apply the developed model to study infinite two-dimensional rectangular periodic arrays of spherical silicon nanoparticles supporting the dipole and quadrupole resonant responses. The correctness and accuracy of the analytical model are confirmed by the agreement of its results with the results of full-wave numerical simulations. Using the developed model, we show the electromagnetic coupling between electric dipole and magnetic quadrupole moments as well as between magnetic dipole and electric quadrupole moments even for the case of an infinite rectangular periodic array of spherical nanoparticles. The strong suppression of the dipole or quadrupole moment due to the coupling effects is demonstrated and discussed for spherical nanoparticle arrays. The analytical expressions for the reflection and transmission coefficients written with the effective dipole and quadrupole polarizabilities are derived for normal light incidences and zero-order diffraction. The derived expressions are applied to explain the lattice anapole (invisibility) states when the incident light is transmitted unperturbed through the silicon nanoparticle array. The important role of dipole and quadrupole excitations in scattering compensation resulting in the lattice anapole effect is explicitly demonstrated. The presented approach can be used for designing metasurfaces and further utilizing them in developing ultrathin functional optical elements.

Multiresolution-based adaptive central high resolution schemes for modeling of nonlinear propagating fronts

A class of wavelet-based methods, which combine adaptive grids together with second-order central and central-upwind high-resolution schemes, is introduced for accurate solution of first order hyperbolic systems of conservation laws and related equations. It is shown that the proposed class recovers stability which otherwise may be lost when the underlying central schemes are utilized over non-uniform grids. For simulations on irregular grids, both full-discretized and semi-discretized forms are derived; in particular, the effect of using certain shifts of the center of the computational allow to use standard slope limiters on non-uniform cells. Thereafter, the questions of numerical entropy production, local truncation errors, and the Total Variation Diminishing (TVD) criterion for scalar equations, are investigated. Central schemes are sensitives for irregular grids. To cure this drawback in the present context of multiresolution, the adapted grid is locally modified around high-gradient zones by adding new neighboring points. For an adapted point of resolution scale j, the new points are locally added in both resolution j and all successive coarser resolutions. It is shown that this simple grid modification improves stability of numerical solutions; this, however, comes at the expense that cell-centered central and central-upwind high resolution schemes, may not satisfy the TVD property. Finally, we present numerical simulations for both scalar and systems of non-linear conservation laws which confirm the simplicity and efficiency of the proposed method. These simulations demonstrate the high accuracy, the entropy production of wavelet-based algorithms which can effectively detect high gradient zones of shock waves, rarefaction regions, and contact discontinuities.

Numerical analysis of the flow field and separation performance in hydrocyclones with different vortex finder wall thickness

High separation sharpness of hydrocyclones is an ultimate goal for the classification process and has attracted considerable attention. The existence of some special flow patterns, such as short-circuit flow and circulation flow, play an important role in the separation process and have not been clearly understood. This paper presents a numerical study of the effects of vortex finder wall thickness on the flow field and separation performance. More importantly, the formations and effects of short-circuit flow, circulation flow, and axial velocity wave zone (AVWZ) were investigated and understood. The simulation results were analyzed in terms of pressure drop, water velocity, separation efficiency, and particle distribution. The results indicate that a thicker vortex finder wall could reduce pressure drop, tangential velocity magnitudes, and the flow rates of both short-circuit flow and circulation flow but increase the fluctuations of axial and radial velocities especially beneath the vortex finder where the AVWZ is formed. The leakage effect of short-circuit flow on sub-coarse particles is less significant than the fluctuation effect of AVWZ. The circulation flow in pre-separation space is beneficial to re-separate the sub-fine and sub-coarse particles to improve the separation sharpness. Consequently, the hydrocyclone with a thin-walled vortex finder is more beneficial for efficient classification.

Consequence assessment of explosions for fuel-air mixtures at hazardous production facilities

The article reviewed one of the known accidents with explosions of fuel assemblies both in domestic and foreign enterprises, and analyzed the causes of its occurrence. With the help of several computational methods, the sizes of the zones of air-shock wave (ASW) were determined and compared with the “real” data, and situational plans with zones of destruction were constructed.

Dynamics of inhomogeneous elastic half-space under moving load

Wave processes in an elastic half-space covered with an elastic layer and (or) a thin elastic plate are considered in the paper. External load moves along the free surface. In the stationary statement, the waveguide properties of the system are determined. The multiple roots of the dispersion equations are revealed and the critical load velocities, leading to the initiation of resonant processes, are determined. In the case when the load moves with the velocity of the Rayleigh wave, additional resonances determined by the structure can be realized in the structure under consideration. It is revealed that Rayleigh resonance exists for long waves only. Numerical solutions are obtained that make it possible to trace the development of resonant excitations. The models of simple structures that have dispersive properties in the medium wave zone are analyzed, such as a thin plate on an elastic base; a model with an attached inertial medium. Analytical solutions have been obtained for these models. Computer simulations conducted simultaneously allow us to analyze the quantitative features of process throughout the entire time period of the load effect. The numerical and asymptotic solutions are compared.

VALIDATION OF UNSTRUCTURED WAVEWATCH III FOR NEARSHORE WAVES

Unstructured wave model grids in the nearshore coastal region provide flexibility and efficiency to resolve complex shorelines and high-gradient wave zones to drive nearshore circulation, wave setup and wave-driven sediment transport. Recent improvements to the unstructured version of WAVEWATCH III (WW3) (WW3DG 2016) to support nearshore application include an implicit solution scheme and domain decomposition for multi-scale spatial coverage over approximately three orders of magnitude. The hybrid approach to parallelization involves spectral partitioning for advection in geographical space and domain decomposition for spectral advection and the source term integration. The advection part of wave action equation is integrated fully implicitly, and a new convergent action limiter derived from Komen et al. (1994) and Hersbach and Janssen (1999) is applied. New Block-Jacobi and Block-Gauss-Seidel solvers are applied with improved convergence. The purpose of this paper is to evaluate the upgraded unstructured WW3 for nearshore application.

Effect of the Annular Multi‐Point Initiation Control Parameters on Jet Formation

AbstractThis work investigates the application of an annular multi‐point initiation explosive network to a jet‐shaped charge. The Whitham method was employed to calculate the pressure and region of the Mach wave zone at different initiation diameters. LS‐DYNA software was used to investigate the effects of the control parameters for the annular multi‐point initiation (i. e., number of initiation points, initiation diameter and initiation synchronicity error) on the performance of the jet (i. e., formation and tip velocity). Results indicated that when there are eight or more initiation points, the jet formed under the multi‐point initiation is similar to the result for a peripherally initiated charge. As the initiation diameter increased, the range of the Mach wave zone decreased in size, but the pressure of the Mach wave and the length and the tip velocity of the jet increased, aiding the formation of the jet, increasing the jet penetration capability and improving the utilization rate of the shaped charge.

On the wave zone of synchrotron radiation.

The extension of the wave zone of synchrotron radiation is studied.

On choosing the start time of binary black hole ringdowns

The final stage of a binary black hole merger is ringdown, in which the system is described by a Kerr black hole with quasinormal mode perturbations. It is far from straightforward to identify the time at which the ringdown begins. Yet determining this time is important for precision tests of the general theory of relativity that compare an observed signal with quasinormal mode descriptions of the ringdown, such as tests of the no-hair theorem. We present an algorithmic method to analyze the choice of ringdown start time in the observed waveform. This method is based on determining how close the strong field is to a Kerr black hole (Kerrness). Using numerical relativity simulations, we characterize the Kerrness of the strong-field region close to the black hole using a set of local, gauge-invariant geometric and algebraic conditions that measure local isometry to Kerr. We produce a map that associates each time in the gravitational waveform with a value of each of these Kerrness measures; this map is produced by following outgoing null characteristics from the strong and near-field regions to the wave zone. We perform this analysis on a numerical relativity simulation with parameters consistent with GW150914- the first gravitational wave detection. We find that the choice of ringdown start time of $3\,\mathrm{ms}$ after merger used in the GW150914 study to test general relativity corresponds to a high dimensionless perturbation amplitude of $ \sim 7.5 \times 10^{-3}$ in the strong-field region. This suggests that in higher signal-to-noise detections, one would need to start analyzing the signal at a later time for studies that depend on the validity of black hole perturbation theory.