Perpendicular Wave Research Articles

Processes controlling the dispersion and beaching of floating marine debris in the Barcelona coastal region

IntroductionCoastal areas are considered potential sinks for plastic in marine environments. Data from a Lagrangian numerical simulation at a coastal scale using high-resolution hydrodynamic information and observational data of river debris discharge were analysed to determine the environmental variables from meteorological forcing or coastline orientation contributing to particle beaching.MethodA beaching likelihood parameter was developed to quantitatively measure the propensity for an area to receive or accumulate particles from a known outflow source. Statistical analyses of particle beaching were conducted to reveal possible relationships with hydrodynamic variables. A debris mass budget was calculated from the river release observational data used in the simulation.ResultsAreas close to the release points received the highest amounts of particles and also registered the highest beaching likelihood values. Significant wave height mildly affected particle beaching (Pearson’s r=0.36). Relative perpendicular wave directions promoted beaching in coastlines with lower azimuths (vertical orientation), whereas those with higher azimuths (horizontal orientation) were more affected by relative alongshore wave directions. The mass contribution from river discharge on beaches where cleanup data was available was 6.0% of the total debris collected.DiscussionThe beaching likelihood parameter revealed the influence of coastal geometry on particle deposition in an area. Comparisons with other studies regarding beaching amounts and particle residence times are challenging due to the scale difference. The complexity of the beaching process makes it difficult to establish relationships with hydrodynamic variables, although a clear association between the coastline orientation and wave direction was established. The debris mass contribution from the two rivers included in the simulation was two orders of magnitude lower than indicated in other studies for the area.

Hydrodynamic Performance of Half Pipe Breakwaters Experimentally and Numerically

The main objective of constructing barriers is to safeguard harbours and shores from waves and sea currents. This paper aims at presenting a study on innovative and non-traditional alternatives to breakwaters, experimentally and numerically, to assess the hydrodynamic efficiency of the suggested models in order to choose the most appropriate one. Two models of semi-submersible-type breakwaters have been studied, in the form of a cross-section of a half pipe with an internal diameter and thickness of 30.00 and 1.00 cm, respectively. Model (a) is a circular half-pipe with an upward concave, whereas model (b) has a sideways concave towards the water. Several scenarios for the breakwaters suggested in this study have been simulated using FLOW 3D. The results indicate that the transmission coefficient (Tc), provided by model (b), is 3-7% lower than model (a), while the reflection coefficient (Rc) values for model (b) are 4-8% higher than model (a). The results show that model (b) has a 10% lower (Tc) at d/h = 0.80 compared to d/h = 0.60, while (Rc) is 8% higher at d/h = 0.80 than at d/h = 0.60 for the same model. The suggested breakwater reduces inclined waves' energy more quickly than perpendicular waves. Regarding the hydrodynamic performance, the proposed breakwater in model (b) is shown to be more efficient and effective than the breakwater in model (a), so it is recommended to use it due to its effectiveness in providing protection for coastal wave zones and benefiting from the energy of waves to generate electricity.

Vortex Motion on the Surface of Shallow and Deep Water

The attenuation of vortex motion on the surface of shallow and deep water is investigated. The vortex flow was formed by two mutually perpendicular waves excited by plungers at a frequency of 6 Hz (wavelength λ = 5.6 cm) on the surface of water measuring 70 × 70 cm and depth h. After reaching a stationary state in the vortex system, the wave pumping was switched off, and the attenuation of the surface flow was recorded. On the surface of shallow water, λ/2π ≈ h, when the characteristic size of the vortices L exceeds the depth of the liquid, L h, the time dependence of the energy of the vortex flow Е(t) is described by an exponential function at all pumping levels, and the dependence of the enstrophy Ф(t) = Ω2(t) has an exponential dependence only in the range of wave vectors 0–0.3 см–1. On the surface of deep water λ/2π h, L ≈ h dependence Е(t) and Ф(t) are far from exponential in all ranges of wave numbers. At high pumping levels, the dependencies Е(t) and Ф(t) are nonmonotonic, which can be attributed to the influence of volumetric flows.

High-latitude Observations of Dissipation-range Turbulence by the Ulysses Spacecraft during the Solar Minimum of 1993–96: The Spectral Break and Anisotropy

We examine Ulysses magnetic field observations from 1993 to 1996 as the spacecraft made its first fast-latitude scan from the southern to the northern hemisphere. Most of the observations we use are representative of high-latitude solar minimum conditions. We examine magnetic field power spectra characteristics of interplanetary turbulence at high frequencies, where the spectrum breaks from an inertial range into the ion dissipation range. The onset and spectral index of the dissipation spectrum are consistent with low-latitude observations at 1 au. Both ranges have a ratio of power in perpendicular magnetic field components to parallel components near 3. The power spectrum ratio test developed by Bieber et al. for single-spacecraft analyses that determines the underlying anisotropy of the wave vectors yields only marginally more energy associated with field-aligned wave vectors than perpendicular wave vectors when comparing the inertial and dissipation-range spectra. The lack of significant change in the anisotropies between the inertial and dissipation ranges contrasts strongly with the turbulence found typically for 1 au near-ecliptic observations, where significant differences in both anisotropies are observed.

Gyrokinetic linear simulation of feedback instability in dipole magnetosphere

We perform a novel linear simulation of the feedback instability by applying a gyrokinetic model to the magnetosphere, where the geomagnetic field is modeled by a dipole magnetic field. In order to avoid huge numerical calculation costs, the effect of the fluctuating mirror force is neglected. It is found that kinetic effects, such as the finite Larmor radius effect and the electron Landau damping, strongly stabilize the feedback instability and form a peak in the perpendicular wave number spectrum of the growth rate. During the linear growth, it is observed that electron free energy has a much larger value than the electromagnetic field perturbation energy. Since such large electron free energy may lead to electron heating and acceleration, it is important to understand its generation mechanism. Analyses based on the energy conservation reveal that the coupling of the non-uniformity of the equilibrium fields along the geomagnetic field and the fluctuating electron distribution gives rise to thermodynamic power generating the electron free energy. A fine velocity space structure around an average Alfvén velocity of the fluctuating electron distribution mainly contributes to drive the thermodynamic power.

Theoretical investigation on a heaving wave energy converter-dual-arc breakwater integration system array

The hydrodynamic performance of an array of heaving wave energy converter (WEC)-dual-arc breakwater integration systems was investigated using a theoretical model in the present paper based on the potential flow theory, with each dual-arc breakwater consisting of a bottom-mounted inner solid and outer perforated arc-shaped cylinder. The multiple scattering problem was solved using a hybrid iterative method. The mean transmission coefficient was introduced to quantify the wave attenuation performance. After successfully validating the theoretical model, the array effect and the hydrodynamic characteristics of the proposed integration system array are investigated. Focusing on the layout of a linear equidistant column, the calculation results indicate that the WEC and dual-arc breakwater array have mutual benefits in enhancing the wave energy extraction and wave attenuation performance. Compared to an array of bottom-mounted solid and porous cylinders, the proposed integration system array provides much better protection to the leeward region except at a very low wave frequency. In the considered frequency region, a closely arranged integration system array under the perpendicular incident waves has a very constructive array effect on the overall performance. For two staggered columns of integration systems, the wave energy absorption of the leeward column is improved and the sheltering effect to the leeward region is better at a high frequency as compared to the one-column layout; in contrast, the overall performance for two aligned columns is better at a low frequency.

Duality of a coiled phononic crystal enables reflectionless interfaces

Recently, it has been demonstrated that one-dimensional bar-based phononic crystals can exhibit subwavelength Bragg bandgaps by coiling the bars and locking the nodal rotational degrees of freedom to create what is termed a coiled phononic crystal (CPnC) [C. L. Willey et al., Phys. Rev. Appl. 18, 014035 (2022)]. Here, it is shown that the CPnC exhibits duality of its dispersion curves relative to its coiling/twist angle, meaning that the dispersion curves are symmetric about a particular coiling/twist angle defined configuration. An exciting implication of this finding is that under a certain set of constraints, segments of dual unit cells with perpendicular wave propagation directions can be connected such that their wave transmission is equivalent to a finite CPnC entirely composed of identical unit cells with parallel wave propagation directions. The ability to link unit cells with different wave propagation orientations, but the same dispersion/dynamic stiffness, is used to create an elastic hierarchically coiled phononic crystal based on a fractal space-filling curve design. The novelty of this work is that it numerically demonstrates reflectionless wave propagation in large fractal architectures (created from specific combinations of dual unit cells) such that regular phononic properties (i.e., passbands and bandgaps) are preserved, allowing for propagation of broadband signals and filtering.

Migration of Fast Magnetosonic Waves in the Magnetosphere With a Plasmaspheric Plume

AbstractPlasmaspheric density structures are considered to control the propagation trajectories of fast magnetosonic (MS) waves in the inner magnetosphere. However, whether the plasmaspheric plume can effectively alter the propagation of MS waves remains unknown. Based on the analytical model of plasma density, ray tracing simulations are performed to investigate the propagation of exactly perpendicular MS waves in the equatorial plane in the magnetosphere containing a plasmaspheric plume. We find that plasmatrough and plume MS waves propagating toward the plasmaspheric plume can be reflected into the plasmaspheric core by the plume, then potentially migrating globally and thus quasi‐trapped inside the plasmaspheric core. The simulations also indicate that lower‐frequency MS waves approaching the plasmaspheric plume are more easily reflected and quasi‐trapped inside the plasmaspheric core. Our findings illustrate a previously unexplored way that plasmatrough MS waves could access and be trapped inside the plasmaspheric core via azimuthal plasmaspheric density structures.

Small-amplitude Compressible Magnetohydrodynamic Turbulence Modulated by Collisionless Damping in Earth’s Magnetosheath: Observation Matches Theory

Plasma turbulence is a ubiquitous dynamical process that transfers energy across many spatial and temporal scales and affects energetic particle transport. Recent advances in the understanding of compressible magnetohydrodynamic (MHD) turbulence demonstrate the important role of damping in shaping energy distributions on small scales, yet its observational evidence is still lacking. This study provides the first observational evidence of substantial collisionless damping (CD) modulation on the small-amplitude compressible MHD turbulence cascade in Earth’s magnetosheath using four Cluster spacecraft. Based on an improved compressible MHD decomposition algorithm, turbulence is decomposed into three eigenmodes: incompressible Alfvén modes and compressible slow and fast (magnetosonic) modes. Our observations demonstrate that CD enhances the anisotropy of compressible MHD modes because CD has a strong dependence on wave propagation angle. The wavenumber distributions of slow modes are mainly stretched perpendicular to the background magnetic field ( B 0) and weakly modulated by CD. In contrast, fast modes are subjected to a more significant CD modulation. Fast modes exhibit a weak, scale-independent anisotropy above the CD truncation scale. Below the CD truncation scale, the anisotropy of fast modes enhances as wavenumbers increase. As a result, fast-mode fractions in the total energy of compressible modes decrease with the increase of perpendicular wavenumber (to B 0) or wave propagation angle. Our findings reveal how the turbulence cascade is shaped by CD and its consequences for anisotropies in the space environment.

Generation of Quantum Vortices by Waves on the Surface of Superfluid Helium

The formation of quantum vortices by two mutually perpendicular waves excited on the surface of superfluid helium has been observed. The interaction of negative charges injected under the surface of He-II with the vortex flow of the liquid, which is formed by surface waves at frequencies from 20 to 49.9 Hz, in the temperature range of 1.5–2.17 K has been studied experimentally by analyzing the current distribution detected by vertically oriented segments of a receiving collector. The efficient capture of injected charges by quantum vortices has been observed at a temperature ofT= 1.5 K, which leads to a significant redistribution of currents between segments of the receiving collector. Charges leave traps on quantum vortices at temperatures nearT= 1.7 K. With a further increase in the temperature, injected charges are scattered on vortex flows of the normal component, which are generated by surface waves.

Generation of Quantum Vortices by Waves on the Surface of Superfluid Helium

The formation of quantum vortices by two mutually perpendicular waves excited on the surface of superfluid helium has been observed. The interaction of negative charges injected under the surface of He-II with the vortex flow of the liquid, which is formed by surface waves at frequencies from 20 to 49.9 Hz, in the temperature range of 1.5–2.17 K has been studied experimentally by analyzing the current distribution detected by vertically oriented segments of a receiving collector. The efficient capture of injected charges by quantum vortices has been observed at a temperature of T = 1.5 K, which leads to a significant redistribution of currents between segments of the receiving collector. Charges leave traps on quantum vortices at temperatures near T = 1.7 K. With a further increase in the temperature, injected charges are scattered on vortex flows of the normal component, which are generated by surface waves.

STABILITY OF RUBBLE MOUND STRUCTURES UNDER OBLIQUE WAVE ATTACK

Stability formulae for armour layers of rubble mound breakwaters are generally developed for perpendicular wave attack and do not include effects of oblique waves. Waves usually attack breakwater obliquely as the sea wave is three dimensional. Several studies have been performed to investigate the effect of wave angle (beta) on the armor stability. Galland (1994), Yu et al. (2002), Wolters and Van Gent (2010) and van Gent (2014) performed laboratory experiments to consider effects of oblique waves on the stability of armour layers. They performed tests with long-crested and/or short-crested waves on rock and concrete armours. The aim of this study is to find an appropriate and compatible reduction factor for EBV stability formulae.

ETG turbulence in a tokamak pedestal

This paper explores the fundamental characteristics of electron-temperature-gradient (ETG)-driven turbulence in the tokamak pedestal. The extreme gradients in the pedestal produce linear instabilities and nonlinear turbulence that are distinct from the corresponding ETG phenomenology in the core plasma. The linear system exhibits multiple (greater than ten) unstable eigenmodes at each perpendicular wave vector, representing different toroidal and slab branches of the ETG instability. Proper orthogonal decomposition of the nonlinear fluctuations reveals no clear one-to-one correspondence between the linear and nonlinear modes for most wave vectors. Moreover, nonlinear frequencies deviate strongly from those of the linear instabilities, with spectra peaking at positive frequencies, which is opposite the sign of the ETG instability. The picture that emerges is one in which the linear properties are preserved only in a narrow range of k-space. Outside this range, nonlinear processes produce strong deviations from both the linear frequencies and eigenmode structures. This is interpreted in the context of critical balance, which enforces alignment between the parallel scales and fluctuation frequencies. We also investigate the nonlinear saturation processes. We observe a direct energy cascade from the injection scale to smaller scales in both perpendicular directions. However, in the bi-normal direction, there is also nonlocal inverse energy transfer to larger scales. Neither streamers nor zonal flows dominate the saturation.

Harnessing Skyrmion Hall Effect by Thickness Gradients in Wedge-Shaped Samples of Cubic Helimagnets.

The skyrmion Hall effect, which is regarded as a significant hurdle for skyrmion implementation in thin-film racetrack devices, is theoretically shown to be suppressed in wedge-shaped nanostructures of cubic helimagnets. Under an applied electric current, ordinary isolated skyrmions with the topological charge 1 were found to move along the straight trajectories parallel to the wedge boundaries. Depending on the current density, such skyrmion tracks are located at different thicknesses uphill along the wedge. Numerical simulations show that such an equilibrium is achieved due to the balance between the Magnus force, which instigates skyrmion shift towards the wedge elevation, and the force, which restores the skyrmion position near the sharp wedge boundary due to the minimum of the edge-skyrmion interaction potential. Current-driven dynamics is found to be highly non-linear and to rest on the internal properties of isolated skyrmions in wedge geometries; both the skyrmion size and the helicity are modified in a non-trivial way with an increasing sample thickness. In addition, we supplement the well-known theoretical phase diagram of states in thin layers of chiral magnets with new characteristic lines; in particular, we demonstrate the second-order phase transition between the helical and conical phases with mutually perpendicular wave vectors. Our results are useful from both the fundamental point of view, since they systematize the internal properties of isolated skyrmions, and from the point of view of applications, since they point to the parameter region, where the skyrmion dynamics could be utilized.

Numerical study on dynamic analysis of a nine-module floating aquaculture platform under irregular waves

A numerical study of the dynamics of a nine-module floating aquaculture platform in irregular waves is proposed, to examine the effect of the connector type between net cages and incident wave direction on the hydrodynamic response. A numerical model based on the coupled boundary element method and lumped-mass model was used to simulate the dynamic behavior of the aquaculture platform. Time-domain statistical analysis, and time-frequency analysis based on Hilbert-Huang transform on the motion responses of net cages and the mooring force responses of the platform were then carried out. The results indicate that the mooring system has a decisive influence on the frequency-domain characteristics of surge motion, while the influence of connector can be ignored. The surge motion under flexible hawser connector is less sensitive to wave incident direction, while the wave direction has a greater impact on surge motion under spherical joint connector. The amplitudes of pitch motion under two different connectors decrease significantly under oblique incident waves, compared with perpendicular incident wave condition. The wave incident direction has little effect on the overall mooring force response of the platform. The mooring force responses at different positions show completely different frequency characteristics when the cages are connected by spherical joints. The larger the pitch response of the cage, the smaller the mooring force response of the mooring chain connected to the net cage. There is a positive correlation between the gravity frequency of the mooring force response and the gravity frequency of the pitch response of the net cage.

On the Stability of Rubble Mound Structures under Oblique Wave Attack

Slope stability formulae for rubble mound structures are usually developed for head-on conditions. Often, the effects of oblique waves are neglected, mainly because it is assumed that for oblique wave attack, the reduction in damage compared to perpendicular wave attack is insignificant. When the incident waves are oblique, the required armour size can be reduced compared to the perpendicular wave attack case. Therefore, it is important to consider the wave obliquity influence on slope stability formulae as a reduction factor. One of the most recent formulae for estimating the stability of rock-armoured slopes, referred to as Etemad-Shahidi et al. (2020), was proposed for perpendicular wave attack. The aim of this study is to develop a suitable wave obliquity reduction factor for the above-mentioned stability formula. To achieve this, first, laboratory experiment datasets from existing reliable studies were selected and analysed. Then, previously suggested reduction factors were evaluated and a suitable reduction factor for the mentioned stability formula were suggested. The suggested reduction factor includes the effect of wave obliquity and directional spreading explicitly. It is shown that the stability prediction is improved by using the wave obliquity reduction factor.

About definition of modes and magnetosonic heating in a plasma's flow: Especial cases of perpendicular and nearly perpendicular wave vector and magnetic field

AbstractDynamics of hydrodynamic perturbations in a plasma depend strongly on an angle between the wave vector and equilibrium straight magnetic field. The case of perpendicular propagation is especial. There are only two (fast) magnetosonic modes since two (slow) ones degenerate into the stationary one with zero speed of propagation. This demands individual definition of wave modes by the links of hydrodynamic relations. These links are not limiting case of the relations in the case of non‐zero angle. The nonlinear excitation of the entropy mode in the field of intense magnetosonic perturbations is also unusual. Bulk and shear viscosity and thermal conduction are considered as the damping mechanisms in a weakly nonlinear flow. The leading‐order dynamic equation is derived which governs perturbation of density in the entropy mode. The links of magnetosonic perturbations and magnetosonic heating may be indicators of plasma‐, geometry of a flow, damping coefficients and type of wave motion. The “almost resonant” character of magnetosonic heating excited by the slow magnetosonic wave in the course of nearly perpendicular wave propagation, is discussed.

Generation of an obliquely propagating shear alfven wave in dusty plasma by an ion beam

AbstractIon beam‐dusty plasma interaction leads to significant changes in the dispersion relation of shear Alfven wave depending on the beam, dust grain, and plasma parameters. Hydrogen ion beam particles interact with the shear Alfven wave via cyclotron interaction when they counter‐propagate with the wave and they can also interact with the co‐propagating wave via Cerenkov interaction. The interaction causes beam as well as plasma density fluctuations and gives rise to perpendicular currents. We have analytically obtained the dispersion relation and the growth/damping rate expressions for obliquely propagating shear Alfven waves in dusty plasma. The effect of beam velocity, magnetic field, wave number, dust particle density, and dust charge fluctuations are discussed. It is shown that both the wave frequency and the maximum growth rate decrease with an increase in beam velocity and the variations are different for parallel and perpendicular wave numbers. The dust particles enhance the frequency and maximum growth rate while the dust charge fluctuations induce damping. The results are in good agreement with the experimental observations.

Large Anomalous Frequency Shift in Perpendicular Standing Spin Wave Modes in BiYIG Films Induced by Thin Metallic Overlayers.

Interface-driven effects on magnon dynamics are studied in magnetic insulator-metal bilayers using Brillouin light scattering. It is found that the Damon-Eshbach modes exhibit a significant frequency shift due to interfacial anisotropy generated by thin metallic overlayers. In addition, an unexpectedly large shift in the perpendicular standing spin wave mode frequencies is also observed, which cannot be explained by anisotropy-induced mode stiffening or surface pinning. Rather, it is suggested that additional confinement may result from spin pumping at the insulator-metal interface, which results in a locally overdamped interface region. These results uncover previously unidentified interface-driven changes in magnetization dynamics that may be exploited to locally control and modulate magnonic properties in thin-film heterostructures.

Non-Hydrostatic Modelling of Coastal Flooding in Port Environments

Understanding key flooding processes such as wave overtopping and overflow (i.e., water flows over a structure when the crest level of the structure is lower than the water level in front) is crucial for coastal management and coastal safety assessment. In port and harbour environments, waves are not only perpendicular to the coastal structure but also very oblique, with wavefronts almost perpendicular to the main infrastructures in the harbour docks. Propagation and wave–structure interaction of such perpendicular and (very) oblique waves need to be appropriately modelled to estimate wave overtopping properly. Overflow can also be critical for estimating flooding behind any coastal defence. In this study, such oblique and parallel waves (i.e., main wave direction is parallel to the structures) are modelled in a non-hydrostatic wave model and validated with physical model tests in the literature. On top, overflow is also modelled and validated using an existing empirical formula. The model gives convincing behaviours on the wave overtopping and overflow.