Real Wave Research Articles

Validation and calibration of partitioned integral ocean wave parameters from co-polarized synthetic aperture radar data

The inversion of wave spectrum is the embodiment of the fine observation of ocean swells by synthetic aperture radar. Due to the nonlinear distortion from velocity bunching, the operational Sentinel-1 Wave Mode (WV) level-2 (L2) Ocean (OCN) wave products retrieved by quasi-linear inversion are still quite different from the real wave spectrum, requiring further calibration. Limited by the azimuth cut-off, the quasi-linear inversed wave spectrum mostly concentrates on swells with a wavelength longer than 150 m. 2D spectral partitioning separates different swell systems, denoted as partitions in the Sentinel-1 WV L2 OCN product. We compared and calibrated the Sentinel-1 WV L2 OCN products' swell partitions (More specifically partitioned integral ocean wave parameters: partitioned wave height, partitioned wavelength, and partitioned wave direction) with WAVEWATCH III (WW3) in different polarization modes (HH and VV polarization) and different incidence angles (∼23°-WV1 and ∼ 36°-WV2). The accuracy of swell partitions in the OCN products varies with peak wave direction relative to the Sentinel-1 flight direction, and it is difficult to calibrate the partitions derived from quasi-linear inversion unless deleting partitions severely distorted by nonlinearity and large-scale features. A machine learning method is proposed to calibrate the wave partitions. Spectral distances of collocated Sentinel-1 and WW3 partition pairs larger than two are considered “bad” partitions to be filtered. Inputting high-dimensional features (twenty-one features) derived from Sentinel-1 WV L2 OCN products into the extreme gradient boosting (XGBoost) model can effectively reduce the bias (root-mean-square error, RMSE) of significant wave height (SWH) of all the partitions from ∼0.10 m (∼0.70 m) to ∼0.00 m (∼0.46 m) and the bias (RMSE) of wavelengths of all the partitions from ∼20 m (∼35 m) to ∼0.20 m (∼26 m) compared with WW3 swell partitions. This method improves the precision of the wave partition and retains more partitions in the Sentinel-1 WV L2 OCN products than previous studies, especially for wave partitions with moderate wave height (< 4 m), potentially improving the understanding of swell dynamics globally.

Ab initio calculation of muon capture on Mg24

In this work we study ordinary muon capture (OMC) on $^{24}$Mg from a first principles perspective. Starting from a particular two- and three-nucleon interaction derived from chiral effective field theory, we use the valence-space in-medium similarity renormalization group (VS-IMSRG) framework to construct effective Hamiltonians and muon-capture operators which nonperturbatively account for many-body physics outside the valence space. The obtained nuclear matrix elements are compared against those from the phenomenological shell model. The impact of including the correlations from the nuclear shell model (NSM) as well as including the induced two-body part is studied in detail. Furthermore, the effects of realistic bound-muon wave function on the operators is studied. Finally, predictions for capture rates to the lowest excited states in $^{24}$Na are given and compared with available data. It is found that the spectroscopic properties of $^{24}$Mg and its OMC daughter $^{24}$Na are fairly well described by both the NSM and VS-IMSRG, and that the effect of the hadronic two-body currents significantly reduces the OMC rates. Both models have some difficulties in matching the measured OMC rates, especially for the $2^+$ final states. This calls for further studies in other light nuclei with available OMC data.

Fragility analysis of nuclear power plant structure under real and spectrum-compatible seismic waves considering soil-structure interaction effect

Both the real and spectrum-compatible seismic waves are widely used as input loads in the seismic assessment of critical structures in engineering applications, which are also allowed by international codes. However, the effect of the real seismic waves and spectrum-compatible seismic waves generated by different methods on the dynamic responses of structures has not been thoroughly emphasized. This study focused on quantitatively comparing the dynamic responses and fragility of the AP1000 nuclear power plant under real and spectrum-compatible seismic waves. Real and spectrum-compatible seismic waves generated by the modification and synthetic methods were used to perform the time history analysis. The effects of three input motion types on a high-accuracy soil–structure interaction system model were investigated based on various dynamic response indexes. The fragility assessment and maximum tension strain contours of the AP1000 nuclear power plant subjected to the three types of seismic waves were also presented to evaluate the influence of the input motions. The results revealed that spectrum-compatible seismic waves can cause larger dynamic responses than real seismic waves at the same peak ground acceleration level. Additionally, although some response indexes, such as strain energy, are sensitive to the input motions when the nuclear power plant is in a nonlinear state, the generation methods of spectrum-compatible seismic waves have insignificant effects on most dynamic response indexes, fragility assessment, and damaged zone locations.

Logarithmic catastrophes and Stokes’s phenomenon in waves at horizons

Waves propagating near an event horizon display interesting features including logarithmic phase singularities and caustics. We consider an acoustic horizon in a flowing Bose–Einstein condensate where the elementary excitations obey the Bogoliubov dispersion relation. In the Hamiltonian ray theory the solutions undergo a broken pitchfork bifurcation near the horizon and one might therefore expect the associated wave structure to be given by a Pearcey function, this being the universal wave function that dresses catastrophes with two control parameters. However, the wave function is in fact an Airy-type function supplemented by a logarithmic phase term, a novel type of wave catastrophe. Similar wave functions arise in aeroacoustic flows from jet engines, path integrals in radio astronomy, and also gravitational horizons if dispersion which violates Lorentz symmetry in the UV is included. The approach we take differs from most previous authors in that we analyze the behavior of the integral representation of the wave function using exponential coordinates. This allows for a different treatment of the branch cuts and gives rise to an analysis based purely on saddlepoint expansions. We are thereby able to resolve the multiple real and complex waves that interact at the horizon and its companion caustic. We find that the horizon is a physical manifestation of a Stokes surface, marking the place where a wave is born, and that the horizon and the caustic do not in general coincide: the finite spatial region between them delineates a broadened horizon.

LQG control for hydrodynamic compensation on large floating wind turbines

This work proposes a novel Linear Quadratic Gaussian (LQG)-based blade pitch control method for floating offshore wind turbines, in which a state-space model of the turbine and water hydrodynamics is included in the LQG design. The actuation considered is collective blade pitch control with the objective of generator power stabilisation and platform motion reduction. A linear Kalman filter is used to estimate un-measurable states relating to wave excitation and radiation through measurements of generator speed, platform pitch, and wind disturbance. Controller design models were validated with the full order nonlinear model under various testing conditions. The new controller design is tested on a nonlinear high-fidelity simulation model of the 15 Mega-Watt (MW) floating semi-submersible wind turbine. In simulations with realistic stochastic wind and wave disturbances, the new controller achieves 32% lower generator speed Root Mean Square Error (RMSE) and 16% lower platform pitch RMSE compared to a standard LQG controller that does not include hydrodynamic states, for equivalent levels of pitch actuation and with a 2°/sec rate limit on pitch. The inclusion of hydrodynamics in the controller design not only reduced platform pitching fluctuation, but also had a strong effect of hub-height factors such as the generator speed.

Simulating transport and distribution of marine macro-plastic in the Baltic Sea.

We simulated the spatial distribution and dynamics of macro plastic in the Baltic Sea, using a new Lagrangian approach called the dynamical renormalization resampling scheme (DRRS). This approach extends the super-individual simulation technique, so the weight-per-individual is dynamic rather than fixed. The simulations were based on a mapping of the macro plastic sources along the Baltic coast line, and a five year time series of realistic wind, wave and current data to resolve time-variability in the transport and spatial distribution of macro plastics in the Baltic Sea. The model setup has been validated against beach litter observations and was able to reproduce some major spatial trends in macroplastic distributions. We also simulated plastic dispersal using Green's functions (pollution plumes) for individual sources. e.g. rivers, and found a significant variation in the spatial range of Green's functions corresponding to different pollution sources. We determined a significant temporal variability (up to 7 times the average) in the plastic concentration locally, which needs to be taken into account when assessing the ecological impact of marine litter. Accumulation patterns and litter wave formation were observed to be driven by an interplay between positive buoyancy, coastal boundaries and varying directions of physical forcing. Finally we determined the range of wind drag coefficients for floating plastic, where the dynamics is mostly directly wind driven, as opposed to indirectly by surface currents and waves. This study suggests that patterns of litter sorting by transport processes should be observable in many coastal and off-shore environments.

Stationary Waves Weaken and Delay the Near-Surface Response to Stratospheric Ozone Depletion

Abstract An intermediate-complexity moist general circulation model is used to investigate the factors controlling the magnitude of the surface impact from Southern Hemisphere springtime ozone depletion. In contrast to previous idealized studies, a model with full radiation is used; furthermore, the model can be run with a varied representation of the surface, from a zonally uniform aquaplanet to a configuration with realistic stationary waves. The model captures the observed summertime positive Southern Annular Mode response to stratospheric ozone depletion. While synoptic waves dominate the long-term poleward jet shift, the initial response includes changes in planetary waves that simultaneously moderate the polar cap cooling (i.e., a negative feedback) and also constitute nearly one-half of the initial momentum flux response that shifts the jet poleward. The net effect is that stationary waves weaken the circulation response to ozone depletion in both the stratosphere and troposphere and also delay the response until summer rather than spring when ozone depletion peaks. It is also found that Antarctic surface cooling in response to ozone depletion helps to strengthen the poleward shift; however, shortwave surface effects of ozone are not critical. These surface temperature and stationary wave feedbacks are strong enough to overwhelm the previously recognized jet latitude/persistence feedback, potentially explaining why some recent comprehensive models do not exhibit a clear relationship between jet latitude/persistence and the magnitude of the response to ozone. The jet response is shown to be linear with respect to the magnitude of the imposed stratospheric perturbation, demonstrating the usefulness of interannual variability in ozone depletion for subseasonal forecasting.

Half-plane diffraction problems on a triangular lattice

We investigate thin-slit diffraction problems for two-dimensional lattice waves. Namely, Dirichlet problems for the two-dimensional discrete Helmholtz equation on the triangular lattice in a half-plane are studied. Using the notion of the radiating solution, we prove the existence and uniqueness of a solution for the real wave number $$k\in (0,3)\backslash \{2\sqrt{2}\}$$ without passing to the complex wave number. Besides, an exact representation formula for the solution is derived. Here, we develop a numerical calculation method and demonstrate by example the effectiveness of our approach related to the propagation of wavefronts in metamaterials through two small openings.

Photon Structure and Wave Function from the Vector Potential Quantization

A photon structure is advanced based on the experimental evidence and the vector potential quantization at a single photon level. It is shown that the photon is neither a point particle nor an infinite wave but behaves rather like a local “wave-corpuscle” extended over a wavelength, occupying a minimum quantization volume and guided by a non-local vector potential real wave function. The quantized vector potential oscillates over a wavelength with circular left or right polarization giving birth to orthogonal magnetic and electric fields whose amplitudes are proportional to the square of the frequency. The energy and momentum are carried by the local wave-corpuscle guided by the non-local vector potential wave function suitably normalized.

Theoretical study on photodissociation dynamics of vibrational excited states of H2S in the first absorption band

The photodissociation quantum dynamics for the first absorption band of H2S in different initial vibrational states have been investigated using Chebyshev real wave packet method. Because of the difference of the wave functions for the initial vibrational states, the calculated absorption spectra and the distributions of vibrational and rotational state of the products display different dynamic characteristics. The width and peak position of the absorption spectra for initial stretching excited states (1,0,0) and (0,0,1) are different from that of the vibrational ground state, while the (0,1,0) vibrational state has two almost equally high peaks in its absorption spectrum because of the change of wave function in angular coordinate. The product vibrational state distribution for (0,1,0) initial state weakly depends on the excitation energy and is dominated by the products of v=0, but SH(v=1) fragment is dominant at lower energy for (1,0,0) and (0,0,1) vibrational states. The rotational state distributions of products are very cold with the peak at j=l for these four states and weakly depend on the total energy. Besides, the rotational state distribution from (0,1,0) vibrational state displays strong oscillation, and its anisotropic parameter with rotational quantum numbers is also different from that of the other three vibrational states.

On the wave height distribution of waves and wave packets around a reef lagoon of the South China Sea

The wave height distributions of raw waves and wave packets around a reef lagoon of the South China Sea are discussed in this paper. The wave height ratio ρ=H3/m0 is used to assess how far the real wave height distribution deviates from the Rayleigh distribution. The results demonstrate a tendency for raw wave height ratios to decline with the steepness μ=kzHs when μ<0.2, where kz is the wave number referred to the mean zero-cross period Tz based on the linear dispersion relation. The connection, however, is rather shaky. On the other hand, the relative entropy εe, which describes the spectral bandwidth, appears to control the wave height ratios ρ. The variational mode decomposition approach is then used to separate the original raw waves into separate wave packets. Meanwhile, the influence of the relative entropy on ρ is eliminated. With respect to the wave packets, ρ decreases with μ. Based on observations, an empirical relationship between ρ and μ is proposed, and a modified Rayleigh distribution (MRD) is also put forward. MRD model accurately predicts the observations when H2/m0<20.

Wave condition preview assisted real-time nonlinear predictive control of point-absorbing wave energy converter based on long short-term memory recurrent neural identification

A real-time nonlinear model predictive controller is presented for point-absorbing wave energy converter (PA-WEC) to maintain the optimal wave energy extraction by tracking the reference PA-WEC velocity. In order to reduce computational cost, the predictive controller is designed using wave condition preview and the Taylor series expansion based nonlinear optimization to determine the q-axis current control signals while the constraints on both the device velocity and q-axis current are respected. The dynamics of the PA-WEC is modeled and details of the nonlinear model predictive controller are presented. A pragmatic method is proposed to obtain the optimal reference PA-WEC velocity by observing the time instants when the excitation force passes a threshold. A long short-term memory recurrent neural network (LSTM-RNN) identifier is designed to identify the wave condition term for implementing the controller. The overall stability of the closed control system including the predictive control and the LSTM-RNN identifier is proved. The proposed nonlinear predictive controller is validated under realistic wave conditions. The results indicate that the proposed control allows higher PA-WEC power production than the conventional control under representative irregular wave conditions.

Proposed Experiments to Clarify the Real Nature of the Quantum Waves

The nature of quantum waves, whether they are real physical waves or, on the contrary, mere probability waves, has been a very controversial theme since the beginning of quantum theory. Here we present some possible experiments that may clarify the problem.

Coherent J/ψ Electroproduction on He4 and He3 at the Electron-Ion Collider: Probing Nuclear Shadowing One Nucleon at a Time

While the phenomenon of gluon nuclear shadowing at small x has been getting confirmation in QCD analyses of various LHC measurements involving heavy nuclei, it has not been possible so far to establish experimentally the number of target nucleons responsible for nuclear shadowing in a given process. To address this issue, we study coherent J/ψ electroproduction on ^{4}He and ^{3}He in the kinematics of a future electron-ion collider and show that this process has the power to disentangle the contributions of the interaction with a specific number of nucleons k, in particular, with two nucleons at the momentum transfer t≠0. We predict a dramatic shift of the t dependence of the differential cross section toward smaller values of |t| due to a nontrivial correlation between x and k. This calculation, which makes use for the first time of realistic wave functions, provides a stringent test of models of nuclear shadowing and a novel probe of the 3D imaging of gluons in light nuclei. In addition, thanks to this analysis, unique information on the real part of the corresponding scattering amplitude could be accessed.

Equatorial waves resolved by balloon-borne Global Navigation Satellite System radio occultation in the Strateole-2 campaign

Abstract. Current climate models have difficulty representing realistic wave–mean flow interactions, partly because the contribution from waves with fine vertical scales is poorly known. There are few direct observations of these waves, and most models have difficulty resolving them. This observational challenge cannot be addressed by satellite or sparse ground-based methods. The Strateole-2 long-duration stratospheric superpressure balloons that float with the horizontal wind on constant-density surfaces provide a unique platform for wave observations across a broad range of spatial and temporal scales. For the first time, balloon-borne Global Navigation Satellite System (GNSS) radio occultation (RO) is used to provide high-vertical-resolution equatorial wave observations. By tracking navigation signal refractive delays from GPS satellites near the horizon, 40–50 temperature profiles were retrieved daily, from balloon flight altitude (∼20 km) down to 6–8 km altitude, forming an orthogonal pattern of observations over a broad area (±400–500 km) surrounding the flight track. The refractivity profiles show an excellent agreement of better than 0.2 % with co-located radiosonde, spaceborne COSMIC-2 RO, and reanalysis products. The 200–500 m vertical resolution and the spatial and temporal continuity of sampling make it possible to extract properties of Kelvin waves and gravity waves with vertical wavelengths as short as 2–3 km. The results illustrate the difference in the Kelvin wave period (20 vs. 16 d) in the Lagrangian versus ground-fixed reference and as much as a 20 % difference in amplitude compared to COSMIC-2, both of which impact estimates of momentum flux. A small dataset from the extra Galileo, GLONASS, and BeiDou constellations demonstrates the feasibility of nearly doubling the sampling density in planned follow-on campaigns when data with full equatorial coverage will contribute to a better estimate of wave forcing on the quasi-biennial oscillation (QBO) and improved QBO representation in models.

Numerical Analysis of the Available Power in an Overtopping Wave Energy Converter Subjected to a Sea State of the Coastal Region of Tramandaí, Brazil

The present work proposes a numerical study of an overtopping wave energy converter. The goal of this study is to evaluate the theoretical power that can be converted by an overtopping device subjected to sea waves in the coastal region of Tramandaí, Brazil. For this, realistic irregular waves were generated using the WaveMIMO methodology, which allows numerical simulation of sea waves through the imposition of transient discrete data as prescribed velocity. For the numerical analysis, a two-dimensional computational model was employed using Fluent, where the device was inserted into a wave channel. The volume of the fluid multiphase model was used for the treatment of the air–water interaction. The results indicated that the free surface elevation obtained using the WaveMIMO methodology, which converts a realistic sea state into a free surface elevation series, was adequately represented. The evaluation of the theoretical power of the overtopping device during around 45 min indicated that 471.28 W was obtained. In addition, a monthly generation projection showed that this device would supply 100% of the electricity demand of a school in the city of Tramandaí. These results demonstrated that the conversion of sea wave energy into electrical energy can contribute to supplying electricity demand, especially for coastal cities.

Small Scale CLTs for the Nodal Length of Monochromatic Waves

We consider Berry's random planar wave model (1977) for a positive Laplace eigenvalue $E>0$, both in the real and complex case, and prove limit theorems for the nodal statistics associated with a smooth compact domain, in the high-energy limit ($E\to \infty$). Our main result is that both the nodal length (real case) and the number of nodal intersections (complex case) verify a Central Limit Theorem, which is in sharp contrast with the non-Gaussian behaviour observed for real and complex arithmetic random waves on the flat $2$-torus, see Marinucci et al. (2016) and Dalmao et al. (2016). Our findings can be naturally reformulated in terms of the nodal statistics of a single random wave restricted to a compact domain diverging to the whole plane. As such, they can be fruitfully combined with the recent results by Canzani and Hanin (2016), in order to show that, at any point of isotropic scaling and for energy levels diverging sufficently fast, the nodal length of any Gaussian pullback monochromatic wave verifies a central limit theorem with the same scaling as Berry's model. As a remarkable byproduct of our analysis, we rigorously confirm the asymptotic behaviour for the variances of the nodal length and of the number of nodal intersections of isotropic random waves, as derived in Berry (2002).

Numerical simulation of borehole 3D scanning acoustic imaging using scattered waves

Oil and gas exploration increasingly requires high-resolution imaging of small, irregularly shaped, and highly heterogeneous well-side complex and abnormal geo-bodies. Conventional borehole acoustic imaging is often unable to accurately obtain the position and azimuth of small-scale abnormal geo-bodies. This study presents an inversion method that uses scattered waves for borehole 3D acoustic imaging and an implementation scheme that combines plane and spherical scanning imaging. The finite-difference time-domain method was used to simulate the acoustic fields for borehole azimuthal acoustic imaging of one and two caves next to a well. The proposed inversion method of 3D spatial scanning based on multi-mode wave information was validated through numerical simulations investigating the effect of different parameters on the imaging results. The simulation results show that the cave-scattered waves include the PP-, PS-, SP-, and SS-waves. When plane scanning imaging is performed based on a single wave mode, the other wave modes become interference factors. After the weighted processing of the PP-, PS-, SP-, and SS-waves, plane scanning imaging based on multi-mode scattered acoustic waves is shown to weaken pseudo-solutions, enhance the signal-to-noise ratio, and improve the radial and axial positioning accuracy of scatterers. When the scatterer is close to the borehole axis, the echo received by the receiver is not a real plane wave. In contrast with the 3D slowness time coherence (STC) and beamforming methods, spherical scanning imaging based on single-mode scattered acoustic waves completely considers this fact, which improves its azimuth positioning accuracy. Furthermore, spherical scanning imaging based on multi-mode scattered acoustic waves accurately estimates the azimuth of caves beside a well with a high imaging resolution. Finally, numerical simulation results were validated using the field measurement data of a well, and the actual imaging effect of the new method was tested. Therefore, rather than using single-mode reflected waves with limited information, the proposed method of scanning imaging using scattered acoustic waves can substantially improve the imaging resolution and positioning accuracy of small-scale abnormal geo-bodies beside a well and enhance the detection range.

Numerical Study of Influences of Onshore Wind on Hydrodynamic Processes of Solitary Wave over Fringing Reef

Many post-disaster surveys have reported on the natural function and effectiveness of fringing reef in preventing the shoreline from the inundation caused by severe weather events. Prior studies mainly focus on the wave propagating, transforming, and breaking on the fringing reefs by assuming that ocean waves propagate in an ideal environment where the wind is absent. However, in the real severe ocean environment, huge surges and waves always occur simultaneously with the strong winds. The wave profile can be easily reshaped by the strong winds, which can also significantly affect the way that ocean waves propagate on the fringing reefs. Therefore, it is necessary to study the hydrodynamics of fringing reefs under the combined action of wind and waves. To study the influences of the onshore wind on the hydrodynamics of solitary wave on the fringing reef, the finite volume method is applied to solve the governing equations of two-phase incompressible flow and a high-resolution numerical wind-wave tank is established in this study. Effects of several main factors are analyzed in detail. The research results show that the onshore wind can significantly increase the maximum wave runup height (maximum by 38.49%) and decrease the wave reflection coefficient of solitary wave (maximum by 8.66%). It is hoped that the research results of this study can enhance the understandings on the hydrodynamics of ocean waves on the fringing reefs during severe weather events.

Modeling and Sliding-Mode Control for Launch and Recovery System in Predictable Sea States With Feasibility Check for Collision Avoidance

This article investigates a deterministic sea wave prediction-based noncausal control scheme for the launch and recovery (L&R) from a mother ship of small rigid-hulled inflatable boats (RHIBs) for maritime rescue missions. The proposed control scheme achieves an automatic hoisting process ensuring that no collisions occur between the RHIB and mothership hull by using the cable tension force as the manipulated control input. A state-space model of the L&R system is established for the first time where the wave forces and external disturbances such as wind acting on both the mothership and the small boat are fully considered. A fast and safe recovery is ensured by a fixed-time convergent sliding-mode controller, which shortens the cable length to a target value with zero terminal velocity at a predefined time instant subject to unknown disturbances and model mismatches. Since the overall dynamics of the swing angle is underactuated, a feasibility check is proposed to avoid collisions between two vessels and overlarge angular velocities by determining a proper time instant to initiate the hoisting process. To cope with the model mismatch and the external disturbance, the constraints on the swing angle and angular velocity are tightened to ensure safety. The stability of the proposed controller is proven and details of the feasibility check are given. The fidelity of the model and the effectiveness of the proposed scheme are demonstrated in simulation where a realistic sea wave is applied.