Generation Of Waves Research Articles

The potential of pulsed electromagnetic field-generated shock waves for reducing microbial load and improving homogenization in raw milk

Milk is a highly nutritious food essential for human consumption. However, traditional thermal processing methods can reduce its nutritional value and cause unwanted changes. The use of shock waves produced by pulsed electromagnetic fields (PEMFs) has been explored as a means to reduce pathogenic microorganisms. The effect of shock wave treatment on microbial load and particle distribution in packaged fresh cow's milk was investigated. Additionally, the impact of shock wave treatment on Salmonella enterica counts in a bacterial suspension of phosphate-buffered saline (PBS) was evaluated, as this bacterium is a significant milkborne pathogen. Treatment with 1000 impulses from an electromagnetic shock wave generator resulted in a 0.7-log reduction in the total bacterial count of milk. In a separate experiment, a 300-impulse shock wave treatment applied to a Salmonella enterica suspension achieved a 3-log reduction in bacterial counts. Furthermore, shock wave treatment resulted in a decrease in milk particle size compared to untreated milk. Notably, the volume of milk used in this study aligns with commercially available packaged products, enhancing the experiment's industrial relevance. The use of PEMF to generate shock waves could provide a novel approach for future studies focused on reducing the microbial load of milk and improving its homogenization.

Strong enhancement of third harmonic generation from a Tamm plasmon multilayer structure with WS2.

Improving the conversion efficiency is particularly important for the generation and applications of harmonic waves in optical microstructures. Herein, we propose to enhance the efficiency of third harmonic generation by integrating a monolayer WS2 with the metal/dielectric/photonic crystal multilayer structure. The numerical simulations show that the multilayer structure enables to generate the Tamm plasmon mode between the metal film and photonic crystal around the telecommunication wavelength, which is consistent with the experimental result. By measuring with a self-built nonlinear optical micro-spectroscopy system, we find that the third harmonic signal can be reinforced by 16-fold through inserting the monolayer WS2 in the dielectric spacer. This work will provide a new way for improving nonlinear optical response, especially THG in multilayer photonic microstructures.

Bifurcation analysis of electron-acoustic waves in electron beam-plasma with suprathermal electrons

It has investigated the properties of nonlinear electron-acoustic waves propagating in a four-component collisionless, unmagnetized plasma. The system consists of cool inertial background electrons of temperature T c , the cool inertial electron beam of temperature T b , hot inertialess suprathermal electrons modeled by a κ-distribution of temperature T h , and ions. The nonlinear modified Korteweg-de Vries-Burgers (mKdV-Burgers) equation that characterizes the electron acoustic waves in such a plasma model is derived. The wave solutions of the resultant mKdV-Burgers equation are investigated using planar dynamical system bifurcation theory. The unperturbed hot, cool, and beam electron densities and the superthermal electron parameter are revealed to have a considerable influence on the nonlinear electron-acoustic traveling waves and the associated electric fields. The system evolves also monotonic shock waves when the dissipation term dominates over the dispersion term. The current model might be useful for understanding the generation of nonlinear electron-acoustic waves in a variety of astrophysical plasma settings, including the Earth's magnetosphere.

Internal waves generated from asymmetric topographies

Previous experimental and theoretical research on tidally generated internal waves over oceanic topography has often used symmetric topographic profiles. However, due to the complex nature of real ocean topography, the effect of asymmetry cannot be overlooked. Studies have shown that topographic complexities, including asymmetry, can have a significant impact on internal wave generation, but topographic asymmetry has not yet been explored in a systematic manner. This work presents a comparison of tidally generated internal waves from nine different two-dimensional asymmetric topographies, consisting of a steeper Gaussian curve on one side, and a wider Gaussian curve on the other. The amplitude of the wider curve varies from 60% of the steeper curve to its equivalent. Two oscillation frequencies are tested. Kinetic energy density in tidally generated internal waves on each side of the topography is compared qualitatively and quantitatively, in both physical and Fourier space. When compared to similar symmetric topographies, waves generated by the asymmetric topographies varied distinctly in both magnitude and wavenumber distribution of kinetic energy density. Waves on the relatively steep side of the topography contain up to 50% more kinetic energy than on the wider side. However, there is very little kinetic energy at the higher wavenumbers associated with the steeper topography. Instead, the internal wavefield is dominated by lower wavenumbers, 50%–90% of the kinetic energy density is contained in wavelengths corresponding to the wider side of the topography. Decreasing the amplitude of the wider curve does not make an appreciable difference in the kinetic energy density spectrum. Thus, the differences quantified here are due solely to changing slope and show the effect which relatively slight asymmetry has on internal wave generation.

Edge-Terminated AlGaN/GaN/AlGaN Multi-Quantum Well Impact Avalanche Transit Time Sources for Terahertz Wave Generation

Edge-Terminated AlGaN/GaN/AlGaN Multi-Quantum Well Impact Avalanche Transit Time Sources for Terahertz Wave Generation

Gravitational waves from a scotogenic two-loop neutrino mass model

We propose a framework to account for neutrino masses at the two-loop level. This mechanism introduces new scalars and Majorana fermions to the Standard Model. It assumes the existence of a global U(1)×Z2 symmetry which after partial breaking provides the stability of the dark matter candidates of the theory. The rich structure of the potential allows for the possibility of first-order phase transitions (FOPTs) in the early Universe which can lead to the generation of primordial gravitational waves. Taking into account relevant constraints from lepton flavor violation, neutrino physics, as well as the trilinear Higgs couplings at next-to-leading order accuracy, we have found a wide range of possible FOPTs which are strong enough to be probed at the proposed gravitational-wave interferometer experiments such as LISA. Published by the American Physical Society 2024

Airblast observations and near-field modeling of the large surface explosion coupling experiment

Seismoacoustic wave generation for two consecutive surface chemical explosions of the same yield (approximately 1 ton TNT-equivalent) was studied during the Large Surface Explosion Coupling Experiment (LSECE) conducted at Yucca Flat on the Nevada National Security Site (NNSS) site in alluvium geology. We have performed numerical simulations for both chemical explosions to investigate how the non-central source initiation, site topography and soil mechanical properties affect the evolution of the explosion (fireball and cloud), its crater, and variations in the generated blast waves. The results can be used to improve the understanding of surface explosions and their effects and how those effects can be used to infer source information such as explosive yield and emplacement. We find that the non-central detonation of the explosive cube results in non-axisymmetric blast overpressures which persist through the strong and weak shock regimes, in this case out to 200 m and more. The pattern of the secondary shock (i.e., shock created due to slowing explosive products within the expanding fireball) is also affected and its arrival relative to the main shock and may be indicative of explosive type due to its dependence on the explosive products ratio of heats. Small reflections are visible within the overpressure signal that are most probably due to small artifacts in blast path. Importantly, the fireball growth, cavity generation, and cloud formation also depart from spherical and ideal approximations due to ground interactions and material dependence, which shows the importance of realistic geomaterial models for accurate prediction. The asymmetry in peak overpressure is diminished for the second chemical explosion, which was placed in the crater of the first. Numerical modeling shows that the explosive jetting created by the non-central detonation is reduced upon interaction with the crater walls and this has the effect of making the blast generation more axisymmetric.

Whistler‐Mode Wave Generation During Interplanetary Shock Events in the Earth's Lunar Plasma Environment

AbstractWhistler‐mode waves are commonly observed within the lunar environment, while their variations during Interplanetary (IP) shocks are not fully understood yet. In this paper, we analyze two IP shock events observed by Acceleration, Reconnection, Turbulence and Electrodynamics of the Moons Interaction with the Sun (ARTEMIS) satellites while the Moon was exposed to the solar wind. In the first event, ARTEMIS detected whistler‐mode wave intensification, accompanied by sharply increased hot electron flux and anisotropy across the shock ramp. The potential reflection or backscattering of electrons by the lunar crustal magnetic field is found to be favorable for whistler‐mode wave intensification. In the second event, a magnetic field line rotation around the shock region was observed and correlated with whistler‐mode wave intensification. The wave growth rates calculated using linear theory agree well with the observed wave spectra. Our study highlights the significance of magnetic field variations and anisotropic hot electron distributions in generating whistler‐mode waves in the lunar plasma environment following IP shock arrivals.

Vortex bursting and associated twist dynamics on helical vortex tubes and vortex rings

The interaction of opposite-signed twist waves on vortex tubes can lead to vortex bursting, a process where the core expands into a double ring-like structure with strong swirling flows. Previous works have studied vortex bursting on rectilinear vortices by axially perturbing the initial core size to generate the twist waves, and observed largely axisymmetric bursting dynamics. In this work, we numerically study bursting on vortical structures with curved centrelines, analysing the interaction between the centreline dynamics, twist wave generation and propagation, and vortex bursting. We focus on axially perturbed helical vortex tubes with small radius-to-pitch ratios up to $0.0625$ , as well as vortex rings with a large radius-to-core size ratio $10$ , both at a circulation-based Reynolds number $5000$ . The results show that though the initial twist wave propagation speeds are relatively unaffected by the curvature and torsion of the centreline, the bursting process is altered significantly compared with rectilinear vortices. The self-induced rotation of the centreline of the helical tube induces a non-axisymmetric distortion of the bursting structure, which rapidly breaks up the vortex core into small-scale helical structures. A similar destabilization of the bursting structure also occurs on vortex rings. The enstrophy increase and accelerated energy decay associated with bursting are predominantly determined by the twist wave strength, rather than the curvature and torsion of the centreline. Combined, our findings imply that bursting could play an important role in transferring and dissipating energy of vortical structures in wakes, and turbulent flows in general.

Large-Scale Laboratory Experiments On The Wave Generation Due To The Collapse Of Partially And Fully Submerged Granular Columns

Landslides that occur in coastal environments can drive cascading consequences such as wave forces, flooding, and infrastructure damage to coastal communities. It can be difficult to classify these slides as subaerial or submarine, and the mechanics of wave generation associated with partially submerged failures are not well understood. Limited physical modelling has been conducted that encompasses both the triggering of granular landslides and subsequent waves associated with partially and fully submerged mass movements. To date, laboratory work investigating tsunamis generated by submarine landslides has focused on the wave formed in the direction of the mass movement (seaward direction) for rigid block experiments (eg. Rzadkiewicz, 1997) and deformable slide masses (e.g. Grilli et al., 2017, Takabatake, 2020, Bullard et al., 2023). From these experimental data sets, predictive relationships connecting slide acceleration, mass, and initial submergence depth to the amplitude of the wave formed have been presented for the seaward wave. Such relationships have not been presented for the landward directed wave, which propagates in the opposite direction of the submarine landslide motion. Further, not all landslides are easily classified as either subaerial or submarine. Consider the 2018 Anak Krakatoa landslide in which the sliding surface was estimated to be 100 m below sea level (Pakoksung et al., 2020), resulting in one third of the total collapse being submerged. In comparison to the end-member conditions of subaerial and submarine failures, the mechanics of wave generation associated with partially submerged failures is much less clear. Granular column collapse experiments provide an idealized experimental framework to explore momentum transfer processes and the resulting waves generated in partially submerged and fully submerged conditions. Work by Cabrera et al., (2020) made use of granular collapse experiments of partially to fully submerged columns to derive a continuous momentum-based function to estimate the maximum seaward wave amplitude based on the initial column submergence ratio (Hw/Ho). However, these experiments were conducted at a small-scale (Ho = 0.15 m) with a width of one particle (2.4 mm diameter). To address this research gap, a series of 22 large-scale granular collapse experiments were conducted by releasing columns of river stone (0.75 m and 0.50 m high) into a laboratory flume reservoir with water depths ranging up to 1.10 m to explore the wave generation and runup processes in both seaward and landward directions. The columns were released by a rapid pneumatically actuated vertical rising gate designed to enable the near instantaneous loss of support of the source volumes resulting in granular collapse. The failure mechanics were captured with high-speed cameras (Figure 1a,b) and wave amplitudes were measured using wave capacitance gauges (Figure 1c,d). This work also provides the first experimental data set of the landward propagating wave and runup associated with submerged granular collapse experiments. Overall, the seaward wave amplitudes measured in these highly-instrumented, large-scale physical models agree with empirical relationships developed in a previous study using smaller-scale models.

Considerations for designing a new wave generator system in an existing flume

Van Halteren Technologies Boxtel B.V. (formerly known as Bosch Rexroth B.V.) has designed, manufactured, installed, and commissioned the new electrical driven wave generator system in the existing Large Wave Flume (GWK) at FZK in Hannover. The aim of the replacement was designing a new wave generator system, with optimized performance in the given space in the existing flume, and replace the hydraulics for an electrically driven system. The width and depth of the flume are five and seven meters respectively. The water depth is variable up to five meters. In order to get the most out of the finite length of the flume the space for the wave maker is limited. Given the limited space for the wave maker we had to apply a dry back wave generator system which has the advantage of a rather compact design compared to a wet back wave generator. This also introduced challenges such as a seal system around the moving wave segment at the side walls and floor as well as a compensator for compensating the static force of the variable water depth. The hydrodynamic forces are provided by the electrically driven system. The wave generator has been provided with an Active Reflection Compensation system (ARC) for compensating the reflected waves traveling to the wave segment. This ARC must be capable to handle variable water depths, even when the water depth is changed in order to simulate high and low water conditions.

2D Model For Addu City Project - Wave Transformation Over Reef Flat

Van Oord DMC was awarded the Contract for the Reclamation by Dredging and Shore Protection works for land in Addu City by The Ministry of National Planning, Housing and Infrastructure of the Maldives. The Scope of Works consists of the Design and Construction of (among others) Reclamation and Shore Protection Works on various locations in the Addu City atoll. The project execution started in 2022 and has been finalized at the end of 2023. The design of the Shore Protection Works has been verified in 2022 by means of 2D physical model testing in the wave flume of DHI in Denmark. Cross-sections of shore protection works for three different reclamation areas have been tested, where this abstract will focus on 2 locations at the outside of the atoll: Maradhoo and Four Lane Link Road (4LLR). All dimensions given in this abstract are prototype values, unless otherwise specified. The length scale of the both models was selected at 1:30. The foreshore of the 2 tested cross-sections is very typical for atolls, consisting of a relatively shallow reef flat followed by a very steep slope to deep water. The modelled foreshores are presented in Figure 1. This figure also shows the locations of the wave gauges, which were placed both offshore (near the wave generator) and on top of the reef flat (in front of the structure). The tested seabed levels directly at the toe of the 4LLR and Maradhoo structures were MSL-0.70m and MSL-0.40m respectively. The target wave conditions were defined in deep water (in front of the wave generator), with design wave heights (Hm0) between 3.8m and 4.4m and 120% overload conditions. The tested peak wave periods (Tp) varied between 11.9s and 19.7s.

The Surviwec Project: An Open-Source Experimental Database For Extreme Loads On A Moored Cylinder Under Regular And Focused Waves

In this work, we introduce a novel open-source experimental database focused on the dynamic response of a moored floater under both regular and focused waves. The database provides detailed information about the motion (6 DOF) of a cylindrical floating body anchored using two distinct mooring configurations. The former configuration employs four tension legs evenly distributed around the perimeter of the float. The latter, utilizes catenary connections made of steel chains. This database holds significance in three key aspects. Firstly, by leveraging one of the largest wave facilities in Europe for wave generation, the wave-structure interaction is studied on a large scale (approx. 1:10 ratio). Due to this, scale effects are minimized. Secondly, the database captures critical hydrodynamic loads, including slamming and overtopping induced by extreme waves, as well as snap loads in the mooring lines. These represent unique features of the dataset. Lastly, the tests are conducted with meticulous consideration for subsequent analytical or numerical validations: preliminary tests with regular waves are followed by investigations under extreme sea states represented by focused waves.

Generation of bidirectional shear horizontal guided waves by size optimization of face-shear piezoelectric transducers

Generating directional guided waves helps to avoid unwanted reflections while providing location information for defects. Bidirectional waves focus wave beams in two opposite directions, which can be applied for generating circumferential zero-order shear horizontal (SH0) waves for large-diameter pipe inspection. In this paper, a novel method for generating bidirectional SH0 waves through size optimization using face-shear (d24) lead zirconate titanate (PZT) transducer is proposed. A theoretical model is established based on the shear-lag model and the Huygens principle, which describes the generation and propagation of SH0 waves in thin plate by bonded d24 PZT transducer. The theoretical model is validated by multi-physics finite element (FE) simulation results in terms of SH0 displacement wavefield. Based on the theoretical model, the performance of bidirectional SH0 wave generation is studied. The maximum bidirectional ratio that can be achieved by d24 PZT within a size range (1–25 mm) under a five-cycle sinusoid tone-burst excitation at a center frequency range (50–300 kHz) is studied. Results show that over 20 dB effect can be achieved at the PZT with a specific aspect ratio. Laboratory experiments are conducted using d24 PZT transducers at 50–300 kHz to validate the effect of bidirectional wave generation in practical detection scenarios. Experimental results show effects of over 20 dB within a certain frequency range can be achieved when using a PZT with a large aspect ratio, which agree well with the theoretical predictions.

Generation of interfacial waves by rotating magnetic fields

Generation of interfacial waves by rotating magnetic fields

Enhanced picosecond terahertz wave generation based on cascade effects in a terahertz parametric generator

Abstract Enhanced terahertz wave generation via Stokes cascaded process has been demonstrated using a picosecond pulse pumped terahertz parametric generation at 1 kHz repetition rate. Clear cascade-saturation of terahertz output was observed, and the corresponded cascade-Stokes spectra were analyzed. The maximum terahertz wave average power was 22 μW under the pump power of 30 W, whereas the maximum power conversion efficiency was 8×10-7 under the pump power of 21 W. The THz power fluctuation was measured to be about 1% in 20 min. This THz parametric source with a relative stable output is suitable for a variety of practical applications.

Experimental and numerical study on freak wave using the Peregrine breather

The evolution of the Peregrine breather (PB) in a wave tank is experimentally studied under water depths k0h (where k0 represents the wave number and h the water depth) ranging from 4.35 to 5.24. Additionally, the initial wave steepness, ε0=k0a0 (with a0 being the background wave amplitude), was varied within the range of 0.077 to 0.116. Comparative analysis between the experimental observations and the numerical simulations, conducted using the high-order nonlinear Schrödinger equation (HNLSE), revealed that the HNLSE proficiently captures intricate details of wave field evolution, including a pronounced left–right asymmetry in surface elevations. The numerical outcomes demonstrated a high degree of consistency with the experimental data. Furthermore, numerical methodologies were employed to examine the fluctuation of wave height relative to water depth. The results of these simulations suggested that as water depth transitions from shallow to deeper conditions, the wave height amplification factor diminishes, eventually stabilizing. This implies that under shallower water conditions, there is a propensity for larger wave generation.

Performance Assessment Of Two Active Absorption Systems In A Large Wave Flume

The quality of most coastal or ocean laboratory experiment depends on the accuracy, uniformity and stability of the generated waves. Generation of waves in the laboratory seems simple, but it should consider the spatio-temporal variability of the wave profile. As they propagate, waves interact with the boundaries, i.e. changes in water depth, lateral walls, test specimens, instrument supporting structures, passive absorbers, etc., as well as with varying hydrodynamic conditions (wave-induced currents, wave-wave interactions, or nonlinear energy transfer, among others). Reflected, scattered and radiated waves may propagate back to the wave generator and reflect back. Re-reflections from the wave generator may be a non-realistic representation of the intended wave field, to the extent that the total energy content in the testing facility may increase significantly and uncontrollably. Theoretically, for weakly nonlinear unidirectional waves propagating over a relatively small number of wavelengths, and as long as the still water depth and facility width does not change, the wave properties should remain constant in space and time, which can be identified as the uniformity and stability of the waves. Under these conditions, nonuniform or unsteady wave properties can be associated to an inadequate selection of the wave theory (Airy, Stokes n-order, Cnoidal, Stream Function, etc., e.g. Fenton 1999), the approximation of the wave generation technique (first or second order, nonlinear - see e.g. Mohtat et al., 2020), formation of wave instabilities (e.g. Benjamin-Feir, 1967), wave reflection, scattering or radiation, and the performance of the active wave absorption system. It can be said that the performance of the active wave absorption control system is one of the responsible factors that can affect directly the quality of the generated waves. Many laboratories have implemented different passive and active wave absorption systems, but the performance on the uniformity and stability of the generated waves, as well as the performance of the active wave absorption system used, have not been assessed in a systematic way, and related published data and information is quite scarce, with few interesting exceptions, e.g. (Lykke-Andersen, 2016; Spinneken 2010; Schäffer and Skourup 1996). However, a direct comparison among the different available active wave absorption control systems is still missing. This paper presents a thorough experimental study on the performance assessment of two different active wave absorption control systems (MTS and Awasys7) as a means to establish the quality of the experiment in terms of the uniformity (space) and stability (time) of generated wave parameters (descriptors) in the laboratory.

Terahertz wave radiation simulation in the Fe thin film*

Femtosecond laser (FL) induced terahertz (THz) source is a new type of THz source based on injecting FL beams into ferromagnetic thin films by nonlinear effects to generate THz wave. It has a wider bandwidth compared to the traditional THz source, which provides higher flexibility and tunability in the application. In this paper, the three-temperature model and the stochastic Landau Lifshitz Gilbert equation at the atomic level are applied to simulate THz wave generation in Fe thin film induced by FL. Simulation results show that under a FL irradiance of 2 J m−2, the maximum demagnetization of the Fe thin film reaches 8.7%. The electromagnetic waves generated completely cover the THz band (0.1–10 THz), which fully satisfied the application requirements of the THz technology, verifying the feasibility of FL inducing the Fe thin film as a THz source. However, when the Fe thin film is overheated, it will be difficult for FL to excite valuable THz waves. Therefore, additional cooling devices are needed to keep the THz source in a workable temperature state, or to use ferromagnetic materials with magnetic moments that can quickly recover to saturation.

Symmetry Reduction of Molecular Shape of Cationic Chromophores for High‐Performance Terahertz Generators

AbstractThe symmetry reduction of molecular shape of cationic chromophores as a design strategy to develop organic terahertz (THz) generators is used. Electron donating group (EDG) with an asymmetric shape is introduced into two types of cationic styryl‐quinolinium chromophores, leading to the development of several novel non‐centrosymmetric crystals with high macroscopic optical nonlinearity. In contrast, when an EDG with a symmetric shape is introduced, centrosymmetric crystal structure is obtained in all investigated crystals. For THz wave generation, crystals based on asymmetrically shaped EDG exhibit several optimal crystal characteristics, including a plate‐shape morphology, a large size, and an in‐plane polar axis. Furthermore, over the entire range of molecular phonon vibrations, 0.5–4 THz, the steric hindrance group in the asymmetrically shaped EDG has a strong influence on the suppression of THz phonon vibrations, leading to a low THz absorption coefficient. The crystals based on asymmetrically shaped EDG generate an ≈40 times stronger THz electric field than the inorganic ZnTe crystal and very broad THz spectra, extending up to 16 THz. Thus, the symmetry reduction of the molecular shape of cationic chromophores through the introduction of an asymmetrically shaped EDG is an effective design approach for the development of novel organic THz crystals.