Excitation Of Waves Research Articles

Sound transmission across locally resonant honeycomb sandwich meta-structures with large spatial periodicity.

Honeycomb sandwich structures have been widely used in the field of engineering owing to their outstanding mechanical properties. However, for a honeycomb sandwich structure with large spatial periodicity, there is a low-frequency sound insulation valley. Here, the sound transmission across locally resonant honeycomb sandwich meta-structures was investigated to overcome this sound-insulation valley. An analytical model was developed based on the space-harmonic approach and the low-frequency sound insulation valley was determined analytically and numerically. The results indicate that the resonator distributed at the center of the face panel has a significant impact on the sound transmission performance of the honeycomb sandwich structure, whereas the resonator distributed on the wall of the honeycomb core does not contribute to overcoming this sound-insulation valley. Based on the research results, a design strategy for overcoming this sound-insulation valley was determined by tuning the damping parameter and constructing graded resonators. Moreover, sound transmission under the excitation of oblique incidence sound waves was also investigated. Compared with the method of filling porous materials, the proposed design method is more effective, and more importantly, the mass of the resonator is only 1.23% of that of the porous materials.

Numerical simulations of drill-string responses for downhole acoustic telemetry

In petroleum engineering, one major challenge for logging while drilling is that the transmission rate of downhole telemetry is too low for real-time evaluations. Downhole acoustic telemetry (DAT) uses acoustic guided waves in a drill string with periodic structures to transmit measurement data, expected to break through low-speed telemetry limitations. However, the lack of effective modeling methods makes the channel response difficult to predict, severely restricting equipment development and field applications. We propose a novel modeling approach to study the responses of the DAT channel. Excitation and propagation mechanisms of the mode waves in the DAT channel are investigated. The 2-D modeling issue is approximated to the 1-D plane-wave propagation along the borehole, considering transmission, reflection, and interconversion of the drill-string and fluid waves. The coefficients of each wave component and the full-wave channel function are derived from the transfer matrix. The efficiency and accuracy of the proposed means are validated by comparison with the finite difference. Numerical results show that the fluid-solid coupling leads to a generalized multipath effect in the DAT channel, making the acoustic responses exhibit discrete bandgaps and nonlinear phase distortion. This study provides a basis for frequency band selection and design for DAT systems.

Dynamic performance of submerged floating tunnel with different mooring styles subjected to anchor cable failure

Submerged floating tunnels (SFTs) are novel structures for transportation across long- and deep-strait regions. Owing to severe wave and current excitation as well as the effects of underwater structures and corrosion, the risk of local anchor cable failure is high, which can result in the progressive failure of the entire structure. In this study, experimental and numerical investigations are conducted to analyze the dynamic behavior of an SFT with different mooring styles under local cable failure. A custom-designed cable failure device and the birth-and-death element method are used to simulate cable failure (i.e., progressive failure) via experiments and numerical simulation, respectively. A physical-scale segmental model of an SFT with different mooring styles under anchor cable failure is developed in this study. A segmental and entire-length mathematical model is developed using the ANSYS program to perform the numerical simulation. The results of the segmental numerical and experimental models indicate good agreement. The dynamic response of an SFT with different mooring styles under cable failure is comprehensively investigated by investigating the effects of key parameters (wave period, buoyant weight ratio, and cable failure mechanism). Moreover, the progressive failure of the SFT under cable failure is investigated via a segment model test and a numerical simulation of its entire length. The present study can serve as a reference for the safer designs of the SFT mooring style.

PERTURBATIONS FAR FIELDS OF THE INTERFACE SURFACE OF THE DEEP OCEAN AND THE ICE COVER FROM LOCALIZED SOURCES

The problem of far wave fields arising at the interface between ice and an infinitely deep homogeneous liquid in the flow around a localized source of perturbations is solved. An integral representation of the solution is obtained and, using the stationary phase method, an asymptotic representation of the solution is constructed for various modes of wave generation. Numerical calculations show that with a change in the flow velocities and ice thickness, a noticeable qualitative rearrangement of the phase patterns of the excited far wave fields at the interface between ice and liquid occurs.

Implementation of EBG Structure to Reduce Surface Wave Excitations for IoT Range Applications

This paper presents the design of antenna for Internet of Things (IoT) applications. The performance of conventional antenna is limited by surface waves due to which it produces a low gain. An attempt is made to reduce the surface wave excitations in conventional antennas with the use of integration of Electromagnetic Band Gap (EBG) cells. The proposed work involves the design of Edge via EBG unit cell at 5.2 GHz and it is simulated with High Frequency Structure Simulator (HFSS) software. The simulation results show that the gain is enhanced by 10% and S11 is reduced by 72%, approximately in the rectangular microstrip patch antenna with Edge via EBGs.

Three-dimensional shape optimization of a submerged body under wave diffraction

This study explores the use of shape optimization to reduce wave forces on a submerged floating body subjected to wave diffraction. To this end, gradient-based shape optimization is adopted, in which dimensionless wave excitation forces are the optimization objective. A shape parameterization method based on the Fourier-series expansion is developed that permits the representation of an arbitrary three-dimensional floating body. The discrete adjoint method is utilized to calculate the gradient of the objective function with respect to the shape parameters. Using three-dimensional shape optimization, taking the initial shape to be a hemisphere, a significant reduction in surge, heave, and pitch wave forces is achieved, with a maximum reduction of 48.40%, 68.43%, and 46.22%, respectively. Furthermore, optimization effectively suppresses wave run-up, with a maximum reduction of 15.62%. A comprehensive analysis of parameters is performed to reveal the effects of wave number, incident angle, and shape parameters on the final optimized shape and wave load characteristics. This study provides a solid guide to the optimization of floating offshore platforms and the development of innovative structural systems.

Double-gradient seismic metamaterials with zero-frequency bandgap characteristic in a layered soil medium

Seismic metamaterials (SMs) are an artificially composite material designed within the sub-wavelength range. To attenuate low-frequency seismic surface waves, a metamaterial structural unit composed of a lead core and an auxetic foam coating layer was proposed; the higher impedance ratio results in the creation of a zero-frequency bandgap under layered soil conditions. To broaden the attenuation zone (AZ), double-gradient seismic metamaterials (DGSMs) were designed. The frequency domain analysis indicates that the attenuation area covering the range of 0–10 Hz is 89.8%. Through displacement-field analysis, the attenuation mechanism of DGSM on specific frequency surface waves can be fully explained. Finally, Taft seismic wave excitation is input for time history analysis, and the acceleration amplitude within 0–2 Hz decreases by 58.6%, which verifies the effectiveness of DGSMs in attenuation of low-frequency seismic waves.

Plasmasphere Control of ULF Wave Distribution at Different Geomagnetic Conditions

AbstractMagnetic storms and substorms cause global disturbances in the Earth's magnetosphere. Plasma clouds injected from the magnetotail during storm or substorm drift around the Earth and generate ultra‐low frequency (ULF) waves via various mechanisms. At the same time, the inner part of the magnetosphere called plasmasphere is filled with cold particles and its characteristics are sensitive to the geomagnetic activity level. Previous theoretical and some observational studies suggested plasmasphere and its boundary, plasmapause, are special regions for ULF waves to interact with charged particles. We present a statistical analysis of ULF waves during different geomagnetic conditions. We utilized Arase satellite magnetic field and electron density measurements from March 2017 to December 2020 to investigate spatial distribution of ULF waves and its dependence on the plasmapause location. A 1–2 RE gap between the plasmapause and a region of high transverse waves occurrence rate was found. This gap keeps during quiet geomagnetic conditions when plasmasphere expands, and we concluded that the plasmapause controls the ULF wave distribution in the magnetosphere. ULF wave occurrence rate significantly decreases at quiet time, but dayside and dawnside maxima still occur for poloidal and compressional, and toroidal waves, respectively. Thus, we can distinguish internally and externally excited waves. Average wave frequency distribution revealed field‐line resonance character of toroidal waves as frequency increases toward the Earth. Poloidal and compressional waves distributions clearly distinguish low frequency externally excited waves and high frequency storm‐time pulsations.

Nonlinear wave excitations in the (2+1)-D asymmetric Nizhnik-Novikov-Veselov system

The (2+1)-dimensional nonlinear asymmetric Nizhnik-Novikov-Veselov system is one of the extended versions of the Korteweg-de Vries equation, and as such of considerable significance in nonlinear wave dynamics. In this work, it is transformed into a bilinear form by using the Hirota transformation and then treated by the variable separation method. In particular, by separating variables in a specific manner, a class of solutions is obtained, which are constructed with the help of three auxiliary functions, Py, Ry, and Qxt. By selecting the three functions conveniently, we obtain novel nonlinear excitations for the asymmetric Nizhnik-Novikov-Veselov system. To make our results more explicit and interesting, various types of nonlinear profiles were displayed, colloquially named as the parallelogram, walnut, dark breather, half-moon breather, and the top-compressed quadrilateral breather structures. It is found that these local wave packets can be well controlled by appropriately selecting the three auxiliary functions, and that the variable separation approach can be extended to other high-dimensional nonlinear systems.

Features of Catheter Treatment of Non-Isthmus-Dependent Atrial Flutter

Atrial flutter (AF) is caused by the re-circulation of the wave of electrical excitation of the myocardium (reentry) around the anatomical substrate which circulates within the atrial tissues. This is always a macro re-entry. Such an anatomical barrier, around which circulation can occur, can be the superior or inferior vena cava, rings of the tricuspid or mitral valves, the mouth of the coronary sinus, pulmonary veins, postoperative scar.
 The aim. To determine the specifics of elimination, success rate, and long-term outcome with various preablation and postablation diagnostic techniques for non-isthmus-dependent atrial flutter (NIDAFL).
 Materials and methods. The study included 26 patients who underwent radiofrequency ablation of atypical NIDAFL.
 Results. As a result of radiofrequency ablation, a sinus rhythm was restored in 17 patients during the procedure. In 7 cases, when the typical, isthmus-dependent AF was removed, the tachycardia cycle and the morphology of the R wave changed. Mapping showed that in 7 cases the direction of the re-entry front changed, and instead of the circulation of excitation through the cavatricuspid isthmus, it then passed around the atriotomy scar. In 2 cases, a change in the cardiac cycle was observed after radiofrequency ablation, but the excitation circulation was the same around the atriotomy scar, only the tachycardia cycle increased. As a result of the use of our techniques, arrhythmia was eliminated in all 21 patients with an atriotomy AF during one procedure. Five patients with AF of a different localization of the re-entry circuit also had their arrhythmia eliminated, although 8 procedures (for five patients) were performed (on average 1.6). There were no complications. During the follow-up period of 1.8±0.7 years, 2 patients had a recurrence of arrhythmia, and they underwent a repeat procedure to eliminate the arrhythmia. One patient developed typical AF that had not been observed before, which was successfully eliminated.
 Conclusion. Catheter treatment of atypical NIDAFL is quite a non-trivial task, because, as our experience shows, several types of tachycardia occur in a significant number of patients. In cases of restoration of sinus rhythm as a result of the application, it is necessary to check the inducibility of another arrhythmia. But despite everything, catheter removal of NIDAFL is quite effective, especially for atriotomy AF, although it requires more X-ray exposure and a relatively large number of applications. The use of navigation systems has helped to improve the results of such interventions in more complex cases.

Metasurface characterization based on eigenmode analysis and averaging of electromagnetic fields

A fully numerical homogenization technique for the retrieval of the effective surface susceptibilities of a periodic composite metasurface is developed in this work. We utilize the so-called dual field-flux finite element formulation scheme to accurately calculate the eigenmodes of a composite periodic metasurface, a scheme that possesses a crucial advantage: The capability of evaluating all field components and their derivatives accurately and with the same order of approximation is a requirement for our proposed technique. Next, we derive the generalized sheet transition condition equations for a general bianisotropic metasurface, which correlate the field components on either sides of the metasurface with its surface susceptibilities. At this point, we establish a new field averaging scheme for the acquisition of the average field components of the modes supported by the metasurface. Combining this computational information, we derive a set of linear algebraic equations based on the GSTCs and the average electromagnetic fields and numerically solve it, so as to obtain the effective surface susceptibilities of a bianisotropic metasurface. Comparison with the results of other techniques in the literature shows very good agreement, relatively to the resonance behavior of the returned values and their position at the frequency spectrum. The advantages that distinguish the proposed technique over other related methods are its foundation on the intrinsic modal information of the eigenmodes supported by the metasurface and its independence of any wave excitation schemes or involvement of analytical polarizability calculations.

Testing and Analysis of Surrounding Buildings during the Operation of Seismic Simulation Shaking Table

This paper focuses on the transmission of vibration response of the seismic simulation shaking table system at Southeast University, and analyzes the effect of this response on the surrounding building. The location of the building is less than 10 m away from the laboratory where the shaking table is located, and during the maximum load test, a student reported that the vibration caused him a sense of discomfort, as well as the shaking of office objects on desktops on high floors, which caused panic. For these reasons, multiple three-directional vibration sensors were placed around the shaking table system and on the 1st, 8th, and 16th floors of the building. Test the vibration response transfer and the vibration response of the building floor while the exercise table is in operation. The test results show that the vibration-weighted acceleration levels of some floors exceed the code limits under sinusoidal wave conditions, which was the cause of the discomfort. The floors will have an amplifying effect on the lateral vibration. For seismic wave excitation, all measurement points of the building meet the limit values required by the GB 50868-2013 Standard for allowable vibration of building engineering. This study can provide a data reference for future shaking table system commissioning and operation.

Roughness induced transition delay in a swept-wing boundary layer in presence of freestream disturbances, Part 2: Acoustic stabilization

Results of experimental investigations on control of the laminar–turbulent transition location in a 45-degree swept-wing boundary layer by the distributed micro-sized roughness (MSR) elements in presence of freestream perturbations are discussed in this two-part work. Part 1 of this study Borodulin et al. (2023) is devoted to the freestream turbulence effects, while Part 2 (the present paper) concentrates on consideration of the acoustic waves’ effects. This paper contains: (i) a complementary description of the experimental setup and measurement techniques related to the acoustic excitation and (ii) the results of studies of the freestream acoustic-field effects on the MSR transition control. The robustness of the MSR transition-control mechanism has been studied by altering the wind-tunnel flow quality: by introducing a significant background sound and/or by simultaneous variation of both the freestream turbulence level and the level of the acoustic wave excitation. At enhanced freestream turbulence, the laminar–turbulent transition is found to move upstream regardless of the sound level and frequency, while the MSR-elements lost their effectiveness in transition control in all cases. At low freestream turbulence levels and in absence of the MSR, the acoustic waves did not affect basically the transition location. However, if the laminar–turbulent transition was delayed by the MSR, the sound of a certain frequency was found to be able to cause a significant additional transition delay.

Excitation of upper hybrid wave by cross focused q-Gaussian laser beams in graded index plasma channel

Excitation of upper hybrid wave by cross focused q-Gaussian laser beams in graded index plasma channel

Amplified Spontaneous Emission from Optical Fibers Containing Anisotropic Morphology CdSe/CdS Quantum Dots Under Continuous Wave Excitation

Fiber laser field is typically dominated by rare earth ions as gain material in the core of a silica optical waveguide. Due to their specific emission wavelengths, rare‐earth‐doped fiber lasers are available only at few predefined wavelengths. However, quantum dots (QDs) are materials which show tunable emission with change in size and composition. Due to such tunability, QDs seem to be promising candidates for obtaining fiber lasers at a spectrum of wavelengths which is not possible using rare earth ions. To replace rare earth ions with QDs, it is of paramount importance that QDs show signatures of optical gain. Herein, the synthesis of asymmetric pod‐shaped CdSe/CdS QDs is reported, which demonstrate efficient gain on pumping. The intrinsic gain properties of the QDs are evaluated through transient absorption (TA) spectroscopy. Later, the exquisite QDs are used to fabricate specialty fibers from which amplified spontaneous emission (ASE) is obtained using continuous wave laser pump at room temperature. Finally, emission signal stability is checked by studying photobleaching and controlling the concentration of the QDs.

The role of magnetic waves in tangent cylinder convection

The secular variation of the geomagnetic field suggests that there are anticyclonic polar vortices in the Earth's core. Under the influence of a magnetic field, the polar azimuthal flow is thought to be produced by one or more coherent upwellings within the tangent cylinder, offset from the rotation axis. In this study, convection within the tangent cylinder in rapidly rotating dynamos is investigated through the analysis of forced magnetic waves. The first part of the study investigates the evolution of an isolated buoyancy disturbance in an unstably stratified rotating fluid subjected to an axial magnetic field. It is shown that the axial flow intensity of the slow Magnetic-Archimedean-Coriolis (MAC) waves becomes comparable to that of the fast MAC waves when |ωM/ωC|∼0.1, where ωM and ωC are the Alfvén wave and inertial wave frequencies respectively. In spherical shell dynamo simulations, the isolated upwellings within the tangent cylinder are shown to originate from the localized excitation of slow MAC waves in the dipole-dominated regime. Axial flow measurements in turn reveal the approximate parity between the slow and fast wave intensities in this regime, which corresponds to the existence of strong polar vortices in the Earth's core. To obtain the observed peak azimuthal motions of 0.6–0.9∘yr−1, the Rayleigh number in the low-inertia geodynamo must be ∼103 times the Rayleigh number for the onset of nonmagnetic convection. However, if the forcing is so strong as to cause polarity reversals, the field within the tangent cylinder decays away, and the convection takes the form of an ensemble of plumes supported entirely by the fast waves of frequency ω∼ωC. The resulting weak polar circulation is comparable to that obtained in nonmagnetic convection.

Emergent Magnonic Materials: Challenges and Opportunities.

Advances in information technology are hindered by energy dissipation from Joule losses associated with charge transport. In contrast, the process of information based on spin waves propagation (magnons) in magnetic materials is dissipationless. Low damping of spin wave excitations is essential to control the propagation length of magnons. Ferrimagnetic Y3Fe5O12 garnets (YIG) exhibit the lowest magnetic damping constants. However, to attain the lowest damping constant, epitaxial growth of YIG on single crystal substrates of Gd3Ga5O12 at elevated temperatures is required, which hinders their CMOS integration in electronic devices. Furthermore, their low saturation magnetization and magnetocrystalline anisotropy are challenging for nanoscale device applications. In the search for alternative material systems, polycrystalline ferromagnetic Co25Fe75 alloy films and ferrimagnetic spinel ferrites, such as MgAl0.5Fe1.5O4 (MAFO), have emerged as potential candidates. Their damping constants are comparable, although they are at least one order of magnitude higher than YIG's. However, Co25Fe75 alloy thin film growth is CMOS compatible, and its magnon diffusion length is 20× longer than in MAFO. In addition, MAFO requires epitaxial growth on lattice-matched MgAl2O4 substrates. We discuss the material properties that control the Gilbert damping constant in CoxFe1-x alloys and MAFO and conclude that CoxFe1-x alloy thin films bring us closer to the realization of the exploitation of spin waves for magnonics.

Magnetic Reconnection in the Martian Magnetotail: Occurrence Rate and Impact on Ion Loss

AbstractThe current sheet is crucial in releasing magnetic free energy in cosmic plasmas via fast magnetic reconnection or wave excitation. This research investigates the characteristics of the Martian tail current sheet by analyzing data acquired from the Mars Atmosphere and Volatile EvolutioN spacecraft over 7 years. For the first time, we find that approximately 15% of the current sheet events display reconnection signatures, including Hall magnetic fields and fast proton flows. These reconnecting current sheets are detected more frequently on Mars than on Earth. The Martian tail current sheet is first demonstrated to be on the proton scale, which can explain the high reconnection occurrence rate. The research also reveals that the current sheets are thinner in regions closer to Mars and in the –E hemisphere. On average, reconnecting current sheets carry high fluxes of protons rather than oxygen ions.

Machine-Learning Approach for Prognosis of Oscillating Water Column Wave Generators

Wave excitations cause structural vibrations on the Oscillating Water Columns (OWC) lowering the power generated and reducing the life expectancy. The problem of generator deterioration has been considered for the Mutriku MOWC plant and a machine learning-based approach for prognosis and fault characterization has been proposed. In particular, the use of k-Nearest Neighbor (kNN) models for predicting the time to failure of OWC generators has been proposed. The analysis is based on data collected from sensors that measure various operational parameters of the turbines. The results demonstrate that the proposed kNN model is an excellent choice for reducing maintenance costs by enabling maintenance scheduling months in advance. The model's high accuracy in predicting generator failures allows for timely and cost-effective maintenance, preventing costly breakdowns and improving turbine efficiency. The results highlight the potential of machine learning-based approaches for addressing maintenance challenges in the energy sector and underscore the importance of proactive maintenance strategies in reducing operational costs and maximizing energy production.

Excitation of exchange spin waves in the transition layer of the two-layer ferrite-ferrite structure

The possibility of intense excitation of exchange spin waves in a tangentially magnetized two-layer epitaxial film of iron yttrium garnet is demonstrated. The waves are excited in a thin transition layer at the interface between the ferrite layers, propagate into the doped layer with reduced magnetization, and reflect from its opposite surface. In continuous excitation mode, they can be observed as a series of spin wave resonance peaks. Mathematical processing of the measured frequencies of resonance peaks allows for the calculation of the magnetization profile of the doped layer and the modeling of the excitation and propagation processes of exchange spin waves. The proposed methodology of mathematical processing can be applied for non-destructive control of the layered structure of epitaxial ferrite structures.