Wave Response Research Articles

Design of X-band bicontrollable metasurface absorber comprising graphene pixels on copper-backed YIG substrate

The plane wave response of a bicontrollable metasurface absorber with graphene-patched pixels was simulated in the X band using commercial software. Each square meta-atom is a 4 × 4 array of 16 pixels, some patched with graphene and the others unpatched. The pixels are arranged on a PVC skin which is placed on a copper-backed YIG substrate. Graphene provides electrostatic controllability and YIG provides magnetostatic controllability. Our design delivers absorptance ≥0.9 over a 100-MHz spectral regime in the X band, with 360 MHz kA−1 m magnetostatic controllability rate and 1 MHz V−1μm electrostatic controllability rate. Notably, electrostatic control via graphene in the GHz range is novel.

Level-Set and Learn: Convolutional Neural Network for Classification of Elements to Identify an Arbitrary Number of Voids in a 2D Solid Using Elastic Waves

We present a new convolutional neural network (CNN)-based element-wise classification method to detect a random number of voids with arbitrary shapes in a two-dimensional (2D) plane-strain solid subjected to elastodynamics. We consider that an elastic wave source excites the solid including a random number of voids, and wave responses are measured by sensors placed around the solid. We present a CNN for resolving the inverse problem, which is formulated as an element-wise classification problem. The CNN is trained to classify each element into a regular or void element from measured wave signals. Element-wise binary classification enables the identification of targeted voids of any shapes and any number without prior knowledge or hint about their locations, shape types, and numbers, while existing methods rely on such prior information. To this end, we generate training data consisting of input-layer features (i.e., measured wave signals at sensors) and output-layer features (i.e., element types of all elements). When the training data are generated, we utilize the level-set method to avoid an expensive remeshing process, which is otherwise needed for each different configuration of voids. We also analyze how effectively the CNN performs on blind test data from a non-level-set wave solver that explicitly models the boundary of voids using an unstructured, fine mesh. Numerical results show that the suggested approach can detect the locations, shapes, and sizes of multiple elliptical and circular voids in the 2D solid domain in the test data set as well as a blind test data set.

Photomechanical and Thermal Wave Responses of a Two-Temperature Semiconductor Model with Moisture Diffusivity Process

Photomechanical and Thermal Wave Responses of a Two-Temperature Semiconductor Model with Moisture Diffusivity Process

Shear Wave-Induced Friction at Periodic Interfaces for Programmable Mechanical Responses

Abstract Nonlinear phononic materials enable superior wave responses by combining nonlinearity with their inherent periodicity, creating opportunities for the development of novel acoustic devices. However, the field has largely focused on reversible nonlinearities, whereas the role of hysteretic nonlinearity remains unexplored. In this work, we investigate nonlinear shear wave responses arising from the hysteretic nonlinearity of frictional rough contacts, and harness these responses to enable programmable functions. By using a numerical approach, we solve the strongly nonlinear problem of shear wave propagation through a single contact and a periodic array of contacts, accounting for frictional effects. Specifically, the Jenkin friction model with experimentally obtained properties is used to capture the effects of stick–slip transition at the contacts. Results show that friction gives rise to shear-polarized eigenstrains, which are residual static deformations within the system. We then demonstrate how eigenstrain generation in multiple contacts can enable programmable functionalities such as an acoustically controlled mechanical switch, precision position control, and surface reconfigurability. Overall, our findings open new avenues for designing smart materials and devices with advanced functionalities via acoustic waves using the hysteretic nonlinearity of frictional contacts.

Monitoring of the Bond State between the Concrete-Filled Steel Tube Pile and Surrounding Soil

The bonding state of the pile-soil interaction is complex. Traditional monitoring methods and tools have not been fully applied to monitor and evaluate it although it affects the lifecycle safety of the pile. In this study, a health monitoring method is proposed to evaluate the bonding state of the pile-soil contact area; it is a transient impact response method based on piezoelectric ceramic sensors to monitor the pile-soil bonding state. During the test, different damage degrees of the pile-soil bonding state were simulated by considering the working conditions of different soil densities and different crack depths as examples. A horizontal transient impact stress was applied to the pile top, and a piezoelectric ceramic sensor embedded in the pile detected the stress wave. As the stress wave response differs in different damage conditions, an energy index was established to quantitatively monitor the degree of damage.

Prompt responses of magnetospheric whistler-mode waves to solar wind dynamic pressure pulses

Whistler-mode waves play a critical role in shaping the Earth’s radiation belts, and their spatiotemporal distribution is vital for forecasting and modeling geospace weather. Previous works have extensively investigated the influences of geomagnetic activities, such as storms and substorms, on the modification of whistler-mode waves, but the direct impacts of solar wind disturbances have received relatively less attention. Recently, increasing research has highlighted the prompt impacts of solar wind dynamic pressure pulses on magnetospheric whistler-mode waves. This paper reviews the current progress in this field, specifically the prompt responses of chorus waves and plasmaspheric hiss to the solar wind dynamic pressure pulses. It will summarize the underlying mechanisms and pose some outstanding questions.

Experimental study on the motion reduction performance of a small suspension catamaran exploiting an active skyhook control strategy

A nine degrees of freedom suspension catamaran has been developed. The ship is so designed that the heave, pitch, and roll motions of the cabin are separable from those of the twin-hull. One brushed DC motor/generator (M/G) is employed at each of the four suspending locations to produce control force. An active skyhook control strategy utilizing proportional-only control is proposed to calculate the desired control input to reduce the cabin’s local vertical velocity and thus improve ride comfort. The mechanical responses of the suspension unit and the performance of the control system are verified through a group of bench tests. The ship motion responses in regular waves are investigated through a series of towing tank experiments. It is found that the proposed control strategy had significant effectiveness on motion reduction of heave and pitch of the cabin in head waves, but a small contribution to the roll motion reduction in beam waves except in the vicinity of the cabin’s natural roll frequency. In head waves, the average motion reduction ratios of the heave and pitch of the cabin both exceeded 50% at zero forward speed, which at 1.5m/s were 39% and 71%, respectively. In beam waves, the average motion reduction ratios of the heave and roll of the cabin were 62% and −57%, respectively.

On the 3D turbulence regime in a Tokamak plasma edge

We derive a reduced model for the electrostatic turbulence in a Tokamak edge, when dealing with a resistive plasma and neglecting the spatial gradient of the background density which triggers the linear drift wave response. The obtained dynamics, de facto equivalent to a Hasegawa–Wakatani model, is characterized by a constitutive relation between the electric potential Laplacian and the density, which allows to deal with a single 3D equation governing the electric potential fluctuations. We study the evolution of the model, by separating the n=0 (n indicating toroidal-like number) mode from all the other ones. Then, we linearize the dynamics of the n≠0 modes around the steady 2D spectrum, which describes the spectral features of the electrostatic 2D turbulence. We theoretically and numerically demonstrate the existence of decaying branch of the 3D turbulence, having such a 2D steady spectrum as a natural attractor. This result suggests that the basic constituent of the self-sustained non-linear drift response in the plasma edge has to be individualized in the non-linear 2D electrostatic turbulence.

Accurate Modeling and Wave Propagation Analysis of Cracked Slender Structural Members by the Spectral Element Method

The analysis of elastic wave propagation in cracked structures is very useful in the crack detection by the ultrasonic guided wave method. This study presents an accurate spectral element modeling method for cracked slender structural members by using refined waveguide models and a more realistic crack model. Firstly, a spatial spectral beam element model is established for uncracked slender structural member based on the Love rod theory, the modified Timoshenko beam theory, and the Saint-Venant’s torsion theory. Then, the complete local additional flexibility matrix for crack in the structural member with rectangular cross section is derived from the theory of elastic fracture mechanics, and a two-node condensed spectral element model considering the stiffness coupling effect caused by the crack is established for cracked slender structural member. The wave response in cracked structures is solved by the numerical inverse Laplace transformation method. A thorough comparison of the wave responses in cracked structural member evaluated by the presented spectral element model and the 3D solid finite element model is given in the numerical example, which verifies the accuracy and high efficiency of the presented method.

The response of the North Pacific jet and stratosphere-to-troposphere transport of ozone over western North America to RCP8.5 climate forcing

Abstract. Stratosphere-to-troposphere transport (STT) is an important source of ozone for the troposphere, particularly over western North America. STT in this region is predominantly controlled by a combination of the variability and location of the Pacific jet stream and the amount of ozone in the lower stratosphere, two factors which are likely to change if greenhouse gas concentrations continue to increase. Here we use Whole Atmosphere Community Climate Model experiments with a tracer of stratospheric ozone (O3S) to study how end-of-the-century Representative Concentration Pathway (RCP) 8.5 sea surface temperatures (SSTs) and greenhouse gases (GHGs), in isolation and in combination, influence STT of ozone over western North America relative to a preindustrial control background state. We find that O3S increases by up to 37 % during late winter at 700 hPa over western North America in response to RCP8.5 forcing, with the increases tapering off somewhat during spring and summer. When this response to RCP8.5 greenhouse gas forcing is decomposed into the contributions made by future SSTs alone versus future GHGs alone, the latter are found to be primarily responsible for these O3S changes. Both the future SSTs alone and the future GHGs alone accelerate the Brewer–Dobson circulation, which modifies extratropical lower-stratospheric ozone mixing ratios. While the future GHGs alone promote a more zonally symmetric lower-stratospheric ozone change due to enhanced ozone production and some transport, the future SSTs alone increase lower-stratospheric ozone predominantly over the North Pacific via transport associated with a stationary planetary-scale wave. Ozone accumulates in the trough of this anomalous wave and is reduced over the wave's ridges, illustrating that the composition of the lower-stratospheric ozone reservoir in the future is dependent on the phase and position of the stationary planetary-scale wave response to future SSTs alone, in addition to the poleward mass transport provided by the accelerated Brewer–Dobson circulation. Further, the future SSTs alone account for most changes to the large-scale circulation in the troposphere and stratosphere compared to the effect of future GHGs alone. These changes include modifying the position and speed of the future North Pacific jet, lifting the tropopause, accelerating both the Brewer–Dobson circulation's shallow and deep branches, and enhancing two-way isentropic mixing in the stratosphere.

Study of Diameter-to-Draft Ratio of Pitch Point Absorber as Wave Energy Converter in Indonesia Waters Based on Boundary Element Method

Recently, harnessing the energy from low wave energy density areas is concerned to deal with renewable energy targets. The previous study proposed a pitch point absorber with a submerged sectional equivalent area as the design parameter. However, that parameter did not suggest the best sectional area and did not directly correlate with the theory of structure hydrodynamic. Thus, this research proposes the diameter-to-draft ratio as a design parameter for the pitch point absorber. The study was conducted numerically using Boundary Element Method software to investigate diffraction characteristics of the device and analyze structure response in irregular waves. The model was modified with five different diameters and ratios. JONSWAP Spectrum was used to generate wave elevation with a 2-m significant wave height and 10-second peak period. The time domain simulation was set at 10.800 seconds. The result of this study showed that the highest responses occurred when the diameter-to-draft ratio was 5 because it has the closest structure natural frequency to assumed wave frequency, which makes it easier to resonate. In all diameters, the higher ratio affects the range of the structure natural frequency getting farther from the assumed wave, so the responses become smaller.

Approach for Near-Real-Time Pipe Burst Detection and Location Estimation Utilizing Any Sequence of Harmonics of the Transient Pressure Signal

The purpose of the paper is to present an approach for real-time pipe burst detection and location estimation, based on the changes in the harmonics and analysis of the corresponding damping that is caused by the burst. The amplitude of each resonance response of the transient pressure wave caused by the burst is damped differently due to the occurrence of the burst. However, utilizing higher order harmonics beyond the first few fundamental frequencies has not previously been possible as it leads to an increasing number of possible solutions to the burst location, which limits the application of the method. An algorithm for damping analysis has been developed which overcomes this limitation, and is able to exclude most of the incorrect solutions when utilizing the information contained in higher order harmonics. Additionally, the gap between data windows can be set so that it enables the real-time data analysis by letting the window gap equal the reciprocal of the sampling rate. Therefore, this algorithm makes utilizing any sequence of harmonics of the signal be possible for real-time burst detection and location estimation. The approach has been verified both numerically and experimentally with acceptable accuracy.

Oscillatory behaviors of multiple shock waves to upstream disturbances

The oscillatory response of multiple shock waves to upstream disturbances in a supersonic flow is studied numerically in a constant area rectangular duct. The flow is accelerated through a nozzle with an exit Mach number of 1.75 and continues in the constant area duct, where multiple shock waves are formed. To investigate the effect of upstream disturbance on shock oscillations, three parameters are varied systematically: upstream turbulent intensity, frequency of upstream pressure fluctuation, and amplitude of upstream pressure fluctuation. The wall shear stress variation along the duct length provides the location of separation and reattachment points in the flow field. The wall pressure frequency spectra were used to investigate the low-frequency unsteadiness in shock oscillations. The power spectral density of the wall static pressure and the probability density function (PDF) of shock location are analyzed, and the results suggest that as the upstream turbulent intensity is increased, the dominant frequency of oscillation is increased and the shock oscillations become more symmetrical. As the upstream disturbance frequency is increased, the shock oscillations become more symmetrical and follow the Gaussian curve closely. The shock wave oscillates with the same upstream excitation frequency when the upstream disturbance amplitude is increased. At large values of upstream disturbance amplitude, the PDF shows a large deviation from the Gaussian, and the rms amplitude of shock oscillation increases monotonously. At higher amplitudes of upstream disturbance excitation, the traces of shock train leading-edge location display path-dependence characteristics.

Non-Abelian mechanics of elastic waves in Kagome metamaterials with internal microstructures

In this work, the duality of mechanical Kagome lattices with internal microstructures is studied and its non-Abelian characteristics of wave packet evolution are discussed. Based on Bloch's theorem, the dynamical and duality matrices are obtained during elastic wave propagation. By regulating the twisting angles of the Kagome lattices and internal microstructures, global twofold degeneracy and unequal Berry phase can be obtained. A fourfold degeneracy appears at Γ point when the mechanical metamaterial is subjected to a special twisting state. Numerical calculations of non-Abelian mechanics and duality are performed, in which band structures with special twisting angles are the same. In addition, the solution of the Wilson operator is derived by the elastic wave equation and gauge transformation, which has non-exchangeable product and leads to the non-Abelian Berry curvature. If the time-reversal symmetry is broken, non-commutative elastic wave responses can be generated. The generalized polarization and wave propagation become different when the acting sequences of external forces are exchanged.

Global Dynamical Network of the Spatially Correlated Pc2 Wave Response for the 2015 St. Patrick's Day Storm

AbstractWe show the global dynamics of spatial correlation of Pc2 wave activity can track the evolution of the 2015 St. Patrick's Day geomagnetic storm for an 8 hr time window around onset. The global spatially coherent response is tracked by forming a dynamical network from 1 s data using the full set of 100+ ground‐based magnetometer stations collated by SuperMAG and Intermagnet. The pattern of spatial coherence is captured by network parameters which in turn track the evolution of the storm. At onset interplanetary magnetic field (IMF) Bz > 0 and Pc2 power increases, we find a global response with stations correlated over both local and global distances. Following onset, whilst Bz > 0, the network response is confined to the day‐side. When IMF Bz < 0, there is a strong local response at high latitudes, consistent with the onset of polar cap convection driven by day‐side reconnection. The spatially coherent response as revealed by the network grows and is maximal when auroral (SuperMAG electrojet) and ring current (SuperMAG ring current) 1 min resolution geomagnetic indices peak, consistent with an active electrojet and ring‐current. Throughout the storm there is a coherent response both in stations located along lines of constant geomagnetic longitude, between hemispheres, and across magnetic local time. The network does not simply track average Pc2 wave power, it is characterized by network parameters which track the storm evolution. This is the first study to parameterize global Pc2 wave correlation and offers the possibility of statistical studies across multiple events and comparison with, and validation of, space weather models.

The Response of Auroral-Oval Waves to CIR-Driven Recurrent Storms: FY-3E/ACMag Observations

Alfven-branch waves provide an efficient means for transporting energy into the auroral oval. Here, we report observations of these waves obtained by the Fengyun-3E (FY-3E)/ACMag instruments, which are designed to detect three-dimensional AC magnetic fields in the 0.05–25 Hz band. The observations suggest that broadband waves are a permanent feature of the auroral oval, although their amplitude and locations vary with the global state of the magnetosphere. We primarily focus on the data obtained from 10 July 2021 to 26 August 2021, during which a series of recurrent storms driven by solar wind corotating interaction regions (CIRs) occurred. Analysis of the observations shows that the auroral-oval waves grow in amplitude (1–3 orders of magnitude) and shift to lower latitude (∼10°) immediately following the decrease in the SYM-H index in each storm. Further investigation reveals the response of the auroral-oval waves has a time scale equal to or less than FY-3E’s effective revisiting time, which is about 45 min. The observations presented in this paper confirm that the FY-3E/ACMag instruments provide a high-resolution monitor of the auroral-oval waves and could further our understanding of auroral physics.

Formulation of ship roll damping models from free-decay data

Estimation of roll damping of a ship is essential to the prediction of its response in waves. The formulation of ship roll damping models from experiment or CFD data involves two parts: the determination of the model form and the calculation of the model coefficients, and both have significant influences on damping accuracy. To improve the roll motion prediction of a particular ship, this paper made an investigation of the typical damping models and its influence factors based on benchmark experiment data. The results show that the typical damping models can not reflect the fluid physics of roll motion. A conclusion is given that all roll angle, angular roll velocity, and angular roll acceleration should be considered in damping model determination. For the convenience of solving the roll motion equation, damping models with angle and angular velocity as independent variables are proposed due to the coupling of the angle, angular velocity, and the angular acceleration in roll. A procedure of damping model formulation is developed based on the Prony-SS method which was introduced into roll damping identification recently. Examples that follow the procedure show good performance. Furthermore, forward speed and flow memory effects on ship roll damping are discussed.

A numerical study on the added resistance and motion of a ship in bow quartering waves using a soft spring system

The prediction of resistance performance in oblique waves have been a key issue for the accurate estimation of added resistance of ships in the actual operating state. Therefore, in this paper, the added resistance of a large tanker in the bow quartering waves (180⁰, 150⁰, 120⁰) was studied by applying a computational fluid dynamics (CFD) solver based on the unsteady Reynolds-averaged Navier-Stokes equations. In addition, the forces and motion responses in bow quartering waves according to the captive test (heave, roll, and pitch free) and soft spring test (6 DOF) were investigated. To validate the CFD results, it was compared with the model test results showing good agreement. The maximum value of the added resistance was observed between 180⁰ and 150⁰, and it decreased sharply at 120⁰. The peak of the added resistance moved to a shorter wave region. The differences in added resistance, heave, and pitch motions in oblique wave according to the degree of freedom were insignificant. However, the discrepancy in roll motion occurred due to the forces and moments differences caused by the degree of freedom. The tendency of added resistance in the bow quartering waves and the forces and motion responses according to the degree of freedom were also investigated.

Wave propagation analysis in laminated composite periodic frame structures using spectral finite element method

In this article, wave propagation in a one-dimensional (1-D) composite periodic frame structure is analyzed using spectral finite elements (SFE) method together with Bloch’s theorem. Each element in the periodic frame structure is modeled as a first-order shear deformation theory (FSDT) beam element and wave equations for the beam elements are derived using FSDT considering axial, flexural, and shear deformations. Next, these equations are solved using the frequency domain SFE method to obtain an elemental dynamic stiffness matrix which on assembly gives the dynamic stiffness matrix for the unit cell of the periodic structure. A polynomial eigenvalue problem is formulated thereafter using Bloch’s theorem to evaluate the dispersion coefficients and wave amplitude ratios. Finally, the entire periodic frame is modeled as homogenized two-noded elements capturing the wave response of the PS with a drastic reduction in computational cost. The results obtained using the present method are validated with finite element simulation using ANSYS mechanical Ansys Parametric Design Language (APDL). The frequency band gaps observed in the frequency domain responses are investigated and corroborated with those predicted by the dispersion relations. This is followed by a detailed parametric study on the influence of different parameters on the band gap characteristics. The present method provides a scheme of wave propagation analysis of composite periodic frames with substantial computational efficiency.

An Offshore Solar Irradiance Calculator (OSIC) Applied to Photovoltaic Tracking Systems

Offshore photovoltaic installations are the future technology in solar energy since they enable the use of the large amount of maritime space, which is especially important when land space is not available. Various research groups are working to create viable installations. However, there are currently no tools available that an offshore system designer can use to quantify the effect of wave response motion on offshore photovoltaic installations. This research presents a new simulation tool termed the Offshore Solar Irradiance Calculator (OSIC) that is able to quantify this effect. Furthermore, a yearly parametric analysis is presented to show the effects of a characteristic wave equation on different offshore tracking systems; namely, horizontal single-axis tracking, vertical single-axis tracking and dual-axis tracking. Finally, another parametric analysis is presented to show the effects of varying wave amplitudes of oscillations on the incident irradiance received by these tracking systems.