Wave Theory Research Articles

Kinetic characteristics of a moored floating structure with a liquid column vibration absorber (LCVA)

ABSTRACT The pitch motion of offshore floating structures under external forces is critical. This study examines the effectiveness of a liquid column vibration absorber (LCVA), a passive damping device with an oscillating liquid in a U-tube, in mitigating pitch motion and vibration. A motion equation describing the LCVA-structure interaction was derived, and a two-dimensional numerical model based on the boundary element method and Airy wave theory was developed. Flume experiments validated the numerical results. Parametric analyses investigated the effects of LCVA and structural characteristics, including the cross-section and water level of the vertical liquid column, as well as the floating structure's draft and length. Results show that an LCVA can reduce pitch motion amplitude by approximately 75%. Structural parameters significantly affect heave motion, while vertical water level strongly influences pitch. Thus, proper LCVA tuning can effectively mitigate pitch motion. Additionally, the floating structure's pitch interacts with the liquid column's amplitude.

The disrupting and growing open cluster spiral arm patterns of the Milky Way

Abstract Star clusters provide unique advantages for investigating Galactic spiral arms, particularly due to their precise ages, positions, and kinematic properties, which are further enhanced by ongoing updates from the astrometric data. In this study, we employ the latest extensive catalogue of open clusters from Gaia DR3 to examine the positional deviations of clusters belonging to different age groups. Additionally, we employ dynamical simulations to probe the evolutionary behavior of spiral arm positions. Our analysis reveals an absence of a theoretical age pattern in the spiral arms traced by open clusters, and the pattern speeds of the spiral arms are consistent with the rotation curve. Both of these results do not align with the predictions of quasi-stationary density wave theory, suggesting a more dynamic or transient arm scenario for the Milky Way. From this perspective, combined with vertex deviation estimates, it appears that the Local arm is in a state of growth. In contrast, the Sagittarius-Carina arm and the Perseus arm exhibit opposing trends. Consequently, we speculate that the Galactic stellar disk does not exhibit a grand-design spiral pattern with a fixed pattern speed, but rather manifests as a multi-armed structure with arms that continuously emerge and dissipate.

Field–particle energy transfer during chorus emissions in space

Chorus waves are some of the strongest electromagnetic emissions naturally occurring in space and can cause radiation that is hazardous to humans and satellites1, 2–3. Although chorus waves have attracted extreme interest and been intensively studied for decades4, 5, 6–7, their generation and evolution remain highly debated7. Here, in contrast to the conventional expectation that chorus waves are governed by planetary magnetic dipolar fields5,7, we report observations of repetitive, rising-tone chorus waves in the terrestrial neutral sheet, where the effects of the magnetic dipole are absent. Using high-cadence data from NASA’s MMS mission, we present ultrafast measurements of the wave fields and three-dimensional electron distributions within the waves, which provides evidence for chorus–electron interactions and the development of electron holes in the wave phase space. We found that the waves are associated with resonant currents antiparallel to the wave magnetic field, as predicted by nonlinear wave theory. We estimated the nonlinear field–particle energy transfer inside the waves, finding that the waves extract energy from local thermal electrons, in line with the positive growth rate of the waves derived from an instability analysis. Our observations may help to resolve long-standing controversies regarding chorus emissions and in gaining an understanding of the energy transport observed in space and astrophysical environments.

Determinants of Human Corneal Mechanical Wave Dispersion for In Vivo Optical Coherence Elastography.

To characterize frequency-dependent wave speed dispersion in the human cornea using microliter air-pulse optical coherence elastography (OCE), and to evaluate the applicability of Lamb wave theory for determining corneal elastic modulus using high-frequency symmetric (S0) and anti-symmetric (A0) guided waves in cornea. Wave speed dispersion analysis for transient (0.5 ms) microliter air-pulse stimulation was performed in four rabbit eyes ex vivo and compared to air-coupled ultrasound excitation. The effects of stimulation angle and sample geometry on the dispersion were evaluated in corneal phantoms. Corneal wave speed dispersion was measured in 36 healthy human eyes in vivo. Air-pulse-induced dispersion was comparable to ultrasound-induced dispersion between 0.7 and 5 kHz (mean-difference ± 1.96 × SD: 0.006 ± 0.5m/s) in ex vivo rabbit corneas. Stimulation 0° relative to the surface normal generated A0 Lamb waves in corneal tissue phantoms, while oblique stimulation (35° and 65°) generated S0 waves. Stimulating normal to the human corneal apex in vivo (0°) induced A0 waves, plateauing at 10.87 to 13.63m/s at 4 kHz, and when obliquely stimulated at the periphery (65°), produced S0 waves, plateauing at 13.10 to 15.98m/s at 4 kHz. Air-pulse OCE can be used to measure human corneal Lamb wave dispersion of A0 and S0 propagation modes in vivo. These modes are selectively excited by changing the stimulation angle. Accounting for wave speed dispersion enables reliable estimation of corneal elastic modulus in vivo. This work demonstrates the feasibility of air-pulse stimulation for robust OCE measurements of corneal stiffness in vivo for disease detection and therapy evaluation.

Comparison study of seismic-tsunami performance for coastal bridges with different RC sacrificial shear keys

Simple-support bridges are employed in offshore regions as integral component of coastal transportation networks. However, these bridges are vulnerable to the combined effects of earthquakes and ensuing tsunami waves due to weak lateral resistance. Reinforced concrete (RC) shear keys have been widely utilized to strengthen bridges by providing extra constraints to the superstructure. While the seismic performance of RC shear keys has been extensively studied, their effectiveness under the sequential action of both hazards remains seldom addressed yet. Therefore, this study aims to compare the seismic-tsunami response of bridges with different RC shear keys. To this regard, a novel envelope curve model was developed for the diagonal failure shear key, with emphasis on their distinct behaviors under seismic and tsunami impacts. OpenSees platform was employed, with natural ground motions and second-order solitary wave theory adopted for seismic and tsunami modeling, respectively. The shear key under each hazard was simulated using an Update Material approach to account for the distinct mechanical property. Subsequently, a parametric study was carried out to compare various factors, including shear key failure modes and strength, as well as wave conditions. The analysis result showed that the maximum strength of RC shear keys can significantly affect bridge performance, while the failure mode also contributes. In addition, the wave condition can largely affect the time-history and maximum deformation depending on water depths. Furthermore, the recommendations for shear key design against sequential seismic-tsunami hazards were provided.

Application of Stokes’ higher order theory and JONSWAP spectrum in modelling extreme wave events validation with historical data

Accurately modelling wave elevations is critical for the design and safety of offshore structures. This study explores the application of Stokes’ 5th Order Wave Theory and JONSWAP (Joint North Sea Wave Project) spectrum to simulate wave conditions similar to those experienced during the Draugen Ringing Event. Hindcasting on the dataset collected form Norwegian Meteorological Institute sensor system Draugen is performed. Through rigorous analysis performed by integrating these models, we aim to validate their accuracy and reliability against empirical data. The methodology includes generating the JONSWAP spectrum based on significant wave heights and peak periods, followed by computing wave surface elevations using Stokes’ 5th Order Wave Theory and spectral analysis. The outcome of the analysis shows a strong correlation between the modelled irregular wave elevations and actual wave data, demonstrating the effectiveness of these models.

Bifurcation and Exact Solutions of a Concatenation Physical Model

To find the exact explicit solution of the concatenation model, the corresponding differential system of the amplitude component is used, which is a planar dynamical system with a singular straight line. In this paper, by using the techniques from dynamical systems and singular traveling wave theory developed by Li and Chen [2007], its corresponding traveling wave system is solved and analyzed, obtaining the corresponding phase portraits and showing the dynamical behavior of the amplitude component. Under different parameter conditions, exact explicit solitary wave solutions, periodic wave solutions, kink and anti-kink wave solutions, compacton solutions, as well as peakons and periodic peakons, are found explicitly.

Propagation of lump and traveling wave solutions to the (4 + 1)-dimensional Fokas equation arising in mathematical physics

In this paper, the [Formula: see text]-dimensional Fokas model is investigated analytically with extensive applications in nonlinear wave theory including the evolution of a three-dimensional wave packet in water with a finite depth, and surface waves and internal waves in straits or channels of varied depth and width. Applying the Hirota bilinear approach, the lump wave solitons and interaction of lump with periodic waves, the interactions of lump wave along single, double-kink solitons as well as the interactions of lump, periodic along double-kink solitons of the governing model are developed. Additionally, by using the extended tanh function technique, certain new traveling wave solitons are established. The physical nature of several solitons is illustrated by drawing the 3D, contours and 2D plots. Consequently, a set of periodic, bright, dark, rational as well as elliptic function solitons are constructed. The employed techniques seem to be more effective and well organized to build some interesting analytical wave solitons to several appealing nonlinear models.

Modeling the motion of a ship with suspended cargo

The stability of a vessel determines its ability to safely navigate in any sea state. In the process of studying the dynamics of a vessel in rough seas, the method of mathematical modeling based on the linear theory of waves and rolling has been used. The models allow obtaining calculation formulas and methods used to analyze the rolling of vessels with shifting cargo on board (liquid, bulk, suspended). The effect of suspended cargo on the seaworthiness of a vessel is currently considered only when solving problems of static stability. When solving problems of dynamics, mathematical models of the roll of a vessel with suspended cargo in calm water and regular waves have been proposed, and linear differential equations of the roll of a vessel with suspended cargo have been obtained. The presence of suspended cargo on a vessel significantly changes the parameters of the roll due to the occurrence of heeling and variable moments of inertia of the vessel. The proposed mathematical methods allow simulating the roll in any regular waves, taking into account arbitrary values of the transverse metacentric height, cargo weight and suspension length.

A Rational Design Method for the Nagoya Type-III Antenna

The current study, as part of a PhD project on the design of a helicon thruster, aims to provide a rational methodology for the design of the helicon thruster’s main component, i.e., the helicon antenna. A helicon thruster is an innovative electrodeless plasma thruster that works by exciting helicon waves in a magnetized plasma, and its antenna is capable of producing a uniform, low-temperature, high-density plasma. A magnetic nozzle is used to accelerate the exhaust plasma in order to generate a propulsive thrust. In this paper, we consider a simple helicon antenna, specifically the Nagoya type-III antenna. We consider a common experimental setup consisting of a quartz tube with finite length containing a uniform magnetized plasma and a Nagoya type-III antenna placed at the tube centre. Considering previous studies on helicon waves theory, we compare three different design methods, each based on simplifying different modelling assumptions, and evaluate the predictions of these models with results from full-wave 3D simulations. In particular, we concentrate on deriving a rational design method for the helicon antenna length, given the dimension of the quartz tube and the desired target plasma parameters. This work aims to provide a practical and fast method for dimensioning the antenna length, useful for initializing more accurate but computationally heavier full-wave simulations in 3D geometry or simply for a rapid prototyping of the helicon antenna. These results can be useful for the development of a helicon thruster but also for the design of a high-density radiofrequency plasma source.

Numerical simulation and experimental investigation of the propagation law of plasma pulse shock waves

Abstract Plasma pulse shock wave rock-breaking technology represents a novel approach to rock fracturing. Present research on this subject largely addresses rocks and electrodes, yet often neglects the critical influence of shock waves in the rock-breaking process. Therefore, it is necessary to further study the propagation law of the shock wave and its reflection and transmission. This paper undertakes experimental simulations using the RHT rock model to explore the propagation process of plasma pulse shock waves based on two variables: the medium and the shape of the electrode. Integrated with one-dimensional stress wave theory, the study examines the impact of four specific parameters—dielectric thickness, surrounding rock height, surrounding rock density, and surrounding rock porosity—on the reflection and transmission rates of shock waves. Pressure data collected from experimental platform are utilized to validate the study’s conclusions. The findings indicate that the propagation behaviors of shock waves differ significantly between water and air mediums. The shape of the electrode causes significant differences in the pressure exerted by the shock wave at the same location. Both the thickness of the dielectric and the porosity of the surrounding rock show a positive correlation with the reflection coefficient and a negative correlation with the transmission coefficient, while the density of the surrounding rock exhibits an inverse relationship. The height of the surrounding rock is irrelevant to both reflection and transmission coefficients.

Rock-Breaking Mechanism and Application of Combined Long and Short Holes in Parallel Holes Cut in Small-Section Tunnels

In order to address the issue of limited excavation footage in the drilling and blasting of a water diversion tunnel with a cross-section of approximately 10 m2, which is unable to meet the demands of rapid construction, a blasting method combining long and short straight-hole cutting was proposed based on the theories of elastic mechanics, blasting craters, explosive gas and stress waves. A mechanical model was established to elucidate the parameter design method and cavity formation principle of the combined cutting. Numerical simulation and field tests were employed to analyze the rock-breaking process of combined cutting, with a view to comparing the blasting effect differences between the traditional inclined cutting method and the combined cutting method. The research results indicate that during the blasting process with combined long and short straight-hole cutting, the uncharged portion of the deep hole can serve as an empty hole during the subsequent blasting of the shallow hole. The concentration of stress at the wall of the empty hole and the superposition of reflected and incident waves serve to enhance the rock-breaking effect of the shallow hole, with the enhancement being influenced by the diameter of the hole and the distance between it and the empty hole. The preferential detonation of the shallow hole can provide a smaller resistance line and free surface distance for deep hole detonation, creating favorable conditions for rock fragmentation in deep hole blasting, making it easier for the rock in the cutting area to be thrown out and increasing the utilization rate of the blast holes. The shape of the formed cavity is a long strip-shaped cube, with its volume being influenced by the spacing between each group of deep and shallow holes. The rock mass damage is most severe in the vertical direction, while the rock mass damage at the center of the upper and lower edges is relatively weaker. In order to optimize the utilization of blasting energy, it is essential to select an appropriate spacing between each group of blast holes. In comparison to the utilization of traditional inclined cuts, the implementation of combined long and short holes has been observed to result in a greater extent of blasting footage and relatively lower explosive consumption. These research findings provide a reference point for the rapid and efficient construction of small-section tunnel engineering, as well as the design of straight-hole cut blasting with reduced consumption.

Interplay of Spin Nernst Effect and Entanglement Negativity in Layered Ferrimagnets: A Study via Exact Diagonalization.

In this paper, we analyzed the influence of the spin Nernst effect on quantum correlation in a layered ferrimagnetic model. In the study of three-dimensional ferrimagnets, the focus is on materials with a specific arrangement of spins, where the neighboring spins are parallel and the others are antiparallel. The anisotropic nature of these materials means that the interactions between spins depend on their relative orientations in different directions. We analyzed the effect of magnon bands induced by the coupling parameters on entanglement negativity. The influence of the coupling parameters of the topologic phase transition on quantum entanglement is investigated as well. Numerical simulations using the Lanczos algorithm and exact diagonalization for different lattice sizes are compared with the results of spin wave theory.

On the transverse-traceless gauge condition when matter is presented

The transverse-traceless gauge condition is an important concept in the theory of gravitational waves. It is well known that a vacuum is one of the key conditions to guarantee the existence of the transverse-traceless gauge. Although it is thin, the interstellar medium is ubiquitous in the Universe. Therefore, it is important to understand the concept of gravitational waves when matter is presented. Bondi–Metzner–Sachs theory has solved the gauge problem related to gravitational waves. But it does not help with cases when the gravitational wave propagates in matter. This paper discusses possible extensions of the transverse-traceless gauge condition to Minkowski perturbation with matter presented.

Metasurface absorber for millimeter waves: a deep learning-optimized approach for enhancing the isolation of wideband dual-port MIMO antennas

In this communication, the concept of metasurface absorber is utilized to enhance the isolation in the dual port multiple-input multiple-output (MIMO) antenna specially designed for a wideband millimeter wave operation. The frequency of operation of the designed module is 32.5–42.5 GHz with sufficient gain attributes. The designed metasurface array consists of two circular rings on two different layers. The concept of deep learning is utilized to optimize the dimensional configuration of the metasurface to achieve the maximum absorption of electromagnetic waves in the band of interest. The suppression of mutual coupling by double-ring metasurface is analyzed with the help of the wave theory concept. In contrast to previous decoupling methods using metasurfaces, the suggested metasurface is intended to be in the same plane as the array. The findings demonstrate the capability of effectively separating antenna elements in wideband MIMO antenna without compromising the geometrical complexity. Diversity metrics such as envelope correlation coefficient (ECC), mean effective gain (MEG), channel capacity loss (CCL), and total active reflection coefficient (TARC) for the proposed frequency range are also used to evaluate the performance of the constructed MIMO antenna. The wideband characteristics with a compact configuration make the design MIMO module a suitable candidate for mm-wave applications. The congruence between simulation and measurement confirms the validity of the suggested design.

Stability analysis of a seabed under combined action of waves and seismic loading

The stability analysis of a seabed under wave and seismic loading is conducted within the framework of yield design theory using the pseudo-static method. The strength properties of the constitutive material are modeled by means of a purely cohesive condition. The loading associated with water waves is modeled through the linear wave theory, whereas the inertial forces induced by the passage of seismic waves is addressed in the framework of pseudo-static method. The material cohesion that increases linearly with dept is adopted in the analysis. A sufficient stability condition is obtained through the static approach of limit analysis, while a necessary condition is determined from the kinematic approach. The effects of seafloor surface inclination, as well as seismic intensity, are analyzed through pseudo-static coefficients. The determination of the limit load obtained through the pseudo-static approach is based on existing literature, particularly when seismic coefficients are not considered.

Seismic Fragility Analysis of Offshore Wind Turbines Considering Site-Specific Ground Responses

This study investigated the seismic performance and assessed the seismic fragility of an existing pentapod suction-bucket-supported offshore wind turbine, focusing on the amplification of earthquake ground motions. A simplified suction bucket–soil interaction model with nonlinear spring elements was employed within a finite element framework, linking the suction bucket and soil to hypothetical points on the OWT structures at the mudline. Unlike conventional approaches using bedrock earthquake records, this study utilized free-field surface motions as input, derived from bedrock ground motions through one-dimensional wave theory propagation to estimate soil-layer-induced amplification effects. The validity of the simplified model was confirmed, enabling effective assessment of seismic vulnerability through fragility curves. These curves revealed that the amplification effect increases the vulnerability of the OWT system, raising the probability of exceeding damage limit states such as horizontal displacement of the tower top, tower stress, and horizontal displacement at the mudline during small to moderate earthquakes, while decreasing this likelihood during strong earthquakes. Comparisons between the Full Model and the simplified Spring Model reveal that the simplified model reduces computational time by approximately 75%, with similar seismic response accuracy, making it a valuable tool for rapid seismic assessments. This research contributes to enhancing seismic design practices for suction-bucket-supported offshore wind turbines by employing a minimalist finite element model approach.

Dynamic Analysis of Fixed Offshore Structures for Wind Turbines

Offshore wind power presents itself as an alternative for complementing and diversifying the Brazilian energy matrix. In this context, fixed jacket-type platforms, widely used by the oil industry, are alternatives for supporting offshore wind turbine towers. However, the unique characteristics of these structures, such as their large dimensions, high centers of mass, and eccentricities of assemblies, as well as the random nature of the loads acting simultaneously on the structure, such as ocean waves, winds, and currents, are challenging components for the engineering of structures built in the marine environment. This article presents some of the main computational models for dynamic structural analysis of fixed offshore wind turbines. In the applied methodology, the sea state is modeled based on second-order Stokes wave theory, where fluid kinematics are calculated from the analysis of random waves in the frequency domain, using the Pierson-Moskowitz spectrum. The aeroelastic-dynamic forces and interactions acting above the free surface were simplified through the adoption of values prescribed in the literature. Finally, structural analysis is carried out using the finite element method, with the jacket bars modeled using plane frame elements. The results obtained in terms of dynamic properties, as well as structural responses, were compared with those extracted from recent works, thus confirming the validity of the chosen methods and consolidating the results for the development of future work.

Propagation characteristics of explosion shock waves in air under different temperature and pressure conditions

Abstract In order to study the propagation characteristics of explosion shock waves in air under different temperature and pressure conditions, stress wave theory and detonation wave theory were first used to analyze the propagation characteristics of shock waves. Combined with numerical simulation results, the propagation characteristics of explosion shock waves were comprehensively analyzed and verified. The following conclusion was drawn: the higher the pressure, the larger the peak value of shock waves at the same spatial position, and the greater the specific impulse of shock waves, Shortening of shock wave propagation distance; The higher the temperature, the less the peak pressure changes at the same spatial position, the smaller the specific impulse of the shock wave, and the longer the propagation distance of the shock wave.

Prediction of fragment impact energy release overpressure based on machine learning

Abstract The overpressure within a quasi-sealed chamber serves as a crucial metric for assessing the energy release behavior and impact potential of energetic fragments. Combining one-dimensional shock wave theory and material microparameters, different machine learning models were trained to predict the overpressure generated by different energetic fragments. The final results demonstrate that the RF model achieved the highest prediction accuracy, with an RMSE error of 0.0251 MPa. Notably, the mathematical expression generated by symbolic regression only incorporated four features. After iterative training of symbolic regression using four features, the prediction accuracy was notably higher. This accuracy surpassed that of the DT model and KNN model, which were trained with eight features. However, it still fell slightly below the accuracy of the GBDT model, which was also trained with eight features.