Explore the vast range of titles available.

The modulation of chorus waves on several‐second timescales in Earth's magnetosphere plays a crucial role in modulating electron precipitation intensity, leading to the formation of pulsating aurora. However, the physical mechanism underlying chorus modulation remains not fully understood. In this study, we perform self‐consistent particle‐in‐cell simulations with typical magnetospheric plasma parameters to quantify chorus modulation driven by plasma density variations and compressional magnetic field fluctuations. It is demonstrated that chorus modulation is determined by nonlinear wave‐particle interactions, in which the condition for nonlinear wave growth is highly sensitive to background plasma parameters. The resulting electron precipitation in the ∼10–200 keV energy range exhibits modulation on comparable timescales, consistent with observations of pulsating aurora. This study enhances our understanding of how variations in magnetospheric plasma parameters influence chorus wave excitation and the associated particle dynamics.

We study spin wave excitation modes of kπ skyrmion (k = 1, 2, 3) in a magnetic nanodot under an external magnetic field along the z direction using micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation. We find that a transition of kπ skyrmion to other skyrmion-like structures appears under some critical external fields, the corresponding spin wave excitations are simulated for each state under magnetic field. For skyrmion, the frequencies of excitation modes increases and then decreases with the low frequency mode splitting at a critical magnetic field. In addition to the well-known two in-plane rotation modes and an out-of-plane breathing mode of skyrmion, more excitation modes are found with a higher k (k = 2, 3). The excitation modes vary as a function of magnetic field, and the excitation frequencies for different modes exhibit a rapid or slight change depending on the field-induced change of magnetization profile. Our study indicates the rich spin wave excitations for kπ skyrmion and opens up the possibility for theoretical or experimental investigation of magnonics application.

Traditional rigid vehicle model cannot reflect structural local vibration and flexible deformation, which may affect the accuracy in evaluating ride comfort of metro vehicle. Aiming at this issue, this paper proposes a research method of flexible dynamic behavior based on flexible multi-body dynamics (FMBD), considering the structural flexibilities of key parts of metro vehicle in detail, to study the ride comfort of metro vehicle. First, finite element models of carbody and frame are established, which are then reduced by substructure theory and Guyan reduction method. On this basis, the flexible vehicle-track coupled dynamic model is established. After investigating the difference between the flexible model and traditional rigid model, the ride comfort of metro vehicle on straight line and curve line is then evaluated subjected to rail random irregularity, short-wave excitation and long-wave excitation, respectively. Finally, correlations of carbody vibrations at different locations are deeply investigated. Results show that carbody accelerations calculated by flexible model are larger than those obtained by rigid model. The sensitive frequency band of human is obviously reflected and calculated by flexible model, indicating that the ride comfort of metro vehicle can be more accurately evaluated with the flexible vehicle model. Flexible modes and local vibrations are obviously reflected in carbody vibrations. Vibration at PR (point on roof) location is largest, and vibration at PC (point on floor center) location is smallest. Ride comfort is very sensitive to long-wave excitation while is not sensitive to short-wave excitation. It is not accurate enough to evaluate ride comfort of metro vehicle only according to vibration at floor center, and more data at different locations should be concerned, especially vibrations at air spring locations.

In order to simplify the stator winding structure of traditional variable reluctance (VR) resolvers and enhance their performance under high-speed operating conditions, this paper proposes a design for a variable reluctance self-coupling resolver based on ultrahigh-frequency (UHF) square wave excitation. The proposed solution optimizes the traditional winding structure by eliminating the separate excitation winding and integrating both excitation and detection functions into the two-phase sine and cosine windings. By optimizing the arrangement of the sine and cosine windings, a single-layer equal-turn winding design is successfully implemented, significantly simplifying the winding layout and reducing copper usage. In terms of excitation signal, this paper innovatively replaces the traditional sinusoidal excitation with UHF square wave excitation. Compared to sinusoidal excitation, square wave excitation not only generates higher electromotive force (EMF) peaks but also simplifies engineering implementation, reducing the complexity of system hardware. To validate the feasibility and advantages of the proposed structure, a complete experimental testing platform was built, and comparative experiments were conducted under various rotational speeds. The experimental results show that the proposed self-coupling resolver can achieve high-precision rotor position detection across the entire speed range, significantly improving the detection accuracy and dynamic response of traditional methods under high-speed conditions. Ultimately, the design demonstrates strong engineering application potential and provides a new solution for high-precision, high-dynamic response rotor position detection.

Optimal control strategies represent a widespread solution to increase the extracted energy of a Wave Energy Converter (WEC). The aim is to bring the WEC into resonance enhancing the produced power without compromising its reliability and durability. Most of the control algorithms proposed in literature require for the knowledge of the Wave Excitation Force (WEF) generated from the incoming wave field. In practice, WEFs are unknown, and an estimate must be used. This paper investigates the WEF estimation of a non-linear WEC. A model-based and a model-free approach are proposed. First, a Kalman Filter (KF) is implemented considering the WEC linear model and the WEF modelled as an unknown state to be estimated. Second, a feedforward Neural Network (NN) is applied to map the WEC dynamics to the WEF by training the network through a supervised learning algorithm. Both methods are tested for a wide range of irregular sea-states showing promising results in terms of estimation accuracy. Sensitivity and robustness analyses are performed to investigate the estimation error in presence of un-modelled phenomena, model errors and measurement noise.

Transformers’ vibration and noise problems are critical to environmental comfort and reliability of equipment. To reduce the vibration and noise of transformers, the vibration and noise of medium and medium-high transformer cores under Maxwell force and magnetostriction were analyzed. A three-dimensional magneto-mechanical-acoustic coupled finite element model was established under sinusoidal and rectangular wave excitation. The deformation, vibration acceleration, and sound pressure distribution were analyzed under the Maxwell force and the magnetostrictive force of medium and medium-high transformers. A vibration noise optimization design architecture for medium and medium-high frequency transformers has been proposed. A transformer core structure with low noise vibration is designed based on the proposed optimization design architecture. The experimental results show that under the sinusoidal excitation, the vibration acceleration in the lamination direction decreases the most, from 18.748 m/s 2 before optimization to 4.89 m/s 2 and under rectangular wave excitation, it decreases from 51.08 m/s 2 before optimization to 13.182 m/s 2 . The proposed method provides a reference for the optimization design of low noise vibration transformers.

As offshore wind turbines develop into deepwater operations, accurately quantifying the impact of stochastic excitation in complex sea environments on offshore wind turbines and conducting structural fatigue reliability analysis has become challenging. In this paper, based on long-term wind–wave reanalysis data from the South China Sea, a novel direct probability integral method (DPIM) is developed for the stochastic response and fatigue reliability analysis of the key components for the floating offshore wind turbine structures, under combined wind–wave excitation. A 5 MW floating offshore wind turbine is considered as the research object, and a comprehensive analysis of the wind turbine system is performed to assess the short-term fatigue damage at the tower base and blade root. The proposed method’s accuracy and efficiency are validated by comparing the results to those obtained from Monte Carlo simulations (MCS) and a subset simulation (SSM). Additionally, a sensitivity analysis is conducted to evaluate the impact of different environmental parameters on fatigue damage, providing valuable insights for the design and operation of FOWTs in varying sea conditions. Furthermore, the results indicate that the fatigue life of floating offshore wind turbine (FOWT) structures under combined wind–wave excitation meets the design requirements. Notably, the fatigue reliability of the wind turbine under aligned wind–wave conditions is lower compared to misaligned wind–wave conditions.

Extensive prior research has delved into the localization of elastic wave energy through defect modes within phononic crystals (PnCs). The amalgamation of defective PnCs with piezoelectric materials has opened new avenues for conceptual innovations catering to energy harvesters, wave filters, and ultrasonic receivers. A recent departure from this conventional paradigm involves designing an ultrasonic actuator that excites elastic waves. However, previous efforts have mostly focused on single-defect scenarios for bending-wave excitation. To push the boundaries, this research takes a step forward by extending PnC design to include double piezoelectric defects. This advancement allows ultrasonic actuators to effectively operate across multiple frequencies. An analytical model originally developed for a single-defect situation via Euler–Bernoulli beam theory is adapted to fit within the framework of a double-defect set-up, predicting wave-excitation performance. Furthermore, a comprehensive study is executed to analyze how changes in input voltage configurations impact the output responses. The ultimate goal is to create ultrasonic transducers that could have practical applications in nondestructive testing for monitoring structural health and in ultrasonic imaging for medical purposes.

It is seen that blisk will be in a nodal diameter vibration state under the engine order excitation, which can be simulated by traveling wave excitation. The nodal diameters rotate on the blisk and it is necessary to identify the specific form of the nodal diameter vibration. Here, based on the determination of nodal diameter vibration parameters, a novel identification method of the nodal diameter vibration was proposed through the experimental test. Specifically, a traveling wave excitation system was built using the LabVIEW control software and noncontact magnetic exciters. Based on the description of resonant state of blisk, the identification principle formulas of the nodal diameter vibration were derived and the identification procedure was given. Taking uncoated and coated blisks as the research objects, the identification method was demonstrated. The identification results showed that the shape, direction, speed, and period of nodal diameter vibration were successfully obtained by the proposed method. In addition, it was found that coatings have a damping effect on blisk. Because of the coating introduction, the blisk vibration response was reduced, the rotation speed of nodal diameter was slowed down, and the rotation period of nodal diameter was increased.

On the basis of the model tests, this paper explores the coupled hydrodynamic performance of the moonpool and the hull. This study aims to compare and analyze the variation in the hull heave response between the piston resonance state of the moonpool under wave excitation and the non-resonance state of the moonpool under wave-current excitation. A novel damping device specifically designed and fabricated for stepped moonpools has been developed. Before and after the installation of the damping device, the free surface response characteristics of the moonpool and heave motion response characteristics of the hull are compared. The findings show a clear correlation between the current speed and heave response characteristics of the hull. During the seakeeping design phase of the drilling vessel, the current speed is an additional critical factor that cannot be disregarded, alongside the moonpool effect. A correlation exists between the fluid dynamics occurring within the moonpool and the heave motion of the vessel hull. A reduction in the amplitude of the motion of the moonpool water results in a decrease in the heave motion of the hull. This study provides a reference for alleviating the seakeeping of a drill ship’s heave response and enhancing the safety and efficiency of the operation.