Decelerating Airy pulse propagation in highly non-instantaneous cubic media

The propagation of decelerating Airy pulses in non-instantaneous cubic medium is investigated both theoretically and numerically. In a Debye model, at variance with the case of accelerating Airy and Gaussian pulses, a decelerating Airy pulse evolves into a single soliton for weak and general non- instantaneous response. Airy pulses can hence be used to control soliton generation by temporal shaping. The effect is critically dependent on the response time, and could be used as a way to measure the Debye type response function. For highly non- instantaneous response, we theoretically find a decelerating Airy pulse is still transformed into Airy wave packet with deceleration. The theoretical predictions are confirmed by numerical simulations

Geometric nonlinear dynamic response of wind turbines with different power performance

As the size of wind turbine blades increases, the influence of geometric nonlinearity on aerodynamic, structural and design of blades becomes more and more serious. In this work, the efficient aero-elastic calculation of large flexible blades is studied. In order to solve the problem of efficient aeroelastic caculation of large flexible blades, this work applied the geometrically exact beam theory based on Legendre spectral finite element and coupled with the blade element momentum theory to establish the aero-elastic analysis model of large flexible blades. This model can efficiently calculate the deformation and load on the blade under aerodynamic loading and fully consider the influence of geometric nonlinearity caused by deformation on aeroelastic ability. Taking NREL 5MW and IEA 15MW wind turbines as examples, the linear and nonlinear dynamic responses of these two wind turbine blades are calculated. The result shows that the neglect of nonlinear effect will bring error. From 5MW wind turbine to 15MW wind turbine, the numerical error increased by 27.88%. The influence of geometric nonlinearity of blades on dynamic responses is analysed, which is of great significance to improve the design level of large-scale wind turbines

Semibrittle seismic deformation in high-temperature mantle mylonite shear zone along the Romanche transform fault

Oceanic transform faults, a key element of plate tectonics, represent the first-order discontinuities along mid-ocean ridges, host large earthquakes, and induce extreme thermal gradients in lithosphere. However, the thermal structure along transform faults and its effects on earthquake generation are poorly understood. Here we report the presence of a 10- to 15-kilometer-thick in-depth band of microseismicity in 10 to 34 kilometer depth range associated with a high-temperature (700\ub0 to 900\ub0C) mantle below the brittle lithosphere along the Romanche mega transform fault in the equatorial Atlantic Ocean. The occurrence of the shallow 2016 moment magnitude 7.1 supershear rupture earthquake and these deep microearthquakes indicate that although large earthquakes occur in the upper brittle lithosphere, a substantial amount of deformation is accommodated in the semibrittle mylonitic mantle that resides at depths below the 600\ub0C isotherm. We also observe a rapid westward deepening of this band of seismicity indicating a strong lateral heterogeneity

Highly efficient room-temperature nonvolatile magnetic switching by current in Fe3GaTe2 thin flakes

Effectively tuning magnetic state by using current is essential for novel spintronic devices. Magnetic van der Waals (vdW) materials have shown superior properties for the applications of magnetic information storage based on the efficient spin torque effect. However, for most of known vdW ferromagnets, the ferromagnetic transition temperatures lower than room temperature strongly impede their applications and the room-temperature vdW spintronic device with low energy consumption is still a long-sought goal. Here, we realize the highly efficient room-temperature nonvolatile magnetic switching by current in a single-material device based on vdW ferromagnet Fe3GaTe2. Moreover, the switching current density and power dissipation are about 300 and 60000 times smaller than conventional spin-orbit-torque devices of magnet/heavymetal heterostructures. These findings make an important progress on the applications of magnetic vdW materials in the fields of spintronics and magnetic information storage.Comment: 18 page2, 4 figure

A Hybrid Forecast Model for Household Electric Power by Fusing Landmark-Based Spectral Clustering and Deep Learning

Household power load forecasting plays an important role in the operation and planning of power grids. To address the prediction issue of household power consumption in power grids, this paper chooses a time series of historical power consumption as the feature variables and uses landmark-based spectral clustering (LSC) and a deep learning model to cluster and predict the power consumption dataset, respectively. Firstly, the investigated data are reshaped into a matrix and all missing entries are recovered by matrix completion. Secondly, the data samples are divided into three clusters by the LSC method according to the periodicity and regularity of power consumption. Then, all samples in each cluster are expanded via bootstrap aggregating technique. Subsequently, a combination of a convolutional neural network (CNN) and a long short-term memory (LSTM) is employed to predict power consumption. The goal of CNN is to extract the features from input data in sequence learning, and LSTM aims to train and predict the power consumption. Finally, the forecasting performance of the LSC–CNN–LSTM is compared with several other deep learning models to verify its reliability and effectiveness in the field of household power load. The experimental results show that the proposed hybrid method is superior to other state-of-the-art deep learning techniques in forecasting performance

A Hybrid Forecast Model for Household Electric Power by Fusing Landmark-Based Spectral Clustering and Deep Learning

Household power load forecasting plays an important role in the operation and planning of power grids. To address the prediction issue of household power consumption in power grids, this paper chooses a time series of historical power consumption as the feature variables and uses landmark-based spectral clustering (LSC) and a deep learning model to cluster and predict the power consumption dataset, respectively. Firstly, the investigated data are reshaped into a matrix and all missing entries are recovered by matrix completion. Secondly, the data samples are divided into three clusters by the LSC method according to the periodicity and regularity of power consumption. Then, all samples in each cluster are expanded via bootstrap aggregating technique. Subsequently, a combination of a convolutional neural network (CNN) and a long short-term memory (LSTM) is employed to predict power consumption. The goal of CNN is to extract the features from input data in sequence learning, and LSTM aims to train and predict the power consumption. Finally, the forecasting performance of the LSC–CNN–LSTM is compared with several other deep learning models to verify its reliability and effectiveness in the field of household power load. The experimental results show that the proposed hybrid method is superior to other state-of-the-art deep learning techniques in forecasting performance

Characterization of the Wing Tone around the Antennae of a Mosquito-like Model

Mosquitoes’ self-generated air movements around their antennae, especially at the wing-beat frequency, are crucial for both obstacle avoidance and mating communication. However, the characteristics of these air movements are not well clarified. In this study, the air movements induced by wing tones (sound generated by flapping wings in flight) around the antennae of a mosquito-like model (Culex quinquefasciatus, male) are investigated using the acoustic analogy method. Both the self-generated wing tone and the wing tone reflected from the ground are calculated. Given that the tiny changes in direction and magnitude of air movements can be detected by the mosquito’s antennae, a novel method is introduced to intuitively characterize the air movements induced by the wing tone. The air movements are decomposed into two basic modes (oscillation and revolution). Our results show that, without considering the scattering on the mosquito’s body, the self-generated sound wave of the wing-beat frequency around the antennae mainly induces air oscillation, with the velocity amplitude exceeding the mosquito’s hearing threshold of the male wingbeat frequency by two orders of magnitude. Moreover, when the model is positioned at a distance from the ground greater than approximately two wing lengths, the reflected sound wave at the male wingbeat frequency attenuates below the hearing threshold. That is, the role of reflected wing tone in the mosquito’s obstacle avoidance mechanism appears negligible. Our findings and method may provide insight into how mosquitoes avoid obstacles when their vision is unavailable and inspire the development of collision avoidance systems in micro-aerial vehicles

Finite-wing-analogy formula for compressibility correction to pressure coefficient of an underwater vehicle model at low Mach number

Wind tunnels are usually used to investigate the flows and forces associated with underwater vehicles when free-surface effects can be ignored. However, because of the large differences between air and water in density and viscosity, the freestream Mach number in a wind tunnel is much higher than that in a water tunnel or towing tank at the same Reynolds number. Therefore, compressibility correction is required for accurate measurement compatibility between wind tunnels and water tunnels or towing tanks. In the study reported here, the flows and forces associated with an underwater vehicle model at different Mach numbers were investigated by solving the Navier-Stokes equations for compressible flow numerically as virtual-wind tunnel experiments. The freestream Mach number Ma varies from 0.004 to 0.5. The distribution of the pressure coefficient on the hull and the effects of Ma on the peaks of the pressure coefficient are discussed in detail. The performances of the Prandtl-Glauert rule, the Karman-Tsien rule, and the Laitone rule for compressibility correction to the pressure coefficient of underwater vehicles are assessed. Defining the average correction factor with larger values for better correction effect, the values for these three compressibility correction formulas are 0.51, 0.38, and 0.23, respectively. A finite-wing-analogy formula to improve the compressibility correction to the pressure coefficient at low Ma is proposed. Inspired by the finite-wing correction to the lift slope of airfoils, the proposed formula offers good convergence of the pressure coefficient and highly accurate compressibility correction with an average correction factor of 0.84

A frequency-domain formulation for predicting multi-frequency noise generated by flows with periodically moving boundaries

A frequency-domain formulation is proposed to compute the far-field noise generated by flows with periodically oscillating or rotating boundaries. The proposed formulation significantly enhances the efficiency of the frequency-domain method in handling the multi-frequency sources with nonrectilinear motion. The novelty of the proposed method is that the frequency- and time-dependent components of the Ffowcs Williams and Hawkings (FW-H) integral are separated by using the far-field asymptotic Green's function. The separation of the frequency- and time-dependent components avoids the need for an expensive time integration in computing the multi-frequency noise generated by flows with periodically moving boundaries. They proposed only one Fourier transform computation in obtaining the noise at different frequencies. The efficiency of the proposed formulation is investigated by analyzing the required number of floating-point operations. Its validity is examined by computing the noise from rotating or oscillating permeable boundaries around composite monopoles and a flapping wing. The proposed formulation is applicable to the FW-H integral with periodically oscillating or rotating boundaries when the maximum velocity on the moving boundary is subsonic