Experimental research on the instability propagation characteristics of liquid kerosene rotating detonation wave

In order to study the instability propagation characteristics of the liquid kerosene rotating detonation wave(RDW),a series of experimental tests were carried out on the rotating detonation combustor(RDC)with air-heater.The fuel and oxidizer are room-temperature liquid kerosene and preheated oxygenenriched air,respectively.The experimental tests keep the equivalence ratio of 0.81 and the oxygen mass fraction of 35%unchanged,and the total mass flow rate is maintained at about 1000 g/s,changing the total temperature of the oxygen-enriched air from 620 K to 860 K.Three different types of instability were observed in the experiments:temporal and spatial instability,mode transition and re-initiation.The interaction between RDW and supply plenum may be the main reason for the fluctuations of detonation wave velocity and pressure peaks with time.Moreover,the inconsistent mixing of fuel and oxidizer at different circumferential positions is related to RDW oscillate spatially.The phenomenon of single-double-single wave transition is analyzed.During the transition,the initial RDW weakens until disappears,and the compression wave strengthens until it becomes a new RDWand propagates steadily.The increased deflagration between the detonation products and the fresh gas layer caused by excessively high temperature is one of the reasons for the RDC quenching and re-initiation.

Study on Propagation Characteristics of Plasma Surface Wave in Medium Tube

Axial propagation characteristics of the axisymmetric surface wave along the plasma in the medium tube were studied. The expressions of electromagnetic field inside and outside the medium tube were deduced. Also, the impacts of several factors, such as plasma density, signal frequency, inner radius of medium tube, collision frequency, etc., on plasma surface wave propa- gation were numerically simulated. The results show that, the properties of plasma with higher density and lower gas pressure are closer to those of metal conductor. Furthermore, larger radius of medium tube and lower signal frequency are better for surface wave propagation. However, the effect of collision frequency is not obvious. The optimized experimental parameters can be chosen as the plasma density of about 10^17 m^-3 and the medium radius between 11 mm and 19 mm.

Gaussian beamed millimetre wave propagation characteristics due to reflecting behaviour in circle tunnel

Propagation characterization is one of the main building blocks for millimetre wave （MMW） communication. The Gaussian beam has attractive features to become a prospective wave form for millimetre radio communication, especially for the utility inside tunnels. A ray tracing method embedded with spectral features of Gaussian beam is employed to analyze mil- limetre wave propagation in a circle tunnel in this paper. In consideration of geometrical figure of the tunnel, the superposition behaviour of direct and reflective beams is analyzed via simplified approximation of Gaussian beam spectral feature. Then the propagation models are established to derive amplitude, phase, and delay spread of received wave. A typical straight tunnel model is used to simulate the propagation behaviour, where strong multi-path effect with deeply fading of signal intensity and dramatically enhancing of delay spread emerges. For investigation of the spectral feature of the multi-path effect, a reflection loss of 14 dB is taken into consideration at a designated point. To analyze the influences of frequency and transmission distance, the propagation characteristics at three different frequencies of 45 GHz, 65 GHz and 85 GHz are compared with the beam travelling down the tunnel. In addition, three different reflection losses of 14 dB, 20 dB, and 26 dB at the frequency of 65 GHz are also investigated to research the influence of the reflecting coefficient.

Detonation Propagation Characteristics of Superposition Explosive Materials

In order to investigate detonation propagation characteristics of different charge patterns,the detonation velocities of superposition strip shaped charges made up of a detonating cord and explosives were measured by a detonation velocity measuring instrument under conditions of different ignition.The experimental results and theoretical analysis show that the maximum detonation propagation velocity depends on the explosive materials with the maximum velocity among all the explosive materials.Using detonating cord in a superposition charge can shorten detonation propagation time and improve the efficiency of explosive energy.The measurement method of detonation propagation velocity and experimental results are presented and investigated.

Lateral stress-induced propagation characteristics in photonic crystal fibres

Using the finite element method, this paper investigates lateral stress-induced propagation characteristics in a photonic crystal fibre of hexagonal symmetry. The results of simulation show the strong stress dependence of effective index of the fundamental guided mode, phase modal birefringence and confinement loss. It also finds that the contribution of the geometrical effect that is related only to deformation of the photonic crystal fibre and the stress-related contribution to phase modal birefringence and confinement loss are entirely different. Furthermore, polarization-dependent stress sensitivity of confinement loss is proposed in this paper.

The Propagation Characteristics of the Electron Beam with Initial Modulation

The propagation characteristics of the beam under various initial conditions are in-vestigated by means of PIC method.The influences of density modulation and velocity modulationon the propagation characteristics are discussed and compared.The results reveal that by chang-iug the amplitude of the two kinds of modulations and the phase difference between them,the

Experiment on Leader Propagation Characteristics of Air Gaps in UHVDC Transmission Towers Under Positive Switching Impulse Voltages

Rapid developments in EHV/UHV transmission systems require a deeper understanding of the mechanism of long air gap discharge.Leader propagation is one of the main processes in long gap breakdown.In this paper,the leader propagation characteristics of real size±800 kV UHVDC transmission tower gaps under positive switching impulse voltages(185/2290μs)are investigated.An integrated observation platform consisting of an impulse voltage divider,a coaxial shunt,a high-speed video camera,and a set of integrated optical electric field sensors(IOES),is established.The waveforms of impulse voltage,discharge current,electric field variation at specific positions,and time-resolved photographs of discharge morphology are recorded.Axial leader velocity and the relationship between leader advancements and injected charge are obtained.The typical value of leader stable propagation velocity is 1.7–2.2 cm/μs,which varies slightly with the gap length and applied voltage amplitude.The leader velocity in the re-illumination process is much higher,and is seen as varying from 5 cm/μs to 30 cm/μs,with an average value around 10 cm/μs.The charge in leader channel per unit length is 20–40μC/m,which illustrates a near-direct proportion relationship between discharge current and leader velocity.The observed parameters are important for further simulation of the tower gap breakdown processes.

Propagation Characteristics of Elastic Wave in Layered Medium and Applications of Impact Imaging Method

It is an important subject to probe the structure in the medium by various kinds of detection methods in the geotechnical engineering. Based on the propagation theory of elastic wave in half-space layered medium, the propagation characteristics of elastic wave in layered medium with different elastic parameters are discussed using dynamic analysis of finite element method. It is known that the S-wave velocity, density and thickness of layer are related to the properties of the elastic wave including waveform characteristics, spectral characteristics and time-frequency characteristics. We pay special attention to the structure with low velocity interlayer. The impact imaging method is applied to the grouting construction of the immersed tube tunnel. Data acquisition and analytical method are introduced in detail. The grouting effects can be qualitatively evaluated by comparing the characteristics of elastic wave before grouting with those after grouting. Finally, a quantitative evaluation is obtained according to the relationship between energy response of elastic wave and impedance ratio.

Generation and propagation characteristics of electromagnetic vortices in radio frequency

Electromagnetic vortices, which describe the orbital angular momentum(OAM) carrying waves with a helical phase front, have recently attracted much interest in a radio frequency domain due to their potential applications in many diverse areas. In an OAM-based scenario, the antenna for OAM mode multiplexing/demultiplexing plays an essential role in controlling the overall system performance. In this paper, we demonstrated theoretically and experimentally an easily realized OAM antenna based on the traveling-wave circular loop structure for efficiently multiplexing/demultiplexing multiple OAM modes; in addition, its general propagation characteristics including the polarization, divergence, and radiation pattern are mathematically analyzed. Schemes for antenna size reduction and various radiation pattern manipulations have also been discussed to realize a more flexible and compact system.

Propagation characteristics of six-core photonic liquid crystal fibers

We demonstrate a new kind of multi-core photonic liquid crystal fibers (PLCFs) which have six liquid crystal cores arrayed in the ring-type geometry and separated by the air holes. Through analyzing the structure of this kind of PLCFs, it can be found that they have the ability to resist the structure deformation. Due to the effective index of the liquid crystal can be adjusted by temperature and wavelength, the energy in the six liquid crystal cores is increased with the temperature increasing and wavelength decreasing. The effective index of the PLCFs is decreased, the effective fundamental mode area is increased and the dispersion properties are gently affected with the wavelength increasing and temperature decreasing.

Propagation characteristics of laser-generated like-Rayleigh waves in viscoelastic adhesive coating/substrate structures

The propagation characteristics of laser-generated like-Rayleigh waves in viscoelastic adhesive coating/substrate structures were studied.Considering the viscoelasticity of the coating and substrate,we have established the finite element models in frequency domain for the laser-generated like-Rayleigh waves in the epoxy coating/aluminum substrate,epoxy coating/brass substrate,and epoxy coating/foam substrate structures,respectively.In addition,we have investigated the waveform and propagation characteristics of the like-Rayleigh waves and studied the influences of the coating transparency,coating thickness,coating viscoelasticity,and substrate viscoelasticity on the propagation characteristics of the like-Rayleigh waves.Moreover,we have verified the results by the theoretical phase velocity and attenuation curves.The results show that the coating viscoelasticity induces the attenuation characteristics of the higher frequencies of the like-Rayleigh waves,but has little effect on the lower frequencies,and the substrate viscoelasticity has the influences on both the higher and lower frequencies of the like-Rayleigh waves,especially the lower frequencies.Furthermore,the mode and dispersive characteristics of the like-Rayleigh waves are closely related to the substrates.This study provides a useful theoretical basis for inverting mechanical parameters and evaluating the adhesive quality of the viscoelastic adhesive coating/substrate structures.

Effect of the structural parameters of photonic crystal fibers on propagation characteristics

Using a full-vector finite-difference time-domain （FDTD） method, this article explores the propagation characteristics of photonic crystal fiber （PCF） theoretically. The dependence of structural parameters on the effective index of the fundamental guided mode, effective index of the fundamental cladding mode, mode field diameter, confinement loss, effective mode area, and chromatic dispersion in PCF have been studied, respectively. The research presents a reference for designing of PCF with a specific purpose.

FORMATION MECHANISM AND PROPAGATION CHARACTERISTICS OF THE EQUATORIAL THERMALLY-FORCED SHORT-TERM CLIMATIC OSCILLATION DURING THE NORTHERN SUMMER

In this study, in order to investigate the global climatic oscillations forced by sea surface temperature (SST) anomalies over equatorial central-eastern Pacific, two numerical schemes with different SST distri-butions (normal and anomalous cases) are tested by using a nine-layer global spectral model. Experiment results show that (i) in northern summer, a wave train that is similar to the teleconnection pattern suggested by Nitta (1987) and Huang (1987) in the Northern Hemisphere and another one in the Southern Hemisphere are reproduced; (ii) simulated results suggest that the response of atmosphere in middle-high latitudes of both hemispheres to an anomalous heating source is more sensitive in tropical western Pacific than in equatorial central-eastern Pacific; and (iii) in northern summer, the formation of low-frequency oscillations on monthly (seasonal) time scale results from energy dispersion as well as interactions between eddies and zonal flow; and between eddies.

Study on plasma expansion model of primary discharge on spacecraft solar array

In the space plasma environment, primary discharge may occur on the solar array and evolve into a destructive sustained arc, which threatens the safe operation of the spacecraft. Based on the plasma expansion fluid theory, a new multicomponent plasma expansion model is proposed in this study, which takes into account the effects of ion species, ion number, initial discharge current, and Low Earth Orbit(LEO) plasma environment. The expansion simulation of single-component and multicomponent ions is carried out respectively, and the variations of plasma number density, expansion distance, and speed during the expansion process are obtained.Compared with the experimental results, the evolution of propagation distance and speed is closed and the error is within a reasonable range, which verifies the validity and rationality of the model. The propagation characteristics of the primary discharge on the solar array surface and the influence of the initial value on the maximum propagation distance and the propagation current peaks are investigated. This study can provide important theoretical support for the propagation and evolution of the primary discharge and the key behavior of the transition to secondary discharge on spacecraft solar array.

Laboratory-scale investigation of response characteristics of liquid-filled rock joints with different joint inclinations under dynamic loading

In underground rock engineering,water-bearing faults may be subjected to dynamic loading,resulting in the coupling of hydraulic and dynamic hazards.Understanding the interaction mechanism between the stress waves induced by dynamic loadings and liquid-filled rock joints is therefore crucial.In this study,an auxiliary device for simulating the liquid-filled layer was developed to analyze the dynamic response characteristics of liquid-filled rock joints in laboratory.Granite and polymethyl methacrylate(PMMA)specimens were chosen for testing,and high-amplitude shock waves induced by a split Hopkinson pressure bar(SHPB)were used to produce dynamic loadings.Impact loading tests were conducted on liquid-filled rock joints with different joint inclinations.The energy propagation coefficient and peak liquid pressure were proposed to investigate the energy propagation and attenuation of waves propagating across the joints,as well as the dynamic response characteristics of the liquid in the liquid-filled rock joints.For the inclination angle range considered herein,the experimental results showed that the energy propagation coefficient gently diminished with increasing joint inclination,and smaller coefficient values were obtained for granite specimens compared with PMMA specimens.The peak liquid pressure exhibited a gradually decreasing trend with increasing joint inclination,and the peak pressure for granite specimens was slightly higher than that for PMMA specimens.Overall,this paper may provide a considerably better method for studying liquid-filled rock joints at the laboratory scale,and serves as a guide for interpreting the underlying mechanisms for interactions between stress waves and liquid-filled rock joints.

A Predictive 6G Network with Environment Sensing Enhancement:From Radio Wave Propagation Perspective

In order to support the future digital society,sixth generation(6G)network faces the challenge to work efficiently and flexibly in a wider range of scenarios.The traditional way of system design is to sequentially get the electromagnetic wave propagation model of typical scenarios firstly and then do the network design by simulation offline,which obviously leads to a 6G network lacking of adaptation to dynamic environments.Recently,with the aid of sensing enhancement,more environment information can be obtained.Based on this,from radio wave propagation perspective,we propose a predictive 6G network with environment sensing enhancement,the electromagnetic wave propagation characteristics prediction enabled network(EWave Net),to further release the potential of 6G.To this end,a prediction plane is created to sense,predict and utilize the physical environment information in EWave Net to realize the electromagnetic wave propagation characteristics prediction timely.A two-level closed feedback workflow is also designed to enhance the sensing and prediction ability for EWave Net.Several promising application cases of EWave Net are analyzed and the open issues to achieve this goal are addressed finally.

Solitary Wave Propagation Influenced by Submerged Breakwater

The form of Boussinesq equation derived by Nwogu （1993） using velocity at an arbitrary distance and surface elevation as variables is used to simulate wave surface elevation changes. In the numerical experiment, water depth was divided into five layers with six layer interfaces to simulate velocity at each layer interface. Besides, a physical experiment was carried out to validate numerical model and study solitary wave propagation.“Water column collapsing”method （WCCM） was used to generate solitary wave. A series of wave gauges around an impervious breakwater were set-up in the flume to measure the solitary wave shoaling, run-up, and breaking processes. The results show that the measured data and simulated data are in good agreement. Moreover, simulated and measured surface elevations were analyzed by the wavelet transform method. It shows that different wave frequencies stratified in the wavelet amplitude spectrum. Finally, horizontal and vertical velocities of each layer interface were analyzed in the process of solitary wave propagation through submerged breakwater.

Research on phase shift characteristics of electromagnetic wave in plasma

The phase shift characteristics reflect the state change of electromagnetic wave in plasma sheath and can be used to reveal deeply the action mechanism between electromagnetic wave and plasma sheath.In this paper,the phase shift characteristics of electromagnetic wave propagation in plasma were investigated.Firstly,the impact factors of phase shift including electron density,collision frequency and incident frequency were discussed.Then,the plasma with different electron density distribution profiles were employed to investigate the influence on the phase shift characteristics.In a real case,the plasma sheath around the hypersonic vehicle will affect and even break down the communication.Based on the hypersonic vehicle model,we studied the electromagnetic wave phase shift under different flight altitude,speed,and attack angle.The results indicate that the phase shift is inversely proportional to the flight altitude and positively proportional to the flight speed and attack angle.Our work provides a theoretical guidance for the further research of phase shift characteristics and parameters inversion in plasma.

Mechanical properties and failure characteristics of fractured sandstone with grouting and anchorage

Based on uniaxial compression experimental results on fractured sandstone with grouting and anchorage, we studied the strength and deformation properties, the failure model, crack formation and evolution laws of fractured sandstone under different conditions of anchorage. The experimental results show that the strength and elastic modulus of fractured sandstone with different fracture angles are significantly lower than those of intact sandstone. Compared with the fractured samples without anchorage,the peak strength, residual strength, peak and ultimate axial strain of fractured sandstone under different anchorage increase by 64.5–320.0%, 62.8–493.0%, and 31.6–181.4%, respectively. The number of bolts and degree of pre-stress has certain effects on the peak strength and failure model of fractured sandstone. The peak strength of fractured sandstone under different anchorage increases to some extent, and the failure model of fractured sandstone also transforms from tensile failure to tensile–shear mixed failure with the number of bolts. The pre-stress can restrain the formation and evolution process of tensile cracks, delay the failure process of fractured sandstone under anchorage and impel the transformation of failure model from brittle failure to plastic failure.

ELM-Based Impact Analysis of Meteorological Parameters on the Radio Transmission of X-Band over the Qiongzhou Strait of China

Communication in the evaporation duct layer is greatly affected by the variation of meteorological parameters.Based on the experimental result of the radio transmission of the X-band over the Qiongzhou Strait of China,the characteristic of the duct and its influence on the transmission effect is analyzed.The results indicate that the evaporation duct height(EDH)has a negative Spearman’s rank correlation of-0.90 with the relative humidity and a positive correlation coefficient of 0.84 with the wind speed.Based on the Extreme Learning Machine(ELM)network,we proposed a Met-ELM model that can provide efficient support in predicting propagation characteristics at nighttime.The predicted results of the MetELM model are consistent with the measurements;the root-mean-square-error is 1.66 dB,with the correlation coefficient reaching 0.96,while the proportion of mean absolute error less than 2 dB has reached81.41%.The data-derived Met-ELM model shows great accuracy in predicting propagation characteristics at nighttime,which also meets the acceptable requirements for radio wave propagation.