Direct Generation of Intense Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate,removing exclusions from molten metals and refining solidification structures during metallurgical processing of materials. In the present study, two electromagnetic methods are proposed to generate intense compression wavesdirectly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a staticmagnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical modelbased on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distributions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to thatof the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagneticforce. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure transducerunder various conditions. The observed results approximately agreed with the predictions derived from the theoreticalanalyses and calculations. Moreover, the effect of the generated waves on improvement of solidification structureswas also examined. It shows that the generated compression waves can refine solidification structures when they wereapplied to solidification process of Sn-Pb alloy. This study indicates a new method to generate compression wavesby imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves canprobably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.

Attenuation and Distortion of Compression Waves Propagating in Very Long Tube

A lot of phenomena related to propagating various waves are seen when the high-speed train goes through the tunnel,the gas pipeline is broken due to an accident or the air brake of the wagon operates.For instance,a compression wave generated ahead of a high-speed train entering a tunnel propagates to the tunnel exit and spouts as a micro pressure wave,which causes an exploding sound.In order to estimate the magnitude correctly,the mechanism of the attenuation and distortion of a compression wave propagating along a very long tunnel must be understood and the experimental information on these phenomena is required.An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube.Experimental results show that the strength of a compression wave decreases with distance.The attenuation and distortion of compression waves are affected by the initial waveform of the compression wave and by the unsteady boundary layer induced by the propagating wave.The shape of a compression wave becomes different with the propagating distance;that is,a shock wave appears just head of a wavefront and an overshoot on pressure distribution is observed behind a shock wave due to the transition of the unsteady boundary layer.

Characteristics of a compression wave propagating over porous plate wall in a high-speed railway tunnel

A pressure wave is generated ahead of a high-speed train, while entering a tunnel. This pressure wave propagates to the tunnel exit and spouts as a micro-pressure wave, which causes an exploding sound. From the fact that the ballast track tunnel has smaller noise than the slab track tunnel, we have suggested a new inner tunnel model to decrease the noise of the micro-pressure wave, using the ballast effect. Experimental and numerical investigations are carded out to clarify the attenuation and distortion of propagating compression wave over porous plate wall in a model tunnel. Data shows that the strength of the compression wave and a maximum pressure gradient of the compression wave was weakened. These data shows the possibility of the present alleviative method using the porous plate wall in a tunnel.

Compressional Wave Velocities in Some Volcanic Rocks at Pressure up to 4.5 GPa

Compressional wave velocities in some Mesozoic and Cenozoic volcanic rocks from Qinling Dabie orogenic belt were measured at room temperature and high pressure (up to 4.5 GPa). Compressional wave velocities of these rocks increase with the increasing of pressure. The experiment data indicate that the pressure at which the microcracks in these rocks finally close is up to 2.0 GPa. The empirical relationships between compressional wave velocities at high pressure and oxide mass fractions, heat productions and densities at room temperature and 100 kPa of these rocks are discussed. It is likely that there does not always exist linear relationship between compressional wave velocities and oxide mass fractions. New heat production data of volcanic rock samples from the Qinling Dabie orogenic belt do not follow the empirical relationship between heat production and seismic velocity for rocks. It is dangerous to use these empirical relations to predicate the modal chemical composition, density and heat production of the lithosphere.

The phase relations between the first arrivals of compressional and shear waves, and their signification to full wave logging

This paper describes the three phenomena observed in full wave experiments： 1. the amplitudes （absolute value） of the first compressional and shear arrivals have the same variation rules; 2. the phases of the first compressional and shear arrivals are always opposite to each other; and 3. the amplitude variation periods of the first compressional and shear arrivals are 2π. A full analysis and interpretation points out that these phenomena should appear under the full wave logging condition. Hence,the basis of using phase diffrences to extract useful information from the full wave is found.

Compressional elastic wave velocities of serpentinized pyroxenite at high pressures and high temperatures and its geological significance

Center for Analysis and Prediction, China Seismological Bureau, Beijing 100036, China 2) Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China

Transmission ratio (T_n) in the radian direction normal to joints in 2-D compressional wave propagation in rock masses

The transmission ratio along the radian direction normal to the joints was studied in the Universal Distinct Element Code （UDEC）. The variation of the transmission ratio with the ratio of joint spacing to wavelength was generalized into a general curve, which was determined by two critical points. The relationship between the two critical points and the affecting factors, quantity of joints and the normalized normal stiffness of joints, were obtained. A prediction model of the transmission ratio in the radian direction normal to the joints was proposed. The proposed model was applied to a field explosion test. The estimated values of the peak particle velocity from the prediction model were compared with the field records. The comparisons showed that the prediction model of the transmission ratio in the direction normal to the joints in the process of 2-D compressional wave propagation through multiple parallel joints is reliable.

Porosity Estimation from Compressional Wave Velocity： A Study Based on Egyptian Carbonate Samples

The porosity of a rock is one of the most important reservoir properties. It controls the reservoir storage capacity. In other words, porosity quantifies the amount of fluids that the rock can store. Most of the world＇s giant fields produce hydrocarbons from carbonate reservoirs. Carbonate rocks contain more than 50% of the world＇s hydrocarbon reserves. Porosity and compressional wave velocity of 41 carbonate samples were determined under ambient conditions in laboratory. The samples were collected from seven shallow wells in west Tushka area, south Western Desert, Egypt. This paper evaluates the well known Wyllie and Raymer equations, an empirical linear equation, and a generalized model for porosity estimation from compressional wave velocity of saturated carbonate samples. Based on the comparison of the predicting identified to provide the most reliable porosity estimation. qualities, the Raymer equation and the empirical linear equation were

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.

THE INTERACTION BETWEEN SHOCK WAVES AND FOAM IN A SHOCK TUBE

An experimental study and a numerical simulation were conducted to investigate the mechanical and thermodynamic processes involved in the interaction between shock waves and low density foam. The experiment was done in a stainless shock tube (80 mm in inner diameter, 10 mm in wall thickness and 5 360 mm in length). The velocities of the incident and reflected compression waves in the foam were measured by using piezo-ceramic pressure sensors. The end-wall peak pressure behind the reflected wave in the foam was measured by using a crystal piezoelectric sensor. It is suggested that the high end-wall pressure may be caused by a rapid contact between the foam and the end-wall surface. Both open-cell and closed-cell foams with different length and density were tested. Through comparing the numerical and experimental end-wall pressure, the permeability coefficients α and β are quantitatively determined.

Diffraction of plane SV waves by a cavity in poroelastic half-space

This paper presents an indirect boundary integration equation method for diffraction of plane SV waves by a 2-D cavity in a poroelastic half-space.The Green＇s functions of compressive and shear wave sources are derived based on Biot＇s theory. The scattered waves are constructed using fictitious wave sources close to the boundary of the cavity, and their magnitudes are determined by the boundary conditions. Verification of the accuracy is performed by： （1） checking the satisfaction extent of the boundary conditions, （2） comparing the degenerated solutions of a single-phased case with well- known solutions, and （3） examining the numerical stability of the solutions. The nature of diffraction of plane SV waves around a cavity in a poroelastic half-space is investigated by numerical examples.

Diffraction of plane P waves by a canyon of arbitrary shape in poroelastic half-space (Ⅰ): Formulation

This paper presents an indirect boundary integration equation method for diffraction of plane P waves by a two-dimensional canyon of arbitrary shape in poroelastic half-space. The Green＇s functions of compressional and shear wave sources in poroelastic half-space are derived based on Biot＇s theory. The scattered waves are constructed using the fictitious wave sources close to the boundary of the canyon, and magnitude of the fictitious wave sources are determined by the boundary conditions. The precision of the method is verified by the satisfaction extent of boundary conditions, the comparison between the degenerated solutions of single-phased half-space and the well-known solutions, and the numerical stability of the method.

Compressive and Rarefactive Waves in Dust Plasma with Non-thermal Ions

The governing equation of the dust fluid with non-thermal ions and variable dust charge on dust particles in hot dust plasmas is obtained. Both the compressive and rarefactive waves in this system are investigated. They can be determined by plasma parameters including the temperatures of （lust fluid, ions and electrons, as well as the non-thermal parameter of ions, and the number densities of the dust particles, the ions and the electrons, etc.

Numerical study on maximum rebound ratio in blasting wave propagation along radian direction normal to joints

In the process of 2-D compressional wave propagation in a rock mass with multiple parallel joints along the radian direction normal to the joints, the maximum possible wave amplitude corresponding to the points between the two adjacent joints in the joint set is controlled by superposition of the multiple transmitted and the reflected waves, measured by the maximum rebound ratio. Parametric studies on the maximum rebound ratio along the radian direction normal to the joints were performed in universal distinct element code. The results show that the maximum rebound ratio is influenced by three factors, i.e., the normalized normal stiffness of joints, the ratio of joint spacing to wavelength and the joint from which the wave rebounds. The relationship between the maximum rebound ratio and the influence factors is generalized into five charts. Those charts can be used as the prediction model for estimating the maximum rebound ratio.

Experimental study of the relationship between fluid density and saturation and sonic wave velocity of rock samples from the WXS Depression,South China Sea

The relationship between fluid density and saturation and sonic wave velocity of rock samples taken from the WXS Depression in the South China Sea was studied by an oil-water replacement experiment under simulated in-situ temperature and pressure conditions.Two kinds of low-density oils（0.691 and 0.749 g/cm^3） and two kinds of high-density oils（0.834 and 0.873 g/cm^3） were used to saturate the rock samples at different oil-saturation states,and the saturated P- and S-wave velocities were measured.Through Gassmann＇s equation,the theoretical P- and S-wave velocities were also calculated by the fluid replacement method.With the comparison of the measured values and the theoretical values, this study comes to the following conclusions.（1） With the increase of oil saturation and the decrease of water saturation,the P-wave velocity of rock samples saturated by low-density oil increases and the changing rule is in accord with the effective fluid theory;the P-wave velocity of rock samples saturated by high-density oil decreases and the changing rule goes against the theory.（2） With the increase of oil density（namely 0.691→0.749→0.834→0.873 g/cm^3） when oil saturation is unchanged,P-wave velocity increases gradually.（3） The S-wave velocity is always stable and is not affected by the change of oil density and saturation.The results can be used to constrain pre-stack seismic inversion,and the variation rule of sonic wave velocity is valuable for hydrocarbon identification in the study area.

A high order boundary scheme to simulate complex moving rigid body under impingement of shock wave

In the paper, we study a high order numerical boundary scheme for solving the complex moving boundary problem on a fixed Cartesian mesh, and numerically investigate the moving rigid body with the complex boundary under the impingement of an inviscid shock wave. Based on the high order inverse Lax-Wendroff(ILW) procedure developed in the previous work(TAN, S. and SHU, C. W. A high order moving boundary treatment for compressible inviscid flows. Journal of Computational Physics, 230(15),6023–6036(2011)), in which the authors only considered the translation of the rigid body,we consider both translation and rotation of the body in this paper. In particular, we reformulate the material derivative on the moving boundary with no-penetration condition, and the newly obtained formula plays a key role in the proposed algorithm. Several numerical examples, including cylinder, elliptic cylinder, and NACA0012 airfoil, are given to indicate the effectiveness and robustness of the present method.

Simulation of thermoacoustic waves by a pressure-based algorithm for compressible flows

A modified SIMPLEC method which can solve compressible flows at low Mach number is introduced and used to study thermoacoustic waves induced by a rapid change of temperature at a solid wall and alternating- direction flows generated by thermoacoustic effects in a ta- pered resonator. The results indicate that the algorithm adopted in this paper can be used for calculating com- pressible flows and thermoacoustic waves. It is found that the pressure and velocity in the resonator behave as stand- ing waves, and the tapered resonator can suppress high- frequency harmonic waves as observed in a cylindrical res- onator.

Freezing and thawing effects of sand-silt mixtures on elastic waves

Freezing and thawing during the winter season change soil properties such as density. The density change in the particulate media influences soil stiffness. In addition, freezing of partially or fully saturated soils changes the soil matrix from a particulate media to a continuum. The goal of this study is to investigate the cyclic freezing and thawing effects on elastic waves. Sand-silt mixtures with 10% silt fraction in weight and 40% saturation are prepared. The sand-silt mixtures are placed in a nylon cell, onto which a pair of bender elements and a pair of piezoelectric disk elements are installed for the measurement of shear and compressional waves, respectively. The temperature of the mixtures decreases from 20 ℃ to -10 ℃ to freezing. The frozen sample is gradually thawed at room temperature （20 ℃）, These freezing-thawing processes are repeated three times. The test result shows that the shear and compressional wave velocities significantly increase when the specimen is frozen. When the temperature is greater than 0 ℃, the elastic wave velocities are lower during thawing than during freezing due to soil structure change. This study demonstrates that soil strucre change during the winter season may be effectively estimated from elastic waves.

基于特征变量扩展的含气饱和度随机森林预测方法

采用数据驱动的方式,提出了一种基于随机森林机器学习算法训练出含气饱和度地震预测方法,并将该方法应用于中国西部复杂天然气藏中,分别对单井资料和二维地震资料进行了含气饱和度预测与分析。研究结果表明:(1)抽取井旁道纵波速度、横波速度和密度3个弹性参数叠前地震反演结果作为基本特征变量样本,引入边界合成少数类过采样技术对基本特征变量样本和对应的含气饱和度样本进行平衡化处理;利用扩展弹性阻抗结合数学变换自动生成一系列的扩展变量;再利用随机森林对特征变量进行含气饱和度预测重要性排名,并优选重要性较高的特征变量进行含气饱和度随机森林训练。(2)该方法大幅减少了特征变量提取和优选的人工工作量,且有效减少了信息冗余以及因含气饱和度样本不平衡导致的训练偏倚问题,有效增强了随机森林算法在含气饱和度地震预测方面的能力。(3)实际单井应用中预测的含气饱和度与测井解释的含气饱和度的相关系数可达0.9855;在二维地震资料应用中,该方法比基于常规未平衡化的11个弹性参数作为随机森林输入预测出的含气饱和度精度更高。

Dust Acoustic Compressive Waves in a Warm Dusty Plasma Having Non-Thermal Ions and Non-Isothermal Electrons

In this article an investigation is presented on the properties of dust acoustic（DA）compressive solitary wave propagation in an adiabatic dusty plasma,including the effect of nonthermal positive and negative ions and non-isothermal electrons.The reductive perturbation method has been employed to derive the lower degree modified Kadomtsev-Petviashivili（mK-P）,3D Schamel-Korteweg-de-Vries equation or modified Kadomtsev-Petviashivili（mK-P） equations for dust acoustic solitary waves in a homogeneous,unmagnetized and collisionless plasma whose constituents are non-isothermal electrons,singly charged positive and negative non-thermal ions and massive charged dust particles.The stationary analytical solutions of the lower degree mK-P and mK-P equations are numerically analyzed,where the effect of various dusty plasma constituents on DA solitary wave propagation is taken into account.It is observed that both the ions in dusty plasma play a key role in the formation of DA compressive solitary waves,and also the ion concentration and non-isothermal electrons control the transformation of the compressive potentials of the waves.