The method of reverberation-ray matrix (MRRM) is extended and modified for the analysis of free wave propagation in anisotropic layered elastic media. A general, numerically stable formulation is established within ...The method of reverberation-ray matrix (MRRM) is extended and modified for the analysis of free wave propagation in anisotropic layered elastic media. A general, numerically stable formulation is established within the state space framework. The compatibility of physical variables in local dual coordinates gives the phase relation, from which exponentially growing functions are excluded. The interface and boundary conditions lead to the scattering relation, which avoids matrix inversion operation. Numerical examples are given to show the high accuracy of the present MRRM.展开更多
Polar mesosphere summer echoes (PMSE) are very strong radar echoes from alti- tudes close to the polar summer mesopause. The data from sounding rocket campaigns indicate that the radar signal to noise ratio (SNR),...Polar mesosphere summer echoes (PMSE) are very strong radar echoes from alti- tudes close to the polar summer mesopause. The data from sounding rocket campaigns indicate that the radar signal to noise ratio (SNR), electron density and dust charge density of polar meso- sphere in summer show obvious layered structure. In this paper the theory of wave propagation in layered media is used to study the reflectance and SNR at each layer in polar mesosphere. The calculated SNR using theory of dusty plasma is found in good agreement with the experimental result, which may imply that the intensity of the radar echoes reflected by the layered structure in polar mesosphere where polar mesosphere summer echoes used to occur can interpret partially the phenomenon of PMSE. In other words, reflection may play an important role in the occurrence of PMSE.展开更多
Compared to single layer porous media,fluid flow through layered porous media(LPMs)with contrasting pore space structures is more complex.This study constructed three-dimensional(3-D)pore-scale LPMs with different gra...Compared to single layer porous media,fluid flow through layered porous media(LPMs)with contrasting pore space structures is more complex.This study constructed three-dimensional(3-D)pore-scale LPMs with different grain size ratios of 1.20,1.47,and 1.76.The flow behavior in the constructed LPMs and single layer porous media was numerically investigated.A total of 178 numerical experimental data were collected in LPMs and single layer porous media.In all cases,two different flow regimes(i.e.,Darcy and Non-Darcy)were observed.The influence of the interface of layers on Non-Darcy flow behavior in LPMs was analyzed based pore-scale flow data.It was found that the available correlations based on single layer porous media fail to predict the flow behavior in LPMs,especially for LPM with large grain size ratio.The effective permeability,which incorporated the influence of the interface is more accurate than the Kozeny-Carman equation for estimating the Darcy permeability of LPMs.The inertial pressure loss in LPMs,which determines the onset of the Non-Darcy flow,was underestimated when using a power law expression of mean grain size.The constant B,an empirical value in the classical Ergun equation,typically equals 1.75.The inertial pressure loss in LPMs can be significantly different from it in single lager porous media.For Non-Darcy flow in LPMs,it is necessary to consider a modified larger constant B to improve the accuracy of the Ergun empirical equation.展开更多
Dynamic behavior of single pile embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's function f...Dynamic behavior of single pile embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's function for ring loads. The influence of soil anisotropy on the dynamic behavior of piles is examined through a series of parametric studies.展开更多
The electric field, equations of boundary conditions and calculation formula of apparent resistivity are derived for the azimuthal anisotropy layered media with the DC method based on the anisotropic Ohm's law. Ta...The electric field, equations of boundary conditions and calculation formula of apparent resistivity are derived for the azimuthal anisotropy layered media with the DC method based on the anisotropic Ohm's law. Taking the Schlumberger symmetric system as an example and using the recurrence formula of nuclear function, the paper theoretically simulates a model of four layers with the same anisotropy coefficient for each layer. The deep sounding curves of resistivity and the pattern of contours are obtained for the model. The results show that the theoretical formula is correct, and the deep sounding curves not only exhibit the difference of resistivity among layers but also indicate the anisotropy characteristics of layers.展开更多
The method in which a source is set on the surface and electric potential is received in the borehole is called surface-borehole electric potential technique.Technique of surface-borehole electric potential was employ...The method in which a source is set on the surface and electric potential is received in the borehole is called surface-borehole electric potential technique.Technique of surface-borehole electric potential was employed to study electric response of layered formation.The electric potential was obtained by solving Poisson equation with finite difference method.In the course of calculation,forward modeling with finite difference method was realized by adopting bandwidth non-zero storage technique and the incomplete Cholesky conjugate gradient method.The results show that method of surface-borehole can acquire anomalous electric potential corresponding to geo-electric layers.In addition,application of appropriate mathematical operator can improve the resolution.Moreover,overburden low resistivity layers have severe influence on measuring results of surface-borehole electric potential.However,bottom low resistivity layers play a positive role in the measurement.展开更多
采用Apache+PHP+MySQL技术设计开发了三层结构模式的视频直播网站——"武警黄金部队学术交流平台",利用Windows MediaEncoder进行学术交流现场的音视频采集,Windows Media Server进行视频发布,直播和点播的流媒体内容嵌入到H...采用Apache+PHP+MySQL技术设计开发了三层结构模式的视频直播网站——"武警黄金部队学术交流平台",利用Windows MediaEncoder进行学术交流现场的音视频采集,Windows Media Server进行视频发布,直播和点播的流媒体内容嵌入到HTML网页,用户用IE、FireFox等浏览器登录浏览视频直播网页即可实现网络视频直播和点播。展开更多
Magnetohydrodynamic (MHD) bioconvection of an incompressible electrically conducting nanofluid near a vertical wavy surface saturated porous medium containing both nanoparticle and gyrotactic microorganisms is inves...Magnetohydrodynamic (MHD) bioconvection of an incompressible electrically conducting nanofluid near a vertical wavy surface saturated porous medium containing both nanoparticle and gyrotactic microorganisms is investigated. The nanofluid is represented by a model that includes both Brownian motion and thermophoresis effects. A suitable set of non-dimensional variables are used to transform the governing boundary layer equations into a dimensionless form. The resulting nonlinear system is mapped to the vertical flat plate domain, and a non-similar solution is used to the obtained equations. The obtained non-similar system is then solved numerically using the fourth-order Runge-Kutta method. The influence of various physical parameters on the local Nusselt number, the local Sherwood number, the local density number of the motile microorganisms, the dimensionless velocity, the dimensionless temperature, and the rescaled density of motile microorganisms is studied. It is found that the local Nusselt number, the local Sherwood number, and the local density number of the motile microorganisms decrease by increasing either the Grashof number or the magnetic field parameter.展开更多
The ultrasonic attenuation coefficient is one of the most important acoustic parameters to character the performance of a thin layer media, but it can not be measured due to mutual superposition of multiple reflected ...The ultrasonic attenuation coefficient is one of the most important acoustic parameters to character the performance of a thin layer media, but it can not be measured due to mutual superposition of multiple reflected waves at the same interface in ultrasonic testing. Ultrasonic pulse echo and lamb wave to evaluate the thin layer media can not obtain attenuation coefficient at present. In this paper, analytical method was used to study the acoustics characteristic of thin layer media with the ultrasonic echo testing. Meanwhile, the process of ultrasonic attenuation measurement was presented. Simulation and experimental investigation is focused on a thin layer of rubber. Attenuation coefficient was introduced and evaluation mathematics model was established by the two echoes cross-correlation with and without the thin layer media based on the time delay spectrum. It involved the parameters related to the acoustic properties of the thin layer media. Through calculating the sound velocity and acoustic impedance with the evaluation model, it can deduce the relation between the attenuation coefficient and the frequency. Through analyzing the simulation results, it indicated that the attenuation coefficients were invariable with the varying of the frequency. However, the attenuation coefficients increased with the frequency increasing by ultrasonic testing the thin layer of rubber. The reason was that the attenuation factor was not taken into account during the simulation. This method overcomes shortcomings that the traditional ultrasonic testing can not evaluate the thin layer media whose thickness is less than motivation wavelength. It is a new solution to study the attenuation characteristic and on-line nondestructive evaluation in the thin layer media.展开更多
Alternating direction implicit finite difference time domain (ADI-FDTD) method is unconditionally stable and the maximum time step is not limited by the Courant stability condition, but rather by numerical error. Co...Alternating direction implicit finite difference time domain (ADI-FDTD) method is unconditionally stable and the maximum time step is not limited by the Courant stability condition, but rather by numerical error. Compared with the conventional FDTD method, the time step of ADI-FDTD can be enlarged arbitrarily and the CPU cost can be reduced. 2D perfectly matched layer (PML) absorbing boundary condition is proposed to truncate computation space for ADI-FDTD in dispersive media using recursive convolution(RC) method and the 2D PML formulations for dispersive media are derived. ADI-FDTD formulations for dispersive media can be obtained from the simplified PML formulations. The scattering of target in dispersive soil is simulated under sine wave and Gaussian pulse excitations and numerical results of ADI-FDTD with PML are compared with FDTD. Good agreement is observed. At the same time the CPU cost for ADI-FDTD is obviously reduced.展开更多
This work deals with the degradation of AZ31 and AZ91 magnesium alloys when they are exposed to three types of physiological media for seven days at 37°C:Ringer's,Hanks\and simulated body fluid(SBF)solutions....This work deals with the degradation of AZ31 and AZ91 magnesium alloys when they are exposed to three types of physiological media for seven days at 37°C:Ringer's,Hanks\and simulated body fluid(SBF)solutions.A combination of immersions tests and surface characterisation methods were employed to evaluate the attack on the surface,and the stability of the formed corrosion product layers for each alloy/electrolyte system.Measurements of the Mg-ion released into the electrolytes were also carried out in order to be correlated with the degradation of the alloys.Electrochemical impedance spectroscopy(EIS)and potentiodynamic polarisation(PDP)techniques were employed to compare the performance of the alloys in these different aggressive electrolytes.According to the obtained results,the Mg-alloys exposed to Hanks'media were the less affected,which fact was attributed to a higher stability of the corrosion products layer formed in this medium,in comparison of those formed in Ringer's and SBF solutions.In add让ion,the corrosion damage was lower for AZ91 than for AZ31 alloy in all environments due to its higher Al content.The mass loss rates calculated from both immersion tests and electrochemical methods followed the same trend for comparative purposes between alloys.展开更多
Taking the graph of the apparent resistivity Pyx in Lanzhou area, its geomagnetic transfer function variations andthe investigation of moderate-strong local earthquakes as example and from.the viewpoint of seismomagne...Taking the graph of the apparent resistivity Pyx in Lanzhou area, its geomagnetic transfer function variations andthe investigation of moderate-strong local earthquakes as example and from.the viewpoint of seismomagnetic effect,the authors found that subterranean conductivity values might be applied to the division of Lanzhou areafrom the surface downward into four layers, i. e., the anomalous, the transitional,the non-anomalous and theanomalous layer. Only the transfer function modular |A| and |B|,magnetic azimuth ap with its variance ap,and the total variance yi in the anomalous layers showed obvious anomalies with time changes. Thus, it could beconjectured that the anomalous layer was closely associated with the anisotropic variations of conductivity of thesubterranean media in the seismicity area.This phenomenon might provide a way to the further study of itsmechanism. It is needed to study the inherent connotation deeply.展开更多
High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,tempe...High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,temperature field induced by this kind of transducer in multi-layer media will be simulated through solving Pennes equation with finite difference method,and the influence of initial sound pressure,absorption coefficient,and thickness of different layers of biological tissue as well as thermal conductivity parameter on sound focus and temperature distribution will be analyzed,respectively.The results show that the temperature in focus area increases faster while the initial sound pressure and thermal conductivity increase.The absorption coefficient is smaller,the ultrasound intensity in the focus area is bigger,and the size of the focus area is increasing.When the thicknesses of different layers of tissue change,the focus position changes slightly,but the sound intensity of the focus area will change obviously.The temperature in focus area will rise quickly before reaching a threshold,and then the temperature will keep in the threshold range.展开更多
The effect of soil stratification was studied through numerical investigation based on the coupled model of solute transport in deformable unsaturated soil. The theoretical model implied two-way coupled excess pore pr...The effect of soil stratification was studied through numerical investigation based on the coupled model of solute transport in deformable unsaturated soil. The theoretical model implied two-way coupled excess pore pressure and soil deformation based on Biot's consolidation theory as well as a one-way coupled volatile pollutant concentration field developed from the advection-diffusion theory. Embedded in the model, the degree of saturation, fluid compressibility, self-weight of the soil matrix, porosity variance, longitudinal dispersion, and linear sorption were computed. Based on simulation results of a proposed three-layer landfill model using the finite element method, the multi-layer effects are discussed with regard to the hydraulic conductivity, shear modulus, degree of saturation, molecular diffusion coefficient, and thickness of each layer. Generally speaking, contaminants spread faster in a stratified field with a soft and highly permeable top layer; soil parameters of the top layer are more critical than the lower layers but controlling soil thicknesses will alter the results. This numerical investigation showed noticeable impacts of stratified soil properties on solute migration results, demonstrating the importance of correctly modeling layered soil instead of simply assuming the averaged properties across the soil profile.展开更多
The study of wave propagation in finite/infinite media has many applications in geotechnical and structural earthquake engineering and has been a focus of research for the past few decades. This paper presents an anal...The study of wave propagation in finite/infinite media has many applications in geotechnical and structural earthquake engineering and has been a focus of research for the past few decades. This paper presents an analysis of 2D anti- plane problems (Love waves) and 2D in-plane problems (Rayleigh waves) in the frequency domain in media consisting of a near-field irregular and a far-field regular part. The near field part may contain structures and its boundaries with the far-field can be of any shape. In this study, the irregular boundaries of the near-field are treated as consistent boundaries, extending the concept of Lysmer's vertical consistent boundaries. The presented technique is called the Condensed Hyperelements Method (CHM). In this method, the irregular boundary is limited to a vertical boundary at each end that is a consistent boundary at the far-field side. Between the two ends, the medium is discretized with hyperelements. Using static condensation, the stiffness matrix of the far-field is derived for the nodes on the irregular boundary. Examples of the application of the CHM illustrate its excellent accuracy and efficiency.展开更多
基金supported by the National Natural Science Foundation of China(Nos.10725210,10832009 and 10432030)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20060335107)the Program for New Century Excellent Talents in University(No.NCET-05-05010).
文摘The method of reverberation-ray matrix (MRRM) is extended and modified for the analysis of free wave propagation in anisotropic layered elastic media. A general, numerically stable formulation is established within the state space framework. The compatibility of physical variables in local dual coordinates gives the phase relation, from which exponentially growing functions are excluded. The interface and boundary conditions lead to the scattering relation, which avoids matrix inversion operation. Numerical examples are given to show the high accuracy of the present MRRM.
基金supported by National Natural Science Foundation of China (Nos.40831062, 60971034)the Scientific Research Starting Foundation of University of Electronic Science and Technology of China (No.Y02002010401066)
文摘Polar mesosphere summer echoes (PMSE) are very strong radar echoes from alti- tudes close to the polar summer mesopause. The data from sounding rocket campaigns indicate that the radar signal to noise ratio (SNR), electron density and dust charge density of polar meso- sphere in summer show obvious layered structure. In this paper the theory of wave propagation in layered media is used to study the reflectance and SNR at each layer in polar mesosphere. The calculated SNR using theory of dusty plasma is found in good agreement with the experimental result, which may imply that the intensity of the radar echoes reflected by the layered structure in polar mesosphere where polar mesosphere summer echoes used to occur can interpret partially the phenomenon of PMSE. In other words, reflection may play an important role in the occurrence of PMSE.
基金financially supported by the National Key Research and Development Program of China(No.2019YFC1804303)the National Natural Science Foundation of China(Grant Nos.41877171 and 41831289)。
文摘Compared to single layer porous media,fluid flow through layered porous media(LPMs)with contrasting pore space structures is more complex.This study constructed three-dimensional(3-D)pore-scale LPMs with different grain size ratios of 1.20,1.47,and 1.76.The flow behavior in the constructed LPMs and single layer porous media was numerically investigated.A total of 178 numerical experimental data were collected in LPMs and single layer porous media.In all cases,two different flow regimes(i.e.,Darcy and Non-Darcy)were observed.The influence of the interface of layers on Non-Darcy flow behavior in LPMs was analyzed based pore-scale flow data.It was found that the available correlations based on single layer porous media fail to predict the flow behavior in LPMs,especially for LPM with large grain size ratio.The effective permeability,which incorporated the influence of the interface is more accurate than the Kozeny-Carman equation for estimating the Darcy permeability of LPMs.The inertial pressure loss in LPMs,which determines the onset of the Non-Darcy flow,was underestimated when using a power law expression of mean grain size.The constant B,an empirical value in the classical Ergun equation,typically equals 1.75.The inertial pressure loss in LPMs can be significantly different from it in single lager porous media.For Non-Darcy flow in LPMs,it is necessary to consider a modified larger constant B to improve the accuracy of the Ergun empirical equation.
文摘Dynamic behavior of single pile embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's function for ring loads. The influence of soil anisotropy on the dynamic behavior of piles is examined through a series of parametric studies.
基金Joint Seismological Science Foundation of China (2001009) State Natural Science Foundation of China (40074010) the Project MOST under contract 2001BA601B002-02-01.
文摘The electric field, equations of boundary conditions and calculation formula of apparent resistivity are derived for the azimuthal anisotropy layered media with the DC method based on the anisotropic Ohm's law. Taking the Schlumberger symmetric system as an example and using the recurrence formula of nuclear function, the paper theoretically simulates a model of four layers with the same anisotropy coefficient for each layer. The deep sounding curves of resistivity and the pattern of contours are obtained for the model. The results show that the theoretical formula is correct, and the deep sounding curves not only exhibit the difference of resistivity among layers but also indicate the anisotropy characteristics of layers.
基金Supported by ihe Major State Basic Research Development Program of China (973 Program) (2010CB428801, 2010CB428804) the National Science Foundation of China (40972166)+1 种基金 the Major Science and Technology Program for Water Pollution Control and Treatment (2009ZX07212-003) the Technology Development and Applications for Ecology System Reconstruction and Restoration of Yongding River (D08040903700000)
基金Project supported by Global Center of Excellence in Novel Carbon Resource Sciences,Kyushu University,Japan
文摘The method in which a source is set on the surface and electric potential is received in the borehole is called surface-borehole electric potential technique.Technique of surface-borehole electric potential was employed to study electric response of layered formation.The electric potential was obtained by solving Poisson equation with finite difference method.In the course of calculation,forward modeling with finite difference method was realized by adopting bandwidth non-zero storage technique and the incomplete Cholesky conjugate gradient method.The results show that method of surface-borehole can acquire anomalous electric potential corresponding to geo-electric layers.In addition,application of appropriate mathematical operator can improve the resolution.Moreover,overburden low resistivity layers have severe influence on measuring results of surface-borehole electric potential.However,bottom low resistivity layers play a positive role in the measurement.
文摘采用Apache+PHP+MySQL技术设计开发了三层结构模式的视频直播网站——"武警黄金部队学术交流平台",利用Windows MediaEncoder进行学术交流现场的音视频采集,Windows Media Server进行视频发布,直播和点播的流媒体内容嵌入到HTML网页,用户用IE、FireFox等浏览器登录浏览视频直播网页即可实现网络视频直播和点播。
文摘Magnetohydrodynamic (MHD) bioconvection of an incompressible electrically conducting nanofluid near a vertical wavy surface saturated porous medium containing both nanoparticle and gyrotactic microorganisms is investigated. The nanofluid is represented by a model that includes both Brownian motion and thermophoresis effects. A suitable set of non-dimensional variables are used to transform the governing boundary layer equations into a dimensionless form. The resulting nonlinear system is mapped to the vertical flat plate domain, and a non-similar solution is used to the obtained equations. The obtained non-similar system is then solved numerically using the fourth-order Runge-Kutta method. The influence of various physical parameters on the local Nusselt number, the local Sherwood number, the local density number of the motile microorganisms, the dimensionless velocity, the dimensionless temperature, and the rescaled density of motile microorganisms is studied. It is found that the local Nusselt number, the local Sherwood number, and the local density number of the motile microorganisms decrease by increasing either the Grashof number or the magnetic field parameter.
基金supported by National Natural Science Foundation of China (Grant No. 50802009)Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070151024)
文摘The ultrasonic attenuation coefficient is one of the most important acoustic parameters to character the performance of a thin layer media, but it can not be measured due to mutual superposition of multiple reflected waves at the same interface in ultrasonic testing. Ultrasonic pulse echo and lamb wave to evaluate the thin layer media can not obtain attenuation coefficient at present. In this paper, analytical method was used to study the acoustics characteristic of thin layer media with the ultrasonic echo testing. Meanwhile, the process of ultrasonic attenuation measurement was presented. Simulation and experimental investigation is focused on a thin layer of rubber. Attenuation coefficient was introduced and evaluation mathematics model was established by the two echoes cross-correlation with and without the thin layer media based on the time delay spectrum. It involved the parameters related to the acoustic properties of the thin layer media. Through calculating the sound velocity and acoustic impedance with the evaluation model, it can deduce the relation between the attenuation coefficient and the frequency. Through analyzing the simulation results, it indicated that the attenuation coefficients were invariable with the varying of the frequency. However, the attenuation coefficients increased with the frequency increasing by ultrasonic testing the thin layer of rubber. The reason was that the attenuation factor was not taken into account during the simulation. This method overcomes shortcomings that the traditional ultrasonic testing can not evaluate the thin layer media whose thickness is less than motivation wavelength. It is a new solution to study the attenuation characteristic and on-line nondestructive evaluation in the thin layer media.
文摘Alternating direction implicit finite difference time domain (ADI-FDTD) method is unconditionally stable and the maximum time step is not limited by the Courant stability condition, but rather by numerical error. Compared with the conventional FDTD method, the time step of ADI-FDTD can be enlarged arbitrarily and the CPU cost can be reduced. 2D perfectly matched layer (PML) absorbing boundary condition is proposed to truncate computation space for ADI-FDTD in dispersive media using recursive convolution(RC) method and the 2D PML formulations for dispersive media are derived. ADI-FDTD formulations for dispersive media can be obtained from the simplified PML formulations. The scattering of target in dispersive soil is simulated under sine wave and Gaussian pulse excitations and numerical results of ADI-FDTD with PML are compared with FDTD. Good agreement is observed. At the same time the CPU cost for ADI-FDTD is obviously reduced.
文摘This work deals with the degradation of AZ31 and AZ91 magnesium alloys when they are exposed to three types of physiological media for seven days at 37°C:Ringer's,Hanks\and simulated body fluid(SBF)solutions.A combination of immersions tests and surface characterisation methods were employed to evaluate the attack on the surface,and the stability of the formed corrosion product layers for each alloy/electrolyte system.Measurements of the Mg-ion released into the electrolytes were also carried out in order to be correlated with the degradation of the alloys.Electrochemical impedance spectroscopy(EIS)and potentiodynamic polarisation(PDP)techniques were employed to compare the performance of the alloys in these different aggressive electrolytes.According to the obtained results,the Mg-alloys exposed to Hanks'media were the less affected,which fact was attributed to a higher stability of the corrosion products layer formed in this medium,in comparison of those formed in Ringer's and SBF solutions.In add让ion,the corrosion damage was lower for AZ91 than for AZ31 alloy in all environments due to its higher Al content.The mass loss rates calculated from both immersion tests and electrochemical methods followed the same trend for comparative purposes between alloys.
文摘Taking the graph of the apparent resistivity Pyx in Lanzhou area, its geomagnetic transfer function variations andthe investigation of moderate-strong local earthquakes as example and from.the viewpoint of seismomagnetic effect,the authors found that subterranean conductivity values might be applied to the division of Lanzhou areafrom the surface downward into four layers, i. e., the anomalous, the transitional,the non-anomalous and theanomalous layer. Only the transfer function modular |A| and |B|,magnetic azimuth ap with its variance ap,and the total variance yi in the anomalous layers showed obvious anomalies with time changes. Thus, it could beconjectured that the anomalous layer was closely associated with the anisotropic variations of conductivity of thesubterranean media in the seismicity area.This phenomenon might provide a way to the further study of itsmechanism. It is needed to study the inherent connotation deeply.
基金Project(11174077)supported by the National Natural Science Foundation of ChinaProject(11JJ3079)supported by the Hunan Provincial Natural Science Foundation of ChinaProjects(12C0237,11C0844)supported by the Science Research Program of Education Department of Hunan Province,China
文摘High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,temperature field induced by this kind of transducer in multi-layer media will be simulated through solving Pennes equation with finite difference method,and the influence of initial sound pressure,absorption coefficient,and thickness of different layers of biological tissue as well as thermal conductivity parameter on sound focus and temperature distribution will be analyzed,respectively.The results show that the temperature in focus area increases faster while the initial sound pressure and thermal conductivity increase.The absorption coefficient is smaller,the ultrasound intensity in the focus area is bigger,and the size of the focus area is increasing.When the thicknesses of different layers of tissue change,the focus position changes slightly,but the sound intensity of the focus area will change obviously.The temperature in focus area will rise quickly before reaching a threshold,and then the temperature will keep in the threshold range.
文摘The effect of soil stratification was studied through numerical investigation based on the coupled model of solute transport in deformable unsaturated soil. The theoretical model implied two-way coupled excess pore pressure and soil deformation based on Biot's consolidation theory as well as a one-way coupled volatile pollutant concentration field developed from the advection-diffusion theory. Embedded in the model, the degree of saturation, fluid compressibility, self-weight of the soil matrix, porosity variance, longitudinal dispersion, and linear sorption were computed. Based on simulation results of a proposed three-layer landfill model using the finite element method, the multi-layer effects are discussed with regard to the hydraulic conductivity, shear modulus, degree of saturation, molecular diffusion coefficient, and thickness of each layer. Generally speaking, contaminants spread faster in a stratified field with a soft and highly permeable top layer; soil parameters of the top layer are more critical than the lower layers but controlling soil thicknesses will alter the results. This numerical investigation showed noticeable impacts of stratified soil properties on solute migration results, demonstrating the importance of correctly modeling layered soil instead of simply assuming the averaged properties across the soil profile.
文摘The study of wave propagation in finite/infinite media has many applications in geotechnical and structural earthquake engineering and has been a focus of research for the past few decades. This paper presents an analysis of 2D anti- plane problems (Love waves) and 2D in-plane problems (Rayleigh waves) in the frequency domain in media consisting of a near-field irregular and a far-field regular part. The near field part may contain structures and its boundaries with the far-field can be of any shape. In this study, the irregular boundaries of the near-field are treated as consistent boundaries, extending the concept of Lysmer's vertical consistent boundaries. The presented technique is called the Condensed Hyperelements Method (CHM). In this method, the irregular boundary is limited to a vertical boundary at each end that is a consistent boundary at the far-field side. Between the two ends, the medium is discretized with hyperelements. Using static condensation, the stiffness matrix of the far-field is derived for the nodes on the irregular boundary. Examples of the application of the CHM illustrate its excellent accuracy and efficiency.