We establish a patchy saturation model and derive the seismic wave equations for patchy saturated porous media on the basis of Biot＇s equations and Johnson＇s bulk modulus. We solve the equations, obtain the attenuat...We establish a patchy saturation model and derive the seismic wave equations for patchy saturated porous media on the basis of Biot＇s equations and Johnson＇s bulk modulus. We solve the equations, obtain the attenuation coefficients, and analyze the characteristics of wave attenuation in the seismic frequency range. The results suggest that seismic waves show attenuation and dispersion in partially saturated rocks in the low frequency range. With frequency increasing, attenuation increases. The attenuation of P-waves of the second kind is more pronounced in agreement with Biot＇s theory. We also study the effect of porosity, saturation, and inner sphere radius on the attenuation of the P-waves of the first kind and find that attenuation increases with increasing frequency and porosity, and decreases with increasing frequency and degree of saturation. As for the inner sphere radius, wave attenuation is initially increasing with increasing frequency and inner sphere radius less than half the outer radius. Subsequently, wave attenuation decreases with increasing frequency and inner sphere radius is higher than half the outer sphere radius.展开更多
The ion-to-electron temperature ratio is a good indicator of the processes involved in the plasma sheet.Observations have suggested that patchy reconnection and the resulting earthward bursty bulk flows(BBFs)transport...The ion-to-electron temperature ratio is a good indicator of the processes involved in the plasma sheet.Observations have suggested that patchy reconnection and the resulting earthward bursty bulk flows(BBFs)transport may be involved in causing the lower temperature ratios at smaller radial distances during southward IMF periods.In this paper,we estimate theoretically how a patchy magnetic reconnection electric field can accelerate ions and electrons differently.If both ions and electrons are non-adiabatically accelerated only once within each reconnection,the temperature ratio would be preserved.However,when reconnection occurs closer to the Earth where magnetic field lines are shorter,particles mirrored back from the ionosphere can cross the reconnection region more than once within one reconnection;and electrons,moving faster than ions,can have more crossings than do ions,leading to electrons being accelerated more than ions.Thus as particles are transported from tail to the near-Earth by BBFs through multiple reconnection,electrons should be accelerated by the reconnection electric field more times than are ions,which can explain the lower temperature ratios observed closer to the Earth.展开更多
The wave-induced local fluid flow mechanism is relevant to the complex heterogeneity of pore structures in rocks.The analysis of the local fluid flow mechanism is useful for accurately describing the wave propagation ...The wave-induced local fluid flow mechanism is relevant to the complex heterogeneity of pore structures in rocks.The analysis of the local fluid flow mechanism is useful for accurately describing the wave propagation characteristics in reservoir rocks.In the exploration and production of hydrocarbon reservoirs,the real stratum may be partially saturated with a multi-phase fluid mixture in general.Therefore,it is of great significance to investigate the wave velocity dispersion and attenuation features in relation to pore structures and fluids.In this work,the characteristics of fabric microstructures are obtained on the basis of pressure dependency of dry rock moduli using the effective medium theory.A novel anelasticity theoretical model for the wave propagation in a partially-saturated medium is presented by combining the extended Gurevich squirt-flow model and White patchysaturation theory.Numerical simulations are used to analyze wave propagation characteristics that depend on water saturation,external patchy diameter,and viscosity.We consider a tight sandstone from the Qingyang area of the Ordos Basin in west China and perform ultrasonic measurements under partial saturation states and different confining pressures,where the basic properties of the rock are obtained at the full gas saturation.The comparison of experimental data and theoretical modeling results shows a fairly good agreement,indicating that the new theory is effective.展开更多
Coastal vegetation is capable of decreasing wave run-up.However,because of regrowth,decay or man-made damage,coastal vegetation is always distributed in patches,and its internal distribution is often non-uniform.This ...Coastal vegetation is capable of decreasing wave run-up.However,because of regrowth,decay or man-made damage,coastal vegetation is always distributed in patches,and its internal distribution is often non-uniform.This study investigates the effects of patchy vegetation on solitary wave run-up by using a numerical simulation.A numerical model based on fully nonlinear Boussinesq equations is established to simulate the wave propagation on a slope with patchy vegetation.By using the model,the process of solitary wave run-up attenuation due to patchy vegetation is numerically analysed.The numerical results reveal that patchy vegetation can considerably attenuate the wave run-up in an effective manner.In addition,high-density patched vegetation can attenuate the solitary wave run-up more effectively than low-density patched vegetation can.For the same density,patchy vegetation with a uniform distribution has a better attenuation effect on wave run-up compared to that of patchy vegetation with a non-uniform distribution.展开更多
Wave-induced flow is observed as the domi- nated factor for P wave propagation at seismic frequencies. This mechanism has a mesoscopic scale nature. The inhomogeneous unsaturated patches are regarded larger than the p...Wave-induced flow is observed as the domi- nated factor for P wave propagation at seismic frequencies. This mechanism has a mesoscopic scale nature. The inhomogeneous unsaturated patches are regarded larger than the pore size, but smaller than the wavelength. Surface wave, e.g., Rayleigh wave, which propagates along the free surface, generated by the interfering of body waves is also affected by the mesoscopic loss mechanisms. Recent studies have reported that the effect of the wave-induced flow in wave propagation shows a relaxation behavior. Viscoelastic equivalent relaxation function associated with the wave mode can describe the kinetic nature of the attenuation. In this paper, the equivalent viscoelastic relaxation functions are extended to take into account the free surface for the Rayleigh surface wave propagation inpatchy saturated poroelastic media. Numerical results for the frequency-dependent velocity and attenuation and the time-dependent dynamical responses for the equivalent Rayleigh surface wave propagation along an interface between vacuum and patchy saturated porous media are reported in the low-frequency range （0.1-1,000 Hz）. The results show that the dispersion and attenuation and kinetic characteristics of the mesoscopic loss effect for the surface wave can be effectively represented in the equivalent vis- coelastic media. The simulation of surface wave propaga- tion within mesoscopic patches requires solving Blot＇s differential equations in very small grid spaces, involving the conversion of the fast P wave energy diffusion into the Blot slow wave. This procedure requires a very large amount of computer consumption. An efficient equivalent approach for this patchy saturated poroelastic media shows a more convenient way to solve the single phase visco- elastic differential equations.展开更多
We present the phase diagrams for neutral patchy colloidal particles whose surface is decorated by different number of identical patches,where each patch serves as an associating site.The hard-core Lennard-Jones(LJ)po...We present the phase diagrams for neutral patchy colloidal particles whose surface is decorated by different number of identical patches,where each patch serves as an associating site.The hard-core Lennard-Jones(LJ)potential and associating interaction are incorporated into the free energies of patchy particles in phases of the uid(F),random close packing(RCP),and face-centered-cubic(FCC)crystal.A rich phase structure of patchy particles with F-F,F-RCP,and F-FCC transitions can be observed.Meanwhile,the sol-gel transition(SGT)characterizing the connectivity of patchy particles is also investigated.It is shown that,depending on the number of patches and associating energy,the F-F transition might be metastable or stable with respect to the F-RCP and F-FCC transitions.Meanwhile,the critical temperatures,critical densities,triple points,and SGT can be significantly regulated by these factors.展开更多
Phytoplankton patchiness ubiquitously obser- ved in marine ecosystems is a simple phy- sical phenomenon. Only two factors are required for its formation: one is persistent variations of inhomogeneous distributions in ...Phytoplankton patchiness ubiquitously obser- ved in marine ecosystems is a simple phy- sical phenomenon. Only two factors are required for its formation: one is persistent variations of inhomogeneous distributions in the phytopl- ankton population and the other is turbulent stirring by eddies. It is not necessary to assume continuous oscillations such as limit cycles for realization of the first factor. Instead, a certain amount of noise is enough. Random fluctua-tions by environmental noise and turbulent ad-vection by eddies seem to be common in open oceans. Based on these hypotheses, we pro-pose seemingly the simplest method to simulate patchiness formation that can create realistic images. Sufficient noise and turbulence can induce patchiness formation even though the system lies on the stable equilibrium conditions. We tentatively adopt the two-component model with nutrients and phytoplankton, however, the choice of the mathematical model is not essen-tial. The simulation method proposed in this study can be applied to whatever model with stable equilibrium states including one-com-ponent ones.展开更多
基金supported by the National Natural Science Foundation of China(Nos.41204089 and 41174087)the National Science and Technology Major Project(Nos.2011ZX05035-001 and 2011ZX05005-005)the National 863 Program(No.2013AA064201)
文摘We establish a patchy saturation model and derive the seismic wave equations for patchy saturated porous media on the basis of Biot＇s equations and Johnson＇s bulk modulus. We solve the equations, obtain the attenuation coefficients, and analyze the characteristics of wave attenuation in the seismic frequency range. The results suggest that seismic waves show attenuation and dispersion in partially saturated rocks in the low frequency range. With frequency increasing, attenuation increases. The attenuation of P-waves of the second kind is more pronounced in agreement with Biot＇s theory. We also study the effect of porosity, saturation, and inner sphere radius on the attenuation of the P-waves of the first kind and find that attenuation increases with increasing frequency and porosity, and decreases with increasing frequency and degree of saturation. As for the inner sphere radius, wave attenuation is initially increasing with increasing frequency and inner sphere radius less than half the outer radius. Subsequently, wave attenuation decreases with increasing frequency and inner sphere radius is higher than half the outer sphere radius.
基金supported by the National Nature Science Foundation of China (Grant NSFC41374179)supported by NASA (NNX16AJ83G)
文摘The ion-to-electron temperature ratio is a good indicator of the processes involved in the plasma sheet.Observations have suggested that patchy reconnection and the resulting earthward bursty bulk flows(BBFs)transport may be involved in causing the lower temperature ratios at smaller radial distances during southward IMF periods.In this paper,we estimate theoretically how a patchy magnetic reconnection electric field can accelerate ions and electrons differently.If both ions and electrons are non-adiabatically accelerated only once within each reconnection,the temperature ratio would be preserved.However,when reconnection occurs closer to the Earth where magnetic field lines are shorter,particles mirrored back from the ionosphere can cross the reconnection region more than once within one reconnection;and electrons,moving faster than ions,can have more crossings than do ions,leading to electrons being accelerated more than ions.Thus as particles are transported from tail to the near-Earth by BBFs through multiple reconnection,electrons should be accelerated by the reconnection electric field more times than are ions,which can explain the lower temperature ratios observed closer to the Earth.
基金supported by the National Natural Science Foundation of China(Grant no.41704109)the Jiangsu Province Outstanding Youth Fund Project(Grant no.BK20200021).
文摘The wave-induced local fluid flow mechanism is relevant to the complex heterogeneity of pore structures in rocks.The analysis of the local fluid flow mechanism is useful for accurately describing the wave propagation characteristics in reservoir rocks.In the exploration and production of hydrocarbon reservoirs,the real stratum may be partially saturated with a multi-phase fluid mixture in general.Therefore,it is of great significance to investigate the wave velocity dispersion and attenuation features in relation to pore structures and fluids.In this work,the characteristics of fabric microstructures are obtained on the basis of pressure dependency of dry rock moduli using the effective medium theory.A novel anelasticity theoretical model for the wave propagation in a partially-saturated medium is presented by combining the extended Gurevich squirt-flow model and White patchysaturation theory.Numerical simulations are used to analyze wave propagation characteristics that depend on water saturation,external patchy diameter,and viscosity.We consider a tight sandstone from the Qingyang area of the Ordos Basin in west China and perform ultrasonic measurements under partial saturation states and different confining pressures,where the basic properties of the rock are obtained at the full gas saturation.The comparison of experimental data and theoretical modeling results shows a fairly good agreement,indicating that the new theory is effective.
基金The National Natural Science Foundation of China under contract Nos 51579036 and 51779039the Fundamental Research Funds for the Central Universities of China under contract No.DUT19LAB13。
文摘Coastal vegetation is capable of decreasing wave run-up.However,because of regrowth,decay or man-made damage,coastal vegetation is always distributed in patches,and its internal distribution is often non-uniform.This study investigates the effects of patchy vegetation on solitary wave run-up by using a numerical simulation.A numerical model based on fully nonlinear Boussinesq equations is established to simulate the wave propagation on a slope with patchy vegetation.By using the model,the process of solitary wave run-up attenuation due to patchy vegetation is numerically analysed.The numerical results reveal that patchy vegetation can considerably attenuate the wave run-up in an effective manner.In addition,high-density patched vegetation can attenuate the solitary wave run-up more effectively than low-density patched vegetation can.For the same density,patchy vegetation with a uniform distribution has a better attenuation effect on wave run-up compared to that of patchy vegetation with a non-uniform distribution.
基金support by the Natural Basic Research Program of China (the ‘‘973 Project’’,Grant No. 2013CB733303)the National Natural Science Foundation of China (Grant Nos. 41304077, 40974079)+1 种基金Postdoctoral Science Foundation of China (Grant No. 2013M531744)Key Laboratory of Geospace Environment and Geodesy (Grant Nos. 12-02-03)
文摘Wave-induced flow is observed as the domi- nated factor for P wave propagation at seismic frequencies. This mechanism has a mesoscopic scale nature. The inhomogeneous unsaturated patches are regarded larger than the pore size, but smaller than the wavelength. Surface wave, e.g., Rayleigh wave, which propagates along the free surface, generated by the interfering of body waves is also affected by the mesoscopic loss mechanisms. Recent studies have reported that the effect of the wave-induced flow in wave propagation shows a relaxation behavior. Viscoelastic equivalent relaxation function associated with the wave mode can describe the kinetic nature of the attenuation. In this paper, the equivalent viscoelastic relaxation functions are extended to take into account the free surface for the Rayleigh surface wave propagation inpatchy saturated poroelastic media. Numerical results for the frequency-dependent velocity and attenuation and the time-dependent dynamical responses for the equivalent Rayleigh surface wave propagation along an interface between vacuum and patchy saturated porous media are reported in the low-frequency range （0.1-1,000 Hz）. The results show that the dispersion and attenuation and kinetic characteristics of the mesoscopic loss effect for the surface wave can be effectively represented in the equivalent vis- coelastic media. The simulation of surface wave propaga- tion within mesoscopic patches requires solving Blot＇s differential equations in very small grid spaces, involving the conversion of the fast P wave energy diffusion into the Blot slow wave. This procedure requires a very large amount of computer consumption. An efficient equivalent approach for this patchy saturated poroelastic media shows a more convenient way to solve the single phase visco- elastic differential equations.
基金supported by the National Natural Science Foundation of China(No.21374028 and No.21306034)the Natural Science Foundation of Hebei Province(No.B2014201103)+2 种基金the Project for Talent Engineering of Hebei Province(No.A2016015001)the Project for Top Young Talent of Hebei Provincethe Project for Top Young Talent of General Colleges of Hebei Province(No.BJ2017017)
文摘We present the phase diagrams for neutral patchy colloidal particles whose surface is decorated by different number of identical patches,where each patch serves as an associating site.The hard-core Lennard-Jones(LJ)potential and associating interaction are incorporated into the free energies of patchy particles in phases of the uid(F),random close packing(RCP),and face-centered-cubic(FCC)crystal.A rich phase structure of patchy particles with F-F,F-RCP,and F-FCC transitions can be observed.Meanwhile,the sol-gel transition(SGT)characterizing the connectivity of patchy particles is also investigated.It is shown that,depending on the number of patches and associating energy,the F-F transition might be metastable or stable with respect to the F-RCP and F-FCC transitions.Meanwhile,the critical temperatures,critical densities,triple points,and SGT can be significantly regulated by these factors.
文摘Phytoplankton patchiness ubiquitously obser- ved in marine ecosystems is a simple phy- sical phenomenon. Only two factors are required for its formation: one is persistent variations of inhomogeneous distributions in the phytopl- ankton population and the other is turbulent stirring by eddies. It is not necessary to assume continuous oscillations such as limit cycles for realization of the first factor. Instead, a certain amount of noise is enough. Random fluctua-tions by environmental noise and turbulent ad-vection by eddies seem to be common in open oceans. Based on these hypotheses, we pro-pose seemingly the simplest method to simulate patchiness formation that can create realistic images. Sufficient noise and turbulence can induce patchiness formation even though the system lies on the stable equilibrium conditions. We tentatively adopt the two-component model with nutrients and phytoplankton, however, the choice of the mathematical model is not essen-tial. The simulation method proposed in this study can be applied to whatever model with stable equilibrium states including one-com-ponent ones.
