In order to study the evolution laws during the development process of the coal face overburden rock mining-induced fissure,we studied the process of evolution of overburden rock mining-induced fissures and dynamicall...In order to study the evolution laws during the development process of the coal face overburden rock mining-induced fissure,we studied the process of evolution of overburden rock mining-induced fissures and dynamically quantitatively described its fractal laws,based on the high-precision microseismic monitoring method and the nonlinear Fractal Geometry Theory.The results show that:the overburden rock mining-induced fissure fractal dimension experiences two periodic change processes with the coal face advance,namely a Small→ Big→ Small process,which tends to be stable;the functional relationship between the extraction step distance and the overburden rock mining-induced fissure fractal dimension is a cubic curve.The results suggest that the fractal dimension reflects the evolution characteristics of the overburden rock mining-induced fissure,which can be used as an evaluation index of the stability of the overburden rock strata,and it provides theoretical guidance for stability analysis of the overburden rock strata,goaf roof control and the support movements in the mining face.展开更多
Based on Hertz contact theory, contact area parameters between ball and raceway are calculated. Using the Creep theory of Cater and V-J theory, adhesive area and micro-slip area in the contact area are analyzed. It is...Based on Hertz contact theory, contact area parameters between ball and raceway are calculated. Using the Creep theory of Cater and V-J theory, adhesive area and micro-slip area in the contact area are analyzed. It is considered that micro-adhesion wear of micro convex body in the slip area is the main reason for accuracy degradation of a linear ball guide pair. And, the characteristics of the contact area between ball and raceway of slider are characterized using the fractal function. Fractal parameters are obtained using the least squares fitting double logarithmic graph structure function. Considering the lubrication condition between the ball and rail of slider, stress analysis is carried out on the adhesive area. A fractal-creep model of contact surfaces is established in the micro-slip region. The fractal parameters of a certain guide rail are measured, and the wear degradation process of linear rolling guide is simulated. Finally, the relationship between wear and relative tangential velocity, normal load and running mileage of linear ball guide is obtained.展开更多
Evolution and fractal character of the phase morphology of high impact polystyrene/poly（cis-butadiene） rubber （HIPS/PcBR） blends during melting and mixing were investigated using scanning electron microscopy （SEM...Evolution and fractal character of the phase morphology of high impact polystyrene/poly（cis-butadiene） rubber （HIPS/PcBR） blends during melting and mixing were investigated using scanning electron microscopy （SEM）. The characteristic length L was defined as the size of particles of the dispersed phase in blends. Different fractal dimensions, Df and Din, were introduced to study the distribution width of phase dimensions in the dimensionless region and the uniformity of the spatial distribution of particles, respectively. The results showed that the average characteristic length Lm and Df increase as the volume fraction of the dispersed phase increases, when the volume fraction of the dispersed phase is lower than 50%. In other words, the size of particles increases and their distribution in the dimensionless region becomes more uniform. Meanwhile, the uniformity of the spatial distribution becomes more perfect as the volume fraction increases. At a certain composition, Lm decreases in the initial stage of the mixing and levels off in the late stage. In the initial stage, Df becomes large rapidly with the process of blending, which means that the distribution of L in the dimensionless region becomes more uniform. Meanwhile, the spatial distribution tends to be ideal rapidly in the early stage and fluctuates in a definite range in the late stage of the mixing.展开更多
The increasing concern of the health and environmental effects of ultrafine soot particles emitted by modern combustion devices calls for new techniques to monitor such particles. Techniques based on light scattering ...The increasing concern of the health and environmental effects of ultrafine soot particles emitted by modern combustion devices calls for new techniques to monitor such particles. Techniques based on light scattering represent one possible monitoring method. In this study, numerical simulations were conducted to examine the errors involved in soot characterization using light scattering techniques. Specifically, this study focused on examining the error caused by the approximate fractal scattering models based on the Rayleigh-Deybe-Gans theory （the RDG-FA model）. When the angular scattering properties were used to retrieve parameters of soot aggregates （the radius of gyration and the fractal dimension）, the RDG-FA method was observed to cause a relative error of -10% for a representative set of soot parameters. The effects of measurement uncertainties were also investigated. Our results revealed the pattern of the errors： the errors consisted of a relatively constant baseline error caused by the RDG-FA approximation and an error increasing with the measurement uncertainties. These results are expected to be useful in the analysis and interpretation of experimental data, and also in the determination of the accuracy and applicable range of scattering techniques展开更多
基金Financial support for this work,provided by the National Natural Science Foundation of China(No.51304154)the Natural Science Foundation Anhui Province(No.1408085MKL92)
文摘In order to study the evolution laws during the development process of the coal face overburden rock mining-induced fissure,we studied the process of evolution of overburden rock mining-induced fissures and dynamically quantitatively described its fractal laws,based on the high-precision microseismic monitoring method and the nonlinear Fractal Geometry Theory.The results show that:the overburden rock mining-induced fissure fractal dimension experiences two periodic change processes with the coal face advance,namely a Small→ Big→ Small process,which tends to be stable;the functional relationship between the extraction step distance and the overburden rock mining-induced fissure fractal dimension is a cubic curve.The results suggest that the fractal dimension reflects the evolution characteristics of the overburden rock mining-induced fissure,which can be used as an evaluation index of the stability of the overburden rock strata,and it provides theoretical guidance for stability analysis of the overburden rock strata,goaf roof control and the support movements in the mining face.
基金Supported by the National Natural Science Foundation of China(No.51505012,51575014)the Natural Science Foundation of Beijing(No.3154029,KZ201410005010)+1 种基金the Important National Science&Technology Specific Projects of China(No.2012ZX04010021-001-004)Beijing Postdoctoral Research Foundation(No.2015XX-13)
文摘Based on Hertz contact theory, contact area parameters between ball and raceway are calculated. Using the Creep theory of Cater and V-J theory, adhesive area and micro-slip area in the contact area are analyzed. It is considered that micro-adhesion wear of micro convex body in the slip area is the main reason for accuracy degradation of a linear ball guide pair. And, the characteristics of the contact area between ball and raceway of slider are characterized using the fractal function. Fractal parameters are obtained using the least squares fitting double logarithmic graph structure function. Considering the lubrication condition between the ball and rail of slider, stress analysis is carried out on the adhesive area. A fractal-creep model of contact surfaces is established in the micro-slip region. The fractal parameters of a certain guide rail are measured, and the wear degradation process of linear rolling guide is simulated. Finally, the relationship between wear and relative tangential velocity, normal load and running mileage of linear ball guide is obtained.
基金This work was supported by the National Natural Science Foundation of China (No. 50390090).
文摘Evolution and fractal character of the phase morphology of high impact polystyrene/poly（cis-butadiene） rubber （HIPS/PcBR） blends during melting and mixing were investigated using scanning electron microscopy （SEM）. The characteristic length L was defined as the size of particles of the dispersed phase in blends. Different fractal dimensions, Df and Din, were introduced to study the distribution width of phase dimensions in the dimensionless region and the uniformity of the spatial distribution of particles, respectively. The results showed that the average characteristic length Lm and Df increase as the volume fraction of the dispersed phase increases, when the volume fraction of the dispersed phase is lower than 50%. In other words, the size of particles increases and their distribution in the dimensionless region becomes more uniform. Meanwhile, the uniformity of the spatial distribution becomes more perfect as the volume fraction increases. At a certain composition, Lm decreases in the initial stage of the mixing and levels off in the late stage. In the initial stage, Df becomes large rapidly with the process of blending, which means that the distribution of L in the dimensionless region becomes more uniform. Meanwhile, the spatial distribution tends to be ideal rapidly in the early stage and fluctuates in a definite range in the late stage of the mixing.
文摘The increasing concern of the health and environmental effects of ultrafine soot particles emitted by modern combustion devices calls for new techniques to monitor such particles. Techniques based on light scattering represent one possible monitoring method. In this study, numerical simulations were conducted to examine the errors involved in soot characterization using light scattering techniques. Specifically, this study focused on examining the error caused by the approximate fractal scattering models based on the Rayleigh-Deybe-Gans theory （the RDG-FA model）. When the angular scattering properties were used to retrieve parameters of soot aggregates （the radius of gyration and the fractal dimension）, the RDG-FA method was observed to cause a relative error of -10% for a representative set of soot parameters. The effects of measurement uncertainties were also investigated. Our results revealed the pattern of the errors： the errors consisted of a relatively constant baseline error caused by the RDG-FA approximation and an error increasing with the measurement uncertainties. These results are expected to be useful in the analysis and interpretation of experimental data, and also in the determination of the accuracy and applicable range of scattering techniques
