Triaxial creep tests were carried out under seepage pressure by using rock servo-controlled triaxial rheology testing equipment.Based on experimental results,rock rheological properties influenced by seepage-stress co...Triaxial creep tests were carried out under seepage pressure by using rock servo-controlled triaxial rheology testing equipment.Based on experimental results,rock rheological properties influenced by seepage-stress coupling were studied,and variations of seepage rate with time in complete creep processes of rock were analyzed.It is shown that,when the applied stress is less than failure stress level,the creep deformation is not obvious,and its main form is steady-state creep.When applied stress level is greater than or less than but close to fracture stress,it is easier to see the increase of creep deformation and the more obvious accelerative creep characteristics.The circumferential creep deformation is obviously higher than the axial creep deformation.At the stage of steady-state creep,the average of seepage flow rate is about 4.7×10-9 m/s at confining pressure(σ3) of 2 MPa,and is about 3.9×10-9 m/s at σ3 of 6 MPa.It is seen that the seepage flow rate at σ3 of 2 MPa in this case is obviously larger than that at σ3 of 6 MPa.At the stage of creep acceleration,the seepage flow rate is markedly increased with the increase of time.The variation of rock permeability is directly connected to the growth and evolution of creep crack.It is suggested that the permeability coefficient in complete creep processes of rock is not a constant,but is a function of rock creep strain,confining pressure,damage variable and pore water pressure.The results can be considered to provide a reliable reference for the establishment of rock rheological model and parameter identification.展开更多
The seepage property of low-permeability rock is of significant importance for the design and safety analysis of underground cavities. By using a self-developed test system, both permeability and porosity of granite f...The seepage property of low-permeability rock is of significant importance for the design and safety analysis of underground cavities. By using a self-developed test system, both permeability and porosity of granite from an underground oil storage depot were measured. In order to study the influence of rock types on permeability, a tight sandstone was selected as a contrast. The experimental results suggested that the porosity of this granite is less than 5% and permeability is low to 10–20 m^2 within the range of effective stress. During the loading process, both exponential relationship and power law can be utilized to describe the relationship between effective stress and permeability. However, power law matches the experimental data better during the unloading condition. The stress dependent porosity of granite during loading process can be described via an exponential relationship while the match between the model and experimental data can be improved by a power law in unloading paths. The correlation of permeability and porosity can be described in a power law form. Besides, granite shows great different evolution rules in permeability and porosity from sandstone. It is inferred that this difference can be attributed to the preparing of samples and different movements of microstructures subjected to effective stress.展开更多
The microscopic characteristics of skeletal particles in rock and soil media have important effects on macroscopic mechanical properties. A mathematical procedure called spherical harmonic function analysis was here d...The microscopic characteristics of skeletal particles in rock and soil media have important effects on macroscopic mechanical properties. A mathematical procedure called spherical harmonic function analysis was here developed to characterize micromorphology of particles and determine the meso effects in a discrete manner. This method has strong mathematical properties with respect to orthogonality and rotating invariance. It was used here to characterize and reconstruct particle micromorphology in three-dimensional space. The applicability and accuracy of the method were assessed through comparison of basic geometric properties such as volume and surface area. The results show that the micromorphological characteristics of reproduced particles become more and more readily distinguishable as the reproduced order number of spherical harmonic function increases, and the error can be brought below 5% when the order number reaches 10. This level of precision is sharp enough to distinguish the characteristics of real particles. Reconstructed particles of the same size but different reconstructed orders were used to form cylindrical samples, and the stress-strain curves of these samples filled with different-order particles which have their mutual morphological features were compared using PFC3D. Results show that the higher the spherical harmonic order of reconstructed particles, the lower the initial compression modulus and the larger the strain at peak intensity. However, peak strength shows only a random relationship to spherical harmonic order. Microstructure reconstruction was here shown to be an efficient means of numerically simulating of multi-scale rock and soil media and studying the mechanical properties of soil samples.展开更多
Strength of discontinuities with complex structure is an important topic in rock engineering.A large number of studies have shown that fractal is applicable in the description of this discontinuity.Using fractal inter...Strength of discontinuities with complex structure is an important topic in rock engineering.A large number of studies have shown that fractal is applicable in the description of this discontinuity.Using fractal interpolation method for the generation of rock joints,numerical experiments of shear tests of the jointed rock mass model were carried out using FLAC^(3D).The test results show that the real rock joints can be simulated by fractal curves obtained by fractal interpolation.The fractal dimension is an important factor for the characterization of jointed rock mass;test results show that the fractal dimension of rock joints can be related to the equivalent cohesion strength and shear strength of the rock mass.When the fractal dimension of the joint surface is less than critical dimension Dc 1.404,the cohesion strength and shear strength of the rock mass increase as the fractal dimension increases;for larger fractal dimensions,all mechanical parameters decrease as the fractal dimension increases.Joint surfaces with different degrees of roughness were obtained by the fractal interpolation method.Three types of failure modes were observed in the tests:climbing slip failure,climbing gnawing fracture,and non-climbing gnawing fracture.展开更多
Influence of surface topography on the tactile friction of medical compression textiles was studied in this paper. The friction behavior was investigated for three kinds of medical textiles with various structures and...Influence of surface topography on the tactile friction of medical compression textiles was studied in this paper. The friction behavior was investigated for three kinds of medical textiles with various structures and compositions by using a textile friction analyzer under dry condition. In order to simulate the contacts of textiles/human finger, a mechanical skin model with similar texture to the skin and applied normal load oflN were selected. Meanwhile, the 3D surface topography of textiles was measured using a digital microscope. The topographical data were analyzed concerning height distribution and material ratio, and the real contact area was estimated as a function of penetration depth. Results showed that the investigated textiles revealed a significant variation on the friction coefficients, which were ( 0.41 ± 0.01 ) ( polyamide, jersey 2 × 2 ), (0.56 ± 0. 01) (cotton, jersey 2×2) and (0. 47 ± 0. 01) (polyamide, jersey 1 × 1 ), respectively. The textile with higher friction coefficient was found to own a relative compact and homogenous surface and larger contact area, vice versa.展开更多
The common method classifying tactile qualities of fabrics is indirectly based on their difference of purely mechanical and physical properties. When human skin slides across fabric surfaces, the friction interaction ...The common method classifying tactile qualities of fabrics is indirectly based on their difference of purely mechanical and physical properties. When human skin slides across fabric surfaces, the friction interaction between fabrics and skin will occur and trigger the cutaneouS tactile receptors, which are responsible for perceived tactile sensation. By the extracted features from friction- induced vibration signals, this paper presents an anthropomorphic classification method classifying tactile qualities of fabrics. The friction-induced vibration signals are recorded by a three-axis accelerator sensor, and the entice testing procedure is conducted in an anthropomorphic way to obtain vibration signals. The fast Fourier transform (FFT) is applied to analyzing the recoded signals, and then the classification features are extracted from the FFT data by the neurophysiological properties of tactile receptors. The extracted features are used to classify fabric samples by the softness sensation and the roughness sensation, respectively, and the classification performance is checked by a comparison with those in a sensory evaluation procedure. The results showed that the anthropomorphic objective classification method was precise and efficient to clarify tactile qualities of woven fabrics.展开更多
A neurodynamical model for selective visual attention considering orientation preference is proposed.Since orientation preference is one of the most important properties of neurons in the primary visual cortex,it shou...A neurodynamical model for selective visual attention considering orientation preference is proposed.Since orientation preference is one of the most important properties of neurons in the primary visual cortex,it should be fully considered besides external stimuli intensity.By tuning the parameter of orientation preference,the regimes of synchronous dynamics associated with the development of the attention focus are studied.The attention focus is represented by those peripheral neurons that generate spikes synchronously with the central neuron while the activity of other peripheral neurons is suppressed.Such dynamics correspond to the partial synchronization mode.Simulation results show that the model can sequentially select objects with different orientation preferences and has a reliable shift of attention from one object to another,which are consistent with the experimental results that neurons with different orientation preferences are laid out in pinwheel patterns.展开更多
基金Projects(11172090,51009052,51109069) supported by the National Natural Science Foundation of ChinaProject(2011CB013504) supported by the National Basic Research Program of China
文摘Triaxial creep tests were carried out under seepage pressure by using rock servo-controlled triaxial rheology testing equipment.Based on experimental results,rock rheological properties influenced by seepage-stress coupling were studied,and variations of seepage rate with time in complete creep processes of rock were analyzed.It is shown that,when the applied stress is less than failure stress level,the creep deformation is not obvious,and its main form is steady-state creep.When applied stress level is greater than or less than but close to fracture stress,it is easier to see the increase of creep deformation and the more obvious accelerative creep characteristics.The circumferential creep deformation is obviously higher than the axial creep deformation.At the stage of steady-state creep,the average of seepage flow rate is about 4.7×10-9 m/s at confining pressure(σ3) of 2 MPa,and is about 3.9×10-9 m/s at σ3 of 6 MPa.It is seen that the seepage flow rate at σ3 of 2 MPa in this case is obviously larger than that at σ3 of 6 MPa.At the stage of creep acceleration,the seepage flow rate is markedly increased with the increase of time.The variation of rock permeability is directly connected to the growth and evolution of creep crack.It is suggested that the permeability coefficient in complete creep processes of rock is not a constant,but is a function of rock creep strain,confining pressure,damage variable and pore water pressure.The results can be considered to provide a reliable reference for the establishment of rock rheological model and parameter identification.
基金Projects(11172090,51479049,11272113,11572110,51209075)supported by the National Natural Science Foundation of ChinaProject(BK2012809)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(201406710042)supported by China Scholarship Council
文摘The seepage property of low-permeability rock is of significant importance for the design and safety analysis of underground cavities. By using a self-developed test system, both permeability and porosity of granite from an underground oil storage depot were measured. In order to study the influence of rock types on permeability, a tight sandstone was selected as a contrast. The experimental results suggested that the porosity of this granite is less than 5% and permeability is low to 10–20 m^2 within the range of effective stress. During the loading process, both exponential relationship and power law can be utilized to describe the relationship between effective stress and permeability. However, power law matches the experimental data better during the unloading condition. The stress dependent porosity of granite during loading process can be described via an exponential relationship while the match between the model and experimental data can be improved by a power law in unloading paths. The correlation of permeability and porosity can be described in a power law form. Besides, granite shows great different evolution rules in permeability and porosity from sandstone. It is inferred that this difference can be attributed to the preparing of samples and different movements of microstructures subjected to effective stress.
基金Project(2015CB057903)supported by the National Basic Research Program of ChinaProjects(51679071,51309089)supported by the National Natural Science Foundation of China+2 种基金Project(BK20130846)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(2013BAB06B00)supported by the National Key Technology R&D Program,ChinaProject(2015B06014)supported by the Fundamental Research Funds for the Central Universities,China
文摘The microscopic characteristics of skeletal particles in rock and soil media have important effects on macroscopic mechanical properties. A mathematical procedure called spherical harmonic function analysis was here developed to characterize micromorphology of particles and determine the meso effects in a discrete manner. This method has strong mathematical properties with respect to orthogonality and rotating invariance. It was used here to characterize and reconstruct particle micromorphology in three-dimensional space. The applicability and accuracy of the method were assessed through comparison of basic geometric properties such as volume and surface area. The results show that the micromorphological characteristics of reproduced particles become more and more readily distinguishable as the reproduced order number of spherical harmonic function increases, and the error can be brought below 5% when the order number reaches 10. This level of precision is sharp enough to distinguish the characteristics of real particles. Reconstructed particles of the same size but different reconstructed orders were used to form cylindrical samples, and the stress-strain curves of these samples filled with different-order particles which have their mutual morphological features were compared using PFC3D. Results show that the higher the spherical harmonic order of reconstructed particles, the lower the initial compression modulus and the larger the strain at peak intensity. However, peak strength shows only a random relationship to spherical harmonic order. Microstructure reconstruction was here shown to be an efficient means of numerically simulating of multi-scale rock and soil media and studying the mechanical properties of soil samples.
基金Projects(51479049,51209075)supported by the National Natural Science Foundation of China
文摘Strength of discontinuities with complex structure is an important topic in rock engineering.A large number of studies have shown that fractal is applicable in the description of this discontinuity.Using fractal interpolation method for the generation of rock joints,numerical experiments of shear tests of the jointed rock mass model were carried out using FLAC^(3D).The test results show that the real rock joints can be simulated by fractal curves obtained by fractal interpolation.The fractal dimension is an important factor for the characterization of jointed rock mass;test results show that the fractal dimension of rock joints can be related to the equivalent cohesion strength and shear strength of the rock mass.When the fractal dimension of the joint surface is less than critical dimension Dc 1.404,the cohesion strength and shear strength of the rock mass increase as the fractal dimension increases;for larger fractal dimensions,all mechanical parameters decrease as the fractal dimension increases.Joint surfaces with different degrees of roughness were obtained by the fractal interpolation method.Three types of failure modes were observed in the tests:climbing slip failure,climbing gnawing fracture,and non-climbing gnawing fracture.
基金National Natural Science Foundations of China,Natural Science Foundation of Shanghai,China,the Fundamental Research Funds for the Central Universities,China
文摘Influence of surface topography on the tactile friction of medical compression textiles was studied in this paper. The friction behavior was investigated for three kinds of medical textiles with various structures and compositions by using a textile friction analyzer under dry condition. In order to simulate the contacts of textiles/human finger, a mechanical skin model with similar texture to the skin and applied normal load oflN were selected. Meanwhile, the 3D surface topography of textiles was measured using a digital microscope. The topographical data were analyzed concerning height distribution and material ratio, and the real contact area was estimated as a function of penetration depth. Results showed that the investigated textiles revealed a significant variation on the friction coefficients, which were ( 0.41 ± 0.01 ) ( polyamide, jersey 2 × 2 ), (0.56 ± 0. 01) (cotton, jersey 2×2) and (0. 47 ± 0. 01) (polyamide, jersey 1 × 1 ), respectively. The textile with higher friction coefficient was found to own a relative compact and homogenous surface and larger contact area, vice versa.
基金National Natural Science Foundations of China,Natural Science Foundation of Shanghai,China,the Fundamental Research Funds for the Central Universities,China
文摘The common method classifying tactile qualities of fabrics is indirectly based on their difference of purely mechanical and physical properties. When human skin slides across fabric surfaces, the friction interaction between fabrics and skin will occur and trigger the cutaneouS tactile receptors, which are responsible for perceived tactile sensation. By the extracted features from friction- induced vibration signals, this paper presents an anthropomorphic classification method classifying tactile qualities of fabrics. The friction-induced vibration signals are recorded by a three-axis accelerator sensor, and the entice testing procedure is conducted in an anthropomorphic way to obtain vibration signals. The fast Fourier transform (FFT) is applied to analyzing the recoded signals, and then the classification features are extracted from the FFT data by the neurophysiological properties of tactile receptors. The extracted features are used to classify fabric samples by the softness sensation and the roughness sensation, respectively, and the classification performance is checked by a comparison with those in a sensory evaluation procedure. The results showed that the anthropomorphic objective classification method was precise and efficient to clarify tactile qualities of woven fabrics.
基金Supported by the Fundamental Research Funds for the Central Universitiesthe National Natural Science Foundation of China under Grant Nos.10872068 and 11002055.
文摘A neurodynamical model for selective visual attention considering orientation preference is proposed.Since orientation preference is one of the most important properties of neurons in the primary visual cortex,it should be fully considered besides external stimuli intensity.By tuning the parameter of orientation preference,the regimes of synchronous dynamics associated with the development of the attention focus are studied.The attention focus is represented by those peripheral neurons that generate spikes synchronously with the central neuron while the activity of other peripheral neurons is suppressed.Such dynamics correspond to the partial synchronization mode.Simulation results show that the model can sequentially select objects with different orientation preferences and has a reliable shift of attention from one object to another,which are consistent with the experimental results that neurons with different orientation preferences are laid out in pinwheel patterns.