The security challenges from room and pillar gobs include land subsidence, spontaneous combustion of coal pillars and mine flood caused by gob water. To explore the instability mechanism of room and pillar gob, we est...The security challenges from room and pillar gobs include land subsidence, spontaneous combustion of coal pillars and mine flood caused by gob water. To explore the instability mechanism of room and pillar gob, we established a mechanical model of elastic plate on elastic foundation in which pillars and hard roofs were considered as continuous Winkler foundations and elastic plates, respectively. The synergetic instability of pillar and roof system was analyzed based on plate bending theory and catastrophe theory. In addition, mechanical conditions and math criterion of roof failure and overall instability of coal pillar and roof system were given. Through analyzing both advantages and disadvantages of some technologies such as induced caving, filling, gob sealing and isolation, we presented a new filling method named box-filling, in view of box foundation theory, to control the disasters of ground collapse, water inrush and mine fire. In a gob's treatment project in Ordos, safety assessment and filling design of a room and pillar gob have been done by the mechanical model. The results show that the gob will collapse when the pillars' average yield band is wider than 0.93 m, and box-filling can control land collapse, mine flood and mine fire economically and efficiently. So it is worth to study further and popularize.展开更多
Aneurysms can be classified into two main types based on their shape: saccular (spherical) and fusiform (cylindrical). In order to clarify the formation of aneurysms, we analyzed and examined the relationship between ...Aneurysms can be classified into two main types based on their shape: saccular (spherical) and fusiform (cylindrical). In order to clarify the formation of aneurysms, we analyzed and examined the relationship between external force (internal pressure) and deformation (diameter change) of a spherical model using the Neo-Hookean model, which can be used for hyperelastic materials and is similar to Hooke’s law to predict the nonlinear stress-strain behavior of materials with large deformation. For a cylindrical model, we conducted an experiment using a rubber balloon. In the spherical model, the magnitude of the internal pressure Δp value is proportional to G (modulus of rigidity) and t (thickness), and inversely proportional to R (radius of the sphere). In addition, the maximum pressure Δp (max) is reached when λ (=expanded diameter/original diameter) is approximately 1.2, and the change in diameter becomes unstable (nonlinear change) thereafter. In the cylindrical model, localized expansion occurred at λ = 1.32 (λ = 1.98 when compared to the diameter at internal pressure Δp = 0) compared to the nearby uniform diameter, followed by a sudden rapid expansion (unstable expansion jump), forming a distinct bulge, and the radial and longitudinal deformations increased with increasing Δp, leading to the rupture of the balloon. Both models have a starting point where nonlinear deformation changes (rapid expansion) occur, so quantitative observation of the artery’s shape and size is important to prevent aneurysm formation.展开更多
It is well known that plane creeping Couette flow of UCM and Oldroy-B fluids are linearly stable. However, for Burges fluid, which includes UCM and Oldroyd-B fluids as special cases, unstable modes are detected in the...It is well known that plane creeping Couette flow of UCM and Oldroy-B fluids are linearly stable. However, for Burges fluid, which includes UCM and Oldroyd-B fluids as special cases, unstable modes are detected in the present work. The wave speed, critical parameters and perturbation mode are studied for neutral waves. Energy analysis shows that the sustaining of perturbation energy in Poiseuille flow and Couette flow is completely different. At low Reynolds number limit, analytical solutions are obtained for simpli- fied perturbation equations. The essential difference between Burgers fluid and Oldroyd-B fluid is revealed to be the fact that neutral mode exists only in the former.展开更多
Dynamical behaviours of the motion of particles in a periodic potential under a constant driving velocity by a spring at one end are explored. In the stationary case, the stable equilibrium position of the particle ex...Dynamical behaviours of the motion of particles in a periodic potential under a constant driving velocity by a spring at one end are explored. In the stationary case, the stable equilibrium position of the particle experiences an elasticity instability transition. When the driving velocity is nonzero, depending on the elasticity coefficient and the pulling velocity, the system exhibits complicated and interesting dynamics, such as periodic and chaotic motions. The results obtained here may shed light on studies of dynamical processes in sliding friction.展开更多
We study instability of a Newtonian Couette flow past a gel-like film in the limit of vanishing Reynolds number. Three models are explored including one hyperelastic（neo-Hookean） solid, and two viscoelastic（Kelvin...We study instability of a Newtonian Couette flow past a gel-like film in the limit of vanishing Reynolds number. Three models are explored including one hyperelastic（neo-Hookean） solid, and two viscoelastic（Kelvin–Voigt and Zener） solids. Instead of using the conventional Lagrangian description in the solid phase for solving the displacement field, we construct equivalent ‘‘differential＇＇ models in an Eulerian reference frame, and solve for the velocity, pressure, and stress in both fluid and solid phases simultaneously. We find the interfacial instability is driven by the first-normal stress difference in the basestate solution in both hyperelastic and viscoelastic models. For the neo-Hookean solid, when subjected to a shear flow, the interface exhibits a short-wave（finite-wavelength） instability when the film is thin（thick）. In the Kelvin–Voigt and Zener solids where viscous effects are incorporated, instability growth is enhanced at small wavenumber but suppressed at large wavenumber, leading to a dominant finitewavelength instability. In addition, adding surface tension effectively stabilizes the interface to sustain fluid shear.展开更多
基金provided by the National Natural Science Foundation of China (No. 41071273)
文摘The security challenges from room and pillar gobs include land subsidence, spontaneous combustion of coal pillars and mine flood caused by gob water. To explore the instability mechanism of room and pillar gob, we established a mechanical model of elastic plate on elastic foundation in which pillars and hard roofs were considered as continuous Winkler foundations and elastic plates, respectively. The synergetic instability of pillar and roof system was analyzed based on plate bending theory and catastrophe theory. In addition, mechanical conditions and math criterion of roof failure and overall instability of coal pillar and roof system were given. Through analyzing both advantages and disadvantages of some technologies such as induced caving, filling, gob sealing and isolation, we presented a new filling method named box-filling, in view of box foundation theory, to control the disasters of ground collapse, water inrush and mine fire. In a gob's treatment project in Ordos, safety assessment and filling design of a room and pillar gob have been done by the mechanical model. The results show that the gob will collapse when the pillars' average yield band is wider than 0.93 m, and box-filling can control land collapse, mine flood and mine fire economically and efficiently. So it is worth to study further and popularize.
文摘Aneurysms can be classified into two main types based on their shape: saccular (spherical) and fusiform (cylindrical). In order to clarify the formation of aneurysms, we analyzed and examined the relationship between external force (internal pressure) and deformation (diameter change) of a spherical model using the Neo-Hookean model, which can be used for hyperelastic materials and is similar to Hooke’s law to predict the nonlinear stress-strain behavior of materials with large deformation. For a cylindrical model, we conducted an experiment using a rubber balloon. In the spherical model, the magnitude of the internal pressure Δp value is proportional to G (modulus of rigidity) and t (thickness), and inversely proportional to R (radius of the sphere). In addition, the maximum pressure Δp (max) is reached when λ (=expanded diameter/original diameter) is approximately 1.2, and the change in diameter becomes unstable (nonlinear change) thereafter. In the cylindrical model, localized expansion occurred at λ = 1.32 (λ = 1.98 when compared to the diameter at internal pressure Δp = 0) compared to the nearby uniform diameter, followed by a sudden rapid expansion (unstable expansion jump), forming a distinct bulge, and the radial and longitudinal deformations increased with increasing Δp, leading to the rupture of the balloon. Both models have a starting point where nonlinear deformation changes (rapid expansion) occur, so quantitative observation of the artery’s shape and size is important to prevent aneurysm formation.
基金supported by the National Natural Science Foundation of China (11172152)
文摘It is well known that plane creeping Couette flow of UCM and Oldroy-B fluids are linearly stable. However, for Burges fluid, which includes UCM and Oldroyd-B fluids as special cases, unstable modes are detected in the present work. The wave speed, critical parameters and perturbation mode are studied for neutral waves. Energy analysis shows that the sustaining of perturbation energy in Poiseuille flow and Couette flow is completely different. At low Reynolds number limit, analytical solutions are obtained for simpli- fied perturbation equations. The essential difference between Burgers fluid and Oldroyd-B fluid is revealed to be the fact that neutral mode exists only in the former.
基金Project supported in part by the National Natural Science Foundation of China （Grant Nos 70431002 and 10575010）, the Foundation for the Author of National Excellent Doctoral Dissertation of China （Grant No 200120）, and the Teaching and Research Award Program for 0utstanding Young Teachers in Higher Education Institutions, Ministry of Education of China （Grant No 209）.
文摘Dynamical behaviours of the motion of particles in a periodic potential under a constant driving velocity by a spring at one end are explored. In the stationary case, the stable equilibrium position of the particle experiences an elasticity instability transition. When the driving velocity is nonzero, depending on the elasticity coefficient and the pulling velocity, the system exhibits complicated and interesting dynamics, such as periodic and chaotic motions. The results obtained here may shed light on studies of dynamical processes in sliding friction.
基金the National Science Foundation(NSF)(DMS-1619960 and CBET1702987)NSF(CMMI-1538137)
文摘We study instability of a Newtonian Couette flow past a gel-like film in the limit of vanishing Reynolds number. Three models are explored including one hyperelastic（neo-Hookean） solid, and two viscoelastic（Kelvin–Voigt and Zener） solids. Instead of using the conventional Lagrangian description in the solid phase for solving the displacement field, we construct equivalent ‘‘differential＇＇ models in an Eulerian reference frame, and solve for the velocity, pressure, and stress in both fluid and solid phases simultaneously. We find the interfacial instability is driven by the first-normal stress difference in the basestate solution in both hyperelastic and viscoelastic models. For the neo-Hookean solid, when subjected to a shear flow, the interface exhibits a short-wave（finite-wavelength） instability when the film is thin（thick）. In the Kelvin–Voigt and Zener solids where viscous effects are incorporated, instability growth is enhanced at small wavenumber but suppressed at large wavenumber, leading to a dominant finitewavelength instability. In addition, adding surface tension effectively stabilizes the interface to sustain fluid shear.
