为了全面地描述裂缝介质的储层特征、流体性质和各向异性特征,提出了由宽方位叠前道集数据直接获取裂缝介质弹性参数和各向异性梯度参数的振幅随方位角变化(Amplitude Versus Azimuth,AVAZ)反演方法。首先推导了基于杨氏模量、泊松比和...为了全面地描述裂缝介质的储层特征、流体性质和各向异性特征,提出了由宽方位叠前道集数据直接获取裂缝介质弹性参数和各向异性梯度参数的振幅随方位角变化(Amplitude Versus Azimuth,AVAZ)反演方法。首先推导了基于杨氏模量、泊松比和各向异性梯度的各向异性AVO方程,通过与Ruger近似进行对比,分析了该方程的近似精度。然后利用实际测井资料和二维逆掩断层模型建立了不同方位角的合成叠前角度道集,对未加噪声和信噪比为3的宽方位叠前角度道集进行了AVAZ反演方法测试,结果表明,未加噪声和信噪比为3的合成宽方位叠前道集均能反演得到符合地震反演精度的杨氏模量(E),泊松比(σ)和各向异性梯度(Γ),噪声对杨氏模量的反演影响较小,不含噪声时泊松比和各向异性梯度的反演精度更高,与真实值吻合程度较高。展开更多
In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of...In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of non-Newtonian fluid flow in the low permeability porous medium are derived, and the threshold pressure gradient （TPG） is also obtained. It is notable that the TPG （J） and permeability （K） of the porous medium analytically exhibit the scaling behavior J ~ K-D＇r/（l＋Or）, where DT is the fractal dimension for tortuous capillaries. The fractal characteristics of tortuosity for capillaries should be considered in analysis of non-Darcy flow in a low permeability porous medium. The model predictions of TPG show good agreement with those obtained by the available expression and experimental data. The proposed model may be conducible to a better understanding of the mechanism for nonlinear flow in the low permeability porous medium.展开更多
A relatively high formation pressure gradient can exist in seepage flow in low-permeable porous media with a threshold pressure gradient, and a significant error may then be caused in the model computation by neglecti...A relatively high formation pressure gradient can exist in seepage flow in low-permeable porous media with a threshold pressure gradient, and a significant error may then be caused in the model computation by neglecting the quadratic pressure gradient term in the governing equations. Based on these concerns, in consideration of the quadratic pressure gradient term, a basic moving boundary model is constructed for a one-dimensional seepage flow problem with a threshold pressure gradient. Owing to a strong nonlinearity and the existing moving boundary in the mathematical model, a corresponding numerical solution method is presented. First, a spatial coordinate transformation method is adopted in order to transform the system of partial differential equa- tions with moving boundary conditions into a closed system with fixed boundary conditions; then the solution can be sta- bly numerically obtained by a fully implicit finite-difference method. The validity of the numerical method is verified by a published exact analytical solution. Furthermore, to compare with Darcy＇s flow problem, the exact analytical solution for the case of Darcy＇s flow considering the quadratic pressure gradient term is also derived by an inverse Laplace transform. A comparison of these model solutions leads to the conclu- sion that such moving boundary problems must incorporate the quadratic pressure gradient term in their governing equa- tions; the sensitive effects of the quadratic pressure gradient term tend to diminish, with the dimensionless threshold pres- sure gradient increasing for the one-dimensional problem.展开更多
It is difficult to obtain a clear image in underwater turbulence environment with classical imaging methods due to the absorption, scattering, and underwater turbulence on the propagation beam.However, ghost imaging(G...It is difficult to obtain a clear image in underwater turbulence environment with classical imaging methods due to the absorption, scattering, and underwater turbulence on the propagation beam.However, ghost imaging(GI), a nonlocally imaging technique, has shown the turbulence-free ability in atmospheric turbulence by exploiting the second-order correlation between the signal beam and the reference beam.In this paper, we experimentally investigate the imaging quality of GI affected by the underwater environment, where the underwater environment is simulated by a 1 m×0.4 m×0.4 m tank with distilled water.The water temperature is controlled by a heater inside the tank, and a temperature gradient is obtained by putting the heater at different positions of the tank.The water vibration is produced by a heavy force, and the turbid medium is obtained by dissolving very small specks of CaCO3 in the water.A set of Hadamard speckle pattern pairs are generated and modulated on the incident beam, and then the beam illuminates on an unknown object after passing through the simulated underwater environment.With the second-order correlations, the image is reconstructed under different temperature gradients, water vibration, and turbid medium ratios.The results show that GI has the turbulence-free ability under lower temperature gradient, water vibration, and turbid media.The structural similarity image measurement(SSIM)values of the reconstructed images only start to decrease when the temperature gradient is greater than 4.0℃.The same temperature gradient produced at the different positions has a little effect on the quality of the underwater GI.展开更多
The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces.In the past,the influence of roughness has been investigated thoroughly.However,even ...The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces.In the past,the influence of roughness has been investigated thoroughly.However,even in the presence of perfectly smooth surfaces,geometry can come into play in form of the macroscopic shape of the contacting region.Here we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft,adhesive counterpart.When it is carefully pulled off,we find that in contrast to circular shapes,detachment occurs not instantaneously but detachment fronts start at pointed comers and travel inwards,until the final configuration is reached which for macroscopically isotropic shapes is almost circular.For elongated indenters,the final shape resembles the original one with rounded corners.We describe the influence of the shape of the stamp both experimentally and numerically.Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov.It is based on a local,mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of adhesion.The validation of the suggested method is made both by comparison with known analytical solutions and with experiments.The method is applied for simulating the detachment of flat-ended indenters with square,triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to 'brushes'.The method is extended for describing power-law gradient media.展开更多
Air leakage may significantly affect the effectiveness of mine ventilation by in- creasing the cost of ventilation and arousing problems for ventilation management.Fur- thermore,air leakage may accelerate the process ...Air leakage may significantly affect the effectiveness of mine ventilation by in- creasing the cost of ventilation and arousing problems for ventilation management.Fur- thermore,air leakage may accelerate the process of coal spontaneous combustion and cause gas explosion,thus greatly threatens the safety of coal production.The estimation of air leakage,therefore,have great practical significance.For any ventilation system of coal mines,there is a defined pattern of pressure gradient which drived the mine air to flow in the network,drives possible air leakage to go shortcut as well.Air leakage may occur through ventilation structures such as ventilation doors and fractures of the surroun- dig coal and rock of airways.A concept and the relevent calculation method of the pres- sure gradient matrix was put forward to assist the analysis of potential air leakage routes. A simplified example was used to introduce the application principle of'pressure gradient matrix in identifying all the potential air leaking routes,which offers a deeper understand- ing over the ventilation system and the prevention of coal spontaneous combustion.展开更多
文摘为了全面地描述裂缝介质的储层特征、流体性质和各向异性特征,提出了由宽方位叠前道集数据直接获取裂缝介质弹性参数和各向异性梯度参数的振幅随方位角变化(Amplitude Versus Azimuth,AVAZ)反演方法。首先推导了基于杨氏模量、泊松比和各向异性梯度的各向异性AVO方程,通过与Ruger近似进行对比,分析了该方程的近似精度。然后利用实际测井资料和二维逆掩断层模型建立了不同方位角的合成叠前角度道集,对未加噪声和信噪比为3的宽方位叠前角度道集进行了AVAZ反演方法测试,结果表明,未加噪声和信噪比为3的合成宽方位叠前道集均能反演得到符合地震反演精度的杨氏模量(E),泊松比(σ)和各向异性梯度(Γ),噪声对杨氏模量的反演影响较小,不含噪声时泊松比和各向异性梯度的反演精度更高,与真实值吻合程度较高。
基金Project supported by the National Natural Science Foundation of China(Grant No.41102080)the Fundamental Research Funds for the Central Universities,China(Grant Nos.CUG130404 and CUG130103)the Fund from the Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education,China University of Geosciences(Wuhan),China(Grant No.TPR-2013-18)
文摘In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of non-Newtonian fluid flow in the low permeability porous medium are derived, and the threshold pressure gradient （TPG） is also obtained. It is notable that the TPG （J） and permeability （K） of the porous medium analytically exhibit the scaling behavior J ~ K-D＇r/（l＋Or）, where DT is the fractal dimension for tortuous capillaries. The fractal characteristics of tortuosity for capillaries should be considered in analysis of non-Darcy flow in a low permeability porous medium. The model predictions of TPG show good agreement with those obtained by the available expression and experimental data. The proposed model may be conducible to a better understanding of the mechanism for nonlinear flow in the low permeability porous medium.
基金funding by the project (Grant 51404232) sponsored by the National Natural Science Foundation of Chinathe National Science and Technology Major Project (Grant 2011ZX05038003)+1 种基金the China Postdoctoral Science Foundation project (Grant 2014M561074)the China Scholarship Council for its generous financial support of the research
文摘A relatively high formation pressure gradient can exist in seepage flow in low-permeable porous media with a threshold pressure gradient, and a significant error may then be caused in the model computation by neglecting the quadratic pressure gradient term in the governing equations. Based on these concerns, in consideration of the quadratic pressure gradient term, a basic moving boundary model is constructed for a one-dimensional seepage flow problem with a threshold pressure gradient. Owing to a strong nonlinearity and the existing moving boundary in the mathematical model, a corresponding numerical solution method is presented. First, a spatial coordinate transformation method is adopted in order to transform the system of partial differential equa- tions with moving boundary conditions into a closed system with fixed boundary conditions; then the solution can be sta- bly numerically obtained by a fully implicit finite-difference method. The validity of the numerical method is verified by a published exact analytical solution. Furthermore, to compare with Darcy＇s flow problem, the exact analytical solution for the case of Darcy＇s flow considering the quadratic pressure gradient term is also derived by an inverse Laplace transform. A comparison of these model solutions leads to the conclu- sion that such moving boundary problems must incorporate the quadratic pressure gradient term in their governing equa- tions; the sensitive effects of the quadratic pressure gradient term tend to diminish, with the dimensionless threshold pres- sure gradient increasing for the one-dimensional problem.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61871234 and 11847062)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20180755)
文摘It is difficult to obtain a clear image in underwater turbulence environment with classical imaging methods due to the absorption, scattering, and underwater turbulence on the propagation beam.However, ghost imaging(GI), a nonlocally imaging technique, has shown the turbulence-free ability in atmospheric turbulence by exploiting the second-order correlation between the signal beam and the reference beam.In this paper, we experimentally investigate the imaging quality of GI affected by the underwater environment, where the underwater environment is simulated by a 1 m×0.4 m×0.4 m tank with distilled water.The water temperature is controlled by a heater inside the tank, and a temperature gradient is obtained by putting the heater at different positions of the tank.The water vibration is produced by a heavy force, and the turbid medium is obtained by dissolving very small specks of CaCO3 in the water.A set of Hadamard speckle pattern pairs are generated and modulated on the incident beam, and then the beam illuminates on an unknown object after passing through the simulated underwater environment.With the second-order correlations, the image is reconstructed under different temperature gradients, water vibration, and turbid medium ratios.The results show that GI has the turbulence-free ability under lower temperature gradient, water vibration, and turbid media.The structural similarity image measurement(SSIM)values of the reconstructed images only start to decrease when the temperature gradient is greater than 4.0℃.The same temperature gradient produced at the different positions has a little effect on the quality of the underwater GI.
文摘The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces.In the past,the influence of roughness has been investigated thoroughly.However,even in the presence of perfectly smooth surfaces,geometry can come into play in form of the macroscopic shape of the contacting region.Here we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft,adhesive counterpart.When it is carefully pulled off,we find that in contrast to circular shapes,detachment occurs not instantaneously but detachment fronts start at pointed comers and travel inwards,until the final configuration is reached which for macroscopically isotropic shapes is almost circular.For elongated indenters,the final shape resembles the original one with rounded corners.We describe the influence of the shape of the stamp both experimentally and numerically.Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov.It is based on a local,mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of adhesion.The validation of the suggested method is made both by comparison with known analytical solutions and with experiments.The method is applied for simulating the detachment of flat-ended indenters with square,triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to 'brushes'.The method is extended for describing power-law gradient media.
基金the National Natural Science Foundation of China(50174045)the Natural Science Foundation of Shaanxi Province China(2006E205)
文摘Air leakage may significantly affect the effectiveness of mine ventilation by in- creasing the cost of ventilation and arousing problems for ventilation management.Fur- thermore,air leakage may accelerate the process of coal spontaneous combustion and cause gas explosion,thus greatly threatens the safety of coal production.The estimation of air leakage,therefore,have great practical significance.For any ventilation system of coal mines,there is a defined pattern of pressure gradient which drived the mine air to flow in the network,drives possible air leakage to go shortcut as well.Air leakage may occur through ventilation structures such as ventilation doors and fractures of the surroun- dig coal and rock of airways.A concept and the relevent calculation method of the pres- sure gradient matrix was put forward to assist the analysis of potential air leakage routes. A simplified example was used to introduce the application principle of'pressure gradient matrix in identifying all the potential air leaking routes,which offers a deeper understand- ing over the ventilation system and the prevention of coal spontaneous combustion.
