Wheeled mobile robots(WMRs) encounter unavoidable slippage especially on the low adhesion terrain such that the robots stability and accuracy are reduced greatly.To overcome this drawback,this article presents a neura...Wheeled mobile robots(WMRs) encounter unavoidable slippage especially on the low adhesion terrain such that the robots stability and accuracy are reduced greatly.To overcome this drawback,this article presents a neural network(NN) based terminal sliding mode control(TSMC) for WMRs where an augmented ground friction model is reported by which the uncertain friction can be estimated and compensated according to the required performance.In contrast to the existing friction models,the developed augmented ground friction model corresponds to actual fact because not only the effects associated with the mobile platform velocity but also the slippage related to the wheel slip rate are concerned simultaneously.Besides,the presented control approach can combine the merits of both TSMC and radial basis function(RBF) neural networks techniques,thereby providing numerous excellent performances for the closed-loop system,such as finite time convergence and faster friction estimation property.Simulation results validate the proposed friction model and robustness of controller;these research results will improve the autonomy and intelligence of WMRs,particularly when the mobile platform suffers from the sophisticated unstructured environment.展开更多
Using theoretical analysis, the single-phase gas seepage mathematical model influenced by slippage effects was established. The results show that the pressure of producing wells attenuates more violently than the well...Using theoretical analysis, the single-phase gas seepage mathematical model influenced by slippage effects was established. The results show that the pressure of producing wells attenuates more violently than the wells without slippage effects. The decay rate of reservoir pressure is more violent as the Klinkenherg factor increases. The gas prediction output gradually increases as the Klinenberg factor increases when considering gas slippage effects. Through specific examples, analyzed the law of stope pore pressure and gas output forecast changing in a hypotonic reservoir with slippage effects. The results have great theoretical significance in the study of the law of coal-bed methane migration in hypotonic reservoirs and for the exploitation of coal-bed methane.展开更多
When the gas flow in the compact porous medium at low speed,it has slippage effect which is caused by the gas molecular collision whit the solidskeleton.Using the gas transfusion slippage effect at researching the coa...When the gas flow in the compact porous medium at low speed,it has slippage effect which is caused by the gas molecular collision whit the solidskeleton.Using the gas transfusion slippage effect at researching the coal bed transfusion rule,established the transfusion mathematical model of the coal bed which had considered the slippage effect. Observing the influence of the different toencircle presses,the different hole press and the different actual stress to the coal bed by using the three-axles permeameter.Thus sum- marized the transfusion rule of the coal bed.The experiment indicates that the bigger of the surrounding pressure,the more obvious of the slippage effect.At the same condition of axial pressure and the surrounding pressure,with the increase of the hole pressure,the coal permeability became bigger and then smaller.The coal body effective tress and the permeability curve nearly also has the same change tendency.Thus we can draws the conclusion that the transfusion of the gas in the coal bed generally has the slippage effect.展开更多
Although the slippage effect has been extensively studied,most of the previous studies focused on the impact of the slippage effect on apparent permeability within a low pore pressure range,resulting in the inability ...Although the slippage effect has been extensively studied,most of the previous studies focused on the impact of the slippage effect on apparent permeability within a low pore pressure range,resulting in the inability of matching the evolution of permeability in the remaining pressure range.In this paper,a new apparent permeability model that reveals the evolution of permeability under the combined action of effective stress and slippage in the full pore pressure range was proposed.In this model,both intrinsic permeability and slippage coefficient are stress dependent.Three experimental tests with pore pressure lower than 2 MPa and a test with pore pressure at about 10 MPa using cores from the same origin under constant confining stress and constant effective stress are conducted.By comparing experimental data and another apparent permeability model,we proved the fidelity of our newly developed model.Furthermore,the contribution factor of the slippage effect Rslip is used to determine the low pore pressure limit with significant slippage effect.Our results show that both narrow initial pore size and high effective stress increase the critical pore pressure.Finally,the evolutions of the slippage coefficient and the intrinsic permeability under different boundary conditions were analyzed.展开更多
At present,the effects of pore throat structure on micro-scale seepage characteristics of tight gas reservoirs are less researched,and traditional numerical simulation methods are faced with a great number of challeng...At present,the effects of pore throat structure on micro-scale seepage characteristics of tight gas reservoirs are less researched,and traditional numerical simulation methods are faced with a great number of challenges in the study of micro-scale flow.In this paper,the flow pattern of tight gas was studied based on the actual temperature and pressure of tight gas reservoir and the characteristic size of reservoir pore throat,and the rationality of tight gas flow was simulated by means of lattice Boltzmann method.Then,considering the influences of micro-scale effect,slippage effect and other factors,a tight gas flow model was established on the basis of LBGK-D2Q9 model,and its calculation results were compared with the analytical solutions and the numerical solutions listed in the literature.Finally,the influential laws of pore throat structure on the micro-scale seepage characteristics of tight gas were discussed.And the following research results were obtained.First,when the pressure is in the range of 3-70 MPa and the temperature is in the range of 293.15-373.15 K,the Knudsen number(Kn)is less than 0.1 and the gas flow is in the pattern of slippage flow and weak continuous flow.And in this case,it is reasonable to adopt the LBGK-D2Q9 model to simulate tight gas flow.Second,the effect of the characteristic size of the flow channel on the Kn is much greater than that of the pressure change.When the pore-throat ratio is constant,the Kn increases slowly along the throat.And its increasing trend gets more obvious with the increase of pore-throat ratio.Third,the presence of the throat makes the non-linear distribution characteristics of the pressure in the pore throat significant,and the pressure drop mainly lies in the throat.And the higher the pore-throat ratio is,the larger the pressure drop range in the throat is.Fourth,the non-linear distribution of pressure decreases the gas flow speed significantly,thus reducing the mass flow rate in the flow channel.In conclusion,the simulation result of the model established in this paper is highly coincident with the analytical solutions and the numerical solutions calculated by DSMC and IP methods in the literature,which verifies that this proposed model is reliable.The research results reveal the importance of“connecting fracture and expanding throat”in the practical development engineering of tight gas reservoirs.展开更多
A mathematical model of landfill gas migration was established under presumption of the effect of gas slippage. The slippage solutions to the nonlinear mathematical model were accomplished by the perturbation and inte...A mathematical model of landfill gas migration was established under presumption of the effect of gas slippage. The slippage solutions to the nonlinear mathematical model were accomplished by the perturbation and integral transformation method. The distribution law of gas pressure in landfill site was presented under the conditions of considering and neglecting slippage effect. Sensitivity of the model input parameters was analyzed. The model solutions were compared to observation values. Results show that gas slippage effect has a large impact on gas pressure distribution. Landfill gas pressure and pressure gradient considering slippage effect is lower than that neglecting slippage effect, with reasonable agreement between model solution and measured data. It makes clear that the difference between considering and neglecting slippage effect is obvious and the effects of coupling cannot be ignored. The theoretical basis is provided for engineering design of security control and decision making of gas exploitation in landfill site. The solutions give scientific foundation to analyzing well test data in the process of low-permeability oil gas reservoir exploitation.展开更多
Both bulk stress(σ_(i i))and stress path(SP)significantly affect the transportation characteristics of deep gas during reservoir pressure depletion.Therefore,the experimental study of horizontal stress unloading on s...Both bulk stress(σ_(i i))and stress path(SP)significantly affect the transportation characteristics of deep gas during reservoir pressure depletion.Therefore,the experimental study of horizontal stress unloading on seepage behavior of gas-bearing coal under constantσi i-constraints is performed.The results show that coal permeability is affected by horizontal stress anisotropy(σ_(H)≠σh),and the contribution of minor horizontal stress to permeability is related to the differential response of horizontal strain.The slippage phenomenon is prominent in deep high-stress regime,especially in low reservoir pressure.σ_(i i)and SP jointly determine the manifestation of slippage effect and the strength of stress sensitivity(γ)of permeability.Deep reservoir implies an incremental percentage of slip-based permeability,and SP weakens the slippage effect by changing the elastic–plastic state of coal.However,γis negatively correlated with slippage effect.From the Walsh model,narrow(low aspect-ratio)fractures within the coal under unloading SP became the main channel for gas seepage,and bring the effective stress coefficient of permeability(χ)less than 1 for both low-stress elastic and high-stress damaged coal.With the raise of the effective stress,the effect of pore-lined clay particles on permeability was enhanced,inducing an increase inχfor highstress elastic coal.展开更多
A new method for selecting dimensionless relaxation time in the lattice Boltzmann model was proposed based on similarity criterion and gas true physical parameters.At the same time,the dimensionless relaxation time wa...A new method for selecting dimensionless relaxation time in the lattice Boltzmann model was proposed based on similarity criterion and gas true physical parameters.At the same time,the dimensionless relaxation time was modified by considering the influence of the boundary Knudsen layer.On this basis,the second-order slip boundary condition of the wall was considered,and the key parameters in the corresponding combined bounce-back/specular-reflection boundary condition were deduced to build a new model of unconventional gas microscale flow simulation based on the lattice Boltzmann method suitable for high temperatures and high pressures.The simulation results of methane gas flow driven by body force in infinite micro-channels and flow driven by inlet-outlet pressure differential in long straight channels were compared with the numerical and analytical solutions in the literature to verify the accuracy of the model,and the dimensionless relaxation time modification was formally optimized.The results show that the new model can effectively characterize the slippage effect,compression effect,gas density and the effect of boundary Knudsen layer in the micro-scale flow of unconventional natural gas.The new model can achieve a more comprehensive characterization of the real gas flow conditions and can be used as a basic model for the simulation of unconventional gas flow on the micro-nano scale.展开更多
基金supported by the National Natural Science Foundation of China(61573078,61573147)the International S&T Cooperation Program of China(2014DFB70120)the State Key Laboratory of Robotics and System(SKLRS2015ZD06)
文摘Wheeled mobile robots(WMRs) encounter unavoidable slippage especially on the low adhesion terrain such that the robots stability and accuracy are reduced greatly.To overcome this drawback,this article presents a neural network(NN) based terminal sliding mode control(TSMC) for WMRs where an augmented ground friction model is reported by which the uncertain friction can be estimated and compensated according to the required performance.In contrast to the existing friction models,the developed augmented ground friction model corresponds to actual fact because not only the effects associated with the mobile platform velocity but also the slippage related to the wheel slip rate are concerned simultaneously.Besides,the presented control approach can combine the merits of both TSMC and radial basis function(RBF) neural networks techniques,thereby providing numerous excellent performances for the closed-loop system,such as finite time convergence and faster friction estimation property.Simulation results validate the proposed friction model and robustness of controller;these research results will improve the autonomy and intelligence of WMRs,particularly when the mobile platform suffers from the sophisticated unstructured environment.
基金Supported by the Youth Program of the National Natural Science Foundation of China （51004061）
文摘Using theoretical analysis, the single-phase gas seepage mathematical model influenced by slippage effects was established. The results show that the pressure of producing wells attenuates more violently than the wells without slippage effects. The decay rate of reservoir pressure is more violent as the Klinkenherg factor increases. The gas prediction output gradually increases as the Klinenberg factor increases when considering gas slippage effects. Through specific examples, analyzed the law of stope pore pressure and gas output forecast changing in a hypotonic reservoir with slippage effects. The results have great theoretical significance in the study of the law of coal-bed methane migration in hypotonic reservoirs and for the exploitation of coal-bed methane.
基金the National Natural Sciences Fund Subsidization Project of China(50774041)National Important Item of the Natural Sciences Fund Subsidization Project of China(50490275)
文摘When the gas flow in the compact porous medium at low speed,it has slippage effect which is caused by the gas molecular collision whit the solidskeleton.Using the gas transfusion slippage effect at researching the coal bed transfusion rule,established the transfusion mathematical model of the coal bed which had considered the slippage effect. Observing the influence of the different toencircle presses,the different hole press and the different actual stress to the coal bed by using the three-axles permeameter.Thus sum- marized the transfusion rule of the coal bed.The experiment indicates that the bigger of the surrounding pressure,the more obvious of the slippage effect.At the same condition of axial pressure and the surrounding pressure,with the increase of the hole pressure,the coal permeability became bigger and then smaller.The coal body effective tress and the permeability curve nearly also has the same change tendency.Thus we can draws the conclusion that the transfusion of the gas in the coal bed generally has the slippage effect.
基金supported by the National Natural Science Foundation of China(No.52079077)the Natural Science Foundation of Shandong Province(No.ZR2021QE069)China Postdoctoral Science Foundation(No.2019M662402).
文摘Although the slippage effect has been extensively studied,most of the previous studies focused on the impact of the slippage effect on apparent permeability within a low pore pressure range,resulting in the inability of matching the evolution of permeability in the remaining pressure range.In this paper,a new apparent permeability model that reveals the evolution of permeability under the combined action of effective stress and slippage in the full pore pressure range was proposed.In this model,both intrinsic permeability and slippage coefficient are stress dependent.Three experimental tests with pore pressure lower than 2 MPa and a test with pore pressure at about 10 MPa using cores from the same origin under constant confining stress and constant effective stress are conducted.By comparing experimental data and another apparent permeability model,we proved the fidelity of our newly developed model.Furthermore,the contribution factor of the slippage effect Rslip is used to determine the low pore pressure limit with significant slippage effect.Our results show that both narrow initial pore size and high effective stress increase the critical pore pressure.Finally,the evolutions of the slippage coefficient and the intrinsic permeability under different boundary conditions were analyzed.
基金Project supported by the Key Program of National Natural Science Foundation of China“Fundamental study on tight gas reservoir formation drying and tight gas seepage capacity improvement”(No.:51534006).
文摘At present,the effects of pore throat structure on micro-scale seepage characteristics of tight gas reservoirs are less researched,and traditional numerical simulation methods are faced with a great number of challenges in the study of micro-scale flow.In this paper,the flow pattern of tight gas was studied based on the actual temperature and pressure of tight gas reservoir and the characteristic size of reservoir pore throat,and the rationality of tight gas flow was simulated by means of lattice Boltzmann method.Then,considering the influences of micro-scale effect,slippage effect and other factors,a tight gas flow model was established on the basis of LBGK-D2Q9 model,and its calculation results were compared with the analytical solutions and the numerical solutions listed in the literature.Finally,the influential laws of pore throat structure on the micro-scale seepage characteristics of tight gas were discussed.And the following research results were obtained.First,when the pressure is in the range of 3-70 MPa and the temperature is in the range of 293.15-373.15 K,the Knudsen number(Kn)is less than 0.1 and the gas flow is in the pattern of slippage flow and weak continuous flow.And in this case,it is reasonable to adopt the LBGK-D2Q9 model to simulate tight gas flow.Second,the effect of the characteristic size of the flow channel on the Kn is much greater than that of the pressure change.When the pore-throat ratio is constant,the Kn increases slowly along the throat.And its increasing trend gets more obvious with the increase of pore-throat ratio.Third,the presence of the throat makes the non-linear distribution characteristics of the pressure in the pore throat significant,and the pressure drop mainly lies in the throat.And the higher the pore-throat ratio is,the larger the pressure drop range in the throat is.Fourth,the non-linear distribution of pressure decreases the gas flow speed significantly,thus reducing the mass flow rate in the flow channel.In conclusion,the simulation result of the model established in this paper is highly coincident with the analytical solutions and the numerical solutions calculated by DSMC and IP methods in the literature,which verifies that this proposed model is reliable.The research results reveal the importance of“connecting fracture and expanding throat”in the practical development engineering of tight gas reservoirs.
基金Project supported by the National Natural Science Foundation of China (No. 50309015) the Major State Basic Research Development Program of China (973 Program) (No. 2002CB412708) the Sunshine Young Project in Wuhan City of China (No. 20055003059-33) the Open Fund of State Professonal Lab of Geological Hazard Prevention and Engineering Geological Environment Protection (No. GZ2004-011)
文摘A mathematical model of landfill gas migration was established under presumption of the effect of gas slippage. The slippage solutions to the nonlinear mathematical model were accomplished by the perturbation and integral transformation method. The distribution law of gas pressure in landfill site was presented under the conditions of considering and neglecting slippage effect. Sensitivity of the model input parameters was analyzed. The model solutions were compared to observation values. Results show that gas slippage effect has a large impact on gas pressure distribution. Landfill gas pressure and pressure gradient considering slippage effect is lower than that neglecting slippage effect, with reasonable agreement between model solution and measured data. It makes clear that the difference between considering and neglecting slippage effect is obvious and the effects of coupling cannot be ignored. The theoretical basis is provided for engineering design of security control and decision making of gas exploitation in landfill site. The solutions give scientific foundation to analyzing well test data in the process of low-permeability oil gas reservoir exploitation.
基金financially supported by the National Natural Science Foundation of China(Nos.52304265,52174216,and 52274145)the Natural Science Foundation of Jiangsu Province(No.BK20221121)the State Key Laboratory of Mining Disaster Prevention and Control(Shandong University of Science and Technology)and Ministry of Education(No.JMDPC202301)。
文摘Both bulk stress(σ_(i i))and stress path(SP)significantly affect the transportation characteristics of deep gas during reservoir pressure depletion.Therefore,the experimental study of horizontal stress unloading on seepage behavior of gas-bearing coal under constantσi i-constraints is performed.The results show that coal permeability is affected by horizontal stress anisotropy(σ_(H)≠σh),and the contribution of minor horizontal stress to permeability is related to the differential response of horizontal strain.The slippage phenomenon is prominent in deep high-stress regime,especially in low reservoir pressure.σ_(i i)and SP jointly determine the manifestation of slippage effect and the strength of stress sensitivity(γ)of permeability.Deep reservoir implies an incremental percentage of slip-based permeability,and SP weakens the slippage effect by changing the elastic–plastic state of coal.However,γis negatively correlated with slippage effect.From the Walsh model,narrow(low aspect-ratio)fractures within the coal under unloading SP became the main channel for gas seepage,and bring the effective stress coefficient of permeability(χ)less than 1 for both low-stress elastic and high-stress damaged coal.With the raise of the effective stress,the effect of pore-lined clay particles on permeability was enhanced,inducing an increase inχfor highstress elastic coal.
基金Supported by National Natural Science Foundation of China(Key Program)(51534006)National Natural Science Foundation of China(51874251)。
文摘A new method for selecting dimensionless relaxation time in the lattice Boltzmann model was proposed based on similarity criterion and gas true physical parameters.At the same time,the dimensionless relaxation time was modified by considering the influence of the boundary Knudsen layer.On this basis,the second-order slip boundary condition of the wall was considered,and the key parameters in the corresponding combined bounce-back/specular-reflection boundary condition were deduced to build a new model of unconventional gas microscale flow simulation based on the lattice Boltzmann method suitable for high temperatures and high pressures.The simulation results of methane gas flow driven by body force in infinite micro-channels and flow driven by inlet-outlet pressure differential in long straight channels were compared with the numerical and analytical solutions in the literature to verify the accuracy of the model,and the dimensionless relaxation time modification was formally optimized.The results show that the new model can effectively characterize the slippage effect,compression effect,gas density and the effect of boundary Knudsen layer in the micro-scale flow of unconventional natural gas.The new model can achieve a more comprehensive characterization of the real gas flow conditions and can be used as a basic model for the simulation of unconventional gas flow on the micro-nano scale.
