In recent years, with the development of the enhanced oil recovery technique, researchers understood that the foam generation in the underground oil-bearing porous medium can successfully improve oil recovery. One of ...In recent years, with the development of the enhanced oil recovery technique, researchers understood that the foam generation in the underground oil-bearing porous medium can successfully improve oil recovery. One of the important mechanisms of foam generation is the snap-off of gas bubbles in porous media.展开更多
Floating oscillating bodies constitute a large class of wave energy converters, especially for offshore deployment. Usually the Power-Take-Off（PTO） system is a directly linear electric generator or a hydraulic motor...Floating oscillating bodies constitute a large class of wave energy converters, especially for offshore deployment. Usually the Power-Take-Off（PTO） system is a directly linear electric generator or a hydraulic motor that drives an electric generator. The PTO system is simplified as a linear spring and a linear damper. However the conversion is less powerful with wave periods off resonance. Thus, a nonlinear snap-through mechanism with two symmetrically oblique springs and a linear damper is applied in the PTO system. The nonlinear snap-through mechanism is characteristics of negative stiffness and double-well potential. An important nonlinear parameter γ is defined as the ratio of half of the horizontal distance between the two springs to the original length of both springs. Time domain method is applied to the dynamics of wave energy converter in regular waves. And the state space model is used to replace the convolution terms in the time domain equation. The results show that the energy harvested by the nonlinear PTO system is larger than that by linear system for low frequency input. While the power captured by nonlinear converters is slightly smaller than that by linear converters for high frequency input. The wave amplitude, damping coefficient of PTO systems and the nonlinear parameter γ affect power capture performance of nonlinear converters. The oscillation of nonlinear wave energy converters may be local or periodically inter well for certain values of the incident wave frequency and the nonlinear parameter γ, which is different from linear converters characteristics of sinusoidal response in regular waves.展开更多
Double-clamped bistable buckled beams demonstrate great versatility in various fields such as robotics,energy harvesting,and microelectromechanical system(MEMS).However,their design often requires time-consuming and e...Double-clamped bistable buckled beams demonstrate great versatility in various fields such as robotics,energy harvesting,and microelectromechanical system(MEMS).However,their design often requires time-consuming and expensive computations.In this work,we present a method to easily and rapidly design bistable buckled beams subjected to a transverse point force.Based on the Euler–Bernoulli beam theory,we establish a theoretical model of bistable buckled beams to characterize their snapthrough properties.This model is verified against the results from a finite element analysis(FEA)model,with maximum discrepancy less than 7%.By analyzing and simplifying our theoretical model,we derive explicit analytical expressions for critical behavioral values on the force-displacement curve of the beam.These behavioral values include critical force,critical displacement,and travel,which are generally sufficient for characterizing the snapthrough properties of a bistable buckled beam.Based on these analytical formulas,we investigate the influence of a bistable buckled beam's key design parameters,including its actuation position and precompression,on its critical behavioral values,with our results validated by FEA simulations.Our analytical method enables fast and computationally inexpensive design of bistable buckled beams and can guide the design of complicated systems that incorporate bistable mechanisms.展开更多
Water/oil flow characteristics in a water-wet capillary were simulated at the pore scale to increase our understanding on immiscible flow and enhanced oil recovery.Volume of fluid method was used to capture the interf...Water/oil flow characteristics in a water-wet capillary were simulated at the pore scale to increase our understanding on immiscible flow and enhanced oil recovery.Volume of fluid method was used to capture the interface between oil and water and a pore-throat connecting structure was established to investigate the effects of viscosity,interfacial tension(IFT)and capillary number(Ca).The results show that during a water displacement process,an initial continuous oil phase can be snapped off in the water-wet pore due to the capillary effect.By altering the viscosity of the displacing fluid and the IFT between the wetting and non-wetting phases,the snapped-off phenomenon can be eliminated or reduced during the displacement.A stable displacement can be obtained under high Ca number conditions.Different displacement effects can be obtained at the same Ca number due to its significant influence on the flow state,i.e.,snapped-off flow,transient flow and stable flow,and ultralow IFT alone would not ensure a very high recovery rate due to the fingering flow occurrence.A flow chart relating flow states and the corresponding oil recovery factor is established.展开更多
基金Project supported by the National Natural Science Foundation of China
文摘In recent years, with the development of the enhanced oil recovery technique, researchers understood that the foam generation in the underground oil-bearing porous medium can successfully improve oil recovery. One of the important mechanisms of foam generation is the snap-off of gas bubbles in porous media.
基金financially supported by the National Natural Science Foundation of China(Grant No.51239007)the Independent Research Project of State Key Laboratory of Ocean Engineering in Shanghai Jiao Tong University(Grant No.GKZD010023)
文摘Floating oscillating bodies constitute a large class of wave energy converters, especially for offshore deployment. Usually the Power-Take-Off（PTO） system is a directly linear electric generator or a hydraulic motor that drives an electric generator. The PTO system is simplified as a linear spring and a linear damper. However the conversion is less powerful with wave periods off resonance. Thus, a nonlinear snap-through mechanism with two symmetrically oblique springs and a linear damper is applied in the PTO system. The nonlinear snap-through mechanism is characteristics of negative stiffness and double-well potential. An important nonlinear parameter γ is defined as the ratio of half of the horizontal distance between the two springs to the original length of both springs. Time domain method is applied to the dynamics of wave energy converter in regular waves. And the state space model is used to replace the convolution terms in the time domain equation. The results show that the energy harvested by the nonlinear PTO system is larger than that by linear system for low frequency input. While the power captured by nonlinear converters is slightly smaller than that by linear converters for high frequency input. The wave amplitude, damping coefficient of PTO systems and the nonlinear parameter γ affect power capture performance of nonlinear converters. The oscillation of nonlinear wave energy converters may be local or periodically inter well for certain values of the incident wave frequency and the nonlinear parameter γ, which is different from linear converters characteristics of sinusoidal response in regular waves.
基金financial support from the National Science Foundation of the United State (Grants 1752575 and 1644579)
文摘Double-clamped bistable buckled beams demonstrate great versatility in various fields such as robotics,energy harvesting,and microelectromechanical system(MEMS).However,their design often requires time-consuming and expensive computations.In this work,we present a method to easily and rapidly design bistable buckled beams subjected to a transverse point force.Based on the Euler–Bernoulli beam theory,we establish a theoretical model of bistable buckled beams to characterize their snapthrough properties.This model is verified against the results from a finite element analysis(FEA)model,with maximum discrepancy less than 7%.By analyzing and simplifying our theoretical model,we derive explicit analytical expressions for critical behavioral values on the force-displacement curve of the beam.These behavioral values include critical force,critical displacement,and travel,which are generally sufficient for characterizing the snapthrough properties of a bistable buckled beam.Based on these analytical formulas,we investigate the influence of a bistable buckled beam's key design parameters,including its actuation position and precompression,on its critical behavioral values,with our results validated by FEA simulations.Our analytical method enables fast and computationally inexpensive design of bistable buckled beams and can guide the design of complicated systems that incorporate bistable mechanisms.
文摘Water/oil flow characteristics in a water-wet capillary were simulated at the pore scale to increase our understanding on immiscible flow and enhanced oil recovery.Volume of fluid method was used to capture the interface between oil and water and a pore-throat connecting structure was established to investigate the effects of viscosity,interfacial tension(IFT)and capillary number(Ca).The results show that during a water displacement process,an initial continuous oil phase can be snapped off in the water-wet pore due to the capillary effect.By altering the viscosity of the displacing fluid and the IFT between the wetting and non-wetting phases,the snapped-off phenomenon can be eliminated or reduced during the displacement.A stable displacement can be obtained under high Ca number conditions.Different displacement effects can be obtained at the same Ca number due to its significant influence on the flow state,i.e.,snapped-off flow,transient flow and stable flow,and ultralow IFT alone would not ensure a very high recovery rate due to the fingering flow occurrence.A flow chart relating flow states and the corresponding oil recovery factor is established.
