Hybrid wavelength-division-multiplexing(WDM)/time-division-multiplexing(TDM) ethernet passive optical networks(EPONs) can achieve low per-subscriber cost and scalability to increase the number of subscribers. This pap...Hybrid wavelength-division-multiplexing(WDM)/time-division-multiplexing(TDM) ethernet passive optical networks(EPONs) can achieve low per-subscriber cost and scalability to increase the number of subscribers. This paper discusses dynamic wavelength and bandwidth allocation(DWBA) algorithm in hybrid WDM/TDM EPONs.Based on the correlation structure of the variable bit rate(VBR) video traffic,we propose a quality-ofservice (QoS) supported DWBA using adaptive linear traffic prediction.Wavelength and timeslot are allocated dynamically by optical line terminal(OLT) to all optical network units(ONUs) based on the bandwidth requests and the guaranteed service level agreements(SLA) of all ONUs.Mean square error of the predicted average arriving rate of compound video traffic during waiting period is minimized through Wiener-Hopf equation.Simulation results show that the DWBA-adaptive-linear-prediction(DWBA-ALP) algorithm can significantly improve the QoS performances in terms of low delay and high bandwidth utilization.展开更多
Nonlocal decoherence of two qubits due to pure phase damping has been investigated.We have proposeda scheme to keep the entanglement of two qubits from nonlocal decoherence.By applying a series of±π pulses,nonlo...Nonlocal decoherence of two qubits due to pure phase damping has been investigated.We have proposeda scheme to keep the entanglement of two qubits from nonlocal decoherence.By applying a series of±π pulses,nonlocaldecoherence can be thoroughly suppressed.展开更多
This paper focuses on the use of rotary-percussive drilling for hard rocks.In order to improve efficiency and reduce costs,it is essential to understand how operational parameters,bit wear,and drilling performance are...This paper focuses on the use of rotary-percussive drilling for hard rocks.In order to improve efficiency and reduce costs,it is essential to understand how operational parameters,bit wear,and drilling performance are related.A model is presented therein that combines multibody dynamics and discrete element method(DEM)to investigate the influences of operational parameters and bit wear on the rate of penetration and wear characteristics.The model accurately captures the motion of the bit and recreates rock using the cutting sieving result.Field experimental results validate the rod dynamic behavior,rock recreating model,and coupling model in the simulation.The findings indicate that hammer pressure significantly influences the rate of penetration and wear depth of the bit,and there is an optimal range for economical hammer pressure.The wear coefficient has a major effect on the rate of penetration,when wear coefficient is between 1/3 and 2/3.Increasing the wear coefficient can reduce drill bit button pressure and wear depth at the same drill distance.Gauge button loss increases the rate of penetration due to higher pressure on the remaining buttons,which also accelerates destruction of the bit.Furthermore,a more evenly distributed button on the bit enhances the rate of penetration(ROP)when the same number of buttons is lost.展开更多
To optimize the bit selection for large-diameter wellbore in the upper section of an ultra-deep well S-1,a full-well dynamic model integrating drill string vibration and bit rock-breaking was established and then veri...To optimize the bit selection for large-diameter wellbore in the upper section of an ultra-deep well S-1,a full-well dynamic model integrating drill string vibration and bit rock-breaking was established and then verified using measured vibration data of drilling tools and actual rate of penetration(ROP)from Well HT-1 in northern Sichuan Basin.This model was employed to calculate and analyze drill string dynamic characteristics during large-diameter wellbore drilling in the Jurassic Penglaizhen Formation of Well S-1,followed by bit optimization.Research results show that during the drilling in Penglaizhen Formation of Well S-1,considering both the ROP of six candidate bits and the lateral/axial/torsional vibration characteristics of downhole tools,the six-blade dual-row cutter bit with the fastest ROP(average 7.12 m/h)was optimally selected.When using this bit,the downhole tool vibration levels remained at medium-low values.Field data showed over 90%consistency between actual ROP data and dynamic model calculation results after bit placement,demonstrating that the model can be used for bit program screening.展开更多
This paper deals with the theoretic simulation of a drill bit whirling under conditions of its contact interaction with the bore-hole bottom rock plane. The bit is considered to be an absolutely rigid ellipsoidal body...This paper deals with the theoretic simulation of a drill bit whirling under conditions of its contact interaction with the bore-hole bottom rock plane. The bit is considered to be an absolutely rigid ellipsoidal body with uneven surface. It is attached to the lower end of a rotating elastic drill string. In the perturbed state, the bit can roll without sliding on the bore-hole bottom, performing whirling vibrations (the model of dynamic equilibrium with pure rolling when maximum cohesive force does not exceed the ultimate Coulombic friction). To describe these motions, a nonholonomic dynamic model is proposed, constitutive partial differential equations are deduced. With their use, the whirling vibrations of oblong and oblate ellipsoidal bits are analyzed, the functions of cohesive (frictional) forces are calculated. It is shown that the system of elastic drill string and ellipsoidal bit can acquire stable or unstable whirl modes with approaching critical Eulerian values by the parameters of axial force, torque and angular velocity. The analogy of the found modes of motions with ones of the Celtic stones is established. It is shown that the ellipsoidal bits can stop their whirling vibrations and change directions of their circumferential motions in the same manner as the ellipsoidal Celtic stones do. As this takes place, the trajectories of the oblate ellipsoidal bits are characterized by more complicated paths and irregularities.展开更多
An incipient stage of a rotating drill string bit whirl motion proceeding on a well bottom surface is studied on the basis of kinematic （nonholonomic） models of mechanic interaction between the contacting uneven bod...An incipient stage of a rotating drill string bit whirl motion proceeding on a well bottom surface is studied on the basis of kinematic （nonholonomic） models of mechanic interaction between the contacting uneven bodies. The bit is considered to be an absolutely rigid spherical or ellipsoidal body, the well bottom surface can be plane or spherical. It is assumed that the system coaxiality is disturbed through small initial curvature of the drill string, imperfections of the bit and bore-well geometry or the system mass debalance. Linearized equations of the bit whirling are deducted, the frequencies of periodic motions are calculated, and their modes are constructed for different geometric parameters of the spherical and ellipsoidal bits. It is demonstrated that, depending on the system properties, the bit motion can acquire the regimes of forward and backward whMings or to transit to the state of stationary spinning relative to an immovable center of velocities. The most unfavorable and atypical whirling modes are characteristic for oblate eilipsoidal bits and curvilinear surfaces of the well bottom.展开更多
为解决柔性车间内AGV的面对动态障碍物时路径规划不准确的问题,基于位操作方法提出一种跳点搜索(Jump Point Search, JPS)的改进算法。算法采用二进制方式编码化栅格地图,实现障碍物的快速识别;通过位操作方法扩大剪枝规则的应用范围,提...为解决柔性车间内AGV的面对动态障碍物时路径规划不准确的问题,基于位操作方法提出一种跳点搜索(Jump Point Search, JPS)的改进算法。算法采用二进制方式编码化栅格地图,实现障碍物的快速识别;通过位操作方法扩大剪枝规则的应用范围,提升JPS算法中搜寻节点的效率;引入Octile距离模式对算法的启发式函数进行优化,达到降低计算复杂度,提升规划速度目的。分别将改进JPS算法与A*算法、JPS算法进行实验对比,结果表明:在复杂车间环境中,搜索时间、扩展节点数量、规划的路径同比其它两种算法都具有明显优势;在躲避动态障碍物测试中,改进型算法避障成功率为92%,躲避成功次数最高且规划的路径质量最优,同比两种算法综合性能最优。验证了算法的可行性。展开更多
文摘Hybrid wavelength-division-multiplexing(WDM)/time-division-multiplexing(TDM) ethernet passive optical networks(EPONs) can achieve low per-subscriber cost and scalability to increase the number of subscribers. This paper discusses dynamic wavelength and bandwidth allocation(DWBA) algorithm in hybrid WDM/TDM EPONs.Based on the correlation structure of the variable bit rate(VBR) video traffic,we propose a quality-ofservice (QoS) supported DWBA using adaptive linear traffic prediction.Wavelength and timeslot are allocated dynamically by optical line terminal(OLT) to all optical network units(ONUs) based on the bandwidth requests and the guaranteed service level agreements(SLA) of all ONUs.Mean square error of the predicted average arriving rate of compound video traffic during waiting period is minimized through Wiener-Hopf equation.Simulation results show that the DWBA-adaptive-linear-prediction(DWBA-ALP) algorithm can significantly improve the QoS performances in terms of low delay and high bandwidth utilization.
基金Supported by the Natural Science Foundation of Anhui Province of China under Grant No.090412060Natural Science Foundation of the Education Committee of Anhui Province of China under Grant No.KJ2008A029
文摘Nonlocal decoherence of two qubits due to pure phase damping has been investigated.We have proposeda scheme to keep the entanglement of two qubits from nonlocal decoherence.By applying a series of±π pulses,nonlocaldecoherence can be thoroughly suppressed.
基金supported by the National Natural Science Foundation of China Youth Science Foundation of China(Grant No.52308388)the Key Project of High-speed Rail Joint Fund of National Natural Science Foundation of China(Grant No.U1934210).
文摘This paper focuses on the use of rotary-percussive drilling for hard rocks.In order to improve efficiency and reduce costs,it is essential to understand how operational parameters,bit wear,and drilling performance are related.A model is presented therein that combines multibody dynamics and discrete element method(DEM)to investigate the influences of operational parameters and bit wear on the rate of penetration and wear characteristics.The model accurately captures the motion of the bit and recreates rock using the cutting sieving result.Field experimental results validate the rod dynamic behavior,rock recreating model,and coupling model in the simulation.The findings indicate that hammer pressure significantly influences the rate of penetration and wear depth of the bit,and there is an optimal range for economical hammer pressure.The wear coefficient has a major effect on the rate of penetration,when wear coefficient is between 1/3 and 2/3.Increasing the wear coefficient can reduce drill bit button pressure and wear depth at the same drill distance.Gauge button loss increases the rate of penetration due to higher pressure on the remaining buttons,which also accelerates destruction of the bit.Furthermore,a more evenly distributed button on the bit enhances the rate of penetration(ROP)when the same number of buttons is lost.
基金Supported by the National Natural Science Foundation of China(52225401)。
文摘To optimize the bit selection for large-diameter wellbore in the upper section of an ultra-deep well S-1,a full-well dynamic model integrating drill string vibration and bit rock-breaking was established and then verified using measured vibration data of drilling tools and actual rate of penetration(ROP)from Well HT-1 in northern Sichuan Basin.This model was employed to calculate and analyze drill string dynamic characteristics during large-diameter wellbore drilling in the Jurassic Penglaizhen Formation of Well S-1,followed by bit optimization.Research results show that during the drilling in Penglaizhen Formation of Well S-1,considering both the ROP of six candidate bits and the lateral/axial/torsional vibration characteristics of downhole tools,the six-blade dual-row cutter bit with the fastest ROP(average 7.12 m/h)was optimally selected.When using this bit,the downhole tool vibration levels remained at medium-low values.Field data showed over 90%consistency between actual ROP data and dynamic model calculation results after bit placement,demonstrating that the model can be used for bit program screening.
文摘This paper deals with the theoretic simulation of a drill bit whirling under conditions of its contact interaction with the bore-hole bottom rock plane. The bit is considered to be an absolutely rigid ellipsoidal body with uneven surface. It is attached to the lower end of a rotating elastic drill string. In the perturbed state, the bit can roll without sliding on the bore-hole bottom, performing whirling vibrations (the model of dynamic equilibrium with pure rolling when maximum cohesive force does not exceed the ultimate Coulombic friction). To describe these motions, a nonholonomic dynamic model is proposed, constitutive partial differential equations are deduced. With their use, the whirling vibrations of oblong and oblate ellipsoidal bits are analyzed, the functions of cohesive (frictional) forces are calculated. It is shown that the system of elastic drill string and ellipsoidal bit can acquire stable or unstable whirl modes with approaching critical Eulerian values by the parameters of axial force, torque and angular velocity. The analogy of the found modes of motions with ones of the Celtic stones is established. It is shown that the ellipsoidal bits can stop their whirling vibrations and change directions of their circumferential motions in the same manner as the ellipsoidal Celtic stones do. As this takes place, the trajectories of the oblate ellipsoidal bits are characterized by more complicated paths and irregularities.
文摘An incipient stage of a rotating drill string bit whirl motion proceeding on a well bottom surface is studied on the basis of kinematic （nonholonomic） models of mechanic interaction between the contacting uneven bodies. The bit is considered to be an absolutely rigid spherical or ellipsoidal body, the well bottom surface can be plane or spherical. It is assumed that the system coaxiality is disturbed through small initial curvature of the drill string, imperfections of the bit and bore-well geometry or the system mass debalance. Linearized equations of the bit whirling are deducted, the frequencies of periodic motions are calculated, and their modes are constructed for different geometric parameters of the spherical and ellipsoidal bits. It is demonstrated that, depending on the system properties, the bit motion can acquire the regimes of forward and backward whMings or to transit to the state of stationary spinning relative to an immovable center of velocities. The most unfavorable and atypical whirling modes are characteristic for oblate eilipsoidal bits and curvilinear surfaces of the well bottom.
文摘为解决柔性车间内AGV的面对动态障碍物时路径规划不准确的问题,基于位操作方法提出一种跳点搜索(Jump Point Search, JPS)的改进算法。算法采用二进制方式编码化栅格地图,实现障碍物的快速识别;通过位操作方法扩大剪枝规则的应用范围,提升JPS算法中搜寻节点的效率;引入Octile距离模式对算法的启发式函数进行优化,达到降低计算复杂度,提升规划速度目的。分别将改进JPS算法与A*算法、JPS算法进行实验对比,结果表明:在复杂车间环境中,搜索时间、扩展节点数量、规划的路径同比其它两种算法都具有明显优势;在躲避动态障碍物测试中,改进型算法避障成功率为92%,躲避成功次数最高且规划的路径质量最优,同比两种算法综合性能最优。验证了算法的可行性。
