In order to track the desired path as fast as possible,a novel autonomous vehicle path tracking based on model predictive control(MPC)and PID speed control was proposed for high-speed automated vehicles considering th...In order to track the desired path as fast as possible,a novel autonomous vehicle path tracking based on model predictive control(MPC)and PID speed control was proposed for high-speed automated vehicles considering the constraints of vehicle physical limits,in which a forward-backward integration scheme was introduced to generate a time-optimal speed profile subject to the tire-road friction limit.Moreover,this scheme was further extended along one moving prediction window.In the MPC controller,the prediction model was an 8-degree-of-freedom(DOF)vehicle model,while the plant was a 14-DOF vehicle model.For lateral control,a sequence of optimal wheel steering angles was generated from the MPC controller;for longitudinal control,the total wheel torque was generated from the PID speed controller embedded in the MPC framework.The proposed controller was implemented in MATLAB considering arbitrary curves of continuously varying curvature as the reference trajectory.The simulation test results show that the tracking errors are small for vehicle lateral and longitudinal positions and the tracking performances for trajectory and speed are good using the proposed controller.Additionally,the case of extended implementation in one moving prediction window requires shorter travel time than the case implemented along the entire path.展开更多
In order to analyze the complex chemical kinetic mechanism systematically and find out the redundant species and reactions, a numerical platform for mechanism analysis and simplification is established basing on Path ...In order to analyze the complex chemical kinetic mechanism systematically and find out the redundant species and reactions, a numerical platform for mechanism analysis and simplification is established basing on Path Flux Analysis （PFA）. It is used to reduce a detailed mechanism for flame inhibited by phosphorus containing compounds, a reduced mechanism with 65 species and 335 reactions is obtained. The detailed and reduced mechanism are both used to calculate the freely-propagating premix C3H8/air flame with different dimethyl methylphosphonate doped over a wide range of equivalence ratios. The concentration distributions of free radicals and major species are compared, and the results under two different mechanisms agree well. The laminar flame speed obtained by the two mechanisms also matches well, with the maximum relative error introduces as a small value of 1.7%. On the basis of the reduced mechanism validation, the correlativity analysis is conducted between flame speed and flee radical concentrations, which can provide information for target species selection in the further mechanism reduction. By analyzing the species and reactions fluxes, the species and reaction paths which contribute the flame inhibition significantly are determined.展开更多
Reduced graphene oxide is the precursor to produce graphene in a large scale;however,to date,there has been no consensus on the electronic structure of reduced graphene oxide.In this study,we carried out an ab initio ...Reduced graphene oxide is the precursor to produce graphene in a large scale;however,to date,there has been no consensus on the electronic structure of reduced graphene oxide.In this study,we carried out an ab initio molecular dynamics simulation to investigate the adsorption process of hydroxyl groups on graphene surface.During the adsorption process,the OH group needs to firstly pass through a physical adsorption complex with the OH above the bridge site of two carbon atoms,next to surmount a transition state,then to be adsorbed at the atop site of a carbon atom.With a 5×5 graphene surface,up to 6 hydroxyl groups can be adsorbed on the graphene surface,indicating the concentration coverage of the hydroxyl groups on graphene surface is about 12%.The simulation results show that the negative adsorption energy increases linearly as the number of adsorbed hydroxyl groups increases,and the band gap also increases linearly with the number of adsorbed hydroxyl groups.展开更多
The two-dimensional barrier passage is studied in the framework of Langevin statistical reactive dynamics.The optimal incident angle for a particle diffusing in the dissipative non-orthogonal environment with various ...The two-dimensional barrier passage is studied in the framework of Langevin statistical reactive dynamics.The optimal incident angle for a particle diffusing in the dissipative non-orthogonal environment with various strengthsof coupling between the two degrees of freedom is systematically calculated.The optimal diffusion path of the particlein a non-Ohmic damping system is revealed to have a probability to return to the potential valley under the combinedinfluence of the off-diagonal system tensors.展开更多
Formaldehyde and hydrogen peroxide are two important realistic molecules in atmospheric chemistry.We implement path integral Liouville dynamics(PILD)to calculate the dipolederivative autocorrelation function for obtai...Formaldehyde and hydrogen peroxide are two important realistic molecules in atmospheric chemistry.We implement path integral Liouville dynamics(PILD)to calculate the dipolederivative autocorrelation function for obtaining the infrared spectrum.In comparison to exact vibrational frequencies,PILD faithfully captures most nuclear quantum effects in vibrational dynamics as temperature changes and as the isotopic substitution occurs.展开更多
Through-flow method is still widely applied in the revolution of the design of a turbomachinery, which can provide not merely the performance characteristic but also the flow field. In this study,a program based on th...Through-flow method is still widely applied in the revolution of the design of a turbomachinery, which can provide not merely the performance characteristic but also the flow field. In this study,a program based on the through-flow method was proposed, which had been verified by many other numerical examples. So as to improve the accuracy of the calculation, abundant loss and deviation models dependent on the real geometry of engine were put into use,such as: viscous losses,overflow in gaps, leakage from a flow path through seals. By means of this program, the aerodynamic performance of a certain high through-flow commercial fan/booster was investigated. On account of the radial distributions of the relevant parameters, flow deterioration in this machine was speculated. To confirm this surmise, 3-D numerical simulation was carried out with the help of the NUMECA software. Through detailed analysis, the speculation above was demonstrated, which provide sufficient evidence for the conclusion that the through-flow method is an essential and effective method for the performance prediction of the fan/booster.展开更多
We describe a computational approach,incorporating quantum mechanics into enzyme kinetics modeling with a special emphasis on computation of kinetic isotope effects.Two aspects are highlighted:(1) the potential energy...We describe a computational approach,incorporating quantum mechanics into enzyme kinetics modeling with a special emphasis on computation of kinetic isotope effects.Two aspects are highlighted:(1) the potential energy surface is represented by a combined quantum mechanical and molecular mechanical(QM/MM) potential in which the bond forming and breaking processes are modeled by electronic structure theory,and(2) a free energy perturbation method in path integral simulation is used to determine both kinetic isotope effects(KIEs).In this approach,which is called the PI-FEP/UM method,a light(heavy) isotope is mutated into a heavy(light) counterpart in centroid path integral simulations.The method is illustrated in the study of primary and secondary KIEs in two enzyme systems.In the case of nitroalkane oxidase,the enzymatic reaction exhibits enhanced quantum tunneling over that of the uncatalyzed process in water.In the dopa delarboxylase reaction,there appears to be distinguishable primary carbon-13 and secondary deuterium KIEs when the internal proton tautomerism is in the N-protonated or in the O-protonated positions.These examples show that the incorporation of quantum mechanical effects in enzyme kinetics modeling offers an opportunity to accurately and reliably model the mechanisms and free energies of enzymatic reactions.展开更多
The AI-AIN-Si composites were prepared in the gas-in-liquid in situ synthesized flow-reaction-system, which was implemented by a powder metallurgy and reaction sin- tering route. The experimental results showed that A...The AI-AIN-Si composites were prepared in the gas-in-liquid in situ synthesized flow-reaction-system, which was implemented by a powder metallurgy and reaction sin- tering route. The experimental results showed that A1-AIN- 50SiB material （prepared by ball-milling powders） and AI- AIN-50SiM material （prepared by mixing powders） exhibited the semi-continuous Si structures and the isolated Si islands, respectively. Subsequently, the AI-AIN-50Si materials were selected as the model materials by phase identification and microstructure analysis. The dynamic microstructural evolu- tion of AI-AIN-50Si materials was investigated using the computational fluid dynamics （CFD） method. Mathematical models and simulation results showed that the in situ synthesis of AIN was strongly influenced by the structure and the flow- path （（Cg,N2/lg,N2）＋（Cs,AlN/ls,AiN））. The flow paths of AI-AIN-50Si^B material were restricted by the semi-continuous Si. These Si structures can promote the formation of the strong turbulence with gradually weakened fluctuation, so that the in situ synthesis of AIN was interconnected and surrounded by an interpenetrating Si network. In contrast, the flow paths of AI- AIN-50Si^B material can easily pass through the isolated Si due to its mild turbulence with linear relationship. As a result, AIN was separated by the isolated Si and agglomerated in the matrix. Overall, the present work provides new insights into dynamic microstructural evolution in in situ reaction sinter- ing systems.展开更多
The surface diffusion of Pt dimers on Wulff polyhedral clusters with 586-12934 atoms was studied by the embedded atom method. The minimum energy diffusion path and the corresponding energy barrier for dimer diffusion ...The surface diffusion of Pt dimers on Wulff polyhedral clusters with 586-12934 atoms was studied by the embedded atom method. The minimum energy diffusion path and the corresponding energy barrier for dimer diffusion on cluster surfaces were determined through a combination of the quenched Molecular Dynamics and the Nudged Elastic Band method. It was found that the diffusion of a dimer across the step-edge by dissociation and consecutive single-atom exchange with the edge atoms, rather than diffusion over the edge as a unit. Therefore, the step can enhance the dissociation of the dimer. For small Wulff polyhedral clusters containing up to 2000 atoms, the energy barrier for dimer diffusion from the {111} to the {100} facet is almost equal to that for the single adatom diffusion on the flat {111} surface. From the calculated cluster size dependence of the energy barrier, we conclude that the Wulff polyhedral cluster is stable, as the cluster has more than about 2000 atoms.展开更多
基金Project(20180608005600843855-19)supported by the International Graduate Exchange Program of Beijing Institute of Technology,China。
文摘In order to track the desired path as fast as possible,a novel autonomous vehicle path tracking based on model predictive control(MPC)and PID speed control was proposed for high-speed automated vehicles considering the constraints of vehicle physical limits,in which a forward-backward integration scheme was introduced to generate a time-optimal speed profile subject to the tire-road friction limit.Moreover,this scheme was further extended along one moving prediction window.In the MPC controller,the prediction model was an 8-degree-of-freedom(DOF)vehicle model,while the plant was a 14-DOF vehicle model.For lateral control,a sequence of optimal wheel steering angles was generated from the MPC controller;for longitudinal control,the total wheel torque was generated from the PID speed controller embedded in the MPC framework.The proposed controller was implemented in MATLAB considering arbitrary curves of continuously varying curvature as the reference trajectory.The simulation test results show that the tracking errors are small for vehicle lateral and longitudinal positions and the tracking performances for trajectory and speed are good using the proposed controller.Additionally,the case of extended implementation in one moving prediction window requires shorter travel time than the case implemented along the entire path.
基金Supported by the National Natural Science Foundation of China （51176181）, the National Basic Research Program of China （2012CB719704）, and the Research Fund for the Doctoral Program of Higher Education （20123402110047）.
文摘In order to analyze the complex chemical kinetic mechanism systematically and find out the redundant species and reactions, a numerical platform for mechanism analysis and simplification is established basing on Path Flux Analysis （PFA）. It is used to reduce a detailed mechanism for flame inhibited by phosphorus containing compounds, a reduced mechanism with 65 species and 335 reactions is obtained. The detailed and reduced mechanism are both used to calculate the freely-propagating premix C3H8/air flame with different dimethyl methylphosphonate doped over a wide range of equivalence ratios. The concentration distributions of free radicals and major species are compared, and the results under two different mechanisms agree well. The laminar flame speed obtained by the two mechanisms also matches well, with the maximum relative error introduces as a small value of 1.7%. On the basis of the reduced mechanism validation, the correlativity analysis is conducted between flame speed and flee radical concentrations, which can provide information for target species selection in the further mechanism reduction. By analyzing the species and reactions fluxes, the species and reaction paths which contribute the flame inhibition significantly are determined.
基金supported by the National Natural Science Foundation of China(No.11774206)Taishan Scholarship Fund from Shandong Province。
文摘Reduced graphene oxide is the precursor to produce graphene in a large scale;however,to date,there has been no consensus on the electronic structure of reduced graphene oxide.In this study,we carried out an ab initio molecular dynamics simulation to investigate the adsorption process of hydroxyl groups on graphene surface.During the adsorption process,the OH group needs to firstly pass through a physical adsorption complex with the OH above the bridge site of two carbon atoms,next to surmount a transition state,then to be adsorbed at the atop site of a carbon atom.With a 5×5 graphene surface,up to 6 hydroxyl groups can be adsorbed on the graphene surface,indicating the concentration coverage of the hydroxyl groups on graphene surface is about 12%.The simulation results show that the negative adsorption energy increases linearly as the number of adsorbed hydroxyl groups increases,and the band gap also increases linearly with the number of adsorbed hydroxyl groups.
基金Supported by the Scientific Research Starting Foundation of Qufu Normal University and the National Natural Science Foundation of China under Grant No.10847101
文摘The two-dimensional barrier passage is studied in the framework of Langevin statistical reactive dynamics.The optimal incident angle for a particle diffusing in the dissipative non-orthogonal environment with various strengthsof coupling between the two degrees of freedom is systematically calculated.The optimal diffusion path of the particlein a non-Ohmic damping system is revealed to have a probability to return to the potential valley under the combinedinfluence of the off-diagonal system tensors.
文摘Formaldehyde and hydrogen peroxide are two important realistic molecules in atmospheric chemistry.We implement path integral Liouville dynamics(PILD)to calculate the dipolederivative autocorrelation function for obtaining the infrared spectrum.In comparison to exact vibrational frequencies,PILD faithfully captures most nuclear quantum effects in vibrational dynamics as temperature changes and as the isotopic substitution occurs.
基金supported by National Natural Science Foundation of China(51236001)National Basic Research Program of China(2012CB720201)Beijing Natural Science Foundation(No.3151002)
文摘Through-flow method is still widely applied in the revolution of the design of a turbomachinery, which can provide not merely the performance characteristic but also the flow field. In this study,a program based on the through-flow method was proposed, which had been verified by many other numerical examples. So as to improve the accuracy of the calculation, abundant loss and deviation models dependent on the real geometry of engine were put into use,such as: viscous losses,overflow in gaps, leakage from a flow path through seals. By means of this program, the aerodynamic performance of a certain high through-flow commercial fan/booster was investigated. On account of the radial distributions of the relevant parameters, flow deterioration in this machine was speculated. To confirm this surmise, 3-D numerical simulation was carried out with the help of the NUMECA software. Through detailed analysis, the speculation above was demonstrated, which provide sufficient evidence for the conclusion that the through-flow method is an essential and effective method for the performance prediction of the fan/booster.
基金supported in part by the National Institutes of Health (GM46736)
文摘We describe a computational approach,incorporating quantum mechanics into enzyme kinetics modeling with a special emphasis on computation of kinetic isotope effects.Two aspects are highlighted:(1) the potential energy surface is represented by a combined quantum mechanical and molecular mechanical(QM/MM) potential in which the bond forming and breaking processes are modeled by electronic structure theory,and(2) a free energy perturbation method in path integral simulation is used to determine both kinetic isotope effects(KIEs).In this approach,which is called the PI-FEP/UM method,a light(heavy) isotope is mutated into a heavy(light) counterpart in centroid path integral simulations.The method is illustrated in the study of primary and secondary KIEs in two enzyme systems.In the case of nitroalkane oxidase,the enzymatic reaction exhibits enhanced quantum tunneling over that of the uncatalyzed process in water.In the dopa delarboxylase reaction,there appears to be distinguishable primary carbon-13 and secondary deuterium KIEs when the internal proton tautomerism is in the N-protonated or in the O-protonated positions.These examples show that the incorporation of quantum mechanical effects in enzyme kinetics modeling offers an opportunity to accurately and reliably model the mechanisms and free energies of enzymatic reactions.
基金supported by the financial support of the National Natural Science Foundation of China (51171146 and 51101177)the Program for Key Science and Technology Innovative Research Team of Shaanxi Province (2013KCT-05)
文摘The AI-AIN-Si composites were prepared in the gas-in-liquid in situ synthesized flow-reaction-system, which was implemented by a powder metallurgy and reaction sin- tering route. The experimental results showed that A1-AIN- 50SiB material （prepared by ball-milling powders） and AI- AIN-50SiM material （prepared by mixing powders） exhibited the semi-continuous Si structures and the isolated Si islands, respectively. Subsequently, the AI-AIN-50Si materials were selected as the model materials by phase identification and microstructure analysis. The dynamic microstructural evolu- tion of AI-AIN-50Si materials was investigated using the computational fluid dynamics （CFD） method. Mathematical models and simulation results showed that the in situ synthesis of AIN was strongly influenced by the structure and the flow- path （（Cg,N2/lg,N2）＋（Cs,AlN/ls,AiN））. The flow paths of AI-AIN-50Si^B material were restricted by the semi-continuous Si. These Si structures can promote the formation of the strong turbulence with gradually weakened fluctuation, so that the in situ synthesis of AIN was interconnected and surrounded by an interpenetrating Si network. In contrast, the flow paths of AI- AIN-50Si^B material can easily pass through the isolated Si due to its mild turbulence with linear relationship. As a result, AIN was separated by the isolated Si and agglomerated in the matrix. Overall, the present work provides new insights into dynamic microstructural evolution in in situ reaction sinter- ing systems.
基金supported by the National Natural Science Foundation of China (Grant No. 50971058)the Hunan Provincial Natural Science Foundation of China (Grant No. 10JJ3050)
文摘The surface diffusion of Pt dimers on Wulff polyhedral clusters with 586-12934 atoms was studied by the embedded atom method. The minimum energy diffusion path and the corresponding energy barrier for dimer diffusion on cluster surfaces were determined through a combination of the quenched Molecular Dynamics and the Nudged Elastic Band method. It was found that the diffusion of a dimer across the step-edge by dissociation and consecutive single-atom exchange with the edge atoms, rather than diffusion over the edge as a unit. Therefore, the step can enhance the dissociation of the dimer. For small Wulff polyhedral clusters containing up to 2000 atoms, the energy barrier for dimer diffusion from the {111} to the {100} facet is almost equal to that for the single adatom diffusion on the flat {111} surface. From the calculated cluster size dependence of the energy barrier, we conclude that the Wulff polyhedral cluster is stable, as the cluster has more than about 2000 atoms.
