The shell-model molecular dynamics method was applied to simulate the melting temper- atures of SrF2 and BaF2 at elevated temperatures and high pressures. The same method was used to calculate the equations of state f...The shell-model molecular dynamics method was applied to simulate the melting temper- atures of SrF2 and BaF2 at elevated temperatures and high pressures. The same method was used to calculate the equations of state for SrF2 and BaF2 over the pressure range of 0.1 MPa-3 GPa and 0.1 MPa-7 GPa. Compared with previous results for equations of state, the maximum errors are 0.3% and 2.2%, respectively. Considering the pre-melting in the fluorite-type crystals, we made the necessary corrections for the simulated melting temper- atures of SrF2 and BaF2. Consequently, the melting temperatures of SrF2 and BaF2 were obtained for high pressures. The melting temperatures of SrF2 and BaF2 that were obtained by the simulation are in good agreement with available experimental data.展开更多
When underground cavities are subjected to explosive stress waves,a uniquely damaged zone may appear due to the combined effect of dynamic loading and static pre-load stress.In this study,a rate-dependent two-dimensio...When underground cavities are subjected to explosive stress waves,a uniquely damaged zone may appear due to the combined effect of dynamic loading and static pre-load stress.In this study,a rate-dependent two-dimensional rock dynamic constitutive model was established to investigate the dynamic fractures of rocks under different static stress conditions.The effects of the loading rate and peak amplitude of the blasting wave under different confining pressures and the vertical compressive coefficient(K_(0))were considered.The numerical simulated results reproduced the initiation and further propagation of primary radial crack fractures,which were in agreement with the experimental results.The dynamic loading rate,peak amplitude,static vertical compressive coefficient(K_(0))and confining pressure affected the evolution of fractures around the borehole.The heterogeneity parameter(m)plays an important role in the evolution of fractures around the borehole.The crack propagation path became more discontinuous and rougher in a smallerheterogeneity parameter case.展开更多
A numerical investigation of the unsteady motion of a deformed drop released freely in another quiescent liquid contaminated by surfactant is presented in this paper. The finite difference method was used to solve num...A numerical investigation of the unsteady motion of a deformed drop released freely in another quiescent liquid contaminated by surfactant is presented in this paper. The finite difference method was used to solve numerically the coupled time-dependent Navier-Stokes and convective-diffusion equations in a body-fitted orthogonal coordinate system. Numerical simulation was conducted on the experimental cases, in which MIBK drops with the size ranging from 1.24 mm to 1.97 mm rose and accelerated freely in pure water and in dilute sodium dodecyl sulphate (SDS) aqueous solution. The applicability of the numerical scheme was validated by the agreement between the simulation results and the experimental data. Both the numerical and experimental results showed that the velocitytime profile exhibited a maximum rising velocity for drops in SDS solutions, which was close to the terminal velocity in pure water, before it dropped down to a steady-state value. The effect of the sorption kinetics of surfactant on the accelerating motion was also evaluated. It is also suggested that introduction of virtual mass force into the formulation improved obviously the precision of numerical simulation of transient drop motion.展开更多
Based on laboratory tests of artificial fractures in mortar material, established the dynamic constitutive model of normal behaviour of rock fracture,. The tests were systematically conducted under quasi-static and dy...Based on laboratory tests of artificial fractures in mortar material, established the dynamic constitutive model of normal behaviour of rock fracture,. The tests were systematically conducted under quasi-static and dynamic monotonic loading conditions. The fractures were of different numbers of asperities in contact and were subsequently of different initial contact areas, which imitated the natural rock fractures. The rate of compressive load applied normal to the fractures covers a wide range from 10–1 MPa/s (quasi-static) up to 103 MPa/s (highly dynamic). The normal stress-closure responses of fractures were measured for different loading rates. Based on the stress-closure relation curves measured, a nonlinear (hyperbolic) dynamic model of fracture, normal behaviour, termed as dynamic BB model, was proposed, which was modified from the existing BB model of static normal behaviour of fractures by taking into account the effect of loading rate.展开更多
Loading history and age are factors for disc degeneration and disc biomechanics; however, their relationship is unclear. To evaluate disc biomechanics, we conducted an experimental, anatomical and numerical approach t...Loading history and age are factors for disc degeneration and disc biomechanics; however, their relationship is unclear. To evaluate disc biomechanics, we conducted an experimental, anatomical and numerical approach to distinguish discs with mild and severe degeneration. In the experimental procedure, 10 cadaveric lumbar discs are tested to static and dynamic compression, and the elastic and viscous moduli and the dynamic parameters are reported. The morphology of disc degeneration is gained with MRI （magnetic resonance imaging） and used to generate a nonlinear finite element model of a degenerated disc, and assisted with the experimental results in order to numerically investigate the distribution of stresses and strains within the disc. The results show a promising methodology for the study of intervertebral disc biomechanics and in general other tissues, organs and medical devices.展开更多
Distillation column control is widely explored in literature due to its complexity and importance in chemical and petrochemical industries. In this process, pressure represents one of the most important variables to b...Distillation column control is widely explored in literature due to its complexity and importance in chemical and petrochemical industries. In this process, pressure represents one of the most important variables to be controlled. However, there are few studies about how pressure affects the dynamic behavior of distillation columns and most research on distillation column control involve direct manipulation of cooling fluid through the condenser. Nevertheless, such an approach demands constant changes in cooling fluid flowrates that are commonly by the order of tons per hour, which can be difficult to work or even unfeasible in a real plant. Furthermore, this strategy is usually avoided, as it can cause fouling and corrosion acceleration. The hot-vapor bypass strategy fits well as a solution for these issues, eliminating the need to dynamically manipulate cooling fluid flowrates in the condensation unit. This work presents the modeling and simulation of a conventional distillation column for the separation of water and ethanol, in which a comparative study between a conventional pressure control and a control using hot-vapor bypass was performed. The main results were obtained through dynamic simulations which considered various disturbances in the feed stream, and demonstrated superior performance by the hot-vapor bypass system over the usual scheme proposed in literature, while evaluating the lntegral Absolute Error （IAE） norm as the control performance index.展开更多
In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifug...In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifugal pump. A CFD model for cavita- tion steady and unsteady simulation has been calculated using the κ-ω SST turbulence model combining with a multiphase ap- proach, based on a homogeneous model assumption. A truncated form of Rayleigh-Plesset equation is used as a source term for the inter-phase mass transfer. The CFD computational region includes the suction cone, impeller, side chambers and volute, as well as suction and pressure pipes. The results were compared with experimental data under non-cavitation and cavitation conditions and a good agreement was obtained for the global performance, the experimental data of the head and the efficiency are 34.04 m and 74.42% at BEP, respectively, the predicted head is 34.31 m and the predicted efficiency is 73.75%. The analy- sis of inner flow pattern shows that the vortex flow generation in the rear of cavity region is the main reason of the head-drop. Obvious increasing can be observed for the amplitude of the pressure fluctuation at the blade passing frequency with different cavitation situations, and subpeak can be found. Besides, the effects of unsteady flow in the side chambers cannot be neglected for accurately predicting the inner flow of the pump. These results imply that this numerical method is suitable for the cavitat- ing flow in the pump.展开更多
This contribution provides a summary of proposed theoretical and computational studies on excited state dynamics in molecular aggregates, as an important part of the National Natural Science Foundation (NNSF) Major Pr...This contribution provides a summary of proposed theoretical and computational studies on excited state dynamics in molecular aggregates, as an important part of the National Natural Science Foundation (NNSF) Major Project entitled "Theoretical study of the low-lying electronic excited state for molecular aggregates". This study will focus on developments of novel methods to simulate excited state dynamics of molecular aggregates, with the aim of understanding several important chemical physics processes, and providing a solid foundation for predicting the opto-electronic properties of organic functional materials and devices. The contents of this study include: (1) The quantum chemical methods for electronic excited state and electronic couplings targeted for dynamics in molecular aggregates; (2) Methods to construct effective Hamiltonian models, and to solve their dynamics using system-bath approaches; (3) Non-adiabatic mixed quantum-classic methods targeted for molecular aggregates; (4) Theoretical studies of charge and energy transfer, and related spectroscopic phenomena in molecular aggregates.展开更多
The structural and dynamic properties of nanoscale ethanol film on a mica surface are investigated via molecular dynamics simulations. We observe a dense, almost fiat ethanol bilayer formed in the vicinity of the mica...The structural and dynamic properties of nanoscale ethanol film on a mica surface are investigated via molecular dynamics simulations. We observe a dense, almost fiat ethanol bilayer formed in the vicinity of the mica surface, with the hydrophobic alkyl groups pointing outward from the surface. Remarkably, such ethanol bilayer is laterally well-ordered with patterned adsorption sites. Each ethanol molecule in the first layer donates one hydrogen bond to the surface basal oxygen atoms and accepts one hydrogen bond from that in the second layer. The ethanol molecules within the bilayer exhibit constrained lateral mobility and delayed dynamics as compared with bulk ethanol, whereas those on top of the bilayer have bulk-like characteristics.展开更多
We introduce a non-uniform gravity-like force field to control the granular flow state in a quasi-one- dimensional system, and study the system by the molecular dynamics simulation. We find that the granular flow unde...We introduce a non-uniform gravity-like force field to control the granular flow state in a quasi-one- dimensional system, and study the system by the molecular dynamics simulation. We find that the granular flow under non-uniform force field can be well described by a density wave with fixed time period if a fixed partiele number condition is used. The base frequency of the density wave does not depend on the position of the flow, while both the average density and oseillation amplitude of the flow vary continuously with the position. The formation of the density wave results from the aggregation of the granules in the decelerated region and the feed-back mechanism in the fixed particle number condition.展开更多
Based upon the stochastic resonance theory,the formation mechanism of 100-kyr cycles in climate system is numerically studied in the perspective of stochastic dynamics.In this study,firstly we combine the idealized al...Based upon the stochastic resonance theory,the formation mechanism of 100-kyr cycles in climate system is numerically studied in the perspective of stochastic dynamics.In this study,firstly we combine the idealized albedo model with the geological evidence and observation in climate system to construct a new albedo model.Secondly,a bistable nonlinear system is constructed by introducing the albedo model into zero-dimensional energy balance model.Finally,based on this new system,with the solar radiation cycles and stochastic perturbation simultaneously taken into account,the variation of 100-kyr cycles is analyzed by numerical simulations.The results show that,when the noise intensity reaches a certain value,the stochastic resonance can be triggered.However,the noise intensity in this level does not exist in the actual climate system.In order to explain the formation mechanism of 100-kyr glacial-interglacial cycles forced by the weak solar radiation cycles,besides the solar radiation stochastic perturbation,the stochastic dynamic effects of the other "non-solar" radiation stochastic perturbation in the climate change processes should also be considered.The stochastic dynamic simulations taking the two types of stochastic perturbation into consideration show that,when the two types of appropriately observable stochastic perturbation are introduced,the stochastic resonance also can be generated.In this situation,the contribution rate of solar radiation stochastic perturbation is about 38%,which proves the importance of solar radiation stochastic perturbation in the formation of 100-kyr climate cycles.展开更多
Based on the short-range order,it is found that the abundance of the P-centered P-transition-metal clusters are the common feature among the liquid Pd-Cu-Ni-P alloys,and hence this feature alone could not uncover the ...Based on the short-range order,it is found that the abundance of the P-centered P-transition-metal clusters are the common feature among the liquid Pd-Cu-Ni-P alloys,and hence this feature alone could not uncover the underlying mechanisms of the variation of glass forming ability among the liquid alloys.For the so called similar elements such as Cu and Ni,their behaviors are significantly different when interacting with Pd or P atoms.Cu has weak bonding with both Pd and P while Ni has very strong bonding with P but nearly no bonding with Pd.The different bonding characters thus underlie the phenomenon that in the best glass formers the ratio of the two similar elements often deviates from 1:1.Only if the parameters of chemical short-range order of Cu and Ni around P become closest to each other the best glass forming ability is reached.It is also illustrated that the calculated dynamic properties are very helpful to locate the composition of the best glass former.展开更多
基金This work was supported by the National Natural Science Foundation of China （No.10676025） and Research Center of Laser Fusion, China Academy of Engineering Physics.
文摘The shell-model molecular dynamics method was applied to simulate the melting temper- atures of SrF2 and BaF2 at elevated temperatures and high pressures. The same method was used to calculate the equations of state for SrF2 and BaF2 over the pressure range of 0.1 MPa-3 GPa and 0.1 MPa-7 GPa. Compared with previous results for equations of state, the maximum errors are 0.3% and 2.2%, respectively. Considering the pre-melting in the fluorite-type crystals, we made the necessary corrections for the simulated melting temper- atures of SrF2 and BaF2. Consequently, the melting temperatures of SrF2 and BaF2 were obtained for high pressures. The melting temperatures of SrF2 and BaF2 that were obtained by the simulation are in good agreement with available experimental data.
基金Projects(51878190,51779031,51678170)supported by the National Natural Science Foundation of China。
文摘When underground cavities are subjected to explosive stress waves,a uniquely damaged zone may appear due to the combined effect of dynamic loading and static pre-load stress.In this study,a rate-dependent two-dimensional rock dynamic constitutive model was established to investigate the dynamic fractures of rocks under different static stress conditions.The effects of the loading rate and peak amplitude of the blasting wave under different confining pressures and the vertical compressive coefficient(K_(0))were considered.The numerical simulated results reproduced the initiation and further propagation of primary radial crack fractures,which were in agreement with the experimental results.The dynamic loading rate,peak amplitude,static vertical compressive coefficient(K_(0))and confining pressure affected the evolution of fractures around the borehole.The heterogeneity parameter(m)plays an important role in the evolution of fractures around the borehole.The crack propagation path became more discontinuous and rougher in a smallerheterogeneity parameter case.
基金Supported by the National Natural Science Foundation of China(No.20236050)
文摘A numerical investigation of the unsteady motion of a deformed drop released freely in another quiescent liquid contaminated by surfactant is presented in this paper. The finite difference method was used to solve numerically the coupled time-dependent Navier-Stokes and convective-diffusion equations in a body-fitted orthogonal coordinate system. Numerical simulation was conducted on the experimental cases, in which MIBK drops with the size ranging from 1.24 mm to 1.97 mm rose and accelerated freely in pure water and in dilute sodium dodecyl sulphate (SDS) aqueous solution. The applicability of the numerical scheme was validated by the agreement between the simulation results and the experimental data. Both the numerical and experimental results showed that the velocitytime profile exhibited a maximum rising velocity for drops in SDS solutions, which was close to the terminal velocity in pure water, before it dropped down to a steady-state value. The effect of the sorption kinetics of surfactant on the accelerating motion was also evaluated. It is also suggested that introduction of virtual mass force into the formulation improved obviously the precision of numerical simulation of transient drop motion.
文摘Based on laboratory tests of artificial fractures in mortar material, established the dynamic constitutive model of normal behaviour of rock fracture,. The tests were systematically conducted under quasi-static and dynamic monotonic loading conditions. The fractures were of different numbers of asperities in contact and were subsequently of different initial contact areas, which imitated the natural rock fractures. The rate of compressive load applied normal to the fractures covers a wide range from 10–1 MPa/s (quasi-static) up to 103 MPa/s (highly dynamic). The normal stress-closure responses of fractures were measured for different loading rates. Based on the stress-closure relation curves measured, a nonlinear (hyperbolic) dynamic model of fracture, normal behaviour, termed as dynamic BB model, was proposed, which was modified from the existing BB model of static normal behaviour of fractures by taking into account the effect of loading rate.
文摘Loading history and age are factors for disc degeneration and disc biomechanics; however, their relationship is unclear. To evaluate disc biomechanics, we conducted an experimental, anatomical and numerical approach to distinguish discs with mild and severe degeneration. In the experimental procedure, 10 cadaveric lumbar discs are tested to static and dynamic compression, and the elastic and viscous moduli and the dynamic parameters are reported. The morphology of disc degeneration is gained with MRI （magnetic resonance imaging） and used to generate a nonlinear finite element model of a degenerated disc, and assisted with the experimental results in order to numerically investigate the distribution of stresses and strains within the disc. The results show a promising methodology for the study of intervertebral disc biomechanics and in general other tissues, organs and medical devices.
基金the Conselho Nacional de Desenvolvimento Científico e Tecnológico(CNPq)for financial support for this work
文摘Distillation column control is widely explored in literature due to its complexity and importance in chemical and petrochemical industries. In this process, pressure represents one of the most important variables to be controlled. However, there are few studies about how pressure affects the dynamic behavior of distillation columns and most research on distillation column control involve direct manipulation of cooling fluid through the condenser. Nevertheless, such an approach demands constant changes in cooling fluid flowrates that are commonly by the order of tons per hour, which can be difficult to work or even unfeasible in a real plant. Furthermore, this strategy is usually avoided, as it can cause fouling and corrosion acceleration. The hot-vapor bypass strategy fits well as a solution for these issues, eliminating the need to dynamically manipulate cooling fluid flowrates in the condensation unit. This work presents the modeling and simulation of a conventional distillation column for the separation of water and ethanol, in which a comparative study between a conventional pressure control and a control using hot-vapor bypass was performed. The main results were obtained through dynamic simulations which considered various disturbances in the feed stream, and demonstrated superior performance by the hot-vapor bypass system over the usual scheme proposed in literature, while evaluating the lntegral Absolute Error （IAE） norm as the control performance index.
基金supported by the State Key Program of National Natural Science Foundation of China (Grant No. 51239005)the National Science & Technology Pillar Program (Grant No. 2011BAF14B04)the Jiangsu Provincial Project for Innovative Postgraduates of China (Grant No. CXZZ11_0564)
文摘In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifugal pump. A CFD model for cavita- tion steady and unsteady simulation has been calculated using the κ-ω SST turbulence model combining with a multiphase ap- proach, based on a homogeneous model assumption. A truncated form of Rayleigh-Plesset equation is used as a source term for the inter-phase mass transfer. The CFD computational region includes the suction cone, impeller, side chambers and volute, as well as suction and pressure pipes. The results were compared with experimental data under non-cavitation and cavitation conditions and a good agreement was obtained for the global performance, the experimental data of the head and the efficiency are 34.04 m and 74.42% at BEP, respectively, the predicted head is 34.31 m and the predicted efficiency is 73.75%. The analy- sis of inner flow pattern shows that the vortex flow generation in the rear of cavity region is the main reason of the head-drop. Obvious increasing can be observed for the amplitude of the pressure fluctuation at the blade passing frequency with different cavitation situations, and subpeak can be found. Besides, the effects of unsteady flow in the side chambers cannot be neglected for accurately predicting the inner flow of the pump. These results imply that this numerical method is suitable for the cavitat- ing flow in the pump.
基金the National Natural Science Foundation of China (21290194)
文摘This contribution provides a summary of proposed theoretical and computational studies on excited state dynamics in molecular aggregates, as an important part of the National Natural Science Foundation (NNSF) Major Project entitled "Theoretical study of the low-lying electronic excited state for molecular aggregates". This study will focus on developments of novel methods to simulate excited state dynamics of molecular aggregates, with the aim of understanding several important chemical physics processes, and providing a solid foundation for predicting the opto-electronic properties of organic functional materials and devices. The contents of this study include: (1) The quantum chemical methods for electronic excited state and electronic couplings targeted for dynamics in molecular aggregates; (2) Methods to construct effective Hamiltonian models, and to solve their dynamics using system-bath approaches; (3) Non-adiabatic mixed quantum-classic methods targeted for molecular aggregates; (4) Theoretical studies of charge and energy transfer, and related spectroscopic phenomena in molecular aggregates.
基金Supported by Grants from Chinese Academy of Sciences,the National Natural Science Foundation of China under Grant No. 10825520National Basic Research Program of China under Grant No. 2007CB936000China Postdoctoral Science Foundation under Grant No. 20100480645
文摘The structural and dynamic properties of nanoscale ethanol film on a mica surface are investigated via molecular dynamics simulations. We observe a dense, almost fiat ethanol bilayer formed in the vicinity of the mica surface, with the hydrophobic alkyl groups pointing outward from the surface. Remarkably, such ethanol bilayer is laterally well-ordered with patterned adsorption sites. Each ethanol molecule in the first layer donates one hydrogen bond to the surface basal oxygen atoms and accepts one hydrogen bond from that in the second layer. The ethanol molecules within the bilayer exhibit constrained lateral mobility and delayed dynamics as compared with bulk ethanol, whereas those on top of the bilayer have bulk-like characteristics.
基金Supported by the National Basic Research Program of China under Grant No.2009CB930800by the National Natural Science Foundation of China under Grant Nos.10875166 and 11274355
文摘We introduce a non-uniform gravity-like force field to control the granular flow state in a quasi-one- dimensional system, and study the system by the molecular dynamics simulation. We find that the granular flow under non-uniform force field can be well described by a density wave with fixed time period if a fixed partiele number condition is used. The base frequency of the density wave does not depend on the position of the flow, while both the average density and oseillation amplitude of the flow vary continuously with the position. The formation of the density wave results from the aggregation of the granules in the decelerated region and the feed-back mechanism in the fixed particle number condition.
基金supported by the National Natural Science Foundation of China(Grant No.41205083)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘Based upon the stochastic resonance theory,the formation mechanism of 100-kyr cycles in climate system is numerically studied in the perspective of stochastic dynamics.In this study,firstly we combine the idealized albedo model with the geological evidence and observation in climate system to construct a new albedo model.Secondly,a bistable nonlinear system is constructed by introducing the albedo model into zero-dimensional energy balance model.Finally,based on this new system,with the solar radiation cycles and stochastic perturbation simultaneously taken into account,the variation of 100-kyr cycles is analyzed by numerical simulations.The results show that,when the noise intensity reaches a certain value,the stochastic resonance can be triggered.However,the noise intensity in this level does not exist in the actual climate system.In order to explain the formation mechanism of 100-kyr glacial-interglacial cycles forced by the weak solar radiation cycles,besides the solar radiation stochastic perturbation,the stochastic dynamic effects of the other "non-solar" radiation stochastic perturbation in the climate change processes should also be considered.The stochastic dynamic simulations taking the two types of stochastic perturbation into consideration show that,when the two types of appropriately observable stochastic perturbation are introduced,the stochastic resonance also can be generated.In this situation,the contribution rate of solar radiation stochastic perturbation is about 38%,which proves the importance of solar radiation stochastic perturbation in the formation of 100-kyr climate cycles.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50971082 and 50831003)
文摘Based on the short-range order,it is found that the abundance of the P-centered P-transition-metal clusters are the common feature among the liquid Pd-Cu-Ni-P alloys,and hence this feature alone could not uncover the underlying mechanisms of the variation of glass forming ability among the liquid alloys.For the so called similar elements such as Cu and Ni,their behaviors are significantly different when interacting with Pd or P atoms.Cu has weak bonding with both Pd and P while Ni has very strong bonding with P but nearly no bonding with Pd.The different bonding characters thus underlie the phenomenon that in the best glass formers the ratio of the two similar elements often deviates from 1:1.Only if the parameters of chemical short-range order of Cu and Ni around P become closest to each other the best glass forming ability is reached.It is also illustrated that the calculated dynamic properties are very helpful to locate the composition of the best glass former.
