Three-dimensional thermal a nalysis simulation of a horizontal zone refining system is conducted for germanimn semiconductor materials. The considered geometry includes a g＇ral）hite boat filled with germanium placed...Three-dimensional thermal a nalysis simulation of a horizontal zone refining system is conducted for germanimn semiconductor materials. The considered geometry includes a g＇ral）hite boat filled with germanium placed in a cylindrical quartz tube. A flow of Ar and H2 gas mixture is purged througll the tube. A narrow section of the, boat is assmned to be exposed to a constant heat rate produced b v an rf coil located outside the quartz tube. The results of this analysis provide essential information about various parameters such as the shape of tile molten zone, required power and temperature gradient in the system.展开更多
Quantum optimal control(QOC)relies on accurately modeling system dynamics and is often challenged by unknown or inaccessible interactions in real systems.Taking an unknown collective spin system as an example,this wor...Quantum optimal control(QOC)relies on accurately modeling system dynamics and is often challenged by unknown or inaccessible interactions in real systems.Taking an unknown collective spin system as an example,this work introduces a machine-learning-based,data-driven scheme to overcome the challenges encountered,with a trained neural network(NN)assuming the role of a surrogate model that captures the system’s dynamics and subsequently enables QOC to be performed on the NN instead of on the real system.The trained NN surrogate proves effective for practical QOC tasks and is further demonstrated to be adaptable to different experimental conditions,remaining robust across varying system sizes and pulse durations.展开更多
By combining femtoscopic interferometry with an optical deblurring algorithm,we present a novel method to image the source in heavy-ion collisions(HICs),while simultaneously determining the interaction strength betwee...By combining femtoscopic interferometry with an optical deblurring algorithm,we present a novel method to image the source in heavy-ion collisions(HICs),while simultaneously determining the interaction strength between particle pairs.The spatial distribution of the emission source has been reconstructed for protons(p)and antiprotons(^(-)p)from the respective pp and^(-)p^(-)p correlation functions in Au+Au collisions at√S_(NN)=200 GeV.Within experimental uncertainties,protons and antiprotons share the same freeze-out distribution showing higher density in the center compared to the widely assumed Gaussian shape.The results evidence the matter–antimatter symmetry in coordinate space at the freeze-out moment before the nucleons are fully randomized in the collisions.展开更多
We present an assumed enhanced strain finite element framework for the simulation of tensile fracturing processes in transversely isotropic rocks.Fractures along the weak bedding planes and through the anisotropic roc...We present an assumed enhanced strain finite element framework for the simulation of tensile fracturing processes in transversely isotropic rocks.Fractures along the weak bedding planes and through the anisotropic rock matrix are treated with distinct enrichment,and a recently proposed dualmechanism tensile failure criterion for transversely isotropic rocks is adopted to determine crack initiation for the two failure modes.The cohesive crack model is adopted to characterize the response of embedded cracks.As for the numerical implementation of the proposed framework,both algorithms for the update of local history variables at Gauss points and of the global finite element system are derived.Four boundary-value problem simulations are carried out with the proposed framework,including uniaxial tension tests of Argillite,pre-notched square loaded in tension,three-point bending tests on Longmaxi shale,and simulations of tensile cracks induced by a strip load around a tunnel in transversely isotropic rocks.Simulation results reveal that the proposed framework can properly capture the tensile strength anisotropy and the anisotropic evolution of tensile cracks in transversely isotropic rocks.展开更多
This paper presents a finite element framework for imposing frictional contact conditions on embedded fracture faces,implemented by the constant-strain assumed enhanced strain(AES)method,where penalty method is used t...This paper presents a finite element framework for imposing frictional contact conditions on embedded fracture faces,implemented by the constant-strain assumed enhanced strain(AES)method,where penalty method is used to impose both non-penetration constraint and Coulomb’s law of friction.The proposed constant-strain AES method for modeling embedded frictional contact can be cast into an integration algorithm similar to those used in the classical plasticity theory,where displacement jump is calculated from the local traction equilibrium at Gauss point,so the method does not introduce any additional global degrees of freedom.Moreover,constant-strain elements are often desirable in practice because they can be easily created automatically for large-scale engineering applications with complicated geometries.As encountered in other enriched finite element methods for frictional contact,the problem of normal contact pressure oscillations is also observed in the constant-strain AES method.Therefore,we developed a strain-smoothing procedure to effectively mitigate the oscillations.We investigated and verified the proposed AES framework through several numerical examples,and illustrated the capability of this method in solving challenging nonlinear frictional contact problems.展开更多
The 2024 UN Climate Change Conference(COP29)will convene from 11 to 22 November in Baku,Azerbaijan.This year’s conference assumes special significance due to conflicts in some regions,geopolitical tensions and height...The 2024 UN Climate Change Conference(COP29)will convene from 11 to 22 November in Baku,Azerbaijan.This year’s conference assumes special significance due to conflicts in some regions,geopolitical tensions and heightened uncertainties in the world.World leaders are expected to report on the progress in implementing their climate commitments.展开更多
A fuzzy adaptive control method is proposed for a flexible robot manipulator. Due to the structure characteristics of the flexible manipulator, the vibration modes must be controlled to realize the high-precision tip ...A fuzzy adaptive control method is proposed for a flexible robot manipulator. Due to the structure characteristics of the flexible manipulator, the vibration modes must be controlled to realize the high-precision tip position. The Lagrangian principle is utilized to model the dynamic function of the single-degree flexible manipulator incorporating the assumed modes method. Simulation results of the fuzzy adaptive control method in the location control and the trajectory tracking with different tip disturbances are presented and compared with the results of the classic PD control. It shows that the controller can obtain the stable and robust performance.展开更多
Ⅰ.Each of the statements below is followed by four alternative answers.Choose the one that wouldbest complete the statement.1.Polysemy is a common feature peculiar to ___.A.English only B.Chinese only C.all natural l...Ⅰ.Each of the statements below is followed by four alternative answers.Choose the one that wouldbest complete the statement.1.Polysemy is a common feature peculiar to ___.A.English only B.Chinese only C.all natural languages D.some natural languages2.From the ____ point of view,polysemy is assumed to be the result of growth and development of thesemantic structure of one and same word.A.linguistic B.diachronic C.synchronic D.展开更多
A nonlinear dynamic model of a simple nonholonomic system comprising a self-rotating cantilever beam subjected to a unilateral locked or unlocked constraint is established by employing the general Hamilton＇s Variatio...A nonlinear dynamic model of a simple nonholonomic system comprising a self-rotating cantilever beam subjected to a unilateral locked or unlocked constraint is established by employing the general Hamilton＇s Variational Principle. The critical values, at which the trivial equilibrium loses its stability or the unilateral constraint is activated or a saddle-node bifurcation occurs, and the equilibria are investigated by approximately analytical and numerical methods. The results indicate that both the buckled equilibria and the bifurcation mode of the beam are different depending on whether the distance of the clearance of unilateral constraint equals zero or not and whether the unilateral constraint is locked or not. The unidirectional snap-through phenomenon （i.e. catastrophe phenomenon） is destined to occur in the system no matter whether the constraint is lockable or not. The saddle-node bifurcation can occur only on the condition that the unilateral constraint is lockable and its clearance is nonzero. The results obtained by two methods are consistent.展开更多
In the traditional method of earthquake loss estimation, all the social wealthes are classified according to their structural type and occupational use. Inventory data is collected and the total loss is estimated from...In the traditional method of earthquake loss estimation, all the social wealthes are classified according to their structural type and occupational use. Inventory data is collected and the total loss is estimated from each facility class separately. For many regions of the world, however, the vast amount of data required by this method is difficult or impossible to obtain. The traditional method is also unable to estimate quickly the loss from an unexpected disaster earthquake. It is difficult to give the necessary risk information to help the government to rescue and relief the earthquake disaster. This paper proposes a simple estimation method of earthquake loss based on macroscopic economical index of Gross Domestic Product (GDP) and population distribution data. A preliminary nonlinear relation among hazard loss, seismic intensity and social wealth was developed by means of some earthquake disaster records during 1980～1995. This method was applied to analyze several assumed earthquakes. The preliminary analysis results show that the new method is effective and reasonable for quick assessment of earthquake loss.展开更多
Two quite different Saha equations modified to a two-temperature plasma were proposed and employed in many literatures.In order to clear up this confusion phenomenon lasted for a few decades in the community of therma...Two quite different Saha equations modified to a two-temperature plasma were proposed and employed in many literatures.In order to clear up this confusion phenomenon lasted for a few decades in the community of thermal plasma science and technology,this paper re-examines the thermodynamic derivation of the two-temperature Saha equations.It is pointed out that the modified Saha equation deduced by using the minimum Gibbs or Helmholtz free energy is incorrect for the two-temperature plasma.Instead,a more rigorous derivation is presented here from the basic thermodynamic principle that the entropy in an isolated system always assumes its maximum value at chemical equilibrium.展开更多
Reactive oxygen species(ROS)and kynurenines:Kynurenines represent a relatively heterogenous group of tryptophan metabolites(Figure 1 A).The amino acid tryptophan is metabolized in the humans by the kynurenine or serot...Reactive oxygen species(ROS)and kynurenines:Kynurenines represent a relatively heterogenous group of tryptophan metabolites(Figure 1 A).The amino acid tryptophan is metabolized in the humans by the kynurenine or serotonin pathway.For a long time,the kynurenine pathway was assumed primarily to constitute the source for nicotinamide-adenine dinucleotide phosphate,one of the most utilized redox active enzyme cofactors.展开更多
Infertility is a major health issue,affecting approximately 15%of couples of child-bearing age.Although nearly half of idiopathic infertility cases are assumed to have a genetic basis,the underlying causes remain larg...Infertility is a major health issue,affecting approximately 15%of couples of child-bearing age.Although nearly half of idiopathic infertility cases are assumed to have a genetic basis,the underlying causes remain largely unknown in most infertile men.展开更多
This paper proposes a new access architecture onmobile cloud,which introduces a middle layer sitting between mobile devices and their cloud infrastructure.This middle layer is composed of cloudlets which are deployed ...This paper proposes a new access architecture onmobile cloud,which introduces a middle layer sitting between mobile devices and their cloud infrastructure.This middle layer is composed of cloudlets which are deployed by cloud services providers,such as wireless network access points(APs),to improve the performance of mobile cloud servicesand be different from traditional mobile operator mode.Then based on this new architecture.we improve our previous(Attribute-basedencryption) ABE access control scheme on cloud for mobile cloud,which is proposed to offload the main amount of computations to the cloudlet as the function of cloud.Simulationresults demonstratethe new access control scheme takes into consideration response time constraints and network statusof access task execution,while satisfying certain network security for mobile cloud.展开更多
Now,widely distributed modern cats are the descendant of wildcat(Felis silvestris lybica),which are assumed to have originally taken advantage of resources in human settlements,before being tamed in the Near East via ...Now,widely distributed modern cats are the descendant of wildcat(Felis silvestris lybica),which are assumed to have originally taken advantage of resources in human settlements,before being tamed in the Near East via a commensal pathway(Driscoll et al.,2007;Larson and Fuller,2014).展开更多
The formula construction of the unified model with the squirt and the Biot mechanism,i.e.the BISQ model[Geophysics 58(1993)524],is discussed.The inconsistent formula construction caused by the self-contradictions of k...The formula construction of the unified model with the squirt and the Biot mechanism,i.e.the BISQ model[Geophysics 58(1993)524],is discussed.The inconsistent formula construction caused by the self-contradictions of key assumptions is pointed out and demonstrated.Once the deformation of the solid skeleton is assumed to be in the uniaxial mode,the deformation of pore fluid is not able to be non-uniaxial at all,but must be uniaxial.Therefore,the expected results in the BISQ model's paper are doubtful and this model needs to be improved.A combination of the two mechanisms simultaneously in theory is significant and still needs more research.展开更多
We investigate the axisymmetric stagnation-point flow of a viscous fluid over a lubricated surface by imposing a generalized slip condition at the fluid-fluid interface.The power law non-Newtonian fluid is considered ...We investigate the axisymmetric stagnation-point flow of a viscous fluid over a lubricated surface by imposing a generalized slip condition at the fluid-fluid interface.The power law non-Newtonian fluid is considered as a lubricant.The lubrication layer is thin and assumed to have a variable thickness.The transformed nonlinear ordinary differential equation governing the flow is linearized using quasilinearization.The method of superposi-tion is adopted to convert the boundary value problem into an initial value problem and the solution is obtained numerically by using the fourth-order Runge-Kutta method.The results are discussed to see the influence of pertinent parameters.The limiting cases of Navier and no-slip boundary conditions are obtained as the special cases and found to be in excellent agreement with the existing results in the literature.展开更多
The objective of this investigation is to examine the correctness and efficiency of the choice of boundary conditions when using assumed mode approach to simulate flexible multi-body systems. The displacement field du...The objective of this investigation is to examine the correctness and efficiency of the choice of boundary conditions when using assumed mode approach to simulate flexible multi-body systems. The displacement field due to deformation is approximated by the Rayleigh-Ritz assumed modes in floating frame of reference （FFR） formulation. The deformations obtained by the absolute nodal coordinate （ANC） formulation which are transformed by two sets of reference coordinates are introduced as a criterion to verify the accuracy of the simulation results by using the FFR formulation. The relationship between the deformations obtained from different boundary conditions is revealed. Nu- merical simulation examples demonstrate that the assumed modes with cantilevered-free, simply-supported and free- free boundary conditions without inclusion of rigid body modes are suitable for simulation of flexible multi-body system with large over all motion, and the same physical deformation can be obtained using those mode functions, differ only by a coordinate transformation. It is also shown that when using mode shapes with statically indeterminate boundary conditions, significant error may occur. Furthermore, the slider crank mechanism with rigid crank is accurate enough for investigating boundary condition problem of flexible multi-body system, which cost significant less simulating time.展开更多
An analytical approach is used to construct the exact solution of the blast wave problem with generalized geometries in a non-ideal medium.It is assumed that the density ahead of the shock front varies according to a ...An analytical approach is used to construct the exact solution of the blast wave problem with generalized geometries in a non-ideal medium.It is assumed that the density ahead of the shock front varies according to a power of distance from the source of the blast wave.Also,an analytical expression for the total energy in a non-ideal medium is derived.展开更多
文摘Three-dimensional thermal a nalysis simulation of a horizontal zone refining system is conducted for germanimn semiconductor materials. The considered geometry includes a g＇ral）hite boat filled with germanium placed in a cylindrical quartz tube. A flow of Ar and H2 gas mixture is purged througll the tube. A narrow section of the, boat is assmned to be exposed to a constant heat rate produced b v an rf coil located outside the quartz tube. The results of this analysis provide essential information about various parameters such as the shape of tile molten zone, required power and temperature gradient in the system.
基金supported by the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302100)the National Natural Science Foundation of China(Grant Nos.12361131576,92265205,and 92476205).
文摘Quantum optimal control(QOC)relies on accurately modeling system dynamics and is often challenged by unknown or inaccessible interactions in real systems.Taking an unknown collective spin system as an example,this work introduces a machine-learning-based,data-driven scheme to overcome the challenges encountered,with a trained neural network(NN)assuming the role of a surrogate model that captures the system’s dynamics and subsequently enables QOC to be performed on the NN instead of on the real system.The trained NN surrogate proves effective for practical QOC tasks and is further demonstrated to be adaptable to different experimental conditions,remaining robust across varying system sizes and pulse durations.
基金supported by the National Natural Science Foundation of China(Grant Nos.12335008 and 12205160)the support of the Center for High Performance Computing and Initiative Scientific Research Program in Tsinghua University。
文摘By combining femtoscopic interferometry with an optical deblurring algorithm,we present a novel method to image the source in heavy-ion collisions(HICs),while simultaneously determining the interaction strength between particle pairs.The spatial distribution of the emission source has been reconstructed for protons(p)and antiprotons(^(-)p)from the respective pp and^(-)p^(-)p correlation functions in Au+Au collisions at√S_(NN)=200 GeV.Within experimental uncertainties,protons and antiprotons share the same freeze-out distribution showing higher density in the center compared to the widely assumed Gaussian shape.The results evidence the matter–antimatter symmetry in coordinate space at the freeze-out moment before the nucleons are fully randomized in the collisions.
基金supported by the National Natural Science Foundation of China(Grant Nos.52038005 and 52201326)the fellowship of China Postdoctoral Science Foundation(Grant No.2022M721883)Tsinghua University Initiative Scientific Research Program.
文摘We present an assumed enhanced strain finite element framework for the simulation of tensile fracturing processes in transversely isotropic rocks.Fractures along the weak bedding planes and through the anisotropic rock matrix are treated with distinct enrichment,and a recently proposed dualmechanism tensile failure criterion for transversely isotropic rocks is adopted to determine crack initiation for the two failure modes.The cohesive crack model is adopted to characterize the response of embedded cracks.As for the numerical implementation of the proposed framework,both algorithms for the update of local history variables at Gauss points and of the global finite element system are derived.Four boundary-value problem simulations are carried out with the proposed framework,including uniaxial tension tests of Argillite,pre-notched square loaded in tension,three-point bending tests on Longmaxi shale,and simulations of tensile cracks induced by a strip load around a tunnel in transversely isotropic rocks.Simulation results reveal that the proposed framework can properly capture the tensile strength anisotropy and the anisotropic evolution of tensile cracks in transversely isotropic rocks.
基金supported by the Fundamental Research Funds for the Central Universities (Grant No.2021FZZX001-14)and ZJU-ZCCC Institute of Collaborative Innovation (Grant No.ZDJG2021005).
文摘This paper presents a finite element framework for imposing frictional contact conditions on embedded fracture faces,implemented by the constant-strain assumed enhanced strain(AES)method,where penalty method is used to impose both non-penetration constraint and Coulomb’s law of friction.The proposed constant-strain AES method for modeling embedded frictional contact can be cast into an integration algorithm similar to those used in the classical plasticity theory,where displacement jump is calculated from the local traction equilibrium at Gauss point,so the method does not introduce any additional global degrees of freedom.Moreover,constant-strain elements are often desirable in practice because they can be easily created automatically for large-scale engineering applications with complicated geometries.As encountered in other enriched finite element methods for frictional contact,the problem of normal contact pressure oscillations is also observed in the constant-strain AES method.Therefore,we developed a strain-smoothing procedure to effectively mitigate the oscillations.We investigated and verified the proposed AES framework through several numerical examples,and illustrated the capability of this method in solving challenging nonlinear frictional contact problems.
文摘The 2024 UN Climate Change Conference(COP29)will convene from 11 to 22 November in Baku,Azerbaijan.This year’s conference assumes special significance due to conflicts in some regions,geopolitical tensions and heightened uncertainties in the world.World leaders are expected to report on the progress in implementing their climate commitments.
文摘A fuzzy adaptive control method is proposed for a flexible robot manipulator. Due to the structure characteristics of the flexible manipulator, the vibration modes must be controlled to realize the high-precision tip position. The Lagrangian principle is utilized to model the dynamic function of the single-degree flexible manipulator incorporating the assumed modes method. Simulation results of the fuzzy adaptive control method in the location control and the trajectory tracking with different tip disturbances are presented and compared with the results of the classic PD control. It shows that the controller can obtain the stable and robust performance.
文摘Ⅰ.Each of the statements below is followed by four alternative answers.Choose the one that wouldbest complete the statement.1.Polysemy is a common feature peculiar to ___.A.English only B.Chinese only C.all natural languages D.some natural languages2.From the ____ point of view,polysemy is assumed to be the result of growth and development of thesemantic structure of one and same word.A.linguistic B.diachronic C.synchronic D.
基金The project supported by the National Natural Science Foundation of China （10272002） and the Doctoral Program from the Ministry of Education of China （20020001032） The English text was polished by Yunming Chen.
文摘A nonlinear dynamic model of a simple nonholonomic system comprising a self-rotating cantilever beam subjected to a unilateral locked or unlocked constraint is established by employing the general Hamilton＇s Variational Principle. The critical values, at which the trivial equilibrium loses its stability or the unilateral constraint is activated or a saddle-node bifurcation occurs, and the equilibria are investigated by approximately analytical and numerical methods. The results indicate that both the buckled equilibria and the bifurcation mode of the beam are different depending on whether the distance of the clearance of unilateral constraint equals zero or not and whether the unilateral constraint is locked or not. The unidirectional snap-through phenomenon （i.e. catastrophe phenomenon） is destined to occur in the system no matter whether the constraint is lockable or not. The saddle-node bifurcation can occur only on the condition that the unilateral constraint is lockable and its clearance is nonzero. The results obtained by two methods are consistent.
文摘In the traditional method of earthquake loss estimation, all the social wealthes are classified according to their structural type and occupational use. Inventory data is collected and the total loss is estimated from each facility class separately. For many regions of the world, however, the vast amount of data required by this method is difficult or impossible to obtain. The traditional method is also unable to estimate quickly the loss from an unexpected disaster earthquake. It is difficult to give the necessary risk information to help the government to rescue and relief the earthquake disaster. This paper proposes a simple estimation method of earthquake loss based on macroscopic economical index of Gross Domestic Product (GDP) and population distribution data. A preliminary nonlinear relation among hazard loss, seismic intensity and social wealth was developed by means of some earthquake disaster records during 1980～1995. This method was applied to analyze several assumed earthquakes. The preliminary analysis results show that the new method is effective and reasonable for quick assessment of earthquake loss.
基金Supported by the National Natural Science Foundation of China under Grant Nos.59676011 and 59836220.
文摘Two quite different Saha equations modified to a two-temperature plasma were proposed and employed in many literatures.In order to clear up this confusion phenomenon lasted for a few decades in the community of thermal plasma science and technology,this paper re-examines the thermodynamic derivation of the two-temperature Saha equations.It is pointed out that the modified Saha equation deduced by using the minimum Gibbs or Helmholtz free energy is incorrect for the two-temperature plasma.Instead,a more rigorous derivation is presented here from the basic thermodynamic principle that the entropy in an isolated system always assumes its maximum value at chemical equilibrium.
基金funded by Austrian Science Fund(FWF),grant No.P 24630-B21(to VC)。
文摘Reactive oxygen species(ROS)and kynurenines:Kynurenines represent a relatively heterogenous group of tryptophan metabolites(Figure 1 A).The amino acid tryptophan is metabolized in the humans by the kynurenine or serotonin pathway.For a long time,the kynurenine pathway was assumed primarily to constitute the source for nicotinamide-adenine dinucleotide phosphate,one of the most utilized redox active enzyme cofactors.
基金supported by the Fundamental Research Funds for the Central Universities(WK2070080005)。
文摘Infertility is a major health issue,affecting approximately 15%of couples of child-bearing age.Although nearly half of idiopathic infertility cases are assumed to have a genetic basis,the underlying causes remain largely unknown in most infertile men.
基金supported by National Natural Science Foundation of China(No.U 1405254, 61472092)China Postdoctoral Science Foundation(No.2015M581101)National Science and Technology SupportingFoundation of China(No.2014BAH41B00)
文摘This paper proposes a new access architecture onmobile cloud,which introduces a middle layer sitting between mobile devices and their cloud infrastructure.This middle layer is composed of cloudlets which are deployed by cloud services providers,such as wireless network access points(APs),to improve the performance of mobile cloud servicesand be different from traditional mobile operator mode.Then based on this new architecture.we improve our previous(Attribute-basedencryption) ABE access control scheme on cloud for mobile cloud,which is proposed to offload the main amount of computations to the cloudlet as the function of cloud.Simulationresults demonstratethe new access control scheme takes into consideration response time constraints and network statusof access task execution,while satisfying certain network security for mobile cloud.
基金supported by the Chinese Academy of Sciences(CAS)and the Ministry of Finance of the People Republic of China(YSBR-019 and XDB26000000)the National Natural Science Foundation of China(41925009)+1 种基金the Howard Hughes Medical Institute(55008731)the Tencent Foundation(through the XPLORER PRIZE)。
文摘Now,widely distributed modern cats are the descendant of wildcat(Felis silvestris lybica),which are assumed to have originally taken advantage of resources in human settlements,before being tamed in the Near East via a commensal pathway(Driscoll et al.,2007;Larson and Fuller,2014).
基金Supported by the National Natural Science Foundation of China under Grant Nos 11134011 and 40974067State Key Laboratory of Acoustics(CAS)under Grant No SKLOA201108Scientific Forefront and Interdisciplinary Innovation Project of Jilin University.
文摘The formula construction of the unified model with the squirt and the Biot mechanism,i.e.the BISQ model[Geophysics 58(1993)524],is discussed.The inconsistent formula construction caused by the self-contradictions of key assumptions is pointed out and demonstrated.Once the deformation of the solid skeleton is assumed to be in the uniaxial mode,the deformation of pore fluid is not able to be non-uniaxial at all,but must be uniaxial.Therefore,the expected results in the BISQ model's paper are doubtful and this model needs to be improved.A combination of the two mechanisms simultaneously in theory is significant and still needs more research.
基金Supported by the Abdus Salam International Centre for Theoretical Physics,Trieste,Italy.
文摘We investigate the axisymmetric stagnation-point flow of a viscous fluid over a lubricated surface by imposing a generalized slip condition at the fluid-fluid interface.The power law non-Newtonian fluid is considered as a lubricant.The lubrication layer is thin and assumed to have a variable thickness.The transformed nonlinear ordinary differential equation governing the flow is linearized using quasilinearization.The method of superposi-tion is adopted to convert the boundary value problem into an initial value problem and the solution is obtained numerically by using the fourth-order Runge-Kutta method.The results are discussed to see the influence of pertinent parameters.The limiting cases of Navier and no-slip boundary conditions are obtained as the special cases and found to be in excellent agreement with the existing results in the literature.
基金supported by the National Natural Science Foundation of China (10872126)the Research Fund of the Doctoral Program of Higher Education of China (20100073110007)
文摘The objective of this investigation is to examine the correctness and efficiency of the choice of boundary conditions when using assumed mode approach to simulate flexible multi-body systems. The displacement field due to deformation is approximated by the Rayleigh-Ritz assumed modes in floating frame of reference （FFR） formulation. The deformations obtained by the absolute nodal coordinate （ANC） formulation which are transformed by two sets of reference coordinates are introduced as a criterion to verify the accuracy of the simulation results by using the FFR formulation. The relationship between the deformations obtained from different boundary conditions is revealed. Nu- merical simulation examples demonstrate that the assumed modes with cantilevered-free, simply-supported and free- free boundary conditions without inclusion of rigid body modes are suitable for simulation of flexible multi-body system with large over all motion, and the same physical deformation can be obtained using those mode functions, differ only by a coordinate transformation. It is also shown that when using mode shapes with statically indeterminate boundary conditions, significant error may occur. Furthermore, the slider crank mechanism with rigid crank is accurate enough for investigating boundary condition problem of flexible multi-body system, which cost significant less simulating time.
文摘An analytical approach is used to construct the exact solution of the blast wave problem with generalized geometries in a non-ideal medium.It is assumed that the density ahead of the shock front varies according to a power of distance from the source of the blast wave.Also,an analytical expression for the total energy in a non-ideal medium is derived.
