In this paper, a gradient method with momentum for sigma-pi-sigma neural networks (SPSNN) is considered in order to accelerate the convergence of the learning procedure for the network weights. The momentum coefficien...In this paper, a gradient method with momentum for sigma-pi-sigma neural networks (SPSNN) is considered in order to accelerate the convergence of the learning procedure for the network weights. The momentum coefficient is chosen in an adaptive manner, and the corresponding weak convergence and strong convergence results are proved.展开更多
This paper presents an efficient and versatile OpenFOAM(Open-source Field Operation And Manipulation)-based numerical solver for fully resolved simulations that can handle any rigid and deforming bodies moving in the ...This paper presents an efficient and versatile OpenFOAM(Open-source Field Operation And Manipulation)-based numerical solver for fully resolved simulations that can handle any rigid and deforming bodies moving in the fluid.The algorithm used for solving Fluid-Structure Interactions(FSI)involving the immersed structure with changeable shapes is based on the momentum redistribution method.The present approach excludes the need to solve elastic equations,obtain high-accuracy predictions of the flow field and provide a rigorous basis for implementing the Immersed Boundary Method(IBM).The OpenFOAM implementation of the algorithm is discussed along with the design methodology for developing bio-inspired underwater vehicles using the present solver.The computational results are validated with the experimental observations of the two-dimensional and three-dimensional anguilliform swimmer case studies.The study further extended to the three-dimensional hydrodynamics of a bioinspired,self-propelling manta bot.The motion of the body is specified a priori according to the reported experimental observations.The results quantify the vortex formation and shedding processes and enable the identification of the portions of the body responsible for the majority of thrust.The body accelerates from rest to an asymptotic mean forward velocity of 0.2 ms^(-1)in almost 5 s,consistent with experimental observations.It is observed that the developed computational model is capable of performing any motion simulation and manoeuvrability analysis,which are critical for the designers to develop novel unmanned underwater vehicles.展开更多
The impact dynamics of a flexible multibody system is investigated. By using a partition method, the system is divided into two parts, the local impact region and the region away from the impact. The two parts are con...The impact dynamics of a flexible multibody system is investigated. By using a partition method, the system is divided into two parts, the local impact region and the region away from the impact. The two parts are connected by specific boundary conditions, and the system after partition is equivalent to the original system. According to the rigid-flexible coupling dynamic theory of multibody system, system＇s rigid-flexible coupling dynamic equations without impact are derived. A local impulse method for establishing the initial impact conditions is proposed. It satisfies the compatibility con- ditions for contact constraints and the actual physical situation of the impact process of flexible bodies. Based on the contact constraint method, system＇s impact dynamic equa- tions are derived in a differential-algebraic form. The contact/separation criterion and the algorithm are given. An impact dynamic simulation is given. The results show that system＇s dynamic behaviors including the energy, the deformations, the displacements, and the impact force during the impact process change dramatically. The impact makes great effects on the global dynamics of the system during and after impact.展开更多
Rockfalls in reservoirs are prone to induce surges, posing a severe threat to passing vessels and facilities. A scheme combined Single-phase freesurface method(SPF), momentum exchange method(MEM), and Lattice Boltzman...Rockfalls in reservoirs are prone to induce surges, posing a severe threat to passing vessels and facilities. A scheme combined Single-phase freesurface method(SPF), momentum exchange method(MEM), and Lattice Boltzmann method(LBM) is proposed to predict the impact of rockfall-induced surges. First, the LBM-SPF model is used to simulate the motion of the free surface, and the MEM model is used to calculate the hydrodynamic force acting on rock mass. To address the incompatibility issue arising from the coupling of LBM-SPF model and MEM model, a correction scheme inside the solid is induced. The simulation results of the single particle and double particle sedimentation in cavity show the feasibility and accuracy of the method designed in this paper. Moreover, the validation experiments of Scott Russel’s wave generator show that the proposed scheme can simulate wave profile stably. The simulation results emphasize that the waves induced by rockfalls have a significant impact on the safe operation of the Laxiwa dam and the passing vessels in the reservoir.展开更多
In this study,single-particle energy was examined using the finite difference method by taking 208Pb as an example.If the first derivative term in the spherical Dirac equation is discretized using a three-point formul...In this study,single-particle energy was examined using the finite difference method by taking 208Pb as an example.If the first derivative term in the spherical Dirac equation is discretized using a three-point formula,a one-to-one correspondence occurs between the physical and spurious states.Although these energies are exactly the same,the wave functions of the spurious states exhibit a much faster staggering than those of the physical states.Such spurious states can be eliminated when applying the finite difference method by introducing an extra Wilson term into the Hamiltonian.Furthermore,it was also found that the number of spurious states can be reduced if we improve the accuracy of the numerical differential formula.The Dirac equation is then solved in a momentum space in which there is no differential operator,and we found that the spurious states can be completely avoided in the momentum space,even without an extra Wilson term.展开更多
The motivation of this work is to investigate a grooved surface's drag reduction. The viscous flow through a two-dimensional microchannel with the grooved surface is analyzed by the lattice Boltzmann method(LBM). ...The motivation of this work is to investigate a grooved surface's drag reduction. The viscous flow through a two-dimensional microchannel with the grooved surface is analyzed by the lattice Boltzmann method(LBM). The effects of the grooved surface on the streamline patterns, the velocity distributions near wall region and the fluid shear stress distributions on the walls at different Reynolds numbers are studied. In addition, the influences of the groove's geometrical parameters on the grooved surface's drag reduction are discussed. The numerical results confirm the grooved surface's drag reduction and present the drag reduction law of the grooved surface.展开更多
The present work concerns the momentum and heat transmission of the electro-magnetohydrodynamic (E-MHD) boundary layer Darcy-Forchheimer flow of a Sutterby fluid over a linear stretching sheet with slip. The nonlinear...The present work concerns the momentum and heat transmission of the electro-magnetohydrodynamic (E-MHD) boundary layer Darcy-Forchheimer flow of a Sutterby fluid over a linear stretching sheet with slip. The nonlinear equations for the proposed model are analyzed numerically. Suitable techniques are used to transform the coupled nonlinear partial differential equations (PDEs) conforming to the forced balance law, energy, and concentration equations into a nonlinear coupled system of ordinary differential equations (ODEs). Numerical solutions of the transformed nonlinear system are obtained using a shooting method, improved by the Cash and Carp coefficients. The influence of important physical variables on the velocity, the temperature, the heat flux coefficient, and the skin-friction coefficient is verified and analyzed through graphs and tables. From the comprehensive analysis of the present work, it is concluded that by intensifying the magnitude of the Hartmann number, the momentum distribution decays, whereas the thermal profile of fluid increases. Furthermore, it is also shown that by aug- menting the values of the momentum slip parameter, the velocity profile diminishes. It is found that the Sutterby fluid model shows shear thickening and shear thinning behaviors. The momentum profile shows that the magnitude of velocity for the shear thickening case is dominant as compared with the shear thinning case. It is also demonstrated that the Sutterby fluid model reduces to a Newtonian model by fixing the fluid parameter to zero. In view of the limiting case, it is established that the surface drag in the case of the Sutterby model shows a trifling pattern as compared with the classical case.展开更多
In this paper, we report the ground state properties i.e. electron momentum density and X-ray structure factors of fcc-copper are presented. The Am241 Compton spectrometer, which uses 59.54 keV gamma-rays, has been us...In this paper, we report the ground state properties i.e. electron momentum density and X-ray structure factors of fcc-copper are presented. The Am241 Compton spectrometer, which uses 59.54 keV gamma-rays, has been used for the Compton profile measurement. To compare the experimental data, the Compton profiles within the framework of linear combination of atomic orbitals (LCAO) method using Hartree–Fock (HF), density functional (DF) and hybrid B3PW schemes embodied in the CRYSTAL06 code have been computed. Among the various theoretical calculations, it is found that the present experimental data is in very good agreement with the hybrid B3PW scheme. A real-space analysis of the experimental Compton profile shows the metal-like behavior of copper The structure factors for copper are computed using hybrid B3PW scheme and compared with available experimental and theoretical data.展开更多
The common defects of the Roe scheme are the non-physical expansion shock and shock instability. By removing the momentum interpolation mechanism(MIM), an improved method with several advantages has been presented to ...The common defects of the Roe scheme are the non-physical expansion shock and shock instability. By removing the momentum interpolation mechanism(MIM), an improved method with several advantages has been presented to suppress the shock instability. However, it cannot prevent the expansion shock and is incompatible with the traditional curing method for expansion shock. To solve the problem, the traditional curing mechanism is analyzed. Effectiveness of the traditional curing method is discussed,and several defects are identified, one of which leads to incompatibility between curing shock instability and expansion shock. Consequently, an improved Roe scheme is proposed, which is with low computational costs, concise, easy to implement, and robust.More importantly, the proposed scheme can simultaneously solve the problem of shock instability and expansion shock without additional costs.展开更多
文摘In this paper, a gradient method with momentum for sigma-pi-sigma neural networks (SPSNN) is considered in order to accelerate the convergence of the learning procedure for the network weights. The momentum coefficient is chosen in an adaptive manner, and the corresponding weak convergence and strong convergence results are proved.
基金the funding received from Naval Research Board,Marine System Panel to carry out this research work at Shiv Nadar University.Award Number:NRB/4003/PG/400,Recipient:Dr.Santanu Mitra,Ph.D.,Assoc.Professor,Mechanical Engineering Department,Shiv Nadar University.
文摘This paper presents an efficient and versatile OpenFOAM(Open-source Field Operation And Manipulation)-based numerical solver for fully resolved simulations that can handle any rigid and deforming bodies moving in the fluid.The algorithm used for solving Fluid-Structure Interactions(FSI)involving the immersed structure with changeable shapes is based on the momentum redistribution method.The present approach excludes the need to solve elastic equations,obtain high-accuracy predictions of the flow field and provide a rigorous basis for implementing the Immersed Boundary Method(IBM).The OpenFOAM implementation of the algorithm is discussed along with the design methodology for developing bio-inspired underwater vehicles using the present solver.The computational results are validated with the experimental observations of the two-dimensional and three-dimensional anguilliform swimmer case studies.The study further extended to the three-dimensional hydrodynamics of a bioinspired,self-propelling manta bot.The motion of the body is specified a priori according to the reported experimental observations.The results quantify the vortex formation and shedding processes and enable the identification of the portions of the body responsible for the majority of thrust.The body accelerates from rest to an asymptotic mean forward velocity of 0.2 ms^(-1)in almost 5 s,consistent with experimental observations.It is observed that the developed computational model is capable of performing any motion simulation and manoeuvrability analysis,which are critical for the designers to develop novel unmanned underwater vehicles.
基金supported by the National Natural Science Foundation of China(Nos.11132007,11272155,and 10772085)the Fundamental Research Funds for the Central Universities(No.30920130112009)the 333 Project of Jiangsu Province of China(No.BRA2011172)
文摘The impact dynamics of a flexible multibody system is investigated. By using a partition method, the system is divided into two parts, the local impact region and the region away from the impact. The two parts are connected by specific boundary conditions, and the system after partition is equivalent to the original system. According to the rigid-flexible coupling dynamic theory of multibody system, system＇s rigid-flexible coupling dynamic equations without impact are derived. A local impulse method for establishing the initial impact conditions is proposed. It satisfies the compatibility con- ditions for contact constraints and the actual physical situation of the impact process of flexible bodies. Based on the contact constraint method, system＇s impact dynamic equa- tions are derived in a differential-algebraic form. The contact/separation criterion and the algorithm are given. An impact dynamic simulation is given. The results show that system＇s dynamic behaviors including the energy, the deformations, the displacements, and the impact force during the impact process change dramatically. The impact makes great effects on the global dynamics of the system during and after impact.
基金supported by the National Natural Science Foundation of China (Nos.41902290,42007276,41972297)Program of Hundred Promising Innovative Talents in Hebei provincial education office (No.SLRC2019027)Natural Science Foundation of Hebei Province (Nos.D2020202002,D2021202001)。
文摘Rockfalls in reservoirs are prone to induce surges, posing a severe threat to passing vessels and facilities. A scheme combined Single-phase freesurface method(SPF), momentum exchange method(MEM), and Lattice Boltzmann method(LBM) is proposed to predict the impact of rockfall-induced surges. First, the LBM-SPF model is used to simulate the motion of the free surface, and the MEM model is used to calculate the hydrodynamic force acting on rock mass. To address the incompatibility issue arising from the coupling of LBM-SPF model and MEM model, a correction scheme inside the solid is induced. The simulation results of the single particle and double particle sedimentation in cavity show the feasibility and accuracy of the method designed in this paper. Moreover, the validation experiments of Scott Russel’s wave generator show that the proposed scheme can simulate wave profile stably. The simulation results emphasize that the waves induced by rockfalls have a significant impact on the safe operation of the Laxiwa dam and the passing vessels in the reservoir.
基金partly supported by the National Natural Science Foundation of China(No.11875070)the Natural Science Foundation of Anhui Province(No.1908085MA16)
文摘In this study,single-particle energy was examined using the finite difference method by taking 208Pb as an example.If the first derivative term in the spherical Dirac equation is discretized using a three-point formula,a one-to-one correspondence occurs between the physical and spurious states.Although these energies are exactly the same,the wave functions of the spurious states exhibit a much faster staggering than those of the physical states.Such spurious states can be eliminated when applying the finite difference method by introducing an extra Wilson term into the Hamiltonian.Furthermore,it was also found that the number of spurious states can be reduced if we improve the accuracy of the numerical differential formula.The Dirac equation is then solved in a momentum space in which there is no differential operator,and we found that the spurious states can be completely avoided in the momentum space,even without an extra Wilson term.
基金the National Natural Science Foundation of China(Nos.11502210 and 51279165)
文摘The motivation of this work is to investigate a grooved surface's drag reduction. The viscous flow through a two-dimensional microchannel with the grooved surface is analyzed by the lattice Boltzmann method(LBM). The effects of the grooved surface on the streamline patterns, the velocity distributions near wall region and the fluid shear stress distributions on the walls at different Reynolds numbers are studied. In addition, the influences of the groove's geometrical parameters on the grooved surface's drag reduction are discussed. The numerical results confirm the grooved surface's drag reduction and present the drag reduction law of the grooved surface.
文摘The present work concerns the momentum and heat transmission of the electro-magnetohydrodynamic (E-MHD) boundary layer Darcy-Forchheimer flow of a Sutterby fluid over a linear stretching sheet with slip. The nonlinear equations for the proposed model are analyzed numerically. Suitable techniques are used to transform the coupled nonlinear partial differential equations (PDEs) conforming to the forced balance law, energy, and concentration equations into a nonlinear coupled system of ordinary differential equations (ODEs). Numerical solutions of the transformed nonlinear system are obtained using a shooting method, improved by the Cash and Carp coefficients. The influence of important physical variables on the velocity, the temperature, the heat flux coefficient, and the skin-friction coefficient is verified and analyzed through graphs and tables. From the comprehensive analysis of the present work, it is concluded that by intensifying the magnitude of the Hartmann number, the momentum distribution decays, whereas the thermal profile of fluid increases. Furthermore, it is also shown that by aug- menting the values of the momentum slip parameter, the velocity profile diminishes. It is found that the Sutterby fluid model shows shear thickening and shear thinning behaviors. The momentum profile shows that the magnitude of velocity for the shear thickening case is dominant as compared with the shear thinning case. It is also demonstrated that the Sutterby fluid model reduces to a Newtonian model by fixing the fluid parameter to zero. In view of the limiting case, it is established that the surface drag in the case of the Sutterby model shows a trifling pattern as compared with the classical case.
文摘In this paper, we report the ground state properties i.e. electron momentum density and X-ray structure factors of fcc-copper are presented. The Am241 Compton spectrometer, which uses 59.54 keV gamma-rays, has been used for the Compton profile measurement. To compare the experimental data, the Compton profiles within the framework of linear combination of atomic orbitals (LCAO) method using Hartree–Fock (HF), density functional (DF) and hybrid B3PW schemes embodied in the CRYSTAL06 code have been computed. Among the various theoretical calculations, it is found that the present experimental data is in very good agreement with the hybrid B3PW scheme. A real-space analysis of the experimental Compton profile shows the metal-like behavior of copper The structure factors for copper are computed using hybrid B3PW scheme and compared with available experimental and theoretical data.
基金Project supported by the National Natural Science Foundation of China(Nos.51736008 and 51276092)
文摘The common defects of the Roe scheme are the non-physical expansion shock and shock instability. By removing the momentum interpolation mechanism(MIM), an improved method with several advantages has been presented to suppress the shock instability. However, it cannot prevent the expansion shock and is incompatible with the traditional curing method for expansion shock. To solve the problem, the traditional curing mechanism is analyzed. Effectiveness of the traditional curing method is discussed,and several defects are identified, one of which leads to incompatibility between curing shock instability and expansion shock. Consequently, an improved Roe scheme is proposed, which is with low computational costs, concise, easy to implement, and robust.More importantly, the proposed scheme can simultaneously solve the problem of shock instability and expansion shock without additional costs.
