A simple interface element for analyzing contact friction problems is developed. Taking nodal displacements and contact stresses as unknowns, this element can simulate frictional slippage, decoupling and re-bonding of...A simple interface element for analyzing contact friction problems is developed. Taking nodal displacements and contact stresses as unknowns, this element can simulate frictional slippage, decoupling and re-bonding of two bodies initially mating or having gaps at a common interface. The method is based on the Finite Element Method and load incremental theory. The geometric and static constraint conditions on contact surfaces are treated as additional conditions and are included in stiffness equations. This simple element has the advantages of easy implementation into standard finite element programs and fast speed for convergence as well as high accuracy for stress distribution in interface. Undesirable stress oscillations are also investigated whenever large stress gradients exist over the contact surfaces. Exact integration or the conventional Gauss integration scheme used to evaluate the interpolation function matrix of the interface element is found to be the source of the oscillations. Eigenmode analysis demonstrates that the stress behavior of an interface element can be improved by using the Newton-Cotes integration scheme. Finally, the test example of a strip footing problem is presented.展开更多
In the steady operation condition, the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rot...In the steady operation condition, the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rotors, including the radial rotor, the forward-skewed rotor and the back- ward-skewed rotor. The three-dimensional viscous flow fields of the fans are computed. In the experiments, the two-dimensional plane particle image velocimetry （PIV） system is used to measure the flow fields in the tip region of three different pitchwise positions of each fan. The results show that the computational results agree well with the experimental data in the flow field of the tip region of each fan. The tip leakage vortex core segments based on method of the eigenmode analysis can display clearly some characteristics of the tip leakage vortex, such as the origination position of tip leak- age vortex, the development of vortex strength, and so on. Compared with the radial rotor, the other two skewed rotors can increase the stability of the tip leakage vortex and the increment in the forward-skewed rotor is more than that in the backward-skewed one. Among the tip leakage vortices of the three rotors, the velocity of the vortex in the forward-skewed rotor is th6 highest in the circumferential direction and the lowest in the axial direction.展开更多
In recent years,exploring the physical mechanisms of brain functions has been a hot topic in the fields of nonlinear dynamics and complex networks,and many important achievements have been made,mainly based on the cha...In recent years,exploring the physical mechanisms of brain functions has been a hot topic in the fields of nonlinear dynamics and complex networks,and many important achievements have been made,mainly based on the characteristic features of time series of human brain.To speed up the further study of this problem,herein we make a brief review on these important achievements,which includes the aspects of explaining:(i)the mechanism of brain rhythms by network synchronization,(ii)the mechanism of unihemispheric sleep by chimera states,(iii)the fundamental difference between the structural and functional brain networks by remote synchronization,(iv)the mechanism of stronger detection ability of human brain to weak signals by remote firing propagation,and(v)the mechanism of dementia patterns by eigen-microstate analysis.As a brief review,we will mainly focus on the aspects of basic ideas,research histories,and key results but ignore the tedious mathematical derivations.Moreover,some outlooks will be discussed for future studies.展开更多
The twin-barge float-over technique,incorporating a dynamic positioning(DP)system,has been increas-ingly utilized to enhance the installation capacity and efficiency of offshore platforms.But the DP system is not full...The twin-barge float-over technique,incorporating a dynamic positioning(DP)system,has been increas-ingly utilized to enhance the installation capacity and efficiency of offshore platforms.But the DP system is not fully considered during the design stage at present.This study investigates the dynamic responses of a twin-barge float-over system integrating flexible connections and DP system.A numerical model is developed and combined with model-scale experiments to analyze the characteristics of the system.The findings reveal the significant influence of the DP system on the coupled system,leading to harsh oscil-lations in the roll and heave directions.To effectively address this oscillation,a method with eigenmodes analysis and filter adjusting is proposed.The robustness of this method is verified through sensitivity analysis,and further investigation is conducted to analyze the motion response characteristics of the coupled system under varying environmental conditions.The findings and the proposed method in this paper are also applicable to various multi-vessel cooperative transportation scenarios.展开更多
文摘A simple interface element for analyzing contact friction problems is developed. Taking nodal displacements and contact stresses as unknowns, this element can simulate frictional slippage, decoupling and re-bonding of two bodies initially mating or having gaps at a common interface. The method is based on the Finite Element Method and load incremental theory. The geometric and static constraint conditions on contact surfaces are treated as additional conditions and are included in stiffness equations. This simple element has the advantages of easy implementation into standard finite element programs and fast speed for convergence as well as high accuracy for stress distribution in interface. Undesirable stress oscillations are also investigated whenever large stress gradients exist over the contact surfaces. Exact integration or the conventional Gauss integration scheme used to evaluate the interpolation function matrix of the interface element is found to be the source of the oscillations. Eigenmode analysis demonstrates that the stress behavior of an interface element can be improved by using the Newton-Cotes integration scheme. Finally, the test example of a strip footing problem is presented.
基金This project is supported by National Natural Science Foundation of China (No. 50406017).
文摘In the steady operation condition, the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rotors, including the radial rotor, the forward-skewed rotor and the back- ward-skewed rotor. The three-dimensional viscous flow fields of the fans are computed. In the experiments, the two-dimensional plane particle image velocimetry （PIV） system is used to measure the flow fields in the tip region of three different pitchwise positions of each fan. The results show that the computational results agree well with the experimental data in the flow field of the tip region of each fan. The tip leakage vortex core segments based on method of the eigenmode analysis can display clearly some characteristics of the tip leakage vortex, such as the origination position of tip leak- age vortex, the development of vortex strength, and so on. Compared with the radial rotor, the other two skewed rotors can increase the stability of the tip leakage vortex and the increment in the forward-skewed rotor is more than that in the backward-skewed one. Among the tip leakage vortices of the three rotors, the velocity of the vortex in the forward-skewed rotor is th6 highest in the circumferential direction and the lowest in the axial direction.
基金National Natural Science Foundation of China,Grant/Award Numbers:11835003,12175070STI2030-Major Projects,Grant/Award Number:2021ZD0202600。
文摘In recent years,exploring the physical mechanisms of brain functions has been a hot topic in the fields of nonlinear dynamics and complex networks,and many important achievements have been made,mainly based on the characteristic features of time series of human brain.To speed up the further study of this problem,herein we make a brief review on these important achievements,which includes the aspects of explaining:(i)the mechanism of brain rhythms by network synchronization,(ii)the mechanism of unihemispheric sleep by chimera states,(iii)the fundamental difference between the structural and functional brain networks by remote synchronization,(iv)the mechanism of stronger detection ability of human brain to weak signals by remote firing propagation,and(v)the mechanism of dementia patterns by eigen-microstate analysis.As a brief review,we will mainly focus on the aspects of basic ideas,research histories,and key results but ignore the tedious mathematical derivations.Moreover,some outlooks will be discussed for future studies.
基金supported by the National Natural Science Foun-dation of China(Grant nos.U20A20328,42206228)to which the authors are most grateful.
文摘The twin-barge float-over technique,incorporating a dynamic positioning(DP)system,has been increas-ingly utilized to enhance the installation capacity and efficiency of offshore platforms.But the DP system is not fully considered during the design stage at present.This study investigates the dynamic responses of a twin-barge float-over system integrating flexible connections and DP system.A numerical model is developed and combined with model-scale experiments to analyze the characteristics of the system.The findings reveal the significant influence of the DP system on the coupled system,leading to harsh oscil-lations in the roll and heave directions.To effectively address this oscillation,a method with eigenmodes analysis and filter adjusting is proposed.The robustness of this method is verified through sensitivity analysis,and further investigation is conducted to analyze the motion response characteristics of the coupled system under varying environmental conditions.The findings and the proposed method in this paper are also applicable to various multi-vessel cooperative transportation scenarios.
