In this paper,an efficien formulation based on the Lagrangian method is presented to investigate the contact–impact problems of f exible multi-body systems.Generally,the penalty method and the Hertz contact law are t...In this paper,an efficien formulation based on the Lagrangian method is presented to investigate the contact–impact problems of f exible multi-body systems.Generally,the penalty method and the Hertz contact law are the most commonly used methods in engineering applications.However,these methods are highly dependent on various non-physical parameters,which have great effects on the simulation results.Moreover,a tremendous number of degrees of freedom in the contact–impact problems will influenc thenumericalefficien ysignificantl.Withtheconsideration of these two problems,a formulation combining the component mode synthesis method and the Lagrangian method is presented to investigate the contact–impact problems in fl xible multi-body system numerically.Meanwhile,the finit element meshing laws of the contact bodies will be studied preliminarily.A numerical example with experimental verificatio will certify the reliability of the presented formulationincontact–impactanalysis.Furthermore,aseries of numerical investigations explain how great the influenc of the finit element meshing has on the simulation results.Finally the limitations of the element size in different regions are summarized to satisfy both the accuracy and efficien y.展开更多
It is well documented that dietary restriction can prevent many different diseases and extend the life spans of different rodent species. In the previous study, we reported that intermittent fasting (IF) as well as mo...It is well documented that dietary restriction can prevent many different diseases and extend the life spans of different rodent species. In the previous study, we reported that intermittent fasting (IF) as well as moderate dietary restriction ameliorated the allergic dermatitis in ICR mice. In the present study, we demonstrated the ameliorative effects of IF on allergic dermatitis in NC/Nga mice, a strain known as a model for atopic dermatitis. Interestingly, the total number of CD4+CD8+ double positive thymocyte in mice after IF significantly decreased in comparison to that in mice fed ad libitum. Although it was reported that an immunosuppressive compound inhibited the contact allergic response by inducing the CD4+CD25+ regulatory T-cells, IF did not affect regulatory T cells in the present study. These results suggested that CD4+CD8+ double positive thymocytes play an important role in the regulation of allergy by IF in NC/Nga mice.展开更多
According to the character and the condition for shell deformation and force balance, we have set up the mathematical models of the contact angle and the contact pressure distribution between the tyre and the shell, s...According to the character and the condition for shell deformation and force balance, we have set up the mathematical models of the contact angle and the contact pressure distribution between the tyre and the shell, studied The features of a multi-body contact model between the roller and the tyre, and developed the build-up procedure of the contact finite element model between the roller and the tyre. The stress distribution rule of the roller and the tyre is obtained as follows. The contact center is the center of the contact stress circle, and the contact stress is also reduced gradually from the contact center to the contact boundary. The equivalent stress of the tyre varies 5 times per circle, thus making the trye fracture easily.展开更多
A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration character...A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration characteristics of the stator is not affected by the contact process. A modified friction models was used to analyze the contact problems. Firstly, the dynamic normal contact force, interface friction force, and steady-state characteristics were analyzed. Secondly, the influences of the contact layer material, the dynamic characteristics of the stator, and the pre-load on motor performance were simulated. Finally, to validate the contact model, a linear ultrasonic motor based on in-plane modes was used as an example. The corresponding results show that a set of simulation of motor performances based on the proposed contact mechanism is in good agreement with experimental results. This model is helpful to understanding the operation principle of the standing wave linear motor and thus contributes to the design of these types of motor.展开更多
Discontinuous deformation problems are common in rock engineering. Numerical analysis methods based on system models of the discrete body can better solve these problems. One of the most effective solutions is discont...Discontinuous deformation problems are common in rock engineering. Numerical analysis methods based on system models of the discrete body can better solve these problems. One of the most effective solutions is discontinuous deformation analysis （DDA） method, but the DDA method brings about rock embedding problems when it uses the strain assumption in elastic deformation and adopts virtual springs to simulate the contact problems. The multi-body finite element method （FEM） proposed in this paper can solve the problems of contact and deformation of blocks very well because it integrates the FEM and multi-body system dynamics theory. It is therefore a complete method for solving discontinuous deformation problems through balance equations of the contact surface and for simulating the displacement of whole blocks. In this study, this method was successfully used for deformation analysis of underground caverns in stratified rock. The simulation results indicate that the multi-body FEM can show contact forces and the stress states on contact surfaces better than DDA, and that the results calculated with the multi-body FEM are more consistent with engineering practice than those calculated with DDA method.展开更多
基金supported by the National Science Foundation of China (Grants 11132007,11272203)
文摘In this paper,an efficien formulation based on the Lagrangian method is presented to investigate the contact–impact problems of f exible multi-body systems.Generally,the penalty method and the Hertz contact law are the most commonly used methods in engineering applications.However,these methods are highly dependent on various non-physical parameters,which have great effects on the simulation results.Moreover,a tremendous number of degrees of freedom in the contact–impact problems will influenc thenumericalefficien ysignificantl.Withtheconsideration of these two problems,a formulation combining the component mode synthesis method and the Lagrangian method is presented to investigate the contact–impact problems in fl xible multi-body system numerically.Meanwhile,the finit element meshing laws of the contact bodies will be studied preliminarily.A numerical example with experimental verificatio will certify the reliability of the presented formulationincontact–impactanalysis.Furthermore,aseries of numerical investigations explain how great the influenc of the finit element meshing has on the simulation results.Finally the limitations of the element size in different regions are summarized to satisfy both the accuracy and efficien y.
文摘It is well documented that dietary restriction can prevent many different diseases and extend the life spans of different rodent species. In the previous study, we reported that intermittent fasting (IF) as well as moderate dietary restriction ameliorated the allergic dermatitis in ICR mice. In the present study, we demonstrated the ameliorative effects of IF on allergic dermatitis in NC/Nga mice, a strain known as a model for atopic dermatitis. Interestingly, the total number of CD4+CD8+ double positive thymocyte in mice after IF significantly decreased in comparison to that in mice fed ad libitum. Although it was reported that an immunosuppressive compound inhibited the contact allergic response by inducing the CD4+CD25+ regulatory T-cells, IF did not affect regulatory T cells in the present study. These results suggested that CD4+CD8+ double positive thymocytes play an important role in the regulation of allergy by IF in NC/Nga mice.
基金This workis supported by Science and Technology Planin Hunan Education Department Project No.(06C758)
文摘According to the character and the condition for shell deformation and force balance, we have set up the mathematical models of the contact angle and the contact pressure distribution between the tyre and the shell, studied The features of a multi-body contact model between the roller and the tyre, and developed the build-up procedure of the contact finite element model between the roller and the tyre. The stress distribution rule of the roller and the tyre is obtained as follows. The contact center is the center of the contact stress circle, and the contact stress is also reduced gradually from the contact center to the contact boundary. The equivalent stress of the tyre varies 5 times per circle, thus making the trye fracture easily.
基金Funded by the National Basic Research Program (973 program) (No. 2011CB707602)the Digital Manufacturing Equipment and Technology National Key Laboratory,Huazhong University of Science and Technology (No. DMETKF2009002)National Sciences Foundation-Guangdong Natural Science Foundation,China (No.U0934004)
文摘A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration characteristics of the stator is not affected by the contact process. A modified friction models was used to analyze the contact problems. Firstly, the dynamic normal contact force, interface friction force, and steady-state characteristics were analyzed. Secondly, the influences of the contact layer material, the dynamic characteristics of the stator, and the pre-load on motor performance were simulated. Finally, to validate the contact model, a linear ultrasonic motor based on in-plane modes was used as an example. The corresponding results show that a set of simulation of motor performances based on the proposed contact mechanism is in good agreement with experimental results. This model is helpful to understanding the operation principle of the standing wave linear motor and thus contributes to the design of these types of motor.
文摘Discontinuous deformation problems are common in rock engineering. Numerical analysis methods based on system models of the discrete body can better solve these problems. One of the most effective solutions is discontinuous deformation analysis （DDA） method, but the DDA method brings about rock embedding problems when it uses the strain assumption in elastic deformation and adopts virtual springs to simulate the contact problems. The multi-body finite element method （FEM） proposed in this paper can solve the problems of contact and deformation of blocks very well because it integrates the FEM and multi-body system dynamics theory. It is therefore a complete method for solving discontinuous deformation problems through balance equations of the contact surface and for simulating the displacement of whole blocks. In this study, this method was successfully used for deformation analysis of underground caverns in stratified rock. The simulation results indicate that the multi-body FEM can show contact forces and the stress states on contact surfaces better than DDA, and that the results calculated with the multi-body FEM are more consistent with engineering practice than those calculated with DDA method.
