NONLINEAR BAROTROPIC INSTABILITY INCLUDING FRICTION DISSIPATION, THERMAL DRIVING AND LARGE TOPOGRAPHY

From a nonlinear quasi-geostrophic barotropic vorticity equation including frictional dissipation, thermal driving and large topography used by Charney in investigation of the multiple flow equilibria and blocking, using the Serrin-Joseph energy method and the variational principle, we found the nonlinear barotropic stability criteria of the zonal basic flow with the total energy, total enstrophy and their linear combination respectively, and compared the criteria with Charney's results.

Influence of contact curvature on frictional energy dissipation under varying tangential loads

This study investigates the effect of contact surface curvatures on the friction response under varying tangential loadings using a finite element(FE)model.The results showed that the geometry of the surface influences the contact force at the interface and reduces the friction effect through an unsteady distribution of the contact force.The relationship between the friction effect,excitation,and contact surface shape was also examined,revealing a linear inverse relationship between the friction and curvature.The findings provide a comprehensive understanding of the frictional interactions between elastic bodies and highlight the role of curvature as a design parameter for regulating the friction effect.

Experimental study of friction dissipators for seismic protection of building structures

This paper presents the results from unidirectional shaking table tests of two reduced scale steel models of a building frame, with one and two floors, respectively. These frames incorporate friction dissipators at every floor. The inputs are sine-dwells and artificial and registered earthquakes. This study is part of a larger research project aiming to assess the seismic efficiency of friction dissipators by means of an integrated numerical and experimental approach. Inside this framework, the main objectives of these experiments are to： （i） collect a wide range of results to calibrate a numerical model derived within the project, （ii） clarify some of the most controversial issues about friction dissipators （including behavior for inputs containing pulses, capacity to reduce resonance peaks, introduction of high frequencies in the response, and self- generated eccentricities）, （iii） better understand their dynamic behavior, （iv） provide insight on the feasibility and reliability of using simple friction dissipators for seismic protection of building structures and （v） characterize the hysteretic behavior of these devices. Most of these objectives are satisfactorily reached and relevant conclusions are stated.

Energy corrugation in atomic-scale friction on graphite revisited by molecular dynamics simulations

Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite,the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics（MD） simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding（known as energy corrugation） comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces.For relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However,for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.

Research of a Response Precise Algorithm on a System with a Pseudo-viscous Frictional Energy Dissipator

The pseudo-viscous frictional energy dissipator（PVFED） is a new energy dissipator. This dissipator can be widely used in engineering for not only the friction is in direct ratio to velocity, but also the problem of viscous energy dissipator mucilage easily leaked has been overcome. The problem of how to get response of the PVFED sys- tem need to be solved before this dissipator can be used widely in engineering. The response calculation methods of the PVFED system on sina load was researched. Wilson-θ,Newmark-β and a precise integration algorithm was used separately to solve the system response and the calculation result in a different time step was compared. It was found from comparison that three calculation results were almost equivalent in a small time step. Calculation precision of Newmark-β and Wilson-θ was reduced and high calculation precision of a precise integration algorithm was kept in a large time step. The results show that it is an effective way to solve the response of a PVFED system by a precise integration method.

The mechanisms and applications of friction energy dissipation

About 30%of the world's primary energy consumption is in friction.The economic losses caused by friction energy dissipation and wear account for about 2%-7%of its gross domestic product(GDP)for different countries every year.The key to reducing energy consumption is to control the way of energy dissipation in the friction process.However,due to many various factors affecting friction and the lack of efficient detection methods,the energy dissipation mechanism in friction is still a challenging problem.Here,we firstly introduce the classical microscopic mechanism of friction energy dissipation,including phonon dissipation,electron dissipation,and non-contact friction energy dissipation.Then,we attempt to summarize the ultrafast friction energy dissipation and introduce the high-resolution friction energy dissipation detection system,since the origin of friction energy dissipation is essentially related to the ultrafast dynamics of excited electrons and phonons.Finally,the application of friction energy dissipation in representative high-end equipment is discussed,and the potential economic saving is predicted.

Prediction of electrical contact endurance subject to micro-slip wear using friction energy dissipation approach

Fretting wear is a common cause of failure of an electrical contact(EC). In this study, we analyzed in detail the failure of EC induced especially by sliding using the representative electrical terminals. Furthermore, combining the friction energy dissipation theory, we proposed a prediction model to evaluate the electrical connector endurance(ECE) based on the contact stress and geometrical changes during the wear process obtained from a numerical model. The study helps establish that the friction energy dissipation theory is a powerful tool to analyze a contact failure due to wear. The proposed model proves to be effective in predicting the ECE for all considered cases such as micro-slip amplitude, contact force, overturning angle, superficial layer thickness, and friction/wear coefficients.

Impact of Friction Stir Welding (FSW) Process Parameters on Thermal Modeling and Heat Generation of Aluminum Alloy Joints

Friction stir welding （FSW） is a solid-state joining process, where joint properties largely depend on the amount of heat generation during the welding process. The objective of this paper was to develop a numerical thermomechanical model for FSW of aluminum--copper alloy AA2219 and analyze heat generation during the welding process. The thermomechanical model has been developed utilizing ANSYS APDL. The model was verified by comparing simulated temperature profile of three different weld schedules （i.e., different combinations of weld parameters in real weld situations） from simulation with experimental results. Furthermore, the verified model was used to analyze the effect of different weld parameters on heat generation. Among all the weld parameters, the effect of rotational speed on heat generation is the highest.

STUDY OF THE NONLINEAR MECHANISM ABOUT THE FORMATION OF BLOCKING HIGH

In this paper,a nonlinear dynamical system considering the interactions among ultra-long wave,long wave and zonal flow in a baroelinic atmosphere was found.In this system,thermal forcing and frictional dissipation are regarded as the external parameters.The procedure,in which the maps of orbit in phase space,contour of stream function and section of Poincaré mapping are combined with each other,is used to determine the distributions of system states and circulation patterns and to draw the corresponding diagrams.The results show that by using the Galerkin method,there is no essential influence of the increasing of orders of truncated-spectrum in a certain range on the distributions of system states and circulation patterns,but it makes them somewhat complexities.By contrast,the changing of distribution of thermal forcing exerts a great influence on the system.Blocking high links closely with the oscillating of the atmospheric circulation and the meridional growing intensely,while the development of synoptic wave can promote the oscillating.