An efficient formulation based on the Lagrangian method for contact–impact analysis of flexible multi-body system

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.

Fuzzy sliding mode control guidance law with terminal impact angle and acceleration constraints

In this paper, a novel fuzzy sliding mode control（FSMC） guidance law with terminal constraints of miss distance, impact angle and acceleration is presented for a constant speed missile against the stationary or slowly moving target. The proposed guidance law combines the sliding mode control algorithm with a fuzzy logic control scheme for the lag-free system and the first-order lag system. Through using Lyapunov stability theory, we prove the sliding surface converges to zero in finite time. Furthermore, considering the uncertain information and system disturbances, the guidance gains are on-line optimized by fuzzy logic technique. Numerical simulations are performed to demonstrate the performance of the FSMC guidance law and the results illustrate the validity and effectiveness of the proposed guidance law.

Defect-free surface of quartz glass polished in elastic mode by chemical impact reaction

Removal of brittle materials in the brittle or ductile mode inevitably causes damaged or strained surface layers containing cracks, scratches or dislocations. Within elastic deformation, the arrangement of each atom can be recovered back to its original position without any defects introduced. Based on surface hydroxylation and chemisorption theory, material removal mechanism of quartz glass in the elastic mode is analyzed to obtain defect-free surface. Elastic contact condition between nanoparticle and quartz glass surface is confirmed from the Hertz contact theory model. Atoms on the quartz glass surface are removed by chemical bond generated by impact reaction in the elastic mode, so no defects are generated without mechanical process. Experiment was conducted on a numerically controlled system for nanoparticle jet polishing, and one flat quartz glass was polished in the elastic mode. Results show that scratches on the sample surface are completely removed away with no mechanical defects introduced, and microroughness(Ra) is decreased from 1.23 nm to 0.47 nm. Functional group Ce — O — Si on ceria nanoparticles after polishing was detected directly and indirectly by FTIR, XRD and XPS spectra analysis from which the chemical impact reaction is validated.

Geographical Impact and Ecological Restoration Modes of the Spatial Differentiation of Rural Social-Ecosystem Vulnerability:Evidence from Qingpu District in Shanghai

Vulnerability research is the core issue and one of the research hotspots of sustainable development science.Vulnerability and its evaluation framework provide a new perspective for rural social-ecosystem studies.This paper introduced the‘input-output’efficiency theory and constructed the‘SEE-PSR’framework for the analysis of social-ecosystem vulnerability in the rural area in Qingpu District of Shanghai City.The DEA models,spatial autocorrelation model,multivariate logistic regression model,geographical detector and hierarchical cluster model were used to analyze the spatial differences of social-ecosystem vulnerability,and its geographical impact mechanisms and ecological restorations,in 184 administrative villages in this area.The results can be divided into three main points.(1)The results of the‘input-output’efficiency model of the EW-DEA based on entropy weight aggregation crossover was more reliable and accurate for the evaluation of rural social-ecosystem vulnerability.The vulnerability of the social-ecosystems in the administrative villages showed a trend of gradual decline from east to west,with an average value of vulnerability of 0.583,and the vulnerability of social systems had become an important factor in constraining the decrease of the vulnerability of the social-ecosystems in the region.(2)The distances from the center of Shanghai City,from Dianshan Lake,from the center of Qingpu District and from the water area were the four dominant geographical factors affecting the vulnerability of the social-ecosystem in this region.The geographical impacts exhibited the spatial differentiations of systemic structure,the substitution of typological attributes and the transformation level.(3)The geographical factors coupling the impact types of the social-ecosystem vulnerability were divided spatially into 10 types.The geographic multi-factor coupling impact types were dominant,which presented multi-cyclic spatial patterns and were dominated by the central multi-factor which was surrounded by the single factor types on both sides.According to the different types,some feasible ways of ecological restoration were proposed,which drew on the experiences of integrated territory consolidation to remediate the vulnerability of rural social-ecological systems.The results of this study can provide scientific reference for rural spatial reconstruction,regional ecological restoration and sustainable development for the regions characterized by conflict in the‘strict protection of the ecological environment and vigorous development of the economy’.

Impact of nanoparticle-induced scattering of an azimuthally propagating mode on the resonance of whispering gallery microcavities

Optical whispering gallery microcavities with high-quality factors have shown great potential toward achieveing ultrahigh-sensitivity sensing up to a single molecule or nanoparticle, which raises a huge demand on a deep theoretical insight into the crucial phenomena such as the mode shift, mode splitting, and mode broadening in sensing experiments. Here we propose an intuitive model to analyze these phenomena from the viewpoint of the nanoparticle-induced multiple scattering of the azimuthally propagating mode(APM). The model unveils explicit relations between these phenomena and the phase change and energy loss of the APM when scattered at the nanoparticle; the model also explains the observed polarization-dependent preservation of one resonance and the particle-dependent redshift or blueshift. The model indicates that the particle-induced coupling between the pair of unperturbed degenerate whispering gallery modes(WGMs) and the coupling between the WGMs and the free-space radiation modes, which are widely adopted in current theoretical formalisms, are realized via the reflection and scattering-induced free-space radiation of the APM, respectively, and additionally exhibits the contribution of cross coupling between the unperturbed WGMs and other different WGMs to forming the splittingresonant modes, especially for large particles.

Impact of cavity symmetry on mode suppression and increase of free spectral range in solid-state dye microlaser

We describe modeling the solid-state dye laser with the microcavity size comparable to light wavelength. Certain symmetry in the allocation of gain material leads to depletion of odd longitudinal modes that, in turn, increases the tunability range of the microlaser. We provide simple physical explanation for the modeling results.

An erosion model for the discrete element method

A shear impact energy model （SIEM） of erosion suitable for both dilute and dense particle flows is pro- posed based on the shear impact energy of particles in discrete element method （DEM） simulations. A number of DEM simulations are performed to determine the relationship between the shear impact energy predicted by the DEM model and the theoretical erosion energy. Simulation results show that nearly one-quarter of the shear impact energy will be converted to erosion during an impingement. According to the ratio of the shear impact energy to the erosion energy, it is feasible to predict erosion from the shear impact energy, which can be accumulated at each time step for each impingement during the DEM simulation. The total erosion of the target surface can be obtained by summing the volume of material removed from each impingement. The proposed erosion model is validated against experiment and results show that the SIEM combined with DEM accurately predicts abrasive erosions.