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71.
关于第14届材料磨损国际会议的简要评述 总被引:2,自引:2,他引:2
对第14届材料磨损会议重点涉及的生物摩擦学、金属磨损、表面涂层、冲蚀、纳米摩擦学、复合材料以及磨损监测等研究领域的最新进展进行了评述,对摩擦学领域今后的研究重点进行了展望. 相似文献
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一种摩擦学状态在线监测系统的研究 总被引:2,自引:5,他引:2
研制了一种用于船用柴油机的摩擦学状态在线监测系统。它集磨粒监测,润滑油质量监测,柴油机扭矩及时转速监测于一体,利用在线铁谱技术监测润滑油中的铁磁性磨粒,利用容栅型电容传感器在线监测污染物引起的润滑油介电常数的变化,利用光电传感器和随轴转动齿盘产生的脉冲及相位差在线测量柴油机输出轴的扭矩及瞬时转速。此外,该监测系统还可将柴油机的磨损状态与动力状态相关联,监测由于各缸爆排压力变化造成的瞬时转速变化,从 相似文献
75.
Abstract. Active control of oscillations of a suspended cable under transversal wind, described by a constant term and a fluctuating turbulent component, is dealt with. Control of transversal in-plane and out-of-plane oscillations is performed by imposing a longitudinal motion to one support; the control law depends, linearly or quadratically, on measures of displacement and velocity of a selected point. First, the steady-state oscillations around the planar static configuration, determined by the wind constant component, under sinusoidal in-plane and out-of-plane loading are studied, showing the nonlinear behaviour in the regions of primary and parametric resonance and the effects of the control action. Afterwards, attention is focused on the response of the cable to transversal wind turbulence, whose fluctuating component is described by a random process with an assigned spectral density. The effectiveness of longitudinal control is analysed by means of numerical investigations.Sommario. Si analizza il controllo attivo delle oscillazioni di un cavo sospeso, sottoposto all'azione di un vento agente in direzione ortogonale al piano del cavo e descritto mediante un termine di carico costante ed una componente variabile di turbolenza. Il controllo delle oscillazioni piane e spaziali viene realizzato mediante spostamento longitudinale di uno degli appoggi; la legge di controllo dipende linearmente o quadraticamente da misure di spostamento e velocità di un punto prescelto. In una prima fase, vengono studiate le oscillazioni stazionarie sotto carichi sinusoidali agenti rispettivamente nel piano e fuori del piano del cavo, intorno alla configurazione di equilibrio statico determinata dalla presenza della componente costante del vento, mostrando il comportamento nonlineare nelle regioni di risonanza primaria e parametrica e gli effetti dell'azione di controllo. Successivamente, si focalizza l'attenzione sulla risposta del cavo alla componente trasversale di turbolenza del vento, la quale è descritta da un processo stocastico a media nulla con densità spettrale assegnata. L'efficacia del controllo viene analizzata attraverso un'indagine numerica. 相似文献
76.
A framework for the numerical analysis of bridges under wind excitation is outlined. It is based on structural finite element
scheme and cross-sectional wind load models. Two aspects are investigated: (1) how considering the mean steady configuration
in the aerodynamic stability calculation; and (2) the effects of load nonlinearities on structural response. A quasi-steady
load model is adopted, which is able to deal with the considered problems by using experimental data easily available in the
practice. By means of numerical examples, it is pointed out (1) that both the modifications in structural tangential stiffness
and in the aerodynamic coefficients due to the mean steady deformation may affect the aeroelastic stability threshold and
(2) that load linearization may produce an underestimation of the structural response. 相似文献
77.
Alan B. Anderson Guangxing Wang Shoufan Fang George Z. Gertner Burak Gü neralp Don Jones 《Journal of Terramechanics》2005,42(3-4):207-229
We assessed short-term impacts of changes in military training load on vegetative cover at Fort Hood, TX. From 1989 to 1995, permanent field transects were monitored for vegetative cover and land use disturbance using standard army monitoring methods [Land Condition Trend Analysis (LCTA)]. Land use intensity (training load) was quantified and used to develop a model to predict future vegetation cover values. We found that standard Army monitoring methods detected changes in installation resources associated with changes in training load. Increased training loads were associated with increased measures of disturbance, decreased ground cover, and decreased aerial vegetative cover. We found that the spatial pattern of disturbance and vegetation cover remained relatively constant over the study period despite large variations in overall training load. Our model used the consistency in spatial cover patterns over time and the strong relationship between training load and vegetation cover to predict the impact of future training loads on vegetation. 相似文献
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A structural health assessment (SHA) methodology is developed using data acquired from structural health monitoring (SHM) system installed on long-span bridges. A set of fatigue criteria has been proposed for pre-determining the global state of the bridge structure failure due to fatigue. This involves finding the threshold of fatigue initiation, below which the rate of fatigue damage may be undetectable under current technology or it is economically unfeasible. The state-of-art for large structures corresponds to the initiation of macro-cracks caused by the accumulation of damage generated by actual service loads for the case of bridges. In what follows, consideration is given to developing fatigue crack growth criterion based on the concept of the continuum damage mechanics (CDM). Fatigue accumulative is included in the model where a fatigue limit for multi-axial stress state is considered. The proposed criterion advocates the evolution of micro-crack growth up to the stage of macro-crack formulation. Considered are the loading histories that correspond to normal traffic loading for highways and railways, incidental or accident loadings such as those caused by typhoons and effective environmental loadings. The potential sites of damage are determined are discussed. The proposed criterion is applied to analyze the fatigue damage of the Tsing Ma Bridge with online strain history data acquired by the SHM system that is permanently installed in the bridge. 相似文献
80.
The paper discusses local porosity theory and its relation with other geometric characterization methods for porous media such as correlation functions and contact distributions. Special emphasis is placed on the charcterization of geometric observables through Hadwigers theorem in stochastic geometry. The four basic Minkowski functionals are introduced into local porosity theory, and for the first time a relationship is established between the Euler characteristic and the local percolation probabilities. Local porosity distributions and local percolation probabilities provide a scale dependent characterization of the microstructure of porous media that can be used in an effective medium approach to predict transport. 相似文献