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关键词： Event-triggered sampling   Sliding mode control   Super-twisting algorithm   Observation accuracy  

摘要： This paper is concerned with event-triggered sliding mode control (SMC) for uncertain mechanical systems subject to limited communication capacity. We consider the scenario where samplings of the system output and of the control input are generated by two different event-triggered strategies. An event-triggered mechanism is incorporated in the sensor to decide when the position information is transmitted from the sensor to observer. The super-twisting algorithm (STA)-based observer is developed to recover the unmeasured velocities by using event-triggered sampling of the position information. Besides, an SMC law is proposed and an input event-triggered mechanism is introduced to decide when the control signal is transmitted over the network to the actuator side. The stability for the overall closed-loop system is analyzed. It is proved that under the proposed output and input event-triggered strategies, there is no Zeno behavior exhibited. Examples are finally presented to illustrate the effectiveness of the proposed event-triggered STA-based observer and the event-triggered SMC scheme.

ISBN: (纸本)9787030719102

摘要： 磨料磨损属于摩擦学范畴，涉及物理、化学、力学、材料与机械多学科的知识。磨料磨损对工农业生产和人类活动除造成巨大的经济和材料损失外，利用其有利的方面，还可帮助人类进行生产和生活。如何抵抗磨损和有效利用磨损，已成为科学家和工程师的一项重要任务。为此，《磨料磨损》从列举磨料磨损的应用实例开始，重点论述磨损力学、磨料表征、二体磨料磨损原理、三体磨料磨损原理、纳米尺度磨料磨损，以及磨料流加工的基本规律。这些内容是作者几十年来研究成果的归纳与总结。理论上，《磨料磨损》涉及部分力学、物理、材料、计算方法等基础知识在磨料磨损中的应用等。

关键词： Mathematical and Computational Engineering  

摘要： Due to the great challenges of measuring forces directly, identifying dynamic loads based on accessible responses is a crucial problem in engineering, helping ensure integrity and reliability of mechanical structures. Dynamic load identification is a difficult inverse problem due to matrix ill-posedness, noise-sensitivity and computational scale, especially in uncertain structures. Unexpected inaccurate or non-unique solutions may be found if these problems are not well addressed. During the past decades, many methods have been proposed to deal with these problems. This paper tries to provide a comprehensive review of techniques for dynamic load identification, including under ill-posedness and uncertain parameter processing;with an emphasis on the statistical, data science, machine learning, and artificial intelligence aspects. Classical physics-based dynamic load identification theories in frequency and time domain are also introduced. Research challenges and prospects of dynamic load identification in mechanical systems are discussed finally. This review may offer guidelines for dynamic load identification in practical complex structures, as well as possibilities for further researches. Some methods could have broader applicability to other inverse problems.

关键词： Theoretical and Applied Mechanics   Classical and Continuum Physics   Solid Mechanics   Engineering Fluid Dynamics   Vibration   Dynamical Systems   Control   Engineering Thermodynamics   Heat and Mass Transfer  

摘要： This work illustrates how one could apply Lie point symmetries for finding the analytical solution to first-order mechanical systems. Although the classical Lie method constitutes a powerful tool for solving differential equations, an obstacle appears in the case of systems of first-order equations because they admit an infinite number of symmetries, and it is not possible to compute them by following a systematic procedure. To overcome this difficulty, we follow the idea exposed in Nucci (J. Math. Phys. 37: 1772-1775, 1996), Nucci (Electr. J. Diff. Eqn. 12: 87-101, 2005), Nucci (J. Math. Phys. 42: 746, 2001) consisting of transforming the original system to an equivalent system in which one of the equations is of second-order. The presented approach is applied to Hathaway's circular pursuit problem, leading to the analytical solution of the system expressed in terms of the general solution to an Abel equation.

关键词： Theoretical and Applied Mechanics   Classical and Continuum Physics   Solid Mechanics   Engineering Fluid Dynamics   Vibration   Dynamical Systems   Control   Engineering Thermodynamics   Heat and Mass Transfer  

摘要： Routh reduction presents the minimum number of differential equations that uniquely describe the state of nonlinear mechanical systems where the state variables can be separated into essential ones and cyclic ones. This work extends Routh reducibility for a relevant set of controlled mechanical systems. A chain of theorems is presented for identifying the conditions when reduced order rank conditions can be applied for determining the Kalman controllability of Routh reducible mechanical systems where actuation takes place along the cyclic coordinates only, while some of the essential coordinates and their derivatives are observed. Four mechanical examples represent the advantages of using reduced rank conditions to check and/or to exclude linear controllability in such systems.

摘要： 前些日子的金鸡奖,我注意到了获得最佳女配的朱媛媛.她安静地拿奖,安静地离场,没有热搜、没有通稿,甚至连微博都没发.别人趋之若鹜的奖项,对她来说,仿佛只是一枚印章,盖过也就算了. 在近几年热播的电影、影视剧中朱媛媛都有极其精彩的表现,凭实力吸引了观众的眼球.在让她摘得女配大奖的《我的姐姐》这部电影中,她饰演一位为弟弟、为家庭付出了大半生的姑妈.和张子枫相对无言的那个镜头,她一个眼神就道尽了一个姐姐的半生沧桑,令人心疼又唏嘘.当她说出那句"套娃也不必套在同一个套子里"时,她的神情又是那么动人.可以说,朱媛媛不仅演出了一个传统女性身上的隐忍与悲剧,还演出了一个坚强女性的共情能力和生命力.

关键词： 渣浆泵   磨损原因   解决方案  

摘要： 本文通过介绍渣浆泵的磨损分类、机理和原因提出引起渣浆泵磨损的几个重要原因,以及延长渣浆泵的使用寿命、提高渣浆泵的耐磨性、降低选煤厂生产成本的解决方案.

关键词： Los Angeles abrasion   crushed aggregates   machine learning   data analytics  

摘要： Rock aggregates are extensively used in the production of materials such as asphalt concrete and Portland cement concrete. Los Angeles Abrasion (LAA) value is one the basic characteristics of crushed aggregates that reflects their resistance against mechanical abrasive factors such as repeated impact loading. There have been several efforts to estimate the LAA value from surrogate physical and/or mechanical properties of the material. Previous works have mainly focussed on a limited number of data samples and thus may not be generalised to make predictions for different lithologies. Another drawback of the current approaches is that they are often in the form of one-to-one correlations between the LAA and a measure of mechanical behaviour such as the uniaxial strength. This paper investigates the capability of Machine Learning (ML) models for prediction of LAA value. Different material properties have been tested as the input parameters to achieve the best prediction results. It was observed that the ML models perform considerably better for predicting LAA compared to the existing correlations reported in the literature.

关键词： Broadband antireflective coating   Polycarbonate   Abrasion resistance   Environmental stability  

摘要： Polycarbonate (PC) is a durable and transparent optical plastic material commonly used as shatter-resistant alternative to traditional optical glass. Broadband antireflective (AR) coatings with excellent mechanical strength and environmental stability are essential for PC to achieve high light transmission and visual quality. In this work, chloroform vapor treatment was employed to partially embed the silica coating into the PC substrate for adhesion enhancement, which also divided the silica coating layer into bottom and middle layers with different refractive indices. The contact between the silica nanoparticles and the substrate was transformed from "point-contact" to "area-contact", which enhanced the adhesion between coating and PC substrate. After the deposition of a top layer coating consisted of silica nanopar-ticles with smaller diameter, a triple-layer refractive index graded AR structure was constructed. Hexamethyldisilazane vapor surface modification was performed to decrease the surface free energy of top coating layer. The triple-layer coating coated PC exhibits superior antireflection property with an average reflectance of only 0.43% over a wide wavelength range of 400-1000 nm. After 100 times of fric-tion or 5 months of exposure to a contaminated environment, the reflectance of coated PC shows barely noticeable difference, indicating its excellent mechanical strength and environmental stability. (c) 2021 Elsevier Inc. All rights reserved.

关键词： 铜锰铝合金   复合材料   显微硬度   摩擦磨损性能  

摘要： 为改善铜锰铝合金的烧结性能,并提高其在干摩擦下的摩擦磨损性能,以铜包石墨作为自润滑相加入到铜锰铝合金中,采用等离子真空压力烧结方法制备铜锰铝/石墨复合材料,分析铜包石墨含量对复合材料的密度、硬度的影响,探讨不同复合材料在干摩擦和油润滑条件下的摩擦磨损性能。结果表明:相比真空和氢气还原气氛下的烧结方式,等离子体烧结铜锰铝/石墨复合材料具有较高的致密度和硬度,其硬度随铜包石墨含量的增加而降低;在干摩擦和载荷小于20 N条件下,铜包石墨质量分数为6%~8%的复合材料有较好的减摩耐磨性能,在干摩擦条件下可作为自润滑材料使用;在油润滑条件下,不同材料的承载能力均有较大提高,但载荷较大时复合材料的减摩、耐磨和承载能力方面略低于铜锰铝合金。