课程文献中心 更多>>

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。

关键词： 课程思政   教学改革   大国工匠  

摘要： 《机构与机械零件》是智能制造专业群的一门专业基础课,在本门课程中,进行了课程思政改革的探索,通过修订课程标准,教学内容、教学方法手段、考核评价中融入思政元素,具体在绪论、齿轮传动、螺纹连接知识点进行了思政元素的融入,并在课堂中进行了实施。通过课堂实施,学生坚定了“四个自信”,形成了正确的价值观,学生们非常认可课程思政,希望以后继续坚持课程思政教学方式。同时,对推进本专业群的其他课程思政改革起到了借鉴作用。

关键词： 20CrMoH钢   超声表面滚压   显微硬度   残余压应力   摩擦磨损  

摘要： 目的提高20CrMoH钢的耐磨性能。方法设置不同的超声滚压力(700、1000、1300 N)与次数(3、6次),对20CrMoH钢进行超声表面滚压加工。采用扫描电子显微镜、粗糙度测量仪、光学显微镜、显微硬度测量仪、X射线应力分析仪、端面型滑动磨损试验机和3D形貌仪等设备,分别对加工前后试样的表面形貌、粗糙度、金相组织、显微硬度、表面残余压应力和摩擦磨损等性能进行对比分析。结果经过超声表面滚压加工的试样,与未处理试样相比,在各项性能上都有较大的提升。表面形貌更加光整,粗糙度Ra从0.82μm下降至0.331μm;表面显微硬度从760HV_(0.2)提高到856HV_(0.2),提升了12.63%;表面残余压应力从–286 MPa提高到–565 MPa;磨损机制从未处理试样的以磨粒磨损和疲劳磨损为主转变为以磨粒磨损和氧化磨损为主。试样在1000 N的作用力下进行6次超声滚压加工后,材料的耐磨性能最好,与未处理试样相比,稳态平均摩擦系数大幅下降,磨损体积从2.29 mm^(3)减小到0.74 mm^(3),减小了67.69%。结论超声表面滚压加工能有效改善20CrMoH钢试样的表面质量,细化表层晶粒组织,增加表面硬度与表面残余压应力,显著提升材料的耐磨性能。

关键词： 水泵   空蚀磨损   原因   对策  

摘要： 水泵是泵站工程的主要设备,空蚀磨损会严重影响其运行效益和使用寿命。本文概述了高扬程电力提灌泵站水泵空蚀磨损的原因及危害,提出了防范与处理高扬程电力提灌泵站水泵空蚀磨损的对策,包括合理设定水泵吸水高度、选择适宜的机型、调整装机高度、选用优质耐磨材料、创新水泵设计理念、防空蚀磨损喷涂处理、合理选用施工材料、维修水泵设备、做好运维管理工作。

关键词： 冲蚀磨损   凸条形态   风速   入射角   凸条间距  

摘要： 针对目前风沙环境下混凝土壁面从不同风速和风向上存在冲蚀磨损差异性,采用RNG k-ε湍流模型结合离散相(DPM)模型耦合求解,建立了风沙两相流作用下混凝土壁面的冲蚀磨损数值模型。对比混凝土立方体模块的物理冲蚀磨损实验数据,验证了该模型具有较好的准确性和可靠性。后续围绕混凝土表层形态优化设计,详细分析了凸条壁面冲蚀磨损的形成和发展机制,同时深入探讨了凸条数量、间距等相关因素对冲蚀磨损的影响。结果表明,风沙流速度越大,凸条壁面的冲击作用越明显,冲蚀磨损越严重;入射角度越大,凸条壁面的微切削作用越明显,抗冲蚀磨损效果也越好。