关键词： 机械动力学-研究生-教材  

ISBN: (纸本)9787030707246

摘要： 本书主要介绍线性机械结构动力响应预测的基本理论和方法，即机械动力学分析问题。全书共6章，第1章主要介绍机械动力学研究的基本内容及流程。第2章讨论利用普遍动力学方程建立机械系统动力学模型的方法，介绍建立单自由度系统、两自由度系统、多自由度系统和基本连续体动力学模型的方法。第3章分别讨论单自由度系统的解及其性质、多自由度系统和弹性体的模态叠加解及其数值计算方法。第4章专门讨论既适用于传统的链式结构，也适用于连续结构、多体线性离散系统和空间结构的传递矩阵分析法。第5章为动态子结构方法。第6章介绍普遍动力学方程、模态综合法、有限元模型凝聚技术和传递矩阵分析法的工程应用问题。本书主要用作机械工程及相关专业的研究生教材，也可供相关研究人员和工程技术人员参考使用。

关键词： Flow fields  

摘要： The vitreous undergoes physical and biochemical changes with age. The most important of such degenerative changes is vitreous liquefaction or synchysis, in which pockets of liquid known as lacunae form in the vitreous gel. The movement mechanism and characteristics of vitreous liquefaction are quite complex. In this study, the flow dynamics of partial vitreous liquefaction (PVL) as two-phase viscoelastic-Newtonian fluid flow are investigated in the human eye. A reliable three-dimensional (3D) numerical procedure is developed for capturing the interface effects and dynamic characteristics of these two-phase complex fluid flows. In the present work, two different configurations of the PVL including liquefied pocket in the central and the posterior portions of the vitreous cavity are considered. The effects of lens indentation on the flow field and interface deformation of PVL inside the vitreous cavity are investigated. The results show that the curvature of the vitreous cavity due to the lens capsule increases shear and normal stresses in comparison with those for the PVL in a sphere as a simplified model. It is observed that the presence of lens indentation and the location of liquefied region are two factors that can produce conditions of asymmetry inside the vitreous body. In a realistic model of vitreous cavity, although the velocity magnitude inside the liquefied vitreous region increases when the liquefied pocket is in the posterior portion of the vitreous cavity, the stress values and the asymmetric condition of flow field become more significant for the liquefied pocket located close to the posterior lens curvature. Published under an exclusive license by AIP Publishing.

关键词： Antimony(V)   Montmorillonite   Complexation mechanism   Interlayer   Edge surface   First principles molecular dynamics  

摘要： Clay minerals play a vital role in retaining antimony (Sb) by surface complexation, which can largely attenuate its mobility and availability. However, a profound understanding of the environmental process of Sb on clay water interface is insufficient. In this study, aiming to quantitatively revealing the complexation mechanism of Sb(V) onto montmorillonite at the molecular scale, we performed first-principles molecular dynamics (FPMD) simulations to systematically investigate the related structural and energetic information. In interlayer space, [Sb (OH)(6)](-) anion can bind with Ca2+/Na+/Al3+/Fe3+ as stable inner-sphere complexes, and the Sb-Al/Fe complex is much more favorable than Sb-Na/Ca complex. On edge surfaces, the ligand exchange processes on possible sites in a wide range of pH have been examined. At (010) edge, [Sb(OH)(6)](-) was adsorbed as bidentate complex on Al(H2O)(H2O) and Mg-(H2O)(H2O) and monodentate complex on Al-(H2O)(OH), and at (110) edge [Sb(OH)6]- formed monodentate complex on Al-(H2O) and Mg-(H2O). The desorption free energies indicated that the Sb-Al bidentate complex is the most stable and favorable edge species, followed by the Sb-Mg bidentate complex. Overall, this work provides the molecular-scale insights into the fate of antimony in natural environments, and the derived fundamental data contribute to improving the experiment-based surface complexation models (SCM).

关键词： Metals and alloys   High-entropy alloys   Amorphous materials   Powder technology   Crystallization  

摘要： Equiatomic and non-equiatomic AlFeCuZnTi high-entropy alloys (HEAs) were prepared by high energy ball milling of elemental powders. For the equiatomic HEA with chemical composition at the boundary of solid solution and amorphous phase regions, an amorphous phase was obtained at moderate milling times, which was mechano-crystallized into a BCC solid solution by continued milling. For the non-equiatomic HEA with chemical composition well within the solid solution region, the same BCC solid solution was obtained during mechanical alloying. The crystallization kinetics of the amorphous HEA was studied by differential scanning calorimetry (DSC) thermal analysis. The crystallization activation energy (calculated based on the Kissinger equation) was correlated to the mean self-diffusion activation energy of the constituting elements, which was related to the multi-component nature of HEAs.

关键词： magnetic   yarns   self-powered   mechanical sensing particle flow spinning  

摘要： Self-powered fabric electronic devices are critical for next- generation wearable technologies, biomedical applications, and human-machine interfaces. The flexible magnetoelectric strategy is an emerging self-powered approach that can adapt to diverse environments and yield efficient electric outputs. However, there is an urgent need to develop a continuous manufacturing method for fabricating self-powered sensing magnetoelectric yarns with a high magnetic powder ratio and resistance to severe surroundings. In this study, we report particle flow spinning mass-manufactured magnetoelectric yarns for self-powered mechanical sensing. It has been shown that mechanical stretching/bending forces can be sensed and recognized by magnetoelectric yarns without an additional power supply. Through a combination of parameter optimization experiments and Maxwell modeling, we reveal the mechanism behind this mechanical-to-electric conversion capability. We further show that these self-powered sensing magnetoelectric yarns can monitor human motions after being attached to texture clothing. We expect that our results will stimulate further research on fabric electronics in a self-powered manner and will substantially advance the field.

关键词： Calcium silicate  

摘要： Calcium silicate hydrate (C-S-H) is the main hydration product of cementitious materials, often experiencing complex stress conditions in practical applications. Therefore, reactive molecular dynamics methods were used to investigate the mechanical response of the atomistic structure of C-S-H under various uniaxial and biaxial strain conditions. The results of uniaxial simulations show that C-S-H exhibits mechanical anisotropy and tension-compression asymmetry due to its layered atomistic structure. By fitting the stress-strain data, a stress-strain relationship that accurately represents the elastoplasticity of C-S-H was developed. The biaxial yield surface obtained from biaxial simulations was ellipsoidal, again reflecting the anisotropy and asymmetry of C-S-H. Four yield criteria (von Mises, Drucker-Prager, Hill, and Liu-Huang-Stout) were further investigated, and it was found that the Liu-Huang-Stout criterion can effectively capture all the major features of the yield surface. During a uniaxial tensile process in the z direction, multi-crack propagation was observed, which was aggravated and weakened by y direction tensile and compressive strains respectively. The results of chemical bond analyses revealed that, for different strain conditions, the Ca-W-O-S and Ca-S-O-S bonds play different roles in resisting deformation.

关键词： 非圆齿轮   多刚体动力学模型   弹性动力学模型   速度偏差率   Runge-Kutta法  

摘要： 一种非圆齿轮-正弦机构串联组合而成的组合机构理论上可严格实现从动件等速往复运动规律。但由于机械系统的动力学效应和电动机输出特性等因素引起的电动机输出轴的速度波动,会导致从动件等速运动速度发生偏差。文中以该组合机构的主传动系统为研究对象,建立了电动机-主传动系统单自由度多刚体动力学模型,并采用数值法求解其运动微分方程,得到了从启动到稳态运动过程中电动机角速度及正弦机构从动件输出速度变化规律。计算结果表明:额定工况条件下电动机角速度波动率为9.78%,正弦机构从动件输出速度偏差率为0.164%。在此基础上,建立了考虑非圆齿轮轮齿弹性变形的主传动系统弹性动力学模型,采用Runge-Kutta法求解系统运动微分方程,得到了额定工况条件下一个运动周期内从动件的往复运动速度规律,其从动件偏差率增加到0.568%。在需要严格实现等速运动规律的应用场合,系统的动力学效应是不可忽视的。

关键词： 机械动力   潍柴动力   房地产   山东潍坊   市场低迷   山东重工   潍柴集团   材料价格上涨  

摘要： 日前,山东重工·潍柴动力2022年商务大会工程机械动力分会在山东潍坊胜利召开。2021年,潍柴在原材料价格上涨,房地产市场低迷以及新冠疫情出现反复的不利条件下,顶住压力,实现逆势上扬。2021年潍柴集团产销发动机预计突破100万台,其中工程机械动力预计销售达20万台,同比增长超过13%。

关键词： 机械通气   瑞芬太尼   布托啡诺   治疗结果   呼吸动力学  

摘要： 背景目前,为了改善机械通气患者人机协调、保护患者脏器功能,临床上主要采取镇痛、镇静治疗。瑞芬太尼和布托啡诺联用可以减少药物相关不良反应,但二者用于机械通气患者的研究报道较少。目的探讨瑞芬太尼联合布托啡诺在机械通气患者中的应用效果及其对呼吸动力学的影响,以期为机械通气患者选取镇痛、镇静治疗方案提供参考。方法选取2018—2020年华中科技大学协和江北医院重症医学科收治的拟行机械通气的患者200例作为研究对象,采用随机数字表法分为研究组(n=100)和对照组(n=100)。对照组患者给予布托啡诺治疗,研究组患者在对照组基础上联合瑞芬太尼治疗。比较两组患者用药前、用药10 min、用药2 h呼吸动力学指标[气道阻力、动态肺顺应性(Cdyn)、平均气道压(Pmean)、吸气峰压(Ppeak)、自主呼吸频率、每分钟通气量(MV)、呼气潮气量(Vexp)、吸气潮气量(Vins)],用药6、12、18、24 h重症监护疼痛观察工具(CPOT)评分和Ramsay镇静评分,术后苏醒时间(包括拔管时间、睁眼时间、呼吸恢复时间)。结果用药前及用药2 h,两组患者气道阻力、Cdyn、Pmean、Ppeak、自主呼吸频率、MV、Vexp及Vins比较,差异无统计学意义(P>0.05);用药10 min,研究组患者气道阻力、Pmean、Ppeak、自主呼吸频率低于对照组,Cdyn、MV、Vexp及Vins高于对照组(P<0.05)。用药6、12、18、24 h,研究组患者CPOT评分和Ramsay镇静评分均低于对照组(P<0.05)。两组患者术后拔管时间、睁眼时间及呼吸恢复时间比较,差异无统计学意义(P>0.05)。结论瑞芬太尼联合布托啡诺能有效提高机械通气患者的镇痛、镇静效果,对呼吸动力学指标的影响小,且未延长患者术后苏醒时间。

关键词： Capillary infiltration   Porous membranes   Bonding strength   Mechanical properties of membranes  

摘要： Capillary infiltration of porous medium impacts applications across oil recovery, soil science, and hydrology. The infiltration kinetics is typically captured by a range of models that differ in the approximation of pore structures, fluid properties, and filling ratio. Capillary bonding of a porous membrane by a polymer melt is important for membrane device manufacturing. However, both the capillary infiltration kinetics and the resulting bonding strength or mechanical integrity have not been reported. In this work, we measure the kinetics of capillary infiltration of a viscous polypropylene (PP) in polyethersulfone (PES) membranes with a normal pore size of 200 nm and varying degrees of hydrophilicity. The time-dependent infiltration depth was quantified ex situ by imaging the cross-sections of the bonded PP film/PES membranes. The microscopic details of the bonded interface were characterized by high-resolution nanomechanical imaging, while the contact angles of PP on the PES surfaces were measured by the sessile droplet method. The results show that the infiltration kinetics at 180 degrees C is better described by the Cai model that incorporates membrane pore structures (porosity, tortuosity, pore size), compared with the basic Lucas Washburn model intended for isolated cylindrical pores. The infiltration kinetics at 200 degrees C appears significantly slower than the predictions of both models, which is hypothesized to be a result of pore deformation/collapse due to the capillary pressure when the PES approaches the rubbery state. Regardless of bonding temperature, the resulting mechanical integrity of the bonded PP film/PES membrane, as quantified by a modified T-peel test, is dictated by the fracture strength of the membranes and weakly decreases with the increase of infiltration depth.