关键词： 工程机械   动力传动   节能环保   机械效率  

摘要： 现代工程机械种类很多,传动方式也很多,不同的传动方式限定了机械设备的环保水平、机械效率、输出能力,不同的机械能否在机械性能、能源消耗、设备稳定性、后期维护保养等方面满足我们的需要,这就需要我们对各种机械进行认真的分析,选出最优的组合方式,淘汰落后的方式,推动机械工业的发展。

关键词： 动力机械   流体机械   可逆性   工作过程   研究  

摘要： 本文对一些动力设备,比如发电机、热力发动机、水泵水轮机、电动机等,介绍了他们的工作过程,并且对其工作过程的不可逆性和可逆性进行了重点阐述,分析了可不可逆的具体原因,提供了必要的理论依据给科学研究及工程实践。

关键词： 动力设备   旋转设备   交变应力   疲劳强度   固有频率   状态智能监测  

摘要： 以焦化厂导焦除尘风机为例,对于节能改造后调速运行的大型动力旋转设备的疲劳强度进行了计算分析,结果表明,对于承受交变应力的旋转设备,应充分考虑尺寸系数和构件残余应力对所选材料疲劳强度极限值的影响,对其核心部件进行抗疲劳设计和校核工作。同时对激振力与旋转设备固有频率耦合振动的现象作了定性分析和说明。鉴于该类设备对生产工艺和产能实现的重要程度,引入了设备状态智能监测系统,对该系统的架构和功能作了阐述,并确定了下一步的主要研究方向。

关键词： 空化   螺旋槽   小扰动法   有限单元法   动力系数  

摘要： 考虑液膜空化效应的影响,研究螺旋槽液体润滑机械密封的动力学特性.基于液体润滑理论和小扰动法,建立了考虑液膜空化的密封微扰膜压控制方程,采用有限单元法对端面液膜三自由度微扰下的液膜刚度和阻尼系数进行了数值求解,分析了不同参数对液膜密封动力系数的影响.螺旋槽深度在10μm左右、槽坝比在0.75左右、槽宽比在0.4左右,螺旋角在9°左右时液膜具有最大的轴向和角向刚度系数.螺旋槽深度在5μm左右、槽宽比在0.6左右、螺旋角在20°左右时,两角向交叉阻尼绝对值最大.初始偏角的存在使密封压力呈现非对称性,从而使两角向动力系数绝对值不再相等.液膜轴向刚度kzz在数量级上远大于其余液膜刚度值,液膜轴向阻尼d_(zz)、角向阻尼d_(αα)和d_(ββ)远大于液膜其余阻尼值且随着转速和间隙的增大而减小.

关键词： 悬置测试   仿真   减振  

摘要： 本文对悬置供应商提供的悬置参数进行测试验证,充分了解各供应商厂家提供的悬置的性能参数是否满足悬置设计需求,为今后动力总成的仿真分析和减振设计提供必要的参数。

关键词： Calcium silicate  

摘要： Efforts to tune the performance of organic/inorganic composites are hindered owing to a lack of knowledge related to the interfacial interaction mechanisms. Here we investigated the interfacial structure, dynamics, energetics and mechanical properties between calcium silicate hydrates (C-S-H) and polymers by molecular dynamics (MD) simulation. In this work, polyethylene glycol (PEG), polyvinyl alcohol (PVA) and polyacrylic acid (PAA) are intercalated into nanometer channel of C-S-H sheets to construct the model of polymer/C-S-H composite. In the interfacial region, the calcium ions near the surface of C-S-H play mediating role in bridging the functional groups in the polymers and oxygen in the silicate chains by forming O-s-Ca-O-p bond. In addition to ionic bonding, the bridging oxygen (C-O-C) in the PEG, hydroxyl (C-OH) in the PVA and carboxyl groups (-COOH) in the PAA provide plenty oxygen sites to form H-bonds with silicate hydroxyl, interlayer water and calcium hydroxyl in C-S-H substrate. The interfacial binding energy is dependent on polarity of functional groups in the polymers, the stability of the H-bond and Ca-O bond, ranking in the following order: E(PAA) > E(PVA) > E(PEG). The PVA with small number of H-bonds formed between oxygen in PVA and water molecules, resulting in increasing the mobility of confined water in the interlayer region. On the other hand, PAA and PVA, with strong polarity, can provide more number of non-bridging oxygen sites that widely distributed along the polymer chains to associate with more calcium ions and H-bonds. Furthermore, uniaxial tensile test is utilized to study the mechanical behavior of the composites. The incorporation of polymers, strengthening the H-bonds in the interfacial region and healing the defective silicate chains, can inhibit the crack growth during the loading process, which both enhance the cohesive strength and ductility of the C-S-H gel. In particular, the intercalated PAA increases the Young's modulus, t

关键词： 巧用   机械能   守恒  

摘要： 机械能守恒定律是解答有关能量问题的常用方法,但是应用该定律时一定要选好研究对象,用守恒条件来判断是否守恒,而且要指明该系统是在哪个过程中守恒,如果忽视过程中的细节,很可能造成错解。

关键词： Mechanical systems   Forward dynamics   Inverse dynamics   Holonomic and nonholonomic constraints   Uderactuated robots   Udwadia-Kalaba equations   Underactuation Equivalence Principle  

摘要： This paper deals with the dynamics and control of underactuated nonholonomic mechanical systems. It is shown in this investigation that the same analytical methods can be used for effectively solving both the forward and the inverse dynamic problems relative to underactuated mechanical systems subjected to a general set of holonomic and/or nonholonomic algebraic constraint equations. The approach developed in this work is based on the combination of two fundamental methods of analytical dynamics, namely the Udwadia-Kalaba equations and the Underactuation Equivalence Principle. While the Udwadia-Kalaba equations represent a fundamental mathematical tool of classical mechanics, the Underactuation Equivalence Principle is a new method recently discovered in the field of analytical dynamics and is associated with nonholonomic mechanical systems. In the paper, these two important analytical methods are discussed in detail. Furthermore, numerical experiments are performed in this investigation in order to demonstrate the effectiveness of the proposed approach considering as an illustrative example of a dynamic model a mobile robot.

关键词： HEART failure  

摘要： Purpose Mechanical circulatory support (MCS) is a non-obvious therapy for heart failure with preserved ejection fraction (HFpEF) because ventricular systolic function is not reduced. We hypothesize MCS of the left ventricle (LV) or left atrium (LA) can improve the hemodynamics in HFpEF including when pulmonary arterial hypertension (PH) is *** Hemodynamic conditions of HFpEF ± PH were recreated on a mock circulation loop (MCL) with a tunable resistance, arterial compliance, peripheral resistance, inertance, venous compliance, and replication of the Frank-Starling mechanism. Hemodynamic parameters were recorded, including atrial and ventricular pressures, ventricular volumes, ejection fraction, and cardiac output. A HeartWare HVAD™ (Medtronic, MN) was used in two different support configurations: 1) LV to aorta (Ao) and 2) LA to Ao. The pump speed was titrated to achieve systemic flow (Qs) of 4.0 L/min and 4.5 L/*** Conditions typically seen in patients with HFpEF ± PH were created in the MCL with complete hemodynamic profiles including HVAD support seen in Table1. In both configurations and regardless of PH status, further Qs augmentation was associated with a reduction in LV end-diastolic pressure, LA pressure and mean pulmonary artery pressure. In the LV to Ao configuration, LV volumes decreased, and ejection fraction improved. In the LA to Ao configuration, LV volumes increased. In the LV to Ao configuration, pressure-volume loop (PVL) data show a reduction in pressure-volume area including a decrease in both stroke work and potential energy. In LA to Ao configuration, PVL data show a decrease in stroke work but an increase in potential energy. This study was not designed to evaluate for suction *** In HFpEF ± PH, MCS can increase Qs and reduce LA pressure. As compared to LV decompression, LA decompression does not volume unload the LV. This study shows potential for MCS as a therapeutic alternative for HFpEF.

关键词： COMPUTATIONAL fluid dynamics   FLOW (Fluid dynamics)  

摘要： Purpose Left ventricle assist devices (LVAD) have contributed to improve survival and quality of life in patients with advanced heart failure, in temporary or lifetime support. Despite technological, bio-compatibility and hemodynamic progress, patients with LVAD have still a relevant incidence of adverse events, such as disabling stroke. The outflow cannula (OC) position and angulation, and the anastomosis site seem to modify the flow in the ascending aorta (AA), and consequently the incidence of cerebral embolism and aortic cusps *** We evaluated the combination of LVAD flow and the residual cardiac output pulsatile flow with computational fluid dynamics (CFD) software based on CT Scan *** Two patients with centrifugal pump LVAD underwent CT Scan regardless of this study, respectively at 7 months and 1.5 years after LVAD implant. We analyzed CT images and made a CFD reconstruction of the anastomosis site, to evaluate the flow in AA. At the same time, in a bench validation test we anastomosed a dacron 32 mm graft (reproducing the AA) and a 14 mm graft (reproducing the OC). We simulated the difference in flow and turbulence, according to different angles of the anastomosis, and the alternative distances from the major cranial branches. Following results of the CFD analysis, we can affirm that it is possible to simulate the optimal flow, improving the laminar flow and reducing the turbulence in the aortic lumen. Moreover, based on the desired angle of the aortic-graft anastomosis, the surgeon can perform the anastomosis with the best shape of the OC (cutting the graft with the angle obtained by the CFD simulation, and incising the AA with the right extension).Conclusion The optimized combination of flows could reduce the incidence of thromboembolic events, aortic endothelium stress, and aortic cusps stress/thrombosis. Further studies are necessary to validate this technology in clinical and surgical practice.