船舶水润滑尾轴承结构设计研究进展

水润滑轴承的结构优化可以有效提高轴承的承载能力、冷却散热、减振降噪和摩擦学性能。在概述船舶水润滑尾轴承的优势和存在问题的基础上,分析归纳水润滑尾轴承内衬结构、内衬的厚度和硬度、轴承间隙、长径比、内衬表面粗糙度等结构设计参数的研究进展;以轴位水润滑尾轴承、内衬多层复合水润滑尾轴承和闭式水润滑尾轴承为例,介绍近年来几种新型水润滑尾轴承的结构设计,指出闭式水润滑尾轴承在内河及沿海船舶上具有广阔的应用前景,是未来的研究重点和发展趋势;建议水润滑尾轴承的研究应从以下方面着手,一是从微纳米尺度研究轴承微观界面润滑机制,二是在考虑轴承参数间耦合作用的基础上对轴承进行多目标优化,三是进一步研究闭式水润滑尾轴承及密封装置材料、结构和辅助装置以及水润滑添加剂,四是研究船舶水润滑尾轴承的设计规范,建立一定范围内精度满足工程需要的轴承设计计算经验公式,以简化轴承设计程序。     

2K-H型人字齿周转轮系的免组装设计与成型

为了解决人字齿周转轮系加工、装配的难题,提出利用3D打印技术制造免组装人字齿周转轮系的新工艺。通过理论推导,建立变位系数、齿侧间隙与齿轮基本参数之间的关系。利用建立的关系式,对行星轮进行负变位,设计具有微量齿侧间隙的2K-H型人字齿周转轮系。利用熔融沉积成型实验平台使设计的人字齿周转轮系成型,成型后的人字齿周转轮系齿轮啮合传动正常,设计、制作相应辅件,将其装配成减速步进电机。结果表明,通过合适的间隙设计,可以利用3D打印技术实现人字齿周转轮系的免组装制造,为小尺寸、一体式人字齿周转轮系个性化定制提供了一种具有工业应用前景的全新解决方案。     

Experimental investigation on the performance of multi-tiered geogrid mechanically stabilized earth (MSE) walls with wrap-around facing subjected to earthquake loading

Construction of mechanically stabilized earth (MSE) walls in multi-tiered configurations is a promising solution for increasing the height of such walls. The good performance of this type of walls after recent major earthquakes was reported in a number of technical studies. In the present study, an experimental approach was adopted to compare the seismic performance of single-tiered and multi-tiered MSE walls using physical modeling and through conducting a series of uniaxial shaking table tests. To do so, several geogrid-reinforced soil walls with wrap-around facing (i.e., three-, two-, and single-tiered) with a total height of 10 m were designed in the form of prototypes of 1-m-height wall models. The step-wise intensified sinusoidal waves were applied to the models in 14 typical forms. Comparing the shaking table test results confirmed the post-earthquake advantages of multi-tiered MSE walls. The results revealed that tiered walls exhibited better behaviors under earthquake loading in terms of the seismic stability of the wall, displacement of the wall crest, horizontal displacement of the wall facing, deformation mode and failure mechanism of the wall, settlement of backfill surface, and seismic acceleration responses.     

Degradation analysis of the core components of metal plate proton exchange membrane fuel cell stack under dynamic load cycles

The durability of metal plate proton exchange membrane fuel cell (PEMFC) stack is still an important factor that hinders its large-scale commercial application. In this paper, we have conducted a 1000 h durability test on a 1 kW metal plate PEMFC stack, and explored the degradation of the core components. After 1000 h of dynamic load cycles, the voltage decay percentage of the stack under the current densities of 1000 mA cm^?2 is 5.67%. By analyzing the scanning electron microscopy (SEM) images, the surfaces of the metal plates are contaminated locally by organic matter precipitated from the membrane electrode assembly (MEA). The SEM images of the catalyst coated membrane (CCM) cross section indicate that the MEA has undergone severe degradation, including the agglomeration of the catalyst layer, and the thinning and perforation of the PEM. These are the main factors that cause the rapid increase in hydrogen crossover flow rate and performance decay of the PEMFC stack.     

Experimental study on vibration-induced clamping force reduction in fuel cell structures

When applied to transportation systems, fuel cell structures are exposed to external mechanical disturbance including shocks and harmonic excitations from operating components. To minimize performance degradation from machine operations, the fuel cell structure needs to be examined via vibration reliability tests. In this study, the reduction in the clamping force of the stack by random vibrations was investigated by experiments. The stack mass and gasket were clamped with bolts for vibration tests. The vibration induced shear movements between clamped stacks. To estimate the vibration input magnitudes, the Dirlik method was used. The reduction in the stack clamping force was estimated using the Basquin's power law. The clamping force decreased by the shear vibration input to the stack structure. The degree of clamping force reduction was larger for the heavier stack. When the stacks were separated by the gasket the reduction became smaller. Through the Dirlik method, the vibration reliability of the stack was evaluated. This information provides severity of the external vibration on the stack functionality.     

基于Adam-DBN网络的行星齿轮箱故障诊断方法研究

随着现代机械装备的复杂化,传统的故障诊断方法难以满足表征设备间的复杂映射关系,且在如今大数据背景下面临着维数灾难的问题。文章结合深度置信网络以及梯度优化算法提出了一种基于梯度优化深度置信网络(Adam-DBN),通过数据验证选取最优梯度优化算法对深度置信网络的的梯度算法进行调优。搭建模拟实际工况的行星齿轮箱实验台,通过实验台采集所得数据构成数据集对方法进行验证。实验表明文中提出的方法能够有效提高DBN网络的收敛速度与训练精度,同时具有较高的故障识别准确率。     

Estimating the system efficiency of the multifunctional hydrogen complex at nuclear power plants

The paper deals with the primary current frequency regulation in the energy system (ES) as well as the basic requirements for NPP power units (PUs) under the conditions of involvement into the primary regulation. According to these requirements, NPP operation is related to the unloading and corresponding decrease in efficiency. It has been shown in this connection that combining NPP with a hydrogen complex (HEC) allows excluding the inefficient unloading mode. This enables the steam turbine and reactor equipment to operate in the basic mode at nominal power level. Besides, the conditions for producing and storing hydrogen and oxygen during the day as well as additionally during the night-time of off-peak electrical load may be created, which allows using them for generating peak power.In the paper, the systemic economic benefit as a result of involving NPP combined with HEC into primary regulation of the current frequency in ES with allowance for expending resources for the main equipment has been estimated. In this regard, the paper gives grounds for cyclic loadings of HEC main equipment including metal tanks for storing hydrogen and oxygen, compressors, hydrogen-oxygen combustion chamber (HOCC) for hydrogen-steam superheating of the actuating medium in the NPP steam turbine cycle. Methodological grounds for evaluating the equipment endurance under cyclic loading with involving into the primary frequency regulation by the criterion of the fatigue crack growth rate are described. It has been shown that in terms of HEC equipment, the highest load intensity occurs in HOCC due to high thermal stresses.Also, the systemic economic benefit has been estimated, and the impact of the equipment deterioration under conditions of cyclic loading has been demonstrated. It is shown that when combining NPP PUs with HEC, the efficiency of primary regulation may significantly depend on such factors as the cost of equipment exposed to cyclic loads, the frequency and intensity of cyclic loads, and the relation between the peak electricity tariff and the cost price of electric energy produced by NPP.It has been shown on the basis of novel methods for estimating the efficiency of involving NPP with HEC into the primary frequency regulation with allowance for damage to the equipment, that the use of HEC may provide a considerable economic benefit, as compared to the version of NPP unloading when involving directly into frequency regulation.     

Pt-based trimetallic nanocrystals with high proportions of M (M=Fe,Ni) metals for catalyzing oxygen reduction reaction

For boosting oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs), a new type of multi-functional catalyst with high activity, high stability, and low cost has been designed and prepared by introducing high proportions of M (M = Fe, Ni) metals in Pt-based nanoparticles through a microwave-assisted polyol method, followed by thermal annealing process. A uniform dispersion of nanoparticles (5 nm) and a face-centered tetragonal (fct) phase improve the activity and stability of the Pt–Fe–Ni/C catalyst. Owing to differences in the surface energies of the alloying elements, Pt atoms with low surface energy have a tendency to segregate from the subsurface to the surface during the annealing. This tendency exposes the internal Pt atoms to the surface of the nanoparticles in the existence of high proportions of M metals, significantly improving the utilization of Pt. As a cathode catalyst, the Pt–Fe–Ni/C catalyst annealed at 675 °C with a mass activity of 0.73 A/mg_Pt, which is 3.5 times higher than that of the commercial Pt/C catalyst, exhibits an excellent half-cell performance. An accelerated durability test demonstrates that the prepared Pt–Fe–Ni/C-675 catalyst is more stable than the commercial Pt/C. The proposed multi-functional catalyst has great potential for PEMFCs and other applications.     

Two-dimensional temperature distribution estimation for a cross-flow planar solid oxide fuel cell stack

The uniform temperature distribution of a cross-flow planar solid oxide fuel cell (SOFC) stack plays an essential role in stack thermal safety and electrical property. However, because of the strict requirements in stack sealing struture, it is hard to acquire the temperature inside the stack using thermal detection devices within an acceptable cost. Therefore, accurately estimating the two-dimensional (2-D) temperature distribution of the cross-flow stack is crucial for its thermal management. In this paper, Firstly, a 2-D mechanism model of a cross-flow planar SOFC stack is established. The stack is divided into 5*5 nodes along the gas flow directions, which can reflect the stack states with moderate computational burden. Then, experimental test data is utilized to modify and validate the stack model, guaranteeing the model accuracy as well as the reliability of model-based state estimator design. Finally, easily-measured stack inputs and outputs are selected, and a temperature distribution estimator combined with unscented kalman filter (UFK) approach is developed to achieve accurate and fast temperature distribution estimation of a cross-flow SOFC stack. Simulation results demonstrate that the UKF-based temperature distribution estimator can precisely and quickly achieve the temperature distribution estimation of the cross-flow stack under both static state and dynamic state changes and is applicable to cross-flow stacks with different size or cell number as well, the maximum estimated absolute error is less than 0.15 K with an absolute error rate of 0.015%, which indicates the developed estimator has good estimation performances.     

矿用减速器太阳轮齿面PVD表面改性的研究

针对矿用减速器太阳轮接触强度最小安全系数通常小于1.25,即可靠度不理想的问题,对太阳轮常用材料17CrNiMo6进行物理气相沉积(PVD)处理。将其表面附着TiN涂层、TiC复合层,并对这2种涂层进行厚度、硬度、密着力、EDS分析。研究表明:齿面进行PVD表面改性虽然具有粗糙度良好、涂层均匀以及密着力好等优点,但其硬度有所降低。