Effect of metallurgical evolution during post-weld aging treatment on localised corrosion of resistance spot welding joints of A286 superalloy

The combined effect of resistance spot welding and precipitation hardening on the localised corrosion of A286 superalloy is studied. The specimens tested by double loop electrochemical potentiokinetic reactivation were welded in the solution treated condition, and then subjected to different precipitation hardening treatments. For both base metal and weld nugget, the maximum localised corrosion is reached when η phase is clearly observable. The fact that the localised corrosion resistance of weld nugget is different from that shown by base metal may be explained by the segregation of Ni and Ti towards the interdendritic region of weld nugget (studied by using scanning electron microscope/energy dispersive X-ray analysis).     

Cutting parameter optimization for one-step shaft excavation technique based on parallel cutting method

The outcome of the cutting blasting in a one-step shaft excavation is heavily related to the cutting parameters used for parallel cutting method. In this study, the relationships between the cutting parameters (such as the hole spacing L and the empty hole diameter D) and damage zones were investigated by numerical simulation. A damage state index γ was introduced and used to characterize the crushing and crack damage zones through a user-defined subroutine. Two indices, i.e., η₁ and η₂ that can reflect the cutting performance, were also introduced. The simulation results indicate that an optimal value of L can be obtained so that the η₁ and η₂ can reach their optimal states for the best cutting performance. A larger D results in better cutting performance when the L value maintains its best. In addition, the influences of the loading rate and the in-situ stress on the cutting performance were investigated. It is found that an explosive with a high loading rate is suit for cutting blasting. The propagation direction and the length of the tensile cracks are affected by the direction and the magnitude of the maximum principal stress.     

Attitude control of spacecraft simulator without angular velocity measurement

In this paper the attitude control of a spacecraft simulator using Reaction Wheels (RW) as the actuators is investigated. The main goal of the current study is to bring the RWs to the rest at the end of the maneuver without angular velocity measurement. A modified feedback linearization controller is applied by considering the Euler angles of the simulator as the output and the RWs angular momentums as the internal state variables. The stability of the proposed controller and the internal dynamics is analyzed using Lyapunov theory. Two modified sliding mode observers are designed to estimate the angular velocities of the spacecraft attitude control subsystem simulator. The proposed observers do not use the control input and the detailed knowledge of the model and thus it can be implemented easily. The global stability of the system is proved. The proposed controller and observers are finally evaluated numerically and experimentally on an attitude spacecraft simulator.     

Diagnostic of fuel cell air supply subsystems based on pressure signal records and statistical pattern recognition approach

A data-driven and application-oriented diagnosis tool is developed for Fuel Cell (FC) air supply subsystems. A bench emulating a FC air line is built to study normal and abnormal operations (clogged inlet, air leakage, error in compressor speed control) and data are collected using the air pressure transducer, which is usually implemented in FC generators. A pattern recognition approach is then applied to statistical features extracted from the pressure signal. The performance of the diagnosis strategy is evaluated from confusion matrices, associated to graphs and performance indicators. Two examples of compressors, air subsystem managements, and data records are considered to examine the method portability. Best classification rates (>95%) are obtained on test profiles, when the pressure regulation is disabled; fault stamps can thus be found in the pressure signal morphology. Regarding the frequency of data logging, both 1 kHz and 100 Hz values are found effective for fault isolations.     

Uncertainty analysis and robust control of fuel delivery systems considering nitrogen crossover phenomenon

In this paper, the fuel delivery subsystem (FDS) with hydrogen recirculation and anode bleeding is applied in proton exchange membrane fuel cell (PEMFC) system, which is utilized to supply hydrogen to the anode of stack and recirculate fuel back to the supply line. As the diffusion of nitrogen from cathode to anode is inevitable in a real PEMFC during long-term operation. To prevent system performance decline due to nitrogen accumulation. Therefore, this paper firstly develops a control-oriented nonlinear dynamic FDS model involving gas diffusion. Additionally, the FDS is very sensitive to operating environment, uncontrolled operation conditions may cause stack degradation. Specifically, a method based on Monte Carlo simulation is proposed to identify the key parameter boundaries. Then the gas distribution in FDS due to nitrogen crossover is analyzed in detail. After this, a hybrid robust methodology based on sliding mode algorithm is also proposed to maintain adequate hydrogen pressure supply, suitable hydrogen and nitrogen content in the system in presence of nitrogen crossover and renewed uncertainties. Finally, the performance of the presented controller is compared with nonlinear PID (NPID) control and nonlinear multi-input-multi-output (NMIMO) control through a hardware-in-the-loop test bench. Experimental results show that the hybrid controller is accurate and suitable for control purpose, the nitrogen content is restricted to the given range and the variation of output voltage is limited to the desired boundaries, the feasibility and effectiveness are validated.     

一个考核能源消耗的通用程序

用计算机管理是企业中降低能源消耗乃至物质消耗的有效手段。文中分析了对能源消耗的考核方法和数学模型 ,并编制了计算程序     

在Y58A插齿机上加工大质数直齿轮的对数分齿计算方法

介绍了在Y58A插齿机上采用对数分齿计算方法加工大质数直齿轮的计算方法和计算实例。生产实践证明,采用对数分齿计算方法既简单易懂、操作方便,同时又能提高工作效率和保证齿轮的加工精度。     

确保混凝土结构优质工程的相关措施

对原材料、钢筋工程、模板工程、混凝土工程的施工技术措施进行了介绍，并从人力资源管理、设备器具管理、过程管理、经济措施几个方面阐述了质量管理措施，以确保混凝土结构的工程质量。     

五台坪上泉岩溶水系统划分研究

以山西省五台坪上泉岩溶水系统为例，介绍了岩溶水系统的概况，并对甲子湾泉、大湾泉、水泉弯泉等岩溶水系统作了明确划分，提出了岩溶水各亚系统间的相互关系。