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排序方式: 共有8132条查询结果,搜索用时 15 毫秒
1.
为解决电镀砂轮磨削加工中容屑空间不足的问题,采用点胶微粘接的方法制备了磨料有序排布的电镀砂轮,分析了磨料粘接效果和镀层力学性能。通过SEM分析了磨料/镀层/导电胶的结合界面,并进行了干磨削试验。研究结果表明,直径约为磨料粒径40%的胶点可粘接住磨料,单个胶点上粘接多颗磨料的占比小于6%;双脉冲电镀工艺制备的镀层显微硬度大于500HV,表层残余应力小于100MPa,磨料/镀层/导电胶之间的界面贴合紧密,无明显缺陷;砂轮在磨削时没有出现磨料脱落现象。 相似文献
2.
In this study, fluid flow over an array of eight, 0.029 m × 0.029 m, square cross‐section cylinders in an octagonal configuration is studied numerically. The mean force coefficients (drag and lift) and the vortex formation characteristics of the array are calculated numerically by utilizing a three‐dimensional large eddy simulation mathematical model for turbulence. The numerical simulation is performed with commercial software ANSYS Fluent 19R1. To investigate the parametric influences, three spacings between the cylinders (0.07, 0.14, and 0.2 m), two array attack angles (0° and 15°), and two Reynolds numbers (4060 and 45 800) are considered. The results comprise flow patterns and force coefficients' variations with Reynolds numbers. The lift force of the downstream cylinder reaches its maximum at α = 15°, and the drag force of the upstream cylinders finds its peak at α = 0°. It is observed through velocity and viscosity contour plots that vortex formation length near the cylinder increases at higher Reynolds number. Velocity vector plots are also presented to show fluid flow behavior near the cylinder. Furthermore, the predicted mean forces on the cylinders are slightly different for different Reynolds numbers, spacings, and angles of attack. 相似文献
3.
ZHU Sheng-cai 《广东电脑与电讯》2020,1(1-2):49-53
The construction of cybersecurity is an important part of the information construction in university. It is an indispensable
condition to help the information construction and a strong guarantee to serve the information support of teachers and students in uni-
versity. The cybersecurity environment, atmosphere and guarantee ability of university need to be improved. Based on the related
work and achievements of cybersecurity construction, some general schemes are put forward to provide reference for cybersecurity
construction in university. 相似文献
4.
Purushothama Chippar Swaraj D. Lewis Sudhir Rai Amit Sircar 《International Journal of Hydrogen Energy》2018,43(16):8007-8017
In this paper, a three-dimensional model for hydrogen absorption in a metal alloy has been developed, validated against the experimental data in the literature, and then applied to a novel design for a hydrogen storage unit. The proposed design is similar to the fuel cell stack, but here the Membrane Electrode Assembly (MEA) has been replaced by a metal hydride (MH) reactor placed between the flow-field plates. These are stacked together to achieve the required amount of hydrogen storage. The flow-field plates have channels engraved on one side for hydrogen supply and on the other, for coolant/heating medium. It is known that the effectiveness of a hydrogen storage unit is directly related to its heat transfer area, and therefore, the choice of its geometry is very important. The larger the size, the more the resistance to heat transfer. Although, the internal tubular heat exchangers have proven to be effective in heat transfer, they pose severe challenges such as cooling/heating medium leakage due to tube erosion, stresses generated, etc. and they displace the active metal hydride from the tank. The present stacked MH reactor configuration helps to overcome these challenges by stacking small MH reactors together and there is no chance of the cooling/heating medium leaking into the metal hydride. Numerical simulations were performed to investigate the effect of coolant flow rate and percentage of flow-field plate rib area exposed to the MH reactor on temperature evolution and the amount of hydrogen stored. Further, a detailed study was carried out to understand the effect of compartmentalization of the MH reactor on temperature distribution. The results revealed that compartmentalization substantially helps to uniformly distribute the temperature in the metal bed, which is very important to maintain uniform utilization of the metal powder. Consequently, the uniform metal powder density for repeated absorption-desorption cycles without significant loss of its hydrogen storage capabilities. 相似文献
5.
针对尾撑式风洞模型强方向性振动问题,基于异位配置加速度负反馈控制器对风洞模型振动主动控制方法进行研究。首先,通过模态分析得到系统低阶模态振动的强方向性并基于系统特性设计了具有结构耦合性的内嵌压电陶瓷作动器的风洞模型振动主动控制系统。然后,基于异位配置NAF控制器分别设计了针对第二阶模态和前两阶模态的单模态NAF控制算法和双模态NAF控制算法。最后,进行了实验验证,结果表明:双模态NAF控制算法控制效果较好,前两阶模态阻尼比分别提高近13倍和近40倍,镇定时间分别缩短近11s和近26s。 相似文献
6.
Fateme Marandi 《国际生产研究杂志》2019,57(3):722-748
This paper introduces a new integrated multi-factory production and distribution scheduling problem in supply chain management. This supply chain consists of a number of factories joined together in a network configuration. The factories produce intermediate or finished products and supply them to other factories or to end customers that are distributed in various geographical zones. The problem consists of finding a production schedule together with a vehicle routing solution simultaneously to minimise the sum of tardiness cost and transportation cost. A mixed-integer programming model is developed to tackle the small-sized problems using CPLEX, optimally. Due to the NP-hardness, to deal with medium- and large-sized instances, this paper develops a novel Improved Imperialist Competitive Algorithm (IICA) employing a local search based on simulated annealing algorithm. Performance of the proposed IICA is compared with the optimal solution and also with four variants of population-based metaheuristics: Imperialist Competitive Algorithm, Genetic Algorithm, Particle Swarm Optimisation (PSO), and Improved PSO. Based on the computational results, it is statistically shown that quality of the IICA’s solutions is the same as optimal ones solving small problems. It also outperforms other algorithms in finding near-optimal solutions dealing with medium and large instances in a reasonably short running time. 相似文献
7.
To solve the problem of complex,cumbersome and error-prone configuration of security devices caused by the heterogeneous configuration modes in complex networks,a dynamic template-based scheme for translating and configuring policy was proposed.In detail,considering the code’s features,the code-based template for translating policies was constructed to configure the command line conversion,and the keyword comparison method was used to ensure the accuracy of policy configuration.Experiments show that the scalability and the accuracy of the proposed scheme. 相似文献
8.
9.
对一般轴对称曲面零件成形,在平面应力假设和增量理论等条件下,以初始构形为参考构形,采用参数分析方法,得到了等效应变增量的微分方程。由于该微分方程包含了等效应变增量和等效应变增量的一阶导数项,一般情况下,等效应变增量的一阶导数以隐函数的形式存在,难以采用理论方法进行求解,因此,将等效应变增量的一阶导数表示成其自身、等效应变增量以及参变量的函数,根据泰勒级数展开式和积分的定义给出了逐步积分解法,可用于求解轴对称胀形、翻边、拉深等板材成形问题。以圆筒形件和圆锥形件的拉深成形为例,采用增量理论,将总变形分成若干个增量步,逐步加载,跟踪变形质点,累加应变,求解得到了法兰区和凹模圆角区等的应变分布。对分别采用比例加载条件、增量理论计算得到的结果与实验值进行了比较,结果表明,采用增量理论得到的结果更接近实验值。 相似文献
10.
Hui LIAO 《等离子体科学和技术》2019,21(8):85102-29
A series of experimental results of field-reversed configurations (FRCs) on a KMAX (Keda Mirror with AXisymmetricity) tandem mirror machine are reported. Single-side FRC translation processes with three different gas species were measured by avalanche photodiodes. Consistent with the theoretical prediction, the measured FRC speeds were inversely proportional to the square root of the ion mass. However, the speeds of the hydrogen FRC increased even in a uniform magnetic field region while the speeds of the helium and argon FRCs decreased. Possible mechanisms are discussed. The speed of the second pass due to the reflection of the mirror fields was found to be ∼1/3 of the first pass speed. The internal magnetic fields were
measured for a colliding-merging argon FRC, and the results show that, even for very slowmoving FRCs, merging can occur. 相似文献