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91.
《Ergonomics》2012,55(4):405-406
The extension force against resistance was recorded in 23 postures for 12 subjects to find explanations for the decrease in back strength in asymmetric postures. A reduction in muscle force in asymmetric postures was found up to 40%, but was strongly dependent on the plane in which asymmetry occurred, and on the posture to which it referred. A quantitative relationship between the forces exerted in different asymmetric postures is discussed, as a basis for formulating universal ergonomic guidelines for optimal working postures. The reduction in force in different asymmetric postures can be explained by length of the muscle, the activation of the muscle, and the moment angle of the muscle.  相似文献   
92.
Valve stiction is the most frequent cause of loop oscillations. Thus, detecting and quantifying this valve problem is essential to ensuring plant profitability. In this work, a novel one-stage procedure to estimate stiction parameters is proposed using a two-parameter stiction model. The optimisation problem is computed using a global optimisation algorithm. These two propositions make the stiction computation more efficient and computationally faster than the currently available method. The applicability of the proposed approach is illustrated using a large number of simulated and industrial valves. Moreover, to isolate the impact of each proposition, the novel method is compared with the currently available technique, which is based on a two-stage scheme. The results show that the global optimisation algorithm is more efficient than the direct search and genetic algorithms, as previously proposed by Jelali (2008). The two-stage procedure provides a better estimate of the apparent stiction, whereas the one-stage procedure provides a better slipjump value.  相似文献   
93.
Dimensional analysis for planetary mixer: Mixing time and Reynolds numbers   总被引:1,自引:0,他引:1  
Mixing time number is a convenient parameter to characterize mixing performance of stirred tanks. This dimensionless number is now well established for agitated vessels equipped with vertically and centrally mounted impeller for Newtonian as well as for non-Newtonian fluids. To our knowledge, there is more ambiguity concerning its definition for planetary mixers especially when they have dual motion (around two perpendicular axes) to achieve homogenization. In this study, dimensional analysis of mixing time and reliability of the modified Reynolds and mixing time numbers are proposed for such a planetary mixer particularly named as TRIAXE® system. These two numbers are based on the maximum tip speed of mixer as the characteristic velocity. Modified dimensionless numbers are consistent with the definition of conventional Reynolds and mixing numbers (when only one revolving motion around the vertical axis of the mixing device occurs in the vessel).Mixing time experiments with TRIAXE® mixer for highly viscous Newtonian fluids showed that the proposed modified Reynolds and mixing time numbers succeeded to obtain a unique mixing curve irrespective of the different speed ratio chosens. This agreement proves that the proposed modified dimensionless numbers can be well adapted for engineering purposes and they can be used to compare the mixing performance of planetary mixers.  相似文献   
94.
本文用有限元软件ANSYS中的三维梁单元建立了高温高压根阀的计算模型.对模型作模态分析后,用静态法计算了根阀在地震栽荷和自重载荷下的结构反应,并根据ASME规范采用压力面积法计算了根阀阀体在内压作用下的总体一次薄膜应力强度和弯曲应力强度,最后按规范要求对根阀进行了各使用限制条件下的应力组合与评定,评定结果表明根阀的设计满足ASME规范的要求。  相似文献   
95.
本文首先介绍了开关电源的基本工作原理和电路构成,在此基础上,通过试验研究,建立了计算机和电视机等电子设备的静态负荷模型。所得结论,为电力系统稳定分析计算提供了依据。  相似文献   
96.
静止无功补偿装置在输电系统中的应用   总被引:13,自引:0,他引:13  
林海雪 《电力设备》2005,6(10):17-20
阐述了静止无功补偿装置(SVC)对改善电网枢纽点的电压控制;提高静态和暂态稳定性,增加输电能力;抑制系统暂时(工频)过电压;增加阻尼,抑制低频和次同步振荡,提高输电功率;改善直流换流站动态无功补偿性能等功能,以及在国内外高压输电系统中的应用情况,并给出了应用实例.我国电网正处在快速发展阶段,随着输电系统SVC技术国产化的成功,SVC在国内电网中的应用会有广阔前景.  相似文献   
97.
天钢集团中板厂SVC动态无功补偿和谐波滤波系统   总被引:4,自引:0,他引:4  
天津钢铁集团中板厂的负载为冲击性交-交变频机,交-交变频机的谐波除了特征谐波外,还有大量旁频。电网中谐波电流大,功率因数低,电压波动超标。SVC系统为FC TCR系统,通过测试负载电流和普通直流机负载电流,分析频率特性,得出交交变频机的谐波滤波可以按照直流机的滤波装置来设计,同时TCR本身产生的谐波必须予以考虑。  相似文献   
98.
This work gives the exact stiffness coefficients for an high order isotropic beam element. The terms are found directly from the solutions of the differential equations that describe the deformations of the cross-section according to the high order theory, which include cubic variation of the axial displacements over the cross-section of the beam. The model has six degrees of freedom at the two ends, one transverse displacement and two rotations, and the end forces are a shear force and two end moments. Also given are the equivalent end forces and moments for several cases of loading along the member. The components of the end moments are investigated, and are found for exact results. Comparison is made with the Bernoulli-Euler and Timoshenko beam models.  相似文献   
99.
本文介绍了动画设计的基本原理,讨论了Windows位图的显示原理和显示方法。以一个动画制作的程序实例,详细叙述了使用VC 6.0设计多媒体动画软件的方法。  相似文献   
100.
This paper presents an approach to design static output feedback and non-fragile static output feedback H controllers for active vehicle suspensions by using linear matrix inequalities and genetic algorithms. A quarter-car model with active suspension system is considered in this paper. By suitably formulating the minimization problem of the sprung mass acceleration, suspension deflection and tyre deflection, a static output feedback H controller and a non-fragile static output feedback H controller are obtained. The controller gain is naturally constrained in the design process. The approach is validated by numerical simulation which shows that the designed static output feedback H controller can achieve good active suspension performance in spite of its simplicity, and the non-fragile static output feedback H controller has significantly improved the non-fragility characteristics over controller gain variations.  相似文献   
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