基于Fluent的圆柱齿轮流量计的密封性仿真分析

通过对圆柱齿轮流量计进行二维简化建模,用Fluent仿真软件的ICEM CFD模块进行网格划分,利用Fluent仿真软件对圆柱齿轮流量计进行了计算和密封性的仿真分析,得出了其速度矢量分布图,并且给出了各泄漏量的计算公式和每种泄漏所占泄漏总量的百分比,即为以后的整个流量计的设计提供理论依据。,提高流量计的寿命具有重要意义。同时还省去了大量的人工计算过程,极大地加快了计算速度。     

Composite bending-dominated hollow nanolattices: A stiff,cyclable mechanical metamaterial

Manufacturing ultralight and mechanical reliable materials has been a long-time challenge. Ceramic-based mechanical metamaterials provide significant opportunities to reverse their brittle nature and unstable mechanical properties and have great potential as strong, ultralight, and ultrastiff materials. However, the failure of ceramics nanolattice and degradation of strength/modulus with decreasing density are caused by buckling of the struts and failure of the nodes within the nanolattices, especially during cyclic loading. Here, we explore a new class of 3D ceramic-based metamaterials with a high strength–density ratio, stiffness, recoverability, cyclability, and optimal scaling factor. Deformation mode of the fabricated nanolattices has been engineered through the unique material design and architecture tailoring. Bending-dominated hollow nanolattice (B-H-Lattice) structure is employed to take advantages of its flexibility, while a few nanometers of carbonized mussel-inspired bio-polymer (C-PDA) is coherently deposited on ceramics’ nanolayer to enable non-buckling struts and bendable nodes during deformation, resulting in reliable mechanical properties and outperforming the current bending-dominated lattices (B-Lattices) and carbon-based cellulose materials. Meanwhile, the structure has comparable stiffness to stretching-dominated lattices (S-Lattices) while with better cyclability and reliability. The B-H-Lattices exhibit high specific stiffness (>10⁶?Pa·kg^?1·m^?3), low-density (～30?kg/m³), buckling-free recovery at 55% strain, and stable cyclic loading behavior under up to 15% strain. As one of the B-Lattices, the modulus scaling factor reaches 1.27, which is lowest among current B-Lattices. This study suggests that non-buckling behavior and reliable nodes are the key factors that contribute to the outstanding mechanical performance of nanolattice materials. A new concept of engineering the internal deformation behavior of mechanical metamaterial is provided to optimize their mechanical properties in real service conditions.     

基于数字兆欧表自动切换档位的研究与实现

随着电力、电气设备的日益复杂化,对于其安全性能也有了更高的要求,数字兆欧表作为测量绝缘阻值的重要工具,已在工业领域中广泛应用;为了满足测量精度以及兆欧表的可靠性,通过基于S3C2440的嵌入式平台,提出了一种基于数字兆欧表的自动切换档位的实现方案,以达到更加精确的测量;此方案通过判断采集到的电压值选择相应的采样电阻来实现,并结合硬件平台和软件设计,分别介绍了驱动程序和应用程序的编写与测试,并很好地应用到了实际电路中;经测试,能够达到预期的效果,测量精度高,测量误差控制在±2%。     

电火花打孔加工系统

本文介绍了电火花打孔加工系统的工作原理和组成、并对系统中的高压脉冲产生电路的设计进行了详细的阐述     

Property-microstructure correlation in in situ formed Al2O3, TiB2 and Al3Ti mixture-reinforced aluminium composites

The in situ formed Al₂O₃, TiB₂ and Al₃Ti mixture-reinforced aluminium composites were successfully fabricated by the reaction sintering of the TiO₂-B-Al system in a vacuum. With increasing boron content in the TiO₂-B-Al system, the amount of generated TiB₂ in the composites increased and Al₃Ti content decreased. At the same time the distribution uniformity of the in situ formed Al₂O₃ and TiB₂ particulates was obviously improved, and the size of the Al₃Ti particles was reduced. The in situ Al₂O₃ and TiB₂ particulates had sizes from 0.096–1.88 m. The interface between the in situ formed particulates and the aluminium matrix was clean, and no consistent crystallographic orientation relationship was found. The strength and elastic modulus of the composites was significantly improved by lowering the Al₃Ti content. When the boron content in the TiO₂-B-Al system rose, the morphology of the tensile fracture surface of the composites was changed from large fractured Al₃Ti blocks and fine dimples, to fine dimples and pulled-out particulates. The strengthening and fracture of the composites have been modelled.     

Simple procedures of choice in multicriteria problems without precise information about the alternatives’ values

The additive model of multiattribute value theory is widely used in multicriteria choice problems. But often it is not easy to obtain precise values for the scaling weights or the alternatives’ value in each function. Several decision rules which require weaker information, such as ordinal information, have been proposed to select an alternative under these circumstances. We propose new decision rules and test them using Monte-Carlo simulation, considering that there is ordinal information both on the scaling weights and on the alternatives’ values. Results show the new rules constitute a good approximation. We provide guidelines about how to use these rules in a context of selecting a subset of the most promising alternatives, considering the contradictory objectives of keeping a low number of alternatives yet not excluding the best one.     

The DCT-based oscillation detection method for a single time series

This paper proposes a new method based on the discrete cosine transform (DCT), named as the DCT-based method, to detect oscillations for a single time series. The main idea is to isolate different frequency components of the time series via the DCT, and to detect oscillations by checking the regularity of zero-crossings of these isolated components. This method has the following features: (i) usage of only time series information of process variables without additional process knowledge, (ii) ability to deal with slowly varying trends, (iii) robustness to both white and colored noises, (iv) capability to handle the presence of multiple oscillations, and (v) amenability to complete automation without human intervention. Simulation examples and industrial case studies are presented to demonstrate the effectiveness and the above features of the DCT-based method.     

A novel color image watermarking scheme in nonsampled contourlet-domain

Geometric distortion is known as one of the most difficult attacks to resist, for it can desynchronize the location of the watermark and hence causes incorrect watermark detection. It is a challenging work to design a robust color image watermarking scheme against geometric distortions. Based on the support vector regression (SVR) and nonsubsampled contourlet transform (NSCT), we propose a new color image watermarking algorithm with good visual quality and reasonable resistance toward geometric distortions in this paper. Firstly, the geometrically invariant space is constructed by using color image normalization, and a significant region is obtained from the normalized color image by utilizing the invariant centroid theory. Then, the NSCT is performed on the green channel of the significant region. Finally, the digital watermark is embedded into host color image by modifying the low frequency NSCT coefficients, in which the HVS masking is used to control the watermark embedding strength. In watermark detection, according to the high correlation among different channels of the color image, the digital watermark can be recovered by using SVR technique. Experimental results show that the proposed color image watermarking is not only invisible and robust against common image processing operations such as filtering, noise adding, and JPEG compression etc., but also robust against the geometrical distortions.