排气歧管流固耦合仿真与试验

针对发动机排气歧管的断裂问题,对某发动机排气歧管的热负荷进行流固耦合分析,并在台架试验中测量其温度场和应变.考虑热辐射和材料的非线性,建立排气歧管的内流场CFD模型、传热模型和有限元模型,分析得到排气歧管的温度场、应力场和塑性应变云图等.仿真结果与试验结果吻合较好.仿真结果表明排气歧管汇合处的温度最高,塑性应变最大位置与试验测得的断裂危险区域吻合.     

热处理对40CrNiMoA钢板焊接接头组织及力学性能的影响

本文研究了调质工艺对40CrNiMoA钢板焊接接头显微组织及力学性能的影响。试验结果表明,经 830 - 870 °C +550 - 650 °C 调质处理后,40CrNiMoA钢3 mm板90 A 10 V焊接接头的焊缝区、热影响区、母材区的硬度差异显著减小,形成了回火索氏体组织。调质处理温度越高,焊接接头的焊缝区、热影响区与母材区的组织越 均匀,且组织中的碳化物颗粒尺寸增大。40CrNiMoA钢焊接板经850 Y油淬,600 X.回火后,具有较高的强度(905 MPa)和塑性(13. 5% ),综合力学性能最优。     

泄洪洞反弧段末端水力特性指标分布规律

龙抬头式泄洪洞在水利水电工程中应用十分普遍,但是由于反弧段流态复杂,其产生空蚀破坏的原因尚不明晰。对不同泄洪洞体型掺气前后的工况进行三维数值计算,对其水力特性指标的分布规律进行研究。结果表明:随着落差Δz增大,反弧段流速逐步增大,水流空化数逐步减小;反弧半径R的改变对反弧段水力参数的影响有限。掺气水流的反弧段水力学指标主要取决于Δz,而受反弧半径R的影响相对较小。当Δz减小时,反弧段末端的水力参数在掺气前后变化不大,反弧段末端下游30m(等于15倍的挑坎高度)处的掺气水流的流速明显降低,空化数明显增高,掺气水流的保护作用对空腔下游部分的水力参数影响更加明显。在反弧末端有二次流出现,两侧边墙附近存在对称涡,不仅对边墙附近的流速压力分布产生一定影响,也加剧了反弧段内的水力特性的复杂程度。     

A novel reversible robust watermarking algorithm based on chaotic system

Reversible watermarking can be applied to the protection for important digital media, such as medical and military image, it allows the watermark to be extracted and the original image to be restored completely, but reversible watermarking with stronger robustness is seldom discussed in existing literature. In this paper, a novel reversible watermarking algorithm based on chaotic system is proposed; chaotic system is not only used to search space of reversibility of the scheme, but also used to randomly select the position of watermarking embedding. Consequently, the proposed scheme achieves larger threshold space of reversibility and better performance of security. For some specific thresholds, the proposed algorithm is not only reversible, but also has stronger robustness against image compression. The experimental results show that the ergodicity and sensitivity to initial values of chaotic system play an important role in reversible watermarking algorithm, and the proposed scheme can achieve balance between reversibility and robustness with the help of chaotic system.     

Solid-state potentiometric SO2 sensor combining NASICON with V2O5-doped TiO2 electrode

A compact tubular sensor based on NASICON (sodium super ionic conductor) and V₂O₅-doped TiO₂ sensing electrode was designed for the detection of SO₂. In order to reduce the size of the sensor, a thick-film of NASICON was formed on the outer surface of a small Al₂O₃ tube; furthermore, a thin layer of V₂O₅-doped TiO₂ with nanometer size was attached on the NASICON as a sensing electrode. This paper investigated the influence of V₂O₅ doping and sintering temperature on the characteristics of the sensor. The sensor attached with 5 wt% V₂O₅-doped TiO₂ sintered at 600 °C exhibited excellent sensing properties to 1–50 ppm SO₂ in air at 200–400 °C. The EMF value of the sensor was almost proportional to the logarithm of SO₂ concentration and the sensitivity (slope) was −78 mV/decade at 300 °C. It was also seen that the sensor showed a good selectivity to SO₂ against NO, NO₂, CH₄, CO, NH₃ and CO₂. Moreover, the sensor had speedy response kinetics to SO₂ too, the 90% response time to 50 ppm SO₂ was 10 s, and the recovery time was 35 s. On the basis of XPS analysis for the SO₂-adsorbed sensing electrode, a sensing mechanism involving the mixed potential at the sensing electrode was proposed.     

An extended matrix encoding algorithm for steganography of high embedding efficiency

F5 steganography is much different from most of LSB replacement or matching steganographic schemes, because matrix encoding is employed to increase embedding efficiency while reducing the number of necessary changes. By using this scheme, the hidden message inserted into carrier media imperceptibly can be transferred via a more secure subliminal channel. The embedding domain is the quantized DCT coefficients of JPEG image, which makes the scheme be immune to visual attack and statistical attack from the steganalyst. Based on this effective scheme, an extended matrix encoding algorithm is proposed to improve the performance further in this paper. By changing the hash function in matrix encoding and converting the coding mode, the embedding efficiency and embedding rate get increased to a large extent. Eventually, the experimental results demonstrate the extended algorithm is superior to the classic F5 steganography.     

地质雷达滤波参数对图像分析结果的影响

基于探地雷达的基本原理,论述了不同地质雷达数字滤波参数对图像分析结果的影响,得出垂直带通滤波在雷达图像处理中起关键作用.并结合平遥古城墙的工程实例,具体探讨了垂直带通滤波的设置问题,建议根据实际的水文工程地质条件,选择合适的数字滤波参数,以便得到清晰精确的探地雷达图像,为今后的技术应用及探测工作提供了依据和支持.     

供热系统分时分区控制节能实测分析

针对特殊用途的公共建筑在无人情况下仍照常供暖而造成能源浪费的现状,采用分时分区控制系统对实例工程供热系统进行了节能改造.测试分析了改造后系统的节能量、整体节能效果、不同控制方案对住户温度的影响.结果表明,采用分时分区控制后供热系统节能率高达25.8％,锅炉房总节能8.7％,节能效果显著.     

加镍钨粉的活化烧结研究进展

钨具有高密度、高熔点、低的热膨胀系数、优异的导电导热性能以及良好的耐腐蚀性能,在许多领域得到了广泛的应用,但由于熔点高,钨的烧结致密化困难。活化烧结是制备高密度和高性能钨及其合金材料的重要方法,其中添加镍元素是钨粉活化烧结最重要的手段之一。本研究从镍的活化效果、掺杂含量以及活化机理方面综述了镍对钨的活化烧结作用,并提出了添加金属元素的钨粉活化烧结的研究方向。     

直流基体偏压对Al-Cr-Si-N涂层结构和力学性能的影响

采用电弧离子镀技术在不同直流偏压下沉积Al-Cr-Si-N涂层,研究基体偏压对涂层成分、微观结构和性能的影响。结果表明:Al-Cr-Si-N涂层以密排六方结构和面心立方结构的AlN相为主,随着基体负偏压增加,涂层的衍射峰整体向小角度方向偏移:涂层内残余压应力逐渐增加,最大值为-0.77 GPa;涂层硬度和摩擦系数变化不明显。当基体负偏压为-40V时,Al-Cr-Si-N涂层的特征参数H/E和H~3/E~(*2)均达最大值,分别为0.15和0.37GPa,此时涂层具有最佳的耐磨性能,摩擦系数亦最低。