阻火器壳体结构与爆轰火焰状态关系研究

针对大型煤矿瓦斯运输管道甲烷爆轰过程中火焰压力波和速度与阻火器结构的匹配问题,对阻火器壳体结构变化与管道内火焰压力和速度的关系进行了仿真研究,仿真中对不同尺寸的阻火器壳体结构建立了二维几何模型和网格模型,采用RNC k-e湍流模型和通用有限速率燃烧模型,运用FLUENT软件对煤管内可燃气体爆轰过程进行了模拟.得到了阻火器壳体内径尺寸、阻火器内有无障碍物与爆轰火焰压力和速度的变化规律,通过分析阻火器内火焰速度和压力的规律,为管道爆轰阻火器的设计和选型提供更为准确的参考依据.     

PVA改性半纤维素-g-AA/膨润土复合高吸水树脂合成研究

为使再生纤维和造纸行业生产过程中产生的带碱半纤维素废液得到有效利用,解决传统高吸水树脂成本高、耐盐性差、凝胶强度低等问题,以半纤维素、部分中和的丙烯酸、膨润土为原料,过硫酸铵-亚硫酸氢钠为氧化还原引发剂,N,N′-亚甲基双丙烯酰胺为交联剂,引入聚乙烯醇（PVA）,在微波辐射条件下合成了聚乙烯醇改性半纤维素-g-丙烯酸/膨润土半互穿网络高吸水树脂,采用FTIR,TG和SEM对产物结构和性能进行表征和测试,考察PVA的引入及其与黏土的协同作用对树脂网络结构和吸液、保水性能的影响。结果表明：在半纤维素-g-丙烯酸/膨润土基础上引入适量的PVA,可以成功制得聚乙烯醇改性半纤维素-g-丙烯酸/膨润土复合高吸水树脂;当PVA质量分数为3%时,树脂的吸水率和吸盐水率分别提高了40.6%和34.7%;改性后树脂的三维网络结构得到有效改善,表现出良好的吸液性能和保水性能。在纤维素综合利用中,利用半纤维素废碱液制备高吸水树脂,可以变废为宝,经济效益和社会效益明显。     

基于堆叠自编码器神经网络的复合电磁检测铁磁性双层套管腐蚀缺陷分类识别方法

铁磁性双层套管长期服役于恶劣的工作环境,极易出现腐蚀缺陷,定期为服役中的双层套管进行在线检测十分必要,而对管壁腐蚀缺陷位置的分类识别是管道定量检测与维修的前提和基础,实时准确的套管腐蚀缺陷分类识别能力是决定管道在线检测效率的重要因素。针对这一情况,将脉冲远场涡流和脉冲涡流技术相结合,提出了基于堆叠自编码器神经网络的分类方法。通过仿真和实验选取合适特征量作为输入层,实现了内管外壁腐蚀、外管内壁腐蚀和外管外壁腐蚀的分类,实验整体预判精度可达97.5%,结果表明该方法可对双层套管腐蚀缺陷缺陷实施高效、高精度分类识别。     

基于卷积核分解的深度CNN模型结构优化及其在小图像识别中的应用

小图像由于像素少、分辨率低、整幅图像包含信息较少,识别较为困难。目前优秀的深度卷积神经网络模型多为大图像而设计,而用于小图像的模型则存在着层次不够深、难以对特征进行充分抽象的不足。本文基于VGG19模型,依据卷积核分解的原理,设计了一种KDS-DCNN模型,模型深度达到31层,解决了目前超深度模型不能直接用于小图像识别的问题,实验表明该方法不但提升了识别性能,而且还降低了模型的时间复杂度。在CIFAR-10、CIFAR-100和SVHN三个数据集上的验证结果显示,KDS-DCNN模型性能优越,其识别错误率分别降低到29.46%、6.02%和2.17%。     

基于超螺旋精度提升机制的OFDM网络信道噪声消除算法

为解决当前OFDM网络信道噪声消除算法难以规避信道中的窄带莱斯噪声,且抗信道衰落能力不强,以及信道间普遍存在严重的频率干涉问题,提出了一种基于超螺旋精度提升机制的OFDM网络信道噪声消除算法.首先,根据各个传输子信道具有差异化的频率载波特性,将传输子信道等价为接收背景中的接收点,从而构建了超螺旋接收结构,有效消除不同传输子信道间存在的频率干扰特性,降低信道窄带莱斯噪声对信号预发射过程的衰落影响;随后,基于角度识别方式进行锐-钝识别,并结合拐点思想,采用序列重排技术,将待发射信号进行消波处理,并进行自旋精度提升,从而提高了其抗窄带莱斯噪声的性能.仿真实验表明:与常见的超高频精度自适应机制(UHF adaptive,UHFA)、共线度自旋精度提升机制(the degree of accuracy of collinear spin,DACS)相比,本文算法与理想状态下的OFDM功率谱密度曲线最为接近,具有更高的信号增益水平与更低的信道误码率.     

引信自旋式微电机旋转机架抗高过载结构设计

针对炮弹发射过程中的瞬时高过载造成弹道修正引信自旋式微电机旋转机架失效,导致引信无法正常工作的问题,结合当前弹载器件抗过载的主要方法与思路,考虑电机旋转机架的工作特点,根据旋转机架动力学模型和轴承在缓冲设计条件下的吸能原理,基于弹-炮-引信耦合有限元动力学仿真获取了旋转机架轴承的过载特性,结果表明了轴承主要承受轴向过载条件下的惯性力冲击。在此基础上,提出了在轴承处添加铜制缓冲垫片和改变外转子机架的轴肩与底螺尺寸两种抗过载设计方案,并通过弹-炮-引信耦合有限元动力学仿真分别获取了两种方案下球轴承最大应力值随时间的变化。结果表明,添加铜制缓冲垫片无法将球轴承的最大应力降低到轴承钢屈服极限以下,而通过改变外转子机架轴肩与底螺尺寸能成功将球轴承的最大应力值降低至轴承钢屈服极限以下,结合推力轴承形变量判定,该方案满足旋转机架的抗过载设计需求,保证了修正引信在炮弹发射后的正常工作。      

Thermal Resistance Measurement across a Wick Structure Using a Novel Thermosyphon Test Chamber

A novel system is developed for measuring the thermal resistance across thin layers of sintered copper wicks of varying porosity. Wicks to be tested are integrated into a passive vertical thermosyphon system, and the resistance is measured for a series of input power levels. The wicks are sintered to a thermally conducting pedestal above a pool of deionized water and heated from below. The apparent thermal resistance across the wick (from the pedestal/wick interface to the vapor space) under the evaporative operating conditions encountered in heat pipes is measured using thermocouples. The apparent thermal resistance across the wick is measured to be as low as 0.01°C/W, corresponding to an evaporative heat transfer coefficient of greater than 128,000 W/m²K.     

Residual stress in polyethylene pipes

This paper deals with residual stress in polyethylene (PE) pipes as an important factor that influences their lifetime. Residual hoop stress distribution in a PE pipe was determined using a methodology previously carried out by the authors on polypropylene pipes. Axial residual stress magnitude was determined by comparison of experimental data and finite element modelling. Based on the obtained results, a new simplified methodology for determining the residual hoop stress is proposed. The method needs only one circular specimen made of pipe, but, unlike older methods, provides a more precise estimation of residual hoop stress distribution taking into account its exponential shape. Some older results from literature are recalculated using this method and residual hoop stress of various PE pipe grades and dimensions are then compared. To provide an idea of residual hoop stress influence on lifetime of a pipe, a lifetime estimation is carried out for the examined pipe.     

Modelling and simulation of gas dynamics in an exhaust pipe

The gas dynamics in an exhaust pipe is studied. In particular we focus on the warm up of the catalytic converter in very short times after the engine start. This is done by combustion a small unburnt part of the exhaust gas. This process is classically modelled by gas dynamic equations. Compared to the existing literature we improve the (one-dimensional) modelling approach using a small Mach number technique and a network ansatz for the full exhaust pipe. The final simplified model on one hand still describes the main features and on the other hand it is computationally a few orders of magnitude faster than the original model. Performing numerical simulations we compare the new model to the (classical) full model and to experimental results in the literature.