基于多CNN的分块镜piston和tip-tilt误差同步检测方法研究

绝大多数大型望远镜采用分块镜的设计方案,为了获得优质的成像效果,需要控制分块望远镜系统的piston和tip-tilt误差。神经网络误差检测方法相较于传统的检测方法具有一定优势,但存在仅检测单一类型误差的局限性。本文提出一种基于卷积神经网络的piston和tip-tilt误差同步检测方法,通过在出瞳面设置具有离散孔的光阑,引发分段镜反射的子波发生干涉-衍射现象,构建包含丰富piston和tip-tilt误差信息的数据集。通过粗测网络和精测网络级联,满足大范围和高精度同步检测的需求。结果表明,该方法实现了对输入光源相干长度内纳米级的piston误差检测,并对10μrad范围内的tip-tilt误差实现了亚微弧度检测;对40 dB的CCD噪声表现出良好的抗干扰性,对面形误差的允差为0.05λ0RMS(λ0=600 nm),同时对六子镜系统具有可扩展性。本文方法光路简单,操作便利,具有实际意义。

Effect of ultrasonic and mechanical vibration treatments on evolution of Mn-rich phases and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys

Effects of ultrasonic vibration(UV)and mechanical vibration(MV)on the Mn-rich phase modification and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys were investigated.The results show that the UV and UV+MV treatments can significantly refine and fragmentize the microstructures.In addition,UV treatment can significantly passivate the primary Mn-rich Al15Mn3Si2 intermetallics.The formation mechanisms of refinement and passivation of the grains and non-dendrite particles were discussed.Compared with the gravity die-cast alloys,the UV and UV+MV treated alloys exhibit improved tensile and creep resistance at room and elevated temperatures.These results can be attributed to the refinement of theα(Al)grains and the secondary intermetallics,the increased proportion of refined heat-resistant precipitates,and the formation of nano-sized Si particles.The ultimate tensile strength of the UV treated alloys at 350℃ exceeds that of commercial piston alloys.This indicates the high application potential of the developed piston alloys in density diesel engines.

Static and Thermal Analysis of Aluminium (413,390,384 and 332) Piston Using Finite Element Method

The main objective of this research was to examine the suitability of aluminium alloy to design a piston of an internal combustion engine for improvement in weight and cost reduction. The piston was modelled using Autodesk Inventor 2017 software. The modelled piston was then imported into Ansys for further analysis. Static structural and thermal analysis were carried out on the pistons of the four different materials namely: Al 413 alloy, Al 384 alloy, Al 390 alloy and Al332 alloy to determine the total deformation, equivalent Von Mises stress, maximum shear stress, and the safety factor. The results of the study revealed that, aluminium 332 alloy piston deformed less compared to the deformations of aluminium 390 alloy piston, aluminium 384 alloy piston and aluminium 413 alloy piston. The induced Von Mises stresses in the pistons of the four different materials were found to be far lower than the yield strengths of all the materials. Hence, all the selected materials including the implementing material have equal properties to withstand the maximum gas load. All the selected materials were observed to have high thermal conductivity enough to be able to withstand the operating temperature in the engine cylinders.

The Effect of Ignition Parameters on the Combustion Characteristics of an Aviation Piston Engine

A cylinder combustion simulation model was established for a two-stroke aviation piston engine used in a small unmanned aerial vehicle. The influence of different ignition system parameters on the combustion process of aviation kerosene was studied using this model. The research results showed that under the working conditions of 5500 r/min and 50% throttle opening, as the ignition energy increased, the peak values of average cylinder pressure and average temperature increased, and the combustion duration shortened, The advance of the combustion center of gravity increases the tendency of the engine to knock. Under the same operating conditions, as the ignition timing advances, the peak values of average pressure and average temperature in the cylinder increase, gradually approaching the top dead center, and the tendency of engine detonation increases more significantly.

Numerical Wave Channel with Absorbing Wave-Maker

The numerical wave channel has been developed based on the volume of fluid method (VOF) in conjunction with the Navier-Stokes equations. The absorbing wave-maker boundary on the left side of the channel is presented by prescribing velocity reference to linear wave-maker theory. The principle of which is that the numerical wave-maker is designed to move in a way that generates the required incident wave and cancels out any reflected wave that reach it at the same time. On the right side of the channel, the open boundary is set to permit incident waves to be transmitted freely. The parametric studies have been carried out at a range of ratios of water depth to wave length d/ L from 0.124 to 0.219, with wave height in the front of paddle/water depth ratio (H0 / d) from 0.1 to 0.3. Wave height, wave pressure distribution along the channel and velocity field are obtained for both open boundary condition and reflective boundary condition at the other end of the channel. For a reflective case, it is shown that the absorbing wave-maker is very effective in canceling out the reflected wave that reaches the numerical paddle and highly repeatable waves can be generated.

Cavitation recognition of axial piston pumps in noisy environment based on Grad-CAM visualization technique

The cavitation in axial piston pumps threatens the reliability and safety of the overall hydraulic system.Vibration signal can reflect the cavitation conditions in axial piston pumps and it has been combined with machine learning to detect the pump cavitation.However,the vibration signal usually contains noise in real working conditions,which raises concerns about accurate recognition of cavitation in noisy environment.This paper presents an intelligent method to recognise the cavitation in axial piston pumps in noisy environment.First,we train a convolutional neural network(CNN)using the spectrogram images transformed from raw vibration data under different cavitation conditions.Second,we employ the technique of gradient-weighted class activation mapping(Grad-CAM)to visualise class-discriminative regions in the spectrogram image.Finally,we propose a novel image processing method based on Grad-CAM heatmap to automatically remove entrained noise and enhance class features in the spectrogram image.The experimental results show that the proposed method greatly improves the diagnostic performance of the CNN model in noisy environments.The classification accuracy of cavitation conditions increases from 0.50 to 0.89 and from 0.80 to 0.92 at signal-to-noise ratios of 4 and 6 dB,respectively.

Tribological Properties of Ti-DLC Coatings on Piston-pin Surfaces

A magnetically filtered cathode vacuum arc deposition system was used to deposit Ti-doped diamond-like carbon coatings(Ti-DLC)on pin surfaces to improve the wear resistance of high-power density diesel engine piston pins.The coating structure,composition,and morphology were characterised using field emission scanning electron microscopy(FE-SEM),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy,and other techniques.Friction tests were carried out using a universal tribometer to study the tribological properties of pins with or without coatings under dry friction and oil lubrication.The surface morphology and cross-sectional morphology of the Ti-DLC coating show that the coating has a uniform crosssection and good surface properties.The XPS spectrum shows that the coating contains Ti-C,Ti-C*,sp2-C,sp3-C,and C-O/C=O.Raman spectroscopy shows that there is an amorphous carbon phase in the Ti-DLC coating.The friction test shows that the friction temperature increase of the pin with the Ti-DLC coating is lower than that without the coating,especially under dry-friction conditions.At the end of the test,the difierence in temperature increase is 16.7%.The friction coefficient when using high-viscosity lubricating oil with a coating is relatively lower than that without a coating,especially under low-speed and heavy-duty conditions.In the dryfriction state,the coated surface has better wear resistance than the uncoated surface,which primarily manifests as abrasive wear,and the surface without a coating mainly experiences adhesive wear.

基于多目标遗传算法的斜盘式轴向柱塞泵低脉动结构优化设计

由于轴向柱塞泵的非对称结构特性,其输出压力和输出流量存在脉动特性,对液压系统的输出稳定性和可靠性造成影响,因此提出了一种基于多目标遗传算法的斜盘式轴向柱塞泵低脉动结构优化设计方法。首先,通过CFD(computational fluid dynamics,计算流体动力学)仿真分析方法,对轴向柱塞泵上/下死点位的压力-流量脉动的产生机理进行了分析;其次,对阻尼槽结构参数对轴向柱塞泵输出压力-流量脉动的影响规律进行了分析,构建了阻尼槽结构的多目标优化模型;最后,求解了低脉动阻尼槽结构。优化后的结构参数:阻尼槽半径为2.21 mm,阻尼槽长度为10.32 mm,阻尼槽错配角为16.54°。优化后压力脉动率为0.59%,相比于优化前的0.75%降低了0.16%,脉动幅值为0.25 MPa;优化后流量脉动率为12.02%,相比于优化前的5.61%降低了43.59%。研究结果为轴向柱塞泵低脉动结构的优化设计提供了有效的理论支持和实践指导。

基于改进EEMD-MB1DCNN的船用柴油机缸套-活塞环故障诊断

针对船用中高速柴油机缸套-活塞环振动信号非线性非平稳性以及同类型不同损伤程度故障发生时振动信号时频域特征相似、故障难以识别等问题,利用振动信号辨识故障,提出一种基于改进集成经验模态分解方法和多模块一维卷积神经网络端到端缸套-活塞环故障诊断方法,通过设计固有模态分量IMF信息质量筛选准则对EEMD分解出的IMFs进行重新排序,获得包含更多凸显故障特征成分的重构信号,输入到上述神经网络模型,通过振动信号分析并与现有方法比较,评估所设计IMF信息质量筛选准则与所搭建模型的性能,试验结果显示该方法能准确、有效地识别缸套-活塞环故障类型。在判断该易损件同类型不同磨损程度故障诊断中有较高的准确率,能对故障状况进行有效的特征提取与故障分类。

斜盘式轴向柱塞泵空化特性分析

针对斜盘式轴向柱塞泵的空化现象,建立了斜盘式轴向柱塞泵全流域模型,采用计算流体力学方法研究了全流域空化特性分布,分析了排油口负载压力、缸体转速和斜盘倾角等工况参数对全流域空化特性的影响规律。研究表明:空化主要发生在吸油区的吸油口、配流盘和柱塞腔区域,空化随气相体积分数增大而加重;排油口负载压力由10 MPa增至30 MPa,吸油口、配流盘和柱塞腔气相体积分数峰值分别由6.28%增至6.68%、5.91%增至7.13%、10.03%增至11.23%;缸体转速由2 200 r/min增至3 000 r/min,吸油口、配流盘和柱塞腔气相体积分数峰值分别由6.39%增至6.41%、6.26%增至10.54%、7.13%增至10.16%;斜盘倾角由3.64°增至5.64°,吸油口、配流盘和柱塞腔气相体积分数峰值分别由6.34%增至6.41%、14.7%降低至13.9%、10.16%增至11.66%。斜盘式轴向柱塞泵在实际设计中,排油口负载压力、缸体转速和斜盘倾角的取值在合理范围内越低越好,斜盘倾角取值存在最优区间。

水液压泵柱塞副织构单元的润滑及承载特性分析

为研究水基轴向柱塞泵织构化柱塞副的润滑及承载特性,建立了轴向柱塞泵AMESim仿真模型,得出单柱塞往复速度、有效织构区长度与其腔内压力特性间的对应关系。建立织构化柱塞副的简化CFD润滑及承载力模型,分析了单周期内织构单元的压力云图、压力分布曲线及承载力特性曲线,研究了织构半径、深度及形貌对柱塞副润滑及承载特性的影响。结果表明:柱塞表面承载力曲线与柱塞腔压力脉动及压力梯度曲线的规律较为一致,在高压区柱塞承载力高,呈出与压力梯度曲线相应的波动式下降特征,而低压区柱塞承载力较低;仿真条件下,增大织构半径及深度均有助于提高柱塞表面承载力,且织构形貌对承载力影响较大,承载力由高到低的形貌依次为圆柱形、球冠形、菱形、方形和三角形。此外,织构收敛楔和发散楔开口大小分别对织构单元的正压核心和负压核心区的面积影响较大,且横截面为直角过渡的圆柱形织构比圆弧过渡的球冠形织构更利于压力集聚。

等温压缩空气储能技术研究综述

压缩空气储能是一种新型的大型物理储能技术,具有很好的发展前景。介绍了等温压缩空气储能的基本原理,以及关键设备与相关技术的原理及发展现状;对液体活塞、水泵和水轮机进行分析和总结;对等温压缩空气储能的基本原理进行了归纳和说明;分析了现有等温压缩空气储能技术研究进展情况,对系统中液体活塞技术以及水泵和水轮机技术进行分析和总结;对已有的压缩空气储能电站数据进行汇总分析。在此基础上,对等温压缩空气储能技术未来发展方向进行了展望,可为等温压缩空气储能系统中动力设备的选用以及示范项目的推进提供一定的数据参考。

斜盘偏距与交错角对飞机液压柱塞泵运动特性影响分析

飞机上常用的直轴式恒压变量液压柱塞泵,出于降低脉动以及改善高频运动时的稳定性需要,斜盘通常设计有偏心距和交错角。针对存在斜盘偏距和交错角的液压柱塞泵,提出了一种能够综合考虑斜盘偏距、交错角、斜盘倾角及斜盘转动速度的柱塞和滑靴运动特性分析方法。以某型航空液压柱塞泵为对象,对比分析了不同偏心距和交错角情况下柱塞的位移、速度特性,以及滑靴在斜盘平面的运动轨迹。按照液压泵配流盘闭死区设计通用准则确定了配流盘闭死区,对柱塞在闭死区内的运动特性进行了分析,结果表明闭死区内柱塞的运动特性深刻影响液压柱塞泵的输出流量和压力脉动。提出的分析方法能够描述斜盘转动(流量切换)过程中的运动动态特性,具有计算效率高、结果准确度高等特点,可用于液压柱塞泵以降低脉动为目标的设计优化。

OP2S双燃料发动机气口匹配特性研究

对置活塞二冲程(OP2S)发动机是一种结构可调性较高的动力系统,采用等效二冲程方法建立并校验了OP2S柴油机的一维仿真模型,研究了不同甲醇含量下进排气口高度冲程比对OP2S柴油机动力性能、燃油经济性、换气性能和排放性能的影响。结果表明:OP2S柴油机具有换气性能和排放性能的双“trade-off”关系。甲醇含量增加会促进经济性能的提高和动力性能的降低,也会促进扫气效率的增加和捕获率的降低。进排气口的匹配设计是提升OP2S柴油机性能的关键之一。进气口通过增加新鲜空气主动促进燃烧,而排气口通过减少能量和新鲜充量损失被动改善换气性能。随着气口高度的增加,OP2S柴油机的性能曲线具有双转捩点。将性能曲线分为3个区域,其中第2区域为最佳性能区,该区域对应的进/排气口高冲程比分别为0.056~0.122和0.078~0.100。

液压破碎锤活塞横裂机理分析与工艺优化

针对破碎锤中的活塞横裂现象,分析了活塞产生横裂的机理,并提出了一种新的活塞热处理制造工艺。采用硬度计和金相组织显微镜对活塞材料进行分析,得出发生活塞横裂故障部位的材料成分和金相组织符合设计要求,而硬度和硬化层深度低于设计要求。利用ANSYS求解活塞“卡死”情况下的最大应力为1229.8 MPa,超出材料的屈服极限850 MPa,最大应力的位置在活塞横裂处;利用Fluent求解活塞所受的径向不平衡力,在活塞的回油槽中受到的最大径向力为3408 N,最小径向力为10 N,在活塞的进油槽中,最大径向力为15675 N,最小径向力为73 N。结果表明,活塞在径向不平衡力作用下形成的“卡死”现象是活塞发生横裂的主要原因。提出延长活塞的渗碳时间、增加活塞在热处理过程中的校直次数等热处理新工艺,经耐久实验验证,所提工艺可以有效解决活塞横裂问题。

列车活塞风对寒区铁路隧道温度场的影响

研究目的:列车通过隧道会产生活塞风,活塞风会将寒区隧道洞外冷空气带入洞内,导致洞内温度场分布发生变化,若对这种影响认识不到位,会导致洞内抗防冻措施不合理造成冻害发生,影响隧道运营安全。鉴于此,采用理论分析和数值模拟等方法,分析列车活塞风对隧道洞内温度场的影响机制,研究列车活塞风对寒区特长铁路隧道洞内温度场的影响规律,为寒区隧道抗防冻设计提供技术支撑。研究结论:(1)冬季列车通过隧道后,活塞风会引起洞内温度场在短时间内显著变化,列车活塞风对洞内温度场持续影响时间较短,列车通过后,洞内温度场会逐渐恢复,特别是当列车频次较小时,基本可恢复到自然通风条件下状态;(2)行车频次导致洞内纵向负温长度增大或减小率均在1%左右;随着围岩温度的增大,隧道洞内纵向负温长度显著降低,且围岩温度越高,活塞风作用方向对洞内温度场影响越小;(3)考虑活塞风对寒区隧道防寒抗冻影响时,应重点考虑其对两侧水沟抗防冻的影响;由于局部衬砌会出现交替冻融现象,隧道结构设计时,应对衬砌耐久性做一定的考虑;(4)本研究成果可供寒区特长铁路隧道建设参考,特别是单向自然风条件下铁路隧道抗防冻设计。

高速轴向柱塞泵空化机制研究与优化

为降低高速轴向柱塞的空化程度,以某型号轴向柱塞泵为例,利用Pumplinx软件搭建CFD仿真模型,探究不同转速与不同吸油口压力对泵空化程度的影响,并结合MATLAB软件对离散的仿真结果进行拟合,得到转速、吸油口压力与吸油效率的变化规律曲线。研究结果表明:当柱塞腔内气体体积达到12%以上,柱塞泵吸油效率下降甚至无法吸油;通过提高吸油口压力可以有效降低柱塞腔的空化程度,提高柱塞泵吸油效率;为了保证泵在5000~6000 r/min下能够正常吸油且有较高的吸油效率,可以使吸油口压力值介于0.25~0.30 MPa之间,此时柱塞腔空化程度和吸油效率均达到相对稳定。

基于稳态有限元法的组合式活塞疲劳寿命分析

活塞作为柴油机关键部件之一,通过台架试验评估其使用寿命成本昂贵,因此为分析某型号国产研制改进后的柴油机活塞在热-机负荷作用下的疲劳寿命,以该V型增压柴油机的活塞为研究对象,建立活塞连杆机构装配体有限元模型,计算了活塞在热载荷下的温度分布和热-机耦合作用下的应力分布。在此基础上,将实测的柴油机命。计算结果表明,由于活塞头部工作环境恶劣、头部和裙部的接触面受螺栓预紧力挤压,使得活塞的短寿命区出现在燃烧室侧壁面与活塞裙顶部截面突变处;活塞裙部疲劳寿命满足厂商设计使用寿命45000 h,活塞头部仅在特定存活率下满足设计使用寿命45000 h。

轴向变量柱塞泵的噪声特性实验和溯源分析

为分析轴向变量柱塞泵的噪声特性和声源位置,搭建了轴向变量柱塞泵的噪声和振动测试平台,并开展了相关实验.在定转速1660 r/min和定排量75 mL/min下,对被测泵负载压力16、20和24 MPa的噪声和振动信号进行了测试和采集,并进行了频谱分析和偏相干分析,得到了工作时该泵的噪声特性,且实现了准确溯源.结果表明:被测泵的噪声随着负载的增大而逐渐增大;柱塞往复运动、流量倒灌和流量脉动为被测泵的主要噪声源,而轴承振动和主轴旋转为次要噪声源;当特征频率小于200 Hz(低频段)时,被测泵的主要结构噪声源为主轴旋转和单个柱塞往复运动产生的振动;当特征频率大于200 Hz(中、高频段)时,被测泵的主要结构噪声源为柱塞往复运动产生的振动.

内燃机活塞环材料及表面处理技术研究现状与发展趋势

活塞环是内燃机中重要的零部件之一,该部件的摩擦损耗占内燃机总摩擦损失的26%。因此,活塞环材料的选用及其表面处理研究对于优化提升内燃机性能、延长服役寿命具有重要意义。简单介绍并总结了内燃机活塞环常用材料及其发展趋势,详细综述了激光表面织构技术、表面涂层技术以及表面复合技术在内燃机活塞环减摩抗磨方面的研究和应用现状。其中,激光表面织构技术(LST)可起到接纳磨屑、保持油膜等作用,从而降低活塞环表面摩擦和磨损,但由于织构形貌和几何参数特征对摩擦学性能的影响较为复杂,仍需结合实际工况进一步研究并优化。以镀铬、热喷涂、气相沉积及激光熔覆为代表的涂层技术也常用于活塞环的表面强化处理,但涂层材料种类繁多,难以形成统一的行业标准进而规模应用。此外,通过合理复合多种表面处理技术,比如微弧氧化与电泳沉积复合、超声滚压与离子渗氮技术复合、磁控溅射和低温离子渗硫复合等,可实现优势互补、发挥协同作用,有效改善接触表面的摩擦性能,为活塞环的减摩增寿研究开拓了新的思路。最后对未来活塞环材料开发应用及其减摩抗磨方面的研究发展进行了展望。