低温推进剂贮箱气冷屏复合绝热结构综合优化设计

气冷屏复合绝热(VSC)结构可以有效减少低温推进剂蒸发损耗。目前尚缺乏对气冷屏复合绝热结构的综合优化设计,现有的研究方法不能准确反映出漏热量与多层变密度材料导热性能及冷屏屏位之间的关系。为此,考虑多层变密度材料导热系数随冷屏位置的变化,对复合绝热结构进行综合优化设计,研究冷屏位置和多层变密度结构的相互影响规律,分析了最佳层密度与最佳屏位。结果表明,加入气冷屏后,降低中密度区层密度,增加高密度区层密度可以进一步减少漏热量。对于不同的层密度组合,存在一个最佳屏温,当冷屏处于该温度时漏热量最小。     

低温真空多层绝热结构热阻的理论分析

低温下真空多层绝热是非常有效的绝热方式，广泛应用于众多领域的科研和工程实践中。低温下真空多层绝热的影响因素很多，具体包括反射屏之间隔层的材料特性、反射屏的层数、层密度、真空度、捆扎的松紧程度等。运用热阻网络分析了间隔物为纤维材料的低温真空多层绝热结构的热阻组成，对总热阻中固体导热热阻Rconduction(solid)、辐射换热热阻Rradiation、残余气体导热热阻Rconduction(gas）分别建立了理论模型，并进行了理论计算推导，得到了低温下真空多层绝热结构总热阻的计算公式。     

空间燃料贮箱变密度多层绝热结构传热性能研究

为了探究变密度多层绝热结构VDMLI层间结构布置对绝热性能的影响,对火箭低温推进剂储罐外的VDMLI结构建立了传热数学模型,并开展了变工况分析,揭示了不同影响因素,包括热边界温度、层数、层密度等对VDMLI绝热性能的影响。研究发现,热边界温度对VDMLI绝热性能以及温度分布有主要影响;层数在40—60即可满足漏热量要求并且整个绝热结构的质量较轻;变密度结构(VDMLI)比定密度(MLI)具有更轻的重量和较好的绝热效果,从内由外依次是低、中、高密度区,且最优变密度分配比例为低密度区层数占总层数的20%,高密度区约占40%,中密度区占33%—36%。研究内容为VDMLI的实际布置提供了可靠的理论支持。     

航天器变密度多层绝热变工况漏热特性研究

航天器的热控技术在空间应用中至关重要。以探月需求为背景,基于逐层计算法建立了航天器多层绝热材料性能仿真模型,并通过实验进行了验证。对用内热外冷模型变密度填充方式改善多层绝热性能的机制和改善幅度进行了研究。结果表明变密度多层绝热相对于均匀密度多层绝热的漏热量可以减少37.3%。分析了冷边界温度、热边界温度和真空度等因素对绝热性能的影响。     

高真空多层绝热结构层间压力反演

高真空是液氢温区多层绝热的基础，通过不同抽气工艺获得的多层绝热材料层间压力分布，使绝热结构性能有显著差异。为了预测多层绝热材料层间压力分布，并作为抽气工艺的评价依据，基于逐层传热学模型，首先通过理论计算建立由不同层间压力分布对应的温度分布组成样本集，应用截断奇异值分解获得其正交基。再根据某绝热结构样品实测的多层材料层间温度分布，采用吉洪诺夫正则化方法对正交基系数进行回归预测，重构层间压力分布，即反演获得了多层绝热材料的层间压力。通过与给定算例的对比验证，结果表明，采用本方法可以从易于精确测量的层间温度分布反演获得层间压力分布，更精确地预测多层绝热材料的性能。为评价、比较和优化液氢容器高真空多层绝热结构的抽气工艺提供参考。     

轻薄柔性多层隔热材料研究进展

对隔热材料的分类、国内外柔性隔热材料的研究现状及存在的问题进行了概括性的论述,说明了多层柔性隔热材料的设计原理及材料筛选对隔热效果的影响,从而指出SiO2气凝胶是目前固体中最好的隔热材料,高真空多层绝热是当前绝热性最好的一种绝热方式,亦称为"超级绝热",其导热系数比空气的导热系数还要低2个数量级.最后指出了理想轻薄柔性隔热材料的结构与组成.     

非真空条件下柔性多层材料高低温绝热性能实验测量

制作了柔性绝热被,设计和搭建了高温、低温环境测试系统,通过测量多层绝热被内外两侧及外侧附近空气的温度变化,衡量不同配置下多个多层绝热被样品的综合绝热性能。考察了厚度、多层配置方式、气密性等对柔性多层材料在常压下的高低温隔热作用和符合-100℃至+135℃高低温环境应用的柔性多层绝热被的最佳厚度及配置方式。     

用于低温存储系统的多层绝热性能分析

真空多层绝热的性能好坏直接影响到低温贮箱的安全性。根据修正的Lockheed模型,计算冷边界温度、热边界温度、层密度等对均匀层密度多层绝热性能影响,并对三区域变密度的多层绝热性能进行分析,最后针对在轨、地面状态时对低温贮箱漏热方面的要求提出采用复合多层绝热的概念,得出复合多层绝热具有优良的隔热性能。     

几种高真空多层绝热结构低温绝热性能试验分析

介绍了在低温容器上最新应用的两种高真空多层绝热结构,发表了新型多层绝热结构与传统多层绝热结构的导热率试验测试比较数据。详细介绍了新结构所应用的材料及排列组合方法,其导热率可低于0.4W/m2,比传统结构至少降低了50%。     

多层绝热的间隔材料有效低温热导率测试研究

叙述了多层绝热的间隔材料玻璃纤维布、隔热纸的有效低温热导率测试方法,为薄层材料的有效低温热导率测试提供了一种方法,并对测试结果和影响因素,如叠层密度和层密度等进行了讨论分析。     

Concept for thermal insulation arrangement within a flexible cryostat for HTS power cables

The successful application of high temperature superconducting power cables requires improved flexible cryostats with respect to their thermal heat load between environment (300 K) and LN₂ (77 K) operating temperature. Heat transfer through the thermal insulation consists of thermal radiation, solid and residual gas conduction. Considering this heat load contributions, a new concept for the thermal insulation arrangement is presented in this paper. The main advantage of this concept consists in a separation of the thermal insulation and the supporting structure. This separation protects the thermal insulation from degradation by mechanical load. The fraction of solid heat conduction through this support structure is minimised by small contact areas and high heat conduction lengths. Heat transfer due to residual gas conduction is reduced by improved evacuation conditions close to the cold wall. Finally the structure allows subdivision of the multilayer insulation ensuring an optimal number of layers with respect to their insulation thickness, i.e. an optimal layer density.     

真空多层绝热性能测试装置及初步实验验证

建立了一套低温用真空多层绝热材料性能测试装置,用于研究变密度多层绝热材料的特性规律。以内密外疏的层密度分布方式为例,在测试装置充注液氮之后,通过稳态量热法实验研究了真空条件下该布置方式绝热层内不同层位置的温度瞬态和稳态分布规律、单点的降温规律、以及单位面积漏热率情况。考察了稳态温度分布以及单位面积热流随热边界温度的变化特性,并将理论温度分布曲线与实验曲线进行了对比,从而验证层与层模型的准确性。     

《车身阻尼层结构的声灵敏度分析及优化》

车身多层阻尼结构的振动特性及隔吸声特性是影响车室空腔声响应的重要因素。一个简化的车身模型用于研究车身多层结构对车内声压级的影响。通过这个模型,研究了车室空腔声响应与阻尼结构之间的关系。对车身阻尼结构进行了声－结构灵敏度分析,并对优化了阻尼层结构参数。     

高速列车车体轻量化层状复合结构隔声设计

随着高速列车车体结构轻量化的发展,层状复合结构车体在高速列车上得到广泛应用,提高层状复合结构的隔声性能,是高速列车减振降噪的关键技术。基于传递矩阵法,建立"铝板+多孔材料层+空气层+碳纤维增强板"的典型高速列车层状复合结构车体隔声计算分析模型,并分析多孔材料和空气层对层状复合结构车体隔声性能的影响。结果显示,混响声场激励下,在铝板和碳纤维增强版之间仅增加空气层只能提高车体结构高频隔声量,低频部分会由于"板-空气-板"的系统耦合共振,形成显著吻合谷,导致其隔声性能在吻合谷频率处大幅下降。对此,利用多孔材料吸声原理,提出在空气层中增加吸声材料层,抑制隔声吻合低谷,通过优化设计,得出"铝板+空气层+吸声材料+空气层+碳纤维增强板"的优化结构形式,在实现车体轻量化目标同时,可有效提高其隔声性能。     

Enhanced sound insulation and mechanical properties of LDPE/mica composites through multilayered distribution and orientation of the mica

In this work, the composites with multilayered distribution of the mica were fabricated by a multilayer coextrusion technique. The influence of layer number on sound insulation and mechanical properties of multilayered composites was investigated. The distribution, dispersion and orientation of mica particulates in composites were characterized by PLM and SEM. The sound insulation property of composites was measured by four microphone impedance tube. PLM and SEM images showed that the mica was distributed as the multilayered structure along the thickness direction of the composites. With the increase of layer number, more mica aggregates delaminated into thin flakes and aligned parallel to the flow direction. Compared to the conventional composites, the multilayered composites showed the enhanced sound insulation efficiency and mechanical properties. The discontinuity of sound impedance and the improved stiffness were considered to play a crucial role in the improvement of sound transmission loss.     

空间液氦制冷器隔热屏蔽系统设计及优化

以空间液氦制冷器为研究对象,介绍了空间液氦制冷器隔热屏蔽系统的设计思路以及方法,设计了一套以气冷屏为主、包括真空多层绝热和隔热支撑结构在内的隔热屏蔽系统,并编制数值计算程序对其进行了优化。计算结果显示了气冷屏尺寸是影响制冷器内部温度场以及内胆热负荷的关键因素,提出了气冷屏尺寸的优化结果。     

Multilayer modal actuator-based piezoelectric transformers

An innovative, multilayer piezoelectric transformer equipped with a full modal filtering input electrode is reported herein. This modal-shaped electrode, based on the orthogonal property of structural vibration modes, is characterized by full modal filtering to ensure that only the desired vibration mode is excited during operation. The newly developed piezoelectric transformer is comprised of three layers: a multilayered input layer, an insulation layer, and a single output layer. The electrode shape of the input layer is derived from its structural vibration modal shape, which takes advantage of the orthogonal property of the vibration modes to achieve a full modal filtering effect. The insulation layer possesses two functions: first, to couple the mechanical vibration energy between the input and output, and second, to provide electrical insulation between the two layers. To meet the two functions, a low temperature, co-fired ceramic (LTCC) was used to provide the high mechanical rigidity and high electrical insulation. It can be shown that this newly developed piezoelectric transformer has the advantage of possessing a more efficient energy transfer and a wider optimal working frequency range when compared to traditional piezoelectric transformers. A multilayer piezoelectric, transformer-based inverter applicable for use in LCD monitors or portable displays is presented as well.     

Design, fabrication, and analysis of chirped multilayer mirrors for reflection of extreme-ultraviolet attosecond pulses

Chirped Mo/Si multilayer coatings have been designed, fabricated, and characterized for use in extreme-ultraviolet attosecond experiments. By numerically simulating the reflection of the attosecond pulse from a multilayer mirror during the optimization procedure based on a genetic algorithm, we obtain optimized layer designs. We show that normal incidence chirped multilayer mirrors capable of reflecting pulses of approximately 100 attoseconds (as) duration can be designed by enhancing the reflectivity bandwidth and optimizing the phase-shift behavior. The chirped multilayer coatings have been fabricated by electron-beam evaporation in an ultrahigh vacuum in combination with ion-beam polishing of the interfaces and in situ reflectivity measurement for layer thickness control. To analyze the aperiodic layer structure by hard-x-ray reflectometry, we have developed an automatic fitting procedure that allows us to determine the individual layer thicknesses with an error of less than 0.05 nm. The fabricated chirped mirror may be used for production of 150-160 as pulses.     

多层结构的玻璃纤维织物/环氧树脂复合材料的降噪性能评价

根据Kirchhoff-Mindlin理论要求,多层结构面板的隔声性能要考虑到复合结构中流体层和固体层之间的整个交互作用:复杂的声波传递过程中在固体和流体层之间多次反射和系统共振,通过对隔声性能与填充在两层面板之间物质密度的关系,以及对硬质物体的组合和空气层厚度的研究,来探讨评价隔声可变因素及对空腔共振约束的隔声低谷的影响.以玻璃纤维为增强材料,环氧树脂为基体,制备复合树脂板,并设计了多层复合结构,利用混响室-静音箱法对材料隔声性能进行了测试分析.研究表明:多层玻璃纤维织物增强环氧树脂复合材料呈一定的刚性,在各频率的隔声量随着复合材料厚度的增加而增加;声音传播过程中所产生的弯曲波对柔性材料隔声性能的影响远大于对刚性材料的影响.不同颗粒填充多层介质复合材料平均隔声量随材料面密度的增加而增加,与材料面密度的指数成良好的线性相关性.