变密度多层的Lockheed修正模型分析北大核心

基于Lockheed修正模型,对用于低温液体贮箱的变密度多层绝热性能进行理论研究。通过对Lockheed修正模型的分析,计算了贮箱内为不同低温液体时最优层密度随热边界温度的变化情况,研究了不同层密度配置方案时绝热多层的热流密度大小,并对不同方案的绝热效果进行了对比分析。     

气冷屏复合绝热结构传热分析及屏位优化"

由气冷屏、聚氨酯泡沫和变密度多层绝热组成的气冷屏复合绝热结构是一种新型的高效热防护绝热结构,通过对不同环境条件下低温贮箱气冷屏复合绝热结构的传热机理分析,推导了气冷屏复合绝热结构中屏温与屏位的数值计算关系,并在此基础上根据漏热量最小原则对气冷屏复合绝热结构中的屏位进行了优化。结果表明,随着环境条件的不同,气冷屏复合绝热机理不同,气冷屏最优位置也不同。常温常压的地面环境,气冷屏置于SOFI与VD-MLI之间时,低温贮箱漏热量最小,绝热效果最优;真空且温度变化剧烈的空间环境,气冷屏置于VD-MLI最中间时,低温贮箱漏热量最小,绝热效果最优。气冷屏复合绝热结构可进一步降低空间低温贮箱的漏热量,同时能满足地面及空间环境使用要求。     

应用于低温贮箱的变密度多层绝热传热分析

采用Layer-by-Layer传热模型对真空多层绝热结构中的传热过程进行了分析,根据各项(辐射换热、气体导热、固体导热)换热分布情况,提出4区域不同层密度的多层绝热结构,分析了各区域层密度变化对多层绝热性能的影响,得出一个使总热流最小的层密度,研究了其各项换热规律以及受到热边界温度的影响。     

蓄冷能力对液氢贮箱蒸气冷却屏瞬态特性的影响

蒸气冷却屏可有效降低贮箱漏热,延长低温流体贮存时间。为明确间歇性排气下蒸气冷却屏是否有足够的蓄冷能力能够在短时排气过程中充分蓄存/回收低温气体冷量,本文针对液氢贮箱绝热结构建立了耦合真空多层绝热与蒸气冷却屏的瞬态传热模型,研究了间歇性排气下液氢贮箱外部绝热结构和内部气液相的热力参数变化规律,讨论了绝热结构瞬态温度分布随蒸气冷却屏蓄冷能力的变化特性,对比分析了蓄冷能力对蒸气冷却屏绝热性能的影响。     

变密度多层绝热性能测试装置及实验验证

建立了一套变密度多层绝热性能测试装置,用于研究变密度多层绝热技术的特性规律.实验应用低温量热法原理测试了真空度、层密度及热边界温度对变密度多层绝热性能的影响.实验结果与理论计算分析结果相吻合,验证了理论计算分析的准确性.     

多层多屏绝热液氦杜瓦传热分析

分析了不同液氦杜瓦结构,指出多屏多层的杜瓦的优缺点。通过对多屏多层绝热中不同传热方式的逐个分析,建立了一个理论传热模型。依照模型采用数值分析的方式,对多层层数为100层时的传热进行了分析,获得传导冷屏分布方式对传热流密度的影响曲线,并指出多层多屏分布的优化应同时考虑空间和温度两个因素。     

应用于ZBO存储的SOFI/VD-MLI技术研究

低温推进剂长期在轨储存技术是制约航空航天探测不断深入的关键技术之一。基于变密度多层绝热的组合型绝热(SOFI/VD-MLI)技术是泡沫塑料绝热与变密度多层绝热相结合的一种新型绝热方式,其绝热效果好、质量轻,在飞行器地面发射阶段和空间在轨阶段均能发挥良好的绝热作用,广泛用于航天低温推进剂的存储。文中从国内外研究现状、结构原理等方面介绍SOFI/VD-MLI技术,重点分析SOFI/VD-MLI技术的优点和未来研究方向。     

新型被动在轨非连接支撑研究现状

支撑结构是低温贮箱及飞行器杜瓦瓶的关键部件,对低温燃料液体的承装及其漏热有重要影响。文中阐述了低温绝热支撑近几年的研究进展,针对新型被动在轨非连接支撑(简称PODS),就其结构、材料及其他相关问题进行了分析。随着新型被动在轨非连接支撑研究的深入,其在空间及工业低温贮箱领域将会获得广泛应用。     

低温容器绝热真空丧失后的绝热夹层漏热量计算分析

真空丧失对低温容器的安全性是一大威胁,可能会造成严重后果。文中通过实验,利用氮气为破空介质,测得了高真空多层绝热低温容器在真空丧失情况下的排放率,根据测得的排放率计算了热流密度。结果表明,根据测得的排放率,不考虑液体温度变化计算得到的热流密度与考虑液体温度变化计算得到的热流密度之间存在差异。     

低温推进剂贮存中SOFI和MLI实验研究

根据低温推进剂长时间在轨贮存的要求,设计并搭建了绝热系统地面验证测试装置,对绝热系统的热力学性能进行测试。针对55L贮箱,采用了泡沫绝热(spray on foam insulation,SOFI)和多层绝热(multilayer insulation,MLI)结合的复合绝热系统,分别在高真空(5×10^-3Pa以上)和大气压条件下进行了验证实验(液氮作为替代工质)。贮箱外绝热系统为15m m厚泡沫绝热层和45组多层绝热时,高真空条件下液氮日蒸发率为0.77%,多层绝热层表观热导率为1.29×10^-4W/(m·K),据此折算为液氧时日蒸发率为0.55%。将高真空和大气压条件下的实验结果比较发现,泡沫绝热层所占热阻分别为总热阻的0.19%和45.14%。     

Point defects on graphene on metals

Understanding the coupling of graphene with its local environment is critical to be able to integrate it in tomorrow's electronic devices. Here we show how the presence of a metallic substrate affects the properties of an atomically tailored graphene layer. We have deliberately introduced single carbon vacancies on a graphene monolayer grown on a Pt(111) surface and investigated its impact in the electronic, structural, and magnetic properties of the graphene layer. Our low temperature scanning tunneling microscopy studies, complemented by density functional theory, show the existence of a broad electronic resonance above the Fermi energy associated with the vacancies. Vacancy sites become reactive leading to an increase of the coupling between the graphene layer and the metal substrate at these points; this gives rise to a rapid decay of the localized state and the quenching of the magnetic moment associated with carbon vacancies in freestanding graphene layers.     

基于Matlab分析负荷对多联机IPLV的影响

多联机有其特殊的优点,但是不同部分负荷的组合对IPLV的影响仍需进一步研究。文中建立IPLV与部分负荷的相关公式,运用MATLAB软件分析不同卸载级负荷与IPLV的关系,从而确定不同部分负荷的最优组合。     

Note on duality on polarized symplectic manifolds

In this note we use some of the results of [3] to derive a general duality theorem for the cohomologies of foliated structures on a manifold. The result is applied to the special case of a symplectic manifold M on which the foliation is given by a complex polarization F in the sense of geometric quantization. We obtain, for example, a rigorous proof of the fact that for a smooth function ƒ on M whose Hamiltonian vector field leaves F invariant, the spectrum of the corresponding prequantization operator v(ƒ) coincides with the spectrum of its transpose, under the above duality. This latter result was obtained by Simms in [12] under certain hypotheses. Proofs of the validity of those hypotheses are now available in the literature; cf. [3] and [7].     

Space-charge effects on multipactor on a dielectric

Analyzes the effects of space charge shielding on the steady state of a multipactor discharge on a dielectric. Analytic methods are used to obtain an exact function for the potential in the discharge, assuming a Maxwellian distribution of emitted electrons. An equation for the amount of power deposited on the dielectric by the multipactoring electrons, for a given saturation level, is given. A simple method for obtaining the saturation level, for a given material, is obtained     

Remarks on KdV-type flows on star-shaped curves

We study the relation between the centro-affine geometry of star-shaped planar curves and the projective geometry of parametrized maps into RP¹. We show that projectivization induces a map between differential invariants and a bi-Poisson map between Hamiltonian structures. We also show that a Hamiltonian evolution equation for closed star-shaped planar curves, discovered by Pinkall, has the Schwarzian KdV equation as its projectivization. (For both flows, the curvature evolves by the KdV equation.) Using algebro-geometric methods and the relation of group-based moving frames to AKNS-type representations, we construct examples of closed solutions of Pinkall’s flow associated with periodic finite-gap KdV potentials.     

X-ray diffraction on chlorine adsorbed on graphite

Cl₂ layers adsorbed on Grafoil have been investigated by X-ray diffraction between 78 and 285 K. Mono- and submonolayers crystallize in a parallelogram lauttce, incommensurate with the (001) graphite surfaces, the molecules oriented almost perpendicular to the surface. The structure is closely related to that of the (001) planes of three-dimensional solid chlorine. For coverages above the monolayer completion bulk crystalization sets in.