DYNAMIC OPTIMIZATION OF THERMAL STRUCTURE

he temperature distnbution on the surface of a flight vehicle and the va-riation of the modulus of elasticity with respect to temperature are considered. The minimum weight structural design with constraints on frequency, on the coordinates ofmodal nodes and on the upper and lower bounds of the design vanables are studied us-ing Kuhn-Tucker conditions as optimal cntenon. The vanation of the flrst three ordernatural frequencies, modal shapes and minimum structural weight vs temperature gra-dient are discussed. It is pointed out that it is imperative to take into account the effectof aerodynamic heating on structural dynamic optimization. Calculation example showsthat the method obtained is feasible and efficient.

A Study of the Structural Properties and Thermal Stability of Chitosanases EAG1 by Molecular Dynamics Simulations

Chitosanases EAG1, a classical glycoside hydrolase from Bacillus ehimensis, is relatively unstable with higher temperature. This shortcoming seriously restricts its industrial application. Therefore, it is crucial to clarify the theoretical basis of thermo stability and to produce enzymes with high activity and stability. Using the structural modeling and molecular dynamical simulation, residues Leu84, Gly113, Asp116, Ala207 and Leu286 were believed to be the key residues for structural stability. Then the predicted residue Leu84 was mutated to ALA. It was shown that the L84A mutation can improve the thermal stability of chitosanases EAG1. Together with previous studies, mutations of G113C, D116C, A207C and L286C forms two sulfur bonds can change the thermal stability of EAG1. The results suggest that the thermal stability of EAG1 could be engineered by site-directed mutagenesis on the conserved residues. This protocol could be employed for improving thermal stability of other chitosanases EAG1.

Towards dynamic structure of biological complexes at atomic resolution by cryo-EM

Cryo-electron microscopy makes use of transmission electron microscopy to image vitrified biological samples and reconstruct their three-dimensional structures from two-dimensional projections via computational approaches. After over40 years of development, this technique is now reaching its zenith and reforming the research paradigm of modern structural biology. It has been gradually taking over X-ray crystallography as the mainstream method. In this review, we briefly introduce the history of cryo-EM, recent technical development and its potential power to reveal dynamic structures. The technical barriers and possible approaches to tackle the upcoming challenges are discussed.

Thermal-Fluid-Structure Coupling Analysis of Flexible Corrugated Cryogenic Hose

This work presents a numerical investigation of the thermal–fluid–structure coupling behavior of the liquid natural gas(LNG)transported in the flexible corrugated cryogenic hose.A three-dimensional model of the corrugated hose structure composed of multiple layers of different materials is established and coupled with turbulent LNG flow and heat transfer models in the commercial software ANSYS Workbench.The flow transport behavior,heat transfer across the hose layers,and structural response caused by the flow are analyzed.Parametric studies are performed to evaluate the impacts of inlet flow rate and thermal conductivity of insulation material on the temperature and structural stress of the corrugated hose.The study found that,compared with a regular operating condition,higher inlet flow velocities not only suppress the heat gain of the LNG but also lower the flow-induced structural stress.The insulation layer exhibits excellent performance in maintaining the temperature at the fluid–structure interface,showing little temperature change with respect to material thermal conductivity and ambient temperature.The simulation results may contribute to the research and design of the flexible corrugated cryogenic hoses and provide guidance for safer and more efficient field operations.

Thermal conductivity of carbon nanoring linked graphene sheets:A molecular dynamics investigation

Improving the thermal conduction across graphene sheets is of great importance for their applications in thermal management. In this paper, thermal transport across a hybrid structure lbrmed by two graphene nanoribbons and carbon nanorings （CNRs） was investigated by molecular dynamics simulations. The effects of linker diameter, number, and height on thermal conductivity of the CNRs-graphene hybrid structures were studied respectively, and the CNRs were found effective in transmitting the phonon modes of GNRs. The hybrid structure with 2 linkers showed the highest thermal conductivity of 68.8 W·m^-1·K^-1. Our work presents important insight into fundamental principles governing the thermal conduction across CNR junctions and provides useful guideline for designing CNR-graphene structure with superior thermal conductivity.

Towards full predictions of temperature dynamics in McNary Dam forebay using OpenFOAM

Hydroelectric facilities impact water temperature; low velocities in a reservoir increase residence time and enhance heat exchange in surface layers. In this study, an unsteady three-dimensional model was developed to predict the temperatm＇e dynamics in the McNary Dam forebay. The model is based on the open-source code OpenFOAM. RANS equations with the Boussinesq approximation were used to solve the flow field. A： realizable k-ε model that accounts for the production of wind turbulence was developed. Solar radiation and convective heat transfer at the free surface were included. The result of the model was compared with the field data collected on August 18, 2004. Changes in diurnal stratification were adequately predicted by the model. Observed vertical and lateral temperature distributions were accurately captured. Results indicate that the model can be used as a numerical tool to assess structural and operational alternatives to reduce the forebay temperature.

Dynamic rupture of metal sheet subjected to laser irradiation and tangential subsonic airflow

To reproduce the premature rupture process of metal sheet subjected to laser irradiation with subsonic airflow,which is an interesting phenomenon observed in the experiments given by Lawrence Livermore National Laboratory,a coupled numerical model considering the interaction and evolution of metal elastoplastic deformation and aerodynamic pressure profile is presented.With the thermal elastoplastic constitutive relationship and failure criterion,the simulated failure modes and dynamic rupture process are basically consistent with the experimental results,indicating plastic flow and multiple fracturing is the main failure mechanism.Compared with the case of non-airflow,subsonic airflow not only accelerates deformation,but also turns the bugle deformation,plastic strain and rupture mode into asymmetric.

THE INFLUENCE OF DRAWING CONDITIONS OF PET POY ON STRUCTURE AND PROPERTY OF THE FIBER

Drawing tests upon PET POY have been made by using dynamic thermal stress analyser,which show that the dynamic thermal stress of fiber is readily affected by drawing conditions. Aseries of samples have been obtained under different drawing velocities, drawing temperatures anddraw ratios. The variations of structural factors of fiber such as the orientation, crystallinity,crystallite size and the thermal shrinkage have been measured. It is proved through experimentsthat the thermal shrinkage（Y） of the drawn fiber of PET POY is influenced by the orientation （rep-resented by sonic velocity x1） and crystallinity （x2） of the fiber. The quantitative relationship is es-tablished using the binary regression method: Y=10.2246+2.2030x1-26.2670x2 The mechanical properties such as tenacity, elongation, yield stress, initial modulus and the te-nacity at 10% elongation, etc. have also been measured. The relations between the tenacity at 10%elongation （D） and drawing velocity（V）, draw ratio （DR）, drawing temperature （T）, and sonic ve-locity and crystallinity have been obtained using a method of mathematical statistics: D=4.594-0.009 6V , D=-8.937+7.170DR, D=2.866+0.00629T, D=-7.34+2.866x1+6.314x2 These equations fit well with data from the experiments. This work will be benefical to the control of quality of products and the development of newproducts.

CAP1400核主泵叶轮动应力计算及疲劳寿命预测

为实现核主泵叶轮疲劳寿命预测,考虑叶轮高温高压的恶劣运行工况建立流-热-固耦合计算模型,应用ANSYS CFX软件对核主泵叶轮内部流动的压力载荷和温度载荷进行非定常数值计算,在ANSYS Workbench中实现载荷向结构的传递,并对叶轮动力响应疲劳载荷开展研究.利用雨流计数法对叶片危险部位的载荷数据进行统计分析,进一步结合Palmgren-Miner理论对核主泵叶轮的最小疲劳寿命周期进行预测.研究结果表明:叶轮在旋转过程中承受周期性交变应力的作用;叶轮叶片进、出口边与前、后盖板交接处容易发生内部应力集中,最大应力出现在叶片出口边与前盖板交接处,为142.57 MPa;叶片各危险部位承受应力波峰和波谷的时间基本一致;叶轮产生的疲劳为应力疲劳,疲劳破坏首先发生在叶片进口边与后盖板交接处;计算得到叶轮的疲劳寿命为277.94 a.研究结果可为叶轮的动态强度优化和疲劳设计提供一定参考.

A comprehensive physical pattern of land-air dynamic and thermal structure on the Qinghai-Xizang Plateau

According to the boundary layer observations of three stations (Garze, Damxung and Qamdu) and relevant earth satellite, radiosonde and surface observations during the intensive observational period (IOP) of the second Tibetan (Qinghai-Xizang) Plateau Experiment of atmospheric science (TIPEX), the land-air physical process and dynamic model on the Tibetan Plateau were comprehensively analyzed in this study. The dynamic characteristics of boundary layer and the rules of turbulent motion on the plateau were illustrated. The characteristics of distributions of wind speed and direction with mutiple-layer structure and deep convective mixed layer on the plateau, the strong buoyancy effect in turbulent motion on the plateau on which the air density is obviously smaller than on the plain, and the Ekman spiral and its dynamic pump effect of the plateau deep boundary layer have been found. The local static distribution of water vapor and the horizontal advection of water vapor in the plateau boundary layer were studied. The abnomal thermodynamic structure on the plateau surface and boundary layer, including the plateau strong radiation phenomenon and strong heating source characteristics of the middle plateau, was also analyzed. The authors synthesized the above dynamic and thermodynamic structures of both surface and boundary layers on the plateau and posed the comprehensive physical model of the turbulence and convective mixture mechanism on the plateau boundary layer. The characteristics of formation, development and movement for convective cloud cluster over the plateau influencing floods in the Yangtze River area of China were studied. The conceptual model of dynamic and thermodynamic structures of turbulent motion and convective plume related to the frequent occurrence of 'pop-corn-like' cloud system is given as well.

Enhancing thermal transport in multilayer structures:A molecular dynamics study on Lennard−Jones solids

We investigate the thermal transport properties of three kinds of multilayer structures:a perfect superlattice(SL)structure,a quasi-periodic multilayer structure consisted of two superlattice(2SL)structures with different periods,and a random multilayer(RML)structure.Our simulation results show that there exists a large number of aperiodic multilayer structures that have effective thermal conductivity higher than that of the SL counterpart,showing enhancement ratio in the effective thermal conductivity up to 193%.Surprisingly,some RML structures also exhibit enhanced thermal transport than the SL counterpart even in the presence of phonon localization.The detailed analysis on the underlying mechanism reveals that such peculiar enhancement is caused by the synergistic effect of coherent and incoherent phonon transport,which can be tuned by the structural configuration.Combined with molecular dynamics simulations and the machine learning technique,we further reveal that the enhancement effect of the effective thermal conductivity by 2SL structure is more significant when the period of SL structure is close to the critical transition period between the coherent and incoherent phonon transport regimes.Our study proposes a novel strategy to enhance the thermal transport in multilayer structures by regulating the wave-particle duality of phonons via the structure optimization,which might provide valuable insights to the thermal management in devices with densely packed interfaces.

Responses of thermal structure and vertical dynamic structure of South China Sea to Typhoon Chanchu

The response of the South China Sea（SCS） to Typhoon Chanchu（2006） was examined using the MM5 and POM model. In the POM model, sea surface boundary conditions were forced by the simulation wind field from MM5, the velocity forcing was introduced in the eastern boundary and the computational schemes of heat fluxes at the surface were introduced. Comparison with the observation data shows that the simulated results are reliable. In the response process of the SCS to Typhoon Chanchu, the influence of the heat fluxes on thermal structure of the SCS was regionally different. Strong wind forcing would lead to upwelling phenomenon in the lateral boundary of deep water basin. Furthermore, the Ekman pumping theory was used to discuss subsurface upwelling and downwelling phenomenon in typhoon forced stage.

酶解-动态高压微射流制备纳米淀粉及对其结构性质的影响

为探究蜡质玉米淀粉(WMS)经普鲁兰酶协同动态超高压微射流技术(P-DHPM)制备纳米淀粉后对其结构及性质的变化规律,本文探讨了处理前后淀粉微观结构、结晶结构、分子结构、粒径、分子量及热性能的变化趋势。结果表明,随着酶解时间的增加,淀粉圆球形颗粒变碎片状、结晶结构逐渐消失、淀粉短程有序性增加、分子量显著(P<0.05)减小;同时,淀粉糊化峰值温度由71.23℃降低至55.81℃,糊化焓值(ΔH)显著(P<0.05)减小至4.68 J/g;酶解淀粉进一步经微射流处理后,粒径降低至纳米级,淀粉颗粒变成更加无规则的小碎片,糊化峰值温度(T_p)降低至55.37℃,糊化焓值(ΔH)增大至14.13 J/g。通过酶解-微射流技术处理WMS淀粉,可制备得到粒径可控且具有短程有序的纳米尺寸淀粉颗粒,提供了一种环境友好、操作简单的制备方法,同时为继续探讨其在淀粉纳米乳液及淀粉基活性包装材料中的应用奠定基础。

Carbon honeycomb structure with high axial thermal transport and strong robustness

Thermal transport properties of low-dimensional nanomaterials are highly anisotropic and sensitive to the structural disorder,which can greatly limit their applications in heat dissipation.In this work,we unveil that the carbon honeycomb structures which have high in-plane thermal conductivity simultaneously possess high axial thermal conductivity.Based on non-equilibrium molecular dynamics simulations,we find that the intrinsic axial thermal conductivity of carbon honeycomb structure reaches 746 W·m^(-1)·K^(-1)at room temperature,comparable to that of good heat dissipation materials such as hexagonal boron nitride.By comparing the phonon transmission spectrum between carbon honeycombs and few layer graphene,the physical mechanism responsible for the high axial thermal conductivity of carbon honeycombs is discussed.More importantly,our simulation results further demonstrate that the high axial thermal conductivity of carbon honeycomb structure is robust to the structural disorder,which is a common issue during the mass production of the carbon honeycomb structure.Our study suggests that the carbon honeycomb structure has unique advantages to serve as the thermal management material for practical applications.

Analysis on Thermal Current Field in Powertrain Cabin of Tracked Vehicles With Electric Transmission System Configuration-2

The electric transmission system congfiguration-2 is one of the main electric drives for tracked vehicles. The geometrical model for the power-train cabin is established and the preliminary design for its cooling system is implemented. The mathematic model is established for thermal current field computation, simulation and analysis in the powertrain cabin. The three-dimensional structure of the powertrain cabin is optimized. The validity of the cooling system design is proved. The foundation for optimizing the whole electric transmission system configuration is laid.

热-水-力作用下圆孔花岗岩的动态损伤特征及结构模型

基于深层地热能开采时储能区井筒围岩所处的工程环境,采用高温加热、不同温度水浸泡、加热-循环次数及径向冲击加载的方法模拟井筒围岩经历的高温、遇水、循环采热及热冲击等造成的动力扰动等物理力学条件。同时,以不同内孔直径的同心圆孔岩样模拟深层地热井,采用分离式霍普金森压杆试验系统开展热-水-力作用下圆孔花岗岩的动态力学试验,并结合VIC-3D非接触应变测量及数值模拟分析技术监测冲击过程中圆孔岩样裂隙萌发、形成的历程和表面应变演化的规律,揭示热-水-力作用下圆孔岩样的动态损伤破坏机制。研究结果表明:径向冲击荷载作用下圆孔花岗岩先后经历弹性变形、塑性变形、结构失稳破坏3个典型阶段;内孔直径、加热温度、浸水温度、加热-浸水循环次数4因素都弱化了圆孔花岗岩抗外界荷载的能力,但未改变其整体的变形演化规律;圆孔花岗岩的破坏模式是动态拉伸破坏,先沿冲击方向由内孔壁向岩样外壁,再垂直冲击方向由岩样外壁向内孔壁萌发、贯通裂纹,形成近垂直的两组破裂面。最后,基于圆孔花岗岩的损伤变形特征及历程,在一定假设基础上,建立动态损伤结构模型,推演了结构方程,并结合试验结果确定了方程参数,通过对比分析发现,理论拟合曲线与试验曲线具有较好的一致性,验证构建的圆孔花岗岩动态损伤结构模型是合理的。研究成果不仅揭示了圆孔结构岩样的损伤破坏机制,也可为预测深部储能区地热井筒围岩损伤变形规律提供理论参考,具有一定的科学和工程实践意义。

围护结构动态热响应机理及应用

动态性是围护结构传热的本质属性,动态热响应机理是其动态运行规律的体现。围护结构在夏季的动态性比在冬季表现更为典型,因此该文开展隔热建筑的围护结构动态性机理及应用研究。通过研究围护结构的动态热响应机理提出围护结构最大防热量G_(max),该指标兼顾多种工况下围护结构热性能的评价。以夏热冬冷地区的重庆为例进行模拟分析。研究发现:G_(max)<60 W/m^(2)时,提升墙体最大防热量可有效提升其动态热响应性能;G_(max)在60~90 W/m^(2)之间时,提升墙体最大防热量可较少提升其动态热响应性能;G_(max)>90 W/m^(2)时,提升墙体最大防热量反而会降低其动态热响应性能。

GH4720Li合金粗晶组织热变形细化预测研究

目的研究不同变形参数下GH4720Li合金动态再结晶行为,建立GH4720Li合金粗晶组织动态再结晶细化的预测模型,为铸态初轧GH4720Li合金锻造工艺参数制定、粗晶组织消除、细晶组织获得提供理论支撑。方法在温度为1030~1150℃、应变速率为0.01~10 s^(-1)条件下,对铸态初轧GH4720Li合金粗晶组织进行了热压缩实验,分析了不同变形参数下合金的动态再结晶行为。研究了合金动态再结晶演化机制,构建了GH4720Li合金粗晶组织动态再结晶预测模型和晶粒尺寸模型,并结合实验对模型的准确性进行了验证。结果在合金热压缩过程中,流变应力表现出明显的加工硬化、动态回复和动态再结晶软化平衡特征,粗晶组织动态再结晶细化程度可以通过流变应力变化间接反映。根据应力-应变数据计算得到合金的热变形激活能为1230.48 kJ/mol,确定了Z参数与峰值应变和临界应变之间的关系,发现峰值应变和临界应变与Z参数均呈线性关系。通过观察合金微观组织发现,在变形过程中发生了非连续动态再结晶和连续动态再结晶,2种变形机制共同影响着粗晶组织的演化,所建立的动态再结晶细化模型和动态再结晶晶粒尺寸模型与实验值最大相对误差仅为8.5%和8.9%。结论所建模型的预测结果与实验结果基本一致,模型预测值具有较高的准确性,可以利用所建模型对合金动态再结晶细化进行定量预测。

辐射制冷技术的物理基础与研究进展

随着现代社会能源与极端气候问题日益严峻,零能耗的辐射制冷技术越来越受到人们的关注与重视。从2014年日间辐射制冷首次被实验实现以来,辐射制冷技术已从结构设计、材料选择、制备工艺、集成应用等多个角度被广泛研究,产生了包括镀膜、涂层、柔性薄膜、织物等多种类型的器件。新的研究也越来越重视辐射制冷在场景兼容性以及环境、气候自适应性等方面的需求。开发多场景兼容、自适应环境变化且具有动态热调控能力的新型辐射制冷器件,对辐射制冷技术的实用化以及能源、医疗、工业生产等领域都有着重要意义。本文围绕辐射制冷技术所运用的基础物理原理与光子学结构设计,综述了辐射制冷器件的基本技术与其在场景兼容、温度自适应热调控等方面的进展。首先介绍了辐射制冷技术的原理与基本设计方法,随后重点介绍了一些典型的辐射制冷结构以及实现多场景兼容与自适应动态调控辐射制冷器件的主要进展,最后对辐射制冷器件的发展进行了总结与展望。

颗粒团聚状态对纳米流体热导率的影响

纳米流体由基液与纳米颗粒组成,因具有优良的热物性而受到广泛关注。颗粒团聚是纳米流体的主要特征之一,对热导率影响显著。目前,通过实验手段很难观察到纳米流体中颗粒由均匀分散到团聚这一过程的微观变化。以铜(Cu)/氩(Ar)纳米流体为研究对象,基于非平衡分子动力学(NEMD)方法对颗粒团聚过程中基液原子的布朗运动及界面层性质进行模拟研究,通过分析均方位移(MSD)及数密度等微观参数得到团聚状态对热导率的影响。结果表明,当颗粒由均匀分散到完全团聚时,热导率逐渐增大,并在团聚时呈现最大值。在完全团聚状态下,基液原子的MSD值比均匀分散状态提高了3%,说明基液原子的布朗运动逐渐增强;同时,界面层的MSD值下降了22%,表明界面层原子活跃程度降低,界面层趋于稳定。通过改变初始颗粒质心距离可将团聚结构分为反应限制团聚(21A,1A=0.1nm)与扩散限制团聚(22A)两种类型。当界面层的数密度由67nm^(-3)升高到72nm^(-3),反应限制团聚向扩散团聚转变;当从67nm^(-3)降至62nm^(-3),扩散限制团聚向反应限制团聚转变,因此界面层密度是影响纳米颗粒团聚结构的主要因素之一。