树状分支传热结构层次生长优化设计技术

To design heat transfer structures for high heat flux electronic components with small space, reasonable heat transfer channel layout was the most effective approach. Aiming at the complex geometry boundaries and difficult-to-manufacture for heat transfer structures designed by topology optimization, a hierarchy growth method for optimal design of branching heat transfer structure inspired by hierarchical characteristics of natural vein branching system was suggested. Different growth control criteria were adopted for principal channels and lateral channels, which grew in succession to form heat transfer structures. Specifically, space colonization algorithm with temperature information was applied to the growth of principal channels, and the law of minimal thermal resistance was applied to control the growth of lateral channels. Several typical 2D or 3D design problems were studied by the suggested method, and the design results were compared with those of SIMP method. The results show that the heat transfer structure by hierarchy growth method has simple and clear geometry boundary, no tiny channel and gray element, therefore it is easy to be manufactured, and has good thermal performance.     

Topology optimum design of unimorph piezoelectric cantilevered Mindlin plates as a vibrating electric harvester

An FEM-based topology optimization approach is proposed to calculate the topologies of a substrate plate and a piezoelectric layer used for vibrating unimorph cantilevered plate-like electricity generators (energy harvesters). The Mindlin plate theory was combined with a topology optimization algorithm to consider the shear effect. Each optimum topology for a plate and a piezoelectric layer is computed and combined by reflecting the natural frequencies of the substrate plate, electromechanical couplings of piezoelectric materials, tip masses and method of moving asymptotes. The piezoelectric coefficients such as elasticity, piezoelectric coupling and capacitance are interpolated by element density variables. The cantilevered plate generators with optimal topologies were designed for three piezoelectric materials such as PZT, PMN-PT and PMN-PT single crystal fiber MFC, and their voltage outputs were compared using a developed FEM-based optimization code to investigate the suitable material for harvesters.     

Shape optimization of two-dimensional thermal conducting solid using boundary integral equation formulation

A method for shape design sensitivity analysis of two-dimensional thermal conducting solid is presented using the material derivative concept and the adjoint variable method. A general thermal boundary condition with heat convection is considered in addition to prescribed temperature and heat flux. The method for deriving the sensitivity formula is based on standard direct boundary integral equation formulation. The sensitivity of a general functional depending on temperature and heat flux is considered. The method is then applied to obtain the sensitivity analysis is demonstrated by a hollow cylinder problem with exact solution. A weight minimization problem of a thermal diffuser is considered as a practical application. The sensitivity by the presented method is compared with that by finite differences and an optimal shape is found by use of an optimization routine.     

基于裸芯片封装的金刚石/铜复合材料基板性能研究

基板是裸芯片封装中热传导的关键环节。随着微电子技术的发展,组件热流密度越来越大,对新型基板材料的要求越来越高,要求具有高的热导率、低的热膨胀系数以及较低的密度。金刚石/铜复合材料作为新一代基板材料正得到愈来愈多的关注。文中分别通过实验和计算机仿真分析了金刚石/铜复合材料的镀覆性、焊接性以及作为基板材料的热性能。结果表明...     

Thermoelastic stability of duplex heat exchanger tubes

When duplex tubes are used for heat exchange purposes, thermal distortion affects the contact pressure and, hence, the thermal contact resistance at the interface. The resulting coupling between the thermal and thermoelastic fields for the system can lead to instability and non-uniqueness of the steady-state solution and, hence, to erratic heat transfer performance.Stability of the system is investigated by determining the conditions under which a small (axisymmetric or non-axisymmetric) perturbation on the steady state can grow exponentially in time. Substitution into the governing heat conduction and thermoelastic equations enables the unknown functions to be determined except for a set of arbitrary constants, which are then determined from the thermal and mechanical boundary conditions, including a statement of the relation between thermal contact resistance and pressure, linearized for small perturbations about the steady state.Results are presented for a range of material combinations and for both directions of steady state heat flux. It is shown that unstable axisymmetric perturbations can only occur for inward heat flow and, hence, the stability boundary for outward heat flow is always associated with a non-axisymmetric mode. In the latter case, the circumferential wavelength of the critical mode is generally about twice the tube thickness and a good approximation to the stability boundary can be obtained using previously published results for the stability of two plane layers in thermoelastic contact.For inward heat flow, the critical heat flux for axisymmetric perturbations is independent of the mean contact resistance, whereas that for non-axisymmetric modes increases with contact resistance. Thus, the stability boundary in this case is determined by non-axisymmetric modes for small values of contact resistance and by axisymmetric modes for large contact resistance.     

Notes on contributors

The local maxima of frictional heat flux are often substantially larger than the apparent rubbing interface average heat flux. This causes potentially large thermal stresses in the rub zone. The physical and mathematical constraints prevalent in this situation are considered together with the parametric senstivities involved. In particular, a characteristic non-dimensional rub time, non-dimensional surface temperature and non-dimensional thermalto-mechanical stress ratio are proposed to gauge the degree of thermal effects in various rubbing configurations. As an aid to understanding the present results and a means of investigating these phenomena further in the future, a computer program is discussed which solves for non-dimensional rub zone temperature and stress versus time for an arbitrary set of uniform asperity sizes and spacings, rubbing element material properties and rub boundary conditions.     

自热式印制板加热性能分析与评估

针对星载电子设备集成化、轻量化设计需求,基于机热一体化设计了一种自热式印制板,通过在多层印制板中埋置加热电阻实现其自加热功能.采用仿真分析,研究了印制板加热电阻布局、导热性能以及结构参数等对加热性能和力学特性的影响,完成自热式印制板样件研制和加热性能评估.研究结果表明,对印制板电路布局、结构参数进行优化设计,可以实现印制板温控区域良好的温度均匀性,满足航天产品温控要求.     

热-机荷载作用的P-FGM扁球壳跳跃屈曲分析

基于经典壳体理论和Sanders非线性应变-位移关系,导出了幂律型功能梯度材料(P-FGM)扁球壳在热-机械荷载作用下的几何非线性常微分控制方程。推导过程考虑了沿厚度存在一维热传导温度场和法向均布荷载作用。采用打靶法求解了由控制方程和固定夹紧边界条件构成的两点边值问题。得到了FGM扁球壳的一些典型的屈曲平衡路径和双稳态构形。对热-机械荷载作用的FGM扁球壳的跳跃屈曲行为进行了参数影响分析。结果表明：温度上升时,球壳上临界荷载显著增加、下临界荷载变化不明显。梯度指数增加时,球壳上、下临界荷载均显著减小。组分材料模量增加时,球壳上、下临界荷载均显著增加。当底圆半径和厚度给定时,随壳体中面曲率半径增加,球壳上、下临界荷载均显著增加。当中面曲率半径和厚度给定时,随底圆半径增加,球壳下临界荷载显著减小,上临界荷载几乎不变。     

Experimental and numerical studies on the thermal analysis of the plate in indirectly fired continuous heat treatment furnace

Experimental and numerical studies were performed by considering convective and radiative heat transfer to predict the transient thermal behavior of a plate in an indirectly fired continuous heat treatment furnace. The temperature profiles in the plate were determined by solving the transient one-dimensional heat conduction equation in conjunction with appropriate boundary conditions by using a time marching scheme. The results obtained from the transient analysis were substantiated by comparing with experimental results. Additionally, parametric investigations were performed to examine how the thermal behavior of the plate is affected by plate and refractory emissivities, charging temperature and residence time of the plate, gas temperature of the work and drive sides of the heat treatment furnace, and plate thickness. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Young-Deuk Kim is a graduate student at Hanyang University in Seoul, Korea. He earned his B.S. in Mechanical Engineering from Korea Maritime University in 2002 and his M.S. in mechanical engineering from Hanyang university in 2004. His current research areas are modeling of automotive aftertreatment catalysts, optimal design of thermal systems, and phase change modeling with free surface flow. Deok-Hong Kang is a senior researcher at the RIST (Research Institute of Industrial Science and Technology) in Pohang, Korea. He earned his B.S. and M.S. in mechanical engineering from Hanyang University in 1989 and 1993, respectively, and his Ph.D. in mechanical engineering from POSTECH in 2004. His current research areas are mathematical modeling for combustion control, furnace optimization control system, and energy saving engineering in all kinds of furnaces. Woo-Seung Kim is a professor in mechanical engineering at Hanyang University in Ansan, Korea. He earned his B.S. in Mechanical Engineering in 1981 from Hanyang University and his M.S. and Ph.D. in mechanical engineering from North Carolina State University in 1986 and 1989, respectively. His current research areas are modeling of automotive aftertreatment systems, inverse heat transfer problems, optimal design of thermal systems, and phase change heat transfer problems with free surface flow.     

用拓扑优化方法进行热传导散热体的结构优化设计

分析了拓扑优化中的材料密度方法和优化准则数值求解算法,将结构力学中的拓扑优化方法应用到热传导结构的优化设计中,建立了热传导结构的拓扑优化数学模型,以设计具有最佳散热效果情况下的结构拓扑分布,为传热体的结构优化设计提供了一种有效的新思路和方法。     

Thermomechanical coupling of rough contact asperities sliding at very high velocity

A model has been developed to study dry friction for a steel tribopair for a large range of sliding velocity. From the topology of two parts in contact, a true contact surface is defined as a set of asperities. Each adhesive junction is associated to a local heat source in the thermal problem that is solved by Green׳s function techniques. The mechanical problem is treated by considering the adiabatic shearing process of these asperities. The coupling of thermal and shearing effects is then performed by using a homogenisation approach. Outcomes, such as the average thermal response on the contact area, appear to be in good agreement with those of the literature. Velocity dependence of the heat flux distribution between parts in contact is highlighted. The temperature profile in both solids in contact, as well as the local shear stress field, is determined at any friction time.     

Power performance of circular piezoelectric diaphragm generators

Energy generation performance of a piezoelectric generator depends mainly on several elements such as the structural style, boundary conditions, geometry parameters, materials, vibration-source frequency, and external load. To obtain the optimal energy-harvesting device, the Raleigh method is used to establish the analysis model of circular piezoelectric composite diaphragms. Simply supported and clamped boundary conditions were considered. The relationships between the output power and the structural parameters of piezoelectric composite diaphragms, and the external load resistance and frequency were shown. Given the correlative material parameters and boundary conditions, the output power, using structural parameters, external load, or vibrating frequency as variables, can be calculated. Simulation results show that there are optimal structural parameters and load for a composite diaphragm to achieve the maximum output power. A piezoelectric diaphragm generator with given dimensions tends to achieve higher output power under clamped boundary conditions than that under simply supported boundary conditions.     

相变薄膜热物性对电子设备热控的影响

相变热控技术是被动热控的重要方法之一。文中对利用柔性相变薄膜材料进行电子设备热控进行了实验研究和数值模拟,获得了相变材料热物性参数和结构参数对热控性能的影响规律。研究结果表明,相变材料的比热容和相变潜热对热控性能的影响较小,材料的热导率、厚度以及来自芯片的热流密度和热源面积因子对热控有较大影响;当系统达到热平衡时,热源中心温度与相变材料热导率、厚度以及热源面积因子成负相关,与热流密度成正相关。     

空间光学遥感器热平衡试验装置的设计

热平衡试验是空间光学遥感器研制中的重要试验内容.需要创造一个地面模拟试验环境和条件,来代替空间高真空和超低温的环境.按照试验规范,在模拟真空冷黑、空间外热流和热边界条件下对空间光学遥感器系统进行热平衡试验.这项技术涉及到试验对象的轨道参数、结构、材料表面特性、轨道外热流计算、轨道外热流模拟、真空冷黑、热边界条件、热计算和热设计等因素.在对上述各项因素综合研究的基础上,提出了用于空间光学遥感器热平衡试验的装置,并用AutoCAD软件完成了其结构设计.简述了该试验装置的构造、特点和设计方法.     

基于并行策略的多材料柔顺机构多目标拓扑优化*

多材料柔顺机构能够让设计者充分利用各种材料的优良属性,在力,位移,以及能量转移等方面获得更大的设计自由度,因而受到重视。针对受到广泛研究的柔顺机构,结合多目标拓扑优化的方法,提出相应的基于并行策略的求解模型。该方法的核心是将一个复杂的多材料多目标问题离散成为单材料子问题,然后并行求解,再根据整体目标的需要,对所有子问题的解进行调整以得到原始问题的解。针对多目标情形,提出新的材料与输出目标关系,从而在将多材料问题离散成单材料子问题的同时,也将多目标问题离散成单目标子问题。对所有的单材料单目标子问题采用各向同性材料的刚度插值-惩罚法并行独立求解。以上方法有其独特优势：在理论和实践上都比较简单,可以处理任意多种材料,可以避免零碎的拓扑结构因而有利于制造。通过算例说明了此方法的有效性。研究结果表明,该方法在某些输出需要特定材料的设计场合更具优势。     

Power performance of circular piezoelectric diaphragm generators

Energy generation performance of a piezoelectric generator depends mainly on several elements such as the structural style, boundary conditions, geometry parameters, materials, vibration-source frequency, and external load. To obtain the optimal energy-harvesting device, the Raleigh method is used to establish the analysis model of circular piezoelectric composite diaphragms. Simply supported and clamped boundary conditions were considered. The relationships between the output power and the structural parameters of piezoelectric composite diaphragms, and the external load resistance and frequency were shown. Given the correlative material parameters and boundary conditions, the output power, using structural parameters, external load, or vibrating frequency as variables, can be calculated. Simulation results show that there are optimal structural parameters and load for a composite diaphragm to achieve the maximum output power. A piezoelectric diaphragm generator with given dimensions tends to achieve higher output power under clamped boundary conditions than that under simply supported boundary conditions.     

A numerical study on the conjugate natural convection in a circular pipe containing water

In this paper, the effect of material property of pipe on the conjugate natural convection in a circular pipe containing water was investigated by solving the unsteady incompressible Navier-Stokes equations coupled with energy equations of the water and pipe. Natural convection and conduction of water inside the pipe was coupled with the conduction of the pipe whose bottom was subject to uniform heat source. From the present grid resolution and time-step independent solutions, it has been confirmed that the water temperature inside a PVC pipe was higher than that inside a steel pipe due to the smaller heat capacity of PVC and that the streamline patterns of the two cases were found to be opposite because the thermal diffusivity of steel (PVC) is larger (smaller) than that of water such that steel (PVC) pipe is heated faster (slower) than water. Furthermore, a quantitative comparison of heat flux to water was performed by examining the distributions of the heat flux along the inside walls of steel/PVC. The average temperature of water inside steel was found to be higher than that inside PVC at the initial stage of heating. On the other hand, PVC provided a larger heat flux to water when it reached a steady value.     

考虑拓扑相关热载荷的散热结构多相材料拓扑优化设计

针对热传导拓扑优化设计过程中拓扑相关热载荷问题,以结构散热弱度为目标函数,体积分数为约束条件,构建了多相材料散热结构拓扑优化数学模型。采用一种基于变密度理论的有序固体各向同性微结构材料惩罚模型法构建多相材料插值模型,分别进行拓扑相关热载荷与拓扑独立热载荷作用下的灵敏度分析,借助优化准则法推导设计变量的迭代格式,引入偏微分方程过滤方法抑制优化过程中出现的数值不稳定现象。通过2D与3D数值模型计算,获得考虑拓扑相关热载荷、拓扑独立热载荷以及耦合拓扑独立/相关热载荷在不同边界条件下对拓扑优化结果的影响规律。结果证明了所提方法在解决拓扑相关热载荷作用下散热结构多相材料拓扑优化设计问题方面的有效性与可行性。     

An integrated approach to evaluating the tribo-contact for coated cutting inserts

The orthogonal machining process when end turning medium carbon and austenitic stainless steels with cemented WC-Co tools coated with single-layer (TiC), two-layer (TiC/TiN), and three-layer (TiC/Al₂O₃/TiN) hard thin films was investigated. Extensive experimental investigations including the thermal, mechanical and tribological responses of the tribo-contact between the coating–substrate system and the chip, under different cutting conditions, were carried out. The study sheds light on the cutting forces, the interface temperatures and the tribo-contact conditions, including the friction energy dissipated at the tool–chip interface, the frictional heat flux conducting into either the chip or the insert, the mean coefficient of sliding friction and the contact loads exerted on the tool rake face. Finally, it was demonstrated how the intrinsic coating properties control the heat flux flowing into both components of such a closed tribo-system and the mechanical stresses on the contact area.     

Minimising heat dissipation in ultrasonic piezomotors by working in a resonant mode

Heat dissipation in ultrasonic motors should be limited, especially in precision applications since it causes thermal deformations. Therefore, an easy-to-understand mechanical model was developed to simulate heat dissipation in an ultrasonic motor. This model involves the dielectric, piezoelectric and mechanical hysteretic losses of the piezoelectric material. Both the model and the experiments lead to the same recommendations to minimise the heat dissipation for ultrasonic motors. Large piezoactuators, exciting passive structures at high resonance frequencies result in a minimum heat dissipation. Furthermore, it was shown that the optimal frequency regarding minimal heat dissipation lies between the resonance and the antiresonance frequency of the system, close to the resonance frequency.