THERMOELASTIC TOPOLOGY OPTIMIZATION FOR PROBLEMS WITH VARYING TEMPERATURE FIELDS

Elastic structures that exist in a thermal environment usually experience complex steady-state or transient heat conduction, whereby operational temperatures and stresses may change with time, heat sources, and thermal or kinematic boundary conditions. This article proposes an evolutionary optimization procedure for topology design involving thermoelasticity in which finite element heat analysis, finite element thermoelastic analysis, and subsequently design modification are iteratively carried out. To achieve as efficacious a material usage as possible, the relative efficiency of an element is defined in terms of its thermal stress level. In this article, design cases with uniform temperature fields, nonuniform temperature fields subjected to single or multiple heat load cases, and transient temperature fields are studied. The examples presented show the capabilities of the proposed procedure to solve various thermoelastic problems under varying temperature fields.     

Temperature-Constrained Topology Optimization of Transient Heat Conduction Problems

A regional temperature measure model is constructed to obtain a small number of temperature constraints for local transient temperature control. The temperature sensitivity is derived using the adjoint variable method. The multiple temperature criteria and three-phase topology optimization are further investigated for transient heat conduction design. The material layout design of transient heat conduction is replaced by a static optimization problem, which is subsequently solved by the method of moving asymptotes. Finally, several numerical examples are provided to demonstrate the feasibility and validity of the proposed topology optimization for transient heat conduction problems.     

基于有限元方法的横掠错排光滑管束传热与流动特性研究

使用有限元方法对横掠不同型式措排光滑管束进行了计算分析，绘制了速度场和温度场的色差梯度图，比较了它们的传热与流动性能。有限元分析方法作为热分析和流动分析研究的有力工具，可以与实验研究相结合作为研究管束传热与流动性能的一种新方法。研究结果对于横掠光滑管束的优化设计具有一定的指导意义。     

Simulation and experimental validation of heat transfer in a novel hybrid solar panel

A hybrid solar panel has been invented to integrate photovoltaic (PV) cells onto a substrate through a functionally graded material (FGM) with water tubes cast inside, through which water serves as both heat sink and solar heat collector. Therefore, the PV cells can work at a relatively low temperature while the heat conduction to the substrate can be minimized. Solar panel prototypes have been fabricated and tested at different water flow rates and solar irradiation intensities. The temperature distribution in the solar panel is measured and simulated to evaluate the performance of the solar panel. The finite element simulation results are very consistent with the experimental data. The understanding of heat transfer in the hybrid solar panel prototypes will provide a foundation for future solar panel design and optimization. The finite element model is general and can be extended for different material design and other size of panels.     

Topological design of channels for squeeze flow optimization of thermal interface materials

Performance of thermal interface materials (TIMs) used between a microelectronic device and its associated heat spreader is largely dependent on the bulk thermal conductivity of the TIM, but the bond-line thickness (BLT) of the applied material as well as the interfacial contact resistances are also significant contributors to overall performance. Hierarchically Nested Channels (HNCs), created by modifying the surface topology of the chip or the heatsink with hierarchical arrangements of microchannels in order to improve flow, have been proposed to reduce both the required squeezing force and the final BLT at the interfaces. In the present work, a topological optimization framework that enables the design of channel arrangements is developed. The framework is based on a resistance network approximation to Newtonian squeeze flow. The approximation, validated against finite element (FE) solutions, allows efficient, design-oriented solutions for squeeze flow in complex geometries. A comprehensive design sensitivity analysis exploiting the resistance network approximation is also developed and implemented. The resistance approximation and the sensitivity analysis is used to build an automated optimal channel design framework. A Pareto optimal problem formulation for the design of channels is posed and the optimal solution is demonstrated using the framework.     

Sensitivity analysis in shape optimization design for a pressure vessel

This paper discusses the sensitivity analysis for a finite element model during shape optimization design for a pressure vessel. The derivative of a stiffness matrix and various load rankings with respect to design variables are obtained. Because the information resulting from the finite element analysis is fully utilized in this method, the programs are greatly simplified so that it becomes possible to carry out the shape optimization with comparatively more variables. The conclusion is illustrated by an example.     

Control of macrosegregation during the solidification of alloys using magnetic fields

Numerical modeling of convection damping and macrosegregation suppression during solidification of alloys with prominent mushy zones through the use of tailored magnetic fields is demonstrated here. Macrosegregation leads to commonly observed defects such as freckles, channels and segregates in cast alloys that severely affect the performance and suitability of the alloy for further applications. The current work demonstrates the successful use of magnetic fields in suppressing thermosolutal convection and eliminating some of these defects in solidifying metallic alloys. The computational model presented utilizes volume-averaged governing transport equations and stabilized finite element techniques to discretize these equations. A finite-dimensional optimization problem, based on the continuum sensitivity method is considered to design the time history of the imposed magnetic field required to effectively damp convection. The coefficients that determine this time variation are the main design parameters of this optimization problem. Continuum sensitivity equations are derived by design-differentiating the governing equations of the direct problem. The cost functional here is given by the square of the L₂ norm of an expression representing the deviation of the volume-averaged velocity corresponding to conditions of convection less growth. The cost functional minimization process is realized through a non-linear conjugate gradient algorithm that utilizes finite element solutions of the continuum direct and sensitivity problems. Design of the time history of the imposed magnetic field is highlighted through different examples with the main objective being the suppression of convection and macrosegregation during alloy solidification.     

Sensitivity analysis in thermoelastic problems using the complex finite element method

This article presents the complex finite element method (ZFEM) for the sensitivity analysis of thermoelastic systems. ZFEM, based on the complex Taylor series approach, performs finite element procedures using complex variables such that the response variables (temperature, stress) and their sensitivities with respect to an input parameter of interest (shape, mechanical and thermal properties, loading) are obtained simultaneously. ZFEM offers significant advantages over alternative sensitivity analyses that require direct derivations of the sensitivity formulae, multiple runs, and/or remeshing. To verify the numerical implementation, a hollow cylinder with convective boundary conditions on the inside and outside surface was considered. First-order derivatives of the stress fields were compared with exact solutions to demonstrate the accuracy of ZFEM sensitivities. The results indicate that the ZFEM-based derivatives are of high accuracy, thereby showing its applicability in the design and analysis of thermoelastic problems.     

拓扑优化理论在活塞结构设计中的应用

建立了某高速发动机活塞的变密度法拓扑优化数学模型,以活塞销座和推力面之间的区域为优化区域,在保证裙部变形稳定性的前提下,利用HyperW orks软件对该区域的活塞结构进行了拓扑优化。材料密度相同时,优化后的活塞质量仅为原来活塞质量的70%左右。对优化前后活塞裙部型线的稳定性进行了比较和分析,优化后活塞的纵截面型线基本上未发生改变,而横截面型线是一条近似水平线,对应的活塞横截面接近正圆,表明拓扑优化能明显改善活塞裙部对变形的适应性。对优化模型进行了有限元静力学分析,结果表明优化前后活塞的应力和整体变形趋势符合实际情况,验证了模型的合理性。     

Numerical simulation of laser-induced transient temperature field in film-substrate system by finite element method

The transient temperature fields generated by a pulsed laser in film-substrate system are obtained by using the finite element method. Time integrations of the semi-discrete finite element equations are achieved by using approximate one order derivative of temperature. The temperature dependences of material properties are taken into account, which has a great influence on the temperature fields indicated by the numerical results. The pulsed laser-induced transient temperature fields in aluminum/methyl-methacrylate system and aluminum/copper system are obtained, which will be useful in the research on thermoelastic excitation of laser ultrasonic waves in film-substrate system.     

Accuracy of an efficient framework for structural analysis of wind turbine blades

This paper presents a novel framework for the structural design and analysis of wind turbine blades and establishes its accuracy. The framework is based on a beam model composed of two parts—a 2D finite element‐based cross‐section analysis tool and a 3D beam finite element model. The cross‐section analysis tool is able to capture the effects stemming from material anisotropy and inhomogeneity for sections of arbitrary geometry. The proposed framework is very efficient and therefore ideally suited for integration within wind turbine aeroelastic design and analysis tools. A number of benchmark examples are presented comparing the results from the proposed beam model to 3D shell and solid finite element models. The examples considered include a square prismatic beam, an entire wind turbine rotor blade and a detailed wind turbine blade cross section. Phenomena at both the blade length scale—deformation and eigenfrequencies—and cross section scale—3D material strain and stress fields—are analyzed. Furthermore, the effect of the different assumptions regarding the boundary conditions is discussed in detail. The benchmark examples show excellent agreement suggesting that the proposed framework is a highly efficient alternative to 3D finite element models for structural analysis of wind turbine blades. Copyright © 2015 John Wiley & Sons, Ltd.     

燃机涡轮盘三维瞬态温度及应力场计算分析

用通用有限元计算程序ANSYS对某燃气轮机启动过程中透平第一级涡轮盘的三维模型瞬态温度和应力场进行计算.计算中考虑了材料的非线性,惯性力和温度场边界条件.分析了温度和应力场特点,提出了改进设计的建议.计算结果可为涡轮盘疲劳寿命预测提供依据.图6参3     

基于BP神经网络和分解技术的汽轮机叶片可靠性反求设计

汽轮机叶片可靠性反求设计旨在确定叶片未知概率设计参数以满足给定的可靠度要求.针对叶片功能函数为随机变量隐性函数的情况,提出了基于有限元、BP神经网络和分解技术的可靠性反求设计方法,该方法将有限元和BP神经网络相结合以构造功能函数与随机输入变量之间的近似解析表达式,运用分解技术,将求解随机设计参数的全局优化问题分解为主问题和子问题,通过子问题直接调用标准优化工具箱得到可靠性指标,并运用分解迭代技术对主问题求解,从而得到随机设计参数及目标可靠性指标对各随机变量的敏感性.以某实验台汽轮机等直叶片为例,阐述了该方法的具体实施过程.该方法数学描述简单,并可直接应用标准优化程序,成功地解决了隐性功能函数下叶片可靠性反求设计,具有较好的工程应用价值.     

Influences of filling process on the thermal-mechanical behavior of composite overwrapped pressure vessel for hydrogen

Temperature rise is an important issue during the fast filling of composite overwrapped pressure vessel for hydrogen. Due to different temperature and thermal expansion coefficients at different parts, thermal-mechanical coupling effects exist. In this work, a fluid-thermal-solid coupling analysis method is proposed for the thermal-mechanical behavior of composite overwrapped pressure vessel in the process of filling. Firstly, a computational fluid dynamics analysis is performed to study the temperature rise and compared with analytical solution. Then a finite element model is set up and validated. The temperature field from the computational fluid dynamics model is exported to the finite element model as boundary condition. By this method, the influences of filling rate, inlet location and geometry on the thermal-mechanical stress field are studied. The results of this work can provide guidance for the design of composite overwrapped pressure vessel and the optimization of filling process.     

Thermal and Structural Response of RCC Dams During Their Service Life

Roller compacted concrete (RCC) dams are vulnerable to cracking as a result of high tensile stresses due to material properties, thermal and mechanical loads. Making reliable prediction of stress fields, and thereby temperature cracking risk form an important part of the material modelling. The present study figures out the changes in thermal stresses and crack fields of the Kinta RCC dam at the end of the construction and its service life. Water temperature at various levels of the reservoir and its fluctuations were considered in the present study. The developed finite element program has been used in the analysis. Based on the obtained results, it is revealed that there is an increase in the thermal stresses after some years of dam completion. However, their location and distribution are mostly similar.     

A boundary element approach for topology design in diffusive problems containing heat sources

The objective of this work is to present the application of a hard-kill material removal algorithm for topology optimization of heat transfer problems containing localized sources. The boundary element method is used to solve the governing equations. A topological-shape sensitivity approach is used to select the points showing the lowest sensitivities, where material is removed by opening a cavity. As the iterative process evolutes, the original domain has holes progressively punched out, until a given stop criteria is achieved. Both isotropic and orthotropic two-dimensional benchmarks are presented and analyzed. Because the BEM does not employ domain meshes in linear cases, the resulting topologies are completely devoid of intermediary material densities. Although the drawbacks of hard-kill methods are still present, the approach opens an interesting field of investigation for integral equation methods.     

System modeling methodology and analyses for materials-based hydrogen storage

In the global efforts to develop advanced materials-based hydrogen storage, the various on-board reversible hydrides, adsorbents and chemical storage candidate materials and systems each have their individual strengths and weaknesses. An overarching challenge in associated research and development is to devise material/system architectures which satisfy all requirements for viability in a particular application area, such as light-duty vehicular transportation. System modeling at the level which encompasses not only the storage material and vessel/reactor, but also integration with a fuel cell and balance-of-plant components, provides a more complete assessment of viability and guides options for improvement. The current work covers the methodology developed for conducting such system modeling consistently across multiple organizations and will present performance results from studies focused on reversible hydride systems. Connecting this high level modeling to more detailed finite element design simulations will be one aspect of our framework approach. The complex hydride NaAlH₄ is representative of novel materials under development and will be used as the basis for properties, such as temperature dependent kinetics, which influence the integrated system configurations and component sizing. While system charging is included through the sizing of certain components, emphasis is placed on hydrogen discharge by the storage system, interrogated through drive cycle transients. Comparisons of performance relative to requirements, including effective gravimetric capacity, effective volumetric density and energy utilization, are given for the baseline material and for a sensitivity study on material density.     

铺层材料单层厚度对风力机叶片低阶模态频率的影响分析

针对大型风力机叶片铺层材料单层厚度对叶片模态频率的影响作用,对铺层材料单层厚度间的耦合机制进行研究。采用Box-Behnken法设计实验,建立叶片铺层单层厚度与其第一阶模态频率间的响应面模型,揭示叶片不同铺层材料单层厚度对模态频率的影响规律。以叶片前两阶模态频率为优化目标、以铺层材料单层厚度为设计变量建立优化数学模型,并采用遗传算法与有限元法结合进行全局寻优。以某企业1.5 MW叶片为算例,结果表明,优化后叶片第一阶挥舞、摆振频率均提高了0.07 Hz。     

Computational design of metadevices for heat flux manipulation considering the transient regime

The present work introduces the optimization-based approach for the design of metadevices to manipulate the heat flux in transient regime. It consists of solving a continuous, nonlinear, constrained, large-scale optimization problem where the objective function (to be minimized) is the error in accomplishing a given heat flux manipulation task along a transient heat conduction process. The response of the metadevice is modeled by using the finite element method, and its design is characterized by a set of parameters defining the material at all the finite elements in the device. These parameters are the design variables of the optimization problem, being chosen from an admissible design set in order to guarantee the feasibility of the optimal solution. As an example, this optimization-based approach is applied to the design of a heat flux shielding metadevice. Compared to a metadevice designed under the classical thermodynamics transformation approach and intuition, the current device performs the shielding task with considerably higher success. In order to highlight the versatility of the proposed optimization-based design method, this approach is also applied to the design of metadevices to satisfy multiple different simultaneous tasks, particularly shielding and cloaking.     

Design Considerations of a Direct Drive Brushless Machine With Concentrated Windings

This paper discusses the performance attributes of the open-slot, modular-wound, external-rotor, topology of electrical machine. Combinations of pole and slot numbers are presented for which the winding factor is maximal and torque ripple is minimal. An optimization of the magnetic circuit design of six promising pole-slot configurations is undertaken using a parametric finite element model (FEM) combined with a genetic algorithm (GA). These designs are benchmarked against a conventional 1.5 slots/pole external-rotor brushless dc machine. These candidate electrical machine versions are characterized by having the same external-rotor diameter, total slot area available for the winding and by equal volumes of permanent magnet (PM). Based on the analysis, the most promising motor structure was selected and a prototype wheel-hub motor has been built for application in a small electrical vehicle. Test data from the prototype is used to validate the findings of the initial analyses and practically demonstrate the attributes of the topology.