Stress-based design of thermal structures via topology optimization

The design of thermal structures in the aerospace industry, including exhaust structures on embedded engine aircraft and hypersonic thermal protection systems, poses a number of complex design challenges. These challenges are particularly well addressed by the material layout capabilities of structural topology optimization; however, no topology optimization methods are readily available with the necessary thermoelastic considerations for these problems. This is due in large part to the emphasis on cases of maximum stiffness design for structures subjected to externally applied mechanical loads in the majority of topology optimization applications. In addition, while limited work in the literature has investigated thermoelastic topology optimization, a direct treatment of thermal stresses is not well documented. Such a treatment is critical in the design of thermal structures where excessive thermal stresses are a primary failure mode. In this paper, we present a method for the topology optimization of structures with combined mechanical and thermoelastic (temperature) loads that are subject to stress constraints. We present the necessary steps needed to address both the design-dependent thermal loads and accommodate the challenges of stress-based design criteria. A relaxation technique is utilized to remove the singularity phenomenon in stresses and the large number of stress constraints is handled using a scaled aggregation technique that has been shown previously to satisfy prescribed stress limits in mechanical problems. Finally, the stress-based thermoelastic formulation is applied to two numerical example problems to demonstrate its effectiveness.     

柔性Flow-Shop调度的遗传算法优化

柔性Flow-shop调度问题（Flexible Flow-shop Scheduling Problem,FFSP）是一般Flow-shop调度问题的推广,由于在某些工序上存在并行机器,所以比一般的Flow-shop调度问题更复杂。为了有效地解决柔性Flow-shop调度问题,用遗传算法求解,给出了一种改进的编码方法,能够保证个体的合法性;并根据编码方法提出了矩阵解码方法。最后以某汽车发动机厂金加工车间的生产调度实例进行仿真,通过比较表明了算法的有效性。     

Efficient size and shape optimization of truss structures subject to stress and local buckling constraints using sequential linear programming

The advance in digital fabrication technologies and additive manufacturing allows for the fabrication of complex truss structure designs but at the same time posing challenging structural optimization problems to capitalize on this new design freedom. In response to this, an iterative approach in which Sequential Linear Programming (SLP) is used to simultaneously solve a size and shape optimization sub-problem subject to local stress and Euler buckling constraints is proposed in this work. To accomplish this, a first order Taylor expansion for the nodal movement and the buckling constraint is derived to conform to the SLP problem formulation. At each iteration a post-processing step is initiated to map a design vector to the exact buckling constraint boundary in order to facilitate the overall efficiency. The method is verified against an exact non-linear optimization problem formulation on a range of benchmark examples obtained from the literature. The results show that the proposed method produces optimized designs that are either close or identical to the solutions obtained by the non-linear problem formulation while significantly decreasing the computational time. This enables more efficient size and shape optimization of truss structures considering practical engineering constraints.     

基于图像分析的粘接质量评价系统设计

目前对发动机防热结构件的粘接质量的判断采用电磁超声波进行无损检测,检测人员只能通过超声波返回的A波波形进行粘接缺陷的评估;这种检测方法效率低,准确度低,对人员要求高且无法实现在线检测,严重影响产品量产;针对此类情况,采用数据可视化、智能图像分析的方法,建立一套粘接质量评价系统;系统包含了对测量结果数据进行过滤处理;根据工件尺寸按照法线函数展开成二维模型;为二维模型填充缺陷信息从而实现粘接效果可视化;采用二值法建立缺陷矩阵;通过粒子法求解缺陷的面积;采用缺陷矩阵扩张的方法,解决相邻缺陷的识别问题;再通过特征值数组的方法解决从3D展开至2D时展开边界切割缺陷区域的问题,从而完整地描述发动机防热结构件粘接质量的全面特征,为粘接质量评价提供了直接依据。     

FTP服务器枢纽中的文件处理引擎设计

为改善大型运营支撑系统之间文件传输效率低下的状况,在FTP服务器枢纽模型中,设计文件处理引擎。通过智能向导模式实现业务注册,建立后台驱动模块实现高效文件传输,采用MD5算法解决文件迁移过程中的完整性校验问题,利用Java线程池控制技术提高引擎多线程并发处理能力。该引擎设计较好地解决了FTP服务器枢纽分层结构之间的协调控制问题,具有较高的实用价值。     

元搜索引擎在油田领域信息分布式搜索的应用

当前大型集中式企业搜索引擎面临规模扩展、数据更新快速和用户需求专业化、多样化等一系列挑战。因此,在整个油田内建立一个高效、高质量的分布式搜索引擎体系架构,并保证不破坏各公司原有企业搜索引擎的基础之上,实现数据共享变得越来越重要。通过分析油田内部公司搜索引擎现状,结合元搜索引擎技术,提出构建一个合理的油田内部分布式搜索引擎体系架构的解决方案。主要从接口规范,查询调度,排序策略三个方面入手,解决分布式搜索引擎在油田应用查询中存在的问题。     

Evolutionary Learning of Dynamic Naive Bayesian Classifiers

Many problems such as voice recognition, speech recognition and many other tasks have been tackled with Hidden Markov Models (HMMs). These problems can also be dealt with an extension of the Naive Bayesian Classifier (NBC) known as Dynamic NBC (DNBC). From a dynamic Bayesian network (DBN) perspective, in a DNBC at each time there is a NBC. NBCs work well in data sets with independent attributes. However, they perform poorly when the attributes are dependent or when there are one or more irrelevant attributes which are dependent of some relevant ones. Therefore, to increase this classifier accuracy, we need a method to design network structures that can capture the dependencies and get rid of irrelevant attributes. Furthermore, when we deal with dynamical processes there are temporal relations that should be considered in the network design. In order to learn automatically these models from data and increase the classifier accuracy we propose an evolutionary optimization algorithm to solve this design problem. We introduce a new encoding scheme and new genetic operators which are natural extensions of previously proposed encoding and operators for grouping problems. The design methodology is applied to solve the recognition problem for nine hand gestures. Experimental results show that the evolved network has higher average classification accuracy than the basic DNBC and a HMM.     

Resonant operation and cycle work from a MEMS-based micro-heat engine

The documentation of a new engine thermodynamic cycle on the micro-scale is presented. This new cycle is the result of resonant operation and cycle work production from a MEMS-based micro-heat engine. The engine is constructed of two thin membranes surrounding a cavity filled with working fluid. This new thermodynamic cycle is shown to include nearly constant volume pressure increase, expansion, heat rejection, and compression components. A thermal switch is integrated with the micro-engine to control heat rejection. The micro-engine is shown to produce up to 6.7 μW of cyclic mechanical power when operated on this cycle. Micro-engine natural frequency is shown to vary from 90 to 140 Hz. The Micro-engine is shown to operate across a low temperature gradient of 1.5°C.     

Optimal topology design of structures under dynamic loads

When elastic structures are subjected to dynamic loads, a propagation problem is considered to predict structural transient response. To achieve better dynamic performance, it is important to establish an optimum structural design method. Previous work focused on minimizing the structural weight subject to dynamic constraints on displacement, stress, frequency, and member size. Even though these methods made it possible to obtain the optimal size and shape of a structure, it is necessary to obtain an optimal topology for a truly optimal design. In this paper, the homogenization design method is utilized to generate the optimal topology for structures and an explicit direct integration scheme is employed to solve the linear transient problems. The optimization problem is formulated to find the best configuration of structures that minimizes the dynamic compliance within a specified time interval. Examples demonstrate that the homogenization design method can be extended to the optimal topology design method of structures under impact loads.Presented at WCSMO-2, held in Zakopane, Poland, 1997     

一种基于规则的双层四边通道布线专家系统原型

四边通道布线问题(switchbox routing problem)是VLSI布图设计(layout)中的一个关键问题。从计算的观点看,它是一个NP-hard问题。因此,基于知识的方法是解决这一问题的有效方法。 本文中,提出了一种以PROLOG为核心的基于规则的双层四边通道布线专家系统的原型(prototype)。它能把人类布线专家的规划、推理能力及布线经验同计算机的高速数据处理能力有机地结合起来,从而取得较高的布线效率和布通率。     

Terminal sliding mode control of rail pressure for gasoline direct injection engines

The desired fuel rail pressure is a crucial factor for guaranteeing the gasoline direct injection (GDI) engine to work stably. In order to solve the rail pressure control problem, the detailed nonlinear model of GDI is derived and reasonable simplification of this model is carried out for the following controller design. Terminal sliding mode control strategy is proposed to design the rail pressure controller with Lyapunov stability. The designed approach with the fast terminal sliding mode surface makes the system have the capacity of global fast convergence and achieves precise tracking control. To demonstrate the validity of the designed control method, simulations are conducted by tracking the different reference rail pressures. Results show that the designed controller tracks the given reference accurately and has strong robustness.     

Thermal-aware floorplanner for 3D IC,including TSVs,liquid microchannels and thermal domains optimization

3D stacked technology has emerged as an effective mechanism to overcome physical limits and communication delays found in 2D integration. However, 3D technology also presents several drawbacks that prevent its smooth application. Two of the major concerns are heat reduction and power density distribution. In our work, we propose a novel 3D thermal-aware floorplanner that includes: (1) an effective thermal-aware process with three different evolutionary algorithms that aim to solve the soft computing problem of optimizing the placement of functional units and through silicon vias, as well as the smooth inclusion of active cooling systems and new design strategies, (2) an approximated thermal model inside the optimization loop, (3) an optimizer for active cooling (liquid channels), and (4) a novel technique based on air channel placement designed to isolate thermal domains have been also proposed. The experimental work is conducted for a realistic many-core single-chip architecture based on the Niagara design. Results show promising improvements of the thermal and reliability metrics, and also show optimal scaling capabilities to target future-trend many-core systems.     

Optimizing Flight Trajectories for Space Vehicles with an Additional Fuel Tank. II

We solve the optimization problem for space trajectories of spacecraft flights with an auxiliary fuel tank from a low round orbit of a man-made Earth satellite to a geotransitional orbit. Control over the spacecraft motion is performed with a jet engine of bounded thrust. To discard the auxiliary tank, one has to turn off the engine, which takes some known time. The mass of the discarded tank is assumed to be proportional to the mass of fuel spent, and the mass of the engine and additional constructions is proportional to the thrust-to-weight ratio. We minimize the value of injection impulse needed to transfer to the geostationary orbit for a given useful mass.In the second part of the paper the problem at hand is formalized as an optimal control problem for a collection of dynamical systems and is solved based on the corresponding maximum principle. In this work we solve boundary problems of the maximum principle numerically with the shooting method. As a result of solving the problem, we construct one- and two-revolution Pontryagin extremals. We perform a series of parametric computations that are used to determine optimal parameters of the spacecraft construction: the best thrust-to-weight ratio and the best distribution of fuel among the tanks.     

Multi-dimensional optimization of functionally graded material composition using polynomial expansion of the volume fraction

The work of this paper proposes a method for multi-dimensional optimization of functionally graded materials (FGMs) composition. The method is based on using polynomial expansion of the volume fraction of the constituent materials. In this approach, the design variables are the coefficients of the polynomial expansion which to be determined through the optimization process. This method provides much more flexibility in the design compared to the methods based on the power-law, or the exponential-law which will in turn lead to more optimal designs. Also it requires much less number of design variables compared to the grid based approaches which is also utilized for two-dimensional optimization of FGMs structures. As an application of the proposed method, the optimization of a simply supported Aluminum plate reinforced with Silicon Carbide nano-particles is considered. Cost plays a very important role for this type of structures, since the cost of the reinforcements such as Silicon Carbide nano-particles, or carbon nano-tubes is too high. So the aim of the optimization process is to minimize the amount of the reinforcement required to satisfy certain performance criteria. Both static, and dynamic cases are considered in this work; a plate under a transverse pressure distribution is considered as the static case, and the panel flutter problem as the dynamic case.     

一类非线性输出反馈系统的自适应输出调节问题

本文讨论一类非线性系统的全局鲁棒输出调节问题.假定被控非线性系统的系统输入方向未知,且产生参考或扰动信号的外部系统含未知参数,这为控制律的设计带来了挑战.文章使用自适应控制方法和内模原理,解决了一类相对阶为1的非线性输出反馈系统的输出调节问题,并将结果应用于处理Lorenz系统的渐近跟踪问题.     

通用无线传感器网络节点平台设计

随着传感网研究的深入,传感器节点运行的实际应用日趋复杂,对实验平台要求也相应提高。为解决该问题,设计了新一代通用传感网感知节点平台NPUMOTE3,提高了节点的处理、存储和传输能力,同时易于扩展、便于使用,可满足当前科研、教学与生产中的不同需求。     

Path planning of modular robots on various terrains using Q-learning versus optimization algorithms

Self-reconfigurable modular robots (SRMRs) have recently attracted considerable attention because of their numerous potential applications in the real world. In this paper, we draw a comprehensive comparison among five different algorithms in path planning of a novel SRMR system called ACMoD through an environment comprised of various terrains in a static condition. The contribution of this work is that the reconfiguration ability of ACMoD has been taken into account. This consideration, though raises new algorithmic challenges, equips the robot with new capability to pass difficult terrains rather than bypassing them, and consequently the robot can achieve better performance in terms of traversal time and energy consumption. In this work, four different optimization algorithms, including Adaptive Genetic Algorithm, Elitist Ant System, Dijkstra and Dynamic Weighting A*, along with a well-known reinforcement learning algorithm called Q-Learning, are proposed to solve this path planning problem. The outputs of these algorithms are the optimal path through the environment and the associated configuration on each segment of the path. The challenges involved in mapping the path planning problem to each algorithm are discussed in full details. Eventually, all algorithms are compared in terms of the quality of their solutions and convergence rate.     

连续体结构的参数化水平集统一优化

针对传统分步式结构优化设计的不足,提出一种同时进行结构拓扑、形状和尺寸统一优化的设计方法.首先采用水平集函数描述统一的结构优化模型和几何尺寸边界,通过引入紧支径向插值基函数将结构拓扑优化变量、形状优化变量和尺寸优化变量变换为基函数的扩展系数;然后取该扩展系数为设计变量,借助一种参数的变化表达3种优化要素对结构性能的影响,将复杂的多变量优化问题变换为相对简单的参数优化问题,有利于与相对成熟的优化算法相结合提高求解效率;进一步用R函数将其融合为一个整体,构造出统一优化模型,并用最优化准则法进行求解.最后通过数值案例证明了该方法的有效性和精确性.     

虚拟现实引擎的设计与实现

真实感和实时性是虚拟现实技术中相互对立着的关键和核心。该文从引擎的底层细节开始讨论,侧重引擎实时性的要求,分析、提出了引擎所应具有的“驱动性”、“完整性”和“独立性”的特征,着重介绍了实时虚拟现实引擎中的若干关键技术,最后给出了一个室内场景三维图形引擎及其应用的实例。