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模拟跨声速湍流的线性和非线性涡粘性湍流模式 总被引：1，自引：0，他引：1
讨论应用线性和非线性涡粘性湍流模式计算跨声速湍流 .用于比较的 3个线性湍流模式是Shih和Lumley的k ε模式 ,CMOTT模式和SST模式 .2个非线性模式是Shih ,Zhu和Lumleyd的二阶模式 ,以及Shih等的三阶模式 .计算的典型流动是绕凸起的跨声速流动 ,该流动的特征是激波与边界层相互作用且伴有流动分离 .计算结果表明非线性湍流模式具有明显的优势 . 相似文献
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研究了标准k ε模式 ,双尺度湍流模式 ,并对其在壁面附近作出长度尺度修正 在此基础上 ,选择了几个基准流动 :二维可压缩拐角、锥柱裙组合体绕流和斜激波 /平板湍流边界层干扰 ,进行数值计算 .通过数值计算和实验结果的比较 ,发现修正湍流模式对流动分离、摩阻和热流的计算具有更好的效果 . 相似文献
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本文介绍过去十年我们在湍流实验研究中取得的某些进展。如边界层湍流中的高阶共振干涉,二维混合层中的转捩过程,拟序结构和近声场的相互作用,不稳定波辐射噪声,自由气流中的湍流对湍流分离的影响等。某些关于湍流模式理论以及粒子群和湍流相互作用的实验研究将在不久可得到某些有意义的结果。 相似文献
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《中国科技信息》2015,(1):5
本项目采用沈阳空气动力研究所研发的航空并行CFD计算平台,进行标准明星并行评估计算。该软件可广泛应用于飞行器的亚、跨、超和高超音速的气动力学计算和一些特殊气体动力学问题如直升机旋翼、导弹发射、座舱弹射、投弹、机动和气动弹性等。传统的飞行器气动布局设计主要依赖理论研究估算、设计师的经验以及大量的风洞试验结果,风洞试验是主要设计工具。计算机技术的迅猛发展推动了航空空气动力学的革命。目前正在大力发展的计算流体力学将以突破对黏流流场物理现象的模拟能力为重点,尤其是精确预测流动分离点和转捩过程以及湍流流动。随着中国航天航空事业的快速发展,尤其是载人航天技术的巨大成功,我国科技人员对空气动力学的数值模拟研究提出了越来越多的需求,常规的计算能力远远无法满足复杂的大型飞行器设计所带来的巨大需求。 相似文献
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本文综述了近年来用分叉和混沌的观点来研究湍流的发生与发展的机理所取得的某些进展。重点介绍了以下三方面的研究成果:1.用分叉与混沌的观点来解释湍流转捩的根本机制。2.用奇怪吸引子和分形的观点来解释湍流运动的不规则性和无序性。揭示湍流运动是流体内在随机性的表现。3.用拉格朗日观点来研究流体的运动,探讨在物理空间内混沌运动与湍流运动之间的密切关系。 相似文献
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Turbulence is a universal form of fluid motion. It is the key issue in fluid mechanics. Very recently, it has become a bottleneck in some key engineering research of national importance, such as aeronautics, astronautics and navigation. Developed turbulence and the onset of turbulence, i.e. transition, are two interrelated parts of turbulence. The hypersonic boundary-layer transition is a strategic focus in the fluid mechanics community. This article reviews recent developments in the study of the hypersonic boundary-layer transition, research facilities and experimental techniques. The hypersonic quiet wind tunnel is introduced as a necessary device to obtain real flight data in near space. Near-wall measurement techniques, such as temperature-sensitive paint, near-wall particle image velocimetry and Rayleigh-scattering visualization, are shown. The most important issues in the recent development of the transition in the hypersonic boundary layer are addressed. The instability and nonlinear interaction of different instability modes are discussed. The recent contributions from China, especially at Peking University, are also introduced. 相似文献
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In this paper, the numerical solution of differential-algebraic equations is considered by Padé approximation method. We applied this method to an example which is a physical model problem. Firstly the physical model problem has been converted to power series, then the numerical solution of physical model problem was put into Padé series form. Thus we obtained numerical solution of physical model problem. 相似文献
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《Journal of The Franklin Institute》2023,360(12):9115-9138
In this paper, active disturbance rejection control (ADRC) based on a neural network has been investigated for the attitude control of the hypersonic vehicle (HV) with uncertain disturbances, which are regarded as a strongly time-varying, nonlinear, and coupled system. The structure of nonlinear state error feedback (NLSEF) with an Extended State Observer (NLSEF+ESO) utilized in ADRC is considered to have good disturbance resistance ability in engineering applications with less dependence on the mathematical model of the system. However, the strong coupling of the HV makes it complicated to separately design ADRC for each channel. In addition, the bandwidth and parameters of the ESO can seriously affect the performance of the ADRC, while jitter occurs when they are not well matched. A cascade active-rejection control scheme is designed by introducing the Radial Basis Function (RBF) Neural Network to substitute the ESO in ADRC, which mitigates the shortcoming of ADRC in addressing the control problems of the MIMO system with coupling disturbances. The NNESO can adapt well to disturbance characteristics through online training and fitting and can effectively reduce the jitter of the control. The stability of the NNESO is proved by Lyapunov stability theory, and the numerical simulations are presented to demonstrate the effectiveness of our theoretical results. In summary, the proposed NNESO-based cascade ADRC is an effective method for solving the problem of HV control with better disturbance resistance. 相似文献
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资源定价改革是今后改革的重点突破领域。天然气作为一种重要的资源,其定价方式变革将推动中国天然气市场发展路径和走向,是整个天然气市场改革至关重要的一环。本文在经典的古诺模型基础上,通过变分不等式转换揭示了生产商、销售商与消费者这三个市场主体在天然气网络市场中的相互作用机制,并由此建立了天然气市场均衡模型;进而探讨了在成本异质性、多气源竞争以及政府限价三种不同情景下均衡价格与社会福利水平的变化;最后以上海市为例进行了实证分析。研究表明:①从社会福利最大化的角度看,中国天然气均衡价格受到上游竞争程度、管输成本、生产成本等因素的影响。推动上游企业降低成本并不能有利于全社会福利水平的改善,政府限价的长期均衡结果是导致需求的膨胀,进一步加剧了短缺;②定价方式的改革对于天然气均衡价格和均衡量影响程度不一。自由竞争的定价方式将驱离成本最高的气源。而中国当前采取的净回值定价改革发挥了需求函数的作用,有利于天然气产业链上下游的平稳发展;③天然气净回值法定价与市场自由竞争定价的效果相等,说明在目前天然气供需存在缺口、市场发育不完全的情况下,净回值法是一种有效的价格改革的过渡方式。过渡的条件是天然气管网的互联互通,形成区域节点价格。 相似文献
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A novel adaptive control with σ-modification for uncertain nonlinear systems is proposed in the paper. The application of conventional adaptive control is severely limited by the problems of construction of Lyapunov function and parameter drift because of non-parametric uncertainties. The proposed adaptive control that is on the basis of the immersion and invariance theory and σ-modification can be used to deal with these problems to some extent. It turns out to be a structured design method without requiring a Lyapunov function in the design level and robust to non-parametric uncertainties. Moreover, constrained command filter backstepping is adopted to meet the amplitude and rate constraints on the states and actuators. The uniformly ultimately bounded stability of the closed-loop system has been analyzed by Lyapunov theory with parametric and non-parametric uncertainties of the controlled model. To demonstrate the design flexibility, the method is applied to the position tracking control system design of a mass-damper-spring system and the flight control system design of a scramjet-powered air-breathing hypersonic vehicle. Finally, the effectiveness of the proposed adaptive control method is illustrated by numerical simulations. 相似文献
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为了保证工程项目组合决策流程的顺利实施,将多主体系统应用于决策流程中,构建了基于多主体的工程项目组合决策流程模型。将具有自适应能力的决策主体作为模型的核心单元,设计了决策主体的逻辑结构和行为推理算法,并将工程项目组合决策流程划分为企业战略评定、单个项目评价、项目组合选择优化、项目组合执行控制以及项目组合调整5个阶段,分析了每个阶段的具体功能。最后通过模型在某建筑企业的具体应用证明了其有效性。 相似文献
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基于互惠动机的个体间隐性知识转移研究 总被引：24，自引：2，他引：22
个体间隐性知识转移是隐性知识转移、知识转移与知识管理的主体内容。隐性知识的非编码性、垄断性和知识主体的诚信缺失性决定了个体间的隐性知识转移契约存在软性约束,从而引致知识转移困境的存在,而传统的激励机制不是解决这一困境的最佳方式。互惠性偏好正逐渐成为经济学研究的热点问题,并对传统的“经济人”假设提出了挑战。隐性知识转移模型与委托-代理模型具有天然的拟合性,通过互惠性假设的植入,可以对基于知识转移的传统委托-代理模型实施优化性改造。知识转入方可以充分利用知识转出方非理性的互惠性偏好来获取更高的知识转移价值,从而实现个体间隐性知识转移效率的提高。 相似文献
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施工方案优化是建筑施工中一项重要任务,施工方法的选择直接决定着工程的安全、质量、经济等各项效益指标,施工方案比选在工程中起着举足轻重的作用。本文立足系统的角度从安全、质量、经济、技术本身等各因素构建施工方案评价模型,为施工方案比选及后评价提供了良好评价模型,并结合工程实践对施工方案的比选和评价作了实证研究。 相似文献