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《Simulation Modelling Practice and Theory》2003,11(5-6):315-351
A numerical model of the air flow problem around the girder of a long-span bridge is presented. The model is based on a finite volume formulation and it is able to simulate steady and non-steady wind loading conditions on the structure under the simplifying assumption, which is plausible for bridges with long spans, of a two-dimensional-like approaching flow. For a given bridge deck cross-section the proposed model allows the numerical evaluation of the flutter derivatives, which is useful to characterize in an analytical way the stability conditions of the overall wind-induced bridge response. In order to obtain satisfactory accuracy and stability of the numerical solution, a two-equation k–ϵ RNG turbulence model and special boundary conditions are employed. The accuracy and applicability of the model to wind engineering problems are successfully assessed by computing the aerodynamic behaviour of some simple cross-section shapes. Numerical results are also obtained for typical long-span bridge cross-sections and the comparison with the available wind tunnel measurements shows a good agreement. 相似文献
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The prime objective of the paper is to overcome the conventional restriction to the field of rational functions as far as the algebraic design of control systems is concerned. By adopting the affine parameterization approach from algebraic control synthesis for the controllers given as the so-called RQ-meromorphic functions an algebraic solution to time-delay system control design is opened where neither an introduction of 2D transfer functions nor the assumption of commensurate delays is needed. The proposed design results in controllers combining both the integrators and delayers due to this property referred to as anisochronic. 相似文献
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目前设计的自由射流风洞系统加热气流模拟软件测量得出的气流面受力值容易发生耦合共振,导致测量流量误差较大;为解决上述问题,基于LabVIEW设计一种新的自由射流风洞系统加热气流模拟软件,软件程序包括自由射流风洞系统加热气流流量调节、加热气流时序控制、气流模拟软件等,通过与采集节点的配合完成数据采集、处理、分析等工作;利用Lab-VIEW技术,在程序软面板显示加热气流压力、增益频率等数据,直观地表现加热气流的压力大小以及变化;根据加热气流模拟软件,简化开发测试以及控制系统的程序,使软件调试过程更加简单,容易操作,实现了软件测试程序以及控制程序流程开发的平台化和通用化;实验结果表明,基于LabVIEW的自由射流风洞系统加热气流模拟软件能够减少气流面受力值耦合共振,测量误差在0.2%以内,实现自由射流风洞系统加热气流的准确模拟. 相似文献
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The study of general linear multivariable systems, with possibly different controlled and measured outputs, is continued in this part of the paper. The structure matrices, defined in Part I, are used to solve the feedback realization problem. Feedback realizable transfer functions are then used to solve problems of "regulator type." It is shown that the solutions to problems like disturbance deeoupling, output regulation, and pole placement are all special cases of the solution to a more general problem. Finally, it is shown how the results of Part I and Part II can be combined to solve problems of "servo type" and of "regulator type" simultaneously. 相似文献
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Luca Ballestra Stefano Micheletti Riccardo Sacco Fausto Saleri 《Computing and Visualization in Science》2001,4(2):79-86
We deal with a hydrodynamic model for semiconductors with a physical viscosity in the momentum/energy equations. The discretization
uses a first-order finite difference scheme with upwinding based on the characteristic variables. We perform a stability analysis
of the numerical method applied to a linearized incompletely parabolic system assuming vanishing viscosity in one space dimension
although the analysis can be extended to the two dimensional case. A thorough numerical parametric study as a function of
the heat conductivity and of the momentum viscosity is carried out in order to investigate their effect on the development
of shocks in both one and two space dimensions.
Received: 30 January 2001 / Accepted: 30 May 2001 相似文献
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Frequency-domain design of pid controllers for stable and unstable systems with time delay 总被引:13,自引:0,他引:13
An approach for tuning PID-type controllers is developed for single input single-output, linear time-invariant systems, based on an extension to the method of D-partition. This method permits design for simultaneous minimum gain and phase margin requirements. It also allows design for specified maximum gain and phase cross-over frequencies of the controlled system. The technique can be applied to systems with stable or unstable plants as well as to irrational systems with significant time delay. Another advantage of the method is that it can be used for various controller configurations including derivative in the feedback path. Three examples illustrate the tuning method. 相似文献
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Mrdjan Jankovic Author Vitae 《Automatica》2010,46(3):510-517
This paper presents a recursive method to design state and output feedback controllers for MIMO, block-feedforward linear systems with delays in the inputs, outputs, and interconnections between the blocks. The resulting controller is of predictor-type, which means that it contains finite integrals over past state and input values. The method is a generalization of the well-known model reduction approach for systems with input delay. A recursive procedure replaces delay terms with non-delay ones step by step, from the top of the cascade structure down. Controller gains are computed for the proxy system without delays, while the construction guarantees the same closed loop poles for the delay system and the proxy one. The observer is designed by applying the duality argument and the separation principle is also shown to apply. 相似文献
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Recent studies have shown that people prefer to age in their familiar environments, thus guiding designers to provide a safe and functionally appropriate environment for ageing people, regardless of their physical conditions or limitations. Therefore, a participatory design model is proposed where human beings can improve their quality of life by promoting independence, as well as safety, useability and attractiveness of the residence. Brainstorming, scenario building, unstructured interviews, sketching and videotaping are used as techniques in the participatory design sessions. Quality deployment matrices are employed to find the relationships between the elderly user's requirements and design specifications. A case study was devised to apply and test the conceptual model phase of the proposed model. 相似文献
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Cristina I. Muresan Abhishek Dutta Zehra Pinar Anca Maxim Clara M. Ionescu 《International journal of control》2016,89(3):579-593
This paper presents two tuning algorithms for fractional-order internal model control (IMC) controllers for time delay processes. The two tuning algorithms are based on two specific closed-loop control configurations: the IMC control structure and the Smith predictor structure. In the latter, the equivalency between IMC and Smith predictor control structures is used to tune a fractional-order IMC controller as the primary controller of the Smith predictor structure. Fractional-order IMC controllers are designed in both cases in order to enhance the closed-loop performance and robustness of classical integer order IMC controllers. The tuning procedures are exemplified for both single-input-single-output as well as multivariable processes, described by first-order and second-order transfer functions with time delays. Different numerical examples are provided, including a general multivariable time delay process. Integer order IMC controllers are designed in each case, as well as fractional-order IMC controllers. The simulation results show that the proposed fractional-order IMC controller ensures an increased robustness to modelling uncertainties. Experimental results are also provided, for the design of a multivariable fractional-order IMC controller in a Smith predictor structure for a quadruple-tank system. 相似文献
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《Advances in Engineering Software》2007,38(3):182-192
The development of a new framework for numerical simulations is presented as one of the possible ways to increase the usability and the speed of development of numerical simulation tools.One of the main differences between the new framework and existing systems is that the new system is capable of performing all operations at run-time. Modules are detected, loaded and used at run-time. The framework needs no prior knowledge of the type and availability of components, thereby increasing the flexibility of the system.The functionality of the framework is demonstrated with the implementation of a simple set of components which, when coupled, form the basis for a numerical simulation. 相似文献
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J.-E. Hernández-Díez S. Mondié S.-I. Niculescu E.J. González-Galván 《International journal of control》2018,91(4):907-925
This paper focuses on the design of P-δ controllers for single-input-single-output linear time-invariant systems. The basis of this work is a geometric approach allowing to partitioning the parameter space in regions with constant number of unstable roots. This methodology defines the hyper-planes separating the aforementioned regions and characterises the way in which the number of unstable roots changes when crossing such a hyper-plane. The main contribution of the paper is that it provides an explicit tool to find P-δ gains ensuring the stability of the closed-loop system. In addition, the proposed methodology allows to design a non-fragile controller with a desired exponential decay rate σ. Several numerical examples illustrate the results and a haptic experimental set-up shows the effectiveness of P-δ controllers. 相似文献
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João B.P. Falcão Filho 《Computers & Fluids》2008,37(10):1276-1308
Numerical prediction of an injection process was successfully performed. The physical problem corresponds to the mixing of a number of parallel supersonic jets with a subsonic main stream, in the presence of solid walls. In practice, this arrangement is to be used as a boosting device in a transonic wind tunnel, with the ultimate objective of extending the tunnel’s envelope without penalizing the main compressor. Five supersonic nozzles are installed at the floor and five at the ceiling of the transition module’s entrance section. Due to the great difference between cross-sectional typical lengths of nozzles and tunnel, the numerical tool has to have a three-dimensional capability. The core of the code is an adaptation of the finite-difference diagonal algorithm, and turbulence effects are properly tackled by the use of the Spalart and Allmaras one-equation scheme. Some simplifications were adopted in order to render the problem minimally tractable, especially in this initial numerical simulation stage, which is the reporting objective of this article. Albeit this, and due to the magnitude of the problem in hand, these simplifying initiatives were not sufficient to bring the calculations down to a scale of reasonable computer costs. Hence, a sequence of grids, coupled with a division of the computational domain, was adopted. Boundary conditions were thoroughly worked, especially the ones related to the domain of calculation’s entrance plane. This plane is important because of the many viscous gradient regions that project against it. Among the many settings under which a tunnel can operate there is one defined as the “design condition”, or else as the “design point”, as it is sometimes called. For a tunnel equipped with an injection system, the design point asks (besides many other specifications) for equal static pressures at the section where the supersonic jet meets for the first time the main stream coming from the tunnel circuit. We have simulated five different operating settings of the tunnel and among them the design condition. Therefore, we have results for the design as well as for many off-design points. The idea was to simulate the many tunnel settings and also to test the code’s ability to handle all these different situations. The code was duly validated and verified, and in the sequel the steady flow field in the mixing region was calculated. Many interesting and very important results were obtained, among which we would point out the existence of compression and expansion domes at the supersonic regions, the calculation of the many engineering parameters related to the injection process, and especially the determination of the injection’s gain threshold. 相似文献
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基于数值计算的高速列车气动阻力风洞试验缩比模型选取方法 总被引:2,自引:0,他引:2
为给高速列车气动阻力风洞试验模型选取提供更多的参考依据,通过计算流体力学(Computational Fluid Dynamics,CFD)方法,研究不同比例的高速列车缩比模型对气动阻力风洞试验结果的影响.首先,计算得到开口式风洞测试段的静压系数分布曲线,为高速列车气动阻力测量试验模型的长度选择以及摆放位置提供依据;其次,通过数值计算得到全尺寸模型列车在明线运行时,以及不同比例的模型列车在风洞中运行工况下的气动阻力信息,并从阻塞效应和雷诺数的变化,以及风洞试验段内静压分布的影响这3个方面对列车模型的气动阻力结果进行分析,得到在所研究风洞中较合理的列车缩比模型比例选取范围.这种以CFD为基础进行数值仿真,选取风洞试验中列车模型比例及试验测试位置的方法,为在地面交通工具风洞中进行高速列车模型气动阻力试验的缩比模型选取提供一定依据. 相似文献
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《Computers & Mathematics with Applications》1999,37(11-12):123-131
In this paper, an analytical and numerical formulation for observed satellite radiances from space is provided, allowing for the radiation effect due to the adjacent rugged terrain. Up to now the atmospheric effect on the satellite images has been dealt with in the case of flat terrain. In this present paper, an allowance for the multiple reflection of light by the adjacent mountainous terrain has been taken into account approximately using the mean background albedo. Then, the validity of the numerical approximate solution is discussed for several cases of typical surface reflection examples, with respect to the atmospheric and topographic correction problem. 相似文献
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建立了黄浦江某大型越江隧道的三维精细非线性有限元模型,采用接触均衡的并行计算技术,解决了大型隧道工程数值模拟时规模庞大的问题。数值模拟了越江隧道的静应力场,比较了两种不同分区方案对并行加速比的影响。数值模拟结果能够为大型隧道工程设计提供参考依据。 相似文献
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多普勒测风激光雷达是大气风场探测的重要手段。本文以光纤Mach-Zehnder干涉仪作为测风激光雷达系统的鉴频器,设计并建立了风速模拟探测激光雷达的自校正式实验系统,采用可控转速机械转轮产生的线速度引起激光多普勒频移的方法模拟大气风场。其主要由激光发射系统、模拟风场系统和光电探测系统组成。初步利用种子激光器的可调节波长实现了系统输出强度变化,通过能量探测方式验证了光纤Mach-Zehnder干涉仪透过率谱强度曲线,实验分析结果验证了鉴频系统的可靠性,并进一步实现了鉴频系统光程差精确校正。 相似文献