An optimality criteria algorithm for tall steel building design using commercial standard sections

Grierson and Chan (1991a, b) recently presented an efficient optimality criteria (OC) technique for the optimum design of large-scale tall steel building frameworks. In this paper, further developments of the technique are described concerning a detailed procedure to assign optimum discrete section sizes to structural members. A 60-storey, 7-bay framework example is presented to illustrate the practical applicability and efficiency of the proposed design optimization algorithm.Presented at NATO ASI Optimization of Large Structural Systems, Berchtesgaden, Germany, Sept. 23 – Oct. 4, 1991     

交通流多格点预估格子模型与数值仿真

考虑驾驶员对多格点交通流量预估效应,建立了新的交通流多格点预估格子模型。通过线性稳定性分析获得了改进模型的稳定性条件。通过非线性分析得到了扭结—反扭结密度波解,得到了交通流相空间的三个区域:稳定区域、亚稳定区域和不稳定区域。数值仿真验证了考虑驾驶员对多格点的预估效应,能够进一步提高交通流的稳定性。     

A numerical model for wind loads simulation on long-span bridges

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.     

A scenario for the development and implementation of a building product model standard

Product models offer a promising method for structuring data describing a building in the databases which will be used in the computer integrated construction process of the next century.In order to define product model standards which completely describe modern buildings, many years of theoretical and experimental work are needed. In order to ensure industrial backing for the work needed to develop full standards, it seems prudent to organize such work on a step by step basis where partial standards can be agreed on and implemented rather quickly.In addition to the international work being carried out within the ISO/STEP working group, it is possible to obtain results on a national basis, provided there is a large enough consensus within the construction industry on what ought to be done.In Finland the basic principles of a building product model, the RATAS-model, have been defined. The model uses a data model consisting of such concepts as objects, attributes, relationships and it describes the building with a five-level abstraction hierarchy starting with the building object. At present a number of prototypes are being developed based on the RATAS-model. These prototypes are developed using different types of application software: relational databases, hypermedia, drafting systems etc., but they all utilize the same conceptual information structure.     

An improved valve stiction simulation model based on ISA standard tests

The Choudhury valve model is a widely adopted data-driven model to study the behaviour of valve stiction. A recent study (Garcia, 2008) revealed that valve stiction simulation based on Choudhury’s simulation model (Choudhury, Thornhill, & Shah, 2005) fails to pass eight out of fifteen Industry Standard Architecture (ISA) standard tests (ISA, 2000, ISA, 2006) for real control valves. In this study, the ISA testing results are further elaborated for this model. It is found that three minor deficiencies lead to the discrepancies between the Choudhury Model outputs and the expected ones when (i) the valve input signal changes the direction of travel, (ii) the initial stem position does not stay on the working curves l₁ and l₂, and (iii) the valve input signal changes in a ramp–pause–ramp manner. To address the above deficiencies, an improved version of the Choudhury Model, termed as XCH Model, is proposed. Assessments along with the ISA standards presented by Garcia (2008) demonstrate the proposed XCH Model passes all the ISA standard tests and thus provides a more realistic simulation of a real industrial valve being able to exhibit stiction behaviour.     

交通流多预期延迟模型与数值仿真

为了更准确地描述交通流,考虑驾驶员反应延迟时间和前车信息的非均衡使用,建立一种多预期延迟跟驰模型。线性稳定性分析表明,驾驶员反应延迟时间的增加会降低交通流的稳定性,多个前车信息的使用可以提高交通流的稳定性。数值仿真的结果表明,减少司机的反映延迟时间和适当地增加前车信息都能提高交通流的稳定性。为尽可能少地引入输入变量,不均衡地利用前车的车间距和速度差信息是必要的。理论和数值模拟的结果均表明驾驶员反应延迟在交通拥堵的形成过程中起着重要作用。     

串列双索气弹模型的风洞试验研究

为研究斜拉桥串列拉索或悬索桥无吊杆串列主缆在风荷载作用下的相互干扰情况,通过自行设计的拉索试验装置,对两串列拉索进行了一系列的气弹模型风洞试验.试验得到索间距W/D在5.85～20变化(W为拉索中心距,D为拉索直径),风偏角在-90°～90°范围内变化时上下游索的一些响应特性.试验观测到了明显的尾流驰振现象,且试验结果表明索间距与风偏角的变化对串列拉索是否出现尾流驰振都有明显的影响.在发生尾流驰振时,以下游索面外的振动为主,且其临界风速随索间距W/D变小而降低;在同一索间距下,0°风偏角为最不利状态,且负风偏角比正风偏角更容易发生尾流驰振.     

Layer average relative humidity from SAPHIR on board Megha-Tropiques: validation with numerical model analyses

Subsequent to the launch of the Sondeur Atmosphérique du Profil d’Humidité Intertropicale par Radiométrie (SAPHIR) sensor on board the Megha-Tropiques satellite on 12 October 2011 from Satish Dhawan Space Centre, Indian Space Research Organization (ISRO), Shriharikota, India, the validation of layer averaged relative humidity (LARH) retrieved from SAPHIR has been initiated in different phases along with other retrieved parameters. The Megha-Tropiques is a joint satellite mission executed by the Indian Space Research Organization (ISRO) and the Centre National d’Etudes Spatiales (CNES), and is primarily devoted to study the tropical atmospheric processes influencing both weather and climate. The present study focuses on a validation campaign, where the validation of LARH derived from SAPHIR is carried out with three different numerical model analyses: the European Centre for Medium Range Weather Forecasts (ECMWF) model, the National Centers for Environmental Prediction (NCEP) model, and the National Centre for Medium Range Weather Forecasting (NCMRWF) model, over a period of six months from January 2013 to June 2013. It is observed that the root mean square difference (RMSD) of LARH has improved considerably for layers 1, 2, 3, and 6, and some marginal changes for layers 4 and 5, when a bias correction is applied to the data. The RMSD of SAPHIR LARH after correcting for bias is well within the range of the mission goal of 20% accuracy.     

Mathematical model and numerical simulation of the liquid fluidization of polydisperse solid particle mixtures

A mathematical model for the fluidization of polydisperse suspensions is developed. The stationary concentration configurations for a given fluidizing velocity are analyzed and a mixing condition for bed inversion is derived. A central finite difference scheme is applied to the simulation of the fluidization of a bidisperse suspension. The numerical simulations agree with the experimentally reported qualitative behaviour of fluidized suspensions such as bed expansion and bed inversion.     

Quantum computer simulation using the CUDA programming model

Quantum computing emerges as a field that captures a great theoretical interest. Its simulation represents a problem with high memory and computational requirements which makes advisable the use of parallel platforms. In this work we deal with the simulation of an ideal quantum computer on the Compute Unified Device Architecture (CUDA), as such a problem can benefit from the high computational capacities of Graphics Processing Units (GPU). After all, modern GPUs are becoming very powerful computational architectures which is causing a growing interest in their application for general purpose. CUDA provides an execution model oriented towards a more general exploitation of the GPU allowing to use it as a massively parallel SIMT (Single-Instruction Multiple-Thread) multiprocessor. A simulator that takes into account memory reference locality issues is proposed, showing that the challenge of achieving a high performance depends strongly on the explicit exploitation of memory hierarchy. Several strategies have been experimentally evaluated obtaining good performance results in comparison with conventional platforms.     

Aerodynamic noise simulation of the flow past an airfoil trailing-edge using a hybrid zonal RANS-LES

This paper document the evaluation of a zonal RANS-LES approach for the prediction of broadband and tonal noise generated by the flow past an airfoil trailing edge at a high Reynolds number. A multi-domain decomposition is considered, where the acoustic sources are resolved with a LES sub-domain embedded in the RANS domain. At the RANS-LES interface, a stochastic vortex method is used to generate synthetic turbulent perturbations. The simulations are performed with the general-purpose unstructured control-volume code FLUENT. The far-field noise is calculated using the aeroacoustic analogy of Ffowcs-Williams and Hawkings. The results of the simulation are compared with available acoustic and mean velocity measurements. The investigation demonstrates the ability of this approach to predict the aerodynamic and aeroacoustic properties of the flow. Two simulations are performed in order to address the sensitivity of the results to the perturbation model. The comparison clearly indicates the critical influence of the model.     

带自控能力的捕食模型正解存在性与数值模拟

在齐次Dirichlet边界条件下,研究一类低密度食饵下,捕食者具有自控能力的捕食模型平衡态正解存在性。通过连续延拓意义下建立的连续算子,利用度理论给出了平衡态正解存在的充分条件,并对理论结果进行数值模拟。研究结果表明,只要捕食者和食饵的生长率适当大,则捕食者和食饵可以共存。     

基于数值计算模型的MMC半桥型子模块仿真方法

模块化多电平换流器（MMC）的各半桥子模块均由两个开关组（1个IGBT和1个反并联的二极管）构成。针对MMC在包含的子模块规模较大的情况下,对采用电路模型分割法对MMC进行分割后的子模块进行仿真求解时仍然会占用较多资源,效率不高的问题,提出了基于数值计算模型的MMC半桥子模块仿真验证方法。首先通过分析三相MMC及其半桥子模块（HBSM）的工作机制,把半桥型子模块中的两个开关组等效为在高、低阻态不断切换的等效电阻并给出了其等效电路。然后针对电容支路的离散化问题,根据梯形积分法推导了MMC半桥型子模块的数值求解公式,给出了数值计算电路模型。最后基于MATLAB仿真平台建立了基于数值计算模型的半桥子模块仿真验证模型,通过与详细模型子模块的仿真波形对比分析,结果表明了所建立的子模块数值计算模型是可行的。     

Mapping of industry building product model for detailed thermal simulation and analysis

Industry Foundation Classes (IFC) is an emerging data standard that promotes the interoperability of digital building product object models, or building product models (BPMs). Implementing IFC-based applications allows reducing data duplication, especially in the aspect of building geometry. With appropriate data mapping engines, an existing BPM may be readily used for performance-based simulation which requires significantly less effort compared with the traditional means. As a result, it is possible to make use of many available proprietary tools to provide additional services such as early-stage building design support. SEMPER-II (S2), which is an active, multi-domain, space-based, object-oriented design support tool for integrated building performance computing, was developed before the IFC standard was established. In order to perform building performance simulations based on the IFC compliant data models expressed through the eXtensible Markup Language (XML) based formats, an add-on data mapping engine has been developed as a front-end application in S2. The data mapping engine extracts all necessary information embedded in the XML data files, which is obtained directly from IFC compliant CAD drawings, and converts the data into the internal data format of S2.This process demonstrates a seamless link between an IFC compliant industry building product model (e.g. CAD) and the Shared Object Model (SOM) of S2 to facilitate building performance simulations.     

On a viscous-hydrodynamic model for semiconductors: numerical simulation and stability analysis

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     

Dimensional reduction of 3D building models using graph theory and its application in building energy simulation

Since the various people involved in the design process for a building project tend to hold conflicting views, this inevitably leads to a range of disparate models for planning and calculation purposes. In order to interpret the relevant geometrical, topological and semantical data for any given building model, we identify a structural component graph, a graph of room faces, a room graph and a relational object graph as aids and explain algorithms to derive these relations. We start with a building model by transferring its geometrical, topological and semantical data into a volume model, decomposing the latter into a so-called connection model and then extracting all air volume bodies and hulls of the model by means of further decomposition into elementary cyclic connection components. The technique is demonstrated within the scope of building energy simulation by deriving both a dimensionally reduced object model required for setting up a thermal multizone model and a geometrical model for defining single or multiple computational fluid dynamic domains in a building together with incidence matrices correlating these models. The algorithm is basically applicable to any building energy simulation tool.

非平稳随机路面模拟与分析

汽车的主要激励来自路面,对路面不平度的模拟和分析,是进行汽车行驶平顺性分析的基础.本文在回顾随机路面模拟和对非平稳随机过程描述的基础上,导出了非平稳随机过程功率谱密度存在的充要条件和Wiener过程的功率谱密度,并用Wiener过程模拟生成了非平稳随机路面.基于小波理论,对非平稳随机过程的路面激励进行了一维离散二进小波分解,有效地把路面激励信号中的平稳成分与非平稳成分、低频成分与高频成分等分离开.     

Crowd simulation using DC model and density information

Realistic crowd simulation is an important issue for the production of virtual worlds for games, crowd management, public space design, education, entertainment or architectural and urban planning. In this paper, crowd simulation is considered from two aspects: intra-group simulation and inter-group simulation. We propose a unified framework for crowd simulation in real-time virtual environment. Based on this framework, for intra-group simulation, we propose a novel density-based information crowd simulation to collision-free. For inter-group simulation, we propose a novel discrete choice (DC) model to realistic simulation of crowds and path planning. Meanwhile, we also propose a variable bounding box method for intra-group/inter-groups intersection problem. The simulation results show that the developed framework allows different group structures to be easily modeled. And the proposed framework could be used for real-time navigation of many moving crowd in complicated virtual environments.     

Effects of amplitude-dependent damping and time constant on wind-induced responses of super tall building

Full-scale measurements of wind-induced responses of a 79-storey tall building, Di Wang Tower, were conducted during the passages of several typhoons. The amplitude-dependent damping ratios of the super tall building were obtained from the measurements. A Monte Carlo simulation procedure was developed in this study to generate fluctuating along-wind and across-wind forces acting on this building. The wind-induced responses of Di Wang Tower were numerically evaluated in time domain on the basis of the generated fluctuating wind forces and the established finite element model of the building. The predicted dynamic responses of the building using the actual amplitude-dependent damping characteristics were compared to those computed with constant damping parameters assumed by the structural designers to evaluate the adequacy of current design practices and to investigate the effect of amplitude-dependent damping on the wind-induced responses. Finally, the effect of time constant on the wind-induced responses of Di Wang Tower was studied by comparing the time domain computational results with those from conventional spectral analysis method. Some of the research findings resulted from this combined experimental and numerical study are expected to be of interest and practical use to professionals and researchers involved in the design and analysis of super tall buildings.     

Direct numerical simulation of compressible turbulent channel flows using the discontinuous Galerkin method

Direct numerical simulation of turbulent channel flows between isothermal walls have been carried out using discontinuous Galerkin method. Three Mach numbers are considered (0.2, 0.7, and 1.5) at a fixed Reynolds number ≈2800, based on the bulk velocity, bulk density, half channel width, and dynamic viscosity at the wall. Power law and log-law with the scaling of the mean streamwise velocity are considered to study their performance on compressible flows and their dependence on Mach numbers. It indicates that power law seems slightly better and less dependent on Mach number than the log-law in the overlap region. Mach number effects on the second-order (velocity, pressure, density, temperature, shear stress, and vorticity fluctuations) and higher-order (skewness and flatness of velocity, pressure, density, and temperature fluctuations) statistics are explored and discussed. Both inner (that is wall variables) and outer (that is global) scalings (with Mach number) are considered. It is found that for some second-order statistics (i.e. velocity, density, and temperature), the outer scaling collapses better than the inner scaling. It is also found that near-wall large-scale motions are affected by Mach number. The near-wall spanwise streak spacing increases with increasing Mach number. Iso-surfaces of the second invariant of the velocity gradient tensor are more sparsely distributed and elongated as Mach number increases, which is similar to the distribution of near-wall low speed streaks.