Efficient model reduction in non-linear dynamics using the Karhunen-Loève expansion and dual-weighted-residual methods

 We look at the task of computing the time-evolution of a non-linear system for a long time, in our case under random external influences. Our specific example is the fatigue evaluation of a wind turbine. To facilitate such a computation, we look at a reduction of the computational effort by projecting everything on a low-dimensional basis. In this case we take the Karhunen-Loève basis generated from running the model a little while under the random loading. It is important that the error which is caused by this reduction process can be controlled. We estimate the error by dual or adjoint methods. This in turn allows the process of model reduction to be performed adaptively. Dedicated to the memory of Prof. Mike Crisfield, for his cheerfulness and cooperation as a colleague and friend over many years.     

生态环境的规划设计

本文论述了生态环境规划设计的基本理论、以生态理论为指导,提出了营造生态环境的几种方法。     

A reactive molecular dynamics model of thermal decomposition in polymers: I. Poly(methyl methacrylate)

The theory and implementation of reactive molecular dynamics (RMD) are presented. The capabilities of RMD and its potential use as a tool for investigating the mechanisms of thermal transformations in materials are demonstrated by presenting results from simulations of the thermal degradation of poly(methyl methacrylate) (PMMA). While it is known that depolymerization must be the major decomposition channel for PMMA, there are unanswered questions about the nature of the initiation reaction and the relative reactivities of the tertiary and primary radicals formed in the degradation process. The results of our RMD simulations, performed directly in the condensed phase, are consistent with available experimental information. They also provide new insights into the mechanism of the thermally induced conversion of this polymer into its constituent monomers.     

Validation of a Three-Dimensional Computational Fluid Dynamics Model of a Contact Tank

A three-dimensional (3D) computational fluid dynamics (CFD) model of a contact tank is presented in this paper. The model results are compared against 3D velocities and flow through curve (FTC) data, representing a tracer concentration profile, from a 1:8 scale physical model. The objective is to demonstrate that CFD models can simulate both the FTC and the 3D velocity field quite well. Simultaneous validation of velocities and FTC is important in ascertaining the predictive capabilities of CFD models, as physical model studies indicate that different baffle arrangements can lead to similar FTCs. Therefore, a good prediction of only FTC, as presented in previous 3D CFD model studies, does not necessarily imply a correct simulation of the flow field.     

浅析建筑小品与植物的关系

着重介绍了园林植物与建筑小品的配置的方法。建筑小品与植物一起配置,不仅可以获得和谐优美的景观,而且还可突出单体达不到的功能效果。     

水解聚马来酸酐的微观阻垢机理研究

利用分子模拟方法优化了水解聚马来酸酐的构型,模拟了水解程度不同时各聚合物与碳酸钙晶体之间的相互作用,并计算了其作用能量和原子键距的变化。计算结果显示:所有阻垢剂分子均逐渐接近方解石晶体,阻垢剂分子链中的活性羧酸基团与Ca2 螯合,某些基团与Ca2 离子的键距越来越趋近,占据晶体的晶格生长点或嵌入晶体内部,同时分子结构存在小幅度的变形;说明该聚合物的阻垢机理是抑制晶体成核即抑制碳酸钙的长大,同时使晶体晶格扭曲畸变使垢松软。作用后动能、势能和总能量均有不同程度的降低,趋于更稳定的构型,并随着水解度的增大,阻垢作用更加明显。     

Tools for dynamic analysis of the general large power system using time-varying phasors

This paper extends the applicable range of phasors for transient analysis from the traditional slow quasi-stationary range to accommodate fast speeds up to the carrier frequency. Rigorous phasor calculus is developed for time varying low pass phasor signals whose bandwidths are less than the 60 Hz carrier frequency. Symmetrical components technique for analysing quasi-stationary unbalanced power system transients is extended to cover the low pass time-varying phasors. It is also proved that the time varying phasors can be used for computing the fast electromagnetic transients within the linear RLC lumped parameter representation of the transmission network irrespective of the transient speeds. In linear networks, this time-varying phasor concept unifies two classical approaches: (1) transient analysis using instantaneous currents and voltages, and (2) steady state analysis using traditional phasors, into analysing both behaviours precisely using the time-varying phasors.     

中国泥沙研究的几个问题

几千年来泥沙一直是中国河流治理和灾害防治中的难题。众所周知，黄河频繁的迁徙和洪水灾害就是泥沙淤积的结果。中国学者在黄河治理和土壤侵蚀、水库淤积、河口海岸泥沙漂移、泥石流灾害防治等方面进行了大量研究工作，促进了学科发展，取得了举世瞩目的成就。本文概述这些泥沙问题、治理方略和研究成果。在21世纪，泥沙研究将面临新的挑战。泥沙理论研究方面，非恒定流输沙、环境泥沙学、生态泥沙学和经济泥沙学将成为新的生长点。为了检阅现有泥沙理论和研究方法，国家大量投资对三峡工程建设中和建设后的泥沙运动和沉积规律进行大规模的测量。中国的泥沙研究将有一个新的飞跃。     

Heat transfer and flow of He II in narrow channels

Heat transfer and fluid flow of He II in a long, narrow channel connected to a bath that supplies a constant supply of heat have been investigated by numerical simulations by using the simplified model of Kitamura et al. [Cryogenics 37 (1) (1997) 1]. Such channels are used to cool compact, stable, low-temperature magnets. The fluid flow is driven by natural convection and the mutual friction between the normal fluid and the superfluid.In this model, the thermomechanical effect and the Goter-Mellink mutual friction balance each other. A consequence of this balance is that the velocity and temperature distributions of He II can be characterized by a dimensionless, dependent parameter equal to the ratio of the fluid speeds of internal convection to the total fluid flow. After a sudden application of heat flux, the internal convection dominates over the total fluid flow until the establishment of steady-state temperature gradients. This predicts that the time required to set up the steady-state total fluid flow is proportional to the total heat capacity in the channel.     

水管理策略对土壤水盐动态和区域地下排水影响的模拟评价

以宁夏惠农灌区平罗试验区为对象，基于田间观测与灌溉试验结果，在田间尺度采用SWAP模型开展不同地下水调控深度与灌溉制度相结合的水管理方案下土壤水盐动态的模拟，在区域尺度采用MODFLOW模型进行不同水管理方案对区域地下排水量影响的模拟评价，据此分析土壤水盐动态过程和农田排水系统的作用，对拟定的各种水管理方案进行评价。结果表明，现状灌溉用水量虽有助于减少表土盐分积聚，但地下排水量占灌溉用水量的39．4％；现状灌溉用水量减少50％时，浅埋地下水位会加重表土积盐；现状灌溉用水量减少25％时，作物根区没有产生明显的积盐，地下排水量减少31．4％。因此，较为合理的水管理方案是将现状灌水量减少25％的同时将地下水埋深控制在70cm以下，才能达到节水、增产、改善农田水土环境的目标。