The use of small‐format and low‐altitude aerial photos for the realization of high‐resolution DEMs in mountainous areas: application to the Super‐Sauze earthflow (Alpes‐de‐Haute‐Provence,France)

Geomorphologists have to make choices and compromises, as acquisition techniques of geometrical information are numerous, depending on the specific complexity of the targeted three‐dimensional objects and the requirements of the end user. This article presents the methodology and the results over a well known and documented site. This ready‐to‐use, low‐altitude, aerial photo methodology reveals itself to be a satisfying compromise between cost, accuracy and difficulty of implementation. The selected equipment package is light enough to enable a quick reaction to unexpected events and the tools and methods are competitive with field acquisition techniques. An evaluation has demonstrated a sub‐metric accuracy for the final result. Copyright © 2002 John Wiley & Sons, Ltd.     

Active interaction control of civil structures. Part 2: MDOF systems

In this paper, the performance of active interaction control (AIC) algorithms is assessed within the context of two realistic building models. The AIC control approach is proposed as a semi‐active means of mitigating the structural response during large earthquakes. To implement the AIC control algorithms into MDOF systems, the modal control (MC) approach that directs the control effort to certain dominant response modes is formulated and utilized herein. Two structures, a 3‐storey building and a 9‐storey steel‐framed benchmark building controlled by the AIC algorithms are analysed for two historical earthquake records. The results of numerical simulation verify the efficacy of the AIC control algorithms in controlling vibration of building structures during large earthquakes. Copyright © 2001 John Wiley & Sons, Ltd.     

Re‐shaping hysteretic behaviour—spectral analysis and design equations for semi‐active structures

Semi‐active dampers offer significant capability to reduce dynamic wind and seismic structural response. A novel resetable device with independent valve control laws that enables semi‐active re‐shaping of the overall structural hysteretic behaviour has been recently developed, and a one‐fifth scale prototype experimentally validated. This research statistically analyses three methods of re‐shaping structural hysteretic dynamics in a performance‐based seismic design context. Displacement, structural force, and total base‐shear response reduction factor spectra are obtained for suites of ground motions from the SAC project. Results indicate that the reduction factors are suite invariant. Resisting all motion adds damping in all four quadrants and showed 40–60% reductions in the structural force and displacement at the cost of a 20–60% increase in total base‐shear. Resisting only motion away from equilibrium adds damping in quadrants 1 and 3, and provides reductions of 20–40%, with a 20–50% increase in total base‐shear. However, only resisting motion towards equilibrium adds damping in quadrants 2 and 4 only, for which the structural responses and total base‐shear are reduced 20–40%. The spectral analysis results are used to create empirical reduction factor equations suitable for use in performance based design methods, creating an avenue for designing these devices into structural applications. Overall, the reductions in both response and base‐shear indicate the potential appeal of this semi‐active hysteresis sculpting approach for seismic retrofit applications—largely due to the reduction of the structural force and overturning demands on the foundation system. Copyright © 2006 John Wiley & Sons, Ltd.     

Performance of a real‐time pseudodynamic test system considering nonlinear structural response

This paper presents the implementation details of a real‐time pseudodynamic test system that adopts an implicit time integration scheme. The basic configuration of the system is presented. Physical tests were conducted to evaluate the performance of the system and validate a theoretical system model that incorporates the dynamics and nonlinearity of a test structure and servo‐hydraulic actuators, control algorithm, actuator delay compensation methods, and the flexibility of an actuator reaction system. The robustness and accuracy of the computational scheme under displacement control errors and severe structural softening are examined with numerical simulations using the model. Different delay compensation schemes have been implemented and compared. One of the schemes also compensates for the deformation of an actuator reaction system. It has been shown that the test method is able to attain a good performance in terms of numerical stability and accuracy. However, it has been shown that test results obtained with this method can underestimate the inelastic displacement drift when severe strain softening develops in a test structure. This can be attributed to the fact that the numerical damping effect introduced by convergence errors becomes more significant as a structure softens. In a real‐time test, a significant portion of the convergence errors is caused by the time delay in actuator response. Hence, a softening structure demands higher precision in displacement control. Copyright © 2007 John Wiley & Sons, Ltd.     

JFNK方法在求解全隐式一维非线性平流方程中的应用

JFNK(Jacobian-free Newton-Krylov)方法是由Newton迭代方法和Krylov子空间迭代方法构成的嵌套迭代方法。作者以全隐式差分的一维非线性平流方程（亦称无粘Burgers方程）探讨采用全隐式格式计算的必要性和JFNK方法的有效性。模拟结果表明, 隐式结果比显式和半隐式结果在稳定度和精度方面较大的优越性, 特别是模拟气流强的系统以及要素空间分布具有较大梯度的系统。     

浅层顶管施工引起的土体移动

顶管施工引起包括地面沉降和土的轴向移动在内的土的运动。 土的这些运动可能导致邻近构筑物和管线的损坏。 理论分析和现场实测都显示, 在类似于上海等地的软土地层中顶管施工, 顶管周围土的运动问题是三维的。 基于半解析数值方法的基本原理, 将轴向离散而在径向和环向选取位移函数, 构造了解析解函数。 给出了包括位移函数、刚度矩阵和荷载矩阵在内的理论分析过程, 从而建立了半解析单元法。 利用半解析单元法将顶管施工中三维土运动问题转化成一维数值计算 。 利用所建立的半解析单元法, 就软土地层中顶管工程实例计算了施工所引起的土体位移。 结果表明, 半解析元法用于计算顶管施工中顶管周围土的移动, 可以得到较为满意的结果。 由于计算所需要的单元数减少, 处理该问题所需要的时间也明显减少。 根据分析与计算结果还得到了一些有价值的结论。     

某水电站地下厂房洞室群围岩稳定分析

采用有限元方法反演某水电站地下厂房厂区初始地应力场。采用Zienkiewicz-Pande的双曲线屈服准则,对某水电站地下厂房洞室群的开挖过程进行了三维弹塑性有限元模拟。为反映锚固支护对围岩的加固作用和评价地下厂房洞室群支护参数的合理性,提出了可以考虑抗剪作用的隐式锚杆单元和可以考虑预应力效果隐式锚索单元。计算结果表明,该洞室群在洞室布局、开挖顺序和支护参数等方面是合理的,各主要洞室群的稳定性总体较好。     

The importance of surface controls on overland flow connectivity in semi‐arid environments: results from a numerical experimental approach

In semi‐arid environments, the characteristics of the land surface determine how rainfall is transformed into surface runoff and influences how this runoff moves from the hillslopes into river channels. Whether or not water reaches the river channel is determined by the hydrological connectivity. This paper uses a numerical experiment‐based approach to systematically assess the effects of slope length, gradient, flow path convergence, infiltration rates and vegetation patterns on the generation and connectivity of runoff. The experiments were performed with the Connectivity of Runoff Model, 2D version distributed, physically based, hydrological model. The experiments presented are set within a semi‐arid environment, characteristic of south‐eastern Spain, which is subject to low frequency high rainfall intensity storm events. As a result, the dominant hydrological processes are infiltration excess runoff generation and surface flow dynamics. The results from the modelling experiments demonstrate that three surface factors are important in determining the form of the discharge hydrograph: the slope length, the slope gradient and the infiltration characteristics at the hillslope‐channel connection. These factors are all related to the time required for generated runoff to reach an efficient flow channel, because once in this channel, the transmission losses significantly decrease. Because these factors are distributed across the landscape, they have a fundamental role in controlling the landscape hydrological response to storm events. Copyright © 2013 John Wiley & Sons, Ltd.     

基于新型LE水平跳点网格的阴阳网格平流方案设计

为了模拟球面平流传输过程,本文基于球面阴阳重叠网格设计了一种两时间层半拉格朗日平流方案.该方案在球面坐标下采用新型的LE水平跳点网格,同时针对阴阳网格重叠区,采用了不同插值方法进行比较分析,且进行了相关的理想数值试验对方案设计效果进行评估.数值试验表明方案设计是成功的,阴阳网格重叠区平流对插值方案比较敏感;半拉格朗日方案能较好地模拟球面刚体平流和变形涡旋的结构、位置及演变过程,并具有较好的数值稳定性和较高的数值精度.     

基于扩展单调速率算法的水下平台通信系统

针对水下平台工作环境复杂、通信实时性和可靠性要求高的特点,设计了一套分布式冗余通信系统。该通信系统以西门子PLC S7-400H和工控机为主控制器,基于波分复用技术建立了冗余的光纤传输通路;同时提出了一种新型的扩展单调速率算法,对水下平台的任务进行了优先级分配,并基于此算法进行了通信系统软件设计。经过可靠性分析和半实物仿真试验验证,该通信系统的实时性、可靠性及冗余机制符合设计要求,可以成功应用于水下平台,效果良好。