半潜式钻井平台复合锚泊系统组分配比优化设计

从提高锚泊系统收放时效性入手,提出了一种半潜式钻井平台复合式锚泊系统组分配比优化设计方法,旨在尽可能降低复合式锚泊系统的钢链配比长度,提高收放效率。结合锚泊系统设计参数,制定优化设计准则,建立优化分析流程,采用ANSYS-AQWA建立锚泊定位半潜式平台水动力分析模型,获得平台运动参数和锚链动力参数,对平台漂移量、锚链最小安全系数、走锚临界张力、锚链最小卧底长度和起锚力进行无量纲指标分析,并综合考虑张力倾角与预张力对优化结果的影响,获得复合式锚泊系统钢链与钢缆的最优配比关系,确定最优钢链长度为395 m,较原钢链长度缩短225 m,钢链收放时间降低36%,进一步提高锚泊系统收放时效性,并降低平台可变荷载。     

基于小波变换的半方差函数影像匹配方法

基于小波变换的半方差函数影像匹配方法,该方法在小波变换的基础上,根据小波方差计算出影像特征最多的分解层,在该层上进行初匹配得到候选同名点。利用半方差函数匹配方法对同名点进行精细匹配,既节省了时间又达到了精确匹配的目的,为影像匹配提供一种新方法。     

Active interaction control of civil structures. Part 1: SDOF systems

This paper presents a family of semi‐active control algorithms termed as active interaction control (AIC) used for seismic response control of civil structures. AIC control algorithms include active interface damping (AID), optimal connection strategy (OCS) and tuned interaction damping (TID). A typical SDOF AIC system consists of a primary structure, an auxiliary structure and an interaction element. The auxiliary structure typically has stiffness comparable to that of the primary structure while its natural frequency is much higher than that of the primary structure. Interactions between the primary and the auxiliary structures are defined by specific AIC control logic such that vibrational energy is extracted from the primary structure into the auxiliary structure during a locking phase and dissipated in the auxiliary structure in the subsequent unlocking phase. The stability of AIC control algorithms is shown using the Lyapunov direct method. The efficacy of AIC control algorithms is demonstrated by the results of numerical simulations of SDOF systems subjected to seismic ground motions. Practical issues such as sampling period and time delay are also investigated in this study. Copyright © 2001 John Wiley & Sons, Ltd.     

Airborne dust deposition in the Okavango Delta,Botswana, and its impact on landforms

This study investigated the local‐scale generation and movement of dust in the seasonal swamps of the Okavango Delta, Botswana, with a view to examining possible transfer of material between ?ood plains and islands. It was found that most of the dust load was carried in the lowest 3 m of the air column, and consisted mainly of amorphous silica, indicating that dust was generated largely on the ?ood plains. Dust loads were found to be highest above the ?ood plains and lowest over the interiors of islands, probably due to the baf?ing effect of the island trees on wind velocity. The contrast in dust loads between islands and ?ood plains suggests that there is a net transfer of dust from ?ood plains to islands, but it was not possible to quantify this transfer. It is evident, however, that ?ood plains experience net erosion and islands net aggradation. A strong seasonality in dust loads was observed, with the maximum dust loads coinciding with maximum wind velocity in October. This also coincides with peak seasonal ?ooding in the delta, and only non‐inundated ?ood plains are capable of generating dust. Years of low ?ood therefore appear to be more dusty. There may also be transfer of material from higher‐lying to lower‐lying ?ood plains, which may reduce the topographic contrast on the ?ood plains. Copyright © 2004 John Wiley & Sons, Ltd.     

Semi‐active control of sliding isolated bridges using MR dampers: an experimental and numerical study

Sliding base‐isolation systems used in bridges reduce pier drifts, but at the expense of increased bearing displacements under near‐source pulse‐type earthquakes. It is common practice to incorporate supplemental passive non‐linear dampers into the isolation system to counter increased bearing displacements. Non‐linear passive dampers can certainly reduce bearing displacements, but only with increased isolation level forces and pier drifts. The semi‐active controllable non‐linear dampers, which can vary damping in real time, can reduce bearing displacements without further increase in forces and pier drifts; and hence deserve investigation. In this study performance of such a ‘smart’ sliding isolation system, used in a 1:20 scaled bridge model, employing semi‐active controllable magneto‐rheological (MR) dampers is investigated, analytically and experimentally, under several near‐fault earthquakes. A non‐linear analytical model, which incorporates the non‐linearities of sliding bearings and the MR damper, is developed. A Lyapunov control algorithm for control of the MR damper is developed and implemented in shake table tests. Analytical and shake table test results are compared. It is shown that the smart MR damper reduces bearing displacements further than the passive low‐ and high‐damping cases, while maintaining isolation level forces less than the passive high‐damping case. Copyright © 2005 John Wiley & Sons, Ltd.     

结构可变阻尼半主动控制

本文阐述了结构半主动控制的概念，并介绍了国内外有关结构半主动控制的研究状态，阐述了几种有关结构半主动控制的算法，包括基于经典最优控制的控制律及算法，基于变结构系统理论的滑动模太控制算法和非线性奇次系统的ｂａｎｇ－ｂａｎｇ控制算法。重点阐述了变结构系统理论和滑移面的确定及控制律的设计。     

Full‐scale experimental verification of resetable semi‐active stiffness dampers

Because of many advantages over other control systems, semi‐active control devices have received considerable attention for applications to civil infrastructures. A variety of different semi‐active control devices have been studied for applications to buildings and bridges subject to strong winds and earthquakes. Recently, a new semi‐active control device, referred to as the resetable semi‐active stiffness damper (RSASD), has been proposed and studied at the University of California, Irvine (UCI). It has been demonstrated by simulation results that such a RSASD is quite effective in protecting civil engineering structures against earthquakes, including detrimental near‐field earthquakes. In this paper, full‐scale hardware for RSASD is designed and manufactured using pressurized gas. Experimental tests on full‐scale RSASDs have been conducted to verify the hysteretic behaviours (energy dissipation characteristics) and the relation between the damper stiffness and the gas pressure. The correlation between the experimental results of the hysteresis loops of RASADs and that of the theoretical ones has been assessed qualitatively. Experimental results further show the linear relation between the gas pressure and the stiffness of the RSASD as theoretically predicted. Finally, shake table tests have also been conducted using an almost full‐scale 3‐storey steel frame model equipped with full‐scale RSASDs at the National Center for Research on Earthquake Engineering (NCREE), Taipei, Taiwan, and the results are presented. Experimental results demonstrate the performance of RSASDs in reducing the responses of the large‐scale building model subject to several near‐field earthquakes. Copyright © 2007 John Wiley & Sons, Ltd.     

全(半)自动地形因子智能提取方法研究与设计实现

结合工作流思想,采用XML建模语言实现支撑全(半)自动地形因子智能提取模型的设计与过程描述。结合地形因子提取算子体系与模型,建立全(半)自动地形因子智能提取系统,并以地面起伏度提取为实验样例,通过流程组合、因子模型建立、参数配置、程序驱动执行等环节实现地形因子流程化、全(半)自动智能提取。系统解耦流程、算法以及专业软件对传统地形因子提取模式的捆绑,通过订制提取模型,灵活提取专题地形因子,提取效率、精度与扩展性较为理想。     

Spatial patterns of soil water balance on intensively cultivated hillslopes in a semi‐arid environment: the impact of rock fragments and soil thickness

During past decades, a diverse system of subsistence agriculture in south‐east Spain (annual rainfall of less than 300 mm) has been overturned in favour of large‐scale plantations of almond trees without consideration for topography and related spatial patterns in soil hydrological properties. The objective of this paper is to investigate the spatial pattern in soil physical properties induced by this cultivation system, and to highlight its impact on the water balance. Soil properties were recorded along hillslopes with shallow soils developed on slates and greywackes in the upper part of the Guadelentin drainage basin (Murcia region). Frequent tillage of these almond plantations covering entire hillslopes has resulted in denudation by tillage erosion on the topographic convexities, as well as transport of rock fragments and fine earth along the slopes. These processes have created a systematic spatial pattern of soil thickness and rock fragment content: shallow and stony soils on the topographic convexities and deep soils with a rock fragment mulch in the concavities at the foot of the slopes. At the same time, a negative relationship between rock fragment content and fine earth bulk density was observed. The impact of this spatial pattern in soil properties on the water balance was evaluated using the PATTERN one‐dimensional hydrological and plant growth model. The model simulates the water balance of soil profiles covering the observed variation in soil thickness, stoniness and bulk density. The model results indicate that the highest rates of infiltration, evaporation and drainage, as well as the lowest rates of overland flow are restricted to shallow soils on the hilltops. In contrast, the deeper soils in the valley bottoms produce a more stable moisture regime than shallower soils, which tend to saturate and dry out quickly. These model results are in agreement with the spatial patterns of almond productivity: an asymptotic increase with soil thickness. Copyright © 2000 John Wiley & Sons, Ltd.