一种基于能量的振动主动控制新方法     

刘志军  周星德 《地震工程与工程振动》2007,27(1):125-129

为了防止控制过程中作动器出现饱和现象,本文提出了一种基于能量的新的振动主动控制策略。该方法是通过比较容许能量与实际能量来确定结构控制力的大小,而其方向是通过对能量求导确定。由于不需要求解线性矩阵不等式,所以计算简单,操作方便。并且当采用同样容量限的多个作动器时,控制输出力一致,从而避免设计多个控制系统,简化了控制器设计。此外,由于采用阶跃控制,控制系统便于实现。最后,以六层建筑物为例来说明本文方法的可行性。  相似文献   

高层结构考虑土与地下室相互作用的振动台试验和理论分析     

沈朝勇  周福霖  黄襄云  罗学海  陈建秋  任珉  金建敏 《地震工程与工程振动》2007,27(6):148-153

采用振动台试验研究了土与地下室相互作用对带多层地下室高层错位转换结构地震反应的影响。在7度小震阶段对比研究了其地下室周围有土及砂等介质约束和无约束情况下的动力特性和动力反应。在7度中震及大震阶段,土与地下室相互碰撞现象被发现。采用有限元方法非线性模拟了土与地下室相互碰撞对高层结构反应的影响。试验及分析表明,水平地震作用下土与地下室相互碰撞会对高层结构,特别是在±0.000附近部位产生不利反应,大震作用下并能造成一定程度的破坏。  相似文献   

雷州半岛灯楼角珊瑚岸礁的特征   总被引：21，自引：0，他引：21  

赵焕庭  王丽荣  宋朝景  余克服  袁家义 《海洋地质与第四纪地质》2002,22(2):35-40

雷州半岛西南海岸的珊瑚礁是中国大陆唯一的全新世中期之初海侵以来形成的岸礁，灯楼角岸段岸礁沿灯楼角岬角两侧共长11.5km,宽500-1000m，厚约5m，珊瑚化石的优势种是Gonioporasp。本海区的海水温度，盐度，透明度和环境质量，均适合造礁石珊瑚生长，采集到活珊瑚8科16属25种，其中优势种是Acropora humilis,Porites lutea,Prities pukoensis和Favia speciosa。岸礁可分为礁坪和礁前向海坡两个地貌单元。内礁坪上有薄层细砂堆积的“沙帽”，主要由陆源碎屑沉积物，其次为生物碎屑组成。礁的^14C年龄主要为7120-4040aBP。在全球变化引起表层海水温度增高和海平面上升的条件下，由于大陆架深层水的影响，琼州海峡的沿岸水受到调节，夏季不致过热，冬季不致过冷，所以本区造礁石珊瑚仍能生长和繁殖，珊瑚礁仍存在和发展。  相似文献   

用全站仪对建筑物倾斜度进行监测的误差分析   总被引：2，自引：0，他引：2  

陈礼伟  牟瑞芳 《四川测绘》2000,23(1):38-40

本文在全站仪自由设站基础上，推导了空间任意两点连线方向角γ的测试误差计算公式，并编制了相应的计算程序，通过计算分析认为：（１）方向角γ的测试误差不仅与测点的斜距、天顶距及水平方向量的测试误差有关，而且与测点的布置有关；（２）如果测点布置合理，可以用全站仪对建筑物的华斜进行监测。  相似文献   

应用沉降速率推算剩余沉降及卸载时间   总被引：4，自引：0，他引：4  

张长生  张伯友  刘国楠  魏勇作 《地球科学与环境学报》2005,27(4):28-32

在地基处理工程中工后沉降和沉降速率是卸载的重要标准，次固结沉降可以估算在一定范围内，工后沉降满足要求与否则主要由剩余主固结沉降控制。基于砂进固结理论和Asaoka方法可以推算出在堆载预压任意时间的沉降速率，运用沉降速率和剩余主固结沉降的关系，就可以推算出任意时间的主固结剩余沉降及卸载时间。在深圳—香港西部通道填海及地基处理工程中，此方法应用效果较好。  相似文献   

层状地基中桩的轴向静载沉降特性   总被引：3，自引：0，他引：3  

江兴旺  邵江  周德培 《地球科学与环境学报》2006,28(3):70-73

采用双折线荷载传递函数,根据桩在竖向静载下的荷载分布与传递规律,运用功的互等定律,导出了一组确定层状地基中桩的轴向荷载沉降曲线的解析简化递推算式,可根据桩侧介质的分布情况和桩的形状对桩进行沉降分析模拟,能较精确确定桩的轴向静载沉降曲线,同时推导了桩顶刚度系数的迭代公式,以此为基础可确定桩的承载力。结合运用实例进行了论证,说明了方法的有效性和正确性。  相似文献   

Spatial Pattern of Rural Settlements in the Upper Reaches of the Minjiang River——a Case Study in Maoxian County, Sichuan   总被引：1，自引：1，他引：0  

FENG Wenlan  LI Ainong Chengdu Institute of Mountain Hazards  Environment  Chinese Academy of Sciences  Chengdu  Sichuan  China Graduate School of Chinese Academy of Sciences  Beijing  China 《山地科学学报》2007,4(2):146-154

A quantitative analysis of the spatial pattern of rural settlements in the upper reaches of the Minjiang River was made with the major data sources being the relevant ETM image and the national geographical database of China (including contour line, river and road) at the scale of 1:250 000, and using image interpretation and field investigation to obtain spatial information on rural settlements. The results of the spatial analysis technique of GIS and correlation analysis showed that most settlements (78.2 %) were located in the mountain area at 1500 ~ 2700 m altitude, and almost half in the arid valley area. More than 80.0 % of settlements had their slopes above 15°. Most settlements had good access to water resources, roads and communications, and tended to cluster close to the road network rather than the river. About half of the rural settlements in the study area were relatively concentrated, while the others were decentralized. Those with higher altitude usually had land with steep slope, inconvenient water and road accesses, and were located far apart from each other. In view of such a situation, further research should be done to make reasonablecountermeasures on these settlements for better living conditions and ecosystem stability.  相似文献   

多层建筑基础隔震的减震效果分析     

雷静雅  汪芳  罗登贵  何涛 《大地测量与地球动力学》2007,27(Z1):71-73

介绍基础隔震结构的工作原理和两种计算模型，结合工程实例采用时程分析法和Matlab程序模拟计算结构隔震和不隔震时的顶层响应，计算结果表明多层建筑采用基础隔震可以有效地降低结构的地震反应。  相似文献   

Occupational paths towards commercial agriculture: The key roles of farm pluriactivity and the commons     

Ward Anseeuw  Catherine Laurent 《Journal of Arid Environments》2007,70(4):659

In South Africa, “black” and “coloured” farmers engaged in several occupational activities are often considered as being “not interested in farming” or “not serious”. However, in Namaqualand the large majority of “coloured” farmers and especially the most successful ones are pluriactive and have off-farm incomes. Investigations were therefore carried out in that region to better understand the role of pluriactivity. Observations focus on middle-income households from the mining sector entering into small-scale commercial farming. Based on surveys in both non-farm and farm sectors, the results show that, for many households, access to sufficient farm assets depends strongly on the employment situation of the sector of origin and requires a level of investment which can be reached only progressively. This obliges these households to rely on off-farm incomes and communal land at least during the early transitional stage. These results stress the importance of taking into account the diversity of paths and of differentiating the various stages in the transitional period between two occupational activities. Finally, the paper emphasises the importance of taking these specific situations into consideration in the management of the commons.  相似文献   

Tracking the Settlement of North African Immigrants: speculations on the social and cultural impacts of a newly arrived immigrant group     

Rebecca-Lea Perrin 《The Australian geographer》2007,38(2):253-273

In the past five years Australia has experienced a dramatic increase in the number of North African arrivals. The majority of North African arrivals for the past 4 years have arrived as humanitarian entrants. This migration stream reflected a shift in the regional focus of the humanitarian program towards Africa. The majority of North African arrivals since 2000–01 have been from Sudan. The States of New South Wales and Victoria received the highest proportions of these arrivals. Key issues, and important research topics for social scientists, are at least threefold. First, the domestic politics and international geopolitics of this humanitarian flow need critical analysis. Second, the suitability of settlement services needs to be assessed. Specifically, the effects and merit of privatising service provision to these refugees requires rigorous scholarly assessment. Finally, more needs to be known about the cultural adaptation of this group, especially youth. Research into the experiences of racism and, relatedly, the existence and appropriateness of anti-racism initiatives is required.  相似文献