土壤热异常对地表能量平衡影响初探

将来自土壤深部的热通量引入off line的陆面过程模式 (NCAR—LSM ) ,通过长达 2a的数值试验对比分析了它对各层次土壤温度和地表能量平衡的影响。　　在土壤底部引入 5W /m2 的热通量使底层土壤显著升温 ,但升温随着接近表层而迅速衰减。积分 3个月后 ,由地下进入地表的热流量增幅可达 1W/m2 以上 ,并持续增大到 5W /m2 ,地表最大升温约 0 .5K ,同时地表感热、蒸发潜热及长波辐射通量均有 1W /m2 左右的正异常 ;若将土壤热传导系数放大一个量级以加速热量交换 ,则地表升温提高到 1K以上 ,长波辐射增加 3W /m2 以上 ,超过了气溶胶全球平均的辐射效应。结果表明 :一定量值的土壤热异常对地表能量平衡和短期气候变化 (10 -1～ 10 1a)有着不可忽略的影响。同时 ,深入的资料分析、完善的陆面过程模式以及它与大气模式的耦合试验也是亟待进行的相关工作。     

土壤热异常影响地表能量平衡的个例分析和数值模拟

The statistical relationship between soil thermal anomaly and short-term climate change is presented based on a typical case study. Furthermore, possible physical mechanisms behind the relationship are revealed through using an off-line land surface model with a reasonable soil thermal forcing at the bottom of the soil layer.In the first experiment, the given heat flux is 5 W m-2 at the bottom of the soil layer (in depth of 6.3 m)for 3 months, while only a positive ground temperature anomaly of 0.06℃ can be found compared to the control run. The anomaly, however, could reach 0.65℃ if the soil thermal conductivity was one order of magnitude larger. It could be even as large as 0.81℃ assuming the heat flux at bottom is 10 W m-2. Meanwhile, an increase of about 10 W m-2 was detected both for heat flux in soil and sensible heat on land surface, which is not neglectable to the short-term climate change. The results show that considerable response in land surface energy budget could be expected when the soil thermal forcing reaches a certain spatial-tem poral scale. Therefore, land surface models should not ignore the upward heat flux from the bottom of the soil layer. Moreover, integration for a longer period of time and coupled land-atmosphere model are also necessary for the better understanding of this issue.     

Optimal design of passive energy dissipation systems based on H∞ and H2 performances

Passive energy dissipation devices (EDDs), such as viscous dampers, viscoelastic dampers, etc., have been used to effectively reduce the dynamic response of civil infrastructures, such as buildings and bridges, subject to earthquakes and strong winds. The design of these passive energy dissipation devices (EDDs) involves the determination of the optimal locations and the corresponding capacities. In this paper, we present two optimal design methodologies for passive EDDs based on active control theories, including H_∞ and H₂ performances, respectively. The optimal design methodologies presented are capable of determining the optimal locations and the corresponding capacities of EDDs. Emphasis is placed on the application of linear matrix inequality (LMI) for the effective design of passive EDDs using the popular MATLAB toolboxes. One important advantage of the proposed approaches is that the computation of the structural response is not needed in the design process. The proposed optimal design methodologies have been applied to: (i) a 10‐storey building and a 24‐storey building both subject to earthquake excitations, and (ii) a 76‐storey wind‐excited benchmark building, to demonstrate the advantages of the proposed design methodologies over the conventional equal capacity design. Copyright © 2002 John Wiley & Sons, Ltd.     

Nonlinear earthquake response analysis and energy calculation for seismic slit shear wall structures

Based on the concept of structural passive control, a new type of slit shear wall, with improved seismic performance when compared to an ordinary solid shear wall, was proposed by the authors in 1996. The idea has been verified by a series of pseudo-static and dynamic tests. In this paper a macro numerical model is developed for the wall element and the energy dissipation device. Then, nonlinear time history analysis is carried out for a 10-story slit shear wall model tested on a shaking table. Furthermore, the seismic input energy and the individual energy dissipated by the components are calculated by a method based on Newmark-β assumptions for this shear wall model, and the advantages of this shear wall are further demonstrated by the calculation results from the viewpoint of energy. Finally, according to the seismic damage criterion on the basis of plastic accumulative energy and maximum response, the optimal analysis is carried out to select design parameters for the energy dissipation device.     

钢筋砼摩擦耗能支撑框架结构的单元刚度和力学模型分析

为研究钢筋砼摩擦耗能支撑框架结构的动力反应性能 ,对其中的摩擦耗能器单元和框架杆单元的单元刚度和力学模型做了分析。钢筋砼摩擦耗能支撑单元由支撑杆单元和钢板—橡胶摩擦耗能器单元组成 ,支撑单元可取空间杆单元 ,摩擦耗能器单元为平面应力矩形单元。摩擦耗能器单元的剪切恢复力曲线为理想的弹塑性曲线 ,根据耗能器单元的力学模型 ,可确定其在每一时刻的刚度 ;框架结构空间杆单元的恢复力模型采用双线型模型 ,根据杆单元的力学模型 ,可确定其在每一时刻的刚度。并利用所编制的程序对十层单榀两跨空间普通框架和摩擦耗能支撑框架在地震作用下进行了弹塑性反应时程分析 ,结果表明耗能支撑框架的顶层最大位移明显小于普通框架     

青藏高原土壤水热分布特征及冻融过程在季节转换中的作用

利用GAME-Tibet期间所取得的高分辩率土壤温度和含水量资料，对青藏高原（主要是藏北高原）土壤水热分布特征及冻融过程在季节转换中的作用进行了分析。指出藏北高原4cm学深处土壤在10月份开始冻结，次年4-5月份开始消融，冻结持续时间长达5-7个月。冻结过程有利于土壤维持其水分，因此，在刚刚开始消融时土壤含水量仍然很高。从而为夏季风爆发前土壤通过蒸发向大气提供水分打下了基础。指出土壤冻融过程可能在高原季节转换中起着重要作用。     

经济全球化与国家能源安全

经济全球化进程的加快对国家经济安全提出了挑战。其中能源安全问题引起我国的关注。伴随着我国经济的快速增长和人民生活水平的提高，我国对能源的依赖程度不断提高。加强能源安全已成为21世纪中国经济社会可持续发展的重要问题之一。     

天然气水合物研究现状与展望

自20世纪90年代以来,世界各国对潜力巨大的新型能源———天然气水合物的研究做了大量的投入,已经取得了重大进展。本文在阐述国外天然气水合物的研究现状的同时,重点介绍了我国在天然气水合物勘探开发和实验模拟方面取得的一些进展,并展望其在能源、环境和其它研究领域的发展前景。     

A quantitative study of the energy release in the aftershocks of the Bhuj earthquake, 2001, India, using Lg phase

The devastating earthquake on 26 January 2001 at Bhuj, India, resulted in large-scale death and destruction of properties of several million US dollars. The moment magnitude of the earthquake was 7.7 and its maximum focal intensity exceeded X in MM scale. The rate of aftershocks of this earthquake, recorded at Gauribidanur seismic array station (GBA), shows a monotonic decay with time superposed with oscillations. For the Indian continent the Lg phase is a prominent arrival at regional distances. The estimate of Lg amplitude is obtained by optimally fitting the Lg wave train to a exponential decay curve. The logarithm of these amplitudes and logarithm of root mean square (rms) value of actual amplitudes of the Lg are calibrated with USGS m_b to create a local m_bLg magnitude scale. The energy released from these aftershocks is calculated from the rms value of Lg phase. The plot of cumulative energy release with time follows the power law of the form t^p, superposed with oscillations. The exponent of the power law, p, is estimated both by a time-window scanning method and by an interpolation method. The value of p is 0.434 for time-window scanning method and 0.432 for the interpolation method. The predominant periods found in the oscillatory part of the cumulative energy, obtained by differencing the observed from the power law fit, are 10.6, 7.9, 5.4, 4.6 and 3.5 h for time-window scanning method. The corresponding periods for interpolation method are 13.4, 11.5, 7.4, 4.2, 3.5, 2.6 and 2.4 h.     

Optimal distribution of linear control intensity over the frequency range

In this paper, a control strategy for structural systems is proposed and developed in the frequency domain. The algorithm is substantially based on a linear derivative feedback and a convolution of the control parameter, whose distribution in the frequency field is chosen in such a manner as to comply with the requirements of an ad hoc formulated constrained optimum problem, with the response data monitored until the instant of control action application. Some numerical testing is carried out by referring to given recorded accelerograms, showing a good performance of the proposed approach. Copyright © 2002 John Wiley & Sons, Ltd.