Evaluation of response and energy in actively controlled structures

A computational method of energy evaluation is derived to study the elastic responses and energy distribution of actively controlled single‐degree‐of‐freedom (SDOF) structures during earthquakes. Contrary to the common perception that applying active control force pumps energy into the structure, the applied control force can actually reduce the energy in the structure by reducing the input energy from earthquakes to the structure. In addition, applying control force can dissipate a large amount of energy in the structure when this control force is applied in the direction opposite to the displacement and velocity responses. To demonstrate this energy mechanism in active controlled structures, the two most popular control algorithms, optimal linear control (OLC) and instantaneous optimal control (IOC) algorithms, are used to calculate the control response and energy spectra. One‐step time delay is incorporated into the algorithms to take into consideration the practical aspect of active control. The effects of different earthquakes and damping ratios on control energy and response spectra are studied. These studies show that both OLC and IOC are very effective in reducing the structural displacement and velocity responses by reducing the input earthquake energy as well as dissipating a large amount of energy in the structure. Copyright © 2001 John Wiley & Sons, Ltd.     

Effectiveness of structural control based on control energy perspectives

A computational algorithm for maximizing the control efficiency in actively controlling the elastic structural responses during earthquake is proposed. Study of optimal linear control using a single degree of freedom shows that applying active control is very effective in reducing the structural displacement and velocity responses for long‐period structures, but at the same time it has an adverse effect in increasing the absolute acceleration response. The extent of this adverse effect reduces the effectiveness of the control system, and therefore it poses a limit on the maximum control force in order to provide maximum control efficiency. In view of this shortcoming, maximum control energy dissipation is used to define the most effective optimal linear control law. Less displacement and velocity response are expected as larger control force is applied, but there is always a limit that maximum control energy can be dissipated. This study shows that this limit depends on the structural characteristics as well as the input ground motion, and a general trend is that the maximum control energy decreases as damping increases. Finally, application of the proposed algorithm on a six‐storey hospital building is presented to show the effectiveness of using optimal linear control on a multi‐degree‐of‐freedom system from the control energy perspectives. Copyright © 2001 John Wiley & Sons, Ltd.     

Geological barrier– a natural rock stratum for preventing confined karst water from flowing into mines in North China

Coalfields in North China encompassing more than ten Provinces contain six to seven coal seams in the Permo-Carboniferous strata. The lower three seams, accounting for 37% of the total reserves, are threatened with karst water from the underlain Ordovician limestone. Hundreds of water inrush incidences have occurred in which a large amount of water suddenly flows into tunnels or working faces under high potentiometric pressure and over 30 mines have been flooded over the last 20 years. Large-scale dewatering or depressurizing of the karst aquifer was considered essential to avoid water inrushes and keep the mines safely operational. This practice has caused sinkholes, dry springs, water supply shortage, and groundwater contamination in the surrounding areas, which is environmentally not permitted. One of the alternative water control measures is to make full use of the rock layer between the coal seam and the karst aquifer as a geological barrier. Similar to the application in the nuclear industry where a geological barrier is used to contain radioactive wastes, the barrier of this application is considered a hydraulic barrier as well with the objective to prevent or constrain water flow from the underlying aquifer into mines. Its effectiveness to constrain water flow is described by a parameter referred to as hydrofracturing pressure (P_hf). When the water pressure in the underlying aquifer exceeds P_hf, a wedging effect takes place within the fractures of the geological barrier and, as a result, water inrush occurs. In-situ hydrofracturing tests were used to determine P_hf in bauxite and silty sandstone at tunnels. The P_hf in the silty sandstone is larger than that in the bauxite but they both vary with depth (distance from the bottom of the tunnel). Based on the test results, a new safety criterion for water inrush was derived for mines and it has been successfully applied to mining practices with the minimum effort of dewatering in the karst aquifer. The same criterion can also be applied to tunneling and quarrying in areas with similar geological conditions.     

Ocean Ridge Granite and Its Geochemical Characteristics in Western Qinghai—Xizang Plateau

In our work,ocean ridge granite,i.e., Oytan plagiogranite massif,was discovered in western Qinghai-Xizang plateau.It intruded into the basic lava of the Oytag ophiolite suite and it was formed a little later than the (ultra)mafic rocks of the Oytag ophiolite suite.The Oytang plagiogranite possesses the geochemical characteristics of mantle-source granite and was formed in the “supre-subduction zone”(SSZ)ocean ridge environment,like the ocean ridge granite of Troodos,Cypus.     

Geochemistry of Basic Dykes in Wudang Block and Its Tectonic Significance

Geochemical characteristics of the Neoproterozoic basic dykes widely exposed in the Wudang block of South Qinling show that the dykes possess the characteristics of continental tholeiitic basalts and were formed in a setting of continental rifting.Therefore,there was an ancient continental block in the areas of southern Qinling and Yangtze block during the Jinning period,and an important firting event of this ancient block occurred in the Early Neoproterozoic.     

插值计算不规则图形面积的方法选择

采用实际的不规则图形作为评价图形，讨论了几种不同插值方法的面积计算精度，得出了对实际工作指导意义的结论。     

自动搜索最小多边形算法的研究

多边形的自动搜索是ＧＩＳ空间分析的基本算法之一，同时也在地籍拆宗、导线网闭合环的闭合差计算等领域有着重要的作用。本文依据一般的图形数据结构，提出了一种结点标记的搜索算法，利用该算法可自动搜索出所有独立的最小多边形。     

VARIABILITY OF AEROSOL OPTICAL PROPERTIES OVER HEFEI DURING SEPTEMBER 1993 TO SEPTEMBER 1994

An 8-wavelength sun-photometer has been operated at Hefei (31.31°N, 117.17°E) to monitoroptical properties of atmospheric aerosols. Altogether 133 solar spectral extinction data were ob-tained on clear days during the period from September 1993 through September 1994, In this pa-per, the feature of the sun-photometer is briefly described. A relative aureole method is intro-duced. which can be used to monitor temporal evolution of aerosol loading during the sun-pho-tometer calibration period. Temporal variabilities of spectral aerosol optical depths and Angstromturbidity parameters are presented. Relation of these variabilities with synoptic and local meteoro-logical conditions are analyzed and discussed, From measured spectral aerosol optical depths undersome representative atmospheric conditions, columnar aerosol size distributions have been retrievedby a linearly constrained inversion method. These typical columnar aerosol size distributions are al-so presented and discussed.     

MEASUREMENTS AND MODEL SIMULATIONS OF SURFACE OZONE VARIATIONS AT DIFFERENT BACKGROUND CONCENTRATIONS OF THE PRECURSORS

Ozone photochemical production and loss in very different environments at Waliguan baselinestation and Lin'an background station were simulated by using the measurement data and photo-chemical box model.The results show that net ozone photochemical production rate is negative,about 0.5 ppb/d,at Waliguan baseline sation,because of very low precursor concentrations.Butat Lin'an background station,the net photochemical ozone production is positive,about 2—3 ppb/h.which is very closed with the measurement at Lin'an.That means ozone production was con-trolled by photochemical reactions at Lin'an background station,because of the higher precursorconcentrations.The net destruction rate,at Waliguan Mt.,is not large,so that future increase inanthropogenic emission of reactive nitrogen will lead to larger production rates of steady-state O_3concentration.     

雨滴尺度谱谱参数和形状因子的分析

作者计算了３次降不过程的雨滴尺度谱参数，并进行Ｍ－Ｐ分布拟合和Г分布拟合。同时还计算了雨滴谱形状因子Ｓ（Ｚ，Ｒ），分析了形状因子与雨强之间的关系。