基于Hilbert-Huang变换和随机减量技术的模态参数识别

傅里叶分析的信号处理方法对非线性、非平稳信号的处理能力差,传统的模态参数识别方法也存在阻尼比识别精度不高的问题。基于Hilbert-Huang变换和随机减量技术提出了一种新的、实用的模态参数识别方法,首先对结构振动信号进行滤波处理和经验模态分解,得到若干阶本征模态响应,然后利用随机减量技术提取自由衰减响应,进而由Hilbert-Huang变换得到信号的瞬时特性,最后结合模态识别的基本理论识别结构的模态频率和模态阻尼比。为了验证这一方法的有效性,对12层钢筋混凝土框架模型振动台试验一测点的加速度记录进行了处理,识别了模态参数,识别结果与其它识别方法及有限元分析结果的对比表明该方法识别模态频率是可靠的,而模态阻尼比识别的精准性仍然难以确认。     

汶川地震诱发滑坡的地震动加速度评判标准

通过对汶川MS8.0地震强震记录资料的计算分析,给出一个与地震诱发滑坡关系比较密切的地震动加速度参数--最大临界加速度.分析表明,最大临界加速度与地震滑坡的相关性高于峰值加速度,而且可以消除峰值加速度作为判据使用时存在的问题.利用汶川地震强震资料建立了该参数在震区的衰减关系,由衰减关系得到的地震滑坡影响区域与汶川地震滑...     

系统锚杆对地下厂房洞室群稳定性影响的数值分析

以某水电站地下厂房工程为实例,采用数值分析方法,通过对比厂房洞室群是否施加系统锚杆的差别,获得系统锚杆对洞室群稳定性的影响.结果表明,施加系统锚杆对围岩主应力影响小,但能平均降低围岩位移28.07％,降低拱顶和拱角处围岩位移34％以上,降低主厂房和尾闸室边墙塑性破坏区深度2.2～4.8m,在一定程度上提高洞室群的整体稳...     

东胜煤田含煤岩系层序地层特征与聚煤规律分析——以东胜煤田阿不亥煤炭勘查区为例

研究区含煤岩系主要为侏罗系中统延安组,通过煤岩层研究和对比,认为延安组本身为一个完整的层序,可分为三个体系域、五个小层序组和18个小层序;体系域、小层序组和小层序之间的转换面是聚煤的主要层位。含煤地层可编号18层煤,其中可采煤层15层,根据层序地层分析和含煤岩系沉积特点,将含煤地层分为三个岩性段,5个煤组,相对应三个聚煤期和5个成因单元。该区的聚煤作用主要受到沉积环境、古地形和古构造的控制。     

The significance of Gobi desert surfaces for dust emissions in China: an experimental study

A series of experiments to determine the direct emission of dust-sized particles from Gobi surfaces by clean wind (wind without sand), and the potential for aeolian abrasion of Gobi surfaces and beds of gravel and mobile sand to produce fine (<100 μm) and dust-sized (<10 μm, PM₁₀) particles under sand-laden winds were conducted. Parent material was obtained from Gobi areas of the Ala Shan Plateau, the region with high dust emissions in arid China. The fine particles produced by aeolian processes were collected using sand traps and sieved the captured materials to exclude particles >100 μm in diameter and then PM₁₀ by sedimentation was acquired. The Gobi surface provided most of the emitted fine particles during the initial dust emission processes, but subsequently, release of the clay coatings of particles by abrasion becomes the dominant source of fine materials. Under sand-laden winds, PM₁₀ production rates produced by aeolian abrasion of Gobi surfaces ranged between 0.002 and 0.244% of blown materials. After removal of sand, silt, or clay with low resistance to erosion from the Gobi surfaces by the wind, the PM₁₀ production rates caused by aeolian abrasion were similar to those from gravel and sand beds. The results also indicated that after the dust-sized particles with low resistance to erosion were removed, the production of dust-sized particles was unrelated to wind velocity. Under aeolian processes, Gobi deserts in this region therefore play a major role in dust emissions from arid and semiarid China.     

Shifting farming-pastoral ecotone in China under climate and land use changes

Meteorological records show a rise in temperature and decrease in precipitation in most parts of the farming-pastoral ecotone of Northern China over the last 50 years. During the last quarter of the 20th Century, the agrarian sector went through a series of reforms and changes in government policies on land use that have led to extensive changes in land cover. The objective of this study was to redefine the location and analyze the boundary variations under the effects of climate and land use changes in the farming-pastoral ecotone of Northern China. The results showed that the location of study area has been redefined as both a climatic ecotone from the perspective of suitability of precipitation and temperature for agricultural crops and vegetation growth, and also a land use ecotone based on the impacts of farmland restructuring by government policies on land use. In recent decades, the climatic boundary has moved southeast while the land use boundary has moved northwest, showing opposing directions of change. The extent of boundary changes in the northeast and northern sections are far greater than in the northwestern section of the farming-pastoral ecotone of Northern China.     

Large-scale rock landslide slip surface location analysis and strength parameters evaluation

Large-scale rock landslides have huge impacts on various large-scale rock engineering and project operations. They are also important aspects evaluating geological disasters. In the initial evaluations on the stability of large-scale rock landslides, in most cases, it is difficult to conduct evaluation or to have accurate evaluations because most of large-scale rock landslides are huge in size, high in slopes, and located in the canyon of mountains, which makes the exploration very difficult and thus hard to get credible data on slip surface form, location, depth and strength. This paper describes the Badi landslide happened along the Lancang River, and systematically introduces methods to analyze and verify large-scale slip surface form using terrain conditions surrounding the large-scale landslide, shape of the slide walls, and development patterns of streams and gully. This paper also introduces ways to obtain strength parameters of slip surface with the soil in the slide zone by using the principles of stress state, principles of gravity compaction, structure regeneration and strength regeneration. It is confirmed that analyzed results to the slip surface are basically consistent with the exploration results. The methods introduced here have been successfully applied to evaluate the stability of Badi large-scale rock landslide and have been applied in engineering practices.     

The optical periodic analysis of BL Lac object AO 0235+164

BL Lac object AO 0235+164 is a well-known object. We collect a large number of effective observation in B, V, R and I band from historical literatures. The possible periods are analyzed by means of discrete correlation function (DCF) method, structure function (SF) method and Jurkevich (J-K) method. The results show that there are possible periodic variations of 2.63–2.66 years in B band, 2.79–2.84 years in V band, 2.57–2.87 years in R band, 2.62–2.88 years in I band, respectively.     

基于光谱分析和综合阈值的FY-3/MERSI云检测

云检测是卫星遥感影像应用中的重要环节。为了获取FY-3中分辨率光谱成像仪(Medium Resolution Spectral Imager,MERSI)传感器精确的云掩膜数据,在分析云与植被、水体、裸露地表等地物在不同波段光谱差异的基础上,结合FY-3/MERSI数据的通道特性,构建基于多光谱和综合阈值的云检测算法。采用热红外通道亮温(CH_5)检测出高云,使用云检测指数(Normalized Cloud Detection Index,I_(NCD))和可见光波段反射率(CH_3)检测中低云。利用江西地区的FY-3/MERSI数据进行应用,将检测结果与其他算法、人机交互解译结果进行了对比分析。结果表明,该算法对FY-3/MERSI影像上的云区具有较好的检测效果,同时利用地面气象观测资料进行验证,检测精度均高于88%,能够满足当前云检测精度需求。     

Distribution characteristics,exploration and development,geological theories research progress and exploration directions of shale gas in China

The shale gas resources in China have great potential and the geological resources of shale gas is over 100×10¹²m³,which includes about 20×10¹²m³ of recoverable resources.Organic-rich shales can be divided into three types according to their sedimentary environments,namely marine,marine-continental transitional,and continental shales,which are distributed in 13 stratigraphic systems from the Mesoproterozoic to the Cenozoic.The Sichuan Basin and its surrounding areas have the highest geological resources of shale gas,and the commercial development of shale gas has been achieved in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in these areas,with a shale gas production of up to 20×10⁹m³ in 2020.China has seen rapid shale gas exploration and development over the last five years,successively achieving breakthroughs and important findings in many areas and strata.The details are as follows.(1)Large-scale development of middle-shallow shale gas(burial depth:less than 3500 m)has been realized,with the productivity having rapidly increased;(2)breakthroughs have been constantly made in the development of deep shale gas(burial depth:3500-4500 m),and the ultradeep shale gas(burial depth:greater than 4500 m)is under testing;(3)breakthroughs have been made in the development of normal-pressure shale gas,and the assessment of the shale gas in complex tectonic areas is being accelerated;(4)shale gas has been frequently discovered in new areas and new strata,exhibiting a great prospect.Based on the exploration and development practice,three aspects of consensus have been gradually reached on the research progress in the geological theories of shale gas achieved in China.(1)in terms of deep-water fine-grained sediments,organic-rich shales are the base for the formation of shale gas;(2)in terms of high-quality reservoirs,the development of micro-nano organic matter-hosted pores serves as the core of shale gas accumulation;(3)in terms of preservation conditions,weak structural transformation,a moderate degree of thermal evolution,and a high pressure coefficient are the key to shale gas enrichment.As a type of important low-carbon fossil energy,shale gas will play an increasingly important role in achieving the strategic goals of peak carbon dioxide emissions and carbon neutrality.Based on the in-depth study of shale gas geological conditions and current exploration progress,three important directions for shale gas exploration in China in the next five years are put forward.