Discontinuous analysis of softening solids under impact loading

Softening solids are analysed under impact loading using a new numerical method which allows displacement discontinuities to propagate arbitrarily through a finite element mesh. The Dirac‐delta distributions that arise in the strain field of classical continuum theory in the presence of strain softening are interpreted as discontinuities in the displacement field. A new finite element procedure with Heaviside jumps added to the underlying displacement interpolation basis is able to capture displacement jumps independent of the spatial discretisation. The amplitudes of displacement jumps are represented by extra degrees of freedom at existing nodes. Numerical results for mode‐I and mode‐II failure due to impact loading are presented. The numerical results highlight the objectivity of the approach with respect to spatial discretisation under dynamic loading conditions. Copyright © 2001 John Wiley & Sons, Ltd.     

中国黄海西岸海陆风循环结构研究

陆海风是由于海陆表面之间的比热容不同而导致的昼夜热量分布差异,从而在海岸附近引发的大气中尺度循环系统.本文利用多普勒风激光雷达Windcube100s首次对黄海西海岸的海陆风的循环结构进行了观测研究.在2018年8月31日至9月28日观测期间发现,海陆风发展高度一般在700 m至1300 m.海陆风转化持续的时间为6小时至8小时.在425m高度,海风水平风速出现最大值,平均为5.6 m s-1.陆风最大水平风速出现在370m,约为4.5 m s-1.最大风切变指数在1300m处,为2.84;在陆风向海风转换过程中,最大风切变指数在700m处,为1.28.在同一高度上,风切变指数在海风盛行和陆风盛行时的差值范围为0.2-3.6,风切变能反映出海陆风的发展高度.     

A new presentation of the Indian Ocean shallow overturning circulation from a vertical perspective

由于印尼贯穿流干扰了南印度洋经向翻转环流的计算,本文应用垂向翻转流函数来诊断印度洋浅层经向翻转环流.基于海洋环流模拟产品(OFES),本文探讨了垂向流函数相比经向翻转流函数的改进.研究结果表明垂向翻转流函数能平滑连接南北印度洋的翻转环流,包括完整的副热带翻转环流和跨赤道翻转环流.经向翻转流函数低估了印度洋浅层翻转环流;而垂向翻转流函数表示的印度洋浅层翻转环流受印尼贯穿流影响更小,其评估的印度洋浅层翻转环流强度约13 Sv,其中副热带翻转环流强度约8 Sv(1 Sv ≡ 106 m3 s-1).此外,垂向翻转流函数在印度洋南开边界(30°S～34°S)上600 m层表现为顺时针翻转结构,其强度约-5 Sv,可能对应风驱的副热带流系.因此,垂向翻转流函数提供了一种新方法来评估印度洋浅层翻转环流.     

小区域地壳变形监测与分析研究

介绍了小区域GPS地壳形变监测网建立、观测和数据处理方法,提出了一种平面直角坐标下位移—应变关系计算模型,得到监测区的位移场、应变场及断层活动方式,进一步得到主应变及方向、最大剪应变、面膨胀等应变参量及应力。     

2021年青海玛多MW7.4地震GNSS同震形变场及其断层滑动分布

2021年5月22日青海玛多M_W7.4地震作为发生在巴颜喀拉块体内部的一次强震,再次引起了人们对该地区地震活动性的强烈关注.本文基于震后GNSS流动观测和区域连续GNSS站资料,解算了106个站点的同震形变及其中17个站点的高频形变波形.同震形变场显示玛多地震具有典型的左旋走滑特征,GNSS观测到的最大同震位移达到1.2 m.GNSS与InSAR数据相符度较高,GNSS提供了准确的近场形变信息.基于GNSS同震形变场,本文反演了断层滑动分布,并计算了发震断层上产生的库仑应力变化.结果表明,发震断层的滑动破裂存在多个凹凸体,破裂分段特征明显且出露地表,与野外地表破裂考察和余震分布吻合,主体破裂位于断层面0~10 km的浅部区域,最大滑动量达到4.6 m,地震矩1.63×10²⁰N·m,矩震级为M_W7.4;发震断层上静态库仑应力增加区域与余震分布具有一致性,说明余震主要是由静态库仑应力加载而触发的.     

Probabilistic estimation of inelastic displacement demands in soil–structure interaction systems on cohesive soils

Inelastic displacement ratios (IDRs) of nonlinear soil–structure interaction (SSI) systems located at sites with cohesive soils are investigated in this study. To capture the effects of inelastic cyclic behavior of the supporting soil, the Beam on Nonlinear Winkler Foundation (BNWF) model is used. The superstructure is modeled using an inelastic single-degree-of-freedom (SDOF) system model. Nonlinear SSI systems representing various combinations of unconfined compressive strengths and shear wave velocities are considered in the analysis. A set of strong ground motions recorded at sites with soft to stiff soils is used for considering the record-to-record variability of IDRs. It is observed that IDRs for nonlinear SSI systems are sensitive to the strength and the stiffness properties of both the soil and the structure. For the case of SSI systems on the top of cohesive soils, the compressive strength of the soil has a significant impact on the IDRs, which cannot be captured by considering only the shear wave velocity of the soil. Based on the results of nonlinear time-history analysis, a new equation is proposed for estimating the mean and the dispersion of IDRs of SSI systems depending on the characteristic properties of the supporting soil, dimensions of the foundation, and properties of the superstructure. A probabilistic framework is presented for the performance-based seismic design of SSI systems located at sites with cohesive soils.     

地磁逐日比异常电磁学成因的进一步分析

基于地磁逐日比异常期间地磁垂直分量日变化幅度变大或变小的统计结果,发现地磁逐日比高值异常是由异常日的地磁垂直分量日变化幅度变小和异常前一天的日变化幅度变大所致。其中,异常日的日变化幅度变小可能是地磁逐日比异常的主要因素,但异常前一天的日变化幅度变大也是异常成立的重要因素。此外,引用前人感应电流假说,结合统计结果进行了机理解释,研究结论进一步证实了前人对该方法的机理推测。     

Horizontal and vertical fluxes of particulate matter during wind erosion on arable land in the province La Pampa,Argentina

A detailed analysis of horizontal and vertical particulate matter (PM) fluxes during wind erosion has been done, based on measurements of PM smaller than 10, 2.5, and 1.0 μm, at windward and leeward positions on a measuring field. The three fractions of PM measurement are differently influenced by the increasing wind and shear velocities of the wind. The measured concentrations of the coarser fractions of the fine dust, PM₁₀, and PM_2.5, increase with wind and shear velocity, whereas the PM_1.0 concentrations show no clear correlation to the shear velocity. The share of PM_2.5 on PM₁₀ depends on the measurement height and wind speed and varies between 4 and 12 m/s at the 1 m height ranging from 25% to 7% (average 10%), and at the 4 m height from 39% to 23% (average 30%). Although general relationships between wind speed, PM concentration, and horizontal and vertical fluxes could be found, the contribution of the measuring field was very low, as balances of incoming and outgoing fluxes show. Consequently, the measured PM concentrations are determined from a variety of sources, such as traffic on unpaved roads, cattle drives, tillage operations, and wind erosion, and thus, represent all components of land use and landscape structure in the near and far surroundings of the measuring field. The current results may reflect factors from the landscape scale rather than the influence of field-related variables. The measuring devices used to monitor PM concentrations showed differences of up to 20%, which led to considerable deviations when determining total balances. Differences up to 67% between the calculated fluxes prove the necessity of a previous calibration of the devices used.     

CO2注气压力对瓦斯扩散系数影响规律实验研究

煤层CH₄解吸效率低、扩散慢的特点严重制约着煤层瓦斯抽采的效率,为解决低透气性煤层瓦斯抽采困难的问题,选取晋城赵庄煤矿煤样,研究不同注气压力对驱替CH₄过程的影响以及驱替过程中CH₄扩散系数的变化规律,利用自主研发的CO₂驱替CH₄试验平台,在0.6、0.8、1.0 MPa等不同注气压力条件下分别进行CO₂驱替CH₄实验。结果表明:驱替压力越大,达到最大CH₄排放量的时间越短,CO₂突破时间越快,置换效率越大,驱替效果越好;CH₄气体驱替过程分为3个阶段,先急剧增加再缓慢增加最后保持平稳;在同一注气压力下,瓦斯扩散系数随时间呈先增大后减小的变化规律,注气压力为0.6、0.8、1.0 MPa时,瓦斯扩散系数的最大值分别为2.27×10-5、3.36×10-5、4.62×10-5 cm2/s。从实验结果可知,不同注气压力下,CO₂对CH₄主要起到驱替作用、置换吸附-解吸作用及稀释驱替作用;每个阶段的CH₄气体运移情况不同,根据实验阶段合理调整注气流量、压力等参数,使注驱技术搭配更高效。研究结果对CO₂深埋与瓦斯（煤层气）高效抽采具有理论指导意义。      

2018年一次非典型梅雨锋暴雨过程诊断分析

利用常规地面气象观测资料、NCEP/NCAR FNL 1°×1°网格点逐6 h再分析资料,对2018年6月20日浙江省一次暴雨过程的主要环流系统、等熵位涡、垂直螺旋度等进行了天气动力学诊断分析。结果表明：850 hPa低涡切变、对流层中层冷空气、200 hPa南亚高压、副热带高压是此次暴雨过程发生的主要影响系统;700 hPa上的正垂直螺旋度中心对暴雨的发生有良好的指示意义;等熵位涡的演变和形态对冷空气活动有较好的视踪作用,等熵位涡中心两侧气流辐合,有利于低压系统发展,高层等熵位涡与冷空气活动有较好的对应关系,等熵位涡大值区偏南侧的移动与强降水落区有较好的对应关系。