最小剪力系数及其调整方法对超高层建筑地震响应的影响

超高层结构地震剪力响应由振型分解反应谱法得到的结果经常不能满足规定的最小剪力系数要求。为此,文章简述剪力系数的概念和调整方法,以具有不同剪力系数的两个模型对比分析结构弹性、弹塑性地震响应差异,探讨剪力系数对超高层结构地震响应的影响。以通过强度和刚度调整使最小剪力系数满足规范要求的两个模型,分析不同调整方法引起的结构响应的合理性。结果表明:满足最小剪力系数的结构的弹性基底剪力大、层间位移角较小,结构的弹塑性位移响应也较小,受力状态优于不满足最小剪力系数的结构,安全性得到了提高。结构弹性倾覆力矩需求和弹塑性基底剪力按刚度调整大于按强度调整;结构弹塑性最大顶点位移和层间位移角响应相差不大,但出现刚度大\,层间位移角也大的与抗震理论相悖的情况;在满足抗震要求的情况下,构件的受力状态则是按强度调整更优,构件截面更加经济合理。     

Experiment on morphological and hydraulic adjustments of step-pool unit to flow increase

Exceptional flood events with a return period of about 50 years can be destructive to step-pool channel segments. However, field investigations and flume experiments have not examined the hydraulic and morphological feedbacks of step-pool morphology during unsteady hydrographs of exceptional flood events. We performed a series of flume experiments with a manually constructed step model, perturbed with three hydrographs that varied in the rate of water supply change. The bed texture, topography, flow regimes, surface flow field and water depth were characterized and measured as the flow rate was increased during the experiments. A distinct pool feature emerged downstream of the manually constructed step when the flow rate exceeded the threshold scaled to the peaks of ordinary flood events in well-graded mountain streams. The pool feature was modified in several different ways with flow rate increase. The bed surface steadily coarsened, micro-bedforms developed and became more pronounced, the bed topography became more spatially complex based on analysis using the Hurst exponent, and last, pool depth steadily increased. Pool modification was also linked to the flow regime: the impinging jet regime led to grain size segmentation in the pool while the jump regime contributed to decelerating flow velocity. The steeper rising limb of hydrograph led to a less developed pool feature, with smaller sized micro-bedforms in the pool bottom to outlet, and higher discharge threshold for distinct coarsening and scouring in the pool. The estimated energy dissipation within the step-pool unit decreased as a power function from low to high flow, quantified as the ratio h_c/H_S, where h_c is the critical water depth and H_S is scour depth. Our results highlight the interaction between morphology, hydraulics, and energy dissipation of step-pool unit and the crucial role of hydrograph shape on the interaction during flow increase © 2019 John Wiley & Sons, Ltd.     

Geomorphic evolution of the Qingshuigou channel of the Yellow River Delta in response to changing water and sediment regimes and human interventions

Delta channels are important landforms at the interface of sediment transfer from terrestrial to oceanic realms and affect large, and often vulnerable, human populations. Understanding these dynamics is pressing because delta processes are sensitive to climate change and human activity via adjustments in, for example, mean sea level and water/sediment regimes. Data collected over a 40-year period along a 110-km distributary channel of the Yellow River Delta offer an ideal opportunity to investigate morphological responses to changing water and sediment regimes and intensive human activity. Complementary data from the delta front provide an opportunity to explore the interaction between delta channel geomorphology and delta-front erosion–accretion patterns. Cross-section dimensions and shape, longitudinal gradation and a sediment budget are used to quantify spatial and temporal morphological change along the Qingshuigou channel. Distinctive periods of channel change are identified, and analysis provides a detailed understanding of the temporal and spatial adjustments of the channel to specific human interventions, including two artificial channel diversions and changes in water and sediment supply driven by river management, and downstream delta-front development. Adjustments to the diversions included a short-lived period of erosion upstream and significant erosion in the newly activated channel, which progressed downstream. Channel geomorphology widened and deepened during periods when management increased water yield and decreased sediment supply, and narrowed and shallowed during periods when management reduced water yield and the sediment load. Changes along the channel are driven by both upstream and downstream forcing. Finally, there is some evidence that changing delta-front erosion–accretion patterns played an important role in the geomorphic evolution of the deltaic channel; an area that requires further investigation. © 2020 John Wiley & Sons, Ltd.     

复测水准网动态平差及其在川滇地区垂直地壳形变中的应用

以1995—2016年川滇地区实测水准资料为例,分别采用动态经典平差、拟稳平差、伪逆平差和GPS速率约束平差4种平差方法进行平差计算,分析探讨4种平差方法在水准网平差处理时的适用条件及优缺点;最后分析了1995—2016年川滇地区的地壳垂直形变特征。结果表明:①在条件具备的情况下,GPS速率约束平差优于动态经典平差、拟稳平差和伪逆平差,主要体现在GPS速率可知、平差后速率误差明显减小,且能有效地抑制误差的传播与积累;而拟稳平差、伪逆平差虽优于动态经典平差,但同样存在着基准假定的问题;②1995—2016年川滇地区整体处于差异隆升阶段,只有四川盆地、滇西北和滇南少部分区域下沉,跨断裂剖面结果显示几条断裂带以继承性运动为主。     

稀无控制点无人机遥感影像几何定位方法研究

无人机以机动灵活、作业周期短和成本低等优势被广泛应用于基础测绘等领域。然而无人机航摄系统采集像片通过传统方法需要密集分布控制点,导致作业成本增加及生产效率下降影响经济效益。为此,在考虑到航测相机曝光延迟的基础上提出基于GPS辅助空中三角测量的稀无地面控制点的无人机遥感影像高精度几何定位方法,并通过实际测试生产数字线划图(DLG)和数字正射影像图(DOM),可满足1∶1000地形图测绘的技术要求,其高效率、低成本的生产模式较常规方法更具有推广意义,尤其是在西部测图以及岛礁测量人烟稀少人员很难或无法到达且使用常规测量方法无法满足成图要求的区域。     

不同类型卫星影像区域网平差方法

传统卫星影像纠正常针对单景影像,且需要一定数量的外业控制点作为参考,严重制约了正射纠正效率。本文提出了一种卫星影像区域网平差方法,利用影像间的连接点进行RPC模型的前方交会,并用少量控制点进行仿射变换,实现了多轨多景卫星影像的区域网平差。经测试,本文方法可有效减少外业控制点,提高卫星影像正射纠正效率。     

真空管磁浮列车T形槽轨平顺度检测方法研究及应用

针对T形槽轨平顺度的测量、分析与调整方法进行了研究,旨在解决T形槽轨建设中难以对其平顺度进行检测和分析的问题采用自由测站测量技术在管内构建高精度三维控制网.解决了因管内环境条件限制而难以建立测量基准的问题;基于此控制网,釆用自由设站测呈与极坐标测址法相结合的技术测得槽轨上各测点的三维坐标,为槽轨平顺度的分析提供了基础数据;为对槽轨平顺度质量进行判定,运用统计分析方法将槽轨上各测点的偏差悄况量化为4项统计指标.结果表明选用的4项指标能够定量和全面地反映槽轨平顺度质量;为提高槽轨平顺度,提出了基于槽轨上各测点的偏差计算调整量和据此对槽轨进行精调的方法.结果表明该方法能显著提高槽轨平顺度。     

数字摄影测量实践教学体系及教学资源构建

针对当前数字摄影测量实践教学中存在的与生产实际脱节、学生创新实践能力不强等问题,对数字摄影测量的实践教学进行改革。紧跟当前数字摄影测量新技术的发展趋势,建立反映当前数字摄影测量最新发展的教学体系,构建一批有特色、有一定创新性的案例式实践教学项目,建立完备的实践教学指导材料,在此基础上构建一批实践教学资源。通过实践教学改革,丰富摄影测量实践教学内容,发展学生的创新思维和数据处理综合应用能力。     

基准网辅助的大区域卫星影像区域网平差技术

针对目前使用数字正射影像图(DOM)作为控制资料,纠正卫星影像,容易造成几何形变的误差传递的问题,该文提出了构建原始影像基准网,进行大区域卫星影像区域网平差的方法。该方法使用外业控制点作为地面控制资料,激光点云生产的数字高程模型(DEM)数据作为高程资料,利用区域网平差技术解算基准网影像的有理多项式系数(RPC)文件,配合DEM辅助弱连接点检测技术增强基准网的稳健性,而后利用高精度连接点匹配基准网解算同源待平差影像的RPC文件。该文使用该方法建立了基于39景高分二号影像的河南安阳、鹤壁地区的基准网,并对两景新增影像进行平差处理。结果表明,平面中误差为1.6m,达到1∶10 000数字正射影像生产的精度要求,相邻影像之间的几何拼接精度优于1个像素,满足了无缝拼接。     

网形结构对重力数据分析结果的影响

为分析网形结构对重力网平差结果的影响,利用北天山测网改造后的最新4期流动重力观测数据,分析测网中存在长支线对整网数据处理结果的影响。结果显示,长支线的存在使北天山最大异常变化达到260 μGal。将支线连成闭合环再进行平差计算,得到的最大重力变化量减小到60 μGal,表明测线上的误差积累导致支线末端测点重力值可靠性差,严重影响异常重力变化的识别。由于观测原因形成长支线时,为正确识别异常信息,采取适当的数据处理方法,将支线连接成闭合环,可以有效提高测网整体平差结果的可靠性。