基于FPGA的自动门限线谱检测研究

由于海洋环境噪声的起伏变化,采用固定门限来进行线谱检测容易造成线谱的漏报或伪峰的误识。根据背景噪声方差的变化采取自动门限可更好地适应背景的变化,能使线谱检测达到更好的效果。通过仿真对采用固定门限和自动门限的检测方法进行了研究和分析,验证了自动门限法的有效性,并采用 FPGA 实现了自动门限线谱检测算法。     

基于海空磁力测量数据的向下延拓方法比较

地磁场的向下延拓是实现磁场数据空间转换的主要手段,是多源海洋磁力测量数据融合和构建三维海洋磁空间背景场模型的关键技术.在分析频域位场向下延拓方法原理基础上,分别采用了4种向下延拓方法将300m高度磁测数据延拓至200m高度,并与同一海区200m高度实测数据对比,以检验各延拓方法的计算效果,为构建三维海洋磁空间背景场模型...     

砂卵(砾)石动剪切模量比与阻尼比的试验研究

砂卵(砾)石的动剪切模量比和阻尼比是河谷地貌场地地震反应分析的重要参数,对设计地震动参数的确定有重要影响。本文利用商洛市地震小区划项目砂卵石的动三轴试验结果,结合其他砂卵(砾)石动三轴试验结果,分组统计得到了稍密、中密、密实砂卵(砾)动三轴试验的推荐结果。建立了典型场地模型,研究了其动剪切模量比和阻尼比的不确定性对场地地震反应的影响。研究表明:动剪切模量比、阻尼比平均值±1倍标准差的不确定性对砂卵石场地峰值加速度的影响较小,说明了分组及统计结果的合理性;不同概率水平下,动剪模量比、阻尼比的变化导致高频部分反应谱有明显差异,0.04-0.1s的反应谱变化范围在20%左右,但对大于1.0s的长周期反应谱影响很小。针对砂卵(砾)石动剪切模量比和阻尼比的研究对提高工程场地设计地震动参数的可靠性具有重要意义。     

波力电站岩坎爆破的技术与工艺

本文根据波力电站岩坎爆破的特点,提出了用多段毫秒雷管一次起爆进行周边预裂爆破、深孔削坡爆破和主坎斜孔抛掷爆破的程序,建立了药量计算的公式,分析了爆破震动对波力电站气室和机房的影响,论述了波力电站岩坎爆破的技术理论与工艺方法。     

2012 - 2017年伊犁河谷冬季降水日变化特征

利用2012 - 2017年冬季伊犁河谷10个国家气象站逐小时降水资料, 分析了伊犁河谷不同区域降水日变化特征, 结果表明： 冬季伊犁河谷西部和中部地区降水量日变化呈单峰型, 北京时间09：00 - 12：00是主要的峰值时段; 其他地区降水量日变化单峰特征不显著。伊犁河谷大部分地区降水量与降水频次的关系比降水量与降水强度的关系更为密切。伊犁河谷冬季降水事件以6 h以内的短历时降水为主, 但其对冬季总降水量的贡献率不足30%; 持续12 h以上的长持续性降水事件发生次数虽少, 但它是伊犁河谷冬季总降水量的主要贡献者。短历时和持续性降水事件是伊犁河谷西部地区降水量日变化主峰的重要贡献者; 持续性和长持续性降水事件是伊犁河谷中部及北部地区降水量日变化峰值的重要贡献者; 伊犁河谷西南部地区冬季降水日循环与降水持续性之间的关系不显著。     

Experimental investigation on scour topography around high-rise structure foundations

The current study aims to investigate the characteristics of scour topography around High-Rise Structure Foundations(HRSFs)via physical modeling tests.Clear-water scour tests with a uniform non-cohesive bed are modeled under the action of unidirectional steady flows.Time variations of the erosion and deposition topography are measured.The results show that deposition downstream of the first dune behind the HRSF is not located on the centerline of the wake.The deposition pattern indicates that a long steady wake region exists behind the permeable foundation.The scour depth around an HRSF is much less than that around a monopile because of the structural permeability,which gives rise to the bleed flow and a weakened downflow and horseshoe vortex.Additionally,the asymmetry of the HRSF affects the scour rate but not the final equilibrium scour depth.The average scour slope decreases along the direction of the flow.On the contrary,the scour radial distance increases along the direction of the flow,with the average value changing from 1.36De to 2.35De(where De is the equivalent diameter of the foundation).Furthermore,the scour hole around the HRSF is serrated rather than smooth owing to the presence of multiple piles.Empirical formulae are suggested for estimating the evolution of scour depth and volume.These laboratory experiments provide reference information for relevant numerical modeling studies and can be applied to guide engineering designs in an ocean area.     

Post-rifting magmatism and the drowned reefs in the Xisha Archipelago domain

Fourteen isolated drowned reefs have been identified around the Xisha Uplift by multibeam and seismic data. The drowning processes of these reefs can be divided into three different stages, which correspond to three different accelerated tectonic subsidence periods. The drowning of the Xisha reefs is the result of the combined action of tectonic subsidence and sea level fluctuations, and the tectonic subsidence rate had to remain above 0.2 mm yr~(-1 )for a long time. Three abrupt accelerated tectonic subsidence events that occurred in the late Miocene, Pliocene and early Quaternary in the Xisha Uplift were closely related to the thermal subsidence processes after three stages of post-rifting magmatism. The magmatism of the middle Miocene and the following thermal subsidence resulted in the drowning of reefs in the northwestern Xisha uplift(Zone A). During the early Pliocene, massive magmatic intrusions and volcanic eruptions occurred in the Xisha Uplift. Then, the subsequent thermal subsidence started the drowning process of reefs in the northeastern and western regions of the Xisha Uplift(Zone B and C). During the early Quaternary, large-scale magmatism also occurred in the Xisha Uplift. The subsequent thermal subsidence resulted in a new rapid tectonic subsidence, which caused the reefs in the southern and southeastern regions of the Xisha Uplift to drown(Zone D and E).     

弧板式透空堤消浪性能影响因素数值研究

弧板式透空堤是由弧型板组成的新型防波堤结构。为探讨其透射系数的影响因素,利用Fluent软件基于N-S方程构建了波浪与板式透空堤相互作用的数值模型,讨论了相对潜深、入射波周期、相对波高、相对板宽和结构型式对透射系数的影响。结果表明:弧板式透空堤的透射系数随着相对波高和入射波周期的增大而增大,在静水面附近透射系数最小,尤以静水面和略高于静水面时的消浪效果最佳;在相同波浪要素条件下,静水面及其上0.02 m和0.04 m位置处,弧板式透空堤的消浪效果明显优于平板式透空堤。     

中国城市韧性综合评估及其时空分异特征

城市韧性对城市健康发展具有显著影响。本文从经济、社会、生态、基础设施等4个系统构建城市韧性综合测度指标体系,对我国地级以上城市韧性进行定量评估,揭示其时空分异特征,并对典型样带区进行影响因素探讨。结果表明：城市韧性子系统间逐步趋于均衡,但经济、生态、基础设施、社会子系统发展趋势存在显著差异,经济子系统占据主导地位,其他子系统位序转换加剧;城市韧性水平集聚趋势减弱,各子系统空间发展格局多样化;城市韧性发展空间异质性显著,中低、低韧性水平城市居于主导地位,东部地区整体高于中西部地区;城市韧性“集群化”空间分异特征显现,城市群地区的韧性高于其他地区;东部沿海样带受城市活力影响显著、在南北方向上变化相对缓慢,长江沿岸样带在经济大发展背景下呈现出明显的东西分异特征,而胡焕庸线沿线样带无明显差异、但其整体受城市扩张因素影响最为显著。     

Wind stress forcing of the North Sea 'pole tide'

We conduct numerical simulations of the wind forcing of sea level variations in the North Sea using a barotropic ocean model with realistic geography and bathymetry to examine the forcing of the 14 month 'pole tide', which is known to be anomalously large along the Denmark–Netherlands coast. The simulation input is the monthly mean surface wind stress field from the National Centers for Environmental Prediction (NCEP) reanalysis for the 40 year period 1958–1997. The ocean model output sea level response is then compared with 10 coastal tide gauge records from the Permanent Service for Mean Sea Level (PSMSL) over the same period of time. Besides the strong seasonal variations, several prominent quasi-periodicities exist near 7 years, 3 years, 14 months, 9 months and 6.5 months. Correlations and spectral analyses show remarkable agreement between the model output and the observations, particularly in the 14 month, or Chandler, period band. The latter indicates that the enhanced pole tide found in the North Sea along the Denmark–Netherlands coast is actually the coastal set-up response to wind stress forcing with a periodicity of around 14 months. We find no need to invoke a geophysical explanation involving resonance enhancement of the pole tide in the North Sea to explain the observations.