基于约束最小二乘的三维点云墙体重建     

周刚  李霖 《地理信息世界》2021,28(1):26-33

近年来,基于点云的室内三维重建在各个领域得到了越来越多的关注.然而通过点云重建室内模型仍有许多问题需要解决:①重建模型的几何特征约束性较差;②模型几何特征拓扑重构复杂;③模型多为表面模型未构建实体模型.针对以上问题,提出了一种基于约束最小二乘的线特征方法实现室内墙体的重建.首先采用局部最小二乘拟合和全局区域生长的思想从点云提取线特征.然后基于约束最小二乘的思想构造全局约束矩阵约束线特征,通过固定区域线段相交方法重构拓扑关系.最后,构造线段缓冲区确定内外墙线重建墙体模型.通过几组数据进行实验,结果表明该方法重建的墙体模型具有几何结构完整和特征约束性强的特点.  相似文献   

开挖前降水引发基坑变形机制模型试验研究     

曾超峰  薛秀丽  宋伟炜  李淼坤  白宁 《岩土力学》2020,41(9):2963-2972

现有基坑相关研究主要关注土方开挖过程引起的变形，认为围护结构变形起点是土方第1次开挖。然而，一些工程实测表明，基坑开挖前降水阶段即可引起围护结构及周边地层发生厘米级的变形。显然，未考虑开挖前变形的基坑监测数据将低估基坑施工的环境效应。为了研究基坑开挖前降水引发基坑变形的机制，开展了室内模型试验，对基坑开挖前降水过程进行了缩尺精细化模拟。通过微型降水井的设置与调控，模型试验真实再现了实际基坑降水过程中井流效应对围护结构受力变形的影响。试验过程中发现，随着降水的进行，坑外降水漏斗不断扩展，围护结构悬臂式侧移及坑外拱肩式地面沉降也随之产生。另外，降水导致墙前水压力明显减小，并诱发墙前侧向总压力重分布（以减小为主），围护结构为此发生指向坑内的悬臂式运动以寻求新的受力平衡，并通过墙后土体损失诱发坑外地层变形。  相似文献   

Temporal-Spatial Variation of Surface Suspended Matter and Controlling Factors in the Inner Shelf of the East China Sea in Winter     

MIN Jianxiong  LI Guangxue  DING Dong  QIAO Lulu  MA Yanyan  YANG Gang  ZHANG Yaqi  ZHANG Lei  LI Shuhao 《中国海洋大学学报(英文版)》2019,(1)

Based on the observed surface suspended matter in the East China Sea in February 2007 and June 2015, an empirical model was established using L1 b's band 4 data to retrieve surface suspended matter from the Moderate Resolution Imagine Spectroradiometer Terra imagery. The squared correlation coefficient is 0.8358, and the root mean square error is 0.4285 mg L-1. The model reflects the distribution characteristics of surface suspended matter in the inner shelf of the East China Sea. In this paper, the satellite images of the study area were retrieved in January from 2001 to 2015, and the monthly distribution of surface suspended matter were obtained. The inter-annual distribution of the study area is similar, and the concentration of surface suspended matter is higher near the shore than offshore. A large amount of surface suspended matter is transported southeast under the influence of Zhejiang and Fujian coastal current and Taiwan warm current. Only a small amount of surface suspension can reach the Kuroshio area. The surface suspended matter concentration changes obviously near the estuary because of the effect of differences in the flux of the Yangtze River. Meanwhile, winter monsoon, temperature front, El Ni?o events, and other factors affect the distribution of surface suspended matter in 100 m isobath to coastal water but minimally influence the distribution in 100 m isobath to deep sea.  相似文献   

Extraction of Lithium from Salt Lake Brine using N523-TBP Mixture System   总被引：1，自引：1，他引：0       下载免费PDF全文

SHI Dong  LI Li-juan  LI Jin-feng  JI Lian-min  SONG Fu-gen  PENG Xiao-wu  ZHANG Li-cheng  ZHANG Yu-ze  LI Hui-fang  SONG Xue-xue  NIE Feng  ZENG Zhong-min  LIU Zhi-qi  GUO Fan 《盐湖研究》2019,27(2):95-110

In this work,problems encountered by tri-butyl phosphate( TBP) in the industrialization of lithium extraction from salt lake brine were discussed in detail. The behavior of N,N-bi-( 2-ethylhexyl) acetamide( N523) during lithium extraction was investigated,and its disadvantages were analyzed in the view of practical application. An N523-TBP mixture extraction system was proposed to alleviate or avoid the defects that N523 and TBP met when they were used separately. The optimal composition of this mixture extraction system was determined to be 20% N523-30% TBP-50% kerosene.The effects of brine acidity,Fe/Li molarity ratio,phase ratio and chloride ion concentration on lithium extraction efficiency were discussed. The operation conditions in single-stage extraction were optimized as brine acidity = 0. 05 mol/L,Fe/Li molarity ratio = 1. 3,and phase ratio = 2. The high concentration of chloride ions in brine was beneficial for the extraction of lithium. The structure of the extracted complex was proposed as( LiFeCl_4·n N523·m TBP)·( 2-n) N523·( 2-m) TBP( m + n = 2) by chemical analysis and slope-fitting methods. The extraction thermodynamic functions were calculated preliminarily,and the results suggested that the extraction process was an exothermic( ΔH 0) and spontaneous( ΔG 0) reaction,and the degree of disorder increased( ΔS 0) during the extraction process. This work will give some guidance to the lithium industry of Qinghai in both the fundamental theory and practical application.  相似文献   

Morphodynamics of an Artificial Cobble Beach in Tianquan Bay,Xiamen, China     

SHU Fangfang  CAI Feng  QI Hongshuai  LIU Jianhui  LEI Gang  ZHENG Jixiang 《中国海洋大学学报(英文版)》2019,(4)

By tracking and monitoring the profile configuration, topography, and hydrodynamic factors of an artificial cobble beach in Tianquan Bay, Xiamen, China over three consecutive years after its completion, we analyzed the evolution of its profile configuration and plane morphology, and its storm response characteristics. The evolution of the profile configuration of the artificial cobble beach in Tianquan Bay can be divided into four stages. The beach was unstable during the initial stage after the beach nourishment the profile configuration changed obviously, and an upper concave composite cobble beach formed gradually, which was characterized by a steep upper part and a gentle lower part. In the second stage, the cobble beach approached dynamic equilibrium with minor changes in the profile configuration. At the third stage the beach was in a high-energy state under the influence of Typhoon Meranti, and the response of the artificial cobble beach differed significantly from that of the low-tide terrace sandy beach. Within a short time, there was net onshore transport of cobbles in the cross-shore direction. The beach face was eroded, the beach berm was accumulated, and the slope of the beach was steepened considerably. In the alongshore direction, there was notable transport of cobbles on the beach from east to west along the shore, and the total volume of the beach decreased by 4.5×103 m~3, which accounted for 50% of the total amount of beach volume lost within three years. The fourth stage was the restoration stage after the typhoon, characterized by a little gentler profile slope and the increase in width and the decrease in height of beach berm. Because of the action of waves and the wave-driven longshore current caused by the specific terrain and landform conditions along the coast(e.g., coastal headlands, near-shore artificial structures, and reefs), the coastline of the artificial cobble beach gradually evolved from being essentially parallel to the artificial coast upon completion to a slightly curved parabolic shape, and three distinct erosion hotspots were formed on the west side of the cape and the artificial drainpipe, and the reefs. Generally, the adoption of cobbles for beach nourishment on this macro-tidal coast beach with severe erosion has yielded excellent stability and adaptability.  相似文献   

Environmental changes in the north‐east Sunda region over the last 40 000 years     

Chuanxiu Luo  Simon Haberle  Zhuo Zheng  Rong Xiang  Chixin Chen  Gang Lin  Kumar Sazal 《第四纪科学杂志》2019,34(3):245-257

  相似文献   

榍石LA-SF-ICP-MS U-Pb定年及对结晶和封闭温度的指示   总被引：1，自引：0，他引：1  

赵令浩  曾令森  詹秀春  胡明月  袁继海  孙冬阳  张立飞 《岩石学报》2020,36(10):2983-2994

榍石富含U、Th，贫Pb，是U-Pb定年的理想矿物之一。本文采用激光剥蚀-高分辨等离子体质谱建立榍石U-Pb定年方法，采用25~30μm激光斑束，准确测定榍石U-Pb标准样品BLR-1（~1048Ma）、OLT-1（~1014Ma）和Pakistan（~21.4Ma），以及年轻榍石样品（<100Ma）U-Pb年龄，提高了检测准确性和空间分辨率。综合对比共生锆石和榍石U-Pb年龄、榍石颗粒微量元素和U-Pb年龄环带及不同成分岩浆岩（SiO₂含量48.1%~77.0%）中岩浆榍石的结晶温度，结果表明：岩浆演化过程中，榍石具有宽泛的结晶温度（600~900℃，峰值~750℃），主要集中于岩浆演化中晚期结晶，榍石U-Pb同位素封闭温度接近或略低于锆石，因此同一岩浆体系中锆石与榍石的年龄差异可能反映了该熔体较晚达到榍石饱和，而非熔体热演化历史或封闭温度信息。  相似文献   

九龙江口浮游植物群体对盐度胁迫的快速适应     

李刚 《海洋学报(英文版)》2019,38(8):78-85

Mixing of freshwater and seawater creates the well-known salinity gradients along the estuaries. In order to investigate how phytoplankton respond to the acute salinity changes, we exposed natural phytoplankton assemblies from the Jiulong River Estuary to differential saline field water while continuously monitoring their photosynthetic performances under both indoor-and outdoor-growth conditions. When the natural cell assemblies from salinity 30 field water were exposed to series low saline field water(salinity 25, 17, 13 and 7.5), the effective Photosystem II quantum yield(ΔF/F_m′) decreased sharply, e.g., to one-fifth of its initials after 5 min exposure to salinity 7.5 field water, and then increased fast during the following 40 min and almost completely recovered after 320 min. During such an exposure process, non-photochemical quenching(NPQ) sharply increased from 0 to 0.85 within 5 min, and then decreased to nearly 0 within the following 70 min. When these cells re-acclimated to salinity 7.5 field water were exposed to series high saline field water(salinity 13, 17, 25 and 30), a similar response pattern was observed, with the decreased ΔF/F_m′ accompanied with increased NPQ, and followed by the recovery-induced increase in ΔF/F_m′ and decrease in NPQ. A similar response pattern as ΔF/F_m′to the acute osmotic stress was also observed in the photosynthetic carbon fixation capacity according to radiocarbon(~(14)C) incorporation. Our results indicate that estuarine phytoplankton assemblies could rapidly recover from the acute osmotic stress, implying a potential cause for their frequent blooms in coastal-estuarine waters where despite drastically varying salinity, available nutrients are abundant due to the land-derived runoffs or mixing-caused relaxations from sediments.  相似文献   

2018年秦皇岛风暴潮前后岸基站及浮标主要水质参数变化分析     

马方方  王刚  毕玉明  周秋伶  桓清柳 《海洋技术学报》2019,38(6):68-74

对2018年8月秦皇岛风暴潮期间3个入海口岸基站及邻近海域浮标的监测数据进行分析,结果显示:风暴潮导致入海口水体中COD、总磷、总氮和氨氮含量均明显升高;风暴潮2 d之后,3个入海口邻近海域均发生赤潮,此次赤潮的发生与风暴潮导致陆源入海污染物骤然大幅升高有关。此次风暴潮导致秦皇岛人造河口、大蒲河口和七里海3个岸基监测站的COD监测日均值最高分别达到15.83 mg/L、8.70 mg/L和7.92 mg/L,约升高至前期的2倍、1.5倍和2倍;人造河口总氮变化不大,大蒲河口和七里海总氮升高30%左右;大蒲河口总磷变化不大,人造河口总磷为前期的3.5倍,升高幅度最大,七里海总磷为风暴潮之前两日的2倍,但未超过前一周的最高浓度;风暴潮当天及第二天,人造河口、大蒲河口、七里海氨氮日均值陆续达到最高,分别为2.34 mg/L、1.11 mg/L和0.12 mg/L,分别为风暴潮前两日的7倍、3.5倍和10倍。风暴潮过后,入海口临近海域发生赤潮,浮标监测到叶绿素a最高值为76.4μg/L,pH和溶解氧也大幅升高。分析表明,此次风暴潮导致的入海口污染物突然大幅升高为风暴潮之后的赤潮发生提供了充足的营养基础。  相似文献   

塑性极限分析鱼雷锚锚尖贯入阻力     

瑜璐  杨庆  杨钢  张金利 《岩土力学》2020,41(6):1953-1962

鱼雷锚安装过程中,锚尖形状影响尖部贯入阻力进而影响贯入深度。基于塑性极限分析理论下限法分析不同锚尖长径比x的椭圆形锚尖的贯入阻力和贯入阻力系数,并考虑了贯入深度、锚-土界面摩擦对贯入阻力以及贯入阻力系数的影响。结果表明:(1)锚-土界面光滑时,锚尖贯入阻力系数随着锚尖长径比的增大而减小;锚-土界面粗糙时,锚尖贯入阻力系数随着锚尖长径比的增大而增大。(2)摩擦力对贯入阻力系数的影响随着ξ增大而增大。(3)随着埋置深度增加,贯入阻力系数受x影响最小时所对应的摩擦系数逐渐减小。(4)当锚-土界面摩擦系数ω 0.75时,工程中可选用ξ1的锚尖用以减小端部贯入阻力;当ω0.26时,ξ1的锚尖提供更小的端部贯入阻力。锚尖长径比ξ=0和ξ=1的下限解与前人研究的桩基和圆形结构的理论解较为一致,进一步验证了所提出的椭圆形锚尖下限法模型的可行性。  相似文献