Feedback control system for blow-out preventer positioning     

《Applied Ocean Research》2019

During the drilling of ultra-deep-water subsea petroleum wells, a blow-out preventer (BOP), a piece of safety equipment, must be assembled on the wellhead. The BOP is suspended using the drilling riser during the wellhead approach operation, and the riser's top end is connected to the floating platform rig. This article presents a feedback control system for the automatic approach of the BOP to the wellhead. Compared to state-of-the-art controls, ours does not require ancillary thrusters installed alongside the riser nor inclination sensors atop of the drilling riser. Additionally, our proposed control embeds a closed-loop dynamic positioning system, thus retaining the characteristics of the original control system and adding an extra closed-loop. This eases implementation of the BOP approach control to an existing platform. To calculate the optimal gains for the BOP controller, we assume a linear system for the riser, including only the pendulum-shape. The simulation is carried out using nonlinear models for both riser and floating platform. We assume an International Towing Tank Conference standard semi-submersible platform, coupled with a 3000-m free-hanging vertical riser for the time-domain simulation. The results show the BOP tracking to be a step-shaped input signal under current and wave loads. A discussion of the performance of feedback control under different environmental loads is also included.  相似文献   

湖南省似大地水准面2017模型及精度分析     

董明旭  李建成  华亮春  姜卫平  尹昊华  敖敏思  曾翔强 《大地测量与地球动力学》2019,39(1):66-71

利用近7万个湖南及邻近省份重力观测数据、502个GNSS/水准控制点及数字高程模型，以EIGEN-6C4全球重力场模型作参考重力场，采用顾及地球曲率影响的各类地形质量位及引力的第二类Helmert凝集法严密算法，利用高分辨率地形数据恢复甚短波扰动重力场，确定空间分辨率2′×2′的高精度湖南省似大地水准面模型（HNGG2017）。经外部检核，模型整体精度均优于±0.022 m。与历史模型相比，新模型在湖南北部常德汉寿、西南部永州江永等地区精度得到显著改善。  相似文献   

基于低成本单频u-blox接收机的GPS/BDS定向性能分析     

李江卫  马立烨  吴仁攀  孙伟  吴多 《大地测量与地球动力学》2019,39(3):279-284

针对高精度GNSS定向应用场景，通过实验对比对低成本单频u-blox接收机的数据质量和解算精度。结果表明，u-blox接收机GPS、BDS观测值的信噪比略低于测量型接收机；伪距精度分别为0.91 m、0.56 m，相位精度分别为1.35 cm、1.20 cm。在静态观测环境下，u-blox的定向精度可以达到航向0.2°/m和俯仰0.4°/m；动态环境下解算结果稍差，但也可以达到航向0.3°/m和俯仰0.6°/m，略低于高成本测量型接收机单频数据的实时动态定向精度。  相似文献   

徕卡RTC360三维激光扫描仪在竣工测量中的应用     

汪晓慧  吴晓培 《测绘通报》2019,(10):150-154,159

徕卡RTC360不仅操作简单、扫描速度快，而且非常智能。可以实时跟踪计算两个连续站点间的相对位置，点云实时预拼接。后期搭配Register360智能拼接软件，点云智能拼接处理，无需人工干预，简单高效。  相似文献   

利用远震研究四川盆地及其周缘瑞利面波相速度和方位各向异性          下载免费PDF全文

王小龙  雷兴林  马胜利  张烨  郭志  闻学泽 《地球物理学报》2020,63(2):445-459

基于四川盆地及周边的245个宽频带台站2010年9月—2014年9月期间的远震记录,提取双台路径瑞利面波相速度频散资料,反演得到四川盆地20～120s的高分辨率瑞利面波相速度及各向异性空间分布.在丰富区域地球物理基础数据的同时,结合已有研究成果对地壳上地幔变形耦合进行探讨,结果表明短周期(20～30s)的相速度分布与四川盆地的地质构造特征相吻合,作为川滇地块、松潘—甘孜地块和四川盆地之间的边界——龙门山断裂带和鲜水河断裂带对上述三个地块上地壳的速度结构具有明显的控制作用;松潘—甘孜地块,特别是川滇地块中下地壳普遍表现为明显的低速异常,表明中下地壳相对软弱;而四川盆地的中下地壳整体呈现相对高速,表明四川盆地具有相对坚硬的中下地壳.研究区域东南角接近北扬子地块与南扬子地块的缝合部位,呈现高速异常.四川盆地南部和东南邻区不同周期均具有较强的各向异性,且快波方向较为一致,反映这些地区不同深度变形耦合较好.四川盆地西部、北部及东北部邻区,不同周期的各向异性快波方向变化较大,不同深度变形耦合较差.这些特征与绕喜马拉雅东构造结的物质流动被扬子地块的高速地壳阻挡的宏观认识基本一致.  相似文献   

Estuarine biofilm patterns: Modern analogues for Precambrian self-organization     

Roeland C. van de Vijsel  Jim van Belzen  Tjeerd J. Bouma  Daphne van der Wal  Valentina Cusseddu  Sam J. Purkis  Max Rietkerk  Johan van de Koppel 《地球表面变化过程与地形》2020,45(5):1141-1154

This field and laboratory study examines whether regularly patterned biofilms on present-day intertidal flats are equivalent to microbially induced bedforms found in geological records dating back to the onset of life on Earth. Algal mats of filamentous Vaucheria species, functionally similar to microbial biofilms, cover the topographic highs of regularly spaced ridge–runnel bedforms. As regular patterning is typically associated with self-organization processes, indicators of self-organization are tested and found to support this hypothesis. The measurements suggest that biofilm-induced sediment trapping and biostabilization enhance bedform relief, strength and multi-year persistence. This demonstrates the importance of primitive organisms for sedimentary landscape development. Algal-covered ridges consist of wavy-crinkly laminated sedimentary deposits that resemble the layered structure of fossil stromatolites and microbially induced sedimentary structures. In addition to layering, both the morphological pattern and the suggested formation mechanism of the recent bedforms are strikingly similar to microbialite strata found in rock records from the Precambrian onwards. This implies that self-organization was an important morphological process in times when biofilms were the predominant sessile ecosystem. These findings furthermore emphasize that self-organization dynamics, such as critical transitions invoking ecosystem emergence or collapse, might have been captured in fossil microbialites, influencing their laminae. This notion may be important for paleoenvironmental reconstructions based on such strata. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Use of local and global maps of forest canopy height and aboveground biomass to enhance local estimates of biomass in miombo woodlands in Tanzania     

《International Journal of Applied Earth Observation and Geoinformation》2020

Field surveys are often a primary source of aboveground biomass (AGB) data, but plot-based estimates of parameters related to AGB are often not sufficiently precise, particularly not in tropical countries. Remotely sensed data may complement field data and thus help to increase the precision of estimates and circumvent some of the problems with missing sample observations in inaccessible areas. Here, we report the results of a study conducted in a 15,867 km² area in the dry miombo woodlands of Tanzania, to quantify the contribution of existing canopy height and biomass maps to improving the precision of canopy height and AGB estimates locally. A local and a global height map and three global biomass maps, and a probability sample of 513 inventory plots were subject to analysis. Model-assisted sampling estimators were used to estimate mean height and AGB across the study area using the original maps and then with the maps calibrated with local inventory plots. Large systematic map errors – positive or negative – were found for all the maps, with systematic errors as great as 60–70 %. The maps contributed nothing or even negatively to the precision of mean height and mean AGB estimates. However, after being calibrated locally, the maps contributed substantially to increasing the precision of both mean height and mean AGB estimates, with relative efficiencies (variance of the field-based estimates relative to the variance of the map-assisted estimates) of 1.3–2.7 for the overall estimates. The study, although focused on a relatively small area of dry tropical forests, illustrates the potential strengths and weaknesses of existing global forest height and biomass maps based on remotely sensed data and universal prediction models. Our results suggest that the use of regional or local inventory data for calibration can substantially increase the precision of map-based estimates and their applications in assessing forest carbon stocks for emission reduction programs and policy and financial decisions.  相似文献   

数字正射影像结合LiDAR数据在山区测绘中的应用     

严慧敏 《测绘通报》2020,(1):115-119

随着信息化社会的到来，现代水利测绘已经由传统测绘向信息化测绘发展，无人机技术应用于测绘行业推进了信息化测绘进程。本文探讨了如何有效利用无人机技术解决测绘领域在山区遇到的问题。固定翼无人机能及时获取地面数字正射影像数据，捕获裸露地面的平面和高程，但是无法获取植被覆盖下的地表高程信息，因此，本文通过机载激光雷达获取植被覆盖下的LiDAR点云数据；将二者数据相结合，再通过EPS软件生成三维地表模型，可以快速获取任何测区地物和地形数据，不仅提高了工作效率，还降低了外业劳动强度。  相似文献   

基于点云滤波的DOM自动生产算法     

白世晗  刘斌  白少云  顾世祥  邢宽平 《测绘通报》2020,(2):82

针对目前生产高精度DOM生成效率低、人工编辑干预较大等现状，提出了一种基于点云滤波的DOM自动生产方式。该方法通过对空三解算后的影像匹配密集点云DSM，使用基于TIN的加密滤波方式进行滤波计算，解决了滤波后空洞区域插值问题，制作出满足微分纠正需求的DEM模型，并基于该模型进行微分纠正生成DOM成果。通过选取ISPRS城区试验数据和实际工程山区数据进行验证，证明该算法不仅提高了效率，同时优化了成果质量，DOM成果精度符合规范要求。  相似文献   

地理科学与资源研究所80年回顾及展望     

葛全胜  廖小罕  高星  封志明  刘卫东  廖晓勇  诸云强 《地理学报》2020,75(12):2537-2546

2020年中国科学院地理科学与资源研究所建所80周年。回眸80年,从1940年重庆北碚成立的中国地理研究所,到1953年重新组建的中国科学院地理研究所和1956年成立的中国科学院自然资源综合考察委员会,再到1999年地理研究所和自然资源综合考察委员会整合形成现在的地理科学与资源研究所,几经变迁,历经三代人努力,研究所始终如一,求真务实,开拓进取,推动着地理科学与资源科学的创新发展,为国家建设发展和生态文明进步做出了重要贡献。适逢建所80周年,本文回顾地理资源所发展历程,总结取得的重要科研成果,并展望未来发展。  相似文献