拖曳锚在海床中运动特性的大变形有限元分析

拖曳锚由于其承载性能和深水中便于安装被广泛应用于海洋工程系泊系统中,如:适用于悬链式系泊系统的传统拖曳锚和适用于绷紧式系泊系统的法向承力锚。拖曳锚安装过程中涉及诸多运动特性:锚板运动方向、系缆点处拖曳力和拖曳角及运动轨迹。基于大变形有限元分析技术耦合的欧拉-拉格朗日法,并引入缆绳方程,建立起锚-缆绳-海床土耦合作用的有限元分析模型;模拟了拖曳锚在均质和线性强度黏土中的嵌入安装过程,研究了锚板运动方向、系缆点处拖曳力和拖曳角及运动轨迹等运动特性;通过与已有的有限元分析方法及理论方法进行对比,验证了该分析模型的有效性;与已有的有限元分析方法相比,提出的分析模型有效地提高了计算效率。     

法向承力锚(VLA)--一种适用于深海工程的新型系泊基础

深水系泊基础是深水系泊系统的重要组成,随着海洋油气资源开发的加速发展,深水系泊系统的关键技术成为国际海洋油气资源开发的重要研究领域.法向承力锚（VLA）是一种崭新的适用于深海油气资源开发的系泊基础形式,论文对其应用、性能特点、工作原理、安装与回收以及计算分析方法等进行了全面介绍,以期对科研人员进一步认识深水系泊系统的关键技术有所帮助,并对国内深水系泊系统的研发起到一定的借鉴作用.     

结构海床耦合系统动力分析数值模型及考察

基于改进的哈丁模型建立了结构海床耦合系统的等效线性化动力分析模型。等效阻尼比是对土体进行等效线性化分析的重要组成,论文着重对土体阻尼对结构海床耦合系统的影响效应进行了考察。接触面分离力是运用滑动库仑摩擦模型进行接触面效应模拟的重要参数,在以前的工作基础上,文中提出了新的结构-海床接触面分离力模型并进行了考察,使其更符合实际情况     

钢悬链式立管管土耦合作用的吸力效应研究

钢悬链式立管（steel catenary riser,简称SCR）的流线段敷设在海床上,在浮体运动和环境荷载作用下管线作拔出海床的上升运动时,软质海床的黏性性质将阻碍管线的拔出而表现出吸力效应。吸力的大小与管线的拔出速度和管土循环作用次数、土的重塑时间等相关。基于现有试验数据拟合得到吸力数值模型,用于改进立管动力分析程序,研究立管拔出速度和管径等对触地区吸力分布、动态响应和疲劳寿命的影响。结果表明：海床土吸力对立管触地区应力特别是弯曲应力的影响较大,二者的变化趋势相似;管径的影响主要体现在贯入深度与管径的相对大小,同一贯入速度下,管径越小则相对贯入深度越大,拔出位移与吸力也会越大,反之则越小;立管的拔出速度是影响海床吸力最大值和拔出位移的主要因素,土吸力和拔出位移随拔出速度的增大而增大,导致触地区的疲劳损伤加剧。因此,探究管土耦合作用的吸力效应及其对SCR触地区疲劳损伤的影响,可为SCR与复杂海床相互作用及工程应用提供重要参考。     

板翼动力锚水中自由下落过程数值模拟

板翼动力锚是依靠自重完成安装并靠自重和海床土的抗力来锚固的新型动力锚。板翼动力锚在水中自由下落的阻力决定了锚到达海床表面时的速度,进而直接决定了锚贯入海床中的深度以及它能提供的承载力。板翼动力锚的形状比较复杂,采用计算流体动力学的方法研究板翼动力锚的下落速度、水平位移和转角与下落位移的关系。计算结果表明:板翼动力锚的拖曳阻力系数约为0.93~1.12之间;在沉贯过程中应使加载臂与翼板共面以减少阻力;板翼动力锚的终端速度约为28 m/s。     

法向承力锚拖曳安装过程的整体模拟

法向承力锚(Vertically Loaded Plate Anchor,VLA)是一种适用于深水的新型系泊基础,它的拖曳安装过程直接决定了其系泊定位的精度和锚体的最终承载能力。综合考虑VLA锚体、锚泊线和上部船体的运动,建立了一种新的准静力整体分析模型。模型包括不断贯入海床的锚体、锚泊线(土中反悬链段和水中悬链段)和安装船体三部分,针对确定的锚泊线长度,安装船运动张紧锚泊线进行安装的过程,计算了此过程中锚体的运动轨迹、锚泊线形态和作用在船体上的锚泊线张力矢量的变化,重点分析了不同抛链长度和海床土体的参数对安装过程控制的影响,发现链长与水深之比达到5时,接近极限贯入深度。     

法向承力锚极限抗拔力特性

法向承力锚是一种新型的适用于深海工程的系泊基础,其极限抗拔力是锚在工程应用中的关键指标。尝试用两种不同的方法评估法向承力锚的极限抗拔力,其一是基于塑性上限分析理论;其二是运用非线性有限元数值方法。与已有的经验公式相比,所建立的计算模型不仅可考虑海床土性质,还能反映锚板定位(嵌入深度及角度)以及系缆力角度对锚极限抗拔力的影响。在与已有评估方法进行比较的基础上,还特别对锚板的嵌入深度、角度以及系缆力角度变化对极限抗拔力的影响规律进行了分析,对三种方法的适用性进行了评述。     

霍尔锚抛锚深度模型试验研究

河床或海床中会布设光缆、管线、隧洞等结构物,如果该水域上有船只抛锚,就要考虑抛锚对结构物安全的影响。通过模型试验探究了霍尔锚在黏土中的抛锚深度,研究了贯入速度、锚重以及土强度对抛锚深度的影响。在模型试验中,用MEMS加速度传感器捕捉锚在土中运动时的加速度,并由加速度积分得到锚的下落速度及对应的下落位移。模型试验结果表明:当霍尔锚以极限速度贯入软黏土中时,17.8 t锚在强度为7.5 k Pa土中的贯入深度为4.0 m; 42 t锚在强度为8.3 k Pa的土中贯入深度为6.7 m。根据试验结果建立了霍尔锚在土中动力贯入时的运动微分方程,分析了作用在锚上的各项受力,并预测了抛锚深度。此外,根据模型试验结果,建立了抛锚深度和锚的总能量之间的经验公式。     

新型动力安装锚水动力学特性模型试验研究

相比于已有动力锚(鱼雷锚、多向受荷锚等),新型轻质动力安装锚借助助推器安装,具有质量轻、埋深大、承载效率高、在海床中下潜容易等特点。良好的水动力学特性(较小的拖曳阻力系数及稳定的下落垂直度)是确保动力安装锚准确、有效地安装到指定地点并贯入到设计深度的前提。通过4组10个工况的模型试验,研究了轻质动力安装锚的终端速度和拖曳阻力系数,及轻质动力安装锚和助推器的组合锚在水中自由下落时的方向稳定性。试验结果表明:优化后轻质动力安装锚的拖曳阻力系数为0.51~0.55,这有助于提高组合锚在水中的下落速度,从而提升组合锚的沉贯深度;增大助推器尾翼展弦比和选用轻质材料制作尾翼能减小组合锚的下落偏角,提高组合锚的方向稳定性。     

霍尔锚在粉细砂中抛锚深度模型试验

航船应急抛锚时锚板贯入土体可能会影响河床或海床中的结构物甚者造成破坏,因此在通航频繁的航道,结构物埋深的设计需要充分考虑应急抛锚时锚板的贯入深度。本文通过缩尺模型试验模拟了霍尔锚在中等密实度粉细砂中的抛锚贯入过程,研究了不同抛锚速度(1.15～4.4 m/s)及粉细砂相对密实度(0.45～0.65)对抛锚贯入深度的影响;基于太沙基极限承载力理论和能量守恒定律,推导出霍尔锚在粉细砂土中贯入深度的表达式,与模型试验结果对比显示理论计算结果偏于保守。基于试验结果提出修正系数,修正后的理论公式能够较好地快速预测霍尔锚在中等密实度粉细砂中的贯入深度。研究结果为粉细砂土河床或海床中的结构物埋深设计提供了一定的技术参考。     

沿岸多模式GNSS三维水深测量方法研究

在沿岸水下地形测量中,高程控制是难点,在远离岸边的区域,不仅布设潮位站困难,而且潮位站水位改正的精度也难以保证,为提高沿岸水域测量的可靠性和灵活性,在河口区域的水深测量项目中进行了RTK、PPK、PPP3种模式的同步作业方式研究。结果表明,基于GNSS多模式三维水深测量的方法能有效提高水位改正的精度和可靠性。无论测区离岸距离多远,可以同步采用RTK、PPK和PPP的方式进行高程控制,这3种模式的高程测量差值均方差接近0.10m,精度能满足沿岸水域一般比例尺地形测量的高程精度要求。     

Leveling the Sea Surface Using a GPS-Catamaran

In the framework of the TOPEX/Poseidon and Jason-1 CNES-NASA missions, two probative experiments have been conducted at the Corsica absolute calibration site in order to determine the local marine geoid slope under the ascending TOPEX/Poseidon and Jason-1 ground track (No. 85). An improved determination of the geoid slope was needed to better extrapolate the offshore (open-ocean) altimetric data to on-shore tide-gauge locations. This in turn improves the overall precision of the calibration process. The first experiment, in 1998, used GPS buoys. Because the time required to cover the extended area with GPS buoys was thought to be prohibitive, we decided to build a catamaran with two GPS systems onboard. Tracked by a boat at a constant speed, this innovative system permitted us to cover an area of about 20 km long and 5.4 km wide centered on the satellites' ground track. Results from an experiment in 1999 show very good consistency between GPS receivers: filtered sea-surface height differences have a mean bias of -0.2 cm and a standard deviation of 1.2 cm. No systematic error or distortions have been observed and crossover differences have a mean value of 0.2 cm with a standard deviation of 2.7 cm. Comparisons with tide gauges data show a bias of 1.9 cm with a standard deviation of less than 0.5 cm. However, this bias, attributable in large part to the effect of the catamaran speed on the waterline, does not affect the geoid slope determination which is used in the altimeter calibration process. The GPS-deduced geoid slope was then incorporated in the altimeter calibration process, yielding a significant improvement (from 4.9 to 3.3 cm RMS) in the agreement of altimeter bias determinations from repeated overflight measurements.     

Seasonal and spatial variations of kinematic parameters of internal solitary waves in the Andaman Sea

The horizontally variable density stratification and background currents are taken into the variable-coefficent extended Korteweg-de Vries(evKdV) theory to obtain the geographical and seasonal distribution of kinematic parameters of internal solitary waves in the Andaman Sea(AS). The kinematic parameters include phase speed,dispersion parameter, quadratic and cubic nonlinear parameters. It shows that the phase speed and dispersion parameter are mainly determined by the topographic feature and ha...     

Ibiza Absolute Calibration Experiment: Survey and Preliminary Results

Within the framework of a project comprising part of the Spanish Space Program related to the JASON-1 CNES (Centre National d'Etudes Spatiales)/NASA (National Aeronautics and Space Administration) mission, a campaign was conducted from June 9–17, 2003, on the Absolute Calibration Site of the island of Ibiza. The objective was to determine the local marine geoid slope under the ascending (187) and descending (248) Jason-1 ground tracks, in order to allow a better extrapolation of the open-ocean altimetric data with on-shore tide gauge locations, and thereby improve the overall precision of the calibration process. For this we have used a catamaran with two GPS antennas onboard, following the Corsica/Senetosa design (Bonnefond et al. 2003a Bonnefond, P., Exertier, P., Laurain, O., Menard, Y., Orsoni, A., Jeansou, E., Haines, B., Kubitschek, D. and Born, G. 2003a. Leveling Sea Surface using a GPS catamaran. Marine Geodesy, 26(3–4): 319–334. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]). Five GPS reference stations were deployed in order to reduce the distance between the areas covered by the catamaran and the fixed GPS receiver used in the kinematic process. The geodetic activities (e.g., GPS, leveling) have enabled the building of a very accurate (few mm) network in a reference frame compatible with the satellite altimetry missions (ITRF 2000). The GPS kinematic data were processed using two different software programmes, allowing checking of the consistency of the solutions. If the standard deviation of the differences (3.3 cm) is close to the kinematic process precision, they exhibit some large values (up to 14 cm). These large discrepancies have been reduced using a weighting based on the crossover differences. Inasmuch as the distances between the tide gauges and the areas covered by the GPS catamaran were becoming large, we have used the MOG2D ocean model (Carrère and Lyard 2003 Carrère, L. and Lyard, F. 2003. Modelling the barotropic response of the global ocean to atmospheric wind and pressure forcing—comparisons with observations. Geophys. Res. Letters, 30(6) [Google Scholar]) to correct the sea surface from tides. In the farthest areas, the crossover differences show an improvement by a factor of two. Finally, we also present preliminary results on Jason-1 altimeter calibration using the derived marine geoid. From this analysis, the altimeter bias is estimated to be 120 ± 5 mm. The quality of this first result validates the whole GPS-based marine geoid processing, for which the accuracy is estimated to be better than 3 cm rms at crossovers.     

Leveling the Sea Surface Using a GPS-Catamaran Special Issue: Jason-1 Calibration/Validation

In the framework of the TOPEX/Poseidon and Jason-1 CNES-NASA missions, two probative experiments have been conducted at the Corsica absolute calibration site in order to determine the local marine geoid slope under the ascending TOPEX/Poseidon and Jason-1 ground track (No. 85). An improved determination of the geoid slope was needed to better extrapolate the offshore (open-ocean) altimetric data to on-shore tide-gauge locations. This in turn improves the overall precision of the calibration process. The first experiment, in 1998, used GPS buoys. Because the time required to cover the extended area with GPS buoys was thought to be prohibitive, we decided to build a catamaran with two GPS systems onboard. Tracked by a boat at a constant speed, this innovative system permitted us to cover an area of about 20 km long and 5.4 km wide centered on the satellites' ground track. Results from an experiment in 1999 show very good consistency between GPS receivers: filtered sea-surface height differences have a mean bias of ?0.2 cm and a standard deviation of 1.2 cm. No systematic error or distortions have been observed and crossover differences have a mean value of 0.2 cm with a standard deviation of 2.7 cm. Comparisons with tide gauges data show a bias of 1.9 cm with a standard deviation of less than 0.5 cm. However, this bias, attributable in large part to the effect of the catamaran speed on the waterline, does not affect the geoid slope determination which is used in the altimeter calibration process. The GPS-deduced geoid slope was then incorporated in the altimeter calibration process, yielding a significant improvement (from 4.9 to 3.3 cm RMS) in the agreement of altimeter bias determinations from repeated overflight measurements.     

基于双差动态定位的近实时潮位变化反演

基于GAMIT TRACK双差动态定位模块计算海洋潮汐.将不同基线组合下的计算结果分别与压力式验潮仪记录值比对,验证该方法的可行性和适应性;比较不同星历和基线组合的结果,得出在150km基线以内,采用IGS最终星历得到的潮位变化结果精度最高,但不具备实时性;超快速星历结果精度稍次之,可以用于实时GPS验潮;广播星历结果...     

Ocean Tides Observed from A GPS Receiver on Floating Sea Ice Near Chinese Zhongshan Station,Antarctica

Due to limit of coverage in TOPEX/Poseidon (T/P) satellite and sparseness of in-situ tide gauges around Antarctica, the accuracy of global ocean tide models in Antarctic seas is relatively poorer than in low- and mid-latitude regions. To better understand ocean tides in Prydz Bay, east Antarctica, a GPS receiver was deployed on floating sea ice to measure tide-induced ice motion in multiple campaigns. Four online Precise Point Positioning (PPP) services are used to process the GPS data in the kinematic PPP mode, and UTide software is used to separate the major tidal constituents. Comparison between results from different processing methods (relative processing solutions from Track, kinematic PPP solutions from online services) and with bottom pressure gauge (BPG) shows that, high-accuracy tidal information can be obtained from GPS observations on floating sea ice, the root-sum-square (RSS) for the eight major constituents (O1, K1, P1, Q1, M2, S2, N2, K2) is below 4 cm. We have also studied the impacts of data span and filter edge effects at daily boundaries on the accuracy of tide estimates, and found that to obtain reliable tide estimates and neglect the filter edge effects, continuous observation longer than 30 days is necessary. Our study suggests that GPS provides an independent method to estimate tides in Prydz Bay, and can be an alternative to tidal gauges, which are costly and hard to maintain in Antarctica.     

Estimation of annual variation of water vapor in the Arctic Ocean between 80°–87°N using shipborne GPS data based on kinematic precise point positioning

The measurement of atmospheric water vapor(WV) content and variability is important for meteorological and climatological research. A technique for the remote sensing of atmospheric WV content using ground-based Global Positioning System(GPS) has become available, which can routinely achieve accuracies for integrated WV content of 1–2 kg/m2. Some experimental work has shown that the accuracy of WV measurements from a moving platform is comparable to that of(static) land-based receivers. Extending this technique into the marine environment on a moving platform would be greatly beneficial for many aspects of meteorological research, such as the calibration of satellite data, investigation of the air-sea interface, as well as forecasting and climatological studies. In this study, kinematic precise point positioning has been developed to investigate WV in the Arctic Ocean(80°–87°N) and annual variations are obtained for 2008 and 2012 that are identical to those related to the enhanced greenhouse effect.     

GPS buoy and pressure transducer results from the August 1990 Texaco Harvest Oil Platform Experiment

The Texaco Harvest Oil Platform Experiment took place August 22–28, 1990, off Point Conception, California. This platform has been designated as the NASA/JPL verification site for the TOPEX radar altimeter, which is to be launched in mid‐1992. The purpose of the experiment was to obtain measurements from GPS and other instrumentation that will be used at the site for the verification activities, and to determine the potential effects of the platform environment on the quality of the measurements. In conjunction with this experiment, a buoy equipped with a GPS receiver was floated in the vicinity of the platform for the purpose of measuring sea‐level change and waves relative to a reference receiver located on the platform. A pressure transducer installed at the site also provided sea‐level change and wave measurements relative to the platform. We present the data collection, processing, and analysis results comparing the GPS‐buoy and pressure transducer data. The GPS‐determined sea‐surface height measurements show 1.3‐cm agreement when compared with transducer‐determined heights taken over the same period of time. Low‐rate (15‐s) data were used to measure the change in sea‐level height due to tides, while high‐rate (1‐s) measurements provided temporal resolution sufficient for determining wave spectra.