Effect of the sloping seabed on 3D soil-spudcan interaction using a material point-finite element(MPM-FEM)model

The sloping seabed affects the bearing capacity and failure mechanism of soil,which may compromise the stability and safety of offshore structures such as jack-up platforms.This paper employs a coupled model combining the material point method and finite element method(MPM-FEM)to analyze the impact of sloping seabeds on the three-dimensional soil-spudcan interaction.The MPM-FEM model implements the B¯approach to solve the challenge of volumetric locking due to the incompressibility constraints imposed by yield criterion.It is validated against the centrifuge results.The effects of sloping seabeds on penetration resistance,soil flow pattern,lateral response,stress distribution,and failure mechanism are discussed.The soil mainly undergoes overall failure when the ratio of penetration depth to spudcan diameter(i.e.D P/D)is between 0 and 0.25.As the slope angle increases,the soil on the side of lower slope is expelled further,resulting in an asymmetric stress distribution and a larger horizontal sliding force of soil.When D P/D increases to 0.75,the soil transitions to localized plastic flow failure,and the range of soil flow affected by the spudcan penetration decreases.The results show that,when the slope angle increases,the lateral displacement and stress distribution on the lower slope of a sloping seabed is significantly larger than that of a horizontal seabed,impacting the spudcan and surrounding soil behavior.The study suggests that the seabed slope significantly affects the range of soil flow and failure at shallow penetration,indicating that the slope angle should be taken into account in the design and installation of offshore jack-up rigs,particularly in areas with sloping seabeds.

Numerical modeling of seabed morphological effects from the construction of artificial islands in Danzhou, Hainan

Haihua Islands is a large artificial island in Danzhou, Hainan. The construction of Haihua Islands changes the hYdrodynamic environment of Yangpu waters, and further affects its morphological change. Delft3D is used to set up a two dimensional nested hydrodynamic and sediment model for Yangpu waters in this paper, and this paper focuses on simulating the velocity and morphological change due to the construction of Haihua Islands after the verification of the model. The seabed deposition is small because of low suspended sediment concentration and less sand source near Yangpu waters. The bed level erodes in the south area of Xiaochan Reef and the Yangpu channel due to the velocity increase in the area.

A Coupling Model of Nonlinear Wave and Sandy Seabed Dynamic Interaction

In the paper, a weak coupling numerical model is developed for the study of the nonlinear dynamic interaction between water waves and permeable sandy seabed. The wave field solveris based on the VOF （Volume of Fluid） method for continuity equation and the two-dimensional Reynolds Averaged Navier Stokes （RANS） equations with a k-ε closure. The free surface of cnoidal wave is traced through the PLIC-VOF （P/ecewise Linear/nterface Construction）. Blot＇s equations have been applied to solve the sandy seabed, and the u-p fmite dement formulations are derived by the application of the Galerkin weighted-residual procedure. The continuity of the pressure on the interface between fluid and porous medium domains is considered. Laboratory tests were performed to verify the proposed numerical model, and it is shown that the pore-water pressures and the wave heights computed by the VOF-FEM models are in good agreement with the experimental results. It is found that the proposed model is effective in predicting the seabed-nonlinear wave interaction and is able to handle the wave-breakwater-seabed interaction problem.

Fractional-order Maxwell model of seabed mud and its effect on surface-wave damping

A fractional-order Maxwell model is used to describe the viscoelastic seabed mud. The experimental data of the real mud well fit the results of the fractional-order Maxwell model that has fewer parameters than the traditional model. The model is then used to investigate the effect of the mud on the surface-wave damping. The damping rate of a linear monochromatic wave is obtained. The elastic resonance of the mud layer is observed, which leads to the peaks in the damping rate. The damping rate is a sum of the modal damping rates, which indicates the wave damping induced by the mud motion of particular modes. The analysis shows that near the resonance, the total damping rate is dominated by the damping rate of the corresponding mode.

Coupling model for waves propagating over a porous seabed

The wave-seabed interaction issue is of great importance for the design of foundation around marine infrastructures. Most previous investigations for such a problem have been limited to uncoupled or one- way coupled methods connecting two separated wave and seabed sub models with the continuity of pressures at the seabed surface. In this study, a strongly coupled model was proposed to realize both wave and seabed processes in a same program and to calculate the wave fields and seabed response simultaneously. The information between wave fields and seabed fields were strongly shared and thus results in a more profound investigation of the mechanism of the wave-seabed interaction. In this letter, the wave and seabed models were validated with previous experimental tests. Then, a set of application of present model were discussed in prediction of the wave-induced seabed response. Numerical results show the wave-induced liquefaction area of coupled model is smaller than that of uncoupled model.

Development of the artificial seabed technology and implementation pretrial well in the South China Sea

This paper introduces the recent highly significant activity of China Oilfield Services Ltd. （COSL） in the South China Sea, where COSL conducted pretrial drilling in June of 2008. The paper discusses some key research and new practices which led to the fabrication of related equipment which was evaluated in the trial. The market for deepwater drilling in the world has grown over the past 10 years but there are few drilling vessels or platforms suitable for drilling in deepwater or super deepwater. China needs equipment capable of deepwater drilling operations. COSL has some semisubmersible platforms, but they are only considered suitable for operations in water depths less than 475 m. An enabling technology, referred to as an artificial seabed, has been under development by COSL since 2004, and it applies the research results and experiences of many experts in deepwater drilling. COSL hopes this technology will allow drilling to depths of approximately 1 000-1 500m with its current platforms. The paper presents research progress and improvements in fabrication and necessary upgrades to equipment for extending deepwater drilling. The pretrial well was executed at a water depth of nearly 500m. COSL will drill the trial well around 2009 at the same location in the South China Sea.

Numerical investigation of non-cohesive seabed response around a mono-pile by crossing wave-current

The interaction between waves and currents in the ocean often complicates the flow field around structures.In this study,a three-dimensional integrated numerical model was established to investigate the seabed response and liquefaction around a mono-pile under different wave-current interaction angles.In the present model,the Reynolds-averaged Navier-Stokes equations were used to simulate the flow field,and the Biot's poro-elastic theory was adopted to calculate the seabed response caused by crossing wave-current loading.Unlike previous studies,the load on the mono-pile was considered,and the wave-current interaction angle was extended to 180°,which was more in line with practical engineering problems.The numerical results were in a good agreement with the experimental measurements.The results indicated that waves interacted with currents in a large angle could result in a large momentary liquefaction depth of the seabed.The parametric studies proved that the position of the front and two sides of the pile was relatively safer compared with that of the leeside of the pile,and the surface of the seabed downstream of the pile was liable to liquefy.

Nonlinear Analysis of Flexible and Steel Catenary Risers with Internal Flow and Seabed Interaction Effects

Flexible risers and steel catenary risers often provide unique riser solutions for today’s deepwater field development. Accurate analysis of these slender structures, in which there are high-speed HP/HT internal flows, is critical to ensure personnel and asset safety. In this study, a special global coordinate-based FEM rod model was adopted to identify and quantify the effects of internal flow and hydrostatic pressure on both flexible and deepwater steel catenary risers, with emphasis on the latter. By incorporating internal flow induced forces into the model, it was found that the internal flow contributes a new term to the effective tension expression. For flexible risers in shallow water, internal flow and hydrostatic pressure made virtually no change to effective tension by merely altering the riser wall tension. In deep water the internal pressure wielded a dominant role in governing the riser effective tension and furthering the static configuration, while the effect of inflow velocity was negligible. With respect to the riser seabed interaction, both the seabed support and friction effect were considered, with the former modeled by a nonlinear quadratic spring, allowing for a consistent derivation of the tangent stiffness matrix. The presented application examples show that the nonlinear quadratic spring is, when using the catenary solution as an initial static profile, an efficient way to model the quasi-Winkler-type elastic seabed foundation in this finite element scheme.

YOLOv5-Based Seabed Sediment Recognition Method for Side-Scan Sonar Imagery

Seabed sediment recognition is vital for the exploitation of marine resources.Side-scan sonar(SSS)is an excellent tool for acquiring the imagery of seafloor topography.Combined with ocean surface sampling,it provides detailed and accurate images of marine substrate features.Most of the processing of SSS imagery works around limited sampling stations and requires manual interpretation to complete the classification of seabed sediment imagery.In complex sea areas,with manual interpretation,small targets are often lost due to a large amount of information.To date,studies related to the automatic recognition of seabed sediments are still few.This paper proposes a seabed sediment recognition method based on You Only Look Once version 5 and SSS imagery to perform real-time sedi-ment classification and localization for accuracy,particularly on small targets and faster speeds.We used methods such as changing the dataset size,epoch,and optimizer and adding multiscale training to overcome the challenges of having a small sample and a low accuracy.With these methods,we improved the results on mean average precision by 8.98%and F1 score by 11.12%compared with the original method.In addition,the detection speed was approximately 100 frames per second,which is faster than that of previous methods.This speed enabled us to achieve real-time seabed sediment recognition from SSS imagery.

An Experi mental Study on Wave-Induced Dynamic Stresses in Seabed

A series of hydraulic model tests with horizontal movable seabed under regular wave actions have been carried out to investigate the dynamic interactions between water waves and seabed soil. Seabed dynamic stresses from experiments are, tound to differ from theoretical resuhs. The response of p0 in permeable seabed has a small decay and phase shift to the nonlinear wave actions, and the dynamic stresses, σs/p0, σh/p0 and u/p0, contain different phase shift characteristics. Such phenomena will strongly affect the dynamic stress path in seabed. If the phase shifts of σs. and σh are neglected, the stress path will become a straight line; otherwise, it will become an elliptical curve. In phase shift cases, the long axis of the p - q diagram will be shortened when the depth increases, and the short axis will become longer when the phase shift increases. For the p＇ - q＇ diagram, the larger the phase lag of u, the longer the short axis. Relative results offer useful information for the analysis of seabed stability.

基于Pasternak海床模型的椭圆余弦波浪荷载作用下埋置管线动力响应解析解

通过两阶段分析方法,针对椭圆余弦波作用下埋置管线的动力响应进行了探究。基于椭圆余弦波理论,采用Biot固结方程推导了非线性波浪作用下浅水区埋置管线所受的周期波浪压力;将管线考虑为动力Pasternak海床模型上的Euler-Bernoulli梁,将波浪动荷载施加到管线上获得无限长管线的动力响应偏微分控制方程;利用Fourier变换和Laplace变换并借助卷积定理得到管线挠度、速度、加速度、转角、弯矩和剪力的动力响应解。通过与三维有限元数值算例及既有试验结果对比验证了解析解的正确性与适用性。对椭圆余弦波作用下埋置管线的动力响应特性进行了敏感参数分析,结果表明:波浪高度H显著影响了波面形状与海床内波浪力大小,不同浪高下管线转角、弯矩和剪力的变化更明显,而挠度、速度和加速度响应敏感性则较低。

浅海海底浅层微小目标体高精度探测技术研究

浅海海底浅层微小目标体一般体积小、埋深较浅,且由于其材料制作上的特殊性,目前应用水声探测方法达不到较好的探测效果。本文从地声数值模拟角度出发,研究如何通过多道地震这一地声探测手段来实现对海底浅层微小目标体的高精度探测。首先,基于波动理论的高阶交错网格有限差分法实现对于微小目标体的正演模拟,探索不同激发主频、不同海底形态、不同掩埋深度情况下浅海微小目标体的地声传播响应特征,总结微小目标体在不同条件下的地声传播规律;其次,通过成像精度更高的逆时偏移技术,实现对于微小目标体的位置、形态的高精度成像。不同浅海微小目标体模型的试算结果表明,采用多道地震的地声探测手段,能够实现对于浅海微小目标体的高精度探测,探测的微小目标体成像位置准确、形态表征良好。

适合渗透海床波浪运动的三维Boussinesq型方程

为考虑孔隙介质对波浪传播变形带来的衰减效应,在渗透介质流体的控制方程中引入线性阻力、非线性阻力和惯性力。自由表面采用精确的运动学和动力学边界条件,水底边界条件采用精确的动力学边界条件,自由水体和渗透介质水体之间满足垂向速度连续、水平速度满足动量相等条件。首先推导最高空间导数为3的以两组计算速度表达的适合单层渗透海床波浪运动的三维Boussinesq型水波方程。其次,对新给出的方程进行傅里叶分析,并将方程的相速度及衰减率与Stokes线性波的解析解进行比较。在1%误差下,相对水深h_(2)/h_(1)=0.1~10,方程的解析解在无因次水深h_(1)/L<1.0(深水波长L=gT^(2)(/2π))范围内与Stokes线性波的解析解都有较好的吻合,这超过了历史文献中任一个Boussinesq型水波方程的适用范围。进而建立立面二维水槽数值模型,并利用预报-校正-迭代的有限差分方法对数值模型进行求解,在变量对时间的导数求解中选择混合四阶AdamsBashforth-Moulton格式。最后,利用数值模拟再现波浪在渗透地形上的传播变形,并与相关试验结果进行比较,二者吻合程度较高。

钢圆筒防护装置周围海床冲淤试验研究

通航区内水下油气生产系统需安装在海床下的钢圆筒防护装置内,以避免往来船舶抛锚、渔业活动等对油气开发设备产生破坏。为揭示海床下钢圆筒防护装置局部冲淤特性,同时验证工程设计方案的可靠性,基于通航区海床下水下生产系统钢圆筒防护装置,对周围土体冲淤特性开展试验研究。根据工程区域现场土样的级配资料配制现场土样,并对不同回填土质的水动力特性进行敏感性分析,得到不同回填土质临界起动流速,为工程回填材料选择提供参考。同时针对平整海床、凸出式和齐平式防护装置类型,开展模型试验研究。结果表明,基于工程场址土壤条件,在安装钢圆筒防护装置、设置回填材料等各种情况下冲淤量很小,均不会发生明显的冲淤现象。现场实测验证了设计方案冲淤试验结果的可靠性。研究结果可为海床下防护结构的设计提供参考。

海床砂土源热泵毛细管前端换热器换热性能研究

海床砂土源热泵是典型的清洁能源供能系统之一。为探究其毛细管前端换热器的换热性能,利用Matlab软件构建了换热器各个毛细管的数值传热模型,并基于该模型分析了管席不同位置处毛细管出口温度变化情况以及毛细管间距、埋深、管长对换热器换热性能的影响。模拟结果表明:当换热达到稳定时,管席顶部管和底部管的换热效果均优于中间各管的换热效果,并且毛细管间距、埋深和管长的增加有利于毛细管换热器换热性能的提升,毛细管间距从20 mm增大到60 mm时,冬夏季毛细管换热量分别增加了51.9%和17.8%,埋深从0.5 m增大到2.5 m时,冬夏季毛细管换热量分别增加了74.3%和53.9%,管长从0.5 m增大到3.0 m时,冬夏季换热量则均扩大了3.9倍。研究可为海床砂土源热泵前端换热器的设计提供理论支撑。

基于全球测深数据的中国海岸线周边海域数字水深模型融合

数字水深模型(Digital Bathymetric Models,简称“DBMs”),是近海工程建设、资源开发、环境保护等领域的重要基础地理信息数据。现有全球公开DBMs产品如GEBCO(The General Bathymetric Chart of the Oceans)、SRTM(The Shuttle Radar Topography Mission)、ETOPO(Earth Topography)等在不同海域的数据类型、数据来源和产品精度均存在差异。为利用全球测深数据和DBMs产品重建中国近海水深模型,本文提出一种基于水深分区的加权融合重建框架。首先,从5个维度(整体精度、不同水深、航线剖面、地理分区、局部细节)对比分析6种常用DBMs产品的可靠性和适用性;然后,顾及水深和地形特征对研究区进行分割和分区,并选取分区内最优DBMs产品,以最小误差为约束进行最优加权融合;最后,对融合结果进行实测值恢复、平滑滤波等后处理,形成中国海岸线周边近海海域15″分辨率高精度无缝水深模型。结果表明,融合结果相比SRTM30_PLUS、GEBCO_2022、SRTM15_V2.5.5和ETOPO_2022均方根误差降低了27%、14%、14%和13%,地形细节也得到保留,证明了该融合框架的可行性,可为多数据集大规模海底地形的融合重建和及时更新提供参考。

基于底质分类的浅海海域遥感水深反演

近年来,卫星遥感影像水深反演一直是国内外研究热点,以往的遥感影像水深反演模型多基于底质均一的条件,缺乏对混合海底底质的研究。针对此问题,本文提出基于底质分类视角的遥感影像水深反演模型。以中国海南岛周边的蜈支洲岛与附近卫星影像为试验数据,对其进行预处理与底质分类后,分别使用双向长短期记忆网络(Bi-LSTM)模型、Stumpf模型与一维卷积神经网络(1D-CNN)模型进行水深反演,分析底质分类前后水深反演结果与不同模型的水深反演结果。结果表明,不同模型在底质分类后水深反演精度均高于底质分类前水深反演精度。Bi-LSTM模型的水深反演精度最高,底质分类后遥感影像水深反演的平均绝对误差、均方根误差与决定系数分别为0.333 m、0.474 m、0.814 m,均优于对比模型。

用阴影法观察水声模型的声场

我们建立了一套用于显示模拟海底反射声场的光学系统．实验水声模型是由水－玻璃粉－玻璃－铝组成的三层模拟海底结构，声源是一个管状换能器，其轴线平行于分界面．实验用这套系统记录了从水下三个界面反射的六组波的声场图像，并且分辨出了它们各自的传播路径。从声场图像也可以得出水－玻璃粉界面、玻璃粉－玻璃界面的面波声速，玻璃粉和玻璃中的体波声速以及它们的厚度，结果与预先测出的参数符合．

深海底履带机器车建模及仿真研究

考虑深海底履带机器车的特殊工作环境、车体的特殊设计 ,建立了深海底履带机器车的动力学模型 .使用MADYMO多刚体动力学仿真软件 ,建立了深海底履带机器车结构模型 ,进行了仿真分析 .与实验结果进行了比较 .

皮影动画中人物运动的特性分析与实现

为了利用现代数字动画技术,将我国传统的皮影戏与动画有机地结合在一起,提出了利用三维动画制作软件,实现数字皮影的人物运动。首先通过对我国传统皮影人物运动的细致分析,总结传统影人的运动规律,指出传统皮影运动的特点及实现数字皮影人物运动的难点。在此基础上利用三维动画制作软件3DSMAX,建立数字皮影动画人物角色模块,以建立影人骨骼树的方法,来解决数字影人运动的难点问题。最后,实例表明了该方法的可行性。