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Physics-based and Machine learning predictions of maneuvering forces in unsteady inflow conditions 非定常流入条件下机动力的物理和机器学习预测
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6832
Rodrigo Vilumbrales Garcia, G. Weymouth, B. Ganapathisubramani
Multi-vessel coordination and controlled maneuvering through upstream wakes is important to a wide range of marine applications; from surface ships to autonomous underwater vehicles. In this work we study the predictive performance of physics-based and machine-learning (ML) models for unsteady inflow maneuvering forces using tandem flapping foils as a model system. Two physics-based approaches, one following simple quasi-steady assumptions and another that modifies classical Theodorsen, are found to perform fairly well when there are only mild interactions with the upstream wake, with minimum error levels of around 6%. However, this error increases to 40% when there is strong wake interaction. Three ML models were trained and tested; a Long Short-Term Memory (LSTM) model, a Neural Ordinary Differential Equations (NODE) model, and a Sparse Identification of Nonlinear Dynamics (SINDy) approach. We find that all three models can match the low error of the physics-based for mild inflow unsteadiness and are capable of improving the predictions in the case of strong interactions, reducing the error levels below 20%. While these ML models require substantial training data and care in choosing their meta-parameters, their predictions do prove to be more reliable for a wider range of unsteadiness conditions as well as potentially still producing human-interpretable models (in the case of SINDy), making them an interesting research direction for further study.
多船协调和通过上游尾流的控制机动对于广泛的海洋应用具有重要意义。从水面舰艇到自主水下航行器。在这项工作中,我们研究了基于物理和机器学习(ML)模型的非定常流入机动力的预测性能,使用串列扑翼作为模型系统。两种基于物理的方法,一种遵循简单的准稳定假设,另一种修改了经典的Theodorsen,当与上游尾流只有轻微的相互作用时,发现表现相当好,最小误差水平约为6%。然而,当存在强烈的尾迹相互作用时,该误差增加到40%。对三个ML模型进行了训练和测试;一种长短期记忆(LSTM)模型,一种神经常微分方程(NODE)模型,以及一种非线性动力学稀疏辨识(SINDy)方法。我们发现,这三种模型都可以匹配基于物理的低误差的温和流入不稳定,并且能够在强相互作用的情况下改进预测,将误差水平降低到20%以下。虽然这些机器学习模型在选择元参数时需要大量的训练数据和谨慎,但它们的预测确实被证明在更大范围的不稳定条件下更可靠,并且可能仍然产生人类可解释的模型(在SINDy的情况下),这使它们成为一个有趣的研究方向。
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引用次数: 0
Analysis of biomimetic stream energy device based on flapping foils 基于扑翼的仿生流能装置分析
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6841
Iro Malefaki, D. Anevlavi, K. Belibassakis
. In this work, the performance of biomimetic device that consists of including a rotating, vertically mounted, biomimetic wing, supported by an arm linked at a pivot point on the mid-chord is evaluated using a numerical model is considered and results are presented concerning the performance. Activated by a controllable self-pitching motion, the system performs angular oscillations around the vertical axis in incoming flow. The performance of the above flapping-foil, biomimetic flow energy harvester, is calculated and the results are compared against experimental data. By systematical application of the model the power extraction and efficiency of the system is presented for various cases including different geometric, mechanical, and kinematic parameters, and the optimal performance of the system is determined. Also comparisons of the calculated performance are presented against predictions for other tidal energy devices, such as the stream energy converters based on the vortex-induced angular oscillations of a cylinder.
. 在这项工作中,仿生装置的性能包括一个旋转的,垂直安装的仿生机翼,由连接在中弦枢轴点的手臂支撑,使用数值模型进行了评估,并给出了有关性能的结果。该系统由可控的自俯仰运动激活,在流入气流中围绕垂直轴进行角振荡。对所设计的扑翼型仿生流能收集器进行了性能计算,并与实验数据进行了比较。通过系统地应用该模型,给出了不同几何、力学和运动参数情况下系统的功率提取和效率,并确定了系统的最优性能。此外,还将计算的性能与其他潮汐能装置的预测结果进行了比较,例如基于涡流诱导的圆柱体角振荡的流能转换器。
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引用次数: 0
Wave calibration in numerical wave tanks using AI methods 人工智能方法在数值波槽中的波浪标定
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6826
C. Gillan, P. Schmitt, C. Finnegan
Analytical solutions for numerical wavetanks are limited presently to a simple bathymetry and third order accuracy. Furthermore, tanks are generally characterised using linear transfer functions to relate the wavemaker forcing amplitude to wave elevation at a probe located in the wavetank. This paper reports on a numerical wavetank implemented using the OpenFOAM software package. The aim of the research is to train neural networks to represent non-linear transfer functions mapping a desired wave surface-elevation time-trace at a probe to the wavemaker input required to create it.
目前数值波槽的解析解仅限于简单的测深和三阶精度。此外,储罐通常使用线性传递函数来描述位于储罐内的探头处的制波器强迫振幅与波高之间的关系。本文报道了一个用OpenFOAM软件包实现的数值波槽。该研究的目的是训练神经网络来表示非线性传递函数,将探测器所需的波面高程时间轨迹映射到创建它所需的波源输入。
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引用次数: 0
Numerical prediction of propeller induced hull pressure pulses using RANS and IDDES 基于RANS和IDDES的螺旋桨诱导船体压力脉动数值预测
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6860
M. Ge, U. Svennberg, R. Bensow
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引用次数: 1
Stability and transition of the wake of a hydrokinetic axial-flow turbine 水动轴流式涡轮尾迹的稳定性和转捩
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6797
A. Posa, R. Broglia
A Large-Eddy Simulation study is reported on the wake generated by the rotor of an axial-flow hydrokinetic turbine. The resolution of the computational grid, composed of about 1.9 billion points, enabled us to capture in detail the phenomena of instability of the tip vortices, including long-wave and short-wave instabilities and mutual inductance. We found that these phenomena trigger the process of wake recovery, starting when the coherence of the tip vortices is lost. This allows the free-stream momentum to penetrate into the wake core via both radial inward flows and turbulent mixing.
本文对轴流式水轮机转子尾迹进行了大涡模拟研究。由约19亿个点组成的计算网格的分辨率使我们能够详细地捕捉到尖端涡的不稳定现象,包括长波和短波不稳定以及互感。我们发现这些现象触发了尾迹恢复过程,从叶尖涡的相干性丧失开始。这允许自由流动量通过径向向内流动和湍流混合穿透尾流核心。
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引用次数: 0
Geometric Convolutional Neural Networks – A Journey to Surrogate Modelling of Maritime CFD 几何卷积神经网络-海事CFD代理建模之旅
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6838
Asad Abbas, A. Rafiee, M. Haase, A. Malcolm
. Computational Fluid Dynamics (CFD) has become an indispensable tool in the field of engineering design evaluation and optimisation. Existing numerical simulation methods are computationally expensive, memory demanding and time-consuming, thus limiting design space exploration and forbid generative design. In order to overcome these challenges, we propose a deep learning based surrogate modeling in-lieu of CFD simulations. Our proposed framework can predict flow fields (e.g pressure field) on the surface of the geometry as well as any overall scalar parameters (e.g drag force) given a three-dimensional shape input. It can also provide uncertainty quantification over predictions. Finally, we demonstrate that our proposed surrogate modelling does not require pre-processing of the input geometry and also outperforms state-of-the-art models in prediction accuracy. When comparing a dataset on aerodynamic drag of car geometries, we show that our model reduced the error standard deviation by a factor of ≈ 2 . 5 compared to a Gaussian Process-based surrogate model.
. 计算流体力学(CFD)已成为工程设计评估和优化领域不可或缺的工具。现有的数值模拟方法计算量大、内存要求高、耗时长,限制了设计空间的探索,不利于生成式设计。为了克服这些挑战,我们提出了一种基于深度学习的代理模型来代替CFD模拟。我们提出的框架可以预测给定三维形状输入的几何表面上的流场(例如压力场)以及任何整体标量参数(例如阻力)。它还可以为预测提供不确定性量化。最后,我们证明了我们提出的代理模型不需要对输入几何形状进行预处理,并且在预测精度方面也优于最先进的模型。当比较汽车几何形状的空气动力学阻力数据集时,我们发现我们的模型将误差标准差降低了≈2。5与基于高斯过程的代理模型相比。
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引用次数: 2
Numerical and experimental investigation of the integrated system of floating wind and wave energy converters 浮动式风波能转换器集成系统的数值与实验研究
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6776
Ling Wan
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引用次数: 0
CFD verification and validation of added resistance and seakeeping response in regular oblique waves with varying wave length 变波长规则斜波附加阻力和耐波性响应的CFD验证与验证
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6786
H. Mikkelsen, Yanlin Shao, Jens Honoré Walther
The importance of CFD is increasing in marine hydrodynamics in studying seakeeping and added resistance of ships. While extensive numerical studies have been reported for various ships in head seas in the literature, much fewer CFD studies are found for oblique waves, which in practice is very important in, for instance, estimating required power and manoeuvrability of ships in realistic sea states. In this paper, the added resistance and motion responses for the KCS container ship in regular waves are studied and validated systematically for five wave headings and six wavelengths using CFD. The ship is free to heave, pitch, and roll. Implementations to the commercial CFD code are made to fix the yaw and surge motions. Extensive verification of the CFD model finds the estimated spatial and temporal discretization errors to be less than 5 %. Results of the verified CFD model are compared with up to three sets of experimental data sets, Potential Flow (PF) and existing CFD results from the literature. In general, the present CFD results show significantly better agreement with the experiments than previously published CFD results. The agreement between the present CFD model and experiments is better for the headings, where the uncertainties of the experiments are smallest. Present CFD results confirm previous published numerical findings that the experimental roll motion is excessive for the 45 ◦ heading. and validation of seakeeping responses and added resistance of the KCS container ship in regular oblique waves by using a CFD approach with turbulence modelling. Convergence studies of both the temporal and spatial discretization errors are presented. Discussions are made to determine affordable time steps and mesh sizes while to keep the discretization errors acceptable. The yaw and surge motions are constrained by user-implementations in the commercial software, which consist of additions of springs and concentrated forces/moment to cancel the fluid forces and moments. The mesh and time step convergence studies shows that the sum of the spatial and temporal discretization errors for an affordable calculation is less than 5 %, which is smaller than the average standard deviation of the experiments by (Sanada et al., 2021). A study of
在海洋流体力学中,CFD在研究船舶的耐波性和附加阻力方面的重要性日益增加。虽然文献中对各种船舶在首海中进行了大量的数值研究,但对斜波进行的CFD研究却少得多,而斜波在实际中非常重要,例如,在实际海况中估计船舶所需的功率和机动性。本文利用CFD对KCS集装箱船在规则波中5个波头、6个波长的附加阻力和运动响应进行了系统研究和验证。这艘船可以自由地颠簸、倾斜和翻滚。实现了商业CFD代码来固定偏航和浪涌运动。对CFD模型的广泛验证发现,估计的空间和时间离散误差小于5%。将验证的CFD模型的结果与多达三组实验数据集、势流(PF)和现有文献中的CFD结果进行了比较。总的来说,本文的计算结果与实验结果的吻合程度明显优于先前发表的计算结果。对于试验不确定度最小的船首,计算模型与试验结果吻合较好。目前的CFD结果证实了先前发表的数值研究结果,即实验滚转运动对于45◦航向是过度的。并利用CFD方法和湍流模型验证了KCS集装箱船在规则斜波中的耐波响应和附加阻力。给出了时间离散误差和空间离散误差的收敛性研究。讨论了确定可承受的时间步长和网格尺寸,同时保持可接受的离散误差。偏航和浪涌运动由用户在商业软件中实现的约束,其中包括添加弹簧和集中力/力矩来抵消流体力和力矩。网格和时间步收敛研究表明,可负担计算的空间和时间离散化误差之和小于5%,小于(Sanada et al., 2021)实验的平均标准差。的研究
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引用次数: 4
Numerical studies of offshore performance of floating protective barriers in waves and currents 波浪和海流中浮式防护屏障近海性能的数值研究
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6844
A. Knysh, John W. Coyle, J. Decew, Andrew Drach, M. Swift, I. Tsukrov
Finite element modeling was applied to evaluate the performance of Triton® floating protective barrier designed by HALO Maritime Defense Systems (US) and used to provide essential protection to critical governmental, commercial, and private assets vulnerable to water-borne intrusion, such as liquefied natural gas terminals, tankers, etc. The numerical model created with Hydro-FE software was validated by physical tests and field deployment observations. Physical tests of a scaled barrier model were conducted in Chase Ocean Engineering Laboratory wave tank at the University of New Hampshire to measure response of the structure and its mooring to different single-frequency waves directed parallel and normal to the model. The field deployment of the full-scale barrier performed south-southwest of White Island, Isles of Shoals, New Hampshire, provided information on its dynamic behavior under monitored environmental conditions. Good correspondence between numerical, physical and field studies was observed. The validated numerical model of the barrier was then used to investigate its performance and seaworthiness in other current and wave conditions with different mooring pretension scenarios.
有限元建模应用于评估由HALO海事防御系统(美国)设计的Triton®浮动防护屏障的性能,并用于为易受水性入侵的关键政府,商业和私人资产提供必要的保护,如液化天然气终端,油轮等。利用Hydro-FE软件建立的数值模型通过物理测试和现场部署观察得到了验证。在新罕布什尔大学的Chase Ocean Engineering Laboratory波浪槽中对一个比例屏障模型进行了物理测试,以测量结构及其系泊对与模型平行和垂直的不同单频波的响应。在新罕布什尔州的White Island, Isles of Shoals的西南偏南进行了全尺寸屏障的现场部署,提供了在监测环境条件下其动态行为的信息。在数值、物理和实地研究之间观察到良好的对应关系。然后,利用验证的数值模型,研究了在其他水流和波浪条件下,不同系泊预张力情况下,屏障的性能和适航性。
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引用次数: 0
Analysis of a floating wave energy converter interaction with waves using the Overset framework 利用Overset框架分析浮波能量转换器与波浪的相互作用
Pub Date : 2022-01-31 DOI: 10.2218/marine2021.6791
G. Barajas, Javier L. Lara, B. Di Paolo, I. Losada
. The aim of this work is to validate and analyze with the numerical model OpenFOAM, the nonlinear interaction of a WEC under regular waves using the Overset framework. Previous techniques, such as deforming grid approaches, present problems to handle large body motions when modelling wave-structure interactions. Therefore, by means of the Overset mesh technique, the interaction of a moored floating wave energy converter in free and moored decay tests and under regular waves are analyzed. Numerical results are compared with experimental data for validation and discussed. MooDy Library is used to compute the mooring restraints.
. 本工作的目的是利用Overset框架对规则波下WEC的非线性相互作用进行数值模型OpenFOAM验证和分析。以前的技术,如变形网格方法,在模拟波-结构相互作用时,在处理大的身体运动方面存在问题。因此,采用超置网格技术,分析了系泊浮波能量转换器在自由和系泊衰减试验以及规则波下的相互作用。将数值结果与实验数据进行了比较,并进行了讨论。穆迪库用于计算系泊约束。
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引用次数: 1
期刊
The 9th Conference on Computational Methods in Marine Engineering (Marine 2021)
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