Simulation of Ship-wave-ice Interactions in the Arctic

Global climate change is presenting opportunities for new networks of maritime transportation through the Arctic. However, these sea routes are often infested by floating sea ice, which brings uncertainties to shipping operators, designers and builders. This work aimed to develop reliable simulation approaches for shipping scenarios in the presence of sea ice and investigate the associated changes to ship calm water resistance. For this purpose, computational fluid dynamics and ice solid mechanics were combined to model the potential ship-wave-ice interactions. Specifically, models were developed to simulate the two primary scenarios of a cargo ship operating in the Arctic, respectively a waterway with floating ice floes and an open-water channel created by icebreakers. Additionally, to build understanding of the Arctic sea condition, two other models were developed simulating the interaction of ocean waves with a rigid ice floe and then an elastic ice sheet, which provided a new solver capable of modelling hydroelastic fluid-structure interactions. Based on validation against experiments, these models provided the ability to accurately predict the ship-wave-ice interactions and the ice-induced resistance changes. Through conducting a systematic series of simulations, it was found that ice floes can increase the ship resistance by the same order of magnitude as the open water resistance, but this is strongly dictated by the ship beam, ice concentration, ice thickness and floe diameter. An open-water ice channel was found to increase the ship resistance by up to 15% compared to the situation without ice, particularly when the channel width is less than 2.5 times the ship beam and the ice thickness is greater than 5% of the ship draught. Moreover, this work developed a procedure to derive simple ice-resistance equations from the simulation results, enabling fast prediction of ship fuel consumption in sea ice fields and incorporation into a new Arctic Voyage Planning Tool

A Review of Computational Simulation Methods for a Ship Advancing in Broken Ice

Apart from breaking level ice, polar ships can interact with broken ice in various scenarios. In recent years, computational simulation models have increasingly been used for the evaluation of ship operability under broken ice conditions, presenting some challenging issues. This paper reviews existing simulation methods used to estimate ship performance and ice loads for ships advancing continuously in broken ice fields. Models for different types of broken ice, including ice floes, ice ridges, brash ice, and sliding ice pieces, are reviewed separately. A ship’s response in broken ice is divided into two categories: resistance, which relates to the overall ship performance, and local loads, which relates to structural safety. This review shows that most existing models are proposed for unbreakable ice particles, which are only applicable to broken ice of small size; most models treat fluid flow with extensive simplification, which does not reflect the influence of a ship’s wake or bow waves, and most models are aimed at resistance estimation, adopting elastic or viscoelastic contact models which do not include ice crushing. As for future work, it is suggested that more effort should be assigned to simulating a ship’s interaction with ice ridges and sliding ice pieces, the modelling of breakable ice floes, and the coupling of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). More attention to the local ice load estimation is also encouraged

Topology optimisation of offshore wind turbine jacket foundation for fatigue life and mass reduction

Offshore wind turbines are frequently regarded as a pricey source of electricity, and efforts are being made to lower both capital and operational costs by developing lighter and more robust structures. This paper presents a topology optimisation method to obtain a novel jacket foundation design by finding the optimum load path on the structure. The OC4 jacket model was computationally simulated considering the Aero-Hydro-Servo-Elastic loads, and the topology optimisation method was used to obtain a series of new designs. The structural optimisation is performed based on the dynamic response of the jacket, whilst restrained by relevant international design standards. In particular, time-domain fatigue simulations were performed to assess the structural integrity of the topology-optimised jacket for the first time. As a result, a range of optimised models with various thickness and diameter options are presented, which are shown to be rational and verify the optimisation procedure. The structural performance of the optimised geometry demonstrates the original jacket foundation is conservative, and the selection of optimised geometry achieved a mass reduction of 35.2% and simultaneously realised a 37.2% better fatigue life. The overall optimisation procedure and results provide useful practicalities for the design of offshore wind turbine foundations and potentially facilitate the structural integrity and cost reduction of the relevant industry

Waves and structural strain induced by a uniform current flow underneath a semi-infinite floating solar coverage

Floating solar panels installed on water reservoirs will be an increasingly popular renewable energy scenario. However, a significant current flow will occur when the reservoir gate is open to release water. Such a current flow can cause complex fluid-structure interaction at the edge of the solar panels, reversely analogized to a ship advancing through calm water, signifying the generation of a stern wave. This wave can damage the solar panels, which needs to be investigated to ensure operational safety. In this context, the present paper analyzes a mixed boundary problem of a uniform flow passing through a two-dimensional semi-infinite elastic plate using an analytical approach—the Wiener-Hopf technique. The mathematical model is based on the linearized velocity potential for fluid flow and the Kirchhoff-Love plate theory for an elastic plate. Three different edge conditions are considered here, namely, clamped, simply supported, and free. Extensive results and discussions are provided for the amplitudes of the propagation wave, and principal strain in the elastic thin plate. In particular, significant “resonance” fluid-structure interactions are found when the current speed is at certain special magnitudes. To support straightforward industrial applications, these special flow rates are given as a water depth Froude number. Overall, this study can provide valuable insights for floating solar projects on water reservoirs to control the water-release rate, thus minimizing the potential structural problems.L.H. acknowledges grants received from Innovate UK (No. 10048187, 10079774, 10081314), the Royal Society (IEC\ NSFC\ 223253, RG\R2\232462), and UK Department for Transport (TRIG2023 – No. 30066).Physical Review Fluid

Energy efficiency analysis of a deformable wave energy converter using fully coupled dynamic simulations

Deformable wave energy converters have significant potential for application as flexible material that can mitigate structural issues, while how to design the dimensions and choose an optimal deployment location remain unclear. In this paper, fully coupled computational fluid dynamics and computational solid mechanics were used to simulate the dynamic interactions between ocean waves and a deformable wave energy converter. The simulation results showed that the relative length to wave, deployment depth and aspect ratio of the device have significant effects on the energy conversion efficiency. By calculating the energy captured per unit width of the device, the energy efficiency was found to be up to 138%. The optimal energy conversion efficiencies were achieved when the structure length was 0.25, 0.5 or 0.75 of the dominating wavelength and submerged at a corresponding suitable depth. The aspect ratio and maximum stress inside the wave energy converter showed a nonlinear trend, with potential optimal points revealed. The simulation approach and results support the future design and optimisation of flexiable wave energy converters or other marine structures with notable deformations

Recent advances in mechanical analysis and design of dynamic power cables for floating offshore wind turbines

This review paper presents a comprehensive analysis of the mechanical design and analysis of dynamic power cables for marine renewable energy applications, focusing on research from the last two decades. The review covers key aspects such as mechanical properties, failure mechanisms, fatigue analysis, experimental studies, local cable analysis, and global load analysis. The study aims to provide a concise summary of the state-of-the-art, identifying recent advancements and research gaps in the field. The methodology involves a systematic review of relevant literature, including journal articles, conference papers, and industry reports. The findings are synthesised to provide insights into the current understanding of power cable design and analysis, as well as to highlight areas requiring further research and development. The review is intended to serve as a valuable resource for researchers, engineers, and stakeholders in the marine renewable energy sector, contributing to the development of more reliable and cost-effective dynamic power cable solutions.Ocean Engineerin

Floating solar power loss due to motions induced by ocean waves: An experimental study

Whilst there is an interest in floating solar energy systems in coastal and offshore regions to utilise available sea space, they are subject to ocean waves that introduce constant momentum. Consequently, solar panels undergo periodic motions with the waves, causing a continuous change in tilt angle. The tilt angle variation is a sub-optimal process and leads to a loss of energy harnessing efficiency. To investigate this phenomenon, the present study innovatively installed a solar simulator on top of a wave tank. The solar simulator was used to generate high-strength light beams, under which, a floating solar unit was subject to periodic incident waves. Wave-induced motions to the solar system as well as the output power were measured. A systematic analysis of the results indicated that a floating solar unit can have significantly lower power output in waves, compared to its calm-water counterpart. An evident link was established between the wave-induced power loss and the wave-induced rotational movement of the panel. An empirical equation was derived which shows the power loss is predictable through the rotational amplitude. The results also highlight the importance of implementing wave attenuation technologies such as breakwaters to minimise wave-induced motions to floating solar systems. Overall, this research presents a novel experimental approach to assess the difference of floating solar power in ocean-wave versus calm-water scenarios, providing valuable insights for future solar projects on the ocean

Towards a full-scale CFD guideline for simulating a ship advancing in open water

Computational Fluid Dynamics (CFD) simulations of a ship’s operations are generally conducted at model scale, but the reduced scale changes the fluid behaviour around the ship. Whilst ideally ship simulations should be run directly at full scale, a guide has not been published to advise on the suitable setups that can provide accurate results while minimizing the computational cost. To address this, the present work explores an optimal approach for full-scale ship simulations. Extensive sensitivity studies were conducted on relevant computational setups to investigate their influences on the prediction of ship resistance, ship-generated waves as well as the boundary-layer flow of the hull. A set of CFD setups for full-scale ship simulations in open water was recommended. It was demonstrated that the ideal Y+ and Courant numbers in full scale are evidently different from those given in current model-scale CFD guidelines, indicating the necessity to establish full-scale CFD guidelines separately

Fluid-structure interaction of a large ice sheet in waves

With global warming, the ice-covered areas in the Arctic are being transformed into open water. This provides increased impetus for extensive maritime activities and attracts research interests in sea ice modelling. In the polar region, ice sheets can be several kilometres long and subjected to the effects of ocean waves. As its thickness to length ratio is very small, the wave response of such a large ice sheet, known as its hydroelastic response, is dominated by an elastic deformation rather than rigid body motions. In the past 25 years, sea ice hydroelasticity has been widely studied by theoretical models; however, recent experiments indicate that the ideal assumptions used for these theoretical models can cause considerable inaccuracies. This work proposes a numerical approach based on OpenFOAM to simulate the hydroelastic wave-ice interaction, with the Navier-Stokes equations describing the fluid domain, the St. Venant Kirchhoff solid model governing the ice deformation and a coupling scheme to achieve the fluid-structure interaction. Following validation against experiments, the proposed model has been shown capable of capturing phenomena that have not been included in current theoretical models. In particular, the developed model shows the capability to predict overwash, which is a ubiquitous polar phenomenon reported to be a key gap. The present model has the potential to be used to study wave-ice behaviours and the coupled wave-ice effect on marine structures.Comment: 23 pages 9 figures, submitted journal pape