Subsea Cables Research Articles

Combined layout and cable optimization of offshore wind farms

Reducing wind energy costs is a crucial goal to promote renewable energy and reduce dependencies on fossil fuels, both to fight climate change and to increase energy independence. Two main optimization problems arise during the design of offshore wind farms: the Wind Farm Layout Optimization (WFLO) problem and the Wind Farm Cable Routing (WFCR) problem. The goal of WFLO is to find the optimal turbine locations within a given area to maximize revenues from energy production minus construction costs. The goal of WFCR is to minimize the costs of subsea cables that transfer the electricity produced by turbines. Traditionally, the two NP-hard problems have been studied separately and are solved sequentially, despite being strongly related. The output of WFLO defines the input to WFCR, and their goals are opposing: while larger distances between turbines have a positive effect on WFLO due to reduced wake losses, they negatively impact the cable costs in WFCR. Hence, we study the combined optimization problem, unifying the two problems. We propose a novel heuristic that uses a combined local search to modify solutions of WFLO and WFCR simultaneously. While the combined approach is more computationally demanding than the sequential approach, the proposed method solves industry-scale problems and improves up to 12 million Euro the Net Present Value (NPV) of wind parks, particularly when the energy density is low. Furthermore, the combined approach reduces the up-front investment costs by up to 10%, significantly reducing investment risks, and enabling a faster expansion of wind energy.

Ground-Return Parameters of Submarine Cables Buried in the Seabed

The computation of sea/seabed-return distributed parameters of subsea cables is a relevant topic due to the growing importance of submarine connections. This article presents for the first time new formulas for the computation of self and mutual ground impedances and admittances for submarine cables buried in the seabed. The original theory developed by Sunde is applied to a three-media model with air, sea, and seabed. Referring to the practical installation practice of the Italian transmission system operator Terna S.p.A., we compare the prediction of the available models and assess the effect of the different approximations on the computation of the per unit length ground parameters. Finally, we define the limits of applicability of the available models that differ in accuracy and complexity.

Advances in Marine Intelligent Electromagnetic Detection System, Technology, and Applications: A Review

This paper introduces the current state of the art in marine intelligent electromagnetic detection sensors, systems and platforms for the detection and health monitoring of offshore structures, especially for subsea cables and pipelines. The presented survey is by no means exhaustive, but introduce some notable results and relevant techniques in the detection and inspection of marine structure electromagnetic monitoring fields. Particularly, this paper presents a review of the main research works focusing on electromagnetic detection techniques and intelligent marine vehicles for subsea cables. The marine electromagnetic exploration techniques are elaborated as active and passive detections based on different electromagnetic field generation and sensing principles. The pulse induction-based detection method for subsea ferromagnetic lines detection, transient and controlled-source electromagnetic systems in marine geological fields under the category of active detection approach, are reviewed. According to the classical applications on subsea cable-like target inspection, the passive detection approach is detailed classified as crisscrossing detection and along-tracking detection, which are characterised by different trajectories of detection vehicles. Finally, the paper discusses the marine electromagnetic detection techniques in general and highlights challenges that need to be addressed in developing detection vehicles with lower electromagnetic noises and advanced autonomy on carrying out detection missions.

Subsea Cables as Enablers of a Next Generation Global Ocean Sensing System

The ocean is vast, complex, and increasingly threatened by human activities. There is an urgent need to find complementary ways to gather extensive information and promote the comprehensive understanding and management of the ocean. In addition, as coastal populations grow, these regions are becoming more vulnerable to hazardous natural events. The global network of subsea cables provides an opportunity to support a holistic ocean observation system, in particular, to anticipate and provide warning about hazards and to prepare responses to catastrophic events. Large-scale and widespread ocean monitoring may also enable the oversight and tracing of global phenomena that have local impacts.

Numerical Simulation of a Three-dimensional Subsea Cable with Buoyancy Module

Extreme formation of slacks and entanglement with risers induced from a small diameter and high structural flexibility of subsea cable is often being a huge challenge in subsea cable installation. In many cases, the cable is prone to breaking, bending, or twisting due to the rough and dynamic underwater condition. One of the alternatives is the use of buoyancy module to facilitate the cable installation and to reduce cable tension and false slacks. This paper proposes reliable three-dimensional mathematical model and simulation to specifically investigate the behaviour of subsea cable with buoyancy module during laying operation. A finite difference method (FDM) and optimization algorithm is used to discretize the formulation and simulate this type of subsea cable problem concerning on the tensional analysis. The methodology is specifically designed to allow cable configuration to be changed over time as a result from the buoyancy module. The viability subsea cable configuration with existence of buoyancy module has been showed successfully reduce the cable tension especially at the hang-off section.

SMART Cables Observing the Oceans and Earth

Abstract The Joint Task Force, Science Monitoring And Reliable Telecommunications (SMART) Subsea Cables is working to integrate environmental sensors (temperature, pressure, seismic acceleration) into submarine telecommunications cables. This will support climate and ocean observation, sea-level monitoring, observations of Earth structure, tsunami and earthquake early warning, and disaster risk reduction. Recent advances include regional SMART pilot systems that are the initial steps to trans-ocean and global implementation. Building on the OceanObs'19conference and community white paper (<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.3389/fmars.2019.00424">https://doi.org/10.3389/fmars.2019.00424</ext-link>), this paper presents an overview of the initiative and a description of ongoing projects including: InSea wet demonstration project off Sicily; Vanuatu and New Caledonia; Indonesia; CAM-2 ring system connecting the Portuguese mainland, Azores, and Madeira; New Zealand; and Antarctica. In addition to the diverse scientific and societal benefits, the telecommunications industry's mission of societal connectivity will also benefit because environmental awareness improves both individual cable system integrity and the resilience of the overall global communications network.

Fluid–Structure Interaction Analysis and Verification Test for Soil Penetration to Determine the Burial Depth of Subsea HVDC Cable

Recently, there have been frequent reports of subsea cable breakage accidents caused by the drop of an anchor pile for aquaculture works involving subsea cables for high-voltage direct current (HVDC) transmission embedded in the southwest sea of Korea. To determine the burial depth that can ensure the safety of subsea HVDC cables embedded under the seabed from the drop of anchor files, the soil penetration characteristics of anchor piles should be reasonably estimated. In the present study, the penetration characteristics of anchor piles into the soil under which subsea HVDC cables are embedded were evaluated using numerical simulations and field verification tests. The numerical simulation for the soil penetration phenomena of anchor piles was carried out using the fluid–structure interaction analysis method using the general purpose nonlinear finite element analysis code based on explicit time integration. Regarding the soil into which anchor piles penetrate, three types of soil—a clay layer, a sand layer, and a clay–sand mixed layer—were considered, which are the representative soil types in the southwest sea of Korea, where many subsea HVDC cables have been embedded. The result of fluid–structure interaction analysis showed that the maximum penetration into the clay layer was higher than that into the sand layer and the clay–sand mixed layer by 86.3% and 36.4% or more, respectively. The error rates of the field verification test and the fluid–structure interaction analysis were found to be 9.8%, 2.4%, and 2.4% in the clay layer, the sand layer, and the clay–sand mixed layer, respectively, which were found to be reasonable levels when considering that it was the numerical simulation for the soil penetration of an anchor pile resulting from drop impacts. The penetration depths of anchor piles were found to be the deepest in the clay layer, showing values of 3.9 to 4.1 m, and those in the sand layer were the shallowest, showing values of 1.9 to 2.1 m.

New developments in submarine cable technology can facilitate acoustics in Polar regions and on the global scale

The subsea telecommunications cable industry is expanding their present single purpose infrastructure to include ocean observing capability. Science Monitoring And Reliable Telecommunications (SMART) Subsea Cables is working to integrate temperature, pressure, and seismic acceleration sensors into commercial cables (∼70 km spacing) to support climate and ocean observation, sea level monitoring, and tsunami and earthquake early warning on the global scale. Furthermore, telecom rated branching cables with power feed units supporting multipurpose “nodes” are becoming a reality. Acoustic capability can be integral to both. Major uses of these nodes include supporting low frequency transceivers enabling basin scale tomography and geo-positioning of mobile assets and docking for autonomous undersea vehicles (AUVs). Enabled by cabled power, these would be part of the fixed/mobile acoustic tomography system measuring ocean heat content at the speed of sound and more generally for transporting energy, data, and acquiring multidisciplinary data throughout a large volume of the ocean. Both variants and hybrids between can support the necessary acoustics contribution to ocean observing. Two proposed systems can support polar applications: Far North Fiber Express connecting Norway/Finland/Ireland with Japan via the Canadian Northwest Passage, and the NSF proposed SMART cable connecting New Zealand with McMurdo Base, Antarctica.

Analysis of the first onshore wind farm installation near the Morocco-United Kingdom green energy export project

Morocco put an enthusiastic plan aim to develop its energy resources to meet the expanding local demand each year. Morocco's vision for 2030 gives a central role to the development of renewable energies in the light of increasing the investment in clean energy by reducing the reliance on oil and its derivatives. This article analyzes the wind energy potential in the Tiznit province with 24-years wind speed data at a height of 10 m using two-parameter Weibull distribution with the intention of developing this desert region that suffers from long dry seasons and poor developed energy resources. The choice of this province is justified by the benefit of the inauguration of a large renewable energy project, between Morocco and the United Kingdom, for the export of green energy using four subsea cables HVDC, each 3800 km long. This cable will follow the shallow water route from the Moroccan site (Guelmim-Oued Noun) to a grid location in Great Britain (Alverdiscott in Devon), passing through Spain, Portugal and France. The main advantage of this location is a significant reduction in maintenance costs and other costs associated with wind energy in the region. The results proved that the development of the onshore wind sector in the Tiznit province is beneficial. Wind speed and energy density were calculated on a monthly average. The performance indicators used in the analysis showed that the VESTAS V82-0.9 MW-70 m wind turbine, among the four technologies selected, provided the best capacity factor of 36.91 % and an annual power production of 3.0 GWh. Based on the Present Value Cost method, the economics aspects was discussed. As a result, the production cost in the Tiznit province for one kWh is 3.8 US cent.

Magnetic fields produced by subsea high-voltage direct current cables reduce swimming activity of haddock larvae (Melanogrammus aeglefinus).

High-voltage direct current (HVDC) subsea cables are used to transport power between locations and from/to nearshore and offshore facilities. HVDC cables produce magnetic fields (B-fields) that could impact marine fish. Atlantic haddock (Melanogrammus aeglefinus) is a demersal fish that is at risk of exposure to anthropogenic B-fields. Their larvae drift over the continental shelf, and use the Earth's magnetic field for orientation during dispersal. Therefore, anthropogenic magnetic fields from HVDC cables could alter their behavior. We tested the behavior of 92 haddock larvae using a setup designed to simulate the scenario of larvae drifting past a B-field in the intensity range of that produced by a DC subsea cable. We exposed the larvae to a B-field intensity ranging from 50 to 150 µT in a raceway tank. Exposure to the B-field did not affect the spatial distribution of haddock larvae in the raceway. Larvae were categorized by differences in their exploratory behavior in the raceway. The majority (78%) of larvae were nonexploratory, and exposure to the artificial B-field reduced their median swimming speed by 60% and decreased their median acceleration by 38%. There was no effect on swimming of the smaller proportion (22%) of exploratory larvae. These observations support the conclusion that the swimming performance of nonexploratory haddock larvae would be reduced following exposure to B-field from HVDC cables. The selective impact on nonexploratory individuals, and the lack of impact on exploratory individuals, could have population-scale implications for haddock in the wild.

Modelling and analysis of offshore energy hubs

Clean offshore energy hubs may become pivotal for efficient offshore wind power generation and distribution. In addition, offshore energy hubs may provide decarbonised energy supply for maritime transport, oil and gas recovery, and offshore farming, while also enabling conversion and storage of liquefied decarbonised energy carriers for export. In this paper, the role of offshore energy hubs is investigated in the transition of an offshore energy system towards zero-emission energy supply. A mixed-integer linear programming model is developed for investment planning and operational optimisation to achieve decarbonisation at minimum cost. We consider offshore wind, solar, energy hubs and subsea cables. A sensitivity analysis is conducted on CO2 tax, CO2 budget and the capacity of power from shore. The results show that: (a) a hard carbon cap is necessary for stimulating a zero-emission offshore energy system, (b) offshore wind integration and power from shore can more than halve current emissions, but offshore energy hubs with storage may be necessary for zero-emission production, and (c) at certain CO2 tax levels, the system with offshore energy hubs can potentially reduce CO2 emissions by 49% and energy losses by 10%, compared to a system with only offshore renewables, gas turbines and power from shore.

Hydrodynamic forces on subsea cables immersed in wave boundary layers

This paper investigates the hydrodynamic forces on small-diameter cables (50 mm ≤ D ≤ 200 mm) under wave conditions. A total of 87 experimental tests are conducted in the parameter ranges of 20 ≤ KC ≤ 2000, 10 4 ≤ Re p ≤ 10 5 , 10 ≤ β ≤ 1 000 and 0.001 < k s / D ≤ 2.6, where KC is the Keulegan–Carpenter number, Re p is the Reynolds number defined with the cable diameter and peak freestream velocity, β is the Stokes number and β = Re p / KC , and k s / D is the ratio between the seabed roughness and cable diameter. The results show that wave boundary layers significantly affect the forces on cables in contact with the seabed. The variations in the force coefficients with the governing parameters of KC and k s / D are interpreted based on the characteristic wave boundary layer features, namely, velocity deficit (reduction) and wall turbulence. Two counteracting mechanisms influence the force coefficients: velocity reduction in the wave boundary layer decreases the force coefficients, whereas strong wall turbulence from the seabed increases the force coefficients. Empirical formulas for evaluating the force coefficients of an on-bottom cable immersed in a wave boundary layer are proposed based on the present results. • A more accurate and economic design method is proposed to quantify the hydrodynamic forces on power transmission cables under waves. • In this method, the effects of KC , k s / D and Re p are quantified. • The influences of wave boundary layers on cable hydrodynamics are made clear.

Magnetic fields generated by the DC cables of offshore wind farms have no effect on spatial distribution or swimming behavior of lesser sandeel larvae (Ammodytes marinus)

In the North Sea, the number and size of offshore wind (OW) turbines, together with the associated network of High Voltage Direct Current (HVDC) subsea cables, will increase rapidly over the coming years. HVDC cables produce magnetic fields (MFs) that might have an impact on marine animals that encounter them. One of the fish species that is at risk of exposure to MF associated with OW is the lesser sandeel (Ammodytes marinus), a keystone species of the North Sea basin. Lesser sandeel could be exposed to MF as larvae, when they drift in proximity of OW turbines. Whether MFs impact the behavior of lesser sandeel larvae, with possible downstream effects on their dispersal and survival, is unknown. We tested the behavior of 56 lesser sandeel larvae, using a setup designed to simulate the scenario of larvae drifting past a DC cable. We exposed the larvae to a MF intensity gradient (150-50 μT) that is within the range of MFs produced by HVDC subsea cables. Exposure to the MF gradient did not affect the spatial distribution of lesser sandeel larvae in a raceway tank 50 cm long, 7 cm wide and 3.5 cm deep. Nor did the MF alter their swimming speed, acceleration or distance moved. These results show that static MF from DC cables would not impact behavior of lesser sandeel larvae during the larval period of their life although it does not exclude the possibility that later life stages could be affected.

Contributing to regional decarbonization: Australia's potential to supply zero-carbon commodities to the Asia-Pacific

The Asia-Pacific has experienced prodigious growth in energy use and is by far the world's largest greenhouse-gas emitting region. Australia has played a leading role in meeting the region's energy and resource needs, becoming the world's largest exporter of coal, liquefied natural gas, iron ore, and alumina. Our analysis shows that these exports are tied to sizeable consequential emissions at the point of use or processing, accounting for about 8.6% of the total greenhouse gas emissions of the Asia-Pacific. The paper investigates three pathways by which Australia could instead export zero-carbon energy and products: direct exports of renewable electricity via sub-sea cables, exports of zero-carbon fuels such as green hydrogen, and the export of “green” metals processed from Australian ores using renewable energy. Carrying out robust, high-level calculations we find that Australia has the land and renewable energy resources to become a key exporter of these commodities. Realization of this potential relies on ongoing cost reductions, growing demand-side interest linked to meeting ambitious emission reduction targets in the region, and the development of cross-border frameworks for clean energy trade. If it were to achieve this goal, Australia could make a sizeable contribution to regional decarbonization via renewable-energy based exports.

SMART Subsea Cables for Observing the Earth and Ocean, Mitigating Environmental Hazards, and Supporting the Blue Economy

The Joint Task Force, Science Monitoring And Reliable Telecommunications (JTF SMART) Subsea Cables, is working to integrate environmental sensors for ocean bottom temperature, pressure, and seismic acceleration into submarine telecommunications cables. The purpose of SMART Cables is to support climate and ocean observation, sea level monitoring, observations of Earth structure, and tsunami and earthquake early warning and disaster risk reduction, including hazard quantification. Recent advances include regional SMART pilot systems that are the first steps to trans-ocean and global implementation. Examples of pilots include: InSEA wet demonstration project off Sicily at the European Multidisciplinary Seafloor and water column Observatory Western Ionian Facility; New Caledonia and Vanuatu; French Polynesia Natitua South system connecting Tahiti to Tubaui to the south; Indonesia starting with short pilot systems working toward systems for the Sumatra-Java megathrust zone; and the CAM-2 ring system connecting Lisbon, Azores, and Madeira. This paper describes observing system simulations for these and other regions. Funding reflects a blend of government, development bank, philanthropic foundation, and commercial contributions. In addition to notable scientific and societal benefits, the telecommunications enterprise’s mission of global connectivity will benefit directly, as environmental awareness improves both the integrity of individual cable systems as well as the resilience of the overall global communications network. SMART cables support the outcomes of a predicted, safe, and transparent ocean as envisioned by the UN Decade of Ocean Science for Sustainable Development and the Blue Economy. As a continuation of the OceanObs’19 conference and community white paper (Howe et al., 2019, doi: 10.3389/fmars.2019.00424), an overview of the SMART programme and a description of the status of ongoing projects are given.

In-situ tensile and fatigue behavior of electrical grade Cu alloy for subsea cables

Distribution of electrical energy through subsea power cables has an increasingly important role in the renewable power generation. The majority of the subsea cables uses copper (Cu) as a conductor material. Cables suspended from sea level to sea floor are subjected to both static and cyclic loads that can introduce microstructural damage due to fatigue, creep and their interaction. In addition, since the manufacturing process of the stranded conductor results in Cu-materials with superficial irregularities and metallurgical anisotropy, the material performances need to be carefully addressed in order to reliably assess the wires life. In order to provide a deeper insight into the occurring damage mechanisms, monotonic and cyclic tests of micro-sized Cu tensile specimens were carried out using in-situ micromechanical testing, inside a scanning electron microscopy (SEM) equipped with an electron backscatter diffraction. Tensile and cyclic loading behavior are discussed in correlation with the damage mechanisms observed directly and post-mortem. The twin boundary fraction in the microstructure is found to be linked to the deformation status, and thus can potentially be used as an indicator for predicting the remaining life of the material under service conditions.

Analysis of Three-Core Composite Submarine Cable Damage Due to Ship Anchor

Suspended submarine cables are prone to likely mechanical damages due to ship anchors, which represent a significant threat to the reliability of power transmission and information communication networks. This paper is aimed at presenting a detailed investigation to the dynamic response of a ship anchor impacting the suspended section a submarine cable in order to reduce the risk of cable damage. In this regard, a three-dimensional and dual nonlinear model of the anchor affecting a subsea cable is established using ABAQUS finite element analysis software. The damage effect due to the ship anchor on the suspended and buried-in-soil sections of the cable is studied. Results show that when a ship anchor hits a suspended section of the subsea cable, the mechanical stress is concentrated at the impacted point and is progressing to both sides of the suspended section with a significant cable deformation. On the other hand, the buried section of the cable suffers from a short impact process, and the deformation is relatively small. To reduce this impact effectively, a detailed technical comparison of two common dumping and filling methods is conducted, and the better protection method is proposed.

Deriving an experimental and analytical relation between the core and fiber temperatures of a 3P XLPE cable

Every submarine power cable contains a fiber-optic assembly. Most windfarms have a distributed temperature sensing (DTS) device for continuous temperature monitoring. Using real-time thermal rating (RTTR) the performance of subsea cables can be increased or a less expensive cable can be installed.The experiments aimed to establish the relation between the fiber and core (or conductor) temperatures in the cable. Fiber temperature was obtained using a DTS interrogator; thermocouples installed in the conductors yielded the core temperature data. The cable used in this test was a 20 meter-long 1800 mm2, 1000 A export cable.These experiments validated a new RTTR model proposed by Marlinks: a thermal RC-ladder model based on finite-element (FEM) calculations. Better suited to the complexity of the spacer geometry and existence of the fiber node, the Marlinks-developed model is considered to be more accurate than the industry standard.

Life Cycle Climate Change Impact of a Cost-Optimal HVDC Connection to Import Solar Energy from Australia to Singapore

This paper aims to evaluate the life cycle greenhouse gas (GHG) emissions of importing electrical power into Singapore, generated from a large-scale solar photovoltaic (PV) power plant in Australia, through a long-distance subsea high-voltage direct current (HVDC) cable. A cost optimization model was developed to estimate the capacities of the system components. A comprehensive life cycle assessment model was built to estimate emissions of manufacturing and use of these components. Our evaluation shows that, for covering one fifth of Singapore’s electrical energy needs, a system with an installed capacity of 13GWPV, 17 GWh battery storage and 3.2GW subsea cable is required. The life cycle GHG emissions of such a system are estimated to be 110gCO2eq/kWh, with the majority coming from the manufacturing of solar PV panels. Cable manufacturing does not contribute largely toward GHG emissions. By varying full-load hours and cable lengths, it was assessed that sites closer to Singapore might provide the same energy at same/lower carbon footprint and reduced cost, despite the lower insolation as compared to Australia. However, these sites could cause greater emissions from land use changes than the deserts of Australia, offsetting the advantages of a shorter HVDC cable.

A call to assess the impacts of electromagnetic fields from subsea cables on the movement ecology of marine migrants

AbstractThe number of subsea cables in the marine environment is likely to grow substantially in the near future. Arrays of energy‐generating windmills or wave power generators are planned for installation in the coastal waters of many countries worldwide. The electricity generated by these and other marine energy sources will be transported to shore through cables with the current and voltage creating electromagnetic fields (EMFs). Furthermore, there are also plans for the installation of undersea cables to interconnect countries and islands for the purpose of sharing power and communications. These also will generate EMFs in the marine environment. While shielding can negate the presence of direct electric fields, induced electric and magnetic fields readily penetrate into the water column. Cables carrying electric current produce anomalies in the earth's main field, which could have the potential for disrupting the migrations of fishes and diverse marine animals that rely on magnetic cues for orientation or navigation. Studies designed to test how these anthropogenic magnetic fields disrupt magnetic orientation have only recently started to be conducted. Given the cultural, economic, and conservation value of many of the species potentially at risk, such work should be immediately prioritized.