Abstract Seafloor Massive Sulfides have been expected to be future mineral resources. To promote the development of Seafloor Massive Sulfides, Seafloor Mineral Processing, a method of extracting valuable minerals from the ores on deep seafloor using flotation to reduce the lifting cost of ores from the seafloor to the sea surface, was proposed. To apply flotation for the seafloor mineral processing, a measurement method of bubble size applicable to deep-sea conditions has been desired because it is necessary to generate fine air bubbles suitable to flotation under pressure conditions on deep seafloor. Then, the authors have studied on bubble size measurement by image analysis, which is expected to be applicable to deep-sea conditions. At the first phase of this study, photographic conditions suitable to image analysis of air bubbles were distinguished. Air bubbles were generated by using a porous nozzle at some air flow rates in a bubble column with a rectangular cross-section. Video images of air bubbles were taken by using both high-speed camera and video camera with a low frame rate. Bubble size was measured by binarizing the video images of bubbles. Under optimal photographic conditions, bubble size was obtained from not only the high-speed camera but also the video camera; and both size data agreed relatively well, which implies that bubble size measurement by using image analysis would be applicable to deep-sea conditions. At the second phase, experiments were carried out under high-pressure conditions up to 2.4 MPa. Single bubble generation by using a capillary nozzle in a small pressure chamber with a sight glass was observed by using a digital microscope. Bubble size measurement by image analysis was carried out by the procedure established at the first phase. While the process of bubble generation at the high pressures was similar to that at the atmospheric pressure, the bubble size was decreased as the pressure rose. The result implies there is a strong correlation between the pressure and the bubble size.

Abstract Aquaculture is currently the fastest growing food sector in the world and the open oceans are seen as one of the most likely areas for large-scale expansion [1], [2], [3]. The global demand for seafood is continuing to rise sharply, driven by both population growth and increased per capita consumption, whilst wild-capture fisheries are constrained in their potential to produce more seafood. A recently funded EC project, the Blue Growth Farm – BGF (GA n. 774426, 1 st June 2018 – 30 th September 2021) aims at contributing to this world need with an original solution. The Blue Growth Farm proposes an efficient, cost-competitive and environmentally friendly multi-purpose offshore farm concept. It is based on a modular floating structure, moored to the seabed, meeting requirements of efficiency, cost-competitiveness and environmental friendless, where automated aquaculture and renewable energy production systems are integrated and engineered for profitable applications in the open sea. In the present paper, the overall engineering approach developed to carry out the research work is presented, described and justified. Different technical and scientific challenges are addressed through an integrated industrial engineering design approach, where all disciplines are tuned to achieve the Blue Growth Farm main targets. These are represented by: i) guaranteeing expected nominal fish production thanks to advanced automation and remote control capabilities; ii) minimizing the pollution introduced at marine ecosystem level when exploiting the marine natural resources, whilst increasing the social acceptance and users community agreement; iii) maximizing the electricity production in the Blue Growth Farm potential installation area ecosystem to provide energy supply to the on-board electrical equipment and to dispatch the extra produced electric energy to the land network. Preliminary engineering design results are promising to demonstrate effective increase of safety and efficiency by reducing on-board human effort and consequently risks at offshore, thus to make commercial-scale open ocean farming a reality. The present paper introduces overall concepts and design methodology whilst other companion works submitted at OMAE2019 [4], [5], [6] provide insight of specific aspects of the Blue Growth Farm project elaborated during the first six months activity.

Abstract The touch down zone (TDZ) of steel catenary riser (SCR) is subject to fatigue damage. As a significant fatigue indicator, the variation of the stress range largely depends on the instantaneous changing bending moment. In this paper, a non-linear interaction model between seafloor and SCR is developed to consider the formation of trench at TDZ and its effect on the variation of bending moment. The seafloor soil is modeled by the nonlinear springs, whose stiffness is calculated according to nonlinear load-deflection relationship, such that the effect of cyclic loading can be simulated. The modeling of trench evolution and bending moment variation near the touchdown point (TDP) under cyclic loading are further conducted using the finite element software ABAQUS. The results show that the trench shaping is related to the uplift displacement of SCR and its number of cycles. The dependence of the bending moment on the displacement cycles near TDP is also investigated.

Abstract Seafloor Massive Sulfides have been expected to be future mineral resources. The grade of valuable metallic elements in ores of Seafloor Massive Sulfides is usually small percentage. If valuable minerals can be extracted from the ores on deep seafloor, the total mining cost can be reduced significantly. The authors proposed Seafloor Mineral Processing, where ores are to be ground into fine particles and separated into concentrates and tailings on seafloor. The Seafloor Mineral Processing system consists of processing units for unit operations such as grinding and separation. To investigate the applicability of flotation, which is a method to separate ore particles by using the difference in wettability of minerals, to the separation unit, measurements of contact angles of sulfide minerals at high pressures were carried out. The results suggested that the contact angles of the minerals would have relationships with pressure in depending on the kind of minerals and solutions. In addition, applying Laser-Induced breakdown Spectroscopy (LIBS), an optical method for elemental analysis, to measurement of metal grade of ore particles handled as slurry in the processing units was also investigated. Signals assigned to copper, zinc, and lead were successfully detected in the spectra obtained from ore particles in slurry flow.

Abstract The submerged floating pipeline is floating at a certain ocean depth with tethers anchored to the seabed. This novel concept of pipeline can be a promising solution for challenging seabed conditions. Because the pipeline is floating at the mid-deep water and does not interact directly with the seabed, there is no need to do any seabed intervention work and wave forces on the pipeline can also be ignored. But the dynamic response of this type of pipeline under strong currents poses several challenges for design of floating pipeline. This work investigates the parametric resonance of submerged floating pipeline between two floating structures. The parametric resonance can lead to the huge motions and fatigue damage of the pipeline. Thus, it is essential to investigate the parametric resonance of the submerged floating pipeline system under combined parametric and vortex excitations considering uncertainties. Hill’s equation of dynamic responses of the pipeline are derived and hill stability diagrams are used to analyses the corresponding motion stability. The effect of the significant uncertain factors on the probability of the parametric stability is investigated using the metamodel method. According to analyses, some effective measures are given to the designers to avoid the parametric instability for the submerged floating pipeline design.

Abstract Japan Oil, Gas and Metals National Corporation (JOGMEC) has been conducting R&D of production system for Seafloor Massive Sulfides (SMS) mining. In order to reach commercialization stage in SMS development, the pipe wear due to slurry flow is one of many technical issues to be solved. In the present paper, the authors conducted the large scale experiment using full scale pipes to obtain the various data on pipe wear, and investigated the pipe wear amount in commercial operation. In the experiment, SUS 304 and UHPE were used for the inner materials of test pieces. In addition, the test pieces were installed in the vertical, horizontal and inclined section. Then the authors estimated the thickness reduction of pipe due to slurry flow based on the experimental results.

Abstract A new riser system concept is being investigated for deep-water application. This is the Branched Riser Systems with its three types: the Branched Steel Catenary Riser (BSCR) System, the Branched Steel Lazy Wave Riser (BSLWR) System and the Branched Lazy Wave Hybrid Riser (BLWHR) Systems. The branched riser system consists of a large bore pipe, which is terminated at an optimized water depth considering the minimum wall thickness requirement from burst and collapse criteria. The larger bore riser pipe is extended from this cut off water depth to the seabed by two smaller riser pipes via a connecting component (connector). The concept draws benefits from the performance of smaller riser bore pipe in strength and fatigue performance besides the opportunities provided by larger bore pipe for maximum flow throughput and vessel top decongestion. Preliminary results from ongoing investigation of type 1 (BSCR) of the branched riser systems, using a 12-inch pipe in combination with two 8-inch riser pipes in a water depth of 3,000m for a cut off water depth of 1500m, indicates a reduction in overall riser weight, stress utilization and fatigue damage at the riser hang off (HO) and touch down zone (TDZ). Results obtained indicate that possible benefits can be achieved through a combination of advantages of smaller and larger bore riser pipe and justifies further research interest on the novel riser concept.

Abstract Traditional subsea mining systems use a heavy subsea crawler, which has a big drill and scrapes the mineral deposit horizontally and have limitations of seafloor inclination, roughness and softness. Those traditional systems also have issues from operational and economical points of view. Furthermore, traditional on-board drilling machines and seabed drilling machines are used for core sampling by drilling to analyze mineral contents of seafloor deposits at the stage of mineral resource estimation before the production but operational and economical efficiencies are required to those traditional systems as well. The objective of this research is to develop an innovative Self-Walking Vertical Mining System (SW-VMS) that overcomes these issues. The system is a fully submerged eight-legged jack up platform and is able to walk autonomously on a rough, soft and inclined seafloor. The SW-VMS can be used both as the mining system to mine seafloor deposits and as the sample drilling system to analyze mineral contents in-situ and on-land efficiently before the mining with a DTH drilling unit. This paper introduces the detail of the SW-VMS as the mining system at first and then introduces the concept of the SW-VMS as the sample drilling system and finally the results of the scale model test of the SW-VMS on-land are shown. The scale model test has been carried out to confirm the walking ability of the SW-VMS from the structural and autonomous control points of view. The scale of the test model is approximately 1/40 of the preliminary design of the SW-VMS which has been already completed. The test consists of test cases of walking on a flat foundation, on a flat foundation including partially soft foundations and on inclined foundations of up to 45 degrees.

Abstract Subsea pipelines operating under high pressures and temperatures are typically buried to protect from the environmental impacts and to prevent the instigation of global buckling. As the seabed profile is generally uneven, certain initial imperfections generally exist along the pipeline. As the pipe traverses in shallow waters, the seabed can be subjected to hydrodynamic loads caused by surface gravity waves. The hydrodynamic pressure, which typically depends on the wave height and water depth, leads to the development of pore pressures within the soil medium. This gradient of the pore pressures can cause significant uplift forces on the pipe, which may initiate the buckling in the vicinity of the imperfection. This study focuses on understanding the influence of these wave induced uplift forces on the buckling of the initial imperfect pipelines. Four typical imperfection profiles are considered in the study. The influence of imperfection shape on the buckling behavior is compared for surface laid and buried pipelines. Thereafter buckling behavior of the considered imperfect pipelines is studied with and without consideration of wave loads for a range of wave particulars and burial depths. The wave forces on the pipeline are estimated by solving Biot’s consolidation equations using finite element software COMSOL and the buckling studies are carried out using ABAQUS.

Abstract The on-bottom stability design of subsea pipelines and cables is important to ensure safety and reliability but can be challenging to achieve, particularly for renewable energy projects which are preferentially located in high energy metocean environments. Often these conditions lead to the seabed being stripped of all loose sediment, leaving the cables to rest on exposed bedrock where roughness features can be similar in size to the cables. As offshore renewable energy projects progress from concept demonstration to commercial-scale developments, new approaches are needed to capture the relevant physics for small diameter cables on rocky seabeds to reduce the costs and risks of export power transmission and increase operational reliability. These same considerations also apply to the cables and small diameter pipes — such as umbilicals — required by oil and gas projects located on rocky seabeds. Recent experimental testing using the University of Western Australia’s unique Large O-tube has enabled the experimental measurement of hydrodynamic forces on small diameter cables and pipes in proximity to smooth and rough beds. The tested conditions extend well beyond the existing published parameter range including much higher KC conditions together with seabed roughness which is comparable in size to the diameter. The results provide design data of great relevance to the ongoing development of marine renewable and conventional oil and gas projects, especially on rocky seabeds. This paper presents a summary of the existing knowledge on the subject as a preface to preliminary test results and gives tentative conclusions on the likely outcomes from this work.

Abstract This paper is based on the experience made during the engineering, fabrication and installation of rigid spools used to tie-in production lines (10”) to manifolds, in 650m max water depth, on a project recently completed in West Africa. The design of tie-in spools needs to accommodate the operation and environmental loads, and the installation, fabrication, metrology and, if applicable, also stack up tolerances. This may require spools of large sizes/weights and complex geometries, with associated fabrication and installation costs that significantly contribute to the overall costs of a project. This paper is focused on the process that was followed during the execution of the RFI (Risers Flowlines Installation) EPCI (Engineering Procurement Construction Installation) contract. To find workable configurations of the spools, such not to compromise the execution of the project, was a major challenge. Horizontal connection systems were to be used. Configurations of the spools, initially designed to be in contact with the seabed (“seabed-supported” design) turned to be by far more complex than the geometries estimated before the start of the detailed engineering, and which had been the basis for laying down the execution schedule of the project. Spools suspended between the horizontal hubs (“free-spanning” design) were finally chosen, which significantly simplified the fabrication and the installation. A key driver of the design was to keep the interface loads within the maximum permissible values specified for the connectors. The feedbacks from the fabrication and the installation are included in the paper, and the lessons learned are provided. Alternative solutions — based on use of flexible pipes — are also discussed.

Abstract Rigid pipelay vessels use two types of equipment to hold the pipe under tension while it is being deployed on the seabed: tensioners and hang-off clamps (HOC). Tensioners are used to maintain tension while paying out the pipe behind the vessel, while the HOC holds the pipe statically during welding operations. For both pieces of equipment, the tension is held through frictional pads in contact with the pipe. With the necessity to reach greater water depths leading to an overall increase of pipeline weights and stiffness (and therefore top tension), the installation of rigid pipelines has become more challenging. In other cases, such as pipe-in-pipe (PiP), carrier pipe wall thicknesses are often optimised as much as possible while lower grade materials are selected to reduce costs, making it more difficult to provide pipelay equipment settings that can satisfy both grip and pipe local integrity requirements. Simple hand calculations and basic equipment modelling are not sufficient to provide safe equipment settings and optimised allowable sea states. The new DNVGL-ST-N001 [1] (Marine Operations and Marine Warranty) also increases scrutiny on pipelay equipment and pipe interaction, making it imperative to develop more in-depth methodologies for settings calculation. This paper gives an overview of a robust methodology for pipelay equipment settings and demonstrates through practical examples how it improves safety while optimising operations, therefore enabling more efficient pipelay operations and reducing waiting on weather.

Abstract Maintaining and retaining a quality sandy beach is a primary requirement for attracting people and tourists in any coastal country. Tourism Enterprises Company (TEC) in Kuwait owns 230 m long sandy beach in Ras Al-Ardh Sea Club, Salmiya, Kuwait. The beach has been eroding because of strong hydrodynamics forces from waves and currents. TEC wants to develop a stable sandy beach of 30 m wide. Kuwait Institute for Scientific Research (KISR), Kuwait is assigned to carry out the required scientific studies. In order to make sure a stable quality beach will exist, KISR has carried out the needed studies, which involves the field measurements such as bbathymetry survey, current and tidal variations, physical characteristics of beach soil, beach and sea bed profile, establishing the design parameters such as waves, currents, tide and wind. Hydrodynamic model study using DELFT3D model for the present and for the proposed extended groin conditions with beach nourishment were carried out. Also numerical modeling using GENESIS model to understand the future shore line changes due to the proposed development was carried out. Design of Groins to estimate the weight of armor units and weight of inner layers were carried out. The particle size and quantity of sand needed for reclamation of 30 m wide beach was estimated. Based on the study, it is recommended that the sandy soil to be used for 30 m wide beach nourishment should have D 50 greater than 0.42 mm (say 0.5 mm) and D 10 greater than 0.25 mm. The borrow pit much be selected by keeping this soil characters in mind. It is recommended to use a submerged offshore breakwater in order to retain the beach sand in place and for reducing the maintenance nourishment. Otherwise, large quantity of the capital nourished beach sand will escape into the deeper water due to strong current coupled with waves and steep seabed slopes. Environmental Impact Study was carried out as per Kuwait Environment Public Authority requirements to bring out the impacts due to beach filling and the construction submerged offshore barrier and extension of east groin for a distance of 30 m. TEC will implement the recommendations for developing the beach in Ras Al-Ardh sea club and will be useful to attract more people to use this beach.

Abstract A new method for deriving extreme soliton current criteria for offshore engineering applications is described. The primary data source was site specific measurement close to the continental shelf break where metocean criteria were required. A dedicated oceanographic mooring was designed to quantify solitons, with rapidly sampled measurement of seawater temperature and velocities through the vertical. As described in two previous OMAE papers, quantification of soliton velocity profiles was achieved via temperature measurement and theory, with measured velocities playing a secondary role in critical validation. The previous methodology was extended in the present study, with separate contributions quantified from variations in soliton amplitude and water column density structure. The nonlinear Fourier techniques first described in OMAE 2017 were again used to reduce uncertainty in estimates of extreme soliton amplitude. In a new development, the long-term distribution of the density structure contribution was quantified using a calibrated hindcast of seawater temperature. Extreme conditions were defined at the boundary of a MITgcm model domain. This sophisticated model was then used to estimate extreme soliton velocities, through the water column and a few metres above the seabed, at a wide range of shallower target locations.

Abstract This study aims at the numerical analysis of wave characteristics when a wave propagates on the porous slope seabed. Numerical wave tank technique was developed using boundary element method with constant panels on the boundary. The fluid was satisfied with potential flow conditions and Darcy’s law was applied for porous intersection. Two computational domain method, which consists of fluid and porous domains, was used to simulate the propagating waves over a sloped seabed having a permeability. To consider fluid-porous boundary interaction, three-step boundary value problems were calculated. The wave amplitude decreased along the free surface as the wave propagated over a sloped bottom. The wave reflection and transmission by subsea structures were also analyzed.

Abstract Artificial reefs (ARs) are structures constructed on the seabed to attract and concentrate fish and to potentially improve and rehabilitate coastal ecosystems. In order to investigate the hydrodynamic characteristics of ARs, a series of model experiments of cubic artificial reefs are carried out in the flume. The model reefs are made of acrylic material with different shapes of opening and various open-area ratios. The hydrodynamic forces of the models are measured in the experiments. The changes of drag coefficient with respect to the open-area ratio and the flow-facing angle of attack are investigated and discussed respectively.

Abstract To mitigate global warming, it is necessary to emit less CO 2 into the atmosphere and the Carbon dioxide Capture and Storage (CCS) attracts attention these days as one of the solutions against the problem. Off Tomakomai coast, Japan, a CCS project has been demonstrated since 2016. However, there may be a risk of CO 2 leakage and consequent seepage from the seafloor, even if the probability of such an event is almost nil. In this research, we assumed that CO 2 seeps from multiple points on the seafloor and aimed at estimating the seepage locations, time and fluxes, by using CO 2 concentration data observed by several sensors set on the seafloor. We adopted the adjoint marginal sensitivity method, which is a probabilistic time-backward method: an adjoint location probability is released by each sensor and spreads in the time-backward direction. The adjoint location probabilities are used to estimate the seepage fluxes. We also combined the least squares method with the adjoint marginal sensitivity method to estimate the seepage fluxes. We considered that CO 2 seeps from 2 points in 2-dimensional horizontal domains as test calculations with changing seepage flux ratios, such as 1:1, 1:0.1 or 1:0.01.

Abstract Artificial reefs (ARs) are purposely submerged in natural aquatic environments to provide additional habitat for fish. The reasonable layout of ARs on the sea floor can effectively enhance and support important marine species. This research involves a three-dimensional numerical simulation to analyze the flow effect of three types of AR layouts based on computational fluid dynamics. Through numerical simulation of the flow past the reefs, we can determine the scale of the upwelling and back-eddy flow. Based on the simulation data, the rational transverse distance between two cross-shaped artificial reefs (CSARs) is 6L (L is the length of the single reef), which is used to design the layouts of CSARs. Five indicators have been used to evaluate the flow field effect of these three layouts. According to the comparison of five indications for different layouts of CSAR, it is more reasonable to divide the AR layouts into two categories: upwelling layout and back eddy layout. Finally, the sphere of influence of the AR layouts on the fisheries resource is also discussed.

Abstract Water wave propagation over shallowly submerged structures is of much interest in the context of submerged wave energy devices, breakwaters or barrier reefs. This work examines waves passing over a two-dimensional shallowly submerged fixed step extending to the seabed. The problem has been modelled in CFD using the open source toolbox OpenFoam utilising the Reynolds Averaged Navier-Stokes Equations. These simulations are compared to experimental work from a previous study as means of validation and extended to larger amplitude waves for a single incident wave frequency. The flow over the step is characterised and examined in the context of developing an efficient hybrid numerical model for the problem.

Abstract Indonesia is a main country supplying coal in the Asia-Pacific region, it is important to ensure a stable coal supply to Japan. Because the topography of the seabed near East Kalimantan Island, Indonesia’s main coal production area, is shallow, it is difficult for bulk carriers to reach the coast. Therefore, Large-Scale Floating Coal Transshipment Station (LFTS) was proposed, which will be used as a relay base between coal-barging barges from land and bulk carriers offshore. Installing an LFTS offshore from East Kalimantan is expected to improve coal transport productivity. LFTS can store coal equivalent to five times the capacity of one bulk carrier (total 500,000T), and can accommodate 2 bulk carriers at the same time during offloading. The scale of LFTS is 590m × 160m. The LFTS has a flat spread and the elastic behavior becomes the dominant Structure. The upper part of the LFTS is different rigidity partly because the partition wall to be loaded by dividing the coal into each quality is provided. Loaded coal not only changes the draft of the LFTS but also greatly deforms the LFTS and is expected to cause local stress concentration on the structural members. Therefore, this paper investigates wave response characteristics and stress characteristics with the coal loading of the LFTS, and then evaluation of structural strength by limit state design method. In this study, linear potential theory and the finite element method (FEM) were used to analyze the static hydroelastic motion under various coal loading condition and wave response of LFTS. And, to grasp the local stress concentration occurring inside the LFTS by using the response results, a detailed model modeling a complicated internal structure was prepared. Zooming analysis which is a method of giving the deformation result by the whole model of LFTS as forced displacement to the local detailed model was carried out. As a result, depending on the coal loading condition and wave conditions, it became clear that LFTS will be in a tough situation.