|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
This paper is one of seven papers that will be included in the special session: Floating Memories - Look Back to Leap Forward. The focus for this paper is on the Tension Leg Platform (TLP), one of the four major platform types that include the Floating Production Storage and Offloading platform (FPSO), the semisubmersible floating production system (Semi) and the Spar platform. The paper summarizes the evolution of the TLP over three and half decades, and provides a thirty-five year retrospective of the progression of TLP technology, including hull shapes, tendon connectors, flex elements, and riser systems. It will walk through the evolution of understanding, analytical methods, and model testing to assess the complex global performance of a TLP, and the unique challenges of system dynamic resonant excitation, the so-called "ringing" and "springing" phenomena. The TLP was a game-changer in bringing dry tree wells to floating platforms, leveraging dry tree drilling and well control methods from a generation of fixed platforms, and enabling multiple top-tensioned production and drilling risers in close proximity due to the limited tensioner stroke not possible on a drill ship or semisubmersible. The TLP has shown its applicability in water depths from the Hutton TLP (1982) in barely 150 m of water in the North Sea, to the Big Foot TLP installed in 1584 m of water in the Gulf of Mexico in 2018, the deepest TLP to date. And it has shown its flexibility in size ranging from the smallest mini-TLP's of 10,000 tonnes displacement, to the North Sea concrete hulled Heidrun TLP of 290,000 tonnes.
This article reviews different types of forcing zones (sponge layers, damping zones, relaxation zones, etc.) as used in finite volume-based flow simulations to reduce undesired wave reflections at domain boundaries, with special focus on the case of strongly reflecting bodies subjected to long-crested incidence waves. Limitations and possible sources of errors are discussed. A novel forcing-zone arrangement is presented and validated via three-dimensional (3D) flow simulations. Furthermore, a recently published theory for predicting the forcing-zone behavior was investigated with regard to its relevance for practical 3D hydrodynamics problems. It was found that the theory can be used to optimally tune the case-dependent parameters of the forcing zones before running the simulations.
Wave reflections at the boundaries of the computational domain can cause significant errors in flow simulations, and must therefore be reduced. In contrast to boundary element codes, where much progress in this respect has been made decades ago (see e.g., Clement 1996; Grilli &Horillo 1997), for finite volume-based flow solvers, there are many unresolved questions, especially:
1) How to reliably reduce reflections and disturbances from the domain boundaries?
2) How to predict the amount of undesired wave reflection before running the simulation?
This work aims to provide further insight to these questions for flow simulations based on Navier-Stokes-type equations (Reynolds-averaged Navier-Stokes, Euler equations, Large Eddy Simulations, etc.), when using forcing zones to reduce undesired reflections. The term “forcing zones” is used here to describe approaches that gradually force the solution in the vicinity of the boundary towards some reference solution, as described in Section 2; some examples are absorbing layers, sponge layers, damping zones, relaxation zones, or the Euler overlay method (Mayer et al. 1998; Park et al. 1999; Chen et al. 2006; Choi &Yoon 2009; Jacobsen et al. 2012; Kimet al. 2012; Schmitt & Elsaesser 2015; Perić & Abdel-Maksoud 2016a; Vukčević et al. 2016).
External floating roof crude oil storage tanks are widely used in the Oil & Gas industry due to many advantages. Floating roofs in storage tanks are well-known in minimizing product losses due to evaporation. The floating roof systems also mitigate fire risk by eliminating vapor space beneath the roof. However, the operation of such massive structures brings different challenges. This paper reveals the relation between floating roof mechanical deformation and tank floor settlement. This research studies a real case of a floating roof storage tank. The double deck floating roof experienced an excessive mechanical distortion in form of bulges and undulations at roof lower deck. A Finite Element (FE) Analysis studied the relation between tank bottom plate settlement and roof deformation while roof is in parking position. The roof bulges were dimensionally surveyed and compared with FE results. The FE Analysis results of stresses and strains were utilized to decide the integrity condition of the tank roof and to study the behavior of the existing bulges for continued operation of the tank roof.
During storage tank major overhaul, bulges were reported in the lower deck of the floating roof with 50-100 mm depth. The bulges are in form of waviness and they are more severe in the roof middle pontoons. The simulation results showed that while the roof is parked over a floor with non-uniform settlement, some of the roof supporting legs will be engaged with the tank floor earlier. This will lead to a non-uniform weight distribution of the tank roof over the legs, and overloading the roof lower deck with bending stresses. The FE results were able to define the location of the induced high stresses that may lead to cracking in the welding lines of the roof lower deck plates. It was decided to conduct a magnetic particle inspection at those critical lines to ensure they are crack-free. Results showed that the stress levels in the roof will reduce dramatically after refilling the tank and floating the deformed roof, this is due to the redistribution of the roof weight uniformly over the product surface. After refilling the tank, plates with elastic bulges will recover and plastically deformed bulges will have lower stress levels. The assessment concluded that storage tank floating roof is fit for service. The relation between storage tank floor settlements and floating roof deformations has never been analyzed to this depth of engineering analysis. The storage tanks international codes state that bulge sizes in the floating roof shall be kept as minimal without providing any acceptance criteria. This research quantifies the acceptance limits of floating roof bulges based on an advanced engineering simulation.
Choi, Won-Hyuk (Daewoo Shipbuilding & Marine Engineering Co., Ltd.) | Kim, Dong-Kyoon (Daewoo Shipbuilding & Marine Engineering Co., Ltd.) | Baik, Yong-Sun (Daewoo Shipbuilding & Marine Engineering Co., Ltd.) | Moon, Seung-Han (Daewoo Shipbuilding & Marine Engineering Co., Ltd.)
Current offshore market pursues an extreme cost and schedule innovative business model and requests optimum design within tight project budget. This is also valid for semi-submersible unit.
This paper discusses several widely adopted conservative assumptions used for semi-submersible unit hull design and proposes a reasonable strength assessment approach based on realistic procedure and Class rule requirement. Some engineering companies, therefore, suggest existing methodology which follows conservative approach with regard to global and local stress combination, normal stress derivation from load cases and observing area for result application. However, there are few explicit and logical references and current market leads to entire optimum design as long as reliable design against various design conditions are maintained.
In this paper, the comparison between proposed approach and existing methodology is to be discussed, which given suggestion has practical characteristics with structural strength assessment point of view for semi-submersible unit. Consequently, the feasibility of the proposed methodology and resultant structural scantlings and weight are presented by comparison of the two (2) methodologies throughout mentioned stress extraction from FE analysis.
Referring previous design for semi-submersible unit of drilling rig, LUW usually has been increased to secure VDL based on the designated stability requirements such as Norwegian Maritime Directorate (NMD) mainly because outfitting weights such as E&I, piping, HVAC, mechanical and drilling equipment have been increased in comparison to FEED or basic design due to design development during detail design, discrepancies, omission, and errors in early stage design. Furthermore, higher VCG of the unit because of the increased outfitting weight, which is concentrated on Deck Box positioned on top, may not be satisfied with the stability criteria due to no ballast margin. And structural steel weight should be increased because the structure should be reinforced due to the increased outfitting weight and arrangement. Furthermore, the structural appurtenance such as sponson and blister, to increase buoyancy capacity, may be incorporated to meet stability criteria, in which the consistent draft should be maintained for drilling operation. The final weight variation is shown in Fig. 1 in comparison to one of FEED of previous projects, which indicates weight proportion and increasing ratio of each discipline. It can be said that structural weight in FEED design does not changed significantly up to final design stage while piping, HVAC, and E&I weight is increased quite a lot in comparison to FEED, e.g. piping increased weight of 90% above.
The growing maturity of offshore wind energy and in particular floating foundation to support Wind Turbine Generators (WTG) has allowed novel concepts to be examined which some years ago were considered unfeasible. One such concept is the use of a toroidal shaped hull structure as a pontoon for its enhanced motion keeping properties. This paper examines the current sub-structures in use and proposed for floating wind turbines. A hydrodynamic analysis is performed on a toroidal pontoon using numerical methods and the results presented. The merits of using a vertical axis WTG are also considered.
The floating hull concept is well proven in the oil and gas industry, namely the semi-submersible design. The main structure of the vessel or structure is located below the ocean surface giving a number of advantages over traditional structures, which usually have the hull form close to the water surface. For instance, the advantages of having the main structure below the water surface includes: reduced wave loads, (since the wave kinematics decay exponentially with depth) and longer natural periods of motion, hence a reduced response motion. Also the deep submergence of the pontoons combined with a structure made up of pontoons, columns and bracing yields the above characterization of low motion response to waves. However, the floating wind farm application requires considerably larger semi-submersible structures with deeper drafts and larger displacements. Given these characteristics it was found that waves contribute to the majority of the rigid-body motion-inducing dynamic loads of a large floating structure (Henderson, 1997). Technical challenges are related to minimizing the wave-induced motion and understanding the coupling between support structure and the wind turbine and achieving static and dynamic stability. The idea for the Multiple Unit Floating Offshore Wind Farm (MUFOW) concept was originally developed at UCL (University of College London) in the early 1990s (Musial, 2003). While it was concluded that such a support structure was not cost-effective to support wind farms, cost analysis was never done for the support structure of a ‘hybrid’ incorporating both wind and wave energy, which would most certainly increase the cost-effectiveness. Nonetheless, recent advancements in the Vertical Axis Wind Turbines (VAWT) and continued research in particular the benefits of combing the VAWT with a floater produces an improved case.
Colorado-Moreno, Adrian Isidro (Universidad Veracruzana) | Rodriguez-Cruz, Maria Alejandra (Universidad Veracruzana) | Cruces-Giron, Aldo R. (Mexican Petroleum Institute) | Hernandez-Hernandez, Jose (Universidad Veracruzana) | Felix-Gonzalez, Ivan (Mexican Petroleum Institute)
In recent years, the wind power capacity installed in Mexico has increased considerably onshore, but it lacks offshore wind installations, despite it has an extended territory to exploit the offshore wind resources. The proposal of this study is the numerical hydrodynamic evaluation of a preliminary concept design of a semisubmersible platform to support wind turbines through a parametric study. The hydrodynamic analysis considers two locations to assess the RAOs and maximum responses of models in operation and extreme conditions.
In Mexico, the main fuel consumption for primary energy generation in 2017 was equivalent to 189.3 million tonnes of oil of which 45.9% came from the consumption of oil, 39.8% natural gas, 6.9% coal, 1.3% nuclear energy, 3.8% hydro-electricity and 2.3% renewables (BP, 2018). By the end of 2017, SENER1 (2018) informed that the power generation installed capacity 75,585 MW, of which 70.5% came from conventional technologies (e.g. combined cycle) and 29.5% from clean technologies (e.g. solar energy and wind energy). For 2032, the power generation installed capacity is expected to increase by 73.0% or 130,292 MW (SENER1, 2018).
Wind energy has generated high interest and relevance since most of the countries around the world have extensive research, on this generation technologies due to its, cost-effectiveness and reliability when compared to other renewable technologies. Last decade, the wind power global capacity raised from 74 GW to 487 GW (Renewables 21 Global Status Report, 2017). A previous study about renewable energy Mexico (Perez et. al 2017) mentioned that the country has favorable winds in its extensive territory although the low power generation installed capacity which is lower than other countries with less territory, such as Germany and Spain. The power generation wind installed capacity was 4.2 GW in 2017 and expected 14.8 GW in 2032 (SENER2, 2018).
The available types of supports for offshore wind turbines depend on the meteorological (e.g. winds) and oceanographic (e.g. water depth) characteristics of the place of installation and the wind turbine power. Henderson & Witcher (2010) mentioned the advantages of the floating substructures and their benefits compared with fixed substructures. For the floating substructures are wide varieties of technical solutions available in terms of design, less cost in deeper waters, better flexibility with regards to construction and installation procedures and easy removal and decommissioning.
Floating mega islands can provide an attractive solution for creating temporal or more permanent space in coastal areas with a high demand for real estate. Also at open sea in the vicinity of wind farms, fish farms or logistical cross points, a floating mega island could be used as a hub, eliminating costly transfers to shore. One of the aspects which needs to be understood is the wave induced motion of such a floating mega island. A piece-wise flexible island has been model tested at MARIN as described in Waals (2018). The motion behaviour, mooring loads and connector loads in mild and severe sea states has been investigated. In Otto (2019), the motion behaviour is described and explained by comparing model test results with numerical simulations. An interesting aspect in this is the relative importance of wave diffraction, wave radiation and the dissipation of energy in the construction. In the present paper, design optimizations have been performed by varying the draft, size and shape of the islands, making use of the numerical procedure as described in Otto (2019).
Artificial islands could be a way to support human activities at sea on the longer term. With an increasing population near the coast and a rising sea level the ocean becomes an interesting alternative for activities on land. Societal challenges, such as the production of renewable energy and the production of seafood on large scale, could be future applications of artificial islands. Depending on the water depth artificial islands could be constructed as reclaimed land, floating or as a hybrid concept.
Alternative fuels such as hydrogen, ammonia or synthetic methane are being studied as alternative for fossil fuels on ships. These synthetic fuels could be produced on islands from renewable electricity that is generated offshore. In the future, floating islands could serve as an energy hub and this could be combined with an (air)port to support the transition towards zero emission transport.
The ambitious intervention plan along the E39 European road in Norway has given the possibility to evaluate special structures to cross the deep and wide Norwegian fjords. Among them, the Submerged Floating Tube Bridge, a submerged structure floating at a defined position below the sea level. The first study was completed in 2011, demonstrating that a twin tube bridge was a feasible solution for crossing the Sognefjord, the deepest fjord along the west coast of Norway. After that, several feasibilities studies have been carried out by the Norwegian Public Road Administration (NPRA) raising the knowledge on this special bridge.
The present paper focuses on the experience of the NPRA in studying the SFTB, highlighting the challenges that the designers had to face in the study of the structure in the Norwegian environment. The position of the fjords respect to the open sea, the geographical conditions and the local environmental loads have strongly influenced the characteristics of the structure and the choices done in every step of the design. In addition, special requirements for some of the Norwegian fjords needed to be considered, including special loads in the design, like the impact of submarines on the structure. Safety issues and the need of lowering the maintenance for the design life of the structure have also strongly affected the final shape and configuration of the bridges.
The experience grown in the NPRA with these studies allows to make some general considerations and suggestions for the designers, depending on the specific requirements for the structure. Furthermore, suggestions based on the Norwegian experience can be done also with the purpose of optimizing the final cost of the SFTB.
The need of improvements for the E39 road in Norway allowed to develop, in the recent years, several studies on the Submerged Floating Tube Bridge (SFTB). The Norwegian Public Road Administration (NPRA) has put a lot of effort in disseminating the results of its research, in order to raise the international knowledge on this particular structure. The present paper summarizes the main achievements of the “Norwegian experience” in the design of the SFTB.
The paper considers the technologies of the perspective marine industrial complex of aquaculture with energy supply from renewable sources. Technological schemes of structures and devices of the onshore plant for the cultivation of hydrobionts, a marine underwater farm and a supply vessel for working with marine plantations are presented. A universal autonomous mobile wave device is presented as a variant of using the energy of waves of the open ocean.
Currently, self-contained, civilian, volatile devices for navigational equipment of the seas, research submarine and surface autonomous devices, mainly receive power from batteries. The number of these facilities is more than one million and the priority task is to prevent adverse ecological consequences of energy supply for the world ocean, regardless of costs. For these purposes, separate developments are used for solar energy, wind energy, waves, currents, temperature differences and salinity of sea water. The optimal result will be the transfer of production and processing ships to hydrogen technologies. A more complex factor threatening the Earth's ecology is due to the rapid growth of industrial coastal marine aquaculture enterprises.
PERSPECTIVE COMPLEX OF MARICULTURE
A comprehensive program for the development of marine aquaculture technologies is required, taking into account the need for clean energy and the future creation of marine underwater plantations, while preserving the coastal environment and local aquatic organisms.Modular plant for breeding hydrobionts
The future network complex developed by Loshchenkov, Knyazhev (2014) for the coasts of the Far East of Russia can serve as a contribution to the development of the Program. The complex contains a coastal enterprise for the cultivation of hydrobionts, bottom plantations in the natural environment and underwater plantations in the water column in the shelf zone.
Coastal breeding plant, due to placement in remote, inaccessible ecologically clean areas of the coast, with valuable local species, is semi-automatic, in a modular design. The plant is located, after studying local geological, meteorological, hydrological and hydrobiological parameters in the places of maximum energy flows, Pool modules and energy modules are manufactured depending on the type of hydrobiont and local natural renewable energy sources. The scheme of the plant for the cultivation of hydrobionts on island of Popov of the Peter the Great Gulf developed for the mariculture enterprise is shown in Fig. 1.
Zhao, Xuanlie (Dalian University of Technology) | Ning, Dezhi (Dalian University of Technology) | Johanning, Lars (Dalian University of Technology, University of Exeter) | Teng, Bin (Dalian University of Technology)
High construction-cost is one of the barriers that limited the developments of wave energy utilization. Integrating wave energy converters (WECs) into other marine structures may reduce the construction cost of WECs effectively. In this paper, an integrated system with a medium array (11 devices) of heaving point absorber WECs (PAWECs) arranged at the weather side of a fixed pontoon-type structure is proposed. The hydrodynamics of the PAWECs are investigated numerically by using higher-order boundary element method (HOBEM) code package (i.e., WAFDUT), which is developed based on linear potential flow theory. The hydrodynamic performance (including interaction factor, wave exciting force and heave response) of the WEC array with the rear pontoon is investigated with focus on the influence of the spacing between the WEC array and the pontoon (WEC-pontoon spacing). For sake of comparisons, the results corresponding to the isolated WEC array, i.e., without the pontoon, are presented. Results show that the performance of the pontoon-integrated WEC array performs better than that without the pontoon.
One obstacle that limits the wave energy utilization is the high construction cost. Integrations of wave energy converters (WECs) and other marine structures (such as breakwaters, offshore wind turbine, offshore platforms, etc.) have attracted much attention for its advantage of cost-sharing (Mustapa et al., 2017; Astariz and Iglesias, 2015; Favaretto et al., 2017). The cost reduction of WECs caused by the integration scheme may enhance the competitiveness of the wave energy converters. Pontoon-type structures are very common in offshore engineering, such as breakwaters, floating docks, ships, etc. In addition to the sharing of the infrastructures of both aspects, the WEC devices can provide power to the offshore operation in a convenient way.
It is understood that, for the pontoon-type structures, the wave conditions at the weather side can be described as the superposition of the incident waves and the reflected waves caused by the pontoon. Thus, it is expected that the energy conversion efficiency of the WECs can be improved. There are some cutting edge studies on improving the efficiency of WECs (mainly including oscillating water column WECs and heaving point absorber WECs) by using the reflection of costal structures. The detailed investigations can be found in Howe and Nader (2017), McIver and Evans (1988), Mavrakos et al. (2004), Schay et al. (2013) and Zhao et al. (2017).