A semi-submersible floating structure includes a horizontal platform with a symmetrical arrangement of buoyant bodies extending vertically downwardly from the platform. The buoyant bodies consist of a tubular column secured by a bending-resistant connection to the platform with a closed container secured to and extending downwardly from the lower end of the tubular column. The horizontal cross-sectional area of the closed container is for most of its vertical height greater than the transverse cross -sectional area of the tubular column. At least the lower portion of the closed container has a curvilinear surface. An annular wall extends around and is spaced radially outwardly from each of the closed containers and the wall, in combination with the enclosed container, forms an annular chamber therebetween open at the bottom and closed at the top. The platform and the buoyant bodies are formed of reinforced concrete or prestressed concrete.
... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false Thunder Horse Semi-Submersible... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.843 Thunder Horse Semi-Submersible safety zone. (a) Description. Thunder Horse Semi-Submersible, Mississippi Canyon 778 (MC...
... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false Thunder Horse Semi-Submersible... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.843 Thunder Horse Semi-Submersible safety zone. (a) Description. Thunder Horse Semi-Submersible, Mississippi Canyon 778 (MC...
... 33 Navigation and Navigable Waters 2 2012-07-01 2012-07-01 false Thunder Horse Semi-Submersible... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.843 Thunder Horse Semi-Submersible safety zone. (a) Description. Thunder Horse Semi-Submersible, Mississippi Canyon 778 (MC...
... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Thunder Horse Semi-Submersible... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.843 Thunder Horse Semi-Submersible safety zone. (a) Description. Thunder Horse Semi-Submersible, Mississippi Canyon 778 (MC...
... 33 Navigation and Navigable Waters 2 2014-07-01 2014-07-01 false Thunder Horse Semi-Submersible... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.843 Thunder Horse Semi-Submersible safety zone. (a) Description. Thunder Horse Semi-Submersible, Mississippi Canyon 778 (MC...
... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false Atlantis Semi-Submersible safety... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.841 Atlantis Semi-Submersible safety zone. (a) Description. Atlantis Semi-Submersible, Green Canyon 787 (GC 787), located at...
... 33 Navigation and Navigable Waters 2 2014-07-01 2014-07-01 false Atlantis Semi-Submersible safety... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.841 Atlantis Semi-Submersible safety zone. (a) Description. Atlantis Semi-Submersible, Green Canyon 787 (GC 787), located at...
... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false Atlantis Semi-Submersible safety... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.841 Atlantis Semi-Submersible safety zone. (a) Description. Atlantis Semi-Submersible, Green Canyon 787 (GC 787), located at...
... 33 Navigation and Navigable Waters 2 2012-07-01 2012-07-01 false Atlantis Semi-Submersible safety... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.841 Atlantis Semi-Submersible safety zone. (a) Description. Atlantis Semi-Submersible, Green Canyon 787 (GC 787), located at...
... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Atlantis Semi-Submersible safety... SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES SAFETY ZONES § 147.841 Atlantis Semi-Submersible safety zone. (a) Description. Atlantis Semi-Submersible, Green Canyon 787 (GC 787), located at...
Noble, P.G.; Singh, D.
A preliminary research project has been carried out to determine the effect of small ice floes on a semi-submersible drilling unit. Physical model tests have been conducted with two main objectives: first, to determine the ability of the columns to prevent ice from passing between them (arching) and thus minimizing the chance of riser damage, and second, to determine the total ice load on the semi-submersible during interaction with ice field concentrations. Three models were used, representing one half of a four, six or eight-legged semi-submersible platform. The dimensions and spacing of the columns were such that the heave and pitch responses were kept constant. The tests were conducted at a model scale of 1:30 using synthetic ice. Test results showed the maximum load measured on a four-legged semisubmersible model, at 100 percent ice floe concentration, was on the order of half of that measured on six or eight-legged semi-submersible models. Also the ice loads on a four-legged semi-submersible model at lower ice floe concentration were substantially less than those for six or eight-legged semi-submersible models. The total ice load on semi-submersible models is found to be a function of ice floe concentration. Up to about 75 percent ice concentration, ice loads varied linearly. Beyond that, the loads increased exponentially for all semi-submersible models.
Sharma, R.; Kim, Tae-Wan; Sha, O. P.; Misra, S. C.
Availability of economic and efficient energy resources is crucial to a nation's development. Because of their low cost and advancement in drilling and exploration technologies, oil and gas based energy systems are the most widely used energy source throughout the world. The inexpensive oil and gas based energy systems are used for everything, i.e., from transportation of goods and people to the harvesting of crops for food. As the energy demand continues to rise, there is strong need for inexpensive energy solutions. An offshore platform is a large structure that is used to house workers and machinery needed to drill wells in the ocean bed, extract oil and/or natural gas, process the produced fluids, and ship or pipe them to shore. Depending on the circumstances, the offshore platform can be fixed (to the ocean floor) or can consist of an artificial island or can float. Semi-submersibles are used for various purposes in offshore and marine engineering, e.g. crane vessels, drilling vessels, tourist vessels, production platforms and accommodation facilities, etc. The challenges of deepwater drilling have further motivated the researchers to design optimum choices for semi-submersibles for a chosen operating depth. In our series of eight papers, we discuss the design and production aspects of all the types of offshore platforms. In the present part I, we present an introduction and critical analysis of semi-submersibles.
Tranter, P. )
Tender-assisted drilling (TAD) involves the use of tender support vessel (TSV) during the drilling phase of platform development to provide drilling utilities to the platform-mounted drilling package. The TSV provides facilities such as mud mixing, storage, pumping, bulk storage, hotel accommodations, and power. Thus, the platform topsides and jacket weight and size can be smaller and less expensive. The paper discusses the advantages and disadvantages of TAD, then describes the TAD vessel, semisubmersible, platform cost savings, accommodations, drilling and workovers, and field experience.
Hadley, I.; Sinclair, C.I.K.; Magne, E.
This paper describes the life extension of a semi-submersible drilling rig built in the early 1970`s. A nominal design life of 20 years was estimated at the time of building; however, in the interim period, numerous improvements have been made in fatigue life estimation ad life improvement techniques, raising the possibility that a further 20 years of operation could be considered. The life extension strategy made use of a number of aspects of offshore technology which were not available at the time of construction of the rig. Finite element studies and results from offshore research programs were used to gauge the effect of fatigue life improvement techniques. The program demonstrated the feasibility of extending the operation of the rig for a further 20 years, with the interval between in-service inspection increased to every five years. It also provided a valuable database of fracture toughness data for the rig materials, which may be used in future work to address reliability issues.
Robertson, A.; Jonkman, J.; Masciola, M.; Song, H.; Goupee, A.; Coulling, A.; Luan, C.
Phase II of the Offshore Code Comparison Collaboration Continuation (OC4) project involved modeling of a semisubmersible floating offshore wind system as shown below. This report documents the specifications of the floating system, which were needed by the OC4 participants for building aero-hydro-servo-elastic models.
Benitz, M. A.; Schmidt, D. P.; Lackner, M. A.; Stewart, G. M.; Jonkman, J.; Robertson, A.
Computational fluid dynamics (CFD) simulations were carried out on the OC4-DeepCwind semi-submersible to obtain a better understanding of how to set hydrodynamic coefficients for the structure when using an engineering tool such as FAST to model the system. The focus here was on the drag behavior and the effects of the free-surface, free-ends and multi-member arrangement of the semi-submersible structure. These effects are investigated through code-to-code comparisons and flow visualizations. The implications on mean load predictions from engineering tools are addressed. The work presented here suggests that selection of drag coefficients should take into consideration a variety of geometric factors. Furthermore, CFD simulations demonstrate large time-varying loads due to vortex shedding, which FAST's hydrodynamic module, HydroDyn, does not model. The implications of these oscillatory loads on the fatigue life needs to be addressed.
Gueydon, S.; Duarte, T.; Jonkman, J.; Bayati, I.; Sarmento, A.
As offshore wind projects move to deeper waters, floating platforms become the most feasible solution for supporting the turbines. The oil and gas industry has gained experience with floating platforms that can be applied to offshore wind projects. This paper focuses on the analysis of second-order wave loading on semisubmersible platforms. Semisubmersibles, which are being chosen for different floating offshore wind concepts, are particularly prone to slow-drift motions. The slack catenary moorings usually result in large natural periods for surge and sway motions (more than 100 s), which are in the range of the second-order difference-frequency excitation force. Modeling these complex structures requires coupled design codes. Codes have been developed that include turbine aerodynamics, hydrodynamic forces on the platform, restoring forces from the mooring lines, flexibility of the turbine, and the influence of the turbine control system. In this paper two different codes are employed: FAST, which was developed by the National Renewable Energy Laboratory, and aNySIM, which was developed by the Maritime Research Institute Netherlands. The hydrodynamic loads are based on potential-flow theory, up to the second order. Hydrodynamic coefficients for wave excitation, radiation, and hydrostatic forces are obtained with two different panel codes, WAMIT (developed by the Massachusetts Institute of Technology) and DIFFRAC (developed by MARIN). The semisubmersible platform, developed for the International Energy Agency Wind Task 30 Offshore Code Comparison Collaboration Continuation project is used as a reference platform. Irregular waves are used to compare the behavior of this platform under slow-drift excitation loads. The results from this paper highlight the effects of these loads on semisubmersible-type platforms, which represent a promising solution for the commercial development of the offshore deepwater wind resource.
Ferrari, J.A. Jr.; Morooka, C.K.
There are a few calculation programs around the world used for determining the main aspects of the Mooring Design of Semi-Submersible Platforms . These programs bold a worldwide acknowledgement and their results are actually reliable. But they require many runs to get a solution that comply with the Classification Society requirements. This paper presents some procedures in order to optimize the semi-submersible mooring design as well as to make it automatic. Regarding the optimization philosophies, the following aspects are treated: (1) the optimization of the platform heading and the mooring pattern based on the spreading of the environmental forces; (2) the searching for the optimum mooring line composition in an automatic mode. Basically, the paper`s main goal is to introduce some methods to find the lowest cost solution for the mooring system in a short time. All of these methods were computationally implemented creating the intelligent system named PROANC, which deals with the semi-submersible mooring design in a quasi-static and deterministic approach. It should be noted that the proposed system exerts a strong appeal as a design tool for feasibility studies of a given oil field and its quasi-static results can be directly applied to a mooring program capable of performing dynamic analysis. Finally some simulations are executed for different water depths and its final results, including the expended time to run, are presented in order to prove the PROANC system wide potential as a design tool.
Bayati, I.; Jonkman, J.; Robertson, A.; Platt, A.
The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of the system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the MARIN offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST in the future. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method has been applied to the OC4-DeepCwind semisubmersible platform, supporting the NREL 5-MW baseline wind turbine. The loads and response of the system due to the second-order hydrodynamics are analysed and compared to first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.
Xie, Shengbai; Yang, Di; Liu, Yi; Shen, Lian
Wind forcing makes a vital contribution to the hydrodynamic loads on structures at sea. The flow physics is complex, involving interactions among surface water waves, turbulent wind, and semi-submersed object. We perform a simulation-based study on a canonical problem of wind past a semi-submersed rectangular prism with the focus on the wave effect, which is an essential factor in wind loads at sea but has been elusive. To tackle this problem, we develop a hybrid simulation method consisting of two parts: a precursor simulation of coupled wind and wave motions in the far field upstream to provide physical inflow condition, and a near-field simulation of the air and water motions around the object. The simulation method is validated through numerical tests and comparisons with data from the literature for different aspects of the code. This hybrid simulation method is then applied to study the effect of surface wave motions on the wind load on the object. Various wave conditions are considered, including pure wind-sea satisfying the Joint North Sea Wave Project spectrum as well as wind-sea mixed with long-wavelength ocean swells. The simulation results exhibit significant oscillations in the wind load on the object. The oscillations are found to correlate well with the incident wave motions and are particularly strong in the presence of swells. The underlying mechanism is explained through analyses on variations of wind speed with different wave phases and wave-correlated flow patterns of the wind when it impinges on the object. Our simulations also indicate that waves have an appreciable effect on the wake behind the object.
Du, Junfeng; Wang, Shuqing; Chang, Anteng; Li, Huajun
Assessing the fatigue life of mooring systems is important for deep water structures. In this paper, a comprehensive fatigue analysis is conducted on the mooring lines applied in a semi-submersible platform with special focus on the low frequency (LF) fatigue damage. Several influential factors, including water depth, wave spectral parameters, and riser system, are considered. Numerical simulation of a semi-submersible platform with the mooring/riser system is executed under different conditions, and the fatigue damage of mooring lines is assessed by using the time domain analysis method as a benchmark. The effects of these factors on the mooring line tension and the fatigue damage are investigated and discussed in detail. Research results indicate that the LF fatigue damage only accounts for a very small portion of the total damage, although the LF components dominate the global motion response and the mooring line tension of the semi-submersible platform. However, it is demonstrated that the LF fatigue damage is clearly affected by the influential factors. The increase in water depth and spectral peak periods, and the existence of risers can weaken the contribution of the LF components to the mooring line fatigue damage, while the fatigue damage due to the LF components increases with the increase of significant wave height.
Zhang, Dagang; Sun, Weiying; Fan, Zhixia
Transportation of tension leg platform (TLP) structures for a long distance has always been associated with the use of a heavy semi-transport vessel. The requirements of this type of vessel are always special, and their availability is limited. To prepare for the future development of South China Sea deepwater projects, the China Offshore Oil Engineering Corporation has recently built a heavy lift transport vessel-Hai Yang Shi You 278. This semi-submersible vessel has a displacement capacity of 50k DWT, and a breath of 42 meters. Understanding the vessel's applicability and preparing it for use in future deepwater projects are becoming imminent needs. This paper reviews the current critical issues associated with TLP transportation and performs detailed analysis of the designed TLP during load-out and transportation. The newly built COOEC transportation vessel HYSY 278 was applied to dry transport of the TLP structure from the COOEC fabrication yard in Qingdao to an oil field in South China Sea. The entire process included the load-out of the TLP structure from the landsite of the fabrication yard, the offloading and float-on of the platform from the vessel, the dry transport of the TLP over a long distance, and the final offloading of the platform. Both hydrodynamic and structure analysis were performed to evaluate the behavior of the transport vessel and TLP structure. Special attention was paid to critical areas associated with the use of this new vessel, along with any potential limitations. The results demonstrate that HYSY 278 can effectively be used for transporting the structure with proper arrangement and well-prepared operation. The procedure and details were presented on the basis of the study results. Special attention was also given to discussion on future use based on the results from the analysis.
Robertson, A.; Jonkman, J.; Musial, W.; Vorpahl, F.; Popko, W.
Offshore wind turbines are designed and analyzed using comprehensive simulation tools that account for the coupled dynamics of the wind inflow, aerodynamics, elasticity, and controls of the turbine, along with the incident waves, sea current, hydrodynamics, and foundation dynamics of the support structure. The Offshore Code Comparison Collaboration (OC3), which operated under the International Energy Agency (IEA) Wind Task 23, was established to verify the accuracy of these simulation tools . This work was then extended under the Offshore Code Comparison Collaboration, Continuation (OC4) project under IEA Wind Task 30 . Both of these projects sought to verify the accuracy of offshore wind turbine dynamics simulation tools (or codes) through code-to-code comparison of simulated responses of various offshore structures. This paper describes the latest findings from Phase II of the OC4 project, which involved the analysis of a 5-MW turbine supported by a floating semisubmersible. Twenty-two different organizations from 11 different countries submitted results using 24 different simulation tools. The variety of organizations contributing to the project brought together expertise from both the offshore structure and wind energy communities. Twenty-one different load cases were examined, encompassing varying levels of model complexity and a variety of metocean conditions. Differences in the results demonstrate the importance and accuracy of the various modeling approaches used. Significant findings include the importance of mooring dynamics to the mooring loads, the role nonlinear hydrodynamic terms play in calculating drift forces for the platform motions, and the difference between global (at the platform level) and local (at the member level) modeling of viscous drag. The results from this project will help guide development and improvement efforts for these tools to ensure that they are providing the accurate information needed to support the design and
Nakamura, Masahiro; Yokokura, Kozo; Nakamura, Arata
Deepwater petroleum development is increasing throughout the world. Complete evaluation of deepwater oil fields prior to development is extremely important, but difficult due to harsh conditions and deepwater. Extended well testing and early production of a field will allow complete evaluation, reducing risk prior to long term commitments. Conceptual design and studies for a semisubmersible type deepwater drilling, early production and testing system with 100,000 bbl storage (DEPTS) that will allow this have been completed. Needs analysis were performed and several potential concepts compared. Sizing and costing of the semisubmersible unit, mooring, and riser systems as well as selection of the drilling, production, and storage units were carried out. The unique aspect of the system is that the combination of drilling, production facilities, and storage on the same vessel will allow the system to be applied across the early phases of offshore oil field development from drilling to early production. With storage integrated into the vessel, oil production can continue in the most extreme conditions. The system`s intended operational area will be the deepwater fields of Asia and Oceania. Studies have been carried out showing the technical and economic feasibility of the system in deepwater up to 2,000 m.
Song, Xun-cheng; Liu, Yong-wang; Guan, Zhi-chuan
Offshore wellbore temperature field is significant to drilling fluids program, equipment selection, evaluations on potential risks caused by casing thermal stress, etc. This paper mainly describes the theoretical basis, module structure and field verification of the simulator WHTSubmersible. This computer program is a useful tool for estimating transient temperature distribution of circulating drilling fluid on semi-submersible platform. WHTSubmersible is based on a mathematical model which is developed to consider radial and axial two-dimensional heat exchange of the inner drill pipe, the annulus, the drill pipe wall, the sea water and the formation in the process of drilling fluid circulation. The solution of the discrete equations is based on finite volume method with an implicit scheme. This scheme serves to demonstrate the numerical solution procedure. Besides, the simulator also considers the heating generated by drilling fluid circulation friction, drill bit penetrating rocks, friction between the drill column and the borehole wall, and the temperature effect on thermal physical properties and rheology of the drilling fluid. These measures ensure more accurate results. The simulator has been programmed as a dynamic link library using Visual C++, the routine interface is simple, which can be connected with other computer programs conveniently. The simulator is validated with an actual well temperature filed developed on a semi-submersible platform in South China, and the error is less than 5 %.
Murray, J.J.; Spencer, D.
Physical model tests were carried out on a scale model of a semisubmersible and a monohull tanker in drifting pack ice. The tests covered a range of drift velocities, directions and ice concentrations. The models were tested in both a fully restrained and moored condition. Data from the experiments were used to develop a semi-empirical numerical model to predict maximum global loads on the mooring system. These results were compared with the maximum loads on the mooring system caused by hydrodynamic forces (waves and current) predicted from a linear numerical model for waves. Analysis results showed that the maximum mooring loads due to the pack ice on the semisubmersible were considerably higher than those caused by the hydrodynamic forces on the same vessel. Also, the maximum mooring loads due to pack ice on the tanker were close to the maximum mooring loads caused by the hydrodynamic forces. Maximum mooring loads related to pack ice forces were realized in ice concentrations of 10/10 coverage while for concentrations less than 6/10 coverage loads attributed to pack ice were negligible in comparison to the hydrodynamic forces. The paper also presents a number of recommendations, based on these findings, to improve the performance of both vessel types and to advance the general state-of-the-art for analysis procedures related to offshore vessel moored in pack ice.
Park, Jinmo; Kim, Nakwan
In this paper, we employ a dynamics modeling method for investigating a multi-body dynamics system of semi-submersible autonomous underwater vehicles consisting of a towing vehicle operated near the water surface, a tow cable, and a towfish. The towfish, which is towed by a marine cable for the purposes of exploration or mine hunting, is modeled with a Six-Degree-of-Freedom (6-DOF) equation of motion that reflects its hydrodynamics characteristics. The towing cable, which can experience large displacements and deformations, is modeled using an absolute nodal coordinate formulation. To reflect the hydrodynamic characteristics of the cable during motion, the hydrodynamic force due to added mass and the drag force are imposed. To verify the completeness of the modeling, a few simple numerical simulations were conducted, and the results confirm the physical plausibility of the model.
Robertson, A.; Jonkman, J.; Vorpahl, F.; Popko, W.; Qvist, J.; Froyd, L.; Chen, X.; Azcona, J.; Uzungoglu, E.; Guedes Soares, C.; Luan, C.; Yutong, H.; Pengcheng, F.; Yde, A.; Larsen, T.; Nichols, J.; Buils, R.; Lei, L.; Anders Nygard, T.; et al.
Offshore wind turbines are designed and analyzed using comprehensive simulation tools (or codes) that account for the coupled dynamics of the wind inflow, aerodynamics, elasticity, and controls of the turbine, along with the incident waves, sea current, hydrodynamics, and foundation dynamics of the support structure. This paper describes the latest findings of the code-to-code verification activities of the Offshore Code Comparison Collaboration, Continuation (OC4) project, which operates under the International Energy Agency (IEA) Wind Task 30. In the latest phase of the project, participants used an assortment of simulation codes to model the coupled dynamic response of a 5-MW wind turbine installed on a floating semisubmersible in 200 m of water. Code predictions were compared from load-case simulations selected to test different model features. The comparisons have resulted in a greater understanding of offshore floating wind turbine dynamics and modeling techniques, and better knowledge of the validity of various approximations. The lessons learned from this exercise have improved the participants? codes, thus improving the standard of offshore wind turbine modeling.
Ng, Peter K L; Ahyong, Shane T
A new genus and new species of pseudozioid crab of the family Pilumnoididae is described from a fouling community on a semisubmersible oil platform in Singapore that had been operating in the Timor Sea and South China Sea. Setozius incertus gen. et sp. nov. superficially resembles species of Pilumnus (Pilumnidae, Pilumnoidea) but has male first and second gonopod structures characteristic of the Pseudozioidea. The form of the carapace, male anterior thoracic sternum and male abdomen indicates that it should be classified in the Pilumnoididae. Setozius is the first member of the family to be recorded from the Indo-West Pacific; all other known pilumnoidids occur in the Atlantic and eastern Pacific. PMID:25243306
Benitz, M. A.; Schmidt, D. P.; Lackner, M. A.; Stewart, G. M.; Jonkman, J.; Robertson, A.
Hydrodynamic loads on the platforms of floating offshore wind turbines are often predicted with computer-aided engineering tools that employ Morison's equation and/or potential-flow theory. This work compares results from one such tool, FAST, NREL's wind turbine computer-aided engineering tool, and the computational fluid dynamics package, OpenFOAM, for the OC4-DeepCwind semi-submersible analyzed in the International Energy Agency Wind Task 30 project. Load predictions from HydroDyn, the offshore hydrodynamics module of FAST, are compared with high-fidelity results from OpenFOAM. HydroDyn uses a combination of Morison's equations and potential flow to predict the hydrodynamic forces on the structure. The implications of the assumptions in HydroDyn are evaluated based on this code-to-code comparison.
Couling, A. J.; Goupee, A. J.; Robertson, A. N.; Jonkman, J. M.
To better access the abundant offshore wind resource, efforts across the world are being undertaken to develop and improve floating offshore wind turbine technologies. A critical aspect of creating reliable, mature floating wind turbine technology is the development, verification, and validation of efficient computer-aided-engineering (CAE) tools that can be relied upon in the design process. The National Renewable Energy Laboratory (NREL) has created a comprehensive, coupled analysis CAE tool for floating wind turbines, FAST, which has been verified and utilized in numerous floating wind turbine studies. Several efforts are currently underway that leverage the extensive 1/50th-scale DeepCwind wind/wave basin model test dataset, obtained at the Maritime Research Institute Netherlands (MARIN) in 2011, to validate the floating platform functionality of FAST to complement its already validated aerodynamic and structural simulation capabilities. In this paper, further work is undertaken to continue this validation. In particular, the ability of FAST to replicate global response behaviors associated with dynamic wind forces, second-order difference-frequency wave-diffraction forces and their interaction with one another are investigated.
A subsea template is installed by a method which includes the steps of securing the template in a position beneath the deck of a semi-submersible drilling vessel, moving the semi-submersible drilling vessel to an appropriate offshore site and subsequently lowering the template from the semi-submersible to the sea bed. In addition, at least three anchorage templates may be loaded onto one or both of the pontoons of the semi-submersible drilling vessel at its original position and are subsequently lowered from the pontoons to their respective locations on the sea bed after the semi-submersible has moved to the offshore site.
... Mobile Offshore Drilling Units (MODUs): Drill ship MODUs 6,710 Submersible MODUs 4,695 Self-elevating MODUs 4,695 Semi-submersible MODUs 8,050 Nautical School Vessels: Length not greater than 100 feet...
... Mobile Offshore Drilling Units (MODUs): Drill ship MODUs 6,710 Submersible MODUs 4,695 Self-elevating MODUs 4,695 Semi-submersible MODUs 8,050 Nautical School Vessels: Length not greater than 100 feet...
... Mobile Offshore Drilling Units (MODUs): Drill ship MODUs 6,710 Submersible MODUs 4,695 Self-elevating MODUs 4,695 Semi-submersible MODUs 8,050 Nautical School Vessels: Length not greater than 100 feet...
Bowie, R.D.; Richardson, K.L.
Floating Production Systems (FPSs) can be either, custom built or a converted semi-submersible, tanker or barge. The paper describes the necessary steps to be taken for the Classification and Certification of FPSs and FPSOS. The paper outlines the latest Classification and certification requirements for both semi-submersible and ship type FPSS. Classification and regulatory requirements for the Hull Structure, Stability, Station Keeping, Shipboard and Production Systems are discussed.
The behavior of a moored open bottom floating platform has been investigated by a series of model tests at the wave basin of CSSRC (69 x 46 x 4m). The model tests were divided into two versions, i.e., version 1 for a conventional semi-submersible and version 2 for an open bottom floating platform. Comparison was made under the same mooring and environmental conditions including waves, steady wind and current. The results of model tests indicate that the open bottom floating platform is more stable and with less mooring loads than the conventional semi-submersible.
Peavy, M.A.; Fahel, R.A. )
This paper provides a technical comparison of jet-pump and nitrogen lift during the drillstem tests (DST's) of a low-gravity, high-viscosity crude on a semisubmersible drilling vessel. Eight DST testing sequences are presented to demonstrate that jet-pump-lift operations are better suited than nitrogen-lift techniques for obtaining reservoir data during Monterey DST's.
... 22 Foreign Relations 1 2014-04-01 2014-04-01 false Submersible vessels. 121.14 Section 121.14... MUNITIONS LIST Enumeration of Articles § 121.14 Submersible vessels. (a) In USML Category XX, submersible and semi-submersible vessels are those, manned or unmanned, tethered or untethered, that: (1)...
Edwards, R.Y.; Johnson, T.L.; Johnson, R.P.
This paper describes large scale hydrodynamic model tests of the Enserch Exploration Garden Banks 388 Floating Production Facility (FPF). This unique facility consists of a semi-submersible connected to a template on the sea floor 2,096 feet below the surface through a buoyant, free standing ``rigid`` riser. The top of the riser and its manifold are located well below the surface to minimize the forces exerted on the riser by waves. Numerous flexible conductors connect the semi-submersible to the manifold on the top of the riser. The emphasis of the model test program was to confirm the estimates of: The structural response of the buoyant, rigid production riser and an adjacent drilling riser; The relative displacements between the semisubmersible and the production riser; The relative displacements between the production riser and drilling riser; and The forces which must be endured by the tensioners and flexible hoses which join the semi-submersible to the production riser. The paper describes the planning and preparation of the model components, the unique aspects of the simulation of the environments and the structural properties of the models, the execution of the experiments and the handling of the large number of measurements necessary to characterize the response of the multi-component system. Finally, the data analysis tools which were employed to provide an understanding of the responses of the system are discussed. 22 figs., 1 tab.
The bibliography contains citations concerning the technology and environmental impacts of dredging. Equipment, including semi-submersible cutter platforms, is described. Other topics include sediment movement, factors affecting sediment movement, the disposal of dredged material, and computer models predicting the fate of the dredged materials. The environmental impacts of the dredged areas and the effects of ocean dumping of dredged material are also discussed. (Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)
The bibliography contains citations concerning the technology and environmental impacts of dredging. Equipment, including semi-submersible cutter platforms, is described. Other topics include sediment movement, factors affecting sediment movement, the disposal of dredged material, and computer models predicting the fate of the dredged materials. The environmental impacts of the dredged areas and the effects of ocean dumping of dredged material are also discussed. (Contains 250 citations and includes a subject term index and title list.)
Zhang, Dagang; Chen, Yongjun; Zhang, Tianyu
This paper studies the current available options for floating production platforms in developing deepwater oil fields and the potential development models of future oil and gas exploration in the South China Sea. A detailed review of current deepwater platforms worldwide was performed through the examples of industry projects, and the pros and cons of each platform are discussed. Four types of platforms are currently used for the deepwater development: tension leg platform, Spar, semi-submersible platform, and the floating production system offloading. Among these, the TLP and Spar can be used for dry tree applications, and have gained popularity in recent years. The dry tree application enables the extension of the drilling application for fixed platforms into floating systems, and greatly reduces the cost and complexity of the subsea operation. Newly built wet tree semi-submersible production platforms for ultra deepwater are also getting their application, mainly due to the much needed payload for deepwater making the conversion of the old drilling semi-submersible platforms impossible. These platforms have been used in different fields around the world for different environments; each has its own advantages and disadvantages. There are many challenges with the successful use of these floating platforms. A lot of lessons have been learned and extensive experience accumulated through the many project applications. Key technologies are being reviewed for the successful use of floating platforms for field development, and potential future development needs are being discussed. Some of the technologies and experience of platform applications can be well used for the development of the South China Sea oil and gas field.
Malme, C.I.; Miles, P.R.; Tyack, P.; Clark, C.W.; Bird, J.E.
An investigation was made of the potential effects of underwater noise from petroleum-industry activities on the behavior of feeding humpback whales in Frederick Sound and Stephens Passage, Alaska in August, 1984. Test sounds were a 100 cu. in. air gun and playbacks of recorded drillship, drilling platform, production platform, semi-submersible drill rig, and helicopter fly-over noise. Sound source levels and acoustic propagation losses were measured. The movement patterns of whales were determined by observations of whale-surfacing positions.
Much exploration drilling is done in subarctic waters around the world, and this will be important in the future. Special demands will be made on the drilling structures to enable them to withstand collisions with drifting ice. A Newfoundland Certificate of Fitness, for example, says a vessel must be able to tolerate collision with the largest iceberg that can be undetectable by radar, with out the danger of platform collapse. The iceberg in this case is defined as having a weight of 5000 tons and a drifting velocity of 2 meters/second. Devices to prevent ice damage to the trusses of semisubmersibles are discussed.
The ability of floating platforms and tankers to operate in the Hibernia environment is discussed. The basic environmental difference between the fixed and floating concept is that the floating systems are unable to withstand impact from heavy ice floes or large icebergs. Therefore, they are designed to utilize safe, reliable quick-disconnect systems, which permit them to evacuate the area when encroaching ice presents a potential hazard. Floating production systems being considered for Hibernia involve ship-type vessels, conventional semisubmersibles, and some form of floating storage and loading facility.
Salton, Jonathan R.; Buttz, James H.; Garretson, Justin; Hayward, David R.; Hobart, Clinton G.; Deuel, Jr., Jamieson K.
A robotic vehicle having two or more tracked mobility platforms that are mechanically linked together with a two-dimensional coupling, thereby forming a composite vehicle of increased mobility. The robotic vehicle is operative in hazardous environments and can be capable of semi-submersible operation. The robotic vehicle is capable of remote controlled operation via radio frequency and/or fiber optic communication link to a remote operator control unit. The tracks have a plurality of track-edge scallop cut-outs that allow the tracks to easily grab onto and roll across railroad tracks, especially when crossing the railroad tracks at an oblique angle.
Lewis, G. ); DeGruy, P. ); Avery, L. )
Damage to Texaco Pipeline Inc.'s Eugene Island Pipeline System (EIPS) in last year's Hurricane Andrew prompted a complex repair project unique for the Gulf of Mexico. Damage, suffered when the anchor of a runaway semisubmersible drilling rig crashed into the 20-in. EPIS during the height of the storm, caused the pipeline to fail under pressure within 48 hr. after start-up following the storm. The paper describes the importance of the EIPS; system safety; Andrew's damage; locating the leak; repair options; the chosen system; mechanical bonding; end connectors and ball flanges; and diving operations.
In one of the largest offshore skidding operations ever undertaken in the UK, a unique system of submersible pumps linked through central control stations was used to load out the deck of a new-built semisubmersible rig onto three barges. Ninety-three submersible pumps and a hydraulic track system were required to move the deck onto the 100 x 14 x 7.5-meter barges. The most critical task was to maintain the barges at a constant level as they took on the load. The problem was overcome with combined dewatering and ballasting actions, carried out simultaneously from each control center and from each barge.
Barber, Bryan; Kahn, Laura; Wong, David
Offshore operations such as oil drilling and radar monitoring require semisubmersible platforms to remain stationary at specific locations in the Gulf of Mexico. Ocean currents, wind, and waves in the Gulf of Mexico tend to move platforms away from their desired locations. A computer model was created to predict the station keeping requirements of a platform. The computer simulation uses remote sensing data from satellites and buoys as input. A background of the project, alternate approaches to the project, and the details of the simulation are presented.
The worldwide semisubmersible drilling rig fleet is approaching retirement. But replacement is not an attractive option even though dayrates are reaching record highs. In 1991, Schlumberger Sedco Forex managers decided that an alternative might exist if regulators and insurers could be convinced to extend rig life expectancy through restoration. Sedco Forex chose their No. 704 semisubmersible, an 18-year North Sea veteran, to test their process. The first step was to determine what required restoration, meaning fatigue life analysis of each weld on the huge vessel. If inspected, the task would be unacceptably time-consuming and of questionable accuracy. Instead a suite of computer programs modeled the stress seen by each weld, statistically estimated the sea states seen by the rig throughout its North Sea service and calibrated a beam-element model on which to run their computer simulations. The elastic stiffness of the structure and detailed stress analysis of each weld was performed with ANSYS, a commercially available finite-element analysis program. The use of computer codes to evaluate service life extension is described.
Any activity requiring the development of the HLLV can benefit by operations from an offshore space center (OSC) since operating near the equator provides a twenty percent increase in payload in an ecliptic plan orbit. Some OSC concepts considered include a moored floating (semisubmersible) design, a stationary design supported by fixed piles, and a combination of these two. The facility supports: a 15,000 foot long, 300 foot wide runway, designed to accommodate a two staged winged launch vehicle, with a one million pound payload capacity to low earth orbit, an industrial area for HLLV maintenance, an airport terminal, control and operation center, and observation tower, liquid hydrogen and liquid oxygen production and storage, and fuel storage platforms, a power generation station, docks with an unloading area, two separate launch sites, and living accommodations for 10,000 people. Potential sites include the Paramount Seamount in the Pacific Ocean off the north coast of South America. Cost estimates are considered.
Rig designers and owners continue to fine-tune a variety of sophisticated new generation semisubmersible and jackup designs that will go into production once supply catches up with demand, later in the decade. The units will be designed to meet the latest international safety requirements, be more highly specialized that most existing rigs, and they will be expensive. Rising oil prices and improved rig utilization will be the catalysts to spur future rig orders. Over the longer term, the aging semi fleet will need to be upgraded or replaced beginning in the second half of the deacade. Rig life extension programs will be economically justified for many rigs, but new construction will pay a significant role in the semi fleet this decade. Many rig designs will be capable of ultra-deep-water drilling and production in water depths as deep as 10,000 feet. Additional designs concepts and projects are discussed.
Triantafyllou, M. S.; Bodson, M.
The present investigation is concerned with the prediction of the future behavior of a vessel within some confidence bounds at a specific instant of time, taking into account an interval of a few seconds. The ability to predict accurately the motions of a vessel can reduce significantly the probability of failure of operations in rough seas. The investigation was started as part of an effort to ensure safe landing of aircraft on relatively small vessels. However, the basic principles involved in the study are the same for any offshore operation, such as carbo transfer in the open sea, structure installation, and floating crane operation. The Kalman filter is a powerful tool for achieving the goals of the prediction procedure. Attention is given to a linear optimal predictor, the equations of motion of the vessel, the wave spectrum, rational approximation, the use of Kalman filter and predictor in an application for a ship, and the motions of a semisubmersible.
Makino, Yoshiyuki; Kagoura, Toru; Ishii, Kenichi; Fuku, Tadashi; Kawakama, E.H.; Yamaguchi, Takumi
In the floating oil production system that is commonly sued in fields 400 m deep or greater, flexible pipes are increasingly used to transport the crude oil and natural gas from the well head to semisubmersibles or tankers, and they are thus indispensable part of the transport system. As offshore wells are brought in at greater depths, the production system facilities is aimed to become smaller and the applications for flexible pipes, with their fast and low cost installation, are certain to increase. In 1993, Furukawa Electric delivered flexible pipes to PETROBRAS for use in deep offshore oil field at 500 m of water depth. This paper presents flexible pipe design points, development item, type approval and verification for deepwater applications.
Gudmestad, O.T.; Pollard, N.
For development of offshore fields, the operator must select production concepts. As several options like subsea templates, floating production and storage concepts, semisubmersibles and steel platforms etc. are available, this paper will review the specifics of one of the possible concepts, the concrete platform. The application of offshore concrete platforms is gaining renewed interest world wide. Several operators are presently carrying out comparisons between offshore concrete structures and jacket support structures. This evaluation includes considerations related to constructability incorporating studies of potential construction sites, and infrastructures as well as availability of materials. This paper summarizes requirements for carrying out an offshore concrete platform construction project and will be useful to those interested in concrete projects.
Letourneur, O.; Falcimaigne, J.
The floating production platforms operating in the North Sea are adapted from drilling semisubmersibles which allow only a limited payload capacity. Experience of concrete production platforms constructed for the North Sea has led Sea Tank Co. to propose a floating platform which offers large payload and oil storage capacities similar to those of existing fixed platforms. Sea Tank Co. and Institut Francais du Petrole joined forces in early 1976 to study the feasibility of a concrete floating production platform incorporating the structure and the production riser together. The results of this 3-yr program show that the concrete floating structure is economically attractive for permanent utilization on a production site. Furthermore, concrete has definite advantages over other materials, in its long term behavior.
Hall, J.E.; Sheng, W.Z.; Krenek, M.J.; Douglas, L.D.; Macfarlane, A.M.; Mohr, H.O.
The Liuhua 11-1 Field is being developed using 20 subsea-completed wells. The development capitalizes on an innovative Modular Building Block method that does not require a seafloor template structure for the field`s diverless subsea production system. The modular assemblies are installed on the seafloor from semi-submersible floating production system while simultaneous in-field drilling and well completion activities are conducted. Electrical pumps downhole drive produced fluids through subsea pipelines to a floating production, storage, and offloading facility. The Liuhua 11-1 Development subsea system uses new and emerging diverless technology in several key areas. These include: a modular seafloor commingling production manifold system for multiple wells; wet-mateable electrical power connectors; horizontal spool trees and associated running tools; remotely operated vehicle (ROV) intervention packages; on-site-fabricated, rigid flowline and pipeline connections; and ROV-deployed, control-umbilical jumpers and instrument packages.
Browning, J. R.; Jonkman, J.; Robertson, A.; Goupee, A. J.
In 2007, the FAST wind turbine simulation tool, developed and maintained by the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL), was expanded to include capabilities that are suitable for modeling floating offshore wind turbines. In an effort to validate FAST and other offshore wind energy modeling tools, DOE funded the DeepCwind project that tested three prototype floating wind turbines at 1/50th scale in a wave basin, including a semisubmersible, a tension-leg platform, and a spar buoy. This paper describes the use of the results of the spar wave basin tests to calibrate and validate the FAST offshore floating simulation tool, and presents some initial results of simulated dynamic responses of the spar to several combinations of wind and sea states.
Zhu, Jianxun; Sun, Liping; Liu, Shengnan; Kang, Jichuang
This paper focuses on the research of a semi-submersible platform equipped with a DP-assisted mooring system. Based on the working principles of the DP-assisted mooring system and the model of the platform motion, a time domain simulation program is applied to analyze the impact, in the case of one line failure, on the platform motion, power consumption of the thrusters and the tension of the mooring lines. The results show that, under the 10-year wind dominant, a one line failure will have little impact on the tension of the mooring lines. When the failure line is windward, the power consumption will increase greatly with a weakened position of accuracy. However when the failure line is leeward, the power consumption will be reduced with a partly strengthened position of accuracy.
Hopkins, Grant A; Forrest, Barrie M
The potential for oil rigs to transport diverse, reef-like communities around the globe makes them high risk vectors for the inadvertent spread of non-indigenous species (NIS). This paper describes two case studies where a suite of pre-border management approaches was applied to semi-submersible drilling rigs. In the first case study, a drilling rig was defouled in-water prior to departure from New Zealand to Australia. Risk mitigation measures were successful in reducing biosecurity risks to the recipient region, but they resulted in the unintentional introduction of the non-indigenous brown mussel (Perna perna) to New Zealand when the rig was defouled in-water by divers. In the second case study, lessons learned from this high-profile incursion resulted in a more structured approach to pre-border management, and this serves as a useful template for future rig transfers. PMID:20696440
Frase, J.R.; Liang, X.Q.; Clark, L.E.
The Nanhai Tiao Zhan is a major component of the Liuhua 11-1 Development System. It is a modified drilling semi-submersible specially converted to maintain station in a severe typhoon environment, drill and complete horizontal subsea wells, supply power for downhole electrical submersible pumps, and support installation and maintenance of the unique Liuhua 11-1 subsea production system. Final design and conversion of the Nanhai Tiao Zhan was accomplished in approximately two years. In the first year, a major engineering effort produced plans and specifications for converting a Sedco 700 series mobile offshore drilling unit into the floating production system Nanhai Tiao Zhan. The second year of the project entailed procurement and construction activities associated with the unit`s conversion and refurbishment. The project was accomplished on schedule within its original budget.
Harvey, D. G.
Any activity requiring the development of the HLLV can benefit by operations from an offshore space center (OSC) since operating near the equator provides a twenty percent increase in payload in an ecliptic plan orbit. Some OSC concepts considered include a moored floating (semisubmersible) design, a stationary design supported by fixed piles, and a combination of these two. The facility supports: a 15,000 foot long, 300 foot wide runway, designed to accommodate a two staged winged launch vehicle, with a one million pound payload capacity to low earth orbit; an industrial area for HLLV maintenance; an airport terminal, control and operation center, and observation tower; liquid hydrogen and liquid oxygen production and storage, and fuel storage platforms; a power generation station, docks with an unloading area; two separate launch sites; and living accommodations for 10,000 people. Potential sites include the Paramount Seamount in the Pacific Ocean off the north coast of South America. Cost estimates are considered.
A new solids control system, consisting of four new shakers and a dryer in parallel all discharging into another dryer, significantly reduced the oil on the cuttings in a nine-well offshore drilling program. Cleaned, slurrified cuttings were then discharged overboard. In November 1994, Oiltools (Europe) Ltd. received contracts to upgrade the solids control systems on Sedco Forex`s Sedco 711 and Sovereign Explorer semisubmersible drilling vessels. Sedco Forex required systems that would meet the reduced oil-on-cuttings (OOC) disposal limit of less than 80 g/kg set by the operator, while staying efficient and economical to operate and maintain. In addition, all solids were required to be slurrified for pumping overboard to ensure dispersal away from the subsea center. This article highlights the equipment used and the savings realized on the Sovereign Explorer after the first three wells of a nine-well program.
Brand, P.J.; Clyne, P.A.; Kirkwood, F.G.; Williams, P.W.
In Oct. 1970, BP`s semisubmersible drilling rig SeaQuest struck oil in Upper Paleocene (Tertiary) sandstones of U.K. Continental Shelf Block 21/10. Four appraisal wells drilled in 1970 and 1971 delineated a large oil reservoir at a depth of 7,000 ft., covering an area of 36 sq miles. The maximum thickness of the oil-bearing sandstone was estimated at 614 ft. Reserves were calculated to be 1,800 MMSTB from an oil in place (OIP) of 4,600 MMSTB, and production was projected to continue until Year 2000. In 1971, Shell/Esso drilled a successful well, Well 22/6-1, that demonstrated the southeastern extension of the field into Block 22/6. The field is a four-way-dip-closed anticline that overlies the Forties-Montrose Ridge and is close to the junction of the Central, South Viking, and Witch Ground grabens. The reservoir occurs in thick Upper Paleocene sandstones deposited as a sand-rich submarine fan sequence. This paper describes how the development of the Forties field has evolved over the past 20 years, the current issues and activities, and the direction for the future.
Describes installation of 3 satellite subsea trees in 500 ft of water from a semisubmersible drilling rig. These wet, diver-assist trees are part of Phillips Petroleum's early development and production program (EDPP) for the Espoir field offshore Ivory Coast, with plans calling for 5 satellite wells with downhole completion equipment and subsea production trees. Diagram shows how a converted jackup, Dan Duke, supports equipment to handle production from subsea wells. Table gives time breakdown of subsea tree installation. Before mobilizing the subsea trees, control system, and tubulars to the rig, a study of deck layout, payloads, and traffic patterns was performed. Concludes that, based on experience in this project and the cost differences between purchase and installation costs, final success is 90% dependent on informed and trained field personnel after engineering, design, and manufacturing; attention to installation procedures and training of field and operational personnel are as critical or more critical than design changes to equipment; and selection of a supplier for high technology equipment, based on a low bid alone, may not translate into lower installation costs.
Pipa, Daniel; Morikawa, Sérgio; Pires, Gustavo; Camerini, Claudio; Santos, JoãoMárcio
Flexible riser is a class of flexible pipes which is used to connect subsea pipelines to floating offshore installations, such as FPSOs (floating production/storage/off-loading unit) and SS (semisubmersible) platforms, in oil and gas production. Flexible risers are multilayered pipes typically comprising an inner flexible metal carcass surrounded by polymer layers and spiral wound steel ligaments, also referred to as armor wires. Since these armor wires are made of steel, their magnetic properties are sensitive to the stress they are subjected to. By measuring their magnetic properties in a nonintrusive manner, it is possible to compare the stress in the armor wires, thus allowing the identification of damaged ones. However, one encounters several sources of noise when measuring electromagnetic properties contactlessly, such as movement between specimen and probe, and magnetic noise. This paper describes the development of a new technique for automatic monitoring of armor layers of flexible risers. The proposed approach aims to minimize these current uncertainties by combining electromagnetic measurements with optical strain gage data through a recursive least squares (RLSs) adaptive filter.
Stacey, A.; Sharp, J.V.
The re-assessment of existing North Sea structures is an increasingly important issue as the age of platforms increases. Over 50 from a total of approximately 180 fixed installations in the UK sector are now over 15 years old. Fatigue damage has been the main reason for repairs to North Sea structures and the risk of this continues. The fatigue guidance of the Offshore Safety Division of the Health and Safety Executive (HSE) has recently been revised and published. Fundamental changes have been made to this guidance with several new recommendations including joint classification, basic design S-N curves for welded joints, the thickness effect, the effects of environment and the treatment of low and high stress ranges. To quantify the effects of the new guidance on the fatigue life assessment of offshore strictures, the HSE commissioned a study which included a deep water and a shallow water fixed steel structure and a twin-pontoon semi-submersible. These structures are typical of those operating in the North Sea. These were re-assessed with respect to fatigue lives and the results compared with predictions based on the 1990 guidance. The results and general conclusions are presented in this paper.
A data warehouse adopted from the POSC/Caesar data model will manage the life-cycle information for the offshore Norway Aasgard project. The Aasgard project comprises the Midgard, Smorbukk, and Smorbukk South fields, which lie in 780--985 ft of water. A semisubmersible production facility will handle gas exports, scheduled to begin in 2000. Statoil estimates that recoverable reserves in the fields are 7.5 tcf of gas and 780 million bbl of oil. Notia software components include: the Intergraph asset and information management (AIM) product; the P/C PDM and P/C RDL models; a data mapping, translation, and import toolkit; the application programming interface (API); and query and browser clients. Intergraph describes AIM, with its object management framework (OMF) from metaphase technology, as the engine upon which Notia is based. The P/C PDM defines the data terminology and structure. A dictionary of standard petrochemical data items, the P/C RDL, defines the various activities, materials, components, and relationships among these items. The API allows users to develop additional functionality, and the toolkit provides resources for translating and mapping data from existing sources into a neutral format so that administrators can prepopulate the data warehouse. A worldwide web browser client allows users to query the data warehouse and display results in a variety of configurable formats, including virtual data sheets.
Ward, R.J. Jr.
The recent boom in day rates for rigs capable of drilling in deep water and harsh environments has created a frenzy of rig refurbishment activity in shipyards located in US Gulf states. In most instances, the destination for the rigs upon completion is the US Outer Continental Shelf (USOCS) in the Gulf of Mexico. The problem faced by contractors/operators planning to use US shipyards is that this circumstance has caused difficulty in shielding rigs and their foreign-sourced components from US Customs duties. Under US Customs law, a bona fide exportation requires severance from US commerce and joining to the commerce of some foreign country or, in the case of a vessel supply, a qualifying international voyage. The USOCS does not qualify as an exportation, nor do movements to drilling sites located on it qualify as an international voyage. Described here are two possible solutions to this economic dilemma and an example of how the foreign trade zone solution was applied by Global marine in its plans for upgrading some of its semisubmersible drilling rigs for deepwater USOCS work.
Robertson, A. N.; Jonkman, J. M.; Masciola, M. D.; Molta, P.; Goupee, A. J.; Coulling, A. J.; Prowell, I.; Browning, J.
The DeepCwind consortium is a group of universities, national labs, and companies funded under a research initiative by the U.S. Department of Energy (DOE) to support the research and development of floating offshore wind power. The two main objectives of the project are to better understand the complex dynamic behavior of floating offshore wind systems and to create experimental data for use in validating the tools used in modeling these systems. In support of these objectives, the DeepCwind consortium conducted a model test campaign in 2011 of three generic floating wind systems, a tension-leg platform (TLP), a spar-buoy (spar), and a semisubmersible (semi). Each of the three platforms was designed to support a 1/50th-scale model of a 5 MW wind turbine and was tested under a variety of wind/wave conditions. The focus of this paper is to summarize the work done by consortium members in analyzing the data obtained from the test campaign and its use for validating the offshore wind modeling tool, FAST.
Concrete platform expertise developed by Norwegian Contractors has been applied to a floating production concept thought to offer considerable potential for marginal and deep-water oil fields. The design is based on a multicell Monotower solution and represents the outcome of studies reaching back to 1978. This work has focused chiefly on devising a production system for Gulf's gas/condensate discovery in 380 m water on Norwegian North Sea Block 35/8. Components covered by the conceptual design study include the catenary anchored concrete floater with condensate storage, subsea and riser systems for high-pressure gas production and topside facilities for gas and condensate treatment. A system also has been developed for periodic direct loading of condensate into a shuttle tanker, which is allowed to weathervane through 360/sup 0/ around the platform. Claimed to offer better motion characteristics than a conventional semisubmersible, the weight-stable platform comprises a series of cylindrical columns arranged in a circle, an inner ring of moonpool cells and a cantilevered base for storage.
Welaya, Yousri M. A.; Elhewy, Ahmed; Hegazy, Mohamed
Since the first jack-up was built, jackups have become the most popular type of mobile offshore drilling unit (MODU) for offshore exploration and development purposes in shallow water. The most pivotal component of the jack-up unit is the leg, which can directly affect the global performance of the unit. In this paper, an investigation into extending the length of the jack up leg is carried out in order to study the enhancement of the rig capability to drill in deeper water approaching the range of the Semisubmersible Drilling Unit (SSDU) (300-1000ft). A study of the performance of a deep-water jack-up unit is performed with different leg lengths. Typical leg scantling dimensions and identical external loads are assigned, and then a detailed Finite Element Analysis (FEA) model is created in order to simulate the jack-up leg unit's structural behavior. A Multi-point Constraint (MPC) element together with the spring element is used to deal with the boundary conditions. Finally, a comparative analysis for five leg lengths is carried out to illustrate their performance, including the ultimate static strength, and weight.
The economic exploitation of marginal offshore fields through production systems based on the use of articulated columns has been the subject of an intensive two year development project executed by Taywood Engineering Ltd. A range of systems for Continental Shelf water depths have been evaluated in detail, and their possible extension into deeper waters has been investigated. This paper outlines the detailed engineering development to conceptual design level of two floating production systems, one employing a heavy duty semi-submersible, the other employing a converted tanker, both permanently linked to articulated columns. Descriptions are given of the extensive development of computer software to enable the accurate predicition of environmental loadings and system motion responses, and of the validation of this software using in-house wave tank model testing facilities. In the development of both designs, emphasis has been placed on enhancing the recovery and profitability of the field by offering improved reservoir control and cost-effective fabrication techniques, without introducing innovative technology. First-order cost estimate and economic analyses of the two systems are presented for particular reference fields to enable their comparison against current systems.
Brands, K.W.; Ball, I.G.; Cegielski, E.J.; Gresham, J.S.; Saunders, D.N.
This paper outlines the overall project for development and installation of a low-profile, caisson-installed subsea Christmas tree. After various design studies and laboratory and field tests of key components, a system for installation inside a 30-in. conductor was ordered in July 1978 from Cameron Iron Works Inc. The system is designed to have all critical-pressure-containing components below the mudline and, with the reduced profile (height) above seabed, provides for improved safety of satellite underwater wells from damage by anchors, trawl boards, and even icebergs. In addition to the innovative nature of the tree design, the completion includes improved 3 1/2-in. through flowline (TFL) pumpdown completion equipment with deep set safety valves and a dual detachable packer head for simplified workover capability. The all-hydraulic control system incorporates a new design of sequencing valve for both Christmas tree control and remote flowline connection. A semisubmersible drilling rig was used to initiate the first end flowline connection at the wellhead for subsequent tie-in to the prelaid, surface-towed, all-welded subsea pipeline bundle.
Webb, R.M.; Thomas, D.B.J.; Geronimi, C.
Monitoring, inspection and maintenance of offshore structures is undertaken to satisfy owners stringent operational requirements, together with the requirements of government regulations, Certifying Authorities and insurance underwriters. The immense costs of offshore inspection and maintenance work has resulted in a growing need for engineers to consider these problems much earlier in the design stages than previously thought necessary and to be aware of future subsea tasks which may need to be performed during the life of an installation. This is particularly so for platforms going beyond the range of divers and those using new structural systems. The paper reviews the requirements for critical components of a compliant tower, a Deep draught Semi-submersible and a SPAR platform in 900 m of water. The assessment is based on the following top down process: (1) identify the structural components of the structure; (2) for each component identify failure or degradation mechanisms; (3) for each failure or degradation mechanism identify the monitoring, inspection and maintenance requirements; (4) for each requirement review available techniques and equipment, identify feasibility in 900 m or advances that are required before feasibility is proved. A simple tabular form enables easy interpretation of the results.
Liu, Mingyue; Xiao, Longfei; Yang, Lijun
The Deep Draft Semi-Submersible (DDS) concepts are known for their favourable vertical motion performance. However, the DDS may experience critical Vortex-Induced Motion (VIM) stemming from the fluctuating forces on the columns. In order to investigate the current-induced excitation forces of VIM, an experimental study of flow characteristics around four square-section cylinders in a square configuration is presented. A number of column spacing ratios and array attack angles were considered to investigate the parametric influences. The results comprise flow patterns, drag and lift forces, as well as Strouhal numbers. It is shown that both the drag and lift forces acting on the cylinders are slightly different between the various L/D values, and the fluctuating forces peak at L/D = 4.14. The lift force of downstream cylinders reaches its maximum at around α = 15°. Furthermore, the flow around circular-section-cylinder arrays is also discussed in comparison with that of square cylinders.
Scurtu, I. C.
Manufacturing steps for a modern three - column semi-submersible structure are delivered using CFD/CAE software and actual Froude scaled model testing. The three- column offshore is part of the Wind Float Project already realized as prototype for wind energy extraction in water depths more than 40 meters, and the actual model will not consider the wind turbine. The model will have heave plates for a smaller heave motion in order to compare it with the case without heave plates. The heave plates will be part of the Froude scale model.. Using a smaller model will determine a smaller heave motion and this will affect predictions of the vertical movement of the three- column offshore structure in real sea. The Froude criterion is used for the time, speed and acceleration scale. The scale model is manufactured from steel and fiberglass and all parts are subjected to software analysis in order to get the smallest stress in connections inside the model. The model mass was restricted by scale dimensions and also the vertical position of centre gravity will be considered during the manufacturing and design process of the Froude scale offshore structure. All conditions must converge in model manufacturing and design in order to get the best results to compare with real sea states and heave motion data.
Hughes, O. F.
Ocean-going vehicles and platforms are among the largest structures in the world and are subjected to relatively harsh conditions of motions and loads. Some of them, such as semi-submersible platforms, are a relatively new type of structure and hence there is no formal, well evolved and established structural design code as there is for more traditional structures. More recently, efforts have also been made to develop a design method of this type for ships and other ocean structures. One of the many advantages of a rationally based design method is versatility; it can be used for structures that have widely differing purposes, measures of merit, shapes and sizes. The purpose is to describe a rationally based design method that has been developed within the field of ocean structures, in order that persons dealing with other types of structure can judge whether and to what extent its various features may be useful for those other types. Also, even though some features may not be applicable they might stimulate some useful ideas.
The ongoing oil spill from the blown-out well by the name of Macondo, drilled by the ill-fated rig Deepwater Horizon, has many features in common with another blowout in the Mexican Gulf that happened three decades ago. Then the oil gushed out from the Ixtoc I well drilled by the Sedco 135-F semi-submersible rig. In the years between these catastrophes, the source and nature of oil spills have undergone large changes. Huge spills from tankers that ran aground or collided used to be what caught the headlines and caused large ecological damage. The number and size of such accidental spills have decreased significantly. Instead, spills from ageing, ill-maintained or sabotaged pipelines have increased, and places like Arctic Russia, the Niger Delta, and the northwestern Amazon have become sites of reoccurring oil pollution. As for blowouts, there is no clear trend with regard to the number of incidences or amounts of spilled oil, but deepwater blowouts are much harder to cap and thus tend to go on longer and result in the release of larger quantities of oil. Also, oil exploration and extraction is moving into ever-deeper water and into stormier and icier seas, increasing potential risks. The risk for reoccurring spills like the two huge Mexican Gulf ones is eminent and must be reduced. PMID:21053719
This patent describes a method of mooring an offshore platform in a body of water having a surface and a floor comprising the steps of: locating anchoring means on the floor of the body of water, the anchoring means adapted for receipt of mooring tendons through a side entry opening therein; stationing a semi-submersible floating structure on the surface of the body of water above the anchoring means. The floating structure consists of external tendon receptacles adapted for side entry receipt of the plurality of mooring tendons, the tendon receptacles being located at an initial distance above the anchoring means; providing one piece, substantially rigid tendons disposed substantially horizontally near the surface and adjacent the floating structure, the tendons having enlarged top and bottom end connectors and an actual length which is greater than the initial distance; swinging the enlarged bottom end connector of one of the tendons downwardly into a position adjacent one of the plurality of anchoring means; pulling the enlarged bottom end connector of one of the tendons through the side opening in one of the anchoring means.
Walker, Nan D.; Huh, Oscar K.; Rouse, Lawrence J.; Murray, Stephen P.
In early October 1992, satellite-derived sea surface temperature data revealed a 200 km long and 10- to 30-km-wide stream of cool water flowing toward the southwest from the Mississippi River delta region. Satellite imagery and in situ measurements have enabled a detailed study of the squirt's kinematics and subsurface characteristics over a 2-week period. In its early stages, the squirt appeared as a narrow, high-speed (>75 cm/s) jet of water which flowed westward over the Mississippi Canyon, forcing a semi-submersible drilling rig to suspend operations from October 2 to 4. After crossing back onto the shelf, the squirt spread laterally, yielding a mushroom-shaped feature, 75 km wide, which consisted of counter-rotating vortices. Northeasterly wind forcing (averaging 10-15 m/s) and water level setup east of the delta appear to have been the primary mechanisms for evolution of the high-velocity currents. Satellite and in situ measurements demonstrate that the dipole eddy was comprised of a cool, low-salinity, low-density water mass at least 26 m deep in the center and 16 m deep along its margins. This event demonstrates that strong northeasterly winds over the northern Gulf of Mexico can initiate along-shelf and off-shelf flows of cooler coastal waters, contributing significantly to seasonal cooling and freshening of the continental shelf and to shelf/slope exchanges of water. During this event, approximately 100 km3 of inner shelf and river water was transported off the continental shelf, a volume equivalent to 17% of the average annual discharge of the Mississippi and Atchafalaya Rivers.
Wendt, F.; Robertson, A.; Jonkman, J.; Hayman, G.
In the latest release of NREL's wind turbine aero-hydro-servo-elastic simulation software, FAST v8, several new capabilities and major changes were introduced. FAST has been significantly altered to improve the simulator's modularity and to include new functionalities in the form of modules in the FAST v8 framework. This paper is focused on the improvements made for the modeling of floating offshore wind systems. The most significant change was to the hydrodynamic load calculation algorithms, which are embedded in the HydroDyn module. HydroDyn is now capable of applying strip-theory (via an extension of Morison's equation) at the member level for user-defined geometries. Users may now use a strip-theory-only approach for applying the hydrodynamic loads, as well as the previous potential-flow (radiation/diffraction) approach and a hybrid combination of both methods (radiation/diffraction and the drag component of Morison's equation). Second-order hydrodynamic implementations in both the wave kinematics used by the strip-theory solution and the wave-excitation loads in the potential-flow solution were also added to HydroDyn. The new floating capabilities were verified through a direct code-to-code comparison. We conducted a series of simulations of the International Energy Agency Wind Task 30 Offshore Code Comparison Collaboration Continuation (OC4) floating semisubmersible model and compared the wind turbine response predicted by FAST v8, the corresponding FAST v7 results, and results from other participants in the OC4 project. We found good agreement between FAST v7 and FAST v8 when using the linear radiation/diffraction modeling approach. The strip-theory-based approach inherently differs from the radiation/diffraction approach used in FAST v7 and we identified and characterized the differences. Enabling the second-order effects significantly improved the agreement between FAST v8 and the other OC4 participants.
Sun, Wei-ying; Zhang, Da-gang; Fan, Zhi-xia
Transportation of floating structures for long distance has always been associated with the use of heavy semi transport vessel. The requirements of this type of vessel are always special, and its availability is limited. To prepare for the future development of the South China Sea deepwater projects, COOEC has recently built a heavy lift transport vessel — Hai Yang Shi You 278 (HYSY278). This semi-submersible vessel has displacement capacity of 50k DWT, and a breath of 42 m. Understanding the vessel's applicability and preparing its use for future deepwater projects are becoming imminent need. This paper reviews the critical issues associated with the floating structure transportation and performs detailed analysis of two designed floating structures during transportation. The newly built COOEC transportation vessel HYSY278 will be used to dry transport the floating structures from COOEC fabrication yard in Qingdao to the oil field in the South China Sea. The entire process will start with load-out/float-off the floating structures from the construction sites, offload the platform from the vessel if needed, dry transport floating structures through a long distance, and finally offload the platform. Both hydrodynamic and structural analyses are performed to evaluate transport vessel and floating structures. Critical issues associated with the transportation and offloading of platform from the vessel will be studied in detail. Detailed study is performed to evaluate the response of the system during this phase and additional work needed to make the vessel feasible for use of this purpose. The results demonstrate that with proper modifications, HYSY278 can effectively be used for transporting structures with proper arrangement and well-prepared operation. The procedure and details are presented on the basis of study results. Special attentions associated with future use will also be discussed based on the results from analysis.
Browning, J. R.; Jonkman, J.; Robertson, A.; Goupee, A. J.
In this study, high-quality computer simulations are required when designing floating wind turbines because of the complex dynamic responses that are inherent with a high number of degrees of freedom and variable metocean conditions. In 2007, the FAST wind turbine simulation tool, developed and maintained by the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL), was expanded to include capabilities that are suitable for modeling floating offshore wind turbines. In an effort to validate FAST and other offshore wind energy modeling tools, DOE funded the DeepCwind project that tested three prototype floating wind turbines at 1/50th scale in a wave basin, including a semisubmersible, a tension-leg platform, and a spar buoy. This paper describes the use of the results of the spar wave basin tests to calibrate and validate the FAST offshore floating simulation tool, and presents some initial results of simulated dynamic responses of the spar to several combinations of wind and sea states. Wave basin tests with the spar attached to a scale model of the NREL 5-megawatt reference wind turbine were performed at the Maritime Research Institute Netherlands under the DeepCwind project. This project included free-decay tests, tests with steady or turbulent wind and still water (both periodic and irregular waves with no wind), and combined wind/wave tests. The resulting data from the 1/50th model was scaled using Froude scaling to full size and used to calibrate and validate a full-size simulated model in FAST. Results of the model calibration and validation include successes, subtleties, and limitations of both wave basin testing and FAST modeling capabilities.
Browning, J. R.; Jonkman, J.; Robertson, A.; Goupee, A. J.
High-quality computer simulations are required when designing floating wind turbines because of the complex dynamic responses that are inherent with a high number of degrees of freedom and variable metocean conditions. In 2007, the FAST wind turbine simulation tool, developed and maintained by the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL), was expanded to include capabilities that are suitable for modeling floating offshore wind turbines. In an effort to validate FAST and other offshore wind energy modeling tools, DOE funded the DeepCwind project that tested three prototype floating wind turbines at 1/50th scale in a wave basin, including a semisubmersible, a tension-leg platform, and a spar buoy. This paper describes the use of the results of the spar wave basin tests to calibrate and validate the FAST offshore floating simulation tool, and presents some initial results of simulated dynamic responses of the spar to several combinations of wind and sea states. Wave basin tests with the spar attached to a scale model of the NREL 5-megawatt reference wind turbine were performed at the Maritime Research Institute Netherlands under the DeepCwind project. This project included free-decay tests, tests with steady or turbulent wind and still water (both periodic and irregular waves with no wind), and combined wind/wave tests. The resulting data from the 1/50th model was scaled using Froude scaling to full size and used to calibrate and validate a full-size simulated model in FAST. Results of the model calibration and validation include successes, subtleties, and limitations of both wave basin testing and FAST modeling capabilities.
Browning, J. R.; Jonkman, J.; Robertson, A.; Goupee, A. J.
In this study, high-quality computer simulations are required when designing floating wind turbines because of the complex dynamic responses that are inherent with a high number of degrees of freedom and variable metocean conditions. In 2007, the FAST wind turbine simulation tool, developed and maintained by the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL), was expanded to include capabilities that are suitable for modeling floating offshore wind turbines. In an effort to validate FAST and other offshore wind energy modeling tools, DOE funded the DeepCwind project that tested three prototype floating wind turbines at 1/50th scale inmore » a wave basin, including a semisubmersible, a tension-leg platform, and a spar buoy. This paper describes the use of the results of the spar wave basin tests to calibrate and validate the FAST offshore floating simulation tool, and presents some initial results of simulated dynamic responses of the spar to several combinations of wind and sea states. Wave basin tests with the spar attached to a scale model of the NREL 5-megawatt reference wind turbine were performed at the Maritime Research Institute Netherlands under the DeepCwind project. This project included free-decay tests, tests with steady or turbulent wind and still water (both periodic and irregular waves with no wind), and combined wind/wave tests. The resulting data from the 1/50th model was scaled using Froude scaling to full size and used to calibrate and validate a full-size simulated model in FAST. Results of the model calibration and validation include successes, subtleties, and limitations of both wave basin testing and FAST modeling capabilities.« less
A marine riser is disclosed including a uniquely designed three element connection structure and associated connecting and releasing means for the inhibiting of fatigue failure caused by moments and axial loads resulting from relative motion between the fixed ocean bottom and a floating drilling platform or ship, such as a semisubmersible rig. The system includes a preloaded connection including a female member and a male member coaxially aligned and held in compression by a nut placed in tension. The connection holds riser pipe sections together. The connection is preloaded through a tool to a degree such that when a load equal to the yield strength of the pipe section material is applied to the pipe sections joined by the connector, the compressed faces of the male and female members do not separate from each other. The degree of preload would be sufficient to maintain the contact between the compressed faces under expected working loads of the pipe sections. The tool operates in conjunction with lugs located on the nut and a flange or platform with mounting holes located on the male member. A lock is provided on the nut to prevent the disengagement of the male and female members after they are brought into compression by the nut. The position of the lock relative to the nut lugs determines the sustained preload of the connection. Seals are provided between the male and female member to prevent leakage of fluid between the interior of the riser connector and the surrounding environment. The connector also includes provision for the support and connection of sections of kill and choke lines.
Yoshida, Koichiro; Suzuki, Hideyuki; Nam, D.; Hineno, Motohiro; Ishida, Shigeki
This paper presents an active control of coupled dynamic responses of the hull and the tendon of TLP. In a deepwater TLP, the restoring force becomes smaller and the natural frequency of the system decreases with increasing water depth. There is a possibility that the dynamic response of tendon, which is induced by the hull motion, can be significant. Furthermore the motion of TLP due to wave drifting force can be comparable or larger than wave induced motion. This low-frequency response can be controlled by conventional DPS thrusters. The operability is improved and the tendon and the riser are protected from structural damage. The low-frequency motion is induced by small wave drifting force and can be controlled by small control force. The first order wave force is very large and control of this high-frequency response is not practical. The control method is optimal control and the low-frequency hull motion and the bending strain of the tendon are controlled. The high-frequency response is removed from the control system by low pass filters. The effectiveness of control is verified by experiment with a 1/100 scale model of JOIA (Japan Ocean Industries Association)-TLP. The hull motion is measured by an ultrasonic ranging sensor and the control force is generated by two thrusters built in the TLP model. Average control force required for the control is about 1/200 of the hull weight, which is slightly larger than the value of the conventional DPS thrust of a semi-submersible.
Kanner, Samuel Adam Chinman
The design and operation of two counter-rotating vertical-axis wind turbines on a floating, semi-submersible platform is studied. The technology, called the Multiple Integrated and Synchronized Turbines (MIST) platform has the potential to reduce the cost of offshore wind energy per unit of installed capacity. Attached to the platform are closely-spaced, counter-rotating turbines, which can achieve a higher power density per planform area because of synergistic interaction effects. The purpose of the research is to control the orientation of the platform and rotational speeds of the turbines by modifying the energy absorbed by each of the generators of the turbines. To analyze the various aspects of the platform and wind turbines, the analysis is drawn from the fields of hydrodynamics, electromagnetics, aerodynamics and control theory. To study the hydrodynamics of the floating platform in incident monochromatic waves, potential theory is utilized, taking into account the slow-drift yaw motion of the platform. Steady, second-order moments that are spatially dependent (i.e., dependent on the platform's yaw orientation relative to the incident waves) are given special attention since there are no natural restoring yaw moment. The aerodynamics of the counter-rotating turbines are studied in collaboration with researchers at the UC Berkeley Mathematics Department using a high-order, implicit, large-eddy simulation. An element flipping technique is utilized to extend the method to a domain with counter-rotating turbines and the effects from the closely-spaced turbines is compared with existing experimental data. Hybrid testing techniques on a model platform are utilized to prove the controllability of the platform in lieu of a wind-wave tank. A 1:82 model-scale floating platform is fabricated and tested at the UC Berkeley Physical-Model Testing Facility. The vertical-axis wind turbines are simulated by spinning, controllable actuators that can be updated in real-time of
Butler, P. ); Emmerson, J.G. ); Berg, Van Den R. )
Submarine pipelines have been installed all over the world, in diameters ranging from 76 mm (3 in.) up to 1270 mm (50 in.) or more and in water depths up to 500 m (1600 ft) using the S-lay method. In the 1950s, the J-lay concept was developed. With the J-lay technique, the pipe is suspended near vertically from the lay barge, thus reducing the horizontal force required to prevent pipe buckling. The J-lay technique has obvious advantages for deep-water applications where it is possible to eliminate the use of anchors by using dynamic positioning. The main drawback of the J-lay technique is that the near vertical pipe is difficult to handle and multiple workstations cannot be used. Only one length of pipe can be welded onto the pipeline at a time and subsequent inspection and coating must be done before the next weld can be made, resulting in low production rates compared to that achieved by S-lay barges. In 1989, Heerema, A Dutch company, which operates a fleet of semi-submersible crane vessels (SSCV) used for the installation of offshore oil and gas production platforms, decided to diversify into marine pipe laying. Realizing direct competition with established pipe lay contractors using S-lay barges could not be commercially competitive, an innovative J-lay system was designed which took advantage of the unique capabilities of the SSCV. Although the J-lay concept was some 30 years old, no functional system had been constructed as there was no immediate market for it, especially one which could justify inferior productivity when compared to S-lay barges. Heerema's solution to this limitation was to maximize the length of each piece of pipe added to the pipeline. By fabricating the pipe on shore into lengths up to 72 m (240 ft) and using the massive crane capacity (4000 tons) of the SSCV to lift each pipe string into position for welding, they could compensate for a lower productivity rate.