Motion of a Large Disconnectable Buoy Within FPSO Turret Moon-Pool

2014 ◽  
Author(s):  
Sean Bian ◽  
Steve Leverette
Keyword(s):  
Deep Water ◽  
Structural Integrity ◽  
Structure Design ◽  
Rational Approximations ◽  
Offshore Engineering ◽  
Close Proximity ◽  
Design Loads ◽  
Numerical Tool ◽  
Moon Pool ◽  
Fully Coupled

The disconnectable buoy turret mooring (BTM) for an FPSO has been a proven technology for areas where hurricane and seasonal cyclones are predominant, or are subject to ice features which need to be avoided. With the requirements of large buoy payload from deep water moorings and heavy risers, the disconnectable buoy size can be substantial. Recent projects are considering buoy net displacements well above 5000Te. The increased buoy size imposes large inertia loads on the supporting structure and mechanical connectors when connected, and possibly more so on the structural integrity and winching system during disconnect and reconnect operations. In order to provide structure design loads as well as to estimate safe operational windows and procedures, it is desirable to understand the physical properties of 2-body motions when the buoy and ship are close enough to have significant interactions. This paper focuses on the hydrodynamic and structural (Winch, Mooring/riser, Fender/bumper etc.) interactions with the buoy operating in close proximity to the turret. Since the readily available offshore engineering tools have limitations to deal with close body hydro-interaction, particularly with the presence of moon-pool resonances, rational approximations are derived for hydrodynamic forces during pull-in and disconnection of the buoy. To analyze fully coupled motions and loads in combined environmental conditions, a typical diffraction/convolution based numerical tool (AQWA) is extended by a custom defined external force function. This analysis allows simulating the real time motions during disconnect, reconnect, or at suspended elevations. Various findings from dedicated model tests and analyses are presented and discussed with implications for configuring and operating the disconnectable buoy system.

Effective Power and Speed Loss of Underwater Vehicles in Close Proximity to Regular Waves

2017 ◽  
Author(s):  
Stefan Daum ◽  
Martin Greve ◽  
Renato Skejic
Keyword(s):  
Free Surface ◽  
Deep Water ◽  
Water Waves ◽  
Underwater Vehicles ◽  
Total Resistance ◽  
Wave Load ◽  
Regular Waves ◽  
Effective Power ◽  
Close Proximity ◽  
Deep Water Waves

The present study is focused on performance issues of underwater vehicles near the free surface and gives insight into the analysis of a speed loss in regular deep water waves. Predictions of the speed loss are based on the evaluation of the total resistance and effective power in calm water and preselected regular wave fields w.r.t. the non-dimensional wave to body length ratio. It has been assumed that the water is sufficiently deep and that the vehicle is operating in a range of small to moderate Froude numbers by moving forward on a straight-line course with a defined encounter angle of incident regular waves. A modified version of the Doctors & Days [1] method as presented in Skejic and Jullumstrø [2] is used for the determination of the total resistance and consequently the effective power. In particular, the wave-making resistance is estimated by using different approaches covering simplified methods, i.e. Michell’s thin ship theory with the inclusion of viscosity effects Tuck [3] and Lazauskas [4] as well as boundary element methods, i.e. 3D Rankine source calculations according to Hess and Smith [5]. These methods are based on the linear potential fluid flow and are compared to fully viscous finite volume methods for selected geometries. The wave resistance models are verified and validated by published data of a prolate spheroid and one appropriate axisymmetric submarine model. Added resistance in regular deep water waves is obtained through evaluation of the surge mean second-order wave load. For this purpose, two different theoretical models based on potential flow theory are used: Loukakis and Sclavounos [6] and Salvesen et. al. [7]. The considered theories cover the whole range of important wavelengths for an underwater vehicle advancing in close proximity to the free surface. Comparisons between the outlined wave load theories and available theoretical and experimental data were carried out for a submerged submarine and a horizontal cylinder. Finally, the effective power and speed loss are discussed from a submarine operational point of view where the mentioned parameters directly influence mission requirements in a seaway. All presented results are carried out from the perspective of accuracy and efficiency within common engineering practice. By concluding current investigations in regular waves an outlook will be drawn to the application of advancing underwater vehicles in more realistic sea conditions.

A Symmetry Analysis of Design Structure: 1,000 Years of Continuity and Change in Puebloan Ceramic Design

2010 ◽  
Vol 75 (4) ◽  
pp. 743-772 ◽  
Author(s):  
Dorothy K. Washburn ◽  
Donald W. Crowe ◽  
Richard V.N. Ahlstrom
Keyword(s):  
Social Relationships ◽  
Structural Integrity ◽  
Structure Design ◽  
American Southwest ◽  
Agricultural Communities ◽  
Continuity And Change ◽  
15Th Century ◽  
Design Structure ◽  
Settlement Type ◽  
Ceramic Design

This paper postulates that cultural entities with long term structural integrity are characterized by symmetrical relationships between and among the constituent sectors of society. We demonstrate how such social relationships are embedded in the symmetrical arrangements of motifs in geometric design. We test this premise with an analysis of 1000 years of ceramic design from the northern American Southwest, AD 600-1600, with a description of the continuities and changes in the plane pattern symmetries that structure design. Two major points of change in symmetry use at c. AD 900 and AD 1300 correlate with changes in settlement type from pithouses to unit pueblos and from unit pueblos to multi-storied plaza oriented pueblos that accompanied adjustments to changes in environmental conditions. We propose that in the American Southwest the predominant use of bifold symmetry is a structural metaphor for the reciprocal social relationships basic to the organization of small puebloan agricultural communities and that the changes in these symmetries reflect the changing integration of the household into an increasingly complex social system. This interpretation of the meaning of design structure is derived from cosmological principles embedded in 20th century ritual songs of the Hopi, descendents of the prehistoric puebloans, as well as depicted in images in their 15th century kiva wall murals. We present this interpretation of the sequence of pueblo development in the American Southwest in terms of the changing symmetrical nature of the social relationships that integrated the agricultural communities as an example of the insights possible with this new approach to design analysis.

Numerical and Experimental Tools for Offshore DP Operations

2011 ◽  
Author(s):  
Fabiano P. Rampazzo ◽  
Joa˜o Luis B. Silva ◽  
Daniel P. Vieira ◽  
Antonio L. Pacifico ◽  
Lazaro Moratelli Junior ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Experimental Tests ◽  
Coupled System ◽  
Coupled Analysis ◽  
Cfd Analysis ◽  
Maximum Condition ◽  
Commercial Code ◽  
Close Proximity ◽  
Fully Coupled ◽  
Two Bodies

DP crane vessel operation can be analyzed based on the uncoupled system or considering the fully coupled system. Parameters such as top-crane acceleration, thruster capability and vessel motions are evaluated for several environmental conditions. Numerical and experimental tools are used and the important result of this analysis is the maximum condition in such that the operation can be safely executed. Those operations are critical, since the vessel is kept in close proximity with other unit and large loads are transported in a pendulum configuration. A precise positioning of the crane-vessel is required, in order to avoid unsafe relative motions, as well as keep the load being transported on a stable position. The uncoupled analysis approach does not consider the influence of the other unit in the crane vessel. This paper presents a methodology for evaluating a DP crane vessel in the offshore operations (DP crane vessel, load being transported, mooring and assistance lines, platform) considering the fully coupled method based on integration of the in house codes with the commercial code WAMIT® system. The methodology is based on the integration of numerical and experimental tools. The dimensions of the transported modules and the proximity of the vessels change the behavior of the vessel motions and line tensions. So, a full nonlinear time domain simulator (TPN – Numerical Offshore Tank) is used to perform the coupled analysis of the system subjected to several environmental conditions, considering also the dynamics of the suspended load and the hydrodynamic interference between the bodies. In order to calibrate the numerical model, several experimental tests are performed such as wind tests with some positions of the crane, tests in towing tanks to evaluated the current effects, thrusters tests to calibrate DP algorithm and wave test with the two bodies. In some cases a complementary CFD analysis is requested in order to evaluate the current and wind shadow effect. Several alternative relative positions between the vessels can be evaluated. This methodology results a more accurate estimative of the system performance.

scholarly journals STRUCTURAL DESIGN PROCEDURES FOR CONCRETE ARMOUR UNITS

1984 ◽  
Vol 1 (19) ◽  
pp. 172 ◽  
Author(s):  
Kevin R. Hall ◽  
W.F. Baird ◽  
D.J. Turcke
Keyword(s):  
Structural Design ◽  
Rational Design ◽  
Structural Integrity ◽  
Design Procedure ◽  
Analytical Techniques ◽  
Structural Performance ◽  
Design Procedures ◽  
Design Loads ◽  
Resultant Stress ◽  
Hydraulic Stability

A rational design procedure for rubblemound breakwater protection which will ensure both the structural integrity and hydraulic stability of individual concrete armour units and the overall armour system is presented. The procedure involves new experimental techniques for measuring strains in model concrete armour units in a hydraulic model of a breakwater subjected to simulated prototype wave attack and analytical techniques for determining equivalent prototype loads on units. Selected design loads are used to define the resultant stress distribution to allow the designer to take the necessary measures to ensure the structural performance of the unit in a breakwater environment•

Concrete LNG GBS Terminal Ship Collision Study

2008 ◽  
Author(s):  
Fuqiang Wu ◽  
Frank Puskar ◽  
Pascinthe Saad
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Structural Integrity ◽  
Impact Resistance ◽  
Liquefied Natural Gas ◽  
Element Analysis ◽  
Benchmark Tests ◽  
Ship Collision ◽  
Numerical Tool ◽  
The Impact

Concrete Gravity Based Structure (GBS) provides an opportunity for the storage of Liquefied Natural Gas (LNG) and represents one of the key elements of an LNG receiving and regasification terminal. The impact resistance of an offshore LNG GBS against accidental ship collision needs to be evaluated. Nonlinear elasto-plastic Finite Element Analysis (FEA) provides a useful numerical tool to assess the damage and evaluate the overall structural integrity of the GBS following a ship collision. In the work presented, a large capacity tanker was modeled using FEA and simulated to collide into a prototype concrete LNG GBS. An efficient, two-step approach was applied to estimate the damage levels caused by the striking tanker considering different approach speeds. Various benchmark tests were conducted to validate the steel and concrete FEA models to ensure the reliability of the analysis. The simulation shows that certain collisions can cause damage to both the tanker bow and the LNG GBS, depending upon the collision speed and the configuration of the colliding bodies. However, these collisions do not always result in a breach of the LNG containment. The results of this type of assessment can be used to assist in designing the LNG GBS to improve its impact resistance. The results can also be used in risk studies typical of these types of facilities.

Bend Stiffener Design for Umbilicals

2011 ◽  
Author(s):  
Nils So̸dahl ◽  
Torfinn Ottesen
Keyword(s):  
Structural Integrity ◽  
Fatigue Loading ◽  
General Description ◽  
Loading Conditions ◽  
Optimization Scheme ◽  
Capacity Curve ◽  
Relative Angle ◽  
Compliant Structure ◽  
Extreme Load ◽  
Design Loads

A crucial design issue for compliant risers and umbilicals for dynamic applications is termination of the compliant structure to a rigid structure. A practical way to solve this problem is to introduce a properly designed bend stiffener to limit the stresses in the compliant structure due to bending at the supports. The bend stiffener provides a gradually increase of the bending stiffness from the rather small value of the compliant structure to a significantly larger value that can be rigidly connected without compromising the structural integrity of the compliant structure. Hence, the bend stiffener geometry needs to be designed to fulfill the design requirements for extreme as well as fatigue loading conditions for the compliant structure. Furthermore, it is required that the bend stiffener is as short as possible to limit costs, support forces, and enable fabrication and installation. The main focus of this paper is to outline an optimization scheme for bend stiffeners to meet design criteria for extreme loading conditions. Measures to provide an adequate fatigue performance of bend stiffeners are also discussed. The loads on the bend stiffener are governed by effective tension and relative angle close to the support (i.e. direction of effective tension relative to the longitudinal direction of the compliant structure at the support). Combinations of effective tension and relative angle aggregated for all relevant extreme load conditions define the design loads on the bend stiffener. The capacity of the compliant structure is governed by a capacity curve expressing the allowable curvature as function of the effective tension. A general optimization scheme is outlined accounting for a general description of the design loads as well as the capacity curve. The optimization methodology is based on a general purpose optimization algorithm utilizing a tailor made non-linear static finite element solver to describe the response of the bend stiffener and the compliant structure. Non-dimensional design curves are also presented based on a simplified conservative description of the design loads and the capacity. This allows for easy practical sizing of bend stiffeners without the need for sophisticated optimization software.

CORROSION ON DEEP GULF SHIPWRECKS OF WORLD WAR II1

2005 ◽  
Vol 2005 (1) ◽  
pp. 387-383
Author(s):  
Michael L. Overfield
Keyword(s):  
World War Ii ◽  
Structural Integrity ◽  
Artificial Reef ◽  
Degradation Process ◽  
Management Plan ◽  
Management Service ◽  
World War ◽  
Close Proximity ◽  
Protection Strategies ◽  
Biological Corrosion

ABSTRACT During the summer of 2004, National Oceanic and Atmospheric Administration's (NOAA) National Marine Sanctuary Program (NMSP) participated with Minerals Management Service (MMS), NOAA's Office of Ocean Exploration (NOAA OE) and C&C Technologies, under the auspices of the National Oceanographic Partnership Program (NOPP), in an investigation to study the “artificial reef effect” of manmade structures in differing depths, and conversely, the effect of the environment on those structures over the course of 60 years, by studying six steel-hulled vessels sunk in the Gulf of Mexico. The National Marine Sanctuary used this opportunity to conduct research on the effects of corrosion on the six vessels identified for study. Corrosion on Deep Gulf Shipwrecks of World War II project represents Phase II of NOAA's RUST database project. Through this study, we addressed the following questions:Does depth of a wreck effect state of corrosion?Is this primarily a chemical, physical or biological process?Do ferrous-hulled shipwrecks follow a fairly consistent degradation process as they age?Is it possible to attach a specific timeline to the degradation scale? The corrosion processes affecting the structural integrity of these vessels is important for two reasons. If we begin to gain an understanding on the corrosive processes at work, we may be able to develop an approximate time line on the eventual fate of these vessels. Second, applying this corrosion timeline, it may enable us to anticipate when tanks and holds containing fuel oils or other hazardous materials will fail and release their cargos into the environment. Using this information, resource protection personnel can assess sites and determine which vessels are considered for direct intervention such as the removal of the threat sources, isolation of the threat, and management plan development or establishment of a monitoring protocol for the site. The survey has added valuable assessment data on steel-hulled vessels and contributes to our understanding of both chemical and biological corrosion in the marine environment. The survey also contributes to the field of underwater research, allowing interpretation and peer review of the results, provides baseline data to examine long-term protection strategies for National Marine Sanctuaries currently threatened by shipwrecks containing oil within or in close proximity to their boundaries.

Reassessment of Dynamically Stable Pipelines Accounting for Potential Clashing With New Assets

2013 ◽  
Author(s):  
Daniel Carneiro ◽  
Sabine Powell ◽  
David Timmins ◽  
Pier Bruzzo
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
State Of The Art ◽  
Design Criterion ◽  
Original Design ◽  
North West ◽  
Analysis Techniques ◽  
Close Proximity ◽  
Lateral Displacements ◽  
Subsea Pipelines

Since mid-1980’s, guidelines permit the design of rigid subsea pipelines allowing significant lateral displacements under extreme environmental conditions. Such a design criterion might bring issues not foreseen in the original design when future assets are to be installed in close proximity — for example pipeline crossings, hot-tap tie-ins or parallel lines using the same corridor. Although not limited to any particular region of the globe, this issue has been showing increasing relevance in the Australian North West Shelf over the last few years. The combination of environmental and geotechnical conditions in that region has led to significant advances in engineering design techniques, and to audacious projects which made viable a number of important subsea pipelines which have been designed to be dynamically stable. As this oil and gas province matures, the installed infrastructure in the region forms part of an increasingly complex subsea network. The design of new subsea assets close to, crossing, or tying into these dynamically stable pipelines require the reassessment of the existing infrastructure for potential clashing conditions. This paper discusses the techniques and integrity criteria available for reassessing dynamically stable pipelines whose originally expected displacements may be incompatible with new required infrastructure. Although the criteria for confirming the structural integrity is, and has to be, grounded on established design codes, the assessment often require advanced engineering and state-of-the-art analysis techniques.

scholarly journals STRUCTURAL BEHAVIOUR OF FULLY COUPLED SPAR–MOORING SYSTEM UNDER EXTREME WAVE LOADING

2014 ◽  
Vol 19 (Supplement_1) ◽  
pp. S69-S77 ◽  
Author(s):  
A. B. M. Saiful Islam ◽  
Mohammed Jameel ◽  
Suhail Ahmad ◽  
Mohd Zamin Jumaat ◽  
V. John Kurian
Keyword(s):  
Response Time ◽  
Deep Water ◽  
Mooring Line ◽  
Mooring System ◽  
Wave Loading ◽  
Extreme Wave ◽  
Spar Platform ◽  
Mooring Lines ◽  
Time Histories ◽  
Fully Coupled

Floating spar platform has been proven to be an economical and efficient type of offshore oil and gas exploration structure in deep and ultra-deep seas. Associated nonlinearities, coupled action, damping effect and extreme sea environments may modify its structural responses. In this study, fully coupled spar–mooring system is modelled integrating mooring lines with the cylindrical spar hull. Rigid beam element simulates large cylindrical spar hull and catenary mooring lines are configured by hybrid beam elements. Nonlinear finite element analysis is performed under extreme wave loading at severe deep sea. Morison's equation has been used to calculate the wave forces. Spar responses and mooring line tensions have been evaluated. Though the maximum mooring line tensions are larger at severe sea-state, it becomes regular after one hour of wave loading. The response time histories in surge, heave, pitch and the maximum mooring tension gradually decreases even after attaining steady state. It is because of damping due to heavier and longer mooring lines in coupled spar–mooring system under deep water conditions. The relatively lesser values of response time histories in surge, heave, pitch and the maximum mooring tension under extreme wave loading shows the suitability of a spar platform for deep water harsh and uncertain environmental conditions.

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