bluuebunny/crossref_metadata_2025 huggingface dataset:
Overview of Tacoma Narrows Bridge Floating Caisson Design
Authors: Krishna M. Sri , Chakrabarti Partha , Chakrabarti Subrata K. , Mukkamala Adinarayana , Anavekar Nagaraj
Published: January 2009

Tacoma Narrows Constructors is building a new suspension bridge in Tacoma, close to Seattle, Washington State, USA next to an existing bridge at the location. The new bridge is being built just south of the existing bridge. This new bridge will be built on towers mounted on two caissons. The caissons are towed to the site from the harbor with the cutting edge, first full lift, and the second and third exterior lifts. The piers are constructed on site up to their full height as floating caissons at varying drafts. During the construction, the floating caissons on both ends of the new bridge are moored in place with 32 catenary mooring lines. The current flow due to ebb and flood tide in the narrows is very high. This high current and the consequent vortex-induced dynamic forces provided a technical challenge in the design of the caisson and its mooring system whose dimensions are of similar order of magnitude as typical offshore structures exposed to severe environment. This paper provides an overview of this challenge, and describes the steps taken in overcoming these difficulties. The design procedure adopted of the moored caisson system and the piers in the overall scheme of the Tacoma Narrows Bridge are summarized. This overview stresses the practical side of towing, mooring and in place construction of the caissons. Some of the critical areas of associated design challenges and their solution techniques are highlighted.
Current Forces on a Large Pier Near an Existing Pier
Authors: Chakrabarti Subrata K. , McBride Mark
Published: January 2009

A new suspension bridge is being built over the Tacoma Narrows, Washington. The bridge will be placed on a structure mounted on 2 large concrete caissons, which will be exposed to strong currents. The piers are of rectangular section with chamfered edges in the upper portion. The caissons are being built at site while floating and moored in high currents. There are no known analytical methods or experimental data available on such structures at high Reynolds number. In order to determine the forces on the caisson due to current, a series of scaled physical model tests of one of the caissons was carried out. The forces on the new caisson were measured in the presence of the existing bridge pier and the bottom contours of the Narrows were accurately modeled. The model scale was chosen as 1:100 and the tests were performed for the caisson at different drafts. This paper describes the test setup, and measurement system for a series of fixed caisson tests and demonstrates the consistency of the test data. The measured inline drag and transverse lift forces on the fixed caisson at different drafts are presented and the effect of the fluid velocity and flow vorticity on the frequency contents in the forces is discussed. The interaction effect of the neighboring existing pier on the current forces of the new caisson is investigated. Since the measured forces were applied in the design analysis of the caissons, the scaling effect of the model test is also discussed. This paper is accompanied by two other papers, which form a group of three papers related to the project describing the current excitation on the caisson and the associated caisson responses. The other two papers in succession are ref. [1] and ref. [2]. The paper in ref. [1] describes the numerical computation of the current forces on the caisson by a 3-D CFD analysis, while the ref. [2] uses the information from these two papers to determine the motion response of the caissons and the mooring line tensions.
Ocean Energy in British Columbia, Canada: Risk and Rewards
Authors: Nielsen Niels , Blaikie Neil
Published: January 2009

The development of Ocean Wave Energy is a leading edge use of primarily existing concepts and technology in a potentially hostile environment. Spawned in part by other offshore industrial and energy related developments, the challenge for ocean wave technology companies has been to harness the huge amounts of this available energy in a safe and efficient manner. With the West Coast of BC having excellent resource potential, electric utilities, power developers and governments have a particular interest in whether Ocean Wave Energy technology has advanced sufficiently to enable development at the near commercial level as a potential future source of renewable energy. This paper will discuss the ocean wave energy potential for BC, how it might be developed, the rewards of successful implementation and the risks that need to be managed.
Evaluation of Mechanisms of Ice Adhesion on Power Network Equipment
Authors: Kasaai Mohammad R. , Farzaneh Masoud
Published: January 2009

The objective of this study is to review the mechanisms of ice adhesion to cables and insulators, with a special emphasis on aluminum and ceramic materials, as these devices are made from these materials. This review shows that the physico-chemical interactions and mechanical interlock contribute to the mechanisms of ice adhesion to surfaces. The physico-chemical mechanisms of ice adhesion to surfaces are classified into three main categories: dipole-dipole or ion-dipole interactions; hydrogen bond; and van der Waals interactions. The interfacial adhesion strength of ice/metals or ice/ceramic insulators is greater than the strength of ice. This indicates that the strength between ice and the material surfaces is greater than hydrogen bonds of ice itself. The mechanical mechanism involves the penetration of liquid water into cavities and pores on the surface of the substrate and expansion of ice during solidification, resulting in an anchor effect and the establishment of a strong bond between ice and surface.
Doppler Spectra of Microwave Backscatter From Water Surface
Authors: Rheem Chang-Kyu , Kobayashi Hidetaka , Yamanishi Kazuomi
Published: January 2009

This paper describes the experimental results of microwave backscattering at water surfaces. Active microwave remote sensing is one of the useful techniques for sea surface measurement. For example, it enables us to know the wind vector on global scale. A principle of measurement is that the microwave backscattering depends on the wind speed. Therefore understanding of the phenomena of microwave scattering at sea surface in detail is indispensable for improvement of measuring accuracy. The purpose of the research is to investigate the characteristics of microwave scattering at various water surface conditions. Water surface was generated by wind and currents, microwave backscattering at that surface was measured by X and C-band microwave scatterometer. The experimental results were summarized in scattering coefficients and Doppler spectra. X-band microwave was more sensitive at wind wave surface than C-band. The mean frequency of Doppler spectrum of backscattering microwave was corresponded to the phase velocity of the mean water surface wave and the bandwidth of Doppler spectrum had close relation to the orbital velocity of the mean wave. A current had no effect on the scattering coefficient, but the Doppler spectrum was shifted to the side corresponding to current direction.
Reliability Analysis of the Burst of Elastic/Plastic Tubes
Authors: Li Guang , Nordgren R. P.
Published: January 2009

The computational method presented in this paper provides an efficient solution to the reliability problem of burst of pipes with random geometric imperfections. The statistical characterization of the geometric imperfections is based on measured data from seamless pipes. Application of the Model-Correction-Factor Method (MCFM) proves that the burst pressure for a given pipe depends almost entirely on its minimum wall thickness. Thus, the burst reliability problem becomes one of determining the probability distribution of minimum wall thickness from the imperfection statistics. This problem is solved approximately by application of reliability theory and a novel homogenization technique. The accuracy of this method is verified through computationally inefficient Monte Carlo simulation for selected cases.
Use of Composite Materials in Protecting and Maintaining Subsea Equipment
Authors: Wang Wen-Tsuen , Watkins Lou
Published: January 2009

This paper summarizes many years of experience in designing and testing composite materials for use on offshore oil and gas pipelines and production equipment. It is the authors’ position that properly designed coatings and coverings can materially extend the life and safety of subsea equipment, whereas improper design can often contribute to premature failure and endanger both equipment and personnel. The principal applications of the authors’ research fall into four areas: (1) Buoyancy – providing buoyant lift to offset excessive weight of equipment in water; (2) Controlled Strength – providing precision compressibility to mitigate possible downhole annular pressure damage (3) Insulation – providing thermal protection against heat loss; and (4) Corrosion Protection – ensuring that all coatings work with (rather than against) cathodic protection systems. The potential for catastrophic damage in any or all of these areas is increasing daily as production moves into deeper water and hotter, higher-pressure wells. The paper presents case studies, cites test evidence, and suggests guidelines for designing composite materials that enhance safety in each of the subject areas. The resulting information will be useful to engineers, supervisors, and managers whose responsibility includes offshore design, maintenance, and safety.
Direct Strength Analysis of Semi-Submersible Platform Structures
Authors: Zhang Haibin , Ren Huilong , Dai Yangshan
Published: January 2009

A kind of direct strength analysis method of semi-submersible platform structures is presented in this paper. With the differences in shape of pontoon, column and beam being considered, the method of accumulative chord length cubic parameter spline function combined with analytic expression is adopted to generate the mesh of platform wet surface. The hydrodynamic coefficients of the platform are calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for platforms with low forward speed. The equations of platform motions are established and solved in frequency domain, and the responses of wave-induced loads on the platforms are calculated. According to the mesh of hydrodynamic computation, the fluid dynamic pressure field of platform wet surface is built, and the pressure loads on shell elements in the finite element model of the structure are calculated by the interpolation method. The calculation conditions and loads in the finite element analysis (FEA) of the platform structures are determined according to the design wave analysis approach. A computer program based on this method has been developed, and a calculation example of semi-submersible platform is illustrated. Analysis results show that this method is a satisfying approach for wave load computation and direct strength analysis of the semi-submersible platforms.
Design and Fabrication of a Collective and Cyclic Pitch Propeller
Authors: Humphrey T. Charles , Bose Neil , Williams Christopher , Snow Michael
Published: January 2009

Helicopters achieve three-dimensional flight using a rotor capable of both collective and cyclic pitch. It was proposed that this type of propulsion system could propel and maneuver an underwater vehicle. A collective pitch and cyclic pitch propeller (CPCPP) was designed and developed as a full scale-working prototype for autonomous underwater vehicle (AUV) propulsion. This paper discusses the design and construction aspects of the CPCPP.
AUV DeepC: Technology Platform for the Atlas Elektronik AUV Family
Authors: Hornfeld Willi
Published: January 2009

ATLAS ELEKTRONIK has a long tradition in the development and manufacture of naval systems and marine technologies like mine-countermeasure boats, integrated sonar, command and control systems and unmanned underwater vehicles (UUVs). One of the latest UUV-product development is the autonomous underwater vehicle, called DeepC with the main features: • Mission depth till 4000 m (Crush: 6000 m); • Weight in air 2.4 to  ; • Cruise speed 4 kts; • Maximum speed 6 kts; • Mission time up to 60 hours; • Operating range up to 400 km; • Payloads 250 kg. The development was started on Jan. 1st 2001 and will be finalized end of 2004 with the deep water tests. DeepC (www.deepc-auv.de) is a high efficient deep diving autonomous underwater vehicle system with long endurance for a lot of applications. Many actions that would normally require high cost ROV systems or which are not possible (e.g. under ice investigations) can now be accomplished using DeepC, at less cost and manpower. The main performance parameters of the DeepC system are in general: • Autonomous mission execution; • Low weight; • High manoeuvrability; • Hover capability; • Modular design; • Containerised Payload; • Deployment from vessels of opportunity; • Obstacle avoidance; • In mission re-planning capability; • Precise navigation; • Advanced diagnosis and fault recovery system. With these performance takes the DeepC system an international top place on the AUV sector and has in the framework of the ATLAS ELEKTRONIK AUV family philosophy a key position: it is the technological basis and highlight of the AUV family, contains the equipment with the most fastidious technologies and is now in the final phase of the development. The second member of the AUV family is the SeaOtter Mk 1, a vehicle system based on an ATLAS MARIDAN development. This AUV is extensively tested, qualified and successfully introduced at the market in its basic version. With the help of the DeepC, technology upgrades are planned which will lead to a substantial performance increase. The AUV of the third generation represents the SeaOtter Mk 2, whose development was up-to-date started and which bundles both, the DeepC technology and the operational experience of the SeaOtter Mk 1.
Alternative Wave-Induced Force and Moment Expressions for a Fixed, Vertical, Truncated, Circular Cylinder in Waters of Finite Depth
Authors: McCormick Michael E. , Cerquetti Jeffrey
Published: January 2009

Two user-friendly expressions for the horizontal and vertical wave-induced forces on fixed, truncated circular cylinders are presented. The approximation of the horizontal force is that of van Oortmerssen, and that of the vertical force is based on a solution of the Laplace equation with a matching radial-force condition at the internal-external interface. The velocity potential resulting from the solution is assumed to be finite at the origin of the radial coordinate. Results obtained from both approximations are compared with results obtained from the rigorous analysis of Garrett. Also, results from the Froude-Krylov approximation for the vertical force are presented for the sake of comparison. The van Oortmerssen are shown to coalesce with the Garrett results for ka > 1.5, while the vertical force results compare well over the ka range studied.
Advances in Design and Installation Analysis of Pipelines in Congested Areas With Rough Seabed Topography
Authors: Sævik Svein , Giertsen Egil , Berntsen Vidar
Published: January 2009

The present paper addresses a method for simulation of deepwater pipeline installation in offshore fields with rough seabed topography focusing on verification of installation feasibility. The method enables 3D pipe lay analysis to be carried out as a set of subsequent static analyses where the vessel is moved forward automatically considering the restraints from lay vessel departure angle and arbitrarily curved pipe routing. The analysis includes the effect of seabed topography from survey data and variable seabed conditions. The numerical algorithm is seamlessly integrated with 3D graphics for visualization of both the seabed terrain and the structural response of the pipe as the vessel is moving forward. The numerical method is based on finite elements that are formulated by applying the Principle of Virtual Displacements. Large deformations, non-linear geometry and contact effects are taken into account. In addition, elastic and elastic-plastic material models are allowed for, both for the pipe and the seabed contact elements. The paper focuses on the procedure including a brief theory description addressing the specialities needed in this case with respect to kinematics, material models and finite element formulation. The developed procedure is then demonstrated both by analytical and real pipeline installation test examples.
A New Spectral Method for Modeling Dynamic Ice Actions
Authors: Ka¨rna¨ Tuomo , Qu Yan , Ku¨hnlein Walter L.
Published: January 2009

This paper presents a method of evaluating the response of a vertical offshore structure that is subjected to dynamic ice actions. The model concerns a loading scenario where a uniform ice sheet is drifting and crushing against the structure. Full scale data obtained at the lighthouse Norstro¨msgrund is used in the derivation of a method that applies both to narrow and wide structures. A large amount of events with directly measured local forces was used to derive formulas for spectral density functions of the ice force. A non-dimensional formula that was derived for the autospectrum applies for all ice thicknesses. Coherence functions are used to define the cross-spectra of the local ice forces. The two kind of spectral density functions for local forces can be used to evaluate the spectral density of the total ice force. The method takes account of both the spatial and time correlation between the local forces. Accordingly, the model provides a tool to consider the non-simultaneous characteristics of the local ice pressures while assessing the total ice force. The model can be used in conjunction with general purpose FE programs to evaluate the dynamic response of an offshore structure.
Ultramonit: A New Concept for Monitoring Using Ultrasonics
Authors: Baltzersen O̸ystein , Solstad Arne , Daaland Alf , Holberg Jens Kristian
Published: January 2009

Recent developments in the fields of electronics, computer systems and communication technology have enabled the use of many new concepts within inspection and monitoring. ULTRAMONIT is one such example where we try to extend the use of ultrasonic measurements in terms of accuracy and what we can measure. In this concept, an array of ultrasonic sensors is placed permanently onto the pipe. The location of these sensors will typically be in a field joint directly at, or close to a weld, and the objective will be to monitor for corrosion attacks and cracks. Permanently installed sensors are advantageous as exact position, orientation and acoustic coupling are maintained between surveys. Compared to conventional ultrasonic inspection, this means significantly improved possibilities for high-resolution trend analysis of the data. Under good conditions, UT wall-thickness can be measured with a resolution in the order of 0.01 mm. Using fixed sensors; such very high resolution could be made available for monitoring purposes. Two versions of this system are developed, one for use on subsea pipelines, and one for use topside or on land facilities. ULTRAMONIT Subsea is implemented as an instrumented pipeline clamp, where the required electronics and sensors are placed and protected in a rugged steel structure. Reliability has been a key objective for this concept, and has been addressed by keeping the permanently installed electronics as simple as possible, while making the more complicated parts of the instrumentation accessible in an ROV carried unit. This ROV is used for interrogation with the sensors by use of a specially developed inductive coupler, which provides power, analog signal for the ultrasonic transducers, and digital communication for the signal multiplexer. This unit is controlled digitally and the number of channels is only limited by signal degradation due to total spanned length of analog cable, as the channel count gets very high. Our prototype has 48 channels in one row of sensors around the circumference of a 10” pipe, but both HW and SW is ready for any practical number of channels. ULTRAMONIT Subsea will be lab-tested at the Statoil R&D center in Trondheim, and a topside/land facilities version of this same system is being installed on a 12” pipe at the Ka˚rsto̸ gas processing plant. Both tests will commence in December 2003, and continue through 2004. Results from these tests will be presented at the conference.
Viscous Drift Forces on a Semi-Submersible Type Mega-Float Comprised of Circular Cylinders
Authors: Sunahara Shunji
Published: January 2009

An estimation of the wave drift forces acting on a semi-submersible type Mega-float supported by very many columns is very important in order to design its mooring system. It is known that the wave drift forces acting on a train of multiple vertical circular cylinders may be determined using the potential flow theory. However, it has recently been reported that the large wave drift forces acting on a large scale model of a semi-submersible type Mega-float, comprised of many simple circular cylinders, for long wave periods, cannot be explained by the potential flow theory. In addition the forces seem to have a significant influence on the design of its mooring system. At first, it seemed that the measured forces were viscous drift forces. The viscous drift forces are in proportion to the square of the wave particle velocity or the cube of the wave height. Of course, the existence of viscous drift forces has already been established, but it was considered that the forces acting are conditional in that the flow is apt to shed, for example on complex under-water shapes, on radiation problem, in larger height or longer period waves. Also it was thought that the forces acting on simple circular cylinders were negligibly small from the viewpoint of engineering applications. Finally, it was not accurately verified that the forces were viscous drift forces. In this study, model tests were carried out. The wave loads acting on a 16-column platform model and the hydrodynamic forces acting on each column of the model were simultaneously measured. The contribution of the viscous drift force component on the wave drift force acting on a train of vertical circular cylinders was also investigated in detail. It was confirmed that significant viscous drift forces act on circular cylinders for long wave periods. Furthermore an applicable region of viscous and potential components of the wave drift forces acting on vertical circular cylinders was obtained.
On the Influence From Hydrodynamic Forces on Speed and Footprint for a Falling Riser
Authors: Berntsen Vidar , Larsen Carl M. , Passano Elizabeth , De Moura Jorge Nilo , Roberto Jose´
Published: January 2009

This paper presents analysis method and key results from dynamic simulations of a drilling riser on 1900 metres water depth after release of upper end. Key results are the geometry of the collapsed riser on the seafloor (footprint) and the impact speed of the riser when hitting the seafloor. The purpose of the study has been to investigate the influence on the results from operational and model parameters such as vessel offset relative to the riser base, current speed, hydrodynamic load model, material model and interaction between the riser and the seafloor. The main conclusion from the study is that most trends from parameter variations are weak and often overshadowed by a more stochastic variation caused by the inherent complexity of the mechanical behaviour during collapse.
Aluminum Drill Pipe Fatigue Analysis
Authors: Miscow Guilherme Farias , Pla´cido Joa˜o Carlos Ribeiro , Valada˜o de Miranda Paulo Emi´lio , Netto Theodoro Antoun
Published: January 2009

While drilling extended reach wells, the weight per foot of the drill string is a critical design parameter that can limit the depth to be reached. One practical solution is the use of drill pipes made of alternative materials to the conventional steel drill pipes. The most direct options are titanium and aluminum. Titanium is in general impaired due to its high cost, although the titanium alloy Ti-6Al4V has already been used in the airplane industry. More recently, Russia has been manufacturing drill pipes using aluminum alloys of the system Al-Cu-Mg, similar to alloys 2024, also used in airplanes. These pipes present a reasonable commercial cost. Drill pipe fatigue damage occurs under cyclic loading conditions due to, for instance, rotation in curved sections of the well. Failures caused by crack nucleation and propagation are one of the highest risks to the structural integrity of these pipes. Usually, failure mechanisms develop in the transition region of the tool joint. Several mechanical and metallurgical factors affect the fatigue life of drill pipes. The former are mainly geometric discontinuities such as transition zones, pits and slip marks. The latter are related to the size and distribution of crystalline grains, phases and second phase particles (inclusions). In this study, the roles played by both factors in the fatigue life of drill pipes are studied through an experimental test program. The fundamental fatigue mechanisms are investigated via laboratory tests in small-scale coupons performed in an opto-mechanical fatigue apparatus. Additionally, full-scale fatigue testes on three aluminum drill pipes were performed. The pipes tested are being used in the horizontal section of some extended reach wells in the Northeast of Brazil.
Air-Pressure Characteristics of Aircushion Supported Large Floating Structures
Authors: Ikoma Tomoki , Masuda Koichi , Rheem Chang-Kyu , Maeda Hisaaki , Iwasa Ryo
Published: January 2009

Air-pressure characteristics of air supported fixed floating structures are described in this paper. The theoretical prediction method of responses of the aircushion type floating structure in waves has been proposed. The adiabatic compression is assumed to the prediction method. In this study, model experiments using two aircushion type models are carried out in the wave tank. Then, pressures in the aircushion and the wave exciting force of heave are measured. It is verified to assume spatially uniformly distribution to pressure distribution from explorations by using the experimental results of the pressure and the phase difference. In addition, effects of the initial pressure of the aircushion and the draft of the skirt bounding the aircushion and/or water are little.
Reliability Calibration of a Waves–Icebergs Interaction Load Combination Factor
Authors: Foschi Ricardo O. , Isaacson Michael , Allyn Norman
Published: January 2009

The Canadian Standards Association [1] has developed and published a code for the design and construction of fixed offshore structures. One of the limit states relates to the combined effects of waves and iceberg collision loading. The Code uses a load combination factor to determine the design load effect. The present paper describes a recent study on the appropriateness of the recommended value of the combination factor. The study involves a numerical analysis in which loads have been calculated, at different probability levels, for a range of iceberg and wave parameters, considering waves alone, an iceberg alone, and an iceberg and waves in combination. The paper thereby makes recommendations for the load combination factor as a function of iceberg and sea state parameters.
Numerical Simulation of the Mooring Procedures of the BGL-1 Pipeline Launching Barge
Authors: Masetti Isai´as Quaresma , Barros Claudio R. Mansur , Jacob Breno Pinheiro , Albrecht Carl Horst , de Lima Beatriz S. L. Pires , Sparano Joa˜o Vicente
Published: January 2009

The objective of this paper is to present the application of a computational tool intended to help the crew of the BGL-1 pipeline launching barge to develop safe mooring procedures. This tool is able to calculate the deformed catenary configuration of all mooring lines, regarding the subsea layout and the local environmental conditions, and taking into account one or more buoys attached to the mooring lines in order to avoid interference and accidents with subsea obstacles. One of the main characteristics of this computational tool is the fact that it is able to incorporate the correct definition of the seabed from bathymetric curves, and to automatically consider the position of the subsea obstacles, and possible interferences between the mooring lines and the obstacles. This is performed through a specialized interface with the SGO (Obstacles Management System) database system. This system, developed by Petrobras, contains frequently updated information about the bathymetry and position of subsea obstacles, gathered by a special vessel equipped with a ROV (Remote Operated Vehicle). Case studies will be presented, in order to illustrate the application of the system to the design of actual mooring procedures.
A Method for Structural Design of Pontoon Type VLFS Based on Collapse Behavior and Reliability Analysis
Authors: Okada Hiroo , Masaoka Koji , Tsubogo Takashi , Katsura Shinji , Kawamata Shin-Ichi
Published: January 2009

This paper deals with a simplified method for the preliminary design of pontoon-type very large floating structures (VLFS), which are supposed floating airport, based on collapse behavior and reliability analysis in irregular waves. Firstly, a simplified estimation method is presented for the probabilistic load effect model of VLFS under irregular sea-state conditions. Next, limit state conditions are shortly presented for the buckling and ultimate collapse strength of stiffened plates under combined compression, shear and lateral pressure in the deck, bulkhead and bottom parts of VLFS, especially, by using a simplified estimation formula. Then, the validity is shown by non-linear finite element method. Finally, dominant limit state modes of 5,000m-class VLFS under combined loads with bending moment, shear force and lateral pressure are obtained by applying the above methods. Then, the features of the collapse behavior and reliability level are investigated by using above calculation results. Effects of design parameters such as yield stress, plate thickness, stiffener and bulkhead space are also investigated using sensitivity analysis.
Using a Nonlinear Spectral Model for Preparing Three-Dimensional Wave Experiments
Authors: Bonnefoy Fe´licien , Le Touze´ David , Ferrant Pierre
Published: January 2009

We are interested in an original numerical model based on a spectral approach and able to simulate the focalisation of waves in a wavetank. Such a technique involves fast FFT resolution, permitting accurate simulations of the target wave fields at low cost. This model is specifically designed to fit with experimental conditions, accounting for the physical wavetank geometry including the absorbing beach, sidewalls, and the snake-type wavemaker. The nonlinear equations are developed in perturbation series up to second order in wave steepness. An additional potential is employed to model the generator of the wave tank. Simulations start from rest in the basin, requiring no initial wave patterns as in other spectral models. Firstly, we consider two dimensional spectra to check the ability of the model to reproduce irregular waves. Secondly, cases of wave trains geometrically focusing at a given location of the test area are simulated. Finally, directional sea spectra are generated with imposing a focalisation of the phases at a given time.
Nonlinear Hydroelastic Response of a Two-Dimensional Mat-Type VLFS by the Green-Naghdi Theory
Authors: Xia Dingwu , Ertekin R. Cengiz , Kim Jang Whan
Published: January 2009

The two-dimensional, nonlinear hydroelasticity of a mat-type VLFS is studied within the scope of linear beam theory for the structure and the nonlinear, Level I Green-Naghdi (GN) theory for the fluid. The beam equation and the GN equations are coupled through the kinematic and dynamic boundary conditions to obtain a new set of modified GN equations. These equations model long-wave motion beneath an elastic plate. A set of jump conditions that are necessary for the continuity (or the matching) of the solutions in the open water region and that under the structure is newly derived through the use of the postulated conservation laws of mass, momentum and mechanical energy. The resulting governing equations, subjected to the boundary and jump conditions, are solved by the finite-difference method in the time domain. The present model is applicable, for example, to the study of the hydroelastic response of a mat-type VLFS under the action of a solitary wave, or a frontal tsunami wave. Good agreement is observed between the present results and other published theoretical and numerical predictions, as well as experimental data. The nonlinear results show that consideration of nonlinearity is important for accurate predictions of the bending moment of the floating elastic plate. It is also found that the rigidity of the structure also greatly affects the bending moment and displacement of the structure in this nonlinear theory.
Bending Moments of an FPSO in Rogue Waves
Authors: Clauss Gu¨nther F. , Schmittner Christian E. , Hennig Janou , Guedes Soares Carlos , Fonseca Nuno , Pascoal Ricardo
Published: January 2009

The increasing numbers of reported rogue waves with extreme crest and wave heights and unusual group pattern with the consequence of severe damages raise the question if such exceptional events have to be considered routinely for the design of ships and offshore structures. For the investigation of the effects of rogue wave impacts time domain simulation methods are required in addition to traditional frequency domain methods which may not be sufficient to consider these extreme events. In this paper the vertical bending moments at the midship section of an FPSO are investigated using state of the art numerical simulation tools in combination with experiments. For the seakeeping tests the extremely high New Year Wave (registered in the North Sea) is generated in the wave tank, and motions and structural forces are analyzed at model scale. For validation the results are evaluated deterministically and compared to numerical simulations. The time domain calculation allows to artificially change local wave characteristics. The steepness of the selected rogue wave is varied and the influence on wave induced loads is studied. A comparison with standard procedures of seakeeping analysis and classification rules closes the paper.
Submergence and Wave Impact Loads During Dry Transportation of an Offshore Structure
Authors: Mansour Alaa M. , Huang Edward W. , Chianis John W.
Published: January 2009

In this paper, the submergence and wave impact loads acting on an offshore structure when transported on a heavy lift vessel has been experimentally studied. The nonlinear global system response under the effect of direct wave loads on the cargo has been investigated. An approach is developed to derive the global direct wave loads time history acting on the cargo in three-dimensions and correlate them to the submergence event. Numerical results are presented to illustrate this approach. Seafastening loads time history are also presented and correlated to the submergence event. Cargo Stability requirements against uplift and overturning on the vessel have been examined and reported.
Analysis Guidelines and Application of a Riser-Soil Interaction Model Including Trench Effects
Authors: Leira Bernt J. , Passano Elizabeth , Karunakaran Daniel , Farnes Knut-Aril , Giertsen Egil
Published: January 2009

A general overview of design aspects related to metal catenary risers is first given. Response characteristics of these types of riser configurations are considered. It is subsequently focused on models for soil-pipe interaction, which have a strong influence on computed riser stresses in the touch-down region. The so-called CARISIMA models for riser-soil interaction in relation to horizontal and vertical motion (i.e.horizontal resistance and suction) are presented. Inherent limitations of the models are summarised. Basic input parameters are described, considerations relevant for establishment of initial trench profile are given, and examples of riser response analysis are presented. Typical behaviour of the numerical models which is observed in the example analyses is also reported.
Background to DNV Recommended Practice DNV-RP-C201 Buckling Strength of Plated Structures
Authors: Solland Gunnar , Jensen Pa˚l Georg
Published: January 2009

The new DNV Recommended Practice on Buckling of Plated Structures (RP-C201) was issued in October 2002. It supersedes the plate part of the widely used DNV Classification Notes 30.1 on Buckling Strength Analysis. The RP covers unstiffened plate elements as well as orthogonal stiffened panels. The recommendations cover both in plane biaxial compression stresses and shear stresses as well as lateral pressure (hydrostatic pressure) even if acting simultaneously. The RP is part of the new series of DNV offshore standards and is intended for design of structures like semi-submersibles, topside structures, FPSOs jack-up rigs etc. The 2004 revision of the Norsok N-004 code will make reference to the RP-C201 with regard to buckling of stiffened plates. The RP is developed on the basis of continuous research activity at DNV within the field of buckling of plated structures for the last 30 years. Feed back from users of Classification Note 30.1 has also been an important element in the development. The result is a new set of design recommendations that leads to more cost effective structures and a more consistent level of structural reliability. This paper describes main features of the RP and the principles for the design checks. It presents the range of application and the background for the various recommendations. Also included are comparisons to other codes and laboratory test.
Cost Optimizations of Gas Detector Systems
Authors: Huser Asmund , Oliveira Luiz Fernando , Dalheim Joar
Published: January 2009

An improved procedure for optimization of flammable gas detector systems in process plant modules is presented in the paper. The main features of the new procedure are that it uses a detailed explosion Quantitative Risk Analysis (QRA) model to obtain the risk reducing effects of applying more gas detectors; and it uses detailed transient Computational Fluid Dynamics (CFD) simulations to assess the most effective locations of the gas detectors. This results in a cost optimized solution which gives the minimum fire and explosion risk, at the lowest cost. A field example is included where it is indicated that with the optimal number of gas detectors, the total costs of fire and explosion accidents are reduced by 18% compared to having no gas detection system at all.
Non-Linear Wave Diffraction Around a Moored Ship
Authors: Zang J. , Gibson R. , Taylor P. H. , Eatock Taylor R. , Swan C.
Published: January 2009

The objective of this research, part of the FP5 REBASDO Programme, is to examine the effects of directional wave spreading on the nonlinear hydrodynamic loads and the wave run-up around the bow of a floating vessel (FPSO) in random seas. In this work, the non-linear wave scattering problem is solved by employing a quadratic boundary element method. An existing scheme (DIFFRACT developed in Oxford) has been extended to deal with uni-directional and directional bi-chromatic input wave systems, calculating second-order wave diffraction under regular waves and focused wave groups. The second order wave interaction with a floating vessel in a unidirectional focused wave group is presented in this paper. Comparison of numerical results and the experimental measurements conducted at Imperial College shows excellent agreement. The second-order free surface components at the bow of the ship are very significant, and cannot be neglected if one requires accurate prediction of the wave-structure interaction; otherwise a major underestimation of the wave impact on the structure could occur.
Qualification of Subsea Thermal Insulation for Extreme Temperatures
Authors: Melve Bjo̸rn , Ali Dana , Hu¨bert Jan-Christian , Hommedal Steinar
Published: January 2009

The Kristin field in the Norwegian Sea have a flowing wellhead temperature of 162 °C. This is believed to be the maximum temperature for an insulated subsea wellhead experienced to date. An extensive qualification program for the corrosion coating and thermal insulation was performed including accelerated ageing in water at elevated temperatures. The most critical test was the insulated hot plate test with holes down to the steel surface. For the extreme temperature of 162 °C a phenolic syntactic foam system showed the “least worse” results, and was chosen as the insulation system.
Model Tests With an FPSO in Design Environmental Conditions
Authors: Skourup Jesper , Sterndorff Martin J. , Smith Susan F. , Cheng Xiaoming , Ahilan R. V. , G. Soares Carlos , Pascoal Ricardo
Published: January 2009

An extensive model test programme has been carried out with a turret moored FPSO model in design environmental conditions. The model tests were carried out in the 3D offshore wave basin at DHI Water & Environment at a scale of 1:80. The objectives of the model tests were two-fold: 1. To determine quadratic transfer functions for the slow-drift forces. 2. To determine the turret moored FPSO response in design environmental conditions with wave spreading. The model tests were made with a wide range of monochromatic and bi-chromatic wave conditions and also with long- and short-crested irregular wave conditions. For the tests in design conditions the irregular waves were combined with the corresponding wind condition. The model (which was segmented into two parts) was equipped with instruments to measure forces in mooring lines and turret, 6 dof motions of the FPSO, bending moments on the FPSO hull and wave run-up on the FPSO model. The present paper describes the details of the experimental work and the measurements made in the tests. Comparisons between model test results themselves to demonstrate the effects of wave spreading on the responses and comparisons to numerical results are given. The model test programme is part of the REBASDO project, funded by the European Union, and involving companies and institutions from several European Countries. The overall objective with the REBASDO project is to develop met-ocean and hydrodynamic models, which will capture the significant features of directional wave effects on FPSO design so that relevant enhancements in the design process can be incorporated in the future.
Fatigue Design Criteria for Small Super Duplex Steel Pipes
Authors: Kristoffersen Steinar , Haagensen Per J.
Published: January 2009

Stainless steel pipes ranging in sizes from approximately 10 to 100 mm OD are used extensively in umbilicals for the control and monitoring of underwater installations for oil and gas production. Umbilicals are subjected to tensile loads as well as variable amplitude loading from wave and current actions. Fatigue is therefore a critical issue in the design of umbilical components. Sea water resistant high strength super duplex steel with ultimate strength of typically 800 to 900 MPa is used to save weight and reduce the wall thickness. Some umbilicals installed by Statoil have design pressure up to 1035 bar, which in combination with large dynamic loads from floating production units makes fatigue design of the umbilicals a challenging issue. While the fatigue performance of butt welded pipes for pipelines and risers are established and implemented in design guidance and codes, the experimental basis for design of small diameter piping made of high strength materials is not well documented in the open literature. However, unpublished data from in-house investigations indicate that small pipes in super duplex steel perform significantly better than larger diameter pipes in lower strength materials. It is therefore apparently scope for a “thinness effect”, i.e. a bonus effect that could be applied to the data for large diameter pipes in current codes to account for the higher S-N curves for small stainless steel pipes. This paper reviews some of the fatigue data for piping and compares these data with experimental evidence from a joint industry project. Tentative fatigue design guidance for small diameter super duplex steel piping is presented. Questions concerning special issues such as the possible influence of wall thickness, mean stress and pre-straining due to reeling are discussed.
Environmental Forces on Offshore LNG Terminals: The Complications of Shallow Water
Authors: Forrsitall George Z.
Published: January 2009

Construction of large and expensive facilities in relatively shallow water demands that additional effort be paid to the extreme environmental conditions expected there. A review of the literature on waves in shallow water shows that many processes must be considered there which are not important in deep water. Bottom friction under waves depends on the detailed bottom conditions and parameterizing it properly may require calibration to local measurements. The limits on wave heights over the nearly flat bottoms that are common in water depths of 10–30 m are poorly known. Additional laboratory and field measurements appear to be necessary before depth limited waves can be confidently specified. The structures often respond differently to wave from different directions, so directional criteria could be useful. Commonly used methods of specifying directional criteria are un-conservative, but it is possible to adjust them so that the overall reliability of the structure is preserved.
Full Size Fatigue Crack-Growth Testing for Girth Welds
Authors: Gioielli Paulo , Buitrago Jaime
Published: January 2009

Fatigue crack-growth modeling has a significant impact in establishing defect acceptance criteria for the inspection of fracture-critical, girth-welded components, such as risers and tendons. ExxonMobil has developed an experimental technique to generate crack-growth data, in actual welded tubulars, that account for the particular material properties, geometry, and residual stresses. The technique is fully compatible with conventional fracture mechanics models. It uses a series of pre-designed notches made around the welds on a production quality, full-scale specimen that is tested efficiently in a resonant fatigue setup. The crack development from notches is monitored during testing and evaluated post-mortem. Given its simplicity and high loading frequency, the technique provides growth data germane to the component at hand at a lower cost and faster than standard, small-scale tests.
Maximum Wave Height Distribution in a Sea State: Effects of Record Length and Spectral Peakedness
Authors: Rodri´guez Germa´n , Pacheco Mercedes , Guedes Soares Carlos
Published: January 2009

The probability distribution of the maximum wave height in a sea state is examined in terms of the spectral peakedness and the sea state duration. The study is based on the analysis of numerically simulated gaussian wave records with given target spectra to fulfill the long duration and stationarity jointly required conditions, seldom found in nature. Results indicate a clear dependence of the probability distribution structure and location on the record length and the spectral shape.
Measurement of the Aerodynamic Pressures Produced by Passing Trains
Authors: MacNeill Robert A. , Holmes Samuel , Lee Harvey S.
Published: January 2009

This paper describes measurement of the aerodynamic pressures produced by a Bombardier High-Speed Non-Electric Locomotive (HSNEL) on an adjacent stationary double-stack freight car. Static pressures are measured on the near and far-side faces of the freight containers over a range of locomotive speeds from 60 to 130 mph. This data is also compared with the pressures predicted by computational fluid dynamics (CFD) simulations.