bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Modeling of Transient Temperature and Residual Stress Distribution Analysis in Multi-Pass Welding Process
Authors: Fu Guang-Ming , An Chen , Lourenço Marcelo Igor , Duan Meng-Lan , Estefen Segen F.
Published: August 2013

The residual stress and deformation due to the welding process have significant influences on the service performance of the welded deepwater platform hull. An exact prediction of transient temperature distribution is the important prerequisite to ensure the simulation accuracy of the welding residual stress and deformation fields, especially in the multi-pass welding process. Although the transient temperature distribution and residual stress distribution was studied in the past by various authors, the literature on 3D finite element (FE) simulation of multi-pass welding process is limited. In this paper, a FE model is developed to analyze the transient temperature and residual stress distribution of AH36 steel sheets in multi-pass welding process. A moving heat source model based on Goldak’s double-ellipsoidal heat flux distribution is employed for the heated plates. The addition of the volumetric heat source into the FE model and its movement along the welding pass are realized through a dedicated FORTRAN subroutine. The element birth and death technique in Abaqus/Standard is employed to simulate the weld filler variation with time in welded joints. The transient temperature calculated in the first stage is utilized as the input to the residual stress and distortion due to thermal shrinkage during the welding process and subsequent cooling. The results show good agreements between the temperature distribution and the geometry of weld pool obtained in the present work and those previously reported. Finally, a parametric study is performed to investigate the effect of welding variables, such as geometric parameters of Goldak’s heat source model, welding speed, pre-heat temperature and power input in the multi-pass welds, on the residual stress and distortion of the steel sheets.
Development of an Innovative Real-Time Simulator for DP-Shuttle Tanker / FPSO Offshore Connection Operation
Authors: Tannuri Eduardo A. , Makiyama Humberto S. , Rateiro Felipe , Fucatu Carlos H. , Taniguchi Denis , Masetti Isaias Q.
Published: August 2013

This paper discusses the prerequisites and the technical aspects of an innovative real-time simulator for DP-shuttle tanker and FPSO offshore connection operation. This simulator was developed by means of a partnership between the University of Sao Paulo and Petrobras. The software is based on the TPN (Numerical Offshore Tank) numerical code which had several modifications, in order perform real-time simulations. The mathematical models considered in the simulator and the computer architecture (hardware and software) will be presented.
Unsteady RANS Simulation of Flow Around a 5:1 Rectangular Cylinder at High Reynolds Numbers
Authors: Ong Muk Chen
Published: August 2013

The unsteady flows around a stationary two dimensional rectangular cylinder with chord-to-thickness ratio B/D = 5.0 at high Reynolds numbers, ReB = 5×105, 1×106, 1.5×106 and 2×106 (based on the free stream velocity and the chord length), are investigated numerically by solving the Unsteady Reynolds-Averaged Navier Stokes (URANS) equations with a standard high Reynolds number k-ε turbulence model. The objective of the present study is to evaluate whether the model is applicable for engineering design within this flow regime. Hydrodynamic results (such as time-averaged drag coefficient, root-mean-square of fluctuating lift coefficient, Strouhal number and mean pressure distribution around the rectangular cylinder) are compared with published experimental data. The mechanism of vortex shedding is also discussed.
DP Cooperative Control for Subsea Installation With Multiple Vessels: An Illustrative Case Study Based on Numerical Simulations
Authors: Oshiro Anderson T. , Tannuri Eduardo A. , Fucatu Carlos H. , Neves Cassiano R. , dos Santos Melquisedec F.
Published: August 2013

This paper presents the development of cooperative control technique applied to vessels equipped with dynamic positioning (DP) system. An illustrative case study is suggested: the launching of subsea equipment using two DP vessels. In this example, the cooperative system controls the relative distance between the DP vessels. One of the advantages of this method is the increase of operation’s safety and operational window, since, among other factors, the tension in the launching cable is reduced by half.

Initially, it was proposed the control of vessels relative positions, trying to keep the movements at the top of the A-frames in counter-phase. This avoids the slackening of the launching cable. For this, an algorithm based on phase estimator (Hilbert transform) associated with a PD control was implemented. The results showed that for regular waves this strategy was effective.

A dynamic mapping was then obtained using simplified 2D simulator, previously validated by comparison with experimental tests. In these maps, two regions are defined — occurrence or non-occurrence of cable slackening — as a function of the distance of the vessels and the depth of the subsea equipment. This map defines the proper set-point for the DP systems for each depth of the subsea equipment. This map is used to define the best relative position for the vessels.

In addition, the hoisting control receives the measurements of the vertical motion at the top of the A-frame, and compensates its motion, trying to maintain a constant lowering velocity. This control was implemented considering errors of 10% and delay of 0.5s in the measurements. The results confirmed that the control is able to eliminate the tension peaks and the occurrence of slackening in the launching cable.

The conclusion is that the appropriate control strategy, considering regular waves, is to combine the control of both position of the vessels and hoisting of the cable. Therefore the position control, coupled with dynamic mapping, defines the “optimal path” to be followed during the line hoisting, trying to keep the vessels as close as possible to the “no slackening” region.
Impacts of Waterway Regulation Engineering on Saltwater Intrusion in the Modaomen Estuary
Authors: Zhu Yuliang , Xu Chencheng , Wei Xiaoyan
Published: August 2013

A large-scale waterway regulation project, which is the main approach for people to manage coastal and estuary area will be imperative due to the high-speed economic development in Guangdong Province. The project will change the topography in the estuary region and influence the hydrodynamic conditions there. The Modaomen waterway, as the main access to the sea of Xijiang River, plays a key role in connecting outer sea. During recent years, a remarkable deterioration of tide intrusion occurred resulting in negative effect on water resource utilization in industry, agriculture and local people’s lives and therefore it is of great significance to study on the tide intrusion caused by dredging project.

This paper analyses measured Modaomen hydrological data and exhibits the temporal and spatial distribution of salinity and characteristics of fresh and salinity water mixing, as well as the correlation between salinity, water level and suspended sediment concentration in the Modaomen region. Based on the establishment of high-precision three-dimensional salinity mathematical model in Modaomen region, this paper calculates various engineering plans and examines the changes of flow field and tidal saltwater intrusion, which provides elementary base for implementation of the waterway regulation engineering. During the process of calculation, the terrain, the border and validation data that adopted in this paper is relatively new and have high reliability.

The study indicates that the salinity degree has a merely minor increase after projects indeed in the estuary to provide situation for tide intrusion. However, the influence is little and it fails to be the chief reasons responsible for the depravation of tide intrusion in the Modaomen estuary recent years.
A Surrogate Model for Evaluation of Maximum Normalized Dynamic Load Factor in Moving Load Model for Pipeline Spanning due to Slug Flow
Authors: Sultan Ibrahim A. , Reda Ahmed M. , Forbes Gareth L.
Published: August 2013

Understanding the problem of slug-flow-induced fatigue damage is of particular importance to the reliable operation of pipelines. Slug flow, across unsupported pipeline spans, produces dynamic vibrations in the pipeline resulting in cyclical fatigue stresses. These dynamic effects will cause the pipeline to fail at a point of stress concentration if proper design procedure is not followed.

The response of a pipeline span, under the passage of slug flow, can be represented by dynamic load factors that are functions of the speed ratio and damping characteristics of the span. The aspects of these functional relationships are investigated, in this paper by conducting multiple simulations at different speed ratios and damping factors. The data obtained from the steady state Fourier expansion will, consequently, be used to produce a surrogate model with a level of accuracy that adequately qualifies it for use in determining dynamic loading of pipelines.

The closed-form surrogate model can be used to eliminate the need to employ costly mathematical procedures or finite element packages for the analysis. The model will also provide a solid ground for optimization studies and help designers gain an insight into how various model parameters impact the system response. This paper will demonstrate the aspects of a proposed surrogate model and endeavor to obtain parameter domains within which the model’s reliability is ensured. A numerical example will be demonstrated to prove the concepts presented in the paper and confirm the validity of the proposed model.
Relationship Between Manganese Nodule Distribution and Deep-Sea Sediment Properties in the Northeastern Pacific
Authors: Chi Sang-Bum , Kim Wonnyon , Park Cheong-Kee , Yoo Chanmin , Ko Youngtak , Moon Jai-Woon
Published: August 2013

In order to identify a potential relationship between the spatial distribution of Mn-nodule and deep-sea sediment properties in the Clarion-Clipperton fracture zone of the northeastern Pacific, physico-chemical properties of deep-sea sediments and photos of sea-floor are analyzed. In general, sediment types in the area show dramatic changes with latitude. Compared to the middle sector (8–12°N) covered with biogenic siliceous sediments, the northern (16–17°N) and southern (5–6°N) areas are dominated by pelagic red clays and calcareous sediments, respectively. Such a difference in sediment types probably produces regional-scale variations in Mn-nodule occurrence with latitude (5–17°N) along longitude (131.5°W). According to the photographic examination, manganese nodules are well exposed on the sea floor in the latitude of >8°N. In connection with the dominant oceanic environment, such observation indicates that calcareous sediments cover the diagenic nodules due to higher primary productivity and sedimentation rate in the latitude of <8°N. In addition, sediments in the latitude of 8–12°N show relatively high shear strength. Considering the operation of miner and environmental effect, highly consolidated B2 and C1 areas (8–12°N), showing higher nodule contents and relatively lower primary productivity, are the most plausible site for commercial mining.
Simulation of the Mooring Vessels in Tsunamis Using the MPS Method Considers Leading Wave and Backwash
Authors: Masuda Mitsuhiro , Minami Kiyokazu , Masuda Koichi , Ikoma Tomoki
Published: August 2013

The present paper describes the simulation of behavior of mooring vessels in tsunami using the 3-D MPS (Moving Particle Semi-implicit) Method for considering leading wave and backwash effect. The chain of a disaster is brought about by two kinds of tsunami. The chain of disaster means breaking the mooring tether, grounding on a wharf, drift to continental areas, the collision with building by leading wave and the outflow of the floating matter by backwash. In this research, the 3D-MPS method is applied, and the bore like wave is applied as an assumed tsunami. The expression of backwash is tried by water pillar collapse. The present calculation results are compared with the experimental results and the applicability of the MPS method is discussed. In addition, the vehicle is arranged on a wharf, and the chain of disaster is simulated.
Modeling and Inspection Applications of a Coastal Distributed Autonomous Sensor Network
Authors: Patrikalakis Nicholas M. , Leighton Joshua , Papadopoulos Georgios , Weymouth Gabriel , Kurniawati Hanna , Valdivia y Alvarado Pablo , Taher Tawfiq , Khan Rubaina
Published: August 2013

Real time in-situ measurements are essential for monitoring and understanding physical and biochemical changes within ocean environments. Phenomena of interest usually display spatial and temporal dynamics that span different scales. As a result, a combination of different vehicles, sensors, and advanced control algorithms are required in oceanographic monitoring systems. In this study our group presents the design of a distributed heterogeneous autonomous sensor network that combines underwater, surface, and aerial robotic vehicles along with advanced sensor payloads, planning algorithms and learning principles to successfully operate across the scales and constraints found in coastal environments. Examples where the robotic sensor network is used to localize algal blooms and collect modeling data in the coastal regions of the island nation of Singapore and to construct 3D models of marine structures for inspection and harbor navigation are presented. The system was successfully tested in seawater environments around Singapore where the water current is around 1–2m/s.
The Application of a “Giant” Floating Wave Barrier for Offshore Installation Work
Authors: Billingy Sean S. , Vermeulen Kees-Jan , Kortekaas Peter
Published: August 2013

When focusing on offshore installation work, it can be seen that there has been a shift from one-off installations for the oil and gas industry to repetitive installations of, for instance, offshore renewables. An important aspect, which plays a large part in the success rate of these repetitive installations, is the workability of the installation vessels.

SMIT understands the importance of workability and is looking into ways to increase the workability of their sheerlegs crane barges in an offshore environment. A proposed method to increase the workability is the use of a floating wave barrier (FWB). This FWB can be a specific structure designed for this purpose, or, as in this case, a barge used for the transportation of the structures that will then be installed by the sheerlegs crane barge.

This paper discusses the effects of a FWB on the first-order motions of the sheerlegs crane barge. Dependent on the environmental conditions, the use of a FWB can decrease the first-order motions of the vessel and increase its workability on that particular phase in the total installation sequence. When applied on the phase with the lowest workability in the installation process, this can result in a higher overall workability. The limits of the use of a FWB are also discussed, particularly with respect to wave height and period.
Application of Deterministic and Probabilistic Methods in Pipeline Lateral Buckling Design
Authors: Zeitoun Hammam , Branković Maša , Shim Edwin , Chin EuJeen , Anderson Benjamin
Published: August 2013

Subsea pipelines lateral buckling design has significantly evolved over the last years as more pipeline projects have moved into more challenging environments and into high temperature / high pressure (HT/HP) design application. Knowledge and understanding of pipeline lateral buckling has improved with design application resulting in refined and enhanced design approaches. Using current design approaches, it is now quite acceptable to control lateral buckle formation along the pipeline by using buckle triggers or to allow uncontrolled lateral buckles, provided that the various design limit states are satisfied.

A number of design methodologies can be used to check the acceptability of uncontrolled buckling or to design for controlled buckling including deterministic, probabilistic buckle formation and full Structural Reliability Assessment (SRA) methods. Using SRA or probabilistic methods is usually an attractive design option as lateral buckling design involves dealing with a large number of uncertainties and variation in design parameters. These methods help to ensure the reliability of the proposed buckle initiation scheme. However, the use of these methods is also associated with a number of challenges such as the need to identify key parameters influencing the design and quantifying their uncertainties. Deterministic design approaches on the other hand are simpler to apply. However, they do not provide means to quantify the reliability of the proposed buckling scheme or the design risks. The choice of input parameters in a deterministic design is also relatively subjective which can possibly result in an overly conservative or unconservative design solution depending on the adopted design approach, selected design parameters and pipeline system being considered.

Design guidelines and recommended practices such as SAFEBUCK (20) offer comprehensive guidelines to design for lateral buckling. However when faced with a range of complex variables, the designer needs to be aware of the effect of these parameters on the overall design.

This paper describes the application of Deterministic and Probabilistic design approaches in lateral buckling design. The paper starts by describing these approaches, their advantages and limitations. The paper then explores a number of key uncertainties and variation in design parameters that the designer is faced with and its effect on the pipeline response.
Statistics of Wave Orbital Velocity in Deep Water Random Directional Wave Fields
Authors: Toffoli A. , Bitner-Gregersen E. M. , Suslov S. A. , Onorato M.
Published: August 2013

A direct numerical simulation method is used to monitor the evolution of nonlinear random directional wave fields. The aim is to investigate the combined effect of high order nonlinearity and directional energy distribution on the statistics of wave orbital velocity. Results show that the development of modulational wave instability and the concurrent formation of large amplitude waves lead to a substantial departure of the statistics of the horizontal velocity from the Normal (or Gaussian) probability density function when the wave field is long crested. As short crestedness increases, departure from the Normal distribution gradually diminishes and eventually vanishes for sufficiently broad directional spreading.
NorMoor JIP: On Safe Mooring Line Design
Authors: Okkenhaug Siril , Mathisen Jan , Hørte Torfinn
Published: August 2013

DNV is currently running a Joint Industry Project, “NorMoor JIP”, on calibration of safety factors for mooring lines together with several oil companies, engineering companies, rig-owners, manufacturers of mooring line components and Norwegian authorities.

Our motivation for initiating a study on mooring line safety factors started out with questions raised with regards to the safety level given by the Norwegian regulations. However, this is equally important for other mooring regulations like ISO, API and class-regulations. What we see is that the mooring standards are interpreted and applied in different ways. The reliability level implied by the regulations is not known, and the present safety factors were set when frequency domain analysis was prevalent while time domain analysis is often applied today.

DNV carried out the DeepMoor JIP [9] during 1995–2000 using frequency domain analysis and reliability-based calibration. Now, a decade later, the increase in computing capacity makes it feasible to carry out a similar calibration for time-domain analysis of the mooring systems.

The objective of the project work is to investigate and compare the characteristic line tension calculated according to design standards with the annual extreme value distribution of the line tension. Further, to calibrate safety factors for mooring line design for the ultimate limit state (ULS) as a function of the target probability of failure.

The original proposal for this JIP included calculations for chain and wire rope moorings on a typical drill rig and a turret moored FPSO at three different water depths at Haltenbanken. However, since this JIP has been very well received in the industry, the scope has been extended to include calculations for a production semisubmersible, for fibre rope systems and for Gulf of Mexico environmental conditions.

This paper will focus on the reasons for doing this calibration study, and the importance of seeking to agree on unified calculation recipes and requirements. Preliminary results for characteristic tension and annual extreme value distributions of tension for some designs are presented and discussed. The calibration of safety factors will be carried out later in the project when all designs are finalized.
Residual Strength Analysis for Rapid Response Damage Assessment (RRDA) of Steel Ship Structures
Authors: Lee AiKuo , VanDerHorn Eric , Wang Ge
Published: August 2013

Numerical and experimental simulations for residual strength analysis of ship structures have recently been investigated in the marine industry. The technology of residual strength analysis is mature enough to assist ocean-going vessels shortly after experiencing a damage incident. The analysis can be used to evaluate the remedial actions necessary to minimize the risk of further damage during stabilization efforts and allow for the eventual transit to a repair facility. In 2010, the American Bureau of Shipping (ABS) implemented enhancements to its Rapid Response Damage Assessment (RRDA) program, in particular to the evaluation of residual strength. An integrated software system was developed to quickly and efficiently provide guidance to the ship owner through the utilization of the analysis results.

This paper highlights the residual strength analysis results of several actual RRDA cases evaluated in recent years. These results were obtained from the application of an analysis software system, which includes the ability to perform timely calculations of the hull girder ultimate strength, hull girder shear stress, buckling and local strength in the damaged condition. This paper also provides an example of the use of analysis data to provide recommendations for remedial actions during a response. The strengths and weaknesses of this current analysis procedure are discussed and conclusions about the use of this software tool in damage scenarios are evaluated by comparing the analysis results with the outcomes of the presented cases.
Assessment of Hydrostatic Collapse of Submarine Pipelines: The Classical Approach Revisited
Authors: Benjamin Adilson C. , Cunha Divino J. S.
Published: August 2013

In order to improve the assessment of the hydrostatic collapse of deepwater pipelines a new method named, RCA (Renewed Classical Approach) method, was developed. The development of this method, which is a modified version of the DNV method, was based on the results of several nonlinear Finite Element (FE) analyses.

In this paper the development of the RCA method is presented. Initially an overview of the classical approach is presented. Then two assessment methods are presented (the DNV method and the RCA method) and the FE modeling is described. Finally the collapse pressures predicted by the assessment methods are compared with those predicted by the FE models.
A Semi-Empirical Wave Crest Distribution of Random Directional Wave Fields
Authors: Bitner-Gregersen Elzbieta M. , Toffoli Alessandro
Published: August 2013

Laboratory data of random directional wave fields have been used to investigate the combined effect of higher order nonlinearity and directional spreading on the wave crest distribution. Different sea states with a variety of combination of steepness and directional spreading have been considered, ranging from long to short crested wave fields. The analysis is also supported by numerical simulations. A 2-parameter Weibull distribution has been fitted to the experimental data and the related parameters have been parameterized as a function of a general version of the Benjamin-Feir Index for directional sea states recently presented by Mori et al. [1]. Long-term distributions of the one-dimensional and two-dimensional Benjamin-Feir Index have been studied based on the hindcast data from the North Atlantic and probabilistic models to describe them are proposed.
Comparative Dynamic Response Analysis of a Fixed Offshore Platform Using Deterministic and Spectral Wave Approaches
Authors: Hafez K. A. , Aboul-Fadl W. , Leheta H. W.
Published: August 2013

This paper investigates numerically the dynamic response of a fixed offshore platform, namely WHP, in a 2D irregular seaway using both deterministic and spectral design wave approaches. The long-crested irregular seaway is defined by Pierson Moskowitz (PM) spectrum with parameters suiting the WHP installation site. The platform dry weight is 10200 tonnes, sitting on 4 legs wellhead structure, and already installed in Hong Long field of Vietnam coast of South China Sea in a location of 45.47 meters water depth. The platform is supported on piles driven through its legs up to 100 meters protrusion into the seabed. The major construction components of WHP platform are prefabricated piles, jacket, deck, topside, helideck, boat-landing, and a number of J-tubes and risers. A 3D finite element model (FEM) of the platform is created to perform a comparative static and dynamic structural analysis of its response. The numerical results obtained from the deterministic and spectral design wave approaches are compared against each other, and partially validated against the actual platform measurements to introduce a reliable and meaningful interpretation of the numerical results. Finally, for the whole effort to be demonstrated efficiently a few conclusions are introduced and some future recommendations are proposed.
Probabilistic Condition Assessment of Aging Equipment Considering the Effect of Operating Conditions and Maintenance
Authors: Ramírez Pedro A. Pérez , Johnsen Roy , Utne Ingrid B.
Published: August 2013

Assessing the technical condition and remaining useful life of aging equipment is crucial for the life extension of O&G facilities. In order to perform a reliable assessment, models describing the degradation of the equipment are necessary. However, the use of accurate physical models for this purpose may be challenging. Some reasons are that the equipment can be exposed to various degradation mechanisms, which may be influenced by different operating conditions, and that the operational data may be scarce. This paper presents a systematic approach for modelling different degradation mechanisms, assessing the technical condition of a component, and quantifying the expected remaining useful life. The quantification is performed using a Bayesian network. Finally, the application of the proposed model is illustrated with the analysis of a fire water pump.
Composite Drilling Riser on Heidrun: A Decade in Operational Experience
Authors: Melve Bjørn , Nedrelid Kristin , Tanem Siv Arna , Kroknes Lasse , Myrmel Stein H.
Published: August 2013

A drilling riser joint with carbon fibre in the main structural body and titanium end flanges was put into service at the Heidrun TLP in 2001. The joint has an internal titanium liner. The joint was the first implementation of an offshore composite riser and was the end result of the Compriser project.

The composite riser joint has an internal diameter of 560 mm (22”) and is 15 m (48 ft) long. The joint is a part of the marine riser. The joint has been in service for ten years and has been treated as its metallic counterparts.

At the periodic inspection done in 2010, it was decided that the external layer needed refurbishment.

Inspection and pressure testing showed that the properties of the joint had not changed during service.
Detailed Analysis of Clump-Weight Interference With Subsea Pipelines
Authors: Maalø Kristian , Alsos Hagbart S. , Sævik Svein
Published: August 2013

This paper focuses on the interference between pipelines and fishing gear such as clump weights. The objective is to examine the clump weight behavior as it is pulled across pipelines. Numerical analyses which simulate the integrated response between clump weight and pipelines are performed [1] and compared with actual tests performed by Statoil during 2004 for the Kristin field development. The experiments involved scaled down pull-over tests over idealized free spanning pipelines.

A detailed model of the experimental model setup is established using the nonlinear finite element software SIMLA. Simulations are carried out for trawl gear interference with pipelines in various idealized free-span conditions. In each case the models force-displacement responses are compared with normalized test results.

Finally, trawl interference with a full scale 1000 m pipeline section resting on uneven seabed is studied. The interaction forces from fully integrated pipeline-trawl analyses are compared directly with design interference loads from DNV-RP-F111, [2]. The objective of this is to quantify the potential safety margin provided by DNV-RP-F111.
Development of a Test Methodology and a Design Tool to Predict the Wear Rate of Flexible Risers Outer Sheaths Installed in I-Tubes
Authors: Pires Fabio , Nogueira Victor , Aquino Fabio , Clevelario Judimar , Sheldrake Terry , Takey Thyago
Published: August 2013

The interface between the flexible risers and I tubes installed in floating production units is being considered by the industry as a critical region regarding wearing due to its geometric characteristics and high contact loads between the flexible risers and I-tube interface equipment. During the past few years some instances of outer sheath damage were reported by the offshore industry.

Such occurrences have been responsible for the unplanned maintenance of flexible pipes and production loss. Based on this scenario, Wellstream has developed and incorporated into its regular supplies, a new model of riser interface equipment with a replaceable polymeric liner, which has been qualified through a full-scale test program and demonstrated to be adequate in protecting the flexible pipe’s outer sheaths [1].

Although the developed equipment was originally designed to allow the replacement of the polymeric liner, which acts as a sacrificial part, the planning of periodic inspections and the determination of the optimum liner thickness could not be reliably performed due to the lack of solid experimental data regarding the wear rates of the polymer pairs and the contact pressures expected for that region. As part of an internal research program, a FEA model has been developed and calibrated in order to allow the assessment of the contact pressure between the flexible pipe’s outer sheath and the I-tube interface equipment for the actual contact pressures generated by the field fatigue loads, supporting the development of a midscale test program to determine the wear rates of the polymeric materials pairs as a function of the contact pressure [2].

The determination of these two main variables allowed the definition and conception of a dedicated design tool and the generation of experimental data to the flexible riser interface equipment and its polymeric liner, increasing the reliability of the flexible risers installed in I-tubes.

This paper presents a discussion regarding the contact pressures experienced by the flexible pipe sample in service, the basis for the experimental test program and the concept of the developed design tool.
Computational Fluid Dynamics Study for Modeling Vortex Induced Vibrations Using High Fidelity Turbulence Models
Authors: Agrawal Madhusuden , Elyyan Mohammad A.
Published: August 2013

Flow over smooth cylinder at very high Reynolds number, ReD = 2×106, is simulated using the unsteady Scale Adaptive Simulation (SAS) turbulence model. Flow structures and vortex shedding were accurately captured. Grid sensitivity study was performed to compare averaged drag coefficient for a conformal fine mesh as well as non-conformal coarse mesh. Predicted value of drag coefficient was within 8% of the experimental value and Strouhal number compared well with the experimental observations.
X-Stream: An Innovative Pipeline Solution to the Challenges of Extreme Water Depths
Authors: Diniz Flávio L. B. , Raposo Celso V. , Neto Mario Caruso , Pitt David , Venas Asle , Stahl Selim , Borsheim Lars
Published: August 2013

In South America, the recent fields discovered in the pre-salt area are located more than 300km away from the coast, which makes exploring and especially the transportation of associated gas a major challenge in the coming years. Several issues are related to this problem:

• distance to shore (more than 300 km) and ultra-deepwater (more than 2000 m);

• vessel time and capacity (reduced number of boats/offshore units with capacity to install pipelines in deepwater);

• increasing demand for these vessels worldwide;

• flaring restrictions in accordance with Brazilian National Petroleum Agency (ANP).

Deepwater pipelines have traditionally been built using very thick pipe walls, requiring large quantities of steel and special equipment for milling and pipe laying.

This paper presents an innovative gas transportation concept for long distance in ultra-deep waters (X-Stream Pipeline Concept). A way to potentially reduce the required wall thickness of deep water pipelines by controlling in the differential pressure across the pipe wall (and thus allowing for a reduction in the pipeline wall thickness).

This concept is also applicable in other deepwater exploratory frontiers, for instance: Gulf of Mexico and West Africa.
Increasing the Operation Window for Drilling Risers on DP Vessels by Monitoring Riser Angles
Authors: Rustad Anne M. , Ervik Anna K. , Sørensen Asgeir J. , Larsen Carl M.
Published: August 2013

Drilling operations are taking place in ever deeper waters and harsher environments using dynamically positioned (DP) vessels. A DP control system maintains the vessel in a fixed position or pre-determined track exclusively by means of active thrusters based on measured position from satellites and hydroacoustics. In particular, two failure scenarios are critical for safe DP operations: drift-off with loss of thrust and drive-off with unstable thruster usage. For drilling operations; ensuring safe emergency disconnect (ESD) when needed and avoiding unnecessary disconnecting when not needed, both the drilling riser behavior and the vessel offsets are of main concern. Concerning the time required to correctly decide and execute ESD drive-off is considered as most critical. It is important to ensure safe operations, maximize operability and avoid disconnection of the riser as far as possible.

In this paper we will investigate riser and vessel dynamics during drive-off in order to increase the operation window that is normally defined from quasi-static considerations. Our analyses show that the traditional limits for vessel offset might be too conservative, and that more realistic criteria can be found by taking riser dynamics during transition into account.
Breaking Wave Kinematics and Resulting Slamming Pressures on a Vertical Column
Authors: Stansberg Carl Trygve , Berget Kjetil , Graczyk Mateusz , Muthanna Chittiappa , Pakozdi Csaba
Published: August 2013

A need has been identified to improve the knowledge about extreme slamming loads from breaking waves on vertical columns, such as offshore platforms and wind turbine foundations. Due to strongly nonlinear physical mechanisms and large statistical variability, more and improved experimental data are needed, as well as better qualified design procedures. In this paper, model test data and CFD simulations from a recent study with a fixed vertical column are compared and investigated in more detail. Selected individual extreme slamming events due to energetic breaking waves in 1:40 and 1:125 scaled model tests are presented and considered. Waves correspond approximately to extreme breaking wave occurrences in steep energetic sea states with 10-4 annual probability in the Norwegian sector.

Slamming pressures on the column wall are measured in time and space by means of a 7 × 7 pressure sensor array covering 19m2 (full scale). Significant spatial variations are observed. When spatially averaged over the array, the observed highest pressures are typically in the range 1MPa–3MPa (full scale), while smaller measuring areas give higher values. This compares roughly to levels found from recent results in the literature; although exact comparison is difficult due to statistical uncertainty issues. Experiences obtained from parallel CFD and PIV activities are also compared to the experiments, from which free-surface particle velocities up to 25m/s (full scale) are estimated in the worst cases. Finally, a simple empirical formula for a slamming coefficient depending on the actual pressure integration area is suggested based on the results.
Intervention Vessel for Barents Sea Operation
Authors: Berg Tor Einar , Berge Bjørn Ola , Borgen Henning , Hänninen Saara
Published: August 2013

This paper describes work done to specify, design and test an offshore intervention vessel for operation off northern Norway and in the Norwegian part of the Barents Sea on an all-year basis. The design has been developed basedon input from manufacturers of subsea systems, owners of offshore vessels and Statoil. Research and development effort have been shared between research institutes (MARINTEK and VTT), the Norwegian University of Science and Technology (NTNU), Statoil, STX OSV and Aker Arctic Technology. The work has been done as a part of the Norwegian Research Council supported project “Construction and intervention vessels for Arctic oil and gas – CIVArctic).
Numerical Simulation of a Floater in a Broken-Ice Field: Part I — Model Description
Authors: Metrikin Ivan , Lu Wenjun , Lubbad Raed , Løset Sveinung , Kashafutdinov Marat
Published: August 2013

This paper presents a novel concept for simulating the ice-floater interaction process. The concept is based on a mathematical model which emphasizes the station-keeping scenario, i.e. when the relative velocity between the floater and the ice is comparatively small. This means that the model is geared towards such applications as dynamic positioning in ice and ice management.

The concept is based on coupling the rigid multibody simulations with the Finite Element Method (FEM) simulations. The rigid multibody simulation is implemented through a physics engine which is used to model the dynamic behaviour of rigid bodies which undergo large translational and rotational displacements (the floater and the ice floes). The FEM is used to simulate the material behaviour of the ice and the fluid, i.e. the ice breaking and the hydrodynamics of the ice floes. Within this framework, the physics engine is responsible for dynamically detecting the contacts between the objects in the calculation domain, and the FEM software is responsible for calculating the contact forces. The concept is applicable for simulations in a three-dimensional space (3D).

The model described in this paper is divided into two main parts: the mathematical ice model and the mathematical floater model. The mathematical ice model allows modelling both intact level ice and discontinuous ice within a single framework. However, the primary focus of this paper is placed on modelling the broken ice conditions. A floater is modelled as a rigid body with 6 degrees of freedom, i.e. no deformations of the floater’s hull are allowed. Nevertheless, the hydrodynamics of the floater and the ice is considered within the outlined model.

The presented approach allows implementing realistic, high fidelity 3D simulations of the ice-fluid-structure interaction process.
Dynamic Analysis for a Pipe-in-Pipe Riser System
Authors: Cheng Yongming , Qi Tao , Chen Xiaoxian
Published: August 2013

A Pipe-In-Pipe (PIP) riser system is widely used in the offshore industry. A typical top tensioned riser system consists of an outer casing, inner casing and tubing. A PIP thermal insulation technology is often used to satisfy stringent insulation requirements and to maintain an acceptable global performance for pipe-in-pipe steel catenary risers. This paper investigates dynamic analysis for a PIP riser system.

This paper first presents a theoretical formulation for a PIP riser system coupled with fluids in the annuli and centralizers between pipes. Hydrodynamic forces associated with the viscous fluid in between concentric cylinders are considered. An effective dynamic stiffness matrix method is then developed to evaluate the added mass and damping influence of the fluid on the natural frequencies and the dynamic response of the coupled riser system.

The composite model approach is commonly used for modeling concentric PIP riser systems. In reality, however, the riser pipes may contact with the outer pipe at the connectors and centralizers under dynamic loading. This paper then discusses a detailed PIP finite element model to capture the coupling effects of centralizers with gaps.

Examples are used to illustrate the dynamic behavior of a PIP riser system. The first example shows the frequency response of a PIP riser coupled through the fluid in the annulus and centralizers distributed longitudinally. The second one represents a PIP riser system coupled through centralizers with gaps. The analysis was performed by using the FEA program ABAQUS.
Establishment of Testing Methodology for Forge Welded Tubular Products
Authors: Marimuthu Ganesan S. , Moe Per Thomas , Salberg Bjarne , Audestad Jan Inge
Published: August 2013

A state-of-the-art small-scale solid state forge welding machine has been fabricated for checking weldability by Shielded Active Gas Forge Welding (SAG-FW) of tubular products applicable predominantly for, but not limited to offshore Industries. Effective, fast and inexpensive welding and testing of joints make this small-scale method suitable for evaluating weldability of a material before starting regular qualification and fabrication in a full-scale welding machine normally located in spool base or offshore. The small-scale machine provides a complete package for pre-qualification studies, including assessment of welding conditions, material flow behavior, heat treatment options. However, there are considerable challenges relating to application of international standards of testing as well as interpretation and use of results in the context of large-scale welding. In this paper results from small-scale welding and weld characterization of an API 5L X65 quality are presented. First, a detailed test plan for analyzing the weld is outlined. This procedure is subsequently applied for checking the welds to be produced in the full-scale machine. Short-comings in using the small-scale process as well as the possible remedies are discussed in detail.
Estimating Design Levels for Strongly Nonlinear Response
Authors: Johannessen Thomas B. , Hagen Øistein
Published: August 2013

The present paper is concerned with the accurate estimation of wave induced design responses in model test campaigns where only a relatively low number of seastates can be simulated.

Three response types are considered, namely an essentially linear response type such as the linear elevation of wave crests, a weakly nonlinear response type such as the second order crest elevation, and finally a discontinuous badly behaved response type such as wave in deck loading.

For each of these response types, the 100 year and 10 000 year response levels are calculated for a Norwegian Sea environment. The fractiles at which these response levels occur at the governing seastate along the 100 year and 10 000 year contours, are also calculated.

Having established these quantities, the efficiency of three methods is evaluated. Firstly an extreme value approach with a Gumbel assumption is considered and it is evaluated how many three hour simulations are required to obtain a good estimate of the relevant fractile levels in the governing seastate. Similarly, a peak over threshold analysis of maxima is considered and the number of seastates required is compared with the Gumbel results.

Finally, the 100 year and 10 000 year response levels are estimated directly by employing an iterative procedure on the probability integral of the long term distribution of the responses together with a simple interpolation procedure. It is found that the latter procedure is efficient, particularly for strongly nonlinear response types.
Lateral Buckling of Deepwater Pipelines in Operation
Authors: Urthaler Yetzirah , Watson Ryan , Davis Jonathan
Published: August 2013

Deepwater pipeline systems are regularly designed to operate under high pressure and high temperature (HPHT) conditions. These operating environments typically mean that the systems are susceptible to Euler buckling, more commonly referred to as lateral buckling. An effective design solution, promoted by the SAFEBUCK JIP [1],[2] and now regularly adopted within the industry, is to accommodate the thermal expansion with planned buckle sites, thereby controlling the loads within the system.

Traditionally, operators have spent a great deal of resources in designing, manufacturing and installing pipeline systems. However, it is equally important to demonstrate that the system is fit for service and that operational loads do not exceed the extreme design cases. In some instances, there have been a number of instances where lateral buckling has caused full bore rupture in offshore pipelines. In order to verify the long-term integrity of a pipeline system, it is essential to confirm the location, mode shape and amplitude of both the planned and rogue (unplanned) lateral buckles. This can be accomplished via pipeline surveys. Recent pipeline survey work was conducted on a pipeline system in the Gulf of Mexico. The data exhibited some areas of unexpected performance, which highlights the fact that operating uncertainty exists and that lateral buckling is an unstable phenomenon. The design Finite Element (FE) models were calibrated using the measured buckle shapes, and the fatigue life was estimated using recorded operational pressure and temperature data. The survey work performed has proven invaluable when assessing the long-term integrity of the pipeline system.

This paper presents a review of the methods used for surveying a pipeline system in the Gulf of Mexico, a summary of the results obtained from the subsequent analysis and pipeline FE model calibration, as well as ‘lessons learned’ for future projects with similar design challenges.