bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.