bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time Series Analysis of Significant Wave Height Data for Identification of Trends in the Ocean Wave Climate
Authors: Vanem Erik , Walker Sam-Erik 
Published: November 2013

Reliable return period estimates of sea state parameters such as the significant wave height is of great importance in marine structural design and ocean engineering. Hence, time series of significant wave height have been extensively studied in recent years. However, with the possibility of an ongoing change in the global climate, this might influence the ocean wave climate as well and it would be of great interest to analyze long time series to see if any long-term trends can be detected.
In this paper, long time series of significant wave height stemming from the ERA-40 reanalysis project, containing 6-hourly data over a period of more than 44 years are investigated with the purpose of identifying long term trends. Different time series analysis methods are employed, i.e. seasonal ARIMA, multiple linear regression, the Theil-Sen estimator and generalized additive models, and the results are discussed. These results are then compared to previous studies; in particular results are compared to a recent study where a spatio-temporal stochastic model was applied to the same data. However, in the current analysis, the spatial dimension has been reduced and spatial minima, mean and maxima have been analysed for temporal trends.
Overall, increasing trends in the wave climate have been identified by most of the modelling approaches explored in the paper, although some of the trends are not statistically significant at the 95% level. Based on the results presented in this paper, it may be argued that there is evidence of a roughening trend in the recent ocean wave climate, and more detailed analyses of individual months and seasons indicate that these trends might be mostly due to trends during the winter months.
Tracking of Buoyancy Flux of Underwater Plumes for Identification, Close Visual Inspection and Repair of Leaking Underwater Pipelines in Muddy Waters
Authors: Agbakwuru Jasper A. , Gudmestad Ove T. , Groenli John , Skjæveland Helge 
Published: November 2013

The importance of close visual inspection of leaking sections of pipelines prior to repair activities cannot be over-emphasized. Underwater optical cameras are important gadgets for most underwater inspection vehicles and submarines. However, the optical camera ordinarily immersed in a gaseous or liquid plume in muddy water condition will see no reliable trace but nearly blank or the scatter of diffused light of illuminating lamps. The implication is that underwater water tools that could be used in clear water to inspect and identify point of leaks on pressure containment structures would not be useful when such structure is installed in muddy or poor underwater visibility conditions.
Recent developments have demonstrated a diver assisted technique of close visual inspection of leaking containments structures installed in muddy water using clean water injection. This present paper demonstrates a technique of tracking and identifying leaking points on pipelines installed in unclear/muddy water conditions using optical cameras installed in a novel manner. The method leads a remotely operated or hyperbaric system to the point of leak in muddy water conditions for close visual inspection and subsequent repair.
The tool performance is validated in a muddy water of Secchi measure of less than 1 cm and in a number of trials, the tool is found sitting at the leak point. Secchi measure is the visual depth into the water column.
Forces that could be found in the plume and the consequences of buoyancy loss to floating or submarine equipment are also examined. Some techniques using remotely operated vehicles and manned hyperbaric bells for leak identification, close visual inspection and repair of pipelines installed in muddy water using the benefit of this presented methodology are proposed and discussed.
Experimental Analysis and Modelling of the Thermomechanical Behaviour of Field Joint of Thermally Insulated Pipeline
Authors: Phan V. T. , Cognard J. Y. , Choqueuse D. 
Published: November 2013

Ultra Deep offshore oil exploitation (down to 3000 meters depth) presents new challenges to offshore engineering and operating companies. Flow assurance and particularly the selection of insulation materials to be applied to pipe lines are of primary importance, and are the focus of much industry interest for deepwater applications.
In this field, particular attention is now focussed on the long term behaviour of the assembly between coated field joints and parent coating material which appears to be critical for in-service durability. A field joint is the uncoated area that results when two pipe sections with coating cutbacks are assembled by welding.
The in-service environmental conditions of the structure are severe and include high hydrostatic pressure up to 30 MPa and large thermal gradients through the thickness of the material (inner temperature up to 100°C and external temperature 4°C). This study aims to establish a model allowing the thermo-mechanical behaviour of the assembly to be evaluated and to describe the experimental protocol required in order to identify the model parameters.
First, the mechanical behaviour of the parent coating (usually glass syntactic polypropylene material) and coated field joint material are determined using hydrostatic compression tests (static and creep) at different temperatures and Dynamic Mechanical Analysis (DMA).
Then, a thermo-mechanical model of the parent material allowing hydrostatic creep deformation is developed and implemented in Comsol Multiphysic ™ software. A global model of the structure under service conditions, from the manufacturing process to the in service conditions, is then proposed and allows the strain distribution in the structure to be predicted. This distribution highlights the critical area of the assembly which is the bond between the parent coating material and the field joint coating.
Challenging Design Confronted in a Deepwater/HPHT PiP Tie-Back Flowline System
Authors: Sun Jason , Jakl Sandra , Shi Han 
Published: November 2013

A challenging problem that pipeline industry has to face in deepwater is the high energy reservoir with high pressure and high temperature. For piping, flowline, and riser, High Pressure (HP) leads to much thicker pipe wall that increases manufacturing and installation cost. High Temperature (HT) has even wider impact on design since the flowline system has to operate over a greater temperature range between non-producing situations such as installation and shut down, and the maximum production flow.
Subsea tie-back to the existing floating production facility, generally named as Brown Field Development, has many engineering and financial advantages. It becomes more popular in the Gulf of Mexico (GoM), North Sea, and West African due to the economical benefits. This paper presents some of the design challenges of a deepwater subsea tie-back project, which is composed of an 8″ by 12″ pipe-in-pipe (PiP) flowline loop from three (3) subsea fields to a semi-submersible platform located in the GoM at a water depth of 2,000m (∼6,600ft). Some of key efforts are worth to mention:
• Mitigation of thermal expansion and global buckling as facing very soft clay soil;
• Transition tie-in of PiP to structure piping - a valiant strength design to meet the deepwater installation loading;
• PiP inner pipe lock-in compressive load - effect of flowline (non-bonded) section length variation and locked-in stress;
• Tight installation target box for the separately installed structure mudmat and upper module.
This paper presents the solutions that Project team has generated to address these design/installation challenges. Lessons learned from the designs and installations are also presented. Advanced analysis tool — FEA are utilized through the entire design stage, from global 3-D flowline modeling to local component strength design.
Dynamic Positioning Simulation of a Simplified FPSO in Waves
Authors: Zhan Dexin , Very Stephen , Bass Don , Millan James 
Published: November 2013

This paper presents a numerical station-keeping simulation in waves (regular and irregular waves) for a simplified FPSO with two DP systems. The main difference of the simulation with these two DP systems was that the first DP system (called MOT DP in this paper) was included in a seakeeping simulation code (MOTSIM) while another DP system (called IOT DP, developed by NRC/IOT) was an external system and installed on another computer (which was the same as the one used to control the vessel in physical model experiments). In order to exchange command messages between the simulation code (MOTSIM) and the IOT DP system, a communication code executed in the same time step was developed by using Windows™ socket functions.
By using these two DP systems a station-keeping simulation for a 1:40 scale model FPSO with six azimuthing thrusters was conducted in regular and irregular waves and wind. The seakeeping RAO results in regular waves were compared between these two DP systems, and also with physical model experiments with external IOT DP system and analysis using a commercial linear, 3-dimensional panel code, HydroStar. In irregular waves a mean station keeping force Fx, Fy in horizontal plane was calculated and its total mean force was compared with results from the physical model experiments. Finally, a discussion between these two DP systems was provided.
Advanced Numerical and Analytical Tools for J-Tube Pull-In Through Multiple Bends
Authors: Fan Chengye , Wang James , Banneyake Ranil 
Published: November 2013

J-tube pull-in is a conventional riser installation method used for connecting pipelines to offshore platforms. In general the J-tube pull-in analysis is performed either using simplified analytical models or finite element method. Finite element (FE) tools become more important for the scenarios with complicated J-tube design, because of its flexibility in adapting material properties, 3D geometry, and multiple bends.
Conventional FE models employ tube-to-tube contact elements (ITT elements in Abaqus) to model the contact between J-tube and riser, where both J-tube and riser are all modeled as beams. In this paper, a new FE model is developed that modeled the J-tube as a surface. The new model was benchmarked with the conventional ITT element model and shows a better performance in terms of convergence speed using a simple geometry. The new model was further applied to a 3D multiple bends J-tube application. The impacts from J-tube size, J-tube bend radius, number of bends, and material yield strength were also studied. The outcome of this analysis provides guidance for effective and reliable J-tube pull-in studies.
A Comparison of Two Wave Models and Their Influence on Fatigue Damage in Ship Structures
Authors: Mao Wengang , Prasetyo Fredhi Agung , Ringsberg Jonas W. , Osawa Naoki 
Published: November 2013

In the maritime industry, fatigue failure is one of the most significant failure modes for ship structures. The fatigue damage in ship structures is mainly caused by the variation of wave loadings applied on ships, leading to variable structural stresses. Therefore, a reliable description of wave environments encountered during a ship’s service life is essential for accurate fatigue assessment of ship structures. Besides the wave scatter diagram provided by classification society rules, different statistical wave models have also been built up to model wave environments along arbitrary ship routes. The wave models could provide more specific wave environment for any chosen sailing routes of an individual ship. They may have the potential to be used for some practical applications, such as conceptual ship fatigue design, remaining fatigue life prediction when a ship plans to change its original trade region, and crack maintenance planning etc.
Since the development of these models may be based on different sources, e.g. satellite measurements, hindcast data, buoys, etc., the reliability and consistence of wave generations from various wave models must be validated by the measured wave environments in order to be used for those practical applications. In this paper, waves generated from two different wave models, one based on hindcast data and one mainly on satellite data, are compared with measured wave environments encountered by a 2800 TEU container vessel on the North Atlantic route. These wave models are used in the calculation of the fatigue damage in the vessel. The results obtained using waves generated from the two wave models are compared with the fatigue damage calculated based on strain measurements in the ship. Recommendations for future development of the wave models and further investigation to make the applications more realistic for ship fatigue assessment are also presented.
Modeling Suction Pile Lowering Through the Splash Zone
Authors: Gordon Robert B. , Grytøyr Guttorm , Dhaigude Mayuresh 
Published: November 2013

This paper describes a direct time domain modeling procedure for suction pile lowering through the splash zone. The paper specifically addresses pile lowering from a relatively small installation vessel with the pile oriented with its long axis nearly parallel to the water surface. The model consists of time domain simulation of the crane/wire/sling/pile system. This system is subjected to vessel motions at the crane tip, hydrodynamic loading on the pile, and pile flooding.
The paper also describes the sensitivity of winch wire tension to seastate, lowering velocity and hydrodynamic model coefficients, and suction pile characteristics.
Finally, a brief comparison is made between this model and others that have been proposed within the industry, some of which have been incorporated in design standards and guidelines such as DNV-RP-H103.
Analytical Hierarchy Process (AHP) for Selecting and Designing a Mini LNG Plant: A Case Study of Batam Indonesia
Authors: Artana Ketut Buda , Putranta Dinariyana Dwi , Arief Irfan Syarief , MadeAriana I 
Published: November 2013

Increase in demand for clean energy is one of the strategic issues in Indonesia nowadays, considering the significant economic growth of the country. A conventional LNG supply chain is not the best solution taking into consideration its high investment. The possibility of using a small scale LNG supply chain concept (Mini LNG) is recently sought by the government and private sectors in Indonesia. It is even more promising when we consider the amounts and number of stranded gas fields in the country. One of the main obstacles to the development plan is the geographical position of Indonesia as an archipelagic country.
This paper presents a case study of LNG supply chain model of 10 mmscfd Gas Sales Agreement (GSA) in Batam and its design of LNG transportation model from Batam to Siantan-West Kalimantan [1]. The distance between Batam and Siantan is approximately 392 nautical miles. Two main objectives are covered in this paper. The first one is an implementation of the Analytical Hierarchy Process (AHP) to select the best location for mini LNG plant, and the second one is to design the LNG supply chain model based on optimization approach.
The AHP model uses a pairwise comparison of 4 (four) qualitative attributes and 14 (fourteen) sub-attributes. 3 alternatives of location for mini LNG plant are evaluated, namely: Tanjung Uncang, Pemping Island and Janda Berhias Island. A sensitivity analysis by varying the weight of some critical attributes is also conducted to ensure that preferred location is sensitively selected with minimum error.
The optimization of the LNG supply chain model is carried out by means of Gradually Reduced Gradient (GRG) methods. The Objective is to attain one design that will minimize investment (cost). Decision variables of the model are LNG plant capacity, storage tank capacity in loading and receiving terminal, vessel size, number of round trip, number of operating vessels, regasification capacity at the receiving terminal, and others.
The Extremal Dependence of Storm Severity, Wind Speed and Surface Level Pressure in the Northern North Sea
Authors: Towe Ross , Eastoe Emma , Tawn Jonathan , Wu Yanyun , Jonathan Philip 
Published: November 2013

Characterising the joint distribution of extremes of significant wave height and wind speed is critical for reliable design and assessment of marine structures. The extremal dependence of pairs of oceanographic variables can be characterised using one of a number of summary statistics, which describe the two different types of extremal dependence. Quantifying the type of extremal dependence is an essential pre-requisite to joint or spatial extreme value modelling, and ensures that appropriate model forms are employed.
We estimate extremal dependence between storm peak significant wave height and storm peak wind speed (Hs, WS) for locations in a region of the northern North Sea. However, since the extremal dependence itself may vary with storm direction, we introduce new covariate-dependent forms of the extremal dependence measures that account for the direction of the storm.
We discuss the implications of all of the estimates for marine design, including specification of joint design criteria for extended spatial domains, and statistical downscaling to incorporate the effects of climate change on design specification.
Simulating the Financial Cost of a Deepwater Loss of Well Control
Authors: Black Jared L. , Hinrichsen Eckhard , Zenteno Alfredo Tello 
Published: November 2013

An international oil company developed a deep water exploratory drilling program scheduled to start in 2011. The company’s safety department required a financial risk analysis of the drilling program to aid in establishing insurance coverage levels. The purpose was to establish a probability cost distribution associated with a lost well control (LWC) incident. A numerical probabilistic simulation approach was deemed necessary since historical LWC cost data were insufficient for statistical analysis.
A ten branch fault tree with up to 38 elements (events) per branch was selected to represent the range of damage conditions that could follow a LWC incident. Probability density functions representing each event’s cost range were selected using a best fit procedure. The simulation procedure randomly selected a tree branch and then passed through the branch selecting costs randomly from each event’s cost-probability distribution. Event costs were summed to provide a total LWC cost for that simulation run. The simulation was repeated multiple times providing a suite of LWC total cost values. These data were then evaluated statistically to establish a LWC cost probability distribution. These results were used by the company’s risk division as an aid in determining the level of insurance to acquire.
Safety Factors Calibration for Wall Thickness Design of Ultra Deepwater Pipelines
Authors: Oazen Eduardo , Antunes Bruno R. , Cardoso Carlos O. , Solano Rafael F. 
Published: November 2013

Wall thickness often presents a considerable influence in offshore pipeline capital expenditure (CAPEX). This influence is enhanced in design of ultra deepwater trunk lines of large diameter, where any wall thickness increase provides a huge impact on project costs. In ultra deepwater scenarios, thicker pipelines may eventually implicate not only in higher costs, but may also compromise the project feasibility due to installation load constraints related to laying vessels availability.
One potential way to reduce the pipeline wall thickness is to calibrate fitness-for-purpose safety factors through application of structural reliability methods, instead of utilizing the standardized safety factors presented in international codes. Since mid-nineties, several offshore pipeline design codes have been allowing the calibration of safety factors by structural reliability analysis. The purpose of such an allowance is that structural reliability methods would eliminate some eventual conservatism presented in the safety factors proposed by codes. Although this enables the achievement of optimized safety factors, more than fifteen years have passed and only few pipeline projects have taken advantage of the benefits of safety factor calibration.
This paper evaluates which potential benefits are available through safety factor calibration, particularly for wall thickness reduction purposes in ultra deepwater pipeline design. Calibrated safety factors are presented for some scenarios related to ultra deepwater export pipelines, considering “system collapse criteria” limit state. The calibrated safety factors are compared with the standardized safety factors presented by international pipeline design codes. The potential for safety factor reduction by the utilization of linepipes with more stringent manufacturing tolerances and the consideration of the thermal ageing imposed by coating application are also discussed.
Safety Factor for Use in the Fatigue Crack Growth Assessment of Pipeline Weld Integrity and Engineering Critical Assessments
Authors: Sriskandarajah T. , Zhou Daowu , Hobbs George , Roberts Graeme 
Published: November 2013

Engineering critical assessments (ECA) are routinely used to provide defect acceptance criteria for pipeline welds. The fatigue crack growth evaluation as part of ECA involves the use of a safety factor applied to the number of cycles of a given stress spectrum. It has been routinely presumed that a safety factor value of half of the corresponding safety factor used for S-N fatigue should be used in the ECA. For example, this was suggested in DNV OS F101 earlier than the 2012 edition.
This paper presents a rationale and example calculations as to why a safety factor of 1.0 for fatigue crack growth is wholly appropriate for design stage calculations (for re-assessment when the various parameters are well defined then it could be appropriate to use a higher safety factor for the cycle counts). A probabilistic approach accounting for the statistical coincidence of misalignment, defect size, weld under maximum loading, etc is described in this paper. The probabilistic approach (based on fatigue crack growth) was compared with the S-N fatigue calculation and the deterministic ECA result. The results demonstrate that the probability of occurrence of fatigue failure using the probabilistic ECA approach with safety factor of 1 is far less than the DNV-OS-F101 requirement of 25 × 10−4 for medium safety class.
This conclusion presumes that in the standard ECA, a worst onerous selection is made from the range of input parameters, e.g. wall thickness, misalignment, defect location etc.