bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of Residual Life of Existing Offshore Platforms in Western Offshore, India
Authors: Renugadevi A. , Nallayarasu S. , Karunanithi S. 
Published: October 2021

Abstract
Western offshore oil field in India has nearly 300 offshore platforms for oil and gas exploration, of which almost 50% of platforms have outlived their life. Life extension of these platforms has become essential for further production activities. In many cases, design level analyses combined with ultimate strength assessment, life extension has been granted. However, risk-based assessment based on the probability of failure based on available reserve strength linked to additional life extension could be a logical method. The Reserve Strength Ratio (RSR) is defined as a ratio of reserve capacity of the jacket structure and the design level environmental loads (1 year or 5year or 10 year or 100-year return period). The encounter probability of these design storms for the life extension period has been established probability for the extension period has been used as a threshold to determining the required RSR using the probability of collapse. For the present study, four typical aged wellhead platforms with different water depths are selected, and RSR is evaluated by carrying out push over analysis. The Monte Carlo Simulation method is used to generate the statistical values of RSR. The probability of failure is then calculated by First Order Reliability Method (FORM) using MATLAB for different RSR values. Reassessment criteria for the existing offshore platforms have been described from the reliability analysis results based on probability failure and encounter probability.
RMS Control of Response of Jacket Structure Using Tuned Liquid Column Ball Gas Damper Under Random Ocean Waves
Authors: Jothinathan Satheesh , Kumar Deepak 
Published: October 2021

Abstract
Jacket structures are one of the most important offshore structures for extracting oil and gas. The fatigue life is affected due to the continuous dynamic wave force experienced by the structure. Generally, the structure is designed so that the dynamic response is small, which increases the cost. So, controlling its response is a good alternative to increase its life span. In this work, a simplified jacket structure under a random sea state is controlled for its response using a tuned liquid column ball gas damper (TLCBGD). The jacket structure in a water depth of 60m is modeled in a surge degree of freedom. The parameters of TLCBGD are optimized using a genetic algorithm for achieving better control in response quantities. For the analysis purpose, the wave is considered stochastic and presented by Pierson–Moskowitz (PM) spectrum of significant wave height 10m. In such a case, the jacket structure response can be presented using the root mean square (RMS) values obtained from the Lyapunov technique. Based on the random vibration analysis theory, the Lyapunov method can be employed to obtain the RMS of the system driven directly without solving the governing differential equation. This method requires the system to be driven by white noise. So, in this study, filters are developed to get the required narrow banded ocean spectrum. It is noticed that the response quantity is highly sensitive to the filter parameters. This is because a slight change in excitation parameters and a change in filter parameters near the system’s natural frequency affect the response significantly. Further, it is seen that the use of the genetic algorithm for tuning the TLCBGD gives very good control on the response quantity of the jacket structure.
Optimization of Segmented Wave-Maker Control to Generate Spatially Uniform Regular Waves in a Rounded-Rectangular Wave Basin
Authors: Ota Daichi , Houtani Hidetaka , Sawada Hiroshi , Taguchi Harukuni 
Published: October 2021

Abstract
A wave field in a wave basin inevitably has spatial variation due to the wave’s cylindrical propagation property. Therefore, we aimed to develop an optimization method for the control of wave-makers to produce a spatially uniform wave field in a specified test zone inside a wave basin with an arbitrary arrangement of wave-makers. The optimization is based on the simulated annealing algorithm, a method for finding a globally optimal solution, which was combined with a numerical wave basin based on linear wave-maker theory. A wave generation experiment was performed in the actual sea model basin (80 m long, 40 m wide, and 4.5 m deep) at the National Maritime Research Institute to validate the proposed optimization method. A case study was conducted with a long-crested regular-wave with a wave height of 10 cm, wavelength of 4.0 m, and wave direction of 180 degrees, which corresponds to the longitudinal direction of the wave basin. A 40-m × 14-m test zone was set in the middle of the wave basin. The experimental results with and without the proposed optimization were compared, which confirmed that the spatial uniformity of the wave field was improved, and the coefficient of variation for the wave height in the test zone decreased from 0.127 to 0.029.
Calibration of a Time-Domain Hydrodynamic Model for A 12 MW Semi-Submersible Floating Wind Turbine
Authors: Silva de Souza Carlos Eduardo , Fonseca Nuno , Berthelsen Petter Andreas , Thys Maxime 
Published: October 2021

Abstract
Design optimization of mooring systems is an important step towards the reduction of costs for the floating wind turbine (FWT) industry. Accurate prediction of slowly-varying horizontal motions is needed, but there are still questions regarding the most adequate models for low-frequency wave excitation, and damping, for typical FWT concepts. To fill this gap, it is fundamental to compare existing load models against model tests results. This paper describes a calibration procedure for a three-columns semi-submersible FWT, based on adjustment of a time-domain numerical model to experimental results in decay tests, and tests in waves. First, the numerical model and underlying assumptions are introduced. The model is then validated against experimental data, such that the adequate load models are chosen and adjusted. In this step, Newman’s approximation is adopted for the second-order wave loads, using wave drift coefficients obtained from the experiments. Calm-water viscous damping is represented as a linear and quadratic model, and adjusted based on decay tests. Additional damping from waves is then adjusted for each sea state, consisting of a combination of a wave drift damping component, and one component with viscous nature. Finally, a parameterization procedure is proposed for generalizing the results to sea states not considered in the tests.
A Well-Based Field Development Redefinition of Unconventional Reservoirs Through Unconventionality Index: Utilizing Machine Learning
Authors: Aldhuhoori Mohammed , Belhaj Hadi , Ghosh Bisweswar , Alkuwaiti Hamda , Qaddoura Rabab 
Published: October 2021

Abstract
The intriguing aspect of this study is to include illustrative and realistic well-based matrix to efficiently evaluate, characterize and develop Unconventional reservoirs (UCRs). This research targets a newly assessment in redefining UCRs, and developing a well-based tool to evaluate, characterize and predict the performance of tight UCRs. In this study, permeability and viscosity are used to develop the Unconventionality Index (UI) to reflect the combined causes of low mobility from UCRs. Machine learning is applied to synthesize a novel comprehensive understanding of UCRs modeling. A distinct pattern is developed for to distinguish between UCRs and CRs to show the Recovery Factor (RF) / UI dependency. Consequently, to establish such relationship, data from major UCRs producers were examined and utilized. In addition, UCRs classification matrix has been developed utilizing actual UCRs data from different reservoirs. Furthermore, a unique Unconventionality Index has been established to classify UCRs, determine reasons of unconventionality and ascertain efficient method/s of development. Subsequently, a correlation between different rock and fluid properties incorporating UI and recovery factor has been attained.
Wave Impact Loads on the Bottom of Flat Decks
Authors: de Oliveira Costa Daniel , Perim Julia Araújo , Camargo Bruno Guedes , Sena Sales Junior Joel , Fernandes Antonio Carlos , Corrêa Rodrigo dos Santos 
Published: October 2021

Abstract
Slamming events due to wave impact on the underside of decks might lead to severe and potentially harmful local and/or global loads in offshore structures. The strong nonlinearities during the impact require a robust method for accessing the loads and hinder the use of analytical models. The use of computation fluid dynamics (CFD) is an interesting alternative to estimate the impact loads, but validation through experimental data is still essential.
The present work focuses on a flat-bottomed model fixed over the mean free surface level submitted to regular incoming waves. The proposal is to reproduce previous studies through CFD and model tests in a different reduced scale to provide extra validation and to identify possible non-potential scale effects such as air compressibility. Numerical simulations are performed in both experiments’ scales.
The numerical analysis is performed with a marine dedicated flow solver, FINE™/Marine from NUMECA, which features an unsteady Reynolds-averaged Navier-Stokes (URANS) solver and a finite volume method to build spatial discretization. The multiphase flow is represented through the Volume of Fluid (VOF) method for incompressible and nonmiscible fluids. The new model tests were performed at the wave channel of the Laboratory of Waves and Currents (LOC/COPPE – UFRJ), at the Federal University of Rio de Janeiro.
Corrosion Products and Surface Morphology for Coated, Uncoated, and Insulated A333 Steel Pipelines in Marine Harsh Environment
Authors: Hillier Alan , Khan Faisal , Caines Susan 
Published: October 2021

Abstract
In situ studies with CUI and corrosion under coating is rare, especially for full scale tests in marine harsh environment. A333 low temperature carbon steel is selected for its versatile use in cold environments. This material is not widely studied in marine environment. Therefore, this work reports corrosion type, products, morphology and mechanism for thirty-six model pipelines (insulated, uninsulated, coated and uncoated) placed at Argentia, NL. Corrosion products were identified using x-ray diffraction (XRD). The detection and semi-quantification of elements on pipe surfaces was performed using energy disruptive spectroscopy (EDS) which was coupled to a scanning electron microscope (SEM). SEM images confirmed the formation of characteristic morphological structures such as sandy crystal (lepidocrocite γ-FeOOH), cotton ball (goethite α-FeOOH), and small grain (akageneite β-FeOOH) structures. For insulated uncoated pipes, the main phases were goethite, akageneite, and hematite(α-Fe2O3). For uncoated uninsulated pipes, akageneite, goethite, and hematite were detected as main phases. For coated pipes, goethite was the main phase. When ferrihydrite was detected with akageneite, there was less lepidocrocite and goethite than when ferrihydrite was not present. Uncoated pipes had deepest pits and highest corrosion rates as previously reported in [1]. Magnetite (Fe3O4) was present in these samples only in year two. Magnetite is a passive oxide formed on the iron surface but can also be a product of microbial reduction of ferrihydrite in certain conditions. A proposed mechanism for the high corrosion rate and pits in uncoated pipes is due to the increased localized corrosion from akageneite due to excess chloride and moisture from seawater spray as well as stabilized ferrihydrite limiting goethite formation, thus reducing steel pipe surface passivity.
Examination on Flaw Interactions in a Plate Subjected to Tensile and Bending Loads
Authors: Im Yeong Cheol , Kim Myung Hyun 
Published: October 2021

Abstract
Engineering Critical Assessment (ECA) procedure, which is a method to evaluate the integrity of various structures with embedded crack, surface crack and multiple cracks and so on. In BS7910, the acceptability of flaws in metallic structures is typically dealt with in terms of stress intensity factor solution. For the case with more than two flaws, BS7910 provides various flaw interaction rules. While such flaw interaction rules are developed based on many parametric studies, it is generally known to lead to very conservative results. In this study, the stress intensity factor solutions in a plate with multiple cracks are evaluated. Target structure is a simple plate subjected to tensile and bending loads, and a series of finite element analysis is carried out using ABAQUS. In addition, the results are validated against previous studies available in literatures. Based on the study, the distance criteria for multiple cracks in PD6493 and BS 7910 are found to be overly conservative. Therefore, a parametric investigation regarding the distance between multiple cracks is examined to reduce the overly conservative estimation in existing standards.
Reliability and Cost Estimation for Maintenance Planning of Oil and Gas Assets
Authors: Nithin Anu Hanish , Obisesan Abayomi , Sriramula Srinivas , Ebinum Terry 
Published: October 2021

Abstract
Safety and reliability of the assets in the Oil and Gas sector is considered critical to maximize availability and minimize downtime in production and operations. The industry, due to ageing assets, are re-visiting the maintenance planning of critical equipment through Reliability-Centered Maintenance (RCM). The RCM process comprises of the hierarchical structuring of technical objects according to their functional locations and further dividing them into their maintainable items and components. Generally, a criticality matrix is developed that would identify the highly critical assets based on criteria such as cost, production, safety, and environment. The Failure Modes and Effects Analysis (FMEA) is then performed for the identified functions, functional failures, and likely failure modes of each component of the asset. The failure modes can be identified from first principles and historical failure data from the asset owner or databases such as the Offshore Reliability Database (OREDA). The failure modes, mechanisms and causes are defined in accordance with International Standards such as ISO14224. The failure characteristics such as the hidden or evident nature of the failure modes, along with the occurrence of the failure within the bathtub curve, would help in deciding the right maintenance strategies such as condition-based, fixed-time, fault-finding intervals, run to failure or redesign. The maintenance tasks are then developed as a mitigation against each failure mode. Efficient and effective asset management strategies are achieved through the allocation of resources such as the labor, tools and materials required to execute the maintenance task. The maintenance tasks are grouped together based on the maintenance time intervals and the resulting maintenance plans are fed into the Computerized Maintenance Management System (CMMS) to manage the maintenance process and track the implementation of the maintenance tasks on site. The maintenance time intervals are allocated mainly based on the current industrial practices and may be qualitative in nature. This paper aims to quantitatively determine the right maintenance intervals by analyzing the historical failure data and determining the Mean Time Between Failures (MTBF) and Mean Time to Repair (MTTR). Cost and reliability analysis of the maintenance scenarios based on best industry practices and statistical analysis is determined. This helps with the decision-making process by improving the maintenance task intervals based on planned and unplanned maintenance downtime. A case study of an asset from the Oil and Gas sector is provided for demonstrating the proposed approach.
Seismic Design for Offshore Wind Farms – Lessons Learnt From the ACE Joint Industry Project
Authors: Klose Marcus , Wang Junkan , Ku Albert 
Published: October 2021

Abstract
In the past, most of the offshore wind farms have been installed in European countries. In contrast to offshore wind projects in European waters, it became clear that the impact from earthquakes is expected to be one of the major design drivers for the wind turbines and their support structures in other areas of the world. This topic is of high importance in offshore markets in the Asian Pacific region like China, Taiwan, Japan, Korea as well as parts of the United States. So far, seismic design for wind turbines is not described in large details in existing wind energy standards while local as well as international offshore oil & gas standards do not consider the specifics of modern wind turbines. In 2019, DNV GL started a Joint Industry Project (JIP) called “ACE -Alleviating Cyclone and Earthquake challenges for wind farms”. Based on the project results, a Recommended Practice (RP) for seismic design of wind turbines and their support structures will be developed. It will supplement existing standards like DNVGL-ST-0126, DNVGL-ST-0437 and the IEC 61400 series. This paper addresses the area of seismic load calculation and the details of combining earthquake impact with other environmental loads. Different options of analysis, particularly time-domain simulations with integrated models or submodelling techniques using superelements will be presented. Seismic ground motions using a uniform profile or depth-varying input profile are discussed. Finally, the seismic load design return period is addressed.
Iceberg Load Software Update Using 2019 Iceberg Profile Dataset
Authors: Stuckey Paul , Fuglem Mark , Younan Adel , Shayanfar Hamid , Huang Yujian , Liu Lei , King Tony 
Published: October 2021

Abstract
The Iceberg Loads Software (ILS) was developed initially to determine design iceberg loads for the Hebron Gravity Base Structure (GBS). The ILS framework has since been adapted for assessing iceberg loads on other structures such as the West White Rose Platform, subsea protection structures, pipelines laid on the seabed and floating production structures (spars and FPSOs). When the ILS was developed, the available iceberg geometry dataset (collected in the 1980s) was relatively limited, which required certain assumptions (i.e., flat wall interaction) and parametrizations (i.e., length distribution, length/draft/mass relationships, eccentricity, etc.) in the formulation of the interaction model. Renewed iceberg profile collection began in 2012, with ongoing improvements in the data collection methodology such that, of the 200 iceberg profiles collected from 2012 onwards, 134 were collected in 2019. The profile data were collected using LiDAR for the iceberg sail and multibeam sonar for the keel. The ILS has been updated using the recent three dimensional (3D) profiles, and a comparison of original versus updated iceberg load distributions for a generic structure show a decrease in loads. Updated ILS loads are compared with another iceberg load analysis tool that directly incorporates iceberg profile data rather than relying on some of the assumptions and parametrizations used in the original ILS formulation. This comparison shows some differences, particularly for extreme loads, which are the subject of on-going investigation.
Buckling Analysis of Torpedo’s Cylindrical Shell
Authors: Siva Sankara Rao Yemineni , Mallikarjuna Rao Kutchibotla , Subba Rao V. V. 
Published: October 2021

Abstract
Torpedo is a self-propelled weapon. It can be launched above or below the water surface. Torpedo’s different internal parts are housed in cylindrical, conical and spherical shell structures. Underwater applications require the minimization of the structural weight of shell structure for increased buckling strength, speed, and operating distance. To serve this purpose lightweight material such as Al-Cu alloy is preferred for the manufacturing of torpedo’s cylindrical shell. Here in the present investigation, unstiffened cylindrical shell structural member of the torpedo is considered for the evaluation of its linear buckling strength when the torpedo is subjected to hydro-static pressure under the sea water. Linear buckling analysis which is also called Eigen buckling analysis is done on unstiffened cylindrical shell geometry by using ANSYS R14.5 software. The values obtained for linear buckling strength from empirical equations mentioned in British Standards Institution, BS 5500 (now superseded by PD 5500) ‘Unfired Fusion Welded Pressure Vessels’ are validated with those results from ANSYS R14.5 and are observed to be closer to each other. The variation of the failure stress of an unstiffened cylindrical shell due to buckling for the variation of its thickness is also observed using both the empirical and simulation using ANSYS R14.5 approaches and are compared using the corresponding plots. And also, the critical buckling pressures of an unstiffened cylindrical shell with a constant thickness for the formation of different number of lobes for the simply supported boundary conditions are calculated by using empirical relations and this variation is observed using the corresponding plot. For these analyses numerical examples are considered.
Effects of Hull Geometry and Tightness of Turns on Ship Maneuverability: An OSIS-IHI Simulation
Authors: Lau Michael 
Published: October 2021

Abstract
OSIS-IHI (Ocean Structure Interaction Simulator – Ice-Hull Interaction) is a ship maneuvering in ice modeling software developed at OCRE for a marine simulator and ship performance assessment applications. A series of OSIS-IHI simulations is conducted to explain the maneuvering behavior observed of the USCGC Polar Icebreaker indicative design previously tested at the centre. The simulation is conducted with the original and a modified version of the USCGC Icebreaker Healy. The Icebreaker USCGC Healy was equipped with doublescrew conventional propellers. The hull geometry of the OSIS-Healy model is appropriately modified to mimic the hull form of two indicated design versions in question and its propulsion units replaced by twin pods prior to studying its maneuverability in order to shed light on the apparently poor maneuvering performance of the podded version of the indicative design. The modified version extends the mid-body leaving just 7.5 % of hull that constitutes the stern section. It is hypothesized that the extended mid-section cost large resisting moment against turning due to the increase of ice breaking at the aft shoulder and mid-body. This hypothesis is validated numerically to explain the poor maneuverability exhibited by the extended mid-body design, based on consideration of ice-hull interaction geometry and basic mechanics of ice breaking as well as existing anecdotal test evidences. This paper presents result of the simulation to explore effects of hull geometry and tightness of turns on ship maneuverability. Important insights gained are summarized and recommendation for further work given.