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Results
SCR Fatigue Mitigation Options for Life Extension
Wemimo, Oluwasegun (Shell Nigeria Exploration and Production Company, Lagos, Nigeria) | Osadebe, Olisaemeka (Shell Nigeria Exploration and Production Company, Lagos, Nigeria) | Amuda, Daniel (Shell Nigeria Exploration and Production Company, Lagos, Nigeria) | Bhat, Shankar (Shell Nigeria Exploration and Production Company, Lagos, Nigeria) | Ugbelase, John (Shell Nigeria Exploration and Production Company, Lagos, Nigeria)
Abstract Steel Catenary Risers (SCRs) are typically designed to meet requirement for the field life. However, with a possibility for an opportunity for life extension (LE), a remaining life reassessment (RLA) is necessary to be carried out to explore options to extend the life within the SCR integrity framework requirements. It is noted that replacing the whole or specific portion of length of the SCR is not considered as an economically and practically viable option. Several SCR fatigue damage reduction options have been explored for life extension considerations in the industry and the practicality of implementing them to specific field leads to only few choices due to the complexities involved in executing these options. The complexities arise in the execution as the fatigue damage reduction options will require careful re-assessment of floating system performance that includes floater motion, global riser behavior, and mooring system performance. This paper aims to present findings from the fatigue re-assessment as well as the thought process and needed considerations to selecting a mitigation option that is purpose-fit given the value drivers as well as constraints for a typical floater in West Africa deep-water. This is considering that within the West of Africa deep-water fields, this is the first time a practical approach is given to solve the fatigue life extension The fatigue reassessment incorporates as-occurred data parameters that affect global system performance of the SCRs. The fatigue mitigation options considered are repositioning of floater, use of buoyancy modules at midsections of the SCR, and increase in Vortex Induced Vibration (VIV) strakes coverage length. Each of these considered options are analyzed with pros and cons of each option, reviewed to arrive at a purpose fit option. This paper further gives practical insight to how oil and gas industry operators in the Gulf of Guinea region who are considering SCR life extension, can see to integrate methodological steps in seeking solutions to extending field life while maintaining asset integrity. It also highlights the impact of technology and digitalization on asset integrity management. This strategy provides affordability to create earnings from today's energy to fund the energy for future needs.
- Africa > Nigeria (0.29)
- Africa > West Africa (0.24)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Risers (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Floating production systems (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
Abstract DeepStar® is an operator-funded Research & Development joint industry consortium including members of the oil community such as oil & gas companies, vendors, regulators, and academic/research institutes working in multidisciplinary technology areas. The DeepStar Project has been in continuous operation since its inception in 1991 and has focused on issues and technologies required to successfully tackle future development and production challenges identified by its members. The focus of this manuscript and extension, the presentation, will be on the numerous projects that were the baseline for current industry standards. The DeepStar program is split into six technical areas of focus from subsurface and drilling to topside and autonomous operations and everything in between. The manuscript will be written focusing on those technical areas and the supporting projects in which final documents are used within the standards. The emphasis will be on three strategic areas of interest for our DeepStar members; first Integrity Management and the integration of our guidelines into the 1) API RP 2SIM Structural Integrity Management of Fixed Offshore Structures, 2) API RP 2RIM Integrity Management of Risers from Floating Production Systems and 3) API RP 2 MIM Mooring Integrity Management. The second topic is DeepStar work on AUV interface standards and the integration of our work into API RP 17H and into the SWIG JIP. The final topic highlighted within the session on Standards is DeepStar’ continuous work on Subsea Chemical Storage and Distribution Systems Subsea to which DeepStar has developed the business case, background requirements, field case studies, and funding commercialization development on this topic since 2010. This manuscript outlines DeepStar’ strategies, projects, and accomplishments through a collaborative effort amongst operators, engineering firms, manufactories, academic intuitions, and government regulators. Through this joint effort, members have been able to minimize the cost and risk of industry-wide engagement and technology development, while at the same time making the most of the organization's particular technology achievements. This aligns with DeepStar’ vision for the development of deepwater technology, which is closely tied to the development and qualification of advanced technologies and gaining acceptance within the oil & gas community. DeepStar has continuously confronted industry-wide issues and provided a forum for discussion and technology acceleration.
Committee I.2: Loads
Hermundstad, Ole Andreas (_) | Chai, Shuhong (_) | de Hauteclocque, Guillaume (_) | Dong, Sheng (_) | Fang, Chih-Chung (_) | Johannessen, Thomas B. (_) | Morooka, Celso (_) | Oka, Masayoshi (_) | Prpic-Oršic, Jasna (_) | Sacchet, Alessandro (_) | Sazidy, Mahmud (_) | Ugurlu, Bahadir (_) | Vettor, Roberto (_) | Wellens, Peter (_)
Committee Mandate Concern for the environmental and operational loads from waves, wind, current, ice, slamming, sloshing, green water, weight distribution and any other operational factors. Consideration shall be given to deterministic and statistical load predictions based on model experiments, full-scale measurements and theoretical methods. Uncertainties in load estimations shall be highlighted. The committee is encouraged to cooperate with the corresponding ITTC committee. Introduction The content of this committee's report is composed in accordance with its mandate by the expertise of its members. Compared to previous reports of the Loads committee the structure is slightly altered, while the topics covered remain basically the same, except that the present report covers ice loads more extensively, while giving less attention to hydroelasticity in waves. There is one section for each of the main types of loads acting on a ship or offshore structure. Hence, Section 2 focuses on wave loads, Section 3 on current and wind loads, while Section 4 concerns ice loads. Next, Section 5 is of a more generic character, concerned with characteristic loads and uncertainty. Finally, Section 6 is devoted to special topics, of which there was only one contribution, namely loads on free-fall lifeboats. Within each of the sections 2 – 5 there is generally one part focusing on ships and another part focusing on stationary offshore structures. On the lowest level we have distinguished between the different ways of assessing the loads, namely theoretical/numerical methods, laboratory tests and full-scale measurements, although this subdivision is not followed consistently through all sections. In the section on wave loads, a distinction is made between potential theory methods and field methods. The latter group contains numerical methods for solving the Navier-Stokes equations in some form, assessing the flow in the entire fluid field. Potential formulations normally use boundary element methods, although field methods can also be used with potential theory (e.g, Amini-Afshar et al. 2019). The committee has performed a benchmark study on heave/pitch motions and vertical bending moments for a large containership at zero speed in steep regular waves. Existing experimental results have been compared with numerical simulations performed by some of the committee members to investigate the performance of various numerical linear and nonlinear methods, ranging from strip theories to SPH and RANSE solvers. This study is presented in an appendix to the report. To avoid unnecessary overlap with other ISSC committees the focus has been on loads and rigid body responses. Structural dynamic responses, such as springing and whipping of ships, are left to the Dynamic Response Committee, but vortex-induced vibrations of slender structures and ice-induced vibrations are considered in the present report. Loads on offshore wind turbines (OWT) are covered to some extent, although the Offshore Renewable Energy Committee deals with OWT in general.
- North America > United States (1.00)
- Europe (1.00)
- Asia > China (0.67)
- Research Report > New Finding (1.00)
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- Overview > Innovation (0.92)
- Transportation > Marine (1.00)
- Energy > Renewable > Wind (1.00)
- Energy > Renewable > Ocean Energy (1.00)
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- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5504/12 > Tyra Field (0.99)
- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5504/11 > Tyra Field (0.99)
- North America > United States > Colorado > Ice Field (0.98)
Committee V.7: Structural Longevity
Lazakis, Iraklis (_) | Leira, Bernt (_) | Chen, Nianzhong (_) | Drumond, Geovana (_) | Lee, Chi-Fang (_) | Jurisic, Paul (_) | Liu, Bin (_) | Mondoro, Alysson (_) | Pahlavan, Pooria (_) | Shi, Xinghua (_) | Song, Ha Cheol (_) | Sugimura, Tadashi (_) | Jochum, Christian (_) | Coppola, Tommaso (_)
Committee Mandate Concern for the structural longevity of ship, offshore and other marine structures. This shall include diagnosis and prognosis of structural health, prevention of structural failures such as corrosion and fatigue, and structural rehabilitation. The focus shall be on methodologies translating monitoring data into operational and life-cycle management advice. The research and development in passive, latent and active systems including their sensors and actuators shall be addressed. Introduction 1.1 Background & Mandate The ISSC Committee V.7 on structural longevity of ship, offshore and other marine structures have been looking into all aspects related to the diagnosis and prognosis of structural health, prevention of structural failures such as corrosion and fatigue, while also considering the work performed on lifecycle management and maintenance aspects over the last 4 years. The latter refer to also incorporating approaches and techniques associated to the development of software and hardware tools for the inspection and monitoring of ship and offshore structures. In this Committee’s report, particular emphasis has been placed on the elaboration of the available studies and most recent developments with regards to inspection and monitoring and offshore structures longevity methods and applications, expanding on the previous Committee work (ISSC, 2018). Moreover, when delivering the mandate of this work, the authors have acknowledged that potential overlaps may occur with regards to Committee III.1 Ultimate Strength, Committee III.2 Fatigue and Fracture, Committee IV.2 Design methods and Committee V.4 Offshore Renewable Energy. In this respect, all efforts have been made in order to minimize the overlap of work while if any of such similarities exist, this is done in the spirit of complementarity supporting the structural longevity of ship, offshore and any other marine structures as presented in this Committee’s mandate. 1.2 Report content The present report consists of six chapters. Each chapter provides thorough critical examination of the available literature while useful conclusions and recommendations for future direction are provided at the end of the Committee report. In this respect, following an introductory chapter that provides an overview on the Committee’s mandate and brief summary of the report content, Chapter 2 investigates the lifecycle assessment and management for structural longevity approaches and tools, considering the particular areas of lifecycle assessment and maintenance management. Data-driven maintenance and relevant approaches such as digital twin applications, iFEM, and reliability-based research efforts are covered as well. In Chapter 3, the trends and developments in inspection and monitoring techniques to improve the structural longevity of ship and offshore structures are highlighted. These concepts are complemented by the examination of hull monitoring systems, remote and autonomous testing and sensors applications for structural monitoring; the employment of artificial intelligence (AI) applications and cloud-based data acquisition and management systems. Chapter 4 specifically considers the models and applications developed in relation to offshore structures updating the work performed in the previous ISSC committee report. The review looks into the aspects of deterioration mechanisms (corrosion, crack growth, erosion and wear), mechanical limit states, implementation of methods and procedures for safe operation and aspects of risk-based integrity management of offshore structures. Furthermore, Chapter 5 explores the available literature with regards to the ships and offshore structural longevity methods and examples. In particular covering the aspects of prediction of longevity, failure modes contributing to longevity assessment and also presenting a more detailed case of a polar supply and research vessel. Finally, Chapter 6 summarises the concluding remarks of the structural longevity report and offers a number of recommendations and directions for future research and applications related to ship, offshore and other marine structures.
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- Asia > Middle East > Saudi Arabia (0.28)
- Summary/Review (1.00)
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- Research Report > Experimental Study (0.92)
- Overview > Innovation (0.67)
- Transportation > Marine (1.00)
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
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- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- (9 more...)
Committee V.2: Experimental Methods
Ehlers, Soren (_) | Abdussamie, Nagi (_) | Branner, Kim (_) | Fu, ShiXiao (_) | Hoogeland, Martijn (_) | Kolari, Kari (_) | Lara, Paul (_) | Michailides, Constantine (_) | Murayama, Hideaki (_) | Rizzo, Cesare (_) | Seo, Jung Kwan (_) | Kaeding, Patrick (_)
Committee Mandate Concern for advances in structural model testing and full-scale experimentation and in-service monitoring and their role in the design, construction, inspection and maintenance of ship and offshore structures. This shall include new developments in: best practice and uncertainty analysis; experimental techniques; full field imaging and sensor systems; big data applications for ship and offshore structures; and correlation between model, full-scale and numerical datasets. Introduction Design methods and rule requirements have to be benchmarked with experimental or service history data. The Goal Based Standards (GBS) approach by IMO, see e.g., IMO Res. 296(87), 454(100) or MSC.1/Circ.1394, require benchmarking of standards by measuring the performance of methodologies, assessments, criteria and requirements by using indicators that can be compared with an accepted standard or with experimental and/or service history data, performance levels or outcomes known to be reliable. This approach calls for a systemic use of experimental results and monitoring of data from ships during construction, in-service and possibly from the end of the life cycle. Thus, the elaboration of experimental outcomes and the handover of information into engineering and management practice need to be further addressed and standardized to fully exploit their potential. Further, the continues growth of complexity in ship and offshore structures potentially designed outside the range of empirical references calls for reliable means of validation. While computer simulations are continuously improving at the same time, their improvement to a large extent depends on a physical understanding of the underlying phenomena to be captured. Therefore, experimental investigations are essential in driving further developments and innovations through their accurate feedback when performed correctly and meaningful. The latter is however challenging, especially with increased complexity of the phenomena to be investigated. Therefore, this report summarizes the expertise of the contributing authors with respect to their corresponding research fields. The report seeks to give a general overview of the specific experiments dealt with therein, presents the latest publications, possible obstacles to be addressed and closes with future recommendations for further developments and integration of the experiments into engineering practice and scientific developments. The report at first covers a section on scaling laws relevant to any experiment followed by specific testing concerning: digital image correlation (DIC), hydrodynamics of flexible structures, wave-in-deck, hybrid models, friction, vibrations, fatigue at low temperatures, corrosion, large scale impact, large scale wind turbine blades, full-scale ice loads, health monitoring and digital twin models. Further, a benchmark study on free vibrations of a cantilever beam is carried out to demonstrate the vast possibilities to carry out such seemingly simple experiment followed by a discussion of the results achieved. The report is concluded with a summary and an outline of further research and development recommendations.
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- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
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Design for preventing or minimizing the effects of accidents is termed accidental limit states (ALS) design and is characterized by preventing/minimizing loss of life, environmental damage, and loss of the structure. Collision, grounding, dropped objects, explosion, and fire are traditional accident categories.
- South America > Brazil (1.00)
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- (3 more...)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Sedimentary Geology > Depositional Environment (0.67)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.67)
- Transportation > Marine (1.00)
- Transportation > Infrastructure & Services (1.00)
- Transportation > Ground (1.00)
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- South America > Brazil > Campos Basin (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Viosca Knoll > Block 786 > Petronius Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Mississippi Canyon > Block 392 > Appomattox Field (0.99)
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Committee IV.1: Design Principles and Criteria
Collette, Matthew (_) | Caridis, Piero (_) | Georgiev, Petar (_) | Hørte, Torfinn (_) | Jeong, Han Koo (_) | Kurt, Rafet emek (_) | Ilnytskiy, Igor (_) | Okada, Tetsuo (_) | Randall, Charles (_) | Sekulski, Zbigniew (_) | Sidari, Matteo (_) | Zhan, Zhihu (_) | Zhu, Ling (_)
Committee Mandate Concern for the quantification of general sustainability criteria in economic, societal and environmental terms for marine structures and for the development of appropriate principles for rational life-cycle design using these criteria. Special attention should be given to the issue of Goal-Based Standards as concerns their objectives and requirements and plans for implementation. Possible differences with the safety requirements in existing standards developed for the offshore, maritime and other relevant industries and of the current regulatory framework for ship structures shall be considered. Role of reliability-based design codes and requirements as well as their calibration to established safety levels. Introduction Design principles and criteria form the framework for assessing marine structures against societal sustainability goals for economic, social, and environmental performance. Design principles and criteria seek to link the analytic tools and data sources discussed in other ISSC committees into a framework for practical evaluation, comparison, and decision-making for proposed marine structures. Similar to other committees, the work on principles and criteria is largely evolutionary. After a burst of development surrounding the introduction of goal-based standards and increased use of risk in the approval process in the 2003-2015 timeframe, recent developments in principles and criteria have occurred over a broader range of topics. For the current mandate period, the committee chose a report structure that extended on several themes from the 2018 report, as well as exploring some areas of our mandate that have not received significant attention recently. The committee report begins with an introduction to principles and criteria, followed by an extensive discussion of sustainability criteria, including the growing push to decarbonize the maritime industry. While further structural design improvements appear to have limited impact on decarbonization, understanding these developments is critical to planning future structural systems and accommodating potential green fuels which may impose their own unique material, structural, and risk assessments. Work on Goal Based Standards and international regulations has been largely evolutionary in the mandate period. To provide an overview of the activities at IMO and with class societies, we departed from past convention and structured the overview to mirror the other sections in our report. Three areas of continuity were selected from the 2018 report, based on rapid developments in these areas or a desire to extend beyond what the 2018 report was able to cover. The growing use of digital twin monitoring systems is reviewed, with a focus on systems for wave climate reconstruction. While direct integration of these systems into criteria is still in development, this field is moving quickly in this direction, and we felt it was essential to continue to chronicle its growth. Work on accidental limit states was also highlighted. Recent ISSC reports from both technical and specialist committees have highlighted technical developments in modelling such limit states. In this work, we have highlighted the extensions of these methods into practical criteria. The 2018 report explored the concept of human factors applied to the engineering process itself, instead of the operational phase. The 2018 chapter revealed that little work was ongoing in this area, but the feedback from the 2018 report suggested that a broader focus on human factors would be welcome, which is presented in our penultimate chapter. Finally, in reviewing the past IV.1 reports, it was clear that the portion of the mandate covering structural reliability has only received passing treatment for several cycles. In this cycle, the committee returned to a deeper focus on reliability, covering both recent developments in publication, along with example calculations. As digital twins and in-service monitoring proliferate, updatable reliability calculations may become more common, reliability approaches continue to be an important part of the principles and criteria landscape. Principles and criteria are inherently linked to both algorithmic formulations and computation tools. Thus, our report should be read in conjunction with several additional ISSC reports which cover fundamental developments in related fields. The work on digital twins is complemented by the work of specialist committee V.7 on Structural Longevity. The work on accidental loading is complemented by specialist committee V.1. Finally, owing to the tight coupling between design principles and design tools, the report of committee IV.2 also complements the work here.
- Asia (1.00)
- Europe > United Kingdom > Scotland (0.28)
- North America > United States > Texas (0.27)
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (1.00)
- Overview (1.00)
- Transportation > Marine (1.00)
- Transportation > Freight & Logistics Services > Shipping > Tanker (1.00)
- Transportation > Air (1.00)
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Management > Risk Management and Decision-Making > Risk, uncertainty, and risk assessment (1.00)
- Health, Safety, Environment & Sustainability > Sustainability/Social Responsibility > Sustainable development (1.00)
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"In offshore and coastal engineering, metocean refers to the syllabic abbreviation of meteorology and (physical) oceanography" (Wikipedia). Metocean research covers dynamics of the oceaninterface environments: the air-sea surface, atmospheric boundary layer, upper ocean, the sea bed within the wavelength proximity (~100 m for wind-generated waves), and coastal areas. Metocean disciplines broadly comprise maritime engineering, marine meteorology, wave forecast, operational oceanography, oceanic climate, sediment transport, coastal morphology, and specialised technological disciplines for in-situ and remote sensing observations. Metocean applications incorporate offshore, coastal and Arctic engineering; navigation, shipping and naval architecture; marine search and rescue; environmental instrumentation, among others. Often, both for design and operational purposes the ISSC community is interested in Metocean Extremes which include extreme conditions (such as extreme tropical or extra-tropical cyclones), extreme events (such as rogue waves) and extreme environments (such as Marginal Ice Zone, MIZ). Certain Metocean conditions appear extreme, depending on applications (e.g.
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- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Sedimentary Geology > Depositional Environment (0.67)
- Geophysics > Electromagnetic Surveying (0.65)
- Geophysics > Seismic Surveying > Seismic Modeling (0.45)
- Transportation > Passenger (1.00)
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- Transportation > Infrastructure & Services (1.00)
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- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5504/12 > Tyra Field (0.99)
- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5504/11 > Tyra Field (0.99)
- North America > United States > Colorado > Ice Field (0.98)
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- Well Drilling > Well Planning > Trajectory design (1.00)
- Well Drilling > Drillstring Design > Drill pipe selection (1.00)
- Well Drilling > Drilling Operations (1.00)
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Committee II.2: Dynamic Response
Storhaug, Gaute (_) | Paiva, Andre (_) | Dessi, Daniele (_) | Zhang, Guiyong (_) | Drummen, Ingo (_) | Moro, Lorenzo (_) | Holtmann, Michael (_) | Shyu, Rong-Juin (_) | Wang, Shan (_) | Dhavalikar, Sharad (_) | Wang, Sue (_) | Sævik, Svein (_) | Wu, WenWei (_) | Huh, Young-Cheol (_) | Yamada, Yasuhira (_)
Committee Mandate Concern for the dynamic response of ship and offshore structures as required for safety and serviceability assessments, including habitability. This should include steady state, transient and random responses. Attention shall be given to dynamic responses resulting from environmental, machinery and propeller excitation. Uncertainties should be highlighted in numerical analysis, modelling and measurements. Introduction Dynamic response refers to structural vibration or noise. The excitation sources can be environmental, mechanical, or accidental, which may result in structural damage or discomfort. The dynamic response is documented by measurements or numerical approach, and rules and standards may require mitigating actions. The group consist of 5 members from the academia and 10 from the industry. Their competence is mainly related to ships, which may result in a bias on offshore references. With a long history in ISSC, again ships and offshore structures are handled separately, but with a common chapter on monitoring and digitalization. The report is divided into topics depending on the excitation source, but with a separate subsection on noise, damping and mitigating actions and standards. This report includes references from fall 2017 with focus on new knowledge of industrial interest. Overlap with other committees is reduced: - VLFS – Very large floating structures are covered by (V.6) Ocean Space Utilization. - Structures for renewable energy are covered by (V.4) Offshore Renewable Energy. - Hydroelastic plastic response is covered by (III.1) Ultimate Strength. - Accidental loads are included, but plastic deformations are covered by (V.1) ALS - Monitoring and digitalization may have a different focus than from other committees. - The excitation sources are covered by (I.2) Loads. - Rules, standards, and guidelines may overlap in more general cases. - Standard applications frequently solved have low focus. Finally, a benchmark is done on structure borne noise comparing numerical calculations with full scale measurements of an accommodation. The degree of variation, error, and uncertainty in the estimates by different methods and organizations are revealed.
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- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Risers (1.00)
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Time Domain Dynamic Response of Coupled Platform-Mooring-Riser System Under Mooring Failure
Yu, Yang (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University) | Zhao, Mingren (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University) | Yu, Jianxing (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University) | Liu, Cheng (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University) | Li, Zhenmian (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin Key Laboratory of Port and Ocean Engineering, Tianjin University)
ABSTRACT This paper has investigated the effect of mooring failure on the global performance of a typical offshore structure under regular surface wave. A self-developed time domain program has been set up to capture the transient response of the system when one or several mooring lines are simultaneously disconnected from fairlead. The results indicate that the whole response could be divided into healthy stage, transient stage and steady stage accordingly. The low frequency of platform is almost decreased with increasing number of broken cables due to the reduced stiffness. The remaining mooring lines on the up-wave side and close to the broken position would exhibit profoundly increasing tension range. The riser tension is less affected by mooring failure due to its vertical configuration and low tension level compared to mooring tension. INTRODUCTION A typical floating offshore system usually concerns three subsystems: the top platform, the mooring system and riser system. They influence each other and respond to environmental loading in a complex way. The positioning mooring lines are likely to be broken when subject to harsh conditions in deeper water, which could result in the instability of production system or even offshore accident. Therefore, an accurate description of the system dynamics under the failure of mooring lines could be a challenging but essential problem. A majority of researchers have demonstrated the theory of the coupled floating system and conducted its performance under broken moorings / risers. Veritas (2010) introduced 2 methods for the dynamics of coupled system: fully coupled analysis, that is the mass/damping/stiffness matrixes of riser and platform are assembled together to realize an overall solution, and efficient analysis, which means that the forces and moments induced by the moorings or risers will act on the platform. Meanwhile, the motions of upper nodes from these slender structures will keep consistent with those of connection points on the platform hull. Liu, et al (2016) combined the ABAQUS modular for riser and self-developed FORTRAN modular for drilling platform and exchanged data with each other to consider the coupled effect. Caire (2012) employed the coupled analysis based on SESAM and compared the results between the coupled and de-coupled method. Hao, et al. (2020) mainly studied the hydraulic pneumatic tensioner in TLP-TTR system under its local failure based on AQWA. Cheng, et al. (2021) conducted the detailed response of TLP, i.e., time series, spectral analysis, phase diagrams and tendon stiffness, under the condition of tendon broken. Chuang, et al. (2020; 2021) investigated the mooring disconnection in the SEMI-mooring-riser system, aiming at the response of platform, tension of remaining lines and risk of riser clashing. More broadly, Bae, et al. (2017) carried out a complex simulation of floating wind turbine with broken mooring line considering the aerohydro-mooring coupled effect in the accident.