bluuebunny/crossref_metadata_2025 huggingface dataset:
MCMC Based Probabilistic Wave Spectrum Estimation Using Onboard Measurement Data
Authors: Park Myong-Jin , Kim Yooil
Published: October 2022

Probabilistic wave model is not only more suitable to describe uncertainties affecting structural reliability than deterministic wave model but also used to calculate probabilistic motion and structural response, which are able to facilitate the evaluation of structural reliability. In this regards, efforts have been made in this research to estimate the probabilistic wave spectrum using onboard measurement data. Firstly, Markov chain Monte Carlo simulation, which archives sampling from arbitrary probability density function of wave parameter as a random variable, was adopted as a probabilistic optimization method. Prior distribution and constraints of wave parameter were defined according to design wave model and previous wave observations. Previous wave observations consist of full-scale measurements obtained from 14,000 TEU container ship and MetOcean data of actual sea. Secondly, Numerical case study was performed for checking the validity of the proposed method. Data based on numerical simulations were generated by combining assumed wave spectrum and response amplitude operator, with some noise added. Finally, the proposed method was applied to full-scale measurements gathered from 14,000 TEU container ship, then, the calculated wave spectrum, motion and structural response were compared with full-scale measurements.
ISM-Based Study on the Constraints of Yangtze River Mainline Fleet Transportation Development in the Context of Green Intelligence
Authors: Yang Yinhua , Jin Yan
Published: October 2022

To explore the applicability of the explanatory structure model in the analysis of the water transportation system, the study of fleet development constraints of the Yangtze River mainline is studied as an example. Based on defining the fleet transportation system boundary and summarizing each influencing factor, the standard ISM deconstruction method is used to obtain the hierarchical relationship among the influencing factors. The structural hierarchical relationship of the constraints to the development of fleet transportation on the Yangtze River mainline is analyzed, and the root factors that restrict its development are found to be: fleet size and new logistics pattern. The results show that the explanatory structure model can better analyze the hierarchical relationship between the factors of the water transportation system. Based on this, and in the context of the current major strategic decision of “carbon peak, carbon-neutral”, the paper finally proposes a new fleet transportation mode combining single vessel and fleet characteristics as a solution to the root causes, which can be an efficient and green transportation option for the Yangtze River mainline cargo transportation market.
Numerical Simulation of a Subsea Pipeline Subjected to Near-Field Underwater Explosion Loads With the Coupled Eulerian-Lagrangian (CEL) Method
Authors: Liu Zhenhui , Igland Ragnar
Published: October 2022

An underwater unexploded ordnance (UXO) for example a mine filled with trinitrotoluene (also known as TNT), may present a potential threat to subsea structures. An explosion is a complicated physical phenomenon as it involves the interactions among water, seabed, the structure, and the explosive ordnance. The relevance of the paper is the need for removal of a large number of UXO on the Norwegian continental shelf during the installation of subsea pipelines. Numerical simulations have been used to calculate the effect of an explosion, but normally with an assumption of free explosion space. The seabed effects are simply considered by exaggerating the explosive weight with an empirical factor. This paper tries to include the real seabed effects in a near-field explosion underwater explosion events by using the Coupled Eulerian-Lagrangian (CEL) method. The effect of water, soil and the TNT are approached by using the Eulerian formulation with specified Equation of status (EOS). The Us-Up’s form of Mie-Gruneisen equation is used for the water and soil. The soil’s strength is described by linear Drucker-Prager yielding function. The Jones-Wilkins-Lee (JWL) equation of state is used for TNT. The steel is approached by shell elements in a Lagrangian scheme. The strain rate effects have been considered through the Cowper and Symonds equation. The coupling between Eulerian and Lagrangian formulation is done by the general contact features provided by Abaqus Explicit solver. The simulation results are discussed in details with respect to the water, soil and pipeline deformations respectively. Additionally, the axial force is also discussed. It is shown that the seabed plays an important role during the explosion and the empirical factor used to exaggerate the TNT mass is over-conservative. In the near-field explosion, the existence of soil may be beneficial to the pipeline’s damage. Global effects may be also triggered due to the large axial force generated during the explosion.
Safety Evaluation Technique of Annular Pressure in Offshore High-Temperature High-Pressure Gas Wells
Authors: Li Yanjun , Liu Shujie , Gao Deli , Zhang Zhi , Long Yang
Published: October 2022

The high-temperature high-pressure (HTHP) nature gas reserves in the South China Sea are 15 trillion cubic meters, accounting for approximately one-third of the total oil and gas resources in the South China Sea. There are many leak risk points of the HTHP wellbore, so it is very difficult to guarantee the wellbore integrity, and the annular pressure seriously threatens the test and construction security. Based on the safety assessment technology study of the annular pressure offshore HTHP gas fields, this paper designed the whole-life-cycle annular pressure management model and operation measures, developed the risk assessment technology of wellbore integrity, compiled the annular pressure diagnosis model, developed the calculation software of annular pressure critical control value, etc. And then, the critical control value of wellbore pressure can be calculated much more quickly and accurately for different production time, which could better manage the wellbore pressure risk and ensure the wellbore integrity. The safety assessment technology study result in the paper has been applied successfully in Yingqiong (YQ) Basin and achieved “zero” annular pressure during the on-site drilling, completion, and production operations.
Assessment of Situation Awareness for Seafarers Using Eye-Tracking Data
Authors: Virdi S. S. , Ng Yong Thiang , Liu Yisi , Tan Kelvin , Zhang Daniel
Published: October 2022

Situation Awareness (SA) is the perception of the current situation, comprehension of its meaning, and projection of what is going to happen in the near future. It is crucial for navigators to possess high SA in a navigational Bridge to mitigate the risk of human errors and to improve navigational safety. However, the current methodology to assess SA mainly rely on human experts, which might bring in potential problems such as bias, work overload, and it is also hard for the human experts to capture every fine detail of the behaviour of the seafarers being assessed. To overcome these, an objective and automated way to assess Situation Awareness is needed. In this work, eye-tracking data is used for the assessment of SA. With the eye tracking device, it is possible to localize where the navigator is looking at, and by applying computer vision with deep learning algorithm, the ongoing activity being executed by the navigator could be identified. In total 7 activities (using RADAR, ECDIS, checking of ship’s heading, and speed, checking data on Echo Sounder, and data related to ships maneuvering, and others) can be recognized which are used as indicators of SA. A set of training data was recorded using Tobii Pro Glasses 3 to train the deep learning algorithm and test the classification accuracy. To further verify the proposed eye-tracking based assessment, a preliminary experiment has been designed and carried out. Five subjects were recruited for data collection. A full-mission Advanced Navigation Research Simulator (ANRS) was used to provide scenarios for both training data collection and preliminary experiment. From the initial results, it shows that a recognition accuracy of > 99% can be achieved, which gives positive support to the eye-tracking based recognition. The analytics results using data from preliminary experiment also show great potential in using eye-tracking to assess SA of navigators. The proposed assessment could be used in both simulator and on-board and for multiple purposes such as performance evaluation, promotion to the next rank, and Continuing Professional Development.
Influence of Gap Width and Artificial Damping on Gap Resonance
Authors: Ekerhovd Ivan , Ong Muk Chen , Zhao Wenhua
Published: October 2022

Side-by-side offloading between two vessels in offshore operations, creates a narrow gap where blistering free surface motions may be excited due to resonant responses. The present study investigates what influence gap width and artificial damping has on these motions. We run a series of numerical simulations, based on a 3D linear potential flow solver using a numerically validated model from our previous work. The model is meant to simulate a floating liquefied natural gas (FLNG) facility, an LNG carrier, and the narrow gap created between them. In this study, the resonant fluid motions in the gap are investigated based on a configuration where both vessels are fixed. The results show a significant impact on the response of the gap resonance with diverse gap widths. By applying artificial damping to the free surface, we found that there is no significant effect on the resonant motions of the gap surface after the gap width reaches a significant fraction of one ship breadth.
Scenario-Based Risk Management for Arctic Waters
Authors: Bergström Martin , Browne Thomas , Ehlers Sören , Helle Inari , Herrnring Hauke , Khan Faisal , Kubiczek Jan , Kujala Pentti , Kõrgesaar Mihkel , Leira Bernt Johan , Parviainen Tuuli , Polojärvi Arttu , Suominen Mikko , Taylor Rocky , Tuhkuri Jukka , Vanhatalo Jarno , Veitch Brian
Published: October 2022

Arctic shipping is growing driven by a demand for natural resources, climate change, and technological development, among other factors. While this provides many benefits for society, it also entails risks for people, the environment, and property. The purpose of this article is to assist ship designers, operators, owners, and other stakeholders in managing those risks by defining a comprehensive approach to scenario-based risk management for Arctic waters. The approach covers both the management of short-term operational risks, as well as of risks related to a ship’s long-term extreme (design) ice loads and structural response. For operational risk management, a further developed version of the established Polar Operational Limitations Assessment Risk Indexing System (POLARIS) method is defined. In contrast to the established method, the further developed version considers the consequences of potential accidental events. For managing risks related to a ship’s long-term extreme ice loads and structural response, guidelines are provided for the application of existing methods of assessing ice loads, including analytical, numerical, and semi-empirical methods. In addition, to support the design of ice class ship structures, a new approach based on closed-form expressions is defined that can be used in the conceptual design phase to determine preliminary scantlings of primary hull structural members (e.g., transverse web frames).
Calculation of Thrust and Torque of a Tandem Propeller Using a Combined Vortex Lattice Lifting Line Method
Authors: Büsken Andreas , Krüger Stefan
Published: October 2022

This paper describes two procedures for the calculation of thrust and torque coefficients of a tandem propeller. Both procedures are based on a Combined Method, which consists of a Vortex Lattice calculation combined with an extended Goldstein approach. The first procedure performs individual calculations for the two propellers. To account for the interaction of the two propellers the consecutive calculations are linked. Since the linked procedure includes some simplifications it can be used only for calculations in homogeneous inflow. To perform calculations in inhomogeneous inflow or account for additional effects the second procedure is implemented, which carries out the combined calculation for the whole tandem propeller. This allows the direct calculation of the propellers’ influence on each other. The results of the two procedures are compared to measured data from open water tests.
Investigating Hull Blockage and Thruster-Hull Effects on an ASD Tug
Authors: Yiew Lucas J. , Taskar Bhushan , Zheng Yingying , Magee Allan R.
Published: October 2022

Interactions between a vessel’s hull and its propulsor are important design and engineering considerations. For vessels equipped with azimuthing propulsors, these interactions are compounded due to the ability of propulsors to direct thrust over a wider arc, even into its own hull. In this study, we examine the interactions between a pair of thrusters and the hull of an azimuthing stern drive (ASD) tug. Specifically, we analyse thruster-on-hull effects, which can materialise as increases in hull drag when flow around the hull is altered by a thruster, or when thrust is vectored towards the hull and impeded by hull surfaces. A series of captive model tests were conducted to evaluate these effects using static and dynamic planar motion mechanism (PMM) tests, in both bare hull and appended hull configurations. Results from this study identify the conditions contributing to thruster-on-hull interactions, and provide further insights into physical mechanisms affecting thruster and hull performances in different flow regimes.
Numerical Evaluation of the Thermal Performance of Modern Offshore Wind Farm Cables Installed in J-Tubes
Authors: Delizisis Panagiotis , Kokkinos Charilaos , Chatzipetros Dimitrios , Pettas Dionisis , Chrysochos Andreas I. , Loukas Konstantinos
Published: October 2022

The submarine cables used to interconnect Offshore Wind-Farms (OWFs) with the mainland typically pass through large, metallic risers having a J-shape when approaching the Wind Turbine Generators (WTGs). These so-called “J-Tubes” consist of three main parts: water, air and platform sections. The air-section is typically sealed at both ends for practical reasons: its bottom is bounded by the water surface, while the top end by means of the armor hang-off cap. Hence, the cable may experience adverse thermal conditions within this enclosed section and the latter is likely to be the thermal bottleneck of the entire subsea route. Unfortunately, no Standardized method currently exists to calculate the current rating of cables installed in J-Tubes. This paper evaluates the applicability of the semi-empirical formulae existing in literature given the modern export cable and J-Tube designs presently used, which in many cases can give Ra numbers substantially higher than 2.3 · 106. Computational Fluid Dynamics (CFD) coupled with heat transfer analysis is employed for this purpose, while simpler heat transfer models applying the existing analytical methods are also used for comparison purposes. Furthermore, the cable is represented in a more realistic way and the convective heat transfer in the filler interior is also considered. As demonstrated in the paper, the use of analytical methods gives relatively good results for lower Ra numbers compared to the more realistic numerical models developed. However, the analytical methods may lead to very optimistic conductor temperature values when Ra becomes higher than 2.3 · 106, thus making their use rather questionable for larger J-tubes.
Proposal for Cyclic Riser Load Methodology Using High-Resolution Current Data
Authors: Moldestad Lasse , Reinås Lorents , Sætre Stian , Johnsen Øistein
Published: October 2022

Both in riser design and life extension exercises, analytical models are used to determine loads and load effects. For cyclic load assessments it is known that applied current load is an important modelling factor. In guidelines and codes for riser systems, such as DNV-RP-E104 and DNV-RP-F204, the prescribed methodology for including current in the analytical models is usually limited to scenarios with limited available statistical current data. This typically has the effect that the intended approach becomes to implement current conservatively in the analytical models, commonly applying a low current velocity. This paper presents results and findings from case studies of top tension marine drilling risers in shallow water, analyzed using 2D wave energy spectra with alternative approaches for current: high-resolution current velocity and direction data approach, and typical current loading approaches based on DNV-RP-E104. The different approaches are further investigated and supplemented by parameter sensitivity assessments. Based on the above, a methodology is proposed on how to implement current loading for cyclic load analysis when high-resolution current data is available, and the potential benefit of the improved prediction is shown. The motivation behind the proposed methodology is to provide an improved cyclic load prediction method for scenarios where high-resolution current data is available. This may be of particular interest for life extension exercises where historic cyclic riser loads can be reassessed based on historical environment and operational data.
State of the Art in New Semisubmersible Platform Concepts
Authors: Wang Tianying , Cui Qing
Published: October 2022

The semisubmersible platform (Semi) shows superior performance to the Spar, TLP and FPSO owing to its unique and reasonable structure and shape, and thus is one of the most vital and promising equipment for deepsea oil and gas development. Nevertheless, its inherent disadvantages have been gradually revealed through six decades of extensive engineering practices and in-depth research. Much innovative work has been carried out during recent two decades to improve its overall performance and maximize its safety and operability to utilize it in supervisor ways. Firstly, the shape features of a conventional Semi and the operation requirements in different phases during the whole life cycle of a Semi were summarized. Then, the factors affecting the stability and the motion performance of a Semi and their internal relationship were studied according to the principles of hydrostatics and hydrodynamics. After that, representative innovative conceptual Semi designs in the academic papers and the patent documents were reviewed. Finally, the directions for further innovation and growth of the Semi were predicted. This paper aims to provide some inspiration and reference to the experts and scholars engaged in deepwater offshore field development and innovative research on the floating structures.
Aspects of Collision Response of Long-Span Floating Bridges
Authors: Storheim Martin , Dørum Cato
Published: October 2022

Ship collisions are a notable hazard for any bridge spanning a water way. Globally, one sees an increase in the number of planned floating bridges. These long-span floating bridges have unique aspects when exposed to ship collision events due to their size, flexibility, mooring configuration and hydrodynamic effects. A large analysis scope was performed during the Ferry-free E39-project for the Bjørnafjorden crossing in Norway, of which key findings are discussed in this paper. Aspects of analysis methodology and the connection between lateral flexibility and hydrodynamic damping are discussed, as well as residual strength considerations for the bridge in damaged condition.
A Risk-Based Approach to Determine Mobile Offshore Drilling Unit Disconnect Criteria
Authors: Garlid Stian , Hørte Torfinn , Reinås Lorents
Published: October 2022

This paper investigated the feasibility of using structural reliability analysis (SRA) methodology to determine a mobile offshore drilling unit risk-based disconnect criteria. A notational harsh environment shallow water mobile offshore drilling unit (MODU) drilling operation case study has modelled weather conditions that result in significant nonlinear dynamic response. From this case study we have found the use of SRA methodology for establishing risk-based operation specific operating criteria feasible. We advocate operational criteria with a quantified probability of exceedance to be useful to decision makers seeking risk-based operations criteria. For this reason, this paper proposes a generic approach for using SRA intended for a range of marine operations specific operating criteria, e.g., MODU connected to a subsea well or vessel to vessel transfer.
Oil and Gas Technologies as Key Elements for a Viable Deep Sea Mining Industry
Authors: Tjåland Egil , Ellefmo Steinar Løve , Aasly Kurt , Gjersvik Tor Berge , Fichler Christine
Published: October 2022

Deep-marine mineral deposits, including polymetallic nodules, seafloor massive sulfides, and cobalt rich manganese crusts, are known down to 6000 meters water depths. Challenges of such extreme water depths, long distances from supply bases and the need for cost-effective technical solutions, share many similarities with challenges in the oil and gas industry. As in the case of oil and gas, the resource estimation of mineral resources depends to a large extent on geophysical measurements, including seismic and electro-magnetic measurements. Production of deep-marine mineral deposits can draw on experiences from oil and gas production from ultradeep water depths, and transportation of ore from the sea bottom can use riser technology employed in oil and gas projects. Floating Production Storage and Offloading vessels used by the oil and gas industry can be utilized to store ore from seabed mining before transport to onshore mineral processing facilities or, less likely, for mineral processing on the seabed, or onboard the Floating Production Storage and Offloading vessel. However, the large sea depths and the high investments needed to achieve a minimal ecological footprint, will need many innovations and new solutions. Such challenges are similar to what the oil and gas industry has developed for oil and gas exploration and production in deep water. Here we show how technologies from the oil and gas industry can be applied for deep sea mineral extraction.
Fatigue Assessment of Pump Tower in LNG Membrane Tanks
Authors: Storhaug Gaute , Sun Hui , Zang Yuelong , Rognebakke Olav
Published: October 2022

Membrane tanks are used for marine transport and storage of LNG, while LNG fuel tanks is an emerging application. LNG carriers operate with almost full or almost empty membrane tanks, while storage tanks on FSRUs and fuel tanks experience all filling levels. Partly filling may give rise to increased sloshing responses on the pump tower structure inside.

DNV has published rules for alternative survey arrangement for FSRU/FSUs, which opens for longer tank inspection intervals. This alternative survey arrangement can be applied provided that the damage risk is less or equivalent to regular tank inspections intervals as an LNG carrier. The challenge is how to assess this equivalence. A definition of the reference vessel and trade is required.

This paper addresses a new proposed methodology to quantify the relative pump tower fatigue. It is built up of several steps that will be explained including hydrodynamics, satellite tracking, CFD, load combination, fatigue analysis and visualization. This is first done for a representative LNG ship and trade. The methodology is then applied for an FSRU. Combinations of filling levels relevant for the FSRU and artificial wave environments are studied to quantify when the resulting fatigue may exceed the LNG carrier reference case. Uncertainties and challenges are discussed.
Experimental and Numerical Investigation on the Dynamic Response of Platform for a Spar-Type Floating Wind Turbine Under Aerodynamic and Hydrodynamic Forces
Authors: Wang Baoxuan , Liang Xu , Jiang Xue
Published: October 2022

Developing floating offshore wind turbines (FOWTs) operating in the deep sea is crucial for reducing carbon emissions and exploiting marine renewable energy. Compared with a fixed-bottom wind turbine, the FOWT with a moving floating platform faces more complex external environment and challenging operating conditions. Its 6-DOF motions with long periods and significant amplitudes will, in turn, affect the dynamic response and performance of FOWT. Therefore, it is necessary to take a deep insight into the dynamic response of floating platforms for FOWTs under aerodynamic and hydrodynamic forces. In this regard, the present study carried out a series of tank tests based on a scaled spar-type FOWT, employing AI-based software-in-the-loop hybrid testing method. Tests were performed in wave-only cases, wind-only cases and combined wind-wave cases to investigate the effect of wave frequency and wind speed on platform motions. Corresponding simulations were also conducted to compare with the test results. In this study, attention was focused on the law reflected by test results and evaluating the applicability and validity of the employed hybrid testing approach. Results show that the natural frequency of yaw can be affected by constant thrust force generated by fan. Wind speed rather than regular wave frequencies have a significant impact on the mean value of platform motions. The amplitude and standard deviation of motions are simultaneously controlled by wind speed and wave frequency. The spectral peak frequencies of surge, sway and yaw are wind-speed dependent in wind-only cases. With the increase of wave frequency, the spectral peak frequencies of 6-DOF motions gradually change from wave frequency into their own natural frequencies. Moreover, numerical calculations generally coincide with the testing results. This work attempts to provide reference and guide for understanding the dynamic response of FOWTs and develop a more reliable hybrid scaled testing method.
Short-Term Forecasting of Surface Wave Elevation Based On an Autoregressive Model
Authors: Chen Jialun , Zhao Wenhua , Milne Ian , Draper Scott
Published: October 2022

Predicting ocean wave elevations on a wave-by-wave basis has been gaining increased attention recently. It has the potential to improve the efficiency and safety of a wide range of offshore operations, such as crane lifts and control of wave energy converters. This study investigates the use of a data-driven technique, specifically the autoregressive model, to predict surface wave elevation in the ocean based only on past measurements at a specific location. The confidence interval of the prediction is provided to quantify uncertainty. The influence of bandwidth on prediction and the cut-off frequency, which is a compromise between improvement in the prediction accuracy and the quantity of discarded wave components is also explored. In this study, the data are digitally filtered into low- and high-pass components. The prediction demonstrates significant improvement in accuracy and prediction horizon compared to the original unfiltered prediction results.
On Design Parameters for Accidental Ice Loading on Ship Hulls
Authors: Leira Bernt J. , Chai Wei , Radhakrishnan Gowtham
Published: October 2022

Ice ridges and icebergs generally pose a major threat to both ships and offshore facilities that operate in Polar regions. In many cases these features will govern the structural design loads. It is not practical or feasible to design a ship to withstand any possible ice impact load without damage, so following the principles of risk-based design, the tolerable consequences of an impact should be determined also considering the associated probability of occurrence. The following limit state design criteria are usually applied in structural design: (i) Serviceability Limit States (ii) Ultimate Limit States (ULS) (iii)Fatigue Limit States (FLS) (iv)Abnormal/Accidental Limit States (ALS). The ALS corresponds to impact events with a very low probability to occur, and its intention is to ensure that a ship hull structure does not suffer from a complete loss of integrity.

It is natural to consider methods that can serve to reduce the number of relevant load cases to be analysed, and to identify the most likely combinations of the relevant design parameters. Accordingly, the so-called environmental contour method becomes of significant interest. Utilization of this approach is illustrated in connection with the ULS and ALS in the present paper.
Propulsive Performance of Morphing and Heaving Foil
Authors: Dev Singh Pragalbh , Neogi Ishan , Niral Shah Vardhan , Joshi Vaibhav
Published: October 2022

Biological locomotion, observed in the flexible wings of birds and insects, bodies and fins of aquatic mammals and fishes, consists of their ability to morph the wings/fins. The morphing capability holds significance in the ability of fishes to swim upstream without spending too much energy and that of birds to glide for extended periods of time. Simplifying the wing or fins to a foil, morphing refers to the ability of the foil to change its camber smoothly, without sharp bends on the foil surface. This allows precise control over flow separation and vortex shedding. Compared to conventional trailing-edge extensions or flaps, used in rudders and elevators in submarines and ships, morphing foils provide better control of thrust and lift characteristics. This study aims at understanding the importance of the morphing of foil combined with a sinusoidal heaving motion on thrust generation. A two-dimensional variational stabilized Petrov-Galerkin moving mesh framework is utilized for modelling the incompressible low Reynolds number flow across the flapping foil. The morphing motion is characterized by the extent of morphing, measured as an angle of deviation from the initial camber, and the point of initiation of morphing on the foil as a percentage of its chord length. The effect of the foil morphing and the heaving motion on the propulsive performance are investigated. The extent of morphing is varied from −30° and 30°, and the point of initiation ranges from 15% to 50% of the chord. The Reynolds and Strouhal numbers for the study are 1100 and 0.2, respectively. The results from the current work can pave the way for enhanced engineering designs in bio-mimetics and give insights on design conditions for optimal thrust performance.
Sensor Data for Maintenance Planning of Topside Piping
Authors: Horn Agnes Marie , Wiggen Frode , Gustafsson Sandra
Published: October 2022

The wish to better know the condition of equipment and thus be able to plan and perform maintenance before a critical failure occurs has existed for many years. Early leak detection of liquid and gas from topside process piping is a critical task for economical and safety reasons. For an operator, there is a need to accurately detect, and localize leaks to timely recover them cost-effectively, or the most viable solution to be able to prevent leaks to happen. The latter named prognostic maintenance, condition-based maintenance or predictive maintenance represents a well-known method where the goal is to ensure preventive measures are taken in due time where leak may happen in a piping system.

There is a rapid development in sensor technologies, algorithm development, data storage systems, data transfer, data processing and computing power. The robustness and reliability of electronic components is constantly improving while the cost is decreasing. To ‘unhide’ hidden failures through condition knowledge and thus reduce inspection and unnecessary repairs and testing efforts on critical (e.g. safety) equipment is a compelling need for the Energy sector today. Digitalization is currently boosting this technology both within model-based prognostics, data-driven prognostics, and hybrid solutions. To make use of this development, classical understanding of fatigue, corrosion and moisture penetration on piping systems must be combined with several IT-related disciplines. The paper will discuss the latest state-of-the art related to sensor monitoring systems with the aim to provide sound recommendations related to fatigue, corrosion and moisture penetration on piping system for topside process piping.
On the Quality of Laboratory Water Waves Generated Mechanically by Flap Wavemakers
Authors: Fouques Sébastien , Akselsen Andreas , Harris Trevor , Brett Kent
Published: October 2022

In laboratories such as ocean basins, surface waves are generated mechanically by imposing an oscillatory motion on one or several vertical boundaries. The shape and characteristics of the wavemaker have a direct impact on the wave heights and periods that can be generated, but also on the quality of the waves obtained in the basin. Here, quality is defined in terms of spurious waves generation, meaning it is directly related to the predictability of the wave field in the basin. Additional factors affecting wave quality can be either mechanical, like the precision of the imposed flap motion, or hydrodynamic, like the amplitude of the flap angle.

In this paper, we investigate the quality of waves generated mechanically by several types of flap-wavemakers, including double-hinged and single-hinged ones, with various hinge depths. The amplitude of second-order spurious waves is evaluated analytically and compared to laboratory experiments carried out in SINTEF’s ocean basin. Third-order effects that results from using a second-order correction of the flap motion are also addressed. Then, the ability of deep-hinged wavemakers to generate short waves, either steep or with small amplitudes, is assessed based on measurements performed at NRC’s towing tank facility. Finally, recommendations on choosing a wavemaker design are proposed.
General Review and Analysis of Research in CEARCTIC and CEPOLAR Projects
Authors: Lu Liangliang , Kuikka Sakari , Kujala Pentti
Published: October 2022

With the climate change and the decreasing of Arctic sea ice, Arctic shipping receives increasing attentions from both the industries and academia due to a large amount of uncertainties involved. CEARCTIC (Centre of Excellence for Arctic Shipping and Operations) and CEPOLAR (Centre of Excellence for Scenario-based Risk Management in Polar Waters) projects are therefore established and worked continuously from year 2013 to 2022, focusing on various fields regarding safe Arctic shipping. Extensive research work has been carried out in CEARCTIC and CEPOLAR framework during the multi-year projects towards safe Arctic shipping. The outcomes are mainly published in scientific journal and conference papers, where various subjects, research directions and methods have been focused and applied. Therefore, it is vital to review the research to better understand the status and overall research of Arctic shipping. This paper aims to review and analyze the research papers published in the framework of the projects, from the viewpoint of research topics, research methods, practical purposes, and risk governance so that a general picture of research on the Arctic shipping can be seen from these perspectives. Based on review and analysis, potential gaps and clues for future research directions towards the Arctic shipping can also be identified.
Towards a Market and Industrially Driven Green Transition of the Norwegian Oil and Gas Industry
Authors: Skorpa Ragnhild , Sørum Lars , Ytrehus Jan David
Published: October 2022

On a world basis, the Norwegian oil and gas industry accounted for 2.5% of the global production in 2020, and even though the CO2 equivalent per unit barrel produced is among the lowest in the world, over 25% of the domestic emissions (scope 1 emissions) in Norway are related to offshore oil and gas production. The oil and gas industry are now undergoing a green transition with high emission reduction ambitions. The aims are a 50% emission reduction by 2030, and towards zero for 2050. With this they are transitioning from exclusive traditional oil and gas to energy supply with a broader portfolio. This includes integrating renewables such as wind, solar and electrification, both research- and operational wise, and optimize production of oil and gas.

Important aspects for acceleration of the green shift in general, will be the ability to develop, adopt and implement new and sustainable technology fast. Specifically, the emission reductions in oil and gas production will be achieved through integrating renewables, system integration, enhanced energy efficiency, novel technologies and general improvements through competence optimalization, digitalization etc. These initiatives are strengthened through earmarking of funding from remedies, to accelerate transition to a sustainable oil and gas industry.

This paper describes and discusses how Norwegian R&D support and efforts represents important parts of the ongoing green transition of the oil and gas industry in Norway.
Input-Unknown Estimation for Arrays of Wave Energy Conversion Systems via LTI Synthesis
Authors: Papini Guglielmo , Pasta Edoardo , Paduano Bruno , Faedo Nicolás , Mattiazzo Giuliana
Published: October 2022

The incoming menace of global overheating and depletion of fossil fuels, highlight the need for alternative, renewable, energy sources. In this context, ocean wave energy has a massive potential to contribute towards global decarbonisation. In optimising wave energy converters (WEC) productivity, state-of-the-art, model-based optimal control techniques are fundamental to enhance energy absorption efficiency. However, the vast majority of these optimal approaches inherently require wave excitation force estimators. In particular, in array configurations, the interaction between WEC devices has to be taken into account to achieve a consistent excitation force estimation. In this paper, a linear time-invariant (LTI) estimation approach for a WEC farm is proposed. The technique proposed is based upon the so-called ‘simple and effective estimator’, recently presented in the WEC literature, which reformulates the wave excitation force estimation problem as a traditional tracking loop. The results show that the proposed approach provides accurate estimates of the exciting force for every device in the array, with almost no design effort, and mild computational requirements.
An Impact Load Identification Method Based on Green’s Kernel Function
Authors: Zhou Xueqian , Xu Yishi , Yang Yu , Lu Gang , Ren Huilong
Published: October 2022

Ships and offshore platform structures experience complex dynamic loads during their lifetime. Impact loads is one of the types of dynamics loads where the duration of action is very short. The relative velocity between impacting body and the structure being impacted is usually high, and which may have a significant influence on the safety of ship structures. The load, as an input of structure calculation, plays an important role during the calculation progress and directly influences the accuracy of the result. Identification of the loads acting on the structures are important for structure design, analysis of strength, estimation of fatigue life and also data driven models of structures, however, most of these types of loads are difficult to identify. A possible approach is to measure the response of the ship structure, and then identify the location of action and the time histories with load identification techniques. In this study, a Green’s kernel function based time-domain inverse method for estimating the impact load is studied. The Tikhonov regularization method and TSVD method are used to deal with the ill-conditioned problem in the inversion, and the ill-conditionness of the matrix is reduced to a certain extent so as to improve the identification accuracy. An Improved Maxwell-Betti method is used to identify the location of impact load at an unknown position. The proposed method is validated through numerical simulation and experiment for a typical structure used in naval architecture and ocean engineering.
A Study on the Error Characteristics and Compensation Algorithm for Strain Gauge in Ship Structure Monitoring Systems
Authors: Zhou Xueqian , Yang Yu , Xu Yishi , Li Chenfeng , Ren Huilong
Published: October 2022

The ship structural stress monitoring system is one of the main technical approaches to realize intelligent ship hull structure, and it has been applied to high-performance ships and large-scale merchant cargo ships in recent years. The structure monitoring system can not only serve as the input of data-driven digital twin models of ships structures, but is also the basis for the derived decision support system. For this reason, it is crucially important to obtain accurate stress in the structure, and the error characteristics of strain gauges under possible combinations of load and temperature that a ship may undergo must be investigated. For a ship structure, the error characteristics of the strain gauges can be investigated by comparing the measures from the strain gauges installed on the ship and the stress obtained from numerical simulation. A neural network to compensate the errors of the strain gauges can be trained through measures from strain gauges and the numerical results for the stress at the same location. In this study, the analysis of the performance and the error characteristics of the strain gauges on a beam test piece are conducted. An experimental investigation of the response of two types of fiber Bragg grating strain gauge at different temperatures and different loads are conducted in the same approach. The performance and error characteristics of the strain gauges under different loads and temperatures are analyzed. Based on the analysis of error characteristics, various BP neural networks are constructed to compensate the errors of the strain gauges. Comparison of compensation results and experimental results of two types of fiber Bragg grating strain gauge shows that the proposed method can effectively reduce the influence of the error on the accuracy of the gauge. Application of this method requires the training samples of measures and numerical results for the stresses under known static loading conditions like berthed in a harbor or moving in calm water. Thus it is feasible to update the neural networks for the compensation of errors during the operation of ships.
Wave Impact on Semi-Submersible Units: A Review of Design Standards
Authors: Gopalakrishnakurup Renjeev
Published: October 2022

On 15 February 1982, the damage sustained by the portholes on the ballast control room onboard the drilling rig Ocean Ranger during a storm kick started a chain of events that resulted in the loss of 84 lives and the rig. The event led to an update of MODU Code that govern the design of Mobile Offshore Drilling Units. Semi-submersible mobile offshore units have evolved in their design and utility since 1982. Most recently, on 30 December 2015, a fatality occurred onboard COSL Innovator when a storm hit the unit. The incident led to changes in the assessment of airgap and structural adequacy of existing designs operating in harsh environment such as North Sea. A comprehensive assessment of the consequences of wave impact on the deck structure of a semi-submersible is still required to understand the safety and reliability of such units subjected to similar incidents. This review paper is an attempt to list important design aspects of Semi-submersible mobile offshore units affected by wave impact on the deck and the current design requirements. Some of the important aspects that require consideration are stability, watertight integrity, local and global structural strength, stationkeeping, impact on safety critical equipment and control systems and safety of persons in living area subjected to wave impact.
Analysis of Chain Fatigue Test Data for New and Used Mooring Chains
Authors: Hørte Torfinn , Yang Limin , Okkenhaug Siril
Published: October 2022

DNV is currently running a Joint Industry Project, “NorMoor JIP”, which is now approaching the end of phase 3. In this phase the fatigue limit state of mooring lines with studless chains for permanent units has got the main attention, where a new design method and safety factors for fatigue has been calibrated using structural reliability analyses. Phases 1 and 2 was covering the ultimate and accidental limit states respectively. The JIP has participants from energy companies, engineering companies, rig-owners, manufacturers and marine authorities. It is a global study covering Gulf of Mexico, Northern Europe and Brazil waters.

The focus in the present paper is on the chain fatigue strength. NorMoor JIP has obtained access to a large number of tension-tension fatigue test data for studless chain of various sizes, both new and used. The tests are carried out at different mean load levels and load ranges and provide a unique opportunity to study how the fatigue strength is influenced by mean load and degree of corrosion. Considerations have also been made to obtain consistency in the test results for tests with different number of links in the test sample.

The main result from analyzing the test data is an S-N based fatigue strength formulation, where the nominal stress range versus number of cycles to failure is given as a function of nominal mean stress and corrosion category. The data support keeping the slope of the S-N curve at m = 3, hence, logA is fitted to the data as a function of mean stress and corrosion category. The overall fit to all data has been checked for sub-groups of data such as new chain, used chain of different corrosion category, different chain diameter and different mean load. Prior to performing the fit, the test data were adjusted to represent number of cycles to failure for the weakest out of 6 links. This adjustment was implemented for tests with number of links different from 6 and is based on extreme value statistics. For corrosion, seven corrosion categories are used, based on guidance provided by the LifeMoor project at Sintef/NTNU. More work is needed to more precisely specify the categories. The formulation proposed uses nominal stress based on the reference diameter for new chain.

A series of 3 papers is published at the OMAE2022 documenting the work done in the NorMoor Phase 3 on the fatigue limit state of mooring lines. Additional to the strength formulation from the present paper, the importance sampling method, developed in NorMoor and presented in OMAE2022-81441, is used in the structural reliability analysis and code calibration presented in OMAE2022-81463.