bluuebunny/crossref_metadata_2025 huggingface dataset:
Conceptual Design and Model Tests for a Mid-Water Floating Hyperloop Tunnel
Authors: Kemp L. J. , Otto W. J. , Waals O. J.
Published: December 2020

Aviation has a significant impact on the global emission of greenhouse gasses. On the Northern Atlantic route alone there are over 2,500 crossings daily. This illustrates the high demand for connecting people. It is expected that this demand will only increase in the future, which will increase the emissions due to aviation even further. An alternative way for connecting people can be the hyperloop, which obtains comparable speeds while using a fraction of the energy. For intercontinental connections a tunnel would be necessary.

In this study, a conceptual design of a mid-water floating hyperloop tunnel is made and tested on model scale at MARIN. In the present paper the results are discussed of model tests on a mid-water floating tunnel in Atlantic storm conditions at various wave directions and tunnel depths.

The conceptual design of the tunnel is based on (nearly) available technology. One kilometer tunnel segments with a diameter of 11 m are connected to construct a tunnel length of > 5,000 km. Model basin tests are performed on scale 1:110, where a scale model of 140 m length is tested. The tunnel is designed as a neutral buoyant tunnel to reduce complexity and costs for the mooring system. The motions, deformations and mooring line tensions for the tunnel segments are measured by force transducers, accelerometers and an optical measurement system.

Due to flexibility of the slender tunnel segments in combination with a soft mooring system, the tunnel tends to following the incoming waves for certain tunnel depths and wave directions. Only small motions and deformations are allowed for a hyperloop capsule to travel on high speed. The conceptual tests show first results on tunnel depth, structural and geometrical design of an hyperloop tunnel and mooring system.
Basic Research on the Influence of Descent Flow From Small Unmanned Aerial Vehicle (Quadcopter) on a Small Floating Body
Authors: Ji Mingyao , Srinivasamurthy Sharath , Nihei Yasunori
Published: December 2020

Currently, unmanned aerial vehicles (UAV), are playing an active role in various situations. However, because of its size and other limitations, the commonly used UAVs (from now on, just called as drone) do not have the long endurance capabilities of large aircraft. Of course, long flight is not the original intention of its design, but flexibility is its main characteristic. This results in the need for frequent replacement and recharging of battery equipment. It may be easy to replace the batteries on land, but it will be more difficult to do the same offshore. Also, there is always the danger of drone falling into the water due to insufficient power. To overcome this problem, it is imagined to place a floating body such that the drone can be docked as and when necessary while flying over the water for maintenance and battery replacement.

Therefore, in this preliminary study, we aim to model the basic physical phenomena mainly on how the drone’s descent flow affects structures such as small floating bodies. The effects of drone descent flow on a small floating body and resulting load distribution was investigated both experimentally and numerically. Further, the mechanism of drone descent flow was examined in detail.

The drift simulation of the floating body due to the drone descent flow was performed with high accuracy, and the model of the drone’s descent flow became clear.
Design of Dynamic High Voltage Cables for Floating Substation
Authors: Guignier Lucie , Mariani Riccardo , Cottet-Emard Arthur , Toumit Stéphane , Choisnet Thomas
Published: December 2020

This paper presents the design and performance assessment of 220kV dynamic export cables for a floating substation characterized by a ring-shaped floater known as Damping Pool.

The main originality of the design presented is that the cables considered have dry conductors. They are shielded from the water by a longitudinally welded corrugated copper sheath. Similar cables have been operating at lower voltage levels and thus with thinner insulation thicknesses.

The export cable configuration has been designed considering environmental conditions representative of both the Central North Sea, Pacific Coast of Japan or the US, in 100m water depth. Ultimate and fatigue limit-state design verification of the configuration are made through nonlinear time-domain analysis using coupled models comprising the floating substation hull, the mooring system and dynamic export cables. Fatigue limit-state design verification is based on the fatigue properties of the cable section, combined with appropriate S-N curves of the armour layers and metallic screen-sheath.

Design verifications show that the dynamic export cable configuration proposed could satisfactorily meet the performance requirements for a service life over 25 years, considering proven cable equipment such as a bend stiffener remaining within today’s manufacturer molding capacities.
Numerical Wave Tank Simulation of a Variable Geometry Wave Energy Converter
Authors: Zou Shangyan , Abdelkhalik Ossama
Published: December 2020

This paper presents a high-fidelity numerical wave tank simulation for Variable Geometry Wave Energy Converters (VG-WECs). Typically, wave energy converters require reactive power to optimize the energy conversion, which significantly jeopardizes the economic index of the system. The proposed VGWECs allows comprehensive shape-changing not only in response to ocean climate but also to reduce the reactive power requirements on the power take-off (PTO) unit. This design aims at eliminating reactive power with minimal impact on optimality in terms of energy production. To investigate the dynamic behavior of the VGWEC, this model is simulated in a Computational Fluid Dynamics (CFD) based Numerical Wave Tank (CNWT) using ANSYS 2-way Fluid Structure Interaction (FSI) tool. The interaction between irregular waves and the VGWEC is simulated. The numerical results show that the proposed VGWEC has large deformation and motion in response to the incoming wave. This highly nonlinear interaction between waves and VGWEC can be leveraged to eliminate reactive power.
Out-of-Plane Bending (OPB) Test of Large Diameter Mooring Chains
Authors: Barros P. , Carlberg E. , Høgsæt I. S. , Karimi M. R. , Braun J. , Gooijer E. , Vargas P.
Published: December 2020

Chevron Corporation and Bluewater Energy Services (BES) performed a chain out-of-plane bending (OPB) test, called OPB MAX hereafter, at DNV GL’s laboratory in Høvik-Norway. The test was performed to study the OPB phenomenon for a chain diameter which was larger than the maximum diameter tested by the OPB JIP. The goal was to understand chain OPB physics for such a large diameter, measure interlink stiffness and maximum sliding moments and validate BES’ in-house finite element model. The current study is a collaboration between all involved parties and the results will be presented in three papers. The first paper summarizes the test setup and instrumentation. The second paper describes the test results, compares them with the OPB JIP estimations and tries to describe the chain OPB physics. The third and the last paper presents the FEA results performed by BES’ in-house finite element model. This paper is the first of the three and focuses on the test setup and instrumentation.

The testing machine has been developed by DNV GL and is capable of applying tensions up to 350 t and interlink rotations in the range of ±3 degrees. Two 7-link chain specimens of R4 and R4s grades, both with the nominal diameter of 168 mm were tested at five tension levels from 150, to 350 t. Testing was performed in both wet and dry conditions. Twenty strain gauges were used to measure 3 OPB and 2 IPB moments at 5 mid-link positions. Twelve strain gauge rosettes were used on 3 links to evaluate SCF’s on the OPB hotspots. Seven inclinometers were used to monitor link rotations. DNV GL utilized a digital image processing tool to capture relative movements of chain links and developed a specific data processing tool to calculate the interlink stiffness, perform statistical analysis and provide several levels of data evaluation and comparison between the tests.

The paper will provide a description of the test matrix and test objectives are given with the background of the previously performed OPB tests. Next a detailed description of the test rig is presented including the utilized instrumentation. Finally, an explanation of the implemented real-time test monitoring and the performed post-processing on the readings, in line with the test objectives is mentioned. The initial test results are briefly provided at the end.
Do Vessels Remain Within Their Operational Limitations in Ice? Analyzing the Risks of Vessels Operating in the Kara Sea Region Using POLARIS
Authors: Panchi Nabil , Kim Ekaterina , Xu Sheng
Published: December 2020

This study investigates whether the vessels remain within their operational limitations in ice using the risk index calculated based on the Polar Operational Limitations Assessment Risk Indexing System (POLARIS) — an acceptable methodology for the assessment of operational limitations in ice infested waters, referenced in the Polar Code of the International Maritime Organization (IMO). The speeds and positions of the vessels in the Kara Sea region were analyzed from January through April for 2017–2019 using the navigational data provided by the Northern Sea Route Administration. For each vessel, except for the icebreakers, the risk index based on POLARIS was calculated using the open-access ice information that was provided by the Arctic and Antarctic Research Institute in Russia. The variation of risk index was analyzed with respect to various parameters such as the ice-class of the vessel, the reported operating speed of the vessel, and the built year of the vessel. Furthermore, we explored the limitations of the risk assessment system as well as the limitations of the available ice information and its implications on the risk assessment system. This paper reports preliminary results from the analysis.
Development of a Simulation Environment for Hybrid Propulsion Drive Trains: Utilization of a Holistic Approach to Predict the Dynamic Behavior in the Early Design Stage
Authors: Jannsen Leif-Erik
Published: December 2020

This paper covers the generic procedure for the creation and usage of a complete system simulation for propulsion systems of ships with focus on complex hybrid systems. Due to the large number of available components and challenging operational profiles, there is no longer a single best solution, especially in specialized shipbuilding. On top of that even minor changes in the propulsion system can have a substantial impact on plant performance and vessel behavior. Thus, the early design stage is crucial. The design procedure usually incorporates the selection and dimensioning of available components and concepts. Once this has been done, the dynamic behavior can be analyzed using the developed system simulation environment. With the knowledge gained the needed alterations in the concept can be identified and implemented in the subsequent design iteration circle. Based on the example of an offshore anchor handling vessel, the integration potential of a hybrid propulsion system is examined and evaluated according to the aforementioned procedure. The applied tool is a system simulation environment developed in the Department of Marine Engineering, consisting of a distributed co-simulation of the existing ship design environment E4 and Matlab® Simulink®.
Fretting Fatigue Design of Subsea Connectors: Matching Results Between Pairs of Tests
Authors: Blades L. E. , Hills D. A. , Wormsen A. , Macdonald K. A.
Published: December 2020

The upper end of a subsea wellhead system has an external wellhead hub profile. The standardised H4 profile is widely used. A wellhead connector is latched on the wellhead profile by use of locking devices with a matching internal profile (e.g. clamps, sections and dogs). Large contact loads are set up when latching the connector on this wellhead profile with the objective of withstanding internal pressure and wave-induced cyclic bending loads while avoiding hub separation. Fretting fatigue is an additional phenomenon to that of conventional high-cycle fatigue (fatigue crack initiation from the wellhead profile grooves) that should be addressed as part of the design documentation.

Methods have been developed to match the key parameters in this contact to a laboratory test. Here, the strength of the effect of each of the matched loading parameters was assessed. Specimens were manufactured from wellhead housing and locking dog steels. The fretting fatigue tests were performed using loads representative of a preloaded connector. Validation of these methods would enable the use of fretting fatigue data determined for one geometry to be used in fatigue life prediction of another.
MIL and MIRO Diagrams for Risk-Based Positioning of Drilling Rigs With Dynamic Positioning System
Authors: Maturana Marcos Coelho , Souza Victor Rafael , Mesa Valentina Clavijo , Martins Marcelo Ramos , Oshiro Anderson Takehiro , Schleder Adriana Miralles
Published: December 2020

Currently, most offshore oil exploration operations are performed by Dynamically Positioned (DP) units; in Brazil, the use of these units is traditional in drilling operations (DP drilling rigs). The advent of DP systems, which allow the vessel to maintain a certain position without the need for anchor lines, has brought great flexibility to the oil field; however, usually in drilling areas, there are a large number of operations being performed simultaneously and subject to weather conditions and a failure of the DP system may cause these vessels to drift, which may occasionally result in a collision with other field equipment or vessels, causing material, personal and environmental damage.

In this context, it is necessary to analyze what would be the best positioning points for these units according to the configuration of potential obstacles present in the area (such as risers, anchor systems and floating production systems), the characteristics of the DP unit and the expected environmental conditions. It is vital to know the risk of collision associated with the positioning of these units. The risk of collision will depend mainly on the meteo-oceanographic variables of the operating region, the hydrodynamic characteristics of the unit, the DP system reliability and its repair time, and the distribution of obstacles in the area.

The objective of the ongoing research is the development of a methodology to define the risk associated with the positioning of the DP units, through a statistical method and a validated drift mathematical model under the influence of environmental agents. The proposed methodology allows us to demonstrate compliance with a widely accepted RAC (Risk Acceptance Criterion). The developed methodology proposes the use of two instruments: Location Iso-Probability Maps (MIL) and Operational Iso-Risk Maps (MIRO), to synthesize the information to the decision making about the operation of the DP units at a specific location, considering the overall collision risk (at MIRO) and the probability of the rig being at a specific location (at MIL).
Decompression Analysis of Multi-Layered Barrier Flexible Pipes Under Catenary Configuration
Authors: Gonzalez Gabriel Mattos , de Sousa José Renato Mendes
Published: December 2020

Periodic shutdowns, which decompress service pressure down to atmospheric pressure, are common in offshore flexible pipe systems. In high pressure and high temperature operations, the use of multi-layer barrier flexible pipes is also common. A multi-layer barrier usually combines inner sacrificial and pressure sheaths and, under certain circumstances, the annular gap between these sheaths is filled with fluid. When this fluid is trapped in this gap, which may occur due to a rapid decompression on shutdown operations or an accidental opening of an upstream valve, the flexible pipe system may fail. The trapped fluid tends to be released slower than the fluid that transiently flows under the bore thus generating a differential pressure, which is function of the rate of decompression, and may induce the collapse of the inner carcass. Therefore, the assessment of the magnitude of this differential pressure is crucial to prevent safe decompression rates. This article describes a numerical model, based on finite differences, to predict the differential pressure magnitude for risers in catenary configurations. The model is developed considering fundamental fluid dynamics principles, such as the conservation equations, for a one-dimensional geometry. The results are compared to previously published literature data for a given 4” flexible pipes under two different geometric configurations (horizontal and catenary). The results from the proposed model agreed quite well with those from a previous proposed approach for horizontal configurations, while the catenary configuration analyses evidenced the impact of the gravity parcel on the differential pressure between the pressure sheath and the bore of the pipe.
Dynamic Analysis of a Progressing Cavity Pump System Using Bond Graphs
Authors: De Moura Jeronimo , Rideout Geoff , Butt Stephen D.
Published: December 2020

One commonly used pump in the petroleum sector is the Progressing Cavity Pump (PCP). The PCP is a type of positive displacement pump that is used as an artificial lifting system which consists of a helical rotor and elastomeric stator. A mathematical solution to a PCP system model requires that we solve a partial differential equation system. The solution is inherently complex and requires considerable computational time. This paper uses the bond graph formalism, which is based on energy and information flow, to implement a model of a PCP system. Its purpose is to predict the dynamic response of the PCP system when it is subjected to a specific reservoir condition. Specifically focusing on the rod string, the torsional effects are captured by a lumped segment approximation. The software 20-Sim© was used to simulate a realistic PCP system application scenario. The model presented in this paper is able to determine the prime mover, rod string, and other component requirements. This paper shows that the multi-body lumped segment model is a useful way to simulate the rod string performance. The bond graph is effective at modeling the PCP system which contains elements from different energy domains.
Time Domain Turret Load and Motion Analyses for a FPSO
Authors: Kim Hyoungchul , Koo Bonjun , Kyoung Johyun
Published: December 2020

Fully coupled time domain turret/FPSO simulations are conducted using TechnipFMC proprietary software MLTSIM. To analyze hydrodynamic interactions and mechanical coupling effects between an FPSO and its turret, a multi-body interaction model is developed and analyzed. In the multi-body interaction model, full coupled hydrodynamic interactions are considered, and the bearing connections are modeled with nonlinear springs and frictional damping. The global performance analysis results are systematically compared with model test results (Kim et al. [1]), and hydrodynamic loads and mechanical coupling loads on the turret are presented in this paper.
Calculating Frictional Losses in Belleville Springs by Geometrical Interpolation
Authors: Maharjan Dipesh , Shah Shaheen , Abugharara Abdelsalam , Butt Stephen
Published: December 2020

The use of Belleville springs has been proven to be beneficial in tackling the problems related to elastic interaction, creep, differential thermal expansion or in the isolation of seismic vibrations in bolted joints. Because of its high and easily variable spring rates, the use of these springs can also be observed in passive vibration assisted rotary drilling (VARD) tools. Because of relative movement of spring with respect to supporting surfaces and the mating spring surfaces, frictional losses in the spring take place during each compression and relaxation cycle leading to a slightly different load-deflection curve from what has been defined in the literature. The geometry of the spring combined with different stacking configurations complicate the study of frictional losses in these kinds of springs.

This work presents a new method to calculate the displacement of different points of Belleville springs during its loading and unloading using geometrical interpolation method. The results of spring displacement are then used to develop a model to calculate frictional load as a function of spring deflection, which is used to analyse load-deflection curves of springs with different dimensional and frictional parameters. The developed methodology is used to plot and understand characteristics curves of four different kind of Belleville springs; High Load, Standard, Force Limiting and Force Adjusting Belleville springs by plotting the graphs for different free-height to thickness and diameter ratios. In the later section of the paper, the proposed methodology has been used to visualize the load-deflection characteristics of Belleville springs used in the p-VARD tool of the Large Drilling Simulator, one of the state-of-the-art drilling simulators at Memorial University of Newfoundland. Results show that understanding of the characteristic curves of different spring configuration helps to plan to drill with desired WOB using a p-VARD tool.
Vessel/Stinger/Pipeline Fully Coupled Analysis for Pipelaying Operation
Authors: Koo Bonjun , Tu Qin , Wang Jiaqi , Mathakari Sachin
Published: December 2020

During pipelaying operations, dynamic performance of the stinger due to vessel motion has a strong impact on the stinger capacity estimation. However, the conventional stinger structural design is based on the maximum load on the roller boxes corresponding to a target top tension value. In addition, the installation analysis uses the uncoupled vessel motion Response Amplitude Operators (RAOs) to calculate the motion induced loads on the stinger and the pipeline.

Since the maximum loads on the stinger are conservatively estimated by linearly superimposing maximum forces from different loading conditions, the conventional design and analysis approach leads to either over-design of the stinger structure or underestimation of the stinger capacity.

To improve conventional pipelaying design and analysis methodologies, a time domain vessel/stinger/pipeline Fully Coupled Analysis (FCA) is presented in this study. The new analysis procedure significantly improved the stinger operation limit compared to the conventional design and analysis procedure.
Hydrodynamic Loads on Net Panels With Different Solidities
Authors: Føre Heidi Moe , Endresen Per Christian , Norvik Carina , Lader Pål
Published: December 2020

Drag forces on nets represent the largest contribution to hydrodynamic loads on traditional fish farms, and will have a large impact on total loads on new designs utilizing netting as containment method. Precise methods for estimation of drag loads are needed.

This paper gives new knowledge on hydrodynamic forces acting on aquaculture nets. It presents results from towing tests, including updated drag and lift coefficients for Raschel knitted netting materials used in nets for aquaculture, and quantify wake effect. The results include high solidity nets and high towing velocities.

It was found that drag loads were close to proportional with the netting solidity for netting solidities ranging from 0.15 to 0.32. The wake effect is quantified through the average velocity reduction factor, which is given as a linear function of solidity.

Much of previously published data are close to the data found through these tests. However, for high solidity nets, the deviation is significant. Therefore, previously published data and models may overestimate drag loads for high solidity nets.
Benefit From Structural Reliability Analysis in Risk Evaluation of Collapse of Externally Supported Casing
Authors: Hørte Torfinn , Bjørset Arve , Zaharie Dan Tudor , Pettersen Sune
Published: December 2020

Casing collapse capacity was identified by Equinor as a critical operational parameter on one of its fields in production. This led to re-evaluation and detailed studies of the overall well design, specifically the production casing’s collapse capacity, together with consequence and risk evaluations in case of a potential casing failure. As an important and useful input to the risk evaluations, the present paper presents a structural reliability analysis for casing collapse.

Initially, the casing collapse capacity was evaluated using API TR 5C3 / ISO 10400 [1], with insufficient capacity being documented. In order to investigate further, physical material testing and collapse testing were performed. Two kinds of collapse tests have been performed: i) tests of unsupported pipe and ii) test of pipes with external support from the cement and formation surrounding the pipe. While a paper from 2018 (OMAE2018-78767) considered casings without external support, the present paper pays attention towards supported pipes. Five collapse tests have been performed where test lengths of the 9 5/8” casing were installed inside a thick-walled pipe that simulates the support. A small gap leaves an annulus between the casing and the supporting pipe, allowing a controlled pressure to increase until collapse. The tests have been simulated by finite element analyses. Good correspondence was obtained, providing confidence that FE simulations can be used to predict the collapse capacity of supported pipes.

While the tests were only performed for an idealized case with support around the whole circumference, a large number of FE simulations have been carried out for different combinations of support conditions together with variations in pipe ovality and internal wear from drilling. Ideally, the space between the casing and the rock formation is filled by cement. However, in practice there may be channels where there is no cement, likely to occur if the casing is eccentric in the well bore during cementing. These results from these FE simulations have been used to generate a response surface. Subsequent structural reliability analyses have been performed, in which well specific uncertainty associated with the above parameters is considered. Measurements and logging are used to minimize the uncertainty in these inputs and thereby leading to a reduction in the calculated failure probability. The probability of casing collapse is calculated conditional on different magnitude of the differential pressure of the pipe.

By using SRA the potential over-conservatism in the conventional deterministic analysis is avoided. The SRA results were used to assist in the risk evaluation resulting in an allowance for continued production on existing wells.
Offshore Breakwaters for LNG and Bulk Terminals: A Design Methodology for Determining Breakwater Layout
Authors: Youssef Khali , El Chahal Ghassan , Saadali Nadjib
Published: December 2020

Over the last decades LNG and bulk terminals have been constructed in many countries. Many of these terminals have been located in sheltered sites without significant influence of swell and wind seas. As the worldwide gas market continues to grow supplying domestic, industrial and power plant projects, there is a continuous interest in new LNG terminals. With the growing gas demand LNG terminals are planned at exposed sites where the need of a breakwater is important for the ability of the facility to maintain operations and to ensure survivability of the terminal infrastructure. Studies are carried out for LNG terminal concept with the main focus on the need for a breakwater protecting the facility which will have significant impact on the CAPEX (Capital Expenditure). The mooring layout of the FSU/FSRU and LNG carrier whether perpendicular or parallel to the breakwater in addition to the planned operations determine the protection area behind the breakwater.

The objective of this study is to establish design curves relating the different environmental and terminal parameters such as wave conditions, berthing facility layout, protection area and breakwater layout. These curves are derived based on the results of numerical simulations for wave transformation process of offshore waves propagating inside the terminal area. More than 700 cases are carried out in this study considering a range of wave periods, breakwater lengths, breakwater type (caisson and rubble mound), facility area dimensions and two incoming waves direction, i.e perpendicular and oblique. The simulations are carried out using the software REFONDE which is based on resolving the mild slope equation for irregular waves. The results of the study are presented in the form of curves and generalized to be used by terminal developers, designers and contractors for general guidance in future projects.

Up to the authors’ knowledge, such curves for the design of marine terminals are not available at present. From this overview, a design methodology is developed to determine breakwater layouts during the early planning phase of project considering wave conditions, facility layout and terminal operations.
Robust Method for Wellhead Loads Estimation Based on Lower Stack Motion Measurements
Authors: Cetin Ali , Holden Harald , Solum Vegard R.
Published: December 2020

Estimating wellhead loads from lower stack motion measurements is a practical and cost-effective approach. In this paper, a new method is proposed, which is based on system identification techniques rather than Newtonian mechanics, thus omitting reliance on uncertain and variable quantities such as lowerflex joint stiffness/damping, riser and drill pipe tension etc. The proposed method is simple and easy to apply, while maintaining accuracy. Both simulation and real-world measurement data are utilized to demonstrate and evaluate the method.
Monitoring and Performance Evaluation of Plastic Cleanup Systems: Part II — Results and Analysis
Authors: Sainte-Rose Bruno , Wrenger Hendrik , Soares Ivan , Mosneron-Dupin Cosme , Duval Clara , Planchat Alban
Published: December 2020

The Ocean Cleanup Foundation is developing floating barrier systems to concentrate and extract buoyant plastic from the global accumulation zones. In that context, two cleanup systems have been designed, built and deployed in the Great Pacific Garbage Patch since 2018 to evaluate their performance in the field for which a large amount of data has been collected. This data serves to validate and calibrate numerical models that will be used to develop future generations of cleanup systems.

The main performance indicator in scrutiny is the field efficiency which can be derived from on the one hand the barrier horizontal motion in terms of displacement and span heading and on the other hand the plastic transport around and inside the barrier. After a first part dedicated to the presentation of the experimental campaign carried out to evaluate the field efficiency of the second cleanup system, this second part is dedicated to the presentation of some results and analysis performed to evaluate the interception efficiency.

This paper first focuses on the cross comparison of two measurement techniques to evaluate the barrier span length and heading, second the metocean models in terms of waves and wind are presented and compared against the available metocean measurements. Then, a multi-linear model is proposed to evaluate the barrier dynamics from the background metocean conditions and applied to the analysis of the barrier in the lifting bag configuration. Finally, the multi-linear model is compared to measured relative speed for all the drifter tests carried out in the campaign the whole test campaign.
Machine Learning Models With Engineering Insight: Case Studies From the Oil and Gas Industry
Authors: Chakraborty Ishita , Kluk Daniel , McNeill Scot
Published: December 2020

Machine learning is gaining rapid popularity as a tool of choice for applications in almost every field. In the oil and gas industry, machine learning is used as a tool for solving problems which could not be solved by traditional methods or for providing a cost-effective and faster data driven solution. Engineering expertise and knowledge of fundamentals remain relevant and necessary to draw meaningful conclusions from the data-based models. Two case studies are presented in different applications that will illustrate the importance of using engineering domain knowledge for feature extraction and feature manipulation in creating insightful machine learning models. The first case study involves condition-based monitoring (CBM) of pumps. A variety of pumps are employed in all aspects of the oilfield life cycle, such as drilling, completion (including hydraulic fracturing), production, and intervention. There is no well-established method to monitor the pump fault states as they are operating based on sensor feedback. As a result, maintenance is performed either prematurely or reactively, both of which result in wasteful downtime and unnecessary expense. A machine learning based neural network model is used for identifying different fault states in a triplex pump from measured pressure sensor data. In the second case study, failures of mooring lines of an offshore floating production unit are predicted from the vessel position data. Identifying a damaged mooring line can be critical for the structural health of the floating production system. In offshore floating platforms, mooring line tension is highly correlated to a vessel’s motions. The vessel position data is created from running coupled analysis models. A K-Nearest-Neighbor (KNN) classifier model is trained to predict mooring line failures. In all the case studies, the importance of combining a deep understanding of the physics of the problem with machine learning tools is emphasized.
Second Order Difference Frequency Wave-Current Loading Using Kelvin-Newman Approximation
Authors: Bakti Farid P. , Kim Moo-Hyun
Published: December 2020

Kelvin & Newman introduced a linearization method to include the current (or forward speed) effect into the diffraction & radiation wave field for large-slender floating bodies. The K-N method assumes a steady far-field current while disregarding the steady potential field due to the presence of the body. The method is proven to be reliable when the Froude number is relatively small, the body shape is relatively slender (∂∂x≪∂∂y,∂∂z), and the sea condition is mild. This requirement is fulfilled for typical FPSOs and ship-shaped vessels in a typical current (or forward speed) condition. Several studies suggested that the presence of the current might change the first order hydrodynamic coefficients such as the first order diffraction force, added mass, and radiation damping. Currents also contributed to a change in the second-order slowly-varying drift force. However, the effect of current in the second-order difference-frequency force is yet to be investigated. By expanding the Kelvin-Newman approximation up to the second order, and solving the problem in the frequency domain, we can save computational time while expanding the accuracy of the scheme.

The second order quadratic force is the main focus of this study, since it is the main contributor to the total second order difference frequency forces especially near the diagonal. By implementing the Kelvin-Newman wave current interaction approach up to the wave’s second order, we can assess the performance of the Kelvin-Newman wave current interaction formulation in various sea conditions.
A Convenient Technology to Calculate Geomechanical Properties From Drilling Data
Authors: Tahmeen Mazeda , Hareland Geir , Hayes John P.
Published: December 2020

The multistage hydraulic fracturing is the best practice to stimulate unconventional hydrocarbon reservoirs for optimal production. Recent studies suggested that selective stimulation design could significantly increase production rates at a reduced cost rather than using non-selective geometric stages. An optimal design needs detailed logging and core information to selectively perforate and optimize the stimulation treatment. In most cases, the non-selective evenly spaced geometric stimulation design is used, primarily due to the time consuming and expensive conventional logging tools and techniques.

In this article, a 3D wellbore friction model is used to estimate the effective downhole weight on bit (DWOB) from the drilling data, directional survey data and drill string information. The estimated DWOB is used as an input to the inverted rate of penetration (ROP) model along with other drilling data, drill bit specifications and reservoir specific formation constants, to calculate rock mechanical and reservoir properties including, compressive strength, Young’s modulus, porosity, permeability and Poisson’s ratio without the use of expensive downhole logging tools. The rock brittleness index is calculated from the relationship between Young’s modulus and Poisson’s ratio based on the definitions of rock brittleness used in recent years.

The field data from horizontal drilling of three sample wells were used to investigate the geomechanical properties in the Montney shale formation and the lower Eagle Ford formation in North America. The calculated geomechanical properties were compared to the corresponding test analysis on cores. The authors investigated the rock brittleness index from the sample well data drilled horizontally in the lower Eagle Ford formation. This novel technology could help geologists and reservoir engineers better exploit unconventional reservoirs leading to optimal selective stimulations and greater net present value (NPV).
Relative Motion During Single Blade Installation: Measurements From the North Sea
Authors: Sander Aljoscha , Haselsteiner Andreas F. , Barat Kader , Janssen Michael , Oelker Stephan , Ohlendorf Jan-Hendrik , Thoben Klaus-Dieter
Published: December 2020

During single blade installation in offshore wind farms, relative motion between nacelle and blade root due to wind and wave excitation pose a significant challenge. Wave excitation can be modelled considerably well by employing state-of-the-art simulation tools and can, therefore, be included in installation planning. Other phenomena, such as flow-induced vibrations are hard to capture and hence challenging to account for when defining installation procedures and limitations. Here, we present measurements conducted during the installation of an offshore wind farm consisting of multi-megawatt turbines installed on monopile foundations in the North Sea. A custom-built sensor capturing linear & angular acceleration and GPS-data was deployed atop the nacelle. Both partially and fully assembled turbines displayed complex oscillation orbits, swiftly changing amplitude and direction. Mean nacelle deflection correlated strongly with significant wave height as well as mean wind speed. As wind speed and significant wave height showed a strong correlation as well, it is difficult to discern which load drives the observed relative motions. While wind loads are significantly smaller than wave loads on partially assembled turbines under installation conditions, additional momentum induced by vortex shedding may prove sufficient to cause the observed effects.
Algorithms for Supervised Machine Learning-Based Structural Performance Evaluation Framework
Authors: Wang Xiaowei , Heo YeongAe
Published: December 2020

Machine learning (ML) approaches have gained increasing attention in the structural engineering field to evaluate structural performance using structural health monitoring (SHM) data. Supervised ML approaches can accelerate the learning process by using labeled training datasets to map an input to output dataset. But, SHM data are not informative to drive a mapping function to determine the real-world performance of large-scale complex structures in particular for future events. To leverage a framework for evaluating the system-level structural performance, this study couples supervised ML approaches with an advanced finite element (FE) model considering pre- and post-event model validation and updating. A well-instrumented system experiencing multiple seismic events is employed as a case study to demonstrate the proposed framework. An FE model of the instrumented system is created and validated using pre-event SHM datasets. Numerical data obtained from the FE model are used for datasets to develop ML prediction models, which are then validated by a post-event SHM dataset. Eight popular ML algorithms are examined and compared to shed light on the effectiveness of the ML algorithms for the proposed framework. The case study results indicate that the Random Forests and Neural Network algorithms provide better estimation for the structural system. The results also imply the need of post-event updating for numerical models used in the case study.
SPIRE: Flexible Riser Condition Monitoring System Applied to Pre-Salt Fields With High CO2
Authors: Brandão M. O. , Lima J. , Almeida E. , Borges O. , McCarthy J. , Nott P. , McNab J.
Published: December 2020

The development of Brazil’s Offshore fields has been performed using flexible pipes because this pipe technology offers significantly increased flexibility, enabling the movement of pipes between wells and reducing lead time to bring a well onstream as compared to rigid pipe solutions. In addition, the decision of where exactly to drill development wells can be delayed, thus making the drilling campaigns easier, cheaper and faster [1].

With the increased activity in Pre-Salt, some challenges to flexible pipes were uncovered and needed to be addressed, notably oil composition and corrosive agents, e.g. H2S, and, specifically for the case of this paper, CO2. At high pressures, such as found in pre-Salt fields, these contaminants create new Stress Corrosion Cracking (SCC) failure modes and several mitigation measures have been adopted to overcome them, focused either on the installed fleet or on the next generation of pipes to be delivered. SCC is a condition that induces failure in the pipes’ metallic layers, but it needs three elements to occur: water, tensile stress exceeding a critical level and a susceptible material. If one of these three elements is suppressed, the phenomena does not to happen.

This paper will cover and present a technology developed to detect the annulus water condition — dry or flooded — and thereby allow a correct integrity management strategy to be adopted. The technology is based on an embedded sensing system together with topside equipment to read the status. The use of such a system is important for the next generation of flexible pipes as it will allow better management of the fleet, with the required measurements performed from the production unit without the need of any support vessel and hence at a reduced cost.
Effect of Annealing Temperature on Physical Features of PVDF Pipe Material
Authors: Rabello Nascimento Christine , Costa Celio A. , Gervasoni Chaves Érica , Teixeira Sylvia , Bertolino Luiz Carlos
Published: December 2020

A PVDF grade typically used in off-shore applications was annealed at 70, 90 and 120°C. The samples were characterized and it was observed a small change in the crystallinity, but, on the other hand, the Elastic modulus of the sample annealed at 120°C increased from 1.52 to 1.85 GPa. The relaxations observed by Dynamic Mechanical Analysis (DMA) indicate that a morphological change took place at annealing process, which led to a stiffness rises of amorphous phase.
A Fundamental Study on Motion Characteristics of the Large-Scale Floating Coal Transshipment Station by Elastic Mooring Lines
Authors: Eto Hiroaki , Sekiguchi Ryo , Kashima Hitomi , Ikoma Tomoki , Aida Yasuhiro , Masuda Koichi
Published: December 2020

This paper describes the motion characteristics and cargo handling efficiency of the Large-Scale Floating Coal Transshipment Station (LFTS). Indonesia is the main country supplying coal in the Asia-Pacific region, it is important to ensure stable coal supply to Japan. Because the topography of the seabed near East Kalimantan Island, Indonesia’s main coal production area, is shallow, it is difficult for bulk carriers to reach the coast. And then, Large-scale Floating Transposition Station for Loading Coal (hereafter LFTS) was proposed, which will be used as a transposition station between small coal barge coming down the river and bulk carriers stay offshore. By installing LFTS, improvement of coal transport efficiency is expected.

As a previous study, the motion characteristics of LFTS using a catenary chain in its mooring system were grasped. However, LFTS can carry up to 500,000 tons of coal, and the draft of LFTS tends to change greatly depending on the coal loading conditions. Besides, the tidal difference in the sea area where the LFTS is installed is about 2 m, and the mounting position of the mooring system on the LFTS side moves up and down by about 10 m at maximum due to changes in the draft and tidal differences. For this reason, when the mounting position of the mooring system is in the lowest state, the mooring line is loosened and the horizontal force is reduced, and it is considered that sufficient restraining force is not exhibited. And, when the mounting position of the mooring system becomes high, the mooring line tension increases and the mooring line may break in some cases.

Therefore, in this study, an attempt was made to use an elastic mooring line as a mooring system for LFTS. An elastic mooring line is a mooring line that incorporates a highly stretchable material between mooring lines that connect anchors and floating body. Even if the mooring line attached to the LFTS moves up and down, an appropriate tension always acts on the elastic mooring line, and it can be expected to suppress the oscillation of the floating body and prevent the mooring line from breaking due to excessive tension. However, elastic mooring lines are mainly used for mooring small structures such as piers and aquaculture facilities, but there are no examples where these mooring lines have been applied to structures over 500m like LFTS. Therefore, elastic mooring lines are adopted for the mooring system of LFTS, systematically calculated according to various setting conditions of elastic mooring lines, and it is grasped whether elastic mooring lines can be applied to LFTS, and the motion characteristics of LFTS moored by elastic mooring lines was also grasped.
Investigating the Impact of Power-Take-Off System Parameters and Control Law on a Rotational Wave Energy Converter’s Peak-to-Average Power Ratio Reduction
Authors: Karayaka H. Bora , Yu Yi-Hsiang , Tom Nathan , Muljadi Eduard
Published: December 2020

Due to the irregular nature of real waves, the power captured in a wave energy converter (WEC) system is highly variable. This is an important barrier to the effective use of WECs. To address this challenge, this study focuses on a rotational WEC power-take-off system in which high-speed and high-efficiency generators along with a torque/power smoothing inertia element can be effectively utilized. In the first phase of this study, the U.S. Department of Energy’s reference model 3 (WEC-Sim RM3; two-body point absorber), along with a slider-crank WEC, were integrated for linear to rotational conversion. Relative motion between the float and spar in RM3 was the driving force for this slider-crank WEC, which is connected to a motor/generator set through a gearbox. RM3 geometry was scaled down by 25 times to work within the limits of the physical motor/generator set used in the experimentation. Once the integration in a hardware-in-the-loop simulation environment was successfully completed, data on the peak-to-average power ratio was collected for various wave conditions including regular and irregular waves. The control algorithm designed to keep the system in resonance with waves was able to maintain relatively high speed depending on the specific gear ratio and wave period. Initial results with hardware-in-the-loop simulations reveal that gear ratio and crank radius have a strong impact on the peak-to-average power ratio. In addition, it was found that output power from the generator was maximized at a larger gear ratio, as the crank radius was increased.