bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Model Development of a Variable-Geometry Attenuator Wave Energy Converter
Authors: Pardonner Davy , Tom Nathan , Guo Yi
Published: December 2020

Because the wave energy industry is still in its infancy, an optimal design for wave energy converters (WECs) has yet to be established; more work is needed to explore various cost-reduction pathways. The primary cost-reduction pathway considered for this work is the optimization of the geometric profile on an attenuator WEC to maximize power production while, at the same time, minimizing capital expenditures through the use of variable-geometry modules. In this investigation, the variable-geometry modules consist of inflatable bags placed on either side of a base central steel cylinder that would be inflated in low-moderate sea states to maximize power capture and then deflated in moderate-extreme sea states to minimize wave loading. The numerical model and simulation of the attenuator WEC were developed and completed using WEC-Sim, which is an open-source code that is appropriate for use in evaluating the dynamic response of the different WEC models in operational seas. The power production estimates were obtained from the Wave Energy Prize (WEP) sea states, which are representative of U. S. deployment sites, to calculate the average climate capture width that is used in the WEP ACE calculation. Preliminary capital expenditure costs were obtained assuming the base central steel cylinder mass was equal to the fluid displaced mass, minus the mass of the variable-geometry bags. The additional weight required to offset the additional buoyancy from the variable-geometry bags was assumed to come from the addition of seawater ballast. The variable-geometry attenuator model was found to have a similar power capture efficiency as a fixed-body model, but is expected to have a lower characteristic capital expenditure given its more streamlined profile, which demonstrates that variable-geometry modules may provide a realistic cost-reduction pathway to help design a more cost-competitive WEC.
Field Trials of Suction-Assisted Installation of Circular Steel Pipe Cofferdam in Silty Sand
Authors: Kim Jae-Hyun , Xin Zhenhua , Lee Ju-Hyung
Published: December 2020

The cofferdam is the temporary barrier to stop the flow of water from a construction site work such as a support column foundation at a river or offshore. It allows for working in the dry condition when the construction is done adjacent or within the waters. However, it is a major cause of delays and increased construction costs because additional works are required to stop the water flow. Recently, in order to overcome the limitations of the conventional cofferdam methods such as sheet pile or caisson tube cofferdams, a large-diameter steel pipe cofferdam method has been proposed which can be installed quickly using suction installation method. The steel pipe cofferdam method is characterized in that the top-lid of the steel pipe is located above the sea level in order to use it as a water barrier, unlike conventional suction buckets where the whole structures are submerged. In this study, the circular steel pipe cofferdam with a 5 m inner diameter was fabricated and the installation tests were conducted on silty sand at the Saemaguem test site. During the experiment, variations of suction pressure and inclination of the steel pipe cofferdam were measured and post-analyzed. This study verified the new steel pipe cofferdam method and confirmed that the suction installation method can be successfully used for various purposes on the offshore structures.
Research on the Static and Dynamics Characteristics of Soft Yoke Mooring System Based on Multi-Rigid Body Interaction
Authors: Wang Hongwei , Zhang Zizhao , Ma Gang , Ma Rongtai , Yang Jie
Published: December 2020

Select the common mooring system-soft yoke mooring system as the research object. The soft yoke mooring system is regarded as a structure composed of multiple rigid bodies, and the theoretical analysis of multi-body dynamics is used to discuss the interaction of multi-rigid bodies.

The classical HYSY113 FPSO is selected as an example, for the soft yoke mooring system, the stiffness characteristics and static restoring force curved compared with those of software OrcaFlex, and they are in good agreement, which verify the reliability of the formula derived, and it is a prerequisite for the accurate simulations in further steps. Coupled analysis to the whole system in time domain is also carried out both in OrcaFlex and AQWA, and the representative response of the FPSO under different environmental conditions is compared, the results are consistent well with each other. It is a good reference for the future study in this field. Good static characteristics are a prerequisite for accurate analysis of time-domain motion. By comparing the results in the time domain, it is found that under the same working conditions, the analysis results calculated by different commercial software (AQWA and OrcaFlex) may be different. We need to perform design analysis based on the characteristics of the software.
The Role of Engineering Critical Assessment in the Life Extension of Risers Connected to Floating Systems
Authors: Mekha Basim , Gordon Robin
Published: December 2020

As many offshore production systems approach the end of their original Design Life, Operators are faced with the choice of either decommissioning or demonstrating that the original Design Life can be extended (Life Extension). Life extension requires the Operator to perform detailed engineering analyses to verify that the system can be operated safely over the period of Life Extension. In many cases this requires detailed fatigue analysis and inspection programs to demonstrate that original fabrication flaws or fatigue cracks that may have existed during the welding of the riser joints or initiated over the original Design Life will not grow to a critical size resulting in failure.

Engineering Critical Assessment (ECA) is now routinely applied in the design and fabrication of new offshore riser systems to develop girth weld flaw acceptance criteria. The resulting flaw acceptance criteria ensure that fabrication flaws will not extend to a critical size over the Design Life and thus the riser still meet its calculated fatigue life. Although ECA procedures for new construction are well established and standard practices have been adopted throughout the industry, ECA procedures for Life Extension have not yet evolved to the same level of acceptance.

This paper will review specific issues associated with applying ECA to support Life Extension of offshore Riser Systems. The paper will provide the overall ECA philosophy and methodology for life extension to be adopted for the historical (hindcast or Phase 1) and future (forecast or Phase 2) analysis of the risers. Some thoughts will also be given to the approach implemented to take advantage of the actual weld fabrication data with the focus on the fatigue critical sections of the risers. Finally, the paper will address the requirements for riser in-situ inspection and how the results could be analyzed and applied to the life extension analysis in conjunction with the ECA analysis.
Experimental Study on the Flow Around a Rotating Cylinder
Authors: Rheem Chang-Kyu
Published: December 2020

The flow around a rotating cylinder has been investigated at the experimental water basins. The tangential velocity generated by the rotation of the cylinder decreases linearly with the logarithmic value of the distance from the cylinder surface, and has a constant distribution in the radial direction regardless of the rotation speed. The distance at which the tangential velocity becomes zero is about 4.35 times of the cylinder radius from the cylinder center. The energy transfer is greater near the cylinder than far from the cylinder and proportional to the proportionality coefficient A of the linear equation of velocity distribution. In a narrow water basin, the influence of the rotation is not absorbed completely to the water and a flow was formed in the water basin.
Hydrokinetic Energy Conversion by Flow-Induced Oscillation of Two Tandem-Cylinders of Different Stiffness
Authors: Yuan Wenyong , Sun Hai , Beltsos Nicholas , Bernitsas Michael M.
Published: December 2020

The VIVACE (Vortex-Induced Vibration for Aquatic Clean Energy) Converter harnesses hydrokinetic energy by enhancing flow-induced oscillations (FIOs) of elastically supported rigid cylinders in a river, tide, or ocean current. The harnessing power depends on the intensity of the oscillation, which is a consequence of the flow-structure interaction. The inflow condition for the downstream (2nd) cylinder is slowed down and perturbed by the upstream (1st) cylinder, due to the shielding effect. Therefore, the optimal structural parameters, i.e., stiffness and damping ratio, for the 2nd cylinder may be different from the 1st cylinder, in terms of energy harnessing.

To improve the performance of the VIVACE Converter, a series of experiments are conducted in a recirculating water channel, with various stiffness combinations of two cylinders in tandem. Three center-to-center spacings, six damping ratios, and seven combinations of spring stiffness are tested. The stiffness of the 1st cylinder, K1, is 600 N/m or 1,000 N/m, while the stiffness of the 2nd cylinder, K2, varies from 400 N/m to 1,200 N/m in increments of 200N/m. Results show that K2 does not affect the energy harnessing power in vortex-induced vibration (VIV) occurring at low speeds, but has great influence on the harnessing power at higher velocities in the transition region from VIV to galloping and in galloping. Decreasing K2 onsets and enhances galloping at lower flow velocity and harnesses up to 110% more energy than the case of K1 = K2. For K1 = 1,000 N/m, the harnessed power is the same for all the combinations of K1 and K2. The overall performance is best when K1 = K2. As spacing increases, the impact of K2 is diminished as explain by the dependence of power on the amplitude and frequency of cylinder oscillations.
Retracted: “Numerical Simulation and Experimental Research of Hydrophone Flow Noise” [ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering, Volume 6B: Ocean Engineering, Virtual, Online, August 3–7, 2020, Conference Sponsors: Ocean, Offshore and Arctic Engineering Division, ISBN: 978-0-7918-8438-6, Copyright © 2020 by ASME. Paper No. OMAE2020-19121, V06BT06A057; 7 pages; doi: 10.1115/OMAE2020-19121]
Authors: ASME
Published: December 2020

This paper was removed from publication at the author’s request. January 15, 2021.

Copyright © 2021 by ASME
World’s First Carbon Sequestration Project in Salt Caverns Built Offshore in Ultra Deep Water in Brazil
Authors: da Costa Pedro Vassalo Maia , da Costa Alvaro Maia , Meneghini Julio Romano , Nishimoto Kazuo , Assi Gustavo , Ebecken Nelson Francisco Favilla , Pinguelli Rosa Luiz , Miranda Antonio Carlos de Oliveira , Goulart Mariana Barbero Ribeiro , Bergsten Andre , Brandão Camila
Published: December 2020

In 2006, giant oilfields were discovered in Brazil in a water depth of ∼ 2200 m and under a caprock of 2000 m of continues salt rock overlaying the reservoirs, called pre-salt. Currently more than a half of the Brazilian oil and gas production comes from these reservoirs. However, some of these assets have big Oil & Gas ratio with a high level of CO2 contamination, which are currently being reinjected in the reservoirs. This procedure gradually increases the CO2 content associated with the oil extracted, reducing well productivity and leading to high costs of CO2 and CH4 separation by the membrane technology. The Research Center for Gas Innovation (RCGI) located at the State University of São Paulo in Brasil, sponsored by Shell Brazil, is developing a technology that uses the thick layer of salt rock overlying the pre-salt reservoirs to build caverns where the contaminated gas will be injected and decontaminated. After 2 years of extensive research, several studies have been carried out to analyze the main critical aspects of the technology in order to evaluate its feasibility, and now it has been decided to advance to the field proof stage. The salt dome studied can accommodate the construction of 15 caverns, thus providing the confinement of approximately 108 million tons of CO2. Before the system be construct in full scale, it was decided to initially build an experimental cavern with smaller size to obtain field parameters of the final design of the caverns. This paper describes this development denominated Offshore Salt Cavern Ultra-deep Water CCS System, that aims to perform the natural gas storage, a natural gravitational separation between CO2 / CH4 inside the caverns, and the confinement of CO2 (CCS). It presents important results related to structural integrity analysis of the giant and experimental caverns, well design using the same methodology applied in more than 200 projects of the pre-salt oil wells, instrumentation plan of the experimental cavern, storage capacities and other relevant data. If the economics proves feasible, this offshore gas storage station will be the first of its kind and possibly the biggest CCS Project in the world.
A Random Method for Calculation of Hoisting Drag
Authors: Qiu Hongyuan , Yang Jianming , Rideout Geoff , Butt Stephen
Published: December 2020

In reality, downhole conditions are highly unpredictable due to many uncertain and inconsistent factors, such as the uncertainty of the friction and contact between drillstring and bore-hole. As friction and contact are crucial components in torque and drag calculation, it is meaningful and practical to consider their uncertainty. This paper presents a random method for calculation of hoisting drag. Firstly, the finite element method (FEM) is used for hoisting drag calculation of a directional drilling well using Adanoy’s method in the deterministic case. Then two strategies are taken to model the random component in the downhole. The first strategy considers the randomness of the downhole friction. Instead of being a deterministic value, the friction coefficient is considered as Gaussian. The second strategy considers the randomness of contact between drillstring and wellbore. As a result, the drillstring is no longer continuously contacting with the wellbore in the curved section of well profile, which can help avoid overestimating torque and drag. Parametric studies on both strategies are conducted. Monte Carlo (MC) simulation is employed for statistical analysis. The probability density distributions and mean values of drag will be studied. The methodology can be extended into torque or drag calculation in lowering, ream in and ream out drilling conditions. Results from this paper indicate that surface hoisting drag is nearly Gaussian when the friction coefficient is Gaussian. The contact loss leads to considerable reduction in the surface hoisting drag when contact uncertainty is considered. The work of this paper will help estimate the range of surface drag and torque, which allows the well planner to develop a risk assessment for a challenging well trajectory.
Optimization of Both the Layout of an Array and the Buoy Dimension for Two Types of Arrays
Authors: Lyu Jianyang , Abdelkhalik Ossama , Zou Shangyan
Published: December 2020

This paper explores optimal configuration of both dimension and layout of Wave Energy Converter (WEC) arrays with full interaction and exact hydrodynamics. Arrays in this research contain devices that operate in heave mode and also devices that operate in pitch mode. The hydrodynamic interaction between buoys in the array is studied and higher q-factors is achieved using optimization. This study includes optimization results for arrays of only heave-mode buoys and hybrid arrays of 2 types of devices that has been mentioned above. Each of the heave-mode arrays contain 3, 5, and 7 buoys respectively while the hybrid arrays have arbitrarily selected configurations of the type of devices for comparison. This simulation uses impedance matching control which provides theoretical maximum level of power. The results indicates it is essential to optimize array layout simultaneously with the dimension of each buoy. Meanwhile, the mode of motion of the devices in an array is a significant factor in designing the array under complex ocean environment, and better performance of the array is achieved when the configuration is selected properly.
Numerical Investigation on Behaviors of Stiffened Large Suction Cap for Offshore Suction Cofferdam
Authors: Kim Jeongsoo , Jeong Yeon-Ju , Park Min-Su , Song Sunghoon
Published: December 2020

This study introduces a large offshore cofferdam installed by suction, unlike conventional ones such as a sheet-pile type, and proposes an effective suction cap for the cofferdam. In structural design view of the cofferdam, there are several critical issues due to its large size. This study conducted structural analyses of stiffened caps for large offshore suction cofferdam using fully nonlinear finite element models, and analyzed changes in behaviors of the cap due to stiffener arrangements to provide design insights. For finite element models, the diameter and the thickness of the suction cap (circular plate only) are 20m and 0.07m, respectively. Suction pressure on the cap was assumed to be 100kPa, all parts of the cofferdam except the cap are considered as boundary conditions. By investigating conventional suction anchors, several stiffener arrangement patterns on the cap of suction cofferdam were derived, and each arrangement was estimated by comparing stress and deformation of the cap. Also, reaction distributions on the edge of the cap were investigated to analyze effects of the stiffener arrangement on the interface behaviors between cap and cofferdam.
Development and Verification of Modeling Practice for CFD Calculations to Obtain Current Loads on FPSO
Authors: Koop Arjen , Yeon SeongMo , Yu Kai , Loubeyre Sebastien , Xu Wei , Huang Jerry , Vinayan Vimal , Agrawal Madhusuden , Kim Jang
Published: December 2020

Current loads are important input parameters for mooring studies. To accurately predict the motions of moored vessels these quantities should be determined with confidence in the values. Traditionally, these quantities have been determined using model tests in water basins or in wind tunnels. With recent advancements in CFD modeling, the offshore industry has started using CFD as an alternative tool to compute current loads on FPSO’s. In order to help adopt CFD as a widely accepted tool, there is a need to develop confidence in CFD predictions. Therefore, a practical CFD Modeling Practice is developed within the Reproducible Offshore CFD JIP. The Modeling Practice describes the geometry modeling, computational mesh, model set-up and post-processing for these types of CFD calculations. This Modeling Practice is verified and validated by five independent verifiers against model test data, such that reproducible and accurate results can be obtained by following the Modeling Practice.

This paper provides an overview of the developed Modeling Practice and the calculated CFD results from the verifiers. The CFD Modeling Practice is benchmarked against available model test results for a barge-type and a tanker-shaped FPSO. By following this Modeling Practice, the CFD predictions for CY and CMZ are within 10% from all verifiers and within 10% from the model test results. Larger differences may be obtained for CX, depending on local grid resolution and turbulence model used, but also due to larger experimental uncertainty for this quantity.
A Generic Allocation Algorithm for Optimal 6dof Motion Control Including Interaction Effects and Physical Limitations
Authors: van Daalen Ed
Published: December 2020

In this paper we consider the allocation problem within the context of optimal motion control for floating or submerged bodies. The purpose of our research is to develop an allocation algorithm which allows for (1) multiple bodies with up to six modes for each body, (2) arbitrary actuator types — azimuthing thrusters, propeller-rudder systems etc., (3) arbitrary objective functions, (4) interaction effects such as forbidden zones, and (5) physical limitations such as saturation.

Some ideas presented in [1, 2] were generalised to more widely applicable concepts. Each body has an arbitrary number of actuators, each actuator has an arbitrary number of degrees of freedom. Interaction effects are modelled by means of state-dependent effectivity coefficients. Coupled states, such as propeller thrust and torque, are modelled as linearised constraints. The constrained optimization problem is solved with a combination of Sequential Quadratic Programming and Steepest Descent methods.

The Python implementation is coupled with MARIN’s extensible modelling framework (XMF). We demonstrate the generic allocation algorithm for an underwater vehicle with multiple actuator types, physical limitations and coupled states and for a surface vessel with two propeller-rudder systems and a bow tunnel thruster. The results show that the allocation algorithm is able to handle complex configurations with specific physical limitations and coupled modes while adopting a generic approach.
Development of a Protocol to Couple Wave and CFD Solvers Towards Reproducible CFD Modeling Practices for Offshore Applications
Authors: Bouscasse Benjamin , Ducrozet Guillaume , Kim Jang Whan , Lim Hojoon , Choi Young Myung , Bockman Arne , Pakozdi Csaba , Croonenborghs Eloïse , Bihs Hans
Published: December 2020

Generating waves inside the CFD domain is a topic of interest in the offshore and naval industry. For practical reasons it is useful to use a potential wave kinematic solver (PWKS) to generate incident waves and use this solution to initialize and propagate incident waves in the CFD solver. Protocols to transfer the wave data from PWKS to CFD solver have been developed to ensure the reproduction of the wave kinematics from a PWKS in CFD solvers. Based on the survey results from a number of PWKS and CFD solvers available, the paper presents the various ways to express the solution and what is needed to reconstruct the fields needed in the CFD.
Using Data Science and Artificial Intelligence to Enable Technology-Driven Offshore Opportunities
Authors: Nanda Subrat , Bhatia Meenakshi A.
Published: December 2020

Recent developments in data science are enabling new opportunities for marine and offshore operators to adopt a more effective asset management strategy. The crux of this strategy is to combine data analytics with maintenance records and operational experience to reduce unplanned downtime. This case study focuses on the assimilation and utilization of diverse and mostly unstructured data, which up until now was largely untapped in the marine and offshore industries. The information extracted from such sources is used to identify key trends in equipment reliability and to improve the understanding of assets’ conditions. Such insights are particularly useful for marine and offshore operators in making critical decisions relating to machinery: optimal resource allocation; proactive planning for planned maintenance events and maximizing overall asset availability. From a Classification Society’s perspective such as American Bureau of Shipping (ABS), this allows operators and/or owners to derive Class-based benefits like Condition-Based Maintenance (CBM).
Utilising Advanced Digital Technologies to Provide Automated Drilling Riser Fatigue Tracking to Support Condition Based Maintenance
Authors: Bohan Paul , Lang Donogh , Williams Dara
Published: December 2020

The traditional industry approach to drilling riser joint inspection and maintenance has centered on recertification of riser joints at fixed five-yearly intervals. There are significant potential efficiencies to be gained from moving to a condition-based maintenance regime where inspection intervals are determined based on the actual usage of the riser joint. One of the critical factors driving the requirement for inspection is the fatigue damage sustained by the riser joint during use.

This paper describes a unique drilling riser joint fatigue tracking system that uses the latest digital technologies, advanced automation processes and a state-of-the-art finite element model of the drilling riser to provide an accurate and efficient solution to the challenge of long-term riser joint fatigue tracking. The architecture and operation of the system is described in detail and the application of a fracture mechanics-based approach to fatigue calculation versus the traditional S-N curve-based approach is discussed.
Utilization of Ocean Water for CO2 Capture via Amine Scrubbing
Authors: Ratanpara Abhishek P. , Shaw Alexander , Deshpande Sanat , Kim Myeongsub
Published: December 2020

As the consumption of fossil fuel resources has continuously increased to meet global fuel demands for power generation, atmospheric emissions of greenhouse gases, particularly carbon dioxide (CO2), have rapidly increased over the last century. Increased CO2 emissions have caused serious international concerns about global warming, sea-level rise, and ocean acidification. Although post-combustion carbon capture technology that separates CO2 from flue gas in fossil fuel-fired power plants has contributed to significant migration of atmospheric CO2 emissions, this approach generates considerable amounts of toxic wastewater containing a heavy chemical which is difficult to treat, raises concerns about acute corrosion of metal structures in the facility, and waste of significant amounts of freshwater. In this research, we are particularly interested in reducing the use of freshwater for CO2 capture and generating carbonate minerals, byproducts of CO2 with calcium (Ca2+) or magnesium ions (Mg2+) in ocean water which are useful building blocks for marine animals, such as seashells and coral reefs. In our experimental approach, we attempted to use ocean water with different monoethanolamine (MEA) concentrations and compared the CO2 capturing efficiency with that in DI water. We found that there are considerable benefits of the use of ocean water in CO2 dissolution, showing that a replacement of freshwater with ocean water would be a possible option. In the future, we will further enhance the dissolution of CO2 in ocean water by using nanoparticle catalysts without using MEA, which will be an environmentally friendly method for CO2 capture.
Optimization Design of the Cross-Section of the Umbilical Based on the Pseudo Mechanical Mechanism
Authors: Yang Zhixun , Yin Xu , Shi Dongyan , Yan Jun , Wang Lifu , Lu Qingzhen , Yue Qianjin
Published: December 2020

Umbilical is a critical equipment in subsea production system for extracting offshore hydrocarbon resources, providing electrical and hydraulic power, control signal transmission and chemical injection. A diversity of components such as electrical cables, optical cables, steel tubes and filler bodies compose the cross-section of an umbilical. Different components perform different physical properties, so different cross-sections will present different geometrical characteristic, carrying capacities, thermal distribution, the cost and the ease of manufacture. Therefore, the cross-sectional design of the umbilical is a typical multi-objective optimization problem. The methodology of pseudo mechanical mechanism is introduced in this paper. Pseudo forces are assumed based on geometrical characteristics, carrying capacities and thermal productivities of different electrical cables, optical cables, steel tube and filler bodies. Each component is analogized to a sphere with different diameters on a funnel surface. Moreover, potential energy and interaction force between different components are defined to avoid the overlap and congestion. Then, the pseudo mechanical model is established and mathematics description is presented corresponding to the cross-section of an umbilical. Iteration algorithm procedure is given to solve this problem. Finally, a case of an umbilical is studied and the optimal cross-section is obtained, which is compared with the result used in practical engineering. It is shown that the methodology of the pseudo mechanical mechanism is effective to obtain the optimal design of cross-section of an umbilical.
Assessment of a Polyamide Used in Flexible Pipes After Aging in Deoxygenated Water
Authors: Costa Danyelle , Oliveira Geovanio , Cirilo Leilane , Costa Marysilvia
Published: December 2020

A high-performance polyamide grade of easy processability which presents excellent thermal and mechanical properties such as resistance to fatigue and creep is studied in this work. An accelerated aging of Polyamide 12 samples was performed in stainless steel autoclaves at 120°C in deoxygenated water at pH 8.7 in order to shorten the aging time and avoid oxidation. The samples were retrieved at distinct aging times which were enough to reach the asymptotic portion of the curve of corrected inherent viscosity (CIV) versus aging time. CIV measurements track modifications of the molecular weight due to hydrolysis. Afterwards, the samples were analyzed through their cross section in the core and edge layer in order to investigate changes due to diffusion effects. Differential scanning calorimetry (DSC) analysis assesses the degree of crystallinity and melting temperature. Thermogravimetric analysis (TGA) was employed in order to investigate changes in the thermal stability and the stage of degradation of the samples. Unlike conventional volumetric analysis techniques, the instrumented indentation tests (IIT) in micro-scale were performed to measure the mechanical properties such as elastic modulus (EIT) and hardness (HIT) along the thickness aiming to detect properties gradient between surface and core. The CIV measurements showed a decrease of 46.3% in the aged sample during the maximum aging time compared to the reference material.
Development of a GIS-Based System for Three-Dimensional Spatial Modeling of Offshore Site Investigation Information
Authors: Kim Mingi , Chung Choong-Ki
Published: December 2020

Offshore site investigation is time-consuming and relatively expensive compared to onshore site investigation, because it is affected by severe weather conditions and has low accessibility from the land. Due to these economic and spatial-temporal constraints, it is essential to integrate the available site investigation information for the planning and design of offshore infrastructures. In this study, a GIS-based system was developed to manage and utilize the offshore site investigation data using opensource software. The system mainly performs the function of modeling the geo-information in three dimensions based on the offshore site investigation database. Through the input module, borehole data, geophysical survey data and numerical terrain information are standardized and stored in the database. The three-dimensional spatial modeling module performs outlier analysis of borehole data, subsurface geo-layer stratification, and interpolation of geotechnical properties. For the geo-layer stratification, the geostatistical integration method of borehole and geophysical datasets is adopted as well as conventional geostatistical methods. The optimization method of the results from geostatistical conditional simulation can be used for three-dimensional modeling of geotechnical property. The geoinformation predicted by the analysis module is inserted back into the database. Although this system is designed for offshore site investigation information, it can be used to manage inland and onshore site investigation information. Three-dimensional spatial modeling of site investigation information of an expressway construction site in South Korea was carried out using the developed system and its applicability was verified.
Development and Validation of Passive Yaw in the Open-Source WEC-Sim Code
Authors: Forbush Dominic D. , Ruehl Kelley , Ogden David , van Rij Jennifer , Yu Yi-Hsiang , Tom Nathan
Published: December 2020

A passive yaw implementation is developed, validated, and explored for the WEC-Sim, an open-source wave energy converter modeling tool that works within MATLAB/Simulink. The Reference Model 5 (RM5) is selected for this investigation, and a WEC-Sim model of the device is modified to allow yaw motion. A boundary element method (BEM) code was used to calculate the excitation force coefficients for a range of wave headings. An algorithm was implemented in WEC-Sim to determine the equivalent wave heading from a body’s instantaneous yaw angle and interpolate the appropriate excitation coefficients to ensure the correct time-domain excitation force. This approach is able to determine excitation force for a body undergoing large yaw displacement. For the mathematically simple case of regular wave excitation, the dynamic equation was integrated numerically and found to closely approximate the results from this implementation in WEC-Sim. A case study is presented for the same device in irregular waves. In this case, computation time is increased by 32x when this interpolation is performed at every time step. To reduce this expense, a threshold yaw displacement can be set to reduce the number of interpolations performed. A threshold of 0.01° was found to increase computation time by only 22x without significantly affecting time domain results. Similar amplitude spectra for yaw force and displacements are observed for all threshold values less than 1°, for which computation time is only increased by 2.2x.
CFD Investigation on the Hydrodynamic Characteristics of Blended Wing Unmanned Underwater Gliders With Emphasis on the Control Surfaces
Authors: Guggilla Mukesh , Rajagopalan Vijayakumar
Published: December 2020

Underwater Gliders are unique buoyancy propelled oceanographic profiling vehicles. Their speed and endurance in longitudinal motion are affected by the symmetry, sweep dihedral angle and span of the control surfaces. In the low-velocity regime, these parameters can be varied to examine the flow around the glider. They also affect the lift-to-drag ratio (L/D) essential for the manoeuvring path in longitudinal and transverse motions. In this paper, the sweep angle of the main wing of a blended wing autonomous underwater glider configuration is varied as 10°, 15°, 30°, 45° and 60° and the resulting hull forms are numerically simulated in the commercial software, STARCCM+. The main wing is a tapered NACA0018 section (taken as per the general arrangement requirement) with 1.5m chord at the root and 0. 1m at the tip. The numerical model is validated using the CFD results of NACA0012 airfoil from Sun.C et al, 2015 [1]. The hydrodynamic forces are obtained by varying the angle of attack (α) of the body from −15° to 15°, for flow velocity of 0.4m/s. The hydrodynamic coefficients (lift-to-drag ratios) and flow physics around the wing are analyzed to arrive at an optimum Lift-to-drag ratio for increased endurance.
In Service Experiences With Ship-Shaped Floating Production Units
Authors: Halsne Marita , Oma Narve , Ersdal Gerhard , Kvitrud Arne , Leonhardsen Roger L. , Langøy Morten , Andersen Terje , Bjørheim Lars G.
Published: December 2020

FPSOs and FSOs have been used on the Norwegian continental shelf for petroleum production, storage and offloading since the 1980’s and have been increasingly common since the end of the 1990’s. During these years a significant amount of experience has been gathered.

On the Norwegian Continental Shelf (NCS) shipowners and operators are obliged to report damages and incidents to the Petroleum Safety Authority Norway (PSA).

This article gives an overview of reported incidents related to the structural and maritime systems on offshore ship shaped units in the petroleum activity (FPSOs and FSOs) on the Norwegian Continental Shelf. Reported incidents are summarised with a focus on the period 2000 to 2019. The incidents include cracks, dents, corrosion, turret incidents, green water, position keeping systems, stability and ballasting, collisions and incidents related to the offloading systems as reported by operators and shipowners to the PSA.

A summary of the reported damages and incidents are discussed with respect to common causes based on available data. The importance and the possible consequences of such incidents are further discussed.
Characterization of the Rheological Behavior of Drilling Fluids
Authors: Cayeux Eric , Leulseged Amare
Published: December 2020

It is nowadays well accepted that the steady state rheological behavior of drilling fluids must be modelled by at least three parameters. One of the most often used models is the yield power law, also referred as the Herschel-Bulkley model. Other models have been proposed like the one from Robertson-Stiff, while other industries have used other three-parameter models such as the one from Heinz-Casson.

Some studies have been made to compare the degree of agreement between different rheological models and rheometer measurements but in most cases, already published works have only used mechanical rheometers that have a limited number of speeds and precision. For this paper, we have taken measurements with a scientific rheometer in well-controlled conditions of temperature and evaporation, and for relevant shear rates that are representative to normally encountered drilling operation conditions. Care has been made to minimize the effect of thixotropy on measurements, as the shear stress response of drilling fluids depends on its shear history. Measurements have been made at different temperatures, for various drilling fluid systems (both water and oil-based), and with variable levels of solid contents.

Also, the shear rate reported by the rheometer itself, is corrected to account for the fact that the rheometer estimates the wall shear rate on the assumption that the tested fluid is Newtonian. A measure of proximity between the measurements and a rheological model is defined, thereby allowing the ranking of different rheological behavior model candidates. Based on the 469 rheograms of various drilling fluids that have been analyzed, it appears that the Heinz-Casson model describes most accurately the rheological behavior of the fluid samples, followed by the model of Carreau, Herschel-Bulkley and Robertson-Stiff, in decreasing order of fidelity.
The Status of Arctic Offshore Pipeline Standards and Technology
Authors: Paulin Mike , Caines Jonathan , Davis Amy , DeGeer Duane , Cowin Todd
Published: December 2020

Offshore pipelines in an Arctic or ice-covered environment face unique challenges different from traditional subsea pipeline design. In 2018, Intecsea as lead consultancy delivered a report to the US Bureau of Safety and Environmental Enforcement (BSEE) Alaska Region which provided a comprehensive review and gap analysis of the Status of Arctic Pipeline Standards and Technology. The objective of this study was to provide BSEE with a comprehensive review and gap analysis of current offshore Arctic pipeline design standards, codes and regulations pertaining to design and development of offshore pipelines in the Arctic, and to report on the state-of-the-art and emerging technologies for offshore pipelines in Arctic applications. Project development information from nine existing offshore Arctic pipelines in the U.S., Canada, and Russia was summarized, as well as guidelines and industry best-practice for monitoring and leak detection.

This paper provides an overview of the results of this study; what offshore Arctic-specific pipeline design and construction challenges may entail, how they have been overcome in past projects, perceived gaps in regulations, and technology advancements that may help with future developments. This paper also summarizes the results of a comprehensive review and gap analysis of Arctic pipeline standards, assessment of the suitability of a single-walled versus pipe-in-pipe system for Arctic applications and presents information on some of the advancements in pipeline design, installation, operations and repair solutions that may be applicable to an Arctic environment.
Modelling Wave-Current-Turbulence Interactions for Tidal Energy Applications
Authors: Venugopal Vengatesan , Vögler Arne
Published: December 2020

This paper presents the nature of turbulence parameters produced from 3-dimensional numerical simulations using an ocean scale wave-tidal current model applied to tidal energy sites in the Orkney waters in the United Kingdom. The MIKE 21/3 coupled wave-current model is chosen for this study. The numerical modelling study is conducted in two stages. First, a North Atlantic Ocean large-scale wave model is employed to simulate wave parameters. Spatial and temporal wind speeds extracted from the European Centre for Medium Range Weather Forecast (ECMWF) is utilised to drive the North Atlantic wave model. Secondly, the wave parameters produced from the North Atlantic model are used as boundary conditions to run a coupled wave-tidal current model. A turbulence model representing the turbulence and eddy viscosity within the coupled model is chosen and the turbulence kinetic energy (TKE) due to wave-current interactions are computed. The coupled model is calibrated with Acoustic Doppler and Current Profiler (ADCP) measurements deployed close to a tidal energy site in the Inner Sound of the Pentland Firth.

The model output parameters such as the current speed, TKE, horizontal and vertical eddy viscosities, significant wave height, peak wave period and wave directions are presented, and, their characteristics are discussed in detail.
Occurrence Frequency of a Triple Rogue Wave Group in the Ocean
Authors: Bitner-Gregersen Elzbieta M. , Gramstad Odin , Magnusson Anne Karin , Sames Pierre C.
Published: December 2020

At 18:20 November 30, 2018, a triple rogue wave group was recorded in the central North Sea. These three consecutive rogue waves, subsequently called “Justine Three Sisters”, were recorded at a single point by a SAAB REX radar. The Norwegian Meteorological Institute’s operational wave forecast model and WAMOS marine radar’s measurements show that they appeared in a crossing sea condition with angle between wind sea and swell being 60 degrees, with swell energy much lower than the wind sea energy but with approximately the same peak frequency. We use the nonlinear wave model HOSM (Higher Order Spectral Method) to investigate frequency of occurrence of such an event in the ocean. Input to the simulations has been a wave frequency-directional spectrum generated by the operational wave forecast model of the Norwegian Meteorological Institute having 4 km resolution. The investigations show that occurrence of three consecutive rogue waves at a single point is a very seldom event in the ocean, which can, however, be reproduced in time domain HOSM simulations if sufficient number of realizations is performed. With the HOSM model being able to capture essential physics of ocean waves, we can assume to predict occurrence frequency from simulations. The study demonstrates also the effect of sampling variability on sea surface elevation and illustrates limitation of single point measurements, using the sea state in which “Justine Three Sisters” occurred as an example. Importance of using spacetime statistics in description of ocean waves as well as in design and operations of marine structures is also discussed.
A Numerical Investigation Into Hydrodynamic Interaction Coefficients for Multiple Freely Floating Bodies in Waves
Authors: Ali Mir Tareque
Published: December 2020

When two or more bodies are floating in waves in each other’s vicinity, the fluid loading on the separate bodies will be influenced by the presence of the neighboring bodies. The wave loads on each body are affected, because of sheltering or wave-reflection effects due to the presence of surrounding floating body, while additional loads are exerted by the radiated waves, which are produced by the motions of the neighboring bodies. For a multi-body system, it is important to accurately compute the hydrodynamic coefficients and interaction coefficients, since these parameters will be used later to solve the 6xN simultaneous equations to predict the motion responses (where N is the number of freely floating bodies in the multi-body system). This paper aims to investigate the hydrodynamic interaction coefficients for two three dimensional (3-D) bodies floating freely in each other’s vicinity. Since the nature of hydrodynamic interaction is rather complex, it is usually recommended to study this complicated phenomenon using numerically accurate scheme. A computer code developed using 3-D source distribution method which is based on linear three-dimensional potential theory is used and the validation of the computer code has been justified by comparing the present results with that of the published ones for hydrodynamic coefficients and interaction coefficients of two bodies closely floating in regular waves. The calculated results for box-cylinder model are compared with the published results and the agreement is quite satisfactory. Numerical simulations are further conducted for two closely floating rectangular barges of side-by-side position in regular waves. During the computations of hydrodynamic coefficients and interaction coefficients for multi-body model, the separation distance between the floating bodies have been varied. Finally, some conclusions are drawn on the basis of the present analysis.
Investigation of Stick-Slip Severity in a Coupled Axial-Torsional Drillstring Dynamics Using a Two DOF Finite Element Model
Authors: Wiktorski Ekaterina , Sui Dan
Published: December 2020

Drilling industry focuses nowadays on process optimization and cost reduction. Unwanted events should be predicted and avoided to increase drilling efficiency, improve safety, and save costs. Development and application of mathematical models enable us to understand the dynamics of the drilling process, learn parameter interaction and regulate system behavior. It is also a way to reduce the risk of occurrence of such events or mitigate negative outcomes.

Challenges in two-dimensional modeling of drillstring vibrations include: (1) correct and precise interpretation of coupled two-dimensional motion, (2) use of sub-models, as down-hole weight on bit (WOB) model, downhole torque on bit (TOB) model and friction model, and (3) proper definition of associated boundary conditions. In this paper, we propose a two-dimensional axial-torsional model that considers these criteria. We present a new way to calculate downhole WOB, which can be used as an alternative to a constant WOB value. Dynamic boundary conditions are introduced to represent the respective phases of stick-slip. The model is formulated using the finite element method and intended for vertical wells. The main goal for developing this model is evaluation of the effect of surface rotational and axial velocities on the downhole drill bit dynamics. A dimensionless parameter, stick-slip severity, is used to represent the intensity of torsional oscillations.

The developed model is based on mathematical relations and defined boundary conditions, which describe the dynamics of drillstring during stick-slip events. The model allows to study the effect of up to twelve input parameters on stick-slip severity to determine a suitable range. Results presented in this paper show that axial velocity applied from the surface may cause initiation of stick-slip, which in turn provokes axial vibrations. Increase in surface axial velocity leads to higher amplitude of downhole torsional oscillations. To mitigate stick-slip, surface rotational velocity should be increased.