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research-article  
Rodolfo Marcilli Perissinotto, William Monte Verde, Jorge Luiz Biazussi, Marcelo Souza Castro and Antonio C. Bannwart
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4042000
The objective of this research is to investigate the velocity of oil drops within the impeller of an electrical submersible pump (ESP) working with oil-in-water dispersion flows at different operational conditions. An experimental study was conducted using an ESP prototype with a transparent shell designed to enable flow visualization within the impeller channels. The tests were performed at three rotational speeds, 600, 900, 1200 rpm, for three water flow rates, 80%, 100%, 120% of the best efficiency point (BEP). A highspeed camera with a lighting set captured images of the oil-in-water dispersion at 1000 frames per second. The images observation suggests the presence of a turbulent flow in the impeller. The turbulence, associated with high rotation Reynolds numbers, causes the oil drops to become smaller as the impeller rotational speed and the water flow rate increase. Despite this rotating environment, the oil drops generally have a spherical shape. Regarding the kinematics, the images processing reveals that the velocity of oil drops has a magnitude around a unit of m/s. The velocity depends on the oil drop position in the channel: oil drops that stay close to a suction blade have significantly higher velocities than oil drops that stay close to a pressure blade. Considering a complex flow with water velocity profiles and pressure gradients, the analysis of oil velocity curves indicates the occurrence of accelerations that may be caused by drag and pressure forces acting on the oil drops.
TOPICS: Impellers, Two-phase flow, Experimental analysis, Water, Flow (Dynamics), Turbulence, Blades, Pressure, Rotation, Pressure gradient, Shapes, Shells, Submersibles, Transparency, Suction, Drag (Fluid dynamics), Reynolds number, Flow visualization, Engineering prototypes, Pumps, Kinematics
research-article  
Xiaoxian Guo, Zhen Gao, Xin Li, Jianmin Yang and Torgeir Moan
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041998
A coupled numerical model has been developed and validated to study the fluid-structural interaction responses of a three-bladed tidal turbine in aligned waves and current. The unsteady blade element momentum (BEM) theory was combined with modal analysis for hydro-elastic calculation. Both the loading and deflection of the blade were studied. The dynamic loading on the blade due to structural deformation was much smaller than the wave-induced loading under linear wave conditions for the given condition.? The linear response amplitude operators (RAOs) of the loads and the blade tip deflections were obtained and used to predict the linear responses. Although both sum- and difference-frequency responses can be identified from time domain simulations, the wave-induced load and the deflection of the blade are dominated by the first-order contributions. The maximum deflection of the blade tip could reach 1.3 m (203%of the means) in the flapwise direction and 0.35 m (210%of the mean) in the edgewise direction with a wave peak period of 11.3 s and significant wave height of 5.5 m.
TOPICS: Waves, Blades, Deflection, Tidal turbines, Stress, Significant wave heights, Modal analysis, Dynamic testing (Materials), Boundary element methods, Engineering simulation, Momentum, Deformation, Fluids, Computer simulation, Simulation
research-article  
Amir R. Nejad, Erin E. Bachynski and Torgeir Moan
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041996
Common industrial practice for designing floating wind turbines is to set an operational limit for the tower-top axial acceleration, normally in the range of 0.2-0.3g, which is typically understood to be related to the safety of turbine components. This paper investigates the rationality of the tower-top acceleration limit by evaluating the correlation between acceleration and drivetrain responses. A 5 MW reference drivetrain is selected and modelled on a spar-type floating wind turbine in 320 m water depth. A range of environmental conditions are selected based on the long-term distribution of wind speed, significant wave height, and peak period from hindcast data for the Northern North Sea. For each condition, global analysis using an aero-hydro-servo-elastic tool is carried out for six one-hour realizations. The global analysis results provide useful information on their own - regarding the correlation between environmental condition and tower top acceleration, and correlation between tower top acceleration and other responses of interest - which are used as input in a decoupled analysis approach. The load effects and motions from the global analysis are applied on a detailed drivetrain model in a multi-body system (MBS) analysis tool. The local responses on bearings are then obtained from MBS analysis and post-processed for the correlation study. Although the maximum acceleration provides a good indication of the wave-induced loads, it is not seen to be a good predictor for significant fatigue damage on the main bearings in this case.
TOPICS: Spar platforms, Floating wind turbines, Wing spars, Stress, Bearings, Design, Turbine components, Fatigue damage, Waves, Servomechanisms, Safety, Wind velocity, North Sea, Significant wave heights, Water
research-article  
Samuel Kanner, Elena Koukina and Ronald W. Yeung
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041995
Real-time hybrid testing of floating wind turbines is con- ducted at model-scale. The semi-submersible, triangular plat-form, similar to WindFloat is built instead to support two vertical-axis wind turbines (VAWTs). On account of incongruous scaling issues between the aerodynamic and the hydrodynamic loading, the wind turbines are not constructed at the same scale as the floater support. Instead, remote-controlled (RC) plane motors and propellers are used as actuators to mimic only the tangential forces on the wind-turbine blades, which are attached to the physical (floater-support) model. On a VAWT, the tangential force, proportional to the torque on the turbine is applied, as this mimics the power production. A control algorithm is implemented using the wind-turbine generators to optimize the platform heading and hence, the theoretical power absorbed by the wind turbines. This experimental approach only seeks to recreate the aerodynamic force which contributes to the power production. In doing so, the generator control algorithm can thus be validated. The advantages and drawbacks of this hybrid simulation technique are discussed, including the need for low inertia actuators, which can quickly respond to control signals.
TOPICS: Optimization, Testing, Floating wind turbines, Wind turbines, Vertical axis wind turbines, Control algorithms, Actuators, Energy generation, Generators, Propellers, Signals, Turbines, Blades, Inertia (Mechanics), Torque, Aerodynamics, Motors, Simulation, Semi-submersible offshore structures, Fluid-dynamic forces
research-article  
Tomoaki Utsunomiya, Iku Sato, Osamu Kobayashi, Takashi Shiraishi and Takashi Harada
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041994
In this paper, numerical modelling and analysis of a hybrid-spar floating wind turbine is presented. The hybrid-spar consists of steel at the upper part and precast prestressed concrete (PC) at the lower part. Such a configuration is referred to as a hybrid-spar in this paper. The hybrid spar was successfully installed offshore of Kabashima island, Goto city, Nagasaki prefecture, Japan on October 18, 2013 (see OMAE2015-41544 [1] for details). In this paper, some details on numerical modelling of the hybrid-spar for design load analysis are presented. Then, the validation of the numerical analysis model is presented for a full-scale hybrid-spar model with 2 MW wind turbine. The comparison has been made for the natural periods and the response during rated power production test. Basically, both comparisons have shown good agreement between the measured values and the simulation, showing reliability of the developed code and the numerical model.
TOPICS: Modeling, Spar platforms, Floating wind turbines, Wing spars, Wind turbines, Numerical analysis, Steel, Computer simulation, Reliability, Prestressed concrete, Simulation, Stress, Ocean engineering, Design, Energy generation
research-article  
Inge Lotsberg
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041993
Fatigue design standards for offshore structures became needed with development of offshore structures in harsh environments like the North Sea during the 1970s. The need for fatigue design of ship structures became increased as more high strength steel was being used in these structures during the 1970s. New types of structures and structural components have been developed like tension leg platforms, floating production platforms and support structures for wind turbines. These structures are subjected to significant dynamic loading such that fatigue design becomes the main issue and relevant fatigue design standards are needed. This paper gives an overview of the development of fatigue design standards for marine structures over the last 40 years.
TOPICS: Fatigue design, Marine structures, Offshore structures, Dynamic testing (Materials), Structural elements (Construction), High strength steel, Ships, Wind turbines, Tension-leg platforms, North Sea
research-article  
Yanyan Sha, J⊘rgen Amdahl and Cato D⊘rum
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041992
The Norwegian Public Roads Administration is running a project 'Ferry Free Coastal Route E39' to replace existing ferry crossings by bridges across eight fjords in western Norway. Since most of the fjords are wide and deep, construction of traditional bridges with fixed foundations is not possible. Therefore, floating bridge concepts are proposed for the fjord-crossing project. Since the floating foundations of the bridges are close to the water surface, the concern of accidental ship collisions is raised. Considering the displacement and speed of the passing ships and the significant compliance of the bridge, interaction between the bridge and the ship can be significant should a collision occur. Many studies have been conducted on ship collision with bridge structures with a special focus on bridge piers. However, the research on ship collision with bridge girders is quite limited. The purpose of this study is to investigate the collision response of a floating bridge for ship-girder collision events. Both the local structural damage and the global dynamic response of the bridge are assessed. Local structural deformation and damage are first investigated by numerical simulations with detailed finite element models in LS-DYNA. Subsequently, the bridge global response to the collision loads is analyzed in USFOS using the force-deformation curves form the local analyses. By combining the local and global analysis results, a comprehensive overview of the bridge response during ship-girder collisions can be obtained.
TOPICS: Bridges (Structures), Girders, Collisions (Physics), Ships, Deformation, Damage, Water, Shorelines, Piers (Structural), Displacement, Dynamic response, Finite element model, Roads, Computer simulation, Construction, Stress
research-article  
Kazuhiro Iijima, Rika Ueda, Hitoi Tamaru and Masahiko Fujikubo
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041997
In this paper, the effect of weather routing and ship operations on the extreme vertical bending moment in a 6000TEU class large container ship which is operated in North Atlantic Ocean, is addressed. Direct time-domain nonlinear response simulation method taking account of the wave-induced vibrations is used in a combined manner with voyage simulations based on 10 years of meteorological data in the area. The probability distribution of the ship's operational parameters conditional upon the meteorological conditions, is considered. It is clarified that the severest wave condition with the significant wave height over 16m in the area, may not be encountered by the ship due to the weather routing and the extreme value is determined mostly by the wave condition much milder than the severest in the area. It is also found out that the ship speed assumed in the most contributing sea state strongly affects the extreme value of the total vertical bending moment since the wave-induced vibrations in the ship tends to be excited at faster speed.
TOPICS: Waves, Vibration, Ships, Simulation, Meteorology, Containers, Statistical distributions, Seas, North Atlantic Ocean, Significant wave heights
research-article  
Yordan Garbatov and Carlos Guedes Soares
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041991
The objective of the present study is to identify the most suitable corrosion degradation model, fitted with real corrosion depth measurement data sets and to reproduce the corroded steel plate surface as a function of time and spatial distribution using advanced statistical methods. An approach for adequately identifying the best-fitted model to real corrosion depth measurement data sets is employed. Two distinct statistical methods for generating a statistical representation of a corroded plate surface in the case of significant and insignificant correlation of the corrosion degradation are provided. A sequence dependent data analysis is performed based on the fast Fourier transform, which is used as an input for a random field modelling of corroded steel plate surfaces. The output of this study represents very important information about the corroded plate surface topology that can be used in any advanced finite element analyses of structural integrity assessment. The formulations can be adapted to any structural components and corrosion environments.
TOPICS: Steel, Corrosion, Modeling, Plates (structures), Fast Fourier transforms, Topology, Finite element analysis, Structural elements (Construction)
research-article  
Nicholas Fantuzzi and Fabio Borgia
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041999
Pistons are fundamental structural elements in any engineering practices such as mechanical, civil, aerospace and offshore engineering. Their strength strongly depends on buckling load and such information is a major requirement in the design process. Euler's linear buckling equation is the most common and most used model in design. It is well suited for linear elastic members without geometrical imperfections and nonlinear behavior. Several analytical and experimental investigations of typical hydraulic cylinders have been carried out through the years but most of the available standards still use a linear approach with many simplifications. Pistons are slender beams with not-uniform cross-section, which need a stronger effort than the classical Euler's approach. The present paper aims to discuss limitations of current DNV standards for piston design in offshore technologies when compared to classical numerical approaches and reference results provided by the existing literature.
TOPICS: Buckling, Pistons, Design, Offshore technology, Structural elements (Construction), Stress, Hydraulic cylinders, Ocean engineering, Aerospace industry
research-article  
Miguel Alfonso Calderon Ibarra, Fernando Jorge Mendes de Sousa, Luís Volnei Sudati Sagrilo and Ying Min Low
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041893
Short-term extreme response estimates are required in many areas of ocean and offshore engineering, such as steel risers design. As in many cases the response in non-Gaussian, a theoretical solution is usually not readily available for this purpose. Hermite transformation and Weibull-based models, among others, are some alternatives that have been used in connection with sampled response time series. In this work a new approach is investigated. Recently, a four-parameter distribution known as the shifted generalized lognormal distribution (SGLD) has been presented in the literature. One of its main advantages is that it covers regions of skewness-kurtosis not covered by other distributions of common use in engineering. In this paper, the performance of this distribution is evaluated in the extreme values' estimation of the utilization ratios of steel riser sections. Three alternatives for using SGLD are investigated in two case studies of different dynamic behavior. The first one is a SLWR (steel-lazy wave riser) connected to a turret-moored FPSO in 914m water depth, and the second is a SLWR connected to a spread-mooring FPSO in a water depth of 1400m. The results obtained by the SGLD-based analysis, which considered several simulation lengths, are compared to those obtained by means of an extreme value distribution fitted to episodical extremes obtained from many distinct realizations. The results of a traditional Weibull-fitting approach to the response peaks and those obtained with and Hermite transformation-based model are also presented for comparison.
TOPICS: Risers (Casting), Steel, Pipeline risers, Mooring, Water, FPSO, Log normal distribution, Simulation, Waves, Ocean engineering, Design, Fittings, Oceans, Time series
research-article  
Piotr Domagalski, Lars Morten Bardal and Lars Satran
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041816
This paper presents an analysis of stratification dependent mean velocity profiles measured in a Norwegian coastal wind climate, and its comparison with models available in the literature. For this purpose we use 3 years of observations from a 100 m meteorological mast located at the Fr⊘ya island (150 km west of Trondheim, Norway), equipped with a set of 2D ultrasonic anemometers. The presented analysis is preceded by a general description of the site wind climate, the atmospheric stratification, the surface roughness, and the surface layer height. Finally, the measured wind velocity profile is compared with selected models: the basic power and logarithmic law and the stability-corrected models: stability-corrected logarithmic wind profile, the Panofsky&Dutton model, the Peña boundary layer height corrected model and the correlation based Smedman and Högström model.
TOPICS: Wind, Climate, Stability, Wind velocity, Surface roughness, Boundary layers, Shorelines, Meteorology
research-article  
Diego Garcia Giraldo and Ronald W. Yeung
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041770
The Deepwater Horizon Mobile Offshore Drilling Unit (MODU) was one of several classes of floatable drilling systems. The explosion on April 20, 2010 led to fatalities and the worst oil spill in the USA. We present an independent estimate of the oil-flow rate into The Gulf caused by the drill-pipe rupture. We employed the NASA Moderate-Resolution Imaging-Spectroradiometer (MODIS) satellite photographs, starting from the days immediately following the disaster, to determine the magnitude of spill. From these images, we obtained the surface area of the spill and calculated the oil flow-rate by two different methods based on contrasting luminance within that area. The first assumes a constant thickness for the total area with upper and lower bounds for the thickness. The second separates the area into different patches based on the luminance levels of each. The probability-density function (PDF) of such luminance plots showed natural groupings, allowing patches be identifiable. Each patch maps to a specific thickness. This second approach provides a more accurate average thickness. With the assumption that evaporation and other loss amounted to ~40% of the spill, we obtained, from the first method, a flow rate ranging from 9,300 barrels per day (BPD) to 93,000 BPD. A value of 51,200 BPD was obtained using patch-separation method. This latter estimate was a plausible value, obtained from the current analysis, but with no details presented in an Extended Abstract in OMAE2012, is remarkably consistent with the "official US-Govt. estimates."
TOPICS: Flow (Dynamics), Gulf of Mexico, Satellites, Brightness (Photometry), Mobile offshore drilling units, Density, Imaging, NASA, Disasters, Evaporation, Pipes, Probability, Rupture, Separation (Technology), Explosions, Drills (Tools), Drilling, Resolution (Optics)
research-article  
Erik Veitch, David Molyneux, Jennifer Smith and Brian Veitch
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041761
The research investigates the influence of human expertise on the effectiveness of ice management operations. The key contribution is an experimental method for investigating human factor issues in an operational setting. Ice management is defined as a systematic operation that enables a marine operation to proceed safely in the presence of sea ice. In this study, effectiveness of ice management operations was assessed in terms of ability to modify the presence of pack ice around an offshore structure. This was accomplished in a full-mission marine simulator as the venue for a systematic investigation. In the simulator, volunteer participants from a range of seafaring experience levels were tasked with individually completing ice management tasks. Recorded from 36 individuals' simulations, we compared ice management effectiveness metrics against two independent variables: i) experience level of the participant, categorized as either cadet or seafarer, and ii) ice severity, measured in ice concentration. The results showed a significant difference in ice management effectiveness between experience categories. We examined what the seafarers did that made them more effective and characterized their operational tactics. The research provides insight into the relative importance of vessel operator skills in contributing to effective ice management, as well as how this relative importance changes as ice conditions vary from mild to severe. This may have implications for training in the nautical sciences and could help to inform good practices in ice management.
TOPICS: Bridges (Structures), Ice, Sea ice, Vessels, Simulation, Offshore structures, Engineering simulation, Human factors
research-article  
Jungao Wang, Rohan Joseph, Muk Chen Ong and Jasna B. Jakobsen
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041732
A free-hanging riser is a typical riser configuration seen in the disconnected drilling riser, the water-intake riser and the deep-sea mining riser. In offshore productions, these marine risers will move back and forth in water and further generate an equivalent oscillatory current around themselves, due to the vessel motions. Both in full-scale marine operations and model tests, it has been reported that such oscillatory current leads to riser vortex-induced vibration (VIV) and therefore causes structural fatigue damage. Recently, there have been some attempts to numerically predict vessel motion-induced VIV on the compliant production risers, with emphasize on relatively large Keulegan-Carpenter (KC) numbers. In the real marine operations, the risers experience small KC number scenarios during most of their service life. Therefore, the investigation of vessel motion-induced VIV under small KC number is of great significance, especially considering its contribution to the fatigue damage. In this paper, numerical investigation of VIV of a free-hanging riser attached to a floating vessel is carried out. A new response frequency model for vessel motion-induced VIV under small KC numbers is proposed and implemented in VIVANA. Validation of the proposed numerical methodology is performed against the published experimental results, where a good agreement is achieved.
TOPICS: Risers (Casting), Pipeline risers, Vessels, Vortex-induced vibration, Water, Fatigue damage, Marine drilling risers, Seas, Ocean engineering, Mining, Service life (Equipment)
research-article  
Yonghee Ryu, Bassam Burgan, Jaewoong Choi and Hee Sung Lee
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041718
A gas explosion in an offshore platform may result in loss of life, environmental impact, and critical damage to the facilities. In case of a strong explosion, certain safety critical structural elements of these facilities have to be designed to withstand high explosion loads. The present study discusses novel methodologies in explosion risk assessment for the safety critical structural elements and introduces a coupled Eulerian-Lagrangian (CEL) method to improve the accuracy of the dynamic structural response under the explosion loading. The design accidental load is defined by explosion risk analyses in terms of drag pressure, differential pressure, and overpressure. In the existing methods, an explosion pressure-time history is commonly simplified as a triangular shape and uniformly applied to the surface of structures. As a result, these methods cannot account for the interaction between elastic waves (normally solved by the Lagrangian method) in the structure and compression waves (normally solved by the Eulerian method) in air medium. The proposed CEL method, which is experimentally validated, leads to realistic predictions of dynamic response of structures compared to the existing methods. The plastic strains derived from the CEL analysis can be approximately 50% lower than the results of Lagrangian analysis. Therefore, significant potential weight reduction can be achieved using the CEL method for a gas explosion analysis.
TOPICS: Explosions, Safety, Offshore platforms, Pressure, Structural elements (Construction), Stress, Waves, Elastic waves, Blast effect, Design, Risk analysis, Compression, Dynamic response, Risk assessment, Shapes, Weight (Mass), Drag (Fluid dynamics), Damage
research-article  
David H. Menéndez Arán, Ye Tian and Spyros A. Kinnas
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041669
This paper describes the use of a lifting line model in order to determine the optimum loading on a marine turbine's blades. The influence of the wake and its geometry is represented through the use of a full wake alignment model. The effects of viscous drag are included through a drag-to-lift ratio. The results obtained for different number of blades and rotational velocities are compared. Various types of constraints are imposed in the optimization method in order to avoid abrupt changes in the designed blade shape. Once the optimum loading has been determined, the blade geometry is generated for given chord, thickness and camber distributions. Finally, a vortex-lattice method is used to verify the power coefficient of the designed turbines.
TOPICS: Turbine blades, Wakes, Blades, Geometry, Drag (Fluid dynamics), Shapes, Chords (Trusses), Optimization, Turbines, Vortices
research-article  
Sondre Sanden T⊘rdal and Geir Hovland
J. Offshore Mech. Arct. Eng   doi: 10.1115/1.4041643
In this paper a solution for estimating the relative position and orientation between two ships in 6 degrees of freedom using sensor fusion and an Extended Kalman filter approach is presented. Two different sensor types, based on time-of-flight and inertial measurement principles, were combined to create a reliable and redundant estimate of the relative motion between the ships. An accurate and reliable relative motion estimate is expected to be a key enabler for future ship-to-ship operations, such as autonomous load transfer and handling. The proposed sensor fusion algorithm was tested with real sensors (two motion reference units and a laser tracker) and an experimental setup consisting of two Stewart platforms in the Norwegian Motion Laboratory which represents an approximate scale of 1:10 when compared to real life ship-to-ship operations.
TOPICS: Sensors, Kalman filters, Ships, State estimation, Flight, Stress, Degrees of freedom, Algorithms, Lasers

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