bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Comparison of Three Floating Wind Turbine Concepts
Authors: Goupee Andrew J. , Koo Bonjun , Kimball Richard W. , Lambrakos Kostas F. , Dagher Habib J. 
Published: August 2013

Beyond many of the Earth’s coasts exist a vast deepwater wind resource that can be tapped to provide substantial amounts of clean, renewable energy. However, much of this resource resides in waters deeper than 60 m where current fixed bottom wind turbine technology is no longer economically viable. As a result, many are looking to floating wind turbines as a means of harnessing this deepwater offshore wind resource. The preferred floating platform technology for this application, however, is currently up for debate.
To begin the process of assessing the relative advantages of various platform concepts for floating wind turbines, 1/50th scale model tests in a wind/wave basin were performed at MARIN (Maritime Research Institute Netherlands) of three floating wind turbine concepts. The Froude scaled tests simulated the behavior of the 126 m rotor diameter NREL (National Renewable Energy Lab) 5 MW, horizontal axis Reference Wind Turbine attached via a flexible tower in turn to three distinct platforms, these being a tension leg-platform, a spar-buoy and a semi-submersible. A large number of tests were performed ranging from simple free-decay tests to complex operating conditions with irregular sea states and dynamic winds. The high-quality wind environments, unique to these tests, were realized in the offshore basin via a novel wind machine which exhibited low swirl and turbulence intensity in the flow field. Recorded data from the floating wind turbine models include rotor torque and position, tower top and base forces and moments, mooring line tensions, six-axis platform motions and accelerations at key locations on the nacelle, tower, and platform. A comprehensive overview of the test program, including basic system identification results, is covered in an associated paper in this conference.
In this paper, the results of a comprehensive data analysis are presented which illuminate the unique coupled system behavior of the three floating wind turbines subjected to combined wind and wave environments. The relative performance of each of the three systems is discussed with an emphasis placed on global motions, flexible tower dynamics and mooring system response. The results demonstrate the unique advantages and disadvantages of each floating wind turbine platform.
Detailed FSI Analysis Methodology for Subsea Piping Components
Authors: Chica Leonardo , Pascali Raresh , Jukes Paul , Ozturk Burak , Gamino Marcus , Smith Kevin 
Published: August 2013

Flow Induced Vibration (FIV) is one of the important phenomena that contribute to failure of subsea piping components. This paper addresses a detailed methodology to analyze the structural response caused by unsteady multiphase flow within a pipe. This fluid-structure interaction (FSI) study was conducted in a two-bend model of a rigid M-shaped jumper to estimate the stresses and pressure fluctuations and determine the level of risk of failure.
Initially, a risk assessment method was carried out to determine the likelihood of failure (LOF) due to flow induced turbulence. Following the screening method, a detailed “two-way coupling” FSI study is recommended. Coupling the Finite Element Analysis (FEA) program with the Computational Fluid Dynamics (CFD) program allows to perform the following assessments:
• Strength check (Allowable stress);
• Fatigue analysis, and;
• Engineering criticality assessment of welds.
The two-way coupling analysis also compares the structural natural frequencies to the slug frequencies. Depending on the percentage difference between the two frequencies, a conclusion can be drawn in terms of level of risk and address whether assessing FIV fatigue damage should be required for future examination.
Loads From Currents and Waves on Net Structures
Authors: Berstad Are Johan , Walaunet Jørgen , Heimstad Line Fludal 
Published: August 2013

The aquaculture industry has increased rapidly the last 20 years. In almost all fish farms, the fish is held captured in net cages. Net structures are built up with twines as shown in Figure 1.
Various parameters of importance for the loads to nets such as solidity, Reynolds number, flow angle relative to mesh and increased flow around twines compared to single twines. This paper outlines such effects.
This paper consider loads to net panels considering the net a sum of twines and then sum the forces twine by twine. Based on this approach the paper presents a calculation method for net meshes. The presented load formulation is valid for rectangular and diamond shaped meshes and is valid for any 3D orientation of flow relative to mesh.
The presented method for load calculation includes methodology for deriving the forces to a net structure based on knowledge of drag resistance for an individual twine. This methodology is compared with other published formulae and empirical data.
A formula is presented based on a twine in wake consideration. The presented formula is compared to measurements for test cases both in terms of a net panel and for a full cage model. Results show good agreement.
Experimental Evaluation of Vortex Induced Vibration Response of Straked Pipes in Tandem Arrangements
Authors: Blumberg Matthew , Tellier Elizabeth , Deka Dhyanjyoti , Zhou Tongming 
Published: August 2013

Vortex induced vibration (VIV) due to steady current flow can be a significant driver in the design of offshore riser systems, affecting riser global configuration, component details and overall subsea architecture. Helical strakes are known to reduce VIV but the degree of effectiveness can vary considerably depending on strake pitch, fin height and more importantly, current flow regime. In addition, the amplitude of VIV and the effectiveness of VIV suppression strakes depends on the inclination of flow to the riser (incidence angle) and presence of wake effects from adjacent risers. Test and field data regarding suppression of riser VIV by strakes is not extensively available in the public domain. This is primarily due to the proprietary nature of the tests conducted in industry. In this paper, a program of testing is devised to better understand strake effectiveness as a function of current incidence angle and the presence of adjacent risers.
Experiments have been conducted on single and tandem pipe arrangements in air in order to evaluate strake suppression efficiency. Aluminium cylinders are tested in a wind tunnel in the structures laboratory of The University of Western Australia (UWA). Two sets of experiments are conducted: the first to evaluate cylinder VIV response at angles of incidence ranging from 30 to 90 degrees and the second to evaluate VIV response of the downstream pipe in a dual pipe arrangement with varying spacing between the pipes. In both cases the bare cylinders are first tested at varying flow speeds. Helical strakes are then added to the single cylinder, and downstream cylinder in the tandem pipe test, and the vibration response is recorded at varying flow speeds.
From the experimentation, it can be seen that downstream cylinder motions are amplified by wake induced instability. This phenomenon is of particular concern for tightly spaced top-tensioned risers (TTR) in wellbays of tension leg platforms (TLP) and deep draft floaters. The VIV motion of the downstream, bare, wake-affected pipe, is magnified to approximately 1.3–2 times the motion of a single bare pipe. When strakes are added to the downstream cylinder, the magnification factor of the downstream cylinder response is largely increased due to the wake of the upstream bare cylinder. However, the actual VIV motions of the downstream cylinder are largely reduced when strakes are incorporated. The present work demonstrates that helical strakes provide an effective means of suppressing vortex induced vibrations of risers in riser arrays, though the degree of effectiveness is reduced in a downstream tubular compared to suppression levels for single pipes.
Ice Model Tests in Context of the Investment Value of an Offshore Vessel
Authors: von Bock und Polach Rüdiger , Janardanan Vinod , Ehlers Sören 
Published: August 2013

Offshore activities and shipping in Arctic regions increased significantly in the past decade due to fossil resources. These areas hold about 15% of the worlds oil and gas. Exploration or transportation in such harsh Arctic environments possesses additional risks for the crew, the material and the environment. Hence, ships need to be able to handle low temperatures and ice impacts. Ice class certificates issued by classification societies reflect the ships level of ice capability. They are further required to be admitted to ice covered waters or particular regions in seasons with a certain probability of ice occurrence. In most cases, offshore operations are not continued in ice and ships need to transit through ice after abandoning a site upon ice arrival. However, the daily costs of such specialized vessels are high with up to 0.5M$ day that are not reimbursed in downtimes or transit. Therefore, in Northern Arctic regions a higher ice class can significantly enhance the ships workability and therewith its economic value.
The lower Polar ice classes, respectively Baltic ice classes, can only be determined analytically with empirically validated formulae for common cargo ships. Other ship types and ships with low L/B ratios are typically required to prove their ice capability through ice model tests. Nevertheless, ice model tests determine only the ice class of the propulsion system, whereas the ice class of the hull structure is determined by calculations. Furthermore, ice model tests are typically conducted towards the end of the design phase where eventual modifications are expensive and potentially threaten the construction schedule of the vessel. Often steel and equipment have already been procured and the manufacturing has begun. This paper presents an iterative procedure of ice model testing and design updates in order to enhance the performance of a particular offshore vessel to meet the requirements for a particular ice class. Thereby, it will be shown how an increase in investment costs for the design changes is compensated by the increasing value of the ships capabilities due to the higher ice class. Furthermore, the drop in value of the ship for the next lower ice class will be indicated as well as the economic consequences should the ship fail to reach the targeted ice class.
A Semi-Analytical Method With Dissipation for Fluid Resonances
Authors: Ten Igor , Lu Lin , Chen Xiao-Bo 
Published: August 2013

A semi-analytical method with dissipation based on the fluid domain decomposition and the expansion of eigenfunctions associated with each domain is developed to analyze the hydrodynamic interaction between floating bodies. The particular cases of moonpool resonance with thin wall (two sides of each wall are “back to back”) and gap resonance with small distance (gap sides of two bodies are “face to face”) are studied with attention on the frequency and amplitude of the fluid resonances.
The dissipation is introduced by a drop of the dynamic pressure across the control surfaces proportional to the normal velocity, which play the role of the dissipative surfaces defined in [1].
Influence of the Ice Concentration on the Ice Loads on the Hull of a Ship in a Managed Ice Field
Authors: van der Werff Solange , Haase Andrea , Huijsmans René , Zhang Qin 
Published: August 2013

The research and development project DYPIC (Dynamic Positioning in Ice) focuses on the challenges related to DP operations in Arctic environment. At the HSVA (Hamburg Ship Model Basin, Germany), model tests in ice were carried out using two configurations; one where the model was fixed to the towing carriage, and a free floating configuration, where the model ship was controlled by a DP system scaled to model parameters.
During the model tests a number of parameters were systematically varied. Model ship velocity and yaw angle were the parameters related to the controlling of the model. In addition, the ice field characteristics were varied by applying two variations in ice floe size and two variations in concentration, resulting in four different ice field descriptions. The ice thickness was remained constant for all test implementations. Every test run with a particular controlling (velocity and heading) profile was executed in each of the four ice fields.
In order to develop a DP controller which is optimally adjusted to the environment in which the system operates, it is important to find relations between the characteristics of the ice field and the forces they apply on the hull of the vessel or construction. An assessment of the measurements and observations during the testing is the basis of a study which has the objective to find how the ice field appearance and the ice loads on a structure relate to each other.
Coupled Analysis Approach in OTEC System Design
Authors: Shi Shan , Halkyard John , Kurup Nishu , Jiang Lei 
Published: August 2013

Ocean Thermal Energy Conversion (OTEC) technologies based on floating platforms generate electrical energy by utilizing the temperature difference between the deep ocean water and the surface water. One typical offshore floating OTEC system uses the temperature difference to drive a heat engine, utilizing a closed-loop Rankine cycle with a working fluid such as ammonia (NH3). Cold water is pumped through a large flexible pipe from approximately 1000m depth to heat exchangers which condense the ammonia vapor. Warm water from the surface is pumped through heat exchangers to evaporate the liquid ammonia to drive the turbine.
An OTEC floating platform could be a semisubmersible, a spar, or other typical offshore hull form with a taut or a catenary mooring system. As opposed to oil and gas production platforms, the OTEC system consists of a large diameter cold water pipe (CWP) which will participate in the global performance of the floating platform. Its unique behavior also includes the contribution of CWP entrained water which behaves differently in lateral and vertical directions due to its open bottom design. The hydrodynamic behavior of the large scale cold water pipe is an important consideration in the system design and analysis. The study presented in this work includes the application of a fully coupled analysis program with an accurate cold water pipe dynamic model in OTEC floating system analysis. The study could be useful for future guidance and reference on OTEC floating platform designs.
Model Experiment of a SPAR Type Offshore Wind Turbine in Storm Condition
Authors: Kokubun Kentaroh , Ishida Shigesuke , Nimura Tadashi , Chujo Toshiki , Yoshida Shigeo , Utsunomiya Tomoaki 
Published: August 2013

Wind power has the primary potential among renewable energies. Because Japan consists of little flat land and little shallow coast, floating wind turbine must be developed to make wind farms in Japan. Therefore, Japanese national demonstration project of Floating Offshore Wind Turbine (FOWT) was started in 2010FY by Ministry of the Environment and a SPAR-type FOWT is under construction at present.
The floater is planned to be hybrid, consists of upper part by steal and lower part by pre-stressed concrete. Four fins are attached around the floater to suppress yaw motion. The floater is moored by three catenary chains.
In order to confirm the safety of the FOWT in storm condition, experiments of a scale of 1/34.5 model were carried out at Ocean Engineering Basin of National Maritime Research Institute (NMRI), Japan. The draft of SPAR, the height of hub above sea level and the diameter of rotor of the model are 1.07m, 0.68m and 0.64m, respectively. In all experiments, blades are fixed to the hub under feathering condition and the hub is irrotational and fixed to the tower because this wind turbine is assumed to be under the storm condition, but wind blows transversely to the nacelle to give the maximum wind force. Water depth of the basin is smaller than the planned sea area on a reduced scale of model, therefore, springs and wires were used instead of chains in order to correspond to characteristics of horizontal mooring tension.
Environmental forces are wind, wave and current in 50-year return period. Tensions of the 3 moorings and the motion of the model are measured in condition of wind and/or wave and/or current. Three kinds of direction of wind are adopted. One is the same direction as the wave and current, another is perpendicular to the wave and current, and the other is against to the wave and current.
Besides the intact conditions a mooring-line-cut experiment in a storm condition was also conducted. Moreover, the effect of vortex induced motion (VIM), which occurs in current, was discussed. The results of the model experiment are reported to show the sufficient safety of this FOWT.
Development and Qualification of Diffusion Bonding Procedures for Microchannel Heat Exchangers
Authors: Li Xiuqing 
Published: August 2013

One of the unique features of Heatric’s heat exchangers is to join flat metal plates through diffusion bonding. Extensive work has been carried out on developing and qualifying robust process procedures for manufacturing this type of heat exchanger.
This paper discusses the important factors affecting diffusion bonding. These include material properties, surface preparation, bonding parameters (pressure, temperature, time and atmosphere) and post bond heat treatment. Material properties will focus on SS316L, 22Cr duplex and alloy 617.
To get ASME approval for using diffusion bonding in the construction of heat exchangers (U stamp certification), the bonding procedure qualification tests must be carried out in accordance with the code requirements. As an example, results from 22Cr duplex test blocks are presented in this paper.
Risk Analysis of the Construction Process of Cascade 5 Well
Authors: Jacinto Carlos Magno Couto 
Published: August 2013

This paper presents the HAZID/HAZOP [1,2,3,4] applied in risk analysis for the Cascade 5 well and this methodology main results, including possible failure or deviation events during the well construction, their causes and detection resources, consequences, criticality, and recommendations for mitigating safety risks.
The HAZID/HAZOP is a systematic method to analyze step by step each well operation, mapping possible deviation processes and proposing recommendations either to prevent causes or mitigate consequences.
The probabilities of some final events in the phases Liner 10”, Logging 12.25” and contingencies, were out of the ALARP (as low as reasonably practicable) [1] levels of risk tolerance, and it was recommended the improvement of the safeguards in these phases using BOP tests program designed.
The greater number of subsea control system failures compared to those that occurred on surface testing is believed to be primarily due to system complexity and hydrostatic issues that come into play in deeper water.
It is important to keep in mind that control system failures are discovered during function tests. In fact, a very large percentage of all failures could have been identified with only a simple function test.
It is important to distinguish between those failures that are found from pressure and those found from function testing.
In this study it was calculated the interval of tests of the security system (BOP) for the period of 100 days of mission, in order to get an average unavailability within the ALARP level (10e−8, 10e−4).
Following this approach it may be possible to avoid kicks and blowouts, saving costs and time in the well construction process.
A Flexible Seafloor Carpet for High-Performance Wave Energy Extraction
Authors: Alam Mohammad-Reza 
Published: August 2013

Similar to the mechanism by which a visco-elastic mud damps the energy of overpassing surface waves, if the near-shore seafloor is carpeted by an elastic thin material attached to generators (i.e. dampers) a high fraction of surface wave energy can be absorbed. Here we present analytical modeling of the flexible carpet wave energy converter and show that a high efficiency is achievable. Expressions for optimal damping and stiffness coefficients are derived and different modes of oscillations are discussed. The presented wave energy conversion scheme is completely under the water surface hence imposes minimal danger to boats and the sea life (i.e. no mammal entanglement). The carpet is survivable against high momentum of storm surges and in fact can perform well under very energetic (e.g. stormy) sea conditions, when most existing wave energy devices are needed to shelter themselves by going into an idle mode.
I am honored to be a colleague of Prof. Ronald Yeung at the University of California, Berkeley. He is a world renowned scientist of ship hydrodynamics with several valuable and key contributions to the field. This manuscript on a new ocean wave energy extraction scheme is due to Ron’s recent interest in the field of ocean renewable energy. I am looking forward to years of working closely with him. Thank you Ron.
Factors Influencing the Design and Construction of LNG Storage Tanks
Authors: Saad Pascinthe 
Published: August 2013

A number of LNG storage tank designs have been implemented on past and current projects. Such designs include full containment tanks with a 9%Ni inner liner for primary containment and storage of LNG at cryogenic temperature, a carbon steel liner for secondary liquid containment, thermal corner protection and vapor barriers on the inner tank and a concrete outer tank for resistance to external loads.
LNG storage tanks are a key component of an LNG liquefaction or regasification facility and there is only a handful of specialized contractors that possess the tank technology and track record of the materials involved and the construction know how required for successful execution. This paper will focus on factors influencing LNG storage tanks design selection and construction execution strategies which can be a function of functional requirements as well as project location.