bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Modal Analysis of Jacket-Type Platforms Using Data-Driven Stochastic Subspace Identification Method
Authors: Xin Junfeng , Hu Sau-Lon James , Li Huajun
Published: August 2013

Employing efficient techniques to accurately identify the modal parameters of new and aging offshore structures has been of interest to the offshore industry for decades. Early methods of modal identification were developed for the frequency domain. The new trend is to employ either input-output or output-only time-domain modal identification methods. Under the assumption that the excitation input is a zero-mean Gaussian white noise process, a modern output-only method that allows direct application to the response time series is the data-driven stochastic subspace identification (SSI-data) method. The main objective of this paper is to evaluate the performance of the SSI-data method using the test data measured from a physical model of a realistic offshore jacket-type platform. Response acceleration data associated with three different excitation mechanisms are investigated: impact loading, step relaxation and white noise ground motion. Although the SSI-data method has been theoretically developed, and often perceived to be only valid, for the ambient noise testing environment, it is shown in this study that the SSI-data method also performs well using data from either the impact loading or step relaxation tests.
Performance Enhancements and Validations of the UC-Berkeley Ocean-Wave Energy Extractor
Authors: Tom Nathan , Yeung Ronald W.
Published: August 2013

This paper evaluates two aspects of enhancements made to the UC-Berkeley ocean-wave energy extraction device first presented in [1]. First, the differences in hydrodynamic performance between flat- and hemispherical bottom floaters were investigated theoretically using UC Berkeley 2-D viscous-flow solver: FSRVM [2]. The predicted enhancement was compared with experimental results, demonstrating that an increase in motion of over 50% was realizable. Second, important modifications to the design, fabrication, and material of the rotor and stator of the permanent magnet linear generator (PMLG) were made with the aim of increasing both power output and mechanical-to-electrical conversion efficiency, ηel. Increased power extraction and efficiency were achieved, doubling what had been previously reported. The non-linear relationship between the generator damping and the magnet-coil gap width was also investigated to verify that the conditions for optimum power extraction presented in [1] were achievable with the PMLG. Experimental results, obtained from testing the coupled floater and PMLG system in the UC-Berkeley wave tank, revealed that measured capture widths were more than double those from the previous design. These results further confirmed that matching of the generator and floater damping significantly increased the global efficiency of the extraction process.
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.
Study on the Spatial Characteristic and Refuge Action in the Offing Earthquake of the Tohoku District Pacific Ocean
Authors: Terasaki Yasuo , Hanai Kenta , Miyazaki Wataru , Kondo Takeo , Sugahara Masashi , Yamamoto Kazukiyo
Published: August 2013

At 14:46 on March 11, 2011, massive tsunami waves triggered by the 2011 earthquake off the Pacific coast of Tohoku brought destructive damage to Pacific coastal areas. Considering that about 90% of the deaths were related to tsunami wave drowning, it is important to move to heights as quickly as possible to survive tsunami waves. Spatial characteristics, such as the number of evacuation sites, the locations of evacuation sites, the slopes of evacuation routes, and city block morphologies, will constitute factors that greatly affect evacuation behavior. In this study, we consulted disaster victims to understand what kind of evacuation behaviors they exhibited and analyzed those evacuation behaviors based on the regional distribution of evacuation sites as seen from city streets. The obtained results showed that the positional relationships between city blocks and evacuation sites are influential in determining means of evacuation and behavior patterns at the time of evacuation. Accordingly, it was found that an appropriate distribution of evacuation sites in city blocks is required for future coastal areas.
The Mooring Bay Concept for LNG Loading in Harsh and Ice Conditions
Authors: Hoog Sven , Berger Joachim , Myland Johannes , Clauss Günther F. , Testa Daniel , Sprenger Florian
Published: August 2013

The demand for natural gas from offshore fields is continuously increasing. Especially future production from Arctic waters comes into focus in context with global warming effects leading to the development of a dedicated technology. Relevant approaches work with floating turret moored production terminals (FLNG) receiving gas via flexible risers from subsea or onshore fields. These terminals provide on-board gas treatment and liquefaction facilities as well as huge storage capabilities for LNG (Liquefied Natural Gas), LPG (Liquefied Petrol Gases) and condensate. Products are transferred to periodically operating shuttle tankers for onshore supply reducing the need for local onshore processing plants providing increased production flexibility (future movability or adaptation of capacity). Nevertheless, in case of harsh environmental conditions or ice coverage the offshore transfer of cryogenic liquids between the terminal and the tankers becomes a major challenge. In the framework of the joint research project MPLS20 ([1]), an innovative offshore mooring and cargo transfer system has been developed and analyzed. MPLS20 is developed by the project partners Nexans ([2]) and Brugg ([3]), leading manufacturers of vacuum insulated, flexible cryogenic transfer pipes, IMPaC ([4]), an innovative engineering company that has been involved in many projects for the international oil and gas industry for more than 25 years and the Technical University (TU) Berlin, Department of Land- and Sea Transportation Systems (NAOE, [5]), with great expertise in numerical analyses and model tests. The overall system is based on IMPaC’s patented and certified offshore ‘Mooring Bay’ concept allowing mooring of the vessels in tandem configuration and simultaneous handling and operation of up to six flexible transfer pipes in full aerial mode. The concept is outlined to operate with flexible transfer lines with 16-inch inner diameter like the newly designed and certified corrugated pipes from Nexans and Brugg. The mooring concept and its major subsystems have proven their operability by means of extensive numerical analysis, model tests and a professional ship handling simulator resulting in an overall transfer solution suitable to be used especially under Arctic conditions like addressed by the EU joint research project ACCESS (http://access-eu.org/). The paper introduces the new offshore LNG transfer system and focuses especially on its safe and reliable operability in the Arctic — with ice coverage as well as in open water conditions.
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.
3-D Numerical Modeling of Wave Run-Up on Monopiles
Authors: Peng Zhong , Wellens Peter , Raaijmakers Tim
Published: August 2013

A 3-D ComFLOW model is used to investigate regular wave and irregular wave run-up on a monopile foundation. ComFLOW model results are in good agreement with measurements of De Vos et al. (2007). Our study shows that the wave run-up is strongly dependent on the wave nonlinearity. A set of non-dimensional, simple formulae have been derived to relate wave run-up to the structure diameter and Ursell number. These new formulae can be used to predict the wave run-up on a monopile foundation in the design phase.
Digital Image Processing for Sea Ice Observations in Support to Arctic DP Operations
Authors: Zhang Qin , Skjetne Roger , Løset Sveinung , Marchenko Aleksey
Published: August 2013

Various types of remotely sensed data and imaging technology will aid the development of sea ice observation to support estimation of ice forces that are critical to Dynamic Positioning (DP) operations in Arctic waters. The use of cameras as sensors on mobile sensor platforms such as unmanned aerial vehicles in Arctic DP operations will be explored for measurements of ice statistics and ice properties. Several image processing algorithms are adopted to analyze ice concentration, ice floe boundaries, and ice types. The resulting image processing methods for ice observation, including a discussion of possibilities, limitations, and further improvements, are presented in this paper.
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].
Fairing Evaluation Based on Numerical Simulation
Authors: Pontaza Juan P. , Kotikanyadanam Mohan , Moeleker Piet , Menon Raghu G. , Bhat Shankar
Published: August 2013

It is well established that strakes are effective at suppressing vortex-induced vibrations (VIV). Fairings are an attractive alternative to helical strakes, because they are a low drag VIV suppression solution. The paper presents an evaluation of a fairing design, based on numerical simulations — to be complemented at a later stage with current tank testing. This paper documents the computational fluid dynamics (CFD) and finite element analysis (FEA) of the evaluation: (1) 3-D CFD in the laboratory scale: 4.5 inch pipe, 3 ft/s current speed, (2) 3-D CFD in the full scale: 14 inch riser, 4 knots current speed, and (3) 3-D FEA of the full-scale fairing module latching mechanism, under service loads corresponding to 4 knots current speed. The analysis results show that the fairing design (1) is effective at suppressing VIV, (2) yields a low drag coefficient (0.52 at Re ∼ 106), and (3) its latching mechanism is adequate for use in calm sea states with 4 knots current speeds.
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.
Characterization of the Accuracy of the MFL Pipeline Inspection Tools
Authors: Salama Mamdouh M. , Nestleroth Bruce J. , Maes Marc A. , Rodriguez Carlos , Blumer Dave
Published: August 2013

Magnetic flux leakage (MFL) intelligent pigs are the most common tools used for pipeline inspection. But, the MFL inspection results are subject to various sources of uncertainties which must be quantified and accounted for in the integrity assessment of the inspected pipeline. A series of pull-through tests (PTT) of seven MFL tools from four service providers was performed on a 12-inch diameter pipe containing preexisting internal corrosion defects of various length, width, and depth, and located in a variety of circumferential and longitudinal positions. The results of these tests are used to quantify the detectability statistics and the sizing uncertainties of the different tools for future use in developing calibrated probabilistic models for reliability based inspection, quantitative risk assessment and life extension studies for pipelines.
Dilution Control of Weld Overlay Superalloys Using Taguchi Method
Authors: Silva Cleiton Carvalho , de Miranda Edvan Cordeiro , Motta Marcelo Ferreira , de Miranda Hélio Cordeiro , Farias Jesualdo Pereira
Published: August 2013

The objective of this work was to optimize the operational conditions aiming to deposit weld overlays with a minimal dilution and iron content as low as possible, and a thickness of weld higher than 3 mm just in a single layer. The alloys studied were Inconel 625, Hastelloy C276 and Inconel 686. The ASTM A516 Gr 60 steel was used as substrate. The welds were performed by GTAW cold wire feed process. The Taguchi method was applied to design the experiments and to evaluate the influence of the variables. The results showed that the arc oscillation (weaving) has a strong effect on the penetration and dilution of welds. The confirmation test for the optimal settings indicated that the additive model of the Taguchi method was not only confirmed the excellent reproducibility, but also provides sufficient confidence in the factorial effects.
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.
Hydrodynamic Analysis of a Vertical Axisymmetric Oscillating Water Column Device Floating in Finite Depth Waters
Authors: Mavrakos Spyros A. , Konispoliatis Dimitrios N.
Published: August 2013

A floating oscillating water column device (OWC) consists of a vertical cylinder, with a finite wall thickness, partly submerged as an open-bottom chamber in which air is trapped above the inner water free surface. The chamber is connected with the outer atmosphere by a duct housing an air turbine. Forced by incident waves from any direction, the water surface inside pushes the dry air above through a Wells turbine system to generate power. In the present contribution the volume flows, the wave forces, the added mass and damping coefficients and the mean second-order loads for various configurations of OWC devices are being presented. Finally, it is tested how differentiations in the device’s geometry (wall thickness, draught, shape of the chamber, turbine characterises) affect the inner pressure and as a result the absorbed power by the device.
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.
Analysis of PIV Tests Results of the Vortex Self Induced Vibration (VSIV) of a Cylinder
Authors: Fernandes Antonio Carlos , Sefat Sina Mirzaei , Cascão Luis V. , Franciss Ricardo
Published: August 2013

The Vortex Self Induced Vibration (VSIV) of cylinders is a phenomenon which occurs in the nature with devices such as Steel Catenary Risers (SRCs) in the deep offshore connected to floating platforms. The devices oscillate transversely due the own vertical motion. This is a currentless (therefore different form VIV) problem. To gain more insight into the nature of VSIV problem, an experimental apparatus was constructed which measure the transversal and response associated with vortex-induced vibration of a totally submerged horizontal cylinder hang on horizontally elastic support under the influence of vertical harmonic oscillating motion. The experiments were conducted in a tank at the LOC/COPPE/UFRJ (Laboratory of Waves and Current of COPPE, Federal University of Rio de Janeiro). The VSIV phenomena of the cylinder in different exciting amplitudes and exciting frequencies could generate different vertical trajectories of VSIV motion such as oval-shape, eight-shape and etc. This paper aims to describe the behavior of the flow around the cylinder during the VSIV motion based on the PIV tests on VSIV motion for different Keulegan-Carpenter numbers and for several exciting frequencies.
Physical and Theoretical Modeling of Surface-Piercing Hydrofoils for a High-Speed Unmanned Surface Vessel
Authors: Brizzolara Stefano , Young Yin Lu
Published: August 2013

The objective of this work is to investigate the performance of two pairs of negative dihedral surface-piercing (SP) hydrofoils designed especially for an unmanned surface vessel with a top speed of 120 knots in sea state two. Physical modeling of a 1/6-scaled model of the SP hydrofoil was conducted at the free-surface cavitation tunnel at the Technical University of Berlin (TUB). The SP hydrofoil feature a new type of super-cavitating profile with an annex tapered trailing edge to achieve good efficiencies in foil born conditions (60–120 knots, super-cavitating/ super-ventilated regimes), as well as at take-off speeds (25–40 knots, wetted and/or partial-cavitating regimes). Preliminary results showed interesting anomalies in the trends of the measured forces with respect to the cavitation number and angle of attack for a wide range of inflow speeds. Details of the experimental study are presented along with numerical predictions obtained using finite volume RANSE solver with a volume of fluid technique to allow for a mixture flow with air/vapor and water phases. Explanation of the anomalies in the hydrodynamic performance is given.
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.
A Review on Experimental Research on Natural Gas Production From the Hydrate With CO2
Authors: Xu Kun , Zhao Jiafei , Liu Di , Song Yongchen , Liu Weiguo , Xue Kaihua , Ye Chencheng , Zhu Yiming
Published: August 2013

In this paper, the experimental researches on replacement of CH4 in the hydrate by use of CO2 reported by researchers both at home and abroad are summarized and analyzed, and the advantages and disadvantages of this method on natural gas production from hydrate is discussed. The latest progresses of CH4 replacement experiment with gaseous CO2, liquid CO2 and CO2 emulsion are present, and the superiority of CO2 emulsion on replacement of CH4 is emphasized. Moreover, the latest experimental research on preparation of CO2 emulsion is introduced, and the key technologies on the replacement of CH4 hydrate with different states of CO2 are indicated.
Tensile Strain Capacity of X80 Girth Welded Linepipes and Crack Growth Analysis
Authors: Igi Satoshi , Sakimoto Takahiro , Endo Shigeru , Muraoka Ryuji , Arakawa Takekazu
Published: August 2013

This paper examines the tensile strain capacity of girth welded pipelines. A pressurized and no pressurized full-pipe tension tests were conducted together with FE analyses in order to investigate the strain behavior of pipe under large axial loading with high internal pressure. The critical tensile strain drastically decreased under a high internal pressure condition. Single edge notch tension (SENT) tests with shallow notched specimens were also performed to obtain the material resistance curve (R-curve), and a series of FE analyses was conducted to obtain the crack driving force for ductile crack propagation. The R-curve and crack driving force curve were used in predicting the tensile strain limit of X80 girth welded pipe with a surface defect in the HAZ. The predicted critical tensile strain showed good agreement with that obtained in the pressurized and no pressurized full-pipe tension test.
Experimental Study of Uniaxial Compressive Strength of Gas Hydrate-Bearing Sediment at Constant Strain Rate
Authors: Nie Xiongfei , Liu Weiguo , Song Yongchen , Zhao Jiafei , Wang Rui
Published: August 2013

The uniaxial compressive tests are conducted on synthetic gas hydrate-bearing sediment samples by using the low-temperature high-pressure triaxial test system. The effects of the temperature, the strain rate and the failure time on the uniaxial compressive strength of hydrate sediment are measured. The results indicate that: (a) The uniaxial compressive strength is sensitive to the change of temperature and increases exponentially as temperature decreases. (b) The uniaxial compressive strength of hydrate sediment changes with the strain rate obviously, and increases with the strain rate increasing following a power function. (c) The uniaxial compressive strength increases with the failure time decreasing following a power function.
Image Processing for the Analysis of an Evolving Broken-Ice Field in Model Testing
Authors: Zhang Qin , van der Werff Solange , Metrikin Ivan , Løset Sveinung , Skjetne Roger
Published: August 2013

Dynamic positioning (DP) experiments in model ice were carried out in the ice tank at the Hamburg Ship Model Basin (HSVA) in the summer of 2011. In these experiments the behavior of two different ships in a broken-ice field were studied. One of the main parameters characterizing a broken-ice field is the ice concentration, defined as the fraction of the total water area covered by ice. In this paper, image processing techniques are applied to derive the ice concentration in the model basin. Several points in time are analyzed in order to describe the evolution of the ice field. The applied techniques include methods for identifying individual ice floes and calculating the ice concentration in the vicinity of the model ship. Ice floe boundaries are then obtained, and the ice floe size distribution and shape factor may further be extracted from the images. The image processing methods applied in this work are object extraction and edge detection algorithms, which are further customized to ice identification. The obtained results can be used for relating the ice field characteristics to the model test results, such as the vessel’s displacements and the corresponding ice forces.
A Study of Hydrocarbon Releases in the Gulf of Mexico, 1996 Thru 2010
Authors: Smith Louise Matilde , Smith John Rogers , Pattee Lauren , Langlinais Julius
Published: August 2013

The events surrounding the Deepwater Horizon (Macondo) disaster have changed the face of deepwater operations. Safety and environmental systems (SEMS) plans and capping or containment capabilities are required to meet current Bureau of Safety and Environmental Enforcement (BSEE) permitting requirements for the Gulf of Mexico (GOM). More generally, industry must identify the operational risks associated with future deepwater operations and specify their plans for responding to those risks, in order to maximize the effectiveness of methods to prevent and respond to potential future releases of hazardous, polluting hydrocarbons. This paper describes a study of public BSEE (previously MMS and BOEMRE) data on incidents involving releases of formation fluids to the environment. The purpose of this study was to provide a factual basis for identifying the operational risk of hydrocarbon releases in offshore operations as a starting point for additional work on identifying opportunities to reduce the frequency, severity, and consequences of such releases, especially for deepwater operations.

Incidents reported over the past 15 years were reviewed and organized in a spreadsheet. A total of 90 non-pipeline incidents were identified as including enough description to be useful. Most of these incidents were spills greater than 50 barrels (bbls), but blowouts, fires, and explosions are important and included. To the extent possible, the review determined: the flow path taken from the formation to the point in the well or production system where the fluids were released, the release point, the barriers that were used to reestablish control, and what can these events tell us about potential future deepwater events.

It is notable that most of these releases occurred in shelf operations rather than deepwater (water depth ≥ 1,000 ft), which was expected due to the much larger number of wells on the GOM shelf. Nearly two-thirds of the releases happened during active drilling, completion, workover, or well-servicing operations. The remaining events occurred during other operations, particularly production, and include two spills after the wells were plugged and abandoned (P&A’d). The number of blowouts per year was relatively small, varying from 2 to 9 for the 15 year period. The number of blowouts has remained roughly constant despite the recent decrease in the rig activity level. Similarly, the size of most spills was relatively small, if the Macondo event is excluded. Nevertheless, the data gives a factual basis for identifying the kinds of events that could lead to future catastrophes if not prevented or identified and controlled successfully.
3D Simulation of Vortex Shedding Past Tapered Circular Cylinders in Subcritical Reynolds Numbers
Authors: Tamimi V. , Zeinoddini M. , Bakhtiari A. , Golestani M.
Published: August 2013

In this paper results from simulating the vortex shedding phenomena behind a fixed tapered circular cylinder, at relatively high Reynolds numbers, are reported. Ansys-CFX computational fluid dynamics model, based on solving three-dimensional (3D) incompressible transient Navier Stokes equations, is employed for this purpose.

The geometries applied in the models resemble those used in wind tunnel experiments by other researchers. The taper slope along the cylinder span is uniform with a tangent of 24:1. The diameter at mid-span of the cylinder equals to 0.0389 m. The Reynolds number (based on the mid-span diameter) is around 29,000. The computational model has first been calibrated against experiments for uniform 3D cylinders as well as results from a Direct Numerical Simulation of turbulent wake with vortex shedding past a uniform circular cylinder, as obtained by other researchers.

The main flow characteristics for tapered cylinders such as vortex dislocations and splitting, cellular vortex shedding, oblique vortex shedding and the variation of the vorticity patterns along the tapered cylinder could be obtained from the simulations.
Development of the Fish Cage Installed in Variable Depths
Authors: Shimizu Hiroki , Kitazawa Daisuke , Mizukami Yoichi
Published: August 2013

Aquaculture is expected to play a key role in the increase in fishery production in the future. Because of environmental and coastal utilization issues, however, it is necessary for us to operate cultivation in exposed area for more fishery production, where the fish cage and its mooring system face severe environmental condition such as typhoon. In that area the fish cage should be submerged to protect it from high waves since the influence of waves is reduced in deeper water. Nevertheless, the technologies for open ocean aquaculture are still in the phase of being developed. For example, in general operating systems, a fish cage is floated or submerged on the basis of the framework which is fixed by buoys and anchors. In the exposed area, however, buoys are broken by waves, resulting in the high maintenance cost. Our research aims at creating the new mooring system of a fish cage. The fish cage is moored without the framework in various depths. Buoys can be submerged so that the maintenance cost of the mooring system must be reduced. The feasibility of the mooring system is examined by smaller-scale water tank testing and simple numerical analysis. First the behavior of the mooring system in still water was examined by both numerical analysis and tank model testing. As a result, the fish cage can be submerged at an arbitrary depth only by changing the ratio of the buoyancy to the weight of the fish cage. Then, using a new model of a fish cage, towing test was carried out to estimate the drag force. The drag force is proportional to the 1.5 powered velocity of water current, which is different from the second powered velocity usually used in numerical analysis. This discrepancy may be attributed to the lack of measured data. It should be also noted change in the attacking angle of water current can influence the drag force. Finally, towing test of the mooring system was carried out at the various towing speeds to examine the change in the geometrical formation of the system. At the higher towing speed fish cage is more submerged due to the increase of drag force. In addition, the fish cage begins inclining just after towing. The drag force must vary since the projected area changes due to the inclination of the fish cage and to the deformation of the net. However, the forces on the fish cage are balanced again so that the geometrical formation becomes stable. As future studies, the experimental result will be compared with the analytical one, in which the effect of drag force will be added to the balance of forces on the fish cage. The water tank has a wave maker, so waves will be added to the water current since wave-induced forces work on the fish cage submerged near water surface.
Dynamic Response of an Offshore Wind Turbine System Using Coupled and Limited Coupled Methods
Authors: Yan Fasuo , Peng Cheng , Zhang Jun , Wang Dagang
Published: August 2013

Offshore turbines are gaining attention as means to capture the immense and relatively calm wind resources available over deep waters. A coupled dynamic analysis is required to evaluate the interactions between the wind turbine, floating hull and its mooring system. In this study, a coupled hydro-aero dynamic response analysis of a floating wind turbine system (NREL offshore-5MW baseline wind turbine) is carried out. A numerical code, known as COUPLE, has been extended to collaborate with FAST for the simulation of the dynamic interaction. Two methods were used in the analysis; one is coupled method and the other is limited coupled method. In the coupled method, the two codes are linked at each time step to solve the whole floating system. The limited coupled method assumes wind load is from a turbine installed on top of a fixed base, namely it doesn’t consider real-time configuration of floating carrier at each time step. Coupled technique is also mentioned to integrate the hydro-aero dynamic analysis in this paper. Six-degrees of freedom motion and mooring tensions are presented and compared. The numerical results derived in this study may provide crucial information for the design of a floating wind turbine in the future.
Computational Modeling of Rolling Cams for Wave-Energy Capture in a Viscous Fluid
Authors: Jiang Yichen , Yeung Ronald W.
Published: August 2013

The performance of an unsymmetrical rolling cam as an ocean-wave energy extractor was studied experimentally by Salter (1974) and then analyzed from the hydrodynamics standpoint by a number of workers in the 70’s (e.g. Evans, 1976). The analysis was carried out on the basis of inviscid-fluid theory and the energy-absorbing efficiency was found to approach 100%. This well-known result did not account for the presence of viscosity, which alters not only fluid damping but also, to some extent, the added-inertia characteristics. How fluid viscosity may alter these conclusions and reduce the energy-extraction effectiveness is examined in this paper, for two rolling-cam shapes: a smooth “Eyeball Cam” with a simple mathematical form and a “Keeled Cam” with a single sharp-edged bilge keel. The solution methodology involved the Free-Surface Random-Vortex Method (FSRVM), reviewed by Yeung (2002). Frequency-domain solutions in inviscid fluid were first sought for these two shapes as baseline performance metrics. As expected, without viscosity, both shapes perform exceedingly well in terms of extraction efficiency. The hydrodynamic properties of these two shapes were then examined in a real, viscous fluid, under a high Reynolds-number assumption. The added moment of inertia and damping are noted to be changed, especially for the Keeled Cam. With the power-take-off (PTO) damping chosen based on the viscous-fluid results, time-domain solutions are developed to understand the behavior of the rolling motion, the effects of PTO damping, and the effects of the cam shapes. These assessments can be effectively made with FSRVM as the computational engine, even at motion of fairly large amplitude, for which an actual system may need to be designed.