bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model Tests With the HVS Semisubmersible for Dry Tree Application
Authors: Kyoung Johyun , Yang Chan-Kyu , Lambrakos Kostas , O’Sullivan Jim 
Published: September 2014

The global hull motion performance of the HVS semisubmersible for dry tree application is investigated with model tests. The HVS semisubmersible, which has been validated for low heave motion and VIM (Vortex Induced Motion) response, was modified for dry tree application. As a base case, the modification includes a keel plate with riser keel guides at the level of the pontoons. The keel plate is optimally designed to increase the hull heave period to compensate for the heave period reduction in the HVS semisubmersible due to the riser tensioners for the dry tree application. The plate also provides additional viscous damping that decreases the heave response at the heave natural period.
The model tests were performed to investigate the in-place hull motion performance for the Gulf of Mexico environmental conditions. The pneumatic riser tensioners were modeled using a spring with dual stiffness. Because of the water depth limit in the wave basin, a truncated mooring was used to simulate the full scale prototype mooring system.
An alternate modification to the HVS semisubmersible that includes pontoon plates was also tested and the measured response was compared to the response of the base case. The measured hull responses were correlated with MLTSIM, a Technip in-house nonlinear time-domain 6-DOF motion analysis program.
Modelling of Ice Growth and Transport on a Regional Scale, With Application to Fountain Lake, Minnesota, USA
Authors: de Goede Erik , Wagner Tim , de Graaff Reimer , Sheets Ben 
Published: September 2014

Numerical modelling of ice growth and transport on regional scales such as lakes, estuaries, or coastal seas can provide crucial input for the planning and design of offshore structures in arctic, sub-arctic, or even mid-latitude regions. It is in these regions that the total loading of ice on infrastructure such as platforms, sea defense structures, sub-sea pipelines, or wind turbines may exceed the total loading of waves and currents, and may therefore determine the design. Thus, the interaction of ice with planned structures might be significant, and accurate models of ice dynamics would be invaluable to engineering in these regions. There is, however, a general lack of ice models that can be applied to study these complex integral physical processes at regional scales. Typically, ice modelling focusses on either large oceanic scales using climate models, or on local scales to study small-scale ice-structure interactions. The regional scale model presented in this paper is targeted at bridging this scale gap.
This paper describes the implementation of an ice module in Delft3D. Delft3D is a flexible integrated modelling suite, which simulates two- and three-dimensional flow, sediment transport, morphology, waves, spills, water quality, and ecology, and is capable of handling the interactions between these processes. By dynamically coupling an ice module with these existing modules it becomes possible to not only predict the growth, melting, and transport of open-water ice and associated hydrodynamics, but also to study the interaction of ice with, for example, river banks, the seabed, water quality, or spills of fine sediments or oil. This paper presents the major concepts of the new Delft3D ice module, as well as example applications for various lakes in The Netherlands and Fountain Lake, in Minnesota, USA. Finally, a hypothetical case of ice transport modelling is presented.
Ice Model Tests With a Compliant Cylindrical Structure to Investigate Ice-Induced Vibrations
Authors: Ziemer Gesa , Evers Karl-Ulrich 
Published: September 2014

A compliant cylindrical structure has been built and tested in a series of model tests in ice in the Large Ice Model Basin at HSVA. The structure’s stiffness in ice plane is higher in ice-drift direction than crosswise, enabling the model to vibrate in different oscillation patterns.
In total, 4 ice sheets have been used to perform tests in different ice thickness, covering a wide range of ice drift velocities between 0.005 and 0.15 m/s in model scale. Several events of ice-induced vibrations were observed throughout the test campaign. Oscillations are found to reach different types of beginning steady-state, mainly depending on ice drift velocity and ice thickness. Dynamic amplification of structural response in ice plane as well as ratio of static and dynamic forces is highly dependent on the type of vibration. While the dynamic amplification is highest when the ice load’s frequency equals the first natural frequency of the structure, the highest dynamic forces occur when the crushing frequency is an integer fraction of the natural frequency.
The paper describes the design of the test set-up, instrumentation and calibration, performance and analysis of conducted tests, and general findings.
Hybrid Riser Resistance to In-Service Fatigue Loading
Authors: Iob Francesco , Mecozzi Elisabetta , Di Vito Luigi , Darcis Philippe , Marines-Garcia Israel , Quintanilla-Carmona Hector M. 
Published: September 2014

Riser systems are subjected to complex loading spectra. A wide range of amplitude loading are induced by naturally complex sea states. The complex loading spectrum differs sensibly from the constant amplitude loading commonly adopted for qualification of the product (riser pipe and its girth welds or threaded connections).
The present paper reports numerical calculations and a comparison of the actual fatigue loading experienced by different riser systems, Steel Catenary Risers (SCR), Lazy Wave Riser (LWR), Hybrid Risers (HR). For the Hybrid riser system, a good fatigue resistance, due to the vessel and wave first motion decoupling, is obtained. On the other hand, the phenomenon of cross flow vibration induced by Vortex Induced Vibrations (VIV), could significantly affect the hybrid riser fatigue performance. In this case, a sensitivity analysis has been performed to evaluate the influence of different parameters, on the applied fatigue loading, like: riser tension, hydro diameter (i.e. external pipe diameter including coating), riser wall thickness, current velocity.
The HR variable amplitude loading spectrum, derived from in-service conditions, referred to Gulf of Mexico scenario, has been calculated and applied in laboratory tests on girth welds of X65, 10.75″ OD, 25.4 mm WT riser. Furthermore, the fatigue performance of these tests has been compared to analogous tests on samples subjected to constant and variable amplitude loading available from previous work on SCR system[1].
Towards an Operational Stereo System for Directional Wave Measurements From Moving Platforms
Authors: Benetazzo Alvise , Bergamasco Filippo , Barbariol Francesco , Torsello Andrea , Carniel Sandro , Sclavo Mauro 
Published: September 2014

Stereo video imaging of water surface has become an effective instrumentation to gather wind waves 3-D data from small to medium range spatial scales. Indeed, recent applications of stereo techniques provided new insights of space-time distributions of sea wave elevations, small scale wave statistics, and directional wave spectra. Like most photogrammetric applications, an accurate calibration of the optical acquisition machinery is required to provide a low-noise, precise and reliable surface reconstruction adequate to extract meaningful wavy surfaces. However, for practical open field applications, there is a strong interest to provide a calibration procedure apt to be performed in an uncomfortable environment in which it may be unfeasible to take apart or even physically access the device.
Here, we propose a stereo pipeline suitable for 3-D wave measurements from fixed and moving platforms. In particular, within the Wave Acquisition Stereo System (WASS) framework, we contemplated a self-calibration technique for a robust estimation of the stereo extrinsic parameters, a fast dense stereo correspondence algorithm, and a two-step correction of the cameras motion. As for other applications, wave information collected by WASS includes synthetic wave parameters (e.g., significant wave height, wave periods, and directions), wavenumber and frequency-direction spectra, spatial distribution of wave elevations, heights, and lengths.
The new pipeline features has been firstly assessed by installing WASS on top of the “Acqua Alta” oceanographic tower in the northern Adriatic Sea (Italy) and comparing WASS measurements against those acquired at the tower with reference instrumentation. Afterwards, the stereo system has been mounted on board the R/V “Urania” during a cruise on April 2013 in the southern Adriatic Sea. During the cruise, to correct for ship’s motion, WASS has been synchronized to the motion unit used for the vessel’s navigation. For validation, sea wave state gathered by WASS has been compared to theoretical models and results from the numerical wave model SWAN.
Results presented show that the accuracy of 3-D waves provided by the new algorithms is comparable to that of other WASS applications, although significantly reducing the installation effort and the computational time by more than one order of magnitude. Additionally, encompassing for ship’s motion makes stereo system a perspective instrumentation for operational wave measuring from research and opportunity vessels. The manuscript is completed by a discussion on the limitations and troubleshooting related to the proposed pipeline.
From Egg-Code to Actual Ice Field Flow Definition
Authors: van der Werff Solange , van der Nat Clemens , Wiersema Ed , Cammaert Gus , Jolles Wim 
Published: September 2014

The Arctic Operations Handbook JIP [1] is an initiative of the Dutch offshore industry to investigate available existing standards and guidelines related to typical offshore contractor operations in Arctic conditions. The JIP identified that guidelines are required for the evaluation of the flow of ice around floating structures, and eventually to predict the resulting ice loads as input to workability studies. A pilot study called IceStream was set up as a first step towards developing guides and tools for ice flow behaviour prediction. This paper describes ice field definition and visualization as conducted within this pilot project.
In the process of developing guides and tools, the objective of IceStream is to obtain a description of the geometry of an ice field, similar to open water conditions. These definitions, indicating the severity of the conditions, are needed as a basis for the determination of operational limits, and serve as an input for numerical prediction models. The ‘egg-code’ [2] principle is identified to be a good starting point when focussing on level ice, as it contains a limited but sufficient number of parameters to indicate the ice field characteristics.
The applicability of the egg-code in numerical modelling is demonstrated by the development of an algorithm which translates egg-code parameters together with floe size distribution parameters into an ice field visualisation that complies with these parameters. The floe size distribution parameters are established from field observation studies. The ice field is defined by a set of ice particles, each particle represented by its area and ice thickness. Other properties (such as bending and crushing strength) can be assigned to the ice particles as well.
Based on the ice field definition, Voronoi Treemapping is used to visualize the ice field. An additional parameter in this treemapping is required to indicate the distribution of ice floes over the domain (or ice cluster formation). Sea ice fields with any ice concentration between open water and 10/10th can be generated in this way. The result is an ice field consisting of random shaped (convex) ice particles with individual properties that comply with the given egg-code. The generated set of ice floes has shown to be a suitable input in the numerical modelling of an ice field approaching a floating structure.
Influence of Apparent Roughness on Pipeline Design Conditions Under Combined Waves and Current
Authors: Jones Oliver , Zyserman Julio A. , Wu Yushi 
Published: September 2014

The oscillatory nature of waves generates a thin boundary layer above the sea bed in which the fluid velocity decreases from its free stream value to zero at the bed. The wave boundary layer thickness is small compared to the current-alone boundary layer (which typically extends throughout the water depth) and, as such, is characterized by a zone of high shear velocity and associated high levels of turbulence. Strong turbulence intensities within the wave-induced boundary layer have an impact on the ambient current field, which experiences an increase in bottom resistance (the so-called ‘apparent roughness’) due to the presence of the turbulent boundary layer.
For currents on the continental shelf, it is well known that the effect of wave-enhanced bottom friction (or “apparent roughness”) is important in controlling the near-bed current speed and turbulent mixing. It can thus be reasonably expected that accounting for this apparent roughness will influence the design basis for sub-marine pipelines that cross the continental shelf. In this paper, we implement — and then demonstrate — the effect of wave-related apparent roughness on currents with the aim of providing a more accurate design basis for pipelines on the continental shelf.
SMIS - Subsea Monitoring via Intelligent Swarms, Design Challenges of an Autonomous Seabed Station
Authors: Boeck Florin , Golz Matthias , Ritz Sebastian , Holbach Gerd 
Published: September 2014

This paper presents the joint research project “SMIS” with focus on the requirements and the design of the seabed station. A major issue for all autonomous subsea systems is the problem of limited battery capacity due to design boundary conditions. SMIS counteracts this by deploying an autonomous power-carrying vehicle, similar to a mobile petrol station, to extend the operation time for the AUVs.
The demands of the autonomous seabed station include the unguided submerge through 6000 m water column, a safe landing on suitable ground without excessive power consumption and a reliable docking mechanism for power transmission to AUVs on the sea floor. Moreover, the communication between the SMIS vehicle fleet for georeference and path guidance during the AUV operation is essential. A modular design also allows operation in ROV mode, which expands the field of application.
A Comparative Study of a Free Span Pipeline Through Numerical Simulations
Authors: dos Santos Marcus V. F. , Morooka Celso K. , Caire Marcelo , Franciss Ricardo , Matt Cyntia G. C. 
Published: September 2014

A subsea pipeline has an important role to produce oil and gas from an offshore petroleum field, connecting a petroleum facility at the open sea and a near shore terminal at the coast. Very often, the pipeline passes over areas with uneven seafloor, and it may present free span portions. The main aim of the present work is improvements on the understanding of undesirable effects of vibrations in a subsea pipeline which presents free span portions along its length. This understanding is fundamental for the safe design and operation of the pipeline with possible reduction of its fatigue life.
Dynamic loads can occur as a consequence of the presence of sea currents acting on portions of the pipeline with free spans. Due to this hydrodynamic current loads, the pipeline structure may oscillate in the same direction of the current (In-line) and, in its transverse direction (Cross-Line). This dynamic response at the free span is mainly caused by the Vortex Induced Vibration (VIV). It is very important for the pipeline design because it can result extreme unacceptable stresses as well as in exceeding limits for the fatigue damage of the pipeline. And, this problem of VIV is still not been completely understood.
In the present paper, different models to estimate VIV forces due to sea current are discussed. For this purpose, different computer programs were used to predict vibrations in the transverse direction of the current incidence direction, caused by the vortex shedding in a free span of the pipeline. Simulations of the dynamic behavior of a free span portion of the pipeline were carried out by two approaches, respectively: an empirical hydrodynamic VIV force model, in frequency domain and, a semi-empirical VIV force model based on the lift coefficient and Strouhal number, in time domain. Simulations results are analyzed through comparisons with experimental data and also limitations of the each model are discussed.
Flowline Bundle Concept for JZ 9-3 Field Development
Authors: Cao Jing , Sha Yong , Li Liwei 
Published: September 2014

Flowline bundle system consisting of carrier pipe, sleeve pipe and internal flowlines offers smart solution for the infield transportation of oil and gas. Due to its features, flowline bundle offers a couple of advantages over conventional flowline in particular for cases where multi-flowlines and high thermal performance are of great interests. The main benefits and advantages of such system include excellent thermal performance to prevent wax formation and hydrates, multiple bundled flowlines, mechanical and corrosion protection, potential reuse, fabricated onshore, as well as towing installation without the requirement of professional pipelay vessel etc. Flowline bundle system can be a smart solution for certain applications, which can be safe and cost effective solution.
The objective of this paper is to present the feasibility study of flowline bundle concept for the JZ 9-3 West Development project in Bohai Bay, Offshore China. This study covers engineering design, fabrication, and offshore towing installation. Design and installation results have been presented and the feasibility of flowline bundle concept has been fully demonstrated for the JZ 9-3 West field development.
Hydrostatic Collapse Pressure and Radial Collapse Force Comparisons for Ultra-Deepwater Pipelines
Authors: Rosas Marco A. P. , Souza Ana Paula F. , Rodrigues Marcos V. , da Silva Danilo Machado L. 
Published: September 2014

In this paper the behavior and the relationship between hydrostatic collapse pressure and diametrically opposed radial compressive force for pipelines were analyzed. This study presents an introduction of a research work aimed to assess the pipeline collapse pressure based on the radial collapse force.
Initially the hydrostatic collapse pressure is analyzed, for pipes with different diameter to wall thickness ratio (D/t) and ovalities, using classical assessment (DNV method) and numerical models (FE). Then, the compressive radial force is also analyzed using numerical models validated by a small-scale ring specimen test. After that, the relationship between hydrostatic collapse pressure and compressive radial force is discussed. These first results show that the radial force is a quadratic function of the collapse pressure.
On the Performance of an Array of Floating Wave Energy Converters for Different Water Depths
Authors: McCallum Peter , Venugopal Vengatesan , Forehand David , Sykes Rebecca 
Published: September 2014

A frequency domain hydrodynamic assessment was carried out using WAMIT on buoy type wave energy converters (WECs), constrained to move in heave only. Control of the power take-off (PTO) system has been established through real control (damping resistance only) for an isolated WEC. This fixed value has then been applied to all WECs in an array of ten devices, set out in two rows. The array has been tested in six water depths, represented by the relative water depth d/λ0, ranging from 0.25 to infinite depth, where λ0 is the resonant wavelength of an isolated WEC in infinitely deep water. Incremental reductions in water depth, result in an drop in peak q̄-factor, which was also marked with a small shift in ka. It was deemed appropriate here to re-tune the PTO settings for the different water depths.
The various interactions within the array were examined in more detail by considering the radiation forces between WECs. Results are presented, highlighting the most significant device interactions due to the variations in water depth. The growth and shift in ka of the peak forces are also evident in shallower water. Depth modified JONSWAP and Pierson-Moskowitz spectra have also been applied in order to calculate mean power production estimates for the various water depths.
For the particular array and conditions considered, there was a clear downward trend in power captured when moving into progressively shallower water. This was in part due to the reduction in total energy available in the shallower spectra, but also because the frequency of peak performance of the array has shifted significantly.
Reliability-Based Calibration of Partial Safety Factors for the Horizontal Axis Tidal Turbine Standard for Certification
Authors: Simeon Gaizka Zarraonandia , Ferreira Claudio Bittencourt 
Published: September 2014

Tidal energy is nowadays one of the fastest growing types of marine renewable energy. In particular, horizontal axis tidal turbines (HATT) are the most advanced designs and the most appropriate for standardisation. It is however, in the interest of the industry to provide a set of standard practises in order to help in the process of designing this type of marine converters. DNV GL is producing this standard with the support of Alstom and as part of the ReDAPT project commissioned and co-funded by the ETI (Energy Technologies Institute).
The work undertaken by DNV GL to produce this standard involves the identification of the uncertainties that designers need to address during the design process. Unlike other marine structures, HATTs are usually located in very energetic areas where no other marine structure has been before. Site characterisation is one of the largest sources of uncertainty e.g. turbulence. Key inputs like turbine inflow conditions or predictions of extreme values are still grey areas due to the limited site measurements and the uncertainty of the metocean models. Numerical models of HATTs are still quite uncertain often dependent on experience of the people running them. As part of ReDAPT project there is an ongoing effort in validation and evaluation of the accuracy of these numerical models and some of the results are used in this calibration study.
The new standard for HATTs deals with the loading uncertainty in a whole new way by introducing a new parameter that is added to the traditional partial safety factors for loads. This new standard uses the traditional safety factors from the offshore structures standards and allows changing them based on the level of uncertainty that was introduced during the design process.
This paper describes the process of calibration of the partial safety factors in ULS for loads of HATTs that was part of the work in the creation of the new standard. The reliability based calibration involved the formulation of failure criteria, the identification of stochastic variables in the failure criteria, calculation of reliability against failure and ultimately the new set of partial safety factors for loads and a methodology for adjustment of the factors in a case by case basis.