bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Investigation on the Load Carrying Behavior of Large Ship Windows
Authors: Fricke Wolfgang , Gerlach Bjarne , Guiard Matthias
Published: September 2014

Aboard ships windows are exposed to static as well as dynamic loads, e.g. impact loads. Failure can lead to serious consequences. Therefore two research projects were initiated in order to analyze the load carrying behavior of windows. In addition to quasi-static ultimate load tests and drop tests with water filled rubber bags special attention is paid to the Finite Element (FE) modeling. In particular the response — stresses and deformations — to quasi-static lateral loads can be calculated with good agreement to test results. Hence FE calculations can be useful to determine and compare failure mechanisms of different window designs. An ultimate load range can be estimated by taking into account the breaking strength range of glass. A comparison between FE calculations and results of the impact tests showed that these are sensitive to conditions which could hardly be measured during the test, e.g. the shape of the approaching water-filled rubber bag. Varying of parameters eventually yielded that window response to impact loads can also be calculated sufficiently, at least, to evaluate different window designs. Further investigations on this topic are in progress.
Similarity of Rudder Effectiveness and Speed Response of a Free-Running Model Ship
Authors: Ueno Michio , Tsukada Yoshiaki
Published: September 2014

The authors had proposed a method, rudder effectiveness correction, to realize full-scale equivalent manoeuvring motion using scale models with the auxiliary thruster. In the method they introduced the rudder effectiveness correction factor to make the effective inflow velocity to rudder defined in a steady straight course similar to a corresponding full-scale ship. The method assumes the factor constant during manoeuvring motion for a model ship running at a constant propeller rate of revolution. In this report the authors propose by a numerical approach a detailed method ensuring more precisely the similarity of manoeuvring motion than the former one. The detailed method takes into account the similarities both of the speed response and rudder effectiveness. The time-varying control both of the propeller rate of revolution and rudder effectiveness correction factor, based on the new method, enables scale model ships to realize the similar manoeuvring motion to full-scale ships more accurately. Simulation calculations using the modular mathematical model of manoeuvring motion clarifies how well the detailed method raise the precision of the full-scale equivalent manoeuvring motion in free-running model ship testing comparing with the former method.
Risk-Based Approach for the Development of Guidelines and Standards on Combined Marine Renewable Energy Platforms
Authors: Macadré Laura-Mae , O’Sullivan Keith , Breuillard Antoine , le Diraison Stéphane
Published: September 2014

The combination of Marine Renewable Energy (MRE) technologies such as wave or current devices with offshore wind, a more mature technology, could enable pooling of R&D efforts and reducing costs (grid connection, moorings, maintenance activities…). Moreover, the different characteristics of the wind, wave and current resources could be complementary and provide a smoothing effect on the power production. Therefore, the EU FP7 project -MARINA Platform- aims at studying concepts of combined platforms integrating different types of MRE devices.

Many challenges are induced by these innovative platforms and guidelines and standards will be required to ensure safety, reliability and quality. However, as the concepts are only at the development stage, no standards have been written for these combined platforms so far.

This paper presents a new approach proposed by Bureau Veritas within the scope of the MARINA project for the development of guidelines and standards dedicated to combined MRE platforms. Existing literature on standards about MRE and related sectors, like shipping, wind energy and offshore oil & gas, forms a good basis to be exploited. In addition, risk assessment and qualification of new technology might be considered as a complement to standards to support the design of novel offshore concepts. Therefore, the presented methodology combines the use of existing standards from MRE and related sectors with a risk-based approach for the most innovative and unknown parts of the platform. A global risk assessment is performed in parallel for a whole review of the system.
Innovation for a Reduction of the Yaw Moment on a Floating Platform With a Vertical-Axis Wind Turbine
Authors: Kanner Samuel , Yeung Ronald W.
Published: September 2014

Three designs of a floating spar platform for a vertical-axis wind turbine (VAWT) are considered, including two novel designs. The novel designs convert the rotary motion of the platform to a translational motion (namely, heave), to reduce the maximum yaw stiffness requirements of the mooring system. In typical operational conditions of a VAWT, the mooring system needs to be stiff to prevent the yaw rotation of the platform, allowing power to be taken off from the rotary electromagnetic generator. The first design considered is a simple spar platform with mooring lines in a spread-mooring configuration. The second design, a novel design, incorporates a lead-screw to couple the rotational motion to a translational motion. This design can take advantage of the hydrostatic restoring force present in heave to reduce the mooring stiffness. The third design, also a novel design, uses a spar-torus combination platform and a lead-screw to counteract the torque on the stator of the generator. Numerical models in the time domain are developed to simulate the dynamics of these three platforms in regular waves and constant-wind conditions and the results are reported. It was found that the stiffness requirements of the second design can be reduced by 25% without changing the transient dynamics. If the wave climate is energetic enough, the third design can not only reduce the yaw stiffness requirements but also increase the mean power produced. Advantages and disadvantages of each design due to the relative complexity of each system, as well as the mooring, generator, and platform dynamics are discussed.
Development of an Approach Towards Mission-Based Design of Arctic Maritime Transport Systems
Authors: Bergström Martin , Ehlers Sören , Erikstad Stein Ove , Erceg Sandro , Bambulyak Alexei
Published: September 2014

This paper describes an approach that utilizes a discrete event simulation tool and ice data from a numerical ice prediction model to enable mission-based design of arctic maritime transport systems consisting of a single or multiple arctic cargo ships.

For a specific vessel design and route, the developed approach makes it possible to simulate how the transit time varies over time due to both varying ice conditions and stochastic factors such as the weather. Thus, for a given transport scenario (route, transport demand, and period of time), the approach can be used to determine a suitable vessel capacity, propulsion power, and ice class. When necessary, the approach can be used to analyze and design more complex transport system consisting of multiple vessels and routes.

A case study is carried out to demonstrate how the approach could be applied in practice. The outcome of the case study indicates that the approach generates realistic figures, and that it is flexible enough to make it possible to vary the number of included parameters and variables as needed.
Numerical Analysis of Failed Forecasts of Waves Under Low Pressures From Viewpoint of Ship Operation
Authors: Sasa Kenji , Chen Chen , Shiotani Shigeaki , Ohsawa Teruo , Terada Daisuke
Published: September 2014

Today, weather routing becomes more important under the current situation of international maritime transportation. However, the authors reveal that the current systems are not necessarily sufficiently reliable. It is also worthwhile to consider the background of the difficulty in numerically forecasting winds and waves. Here, two failed cases of wave forecasts are verified using WRF and SWAN, two numerical meso-meteorology models. In both failed cases, low pressures developed from the southern sea area of Japan with a northeast direction. First, wind direction can be reproduced correctly, even if the resolution of the simulation is changed. Second, if the resolution is insufficient, wind speed will be underestimated as smaller than the observed values. At the same time, wave height tends to be underestimated as compared to observed values, too. This is the feasibility study for improving the forecasting of wave growth pattern due to developing low pressures from the viewpoint of safe ship operation.
Numerical Assessment on Wave Energy Resources in Coastal Waters of Northeastern Taiwan
Authors: Tzang Shiaw-Yih , Chen Yung-Lung , Hsu Tai-Wen , Chen Da-Wei , Wang Chun-Chih , Lin Chen-Chou
Published: September 2014

To assess wave power resources at a marine energy test site in Keelung coastal waters, the SWAN (Simulating WAve Nearshore) model [1; 2] is applied to obtain wave conditions for assessing the wave energy resources. The ocean surface wind velocity by CCMP (Cross-Calibrated Mutli-Platform) is first adopted in SWAN model simulation. Comparisons with field measurements of AWCP (Acoustic Water Column Profiler) station in Port of Keelung and of ADCP (Acoustic Doppler Current Profiler) station offshore NTOU (National Taiwan Ocean University) during periods form Jul 1st to Dec 31st of 2010, show that simulated significant wave heights agree well with measured values except in periods of typhoons and strong northeastern monsoons. However, the simulated peak periods are generally underestimated than the measurements. The same results can also be seen in simulated wave energies. The resulting simulated wave energies agree with measurements better at NTOU test site than at Keelung station.
The Development of Meteorological and Oceanographic Data Collection and Recording System Operating on Training Ship
Authors: Fujii Michio , Hayashi Mitsuru , Urakami Misako , Wakabayashi Nobukazu
Published: September 2014

The observation at sea for marine meteorology is achieved by weather reports from merchant ship’s crew every 3 or 6 hours, mainly. However, the number of available observation data is insufficient for weather forecasting and marine environmental simulation, compared with landside. Nowadays, the special data collection function is required if the automatic observation data collection system is installed on ship. But, it is difficult to install special equipment onto general merchant ship. Therefore, we develop a prototype marine observation system, which can be installed various types of ships easily without any special data collection function for improving data collection source and/or period of the observation at sea.

In this paper, a) the configuration of high reliability and durability marine observation system by using general-purpose PC and general meteorological / oceanographic sensors, b) outlook of utilizing the data, which collected by this system, are described.
Impact Resistance Cryogenic Bunker Fuel Tanks
Authors: Voormeeren Lars O. , Atli-Veltin Bilim , Vredeveldt Alex W.
Published: September 2014

The increasing use of liquefied natural gas (LNG) as bunker fuel in ships, calls for an elaborate study regarding the risks involved. One particular issue is the vulnerability of cryogenic LNG storage tanks with respect to impact loadings, such as ship collisions and dropped objects. This requires an understanding of the impact resistance of the storage tanks and the actual loads to be expected. No substantial literature exists on the actual energy absorbing capacity (crashworthiness) of cryogenic tanks. Main issues are material properties under cryogenic/ moderate strain rate conditions and failure mechanisms associated with large deformation - fluid structure interaction, in particular the liquid-full condition.

This paper reports material properties of stainless steel 304 at both ambient and cryogenic conditions. Also the effect of strain rate is addressed. Moreover, it describes and compares two approaches of predicting the effect of the ‘liquid-full’ condition on the impact resistance of LNG storage tanks. The first approach follows a multi-material Arbitrary-Lagrangian-Eulerian (ALE) formulation, whereas the second approach captures the fluid-structure interaction through an analytical loading subroutine, calculating the internal pressure as a function of tank volume decrease. Results of impact experiments on partially liquid-filled small-scale storage tanks are presented. The calculation methods have been validated against the experimental results. The results of the validation show that the crashworthiness of stainless steel (cryogenic) storage tanks can be well predicted through both the ALE and the analytical formulation.
On Determination of Acceptable Safety Class in Design of Pipe-In-Pipe (PIP) Systems
Authors: Manouchehri Soheil , Hardouin Guillaume , Kaye David , Potter Jason
Published: September 2014

Pipe-In-Pipe (PIP) systems are increasingly used in subsea oil and gas production where a low Overall Heat Transfer Coefficient (OHTC) is required. A PIP system is primarily composed of an insulated inner pipe which carries the production fluid and an outer pipe that protects the insulation material from the seawater environment. This provides a dry environment within the annulus and therefore allows the use of high quality dry insulation system. In addition, from a safety point of view, it provides additional structural integrity and a protective barrier which safeguards the pipeline from loss of containment to the environment.

Genesis has designed a number of PIP systems in accordance with the recognized subsea pipeline design codes including DNV-OS-F101 [1]. In section 13 F100 of the 2013 revision, a short section has been included in which PIP systems are discussed and overall design requirements for such systems are provided. It has also been stated that the inner and outer pipes need to have the same Safety Class (SC) unless it can be documented otherwise.

This paper looks at the selection of appropriate SC for the outer pipe in a design of PIP systems based on an assessment of different limit states, associated failure modes and consequences. Firstly, the fundamentals of selecting an acceptable SC for a PIP system are discussed. Then, different limit states and most probable failure modes that might occur under operational conditions are examined (in accordance with the requirements of [1]) and conclusions are presented and discussed. It is concluded that the SC of the outer pipe of a PIP system may be lower than that of the inner pipe, depending on the failure mode and approach adopted by the designer.
Green Water Phenomena on a Twin-Hull FLNG Concept
Authors: van ‘t Veer Riaan , Vlasveld Ebert
Published: September 2014

This paper investigates — based on model tests and potential flow calculations — several phenomena associated with the green water problem in severe sea states. The topics investigated are: the wave characteristics of the severe and steep sea states, the behavior of the vessel in these waves, the relative motions at the bow and the height of water on deck.

The green water problem is of interest since many floaters used for the oil and gas production by the offshore industry are permanently moored for typically 20 years or more, and they will experience severe storm conditions with large wave heights.

The investigations concern an unusual vessel type: SBM’s innovative midscale Twin-Hull FLNG concept [1]. The floater concept is to join two (standard) LNG carriers together to obtain sufficient storage volume and process deck space. The concept is under development and one aspect, from operability point of view, is the probability for green water. For this purpose a first model test campaign has been carried out.

The Twin-Hull FLNG concept has been tested in extreme sea states which are typical for offshore Brazil and East-Africa.

Linear potential flow calculations were applied to predict the freeboard exceedance based on relative motion amplitude operators. The correlation to the measured data is discussed.

Although the research is dedicated to the Twin-Hull FLNG vessel, the observed phenomena are considered applicable to any stationary vessel in general.
Shock Response of Ship Section to Underwater Explosion With the Cavitation Effect
Authors: Ying-yu Chen , Yao Xiongliang , Wei Xiao , Xiang-dong Liu
Published: September 2014

Besides the shock wave load and the gas bubble pulse load, cavitation effect has a significant influence on the ships subjected to underwater explosion. The goal of this research is to investigate the cavitation effect on the response of ship section using acoustic-structural arithmetic. Comparison between the structure response considering the cavitation effect and not, the formation mechanism of cavitation zone are discussed. The simulation results show acoustic-structural arithmetic can be used to numerical simulate the dynamic response of simple structure and ship section subjected to underwater explosion with the consideration of cavitation effect. And it also can be used to capture the cavitation in the water. Meanwhile, the simulation results show that cavitation zone generated by underwater explosion is very large, and the reloading effect is obvious with the consideration of cavitation effect. The vibration of the ship structure is more severe with the reloading, and thus more serious damage occurs as the result of the prolonged loading time.
Tow Forces for Emergency Towing of Containerships
Authors: Shigunov Vladimir , Schellin Thomas E.
Published: September 2014

For a series of five containerships of differing capacities (707, 3400, 5300, 14000 and 18000 TEU) systematic computations were performed to estimate the tow force required in an emergency. Time-average ship positions with respect to the given waves, wind and current directions and the corresponding time-average forces were considered. Current speed was considered to include also towing speed. Directionally aligned as well as not aligned wind and waves were investigated. Wave height, wind speed, and wave and wind direction relative to current direction were systematically varied. Wind speeds based on the Beaufort wind force scale corresponded to significant wave heights for a fully arisen sea. Waves were assumed to be irregular short-crested seaways described by a JONSWAP spectrum with peak parameter 3.3 and cosine squared directional spreading. For each combination of current speed, wave direction, significant wave height and peak wave period, the required tow force and the associated drift angle were calculated. Tow force calculations were based on the solution of equilibrium equations in the horizontal plane. A RANS solver for current and wind forces and a Rankine source-patch method for drift forces in waves computed hydrodynamic forces and moments. Tow forces accounted for steady (calm-water) hydrodynamic forces and moments, constant wind forces and moments, and time-average wave drift forces and moments. Rudder and propeller forces and towline forces were neglected.
End Fitting Effect on Tensile Armor Stress Evaluation in Bent Flexible Pipe
Authors: Zhu Linfa , Tan Zhimin
Published: September 2014

The stress evaluation of tensile armor layer in bent unbonded flexible pipe due to end fitting termination is investigated. A preliminary mathematical stress analysis model which accounts for the boundary condition at the end fitting interface is developed. Two shifting parameters are introduced to correct the friction field acting on the tensile wires. Closed form solutions are obtained for the modified friction force, axial stress and displacement. The validity of this model is investigated through a comparison with results obtained using a 3D finite element model. The relationship between the shifting parameters and the initial hoop position of wires is discussed. Studies of local stress elevation on wires with different initial hoop positions are conducted. The results show that end fitting effect could causes a significant stress elevation in a large amount of tensile wires if heavy pipe bending is permitted at the end fitting vicinity.
Hydrodynamic Performance of a Novel Free Surface Pitching Breakwater
Authors: Venugopal Vengatesan , Zlatev Stefan
Published: September 2014

A new concept floating breakwater was developed and tested to evaluate its hydrodynamic performance in this paper. This innovative floating breakwater has a rocking body shape which could also be used as a wave power device. A scale model was tested in a wave flume under regular and irregular wave conditions for various combinations of wave frequencies and wave heights. The breakwater has been tested for three immersion depths of 0.05 m, 0.09 m and 0.13 m from still water level. The measured transmitted and reflected waves were used to evaluate the coefficients of transmission (CT), reflection (CR) and dissipation (CL). The results illustrated that the breakwater model performed at its best when submerged at 0.13m, as this immersion depth produced lower coefficients of transmission (CT), lower reflection coefficients (CR) and higher energy dissipation (CL) coefficients. The comparison between regular and irregular waves produced similar ranges of transmission, reflection and energy coefficients.
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.
Marine Energy Resource Assessment for Orkney and Pentland Waters With a Coupled Wave and Tidal Flow Model
Authors: Venugopal Vengatesan , Nemalidinne Reddy
Published: September 2014

Some preliminary results obtained from a coupled wave and 3D tidal flow numerical model, applied to the Orkney and Pentland waters in the Scottish region of the United Kingdom, are reported in this paper. The coupled wave and flow model was applied to the Orkney Islands comprising a domain of 1.25°W – 5°W and 58.25° N – 59.75°N. The model was run by boundary inputs of wind and water level extracted from European Centre for Medium Range Weather Forecasts (ECMWF) and Danish Hydraulic Institute’s (DHI) global tidal model respectively. The model has been calibrated and validated with wave buoy and ADCP (Acoustic Doppler and Current Profiler) measurements. The depth-wise current velocity components predicted by the model were compared with ADCP measurements for three sites in the Pentland Firth. The results indicated that the coupled model worked well and the tidal current velocities from the model correlated well with ADCP measurements at different depths.
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.
Investigating LiDAR Sensing Errors for Wind Turbines Loads Reduction
Authors: Bayon Benoit , Chauvin Jonathan
Published: September 2014

LiDAR sensors are a promising technology for a reliable measurement of the incoming wind. This is especially useful for applications such as antennas and wind turbines. For wind turbines, the use of this sensor provides the information of the rotor wind speed which can be used in dedicated control laws to improve the wind turbine performance, mainly on the mechanical loads and extreme moments. However the provided information is not flawless. Several error sources exist and degrade the wind information. As a consequence, the performance of the blade pitch control law is reduced. In this paper, an insight of the LiDAR measurement error sources is provided through the establishment of a frequency domain model. The impact of these errors on the performance of a blade pitch control law is investigated, along with the comparison with a standard control law.
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.
Experimental Investigation vs Numerical Simulation of the Dynamic Response of a Moored Floating Structure to Waves
Authors: Dessi Daniele , Minna Sara Siniscalchi
Published: September 2014

A combined numerical/theoretical investigation of a moored floating structure response to incoming waves is presented. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used as a multipurpose platform for hosting wind-turbines, aquaculture farms or wave-energy converters. The dynamic wave response is investigated with numerical simulations in regular and irregular waves, showing a good agreement with experiments in terms of time histories of pitch, heave and surge motions as well as of the mooring line forces. To highlight the dynamical behavior of this complex configuration, the proper orthogonal decomposition is used for extracting the principal modes by which the moored structure oscillates in waves giving further insights about the way waves excites the structure.
Effect of Flap Type Wave Energy Converters on the Response of a Semi-Submersible Wind Turbine in Operational Conditions
Authors: Michailides Constantine , Luan Chenyu , Gao Zhen , Moan Torgeir
Published: September 2014

In the present paper the effect of flap type wave energy converters on the response of a floating semi-submersible wind turbine is investigated and reported. Two different layouts with regard to the number of rotating flaps that are utilized are considered and compared with the case of a pure floating semi-submersible wind turbine. Comparisons of response in terms of stability, motions and internal loads are made for selected environmental conditions. The combined operation of the rotating flaps results in an increase of the produced power without affecting significantly selected critical response quantities of the semi-submersible platform.
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.
Design and Analysis of Trochoidal Propulsors Using Nonlinear Programming Optimization Techniques
Authors: Roesler Bernard T. , Francsiquez Manaure , Epps Brenden P.
Published: September 2014

Flapping foil propulsors may increase the propulsive efficiency of large shipping vessels. This paper presents the design of a notional propulsor for an inland waterway vessel. Calculations for the trochoidal propulsor are performed using a lumped, two-dimensional model, which includes the influence of the free vortex wake, as well as approximations to account for three-dimensional effects. The numerical model is used to optimize the foil pitch function in order to achieve the highest efficiency for given geometric and operational parameters. Foil-to-foil interactions are studied for multiple-foil propulsors to determine effects of blade number on hydrodynamic efficiency. Considerations of packaging options for a trochoidal propulsor are explored. The results presented herein can also be applied to large- and mid-sized ships, such as international shipping vessels, fishing vessels, cruise liners, and military ships.
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.