bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of the Geometric Tunability of a WEC From a Worldwide Perspective
Authors: de Andrés Adrián D. , Guanche Raúl , Vidal César , Losada Íñigo J. 
Published: September 2014

Nowadays the goal of WEC developers is to reduce the price of the harvested energy for its own technology, via either decreasing the cost of WECs or increasing the power production. In order to increase the power production of a particular WEC, usually the WECs are tuned with the wave climate at the target location. However, in order to achieve the maximum profitability, the WECs must be able to be deployed in a bunch of locations with different wave climates. Therefore WECs must be flexible to be adapted to different kind of locations.
The matchability of a device could be achieved via the PTO control or changing the geometric characteristics of a particular device. In this study, an analysis about how the geometric tuning of a generic wave energy converter affects to different climate scenarios is performed.
Firstly, a generic wave energy converter is assumed to be formed by an array of floating cylinders that absorb in heave. Three options are proposed in the present study, a cylinder with its natural period on 4 s, typical of enclosed seas, another option with a natural period of 8 s (mean Atlantic swell) and an option that is tunable as a function of the location in order to evaluate the influence of tuning on the power performance.
The power matrix is computed with a frequency domain model and then, the converters are evaluated worldwide, taking the met-ocean data from a global reanalysis database (GOW) from Reguero et al (2012). The results are presented in terms of two main indicators, on one hand, the capture width ratio, that evaluates the efficiency of the converter on each location, and the kW/Ton parameter that evaluates the efficiency of the converter on “economic” terms.
Finally, tuning a converter for each location of deployment resulted positive in terms of capture width ratio, however regarding the kW/Ton indicator tuning resulted useless due to the heaviness of the structures needed to tune the converter with high peak periods. The number of suitable locations (in terms of an acceptable kW/Ton indicator) was higher as the mass of the structure is reduced, regardless of the natural period of the converter, thanks to a good performance of high natural periods converters.
The Design Limitations of a Circular Wave Pool
Authors: Schmied Steven A. , Binns Jonathan R. , Renilson Martin R. , Thomas Giles A. , Macfarlane Gregor J. , Huijsmans Rene 
Published: September 2014

In this paper, the design of a circular wave pool that produces continuously breaking waves is discussed, whereby a pressure source is rotated within an annular wave pool. The concept was that the pressure source generates non-breaking waves that propagate inward to the inner ring of the annulus, where a sloping bathymetry (beach) triggers wave breaking. In order to refine the technique, research was conducted to better understand the mechanics of waves generated by moving pressure sources in a constrained waterway, the transformation of these waves as they travel across the channel and the effect of the sloping beach on the wave quality for surfing.
The quality of the waves was defined in terms of wave height, speed and shape, with the aim to create plunging waves, known as “barrels”, that are highly desired by surfers.
A predominantly experimental approach was undertaken to determine the required design parameter values and their limitations. Scale model experimental results were previously presented at OMAE 2011 and OMAE2013.
This paper presents the steps to design the pool using the empirical analysis and experimental results are presented. The effect of the pressure source and pool bathymetry on the currents formed in the pool, are also presented. Through this design process, high quality continuous breaking waves with the desired plunging shape were able to be generated.
Finally, the authors are planning to use the facilities and techniques developed to investigate the complexities of predefined wave fields, including the three dimensional (3D) details of the velocity, pressure and turbulence fields beneath. Understanding these complexities within multidimensional wave patterns is the key to analysing a number of different fields, including wave resistance of ships; wave disturbances to other maritime users; bank erosion; wave signal tracking; and wave structure interaction.
Lessons Learned From Auditing Structural Integrity Management
Authors: Ersdal Gerhard , Galbraith David , Sharp John 
Published: September 2014

As part of its regulatory duties the Norwegian Petroleum Safety Authority (PSA) periodically undertakes audits of the Structural Integrity Management (SIM) functions of the operators of facilities within the Norwegian offshore jurisdiction; typically one or two audits of reasonable detail are undertaken each year, but in addition PSA have also tried a series of mini-audits based purely on interviews without examination of evidence.
In many cases certain aspects of the SIM cause the auditors some concern and there is a degree of consistency about those aspects of SIM causing such concern, and on occasion become formal “findings” of the audits. In general the actual execution of SIM activities are performed adequately, but the full understanding of the purpose of SIM and realistic intent and expectation are missing. A particular concern of the auditors is the anticipation of structural form-specific accidental and abnormal events and their incorporation into the SIM.
This paper will provide a summary of the more important lessons learnt over several years of auditing, in an attempt to provide industry with a better understanding of the regulator’s expectations of SIM, particularly for installations that are ageing or have unique features.
Analysis of the Loads on and Dynamic Response of a Floating Flexible Tube in Waves and Currents
Authors: Genzman Grant N. , Fredriksson David W. , Schultz Michael P. , Trent Jonathan D. 
Published: September 2014

Recently proposed offshore structure designs for wastewater treatment and algae biomass production may incorporate floating flexible tubes. In one configuration, the tubes float at the surface and contain a fluid and algae mixture. The purpose of this study is to analyze the loads on and dynamic response of such tubes in varying environmental conditions, specifically waves and currents.
The approach includes both physical and numerical modeling techniques. Physical models at a scale of 1:4.21 (model to prototype) and two fill levels (50% and 95%) were tested in wave and towing tank facilities in the Hydromechanics Laboratory at the United States Naval Academy. The models were towed at a range of scaled speeds to represent currents and subjected to scaled wave conditions in one of the tanks. During these tests, attachment loads were measured and dynamic response was evaluated.
In addition to the physical modeling approach, Computational Fluid Dynamics (CFD) simulations were performed to assess steady drag measurements at the 1:4.21 scale and the results were compared to the experimental tests. The CFD modeling results were comparable to those obtained from the physical modeling tests, at least at the higher fill levels that were analyzed.
The results indicated that the model response tended to follow the wave forcing more at the middle wave frequencies. For both fill levels, the response of the forward end of model increased with wave frequency while the response of the rear end of the model remained rather consistent across the frequencies tested. The results did not indicate a significant difference in dynamic response when the model was tested in both waves and current. The average attachment loads, however, were higher when the model was tested in waves and a current than in waves only. The attachment loads were also higher in wave and current conditions that included a faster current or lower-frequency (larger) waves.
The intent of the project, through both modeling methods, was to increase the understanding of the loads on and the response of a floating tube in waves and currents. Future work could include an increase number of replicates for better accuracy, additional test frequencies and tow speeds, alternate attachment techniques, and testing at larger scales for comparison.
Experimental Data on the Systematic Variation of the Internal Damping Inside a U-Shaped Anti-Roll Tank
Authors: Gunsing Michiel , Carette Nicolas , Kapsenberg Geert 
Published: September 2014

Anti-Roll Tanks (ARTs) can be a successful device to reduce ship roll motion (Figure 1), but the tank has to be properly designed. A good design includes an appropriate number of damping devices in the tank to reduce the water motions at resonance and to increase the frequency range over which the tank works efficiently. It is difficult to accurately predict the effect of different damping devices on the roll damping moment of the tank; usually tests on a rotating table, so called bench tests, are performed for each individual design.
Nowadays, CFD (see e.g. [1]) calculations solving the URANS equations can predict the effect of damping devices on the roll motion of the tank. In order to validate such codes a series of experiments with a U-type ART on a rotating table have been carried out where the interior arrangement in the duct of the tank has been varied. The set-up of the experiment, the measurement system and the results of the experiments are presented and discussed in this publication; the raw data of the experiments are also made available.
A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures
Authors: Lu Xin , Kumar Pankaj , Bahuguni Anand , Wu Yanling 
Published: September 2014

The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms.
The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications.
We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.
Deep Water Installation, Hydrodynamic Aspects and Practical Considerations
Authors: van Dijk Radboud , van Zandwijk Kees , Harmsen Eelco 
Published: September 2014

The past decade has shown a fast growing subsea production market tending to complete factories on the sea floor involving ever more complicated infrastructure and increasing size and weight components to be installed. The water depth of this market typically ranges between 1000 and 3000m. This new subsea market triggers a need for increased deep water lowering capacity to enable safe, fast and efficient installation of this infrastructure.
The authors’ company has gained extensive experience in the field of deep water installation over the past 15 years, ranging from complex mooring foundations to the installation of large subsea production units in up to 3000m water depth. This experience is used and further deployed in the specification of new and higher capacity deep water lowering systems for recent and upcoming investments.
The paper will share a number of the contractor’s considerations with respect to a state-of-the-art deep water lowering system meeting the needs of today’s subsea production market. The paper will address the challenges associated with the various stages of deep water installation, choices made in type of ropes (steel versus fiber), pros and cons of various floater types that can be used as an installation platform and the need for and effect of passive or active heave compensation.
Estimation of Failure Parameters for Finite Element Simulations Based on a Single State of Stress and Arbitrary Stress-Strain Relation
Authors: Voormeeren Lars O. , Walters Carey L. , Tang Lisa , Vredeveldt Alex W. 
Published: September 2014

Crash analysis in the maritime and offshore industry typically relies on failure criteria that are based only on uniaxial states of stress. However, it is well known that the failure strain depends on the state of stress, and the state of stress in ship collisions is not necessarily uniaxial. Although more detailed failure models are routine in other industries, the cost of finding the parameters for these models remains a barrier within the maritime and offshore industry. This paper explores an approach of applying the Modified Mohr-Coulomb (MMC) failure criterion based on a single tension test. This is based on the observation that there is only a single independent calibration parameters when a von Mises yield locus and plane stress are assumed. The MMC yield condition is also generalized by applying it to an arbitrary stress versus strain relationship, which does not follow the power hardening law.
Results of impact tests on small-scale cryogenic storage tanks filled with water and air are presented and are used to validate the adjustments made above. This validation test also shows how the above findings can be applied to storage tanks for LNG fuel on inland waterway ships.
Hull Structural Analysis of Turret-Moored FPSOs Considering Hull–Turret Interaction
Authors: Lee Ki-Myung , Choi Won-Hyuk , Kim Hyun Soo , Moon Seung Han , Kim Jin Tae 
Published: September 2014

For turret-moored ship-type offshore structures such as floating production storage and offloading (FPSO) units, the hull structure is affected by mooring and riser loads that are transferred through turret systems, in addition to environmental loads on the hull itself. Moreover, the existence of turret structures has an influence on the structural behavior of the hull around the turret system. In the structural design of FPSOs, the turret structure and its loads are considered in a direct analysis of hull structure for a realistic strength assessment of FPSOs.
This paper investigates several specific techniques for hull structural analysis considering the interaction with the turret system. The linear gap function is utilized to represent the nonlinear contact behavior between the hull and turret structures. The linear superposition of structural responses is also adapted, and its validity is demonstrated in the case of hull–turret contact problems. These studies conclude that the hull structures with turret systems that involve contact nonlinearity in their interface can be assessed using the conventional hull strength assessment based on linear analysis. Moreover, by including the turret model directly in hull structural analysis, the uncertainty arising from hull–turret interface loads can be reduced, and a robust and adaptive design procedure can be set up in the detailed engineering stages.
Modelling Installation and Construction of Offshore Wind Farms
Authors: Stempinski Florian , Wenzel Sebastian , Lüking Jan , Martens Luigi , Hortamani Mahboubeh 
Published: September 2014

While the offshore climate in the North Sea bears a great potential for the exploitation of reliable and powerful wind energy it poses a challenge for the constructors of offshore wind farms. Large heavy lift jack-up vessels (HLJV) are employed to transport the components of the wind energy converters to the offshore location. After a preloading and jacking procedure, subsea lifts of tripod foundations weighing up to 950tons as well as tower and nacelle installations at large heights need to be undertaken. As typical offshore wind farms consist of 80 or more separate wind turbines the installation works are conducted in a serial manner — often through the winter season. Thus, many critical offshore operations are conducted consecutively on the basis of daily or weekly weather reports. These operations cannot rely on optimal weather conditions therefore planning and engineering has to cover appropriate wind and wave conditions taking into account contingencies for uncertainties in the reliability of weather windows as well as in the soil conditions.
This paper shows how the weather criteria derived from numerical seakeeping and structural simulations are taken into a project simulation model covering 90 separate serial installations. Based on hindcast re-analyses installation simulations are conducted in multi-seasonal weather scenarios. This enables the quantification of the suitability of a particular marine spread and its associated installation processes in combination. The risk profile of weather related delays are derived.
Reliable and Efficient Injury Assessment for Free-Fall Lifeboat Occupants During Water Entry: Correlation Study Between Lifeboat Acceleration Indicators and Simulated Human Injury Responses
Authors: van Dam E. , Uittenbogaard J. , Reinholdtsen S. A. , Fouques S. , Sauder T. 
Published: September 2014

The evacuation of personnel from an offshore installation in severe weather conditions is generally ensured by free-fall lifeboats. During the water entry phase of the launch, the lifeboat may be subject to large acceleration loads that may cause harmful acceleration-induced loads on the occupants.
The present/common methodology for assessing the occupant safety of free-fall lifeboats uses one single characteristic launch to perform injury risk analysis for a given free-fall lifeboat launch condition that includes e.g. weather conditions, lifeboat and host installation loading conditions.
This paper describes an alternative methodology to fully assess the risk of injury for lifeboat occupants during water entry by introducing a correlation model between acceleration load indicators and injury responses. The results are presented in terms of seating matrices showing critical seat rows, in which the probability of being injured exceeds a pre-defined threshold.
Type Classification for Horizontal Axis Tidal Turbine (HATT): An Important Step Towards Commercialisation
Authors: Bittencourt Claudio , Argyriadis Kimon , Steiniger Michael 
Published: September 2014

One key aspect of serial production is to define a set of parameters that can define the limits and conditions that product can be used. Type certification is applied to serial production such as wind turbines when the matching of the site characteristics and the turbine design conditions is summarised in a short description of the site parameters that fundamentally describes the wind conditions (energy and turbulence). This easy matching is used by all stakeholders in assessing the suitability of different turbines to a specific project development. However, type classification is also important to optimise the design, manufacturing, installation and maintenance costs by setting key parameters to production of turbines with same characteristics (scale factor).
The same applies to tidal turbines. Although, at the present phase of development, serial production is not yet a main driver and designs are mainly carried out with specific sites in mind, it is useful to develop a type classification now to support generic design parameters and that can be tested for future serial production and matching sites with serial products.
While for wind turbines, the set of key parameters is reasonably simple [1], for tidal there are a number of environmental conditions (for example waves, astronomical tide, current turbulence, water depth, etc), and parameters (such as hub height related to the seabed and sea surface) which must be considered within the design of a HATT, parameters which may also be utilised in the construction of generic type classes for Tidal Turbines.
Thus, the identification of generic type classes for HATTs is dependent upon the ability (by conjunction of assumptions, formulations, etc.) to distil the existing extensive list of site / HATT parameters down to a minimum number of key parameters upon which a simple but robust set of generic type classes could be based.
Whilst it is recognised that adjustments of type classes may be required in the future, a first approach will be presented in the DNV GL Standard for Certification of HATT developed under the ReDAPT project and it is described in detail in this paper. The ReDAPT project is commissioned and co-funded by the ETI (Energy Technologies Institute).
Numerical and Experimental Research on a Podded Propulsor
Authors: Islam Mohammed , Ryan Ron , Molynuex David 
Published: September 2014

This paper presents methodologies and some results of a numerical and experimental program to evaluate the effects of static azimuthing conditions on the propulsive characteristics of a puller podded propulsor in open water. In the experimental effort, the model propulsor was instrumented to measure thrust, torque and rotational speed of the propeller, and three orthogonal forces and moments, and azimuthing angle of the pod. The experimental results included the bare propeller (ahead only) and the combined propeller and pod over a range of advance coefficients at various static azimuthing angles in the range of −180° to 180°.
A complementary numerical study is being carried out to predict the hydrodynamic forces of podded propulsor in static azimuthing conditions. A Reynolds-Averaged Navier Stokes solver is used to predict the propulsive performance of the bare propeller as well as the podded propulsor system. The thrust and torque for the bare propeller were compared to the corresponding measurements. The propeller thrust and torque as well as the loads on the pod in straight-ahead condition and at static azimuthing angles were then compared with the measurements. Preliminary analysis demonstrates that the RANS solver could predict the performance coefficients of the bare propeller as well as the podded propulsor in straight-ahead and static azimuthing angles in puller configurations.