bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physical and Numerical Modelling of Mooring Forces and Displacements of a Wave Activated Body Energy Converter
Authors: Angelelli Elisa , Zanuttigh Barbara , Martinelli Luca , Ferri Francesco 
Published: September 2014

The paper analyses the forces on the mooring system and the device motions of a floating Wave Activated Body Energy Converter under ordinary and extreme wave conditions. The investigation has been carried out with physical and numerical approaches. The physical tests were performed in 1:60 scale in the shallow-water wave tank of Aalborg University, whereas the numerical simulations were performed in 1:1 scale with the AQWA code developed by ANSYS. The spread mooring system tested in the laboratory allowed for an efficient device keeping while minimising the space. The loads on the moorings increase with increasing the significant wave height and show a modest trend with the peak wave length.
These experimental measurements were compared with the numerical results, suggesting that AQWA model is able to accurately reproduce the standard deviation of the forces on the mooring lines. From the simulations it is highlighted that the device should work far from resonance condition, because when the typical wave period is near to the natural period (in surge) the forces acting on the mooring lines increase, resulting in a high level of energy loss.
Derivation of Wave Height and Peak Period Statistics Accounting for Physical Limitations
Authors: Melis Cécile , Bonnaffoux Guillaume 
Published: September 2014

When assessing the joint-probability of significant wave height and peak period, (Hs,Tp) measured over years at a given site, it is customary to fit a log-normal distribution to assess Tp dependence on Hs. The parameters of this distribution are then used either to compute N-year return period design curves in order to compute extreme response by means of short-term analysis, or response distributions, by means of response-based analysis.
The main drawback of the Log-Normal distribution to represent the variability of Tp wrt. Hs is that its lower bound is zero, while physics tell us that wave steepness cannot be infinite, hence the lower bound, Tplim(Hs) should be greater than zero. If the distribution is kept unbounded, the resulting statistical fitting tends to predict occurrences of sea-states with (Hs,Tp) pairs having unphysical or unlikely steepness. This is particularly true in the range of 10–15s, where some ship-shaped units mooring systems responses are at their maximum.
Attempts have been made in the past to introduce a lower bound to the log-normal distribution, for instance by Drago et al, [1], by shifting it by a predefined value of limit steepness. By doing so, some points of the original dataset had to be discarded as they were falling below the lower bound. An evolution of their methodology is proposed in this paper, which uses the points of the dataset in a relevant region which will be defined hereafter, and then uses this limit to shift the Log-Normal distribution. The obtained environmental contours are then compared against observed data to check which one fits most accurately the original set of measured (Hs,Tp) pairs.
Viscoelasticity and Drilling Fluid Performance
Authors: Lee John , Tehrani Ahmadi , Young Steve , Nguyen Christine 
Published: September 2014

Viscoelastic properties of drilling fluids are not often measured due to a lack of understanding of their impact on fluid performance as well as a lack of field equipment suitable for such measurements. A study has been conducted recently to evaluate the viscoelastic properties of xanthan gum and invert drilling fluids and their impact on barite suspension quality and rheology. Both a Brookfield YR-1 rheometer and a Bohlin Gemini 150 rheometer were used to generate data for comparison. The impact of viscoelasticity on steady-state rheology, thixotropy and shear thinning was evaluated using a multi-speed rheometer. A soon-to-be-adopted API recommended procedure was used to measure the barite sag tendency under dynamic conditions.
Aqueous solutions of xanthan gum showed that viscoelasticity, shear thinning and thixotropy increased with increasing polymer concentration. When the solutions were weighed up with barite, they became more viscoelastic, slightly more thixotropic, but less shear thinning. Proper suspension of barite was observed at a xanthan gum concentration of 2 lb/bbl without any other additives.
Compared to xanthan-barite suspensions, invert drilling fluids of similar density exhibited a greater viscoelasticity but less thixotropy and shear thinning. Treatment of invert drilling fluids with viscoelastic polymers resulted in a further enhancement of viscoelasticity and thixotropy, but a slight deterioration in shear thinning. Barite suspension quality showed a certain degree of correlation with viscoelasticity as well as steady-state rheology; however, these properties were temperature dependent for invert drilling fluids.
Hydraulic analyses indicated that viscoelastic additives can impact fluid viscosity thus affecting pressure loss, equivalent circulating density and hole cleaning. Viscoelasticity enhancement may be used to improve barite suspension quality under certain conditions, but its impact on hydraulics must be carefully considered.
Wave Energy Assessment and Wind Correlation for the North Region of Scotland, Hindcast Resource and Calibration, Investigating for Improvements of Physical Model for Adaptation to Temporal Correlation
Authors: Lavidas George , Venugopal Vengatesan , Friedrich Daniel , Argawal Atul 
Published: September 2014

Wave energy sites around Scotland, are considered one of the most energetic waters, as they are exposed to the Atlantic Ocean. The amount of energy reaching the shoreline provides an opportunity for wave energy deployments.
Currently, considerations on wave devices expect them to be installed at nearshore locations. That means that the potential wave resource has to be investigated, since deep to shallow water interactions alter the shape of propagated waves. Resource assessment for these regions is essential in order to estimate the available and extractable energy resource. Although several numerical models exist for wave modelling, not all are suitable for nearshore applications.
For the present work, the nearshore wave model SWAN has been used to simulate waves for the Hebridean region. The set-up, calibration and validation of the model are discussed. The resulting wave conditions are compared with buoy measurements. Results indicate that the modelling technique performed well.
Application of Focusing Wave Groups in Model Testing Practice
Authors: Schmittner Christian , Brouwer Joris , Hennig Janou 
Published: September 2014

For hydrodynamic model testing different types of model waves are applied, where the most common ones are regular (monochromatic) and irregular (multichromatic) waves. In addition to these wave types the application of focusing wave groups, which are also often denoted as wave packages or transient wave packets, can give insight into aspects that cannot be assessed by the conventional model waves.
This paper describes the different applications of focusing wave groups for hydrodynamic model testing. The paper starts with the historical background, followed by a theoretical description and the generation procedure.
The main part of the paper is dedicated to the practical application of focusing wave groups in the basin. Items that will be described are a) the derivation of transfer functions for floating structures and for anti-roll tanks b) the determination of hydraulic and electrical transfer function of wave makers c) the verification of position and calibration of wave probes in the basin d) the generation of extreme wave events e) the assessment of reflection coefficient of beaches f) the investigation of non-linear aspects of transfer functions.
Finally, characteristics of the analysis of focusing waves are introduced and compared to conventional methods based on regular and irregular waves.
Experimental Study of Cuttings Transport Efficiency of Water Based Drilling Fluids
Authors: Ytrehus Jan David , Taghipour Ali , Lund Bjørnar , Werner Benjamin , Opedal Nils , Saasen Arild , Ibragimova Zalpato 
Published: September 2014

One important requirement for a drilling fluid is the ability to transport the cuttings out of the borehole. Improved hole cleaning is a key to solve several challenges in the drilling industry and will allow both longer wells and improved quality of well construction. It has been observed, however, that drilling fluids with similar properties according to the API standard can have significantly different behavior with respect to hole cleaning performance. The reasons for this are not fully understood.
This paper presents results from laboratory tests where water based drilling fluids with similar rheological properties according to API measurements have been tested for their hole cleaning capabilities in a full scale flow loop. Thorough investigation of the viscoelastic properties of the fluids were performed with, among other instruments, a Paar-Physica rheometer.
Improved understanding of the fluid properties relevant to hole cleaning performance will help develop better models of wellbore hydraulics used in planning of well operations. Eventually this may lead to higher ROP with water based drilling fluids as obtained with oil based drilling fluids. This may ease cuttings handling in many operations and thereby significantly reduce the drilling cost using (normally) more environmentally friendly fluids.
The experiments have been conducted as part of an industry-sponsored research project where understanding the hole cleaning performance of various oil and water based drilling fluids is the aim. The experiments have been performed under realistic conditions. The flow loop includes a 12 meter long test section with 2″ OD freely rotating drillstring inside a 4″ ID wellbore made of concrete. Sand particles were injected while circulating the drilling fluid through the test section in horizontal position.
A New Riser Fatigue Monitoring Methodology Based on Measured Accelerations
Authors: Ge Michael Long , Kannala Jomon , Li Songcheng , Maheshwari Himanshu , Campbell Mike 
Published: September 2014

In support of its commitment to safe and reliable operations, BP has been continuously developing a program to assess and maintain structural integrity for offshore drilling risers and conductors. This paper presents recent efforts by BP, in conjunction with 2H Offshore, to develop a new fatigue monitoring methodology for drilling riser systems due to both wave and vortex-induced-vibration (VIV) damage.
BP has been monitoring structural response, including the fatigue damage, of riser systems in the Gulf of Mexico over the past ten years. To date, the focus has predominantly been on determining the fatigue damage due to VIV, since VIV and its effects on structural response are considered a not well-understood phenomenon. In addition to VIV fatigue, direct wave loading and vessel motions also contribute to the total fatigue damage, and sometimes wave fatigue may have a larger contribution than VIV fatigue damage. Therefore, it is necessary to determine fatigue due to both wave and VIV effects to confirm the long-term fatigue integrity of the drilling risers.
To take full advantage of the accumulated monitoring data, a new fatigue monitoring methodology was developed using an analytical solution to account for the damage due to both wave and VIV effects. With this method, the measured acceleration data are converted into curvature, and then fatigue damage along the length of riser and conductor are calculated. This new methodology has been validated with both finite element analysis (FEA) and field data, and sensitivities to various parameters have been considered.
Enhanced Collapse Resistance of Compressed Steel Pipes
Authors: Krishnan Venkat R. , Baker David A. 
Published: September 2014

Pipe collapse is a primary design consideration for deep water locations and offshore areas with sharp seabed curvatures or spans, where bending reduces collapse resistance due to ovalization. Previous numerical and experimental work has shown that collapse resistance of steel pipes can be enhanced significantly by using compression instead of expansion during the final stage of the pipe forming process.
ExxonMobil has recently undertaken a rigorous numerical modeling and experimental testing program to investigate the collapse resistance of compressed (JCOC) steel pipes under combined loading of external pressure and bending, and this paper presents the main results from the program. The first part of the paper presents results of sensitivity studies from three dimensional (3D) finite element analyses (FEA) of the pipe forming process, and the second part focuses on the collapse modeling under combined loading as well as a comparison of the numerical results with the experiments. The results indicate that the collapse envelope for steel pipes under combined external pressure and bending can be enhanced by up to 35% by adopting pipe compression rather than expansion as the final step of the forming process.
Transient Wave Packets: New Application in CFD-Methods
Authors: Clauss Günther F. , Stuppe Sven , Dudek Matthias 
Published: September 2014

Detailed knowledge of motion and seakeeping behaviour in an early design stage is indispensable in modern layout of marine offshore structures. Therefore, numerical methods are used to calculate the Response Amplitude Operators (RAO), which are generally based on potential theory or the Reynolds-Averaged-Navier-Stokes-Equation (RANSE).
Calculations with potential-codes are commonly used, well established and time-saving. Main disadvantages are the neglect of viscous effects and the hull structure above the still water level. By using RANSE-methods, these nonlinear effects can be investigated in detail, but at the price of calculation time and extensive grid generation. To achieve sufficient RAOs in frequency domain, time-consuming and intensive calculations would be necessary with these CFD-methods, using seastate applications with regular or irregular waves only. Therefore, these methods are not convenient for standard motion analysis by now.
Transient Wave Packets (TWP) represent an approved method at model tests, revealing the entire RAO for any offshore structure within one single, short test run. Main advantage of this technique is the accurate predictability and short superposition in space and time. Containing all elementary wavelengths of the generated initial wave spectra, the TWP-method could be used in RANSE-methods, implementing all necessary initial conditions to the CFD-solver. To reduce the calculation effort to a minimum in space and time, the superimposed wave train is generated near the investigated offshore structure by using modified, linear wave theory in spatial domain.
To present this method by means of a practical example, the motion and sloshing behaviour of an offshore LNG-carrier (LNGC) are investigated in detail. For validation purpose, all results are compared to model tests, conducted in the seakeeping basin at Technische Universität Berlin (TUB), as well as numerical results of the potential theory solver WAMIT.
Life-Cycle Assessment of Flexible Risers
Authors: Fergestad Dag , Løtveit Svein Are , Leira Bernt J. 
Published: September 2014

The number of flexible pipes in operation is increasing due to new field developments and the desire to extend the lifetime of existing fields. There have been many challenges with respect to long term operation of such pipes, in many cases with the need to replace or repair before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing.
The present paper summarizes state of the art technology related to operation of flexible pipes and some recent research and development activities that contribute to resolving these issues. In particular, the following topics are addressed:
• Fatigue testing of flexible pipes subjected to corrosion damage during operation
• Development of improved numerical models and methods for assessment of the residual capacity of flexible pipes
• Integrity assessment of flexible pipes also applying quantified risk and reliability assessment
• Repair methods for damaged pipe sections
In addition, an outline is given of a Handbook (ref. Handbook 2014) which addresses the various topics related to life-cycle design and operation of flexible pipes, see Appendix. Future prioritized research efforts with focus on some of the topical issues given in the list above are finally addressed.
Wind/Wave Basin Verification of a Performance-Matched Scale-Model Wind Turbine on a Floating Offshore Wind Turbine Platform
Authors: Kimball Richard , Goupee Andrew J. , Fowler Matthew J. , de Ridder Erik-Jan , Helder Joop 
Published: September 2014

In 2011, the DeepCwind Consortium performed 1/50th-scale model tests on three offshore floating wind platforms at the Maritime Research Institute Netherlands (MARIN) using a geometrically scaled model of the National Renewable Energy Laboratory (NREL) 5 MW reference turbine. However, due to the severe mismatch in Reynolds number between full scale and model scale, the strictly Froude-scaled, geometrically-similar (geo-sim) wind turbine underperformed greatly, which required significant modification of test wind speeds to match key wind turbine aerodynamic loads, such as thrust. The conclusion from these prior efforts was to abandon a geometrically similar model turbine and use a performance-matched turbine model in its place, keeping mass and inertia properties properly scaled, but utilizing modified blade geometries to achieve required performance at the lower Reynolds numbers of the Froude scaled model. To this end, the University of Maine and MARIN worked in parallel to develop performance-matched turbines designed to emulate the full scale performance of the NREL 5 MW reference turbine at model scale conditions. An overview of this performance-matched wind turbine design methodology is presented and examples of performance-matched turbines are provided.
The DeepCwind semi-submersible platform was retested at MARIN in 2013 using the MARIN Stock Wind Turbine (MSWT), which was designed to closely emulate the performance of the original NREL 5 MW turbine. This work compares the wind turbine performance of the MSWT to the previously used geometrically scaled NREL 5 MW turbine. Additionally, turbine performance testing of the 1/50th-scale MSWT was completed at MARIN and a 1/130th-scale model was tested at the University of Maine under Reynolds numbers corresponding to the Froude-scaled model test conditions. Results from these tests are provided to demonstrate effects on model test fidelity. Comparisons of the performance response of the geometrically matched turbine to the performance-matched turbines are also presented to illustrate the performance-matched turbine methodology. Lastly, examples of the fully dynamic floating system performance using the original geometrically scaled NREL 5 MW turbine and the MSWT are investigated to illustrate the implementation of the model test procedure as well as the effects of turbine performance on floater response. Using the procedures employed for the MARIN tests as a guide, the results of this work support the development of protocols for properly designing scale model wind turbines that emulate the full scale design for Froude-scale wind/wave basin tests of floating offshore wind turbines.
Ship Structural Design Support Methodology for the Reliability Based Design Optimization (RBDO)
Authors: Žanić Vedran , Pirić Karlo , Prebeg Pero 
Published: September 2014

The objective of the paper is to present the structural design support system (DeSS) rationale for the reliability based design optimization (RBDO) in the concept design phase. Basic steps are as follows:
• Interactive identification of the design problem (design variables, constraints, objectives) as well as design problem variates and their distribution parameters. Safety related design criteria are used as objectives and as constraints in the presented procedure;
• Calculation of the cross section ultimate longitudinal strength criteria based on the extended Smith’s method; based on the Report SSC-398;
• Selection of non-dominated designs (Pareto-optimal, NDD points) for the given deterministic design criteria;
• Calculation of reliability/deterministic safety measures. Novel FASTREL code, based on the Dimension Reduction Method (DRM) is used for the reliability calculations;
• Generation of insight into the Multi Attribute Decision Making (MADM) process with 5D graphic presentation of designs in design and attribute spaces in the interactive OCTOPUS Designer (Demak/DeView) IT modules.
Practical application of the developed concept design methodology and of the design environment to the structural design of the verifiable test example corresponding to SSC-398 report. DeSS was used in fast generation of optimal designs using MODM (MOSLP) and MADM (MOPSO) techniques. To speed up the RBDO design process deterministic and probabilistic formulations of design problem were run concurrently and supporting each other are presented using the safety related design attributes (deterministic and reliability based) for the NDD supported decision-making technique.
Development and Application of Trim Optimization and Parametric Study Using an Evaluation System (SoLuTion) Based on the RANS for Improvement of EEOI
Authors: Lee Jisun , Yoo Seonoh , Choi Sangkyu , Kim Heetaek , Hong Chunbeom , Seo Jongsoo 
Published: September 2014

In general, the speed power performance of ships is optimized for design speed and draught in accordance with the contract condition. But, the contract condition may not be always the same as the actual operating condition. Therefore, in order to reduce the fuel consumption practically, it is necessary to optimize the performance under various conditions considering the actual voyage. This is the reason that the trim optimization covering various operating profiles becomes the main issue in reducing fuel oil consumption.
In this paper, a numerical study is carried out to optimize trim conditions through the computational evaluation system called SoLuTion developed by Samsung Heavy Industries Co. (SHI) with variation in draught, ship speed and voyage trim. In order to get more accurate results in resistance and self-propulsion performance, the Reynolds-Averaged Navier-Stokes (RANS) equations including Volume of the Fluid (VOF) method by Hirt and Nichols (1981) for free-surface boundary condition and moving mesh technique for propeller rotation effect are employed as governing equations. Reynolds Stresses Model (RSM) with the wall function is applied as a turbulence model for turbulent flow computation.
Through this study, the followings are the main three factors to be considered in evaluation of the quantitatively accurate speed performance by varying the draught, speed and voyage trim. First, the distance from hull surface to the first grid point should be adjusted to eliminate the effects of frictional resistance. Second, the grid system should be generated to avoid the grid dependency on variation of draught. Finally, the running trim and sinkage of the voyage conditions should be considered. The results of the trim optimization performed numerically are well-matched with the towing test results conducted at Samsung Ship Model Basin(SSMB). As the results of this study, it is confirmed that SoLuTion is a useful and efficient tool for trim optimization and the provided optimum trim will be able to contribute to fuel savings under the operating conditions. From trim optimization study, it is found that there is certain level of effects due to the bulb and transom immersion to find the optimum trim condition. Also SoLuTion is applicable not only to trim optimization but also to parametric studies in optimum shape of the ships considering the actual operating profile.