bluuebunny/crossref_metadata_2025_split huggingface dataset:
Efficient Wave Modeling Using Non-Hydrostatic Pressure Distribution and Free Surface Tracking on Fixed Grids
Authors: Bihs Hans , Kamath Arun , Aggarwal Ankit , Pakozdi Csaba 
Published: September 2018

For the estimation of wave loads on offshore structures, relevant extreme wave events need to be identified. In order to achieve this, long term wave simulations of relatively large scales need to be performed. Computational Fluid Dynamics (CFD) based Numerical Wave Tanks (NWT) with an interface capturing two-phase flow approach typically require too large computational resources to achieve this efficiently. They are more suitable for the near-field hydrodynamics of steep and breaking wave impacts on the structures. In the current paper, a three-dimensional non-hydrostatic wave model is presented. While it also solves the Navier-Stokes equations, it employs an interface tracking method for the calculation of the free surface location. The algorithm for the simulation of the free surface is based on the continuity of the horizontal velocities along the vertical water column. With this approach, relatively fewer cells are needed in the vicinity of the air-water interface compared to CFD based NWTs. With coarser grids and larger time steps, the wave propagation can be accurately predicted. The numerical model solves the governing equations on an rectilinear grid, which allows for the employment of high-order finite differences. For time stepping, a fractional step method with implicit treatment of the diffusion terms is employed. The projection method is used for the calculation of the non-hydrostatic pressure. The resulting Poisson equation is solved with Hypres geometric multigrid preconditioned conjugated gradient algorithm. The numerical model is parallelized following the domain decomposition strategy and MPI communication between the individual processors.
In the current paper, the capabilities of the new wave model are presented by comparing the wave propagation in the tank with the CFD approach in a 2D simulation. Further, a 3D simulation is carried out to determine the wave forces on a vertical cylinder. The calculated wave forces using the new approach is compared to that obtained using the CFD approach and experimental data. It is seen that the new approach provides a similar accuracy to that from the CFD approach while providing a large reduction in the time taken for the simulation. The gain is calculated to be about 4.5 for the 2D simulation and about 7.1 for the 3D simulation.
Reeled CRA Clad/Lined Pipeline Installation: Seastate Optimisation From Fatigue and Fracture Perspective
Authors: Zhou Daowu , Sriskandarajah T. , Bowlby Heidi , Skorpen Ove 
Published: September 2018

The deformation mechanism in reel-lay of corrosive resistance alloy (CRA) clad/lined pipes can facilitate defect tearing and low cycle fatigue crack growth in the girth welds. Pipe-lay after straightening will subject the CRA welds to high cycle fatigue. The permissible seastate for installation will be governed by failure limit states such as local collapse, wrinkling of the liner, fatigue and fracture.
By means of a recently completed offshore project in North Sea, this paper discusses seastate optimisation when installing pipelines with CRA girth welds, from a fatigue and fracture perspective. The additional limiting requirement in CRA welds to maintain CRA liner integrity can lead to significant assessment work since all critical welds shall be examined. AUT scanned defect data were utilised to maximise permissible seastates based on fatigue allowance from a fatigue crack growth calculation.
An alternative simplified approach to derive the crack growth based on a superposition method is studied. It enables a straightforward real-time prediction of crack growth and has the potential to be used during the offshore campaign to improve the installation flexibility.
Post-installation fracture assessment under more critical seastates is examined for CRA partial over-matching welds. A comparison of CDF between conventional ECA procedure and 3D FE is provided.
Fatigue Analysis of a 12-MW Wind Turbine Blade
Authors: Ahn Hyeonjeong , Shin Hyunkyoung 
Published: September 2018

In 2017, the MHI Vestas released a 9.5-MW offshore wind turbine. It is also actively researching and developing a 10-MW offshore wind turbine. As the capacity of a wind turbine increases, the sizes of all its system components, including length and weight, correspondingly increase. Consequently, as a wind turbine becomes larger, it becomes necessary to analyze the fatigue load applied to its entire system. The first reason for such an analysis is to achieve a safe but not overly designed large wind turbine. Second, most wind turbine accidents involve aging turbines and are related to fatigue analysis.
Accordingly, the purpose of fatigue analysis is to safely design a wind turbine that sustains repeated loads within its design life. In this study, the blades and loads for the fatigue analysis of a 12-MW floating offshore wind turbine are calculated based on the National Renewable Energy Laboratory (NREL) 5-MW wind turbine blades. The calculated loads are applied to the Markov matrix through a preprocessing, such as the cycle counting method. Finally, the equivalent fatigue load is estimated based on both mean and range.
In this study, only the equivalent fatigue load on the turbine blade is calculated. However, if fatigue analysis is to be performed for all parts using equivalent loads, it is possible to design the wind turbine to fully withstand such loads throughout its design life, and prevent the overdesign of each part as well.
Hybrid Tool to Prevent Ship Propeller Erosion
Authors: Llull T. , Mujal-Colilles A. , Castells M. , Gironella X. , Martínez de Osés X. , Martín A. , Sánchez Arcilla A. 
Published: September 2018

The present contribution aims to implement a new methodology to prevent Roll on-Roll off vessels (RO-RO) from causing severe scouring actions. The methodology combines field, experimental, theoretical and numerical tools exchanging information to establish the manoeuvre potential scouring damage. The main contribution is the introduction of a manoeuvre ship simulator to obtain variables that otherwise cannot be obtained in field studies. These variables, all related to ship’s propeller behaviour, are the rotational speed, the pitch ratio and the engine power during the whole manoeuvre.
Results show an over-prediction of the theoretical and experimental axial velocity and maximum erosion depth, indicating their clear limitations and the necessity of accurate data to apply the method. The methodology used with the key incorporation of the manoeuvre simulator is revealed to be a very useful tool to study new manoeuvres (including the possibility to work with a single or a couple of tugboats during the docking and undocking manoeuvres) to prevent propeller scouring actions.
Comparison of Taut and Catenary Mooring Systems for Finfish Aquaculture
Authors: Turner Adam A. , Steinke Dean M. , Nicoll Ryan S. , Stenmark Patrik 
Published: September 2018

Finfish aquaculture has been expanding in areas like Norway and Canada over the last 20 years, and is projected to expand further in the next decades as the planet’s population and demand for seafood increases. Finding appropriate salmon farm sites is becoming increasingly difficult, as there are fewer protected nearshore locations available for development. As a result, there is interest in increased utilization of existing leases (i.e. permitted sites). These leases have a boundary in which the anchors and mooring lines must be contained. Reducing the footprint of the mooring arrangement will allow for an increased utilization of existing leases. A possible method to reduce the footprint of a spread moored salmon farm is to use a taut mooring rather than a chain catenary mooring. This requires the use of mooring materials and components that allows for handling of tidal elevation changes and wave action. This paper investigates the performance of a taut moored configuration with integrated Seaflex elastomeric mooring components in comparison with a conventional chain catenary configuration using dynamic analysis.
The results show that a reduced footprint taut mooring configuration with integrated elastomeric mooring components can be substituted for a typical chain catenary mooring with no significant increase in peak mooring line loads at extreme sea states and significant reduction in peak loading at moderate and calm seastates.
Probabilistic Wall Thickness Verification for the TurkStream Pipeline
Authors: Liu Ping , Meijer Arjen , DeGeer Duane , Jurdik Erich , Chaudhuri Jay , Zhou Shirley 
Published: September 2018

The TurkStream pipeline system is currently being constructed across the Black Sea for supply of natural gas from the Russian coast near Anapa to landfall on the Turkish coastline. The pipeline design is extremely challenging from a technical perspective with water depths along most of the route exceeding 2200m, difficult seabed conditions with steep slopes and geohazard risks, a potentially aggressive and corrosive subsea environment, and high gas deliveries requiring a large pipeline diameter.
The combination of diameter, wall thickness, and quality requirements for the TurkStream linepipe is at the limit of leading mills around the world, and outside their normal production envelope. In order to demonstrate that the manufactured linepipe will meet target reliability levels, a material development program was completed, which included a major testing program involving testing prototype TurkStream pipes manufactured by both the UOE and JCOE methods of linepipe fabrication. The results from this test program formed the basis for a probabilistic verification of the pipeline wall thickness.
This paper presents the reliability-based verification of the wall thickness for the TurkStream subsea pipelines. The collapse limit state was identified as the governing mode of failure, and was defined by a collapse prediction formula developed specifically for the TurkStream pipelines. The model was verified by full-scale tests from the test program, and then used to define the failure surface of the collapse envelope due to external pressure and bending.
The probabilistic analyses resulted in reliability levels that exceed design code requirements. In addition, these analyses highlighted the need for certain criteria to be met during coated linepipe production. These requirements are summarized in this paper.
Development of Acoustic Communication and Positioning System for Operation of Multiple AUVs
Authors: Watanabe Yoshitaka , Meguro Koji , Deguchi Mitsuyasu , Shimura Takuya 
Published: September 2018

In underwater observation using an autonomous underwater vehicle (AUV), a support vessel typically monitors the AUV to support the observation. The AUV have to be positioned to be tracked by the vessel and informed the positioning result for navigation with acoustic communication. This process is significant especially in deep water. The AUV uplinks to inform its status and transmit some observation data in real time, and sometimes be commanded to change the observation plan by downlink from the vessel. Authors planned to use an autonomous surface vehicle (ASV) to track and monitor multiple AUVs for efficient observation. An acoustic multi-access communication and positioning system have developed as one of the elemental technologies for the observation system.
The developed acoustic system achieves multi-access with frequency division multiple access (FDMA) method, and the ASV can monitor up to three AUVs simultaneously. Positioning is performed with super short baseline (SSBL) method. The acoustic device has operation mode in which positioning and communication functions are integrated, called as auto mode. In auto mode, uplink packets can be very close and the AUV can uplinks efficiently, and timing of downlink is calculated from positioning result appropriately.
Results of two sea trials are shown. The precision of positioning was enough to track the AUV. However random error was much larger than that of SSBL of the vessel, hence some precise method is necessary to keep the quality of observation data high. Communication and auto mode sequence worked well in the sea trial.
Long Term Analysis of Steep and Breaking Wave Properties by Event Matching
Authors: Johannessen Thomas B. , Lande Øystein 
Published: September 2018

Offshore structures are typically required to withstand extreme and abnormal load effects with annual probabilities of occurrence of 10−2 and 10−4 respectively. For linear or weakly nonlinear problems, the load effects with the prescribed annual probabilities of occurrence are typically estimated as a relatively rare occurrence in the short term distribution of 100 year and 10 000 year seastates. For strongly nonlinear load effects, it is not given that an extreme seastate can be used reliably to estimate the characteristic load effect. The governing load may occur as an extremely rare event in a much lower seastate. In attempting to model the load effect in an extreme seastate, the relevant short term probability level is not known nor is it known whether the physics of the wave loading is captured correctly in an extreme seastate. Examples of such strongly nonlinear load effects are slamming loads on large volume offshore structures or wave in deck loads on jacket structures subject to seabed subsidence.
The present paper is concerned with the long term distribution of strongly nonlinear load effects and a methodology is proposed which incorporates CFD analysis in a long term Monte Carlo analysis of crest elevations and wave kinematics. Based on a long term time domain simulation of a linear surface elevation, a selection of events is run in CFD in order to obtain a database of linear and corresponding fully nonlinear wave fields with the possibility of wave breaking included. In the subsequent long term analysis, a large linear event is then replaced by the closest matching event in the database. A technique is developed to Froude scale the database results and shift the origin in time and plane so that the database of typically only 100 events give a close match to all the events in the simulation.
The method is applied to the simple case of drag loading on a cylinder which is truncated above the still water level such that only the largest waves impact with the structure. It is observed that whereas the Event Matching method agree well with a second order model for return periods lower than 100 years, the loading on the cylinder is significantly larger for longer return periods. The deviation is caused by the increasing dominance of wave braking in the largest crest and illustrates the importance of incorporating wave breaking in the analysis of wave in deck loading problems.
A 2D Experimental and Numerical Study of Moonpools With Recess
Authors: Ravinthrakumar Senthuran , Kristiansen Trygve , Ommani Babak 
Published: September 2018

Moonpool resonance is investigated in a two-dimensional setting in terms of regular, forced heave motions of a model with moonpool with different rectangular-shaped recess configurations. A recess is a reduced draft zone in the moonpool. Dedicated experiments were carried out. The model consisted of two boxes of 40 cm width each, with a distance of 20 cm between them. Recess configurations varying between 5 cm to 10 cm in length and 5 cm in height were tested. Different drafts were also tested. The free-surface elevation inside the moonpool was measured at eight locations.
A large number of forcing periods, and five forcing amplitudes were tested. A time-domain Boundary Element Method (BEM) code based on linear potential flow theory was implemented to investigate the resonance periods, mode shapes as well as the moonpool response as predicted by (linear) potential flow theory. Dominant physical effects were discussed, in particular damping due to flow separation from the sharp corners of the moonpool inlet and recess. The effect of the recess on the piston-mode behavior is discussed. BEM simulations where the effect of flow separation is empirically modelled were also conducted.
The non-dimensional moonpool response suggests strong viscous damping at piston-mode resonance. The viscous BEM simulations demonstrate improvement over inviscid BEM, although further improvement of the method is needed. The piston mode shapes are clearly different from the near flat free-surface elevation for a moonpool without recess, consistent with recently published theory.
Quantification of Multiple Factors and Interaction Effects on Drilling Fluid Invasion
Authors: Ezeakacha Chinedum Peter , Salehi Saeed , Kiran Raj 
Published: September 2018

Water-based drilling mud is one of the commonly used fluid systems for drilling operations. The loss of drilling fluid in porous media and fractured formations have been one of the industry’s focus in the past decades. However, the dynamics and constantly changing wellbore conditions push the boundaries for more research into accurate quantification and mitigation methods for fluid loss. In the design and development of drilling fluids, most test conditions are kept constant during fluids property testing. Drilling fluid loss and rheological parameters are determined experimentally at constant test conditions, and according to the combination of mud additives, rather than a comprehensive approach. In addition, conventional methods of quantifying drilling fluid loss properties for field application can be is time-consuming, considering that multiple factors impact fluid loss.
This study presents a statistical engineering approach for pore-scale characterization of water-based mud (WBM) invasion. The methods used in this research are: special case of factorial design of experiment (DoE), analysis of variance (ANOVA), and regression. Important field parameters based on previous studies and industry recommendations were carefully integrated in the DoE and result analyses. These parameters include but not limited to: porous media type, temperature, type of lost circulation material (LCM), concentration of LCM, drilling string rotary speed, and eccentricity. Ceramic filter tubes were used for the first set of experiments and Upper Grey sandstone rock samples were used for the second set of experiments. The statistical analyses performed in this study were based on a 95% confidence interval (CI). The results show that for single factor interpretation, increase in temperature and rotary speed increased dynamic fluid invasion significantly. Increase in LCM concentration resulted to a significant decrease in fluid invasion. LCM concentration and rotary speed interaction revealed a significant decrease in fluid invasion. LCM concentration and temperature interaction significantly increased fluid invasion. Rotary speed and temperature interaction also increased fluid invasion significantly. The three-factor interaction effect of LCM concentration, rotary speed, and temperature was not significant in reducing fluid invasion. For the conditions used in this study, the regression analysis showed that dynamic fluid invasion in Upper Grey sandstone can be explained from variation in LCM concentration and rotary speed. The results and methods from this study can provide reliable information for drilling fluids design and selecting operating conditions for field application.
Laboratory Test on Cement Plug Integrity
Authors: Opedal Nils , Corina Anisa Noor , Vrålstad Torbjørn 
Published: September 2018

A recurring issue in the petroleum industry is the performance of cement in relation to its primary role of providing zonal isolation. Enhanced understanding of this subject offers the possibility to improve the planning and design of the cementing job to minimizing the risk of poor bonding of cement and loss of well integrity. The design and execution of the cement job is by no means an easy task, mainly due to the complexity of the material and process, and the variety in conditions one can encounter downhole. Thus, screening of different materials and conditions is necessary to optimize the success of a cement operation.
This work focused on experimentally testing cement plugs to be able to understand the sealing ability of cement to a casing at relevant temperatures and pressures. A built-for-purpose test setup was designed and assembled, and the goal of this work was to test this new setup and to establish a proper baseline for future test on various cement systems.
The setup consists of a test cell containing the cement plug, an automated pressure regulator used for generating a pressure differential across the cement plug and flow meters to measure the flow rate through the cement plug. The output data from the tests is the differential pressure needed to have breakthrough of gas, and the connection between the flow rate and differential pressure across the cement plug. The possible manipulated variables for the test setup is the cement type and casing surface properties.
An Assessment of Load and Response for Horizontal Slamming Loads From Model Scale Experiments
Authors: Storheim Martin , Lian Gunnar 
Published: September 2018

Steep breaking waves can result in high impact loads on offshore structures, and several model test campaigns have been conducted to assess the effect of horizontal wave slamming. High loads have been measured, and they can be challenging to withstand without significant deformation.
For wave slamming problems it is common to estimate the characteristic slamming load and assume that this will give an equivalent characteristic response. One challenge related to the slamming load is that it has a large variability in load level, the duration of the load and the shape of the overall load pulse. This variability can have a large impact on the estimated response to the characteristic load, causing a similar or larger variability in response. Due to the sensitivity to the structural response, it may be difficult to interpret large amounts of such data to arrive at a relevant design load without making overly conservative assumptions.
This paper investigates the sensitivity of the structural response to assumptions made in the material modelling and how the short term variability is affected if we instead of load use response indicators such as plastic strain and max deformation to arrive at a characteristic load. For this purpose, a simplified dynamic response model is created, and the recorded wave impact events can then be evaluated based on the predicted structural response from the simplified model.
It was found that the structural response is sensitive to the structural configuration. The assumed material behavior and hydro-elastoplastic effects were identified to greatly affect the structural response. A reasonable approach to arrive at the q-annual response seems to be to first estimate the q-annual extreme slamming load, and then run the structural analysis on several of the measured slamming time series with the estimated q-annual extreme pressure.