bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nearshore Wave Modelling in a Norwegian Fjord
Authors: Stefanakos Christos N. , Furevik Birgitte R. , Knutsen Øyvind , Christakos Konstantinos 
Published: December 2020

Abstract
Phase averaged wave models is a good supplement of in situ measurements for the study of wave climate in a specific location. In spite of having been tested in smoothly varying coastal areas, they haven’t previously been systematically validated in complex topography (coastline and bathymetry) such as Norwegian fjords, due to lack of measurements. However, in planning for large fjord crossings, the Norwegian Public Roads Administration have launched a number of buoys which allow for validation of model setup.
In the present work, nearshore wave conditions in the area of Sulafjord, central Norway, are investigated as derived from numerical modelling with several different setups, and are compared against in situ buoy measurements with good accordance. The analysis is carried out by transferring offshore wave conditions to the nearshore area by successive applications of the well-known third-generation wave model SWAN. As input has been used a very detailed bathymetry of the area, and time series of wind and wave parameters derived from ERA5 and NORA10 datasets. Various scenarios reconstructing the wave input spectra have been considered.
Application of Fractional Calculus in Modelling Viscoelastic Foundation of Ship Structures for Passive Vibration Control
Authors: Praharaj R. K. , Datta N. 
Published: December 2020

Abstract
Viscoelastic materials (VEM) are often used in the ship floors to dampen the noise and vibration induced by machinery (engines, pumps, alternators) and live loads (human traffic and liquid movement in pipelines). Therefore, accurate modeling of such materials is important for the iterative design-analysis process. VEM exhibits both time and frequency-dependent properties. Traditionally, integer-order viscoelastic mechanical models are used to describe the rheological properties of the viscoelastic materials. However, such models find difficulties in predicting the rheological characteristics since their kernel functions are a combination of exponential functions. For instance, the integer-order Maxwell model is good at describing the stress relaxation behavior while is poor in capturing creep, and vice-versa for the integer-order Kelvin-Voigt model. However, the fractional-order mechanical model can overcome the above problem with a fewer number of model parameters. Therefore, in this paper, the fractional derivative-based Kelvin-Voigt mechanical model is employed to describe the time-dependent vibratory behavior of the VEM. To validate the effectiveness of the above model, a thin elastic plate bonded with a thin layer of VEM, subject to a concentrated impact load, is studied. Galerkin’s method and Triangular strip matrix approach are used to solve the partial fractional differential equations of motion. The semi-analytical approach of modal superposition is used to generate the response, whose first dynamic overshoot of displacement is crucial to contain the dynamic stress within the working stress level. This bypasses the computationally expensive Finite Element Method. Additionally, ANSYS is limited to the integer-order damping model only. This analysis gives insights into the efficacy of the VEM chosen for passive vibration control of structural components of ship hulls. A case study for free vibration is done with a commercially available VEM, which is used as surface flooring to cover steel plates of ship hulls, thereby acting as vibration dampers. Free vibration results show that the damping coefficient of the plate foundation system increases with increasing the order of the derivative. In addition, the amplitude of the transient response decreases with the order of the derivative. Thus, the classical integer-order mechanical model overestimates the damping of the viscoelastic materials, which leads to underestimating the displacement and associated stresses. The results are verified with literature and ANSYS.
Machine Learning for Subsea Pipeline Reeling Mechanics
Authors: Giry Eric , Cocault-Duverger Vincent , Pauthenet Martin , Chec Laurent 
Published: December 2020

Abstract
Installation of subsea pipelines using reeling process is an attractive method. The pipeline is welded in long segments, typically several kilometers in length, and reeled onto a large diameter drum. The pipeline is then transported onto such reel to the offshore site where it is unreeled and lowered on the seabed. The deformation imposed on the pipeline while spooled onto the drum needs to be controlled so that local buckling is avoided.
Mitigation of such failure is generally provided by proper pipeline design & reeling operation parameters. Buckling stems from excessive strain concentration near the circumferential weld area resulting from strength discontinuity at pipeline joints, mainly depending on steel wall thickness and yield strength. This requires the characterization of critical mismatches obtained by trial and error. Such method is a long process since each “trial” requires a complete Finite Element Analysis run. Such simulations are complex and lengthy. Occasionally, this can drive the selection of the pipeline minimum wall thickness, which is a key parameter for progressing the project. The timeframe of such method is therefore not compatible with such a key decision.
The paper discusses the use of approximation models to capitalize on the data and alleviate the design cost. To do so, design of experiments and automation of the computational tool chain are implemented.
It is demonstrated that initial complex chain of FEA computational process can be replaced using design space description and exploration techniques such as design of experiments combined with advanced statistical regression techniques in order to provide an approximation model. This paper presents the implementation of such methodology and the results are discussed.
Pressure Testing of Barrier Integrity
Authors: Raaen Arne M. , Fjær Erling 
Published: December 2020

Abstract
Plug and abandonment of a well is expected to ensure that the sealing integrity of the cap rock is restored. This also implies that the annulus between casing and rock is sealed off. Some formations may under the right conditions close in on the casing, providing a highly valuable contribution to the sealing. Although acoustic tools may be used to evaluate whether there is casing contact, the hydraulic integrity of such a barrier must be established by field testing for all potential formations.
While the main focus here is on natural shale barriers, the analysis and conclusions apply equally well to testing of cement based and other barriers.
This paper discusses two pressure integrity tests that are used for this purpose, the XLOT-type test and the communications test. The test procedures are outlined, and the expected sensitivity is estimated. In particular, it is shown that temperature effects may complicate test interpretation, possibly giving both false acceptance and false rejections of tests. Hence, it is of vital importance to include temperature measurements in the evaluation of the tests.
It is estimated that the leakage detection limit of both tests is significantly higher than the target value needed to ensure that sealing integrity has been restored. This calls for improvements of the testing procedures.
Accuracy of Simplified Methods for Fatigue Damage Estimation of Exposed Fish Farms
Authors: Slagstad Martin , Takle Bore Pål , Amdahl Jørgen 
Published: December 2020

Abstract
Fish farms are being placed in more exposed locations than earlier, encouraged by the “development licenses” that the Norwegian Directorate of Fisheries have introduced. Traditional design methods for estimating fatigue damage for fish farms are based on formulations given in the code NS - 9415 Marine fish farms. These methods are initially developed for sheltered areas and may not give an adequate level of safety in more exposed locations, where the dynamic response from waves is of greater importance. Accurate calculations using state of the art methods are very time consuming both with respect to man hours, but especially with regard to CPU consumption. Hence, for practical design, simplified procedures, such as combination of the design wave method with an assumed Weibull distribution, are often used to limit the complexity of the analysis as well as the costs. To the authors knowledge, the accuracy of such simplified methods is not well documented for exposed fish farms and with limited full-scale experience it is difficult to conclude that the desired safety level is achieved. This paper addresses this problem by investigating the accuracy of simplified methods to estimate the fatigue damage. A case study of a modern fish farm concept for exposed waters is performed where the simplified methods are compared to more complex time-domain analyses using state of the art modeling techniques.
Numerical Simulation of Cone Penetration Tests Inside Suction Caisson Foundations in Sand
Authors: Stapelfeldt Marc , Alkateeb Diaa , Grabe Jürgen , Bienen Britta 
Published: December 2020

Abstract
Offshore wind is increasingly utilised as a renewable energy source. A growing number of bottom fixed wind turbines installed offshore are supported by suction caisson foundations. The suction-assisted installation remains a source of uncertainty towards the in-service performance due to the unknown post-installation soil plug state. Cone penetration tests within the suction caisson can help to improve the reliability. Therefore, cone penetration tests were employed in centrifuge tests to investigate the plug state in a previously installed suction caisson. However, the performance of a cone penetration test in a small-scale experiment is connected to uncertainties: A relatively large diameter device is required to conduct the cone penetration test — especially in a centrifuge test. Different finite element models are developed in order to visualise and investigate a cone penetration test inside a suction caisson. The numerical analysis results are validated through the back-calculation of centrifuge cone penetration tests. The results of the simulated cone penetration tests inside a suction caisson are evaluated and compared to the centrifuge experiments. This investigation reinforces the scope of the centrifuge experiments and emphasises a considerable effect of the pressure transferral through the caisson lid in the soil plug state. Hence, the results of this study reduce existing uncertainties regarding possible suction installation effects on the in-service performance of caisson foundations.
Collision Experiments of Ship Models in Water Tank
Authors: Xu Lijun , Zhu Ling , Wang Xiangbiao , Pedersen Preben Terndrup 
Published: December 2020

Abstract
The consequences of ship collision could be very serious, causing lots of human casualties, environmental pollution and huge economic losses. It is essential to study the collision process including two ships in water. In the past, most ship collision tests are based on the study of collision damage of local structures and there are few experiments considering the motion response of ships during the collision process. Actually, the interaction between the fluid and structure does have effects on the collision consequences. In this paper, the collision experiments of ship models are conducted in a water tank, with particular attention on structure in the collision region. Considering the coupling effect of external dynamics and internal mechanics, the dynamic responses of ships during collision are studied. The failure mode and deformation damage characteristics of ship’s side structure in collision region are also assessed. On this basis, the time history of collision forces, the damage extent of the struck structure and the energy absorption are analyzed and then the influence of velocity and ship’s mass on the results are evaluated. It provides valuable test data for validation of numerical simulation and theoretical studies.
Methodology for Mitigation of Armour Wire Bird Caging in Offshore Wind Export Cables
Authors: Connaire Adrian , Killeen Caitríona , Savitsky Ivan , Anwasi Richard , Nestor Ruairí 
Published: December 2020

Abstract
Subsea export power transmission cables for offshore wind farms are being installed more extensively year-on-year due to the increasing demands for power output from renewable sources. With the increasing number of installations, the number of cable failures during installation has increased. One failure mode involves the temporary or permanent radial deformation of armour wires otherwise known as armour wire bird caging which occurs from a combination of twist, bending and compression loads which build up in a cable. This failure mode can lead to significant remediation costs and schedule delays for projects affected.
In this paper, the authors present a method for predicting armour wire bird caging for generic installation configurations based on a review of the root causes from several historical bird caging failure instances. Various numerical models and analyses which simulate the installation conditions are described. The models simulate key response mechanisms including bending-induced twist and inter-layer separation within a cable. Cable loading conditions are compared with cable bird caging limits and the parameters which influence the onset of bird caging are identified. Based on a range of sensitivity analyses, handling curves to assist with installation are developed and a full-scale test validation programme is proposed. This work was performed for a project which received financial and technical support from The Carbon Trust’s Offshore Wind Accelerator (OWA), a collaborative R&D programme funded by nine leading offshore wind developers (EnBW, Equinor, Innogy, Ørsted, RWE, SPR, Shell, SSE, Vattenfall) and the Scottish Government.
Ship As a Wave Buoy: Estimating Full Directional Wave Spectra From In-Service Ship Motion Measurements Using Deep Learning
Authors: Scholcz T. P. , Mak B. 
Published: December 2020

Abstract
The ocean wave directional spectrum is an important wave characteristic for maritime safety and navigation. Accurate estimation of directional spectra in real-time is a challenge. In this study we aim to reconstruct the directional spectra from ship motions using a deep convolutional encoding-decoding neural network. In-service measurements of ship motions and wave spectra from a WAMOS II wave scanning radar were used to train the neural network. The data was collected from a frigate type ship for a period of two years. We demonstrate that the deep convolutional encoding-decoding neural network is successful in predicting the directional spectra in real-time. At the same time, we conclude that more data is needed for a better prediction performance, including a more complete coverage of operational conditions.
Experimental Study on the Wall Factor for Rod-Shaped Proppant Settling in Vertical Fracture
Authors: Zhu Zhaopeng , Song Xianzhi , Yao Xuezhe , Zhu Shuo , Jing Silin 
Published: December 2020

Abstract
Hydraulic fracturing is an important technology to improve oil and gas production. In recent years, rod-shaped proppant has received increasing attention for its advantages in avoiding fracture closure and enhancing conductivity. Due to its special shape, the settling process in the fracture is more complicated than that of a spherical proppant. Accurate description of the wall factor of fracture on the settling rod-shaped proppant is pivotal in predicting the transport distance of rod-shaped proppant and improving the effect of fracturing. However, few researches have been reported about the fracture wall factor on the settling rod-shaped proppant. In this study, the transparent fracture model with different width and a high-speed camera were used to record the settling process of the rod-shaped proppant in the fracture. A total of 215 tests were carried out to analyze the effects of fluid properties, the equivalent dimensionless diameter, sphericity, and Reynolds number on the wall factor, involving the ranges of the equivalent dimensionless diameter and the particle Reynolds number are 0.03 to 1.47 and 0.03–1354.14, respectively. The settling processes of rod-shaped proppant under horizontal and vertical states were studied, and two wall factor models for the two states were established, respectively. The results show that the wall factor is a function of both the equivalent dimensionless diameter and Reynolds number. Finally, the prediction models of wall factor with the prediction error of 1.70 and 4.44% are established for these two Reynolds number regions, respectively. The results of this study can further improve the performance of rod-shaped proppant in hydraulic fracturing.
Stinger Structural Analysis Using Fully Coupled Model for Pipelay Operations
Authors: Gupta Anupam , Tallavajhula Sudhakar , Mathakari Sachin 
Published: December 2020

Abstract
With the growing demands and increasing challenges in deep-water pipeline installation, it is increasingly important to optimize stinger capacity assessment procedure for higher level of accuracy and cost-efficiency as compared to the traditional approach which is highly conservative.
The traditional approach combines maximum stresses from three different analyses for environmental loads, vessel motions and pipeline forces to calculate the dynamic performance of a stinger. This approach ignores the coupled behavior between stinger, vessel and pipeline leading to conservative results and over-design which significantly underestimates the operational limits of the stinger structure.
The main objective of this study is to develop a simple yet optimized and accurate stinger design and analysis procedure by considering the combined effect of vessel motion, pipeline forces and environmental loading on stinger structure. This is achieved by performing a Fully Coupled Analysis (FCA) in time domain, with capability to capture the impact of stiffness and hydro-elastic properties of stinger and pipeline. The fully coupled model also allows inclusion of hydrodynamic loads on installation vessel as compared to use of vessel motion RAOs in the traditional approach. Forces from this time-history analysis are extracted and mapped onto the structural model to check for structural strength using API and AISC codes.
This paper presents a comparison between structural analysis results obtained from Fully Coupled Analysis (FCA) and traditional approach. Results from the FCA procedure have shown significant improvement in the operational limits of stinger.
Monitoring and Performance Evaluation of Plastic Cleanup Systems: Part I — Description of the Experimental Campaign
Authors: Sainte-Rose Bruno , Wrenger Hendrik , Limburg Hans , Fourny Arthur , Tjallema Arjen 
Published: December 2020

Abstract
The Ocean Cleanup Foundation is developing floating barrier systems to concentrate and extract buoyant plastic from the global accumulation zones located in the subtropical convergence zones in the world’s oceans. In that context, two cleanup systems have been designed, built and deployed in the Great Pacific Garbage Patch since 2018 to evaluate their performance in the field. During those campaigns, a large amount of data in terms of system displacement and environmental conditions has been collected. This data serves to further validate and calibrate numerical models that will be used to develop future generations of cleanup systems.
The main performance indicator in scrutiny is the field efficiency which can be derived from on the one hand the barrier horizontal motion in terms of displacement and span heading and on the other hand the plastic transport around and inside the barrier. This information then needs to be correlated to the background environmental conditions to evaluate the barrier’s efficiency over a longer deployment period and allow multi-decadal hindcast analysis. describe both the experimental and numerical work, this paper is split in two parts. This first part is dedicated to the presentation of the experimental setup in terms of barrier displacement, environmental conditions and surface transport measurements.
This paper details the techniques employed to carry out those measurements, how they are processed but also the short comings of some measurement methods.
Energy Harvesting From the Tidal Currents Using a Mangrove-Like System
Authors: Kazemi Amirkhosro , Curet Oscar , Gómez Daniel , Castillo Eduardo E. 
Published: December 2020

Abstract
Tidal energy has the potential for future electricity generation to be widely used in intercostal areas during the rise and fall of tides. Inspired by mangrove roots, we designed a novel device to harvest hydrokinetic energy from tidal currents. This device consists an oscillating cylinder, partially submerged in a flow of water and an electric generator composed of a fixed magnet and a coil attached to the cylinder pivoted at its top by a thin flexible steel plate. This energy harvesting system is considered as one-degree-of-freedom vortex-induced vibration (VIV). The oscillation amplitude of the cylinder tip was recorded with a high-speed camera and 2-D PIV measurements were made to explore the hydrodynamic interaction within the devices for Reynolds numbers ranging from 200 to 1500 (based on cylinder diameter) consistent with biological velocity in tidal flows. We analyzed the kinematics as well as the power generation of the device for different stiffness of the plate. We observed that the cylinder was unmoved for low water velocities; however, by increasing the flow velocity the oscillations increase and reached a maximum value; similar fashion was observed for all stiffness. It was found that for a specific range of reduced velocity (0 &lt; Ur &lt; 3.5) the device worked in its optimal range in which the amplitude of oscillations and the efficacy of the system reach the highest values. This analysis of VIV correlated with oscillations will be fundamental for future bio-inspired energy harvesting devices. These renewable energy devices could have applications to power small actuators or sensors to monitor coastal infrastructure.
Clamping Effect on the Welding Deformations in Dissimilar Welded Pipes (Joints) With Varied Thicknesses: Axial and Radial Shrinkage
Authors: Kogo Bridget , Wang Bin , Chizari Mahmoud 
Published: December 2020

Abstract
This study investigates and evaluates the welding residual stresses and deformations in the dissimilar material MSSS metals in order to verify the clamping effect on the residual stresses and deformations and entails comparison with the finite element simulation, the critically reflected longitudinal ultrasonic stress measurement and the hole-drilling residual stresses in a Butt-welded plate courtesy of Javadi et al [1]. The angular shrinkage measurement and vertical displacement were used to achieve this objective. The outcome of the study proved that the measurement of residual stress using protractor is an effective way of differentiating the influence of clamps on the longitudinal stresses.