bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies About Design of Rear Stator of Ducted Propeller Using CFD
Authors: Feng Dakui , Zhang Hang , Sun Yue , Wang Qing , Hu Xiaofei
Published: November 2019

Ducted propeller designs are becoming more popular because of their high efficiency, resistance to cavitation and low radiated noise. In this paper, unsteady RANS simulations are carried out for the design of rear stators for ducted propeller to improve its hydrodynamic performance. The design of rear stator is carried out based on the wake field behind propellers. The two-dimensional airfoil modified from NACA4603 is studied to obtain the angle of attack that makes thrust on stators maximum. The analyses are performed at different angles of attack, using commercial computational fluid dynamics (CFD) solver STAR-CCM+ to solve URANS equations. URANS equations are discretized by finite volume method and solved by PISO algorithm. Simulations have been made using unstructured grid with mesh moving technique. The simulation results indicate that the total thrust coefficient and efficiency of modified ducted propeller have been improved by 7.32% and 5.72% respectively compared with the parent one. The simulation results show that the design method is reasonable and feasible.
Wave Impact Loads Prediction With Compressible Air Effects Using CFD
Authors: Gatin I. , Liu S. , Vladimir N. , Jasak H.
Published: November 2019

A computational method for predicting wave impact loads where compressible air effects might be present is presented in this paper. The method is a Finite Volume based Computational Fluid Dynamics method where air is modelled as a compressible ideal gas while water is treated as incompressible. Special numerical treatment of the interface based on the Ghost Fluid Method enables capturing the sharp transition in compressible properties of air and water across the free surface, making the method accurate for predicting trapped air pockets during wave impacts or slamming. The approach enables predicting impacts where trapped air pockets play an important role in the loading of the structure due to the capacity to absorb and redistribute wave impact energy. The present approach is validated on a falling water slamming case where trapped air compression is present. Next, a full scale wave breaking impact on a vertical wall is simulated and the results compared to experimental measurements, with trapped air compression effects. Finally, the method is applied on a breakwater green water loading calculation of an Ultra Large Container Ship in an extreme focused wave impact based on the Response Conditioned Wave theory. Motion of the container vessel is calculated directly during the simulation. The calculation is shown to be computed with limited computer resources in reasonable amount of time. Overall the approach proved to be accurate, robust and efficient, providing a tool for assessing wave impact loads with or without compressible air effects.
A Validation of a Pivoted Point Absorber Type Wave Energy Converter Using CFD
Authors: Yang Injun , Tezdogan Tahsin , Incecik Atilla
Published: November 2019

Wave energy is sustainable and clean energy, so it has great potential to be an eco-friendly and lasting renewable energy resource in the future. Recently, a number of researchers have investigated different types of wave energy converters (WECs) using numerical models such as potential theory and Computational Fluid Dynamics (CFD) to enhance the efficiency of such devices. In this paper, a validation of a point absorber type WECs is investigated to capture the movement of the WEC system and to measure the moment on the WEC system. The WEC consists of a lever and a buoy. The geometry is the same as the existing experimental geometry of the reference in order to validate the present numerical simulation. The buoy is connected to the lever and has a hinge on the connection point. Besides, another hinge is installed in the middle of the lever, and the WEC system rotates in the pitch direction. The commercial CFD package Star-CCM+, which solves Reynolds-Averaged Navier-Stokes equations, is employed in this study. In the initial stages of this research, a validation study against published experimental results was conducted. The rotational displacement and the moment on the buoy were compared with the existing experimental data of the reference. The result shows good agreement. In the near future, a study on a new pivoted point absorber WEC device regarding the buoy shape of the WEC device and an operation principle will be performed based on this numerical study.
Linear Evolution of a Narrow-Banded Surface Gravity Wavepacket Over an Infinite Step
Authors: Li Yan , Adcock Thomas A. A. , van den Bremer Ton S.
Published: November 2019

This paper focuses on the classical and fundamental problem of waves propagating over an infinite step in finite water depth. Specifically, this paper aims to extend classical narrow-banded wave theory for constant water depth which uses a multiple-scales expansion to the case of an abrupt change in the water depth, known as an infinite step. This paper derives the linear evolution equations and is the first step towards the calculation of second-order and higher-order effects for wavepackets travelling over a step using commonly employed envelope-type evolution equations, in particular the bound sub- and super-harmonics at second order.
Vortex Induced Vibration of a Steel Catenary Riser Under Out-of-Plane Current: An Experimental Study
Authors: Xu Yuwang , Wang Jungao , Ren Haojie , Zhang Mengmeng , Fu Shixiao
Published: November 2019

To investigate the VIV characteristics and to further develop the corresponding numerical predictions of a steel catenary riser under out-of-plane current, a large-scale model of a steel catenary riser was towing in an ocean basin at various speeds and directions. Fiber Bragg grating strain sensors are instrumented on the riser model to measure both in-plane and out-of-plane responses. The vortex-induced vibration responses of the steel catenary riser under out-of-plane current, i.e., the oscillating amplitude, the response frequency, and the traveling wave phenomenon, are compared with those under the in-plane current.
A Probabilistic Approach to Tropical Cyclone Modelling
Authors: Grey Stephen , Liu Ye
Published: November 2019

Tropical cyclones are highly variable and, in many areas of the world, are the main cause of extreme wind and associated waves, surge and current conditions. At a given location, cyclones that cause a significant impact are relatively rare but severe events, which means that the number of historical events for which data are available is often quite small. In addition, the effects, particularly surge, can be relatively localized and affected by the local bathymetry and topography. This causes considerable difficulty in making quantitative predictions of extreme events for design of offshore or coastal structures in areas affected by tropical cyclones.

A new probabilistic method has been developed to increase the sample of tropical cyclones by producing 10,000 years of synthetic cyclone tracks with a range of paths, intensities and sizes based on Hall and Jewson [1] and Casson and Coles [2]. From this set of synthetic tracks, those tropical cyclones most likely to affect the site of interest are modelled using time-varying wind fields based on the Holland model [3] with surge, current and waves then modelled using the hydrodynamic model TELEMAC-2D coupled to the SWAN wave model. As it is impractical to model 10,000 years of tropical cyclones, a Gaussian process emulator is employed to relate the resultant conditions to parameters defining the cyclones, such as track position, heading, intensity and radius to maximum wind.

The result is a synthesized 10,000 years of cyclone events from which design conditions for a range of return periods can be predicted with a greater degree of certainty than by extrapolating from historical events.
Quantification of Predicted Wave Forces From Distant Elevation Measurements
Authors: Hallowell Spencer T. , Arwade Sanjay R. , Johlas Hannah , Lomonaco Pedro , Myers Andrew
Published: November 2019

The vast spatial scale of offshore structures causes wave loading to be correlated amongst nearby structural members. Certain engineering activities including health monitoring, maintenance, and preliminary design of offshore structures requires the prediction of wave forces on said structural members. The high cost and low availability of environmental wave measurements requires the reconstruction of wave kinematics and force profiles to accurately capture the forcing history on offshore structures. A method for predicting wave forces on a cylinder from nearby wave elevation measurements is proposed. The formulation utilizes the Fast Fourier Transform to calculate wave kinematics propagation in the frequency domain and applies the kinematics to the Morison equation for calculation of cylinder forces. The prediction equations are applied to three types of waves: regular periodic waves, random irregular waves, and solitary breaking waves, and the error in both elevation prediction and force prediction when compared to measured values is calculated. The force prediction equations were shown to perform best for small wave heights, with errors as low as 5% in the force predictions for small regular and irregular waves. The error in force prediction increases nonlinearly with the increase in wave height due to the deficiencies of the linear dispersion relationship used in the formulation.
Nonlinear Airy Wave Pulses on the Sea Surface
Authors: Shugan Igor , Kuznetsov Sergei , Saprykina Yana , Chen Yang-Yih
Published: November 2019

The possibility of self-acceleration of the water-wave pulse with a permanent envelope in the form of the nonlinear Airy function during its long propagation in deep water is experimentally and theoretically analyzed. This wave packet has amazing properties — accelerates without any external force, and preserves shape in a dispersive medium. The inverted Airy envelope wave function can propagate at velocity that is faster than the group velocity. We experimentally study the behavior of Airy water-wave pulses in a super-tank and long scaled propagation, to investigate its main properties, nonlinear effects and stability. Theoretical modeling analysis is based on the nonlinear Schrodinger equation. We investigate the scope of applicability, feasibility and stability conditions of nonlinear Airy wave trains in the deep water conditions; defining regimes of self-acceleration of the main pulse, immutability shape of Airy envelope; assessing the impact of nonlinearity and dissipation on the propagation of Airy waves. We analyzed the influence of the initial pulse characteristics on self-acceleration of wave packet and the stability of the envelope form. The anticipated results allow extending the physical understanding of the evolution of nonlinear dispersive waves in a wide range of initial conditions and at different spatial and temporal scales, from both theoretical and experimental points of view. Steep waves start to become an unstable, we observe spectrum widening and downshifting. Wave propagation is accompained by the intensive wave breaking and the generation of water-wave solitons.
Parameter Calibration for Continuum Damage Mechanics Models to Simulate Ductile Fracture of High Strength Pipeline Steels
Authors: Van den Abeele Filip
Published: November 2019

The ability to arrest a running crack is one of the key features in the safe design of pipeline systems. In the industry design codes, the crack arrest properties of a pipeline should meet two requirements: crack propagation has to occur in a ductile fashion, and enough energy should be dissipated during propagation. While the first criterion is assessed by the Battelle Drop Weight Tear Test (BDWTT) at low temperatures, the latter requirement is converted into a lower bound for the impact energy absorbed during a Charpy V-notch (CVN) impact test. However, the introduction of high strength pipelines steels (X70 and beyond) has revealed that the commonly used relations based on BDWTT and CVN no longer hold. For such scenarios, Continuum Damage Mechanics (CDM) models provide promising potential to obtain a more profound understanding of the mechanisms that govern ductile crack propagation in high strength pipeline steels.

In recent years, different types of CDM models have been used to simulate ductile fracture of pipeline steels. This paper focuses on two of these models, i.e. the Gurson-Tvergaard-Needleman (GTN) model and the Modified Bai-Wierzbicki (MBW) model. The GTN model is based on the computation of void growth according to Rice and Tracey, and account for the local softening of the material due to void nucleation, growth and subsequent coalescence. The MBW model is a fully coupled damage model, where the yield surface depends on both the stress triaxiality and the Lode angle. Although both models can predict ductile fracture propagation, their widespread application in pipeline design is hampered by the large number of input parameters to be calibrated. The GTN model requires 10 input parameters, i.e. 3 Tvergaard damage parameters, 4 porosity parameters and 3 parameters to describe void nucleation.

Whereas the Modified Mohr-Coulomb model originally proposed by Bai and Wierzbicki uses merely 2 parameters, the extended MBW model requires no less than 18 parameters to be calibrated: 11 plasticity parameters (5 stress + 3 strain rate + 3 temperature) and 7 damage parameters (4 initiation + 1 propagation + 2 failure).

In this paper, different numerical/experimental strategies to calibrate these parameter sets are reviewed and compared. Sensitivity analyses are performed to assess the influence of the different input parameters on the model predictions. For both GTN and MBW models, the robustness and uniqueness of the calibrated parameter sets is investigated. Recommendations on optimum parameter values are derived, with special emphasis on high strength pipeline steels.
Estimation of Roll Damping Coefficients Based on Model Tests Responses of a FPSO in Waves
Authors: Rodríguez Claudio A. , Esperança Paulo T. T. , Oliveira Mauro C.
Published: November 2019

Roll damping estimation is of great concern for the prediction of motions in waves of ship and offshore platforms, especially when viscous effects are relevant. Although this problem dates back to the times of William Froude, it has regained much attention in the context of the development of the second-generation intact stability criteria of ships, especially because there are still not accurate and efficient tools for roll damping prediction. For offshore applications, a common approach for roll damping estimation is to perform roll decay tests with scale models in calm water and then use the resultant values in the roll equation to predict motions in waves. However, for some wave conditions, the damping coefficients obtained from those tests may not be representative of the actual damping in waves. To assess the influence of wave conditions in the roll damping coefficients, the present work proposes a simplified hybrid approach that combines experimental results from model tests with numerical predictions of roll motion in waves. The numerical tool adopted here is based on a frequency domain single-degree-of-freedom model with linearized external damping that includes viscous effects. A series of experimental model tests with a typical FPSO hull in regular and irregular has been analyzed to obtain the roll damping coefficients in waves. These results are compared with those from decay tests in calm-water as well as from semi-empirical predictions based on Ikeda’s method. Despite the linearized assumption, it is expected that the damping coefficients from wave tests provide a more realistic representation of the roll dynamics than those from typical decay tests.
Development of a Control Strategy for Underway Tandem-Like Oil Transfer Operation Between a Conventional and a DP Tanker
Authors: Moreno Felipe M. , Amendola José , Tannuri Eduardo A. , Ferreira Marcos D.
Published: November 2019

Ship-to-ship (STS) operations have been widely applied for oil and cargo transfer in order to improve operational efficiency and reduce operational costs. Brazil has seen an increase in underway Ship-to-Ship operations due to the lack of available berths and terminals. The transfer operation is carried in sheltered locations in Brazil and abroad, but still has issues such as cable ruptures and high downtimes due to environmental conditions. This work proposes the development and validation of a control system for an innovative configuration for oil transfer between a DP shuttle and a conventional tanker, using a modified tandem configuration. The conventional vessel is underway and the DP vessel follows it with a lateral offset that provides a safe route for escape in case of any failure. The focus of the present paper is the control system design applied to the DP vessel that ensures the safe operation inside the offloading site. This control applies two individual sliding mode controllers for rudder and thruster control, with coefficients obtained from numerical simulations, associated with a line-of-sight strategy for course and speed over ground controllers. The set-point for the controller is obtained from the conventional vessel that is navigating ahead from the controlled vessel. Control performance and operation safety are evaluated through a set of real-time simulations of the transfer operation, where performance is evaluated through measurement of the Bow Loading System point position in both straight line navigation and in a 10km radius curve. The control robustness is evaluated by varying the environmental conditions in the simulations. Safety issues are also considered by evaluating the possibility of evasive maneuvers in case of component failure.
Detection of Mooring Line Failure of a Spread-Moored FPSO: Part 2 — Global Performance Analysis Using MLTSIM
Authors: Kyoung Johyun , Lim Ho-Joon , Sidarta Djoni E. , Tcherniguin Nicolas , Lefebvre Timothee
Published: November 2019

This paper presents Part 2 in the development of an Artificial Neural Network (ANN) model for detection of mooring line failure of a spread-moored FPSO, global performance analysis used to generate the training and test data for the study.

The development of an ANN model for detection of mooring line failure requires a comprehensive training data that is most practically available from the results of numerical simulations. Time domain analysis is necessary to capture the nonlinear behavior of a moored FPSO system and to represent the behavior of the physical system as accurate as possible. Given the wide range of sea-state conditions, of direction of the sea-states and of draft conditions of the FPSO, the number of time domain simulations is easily larger than 100,000. Therefore, an accurate and numerically efficient tool is necessary for carrying this task.

The FPSO hull motion analysis is performed using MLTSIM, a TechnipFMC in-house, nonlinear time domain floating body motion analysis program. MLTSIM captures various non-linear load and response effects such as mooring stiffness, riser loads, drag and drift forces, as well as various user defined loads. MLTSIM is a numerically efficient and fast time domain solver which can run on both high-performance computing (HPC) system and a single laptop.

Numerical model of a FPSO system has been validated using the results of model tests. In addition, the results of numerical simulations, in terms of hull motions and mooring line tensions, are compared with the results of model tests and a commercial software OrcaFlex. This well-calibrated model is then used for generating the numerical data required for the development of the ANN model.
Parametric Rolling in Regular Head Waves of the KRISO Container Ship: Numerical and Experimental Investigation in Shallow Water
Authors: Tello Ruiz Manases , Villagomez Jose , Delefortrie Guillaume , Lataire Evert , Vantorre Marc
Published: November 2019

The IMO Intact Stability Code considers the parametric rolling phenomenon as one of the stability failure modes because of the larger roll angles attained. This hazardous condition of roll resonance can lead to loss of cargo, passenger discomfort, and even (in the extreme cases) the ship’s capsize. Studies as such are mostly conducted considering wave characteristics corresponding to wave lengths around one ship length (λ ≈ LPP) and wave amplitudes varying from moderate to rough values. These wave characteristics, recognised as main contributors to parametric rolling, are frequently encountered in deep water. Waves with lengths of such magnitudes are also met by modern container ships in areas in close proximity to ports, but with less significant wave amplitudes. In such areas, due to the limited water depth and the relatively large draft of the ships, shallow water effects influence the overall ship behaviour as well.

Studies dedicated to parametric rolling occurrence in shallow water are scarce in literature. In spite of no accidents being yet reported in such scenarios, its occurrence and methods for its prediction require further attention; this in order to prevent any hazardous conditions. The present work investigates the parametric roll phenomenon numerically and experimentally in shallow water. The study is carried out with the KRISO container ship (KCS) hull. The numerical investigation uses methods available in literature to study the susceptibility and severity of parametric rolling. Their applicability to investigate this phenomenon in shallow water is also discussed. The experimental analysis was carried out at the Towing Tank for Manoeuvres in Confined Water at Flanders Hydraulics Research (in co-operation with Ghent University). Model tests comprised a variation of different forward speeds, wave amplitudes and wave lengths (around one LPP). The water depth was fixed to a condition equivalent to a gross under keel clearance (UKC) of 100% of the ship’s draft.
A Design Practice for Subsea Pipeline Subjected to UXO Hazards
Authors: Liu Zhenhui , Igland Ragnar , Bruaseth Sindre , Ercoli-Malacari Luca , Lillebø Odd Arne
Published: November 2019

This paper presents a design practice for the oil export pipeline (OEP) of Johan Sverdrup Oil Field subjected to unexploded ordnance (UXO) hazards during the pipeline installation period. The UXO (unexploded ordnance) is a potential risk to the oil export pipeline due to its significant impulsive pressure load in a short time. Present paper discusses an unfavorable scenario in which the UXOs are identified during the pre-lay survey stage. It may (and it does) happen due to the survey methods chosen between the initial preliminary and the pre-lay survey. Consequently the original design pipeline routing has to be updated in order to minimize the UXOs’ potential damage to the pipeline. A safety distance between pipeline and UXOs shall be established and maintained. To achieve this, advanced numerical simulation was used for assessing the damage of pipeline under UXO explosion loads. The damage is sensitive to the charge weight and the distance between charge and pipeline. The pipeline route was updated accordingly based on the safety distance and actual locations of UXOs. The new route shall also fulfill all design checks. With the updated pipeline routing, the installation could continue without interruption of the project schedule. The identified UXOs will be subject to later removal before startup of production to further ensure the safety of installed pipeline. The overall design process is presented. Some simulation results from Abaqus Explicit solver are shown in the paper. Conclusions and discussions are included, which may be useful for similar projects in the future.
Numerical Simulation of Multidirectional Waves With Full-Spectrum Using DualSPHysics
Authors: Kanehira Taiga , Mutsuda Hidemi , Draycott Samuel , Ingram David M. , Doi Yasuaki
Published: November 2019

The numerical model for circular wave basin were developed using DualSPHysics based on Smoothed Particle Hydrodynamics to generate short-crested wave. The recreation of short-crested wave was achieved using Pierson Moskowitz spectrum and cosin2s spreading function with spreading value s. It is found that this numerical tank model could successfully reproduced not only long-crested but short-crested waves using 168 hinged-flap type wave makers.
URANS Simulation of ONR Tumblehome Parametric Rolling in Regular Head Waves
Authors: Zhang Zhiguo , Guo Lixiang , Wang Shuang , Yuan Ye , Chen Can
Published: November 2019

In this paper, an in-house CFD code HUST-Ship is used for the numerical simulation of parametric rolling phenomena of ONR Tumblehome in regular head wave. Preliminary resistance and roll decay simulations at Fr = 0.2 were carried out and compared with existed INSEAN experimental data. Following, three DOFs’ ship motions in regular head wave with an initial roll angle of 30 degrees was calculated to examine the possibility of occurrence of parametric rolling. Finally, a simulation without initial roll disturbance was performed to investigate its influence to the steady roll amplitude. By conducting fast Fourier transform of the time history of motions, forces and moments, the characteristics are analyzed and co-related with wave frequency. Results can be concluded that the in-house code has the ability to perform the parametric rolling simulation, and that the final steady roll amplitude is not affected by the initial disturbance. In addition, heave and pitch motions are dominantly affected by wave characteristic, roll frequency is about half that of wave, and that forces and moments in x direction exhibit high-order non-linearity.
Numerical Modeling Practice and Verification of the Wind Load Estimation for FPSO and Semi-Submersible
Authors: Yeon SeongMo , Jang Hyunchul , Kim Jang Whan , Kim JooSung , Nam Bo Woo , Huang Zhenjia , O’Sullivan Jim , Kim Hyun Joe , Hong Sa Young
Published: November 2019

This paper summarizes a joint effort, TESK JDP, initiated by TechnipFMC, ExxonMobil Upstream Research Company (EMURC), Samsung Heavy Industries (SHI) and Korea Research Institute of Ships & Ocean Engineering (KRISO) in order to develop reliable modeling practices for the application of Computational Fluid Dynamics (CFD) to the design of the offshore floating structures. The modeling practice for the wind load on offshore floating structures, which was one of the topics in this JDP, was studied and verified against model test results.

The wind load on the offshore floating structures mostly depends on the shape of the wind profile rather than the design wind speed. Much weight is put on the generation and retainment of the wind profile within the computational domain. The modeling practice for generating the wind profile referred to as sustainable atmospheric boundary layer (ABL) or horizontally homogeneous turbulent boundary layer (HHTBL) as well as domain size, mesh strategy, turbulence model are used to perform wind load simulations for a semi-submersible and FPSO respectively as a blind test between JDP members. In order to minimize uncertainties from geometric similarity, special care was taken during the simulation and model test for the FPSO due to the complicated top side modules. Given the modeling practice, the results are compared between JDP members and show consistent tendency. Also, a good agreement was observed for the hydrodynamic coefficients of the wind load for both the FPSO and semi-submersible.
Hydrodynamic Design of a Morphic Autonomous Underwater Vehicle Using Neural Networks
Authors: Becker Quentin , Alam Mohammad-Reza , Immas Alexandre
Published: November 2019

With the advent of Artificial Intelligence and new manufacturing techniques, Autonomous Underwater Vehicles (AUVs) have started to prevail over their manned version in terms of cost efficiency when it comes to accomplish tasks in ocean exploration, offshore platform and ship maintenance or other military missions. As progress has been made over the past years, autonomy remains a topical issue for the untethered AUVs. Drawing its inspiration from nature, this paper aims at minimizing the energy consumed by the device on a specific mission by allowing its shape, parameterized with Bezier curves, to morph throughout time. The framework is restricted to one dimensional trajectories only. A first step consisting of finding the optimal velocity and shapes added mass coefficient in surge as functions of time for a given mission is presented. Then a way of determining the succession of shapes the AUV must take so that it has the right added mass coefficient at any time is proved and used. This last part is made computationally affordable by using a Neural Network instead of a Boundary Element Method to evaluate the hydrodynamic coefficient in surge of the shape. Outliers detection and elimination are being performed on the training dataset to increase the predictive model reliability and robustness.
Investigation of Strain-Based Failure Assessment Based on Reference Strain Method for Welded Pipes
Authors: Lee Jae Sung , Kim Myung Hyun
Published: November 2019

Pipelines are effective means to transport oil and gas. It is essential to maintain the safety of pipelines with the increasing demand for oil and gas resource. Welded pipelines may suffer damage such as cracks during installation and operation, and the consequence evaluation for such damage is very important. Engineering critical assessment (ECA) is the evaluation procedure for structures with flaws and has been widely applied for assessing the pipeline integrity. Although main standards of structural integrity assessment including BS 7910 are stress-based ECA, it is known to produce overly conservative results. In this regard, strain-based ECA has been recently developed.

One of the methods for improving the accuracy of strain-based ECA is the reference strain method. However, only few researches with reference strain method applied to welded pipes are available. Therefore, in this study, a numerical analysis based on the strain-based ECA is performed for strength mismatched girth welded joints with a circumferentially oriented internal surface crack. Equivalent stress-strain curve in BS7910 is employed to reflect the strength mismatch effects in the reference strain. This paper compares the results from the reference strain method and finite element analysis: J-integral and reference strain. Strain capacity of the reference strain method with strength mismatch is also discussed against stress-based ECA.
Experimental and Numerical Analysis of Performance of Oscillating Water Column Wave Energy Converter Applicable to Breakwaters
Authors: Park Sewan , Kim Kyong-Hwan , Nam Bo-Woo , Kim Jeong-Seok , Hong Keyyong
Published: November 2019

In the present study, the primary energy conversion performance of an oscillating water column (OWC) was evaluated through experimental tests and numerical simulations. The experimental tests were performed at an ocean basin located in Korea Research Institute of Ships and Ocean Engineering (KRISO), Korea. A 1/4 scaled OWC chamber model with an orifice to account for the turbine effect was set up at the 3-dimensional basin, and regular wave tests were performed at various incident wave periods. The water surface level inside the chamber, the differential pressure between before and after the orifice, and the airflow speed through the orifice were measured. Computational fluid dynamics (CFD) analysis was performed using the Star-CCM+ commercial software to analyze the performance of the OWC for the same model that was used in the experiment. Detailed flow fields were discussed based on the CFD results, and the numerical and experimental results were compared. The validation results showed good agreement.
Experimental Investigation of Wave Runup on Offshore Intake Wells in a Random Wave Environment
Authors: Prabu Kumar V. , Sundaravadivelu R. , Murali K.
Published: November 2019

The seawater intake system is one of the essential operational units in many industries located in the coastal regions. The selection of the type of intake system to a specific sector depends on the total volume required and the quality of the sea water. The offshore seawater intake wells are a suitable option to meet the large volume water requirement and desired water quality. Sometimes two or more intake wells are installed to supply the large volume of the sea water. Since the increase in spacing between the wells leads to an increase in capital cost, it is predominant important to find the optimum distance between the wells. The present study focuses on the external and internal hydrodynamics of two caisson type offshore intake wells situated in random wave environment. Two wells are fabricated in 1:20 model scale and installed in the shallow wave basin and exposed to the random waves. The outer to outer face distance between two wells changed by concerning the outer diameter (D) of the well such that 1D, 1.5D and 2D. The wave run-up, diffraction wave height and free surface water oscillations inside the wells are measured. The distance between the two intake wells has a significant role in wave run-up and free surface oscillation inside the well. Besides, the H/d have a substantial influence on the wave run-up on the seaward face compared to the side and shoreward face in all three cases. Also, the diffraction wave height is minimum when the wells are separated by 1.5D distance. Moreover, wave run-up and free surface water oscillation are optimum when the separation distance between the wells is 1.5D.
Numerical Simulation of Consecutive Multiple Lateral Impact on the Reinforced Concrete Pier
Authors: Yang Shuai , Xia Xiao-zhou , Zhang Qing , Wang Xue-gang , Ying Zong-quan
Published: November 2019

The consecutive multiple impact resistance of reinforced concrete pier column becomes the most concern in the engineering field. Numerical simulation the process of consecutive multiple lateral impacts is the necessary measures to master the internal mechanism. The fine 3D finite element model is established combining solid element and beam element. The dynamic damage constitutive model of concrete is developed. To react to problem of calculative efficiency and damage accumulation effect, the reduced integration method and full restart analytical method of explicit dynamic analysis strategy is taken using element failure criterion. The translation process of the system energy, the time history value of impact mass acceleration and strain gauge and failure mode of the reinforced concrete pier are compared with the experiment results. The feasibility of the modelling and the validity of the analysis strategy are validated. This study can provide computation basis for research of reinforced concrete structures under consecutive multiple impact.
Time-to-Failure Estimation of Barrier Systems in Permanently Plugged and Abandoned Wells
Authors: Arild Øystein , Lohne Hans Petter , Skadsem Hans Joakim , Ford Eric Patrick , Selvik Jon Tømmerås
Published: November 2019

With the increasing number of aging fields and wells worldwide, a large number of wells will have to permanently plugged and abandoned in the coming decades. Today’s technical solutions on P&A design are primarily driven by legislations or recognized standards such as NORSOK D-10 or the Oil & Gas UK Well Decommissioning Guidelines. The NORSOK D-010 say that the well should be sealing to “eternity” without providing any link between the recommended solution and time-to-failure.

During the last few years, there has been a drive towards a risk-based approach to P&A design. With such an approach, the goodness of a P&A design can be formulated in terms of the associated leakage risk, which consists of two components; i) the time-to-failure of the barrier system and ii) the leakage rate given the barrier system has failed.

When failure data are available, there is a wide range of statistical tools available for establishing the time-to-failure probability distribution. However, barrier failure data on permanently plugged and abandoned wells are scarce in the North Sea region. In order to estimate the time-to-failure for wells in the North Sea region, all relevant information should be taken into account; survival data, expert input and physiochemical degradation models. In this paper, we will show how this can be accomplished by means of a Bayesian reliability approach.

The paper will first describe the general framework for how to perform Bayesian time-to-failure estimation. Thereafter, information pertaining to barrier system lifetime for wells on the Norwegian Continental Shelf (NCS) and relevant assumptions will be discussed. Finally, the methodology will be applied on a synthetic case.
Experimental Research of Wave Transformation on Porous Coral Reef
Authors: Zhu Gancheng , Ren Bing , Wang Yongxue , Wang Chao
Published: November 2019

The influences of reef porosity on wave propagation over coral reef are studied by two-dimensional laboratory experiments. Detailed measurements of wave height and set-up over the reef are carried out under various particle sizes of porous media and incident wave conditions. A comparison of hydrodynamic characteristics between the porous reef and the solid reef is conducted. Based on Gourlay’s [1] model, a dimensionless analysis is conducted to describe the relationship between incident wave conditions and wave set-up over the porous reef.
Local Hard Zones in Sour Service Steels
Authors: Fairchild D. P. , Newbury B. D. , Anderson T. D. , Thirumalai N. S.
Published: November 2019

Hard zones in large diameter pipe have been identified as the cause of the Kashagan pipelines failure, the replacement of which is estimated to cost $3.6B [1–4]. Some hard zone formation mechanisms have been known for years, but one mechanism is “new”, or more precisely, newly recognized. This mechanism can occur during the Thermomechanical Control Processing (TMCP) of plate and specifically during accelerated cooling. The hard microstructure is lath bainite and is isolated in thin (200–500 μm) surface regions. To distinguish the new mechanism from the others these surface regions are given the name local hard zones (LHZs).

There are currently no validated industry standard inspection methods that can be used to detect LHZs. This situation is challenging for an industry that relies on TMCP pipe for sour service applications. This paper explains the LHZ formation mechanism while a companion paper (Newbury, et al [59]) will describe TMCP monitoring techniques that can be used to mitigate the risk of LHZs.
Study on Anchor Leg Installation Sequence of Nanhai Shengli FPSO Under Typhoon Season
Authors: Shen Hui , Wang Huoping , Zhu Weiquan , Wang Deyang
Published: November 2019

Nanhai Shengli (NHSL) FPSO, which is serviced in the South China Sea, was dry-docking to upgrade its internal turret mooring system in the first half of 2018, and the mooring system was re-hooked up to the FPSO subsequently in July. The whole installation of the mooring system will last for more than a month. Based on the metocean data of the South China Sea and operation experience, the mooring system installation may encounter typhoon conditions. The NHSL mooring system consists a 10-legs catenary system. The installation sequence of anchor legs may affect the performance of the mooring system under different intensity typhoon conditions. Steps in the design process of anchor leg installation sequence are described in this paper. Based on the tension and offset derived from the time domain mooring analysis, an optimized installation sequence is obtained in order that the mooring system has a better ability to withstand typhoon conditions.
A 2D Nonlinear Numerical Wave Tank With a Moored Floating Body
Authors: Sun Hui , Helmers Jens B.
Published: November 2019

A 2D nonlinear numerical wave tank is developed to simulate the motion responses of a moored floating body in waves which may experience strongly nonlinear wave-body interactions. The numerical solver is based on a Boundary Element Method which has been developed to solve strongly nonlinear hydrodynamic problems. The method is further developed in this paper to simulate a floating body in waves, where horizontal, vertical and rotational motions can be calculated. An effective algorithm is implemented to separate the added mass forces from the total hydrodynamic forces, thus to make the time domain solution converge more easily. The numerical results for a horizontal circular cylinder in waves are compared with linear theory for small wave steepness for verification and further compared with published model tests and CFD results for high wave steepness as validations.
A Pilot Study on Time-Dependent Dissolution of CO2 in Oil for Prediction of Gas Kick Behaviors in Non-Aqueous Fluids
Authors: Kunju Mahendra , Nielsen James , Chen Yuanhang , Santos Otto L. , Williams Wesley C. , Ribeiro Paulo , Chagas Felipe
Published: November 2019

The influx of gas from formations during drilling or when the well is left undisturbed during tripping, logging, and flow check can dissolve very quickly in Non-aqueous drilling fluids (NAF). The dissolved gas can stay unnoticeable till the gas comes out of solution below bubble point pressure closer to surface. The objective of the paper is to develop a model to predict the time dependent mass transfer of CO2 in oil at subcritical pressures and validate the model using experimental results. Since CO2 is soluble in oil, the interaction between solvent and solute can help us understand the dissolution and mass transfer mechanism of CO2 in oil. A model has been developed by incorporating factors that drive the interaction and the rate of gas loading into the liquid to predict the time-dependent mass transfer. A 1.5 inch vertical low pressure apparatus is used to conduct experiments by injecting CO2 into pressurized static column of oil. Pressure inside the pipe, and mass of CO2 injected are varied to study their effects on mass transfer. Boundary conditions for this model are provided from experimentally obtained data of volumetric mass transfer coefficient of the injected gas and liquid system at gas injection flow rate. The developed time-dependent model has been validated using the data collected from the tests. The volumetric mass transfer coefficient is found to change with pressure. This model can be extended to experiments under high-pressures to replicate the downhole conditions. The model can be modified to include desorption to predict the loading and unloading of gas in NAF, and gas oil ratios at depths along the annulus in a real well.
Application of Nearshore Risk Assessment of Hazard and Vulnerability in Marine Resource Area for National Spatial Planning
Authors: Chien Lien-Kwei , Huang Chi-Wen , Huang Wei-Po , Ku Cheng-Yu , Chang Chih-Hsin
Published: November 2019

Taiwan is surrounded by sea. Thus, with the rapid growth of population, the coastal area can be considered for development in the future to satisfy the needs of the population. Moreover, the marine areas and nearshore areas of Taiwan can be developed and used. Therefore, there is a high concern pertaining to the management and use of marine areas and nearshore areas. The “Coastal Management Law” was announced and implemented in Taiwan on February 4, 2015 and defines the coastal areas in Taiwan. On January 6, 2016, the “National Land Planning Law” was announced, and the national spatial land was divided into four functional zones. This study aimed to designate the marine resource zones. The Ministry of the Interior (Taiwan) announced the national spatial plan on April 30, 2018 and proposed the conditions for the allocation of the marine resource zones. However, the conditions only considered the exclusivity or compatibility of the legal use of the marine areas. Therefore, the results of this study provide details pertaining to the risk level of nearshore areas. In the future, these results could be used as the foundation for the selection of marine resource zones and could be used to propose new plans for the selection conditions of the marine resource zones. The findings of this study can provide the central government agency with a reference for the planning and management of national spatial land.
The Effect of Operational Parameters on Vibration Signals of Wind Turbine Gearboxes
Authors: Koukoura Sofia , Bechhoefer Eric , Carroll James , McDonald Alasdair
Published: November 2019

Vibration signals are widely used in wind turbine drivetrain condition monitoring with the aim of fault detection, optimization of maintenance actions and therefore reduction of operating costs. Signals are most commonly sampled by accelerometers at high frequency for a few seconds. The behavior of these signals varies significantly, even within the same turbine and depends on different parameters. The aim of this paper is to explore the effect of operational and environmental conditions on the vibration signals of wind turbine gearboxes. Parameters such as speed, power and yaw angle are taken into account and the change in vibration signals is examined. The study includes examples from real wind turbines of both normal operation and operation with known gearbox faults. The effects of varying operating conditions are removed using kalman filtering as a state observer. The findings of this paper will aid in understanding wind turbine gearbox vibration signals, making more informed decisions in the presence of faults and improving maintenance decisions.
The Calving Events of Petermann Glacier From 2008 to 2012: Ice Island Drift Characteristics, Assessment of Fracture Events, and Geographical Data Analysis
Authors: Zeinali Torbati Reza , Turnbull Ian D. , Taylor Rocky S. , Mueller Derek
Published: November 2019

The eastern Canadian Arctic is an ice-prone environment that is a vital part of Canadian Arctic shipping lanes. A better understanding of the ice environment and ice characteristics in this region is essential for supporting safe and economical marine activities. This study presents a first analysis of the drift of ice islands that originated from the Petermann Glacier calving events in northwest Greenland between 2008 and 2012. These massive calving events generated numerous smaller ice islands and icebergs through subsequent deterioration and break-up events. Surviving ice features drifted further southward into the Baffin Bay and reached as far as offshore Newfoundland (∼47 °N) for the case of the 2010 calving event. The drift characteristics of Petermann ice islands are evaluated through the analysis of the recently developed Canadian Ice Island Drift, Deterioration and Detection (CI2D3) database. The average drift distance, speed, and directions of the ice islands that resulted from the 2008, 2010, and 2012 calving events were estimated using successive observations of the monitored ice islands in the CI2D3 database. This study also includes an assessment of fracture events, including the total number of ice island break-up events following each massive calving event and the average number of daughter ice islands resulting from each break-up event. A geographical analysis of the data was also performed to present the location of the fracture events, as well as the time series of latitude change of Petermann ice islands from their origin (northwest Greenland ice tongues) to where until they became too small (< 0.25 km2) to be delineated in the CI2D3 database. This information is of particular interest to marine activities in the eastern Canadian Arctic, and oil and gas operations offshore Newfoundland and Labrador.