bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Importance of the Coupling Between Transient Mechanical, Hydraulic and Thermal Effects for the Modelling of Real-Time Drilling Operations
Authors: Dvergsnes Erik Wolden , Cayeux Eric
Published: November 2019

Because of the increased importance for the drilling industry to deliver drilling automation solutions, model-based applications for the analysis and control of the drilling process, have become an attractive approach towards improved performance and increased safety. A critical characteristic for such applications is its ability to perform accurate simulations of the drilling operation in real-time, based on a detailed description of the wellbore.

In a real-time context, the boundary conditions of the drilling system are seldom constant, therefore reinforcing the importance of utilizing transient models of the drilling process instead of steady state ones. Typical domains that require modelling are related to the mechanical, hydraulic and heat transfer aspects of a drilling operation. The time constants of the force-, momentum-, mass- and energy-conservation equations are sufficiently different to allow for solving each of these equations with different time discretization schemes. Yet, side effects influence the results from each other’s and therefore a time coupling shall nevertheless be accounted for.

For instance, for a drilling operation conducted on a floater, the heave induced movement at the top of the string propagates along the drill-string, therefore causing a displacement that induces swab and surge pressure variations, which themselves generate counter-acting forces on the drill-string. In such conditions, both the mechanical and hydraulic frictions generate heat that changes the in situ thermal conditions and therefore the drilling fluid mass density and its rheological behavior. Consequently, heat exchange caused by the drill-string and fluid movements also influences the hydraulic response of the system. Furthermore, thermal expansion will also apply to the drill-string.

In this paper, we discuss recent advances related to the coupling between transient mechanical, hydraulic and thermal models, where a key criterion is that the combined drilling model shall be capable of running in real-time on a standard computer. Incorporating these transient models is considered a necessary step towards improved accuracy of simulations, especially on floaters, where heave effects become important. We illustrate various effects by presenting and discussing several simulations results in detail.
Numerical and Experimental Modelling of Wave Loads on Thin Porous Sheets
Authors: Mackay Ed , Johanning Lars , Ning Dezhi , Qiao Dongsheng
Published: November 2019

This work considers the numerical modelling of wave interaction with thin porous structures, based on tests conducted in simplified conditions. Wave flume tests were conducted to measure the wave loads on thin porous sheets extending over the full water column. The porous sheets tested had a range of porosities, hole separation distances and thicknesses. Numerical and analytic models for the wave forces on the porous sheet are formulated under the assumptions of either a linear or quadratic pressure loss across the porous sheet. An iterative boundary element method (BEM) model is formulated to solve the quadratic pressure loss across the porous sheet.

It is shown that the assumption of a linear pressure loss at the porous boundary is inadequate to capture the variation in the wave load with both wave frequency and amplitude, but that the quadratic model is in good agreement with the measured forces. The porosity of the sheet is shown to have the dominant effect on the wave loads. The hole separation distance affects the phase of the force on the porous wall, but has only a small effect on the amplitude of the force. The sheet thickness is shown to have a small effect on the amplitude of the force but a significant effect on the phase of the force.

The results are of interest for numerical modelling of structures with thin porous boundaries in a wide range of contexts such as breakwaters, aquaculture and offshore structures with porous elements designed to reduce loads.
On Digital Twin Condition Monitoring Approach for Drivetrains in Marine Applications
Authors: Johansen Sigrid S. , Nejad Amir R.
Published: November 2019

A digital twin is a virtual representation of a system containing all information available on site. This paper presents condition monitoring of drivetrains in marine power transmission systems through digital twin approach. A literature review regarding current operations concerning maintenance approaches in todays practices are covered. State-of-the-art fault detection in drivetrains is discussed, founded in condition monitoring, data-based schemes and model-based approaches, and the digital twin approach is introduced. It is debated that a model-based approach utilizing a digital twin could be recommended for fault detection of drivetrains. By employing a digital twin, fault detection would be extended to relatively highly diagnostic and predictive maintenance programme, and operation and maintenance costs could be reduced. A holistic model system approach is considered, and methodologies of digital twin design are covered. A physical-based model rather than a data based model is considered, however there are no clear answer whereas which type is beneficial. That case is mostly answered by the amount of data available. Designing the model introduces several pitfalls depending on the relevant system, and the advantages, disadvantages and appropriate applications are discussed. For a drivetrain it is found that multi-body simulation is advised for the creation of a digital twin model. A digital twin of a simple drivetrain test rig is made, and different modelling approaches were implemented to investigate levels of accuracy. Reference values were derived empirically by attaching sensors to the drivetrain during operation in the test rig. Modelling with a low fidelity model showed high accuracy, however it would lack several modules required for it to be called a digital twin. The higher fidelity model showed that finding the stiffness parameter proves challenging, due to high stiffness sensitivity as the experimental modelling demonstrates.

Two industries that could have significant benefits from implementing digital twins are discussed; the offshore wind industry and shipping. Both have valuable assets, with reliability sensitive systems and high costs of downtime and maintenance. Regarding the shipping industry an industrial case study is done. Area of extra focus is operations of Ro-Ro (roll on-roll off) vessels. The vessels in the case study are managed by Wilhelmsen Ship Management and a discussion of the implementation of digital twins in this sector is comprised in this article.
CO2-Foam Rheology Behavior Under Reservoir Conditions
Authors: Al-Qasim Abdulaziz S. , Kokal Sunil , AlOtaibi Fawaz
Published: November 2019

Super critical carbon dioxide (SC-CO2) flooding is one of the most important enhanced oil recovery (EOR) methods used for conformance control and deep diversion of SC-CO2. It minimizes gravity override of SC-CO2 bypassing oil in the lower part of the formation. This paper investigates the impact of various parameters such as liquid/liquid ratio, different foam qualities and different injection modes on the SC-CO2-foam quality and its rheological properties.

SC-CO2 foam can control the SC-CO2 mobility, enhance the sweep efficiency in reservoirs and improve the conformance control. Experimental results shows that combining foam with supercritical and dense CO2 will reduce the mobility of SC-CO2 to oil and water, stabilize the SC-CO2 injection front and mitigate the gravity override to a great extent resulting in less amount of unwept oil and better displacement efficiency and more recovery gain.

Different set of lab experiments designed and conducted to identify the right ratio that can drastically increase SC-CO2 viscosity. In this work, we explored the rheological properties of SC-CO2 foam/gel chemicals with different pressure and temperature. Two different types of surfactants were tested. The experimental setup and conditions were designed to allow surfactant to mix with SC-CO2 under high reservoir pressure and temperature (HPHT) to create foam to evaluate and screen the foam quality and texture.

The rheological properties of the SC-CO2-foam were investigated by varying the shear rate, shear stress, foam quality, injection modes and foaming agent concentrations at reservoir conditions. The effects of foam quality and liquid/liquid ratio, pressure and temperature on SC-CO2-foam at synthetic brine-environment rheology behavior, stability and mobility of foam were investigated. The foam study experiments were conducted using different scenarios: once by injecting SC-CO2 and surfactant solutions simultaneously and another time by alternate injection of CO2/surfactant solution at different flow rates at different foam qualities. The experimental results have shown that the foam mobility (total mobility of CO2 /surfactant solution) decreased with increasing foam quality ranging from 20% to 80%. The rheological properties of N2-foam were investigated and compared with SC-CO2-foam properties. This was correlated with the images of the high pressure, high temperature (HPHT) foams that were captured through microscope at different time intervals and analyzed to indicate their stability.
CFD Modelling to Investigate Design of a Whaleback-Type Forecastle for Greenwater Protection
Authors: Chen Lifen , Zhang Xiantao , Taylor Paul H. , Draper Scott , Wolgamot Hugh
Published: November 2019

In extreme weather permanently moored FPSOs may be overtopped by large amounts of greenwater, resulting in damage to deck structures and downtime. Thus, the preliminary design process for FPSOs has often included structural protection to mitigate loads from greenwater on deck and ensure structural integrity of top side structures at the bow in harsh sea conditions. This paper numerically investigates greenwater at the bow of an FPSO fitted with a ‘whaleback’ or ‘duck-bill’ shaped forecastle that is represented as an angled extension to the freeboard. In this study, the whaleback forecastle is intended to completely deflect the greenwater flow off the forecastle head. Previously validated numerical models based on OpenFOAM, an open source Computational Fluid Dynamics (CFD) package, are used. The (vertical) run-up height and the forces on the whaleback are analysed based on the CFD results to quantify the effectiveness of the design. It is found that the parameter tan β (FE/λp) that combines the coupled effect of the whaleback geometry and the incoming wave is important for determining the run-up height. The use of this parameter leads to a crude method for fast estimates of the effectiveness of such structures. Increase of the slope of the whaleback forecastle increases the run-up height, thus, increases the horizontal greenwater loading on such structure, however, the direct effect of the slope on the horizontal greenwater loading is found to be limited. An opposite trend is observed for the vertical greenwater loading in which the forecastle slope still plays a significant role even if the effect of run-up height is excluded, as a result of overtopping volume. Additionally, the vertical component of greenwater loading dominates the total greenwater loading on the whaleback forecastle.
Numerical Study of Breaking Waves and Associated Wave Forces on a Jacket Substructure for Offshore Wind Turbines
Authors: Aggarwal Ankit , Martin Tobias , Shirinov Seimur , Bihs Hans , Kamath Arun
Published: November 2019

The interest towards offshore wind energy has grown manifolds in the last few decades. Jacket structures are one of the most widely used substructures in the offshore wind turbine installations for intermediate water depths. Offshore structures are exposed to breaking waves. The interaction of breaking waves with the jackets is quite complicated due to the multiple vertical, horizontal and diagonal members. In the present study, a numerical investigation of the wave hydrodynamics and wave forces exerted by regular breaking waves on a jacket is performed. The open-source CFD code REEF3D is used for this purpose, which raises the possibility to model the breaking process physically. The conducted model-scale laboratory experiments have been performed in the past such that a direct comparison is presented.
Overview of the Lateral Buckling and Walking Designs of Deepwater Pipelines in Offshore Brazil
Authors: Solano Rafael F. , Cardoso Carlos O. , Antunes Bruno R.
Published: November 2019

Last two decades have been marked by a significant evolution on the design of HP/HT subsea pipelines around the world. The HotPipe and SAFEBUCK JIPs can be seen as the first deepened developments in order to obtain safe design guidelines for subsea pipelines systems subjected to global buckling and walking behaviors. The adopted design approach have been to allow exposed pipeline buckles globally on seabed in a safe and controlled manner. Otherwise, the walking phenomenon has been in general mitigated constraining axial displacements by means of anchoring systems.

After several design and installation challenges concerning lateral buckling and pipeline walking behaviors, nowadays there is a significant amount of deepwater pipelines operating with buckle initiators (triggers) as well as walking mitigation devices in offshore Brazil. Oil and gas pipelines, short gathering lines and long export lines, installed by reeling and J-lay methods, in other words different kinds of subsea pipelines have operated on very soft clayey soils and have formed planned lateral buckles as well as rogue buckles.

This paper presents the main characteristics and design challenges of the deepwater pipelines subjected to the lateral buckling behavior, also highlighting mitigation measures to constrain the walking phenomenon of some pipelines. The relevant design results are highlighted as type and number of buckle triggers, buckle spacing, type and locations of walking mitigations. Envelopment of the main design parameters are mapped in order to identify some trends. Finally, survey images of operating pipelines are presented confirming behaviors predicted in the design phase.
Air-Gap Analysis of a Semi-Submersible Considering Full Second Order Effects
Authors: Pan Zhiyuan , Vada Torgeir Kirkhorn , Nestegård Arne
Published: November 2019

In the present paper, a complete and consistent second-order computation of airgap for a semi-submersible is presented. The second-order sum and difference frequency upwell will be calculated and combined with the linear upwell statistically to find the short-term extremes. The phasing of the low frequency surface elevation with respect to the low frequency vertical motion will be considered. The asymmetric characteristics of the surface elevation will be taken care of by the sum frequency surface elevation. By comparing the maximum and minimum extremes of surface elevation in a given sea state at specified off-body points, the “asymmetry factor” up to the second order can be obtained.
Effects of Euler Angles of Vertical Cambered Otter Board on Hydrodynamics Based on Response Surface Methodology and MOGA
Authors: Wang Gang , Wan Rong , Huang Liuyi , Zhao Fenfang , Wang Xinxin , Zhu Wenbin , Wang Lei , Xu Qingchang , Li Yuyan
Published: November 2019

In this present work, effects of three Euler angles (Angle of Attack (AOA), Angle of Trim (AOT), Angle of Pitch (AOP)) of vertical cambered otter board on hydrodynamic characteristics (drag coefficient (Cd), lift coefficient (Cl), center-of-pressure coefficients (Cp)) were studied based on numerical simulation combined with Kriging Response Surface Methodology (KRSM) and Multi-Objective Genetic Algorithm (MOGA). Wind tunnel experiments were carried out to validate the accuracy of response surface based on numerical simulation. It was demonstrated that AOA had prominent effects on Cd and Cl, while AOT and AOP had less effects. The working posture of otter board were recommended to lean inwards (0°∼6°) and forward (−10°∼0°) to improve the lift-drag ratio without sacrificing Cl. The influences of AOT and AOP on positions of center-of-pressure point were less significant than that of AOA and decreasing with the increase of AOA. In addition, response surface of hydrodynamic coefficients around the critical AOA was a decent indicator of occurrence of stall. Finally, three candidate cases were selected to satisfy the high working efficiency by MOGA, which was consistent with the above recommendations. This study provided a scientific reference of response surface experimental investigations methodology and the configuration of Euler angles of otter board.
On Calculating the Crack Growth Within a Single Load-Dwell-Unload Cycle for Metal Structures
Authors: Wang Fang , Zhang Xuezhong , Jiang Zhe , Cui Weicheng
Published: November 2019

Some structures such as components of deep-sea submersibles, will endure cyclic loads with a period of dwell time at high stress level within each loading-unloading cycle. For components subjected to cyclic loads, fatigue life analysis is an important issue. Approaches based on fracture mechanics are reliable, in which choice of crack growth model plays an important role. The commonly-used crack growth rate model can make fatigue crack increment by cycle-by-cycle integration, which neglects the crack length change within a single cycle. Some researchers proposed the concept of crack growth rate model in small time domain to consider the crack growth within one load-unload cycle. However, during the dwell time, the crack increment can also be detected. In this paper, the model in small time domain will be extended to that for a single load-dwell-unload cycle. The model can be applied to calculate the life of metal structures under dwell-fatigue conditions.
Development of a PID Control Strategy for a Compact Autonomous Underwater Vehicle
Authors: Sahoo Avilash , Dwivedy Santosha K. , Robi P. S.
Published: November 2019

This paper presents a proportional-integral-derivative (PID) control strategy for navigation of a compact autonomous underwater vehicle (AUV) developed in-house. The AUV has a closed frame, neutrally buoyant, three-part modular structure made up of glass fibre composite material. Three fix position bi-directional thrusters are used for propulsion. A detailed CAD model of the AUV is developed using the modelling software SOLIDWORKS to estimate different system parameters. Hydrodynamic parameters are estimated from the ANSYS Fluent simulations of the AUV structure. Using the system parameters, a six degrees of freedom (DOF) dynamic model is developed, which is further simplified to a 4 DOF model. A 3D guidance system is developed for path planning using Line-of-Sight (LOS) strategy with way-point navigation. A closed loop PID controller is developed to follow the trajectory developed by the guidance system. The controller is simulated using MATLAB Simulink and the results are discussed.
At-Sea Experiment on Durability and Residual Strength of Polyester Rope for Mooring of Floating Wind Turbine
Authors: Utsunomiya Tomoaki , Sato Iku , Tanaka Koji
Published: November 2019

When using synthetic fiber rope as a mooring line of a floating body such as floating offshore wind turbine (FOWT), it is necessary to carry out characteristic test and to grasp well about strength, stiffness, durability against monotonic and cyclic loadings. In this research, we have made characteristics test of polyester rope based on ISO. Next, based on the obtained characteristic values (mass, stiffness, strength, etc.), the dynamic response analysis of the floating body-mooring system was carried out and the mooring design was carried out. It was actually operated as a floating body mooring line for about 1 year. During the operation period, no abnormality was found, nor appearance damage occurred. After completion of operation for 1 year, the polyester rope was collected and residual strength test was carried out. As a result, no serious deterioration situation such as infiltration of marine organisms or fracture of the strands due to wear between fibers was observed at all. On the other hand, with respect to durability, it was found that the strength reduction was 2.9% from the initial state with respect to the breaking strength.
Study on Mechanical Behavior of Tensile Armor Wires of Marine Flexible Pipes and Cables During Winding Process
Authors: Lu Qingzhen , Wu Shanghua , Wang Dong , Yang Zhixun , Yin Yuanchao , Hu Haitao , Yan Jun , Yue Qianjin
Published: November 2019

In this paper, a mechanical model of armor wire winding process is established to quantify the relationship between the tension force and the internal force of armor wire cross section in winding process. Then based on this model, a method for predicting the residual stress of armor wire cross section after winding is presented. The reasonable winding tension force and the minimum residual stress are discussed. In addition, the reasonable design of the processing equipment is further discussed. This paper provides a useful reference for the evaluation of key parameters and the prediction of residual stress in the processing of tensile armor layer of offshore flexible pipes and cables.
Validation of Numerical Models of the Offshore Wind Turbine From the Alpha Ventus Wind Farm Against Full-Scale Measurements Within OC5 Phase III
Authors: Popko Wojciech , Robertson Amy , Jonkman Jason , Wendt Fabian , Thomas Philipp , Müller Kolja , Kretschmer Matthias , Ruud Hagen Torbjørn , Galinos Christos , Le Dreff Jean-Baptiste , Gilbert Philippe , Auriac Bertrand , Oh Sho , Qvist Jacob , Sørum Stian Høegh , Suja-Thauvin Loup , Shin Hyunkyoung , Molins Climent , Trubat Pau , Bonnet Paul , Bergua Roger , Wang Kai , Fu Pengcheng , Cai Jifeng , Cai Zhisong , Alexandre Armando , Harries Robert
Published: November 2019

The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project validates OWT models against the measurements recorded on a Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. The following operating conditions of the wind turbine were chosen for the validation: (1) Idling below the cut-in wind speed; (2) Rotor-nacelle assembly (RNA) rotation maneuver below the cut-in wind speed; (3) Power production below and above the rated wind speed; and (4) Shutdown. A number of validation load cases were defined based on these operating conditions. The following measurements were used for validation: (1) Strains and accelerations recorded on the support structure; (2) Pitch, yaw, and azimuth angles, generator speed, and electrical power recorded from the RNA. Strains were not directly available from the majority of the OWT simulation tools. Therefore, strains were calculated based on out-of-plane bending moments, axial forces, and cross-sectional properties of the structural members. Also, a number of issues arose during the validation: (1) The need for a thorough quality check of sensor measurements; (2) The sensitivity of the turbine loads to the controller and airfoil properties, which were only approximated in the modeling approach; (3) The importance of estimating and applying an appropriate damping value for the structure; and (4) The importance of wind characteristics beyond turbulence on the loads. The simulation results and measurements were compared in terms of time series, discrete Fourier transforms, power spectral densities, probability density functions of strains and accelerometers. A good match was achieved between the measurements and models set up by OC5 Phase III participants.
The Assessment of Locally Thinned Areas Subject to a Hoop Stress and an Axial Stress: Background to the Guidance Given in Annex G of BS 7910:2013
Authors: Cosham Andrew , Andrews Robert
Published: November 2019

Annex G Assessment of locally thinned areas (LTAs) in BS 7910:2013 is applicable to LTAs in cylinder, a bend and a sphere or vessel end. It can be used to assess the longitudinally-orientated LTA in a cylinder subject to a hoop stress and a circumferentially-orientated LTA in a cylinder subject to an axial stress (due to axial force, in-plane bending moment and internal pressure), and also to assess an LTA subject to a hoop stress and an axial stress.

An outline of the origins of Annex G is given. A comparison with full-scale burst tests of pipes or vessels containing LTAs subject to a hoop stress and an axial stress is presented. It is demonstrated that the method in G.4.3 Hoop stress and axial stress is conservative.
A Numerical Evaluation of the Quadratic Transfer Function for a Floating Structure
Authors: Xie Zhitian , Liu Yujie , Falzarano Jeffrey
Published: November 2019

The second order force of a floating structure can be expressed in terms of a time independent quadratic transfer functions along with the incident wave elevation, through which it is possible to evaluate the second order wave exciting forces in the frequency domain. Newman’s approximation has been widely applied in approximating the elements of the quadratic transfer function matrix while numerically evaluating the second order wave induced force. Through Newman’s approximation, the off-diagonal elements can be numerically approximated with the diagonal elements and thus the numerical calculation efficiency can be enhanced. Newman’s approximation assumes that the off-diagonal elements do not change significantly with the wave frequency and that hydrodynamic phenomenon regarding the low difference frequency are usually of interest. However, it is obviously less satisfying when an element that is close to the diagonal line in the quadratic transfer function matrix shows an extremum if the corresponding wave frequency is close to the natural frequency of the certain motion. In this paper, the full derivation and expression of the second order wave forces and moments applied to a floating structure have been presented, through which the numerical results of the quadratic transfer function matrix including the diagonal and the off-diagonal elements will be illustrated. This work will present the basis of numerically evaluating the second order forces in the frequency domain. The comparisons among various approximations regarding the second order forces in deep water will also be presented as a meaningful reference.
On Signatures and Features of Modulational Instability in Ocean Waves
Authors: Babanin Alexander V.
Published: November 2019

Modulational instability of nonlinear waves in dispersive environments is known across a broad range of physical media, from nonlinear optics to waves in plasmas. Since it was discovered for the surface water waves in the early 60s, it was found responsible for, or able to contribute to the topics of breaking and rogue waves, swell, ice breakup, wave-current interactions and perhaps even spray production. Since the early days, however, the argument continues on whether the modulational instability, which is essentially a one-dimensional phenomenon, is active in directional wave fields (that is whether the realistic directional spectra are narrow enough to maintain such nonlinear behaviours). Here we discuss the distinct features of the evolution of nonlinear surface gravity waves, which should be attributed as signatures to this instability in oceanic wind-generated wave fields. These include: wave-breaking threshold in terms of average steepness; upshifting of the spectral energy prior to breaking; oscillations of wave asymmetry and skewness; energy loss from the carrier waves in the course of the breaking. We will also refer to the linear/nonlinear superposition of waves which is often considered a counterpart (or competing) mechanism responsible for breaking or rogue waves in the ocean. We argue that both mechanisms are physically possible and the question of in situ abnormal waves is a problem of their relative significance in specific circumstances.
Dynamic Response of Spar-Type Floating Offshore Wind Turbine in Freak Wave
Authors: Tang Yougang , Li Yan , Xie Peng , Qu Xiaoqi , Wang Bin
Published: November 2019

Simulations are conducted in time domain to investigate the dynamic response of a SPAR-type floating offshore wind turbine under the scenarios with freak wave. Towards this end, a coupled aero-hydro numerical model is developed. The methodology includes a blade-element-momentum model for aerodynamics, a nonlinear model for hydrodynamics, a nonlinear restoring model of SPAR buoy, and a nonlinear algorithm for mooring cables. The OC3 Hywind SPAR-type FOWT is chosen as an example to study the dynamic response under the freak conditions, while the time series of freak wave is generated by the Random Frequency Components Selection Phase Modulation Method. The motions of platform, the tensions in the mooring lines and the power generation performance are documented in different cases. According to the simulations, it shows that the power coefficient of wind turbine decreased rapidly at the moment when freak wave acted on the floating structure.
Achieving a High Accuracy Numerical Simulations of the Flow Around a Full Scale Ship
Authors: Pena Blanca , Muk-Pavic Ema , Ponkratov Dmitriy
Published: November 2019

The hydrodynamic performance of ships may be improved by the retrofit of Energy Saving Devices (ESDs). These devices are typically seen in the aft part of the ship hull and act by lowering the ship resistance, conditioning the fluid in front of the propeller and/or recovering energy from the rotational swirl of the fluid leaving the propeller.

In the case of a retrofit of an existing ship no straight forward solution exists. In order to find a beneficial design that will improve hydrodynamic performance, a successful and accurate initial assessment of the flow around a hull is of the most importance. Once the flow around the hull is scrutinized in detail, and required flow changes are determined, a ship designer can progress with designing an Energy Saving Device specifically tailored to have a desired effect.

This paper presents a high quality numerical evaluation of the flow around a ship hull in the full scale using a sophisticated DES model that was successfully validated against the sea trials. The findings from the numerical analysis will identify the potential improvements in the hydrodynamic performance of the ship that could be achieved by ESD.
The Characteristics of Numerical Solution of NDDE to Solve the Drill Pipe Stick-Slip
Authors: Katsui Tokihiro , Inoue Tomoya , Sogawa Daisuke , Notani Yusuke
Published: November 2019

The Stick-Slip is one of troublesome problems which happens in scientific drilling. In order to clarify the mechanism of Stick-Slip phenomenon, it is necessary to develop a reliable numerical model [1]-[4] to estimate drill bit motion for various drilling conditions.

We have investigated on an NDDE (Neutral Delay Differential Equation) [5] to solve Stick-Slip of drill pipe [6]-[8]. In order to solve this NDDE, it is necessary to determine the frictional torque acting on the drill bit. In the previous study, we have employed the Balanov’s [4] frictional torque model which is the function of drill bit rotation with four unknown model parameters. This numerical model calculates the Stick-Slip phenomena of the drill pipe model in the laboratory experiments correctly under the appropriate four model parameter settings. On the other hand, it is quite difficult to calculate the actual drill pipe Stick-Slip [9], because the calculated results change drastically depending on the four unknown parameter settings. In the present study, the frictional torque acting on the drill bit is defined as a periodic function and solved the NDDE to calculate the stick-slip of the actual drill pipe. The average, variation and period of the frictional torque on the drill bit were set under the consideration of measured top drive torques. The calculated numerical solutions of the drill bit motion and the top drive torque agreed qualitatively with the measured ones.
Numerical Simulation of Drifting and Run-Up Ice Floes Driven by Tsunami
Authors: Kioka Shinji , Ishida Maiko , Takeuchi Takahiro
Published: November 2019

In order to simulate drifting and run-up ice floes driven by tsunamis, we developed a quasi-3D Discrete Element Method (DEM) in which phenomena unique to granular solids, such as the arch action, jam and pile up of such solids, can be simulated with a small computation load. The validity of the simulation method was verified by hydraulic experiments using synthetic ice. Some numerical simulations of drifting and run-up ice floes driven by a tsunami were performed to investigate the fundamental characteristics of ice run-up and the applicability to actual seas. It was confirmed that the simulation results could estimate risk areas where ice pile up and jam form as well as hazardous areas showing the degree of damage to buildings. Such calculation was expected to be useful for the compilation of hazard maps and the development of disaster mitigation plans in the future.
Analysis of Polyester Reinforced Flexible Composite Pipe Under Internal Pressure
Authors: Sun Xinyu , Bai Yong , Zhang Xiaojie , Liu Chang , Zhao Jiannan
Published: November 2019

In recent years, petroleum and natural gas industry technology continues to develop, so the market demand for polyester fiber reinforced flexible composite pipe is increasing. Polyester reinforced flexible composite pipe is widely used in practical production, which is based on thermoplastic material and winded by polyester fiber. Based on the anisotropic uniformity of polyester reinforced flexible composite pipes, this paper focuses on the mechanical behavior of flexible composite pipes under internal pressure. By using numerical analysis method, the stress-strain change and burst pressure model of polyester reinforced pipe under internal pressure are established. The short-term burst pressure test is carried out to obtain the burst pressure of the reinforced pipe. The finite element analysis software ABAQUS is used to establish finite element model for simulation analysis. According to the generated test data, the correctness of the finite element analysis results is verified. The sensitivity of winding angle and diameter-thickness ratio to the pressure was studied to further understand the mechanical properties of polyester reinforced composite pipe.
Recent Advances in the Prediction and Mitigation of Flow Induced Pulsations in Flexible Risers and Flowlines
Authors: Belfroid S. P. C. , González Díez N. , Korst H.
Published: November 2019

Flow-induced pulsations in flexible risers and flowlines (FLIP) has been the subject of ongoing research roughly over the last two decades. This phenomenon, also called singing, can cause high vibration and cyclic stress levels in the attached up- and downstream pipe systems, thereby imposing serious limitations on the flowrates through the pipes. FLIP occurs when the flow velocity along the flexible is above a certain onset flow velocity. Large pressure pulsations can appear as a result of a feedback loop mechanism established between vortex shedding at the inner cavities and longitudinal acoustic standing waves. Since FLIP is recommended to be avoided in all cases, the main focus of the research has been to understand the phenomenon and build models to predict the onset velocity. An overview of the experiences in the behavior and prediction of onset data on a large number of field cases is given. Recent advances on the theory and prediction of the onset and behavior of flow induced pulsations are discussed. This ranges from new advanced test methods for acoustic source allocation to full large scale experiments. In addition, new and upcoming anti-FLIP technologies as well as possible mitigation actions available to operators are discussed, by introducing recent field experiences as well as large scale tests.
Application of Friction Fatigue Pile Driving Models in GRLWEAP
Authors: Milewski Henry , Kennedy Justin
Published: November 2019

Pile driveability analyses play a crucial part in pile installation planning (hammer sizing, anticipated driving time) and pile design (fatigue concerns). GRLWEAP is one of the predominant pile driving analysis software tools used globally. Traditionally, the offshore community has often wished to use specific SRD prediction methods in driveability analyses. Some of the most popular of these methods (e.g. Alm & Hamre, 2001) employ a ‘friction fatigue’ approach whereby side friction reduces with increasing pile penetration. A past limitation in GRLWEAP has been that friction fatigue methods could not be used in a full driveability analysis, since only a single SRD (valid only for a particular depth of penetration) can be input. This is prohibitive when outputs such as blowcounts are desired at each intermediate penetration depth (e.g. for fatigue analysis), rather than just the final depth.

With the introduction of GRLWEAP’s ‘friction fatigue’ module, a way of modelling friction fatigue is now provided, but the fatigue equations are formulated in a specific way that may not be directly applicable to various friction fatigue approaches. Using the Alm & Hamre (2001) friction fatigue method as an example, an approach is presented that shows how friction fatigue models that are not formulated in the same manner as GRLWEAP’s friction fatigue approach can be converted into a suitable form to allow full implementation in a GRLWEAP driveability analysis. This enables driveability analyses to capture the dynamic nature of the SRD as pile penetration increases, producing results that are valid for all penetrations and circumventing the need for alternative workarounds to capture friction fatigue. The general principles presented herein may be modified on similar principles for other friction fatigue models not explicitly captured within GRLWEAP.
Forced Vibration Tests for In-Line VIV to Assess Partially Strake-Covered Pipeline Spans
Authors: Wu Jie , Yin Decao , Passano Elizabeth , Lie Halvor , Peek Ralf , Sequeiros Octavio E. , Ang Sze Yu , Bernardo Chiara , Atienza Meliza
Published: November 2019

A series of experiments is performed in which a strake-covered rigid cylinder undergoes harmonic purely in-line motion while subject to a uniform “flow” created by towing the test rig along SINTEF Ocean’s towing tank. These tests are performed for a range of frequencies and amplitudes of the harmonic motion, to generate added-mass and excitation functions are derived from the in-phase and 90° out-of-phase components of the hydrodynamic force on the pipe, respectively.

Using these excitation- and added-mass functions in VIVANA together with those from experiments on bare pipe by Aronsen (2007), the in-line VIV response of partially strake-covered pipeline spans is calculated. It is found that as little as 10% strake coverage at the optimal location effectively suppresses pure in-line VIV.

Further advantages of strakes rather than intermediate supports to suppress in-line VIV include: strakes are not affected by the scour which can lower an intermediate support (in addition to creating the span in the first place). Further they do not prevent self-lowering of the pipeline or act as a point of concentration of VIV damage as the spans to each side of the intermediate support grow again.
A Study on the Validity of a One Degree of Freedom Model for Deepwater Subsea Lifts
Authors: Tommasini Rodrigo Batista , Carvalho Leonardo de Oliveira , Pavanello Renato
Published: November 2019

The lowering into deepwater phase of the installation of subsea equipment is analyzed by a one degree of freedom model and also by a multiple degree of freedom model in order to determine the scenarios where the simplified model can be used accurately. The one degree of freedom system is based on the assumption that the lifting cable has a length that varies throughout the time as a function of the payout speed. On the other hand, the multiple degree of freedom system is constructed using the commercial software Orcaflex which uses the line feeding feature to evaluate the continuous lowering of the equipment during the operation. Firstly, possible critical scenarios for the use of the simplified model are obtained by evaluating the total time for longitudinal pressure waves to travel inside the cable and by analyzing the resonance frequencies of the system for different water depths, types of cables, and equipment. Secondly, the one degree and the multiple degree of freedom systems are compared. The results show that high water depth and high mass ratio tends to lead to more critical scenarios for the use of the simplified model, especially when the excitation period is low. Further, the dynamics of the system for different payout speeds is assessed considering the most critical scenario for the use of the simplified model. In this case, the differences between the models are not affected by the speed. It is concluded that the one degree of freedom model should not be considered as an accurate method to analyze subsea lifts for scenarios of high mass ratio, high water depth and low excitation periods, independent of the payout speed considered for the operation. Finally, guidance for the selection between both models is provided.
Modeling a Non-Linear Mooring System for Floating Offshore Wind Using a Hydraulic Cylinder Analogy
Authors: Harrold Magnus J. , Thies Philipp R. , Newsam David , Bittencourt Ferreira Claudio , Johanning Lars
Published: November 2019

The mooring system for a floating offshore wind turbine is a critical sub-system that ensures the safe station keeping of the platform and has a key influence on hydrodynamic stability. R&D efforts have increasingly explored the benefits of nonlinear mooring systems for this application, as they have the potential to reduce the peak mooring loads and fatigue cycling, ultimately reducing the system cost. This paper reports on a hydraulic based mooring component that possesses these characteristics, attributable mostly to the non-linear deformation of a flexible bladder. This is not a typical hydraulic component and, as a consequence, modeling its dynamic performance is non-trivial. This paper addresses this by introducing an analogy to numerically model the system, in which the functionality of the mooring component is compared to that of a hydraulic cylinder. The development of a working model in Simscape Fluids is outlined, and is subsequently used to simulate the IMS in a realistic environment. It is found that the numerical model captures a number of the dynamic performance characteristics observed in a previously tested prototype of the IMS.
Development of 3-Dimensional Fully Nonlinear Potential Flow Planar Wave Tank in Framework of OpenFOAM
Authors: Lin Zaibin , Qian Ling , Bai Wei , Ma Zhihua , Chen Hao , Zhou Jian-Guo
Published: November 2019

A 3-Dimensional numerical wave tank based on the fully nonlinear potential flow theory has been developed in OpenFOAM, where the Laplace equation of velocity potential is discretized by Finite Volume Method. The water surface is tracked by the semi-Eulerian-Lagrangian method, where water particles on the free surface are allowed to move vertically only. The incident wave is generated by specifying velocity profiles at inlet boundary with a ramp function at the beginning of simulation to prevent initial transient disturbance. Additionally, an artificial damping zone is located at the end of wave tank to sufficiently absorb the outgoing waves before reaching downstream boundary. A five-point smoothing technique is applied at the free surface to eliminate the saw-tooth instability. The proposed wave model is validated against theoretical results and experimental data. The developed solver could be coupled with multiphase Navier-Stokes solvers in OpenFOAM in the future to establish an integrated versatile numerical wave tank for studying efficiently wave structure interaction problems.
On Deriving High Pressure Empirical Multiphase Forcing Functions From CFD Analysis
Authors: Macchion Olivier , Belfroid Stefan , Stachyra Leszek , Jensen Atle
Published: November 2019

Computational Fluid Dynamics (CFD) simulations are used to predict the flow-induced forcing in high-pressure multiphase pipe flow. Furthermore, empirical correlations from the literature is compared and validated against computational and experimental results. Based on the CFD results and in conjunction with the reference 6” (internal diameter (ID)) data, new scaling rules are proposed.
Fundamental CFD Study on the Hydrodynamic Performance of the DARPA SUBOFF Submarine
Authors: Takahashi Kenshiro , Sahoo Prasanta K.
Published: November 2019

This study attempts to examine the potential for computational fluid dynamics (CFD) as an estimation tool of the hydrodynamic performance of submarines. The DARPA SUBOFF model is adopted as a benchmark because of its availability of experimental data for validation. The computational modeling is based on the Reynolds Average Navier Stokes (RANS) equations solved by a finite volume method. Verification and validation of the straight-ahead resistance and the forces and moment exerted on the hull in steady translation and turn with a drift angle were conducted in accordance with the published methodology and procedure. The process to have determined the computational setups is described. Furthermore, the computational results as a function of velocity and drift angle are presented and compared with available experimental data. In conclusion, the present CFD method can be used as an estimation tool for the straight-ahead resistance at various velocities in model scale for multiple configurations.
Fatigue Assessment of “Corroded” Mooring Chain
Authors: Baker David A. , Li Zhen , Wang Sue , Zhang Xiying , Shao Yunliang , Li Harry , Zhan Xiaoqin , Zhu Linfang , Tao Xing (Terry)
Published: November 2019

Assessment of corroded mooring chain for continued service is a challenging task faced by industry. Current best practice relies heavily on qualitative inspection information collected during inspection campaign. There has been little investigation into this practice and whether it is an appropriate technique or can be improved. To address this issue, the Fatigue of Corroded Mooring Chains (FoCCs) Joint Industry Project (JIP), initiated in 2016 with fifteen (15) participating organizations, including oil majors, chain manufactures, consulting firms, and classification societies, to examine assessment methods for evaluating remaining fatigue life. JIP teams were formed to progress fatigue testing and finite element objectives. One such team, comprised of ExxonMobil, ABS and Asian Star Anchor Chain, has performed an additional series of fatigue tests beyond the core JIP work effort.

A fatigue test was conducted to 1) demonstrate the utility of finite element analysis in the assessment of fatigue life and 2) demonstrate performance of simulated damage. This unique fatigue test program was conducted on mooring chain with manufactured “corrosion pits” of different dimensions. All chain surface features were digitally recorded and converted into finite element models. These models were subsequently analyzed to compare with test results — both cycle count and failure location. This paper presents the findings from these fatigue tests and finite element analyses and how they can be utilized for assessment of remaining fatigue life.