bluuebunny/crossref_metadata_2025 huggingface dataset:
Smart Communicative Cement: On the Move Towards the Future of Zonal Isolation Monitoring
Authors: Bezerra de Melo Ricardo Cesar , Eid Ramy N.
Published: September 2018

The oil and gas industry, by default, has been pretty conservative when it relates to innovation and drastic changes in mind-set. Mainly focused on the costly drilling and completion steps, some of the “smaller” services have been ignored. As such, Repsol has decided to take a deeper look at nano and micro sensored technologies in other industries and potentially replicate some of this innovation, allowing the industry to take “a step” closer to smarter zonal isolation. In general, the industry is quite aware of well integrity issues that we face. Be it immediate (whilst drilling/completing), within the life of production or even during the abandonment phase. There are many statistics proving that on a global scale, there are well integrity and sustained casing pressure issues on about 30–60% of all drilled wells. And we can confirm that a majority of these are directly related to well-cementing, creating an immense impact(s), that can negatively influence overall HSE, loss of potential reserves and bottom line dollar-amount. The ability to take a close look at well cementing has only proven feasible in a laboratory environment, beyond that, the knowledge and prediction of the actual state of the zonal isolation has proven difficult, confusing or costly. Regardless of the improved best practices, enhanced logging tools or state-of-the-art technological advances in chemicals/systems — we still seem to have that unanswered “gap” — on what actually happened, when it happened and how to avoid it in the future. This paper describes the background, the thought process and the potential advantage of ours proposed ideology, let Alone ongoing R&D efforts to improve the cement isolation quality, measurements and real time monitoring of its properties and integrity during the well life and after abandonment by sensoring it and communicating back to surface.
Improved Stability Design of Subsea Pipelines on Mobile Seabeds: Learnings From the STABLEpipe JIP
Authors: Griffiths Terry , Draper Scott , White David , Cheng Liang , An Hongwei , Fogliani Antonino
Published: September 2018

The on-bottom stability design of subsea pipelines is important to ensure safety and reliability but is challenging to achieve, particularly in Australia due to onerous metocean and seabed conditions, and the prevalence of light gas pipelines. This challenge has been amplified by the fact that industry design guidelines have given no guidance on how to incorporate the potential benefits of seabed mobility, which can lead to lowering and self-burial of the pipeline on a sandy seabed. In this paper, we review the learnings of the STABLEpipe Joint Industry Project (JIP), which was initiated with the aim of developing new design guidelines to assess the on-bottom stability of pipelines on mobile seabeds. The paper summarises the new research undertaken within the STABLEpipe JIP to better predict sedimentation and scour, pipe-fluid interaction and pipe-soil interaction. New design methods to assess the on-bottom stability are also outlined, which have been developed based on the new research. These methods have been adopted in a DNVGL guideline authored by the JIP researchers in collaboration with DNVGL and presently available for use by the JIP participants. Finally, applications of the STABLEpipe JIP outcomes and focus areas for further work are discussed.
A Systematic Design Approach of Gripper’s Hydraulic System Utilized in Offshore Wind Turbine Monopile Installation
Authors: Nejad Amir R. , Li Lin , Acero Wilson Ivan Guachamin , Moan Torgeir
Published: September 2018

This paper presents a systematic approach for designing the hydraulic mechanism as a part of the gripper system employed in offshore wind turbine monopile installation. Traditionally, such equipments used in marine operation are designed based on deterministic approach, selecting actuators and power pack by applying a safety margin which is not explicitly derived from a systematic load/load effect analysis, or a reliability based method. The method in this article offers a systematic way of designing the hydraulic power system, actuators and supporting structure to overcome extreme and fatigue loadings during operation. The design starts with a global analysis and modelling of monopile and installation vessel. The forces and motions from global analysis are then employed for designing hydraulic actuators and power system. A dynamic model of hydraulic system is built to analysis dynamic response in hydraulic system. The results from this local dynamic model can be used in power management and system optimization. The proposed method is a step forward to apply reliability-based design on mechanical components in marine applications through a systematic long-term load and load effect analysis.
Validation and Development of Improved Methods for the Calculation of Wave Loads on XXL Monopiles
Authors: Leimeister Mareike , Dose Bastian
Published: September 2018

With the offshore wind industry aiming to deploy deeper water sites (> 30 m) while still utilizing monopiles, support structures with larger diameters are required. For the design and assessment of so-called XXL monopiles, wave-induced forces, which become more dominant with increasing diameter, have to be determined accurately. Thus, this study focuses on the identification of differences between state-of-the-art theories for wave load calculations with engineering models and the forces exerted on large monopiles from high-precision numerical reference methods. Within the framework of the research project TANDEM (Towards an Advanced Design of Large Monopiles) a 7 m diameter monopile is designed to support Fraunhofer’s IWT-7.5-164. This offshore wind turbine system is used as reference to determine wave-induced loads based on the MacCamy-Fuchs approach, implemented in models in Modelica. Different waves, defined in a simulation matrix, are investigated to elaborate the significance of diffraction effects, as well as the relevance of non-linear effects. The results are compared to CFD (Computational Fluid Dynamics) simulations. Deviations in the wave-induced forces are analyzed, taking into account the different capabilities of the applied tools, trends in the applicability of the engineering model are elaborated, and suggestions for improvement of the code based on state-of-the-art theories are given.
Numerical Simulation of Hydrodynamic Performance of Multi-Hull Catamaran With 3DOF Motion
Authors: Li Rijie , Liu Liwei , Guo Lixiang , Feng Dakui , Wang Xianzhou
Published: September 2018

This paper presents CFD to study the hydrodynamic performance for the high-speed, multi-hull Catamaran advancing in calm water. It uses inhouse computational fluid dynamics (CFD) code to solve RANS equation coupled with six degrees of freedom solid body motion equations. RANS equations are solved by finite difference method and PISO arithmetic. Computations have been made using structured grid with overset technology. Turbulence models used the anisotropic two equations Shear Stress Transport (SST) k-ω model. Single phase level set was used for free surface simulation. A good agreement on the resistance prediction between CFD and experimental fluid dynamics (EFD) has been observed (on the resistance prediction of about 4.0%). Differences between CFD and EFD have been seen for the 3 degrees of freedom (3DOF) motion, whereas larger discrepancy is observed for the sinkage and trim estimation (about 8.0%).
Benchmarking of Analysis Tools for Thruster Assisted Mooring
Authors: Merino Hoyos Daniel , Falkenberg Erik , Stuberg Petter
Published: September 2018

While the size of new built semi-submersibles is steadily increasing, their mooring systems are not experiencing a similar change. Most of the sixth-generation drilling units rely heavily on thruster assisted mooring to increase their operability in harsh environments and shallow waters. Frequency domain programs are commonly used to calculate mooring line tensions in the design analyses. This analysis technique assumes linearity in both the mooring system and the thruster assist controller. The study presented in this paper examines the validity of these assumptions by comparing frequency and time domain analyses in two state-of-the-art analysis programs. The linear thruster assist controller in frequency domain analyses is benchmarked against the Kalman filter-based controller in time domain simulations and against a real thruster assist controller coupled with the time domain software.
Comparative Study of Hydrodynamic Responses of Two Combined Wind Turbine and Wave Energy Converter Systems Under Typical Operational Sea Cases
Authors: Ren Nianxin , Zhu Ying , Ma Zhe , Wu Hongbo
Published: September 2018

In present work, two combined wind turbine (WT) and wave energy converter (WEC) systems have been concerned. One is a fixed-bottom system, referred as “MWWC” (monopile-WT-WEC combination); the other is a floating system, referred as “TWWC” (TLP-WT-WEC-combination). Comparative study of the hydrodynamic responses of the two combined systems has been done by numerical simulations in the time domain. Hydrodynamic loads of the supporting structures and the WEC are calculated by the AQWA code, which is available for modeling multi-body systems including both mechanical and hydrodynamic couplings between the supporting tower and the WEC floater. Firstly, the effect of different power-take-off (PTO) parameters, wave periods and the displacements of the WEC on the performance of the WEC’s wave energy production of the two combined systems under typical wave cases has been investigate, and preliminary optimal values for the PTO damping stiffness of the two combined systems have been obtained and compared; secondly, the effect of the horizontal contact force between the supporting tower and the additional WEC floater of the two combined systems have been further investigated, which is important for both the fatigue and extreme loads design of the supporting tower. Finally, a new strategy for MWWC system by adding horizontal PTO dampers between the supporting tower and the WEC floater has been proposed and investigated, which is helpful for both reducing the horizontal contact force and using the relative horizontal motion to produce power.
VIM Suppression for a FSR With a Co-Centric Porous Sheath Around the Buoyancy Can: Effects of Mesh Orientation and Diameter Ratio
Authors: Crosswell Jessica , Balash Cheslav
Published: September 2018

Here, we experimentally studied the vortex-induced motion (VIM) of a free-standing riser (FSR; 1:65 scale model) with and without a porous metal screen (‘sheath’) placed co-centrically around the buoyancy can (BC). Specifically, we investigated the effects of mesh orientation (square and square rotated 45° in its own plane) and screen-BC diameter ratio (1.1 and 1.2) over a range of flow velocities. BC motions were recorded with a submersible camera; and inline (IL) and cross-flow (CF) amplitudes were then estimated with a motion tracking software. As expected, the installation of the screen changed the natural frequency of the models. Furthermore, the screen increased the reduced velocity at which the lock-in occurred, delaying it by a factor of ∼1.2 and ∼1.4 for the CF and IL respectively. All sheathed models had a prominent reduction in IL amplitudes compared to the bare/unsheathed BC; and at smaller flow velocities, the sheathed models also exhibited significantly lower CF motions, particularly those with a greater screen-BC diameter ratio.
Numerical Simulations of Continuous Icebreaking Process With Different Heel Angles in Level Ice
Authors: Wang Feng , Zou Zao-Jian , Guo Hai-Peng , Ren Yi-Zhou
Published: September 2018

Based on cohesive element method (CEM), the continuous icebreaking process with different heel angles in level ice are simulated in this paper. The simulations are established in FEM software LS-DYNA and an icebreaking tanker - MT Uikku is assumed advancing with the certain heel angle in level ice. Firstly, the comparisons are made between the simulations and the model tests for the cases with zero heel angle. A good agreement is obtained between the simulated and measured data. Then the effects of different heel angles on ice resistance and ice breaking patterns are investigated and analyzed. The results show that ice resistance, average ice breaking length and average broken channel width present increasing trends with the increase of ship heel angle. The applied methods show a wide prospect to predict ice loads on marine structures in the level ice and simulate the ice-structure interaction process.
Dynamic Positioning Reliability Index (DP-RI) and Offline Forecasting of DP-RI During Complex Marine Operations
Authors: Fernandez Charles , Kumar Shashi Bhushan , Lok Woo Wai , Norman Rosemary , Kr. Dev Arun
Published: September 2018

The Dynamic Positioning (DP) System is a complex system with significant levels of integration between many sub-systems to perform diverse control functions. The extent of information managed by each sub-system is enormous. The complex level of integration between sub-systems creates more possible failure scenarios. A systematic analysis of all failure scenarios is tedious and for an operator to handle any such catastrophic situation is breath taking. There are many accidents where a failure in a DP system has resulted in fatalities and environmental pollution. Therefore, reliability assessment of a DP system is critical for safe and efficient operation of marine and offshore vessels.

Traditionally, the reliability of a DP system is assessed during the design stage by methodologies such as Failure Mode Effects and Analysis (FMEA), Proving Trials, Hardware In-the Loop (HIL) testing, Site-Specific Risk Analysis, DP capability Analysis and during operation by annual trials to verify functionality. All these methods are time consuming, involving a lot of human effort and notably no analysis of previous accidents are indicated in the reliability assessment. This imposes in-built uncertainty and risk in DP system during operation.

In this paper, a new concept of Dynamic Positioning Reliability Index (DP-RI) is introduced and a state-of-the-art advisory decision making tool is proposed. This tool is developed based on information from various sources including Offshore Reliability Data (OREDA), International Marine Contractors Association (IMCA) Accident database, DP vendor equipment failure databases, DP System supplier’s manuals, previous system level FMEA and HIL testing results, Site specific risk analysis documents, Project design specification and Operator’s operational experiences. Thus, DP-RI addresses the pitfalls of existing reliability assessment methods and will be an efficient tool in reducing the number of DP-related accidents.
Insights Into Compaction Grouting for Offshore Pile Foundations
Authors: Geißler Peter , Cuéllar Pablo , Hüsken Götz , Kühne Hans-Carsten , Baeßler Matthias
Published: September 2018

The authors are currently investigating the possibility to apply compaction grouting for offshore pile foundations (Jacket piles as well as monopiles) as a possible retrofitting technique for an optimised foundation concept. In this research project, we are developing a design approach aiming to predict the ideal amount and properties of a grout for a specific soil situation and desired improvement of pile bearing capacity after installation and during service time. Both numerical and experimental tests have been carried out to investigate the injection process during which a highly viscous grout is injected into the soil under high pressure to displace and compact the surrounding soil without fracturing it. The implicit Material Point Method (MPM) based on a mixed formulation is the numerical technique chosen to deal with the expected large deformations and the arbitrary shape of the developing grout bulb. The usage of MPM prevents both the need of remeshing and the numerical instability induced by extensive mesh distortion. For validation with experimental results, we have constructed a testing chamber with one transparent sidewall. This chamber enables us to observe the injection process directly at the transparent vertical window and to measure the in-plane soil displacements and strains by means of the Digital Image Correlation (DIC) technique.

The results already reveal the interrelation of soil and grout properties for a successful usage of this common ground improvement technique.
Effect of Tension on Collapse Performance of Flexible Pipes
Authors: Miyazaki Marcelo , Paumier Laurent , Caleyron Fabien
Published: September 2018

This paper investigates the effect of tension on collapse performance of flexible pipes.

In the design of flexible pipelines for offshore field developments, one of the failure modes being associated with external pressure and bending loadings is the hydrostatic collapse. In accordance with standards, TechnipFMC methodology for flexible pipe collapse resistance determination ensures a robust design. The model has an analytical basis, leading to a fast and straightforward use. It has been validated with more than 200 tests performed on all possible pipe constructions on straight and curved configurations.

TechnipFMC and IFP Energies nouvelles have also developed and improved over the past few years a Finite Elements Model dedicated to flexible riser studies. It takes full advantage of the structure periodicities such that a whole riser can be studied with a short length and low CPU cost model associated to specific periodicity conditions. The model is able to represent bent risers in various configurations (bending cycles, internal and external pressure, axial tension, torsion) and has been used for collapse prediction of flexible risers under tension. Additionally, a specific test protocol has been developed to be able to carry out a collapse test associated to tension.

The purpose of this paper is to present the collapse test result, the specific development of the model for collapse and tension and the corresponding calculations performed with the Finite Elements Model on several structures, demonstrating that there is no negative influence of tension on collapse mode. It also gives a better understanding on the interaction between tension in the armor layers and collapse phenomenon.
3-D Numerical Simulations of Subsea Jumper Transporting Intermittent Slug Flows
Authors: Kim Jihyeon , Srinil Narakorn
Published: September 2018

Subsea jumper is the steel pipe structure to connect wellhead and subsea facilities such as manifolds or processing units in order to transport the produced multiphase flows. Generally, the jumper consists of a goalpost with two loop structures and a straight pipe between them, carrying the multiphase oil and gas from the producing well. Due to the jumper pipe characteristic geometry and multi-fluid properties, slug flows may take place, creating problematic fluctuating forces causing the jumper oscillations. Severe dynamic fluctuations cause the risk of pipe deformations and resonances resulting from the hydrodynamic momentum/pressure forces which can lead to unstable operating pressure and decreased production rate. Despite the necessity to design subsea jumper with precise prediction on the process condition and the awareness of slug flow risks, it is challenging to experimentally evaluate, identify and improve the modified design in terms of the facility scale, time and cost efficiency. With increasing high computational performance, numerical analysis provides an alternative approach to simulate multiphase flow-induced force effects on the jumper. The present paper discusses the modelling of 3-D flow simulations in a subsea jumper for understanding the development process of internal slug flows causing hydrodynamic forces acting on the pipe walls and bends. Based on the fluctuating pressure calculated by the fluid solver, dynamic responses of the jumper pipe are assessed by a one-way interaction approach to evaluate deformation and stress. A potential resonance is discussed with the jumper modal analysis. Results from the structural response analyses show dominant multi-modal frequencies due to intermittent slug flow frequencies. Numerical results and observed behaviors may be useful for a comparison with other simulation and experiment.
Adaptive Grid Refinement for Two-Phase Offshore Applications
Authors: van der Plas Peter , Veldman Arthur E. P. , Seubers Henk , Helder Joop , Lam Ka-Wing
Published: September 2018

In the past, the CFD simulation method ComFLOW has been successfully applied in a wide range of offshore applications, involving wave simulations and impact calculations. In many of these calculations the area of interest comprises a small part of the domain and remains fixed in time, which allows for efficient grid refinement by means of grid stretching or static local refinement. However, when trying to accurately resolve the surface dynamics and kinematics of irregular and breaking waves, the resolution requirements are strongly time-dependent and difficult to predict in advance. Efficient grids can only be obtained by means of time-adaptive refinement. A Cartesian block-based refinement approach is followed which allows for efficient grid adaptation, with moderate overhead. An array-based data structure is employed which exploits the semi-structured nature of the Cartesian block grid. Currently we are testing the method with the simulation of lifeboat drops in regular and irregular wave conditions. This poses several challenges such as accurately imposing the incoming waves and modifying the absorbing boundary conditions to support two-phase flow. To reduce the wall-clock time, the simulation method has been parallelized.
Risk of Maritime Traffic in Coastal Waters
Authors: Teixeira A. P. , Guedes Soares C.
Published: September 2018

This paper addresses the broad aspects of safety of maritime transportation from the identification to the management of risks related particularly to the maritime traffic in coastal waters. A brief overview of present-day maritime accident statistics are presented and the methodologies that have been adopted in the maritime sector to analyze ship accidents are reviewed. The paper also reviews the models and tools that have been used for simulation of ship navigation and for accident probability prediction based on Automatic Identification System (AIS) data and the analysis and modelling of the influence of human and organisational factors on ship accidents. The development of maritime risk models based on Bayesian Networks and the various elements that influence an effective response to maritime accidents are also addressed.
Numerical Simulation of Surface Ship Motion in Regular Head Waves
Authors: Guo Lixiang , Wei Peng , Zhang Zhiguo , Sun Yue , Yu Jiawei
Published: September 2018

The motion of surface ship in wave environments is fully three-dimensional unsteady motion and includes complex coupling with hydrodynamic force and dynamic motion of the rigid body. This paper presents simulations of the KCS model with motions involve pitch and heave in regular head waves. Computations were performed with an in-house viscous CFD code to solve RANS equation coupled with six degrees of freedom (6DOF) solid body motion equations and dynamic overset grids designed for ship hydrodynamics. RANS equations are solved by finite difference method and PISO arithmetic. Level-set method is used to simulate the free surface flow. The simulation geometry includes KCS hull and rudder under three conditions with three wave length and wave height combinations and two velocities (Fr = 0.26 and 0.33). Total resistance coefficient CT, heave motion z and pitch angle θ have been compared between CFD and EFD. Comparisons show that pitch and heave are much better predicted than the resistance. In the first section, simulations considered only 2 degrees of freedom (heave and pitch), for the second section, numerical simulation added the rolling motion to study the KCS in regular head waves. The second simulation cases were carried out with the same velocity and wave length and amplitude combination as the first cases. Comparisons of heave and pitch motion between 2DOF simulations and 3DOF simulations were presented in this paper. Results show the difference of heave motion z and pitch angle θ between the 2DOF and 3DOF-simulasions. In both cases the free surface were studied as an example of the flow generated by the ship pitching and heaving.
Experimental Study for the Effect of Appendages on Vortex-Induced Motions of Tension Leg Platform
Authors: Tian Chenling , Liu Mingyue , Wang Shisheng , Wang Xinru , Li Haobo
Published: September 2018

Vortex-induced motions (VIM) of large marine structures have been emerged as hot issues both in engineering and academic fields. Aiming to investigate the effect of the appendages on the VIM phenomenon of the tension leg platforms (TLP), experimental studies were carried out in a towing tank., The tendon pretensions and mass ratio were modeled exactly by using an air-bearing system. Additionally, the motions in vertical plane were almost restricted and the TLP model was allowed to move freely in horizontal plane. The 6-degrees of freedom (6-DOF) motions of the model were recorded by the motion acquisition system, consistent with an acceleration sensor installed at the deck as well as four load cells employed to acquire the restoring forces of the four mooring lines respectively.

This paper presents the VIM responses of the TLP model with bare hull and the model with appendages located at the surface of columns with different relative positions to the current (i.e., 0°, 45°, 90° and 135°, respectively). In addition, the dynamic behaviors are also processed. The results show that the amplitudes of VIM response in the transverse direction are mitigated significantly for the configuration of 45°-appendages, lower than that of the bare hull model about 65 percent but slightly subsided at other locations. Moreover, the appendages at all locations can obviously reduce the amplitudes of the yaw motions, with the maximum decrease of 52 percent of the yaw responses for the configuration of 0°-appendages and 45°-appendages, compared with that of the bare hull model.
Investigation on Mechanical Properties of Fibreglass Reinforced Flexible Pipes Under Torsion
Authors: Fang Pan , Xu Yuxin , Yuan Shuai , Bai Yong , Cheng Peng
Published: September 2018

Fibreglass reinforced flexible pipe (FRFP) is regarded as a great alternative to many bonded flexible pipes in the field of oil or gas transportation in shallow water. This paper describes an analysis of the mechanical behavior of FRFP under torsion. The mechanical behavior of FRFP subjected to pure torsion was investigated by experimental, analytical and numerical methods. Firstly, this paper presents experimental studies of three 10-layer FRFP subjected to torsional load. Torque-torsion angle relations were recorded during this test. Then, a theoretical model based on three-dimensional (3D) anisotropic elasticity theory was proposed to study the mechanical behavior of FRFP. In addition, a finite element model (FEM) including reinforced layers and PE layers was used to simulate the torsional load condition in ABAQUS. Torque-torsion angle relations obtained from these three methods agree well with each other, which illustrates the accuracy and reliability of the analytical model and FEM. The impact of fibreglass winding angle, thickness of reinforced layers and radius-thickness ratio were also studied. Conclusions obtained from this research may be of great practicality to manufacturing engineers.
Analytical Approach on Dynamic Tension of Free Hanging Configuration
Authors: Kanazawa Motoyasu , Wada Ryota , Ozaki Masahiko
Published: September 2018

Free hanging is the most simple and basic model of a flexible riser, and has advantages in terms of low cost and easy operation, installation and maintenance compared to other configurations, such as Lazy-S or Steep-S. However, the dynamic motion of the top end has direct impact on the riser behavior near the touch down zone (TDZ) and causes axial compression. Since flexible pipe is vulnerable to axial compression, we usually adopt buffer configuration like Lazy-S or Steep-S. Some technical means have been made to reduce the axial compression of free hanging, such as non-uniform weight distribution for Steel Catenary Riser (SCR) and heavy material wrapping near TDZ for flexible pipe. Despite the achievements of such research, it is difficult to say that there is a systematic and comprehensive explication on how the parameters of dynamic motion or the configuration of pipe effect the dynamic tension of a riser. Linearized analysis in frequency domain with quite small number of lumped-mass model is discussed in this paper. The simplified linearized analytic solution support or modify empirical knowledge which parameter (weight in air or water, an angle of the riser against still water plane, the motion of the top end or added mass) effect dynamic minimum tension of the riser. The aim of this paper is to provide starting point of analytical approach and show its possibility. Most of the key parameters which are empirically known to estimate dynamic tension of the riser is driven from analytical model in this paper. Comprehensive numerical calculation by Orcaflex is performed to verify the assumptions and support the results.
Experimental Study of Muddy Soil Inside Suction Bucket Foundation by Vacuum Electro-Osmosis
Authors: Puyang Zhang , Hanbo Zhai , Hongyan Ding , Conghuan Le
Published: September 2018

The composite bucket foundation of offshore wind power is a new type of foundation, which has been applied in practical engineering because of its advantages of large-scale prefabrication on land, integrated installation at sea and zero residual recovery. In order to overcome the shaft friction and tip resistance of the suction bucket, great passive suction is often applied during the penetration of the suction bucket. However, the large hydraulic gradient usually leads to seepage failure of the soil on beneath the top plate of the bucket foundation. As a result, the bearing capacity of the top plate of the bucket is often ignored. In this paper, the construction and construction process of composite bucket foundation are introduced, and series of model tests were carried out to reinforce the soil inside of the bucket foundation by the method of the vacuum electro-osmosis. The results show that the combined method of negative pressure and electro-osmosis can effectively improve the undrained shear strength of the soil and reduce the water content of the soil in the bucket foundation. Finally, the reinforcement effect of soil inside bucket foundation is analyzed according to reinforcement of the prototype construction.
Accuracy of Failure Criteria Commonly Used for Ship Collision Simulations
Authors: Villavicencio R. , Liu Bin , Liu Kun
Published: September 2018

The paper summarises observations of the fracture response of small-scale double hull specimens subjected to quasi-static impact loads by means of simulations of the respective experiments. The collision scenarios are used to evaluate the discretisation of the finite element models, and the energy-responses given by various failure criteria commonly selected for collision assessments. Nine double hull specimens are considered in the analysis so that to discuss the advantages and disadvantages of the different failure criterion selected for the comparison. Since a large scatter is observed from the numerical results, a discussion on the reliability of finite element analysis is also provided based on the present study and other research works found in the literature.
A Numerical Investigation of Wedge Angle Effects on a Plunger Type Wave Maker With a Constant Submerged Volume
Authors: Azadian-Kharanjani Zohreh , Nikseresht Amir H. , Bingham Harry B.
Published: September 2018

The effect of wedge angle at a constant submerged volume for a plunger type wave maker on the wave height, wave amplitude ratio and the quality of generated wave is studied numerically for a range of linear wave conditions in this research. The commercial ANSYS-FLUENT finite volume code is used to solve the Navier-Stokes equations using dynamic meshes and a Volume of Fluid (VOF) scheme is used to capture the air-water interface. A second order upwind numerical scheme is used to discretize the convective terms of the momentum equations and the standard SIMPLE algorithm is used for coupling the pressure and velocity based equations. At first the plunger-type wedge shaped wave-maker of Wang is considered numerically for the conditions used in his experiments, over a range of linear wave conditions (H/λ less than or equal to 0.03). After validating the numerical method, the effect of plunger wedge angle on the quality of the generated waves and on the power which is needed to run the wave maker are investigated. From these results, we conclude that the quality of the generated waves reduces with increasing wedge angle, when the submerged volume is fixed.
Simplified FEA Models in the Analysis of the Redistribution of Beneficial Compressive Stresses in Welds During Cyclic Loading
Authors: Josefson B. L. , Alm J. , McDill J. M. J.
Published: September 2018

The fatigue life of welded joints can be improved by modifying the weld toe geometry or by inducing beneficial compressive residual stresses in the weld. However, in the second case, the induced compressive residual stresses may relax when the welded joint is subjected to cyclic loading containing high tensile or compressive stress peaks.

The stability of induced compressive stresses is investigated for a longitudinal gusset made of a S355 steel. Two methods are considered; either carrying out a high frequency mechanical impact (HFMI) treatment after welding or alternatively using low transformation temperature (LTT) electrodes during welding. The specimen is then subjected to a cyclic loading case with one cycle with a tensile peak (with magnitude reaching the local yield stress level) followed by cycles with constant amplitude. A sequential finite element analysis (FEA) is performed thereby preserving the history of the elasto-plastic behavior. Both the welding process and the HFMI treatment are simulated using simplified approaches, i.e., the welding process is simulated by applying a simplified thermal cycle while the HFMI treatment is simulated by a quasi-static contact analysis.

It is shown that using the simplified approaches to modelling both the welding process and HFMI treatment gives results that correlate qualitatively well with the experimental and FEA data available in the literature. Thus, for comparison purposes, simplified models may be sufficient. Both the use of the HFMI treatment and LTT electrodes give approximately the same compressive stress at the weld toe but the extent of the compressive stress zone is deeper for HFMI case.

During cyclic loading it is shown that the beneficial effect of both methods will be substantially reduced if the test specimen is subjected to unexpected peak loads. For the chosen load sequence, with the same maximum local stress at the weld toe, the differences in stress curves of the HFMI-treated specimen and that with LTT electrodes remain. While the LTT electrode gives the lowest (compressive) stress right at the well toe, it is shown that the overall effect of the HFMI treatment is more beneficial.
Pipeline UHB OOS Design With Variable Pressure and Temperature Distributions
Authors: Liu M. , Cross C. , McGrail J.
Published: September 2018

In this paper, the effect is discussed of both pressure and temperature variations and their bearings on the SRA UHB safety factors. A variable peak distribution characterised by probabilities of distinct design and operating conditions is proposed and developed for performing OOS UHB. A routine has been developed recognizing that such a distribution is generally not available in the SRA software. Bearing in mind that friction is an important parameter in the UHB and OOS analysis but not duly considered in the literature to date, an integrated UHB model is introduced in the SRA to account for axial friction. The probabilistic methodology, its implementation and significance are shown through a series of SRA and parametric studies using Monte Carlo simulations. It is demonstrated that a more sensible UHB SRA can be achieved to minimise unnecessary margins, whereby the design parameters can be represented by appropriate probability density functions taking into consideration of maximum design, operating and surge excursion conditions, system availability and reliability levels. Some conclusions and recommendations are presented on the selection of SRA input parameters.
A Comparative Research on Computation Methods for Wave Loads of Semi-Submersible Platform
Authors: Pei Zhiyong , Wu Shenyi , Chen Keqiang , Hu Xiaoming , Wu Weiguo
Published: September 2018

Wave load is one of the main external loads for semi-submersible platform, which is usually calculated by design wave method. In the present research, three design wave methods are investigated and compared on design wave parameters determination of semi-submersible platforms, i.e., the deterministic design wave method, stochastic design wave method and long-term prediction design wave method. Moreover, the specified calculation methods and the detailed wave load computation procedure are summarized considering the load characteristics of global hydrodynamic response. Finally, a semi-submersible platform is regarded as objective and the design wave results of three design wave methods are compared and analyzed. The fundamental research can provide reference for rational selection of wave loads calculation method.
Trajectory Control of a Tethered Underwater Robot System
Authors: Wu Jiaming , Chen Dongjun , Xu Ying , Chen Yuqing , Lu Lihua
Published: September 2018

A three-dimensional hydrodynamic and control model to simulate tethered underwater robot system is proposed. The fluid motion around the moving robot main body with running control ducted propellers is governed by Navier-Stokes equations, and multiple sliding mesh technique is applied to solve the governing equations. The governing equation of umbilical cable connected to the robot is based on the Ablow and Schechter method. The six-degrees-of-freedom equations of motion for underwater vehicle simulations proposed by Gertler and Hargen are adopted to estimate the hydrodynamic performance of the underwater robot. In the model, the feed-forward control algorithm is applied to adjust the length of the umbilical cable according to the robot trajectory control target, the incremental PID control algorithm is adopt to regulate the rotating speeds of the ducted propellers producing appropriate thrusts for the robot control. With the proposed hydrodynamic and control model, hydrodynamic behaviors of the robot under definite trajectory control manipulations are observed numerically.

The numerical results of robot trajectory control simulations indicate that the feed-forward control algorithm for adjusting the length of the umbilical cable, and the incremental PID control algorithm for regulating the rotating speeds of the propellers are feasible and effective, the adjusting the length of the umbilical cable with feed-forward control technique is largely responsible for the vertical trajectory control to the robot, while regulating the rotating speeds of the propellers by the PID control algorithm play a leading role in the horizontal trajectory manipulation, the deviation between the designated trajectory and the control one at each time step is acceptable.
Advanced FE Modelling Approach for Pipeline Hooking Interaction of Dragged Anchors
Authors: Bartolini Lorenzo , Marchionni Lorenzo , Parrella Antonio , Vitali Luigino
Published: September 2018

Offshore pipelines, located in areas with high/medium ship traffic, are exposed to threats such as dragged anchors, dropped objects, sinking ships, etc..

In the last years, there have been a few accidents where subsea pipelines or cables have been hooked and damaged by dragged anchors. These incidents have been caused both by emergency and accidentally dragged anchors. Two of the most serious incidents to pipelines caused by an accidentally dragged anchor involved the Trans Mediterranean gas pipelines in 2008 and the Kvitebjørn gas pipeline in the North Sea in 2007.

The interaction mechanism between the pipeline and an anchor dragging on the seafloor is affected by different parameters (i.e. anchor size, chain length, water depth, soils geo-technics, anchor speed, incident angle between the pipeline and the anchor dragging direction). In common practice, the occurrence of hooking events is assessed by implementing specified interpretative model involving basically typical anchor dimensions for the different ship classes and expected soil pipe interaction scenarios.

Major efforts have been made to develop a 3D Finite Element model with the aim of improving the simulation capabilities of engineers to address and anticipate the mechanism of pipeline and dragged anchor interaction. The model presented in this paper is based on the Coupled Eulerian Lagrangian (CEL) technique. With respect to typical simplified FE models, implementing the seabed as an analytic surface, this advanced technique (i.e. CEL) allows one to model the seabed as a deformable Eulerian domain, in which the anchor (and the pipeline) can penetrate. The seabed settlement and the displacement of soil particles due to anchor motion can be fully calculated.

The FE Model includes the steel pipeline geometry and the external concrete coating, the surrounding water, the deformable seabed and the 3D anchor geometry with its chain.

Scope of this assessment is to improve the understanding of the pipeline and anchor interaction event. In particular the focus is on the mechanisms and dynamics of accidental events which lead to the occurrence of anchor engagement with the pipeline. Eventually, the final goal is to refine and take into due account the contribution of accidentally dragged anchor scenario in the overall procedure for pipeline design against threats posed by commercial ship traffic.

In this paper:

• The state of the art about the classical analysis methodology recommended by standards to evaluate the interaction between the pipeline and the accidental dragged anchors is briefly described;

• A FEM based analysis methodology is drawn and proposed to address the potential for pipeline hooking by the accidentally dragged anchor event;

• A typical application is presented.
Investigation of Monitoring Fish Using Underwater Fish-Eye Camera at the Test Site of Marine Renewable Energy
Authors: Yoshida Takero , Kitazawa Daisuke , Mizukami Yoichi , Chen Qiaochu , Mochizuki Akito
Published: September 2018

Assessment of any significant effects on the local marine environment when considering the installation of a marine renewable energy device is of the utmost importance. In particular, the effect of such device on fish is concerned by local fishermen. To confirm variation of fish before and after installing the device of marine renewable energy, we investigated effective monitoring system using an underwater fish-eye camera. In this paper, visibility of the fish-eye camera was tested off Kamaishi city, Iwate prefecture, Japan, which is a test site of marine renewable energy in Japan. Device of wave power generation is planning to install at this site in the future. We confirmed the visibility of the fish-eye camera using a fish-shaped target by changing the distance between the target and camera. The water depth and photon were simultaneously measured. From the result, the horizontal visibility was discussed, and then we made a plan to observe around wave power generator using this fish-eye camera.
Experimental Investigation Into the Effect of Impact Loading on the Response of Metallic Trapezoidal Corrugated Core Sandwich Panels
Authors: Yang Haifu , Cheng Yuansheng , Zhang Pan , Liu Jun , Chen Kai
Published: September 2018

Sandwich structures with corrugated cores have attracted a lot of interest from industrial and academic fields due to their superior crashworthiness. In this paper, the dynamic response of metallic trapezoidal corrugated core sandwich panels under low-velocity impact loading is studied by conducting drop hammer impact testing. The sandwich panels composed of two thin face skins and trapezoidal corrugated core, were designed and fabricated through folding and laser welding technology. Main attention of present study was placed at the influences of the impact energy, impactor diameter and impact location on the impact force, deformation mechanisms and the permanent deflections of the trapezoidal corrugated core sandwich panels. Results revealed that the impact energy has significant effects on the dynamic response of the sandwich panel, whereas the impact diameter has little effects on it. The deformation mode of the front face sheet differs sharply when the impact location is different. The middle unit cell of corrugated core is compressed to the “M” shape under different low-velocity impact loading.
Short Term Statistics of Hydroelastic Loads of a Containership in Head and Oblique Seas
Authors: Rajendran Suresh , Guedes Soares C.
Published: September 2018

Vertical bending moment (VBM) is an important parameter for the structural safety of any sea going ship. Generally, it is expected that ships encounter largest VBM in head seas. However, when it comes to flexible ships, it is not necessary that the largest VBM always occurs in head sea. It can also occur in oblique waves and high frequency response in waves with shorter period can be as large as the wave frequency response or can be even larger. Studies conducted in the recent past by other researchers has shed some light into this peculiar characteristics of VBM of flexible hulls. Therefore, it will be worthwhile to further investigate to check whether the nonlinear design load calculation of the flexible hull in head seas will lead to conservative results or should be tested for a range of headings with different combinations of wave period in order to estimate the largest VBM acting on the hull. In this paper, the numerical and the measured VBM of an ultra large container ship (ULCS) in low to severe sea states are analyzed and compared. The effect of speed, significant wave height, springing and bow flare slamming on the response is studied. The measured VBM in head and oblique waves are compared and interesting findings are observed.