bluuebunny/crossref_metadata_2025 huggingface dataset:
New Insights Into the Flooding Sequence of the Costa Concordia Accident
Authors: Dankowski Hendrik , Russell Philipp , Krüger Stefan
Published: September 2014

The tragic accident of the Costa Concordia in January 2012 was one of the most severe large passenger ship accident in Europe in recent times followed by a tremendous public interest. We present the results of an in-depth technical investigation of the flooding sequence which lead to the heeling and grounding of the ship.

A fast and explicit numerical flooding simulation method has been developed in the last years to better understand accidents like this one caused by complex and large scale flooding events. The flooding simulation is validated with the help of results from model tests and has been successfully applied to the investigation of several other severe ship accidents. It is based on a quasi-static approach in the time domain which evaluates the hydrostatic equilibrium at each time step. The water fluxes through the openings are computed by a hydraulic model based on the Bernoulli equation. Large and partly flooded openings are taken into account as well as conditional openings like the opening, closing and breaking of doors. The fluxes are integrated in the time domain by a predictor-corrector integration scheme to obtain the water volumes in each compartment involved in the flooding sequence.

Due to the fact that the accident happened in calm water at moderate wind speeds close to the shore of the island Giglio this quasi-static numerical flooding simulation can be applied. The results of the technical investigation of the Costa Concordia accident obtained with the help of the developed method are presented. These results match well with the heel and trim motions observed during the accident and the chain of events which lead to the final position of the vessel on the rocks in front of the island Giglio.

The explicit and direct approach of the method leads to a fast computational run-time of the numerical method. This allows to study several possible accident scenarios within a short period to investigate for example the influence of the opening and closing of watertight doors and to identify a most likely flooding scenario which lead to this tragic accident.
Vortex Shedding From a Ship Hull by Means of Tomographic PIV
Authors: Egeberg Tale F. , Yoon Hyunse , Stern Frederick , Pettersen Bjørnar , Bhushan Shanti
Published: September 2014

The onset and progression of vortices generated by the hull of a surface combatant has been investigated for drift angles of 0, 10 and 20 degrees by means of tomographic particle image velocimetry. Vortices are seen to form on the sonar dome and fore-body of the ship model, as well as on the bilge keels, and on the after-body. Two major streamwise vortex systems were identified: the vortices generated by the sonar dome and the vortices generated on the fore-body of the hull. Leading edge and crossflow vortices form on the bilge keels, and on the windward side, these vortices merge. Vortices are also seen to form on the afterbody of the hull at increased drift angles. Frequency analysis of the sonar dome vortex at drift angle 20 degrees reveals a dominant frequency of approximately 3 Hz.
Consideration of Epistemic Uncertainty in Extreme Wave Height Estimation
Authors: Wada Ryota , Waseda Takuji
Published: September 2014

Extreme value estimation of significant wave height is essential for designing robust and economically efficient ocean structures. But in most cases, the duration of observational wave data is not efficient to make a precise estimation of the extreme value for the desired period. When we focus on hurricane dominated oceans, the situation gets worse. The uncertainty of the extreme value estimation is the main topic of this paper. We use Likelihood-Weighted Method (LWM), a method that can quantify the uncertainty of extreme value estimation in terms of aleatory and epistemic uncertainty. We considered the extreme values of hurricane-dominated regions such as Japan and Gulf of Mexico. Though observational data is available for more than 30 years in Gulf of Mexico, the epistemic uncertainty for 100-year return period value is notably large. Extreme value estimation from 10-year duration of observational data, which is a typical case in Japan, gave a Coefficient of Variance of 43%. This may have impact on the design rules of ocean structures. Also, the consideration of epistemic uncertainty gives rational explanation for the past extreme events, which were considered as abnormal. Expected Extreme Value distribution (EEV), which is the posterior predictive distribution, defined better extreme values considering the epistemic uncertainty.
Applications of Vector Evaluated Genetic Algorithms (VEGA) in Ultimate Limit State Based Ship Structural Design
Authors: Hughes Owen , Ma Ming , Paik Jeom Kee
Published: September 2014

Ship structural design often deals with multiple objectives such as weight, safety, and cost. These objectives usually conflict with each other, and optimizing a particular solution with respect to a single objective can result in unacceptable results with respect to the other objectives. A reasonable solution to a multi-objective problem is to investigate a set of solutions, each of which satisfies the objectives at an acceptable level without being dominated by any other solution. Genetic algorithms have been demonstrated to be particularly effective to determine excellent solutions to these problems. In this paper a multi-objective GA, called Vector Evaluated Genetic Algorithm (VEGA) is formulated and used to optimize a large and complex thin-wall structure (a complete cargo hold of a 200,000 ton oil tanker) on the basis of weight, safety and cost. The structure weight and cost and all of the stresses are calculated using a realistic finite element model. The structure adequacy is then evaluated using the ALPS/ULSAP computer program (Paik and Thayamballi, 2003) which can efficiently evaluate all six ultimate limit states for stiffened panels and grillages. This example was chosen because the initial design is severely inadequate. The results show that the proposed method can perform ultimate strength based structural optimization with multi-objectives, namely minimization of the structural weight and cost and maximization of structural safety, and also that the method is very robust.
Frequency Versus Time Domain Fatigue Analysis of a Semi-Submersible Wind Turbine Tower
Authors: Kvittem Marit I. , Moan Torgeir
Published: September 2014

The current paper addresses a study of a semi-submersible wind turbine, where tower base bending moments and short term tower fatigue damage was estimated by a frequency domain method assuming two-dimensional platform motions. Both a rigid structure assumption and a generalised degree of freedom model for including the first flexible mode of the turbine were investigated. First, response wind- and wave loads were considered separately, then superposition was used to find the response to combined wind and wave loading. The bending moments and fatigue damage obtained by these methods were compared to results from a fully coupled, non-linear time domain analyses.

In this study a three column, catenary moored semi-submersible with the NREL 5MW turbine mounted on one of the columns was modelled. The time domain simulation tool used was Simo-Riflex-AeroDyn from Marintek and CeSOS.

The frequency domain method accounting for a flexible turbine gave a good representation of the tower base bending moment histories for the moderate sea states in these analyses, also for the combined wind and wave analyses. The frequency domain fatigue damage predictions were underestimated by 0–60%, most likely due to the exponential relationship between damage and stress amplitude.
Analysis of the German Navy Stability Standard BV 1030 With Respect to Operability in Heavy Weather
Authors: Krüger Stefan , Hatecke Hannes , Rinke Andreas , Tammen Klaus
Published: September 2014

The stability standard of the German Navy — the BV 1030 — was developed in the mid-sixties of the last century in close cooperation with the German Navy Authorities (now BAIINBw) and the University of Hamburg. Other than the stability standards used for commercial shipping, the BV 1030 is based on righting and heeling lever balances for each individual loading condition of each individual ship. Different types of heeling moments have to be assumed in several combinations and they have to be balanced against the righting levers of the ship. Not only the still water stability curve is subject to this lever balance, but also wave crest and wave trough situations are subject to the stability analysis. The BV 1030 stability standard further requires a minimum stability if the ship is on the wave crest. Since this stability standard is in force, the German Navy never experienced a stability accident. The development of new hull forms with the focus on fuel efficiency has widely brought up new problems in heavy weather, for example the vulnerability for parametric rolling. It was therefore of interest for the German Authorities (BAIIN) whether the existing stability standard has sufficient safety to cover also these phenomena connected to more modern hull forms. Therefore an analysis was carried out in close cooperation between BAIINBw, MARS and TUHH where the operability of several ships of the German Navy was analyzed with numerical sea keeping computations. The nonlinear sea keeping code E4ROLLS was used which allows the computation of time series of the ship motions in irregular, short crested seas. From these computations, operational limits could be derived, or, vice versa, the required stability to guarantee a certain operability. The results showed that the concept of the German BV 1030 stability standard provides a significantly higher safety level compared to IMO standard for commercial ships. The results did also show that for modern hull forms, some adjustments to the existing safety standard were found to be useful to better cope with righting arm fluctuations in longitudinal waves.
Dynamic Mudline Damping for Offshore Wind Turbine Monopiles
Authors: Carswell Wystan , Johansson Jörgen , Løvholt Finn , Arwade Sanjay R. , DeGroot Don J.
Published: September 2014

Fatigue is often a design driver for large (e.g. 5–10 MW) offshore wind turbines (OWTs), necessitating a thorough examination of damping sources: aerodynamic, hydrodynamic, structural, and soil. Of these sources, soil damping has been least considered by researchers with respect to OWTs. Aeroelastic programs, such as the National Renewable Energy Laboratory (NREL) code FAST, are typically used for time history analysis of aerodynamic and hydrodynamic loads experienced by OWTs. To take into account foundation flexibility while minimizing computational expense, reduced-order foundation models such as the mudline stiffness matrix are often used. Mudline stiffness and damping matrices are derived here for the NREL 5MW reference turbine. By recompiling FAST with mudline stiffness and damping matrices, the contribution of soil damping to OWT dynamic behavior is then quantified by comparing time history analysis results including and excluding soil damping.
Wave-in-Deck Load on a Jacket Platform, CFD Calculations Compared With Experiments
Authors: Iwanowski Bogdan , Vestbøstad Tone , Lefranc Marc
Published: September 2014

The paper presents an industrial application of CFD for calculation of Wave-In-Deck load due to an extreme wave.

Particular attention is given to flow kinematics initialization that is necessary to start up a CFD simulation. The applied CFD code, ComFLOW, is a Navier-Stokes equation solver with an improved Volume of Fluid (iVOF) method employed to displace and re-construct fluids free surface.

For incoming waves high enough for a negative air-gap and therefore with Wave-In-Deck loads, a jacket platform was tested in model basin, for both regular and irregular wave cases. One of goals of these model tests was verification of CFD codes. The experimental and computational models of the structure are exactly the same. In the paper, the measured Wave-In-Deck forces are compared with CFD results.
Development of a Novel Time-Frequency Enhanced Volterra System Identification Method for the Modeling of a Nonlinear OWC Wave Energy Converter Under Irregular Sea Wave Excitation
Authors: Gkikas G. D.
Published: September 2014

A system identification method combining the virtues of the Volterra series and Hilbert-Huang transform and developed for the modelling of the nonlinear dynamic pressure fluctuation inside the chamber of an Oscillating Water Column wave energy converter (OWC-WEC) is presented. The proposed method is validated for the case where the excitation corresponds to a general nonlinear stationary signal.
Creation of Warm Model Ice
Authors: Bos R. W. , Huisman T. J. , Brouwer J. , Hagesteijn G. , de Koning Gans H. J.
Published: September 2014

To predict loads on propellers in ice, model tests can be used. Using regular (refrigerated) cold model ice in ice basins is a valid option. However, these tests are expensive, difficult to reproduce and bound to time and location, due to the required cooling in ice model basins. An alternative would be to use warm model ice, a material with the properties of model ice at room temperature. This paper proposes one variety, using only materials available from DIY stores. Based on theoretical propeller-ice interaction models, it is assumed that the loads come from a crushing process. Hence, the compressive strength follows as dominant material property of ice. To match compressive strength of weak cold model ice, a large particle composite is proposed. Expanded Polystyrene (EPS) beads are used as particles, with paraffin as matrix to produce warm ice specimens. The compressive strength of these specimens were measured with a uniaxial compression test and matched with weak model ice. The specimens were designed for in-situ use in model scale propeller impact tests.
Small-Scale Model Tests of a Rubber-Tube Wave Energy Converter With Pneumatic Power Take-Off
Authors: Mendes A. C. , Paredes L. M. A. , Gil F. A. S. , Chaplin J. R.
Published: September 2014

The paper deals with a relatively new concept in wave-energy conversion systems: the Anaconda. This device consists basically of a distensible tube, made out of rubber material, which interacts with the incident waves in order to convey the absorbed energy to some form of power take-off (PTO). In the present case, the bulges inside the rubber tube drive a slug of water towards a vertical shaft referred to as a chimney. The oscillations of the water column inside the chimney induce a pressure oscillation in the pneumatic chamber above that activates an air-turbine. The Anaconda device has been studied extensively by experimental and theoretical means. However, so far, the pneumatic PTO for this device has only been examined within restrictive linear conditions. This study is about a series of 1:100 scale model tests of a freely floating Anaconda in a wave flume, under deep and intermediate water regular waves, for a device equipped with a non-linear PTO. In the model, the pneumatic chamber communicates with the atmosphere through an orifice. Three calibrated orifices of different diameters have been tested. The pressure across the orifice is determined from measurements taken of the amplitude of water column oscillations in the system, by applying Bernoulli’s law. These properties are subsequently used for calculating the power captured from the incident waves. Estimates of power output and energy capture width are presented, as functions of wave frequency, while the device interacts with linear and second-order waves. Our estimates are finally extrapolated to predict prototype performance.
Variations of Hydrodynamic Characteristics With the Perforated Cylinder
Authors: Chandrasekaran Srinivasan , Natarajan Madhavi , Thanu Natarajan Chithambara
Published: September 2014

Presence of the perforated outer cover on the existing column members of offshore platforms reduces the direct wave impact on these members. Such applications are common in the coastal structures where perforated covers are provided on the seaside to dissipate the wave energy and to reduce the pressure on the members. Detailed studies on the variations of the hydrodynamic characteristics on the inner cylinder, encompassed by a perforated outer cover are scarce in the literature. Present study is focused the development of numerical model to investigate the variations in the water particle kinematics on the inner cylinder encompassed by perforated outer cover. Hydrodynamic characteristics are examined along the water depth through computation fluid dynamics (CFD) for perforation ratios (p%) varying in the range of 10 to 15%. Velocity profiles for different wave steepness are developed along with the design charts for the chosen perforation ratios. These design charts can be readily used for estimating the water particle kinematics for perforated members along the water depth.
A Coupled Methodology for Wave-Body Interactions at the Scale of a Farm of Wave Energy Converters Including Irregular Bathymetry
Authors: Charrayre François , Peyrard Christophe , Benoit Michel , Babarit Aurélien
Published: September 2014

Knowledge of the wave perturbation caused by an array of Wave Energy Converters (WEC) is of great concern, in particular for estimating the interaction effects between the various WECs and determining the modification of the wave field at the scale of the array, as well as possible influence on the hydrodynamic conditions in the surroundings. A better knowledge of these interactions will also allow a more efficient layout for future WEC farms. The present work focuses on the interactions of waves with several WECs in an array. Within linear wave theory and in frequency domain, we propose a methodology based on the use of a BEM (Boundary Element Method) model (namely Aquaplus) to solve the radiation-diffraction problem locally around each WEC, and to combine it with a model based on the mild slope equation at the scale of the array. The latter model (ARTEMIS software) solves the Berkhoff’s equation in 2DH domains (2 dimensional code with a z-dependence), considering irregular bathymetries. In fact, the Kochin function (a far field approximation) is used to propagate the perturbations computed by Aquaplus into Artemis, which is well adapted for a circular wave representing the perturbation of an oscillating body. This approximation implies that the method is only suitable for well separated devices. A main advantage of this coupling technique is that Artemis can deal with variable bathymetry. It is important when the wave farm is in shallow water or in nearshore areas. The methodology used for coupling the two models, with the underlying assumptions is detailed first. Validations test-cases are then carried out with simple bodies (namely heaving vertical cylinders) to assess the accuracy and efficiency of the coupling scheme. These tests also allow to analyze and to quantify the magnitude of the interactions between the WECs inside the array.
Three Dimensional Numerical Modelling of Pier Scour Under Current and Waves Using Level Set Method
Authors: Afzal Mohammad Saud , Bihs Hans , Kamath Arun , Arntsen Øivind A.
Published: September 2014

Stability of offshore structures can be threatened by local scouring which could ultimately lead to their failure. As a consequence, knowledge of the scouring mechanism and the accurate prediction of the characteristic scour geometry is very important for the design of such structures. A three-dimensional computational fluid dynamics model is used to calculate the scour and the deposition pattern around a pier for two different boundary conditions: constant discharge and regular waves. The computational fluid dynamics (CFD) model solves Reynolds-Averaged Navier-Stokes (RANS) equations in all three dimensions. The location of the free surface is represented using the level set method, which calculates the complex motion of the free surface in a very realistic manner. For the implementation of waves, the CFD code is used as a numerical wave tank. For the geometric representation of the moveable sediment bed, the level set method is used. The numerical results for the local scour prediction are compared with physical experiments. The performance of the turbulence models, the formulations of the critical shear stress for the sloping bed and the effect of the variation of the sediment time stepping are investigated. The decoupling of the hydrodynamic and the morphodynamic time step is tested and found to be a reasonable assumption. For the two situations of local pier scour under current and wave conditions, the numerical model predicts the general evolution (geometry, location and maximum scour depth) and time development of the scour hole accurately.
The First Standard for Certification of HATT: The Application of Risk Based Approach
Authors: Bittencourt Claudio , Zarraonandia Gaizka , Vinogradov Alexey , Cocho Mathieu
Published: September 2014

As part of the ReDAPT, a project commissioned and co-funded by the ETI (Energy Technologies Institute), the first standard for certification of horizontal axis tidal turbine (HATT) has been commissioned to DNV GL in order to accelerate the development of the tidal technology and its commercialization. Although the development of the standard is limited to one turbine concept and unlike the wind turbines, the possible variations of configurations and the limited track record of the technology provided great challenges to define requirements and parameters to be considered in all aspects of the turbine.

A risk based approach has been used on the different HATT configurations, addressing all the systems, subsystems and main components. The process, as described in the DNV OSS-312 – Certification of Tidal and Wave Energy Converters, addressing technology assessment and FMEA leading to a certification plan and definition of standards from Oil & Gas / Wind to be applied, was implemented in a level of detail sufficient to define the failure modes and associated risks that were the basis for definition of design, construction, commissioning and in-service life requirements.

The work on failure modes and risks as well as data and definitions necessary for an effective risk based process were carried out with the support and assistance of ALSTOM during the ReDAPT project and the experience accumulated by DNV GL in the verification / certification projects carried out so far.

Although every standard has a risk based background (even if based on field experience for many years), this standard has a direct connection between the identified risks and requirements. As the risks can vary for a specific configuration of HATT, technology matures and data is harnessed with the passing of the time, the approach used will allow for a faster and consistent adaptation of the standard now and in the future.

This paper, describes the process in detail, presents the structure used for the risk assessment process, its conclusions and highlights the connection between the findings and the content of the standard.
Fatigue Performance of Grade R4 and R5 Mooring Chains in Seawater
Authors: Fernández Jonathan , Storesund Walther , Navas Jesús
Published: September 2014

With more than 50.000 tons in service to date, the Oil&Gas Industry has the need to understand the tension fatigue performance of grade R5 chains in straight tension, and corroborate the validity of the existing design methods.

The chain fatigue design curves in API and DNV are based on fatigue tests obtained in the nineties and early two thousands. However the tests were performed on lower grades such as ORQ, R3 and R4, and small chains, 76 mm diameter being the largest studless chain tested.

The industry has moved towards the use of large studless chains, especially in permanent units, where chain diameters above 150 mm are not unusual.

This paper gathers information from a full scale fatigue test program on grade R4 and R5 studless chains, performed in seawater and with diameters between 70 mm and 171 mm. The chains being tested are actual production chains supplied for different drilling units and large permanently moored production floating units.

The paper analyses the data and determines tension-tension fatigue curves based on API and DNV methods for computation of cumulative fatigue damage, regardless of other damaging mechanisms. Improved fatigue capacity is obtained with respect to the above recommended design methods.
Effects of Preheat and Interpass Temperature on the Residual Stress and Distortion on the T-Joint Weld
Authors: Fu Guangming , Lourenço Marcelo Igor , Duan Menglan , Estefen Segen F.
Published: September 2014

The finite element model of ABAQUS combined with FORTRAN subroutines was developed to predict the residual stress and deformation of T-joint welds under different preheat and inter-pass temperature. A calibrated and sequentially coupled thermal and mechanical 3D finite element (FE) model is developed, and Goldak’s double ellipsoidal heat source model is implemented into the numerical model. The welding induced imperfections, including the residual stress and distortion are discussed in this paper. The results show that vertical deformation depend significantly on the preheat temperature and inter-pass temperature. The influences of preheat and interpass temperature on the residual stress are not significant.
The Tension Leg Semisubmersible (TLS): The Hybrid TLP-Semisubmersible Floater With the Spar Response
Authors: Mansour Alaa M. , Wu Chunfa , Kumar Dhiraj , Zuccolo Ricardo
Published: September 2014

The Tension Leg Semisubmersible (TLS) floater is the second generation of the Free-Hanging Solid Ballast Semisubmersible (FHSB Semi) design. The FHSB Semi is the state-of-the-art design that maintains the advantages of the conventional Semisubmersibles and provides the motions of Spars. The FHSB Semi design is a conventional semisubmersible with an added feature of a Free-Hanging Solid Ballast tank (SBT) located deep below the hull keel level and connected through four groups of chains (on its four corners) to the semisubmersible hull. During the pre-service conditions, the chains are used to retract the SBT and maintain it at a close proximity to the hull keel to facilitate the transportation and installation operations. Once the semisubmersible is moored in-place, the chain system is operated to lower the SBT to its desired elevation below the hull keel and maintain it permanently connected to the semisubmersible hull during the in-service condition. The SBT provides substantial in-water weight and added mass that significantly reduce the platform response and maintains the chains in tension.

In this paper, detailed description of the Tension Leg Semisubmersible (TLS) design as the second generation of the FHSB Semi is presented. The paper also includes discussions on the proposed project execution plan for the TLS covering the fabrication, transportation and installation as well as the added risks and risk mitigations associated with the new semisubmersible design and execution.

A case study is introduced where a TLS is used as a dry tree host for a field located at 6,000 ft of water in the central Gulf of Mexico (GoM) harsh environment.
Modeling of an Oscillating Wave Surge Converter With Dielectric Elastomer Power Take-Off
Authors: Moretti Giacomo , Forehand David , Vertechy Rocco , Fontana Marco , Ingram David
Published: September 2014

This paper introduces a novel concept of Oscillating Wave Surge Converter, named Poly-Surge, provided with a Dielectric Elastomer Generator (DEG) as Power Take-Off (PTO) system.

DEGs are transducers that employ rubber-like polymers to conceive deformable membrane capacitors capable of directly converting mechanical energy into electricity. In particular, a Parallelogram Shaped DEG is considered.

In the paper, a description of the Poly-Surge is outlined and engineering considerations about the operation and control of the device are presented. In addition, a mathematical model of the system is provided. Linear time-domain hydrodynamics is assumed for the primary interface, while a non linear electro-hyperelastic model is employed for the DEG PTO.

A design approach for the Poly-Surge DEG PTO is introduced which aims at maximizing the energy produced in a year by the device in a reference wave climate, defined by a set of equivalent monochromatic wave conditions. A comparison is done with two other WEC models that employ the same primary interface but are equipped with mathematically linear PTO systems under optimal and suboptimal control. The results show promising performance of annual energy productivity, with slightly reduced values for the Poly-Surge, even if a very basic architecture and control strategy are assumed.
In Situ Investigation of Microstructural Changes in Thermoplastic Composite Pipe Under Compressive Load
Authors: Dodds Neville , Pancholi Ketan , Jha Vineet , Tariq Syed Fawad , Latto James
Published: September 2014

Thermoplastic composite materials are very advantageous as component layers in subsea risers due to their inherent properties such as high strength, low density, fatigue and chemical resistance. However, response of composite materials to applied loading is complex and three-dimensional in nature. The heterogeneous structure of the composite material induces irregular distribution of stress/strain over the cross-section and thus, it is essential for design to use analytical methods capable of determining the stress-strain relationship in three-dimensional space. Currently, most methods rely upon one-dimensional or two-dimensional data collection techniques with macro scale stress / strain observations for experimental validation. In order to ascertain the correct load to the failure, a complete understanding of the material failure at the micro-scale is essential.

In this work, X-ray computed tomography is employed for the in situ observation of micromechanical failure of the composite material under a compressive load. The observed results are compared and validated with the traditional stress-strain data and finite element analysis. It is observed that the damage in the composite material initiates by delamination which grows as the loading progresses. Moreover, the properties and failure modes are highly dependent on the manufacturing process. By gaining further understanding of the failure modes using these methods, the findings can be utilized in optimizing the design of composite riser structures.
Structural Damage Detection With Vibration Characteristics for Subsea Pipelines
Authors: Feng X. , Zhou J.
Published: September 2014

A method based on the vibration transmissibility is presented for subsea pipeline in this paper. Fist, the vibration transmissibility for a pipeline structure was presented theoretically. An outlier analysis algorithm was used to detect the structural damage by using of the transmissibility function calculated with the measured vibration signals. Next, the experimental investigations were carried out to verify the feasibility of the proposed method. The results demonstrate that the local damage in the pipeline can be effectively detected. It is indicated that the transmissibility based approach can be used to monitor the damage or structural deterioration for subsea pipelines.
Research on Bifurcation Control Method and its Application on the Parametric Rolling of Ships in Longitudinal Waves
Authors: Hu Kaiye , Ding Yong , Wang Hongwei
Published: September 2014

In this paper, we propose a bifurcation control method in order to stabilize the trivial steady state in the frequency response of the nonlinear parametric system of ships and try to eliminate jump in the force response, by employing a combined linear-plus-nonlinear feedback control. By theoretically analyzing the modified modulation equations, we show that the unstable region of the trivial steady state of the ship’s parametric rolling motion in longitudinal waves can be shifted and the nonlinear character can be changed, by means of the bifurcation control with the feedback controller. The shift of the unstable region permits the stabilization of the trivial steady state in the frequency response, and the suppression of the discontinuous bifurcation due to the change of the nonlinear character allows the elimination of the jump in the quasistationary force response. By performing numerical simulations, and by comparing the responses of the uncontrolled system and the controlled one, we clarify that the proposed bifurcation control is available for improvement the safety of the ship’s parametric excitation in longitudinal waves.
Development and Validation of a Customizable DP System for a Full Bridge Real Time Simulator
Authors: Queiroz Filho Asdrubal N. , Zimbres Marcelo , Tannuri Eduardo A.
Published: September 2014

This paper presents the development and validation of a customizable Dynamic Positioning (DP) System for a real time full bridge simulator. The Maritime Waterway Simulator (SMH) was developed based on the code of the Numerical Offshore Tank (TPN) simulator. It is able to perform study of maneuvers feasibility and crew training. Many simulated operations such as oil offloading, pipe-laying, support to platforms or station keeping, require a DP system. In order to meet the demand for such a system, a complete system was developed with an important requirement in mind: The DP system of a full bridge simulator must be easily customizable for different types of vessels. In order to validate the developed DP system, a commercial DP system is used for comparison. DP operations with the vessel is conducted with both systems: the in house developed DP and the commercial one. The results obtained with the developed DP system are compared with the one obtained with the commercial system. This comparison demonstrates that the in-house DP system can indeed be used for simulating different types of DP vessels.
A Hybrid 2D-3D CFD Model System for Offshore Pile Groups Subject to Wave Loading
Authors: El Safti Hisham , Bonakdar Lisham , Oumeraci Hocine
Published: September 2014

A hybrid 2D-3D CFD model is developed for studying water wave loads on a slender pile in a pile group. In the hybrid model approach, a one-way link is established between a model for the far-field and another for studying the fluid-structure interaction in the near field. In the far-field a 2D incompressible Navier-Stokes multiphase solver is considered for the proper reproduction of phase-focused (freak) waves produced in physical experiments. The near-field model is a multiphase 3D CFD model that utilizes compressible Navier-Stokes equations to enhance the simulation of entrapped air compressibility effects during breaking wave impact on structures. Both models use the Volume-Of-Fluid (VOF) method to capture the air-water interface and alternatively a RANS or LES turbulence model. An overlap zone is introduced to both models, in which fluid kinematics and surface elevation are sampled from the far-field model and introduced via a relaxation function to the overlap zone in the near-field model. In the 3D model, the use of a relaxation approach provides absorption for reflected waves from the structure. Further, a procedure is outlined to achieve/enhance the 3D model convergence. This is necessary in case of the development of artificial high velocities at water-air interface at the end of a short overlap (relaxation) zone for wave inlet (or near the boundary if only a wave inlet boundary condition is considered). The model system is developed using the OpenFOAM® framework. The overlap zone is implemented as an extension to the waves2Foam [1] toolbox.
Viscous Damping Effects on Heading Stability of Turret-Moored Ships
Authors: Zangeneh Razieh , Thiagarajan Krish P. , Urbina Raul , Tian Zhigang
Published: September 2014

Tankers used for offshore oil production and storage are kept in station by turret mooring systems, enabling the vessels to weathervane in the direction of the dominant environmental loads. These passive weathervaning systems have been observed in model experiments to be ineffective in swell-dominated long wave conditions. Over a range of wavelengths from 0.6 < λ/L < 2 (L – ship length), the vessel was observed to lose heading control in head sea condition, due to a pitchfork bifurcation that is initiated at a critical wavelength of 0.73L. A notable feature of poor heading stability is the existence of a stable equilibrium at a large heading angle (50–60°) with respect to the direction of oncoming waves. With lack of heading control, the ship motions, principally roll, can increase thus affecting onboard operations.

Time domain analysis conducted with no added viscous damping shows reasonable agreement with experimental data for the final heading angle. Further numerical tests reported in a previous paper by the authors showed that small to moderate viscous damping in sway and yaw did not alter the final heading, while the role played by viscous damping in other modes (heave, roll and pitch) needed further investigation. This paper reports on a parametric study on the heading stability of a turret moored tanker using time domain tools. Viscous damping is systematically varied in different modes of motion and its effect on final heading equilibrium is assessed. It is shown that effects of pitch damping are stronger than heave or roll, and can eliminate heading instability altogether.
Numerical Simulation of Solid Particle Erosion in a 90 Degree Bend for Gas Flow
Authors: Zhang Ri , Liu Haixiao
Published: September 2014

Solid particle erosion in piping systems is a serious concern of integrity management in the oil and gas production, which has been widely predicted by the numerical simulation method. In the present work, every step of the comprehensive procedure is verified when applied to predicting the bend erosion for gas flow, and improvements are made by comparing different computational models. Firstly, five turbulent models are implemented to model the flow field in a 90 degree bend for gas flow and examined by the static pressure and velocity profile measured in experiments. Secondly, the particle velocities calculated by fully coupling and one-way coupling are compared with experimental data. Finally, based on the knowledge of flow modeling and particle tracking, four classic erosion equations are introduced to calculate the penetration rates in a 90 degree bend. By comparing with the experimental data available in the literature, it indicates that the k–ε model is the most accurate and effective turbulent model for gas pipe flow; the fully coupling makes the simulation of particle motion closer to measured data; and the Grant and Tabakoff equation presents better performance than other equations.
Ship Motions of KCS in Head Waves With Rotating Propeller Using Overset Grid Method
Authors: Shen Zhirong , Carrica Pablo M. , Wan Decheng
Published: September 2014

The overset grid method has been implemented in the open source code OpenFOAM. The purpose of this work is to validate the overset code in OpenFOAM and demonstrate the capability and flexibility of overset grid approach to solve complex situations. Ship motions of KCS in head waves with and without rotating propeller are investigated using overset grid method in this paper. Two conditions are conducted. The first case involves the model without propeller advancing at a speed of 1.701 m/s, corresponding to Fr = 0.26 and Re = 6.82×106. Incident regular wave of wave length λ = 1.15Lpp and wave height Hw = 0.084m is adopted. A grid convergence study is conducted for the validation of overset grid method. In the second case, a rotating propeller is installed on the KCS model. The seakeeping characteristics of KCS model with rotating propeller in head waves are investigated numerically. The motion responses and propeller thrust and torque are analyzed and compared with experimental data.
Heave Induced Internal Flow Fluctuations in Vertical Transport Systems for Deep Ocean Mining
Authors: Hannot Stephan D. A. , van Wijk Jort M.
Published: September 2014

Deep ocean mining systems will have to operate often in harsh weather conditions with heavy sea states. A typical mining system consists of a Mining Support Vessel (MSV) with a Vertical Transport System (VTS) attached to it. The transport system is a pump pipeline system using centrifugal pumps. The heave motions of the ship are transferred to the pump system due to the riser-ship coupling. Ship motions thus will have a significant influence on the internal flow in the VTS.

In this paper, the influence of heave motions on the internal flow in the VTS for a typical mining system for Seafloor Massive Sulfide (SMS) deposits in Papua New Guinea is analyzed. Data on the wave climate in the PNG region is used to compute the ship motions of a coupled MSV-VTS. The ship motions then are translated into forces acting on the internal flow in order to compute fluctuations in the internal flow. In this way, the workability of the mining system with respect to the system’s production can be assessed.

Based on a detailed analysis of the internal flow in relation to ship motions, the relevance of a coupled analysis for the design of VTS is made clear. This paper provides a method for performing such analyses.
Assessment of Parameters Influencing Lateral Buckling of Deep Subsea Pipe-in-Pipe Pipeline System Using Finite Element Modeling
Authors: Haq M. Masood , Kenny S.
Published: September 2014

The operational requirements for subsea pipeline systems have progressed towards higher design temperatures and pressures (HTHP). To address flow assurance requirements, pipe-in-pipe systems have been developed.

For pipelines laid on the seabed, or with partial embedment, the potential for lateral buckling; in response to operational loads, external forces and boundary conditions, has become a major factor in engineering design. The effective axial force is a key factor governing the global lateral buckling response that is influenced by parameters such as internal and external pressure, and operating and ambient temperature. Other design parameters that influence lateral buckling include global imperfections or out-of-straightness, pipe/soil interaction characteristics and installation conditions. Global buckling reduces the axial load capacity of the pipeline that may impair operations and exceed serviceability limit states.

Results from a numerical parameter study on lateral buckling response of a subsea pipe-in-pipe (PIP) pipeline are presented. The parameters examined include pipe embedment, pipe out-of-straightness (OOS), soil shear strength, soil peak and residual forces and displacements, variation in soil properties distributed along the pipeline route, and external pressure associated with the installation depth. The observed pipe response was a complex relationship with these parameters and kinematic boundary conditions.
Full Scale Reeling Simulation Test of X65 HFW Linepipe
Authors: Sadasue Teruki , Igi Satoshi , Tajika Hisakazu , Oi Kenji , Yabumoto Satoru
Published: September 2014

Reel-lay method is widely recognized cost effective installation process for offshore pipelines. In the process of reel-lay, cyclic plastic strain is expected at pipelines due to reeling, unreeling, aligning and straightening. In order to maintain integrity of pipelines subjected to large bending deformation it is necessary to understand the bending deformability and change in mechanical properties of pipelines.

Advanced HFW (High Frequency electric resistance Welded) linepipe “MightySeam®” has superior low temperature toughness at seam weld and base material and has some advantages in application to offshore pipelines from a viewpoint of change in toughness due to pre-straining, coatings and long time exposure.

In this paper full scale reeling simulation tests of X65 HFW linepipe were conducted in order to study bending deformability and the change in mechanical properties. The tests were performed by bending pipe alternately to reeling former and straitening former with different radii. Girth welding were applied to test pipes in order to investigate effect of strain concentration around girth weld by strength mismatch or weld reinforcement. Small scale reeling simulation tests with/without aging were also conducted and the results were compared to those of full scale reeling simulation tests.

In full scale reeling simulation test, some strain concentration arose around girth weld by strength mismatch and local contact of weld reinforcement to former. Some ovalizations were advanced during tests, however local buckling could not be recognized throughout pipes even if strain concentration occur around girth welds. Tensile properties were changed proportional to last introduced plastic strain as a result of Bauschinger effect and work hardening at strain history. Low temperature toughness of base material and seam weld did not change significantly by pre-straining or aging.
A Study on the Application of Hybrid Panels to Ship Structures
Authors: Yoshikawa Takao , Takaoka Yukichi , Maeda Masahiro
Published: September 2014

The application of hybrid panels composed of polyurethane foam cores and steel faceplates to hull structures was studied.

First, the strength and collapse behavior of the panels were examined using three-point bending tests for hybrid panels with different core densities. Based on the experimental results, low-density core materials, such as those having a density of 300 kg/m3, are recommended for hybrid panels with respect to strength and weight. The structural strength of hybrid panels was investigated through a series of calculations utilizing FEA for beams clamped at both ends under uniform pressure by changing the thickness of the faceplates and core, and the length of the clamped span.

Taking account of the structural advantages of hybrid panel structures, two kinds of applications for hybrid panels are proposed.

One is in the inner bottom structure of bulk carriers. There is the possibility of improving the residual strength of hybrid panels after they are subjected to severe impacts. The dynamic characteristics of hybrid panels were investigated. It was confirmed that the residual deformation of hybrid structures after impact loading is less than that of ordinary stiffened structures of the same weight.

The other application is in the structural members of pressurized LPG (Liquefied Petroleum Gas) tanks. In utilizing hybrid panels in LPG tanks, the difference in rigidity between the core and skin produces a high peak bending stress in the vicinity of the clamped ends. In this paper, measures for the mitigation of this phenomenon are proposed. Also, the difference in rigidity between core and skin also produces weak points in hybrid panels such as the interface between the core and skin-plate. The applicability of hybrid panels in tank systems was examined by numerical methods utilizing the experimental results and it was confirmed that the shear and peel strength of the interface is more than sufficient.