bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
Improvement of Resistance and Wake Field of an Underwater Vehicle by Optimising the Fin-Body Junction Flow With CFD
Authors: Toxopeus Serge , Kuin Roderik , Kerkvliet Maarten , Hoeijmakers Harry , Nienhuis Bart 
Published: September 2014

To control underwater vehicles appendages such as rudders or fins are generally used. These appendages induce added resistance and deteriorate the quality of the inflow to aft control surfaces or propeller, due to the formation of amongst others horseshoe vortices.
In this paper, CFD is used to study the flow around a typical wing-body junction and to obtain insight in how to suppress the horseshoe vortex. For a generic submarine the impact of a range of modifications of the sail on resistance, propulsion and wake field is investigated. Design guidelines regarding the most promising modifications will be given. It will be shown that quite significant improvements of the resistance as well as the wake quality can be obtained by properly designing the junction between the appendage and the hull.
A Study on the Impact Load Acting on an FPSO Bow by Steep Waves
Authors: Hong Sam-Kwon , Lew Jae-Moon , Jung Dong-Woo , Kim Hee-Taek , Lee Dong-Yeon , Seo Jong-Soo 
Published: September 2014

Among offshore floaters used to develop offshore resources, FPSO and FSO have a storage function whereas semi-submersible, Spar and TLP have only production function. The floaters with the storage function such as FPSO and FSO are designed as the typical ship type concept compared to the other floaters with small water plane area.
In order to design the floaters for offshore resource development, it is needed to estimate the seakeeping performance under operating condition and survival conditions and then carry out the structural design based on seakeeping performance results. The environment conditions of 1yr, 10yrs, 100yrs or 1,000 yrs return periods are used based on the metocean data of the installation field to evaluate the seakeeping performance under operating and survival conditions. In general, the wave conditions with the maximum wave heights for each return periods are selected on each wave contour lines in the wave scatter diagram. Then the seakeeping performance is evaluated from the seakeeping model test.
However, it was observed that the wave with the pitch forcing period, where the wave length is close to the ship length, is more important than the wave with the maximum wave height after several accidents caused by the green water in Northern North Sea and Norwegian Sea. Therefore, it became a common practice to include not only the wave conditions with maximum wave heights for each return period but also the wave conditions with the pitch forcing period to evaluate the seakeeping performance for offshore development floaters. Ship type floaters such as FPSO are more likely to experience higher impact force due to the large frontal area accompanied by large heave and pitch motions in head sea and bow quartering seas. Recently, it was reported that in an accident in North Sea of UK sector, the damage at the bow of the FPSO is caused due to the steep waves. Afterwards, studies on the steep waves have been made in several institutes such as UK HSE.
In this study, the effect of the impact load (so called slapping load) by the steep waves acting on the FPSO bow is investigated throughout the model test. For measurement of the pressure and impact force on the frontal area, a bow-shaped panel was fabricated with the pressure and force sensors, and installed on the bow starboard side of the model FPSO. During the model test campaign, the impact load was investigated using the steep waves with Hw/λ greater than 1/16 in addition to the general wave conditions with maximum wave heights.
Consequently, it is confirmed in the model test that the impact loads acting on the FPSO bow are significantly increased with the steep waves (Hw/λ > 1/16) compared to the general wave conditions. Therefore, it is necessary to consider whether the steep waves are additionally included in the wave conditions to estimate the seakeeping performance and how to apply the impact loads acting on the FPSO bow from the steep waves in structure design.
Tidal Current Turbine Wake and Park Layout in Transient Environments
Authors: Arnold Matthias , Cheng Po Wen , Daus Philipp , Biskup Frank 
Published: September 2014

Due to orbital velocities of the waves, the characteristics of tidal current turbines change over time. Therefore the induction factor and subsequent the wake is time dependent. Within the present research this time dependency is investigated by using Computational Fluid Dynamics (CFD) with Virtual Free Surface (VFS) and Actuator Disc (ACD) models.
Based on this setup several different wave and current scenarios are simulated and analyzed with respect to the transient velocities in the turbine wake. Special respect is taken to the velocity undulations radiated by the changing apparent velocities in the rotor plane. These undulations move with the wake of the tidal current turbines and increase the wave loads on 2nd row turbines in a park.
This paper presents an efficient method for simulation of wave and park interactions and investigates dynamic turbine wakes under a large variety of parameters. Based on these simulations a suggestion for a tidal park design with respect to a balance of fatigue loads and power output is concluded.
Bilge Keel Forces and Vortex Shedding: A Numerical Analysis With OpenFOAM
Authors: Piehl Henry , el Moctar Ould 
Published: September 2014

The damping effectiveness of a bilge keel depends on the velocity of the flow and the roll period of the ship. The Morison equation defines the relation between these motion parameter and the forces acting on the bilge keel. Sarpkaya and O’Keefe published in 1996 an article with their results of several flow experiments conducted over a wide range of Keulegan-Carpenter period parameter. They provide the KC dependent drag and inertia coefficients obtained from the measured forces on a bilge keel and discuss the vortex pattern generated by the oscillating bilge keel.
In the present study the CFD code OpenFOAM was used to compute the flow around a bilge keel and the related forces. The numerical and experimental results are compared. Based on the test conditions a finite volume mesh was generated and the flow was computed with a transient, turbulent flow solver. In order to investigate the boundary layer on an oscillating wall and the dissipation of the vortex structures different turbulence models (kωSST, low Re and LES) were used. The experiments were conducted at zero forward speed. However, the computations were performed for different ship speeds.
Green Water on FPSO Predicted by a Practical Engineering Method and Validated Against Model Test Data for Irregular Waves
Authors: Schiller Rafael Vergara , Pâkozdi Csaba , Stansberg Carl Trygve , Yuba Douglas Gustavo Takashi , de Carvalho e Silva Daniel Fonseca 
Published: September 2014

This paper presents a series of numerical analyses performed with the potential theory-based Green Water engineer tool KINEMA3. KINEMA3 was designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in design load analysis. The purpose of the study presented herein is to validate KINEMA3 green water (deck overtopping) predictions in nonlinear irregular waves with results from model tests performed at the TPN (Tanque de Provas Numérico) laboratory at the University of São Paulo, Brazil. Comparisons are made for a selection of irregular wave cases, for two choices of anchoring conditions (free floating vessel and fixed vessel) and for three wave headings (180°, 225° and 270°: head, quartering and beam seas, respectively).
KINEMA3 statistical green water predictions present a general good agreement with observations from the TPN model tests for all wave cases, headings and mooring conditions. Overall, observed trends for occurrence of green water and standard deviation/maximum of relative wave height are successfully reproduced by KINEMA3. In agreement with model test results, it is predicted that green water occurs more frequently for a free floating vessel and for beam seas.
Additional comparisons between KINEMA3 predictions using different FPSO panel models (low-order and high-order models) present negligible differences with respect to green water estimates. The results presented herein demonstrate the robustness of the tool towards the prediction of green water for variable wave headings and sea states, and highlight the capability of KINEMA3 to be employed as an engineering-like tool for fast and multiple estimates of green water in early design studies.
This work is a part of the research project “Green Water and Wave Impact on FPSO” carried out for and in cooperation with PETROBRAS.
Green Water and Wave Impact on FPSOs in Santos Basin: Challenges and Prediction Tools
Authors: Schiller Rafael Vergara , Pâkozdi Csaba , Stansberg Carl Trygve , de Carvalho e Silva Daniel Fonseca 
Published: September 2014

Green water (water-on-deck) and subsequent wave impact is a strongly non-linear, random and complex phenomenon that represents an important factor to be considered in the design of moored vessels and vessels in transit. The Santos Basin, in southeast Brazil, is a new frontier for deep water oil production, where FPSO green water issues are expected to be more important. In this paper, we investigate new green water challenges associated with the Santos Basin. We employ an engineering prediction tool, KINEMA, designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in early design load analysis. We perform a sensitivity study to arbitrary wave directions and present preliminary results from a case study that would be illustrating for the Santos Basin.
Firstly, a comparison between numerical green water predictions and a set of earlier model test data for a Campos Basin case shows satisfactory agreement. A sensitivity study suggests that an empirical tuning factor, which is related to wave amplification and wave-structure interaction, should decrease with increasing wave heading. Then, a preliminary numerical investigation of the green water problem in Santos Basin wave conditions demonstrates that although the wave impact from the largest waves (S-SW) may be avoided by heading the vessel towards S-SW, other wave directions have to be taken into consideration. The results presented herein confirm that multi-directional wave heading is a green water challenge in the Santos Basin. Further studies that address this problem in detail, in special variations in the wave-structure interactions due to wave heading, and for actual particular Santos Basin FPSO’s, are recommended.