bluuebunny/crossref_metadata_2025 huggingface dataset:
Crush Behavior of Multilayered Pipes: Study of Pipe Integrity and Kinematic Assumptions
Authors: Gay Neto Alfredo , Franzini Guilherme Rosa , Martins Clóvis de Arruda , Pesce Celso Pupo , Malta Eduardo Ribeiro
Published: November 2013

The crush of multilayer pipes is an important problem in mechanics. Many types of devices may be used to apply radial forces to keep a pipe fixed when it is loaded in the axial direction. To address this problem, one could use analytical or numerical approaches, dealing with the local bending of each cross section of the pipe. For taking into account the material and geometric nonlinearities, a finite element model can be also used. This work applies a numerical 2D model to address the crush problem caused by shoes applying radial loads in three-layered pipes. The inner and the outer layers are metallic, and the intermediate one polymeric. All the materials are considered to be nonlinear, being the metallic materials elastic-plastic. The polymeric material is assumed to have a nonlinear behavior. The main objective of the work is to study the pipe integrity and discuss the kinematics of the pipe layers when crushed. Two distinct conditions are considered: (i) slippage and gaps formations are allowed between the layers or (ii) the three layers are ideally adhered to each other. The effect of parametric variations of friction between layers is analyzed. This kinematics discussion is addressed by increasing the number of crushing loads applied to the pipe, from two to sixteen loads, from which a limit is inferred. The results and conclusions may be employed as a basis for improving simpler analytical models to face the same problem.
Study of ISO 19901-3 Building Code Correspondence Factor for Eurocode 3
Authors: Neumann Nicolas
Published: November 2013

For topside structures ISO 19901-3 rely on national or regional building codes to derive the resistance of structural components. It is, however, required that the design resistance(s) of the building code is matched to the design resistance(s) of ISO 19902 through the use of a building code correspondence factor Kc. Recently, Kc was proposed in the literature to be taken as 0.95 for the European code for steel structures, Eurocode 3 (EN 1993). The present study does not support this value. Instead a value of 0.86 is derived. This lower value is based on the investigation of a topside project in the North Sea, and intends to cover for the stricter requirements to component resistance in ISO 19902 compared to Eurocode 3 for plastic and compact cross-sections.
Lazy Wave Catenary Risers: Scaling Factors and Analytical Approximation of the Static Stress Range in the Touchdown Zone
Authors: Quéau Lucile M. , Kimiaei Mehrdad , Randolph Mark F.
Published: November 2013

Offshore exploration and production of oil and gas continue to increase and move into ever deeper water. Steel catenary risers (SCRs) are one of the most cost effective type of risers in deep water. However, high sensitivity to vessel motions and hydrodynamic loading in the touchdown zone may limit the feasibility of SCR applications. In recent years, there has been a growing interest in the use of Lazy-wave catenary riser (LWR) due to their better fatigue performance in the touchdown zone through the damping effect of the buoyancy section.

The design of LWR involves numerous parameters that lead to a wide range of configurations. Each of these configurations needs to be evaluated against several criteria with respect to geometry, strength and fatigue for instance. This paper presents how tools recently proposed to improve the design of standard SCRs can be extended to benefit LWR applications. The dimensionless groups governing the structural response of LWRs are established in the aim of easing sensitivity analysis to key input parameters for LWR design, assisting experiments and reducing the number of numerical simulations. Moreover, the DAF (dynamic amplification factor) approach for dynamic response which has previously been explored for SCRs could also be used to simplify design of LWRs. As DAF relies on the analytical determination of static response, this framework shows that analytical boundary layer solutions in conjunction with the use of a Winkler type soil model can efficiently and accurately predict the static stress range of LWRs observed in the TDZ.
Temporary-Creep and Post-Creep Properties of Aquaculture Netting Materials With UHMWPE Fibres
Authors: Moe Føre Heidi , Endresen Per Christian , Jensen Østen
Published: November 2013

This paper presents test results on temporary-creep properties, recovery of strain post creep and post-creep tensile properties of a Raschel knitted netting material with a combination of UHMWPE and Polyester fibres. Specimens of the material were subjected to uniaxial loading over a period of 30 minutes, at a constant creep target load of 10–90 % of average tensile strength. The specimens were wet and tested in room temperature.

The netting structure experienced significant creep strain, with mean values in the range of 1.3–4.5 %, increasing with increased creep target load. Large proportions of the elongation accumulated during on-loading and creep were long lasting and possibly permanent. Tensile tests showed that for the highest creep target load, strength and elongation at break increased by 17 %.

The UHMWPE-netting experienced larger creep strains than PA6-netting for relatively large creep target loads (60–90 % of the average breaking strength), while creep strains were smaller for low loads. PA6-netting had a larger and faster recovery of strain post creep than the UHMWPE-netting, and the length and force at break were not significantly affected by the creep load history.
Fracture Resistance of Ship Longitudinal Members Including Fatigue Crack
Authors: Quéméner Yann , Huang Chien-Hua , Lee Chi-Fang
Published: November 2013

This study investigates the fracture failure of longitudinal members including cracks. Specifically, this study employs the failure assessment diagram methodology to assess the conditions of failure at the crack tip. Based on various crack configurations, this study establishes the analytical formulations of the crack-tip condition that are validated using finite element analyses. In addition, the material toughness is expressed in terms of crack-tip opening displacement. This study evaluates the failure stress of representative cracked members as a function of the crack length. This enables determining critical crack lengths corresponding to the maximum stresses derived from extreme loads. Finally, this study uses simplified fatigue crack growth analyses to characterize the critical crack length in terms of fatigue life. For members located in the deck and bottom regions, the critical crack lengths correspond to the end of the assessed fatigue life. Therefore, the fracture resistance of the longitudinal members is satisfactory as it will not cause the premature loss of the component. This study also provides analytical formulations for crack-tip conditions that could be employed in a reliability study linking fatigue crack growth and fracture under extreme loads.
Drilling Riser VIV Analysis Using Time Domain Code SimVIV
Authors: Sidarta Djoni E.
Published: November 2013

Drilling risers are often subjected to VIV from ocean currents, which may vary in directions over depth. VIV of drilling riser has commonly been analyzed using frequency domain code. This paper presents an alternative tool of analyzing VIV of drilling riser using time domain code SimVIV. With this tool it is possible to apply currents in varying directions over depth.

Measured currents and VIV responses of a drilling riser available in the literature are used in this study. The results of time domain analysis using SimVIV are compared against measured responses. The effect of current directionality over depth on drilling riser VIV response is also analyzed.
Crack Extension Effects on Welding Residual Stress in Fitness for Service Assessment
Authors: Rhee H. Chong
Published: November 2013

In the fitness for service assessment of a welded component with crack like defect, the current industry practices treat the welding residual stress in the same way as the applied operating stress in calculating the crack driving force. Although a growing crack should release the welding residual stress, the same initial residual stress is used in calculating the stress intensity factor solution regardless of the crack depth. Such procedures should result in too conservative solutions, since the crack extension effect on welding residual stress release is ignored in the crack driving force calculation. The present paper discusses the current state of the industry code and standard procedures for welded component defect assessment with a practical example problem solution, along with detailed discussions on the effects of crack growth on the welding residual stress. The objective of the paper is to motivate the industry to improve the code and standard procedures for the weld defect assessment. Also it presents a comparison of crack-like defect assessment results between the current industry procedure and one of newly proposed crack driving force calculation procedures for a crack growing in welding residual stress field, considering the welding residual stress release effects of growing crack. Recommendations for improving the industry code and standard procedures for the weld area defect assessment are provided based the investigation.
Physical and Numerical Modelling of Installation and Pull-Out of Dynamically Penetrating Anchors in Clay and Silt
Authors: Hossain Muhammad Shazzad , Kim Youngho , Wang Dong
Published: November 2013

Dynamically penetrating anchors (DPAs) are a recent type of mooring technology that have been shown to provide a cost-effective alternative to other forms of anchoring system in deep waters. This paper reports the results from a series of model tests undertaken to provide insight into the behavior of DPAs during dynamic installation and monotonic pull-out in normally consolidated clay and calcareous silt. The tests were carried out in a drum centrifuge at 200 g, varying the drop height and hence the terminal velocity. The pull-out angle at the mudline was also varied to encompass various mooring systems.

This paper also reports the results from finite element (FE) analyses simulating dynamic installation of anchors. The 3D large deformation FE (LDFE) analyses were carried out using the Coupled Eulerian-Lagrangian (CEL) approach in the commercial FE package Abaqus/Explicit. A parametric study was undertaken, exploring a range of anchor geometry in terms of diameter, tip angle and number and length of fins; impact velocity and soil strength.

For dynamic installation, two interesting aspects of the soil flow mechanisms were identified: (a) downward soil movement, concentrating around the advancing anchor, being reduced gradually with reducing penetration velocity and more rapidly with increasing number of fins and anchor projected area; (b) mobilisation of end bearing mechanism at the base of the anchor as well as fins, with the latter reduced significantly for shorter fins. The depth of anchor penetration increased as the drop height (and terminal velocity) increases and the soil strength decreases. For static pull-out, the mooring angle at the mudline influenced the pull-out mechanism and the capacity significantly. The anchor rotation and hence the anchor displacement required for attaining maximum capacity reduced as the angle increases.
Strain Based Design: Crossing of Local Features in Arctic Environment
Authors: Bartolini Lorenzo , Bruschi Roberto , Spinazzè Maurizio , Torselletti Enrico , Vitali Luigino
Published: November 2013

In arctic pipeline projects, seismic risk and differential settlements are common, whether local or distributed across long stretches. For buried pipelines, seismic hazards are generally classified as wave propagation hazard (WP) or permanent ground deformation (PGD) hazard. Below ground crossing of seismic faults has been the real challenge in a series of pipeline projects. STress Based Design (STBD) criteria has been used in the past. Application of this method is straightforward as simple linear elastic analysis is required to calculate the load effects in the specified conditions. In the assessment of the structural integrity of a pipeline, load effects are compared with allowable states of stress. Unfortunately, unsatisfactory design, both from economic and safety points of view, may result. StraiN Based Design (SNBD) is an attractive option in these situations.

The use of SNBD in pipeline technology has been widely discussed during the last decade, particularly for offshore applications. In many instances the offshore pipeline engineer can adopt SNBD to avoid onerous measures necessary to meet the traditional STBD criteria. First introduced to make allowance for crossing bottom roughness and harsh environments, more recently for High Pressure/High Temperature (HP/HT) applications, SNBD is currently used in a series of strategic project developments in North America and East Siberia, for both offshore and land pipelines crossing regions affected by ice gouging and geo-hazards from seismic activity such as land slides, active faults, soil lateral spreading due to soil liquefaction etc. Conditions for which SNBD are applicable, as well as permissible deformations in relation to line pipe material and safe operation of the pipeline in the long run, are of major concern.

In this paper, the following is discussed:

• Relevant hazards for arctic land and offshore pipelines such as ice scouring, permafrost thaw, frost heave etc..

• The design approach and design philosophy for Buried Pipeline Crossing active faults. In particular:

○ The Pipeline Crossing Layout of local features to minimize Load Effects;

○ Material and Steel Wall Thickness Selection vs. Crossing Location;

○ Pipeline Deformation Capacity (PDC) Assessment;

○ Pipeline Strain Demand (PSD) Assessment;

○ Pipeline Trench Design including Shape, Back-filling etc. vs. Pipe-Soil and Temperature Effects.
Calculation of Wave Height Dependent Force RAO’s on Submerged Bodies in Close Proximity to the Free Surface
Authors: van Winsen Ivan , Bokhorst Job S. , Huijsmans René H. M.
Published: November 2013

Diffraction calculations overpredict motion RAO’s and force RAO’s in cases where a small layer of water is present on top of a submerged body. This was observed after conducting model tests on a free floating SSCV Thialf and a captive submerged cylinder. A parameter study is done to get a better understanding of why diffraction calculations overpredict the forces in heave direction. From this study it was observed that unrealistically high water elevations existed on top of the cylinder causing the heave forces to be overestimated. A damping lid is therefore implemented to decrease this water elevation. On top of that, a new method is developed to be able to capture the dependency of the force RAO on the wave height. This method uses the instantaneous submergence height (the height of water on top of the submerged body) to determine the time averaged force RAO for a given wave height and wave frequency.
Residual Strength of Dented Stiffened Panels
Authors: Amante Diogo do Amaral , Chujutalli John Alex , Estefen Segen F.
Published: November 2013

The residual compressive strength of dented stiffened panels is investigated. Numerical simulations were performed using the finite elements program ABAQUS. The analysis is carried out in two steps. First the panel indentation damage is imposed using the ABAQUS explicit code program. After the indentation, a compressive load is applied and then the panel residual compressive strength is verified. Local damage was simulated by a dynamic collision due to an object fall. Therefore the distortions and the residual stresses due to the damage are both considered in the subsequent compression analysis. The aim of the work is to study the failure behavior up to and beyond buckling to evaluate the strength loss due to the damage imposed to the panel. The numerical models are represented by shell elements assuming finite membrane strains and large rotations, considering both geometric and material nonlinearities.
Improvements in the Prediction of the Characteristic Wave Pattern of Blunt Ships With Potential Codes
Authors: Will Johannes , Christiansen Jakob
Published: November 2013

Potential flow solvers have been and still are the work horses of computational wave resistance determination. Having matured over more then two decades they seem to have reached their limit of improvement. While the main focus of today’s software development lies on viscous flow solvers, the development of potential codes must not be disregarded, but they should instead be keep up to date with respect to the requirements of today’s and future ship building markets as well as hardware and software capabilities.
Prediction of Ship Response Statistics in Extreme Seas Using Model Test Data and Numerical Simulations Based on the Rankine Panel Method
Authors: Guo Bingjie , Bitner-Gregersen Elzbieta M. , Sun Hui , Helmers Jens Bloch
Published: November 2013

Earlier investigations have indicated that proper prediction of non-linear response due to non-linear waves is important for ship safety in extreme seas. Nonlinearities may increase significantly ship response in steep sea-states. The topic has not been sufficiently investigated yet, particularly when rogue waves are considered. A question remains whether the existing linear codes can predict nonlinear responses with a satisfactory accuracy and how large the deviations from linear predictions are. To indicate it, response statistics have been studied based on the model tests carried out in the Spanish basin CEHIPAR and the sea-keeping tank of the Technical University of Berlin (TUB), and compared with the results derived from numerical simulations using the DNV code WASIM. It is a potential code for wave-ship interaction based on 3D Panel method, which can perform both linear and nonlinear simulations. The numerical simulations with WASIM and the model tests including extreme and rogue waves have been performed on 3 different ship types: Chemical tanker, LNG tanker and a Cruise ship. The analysis includes both regular and irregular waves. Ship motions and bending moments have been studied. The effect of water depth on ship responses is also investigated. The study indicates that nonlinearities may have significant impact on extreme motions and bending moment induced by strongly nonlinear waves. Uncertainties related to the results are also discussed.
Wave Diffraction Forces on Offshore Wind Turbine Piles With an Octagonal Cross Section
Authors: Lim Serena , Tao Longbin
Published: November 2013

Traditional offshore wind turbines are normally supported by circular monopiles which are fabricated by rolling thick plates and welding them longitudinally. Due to the significant capital cost associated with the fabrication of such large circular cylinders, a new recommended innovative design to overcome such problem is introduced by replacing the circular cylinder with a vertical pile of octagonal cross-sectional shape. An efficient and very accurate semi-analytical/numerical solution based on the Scaled Boundary Finite Element Method (SBFEM) is developed to calculate the wave diffraction forces acting on the octagonal cylinders where no fundamental solutions known exist. Compared to the traditional Boundary Element Method (BEM), the SBFEM is free from the irregular frequency difficulty which means that it does not suffer from computational stability problems at sharp corners. The SBFEM solution also exhibits an enormous reduction of elements used to calculate the wave diffraction compared to the Finite Element Method (FEM), hence, a significant reduction in computational time. The SBFEM computation of the diffraction force demonstrates highly accurate results with a small number of surface elements. The presented method shows significant advantages, and is suitable for engineering applications especially the wave-structure interaction in the practical design.
Multidimensional Interpolation Filters Development for Risers’ Database Analysis
Authors: Gonçalves Ricardo Pereira , Lima Edison C. P.
Published: November 2013

This work presents the application of Artificial Intelligence Technology to a database that stores valuable information about structural analysis results of flexible pipes used in Oil and Gas Industry. The main objective is to create a low-cost computational tool capable to infer structural analysis results that can be used as a preliminary design for flexible pipes. This application uses Data Mining concepts for database preprocessing techniques, learning and prediction, multidimensional interpolation algorithms for knowledge gain. The usefulness and the reliability of this methodology are illustrated by means of numerical examples.
The Use of Crosshead Displacement in Determining Fracture Parameters
Authors: Walters Carey L. , Voormeeren Lars O. , Janssen Michael
Published: November 2013

In determining the fracture toughness of a test specimen, standards currently require either locally-measured load-line displacements or clip gage displacements. In order to measure these parameters, secondary sensors generally need to be installed and calibrated, which often comes at a higher cost. As crosshead displacements are automatically measured in most modern material test machines, use of the crosshead measurements alone would be less expensive. Although much criticism exists on the accuracy of this approach in determining CTOD values, the method can still prove sufficiently accurate for many applications. The current paper aims to assess the magnitude of the errors that arise from using the crosshead displacement in fracture mechanics testing of steels with the Single Edge Notched Bending (SENB) specimen geometry. The results show that for steels with sufficiently large toughness, the use of the crosshead displacement to calculate J and convert to CTOD produces results within 10% of calculating the CTOD directly with conventional techniques.
Model Testing and CFD Analysis of 2D Profiles Towards Offshore Applications
Authors: do Vale Machado Lucas , Fernandes Antonio Carlos , Bodstein Gustavo César Rachid
Published: November 2013

In this paper we present numerical and experimental work motivated by the study of a rudder profile with significant levels of lift that provides better performance for the maneuvering and stabilization of a ship. This is the so-called Schilling profile. The analysis of the two-dimensional subsonic steady flow over four profiles was carried out using computational fluid dynamics (CFD) tools with a κ-ω SST turbulence model. We consider three Schilling profiles with different thicknesses and the classical NACA 0015 profile, taken as a reference. Simulation results were compared to our experimental measurements at various angles of attack and two orders of magnitude of the Reynolds number, 5.45 × 104 and 1.09 × 105. The numerical results show general good agreement with experimental data and highlight the distinct behavior of Schilling profile.
Validation of the HVS Semisubmersible Global Performance by Model Tests
Authors: Kyoung Johyun , Yang C. K. , O’Sullivan Jim , Miliante Thiago
Published: November 2013

Validation of the HVS (Heave and VIM Suppressed) semi-submersible’s global performance is carried out through wave basin model tests and correlation with numerical analysis. As an application for a wet-tree floater, Technip designed the HVS semisubmersible to have reduced heave and VIM (Vortex Induced Motion) response. The HVS semisubmersible has blisters attached to the columns. The blister breaks the coherence of the vortex shedding along the length of the column and as a result reduces the VIM response. The redistribution of pontoon volume because of the blister reduces the heave excitation loading. The blister also provides adequate buoyancy for quayside integration.

To validate the improved hull global performance, the wave basin model tests were performed. In the tests, collinear hurricane environments of the Gulf of Mexico were considered for two different headings. Truncated mooring was applied to simulate prototype mooring system. Wind loading was applied by means of a dynamic controlled wind winch. Current was generated by a wire attached to a system of pulleys. The measured hull responses were correlated with MLTSIM, a Technip in-house time-domain nonlinear motion analysis program. Through the correlation with model test results, the improved HVS semisubmersible global motion in hurricane environments is validated.
CFD and Experimental Analysis of Current Forces of Pusher-Barge Systems
Authors: Grassi Ana Giulia F. , Lavieri Rodrigo S. , Pereira Adriano A. P. , Tannuri Eduardo A.
Published: November 2013

The water transportation of cargo is, among several possible modes of transportation, the most economically and environmentally efficient. Adding technology to pusher-barge systems increases the efficiency of this form of transport. It is not only limited to the design and manufacturing process, but extends to the training of commanders and crews. An efficient way to ensure this training is immersion in virtual scenarios that simulate reality. To have realistic response of the simulator to external commands and boundary conditions, it is necessary to understand the hydrodynamics of the pusher-barge system in its various working conditions. This paper presents results and discussions on the hydrodynamics of a river pusher-barge system based on computational results from CFD (Computational Fluid Dynamics) and experimental results from towing tank test using small scale model. Initially the coefficients of current forces acting on the vessel in the horizontal plane (surge, sway and yaw) obtained by the two methods are presented. Several current incident angles were analyzed in the following cases: two drafts (ballasted and full-loaded), three configurations of barges (1 × 1, 2 × 1 and 2 × 2) and two water depths. Next, the results are compared and the divergences due to small difference in geometry and scale effects are analyzed. The hypotheses formulated for possible causes of the divergences are grounded through mathematical and experimental models and simulations. To cancel these effects and perform validation of CFD, new simulations are presented with similar geometry to the model tested.
Relation Between Flow Velocity and Impact Pressure in a Green Water Flow
Authors: Ariyarathne Kusalika , Chang Kuang-An , Mercier Richard
Published: November 2013

Impact pressure due to plunging breaking waves impinging on a simplified model structure was investigated in the laboratory based on two breaking wave conditions: the wall impingement wave condition and the deck impingement wave condition. Pressure, void fraction, and velocities were measured at various locations on the deck surface. Impact pressure was correlated with the mean kinetic energy calculated based on the measured mean velocities and void fraction to obtain the impact coefficient. For the wall impingement wave condition, the relationship between impact pressure and mean kinetic energy is linear with the impact coefficient close to unity. For the deck impingement wave condition, the above relationship does not show good correlation, whereas the impact coefficient was found to be a function of the rate of pressure rise.
Maximum Wave Forces: Evaluation and Case Studies
Authors: Barbaro Giuseppe , Foti Giandomenico , Sicilia Carmelo Luca
Published: November 2013

To define and predict all forces exerted by sea storms on structures is necessary to give support to coastal and offshore engineering.

In this paper the horizontal force on offshore gravity platforms and on breakwaters is analyzed. Two cases study in two different locations are proposed, the first one concerns Italian coasts (Ortona), the second one is in the USA (Alaska). The results will be compared.

The purpose of this paper is to compare recent methods for calculating force on structures with the well-known Morison’s equation and the Goda’s model.

Wave climate was studied using the ISPRA (Istituto Superiore per la Protezione e la Ricerca Ambientale) and NDBC (National Data Buoy Center) measurements.
Motion Monitoring of T-Shaped Launching Barge With LW3-1 Jacket Dry-Towing From Qingdao to South China Sea
Authors: Luo Hanbing , Xie Peng , Zhang Zhi , Yu Dongchi , Li Huailiang , Wang Alan
Published: November 2013

T-shaped launching barge HYSY229 is applied to transport the LW3-1 jacket from Qingdao to South China Sea, which is the largest one in Asia up to now. Two tugs are used for the dry-towing. Because the shape of this barge hull is a little special, it is interesting to investigate the motion responses during the transportation. Meanwhile, real-time motion monitoring is very necessary and important for the owner from the view point of the safety of the dry-towing process. Signals of pitch, roll and accelerations of six degree motions of the barge are monitored during the transportation. The measurements lasted 29 days starting from 27th July to 25th August in 2012. The maximum peak-peak value recorded for roll and pitch motions is 1.64 and 2.38 degrees respectively, which is smaller than the threshold of design value. Moses code is adopted to predict the 1/3 roll and pitch motions of the barge. Results of numerical simulation and motion monitoring are compared in short term sea state using the environmental parameters observed. Fair well agreements are achieved.
Wet Vibration of Axially Loaded Elastically Supported Plates to Moving Loads: Aircraft Landing on Floating Airports
Authors: Datta N. , Thekinen J. D.
Published: November 2013

Dynamic analysis of thin rectangular elastically supported stiffened plates with axial loads is presented. A floating airport is modeled as a horizontal Kirchhoff’s plate, which is elastically supported at the ends; and is subjected to the impact of aircrafts landing and deceleration over its length. This sets the free-free-free-free plate into high-frequency vibration, causing flexural stress waves to travel over the plate. First, the beam natural frequencies and modeshapes in either direction are generated with these complexities. The Eigen value analysis of the governing differential equation is done, using the weighted summation of the product of the beam modes. The accuracy of the frequencies is compared with those from FEA studies. The radiation pressure on the bottom side of the plate is included to reduce the frequencies by the added-mass effect. The plate is then subjected to decelerating shock loads. The vibratory response is analyzed by the computationally efficient normal mode analysis. The amplification factor vs. the taxiing time of the moving load is generated.
A Model Scale Experimental Investigation on Vortex-Self Induced Vibrations (VSIV) of Catenary Risers
Authors: Rateiro Pereira Felipe , Gonçalves Rodolfo T. , Pesce Celso P. , Fujarra André L. C. , Franzini Guilherme R. , Mendes Pedro
Published: November 2013

Vortex Self-Induced Vibrations (VSIV) of a reduced scale model of a catenary riser are experimentally investigated. The riser model dynamics was assessed with a submerged optical motion capture system and significant VSIV were revealed as result of oscillatory vertical motion imposed to the top. Such a behavior recovers similar ones reported in the technical literature by other authors and resembles previous fundamental studies, by Sumer and Fredsoe, with rigid cylinders forced to oscillate in a plane and elastically mounted in the transversal direction. The present experiments are preliminary and pertain to a much more comprehensive experimental set, within a research project aimed at studying the nonlinear dynamic behavior of risers, through experimentally validated analytical and numerical, nonlinear reduced-order models.
Ocean Space Utilization Using Very Large Floating Semi-Submersible
Authors: Srinivasan Nagan , Sundaravadivelu R.
Published: November 2013

Very Large Floating Structures (VLFS) are highly specialized floating structures with variety of applications in the civil engineering of ocean. Their economic design is based on their hydro-elastic behavior due to wave environmental forces. VLFS are extra large in size and mostly extra long in span in the design feature for their applications. For that reason they are mostly modularized into several smaller structures and joined together in the site. The critical problem is the longitudinal bending moment of the long floating vessel in severe wave environment. With the result of that the present available VLFS designs become not economical for applications in hostile-ocean.

This paper presents ocean space utilization using an innovative VLFS with truss pontoon concept. The concept uses a strong deck with strong longitudinal beams to take care of the needed bending moment of the vessel for the survival, standby and operational conditions of the ocean environment. At the submerged bottom just above the keel-tank top, a simple open-frame truss-structure is used instead of a heavy shell type pontoon. The truss-pontoon provides the necessary flow transparency for the reduction of the wave exciting forces and consequently reduces heave amplitude of motions and the vertical acceleration. Each individual columns of the truss pontoon semi-submersible is tuned to have heave-period over 22 sec, independently, such that minimum hydrodynamic-motions are obtained for the overall structure.

The VLFS is designed with minimum heave for the extreme storms unlike the conventional column stabilized semi-submersible unit with conventional pontoon. The paper proposes a new VLFS concept which is feasible for applications in harsh environment. Most importantly cost effective VLFS is achieved. This paper presents the details of the VLFS design, stability, motion, and experimental verification from the physical wave-tank with the scaled-down model. At the end of the paper, a few comprehensive example applications are illustrated.
Motion of OC4 5MW Semi-Submersible Offshore Wind Turbine in Irregular Waves
Authors: Shin Hyunkyoung , Kim Byungcheol , Dam Pham Thanh , Jung Kwangjin
Published: November 2013

The interests in new and renewable energies increase sharply while our world suffers from environmental pollution and energy shortage. Governments and organizations throughout the world have tried to develop those energies to reduce pollution and solve energy crisis. In this study, we carry out a 1:80 scale model test and full scale numerical analysis of the OC4 5MW semi-submersible offshore wind turbine system designed by DeepCwind project. The purpose of this model test and numerical analysis is to predict and evaluate its motion in irregular waves.
Research on the Optimization of the Offset and the Power Consumption for a DP Assisted Mooring System
Authors: Wang Hongchao , Wang Lei , Liu Hanlin
Published: November 2013

DP assisted mooring system is a new positioning system including mooring system and dynamic positioning system. In this paper, two measures are proposed to reduce the offset and the power consumption of a generic semi-submersible platform which is equipped with a DP assisted mooring system during operation. One is to tighten the windward mooring lines and slacken the leeward mooring lines, the other is to reduce or cancel the forbidden angles of the thrusters adjacent to the failed thrusters. Given that the two measures can both reduce the offset and the power consumption of the semi-submersible unit, it is suggested to combine the two measures together to obtain better positioning accuracy. This paper is helpful to engineering practice.
Fatigue Reliability Evaluation of Marine Risers Under Vortex Induced Vibration
Authors: Khan Rizwan A. , Ahmad Suhail
Published: November 2013

Depleting oil reserves in shallow waters, off-shore oil fields are opening the avenues of new ventures in deep sea conditions. A marine riser is a major component of an offshore drilling and production system that are either fixed or floating in nature. Deepwater risers are quite long and significant currents usually excite natural bending mode that is much higher than the fundamental bending mode. In ultra deep environment currents usually change in magnitude and direction with depth, thereby inducing possibility of exciting multiple modes of the riser vibration due to VIV. Vortex induced vibration analysis has been carried out of a long marine riser in a probable deep sea location. To improve the understanding under deepwater harsh environments, the behavior of the riser under these forces is thoroughly investigated. 3D Nonlinear dynamic analysis of riser is obtained in the time domain using finite element software package ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue reliability analyses of riser. Uncertainty modeling, especially of fatigue crack growth parameters, is undertaken using bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using Monte Carlo Simulation. The bi-linear crack growth models are found to lead to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has been thoroughly investigated. These findings implicate inspection schemes for components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment.
A Conceptual Framework for Assessing the Potential of Ocean Mining Sites
Authors: Elosta Hany , Shan Shiliang , Kudla Nicole L. , Yang Kyung-Kyu
Published: November 2013

Ocean mining is considered to be the new offshore frontier and has been the center of research and commercial focus over the past few years. The further development of the ocean mining industry posts challenges in many fields including engineering, economics, environment, law, logistics and supply chain. This research aims to understand the challenges and link these fields by developing a framework for assessing the potential of ocean mining sites. Seabed resources and associated exploration and exploitation technologies are reviewed. Based on this review, it identifies the most promising ocean mining sites, the massive sulphide deposits in inactive hydrothermal vents, along the oceanic ridge in the Exclusive Economic Zone. An online survey is conducted to obtain a broader academic and industrial view on ocean mining. The world’s first commercial ocean mining project developed by Nautilus Minerals Inc. is also analyzed as a case study. Based on the seabed resources review, online survey and case study, the major challenges in ocean mining are presented, covering engineering systems, environmental risk mitigation, economic feasibility, law, logistics and supply chain.
Linear and Nonlinear Sectional Loads With Potential and Field Methods
Authors: von Graefe Alexander , el Moctar Ould , Oberhagemann Jan , Shigunov Vladimir
Published: November 2013

A Rankine source method is applied to predict linear and weakly nonlinear sectional loads of a modern container ship. The method uses solution in the frequency domain, linearised with respect to wave amplitude about the nonlinear steady flow due to forward speed, which accounts for the nonlinear free-surface conditions, ship wave and dynamic trim and sinkage. Weak nonlinearity of the sectional loads in waves (e.g. hogging-sagging asymmetry) is taken into account by pressure extrapolation and integration up to the estimated actual water line. The sectional forces obtained with this method are compared with the results of other methods, including (1) linear Rankine panel method, where flow due to waves is linearised about the double-body flow, (2) linear zero-speed Green function method with correction for forward speed, (3) fully nonlinear simulations based on field-based solution of Reynolds-averaged Navier-Stokes (RANS) equations and (4) model tests. Comparison with RANS solution and model tests shows, that the proposed method can accurately predict sectional loads for small to moderate wave heights.
Improving 3-D Variational Stereo Reconstruction of Oceanic Sea States by Camera Calibration Refinement
Authors: Shih Ping-Chang , Gallego Guillermo , Yezzi Anthony , Fedele Francesco
Published: November 2013

Studies of wave climate, extreme ocean events, turbulence, and the energy dissipation of breaking and non-breaking waves are closely related to the measurements of the ocean surface. To gauge and analyze ocean waves on a computer, we reconstruct their 3-D model by utilizing the concepts of stereoscopic reconstruction and variational optimization. This technique requires a pair of calibrated cameras — cameras whose parameters are estimated for the mathematical projection model from space to an image plane — to take videos of the ocean surface as input. However, the accuracy of camera parameters, including the orientations and the positions of cameras as well as the internal specifications of optics elements, are subject to environmental factors and manual calibration errors. Because the errors of camera parameters magnify the errors of the 3-D reconstruction after projection, we propose a novel algorithm that refines camera parameters, thereby improving the accuracy of variational 3-D reconstruction. We design a multivariate error function that represents discrepancies between captured images and the reprojection of the reconstruction onto the images. As a result of the iteratively diminished error function, the camera parameters and the reconstruction of ocean waves evolve to optimal values. We demonstrate the success of our algorithm by comparing the reconstruction results with the refinement procedure to those without it and show improvements in the statistics and spectrum of the wave reconstruction after the refinement procedure.
Development of a Fatigue Life Assessment Tool for Pipelines With Local Wrinkles
Authors: Bakhtyar F. , Kenny S.
Published: November 2013

Pipelines may be subject to ground movement events or external interference that imposes axial and moment loading into the pipeline. This system demand may cause localized deformation mechanisms to develop, that may be observed as local wrinkling or buckling of the pipe wall. The local buckle amplitude may increase with continued external loading and may fracture due to low cycle fatigue failure caused by operational conditions.

There exists limited data and engineering guidance on the mechanical performance of energy pipelines with a local wrinkle or buckle. The literature suggests the fatigue service life can be significantly reduced by the presence of local wall deformation mechanisms.

In this study, continuum numerical modelling procedures are developed to assess the influence of pipeline damage in the form of a local wrinkle or buckle on the low-cycle fatigue life. The simulation tool is calibrated from the available literature and a parametric study is conducted to examine the influence of wrinkle bend radius, pipe wall thickness, cyclic displacement amplitude, material grade and constitutive models on the pipe mechanical performance.
Reliability Evaluations of an Offshore Platform With Partial Porous Cylinders due to Wave and Seismic Forces
Authors: Park Min-Su , Jeong Youn-Ju , You Young-Jun , Park Jae-Hyun
Published: November 2013

In the present study, the partial porous cylinder, which is composed of a porous part located near free surface and a rigid part bounded top and bottom by impermeable end caps, is suggested to reduce the effect of wave forces. In order to calculate the wave force acting on the partial porous cylinder the fluid domain is divided into three regions, and the scattering wave in each fluid region is expressed by an Eigen-function expansion method. Applying Darcy’s law to the porous boundary condition, the effect of porosity can be simplified. Using the wave and the seismic forces, the dynamic response evaluations of the offshore platform with partial porous cylinders are carried out through the modal analysis and the substructure method based on the effect of soil-structure interaction. The displacement and the bending stress at critical structure members are computed using the Monte Carlo Simulation (MCS). Using the reliability index based on the results from MCS, the reliability evaluations of the offshore platform with partial porous cylinders are examined.
An Auxiliary Thruster for Free-Running Model Ship Test
Authors: Tsukada Yoshiaki , Ueno Michio , Miyazaki Hideki , Takimoto Tadanori
Published: November 2013

The free-running model ship test is an important measure to investigate into ship performance and response in various situations. Its basis is the Froude’s similarity law. Since Reynolds number remains quite different between model ships and full-scale ones, phenomena concerning viscosity cannot be similar.

One of the most specific features related to the viscosity is the friction resistance and thus propeller load that differs to a large extent between model ships and full-scale ones. This difference affects torque and thrust responses in waves and wind, and also rudder effectiveness or manoeuvrability.

The authors have developed a prototype of auxiliary thruster that assists free-running model ships’ propeller. The auxiliary thruster can control its forward force and adjusts the model ship propeller load to arbitrarily time varying target values. The prototype consists of a duct fan, a load cell mounting the duct fan on it, an amplifier for the duct fan, and a PC. The PC controls the auxiliary thrust, or forward force generated by the duct fan, using the model ship speed and the force data measured by the load cell.

This report presents the prototype of auxiliary thruster and its trial test applied to a free-running model ship to study the effect of propeller load on manoeuvrability. The trial test clarified how the auxiliary thrust or the propeller load affects the model ship responses to steering. Theoretical calculations simulating the effect of propeller load corresponding to the trial test confirmed these effects. Applicability of the auxiliary thruster to other free-running model tests is also discussed.
Modeling of Two-Phase Oil/Water Flow in Horizontal Pipeline Using CFD Technique
Authors: Pouraria Hassan , Paik Jeom Kee , Seo Jung Kwan
Published: November 2013

In spite of the importance of the flows of two immiscible liquids in diverse range of process, the existing literature does not cover this topic satisfactorily. In the present study, numerical modeling of dispersed oil-water flow through horizontal pipeline has been carried out using Eulerian-Eulerian approach. Three different turbulence models namely the standard k-ε, RNG k-ε and Reynolds Stress Model (RSM) have been used in this study to identify the best model. Numerical solution was performed using FLUENT 6.3.26 and the results regarding the distribution of volume fraction were compared with published experimental and numerical data. According to the present numerical results, the Reynolds Stress Model can predict the distribution of phases better than the used two-equation turbulence models in this study. Furthermore, it was observed that the present model could predict the trend of pressure drop at different water cuts better than the commonly used homogeneous model. However, the accuracy of the results is not much better than the homogeneous model.