bluuebunny/crossref_metadata_2025_split huggingface dataset:
Importance Rating of Riser-Soil Interaction Effects
Authors: Voie Per Erlend , Skeie Geir , Bergan-Haavik Jens 
Published: September 2014

The fatigue life of risers loaded by wave kinematics, vessel movements, and vortex-induced vibrations, is one of the critical issues when designing floating production systems comprised of a large floating structure attached to the seabed by vertical tethers or mooring lines. It is especially difficult to estimate fatigue stresses due to the interaction between the seabed/soil and the riser because of the high non-linearity of soil response. Adding to the complexity the touchdown zone where the riser contacts the soil often proves to be the critical location for the fatigue life, since the maximum bending stresses usually occur in this part of the riser. Previous studies have also shown fatigue damage to be sensitive to soil stiffness. Although linear elastic soil models provide very useful insights about pipe-soil interaction, they cannot fully describe the complex interaction problem including: trench formation, non-linear soil properties, soil suction, detachment of the pipe from the soil, pipe re-contact with the soil and degradation of soil stiffness, which are evident from full-scale experimental testing and field surveys.
The background for this study is to explore the effect of going beyond the common linear soil model, calculate the riser-soil interaction effects in more detail and identify which interaction effects are the most important for riser response.
Based on consolidating knowledge from conference publications, joint development projects and bearing capacity theory a pipe-soil interaction model accounting for the seemingly most important interaction mechanisms is developed and implemented in ABAQUS. The importance of the many interaction effects is explored through sensitivity studies. Based on the importance rating recommendations are given on what level of model sophistication to choose for different applications e.g. fatigue analysis.
Modeling and Analysis of a 5 MW Semi-Submersible Wind Turbine Combined With Three Flap-Type Wave Energy Converters
Authors: Luan Chenyu , Michailides Constantine , Gao Zhen , Moan Torgeir 
Published: September 2014

Semi-submersible floating structures might be an attractive system to support wind turbines and wave energy converters (WECs) in areas with abundant wind and wave energy resources. The combination of wind turbines and WECs may increase the total power production and reduce the cost of the power.
A concept of a semi-submersible with a 5 MW horizontal axis wind turbine combined with three flap-type WECs is presented in this paper. The concept is named as Semi-submersible Flap Combination (SFC). The WECs of the SFC are inspired by an optimized bottom-fixed rotating flap-type wave energy absorber. Each WEC of SFC includes an elliptical cylinder, two supporting arms, a rotational axis and a power take off (PTO) system.
A time domain numerical modeling method for the SFC is presented. The numerical model is using the state-of-the-art code Simo/Riflex/Aerodyn. Linear rotational damping is introduced to model the effects of the PTO system. The choice of a PTO damping coefficient and of the mass of the elliptical cylinders has a significant effect on the power generated by the WECs. Such effects have been addressed and discussed in the paper through a sensitivity study.
On the Prediction of Fatigue Damage From VIV
Authors: Passano Elizabeth , Larsen Carl M. , Wu Jie 
Published: September 2014

Empirical methods for calculation of response from vortex shedding are based on a set of coefficients that determines response frequencies, excitation force and damping, but also how competing frequencies will appear in time and along a structure. It is easy to formulate a mathematical model for Vortex Induced Vibrations (VIV), but the key challenges are to find the necessary hydrodynamic coefficients and a model for how the active frequencies appear in time and space.
Since the original version of VIVANA was released more than ten years ago, new information has been become available through new test techniques, as well as from new methods for analysis of old tests.
In this study, recent re-examination of the results of the NDP 38 m tests is presented. The observed response behavior is compared to predicted VIV response and fatigue. The consequences of assuming that response frequencies will be active concurrently or consecutively are investigated and predicted response and fatigue are compared to results based on the measurements.
Another method that has provided valuable information has been inverse analysis, by which forces on a flexible beam are estimated from measured strains and/or accelerations. When forces are known, the underlying coefficients can be calculated from the standard equations.
Inverse analysis has been carried out from a set of experiments, and a new set of coefficients has been estimated for use in coefficient based programs such as VIVANA. Initial comparisons between measured and predicted response show that the new coefficients give an improved agreement with regard to amplitudes and frequency composition.
Extended Porosity Rate Function for Frost Heave
Authors: Abdalla Basel , Fan Chengye , Mckinnon Colin , Gaffard Vincent , Audibert-Hayet Annie , Coche Edmond , Eltaher Ayman 
Published: September 2014

Frost heave is a common phenomenon in the Arctic, where soil expands in the direction of heat loss due to ice lens growth upon freezing. It also occurs if a refrigerated structure is buried in unfrozen frost heave-susceptible soil, and thus special considerations are required when designing chilled or LNG pipelines in the Arctic. In the past decades, many theoretical and numerical methods have been developed to predict the frost heave of freezing soil. Among them, the rigid ice model, segregation potential model, and porosity rate function model are the most popular. These frost heave models work well in predicting the soil response during a pure freezing process, but none of these methods consider a thawing and consolidation of soil, which is the opposite but integrated process when the system undergoes the annual temperature cycle.
In this study, efforts are made to extend the porosity rate function to the thawing branch based on reasonable assumptions. With the extended model, a fluctuating surface temperature can be applied on top of the soil surface to simulate a continuous changing ambient temperature. The extended model is realized in ABAQUS with user defined subroutines. It is also validated with test data available in the public domain. As an application example, the extended model is utilized to simulate a chilled gas line buried in frost-susceptible soil to estimate its frost heave over a multi-year operation.
Effect of Anti-Wear Tape on Behavior of Flexible Risers
Authors: Zhou Chongyao , Ye Naiquan , Sævik Svein 
Published: September 2014

The service life of a flexible riser is often dominated by the metallic layers under cyclic bending loads, particularly the tensile armor layers. The effect of the anti-wear tapes is normally omitted during cross section modelling, where a plane-remain-plane assumption is usually used for stick condition. Significant differences have been observed between numerical analysis assuming plane surfaces remain plane and laboratory measurements studying the bending moment versus curvature for a flexible riser which has anti-wear tapes between the two tensile armor layers.
A new shear interaction algorithm has been developed in the numerical model to improve the modeling of the anti-wear tapes by taking the thickness and shear modulus of the anti-wear material into account. The impact of these parameters on the bending behavior of the flexible riser is demonstrated by comparing the numerical analysis results with the laboratory measurements.
Design Study of BOP Shear Rams Based on Validated Simulation Model and Sensitivity Studies
Authors: Tulimilli Bhaskar Rao , Naik Pramod , Chakraborty Arindam , Sawant Sourabh , Whooley Alan 
Published: September 2014

Blowout Preventers (BOP) are safety devices used to prevent uncontrolled flow of liquids and gases during a blowout. Blind Shear Rams (BSR) is one of the critical components of a BOP responsible for shearing the drill pipe and sealing the wellbore during a blowout scenario. Tests were conducted by shearing a drill pipe under non-flowing conditions to obtain the maximum shearing force, shape of sheared drill pipes, shearing time. A FE methodology has been developed to model the shearing process using Abaqus Explicit finite element solver. Simulations were performed to replicate the shop test and the results are compared with the shop test and found to be in good agreement. The current study uses a validated model for evaluating some of the challenges being faced by the BOP shear ram technology. These include drill pipe centralization in the well bore, shearing of a drill pipe subjected to axial tension, compression and buckling, and shearing in flowing well conditions. All these studies are performed and their effect on shearing process is discussed.
The effect of high velocity formation fluid through the drill pipe and annulus in the localized shearing region is also assessed separately by performing Computational Fluid Dynamics (CFD) simulations and it is found that the resistance offered by flowing fluid is not significant compared to the high pressure from accumulators required to shear the pipe. A shear ram design accommodating the results of the study is verified for increased efficiency of the shearing process. The study is conducted as part of a Technology Assessment Programs (TAP) for the Bureau of Safety and Environmental Enforcement (BSEE) in the areas of BOP stack sequencing, monitoring and kick detection.
Combination of Petroleum Correlations and Drift-Flux Approaches: A New Model for Two-Phase Flow Pressure Gradient Calculation for Horizontal and Slightly Inclined Upward Flowlines
Authors: de Melo Vieira Rinaldo Antonio , Garcia Artur Posenato 
Published: September 2014

One-dimensional single-phase flow has only one characteristic velocity, which is the area-averaged velocity. On the other hand, one-dimensional two-phase flow has several characteristics velocities, such as center of volume mixture velocity and center of mass mixture velocity.
Under slip condition, usually they are quite different. In a simple way, one may think that the petroleum correlations and the drift-flux model are an attempt to “adapt” the single-phase momentum equation for a mixture of more than one phase, where the several parameters in the single-phase equation are replaced by average-mixture ones. These two models use different considerations for this “adaptation”. For instance, for friction loss calculation, petroleum correlations use the mixture volume velocity while drift-flux models use the mixture mass velocity.
Normally, the volume velocity is higher than the mass velocity, and petroleum correlations may calculate friction gradients higher than the ones obtained by drift-flux models. This is very important, especially for horizontal and slightly inclined upward flows, where the friction pressure gradient is dominant.
This work compares the pressure gradient evaluated by these two models for horizontal and slightly inclined upward flowlines using available data found in literature. The comparison shows that, depending on the situation, one model gives better results than the other. Based on the results, a new approach for two-phase flow friction calculation is proposed.
The new model represents a combination of the approach used by the Petroleum Correlations and the Drift-Flux Model, using different characteristic velocities (volume, mass and a new one defined by the authors). The new model is very simple to implement and shows good agreement with the tested data.
Development of Hull Sizing System for Tension Leg Platform by Using Optimization Algorithm
Authors: Sugita Toshio 
Published: September 2014

Hull sizing system for tension leg platform (TLP) has been developed by using optimization algorithm. Hull sizing work is vital at the initial design stage of the offshore platforms. It is the driver towards a successful execution of a good design. In order to achieve the objective of producing an efficient and cost effective design, optimization of the hull configurations is very important. An optimized hull needs input from various criteria such as global performance, stability, strength, constructability, installation, etc. During the process of optimizing the design, it is inevitable that the hull configurations go through a number of iterations. Thus, the hull sizing program is developed by using optimization algorithm in order to solve multi-variable problem in the effective way in producing an efficient design in terms of performance, constructability and cost.
The principal dimension of the hull (column and pontoon size) and tendon size are the variables to be optimized. The objective function to be minimized is the sum of the of hull and tendon material weight. At each iteration of the optimization process, the program evaluates the global performance criteria, stability criteria, and simplified global strength criteria. The frequency-domain analysis method is used to perform the global performance analysis. The hydrodynamic coefficients are calculated by applying the boundary element method. Global strength analysis is carried out by using a beam model. Metocean data, water depth, riser information and topside information, such as weight, center of gravity and wind force coefficients, are input constant. A simulated annealing method is used for the optimization algorithm of the hull dimension and tendon size.
The program is being tested for a conventional TLP. The optimized hull shape provided in this program is in line with the existing TLP configurations. Henceforth, the program will be further studied and will be verified to improve its practical utility.
Numerical Simulation of Piggyback Risers Under Steady Current Loading
Authors: Srinivasan Vedanth , Agrawal Madhusuden 
Published: September 2014

With elevated interest in offshore drilling, transportation of production fluid to surface facilities are under heavy scrutiny. Particularly, design of marine risers either in standalone or in a piggyback configuration continues to dominate the focus of the research community in assessing the influence of hydrodynamic drag on its operation. In this study, full three dimensional Computational Fluid Dynamics (CFD) simulations were performed to estimate the flow induced drag on piggyback risers under steady current configurations. The turbulent structures generated in the flow domain are resolved using SST k-omega turbulence modeling approach.
Effect of flow velocities and circumferential position of the smaller cylinder with respect to the larger cylinder, were investigated on drag coefficient. Two different piggyback riser models, with varying cylinder diameters were considered. The predicted drag coefficients under a wide range of Reynolds number were in good agreement with the experimental data. The effect of diameter ratio of the two cylinders and the position of smaller cylinder were identified to play an important role in the generation of flow structures within the domain. Numerical simulations identify and capture key hydrodynamics interference such as drag reduction and vortex shedding patterns that are critical in the design of piggyback riser configurations. For example, the drag coefficient of the largest cylinder is lowest value when it is placed in the wake of the smaller cylinder and the drag on the small cylinder depends significantly on the diameter ratio of the cylinders and their relative position. Further, detailed discussions pertaining to vortex shedding patterns under various model configurations are elaborated. This study clearly demonstrated the applicability of numerical tools to gain insight into the hydrodynamic interaction between two cylinders placed under close proximity.
Performance Prediction of the Rotational Wave Energy Converter Using Single-Bucket Drag Type Turbine
Authors: Akimoto Hiromichi , Kim YongYook , Tanaka Kenji 
Published: September 2014

Because ocean wave propagates along water surface, wave energy resource is measured in the unit of line density (kW/m). It indicates that the output of a Wave Energy Converter (WEC) is proportional to its wave front width when we consider the scaling-up of the device. It will be a problem in the commercialization of a scaled-up WEC because the cost of device increases with size in a higher pace.
With the above consideration, the authors proposed a rotary type wave energy converter. It is a drag type vertical axis water turbine with its rotational axis lying horizontally on the water surface and in parallel to the wave front. To capture the orbital fluid particle motion in wave, the turbine is composed of a bucket and a streamlined counter weight. The device can be linearly extended in the direction parallel to the wave front to obtain the merits of scale. The WEC does not have massive components because the reaction torque of electric generation can be absorbed by a relatively small float system.
This paper provides the numerical test of the device in deep water wave condition. The dependencies of the output to the wave height and the submergence of the rotational axis are checked by the two-dimensional flow simulation.
Noise Footprint: A Proposal Within the Framework of FP7 AQUO Project to Define a Goal Based Approach Towards the Reduction of Underwater Radiated Noise From Shipping
Authors: Baudin Eric , Folegot Thomas , Andre Michel , Audoly Christian , Rizzuto Enrico , Benedetti Lanfranco 
Published: September 2014

The Marine Strategy Framework Directive has officially stated as soon as 2008 the anthropogenic noise due to shipping were to be mitigated. The policy makers, the yards and the ship owners still strongly rely on the expert studies and guidelines to find the appropriate methodology to assess and then mitigate the acoustic pollution impact shipping on the marine biota. To address this issue, the project AQUO “Achieve QUieter Oceans by shipping noise footprint reduction” (www.aquo.eu) started in October 2012 for 3 years. The AQUO project was built in the scope of FP7 European Research Framework. It involves 13 partners from 8 European countries, mixes academic experts, industry representatives from yard, classification society and other acoustic and bio-acoustic specialized bodies.
Addressing the anthropogenic noise pollution into the marine biota is an increasing concern which is logically paired with the increasing commercial maritime traffic. The IMO itself has recently issued a first draft guideline, to be followed up during the next MEPC, addressing this matter.
In parallel to the different achievements that are effective or in progress by standardization bodies or other delegated or assigned work group, the AQUO project aims to finally issue guidelines to be taken as methodological tools. The multi-disciplinary team of this project aims to comply with expectations from the different stakeholders.
First, an overview of the project is given. The objectives and the related project structure are detailed so as to better understand which axes are chosen and studied.
Secondly, it is here proposed to share the recent outcomes of AQUO project. The current status of applied knowledge, related legal decisions as well as standards empowerment are essential to identify the remaining needs and consequent expected efforts. Drawing first the background rationales the noise footprint concept is then detailed. The process followed towards the main objective of mitigating the anthropogenic noise from shipping will be partly revealed and completed by the expected future work to be achieved by 2015.
Effect of Wind Loads on the Performance of Free-Fall Lifeboats
Authors: Sauder Thomas , Croonenborghs Eloise , Fouques Sebastien , Berchiche Nabila , Reinholdtsen Svein-Arne 
Published: September 2014

The paper presents a model describing the launch of free-fall lifeboats from offshore structures in strong environmental wind.
Six-degrees-of-freedom numerical simulations of the lifeboat launch are performed using the free-fall lifeboat simulator VARUNA with a complete set of wind coefficients for the lifeboat. Those wind coefficients are obtained by CFD simulations validated against wind tunnel tests. The lifeboat launch simulations are then verified against time-domain CFD simulations of the whole launch in air until water entry.
It is shown by means of numerical simulations that wind-induced loads on the lifeboat have a strong influence on its kinematics until water entry, and subsequently on the acceleration loads experienced by the occupants, on the structural loads on the lifeboat, and on its forward speed after water exit.
It is concluded that the effect of wind-induced loads on the lifeboat performances should in general be investigated when establishing the operational limits for a given offshore installation.
Non-Conservative Consequences of “Conservative” Assumptions in Ship-Platform Collision Analysis
Authors: Storheim Martin , Amdahl Jørgen 
Published: September 2014

When designing offshore structures it is normally required to withstand a ship impact of a given magnitude without having progressive collapse of the structure. A common assumption when verifying a structure’s crashworthiness is to consider impact from a rigid vessel. This is argued to be a conservative assumption, as the struck structure will have to dissipate all energy. At a given time instant during a real collision, the weakest body will deform. Thus, if the actual strength of the platform is greater than that of the striking vessel, the rigid assumption will be wrong.
For impact between a platform and a supply vessel, contact can occur for both the stem (forecastle structure) and the bulb simultaneously. Analyses show that there is a large difference between the strength of the stem and the bulb structure for conventional supply vessels, both in terms of total force and more importantly the pressure exerted to the struck structure. Thus, while the bulb might be stronger than the struck object, the stem is normally crushed.
If a completely rigid vessel is assumed, the strain energy dissipation in the struck structure in way of the stem would be highly overpredicted, thereby lowering the estimate of the damage caused by the bulb.
This paper investigates the consequences of the rigid assumption by nonlinear finite element analysis. A modern large supply vessel design is checked. The differences between a rigid and a deformable vessel are highlighted, and non-conservative results identified.
Experimental and Numerical Investigation of Seakeeping Performance for Sea-River Ships With Different Hull Fullness
Authors: Kurchukov K. V. , Platonov V. G. , Katunin E. Yu. , Kuznetsov A. A. 
Published: September 2014

Commercial vessels under 5000 dwt, specifically sea-river vessels, constitute a substantial part of the world’s merchant fleet. These vessels are as a rule running between sea, estuary and river ports.
Mostly these vessels are restricted in operation by areas, seasons, distance from port of refuge, wind and wave conditions. In this connection the operational safety of such vessels, which are mainly engaged in carriage of oil products, is a critical issue.
This paper addresses integrated studies on seakeeping of sea-river vessels starting from the early design stage with preliminary CFD estimates and model experiments in wave basin up to the operational sea trials. The wave conditions for analytical and experimental studies are chosen to be as close as possible to the specific ship profile and expected area of operation.
Some conclusions regarding the effect of block coefficient on seakeeping performance of sea-river vessels are made, estimations and experimental data are compared for a ship with extremely large block coefficient and wider operation area (beyond coastal waters), as well as seakeeping performance data recorded at sea during operational voyage of the vessel on the Black sea and Mediterranean sea are given.