bluuebunny/crossref_metadata_2025 huggingface dataset:
Steel Lazy Wave Riser Design for Semi-Submersible in Harsh Environment
Authors: Cheng Jingyun , Cao Peimin
Published: September 2014

Deep draft production semi-submersible with steel lazy wave risers (SLWRs) has been studied for the 2,625ft water depth in harsh environment. The design challenges and feasibility of steel catenary risers (SCRs) for semi-submersible at relatively shallow water and harsh environment are discussed. The benefits of using SLWRs to improve riser strength and fatigue performance are presented. Due to the complexity of SLWR geometry, a systematic configuration approach is introduced to achieve the desired riser performance target. A comparison study on fatigue and strength performance of various riser configurations is performed. The assessment provides design guidance for the optimal solution of the integrated hull, mooring and riser system. It concludes that deep draft production semi-submersible with SLWRs can be a feasible and cost effective solution for field development at water depth range from 2,297ft to 3,281ft in harsh environment.
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.
Simplified Model for the Weight Estimation of Floating Offshore Plant Using the Statistical Method
Authors: Roh Myung-Il , Seo Seong-Ho , Shin Hyun-Kyoung , Ku Nam-Kug , Ha Sol , Kim Ki-Su
Published: September 2014

The weight information of a floating offshore plant, such as an FPSO, is one of the important data to estimate the amount of production material and to determine the production method for its construction. In addition, the weight information is a key factor which affects in the building cost and production period of the offshore plant. Although the importance of the weight has long been recognized, the weight has been roughly estimated by using the existing design and production data, and designer’s experience. To improve this task, a simplified model for the weight estimation of the offshore plant using the statistical method was developed in this study. To do this, various past records to estimate the weight of the offshore plant were collected through the literature survey, and then the correlation analysis and the multiple regression analysis were performed to develop the simplified model for the weight estimation. Finally, to evaluate the applicability of the developed model, it was applied to some examples of the weight estimation of topsides of the offshore plant. The results showed that the developed model can be applied the weight estimation process of the offshore plant at the early design stage.
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.
Challenges With Oil Spill Risk Assessment in Arctic Regions: Shipping Along the Northern Sea Route
Authors: Bambulyak Alexei , von Bock und Polach Rudiger U. Franz , Ehlers Sören , Sydnes Are
Published: September 2014

Arctic regions, and thus ice-covered waters, are continuously getting higher in the national and international political agenda. The world demand in energy resources and the need in development of new transportation routes are pushing industrial activities up North where we see prospects and expectations on one side, and gaps and challenges on the other. Industrial development of the new geographic area is complex, and the priority in transportation is given to marine shipping. For the recent years, transit cargo shipping through the North Eastern Passage or the Northern Sea Route (NSR) increased more than 10 times from 0.11 million tons (4 passages) in 2010 to 1.36 million tons (71 passages) in 2013. Although, the numbers are small compared to global cargo shipping, the sensitive Arctic environment requires the establishment of a oil spill recovery system as well as risk mitigation measures. This, in turn, requires the preceding development of a risk assessment methodology for oil spills in ice-covered waters. Therefore, this paper presents the challenges involved in Arctic shipping along the NSR and identifies the knowledge gaps with respect to environmental risk assessment of accidental oil spill.
Study of Ship-Ice Collision on Ice Breaker ARAON
Authors: Kim Sungchan , Nho Insik , Lee Takkee , Choi Kyungsik
Published: September 2014

The interaction between a ship and sea ice is a complex process depending on the ice properties, the ice geometry and the relative velocity between the ship and the ice. The effect of important parameters such as ship speed and ice thickness on the impact force are studied by means of finite element model. Idealized ice element types are applied to finite element model in order to survey the impact force and the structural response of icebreaker ARAON subjected to sea ices. Interaction behaviors obtained by finite element model considering the varying parameters are also discussed to compare the numerical results with the design data of ARAON.
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.
Free and Forced Vibration Analysis of an Idealized Compliant Tower With Superstructure, due to Current Loads, Wave Excitation, and Earthquake Impulses
Authors: Ankit  , Datta N.
Published: September 2014

A compliant tower (CT) is modeled as a partially dry, partially tapered, damped Timoshenko beam with the superstructure modeled as an eccentric tip mass, and a non-classical damped boundary at the base. The foundation is modeled as a combination of a linear spring and a torsional spring, along with linear and torsional dampers. The mean empty space factor due to the truss type structure of the tower is included. The effect of shear deformation and rotary inertia are included in the vibration analysis; with the non-uniform beam mode-shapes being a weighted sum of the uniform beam mode-shapes. The weights are evaluated by the Rayleigh-Ritz method, using the first ten modes and verified using Finite Element Method (FEM). The superstructure adds to the kinetic energy without affecting the stiffness of the beam, thereby reducing the natural frequencies. The weight of the superstructure acts as an axial compressive load on the beam, reducing its frequencies further. Kelvin-Voigt model of structural damping is included. A part of the structure being underwater, the virtual added inertia is included to calculate the wet natural frequencies. The CT is first subjected to steady current loads of a given velocity profile. The static deflection and overturning moment is estimated for current loads. The CT is then studied for wave excitation at various seas states. Morrison’s equation and Pierson-Moskowitz Spectrum are used to derive the forces for different sea states. The forced vibration analysis of the structure is done via Rayleigh-Ritz method and verified using FEM. The maximum horizontal deflection and shear stress of the base of the superstructure, and the normal/shear stresses at the foundation are analyzed. Finally, the CT is subjected to earthquake excitation, modeled as an arbitrary horizontal impact excitation at the base. The above forced vibration analysis is repeated.
Potential of Michell’s Integral for Ship Wave Resistance
Authors: Tsubogo Takashi
Published: September 2014

The Michell’s integral (Michell 1898) for the wave making resistance of a thin ship has not been used widely in practice, since its accuracy is questioned especially for a Froude number range about 0.2 to 0.35 for conventional ships. We examine calculations by Michell’s integral for some ship forms, e.g. a parabolic strut, Wigley hull and so on. As a result, one reason of the disagreement with experiments is revealed. It must be the gradient of hull form in the depth direction. Then a thin ship theory including the hull gradient effect in the depth direction is presented, which improves slightly in low Froude numbers but needs more computing time than Michell’s integral so as to solve a boundary integral equation.
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.
Reliability Assessment Approach for DCV Aegir Pipeline Installation Analyses
Authors: Karjadi Erwan , Smienk Henk
Published: September 2014

Heerema Marine Contractors (HMC) is entering a new era of pipe laying with the new Deepwater Construction Vessel (DCV) Aegir. This vessel is designed to be able to reel/J-lay pipelines for a wide range of pipe dimension and water depth combinations.

To define the limit of installation workability windows, the pipeline installation analyses (reeling or J-lay method) during the project engineering preparation phase are normally performed based on the consideration that a combination of several “worst case” scenarios will occur at the same time during the installation event. The worst case scenarios are assumed in terms of pipe resistance (geometry/property), positioning of the vessel/equipment, environmental loads, etc. This method of calculations can be considered as the most practical and safe approach.

However, as an accumulation of conservative assumptions is inherently being made within this approach, it can lead to a situation that the pipeline cannot be installed or lead to insufficient workability window for pipeline installation operation. Another shortcoming of this worst case scenario approach is that we are not able to quantify the probability of failure for a certain pipeline installation scenario. The reliability analyses and assessment for pipeline construction/installation as described in the DNV-OS-F101 code [1] can be used as an alternative. The assessment can lead to some relaxations of the pipeline installation workability in a safe manner whilst accepting some level of the risks.

The purpose of this paper is to present the development of reliability assessment approach for pipeline installation analyses for the DCV Aegir. One of the important steps of the development is the setup of a pipeline database based on the as-built pipeline data from HMC’s past projects. The database can be used to estimate the typical distributions of the pipe dimension and properties as input for the reliability analyses.

Three examples are given in this paper, two are related to the reeling pipeline analysis with standard pipe ends and counterbored pipe ends (First Order Reliability Method FORM and Monte Carlo approach) and another example is related to J-lay pipeline installation analysis. The results of the assessments are correlated with the DNV guideline for the acceptance of nominal target probability of failures against the safety classes.
Full-Scale Measurements of Wave and Current Loads on Splitter Fairings
Authors: Spencer Don , Liapis Stergios , Constantinides Yiannis , Islam Mohammed , Edwards Zachary
Published: September 2014

This paper presents measurements of the mechanical loads that splitter fairings on vertical and inclined risers will experience while in the wave zone or due to current drag. A 21″ pipe was utilized for the measurements, which corresponds to prototype size for a production riser and a 1:2.5 scaled model for a 54″ drilling riser. The program had three objectives, (a) to determine the nature of wave and current loading on a riser segment that was fitted with a fairing to provide sufficient internal strength and stiffening; (b) to determine the wave and current loading on the fairing connection system to assist in designing reliable latching systems, and (c) to investigate if the measured loading on the fairings from forced oscillation experiments can be used to simulate loading resulting from wave motion.

Of primary interest was the effect of wave loading on the fairings in prototype or near prototype conditions. One significant impediment to conducting such experiments in a model wave basin was the very limited ability of the basin to generate full scale wave in terms of period or height. However the horizontal component of the oscillatory wave velocity can be simulated by oscillating the fairings at prototype wave periods and amplitudes to obtain the same relative flow condition. One of the fundamental questions that remained prior to the research was whether the novel forced oscillation technique could actually replicate the real world wave induced loads and some experiments were directed at confirming this.

While exploratory in nature, these forced oscillation experiments demonstrated that the test apparatus and methodology were able to replicate the corresponding measurements from the wave experiments, thus providing reliable data to assist in predicting hydrodynamic loading on fairings due to current, forced oscillatory motion, and waves. The basin carriage was successfully used to force the fairings in a prescribed oscillatory motion. The analysis of the measurements of the forced oscillation experiments showed that the inertial force correlated well and was linearly proportional to acceleration while the viscous force was a linear function of velocity. It was demonstrated that the forced oscillation experiments could provide reasonably good estimates of the global loading resulting from wave action. This implies that the experimental technique of replacing wave motion with forced oscillation can be used for design. As a result, prototype or near prototype scale models of fairings can be tested in wave conditions well beyond the capability of model basins. While the global loads due to waves could be predicted from the forced experiments it appeared the latching load were about 70% higher while in waves relative to those recorded during the forced oscillation experiments. This discrepancy could be attributed to free surface effects.
Analysis of Autonomous Underwater Gliders Motion for Ocean Research
Authors: Gao Lei , He Ran , Li Yangge , Zhang Zhiguo
Published: September 2014

Underwater gliders, a type of highly efficient underwater vehicle which uses gravity and buoyancy for propulsion, has been studied for a long time during the last 3 decades. This paper describes the development of the principle dynamic models of a general underwater glider, including hydrodynamic forces and buoyancy effects. The numerical analysis model was developed for the underwater glider motion. Dynamic forces equations including the model’s buoyancy, gravity, and hydrodynamic forces in gliding are derived. Gliding velocities with changes of the net buoyancy are compared. The numerical method was used to calculate the hydrodynamics coefficient of the glider. Dynamic characteristics of the Seaglider and SLOCUM have been used as validation objects for the numerical method. The glide angle is merely the function of the lift/drag ratio and has no relation to the net buoyancy. The gliding velocity would increase when the buoyancy increases.
Investigation of the Influence of Screw Connections in Drill-Strings on the Propagation of Torsional Waves With Respect to Advanced Stick-Slip Controllers
Authors: Kreuzer Edwin , Krumm Ludwig , Pick Marc-André
Published: September 2014

Drill strings are used in the oil and gas industry to search for oil, gas, and geothermal resources and form extremely slender structures which makes them very sensitive to torsional and other vibrations. In order to immensely reduce torsional vibrations along the whole string, a wave based control method was developed at our institute. Numerical simulations and tests at an experimental setup showed very good results, but the implementation in a real drilling rig has not yet been taken place. One apparent difference in a real drill string will be the assembly of many rather short drill pipes, which is unregarded in conventional models and our small test rig. This might lead to improper behavior of our wave based control mechanism and shall be investigated is this paper. We present a model that accounts for a discontinuously built drill string and show the consequences for our advanced control method via numerical simulations.
A Structural Strain Method for Fatigue Evaluation of Welded Components
Authors: Dong Pingsha , Pei Xianjun , Xing Shizhu
Published: September 2014

In this paper, a new structural strain method is presented to extend the early structural stress based master S-N curve method to low cycle fatigue regime in which plastic deformation can be significant while an elastic core is still present. The method is formulated by taking advantage of elastically calculated mesh-insensitive structural stresses based on nodal forces available from finite element solutions. The structural strain definition is consistent with classical plate and shell theory in which a linear through-thickness deformation field is assumed a priori in both elastic and elastic-plastic regimes. With considerations of both yield and equilibrium conditions, the resulting structural strains are analytically solved if assuming elastic and perfectly plastic material behavior. The formulation can be readily extended to strain-hardening materials for which structural strains can be numerically calculated with ease. The method is shown effective in correlating low-cycle fatigue test data of various sources documented in the literature into a single narrow scatter band which is remarkable consistent with the scatter band of the existing master S-N curve adopted ASME B&PV Code since 2007.

With this new method, some of the inconsistencies of the pseudo-elastic structural stress procedure in 2007 ASME Div 2 Code can now be eliminated, such as its use of Neuber’s rule in approximating structural strain beyond yield. More importantly, both low cycle and high cycle fatigue behaviors can now be treated in a unified manner. The earlier mesh-insensitive structural stress based master S-N curve method can now be viewed as an application of the structural strain method in high cycle regime, in which structural strains are linearly related to traction-based structural stresses according to Hook’s law. In low-cycle regime, the structural strain method characterizes fatigue damage directly in terms of structural strains that satisfy linear through-thickness deformation gradient assumption, material nonlinear behavior, and equilibrium conditions. The use of a pseudo-elastic structural stress definition is not fundamental, but merely a means to put low-cycle and high-cycle fatigue test data in a conventional stress-based S-N data representation which is typically preferred in engineering practice, than a strain-based representation.
Collapse Analysis of Offshore Platforms Using Constrained New Waves
Authors: Kimiaei Mehrdad , Edgarth Daud W.
Published: September 2014

Traditionally regular deterministic wave theories are employed to estimate wave loads on offshore platforms but they cannot capture random nature of the sea states. Randomly generated sea surfaces will lead to most accurate results for structural responses due to waves but they are usually based on long duration simulations and hence need excessive computational efforts. Constrained NewWaves (CNWs), with significantly shorter computational time, have recently been used successfully for estimating of structural response of offshore platforms due to waves. For extreme waves, as long as there is no indication of major structural nonlinearity in the system, they have shown reasonably accurate results as an alternative for long duration randomly generated sea surfaces.

This paper is concerned with using CNWs in collapse analysis of offshore platforms under extreme waves where large geometrical and material nonlinearities are expected. It shows how the plastic level of the response, total duration of the loading, the loading pattern and dynamic characteristics of the platform can influence the extreme response and collapse rates of the offshore platforms.
Pipe-Soil Interactions for a Pipeline With Strakes on a Furrowed Seabed
Authors: Brunner Mark , Bai Qiang
Published: September 2014

Although significant pipe-soil interaction information is now available in the industry for shallowly-embedded, cylindrical pipelines on a flat seabed, there is little information available for subsea pipelines with vortex-induced vibration (VIV) suppression strakes on a furrowed seabed.

A heavily furrowed seabed may have multiple free spans that are subjected to seabed currents and potential VIV. To suppress VIV at the free spans, strakes are often applied to the pipeline over the entire length of the furrowed area. At the tops of the furrows, the pipeline will penetrate further into a soft clay seabed due to the weight of adjacent free spans. Significantly different pipe-soil interactions are possible in these areas, especially with the presence of VIV suppression strakes. Accounting for these differences is essential when assessing thermal expansion issues, such as global lateral buckling and pipeline walking.

This paper presents the findings for a test case of a pipeline with strakes on a furrowed seabed and provides suggestions for a user subroutine to be used for a pipeline system with beam elements in a finite-element analysis. The CEL method is first used to assess the impact of straked-pipeline penetration into a flat, soft-clay seabed, then to assess lateral and axial pipe resistances at different penetration depths. This information is used to develop a user subroutine for beam elements to further assess the pipeline on a furrowed seabed, in which the effects of vertical pipeline load and penetration on the lateral soil resistance are included.

The test case also considers a typical analysis for a pipeline subjected to elevated temperature and pressure cycles.
InWave: A New Flexible Design Tool Dedicated to Wave Energy Converters
Authors: Combourieu Adrien , Philippe Maxime , Rongère François , Babarit Aurélien
Published: September 2014

This article presents the novel methodology used in the software InWave to address the problem of wave energy converters (WEC) modelling. The originality compared to other recently developed tools lies in a fast semi-recursive multibody dynamic solver which integrates a flexible hydrodynamic solver.

The multibody solver works in time domain and is fully nonlinear. It solves the dynamic of systems formed of a fixed or free base articulated with any number of bodies that can be floating or not, with branchy structure ([1]).

The integrated hydrodynamic solver is a linear potential flow solver based on boundary elements method. It uses the generalized degrees of freedom approach ([11]). Combined with a relative coordinate parameterization, it allows for a minimization of the number of hydrodynamic boundary value problems that have to be solved, thus allowing a reduction of computational time both for BEM computations and time domain simulations. Time domain reconstruction is performed to link hydrodynamic loads with the multibody dynamic solver. Interaction between bodies through radiation is thus taken into account.

InWave is a complete WEC modelling tool including incident wave generation, multibody dynamic solver, hydrodynamic solver, power take-off and mooring models, post-processing and visualization.

A successful comparison with the linear potential flow solver Aquaplus ([5]) on a basic cylinder test case is carried out.

Finally, a complex test case on a Langlee-like device is presented, comparing InWave results with those from the NumWec project ([2]). A good agreement between both models is found, which increases the confidence in InWave algorithms and implementation.
Reliability of Corroded Pipelines by Enhanced Monte Carlo Simulation
Authors: Leira Bernt J. , Næss Arvid , Næss Ole E. Brandrud
Published: September 2014

The present paper addresses reliability analysis of corroding pipelines considering also system reliability effects. The analysis is performed by utilization of enhanced Monte-Carlo simulation methods which have been found to be very efficient for quantification of system reliability in the case of multiple components with arbitrary correlation levels. The examples which are studied in the paper comprise systems with corrosion defects which are both independent and correlated.
The Effect of the Computational Grid Size on the Prediction of a Flammable Cloud Dispersion
Authors: Miralles Schleder Adriana , Martins Marcelo Ramos , Pastor Ferrer Elsa , Planas Cuchi Eulàlia
Published: September 2014

The consequence analysis is used to define the extent and nature of effects caused by undesired events being of great help when quantifying the damage caused by such events. For the case of leaking of flammable and/or toxic materials, effects are analyzed for explosions, fires and toxicity. Specific models are used to analyze the spills or jets of gas or liquids, gas dispersions, explosions and fires. The central step in the analysis of consequences in such cases is to determine the concentration of the vapor cloud of hazardous substances released into the atmosphere, in space and time. With the computational advances, CFD tools are being used to simulate short and medium scale gas dispersion events, especially in scenarios where there is a complex geometry. However, the accuracy of the simulation strongly depends on diverse simulation parameters, being of particular importance the grid resolution. This study investigates the effects of the computational grid size on the prediction of a cloud dispersion considering both the accuracy and the computational cost.

Experimental data is compared with the predicted values obtained by means of CFD simulation, exploring and discussing the influence of the grid size on cloud concentration the predicted values.

This study contributes to optimize CFD simulation settings concerning grid definition when applied to analyses of consequences in environments with complex geometry.
Numerical Study of Landslide Impact on Submarine Pipelines
Authors: Yuan Feng , Li Lingling , Guo Zhen
Published: September 2014

Offshore pipelines are frequently subjected to the impact of submarine landslides or debris flow, causing large displacement and increase in internal forces. The damage of pipeline has been vastly reported and the pipeline behavior subjected to landslide has also been explored by many researchers. The impact of landslide on pipeline is commonly assumed to be static problem. However, the displacing process of the pipeline under the active landside loading is a kinematic procedure. This work attempts to explore the kinematic process of pipeline based on the vector form intrinsic finite element method. It is found that when the displacement is firstly triggered, it increases very quickly. With the increase of lateral soil resistance and the development of internal forces, the displacement gradually decreases and stabilizes. The comparison with the analytical model reveals obvious difference in tension distribution along the pipeline. Moreover, detailed analysis on the influence of landslide impaction location and the initial pipeline shape is included in the parametric analysis.
Long Term Extreme Analysis of FPSO Mooring Systems Based on Kriging Metamodel
Authors: Wang Aijun , Huang Shan , Barltrop Nigel
Published: September 2014

Establishing statistical distributions of the response extremes is of particular importance for the design of FPSO mooring systems and the related riser design. Long term time domain simulation is the most accurate design approach to determine the extreme responses. It involves, however, coupled dynamic analysis of FPSO mooring system for a large number of sea states and consequently the task is often prohibitively time consuming. To solve this problem, an approach for the long term extreme analysis based on a metamodel in conjunction with the design of experiment methodology is proposed in the paper. In this approach, Latin Hypercube Sampling (LHS) based on the design of experiment method, is performed to select a sub-set of sea states from all sea states. Short term distributions for this sub-set of sea states are simulated and estimated. Kriging metamodel, which can map the relations between the sea states characteristics and the short term distribution parameters, is then applied. The accuracy of the metamodel is investigated. The long term response distribution of moored FPSO systems for all sea states can be predicted based on the metamodel. This approach for the long term extreme analysis of FPSO mooring systems avoids the response analysis over all sea states and can greatly improve the computational efficiency of the long term extreme analysis of FPSO mooring systems.
Top Tensioned Riser Interface With Dry-Tree Semisubmersible
Authors: Xiang Sherry , Cao Peimin , Otten Jeff , Jiang Lei , Bian Sean
Published: September 2014

Dry Tree Semisubmersibles (DTS), with the capability of supporting surface wellheads and allowing drilling and completion through direct vertical access risers, have attracted intense interest from the oil and gas industry. A wet tree deep draft semisubmersible has been carefully reconfigured considering the balance between the overall floater configuration and the tensioner stroke for a harsh environment application. A large amount of simulation efforts have been performed for the optimization of the integrated hull/deck/mooring/riser system. Recently, a basin model test was also successfully completed and further demonstrated its technical feasibility.

The paper presents the overall design of a Top-Tensioned Riser (TTR) system for a DTS application focusing on the complexity of the DTS-TTR interface including ram style tensioning system, riser conductor and riser top assembly design with keel joint, etc. Due to the heavy weight of the TTR system in the ultra-deep water application, the riser top sections are subject to high reaction loads with the DTS in severe environments. The riser system faces the challenge to have a feasible and economic top assembly design. In this paper, an engineered riser conductor pipe is introduced to interface the riser top assembly with hull. The riser conductor pipe, which spans from deck to keel, is integrated with riser top assembly and the tensioner system design. The riser conductor protects the riser in the splash zone and prevents the high reaction loads directly transferring from hull to riser, thus reducing the riser keel joint and tension joint size. The feasibility and performance of the TTR system are demonstrated through the static and dynamic analyses. Pipe-in-pipe (PIP) contact model is employed in the simulation to ensure the dynamic interaction loads between riser and riser conductor are captured. The TTR overall system design consideration for the DTS application is discussed.
Modelling Rheological Behavior of Fresh Cement-Sand Mixtures
Authors: Hoornahad Hooman , Koenders Eduard A. B.
Published: September 2014

In this paper, the effect of the mix composition on rheological behavior of fresh cement-sand mixture is studied by considering a mixture as a two-phase model that is decomposed into a granular and a paste phase. The paste itself is subdivided into void paste and excess paste. Void paste fills the void space between the grains when they are in a fully compacted state while excess paste will use the remaining paste to form a paste layer around each individual grain particle, with equal thickness. By considering each grain particle covered with the excess paste layer as a single element, the rheological behavior of cement-sand mixtures can be related to their inter-element interactions for all sets of particle combinations.