bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Equilibrium Homogeneously Condensing Flow Analyses as Design Tools for Steam Turbines
Authors: Senoo Shigeki , Shikano Yoshio
Published: March 2009

In order to get the details of flow fields in steam turbines, three-dimensional turbulent flow calculations are useful. However in a design procedure, three-dimensional flow calculations are only possible in the last design stage, because they need in-depth boundary conditions of both geometries and flows. At such a late time in the procedure, it is difficult to go back and change main design parameters, such as flow area and stage load. Both three-dimensional flow patterns and non-equilibrium condensation caused by rapid expansions of steam have important roles with respect to steam turbine performance particularly in low-pressure sections. The steam turbine internal efficiency can be improved by taking account of these effects in the early design stage, especially in flow pattern design. This paper describes a multi-stage through-flow calculation technique including both three-dimensional flow efffects and phase changes from vapour to small droplets. To compute the high-speed two phase steam flow, a flux-splitting procedure including non-equilibrium homogeneously condensation is introduced. Three-dimensional blade forces are calculated by using angles of both blade camber and radial lean. The blade camber lines can be decided without in-depth blade geometries. Therefore this computational technique is applicable in the flow pattern design. The calculation results agree well with fully three-dimensional flow calculation and the calculation can predict supersaturating states and Wilson lines which are defined as the maximum supercooling.
Anisotropic Turbulence Modelling of Near Wall Effects Pertinent to Turbomachinery Flows
Authors: Corsini Alessandro , Rispoli Franco
Published: March 2009

A computational study is presented which investigates the predictive performance of two non-linear turbulence closures in simulating the physics pertinent to decelerating turbomachinery flows. The compared approaches are a cubic non-linear k-ε model and an algebraic Reynolds stress model. They have been considered as promising closures for improving the industry CFD state-of-the-art accounting for non-equilibrium effects. The authors adopt a parallel multi-grid algorithm, which is developed with a finite element formulation based on a highly accurate stabilized Petrov-Galerkin method. The finite element formulation is here applied on equal-order Q1-Q1 as well as mixed Q2-Q1 element pairs, and the accuracy of the latter approximation is assessed on near-wall flows simulation. The parallel solution algorithm for Reynolds Averaged Navier-Stokes modeling exploits an overlapping domain decomposition technique based on an “inexact explicit non linear Schwarz method”. The compressor flow considered for model benchmarking is highly challenging because of the transitional nature of the flow and the existence of significant leading- and trailing-edge separations. The potential of non-isotropic closures has been investigated. The algebraic stress model is shown to provide a better base-line for non-equilibrium effects simulation with respect to the cubic k-ε model. As it is shown for the studied compressor cascade, the cubic eddy-viscosity model exhibits some predictive weaknesses, among them an excessive turbulence attenuation that results in un-realistically delayed transition to turbulence.
POD Investigation of Near-Wall Turbulent Structures
Authors: Di Cicca Gaetano Maria , Iollo Angelo , Spazzini Pier Giorgio , Iuso Gaetano , Onorato Michele
Published: March 2009

Experimental data of a turbulent boundary layer developing over a flat plate, obtained by Digital Particle Image Velocimetry (DPIV) technique, are analyzed making use of proper orthogonal decomposition (POD). Different POD definitions have been used in order to check their ability in educing the various structures dominating the near wall region. Results show a specific sensitivity depending on the POD definition adopted.
PIV Investigations of Particle Velocities in the Tongue Region of a Slurry Pump
Authors: Charoenngam P. , Subramanian A. , Kadambi J. R. , Wernet M. , Sankovic J. , Addie G. , Courtwright R.
Published: March 2009

Transport of solid-liquid slurries in pipeline transport over short and medium distances is very important in many industries, including mining related processes. The particle image velocimetry technique was successfully utilized to investigate the velocities and kinetic energy fluctuations of slurry particles at the tongue region of an optically-clear centrifugal pump. The experiments were conducted using 500 micron glass beads at volumetric concentrations of 2.5% and 5% at pump speeds of 725 and 1000 rpm. The fluctuation kinetic energy increased approximately 200% to 500% as the pump speed was increased from 725 rpm to 1000 rpm. The directional impingement mechanism is more significant at the pressure side of the blade, tongue and the casing. This mechanism becomes more important as the speed increases. This suggests that the impeller, tongue and the casing of the slurry pump can wear out quickly, especially with an increase in speed. In this paper the emphasis is on the tongue region. The random impingement mechanism caused by the fluctuation kinetic energy of the solids can play an important role on the erosion of the tongue area.
Stiffness Analysis of Feed Back Spring and Flexure Tube of Jet Pipe Electrohydraulic Servovalve Using Finite Element Method
Authors: Somashekhar S. Hiremath , Singaperumal M. , Krishna Kumar R.
Published: March 2009

In the present paper an attempt has been made to predict the behavior of some precision hydraulic components such as feed back spring and flexure tube. The performance of the valves depends on so many parameters. The feed back spring and flexure tube elements are identified as more critical spring elements in servovalve operation. If these elements are properly designed with respect to stiffness, automatically dynamic performance of the servovalve is improving. Hence an attempt has been made to predict the stiffness of these elements by finite element method. The solid model of these components are carried out in IDEAS-Master modular and simulated by applying the suitable boundary and loading conditions. The stress concentration areas in these components due to loading are shown. The critical affecting dimensional sensitivity analysis is carried out using FEM and results are presented.
Parametric Study of a Turbine Blade Cascade Using a New Parametric Flow Solver Turb’Opty
Authors: Moreau S. , Aubert S. , N’Diaye M. , Ferrand P. , Tournier J. , Rochette M.
Published: March 2009

A new parameterized CFD solver Turb’Opty™ has been developed based on a Taylor series expansion to high order derivatives of the solutions of the discretized Navier-Stokes equations. The method has been successfully applied to the laminar compressible flow field of the T106 turbine blade cascade. Comparisons with the classical CFD results have validated the accuracy of the parameterized solutions obtained by a simple polynomial reconstruction around a reference solution. The CPU efficiency has been emphasized by quickly computing the performance maps (power and losses) of this blade cascade. Wide industrial perspectives of turbomachinery global optimization are finally demonstrated by coupling this method with a simple genetic algorithm.
Momentum Thickness Measurements for Thick Axisymmetric Turbulent Boundary Layers
Authors: Cipolla Kimberly M. , Keith William L.
Published: March 2009

Experimental measurements of the mean wall shear stress and boundary layer momentum thickness on long, thin cylindrical bodies are presented. To date, the spatial growth of the boundary layer and the related boundary layer parameters have not been measured for cases where δ/a (a = cylinder radius) is of order one or greater. Moderate Reynolds numbers (104 < Reθ < 105) encountered in hydrodynamic applications, are considered. Tow tests of cylinders with diameters of 0.89 mm and 2.5 mm and lengths ranging from approximately 30 meters to 150 meters were performed using the High-Speed Seawater Tow Tank at NASA Langley Research Center. The total drag (axial force) was measured at tow speeds ranging from 2.4 to 17.4 m/sec. These data were used to determine the tangential drag coefficients on each test specimen, which were found to be two to three times greater than the values for the corresponding hypothetical flat-plate cases. Using the drag measurements, the turbulent boundary layer momentum thickness at the end of the cylindrical bodies is determined, using a control volume analysis. The results show that for the smallest diameter cylinders, there is no indication of relaminarization, and a fully developed turbulent boundary layer exists. In addition, laser measurements showed no large scale transverse motions (snaking) existed during the tows, and the tow angle was less than 1 degree for all cases, confirming that the cylinders were neutrally buoyant.
Turbulence Measurements Within a Cyclic Flow and Analysis in the Momentum Equation
Authors: Suk Eugene , Fetter Daniel K. , Sullivan Pierre E.
Published: March 2009

Particle Image Velocimetry (PIV) measurements were performed within an optical water analog engine. A unique triggering and data collection system was developed to allow a CCD camera to acquire two consecutive image frames at predetermined crank angles. The water analog engine operated at 15 RPM and had a square cross-section with two circular valved inlets. Measurements were made throughout an entire cycle to determine mean and turbulence statistics and results at 60 crank angle degree are discussed in this paper. Different averaging techniques were used and results between the techniques were compared to provide a number of statistical quantities having large discrepancies in scales and distributions. A study of the equations of motion showed that different averaging techniques results in differing physical interpretations of the flow.
Particle Tracking in Laminar Flow of Molten Aluminum in Straight, Constant Cross-Section Ducts Subjected to Steady, Uniform Electric and Magnetic Fields
Authors: Blaskovich T. , Baliga B. R. , Oliveira L. A.
Published: March 2009

The formulation, testing, and application of some mathematical models and numerical solution methods for tracking electrically non-conducting particles in laminar flow of molten aluminum in straight, constant cross-section ducts subjected to steady, uniform electric and magnetic fields are presented. The separation chamber is a straight duct of constant rectangular cross-section and electrically non-conducting walls. The effects of the induced electric field in the molten aluminum are considered negligible. Attention is focused on the fully-developed flow regime. In the calculation of the inclusion trajectories, consideration is given to drag, gravity, virtual mass, Basset, lift, and electromagnetic forces. A control-volume finite element method is used for the calculation of the fluid flow. A fourth-order Runge-Kutta method and a particle-location and interpolation algorithm are used to calculate the particle velocities and trajectories. Results obtained for a test problem and a demonstration problem are presented and discussed in this paper.
MSR Upgrade at Duane Arnold Uses Modularization to Cut Radiation Exposure and Erection Time
Authors: Sorenson Eric S. , Yarden Abraham L. , Sullivan Chester S. , Tam Clement W.
Published: March 2009

When the BWR at Duane Arnold went on-line, it was rated at 565.7 MWe. Some time ago, due to operational and other problems it was determined that it would be economical to isolate the HP reheaters from service in the double-stage two Moisture Separator Reheaters (MSRs). Duane Arnold is now undergoing an extensive and lengthy life-extension and uprating program, targeted at 16 percent involving many components. After a detailed study involving several alternative approaches to upgrading the MSRs in conjunction with a new, larger HP turbine, they have now been completely redesigned and reconstructed using essentially the original configuration — 2-pass LP and HP reheaters with chevron moisture separator sections, but using advanced technology throughout and in conjunction with the optimization of the uprated turbine generator. In order to minimize component installation time and reduce personnel radiation exposure, the modern Moisture Separation (M.S.) components were “modularized” — installed as four completely preassembled M.S. sections replacing the need for the in-shell installation of multiple small components. This paper covers the many alternative choices considered and details all elements and phases of the final MSR upgrade design and installation process selected. The installation of a new main turbine, oversized in anticipation of an increase in thermal power, was expected to result in a decrease of about 10 MWe due to throttling losses across the turbine control valves. The refurbished MSR with restored second stage reheat was expected to just offset this loss. Post installation testing showed a gain of 4 MWe beyond the offset of the turbine control valve throttling losses. As a result, the net gain over previous operation is therefore 4 MWe even though the new MSR is responsible for gain of about 14 MWe.
Mechanical Properties of Alumina Composite Hardened by Ultra Dispersed Diamonds
Authors: Kireitseu Maksim , Yerakhavets L. , Nemerenco Ion
Published: March 2009

Structure and mechanical properties of composite coatings that contain of 5 to 25% (vol.) of ultra-dispersed diamonds, different alumina phases, and components of SiC, AlN have been investigated. Structure, grains morphology, presence of pores and their distribution, interaction zones were investigated with SEM, X-ray-phase analysis and micro-X-ray-spectral analysis. Material was formed by impulse pressing. It is revealed that the material has variable-porosity, high density, microhardness up to 25 GPa and load rating. XRD analysis shows that the structure includes the diamond phase. To investigate load rating of the material Hertzian contact was used. Ultra-dispersed diamonds strength the structure in general as well as mechanical properties and quality of composite coatings.
A Consideration on Energy Transfer Mechanism Caused Between Impeller Blade and a Fluid Particle in Centrifugal Pump
Authors: Tanaka Takaharu
Published: March 2009

Impeller blade’s rotational motion causes centrifugal force on fluid particle. It directs radial outward. However, the flow rate, that is, radial outward flow is not caused by centrifugal force in centrifugal pump. Tangential forward force, which is in the direction perpendicular to rotational radius, causes tangential forward movement on fluid particle under the radial balance of centrifugal and centripetal forces in the rotating flow passage of centrifugal pump and it causes the flow rate. And the head is caused by centrifugal force and equivalent to centripetal force, which acts on fluid particle radial inward. Which is equivalent to external force at the trailing edge of impeller outlet.
LIF Thermometry in a Sooty Flame: An Application of Excitation-Emission Spectrum
Authors: Miyakawa Taru , Hayashida Kazuhiro , Amagai Kenji , Arai Masataka
Published: March 2009

A new method for the temperature measurement in a sooty flame was developed, based on an excitation scan. A tunable, narrowband ArF excimer laser was used to excite various absorption lines in D2Σ+ ← X2Π(0,1) band of NO. Spectrum of the laser-induced emissions from the flame was obtained by using a spectrograph. In the case of a propane diffusion flame, this emission spectrum consisted of NO and O2 fluorescence, and off-resonance emissions related to the soot particles. These off-resonance emissions were usually stronger than the fluorescence. However the off-resonance emissions in the shorter wavelength region than 250 nm were weaker than the fluorescence. In other words, the ε(0,3) band of NO fluorescence which appeared in the ultra-violet region (around 208nm), was stronger than the off-resonance emissions, and was free from the O2 fluorescence. Therefore, the NO rotational temperature in a sooty flame could be deduced from the excitation spectrum based on the ε(0,3) band. In order to obtain the excitation spectrum based on the ε(0,3) band, an excitation-emission spectrum (EES) was obtained. NO rotational temperature in a propane diffusion flame was derived from this EES.
A Justification for Designing and Operating Pipelines Up to Stresses of 80% SMYS
Authors: McLamb Martin , Hopkins Phil , Marley Mark , Nessim Maher
Published: March 2009

Oil and gas majors are interested in several projects worldwide involving large diameter, long distance gas pipelines that pass through remote locations. Consequently, the majors are investigating the feasibility of operating pipelines of this type at stress levels up to and including 80% of the specified minimum yield strength (SMYS) of the pipe material. This paper summarises a study to investigate the impact upon safety, reliability and integrity of designing and operating pipelines to stresses up to 80% SMYS.
Biomass Combustion Wastes Utilization in Natural Gas Pipeline Construction
Authors: da Silveira Djalma Dias , de Andrade Renato Paula , Heck Airton Lui´s
Published: March 2009

Pipeline construction in rock soils demands an extreme care, under a constructive point-of-view, specially regarding a possible damage to the pipeline coating. Irregular pieces of rock (result of rock blasting) can contribute to this damage. Actual methodologies can be resumed in the utilization of selected soil (extracted from natural areas) as “padding” layer and also to cover the pipeline. Another methodology is mechanical protection utilization (special sleeves and wood grids). This paper proposes the utilization of biomass wastes after burning in Biomass Fire Power Plants as “padding” and “covering” agent, in substitution to the soil extracted from natural areas. The waste studied is produced after the burning of rice husk wastes that are burned in power plants in operation at the South Region of Brazil. Laboratory analyses were conducted and the results are presented and discussed, in terms of pipeline integrity and soil quality effects. Main results of this work are related to the possibility of cost reduction by the utilization of waste as the “padding” and “covering” agents in pipeline construction, as well as the selected soil extraction areas conservation, that can be used to another economical or environmental activity. Another result can be the reducing of mechanical protection elements used during the construction step. Finally, this paper contributes to the development of new initiatives related to alternative materials using in pipeline construction routines, based on cost reduction × environmental sustainability binomial, that can result in more sustainable gas pipeline construction projects.
Development of Two-Fluid Flow Model for Pipeline Decompression
Authors: Zhou X. L. , Moore R. G. , King G. G.
Published: March 2009

Natural gas pipelines have an excellent safety record but on rare occasions they rupture and decompress. When this happens their contents cool rapidly and form two phases. The decompression behaviors of multiphase fluid released from pipeline are not well understood. Pipeline decompression modeling is useful in characterizing the rapid transient flow that occurs when a pipeline ruptures. Numerical simulation can provide detailed data for analyzing the consequences of pipeline bursts and the mechanical performance of pipelines as they decompress. Decompression behavior of fluids is complicated by the formation of two-phase flow due to gas cooling or liquid flashing effects. Based on the time-space-ensemble composite averaging procedure, a two-fluid flow model is derived for simulating high-pressure natural gas pipeline decompression. The composite averaging operator is supported and demonstrated by simple experimental data. A set of constitutive equations is formulated for the closure of the system of equations. The conservation equations along with closure equations are examined for compliance with the second law of thermodynamics. Characteristics analysis is performed to ensure that the set of equations is well-posed mathematically.
Full History Burst Test Through Finite Element Analysis
Authors: Fonzo Andrea , Salvini Pietro , Di Biagio Massimo , Mannucci Gianluca
Published: March 2009

Ductile Fracture propagation phenomena have been widely investigated by researchers in the last years, with particular regard to large metallic structures such as pressurized vessels or gas pipelines. A large number of burst tests have been carried out by Centro Sviluppo Materiali S.p.A. (C.S.M.) in the last decades to identify a set of significant parameters characterizing fracture propagation conditions; the aim is to foresee the behavior (speed and its derivatives) of longitudinal running cracks. The optimal choice of these parameters is strongly helped by appropriate use of Finite Element analysis. To this goal a Finite Element software has been developed, it allows the correct computing of some particular aspects of fracture propagation and the behavior of pressured real gases during decompression. In the present paper a pipeline burst test, carried out on a X100 grade pipeline, and all laboratory tests and data manipulations necessary to build up the whole procedure have been discussed. One of the main objectives is the setting of a procedure able to identify the fracture parameters, when a ductile propagation occurs, avoiding any scatter due to transient effects.
Unconventional Procedure for Purging a Crack-Weakened Pipeline
Authors: Ferioli Jose´ Fernando M. , Pereira Fernando Borja
Published: March 2009

The Arauca´ria to Paranagua´ Pipeline (OLAPA) owned by PETROBRAS, was built in 1976 in Parana´ State, Brazil, connecting an oil refinery nearby the city of Curitiba to a marine terminal near Paranagua´ Seaport. The pipeline had been operating normally for 25 years, moving liquefied petroleum gas (LPG) and diesel fuel to the refinery as well as petrochemical Naphtha and light cycle oil (LCO) in the opposite direction. The second week of February 2001 came along with heavy and continuous summer rain on Parana´ State most of which on a hilly terrain portion crossed by the pipeline, currently regarded as an environment preservation area of the Atlantic Rain Forest. On 16th day, that same month, while the line was on shut in condition, a hardly noticeable landslide across the right-of-way led the pipeline to the complete rupture, succeeded by product spill. Further analysis on the rupture section pointed to circumferential cracks caused by axial stress induced by a slow and steady slide on the adjacent soil. Surveys on other regions possibly affected by similar soil movement on the right-of-way warned operations staff that there could be more weakened sections along the pipeline, therefore pipe failures and product spill might still happen due to the continuation of the rainy season. Product removal became required to avoid environmental threats. The purging procedure should meet two main constrains, i.e., minimize pressure and volume flow through the identified risky locations. This paper describes the planning and execution of such purging process, tailored for a weakened pipeline on an environmental sensitive area, adopting unconventional methods to move liquid products upward high steeps, considering restrains to operational pressures around one third of normal values.
Superhigh Pressure Dense Phase Arctic Pipelines Increase Reliability and Reduce Costs
Authors: King Graeme , Kedge Chris , Zhou Xuelong , Matuszkiewicz Andrzej
Published: March 2009

Differential movement in permafrost terrain due to ground freezing or thawing challenges the reliability of buried pipelines proposed for transporting natural gas from Prudhoe Bay and the Mackenzie Delta. Arctic pipelines designed to operate at conventional pressures (that is, below 10 MPa) are susceptible to wrinkling, bulging, and ovalling due to the differential movements they cause at interfaces between frozen and unfrozen ground and between different types of soil. Arctic pipelines designed to operate at superhigh pressures—defined here as pressures above 25 MPa—can accommodate the differential movements. A fair comparison between large diameter artic pipelines with operating pressures in the range from 10 to 42 MPa was made by accurately simulating flow performance with Greenpipe’s PipeCraft™ software. For any given design flow, superhigh pressure dense phase pipelines have smaller diameters and thicker walls, making them more flexible and better able to handle differential movements. And at superhigh pressures, Joule-Thomson cooling is negligible so that flowing gas stays close to ground temperature, reducing potential for frost heave or thaw settlement in the first place. Although weight per meter of superhigh pressure pipelines is similar to conventional pressure pipelines of similar flow capacity, increased flexibility means they are easier to lift and handle during construction. They also conform more easily to the terrain, resulting in less excavation and less pipe bending to make them fit the contours of the trench. The net result is reduced construction costs. When construction, maintenance and reliability are factored into the selection process, superhigh pressure dense phase pipelines provide a cost effective option for handling the challenges of arctic environments.
First-Time Use of LDSAW X-80 Pipes for High-Pressure and High-Temperature Transmission of Steam
Authors: Bishop M. , Hillenbrand H.-G. , Liessem A. , Reepmeyer O. , Schroeder J.
Published: March 2009

In north-eastern Alberta/Canada, Canadian Natural Resources and others operate systems of steam transmission pipelines to deliver steam to hundreds of oil wells in Alberta. The delivered steam is injected into the well to stimulate the reservoir, enhancing the recovery of heavy oil. Due to changing stimulation techniques it was required to inject up to 3,000m3 per day per well of cold water equivalent steam at a wellhead pressure of 13 MPa. Up to ten wells can receive steam simultaneously. To facilitate the economic movement of this large volume of steam, the installation of a 24NPS steam pipeline was essential and required the innovative application of existing technology. Another requirement was that the pipes must be field-weldable without post-weld heat treatment — a requirement aimed at keeping installation costs low. Several linepipe steel grades including grade X-80 and GRS 550 steels, which are comparable to CSA Gr. 550 steel, were examined for their mechanical properties up to 400°C. Based on this knowledge Europipe delivered the pipes for a steam pipeline of 4,500 m. The line of 24NPS CSA Gr. 550 material operates at a temperature of 354°C and a pressure of 17.2 MPa. The elevated temperature tensile and CVN tests performed during the production of the 24NPS pipes confirmed the results of the preproduction tests of similar steels. Additionally, aging and creep tests with the original material were performed to determine a satisfactory lifetime at the given operating conditions. All tests established that the delivered material is suitable for the application. Also a field welding procedure was developed that did not require post weld heat treatment for the 24NPS CSA Gr. 550 pipes. The 4,500 m of 24NPS Gr. 550 linepipe were successfully installed and placed into service during the summer of 2001.
Uncertainty in Petroleum Field Development Projects
Authors: Chamanski Alexandre A. , Gudmestad Ove T.
Published: March 2009

The development of petroleum fields involves both technical and commercial uncertainties. The technical uncertainties associate with the geological and technical complexity of producing hydrocarbon resources, especially in hostile environments. The commercial uncertainties, in turn, associate with the capital intensity of the petroleum field development projects and the volatility of the petroleum markets. In addition, petroleum field development projects are usually large and complex, and their successful realization requires effective management of numerous activities, and, often, resolving conflicting interests of the parties involved in the projects. A better understanding of uncertainty is therefore essential for successful management of petroleum field development projects. The sample examined in this study included 48 Western and Russian experts in petroleum field development. The experts’ responses to a questionnaire were used to identify the key uncertainty factors in the petroleum field development process and analyze the heterogeneity of the experts’ opinions.
On the Wave and VIV Fatigue of Steel Catenary Risers Connected to Floating Structures
Authors: Mekha Basim B.
Published: March 2009

The Steel Catenary Riser (SCR) concept has been considered as a vital option for most new deepwater field developments around the world. The use of an SCR, as a pipe connecting the export pipeline system and/or remote wells and infield flowline to a floating structure, has given more flexibility and potential to the oil exploration and transportation in water depths where other riser concepts would not tolerate the hydrostatic loads or would have become very costly. Major design concerns of the SCR pipes connected to a floating structure are the dynamic motion and the fatigue damage. The SCRs are very sensitive to the platform or vessel motion characteristics to which they would be attached as well to the environmental loads. The two main sources of fatigue are the random wave sea states and the associated platform motion and vortex induced vibration (VIV) due to current. The wave sea states are represented by wave spectra while the platform motions are applied as first order Response Amplitude Operators (RAOs) and second order slow drift motions. This paper gives a brief introduction about the development of the fatigue analysis methods that have been used to date. Results of parametric studies investigating several effects on the fatigue damage of the SCRs are presented. Some of these effects include flexible joint rotational stiffness, VIV analysis parameters, slow drift motion effects. The results will be for different size risers and fluid contents.
Lifting Effects for Wave Resistance or Sea-Keeping Calculations
Authors: Boin Jean Philippe , Guilbaud Michel , Ba Malick
Published: March 2009

We present the introduction of lifting effects in a code of calculation [1–3] based on a first order panel method using the diffraction-radiation with forward speed Green function satisfying a linearised free-surface condition and the radiation one. A mixed formulation has been used with a source distribution on the hull and a doublet one on the plane of symmetry and the wake of lifting parts of the body, leading to an integral equation derived from the 3 rd Green identity. The Green function and its derivatives are not computed but are directly integrated on elementary panels, segments or semi-infinite strips. Results are presented for semi-submerged ellipsoid, rectangular surface-piercing bodies, Wigley hull, Series 60 ship, sailing boat and military 5415 hull. Global forces, moments but also free surface elevations are compared with the results of other methods and with measurements, either in steady or in unsteady flows in the frequency domain.
Impact of FPSO Heading on Fatigue Design in Non-Collinear Environments
Authors: Nordstrom Christina D. , Lacey Peter B. , Grant Bob , Hee Derek D.
Published: March 2009

To achieve confidence in continuous 20+ year FPSO service without fatigue cracks leading to costly repair offshore or in dry-dock, ExxonMobil has developed a prescriptive Fatigue Methodology Specification (FMS, ref. 5) for new-build FPSOs. An important FMS requirement for turret-moored FPSOs is to determine relative wave headings in non-collinear wind, current and wave environments using a first-principles approach. Based on initial review with FPSO designers, this FMS requirement may pose a significant challenge because appropriately defined met-ocean criteria and efficient analytical design tools are not readily available. To date, FPSO designers typically account for weather-vaning in non-collinear environments by assuming a distribution of relative wave headings based on experience. For example, one assumption is to use 0 degrees (head seas) for 70% of the time and within ±30 degrees off the bow for the remaining 30%. In certain environments, this assumption can lead to a non-conservative fatigue design for hull structural details that are sensitive to beam seas, and an overly conservative fatigue design for details sensitive to head seas. ExxonMobil contracted Moffat & Nichol to develop a time-domain procedure to predict mean FPSO headings by considering wave, wind and current induced loads on the FPSO hull and topsides throughout the FPSO’s 20+ year operational life. A key element of this methodology is a directional representation of met-ocean data, including waves, winds and currents for every 3- or 6-hour sea-state. We have implemented our heading analysis procedure in robust software, which includes processing of the 20+ year met-ocean data in the time domain. Once the FPSO heading time history is known, fatigue lives at critical structural connections are predicted using the spectral fatigue method prescribed in the FMS. To demonstrate the heading methodology and assess its efficiency for project use, an example analysis was performed for an FPSO at a specific geographic location, where relatively strong currents exist. Comparison of predicted FPSO headings and fatigue lives with those using the existing industry practices confirmed the need for a first principles based heading methodology for FPSO fatigue design. The heading and fatigue analysis procedure described here can lead to more accurate, robust fatigue designs for FPSOs in non-collinear environments.
Off-Shore Aquaculture
Authors: Busto Santiago Otamendi
Published: March 2009

A series of problems affecting the fish breedings, the littoral coast area and the companies’ balance sheet are starting to appear in the development of littoral acquaculture. The following document will analize the installation of the Off-Shore ship for the fattening and transport of 2.000 TN of pelagic fish. This ship of big dimensions carries out the breeding in deep waters and in areas far away from the coast so as not to affect the environmental changes (storms, pollution, red tides…). The energy needs of the ship are fulfilled by a windmill and a system that uses the waves’ oscillation energy.
Evaluation of Abrasive Wear of Polymeric Materials Using Single-Pass Pendulum Scratching
Authors: Piza Paes Marcelo Torres , Rego Motta Antonio Marcos , Lontra Filho Lauro Lemos , de Morais Juliano Ose´ias , Franco Sine´sio Domingues
Published: March 2009

Scratching abrasion due to rubbing against the sediment layer is an important degradation mechanism of flexible cable in deep water oil and natural gas exploitation. The present study was initiated to gain relevant data on the wear behaviour of some commercial materials used to externally protect these cables. So, Comparison tests were carried out using the single-point scratching technique, which consists of a sharp point mounted at the extremity of a pendulum. The energy dissipated during the scratching is used to evaluate the relative scratch resistance. The results showed, that the contact geometry strongly affects the specific scratching energy. Using SEM imaging, it was found, that these changes were related to the operating wear mechanisms. The observed wear mechanisms are also compared with those observed on some cables in deep water operations.
Modal Superposition Technique to Predict the Seismic-Pushover Load for Jacket-Type Structures
Authors: Srirengan Kanthi , Chakrabarti Partha , Ghosh Rupak
Published: March 2009

Two novel methods namely the Dominant Modes method and the All Modes method to predict the seismic-pushover load for the jacket-type structures are presented. Both of these methods are based on the linear superposition of the modal reactions. As a preliminary evaluation, the linear elastic response of a jacket structure subjected to seismic-pushover loads is compared with that obtained from the response spectrum analysis. Furthermore, the nonlinear inelastic behavior obtained from the seismic-pushover analysis is compared with that obtained from the nonlinear time-history analysis, for a portal frame subjected to El Centro earthquake motion. When more than one mode is dominant in an excitation direction, both the linear elastic and the nonlinear inelastic responses obtained using the loads generated from the All Modes method are representative of the reference solutions.
Fitness-for-Service Assessment for Weldments of the Natural Gas Pipeline by Using Failure Assessment Diagram
Authors: Lee Jung-Suk , Ju Jang-Bog , Jang Jae-il , Kwon Dongil , Kim Woo-sik
Published: March 2009

There are buried natural gas pipelines of which total length amounts to about 2.1×106m in Korea, and it is very important issue to evaluate FFS (Fitness-for-service) when a crack-like flaw was found in operating pipelines. But, the research about this had not yet been performed in Korea. So, this study constructed a FFS code appropriate to Korean natural gas pipeline through comparing and analyzing API 579 and BS 7910 that are lately. In addition, we developed the user-friendly software based on FFS code, so that field service workers who have little idea about fracture mechanics can use easily. The best merit of this code is that it is possible to evaluate FFS for welding HAZ in Korea natural gas pipeline.
Crew Habitability on Offshore Installations: Comprehensive Guidance
Authors: McCafferty Denise B. , McSweeney Kevin P.
Published: March 2009

In order to meet energy needs the search for oil and gas has led into deeper and deeper water. With installations located farther from shore, the length of stay aboard for crews could also increase. Long stays offshore can challenge crew mental and physical fitness levels which may impact productivity, performance, and safety. To maintain appropriate fitness levels, crews must be provided with properly designed accommodations and workspaces with favorable ambient environmental factors. ABS has developed a comprehensive guide that integrates human factors, ergonomics, and habitability data with accommodations design criteria. The subject of this paper is the production of such a guide, the ABS Guide for Crew Habitability on Offshore Installations, it’s criteria and measurement methodologies.
Some Aspects of Spar Platform Buoyancy Can Loads
Authors: Thompson Hugh , Irani Mehemosh B. , Finn Lyle D.
Published: March 2009

A finite element program is developed to analyze the dynamics of buoyancy cans within the centerwell of Spar platforms. The time domain non-linear finite element model includes the effects of the hydrodynamics of the water within the centerwell, and, the gap between the buoyancy cans and guides. The forces on the buoyancy can guide structure due to Spar motions is studied in the present paper. The theoretical results are validated with experimental and field measurements. 1:20.89 scale model tests are conducted to measure the buoyancy can motions and guide reaction forces for a range of gap sizes and specified Spar motions. A Spar platform is also instrumented to measure the guide forces in actual field conditions. The prototype field data is analyzed and compared with the numerical predictions.
A Nonlinear Coupled-Mode Model for Water Waves Over a General Bathymetry
Authors: Athanassoulis Gerassimos A. , Belibassakis Konstandinos A.
Published: March 2009

A non-linear coupled-mode system of horizontal equations is derived with the aid of Luke’s (1967) variational principle, which models the evolution of nonlinear water waves in intermediate depth over a general bathymetry. The vertical structure of the wave field is exactly represented by means of a local-mode series expansion of the wave potential, Athanassoulis & Belibassakis (2000). This series contains the usual propagating and evanescent modes, plus two additional modes, the free-surface mode and the sloping-bottom mode, enabling to consistently treat the non-vertical end-conditions at the free-surface and the bottom boundaries. The system fully accounts for the effects of non-linearity and dispersion.
A Rational Risk Acceptability Criterion Based on the Life Quality Index
Authors: Rackwitz Ru¨diger
Published: March 2009

Optimization techniques are essential ingredients of reliability-oriented optimal designs of technical facilities. An example of a suitable objective functions in terms of generalized cost is presented. Within FORM/SORM structural reliability analysis can be reduced to an optimization task and some simple algebra. However, instead of a optimization of cost on top of a optimization for the reliability task, a one-level optimization is proposed by adding the Kuhn-Tucker conditions of the reliability problem to general cost-benefit optimization. A rational basis to account for the cost of saving lives based on the recently proposed Life Quality Index is presented. An example illustrates the methodology.
Integration of Geometry Definition and Wave Analysis Software
Authors: Lee C.-H. , Letcher J. S. , Mark R. G. , Newman J. N. , Shook D. M. , Stanley E.
Published: March 2009

In a paper presented at OMA 2001, an extension of the panel code WAMIT was described where the surface geometry of the structure is represented explicitly and the solution for the velocity potential is approximated by higher-order B-splines. This permits an exact representation of the geometry in many applications, and avoids the effort and approximations inherent in preparing traditional low-order panel inputs. However the algorithms for the explicit geometry definition must be coded in special ad hoc subroutines for each type of structure. In the present paper we describe recent work to integrate the programs MultiSurf and WAMIT, in a manner which circumvents the need for special subroutines. In most practical cases this leads to a substantial reduction of the work required to perform computations of wave effects on structures. MultiSurf is a CAD program which enables users to define surface geometry with a high degree of accuracy, efficiency, and generality. It has been used extensively to develop low-order panel input files for ships and offshore structures, as well as for a variety of other marine design applications. The fundamental approach is to represent each part of the surface which is smooth and continuous by a parametric surface ‘patch’, using appropriate surface constructions which allow these patches to be joined robustly. The kernel of MultiSurf, known as RGKernel, includes the necessary code to evaluate surface locations and derivatives. A close integration of MultiSurf and WAMIT has been achieved by linking RGKernel with WAMIT, so that the same geometry can be reproduced during the hydrodynamic analysis. This integration makes it possible for users to define the geometry of structures interactively in MultiSurf, and to transfer this representation to WAMIT without significant extra effort. Thus the hydrodynamic analysis can be performed with exact or highly accurate representations of the geometry, and with the increased accuracy and efficiency inherent in the higher-order solution based on B-spline representation of the potential. After a brief explanation of the methodology, illustrative results are described for several examples. Comparisons are made of the accuracy, efficiency and workload, relative to the conventional use of low-order panels.
On the Effect of Water on Deck on Ship Motion
Authors: Spanos Dimitris , Papanikolaou Apostolos , Tzabiras George
Published: March 2009

The effect of trapped water on deck or the interior compartments of ships on ship motions is closely investigated by use of a non-linear numerical simulation method. The employed method enables the efficient simulation of the wave excited, coupled ship – trapped water motions and proves to be a very valuable tool for the assessment of the survivability of flooded ships in waves. A detailed study has been carried out to more carefully investigate the coupling effects between the ship and the floodwater mass that can be expressed through a resultant interaction force. This interaction force has been approximated both by a simplified model employed by the present simulation method and also by a more accurate CFD code and satisfactory agreement between the results of both approaches has been obtained.
Fatigue of Titanium Welds: Models for Assessment of Defect Sensitivity
Authors: Babalola Olusegun Tunde , Berge Stig
Published: March 2009

Welds produced by the Tungsten Inert Gas (TIG) process in riser grade titanium may contain pores, typically of sub-millimetre dimensions. Fatigue testing has proved that fatigue crack growth may be initiated from even very small pores. The size and existence of pores thus may be a governing factor for fatigue strength. For assessment of inspection and design criteria, tools for calculation of fatigue life from pre-existing pores are required. Numerical models for calculation of fatigue crack growth from internal defects were developed. The models were based on parametric formulae for the stress intensity factor for elliptic cracks in finite thickness plates. Coupons from TIG-welded titanium pipe were fatigue tested, and initial defects were identified and sized by Scanning Electron Microscopy. The test data was used for evaluation of the fracture mechanics models. Inherent uncertainties and limitations for fracture mechanics calculation of fatigue life were identified and discussed. By choosing appropriate values for crack growth threshold the accuracy of the calculated fatigue life was within a factor of two compared to the experimental data.
Fatigue and Ultimate Limit State of Grouted Tubular Joints
Authors: Morahan Darren J. , Lalani Minaz
Published: March 2009

A joint industry project commenced in 1993 to develop a design manual for tubular joints, which are strengthened or repaired through chord grout filling. This project was carried out in two phases and was completed in the late 1990’s. The project comprised the conduct of over 200 SCF and ultimate load tests on large scale as-welded and grouted tubular joints. In addition to the testing programme, studies on offshore deployment were carried out to ensure that complete chord grout filling was achievable for all practical scenarios. The primary reason for carrying out this project is the industry-wide recognition that chord grout filling represents an extremely cost-effective and mechanically efficient method to strengthen or repair tubular joints. Further, it has been recognised that double-skin joints (e.g. pile through leg with annulus grout-filled) are often present in structures and the enhanced strength and fatigue characteristics as a result could be exploited to permit more efficient new platform designs or better estimation of joint performance for existing installations. Although API RP2A [1] and ISO [2] recommendations permit the use of grouted joints, little guidance is provided. The guidance that is provided is based on public domain data and engineering principles. This project was carried out to generate a substantial amount of new data/information, leading to the creation of a detail design manual for grouted joints [3,4].