bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Dynamics Simulation of Nanometric Machining Under Realistic Cutting Conditions
Authors: Promyoo R. , El-Mounayri H. , Yang X.
Published: July 2009

Molecular Dynamics (MD) simulations of nanometric machining of single-crystal copper were conducted at a conventional cutting speed (5m/s) and different depths of cut (0.724 – 2.172 nm). The simulations were carried out to predict cutting forces and investigate the mechanism of chip formation at the nano level. The effect of tool rake angles and depths of cut on the mechanism of chip formation were also investigated. Tools with different rake angles, namely 0°, 5°, 10°, 15°, 30°, and 45°, were used. It was found that the cutting force, thrust force, and the ratio of the thrust force to cutting force decrease with increasing rake angle. However, the ratio of the thrust force to the cutting force is found to be independent of the depth of cut.
Studies of Size Effect on the Formability of a Domed Part in Incremental Forming
Authors: Huang Y. , Cao J. , Smith S. , Woody B. , Ziegert J. , Li M.
Published: July 2009

The failure strain level in a single point incremental forming (SPIF) process is found to be much higher than that in the traditional stamping process. Based on the assumption that forming limits in SPIF are dominated by fracture failure, the Oyane ductile fracture criterion is introduced in this paper to predict the fracture initiation site, and hence the forming limit, given the stress and strain values obtained from finite element simulations. The predicted results compare well with those obtained from the SPIF experiments. Furthermore, this fracture criterion is used to study the size effects in SPIF. Analytical equations are derived to comprehensively consider the effects of design and process parameters on sheet formability including sheet thickness, tool diameter, and incremental depth. Previously published experimental data is used to verify the feasibility of the proposed size effect equation.
Application of Envelop Analysis and Wavelet Transform for Fault Detection in Local Gearboxes Failure
Authors: Gu Dong Sik , Choi Byeong Keun , Kim Byeong Su , Lee Jeong Hwan , Son Jong Duk , Yang Bo Suk , Widod Achmad
Published: July 2009

Vibration analysis is widely used in machinery diagnosis and the wavelet transform has also been implemented in many applications in the condition monitoring of machinery. In contrast to previous applications, this paper examines whether acoustic signal can be used effectively along vibration signal to detect the various local fault, in local fault of gearboxes using the wavelet transform. Moreover, envelop analysis is well known as useful tool for the detection of rolling element bearing fault. In this paper, acoustic emission (AE) sensor is employed to detect gearbox damage by installing them around bearing housing at driven-end side. Signal processing is conducted by wavelet transform and enveloping to detect the fault all at once gearbox and bearing using AE signal. Result of fault detection is presented using some general statistical features and a proposed new feature (RGF: Ratio of Gear Frequency) for gear fault calculated from AE signal with different condition.
A Generic Tool Path Generation Methodology for Incremental Forming
Authors: Malhotra Rajiv , Reddy N. Venkata , Cao Jian
Published: July 2009

This paper presents a generic methodology for tool path generation for an arbitrary component that can be formed by single point incremental forming (SPIF) to obtain required geometrical accuracy. Adaptive slicing concepts used in layered manufacturing have been modified and used for generating tool path for SPIF. Experiments and FEA have been carried out to study the effectiveness of the proposed methodology. Results indicate that the proposed methodology enhances the accuracy achievable in SPIF.
Analytical Modeling of Metal Transfer for GMAW in the Globular Mode
Authors: Ersoy U. , Hu S. J. , Kannatey-Asibu E.
Published: July 2009

A lumped parameter dynamical model is developed to describe the metal transfer for gas metal arc welding (GMAW) in the globular mode. The oscillations of molten drop are modeled using a mass-spring-damper system with variable mass and spring coefficient. An analytical solution is developed for the variable coefficient system to better understand the effect of various model parameters on the drop oscillations. The effect of welding drop motion on the observed current and voltage signals is investigated and the model agrees well with the experimental results. Furthermore, the effect of wire feeding rate (or welding current) on the metal transfer cycle time is studied and the model successfully estimates the cycle times for different wire feeding rates.
Friction Damper for Fatigue Damage Mitigation in Steel Jacket Platforms
Authors: Golafshani A. A. , Gholizad A.
Published: July 2009

The performance of friction dampers to mitigate the wave induced vibrations in jacket type offshore platforms has been investigated in this study. Due to the random nature of ocean waves, a full stochastic analysis method has been intended to evaluate the response of the structures utilized with these devices and also a stochastic linearization technique has been used to take the nonlinear behavior of these hysteretic dampers into account. At last, the developed mathematic formulation has been practiced to evaluate the response of a realistic model and to find out the optimal values for the adjustive parameters of the friction dampers to dissipate the wave induced vibrations of the platform.
The Influence of Spud-Can-Soil Interaction on Non-Linear Dynamic Response of a Three-Leg North-Sea Drilling Jack-Up System
Authors: Emami Azadi M. Reza
Published: July 2009

In the present work, we have studied the effects of jack-up-soil interaction parameters on the global nonlinear dynamic response of jack-up platform. Various support conditions are initially considered for translational as well rotational degrees of freedom of jack-up rig. Then the influence of soil type on the dynamic response of hull is investigated. The soil type is varied between loose to very dense sand and from soft to stiff clays. Meanwhile, the effect of variation of soil’s shear modulus is considered. The effects of spud-can embedment ratio and spud-can apex-angle on the overall dynamic response of jack-up platform are also taken into account.
Research on the Pressure Field and Production Ability of Compound Hydrocyclone
Authors: Li Feng , Jiang Minghu , Zhao Lixin
Published: July 2009

Compound hydrocyclone is an important separation equipment in oilfield waste water treatment. In order to grasp the equipment separation characteristics, its pressure field and production ability research is becoming more and more important. In the process of pressure or pressure drop deduced, the hydrocyclone’s vortex field is divided into two parts: semi-free vortex area and compulsive vortex area. In the free vortex area, the pressure and the pressure drop are all deduced by the tangential equation, the pressure gradient equation and the relationship equation of tangential velocity in the hydrocyclone body and the velocity of the rotary crib. In the compulsive vortex area, the pressure and the pressure drop are deduced by the velocity equation and the hydrocyclone’s separation equation. As to the respect of the production ability, it is fixed on the relationship of the inlet flow-rate, overflow pipe diameter, the main diameter of the compound hydrocyclone, pressure drop and the inlet liquid density. The research indicates that the pressure or the pressure drop are all connected with compound hydrocyclone’s diameter, rotary crib’s running velocity and diameter of the maximum tangential velocity track face. As the results of the research, the ascertained key operators, pressure and the pressure drop, the hydrocyclone’s production ability can provide designing consult for the hydrocyclone designers.
Stochastic Analysis of Vertical Wave Loads on Deck
Authors: Kota Ravikiran S. , Moan Torgeir
Published: July 2009

Vertical loads on a platform deck due to incident random waves — long-crested and Gaussian, are studied. Loads on the deck are due to wave-slamming, added-mass over the wetted length and nonlinear Froude-Krylov components. Reliable estimation of these loads and their duration is important in evaluating their effects on platform response (global or local). Emphasis of the present work is to study statistical measures such as expected maximum/minimum impact load and its duration. Gaussian waves are numerically simulated over several points of a two-dimensional deck in time-domain and each deck-wetting event identified and tracked from its inception to expiry. Forces are modeled using a simplified two-dimensional slamming model following Kaplan’s (1987) approach. Use of von Ka´rma´n method, and hence instantaneous wave profile, enables multiple slamming regions to be considered. Simulated results for expected deck-wetting duration and expected maximum wetted length are then compared against analytical results for one- and two-dimensional stationary Gaussian processes.
Risk Based Fuzzy Modeling of Cost Estimating Relationships for Floating Structures
Authors: Cocodia Erebi
Published: July 2009

The increasing cost of offshore developments involving floating structures has resulted in the need to ensure accurate cost estimates are developed very early in the project lifecycle. A number of conceptual costs estimating approaches exist in the industry however, there are concerns about their accuracy and applicability in the early stages of the project. Cost Estimating Relationships (CERs) that can be applied at the concept development phase of floating structures have therefore been developed. They are derived from the reported cost and weight of existing Floating Production, Storage and Off take (FPSOs) vessels and have been applied to ship based offshore development concepts. These CERs are risk based, to produce varying results on a cost (weight) and schedule basis, such that overestimates/ underestimates are offset by risk ranking, to yield a relatively small error in the cost estimates. The uncertainties identified in the risk ranking of components of the development concepts (and resulting cost estimates) are accounted for by applying fuzzy logic to the CERs. This paper presents some of the results of ongoing research that is expected to contribute significantly to the development of floating offshore structures while improving confidence levels in conceptual cost estimates, thus facilitating a comprehensive front-end evaluation of offshore developments.
FPSO-H Preliminary Design Approach
Authors: Ferraz C. , Oliveira N. G. , Vasconcellos J. M.
Published: July 2009

Brazil Campos Basin is under large offshore oil production activity. Many new giant oil fields are under development. In many oil fields Brazil has been using ship tankers converted as FPSO platform vessel. At this moment four FPSO are in final construction phase to be installed in Campos Basin (P-43, P-48, P-50 and P-54). Many oil cargo tankers are transformed to work as FPSO. Although they are showing good characteristics, some problems are rising. The turret design approach was used in the primary FPSO’s design phase but recently the spread mooring system is also under installation in Campos Basin. Two converted FPSO’s (P-43 and P-48) were installed recently using spreading mooring system. The P-43 was installed at 800 m of water depth in Barracuda field at Campos basin. It is brother P-48 is installed at Caratinga field. Both platforms are designed to produce 300.000 barril/day. New ideas about Floating Production Storage and Offloading (FPSO) system have been in focus since some projects started working in an appropriately FPSO design direction. The Naval Architecture and Marine Engineering Department at COPPE/UFRJ has been investigating a new FPSO design and many ideas are under evaluation. One of these ideas is implement a ballast tank system to improve the floating platform behavior in waves with less structure stress. This paper presents the FPSO-H preliminary design. The aim of this project is investigate a new conception where deck are is used to separate accommodation and production plant. Also, the design applied the idea that the number of tanks should be increased to allow better weight distribution and improve the tanks inspection plain. In addition the design includes ballast tanks to increase the operator ability to control stability and vessel motion. The paper presents a case study of FPSO-H design for a Campos basin field. Graphics and tables shown the main results and recommendations are highlights for future work.
Characterization of Polyester Mooring Lines
Authors: Franc¸ois Michel , Davies Peter
Published: July 2009

Fibre ropes are extensively used in marine applications. One critical area of interest is their application as mooring lines for floating offshore platforms, for which primarily polyester is now employed in various regions (offshore Brazil - now for 10 years, West Africa, Gulf of Mexico). Evaluating the response of the system requires a description of the load-elongation properties of the rope. A practical model involving two sets of stiffness data is currently used, and procedures for their measurement are available. This paper presents an overview of this model, then focuses on recent work on the quasi-static stiffness of polyester ropes. This is addressing the variations of the mean tension in the lines, at a very slow rate, under changing weather conditions. Extensive tests were performed, principally on polyester sub-rope samples. Some tests were also performed on a full size 800-ton MBS rope. Besides standard tests, specific tests were performed over an extended range of loading, to cover the situations that may be found in a wide range of systems and design conditions. The factors (measurement accuracy, test conditions, etc...) affecting the values are discussed along with the presentation of tests and results. Results are interpreted to provide practical data for mooring analysis, in the form of a quasi-static load-elongation characteristic. These results also give a better insight into the visco-elasto-plastic response of polyester fibre ropes. For the dynamic stiffness of polyester ropes, an overview of recent and earlier test data is presented. The dependence of dynamic stiffness on testing parameters is discussed, highlighting mean load as the principal parameter under real stochastic loading, and confirming the current practice for modelling dynamic stiffness in design.
Influence of Fibre Stiffness on Deepwater Mooring Line Response
Authors: Davies Peter , Baron Patrice , Salomon Karine , Bideaud Charles , Labbe´ J.-P. , Toumit Ste´phane , Francois Michel , Grosjean Francois , Bunsell Tony , Moysan A.-G.
Published: July 2009

Polyester fibre ropes are now an accepted solution for deepwater mooring of production platforms and a single high tenacity fibre grade is widely used. Few studies of other fibres have been reported but polyesters can be produced with a range of properties by varying drawing parameters, and other stiffer fibres are also available. This paper presents a study of these alternative fibre rope solutions, performed within the French Mooring Line project. First, in order to obtain the input data necessary for mooring line analyses an extensive test program was performed to characterize polyester, improved polyester, PEN, LCP, aramid and HMPE fibre ropes from yarns up to 800 ton break load ropes. Tests at different scales have allowed property transfer to be quantified. Rope modelling has been used in parallel to examine the influence of material and structural parameters. Then, using these data, a series of analyses was run by engineering contractors, which quantified the benefits of higher stiffness for different supports (semi-submersible, production platform and offloading buoy) down to 2500 meter depth. Under certain conditions the stiffer ropes can result in significantly reduced rope diameter and weight.
A Hydrodynamic Analysis Method for Offshore Discharge Operations
Authors: de Jonge J. B. , Peters O. A. J. , Huijsmans R. H. M.
Published: July 2009

Semi-submersible heavy transport vessels are used for transport of floating cargo. In general discharging takes place in sheltered and/or very benign areas, which are often not the areas of operation for these cargos. To be able to discharge in less benign areas, an R&D project was initiated to capture the problems arising at hydrodynamic interaction between two floating bodies in very close proximity. Comparison of model tests with industry standard 3D-diffraction analysis has shown large discrepancies on the motions on the vessel. Therefore, the first stage of this R&D project is to investigate the effect of the narrow gap between the loading deck and the bottom of the floating cargo, find a better analysis solution and incorporate this in a multi-body hydrodynamic interaction method. To be able to develop this method, first the single body problem in extreme shallow water is investigated. This problem was investigated by Drobyshevski [1], who assumed that a two-dimensional flow describes the flow in the narrow gap, being the under-bottom domain, for which better solution methods are available than 3D-diffraction method. His method is tested and validated with a truncated vertical cylinder with flat bottom in extreme shallow water. Since the Asymptotic Matching Program of Drobyshevski does not include 3D-diffraction for arbitrary shaped structures and is only applicable for single bodies, the new developed Multi Domain Diffraction Method is a combination of two-dimensional flow and general 3D-diffraction, both based on linear potential theory.
International Codes and Standards Applicable to Cost Estimating Relationships for Floating Production Systems
Authors: Cocodia Erebi
Published: July 2009

Offshore development engineers are expected to provide early and accurate cost estimates for floating structures. However, there is a tendency within the industry to forget that the cost estimating process may be guided by relevant international standards to ensure consistency and accuracy. There are a number of industry standards and codes on offshore structures and life cycle cost, which are applicable to cost estimating relationships for floating offshore structures; these standards could be used in the cost estimating aspects of concept selection studies, sensitivity analysis and optimisation in the front-end and development planning stages of an offshore project. This paper summarises the author’s study of the applicability of these relevant international standards and discusses ways of applying these to the Cost Estimating Relationships (CERs) for Floating Production Systems (FPS).
Application of Linearized Morison Load in Pipe Lay Stinger Design
Authors: van ‘t Veer Riaan
Published: July 2009

This paper presents numerical results of ship motions and global stinger loads through a combined hydrodynamic analysis of a pipe lay vessel with submerged stinger. The results of nonlinear time domain simulations are compared to those obtained through linearization of the Morison load on the slender stinger elements. Through linearization, an iterative frequency domain solution scheme is developed reducing analysis time significantly. Response amplitude operators in operating and limiting sea states are shown, including the influence of current velocity. Through nonlinear time domain simulations insight is obtained on the distribution and magnitude of the extreme values.
Impact of Linearization of Bilge Keel Damping on the Early Assessment of Vessel Operability
Authors: Gachet Michael , Kherian Jean-Gregoire
Published: July 2009

This paper investigates the benefits of a method whereby roll damping is assessed for each sea state in a given scatter diagram. Particular emphasis is given to the quadratic damping induced by the vessel bilge keels. For each sea state in a scatter diagram, an iterative process is used to obtain a sea state dependent linearized bilge keel damping. This paper shows the impact of such a refined method on the evaluation of operability for a generic vessel. It also provides a comparison with simpler operability assessment methodology both in terms of overall vessel operability and limiting operational sea states for typical scatter diagrams and operability criteria.
Structural Analysis of an Offshore Jacket Model Under Seismic Excitation
Authors: Correia Helder J. D. , Mendes Anto´nio C. , Oliveira Carlos A. F. S.
Published: July 2009

In the present work the action of earthquakes upon offshore jacket structures is analysed by means of ADINA software. Our case-study refers to an existing model structure, previously constructed at the Laboratory of Fluid Mechanics of UBI, which has been analysed from the hydrodynamic point of view — Mendes et al. [1, 2]. The seismic excitation will be imposed at the base of this model structure, with frequencies and amplitudes corresponding to actual earthquake conditions transposed to the model scale of 1:45. The FEM software is utilised to calculate the natural frequencies of the model and to obtain stresses at selected members, as well as their nodal displacements. Our purpose is to quantify maximum stresses occurring in critical structural members and to verify the survivability criterion. The predictions of the numerical model, in terms of the reaction forces at the base and acceleration at the top of the structure, are then correlated with the experimental measurements performed when the model structure is excited in an especially designed shaking table (Correia [3]), revealing a good agreement between both results.
Effect of Moonpool Hydrodynamics on Spar Heave
Authors: Gupta Himanshu , Blevins Robert , Banon Hugh
Published: July 2009

A Spar is a deep draft platform for oil and gas production and drilling operations. One of the features of the Spar platform is the presence of a moonpool (or centerwell) inside the cylindrical hull structure. A unique aspect of the moonpool in Spars is the presence of partial closure plates at the bottom. The seawater goes in and out of the moonpool though these bottom closure (or guide) plates. Depending on the design of a Spar (e.g., the number of risers), typical period of moonpool vertical oscillation can be close to the peak of extreme seastate spectra. The Spar heave motion is thus coupled with the moonpool water oscillation and presents itself as a two oscillator problem. The complex behavior of moonpool and Spar heave interaction is largely ignored in current practice, via conservative assumptions (this is also due to lack of a mathematical model). A new model describing this interaction between moonpool water oscillation and the Spar heave has been developed in this paper. The results of the new model highlight the importance of the moonpool hydrodynamics in predicting the heave motions of Spars.
An Analytic Method of Underwater Observation Tower Due to Wave Breaking Forces
Authors: Saijo Osamu , Eto Hiroaki , Koto Yutaka
Published: July 2009

Wave breaking forces acting on the nearshore structures, such as the underwater observation tower, are subject to breaking wave forces which leads to response behavior that is characteristically nonlinear. Most of the existing underwater observation towers in Japan were constructed in the wave breaking zone as this zone is abundant with underwater life and presents a fantastic under water scene. Convenient access to the observation tower is typically connected by a bridge connecting the tower to an onshore site. This study reported here presents the develop a structural analysis procedure for an underwater observation tower subject to the breaking wave forces using finite element analysis. The tower structure consists of vertical circular cylindrical form that may be tapered in some cases. A procedure for estimating the breaking wave forces and transferring the appropriate hydrodynamic pressure distribution to each nodal point in the finite element model is presented and discussed. The ratio between the total diffraction wave forces and total breaking wave forces was investigated, and then the breaking wave pressure distribution acting on the structural surface was studied. Using that ratio obtained through the comparative studies, the dynamic analysis was conducted in the various wave periods for a constant water depth. After summarizing these calculation results, an analytic method on underwater observation tower due to wave breaking forces was presented.
Whipping Phenomenon Caused by the Internal Flow Momentum on the Catenary Risers of Offshore Petroleum Fields
Authors: Bordalo Se´rgio N. , Morooka Celso K. , Cavalcante Cesar C. P. , Matt Cyntia G. C. , Franciss Ricardo
Published: July 2009

A laboratory-scale model was designed to investigate the influence of the internal flow of two-phase oil and gas mixtures on the motion of slender risers hanging in catenary configuration used for offshore petroleum production in deep waters. The behavior of the riser arises from the interplay of various dynamic phenomena: the long length and relatively small diameter of the pipeline confers a cable-like elasticity to the system, which, under static loading, assumes a catenary shape; dynamic excitation caused by environmental conditions generates oscillations. The internal flow momentum may impose a natural whipping displacement — compounding swinging and bending — adding to the concerns of stress and fatigue. The internal flow may display different two-phase patterns (bubbles, slugs, intermittent, annular or stratified mixtures) possessing completely different characteristics; also, the flow-induced dynamic loading depends on the flow rates of both oil and gas phases. Although computer codes have been developed to simulate the motion of risers, there is much need for experimental validation. This research attempts to discern the effects of the internal flow, discriminating it from the other dynamic phenomena. Accelerometers and video acquisition were employed to verify the phenomenon and to determine the frequency spectrum of the oscillations.
The Effect of a Dual Draft Hull on the Motion Behaviour of a Pipelay/Heavy-Lift Vessel
Authors: van Kessel J. L. F. , van der Velde W. J.
Published: July 2009

The motion behaviour of a Dual Draft vessel was calculated and experimentaly validated by means of model tests. Both the tests and computations showed that the roll behaviour of a Dual Draft vessel in pipelay / transit mode does not correspond to the usual observed response amplitude operator (RAO), where the roll RAO decreases with increasing wave height due to non-linear damping. When the wider top section of the Dual Draft vessel enters the water due to a roll motion, the buoyancy increases at that side and results in an increase of the excitation moment and roll RAO. Non-linear damping is of significant importance on the ship motions and is particulary noticeable in roll motions. This paper describes the effect of a Dual Draft hull on the motion behaviour of a pipelay / heavy-lift vessel in beam seas. The non-linear damping of a Dual Draft vessel will be discussed and calculations of the motion behaviour will be presented and compared with results of model tests.
Second-Order Wave Loads on a LNG Carrier in Multi-Directional Waves
Authors: Renaud Mathieu , Rezende Fla´via , Waals Olaf , Chen Xiao-Bo , van Dijk Radboud
Published: July 2009

Due to the installation of LNG terminals moored in proximity to the coast, the wave kinematics in shallow water and the consequence on the behavior of those terminals have recently became a major concern of the offshore industry. One key issue is the accurate simulation of the low-frequency motions of LNG carriers, specially the surge, for which the vessel presents low damping, in order to perform the design of the mooring system. The present paper focuses on the effect of wave directionality on second-order slow-drift loads and the related response of the vessel. The paper describes results of model tests in regular cross waves — monochromatic but coming from two directions separated by 90 degrees, as well as bichromatic cross waves. The new “middle field” formulation extended to the case of cross waves, is used to compute the wave drift loads and low-frequency Quadratic Transfer Function (QTF). The results are compared with those from the model tests.
The Influence at Vertical First Order Motions Using Appendages in a Monocolumn Platform
Authors: Matsumoto Fabio Tadao , Gonc¸alves Rodolfo Trentin , Malta Edgard Borges , de Medeiros Higor Felipe , Nishimoto Kazuo , Masetti Isai´as Quaresma
Published: July 2009

Oil discovery in ultra-deep-waters is carrying out the ocean engineering to develop new conceptions of offshore exploration and production systems. A promising alternative is a monocolumn platform with moonpool. Concept design has shown its good stability make feasible the use as offshore solution. In order to solve the problem brings by increase on water deep, the use of steel catenary risers and wellhead dry completion has been shown a good solution because it decreases the maintenance cost. However, this solution needs a very low vertical motion. In general, platform like the monocolumn present resonance on vertical motion (15–20 sec to heave motion, 20–25 sec to roll/pitch motion) close to typical wave energy. This fact is so that designers introduce mechanisms to leave the natural periods out of wave energy. The moonpool as passive absorber motion was a solution found by designers. The water inside moonpool acts out-of-phase with platform motion. This difference on phases can attenuate the platform dynamic response. Other solution is water-line-area (AWL) reduction that reduced the restoring forces and consequently increased the value of vertical motions natural periods. These two alternatives showed very efficient to improve the monocolumn performance. This paper presents the gain, in terms of motions, achieved as the appendages introduction on the platform. These appendages consist of two plates, one in form of a disk and other around it. It can be located on the bottom at platform and inserted inside at the moonpool. Model test conduced on the scaled platform shows that heave and pitch natural period increased approximately 4 seconds when this appendages is allocated on the bottom. Practically any change is noted when it is allocated only inside of the moonpool.
Conceptual Design of Floating Production and Storage With Dry Tree Capability
Authors: Gonc¸alves Rodolfo Trentin , Matsumoto Fabio Tadao , de Medeiros Higor Felipe , Brinati Hernani Luiz , Nishimoto Kazuo , Masetti Isai´as Quaresma
Published: July 2009

This paper introduces a new concept and a preliminary study for a floating unit aimed at exploring and producing oil in ultra deep waters. This platform, which combines two relevant features — great oil storage capacity and dry tree production capability — comprises two bodies with relatively independent heave motions between them. A parametric model is used to define the main design characteristics of the floating units. A set of design alternatives is generated using this procedure. These solutions are evaluated in terms of stability requirements and dynamic response. A mathematical model is developed to estimate the first order heave and pitch motions of the platform. Experimental tests are carried out in order to calibrate this model. The response of each body alone is estimated numerically using WAMIT® code. The paper also includes a preliminary study of the platform mooring system.
SCR Application for Turret Moored FPSOs in West Africa
Authors: Wang Howard H. , Kan Wan C. , Orphee Juan I. , Crawford Mark D. , Sutherland Jim , Gioielli Paulo C. , Miller John E.
Published: July 2009

Turret moored Floating Production Storage and Offloading (FPSO) systems with flexible risers have been successfully used in many deepwater developments in West Africa. However, Steel Catenary Risers (SCR) have not been used on a turret moored FPSO because of concerns with the riser fatigue and compression loading due to the large FPSO motions at the turret location. ExxonMobil has initiated a development program to establish the feasibility of SCRs on turret moored FPSOs. The goal of this work effort is enable the use of SCRs on West African turret-moored FPSOs and thereby expand the riser concept options to bring potential economic advantage for future prospects. Additionally, the SCRs may be needed to comply with local content requirements. The development program consists of identifying the limitations of a conventional SCR design, establishing feasible SCR concepts that meet the strength and fatigue requirements, and pre-qualification of a high fatigue performance welding technology. The program focuses on alternate SCR concepts including SCRs with locally weighted and buoyant sections. This paper presents the SCR concepts and the associated analysis results which demonstrate the elimination of compressive loads in the touch down area and the achievement of adequate weld fatigue performance throughout the riser. This paper further presents the results of the inconel weld pre-qualification program including fatigue tests on large and small diameter pipe to demonstrate enhanced fatigue performance.
Effect of Wave Loading on the Seismic Behavior of a Typical Fixed Jacket-Type Platform
Authors: Omrani Z. , Gharabaghi A. R. M. , Hosseini S. R. , Nouri S.
Published: July 2009

Design of fixed offshore platforms to resist earthquakes involves many of the same problems and issues as other onshore structures. However, there are some important differences that the most important one is the presence of seawater. It influences the mass, stiffness, damping and strength characteristics of the platform, which can have important effects on the structure response characteristics. The entrained water inside the platform elements and the water that is accelerated by the motions of the structure, have very important effects on the mass and damping characteristics of the platform. The presence of other environmental loads, particularly waves can also influence the response of these structures. In this paper, the nonlinear response of a typical jacket type platform, which has been installed in Persian Gulf, under wave and earthquake loadings are studied. The structure is modeled by ANSYS, finite element software. Time histories of different earthquake loadings are applied. Wave characteristics are based on local information. These loadings are applied separately and simultaneously. Moreover, they are applied in the same direction and different directions. The results are compared with each other and the most sever cases are extracted.
VIV Control and Drag Reduction Using the Guided Porosity Concept
Authors: Fernandes Antonio C. , Coelho Fabio M. , Franciss Ricardo , Neto Severino F. S.
Published: July 2009

This paper aims to discuss the effectiveness of a new passive kind of VIV (Vortex Induced Vibrations) suppression. Moreover, the proposed solutions leads to a significant drag reduction when compared with conventional proposals (strakes for instance). The concept of guided porosity is applied in experimental tests conducted with low mass ratio cylindrical models. The works also shows that the job (VIV control and drag reduction) is achieved without moving parts, in contrast with segmented fairings. It also advances in terms of the omnidirectional solution. Initially, the concept is discussed in terms of the potential theory. Then experimental results are presented in terms of displacements and forces.
Fluid-Structure Interaction Simulation Using an Incompressible SPH method
Authors: Rafiee Ashkan , Thiagarajan Krish P.
Published: July 2009

In this paper an incompressible Smoothed Particle Hydrodynamics (SPH) method is proposed for simulation of fluid-structure interaction problems, deploying the pressure Poisson equation to satisfy incompressibility constraints. Viscous fluid flow past rigid and hypoelastic solid surfaces is studied. The fluid is fully coupled with the solid structure that can undergo large structural deformations. A key feature of the proposed scheme is that the no-slip and coupling conditions on the contact surface are satisfied automatically. To alleviate the numerical difficulties encountered when a hypoelastic solid structure is highly stretched, an artificial stress term is incorporated into the momentum equation which reduces the risk of unrealistic fractures in the material. Three challenging test cases, deformation of an elastic plate subjected to time-dependent water pressure, collapse of a water column with an obstacle and breaking dam on a hypoelastic wall are solved to demonstrate the capability of the proposed scheme. The results are in very good agreement with available experimental results.
Experimental Results of Tsunami Bore Forces on Structures
Authors: Robertson I. N. , Riggs H. R. , Mohamed A.
Published: July 2009

A series of experiments has been carried out at the Tsunami Wave Basin (TWB) at Oregon State University (OSU) to determine the effect of tsunami bores on coastal and near-shore structures, especially buildings and bridges. The TWB is equipped with a piston-type wavemaker capable of generating clean solitary waves. The facility was used to model tsunami bores breaking over coastal reefs and their impact on structural components, including columns, walls, and horizontal members, such as building floors and bridge decks. Detailed wave height and velocity measurements were recorded as well. This paper focuses on the fluid forces of a bore impacting a wall/floor system. The experimental setup will be described and force results will be presented. The experimental results provide needed data to validate CFD models that can then be used to determine forces for a wider variety of situations.
Integrated Fatigue Analysis of the GAP Structural System
Authors: Melis Cecile , Laymond Stephane , Jean Philippe
Published: July 2009

MURPHY Sabah Oil Co. Ltd. has developed the Kikeh Field located offshore Malaysia in the South China Sea in a water depth of 1325m. This field development is based on a Floating Production Storage and Offloading unit (FPSO) and a Spar Dry Tree Unit (DTU). Fluids are transported in fluid transfer lines (FTL) using SBM’s newly developed and patented Gravity Actuated Pipe (GAP) system. The GAP is an interesting combination of mooring (tether chains), dynamic steel riser (carrier pipe and flowlines) and steel structures (towheads). Design codes and standards usually address the design of these components separately. One of the challenges of the GAP project is to have a consistent design philosophy for all the components so that the GAP can be treated as an integrated system with homogeneous quality and safety levels. GAP component fatigue analysis is a good example of integrated system design. In the GAP, fatigue loading is applied by the floaters, through the tether chains, to the towheads into the carrier pipe. The fatigue analysis of individual GAP components cannot be performed in isolation — it must be the result of an integrated GAP fatigue analysis. A global model of the GAP is built with towheads modelled as rigid bodies and tether chains and carrier pipe modelled as dynamic lines. This model is used to obtain time series of loads on all components of the GAP. The fatigue of each component is calculated using the same methodology based on stress Response Amplitude Operators (RAOs) for a selected number of combinations of FPSO headings, wave directions, FPSO drafts and fluid densities. This methodology is classical for chains and steel pipes. It is less classical to apply such a detailed methodology for large structures like towheads. The towhead structures are key components that provide connection between tether chains and carrier pipe, flexible jumpers and steel flow lines, carrier pipe and decoupling overhead buoyancy tank. As such, the fatigue analysis of the towhead is as critical as for the tether chains and the carrier pipe. Finite element models of the towheads have been subjected to unit loads from all components attached to them and from the dynamic fluid pressures generated by unit towhead accelerations. Using the loads extracted from hydrodynamics calculations on the global GAP model and the matrix of stress for unit loads, the time domain approach is kept throughout the complete structural assessment of the towheads. This is in order to maintain a high degree of accuracy in the stress prediction. Given the criticality of the carrier pipe, a very detailed Engineering Criticality Assessment (ECA) is performed to define flaw acceptance criteria to be used during the Non Destructive Examination (NDE) campaign.
Coupled Analysis of an FPSO and Dry Tree Unit Connected by a Gravity Actuated Pipe (GAP)
Authors: Naciri Mamoun , Schaegis Helene , Ardoise Guillaume
Published: July 2009

MURPHY Sabah Oil Co. Ltd. has developed the Kikeh Field located offshore Malaysia in the South China Sea in a water depth of 1325m. This field development is based on a Floating Production Storage and Offloading unit (FPSO) and a Spar Dry Tree Unit (DTU). Fluids are transported in fluid transfer lines (FTL) using SBM’s newly developed and patented Gravity Actuated Pipe (GAP) system. To our knowledge this is the first time two large moored floaters are connected together by a slender body closing a gap of 1600m. It was not clear at the beginning of the project to what extent the first and second order motions of the two floaters were coupled, if at all, owing to the presence of the GAP system. To investigate the extent of coupling, both frequency domain (modal analysis) and time domain analyses of the FPSO, GAP system and Dry Tree Unit were performed. The salient features and results are presented.
Gap Onshore Construction: Welding and NDE Challenges
Authors: Pearson Anthony , Laymond Stephane , Werner Mark
Published: July 2009

MURPHY Sabah Oil Co. Ltd. has developed the Kikeh Field located offshore Malaysia in the South China Sea in a water depth of 1325m. This field development is based on a Floating Production Storage and Offloading unit (FPSO) and a Spar Dry Tree Unit (DTU). Fluids are transported in fluid transfer lines (FTL) using SBM’s newly developed and patented Gravity Actuated Pipe (GAP) system. Two key areas in the construction of the Kikeh GAP Fluid Transfer Line were Welding and Non-Destructive Examination (NDE). The welding of flowlines was performed using the Gas Tungsten Arc Welding (GTAW) and Shielded Metal Arc Welding (SMAW) processes. The welding of the carrier pipe utilized the double-sided Submerged Arc Welding (SAW) process for tubular prefabrication and the manual/automated GTAW processes for girth welding in the field. Welding process selection for the carrier pipe was driven by the need for high weld quality in order to provide optimum fatigue performance. Extensive welding procedure development was carried out for the manual/automated GTAW techniques in order to determine optimum welding parameters as this constituted the most critical welding activity. Project specific welding procedure qualification was undertaken for all field welding activities. An Engineering Criticality Assessment (ECA) was performed to determine maximum allowable defect sizes for the welded joints. This ECA established that the welded joints had a low defect tolerance, which consequently dictated the necessity for an NDE technique providing a high level of flaw detection and accurate flaw sizing. Automated Ultrasonic Testing (AUT), using a Phased Array (PA) system based upon the ‘Pulse Echo Method’, enhanced with mapping images and ‘Time of Flight Diffraction’ (TOFD), was therefore nominated as the volumetric inspection method for the carrier pipe. The AUT system capabilities were verified by qualification, prior to mobilization to the field, to determine the system Probability of Detection values (POD) and imperfection height sizing accuracy as well as assessing the AUT operator(s) performance.
Simulation of Vibration Control of Offshore Platforms Under Earthquake Loadings
Authors: Ma Rujian , Wang Jungang , Zhao Dong
Published: July 2009

The simulation of vibration control of offshore platforms under earthquake loadings is performed in this paper by using the ANSYS software, in which the first three order natural frequencies of the platform are controlled by the ETMD system where the parameters of the system are taken in the optimal regions. The results show that the ETMD system can reduce the vibration of the platform effectively under earthquake loadings. Another important conclusion is that reasonable control effects can be obtained by control the first order natural frequency. There are 10% and 20% increase in y and z directions when the first two and three order natural frequencies are controlled simultaneously.
The Air-Water Sloshing Problem: Parametric Studies on Excitation Magnitude and Frequency
Authors: von Bergheim P. , Thiagarajan K. P.
Published: July 2009

The problem of liquid sloshing has gained recent attention with the proliferation of liquefied natural gas (LNG) transport in partially filled tanks of a tanker vessel. In this paper, we first present the rudiments of a linear potential theory for sloshing motions in a two-dimensional rectangular tank due to small amplitude sway motions. We obtain closed form solutions for the Response Amplitude Operator (RAO) of slosh amplitude as a function of frequency. Then we present the computational fluid dynamics (CFD) formulation of the problem using dynamic meshing features. The CFD results for RAO are compared with theory, and good agreement is noticed. The impact pressure time series is compared with published experimental data, and good agreement is seen. Contrary to common observations, we notice that turbulent flow models give better and more accurate results than laminar models. CFD simulations are then performed for a range of excitation amplitudes and frequencies. Pressure contours and water surface elevation are monitored as function of excitation amplitude and frequency, and the regions of impacting vs. non-impacting are delineated.
A Numerical Study on the Impact of Filling Level on Liquid Sloshing Pressures
Authors: Rakshit Dibakar , Repalle Nitin , Putta Jagadeesh , Thiagarajan Krish P.
Published: July 2009

Sloshing is a critical phenomenon in Liquefied Natural Gas (LNG) containments in terms of impact loads on the walls of the tank. The peak impact pressures and its location in the tank during sloshing depend on tank fill levels, period and amplitude of oscillation of the tank. In the present study, numerical investigations were carried out on the sloshing motions in a two-dimensional tank at various fill levels due to sway excitation. The two-phase flow was modeled using finite volumes and the Volume-Of-Fluid (VOF) technique using the commercial software FLUENT®. The fill levels were varied from 10–95%, and the excitation time periods were varied from 0.8–2.8 s for constant sway amplitude of 0.25m (peak-peak) at 1:30 scale. The proposed numerical model gives the average peak pressures and peak pressure locations required for the future experiments to be conducted in a laboratory.