bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulated and Experimental Capture Times of Micro-Scale Pins Collected From a Vibratory Feeder
Authors: Luidens Martha M. , Cipra Raymond J.
Published: May 2009

Challenges occur during micro-scale parts assembly due to the strong influence of electrostatic, van der Waals, capillary, and magnetic forces acting on the bodies, resulting in sticking of micro-scale parts to assembly grippers and to other parts, making part manipulation very difficult. In order to provide insight into the influences of various forces which occur while collecting micro-scale pins on a vibratory feeder, experimental tests were conducted measuring the pin capture times while varying pin length and vibrating amplitude. Based on the results from these experiments and the environment in which the tests were conducted, electrostatic forces and drag forces were found to be the most influential. From the experimental results, modifications were made to an existing impulse-based simulation to incorporate a drag force and an electrostatic force, and simulations were conducted to find the effect of changing pin length and vibrating amplitude on the pin capture times. For one micro-scale pin on the vibratory feeder bowl, both the simulated and experimental results show good correlation for the mean capture time which increases when pin length increases or when the vibrating amplitude of the feeder bowl increases. The simulation results for multiple pins when varying pin length gave mean capture times which did not follow the same trends as the experimental testing; however, due to the stochastic nature of the vibratory system, the simulated results were considered comparable. This difference when looking at multiple pins is potentially attributed to the two-dimensional nature of the simulation.
On the Regulus Associated With the General Displacement of a Line
Authors: Huang Chintien , Kuo Wuchang , Ravani Bahram
Published: May 2009

In the two position theory of finite kinematics, we are concerned with not only the displacement of a rigid body, but also with the displacement of a certain element of the body. This paper deals with the displacement of a line and reveals the regulus that characterizes such a displacement. Residing on a special hyperbolic paraboloid, the regulus is obtained by the intersection of three linear line complexes corresponding to a specific set of basis screws of a 3-system. The degeneration of the regulus when two positions of a line intersect is also discussed. In this paper, the regulus of intersection is obtained geometrically as well as analytically. The discovery of the regulus lays a geometric foundation for dealing with line-based problems in computational kinematics and computational line geometry.
Dynamics Analysis of MEMS-Based Vibratory Angular Rate Sensors Via a Generic Reduced Order Model
Authors: Asokanthan Samuel F. , Cho Jihyun , Wang Tianfu , Chen Yu-Kuang
Published: May 2009

Instabilities in micro sized vibratory angular rate sensors that are subject to periodic fluctuations in input angular rates have been investigated. For the purpose of acquiring stability conditions, dynamic behavior of periodically perturbed linear gyroscopic systems is studied in detail. It is shown that the effects from the centrifugal forces as well as the associated fluctuations are negligible, and based on these findings, a simplified model is proposed. An asymptotic approach based on the method of averaging has been employed for establishing closed-form instability boundary conditions. In particular, onset of instability due to sum-type combination resonance has been found to be occur. A numerical approach based on the maximal-Lyapunov exponent is employed for validating the analytical predictions. Stability predictions have been illustrated via stability diagrams in the excitation amplitude-frequency space. Based on the results from this model, dangerous critical frequencies that depend on the system natural frequencies may be avoided during the design process and useful design specifications can be formulated.
Motion Classification Using Wireless Sensors for Activity Monitoring in Firefighting
Authors: Nguyen Nguyen , Sundararajan V. , Zordan Victor B.
Published: May 2009

Firefighter’ chief reason for entering a burning structure is to search for and rescue potential victims. Currently, their primary method for communication is an often-congested two-way radio which the firefighters use from within a burning building to relay their activities (and other information) to an external battalion chief. In response to discussions with firefighters in the field, we introduce an approach for automatically segmenting and classifying a select set of activities using wireless accelerometers attached to the human body. The activities we focus on are the ones that are most commonly conducted by firefighters and that are important to the battalion chief for understanding the ongoing search and rescue. In our implementation, sensors continuously measure the acceleration of a small number of body segments and transmit data back to a central base station. At runtime, our system classifies data for short intervals, relying on training examples of the activities of interest. We show that our approach can appropriately detect motions in real-time without significant latency using as few as two accelerometers.
The Relation Between Performance, Design Space, Refinement, and Information
Authors: Krus Petter
Published: May 2009

Design in general is about increasing the information of the product/system. Therefore it is natural to investigate the design process from an information theoretical point of view. In this paper the design process is described as an information transformation process, where an initial set of requirements are transformed to a system specification. Performance and cost are both functions of complexity and refinement, which can be expressed in information entropy. There are essentially two ways of increasing the information content in a system. One is to reduce tolerances in the design parameters. The other way is to increase the design space, by introducing more features into the design. Both of these aspects of increasing information content are discussed through the establishment of a formal framework. In this way, the relationship between concept refinement and design space expansion can be viewed in information theoretical terms. The information theoretical model is demonstrated on examples. The model has practical implications for the balance between number of design parameters, and the degree of convergence in design optimization. It can also be used to give a rough estimate of number of parameters that are needed for a specified degree of accuracy in the optimization result, or the number of parameters that are meaningful to use under uncertainty.
Feedforward and Feedback Control of Lane Keeping by the Human Driver
Authors: Zhou Jing , Peng Huei
Published: May 2009

A feedforward/feedback control model of drivers’ lane keeping behavior is presented in this paper. The model is based on the linearized analysis of the driver’s curve negotiation dynamics. In real driving, the driver previews the upcoming road geometry and relies on perceived vehicle states to maintain a desired lateral position. Feedforward and feedback roles are associated with different perceptual cues, and the lane keeping task is formulated into a disturbance rejection problem. Control parameters are determined to reflect natural stable human characteristics. Verification tests in a realistic simulation environment demonstrate the ability of the model to generate driver/vehicle lane keeping responses comparable to those obtained on a simulator. Potentially, the derived control algorithm can also be applied to automatic lane-tracking as long as reliable information regarding vehicle states and upcoming road conditions is accessible.
NiMH Battery Characterization and State-of-Charge Estimation for HEV Applications
Authors: Bornatico Raffaele , Storti Andrea , Mandrioli Leonardo , Zappavigna Annalisa , Guezennec Yann , Rizzoni Giorgio
Published: May 2009

One of the most important challenges for effective energy management in Hybrid Electric Vehicles (HEVs) applications is the capability of correctly estimate the batteries State of Charge (SoC). This task is particularly arduous to accomplish in real-time, due to the complexity and nonlinearities, as well as the inevitable presence of on-board measurements errors. The objective of this paper is to develop a NiMH battery model which accounts for the relevant dynamics related to HEV applications. A detailed series of experiments allowed for system identification to be performed in order to design an equivalent electrical circuit model of the battery, where capacitors take care of voltage relaxations, while resistors model all forms of energy losses. Experimental results are then compared with model prediction, resulting in variances limited to less than 3.5%. Finally, the validated model was inverted to serve as a main component of a proposed SoC estimator, whose performance is of key relevance for effectiveness of HEVs. Results during actual vehicle operations are shown delineating a successful application.
Advanced Tool for Railway Planning and Traffic Control Decision Making
Authors: Sanz Bobi Juan de Dios , Gala´n Lo´pez Ramo´n , Mera Sa´nchez de Pedro Jose´ Manuel , Garzo´n Nu´n˜ez Jorge , Reyes de la Pen˜a Pedro
Published: May 2009

This paper focuses on the difficulties noticed in Railway’s Decision Making processes according to schedule-making and to control tasks on the central operation post of principal railway lines. Traffic density, rail stations’ capacity and human criteria are main factors in order to develop and to obtain a useful tool for helping Railway Administrations in the decision making processes. In this sense, a tool is presented to operate off-line for planning and scheduling; and on-line for common operation on traffic central post. The architecture is oriented to save time in specific modules where operation tools are trained on different scenarios to solve particular ‘events’ which are defined to be critical for the line. The objective is the generation of an optimal operational plan to regulate the line with minimum train delay according to the characteristics of the line (stations, facilities) and vehicles. The results are proven useful for mass-transport, like underground, or open-line topologies with mixed traffic both passenger and freight.
Riser Modeling Scheme for a Load-Sharing Marine Drilling Riser
Authors: Chang Roger , Fisher Ed
Published: May 2009

Typical riser analysis for a marine drilling riser using the conventional composite modeling scheme will have only one line of elements mathematically representing riser pipe and auxiliary lines. The mass and weight of the riser system may be properly modeled. It is up to the analyst to include auxiliary lines’ stiffness, bending and/or axial. The rule of thumb is to ignore them if the riser is not of load-sharing design, otherwise include them. However, even with stiffness included in the model, the composite modeling scheme will not capture the load path correctly. Parametric studies were performed to develop a modeling scheme for a load-sharing marine drilling riser. This paper compares the results by the newly developed modeling scheme with the composite model. Significantly different tension patterns between the two models are observed.
Titanium Stressjoint Design for the Top Connection of a SCR in HPHD
Authors: de Andrade Edmundo Queiroz , Siqueira Elizabeth Frauches Netto , Mourelle Marcio Martins , Caldwell Chris
Published: May 2009

The top connection for the SCRs is one of the main critical points of their design. This situation becomes more challenging principally when there are high pressures and high deep water (HPHD) combined with extreme environmental loads — as is the case in the Gulf of Mexico. PETROBRAS became aware of this problem during the conceptual study of SCRs for ultra-deep waters, where the SWL is in the vicinity of 8200 ft, and with internal pressure of 12100 psi to 15000 psi. With this scenario in mind, a Titanium stressjoint began to be considered as the principal solution to the top connection. Due to this, PETROBRAS — in partnership with RTI ENERGY SYSTEM — developed a study to design a stressjoint model which would validate the SCR. This paper broadly discusses the search for this top connection solution. Dynamic global and local analyses were performed, which led us to the final solution of a titanium and steel mixed stressjoint.
Sour Service Corrosion Fatigue Testing of Flowline Welds
Authors: McMaster Fraser , Thompson Hugh , Zhang Michelle , Walters David , Bowman Jonathan
Published: May 2009

An examination of the corrosion-fatigue behavior of production quality welds in X65-type pipes was performed. Due to the low cycle operational nature of the production flowline system, the fatigue test frequency was substantially lower (0.01Hz vs. 0.33Hz) than typically utilized during corrosion-fatigue testing. Also the tests were performed at higher stress ranges than previous sour service fatigue tests, which to date have targeted riser fatigue loading regimes. Stress-life (S-N) samples were removed from segments of pipe with outside diameters of 10.75 inch (wall thickness of 1.30 inch) and 9.625 inch (wall thickness of 1.26 inch) containing fully inspected, production-quality circumferential welds. Environments examined included laboratory air conditions as well as deoxygenated brine supplemented by a gas mix of H2S and N2. For all environmental tests performed, the dissolved oxygen levels were maintained at less than 10 ppb during all testing. The measured fatigue life decrease in the curved pipe segments was in the range of 8–110 times due to the combined effect of the material and fluid property variables examined. The results of this work clearly illustrated the impact of sour-service corrosion fatigue, in welded carbon steel pipes, to the multitude of variables involved. Nevertheless, the foregoing experimental work clearly demonstrated the importance of performing environmental relevant testing when considering material and process selection for offshore applications.
Ice Gouge Reliability of Offshore Arctic Pipelines
Authors: Younan A. H. , Hamilton J. M. , Weaver J.
Published: May 2009

Offshore arctic pipelines must be designed with adequate reliability against damage or rupture due to the effects of ice features that gouge the seafloor. A common design approach is to bury the pipeline sufficiently deep to avoid contact by a gouging ice keel of a target rare return interval. The effects of sub-gouge soil displacements on pipe stress or strain are also assessed. It is implicitly assumed, in this traditional approach, that ice keels have infinite strength and momentum, so that gouge depths are not limited by ice keel failure and direct contact of ice on pipe results in rupture. However, many first-year ice features may not be strong enough to gouge the soil to the extreme gouge depths. Considering the high cost of incremental pipeline burial depth, it may be desirable to account for limits imposed on extreme gouge depth by soil resistance. Introducing these limits, however, gives rise to additional uncertainty and requires the development of a reliability framework to assess the consequences of direct ice contact on the buried pipe. This paper presents a methodology for evaluating the probability of ice gouging non-performance of a pipeline while explicitly accounting for the ability of the seabed soil to limit ice gouge depth based on the relative strength of soil and ice keel. Non-performance is defined either as ice contact on the pipe or exceedence of some level of acceptable pipe strain when contacted by ice. A three-step approach is followed through the use of nonlinear finite element analysis to estimate pipeline capacity, the statistical characterization of demand from ice gouging events, and the development of a reliability framework combining demand and capacity. Parameters governing the capacity of the pipeline are identified, the sensitivity of the pipeline reliability to various parameters is investigated, and the impact of allowing ice contact on pipeline reliability is presented. Relative merits and risks of allowing ice contact are discussed in the context of pipeline reliability. The presented results and discussions are believed to be of significant help in the development of burial depth criteria for future offshore arctic pipelines, and certainly in the reassessment of existing ones.
The Effect of Flexible Pipe Non-Linear Bending Stiffness Behavior on Bend Stiffener Analysis
Authors: Caire Marcelo , Vaz Murilo Augusto
Published: May 2009

Bend stiffeners are critical components for flexible risers and umbilical cables employed to ensure a safe transition at the riser-vessel interface, avoiding overbending and accumulation of high cyclic fatigue damage. The analysis and design of bend stiffeners usually consider the system as a unique beam, in which the pipe bending response is linear. However, the structural mechanics of these complex layered structures is governed by internal friction mechanisms that yield non-linear moment versus curvature relationship. In fact, the pipe structure exhibits an approximately bi-linear hysteretic bending moment against curvature relationship arising from the progressive activation of friction and consequential slipping between adjacent layers. The flexible pipe bending stiffness substantially reduces after a given critical curvature (i.e., after slip between adjacent layers) is reached. In this paper, the effect of this flexible pipe non-linear response on the bend stiffener design is evaluated. The mathematical formulation and the solution methodology are presented. A set of four non-linear ordinary differential equations is obtained from geometrical compatibility, equilibrium of forces and moments and constitutive equations and a numerical solution is obtained using the shooting method. A finite element analysis is developed to validate the analytical model and to assess the effect of the radial clearance between the structures on the bend stiffener response. A case study is presented for some static loading conditions and it is observed that the bending stiffness bi-linear behavior may not affect the bend stiffener extreme load design results, but it may significantly influence the fatigue analysis.
The Vibration Control of a Combined Anti-Vibration Platform Under the Rare Seismic Wave Forces
Authors: Zhao Dong , Cai Dongmei , Ma Rujian , Qu Zhaofu , Chen Zhonghe , Wang Jungang
Published: May 2009

The combined anti-vibration platform, which was composed of the mega-frame platform (MFP) and the multiple extended tuned mass damper (METMD) system, was simplified as a multiple-degree-of-freedom system for the study of the resonant responses’ decrease of the platforms under the rare seismic wave forces. The METMD system was made up of several ETMD units that had a specific frequencies’ bandwidth. The average frequency was tuned to the platform’s first natural frequency, which was the target frequency to be controlled. So, the offshore platform and the METMD system were simplified to an m+1 DOFs system to be analyzed theoretically. The ratio of the METMD system mass to the platform residual mass was 14% and the ratio of the exciting frequency to the platform’s natural frequency varied between 0.5 and 1.5 The theoretical analysis shows that the platform has the best vibration control effect when the frequencies’ bandwidth is 0.45; the damping coefficient is 0.1 and the number of the ETMDs is 5. In order to analyze the dynamic response of the combined anti-vibration platform under the random seismic loads, the El-Centro, Taft and Qian’an seismic waves were chosen as typical loads and their maximal acceleration values had been adjusted according to 8 level fortification under rarely occurred earthquake. The FEM simulations shows that: 1) the average vibration displacements decrease ratios of the entire platform in the X, Y, Z directions are 80.48%, 61.93% and 64.31% respectively under the El-Centro seismic wave; 2) the X, Y, Z directions average decrease ratios for the entire platform are 84.21%, 49.95% and 56.6% respectively under the Taft seismic wave; 3) the X, Y, Z directions average decrease ratios of the entire platform are 50.09%, 32.645% and 23.34% respectively under the Qian’an seismic wave; and 4) the average displacement decrease ratios of the whole platform in X, Y and Z-direction are 71.59%, 48.18% and 48.08% respectively considering all seismic waves above. So the combined anti-vibration platform has the better ability on the vibration control under the random seismic loads.
Experimental and Numerical Study of Wake Interference and Clashing Between Steel Catenary Risers
Authors: Fontaine E. , Capul J. , Rippol T. , Lespinasse P.
Published: May 2009

The aim of this work is to estimate the risk of clashing between steel catenary risers (SCRs) due to wake interference. More generally, the validity of clearance analysis between risers as recommended by design codes is discussed. Considering the complexity of the problem, theoretical, numerical and experimental approaches have been used jointly. Similitude rules have been investigated to reproduce Wake Induced Oscillations (WIO) at model scale. Different regimes have been identified (stable, unstable and critical) depending on the intensity and effects of WIO. The validity of steady wake models used in the industry is discussed in view of the experimental data. Finally, onset criteria for WIO and clashing are proposed based on comparison between experimental and numerical results.
Visual Assessment of Corroded Condition of Plates With Pitting Corrosion Taking Into Account Residual Strength: In the Case of Webs of Hold Frames of Bulk Carriers
Authors: Nakai Tatsuro , Matsushita Hisao , Yamamoto Norio
Published: May 2009

Corrosion pits with a conical shape are typically observed in hold frames in way of cargo holds of bulk carriers which carry coal and iron ore. The ratio of the diameter to the depth of the typical corrosion pits is in the range between 8–1 and 10–1 and its diameter might become up to 50mm. The evaluation of residual strength of members with large uneven pitting corrosion is difficult compared with that of members with general corrosion. Therefore, it is of crucial importance to develop a method for the evaluation of residual strength of pitted members. The purpose of the present study is to investigate the effect of pitting corrosion on the ultimate strength of steel plates under various loading conditions and explore a method for the evaluation of residual thickness of pitted plates. In the present study, a series of non-linear FE-analyses has been conducted with steel plates with a variety of random pit distributions under various loading conditions such as uni-axial compression, bi-axial compression, shear and combination of these. In these analyses, random pit distributions were calculated by the previously developed corrosion model. It has been shown that equivalent thickness loss, which is defined as thickness loss of uniformly corroded plates with the same ultimate strength as the randomly pitted plates, is smaller than or equal to 1.25 times the average thickness loss. It has been also revealed that the equivalent thickness loss for the ultimate strength under the above-mentioned loading conditions is smaller than average thickness loss at the minimum cross section, where the average thickness loss at the minimum cross section almost corresponds to the equivalent thickness loss for the tensile strength. Based on these findings, a method for the estimation of equivalent thickness loss of pitted plates has been discussed using the thickness diminution-DOP relationship, where DOP (Degree of Pitting Intensity) is defined as the ratio of the pitted surface area to the total surface area.
Prevention and Monitoring of Fatigue-Corrosion of Flexible Risers’ Steel Reinforcements
Authors: Fe´lix-Henry Antoine
Published: May 2009

Flexible pipelines used for oil production on floating platforms are subject to dynamic loads and are designed to ensure no fatigue failure over their service life. Their reinforcing layers are located in a very confined environment called the annular space and are made out of high strength steel wires. If these steel wires are subjected to a wet corrosive environment, corrosion fatigue can become an issue, especially for sour service applications with the presence of H2S and CO2. Over the past years, Flexi France has dedicated a lot of effort not only to predict the composition of the environment in the annular space and the steel wires’ fatigue-corrosion behaviour, but also towards the prevention of corrosion and the monitoring of this annular space. Several innovative solutions recently developed and tested in Flexi France are presented in this paper concerning prevention of annular space flooding by seawater ingress or by diffused water. The paper also presents new designs for integrating monitoring sensors into the pipe structure and corrosion fatigue mitigation methods. Inspection and monitoring methods by integration of sensors or conduits within the pipe structure during its manufacture are now commercially available. These technologies, some of which are already applied on offshore fields, extend the usage limits of high strength steels and increase the fatigue life of dynamic risers. This is of primary importance for demanding applications such as deepwater, high pressure and/or sour service production.
A Cohesive Zone Modeling Approach to Hydrogen Induced Stress Cracking in 25%Cr Duplex Stainless Steel
Authors: Olden Vigdis , Thaulow Christian , Johnsen Roy , O̸stby Erling
Published: May 2009

Hydrogen influenced cohesive zone elements are implemented in finite element (FE) models of rectangular U and V notched tensile specimens. The material description outside the cohesive zone is representative of a fine grained 25% Cr duplex stainless steel, UNS32760-S. A three step procedure consisting of conventional elastic plastic stress analysis, stress driven diffusion analysis and finally cohesive zone fracture initiation analysis makes the basis for the presented work. The applied boundary conditions are representative of mechanical stresses and environmental loads on an oil and gas pipeline in subsea conditions. A linear traction separation law gives reasonably good fit with experimental results for gross stress levels of 0.85–0.9 times the material yield stress. Hydrogen concentration of 40 ppm at the surface and 1 ppm in bulk always gives crack initiation at the surface despite the peak normal stress localized in front of the notch tip.
Applicability Evaluation of SS (Structural Stress) Method on Actual Project
Authors: Kim Kwang-Seok , Kang Joong-Kyoo , Heo Joo-Ho , Lee Sung-Geun
Published: May 2009

The structural stress (SS) method developed by BATTELLE has been studied based on small or mid size scale specimens. In order to apply new method on actual project, the new method such as SS should have application results on actual project. However, SS method didn’t have a lot of application data compared to class procedure using hot spot stress (HSS). In order to find that the SS method for the evaluation of fatigue life can give reasonable results when it is applied under the same loading suggested by classification societies, fatigue lives derived by class and SS method were compared. ABS & DNV’s simplified fatigue analysis method were adopted to check the validity of SS method. Before applying complicated loading of class, static loading case was applied since the class method has their own correlation factor for wave loading. And then simplified fatigue analysis was performed with more complicated loading cases. From the results of fatigue life calculation, it can be said that SS shows reasonable fatigue lives with respect to HSS or notch stress based fatigue lives.
Interaction and Clashing Between Bare or Straked Risers: Analyses of Experimental Data
Authors: Baarholm Rolf , Kristiansen Trygve , Lie Halvor
Published: May 2009

Hydrodynamic interaction and clashing of two long flexible cylinders in uniform steady current have been studied. Model tests have been performed in the towing tank at Marintek in Trondheim. The riser models were free to move in vortex induced vibrations (VIV) and wake induced vibrations (WIO). Model tests were performed both for straked and bare risers, and for risers with and without bumper elements attached. The model tests where presented in an earlier paper. This paper will briefly present the tests while the primary objective of the present paper is to describe advanced analysis and results. The emphasis in the analysis of the recorded data has been to assess the spatial distribution of clashing, the relative impact velocities, WIO and VIV.
The Sensitivity of Set-Up/Set-Down and Wave-Driven Currents to Different Breaking Models
Authors: Newell Carl , Mullarkey Thomas
Published: May 2009

The authors have developed a wave-current interaction model. It includes a wave sub-model based on the elliptic form of the mild slope wave equation with a parabolic mild slope wave equation as a boundary condition. It also includes a hydrodynamic sub-model which has been developed to examine set-up, set-down and currents in the coastal zone. The wave breaking model used in the wave sub-model affects the results of set-up, set-down and current obtained using the hydrodynamic sub-model. This paper examines a number of different breaking models and compares the set-up, set-down and currents obtained using radiation stress values which are calculated from derivatives of velocity potential. The velocity potential is obtained in the wave sub-model using the various breaking models being examined. The results show a number of possible breaking models for set-up and set-down calculation and also shows shortcomings in various breaking models when it comes to calculation of longshore currents.
Computational Tool for the Dynamic Analysis of Flexible Risers Incorporating Bending Hysteresis
Authors: Smith Russell , Carr Tommie , Lane Michael
Published: May 2009

Non-bonded flexible-pipe risers provide a structurally compliant solution in offshore floating production systems for the recovery of oil & gas. The bending stiffness of the flexible pipe is an important property in designing the riser system to safely withstand extreme and fatigue loading conditions. These risers have two fundamentally different bending stiffness properties that depend on if the riser system is pressurized or depressurized. A depressurized riser has a comparatively small linear bending stiffness. Most riser designs apply this stiffness as its produces conservative (large) bending responses. In recent years, the bending response predicted from the depressurized bending stiffness has proven overly conservative and there has been an increasing demand to consider the larger hysteretic bending stiffness of the pressurized riser. The objective is to reduce the conservatism and achieve an approved safe design. Recent developments have advanced the modeling of flexible riser bending with hysteresis and this capability has now been incorporated into an industry standard finite-element riser analysis tool. This paper describes the background of hysteresis in relation to non-bonded flexible pipes and outlines the methodology of the riser motions software that incorporates bending stiffness with hysteresis. Riser systems where the dynamic bending response is critical to the success of the design are the main applications that will benefit from this new technology. Examples include: i.) The dynamic bending response at the seabed touchdown of a deepwater catenary riser. ii.) Bending at an interface with the riser hang-off or subsea tie-in.
Sheath Materials for Direct Electrical Heating Cable: Long Term Testing
Authors: Melve Bjo̸rn
Published: May 2009

A high voltage cable is strapped to the flowlines on the HTHP Kristin field as a part of the direct electric heating (DEH) system. The cable with its components has to function in temperatures above 100 °C since it is connected to the hot flowlines. Four different candidate cable sheath materials were exposed to an accelerated ageing program that simulated the conditions the cable should survive during the twenty years lifetime. The materials were a stiff polypropylene (pipe grade), a rubber modified polypropylene, a thermoplastic elastomer and polyvinylidenfluoride (PVDF). The test conditions were one year exposure in 130 °C oxygenated sea water (8 ppm O2). After the exposure were the mechanical properties of the thermoplastic elastomer significantly degraded and the surface of the material was greasy. The stiff polypropylene was not stable for a long term exposure at these conditions. The rubber modified polypropylene was an acceptable sheath material. The PVDF material was not influenced by the exposure and was the best ranking material.
The Description of Breaking Waves and the Underlying Water Particle Kinematics
Authors: Christou Marios , Swan Chris , Gudmestad Ove T.
Published: May 2009

This paper concerns the numerical description of breaking waves and the resulting water particle kinematics. A fully non-linear multiple flux Boundary Element Method (BEM), developed by Hague & Swan [1], is applied to simulate the extreme nature of overturning waves. This BEM differs from traditional boundary integral approaches in that smoothing is not required and that neither re-gridding nor the redistribution of nodes is performed at any stage during the simulation. Plunging breakers resulting from two types of waves are examined. The first kind is produced by solitary waves propagating up an impermeable plane slope. The second concentrates on a realistic (JONSWAP) sea state spectrum to produce an overturning unidirectional irregular wave group in deep water. The water surface profiles and the resulting water particle kinematics produced by the two types of waves are analysed both qualitatively and quantitatively. Furthermore, the numerical description of the solitary wave is compared to new laboratory observations of the water surface elevation and the validity of existing breaking criteria examined. The practical implications of the findings on extreme wave loading are then addressed.
Theoretical and Experimental Analysis of Air Gap Response and Wave-on-Deck Impact of Floating Offshore Structures
Authors: Kazemi Saeid , Incecik Atilla
Published: May 2009

A comparative study between the theoretical and experimental analysis of air gap response and potential wave-on-deck impact forces of floating offshore structures is the main topic of this study. Both motion of the platform and the local wave elevation are important in air gap responses and wave impact forces. So, accurate and efficient computational analysis of wave induced loads and resulting platform’s responses and wave elevation is important in the prediction of air gap and evaluation of possible wave impact force. Numerical modelling for air gap and wave impact prediction is particularly complicated in the case of floating offshore structures because of their large volume, and the resulting effects of wave diffraction and radiation. Therefore, for new floating platforms, the model tests are often performed as part of their design process. The overall aim of this study is to introduce a simplified numerical method with sufficient accuracy suitable for preliminary design stages of a floating offshore platform to predict the air gap response using hybrid method and to evaluate the vertical wave impact force using Wagner-based method. The results obtained from the proposed method have been compared with those obtained from the experiments carried out in the wave tank of the Newcastle University.
Clashing of Risers and Umbilicals With Tension Leg Platform Tendons
Authors: Mansour Ghiath
Published: May 2009

Clashing of risers and umbilicals with other risers, umbilicals, mooring lines, tendons, the hull, or other objects is a major design issue. Preventing clashing is the preferred course of action; however, clashing between catenary risers or catenary umbilicals and tension leg platform (TLP) tendons is typically more challenging to prevent due to the difference in configuration/stiffness and the light weight in the case of umbilicals. In this article, the effect of parameters such as the hang-off angle, hang-off location, azimuth heading, Drag coefficient and weight on the clashing between TLP tendons and umbilicals is considered. Alternatives to preventing such clashing are also discussed.
The Influence of Pipeline Insulation on Installation Temperature, Effective Force and Pipeline Buckling
Authors: Anderson Murray , Bruton David , Carr Malcolm
Published: May 2009

High-performance insulated pipelines are designed for long cool-down times in operation. During the installation of such pipelines, the heat within the pipe as it leaves the lay vessel is not easily lost to the surrounding seawater. The ambient temperatures on the lay vessel, combined with significant heat input during welding and field joint coating, will result in the pipeline leaving the lay vessel at a temperature well above ambient deck temperature. The insulation system ensures that a significant amount of this heat will remain within the pipeline as it descends to the seabed, resulting in a higher than ambient installation temperature. As the pipeline cools to ambient seabed temperature, it is restrained on the seabed by axial friction thus generating effective tension in the pipeline. The magnitude of the locked in tension will depend on various factors, including the overall heat transfer coefficient, the system heat capacity, the water depth, water column temperature and the lay rate. Any significant locked in tension will influence the buckling behaviour of the pipeline by inhibiting buckle formation and reducing feed-in to lateral buckles. This paper presents a method to assess the temperature loss through the water column during installation of an insulated pipeline and the location, relative to the touchdown point, at which the pipeline becomes fully constrained. The modified as-installed temperature will much improve the accuracy of predicted buckling response at hydro-test or in operation.
Deepwater Spar Steel Catenary Riser Monitoring Strategy
Authors: Natarajan Shreenaath , Podskarbi Mateusz , Karayaka Metin , Howells Hugh
Published: May 2009

Steel catenary risers (SCRs) in deepwater environment exhibit complex dynamic dynamic response governed by various factors such as environmental conditions, vessel motions, soil-structure interaction and material degradation. Uncertainties in the SCR design exist in the design data, analysis methodologies, fabrication, and hence a conservative approach has been adopted to overcome these shortfalls. Recent advances in monitoring systems installed on SCRs provide operator the assurance of the integrity of the SCRs in service, verify the SCR design, and enhance basic understanding of the SCR response. This paper outlines a strategy for monitoring the SCRs to characterize the response due to vessel motions, vortex induced vibrations (VIV), and soil-structure interaction. A detailed example of real-time SCR monitoring system with optimized array of motion and strain measurements is presented. The methodology for sensor selection and optimization is based on linear regression analysis. The measured data processing methods include shape matching the response amplitudes with correlating response frequencies. The principles and methods of measured data interpretation to capture global response shape due to wave and vessel motions induced and VIV are presented. The pipe-soil interaction such as soil stiffness, suction, softening and trenching effects characterized using the strain measurements in the touch down zone are presented. In addition, the methods to calibrate the individual vertical, lateral and axial models for pipe-soil interaction are presented.
Incorporating the Higher Harmonics in VIV Fatigue Predictions
Authors: Jhingran Vikas , Vandiver J. Kim
Published: May 2009

Vortex-Induced Vibrations (VIV) are an important source of fatigue damage for risers in the Oil and Gas industry. Results from resent VIV experiments by Vandiver et al. [1] indicate significant dynamic strain energy at not only the Strouhal frequency, but also its harmonics. In certain regions of the pipe, these higher harmonics accounted for more that half of the measured RMS strain and increased fatigue damage by a factor exceeding twenty. However, the state-of-the-art in VIV prediction only accounts for the vibrations at the Strouhal frequency. Preliminary results from a second set of experiments, described in this paper, confirm the importance of the higher harmonics in fatigue life estimates of pipes. Further, the authors formulate an approach to incorporate the higher harmonics in VIV related fatigue design. Finally, the authors identify the estimation of the higher harmonics, in both location and magnitude, as an important area of ongoing research, the results of which will be required to implement this proposed method.
Oscillations in Moonpool at Static Platform in Waves
Authors: Salman Sadiq , Kang Zhuang , Yao Xiong-Liang
Published: May 2009

Most of the offshore platforms at sea are static and considered as rigid. This paper presents a series of towing tank experimental research to understand the wave and structure interaction for moonpool installed at static platform. It also gives a comparison of results between static platforms in waves and model moving in calm water with forward speed. Study comprised of circular and square shaped moonpool, while square shaped was further investigated for different attack angles varying from 0–45 degrees with an interval of 15°. Time period of incoming waves was increased from 1 s to 3 s with an interval of 1 s. To have a variety of situations to cater for the actual state at sea, wave height was also increased from 40 mm to 80 mm with an interval of 20 mm. For wave height and time period different combinations are presented to get variety of results. Results are given in terms of ‘dB’ for water oscillation pressure, which governs the water motions inside the moonpool, and for that matter it directly relates resonance in moonpool as the natural frequency of water inside the cavity does not change with a change in the velocity of incoming waves rather it is dependents upon the physical properties of the fluid medium, shape of cavity, size of cavity and the draught of water inside the cavity. With an increase in the time period of incoming waves, sound level ‘dB’ in terms of oscillation pressure frequency generated by the circular moonpool also increases. The same phenomenon is observed once the wave height is increased from 40–80 mm; except for one condition i.e., T = 3 s and λ = 80 mm. This shows that longer and higher waves may not always produce higher noise level for circular moonpools; this is not the case for square shaped moonpool. At increasing attack angles for square shaped moonpool, the acoustic level increases slightly for similar wave conditions. Furthermore, while comparing moving model in calm water with forward speed and static model at in coming waves; it was revealed that, square moonpool at different attack angles in calm water with forward speed condition, produces greater noise level once compared with waves-only condition. This phenomenon is unlike in circle moonpool. The results given in this paper are very important structural elements of the offshore platform during the design process.
Advances in the Hydrodynamics of Side-by-Side Moored Vessels
Authors: Pauw Willemijn H. , Huijsmans Rene´ H. M. , Voogt Arjan
Published: May 2009

In this paper a comparison between model basin experiments and results of diffraction computations on side-by-side moored LNG carriers is presented. The computations are based on a new lid method in diffraction codes to suppress non-realistic high wave elevations between the two floating objects. This lid method was originally formulated by Chen (2005). In this method a damping value is added to the free surface by means of a damping parameter. Since no theoretical solution can be found to establish the required value of the damping parameter, model basin experiments have been performed to determine this value. However from the results of the model basin experiments it is shown that it is difficult to obtain one unique value of the lid damping (for the 4m or small gap). The way of tuning the damping value of the lid is crucial. Tuning the damping based on first order results, like motions or wave height RAO’s will lead to a much larger variation in the estimate of the second order sway wave drift force transfer function.
In-Service Repair of Flexible Riser Damage Experience With the North Sea Galley Field
Authors: Anderson Keith , MacLeod Ian , O’Keeffe Brian
Published: May 2009

Routine GVI of the Galley riser system indicated potential damage to the Gas Export riser. This was observed as a steady stream of gas bubbles emanating from within an inverted bellmouth used to constrain riser motion at the Floating Production Facility (FPF) pontoon level. The vented gas volume was consistent with permeated gas rates from the annulus, an indicator of damage to the external sheath of the riser. The inverted bellmouth negated inspection of the riser within, hence the cause of the damage could not be ascertained. To determine the condition of the structure the riser was isolated and raised to allow inspection of the damaged section. This inspection found structural damage to the outer layers of the flexible pipe including corrosion damage of the outer tensile armour wires reducing the structural capacity of the riser. The extent of damage instigated a multi-company, multi-disciplinary team investigation and implementation of unique remedial measures to ensure fit for purpose operations for the remainder of field life. Implementation of the permanent remedial works was performed and successfully completed with reintroduction of the risers to permanent service in January 2006. This paper describes in detail the novel and unique techniques used to repair and re-commission the damaged riser.
Wet Gas Separation in Gas-Liquid Cylindrical Cyclone (GLCC) Separator
Authors: Molina Robiro , Wang Shoubo , Gomez Luis E. , Mohan Ram S. , Shoham Ovadia , Kouba Gene
Published: May 2009

A novel Gas Liquid Cylindrical Cyclone (GLCC©), equipped with an Annular Film Extractor (AFE), for wet gas applications has been developed and studied experimentally and theoretically. Detailed experimental investigation of the modified GLCC has been carried out for low and high pressure conditions. The results show expansion of the operational envelope for liquid carry-over, and improved performance of the modified GLCC. For low pressures, the modified GLCC can remove all the liquid from the gas stream, resulting in zero liquid carry-over. For high pressure conditions, the GLCC with a single AFE has separation efficiency > 80% for gas velocity ratio of < 3. A mechanistic model and an aspect ratio design model for the modified GLCC has been developed, including the analysis of the AFE. The model predictions agree with the experimental data within ± 15% for low pressure and ± 25% for high pressure conditions.