bluuebunny/crossref_metadata_2025 huggingface dataset:
Establishing Correspondence Between Value Functions Used in Market-Based Engineering Design
Authors: Wissmann Luke A. , Donndelinger Joseph A.
Published: July 2009

The benefits of applying market demand models in engineering design have been well established. Arguably the most common approach has been to apply a random utility model, although any representation of market demand based on customers’ responses to surveys or in market situations can be used to this end. In practice, various methods have been used to collect market data through the use of surveys, typically based either on choices from among sets of alternatives or statements of willingness-to-pay. The applicability of the data collected has been limited, however, by the complexity of the relationships between market research methods and market demand models. The prospects of reusing an enormous amount of available market research data and increasing practitioners’ freedom in applying market research data to forecast market demand compel us to investigate the correspondence between market demand models. In this paper, we build on the recent work of Cook and Wissmann to demonstrate a bilateral correspondence between the popular multinomial logit model and Cook’s S-Model. Results from two independent case studies are presented showing that the utility function in a multinomial logit model may be reparameterized as a value function in the S-Model and vice-versa. The techniques demonstrated in this paper for defining direct comparisons between previously incompatible market research methods and demand models provide the practitioner with powerful new capabilities for validating market models, fusing market models to expand customer-based trade spaces, and presenting results to decision-makers in familiar formats.
A General Approach to Robustness Assessment for Multidisciplinary Systems
Authors: Du Xiaoping , Zhang Yi
Published: July 2009

In many engineering applications, both random and interval variables may exist. The mixture of both types of variables has been dealt with in robust design for single disciplinary systems. This work focuses on robustness assessment for general multidisciplinary systems with the presence of both random and interval variables. To alleviate the intensive computational demand, we propose a semi-second-order Taylor expansion method to estimate robustness. A performance function is approximated linearly in terms of random variables, but the interaction terms between random and interval variables are kept. Robustness is measured by the standard deviation of a system performance. The maximum and minimum standard deviations over the interval variables are identified. With proposed method, the impact of both random and interval variables on the system performance can be found efficiently.
Interactive Deformation Through Mesh-Free Stress Analysis in Virtual Reality
Authors: Faas Daniela , Vance Judy M.
Published: July 2009

Virtual reality (VR) techniques are used to create an environment that allows an engineer to modify the shape of a part and see the changes in the stress state immediately. A virtual reality application, Interactive Virtual Design Application (IVDA), that allows fast mesh-free analysis of multiple element types, including two-dimensional (2D) elements, is described in detail. Taylor series approximations and Pre-conditioned Conjugate Gradient (PCG) methods are used with mesh-free analysis to perform quick reanalysis during interactive shape modification. Prior to this work, only 3D elements were incorporated into the method. The addition of 2D elements greatly expands the potential application of this work. Several software packages including VR Juggler, OpenHaptics, OPCODE, Tahoe and OpenGL/GLM/GLUT libraries are combined in the resulting application to handle a variety of elements. This approach also supports concurrent product design and assembly methods prototyping. The addition of 2D analysis capability is discussed in this paper. The method is described and a sample problem presented.
FIDOE: A Framework for Intelligent Distributed Ontologies in Engineering
Authors: Witherell Paul , Krishnamurty Sundar , Grosse Ian R. , Wileden Jack
Published: July 2009

This paper presents FIDOE, a Framework for Intelligent Distributed Ontologies in Engineering. FIDOE consists of a suite of logic rules and templates for interactively developing relationships between properties of linked ontologies. The logical rules embedded in FIDOE automatically operate on various discipline-specific ontologies to systematically identify influences, direct and indirect, of proposed design modifications on other aspects of the design through common domain concepts. Once potential influences are identified, FIDOE enables the user to precisely define the domain relationships, using predefined templates, between the identified domain concepts that enumerate influence types. This tool, thus, provides a pervasive, real time awareness of the implications of design changes during the design process in a distributed environment. The application of FIDOE to distributed and multidisciplinary design problems is detailed with the aid of an industry-provided printed circuit board (PCB) design. Here, commonalities among indirectly connected domain ontologies (electrical, mechanical and thermal domains) are identified using the developed query method and subsequent relationships are defined. These relationships are then applied to provide a collaborative understanding and awareness of the distributed process, all while demonstrating the effectiveness of this approach. This awareness was successfully able to address some previously identified industry concerns, returning promising results while laying a solid foundation for future work.
Employing Automation for Effect Prediction and Exploration in Complex Simulations (EAEPECS)
Authors: Wedgwood Janet , Horiatis Zacharias , Konicki Thaddeus
Published: July 2009

Support of military campaigns requires new approaches for effective generation of desired effects, and continuous adjustment of the actions, for the entire life of the campaign. Military planners are moving to Effects-Based Operations (EBO) [1] to achieve these desired effects for a combination of Diplomatic, Informational, Military, and Economic (DIME) actions. As military planners move from pure military operations to Effects-Based Operations (EBO) [1], they will need tools to enhance their understanding how the desired Political, Military, Economic, Social, Infrastructure, Information (PMESII) effects can be achieved through a combination of Diplomatic, Informational, Military, and Economic (DIME) actions. Engineers at Lockheed Martin Advanced Technology Laboratories are developing the Employing Automation for Effect Prediction and Exploration in Complex Simulations processes as part of their research into the use of Modeling and Simulation to develop and analyze campaign-level effects-based operations. It uses innovative multi-paradigm simulations of DIME actions on models to determine the probable desired effects, as well as the undesirable effects, while developing a better understanding of second and third order effects. In order for this technology to be useful to military analysts and planners, it must be made accessible to non computer scientists. Our goal is to help analysts and planners easily exploit the power of Modeling and Simulation for exploring Effects-Based Operations through automation of scenario development, model instantiation, integration and initialization and Course of Action (COA) development, simulation and analysis.
WeDesign: A Forum-Based Tool for Managing User-Generated Content in Engineering Design and Product Development
Authors: Jakiela Mark J. , Zheng Jing
Published: July 2009

A web forum-based tool for managing user-generated content in engineering design and product development is described. The system is intended to allow a “crowdsourcing” approach, in which large groups perform the work more commonly by individuals. User tests are conducted with an initial implementation, with the system configured in control and “parliamentary” modes. This experiment is done in the setting of a mechanical engineering senior capstone design course. The parliamentary mode is intended to encourage discussion and negotiation among participants, and allows them to design their own work processes. Review of the designs produced together with responses to a survey indicate the system was favorably received, and allowed a group to generate and select concept designs. Future research directions are suggested.
Parameterization of Three-Dimensional Rigid Body Guidance Incorporating Planar Gear Connections in a Spatial Closed-Loop Mechanism With Parallel Consecutive Axes
Authors: Mckinley Javier Rolda´n , Crane Carl , Dooner David B.
Published: July 2009

This paper introduces a reconfigurable closed-loop spatial mechanism that can be applied to repetitive motion tasks. The concept is to incorporate five pairs of non-circular gears into a six degree-of–freedom closed-loop spatial chain. The gear pairs are designed based on given mechanism parameters and a user defined motion specification of a coupler link of the mechanism. It is shown in the paper that planar gear pairs can be used if the spatial closed-loop chain is comprised of six pairs of parallel joint axes, i.e. the first joint axis is parallel to the second, the third is parallel to the fourth, ..., and the eleventh is parallel to the twelfth. This paper presents the synthesis of the gear pairs that satisfy a specified three-dimensional position and orientation need. Numerical approximations were used in the synthesis the non-circular gear pairs by introducing an auxiliary monotonic parameter associated to each end-effector position to parameterize the motion needs. The findings are supported by a computer animation. No previous known literature incorporates planar non-circular gears to fulfill spatial motion generation needs.
A Flexure-Based Bi-Axial Contact-Aided Compliant Mechanism for Spinal Arthroplasty
Authors: Halverson Peter A. , Howell Larry L. , Bowden Anton E.
Published: July 2009

A healthy spinal disc is capable of 3 degrees of rotation and has a force-deflection response that helps to stabilize the spine. Age or trauma can cause the stability of the spine to decrease. Spinal fusion, the current surgical treatment of choice, stabilizes the spine by rigid fixation, reducing spinal mobility at the cost of increased stress at adjacent levels. This paper introduces a compliant mechanism that has the potential to closely mimic the physiological motion profile of the natural spinal disc. Compliant mechanisms have properties that make them well suited for spinal implants that restores the range of motion and the forcedeflection response of the spine. This paper presents an introduction to the biomechanics of the spinal disc, reviews the state of the art in spinal care, and proposes the use of the Flexure-based Bi-Axial Contact-aided (Flex-BAC) compliant mechanism as a spinal arthroplasty device (artificial disc). The Flex-BAC compliant mechanism offers the potential to restore both the kinematics and kinetics of a damaged spinal disc. The disc provides the ability to eliminate wear through rolling. An overview of the device and a preliminary kinematic and kinetic analysis are given.
On the Utilization of the Escape Phenomenon to Realize New Mass Detectors
Authors: Alsaleem Fadi M. , Younis Mohammad I.
Published: July 2009

In this work, we demonstrate the concept of a new type of mass sensor detector. The detector is designed to act as a switch that is triggered if the measured mass exceeds a threshold value. The basic idea of the proposed switch is based on utilizing the escape phenomenon that the nonlinear electrostatic force introduces to the dynamics of a capacitive microcantilever. The detector is excited electrostatically with a frequency near the primary or the sub-harmonics (twice the natural frequency) resonances a way from the instability frequency band (escape phenomenon). By absorbing a threshold mass of a target material, the natural frequency of the cantilever will change in a way that it starts to oscillate in the unstable zone and hence hits the substrate. This action could be utilized to activate, for example, an alarming system indicating that the measured material has exceeded the allowable threshold mass (concentration) value.
Experiences of a US-India Team in Developing a Case Study That Illustrates Technical and Global Issues in Weld Design
Authors: Rajan Pramod , Raju P. K. , Sankar Chetan S.
Published: July 2009

Understanding the real-world issues in the global industry is one of the ways of enhancing the learning experience of engineering students. This paper describes such an experience. This was a collaborative weld design project between Auburn University, Auburn, Alabama, Indian Institute of Technology (IIT), Madras, India and Bharat Heavy Electricals Limited (BHEL), Tiruchirappalli, India. The main problems BHEL faced were (1) Inspection time of the welds, (2) Inaccessibility of the welds, and (3) Detection of kissing bond or pasty weld. Three possible solutions to these problems were identified by the practitioners. In order to bring this real-world issue into engineering classrooms, the authors developed a case study. The authors also developed a multimedia CD-ROM which brings the problem live into class rooms using video, audio and pictures. This case study has been tested with mechanical engineering students. The majority of the students found the use of case studies to be beneficial, particularly because of the group work and applicability to real life situations. The details of the case study and its implementation in an engineering class room at Auburn University are discussed in the paper.
Design of an Automated Calibration System for Electromagnetic Tracking Systems
Authors: Jayaram Sankar , Jayaram Uma , Palmer Craig
Published: July 2009

Electromagnetic tracking systems used in virtual reality applications are subject to tracking error due to magnetic field distortions caused by metallic objects in the environment. The goal of this research was to create and evaluate an automated data collection systems and calibration methods to allow a hands-free calibration of a complex space with multiple physical objects in the environment. The need was for a suitable device to automatically collect data points for the physical reference system without causing further distortion to the magnetic field. The calibration device was designed in order to accurately position the electromagnetic receiver at user-specified grid points throughout the tracking environment, thereby allowing the calculation of position and orientation error at each location. Novel methods were created to avoid collision of the automated calibration device with objects in the environment. The tests showed that the density of calibration and the flexibility achieved with this device far exceed any previous methods used. This research built on our previous efforts to create a software system to assist in manual data collection for calibration.
Narrativity for User Experience Design
Authors: Kiriyama Takashi
Published: July 2009

It is becoming a new challenge for the designer to understand how the user finds meanings in using a product and service. It requires for thinking about a number of situations that may be experienced by various users. A useful method for dealing with situations is persona design. We looked at a persona created by a professional analyst to find that a scenario of the persona is useful to clarity preconditions by which a desired behavior occurs with the persona.
Vortex Sheddings on the Instability at Subsea Suspended Pipeline
Authors: Mestanzade N. , Yilmaz L.
Published: July 2009

The underwater suspended pipeline was investigated for the lateral vibration which is applied for the oscillation of the pipeline part for vortex shedding. Firstly it is defined the tension force at the connection legs on the sea bottom. For definition of the dynamical equation it is used the analogy of the Mathieu Equation. For solution it is used Ince-Struut Diagram. As numerical example it was used the pipeline behavior at the project between Turkey and North Cyprus at the East Mediterranean Sea. In this research the theoretical background is compared with the experimental data of Danish Hydraulic Institute. It shows the good agreement.
Reynolds Number Dependence of Flexible Cylinder VIV Response Data
Authors: Swithenbank Susan B. , Vandiver J. Kim , Larsen Carl Martin , Lie Halvor
Published: July 2009

The response amplitude and the non-dimensional frequency of flexible cylinder vortex-induced vibrations from laboratory and field experiments show significant trends with increasing Reynolds number from 103 to 2 * 105. The analysis uses complex data from experiments with wide variations in the physical parameters of the system, including length-to-diameter ratios from 82 to 4236, tension dominated natural frequencies and bending stiffness dominated natural frequencies, sub-critical and critical Reynolds numbers, different damping coefficients, standing wave and traveling wave vibrations, mode numbers from 1 – 25th, and different mass ratios.
Floating Offshore Wind Turbines: Responses in a Seastate Pareto Optimal Designs and Economic Assessment
Authors: Sclavounos Paul , Tracy Christopher , Lee Sungho
Published: July 2009

Wind is the fastest growing renewable energy source, increasing at an annual rate of 25% with a worldwide installed capacity of 74 GW in 2007. The vast majority of wind power is generated from onshore wind farms. Their growth is however limited by the lack of inexpensive land near major population centers and the visual pollution caused by large wind turbines. Wind energy generated from offshore wind farms is the next frontier. Large sea areas with stronger and steadier winds are available for wind farm development and 5MW wind turbine towers located 20 miles from the coastline are invisible. Current offshore wind turbines are supported by monopoles driven into the seafloor at coastal sites a few miles from shore and in water depths of 10–15m. The primary impediment to their growth is visual pollution and the prohibitive cost of seafloor mounted monopoles in larger water depths. This paper presents a fully coupled dynamic analysis of floating wind turbines that enables a parametric design study of floating wind turbine concepts and mooring systems. Pareto optimal designs are presented that possess a favorable combination of nacelle acceleration, mooring system tension and displacement of the floating structure supporting a five megawatt wind turbine. All concepts are selected so that they float stably while in tow to the offshore wind farm site and prior to their connection to the mooring system. A fully coupled dynamic analysis is carried out of the wind turbine, floater and mooring system in wind and a sea state based on standard computer programs used by the offshore and wind industries. The results of the parametric study are designs that show Pareto fronts for mean square acceleration of the turbine versus key cost drivers for the offshore structure that include the weight of the floating structure and the static plus dynamic mooring line tension. Pareto optimal structures are generally either a narrow deep drafted spar, or a shallow drafted barge ballasted with concrete. The mooring systems include both tension leg and catenary mooring systems. In some of the designs, the RMS acceleration of the wind turbine nacelle can be as low as 0.03 g in a sea state with a significant wave height of ten meters and water depths of up to 200 meters. These structures meet design requirements while possessing a favorable combination of nacelle accleration, total mooring system tension and weight of the floating structure. Their economic assessment is also discussed drawing upon a recent financial analysis of a proposed offshore wind farm.
Simulation of Free Surface Compressible Flows via a Two Fluid Model
Authors: Dias Fre´de´ric , Dutykh Denys , Ghidaglia Jean-Michel
Published: July 2009

The purpose of this communication is to discuss the simulation of a free surface compressible flow between two fluids, typically air and water. We use a two fluid model with the same velocity, pressure and temperature for both phases. In such a numerical model, the free surface becomes a thin three dimensional zone. The present method has at least three advantages: (i) the free-surface treatment is completely implicit; (ii) it can naturally handle wave breaking and other topological changes in the flow; (iii) one can easily vary the Equation of States (EOS) of each fluid (in principle, one can even consider tabulated EOS). Moreover, our model is unconditionally hyperbolic for reasonable EOS.
Benchmarking of VIV Suppression Systems
Authors: Schaudt Kenneth J. , Wajnikonis Christopher , Spencer Don , Xu Jie , Leverette Steve , Masters Rodney
Published: July 2009

A new form of Vortex-Induced Vibration (VIV) suppression device, the AIMS Dual-fin Flow Splitter (ADFS), has been developed, tested and benchmarked against bare-pipe, 5d and 15d pitch strakes and conventional teardrop fairings. Testing included high-mode number in-situ tests as well as low Reynolds number (<300,000) and high Reynolds number (<1.9 million) forced and free tank tests. Finally, wind tunnel tests and in-water Particle Image Velocimetry (PIV) were used to test the hypothesis that the dual-fin flow splitter replaces the oscillating wake of a blunt body with a stable, attached circulation behind the body and between the fins. Such a replacement was hypothesized to result in reduced drag, and the elimination of almost all VIV. The paper will describe the testing program and results, and present the incorporation of the test results into riser models.
Wake Fields Behind Risers Undergoing Vortex-Induced Vibration
Authors: Xu Jie , Spencer Don , Gardner Alex , Molynuex David , Qiu Wei , Bose Neil , Masters Rodney H. , Shanks John
Published: July 2009

This paper presents measurements of the wake field behind three riser models obtained by using a Digital Particle Image Velocimetry (DPIV). The three riser models were a circular rigid cylinder, a cylinder fitted with fairings and a cylinder fitted with strakes. The models were free to vibrate in the cross-flow direction when towed in a uniform flow. The range of tested Reynolds number based on the diameter of the cylinder was from 3×104 to 2.5×105. The measurement results showed that the transverse vibration amplitudes for both the faired and straked cylinder were far less than those of the bare cylinder. Based on the wake flow field comparison between the models tested it was found that the modes of vortex shedding observed behind the bare cylinder did not occur behind either the faired or straked cylinder. This reveals that the vibrations responses of the cylinders are directly related to their wake modes. Strong, regularly shed vortices induce large amplitude vibration and weak, scattered vortices lead small amplitude or no vibration. The different wake patterns are presented for the three cylinders.
Feasibility Study of Disconnectible Drilling Risers
Authors: Li Yousun , Lo King Him , San Martin Hugo Corvalan
Published: July 2009

This study investigates the feasibility of an alternative deepwater drilling riser concept. The riser consists of two segments: a short upper segment suspending from a MODU, and a long freestanding lower segment that can be disconnected from the upper segment. The entire drilling riser can thus be moved to a new drilling location with the riser upper segment directly moved with the MODU and the disconnected lower segment moved by an AHV or heavy duty tug using a heave compensated landing system. The behaviors of this dis-connectible riser are studied. Numerical results demonstrate the feasibility of the dis-connectible riser concept.
Small Scale Model Tests of Ice Gouge in Soft Sandy Silt
Authors: Stava Ingar , Nystro̸m Per R. , Vikse Normann , Gudmestad Ove T. , Liferov Pavel , Gro̸nli John
Published: July 2009

Small scale gouge tests were designed and executed at the University of Stavanger in Norway as a part of master thesis work. A box (2.5 × 2.5 m) was filled with soft sandy silt and several gouge tests were performed. The subgouge soil deformations, the soil mound dimensions and the ratio between initial and residual gouge depth were measured under varying gouge parameters. Vaneshear and T-bar tests were used to estimate soil properties. A pipe segment was buried under the gouge and strains in the pipe were monitored in some of the tests. Test results are presented in this paper, including FE simulations of some of the performed experiments.
Optimization of Mega-Frame Platforms Based on Orthogonal Design
Authors: Zhao Dong , Ma Rijian , Cai Shaoli , Cai Dongmei
Published: July 2009

The orthogonal design was chosen as the mega-frame platform optimizing method to find out the parameters which had the most important effect on the platforms’ performances. The mega-frame platform (MFP) was a new type of anti-vibration platform using the mega-frame theory. It was combined of the major frame and the minor frames. The parameters that had much more important effect on the MFP’ static capability were the number, height, position and stiffness of the major beams and the leg batter, stiffness of the major columns. In this paper, there were six factors, which were the diameter of the major beams (factor A), the leg batter (factor B), the diameter of the major columns (factor C), the position (factor D), the number (factor E) and height (factor F) of the major beams, in the orthogonal design. Two factors, the number and the height of the major beams, had two levels. One factor, the position of the major beams, had three levels. The other three factors had four levels. In order to use the orthogonal table L16(44×23), one level of factor D was repeated. The analyses of the MFPs with different parameters under the same horizontal and vertical unequal loads show that: 1) the most important factor that effects the MFP is the diameter of the major columns, then the leg batter of the major columns; the thirdly and the fourthly factor are the position and the diameter the major beams; the height of the major beam has the least effect on the MFP’s performances; 2) the optimal MFP is C4B3D4A1E2F2. The mode analysis of the optimal MFP shows that the platform has high global stiffness and the equal mass and stiffness distribution. So the MFPs have the overall performance and can avoid the partial breakage under the random external loads.
Modal Analysis of the Ice-Structure Interaction Problem
Authors: Venturella Michael A. , Patil Mayuresh J. , McCue Leigh S.
Published: July 2009

In this paper the authors build upon the single degree of freedom ice-structure interaction model initially proposed by Matlock, et al. (1969, 1971). The model created by Matlock, et al. (1969, 1971), assumed that the primary response of the structure would be in its fundamental mode of vibration. Modal analysis is used in this study, in which the response of each mode is superposed to find the complete modal response of the entire length of a pier subject to incremental ice loading. In Matlock, et al., the physical system is a bottom supported pier modeled as a cantilever beam. Realistic conditions such as ice accumulation on the pier modeled as a point mass and uncertainties in the ice characteristics are introduced in order to provide a stochastic response. The impact of number of modes in modeling is studied as well as dynamics due to fluctuations of ice impact height as a result of typical tidal fluctuations. A Poincare´ based analysis following on the research of Karr, et al. (1992) is employed to identify and periodic behavior of the system response. The intention of this work is to provide a foundation for future work coupling multiple piers and connecting structure for a comprehensive ice-wind-structural dynamics model.
Inspection Considerations for Deepwater Thick-Walled Riser Systems
Authors: Bowman Jonathan , Thompson Hugh , Stevens Donald , Crane James
Published: July 2009

The fatigue loading on deepwater risers results in the need to impose very tight weld acceptance criteria for pipe alignment and flaw sizes. The production of high-pressure, high-temperature reservoirs calls for increasingly thick-walled riser systems. The combination of thicker wall pipe and the maintenance of tight flaw acceptance criteria challenges automated ultrasonic testing (AUT) which is the primary method of riser weld inspection. An understanding of the limitations of the weld inspection system must be determined and accommodated as part of the engineering process and in conjunction with adequate knowledge of the pipe end dimensions can help optimize the inspection process. This paper discusses the challenges associated with the preparation for and inspection of thick-walled riser system welds and the impact this can have on the system design and engineering requirement. In support of the discussion an overview of a recent study to determine the detect-ability and sizing accuracy of an AUT system with thick-wall pipe girth welds is presented. The qualification program is based upon the AUT inspection of seeded defect welds which are subsequently cut into weld rings, re-inspected with an immersion scan and sectioned to determine the size of the flaws present. All AUT inspections are performed under similar conditions to the inspection of the production welds (i.e., no prior knowledge of the nature of the seeded welds).
Reliability Analysis of Oil Tankers With Collision Damage
Authors: Jia Huirong , Moan Torgeir
Published: July 2009

This paper deals with reliability analysis of a damaged tanker conditioned upon collision damage and the damage scenarios following collision. A tanker in full load condition (FLC) and two damage sizes are considered. The ultimate strength of the damaged tanker is assessed by applying Smith’s method, and an interaction equation for vertical and horizontal bending moments (VBM and HBM) is established. The still-water bending moment is calculated by the hydrostatic code ShipShape and the 3D hydrodynamic code WASIM is employed to calculate the wave induced vertical and horizontal bending moments. Correlation between vertical and horizontal bending moments is also considered. An out-crossing rate method is adopted to estimate the failure probability for the vector load effect process, and Monte Carlo simulations are used to account for model uncertainties.
Treatment of Low Stresses in Fatigue Design of Girth Welds Under Spectrum Loading
Authors: Maddox Stephen J.
Published: July 2009

Although the use of Miner’s rule for calculating the cumulative damage due to spectrum loading is well established, there is conflicting evidence as to how stresses below the constant amplitude fatigue limit (CAFL) should be assessed. They are known to be damaging under spectrum loading, but the extent of that damage is not clear. Since such stress levels potentially contribute the majority of the fatigue damage from wave motion and vortex-induced vibration in risers, this issue is highly significant both economically and with respect to safety. Therefore, fatigue tests were performed on strip specimens cut from girth-welded steel pipes under constant and variable amplitude loading to investigate this issue. The test results were assessed on the basis of Miner’s rule used in conjunction with various methods of extrapolating the S-N curve beyond the CAFL to establish the most suitable for correctly representing the damaging effect of stress ranges below it. A fracture mechanics fatigue crack growth analysis was also performed to calculate the fatigue lives expected under the test loading spectrum.
VIV Model Test Data Comparison With Shear7 V4.5
Authors: Yang G. , Frank W. R. , Campbell R. B. , Slocum S. T.
Published: July 2009

The prediction of riser and tendon fatigue damage due to vortex-induced vibration (VIV) remains an active area of research in the offshore industry. In 2003, ExxonMobil performed VIV testing on a 10-m long, 20-mm diameter model in an effort to better understand the mechanics of VIV response of a long flexible pipe. Measured results from these tests, summarized in terms of response frequency, strain, and damage, were published in a series of papers in OTC 2004. Due to the dense array of instrumentation (17 cross flow and 35 inline stations along the riser span) and the use of strain gages in the experiments, the 2003 ExxonMobil data allows for a direct estimation of fatigue response and provides an excellent benchmark for validation of VIV predictions. This paper extends our previous work by comparing the measured test results to simulations of the test conditions (for example, model properties, boundary conditions, and current profiles) using the widely used VIV prediction tool, Shear7. We compared measured and predicted response in terms of a “damage index” for bare, fully straked, and partially straked risers. The damage index, defined as response frequency times the third power of RMS strain ( f×εrms3), is proportional to the fatigue life and thus can be used as a basis to assess the accuracy of predictions. For the comparison work presented in this paper, ExxonMobil has utilized a latest version of Shear7 (version 4.5) which provides added functionality and increased user control over analysis assumptions through assignment of key input parameters. In order to investigate the influence of the analysis assumptions on the predictions, a matrix of 64 distinct input parameter sets was defined. The study indicated that the new “time-sharing” model in general can generate prediction results with reasonable bias and scatter for bare risers. However, prediction errors for straked risers are still high even when the most favorable parameters are selected for the analysis. These comparisons highlight the continuing need for improved formulations with smaller prediction bias and scatter and for high quality benchmarking data and benchmarking methods for objective assessment of VIV prediction accuracy.
Collapse Strength of Damaged Plating
Authors: Nikolov Plamen I.
Published: July 2009

In this paper, based on Finite Element (FE) simulation, the ultimate strength of damaged continuous plating is studied considering the combined effect of residual deflections and stresses. Firstly, damage over plating is simulated resulting to residual deflection in prescribed shape and magnitude accompanied by residual stresses. Then compressive loading is applied and the effect of simultaneous presence of both residual deflections and residual stresses on the plating ultimate strength is studied. It is found that (1) the compressive strength may be significantly overestimated when the damage related residual stresses are not considered, (2) a larger magnitude of initial dishing does not necessary result to a lower ultimate strength. It is shown that the simplified methods in the Common Bulk Carrier Rules need further improvements.
Features of Current Generating System and the Application in New Deepwater Offshore Basin
Authors: Lu Haining , Yang Jianmin , Li Runpei
Published: July 2009

In the paper requirements of reliable offshore model tests on deepwater current modeling in the basin are reviewed. Based on these requirements, some features of current modeling in deepwater offshore basin are discussed, which have been applied to the state-of-the-art deepwater offshore basin of Shanghai Jiao Tong University. The new basin is introduced in detail, including its main particulars, main equipments for ocean environmental modeling etc. As the latest application of current modeling in the basin, external current recirculation and independent layers in vertical direction have been applied in its current generating system. In addition hydraulic performances of the current generating system in the new basin are studied in this paper using both CFD and experimental methods. Current uniformities, turbulence levels and various vertical current profiles etc. in measuring area are investigated individually. It is concluded that good agreements can be obtained between CFD calculation and model tests. Both results show that the hydraulic performances of the current generating system can satisfy the requirements of offshore model tests in deep water. Uniform and constant current flows with low turbulence levels are produced with various current velocities. Several typical vertical current profiles, including uniform and stratified current profiles can be generated in measuring area with satisfactory agreements with the target profiles. In addition some suggestions have also been proposed and accepted during design, construction and operation of the new basin.
Automated Ultrasonic (AUT) and Real-Time Radiographic (RTR) Inspection of Inconel Clad Steel Catenary Risers
Authors: Prentice Garth , Alderton Steve , Tang Zhenzeng
Published: July 2009

This paper describes two proven methods in nondestructive evaluation of Inconel clad steel catenary risers — Automated Ultrasonic Testing (AUT) and Real-time Radiography (RTR). The history of development, qualification and implementation of these two methods are discussed in detail in this paper.
Ship and Ice Collision Modeling and Strength Evaluation of LNG Ship Structure
Authors: Wang Bo , Yu Han-Chang , Basu Roger
Published: July 2009

A collision model has been developed for nonlinear dynamic finite element analysis on an LNG ship and a crushable ice using commercial code DYTRAN. In this modeling, a global LNG ship model has been employed as a deformable body which follows the elastic-plastic constitutive model, and an ice floe has been modeled as a crushable body including material failure. The deformation and failure of the ship structure and the ice as well as the contact force at the contact area between the ship and the ice have been determined from collision simulations. For most ship-ice interaction scenarios, the ice load applied to the ship can be considered as a quasi-static load. The loading capacity of LNG ship hull structure has been investigated applying static ice loads to a local model, which is a whole compartment of a cargo tank in the ship structure including five components such as the side shell plating, longitudinal stiffeners, stringers, web frames, and inner hull. For each ship and ice interaction scenario, loading cases at five varying locations in the local model have been investigated. Numerical results show that different loading location cases cause the structure failure at different components. FE results also indicate that large plastic deformation and buckling failure modes are found in different components of the hull structure. Finally, acceptance criteria and the complete procedure have been developed for the strength evaluation of hull structure in LNG carriers under ice loads.
Nonlinear Behavior of Single Piles in Jacket Type Offshore Platforms Using Incremental Dynamic Analysis
Authors: Asgarian Behrouz , Assareh Mohammad Amin , Alanjari Pejman
Published: July 2009

Offshore platforms are some of those structures which are built to withstand environmental and accidental loads during oil exploitation operation. One of the most usual types of these platforms is the Jacket Type Offshore Platform (JTOP) which can be divided into three important parts, which are Deck, Jacket, and piles. In order to increase the safety, particular attention should be paid to earthquake excitations which are directly applied to the piles of these structures. Nonlinearity in piles and buckling of the struts are important issues which have to be considered by the designers of offshore platforms. Incremental Dynamic Analysis (IDA) is a powerful tool to assess the capacity of a structure upon seismic loads. In this paper incremental dynamic analysis has been implemented on single piles considering soil-pile interactions and free field site response. The use of nonlinear materials and lateral load resisting elements in the incremental dynamic analysis done in this paper has made it possible to get promising insights for incorporation of appropriate limit states and applications of performance based engineering. Special Engineering Demand Parameters (EDP) and Intensity Measures (IM) have been introduced for the single pile dynamic analysis in jacket type offshore platforms.
Corrosion Fatigue of Simulated C-Mn Steel HAZs in Sour Produced Fluids
Authors: Hammond R. I. , Baxter D. P.
Published: July 2009

Steel Catenary Risers are subjected to both fatigue loading (from waves and tides) and corrosive environments (internal and external). The financial benefit of using C-Mn steels for SCRs is significant, therefore there is a need to establish the limitations of the material. These limitations are likely to be controlled by the HAZ, as HAZ microstructures are typically more susceptible than parent steel to cracking during exposure to a sour environment, especially if they have high hardness. Samples of API 5L X65 line pipe steel were heat treated to provide materials exhibiting two microstructures comparable to those seen in girth weld HAZs with two levels of hardness. Fatigue tests were then performed in a sour environment to determine the influence of microstructure, frequency and crack depth on the observed crack growth rate. Tests were performed using a ‘frequency scanning’ technique which involved maintaining a constant ΔK by continually monitoring and shedding the applied load range as crack length increased during the test. Frequency was varied in the range 10–0.01Hz. As there was a concern that the effect of frequency might be masked by an effect of crack depth, a second series of tests was also carried out on each microstructure to explicitly investigate the effect of this latter variable. A stress ratio of 0.5 was used to ensure a relatively high mean stress, to simulate the presence of a tensile residual stress. Test data suggested that harder material exhibited a higher fatigue crack growth rate in the sour environment, and that frequency had only a small effect over the range examined. A second series of tests suggested that crack growth rate was independent of crack depth for crack depths greater than 6mm, although there was some evidence that for shallower flaws the crack growth rate may be higher. It is suggested that when performing fracture mechanics calculations using fatigue crack growth rate data, it is important to ensure that the latter are associated with tests performed on material exhibiting a comparable microstructure to the component being modelled. For relatively shallow flaws it may be the case that crack growth rates in a sour environment are higher (for a given ΔK) than for longer flaws. It should therefore be recognised that in certain applications, defect assessments which use crack growth rate data derived from tests using deeply-cracked specimens may result in non-conservative life predictions.
Fatigue Testing and Analysis of a Deep Water Steel Tube Umbilical
Authors: Dobson Alan , Fogg Dave
Published: July 2009

Rapid analysis of dynamic umbilical structures during the design phase requires a robust mathematical model of the component stresses due to static and alternating loads. The following discusses the validation of a model, through full scale testing, used to assess the stresses and strains present within steel tubes, in umbilical structures typically used in dynamic service in deep waters, such as found in the Gulf of Mexico and offshore West Coast of Africa. The validation focuses upon the complexity of the mathematical model and the influence of tension magnitude the stick-slip mechanism and the stress variation around the circumference of the tubes when under the influence of bending loads.
Cyclic and High Strain Behavior of Titanium Alloys Used for Riser Components
Authors: Baxter C. F. G.
Published: July 2009

Grades 23 and 29 titanium alloys are becoming more commonly used offshore for critical components of riser systems. Many of these components, such as compact flanges, operate at high mean strains due to make-up loads, often close to or above yield. Hitherto, weld fatigue data collected at low mean strains have been used for prediction of fatigue lives of such components. However, these analyses have resulted in short but adequate lives. The objective of this work was, therefore, to derive fatigue data that could be applied to components operating at high strains and over a large range of stress ratios. This necessitated strain-controlled fatigue testing. Cyclic material properties evaluated from the tests are presented. In addition, it was found that sustained strain load, a type of stress relaxation that, unlike normal stress relaxation, does not require elevated temperatures, affected the cyclic behavior It also affects the distribution of make up stresses. This phenomenon was also investigated and it was shown that the cyclic stress/strain curve, readily derived from strain-controlled fatigue tests, accounted for sustained strain load effects.
Wave Statistics and Spectra via a Variational Wave Acquisition Stereo System
Authors: Gallego Guillermo , Benetazzo Alvise , Yezzi Anthony , Fedele Francesco
Published: July 2009

We propose a novel variational Wave Acquisition Stereo System (WASS) that exploits new stereo reconstruction techniques for accurate estimates of the spatio-temporal dynamics of ocean waves. WASS has a significant advantage as a low-cost system in both installation and maintenance. A stereo camera view provides three-dimensional data (both in space and time) whose statistical content is richer than that of a time series retrieved from wave gauges, ultrasonic instruments or buoys, the latter being expensive to install and maintain. Indeed, wave spectra can be easily estimated from the multi-dimensional images obtained with WASS. The estimated spectra present an inertial range that decays as k−2.5, k being the wave number, in agreement with wave turbulence theory (Zakharov 1999, Socquet-Juglard et al. 2005). Further, the empirical probability density functions derived from the reconstructed surface data compare very well with theoretical models (Tayfun & Fedele 2007, Fedele 2008). The variational WASS is a promising technology with broader impacts in offshore engineering since it will enrich the understanding of the statistics of waves for an improved design of offshore structures.
Reliability Based Optimization of Steel Monopod Offshore-Towers
Authors: Karadeniz H. , Togan V. , Vrouwenvelder T.
Published: July 2009

In this work, the implementation of reliability-based optimization (RBO) of a circular steel monopod-offshore-tower with constant and variable diameters (represented by segmentations) and thicknesses is presented. The tower is subjected to the extreme wave loading. For this purpose, the deterministic optimization of the tower is performed with constraints including stress, buckling, and the lowest natural frequency firstly. Then, a reliability-based optimization of the tower is performed. The reliability index is calculated from FORM using a limit state function based on the lowest natural frequency. The mass of the tower is considered as being the objective function; the thickness and diameter of the cross-section of the tower are taken as being design variables of the optimization. The numerical strategy employed for performing the optimization uses the IMSL-Libraries routine that is based on the Sequential Quadratic Programming (SQP). In addition, to check the results obtained from aforementioned procedure, the RBO of the tower is also performed using the genetic algorithms (GA) tool of the MATLAB. Finally, a demonstration of an example monopod tower is presented.