bluuebunny/crossref_metadata_2025 huggingface dataset:
Cognate Space Identification for Forced Response Structural Redesign
Authors: Blouin Vincent Y. , Bernitsas Michael M.
Published: March 2009

LargE Admissibility Perturbations (LEAP) is a general methodology, which solves redesign problems of complex structures with, among others, forced response amplitude constraints. In previous work, two LEAP algorithms, namely the Incremental Method (IM) and the Direct Method (DM), were developed. A powerful feature of LEAP is the general perturbation equations derived in terms of normal modes, the selection of which is a determinant factor for a successful redesign. The normal modes of a structure may be categorized as stretching, bending, torsional, and mixed modes and grouped into cognate spaces. In the context of redesign by LEAP, the physical interpretation of a mode-to-response cognate space lies in the fact that a mode from one space barely affects change in a mode from another space. Perturbation equations require computation of many perturbation terms corresponding to individual modes. Identifying modes with negligible contribution to the change in forced response amplitude eliminates a priori computation of numerous perturbation terms. Two methods of determining mode-to-response cognate space, one for IM and one for DM, are presented and compared. Trade-off between computational time and accuracy is assessed in order to provide practical guidelines to the designer. The developed LEAP redesign algorithms are applied to the redesign of a simple cantilever beam and a complex offshore tower.
Transit Draft Heave and Pitch Motion Analysis of the Mobile Offshore Base (MOB) Using Reverse MI/SO Techniques
Authors: Falzarano Jeffrey , Cheng Jun , Rodrigues William
Published: March 2009

A major design feature of the Mobile Offshore Base (MOB) is its ability to transit anywhere in the world in the required time frame. This means that the MOB must be able to transit in severe environmental conditions. In these extreme sea conditions, a primary cause for concern is the large accelerations that the vessel motions might experience due to the high static stability of the MOB at Transit Draft. Furthermore, since the vessel has minimum freeboard in this condition, it is exposed to green water over the pontoon tops. The submergence of the pontoon deck causes a considerable loss in the vessel’s restoring moment. These concerns have warranted a study by the Office of Naval Research into the Transit Draft Dynamics of the MOB. A part of the research in progress involves the development of a non-linear system modeling and optimization tool utilizing Reverse MI/SO (Multiple-Input/Single Output) techniques. Reverse MI/SO is based on the statistical signal processing of the recorded time histories of the excitation and response of the non-linear multi-degree-of-freedom system. This method of analysis is functional and reliable in identifying an ideal representation of the linear and non-linear terms of the system under consideration. Reverse MI/SO is a frequency domain analysis technique that also provides coherence functions for each of the terms in the model enabling an evaluation of the correctness of the proposed integro-diffrential equation of motion representing the system.
Reliability Based Design Criteria for Installation of Pipelines in the Bay of Campeche, Mexico: Part 1
Authors: Bea Robert , Xu Tao , Heredia-Zavoni Ernesto , Lara Leonel , Burbano Rommel
Published: March 2009

Studies have been performed to propose reliability based design criteria for the installation of pipelines in the Bay of Campeche, Mexico. This paper summarizes the reliability formulations that were used to develop Allowable Stress Design and Load and Resistance Factor Design guidelines for Ultimate Limit State conditions, background on the target reliabilities that were used in the development, and the methods that were used to characterize the demands (loads, displacements) induced in pipelines during their installation. This paper summarizes data that was gathered during the installation of pipelines in the Bay of Campeche to help define the Biases (actual stresses/calculated stresses) associated with the analytical model used to predict installation demands. These results are compared with those published previously based on other field and laboratory tests. A companion paper details the analyses of pipeline Ultimate Limit State capacities and the Biases associated with these capacities.
A Reliability-Based Method for Determining Design Ice Loads on Offshore Structures
Authors: Wu X. , Wang A. T. , Heuer C. E. , Ralston T. D. , Davenport G. F. , Toro G.
Published: March 2009

This paper describes a reliability-based methodology that has been developed at ExxonMobil Upstream Research Company (URC) for determining rational design ice loads on offshore structures. The URC methodology provides a systematic framework to account for Type I (aleatory) and Type II (epistemic) uncertainties in assessing global probabilistic ice hazards. Specifically, a logic-tree based approach is developed to model Type II uncertainties in the assessment of ice hazards. Although the method has general applicability, the present work considers a wide, vertical-sided, gravity-based structure (GBS) in a dynamic, annual ice environment. Both FORM/SORM methods and Monte Carlo simulation are used in the analyses. Results obtained from this reliability-based approach indicate that the modeling of Type II uncertainties plays a significant role in quantifying the ice hazards for determining the design ice load. Further, this effort may potentially reduce over-conservatism in typical deterministic ice load calculations. The probabilistic methodology developed in this study has broad applicability and can provide a rational framework for calculating design ice loads on other types of structures for arctic offshore development.
Verification of TOPEX/Poseidon Wave Data Against Buoys Off the West Coast of Portugal
Authors: Moreira Nuno M. , Pires Henrique Oliveira , Pontes M. Teresa , da Camara Carlos
Published: March 2009

The goals of the present work are to compare TOPEX/Poseidon (T/P) significant wave height (HS) with buoy data off the West Coast of Portugal and to evaluate the performance of wave period algorithms. Altimeter and buoy data are compared according to co-location criteria proposed in literature. A new method for analysing the variation of quality parameters in the space and time domains is presented. The use of wave group velocity as a way of relating space and time lags is also proposed. Local calibrations for T/P HS are computed, with the interval of degradation of TOPEX altimeter considered separately. It is found that an algorithm for mean wave zero-crossing period (ZT) can be used in the region under consideration, the root mean square error (Erms) being lower than 0.7 s if local coefficients are used.
Structural Integrity Evaluation of Jackets Submitted to Through Cracks
Authors: Rouhan Antoine , Schoefs Franck
Published: March 2009

The study of the impact of through cracks on structural integrity of jacket platforms still a challenge. The detection of such cracks is of great importance and a miss, or a spurious indication can lead to maintenance costs overrun. In the context of risk-based inspection and monitoring of such structures, a global methodology is proposed. The detection of large cracks is first addressed. A probabilistic model is proposed, taking into account the in situ inspections performances and the probability of crack presence. This is achieved by the use of the detection theory. Second, a finite element that is able to represent the structural behaviour of through cracked tubular nodes is proposed and a global structural integrity measure is suggested. Finally, inspection results are introduced in order to compute the expected platform structural integrity. It is illustrated by considering FMD inspections results of a tripod structure. Effects of false alarms can then be underlined.
Seismic Behavior of Rubble-Mound Moles on Sandy Marine Sediments
Authors: Adalier K. , Zimmie T. F. , Pamuk A.
Published: March 2009

Recent major seismic events such as Loma Prieta 1989, Kobe 1995, and Izmit 1999 earthquakes continue to demonstrate the damaging effects of liquefaction-induced loss of soil strength and associated damage to waterfront and port structures. This paper presents the experimental results from a series of dynamic centrifuge model tests performed to investigate the seismic behavior of rubble-mound moles resting on loose, clean, sandy marine deposits. Soil response during and after shaking was monitored by miniature accelerometers, pore pressure transducers, and vertical and horizontal displacement gages placed throughout the soil model. Currently, such test results offer a valuable alternative to actual full-scale dynamic response, which is virtually non-existent. It was found that catastrophic failures of even structurally-strong moles are possible if they are underlain by loose liquefiable soils. Densification and usage of a geogrid mat as liquefaction-induced hazards countermeasures are also evaluated. Both methods much improved the liquefaction induced deformations in the foundation and of the mole.
Online Valve Monitoring Systems Used on Off-Shore Platforms in the North Sea
Authors: Juvik Tore , Hermansen Tore , Carr Roger , Hale Stan
Published: March 2009

Monitoring the leakage and condition of Emergency Shutdown Valves (ESVs) on offshore oil and gas platforms is an essential part of maintaining the safety of personnel and protecting the environment. Failure of these valves to operate when they are needed also has an enormous economic impact. The ESVs are intended to isolate each section of the platform in the event of a line break or fire, preventing hydrocarbons from flowing into the affected section. This paper describes a unique approach to monitoring these valves for leakage while the systems are in operation.
System Identification Techniques for Prediction of Fluid Accelerations Under Irregular Waves Based on Free-Surface Elevation Measurements
Authors: Cies´likiewicz Witold , Gudmestad Ove T.
Published: March 2009

A parametric model linking the free-surface elevations with the fluid acceleration field under an irregular wave is developed. In order to estimate the parameters of the model, system identification procedures are applied based on data recorded in a wave tank. The free-surface time series are taken as input data and the output data are components of the particle acceleration vector. The particle acceleration time series were obtained by taking the numerical derivative of the measured orbital velocity time series. A simple algorithm of numerical diffrentiation is proposed. This algorithm gives very accurate values of the particle acceleration and is quite straightforward as the derivative is computed directly in time domain. A linear time-invariant model with the static nonlinearities incorporated at the input side is assumed. This paper demonstrates the results of modelling the horizontal component of the particle acceleration in comparison with the time series calculated from wave kinematics data taken in a wave flume during an earlier experiment using Laser Doppler Velocimetry. The modelled particle acceleration time series compare well with those calculated from the observed velocity time series. This proves the effectiveness of the applied approach. The system identification techniques allow for preparing the model which constructs the wave kinematics (both velocities and accelerations) using the measured time series of only the free-surface elevation. This feature of the proposed approach may be very useful in maritime engineering and oceanography.
A Simplified Method for Response Behavior and Reliability Analysis of Long Submerged Structures With Tension Legs in Irregular Waves
Authors: Katsura Shinji , Okada Hiroo , Masaoka Koji , Tsubogo Takashi , Shimada Kiko
Published: March 2009

This paper deals with the elastic response behavior of marine tunnel structures with tension legs in regular and irregular waves. Firstly, a simplified estimation method for dynamic responses under regular wave conditions is analytically presemed using a simple beam on an elastic foundation. Then, in order to demonstrate the validity of above results, experimental studies are carried out for a marine tunnel structure model with tension legs under wave-induced loads. Next, a simplified estimation method is presented for the elastic response behavior under irregular wave conditions by using above analytical results and combining irregular sea wave spectra. Then, the limit state failure mode of the main structure is presented for estimating the reliability level for cracking failure under extreme wave loads. Finally, the applicability of the methods is investigated through numerical examples carried out for a 1,000m-class marine tunnel structure with tension legs under some irregular sea state conditions. And characteristics of the short-term responses and reliability levels for the cracking failure are numerically shown.
Structural Safety Assessment of Pontoon-Type VLFS Considering Damage of Breakwater
Authors: Fujikubo Masahiko , Xiao Tao-Yun , Yamamura Kazuhiro
Published: March 2009

Structural reliability analysis of a pontoon-type Very Large Floating Structure (VLFS) of rectangular planar shape surrounded by gravity-type breakwater in extreme waves is performed considering the damage of breakwater. Bending and shear collapses are considered for floating structure, while overturning damage for breakwater. The ultimate bending and shear strengths of the floating structure are calculated using Idealized Structural Unit Method (ISUM) and FEM. The calculated failure probability of floating structure is compared with the specified target safety level. It has been found that the considered floating structure is most likely to fail in the bending collapse mode in transverse waves and that the corresponding failure probability satisfies the target level.
Cost Effectiveness of Hull Girder Safety
Authors: Skjong Rolf , Bitner-Gregersen Elzbieta M.
Published: March 2009

The paper presents a cost effectiveness assessment of the safety in a design code for oil tankers. The marginal cost to safety improvements is based on code calibration studies for different target reliabilities. This allows basing the actual target reliability indices on risk acceptance criteria derived from cost effectiveness of the marginal change in scantling requirements. This approach is in agreement with the criteria defined in IMO submissions and used in the ongoing IMO coordinated Formal Safety Assessment studies on bulk carriers. The documentation that cost effectiveness criteria may be applied has previously been submitted to IMO. It is concluded that the method works quite well in the examples that are presented, and that the current codes are in close agreement with decision criteria used for other risk control options. As probabilities calculated by structural reliability methods are notional, it is also advantageous to use marginal costs to safety improvement instead of absolute numbers of probabilities as acceptance criterion. It is indicated that a cost effectiveness criterion may replace the current practice of basing target reliabilities on calibration against previous best practices. Although the basic safety philosophy is changed radically, the study does not indicate that the change in criteria would result in much change in design. The advantage of using the suggested approach is the consistency with ongoing FSA development at IMO.
Analysis of WACSIS Data Using Directional HWM
Authors: Zhang Jun , Zhang Shaosong , Wang Zhongming
Published: March 2009

WACSIS (Wave Crest Sensor Inter-comparison Study) is a Joint Industrial Project (JIP). Many different types of instruments were attached to a steel jacket platform that located in 18 m deep water and about 9 km from the Dutch coast to measure ocean waves during this project. The sensors for measuring wave elevation include Marex and SAAB Radars, a Baylor wave staff, an EMI Laser, a Vlissingen and Marine 300 step gauges. A S4ADW current meter was deployed at 10m below the MWL to measure pressure and particle velocities. In addition, a Directional Waverider Buoy was deployed nearby the platform to provide the information of wave directionality. The Directional Hybrid Wave Model (DHWM) was recently developed to deterministically decompose and predict a directional wave field. By the DHWM, the wave properties nearby the platform can be deterministically predicted based on at least three wave measurements. If the prediction location happens to be same as other instruments whose measurements have not been used for the prediction, then the comparison between the prediction and the measurement by this instrument may reveal the consistency and suitability of this instrument. Several such kind of comparisons are given in this study, indicating the DHWM is valuable to the analysis of field wave measurements.
Implicit Reliability of Ship Structures
Authors: Bitner-Gregersen Elzbietta M. , Hovem Liv , Skjong Rolf
Published: March 2009

Ship structures must be designed with adequate safety and reliability, and their designs must be acceptable from an environmental and economical point of view. Target reliabilities have to be met in the design rules in order to ensure that certain safety levels are reached in design according to the rules. There are several steps involved in a process of determining target reliabilities in agreement with a risk based approach as recommended by Formal Safety Assessment, IMO (1997, 2001). The study concentrates on the second step of FSA, i.e. calculation of the reliability level inherent in existing rules representing past practice when state-of-the-art models for environment, loads, response and capacity are adopted. Buckling of a ship deck in the extreme sagging conditions is considered. The suggested procedure is illustrated by three examples. The reliability calculations are carried out for the ‘as build’ stiffened deck plate thickness. Uncertainties involved in the suggested analysis procedure and their consequences on implicit reliability are presented. Implementation of the results in the risk analysis is discussed.
Some Nonlinear Behaviour of Freak Waves and Envelope Solitons
Authors: Clamond Didier , Grue John
Published: March 2009

The nonlinear Schro¨dinger-like equations are widly used models for investigating the evolution of surface gravity waves with narrow-banded spectra. We numerically compare one of these simplified models with a fully nonlinear one. In particular, we study the long time evolution of wave groups. Although the simplified model predicts the right number of soliton formed, their behaviour and long time evolution is not well described. Solitons interact differently with the two models. During the interaction, freak waves are formed. Their occurence is more frequent with the fully nonlinear model. A more interesting phenomemon is, during the formation of freak waves, the wave envelope oscillates rapidly. This “intermittence” is not at all predicted by any weakly nonlinear model.
Specifying and Testing Fiber Moorings for Harsh Environment Locations
Authors: Stonor Richard W. P. , Ahilan R. V. , Marthinsen Tom
Published: March 2009

Fiber Moorings are increasingly seen as having significant advantages for use in permanent deepwater moorings and several have now been installed worldwide. They have generally been seen to be of particular advantage in areas where the environmental conditions are modest. However the advantages they offer in good position keeping and relatively easy installation are also attractive in harsh environment locations. In order to be accepted for use in fields such as offshore western Norway a thorough review has been undertaken to determine the level of special consideration that should be given to such locations and the selection of fiber rope moorings that will be suitable for such use. The paper describes the characteristics that need special consideration during specification and comments on the additional work that will be required before such moorings can be used at such locations.
Effect of Cement Contents and Curing Periods on Properties of DUT-1 Synthetic Model Ice
Authors: Li Zhijun , Wang Yongxue , Wang Xiwen , Li Guangwei
Published: March 2009

The effect of cement content and curing period on a new kind of synthetic model ice, DUT–1 synthetic model ice is reported. The 450# cement contents were 10%, 11%, 12%, 13%, 14%, 15% and 16% by dry weight of mixture materials. Eight different curing periods were used: 66h, 92h, 115h, 139h, 163h, 186h, 211h and 235h. Physical and mechanical properties such as density, compressive strength, flexural strength, elastic modulus were determined. The cement content was found to increase the density and mechanical parameters with content increasing, whereas curing periods exhibited increasing these parameters to a top value, then decreasing under normal air temperature curing.
Maximum Likelihood Method as a Means to Estimate the Directional Wave Spectrum and the Mean Wave Drift Force on a Dynamically Positioned Vessel
Authors: Waals Olaf J. , Aalbers A. B. , Pinkster J. A.
Published: March 2009

Feed forward in control theory is a method in which real time information about system disturbance is fed into the controller to improve its performance. As such, feed forward of the wave drift forces would improve DP behavior of a ship in terms of fuel consumption as well as position keeping. In the present study the wave drift forces have been divided in a constant part and a low frequent oscillating part. The constant part directly depends on the directional wave energy spectrum. In this paper the directional spectrum and mean drift force will be estimated from six relative wave height measurements on a dynamically positioned vessel. The Extended Maximum Likelihood Method (EMLM) is known to make a reliable estimate of the directional wave spectrum from wave measurements at fixed locations in the wave field. For a wave feed forward application the EMLM had to be implemented on a moving ship. Six relative wave height probes have been installed on board of a shuttle tanker. The EMLM has been applied to these relative motions and the low frequent yawing motion has been taken into account to calculate an earth bound spectral estimate. The estimate for the spectrum is based on a 30min average and is updated every minute in a moving average algorithm. Finally, the mean wave drift force is calculated for the actual heading of the ship.
Deterministic Reproduction of Nonlinear Waves
Authors: Skourup Jesper , Sterndorff Martin J.
Published: March 2009

A method for deterministic reproduction of non-linear long-crested waves has been implemented. The model is used for non-linear reproduction of measured wave time series from a model test programme in a wave flume. Regular waves, irregular waves and focused waves have been reproduced with the model. Based on measured surface elevation time series at one location in the flume the elevation time series and the kinematics have been reproduced at another location using both linear theory and the second order model. The numerical results have been compared with measurements and it is found that the second order model is able to reproduce the correct shape of the waves as they propagate in the flume — even when the waves are highly non-linear.
Fatigue Strength of Titanium Riser Welds: Effects of Material Grade and Weld Method
Authors: Berge Stig , Elde Oddvar I. , Mainc¸on Philippe
Published: March 2009

MARINTEK in co-operation with Institute of Energy Technology (IFE) has carried out a Joint Industry research programme Titanium Risers and Flowlines. The programme consisted of five sub-projects: Design, corrosion, welding, mechanical characterisation and fatigue. The primary results from the programme has been published in a Handbook (1999). The objective of this paper is to report on some of the results from the fatigue sub-project. Girth welded joints from a supplier of titanium pipe were fatigue tested in air. Pipe was welded by the TIG process, in 1G and 5G positions, with ASTM Grade 28 and 29 pipe material. Constant amplitude SN data were obtained. The results were compared with current proposals for fatigue design curves for titanium riser welds.
Experiments and Analysis of Laboratory Generated Steep Waves
Authors: Chakrabarti Subrata K.
Published: March 2009

In many offshore locations, storm generated steep waves are common and the survival of offshore structures in their presence is an important design condition. The design environment in depth-limited waters often includes waves of breaking and near-breaking conditions, in which currents may be present. Experiments were carried out in a wave tank with simulated steep waves with and without steady in-line current in which the wave profiles and the corresponding kinematics were simultaneously measured. The waves included both regular and random waves and often approached the breaking wave height for the water depth. These waves were analyzed by higher-order wave theory. In particular, the regular waves were simulated by the regular and irregular stream function theory. Especially steep wave profiles within the random waves were computed using the irregular stream function theory. The theory allows inclusion of steady current in its formulation for computation of wave kinematics. The correlation of the measured wave kinematics with the higher-order stream function wave theory showed that the wave theory could predict the kinematics of these steep waves (with and without the presence of current) well. However, in breaking waves, the vertical water particle velocity was not predicted well, specially near the trough. The effect of breaking and near-breaking steep waves on a fixed vertical caisson was also studied. The forces measured on the vertical caisson from the wave tank testing were analyzed to determine the effect of these waves and currents on the forces. It was found that the measured forces (and overturning moments) on the caisson model matched fairly well by the proper choice of force coefficients from the design guideline and the nonlinear stream function theory of appropriate order.
Petrobras Operational Excellence Programme
Authors: da Costa Fraga Carlos Tadeu , Mastrangelo Carlos Ferraz
Published: March 2009

This paper addresses actions implemented by Petrobras after the P-36 accident. The purpose of investigations following major accidents is to understand what exactly happened to avoid repetition. It is everyone’s responsibility to adopt practices that mitigate the risks even more in any activities. The P-36 accident was therefore analysed and discussed as transparently and deeply as possible in order that the lessons learned may be translated into safer operations. This is how it is done throughout the oil industry: the lessons learned from major accidents usually cause radical changes to the industry’s practices with regard to change in equipment, design, procedures, behaviours and attitudes. The P-36 Investigation Commission, with technical experts from Petrobras, universities and worker union representatives, audited by a company of international repute, produced several recommendations and identified areas for improvement. This paper discusses how Petrobras considered the commission report and how the areas for improvement are to be addressed. Many recommendations were immediately applicable but others, including some areas for improvement, requiring more detailed planning, were included in an Operational Excellence Programme (PEO – Programa de Exceleˆncia Operacional). This Programme shall be applied to every offshore unit of the company, while taking into account the peculiarities of each Business Unit. This Programme covers actions involving Petrobras design practices, operation, ballast and stability, maintenance, safety and human resources for offshore units and all those actions shall be concluded by December 2002. A detailed description of the actions which go beyond those required by current legislation will also be given, permitting Petrobras to achieve operational excellence in all its offshore units. Furthermore, Petrobras intends to contribute to the ongoing improvement of offshore oil industry practices through widespread dissemination of this Programme, which has already begun.
Probabilistic Models of Uncertainties in Fatigue and Fracture Reliability Analysis
Authors: Zhao W. , Stacey A. , Prakash P.
Published: March 2009

Probabilistic methods enable the modelling of the uncertainties associated with the integrity assessment of structures containing defects to be taken into account. This paper presents a critical review of recent developments in the probabilistic modelling of the uncertainties associated with fatigue and fracture reliability assessment. A number of probabilistic models for the principal parameters in the S-N curve, fatigue crack growth functions and fracture analysis are presented and discussed with particular emphasis on the identification of future needs for the development of suitable code procedures for offshore structures.
Nonlinear Wave Disturbance Around a Vertical Circular Column
Authors: Stansberg C. T. , Braaten H.
Published: March 2009

The wave disturbance close to vertical columns is analysed. In particular, the deviations from linear predictions are investigated, by experimental as well as by numerical methods. Thus a second-order numerical diffraction model is established by means of a diffraction analysis code (WAMIT) and compared to model tests with a single, fixed column with diameter 16m. Tests in regular, bi-chromatic as well as irregular waves are run. Significant nonlinear effects are observed, especially in steep waves, with the maximum elevation in front of the column increasing from 11.5m in a linear prediction to around 19m, in a 12s regular wave with 22m wave height. The main nonlinear effects in front of the column are identified as second-order sum-frequency and difference-frequency terms, plus a significant nonlinear increase in the first harmonic component. The WAMIT prediction of the second-order effects agrees fairly well with the measurements, although with some overprediction and underprediction, respectively, of the sum-frequency and difference-frequency (LF and mean set-up) terms in the steepest waves. For the underprediction of the first harmonic, however, a theory beyond second order is required.
Cost Effective Large Blade Components by Using Carbon Fibres
Authors: Joosse P. A. , van Delft D. R. V. , Kensche Chr. , Soendergaard D. , van den Berg R. M. , Hagg F.
Published: March 2009

Due to the increasing size of wind turbine rotors, especially for offshore wind turbines, the power output and the blade mass are becoming more important. A new type of cheaper carbon fibres is expected to result in a lower blade mass and marginally cheaper blades. In a Joule-funded project, the possibilities for economic use of carbon fibres is determined by establishing material design data, analysing production methods, developing cost-effective blade root joints and assessing blade and turbine costs. The R&D project will be finalised by the end of 2001. Up to now, production processes and promising material combinations have been reviewed, tested and ranked. Basic material design data have been established for the two most-promising material combinations. Due to disappointing fatigue results on Panex/VE, additional testing on four large-tow laminates was performed. The fatigue properties of these showed to be consistent. Later testing on a similar Panex/epoxy laminate, however, revealed much better fatigue behaviour. Joint development and cost assessment are underway and show promising results.
Identification of Synchronous Generator Transfer Functions From Standstill Test Data
Authors: Molenaar David-P. , Bosgra O. H. , Hoeijmakers M. J.
Published: March 2009

The design of a robust frequency converter controller for high dynamic performance of a synchronous generator requires an accurate dynamic model of the electromagnetic part. In this paper a new procedure for identifying the transfer functions of Park’s dq-axis model of a synchronous generator has been developed. It will be shown that the parameters of this model can be easily identified from standstill time-domain data. The validity of the theoretical model has been verified by comparing time-domain simulations with measurements taken from the Lagerwey LW-50/750 direct-drive synchronous generator. It can be concluded that a consistent model estimate of the electromagnetic part of the LW-50/750 generator has been obtained. Ultimate validation, however, will follow after the implementation of the designed frequency converter controller in this wind turbine.
Prediction of acoustic radiation from axisymmetric surfaces with arbitrary boundary conditions using the boundary element method on a distributed computing system
Authors: Wright Louise , Robinson Stephen P. , Humphrey Victor F.
Published: March 2009

This paper presents a computational technique using the boundary element method for prediction of radiated acoustic waves from axisymmetric surfaces with nonaxisymmetric boundary conditions. The aim is to predict the far-field behavior of underwater acoustic transducers based on their measured behavior in the near-field. The technique is valid for all wavenumbers and uses a volume integral method to calculate the singular integrals required by the boundary element formulation. The technique has been implemented on a distributed computing system to take advantage of its parallel nature, which has led to significant reductions in the time required to generate results. Measurement data generated by a pair of free-flooding underwater acoustic transducers encapsulated in a polyurethane polymer have been used to validate the technique against experiment. The dimensions of the outer surface of the transducers (including the polymer coating) were an outer diameter of 98mm with an 18mm wall thickness and a length of 92mm. The transducers were mounted coaxially, giving an overall length of 185mm. The cylinders had resonance frequencies at 13.9 and 27.5kHz, and the data were gathered at these frequencies.
Reconstruction of vibroacoustic responses of a highly nonspherical structure using Helmholtz equation least-squares method
Authors: Lu Huancai , Wu Sean F.
Published: March 2009

The vibroacoustic responses of a highly nonspherical vibrating object are reconstructed using Helmholtz equation least-squares (HELS) method. The objectives of this study are to examine the accuracy of reconstruction and the impacts of various parameters involved in reconstruction using HELS. The test object is a simply supported and baffled thin plate. The reason for selecting this object is that it represents a class of structures that cannot be exactly described by the spherical Hankel functions and spherical harmonics, which are taken as the basis functions in the HELS formulation, yet the analytic solutions to vibroacoustic responses of a baffled plate are readily available so the accuracy of reconstruction can be checked accurately. The input field acoustic pressures for reconstruction are generated by the Rayleigh integral. The reconstructed normal surface velocities are validated against the benchmark values, and the out-of-plane vibration patterns at several natural frequencies are compared with the natural modes of a simply supported plate. The impacts of various parameters such as number of measurement points, measurement distance, location of the origin of the coordinate system, microphone spacing, and ratio of measurement aperture size to the area of source surface of reconstruction on the resultant accuracy of reconstruction are examined.
Simulation of elastic wave scattering in cells and tissues at the microscopic level
Authors: Doyle Timothy E. , Tew Adam T. , Warnick Keith H. , Carruth Brent L.
Published: March 2009

The scattering of longitudinal and shear waves from spherical, nucleated cells and three-dimensional tissues with simple and hierarchical microstructures was numerically modeled at the microscopic level using an iterative multipole approach. The cells were modeled with a concentric core-shell (nucleus-cytoplasm) structure embedded in an extracellular matrix. Using vector multipole expansions and boundary conditions, scattering solutions were derived for single cells with either solid or fluid properties for each of the cell components. Tissues were modeled as structured packings of cells. Multiple scattering between cells was simulated using addition theorems to translate the multipole fields from cell to cell in an iterative process. Backscattering simulations of single cells indicated that changes in the shear properties and nuclear diameter had the greatest effect on the frequency spectra. Simulated wave field images and high-frequency spectra (15–75 MHz) from tissues containing 1211–2137 cells exhibited up to 20% enhancement of the field amplitudes at the plasma membrane, significant changes in spectral features due to neoplastic and other microstructural alterations, and a detection threshold of ∼8.5% infiltration of tumor cells into normal tissue. These findings suggest that histology-based simulations may provide insight into fundamental ultrasound-tissue interactions and help in the development of new medical technologies.
On-axis and far-field sound radiation from resilient flat and dome-shaped radiators
Authors: Aarts Ronald M. , Janssen Augustus J. E. M.
Published: March 2009

On-axis and far-field series expansions are developed for the sound pressure due to an arbitrary, circular symmetric velocity distribution on a flat radiator in an infinite baffle. These expansions are obtained by expanding the velocity distributions in terms of orthogonal polynomials R2n0(σ∕a)=Pn(2(σ∕a)2−1) with Pn the Legendre polynomials. The terms R2n0 give rise to a closed-form expression for the pressure on-axis as well as for the far-field pressure. Furthermore, for a large number of velocity profiles, including those associated with the rigid piston, the simply supported radiator, and the clamped radiators as well as Gaussian radiators, there are closed-form expressions for the required expansion coefficients. In particular, for the rigid, simply supported, and clamped radiators, this results in explicit finite-series expressions for both the on-axis and far-field pressures. In the reverse direction, a method of estimating velocity distributions from (measured) on-axis pressures by matching in terms of expansion coefficients is proposed. Together with the forward far-field computation scheme, this yields a method for far-field loudspeaker assessment from on-axis data (generalized Keele scheme). The forward computation scheme is extended to dome-shaped radiators with arbitrary velocity distributions.
Feeding at a high pitch: Source parameters of narrow band, high-frequency clicks from echolocating off-shore hourglass dolphins and coastal Hector’s dolphins
Authors: Kyhn Line A. , Tougaard J. , Jensen F. , Wahlberg M. , Stone G. , Yoshinaga A. , Beedholm K. , Madsen P. T.
Published: March 2009

Toothed whales depend on echolocation for orientation and prey localization, and source parameters of echolocation clicks from free-ranging animals therefore convey valuable information about the acoustic physiology and behavioral ecology of the recorded species. Recordings of wild hourglass (Lagenorhynchus cruciger) and Hector’s dolphins (Cephalorhynchus hectori) were made in the Drake Passage (between Tierra del Fuego and the Antarctic Peninsular) and Banks Peninsular (Akaroa Harbour, New Zealand) with a four element hydrophone array. Analysis of source parameters shows that both species produce narrow band high-frequency (NBHF) echolocation clicks. Coastal Hector’s dolphins produce clicks with a mean peak frequency of 129 kHz, 3 dB bandwidth of 20 kHz, 57 μs, 10 dB duration, and mean apparent source level (ASL) of 177 dB re 1 μPap.-p.. The oceanic hourglass dolphins produce clicks with mean peak frequency of 126 kHz, 3 dB bandwidth of 8 kHz, 116 μs, 10 dB duration, and a mean estimated ASL of 197 dB re 1 μPap.-p.. Thus, hourglass dolphins apparently produce clicks of higher source level, which should allow them to detect prey at more than twice the distance compared to Hector’s dolphins. The observed source parameter differences within these two NBHF species may be an adaptation to a coastal cluttered environment versus a deep water, pelagic habitat.
Evaluation of a Rapid Immunochromatographic ODK0501 Assay for Detecting
Streptococcus pneumoniae
Antigen in Sputum Samples from Patients with Lower Respiratory Tract Infection
Authors: Izumikawa Koichi , Akamatsu Suguru , Kageyama Akiko , Okada Kiyomi , Kazuyama Yukumasa , Takayanagi Noboru , Nakamura Shigeki , Inoue Yuichi , Higashiyama Yasuhito , Fukushima Kiyoyasu , Ishida Tadashi , Sawai Toyomitsu , Yoshimura Kunihiko , Nakahama Chikara , Ohmichi Mitsuhide , Kakugawa Tomoyuki , Nishioka Yasuhiko , Aoki Nobuki , Seki Masafumi , Kakeya Hiroshi , Yamamoto Yoshihiro , Yanagihara Katsunori , Kohno Shigeru
Published: March 2009

A novel, rapid, and noninvasive test (ODK0501) to detect
Streptococcus pneumoniae
antigen was evaluated in a Japanese multicenter study. ODK0501 uses polyclonal antibodies to detect C polysaccharide of
S. pneumoniae
from sputum samples by an immunochromatographic assay. The utility of ODK0501 was evaluated for 161 adult patients with lower respiratory tract infection between March 2006 and March 2007. Bacterial culture and identification, real-time PCR, and ODK0501 assays were performed on sputum samples, and the Binax Now
Streptococcus pneumoniae
antigen test was performed using urine samples obtained from the same patients. The performances of all tests were compared based on the results of bacterial culture and identification. The sensitivity and specificity of ODK0501 were 89.1% (49/55 samples) and 95.3% (101/106 samples), respectively. We then compared the Binax Now
Streptococcus pneumoniae
antigen test with ODK0501 using samples from 142 patients. The sensitivities of ODK0501 and the Binax Now
S. pneumoniae
antigen test were 90.0% (45/50 samples) and 62.0% (31/50 samples), respectively (
P
= 0.002). The relative quantity of
S. pneumoniae
in expectorated sputum was calculated using real-time PCR and indicated that the possibility of false-positive results for ODK0501 due to indigenous
S. pneumoniae
was low. The positive and negative concordance rates of ODK0501 and Binax Now were 96.8% (30/31 samples) and 21.1% (4/19 samples), respectively. Binax Now was less capable of detecting
S. pneumoniae
antigen among patients with underlying chronic obstructive pulmonary disease. In conclusion, ODK0501 is noninvasive, rapid, and an accurate tool for diagnosing respiratory infection caused by
S. pneumoniae
.
Peripheral Ovine Progressive Pneumonia Provirus Levels Correlate with and Predict Histological Tissue Lesion Severity in Naturally Infected Sheep
Authors: Herrmann-Hoesing Lynn M. , Noh Susan M. , White Stephen N. , Snekvik Kevin R. , Truscott Thomas , Knowles Donald P.
Published: March 2009

Studies were undertaken to determine whether anti-ovine progressive pneumonia virus (OPPV) antibody responses in serum or OPP provirus levels in peripheral blood associate with the degree of histologically measured tissue lesions in naturally OPPV-infected sheep. Sections of formalin-fixed, paraffin-embedded, and hematoxylin- and eosin-stained lung, mammary gland, carpal synovial membrane, and brain tissues from 11 OPPV-infected ewes (mean age of 8.6 years) and 5 OPPV-uninfected ewes (mean age of 6 years) were evaluated for lesion severity. Ovine progressive pneumonia (OPP) provirus levels and anti-OPPV antibody titers in peripheral blood and serum samples, respectively, were measured upon euthanasia and 3 years prior to euthanasia. Both mean peripheral OPP provirus levels and mean serum anti-surface envelope glycoprotein (anti-SU) antibody titers at the time of euthanasia were significantly higher in ewes with moderate to severe histological lesions than in ewes with no to mild histological lesions. However, although mean peripheral blood OPP provirus levels at euthanasia and 3 years prior to euthanasia significantly correlated with the highest histological lesion score for any affected tissue (two-tailed
P
values, 0.03 and 0.02), mean serum anti-SU antibody titers, anti-capsid antibody titers, and anti-transmembrane 90 antibody titers at euthanasia did not show a significant correlation with the highest histological lesion score for any tissue (two-tailed
P
values, 0.32, 0.97, and 0.18, respectively). These data are the first to show that OPP provirus levels predict and correlate with the extent of OPPV-related histological lesions in various OPPV-affected tissues. These findings suggest that peripheral OPP provirus levels quantitatively contribute more to the development of histological lesions than the systemic anti-SU antibody host immune response.
High-Throughput Molecular Determination of
Salmonella enterica
Serovars by Use of Multiplex PCR and Capillary Electrophoresis Analysis
Authors: Leader Brandon T. , Frye Jonathan G. , Hu Jinxin , Fedorka-Cray Paula J. , Boyle David S.
Published: March 2009

Salmonella enterica
is a leading cause of food-borne illness worldwide and is also a major cause of morbidity and mortality in domestic and wild animals. In the current study, a high-throughput molecular assay was developed to determine the most common clinical and nonhuman serovars of
S. enterica
in the United States. Sixteen genomic targets were identified based on their differential distribution among common serovars. Primers were designed to amplify regions of each of these targets in a single multiplex PCR while incorporating a 6-carboxyfluorescein-labeled universal primer to fluorescently label all amplicons. The fluorescently labeled PCR products were separated using capillary electrophoresis, and a
Salmonella
multiplex assay for rapid typing (SMART) code was generated for each isolate, based upon the presence or absence of PCR products generated from each target gene. Seven hundred fifty-one blind clinical isolates of
Salmonella
from Washington State, collected in 2007 and previously serotyped via antisera, were screened with the assay. A total of 89.6% of the isolates were correctly identified based on comparison to a panel of representative SMART codes previously determined for the top 50 most common serovars in the United States. Of the remaining isolates, 6.2% represented isolates that produced a new SMART code for a previously determined serotype, while the final 8.8% were from serotypes not screened in the original panel used to score isolates in the blinded study. This high-throughput multiplex PCR assay allowed simple and accurate typing of the most prevalent clinical serovars of
Salmonella enterica
at a level comparable to that of conventional serotyping, but at a fraction of both the cost and time required per test.