bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Evaluation of Vortex-Induced Vibration of a Riser Bundle With Gaps
Authors: Vandiver J. Kim , Cheng Yongming , Jaiswal Vivek , Sheshadri Aditi , Yu Alan
Published: February 2010

VIV model test results are presented for a bundle of three parallel pipes all lying in the same plane, similar to a riser with large kill and choke lines. The rigid model was attached to a spring-mounted frame in the MIT towing tank. The horizontal model was towed in the tank and allowed to respond in free vibration to vortex-induced vibration in the cross-flow direction. The angle of attack of the model was varied from 0 to 90 degrees. The model was tested with and without helical strakes. Without strakes the model exhibited significant vibration at 0 and 90 degrees angle of attack. Strakes suppressed VIV at all angles of attack.
Strain lntensification Due to Material Discontinuity at Field Joints Adjacent to Thick Wall Insulation Coating
Authors: Roberts Clem , Rathbone Andrew , Timmins David , Cumming Gary , To̸rnes Knut
Published: February 2010

High pressure/high temperature (HP/HT) subsea pipelines are increasingly being designed to buckle in a controlled manner in order to relieve axial loading. HP/HT pipelines often require insulation coating to prevent hydrate formation and to help manage internal corrosion. Thick wall polymer coatings are a common choice of insulation material in such cases. A change in local bending stiffness, for example due to the change in external coating at field joints, can result in strain localisation leading to a higher local curvature than would have occurred in an otherwise homogenous system. Industry knowledge of the influence of thick wall polypropylene is limited. The proportion of total bending stiffness attributed to the coating is much larger than typically observed in non-insulated coating systems. The polymer coating is likely to behave in an elastic manner even at elevated strain levels, i.e. those typically observed in lateral buckles. It is shown herein that significant strain intensification can occur at field joints even when the field joints appear to be of a similar configuration to that of the nominal linepipe coating. This paper presents the results of finite element (FE) analyses (using solid body elements) that have been employed to demonstrate, in highly loaded conditions such as laterally buckled pipelines, the influence of thick wall insulation coatings on strain intensification at field joints. Furthermore analytical equations have been derived as an alternative methodology for calculation of strain intensification at field joints. It is demonstrated that, even in highly loaded conditions, the analytical relationship correlates very well to results determined via the FE technique.
Calculation of Current or Manoeuvring Forces Using a Viscous-Flow Solver
Authors: Toxopeus Serge , Vaz Guilherme
Published: February 2010

To investigate the capabilities of using a viscous-flow solver to calculate current or manoeuvring forces on ship hulls, calculations have been conducted for a test hull under several oblique inflow conditions. All calculations were performed with a single grid topology to reduce the amount of grid generation time. Verification and validation of the predicted loads and flow around the hull has been performed through grid refinement studies and comparison with experiments and results from previous calculations. Furthermore, the influence of unsteady behaviour on the results for large inflow angles is shown. Conclusions are drawn regarding the accuracy of the results and recommendations for improvements and further work are given.
Consolidation of Lumpy Clay Backfill Over Buried Pipelines
Authors: Ghahremani Mahmoud , Brennan Andrew J.
Published: February 2010

Offshore pipelines are usually buried to protect the pipe from external loads. When trenching is achieved by jetting or ploughing, some clayey soils can be cut into distinct lumps and this lumpy soil is then used as the backfill material under which the pipe is buried. To counter the effects of upheaval buckling, the resistance of the soil to pipe uplift must be known. There is still uncertainty about the performance of lumpy backfill in this regard. A series of centrifuge tests were performed with such soils as backfill, utilising a specially designed pore-pressure measuring pipe, to determine the influence of lump size, lump shape and pullout rate on uplift resistance Backfill comprising larger lumps consolidates quicker than if the backfill lumps are smaller. It is also observed that backfill comprising larger lumps provides greater resistance to pipe uplift after consolidation.
Fully Coupled Fluid-Structure Interaction for Offshore Applications
Authors: Jaiman Rajeev K. , Shakib Farzin , Oakley Owen H. , Constantinides Yiannis
Published: February 2010

CAD integrated tools are accelerating product development by incorporating various aspects of physics through coupling with computational aided engineering (CAE) packages. One of the most challenging areas is fluid-structure interaction (FSI) of low mass bodies such as flexible marine risers/cables with vortex-induced vibrations. The focus of this work is on the application of a new Multi-Iterative Coupling (MIC) procedure to couple AcuSolve (fluid solver) with Abaqus (structural solver). The proposed new scheme has superior stability and convergence properties as compared to conventional explicit staggered schemes, especially for low mass-density ratios of structure to fluid. Demonstrations and validation of the scheme are presented and discussed along with additional challenges associated with FSI in production environments. The addition of an FEA solver enables the modeling of the nonlinear aspects of flexible riser VIV, namely, contacts with gaps, multi-body dynamics, seabed interaction, geometric and/or material nonlinearities.
Influence of Multidirectional Irregular Wave Sampling to Second-Order Hydroelastic Responses of VLFS
Authors: Chen Xujun , Moan Torgeir , Tang Xuefeng
Published: February 2010

Hydroelasticity theory considering the second-order fluid forces induced by the coupling of first-order wave potentials is introduced briefly in this paper. Based on this theory, four types of multidirectional irregular wave samplings are introduced, the frequency steps Δω of the four samplings are 0.04, 0.04, 0.02 and 0.01 rad/s, and the corresponding numbers of wave components N are 17, 75, 147 and 285 respectively. The result of principal coordinates and displacements of a very large floating structure (VLFS) for the four types of sampling are presented and discussed. The influence of the sampling is analyzed. The conclusions show that the sampling of the multidirectional irregular waves influence the second-order hydroelastic response of the VLFS. The accuracy and the computer time of the calculating with sampling of frequency step Δω = 0.02 rad/s are acceptable.
Study on Snap Tension in Mooring Lines of Deepwater Platform
Authors: Zhang Su-xia , Tang You-gang , Liu Hai-xiao
Published: February 2010

Based on the theory of impact dynamics, the motion equations for a mooring line-floating body system after and before impact loading are established with consideration of the viscoelastic property of mooring lines. The factors that influence the taut-slack conditions of a mooring system are analyzed through classifying the taut-slack regions, which are defined by nondimensional ratios of displacement, frequency and damping of the system. The mooring lines of Jip spar platform is analyzed, and the snap tension characteristics of mooring lines are given, the factors that influence the maximum tension in mooring lines, including the mass of floating body, length of mooring lines, frequency and amplitude of external excitation, and pretension in mooring lines, are also analyzed through computing the dynamic response of system and parametric study. It is shown that the maximum tension increases with increase of the mass of floating body, external excitation and pretension and decreases with increase of the length of mooring lines, also, it is found that the influence of the nondimensional ratio of damping increases with increase of the pretension in mooring lines.
Efficient Non-Hydrostatic Modeling for Free Surface Waves in Deep and Shallow Water
Authors: Wu Chin H. , Young Chih-Chieh
Published: February 2010

A novel approach that introduces the Boussinesq-type like equations into an implicit non-hydrostatic model, free of irrotational flow assumption, is presented. The basic concept is to obtain an analytical-based form of pressure distribution at the top layer by matching the reference velocity under a virtual grid system with the one under a non-hydrostatic model grid system. Locations of the references velocities are tuned to optimize the linear wave dispersion property in the model. Efficiency of this non-hydrostatic model with Boussinesq-type equations (NHM-BTE) is critically examined through several free-surface wave examples. Overall model results show that NHM-BTE using only a few vertical layers (i.e., two ∼ four) is capable of accurately simulating highly dispersive wave motion and wave transformation over irregular bathymetry.
Jack-Up Installation on an Uneven Seabed: Recommendations From Model Testing in Overconsolidated Clay
Authors: Landon Melissa M. , Gaudin Christophe , Cassidy Mark J.
Published: February 2010

This paper presents results of a laboratory testing program employing a reduced-scaled model of a three-legged jack-up to investigate the influence of an adjacent footprint on spudcan installation. This study focused on the installation of the full jack-up with a single leg located adjacent to a surface discontinuity. This contrasts previous studies that focused on the behavior of a single leg model and aims to account for the coupled interaction of the three legs and hull. The investigation was conducted using a 1:200 model scale jack-up designed to represent an average commonly used field jack-up. It was fully instrumented for leg bending and axial force measurement, and allowed unconstrained horizontal motion and rotation in the plane of foundation-footprint offset. Installation was performed at foundation-footprint centerline offsets of 0.75, 0.89, and 1.0 times the footprint diameter in overconsolidated kaolin clay adjacent to three different footprint types. The three footprint types — spudcan generated, a similarly shaped vertical walled auger generated, and shallow slope — were used to analyze separately the effect of shape and soil disturbance.
Applications of Accurate VIV Response Reconstruction Schemes
Authors: Mukundan Harish , Hover Franz S. , Triantafyllou Michael S.
Published: February 2010

Quantifying vortex-induced vibration of long flexible slender structures exposed to ocean currents is critical to their design, analysis, installation and maintenance. These oscillations often driven at high frequencies for extended time may result in fatigue induced damage. Further, these primarily cross-flow oscillations results in an amplification of drag which may lead to possible riser interference issues especially when dealing with inline motions. Developments in instrumentation and installation of data acquisition systems on board marine risers have made accurate measurement of riser responses possible. On the other hand, recent developments in accurately reconstructing the VIV response of the riser using data from these acquisition systems have opened up entirely new array of methods to accurately interrogate, interpret and further improve VIV modeling of such structures. This paper presents with some depth the accurate reconstruction method developed by the authors and their use to identify new basic features of riser VIV. These include in-situ measurements of fatigue damage, identification of new phenomena and their quantification in empirical prediction codes by improving both the empirical models and empirical databases. Examples demonstrating each use of the reconstruction method are applied to data from a model-scale riser experiment.
Higher Order Boundary Element Method Applied to the Hydrofoil Beneath the Free Surface
Authors: Ghassemi Hassan , Kohansal Ahmad Reza , Ardeshir Abdollah
Published: February 2010

In this paper a three-dimensional numerical model using the higher order boundary element method (HOBEM) is developed to analyze hydrodynamic characteristics of hydrofoils beneath the free surface. The method uses combinations of the source and doublet by linear disctribution on each element of the body and free surface. The geometry of the element is represented by quadratic bilinear elements. The method is applied to three-dimensional hydrofoils of the symmetric Joukowski and NACA4412 profiles moving beneath the free surface in constant speed. Some results (pressure distribution, lift, wave-making drag and wave elevation and wave pattern) are presented. It is shown that this approach is accurate, efficient and the results are in good agreement with the experimental measurements and other calculated results.
Influence of the Reynolds Number on Spar Vortex Induced Motions (VIM): Multiple Scale Model Test Comparisons
Authors: Roddier Dominique , Finnigan Tim , Liapis Stergios
Published: February 2010

There have been a number of publications on spar Vortex-Induced-Motions (VIM) model testing procedures and results over the past few years. All tests allowing full 6 DOF response to date have been done under sub-critical Reynolds Number conditions. Prior to 2006 tests under super-Critical Reynolds Number conditions had only been done with a fully submerged 1 DOF rig. Early in 2006, a series of Spar VIM experiments was undertaken in three different facilities: Force Technology in Denmark, the David Taylor Model Basin in Bethesda Maryland and UC Berkeley in California. The motivation of this work was to investigate the effect of Reynolds Number and hull appurtenances on spar vortex induced motions (VIM) for a vertically moored 6DOF truss spar hull model with strakes. The three series of tests were done at both sub and super-critical Reynolds Numbers, with matching Froude Numbers. In order to assess the importance of appurtenances (chains, pipes and anodes) and current heading on strake effectiveness, tests were done with several sets of appurtenances, and at various headings and reduced velocities. These experiments were unique and groundbreaking in many ways: • For the first time the issue of scalability of Spar VIM experiments has been addressed and tested in a systematic way. • For the first time the effect of appurtenances (pipes, chains and anodes) was systematically tested. • The model tested at the David Taylor Model Basin (DTMB) had a diameter of 5.8′ and a weight of 15,600 lbs. It is the largest spar model ever tested. Furthermore the DTMB tests series is the only supercritical spar VIM performed with a six degree of freedom (6DOF) rig. This paper describes the three model tests campaigns, focusing on the efforts made to ensure three complete geo-similar programs, and on the significant findings of these tests, effectively that the influence of Re is to add some conservativeness in the results as the testing scale is smaller.
Hunting for Rogue Waves in a Three-Dimensional Nonlinear Wavefield: A Direct Simulation-Based Approach
Authors: Xiao Wenting , Liu Yuming , Yue Dick K. P.
Published: February 2010

We describe an investigation of the occurrence, statistics, and generation mechanisms of rogue wave in the open sea using direct three-dimensional phase-resolved nonlinear wavefield simulations. To achieve this we develop an efficient nonlinear wavefield simulation capability based on the high-order spectrum method which solves the primitive phase-resolved Euler equations. The simulations account for nonlinear wave-wave interactions up to an arbitrary high order in the wave steepness and are capable of accounting for effects of bottom bathymetry, variable current, and direct physics-based models for wind input and wave breaking dissipation. We apply direct large-scale simulations to obtain a large number of phase-resolved nonlinear wavefields, initially specified by directional wave spectra. The typical spatial-temporal domain size of such numerical nonlinear wavefields is O(103 km2) over evolution time of O(hr). These spatial and temporal scales account for quartet resonant interactions and partially for quintet resonant interactions among wave components in the wavefield. From the simulated nonlinear wavefields, rogue wave events are identified and their occurrence statistics are studied. It is shown that the classic linear theory (i.e. Rayleigh distribution) significantly underestimates the rogue wave occurrence. Second-order theory improves the Rayleigh prediction, but still underestimates the rogue wave occurrence in wavefields with moderately large wave steepness and relatively narrow directional spreading and spectrum bandwidth. The influence of key wave spectrum parameters (such as significant wave height, directional spreading, effective steepness, and spectrum bandwidth) on the rogue wave occurrence is analyzed. The classification of rogue waves according to their configuration is also obtained. The key characteristics of a rogue wave or rogue wave group in terms of kinematics and surface structure are analyzed and quantified. The nonlinear wave simulations, which provide full three-dimensional kinematics and dynamics of rogue wave events, provide a powerful tool for understanding the underlying mechanisms of their generation. They are elucidated by specific examples.
The Influence of Foundation Modeling Assumptions on Long-Term Load Prediction for Offshore Wind Turbines
Authors: Bush Erica , Manuel Lance
Published: February 2010

The objective of this study is to investigate the effect of alternative monopile foundation models for shallow-water offshore wind turbines on extreme loads associated with 20-year return periods. Foundation models with tower base fixed at the mudline, with apparent fixity points below the mudline, with coupled transverse and lateral springs at the mudline, and with distributed springs over the entire penetration depth of the monopile are compared. We employ a utility-scale 5 MW offshore wind turbine model with a 90-meter hub height in stochastic simulations; the turbine is sited in 20 meters of water. Selected 20-year wind speed and wave height combinations are employed as we study comparative response statistics, power spectra, and probability distributions of extreme loads for the fixed-base and the three different flexible foundation models. A discussion on the varying dynamics, on short-term response statistics, and on extrapolated long-term loads from limited simulation is presented. Sea states involving wind speeds close to the turbine’s rated wind speed are found to control 20-year loads, and the flexible foundation models are found to experience higher extreme loads than the fixed-based case. Overall, the three flexible foundation models appear to yield similar long-term loads based on an Inverse FORM (First-Order Reliability Method) approach for the selected turbine and soil profile used in this study.
Numerical Evaluation for Dynamic Response of Seabed Under Random Wave Loading
Authors: Wang Zhong-Tao , Luan Mao-Tian , Liu Shu-Jie
Published: February 2010

The analysis of dynamic response of seabed due to wave loading is of practical significance in design and construction of marine structures and offshore installations. Recently considerable efforts for this problem have been made with growing interest by many researchers and marine engineers, and many representative results have been achieved. It is obvious that wave loading plays a significant role in the evaluation of construction safety and seabed instability. But there are few results of research and engineering design that can consider the feature of wave loading and soil parameters together. The purpose of this paper is to establish a reasonable numerical model to simulate dynamic response of seabed under random wave loading. The dynamic relation between random wave and seabed can also be described through this model. Comparative studies are principally made between the proposed analysis considering actual feature of ocean situation and conventional analysis based on linear theory of regular wave. The effect of randomness of wave loading on the dynamic response of seabed is investigated. The necessity is also discussed about considering the influence of damping energy on propagating wave by porous seabed. In the conventional analyses of seabed dynamics, wave loading is basically treated as a deterministic process and is usually taken into consideration by using linear theory of regular wave. In fact, ocean wave is of intrinsic randomness in both time sequences and spatial distribution. The random nature of both wave and wave-induced loading will subsequently affect dynamic behavior of seabed. In this paper, the analyses which can consider characteristics of randomness of wave loading and dynamic interaction between seabed and random waves, are formulated in a stochastic framework. Integrated numerical analysis model is established by employing wave spectrum of AVERAGE JONSWAP. The comparative studies are conducted among the methods of conventional random analysis, proposed random analysis, and linear regular wave theory. The results show that the amplitudes of dynamic response of seabed subjected to random wave loading are larger than that of regular linear wave loading. Therefore the stochastic feature of wave loading has to be duly taken into account in the analysis for dynamic response of seabed.
Analytical Cubic Solution to Weakly Nonlinear Interactions Between Surface and Interfacial Waves
Authors: Tahvildari Navid , Jamali Mirmosadegh
Published: February 2010

Resonant interaction between one surface wave and two oblique interfacial waves is analyzed in a three dimensional system of a finite-depth, two-layer fluid. A third order perturbation analysis is carried out to obtain the evolution equations of the waves amplitudes. Taking the waves amplitudes as the perturbation small parameter, the evolution equations of the waves are solved simultaneously to obtain the short and long term behavior of the interfacial waves. In contrast to the second order analysis, the current analysis shows that after an initial exponential growth period, the interfacial waves stop growing and stabilize. Furthermore, the influences of surface wave frequency, density ratio and viscosity in the resonant interaction are investigated. Finally, the analytical results are compared with previous experimental observations.
Effect of Floaters’ Geometry on the Performance Characteristics of Tightly Moored Wave Energy Converters
Authors: Mavrakos Spyros A. , Katsaounis Georgios M. , Apostolidis Michalis S.
Published: February 2010

The paper deals with the investigation of the effect that floaters’ hydrodynamics has on the performance characteristics of tightly moored vertical axisymmetric wave energy converters. Several geometries of WEC’s floaters have been examined by assuming that they have constant displacement. Specifically, a cylindrical body with and without vertical and horizontal skirts at its bottom, a cone and a two–body, piston–like arrangement, which consists of an internal cone and an exterior torus, have been investigated and comparatively assessed. The WEC’s first-order hydrodynamic characteristics, i.e. their exciting wave forces and the correspondent hydrodynamic parameters, are evaluated using a linearized diffraction–radiation semi-analytical method. A dynamical model for evaluating of the floaters’ performance in time domain is developed that properly accounts for the floaters hydrodynamic behavior, the modeling of the hydraulic system and of the power take–off mechanism. The effect of the floaters geometry on the efficiency of the converter is analyzed through the results for the power absorption, under the excitation of several sea states.
Hydrodynamic Properties of a Suction Can Oscillating Near the Free Surface
Authors: Plummer C. , Macfarlane G. , Drobyshevski Y.
Published: February 2010

Offshore operations often require heavy subsea equipment, such as suction piles or cans, to be lowered by a support vessel into the sea. A lifting device must have adequate capacity to withstand the dynamic loads generated by the motions of the vessel and the heave response of the structure. The objective of this study is to determine the added mass and damping of a suction can oscillating in heave near the free surface; knowledge of these hydrodynamic properties is required for the accurate prediction of the dynamic lift forces during the deployment. This project is a logical progression following two similar studies, which investigated these hydrodynamic properties for the suction can in the mid-water position and when approaching the seabed. All three studies involved the conduct of model tests to determine the hydrodynamic properties. Free decay tests were conducted at several heave frequencies, and the added mass, linear and quadratic damping components were determined. In addition, the effect of varying the percentage of open hatch area has been investigated. Test data demonstrates that the heave added mass is strongly dependent on the frequency of motion, and its values are significantly smaller than those measured in the unrestricted flow. From observations, there was no dependency on the motion amplitude, nor did the size of open hatches have notable effect on the added mass. It was observed that when the top plate of the structure was in contact with the free surface a mean “pull down” force appeared. This force is caused by the suction underneath the top plate when the can moves upwards. As opposed to the mid-water position and near the sea floor, the study indicates that the area of open hatches has no noticeable effect on the heave damping when the suction can is oscillating near the free surface.
Underwater Target Recognition Using Time-Frequency Analysis and Elliptical Fuzzy Clustering Classifications
Authors: Ou Hui , Allen John S. , Syrmos Vassilis L.
Published: February 2010

A novel underwater target recognition approach has been developed based on the use of Wigner-type Time-Frequency (TF) analysis and the elliptical Gustafson-Kessel (GK) clustering algorithm. This method is implemented for the acoustic backscattered signals of the targets, and more precisely from the examination of echo formation mechanisms in the TF plane. For each of the training signals, we generate a clustering distribution which represents the signal’s TF characteristics by a small number of clusters. A feature template is created by combining the clustering distributions for the signals from the same training target. In the classification process, we calculate the clustering distribution of the test signal and compare it with the feature templates. The target is discriminated in terms of the best match of the clustering pattern. The advantages of GK clustering are that it allows elliptical-shaped clusters, and it automatically adjusts their shapes according to the distribution of the TF feature patterns. The recognition scheme has been applied to discriminate four spherical shell targets filled with different fluids. The data sets are the simulated acoustic responses from these targets, including the interferences caused by the seafloor interaction. [J. A. Fawcett, W. L. J. Fox, and A. Maguer, J. Acoust. Soc. Am. 104, 3296–3304 (1998)]. To evaluate the system robustness, white Gaussian noise is added to the acoustic responses. More than 95% of correct classification is obtained for high Signal-to-Noise Ratio (SNR), and it is maintained around 70% for very low SNRs.
An Integrated Risk Framework for Large Scale Deployments of Renewable Energy
Authors: Ram Bonnie
Published: February 2010

Assessing the potential environmental and human effects of deploying renewable energy along our coasts, on the Outer Continental Shelf, and in the Great Lakes requires a new risk paradigm. Evaluating potential risks requires a consistent program of research over time that collects relevant data by each sectoral area, such as bat and bird collisions, entanglement with mammals and fish, safety within shipping lanes, etc. Data collection alone, however, will not lead to better decisionmaking. Arriving at a broad and integrated risk profile of environmental and human effects is beyond a linear problem or a scientific decision. It becomes a political decision that must take into account the scientific evidence, comparison to other energy supply options, and stakeholder and public concerns. Risk assessment is not a new approach as it is applied throughout the federal government. The renewable energy area needs to develop and apply a risk assessment framework to support better decisions for deployment. The current approach evaluates potential impacts, sector by sector, or with a National Energy Policy Act (NEPA) document prepared by a federal agency or private developer. This site or project specific analyses are central to a better understanding of risk, but again it does not help the decisionmaker. The decisionmaker needs to better understand the broad spectrum of risk across all potential sites. Though the analyses may be incomplete, expert judgments can determine the level of significance and the research gaps. While renewable energy deployments are small today, marine renewable energy deployments are planned in the ocean over the next decade within North America and large deployment goals are expected in Europe. Now is the time to construct an integrated risk framework that evaluates the sectoral impacts, compares across these impacts, and then compares them to other energy supply options. A central lesson of a risk framework is that risks (sector effects) must be compared across potential effects to develop a transparent evaluation of temporal and spatial impacts of a site or a region. An evaluation of one sector separate from the others leads to skewed perceptions of significant risks. This integrated risk framework would also lead to effective siting strategies that would be based on mitigating the most important risks and employing cost-effective adaptive management practices wherever possible. While the nation moves forward in deploying renewable energy, lessons learned and new data will trigger new problems and new solutions to the potential impacts on the coastal landscape and within the marine environment. This integrated risk framework is presented graphically below to identify the specific analytical steps as well as how these activities will lead to better decisionmaking and smarter siting strategies (see Figure 1).
Wave Height Variation Across Surf Zone of Bar Type Profile
Authors: Hsu Tai-Wen , Lai Kun-Sian
Published: February 2010

Analytical solutions for wave height decay due to shoaling and breaking on a bar type profile are presented. A macroscopic analogy between an idealized surf zone and a hydraulic jump are incorporated in the theory to account for wave transformation and energy dissipation in the surf zone. The theoretical results are fairly compared with laboratory observations. Key parameters that influence wave energy dissipation in the surf zone are investigated.
Hydrodynamics of Multiple Floating Point-Absorber Wave Energy Systems With Inter-Body and Bottom Slack-Mooring Connections
Authors: Vicente Pedro C. , de O. Falca˜o Anto´nio F. , Gato Lui´s M. C. , Justino Paulo A. P.
Published: February 2010

Point absorbers constitute an important class of offshore wave energy converters. If employed in the extensive exploitation of the offshore wave energy resource, they should be deployed in arrays, the distance between elements in the array being possibly tens of meters. In such cases, it may be more convenient that the array is spread moored to the sea bottom through only some of its elements (possibly located in the periphery), while the other array elements are prevented from drifting and colliding with each other by connections to adjacent elements. This kind of mooring arrangement is addressed in the paper in a simplified way by considering an array of two buoys. Two opposed slack-mooring lines connect the floater pair to the bottom, while a third line, from whose mid-point hangs a weight, connects the two buoys pulling them towards each other. The centres of the buoys and the mooring lines are in a vertical plane parallel to the incoming wave direction, so that body and mooring motions are two-dimensional. The whole system — buoys, moorings and power take-off systems (PTOs) — is assumed linear, so that a frequency domain analysis may be employed. In the numerical simulations, two identical hemispherical buoys oscillate in heave and surge, acted upon by the waves, the mooring system and their PTOs. The PTO consists of a linear damper whose force is proportional to the heave velocity. Results from numerical simulations, with regular and irregular waves, are presented for the motions and power absorption of the converters, for different mooring and PTO parameters. Comparisons with the simpler cases of one single buoy in the moored and unmoored situations show significant differences.
Metabolic Regulation Through Acetylation
Authors: Ray L. Bryan
Published: February 2010

Acetylation of metabolic enzymes controls metabolic function in humans and bacteria.
Discovery and Characterization of Inhibitors of
Pseudomonas aeruginosa
Type III Secretion
Authors: Aiello Daniel , Williams John D. , Majgier-Baranowska Helena , Patel Ishan , Peet Norton P. , Huang Jin , Lory Stephen , Bowlin Terry L. , Moir Donald T.
Published: February 2010

The type III secretion system (T3SS) is a clinically important virulence mechanism in
Pseudomonas aeruginosa
that secretes and translocates up to four protein toxin effectors into human cells, facilitating the establishment and dissemination of infections. To discover inhibitors of this important virulence mechanism, we developed two cellular reporter assays and applied them to a library of 80,000 compounds. The primary screen was based on the dependence of the transcription of T3SS operons on the T3SS-mediated secretion of a negative regulator and consisted of a transcriptional fusion of the
Photorhabdus luminescens luxCDABE
operon to the
P. aeruginosa exoT
effector gene. Secondary assays included direct measurements of the T3SS-mediated secretion of a
P. aeruginosa
ExoS effector-β-lactamase fusion protein as well as the detection of the secretion of native ExoS by the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of culture supernatants. Five inhibitors in three chemical classes were demonstrated to inhibit type III secretion selectively with minimal cytotoxicity and with no effects on bacterial growth or on the type II-mediated secretion of elastase. These inhibitors also block the T3SS-mediated secretion of a YopE effector-β-lactamase fusion protein from an attenuated
Yersinia pestis
strain. The most promising of the inhibitors is a phenoxyacetamide that also blocks the T3SS-mediated translocation of effectors into mammalian cells in culture. Preliminary studies of structure-activity relationships in this phenoxyacetamide series demonstrated a strict requirement for the
R
-enantiomer at its stereocenter and indicated tolerance for a variety of substituents on one of its two aromatic rings.
Fluorescence Microscopy Demonstrates Enhanced Targeting of Telavancin to the Division Septum ofStaphylococcus aureus
Authors: Lunde Christopher S. , Rexer Charles H. , Hartouni Stephanie R. , Axt Sabine , Benton Bret M.
Published: February 2010

The cellular binding patterns of fluorescent conjugates of telavancin and vancomycin were evaluated inStaphylococcus aureusby fluorescence microscopy and ratio imaging analysis. Telavancin showed enhanced binding at the division septum compared to vancomycin. This result is consistent with observations that telavancin binds with higher affinity to lipid II than tod-Ala-d-Ala residues in the cell wall, thus demonstrating the preferential binding of telavancin to the site of active cell wall biosynthesis.
An Antimicrobial Peptide That Targets DNA Repair IntermediatesIn VitroInhibitsSalmonellaGrowth within Murine Macrophages
Authors: Su Leo Y. , Willner Dana L. , Segall Anca M.
Published: February 2010

The hexapeptide WRWYCR was previously identified on the basis of its ability to inhibit bacteriophage lambda integrase-mediated recombination by trapping and preventing resolution of the Holliday junction intermediate. This peptide inhibits several unrelated DNA repair enzymes that bind to and process Holliday junctions and branched DNA substrates. WRWYCR and itsdstereoisomer, wrwycr, are bactericidal against both Gram-positive and Gram-negative bacteria, causing the accumulation of DNA breaks, chromosome segregation defects, and the filamentation of cells. DNA repair is a novel target of antibiotics. In the present study, we examined the ability of the peptides to inhibit the growth ofSalmonellain mammalian cells. J774A.1 macrophage-like cells and murine peritoneal macrophages were infected withSalmonella entericaserovar Typhimurium and grown in the presence or absence of peptide. We found that peptide wrwycr reduced the number ofSalmonellacells recovered after 24 h growth in J774A.1 cells by 100 to 1,000 times, depending on the multiplicity of infection. The peptide also inhibitedSalmonellagrowth in peritoneal macrophages, and although higher doses were required, these were not toxic to the host cells. The apparent lower level of potency of the peptide paralleled the lower level of replication ofSalmonellaand the lower level of permeation of the peptide in the peritoneal macrophages than in the J774.1 cells. Treatment with peptide wrwycr elicited the SOS response in a significant fraction of the intracellular bacteria, as would be expected if the mechanism of bacterial killing was the same in pure culture and in host cells. These results represent a proof of principle of the antimicrobial activities of compounds that target DNA repair.
The Stress-Induced Virulence Protein InlH Controls Interleukin-6 Production during Murine Listeriosis
Authors: Personnic Nicolas , Bruck Serawit , Nahori Marie-Anne , Toledo-Arana Alejandro , Nikitas Giorgos , Lecuit Marc , Dussurget Olivier , Cossart Pascale , Bierne Hélène
Published: February 2010

The genome of the pathogenic bacteriumListeria monocytogenescontains a family of genes encoding proteins with a leucine-rich repeat domain. One of these genes,inlH, is a σB-dependent virulence gene of unknown function. Previously,inlHwas proposed to be coexpressed with two adjacent internalin genes,inlGandinlE. Using tiling arrays, we showed thatinlHexpression is monocistronic and specifically induced in stationary phase as well as in the intestinal lumen of mice, independent ofinlGandinlEexpression. Consistent withinlHσB-dependent regulation, surface expression of the InlH protein is induced when bacteria are subjected to thermal, acidic, osmotic, or oxidative stress. Disruption ofinlHincreases the amount of the invasion protein InlA without changinginlAtranscript level, suggesting that there is a link betweeninlHexpression andinlAposttranscriptional regulation. However, in contrast to InlA, InlH does not contribute to bacterial invasion of cultured cellsin vitroor of intestinal cellsin vivo. Strikingly, the reduced virulence ofinlH-deficientL. monocytogenesstrains is accompanied by enhanced production of interleukin-6 (IL-6) in infected tissues during the systemic phase of murine listeriosis but not by enhanced production of any other inflammatory cytokine tested. Since InlH does not modulate IL-6 secretion in macrophages at leastin vitro, it may play a role in other immune cells or contribute to a pathway that modulates survival or activation of IL-6-secreting cells. These results strongly suggest that InlH is a stress-induced surface protein that facilitates pathogen survival in tissues by tempering the inflammatory response.
Cross-Species Protection Mediated by aBordetella bronchisepticaStrain Lacking Antigenic Homologs Present in Acellular Pertussis Vaccines
Authors: Sukumar Neelima , Sloan Gina Parise , Conover Matt S. , Love Cheraton F. , Mattoo Seema , Kock Nancy D. , Deora Rajendar
Published: February 2010

TheBordetellaspecies are Gram-negative bacterial pathogens that are characterized by long-term colonization of the mammalian respiratory tract and are causative agents of respiratory diseases in humans and animals. Despite widespread and efficient vaccination, there has been a world-wide resurgence of pertussis, which remains the leading cause of vaccine-preventable death in developed countries. It has been proposed that current acellular vaccines (Pa) composed of only a few bacterial proteins may be less efficacious because of vaccine-induced antigenic shifts and adaptations. To gain insight into the development of a newer generation of vaccines, we constructed aBordetella bronchisepticastrain (LPaV) that does not express the antigenic homologs included in any of the Pa vaccines currently in use. This strain also lacks adenylate cyclase toxin, an essential virulence factor, and BipA, a surface protein. While LPaV colonized the mouse nose as efficiently as the wild-type strain, it was highly deficient in colonization of the lower respiratory tract and was attenuated in induction of inflammation and injury to the lungs. Strikingly, to our surprise, we found that in an intranasal murine challenge model, LPaV elicited cross-species protection against bothB. bronchisepticaandBordetella pertussis. Our data suggest the presence of immunogenic protective components other than those included in the pertussis vaccine. Combined with the whole-genome sequences of manyBordetellaspp. that are available, the results of this study should serve as a platform for strategic development of the next generation of acellular pertussis vaccines.
Phylogenomics Reveals a DiverseRickettsialesType IV Secretion System
Authors: Gillespie Joseph J. , Brayton Kelly A. , Williams Kelly P. , Quevedo Diaz Marco A. , Brown Wendy C. , Azad Abdu F. , Sobral Bruno W.
Published: February 2010

With an obligate intracellular lifestyle,Alphaproteobacteriaof the orderRickettsialeshave inextricably coevolved with their various eukaryotic hosts, resulting in small, reductive genomes and strict dependency on host resources. Unsurprisingly, large portions ofRickettsialesgenomes encode proteins involved in transport and secretion. One particular transporter that has garnered recent attention from researchers is the type IV secretion system (T4SS). Homologous to the well-studied archetypalvirT4SS ofAgrobacterium tumefaciens, theRickettsialesvirhomolog (rvh) T4SS is characterized primarily by duplication of several of its genes and scattered genomic distribution of all components in several conserved islets. Phylogeny estimation suggests a single event of ancestral acquirement of thervhT4SS, likely from a nonalphaproteobacterial origin. Bioinformatics analysis of over 30Rickettsialesgenome sequences illustrates a conserved corervhscaffold (lacking only avirB5homolog), with lineage-specific diversification of several components (rvhB1,rvhB2, andrvhB9b), likely a result of modifications to cell envelope structure. This coevolution of thervhT4SS and cell envelope morphology is probably driven by adaptations to various host cells, identifying the transporter as an important target for vaccine development. Despite the genetic intractability ofRickettsiales, recent advancements have been made in the characterization of several components of thervhT4SS, as well as its putative regulators and substrates. While current data favor a role in effector translocation, functions in DNA uptake and release and/or conjugation cannot at present be ruled out, especially considering that a mechanism for plasmid transfer inRickettsiaspp. has yet to be proposed.
Patterns of work-related traumatic hand injury among hospitalised workers in the People's Republic of China
Authors: Jin Kezhi , Lombardi David A , Courtney Theodore K , Sorock Gary S , Li Mingqiang , Pan Rong , Wang Xin , Lin Jie , Liang Youxin , Perry Melissa J
Published: February 2010

Objectives

This study describes the type, location and severity of work-related acute traumatic hand injuries of 560 workers treated in 11 hospitals in three economically active cities in the People's Republic of China (PRC) over a 2-year period.

Methods

A structured questionnaire was used to collect participant's information. Log-linear and logistic models were constructed to identify factors associated with injury occurrence and severity, respectively.

Results

Participants (n=560) had a mean age of 31.7 years (SD 10.5), 74.4% were men. 85.4% of participants were employed in manufacturing industries; 51.7% of 750 injuries were to the left hand. The index finger was injured most often and the most severe injury occurred to the right thumb. 68.3% of participants had only a single type of injury (29.7% crushes, 25.7% amputations and 18.5% fractures). Severe injuries occurred most often while working with food products (79.2% severe), furniture (72.2%), non-metallic mineral products (71.4%) and wood products (70.6%). Powered machines were involved in 59.5% of injuries. Injury frequency was associated with gender (male vs female, odds ratio (OR) 2.9, 95% CI 2.4 to 3.5) and company size (≤100 vs >100 employees, OR 2.5, 95% CI 2.1 to 3.1). Injury severity was associated with gender (male vs female OR 0.6, 95% CI 0.4 to 0.9) and powered machine use (OR 2.2, 95% CI 1.3 to 3.7).

Conclusions

The present study suggests that working in manufacturing industries and working with powered machines are the primary sources of severe hand injuries in hospitalised workers in economically active areas of the PRC.
Alcohol involvement among young female drivers in US fatal crashes: unfavourable trends
Authors: Tsai Virginia W , Anderson Craig L , Vaca Federico E
Published: February 2010

Objective

Young men have greater representation in fatal alcohol-related crashes. Recent studies of young women and risky behaviours have raised concerns about the implications this may have for alcohol-related fatal crashes. The objective of this study was to investigate the representation of young female drivers in US alcohol-involved fatal crashes (1995–2007) and to identify trends heralding future negative changes in crash profiles for young female drivers.

Design

Fatal crash data were obtained from the US National Highway Traffic Safety Administration Fatal Analysis Reporting System (FARS). Five age groups were analysed. The FARS multiple imputation dataset was used to estimate the proportion of drivers with blood alcohol, and variance estimates were corrected for the procedure. Linear regression was used to measure trends (1995–2007).

Results

179 891 fatal crashes in all age groups occurred over the study period. The rate of involvement in fatal crashes for young drivers with positive blood alcohol concentrations (BAC) decreased for men and women aged 16 years but increased for women age 19–24 years. Young female drivers had a greater increase than young men in the proportion of alcohol-involved fatal crashes (3.1%, 95% CI 1.9 to 4.3% vs 1.2%, 95% CI 0.2 to 2.1%, p=0.02). Most of the increase occurred in drivers with BAC ≥0.15 g/dl. Drivers with higher BAC had markedly lower safety restraint use. Over time restraint use increased in all BAC groups studied.

Conclusion

Alcohol-involved fatal crash rates in young female drivers aged 19–24 years have increased. However, male drivers continue to surpass women in the number of alcohol-involved fatal crashes. Restraint use decreases markedly with increasing BAC.
A review of operational research studies in forest fire management
Authors: Martell D. L.
Published: February 2010

This paper is a comprehensive review of operational research studies in forest fire management during the years 1961 through 1981. It includes a brief discussion of fire management decision making, summaries of and comments regarding the practical merits of the work that has been done, and suggestions concerning future efforts in this field.