bluuebunny/crossref_metadata_2025 huggingface dataset:
Shaking Table Test on the Improvement Dimension of Permeable Grouting Method for Liquefaction Countermeasure
Authors: Kobayashi Masakazu , Zen Kouki , Chen Guangqi , Kasama Kiyonobu , Hayashi Kentaro
Published: February 2010

In order to clarify an optimum improvement dimension for the permeable-grouting method as a liquefaction countermeasure, a series of shaking table tests have been conducted for improved model grounds with various improvement dimensions. To express the variety of improvement dimensions in field, the model ground was created by dividing it into two types of mesh elements, in which each mesh element was simplified as a liquefiable element (unimproved element) or non-liquefiable element (improved element) respectively. Improvement ratio defined by the volume ratio of improved elements in total elements was set for 0% or 50% and the width of mesh element was 50mm. The acceleration of shaking table was applied by step loading; 100, 200, 300 and 400gal with the sinusoidal wave form of 3Hz. In order to investigate the seismic behavior of the improved ground, pore water pressure transducers and acceleration meters were set in the model ground. The main conclusions obtained from this study are as follows; 1) Both of the ground settlement induced by liquefaction and the acceleration response during seismic loading are greatly affected by the generated excess pore water pressure depending on the improvement dimension. Therefore, the “liquefiable region” in which the excess pore water pressure ratio is more than 0.75 is newly defined to evaluate the effect of improvement dimension on the acceleration response of ground, excess pore water pressure and vertical settlement, 2) As improved element increases in the liquefiable region, both of the excess pore water pressure in liquefiable element and the acceleration response of ground surface decrease. Namely, the improvement ratio in the liquefiable region could be an important index to evaluate the effect of improvement, 3) From the experimental conditions in this paper, it is suggested that 300mm is the best vertical interval and 150mm is the worst one to reduce the ground settlement induced by liquefaction and the vibration of ground.
The Influence of Internal Pressure on Pipeline Natural Frequency
Authors: Massa Andre´ Luiz Lupinacci , Galgoul Nelson Szilard , Guevara Junior Nestor Oscar , Fernandes Antonio Carlos , Coelho Fa´bio Moreira , da Silva Neto Severino Fonseca
Published: February 2010

Galgoul et al. (2004) have written a previous paper in which they have pointed out the conservatism of the latest recommendations for pipeline freespan evaluations, associated to the way the axial force is considered in the determination of the pipeline natural frequency. First because it fails to consider the fact, that the axial force of a sagging pipe, subject to temperature expansion, is much smaller than that of a straight pipe. Second because the effective axial force caused by internal pressure should not be used to determine the pipeline natural frequency. Fyrileiv and Collberg (2005) also discussed this aspect. In order to back up their previous arguments the authors decided to perform some tests an axially restrained pipeline at both ends, which was pressurized in order to justify their claims that these pipelines are not only under tension (and not compression), but also that their natural frequencies increase instead of reducing, although they do bend out because of the pressure, reaching a point of instability. The authors understand the effective axial force concept and the enormous simplifications, which it brings to an otherwise cumbersome problem, but wish to emphasize that these advantages are not unlimited and that this is one of these restrictions. To back up the text results a finite element model has been produced, in which the internal pressure is taken into account as it actually is (and not as an axial force) to show that the pipe wall stresses can only be obtained correctly in this manner.
Study on Negative Skin Friction of Pile Groups Considering Coupled Effect of Surface Load and Soil Consolidation
Authors: Kong Gang-qiang , Yang Qing , Luan Mao-tian
Published: February 2010

The study was performed based on an analysis of model test results of 3×3 pile group and confirmed the reliability and accuracy of determining negative skin friction (NSF) using numerical modeling of fluid-soild interaction. A 3D numerical model with surface load and soil consolidation was established using FLAC3D, which focused on the mechanism of NSF and its influence factors such as friction of pile-soil interface, spacing of pile and time of consolidation. The results obtained under different cases in an engineering practice were finally compared with measured and empirical data, showing that it is necessary to consider surface load and soil consolidation when dealing with NSF. The results also indicated the analysis with surface load and soil consolidation could simulate the developing process of NSF and produce a more accurate outcome — closer to measured data. The NSF increases rapidly at beginning and then slowly down, finally stabilized at a constant as soil consolidation progresses. Due to pile group effects, the piles at the centre had a smaller downdrag and settlement than those at corner or at edges; pile group effects became more obvious when pile spacing decreased.
VIV Hydrodynamic Data Extraction From Field Data
Authors: Chasparis Filippos , Modarres-Sadeghi Yahya , Hover Franz S. , Triantafyllou Michael S. , Contantinides Yiannis , Mukundan Harish
Published: February 2010

In this paper we extend a methodology to extract a VIV hydrodynamic database from field data to accommodate partially straked cylinders. There are two databases, each consisting of the lift and added mass coefficients as functions of reduced velocity and amplitude of response; the first for the bare part of the riser, and the second for the straked part. The field data can be either in the form of acceleration, strain, or a combination of acceleration and strain time traces, together with the shape of the current profile. First, the program VIVA together with a nominal force database obtained from laboratory hydrodynamic experiments is used in order to get an initial prediction of the riser response under a particular flow profile. The nominal databases are then parameterized and altered in a systematic way until the new VIVA predicted response best matches the measured field response, thus resulting in an optimal database. Examples from the Norwegian Deepwater Program VIV experiments demonstrate the effectiveness of the methodology.
Numerical Simulation of Wake Effects in the Lee of a Farm of Wave Energy Converters
Authors: Beels Charlotte , Troch Peter , De Rouck Julien , Versluys Tom , De Backer Griet
Published: February 2010

The contribution of wave energy to the renewable energy supply is rising. To extract a considerable amount of wave power, Wave Energy Converters (WECs) are arranged in several rows or in a ‘farm’. WECs in a farm are interacting (e.g. The presence of other WECs influence the operational behaviour of a single WEC) and the overall power absorption is affected. In this paper wake effects in the lee of a single WEC and multiple WECs of the overtopping type, where the water volume of overtopped waves is first captured in a basin above mean sea level and then drains back to the sea through hydro turbines, are studied in a time-dependent mild-slope equation model. The wake behind a single WEC is investigated for uni- and multi-directional incident waves. The wake becomes wider for larger wave peak periods. An increasing directional spreading results in a faster wave regeneration and a shorter wake behind the WEC. The wake in the lee of multiple WECs is calculated for two different farm lay-outs, i.e. an aligned grid and a staggered grid, with varying lateral and longitudinal spacing. In general, the staggered grid results in the highest overall wave power absorption.
Design Guideline and Acceptance Criteria for the Sag Bend Compression of Steel Catenary Riser
Authors: Ye Wei , Zhang Michelle
Published: February 2010

Although steel catenary riser (SCR) is an efficient riser concept for the deepwater oil and gas production, SCR on a Semi-submersible is susceptible to compression at the sag bend region that may lead to over stress under extreme environmental conditions such as 100-year and 1000-year return hurricane in Gulf of Mexico (GOM). It is one of the challenges to SCR design. The paper covers a wide range of SCRs, ranging from 6 inch to 20 inch outer diameter and including production and export SCRs, under the 100-year and 1000-year return hurricane conditions in GOM. Both linear and nonlinear analysis is performed. The non-dimensional compression and stress/strain coefficients are proposed, and they reveal excellent correlations between them and the compression force and bending stress/strain despite of the different riser size and weight. These coefficients can be used to determine the level of compression and bending stress/strain before the detailed and lengthy calculations, which are very useful as design guidelines. The acceptance criteria for GOM 100-year and 1000-year return hurricanes are discussed. It is recommended that for the nonlinear strain-based design the collapsed-based strain acceptance criteria are not conservative. More stringent nonlinear strain-based criteria are recommended, such as fracture mechanics analysis and accumulated strain analysis to ensure the integrity of the SCR during its life span.
Characterization of the Solid-Fluid Transition of Fine-Grained Sediments
Authors: Boukpeti Nathalie , White David , Randolph Mark , Low Han Eng
Published: February 2010

Characterization of the strength of fine-grained sediments as they evolve from an intact seabed material to a remolded debris flow is essential to adequately model submarine landslides and their impact on pipelines and other seabed infrastructure. In the current literature, two distinct approaches for modelling this material behavior have been considered. In the soil mechanics approach, fine-grained soils are characterized by the undrained shear strength, su. The critical state framework proposes a relation between su and the water content, or void ratio of the soil. In addition, rate effects and strain softening effects are described by multiplying a reference value of su by a function of the shear strain rate or the accumulated shear strain respectively. In the fluid mechanics approach, slurries of fine-grained material are characterized by a yield strength and a viscosity parameter, which describes the change in shear stress with shear strain rate. Empirical relationships have been proposed, which relate the yield strength and the viscosity to the sediment concentration. This paper demonstrates that the two modelling approaches are essentially similar, with only some formal differences. It is proposed that the strength of fine-grained sediments can be modelled in a unified way over the solid and liquid ranges. To support this unified approach, an experimental campaign has been conducted to obtain strength measurements on various clays prepared at different water content. The testing program includes fall cone tests, vane shear tests, miniature penetrometers (T-bar and ball) and viscometer tests. Rate effects and remolding effects are investigated over a wide range of water contents spanning the domains of behavior that are usually defined separately as soil and fluid. The present paper focuses on analyzing the results of fall cone, vane shear and viscometer tests. Analysis of the results shows that the variation in shear strength over the solid and liquid ranges can be described by a unique function of water content — suitably normalized — for a given soil. Furthermore, the effect of strain rate and degree of remolding can be accounted for by multiplying the basic strength parameter by appropriate functions, which are independent of the current water content.
On the Transient and Progressive Flooding Stages of Damaged RO-RO Vessels
Authors: Khaddaj-Mallat Chadi , Rousset Jean-Marc , Ferrant Pierre
Published: February 2010

Roll-On/Roll-Off vessels appear to be sensitive to rapid capsizing due to abrupt ingress of water caused by maritime accidents. As a result of the damage creation, the flooded ship can experience intermediate stages which might be more devastating than the final condition, as the sudden loading could significantly alter the ship stability characteristics. Far from a probabilistic analysis, the present paper aims at contributing to enhance knowledge of the flooding physics by treating some relevant important topics. It sheds light on the transient and progressive flooding stages, focuses on relevant factors and suggests combinations between factors that strongly affect the flooding before the steady state is reached. Furthermore, the authors comment on some points which remain hard to take into consideration, whatever the adopted methodology is, and propose, where found necessary, recommendations for a more reliable assessment of the flooding process. This survey shows that the intermediate flooding phase, which assessment could be adequate in calm water condition, depend upon many factors whose interdependency and effects still require further investigation. May a novel assessment methodology lead us to a better understanding and facilitate, therefore, the framing of new damage stability regulations.
A Novel Vacuum-Insulated Dual-Wall Composite Pipe for Cold Environment Applications
Authors: Ruhl Mark , Juss Kulvinder , Mertiny Pierre
Published: February 2010

Transportation of multiphase flows in hydrocarbon mining and processing, such as in sub-sea flow lines, often requires the fluid to be heated to reduce viscosity and prevent solidification within the pipeline. However, conventional metallic pipelines used in this application are prone to external corrosion from the surrounding oceanic water and internal metal loss caused by corrosion and abrasive particles within the multiphase fluid. Fibre-reinforced polymeric composite pipes are an economical means for mitigating these shortcomings by providing increased corrosion and abrasion resistance. As such, the current paper examines the small-scale preliminary design of a novel vacuum-insulated dual-walled composite pipe as a means of overcoming the aforementioned limitations. The inner and outer walls are based on a recently developed intrinsically-bonded lined-composite pipe; the polymeric liner serves to: (1) prevent degradation of the vacuum created in the annulus between the internally-lined inner and externally-lined outer walls, and (2) help prevent abrasion/corrosion of the composite pipe. Furthermore, by utilizing filament-wound pipes, a health monitoring system can be readily incorporated into the composite structure via electrical or optical fibres. The aim of this article is to: (a) outline the pipe structure, and (b) describe the laboratory based manufacturing and testing protocols.
Decision Support for Offshore Operations in Remote Arctic Areas TOSC: An Optimization Toolbox Based on Bayesian Networks
Authors: Hu¨ffmeier Johannes , Forsman Bjo¨rn , Sandkvist Jim , Rafstedt Johan
Published: February 2010

SSPA Sweden AB has developed a decision support tool for Arctic offshore operations in close cooperation with the ship owner Transatlantic. With their icebreaking offshore supply vessels, Transatlantic has experience in both offshore operations and ice breaking for the Swedish Maritime Administration, which gives them a unique competence for Arctic offshore tasks. Founded on these experiences SSPA has created a toolbox based on Bayesian networks to provide the decision maker with the required competence to plan, dimension and organise offshore operations. The demands on the model given by Transatlantic for this tool were to include an accurate planning possibility, it should be handy and flexible, successively extendable, based scientifically and it should reflect the operators experience and even experience transfer. The developed tool is based on so called Bayesian Networks. With the help of the graphical directed arrows it is possible to describe complex links and relations between: - specific customer demands and service needs, - supply tasks, icebreaking management, anchor handling, towing, etc., - local external environmental conditions, ice, weather, - surrounding infrastructure, base harbours, transports, - external requirements, national rules, permissions, classification requirements, - possible abnormalities, undesired events, danger of accident, - emergency preparedness, redundant resources, - resources, vessels in use, land-based resources, helicopters, etc. By combining risk analysis methodology, statistics and expert judgements the tool belays and incorporates high safety, cost-benefit, well-reasoned strategies, alternative plans of action and purposive solutions.
Fatigue Performance of SMLS SCR Girth Welds: Comparison of Prefabrication-Type WPS
Authors: Darcis Philippe P. , Marines-Garcia Israel , Di Vito Luigi , Richard Gilles , Ruiz Eduardo A. , de Souza Marcos P. , Marques Elsa C. , Dell’Erba Diego N. , Armengol Mariano , Quintanilla Hector
Published: February 2010

The objective of the present research work is focused on evaluating the fatigue performance of different prefabrication welding procedures and determining the best compromise between manufacturing specifications, productivity and fatigue strength. Therefore, a large full scale fatigue campaign was launched at Tenaris to comply with this objective. SMLS SCR pipe (grade X65, outer diameter 10 3/4″, wall thickness 25.4 mm) was selected and manufactured according with the current most challenging offshore specifications and girth joints representative of prefabrication welding were manufactured in 1G position. Two different bevel geometries, two different welding techniques for the root pass and two different welding techniques for fill and cap passes were studied and compared. Finally, a post weld finishing technique has been implemented, aiming to improve the fatigue strength by removal of the weld root and cap reinforcements. Misalignment measurements, with stress concentration factor calculations, and post-tests fractographic investigations have been systematically performed on all the samples after testing. This activity was of paramount importance in determining the causes for fatigue initiation. The tests results demonstrated the important role played by the girth weld root internal geometry on the fatigue strength, the influence of the High-Low, the preferential fatigue initiation sites and the fatigue strength improvement by removal of weld reinforcements.
The Effectiveness of Dynamic Compaction Under Various Water Levels
Authors: Chen Jing-Wen , Chen Fu-Cheng
Published: February 2010

Dynamic compaction is currently regarded as one of the quick but cost-effective method for soil densification to resist the potential of soil liquefaction during earthquake. Most practices and studies reveal the depth of densification is mainly limited by the compaction energy without considering the effect of water table. In this experimental study, the impact performances under both presence and absence of water level without changing the compaction energy were presented. The Single-point Impact Test is developed to perform a series of tests on soils under different water levels and drained conditions. Meanwhile, an automatic cone penetrometer is also developed to evaluate the effectiveness. The boundary effect of soil container used in the test is also discussed. The impact-induced pore pressures and dissipation periods are measured and compared with a field measurement. The relationship between the effective dynamic stresses and corresponding cone resistances in soils is highlighted. The performance of dynamic impacts is evaluated by a term of improvement ratio.
Results From Real Sea Experiment of Ocean Nutrient Enhancer TAKUMI
Authors: Ouchi Kazuyuki
Published: February 2010

Upwelling and scattering Deep Ocean Water (DOW) into the euphotic surface layer has been proposed by many oceanographers as a “fishing ground of artificial upwelling”. So far, however, there are no successful means to make it, because of the following difficulties; the very huge amount of DOW upwelling, the dilution of DOW’s nutrient salts in the sea, enduring the rough sea condition on offshore, the strength of very long riser pipe for upwelling, etc. The MARINO-FORUM 21, sponsored by Japanese government fisheries agency, organized the research and development project of an ocean nutrient enhancer named TAKUMI and real sea experiment using it, since the year of 2000. New technology concept, featuring the density current generator for avoiding dilution of nutrient salts, the spar type submersible floating structure for withstanding against the rough sea condition, and the design and analysis of riser pipe for not only in case of the rough sea but also in case of the upending which is world first challenge of election of steel riser pipe with gravity fall in the sub-sea, was studied and introduced for the design of TAKUMI as a proper Ocean Nutrient Enhancer. TAKUMI that upwells DOW of 100,000m3/day from 200m depth and discharges it into the euphotic layer with Diesel engine was manufactured and set-up at the center of Sagami Bay in Japan, in May 2003. More than five years continuous operation in various sea conditions, which includes very rough sea in typhoon and rapid current, caused by direction change of Kuroshio Current was carried out. Also, the behavior of the nutrient water mass and the pattern of primary production around TAKUMI was investigated using the research vessel Tansei Maru. The results from the real sea experiment lead us to believe that the TAKUMI type artificial DOW upwelling system can be feasible to increase a primary production and make a fishing ground in case of large size system of more than 1,000,000m3/day.
Cooperative Control of a Team of AUVs Using Smoothed Particle Hydrodynamics With Restricted Communication
Authors: Huhn Stephen , Mohseni Kamran
Published: February 2010

In this paper, the problem of controlling a team of AUVs in an environment containing obstacles and under communication restrictions is addressed. The control methodology is decentralized and utilizes Smoothed Particle Hydrodynamics (SPH), which allows each agent to be modeled as a single fluid particle, with forces acting upon it. Studies are conducted concerning the effect of the interpolation kernel’s width to allow uniform distribution of the vehicles in the goal region. The ability to model an adverse region using the SPH methodology is also addressed. Simulations are included that demonstrate the effect that the kernel’s width has on the dynamics of the system, as well as the effect of modeling adverse particles in the domain.
Use of Cryogenic Buoyancy Systems for Controlled Removal of Heavy Objects From the Seabed
Authors: Nicholls-Lee Rachel F. , Turnock Stephen R. , Tan Mingyi , McDonald Paul C. , Shenoi R. Ajit
Published: February 2010

New methods for marine salvage and decommissioning of structures in the open sea are continually being sought in order to improve control and lower operational costs. This paper investigates the concept design of a lightweight cryogenic marine heavy lift buoyancy system. The objective is to be able to lift or lower large displacement objects under full remote control. The opening stages of the project work include the development of a system that will operate to a depth of 350m. As part of the design process for such an arrangement, numerical simulation of the complete system has been undertaken in order to develop mechanical, cryogenic and process control systems. The paper considers the overall design concept and associated system development issues. These are illustrated through use of the time accurate simulation of alternative design configurations that confirm their viability.
Numerical Investigation of the Flow Through and Around a Net Cage
Authors: Shim Kyujin , Klebert Pascal , Fredheim Arne
Published: February 2010

Structure and design of fish cages can be improved by the knowledge of the flow pattern around and inside the net cages. To address this problem, commercially available computational fluid dynamics (CFD) software is used to analyze this problem by calculating the drag and the flow velocity distribution around cylinders with different porosities. The results of these simulations are compared with the data from experiments which have been previously published. Aquaculture cages are very large structures that consist mainly of netting, which can be approximated by small cylinders connected at knots. But due to the large number of these cylinders (millions for a single salmon farming cage), it is computationally expensive to model the exact geometry. Bio fouling is another factor which is of particular interest as fouled nets (lower porosity) can significantly reduce flow of well-oxygenated water reaching the fish during normal rearing conditions. Therefore the numerical approach used to simulate the flow through and around the net cage is to consider it as a circular cylinder with a porous jump boundary. Drag coefficient and flow pattern are compared with available experimental data. Vertical cylinders are used for this study. Different porosities have been used for the simulations as for the experiments (0%, 75%, 82% and 90% open area) in order to simulate the impact of the fouling on the load of the net structures and the flushing of the cage. The results show that a porous jump with a pressure drop proportional to velocity squared has the best agreement with measured data.
Development and In-Sea Performance Testing of a Single Point Mooring Supported Contra-Rotating Tidal Turbine
Authors: Clarke Joe , Grant Andrew , Connor Gary , Johnstone Cameron
Published: February 2010

A 2nd generation, contra-rotating marine current turbine has been developed by the Energy Systems Research Unit at the University of Strathclyde. This system can be tuned to extract energy over a wide range of water depths by “flying” a neutrally-buoyant device from a flexible, tensioned mooring. After successful proof of concept turbine trials, the development programme has moved on to investigate the performance of a scaled prototype system comprising of a dual rotor, contra-rotating turbine directly coupled to a submersible contra-rotating generator; and held on station via a gravity based tensioned mooring system. The turbine/generator assembly was initially tested in a towing tank, before the entire system underwent sea trials initially at the Kyles of Bute in the River Clyde Estuary before being deployed in eth Sound of Islay of eth West Coast of Scotland. An investigation into turbine wake development (an area in which it is hoped that the contra-rotating turbine will have uniquely beneficial properties) has recently begun. Small single-rotor model turbines have been deployed in a flume. Trends observed so far are in accordance with those observed by other researchers.
Measurements in Circular Wave Tank With Active Generators
Authors: Martins Joao Alcino de Andrade
Published: February 2010

This paper discusses some aspects of the new technology in testing tank for Naval and Ocean Engineering developed at NAOE-Osaka University, Japan, based on the concept of active wavemakers all around the tank perimeter [1]. Past and present measurements shown that the wave field is homogeneous with some restrictions and can keep irregular wave more than 50 wave periods. The experimental results for platform model diffraction force are good and agree with theory and also with early tests [7]. The analyses of wave and platform model force measurements prove the new wave tank concept precision, usefulness and reliability.
Dynamic Control of Biologically Inspired Pulsatile Jet Propulsion Thrusters
Authors: Krieg Michael , Mohseni Kamran
Published: February 2010

Inspired by the propulsion techniques employed by squid and other cephalopod, a new type of thruster was designed which utilized pulsatile jet propulsion to generate controlling forces. The thrust production from this jet actuator was characterized in a static environment and seen to be well approximated by a simple fluid slug model. A linear transfer function model was derived to describe the transient dynamics of this thruster being employed in a virtual vehicle simulation; which was developed to test the thruster with unsteady driving signals. It was predicted that an impulsive type of thrust (as is found in our jet actuator) is ideal in a non-linear damping environment, since all of the acceleration is being added to the system while its at its lowest velocity and therefore lowest drag. Due to the extremely nonlinear nature of underwater vehicle environments we developed a scaling system to classify regimes of maneuvers and characterize their dynamics independently. Assuming a simple proportional derivative control algorithm, the vehicle closed loop frequency response was predicted using the transfer function model; which was linearized according to the maneuvering regime. Within the hybrid simulation environment, the closed loop frequency response was tested empirically and seen to be well approximated by the model.
Effects of Fluid Motions in Liquid Tanks on Vessel Motions Using a Simple Panel Method
Authors: Cao Yusong , Zhang Fuwei
Published: February 2010

This paper presents a simple and fast panel method to include the effect of liquid tanks of a vessel in the prediction of the natural frequencies of the vessel motions. The effects are expressed in terms of modifications to the added mass and stiffness matrices of the vessels with the liquids in the tanks assumed being rigid. An application example for a vessel with two internal liquid tanks is demonstrated.
Hydroelastic Response of Wind or Tidal Turbines
Authors: Young Yin L. , Motley Michael R. , Yeung Ronald W.
Published: February 2010

The objective of this work is to develop and validate a coupled boundary element method (BEM)-finite element method (FEM) for the transient hydroelastic analysis of wind or tidal turbines subject to spatially varying inflow. The focus is on tidal turbines, although the methodology is also applicable for the analysis and design of wind turbines. An overview of the formulation for both the fluid and solid domains, and the fluid-structure interaction algorithms, are presented. The model is validated by comparing the predicted thrust and power measurements, and cavitation patterns, with experimental measurements and observations for a 800 mm marine current turbine presented in [1]. Additional numerical results are shown for the same turbine, but scaled up to 20 m in diameter, operating in a tidal boundary layer flow. The results suggest that a special high-strength corrosion resistant material is needed to avoid excessive blade deflection, and to ensure structural integrity. The results also suggest that it is important to consider the dynamic characteristics of the tidal turbine as the natural frequencies of the blades when operating in water are significantly reduced, as compared to when operating in air. Finally, current design challenges for both wind and tidal turbines are discussed.
A Buoy-Based WEC Device to Provide Low Power to Sensors
Authors: Davis Edward P. , Ertekin R. Cengiz , Riggs H. Ronald
Published: February 2010

Remote ocean instrumentation and monitoring techniques often rely on floating buoys with a variety of sensors to acquire time series measurements such as ambient noise, acoustic tracking or communications. The operating lifetime of small remote buoys is limited by onboard battery power. Remote acoustic sensors with hydrophone arrays, onboard RF transmitters, GPS receivers and other support electronics can draw up to 100–200W of continuous power in operation, limiting battery life in many cases to 12 to 24 hours between recharge. Recharging is inconvenient, and often impractical to the point that many compact sonobuoys are designed to scuttle themselves after about a day. The associated cost, as well as the environmental impact of sending large amounts of battery and electronic hardware to the bottom of the ocean, is a strong driver for developing renewable ocean power sources for semi-permanent unattended buoy deployments. In support of this vision, a simple, low-cost buoy size platform capable of generating power by scavenging energy from ocean wave motion is developed and demonstrated. The phase 1 prototype is designed to deliver a minimum of 50W of average power from the wave motion characteristics. The motions and the resulting tension in the mooring line are calculated through a linear potential-based computer program. The heaving-body WEC (Wave Energy Converter) design and the modeling are discussed. The design data and the calculations are presented as part of proof of concept of the power generation mechanism and the buoy.
A Multi-Scale Approach to the Analysis of Ultra Deepwater Unbonded Flexible Risers
Authors: Bahtui Ali , Alfano Giulio , Bahai Hamid
Published: February 2010

The results of a detailed, non-linear finite-element analysis of a small-scale (i.e. 1.7m long) six-layer unbonded flexible riser, accounting for interlayer contact and frictional slip, are used to calibrate a novel, simplified constitutive model for a 3D, non-linear Euler-Bernoulli beam model suitable for large scale analyses (hundreds of meters in length where water depth is more than 1000m). The detailed finite element model contains all the layers, each modeled separately with contact interfaces between them. The finite element model includes the main features of the riser geometry with very little simplifying assumptions made. The detailed finite element model is formulated in the framework of a novel, multi-scale approach potentially suitable for ultra deepwater applications. A simple, three-dimensional Euler-Bernoulli beam element, suitable for large scale analyses, is developed based on a non-linear constitutive law for the beam cross-section relating bending curvatures to the conjugate stress resultants.
Environmental Effect on Fatigue Life of FPSO Hull Structures
Authors: Wang Xiaozhi , Kim Booki , Zhang Yanming , Liao Ping
Published: February 2010

Floating production, storage and offloading systems (FPSOs) have been widely used in the development of offshore oil and gas fields because of their many attractive features. These features include a large work area and storage capacity, mobility (if desired), relatively low construction cost and good stability. They are mostly ship shaped, either converted from existing tankers or purpose built. The hull structural scantling design for tankers may be applicable to FPSOs; however, FPSOs have their own unique characteristics. FPSOs are located at specific locations with a dynamic loading that is quite different from that arising from unrestricted ocean service conditions for tankers. It is also noted that the wave conditions in recent FPSO applications may be very complicated when operating in areas such as those offshore West Africa and offshore Brazil where both seas and swells exist and propagate in different directions. In this paper, the unique FPSO operational aspects, especially the load assessment due to on-site environments will be described. The methodology of handling complicated wave conditions in fatigue assessment will be addressed. Special considerations for converted FPSOs, which need to take into account their operational history as a trading tanker and low cycle fatigue due to FPSO operations, will also be introduced. Case studies will be presented and appropriate analysis methodology will be summarized. The methodology has also been adopted by ABS Guide, see ABS [1].
Two Degrees of Freedom Vortex-Induced Vibrations of a Rigid Circular Cylinder With Varying Natural Frequencies in the X and Y Directions
Authors: Sanchis Arnaud
Published: February 2010

VIV experiments in two degrees of freedom are performed with a new apparatus designed to achieve a very low mass ratio and structural damping (ζ = 0.01). We investigated the influence of the ratio between the natural frequencies in the horizontal (fx) and vertical (fy) directions on the system response. Experiments were conducted at fx/fy = 0.42, 0.87, 1.16, 1.36 and 1.44 with mx* = 2.87 and my* = 1.65. For fx/fy < 1, the amplitude and frequency response were found to be similar to the classical case where fx/fy = 1, except in the transition zone between the upper and lower branches. For fx/fy > 1 however, radical changes were observed in the system response in amplitude, frequency and phase θ between the horizontal and vertical displacements. The most obvious is the appearance of a local maximum of Ay* in the middle of the upper branch. Secondly, the nature of the transition between the upper and lower branches changes from intermittent switching to a hysteretic one. The shape of the figure-of-eights describing the cylinder trajectory is also affected so that the cylinder is moving upstream at the top of its trajectory instead of downstream, indicating a profound modification of the interaction between the two degrees of freedom. Lastly, the range of reduced velocities over which stable, two-degrees-of-freedom oscillations were recorded is greatly increased up to 3.8 < U* < 8.4.
Pharmacokinetics of Clindamycin in Pregnant Women in the Peripartum Period
Authors: Muller Anouk E. , Mouton Johan W. , Oostvogel Paul M. , Dörr P. Joep , Voskuyl Rob A. , DeJongh Joost , Steegers Eric A. P. , Danhof Meindert
Published: February 2010

The study presented here was performed to determine the pharmacokinetics of intravenously administered clindamycin in pregnant women. Seven pregnant women treated with clindamycin were recruited. Maternal blood and arterial and venous umbilical cord blood samples were obtained. Maternal clindamycin concentrations were analyzed by nonlinear mixed-effects modeling with the NONMEM program. The data were best described by a linear three-compartment model. The clearance and the volume of distribution at steady state were 10.0 liters/h and 6.32 × 103liters, respectively. Monte Carlo simulations were performed to determine the area under the concentration curve (AUC) for the free (unbound) drug (f) in maternal serum for 24 h divided by the MIC (fAUC0-24/MIC). At a MIC of 0.5 mg/liter, which is the EUCAST breakpoint, the attainment at the lower 95% confidence interval (CI) was 24.6 if the level of protein binding was 65%, and this value concurred well with the target value of 27. However, for higher degrees of protein binding, as has been described in the literature, the attainment was lower, down to 10.2 for a protein binding level of 85% (lower 95% CI). The concentrations in umbilical cord blood were lower than those in maternal blood. The concentration-time profiles in maternal serum indicate that the level of exposure to clindamycin may be too low in these patients. Together with the lower concentrations in umbilical cord blood, this finding suggests that the current dosing regimen may not be adequate to protect all neonates from group B streptococcal disease.
Compensation of Fitness Costs and Reversibility of Antibiotic Resistance Mutations
Authors: Schulz zur Wiesch Pia , Engelstädter Jan , Bonhoeffer Sebastian
Published: February 2010

Strains of bacterial pathogens that have acquired mutations conferring antibiotic resistance often have a lower growth rate and are less invasive or transmissible initially than their susceptible counterparts. However, fitness costs of resistance mutations can be ameliorated by secondary site mutations. These so-called compensatory mutations may restore fitness in the absence and/or presence of antimicrobials. We review literature data and show that the fitness gains in the absence and presence of antibiotic treatment need not be correlated. The aim of this study is to gain a better conceptual grasp of how compensatory mutations with different fitness gains affect evolutionary trajectories, in particular reversibility. To this end, we developed a theoretical model with which we consider both a resistance and a compensation locus. We propose an intuitively understandable parameterization for the fitness values of the four resulting genotypes (wild type, resistance mutation only, compensatory mutation only, and both mutations) in the absence and presence of treatment. The differential fitness gains, together with the turnover rate and the mutation rate, strongly affected the success of antibacterial treatment, reversibility, and long-term abundance of resistant strains. We therefore propose that experimental studies of compensatory mutations should include fitness measurements of all possible genotypes in both the absence and presence of an antibiotic.
CEM-101 Activity against Gram-Positive Organisms
Authors: Woosley Leah N. , Castanheira Mariana , Jones Ronald N.
Published: February 2010

The
in vitro
activity of CEM-101, a new fluoroketolide, was determined against Gram-positive organisms with various macrolide susceptibility profiles. Experiments for determination of the MICs and minimum bactericidal concentrations (MBCs), timed killing, single-step and multistep mutation rates, the erythromycin induction of resistance, postantibiotic effect (PAE), and drug interactions were performed for CEM-101; and the results were compared to those obtained with telithromycin, macrolides, and lincosamides. The MBCs of CEM-101 remained lower overall than those of telithromycin, and CEM-101 displayed a 2-fold greater potency than the ketolide. Timed-killing curve testing showed that CEM-101 had greater bactericidal activity than telithromycin (a ≥3-log
10
-CFU/ml decrease in the initial inoculum at 24 h) against the staphylococcal isolates tested. The propensity of CEM-101 to cause resistance was low, as determined from the rates of resistance determined in single-step mutational studies (<10
−8
or 10
−9
). In multipassaging studies, mutants of two strains (both of which were USA300 isolates) resistant to CEM-101 emerged. That number was comparable to the number resistant to clindamycin but less than the number resistant to telithromycin. Erythromycin induced CEM-101 resistance in
Staphylococcus aureus
and
Streptococcus pneumoniae
, similar to telithromycin; however, in seven of eight beta-hemolytic streptococci, CEM-101 resistance induction was not observed. CEM-101 showed a significant concentration- and exposure-dependent PAE against the strains tested, with the values ranging from 2.3 to 6.1 h for Gram-positive organisms (these times were longer than those for telithromycin). No antagonism was found in synergy analyses, with enhanced inhibition being most noted for combinations with CEM-101 and ceftriaxone, gentamicin, and trimethoprim-sulfamethoxazole. Overall, this new antimicrobial agent (CEM-101) showed good antimicrobial characteristics compared with those of the agents in its class and exhibited measured parameter values similar or superior to those of utilized comparators, indicating that CEM-101 warrants further clinical evaluation.
Effectiveness of speed enforcement through fixed speed cameras: a time series study
Authors: Novoa Ana M , Pérez Katherine , Santamariña-Rubio Elena , Marí-Dell'Olmo Marc , Tobías Aurelio
Published: February 2010

Objective

To assess the effectiveness of speed cameras in reducing the numbers of crashes and people injured on the arterial roads of Barcelona, and to assess their long-term effectiveness on the beltway.

Methods

Time series analyses were performed separately for the arterial roads and the beltway. The stretches of arterial roads encompassing 500 m before and after the location of a speed camera were considered the enforced stretches, the remaining stretches of arterial roads being considered the comparison group. The outcome measures were the numbers of crashes and of people injured. Quasi-Poisson regression models were fitted, controlling for time trend, seasonality and implementation of other road safety measures.

Results

Both on the enforced and non-enforced arterial road stretches, the risks of crashes and people injured were similar in the two periods. On the beltway, reductions of 30% (95% CI 38% to 20%) and 26% (95% CI 36% to 14%) were observed, respectively.

Conclusions

Speed cameras do not reduce the numbers of crashes or people injured on the arterial roads of Barcelona. However, they are effective in the short and in the long-term on the beltway. Speed enforcement through fixed speed cameras is thus effective in medium–high-speed roads, although effectiveness could not be generalised to roads with lower speed limits and traffic lights.
Measurement and simulation of dwarf mistletoe infection of second-growth western hemlock on southern Vancouver Island
Authors: Bloomberg W. J. , Smith R. B.
Published: February 2010

Infection of western hemlock (Tsugaheterophylla (Raf.) Sarg.) residual overstory and second-growth understory by hemlock dwarf mistletoe (Arceuthobiumtsugense (Rosendahl) G.N. Jones) was analyzed in seven plots on southern Vancouver Island. The number of infections in residual trees ranged from 373 to 4058 and in second-growth trees from 3 to 455. The number in second-growth trees was significantly correlated positively with dbh and tree height and inversely with height/dbh ratio. The percentage of crown length infected varied significantly among plots and was significantly correlated with the number of infections. Vertical distribution of infections in tree crowns did not conform to test distributions; distribution by infection age approximated the Poisson. The range in infection age varied according to height in green crown and length of green crown infected. Mortality of infections varied significantly among plots and was greatest in lower slope sites and least in a drier upper slope site. Proportion of dead infections was a function of height in crown and total length of green crown infected. Data suggest that infection level in second-growth trees was proportional to the number of residuals and was inversely related to percent nonhost species, stand density, and growth rate. The number of infections predicted by a simulation model averaged 107% of the number recorded in residual trees and 128% in second-growth trees. Curves of predicted vertical distribution of infections in crowns were of the same shape as those recorded in plot sample trees. The predicted average age-class distribution of infections approximated Poisson distribution within the same probability range as recorded in plot sample trees. The predicted average dbh of residual and second-growth trees were 90 and 97%, respectively, of the recorded values; predicted average heights were 115 and 101%, respectively, of recorded values. Infection predicted by the model over a range of hypothetical stand, site, and infection conditions was used to elucidate major epidemiological factors that might bear on silvieultural control. Results confirmed the observed effects of number of residuals, stand composition, growth rate, and stand density on infections.
A heuristic weight determination procedure for goal programs used for harvest scheduling models
Authors: Hotvedt James E. , Leuschner William A. , Buhyoff Gregory J.
Published: February 2010

A heuristic, "unstructured" weight determination procedure was developed for harvest scheduling models in which goal programming algorithms are employed. Six noninferior solution sets that included four goals, total volume harvested, total discounted cash flow, total undiscounted cash flow, and total discounted costs, were generated using a complementary linear and goal programming approach. Representatives from a pulp and paper company (The Company) located in the southeastern United States ranked the solution sets from most to least preferred and provided a statement of why they ranked the sets the way they did. Additional noninferior solutions were generated to improve the achievement levels of the initial preferred solution. The procedure contributes to improved forest management decisions by providing the optimal harvest scheduling plan under each of the four goals individually and by providing goal achievement level trade offs under different weight structures. The procedure was well received and instructive to The Company representatives since it was easy to understand and required minimal analytic expertise and time on the part of the decision makers.