bluuebunny/crossref_metadata_2025 huggingface dataset:
Decay of Vibrations Along Deepwater Mooring Lines
Authors: Argyros Alex , Langley Robin S. , Ahilan R. V.
Published: November 2011

Model tests for global design verification of deepwater floating structures cannot be made at reasonable scales. An overview of recent research efforts to tackle this challenge is given first, introducing the concept of line truncation techniques. In such a method the upper sections of each line are modelled in detail, capturing the wave action zone and all coupling effects with the vessel. These terminate to an approximate analytical model, that aims to simulate the remainder of the line. The rationale for this is that in deep water the transverse elastic waves of a line are likely to decay before they are reflected at the seabed. The focus of this paper is the verification of this rationale and the ongoing work, which is considering ways to produce a truncation model. Transverse dynamics of a mooring line are modelled using the equations of motion of an inextensible taut string, submerged in still water, one end fixed at the bottom the other assumed to follow the vessel response, which can be harmonic or random. Nonlinear hydrodynamic damping is included; bending and VIV effects are neglected. A dimensional analysis, supported by exact benchmark numerical solutions, has shown that it is possible to produce a universal curve for the decay of transverse vibrations along the line, which is suitable for any kind of line with any top motion. This has a significant engineering benefit, allowing for a rapid assessment of line dynamics — it is very useful in deciding whether a truncated line model is appropriate, and if so, at which point truncation might be applied. Initial efforts in developing a truncated model show that a linearized numerical solution in the frequency domain matches very closely the exact benchmark.
Fatigue Analysis of a Steel Catenary Riser With Uncertain Seabed Parameters
Authors: Li Feng Zi , Low Ying Min
Published: November 2011

Steel Catenary Risers (SCRs) are commonly employed in deepwater oilfields. The most problematic aspect of fatigue analysis is the touchdown point, in which the dynamic bending stresses are highest and the uncertainties are most pronounced. From a previous study conducted by the authors, it is found that the fatigue damage is extremely sensitive to several seabed parameters. Thus the uncertainties in the seabed parameters should be properly accounted in order to achieve a reliable and economical SCR design. In this work, reliability analysis is performed with three seabed random variables, namely soil stiffness, soil suction, and seabed trench. The efficient First Order Reliability Method (FORM) is employed in conjunction with the Response Surface Method to yield the probability of fatigue failure. The results are then compared with direct numerical integration. Further, the dependency between the different random variables is investigated.
A Bivariate Extreme Value Distribution for Reliability Assessment of Marine Structures
Authors: Leira Bernt J. , Myrhaug Dag , Holm Ha˚vard
Published: November 2011

A bivariate Gumbel distribution is established based on transformation of an existing bivariate Rayleigh distribution. Application of this distribution in relation to reliability assessment of marine structures is subsequently addressed. Linear combinations of the two basic variables which are Gumbel distributed are further considered. The role of the Gumbel distribution in connection with reliability assessment of marine structures is discussed. Comparison with another class of bivariate Gumbel distributions (Gumbel Type A) is also made.
An Experimental Study of Shallow Water Wave Statistics on Mild Bed Slopes
Authors: Katsardi Vasiliki , Swan Chris
Published: November 2011

This paper describes a new series of laboratory observations, undertaken in a purpose built wave flume, in which a number of scaled simulations of realistic ocean spectra were allowed to evolve over a range of mild bed slopes. The purpose of the study was to examine the distribution of wave heights and its dependence on the local water depth, d, the local bed slope, m, and the nature of the input spectrum; the latter considering variations in the spectral peak period, Tp, the spectral bandwidth and the wave steepness. The results of the study show that for mild bed slopes the statistical distributions of wave heights are effectively independent of both the bed slope and the spectral bandwidth. However, the peak period plays a very significant role in the sense that it alters the effective water depth. Following detailed comparisons with the measured data, the statistical distributions for wave heights in relatively deep water are found to be in reasonable agreement with the Forristall [1] and Glukhovskii [2] distributions. For intermediate water depths, the Battjes & Groenendijk [3] distribution works very well. However, for the shallowest water depths none of the existing distributions provides good agreement with the measured data; all leading to an over-estimate of the largest wave heights.
Importance of Added Mass for the Interaction Between IL and CF Vibrations of Free Spanning Pipelines
Authors: Aglen Ida M. , Larsen Carl M.
Published: November 2011

The importance of cross-flow (CF) response generated by vortex induced vibrations (VIV) of free spanning pipelines has long been recognised. The significance of in-line (IL) vibrations has recently been understood and hence also been subjected to research. The combined effect of CF and IL vibrations is, however, still not fully described. This paper highlights the CF-IL interaction with focus on the transition zone from pure IL to CF dominated response, giving special attention to how the added mass influences the interaction. Results from extensive flexible beam tests connected to the Ormen Lange (OL) development have been used as a basis for this study. Trajectories for cross sectional motions from the flexible beam test were identified, and then used as forced motions of a large diameter rigid cylinder exposed to uniform flow. Non-dimensional parameters like Reynolds number (Re), amplitude ratio and reduced frequency were identical for the two tests. Hence, forces found from the forced motion test could be used to find hydrodynamic coefficients valid for the flexible beam case. This paper discusses the results from the flexible beam tests with a relatively short length to diameter ratio (L/D) of 145. Modal analyses by Nielsen et al. (2002) show that the first mode dominates in both directions for these particular tests, even though the IL response frequency is twice the CF frequency. In this paper the added mass variations along the OL flexible beam is studied. Forces acting on 4 different cross sections along the beam are measured for 7 different prototype velocities. For each test the hydrodynamic coefficients are calculated, and the results show how the added mass changes along the beam for increasing velocities, and thereby creates resonance for both IL and CF response. The stability of the added mass coefficient throughout the time series is also evaluated.
Evaluation of Alternatives for Offshore Petroleum Production System in Deep and Ultradeep Water Depth
Authors: Morooka Celso K. , de Carvalho Maria Deolinda B. M.
Published: November 2011

Different equipments combined compose an offshore petroleum production system. Several development alternatives are available for a given offshore petroleum field. The selection of the most suitable system for a given scenario depends on field development characteristics and strategies such as its geographical location, water depth, environmental conditions and knowledge about similar systems already selected and in use for oil and gas production and available infrastructure in around. For the purpose of field production system design a database with types of production platforms, mooring systems, subsea equipments, reservoir main characteristics, type of wells and lifting processes is fundamental. Today, offshore petroleum reservoir production is more and more complex due to several variables involved and requirement needed to meet deep and ultra deep water depth, pre-salt petroleum with aggressive fluid characteristics, fields in remote areas and other environmental issues. Large fields in deep and ultra deep water are particularly challenging due to little availability of suitable platform types, among known concepts such as floating, production, storage and offloading unit (FPSO), semisubmersible, spar and tension leg platform (TLP). In the present paper, a database for worldwide offshore petroleum systems in use has been elaborated by searching data available in the literature. The database is organized for more than three hundred platforms distributed on more than four hundred different offshore oil fields. To serve as a basis for the conceptual design of a field production system, this database contains information such as type of the platform, field location, water depth, days for the first production, type of well, completion, mooring system, riser and offloading system. This information is structured for different water depth and environmental condition, for each field. From this database, analysis has been conducted for distribution of each type of platform by worldwide region, distribution of each type of platform by the offshore field by region, among others analysis. Concept of Utility Functions are applied to represent technological trends and to be helpful in the process. Among the results, a preference for FPSOs and semisubmersible was observed in Brazil offshore, semisubmersible, TLPs and Spars in Gulf of Mexico. In Europe, particularly the North Sea, FPSO, semisubmersible, and few TLPs have been found. In West Africa, most of the field production is based on FPSOs, although some semisubmersible and TLP could be observed. Similar analyses were conducted in other regions. Results and discussions show preferences regarding technology selected by each region, region historical data, and growth of water depth in different fields.
Hydrogen Induced Mechanical Property Behavior of Dissimilar Weld Metal Interfaces
Authors: Fenske Jamey A. , Hukle Martin W. , Newbury Brian D. , Gordon J. R. , Noecker Rick , Robertson Ian M.
Published: November 2011

A series of catastrophic failures between alloy 625 weld metal (referred to as ‘A625’) and AISI 8630 low alloy steel forgings (referred to as ‘8630’) on cathodically-charged subsea equipment demonstrate the need to gain a better understanding of the hydrogen-induced tearing resistance of these interfaces as well as similar types of interfaces also currently used in the field. Other dissimilar metal weld interfaces in use include ASTM A182 F22 (referred to as ‘F22’) welded with A625. Similar metal alternatives are also in use, including F22 welded with low alloy steel (referred to as ‘LAS’). Slow strain rate single-edge notched bend tests under hydrogen charging conditions were used to establish ‘R-curve’ crack growth resistance trends for the F22-A625 and F22-LAS weld metal interfaces. Differences in ‘R-curve’ crack growth behavior between the different weld metal interfaces have been observed and compared to R-curve results from 8630-A625 interfaces. The F22-LAS interface demonstrates the most tearing resistance under slow strain rate after hydrogen charging followed by the F22-A625 and then the 8630-A625 interface. Subtle differences between the weld metal microstructures are described and provide a possible explanation regarding the difference in ‘R-curve’ behavior.
Experience From Norwegian Programme on Ageing and Life Extension
Authors: Ersdal Gerhard , Ho¨rnlund Erik , Spilde Hans
Published: November 2011

In 2005, the Petroleum Safety Authority Norway (PSA), gave special priority to a programme of ageing and life extension. The programme comprised technical investigations into how ageing will reduce the safety of the facilities and how this can be managed, plus cooperation with the petroleum industry to develop standards and guidelines for assessment of ageing facilities for life extension. In addition, audits have looked into the way operators are dealing with the implications of ageing facilities. This paper summarizes the outcome of the programme and the experience gained from it.
Probabilistic Model Application in the Integrated Stability Analysis of Offshore On-Bottom Pipeline
Authors: Youssef Bassem S. , Cassidy Mark J. , Tian Yinghui
Published: November 2011

Offshore pipelines provide the main link between offshore oil and gas fields and hydrocarbon development onshore. Due to their economical installation, untrenched pipelines laid “on-bottom” are finding increased popularity over other types of offshore pipelines. However, the stability of untrenched pipeline design remains the subject of criticism. In many cases around the world, severe loading conditions, such as those during hurricanes, result in severe pipeline damage and disruption of oil and gas supply. In on-bottom pipeline stability analysis, hydrodynamic loads are applied to the pipe structure. The pipe passes these loads onto the supporting soil along its length. A variety of parameters need to be defined to model this loading scenario and to reflect the complicated interaction between the hydrodynamic load, pipe structure and the supporting soil. Moreover, there are uncertainties regarding the input values of these parameters, as any difference in these parameter values will result in a considerable difference in the final pipeline stability result (though the sensitivity to any differences is not well studied). In this study of the offshore pipeline stability, the hydrodynamic loads are estimated using Fourier analysis, which is currently the best practice in hydrodynamic modeling. The pipe-soil interaction is simulated with a force-resultant model, which is derived from a plasticity framework and is based on the results of centrifuge test calibration. The pipeline is modeled using an integrated numerical modeling tool developed by implementing the hydrodynamic load model and force-resultant model codes in the finite element package ABAQUS. Use of the integrated modeling tool allows for the coupling effect of the hydrodynamic-pipe-soil interaction to be accounted for, with the added ability to modify the applied hydrodynamic loads due to pipe movements during the analysis. The main aims of this paper are to demonstrate methods to estimate the probability of exceeding pipeline stability and quantify the importance of the on-bottom pipeline statistical analysis and the sensitivity of the parameters included in the pipeline stability design. After first describing the integrated model and providing an illustrative example of its use these aims are achieved by i) performing probabilistic analysis for a typical pipeline case and investigating the probability of exceeding pipeline stability under different maximum pipeline displacement values; and ii) developing a sensitivity analysis of the input parameters included in the on-bottom pipeline stability and ranking these parameters according to their sensitivity to the pipeline stability design.
Jack-Up Site Assessment: The Voyage to an ISO
Authors: Hoyle Mike J. R. , Stiff John J. , Hunt Rupert J.
Published: November 2011

As a mobile offshore unit, a jack-up can float, self-elevate and then impose proofing loads on the seabed to establish a safe working envelope for subsequent drilling or construction activities. Jack-up site assessment has seen significant advances over the 50 or more years that jack-ups have been deployed offshore. The advances have occurred as a result of both the improvements that have been seen in the analytical tools and also as a result of the many significant strides in our understanding of the physics of the jack-up and the ocean environment. Jack-ups, due to their semi-compliant nature, pose particularly difficult challenges to the designer and operator — more so than most offshore structures. This requires cutting edge technologies to assure that practical solutions can be reached without either too much conservatism or too little safety. These advances have often occurred, or been encouraged, as a result of the engagement of the operators hiring the jack-ups and their technical overseers such as Jan Vugts. Jan was instrumental in initiating the Shell study into jack-up site assessment that resulted in a follow-up JIP which developed the SNAME Recommend Practice. Since then ISO 19905-1 has been under development and Jan has provided both encouragement and also very detailed review comments. This paper charts the voyage from the early days of jack-up site assessment through to the development of the ISO and highlights some of the key technical developments.
Unresolved Enigmas From Shallow Water Model Tests
Authors: Naciri Mamoun , van Dijk Radboud , Waals Olaf
Published: November 2011

Model tests are widely thought as a reliable means of obtaining answers to questions beyond the realm of state-of-the art simulation tools. The author’s experience, no doubt shared with others, has been that whilst providing many answers model tests sometimes raise new questions and unveil phenomena not anticipated at the start. Sometimes these phenomena are investigated in detail and documented (ref [1]), but more often the pressure of project execution prevents enough time to be spent in understanding these phenomena if they are thought to be of secondary importance. This paper will address two such instances of un-resolved and un-explained experimental results. The first instance is drawn from a 2004 model test campaign where an LNG carrier was kept on station by a horizontal mooring in 30m water depth. Un-explained 1st order motion responses were obtained in bow-quartering waves. The second instance is drawn from model tests performed in the context of the HAWAI-JIP in 2006. Un-explained low-frequency sway motions of an LNG carrier were observed during a surge decay tests in shallow water waves. The paper will describe these findings and propose rational explanations.
URANS Simulation of an Appended Hull During Steady Turn With Propeller Represented by an Actuator Disk Model
Authors: Dai Charles M. , Miller Ronald W.
Published: November 2011

This paper reports on the comparison between computational simulations and experimental measurements of a surface vessel in steady turning conditions. The primary purpose of these efforts is to support the development of physics-based high fidelity maneuvering simulation tools by providing accurate and reliable hydrodynamic data with relevance to maneuvering performances. Reynolds Averaged Unsteady Navier Stokes Solver (URANS): CFDSHIPIOWA was used to perform simulations for validation purposes and for better understanding of the fundamental flow physics of a hull under maneuvering conditions. The Propeller effects were simulated using the actuator disk model included in CFDShip-Iowa. The actuator disk model prescribes a circumferential averaged body force with axial and tangential components. No propeller generated side forces are accounted for in the model. This paper examines the effects of actuator disk model on the overall fidelity of a RANS based ship maneuvering simulations. Both experiments and simulations provide physical insights into the complex flow interactions between the hull and various appendages, the rudders and the propellers. The experimental effort consists of flow field measurements using Stereo Particle-Image Velocimetry (SPIV) in the stern region of the model and force and moment measurements on the whole ship and on ship components such as the bilge keels, the rudders, and the propellers. Comparisons between simulations and experimental measurements were made for velocity distributions at different transverse planes along the ship axis and different forces components for hull, appendages and rudders. The actuator disk model does not predict any propeller generated side forces in the code and they need to be taken into account when comparing hull and appendages generated side forces in the simulations. The simulations were compared with experimental results and they both demonstrate the cross flow effect on the transverse forces and the propeller slip streams generated by the propellers during steady turning conditions. The hull forces (include hull, bilge keels, skeg, shafting and strut) predictions were better for large turning circle case as compared with smaller turning circle. Despite flow field simulations appear to capture gross flow features qualitatively; detailed examinations of flow distributions reveal discrepancies in predictions of propeller wake locations and secondary flow structures. The qualitative comparisons for the rudders forces also reveal large discrepancies and it was shown that the primary cause of discrepancies is due to poor predictions of velocity inflow at the rudder plane.
Stability of Temporary Submarine Slopes
Authors: Bubel Julian , Rudolph Christina , Grabe Ju¨rgen
Published: November 2011

Shallow foundation structures for offshore wind turbines offer ecological benefits compared to pile foundations as less noise is emitted at sea floor level during construction process. On the other hand, shallow offshore foundations can rarely be placed on top of the sea floor. Weak soils usually need to be excavated to place the foundation structure on more stable ground and thus, anthropogenic submarine slopes result. Steep but stable slopes meet both economic and ecologic aims as they minimise material movement and sediment disturbance. After Terzaghi [1] the angle β between slope and the horizontal of the ground surface of coarse-grained soil is at most equal to the critical state friction angle φc. However, it can be observed that natural submarine slopes of sandy soils are always much more shallow. Particularly fine-grained, cohesionless or almost cohesionless soils failed in the past, although the slope angle was much smaller than the critical state friction angle φc. Artificial (temporary) slopes do not appear and behave as natural submarine slopes, since the latter are already shaped by perpetual loads of waves, tide and mass movements. Physical simulations of different scales are used to analyse the stability of artificial submarine slopes with sandy soil of the North Sea. The study focuses on gravitational forces and impacts from the excavation processes. The simulations and theoretical considerations result in suggested slope angles for future shallow offshore foundations of wind farms in the North Sea.
The Global Secant Relaxation-Based Accelerated Iteration Procedure for Solution of Nonlinear Finite Element Equation Systems of Offshore Structural Mechanics Problems
Authors: Chen Chang-New
Published: November 2011

A global secant relaxation (GSR)-based accelerated iteration scheme can be used to carry out the incremental/iterative solution of various nonlinear finite element systems of offshore structural mechanics problems. This computation procedure can overcome the possible deficiency of numerical instability caused by local failure existing in the iterative computation. Moreover, this method can efficiently accelerate the convergency of the iterative computation. This incremental/iterative analysis can consistently be carried out to update the response history up to a near ultimate load stage, which is important for investigating the global failure behaviour of a structure under certain external cause, if the constant stiffness is used. Consequently, this method can widely be used to solve general nonlinear problems. Mathematical procedures of Newton-Raphson techniques in finite element methods for nonlinear finite element problems are summarized. These techniques are the Newton-Raphson method, quasi-Newton methods, modified Newton-Raphson methods and accelerated modified Newton-Raphson methods. Numerical results obtained by using various accelerated modified Newton-Raphson methods are used to study the convergency performances of these techniques for material nonlinearity problems and deformation nonlinearity problems, separately.
Application of Formal Safety Assessment to Navigational Risk Evaluation of Yangtze River
Authors: Zhang Di , Yan Xinping , Yang Zaili , Wang Jin
Published: November 2011

Formal safety assessment (FSA), as a structured and systematic risk evaluation methodology, has been gradually and broadly used in the shipping industry nowadays around the world. Concerns have been raised to navigational safety of Yangtze River, known as China’s largest and the world busiest inland waterway. With the national development of the Middle and Western parts of China, the throughput and the passing ships in Yangtze River have been rapidly increasing during the past few decades. Meanwhile, accidents such as collisions, groundings, overturns, oil-spills and fires occur repeatedly, causing serious consequences. In view of this, attempts made in this paper are to evaluate the navigational risk of Yangtze River using the FSA concept and a Bayesian Network (BN) technique, so as to enhance the navigational safety in Yangtze River.
Two-Parameter Elastic-Plastic Fracture Mechanics Analysis of Surface Cracked Plates Under Uniaxial and Biaxial Loading
Authors: Wang Xin
Published: November 2011

In this paper, the J-Q two-parameter elastic-plastic fracture mechanics approach is used to analyse the surface cracked plates under uniaxial and biaxial loading. First, the J-Q characterization of crack front stress fields of surface cracked plates under uniaxial and biaxial tension loadings are discussed. The complete J-Q trajectories for points along the crack fronts as load increases from small-scale yielding to large-scale yielding were obtained. Based on the materials toughness locus, (resistance to fracture JC as a function of Q), the assessments of the onset of cleavage fracture are conducted. The critical location along the 3D crack front, and the corresponding maximum load carrying capacity are obtained. The results are consistent with experimental observations. It is demonstrated the J-Q two-parameter approach is capable of providing comprehensive assessments of cleavage fracture of surface cracked plates under uniaxial/biaxial loadings, capturing all the important aspects of the problem.
Numerical Study of the Influence of Initial Condition in Vortex Induced Vibration of a Circular Cylinder With Two Degree of Freedom
Authors: Ferreira Bruno C. , Vitola Marcelo A. , Wanderley Juan B. V. , Sphaier Sergio H.
Published: November 2011

The vortex-induced vibration (VIV) is a classical problem in ocean engineering. Intensive research on this field for flow around a circular cylinder has been observed, due to practical application, mainly the design of risers, cables and pipelines with free span. The relevance of this phenomenon is related to the structure failure, consequence of large displacement or fatigue. In the present study the influence of initial condition on the vortex induced vibration (VIV) of a circular cylinder with two degree of freedom is investigated by the numerical solution of the slightly compressible formulation of Reynolds Average Navier-Stokes equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates. The k–ε turbulence model is used to simulate the turbulent flow in the wake of the cylinder. Two different initial conditions have been tested, free-stream and continuous reduced velocity increase (using the previous reduced velocity as initial condition for the next value). Results for the phase angle, amplitude, frequency, and lift coefficient are presented. The numerical results have been compared with experimental data of Jauvtis and Williamson [1]. The results indicate that the history of cylinder movement has a important impact in the amplitude oscillation observed in-line and cross-flow, principally in the reduced velocity range associated with the upper branch. Results obtained for the initial and lower branch seems to be independent of the initial condition. Further investigation are necessary to understand the difference observed such as the absence of the jump in the cross-flow oscillation between the initial and upper branch and the absence of in-line oscillation for reduced velocity in the range of 1–4 and the peak of in-line oscillation at reduced velocity 6.0.
A Nonlinear Viscoelastic Model for Polyester Mooring Line Analysis
Authors: Kim J. W. , Kyoung J. H. , Sablok A. , Lambrakos K.
Published: November 2011

A viscoelastic model considering multiple relaxation times and nonlinearity in dynamic stiffness has been developed. The model is based on the Maxwell-Wiechert model, which is an extension of an earlier model based on the standard linear solid (SLS) model. The time-dependent elastic modulus of polyester rope is represented by a 4-term Prony series (MW4 model). Relaxation times and coefficients of the Prony series have been determined from test data of dynamic stiffness at different loading periods. Nonlinearity in dynamic stiffness is considered by iteratively adjusting the dynamic stiffness of polyester rope based on the calculated mean load on the rope. The developed model has been applied in the global performance analysis of a Spar platform moored in deep water. Platform offset and mooring-line tension comparisons between the SLS and the MW4 models are given for intact and broken mooring-line cases.
Parallelization of LBM Code Using CUDA Capable GPU Platform for 3D Single and Two-Sided Non-Facing Lid-Driven Cavity Flow
Authors: Alam Muhammad S. , Cheng Liang
Published: November 2011

In this paper, a lattice Boltzmann model is developed and then parallelized employing a Compute Unified Device Architecture (CUDA) capable nVIDIA GPU platform. Numerical algorithms are developed for the solution of 3D single and two-sided non-facing lid-driven (TSNFL) cavity flow for Re = 10–1000. The algorithms are verified by solving both steady and unsteady 3D cavity and 3D TSNFL flow problems. Excellent agreement is obtained between numerical predictions and results available in literature. The results show that the CUDA-enabled LBM code is computationally efficient. It is observed that the implementation of LBM on a GPU allows at least thirty million lattice updates per second for 3-D lid driven cavity flow. Computations have been carried out for a 2-D lid driven cavity flow too. It is revealed that LBM-GPU calculation achieves 641 million lattice updates per second for the 2-D lid driven cavity flow.
Time-Domain Simulation of Multibody Floating Systems Based on State-Space Modeling Technology
Authors: Yu Xiaochuan , Falzarano Jeffrey M.
Published: November 2011

It is important to study MULTIBODY dynamics when analyzing the transfer of cargo between ships and platforms at sea. The hydrodynamic interactions between multiple bodies in close proximity are expected to be significant and complex. In this paper, two levels of approximation of hydrodynamic coefficients are considered, i.e., the constant coefficient method (CCM) and the impulse response function (IRF). The equations of motion are written in standard state-space format, in which the convolution terms are computed using the trapezoidal rule. Initially, this newly proposed numerical scheme is successfully applied to calculate motion responses of a two-body floating system. The time-domain responses of this multibody floating system in both regular waves and random sea are further verified numerically. In addition, an ideal case of the motion mitigation of this system using Dynamic Positioning (DP) system is also given and discussed. The mean drift force is considered using Newman’s approximation. Numerical study shows that the optimal Linear Quadratic Regulator (LQR) method can help to mitigate the motion responses of this two-body floating system at sea. Finally, this scheme is extended to a three-body floating system, with the relative motions in random seas determined.
Vortex Induced Motion (VIM) Performance of the Multi Column Floater (MCF)–Drilling and Production Unit
Authors: Tahar Arcandra , Finn Lyle
Published: November 2011

This paper presents the VIM model tests of the Multi Column Floater (MCF). The MCF is a new drilling and production deep-draft semisubmersible platform developed by Horton Wison Deepwater in Houston. A vertically restrained well deck or Multi Riser Buoyancy Can (MRBC) configured in the center of the MCF is a technology enabler for dry tree semisubmersible. The MRBC independently supports and tensions the production and drilling risers. The production risers may be a combination of dry tree risers and subsea tree tubing risers. VIM model tests were carried out at the FORCE Technology basin during the period of September-October, 2007 for the internal study. The test emphasis was to understand the physical behavior of the MCF at model scale so that a thorough correlation study could be carried out. The inplace model test analysis as well as comparison with numerical tools has been published in the OMAE2010-20640 paper [1]. VIM performance of the MCF that uses cellular construction for the columns is the focus of this paper. The 1:55.88 scale model tests were conducted. The MCF mooring stiffness, riser stiffness, natural periods and mass properties were closely matched with target full-scale properties. The MCF was tested without strakes. A wide range of towing speeds in 3 headings was covered in the test programs. The VIM response was measured for different reduced velocity (Ur). A total of 38 tests were done.
Large-diameter roll mold fabrication method using a small-diameter quartz roll mold and UV nanoimprint lithography
Authors: Taniguchi Jun , Unno Noriyuki , Maruyama Hiroki
Published: November 2011

The roll-to-roll (RTR) technique is a high-throughput method for nanoimprint lithography (NIL); however, the fabrication of the roll mold for RTR NIL is difficult because of the cylindrical shape of the mold. Roll molds are usually fabricated by rolling up a nickel-plated foil imprinted with a nanopattern, but this method generates a seam. To produce a seamless nanoscale mold, we have previously developed a technique for direct writing with an electron beam (EB) onto a rotating cylindrical substrate. The method uses a cylindrical substrate (the roll mold substrate) coated with a resist that is written upon directly by an EB while the roll mold substrate is rotated in a vacuum. However, the throughput of this technique is very low. In an attempt to overcome this problem, we investigated a roll diameter amplification method using direct transfer from a patterned small mold. The roll mold was made of synthetic quartz, and its diameter was 30 mm. This roll mold was dipped in hydrogen silsesquioxane, which acts as high-resolution negative-type EB resist. The mold coated with the EB resist was subjected to EB lithography at an acceleration voltage of 30 kV and an EB current of 100 nA. After development, 520 nm line patterns were obtained on the quartz roll mold. The transparent roll mold was subsequently used to transfer the pattern directly onto a large mold at a rotation speed of 0.2 rpm, a nip force of 60 N, and a UV dose of 60 mW/cm2. The diameter of the large mold was 150 mm, and the mold was covered with a UV-curable film. The width of the transfer lines was 510 nm. By using a large mold made of the resulting patterned polymer, RTR UV-NIL was carried out at a feed speed of 1 mm/s, a nip pressure of 0.25 MPa, and a UV dose of 87 mW/cm2. The transfer film was the same UV-curable film. The replicated lines widths were 590 nm; this large value was caused by deformation of the polymer mold during the RTR NIL process. The roll diameter amplification method is therefore very effective for RTR UV-NIL, because a small-diameter roll can be used as the master mold.
From DNA to Targeted Therapeutics: Bringing Synthetic Biology to the Clinic
Authors: Chen Yvonne Y. , Smolke Christina D.
Published: October 2011

Recent advances in synthetic biology could address prevailing medical challenges.
Helping the Heart to Heal
Authors: Rytting Erik
Published: October 2011

Liposomes targeted to an angiotensin receptor promote the delivery of drugs to the damaged heart.
Reciprocal Regulation of Cephalosporin Resistance in Enterococcus faecalis
Authors: Kristich Christopher J. , Little Jaime L. , Hall Cherisse L. , Hoff Jessica S.
Published: November 2011

Antibiotic-resistant enterococci are major causes of hospital-acquired infections and therefore represent a serious public health problem. One well-known risk factor for the acquisition of hospital-acquired enterococcal infections is prior therapy with broad-spectrum cephalosporin antibiotics. Enterococci can proliferate in patients undergoing cephalosporin therapy due to intrinsic cephalosporin resistance, a characteristic of the genus
Enterococcus
. However, the molecular basis for cephalosporin resistance in
E. faecalis
has yet to be adequately elucidated. Previously we determined that a putative Ser/Thr kinase, IreK (formerly PrkC), is required for intrinsic cephalosporin resistance in
E. faecalis
. Here we show that kinase activity is required for cephalosporin resistance and, further, that resistance in
E. faecalis
is reciprocally regulated by IreK and IreP, a PP2C-type protein phosphatase encoded immediately upstream of IreK. Mutants of two divergent lineages of
E. faecalis
lacking IreP exhibit remarkable hyperresistance to cephalosporins but not to antibiotics targeting other cellular processes. Further genetic analyses indicate that hyperresistance of the IreP mutant is mediated by the IreK kinase. Additionally, competition experiments reveal that hyperresistant Δ
ireP
mutants exhibit a substantial fitness defect in the absence of antibiotics, providing an evolutionary rationale for the use of a complex signaling system to control intrinsic cephalosporin resistance. These results support a model in which IreK and IreP act antagonistically via protein phosphorylation and dephosphorylation as part of a signal transduction circuit to regulate cellular adaptation to cephalosporin-induced stress.

IMPORTANCE
As a major cause of hospital-acquired infections, antibiotic-resistant enterococci represent a serious public health problem. Enterococci are well-known to exhibit intrinsic resistance to broad-spectrum cephalosporin antibiotics, a trait that enables them to proliferate in patients undergoing cephalosporin therapy, thereby predisposing these patients to acquisition of an enterococcal infection. Thus, inhibition of enterococcal cephalosporin resistance could represent an effective new strategy to prevent the emergence of hospital-acquired enterococcal infections. At this time, however, the molecular basis for cephalosporin resistance in
E. faecalis
is poorly understood. Our results begin to unravel the details of a new phosphorylation-dependent signal transduction system that controls cephalosporin resistance in enterococci. Deeper understanding of the mechanism underlying cephalosporin resistance in
E. faecalis
may enable the development of new therapeutics designed to reduce the incidence of hospital-acquired enterococcal infections.
The National Falls and Bone Health Audit: implications for UK emergency care
Authors: Banerjee Jay , Benger Jonathan , Treml Jonathan , Martin Finbarr C , Grant Rob , Lowe Derek , Potter Jonathan , Husk Janet
Published: November 2011

Introduction

The National Clinical Audit of Falls and Bone Health, coordinated by the Royal College of Physicians, assesses progress in implementing integrated falls services across the UK against national standards and enables benchmarking between service providers. Nationally, falls are a leading contributor towards mortality and morbidity in older people and account for 700 000 visits to emergency departments and 4 million annual bed days in England alone.

Methods

Two rounds of national organisational audit in 2005 and 2008 and one national clinical audit in 2006 were carried out based on indicators developed by a multidisciplinary group.

Results

These showed that management of falls and bone health in older people remains suboptimal in emergency departments and minor injury units and opportunities are being missed in carrying out evidence-based risk assessment and management.

Conclusions

Older people attending emergency departments in the UK following a fall are receiving a poor deal. There is an urgent need to ensure more effective assessment and management to prevent further falls and fractures.
Establishing a pilot bovine viral diarrhoea virus eradication scheme in Somerset
Authors: Booth R. E. , Brownlie J.
Published: October 2011

Beginning in April 2006, 41 farms were recruited onto a pilot Bovine viral diarrhoea virus (BVDV) eradication programme across the south of England with the majority of study herds concentrated in Somerset. Each herd was assessed and where relevant cleared of persistently infected (PI) animals. Seven farms dropped out before whole herd screening could be performed. Of the remaining 34 farms, 20 (59 per cent) were classified as infected although two of these were initially misclassified as BVDV‐free. Over the course of three years, 61 PIs were identified across 16 of the 20 infected farms. 72 per cent of PIs indentified on the first herd test were below two years of age. PI prevalence ranged from 0.2 to 3.1 per cent of infected herds and was highest in herds that did not vaccinate. By the end of 2009, 24/34 (71 per cent) of study farms were BVDV‐free while 10 (29 per cent) remained infected.
Field monitoring of plant-growth-promoting rhizobacteria by colony immunoblotting
Authors: Krishnen Ganisan , Kecskés Mihály L. , Rose Michael T. , Geelan-Small Peter , Amprayn Khanok-on , Pereg Lily , Kennedy Ivan R.
Published: November 2011

Inoculant plant-growth-promoting bacteria are emerging as an important component of sustainable agriculture. There is a need to develop inexpensive methods for enumerating these organisms after their application in the field, to better understand their survival and impacts on yields. Immunoblotting is one potential method to measure viable cells, but the high cost of the conventionally used nylon membranes makes this method prohibitive. In this study, less expensive alternative materials such as filter papers, glossy photo papers, and transparencies for the purpose of colony immunoblotting were evaluated and the best substance was chosen for further studies. Whatman filter paper No. 541 combined with a 0.01 mol·L–1 H2SO4 rinsing step gave similar results to nylon membranes but <20% of the overall cost of the original colony immunoblotting assay. The application of the modified immunoblot method was tested on nonsterile clay soil samples that were spiked with high numbers (>107 CFU·g–1) of the plant-growth-promoting bacteria Pseudomonas fluorescens , Azospirillum brasilense , or Rhizobium leguminosarum . The modified protocol allowed the identification and recovery of over 50% of the inoculated cells of all three strains, amidst a background of the native soil microflora. Subsequently, the survival of P. fluorescens was successfully monitored for several months after application to field-grown rice at Jerilderie, New South Wales, Australia, thus validating the procedure.
ThehtpABoperon ofLegionella pneumophilacannot be deleted in the presence of thegroEchaperonin operon ofEscherichia coli
Authors: Nasrallah Gheyath K. , Gagnon Elizabeth , Orton Dennis J. , Garduño Rafael A.
Published: November 2011

HtpB, the chaperonin of the intracellular bacterial pathogen Legionella pneumophila , displays several virulence-related functions in vitro. To confirm HtpB’s role in vivo, host infections with an htpB deletion mutant would be required. However, we previously reported that the htpAB operon (encoding co-chaperonin and chaperonin) is essential. We attempted here to delete htpAB in a L. pneumophila strain carrying the groE operon (encoding the Escherichia coli co-chaperonin and chaperonin). The groE operon was inserted into the chromosome of L. pneumophila Lp02, and then allelic replacement of htpAB with a gentamicin resistance cassette was attempted. Although numerous potential postallelic replacement transformants showed a correct selection phenotype, we still detected htpAB by PCR and full-size HtpB by immunoblot. Southern blot and PCR analysis indicated that the gentamicin resistance cassette had apparently integrated in a duplicated htpAB region. However, we showed by Southern blot that strain Lp02, and the Lp02 derivative carrying the groE operon, have only one copy of htpAB. These results confirmed that the htpAB operon cannot be deleted, not even in the presence of the groE operon, and suggested that attempts to delete htpAB under strong phenotypic selection result in aberrant genetic recombinations that could involve duplication of the htpAB locus.
TRACKING CONTROL AND THE BACKSTEPPING DESIGN OF SYNCHRONIZATION CONTROLLER FOR CHEN SYSTEM
Authors: WANG XINGYUAN , ZHANG JING
Published: November 2011

This paper presents tracking control and synchronization strategies for Chen system. Two universal controllers, a tracking controller and a synchronization controller based on Backstepping design method were designed. It is proved theoretically that the tracking controller enables the error signal exponentially to converge to zero. The validity of Backstepping synchronization controller is also proved. Numerical simulations further validated the two controllers.
CERTIFIED REDUCED BASIS METHODS FOR NONAFFINE LINEAR TIME-VARYING AND NONLINEAR PARABOLIC PARTIAL DIFFERENTIAL EQUATIONS
Authors: GREPL MARTIN A.
Published: November 2011

We present reduced basis approximations and associated a posteriori error bounds for parabolic partial differential equations involving (i) a nonaffine dependence on the parameter and (ii ) a nonlinear dependence on the field variable. The method employs the Empirical Interpolation Method in order to construct "affine" coefficient-function approximations of the "nonaffine" (or nonlinear) parametrized functions. We consider linear time-invariant as well as linear time-varying nonaffine functions and introduce a new sampling approach to generate the function approximation space for the latter case. Our a posteriori error bounds take both error contributions explicitly into account — the error introduced by the reduced basis approximation and the error induced by the coefficient function interpolation. We show that these bounds are rigorous upper bounds for the approximation error under certain conditions on the function interpolation, thus addressing the demand for certainty of the approximation. As regards efficiency, we develop an offline–online computational procedure for the calculation of the reduced basis approximation and associated error bound. The method is thus ideally suited for the many-query or real-time contexts. Numerical results are presented to confirm and test our approach.
3D IMAGE RECONSTRUCTION FOR SUBMERGED OBJECTS USING RAMP RESPONSE SIGNATURES
Authors: LI W.
Published: November 2011

Underwater acoustical imaging techniques and the inverse analysis of acoustic scattering problems have now found many important engineering applications. Based on the physical optics approximation, the ramp response signal can be proven that it is proportional to the profile function of the scatterer, which is defined as the area of cross section of the object perpendicular to the direction of wave propagation. The image synthesis technique named as the approximate limiting surface technique is applied to generated underwater objects by using the ramp responses of the objects. The modification should be made by an iterative procedure which will adjust the parameters of each surface and will yield a result until the profile functions of this generated image at all looking angles are consistent with the input ones. Several typical objects are presented to demonstrate the process of the 3D image generation and the results indicate that the qualities of the final images are quite acceptable. The further research work is to build an automatic iterative mechanism to generate the final image for a submerged object.