bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamic Study of Submerged Ice Collisions
Authors: Chander Subodh , Akinturk Ayhan , Colbourne Bruce
Published: October 2015

Most of the research done on ice-structure interaction deals with the ice at the sea surface. Whereas majority of ice-strengthened regions of ships and offshore structures are well below the waterline. The aim of this research is to examine the mechanics of ice loads caused by submerged ice blocks colliding with the structure. The kinematics is an essential determinant of the energy that is available to drive the ice crushing process during the collision. The present research aims to develop a model to represent the mechanics of such collisions and set a direction for future work. This study includes experimental and numerical components. Various physical experiments have been conducted using a submerged ice model moving solely due to its buoyancy. Using high speed camera the experiments are recorded and analysed to determine the kinematics of collision. These include location, velocity and acceleration of the model ice as a function of time. In parallel, numerical simulations have being conducted using FLOW 3DTM software. The results of the experiments are used to validate the numerical model of the underwater collision. The results shows that added mass plays an important role during the underwater impact collisions. The paper presents some preliminary results obtained during this research.
Short-Term Operational Sea Ice Forecasting for Arctic Shipping
Authors: Howell Carl , Richard Martin , Barnes Joshua , King Tony
Published: October 2015

The Arctic sea ice is declining in extent, volume and thickness. With this decline comes an increased interest in the two main Arctic shipping routes: Canada’s Northwest Passage (NWP) and Russian Northern Sea Route (NSR). The NWP is the most direct route between Asia and the East coast of North America. Some routes are up to 40% shorter than those using the Suez Canal.

With commercial and contractual implications, Arctic shipping route access needs to be predictable with sufficient lead time to allow optimization. This paper presents a methodology for forecasting the timing and length of the open-water season (by determining freeze-up and break-up dates) on regional scales at key locations in the NWP along with examples of applications.

A suite of statistical models were developed to forecast the timing and length of the open-water season at key locations within the NWP, using a multi-node based quadratic discriminant (QD) approach. Forecasts are feasible up to four weeks in advance. Ensembles of QD models were built for key regions using a feature selection method to select an optimized set of input parameters to better discriminate between two states (i.e., ice or open-water). The set of available features used included observed and modeled environmental, oceanographic and atmospheric parameters. Results of models with a 28-day forecast horizon show that over 59% of predictions for break-up and 79% of predictions for freeze-up fall within a ±4-day range, which is the error on the reference dates derived from the weekly CIS ice charts.
Protecting Offshore Pipelines Against Drifting Ice: A Discussion on Standards and Guidelines
Authors: Barrette Paul , Sudom Denise , Babaei Hossein
Published: October 2015

In freezing waters, seabed gouging ice features (icebergs, pressure ridges) are a threat to offshore pipelines, which must be buried to a safe depth. Several standards and guidelines addressing this issue are examined and compared. The type of information that each code deems significant varies considerably — factors that are important to some code writers are not to others. API RP 2N, CSA-ISO 19906, CSA Z662 and DNV OS F101 direct the users to specific factors that either must or could be considered for design, but do not indicate what is to be done with them. In contrast, the RMRS rules are highly prescriptive. From a code user’s perspective, a comprehensive listing of all factors involved in ice-seabed-pipe interaction might provide better guidance in assessing what needs to be considered. This assessment could also be divided into three distinct operations: determination of design gouge depth, determination of clearance below the design gouge depth, and determination of pipeline response.
Performance Improvement and Similarity Analysis for Torsional Galloping Based Turbine
Authors: Armandei Mohammadmehdi , Fernandes Antonio Carlos
Published: October 2015

This paper addresses the innovative turbine for hydrokinetic energy extraction proposed by (Fernandes and Armandei, 2014). This turbine harvests energy via torsional galloping. The turbine consists of a rectangular flat plate located vertically initially aligned with the water current and connected with a torsional spring. By changing the axis position, some experimental tests are conducted to assess the improvements on the performance of the turbine. It is observed that the optimal position for the elastic axis happens when the axis is located at 0.75 of the chord length from the leading edge. This is in accordance with the ideal axis position obtained from the Theodorsen theory reported in a PhD thesis (Armandei, 2013). Also, in order to have estimate of the performance of the turbine in the scaled-up level, a similarity analysis is made. Then the results are modified to find the estimate for the performance of the array of turbines. The comparison between the estimated power of the torsional galloping turbine and some conventional turbine types gives a general idea about how this turbine would operate in full scale.
Assessment of Pipeline Walking With Coupled Triggering Mechanisms by Finite Element Approach
Authors: Birdas Michail , Srinil Narakorn , Van den Abeele Filip
Published: October 2015

Asymmetric loading/unloading profiles during the start-up and shut-down operations of high pressure high temperature pipelines may cause an accumulated axial displacement over several operational cycles known as Pipeline Walking phenomenon. This pipeline walking can be triggered by several factors e.g. the seabed slope, riser tension and thermal transients. Several studies have been carried out in the literature regarding the influence from individual factors; nevertheless, very little has been made in the evaluation of coupled triggering mechanisms, common for a pipeline segment.

This paper investigates the pipeline walking phenomenon using finite element modelling and analysis software SAGE Profile 3D versus standard analytical formulae. The keys aims are (i) to study the interaction and coupling between the walking triggering mechanisms by comparing coupled and uncoupled analyses, and (ii) to compare the obtained numerical results with analytical predictions, commonly used in the subsea industry. Depending on the pipeline and soil properties, the effect of triggering mechanisms is parametrically investigated with varying pipeline tension and seabed slope for a specific thermal gradient profile.

It is found that the common approach to sum up the individual walking rate by the uncoupled analysis for a combination of any two triggering mechanisms, underestimates the walking phenomenon when compared with the coupled analysis. This highlights how attention must be paid to the interaction mechanism. In addition, this study emphasizes that the analytical models severely overestimate the pipeline walking phenomenon, especially when more than one triggering mechanisms are present.
Offshore Monitoring of Snorre A TLP TTR Jumpers
Authors: Rooney Phelim , Nilsen-Aas Christoffer , Skjerve Haavard , Nedrelid Kristin , Viko Nils Gunnar
Published: October 2015

Four sensors were installed on the Snorre A TLP (Tension Leg Platform) on 16th April 2014 and retrieved on 10th May 2014, to document motions of the vessel, top tensioned riser (TTR) and flexible jumper connecting the TTR (Top Tensioned Riser) with the topside piping. The data recorded represents 3828 data sets. Associated significant wave height and peak period is synchronous data extracted from the Miros wave measurement radar and stored in the environmental data base. The SmartMotion riser sensors are certified for service in the Wellbay. The sensors are modelled into the OrcaFlex (1) “calibration” analysis model in order to simulate the motion responses in the same format as recorded offshore (accelerations and rates of rotation), and to carry out verification of the OrcaFlex model by comparing both raw data and filtered/integrated derivatives. This work provides a basis for life extension of the Jumpers and provides valuable feedback to design and analysis of TLP and Spar Jumpers between TTRs and topside Headers.
Validation of a Software Tool (DROPSIM) to Predict the ‘Drop and Getaway’ Behaviour of a Lifeboat
Authors: Palermo Elia , Tonelli Roberto , Quadvlieg Frans , Scharnke Jule , Drummen Ingo , Teigen Per
Published: October 2015

The purpose of a free fall lifeboat is to evacuate people from platforms in case of emergency, and when other, normal means of evacuation, are not possible. For instance, when the weather is too rough, and evacuation cannot be performed by helicopters, the lifeboats are the last way of escape. It is thus essential to be able to properly assess the operability of a lifeboat and the safety of its occupants upon evacuation.

Over the past four years, methods to quantify the operability limits of a lifeboat were analysed in a research project carried out for Statoil. As part of this project, a prototype software (denominated DROPSIM) was developed to predict the ‘drop and sailaway behaviour’ of a lifeboat. DROPSIM is a simplified method based on strip theory, with the objective to obtain predictions that are consistent with the relevant statistical behaviour of the lifeboat, and for the same target level of probability.

Particularly because DROPSIM is a simplified tool, it is vital to verify that the software is adequate for simulating thousands of random lifeboat drops, yielding robust statistical predictions with sufficient accuracy. In order to show the performance of the simulation tool, an extensive validation procedure was established, based on a large amount of model test and data from other simulation tools. The following topics were considered in the validation:

A. Verification: basic checks, e.g. related to buoyancy without comparison to model tests

B. Consistency of simulated and measured response for basic test cases, including free-falling wedge tests and a variety of impact tests with a bullet shaped model

C. Prediction of the sailaway behaviour of a lifeboat in comparison to model tests

D. Comparison with integrated drop and sailaway model tests in normal and off-design (extreme) conditions in calm water and in waves.

In this paper the results of the validation of DROPSIM are presented and discussed. Another dedicated paper gives insight into the mathematical model of DROPSIM ([1]).
Iceberg Drift Forecast Requirements for Offshore Platforms Utilizing Facility Side-Tracking to Avoid Impacts
Authors: Fuglem Mark , Stuckey Paul , King Tony , Brown Murray
Published: October 2015

A number of solutions have been successfully implemented for producing oil and gas off Canada’s east coast, where impacts by icebergs are a possibility. In future, as operators move further offshore to deeper water and further north where the numbers and sizes of icebergs may increase, new solutions for avoiding impacts will be required to limit ice strengthening requirements and ice related downtime costs. A potential solution is the use of facility side-tracking, where a floating system is designed to move laterally to avoid approaching icebergs. This paper discusses the issues involved including the need for improved short-term iceberg drift forecasting.
Comparison Between Finite Element Model and an Artificial Neural Networks Procedure for Riser Analysis
Authors: de Aguiar Cristiano S. , de Lacerda Thiago Angelo G. , Sagrilo Luis V. S. , Siqueira Wallace B.
Published: October 2015

As exploitation activities moves into fields located in deep water, the industry has been addressing studies aiming at concepts of offshore systems that reduce the influence of environmental loads on risers. The Buoy Support Riser (BSR) system is one of these new proposed concepts. The BSR is composed by a subsurface tethered buoy, where flexible jumpers connect the Floating Production Unit (FPU) to the BSR and Steel Catenary Risers (SCRs). Due to its complexity and non-linearity, this offshore system requires a highly refined finite element model for dynamic analysis, which demands a high computational cost. In order to increase feasibility of the analysis it is proposed a low computational cost methodology based on Artificial Neural Networks (ANN). This work aims to develop a program to train an ANN to predict the jumpers’ dynamic tension from FPU motions without running the finite element model for every time step. In this way, the purpose is to find results as reliable as those achieved in a dynamic analysis with a finite element model. Statistical parameters will be used for this comparison.
Modelling of Sea Storms Associated With Energy Harvesters: Downtime and Energy Losses
Authors: Arena Felice , Laface Valentina , Malara Giovanni , Romolo Alessandra
Published: October 2015

The design of an energy harvester involves achieving the two following objectives: to install a safe structure with a reasonable safety margin; and to install an effective device which is able to capture energy in a variety of environmental conditions. In this context, the long-term modelling of the environmental variables plays a crucial role.

In the context of wave energy harvesters, the occurrence of sea storms is a critical element in the design process. Indeed, its identification is required for determining extreme loads as well as controlled de-activations of the device for preserving the mechanical components into the device.

Considering these issues, the paper proposes an analysis of the wave climate oriented to the determination of the downtime and of the energy losses. Specifically, the paper provides expressions: for calculating the average deactivation time of a wave energy device, given that it must be deactivated if the significant wave height is larger than a certain threshold; and for calculating the energy “lost” (as it is not absorbed by the device) during a storm in which the maximum wave height is larger than the mentioned threshold.

The paper shows that closed-form expressions can be obtained by relying on the Equivalent Triangular Storm (ETS) model and that the adequacy of the estimations improves for larger values of the significant wave height threshold.
Evaluation of Stress Corrosion Cracking Susceptibility of the API 5L X70 Steel in Corn and Sugar Cane Ethanol Environments
Authors: Breitenbach Joseane O. , Renck Tiago S. , Moraes Pedro M. , Kwietniewski Carlos E. Fortis , Strohaecker Telmo R. , Pimenta Gutemberg S. , Baptista Ilson Palmieri
Published: October 2015

The interest in renewable and cleaner fuels has stimulated ethanol production in the last decades. Some of the drivers for that ever increasing production were the Brazilian Alcohol Program, Kyoto Protocol and the replacement in USA of the octane booster MBTE (methyl-tert-buthyl ether) for ethanol. The world’s largest producers of ethanol are The United States of America and Brazil, where the main sources are corn and sugar cane, respectively. Production flow via pipeline is the safest and most cost effective way to connect the producers, usually spread across the country, to the distribution terminals. However, in USA there are evidences that ethanol may have caused stress corrosion cracking (SCC) in pipelines and also in storage tanks. Controversially, in Brazil ethanol has been transported and stored since the 1970’s without any indication of SCC. The aim of this work is to evaluate the susceptibility of the steel API 5L X70 [1] to SCC in different ethanol (corn and sugar cane) using slow strain rate testing (SSRT). These tests were carried out on notched specimens according to NACE TM 0111 [2]. The SSRT results carried out in corn ethanol have shown a considerable reduction of plastic elongation and a mixed fracture micromechanism of quasi-cleavage and intergranular facets clearly indicating a susceptibility of the API 5L X70 steel to SCC. The SSRT also demonstrated that the carbon steel tested here is completely immune to SCC in sugar cane ethanol.
Dynamic Domain Decomposition Strategy Coupling Lattice Boltzmann Methods With Finite Differences Approximations of the Navier-Stokes Equations to Study Bodies in Current
Authors: Colicchio Giuseppina , Lugni Claudio , Greco Marilena , Faltinsen Odd M.
Published: October 2015

A Domain-Decomposition (DD) strategy is proposed for problems involving regions with slow variations of the flow (A) and others where the fluid features undergo rapid changes (B), like in the case of steady current past bodies with pronounced local unsteadiness connected with the vortex shedding from the structures. For an efficient and accurate solution of such problems, the DD couples a Finite Difference solver of the Navier-Stokes equations (FD-NS) with a Multiple Relaxation Time Lattice Boltzmann method (MRT-LBM). Regions A are handled by FD-NS, while zones B are solved by MRT-LBM and the two solvers exchange information within a strong coupling strategy. Present DD strategy is able to deal with a dynamic change of the sub-domains topology. This feature is needed when regions with vorticity shed from the body vary in time for a more flexible and reliable solution strategy. Its performances in terms of accuracy and efficiency have been successfully assessed by comparing the hybrid solver against a full FD-NS solution and experimental data for a 2D circular cylinder in an impulsively started flow.
Entropy Production of Hydrate Transport in Subsea Multiphase Pipeline Flows
Authors: Odukoya Adedoyin , Naterer Greg F.
Published: October 2015

A numerical model is developed to examine the flow conditions of multiphase heat transfer and entropy production during hydrate formation in subsea pipelines. The temperature and pressure gradients of the oil and gas flow in subsea pipelines lead to entropy generation. This paper examines the impacts and effects of thermodynamic irreversibilities on the nucleation and growth processes of hydrate crystals in the pipeline flows. The effects of heat transfer ratio, internal diameter of the pipe, molar gas density, and environment temperature on entropy production in subsea pipelines are predicted and discussed in this paper. The numerical model accounts for the temperature distribution along the axial length of the pipe, reaction kinetics, and mass transfer between the solid and fluid layer. The kinetic energy of the hydrate particles during the coagulation process is analyzed in the numerical model. The results indicate that entropy production is highest at the beginning of the nucleation process. Pipelines with smaller internal radii have a lower rate of hydrate formation in subsea pipelines. The results from the numerical model are verified by comparison with experimental results for structure type II natural gas hydrates.
Analysis of Hydrodynamic Characteristics in the Process of Autonomous Underwater Vehicle Docking
Authors: Du Xiaoxu , Wang Huan
Published: October 2015

The successful operation of an Autonomous Underwater Vehicle (AUV) requires the capability to return to a dock. A number of underwater docking technologies have been proposed and tested in the past. The docking allows the AUV to recharge its batteries, download data and upload new instructions, which is helpful to improve the working time and efficiency. During the underwater docking process, unsteady hydrodynamic interference occurs between the docking device and an AUV. To ensure a successful docking, it is very important that the underwater docking hydrodynamics of AUV is understood. In this paper, numerical simulations based on the computational fluid dynamics (CFD) solutions were carried out for a 1.85m long AUV with maximum 0.2 m in diameter during the docking process. The two-dimensional AUV model without fin and rudder was used in the simulation. The mathematical model based on the Reynolds-averaged Navier-Stokes (RANS) equations was established. The finite volume method (FVM) and the dynamic structured mesh technique were used. SIMPLE algorithm and the k-ε turbulence model in the Descartes coordinates were also adopted. The hydrodynamics characteristics of different docking states were analyzed, such as the different docking velocity, the docking device including baffle or not. The drag coefficients of AUV in the process of docking were computed for various docking conditions, i.e., the AUV moving into the docking in the speed of 1m/s, 2m/s, 5m/s. The results indicate that the drag coefficient increases slowly in the process of AUV getting close to the docking device. When the AUV moves into the docking device, the drag coefficient increases rapidly. Then the drag coefficient decreases rapidly. The drag coefficient decreases with the increase of velocity when AUV enters the docking device. It was also found that the drag coefficient can be effectively reduced by dislodging the baffle of docking device.
A New Approach of Quantifying Top-Tensioned Risers Clashing by Using Wavelet Scalograms
Authors: Xing Shutao , Dai Wentao , Moorthy Dakshina , Li Gangqiang
Published: October 2015

Clashing or colliding can take place between a riser and its adjacent risers or other lines/structures. Clashing is of great concern for the design of top-tensioned riser (TTR) arrays in deep water. Understanding the impact behavior between risers is essential for developing reliable clashing mitigation approaches during design phase. Further, monitoring of risers clashing is useful during operation and installation of the systems.

A critical consideration of clashing monitoring is how to quantify the impact. Traditional methods need a priori information which is difficult to be obtained accurately. This paper proposed a new method of monitoring risers clashing by using wavelet scalograms of dynamic responses that doesn’t need such priori information. The method was investigated through numerical simulation of a pair of TTR risers operated from tension-leg platform (TLP) that are subjected to current and floater motions. The wavelet scalograms of the risers’ velocities and accelerations were utilized to quantify impact. It was verified that the wavelet scalograms can indicate clashing severity quite well.
Numerical Prediction Method for Elasto-Viscoplastic Behavior of Glass Fiber Reinforced Polyurethane Foam Under Various Compressive Loads and Cryogenic Temperatures
Authors: Lee Chi-Seung , Kim Myung-Sung , Choi Kwang-Ho , Kim Myung-Hyun , Lee Jae-Myung
Published: October 2015

In the present study, the material characteristics of a glass fiber-reinforced polyurethane foam (RPUF) which is widely adopted to a liquefied natural gas (LNG) insulation system was investigated by a series of compressive tests under room and cryogenic temperatures. In addition, a temperature- and strain rate-dependent constitutive model was proposed to describe the material nonlinear behavior such as increase of yield stress and plateau according to temperature and strain rate variations. The elasto-viscoplastic model was transformed to an implicit form, and was implemented into the ABAQUS user-defined subroutine, namely, UMAT. Through a number of simulation using the developed subroutine, the various stress-strain relationships of RPUF were numerically predicted, and the material parameters associated with the constitutive model were identified. In order to validate the proposed method, the computational results were compared to a series of test of RPUF.
Wave Carpet Optimization via Real Time Hybrid Modeling
Authors: Börner Thomas , Alam M.-Reza
Published: October 2015

Real time hybrid modeling as a structured approach of implementing a real time control system has been proven as an efficient strategy to assess and optimize wave energy converter. In this paper an existing real time hybrid modeling framework for wave energy converter is reviewed, in which the main problem is divided into multiple sub-domains. Each sub-domain uses a preferred method, e.g. experimentally and/or computationally, which contributes to solve the main initial problem as a whole. An interface including actuators and sensors enables the simultaneously running sub-domains to communicate in a closed control loop in “real time”. Specifically, the entire power takeoff of a novel WEC called the “Wave Carpet”, which is classified as a submerged pressure differential device, is shifted into the computational domain. The interaction of the WEC’s absorber unit with incident waves is left in the experiment due to its highly nonlinear characteristics. An extended setup allows to reveal further optimization potential of the novel converter design as a case study. Results of the converter behavior under variable wave states, and for different characteristics of the simulated PTO units are presented. In particular, the presented results show the expected broad band absorption capability of the Wave Carpet by closer examination of the influence of variable PTO unit resistance coefficients on the total, and also on the individual units’ performance.
Deformation Capacity of Weld Seam of the High Quality HFW Linepipe
Authors: Igi Satoshi , Yabumoto Satoru , Sadasue Teruki , Tajika Hisakazu , Oi Kenji
Published: October 2015

Newly-developed high quality high frequency electric resistance welded (HFW) linepipes have recently been used in pipelines in reel-lay applications and low temperature service environments because of their excellent low temperature weld toughness and cost effectiveness. In order to clarify the applicability of these HFW linepipes to the seismic environment, a series of full-scale tests such as bending test with internal pressure and uniaxial compression test were conducted according to the seismic design code in Japan gas association (JGA).

Based on the above-mentioned full-scale tests, the safety performance of high quality HFW linepipe to apply to the seismic region is discussed in comparison with the mechanical properties in the small-scale tests such as the tensile and compression property of the base material and weld seam, especially focused on the strain capacity of HFW linepipe from the view points of full-scale performance and geometrical imperfection.

Test results of the bending test with internal pressure and the uniaxial compression were complied with the JGA seismic design code for the permanent ground deformation induced by lateral spreading and surface faults.
Simulation on the Dynamic Behavior of the Propulsion System Subjected by Hull Deformation for Large Vessels
Authors: Tian Zhe , Yan Xinping , Zhang Cong , Tan Weizhong
Published: October 2015

This paper aims to investigate the dynamic behavior of the large ship propulsion system subjected by hull deformation. Evident tendency of development of large scale ships was shown that the interaction between the propulsion shaft and ship hull becomes much severer than before. The excited forces caused by severe sea waves have considerable effects on the hull deformation which could have further impact on the shaft propulsion system. On the contrary, the operation quality of ships and the durability of machines are threatened by the malfunctions of shaft propulsion system. As a result the reliability of the vessels has been put in an important position by the companies and the governments all over the world. For scientists, investigating the dynamic behavior of the propulsion system subjected by the hull deformation is a meaningful research to avoid malfunction of machine in navigation. Numerical analysis is now an effective method to analyze some key components on large vessels. Taking the 8530TEU container as an example, a numerical model of the large ship propulsion-hull coupling system is presented in this paper to analyze the dynamic behavior of the ship propulsion system subjected by hull deformation. The hull deformations are obtained under different sea conditions as the exciting forces which are used on the coupling system. Then the dynamical responds of the ship shaft are obtained. Based on the results, suggestions are proposed to ensure the normal operation of the propulsion system in different sea conditions.
Analysis of Torsional Vibration of Large-Scale Ship Propulsion Shafting
Authors: Tan Weizhong , Zhang Cong , Tian Zhe , Yan Xinping
Published: October 2015

This paper is based on the multi-body dynamic coupling theory and finite element theory. A multi-body dynamic coupling model of the large-scale vessel is built and the torsion vibration characteristics of slow-speed ship propulsion shafting are analyzed. The measurements of shafting torsional vibration in the real ship are compared with the results from the simulation model. Then, the differences between measurements and simulation results are analyzed in multi-orders. The analysis result indicates that the simulation results are almost the same with measurements obtained from the real ship, which verify the correctness and feasibility of the model. At the same time, the influence of ship hull deformation on the torsion vibration of ship propulsion shafting is discussed by Adams/Vibration. The analysis shows that the ship hull deformation could cause the significant increase of torsional vibration of ship propulsion shafting.
A Collaborative Approach to Root Cause Analysis: With Reference to Suncor Energy Terra Nova Flexible Flowlines and Risers
Authors: Karabelas George , Redfern Geoff , Jacobs Brad , Roberts Andrew , Fernando Upul , Tink Brian , Varley Mark
Published: October 2015

One riser and two flowline sections installed in the Suncor Energy Terra Nova riser replacement programme were shown to leak during field tests performed after site installation. No hydrocarbon loss occurred nor was there an environmental incident; however, the scheduled production start-up for the pipes was delayed. The pipes were designed and manufactured to comply with API [1] code and had successfully undergone full-scale factory acceptance testing (FAT) at 1.5 times design pressure following manufacture. Investigations confirmed that the leaks in both pipes occurred due to a crack in the polymer (PVDF) barrier within the end-fitting region of the pipe. It was also concluded that the crack in the barrier in these pipes occurred after completion of the FAT and sometime during the transportation, storage and subsequent installation of the pipes in the field. It was identified that the problem in the barrier resulted from an unknown thermo-mechanical loading condition of the pipe during this period, and also related to specific design features of some components in those end-fittings.

The TapRoot Root Cause Analysis (RCA) tool was used to guide the investigation effort and consider all available data. Small and full-scale tests were performed to simulate and understand the end fitting design in the environments and conditions experienced during transport, installation and offshore testing.

What is presented here is a brief outline of the incident and details of the subsequent investigation. The investigation was conducted over a period of 18 months with the participation of all parties involved in the design, manufacture, installation and operation of the flexibles. This paper summarises the investigation process followed, documents the results, discusses the results and outlines the conclusions and recommendations arising from this investigation.
FEA Analysis of Subsea Mooring Suction Anchor Under Operation Condition
Authors: Wang Shuqin , Zhang Jiaping , Malachowski Jim , Hossain Jubair , Colling James
Published: October 2015

The analysis of a mooring suction anchor involves both geotechnical and structural engineering. The design starts with the geotechnical analysis of a mooring suction anchor where the design loads are used to determine the size of the mooring suction anchor.

Typically, a conservative estimate would be made for the soil strength and analysis would involve several layers of soil with different properties. The mooring suction anchor is then designed using the relevant soil parameters for various limit states under the combined vertical, lateral, torsional, and moment loading. Soil pressures or reactions acting on a rigid steel mooring suction anchor for each limit state are calculated. The calculation results are then provided to structural engineers to perform strength analysis to verify the integrity of the anchor. Therefore, it is important to understand how the soil reactions interact with the suction anchor in the structural model.

The current analysis used the soil reaction data developed for an in-place loading condition for a mooring suction anchor. The structure of the mooring suction anchor was modelled using a 3D finite element method. Two studies were performed. The first study performed the regular mapping of the soil pressure to the suction anchor. The second study assumed that all the loads would be applied on the mooring padeye and the bottom of the suction would be fixed. It was presumed that the second study would yield a conservative result. However, the analysis results showed that the second study did not provide a conservative result. Therefore, it is recommended that the care should be taken when making such assumptions in future studies.
Reliability Evaluation of Marine Propulsion Shaft Based on Stress-Strength Interference Theory
Authors: Dong Conglin , Yuan Chengqing , Bai Xiuqin , Yan Xinping , Mao Shuhua
Published: October 2015

Ships play an important role in waterway transportation and ocean development. A core component of a ship is its marine propulsion system, in which the marine propulsion shaft is an important constituent. With the development of large-scale ships, the reliability of the marine propulsion shaft under the extreme sea state has attracted many attentions from the users and scholars. This paper focuses on studying how the action time of the random load and severe sea state influences the reliabilities of the marine propulsion shaft when its strength had not or less degenerated. The stress-strength interference theory was used to evaluate the reliability of the marine propulsion shaft. Firstly, the stresses at the maximum deformation of the marine propulsion shaft under the different sea states were obtained using finite element simulation method. The calculation results fitted well with the actual situation. The action times of the random load and severe sea states had significant effects on the reliability of the marine propulsion shaft. The reliabilities decreased as the actions times increased, and decreased sharply under the severe sea states (sea states 8 and 9). The decreasing trends of the reliability and failure rate became more obvious and steeper when the action times were less than 2000 under the different sea states, and more slowly when the action times were from 2000 to 5000. It believed that the knowledge gained in this study will provide the theoretical model for researching on the reliability evaluation theory of ship propulsion system and protecting the ships completing their missions reliably and safely.
Reduced Order Model for Motion Forecasts of One or More Vessels
Authors: Milewski William M. , Connell Benjamin S. H. , Vinciullo Valerie J. , Kirschner Ivan N.
Published: October 2015

The reduced order model at the heart of the APS Environmental and Ship Motion Forecasting system must retain the accuracy of a higher fidelity seakeeping code while simultaneously meeting computational speed required to provide motion forecasts minutes into the future for two or more ships operating in close proximity. We describe the mathematical formulation of the reduced order model and efficient modeling techniques to construct databases of wave force Response Amplitude Operators and Impulse Response Functions before presenting comparisons between the reduced order model, a higher fidelity seakeeping code called AEGIR, and experimental data for the R/V Melville and two multi-ship configurations.
A more stable transition matrix for acoustic target scattering by elongated objects
Authors: Lim Raymond
Published: October 2015

The transition (T) matrix of Waterman has been very useful for computing fast, accurate acoustic scattering predictions for axisymmetric elastic objects, but this technique is usually limited to fairly smooth objects that are not too aspherical unless complex basis functions or stabilization schemes are used. To ease this limitation, a spherical-basis formulation adapted from approaches proposed recently by Waterman [J. Acoust. Soc. Am. 125(1), 42–51 (2009)] and Doicu, Eremin, and Wriedt [Acoustic and Electromagnetic Scattering Analysis Using Discrete Sources (Academic, London, 2000)] is suggested. This is implemented by simply transforming the high-order outgoing spherical basis functions within standard T-matrix formulations to low-order functions distributed along the object's symmetry axis. A free-field T matrix is produced in a nonstandard form, but computations with it become much more stable for elongated aspherical elastic shapes. Some advantages of this approach over the approaches of Waterman and Doicu, Eremin, and Wriedt are noted, and sample calculations for a 10:1 Al prolate spheroid and a 10:1 Al superspheroid of order 10 are given to demonstrate the enhanced stability.
Explaining the Railsback stretch in terms of the inharmonicity of piano tones and sensory dissonance
Authors: Giordano N.
Published: October 2015

The perceptual results of Plomp and Levelt [J. Acoust. Soc. Am. 38, 548–560 (1965)] for the sensory dissonance of a pair of pure tones are used to estimate the dissonance of pairs of piano tones. By using the spectra of tones measured for a real piano, the effect of the inharmonicity of the tones is included. This leads to a prediction for how the tuning of this piano should deviate from an ideal equal tempered scale so as to give the smallest sensory dissonance and hence give the most pleasing tuning. The results agree with the well known “Railsback stretch,” the average tuning curve produced by skilled piano technicians. The authors' analysis thus gives a quantitative explanation of the magnitude of the Railsback stretch in terms of the human perception of dissonance.
On the inadvisability of using single parameter impedance models for representing the acoustical properties of ground surfaces
Authors: Dragna Didier , Attenborough Keith , Blanc-Benon Philippe
Published: October 2015

Although semi-empirical one parameter models are used widely for representing outdoor ground impedance, they are not physically admissible. Even when corrected to satisfy a passivity condition in respect of surface impedance they do not satisfy the condition that the real part of complex density must be greater than zero. Comparison of predictions with frequency-domain data for short range propagation have indicated that physically admissible models provide superior overall agreement. A two parameter variable porosity model yields better agreement for many grassland surfaces and a two parameter version of the slit pore microstructural impedance model yields better agreement with data obtained over low flow resistivity surfaces such as forest floors and gravel. Impedance models and conditions for physical admissibility are summarised. In addition to those examined previously, the slit pore model is shown to be physically admissible. After providing further examples of the better agreement with short range data that can be achieved using two parameter models, it is shown that differences between frequency domain predictions at longer ranges using physically admissible models rather than one parameter models are significantly greater than those resulting from short range spatial variability and comparable with seasonal variability over grassland.
To beam or not to beam
Authors: Dronca Roxana
Published: October 2015

Radiation therapy for prostate cancer can increase androgen receptor signaling and exacerbate the disease in some patients.
The Connection between Persistent, Disinfectant-Resistant Listeria monocytogenes Strains from Two Geographically Separate Iberian Pork Processing Plants: Evidence from Comparative Genome Analysis
Authors: Ortiz Sagrario , López-Alonso Victoria , Rodríguez Pablo , Martínez-Suárez Joaquín V.
Published: October 2015

The aim of this study was to investigate the basis of the putative persistence of
Listeria monocytogenes
in a new industrial facility dedicated to the processing of ready-to-eat (RTE) Iberian pork products. Quaternary ammonium compounds, which included benzalkonium chloride (BAC), were repeatedly used as surface disinfectants in the processing plant. Clean and disinfected surfaces were sampled to evaluate if resistance to disinfectants was associated with persistence. Of the 14 isolates obtained from product contact and non-product contact surfaces, only five different pulsed-field gel electrophoresis (PFGE) types were identified during the 27-month study period. Two of these PFGE types (S1 and S10-1) were previously identified to be persistent and BAC-resistant (BAC
r
) strains in a geographically separate slaughterhouse belonging to the same company. The remaining three PFGE types, which were first identified in this study, were also BAC
r
. Whole-genome sequencing and
in silico
multilocus sequence typing (MLST) analysis of five BAC
r
isolates of the different PFGE types identified in this study showed that the isolate of the S1 PFGE type belonged to MLST sequence type 31 (ST31), a low-virulence type characterized by mutations in the
inlA
and
prfA
genes. The isolates of the remaining four PFGE types were found to belong to MLST ST121, a persistent type that has been isolated in several countries. The ST121 strains contained the BAC resistance transposon Tn
6188
. The disinfection-resistant
L. monocytogenes
population in this RTE pork product plant comprised two distinct genotypes with different multidrug resistance phenotypes. This work offers insight into the
L. monocytogenes
subtypes associated with persistence in food processing environments.
Comparative Adjuvant Effects of Type II Heat-Labile Enterotoxins in Combination with Two Different Candidate Ricin Toxin Vaccine Antigens
Authors: Vance David J. , Greene Christopher J. , Rong Yinghui , Mandell Lorrie M. , Connell Terry D. , Mantis Nicholas J.
Published: October 2015

Type II heat-labile enterotoxins (HLTs) constitute a promising set of adjuvants that have been shown to enhance humoral and cellular immune responses when coadministered with an array of different proteins, including several pathogen-associated antigens. However, the adjuvant activities of the four best-studied HLTs, LT-IIa, LT-IIb, LT-IIbT13I, and LT-IIc, have never been compared side by side. We therefore conducted immunization studies in which LT-IIa, LT-IIb, LT-IIbT13I, and LT-IIc were coadministered by the intradermal route to mice with two clinically relevant protein subunit vaccine antigens derived from the enzymatic A subunit (RTA) of ricin toxin, RiVax and RVEc. The HLTs were tested with low and high doses of antigen and were assessed for their abilities to stimulate antigen-specific serum IgG titers, ricin toxin-neutralizing activity (TNA), and protective immunity. We found that all four HLTs tested were effective adjuvants when coadministered with RiVax or RVEc. LT-IIa was of particular interest because as little as 0.03 μg when coadministered with RiVax or RVEcproved effective at augmenting ricin toxin-specific serum antibody titers with nominal evidence of local inflammation. Collectively, these results justify the need for further studies into the mechanism(s) underlying LT-IIa adjuvant activity, with the long-term goal of evaluating LT-IIa's activity in humans.
Molecular Characterization of Nonhemolytic and Nonpigmented Group B Streptococci Responsible for Human Invasive Infections
Authors: Six Anne , Firon Arnaud , Plainvert Céline , Caplain Camille , Touak Gérald , Dmytruk Nicolas , Longo Magalie , Letourneur Franck , Fouet Agnès , Trieu-Cuot Patrick , Poyart Claire
Published: October 2015

Group B
Streptococcus
(GBS) is a common commensal bacterium in adults, but is also the leading cause of invasive bacterial infections in neonates in developed countries. The β-hemolysin/cytolysin (β-h/c), which is always associated with the production of an orange-to-red pigment, is a major virulence factor that is also used for GBS diagnosis. A collection of 1,776 independent clinical GBS strains isolated in France between 2006 and 2013 was evaluated on specific medium for β-h/c activity and pigment production. The genomic sequences of nonhemolytic and nonpigmented (NH/NP) strains were analyzed to identify the molecular basis of this phenotype. Gene deletions or complementations were carried out to confirm the genotype-phenotype association. Sixty-three GBS strains (3.5%) were NH/NP, and 47 of these (74.6%) originated from invasive infections, including bacteremia and meningitis, in neonates or adults. The mutations are localized predominantly in the
cyl
operon, encoding the β-h/c pigment biosynthetic pathway and, in the
abx1
gene, encoding a CovSR regulator partner. In conclusion, although usually associated with GBS virulence, β-h/c pigment production is not absolutely required to cause human invasive infections. Caution should therefore be taken in the use of hemolysis and pigmentation as criteria for GBS diagnosis in routine clinical laboratory settings.
Structure/Function Studies Involving the V3 Region of the HIV-1 Envelope Delineate Multiple Factors That Affect Neutralization Sensitivity
Authors: Zolla-Pazner Susan , Cohen Sandra Sharpe , Boyd David , Kong Xiang-Peng , Seaman Michael , Nussenzweig Michel , Klein Florian , Overbaugh Julie , Totrov Max
Published: October 2015

Antibodies (Abs) specific for the V3 loop of the HIV-1 gp120 envelope neutralize most tier 1 and many tier 2 viruses and are present in essentially all HIV-infected individuals as well as immunized humans and animals. Vaccine-induced V3 Abs are associated with reduced HIV infection rates in humans and affect the nature of transmitted viruses in infected vaccinees, despite the fact that V3 is often occluded in the envelope trimer. Here, we link structural and experimental data showing how conformational alterations of the envelope trimer render viruses exceptionally sensitive to V3 Abs. The experiments interrogated the neutralization sensitivity of pseudoviruses with single amino acid mutations in various regions of gp120 that were predicted to alter packing of the V3 loop in the Env trimer. The results indicate that the V3 loop is metastable in the envelope trimer on the virion surface, flickering between states in which V3 is either occluded or available for binding to chemokine receptors (leading to infection) and to V3 Abs (leading to virus neutralization). The spring-loaded V3 in the envelope trimer is easily released by disruption of the stability of the V3 pocket in the unliganded trimer or disruption of favorable V3/pocket interactions. Formation of the V3 pocket requires appropriate positioning of the V1V2 domain, which is, in turn, dependent on the conformation of the bridging sheet and on the stability of the V1V2 B-C strand-connecting loop.

IMPORTANCEThe levels of antibodies to the third variable region (V3) of the HIV envelope protein correlate with reduced HIV infection rates. Previous studies showed that V3 is often occluded, as it sits in a pocket of the envelope trimer on the surface of virions; however, the trimer is flexible, allowing occluded portions of the envelope (like V3) to flicker into an exposed position that binds antibodies. Here we provide a systematic interrogation of mechanisms by which single amino acid changes in various regions of gp120 (i) render viruses sensitive to neutralization by V3 antibodies, (ii) result in altered packing of the V3 loop, and (iii) activate an open conformation that exposes V3 to the effects of V3 Abs. Taken together, these and previous studies explain how V3 antibodies can protect against HIV-1 infection and why they should be one of the targets of vaccine-induced antibodies.