bluuebunny/crossref_metadata_2025 huggingface dataset:
Sphagnum physiology in the context of changing climate: emergent influences of genomics, modelling and host–microbiome interactions on understanding ecosystem function
Authors: WESTON DAVID J. , TIMM COLLIN M. , WALKER ANTHONY P. , GU LIANHONG , MUCHERO WELLINGTON , SCHMUTZ JEREMY , SHAW A. JONATHAN , TUSKAN GERALD A. , WARREN JEFFREY M. , WULLSCHLEGER STAN D.
Published: September 2014

Peatlands harbour more than one‐third of terrestrial carbon leading to the argument that the bryophytes, as major components of peatland ecosystems, store more organic carbon in soils than any other collective plant taxa. Plants of the genus Sphagnum are important components of peatland ecosystems and are potentially vulnerable to changing climatic conditions. However, the response of Sphagnum to rising temperatures, elevated CO2 and shifts in local hydrology have yet to be fully characterized. In this review, we examine Sphagnum biology and ecology and explore the role of this group of keystone species and its associated microbiome in carbon and nitrogen cycling using literature review and model simulations. Several issues are highlighted including the consequences of a variable environment on plant–microbiome interactions, uncertainty associated with CO2 diffusion resistances and the relationship between fixed N and that partitioned to the photosynthetic apparatus. We note that the Sphagnum fallax genome is currently being sequenced and outline potential applications of population‐level genomics and corresponding plant photosynthesis and microbial metabolic modelling techniques. We highlight Sphagnum as a model organism to explore ecosystem response to a changing climate and to define the role that Sphagnum can play at the intersection of physiology, genetics and functional genomics.
Partitioning changes in photosynthetic rate into contributions from different variables
Authors: BUCKLEY THOMAS N. , DIAZ‐ESPEJO ANTONIO
Published: September 2014

Changes in net CO2 assimilation rate (A) are often partitioned into contributions from changes in different variables using an approach that is based on an expression from calculus: namely the definition of the exact differential of A, which states that an infinitesimal change in A (dA) is equal to the sum of infinitesimal changes in each of the underlying variables, each multiplied by the partial derivative of A with respect to the variable. Finite changes in A can thus be partitioned by integrating this sum across a finite interval. The most widely used method of estimating that integral is a coarse discrete approximation that uses partial derivatives of the natural logarithm of A rather than A itself. This yields biased and ambiguous estimates of partitioned changes in A. We present an alternative partitioning approach based on direct numerical integration of dA. The new approach does not require any partial derivatives to be computed, and it can be applied under any conditions to estimate the contributions from changes in any photosynthetic variable. We demonstrate this approach using field measurements of both seasonal and diurnal changes in assimilation rate, and we provide a spreadsheet implementing the new approach.
A New Two‐Bin Policy for Inventory Systems with Differentiated Demand Classes
Authors: Ghosh Sugoutam , Piplani Rajesh , Viswanathan S.
Published: September 2014

We consider an inventory system under continuous review with two demand classes that are different in terms of service level required (or penalty cost incurred for backordering of demand). Prior literature has proposed the critical level rationing (CLR) policy under which the demand from the lower priority class is backordered once inventory falls below the critical level. While this reduces the penalty cost for the higher demand class, the fill rate achieved for the lower priority demand class gets compromised. In this study, we propose a new class of two‐bin (2B) policy for the problem. The proposed 2B policy assigns separate bins of inventory for the two demand classes. The demand for each class is fulfilled from its assigned bin. However, when the bin intended for the higher demand class is empty, the demand from the higher class can still be fulfilled with the inventory from the other bin. The advantage of the 2B policy is that better fill rates are achieved, especially for the lower demand class. Computational results show that the proposed policy is able to provide a much higher service level for the lower priority class demand without increasing the total cost too much and without affecting the service level for the higher priority class. When a service level constrained optimization problem is considered, the 2B policy dominates the CLR policy when the service level difference for the two classes is not too high or the service levels required for both the classes are relatively lower.
Positioning Inventory in Clinical Trial Supply Chains
Authors: Fleischhacker Adam , Ninh Anh , Zhao Yao
Published: September 2014

As a result of slow patient recruitment and high patient costs in the United States, clinical trials are increasingly going global. While recruitment efforts benefit from a larger global footprint, the supply chain has to work harder at getting the right drug supply to the right place at the right time. Certain clinical trial supply chains, especially those supplying biologics, have a combination of unique attributes that have yet to be addressed by existing supply chain models. These attributes include a fixed patient horizon, an inflexible supply process, a unique set of service‐level requirements, and an inability to transfer drug supplies among testing sites. We provide a new class of multi‐echelon inventory models to address these unique aspects. The resulting mathematical program is a nonlinear integer programming problem with chance constraints. Despite this complexity, we develop a solution method that transforms the original formulation into a linear integer equivalent. By analyzing special cases and through numerical study of both real‐life and simulated examples, we demonstrate the effectiveness of the solution and develop insights into inventory positioning and the cost drivers in clinical trial supply chains.
High diversity, expanding populations and purifying selection in phytoplasmas causing coconut lethal yellowing in Mozambique
Authors: Bila J. , Mondjana A. , Samils B. , Högberg N.
Published: September 2014

In this study, the putative phytoplasma species causing coconut lethal yellowing disease in Mozambique and Tanzania were characterized. The 16S rRNA and secA genes were sequenced. Phylogenetic analysis revealed that Mozambican coconut phytoplasmas belong to three different types: ‘Candidatus Phytoplasma palmicola’ 16SrXXII‐A, a second strain that was previously isolated in Tanzania and Kenya (16SrIV‐C), and a third strain that was different from all known lethal yellowing phytoplasma species. The third strain potentially represents a novel species and is closely related to pine phytoplasma. Co‐infection with ‘Ca. Phytoplasma pini’‐related and ‘Ca. Phytoplasma palmicola’ 16SrXXII‐A strains was observed. Furthermore, sequence variation in ‘Ca. Phytoplasma palmicola’ at the population level was consistent with purifying selection and population expansion.
Two‐year stability of individual differences in (para)sympathetic and HPA‐axis responses to public speaking in childhood and adolescence
Authors: van den Bos Esther , Westenberg P. Michiel
Published: September 2014

Long‐term stability of individual differences in stress responses has repeatedly been demonstrated in adults, but few studies have investigated the development of stability in adolescence. The present study was the first to investigate the stability of individual differences in heart rate, parasympathetic (RMSSD, pNN50, HF), sympathetic (LF/HF, SC), and HPA‐axis (salivary cortisol) responses in a youth sample (8–19 years). Responses to public speaking were measured twice over 2 years. Stability was moderate for absolute responses and task delta responses of HR, RMSSD, pNN50, and HF. Stability was lower for SC and task delta responses of LF/HF and cortisol. Anticipation delta responses showed low stability for HR and cortisol. The latter was moderated by age or puberty, so that individual differences were more stable in more mature individuals. The results support the suggestion that stress responses may be reset during adolescence, but only for the HPA axis.
Home Bias in Officiating: Evidence From International Cricket
Authors: Sacheti Abhinav , Gregory-Smith Ian , Paton David
Published: September 2014

We use data on leg before wicket decisions from 1000 test cricket matches to quantify the systematic bias by officials (umpires) to favour home teams. We exploit recent changes in the regulation of test cricket as a series of natural experiments to help to identify whether social pressure from crowds has a causal effect on home bias. Using negative binomial regressions, we find that home umpires favour home teams and that this effect is more pronounced in the later stages of matches.
Validity and reliability of the SPORTS score for shoulder instability
Authors: Blonna Davide , Bellato Enrico , Caranzano Francesco , Bonasia Davide , Marmotti Antongiulio , Rossi Roberto , Castoldi Filippo
Published: September 2014

Purpose: athletes affected by shoulder instability cannot be judged solely according to the criteria used for non-athletes. In order to improve the assessment of shoulder instability surgery outcomes, the SPORTS score was tested in a cohort of athletes.

Methods: ninety-eight athletes at an average follow-up of 4.6 years (range 1-9.2) after open or arthroscopic surgery for recurrent anterior shoulder instability were included in this study. The patients were asked to complete the SPORTS score questionnaire twice, with an interval of 2-3 weeks between the two assessments. The Bland-Altman method and the intra-class correlation coefficient were used to measure reliability. Criterion validity was assessed by calculating the Spearman correlation coefficient between the SPORTS score and the Western Ontario Shoulder Instability Index (WOSI) score, the Rowe score, the Oxford Shoulder Instability Score (OSIS), and the Subjective Shoulder Value (SSV).

Results: the SPORTS score showed excellent test-retest reliability. The systematic error between the first and the second assessment was 0.3 points (95% upper limit of agreement = 2.3 points). The criterion validity was found to be strong for the SPORTS score, which correlated best with the SSV and the “sport, recreation, and work” component of the WOSI score. The SPORTS score had an acceptable floor effect (8%). The ceiling effect was 46%, which was better than the ceiling effects seen with the Rowe, OSIS and WOSI scores.

Conclusions: this study suggests that the SPORTS score is a valid score in the assessment of athletes after surgery for shoulder instability and that it adds important information to the currently available scores.

Level of evidence: Level III, diagnostic study of nonconsecutive patients.
How do massive immobile rotator cuff tears behave after arthroscopic interval slides? Comparison with mobile tears
Authors: Fossati Chiara , Arrigoni Paolo , Ragone Vincenza , Spennacchio Pietro , Banfi Giuseppe , Randelli Filippo , Randelli Pietro
Published: September 2014

Purpose: the aim of this study was to compare clinical outcomes of contracted immobile massive rotator cuff tears mobilised through an arthroscopic interval slide technique versus massive mobile cuff tears directly repaired without any mobilisation.

Methods: twenty-five patients who underwent arthroscopic repair for massive rotator cuff tears with a minimum of 18 months follow-up were included. The patients were retrospectively divided into two groups. In group 1, a single or double interval slide was performed to achieve adequate tendon mobilisation. In group 2 (control group), massive rotator cuff tears were arthroscopically repaired without any additional release. Patients were evaluated with validated outcomes scores: subjective and objective Constant score, a Visual Analogue Scale (VAS) for pain, and single Assessment Numeric Evaluation (SANE).

Results: the two groups were comparable in terms of age, gender and involvement of the dominant arm. The mean follow-up duration was 31 months in group 1 and 28 months in group 2 (p = 0.4). The two groups showed no significant differences in SANE and VAS results (group 1: SANE 77%, VAS 1.3; group 2: SANE 88%, VAS 1.6), or in total Constant score (group1: 66.5 ± 11; group 2: 75 ± 14; p = 0.1) and subjective Constant score (Group 1: 31 ± 5; group 2: 30.8 ± 7; p = 0.9). A significant difference was found for the objective Constant score, which was higher in the control group (group 1: 35.5 ± 7; group 2: 44 ± 8; p = 0.009).

Conclusions: Subjective clinical outcomes of arthroscopic repair with or without interval slides did not differ and were satisfactory. Objectively, immobile cuff tears showed inferior results.The use of interval slides might be considered a first step or an alternative to more invasive procedures for low demanding patients.

Level of evidence: Level III, retrospective comparative study.
First patellar dislocation: from conservative treatment to return to sport
Authors: Respizzi Stefano , Cavallin Ramon
Published: September 2014

Treatment of first patellar dislocation is usually conservative and the subsequent rehabilitation program is based on specifically formulated objectives, which can be divided into different stages: stage 1: resolution of pain, swelling and inflammation; stage 2: recovery of joint motion and flexibility; stage 3: recovery of muscle strength; stage 4: recovery of motor patterns and coordination; and stage 5: recovery of the sportspecific athletic action and return to sporting activity. The aim, in the management of a patient affected by first patellar dislocation, is to achieve the best possible functional recovery: since this is a condition often affecting young athletes, this means returning them to their pre-injury conditions, both in terms of fitness and the level of sporting activity practiced. By proceeding through functional stages, the risk of recurrence of the dislocation can be reduced. The “go-ahead” to resume sporting activity can only be given in the presence of normal results on sport-specific functional tests.
The Drag, Lift and Strouhal Number of a Circular-Section Cylinder With a Conic Disturbance at Subcritical Reynolds Numbers
Authors: Lin Liming , Zhong Xingfu , Wu Yingxiang
Published: September 2014

Through numerical simulations, the flow past a circular-section cylinder with a conic disturbance is investigated at sub-critical Reynolds numbers of 102, 103 and 104. At higher Reynolds numbers, LES is employed in simulating the turbulence transition in the near wake. Computations with a series of parameters, the wavelength and wave steepness, are carried out. Generally, the drag of conic cylinder is gradually increased with the increasing wave steepness and in most cases greater than that of the cylinder without disturbance. However, the total lift in most cases is obviously reduced. The phenomenon of local minimum is found out in variation of drag and lift. The introduction of conic disturbance also leads to the decrease of frequency of vortex shedding as the wave steepness increases.
Numerical CFD-Model of Contact Interactions Between Hummock and Ice Fields for Estimation of Ice Loads on Sakhalin Offshore GBS Platforms
Authors: Sabodash Olga A. , Bekker Alexander T.
Published: September 2014

A two-fluid Eulerian-Eulerian model accounting for the contact interactions between obstruction and hummock, stopped before a structure, and ice floes has been developed. In this work the ice cover is considered to behave as a continuous stream of drifting ice surrounded by the water phase. The technique accounts for the «ice-to-ice» interactions. Consequently, a multiphase computational fluid dynamics (CFD) model is formulated and used for the numerical modeling of the process. The input ice data were obtained from the full-scale observations of the ice conditions in the Piltun-Astokhskoe deposit area during 1989÷2002. Some preliminary results and discussions are presented.
Drop Tests and Modeling of Water Entry of Air-Cavity Hull Sections
Authors: Keehnel Dawn , Matveev Konstantin I.
Published: September 2014

Marine vessels sailing through waves may experience very high loads during slamming events. The present study addresses a novel air-cavity hull configuration that contains air trapped between rigid side hulls and a platform. Laboratory drop tests have been conducted with two-dimensional sections imitating air-cavity hulls. The platform vertical position was the main variable parameter. Time-dependent accelerations and pressure measured at the platform center are reported. Peak values of these variables and their occurrence times are identified. The captured air pockets are found to reduce maximum slamming loads. A simplified mathematical model is applied for simulating the initial phase of the air-cavity hull water entry. The obtained results can be used for seakeeping assessment of air-cavity ships as well as validation of more sophisticated mathematical models for hull slamming.
A New Particle Method for Two-Phase Flows With Large Density Difference
Authors: Koh C. G. , Luo M. , Gao M. , Bai W.
Published: September 2014

A new numerical approach for solving two-phase flows is presented in the framework of the recently developed Consistent Particle Method (CPM). The spatial derivatives along fluid interfaces where abrupt discontinuity of fluid density exists are computed by including neighbor particles of another fluid and applying Taylor series expansion on specific pressure energy. In addition, a new h-adaptive particle selection scheme is proposed to overcome the potential problem of ill-conditioned coefficient matrix of PPE when particles are sparse and non-uniformly spaced. Using this method, water-air sloshing in a closed rectangular tank is studied with experimental validation.
Effects of Attrition due to Water in Cyclically Loaded Grouted Joints
Authors: Schaumann Peter , Raba Alexander , Bechtel Anne
Published: September 2014

According to political goals, electricity from offshore wind farms in Germany will amount to 15 GW by 2030. Most of the wind farms will be located far offshore in water depths larger than 30 m. For such water depths, lattice substructures like jackets or tripods are the preferred solution. The substructures are founded on piles and connected to these by submerged grouted joints. In lattice substructures grouted joints are predominantly loaded by cyclic axial loads. Even though, this connection is well known from the offshore oil and gas industry, comparatively few results on effects of attrition due to water for grouted joints are available.

At the Institute for Steel Construction of the Leibniz University Hannover, Germany, within the joint research project ‘GROWup’ investigations focus on the fatigue performance of grouted joints under predominant axial loading. As part of this research project, cyclic loading tests on small scale grouted joints with shear keys were conducted. The specimens were filled with industrial grout products and tested in a water basin to evaluate the influence of water to the fatigue performance of the connection at small scale. These test results show that the water effect leads to a significant reduction of the fatigue performance of the connection compared to results from tests in dry conditions. Moreover, the impact of water is proportional to the applied test frequency. The results of the structural tests differ from results of pure material specimen tests, on which current code provisions are based.

This paper presents results from the small scale tests on grouted joints with shear keys in dry and submerged conditions. Effects of attrition due to water are shown and their effect is quantified. The results are compared to other published findings. In conclusion the presented investigations underline the importance of the water effect to the fatigue performance of small scale grouted joints. In conclusion, this paper will stimulate discussions on the demand for research on large- and real-scale grouted joints.
Wave Loads Investigation of a VLCC by Experimental and Theoretical Methods
Authors: Wang Xueliang , Hu Jiajun , Gu Xuekang , Ding Jun , Zhao Nan
Published: September 2014

On the large scale the commercial ship development trend indicates that the length of ship becomes longer and longer whilst its hull girder turns into much more flexible than that of small and medium-sized ships. This results in a ship sustaining both springing and slamming responses when travelling at sea. A VLCC is introduced in this paper to study its low and high frequency wave load responses in both full loaded and ballast condition. Experimental and theoretical methods were used to investigate the characteristic of this VLCC’s wave loads. A segmental model with its length more than six meters being connected by two non-uniform beams was used to get the vertical bending moments at each measured cut. A 2D nonlinear theory and a 3D hydroelastic theory were both employed to predict the wave loads responses. The results had been compared between experimental and theoretical methods. It was shown that springing phenomenon was prone to appear when wave amplitude was low and its period was short, especially when wave encounter frequency was an integral multiple of the basic vibration frequency of the ship hull girder. Slamming happened when the wave amplitude was high. However, it was difficult to distinguish slamming or springing or their combination from the wave-induced vibrations because of the small damping ratio in total vibrations. Loading condition has a great influence on wave loads responses especially on the springing behavior. It was found that springing behavior is much more severe in ballast condition than in full loaded condition. The mechanism of it which mentioned in other reference was reconfirmed in this paper.
Investigation of Tensile Armor Wire Breaks in Flexible Risers and a Method for Detection
Authors: Weppenaar Nick , Andersen Bo
Published: September 2014

Tensile armor wire breaks in flexible risers have been studied by measuring strain in wires during a series of full-scale dynamic pipe tension tests. This has resulted in an understanding of wire breaks described by parameters such as time evolution, spatial distribution and the scale of the measured strain change. With the measured strain data wire break events in flexible risers can be detected and discriminated from other events in the pipe structure. Hence, by instrumenting risers with a grid of fiber optical strain sensors embedded in the tensile wires a Wire Break Detection system can be implemented. The test data and the resulting knowledge of how strain variations from a wire break event propagate in a flexible riser are presented.
The Variation of Physical Properties in Frozen Soils at Various Freezing Temperatures
Authors: Kim YoungSeok , Kim Kiju , Hong Seung-Seo , Cho Wanjei
Published: September 2014

Due to the recent climate change, the colder and longer winter is expected in Korea. Besides, the recent participation agreement on the development of the natural gas pipeline in Russia and construction of the second Korean Antarctic research station, the Jangbogo station changes the research interests from the seasonally frozen ground to the permafrost ground. The recent development of the site investigation techniques using wave propagation and electrical resistivity enabled engineers to evaluate the physical properties of the frozen soils and further correlate them to the mechanical properties. However, the physical properties of the frozen ground change when the water in the soil solidifies to ice; this change is particularly notable between 0 and −10°C. Therefore, the physical property changes due to freezing needs to be investigated in terms of wave propagation characteristics and electrical resistivity with regard to the various freezing temperatures. In this study, the characteristics of wave propagation and electrical resistivity of frozen soils are investigated under various sub-zero temperatures. The characteristics of wave propagations are analyzed in terms of compression and shear wave velocities. The electrical resistivity is measured under various sub-zero temperatures to understand the effects of ice, which will further provide the valuable information about the location of the active layer. Furthermore, the evaluated physical properties can be used as basic data for the evaluation of the mechanical properties such as strength and stiffness.
Uncertainty in Stress Concentration Factor Computation for Ship Fatigue Design
Authors: Ogeman Viktor , Mao Wengang , Ringsberg Jonas W.
Published: September 2014

In stress-based fatigue design and analysis of marine structures, a stress concentration factor (SCF) is used to compute the local stress in structural details when the hot-spot approach is used. For a typical steel material, the fatigue damage is computed as proportional to the power 3–5 of the stress values, defined by the chosen S-N curve. This means that a small change in the SCF value can lead to a large difference in the fatigue damage result and corresponding fatigue life prediction. Thus, the methodology used to compute the SCF should be clearly defined in classification society guidelines.

This study presents a review of different direct calculation procedures for how to obtain the SCF based on fatigue assessment guidelines. The effect of different element types and local stress extrapolation methods to the fatigue damage estimation is studied for both longitudinal load and bending load conditions in a container ship. A simple structural detail with cracks observed after only a few years in service is used for the case study. For this structural detail, two alternative methods to compute the local stress for fatigue assessments are compared. The difference in fatigue life prediction using the proposed approaches is compared; with at least 50% difference expected even within the guidelines from the same classification society. It is further discussed how to reduce the SCF with the objective to increase the fatigue life.
Flexible Riser Bending Hysteresis Influence on Bend Stiffener Response
Authors: Caire Marcelo
Published: September 2014

The bending stiffness response is an important parameter in the lifetime assessment of unbounded flexible risers. Its behavior is governed by interlayer friction mechanisms leading to a non-linear moment x curvature relationship that is highly dependent on the internal pressure. In order to investigate its influence on the critical bend stiffener hang-off region response, a detailed finite element analysis is carried out using a specialized tool for a short segment length of a selected 2.5″ ID riser cross section. Different internal pressures are numerically analyzed and the resulting local hysteretic bending response is then adjusted and directly incorporated into a global dynamic analysis tool that uses an equivalent elasto-plastic formulation with a hardening parameter that controls the behavior of the slippage mechanism. A fully coupled irregular wave dynamic analysis is then carried out and the flexible riser curvature distribution response in the bend stiffener region compared for different bending hysteresis models adopted.
Transient Hydrodynamic Forces on a Disconnectable Turret Buoy
Authors: Huang Z. J. , Walker K. M. , Lee S. , Thanyamanta W. , Spencer D.
Published: September 2014

For disconnectable turret-moored FPSOs, accurate prediction of turret buoy and FPSO motions during the buoy disconnection process is essential for safe operations. For deepwater high production rate systems, large size buoys are required to accommodate the large number of risers and heavy mooring legs. Analytical models of hydrodynamic forces on large size buoys must be verified before they are applied to motion predictions. To gain a better understanding of the transient hydrodynamic loads on the buoy and hydrodynamic interactions between the buoy and the hull during disconnection, we conducted a specially designed model test in a tow tank. In the model tests, both the buoy and the FPSO models were forced to oscillate by two independent actuators in calm water and in waves. Summary of test results, computed transient hydrodynamic forces from a simplified approach, a true time-domain transient hydrodynamic analysis based on instantaneous buoy positions, and computational fluid dynamics (CFD) results are presented in this paper.
Comprehensive Qualification Program for the Browse 24 Inch High Temperature Flexible Joint Prototype
Authors: Mekha Basim , Hawkey Ben , Patrick James , Pottorff Todd
Published: September 2014

Flexible Joints have been an essential part of many steel catenary risers (SCRs) as one of the main means for connecting SCRs to the floating facilities in deep water. Since 1994 when the first Flexible Joints were installed on the Augur Tension Leg Platform (TLP), many Flexible Joints have been designed and installed for 6 inch to 24 inch SCRs on all kinds of floating production facilities and in a range of water depths.

Woodside Energy Limited (Woodside), as operator of the Browse LNG Development on behalf of the Browse Joint Venture participants for their original Browse LNG Development concept (Browse to Kimberley subsea development and onshore processing concept), had contemplated using Flexible Joints as top termination units for the high temperature 24 inch Wet Gas Export SCRs. Woodside contracted Oil States Industries, Inc. (OSI) to design, manufacture and test a prototype 24 inch Flexible Joint that would meet the project’s stringent operational and fatigue requirements for 40 years design life. This high temperature 24 inch Flexible Joint was the largest Flexible Joint ever manufactured since its design required bellows and a thermal barrier.

A state-of-the-art qualification program for the high temperature 24 inch Flexible Joint was undertaken to demonstrate its feasibility for use on the 24 inch wet gas export SCRs for the Browse project in approximately 600m water depth. The Flexible Joint prototype was subjected to a comprehensive test program, including axial and rotational tests, hydrotests and a fatigue test, which was developed to cover all aspects of the Flexible Joint design and its components.

In this paper, the details of the high temperature 24 inch Flexible Joint qualification program will be presented with emphasis on the steps taken to successfully complete the program and the lessons learned from the challenges that were encountered. The paper will also provide a summary of the challenges and steps taken to complete the program which presented a unique opportunity to expand on the capability of the industry to go beyond what has been previously accomplished. The program was very challenging in all aspects but succeeded in achieving all of its goals.
Peculiarities of Multi-Legged Platform Operation in Ice Condition
Authors: Karulin Evgeny , Karulina Marina
Published: September 2014

A usage of multi-legged structures in ice conditions involves some peculiarities that should be taken into account both while designing the platform and while planning technological operations nearby it. In 2010–2013 a range of theoretical and experimental studies were performed at the Krylov State Research Centre, St. Petersburg, Russia. The work aimed to investigate main peculiarities of multi-legged structure interaction with ice, such as 1). mutual influence on ice action on each leg, 2) jamming of the inner space between legs and blocking the space between the front legs with ice floes, and 3) arisen yaw moments about the platform vertical axis due to unsymmetrical ice action on the legs. Three series of model tests with various multi-legged structures models were carried out in the Ice Basin. The presented in the paper main results show effect of key parameters on the interaction processes and on the ice action. During the tests the following parameters were varying: distance between the legs, ice drift speed and direction, broken ice concentration and the ice pieces size. Also, the paper contains results of numerical simulations of some tested scenarios in broken ice conditions. The numerical model is based on discrete element method, and it enables to extend a range of the investigations.
Experimental Investigation of Steel Coiled Tubes Performance Under Cyclic Bending
Authors: Lagat Christopher , Roufail Reem , Rasouli Vamegh , Evans Brian , Soe Soren
Published: September 2014

Research is currently being undertaken in Australia to develop new drilling technologies for deep mineral exploration. The Deep Exploration Technologies Cooperative Research Centre (DET CRC) has carried out a comprehensive review of the available drilling technologies in the market. Following the study, coiled tube drilling technology has been suggested as a faster and cheaper method than conventional pipe drilling. This is primarily due to its smaller footprint relative to the standard rotary method, ease of unit mobility, less operating personnel, faster rate of penetration, and faster rig up and rig down times. The steel coiled tubing technology has traditionally been used in the petroleum industry. While there have been several attempts to evaluate the performance of coiled tubes in the oil and gas industry, limited or no attempts have been made to assess its performance in deep hard rock mineral exploration drilling. Therefore, DET CRC is in the process of re-designing the coiled tube rig approach to enable fast and efficient drilling of deep micro-holes in hard rocks. Cyclic bending of the coiled tubing past the yield strength point of the material leads to progressive weakening of the tube, which accordingly leads to rapid reduction of the tube service life [1]. Hence fatigue is an important parameter that needs to be considered in material selection for coiled tube and rig design. A bending machine was designed and manufactured to evaluate the fatigue bending strength of conventional HSLA steel tubes. The machine is capable of measuring and recording the bending/flattening resistant forces of the tubes along with the number of bend/flatten events. It can also measure the strain applied on the tube if needed. In this study, several HSLA steel grades and thicknesses of coiled tubes were tested for fatigue bending strength. Fatigued and non-fatigued tubes had their mechanical property alteration tested using tensile test methods.

This paper presents the fatigue bending machine. The machine is designed to test most material types of coiled tubes. The paper also reports results of the cyclic bending experiments that were performed on selected grades and sizes of conventional HSLA steel coiled tubes. The paper complements and enhances the understanding of the performance of conventional coiled tube material under fatigue bending conditions.
Scale Tests of the GICON®-TLP for Wind Turbines
Authors: Adam F. , Myland T. , Dahlhaus F. , Großmann J.
Published: September 2014

The paper will present the preliminary design of the so called GICON® - Tension Leg Platform (TLP) as an innovative foundation concept for floating offshore wind turbines.

Preliminary results from model basin tests are also shared. This includes the currently ongoing research of comparing calculated and experimental data obtained through extensive wind and wave tank experiments with a scale model of an offshore wind turbine at the Maritime Research Institute Netherlands (MARIN) in June 2013. These tests have provided insights regarding the dynamic characteristics of the GICON®-TLP by analyzing the system’s response to different load cases.

The experiments included wind and wave loads, which represent three different sea states, each with three different directions of inflow. The chosen load cases correspond to the proposed location in the German Baltic Sea where the full scale prototype will be erected.
How Reliable Are the Current Testing Procedures for the Safety Assurance Against Crack Propagation in Seamless Gas Pipelines?
Authors: Nonn Aida , Erdelen-Peppler Marion , Wessel Waldemar , Mahn Denise
Published: September 2014

The worldwide growing energy demand with the exploration of new gas fields has promoted the development of high toughness seamless pipeline steels which should sustain the increasing demands resulting from the complex loading situations. One of the most important prerequisites for safe installation and operation of long distance gas transmission pipelines is the detailed knowledge and characterization of their fracture performance for specific applications. However, recent industry experience has revealed concerns related to the limitations and reliability of current test methods for brittle-to-ductile transition evaluation. Regarding the transition temperature evaluation, the critical issues involve Drop-Weight Tear Testing (DWTT) and full-scale West-Jefferson (WJ) test applied to the smaller pipes with diameter less than 500mm. The DWTT leads frequently to invalid results in terms of abnormal fracture appearance and inverse fracture occurrence. It is still not clear if this behavior is only owed to a testing effect, which material characteristics cause it and how far it reflects the full-scale behavior. Similar observations were made for the West-Jefferson tests, which could not be assessed in the standard manner either. Again, the question was towards testing effects and the behavior of the pipeline transporting gaseous media remains unanswered. Therefore, this paper aims at identifying open questions on basis of a literature study and own experimental results and showing possible ways forward in demonstrating safety in design against propagating fracture.
The Effect of Nickel on Fracture Toughness at Low Temperature for Hydrogen Pre-Charged Steel Samples
Authors: Félix Lorenzo Marzari , da Fonseca José Eduardo Ferreira , Kwietniewski Carlos Fortis , Borges Marcelo Favaro , Haag Jefferson , Dalpiaz Giovanni
Published: September 2014

Production of oil and gas in the Brazilian pre-salt will face several technical challenges. One of them that is a major concern is the presence of CO2 in high concentrations. Indeed, since the local regulatory agency requires increasingly stricter recommendations, it seems unlikely the possibility of simply release CO2 in the atmosphere. Besides that, as it happens since the 1970’s in USA, enhanced oil recovery (EOR) using CO2 might be a great opportunity and has to be considered. If that is the case, as soon as CO2 is separated from the oil in the top side, it has to be pressurized and transported through pipelines into the reservoir. The material of choice for that pipeline would be API 5L X65 since it is widely used and most available. The working pressure can reach up to 500 bar or more and it is an important issue to consider the fact that a suddenly depressurization due to a crack in the pipeline or a failure in a fastener or flange can promote a local abrupt decrease in temperature down to −60°C or even lower. That concern in addition to the fact that cathodic protection has to be used in the pipeline for corrosion control has the potential to produce embrittlement due to a combination of low temperature and hydrogen charging and ultimately lead to a catastrophic failure. The use of nickel to improve steel toughness has been used extensively and some grades or classes of nickel containing steels have been created for special applications. The aim of this work is to evaluate whether a nickel containing steel would be a more suitable material to manufacture high pressure CO2 transporting pipelines, taking in account a possible leak and the corresponding effect of a local and abrupt drop in temperature on the fracture toughness of the material. The effect of hydrogen due to cathodic protection on fracture toughness is also evaluated. The results indicated that under the experimental conditions and materials examined here the 9%wt nickel steel is not sensitive to low temperature and hydrogen, practically maintaining its original fracture toughness.
Numerical Modeling of Unbonded Flexible Risers Under Combined Symmetrical Loads
Authors: Ren Shaofei , Tang Wenyong , Xue Hongxiang , Hu Zhe
Published: September 2014

This paper presents a numerical method to predict the behavior of unbonded flexible risers under symmetrical loads, and takes an eight-layer unbonded flexible riser for the case study. In order to accurately simulate geometric properties of the riser and contact interaction between layers, carcass and zeta layers are modeled as the actual complicated cross-sections, and all layers are modeled by solid element, both contact and friction between layers are taken into consideration. ABAQUS/Explicit is adopted to avoid convergence problem caused by geometric and contact nonlinearities, mass scaling is adopted to avoid long computational time caused by the very detailed finite element model of carcass and zeta layers. Load cases considered in this paper are external pressure coupled with axial tension, axial compression under different lay angles of helical strips and boundary conditions. The results show that numerical results agree well with theoretical results, lay angles of tensile armor layers have a great impact on the axial displacement, but boundary conditions have little effect on the axial displacement.
Reducing Roll Motion by Passive Free Surface Tanks
Authors: Nielsen Christian S. , Nielsen Ulrik D.
Published: September 2014

Roll stabilisation of motorised vessels plays an important part in reducing passenger discomfort and increasing safety and cargo capacity. Passive free surface tanks are considered a low-cost stabilising method, which is efficient at all speeds without increasing hull resistance.

In this study, a mathematical model for evaluating the performance of a passive free surface tank is established. This is done by coupling a roll model to a fluid flow model. As a numerical example, the seakeeping abilities of a container vessel are evaluated. The necessary methods for performing the simulation are presented and the design of a free surface tank is explained.

The effects of the passive free surface tank are evaluated and a significant damping effect is observed, particularly in cases with resonant roll.
Theoretical Investigation on Ice Resistance Prediction Methods for Ships in Level Ice
Authors: Myland Daniela , Ehlers Sören
Published: September 2014

The assessment of the ship performance in ice covered waters has become more and more important in view of the increased interest in Arctic field logistics and transportation. The performance of ice-going or ice breaking ships is usually defined by their ability to proceed in uniform level ice, where good performance means low ice resistance, high propulsion efficiency and continuous ice breaking. In order to assess the ice breaking performance in an early design stage, model tests may be executed or several theoretical methods may be applied to predict the ice resistance may be applied. Due to the physical nature of model tests, all processes, i.e. forces contributing to ice resistance are considered. Thus, the execution of model tests is still the most reliable method to determine the ice resistance. But with regard to the high costs of model tests there is continued demand to gain knowledge on the reliability of theoretical prediction methods. The applicability of the method of choice depends on the underlying assumptions of the method itself and thus the method’s capability to predict and consider physical phenomena of interest.

In this paper model tests are used to evaluate the influence of hull shape parameters and ice conditions on the breaking process, i.e. the ice resistance and the ship performance. Based on the knowledge gained a systematic comparison of existing, representative ice resistance prediction methods is carried out. The methods considered are state-of-the-art techniques which the original publications introduced with sufficient information to allow for their use in this comparison. It focuses on the suitability of the existing methods as engineering tools for the prediction of different components, as well as the total ice resistance itself. The incorporation of the ice resistance contributions in the different prediction methods is presented and differences are identified. On this basis an assessment of the assumptions and simplifications of these different numerical methods is outlined.
A Coupled-Mode Method for Acoustic Propagation and Scattering in Inhomogeneous Ocean Waveguides
Authors: Belibassakis K. A. , Athanassoulis G. A.
Published: September 2014

We consider the problem of acoustic propagation and scattering in inhomogeneous waveguide governed by the Helmholtz equation. We focus on an ideal, cylindrically symmetric ocean waveguide, limited above by an acoustically soft boundary modelling the free surface, and below by a hard boundary modelling the impenetrable seabed with general bottom topography. The wave field is excited by a monochromatic point source, and thus, the present solution is equivalent to the construction of the Green’s function in the inhomogeneous domain. An improved coupled-mode method is developed, based on an enhanced local-mode series for the representation of the acoustic field, which includes an additional mode accounting for the effects of the bottom slope and curvature. The additional mode provides an implicit summation of the slowly convergent part of the series, rendering the remaining part to converge much faster, pemitting truncation of the modal expansions keeping only a few evanescent terms. Using the enhanced representation, in conjunction with an appropriate variational principle, a system of coupled-mode equations on the horizontal plane is derived for the determination of the complex modal-amplitude functions. Numerical results are presented including comparisons with analytical solutions illustrating the role and significance of the additional mode and the efficiency of the present coupled-mode tmodel, which can be naturally extended to treat propagation and scattering problems in three-dimensional, multi-layered ocean acoustic waveguides.