bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Free Surface Nonlinear and Fluid Viscosity on Fluid Resonance in the Narrow Gap
Authors: Jiang Sheng-chao , Zou Li , Sun Tie-zhi , Liu Chang-feng
Published: October 2017

Numerical simulations are carried out for gap resonance problem between two side-by-side non-identical boxes. The linear potential model over-predicts the resonant amplitude in the narrow gap because it not only neglects the energy dissipation due to vortical motion, but also neglect the nonlinearity due to free surface. More relative energy are reflected with the increase of incident wave amplitude, leading to the decrease of relative resonant amplitude and relative energy dissipation in the narrow gap at resonant frequency. When the incident wave frequency is outside a little band to resonant frequency, relative energy dissipation becomes the dominant factor for the decrease of relative wave amplitude in the narrow gap with the increase of incident wave amplitudes. In a word, both the free surface nonlinearity and fluid viscosity play the important, but different, roles on wave resonances in the narrow gap.
Soil Structure Interaction Analysis of a Berthing Structure Under Lateral Loading-By Numerical Approach
Authors: Kavitha Perumalsamy , Sundaravadivelu Ranganathan
Published: October 2017

In coastal and offshore structures, the predominant forces leading to lateral movements are mainly due to waves, currents, winds, berthing forces, mooring forces and lateral earth pressure due to unstable slope as a result of dredging or siltation etc. Due to relative movement between the piles and the soil, the load transfer to pile is a complex soil interaction problem. It is a two way problem and should be solved by structure-soil model with appropriate load displacement characteristics of both the structure and the soil. Pile-soil interaction analysis is carried out by numerical methods based on iterative techniques of equilibrium of forces and moments, based on relative stiffness of pile-soil system. Conventionally API guidelines and Vesic equation are used to analyze the laterally loaded piles. The study of laterally loaded pile in active soil wedge requires a proper assessment of soil structure interaction phenomenon involving the interaction between pile surface and the surrounding soil. The instability of soil wedge can occur due to self-weight, surcharge load, dredging, siltation and earthquake force. The soil structure interaction problem of piles located in active soil wedge has rarely been approached. Laterally loaded piles are analyzed by methods derived from the classical beam on elastic foundation mode in which the soil support is approximated by a series of independent elastic spring. The soil spring constants estimated from API guidelines and Vesic equations are not suitable for piles located in active soil wedge. Hence in this paper, a numerical study is carried out for a berthing structure in dense sand using PLAXIS 3D and STAAD Pro, in order to study the behaviour of piles in active soil wedge.
Fatigue Performance of Friction Welds Manufactured Both in Air and Underwater
Authors: Manteghi Siak , Gibson Dave , Johnston Carol
Published: October 2017

Friction welding is being performed offshore in environments where arc welding may be difficult and where fatigue performance is critical. Friction welding underwater with Remotely Operated Vehicles (ROVs) can greatly reduce the cost of a project compared with using divers and arc welding because the support vessel, which is the major cost component in such an operation, is smaller. This paper describes two different programs of experimental work in which the fatigue endurance of friction welds were found to be better than that which could be expected from arc welded joints of similar geometry. The first program involved experimental work done with 25mm diameter steel bars. It found that, in the as-welded condition, friction welds have high fatigue strength. Residual stress measurements showed that this was due to a beneficial residual stress distribution in which compressive stresses are present at the surface adjacent to the failure site. Further evidence of this was obtained by subjecting some specimens to thermal stress relief. The fatigue strength of the stress relieved specimens was reduced compared with the as-welded joints but nevertheless the fatigue strength of these specimens was still high. The second program involved fatigue tests on friction stud welds in which the friction welding equipment was deployed offshore by divers or ROVs. The test specimens were made up of 19mm diameter studs friction welded onto structural steel plate. As with the first program, the specimens showed high fatigue endurance with results approximating to a DNV Class C1 curve. In some of the tests, the studs were preloaded in tension and results from specimens that were preloaded to the correct value specified for the joint were all stopped as run-outs, with specimens remaining unbroken.
Quasi-Static and Dynamic Deformation of Polymer Coated Pipes
Authors: Vestrum Ole , Kristoffersen Martin , Langseth Magnus , Børvik Tore , Polanco-Loria Mario A. , Ilstad Håvar
Published: October 2017

Offshore pipelines are occasionally subjected to accidental impact loads from trawl gear or anchors, which may damage the pipeline. This study reports the results of material and component tests carried out on offshore steel pipes and an adhering polymer coating. The polymer coating is primarily applied for corrosion protection and thermal insulation. Despite not necessarily being designed for it, the polymer coating does have some structural capacity, and it is this capacity that is the main topic of investigation herein. In design codes and guidelines, coating is traditionally not accounted for when determining the energy absorbed by a pipeline during impact. This makes the estimates provided overly conservative. The goal of this experimental work is then to investigate whether a typical polymer coating makes any significant contribution to the energy absorption properties of a pipeline cross-section during impact. To this end, both dynamic and quasi-static denting tests of full-scale pipe cross-sections are carried out. All pipes tested have a length of approximately 1 m. The sharpest indenter from the guidelines is used, as a sharper indenter is more likely to penetrate compared with a blunter one. Based on the tests, the polymer coating can absorb a notable part of the kinetic energy delivered to the system. More tests with different coating and pipe thicknesses are needed to quantify this effect.
Transverse Deformation of Pressurised Pipes With Different Axial Loads
Authors: Kristoffersen Martin , Børvik Tore , Langseth Magnus , Ilstad Håvar , Levold Erik
Published: October 2017

Pipelines residing on the seabed are exposed to various hazards, one of them being denting, hooking and release of the pipeline by e.g. anchors or trawl gear. As a pipeline is displaced transversely in a hooking event, an axial tensile load resisting the displacement builds up in the pipeline. This study examines the effect of applying three different axial loads (zero, constant, and linearly increasing) to a pipe while simultaneously deforming it transversely. A fairly sharp indenter conforming to the prevailing design codes was used to deform the pipes. These three tests were repeated with an internal pressure of about 100 bar for comparison. Adding an axial load appeared to increase the pipe’s stiffness in terms of the force-displacement curve arising from deforming the pipe transversely. The internal pressure also increased the stiffness, and produced a more local dent in the pipe compared with the unpressurised pipes. All tests were recreated numerically in finite element simulations. Generally, the results of the simulations were in good agreement with the experiments.
Critical Factors Affecting the Capacity of Cylindrical Grouted Connections in Offshore Energy Structures
Authors: Shamsuddoha Md , Hüsken Götz , Baeßler Matthias , Kühne Hans-Carsten , Thiele Marc
Published: October 2017

Current trend suggests that global energy consumption will increase in the future. This growing energy demand and advancement of technology lead to explore all potential offshore fossil and non-fossil energy sources, necessitating erection of exploration and production structures, rigs, platforms and towers, which are susceptible to adverse environmental conditions along with their maintenances. Cylindrical grouted joints provide suitable connections between steel substructure and foundation in these offshore platforms and wind structures especially monopiles for ease of installation. However, these are composite connections with exterior sleeve, interior pile and infill grout. The capacity of these connections is affected by number of factors. The literature over last four decades by numerous researchers has shown the development of these connections with increasingly higher capacities and influences on these capacities due to various factors. This paper provides a comprehensive review on the factors affecting the connection capacity along with technical challenges for the future. Critical aspects and shortcomings of the current connection systems and potential solutions may be sought after for these issues are also discussed.
Development of Fatigue Design Standards for Marine Structures
Authors: Lotsberg Inge
Published: October 2017

Fatigue design standards for offshore structures became needed with development of offshore structures in harsh environments like the North Sea during the 1970s. The Ultimate Limit State had earlier been the most significant design requirement for similar platforms in the Mexican Gulf being less utilized with respect fatigue.

The need for fatigue design of ship structures became increased as more high strength steel was being used in these structures during the 1970s. The analysis method for long term loading and assessment of fatigue capacity has been improved over the years and this has also resulted in need for new and revised design standards.

New types of structures and structural components have been developed like tension leg platforms and support structures for wind turbines. These structures are subjected to significant dynamic loading such that fatigue design becomes the main issue and relevant fatigue design standards are needed.

Fatigue assessment of fixed offshore structures in the North Sea has been standard practice since the 1970s. Fatigue of floating platforms became a requirement after the accident with the Alexander Kielland platform in 1980. Later new types of structures have been installed in the North Sea such as tension leg platforms and floating production ships where fatigue has been an important part of the design. A further challenge with respect to fatigue came with the development of support structures for wind turbines to be installed in the sea.

This paper gives an overview of the development of fatigue design standards for marine structures over the last 40 years. This includes the significance of refined calculation of long term stress range distribution, calculation of hot spot stress, size effect and effect of mean stress effect on fatigue design of ship structures.
On the Axial Holding Capacity of Torpedo Bases in Clay
Authors: de Sousa José Renato M. , Genzani Rachel G. B. C. , Porto Elisabeth C. , Borges Alexandre T. , Nogueira Emmanuel F. , Ellwanger Gilberto B.
Published: October 2017

A torpedo base is a type of conductor casing that embeds into the seabed mainly by free fall using its own weight as driving energy. One of the advantages of this concept is to install the conductor casing before the dynamic positioned (DP) drillship arrival at the location. This reduces the time of the well drilling leading to significant cost saving. However, the need to withstand the challenging loads of the ultra-deep water scenarios pushed the typical torpedo base design to its limit and, consequently, modifications to its original geometry and more accurate design models are needed. Therefore, in this work, a new torpedo base, designed to sustain high axial loads in very soft clays, is analyzed with a three-dimensional finite element (FE) model. This model accounts for the setup-effects of the soil with the use of a previously proposed analytical approach to estimate the stress state of the soil at any time after the installation of the base. The results obtained indicate that the axial holding capacity of the base varies along time. The holding capacity increase rapidly at the beginning of the installation, but this rate reduces after the first days. Depending on soil characteristics, full axial capacity may be reached more than one year after the installation of the base. Moreover, the use of more than four fins welded to the shaft of the conductor casing modifies the shear zone along the base, but does not contribute to a significant increase in the axial holding capacity.
Analysis of Thermally Induced Stresses for Effective Remediation of Lost Circulation Through Drilling Induced Fractures
Authors: Wang Ze , Nielsen James , Chen Yuanhang
Published: October 2017

Lost circulation events during drilling are associated with the initiation of new fractures or the reopening of pre-existing fractures from the wellbore. Practices frequently implemented to combat lost circulation, including wellbore strengthening (WBS), are employed by plugging and propping the newly induced and pre-existing fractures to limit further propagation from the wellbore. One observation that was noted is that there is a discrepancy in the performance of lost circulation prevention methods for different temperatures between the fluids used and the surrounding formation. However, it is not yet fully understood how temperature affects pre-existing fractures and newly initiated fractures during these practices.

This study discusses how the stress state around fractures is influenced by a change in temperature considering fluid flow into a formation through drilling induced fractures. A finite element analysis with a coupled thermal-hydrologic-mechanical processes simulation was established to demonstrate how the stress redistributes around the fractures while considering fluid invasion and heat transmission. The results of the changing thermal stress around the fractures under various scenarios have been investigated. Included in our analysis is the potential risk of reinitiating fractures. The conclusions from this study indicate that a large temperature difference between the formation rock and fluid flow into the fractures could be a major concern when trying to prevent fracture propagation and control lost circulation events. It could potentially diminish the effect of enhanced hoop stress provided by WBS and fracture plugging by lost circulation materials. Such information is important to facilitate a successful management of lost circulation by taking into accounts the thermal impact of different lost circulation prevention approaches. The results from this paper are particularly important when a large temperature difference exists between circulating fluids and surrounding rock as commonly seen in HPHT and deep water wells.
Numerical Investigation of Wave Kinematics Inside Berm Breakwaters With Varying Berm Geometry Using REEF3D
Authors: Sasikumar Athul , Bihs Hans , Kamath Arun , Musch Onno , Arntsen Øivind A.
Published: October 2017

Harbours are important infrastructures for an offshore production chain. These harbours are protected from the actions of sea by breakwaters to ensure safe loading, unloading of vessels and also to protect the infrastructure. One of the important hydrodynamic processes in these regions is the interaction of water waves with permeable breakwaters such as rubble mound breakwaters or berm breakwaters. It is important to study the wave-breakwater interactions in order to have an optimal design of these structures. In current literature, research regarding the design of these structures is majorly based on physical model tests. Empirical formulations are derived based on these test, which can have a relatively narrow range of applicability. In this study a new tool, a three-dimensional numerical model is introduced. Physical and numerical models have limitations that can restrict their independent use. A combined use of both can lead to different forms of improvements: being able to model problems that cannot be modelled by either physical or numerical modelling alone; increasing quality at the same cost or obtaining the same quality at reduced cost.

In this study, the open-source CFD model REEF3D is used to study the design of berm breakwaters. The model uses the Volume averaged Reynolds Averaged Navier-Stokes (VRANS) equations to solve the porous flows. At first the VRANS approach in REEF3D is validated for flow through porous media. A dam break case is simulated for two different porous materials. Comparisons are made for the free surface both inside and outside the porous medium. The numerical model REEF3D is applied to show how to extend the database obtained with purely numerical results, simulating different structural alternatives for the berm in a berm breakwater. Different simulations are conducted with varying berm geometry. The influence of the berm geometry on the pore pressure and velocities are studied. The resulting optimal berm geometry is compared to the geometry according to empirical formulations.
Residual Stresses in Strength Mismatched Welded Pipes
Authors: Mirzaee-Sisan Ali , Wang Junkan
Published: October 2017

It is commonly understood that residual stresses can have significant effects on structural integrity. The extent of such influence varies and is affected by material properties, manufacturing methods and thermal history. Welded components such as pipelines are subject to complex transient temperature fields and associated thermal stresses near the welded regions. These thermal stresses are often high in magnitude and could cause localized yielding around the deposited weld metal. Because of differential thermal expansion/contraction episodes, misfits are introduced into the welded regions which in turn generate residual stresses when the structure has cooled to ambient temperature.

This paper is based on a recently completed Joint Industry Project (JIP) led by DNV GL. It briefly reviews published experimental and numerical studies on residual stresses and strength-mismatched girth welds in pipelines. Several Finite Element Analysis (FEA) models of a reeling simulation have been developed including mapping an initial axial residual stress (transverse to the weld) profile onto a seamless girth-welded pipe. The initial welding residual stress distribution used for mapping was measured along the circumference of the girth welds. The predicted residual stresses after reeling simulation was subsequently compared with experimental measurements.
An Efficient Convex Formulation for Model-Predictive Control on Wave-Energy Converters
Authors: Zhong Qian , Yeung Ronald W.
Published: October 2017

Model-Predictive Control (MPC) has shown its strong potential in maximizing energy extraction for Wave-Energy Converters (WECs) while handling hard constraints. As MPC can solve the optimization problem on-line, it can better account for state changes and reject disturbances from the harsh sea environment. Interests have arisen in applying MPC to an array of WECs, since researchers found that multiple small-size WECs are more economically viable than a single large-size WEC. However, the computational demand is known to be a primary concern for applying MPC in real-time, which can determine the feasibility of such a controller, particularly when it comes to controlling an array of absorbers.

In this paper, we construct a cost function and cast the problem into a Quadratic Programming (QP) with the machinery force being the “optimizer,” for which the convexity can be guaranteed by introducing a penalty term on the slew rate of the machinery force. The optimization problem can then be solved efficiently, and a feasible solution will be assured as the global optima. Constraints on the motion of the WEC and the machinery force will be taken into account. The current MPC will be compared to others existing in literature, including a nonlinear MPC [1] which has been applied in wave-tank tests. The effects of constraints on the control law and the absorbed power are investigated. Performances of the WEC are shown for both regular and irregular wave conditions. The current MPC is found to have good energy-capture capability and is able to broaden the band-width for capturing wave energy. The reactive power required by the PTO system is presented. The additional penalty term provides a tuning parameter, of which the effects on the MPC performance and the reactive power requirement are discussed.
Composite Coiled Tubing for Extended Reach in Horizontal Oil Wells
Authors: Costache Andrei , Berggreen Christian
Published: October 2017

Conventional steel coiled tubing cannot reach along the entire length of very long horizontal oil wells. A lighter and more buoyant coiled tube is made possible using composite materials. The high stiffness to weight ratio of fiber reinforced polymers, coupled with a lower coefficient of friction, has the potential of greatly extending the reach in horizontal oil wells. This study shows how to design composite coiled tubing and gives a comprehensive discussion about the most influential parameters. Several solutions, using glass-fiber and carbon are considered. Finite element models are used to calculate the buckling loads and the corresponding interlaminar stresses. The very positive results obtained during this study show that composite coiled tubing systems are vastly superior to their steel counterparts, and that in the future, these will become the new industry standard.
Development on Most Suitable Removal Method of Radioactive Cesium Adsorbed on Ocean Sludge by Using Fine Bubble and Activating Microorganisms
Authors: Kyoichi Okamoto , Takeshi Toyama , Tomoe Komoriya
Published: October 2017

Fukushima nuclear accident of March 11, 2011, soil and water had been contaminated by radioactive cesium. Moreover, radioactive cesium was found in the ocean sludge in Tokyo Bay flowing from rivers. Cesium which is adsorbed to the sludge cannot be easily removed. One of the authors developed decomposition and purification system, a circulation-type system by fine bubbles, that is, by creating aerobic state, aerobic bacteria are activated resulting to decomposition and purification of ocean sludge. Based on the hypothesis that radioactive cesium is adsorbed on the surface of the sludge deposition. It is considered that cesium can be eluted after decomposing the deposited sludge. Once the cesium is eluted in the water, it can fix to a mineral such as zeolite. Eluting and fixing cesium adsorbed on sludge takes so much time. In this case, the concept of removing the left sludge by flocculation method and then followed by coagulating sedimentation method is studied. In this study, our objects are to show the effectivity and efficiency of using flocculation and coagulating sedimentation in removing radioactive cesium. As the results, we pointed out this method is very good.
Manoeuvring Validation Analysis of the M/F Landegode
Authors: Ross Andrew , Fathi Dariusz
Published: October 2017

A framework is described in which a manoeuvring simulator can be built up from model tests. It is applied to a modern LNG powered RORO ferry, the M/F Landegode, with model tests and computational results being used to make full-scale predictions. These predictions are tested against full-scale manoeuvring performance measurements, and are shown to be of a high quality.
Offloading Operability of Small Scale AG FLNG With Side-by-Side Moored Small Scale LNG Carrier in Offshore West Africa
Authors: Kim Mun-sung , Morilhat Eric , Nguyen X. C. , Kim Bo-hee , Jang Jung-moon , Jeong Hyun-su
Published: October 2017

This study describes one of the technical solutions for Small Scale FLNG (SSFLNG)[1] development specifically designed to monetize Associated Gas (AG) of producing oil fields located within convenient distance of an existing LNG Plant or Port with LNG storage facility. Limited production capacity combined with short range small scale LNG carriers (SSLNGC), provide a cost effective means for LNG production. Ship to ship off-loading operation by loading arm has been considered in AG SSFLNG. Produced LNG is to be off-loaded from the SSFLNG to side-by-side moored SSLNGC. Relative motion and dynamic load acting on loading arm system in side-by-side mooring arrangement is one of key factors to estimate the offloading operability of the AG SSFLNG. In this paper, a numerical two-body motion analysis for the side-by-side moored SSFLNG in frequency- and time-domain is carried out.

Also, the basic engineering work is carried out for the marine loading arms (MLA). Since the MLA reacts approximately as a linear system, it is calculated by a full spectral RAO analysis for each of the worst load cases issued from the spectral ranking. All loads and stresses inside the MLA are verified in accordance with EN1474-1[2] for the situations identified in the previous step. A high level fatigue analysis focused on the cryogenic swivel joints is carried out.

Based on the numerical calculation for relative motion in side-by-side moored FLNG, we have been performed structural assessment for MLA in several environment conditions. The structural integrity of both MLA and the LNGC manifold are validated during offloading for Offshore West Africa.
Numerical Simulation of Dynamic Shoreline Changes Behind a Detached Breakwater by Using an Equilibrium Formula
Authors: Lee Jung Lyul , Hsu John Rong-Chung
Published: October 2017

Salient and tombolo are common features found in the lee of detached breakwaters. The empirical parabolic bay shape equation (PBSE) can be applied when their planform is fully developed, whereas numerical model is required to simulate the dynamic shoreline evolution prior to the planform reaching static equilibrium. This paper reports the excellent performance of PBSE through the comparison with labaratory results and the development of a numerical model for dynamic shoreline change that utilizes the concept of PBSE and equilibrium beach profile. Formulation proposed for sediment transport rate is theoretically compared with that in GENESIS. The governing equation for the combined shoreline response model is based on the one-line beach model, which includes shoreline changes owing to longshore and cross-shore sediment transport. Finally, numerical results reveal, by comparing with an experimental case in the laboratory, that the model is adequate to successively simulating the dynamic evolutions of the shoreline behind a detached breakwater.
Motion Performances of a 5 MW VAWT Supported by Spar Floating Foundation With Heave Plates
Authors: Liu Liqin , Guo Ying , Jin Weichen , Yuan Rui
Published: October 2017

The VAWT (vertical axis wind turbine) has advantages in the development of large-scale offshore wind power. This paper presents a motion study of a 5 MW floating VAWT composed of the Φ type Darrieus wind turbine and a truss spar floating foundation with heave plates. The surge, heave and pitch motion equations considering the effects of retardation function of the floating VAWT were established and solved numerically. Several load cases were carried out to analyze the motion performances of the floating VAWT. The results show that the wind forces have minimal influence on the heave motions of the floating VAWT, while they obviously increase its surge and pitch mean displacements. For LC3, the surge, heave and pitch frequencies of the floating VAWT are dominated by the wave frequencies, and the 2P (twice-per-revolution) response of pitch motions is not significant. For LC4, the 2P response of pitch motions of the floating VAWT are more significant than LC4.
Numerical Investigation of Propeller Noise From Tip Vortex Cavitation
Authors: Zhu Wencai , Gao Hongtao , Song Yuchao
Published: October 2017

In this paper, the Mixture multiphase flow model and the Schnerr-Sauer cavitation model are used to simulate the tip vortex cavitation of the propeller and then to predict the sound pressure level of the propeller. The structured and unstructured grids are adopted in stationary domain and rotating domain, respectively. The moving reference frame model is used in the rotating domain. The open water characteristics of the propeller are calculated by the SST k-ω turbulence model and the isosurface of vorticity magnitude is clearly presented. The results of the calculation are compared with the non-cavitating condition. It shows that the efficiency of the propeller is reduced when the tip vortex cavitation appears. The tip vortex cavitation will lead to increases both in the overall sound pressure in time histories and in the sound pressure level in the frequency domain.
The Consequence Method: An Approach for Estimating Roll Damping in Transportation Fatigue Analyses
Authors: Bøe Tormod , Yang Limin , Falkenberg Erik
Published: October 2017

In order to compute fatigue damage during offshore transports it is necessary to assume a description of the sea states encountered during the voyage. In recent years, it has become a common approach to apply directional long-term scatter diagrams for the transportation route, taking into account vessel speed, course and time of year for the departure.

An important contribution to the transportation fatigue damage is usually the wave induced inertia load. For ship shaped vessels additional viscous damping needs to be included in order to estimate correct roll response. However, since viscous roll damping is non-linear, correct estimation of fatigue damage can only be obtained by computing partial damage for all individual sea states in the scatter diagram. This becomes very time-consuming and is usually not done.

Instead, the roll damping level is tuned to match typical mean sea states in the scatter diagram. The roll damping will then be too low for higher sea states and too large for smaller sea states. When choosing the roll damping level, the aim should be to obtain an overall error in transportation fatigue damage which is minimized.

This paper describes a method to estimate a representative viscous roll damping level for transportation fatigue analyses.
Visual Image Correlation Compared to Discrete Instrumentation for Measurement of Compressive Strains for Strain Based Design
Authors: Bergman Jason , Liu Ming , Timms Chris
Published: October 2017

Strain-based design philosophies have been developed to ensure safe pipeline operation through regions of slope instability, seismic activity or discontinuous permafrost while extending the life expectancy of the pipeline in those zones. Strain-based design methodology typically involves a comparison of the strain demand (estimated conservatively using numerical pipe-soil interaction analysis techniques) to the strain capacity (predicted using experimentally benchmarked models).

This paper presents a comparison of measurement techniques for laboratory testing of critical compressive strain capacity (CCS). The CCS is defined as the strain coinciding with the peak bending moment, averaged over a gauge length often selected as one pipe diameter across the buckle location. As explored in previous work [1], the three most common methods to measure strain on the specimen intrados, with respect to bending, include 1) direct measurement using strain gauges on the intrados with respect to bending, 2) calculation of CCS from the output of discrete instrumentation (DI) including strain gauges and inclinometers; and 3) direct measurement of surface strains using Visual Image Correlation (VIC) techniques.

In 2015 and 2016, the Centre for Reliable Energy Systems (CRES) and C-FER Technologies 1999 Inc. (C-FER) collaborated on a series of full-scale experiments (performed by C-FER) and detailed finite element analysis (FEA) (performed by CRES) intended to assess and understand the effect of various anomalies on the strain capacity of line pipe. To facilitate comparison of the DI strain measurement method and the newer VIC method, these tests were conducted using both methods. The results demonstrate that the VIC technique can provide a more complete measure of the strain field and greater accuracy in cases where uneven strain distributions challenge the assumptions associated with DI methods. High level test data is presented and one test displaying the discrepancy between VIC and DI results is described. Finite element modelling, employed to explore the digression observed between the two strain measurement methods, is also presented and the comparative results of the two strain measurement techniques are discussed.
Nonlinear Ocean Wave Models and Laboratory Simulation of High Seastates and Rogue Waves
Authors: Yim Solomon C. , Osborne Alfred R. , Mohtat Ali
Published: October 2017

With the increasing demand for marine structures, including ships and wave energy devices, to operate in energetic, high seastates, the need for modeling and simulation of nonlinear ocean wave fields in large-scale wave basins is becoming essential. In response to this demand, a number of large-scale wave basins have been placed into operation over the years and larger and more sophisticated new ones are under planning and construction. In this article, the current state of practice and technical issues in modeling and simulation of high seastate ocean waves are summarized. A novel methodology for quantitative evaluation of the suitability of competing linear and nonlinear wave theories for a given wave field with multi-spatial measurements is presented. Preliminary results of an on-going study on wave modeling and analysis of measured data from a wave simulation performance study of the Oregon State University directional wave basin, using nonlinear wave theory (e.g. the nonlinear Schrödinger equation), nonlinear Fourier analysis and inference to the existence of rogue waves, are presented. Suggestions on future development of nonlinear wavemaker theories and numerical modeling and simulation of large-scale wave basin nonlinear wave generation are proposed. The article concludes with some observations and remarks on the importance of using an appropriate wave theory to determine the existence of nonlinear coherence structures, including breathers and rogue waves.
Development of the Hywind Concept
Authors: Skaare Bjørn
Published: October 2017

An overview of the development of the Hywind concept is presented with focus on numerical analysis tools, model and full scale experiments, and control systems.

Several analysis tools have been developed and matured over several years, and verified against model and full scale experiments.

Special purpose control systems have been developed for the Hywind concept for the purpose of stabilization of floater motions as well as motion control.
Simulating Large-Scale Fatigue Test Specimens for Offshore Wind Monopiles
Authors: Brennan Feargal , Kolios Athanasios , Tavares Isaac
Published: October 2017

Size effects are extremely important to understand and accounting for their inclusion in fatigue tests is imperative in order to produce meaningful results. This can however be problematic as in dealing with very large offshore structural details and sections, testing to destruction can involve extremely large loads and gripping arrangements that can be cost prohibitive. It is therefore important to be able to simplify test specimens so that the local detail is retained without losing important size influences.

This paper describes an investigation into whether or not extracted specimens from actual Offshore Wind Monopile Sections are in fact the best choice for fatigue testing. The results are analysed and a recommendation is made for future test programmes involving offshore wind monopile and tower applications.
On the Application of Structural Reliability Analysis
Authors: Hørte Torfinn , Sigurdsson Gudfinnur
Published: October 2017

Structural Reliability Analysis (SRA) is a useful tool in structural engineering. Uncertainty in input parameters and model uncertainties in the analysis predictions are explicitly modelled by random variables. With this methodology, the uncertainties involved are handled in a consistent and transparent way. Compared to a deterministic analysis, SRA provides improved insight in how the various uncertainties involved influence the results. The main results from SRA is the calculated probability of structural failure, but other useful results such as uncertainty importance factors and design points being the most likely combination of all variables at failure represent helpful information.

The present paper illustrates some the features using SRA for two different types of application. The first application is the use of SRA as a tool for code calibration and the second shows the application of SRA to a problem where common practice is likely to be rather conservative and therefore leading to unacceptable results, but where the degree of conservatism is not known.

Two examples are chosen to illustrate code calibration; i.e. hull girder ultimate limit state (ULS) for tankers and ULS for mooring design in the ULS for floating offshore vessels. Code calibration involves both SRA and design analysis following the code. It is shown how the design analysis can be modified in order to better reflect a chosen target reliability level across a selected set of test cases representative for what the code should cover.

Fatigue of subsea wellhead systems is selected as an example of a special case when application of existing rules may lead to unsatisfactory results which are likely to be rather conservative. It is shown how results can be presented in terms of the accumulated probability of fatigue failure as a function of time. This may be a more suitable basis for decision making than a calculated fatigue life from a standard analysis. It is also illustrated how importance factors from the SRA can be used as guidance on how to prioritize effort in order to improve prediction of the fatigue damage.

The present paper is not intended to be detailed in all input and analysis methodology, but draw the attention towards the possibilities and benefits of applying SRA in structural engineering, where the examples are used to illustrate this potential.
Improvement of Ohmic contacts on Ga2O3 through use of ITO-interlayers
Authors: Carey Patrick H. , Yang Jiancheng , Ren Fan , Hays David C. , Pearton Stephen J. , Kuramata Akito , Kravchenko Ivan I.
Published: October 2017

The use of ITO interlayers between Ga2O3 and Ti/Au metallization is shown to produce Ohmic contacts after annealing in the range of 500–600 °C. Without the ITO, similar anneals do not lead to linear current–voltage characteristics. Transmission line measurements were used to extract the specific contact resistance of the Au/Ti/ITO/Ga2O3 stacks as a function of annealing temperature. Sheet, specific contact, and transfer resistances all decreased sharply from as-deposited values with annealing. The minimum transfer resistance and specific contact resistance of 0.60 Ω mm and 6.3 × 10−5 Ω cm2 were achieved after 600 °C annealing, respectively. The conduction band offset between ITO and Ga2O3 is 0.32 eV and is consistent with the improved electron transport across the heterointerface.
Papers of note in
Science Immunology
2
(15)
Authors: Foley John F.
Published: October 2017

This month’s articles highlight the adaptations in the maternal immune system during pregnancy and show how follicular regulatory T cells suppress B cell activation.
Susceptibility of Pseudomonas aeruginosa Dispersed Cells to Antimicrobial Agents Is Dependent on the Dispersion Cue and Class of the Antimicrobial Agent Used
Authors: Chambers Jacob R. , Cherny Kathryn E. , Sauer Karin
Published: October 2017

The biofilm life cycle is characterized by the transition of planktonic cells exhibiting high susceptibly to antimicrobial agents to a biofilm mode of growth characterized by high tolerance to antimicrobials, followed by dispersion of cells from the biofilm back into the environment. Dispersed cells, however, are not identical to planktonic cells but have been characterized as having a unique transitionary phenotype relative to biofilm and planktonic cells, with dispersed cells attaching in a manner similar to exponential-phase cells, but demonstrating gene expression patterns that are distinct from both exponential and stationary-phase planktonic cells. This raised the question whether dispersed cells are as susceptible as planktonic cells and whether the dispersion inducer or the antibiotic class affects the drug susceptibility of dispersed cells. Dispersed cells obtained in response to dispersion cues glutamate and nitric oxide (NO) were thus exposed to tobramycin and colistin. Although NO-induced dispersed cells were as susceptible to colistin and tobramycin as exponential-phase planktonic cells, glutamate-induced dispersed cells were susceptible to tobramycin but resistant to colistin. The difference in colistin susceptibility was independent of cellular c-di-GMP levels, with modulation of c-di-GMP failing to induce dispersion. Instead, drug susceptibility was inversely correlated with LPS modification system and the biofilm-specific transcriptional regulator BrlR. The susceptibility phenotype of glutamate-induced dispersed cells to colistin was found to be reversible, with dispersed cells being rendered as susceptible to colistin within 2 h postdispersion, though additional time was required for dispersed cells to display expression of genes indicative of exponential growth.
In Vitro
Activity of the Novel Lactone Ketolide Nafithromycin (WCK 4873) against Contemporary Clinical Bacteria from a Global Surveillance Program
Authors: Flamm R. K. , Rhomberg P. R. , Sader H. S.
Published: October 2017

Nafithromycin (WCK 4873), a novel antimicrobial agent of the lactone ketolide class, is currently in phase 2 development for treatment of community-acquired bacterial pneumonia (CABP). A total of 4,739 nonduplicate isolates were selected from a 2014 global surveillance program at medical institutions located in 43 countries within the United States, Europe, Latin America, and the Asia-Pacific region. Nafithromycin and comparator agents were used for susceptibility testing by reference broth microdilution methods. Nafithromycin was active against
Staphylococcus aureus
(MIC
50/90
, 0.06/>2 μg/ml), including erythromycin-resistant strains exhibiting an inducible clindamycin resistance phenotype (MIC
50/90
, 0.06/0.06 μg/ml) and telithromycin-susceptible strains (MIC
50/90
, 0.06/0.06 μg/ml), but it exhibited limited activity against most telithromycin-resistant and clindamycin-resistant isolates that were constitutively resistant to macrolides (MIC
50/90
, >2/>2 μg/ml). Nafithromycin was very active (MIC
50/90
, 0.015/0.06 μg/ml) against 1,911
Streptococcus pneumoniae
strains, inhibiting all strains, with MIC values of ≤0.25 μg/ml. Telithromycin susceptibility was 99.9% for
Streptococcus pneumoniae
strains, and nafithromycin was up to 8-fold more potent than telithromycin. Overall, 37.9% of
S. pneumoniae
strains were resistant to erythromycin, and 19.7% were resistant to clindamycin. Nafithromycin was highly active against 606
Streptococcus pyogenes
strains (MIC
50/90
, 0.015/0.015 μg/ml), inhibiting 100.0% of isolates at ≤0.5 μg/ml, and MIC
50/90
values (0.015/0.015 to 0.03 μg/ml) were similar for the 4 geographic regions. Nafithromycin and telithromycin demonstrated comparable
in vitro
activities against 1,002
Haemophilus influenzae
isolates and 504
Moraxella catarrhalis
isolates. Overall, nafithromycin showed potent
in vitro
activity against a broad range of contemporary (2014) global pathogens. These results support the continued clinical development of nafithromycin for treatment of CABP.
Modified Penicillin Molecule with Carbapenem-Like Stereochemistry Specifically Inhibits Class C β-Lactamases
Authors: Pan Xuehua , He Yunjiao , Chen Tianfeng , Chan Kin-Fai , Zhao Yanxiang
Published: October 2017

Bacterial β-lactamases readily inactivate most penicillins and cephalosporins by hydrolyzing and “opening” their signature β-lactam ring. In contrast, carbapenems resist hydrolysis by many serine-based class A, C, and D β-lactamases due to their unique stereochemical features. To improve the resistance profile of penicillins, we synthesized a modified penicillin molecule, MPC-1, by “grafting” carbapenem-like stereochemistry onto the penicillin core. Chemical modifications include the
trans
conformation of hydrogen atoms at C-5 and C-6 instead of
cis
, and a 6-α hydroxyethyl moiety to replace the original 6-β aminoacyl group. MPC-1 selectively inhibits class C β-lactamases, such as P99, by forming a nonhydrolyzable acyl adduct, and its inhibitory potency is ∼2 to 5 times higher than that for clinically used β-lactamase inhibitors clavulanate and sulbactam. The crystal structure of MPC-1 forming the acyl adduct with P99 reveals a novel binding mode for MPC-1 that resembles carbapenem bound in the active site of class A β-lactamases. Furthermore, in this novel binding mode, the carboxyl group of MPC-1 blocks the deacylation reaction by occluding the critical catalytic water molecule and renders the acyl adduct nonhydrolyzable. Our results suggest that by incorporating carbapenem-like stereochemistry, the current collection of over 100 penicillins and cephalosporins can be modified into candidate compounds for development of novel β-lactamase inhibitors.
The Gastrointestinal Tract Is a Major Source of Echinocandin Drug Resistance in a Murine Model of Candida glabrata Colonization and Systemic Dissemination
Authors: Healey Kelley R. , Nagasaki Yoji , Zimmerman Matthew , Kordalewska Milena , Park Steven , Zhao Yanan , Perlin David S.
Published: October 2017

Candida
species are a part of the human microbiome and can cause systemic infection upon immune suppression.
Candida glabrata
infections are increasing and have greater rates of antifungal resistance than other species. Here, we present a
C. glabrata
gastrointestinal (GI) colonization model to explore whether colonized yeast exposed to caspofungin, an echinocandin antifungal, develop characteristic resistance mutations and, upon immunosuppression, breakthrough causing systemic infection. Daily therapeutic dosing (5 mg/kg of body weight) of caspofungin resulted in no reduction in fecal burdens, organ breakthrough rates similar to control groups, and resistance rates (0 to 10%) similar to those reported clinically. Treatment with 20 mg/kg caspofungin initially reduced burdens, but a rebound following 5 to 9 days of treatment was accompanied by high levels of resistance (
FKS1
/
FKS2
mutants). Although breakthrough rates decreased in this group, the same
FKS
mutants were recovered from organs. In an attempt to negate drug tolerance that is critical for resistance development, we cotreated mice with daily caspofungin and the chitin synthase inhibitor nikkomycin Z. The largest reduction (3 log) in GI burdens was obtained within 3 to 5 days of 20 mg/kg caspofungin plus nikkomycin treatment. Yet, echinocandin resistance, characterized by a novel Fks1-L630R substitution, was identified following 5 to 7 days of treatment. Therapeutic caspofungin plus nikkomycin treatment left GI burdens unchanged but significantly reduced organ breakthrough rates (20%;
P
< 0.05). Single-dose pharmacokinetics demonstrated low levels of drug penetration into the GI lumen posttreatment with caspofungin. Overall, we show that
C. glabrata
echinocandin resistance can arise within the GI tract and that resistant mutants can readily disseminate upon immunosuppression.