bluuebunny/crossref_metadata_2025 huggingface dataset:
Consistent VIV Assessment Methodology for Unbonded Flexible Risers
Authors: Ferdi Faycal , Puliafito Marco , Willis Neil
Published: October 2017

One main objective of assessing vortex-induced vibration (VIV) in deep-water (1000 m) riser design analysis is to determine the VIV fatigue damage. Whilst the VIV assessment methodology is well known for steel catenary risers, the unbonded flexible risers require special attention due to their complex composite behaviour. This is especially true when using the superposition modal approach, which is used in Shear7. The VIV response of unbonded flexible risers when modelled by Shear7 is complex and depends on several parameters, mainly: bending stiffness, modal damping and riser configuration.

Flexible risers exhibit a non-linear moment response due to the stick/slip hysteresis phenomena of the metallic wires. For low curvatures, a flexible pipe is characterised by a high bending stiffness. However, when the applied loads exceed a threshold level given by the friction resistance between the layers, slippage between the layers occur and the corresponding bending stiffness is significantly reduced, which leads to higher curvature levels. This behaviour is characterised by the moment-curvature response, which is specific to each cross section and is highly dependent on operating conditions (pressure, temperature), external conditions (temperature and hydrostatic pressure) and riser configuration (tension distribution).

The objective of this paper is to establish a consistent VIV analysis methodology for unbonded flexible risers taking some of the main critical parameters such as bending stiffness, modal damping, riser configuration and environmental loading into account. This methodology has been developed for a large West African offshore project, where different types of flexible risers with different operating conditions have been assessed. The impact of the pre-slip and post-slip bending stiffness on the VIV response has been studied and an energy-based approach has been used to calculate the modal damping associated with the frictional energy loss due to the stick/slip phenomenon. This energy loss is directly dependent on the curvatures extracted from the modes excited by the oceanic currents acting on the risers. Different riser configurations have also been considered to assess the impact of the vessel offset on the VIV curvature response.

Finally, VIV induced fatigue damage of the flexible risers has been determined using both extreme and long term current profiles assuming steady state current in the VIV model. The fatigue damage has been calculated at several critical locations along each flexible riser by converting the curvature histograms obtained from the VIV assessment into stresses using specific S-N data converting stress cycles into aggregated damage benchmarked against wave-induced damage.
Evaluation of Response Amplitude Operator of Ship Roll Motions Based on the Experiments in White Noise Waves
Authors: Bielicki Sebastian , Bednarek Antoni , Kraskowski Marek
Published: October 2017

Evaluation of the response amplitude operator (RAO) function for ship wave frequency motions by means of scale model tests in regular waves is a standard procedure conducted by hydrodynamic model testing institutions. The resulting RAO function allows for evaluating sufficiently reliable seakeeping predictions for low to moderate sea states. However, for standard hull forms, correct prediction of roll motion in irregular wave (and also in regular waves different than these used in the experiment) on the basis of RAO function presents a substantial challenge due to considerable contribution of viscous damping to roll response. In other words, the RAO values depend strongly on the amplitude of the waves used in the experiment, so the final prediction requires careful application of relevant correction of RAO, dependent on the actual significant wave height, for which the prediction is computed. Thus, in order to collect complete data for ship roll prediction, the roll decay test is usually also required. Additional drawback of evaluating the seakeeping prediction on the basis of RAO is the fact that the experiment in regular waves is quite time-consuming, which refers to the experiment itself as well as to the processing. The following paper presents a proposal of the alternative method for experimental evaluation of response amplitude operator of roll motion in beam waves, consisting in exposing the ship model to irregular wave characterized by white noise spectrum, i.e. the spectrum of uniform energy density. In theory, RAO function is equivalent to the square root of the spectrum of the response to white noise wave. The results of experiments in white noise waves were verified on the basis of the results of comprehensive experiments conducted in usual way. Additionally, the effect of non-linearity of viscous damping was widely studied by comparing the calibrated RAO-based predictions with actual response to irregular waves of different heights. As a result, a method for including the non-linear effects in prediction based on white noise was proposed. It was proved that the proposed method is capable of providing equally valuable information in significantly shorter time.
Wake Shielding Model Effect on Riser Dynamic Response
Authors: Fu Ping , Leira Bernt J. , Myrhaug Dag
Published: October 2017

The paper provides a method to estimate the clearance between two flexible risers in tandem arrangement by taking into account the wake interference when subjected to a combined current plus waves flow. The wake interference of a pair of risers due to current is studied by combining the results from global riser analysis software Riflex and Blevin’s wake model [1]. The deflection shapes of a pair of tandem risers with steep-wave configuration, with and without wake interference, are presented and discussed. The effect of the wake interference on dynamic response of a pair of 2D cylinders due to a current plus waves flow is investigated by assuming that the Blevins’ wake model, originally established for cylinders in steady flow, to be valid for current plus waves as well as current-dominant flow conditions. A simplified clearance assessment is also proposed by which a static wake interference effect is considered during the dynamic analysis, and comparisons are made between the two methods.
Experimental Investigation of Power Umbilical Damping
Authors: Ottesen Torfinn
Published: October 2017

Ocean currents may cause vortex induced vibrations (VIV) of deep-water umbilicals and cables. Since the VIV response may give significant contributions to the total fatigue damage it is important to know the structural damping for relevant curvature levels.

A laboratory test has been performed on a 12.5 m long test specimen to determine the damping for a range of curvature levels that are in the vicinity of the stick-slip transition region. The energy input to maintain steady state oscillations with curvature amplitudes in the range 0.0002–0.001 m−1 was measured. The steady state energy input is consistent with damping ratios obtained using the free decay method.

The structural damping depends on construction temperature and curvature and is less for typically low seawater temperature and low curvatures. The transition between the stick- and the slip regime is seen for typical seawater temperature.
Pore Pressure Under a Gravity Based Structure Under the Influence of Waves
Authors: Christensen Erik Damgaard , Carstensen Stefan , Madsen Mikael Thyge , Hesselbjerg Peter Allerød , Nielsen Christel Jeanty
Published: October 2017

The total wave load on a gravity based foundation for offshore wind turbines is influenced by the pore pressure from beneath the structure. The pore pressure is induced by the wave-structure-seabed interaction. Often the uplift force is included in a simplified way in the design of the gravity based foundation. This leads typically to very conservative designs in order to accommodate the uncertainties in the procedure. The experiments shall lead to better prediction models based on for instance CFD model’s with the direct calculation of pressure variations in the seabed and any erosion protection layer. Herewith, it will be possible to get a direct assessment of wave loads on the foundation, also under the seabed level. The study includes experiments as well as numerical analyses. A good agreement between the experimental results and the numerical analyses was found. In the numerical analyses, it was possible to investigate the effect of air content in the pores, which turned out to have an effect on the distribution of the pore pressure.
Autonomous Flow Control Device Modelling and Completion Optimisation
Authors: Eltaher Eltazy , Muradov Khafiz , Davies David , Grassick Peter
Published: October 2017

The functions of the various wellbore completion components and their impact on the given well performance should be fully understood to achieve the full potential of advanced wells completions (AWCs).

Inflow control technology has been a success when installed in many fields. Field trials of the more recently developed Autonomous Flow Control Completions (AFCC) have shown their potential to further improve well performance. However, such (autonomous) discrimination and control of the different fluid phases, presents new modelling challenges that require extension of today’s wellbore/reservoir models and workflows for optimizing the completion design. The modelling challenges associated with this new technology requires more research to correctly quantify their added-value and guide future design improvements in AFCC technology.

This paper discusses how the currently available modelling tools can best designed when only single-phase flow performance data is available. Methods and workflows to improve the modelling accuracy, as well as, to understand the performance of an AFCC in a horizontal well in comparison with passive inflow control technology are presented. Novel methods to visualize and optimize the AFCC are presented and used to optimize the equipment design and identify the technology’s added-value.

Finally, this paper presents a modelling workflow for reservoir and well engineering studies by providing optimal AFCC selection guidelines together with a brief summary of an extension of the work reported here to multi-phase flow in typical AFCCs. Incorrect modelling of the devices Multi-Phase Flow Performance was found to effect the economic evaluation of this promising technology; forming an extra barrier to its early adoption.
A Review of Offshore Decommissioning Regulations in Three Countries: Strengths and Weaknesses
Authors: Fam Mei Ling , Tan Hoon Kiang , Konovessis Dimitrios , Ong Lin Seng
Published: October 2017

The decommissioning of offshore structures around the world will be a persisting problem in the coming decades as many existing structures will exceed their design life, or when the reservoirs are depleted. This paper examines an overview of regulations in countries deemed to be more experienced in decommissioning such as the UK, Norway and the USA. The regulations were identified in terms of three areas: the legal, technical and financial security framework. It is concluded that the majority of the regulations covering the technical section are similar. The major differences are between two overarching philosophies — one that is more prescriptive with stricter requirements and another that is more flexible with a goal-setting regime. Non-technical aspects of decommissioning appear to attract increasing attention from governments, such as decommissioning financial capability, minimisation of costs while meeting regulatory requirements, transfer of liability if other decommissioning options are accepted, and the movement of wastes from offshore to onshore and their subsequent disposal.
Ship Handling Model Validation Using In-Service Measurements
Authors: Abbasi Hoseini Afshin , Steen Sverre
Published: October 2017

In this work, an alternative method is proposed for validation of ship handling models using onboard monitoring data of normal ship operations. If validation data can be collected during ship service, one can obtain a large number of “repetitions” without dedicated sea trials that are expensive. Although the accuracy of each sample will probably be less than in dedicated trials, it might be compensated by the fact that many samples will be available. As a case study, the results of simulation of the research vessel of the Norwegian University of Science and Technology (NTNU), Gunnerus, using MARINTEK’s vessel simulator (VeSim) are presented and evaluated by certain maneuvers identified from Gunnerus onboard measurements. To validate a ship simulator, it is shown that it might be better to investigate the agreement between simulation and full-scale measurements during operations similar to the ones that shall be simulated later, than just validating against standardized maneuvers such as turning circle and zig-zag tests.
Development of Well Intervention Fluid for Removal of Sustained Casing Pressure
Authors: Demirci Efecan , Butler Kristina , Wojtanowicz Andrew K.
Published: October 2017

Sustained Casing Pressure (SCP) is a well integrity problem and its removal is required. Techniques that involve replacing the fluid inside the annulus with a heavier fluid (kill fluid, KF) to stop gas migration have so far failed due to issues resulting from fluid incompatibility. This study aims to develop an intervention fluid compatible with water-based annular fluids. Based on the theory of buoyant slippage, brominated organic fluids have been produced and tested to assess compatibility and performance with multiple physical models. Results showed that the KF was able to settle down in water-based fluids, build up and exert pressure at the bottom. Experiments also exposed the formation of a mixture zone just above the building-up KF column. Lower injection rates and/or larger nozzle sizes decrease KF dispersion, prevent mixture zone formation and increase KF recovery. Intervention fluids developed in this study may revive the defunct bleed-and-lube (B&L) technique that would dramatically reduce the cost of SCP removal or may be used in an alternative process of continuous displacement that would significantly reduce the time of well intervention. Presented in the paper is also a road map for testing the SCP removal process that would lead to development of this technology.
Decision Support Tools for Selection of External Protective Coating for Pipelines
Authors: Yasseri S. , Bahai H. , Rahmati M. T.
Published: October 2017

A good coating is one with high performance and durability; has a low surveillance and maintenance requirement; is easily applied with no health risks and finally is cost effective. It is unlikely that a single type of coating would be able to satisfy all these needs. Thus, a decision support tool is needed to help identify the most appropriate choice. This paper presents three simple methods for this selection process, and allows the judgment of more than one expert to be aggregated in order to reach a consensus. An example is presented which demonstrates the application of these methods, by providing the decision-maker the ability to weigh options and set priorities in deciding on the best compromise solution for a corrosion coating material.
Evaluation of an Offshore Floating Wind Power Project on the Galician Coast
Authors: Díaz Hugo , Rodrigues José Miguel , Guedes Soares C.
Published: October 2017

This paper aims to make a contribution to assessing the viability of offshore wind power projects on the Galician coast. Several of the factors involved in these projects are studied, such as site selection and employed technologies regarding turbine and floating foundations. Estimated costs ‘ analysis and financial evaluation are performed for a chosen solution. Based on the conducted study, an offshore wind farm in Galicia may become valid in a prospect of an electricity tariff to the producer in line with other European countries. Furthermore, an expected decrease of costs of floating platforms once produced in series and of offshore technology as a whole, in addition to incentives, would make the investment much more attractive.
Ship Vertical Loads From Using an Adaptive Mesh Pressure Integration Technique for Froude-Krylov Forces Calculation
Authors: Rodrigues José Miguel , Guedes Soares C.
Published: October 2017

Dynamic vertical bending moments are determined for a military vessel hull in still water and under head waves, with a weakly nonlinear method. The domain for hydrostatic and undisturbed pressures integration is time-variant and generated with a quad-tree adaptive mesh algorithm, on which exact formulations for pressure on polygonal elements are used. Linear radiation and diffraction pressures, on another mesh superimposed with the aforementioned, are calculated with a frequency domain code. Results are compared with published experimental ones for small and large wave heights.
Wave-Energy Conversion Avoiding Destructive Wave Interference
Authors: Falnes Johannes
Published: October 2017

Many of the various proposed wave-energy converter (WEC) units are immersed oscillating bodies, which, in the primary conversion stage, collect input power as the product of two oscillating factors, a velocity and wave-induced force. The latter factor is vulnerable to destructive wave interference, unless the extension of each WEC unit is sufficiently small. Two simple, elementary-mathematical, inequalities express two kinds of upper bounds for the wave power that may be absorbed by an oscillating immersed body. The first upper bound, published in the mid 1970s, is well-known, in contrast to the second one, Budal’s upper bound, which was derived a few years later, and which takes the WEC’s hull volume into consideration. Combining the two different upper bounds and considering also a typical wave climate, we may conclude that for a WEC array plant deployed in the North Atlantic, each point-absorber WEC unit volume should typically be about 300 cubic metre, and its primary-converted power take-off (PTO) capacity should be in the range of 50 to 300 kW. These heaving WEC units, being monopole wave radiators, may have a much higher PTO-capacity-to-immersed-hull-wet-surface ratio than any other type of WEC unit, such as those using dipole-mode (e.g. surge- or pitch-mode) radiation. For large-scale utilization of wave energy, arrays of WEC units are required.
Nonlinear and Dissipative Characteristics of a Combined Random-Cnoidal Wave Field
Authors: Kaihatu James M. , Goertz John T. , Ardani Samira , Sheremet Alex
Published: October 2017

Images of the 2004 Indian Ocean tsunami at landfall shows a leading edge marked by short waves (“fission” waves). These waves appear to be cnoidal in shape and of a temporal and spatial scale in line with the longest swell present in the region, and may interact with the longer waves in the background random wave spectrum. As part of a comprehensive series of experiments, the Large Wave Flume at Oregon State University (USA) was used to generate and measure the properties of cnoidal, random, and combined cnoidal-random wave trains. Both the nonlinear energy transfer characteristics (via bispectral analysis) and dissipation characteristics (via a proxy dissipation function) are studied for all generated wave conditions. It is generally determined that the characteristics of the cnoidal wave dominate the combined cnoidal-random wave signals if the energy of the cnoidal wave is at least equal to that of the random wave.
A Comparison of Biradial and Wells Air Turbines on the Mutriku Breakwater OWC Wave Power Plant
Authors: Henriques J. C. C. , Sheng W. , Falcão A. F. O. , Gato L. M. C.
Published: October 2017

The Mutriku breakwater wave power plant is located in the Bay of Biscay, in Basque Country, Spain. The plant is based on the oscillating water column (OWC) principle and comprises 16 air chambers, each of them equipped with a Wells turbine coupled to an electrical generator with a rated power of 18.5 kW. The IDMEC/IST Wave Energy Group is developing a novel self-rectifying biradial turbine that aims to overcome several limitations of the Wells turbine, namely the sharp drop in efficiency above a critical flow rate. The new turbine is symmetrical with respect to a mid-plane perpendicular to the axis of rotation. The rotor is surrounded by a pair of radial-flow guide vane rows. Each guide vane row is connected to the rotor by an axisymmetric duct whose walls are flat discs. In the framework of the “OPERA” European H2020 Project, the new biradial turbine will be tested at Mutriku and later will be installed and tested on a floating OWC wave energy converter — the OCEANTEC Marmok-5’s — to be deployed at BiMEP demonstration site in September of 2017. The aim of the present paper is to perform critical comparisons of the performance of the new biradial and the Wells turbine that is presently installed at Mutriku. This is based on results from a time-domain numerical model. For the purpose, a new hydrodynamic frequency domain model of the power plant was developed using the well know WAMIT software package. This was used to build a time-domain model based on the Cummins approach.
Full-Scale Validation of a Vessel’s Station-Keeping Capability With DynCap
Authors: Pivano Luca , Nguyen Dong , Smøgeli Øyvind
Published: October 2017

With the steady growth of the number of Dynamic Positioning (DP) vessels, increasingly complex designs and operations, and a decreasing number of experienced DP operators, effective operational risk management tools are key for safer and more efficient operations. One of the key aspects when looking at the operational risks is the estimation of the vessel position and heading after the worst case single failure and in the transient period after the failure has occurred. The aim of this paper is to provide insight about the use of comprehensive dynamic operability analyses performed by time-domain simulations for understanding the vessel performance and limitations, in turn providing valuable and reliable input to operational risk assessment and planning. This paper presents also a comparison with results from full-scale trials.
Application of Outcrops Rock Samples in Laboratory Research of Shale Drilling Fluid Interaction
Authors: Pašić Borivoje , Gaurina-Međimurec Nediljka , Mijić Petar , Barudžija Uroš
Published: October 2017

Shales instability is a result of its mineralogical composition (especially content of different water sensitive clay) and its physico-chemical properties. In different laboratory research of shale/drilling fluid interaction conducted until now, researcher used different shale samples (original rock samples taken by the coring process, drilling cuttings, outcrop samples and artificial rock samples), different laboratory equipment and various inhibitive muds. There are two main problems related to the laboratory testing of shale samples’ quantity and quality. The main task of this paper was to examine the applicability of outcrop rock (shale) samples for laboratory research of shale/drilling fluid interaction. Rock samples were taken at natural shale outcrop on different locations in Croatia. In the first stage of the laboratory research, mineralogical composition and petrophysical properties of used shale samples were tested. In the second stage, shale samples’ swelling in different fluid were examined. After getting results of the shale swelling, new quantity of outcrop shale samples was taken, crushed to drilling cuttings size and placed in roller oven cells previous charged with different fluids. In the last stage, a dried (hot rolled) shale sample was used for preparation of the artificial shale samples. Generated artificial samples were used in further laboratory research.
High Cycle Fatigue Damage Evaluation of Steel Pipelines Based on Microhardness Changes During Cyclic Loads
Authors: Drumond Geovana , Pinheiro Bianca , Pasqualino Ilson , Roudet Francine , Chicot Didier , Decoopman Xavier
Published: October 2017

Fatigue is a major cause of failures concerning metal structures, being capable of causing catastrophic damage to the environment and considerable financial loss. Steel pipelines used in oil and gas industry for hydrocarbon transportation, for instance, are submitted to the action of cyclic loads, being susceptible to undergo fatigue failures. The phenomenon of metal fatigue is a complex process comprising different successive mechanisms. In general, four stages can be identified, representing microcrack initiation (nucleation), microcracking, macrocrack propagation, and final fracture. Fatigue damage prior to nucleation of microcracks is primarily related to localized plastic strain development at or near material surface during cycling. The microhardness of the material shows its ability to resist microplastic deformation caused by indentation or penetration, and is closely related to the material plastic slip capacity. Therefore, the study of changes in material surface microhardness during the different stages of fatigue process can estimate the evolution of the material resistance to microplastic deformations and, consequently, provide relevant information about the cumulated fatigue damage on the surface. The present work is part of a research study being carried out with the aim of proposing a new method based on microstructural changes, represented by a fatigue damage indicator, to predict fatigue life of steel structures submitted to cyclic loads, before macroscopic cracking. In a previous work, the X-ray diffraction technique was used to evaluate these changes. This technique presents several advantages, since it is non-destructive and concerns the surface and subsurface of the material, where major microstructural changes take place during fatigue. The most important parameter obtained by this technique is the full width at half maximum (FWHM) of the diffraction peak, which can provide information about the dislocation network density and estimate microdeformations. It was found that the evolution of this parameter with cycling presents three different stages, associated to the mechanisms of microcrack initiation, microcracking, macrocrack propagation, respectively. Here, the fatigue damage of pipeline steels is evaluated through microhardness testing. Different stages of changes in microhardness are also found and they are correlated to those observed with the X-ray technique and also with transmission electron microscopic (TEM) images from experimental tests performed with a similar material. This correlation can help to corroborate the X-ray diffraction results previously obtained and recommend then this non-destructive technique as the base of the method for predicting fatigue life of steel structures proposed here.
Multi-Purpose Offshore-Platforms: Past, Present and Future Research and Developments
Authors: Leira Bernt J.
Published: October 2017

Energy, fisheries and transport infrastructures are increasingly being established offshore. Facilities such as offshore wind farms may occupy large areas and compete with other users of the maritime space. Accordingly, offshore platforms that can combine many functions within the same infrastructure could offer significant benefits. This applies to economy, optimization of spatial planning and minimization of the impact on the environment.

In the present paper, some proposed innovative designs for multi-use offshore platforms are described. The technical, economical and environmental feasibility of designing, installing, operating, servicing and maintaining such platforms are discussed. The relevant platforms under consideration are targeted towards ocean renewable energy (in particular offshore wind), aquaculture and related transport maritime services.

Innovative designs for multi-use offshore platforms that intend to allow optimal coupling of the various activities and services are highlighted. Issues such as safe and efficient installation, operation, maintenance and monitoring are also briefly discussed in the paper.
Testing Techniques for Establishing Fracture Resistance of Steel in a Sour Environment
Authors: Ali Muhammad S.
Published: October 2017

It is well established that sour operating environments can give rise to significantly reduced fracture toughness of pipelines made of carbon manganese steel. Fracture resistance of a material is usually defined in terms of a fracture resistance curve, commonly known as an R-curve which is determined by testing pre-cracked specimens under a rising load. Fracture resistance data can be derived by the single specimen method, where crack extension is determined using unloading compliance or the multiple specimen method, where crack extension is measured from the fracture face of each specimen and each specimen is taken to a different load level. The fracture resistance behaviour of API 5L X65 grade pipeline steel determined by testing single edge notched bend specimens in a specific sour environment using both single and multiple specimen test methods is reported. The fracture resistance of the steel was found to be highly sensitive to the loading rates (described by the initial rate of increase of stress intensity factor in the elastic range) applied during the fracture resistance tests. It was possible to identify a loading rate slow enough to provide fracture initiation toughness reasonably close to the expected lower bound toughness. It is possible to produce similar R-curves from single and multiple specimen testing methods (if conditions are otherwise the same). Under comparable loading rates and environmental conditions, side grooved specimens resulted in lower fracture toughness as compared to the toughness determined from the plane sided specimens. It was also noticed that there was a weaker correlation between side grooving and toughness at slower loading rates.
Influence on Structural Reliability of Uncertain Extreme Value Estimates
Authors: Reid Stuart , Naess Arvid
Published: October 2017

Loads for the purpose of structural design are often based on estimated extreme values of time-varying loads based on limited amounts of data. Uncertainty in the estimation of the design loads inevitably leads to uncertainty in the resultant levels of structural reliability. In this paper, uncertainty is assessed for estimates of extreme wind loads calculated using statistical methods based on the average conditional exceedance rate (ACER), fitting of a Gumbel distribution and Peaks-Over-Threshold (POT). The ACER method gave the best results, but all the methods gave results which would normally be considered to be sufficiently accurate for engineering applications. However, for structures designed on the basis of the estimated values of V100 or V500, the uncertainty in the estimated design loads produced very uncertain probabilities of failure with a significant increase in their expected value. It is concluded that the uncertain distribution of the probabilities of failure must be taken into account when evaluating structural safety and a ‘fiducial confidence function’ is proposed for this purpose.
Reliability Analysis and Risk-Based Methods for Planning of Operation and Maintenance of Offshore Wind Turbines
Authors: Sørensen John Dalsgaard
Published: October 2017

Reliability analysis and probabilistic models for wind turbines are considered with special focus on structural components and application for reliability-based calibration of partial safety factors. The main design load cases to be considered in design of wind turbine components are presented including the effects of the control system and possible faults due to failure of electrical / mechanical components. Considerations are presented on the target reliability level for wind turbine structural components. Application is shown for reliability-based calibrations of partial safety factors for extreme and fatigue limit states are presented. Operation & Maintenance planning often follows corrective and preventive strategies based on information from condition monitoring and structural health monitoring systems. A reliability- and risk-based approach is presented where a life-cycle approach is used. An example with wind turbine blades is considered using the NORCOWE reference wind farm.
Risk Informed Structural Systems Integrity Management: A Decision Analytical Perspective
Authors: Faber Michael Havbro
Published: October 2017

The present paper is predominantly a conceptual contribution with an appraisal of major developments in risk informed structural integrity management for offshore installations together with a discussion of their merits and the challenges which still lie ahead. Starting point is taken in a selected overview of research and development contributions which have formed the basis for Risk Based Inspection Planning (RBI) as we know it today. Thereafter an outline of the methodical basis for risk informed structural systems integrity management, i.e. the Bayesian decision analysis is provided in summary. The main focus is here directed on RBI for offshore facilities subject to fatigue damages. New ideas and methodical frameworks in the area of robustness and resilience modeling of structural systems are then introduced, and it is outlined how these may adequately be utilized to enhance Structural Integrity Management (SIM). Finally, the concept of Value of Information analysis (VoI) from the Bayesian pre-posterior decision analysis is proposed, as an overarching methodical platform for the planning and optimization of structural Health Monitoring (SHM) activities in the context of SIM at both operational and strategic levels.
Whirling Motion of Monopile Offshore Wind Turbines Subjected to Harmonic and Random Base Excitation
Authors: Cai Zhicheng , Zheng Xiang Yuan
Published: October 2017

In April 2014 a series of 30:1 scaled shake table test of the NREL-5MW monopile offshore wind turbine were conducted. Significant whirling motions were observed during the test [1], which were seldom reported for civil engineering and offshore engineering structures. This study is thereby devoted to revealing the mechanism of the whirling motion of a typical tall monoplie offshore wind turbine.

The original shake table model is simplified into a uniform cantilever beam with a large lumped mass on the top. Two nonlinear coupled integro-differential equations of motion containing cubic nonlinearities due to curvature and inertia are used and solved by both analytical and numerical approaches. The ElCentroExp random base excitation and lateral harmonic base excitations with different amplitudes and frequencies are considered in the analysis to fathom the instability mechanism.

The analysis results show that, for harmonic base excitations with frequency within a specific range, when the amplitude of base excitation and the initial perturbation exceed a certain threshold, stable whirling motion response will be triggered and the motion of shake table model will be controlled by whirling. However, the analysis results also demonstrate that, subjected to the ElCentroExp base excitation or its equivalent lateral harmonic base excitations, neither analytical nor numerical approach can produce whirling motion response, regardless of the damping ratio. The LM model will always show planar motion response. This differs significantly from the observation of shake table model test.
Ship Collision Analysis of a Floating Bridge in Ferry-Free E39 Project
Authors: Sha Yanyan , Amdahl Jørgen
Published: October 2017

The Norwegian Public Roads Administration is running a project ‘Ferry free coastal route E39’ which includes replacing ferry crossings by bridges or tunnels across eight fjords in Western Norway. Since most of the fjords are wide and deep, traditional fixed links are not possible to be constructed. Therefore, floating bridge and tunnel concepts are proposed for the fjord-crossing project. Because floating bridges and tunnels have many structural components close to the water surface, a critical concern of accidental ship collision loads is then raised. Considering the large displacement and high speed of the passing ships, the interactions between the bridge structure and the ship bow can be significant should collision occurs. It is therefore important to carefully evaluate bridge response subjected to ship collision loads in the design process. This paper presents a case study of ship collision analysis of the floating bridge concept for Bjørnafjorden. Two possible collision scenarios, i.e. ship-pontoon and ship-girder collisions, are considered. First, local structural deformation and damage are numerically investigated by detailed finite element models using LS-DYNA. Second, bridge global response under ship collision loads are simulated in USFOS. By combining the local and global analyses, a comprehensive overview of bridge response under ship collision load can be obtained.
Time Domain Modelling of Frequency Dependent Wind and Wave Forces on a Three-Span Suspension Bridge With Two Floating Pylons Using State Space Models
Authors: Xu Yuwang , Øiseth Ole , Moan Torgeir
Published: October 2017

Floating suspension bridges, one of several new designs to make it possible to cross deep and wide fjords, consist of three spans and supported by two tension leg platforms and two fixed traditional concrete pylons. Geometric nonlinearities, nonlinear aerodynamic and hydrodynamic forces and nonlinear mooring systems can become of high importance. Time domain methods are commonly applied when nonlinearities need to be considered. The main challenge in time domain simulation of the floating suspension bridge is the modelling of frequency-dependent aerodynamic self-excited forces and hydrodynamic radiation forces. This paper shows how rational functions fitted to aerodynamic derivatives and hydrodynamic added mass and potential damping can be converted to state space models to transform the frequency-dependent forces to time-domain. A user element is implemented in the software ABAQUS to be able to include the self-excited forces in the dynamic analysis. The element is developed as a one node element that is included in the nodes along the girder and the tension leg platforms. The responses of the floating suspension bridge under turbulent wind forces and first-order wave excitation forces are calculated in a comprehensive case study and compared with results obtained using a multi-mode frequency domain approach to illustrate the performance of the presented time-domain methodology.
Cluster cleaned HOPG by XPS
Authors: Morgan David J.
Published: October 2017

X-ray photoelectron spectroscopy was used to characterize a highly oriented pyrolytic graphite (HOPG) sample. The HOPG was freshly cleaved using Scotch tape prior in the entry lock of the spectrometer and subsequently cleaned using an argon cluster source. This method of cleaning has led to an improved definition of the C KLL Auger signal used for differentiation in the determination of sp2/sp3 ratios according to the method of Lascovich et al. [Appl. Surf. Sci. 78, 17 (1994)].
Realization of a high vacuum evaporation system for wave-length shifter deposition on photo-detector windows
Authors: Bonesini Maurizio , Mazza Roberto , Cervi Tommaso , Menegolli Alessandro , Prata Marco Cesare , Raselli Gian Luca , Rossella Massimo , Spanu Maura Ninuccia , Torti Marta
Published: October 2017

In this paper, the authors present a system based on a vacuum chamber and Knudsen cells that can evaporate organic materials on convex surfaces up to 10 in. diameter, with a good uniformity, in a very short time. This system was successfully used at CERN for the deposition of tetra-phenyl butadiene wavelength shifter on the 8 in. window of 360 Hamamatsu R5912-MOD photomultiplier tubes (PMTs), before their installation inside the ICARUS T600 detector to be used for neutrino physics studies. The quantum efficiency in the vacuum ultraviolet region measured on the whole photocathode shows a good uniformity over the entire PMT active surface with an average value above 10% from 120 to 200 nm.
Spectral response characteristics of transmission-mode alkali telluride photocathodes working from vacuum-ultraviolet to ultraviolet band
Authors: Zhang Xiang , Zhang Yijun , Qian Yunsheng , Feng Cheng , Zhang Jingzhi , Jiang Yunlong , Pan Zhiyun
Published: October 2017

In order to characterize the spectral response of transmission-mode alkali telluride photocathodes, a spectral response measurement system for image intensifiers working from the vacuum-ultraviolet to ultraviolet band is developed. Using this system, the transmittance curves of usual window materials such as quartz, MgF2, and sapphire selected to prepare alkali telluride photocathodes are measured. In addition to the transmittance test function, the spectral response of image intensifiers based on transmission-mode alkali telluride photocathodes, such as Cs2Te, Rb2Te, Cs-K-Te, and Rb-K-Te photocathodes, under the excitation light from 115 to 400 nm is measured. The measured results show that the longwave cutoff wavelength of the Rb2Te photocathode is 313 nm, while that of the Cs2Te photocathode is 342 nm, which could be ascribed to the reduced cathode work function, inversely proportional to the atomic number of the alkali element in uni-alkali telluride photocathodes. Besides, the spectral response values of Cs-K-Te and Rb-K-Te photocathodes are greater than those of Cs2Te and Rb2Te photocathodes, and this case is similar to the multialkali effect of alkali antimonide photocathodes. The cutoff wavelength can get shorter through the combination with an additional K element. Compared with the Rb-K-Te photocathode with the shorter cutoff wavelength, the Cs-K-Te photocathode can achieve higher sensitivity.
Similar abilities of musicians and non-musicians to segregate voices by fundamental frequency
Authors: Deroche Mickael L. D. , Limb Charles J. , Chatterjee Monita , Gracco Vincent L.
Published: October 2017

Musicians can sometimes achieve better speech recognition in noisy backgrounds than non-musicians, a phenomenon referred to as the “musician advantage effect.” In addition, musicians are known to possess a finer sense of pitch than non-musicians. The present study examined the hypothesis that the latter fact could explain the former. Four experiments measured speech reception threshold for a target voice against speech or non-speech maskers. Although differences in fundamental frequency (ΔF0s) were shown to be beneficial even when presented to opposite ears (experiment 1), the authors' attempt to maximize their use by directing the listener's attention to the target F0 led to unexpected impairments (experiment 2) and the authors' attempt to hinder their use by generating uncertainty about the competing F0s led to practically negligible effects (experiments 3 and 4). The benefits drawn from ΔF0s showed surprisingly little malleability for a cue that can be used in the complete absence of energetic masking. In half of the experiments, musicians obtained better thresholds than non-musicians, particularly in speech-on-speech conditions, but they did not reliably obtain larger ΔF0 benefits. Thus, the data do not support the hypothesis that the musician advantage effect is based on greater ability to exploit ΔF0s.
Genome-wide functional analysis reveals central signaling regulators of lymphatic endothelial cell migration and remodeling
Authors: Williams Steven P. , Odell Adam F. , Karnezis Tara , Farnsworth Rae H. , Gould Cathryn M. , Li Jason , Paquet-Fifield Sophie , Harris Nicole C. , Walter Anne , Gregory Julia L. , Lamont Sara F. , Liu Ruofei , Takano Elena A. , Nowell Cameron J. , Bower Neil I. , Resnick Daniel , Smyth Gordon K. , Coultas Leigh , Hogan Benjamin M. , Fox Stephen B. , Mueller Scott N. , Simpson Kaylene J. , Achen Marc G. , Stacker Steven A.
Published: October 2017

The signaling proteins and pathways involved in lymphatic endothelial cell migration are identified through a functional screen.
Papers of note in
Nature
549
(7673)
Authors: VanHook Annalisa M.
Published: October 2017

This week’s articles highlight the role of vitamin C in hematopoietic cells; a source of maternal inflammation that contributes to neurodevelopmental defects; the blocking of a niche factor that promotes the growth of gliomas; and a protein that influences DNA repair pathway choice.
Papers of note in
Science Translational Medicine
9
(409)
Authors: Ferrarelli Leslie K.
Published: October 2017

This week’s articles describe a stem cell–based therapy for chronic kidney disease and targets for treating diabetic nerve pain and acute respiratory distress in critically ill patients.
Papers of note in
Science
357
(6358)
Authors: VanHook Annalisa M.
Published: October 2017

This week’s article shows that the release of oxytocin in the ventral tegmental area influences sociability in mice by stimulating dopaminergic neurons that project to the brain’s reward center.
Functional Characterization of CTX-M-14 and CTX-M-15 β-Lactamases by
In Vitro
DNA Shuffling
Authors: Po Kathy Hiu Laam , Chan Edward Wai Chi , Chen Sheng
Published: October 2017

This work investigated the molecular events driving the evolution of the CTX-M-type β-lactamases by the use of DNA shuffling of fragments of the
bla
CTX-M-14
and
bla
CTX-M-15
genes. Analysis of a total of 51 hybrid enzymes showed that enzymatic activity could be maintained in most cases, yet hybrids that were active possessed fewer amino acid substitutions than those that were inactive, suggesting that point mutations in the constructs rather than reshuffling of the fragments of the two target genes would more likely cause disruption of CTX-M activity. For example, the P
67
L and L
261
P changes in a CTX-M-14 fragment could completely abolish the activity of the enzyme on all antibiotics tested. Structural analysis showed that L
216
was located in the active-site β sheet and might interact with the adjacent hydrophobic residues to stabilize the active-site β sheet and maintain the integrity of the enzyme active site. Likewise, a single amino acid substitution, E
64
K, was found to exhibit a significant suppressive effect on CTX-M-15 activity. Structural analysis showed that E
64
might form a salt bridge with R
44
, disruption of which might affect CTX-M-15 activity. Further analysis of the structure-function relationship of a range of mutant enzymes confirmed that, as can be expected, unstable enzymes lose their activity and avoid selective events. These findings suggest that the distal pockets could also contribute to the activity of the enzymes and may be regarded as alternative targets for inhibitor development.