bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluating multiplexed next‐generation sequencing as a method in palynology for mixed pollen samples
Authors: Keller A. , Danner N. , Grimmer G. , Ankenbrand M. , von der Ohe K. , von der Ohe W. , Rost S. , Härtel S. , Steffan‐Dewenter I.
Published: September 2014

The identification of pollen plays an important role in ecology, palaeo‐climatology, honey quality control and other areas. Currently, expert knowledge and reference collections are essential to identify pollen origin through light microscopy. Pollen identification through molecular sequencing and DNA barcoding has been proposed as an alternative approach, but the assessment of mixed pollen samples originating from multiple plant species is still a tedious and error‐prone task. Next‐generation sequencing has been proposed to avoid this hindrance. In this study we assessed mixed pollen probes through next‐generation sequencing of amplicons from the highly variable, species‐specific internal transcribed spacer 2 region of nuclear ribosomal DNA. Further, we developed a bioinformatic workflow to analyse these high‐throughput data with a newly created reference database. To evaluate the feasibility, we compared results from classical identification based on light microscopy from the same samples with our sequencing results. We assessed in total 16 mixed pollen samples, 14 originated from honeybee colonies and two from solitary bee nests. The sequencing technique resulted in higher taxon richness (deeper assignments and more identified taxa) compared to light microscopy. Abundance estimations from sequencing data were significantly correlated with counted abundances through light microscopy. Simulation analyses of taxon specificity and sensitivity indicate that 96% of taxa present in the database are correctly identifiable at the genus level and 70% at the species level. Next‐generation sequencing thus presents a useful and efficient workflow to identify pollen at the genus and species level without requiring specialised palynological expert knowledge.
Inventory‐Based Dynamic Pricing with Costly Price Adjustment
Authors: Chen Wen , Feng Qi , Seshadri Sridhar
Published: September 2014

We study an average‐cost stochastic inventory control problem in which the firm can replenish inventory and adjust the price at anytime. We establish the optimality to change the price from low to high in each replenishment cycle as inventory is depleted. With costly price adjustment, scale economies of inventory replenishment are reflected in the cycle time instead of lot size—An increased fixed ordering cost leads to an extended replenishment cycle but does not necessarily increase the order quantity. A reduced marginal cost of ordering calls for an increased order quantity, as well as speeding up product selling within a cycle. We derive useful properties of the profit function that allows for reducing computational complexity of the problem. For systems requiring short replenishment cycles, the optimal solution can be easily computed by applying these properties. For systems requiring long replenishment cycles, we further consider a relaxed problem that is computational tractable. Under this relaxation, the sum of fixed ordering cost and price adjustment cost is equal to (greater than, less than) the total inventory holding cost within a replenishment cycle when the inventory holding cost is linear (convex, concave) in the stock level. Moreover, under the optimal solution, the time‐average profit is the same across all price segments when the inventory holding cost is accounted properly. Through a numerical study, we demonstrate that inventory‐based dynamic pricing can lead to significant profit improvement compared with static pricing and limited price adjustment can yield a benefit that is close to unlimited price adjustment. To be able to enjoy the benefit of dynamic pricing, however, it is important to appropriately choose inventory levels at which the price is revised.
Multilevel Multivariate Modelling of Legislative Count Data, with a Hidden Markov Chain
Authors: Lagona Francesco , Maruotti Antonello , Padovano Fabio
Published: September 2014

The production of legislative acts is affected by multiple sources of latent heterogeneity, due to multilevel and multivariate unobserved factors that operate in conjunction with observed covariates at all the levels of the data hierarchy. We account for these factors by estimating a multilevel Poisson regression model for repeated measurements of bivariate counts of executive and ordinary legislative acts, enacted under multiple Italian governments, nested within legislatures. The model integrates discrete bivariate random effects at the legislature level and Markovian sequences of discrete bivariate random effects at the government level. It can be estimated by a computationally feasible expectation–maximization algorithm. It naturally extends a traditional Poisson regression model to allow for multiple outcomes, longitudinal dependence and multilevel data hierarchy. The model is exploited to detect multiple cycles of legislative supply that arise at multiple timescales in a case-study of Italian legislative production.
Consistent Estimation of the Fixed Effects Ordered Logit Model
Authors: Baetschmann Gregori , Staub Kevin E. , Winkelmann Rainer
Published: September 2014

The paper considers panel data methods for estimating ordered logit models with individual-specific correlated unobserved heterogeneity. We show that a popular approach is inconsistent, whereas some consistent and efficient estimators are available, including minimum distance and generalized method-of-moment estimators. A Monte Carlo study reveals the good properties of an alternative estimator that has not been considered in econometric applications before, is simple to implement and almost as efficient. An illustrative application based on data from the German Socio-Economic Panel confirms the large negative effect of unemployment on life satisfaction that has been found in the previous literature.
Genomic Organization and Expression of Immunoglobulin Genes in the Chinese Hamster (Cricetulus griseus)
Authors: Qin T. , Zhu H. , Wang D. , Hao H. , Du W.
Published: September 2014

In science, the hamsters are widely used as a model for studying the human diseases because they display many features like humans. The utility of the Chinese hamster as a biology model can be further enhanced by further characterization of the genes encoding components of the immune system. Here, we report the genomic organization and expression of the Chinese hamster immunoglobulin heavy and light chain genes. The Chinese hamster IgH locus contains 268 VH segments (132 potentially functional genes, 12 ORFs and 124 pseudogenes), 4 DH segments, 6 JH segments, four constant region genes (μ, γ, ε and α) and one reverse δ remnant fragment. The Igκ locus contains only a single Cκ gene, 4 Jκ segments and 48 Vκ segments (15 potentially functional genes and 33 pseudogenes), whereas the Igλ locus contains 4 Cλ genes, but only Cλ3 and Cλ4 each preceded by a Jλ gene segment. A total of 49 Vλ segments (39 potentially functional genes, 3 ORFs and 7 pseudogenes) were identified. Analysis of junctions of the recombined V(D)J transcripts reveals complex diversity in both expressed H and κ sequences, but the microhomology‐directed VJ recombination obviously results in very limited diversity in the Chinese hamster λ gene despite more potential germline‐encoded combinatorial diversity. This is the first study to make a comprehensive analysis of the Ig genes in the Chinese hamster, which provides insights into the Ig genes in placental mammals.
Long-term outcome of low contact stress total knee arthroplasty with different mobile bearing designs
Authors: Solarino Giuseppe , Spinarelli Antonio , Carrozzo Massimiliano , Piazzolla Andrea , Vicenti Giovanni , Moretti Biagio
Published: September 2014

Purpose: to evaluate the differences in clinical outcome and survivorship of three different mobile bearings for total knee arthroplasty.

Methods: a retrospective study was conducted in 60 patients (53 females, 7 males, mean age: 68 years and 5 months) each submitted to total knee replacement using one of the three different mobile bearings of the LCS system (Depuy Johnson & Johnson, Warsaw, IN). The diagnosis was knee osteoarthritis in 57 cases and rheumatoid arthritis in three cases. Three different groups of 20 cases each were identified: total knee arthroplasties with mobile menisci (group 1); total knee arthroplasties with the rotating platform (group 2); and total knee arthroplasties with the anteroposterior glide platform (group 3). As regards the component fixation, 33 implants were cementless, three were cemented, and in 24 only the tibial component was cemented. The patella was not replaced.

Results: although the duration of follow-up differed between the three groups, the clinical and radiological results at final follow-up showed no revision of femoral and/or tibial components for mechanical or septic reasons, and no signs of impending failure. One meniscal bearing, showing polyethylene wear after 17 years, was successfully replaced.

Conclusions: the present retrospective study confirmed the long-term effectiveness of knee implants with mobile bearings, in which the congruity of the surfaces makes it possible to overcome the problem of high contact stresses that may result in polyethylene wear and osteolysis; at the same time, these implants eliminate constraint forces thereby reducing the risk of mechanical loosening.

Level of evidence: Level III, retrospective comparative study.
Inertial sensors to quantify the pivot shift test in the treatment of anterior cruciate ligament injury
Authors: Zaffagnini Stefano , Lopomo Nicola , Signorelli Cecilia , Muccioli Giulio Maria Marcheggiani , Bonanzinga Tommaso , Grassi Alberto , Raggi Federico , Visani Andrea , Marcacci Maurilio
Published: September 2014

The main purpose of this article was to describe in detail, from the perspective of the clinical end user, a previously presented non-invasive methodology, applied in the treatment of anterior cruciate ligament injury, in which inertial sensors are used to quantify the pivot shift test. The outcomes obtained and relative considerations were compared with findings emerging from a review of the relevant updated literature.

The detailed description here provided covers the system, the parameters identified and the testing procedure; it also includes the technical specifications of the hardware, the features introduced in the updated version of the software and the application of the system in clinical practice.

The comparison of the technical considerations and clinical results with the updated literature confirmed the system’s optimal ergonomics, good reproducibility and clinical reliability.

The novel approach here analyzed has been shown to overcome the weaknesses of other available devices and systems. Therefore, since it can be considered a new paradigm in the quantification of pivot shift test, we can recommend its routine use in clinical practice.
Calcific tendinitis of the shoulder
Authors: De Carli Angelo , Pulcinelli Ferdinando , Rose Giacomo , Pitino Dario , Ferretti Andrea
Published: September 2014

Calcific tendinitis is a common disease that predominantly affects individuals aged between 40 and 60 years. Women seem to be more affected than men. Various factors have been suggested to play a role in this condition, such as abnormal activity of the thyroid gland, metabolic diseases (e.g. diabetes), and genetic predisposition. Various etiological hypotheses have been advanced: the degenerative and multiphasic theories are the two most accredited ones. Clinically, calcific tendinitis is characterized by severe, disabling pain which occurs spontaneously, usually in the morning. There can be concomitant stiffness, giving rise to a frozen shoulder-like clinical picture. Conventional radiography of the shoulder is the most appropriate imaging approach. Most cases resolve spontaneously. Many conservative treatments have been reported in the literature, showing varying levels of evidence of efficacy. Arthroscopic surgery is the orthopedic specialist’s last option. It is to be noted that post-surgical pain can persist for many weeks after the operation. Finally, it is important not to forget the variant characterized by osteolytic involvement of the greater tuberosity, which has been associated with a worse clinical outcome, both after conservative treatment and after surgery.
Imaging of articular cartilage: current concepts
Authors: Ronga Mario , Angeretti Gloria , Ferraro Sergio , De Falco Giovanni , Genovese Eugenio , Cherubino Paolo
Published: September 2014

Magnetic resonance imaging (MRI) is the gold standard method for non-invasive assessment of joint cartilage, providing information on the structure, morphology and molecular composition of this tissue. There are certain minimum requirements for a MRI study of cartilage tissue: machines with a high magnetic field (> 1.5 Tesla); the use of surface coils; and the use of T2-weighted, proton density-weighted fast-spin echo (T2 FSE-DP) and 3D fat-suppressed T1-weighted gradient echo (3D-FS T1W GRE) sequences. For better contrast between the different joint structures, MR arthography is a method that can highlight minimal fibrillation or fractures of the articular surface and allow evaluation of the integrity of the native cartilagerepair tissue interface. To assess the biochemical composition of cartilage and cartilage repair tissue, various techniques have been proposed for studying proteoglycans [dGEMRIC, T1rho mapping, sodium (23Na) imaging MRI, etc.], collagen, and water distribution [T2 mapping, “magnetisation transfer contrast”, diffusion-weighted imaging (DWI), and so on]. Several MRI classifications have been proposed for evaluating the processes of joint degeneration (WORMS, BLOKS, ICRS) and post-surgical maturation of repair tissue (MOCART, 3D MOCART). In the future, isotropic 3D sequences set to improve image quality and facilitate the diagnosis of disorders of articular structures adjacent to cartilage.
Locked bilateral posterior fracture-dislocation of the shoulder in an epileptic patient: case report
Authors: Cautero Enrico , Gervasi Enrico
Published: September 2014

Bilateral posterior dislocation of the shoulder, often secondary to seizures, is uncommon, while bilateral posterior fracture-dislocations is rarer still: 0.6 cases among a population of 100,000 people per year. The scientific literature contains very few published reports of cases of bilateral posterior fracture-dislocation of the shoulder, a condition that tends to be sustained by epileptic patients during seizures. The authors presented a case of bilateral posterior fracture-dislocation of the shoulder secondary to a first epileptic seizure episode treated by humeral head replacement with stem less implants on both shoulders, with satisfactory radiographic and clinical outcome.
Non-Linear Wave Runup Along the Side of Ships Causing Green Water Problems: Experiments and First CFD Calculations
Authors: Buchner Bas , van den Berg Joris , Helder Joop , Bunnik Tim
Published: September 2014

Large relative wave motions along the side of a ship can lead to green water on the deck. With a simplified test setup of a thin plate under an angle with the wave direction (to separate non-linear wave run up from motion effects), the non-linear wave reflection along the side of ships is studied in the present paper. These pilot tests with regular and irregular waves gave new insight in the process of non-linear wave run up with plunging and spilling breakers close to the plate. The complex processes observed made clear that linear or second order models will not be able to predict this behavior accurately. Previously [1] it was concluded that CFD methods that allow wave breaking are necessary for a prediction of these important effects. In the present paper a first pilot study is presented with an improved Volume of Fluid (VoF) Method. It is concluded that the method is in principle able to present these relative wave motions, but that a finer gridding is necessary to study the detailed flows.
Application of De-Icing Techniques for Arctic Offshore Production Facilities
Authors: Zaki Rezgar , Barabadi Abbas
Published: September 2014

With increasing energy demand, the oil and gas industry is pushing towards new unexplored remote Arctic areas. More than 25% of undiscovered petroleum reserves are expected to be in the Arctic region. Moreover, it is estimated that approximately 84% of the undiscovered oil and gas occurs offshore. There are numerous challenges and environmental factors that must be overcome before one can conduct oil and gas exploration, and engage production activities in Arctic regions. Superstructure icing from sea spray and atmospheric icing affect operation and maintenance of offshore production facilities in various ways including repair time, failure rate of mechanical and electrical components, power losses, life cycle cost, and safety hazard and can cause downtime in the facilities. These problems are motivating designers, manufacturers and safety researchers to find better practical solutions for ice protection technologies. Many active and passive anti-icing and de-icing techniques have been used in different industries such as electric power. However, Arctic offshore operational conditions provide new challenges for application of these methods and they have limitation of usage due to harsh and sensitive environment and wilderness, lack of infrastructure as well as distance to the market. Hence, such conditions must be considered during design and operation phase for anti-icing and de-icing techniques. This paper discusses how operational conditions of Arctic region can affect the application of available anti-icing and de-icing techniques. Moreover, it will discuss different types of ice accretion and their hazard for the Arctic offshore production facilities.
Computation of Drift Forces for Dynamic Positioning Within the Very Early Design Stage of Offshore Wind Farm Installation Vessels
Authors: Augener Philip H. , Krüger Stefan
Published: September 2014

The German government has decided upon the changeover from fossil and nuclear based electrical power generation to renewable energies. Following from this offshore wind farms are erected in the exclusive economic zones of Germany. For the transportation and installation as well as the maintenance of the wind turbine generators very specialized vessels are needed. The capability of dynamic positioning even in very harsh weather conditions is one of the major design tasks for these vessels. For this reason it is important to know the external loads on the ships during station keeping already in the very early design stage. This paper focuses on the computation of wave drift forces in regular and irregular waves as well as in natural seaway. For validation the results of the introduced calculation procedure are compared to measured drift force data from sea-keeping tests of an Offshore Wind Farm Transport and Installation Vessel.
Pressure Profile in Annulus: Solids Play a Significant Role
Authors: Zhang Feifei , Miska Stefan , Yu Mengjiao , Ozbayoglu Evren , Takach Nicholas
Published: September 2014

In drilling operations, accurate estimation of pressure profile in the wellbore is essential to achieve better bottom hole pressure control. Adjusting the drilling fluid properties and optimizing flow rate require precise knowledge of the pressure profile in the circulation system. Annular pressure profile calculations must consider solids present in the drilling fluid because the solids drilled from formations may have a significant effect on pressure in the wellbore. In cases of high solids fraction or solid pack off, the pressure loss caused by solids is much higher than the friction pressure loss. This paper looks into the effect of solids on the wellbore pressure profile under different conditions. An extensive number of experiments were conducted on a 90-ft-long, 4.5″x8″ full-scale flow loop to simulate field conditions. The effects of solids on pressure profile in the annulus are investigated. In the experimental results, a significant difference is found between the pressure profile with solids and without solids in the wellbore. A practical approach to calculate the pressure profile by considering the effects of solids in the wellbore is developed. This approach is based on the results of solids behavior in the wellbore. Both solids fraction in the well and solids pack off are considered in the proposed approach. The prediction results are in good agreement with the experimental data.

The results of this study show how the pressure profile in the wellbore varies when solids present in the annulus. The pressure gradient with solids can be several times larger than the pure friction loss without solids. A decrease in flow rate may lead to a higher pressure profile and the risk of solids pack off in the wellbore because it increases the solids fraction. Results of this paper may have important applications in drilling operations.
Small and Large Scale Experimental Investigations of Wave Loads on a Slender Pile Within Closely Spaced Neighbouring Piles
Authors: Bonakdar Lisham , Oumeraci Hocine
Published: September 2014

Wave loads on a slender pile within a group of piles are studied by means of (i) large-scale laboratory tests carried out in the Large Wave Flume (GWK) of the Coastal Research Centre (FZK) in Hannover, and (ii) small scale experiments performed in 2 m-wide wave flume of Leichtweiss-Institute for Hydraulic Engineering and Water Resources (LWI), in Braunschweig, Germany. The small scale model tests (LWI) were scaled down (1:6.5) by Froude law from the large scale model tests (GWK). Scale and model effects are examined by comparing the results of small and large scale laboratory tests.
Coupled Analysis of FPSO and CALM Buoy Offloading System in West Africa
Authors: Kang Youwei , Sun Liping , Kang Zhuang , Chai Shuhong
Published: September 2014

FPSO and CALM (Catenary Anchor Leg Mooring) buoy offloading systems are being extensively employed in water field of West Africa. In this paper we did some research on the response of FPSO and CALM offloading systems under special environment conditions in West Africa. It is found that Swell dominate sea state has much larger effects on wave frequency motions of FPSO than responding results introduced by Wind Sea dominate sea state, and squall and current will introduce large horizontal motions of FPSO, such as surge and sway. As for CALM, swell and wind sea mainly affect its heave and roll motions, respectively. Due to its little wind area, CALM does not show great response to Squall which is the extreme environment condition for FPSO though.

By comparing the results from OOL (Oil Offloading Line) dynamic analysis and quasi-static analysis, it could be that OOL dynamic effect has little influence on motions of FPSO. But it can bring large changes of responses of CALM because of its small water displacement which indicates coupled analysis of the whole system is necessary.

Besides, investigations on OOL fatigue have also been done, and the results show that CALM motion plays an important role on fatigue damage and life of OOL under different sea states.
Measurement System for Wave Energy Converter: Design and Implementation
Authors: Lindblad Liselotte , Baudoin Antoine , Leijon Mats
Published: September 2014

A Wave Energy Converter (WEC) measurement system has been constructed and installed with the purpose to measure, log and evaluate the WEC’s performance during operation at sea. The WEC is to be deployed at Uppsala University’s wave power research site in Lysekil on the west coast of Sweden.

In designing such a system the key research objectives has been (1) to study the risk of overheating due to high currents in the stator windings, (2) to evaluate how the WEC’s outer structure withstands drag and bending forces from the buoy line and (3) to construct a detection system which indicates if water leaks into the generator. The measurement system was designed to collect data essential to study these key objectives.

Transducers were used to measure: buoy line force, translator position, phase currents, bending and tensile strain on the generator hull, water level inside generator and the temperature at multiple places inside the generator. The measurement system has been installed and calibrated in the WEC. Furthermore, the design has been evaluated in lab experiments in order to verify the function and accuracy of the different measurements.

This paper presents the underlying research objectives for developing the WEC generator measurement system, together with a description of the technical implementation.
Numerical Simulation of Tsunami Run-Up and Inundation for the 2011 Tōhuku-Oki Tsunami: A Parametric Analysis for Tsunami Run-Up and Wave Height
Authors: Basu Debashis , Sewell Robert , Das Kaushik , Janetzke Ron , Dasgupta Biswajit , Stamatakos John , Waiting Deborah
Published: September 2014

This paper presents computational results for predicting earthquake-generated tsunami from a developed integrated computational framework. The computational framework encompasses the entire spectrum of modeling the earthquake-generated tsunami source, open-sea wave propagation, and wave run-up including inundation and on-shore effects. The present work develops a simplified source model based on pertinent local geologic and tectonic processes, observed seismic data (i.e., data obtained by inversion of seismic waves from seismographic measurements), and geodetic data (i.e., directly measured seafloor and land deformations). These source models estimated configurations of seafloor deformation used as initial waveforms in tsunami simulations. Together with sufficiently accurate and resolved bathymetric and topographic data, they provided the inputs needed to numerically simulate tsunami wave propagation, inundation and coastal impact. The present work systematically analyzes the effect of the tsunami source model on predicted tsunami behavior and the associated variability for the 2011 Tōhuku-Oki tsunami. Simulations were carried out for the 2011 Tōhuku -Oki Tsunami that took place on March 11, 2011, from an MW 9.1 earthquake. The numerical simulations were performed using the fully nonlinear Boussinesq hydrodynamics code, FUNWAVE-TVD (distributed by the University of Delaware). In addition, a sensitivity analysis was also carried out to study the effect of earthquake magnitude on the predicted wave height. The effect of coastal structure on the wave amplification at the shore is also studied. Simulated tsunami results for wave heights are compared to the available observational data from GPS (Global Positioning System) at the central Miyagi location.
Ultimate Shear Strength of Stiffened Panels for Offshore Structures
Authors: Rizzo Nicolau Antonio dos Santos , Amante Diogo do Amaral , Estefen Segen F.
Published: September 2014

Structures in civil, naval and aeronautical engineering commonly use plates that experience shear loading. When subjected to loading, such as shear, axial compression, bending and lateral pressure, many panel designs use stiffeners to reinforce the structure and increase the buckling capacity. Particularly, in the oil industry, platform side shell structures are made up of stiffened panels that experience a considerable amount of shear force. When added to geometrical imperfection (e.g. fabrication or supply vessel collision), this compromises the ultimate strength capability. The aim of the present study is to develop a simplified model, using FEM, to predict the ultimate loading capability of stiffened panels under pure shear stress. Furthermore, an amplified parametric study varying the geometry and initial imperfection was considered to verify such influences. Comparison with several current and published studies yielded positive and conclusive results.
Numerical Study of Wave Slamming on an Oscillating Flap
Authors: Wei Yanji , Henry Alan , Kimmoun Olivier , Dias Frederic
Published: September 2014

Bottom hinged Oscillating Wave Surge Converters (OWSCs) are efficient devices for extracting power from ocean waves. There is limited knowledge about wave slamming on such devices. This paper deals with numerical studies of wave slamming on an oscillating flap to investigate the mechanism of slamming events. In our model, the Navier–Stokes equations are discretized using the Finite Volume method with the Volume of Fluid (VOF) approach for interface capturing. Waves are generated by a flap-type wave maker in the numerical wave tank, and the dynamic mesh method is applied to model the motion of the oscillating flap. Basic mesh and time step refinement studies are performed. The flow characteristics in a slamming event are analysed based on numerical results. Various simulations with different flap densities, water depths and wave amplitudes are performed for a better understanding of the slamming.
Numerical Study of the Flow-Induced Vibration of Two Equal-Diameter Cylinders in Tandem With Varying the Mass Ratio
Authors: Tofa M. Mobassher , Maimun Adi , Ahmed Yasser M. , Jamie Saeed
Published: September 2014

Mass ratio is an important parameter that influences the vortex-induced vibration of circular cylinder, especially for a two degree of freedom system. Numerical simulations have been performed for two equal-diameter cylinders with different mass ratios in tandem arrangement which are subjected to uniform flows in subcritical flow regime. The distances between the upstream and downstream cylinders were three and four times of the cylinder diameter. The purpose of this study is to investigate the effect of upstream cylinder’s mass ratio on the vibration of downstream cylinder. The shear stress transport detached eddy turbulence model has been used for simulating the turbulent flow around the two cylinders. The numerical results of a single cylinder subjected to 2DOF vibration have been compared with the experimental results available for such cases to validate the present study.
Wave Transmission, Reflection and Energy Dissipation Characteristics of Floating and Fixed Pontoon Type Wave Barriers in Random Wave Fields
Authors: Subramaniam Neelamani , Al-Banaa K.
Published: September 2014

Wave transmission, reflection and dissipation characteristics of floating and partially immersed fixed pontoon-type barriers dictate its optimal design. Model scaled experimental investigations were carried out on two different types of wave barriers; one, a floating slack moored pontoon barrier and another, a fixed partially immersed pontoon barrier. The hydrodynamic performances for a wide range of random wave conditions are assessed. The draft of both the pontoon models is kept constant with 12.66% of water depth. JONSWAP spectra was used for random wave generation. The investigations were carried out for incident wave steepness, His/Lp in the range of 0.007 to 0.097, relative water depth, d/Lp in the range of 0.093 to 0.452 and relative width of the breakwater, B/Lp in the range of 0.133 to 0.646. It was found from this study that increasing the relative width of the wave barrier could reduce the wave transmission coefficients and increase the wave reflection and energy dissipation coefficients for both the types of wave barriers. For floating barrier, for short period waves (B/Lp of 0.5 to 0.6), the transmission coefficients were in the range of 0.25 to 0.3 and for long period waves (B/Lp of 0.13 to 0.2), the transmission coefficients were in the range of 0.8 to 0.85. Fixing the barrier in space help to reduce the wave transmission to an extent of 10% to 15%, especially for the long waves. For d/Lp in the range of 0.093 to 0.452, for fixed barrier, the reflection coefficients were in the range of 0.6 to 0.8; whereas for floating barrier, it was only in the range of 0.3 to 0.6. It was found that the wave energy dissipation coefficient is better for floating barrier (0.4 to 0.8) compared to fixed barrier (0.2 to 0.5). For a design wave length of 40 m, in order to reduce 50%, 60%, and 70% of the incident wave height on the lee side, a floating pontoon barrier with width of 17.2 m, 21.6 m and 26.0 m respectively would be needed. For the same condition, barrier widths of 12.4 m, 18.8 m, and 26.0 m would be needed for a partially immersed fixed barrier with a draft of 12.66% of water depth. The data from this study will be useful for the design of floating, as well as partially immersed fixed pontoon type wave barriers.
Numerical Assessment on Primary Wave Energy Conversion of Oscillating Water Columns
Authors: Sheng Wanan , Alcorn Ray , Lewis Tony
Published: September 2014

Oscillating water column (OWC) wave energy converters (WECs) are probably the simplest and most promising wave energy converters due to their good feasibility, reliability and survivability in practical wave energy conversions and also regarded as the most studied and developed when compared to other types of the wave energy converters.

This research aims to develop a reliable numerical tool to assess the performance of the OWC wave energy converters, particularly in the primary wave energy conversion. In the numerical assessment tool, the hydrodynamics of the device and thermodynamics of the air chamber can be studied separately. However, for the complete dynamic system when a power takeoff (PTO) system is applied, these two dynamic systems are fully coupled in time-domain, in which the PTO can have a simple mathematical expression as the relation between the pressure difference across the PTO (the chamber pressure) and its flowrate through the PTO. And the application of a simple PTO pressure-flowrate relation very much simplifies the complicated aerodynamics and thermodynamics in the air turbine system so the whole dynamic system can be simplified.

The methodology has been applied to a generic OWC device and the simulation results have been compared to the experimental data. It is shown that the developed numerical method is reliable in and capable of assessing the primary wave energy conversion of oscillating water columns.
Hydrodynamic Coefficients for Straked Risers
Authors: Nestegård Arne , Voie Per Erlend , Sødahl Nils
Published: September 2014

A considerable challenge in deep water field developments is the possibility of Vortex Induced Vibrations (VIV) of flexible risers due to presence of high currents. The most common remedy is the use of VIV suppression devices such as helical strakes.

The background for this study is the lack of guidelines for estimation of hydrodynamic force coefficients for straked risers. In particular there seems to be no publicly available experimental data on tangential force coefficients for straked risers. Analyses indicate that tangential drag may be important for compliant steel risers, e.g. SCRs and steel lazy-waves risers on high-motion platforms in harsh environments. For large vertical motion of the platform there will be a substantial tangential relative velocity along the riser. Adding strakes to the riser will then effectively increase the tangential drag.

Simplified formulations for hydrodynamic coefficients for straked risers have been derived, including added mass and drag coefficients for both normal and tangential flow. The simplified formulations are derived from basic hydrodynamic theory without experimental calibration except for the drag coefficients for normal flow where the proposed drag coefficients are empirical based on experiments reported in the literature.

An example of a global analysis of straked risers in deep water is presented to demonstrate the effect of tangential drag. Derived formulas for hydrodynamic coefficients to be used in global analysis of straked risers will be implemented in DNV GL Recommended Practices.
A Parametric Study of Wave - Structure Interaction Using the Coupled Transient CFD and Diffraction Methodology
Authors: Jia David , Agrawal Madhusuden , Malachowski Jim
Published: September 2014

This paper is a continuation of our previous paper [1] (OMAE2013-11569) where we demonstrated a state-of-the-art methodology for predicting the motions and loads of subsea equipment and structures during offshore operations basing on time domain simulations of subsea equipment and structures. Instead of relying on simplified equations or empirical formulations to calculate and estimate the hydrodynamics coefficients, or using steady-state CFD simulation on a stationary equipment and structure to predict drag and added masses on submerged structures in traditional approaches, this methodology couples the transient CFD with diffraction analysis. The time domain diffraction simulation is coupled with multiphase CFD simulation of subsea equipment and structures in waves. Transient CFD model with rigid body motion for the equipment and structure calculates added masses, forces and moments on the equipment and structure for diffraction analysis, while diffraction analysis calculates linear and angular velocities for CFD simulation. In this paper, parametric studies are performed to investigate effect of wavelength, wave amplitude and wave current on the motion of a hollow cylinder in waves. The results of the parametric studies in this paper show wave-structure interaction of a hollow cylinder in waves, and the effect of waves and current on the motion of the cylinder and the associated forces. The results provide better understanding of structure motion and associated forces in waves using this coupled methodology. The coupled methodology eliminates the inaccuracy inherited from assumed or calculated hydrodynamic properties that are obtained by using simplified equations or empirical formulations [2], or by using steady-state CFD analyses in traditional decoupled approaches. The results show that the coupled physics of wave and cylinder motion is captured by using this methodology, otherwise is not captured by traditional approaches. This coupled methodology has potential applications in analyses of the motions of subsea equipment and structures in wave during offshore operations.
Influential Study of Opening on the Mechanical Behaviour of an Integrated Superstructure
Authors: Xu Weijun , Wang Longkan , Wang Wei , Yang Nana , Pang Fuzhen
Published: September 2014

This paper concerns the mechanical behavior of an integrated superstructure with opening. Integrated superstructure with different openings was constructed by using ABAQUS code based on DDG 1000 Zumwalt Class multimission destroyer, and simulation calculations with eight cases of the superstructure under slamming load and inertial load were carried out. The influential effects of the opening positions, opening dimensions and opening types on the strength and stiffness of superstructure were explicated. Conclusions are drawn: The strength and stiffness increase with the increase of the opening dimension in the design region in the initial stage, and decrease in the later stage; With the increase of distance between the small opening and the large opening, the strength and stiffness of local structure near the large opening become weaker; the maximum Mises stress and the maximum displacement are larger when the opening is in transverse direction than in longitudinal direction. The maximum Mises stress and maximum displacement occurred at the transition surface and the borders between top and broadside, the value of maximum Mises stress is about 70–90MPa, and the maximum displacement is approximately 5mm.
Latching Control of a Floating Oscillating Water Column Wave Energy Converter in Irregular Waves
Authors: Henriques João C. C. , Chong Juan C. , Falcão António F. O. , Gomes Rui P. F.
Published: September 2014

The paper concerns the phase control by latching of a floating oscillating-water-column (OWC) wave energy converter of spar-buoy type in irregular random waves. The device is equipped with a two-position fast-acting valve in series with the turbine. The instantaneous rotational speed of the turbine is controlled through the power electronics according to a power law relating the electromagnetic torque on the generator rotor to the rotational speed, an algorithm whose adequacy had been numerically tested in earlier papers. Two alternative strategies (1 and 2) for the latching/unlatching timings are investigated. Strategy 1 is based on the knowledge of the zero-crossings of the excitation force on the floater-tube set. This is difficult to implement in practice, since the excitation force can neither be measured directly nor predicted. Strategy 2 uses as input easily measurable physical variables: air pressure in the chamber and turbine rotational speed. Both strategies are investigated by numerical simulation based on a time-domain analysis of a spar-buoy OWC equipped with a self-rectifying radial-flow air turbine of biradial type. Air compressibility in the chamber plays an important role and was modelled as isentropic in a fully non-linear way. Numerical results show that significant gains up to about 28% are achievable through strategy 1, as compared with no phase control. Strategy 2, while being much easier to implement in practice, was found to yield more modest gains (up to about 15%).
Wave Absorption Improvements Inside the Moonpool of a Monocolumn Platform With an Internal Dock
Authors: de Oliveira Allan C. , Malta Edgard B. , Vilameá Eduardo M.
Published: September 2014

Monocolumn platforms are usually considered an alternative concept for drilling and offshore production unit designs. This concept could provide high stability, small motions and also storage capacity. More recently, it was considered for a logistic hub platform design. The use of this concept with an opening for boat docking seems to provide a feasible solution for the people transfer in harsh environments, especially in areas like pre-salt Brazilian offshore fields, which are also very far from the coast. Although the helicopter technology has been improved in recent years to attend transport requirements from shore to the platforms, the use of a hub platform at sea still shows some economical and operational advantages, related to the conventional operations.

Although the sheltered area provided by the interior of the monocolumn platform seems to solve the transfer problem in harsh environments, the hydrodynamic behavior of the moonpool became a problem to be solved during the feasibility studies of the concept, since the moonpool water column elevations tends to be resonant in special cases. To deal with this problem, some attempts were done to absorb the wave energy inside the moonpool and eliminate its resonance, achieving the desired level of absorption. This work shows the attempts and the results obtained, which has proven the feasibility of the concept.
Response of Beams Under the Impact of Freak Waves
Authors: Hu Zhe , Tang Wenyong , Xue Hongxiang , Ren Shaofei
Published: September 2014

Recently the research on freak waves has focused on the formation mechanism as well as the experimental and numerical simulation, however the study of freak waves’ action on marine structures which is often confined to numerical methods is still not much. As beams are often studied as the simplified model of plates for structural safety assessment, in this paper, the response of a beam which is hit by a 2-D freak wave is studied. The freak wave is generated in a numerical wave tank (NWT) which solves the 2-D incompressible Navier-Stokes equations. The freak wave is based on the data of real sea condition in the Sea of Japan. An efficient wave absorbing method which satisfies the mass conservation is applied in the numerical wave tank. The influence of the beam’s motion on the freak wave fluid field is also considered in this paper, as well as different boundary conditions of the beam. It is found that the natural frequency has a great impact on the response of the beam.
Comparative Study on the Collapse Response of Flexible Pipe Using Finite Element Methods
Authors: Cooke Nathan , Kenny Shawn
Published: September 2014

Although the scope and use of flexible pipe systems in deepwater developments is expanding, the mechanical behavior for these environments is not fully understood. This is due to the complex response and interaction between multiple layers within the pipe system that introduces significant difficulties and constraints into the engineering analysis. As future developments look to extend the use of this technology to greater water depths and harsher operating conditions there is a need to develop advanced numerical tools that can evaluate the mechanical integrity of these complex hybrid pipe systems. Availability of increasingly advanced computational packages has enabled substantial improvements to be made in the complexity of simulation tools for combined loading, external pressure collapse and fretting.

This study establishes a foundation for the development of advanced numerical modeling procedures to assess the collapse failure of composite flexible pipe systems for deepwater applications. Here, a continuum finite element model is constructed using the software package ABAQUS/Standard, and studied using non-linear (arc length) methods. The carcass, pressure armor and corresponding polymer layers are represented in detail and modeled with three dimensional solid brick elements in order to examine the interlayer relationships influencing collapse initiation. In many recent studies, an initial geometric imperfection in the form of general ovality is explored as the predominant bifurcation mode. A similar approach is adopted here, coupled with case studies chosen such as to facilitate validation against existing analytical and numerical data. The importance of element selection, contact mechanics, interface properties and initial imperfections on the system mechanical response and performance is presented and compared to the available literature.
Fatigue Design Methodology for Large Mooring Chains Subjected to Out-of-Plane Bending
Authors: Lassen Tom , Aarsnes Jan , Glomnes Einar
Published: September 2014

The present paper presents a fatigue life prediction method for chains subjected to tension and Out-of-Plane-Bending (OPB). The investigation was carried out on a high strength mooring chain segment with a diameter of 165 mm and a steel quality R5. Such chains are used in mooring systems for large Floating Production Storage and Offloading (FPSO) units in harsh weather condition. Due to the fact that the mooring chains are pre-tensioned the wave induced displacements will introduce secondary bending effects about the weak axis in the chain links, particularly in the bilge hang-off area.

In such chains both conventional tension fatigue and fatigue damage accumulation due to Out-of-Plane-Bending (OPB) have to be analyzed. Results from full scale behavior tests, Finite Element Analyses and a case study with simulation of in-service loading are included in the present study. Finally, fatigue life predictions and an operational strategy are presented for a case study for a floater in the Barents Sea. With a target service life of 30 years, the endurance with respect to fatigue damage is a major design criterion for the mooring chain in this case.
Underwater Friction Stud Welding: Evaluating Optimum Parameter Settings for Subsea Intervention Without a Shroud
Authors: Ratnayake R. M. Chandima , Brevik Vegard Alexander
Published: September 2014

Underwater friction stud welding (FRSW) uses a shroud around the stud, controlling extreme cooling rates from the surrounding water. The FRSW commonly requires integration with a remote operating vehicle (ROV) or diving system when it is remotely operated in subsea deployed interventions. A hydraulic FRSW unit has been designed and fabricated to perform FRSW without a shroud via a ROV. Use of the FRSW unit without a shroud indicated significant challenges in welding studs underwater. Hence, an experimental study was initiated to investigate the optimum FRSW parameter values minimizing the inherent challenges. The experimental study was performed to estimate the optimum parameter settings for welding a grade 8.8 bolt on an S235 structural steel plate. This manuscript discusses the experimental approach, results and conclusions reached in the parameter evaluation, estimation and experimentation.