bluuebunny/crossref_metadata_2025 huggingface dataset:
Implication of ultraviolet light in the etiology of uveal melanoma: A review
Authors: Mallet Justin D. , Gendron Sébastien P. , Drigeard Desgarnier Marie‐Catherine , Rochette Patrick J.
Published: August 2013

Uveal melanoma is the most frequent intraocular cancer and the second most common form of melanoma. It metastasizes in half of the patients and the prognostic is poor. Although ultraviolet (UV) radiation is a proven risk factor for skin melanoma, the role of UV light in the etiology of uveal melanoma is still contradictory. We have compared epidemiological and genetic evidences of the potential role of UV radiation in uveal melanoma with data on cutaneous melanoma. Even though frequently mutated genes in skin melanoma (e.g. BRAF) differ from those found in uveal melanoma (i.e. GNAQ, GNA11), their mutation pattern bears strong similarities. Furthermore, we provide new results showing that RAC1, a gene recently found harboring UV‐hallmark mutation in skin melanoma, is also mutated in uveal melanoma. This article aims to review the work done in the last decades to understand the etiology of uveal melanoma and discuss new avenues, which shed some light on the potential role of UV exposure in uveal melanoma.
Blood lead concentrations in sub‐Saharan African children below 6 years: systematic review
Authors: Ngueta Gerard , Ndjaboue Ruth
Published: August 2013

Objective

To assess the geometric mean of blood lead levels in children aged below 6 years living in sub‐Saharan Africa.

Methods

Search strategies were developed in MEDLINE, Web of Science and Google scholar system, supplemented by screening of references from included papers and review articles. Studies including children younger than 6 years residing in sub‐Saharan Africa (SSA) were eligible. The studies were assessed for quality of methods for blood collection, for participants’ recruitment and for quality control for lead analyses. Data were extracted and synthetised by estimating the mean weighted by sample size.

Results

A total of 11 148 published papers were identified with only 16 studies conducted in SSA. Only nine of them were relevant of inclusion criteria. The weighted mean of blood lead levels was 13.1 μg/dl. Five of included studies were classified as being less likely to present selection bias, having performed venipuncture and adequate quality control for lead analyses. The weighted mean from analyses involving only these studies was 16.2 μg/dl. Six of the included studies reported the prevalence of blood lead levels ≥10 μg/dl; levels ranged from 7.0% to 70.9%. Only one study reported the prevalence of blood lead levels ≥5 μg/dl (50%).

Conclusions

The geometric mean of blood lead levels in sub‐Saharan African children is still elevated relative to the US children. The new standard from the Centers for Disease Control and Prevention (5 μg/dl) implies that important efforts should be directed towards the initiation (or reinforcement) of prevention programmes and thorough research studies in sub‐Saharan Africa.
Effect of voluntary hyperventilation with supplemental CO2 on pulmonary O2 uptake and leg blood flow kinetics during moderate‐intensity exercise
Authors: Chin Lisa M. K. , Heigenhauser George J. F. , Paterson Donald H. , Kowalchuk John M.
Published: August 2013

New findings

What is the central question of this study?

Voluntary hyperventilation that induces hypocapnic alkalosis (HYPO) is associated with slowed adaptation of O2 uptake and leg blood flow during moderate exercise; however, it is unknown whether hypocapnia, alkalosis and/or the hyperventilation manoeuvre is related to these observations.

What is the main finding and its importance?

We included a condition with the same work of breathing as HYPO, but the fall in CO2 was prevented by the addition of higher CO2 to the inspirate (normocapnia). This condition demonstrated that hypocapnia/alkalosis was responsible for the slower leg blood flow response; however, the act of hyperventilation itself also had a role to play in the slower O2 uptake kinetics.

Pulmonary O2 uptake () and leg blood flow (LBF) kinetics were examined at the onset of moderate‐intensity exercise, during hyperventilation with and without associated hypocapnic alkalosis. Seven male subjects (25 ± 6 years old; mean ± SD) performed alternate‐leg knee‐extension exercise from baseline to moderate‐intensity exercise (80% of estimated lactate threshold) and completed four to six repetitions for each of the following three conditions: (i) control [CON; end‐tidal partial pressure of CO2 () ∼40 mmHg], i.e. normal breathing with normal inspired CO2 (0.03%); (ii) hypocapnia (HYPO; ∼20 mmHg), i.e. sustained hyperventilation with normal inspired CO2 (0.03%); and (iii) normocapnia (NORMO; ∼40 mmHg), i.e. sustained hyperventilation with elevated inspired CO2 (∼5%). The was measured breath by breath using mass spectrometry and a volume turbine. Femoral artery mean blood velocity was measured by Doppler ultrasound, and LBF was calculated from femoral artery diameter and mean blood velocity. Phase 2 kinetics (τ) was different (P < 0.05) amongst all three conditions (CON, 19 ± 7 s; HYPO, 43 ± 17 s; and NORMO, 30 ± 8 s), while LBF kinetics (τLBF) was slower (P < 0.05) in HYPO (31 ± 9 s) compared with both CON (19 ± 3 s) and NORMO (20 ± 6 s). Similar to previous findings, HYPO was associated with slower and LBF kinetics compared with CON. In the present study, preventing the fall in end‐tidal (NORMO) restored LBF kinetics, but not kinetics, which remained ‘slowed’ relative to CON. These data suggest that the hyperventilation manoeuvre itself (i.e. independent of induced hypocapnic alkalosis) may contribute to the slower kinetics observed during HYPO.
Non‐quantal release of acetylcholine in rat atrial myocardium is inhibited by noradrenaline
Authors: Borodinova Anastasia A. , Abramochkin Denis V. , Sukhova Galina S.
Published: August 2013

New findings

What is the central question of this study?

Is non‐quantal release of ACh in the heart regulated by noradrenaline or does it represent uncontrolled leakage of ACh from cardiac cholinergic fibres?

What is the main finding and its importance?

Cardiac non‐quantal ACh release can be negatively regulated by noradrenaline. This finding suggests that non‐quantal release has physiological relevance and is also important in the context of cholinergic–adrenergic interactions in the heart.

In the mammalian myocardium, ACh, which is the main neurotransmitter of cardiac parasympathetic postganglionic fibres, can be released via both quantal (vesicular) and non‐quantal (non‐vesicular) mechanisms of secretion. Non‐quantal release is continuous and independent of vagus activity and exocytosis of ACh‐containing vesicles. During the incubation of myocardium in the presence of acetylcholinesterase (AChE) inhibitors, non‐quantal ACh release leads to accumulation of ACh in the myocardium and cholinergic effects, which are proportional to the intensity of non‐quantal secretion. The aim of the present study was to reveal whether non‐quantal release of ACh can be modulated by another major cardioregulator, noradrenaline, or whether it represents uncontrolled leakage of ACh from cholinergic fibres. Cholinergic changes of electrical activity induced by the AChE inhibitor paraoxon (5 × 10−6 m) in isolated rat right atrial preparations were determined by means of a standard microlectrode technique and used as a measure of the intensity of non‐quantal release. Noradrenaline (10−7 and 10−6 m) substantially suppressed, but did not abolish, effects of paraoxon via stimulation of α‐adrenoceptors, because all experiments were conducted in the presence of the β‐blocker propranolol (5 × 10−6 m). A blocker of ganglionic transmission, hexamethonium bromide (10−4 m), failed to alter the inhibitory effect of noradrenaline, indicating that only non‐quantal ACh release is suppressed by this neurotransmitter. The effects of noradrenaline could be reduced by the α2‐antagonist yohimbine (10−6 m). However, both the α1‐agonist phenylephrine (10−6 m) and the α2‐agonist clonidine (10−6 m) significantly inhibited the cholinergic effects of paraoxon, indicating the possible involvement of both α‐adrenoceptor subtypes in mediation of the adrenergic inhibition of non‐quantal ACh release. Thus, cardiac non‐quantal ACh release can be negatively regulated by noradrenaline, providing another facet of sympathetic–parasympathetic interaction in the heart.
Enhanced purinergic contractile responses and P2X1 receptor expression in detrusor muscle during cycles of hypoxia–glucopenia and reoxygenation
Authors: Elliott R. A. , Tonnu A. , Ghaffar N. , Taylor A. H. , Tincello D. G. , Norman R. I.
Published: August 2013

New findings

What is the central question of this study?

Given that the bladder in 60% of patients with detrusor overactivity exhibits increased atropine‐resistant contractile responses to nerve stimulation and that high intravesicular pressure is associated with episodes of hypoxia–glucopenia and reperfusion, we asked whether cycles of hypoxia–glucopenia and reoxygenation increases purinergic signalling in the rat bladder in vitro.

What is the main finding and its importance?

Four cycles of hypoxia–glucopenia and reoxygenation augmented atropine‐resistant contractile responses of rat detrusor muscle strips subjected to electrical field stimulation via increased purinoceptor P2X1 expression and ATP release. Purinergic antagonists blocked this augmentation, suggesting a possible therapeutic role for purinergic antagonists in the treatment of detrusor overactivity.

Bladders from patients with detrusor overactivity have an increased atropine‐resistant contractile response to nerve stimulation. The bladder has also been shown to be very susceptible to hypoxia–glucopenia and reperfusion injury, leading to the hypothesis that episodes of hypoxia–glucopenia and reoxygenation result in increased atropine‐resistant responses to nerve stimulation in the detrusor muscle. Detrusor muscle strips were suspended in a Perspex organ bath chamber of volume 0.2 ml perfused with Krebs solution at 37°C aerated with 21% O2, 5% CO2 and the balance nitrogen. Hypoxia–glucopenia was induced by switching perfusion to Krebs solution without glucose, gassed with 95% nitrogen and 5% CO2. Atropine‐resistant contractile responses increased by 40.5 ± 7.3% after four cycles of hypoxia–glucopenia (10 min) and reoxygenation (1 h), whereas α,β‐methylene ATP‐resistant responses did not increase. Expression of P2X1 receptors in the bladder was increased after hypoxia–glucopenia and reoxygenation cycling, and ATP release from stimulated bladder strips during cycling was also increased. Other P2X receptor‐mediated mechanisms may also be involved in the augmentation of bladder contraction during hypoxia–glucopenia and reoxygenation cycling, because a non‐specific P2X antagonist blocked most of the augmented response, whereas a P2X1‐specific antagonist prevented only part of the augmentation of contractile response induced by hypoxia–glucopenia and reoxygenation. In conclusion, four cycles of hypoxia–glucopenia and reoxygenation increased the purinergic, but not the cholinergic, contractile responses to nerve stimulation. Increased P2X1 receptor expression and ATP release may have contributed to the augmentation of contractile response induced by hypoxia–glucopenia and reoxygenation. Purinergic antagonists may, therefore, be a useful therapeutic option for the treatment of overactive bladder with increased purinergic‐mediated contractions.
Strength Behaviour Analysis of an Offshore Brazilian Marine Clay
Authors: Fagundes Diego F. , Rammah Khader I. , Almeida Marcio S. S. , Pequeno Julio , Oliveira Jose Renato M. S. , Borges Ricardo Garske
Published: August 2013

The main purpose of this paper is to describe the geotechnical behaviour of a deep water marine clay obtained from Campos basin oil field located offshore the state of Rio de Janeiro in Brazil. The soil samples were obtained at a depth of about 1500 m using a Kullenberg piston corer. Characterization tests were undertaken on the clay samples, including water content, Atterberg limits, particle size distribution and specific density. Isotropic and anisotropic undrained triaxial tests were also carried out on both normal and over-consolidated samples to assess both the conventional strength and Cam-clay parameters. Additionally, oedometer tests were performed to evaluate the compressibility of both undisturbed and reconstituted soil samples. Finally, a series of T-bar penetrometer tests were performed on the mini-drum geotechnical centrifuge at COPPE, the University of Rio de Janeiro to establish the undrained shear strength profile. The results obtained from the T-bar tests were compared with the theoretical strength curves that were established based on the Cam-clay parameters derived from the laboratory tests. The results obtained in this study indicated a useful methodology to assess and capture the behaviour of marine clay. The assessment of strength behaviour of marine clay is quite essential in modelling of wide range of soil-offshore structure interaction problems such as pipelines, mudmats and anchors.
A Hybrid Analysis Method for Investigating Oil Cleanup Operations at Sea
Authors: Clauss Günther F. , Kosleck Sascha , Sprenger Florian , Stuppe Sven
Published: August 2013

The severe ecological and economical aftermath of the 2010 ‘Deepwater Horizon’ catastrophe in the Gulf of Mexico clearly shows the insufficiency of current oil recovery systems which cannot operate in wave heights above 1.5 m. To prevent emulsification and weathering processes, it is necessary to skim the oil film off the sea surface shortly after the accident. The autonomous SOS (Sea State-independent Oil Skimming System) developed within the framework of the research project SOS3 features high transit velocities, the capability of operating in rough seas and a massive intake of oil polluted water — and is therefore a unique technology. Numerical analyses of realistic oil skimming operations require three-dimensional transient three-phase flow simulations in order to take into account wave-induced ship motions. Due to the computational effort, a simplified approach is chosen for systematic investigations. Model tests at a scale of 1:25 are conducted in two different irregular sea states. In order to represent oil cleanup operations as realistically as possible, towing tests at constant velocities are replaced by a series of experiments with a free-running model. A self powered tug pushes the oil skimming barge and experiences interactions with waves, influencing the velocity and therefore the skimming performance of the SOS. Data from optical motion measurements of the barge is then used as input for two-dimensional CFD simulations. The numerical analyses are focusing on the oil-water-separation process of the realistically moving coupled system in different irregular sea states.
Large Deformation Numerical Simulations Regarding Soil Plugging Behaviour Inside Open-Ended Piles
Authors: Henke Sascha
Published: August 2013

Soil-plugging inside open-ended piles is a well-known phenomenon which increases vertical bearing capacity on the one hand but also leads to increasing driving resistance. There are many different factors affecting the tendency of soil-plug formation like pile diameter, geometry of the pile, installation method, soil density and so on. With the basis of experimental data numerical models to simulate the pile installation process to better understand the mechanisms of soil plugging inside open-ended piles are validated. The validated numerical models are used to examine different aspects regarding the phenomenon of soil plug formation. First, the evolution of internal and external shaft friction is investigated in more detail with focus on pile diameter. Furthermore, the impact of internal reinforcements like internal rings are investigated numerically. The shape of the internal ring is varied throughout this study to evaluate the influence of this key factor on internal stress development.
Numerical Studies of a Floating Cylindrical OWC WEC
Authors: Sheng Wanan , Lewis Anthony , Alcorn Raymond
Published: August 2013

Oscillating water column (OWC) wave energy converters (WECs) are a popular type of wave energy devices. Generally, the OWC WECs have a simple structure and working principle, but with a high conversion efficiency, and a high reliability in power take-off due to a small torque and a high rotation speed for a certain power extraction. The OWC devices convert wave energy into pneumatic energy primarily by producing the pressured and de-pressured air (pneumatic energy) in the air chamber through the motions of the interior water surface in the water column. Conventionally, the pneumatic energy is converted into mechanical energy through an air turbine (in small scaled model, an orifice or porous membrane material is used for non-linear or linear power take-off modelling). However, these processes are very limitedly understood due to the complexities of the hydrodynamics, aerodynamics, and thermodynamics and their coupling effects. Theoretical and numerical attempts are very limited, especially when the coupling effects are included. As a result of the difficulties, in the device development, the most popular and acceptable approach may be the model tests, with different scaling factors in their corresponding development stages, as recommended by the relevant wave energy development protocols. To reduce the dependencies on the physical modelling in the OWC device development, numerical methods are very desirable to accommodate the simulation and assessment of the hydrodynamic and aerodynamic/thermodynamic performances of the OWC WECs. This is the main target of this investigation.

In this numerical simulation, the hydrodynamic performances (including the motions of the structure and the interior water surface in waves) are carried out by employing a conventional boundary element method (i.e., WAMIT in this case) in frequency domain. To include the effects of the airflow passing through an orifice, its aerodynamic performance is much simplified by assuming its effects on the hydrodynamic performance through some extra damping coefficients to the motions of the floating structure and to the motion of the interior water surface. In this way, the interior water surface response can be obtained for the coupling effects of the hydrodynamics and aerodynamics of the OWC WEC. In this regard, an important issue in the numerical simulation is to seek an appropriate representation of the damping levels.
Numerical Simulation of Spudcan Penetration Into Silica Sand and Prediction of Bearing Behaviour
Authors: Pucker Tim , Bienen Britta , Henke Sascha
Published: August 2013

Prediction of the bearing behavior of vertical loaded shallow foundations is typically done using the classical bearing capacity approach. This approach is very sensitive to the friction angle assumed in the calculation. A conservative estimate of the bearing capacity is required for most applications, hence uncertainties in the friction angle may be absorbed by the safety factor applied. Spudcans are used to found mobile jack-up platforms in the oil and gas industry as well as in the offshore wind energy industry. Contrary to the classical approach, the bearing capacity of spudcans has to be predicted accurately. Spudcans are penetrated into the seabed and a continuous bearing failure proceeds until the target capacity is met. A Coupled Eulerian-Lagrangian (CEL) approach is used to simulate the penetration process of spudcans into silica sand. The sand is modeled using a hypoplastic constitutive model to capture the influence of the void ratio and stress state for example. A parametric study of foundation diameter and enclosed cone angle is presented. The numerical model is validated against results from centrifuge experiments of flat and conical circular footings penetrating into silica sand. A first empirical approach to estimate the bearing capacity depending on the diameter and enclosed cone angle is given for silica sand.
On the Effect of Hull Girder Flexibility on the Vertical Wave Bending Moment for Ultra Large Container Vessels
Authors: Vincent Andersen Ingrid Marie , Jensen Jørgen Juncher
Published: August 2013

Currently, a number of very large container ships are being built and more are on order, and some concerns have been expressed about the importance of the reduced hull girder stiffness to the wave-induced loads. The main concern is related to the fatigue life, but also a possible increase in the global hull girder loads as consequence of the increased hull flexibility must be considered. This is especially so as the rules of the classification societies do not explicitly account for the effect of hull flexibility on the global loads. In the present paper an analysis has been carried out for the 9,400 TEU container ship used as case-ship in the EU project TULCS (Tools for Ultra Large Container Ships). A non-linear time-domain strip theory is used for the hydrodynamic analysis of the vertical bending moment amidships in sagging and hogging conditions for a flexible and a rigid modelling of the ship. The theory takes into account non-linear radiation forces (memory effects) through the use of a set of higher order differential equations. The non-linear hydrostatic restoring forces and non-linear Froude-Krylov forces are determined accurately at the instantaneous position of the ship in the waves. Slamming forces are determined by a standard momentum formulation. The hull flexibility is modelled as a non-prismatic Timoshenko beam. Generally, good agreement with experimental results and more accurate numerical predictions has previously been obtained in a number of studies. The statistical analysis is done using the First Order Reliability Method (FORM) supplemented with Monte Carlo simulations. Furthermore, strip-theory calculations are compared to model tests in regular waves of different wave lengths using a segmented, flexible model of the case-ship and good agreement is obtained for the longest of the waves. For the shorter waves the agreement is less good. The discrepancy in the amplitudes of the bending moment can most probably be explained by an underestimation on the effect of momentum slamming in the strip-theory applied.
Fatigue Testing of Full Scale Girth Welded Pipes Under Variable Amplitude Loading
Authors: Zhang Y.-H. , Maddox S. J.
Published: August 2013

In the fatigue design of steel catenary risers there are concerns regarding the fatigue damage to girth welds from low stresses, below the constant amplitude fatigue limit, in the loading spectrum and the validity of Miner’s cumulative damage rule. In both cases there is increasing evidence that current design methods can be non-conservative. These fundamental issues were addressed in a recent JIP. A key feature was development of the resonance fatigue testing rigs to enable them to test full-scale pipes under variable amplitude loading. Such tests were performed under a loading spectrum representative of that experienced by some risers, with many tests lasting over 100 million cycles to investigate the fatigue damage due to small stresses as well as the validity of Miner’s rule. However, the resonance rigs are only capable of producing spectrum loading by gradually increasing or decreasing the applied load, whereas more ‘spiky’ random load sequences may be relevant in practice. Therefore the programme also included fatigue tests in conventional testing machines on strip specimens cut from pipes to compare the two types of loading sequence. This paper presents the results of these tests, conclusions drawn and recommendations for changes to current fatigue design guidance for girth welded pipes regarding the definition of the fatigue limit, allowance for the damaging effect of low stresses and the validity of Miner’s rule.
A Numerical Investigation of Flow Around a Circular Cylinder Near a Flat Boundary
Authors: Neto Mário Caruso , Wanderley Juan B. V.
Published: August 2013

Flow around a pipeline near the seabed still remains relatively unknown in spite of the efforts of many researchers to understand the complicated flow around bluff bodies. The present study contributes to this discussion numerically investigating two-dimensional fluid flow around a circular cylinder near a flat plate. The investigation contemplates Reynolds numbers of 100, 180 and 7000 and a gap ratio (G/D) of 3, 0.6, 0.3 and 0.125. The flow is simulated considering a finite difference and total variation diminishing (TVD) conservative scheme with a Chimera domain division method to solve RANS equations. The k-e turbulence model is used to simulate the turbulent flow in the high Reynolds number case. Results are obtained for force coefficients and flow visualization. The results show a significant variation of flow characteristics with gap ratio and Reynolds number variation.
High Porosity Net Drag at a Low Angle of Attack in Application to a Representative Prawn Trawl
Authors: Balash Cheslav , Bose Neil , Binns Jonathan , Sterling David
Published: August 2013

The presented work investigated the extent by which Reynolds number determines the drag coefficient for high porosity nets at a low angle of attack. A simple prawn trawl model that incorporates the main design features of prawn trawls employed in Australia was developed. Four trawl models of various high porosities were tested in a flume tank with respect to drag and shape over a range of flow velocities. The physical trawl model was analysed as a system of independent plane net sheets, each with an orientation to the flow estimated from analysis of stereo-vision data. The main finding was that the drag coefficient was weakly dependent on the Reynolds number in the range typical for prawn trawl operations, 1000<Re<1700. These combined findings imply that trawler operators can approximately estimate prawn net drag from a function containing trawl twine area, towing speed and spread ratio.
Geotechnical Stability of Gravity Base Foundations for Offshore Wind Turbines on Granular Soils
Authors: Sedlacek Germán , Miehe Alina , Libreros Ana , Heider Yousef
Published: August 2013

Offshore wind energy farms have gained much attention during the last years in Germany and all over the world. In the construction of offshore wind turbines, piled foundations have been mostly used so far. However, gravity base foundations represent a good alternative as they minimize the typical high risks of the offshore works, such as weather-dependent installation, operational safety, construction sequence and performance. The whole wind energy turbine is assembled onshore and promptly transported to the planned location.

In the design of the gravity foundation under cyclic loading conditions, it is essential to avoid inadmissibly large reductions of the subsoil bearing capacity due to the excess pore-water pressure (loss of stability) and tilting of the foundation caused by the accumulation of settlements (loss of serviceability).

This paper provides a description of the soil-mechanical behaviour of gravity base foundations and gives an account of the current available rules and standards for dimensioning foundations of this type. In this regard, a procedure for the geotechnical design of a gravity base foundation is laid out, where this work points out that the existing standards for designing gravity base foundations need to be further developed. Moreover, a brief summary of the results at a full-scale model test, according to the present state of testing and knowledge, are given.
Effect of Water or Soap Solution on Fatigue Crack Growth in Welded Steel
Authors: Dimitriu Radu , Maddox Stephen
Published: August 2013

It is common practice to conduct fatigue tests on full-scale girth welded pipes in resonance bending with a static axial mean stress induced by internal water pressure. Clean tap water is used, which gradually stagnates with time during a long endurance test, and therefore it is generally assumed that it has no significant effect on the fatigue lives of cracks propagating from the inside. However, important conclusions are drawn from such tests, especially when they relate to risers, and therefore there is a need to check this.

In a different context there is a similar need to check the effect of soap solution on fatigue. This is often applied during fatigue tests on welded joints that fail from an accessible weld toe as an aid to crack detection. Furthermore, it may continue to be applied when a crack has been detected in order to produce beachmarks on the fatigue fracture surface by staining.

The present paper presents the results of a series of fatigue crack growth rate (FCGR) tests that aimed to establish the effects of clean water or soap solution on the fatigue performance of welded structural steel. The tests were carried out on standard single edge-notched bend (SENB) specimens machined from girth welds in X65 grade steel pipe. Comparative tests were conducted at ambient temperature in air, tap water, de-ionized water and soap solution environments. Noting the general finding that corrosion-fatigue crack growth rate increases with decrease in load cycling frequency, the influence of frequency between 0.1 and 10Hz was investigated.
Towards a Model for Propeller-Ice Interaction
Authors: Peddle Adam , Dang Jie , van Terwisga Tom
Published: August 2013

A reduced level of Arctic sea ice in recent years has resulted in an increase in commercial interest in shipping through previously inaccessible waters, such as the Northwest Passage. This interest has been significantly reinforced by the fact that vast amounts of natural resources are expected to exist in the Arctic regions. As such, the operation of vessels in ice-covered waters is currently a research topic of great relevance.

Computational methods such as those based on potential flow have become invaluable in the evaluation and optimization of marine propellers, though as of this writing there exists a deficit of proven software tools to evaluate the operation of propellers in icy waters. In order to properly develop a model and a tool, a physical understanding of the involved processes is vital.

A Cooperative Research Ships (CRS) project has been initiated with the ultimate aim of developing a software tool for the evaluation of propellers operating in ice which will operate within the CRS PROCAL environment. The research described in this paper is the first step in the development of such a tool.

This paper is intended to serve primarily as a review of the existing literature on mathematical models of propeller-ice interaction as well as their numerical solutions. Such a study serves as a vital first step in the development of a complete method for propeller ice interaction. In addition to providing an overview of the current level of understanding in the field, this paper intends also to identify which areas are well understood and which require further investigation. It will highlight the strengths and shortcomings of current models with the intention of advancing towards the final model.
Numerical Estimation of Nonlinear Wave Forces on a Multi-Hull Barge Using Finite Element Method
Authors: Senan Aswathy , Krishnankutty P.
Published: August 2013

This paper deals with the estimation of second order wave excitation forces on a free floating triple-hull barge using software developed based on finite element method. The wave-hull interaction nonlinear problem is presented here using the perturbation method, where potential flow theory is used. In the finite element model, the absorbing or nonreflecting far boundary condition is applied at a truncated surface in the form of boundary damper. The software developed for the solution of this nonlinear problem is validated for two and three-dimensional cases for which analytical and other numerical solutions are known. A convergence study on the three-dimensional cylinder problem is carried out to derive a guideline in selecting finite element mesh density and its grading. A triple-hull barge problem is selected here as a practical problem to study the nonlinear wave effects on the forces and motions. A grid independent study on this problem is carried out by using four finite element meshes of different density and grading. The optimum mesh selected from this study is used for further analysis of the problem. Bandwidth optimization is carried out on the generated meshes in order to reduce the computational effort, as the finite element algorithm used here is based on the banded solver technique. The second order wave excitation forces and moments on the barge estimated for different wave steepness (H/Lw - 0.08 to 0.012) in oblique sea condition shows that the second order surge and heave forces amounts up to 49% and 17.5% respectively and the second order yaw moment up to 39% when compared with the first order (linear) wave forces. Similar trend is observed for the forces and moments in beam sea and head sea conditions.
Frequency Components of Vortex Induced Vibrations in Sheared Current
Authors: Larsen Carl M. , Zhao Ziguang , Lie Halvor
Published: August 2013

Vortex induced vibrations (VIV) of long flexible risers subjected to ocean currents are of vital interest to the offshore industry. Although significant efforts have been seen during the last decades, reliable prediction of this complicated fluid structure interaction phenomenon is still a challenge.

The primary objective of this paper is to characterize the frequency components of VIV measured in flexible beams subjected to sheared current, and try to establish a general model for frequency participation for use in semi-empirical models for calculation of fatigue damage from VIV. Experimental data from the well known Hanøytangen tests and the Norwegian Deep-water Programme (NDP) high mode experiments have been used in this study. The present paper is mainly based on results from Ziguang Zhao (2011).

Wavelet analyses are applied to reveal the frequency components in the measured signals. These analyses give information on the time-varying intensity of each active frequency at a specific position on the beam. The dominating frequency and range of other active frequencies are two key parameters from the wavelet analyses that are further used in this work.

By comparing synchronic measurements from various positions along the beam, we can see that neighbor locations often will display the same time-varying peak frequency. However, the response at two positions apart form each other may be dominated by different frequencies. Hence, the time sharing concept needs to be reformulated from describing a frequency variation valid for the total length of a riser, to consider different zones separately. Based on the observation above, a combined time sharing and space sharing model is proposed. The controlling parameters in this model are an energy based parameter that ranks the participating frequencies, a threshold for a frequency candidate to become active, and the length of the excitation zone for each frequency. All parameters can easily be found for cases of practical interest.
Reconstruction and Prediction of Short-Crested Seas Based on the Application of a 3D-FFT on Synthetic Waves: Part 1 — Reconstruction
Authors: Naaijen Peter , Blondel-Couprie Elise
Published: August 2013

This article explores the feasibility of using a 3-dimensional Fast Fourier Transform (3D FFT) to obtain a frequency domain description of a spatio temporal measured short crested wave field. As 3D FFT is also the basic technique behind wave measurements by navigational X-band radars, the frequency components obtained by these radars could be used as initialization of a wave propagation model, enabling deterministic prediction of wave elevation on board of ships / offshore structures. Different methods are presented to use the dispersion relation to filter wave components obtained by the 3D FFT. The effect on the accuracy of data windowing and temporal measurement domain size are explored by simulations with linear synthetic wave data: It is investigated how well a synthetic wave field reconstructs after inverse transforming the filtered frequency components obtained by 3D FFT. A second paper [1] will consider the prediction outside the measurement domain by using the filtered 3D FFT components.
Reconstruction and Prediction of Short-Crested Seas Based on the Application of a 3D-FFT on Synthetic Waves: Part 2 — Prediction
Authors: Blondel-Couprie E. , Naaijen P.
Published: August 2013

This paper is the natural follow-up of the paper [6] also presented at OMAE 2012 by the authors. In [6] the authors describe various linear reconstruction methods for short-crested seas. Each of them is based on a specific analysis technique for the spectral components obtained when applying a 3D Fourier Transform to a series of snap shots of the ocean surface. The efficiency and the accuracy of each method is investigated in [6] for the reconstruction of synthetic images of linear short-crested wave fields.

The purpose of the second part of the paper is to test the most accurate methods described in [6] for the prediction of synthetic linear waves. The predicted wave fields are calculated within a specific area in space and time called the prediction zone, which is determined theoretically. The method for determining the theoretical prediction zone is also described in this part of the paper.
Prediction of Stabilizing Moments and Effects of U-Tube Anti-Roll Tank Geometry Using CFD
Authors: Thanyamanta Worakanok , Molyneux David
Published: August 2013

U-tube type stabilizers have been used in ships and offshore vessels to reduce roll motion. The motion of the fluid in the tank creates moments that counteracts the roll moment of the ship. With space and weight constraints, a well designed U-tube tank is crucial for providing effective stabilization. Geometric parameters play important roles in defining the stabilizing performance of such tanks. The effects of these parameters are sometimes interrelated. Computational Fluid Dynamics (CFD) is a useful tool that can be used to predict stabilizing moments and phase lags of U-tube tanks in a short period of time. In order to use the CFD code reliably, validation is required.

In this paper, a CFD code’s ability to predict stabilizing moments created by fluid in various U-tube tank geometries was validated. The effects of tank parameters on the stabilizing moments were investigated and compared with published experiment data. The results were found to be in good agreement with the model test data. The code can be used to give a preliminary evaluation of tank performance for design purposes.
Hydrokinetic Energy Extraction Potential of a Turbine Array Placed Across the Florida Current
Authors: Duerr Alana E. S. , Dhanak Manhar R.
Published: August 2013

The Florida Current has been noted as a potential resource for ocean hydrokinetic energy. The area encompassed by the geographical extent of Florida Current is substantial compared to the required footprint of an array of hydrokinetic turbines that may be implemented to harness the hydrokinetic energy of the current. A method has been developed to use data from the HYbrid Coordinate Ocean Model (HYCOM) for the Florida Current to identify favorable locations for installation of current turbines. Cross-sectional current data along lines of constant latitude from 25 to 30 °N off of Florida’s east coast have been analyzed. Optimum hydrokinetic turbine array installation sites within the Florida Current were determined, and hydrokinetic turbine array extraction estimates have been made at one of these identified locations.
A Study on Characteristics of Frost Heaving With Soil Samples From Terra Nova in the East Antarctic Region
Authors: Kim YoungSeok , Hong Seung-Seo , Park Jung-Hee , Kang Jae Mo , Lee Jong-Sub
Published: August 2013

The second scientific Antarctica station of South Korea is under construction at Terra Nova Bay located in east Antarctica. The objective of this study is the evaluation of the frost heave susceptibility of soils sampled from the second station site by performing laboratory frost heaving tests. Experiments are carried out with the soil specimens taken from five different areas at Terra Nova Bay. Test specimens are frozen with constant temperatures at the top and bottom of the specimen at −17 °C and 4 °C, respectively. In addition, grain size analyses and unfrozen water tests are also performed for monitoring the characteristics of the water contained in the permafrost. Frost susceptibility is evaluated by standard methods recommended in UK, US and Japan. Experimental results show that the more the fine contents exist in soils, the more frost heave occurs. The result denotes that grain size has a significant effect on frost heave. The results suggest that the frost heaving susceptibility of the frozen ground at the Antarctic site would be effectively evaluated through the grain size and the frost heaving parameters.
Temperature Distribution and Frozen Soil Characteristics at Jangbogo Antarctic Research Station
Authors: Hong Seung-Seo , Kim YoungSeok , Park Jung-Hee , Lee Jangguen , Lee Jong-Sub
Published: August 2013

Temperature monitoring along the depth in construction site of the Jangbogo Antarctic research station (74° 37′S, 164° 12′E) was carried out. The thermal behavior of the frozen ground was investigated. The temperatures were measured during site investigation from February 07, 2011 to February 12, 2011. The temperature profile was analyzed in the frozen ground. The results show that the increase along with the depth. This study demonstrates that the temperature profile obtained at this site could be effective reference for the construction of the research station in the Antarctic.
Benchmark Study on Thruster-Hull Interaction in Current on a Semi-Submersible Crane Vessel
Authors: Ottens Harald , van Dijk Radboud
Published: August 2013

The ability of a DP-vessel to keep its position depends highly on the performance of the DP system. The thrust efficiency of the DP-system depends on the efficiency of the individual thrusters, but also on the interaction of the thruster wake and the hull of the vessel. This thruster-hull interaction becomes even more important when the vessel is a semi-submersible vessel; the thruster wake of the thruster on the upstream pontoon might impinge on the downstream pontoon resulting in high losses in efficiency and reduced DP-capability. Heerema Marine Contractors has two DP-semi-submersible crane vessels; the Thialf and Balder. An assessment of the thrust efficiency of the DP thrusters of these vessels has been made by comparing CFD computations with dedicated model tests.

In previous benchmark studies CFD is used to assess the current loads as well as thruster-hull interaction without current on a semi-submersible vessel. The logical next step is to perform a numerical study on a thruster-hull interaction with current. Similar as the previous benchmark studies the numerical data are validated with a series of dedicated model tests. The model test data include the global forces, the forces on each individual pontoon and the forces of each individual thruster, including the nozzle thrust and propeller thrust. The comparison between the CFD and model test data shows that CFD is able to predict the relevant force components within a sufficient accuracy for engineering purposes.

At present not much is known about the extrapolation of model scale DP-thrust efficiency to full scale DP-thrust efficiency, neither for model test results, nor for CFD results. Scaling CFD from model scale to full scale is not trivial; it involves a significant change in Reynolds number, a different description of boundary layer and poses challenges to meshing and grid. Therefore, validation is required. A first validation study is performed based on data acquired during a transit of SSCV Thialf in Q4 2011. In preparation, CFD simulations are performed for different thrust combinations. These results are compared to full scale observations and, where possible, improvements to the numerical modeling are assessed.

The paper addresses lessons learnt to improve the CFD computations as well as practical aspects and limitations of thrust efficiency modeling, including all interaction effects, using CFD from an engineering perspective.
Centrifuge Study of the Effects of Lattice Leg on Penetration Resistance and Bearing Behavior of Spudcan Foundations in NC Clay
Authors: Li Yu Ping , Lee Fook Hou , Goh Siang Huat , Yi Jiang Tao , Zhang Xi Ying
Published: August 2013

This paper reports the primary results of a centrifuge model study into the possible effects of the lattice leg on the penetration resistance and vertical bearing capacity of spudcan foundations in normally consolidated clay. Up to now, the possible effects of the lattice leg has been largely ignored in both research and design of spudcan foundation. Centrifuge experimental results show that there is an increase in penetration resistance for spudcan footing equipped with lattice leg, in comparison with spudcan footing connected to slender circular column leg as widely used by current research. Larger excess pore water pressure was generated by the spudcan penetration with lattice leg in compare with that without. Moreover, the presence of the lattice leg is shown to affect the cavity depth formed around the penetrated spudcan footing, which is simply assumed completely back flow for spudcan penetration in soft clay by SNAME (2008). It was found that the bearing capacity of spudcan foundation has been further underestimated by SNAME (2008) due to the neglecting of lattice leg effect. Taken altogether, this implies that changes in penetration resistance arising from the lattice leg may be due to the effect of the latter on the backflow pattern. Apart from highlighting the effect of the sleeve with big openings, the results also highlight the possible future use of sleeves to enhance the bearing capacity and possibly reduce the penetration of spudcan foundations in various soil deposits.
Wind Effect Estimation in Side by Side Offloading Operation for FLNG and LNG Carrier Ships
Authors: Fujiwara Toshifumi , Yukawa Kazuhiro , Sato Hiroshi , Otsubo Kazuhisa , Taniguchi Tomoki
Published: August 2013

Liquid Natural Gas resource development is often conducted worldwide. Recently the drilling area has gradually expanded from shallow sea area to the deep ocean. A Floating LNG facility (FLNG) and a LNG carrier ship (LNG) are assumed to operate in the open sea expected to wind, wave and current. In this situation, an operational capability evaluation of the LNG would be needed to grasp the operational weather limitation. The effect of each weather element, i.e. wind, wave and current, giving manoeuvring effect to ships, is expected to assess exactly as external loads. In such a situation, wind interaction effect under the operating condition that a FLNG and a LNG are in same closed area is not clearly understood. This paper treats and proposes one estimation method of wind load for the operation of side-by-side offloading including interaction effect of a FLNG and a LNG. The proposed wind load estimation method based on the wind tunnel experiments represents the shielding effect of the LNG behind the FLNG. Operational assessment on ship manoeuvring under strong wind is calculated using the proposed wind load method in the final stage.