bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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 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.
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.
Physical Modelling of Offshore Structures Founded on Sea Bed
Authors: de Freitas Fagundes Diego , Almeida Maria Cascão F. , Almeida Marcio S. S. , Rammah Khader I. 
Published: August 2013

This work presents an experimental study using centrifuge modelling on mudmat shallow foundations which are mainly used to support offshore subsea equipment. An optimized design of these foundations requires the maximizing of the ratio between the installation and the pull-out resistance of the foundation. International standards, based on classical theories, are often limited and do not meet the complexity of the projects. The bibliography is not yet conclusive about the load capacity factors for this particular problem. In this work, physical modelling has been performed on both perforated and solid mudmats subjected to vertical load and simulating both installation and extraction scenarios.
The soil used in this study is a marine clay taken from the Roncador field at Campos basin located offshore of the state of Rio de Janeiro, Brazil. The physical modelling experiments have been carried out on the mini-drum geotechnical centrifuge at COPPE/UFRJ. The technique of lumps was adopted for the preparation of the soil models and a temporary surcharge using a sand layer has been applied to develop a soil strength profile similar to the one found in the field. The results obtained in this study provided a better understanding of the soil-structure interaction problem with regard to the installation and pull-out resistance of the studied type of foundation focusing on their bearing capacity factors.
The Effect of Exposure Length on Vortex Induced Vibration of Flexible Cylinders
Authors: Rao Zhibiao , Vandiver J. Kim , Jhingran Vikas , Sequeiros Octavio 
Published: August 2013

This paper addresses a practical problem: “What portion of fairing or strake coverage may be lost or damaged, before the operator must take corrective measures?” This paper explores the effect of lost fairings (the exposure length) on Vortex-Induced Vibration (VIV) of flexible cylinders. The source of data is a recent model test, conducted by SHELL Exploration and Production. A 38m long pipe model with varying amounts of fairings was tested. Response as a function of percent exposure length is reported. Unexpected results are also reported: (i) the flexible ribbon fairings used in the experiment did not suppress VIV at speeds above 1 m/s; (ii) Above 1 m/s, a competition was observed between VIV excited in the faired and bare regions of the cylinder, (iii) Unusual traveling wave behavior was documented—waves generated in the bare region periodically changed direction, and exhibited variation in VIV response frequency.
The results of these tests showed that (1) the excitation on the bare and faired regions could be identified by frequency, because the faired region exhibited a much lower Strouhal number; (2) as expected, the response to VIV on the bare region increased with exposure length; (3) the response to VIV on the faired region decreased with exposure length.
Supercritical Group Velocity for Dissipative Waves in Shallow Water
Authors: Jung Tae-Hwa , Lee Changhoon 
Published: August 2013

The group velocity for waves with energy dissipation in shallow water was investigated. In the Eulerian viewpoint, the geometric optics approach was used to get, at the first order, complex-valued wave numbers from given real-valued angular frequency, water depth, and damping coefficient. The phase velocity was obtained as the ratio of angular frequency to realvalued wave number. Then, at the second order, we obtained the energy transport equation which gives the group velocity. We also used the Lagrangian geometric optics approach which gives complex-valued angular frequencies from real-valued wave number, water depth, and damping coefficient.
A noticeable thing was found that the group velocity is always greater than the phase velocity (i.e., supercritical group velocity) in the presence of energy dissipation which is opposite to the conventional theory for non-dissipative waves. The theory was proved through numerical experiments for dissipative bichromatic waves which propagate on a horizontal bed.
Both the wave length and wave energy decrease for waves with energy dissipation. As a result, wave transformation such as shoaling, refraction, and diffraction are all affected by the energy dissipation. This implies that the shoaling, refraction, and diffraction coefficients for dissipative waves are different from the corresponding coefficients for non-dissipative waves. The theory was proved through numerical experiments for dissipative monochromatic waves which propagate normally or obliquely on a planar slope.
Planning for Construction Work in Cold Climate Regions
Authors: Gudmestad Ove T. , Karunakaran Daniel 
Published: August 2013

With increased interests in oil and gas exploration in cold climate regions, it is not realistic that all construction activities can take place during the short summer and work will continue into the early fall and possibly later. The offshore contractors must, therefore, be ready to participate in construction work in these regions during an extended season, i.e. outside the summer season with milder weather conditions. It is also important that some key work-intensive activities (e.g. pipe laying) can start as early as possible in the season.
This paper will discuss the challenges associated with construction work in cold climate regions with emphasis on the physical conditions, in particular with reference to Polar Low Pressures and the potential for icing, as well as the logistics of working long distances from established supply bases.
Large uncertainties in weather forecasts call for proper management decisions accounting for the specifics of the area. Long periods of “waiting on weather” might result and management must have the patience to wait until safe operations can commence.
Emphasis will be on the Barents Sea where recent hydrocarbon findings have proven very encouraging and where a huge area soon will be opened for exploration, following the agreement on the border between Norway and Russia, potentially calling for joint Norwegian–Russian construction projects (Bulakh et al., 2011).