bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic Considerations for a Single-Reheat Cycle SCWR
Authors: Naidin M. C. , Monichan R. , Zirn U. , Gabriel K. , Pioro I.
Published: February 2010

Currently, there are a number of Generation IV SuperCritical Water-cooled nuclear Reactor (SCWR) concepts under development worldwide. The main objectives for developing and utilizing SCWRs are: 1) Increase gross thermal efficiency of current Nuclear Power Plants (NPPs) from 30 – 35% to approximately 45 – 50%, and 2) Decrease capital and operational costs and, in doing so, decrease electrical-energy costs. SCW NPPs will have much higher operating parameters compared to current NPPs (i.e., steam pressures of about 25 MPa and steam outlet temperatures up to 625°C). Additionally, SCWRs will have a simplified flow circuit in which steam generators, steam dryers, steam separators, etc. will be eliminated. Furthermore, SCWRs operating at higher temperatures can facilitate an economical co-generation of hydrogen through thermo-chemical cycles (particularly, the copper-chlorine cycle) or direct high-temperature electrolysis. To decrease significantly the development costs of a SCW NPP, to increase its reliability, and to achieve similar high thermal efficiencies as the advanced fossil steam cycles it should be determined whether SCW NPPs can be designed with a steam-cycle arrangement that closely matches that of mature SuperCritical (SC) fossil-fired thermal power plants (including their SC-turbine technology). The state-of-the-art SC-steam cycles at fossil-fired power plants are designed with a single-steam reheat and regenerative feedwater heating. Due to that, they reach thermal steam-cycle efficiencies up to 54% (i.e., net plant efficiencies of up to 43% on a Higher Heating Value (HHV) Basis). This paper analyzes main parameters and performance in terms of thermal efficiency of a SCW NPP concept based on a direct regenerative steam cycle. To increase the thermal efficiency and to match current SC-turbine parameters, the cycle also includes a single steam-reheat stage. The cycle is comprised of: an SCWR, a SC turbine, which consists of one High-Pressure (HP) cylinder, one Intermediate-Pressure (IP) cylinder and two Low-Pressure (LP) cylinders, one deaerator, ten feedwater heaters, and pumps. Since this option includes a “nuclear” steam-reheat stage, the SCWR is based on a pressure-tube design. A thermal-performance simulation reveals that the overall thermal efficiency is approximately 50%.
Comparison and Improvements of Correlations for Film Boiling in Tubes
Authors: Pelletier E.-L. , Leung L. K. H. , Teyssedou A. , Girard R.
Published: February 2010

Two methodologies to predict film boiling heat-transfer coefficient have been assessed against experimental wall-temperature measurements obtained under steady-state conditions with water flow inside vertical tubes. One of these methodologies employs heat flux as the independent parameter while the other uses wall temperature as the independent parameter. The film boiling heat transfer consists of developing and fully developed film-boiling regions. Film boiling heat-transfer coefficients are predicted using the film boiling look-up tables for fully developed flow. Developing film-boiling effect is accounted for using modification factors to the fully developed heat-transfer coefficient. Wall-temperature distributions along uniformly heated tubes were established using a semi-analytical scheme and compared against measurements. Both methodologies have provided good predictions. However, the overall prediction accuracy for the heat-flux-based correlation is slightly better than that for the wall-temperature-based correlation. Wall temperatures predicted with the heat-flux-based correlation follow closely measurements at the developing post-dryout region. The wall superheat correlation predicts a sharp temperature rise once the critical heat flux is exceeded, resulting in discrepancies between predictions and measurements of wall temperature and overpredictions of the maximum temperature. The wall-temperature-based modification factor for the developing film-boiling region has been revised using the tube heat-transfer database to improve the prediction accuracy of the wall temperature.
Experimental Investigation on Two-Phase Flow Distribution in Multi-Channel Manifold With Two Radial Inlets
Authors: Pang Liping , Sun Baomin , Wang Bo
Published: February 2010

An experimental investigation was conducted to study the two-phase flow distributions in a horizontal cylindrical manifold with two radial inlets and 11 parallel channels. The effects of the different inlet conditions on two-phase flow distribution of parallel channels in the manifold were investigated. The flow rates of air and water in 11 channels were measured under symmetrical and unsymmetrical inlet conditions. Experimental results show that the air and water flow distributions of manifold at channels keep a stable flow ratio when two radial inlet conditions keep symmetrical. Water flow distribution has a significant variation and air flow distribution has a small change when two radial inlet conditions keep unsymmetrical and water superficial velocity increases at right inlet. Water and air flow distribution has a significant variation when two radial inlet conditions keep unsymmetrical and air superficial velocity decreases.
FLUENT Analysis of a ROSA Two-Phase Stratification Test
Authors: Farkas Tatiana , To´th Iva´n
Published: February 2010

One of the OECD ROSA project tests, investigating temperature stratification in the cold legs and the downcomer during ECCS water injection under two-phase natural circulation conditions was analysed with the FLUENT code. The guidance given in the “Best Practice Guidelines for the Use of CFD in Nuclear Reactor Safety Applications” of the OECD GAMA group was followed. The standard k-ε turbulence model of FLUENT was applied along with the VOF (Volume of Fluid) description of the steam/water phases. In order to model the interface of the two phases more closely, transient calculations were performed. Based on a comparison of calculated and measured results, it is found that the standard k-ε turbulence along with the VOF model gave acceptable description of the temperature distribution within the water layer. However, the model under-estimates mixing at the injection point, while it is over-estimated further downstream in the stratified water flow. The condensation model applied in FLUENT strongly under-estimated the subcooling of the steam phase. Insufficient condensation might explain why the downcomer level drops below the cold leg, which was not the case in the test.
Electron and Material Interaction Studies for the Optimization of a Novel Tritium Based Radioisotope Power Source
Authors: Adams Thomas E. , Webster Jeffrey A. , Taleyarkhan Rusi P.
Published: February 2010

Radiation interaction with materials can have beneficial uses, such as in radioisotope power sources where the ionizing particles provide a direct energy source for conversion into electricity; similar to photovoltaic cells. Radioisotope power sources in the past did not succeed: limited low power applications, rapid semi-conductor degradation, availability and cost of suitable radioisotopes. Now, the power generated is compatible with present electronic devices. Novel and compelling need-based applications for long-life radioisotope power sources are emerging in the military, intelligence, commercial and medical markets. However, the net efficiency is still below 10% due to the isotropic emission and self-shielding losses in the source, electron-hole recombination and interactions of a beta particle. Evaluating the effects of beta particle interaction with a p-n junction is the key to optimizing a betavoltaic cell design. The radioisotope source needs to be safe, robust and affordable; a design using tritium and a modified silicon structure could offer a comprehensive and optimal advance to the state-of-the art.
CIAU Methodology and BEPU Applications
Authors: Petruzzi A. , D’Auria F.
Published: February 2010

Best-Estimate calculation results from complex thermal-hydraulic system codes (like Relap5, Cathare, Athlet, Trace, etc..) are affected by unavoidable approximations that are unpredictable without the use of computational tools that account for the various sources of uncertainty. Therefore the use of best-estimate codes within the reactor technology, either for design or safety purposes, implies understanding and accepting the limitations and the deficiencies of those codes. Uncertainties may have different origins ranging from the approximation of the models, to the approximation of the numerical solution, and to the lack of precision of the values adopted for boundary and initial conditions. The amount of uncertainty that affects a calculation may strongly depend upon the codes and the modeling techniques (i.e. the code’s users). A consistent and robust uncertainty methodology must be developed taking into consideration all the above aspects. The CIAU (Code with the capability of Internal Assessment of Uncertainty) and the UMAE (Uncertainty Methodology based on Accuracy Evaluation) methods have been developed by University of Pisa (UNIPI) in the framework of a long lasting research activities started since 80’s and involving several researchers. CIAU is extensively discussed in the available technical literature, Refs. [1, 2, 3, 4, 5, 6, 7], and tens of additional relevant papers, that provide comprehensive details about the method, can be found in the bibliography lists of the above references. Therefore, the present paper supplies only ‘spot-information’ about CIAU and focuses mostly on the applications to some cases of industrial interest. In particular the application of CIAU to the OECD BEMUSE (Best Estimate Methods Uncertainty and Sensitivity Evaluation, [8, 9]) project is discussed and a critical comparison respect with other uncertainty methods (in relation to items like: sources of uncertainties, selection of the input parameters and quantification of their uncertainty ranges, ranking process, etc.) is presented.
Steam-Reheat Option for SCWRs
Authors: Saltanov Eugene , Monichan Romson , Tchernyavskaya Elina , Pioro Igor
Published: February 2010

Concepts of nuclear reactors cooled with water at supercritical pressures were studied as early as the 1950s and 1960s in the USA and Russia. After a 30-year break, the idea of developing nuclear reactors cooled with SuperCritical Water (SCW) became attractive again as the ultimate development path for water cooling. The main objectives of using SCW in nuclear reactors are: 1) to increase the thermal efficiency of modern Nuclear Power Plants (NPPs) from 30 – 35% to about 45 – 48%, and 2) to decrease capital and operational costs and hence decrease electrical energy costs. SCW NPPs will have much higher operating parameters compared to modern NPPs (pressure about 25 MPa and outlet temperature up to 625°C), and a simplified flow circuit, in which steam generators, steam dryers, steam separators, etc., can be eliminated. Also, higher SCW temperatures allow direct thermo-chemical production of hydrogen at low cost, due to increased reaction rates. To achieve higher thermal efficiency a nuclear steam reheat has to be introduced inside a reactor. Currently, all supercritical turbines at thermal power plants have a steam-reheat option. In the 60’s and 70’s, Russia, USA and some other countries have developed and implemented the nuclear steam reheat at subcritical-pressure in experimental reactors. There are some papers, mainly published in the open Russian literature, devoted to this important experience. Pressure-tube or pressure-channel SCW nuclear-reactor concepts are being developed in Canada and Russia for some time. It is obvious that implementation of the nuclear steam reheat at subcritical pressures in pressure-tube reactors is easier task than that in pressure-vessel reactors. Some design features related to the nuclear steam reheat are discussed in this paper. The main conclusion is that the development of SCW pressure-tube nuclear reactors with the nuclear steam reheat is feasible and significant benefits can be expected over other thermal-energy systems.
Numerical Simulation of Breakwaters for Land Reclamation
Authors: Zhang Jian-Min , Zhang Jianhong , Wang Gang , Chen Yang
Published: February 2010

This paper highlights some practical considerations of soil structure interactions in the design of the breakwater for a land reclamation project at Da Ya Bay, Southern China sea, through three-dimensional finite element analysis. A pile-breakwater-foundation system is evaluated during its construction and after construction has been completed. The maximum deflections and moments of the piles take place in the soft marine clay underneath the breakwater. The deformation of the soft soil imposes great impact on the slender pile. Based on the study, it is considered inadequate to solely increase the density and stiffness of the piles, as it will not effectively reduce the deformation of the foundation as well as the moment of the pile. On the contrary, the increased stiffness results in significant increase of the stresses in the pile. Consequently, the deformation of pile should be evaluated in terms of interactions between soil and pile. Improvement of the soft marine clay is also of great importance.
Vortex-Induced Vibrations on Flexible Cylindrical Structures Coupled With Non-Linear Oscillators
Authors: Rosetti Guilherme F. , Nishimoto Kazuo , de Wilde Jaap
Published: February 2010

The recent escalade of the oil prices encourages the search and exploration of new oil fields. This represents a challenge to engineers, due to more difficult conditions of operation in harsh environments and deeper reservoirs. The offshore industry faces, in the edge of technology with new necessities and limiting conditions imposed by the environment, an increase in the cost of production. It is, therefore, of vital importance to have the equipments operating at the most optimized conditions in order to reduce these costs. VIV software developed in the frequency domain was successful in designing risers and pipelines using large safety factors and making conservative assumptions. These tools only predict single-mode vibrations. In this perspective, the present paper describes the results obtained from a new time-domain code developed to assess the vortex-induced vibrations of a long flexible cylinder. A time-domain analysis was chosen because this suits the problem well, since it is able to predict and calculate different modes of vibrations. In the model, a cylinder is divided into elements that can be exposed to an arbitrary current profile. Each of these elements is free to oscillate parallel and transversely to the flow, and is coupled to a pair of van der Pol’s wake oscillators. This simulates the vortex shedding and, therefore, the fluctuating nature of drag and lift coefficient during the occurrence of VIV. The governing equations are solved by 4th-Order Runge-Kutta schemes in time domain. The new time-domain model is compared with small scale model test data from benchmarking.
Inclined Loading Capacity of Embedded Suction Anchors in Clay
Authors: Kim Y. S. , Kim K. O. , Cho Y. , Bang S. , Jones K. D.
Published: February 2010

An analytical solution has been developed to estimate the inclined pullout capacity of an embedded suction anchor in clay seafloor. Validation has been made through comparisons with a limited number of centrifuge model test results. Results indicate that the inclined pullout capacity of an embedded suction anchor in clay decreases as the load inclination angle to the horizontal increases. As the point of the load application moves downward, the inclined pullout capacity increases, reaches its peak, and then starts to decrease.
Boundary Layer and Wake Region Simulation for Low Reynolds Number Flows Around Bluff Bodies Using the Lattice Boltzmann Method
Authors: Hayatdavoodi Masoud
Published: February 2010

Two and three-dimensional flows around solid boundaries are interesting and important subjects to both scientists and engineers. Lattice Boltzmann Method (LBM) is a relatively new computational method to simulate fluid flows by tracking the collision, advection and propagation of mesoscopic fluid particles. LBM is originated from the Cellular automata combined with kinetic theory and the Boltzmann equation. The method solves the explicit finite difference scheme lattice Boltzmann equations which are second order in space and first order in time. LBM does not attempt to solve the Navier-Stokes equations directly, however, it obeys them. The two-dimensional flows around square and circular cylinders are simulated with uniform and nonuniform grid structures using LBM. The boundary-layer growth and wake region physics are captured with small scale details, and the results are discussed in comparison with the available references for Reynolds numbers between 50 and 350. The compatibility of the method to simulate a flow around ship-shaped geometries and a combination of objects is also provided.
Dynamic Triaxial Experimental Study on Wave-Induced Strength Weakening of Subaqueous Yellow River Delta Silty Soil Under Wave Action
Authors: Xu Guohui , Liu Huixin , Wang Xin , Wei Congcong , Zhang Minsheng
Published: February 2010

Silty soil in the Chengbei region of the Yellow River Delta is prone to geological hazards including landslides, collapses, silt flow, etc. The failure of silty soil is closely correlated with its strength change induced by wave action. In this study, dynamic triaxial experiments were employed to explore the relationship between oscillation times and dynamic shear strength of silty soil in the Subaqueous Yellow River Delta by modeling wave-seabed interactions. This paper studies the change law of dynamic shear strength, cohesion and internal friction angle with the oscillation time. The results indicate that the strength weakening of silty soil follows the rule of power function attenuation. In addition, failure modes, variations in pore pressure together with the microstructures are also discussed in this paper through careful observation of the samples.
VIV and WIV Suppression With Parallel Control Plates on a Pair of Circular Cylinders in Tandem
Authors: Assi Gustavo R. S. , Bearman Peter W.
Published: February 2010

Experiments have been carried out on two-dimensional devices fitted to a rigid length of circular cylinder to investigate the efficiency of pivoting parallel plates as wake-induced vibration suppressors. Measurements are presented for a circular cylinder with low mass and damping which is free to respond in the cross-flow direction. It is shown how VIV and WIV can be practically eliminated by using free to rotate parallel plates on a pair of tandem cylinders. Unlike helical strakes, the device achieves VIV suppression with 33% drag reduction when compare to a pair of fixed tandem cylinders at the same Reynolds number. These results prove that suppressors based on parallel plates have great potential to suppress VIV and WIV of offshore structures with considerable drag reduction.
In-Line Motion of Subsea Pipeline Span Models Experiencing Vortex-Shedding
Authors: Lee Li , Allen Don , Pontaza Juan P. , Kopp Frans , Jhingran Vikas
Published: February 2010

Subsea pipeline spans, when experiencing bottom ocean currents, are prone to vortex-induced vibration (VIV). Experiments and computational fluid dynamics (CFD) are conducted to evaluate the effects of the pipe stiffness on its first mode in-line VIV motion, primarily in the reduced velocity range from approximately 1.0 to 4.0. Experimental results also indicated that there was obliqueness in motion trajectories, which could have impacts on VIV design of the free spans. The main findings of this investigation are presented in this paper.
Experimental Investigation and Numerical Modeling of Hydrodynamic Characteristics of a Heaving Sea Cage
Authors: Ito Sho , Tsunoda Tomoyuki , Itakura Hiroshi , Bao Weiguang , Kitazawa Daisuke , Kinoshita Takeshi
Published: February 2010

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore fish cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. In the present study, therefore, we investigated hydrodynamic property of a heaving sea cage as the first step. Forced oscillation tests and wave exciting force tests have been carried out, and numerical modeling have also been made to estimate hydrodynamic characteristics theoretically and to estimate the drag and mass coefficients. Results of the forced oscillation tests show that the added mass and damping coefficient of sea cage models depend on forced oscillation amplitude. This dependence may be mainly attributed to the deformation of net, and we successfully reduce the dependence on the forced oscillation amplitude in the result of reanalysis which takes into account the deformation of net. Results of measured wave exciting force show that wave exciting forces are not linear in wave amplitude. This may be due to the viscous drag effects as well as the deformation of net. On the other hand, we calculated the flow around a sea cage. This is based on velocity potential and supplemented the effect of viscosity by equivalent linearization. In the boundary condition on the sea cage surface, the vertical velocity to the surface is not equal to zero, but determined by the permeate coefficient of the surface. This permeate coefficient is a function of wave amplitude, wave period and porosity of the net. In the future works, deformation of net should be also taken into account in this calculation.
Theoretical and Experimental Study on a Porous Cylinder Floating in Waves
Authors: Zhao Fenfang , Kinoshita Takeshi , Bao Weiguang , Itakura Hiroshi
Published: February 2010

In the present work, the theoretical and experimental study on the interaction of water waves with a truncated circular cylinder is performed. The cylinder partly made of porous materials, possesses a porous sidewall and an impermeable bottom. A non-dimensional parameter b is adopted in the theoretic formulation to describe the porosity, which is not directly related to the opening ratio τ of the porous materials. To validate the theoretical work and computed results, a series of model tests are carried out in a wave basin. Effort is also made to establish an empirical relation between b and τ based on the comparison of the calculation and experimental data. The phenomenon of sloshing mode occurred at certain wave number is investigated as well to find its potential application in breakwaters.
A Convergence Study on Mixed Mode Function: Boundary Element Method for Aircraft-VLFS-Water Interaction Systems Subject to Aircraft Landing Impacts
Authors: Jin J. Z. , Xing J. T.
Published: February 2010

A mixed mode function–boundary element method was developed by the authors to analyze the dynamic behaviour of an integrated aircraft – VLFS – water interaction system exited by aircraft landing impacts. In the mathematical model, the aircraft and VLFS are considered as two elastic structures. The landing gears of the aircraft are modeled by four support units, each of which consists of a linear spring and damper. The water is assumed to be incompressible, inviscid and satisfying a linear free surface wave condition and an undisturbed condition at infinity. The motions of the aircraft and VLFS are described by their respective natural modes. The fluid domain is modelled using a boundary element approach. The coupled fluid–structure equation is solved in the time domain with Newmark approximations. In this paper, the numerical stability of the developed method is investigated. To realize this aim, convergence study is performed in determining the size of retained fluid surface, the number of retained modes of VLFS and the time step used in the time integration scheme.
Drag Coefficients of a Long Flexible Circular Cylinder With Wake Interference
Authors: Huera-Huarte Francisco J.
Published: February 2010

Drag coefficients of the downstream cylinder in a tandem arrangement of two models aligned with the flow are shown in this work. The models, which experienced vortex-induced vibrations with wake interference, had an external diameter of 16 mm and a total length of 1.5 m giving an aspect ratio of about 94. More than 400 runs were carried out in a water flume with only the lower 40% of the models exposed to the current. The flow speed was varied up to 0.75 m/s giving Reynolds numbers in the range from 1200 to 12000. A supporting structure, where the models were attached, allowed changes in the centre to centre distances and in the applied top tensions. Separations of up to 4 diameters were tested with tension variations from 15 to 110 N. Reduced velocities based on the fundamental natural frequency reached values up to 16. The mass ratio of the models was around 1.8 and the combined mass-damping parameter about 0.05.
Shaking Table Test on the Seismic Behavior of Caisson Type Quay-Wall in Application of Ground Solidification Technique
Authors: Kasama Kiyonobu , Zen Kouki , Chen Guangqi , Hayashi Kentaro
Published: February 2010

In order to investigate the effect of ground solidification method for reducing the seismic damage of caisson type quay-wall, a series of shaking table tests in 1g gravitational field were performed in terms of the shear strength and the improvement width of ground solidification. The main conclusions obtained from this study are as follows: 1) Ground solidification behind caisson type quay-wall is effective for reducing the seismic damage of caisson type quay-wall and, however, setting backfill stones in solidified ground is not useful for the stability of quay-wall in current experimental condition for this study. 2) For solidified ground with large shear strength, the seismic behavior of quay-wall sympathizes with solidified ground as if both of solidified ground and quay-wall are a combined structure. Consequently, the seismic earth pressure from liquefied sandy ground is absorbed by solidified ground reducing the seismic earth pressure to quay-wall. 3) A formula to evaluate the sliding safety of caisson type quay-wall with solidified ground is proposed considering the cohesive component of shear strength of solidified ground. Based on the proposed formula, the improvement width for ground solidification method can be reduced from a conventional width in current design code.
An Investigation Into the Non-Linear Effects Resulting From Air Cushions in the Orecon Oscillating Water Column (OWC) Device
Authors: Lye Jim L. , Brown David T. , Johnson Fraser
Published: February 2010

When designing an Oscillating Water Column (OWC) device, the motions and structural responses in waves are of great interest. However, predictions of these motions are complicated by the presence of air chambers above a large proportion of the waterplane area. Modeling the stiffness provided by air cushions at model scale presents a number of problems as air stiffness does not scale according to the laws of Froude scaling. To-date, the closest analogy might be an air-lifted gravity base structure, or crane vessel. However, in an OWC device, the air is not trapped as it is allowed to vent through a turbine. As a result, in still water, none of the mass of the buoy is supported by the air column. However, as the buoy is subjected to waves of increasing height the influence of the air chambers on the motions response becomes more pronounced. Experiments into the behavior of structures with trapped air springs have focused largely on benign sea conditions as the air cushions are generally used in vessels or structures involved with installation operations or similar. In contrast, the behavior of an OWC device must be predicted in all conditions up to, and including, survival conditions. BPP-TECH are providing technical support to the designers of the Orecon MRC wave energy buoy. This buoy uses chambers of varying drafts to generate electricity from the waves. The buoy is tension moored to the sea bed in order to constrain the heave motions to maximize the air pressure within the chambers as waves pass. A series of tank tests were undertaken at the OCEANIDE facility in order to investigate the motions of the buoy while tension moored and also measure the mooring line tensions. This paper will focus on the methods used to represent the air chambers at model scale and will present the results of the tests. A variety of different orifice sizes were used in the test campaign in order to provide a spread of values that would offer an insight into the effect of the air chambers on the motions of the structure in waves.
Effect of Drill-Ship Motions on Core Sample Conditions During the Nankai Trough Seismogenic Zone Experiment
Authors: Shinmoto Yuichi , Wada Kazuyasu
Published: February 2010

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stage 1A, which is a part of the Integrated Ocean Drilling Program (IODP), is a series of expeditions in scientific drilling and coring operations aboard the first riser-equipped deep sea drilling vessel, Chikyu. The objectives are to recover good quality core samples and collect data on undersea properties and drilling conditions, which will also provide valuable information for future expeditions. The coring operations were carried out under harsh drilling and ocean conditions so that core recovery was inconsistent and fluctuated from high to low. Moreover, differences in independent lithology, depth, and the type of coring tools from previous expeditions made it necessary to analyze and optimize drilling parameters with new data. A serious concern in retrieving core samples was the vertical heave motions caused by the drill-ship since the active heave compensator system could not be activated before operations due to the extreme deep sea conditions and only the passive heave compensator was used. The drill string and coring tools are particularly vulnerable to the high heaving movements of the vessel so that the core recovery rate and quality are also adversely affected. The present work presents an analysis of geotechnical information, drilling parameters and the drill-ship motions the NanTroSEIZE expedition in order to optimize core conditions and maintain high core recovery.
Wave Power Statistics for Sea States
Authors: Myrhaug Dag , Leira Bernt J. , Holm Ha˚vard
Published: February 2010

The paper provides a bivariate distribution of wave power and significant wave height, and the statistical aspects of wave power for sea states are discussed. This is relevant for e.g. making assessments of wave power devices and their potential for converting energy from waves. The results can be applied to compare systematically the wave power potential at different locations based on long term statistical description of the wave climate.
Wave Propagation Through a Viscous Fluid Contained in a Prestressed Viscoelastic Tube
Authors: Ma Ye , Ng Chiu-On
Published: February 2010

The oscillatory motions induced by a propagating wave of small amplitude through a viscous incompressible fluid contained in a prestressed and thick-walled viscoelastic tube are studied by a perturbation analysis based on equations of motion in the Lagrangian system. While the finite-amplitude initial displacements of the wall are found at the zeroth order, the wave kinematics and dynamics are determined at the first order as analytical functions of the wall and fluid properties, prestress, and the Womersley number for the cases of a free or tethered tube.
Maintenance Planning of Offshore Wind Turbine Using Condition Monitoring Information
Authors: Rangel-Rami´rez Jose´ G. , So̸rensen John D.
Published: February 2010

Deterioration processes such as fatigue and corrosion are typically affecting offshore structures. To “control” this deterioration, inspection and maintenance activities are developed. Probabilistic methodologies represent an important tool to identify the suitable strategy to inspect and control the deterioration in structures such as offshore wind turbines (OWT). Besides these methods, the integration of condition monitoring information (CMI) can optimize the mitigation activities as an updating tool. In this paper, a framework for risk-based inspection and maintenance planning (RBI) is applied for OWT incorporating CMI, addressing this analysis to fatigue prone details in welded steel joints at jacket or tripod steel support structures for offshore wind turbines. The increase of turbulence in wind farms is taken into account by using a code-based turbulence model. Further, additional modes t integrate CMI in the RBI approach for optimal planning of inspection and maintenance. As part of the results, the life cycle reliabilities and inspection times are calculated, showing that earlier inspections are needed at in-wind farm sites. This is expected due to the wake turbulence increasing the wind load. With the integration of CMI by means Bayesian inference, a slightly change of first inspection times are coming up, influenced by the reduction of the uncertainty and harsher or milder external agents.
Low Cycle Fatigue of Internally Pressurized Corroded Pipes Under Cyclic Bending
Authors: Baeta Marcos Andre´ , Lourenc¸o Marcelo Igor , Netto Theodoro A.
Published: February 2010

Corroded pipes for oil transportation can eventually experience low cycle fatigue failure after some years of operation. The evaluation of the defects caused by corrosion in these pipes is important when deciding for the repair of the line or continuity in operation. Under normal operational conditions, these pipes are subject to constant internal pressure and cyclic load due to bending and/or tension. Under such loading conditions, the region in the pipes with thickness reduction due to corrosion could experience the phenomenon known as ratcheting. The objective of this paper is to present a revision of the available numerical models to treat the ratcheting phenomenon. Experimental tests were developed allowing the evaluation of occurrence of ratcheting in corroded pipes under typical operational load conditions as well as small-scale cyclic tests to obtain the material parameters. Numerical and experimental tests results are compared.
Design and Experimental Study of Hydrocyclone in Series and in Bridge of Downhole Oil/Water Separation System
Authors: Zhang Yong , Jiang Minghu , Zhao Lixin , Li Feng
Published: February 2010

Hydrocyclone, as the core part of the downhole oil/water separation (DOWS) system, has been used for a long time. But some issues restricted it from extensive and long term utilization in terms of reinjection in the same oil well, offshore oil production and so on. The design in this paper solved the puzzle how to arrange the main devices and their flow channels in the comparatively narrow well bore. Some special ideas were designed to accomplish the function to get more handling capacity by connecting hydrocyclones in bridge and to obtain thicker rude oil by connecting hydrocyclones in series. Experimental study has been carried on which shows the hydrocyclones connecting both in series and in bridge can satisfy the corresponding application in DOWS. This study can arouse new efforts to separate more water in well bore than ever which can greatly decrease the burden of water treatment and gain more economic efficiency.
The Effect of Hydrodynamic Action on Sediment Consolidation Process in the Yellow River Estuary
Authors: Yang Xiu-juan , Jia Yonggang , Shan Hongxian
Published: February 2010

By in situ tests, the impaction of the marine hydrodynamics, such as wave and tide, on the rapidly deposited sediments consolidation process was studied. In the tide flat of Diaokou delta-lobe, one 2m×1m×1m test pit was excavated. The fluid sediments imitating the rapidly deposited seabed silts were made in-situ, and an iron plate covered part of the test pit to cut off the effect of the marine hydrodynamics. By field-testing methods, like static cone penetration test, the variation of strength is measured at real time, and the marine hydrodynamics’ impaction on the consolidation process of the sediments in the Yellow River Estuary was studied. It is shown that the self-consolidated sediments’ strength linear increased with the depth. In the consolidation process, in the initial, marine hydrodynamics play a decisive role, about three times as much as self-consolidated in raising the strength of the sea-bed soils, and with the extension of the depth the role of the hydrodynamics reduced. With the continuation of the consolidation process, the trend of the surface sediments’ increased-strength gradually slowed under the water dynamics, while the sediments below 30cm was in opposite ways. As a result, the rapidly deposited silts present a nonuniform consolidation state, and the crust gradually formed. The results have reference in studying the role of the hydrodynamics in the soil consolidation process.
The Study on Property Non-Uniformity of Superficial Sediment at the Yellow River Estuary, China
Authors: Chang Fangqiang , Jia Yonggang , Shan Hongxian , Liu Tao
Published: February 2010

The silt carried by the Yellow River accumulates rapidly at the estuary to form an underwater delta, and the sediment is influenced and transformed continuously by river and ocean dynamic forces. One-meter-deep superficial sediment samples were taken at the Yellow River estuary to measure the basic physical and mechanical properties in the laboratory. The laboratory tests revealed the superficial sediment is over-consolidated and the over-consolidation ratio (OCR) reduces with depth. Soil penetration resistance was measured by a Proctor Penetrometer In-Situ. The results show the strength of superficial sediment appear to be strong non-uniformity (variation), and the strength of Xin Tan and Guang Li Gang region is less than those of the Da Wang Bei and Diao Kou. Then, the extent of soil property non-uniformity in space was calculated according to the Vanmarcke Foundation Random Theory. The vertical non-uniformity size lies between 0.32–0.93m, with little difference between those of terrestrial soils, and the horizontal lies between 12–32m, less than those on land. Finally, the reasons to cause strong non-uniformity are discussed. They are mainly composed of sediment modification by wave and biological activities.
Numerical Simulation of the Installation and Extraction Process of Spudcan Foundations in Clay
Authors: Liu Jun , Hu Yuxia
Published: February 2010

This paper presents results from large displacement finite element analysis for spudcan foundation penetrating into and extracting from normally consolidated (NC) clay. The soil was idealized as an elastic-perfectly plastic material obeying a Mohr-Coulomb yield criterion and the large displacement analysis was carried out using Remeshing and Interpolating Technique with Small Strain (RITSS) model to simulate the full installation and extraction process. The numerical results were compared with centrifuge model test data and existing analytical solutions. A full parametric study was undertaken to quantify the influence on spudcan extraction process from soil strength profile, foundation interface roughness and penetration depth. The extraction results showed that the normalized uplift resistance after spudcan installation was much lower than that from small strain analysis, and it was also lower than that of pre-embedded case. Thus it is necessary to apply RITSS method in spudcan extraction simulation after installation.
WindFloat: A Floating Foundation for Offshore Wind Turbines—Part II: Hydrodynamics Analysis
Authors: Cermelli Christian , Roddier Dominique , Aubault Alexia
Published: February 2010

WindFloat is a floating foundation for very large offshore wind turbines. This paper describes the hydrodynamic analysis of the hull, as well as ongoing work consisting of coupling hull hydrodynamics with wind-turbine aerodynamic forces. Three main approaches are presented in this paper: - The numerical hydrodynamic model of the platform and its mooring system; - Wave tank testing of a scale model of the platform with simplified aerodynamic simulation of the wind turbine; - FAST, an aerodynamic software package for wind turbine analysis with the ability to be coupled to the hydrodynamic model. These conference proceedings include two other papers presenting the design basis and main systems of this floating foundation [1], as well as structural analysis of the hull and mast [2].
Development of Invertebrate Assemblages and Fish on Offshore Wave Power
Authors: Langhamer Olivia , Wilhelmsson Dan , Engstro¨m Jens
Published: February 2010

A significant development of offshore wave power is planned in the future, and its impact on the marine environment is unclear. Solid structures placed on the seabed create new habitats and function as artificial reefs for marine organisms. In this study we investigated the artificial reef effect and fouling impacts on offshore wave power devices deployed at the Swedish west coast. Here, buoys acting as point absorbers on the surface are connected to generators anchored on concrete foundations on the seabed. We studied the influence of surface orientation of the wave power foundations on epibiotic colonisation, and made in situ observations of micro-habitat use by fish and crustaceans over four years of submergence. We also examined fouling assemblages on buoys and calculated the effects of biofouling on the energy absorption of the wave power buoys.
Sea Water Pump Station Basin Mathematical Hydraulic Model Test (CFD Analysis)
Authors: Barzegar Sadegh , Elhami Amiri Alireza , Rahbar Pooyan , Assadi Niazi Mehdi
Published: February 2010

Background and aim: A sea water intake, with original design of the six drum screen and twenty sea water pump intake with very different flow rate connected to header bay. The capacity of Origin Sea water intake including huge pump station and drum screen is 200,000 m3/hr. The purpose of the mathematical hydraulic model test of the sea water pumping station is to verify that the basin allows a good operating condition for each pump. To ensure a good operating condition for each pump, the design of the seawater basin has to insure: • A correct filter working; • Low transversal velocities; • A flow without vortex. Method and material: The mathematical model of the basin allows to know the flow and to verify: • The main dimensions of the pumping station; • The distance between the inlet ducts and the filters; • The distance between the filters and pump chambers. Result: in the first basin, the flow patterns no problems. Only swirl at the exit of culverts and near the free surface, and two areas where the flow has no velocity were observed. In the downstream other filters, we observe also a circulation that generates a tangential velocity. Conclusion: The mathematical model of the sea water pumping station has allowed calculating three cases (without and with filter stopped) for the low water level and nominal flow rate. In most difficult case, we observe some recirculation, mainly near the free surface, without more influence on principal flow. In the three cases, the distribution of the flow rate between the drum screens is uniform; the gap is inferior to 2%. At the entry of the pump chambers, the velocity fluctuations and the angle are low. Consequently, the secondary flows in pump chambers will be limited.
Crest-Height Distribution in Nonlinear Random Wave
Authors: Li Cuilin , Yu Dingyong , Gao Yangyang , Yang Junxian
Published: February 2010

Many empirical and theoretical distribution functions for wave crest heights have been proposed, but there is a lack of agreement. With the development of ocean exploitation, waves crest heights represent a key point in the design of coastal structures, both fixed and floating, for shoreline protection and flood prevention. Waves crest height is the dominant parameter in assessing the likelihood of wave-in-deck impact and its resulting severe damage. Unlike wave heights, wave crests generally appear to be affected by nonlinearities; therefore, linear wave theory could not be satisfied to practical application. It is great significant to estimate a new nonlinear wave crest height distribution model correctly. This paper derives an approximation distribution formula based on Stokes wave theory. The resulting theoretical forms for nonlinear wave crest are compared with observed data and discussed in detail. The results are shown to be in good agreement. Furthermore, the results indicate that the new theoretical distribution has more accurate than other methods presented in this paper (e.g. Rayleigh distribution and Weibull distribution) and appears to have a greater range of applicability.
Long-Term Fatigue and Extreme Design of Steel Risers
Authors: Martins Michele A. L. , Do´ria Andre´ S. , Silveira Eduardo S. S.
Published: February 2010

Environmental loads are the main source of dynamic excitation of offshore structures. Due to the random nature of these loads, one should consider statistical properties when designing such structures. Recent codes for the design of steel risers address the use of environmental contours or full long-term analysis to take into account the statistics of load effects. Moreover, sea states for fatigue design should also be carefully selected so as to include the region of the scatter diagram which most contributes to the total damage. This paper looks into fatigue and ultimate limit states of steel risers. The first part shows a comparative study of three design criteria for extreme statistical analysis. These criteria are based on design storm, environmental contour, and full long-term statistics. A joint probability distribution found in the literature for a Brazilian location was used to describe the correlation between the significant wave height and the zero crossing wave period. The second part deals with the analysis of the coefficient of contribution for fatigue and long-term extreme statistics. Several full time domain analyses were performed and the most important sea state region for each limit state is shown in two examples of steel catenary risers. A discussion about sea state selection is then presented.