bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamic Performance of a Novel Design of Pressurized Fluidized Bed Combustor
Authors: Wang Alan L. T. , Stubington John F.
Published: January 2009

A bench-scale fluidized bed combustor with a novel fluidizing gas injection manifold was successfully built for characterization of Australian black coals under pressurized fluidized bed combustion (PFBC) conditions. The bed of silica sand (mean size 1.3 mm and density 2700 kg/m3) was 40 mm ID with a static height of 75 mm. This facility was designed to operate at 1.6 MPa, 850°C and a fluidizing velocity of 0.9 m/s, identical to those used industrially, in order to match as closely as possible the local hydrodynamic environment around each coal particle in an industrial PFBC. To verify satisfactory hydrodynamic performance with the novel gas injection manifold, the fluidization was directly investigated by measuring differential pressure fluctuations under both ambient and PFBC conditions. In addition, a Perspex cold model was built to simulate at ambient conditions the hydrodynamics of the hot bed in this PFBC facility. The cold model was constructed to a geometric scale of 1.431:1, determined by Glicksman’s scaling law. Under PFBC conditions of 1.6 MPa, 850°C and 0.9 m/s, the bed in UNSW’s PFBC facility operated in a stable bubbling regime and the solids were very well mixed. The bubbles in this PFBC were effectively cloudless and no gas backmixing or slugging occurred; so the gas flow in this bed could be modeled by assuming two phases (bubble and particulate) with plug flow through each phase. The results from the cold model showed that the ratio of Umf for the simulated bed to Umf for the hot PFBC bed matched the conditions proposed by Glicksman’s scaling laws. The bubbles rose along the bed with axial and lateral movements (moving both towards and from the wall), and erupted from the bed surface evenly and randomly at different locations. Two patterns of particle movement were observed in the cold model bed: a circular pattern near the top section, and a rising and falling pattern dominating the particle movement in the lower section created by the rising bubbles.
The Local Heat Balance in a Stationary Fluidized-Bed Furnace Burning Biomass Fuels
Authors: Niklasson Fredrik , Johnsson Filip
Published: January 2009

This work investigates the influence of biomass fuel properties on the local heat balance in a commercial-scale fluidized bed furnace. Experiments with different wood based fuels were performed in the Chalmers 12 MWth circulating fluidized bed boiler, temporarily modified to run under stationary conditions. A two-phase flow model of the bed and splash zone is applied, where the combustion rate in the bed is estimated by global kinetic expressions, limited by gas exchange between oxygen-rich bubbles and a fuel-rich emulsion phase. The outflow of bubbles from the bed is treated as “ghost bubbles” in the splash zone, where the combustion rate is determined from turbulent properties. It is found that a large amount of heat is required for the fuel and air to reach the temperature of the bed, in which the heat from combustion is limited by a low char content of the fuel. This implies that a substantial fraction of the heat from combustion of volatiles in the splash zone has to be transferred back to the bed to keep the bed temperature constant. It is concluded that the moisture content of the fuel does not considerably alter the vertical distribution of heat emitted, as long as the bed temperature is kept constant by means of flue gas recycling.
The Efficient Biomass Waste Incineration Using Advanced FBC Technology
Authors: Lee Seong W. , Zhu Shijun , Liu Yun , Hua Jian , Limpscomb Levi , McLaughlin Melvin
Published: January 2009

A Swirling Fluidized Bed Cambustor (SFBC) hot model with the exhaust gas cleaning equipment was carefully designed and fabricated in this paper. The systematic airflow test was conducted to check the air subsystem connection leaking, control valve, the flow rate and pressure. The air subsystem is adjusted and updated based on the result of the system test. Series fuel combustion experiments were conducted at the different biomass fuels. The overall heat transfer rate and combustion efficiency were calculated. The swirling fluidized bed combustion system burned low heat value biomass (chicken litter) at the relatively high combustion efficiency with low NOx and SOx emissions. The overall heat recovery efficiency is about 45–65%. The combustion efficiency can reach 92% while the sawdust was burned in this waste disposal system. The results indicate that the swirling fluidized bed combustion waste disposal system has a prospect in burning the extra chicken litter in the chicken farm communities with very low emission.
Hydrodynamics of Double-Dipleg Circulating Fluidized Beds for Waste Incineration
Authors: Yun Xiaoyin , Lin Weigang , Wu Shaohua
Published: January 2009

In order to solve the problems of high temperature chlorine induced corrosion and the emission of dioxins, a new type of double-dipleg circulating fluidized bed incinerator is under development at the Institute of Process Engineering, Chinese Academy of Sciences. Understanding the hydrodynamics of such new type of CFB incinerator are of crucial importance for successful design and operation of the system. Experiments have been carried out in a lab-scale double-dipleg circulating fluidized bed to study the hydrodynamics of such system. The investigation is focused on the pressure profile in the loop and residence time distribution of particles with different sizes and densities in the secondary dipleg. The results show that the pressure profile in such system is similar to that in the conventional CFB. The residence time distribution (RTD) function of particles in the second dipleg varies with particle recirculating rate, superficial gas velocity and the characteristics of the particles, such as density and size. The mean residence time of particles decreases sharply with an increase of the particle re-circulating rate and slightly decreases as the superficial gas velocity increases. It appears that the density of particle has a stronger influence on the residence time than the particle size. The lighter particles have a shorter residence time. The residence time distribution function of the particles is described by a tank-in-series model. The implication of the results to the design and operation of the double-dipleg circulating fluidized bed incinerator are discussed.
Design Considerations in the Development of Fuel Cell Power Modules
Authors: Rivard P. , Cargnelli J. , Simpson T. , DelCore R. , Burany S. , Bazzarella R.
Published: January 2009

The commercialization of fuel cell power modules presents a “catch-22”, in that proponents must reduce the cost drastically in order to achieve wide-scale adoption, and wide-scale adoption must occur in order to achieve the learning-curve effects leading to lower costs. Which one is to come first, cost-reduction or wide-scale adoption?
Temperature Measurement Technologies and Their Application in the Research of Fuel Cells
Authors: Wang Mao Hai , Guo Hang , Ma Chong Fang , Ye Fang , Yu Jian , Liu Xuan , Wang Yan , Wang Chao Yang
Published: January 2009

Fuel cells have attracted extensive attention throughout the world in recent years for their high efficiency and high environmental compatibility. Temperature plays a key role in achieving high performance of fuel cells because it deeply influences the activity of catalyst, dehydration of solid polymer membrane, mass transfer and heat management of fuel cells. The temperature distribution has close relationship with current density distribution and lifetime of fuel cells because the uniformity of temperature distribution is a quite important problem for fuel cells. In this paper, a review of temperature measurement technologies that can be used to measure temperature distribution of fuel cells was presented. The measurement of cathode exterior surface temperature fields of a hydrogen proton exchange membrane fuel cell under various operational conditions was conducted by using the technology of infrared thermal imaging. The proton exchange membrane fuel cell structure was designed for uniformity of input heat. A NEC TH5102 thermo tracer was applied to measure the cathode exterior surface temperature distributions of the cell with 5cm2 active area. The experimental results showed that the infrared thermal imaging is an effective method to measure the exterior temperature fields of the PEMFC. The cathode temperature distributions of the cell varied with cell temperatures and flow rates.
Parametric Study of Transport Phenomena in PEM Fuel Cells Using a 3D Computational Model
Authors: Berning T. , Djilali N.
Published: January 2009

This paper presents the results of a parametric study conducted using a three-dimensional, non-isothermal model of a PEM fuel cell. The effect of various operational, geometric and property parameters was investigated in detail. The availability of reliable data for setting various modeling parameters was found to be critical to obtain physically realistic results. In addition to the effect of temperature and pressure, geometrical and material parameters such as the gas-diffusion thickness and porosity as well as the ratio between the channel width and the collector plate land area were investigated in detail, and it was found that the contact resistance plays an important role for the evaluation of the impact of such parameters on the fuel cell performance. The results demonstrate the usefulness of this computational model as a design and optimization tool.
Performance Modeling of PEM Fuel Cell Operated on Reformate
Authors: Zhou Tianhong , Liu Hongtan
Published: January 2009

A three-dimensional mathematical model of PEM fuel cell operated on reformate is developed based on our previous established fuel cell model (Zhou and Liu, 2001), by incorporating the adsorption and oxidation kinetics of CO on platinum surface proposed by Springer et al (1997, 2001). This model is capable of studying the effect of CO poisoning as well as the hydrogen dilution effect by inert gases. The adsorption and oxidation kinetics of CO on platinum surface are incorporated in the source terms of the species equations, thus basic form of the mathematical equations are the same as those used for PEM fuel cell operated on pure hydrogen. With this model, we can obtain detailed information on the CO poisoning and variation of CO and hydrogen concentrations inside the anode. The modeling results from this 3D model revealed many new phenomena that cannot be obtained from previous 1D or 2D models. The model can be used to provide guidance for anode design optimizations. In the paper, results of the effects of various operating and design parameters, such as anode flow rate, gas diffuser porosity, gas diffuser thickness, and the width of the collector plate shoulder, are also presented.
Some Aspects of Mass Transfer Within the Passages of Fuel Cells
Authors: Beale S. B.
Published: January 2009

This paper describes a numerical heat/mass transfer analysis for planar and square duct geometries, found in certain fuel cells. Both developing and fully-developed scalar transport are considered. The solution to the heat/mass transfer problem is presented in terms of normalized conductance as a function of the driving force and wall Reynolds/Peclet numbers.
Analysis and Optimization of a Hybrid MCFC-Steam Turbine Plant
Authors: Lunghi P. , Bove R.
Published: January 2009

Fuel Cells are high efficiently chemical energy conversion devices and their promising high performance are recognized by all the scientific community. Their conversion efficiency can be further enhanced recycling the heat content of the exhaust gas for CHP applications or for a bottoming cycle. For this kind of application, high temperature fuel cells (MCFC and SOFC) particularly suit, because outlet gas temperature is relatively high. In previous works (Desideri U. et al. 2001, Lunghi P. and Ubertini S. 2001, Lunghi P., Bove R. and Desideri U. 2002) the possibility of combining an ambient pressure MCFC with a gas turbine has been deeply investigated. Results showed very promising performance only if new designed turbines will be available for an optimised plants combination. The inlet temperature for gas turbine, in fact, is sensible higher than exhaust gas from fuel cell anode and so additional fuel is needed in the bottoming cycle, leading a system efficiency reducing. For this reason, in a previous work (Lunghi P. and Bove R. 2003) it was analyzed the possibility using as bottoming cycle a Steam Turbine Plant equipped with a HRSG for steam generation. In the present work suitable MCFC and Steam Turbine sizes are chosen and a performance analysis is conducting, through numerical simulations. Results showed very high electric efficiency reachable with this plant configuration.
Characterization of Transmission Properties of 3M LF120C Plastic Optical Light Guide
Authors: Cates M. R. , Jaiswal S. L. , Maxey L. C. , Earl D. D.
Published: January 2009

Transmission studies of 3M optical light guide, type LF120C with nominal 12.6 mm core diameter, were performed to characterize the material for use in hybrid solar lighting applications, in particular for the transport of sunlight from a collector to discrete lighting fixtures (luminaires). The light guide properties studied included: total transmission (in lumens) per unit length, transmission as a function of input angle and wavelength, transmission as a function of bend radius, and transmission through two bends. The preliminary value for total transmission is 96.6% per meter. Angular input begins to drop significantly at angles greater than 25 degrees. Wavelength transmission has significant minima at about 643 and 750 mm. Losses through bends are much greater for light input at large angles. In addition to the data compilations and detailed summaries of measurement findings, the measurement system and error sources are described.
Chemical Kinetics Simulation of High Temperature Hydrocarbons Reforming in a Solar Reactor
Authors: Rubin Rachamim , Karni Jacob , Yeheskel Jacob
Published: January 2009

This study is aimed at developing a simulation model of a solar Volumetric reactor for hydrocarbon reforming, operating at high temperature and pressure. It will then be used to optimize the reactor design and analyze its performance. The model development utilizes previous and on-going experimental work on Volumetric receiver and catalyst development. The reaction’s kinetics are computed, using the CHEMKIN II simulation package. The chemical kinetic modeling of the relevant C-H-O system is based on: (i) Definition of the relevant computation domain and parameters: temperature, pressure, reactant compositions, residence time, and catalyst load, (ii) Utilizing laboratory measurements at 700–1400K and 1–4 bar. to quantify the kinetic parameters for both, H2O, and CO2 reforming of CH4 and for the Reverse Water Shift reaction. Calculated and measured data are compared for three representative cases, showing a good agreement. The results indicate that the Arrhenius method can be a viable and practical way to predict the behavior of steam and CO2 reforming over a range of temperatures and pressures. Furthermore, it is shown that the present approach can provide a method for estimating the desirable dimensions of the reactor for reforming of CH4. Additional, on-going computational and experimental work, which would provide a more accurate simulation, can easily be implemented using the present numerical model.
Modeling Phase Change Materials With Conduction Transfer Functions for Passive Solar Applications
Authors: Barbour Jason P. , Hittle Douglas C.
Published: January 2009

The use of passive solar design in our homes and buildings is one way to offset the ever-increasing dependence on fossil fuels and the resulting pollution to our air, our land, and our waters. A well-designed sunroom has the potential to reduce the annual heating loads by one-third or more. By integrating phase change materials (PCMs) into building elements such as floor tile and wallboard, the benefits of the sunroom can be further enhanced by providing enhanced energy storage. To maximize benefits from PCMs, an engineering analysis tool is needed to provide insight into the most efficient use of this developing technology. Thus far, modeling of the phase change materials has been restricted to finite difference and finite element methods, which are not well suited to inclusion in a comprehensive annual building simulation program such as BLAST or EnergyPlus (BLAST Support Office, 1991; Crawley et al, 2001). Conduction transfer functions (CTFs) have long been used to predict transient heat conduction in such programs (Sowell and Hittle, 1995). Phase changes often do not occur at a single temperature, but do so over a range of temperatures. The phase change energy can be represented by an elevated heat capacity over the temperature range during which the phase change occurs (Kedl, 1991). By calculating an extra set(s) of CTFs for the phase change properties, the CTF method can be extended to include the energy of phase transitions by switching between the two (or more) sets of CTFs. This method can be used to accurately predict the internal and external temperatures of PCM-containing building elements during transient heat conduction. The amount of energy storage and release during a phase transition can also be modeled with this method, although there may be some degree of inaccuracy due to switching between two or more sets of CTFs.
An Optimization Methodology for Zero Net Energy Buildings
Authors: Christensen Craig , Stoltenberg Blaise , Barker Greg
Published: January 2009

A zero net energy building (ZNEB) is grid-tied, net metered and produces as much energy on-site as it uses in a typical year. In this paper, we describe methods to cost optimize designs for ZNEB’s. The goal is to find a constrained optimum, i.e., the minimum-cost design that achieves ZNE. Increased first costs for improved efficiency are balanced against the size of the PV system required to achieve ZNE (where the net-metered PV system is the energy source of last resort, because it is expensive but can meet the remaining load “using the grid for storage”). Discrete building component options are considered within various categories (e.g., walls, ceilings, foundations, glass types, air conditioners, furnaces, etc.). Each category is optimized by balancing the marginal cost of saved energy for efficiency options against the cost of energy from the PV system. Categories are optimized sequentially with iteration to adjust for possible interactions between categories. The process is automated with software that manipulates input files, launches DOE2 simulations, reads the results, and executes the optimization methodology.
Direct and Indirect Solar Energy Utilization in Bioelectrochemical Cells
Authors: Yagishita Tatsuo , Miyano Rinako , Tsukahara Kenichiro , Sawayama Shigeki , Ogi Tomoko
Published: January 2009

The Effect of glucose addition on the current outputs of the electrochemical cells using Synechocystis sp. PCC6714 was investigated under the conditions with or without light. The current outputs increased with higher concentrations of HNQ and glucose. The current under illumination was lower than that in the dark even in the presence of 5 mM HNQ and 1 g 1−1 glucose, or 1 mM HNQ and 10 g 1−1 glucose. However, the coulombic output obtained from integration of the current was higher under illumination than in the dark under the conditions with 5 mM HNQ and 10 g 1−1 glucose. A main organic acid produced during discharge was acetic acid. The amount of acetic acid decreased, when the current outputs increased. Therefore, the current output production might compete with the production of acetic acid. Efficient system could be established by supplying both solar energy and chemical energy simultaneously.
Solar Hydrogen Production: Direct Water Splitting Into Hydrogen and Oxygen by New Photocatalysts Under Visible Light Irradiation
Authors: Arakawa Hironori , Zou Zhigang , Sayama Kazuhiro , Abe Ryu
Published: January 2009

The photocatalytic splitting of water into hydrogen and oxygen using solar energy is one of the most attractive renewable sources of hydrogen fuel. Therefore, considerable efforts have been paid in developing photocatalysts capable of using visible light, which accounts for about 43% of the solar energy. However such a photocatalyst has not been developed so far. We have developed a new Ni-doped indium-tantalum oxide photocatalyst, In1-xNixTaO4 (x = 0.0∼0.2), which induced direct splitting of water into stoichiometric amount of oxygen and hydrogen under visible light irradiation with a quantum yield of about 0.66% at 420.7 nm. We have also developed a new two-step water splitting system using two different semiconductor photocatalysts, Pt/WO3 photocatalyst for oxygen evolution and Pt/SrTiO3(Cr-Ta-doped) photocatalyst for hydrogen evolution, and a redox mediator, I−/IO3−, mimicking the Z-scheme mechanism of the natural photosynthesis. The quantum yield of this system was about 0.1% at 420.7nm. Both photocatalytic methods are the first examples for visible light water splitting system in the world.
The Decline in Mercury Emissions From Solid Waste Management
Authors: Erdheim Ric
Published: January 2009

Mercury pollution is a growing health and environmental concern. The 1997 EPA Mercury Report to Congress identified mercury emissions from solid waste combustors as causing 1/3 of all emissions in the US. The report attributed smaller amounts to emissions from landfill and product breakage. Some states are targeting solid waste management for regulatory action. Mercury use in products has declined by 90% since 1980. The electrical industry has been at the forefront of this decline. Incinerator companies have successfully implemented the requirements for mercury emission controls required by the Clean Air Act Amendments of 1990. As a result, there has been a substantial reduction of mercury emissions from solid waste combustors and these combustors are now a very small source of mercury emissions. This and other actions are resulting in demonstrable declines of mercury in the environment. Proposed state action inappropriately still targets the solid waste system as a source of mercury and consists of programs that are not cost-effective and that have no priorities. The advancements have largely taken place. Industry needs to document and disseminate its achievements. Industry also should foster cost-effective efforts to enhance existing achievements.
Continued Performance and Economic Issues for the Polk County Minnesota Bituminous County Road Constructed With Municipal Solid Waste Combustor Ash
Authors: Lucido Samuel P. , Wilson Willard
Published: January 2009

This paper is a follow up to previous installments presenting environmental, construction, performance and economic issues associated with Polk County CSAH 13. The CSAH 13 project was a demonstration of the use of municipal waste combustor (MWC) ash in bituminous. New structural and cost data is presented. The incorporation of MWC ash into bituminous pavements has been investigated in the United States since the middle 1970s. Thus far, most, if not all of these projects, have attempted to answer the questions: Is it safe? Is it feasible? Or does it provide an acceptable product? The presented project answers these questions on a new level. MWC ash amended bituminous was used to construct a portion of 2.25 miles of road in Northwest Minnesota. Significant environmental and structural testing was performed prior to, during and after construction. Environmental testing on this project has shown that the use of MWC ash in bituminous pavement, as performed, is safe. In addition, economic analysis shows important financial advantages by using ash-amended bituminous. Structural testing showed a 36% increase in stability, 19% increase in flow and a 17% increase in spring season axle load capacity. Improvement in resistance to freeze-thaw cracking was also shown.
Maneuvering and Simulation of a Ship Entering Into the Vancouver Harbor With an Escort Tug
Authors: Li Ye , Calisal Sander M.
Published: January 2009

Ship maneuverability and its prediction in the early design stage become possible and important during last 40 years as a result of some marine accidents involving large ships. Maneuverability standards were developed and proposed by International Maritime Organization (IMO) which provides the performance criteria. Ship simulation technology in particular simulation of ship maneuvering advanced well in recent years. With the availability of numerical or experimental hydrodynamics coefficients, maneuverability of different ships can now be simulated with the help of computer programs. Relatively good agreement was reported by various researchers between simulated results and those obtained from real ship trials. It seems that simulation can now identify acceptable ship maneuvering performance in calm seas. However the effects of the wind and the currents are not that well studied and reported while they are always important factors for ship maneuvering especially in restricted waters. In this study “good” ships are identified by a numerical simulation and then their course keeping in restricted area is studied in calm seas and under wind and current conditions. The simulation work is on ESSO OSAKA 278,000DWT tanker, a well tested ship for regular maneuvering test and for entrance in the Vancouver Harbor under wind and current conditions. The effect of escort tugs on such an operation is also quantified. The range of current and wind speeds for “successful” operation is then established. The detailed analysis and comparison with available experimental results are provided.
Analysis of Offshore Structures Subjected to Various Types of Sea Wave
Authors: Kuntiyawichai K. , Chucheepsakul S. , Lee M. M. K.
Published: January 2009

The principal aim of this paper is to study the dynamic behaviour of offshore platforms subjected to wave loading. A general review of offshore structure, wave loading and their effects on offshore structures are presented. A brief review on the basics of Wavelet analysis is also mentioned in this study. The techniques for modeling wave loading in finite element analyses are described and discussed in detail. A series of 3D analyses were carried out using the ABAQUS finite element software to study the effects on the dynamic response of the change in support conditions at the seabed. The effects of wave height, wave period and wave velocity on platform behaviour were studied. The results from time history analysis are characterized using Wavelet Analysis in order to obtain the response pattern due to wave loading. These analyses allow the frequency response of the jacket structures to be described in the time domain. These results give a clear view on the response of jacket structure. The important parameters on offshore modeling have also been identified and discussed in this paper. The results presented in this study can be used as a guidance for engineer in order to understand the dynamic behaviour of jacket structures subjected to wave loading.
Loading on a Fixed Vertical Slender Cylinder in an Oblique Wave-Current Field
Authors: Zaman M. H. , Baddour R. E.
Published: January 2009

A study of the loading of an oblique wave-current field on a slender cylinder in a 3D flow frame is reported in this paper. The three dimensional expressions describing the characteristics of the combined wave-current field in terms of mass, momentum and energy flux conservation equations are formulated. The parameters before the interaction of the oblique wave-free uniform current and current-free waves are used to formulate the kinematics of the flow field. These expressions are also employed to formulate and calculate the loads imparted by the wave-current fluid flow on a bottom mounted slender vertical cylinder. A comparison of the obtained results due to the present model to those obtained using three other models being used in the offshore industry is shown for a range of the normalized current parameters. One of these three models is proposed by the American Petroleum Institute (API), which is based on a superposition principle. Morison et al equation is deployed for the load computations in all cases. Comparisons among the obtained results in a normalized manner are shown and discussed.
Calculation of Three-Dimensional Flow Field for Moving Pressure Distributions
Authors: Sahin Iskender
Published: January 2009

Three-dimensional flow field generated by a moving surface pressure distribution is calculated with an emphasis on estimating the bottom pressure signature of an air cushion vehicle. Analytical studies yield singularities and periodic functions with large oscillations in the integrals. The singularities are removed by the Cauchy’s residue theorem and the resulting integrals are numerically evaluated by the use of adaptive quadrature integrations.
Diagnosis of the Noise Discipline in Petrobras Offshore Units Projects
Authors: Sztajnbok Ernani L. , Vaz Pinto Luiz Antonio , Lenzi Arcanjo , Guedes Fernando Pedrosa , Vieira de Assis Regina Ce´lia
Published: January 2009

Health, comfort and the job efficiency of the crew of offshore platforms are factors deeply related to the acoustic quality of the places. The acoustic project of platforms include the noise prediction. It is a complex problem, because it involves several noise sources and receptors. Numeric methods such as Boundary Element Method and Finite Element Method are not still fully satisfactory for use in complex acoustic problems. This way, semi-empiric formulas and statistics methods are used in the prediction calculations. This paper describes some aspects of the Petrobras experience, along the years, in the performance of acoustic projects in offshore platforms. Finally, in this work, some important decisions are discussed for improvement of the acoustic quality of those operational units.
Wave Runup on Cylinders Subject to Deep Water Random Waves
Authors: Indrebo Ann Kristin , Niedzwecki John M.
Published: January 2009

The accurate prediction of wave runup on deepwater offshore platform columns is of great importance for design engineers. Although linear predictive models are commonly used in the design and analysis process, many of the important effects are of higher order, and thus can only be accounted for by complex nonlinear models that better reflect the physics of the problem. This study presents a two-parameter Weibull distribution function that utilizes empirical coefficients to model the surface wave runup. Laboratory measurements of irregular waves interacting with vertical platform cylinders were used to obtain the Weibull coefficients necessary for the analytical model. Six data sets with different configurations where the wave elevation was measured close to the test cylinders are analyzed. These data on wave runup in deepwater random waves were generated at similar water depths with identical significant wave heights and spectral peak periods. Statistical parameters, zero crossing analysis and spectral analysis were utilized to characterize and interpret the time series data. The analysis focused on interpreting the tails of the probability distributions by carefully fitting the analytical model to the measured model data. This study demonstrates that the two-parameter Weibull model can be used to accurately model the wave runup on platform cylinders for the range of experimental data investigated in this study.
Converting Kinetic Energy in Small Watercourses Using Direct Drive Generators
Authors: Nilsson Karin , Segergren Erik , Sundberg Jan , Sjo¨stedt Elisabeth , Leijon Mats
Published: January 2009

Tidal currents, ocean currents and unregulated watercourses are all large sources of energy that can be converted into electricity. Several technical and economical solutions within this research area have been demonstrated. In literature there exists two different turbine types, horizontal and vertical axis. The present paper focuses on the design of a permanent magnetized generator directly coupled to a vertical axis turbine. The proposed theoretical concept is adapted to data measurements regarding water current velocities and flow profiles from a Swedish watercourse. A high electromagnetic efficiency of 90% is obtained.
Damping Estimation of Risers Using Time-Frequency Transforms
Authors: Araga˜o Filho Luiz A. C. M. , Magluta Carlos , Roitman Ney
Published: January 2009

Offshore oil exploitation at increasing water depths has been carrying out studies focused on improving riser response prediction. In order to have a safety design of flexible risers it is necessary to evaluate its dynamic characteristics, mainly the damping factor. This parameter is obtained experimentally and the usual techniques sometimes are not appropriated. For these techniques the damping factor is considered constant, but some tests performed in COPPE’s Lab showed that this is not completely true. In order to estimate the damping factors of a multi-degree of freedom system, cross-sections of Continuous Wavelet Transforms (CWT) based on the Morlet wavelet function from time-domain responses are used. The procedures are then tested on signals acquired from the lateral vibration of a flexible riser. Non-linearity analysis capabilities are also verified.
Review and Selection of a Finite Element Simulation Platform for Academic and Industrial Analyses of In-Service Welding Operations
Authors: Lindstro¨m Per R. M. , Faraji Maneli
Published: January 2009

In order find a general platform/environment for simulation of in-service welding operations, a review and analysis of non-linear Finite Element Analysis, FEA, programs have been performed. Free and commercial softwares have been considered and the programs that have been reviewed and evaluated are ABAQUS, CALCULIX, CODE-ASTER, MARC and SYSWELD. Different platforms, i.e. workstation configurations with the associated Operative System, OS, has also been investigated to find an optimised simulation platform solution. To facilitate the selection of a suitable simulation platform, the performance and durability of ABAQUS has been evaluated by means of an in-service weld simulation. The residual weld hoop stresses of the weld simulation have been compared with the results of girth weld experiments from bibliographic sources. To enhance the evaluation process as well as gain experiences of measuring residual weld stresses, two (2) girth welds with measurement of the weld hoop stresses have been carried out. The maximum solving performance of ABAQUS was obtained by means of a tailor-made workstation, configured with the OS Slackware Linux 9.1 and a specially compiled Linux kernel. The findings of the research will be utilized on selection of a FEA-simulation platform that will be used for the purpose of scientific research and industrial development in the field of inservice welding operations.
Fatigue Assessment and Testing of a Repaired Tubular T-Joint
Authors: Haagensen P. J. , Skallerud B.
Published: January 2009

Stress concentration factors (SCF’s) for a T-joint were calculated by parametric equations, finite element analysis, weight functions, and by experimental stress analysis. Fatigue life predictions were made on the basis of computed SCF’s. Fatigue tests were performed to determine crack development and fatigue life. Following crack growth through the thickness, the crack was ground out and the joint repaired by welding and improved by peening. Further testing at a 35% higher load showed that the original fatigue life was restored by the repair.
Impact of Hammock Formations on Vertical Obstructions
Authors: Vershinin Stanislav A. , Truskov Pavel A. , Kouzmitchev Konstantin V.
Published: January 2009

The paper considers scenarios of head-on impact on vertical obstacles and destruction of hummock subsurface parts represented as a discrete spherical-element medium. The issues analyzed include the 2-phase nature of interaction and destruction of a loose and connected medium and also the cyclic pattern of loading and dynamic effects emerging in interaction with the hummock keel. The contact local stress in the subsurface part is determined by solving the Hertz equation which describes the indent of a sphere into a plane slab. Structural bonds are destructed when cohesion vanishes over the sliding plane. In the initial phase, a frozen ice ridge disintegrates as an perfectly plastic body with small angle of cohesion, while the second phase is viewed as dozing the sliding prism as a loose discrete body. This model allows for spatial effects in distortion of the subsurface part of an ice ridge. The dynamic effect is noted to increase with the size of hummock fragments, hummock speed and size.
Dynamic Response of Composite Two-Dimensional Elasticity Problems Solved by DQEM and EDQ Based Time Integration Method
Authors: Chen Chang-New
Published: January 2009

The dynamic response of composite two-dimensional elasticity problems is solved by using the DQEM to the spacial discretization and EDQ to the temporal discretization. In the DQEM discretization, DQ is used to define the discrete element model. Discrete dynamic equilibrium equations defined at interior nodes in all elements, transition conditions defined on the inter-element boundary of two adjacent elements and boundary conditions at the structural boundary form a dynamic equation system at a specified time stage. The dynamic equilibrium equation system can be solved by the direct time integration schemes of time-element by time-element method and stages by stages method which are developed by using EDQ and DQ. Numerical procedures and numerical results are presented.
Experimental Investigation and Finite Element Analysis of the Inversion of Capped End Frusta as Impact Energy Absorbers
Authors: Aljawi A. A. N. , Alghamdi A. A. A. , Abu-Mansour T. M. N.
Published: January 2009

In this paper, an innovative mode of deformation of the frusta is presented and discussed in details. A full experimental investigation for the quasi-static axial inversion of right circular frusta is given. The experimental work includes studying the effect of frusta wall thickness, angle of frusta and material type on the inversion of the frusta. The quasi-static tests were conducted on an Instron Universal testing machine and qualitative dynamic test were carried using Drop Hammer Facility. Finite element (FE) modeling of the inversion mode is carried out by using ABAQUS FE package. Analysis of the deformation modes is examined using a non-linear model of the finite element package. The FE findings are reported and modes of deformation during the inversion of aluminum frusta are described under quasi-static and dynamic cases. Furthermore, a good agreement is reported between the finite element force histories and the experimental results.
Dynamic Response Interaction of Vibrating Offshore Pipeline and Moving Seabed With Varying Geological and Geo-Mechanical Properties
Authors: Olunloyo Vincent O. S. , Oyediran Ayo A. , Osheku Charles A.
Published: January 2009

The dynamic response interaction of a vibrating offshore pipeline on a moving seabed is herein investigated where the pipeline is idealized as a beam vibrating on an elastic foundation. In particular the time history effects on physics of the stress distributions on the dynamic interaction predicted on sea state and waves is studied. The spectral density analysis of responses and stress distributions over time is used to predict the anticipated time for pipe burst using the seabed state. The studies also revealed that in general, the seabed acts either as a damper or as a spring and in particular when we have sedimentation, the seabed geology permits the geo-mechanical property of the sediment cover to act only as a damper. As expected, external excitation will increase the response of these pipes for which an amplification factor has been derived. For soft beds, high transverse vibrations were dampened by increasing the internal fluid velocity whereas they became amplified for hard beds.
Stress Concentration Factors for Stud-Less Mooring Chain Links in Fairleads
Authors: Vargas Pedro M. , Hsu Teh-Min , Lee Wai Kong
Published: January 2009

Mooring chains are critical components of off-shore installations. The fatigue assessment of these components often requires complex calculations to determine the loadings in the mooring chains. Traditionally the loadings can be converted into fatigue lives using S-N curves such as the DnV Posmoor curve, or the API RP2 SK curve. Deep water SPARs undergoing vortex-induced-motion (VIM) in loop current conditions may be subject to higher mean/cyclic loadings with considerably lower fatigue life estimates — compared with earlier installations in which fatigue life estimates were so large that fine tuning fatigue prediction methodologies was only of academic interest. In this case a more accurate evaluation of the fatigue performance of mooring chains is needed. In this study the stress concentration factors (SCFs) of a studless 5.25” (133mm) mooring chain were examined in a seven-pocket fairlead. The chain-fairlead system analyzed in this study had a very tight fit (i.e., was not designed for passing connector links), and the results of this study will, in general, not be applicable to other chain-fairlead combinations without additional study. The computed SCFs of the stud-less link interacting with the fairlead pocket were compared to the corresponding SCFs in a chain link away from the fairlead. The study shows that the maximum SCF ratio is 1.15, significantly less than the upper bound 2.5 value recommended by Det Norske Veritas in OS-E301 in lieu of detailed analyses. This has a significant impact, nearly an order of magnitude, on fatigue life prediction of the chain, justifying the analytical effort. The study also found that the SCF of the chain link in the fairlead is a function of the geometry of the chain and the fairlead. As a result some guidance is provided in this paper with respect to the implications of minimum SCFs on other link and fairlead geometries. This study combines computational efforts from NEL and ChevronTexaco in a two-pronged approach where: 1) NEL provided calculations addressing parametric variations of the chain link angles of the mooring line leaving the fairlead and the chain tension levels, and 2) ChevronTexaco validated simplified modelling assumptions done by NEL to make the parametric problem tractable.
Numerical Study of Landslide-Generated Waves
Authors: Yang Gang , Isaacson Michael
Published: January 2009

A time-domain boundary element method is developed to simulate linear waves generated by a wave paddle or a horizontal-moving landslide of an arbitrary profile. In this approach, a time-integration procedure is used to apply the boundary conditions, and the wave field at each time step is solved by an integral equation method based on Green’s theorem. Numerical models in three dimensions are developed to simulate waves generated by landslides. The models were validated against theoretical and experimental results on comparative wavemaker problems. Numerical simulation results on landslide-generated waves demonstrate a number of features of interest. Design curves for engineering applications are also developed for quick estimate of magnitudes of landslide-generated waves in engineering applications.
Sensitivity of Ferry Services to the Western Isles of Scotland to Changes in Wave Climate
Authors: Woolf David K. , Coll John , Gibb Stuart , Challenor Peter G.
Published: January 2009

The Western Isles of Scotland and the rest of the Highlands and Islands of Scotland is a remote, sparsely populated region with a high dependency on marine activities. In particular, ferry services are vital to the region. At the same time, the seas to the west and north of Scotland are among the roughest in the world during autumn and winter, making maintenance of a reliable ferry service both difficult and expensive. Ferry routes avoid the open ocean, but some waters are exposed to ocean waves. The inter-annual variability of the ocean wave climate to the west is very high, primarily in response to the North Atlantic Oscillation (NAO). This sensitivity to NAO extends to partially sheltered waters and ferry routes. A deterioration in wave climate in response to either natural variability of the NAO, or as a regional response to anthropogenic climate change is distinctly possible. By analyzing the contemporary response to shifts in the NAO, there is predicted to be a disproportionately large increase in ferry service disruption in response to any deterioration in wave climate.
Safety Barriers in Offshore Drill Rigs Derived From Accident Investigation
Authors: Ersdal Gerhard , Friis Hansen Andreas
Published: January 2009

This paper uses historic accidents to identify important barriers for the structural and marine safety of offshore drill rigs. Several accidents and near misses have been evaluated and barriers that failed, did not exist at the time of the accident or that stopped the accident are identified. Based on these analyses and review of anticipated failure modes in standards and regulations, a simplified generic barrier diagram is established. The generic barrier diagram can be used to evaluate current practice and provide input to general safety management. The possible degradation of the barriers with increasing rig age is also evaluated, and the possible effect the degradation might have on the integrity of aging rigs.
Industrial Implementation of Risk Based Inspection Planning Lessons Learned From Experience: Part 2 — The Case of Steel Offshore Structures
Authors: Rouhan Antoine , Goyet Jean , Faber Michael Havbro
Published: January 2009

Risk Based Inspection (RBI) planning methods for structures have been under development for years. They have now reached a maturity allowing their use in an industrial context. The first applications of detailed RBI where devoted to single components and lately applied in a more extensive way to a set of components, using generic approaches. As being the second part of a report on industrial application of RBI, this present paper focused on RBI for fixed steel offshore structures. The challenge here is the full implementation of the method to a whole set of offshore platforms. General questions arise, such as how to use detailed RBI planning that builds inspection plans of details to establish inspection campaigns for a given platform and, in a more general way, how to go from detailed RBI planning to inspection campaigns for a set of platforms. Also, several more technical issues have been raised during the studies, such as fatigue computations, push-over analyses, risk acceptance criteria and scheduling phases. This paper presents part of the experiences gained using and applying these RBI methods to a specific field of jackets.
Use of Spaceborne Synthetic Aperture Radar for Offshore Wave Analysis
Authors: Nieto-Borge Jose´ C. , Lehner Susanne , Schneiderhan Tobias , Schulz-Stellenfleth Johannes , Niedermeier Andreas
Published: January 2009

Spaceborne Synthetic Aperture Radar (SAR) is able to provide sea state information on a global scale by means of the directional wave spectrum. Recent developed algorithms have been developed to obtain additional information in the spatial domain rather than the spectral domain. These methods permit to detect of individual wave heights, wave groupiness in open sea areas, as well as surface wind fields. This work shows the capabilities of spaceborne SAR to extract offshore information about individual waves and wave grouping for areas of about 100 × 100 square kilometers. The methods are applied to ERS-2 SAR images of the North Sea over areas close to the location of some oil platforms. Results obtained in the vicinity of the Ekofisk platform are shown. In addition, ERS-2 SAR images taken on January 1, 1995 over the Draupner platform in the North Sea are analyzed. These SAR images were taken at the approximate time when the wave record known as “new year wave” was measured.