bluuebunny/crossref_metadata_2025 huggingface dataset:
Manufacturing With MicroECM
Authors: Stofesky David B.
Published: October 2008

Electrochemical Machining (ECM) has been widely used as a non-traditional three dimensional machining process for a variety of industrial applications. Electrochemical processing permits material removal of metals as diverse as aluminum, brass, tool steels, stainless steels, and titanium. Using cathodic tooling, a conductive electrolyte flowing through the electrode gap, controllable power source, and Faraday’s Law, predictable volumes of metal can be removed from the anodic substrate. Faraday’s Law states that the rate of material removal is proportional to the process current and application time, while Ohm’s Law states that current is inversely proportional to the impedance of the (electrochemical) circuit. MicroECM™ is an application of the ECM process that involves the removal of miniscule volumes of material from anodic substrates while holding micron level dimensional tolerances. This paper describes the process, its requirements, and typical applications for microECM™.
An Analytical Model of Micro-Endmill Dynamics in the Presence of Tool Setup Errors
Authors: Filiz Sinan , Ozdoganlar O. Burak , Romero Louis A.
Published: October 2008

This paper presents an analytical model of micro-endmill dynamics in the presence of the setup errors. To accurately capture the rotary inertia and shear deformations of non-slender micro-endmills, Timoshenko-beam equations are used to derive the boundary-value problem for transverse vibrations of rotating micro-endmills with setup errors. The numerical solution of the boundary-value problem is obtained through a spectral-Tchebychev method. The model and the spectral-Tchebychev method are validated by comparing the mode shapes and natural frequencies to those from a commercial finite-elements code. The effectiveness of the model is illustrated by applying it to investigate (1) rotational stability of micro-endmills, (2) the effect of tool geometry on mode shapes and natural frequencies, (3) the influence of setup errors, and (4) the dynamic response of the micro-endmills to harmonic forcing. The model can be used for designing micro tools with preferred dynamic characteristics, as well as for modeling and stability analysis of the micromilling process.
3D FEA Simulations of Fused Deposition Modeling Process
Authors: Zhang Yizhuo , Chou Y. Kevin
Published: October 2008

Fused deposition modeling (FDM) is one of layer-manufacturing technologies that have been widely used for rapid prototyping applications in product design and development. Due to the intensive energy, rapid cooling and phase changes, parts made by FDM and other layer-manufacturing processes are deviated from the designed geometry, and some require laborious post-processing. Most severe form inaccuracies such as curl, warping, and delamination are attributed to the residual stress accumulations during prototype fabrications. This study investigates the FDM process, which comprises complicated heat and mass transfer phenomena coupled with mechanical loading and phase changes. A finite element analysis model using element activations has been developed to simulate the mechanical and thermal phenomena in FDM, and further used for residual stress and part distortion simulations. The model has also been used to study the toolpath effects on the FDM process. Toolpath patterns affect the residual stresses not only in the magnitude, but also in the distribution which shows stress concentrations aligned with the primary direction of the toolpath. Experimentally fabricated and measured prototypes show that the part distortion-center shifts distinctly due to different toolpath patterns, which is consistent with the residual stress characteristics in the simulations. From the simulations, it is also shown that the short-raster toolpath results in higher residual stresses, and thus possibly larger distortions, than the long-raster and alternate-raster patterns, both having similar stress distributions and distortion features.
A Signal Processing Technique for Chatter Stability Prediction
Authors: Sbrescia Francesco , Sims Neil D.
Published: October 2008

The frequency response function (FRF) of a CNC machine tool plays a key role the onset of regenerative chatter. The majority of modal testing techniques to measure the tool’s FRF rely on skilled operators and expensive equipment, but can still suffer from poor repeatability and excessive machine down-time. Some efforts have been performed to overcome these issues using non-contact devices but in general these methods do not capture the FRF during the metal cutting process. Consequently the effects of the spindle rotation and preload due to the cutting forces cannot be simultaneously considered. The present paper presents a novel method of predicting the tool’s FRF by exciting the system while cutting, and measuring the forces acting on the tool. A signal processing procedure is used study the stability of the system. Numerical simulations are used to illustrate two possible uses of the approach: prediction of the full stability lobes with no prior knowledge of the material cutting parameters; and prediction of the stable depth of cut at the current spindle speed. The results are then discussed with particular emphasis on the issues concerning practical implementation of the approach.
Single Point Diamond Turning of CVD Coated Silicon Carbide
Authors: Bhattacharya Biswarup , Patten John A. , Jacob Jerry
Published: October 2008

Scratching experiments, using diamond styli and single point diamond tools, were performed to simulate Single Point Diamond Turning (SPDT). The results of these experiments were used to determine if a ductile response is possible, and then to determine the critical depth of cut or penetration depth for the ductile to brittle transition (DBT). The depths of the scratches produced at different loads were measured and correlated to the ductile and brittle response of the material. The DBT depth for Chemically Vapor Deposited (CVD) coated Silicon Carbide (SiC) samples was determined. The analysis for the critical depth (DBT) did confirm the possibility for SPDT of CVD coated SiC in the ductile regime. These results were further used for SPDT of CVD SiC. Post experimental analysis of the machined surface did reveal a final surface roughness of 8–20nm, successfully demonstrating ductile regime machining of CVD coated SiC.
Nanoindentation Assisted Self-Assembly of Quantum Dots
Authors: Taylor Curtis , Stach Eric , Salamo Gregory , Malshe Ajay
Published: October 2008

The ability to pattern quantum dots with high spatial positioning and uniform size is critical for the realization of future electronic devices with novel properties and performance that surpass present technology. This work discusses the exploration of an innovative nanopatterning technique to direct the self-assembly of nanostructures. The technique focuses on perturbing surface strain energy by nanoindentation in order to mechanically bias quantum dot nucleation. Growth of InAs quantum dots on nanoindent templates is performed using molecular beam epitaxy (MBE). The effect of indent spacing and size on the patterned growth is investigated. The structural analysis of the quantum dots including spatial ordering, size, and shape are characterized by ex-situ atomic force microscopy (AFM). Results reveal that the indent patterns clearly bias nucleation with dot structures selectively growing on top of each indent. It is speculated that the biased nucleation is due to a combination of favorable surface strain attributed to subsurface dislocation strain fields and/or multi-atomic step formation at the indent sites, which leads to increased adatom diffusion on the patterned area.
Summary of the Lomellina Energia Project and Review of the Capacity Upgrade Project
Authors: Davis Craig F.
Published: October 2008

This paper presents a summary of the historical performance of the Lomellina Energia (“LE1”) project near Milan Italy and discusses the design improvements to the second unit (“LE2”) that will be implemented during the capacity upgrade project in 2006/2007.
New Waste-to-Energy Projects: Opportunity Knocks!
Authors: Rose John L.
Published: October 2008

Never have conditions been more favorable for the development of new waste-to-energy projects. The record of operating waste-to-energy plants has dispelled all of the objections that had been raised by environmental activists with respect to emissions and residue toxicity. The economics have become positive due to the rising cost of disposal at distant landfills and the increased value of the recovered energy due to sharp increases in the cost of fossil fuels. The threat of global warming and the recognition of the need to reduce reliance on imported fuel sources have made the public aware of the need to make full use of all domestic sources of energy. Regardless of legal definitions, energy from wastes is renewable energy and established technology. Waste-to-energy plants are even now providing more energy then other renewable sources such as biomass, wind, and direct solar combined. What is needed now for the industry to look at the existing technology to see how it can optimize energy recovery, both in capital and operating costs, without compromising environmental performance. Above all, we need a major push to make our case with the public and the politicians who represent it to convince them that waste-to- energy is not only good economics, but good environmental policy as well.
Waste-to-Energy Project Economics and Financing: A Look Into the Factors Influencing the Future
Authors: Clunie Jeffrey F.
Published: October 2008

This paper focuses on significant changes in the overall economics of waste-to-energy (WTE) during the last 30 years. The WTE industry in this country has seen several different business cycles occur since 1975, as different market drivers have caused the industry to rise and fall. This paper compares: (1) those economic factors that were in play in 1975, when the first WTE facility in the United States was built, and the industry was in its infancy; (2) the factors at play when the WTE industry was at its height in 1990; and (3) some of the factors that caused the industry’s steep downward trend since 1994, when the last greenfield WTE facility in the United States was built. The paper will identify changes that have occurred with regard to the pricing of electricity and the ability of public sectors to charge non-market-based tipping fees. The paper discusses the drivers of 2006 and focuses on completed economic factors to be considered when comparing WTE with other waste disposal means. The paper discusses the drivers of 2006 and whether the industry is finally poised to begin an upward turn in the cycle. The paper focuses on the impact of the cost of diesel fuel oil on the overall economics of long-haul transfer, and how that is likely to impact the future development of WTE facilities. The paper also presents a case study of a recent analysis that was undertaken for two counties that were evaluating the financial viability of WTE as compared to other disposal options.
Polycyclic Aromatic Hydrocarbon (PAH) Formation in Thermal Degradation of Styrene Butadiene Copolymer (SBR)
Authors: Kwon Eilhann , Castaldi Marco J.
Published: October 2008

This study has been initiated to quantify the release of the Polycyclic Aromatic Hydrocarbon (PAH) species from Styrene Butadiene Copolymer (SBR) during gasification. The identification and quantification has been determined experimentally using Gas Chromatography/Mass Spectroscopy (GC/MS) coupled to a Thermo-Gravimetric Analysis (TGA) unit. SBR samples were pyrolysed in a TGA unit in a N2 atmosphere. The identities and absolute concentrations of over 32 major and minor species have been established, including a large number of aromatics, substituted aromatics, and PAHs. The light hydrocarbon species also have been determined simultaneously and identified as H2, C2H2, CH4, C2H6, and C4H10 with lower concentrations of other hydrocarbon gases. Significant amounts of ethyl benzene, toluene, and styrene were observed between 330°C and 500°C. The largest PAH detected was the family of C24H14 (molecular weight 302), benzo[ghi]perylene with peak concentrations reaching 0.19 ppmv. The effluent species detected suggest that formation of PAH’s occurs either through hydrocarbon addition reactions or benzene ring re-combination reactions. In addition, the chemical structure of SBR lends itself gas phase release of benzene molecules or radicals, thus facilitating the PAH production route. Preliminary calculations done using MOPAC provided some insight into the energy required to break the benzene ligand bond from the butadiene structure. The measurements supply information on the identities and levels of hazardous air pollutants, and provide useful new data for the development and validation of detailed reaction mechanisms describing their origin and fate.
An Assessment of the Capabilities of the Munters Zeolite Rotor Concentrator to Reduce VOC and Odor Emissions From a Municipal Waste Combustion Facility
Authors: Secunde James M. , Krenitsky Peter
Published: October 2008

Maine Energy Recovery Company is a waste-to-energy facility, firing refuse-derived fuel (RDF) in two B&W boilers to produce steam which is used to generate 22MW of electricity. As part of its on-going effort to study odor generation and enhance their odor control system, Maine Energy discovered that a greater quantity of volatile organic compounds (VOC) are generated by the waste itself than had previously been estimated. The VOCs that were found are primarily light alcohols, such as methanol, ethanol, and butanol, along with compounds such as acetone, methyl ethyl ketone (MEK), benzene, toluene, xylene, and others. These compounds are generated from the operation of diesel-fueled equipment in the facility’s tipping building, and from the decomposition of the waste itself. The VOC generation also has a strong seasonal component, where generation is highest in the warmer summer weather, and lowest in the depths of winter. In the summer of 2005, Maine Energy undertook a pilot scale study of VOC control using a proprietary concentrator technology from Munters Corporation, Zeol Division of Amesbury, Massachusetts. A scaled-down version of their rotary zeolite concentrator was employed at Maine Energy over a six week period from July to September 2005. Numerous samples were taken at the inlet and outlet of the device, and several extended tests were conducted using Fourier-Transform Infrared (FTIR) technology to search for specific organic compounds. The results showed that the device reduced VOC, as well as odors, by approximately 85%, without the benefit of extensive fine-tuning of the device or the process during this limited run. The testing also revealed the need for extensive particulate removal at the inlet to the device, which would have a significant effect on cost efficiency.
The Evolution of Non-Ferrous Recovery at the Solid Waste Authority of Palm Beach County’s North County Resource Recovery Facility
Authors: Schauer Ray , Riley James P.
Published: October 2008

The North County Resource Recovery Facility is a 2,000 tpd refuse derived fuel (RDF) Waste to Energy facility located in West Palm Beach, FL. Palm Beach Resource Recovery Corporation (PBRRC), a wholly owned subsidiary of The Babcock & Wilcox Company (B&W), operates and maintains the facility under a long-term operation and maintenance (O&M) agreement with the Solid Waste Authority of Palm Beach County.
Vitrification of Bottom Ash From AVR MSW Incinerators
Authors: Xiao Y. , Oorsprong M. , Yang Y. , Voncken J. H. L.
Published: October 2008

During incineration of municipal solid waste (MSW), various environmentally harmful elements and heavy metals are liberated either into bottom ash, or carried away with the off-gases and subsequently trapped in fly-ash. If these minor but harmful elements are not properly isolated and immobilized, it can lead to secondary environmental pollution to the air, soil and water. The stricter environmental regulations to be implemented in the near future in the Netherlands require a higher immobilization efficiency of the bottom ash treatment. In the present study, MSW incinerator bottom ash was vitrified at higher temperatures and the slag formed and metal recovered were examined. The behaviour of soluble elements that remain in the slag is evaluated by leaching extraction. The thermodynamics of slag and metal formation is discussed. The results obtained can provide a valuable route to treat the ashes from incinerators, and to make recycling and more efficient utilization of the bottom ash possible.
Numerical Analysis of Size Reduction of Municipal Solid Waste Particles on the Traveling Grate of a Waste-to-Energy Combustion Chamber
Authors: Nakamura Masato , Castaldi Marco J. , Themelis Nickolas J.
Published: October 2008

The size reduction of municipal solid waste (MSW) particles on the reverse acting traveling grate of a waste-to-energy (WTE) combustion chamber was estimated by means of a numerical model combining the particle size distributions (PSD) of MSW and combustion residues and the Shrinking Core Model (SCM). This new integrated model was used to simulate the particle behavior on the grate. During their travel on the moving grate, the sizes of the particles are reduced by combustion, breakage, and compaction. This study shows the calculation of the particle size change using this model and comparison of the numerically derived PSDs of MSW and ash particles with experimental data. There is good agreement between calculated and measured values.
Increasing the Quantity and Quality of Metals Recovered at Waste-to-Energy Facilities
Authors: Sunk Werner , Themelis Nickolas J.
Published: October 2008

The Integrated Waste Services Association (IWSA) compiles annual data of metal recovery by U.S. waste-to-energy (WTE) facilities. The 2004 IWSA survey showed that the U.S. WTEs processed 28.8 million short tons of municipal solid wastes (MSW) and recovered a total of approximately 706,000 tons of ferrous metal scrap, i.e. 2.45% of the MSW stream. The 2001 U.S.E.P.A. report on the characterization of the U.S. wastes reported that MSW contained 7.9% metals. However, some of this metal is collected separately at the household level and a small amount is non-ferrous metal. If it is assumed that the waste stream that is “disposed” in WTE facilities contains on the average 5% of ferrous metals, the ferrous input to all U.S. WTEs is estimated at approximately 1.44 million tons. On this basis, close to 0.7 million tons of metal are not recovered in WTEs. On the same basis, the ferrous metal lost in MSW that is landfilled (247 million tons in the U.S.) is estimated to be about 12 million tons per year. The non-recovered metal at WTEs entails both environmental and economic penalties. Therefore, an industry-university collaborative study is addressed to examining a) current metal recovery before and after combustion; b) potential for increasing metal value by physical processing of the metals recovered, either at WTEs or at a regional facility to be supplied by several WTEs; c) sampling and characterization procedures used in the WTE industry; and d) potential for physical and chemical characterization of different grades of WTE metal scrap. This paper focuses on the first two subjects — the current state of WTE metal recovery and the potential for increasing metal recovery. This work in progress is published in the NAWTEC 14 Proceedings with the objective of stimulating discussion and obtaining useful input from industry and academia concerned with the conservation of non-renewable resources.
Hydrodynamic Coefficients of Cylinders With Strakes in Oscillatory Flows
Authors: Gopalakrishnakurup Renjeev , Clelland David , Huang Shan
Published: October 2008

Hydrodynamic coefficients of cylinders fitted with strakes in oscillatory flows have been investigated. Three different pitch ratios have been tested, i.e. pitch ratios of infinity, 8 and 4. The cylinders are forced to oscillate in otherwise calm water in a water tank. To validate as well as to compare the experiment results, a smooth cylinder is included in the test matrix. Digital signal filtering has been found to influence the results obtained. Hence sine-fitted signals are used for obtaining the coefficients. For cylinders with strakes, it has been found that the coefficients vary little with Reynolds number. It is also concluded that the pitch ratio has a significant impact on the hydrodynamic coefficients.
System Plan Considering Spare Capability Allowed for Weather Conditions for CO2 Marine Transport and Release in Deep Waters
Authors: Ozaki Masahiko , Minamiura Junichi , Ohta Makoto , Sasaki Yuichi , Matsuura Masami
Published: October 2008

Ocean storage of the captured CO2 from fossil fuel burning is a possible option for mitigating the increase of CO2 concentration in the atmosphere. Moving-ship type of CO2 ocean storage is a concept whereby captured CO2 is delivered by ship to a site and injected into the deep ocean by means of a pipe suspended beneath a ship as it slowly moves through the water. In case of bad weather conditions, CO2 marine transport and operation on the sea should be adjourned although CO2 would be captured at the plant every day. It is, therefore, required that the system would have the buffer storage at the port and the extra shipping ability to recover the delay of schedule. Since the large scale of such spare capability might lead to the increase in cost, it is needed to investigate how to plan the system allowed for weather conditions reasonably. In this study, a time series model of sea state through one year is generated for a hypothetic ocean storage site, based on the wind data observed with satellite remote sensing, and simulations of CO2 marine transport and operation on the sea are carried out considering the operational limit of sea state. In this approach, the continuing bad weather days or the frequent occurrences of rough sea condition during the specific season are counted. Three kinds of system are applied for the simulations and compared; 1) CO2 carrier and release ship are used separately and moored tandem for CO2 shift at the site, 2) CO2 carrier and release ship are used separately and moored in parallel for CO2 shift, 3) ship is used as a CO2 carrier and release ship. The third one would not need mooring and CO2 shift operations on the sea which are sensitive to the sea state, but would need long- and every-time operation of pipe handling. The results are assessed as capital and running cost per tonne of CO2.
Investigation of the Influence of Waves and Vessel Motions on the VIV Response of Flexible Risers and Umbilicals From a Fatigue Damage Perspective
Authors: Trarieux F. , Lyons G. J. , Vaz M. , Patel M. H. , Garnham S.
Published: October 2008

The influence of waves and vessel motions on VIV is poorly understood. Investigations into this behaviour require substantial data sets in order to carry out a rigorous parametric analysis since many factors can prove the analysis to be very complex. Whilst the effect of waves might be considered to be relatively straightforward to appraise, the effect of vessel motions is a very delicate task indeed. For example, operating conditions can require the vessel to actively weathervane through the action of thrusters which can potentially affect the measurements. Data from the Foinaven Umbilical Monitoring System (FUMS) have enabled a detailed review of more than 22,000 records of curvature and other key parameters, each of about 7 minutes duration from January to May 2001. A strategy had to be established to process in an efficient manner the very many records. This paper presents the method which was followed in order to select suitable records, which could be compared in terms of varying wave height, current speed and direction. Results from spectral analysis are shown in several configurations of wave, vessel motions and current. From a predictive VIV approach, the analysis was performed using VIVALL which has the capability of generating curvature time-series. A comparison of spectra of measured and theoretical records is presented with commentary. In the second part of this paper, a fatigue damage investigation is presented. Trarieux & Lyons previously reviewed several fatigue methods which can be applied to VIV, and developed a simply applied approach as an alternative to the widely-used rainflow counting method. This alternative method is based on a simply calculated bandwidth parameter which has proven to give interesting insight into the frequency content of the VIV response. The application of this method along with rainflow counting is presented for different cases of varying wave height, vessel motions and current. Conclusions on these various influences on VIV and fatigue are provided.
X-Band Radar as a Tool to Determine Spectral and Single Wave Properties
Authors: Reichert Konstanze , Hessner Katrin , Dannenberg Jens , Traenkmann Ina
Published: October 2008

The Wave Monitoring System WaMoS II was developed for real time measurements of directional ocean waves spectra to monitor the sea state from fixed platforms in deep water or coastal areas as well as from moving vessels. The system is based on a standard marine X-Band radar used for navigation and ship traffic control. WaMoS II digitises the analogous radar signal and analyses the sea clutter information to obtain directional wave spectra from the sea surface in real time even under harsh weather conditions and during night. Spectral sea state parameters such as significant wave height, peak wave period and peak wave direction both for wind sea and swell are derived. Within the EU funded project ‘MaxWave’ and the German project ‘SinSee’ new algorithms were developed to determine sea surface elevation maps from radar images which are used to investigate the spatial and temporal evolution of single waves simultaneously. In this paper a short overview describes the calculation of surface elevation maps and the detection of individual waves. Considering two case studies, the results of spatial single wave detection and corresponding temporal single wave properties are compared and discussed. Individual wave parameters derived from radar images are compared to individual waves measured by a buoy. An application of the method to characterise extreme sea states is discussed.
Wave-Height Distributions and Nonlinear Effects
Authors: Tayfun M. Aziz , Fedele Francesco
Published: October 2008

Theoretical distributions for describing the crest-to-trough heights of linear waves are reviewed briefly. To explore the effects of nonlinearities, these and two approximations that follow from the Tayfun [28] model are generalized to nonlinear waves via the second-order quasi-deterministic model of Fedele and Arena [7]. The potential utility of Gram-Charlier type approximations [17, 18, 29, 31] in representing the statistics of nonlinear wave heights is also explored. All models and a fifth-order Stokes-Rayleigh type model recently proposed by Dawson [5] are compared with linear and nonlinear waves simulated from the JONSWAP spectrum representative of long-crested extreme seas, and also with observational data gathered during two severe storms in the North Sea. The results indicate first that nonlinearities do not appear to affect the crest-to-trough wave heights significantly. Most models and their nonlinear extensions yield similar and reasonable predictions of the data trends observed. The present comparisons do not confirm the efficacy of Gram-Charlier type approximations in modeling the statistics of unusually large wave heights.
Numerical Prediction of Model Podded Propeller-Ice Interaction Loads
Authors: Wang Jungyong , Akinturk Ayhan , Bose Neil
Published: October 2008

As the interest in arctic shipping and arctic exploration of oil and gas is increasing in recent years, the number of ice class vessels is increasing rapidly. Also the choices for propulsion devices are getting wider and these include podded propulsion systems. This study is a framework for the numerical prediction of the ice interaction loads acting on a podded propeller blade. The results of this study will help us to understand the propeller-ice interaction problem more comprehensively. Several studies for propeller-ice interaction have been carried out in the past few decades. Propeller-ice interaction, however, is a complicated process with a high level of uncertainties due to ice properties, ship operating conditions, and environmental conditions. Full-scale measurements involve high costs. In order to overcome these difficulties, model tests were carried out with model ice in an ice tank. The model tests provide well-controlled ice properties and interaction conditions to reduce the uncertainties. The tests were carried out in the ice tank with scaled down model ice at the National Research Council of Canada’s Institute for Ocean Technology. The ice loads acting on the propeller blade were measured with a six-component force and moment load cell fitted to the shaft and one of the propeller blades. Based on the experimental results, a numerical prediction model was developed to estimate the ice loads on the propeller blade. The numerical prediction is composed of three parts: the hydrodynamic calculations including separable and inseparable hydrodynamic loads, and the ice milling loads calculation. The separable and inseparable hydrodynamic loads can be obtained from clear water and blocked flow respectively. The hydrodynamic calculations were done by a low order panel method. The subroutines for calculating the ice milling loads are implemented into the panel method. The numerical prediction model for ice milling loads is described and the results are compared with those of experiments.
Full-Scale Fatigue Test on X60 Spiral Linepipe
Authors: Zhuang Chuanjing , Huo Chunyong , Feng Yaorong
Published: October 2008

Both fluctuation of operation pressure and transmission halt have obvious effect on the lifetime of the pipeline. When there exist flaws in the pipes, cyclic load caused by pressure fluctuation will promote the development of such defects especially as cracks. A full-scale fatigue test was performed on the X60 Spiral Submerged Arc-Welded pipes (Outside Diameter is 660mm), which was pre-manufactured with a small outside surface crack-like flaw. The test result indicated that both defect size and cyclic load magnitude had great effect on crack propagation rate and fatigue lifetime. During the test, the artificial shallow surface defect developed only in depth direction and finally caused the leakage. Comparison of test results between small-size and full-scale fatigue tests showed that small-size test can be used for lifetime prediction of the pipeline although there was some deviation.
Reliability Analysis of Submarine Pressure Hulls With Failure Governed by Inelastic Buckling
Authors: Radha P. , Rajagopalan K.
Published: October 2008

Due to the complexity involved in the inelastic buckling collapse mechanism of stiffened shell structures, the reliability analysis of submarine pressure hull, in which failure is dictated by inelastic effects, assumes great significance among structural engineers. In spite of many years of efforts by different authors to develop good prediction techniques for plastic and elastic-plastic buckling of stiffened shells and also to use the reliability concepts in the submarine pressure hull structures, comprehensive and reliable methods are still scarce. Hence in this paper a rigorous Finite Element analysis of a typical internally ring stiffened submarine pressure hull with failure governed by inelastic overall buckling has been done using the general purpose finite element software NISA. The samples required for each random variable were generated using Random Polar Sampling Technique (RPST) in which the combinations of variates are obtained using a random polar sampling of Latin hypercube sampled values. For the obtained collapse pressures, the reliability of the pressure hull structure has been determined and the effect of mean service loads on reliability has been analysed by taking different Central Safety Factors. The results were validated using Johnson-Ostenfeld Inelastic Correction method and the conclusions are advanced.
Numerical Simulation of Oscillatory Flow Around Two Circular Cylinders of Different Diameters
Authors: An Hongwei , Cheng Liang , Zhao Ming , Dong Guohai
Published: October 2008

A detailed study of oscillatory flow around two circular cylinders of different diameters is carried out numerically. The Reynolds-averaged Navier-Stokes equations are solved using a finite element method (FEM) with a k–ω turbulence closure. The numerical model is validated against oscillatory flows past a single circular cylinder where the experimental data are available in literature. Then it is employed to simulate the flow around two circular cylinders. It’s found that the fluid flow field around two cylinders is different from the single cylinder case, especially when the small cylinder diameter increases. The orientation of the small cylinder and the gap between two cylinders have significant effects on the vortex shedding process and force coefficients on the cylinders.
Motion Response of a Full-Scale Life Raft in Laboratory Tow Experiments
Authors: Mak Lawrence , Simo˜es Re´ Antonio , Kuczora Andrew
Published: October 2008

A 16-person full-scale life raft was towed in a tow tank in calm water, regular and irregular waves. The objectives were to assess the raft motion response, occupant motion, tow force, effect of tow speed, effects of different test variables (drogue deployment, floor inflation, weight distribution and ballast), and the likelihood of occupant motion sickness. Comparisons of RAOs obtained in regular and irregular waves demonstrated that irregular waves could be used as a cost effective means to determine raft response with a high degree of confidence. They also show that the life raft tow performance is different in waves than in calm water. For example, mean tow force is 20% higher in the sea state tested than in calm water. Floor inflation, drogue deployment, even weight distribution and tow speed increase mean tow force and tow force variation about its mean. The data also show that the same ballast types should be used to access the effects of different variables because manikin and water bag ballast produce different results. Measured occupant heave acceleration was about the same as the raft heave acceleration. From occupant heave acceleration, it was estimated that after 20 hours in the raft, 20% of occupants would vomit. Formulae were proposed to predict tow force in different sea states. Mean tow forces predicted using calm water tow resistance and RAOs derived from regular wave tow tests compared well with measured mean tow force in irregular waves.
Pipeline Safety Assessment at Inspection Time
Authors: Alamilla J. , Garci´a-Vargas J. , Oliveros J.
Published: October 2008

This work presents a reliability model for determining the pipeline safety after obtaining information on the corrosion damage of the piping system by non-destructive inspection. The model is used to estimate pipeline system reliability in every region containing detected corrosion defects and the probability of either global system failure or of a given pipeline segment. The global failure probability incorporates the contribution of defects that are undetectable by the inspection tool. For this, the probability density functions of maximum depths and the number of undetected corrosion defects by the inspection tool are also determined. The failure associated to each corrosion defect is determined from the pipeline resistance and fluid pressure. The model is applied to a pipeline segment of a given length showing that defect measurement errors and the contribution of corrosion defects, undetected by inspection tool, can significantly influence the value of failure probability of the system. To calculate the failure probability of the system the directional simulation technique is utilized.
On the Prediction of Hydrodynamic Forces Acting on a Ship Moving at Constant Drift
Authors: Ali N. Sulficker , Dhinesh G. , Murali K. , Anantha Subramanian V.
Published: October 2008

The effect of drift angle on a ship is investigated through towing tank tests and using Computational Fluid Dynamics (CFD). Resistance and wave elevations obtained from the computational study are validated with experimental results. Detailed free surface, mean velocity and pressure flow fields on the hull surface are obtained from the computational study for Fn ranging from 0.16 to 0.22 and for drift angle β = 0, 5 and 10°. The lateral force, yaw moment and asymmetric flow characteristics are brought out in the computational study.
The Equivalent Depth of Wave-Induced Scour Around Offshore Pipelines
Authors: Mousavi Mir Emad , Yeganeh Bakhtiary Abbas , Enshaei Nastaran
Published: October 2008

Physical experiments have been conducted to study the scouring around a pipe over an erodible bed under waves motion. The results show that the depth of the wave-induced scour is reduced when the pipe is installed in a primary depth. It is also indicated that when the primary installation depth of the pipe, |e|, exceeds a specified depth, no scouring occurs underneath the pipe. This specific depth is called the Equivalent Depth of Wave-Induced scour, Se. The equivalent depth of wave-induced scour is estimated as a function of pipe diameter and the Keulegan Carpenter number. Also for prediction of the scour depth with respect to the primary installation depth of the pipe, a new equation is proposed. In addition, new equations are proposed for prediction of the scour width before the pipe is installed. The results and proposed equations are next simplified in the form of diagrams to be used in practice. The experiments cover small KC numbers (KC < 6) that represent deep water conditions. The results can be used either for the design purposes or for calibration of the numerical models.
Behavior of Tensile Wires in Unbonded Flexible Pipe Under Compression and Design Optimization for Prevention
Authors: Tan Zhimin , Loper Cobie , Sheldrake Terry , Karabelas George
Published: October 2008

In ultra deepwaters, helical tensile armour wires under certain loading conditions may exhibit localized deflection in either the radial (out-of-plane) or lateral (in-plane) direction when subjected to significant high axial compression and bending. This phenomenon is often referred to as birdcage buckling. This paper presents the development of a total strain energy approach for modeling the buckling and post-buckling behaviour of these wires and for illustrating the characteristics of such behaviors. The paper presents the summary of the full scale offshore (Deepwater Immersion) DIP tests performed by Wellstream to date, all of which have been successful in resisting the failure modes. In addition, the results of pressure chamber tests are also presented and discussed, especially some of the key test constraints which can have a significant influence on the final result as observed on a recent 10-inch structure chamber test. The presented model provides a tool to define and implement the design criterions against such failure modes. The further validation of the model through comprehensive tests is planned, which is critical to ensure the ability to economically design and optimize flexible pipe structures to prevent this phenomenon, and to facilitate more cost effective products that meet the ultra deepwater design challenges.
A 2-D Vertical Finite-Element Model for Sediment Transport Due to Tidal Flow
Authors: Li Shi Sen , Liu Tao , Li Guojie , Gao Jie
Published: October 2008

An estuarine two-dimensional vertical finite-element model of suspended sediment transport has been established by the sediment conservation equation. The primary objective of the present paper is to develop and verify a 2DV estuarine tidal flow and sediment transport model derived by the moving grid FEM. To this end, finite-element method has been used. An arbitrarily shaped quadrilateral element has been selected. This model has been compared with analytical solution. The tidal flow model was developed by Li and Shi. This represents a step towards developing a general 2DV estuarine model.
Experiment on the Bottom Shear Stress of Sand Ripple Bed Under Wave Action
Authors: Li Shi Sen , Gao Jie , Qin Chongren , Liu Tao
Published: October 2008

When the strength of wave traveling over sandy bed reaches a certain condition, the bed form will be changed, to form the sand ripple bed. The formation mechanism of the bottom shear stress on ripple bed differs from that on plane bed. However investigation on the bottom shear stress on ripple bed is foundation of the investigation on the wave damping with traveling and the sediment transport. Therefor, this investigation is significant. The present paper measured the bottom shear stress directly and gave formulas to calculate the bottom friction factor and shear stress on the ripple bed.
Numerical Analysis on Added Resistance of Ship by 3-D Green Function Method
Authors: Inoue Yoshiyuki , Zakaria N. M. Golam
Published: October 2008

This paper deals with the numerical analysis on added resistance of a ship by 3-D Green Function Method. Linear potential theory has been used to describe the fluid motion and 3-D sink-source technique with forward speed has been applied to determine hydrodynamic forces for surface ship advancing in waves at constant speed. After solving the motion equation in frequency domain, radiation potential due to motion responses have been calculated to obtain the total potential of the flow field. Then, total potential and its derivatives have been obtained to assess the added resistance in waves by near field approach. To show the validity of the numerical code, the present numerical results for motion responses and wave loads on ships have been compared with experimental data as well as some numerical results by different approaches. Then the added resistances given by present numerical calculation by 3-D Green Function have been compared with some classical 2-D methods as well as experimental data for Series 60 ships. Finally the present numerical calculations have been applied for fuller form slow speed vessel where the classical 2-D methods usually fails to give good results due to their inherent limitations. The numerical results suggest that better agreement have been achieved in many cases using present full 3-D Green Function method.
Mean Stress Effect on Fatigue of Welded Joint in FPSOs
Authors: Zhang Bin , Moan Torgeir
Published: October 2008

This paper deals with the mean stress effect on the fatigue life of welded joints in FPSOs. Mean stresses in structural details of FPSOs are composed of residual stresses and mean stresses induced by external service loading conditions. Mean stresses, both the residual stresses and those induced by external load, affect on the fatigue life of structural details. Fatigue strength decreases as tensile mean stress increases. Under compressive mean stresses, fatigue lives are increased. Different fatigue analysis procedures to account for mean stress effect, i.e. JBP, JTP, DNV CN30.7 and IIW procedure, are used to compare the fatigue test data of different specimens representing different typical welded connections in ship-shaped structures from HHI in Korea. In this paper these procedures are compared and an improved procedure explicitly considering of the mean stress effect is also proposed. The fatigue strength of welded joints of FPSO is affected by the initial condition as well as possible redistribution (shake-down) of the residual stresses. The initial condition of welding residual stress and its re-distribution by static preload and cyclic load in the small scale specimens are evaluated with FE analyses and analytical equations, also compared with the test results obtained from measurement based on ordinary sectioning method.
Pontryagin Maximum Principle and Control of a OWC Power Plant
Authors: Justino P. A. P.
Published: October 2008

This paper concerns the analytical formulation and numerical simulation of the control of an oscillating-water-column (OWC) power plant. Pontryagin Maximum Principle (PMP) is applied to an OWC with a throttle valve-latching control is allowed. It is assumed that the rotational speed for the turbo-generator set is variable and thus a control strategy for the generator is taken into account. It is also assumed that the plant has a by-pass valve that prevents aerodynamic stall to occur at the turbine rotor blades. The control aims to maximize the amount of energy delivered to the generator taking into account not only the hydrodynamic performance of the device but also the aerodynamic performance of the turbine and bypass valve. It should be noted that this performance depends on the rotational speed of the turbo-generator set and thus it is related to the control strategy applied to the generator. A wave-to-wire model that includes the two control strategies (generator and throttle valve control) is devised.
Numerical Investigation on the Pull-Out Behaviour of Suction Caissons in Clay
Authors: Zeinoddini Mostafa , Nabipour Mahmood
Published: October 2008

Since their inception suction caisson foundations have presented themselves as proven means of anchoring floating production systems and fixed offshore structures. The pull-out capacity of suction caissons remains a critical issue in their applications, and in order to produce effective designs, reliable methods of predicting the capacity are required. In this paper results from a numerical investigation on the behaviour of the suction caissons in clays against pull-out loading have been presented. Soil nonlinearities, soil/caisson interactions and the effects from the suction on the behaviour have been taken into account. A linear relationship has been observed between the soil cohesion values and the pull-out capacity. Under drained conditions, beyond specific limits of soil cohesion values, the increase in the cohesion value have found to demonstrate no further influence on the pull-out capacity. The soil internal friction angle has been noticed to have an exponential increasing effect on the pull-out capacity. With constant values of the caisson diameter, an increase in the aspect ratio noticed to have a second order effect of the friction originated part and a linear influence on the cohesion originated part of the resistance. With constant values of the caisson length, an increase in the aspect ratio values has found to result in an exponential decrease of the pull-out capacity. Based on the obtained numerical results simple formulations and approximations have been proposed in order to estimate the effects of the studied parameters on the pull-out capacities.
Static Strength of Sleeve Reinforced X-Joints Loaded by Compression Load
Authors: Qi Feng , Tan Jia-Hua
Published: October 2008

In this paper a new method to reinforce X joints is presented depended on the connection between pontoon and leg of semi-submersible. As a part of total research, this paper extends numerical study to sleeve reinforced X-joints subjected to compression load through systematic variation of the main geometric parameters. The load transferring mechanisms and failure modes of such joints, with different sleeve size, are investigated and compared with corresponding un-reinforced joints. Within the range of geometric parameters investigated, the sleeve is observed to provide strength enhancement up to 200% for the corresponding un-reinforced joint. Design recommendations are provided for this joint type.