bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of High Efficiency MCFC/GT Hybrid Power Generation System
Authors: Watanabe T. , Izaki Y. , Mugikura Y. , Yoshikawa M. , Morita H. , Kawase M. , Yoshiba F. , Asano K.
Published: January 2009

A number of cycle simulations, which are applied by Molten Carbonate Fuel Cell (MCFC) power plants combined with gas/steam turbines, prove that it is possible to design very highly efficient power plants. However, the stack performance, the operation technology and the performance estimation technology have not yet been established during the initial development stages. The Central Research Institute of Electric Power Industry (CRIEPI) has performed many cell and stack tests and has evaluated the performance under various operating conditions. The operation, performance analysis and estimation methods have been developed for various pressure ranges. Therefore, the accuracy of the plant power estimation has been improved immensely. CRIEPI has also proposed the application of a Li/Na electrolyte instead of a Li/K to achieve higher voltages and a longer stack life. A 10 kW-class short stack consisting of ten 1-m2 cells with a Li/Na electrolyte was operated for more than 10,000 hours, and a very low voltage decay rate was measured during the governmental program. Based on these accomplishments, field tests on small MCFC/GT (gas turbine) hybrid power plants with capacities of several hundred kW will be initiated in Japan throughout the next years.
Gas Flow and Heat Transfer Analysis for an Anode Duct in Reduced Temperature SOFCs
Authors: Yuan Jinliang , Rokni Masoud , Sunde´n Bengt
Published: January 2009

In this study, a fully three-dimensional calculation method has been further developed to simulate and analyze various processes in a thick anode duct. The composite duct consists of a porous layer, the flow duct and solid current connector. The analysis takes the electrochemical reactions into account. Momentum and heat transport together with gas species equations have been solved by coupled source terms and variable thermo-physical properties (such as density, viscosity, specific heat, etc.) of the fuel gases mixture. The unique fuel cell conditions such as the combined thermal boundary conditions on solid walls, mass transfer (generation and consumption) associated with the electrochemical reaction and gas permeation to / from the porous electrode are applied in the analysis. Results from this study are presented for various governing parameters in order to identify the important factors on the fuel cell performance. It is found that gas species convection has a significant contribution to the gas species transport from / to the active reaction site; consequently characteristics of both gas flow and heat transfer vary widely due to big permeation to the porous layer in the entrance region and species mass concentration related diffusion after a certain distance downstream the inlet.
Development of PEMFC Systems for Space Power Applications
Authors: McCurdy Kerri , Vasquez Arturo , Bradley Karla
Published: January 2009

Space power applications historically include fuel cells due to the high energy storage density of hydrogen and oxygen compared to batteries. Fuel cells are continuously under development to incorporate latest technology and focus on specific details of fuel cells systems relevant to harsh space transportation environments. The National Aeronautics and Space Administration is developing proton exchange membrane fuel cells systems for space power applications because of the potential for longer life, reduction in cost, and increase in safety compared to current alkaline fuel cell technology. Space fuel cell applications utilize oxygen instead of air, which introduces better performance but greater hazards. Circulation of reactants is beneficial for these systems to aid in removal of product water from the fuel cell stack and to humidify reactant fluid streams. Current space fuel cell prototype systems use a simple but effective pump for reactant recirculation known as a gas ejector. A gas ejector uses a high-pressure primary gas supply to produce suction to a secondary fluid at a lower pressure. A gas and water separator is then necessary to remove the fuel cell product water from the unutilized recirculated oxygen. The National Aeronautics and Space Administration is analyzing and testing several different means to separate the oxygen gas and water in both microgravity and increased gravity conditions. This paper addresses specific components and design concerns for proton exchange membrane fuel cell systems for space power applications.
Analogies Between Fuel Cells and Heat Exchangers: From Phenomena to Design Principles
Authors: Haynes Comas , Rooker William , Melbourne Vaughn , Jones Jeffery
Published: January 2009

Fuel cells and heat exchangers have numerous similarities. Both technologies are used to produce an “energy-in-transit.” Heat exchangers foster thermal transport (heat) as a result of thermal potential differences between streams; fuel cells foster charge transport across electrodes (current leading to power) as a result of electrochemical/electric potential differences between the reactant streams and fuel cell electrodes. Additional analogs include series resistance formulations, active regions for transport phenomena and pertinent capacity rates. These similarities have motivated the extension of heat exchanger design philosophies to fuel cells development. Pilot simulations have been done wherein solid oxide fuel cell geometries and process settings are being optimized via electrochemical pinch points, electroactive area optimization (patterned after optimal area allocation within heat exchangers), electrode “fins” for diminished polarization, and electrochemical multi-staging (motivated by heat exchanger network concepts). The prevailing theme has been to bridge methodologies from the mature field of heat exchanger design to improve fuel cell design practices.
Investigation of a Novel Reciprocating Compression Reformer for Use in Solid Oxide Fuel Cell Systems
Authors: Zinn Anthony N. , Gardner Todd H. , Berry David A. , James Robert E. , Shekhawat Dushyant
Published: January 2009

A novel reciprocating compression device has been investigated as a non-catalytic natural gas reformer for solid oxide fuel cell systems. The reciprocating compression reformer is a potential improvement over current reforming technology for select applications due to its high degree of heat integration, its homogenous gas phase reaction environment, and its ability to co-produce shaft work. Performance modeling of the system was conducted to understand component integration and operational characteristics. The reformer was modeled by utilizing GRI mech. in tandem with CHEMKIN. The fuel cell was modeled as an equilibrium reactor assuming constant fuel utilization. The effect on the reformer and the reformer – fuel cell system efficiencies and exit gas concentrations was examined over a range of relative air-to-fuel ratios, 0.2 to 1.0, and at compression ratios of 50 and 100. Results from this study indicate that the reformer – fuel cell system could approach 50% efficiency, if run at low relative air-to-fuel ratios (0.3 to 0.5). With higher air-to-fuel ratios, system efficiencies were shown to continuously decline due to a decrease in the quality of synthesis gas provided to the fuel cell (i.e. more power being produced by the reformer). Optimal operation of the system has been shown to occur at a relative air-to-fuel ratio of approximately 0.775 and to be nearly independent of the compression ratio in the reciprocating compression reformer. Higher efficiencies may be obtained at lower relative air-to-fuel ratios; however, operation below this point may lead to excessive carbon formation as determined from an equilibrium carbon formation analysis.
Circumventing the Challenges of Fuel Cell Powered Automobiles
Authors: Gover James E.
Published: January 2009

The purposes of this paper are (1) to examine the realities of fuel cell development to determine the economic potential of fuel cell applications to transportation and (2) to identify the major challenges as well as the public policies that could lead to the automobile becoming a mobile electric power source that is used to power homes and industry. Several technical and cost issues were identified to have the potential to pose development challenges; however, none are likely to be show-stoppers. If the fuel cell powered vehicle can offer the consumer additional uses for the automobile, e.g., a source of electric power for businesses or it can permit a rapid style change in the automobile by easily replacing the passenger compartment at costs the consumer finds acceptable, the consumer will be willing to spend more on the fuel cell powered vehicle than it spends on combustion engine powered vehicles. If the fuel cell stimulates design changes that makes major contributions to the safety of automobiles and results in substantial reductions in the cost of insurance, that will also promote consumer interest. Of equal importance to these technical issues are public policies that could promote fuel cell power use in automobiles. For example, a desire to reduce our dependence on foreign sources of oil or rapid growth in oil prices could lead to pubic policies that would accelerate the adoption of fuel cells in automobiles.
Water and Thermal Balance in PEM Fuel Cells
Authors: Izenson Michael G. , Hill Roger W.
Published: January 2009

The high energy density available from polymer electrolyte membrane (PEM) fuel cell systems makes them attractive sources of portable power. A key consideration for minimum weight portable power systems is that they must operate simultaneously at water balance (no external water supply) and thermal balance (controlled temperature). Water and thermal management are intimately linked since evaporation is a potent source of cooling. The cell’s electrochemical performance and the ambient environment determine the rates of water production and transport as well as heat generation and removal. This paper presents the basic design relationships that govern water and thermal balance in PEM fuel cell stacks and systems. Hydrogen/air and direct methanol fuel cells are both addressed and compared. Operating conditions for simultaneous water and thermal balance can be specified based on the cell’s electrochemical performance and the operating environment. These conditions can be used to specify the overall size and complexity of the cooling equipment needed in terms of the “UA” product of the heat exchangers. The water balance properties can have strong effects on the size of the thermal management equipment required.
Optimal Outside Airflow Control of Integrated Air Handling Unit System for Large Office Buildings
Authors: Song L. , Liu M.
Published: January 2009

This paper presents the optimal outside air control in the integrated air handling unit system for large commercial buildings (OAHU). The optimal outside air control schedules are developed using the geometric linear optimization method, and expressed as analytical functions of the outside air temperature and enthalpy, the interior zone airflow ratio, and the exterior zone supply air temperature. The optimal outside air control schedules can be applied to both constant and variable air volume systems. When the optimal outside air control schedules are implemented, the OAHU system can significantly improve indoor air quality (IAQ) and use significantly less thermal energy than conventional systems. The geometric optimization method can also be used in other linear HVAC optimizations with non-liner constraint conditions.
Analysis of Pickup/Pulldown Load in Buildings: Part I — Mathematical Analysis
Authors: Saman Namir F. , Shami Usama F. , Mahdi Hashim S.
Published: January 2009

In large commercial buildings, air handlers for HVAC systems are shutdown during unoccupied periods to save on utility bills. During the shutdown time, some of the heating or cooling load accumulates and is stored in the building. Consequently, on start up, there is an added load that must be removed by the HVAC system. The stored load can be divided into preconditioning load (fast load) and storage load (slow load). In this paper, mathematical analysis is used to study the preconditioning and storage loads after system shutdown. The governing mathematical equations, that represent an analytical model, were solved using Laplace transforms. Simplifications to the analysis are presented. It is found that the ratio of storage area to the exposed area plays an important role in the determination of shutdown loads.
Solar Tri-Generation: New Concept of Solar Energy System
Authors: Tanaka Tadayoshi , Ando Yuji , Amano Masatsugu
Published: January 2009

It is general that each of the heat and electricity is individually supplied even if their resources are the same. However, from the viewpoint of the effective use of energy resources, development of co-generation producing both of them is promoted. To enhance more the utilization of energy resources, it is considered to supply three different types of energy from one energy resource. This is a basic concept of tri-generation and we named it first in the world. Tri-generation we proposed supplies heat, electricity and fuel. By this definition, we can easily understand that tri-generation is realized by utilizing solar energy. Therefore, we call it solar tri-generation. In this paper, the methods of system structure and the feature of solar tri-generation are described and we conducted a simplified analysis to make clear the effectiveness of solar tri-generation in the comparison of effective use of solar energy with a solar co-generation consisting of photovoltaic cell modules and photovoltaic/thermal modules. Furthermore, from the viewpoint of CO2 emission reduction, we conducted a simplified analysis to make clear the characteristics of energy consumption in the three systems of a fossil fuel fired co-generation and, a solar co-generation and a tri-generation with fossil fuel fired co-generation.
Numerical Study on the CZ Silicon Melt Convection for High Efficient Solar Cell
Authors: Munakata Tetsuo , Someya Satoshi
Published: January 2009

Conversion efficiency of solar cell is strongly affected by quality of substrate and the quality of substrate is influenced by melt convection if the substrate crystal is grown by melt growth technique. Therefore, melt convection control techniques are important to produce a high quality single crystal. In this paper, we have proposed a high frequency magnetic field applied CZ method and investigated the effect of high frequency magnetic field on silicon melt convection. The result reveals that the high frequency magnetic fields affect the tendency of the melt convection: until certain intensity of the high frequency magnetic field, the melt convection is suppressed and above such intensity of the high frequency magnetic field, the melt convection intensity is enhanced. This result indicates that the melt convection can be controlled by the high frequency magnetic field and the high quality silicon single crystals will be grown by this method.
Brightstar Solid Waste and Energy Recycling Facility: An Innovative Waste to Energy Technology
Authors: Schwarz Stephen C. , Richter Leah K.
Published: January 2009

The Brightstar Environmental Solid Waste and Energy Recycling Facility (SWERF) is a municipal solid waste (MSW) to energy facility utilizing a gasification (pyrolysis) process. At this time, the only operational SWERF is in New South Wales, Australia. While pyrolysis of MSW is not in itself new, the Brightstar technology is believed to have reached a sufficient level of development, and to incorporate sufficient new features, to qualify as new and cutting edge. This paper presents findings from a trip to Australia to inspect the facility, as well as the results of a Request for Proposals process for a municipal client in Florida. Analysis includes process, environmental, and economic factors.
Beneficial Reuse of Municipal Waste-to-Energy Ash as a Landfill Construction Material
Authors: Worobel Bob , Leo Kevin , Gorrie Jason , Thur de Koos Paul
Published: January 2009

The Solid Waste Disposal Authority of Palm Beach County owns a municipal waste-to-energy plant located in West Palm Beach, Florida. Currently, ash generated by the operation of the facility is disposed at the Authority’s adjacent Class I Landfill. In 1998, the Florida Legislature amended certain provisions of the Florida Statutes to encourage the beneficial reuse of municipal waste-to-energy ash in manners that are protective of human health and the environment. To that end, the Florida Department of Environmental Protection developed a document entitled “Guidance for Preparing Municipal Waste-to-Energy Ash Beneficial Use Demonstrations” to assist communities in developing reuse demonstrations. SWA and CDM undertook a project and developed a report in accordance with the Guidance document to demonstrate that reuse of the ash from the SWA’s waste-to-energy facility as a landfill construction material is consistent with the reuse goals set forth by the Legislature. Initial studies were performed to identify locations and quantities for use of ash within the confines of SWA property. Some of these locations included future Class I and Class III Landfill cells and perimeter roadways. It was determined that nearly 3 million cubic yards of landfill space could be saved through beneficial reuse of the ash. An initial analytical screening was performed to test the leaching potential of the eight RCRA metals and compare to applicable groundwater and surface water standards. Overall results were favorable, with some indication that lead could pose potential concern. Geotechnical index testing (grain size, moisture content, and organic content) was performed to determine if ash has similar physical properties to the sand that is currently used on-site. Results indicated that the ash has similar physical properties to the sandy material. This initial testing was performed in accordance with the July 1998 DRAFT version of the guidance document.
Design, Construction, Start-Up and Commissioning of a State-of-the-Art Water-Cooled Grate WtE-Plant for O¨rebro, Sweden
Authors: Adams Bart , Eeraerts Dirk , Christiaens Ivan
Published: January 2009

In 2001, SEGHERS was awarded the contract for the design and construction of the furnace and heat recovery system of a new, 330 tons per day WtE-plant in Orebro¨, Sweden. A wide variety of municipal and industrial wastes (including electronic waste, demolition waste, car fluff, filters, plastic and rubber...) will be treated. The design point corresponds to an average heating value (HHV) of 13.1 MJ/kg (5600 Btu/Lb). The first part of the paper addresses the engineering and construction phase of the project, which took 15 months in total. Key decisions and design options, including the choice and characteristics of a partially water-cooled grate, the use of the cooling water heat (with implications on plant efficiency) and the design features resulting in a low-NOx WtE plant are discussed in detail. The second part of the paper focuses on the construction and commissioning of the plant. Finally, the plant performance is documented. The main results are compared with the guaranteed values and the differences are discussed. The performance of the water-cooled grate is compared to that of other WtE plants.
Optimal Vibration Control Strategy for Offshore Platforms Accounting for AMD Constraints
Authors: Ji Chunyan , Meng Qingmin
Published: January 2009

In order to control the excessive vibration of offshore platforms under wave excitations, an H2 control algorithm was presented in this paper. In the present study, noise terms for generating filtered wave loading and accounting for model uncertainty are separated. In addition, in H2 optimization problem, AMD’s capacities are considered by setting the limits of AMD stroke and maximum input control force. And the formulations of such algorithm are described. In order to investigate the feasibility and effectiveness of the proposed method, a numerical example applied to an offshore platform is presented in this paper. The numerical results demonstrate that the proposed algorithm is effective in reducing the vibration of offshore structure when there are some uncertainties in building the mathematical model of the structure. In addition, AMD designed by the proposed method can keep its operation by choosing appropriate feedback gain among several gain candidates based on the AMD limits.
Second Order Model for Wave Crests Used in Prediction of Green Water Load and Volume on Ships in Random Waves
Authors: Wist Hanne Therese , Myrhaug Dag , Rue Ha˚vard
Published: January 2009

The probability that a wave crest in a random sea will exceed a specified height has long been recognized as important statistics in practical work, e.g., in predicting green water load and volume on a ship. Nonlinear probability density functions for predicting green water load and volume are presented. The models are based on the linear model of [1] in combination with transformation of a second order wave crest height model. The wave crest height model is obtained from second order wave theory for a narrow-banded sea state in combination with transformation of the Rayleigh distribution. Results from the models are compared with model tests of a cargo ship presented in [1].
Development of 550 MPa Yield Strength Steel Plate for Offshore Structures
Authors: Kamo Takahiro , Urabe Takeshi , Ohnishi Kazushi , Nakamura Hirofumi , Okaguchi Shuji , Hamada Masahiko , Suzuki Shuichi
Published: January 2009

Offshore structure steel with high strength of YS550MPa has been investigated. As for offshore structure steel, high toughness in welded joints is required in addition to that in base metal. TMCP type steel of up to YS420MPa grade is used widely, and up to YS500MPa grade is reported in some papers. However, steel of higher strength grade with good toughness and weldability will be beneficial to structures in strict conditions. To reach the YS550MPa requirement, hardening effect by Cu precipitation was utilized. Steel plates were designed with micro-alloyed low C-Mn-Cu-Ni-Cr-Mo system. The combination of the copper precipitation and TMCP technology can increase strength without deteriorating toughness and weldability. Heat treatment for Cu precipitation was carried out to optimize the balance of strength and toughness of the base metal. The developed steel also shows good HAZ CTOD toughness up to 76.2mm thickness in several welding conditions including after PWHT. The newly developed steel has the possibility to increase the flexibility to design large-sized structures.
Floatover Deck Installation: Case Study — Structural Efficiency of Longitudinally and Transversely-Recessed Structures
Authors: O’Neill Lee A. , Fakas Emmanuel , Pinna Rodney , Walsh Timothy
Published: January 2009

Conventional floatover deck (FOD) installation on a jacket substructure requires the top of the structure to be recessed appropriately, either in the longitudinal or transverse direction to accommodate the vessel transporting the deck. The recess direction is very important to the design of the jacket and influences the outfitting of appurtenances, the shape of the deck and the floatover concept as a whole. This study investigates the structural integrity of typical longitudinal and transverse jackets suitable for FOD installation under both inplace and installation conditions. The study also assesses the structural efficiency of the two options under various installation conditions and benchmarks their structural performance against more conventional jackets associated with lift-installed decks.
A Frequency Domain Approach for Random Fatigue Analysis of Steel Catenary Risers at Brazil’s Deep Waters
Authors: Dantas Claudio Marcio Silva , de Siqueira Marcos Queija , Ellwanger Gilberto Bruno , Torres Ana Lu´cia F. Lima , Mourelle Marcio Martins
Published: January 2009

The steel catenary riser was adopted by Petrobras as a cost-effective alternative for oil and gas export and for water injection lines on deepwater fields, where large diameter flexible risers present technical and economic limitations. The installation of the P-18 SCR was a pioneer project of a free-hanging steel catenary riser linked to a semi-submersible [1] and demonstrated the technical feasibility of the concept. Fatigue damage verification is an important issue in SCR design, demanding a high number of loading cases to be analyzed. The random time domain nonlinear analysis is considered an attractive and reliable tool for fatigue analysis as nonlinearities are properly modeled and the random behaviour of environmental loadings is considered. As time domain analysis is high computer time consuming, the frequency domain analysis has been considered as an alternative tool for the initial phases of riser design to be used mainly for fatigue damage verification. This paper presents a methodology developed to perform a linearized frequency domain analysis aiming at fatigue damage verification. Two drilling risers were analyzed with the frequency domain procedure developed. The model of a steel lazy-wave riser was analyzed both in frequency and time domain in order to compare fatigue damage results. The analyses were performed using the Petrobras’s in-house computer codes ANFLEX, ALFREQ and POSFAL developed and implemented as part of projects from CENPES/PETROBRAS with “COPPE/UFRJ -The Engineering Post-Graduating Coordination of the Federal University of Rio de Janeiro”.
Wireless Data Communication for Ocean Bottom Instrumentation
Authors: Shih H.-H. , Sprenke James , French Geoff , Boicourt William C.
Published: January 2009

The National Ocean Service (NOS) of NOAA maintains and operates a Physical Oceanography Real Time System (PORTS®) in the Nation’s major ports, harbors and bays. The traditional way to obtain real-time data from bottom mounted instruments is via underwater cable link. However, it is vulnerable to damages and costly to install and maintain. This paper describes a new approach utilizing wireless data telemetry. The system consists of an ocean bottom instrumentation platform and a data relay surface buoy. The bottom platform contains a RD Instruments (RDI) 1200 KHz acoustic Doppler current profiler (ADCP), a LinkQuest UWM1000 underwater acoustic transmitting modem, and acoustic recovery devices. The surface buoy supports a UWM1000 receiving modem and a Freewave 900MHz spread spectrum line-of-sight radio modem with antenna. The ADCP provides measurements of vertical current profiles at 6-minute interval and surface waves at hourly interval. The underwater acoustic modem transmits at 9.6 K baud rate the current data at the end of each 6-minute sampling, and wave data at the end of each 20-minute sampling. These data are relayed via radio at 48.5 K baud rate to a shore base station located at the University of Maryland’s Horn Point Laboratory about 16 miles away. There the data are then transferred in near-real-time via internet to NOS office in Silver Spring. Data are monitored and archived at both sites. The system was deployed off Taylors Island in the Chesapeake Bay in late July 2003 and was operated reliably through a 8-month period. It demonstrated successfully its measurement concept and capability for real-time monitoring of both currents and waves from a single ADCP instrument. This paper describes the overall system, component testings and field experiences, and presents some sample results.
High Strength Linepipe With Excellent HAZ Toughness
Authors: Okatsu Mitsuhiro , Oi Kenji , Ihara Koichi , Hoshino Toshiyuki
Published: January 2009

The API 5L-X65 steel plates for low temperature service were produced using the thermo-mechanical control process (TMCP) with the optimum micro-alloying addition. Featuring of the additions are as low amount of titanium, calcium, niobium, and vanadium as possible, for high heat affected zone (HAZ) toughness and strength. Controlling titanium and nitrogen and the Ti/N ratio, a large number of TiN dispersed finely are formed in steel and the austenite grain size near a weld fusion line is refined remarkably owing to strong pinning effect of TiN. Calcium addition promotes ferrite nucleation, so that increase in fine polygonal ferrites makes microstructure of HAZ much finer. Niobium and vanadium content are reduced, because carbide precipitates are formed when the coarse grain HAZ is reheated around 700 degree C and the precipitation hardening deteriorates HAZ toughness. The trial manufacturing of the 19.5mm, 26.9mm and 31.4mm thick X65 grade UOE pipes was finalized with the satisfactory results. The toughness of longitudinal submerged-arc welds was more than 50 J in Charpy V-notch impact test at −30°C.
Dynamics of a Linear Generator for Wave Energy Conversion
Authors: Eriksson Mikael , Thorburn Karin , Bernhoff Hans , Leijon Mats
Published: January 2009

A concept is presented where the piston of a seabed based linear generator is directly driven by a buoy on the water surface. A spring is connected to the other end of the piston. Thereby the buoy absorbs energy in two ways. A large number of poles are used as an “electromagnetic gearbox” which gives a high rate of flux change in the stator despite the slow piston motion. The damping force is a function of the velocity and the electric output power. In the studied concept the power from the generator is rectified with a diode bridge. The results of theoretical studies of output power and its interaction with the dynamics of the equation of motion are presented. It is shown that the DC voltage can be tuned to optimize the power production for each wave climate.
Assessing Motion Stress Levels on Board of Fishing Vessels of the Newfoundland Fleet
Authors: Bass Don , Cumming David , Akinturk Ayhan , Molyneux David , Vera Javier , Hopkins Dwayne , Barrett John
Published: January 2009

The aim of this study is to develop a numerical tool that could be used to assess the physical stress levels associated with the vessel motions on board of fishing vessels of the Newfoundland fleet. A number of full-scale sea trials of typical fishing vessels of the fleet are underway to validate the numerical tool. Model experiments are expected to follow in the near future. If desirable correlations between the trials, model tests and the numerical results are obtained, simulations will be performed to obtain typical ‘motion stress’ profiles of various fishing boats over a typical fishing season. This paper presents the preliminary results obtained so far. Sea trials for a 35’ fishing vessel was conducted. Sample results presented in the paper. Motion Induced Interruption (MII), which will be used to assess the physical stress levels has been implemented into the numerical tool and few case studies performed for the 35’ fishing vessel. Results obtained so far seem promising.
Damage Identification in Offshore Platforms Using Frequency Response Functions
Authors: Roitman Ney , Gade´a Anderson S. M. , Magluta Carlos
Published: January 2009

The damage identification problem in offshore platforms, specifically in jacket platforms, has been studied since the seventies. In spite of the effort dispended, there is still no spread out methodology that can be applied in this kind of structure, due its specific characteristics (structural complexity, load and operational conditions, etc.). The development of such methods would be extremely useful to preview structural failures, once this kind of structures is almost completely under water. Most of the developed methods for damage identification use modal parameters, by comparisons of different structural time conditions, and the damage may be expressed through the observed discrepancy. This paper presents a methodology to locate damage based on an iterative method. It was developed an optimization software which uses the Goal Programming Technique to choose the best set of variables that minimizes the difference between experimental and numerical Frequency Response Functions (FRFs), which can better represent the structure situation. Some numerical simulations were performed on a scaled fixed oil platform model to verify the efficiency of the method. The results show that such method is efficient when damages are restricted to a set of optimization variables.
A Case Study Comparison of Surface Extrapolation and Battelle Structural Stress Methodologies
Authors: Healy Brian E.
Published: January 2009

A case study comparison of the surface extrapolation and Battelle structural stress methodologies has been performed on a side shell connection detail typical of a representative FPSO or tanker vessel. Computations of hot spot stress via either method are consistent with current recommended practice. Convergence analysis to determine the hot spot stresses that best serve as fatigue parameters and a fatigue comparison that employs hot spot stresses from the convergence analysis have been executed at various locations around the detail. Results are reported and discussed.
Influence of Oxygen on Electrode Consumption and Penetration in GTA Welding
Authors: Ogawa Yoji , Morita Takao
Published: January 2009

Principle of Gas Tungsten Arc Welding is quite simple. Electron, which is emitted from Tungsten electrode, hits into the metal, and the heat from this impingement produce enough heat for fusion welding. However, actual behaviors are quite complicated. Electron emission is much influenced by physical condition of cathode and ambient circumstance. Considerable electron emits from unbelievable location of the cathode, especially at the ignition stage when the cathode is not enough hot. The anode spot, where main electrons hit into the metal, is also much influenced by surface condition and purity of shielding gas. The anode spot is usually appeared at the center of molten pool where the temperature seems to be maximum value. But, it sometimes moves irregularly or hits on the solid surface. This situation is mainly caused by oxidized layer on the metal or molten pool. Some minor elements on the metal act as a kind of catalytic agent. It sometimes drastically changes weld geometry. An amount of erosion on cathode surface is increased with increased oxygen contents. The penetration depth is also increased with oxygen contents. Plasma condition is also changed, because cathode and anode conditions are closely connected with plasma condition. Dynamic behavior of arc-cathode and arc-anode reactions was observed by ultra-high speed video system in a chamber from vacuum to high pressure, where contents of gas are controlled. Effects of oxygen and minor elements on anode and cathode reactions were considered.
Offshore Arctic Pipeline Oil Spill Risk Assessment
Authors: Dinovitzer A. , Comfort G. , Lazor R. , Hinnah D.
Published: January 2009

While offshore arctic pipelines have been under consideration for more than 25 years, few have been built. Renewed interest in offshore arctic oil and gas has necessitated the design of pipelines capable of both overcoming the technical challenges of the arctic offshore environment and minimizing the risk to it. This paper describes a quantitative risk assessment completed by BMT Fleet Technology Limited on the risk of an oil spill for several design alternatives of the proposed Liberty Pipeline that would be used to transport oil onshore from a production site in the Alaskan Beaufort Sea. For the purposes of the study, risk was defined as the volume of oil expected to be released over the planned pipeline 20-year life. The investigation considered the risks associated with ice gouging, strudel scour, permafrost thaw subsidence, operational failures, corrosion, third party activities and thermal loads leading to upheaval buckling. Event probabilities for these hazards were established through the development of event trees used to combine historic operational failure statistics and those estimated through engineering analysis. A pipeline leakage consequence model was developed to quantify the oil volume released during pipeline failure events associated with rupture, through-wall cracking and pinhole leaks. The model considered secondary containment and the expected performance of leak detection and monitoring systems. The time to leak detection, shut down, and line evacuation were used in estimating the total spill volumes. The paper provides an overview of primary elements of the risk assessment including the hazard identification, reliability analysis and consequence modeling, and describes the challenges involved in this comparative risk analysis completed for this unique environment.
Strain Limits for High Strength Riser Materials
Authors: Baxter Carl , Sherry Andrew , O’Gara David , Beardsmore David
Published: January 2009

High strength materials are being used to increase the capability of dynamic risers to withstand deep water and high pressure flows. Design codes generally require that these materials operate well within their ultimate capability in the main body of the riser, but components of the riser such as screwed connectors and flanges often experience high localized or secondary stresses above yield. These stresses are allowable because they are self-limiting or in strain controlled situations. In addition the main body of the riser may also exceed yield in survival conditions when the riser may be allowed to undergo permanent distortion, but not fracture. However, high strength materials often exhibit lower ductility than traditional steels and as a result, there is a need to understand how these materials behave under high multiaxial stress conditions in order to quantify the true margin of safety in the component. The work reported in this paper focuses on titanium Grade 29, which has been used for tapered stress joints on steel catenary risers, and is now being considered for use in the riser touch down zone on several deepwater projects. The work on burst testing was also part of the validation of Dn V-RP-201, “Design of Titanium Risers”. This paper explores two approaches to determining a material model for failure. The first method used the Rice and Tracy void fraction model but this was found to be geometry dependent for this material and not ideal for failure prediction. A method was developed for determining strain limits under triaxial loading conditions using diffuse necking theory. The theory was applied to burst tests of high-pressure cylinders and gave a good prediction of the burst pressure and strain at failure.
Modeling of Underwater Flexible Structures and Its Application to the Fishing Gear System Simulation
Authors: Lee Chun-Woo , Lee Ju-Hee , Cha Bong-Jin , Kim Hyun-Young , Lee Ji-Hoon
Published: January 2009

This paper describes a physically based model for underwater flexible systems and presents its simulation results. In this study, a flexible structure is divided into a finite number of elements and those elements are connected with flexible lines. The elements of a structure can be modeled using the mass-spring model. The model is described as a nonlinear and stiff equation by considering the elasticity of the lines and external forces. The Newmark β method is used for the numerical integration of the system. It is found that this method offers low computational times and a stable solution. Also introduced is an algorithm to design various flexible systems using computer graphics, an automatic model creating system from the designed plan and a three-dimensional graphics tool that can show the calculated results. Application examples in design and simulation for the commercial fishing gears are presented.
Physical Modeling of Suction Piles in Clay
Authors: Raines Richard D. , Garnier Jacques
Published: January 2009

The behavior of suction piles that are installed by suction into soft Speswhite clay was investigated by model tests in a large geotechnical centrifuge. Many different placement and loading tests were carried out in similar soils, thereby providing a reliable method for evaluating the effects of selected parameters on pile response. Techniques and equipment were developed to prepare normally consolidated clay samples with a high degree of repetitiveness and to measure their characteristics in-flight (e.g., on-board movable Cone Penetrometer device – abbreviated CPT in this paper) in order to simulate deepwater offshore soil conditions. The CPT tests performed in-flight indicate that these objectives were achieved with the soil samples tested. Special devices were developed for this program to apply well-controlled vertical and inclined monotonic and cyclic loads. A well-controlled system was necessary to investigate sustained and cyclic loads for simulating environmental loading conditions on anchor pile moorings for floating production and drilling facilities, or on other facilities used in the storage and off-loading of oil and gas. In the test program, the capacity measured during monotonic loading served as a reference value for establishing a scale factor to be used in applying cyclic and sustained loading. A monotonic load test was always carried out before and after each cyclic or sustained load test in order to quantify any change in capacity due to a given loading event. Issues addressed in the program and discussed in this paper include the effect of suction installation methodologies on pile capacity, and the behavior of piles during inclined monotonic loading and cyclic loading due to simulated Gulf of Mexico hurricane events. Other issues were addressed in the program (e.g., simulated loop current events, effect of a sand layer on suction pile penetration) but are not included in this paper due to space limitations. A number of tests were performed for each loading condition and the data are judged to be robust because of the consistency of the results within the same tub when applying multiple loading sequences, and between tubs when applying a similar test protocol. The experimental data from the test program will be used to update ExxonMobil suction pile design practice, and to validate in-house and contractor numerical models.
Geometrical and Material Non-Linear Formulation for Bend Stiffeners
Authors: Vaz Murilo Augusto , de Lemos Carlos Alberto Duarte
Published: January 2009

A mathematical formulation and a numerical solution for the geometrical and material non-linear analysis of bend stiffeners — employed to protect the upper terminations of flexible risers and subsea umbilical cables — are presented in this paper. The differential equations governing the problem result from geometrical compatibility, equilibrium of forces and moments and material constitutive relations, which can be linear elastic symmetric or non-linear elastic asymmetric. In this latter case, the bending moment versus curvature for each cross-section is calculated and then expressed by a polynomial power series expansion. Hence, a set of four first order non-linear ordinary differential equations is written and boundary conditions are defined at both ends. A one-parameter shooting method is employed and results are presented for a case study where linear elastic symmetric and non-linear elastic asymmetric constitutive models are compared and discussed. It is shown that an accurate analysis of bend stiffeners depends on a precise assessment of the material constitutive property.
Including Roll in the Evaluation of Bending Loads for the Hull Girder in a Seaway
Authors: Rizzuto Enrico
Published: January 2009

The longitudinal strength of the hull girder is traditionally verified by linear superposition of still water (static) loads to wave induced (dynamic) loads. Belonging to the former class, gravitational effects are considered always as directed along the plane of symmetry of the ship, as the static equilibrium position corresponds to the ship floating with a neutral heel angle. This is not the case for a ship in a seaway, as the weight will act in reality along the instantaneous ‘true vertical’, which is not in general contained in the symmetry plane, due to ship motions. The actual direction of the weight force represents one of the non-linear aspects of the seakeeping problem, as the direction of one of the input external forces (weight) depends on the instantaneous roll angle (representing an output of the study). The present paper investigates the above subject, trying to quantify this retro-action effect with reference to the verification of the bending strength of the hull girder. The attention is focussed on the magnitude of the horizontal bending component generated by the inclined direction of the weight force as compared to the bending component induced by waves in the same plane (normal to the plane of symmetry of the ship). The subject is discussed on the basis of a linear seakeeping analysis, which is not able to model properly the non-linear aspects above recalled, but provides anyway as output an estimate of roll motions that can be used to evaluate in a qualitative way how large would be the horizontal load component due to weight, not accounted for in equilibrium equations. The statistical correlation between the wave induced bending load and roll angle is treated with the simplified assumption of a Gaussian joint distribution and a consistent model for the combination of horizontal and vertical bending components is established. The reference situation is chosen as corresponding to the extreme value of the vertical wave induced component, and distribution for the horizontal wave bending component and of roll motion are conditioned to the occurrence of such extreme value. This can be seen as an extension of Turkstra’s rule for the combination of loads to the case of correlated loads. The stochastic model is applied in the evaluation of the hull girder reliability for a test case and the conditioned probability distribution of roll motion at the failure point is derived in order to discuss the influence of a possible inclusion of roll effects in the verification of the hull girder bending strength.
Multibody Techniques in Offshore Dynamics With an Application to a Crane Ship
Authors: den Haan Joost , van Zutphen Hermione
Published: January 2009

In this paper multibody dynamics techniques are reviewed for their applicability to offshore engineering, for example to cases like installation, decommissioning, salvage, offloading, pipe laying and dredging. The basis of every simulation is formed by the equations of motion. Multibody techniques have the advantage over analytical methods that they are generic: the equations of motions are derived by a computer algorithm rather than by hand. This allows for a large variety of systems to be analyzed with a single program. The review shows that the topology dependent semi-recursive velocity transformation method (VTM) provides a computationally efficient method for spatial time domain simulations. As an application a crane vessel payload-pendulation problem is studied. The initial results of this study suggest that multibody techniques in offshore dynamics provide better insight and possibly higher accuracy in response prediction than other methods.
Viscous Wave Interaction Due to Motion of a Surface Wave Over a Sediment Bed
Authors: Jamali Mirmosadegh , Lawrence Greg A.
Published: January 2009

The results of a flume investigation of surface wave motion over a fluidized bed are presented. It is shown that a resonant wave interaction between a surface wave and two interfacial waves at the interface of the fresh water and the fluidized bed is a strong mechanism for instability of the interface and the subsequent mixing of the layers. The interfacial waves are subharmonic to the surface wave and form a standing wave at the interface. The interaction is investigated theoretically using a fully viscous interaction analysis. It is shown that surface wave height and viscous effects are the determining factors in the instability mechanism. The results indicate that the net effect of viscosity on the interaction process is to suppress the interfacial waves.