bluuebunny/crossref_metadata_2025 huggingface dataset:
Ventilation of Gas Turbine Package Enclosures: Design Evaluation Procedure
Authors: Bagheri Hamid , Vahidi Daniel
Published: October 2008

Gas turbine packages provide a major portion of mechanical drive and power supply for the offshore operating oil and gas platforms. These packages are typically installed in acoustic enclosures, which need to be ventilated for both removing the heat rejected from the engine and package components, and properly diluting explosive gasses in case of a leak. Considering importance of safety and reliability of gas turbine equipment operating in the offshore environment, and also near industrial and populated areas, authors of the paper emphasize the need for experimental validation of a CFD prediction practice for effective ventilation of the turbine package enclosures. In a properly designed acoustic enclosure, ventilation system has to prevent overheating of the electrical and engine control components, as well as, dilution of potential fuel leakages to eliminate stagnant zones that could cause an ignition within enclosure. Conversely, an excessive flow of the vent air may result in masking local fuel leakages, which might pass undetected through explosion protection devices. Therefore, the optimum enclosure ventilation design has to be based on proper vent flow distribution to ensure acceptable temperature distribution within the enclosure, proper flow distribution to ensure no stagnation area, combined with appropriate gas detection setting. In order to achieve an optimum enclosure design, rather complex flow and heat transfer phenomena have to be studied to select the optimal configuration of the vent system. Numerical analysis of the enclosures with commercially available CFD codes is usually based on a number of simplifying assumptions and approximations. Therefore, to satisfy critical safety requirements in the offshore environment, authors of the paper emphasize role of experimental validation of the CFD predictions. The presented paper provides details of the enclosure design validation using a CFD study based on an earlier experimental validation of the numerical predictions. A midsize gas turbine package model was selected to demonstrate this procedure. The main features from the actual engine package were included in the CFD model. Effectiveness of ventilation was studied for both cold and heated engine surfaces. CFD analyses were also carried out for local CO2 injection emulating natural gas leakage. Both scenarios with CO2 and natural gas (methane) leakages were considered reducing uncertainty of predictions due to the differences in the density and buoyancy between these gasses. Based on presented study certain improvements in design of the enclosure were recommended and described in the paper.
A Finite-Element Computation for Three-Dimensional Problems of Sloshing in LNG Tank
Authors: Kim J. W. , Sim I. H. , Lee J. M. , Lee Y. B. , Bai K. J.
Published: October 2008

A three-dimensional finite-element method is developed to calculate the impact pressure due to liquid sloshing in LNG tank. A finite-element method presented here is based on a variational principle in velocity-potential formulation, which was developed by Kim et al (ISOPE 2003). The tank motions are extended to the six degrees of freedom motions; both translational and rotational motions. Numerical result for an example of an LNG tank shows good agreement with model test results and three-dimensional effect needs to be considered to estimate correct impact pressure at tank corners.
A New Reliability Evaluation Algorithm Using Response Surface Methodology Combined With Space Mapping Technique
Authors: Zhang Lixin , Jian Zhijun , Xu Zhaohui
Published: October 2008

A new method is proposed to tackle the huge computation cost involved in Successive Response Surface Methodology applied to the reliability analysis, in which Space Mapping technique is combined with Response Surface Methodology. While the new approach is performed, the limit state function is only fitted at the first iteration; at other iterations Space Mapping technique is employed to map the original limit state function into the new ones. Experimental design, corresponding model evaluations and response surface fitting of the limit state function are not done repetitively as what we do while SRSM is used, which leads to the great cutting down of computational efforts.
Climatology, Variability and Extrema of Ocean Waves: The Web-Based KNMI/ERA-40 Wave Atlas
Authors: Sterl Andreas , Caires Sofia
Published: October 2008

The European Centre for Medium Range Weather Forecasts (ECMWF) has recently finished ERA-40, a reanalysis covering the period September 1957 to August 2002. One of the products of ERA-40 consists of 6-hourly global fields of wave parameters like significant wave height and wave period. These data have been generated with the Centre’s WAM wave model. From these results the authors have derived climatologies of important wave parameters, including significant wave height, mean wave period, and extreme significant wave heights. Particular emphasis is on the variability of these parameters, both in space and time. Besides for scientists studying climate change, these results are also important for engineers who have to design maritime constructions. This paper describes the ERA-40 data and gives an overview of the results derived. The results are available on a global 1.5° × 1.5° grid. They are accessible from the web-based KNMI/ERA-40 Wave Atlas at http://www.knmi.nl/waveatlas.
Coupled VIV and Heat Transfer Analyses: Design of VIV Suppression Configuration for the Independence Hub SCRs
Authors: Menon Raghu , Lee Li , Mekha Basim
Published: October 2008

Independence Hub (IH), a semisubmersible production platform in the deepwater Gulf of Mexico is currently under construction and will produce gas and condensate from multiple subsea developments. The platform, installed in some 8000 feet of water, is located in a region of the Gulf that is well known for its severe environment, particularly persistent loop currents that could last several months out of a year. The current profiles are such that there is a significant risk of fatigue failure of the risers due to Vortex Induced Vibration (VIV) and adequate mitigation through installation of VIV suppression devices, such as strakes and fairings, are required. An additional challenge that impacts the topsides facility and flex joint design is the low arrival temperature of the produced gas due to Joule-Thomson (JT) cooling. In the case of a bare riser (one without any VIV suppression), the heat transferred from the ambient seawater to the produced gas is sufficient to exceed the target arrival temperature. However, installing VIV suppression devices along the span of the riser may insulate it, which in turn has the potential to decrease the arrival temperature significantly. This paper will discuss coupled VIV and heat transfer analyses carried out to assess the risk of both VIV and low arrival temperatures for the IH production risers. The heat transfer analyses were carried out rigorously using 3D Computational Fluid Dynamics (CFD) simulations of the riser with and without VIV suppression devices. Helical strakes and short fairings were analyzed and optimum suppression configurations for two production risers that meet both the VIV and thermal requirements are presented. The optimum configuration was also subject to the requirement that the suppressed risers be S-layable. A hybrid suppression design based on both strakes and fairings are presented that meets the fatigue and arrival temperature requirements while minimizing installation risks using the S-lay method.
Simulation of the Mean-Zero-Up-Crossing Wave Period Using Artificial Neural Networks Trained With Simulated Annealing Algorithm
Authors: Bazargan H. , Bahai H. , Aryana F. , Yasseri S. F.
Published: October 2008

The aim of this work is to simulate the 3-houly mean zero-up-crossing wave periods (Tzs) of the sea-states of a future period for a location in the North East Pacific. Seven multi-layer artificial neural networks (ANNs) were trained with simulated annealing algorithm. The output of each ANN was used for estimating each of the 7 parameters of a new distribution, described in Appendix A, called hepta-parameter spline proposed for the conditional distribution of the Tz given some significant wave heights and mean zero-up-crossing wave periods. After estimating the parameters of the conditional distributions, the Tzs have been forecasted from the hepta-parameter spline distributions corresponding to the Tzs of the period.
Seismic Reliability of Jacket Platforms
Authors: Silva-Gonza´lez Francisco L. , Heredia-Zavoni Ernesto
Published: October 2008

The accumulation of fatigue damage produces a deterioration of the structural capacity of offshore marine platforms which increases the risk of a potential failure during a strong earthquake. In this paper a method to calculate the global probability of failure of marine platforms with accumulated fatigue damage subjected to strong earthquakes, is presented.
Estimation of Wave Height Return Periods Using a Nonstationary Time Series Modelling
Authors: Stefanakos Christos N. , Monbet Vale´rie
Published: October 2008

A new method for calculating return periods of various level values from nonstationary time series data is presented. The key-idea of the method is a new definition of the return period, based on the Mean Number of Upcrossings of the level x* (MENU method). The whole procedure is numerically implemented and applied to long-term measured time series of significant wave height. The method is compared with other more classical approaches that take into acount the time dependance for time series of significant wave height. Estimates of the extremal index are given and for each method bootstrap confidence intervals are computed. The predictions obtained by means of MENU method are lower than the traditional predictions. This is in accordance with the results of other methods that take also into account the dependence structure of the examined time series.
Reliability of Burst Limit States for Damaged and Corroded High Strength Pipelines
Authors: Maes Marc A. , Salama Mamdouh M. , Dann Markus
Published: October 2008

High strength steels (X100 and X120) that are being considered for high pressure gas pipelines differ from conventional steels by exhibiting lower work hardening capacity, lower strain to failure and softening of their HAZ. These differences impact burst limit state and tensile limit state, in addition to crack arrest. In this paper, the impact of the variations in mechanical properties on the reliability of pipe limit states involving ductile burst of damaged or corroded pipe is examined. The paper presents the results of burst limit state analysis using state-of-the-art plastic burst models of strain hardening pipe and considering all the uncertainties that impact the margin of safety of pipes subject to internal pressure. Intact pipes, corroded pipes and externally damaged pipes are considered. A case study comparing the differences between normal strength (X60) pipeline and high strength (X100) pipeline is also presented.
Stochastic Analysis of Nonlinear Response of a Moored Structural System Under Narrowband Excitations
Authors: Yim Solomon C. , Yuk Dongjun , Naess Arvid , Shih I.-Ming
Published: October 2008

A semi-analytical method is developed for the stochastic analysis of a nonlinear moored ocean structure subjected to narrowband random waves. The method is then used to investigate the probability distribution of extreme values of the responses. To verify the accuracy and capability of the method in handling complex nonlinear behavior of the nonlinear moored ocean structure, experimental results are employed to calibrate numerical simulations and the resulting probability distributions obtained from the semi-analytical method. A nonlinear-structure nonlinearly damped model is employed to model the moored structure considered and the system coefficients are identified through the reverse multiple-input/single-output technique. An examination of the comparisons indicates that the structural response extreme value probability distributions obtained from the semi-analytical predictions are quite accurate.
Uncertainties in Extreme Wave Height Estimates for Hurricane Dominated Regions
Authors: Jonathan Philip , Ewans Kevin
Published: October 2008

The inherent uncertainties in estimation of extreme wave heights in hurricane-dominated regions are explored using data from the GOMOS Gulf of Mexico hindcast for the period 1900–2005. In particular, the effect of combining correlated values from a neighbourhood of 72 grid locations on extreme wave height estimation is quantified. We show that, based on small data samples, extreme wave heights can be underestimated and that site averaging usually improves estimates. We present a bootstrapping approach to evaluate the uncertainty in extreme wave height estimates. We also argue in favour of modelling supplementary indicators for extreme wave characteristics, such as a high percentile (95%) of the distribution of 100-year significant wave height, in addition to its most probable value, especially for environments where the distribution of 100-year significant wave height may be skewed.
Large-Scale Investigations of Geotextile Sandcontainers Used for Scour Protection of Offshore Monopiles Supporting Wind Energy Turbines
Authors: Gru¨ne Joachim , Sparboom Uwe , Schmidt-Koppenhagen Reinold , Wang Zeya , Oumeraci Hocine
Published: October 2008

An innovative scour protection for monopile structures was proposed by using geotextile sand containers in a research programme started recently. Large-scale model tests on the stability of such alternative scour protection are being performed in the Large Wave Channel (GWK) of the Coastal Research Centre (FZK). First results are reported from basic test series performed with single geotextile sand containers and container groups with different container weights, varied in sizes and percentages of filling. Further an empirical approach on the stability of sand containers is estimated as a first approximation from the results.
Ultra-Low Hydrogen Consumables for Welding of High Strength Steels With 690–750 MPa-Yield Strength
Authors: Liu Stephen , Clasper Craig , Moline Keith , Scott Joe
Published: October 2008

Two fundamental concepts in welding consumable development were explored in this research. The first concept dealt with the introduction of yttrium-containing oxides into the weld metal for microstructural control and hydrogen trapping. The second concept suggested the use of fluoride species to displace hydrogen from the arc. Combining yttrium and fluorides into one single flux-cored consumable to capture the benefit of hydrogen reduction from both ingredients, however, proved to be difficult. The oxygen potential controlled by yttrium clashed with the fluorine potential controlled by KF. Several iterations led to the successful reconciliation of the oxygen potential and fluorine potential and the development of a new generation of flux-cored consumables with exceptional performance. Using CO2 as shielding gas, these consumables successfully produced welds that contained only 0.6 ml H2/100 g weld metal. With a duplex martensite-acicular ferrite microstructure, a weld metal with yield strength of 99 ksi and tensile strength of 108 ksi was obtained. The weld metal exhibited excellent ductility, 21.8% elongation. Impact toughness exceeded the −60 °F requirement by 88%, reaching values of 76 ft-lb. Charpy-V-notch energy at 0 °F testing temperature measured an outstanding average of 89 ft-lbs. Consumables designed using the two fundamental concepts have demonstrated great capability of producing high strength steel welds that met stringent mechanical performance requirements.
The State-of-the-Art Review of Risers’ VIV Fatigue
Authors: Iranpour Mohammad , Taheri Farid
Published: October 2008

As one of the most prominent one, Vortex Induced Vibration (VIV) can create serious fatigue damage in risers used by the offshore industry. In deep waters, where oil and gas exploration and production continue apace, VIV may make the largest contribution to overall riser fatigue damage. Extensive researches have been done to investigate VIV response of risers, and several methods have been proposed for the fatigue life estimation of these structures. This paper addresses some of the methods available in literature for VIV fatigue life estimation of risers, focusing on their main underlying assumptions. The main focus of the study is on the influence of direct action of current on the riser structure. It is observed that riser fatigue life is greatly dependent on different parameters, and any minor change in these parameters would significantly influence the predicted fatigue life. It is illustrated that the available approaches for analyzing VIV fatigue of risers mainly focus on the VIV portion of the task, and indeed less attention is paid to the actual fatigue life analysis using various models. The importance of reconsidering the fatigue damage as a priority when designing risers has been discussed in detail, and recommendations for the future direction of researches on VIV induced fatigue of risers have been proposed.
Integrating 20 Years of Geotechnical Investigation Using Geostatistics: Building a 3D Model of Soil Stratigraphy, Campeche Bay, Gulf of Mexico
Authors: Nu´n˜ez Farfa´n Jaime , Galva´n Garci´a Eduardo , Cruz Roque Diego , Koh Cambranis Wilbert
Published: October 2008

20 years of geotechnical investigation in the Campeche Sound were integrated using geostatistics to build a 3D model of the soil stratigraphy of a 800 km2 area. This model was developed analyzing the data structure and its space variability to conform the analytical model which later on was implemented into a Geographical Information System (GIS) in order to have not only rapid and a friendly access to the model but also to the original geotechnical and geophysical field reports and the location of infrastructure and geohazards in the area. A major part of the work was done by combining the experience and knowledge of the technology used to explore the soils and its evolution in 20 years with the scientific rigor of the geostatistics techniques in order to correlate the soil strata. In this article we present the methodology used to develop the model as well as the results obtained by its implementaion in a GIS.
Deep Water Current Observations in Lankahuasa Area in the Mexican Gulf of Mexico
Authors: Garcia Govea C. , Corte´s Romero Juan Jose´ , Valle Molina O.
Published: October 2008

In preparation for the near future deep-water exploitation in the Mexican oil industry, the Mexican Petroleum Institute and Pemex carried out the first oceanographic sub-surface mooring installation in deep waters, in Lankahuasa area in 1500 m water depth. The aim of this project is to supply the necessary water column information for planning, installation, development and production activities for the Mexican offshore industry. Parameters measured include, current velocities, current direction, internal waves as well as traditional water quality measurements. Profiles of conductivity, temperature and Depth (CTD) from 100 m up to 2,500 m water depths were obtained from cruises where samples were taken over a wide area during January and February 2005. Salinity and density are calculated from CTD data. Oceanographical parameters were measured by 3 ADCP (Acoustic Doppler Current Profile) and by 2 current meters in the entire water column. The oceanographic situation during the deployment was characterized by the presence of an anticyclonic (clockwise rotating) eddy and a cyclonic one in the area, located to the north of 21° N. Both eddies were slowly propagating in a general southward direction.
First Experience in the Next Generation Ice Laboratory for Testing Ships and Structures
Authors: Wilkman Go¨ran , Mattsson Tom , Niini Mikko
Published: October 2008

Ice model testing has a history of almost 50 years. The first basin started operation in the middle of 1950ies in Russia by Arctic and Antarctic Research Institute (AARI). Ever since there has been a number of facilities built worldwide. In Finland the first facility was built by Wa¨rtsila¨ in 1969 for testing tankers intended for North-west passage (Manhattan project). In the eighties new facilities were built in Finland, Germany, Canada, Russia and Japan. In the present facility of Kvaerner Masa-Yards Arctic Technology (MARC) in Helsinki the operation started in 1983 under the name of Wa¨rtsila¨ Arctic Research Centre (WARC). The operation of the facility was originally planned to continue till 2011, but as part of the Helsinki City planning activity it was agreed that the facility is to end its successful work during 2005. In spring 2004 decisions were made by the new parent Aker Yards group and Aker Finnyards (that time Kvaerner Masa-Yards) to build a new facility and establish a separate company to handle ICE ISSUES for the whole Aker group. The new company, Aker Arctic Technology “AARC”, started operation in the beginning of 2005 and the new model testing facility was opened in February 2006. Aker Arctic Technology Inc. is owned by Aker Finnyards, Aker Kvaerner, Wa¨rtsila¨ and ABB. The services of the new company, in addition to the traditional model testing and related issues (environment studies, design bases and ship design concepts) will cover also total vessel design packages. This paper describes the novelties of the new ice model testing facility and reveals technical improvements, lessons learned and possibilities for more enhanced operation. Also the first experience in the new facility will be discussed.
An Equivalent Lateral Force for Continuous Crushing
Authors: Ka¨rna¨ Tuomo , Qu Yan , Yue QianJin
Published: October 2008

This paper addresses a condition where a wide, vertical faced structure is subjected to dynamic actions posed by competent level ice. Loading conditions where the ice fails by continuous crushing are studied. It is widely accepted that the structure reacts reluctantly to very rapidly fluctuating forces. On the other hand, an external force caused by continuous ice crushing is often magnified within the structure. These two effects are considered by deriving an equivalent lateral force. The lateral force is obtained by using a magnification factor. This parameter can also be used as an indicator of the dynamic susceptibility of the structure.
Structural Reliability of a Suezmax Oil Tanker Designed According to New Joint Tanker Project Rules
Authors: Guedes Soares C. , Parunov Josˇko
Published: October 2008

The paper aims at quantifying the changes in notional reliability levels that result from redesigning an existing suezmax tanker to comply with new Joint Tanker Project (JTP) rule requirement for ultimate vertical bending moment capacity. The probability of structural failure is calculated using a first-order reliability method. The evaluation of the wave-induced load effects that occur during long-term operation of the ship in the seaway is carried out in accordance to IACS recommended procedure. Comparative analysis of long-term distributions of vertical wave bending moment calculated by two independent computer seakeeping codes is performed. The still water loads are defined on the basis of a statistical analysis of loading conditions from the loading manual. The ultimate collapse bending moment of the midship cross section, which is used as the basis for the reliability formulation, is evaluated by JTP single-step procedure and by program HULLCOLL for progressive collapse analysis of ship hull-girders. The reliability assessment is performed for “as-built” and “corroded” states of the existing ship and a reinforced design configuration complying with new JTP rules. It is shown that hull-girder failure probability of suezmax tanker reinforced according to new JTP rules is reduced several times. Sensitivity analysis and a parametric study are performed to investigate the variability of results to the change of parameters of pertinent random variables within their plausible ranges.
Analytical Plastic Capacity Formulation for Plates Subject to Ice Loads and Similar Types of Patch Loadings
Authors: Nyseth Ha˚vard , Holtsmark Gabriel
Published: October 2008

The response of plates subjected to patch loads with length/ height less than the dimensions of the plate field is of importance for the design of hulls strengthened for operation in ice covered waters and other comparable types of loading. An analytical plastic capacity formulation for plates subjected to patch loading of any rectangular geometry configuration has been derived, which from comparison with nonlinear finite element analysis is seen implicitly to limit the permanent deflection to be up to 0,40% of the frame spacing. The analytically derived formulations for the plastic bending based load capacity are based on yield line theory. Expressions for single and multiple patch loads are included, where the derivation is based on the assumption that the response for a single patch load is equal to the response from a sequence of identical patch loads located within the same plate field, and spaced a certain minimum distance apart. The expressions may serve as basis for rule requirements for plates subject to ice loads and other types of patch loads. For the considered longitudinally and transversely stiffened plate cases, nonlinear FE calculations show that the proposed plate bending based load capacity formulations generally give rise to permanent deformations in the plate up to 0.40% of the frame spacing, when the plate model analyzed is extended to include adjacent plate fields. Comparisons of nonlinear FE calculations show the pressure-deformation relationship of the single and repeated load patch to be the same within the range of permanent deformations considered. Comparison of the analytically derived plate formula with DNV Arctic Rules and Finnish-Swedish Ice Class Rules (FSICR) indicates that the plate formula of the DNV/FSICR gives similar results for the same load levels. The analytically derived formula, however, provides a more consistent utilization of the plate bending based capacity that is valid for a wider range of patch load geometries. Comparison of the IACS Polar Class (PC) Rules formulation indicates that the IACS plate formulation is increasingly non-conservative for small patch lengths, and that the application should be restricted to cover larger patch lengths only, e.g. l/s > 1,0.
The Analysis of the Mechanical Properties of Welding Joints of High-Strength Steels for Offshore and Ship Structures
Authors: Buglacki Henryk , Kallas Paweł , Pilecki Andrzej , Smajdor Monika
Published: October 2008

As the result of carried out research we proved the point, that in design and construction of ship and off-shore structures, it is possible to determine accurate values of end mechanical properties and microstructure of welded joints of category 420÷690 steel thick plates. The strengthening meters we obtained in the course of work (cementite, solution, precipitation, ferrite grain size) together with end mechanical properties (Rm, Re, A5, Z, KV0, KV20, KV40, KV60) enable us to determine metallurgical agents (chemical composition, Vch, t0, th) which make it possible to meet acceptance requirements of high strength steel. The worked-out correlation equations of welded joints mechanical properties may be helpful in assessing the influence of welding technology (t8/5, Tmax, E) on meeting acceptance requirements. We proposed the equation which can be used for preliminary assessment of currently produced high strength steels weldability (Ce31) and correlation equations used to calculate maximum hardness of HAZ material (HVmax).
Ultimate Strength of Transverse Plate Assemblies Under Uniaxial Loads
Authors: Lui´s Rui M. , Witkowska Malgorzata , Guedes Soares C.
Published: October 2008

This paper deals with the strength of panels composed of three and five plates connected transversely and loaded along the longitudinal direction. First, a comparison between the strength of panels having asymmetric imperfections and of single plates is made, which allows evaluating the ability of the single plate to properly simulate the panel strength. Following this, the results obtained for a panel model having symmetric imperfections are confronted with the results of the asymmetric imperfections. The asymmetrical and symmetrical models of the panel give respectively the lowest and highest strengths possible (imperfections in adjacent plates with different amplitudes have “in between” strengths) allowing to establish limits to the variation of the strength. The results show that using a single plate can be conservative or nonconservative, depending of the plate slenderness and shape of initial deflections. It is concluded that for design purposes it will in general be enough to consider assemblies of three plates, as the results for five plate assemblies are not much different.
A Statistical Analysis of Corrosion Wastage of Transverse Members in Single Hull Tankers
Authors: Thuanboon Swieng , Tordonato David S. , Navidi William , Olson David L. , Mishra Brajendra , Wang Ge
Published: October 2008

Corrosion wastage of structural members in oil tankers over the time causes variability in structural properties. Corrosion is a function of many variables and uncertainties, such as the types of corrosion protection systems used, types of cargo, temperature, humidity, etc. The traditional engineering and analysis, which uses simplified deterministic approaches to account for this time-dependent reliability or risk of aging ship structure, is not suitable. This investigation explores the use of statistical analysis approaches to predict corrosion wastage in oil carrying tankers. Corrosion wastage measurements from transverse members of 115 oil tankers were collected to add to an extensive corrosion wastage database. Lognormal function was found to best fit the collected data when compared to other methods, such as the Weibull function. Linear regression in the form of three mathematical models of corrosion wastage, developed by considering age of ship, coating life, and the location of the transverse members, is used to indicate the relationship between corrosion wastage and age of ship. Corrosion rates were determined by the derivatives of the corrosion wastage. The results show that corrosion wastage may accelerate after twenty years of service. It is expected that the study will help identify which structural members may be more susceptible to corrosion wastage and require more frequent inspection.
On the Occurence of Abnormal Waves in an Offshore Tank
Authors: Anta˜o E. M. , Guedes Soares C.
Published: October 2008

A set of wave data generated in an offshore tank is studied. The set of the largest waves in those sea states is studied with respect to steepness, asymmetry and nonlinearity. It was possible to find some waves that were classified as abnormal or freak according to presently accepted criteria. Their statistics connected to steepness and nonlinearity were determined. Comparison of the nonlinearity as well as statistics of the largest waves in the offshore tank and at sea so as to identify the limitations of the properties of large waves in model basins.
Truss Spar Vortex Induced Motions: Benchmarking of CFD and Model Tests
Authors: Halkyard John , Atluri Sampath , Sirnivas Senu
Published: October 2008

Spar production systems are subject to Vortex Induced Motions (VIM) which may impact mooring and riser design. Helical strakes are employed to mitigate VIM. Model tests are typically required to validate the performance of the strakes. This paper will report on the results of benchmarking studies that have been conducted over the past few years to compare model tests with computational fluid dynamics (CFD). The paper discusses comparisons of CFD with model tests, “best practices” for the use of CFD for these classes of problems and issues related to turbulence modeling and meshing of problems at large Reynold’s numbers. This work is ongoing.
Swept Blade Aerodynamic Effects of Compressor Airfoil
Authors: Xu C. , Amano R. S.
Published: October 2008

To meet the needs of efficient compressor airfoil designs, a CFD prediction of complex 3D flow fields in turbine blade passages has been incorporated in the design process. Owing to the numerous advantages of 3-D CFD technology, a number of compressor manufacturers already adopt a 3D blading technique. In addition, blade lean and sweep have been implemented to increase the blade row efficiency. Experimental studies have shown the advantages of these features. However, most of the experimental results showed other combined features, which makes it difficult to determine the effects of individual features. The development of CFD techniques has made it possible to do three-dimensional turbulent flow analyses in a very short time. In this study, numerical studies are presented to investigate the sweep effects on a transonic compressor airfoil. The focus of this study is to investigate the sweep effects without changing other compressor blade features; i.e. keeping the blade out flow angle and section shape to be the same for all cases. The purpose of the study is to enhance the understanding of the sweep effect in a transonic compressor rotor blade. The results showed that the sweeps redistribute the flow reducing the secondary flow loss, depending on the baseline. It was shown that a forward sweep reduces the tip loading in terms of the static pressure coefficient.
Parts Life Management: Essential for Minimizing Life Cycle Costs
Authors: DellaVilla Salvatore A. , Steele Robert F.
Published: October 2008

This paper will review the issues associated with parts tracking and critical parts life management, discussing the need to implement accurate and efficient processes to develop meaningful and accurate empirical observations.
Design Considerations of Oxy-Fuel Fired Supercritical Pressure Circulating Fluidized Bed Boilers
Authors: Halder Prabir K.
Published: October 2008

Researchers around the globe are focussing on the capture and storage of carbon dioxide generated from the combustion of coal in boilers for power generation. Oxygen fired boilers have the advantage of creating CO2 rich flue gas which enables the CO2 to be captured in a more cost effective manner compared to post combustion capture of CO2 from an air fired boiler. This paper discusses design considerations for oxy-fuel fired supercritical circulating fluidized bed boilers. A 420 MWe supercritical CFB boiler firing coal with oxygen has been considered for the study. An analytical/semi-empirical model has been developed to model fuel combustion and heat transfer in the furnace and convection pass. The fuel burns with oxygen supplied at the bottom of the bed and the fluidization velocity and bed temperature is controlled by flue gas recirculation. The model is used to design the boiler and determine its performance characteristics. The heating surfaces, recirculation ratios and other parameters have been designed to achieve the required boiler capacity. The impact of the CO2 rich flue gas on CFB boiler design is compared with conventional air blown CFB boilers. The study reveals that oxy-fuel combustion in a CFB combustor does not alter the heat transfer characteristics when compared with combustion with air. In the convection bank, oxyfuel combustion increases both convective and radiative components of heat transfer, thereby reducing the size of the heat transfer banks required.
Fast Pyrolysis of Distillated Ashe Juniper Biomass
Authors: Jua´rez Jaime J. , Contreras Victor R. , Haupert Gaston R. , Hill Steven , Daugaard Daren E.
Published: October 2008

Ashe Juniper is one of three major species of juniper native to Texas. Communities of Ashe Juniper occupy over 8 million acres of Texas rangelands and are responsible for herbage reduction, which adversely impacts the livestock carrying capacity. Ashe Juniper wood contains aromatic liquids called essential oils, which are economically beneficial for the personal care products industry. In order to exploit this benefit Texarome, Inc. of Leaky, Texas uses a large-scale steam distillation process to extract aromatic liquids from Ashe Juniper. This process results in a large quantity of Ashe Juniper woodchip waste for which there is few uses. A moderate temperature process known as fast pyrolysis was used to convert steam-distillated Ashe Juniper into a liquid known as bio-oil. An average liquid yield of 40.8% is reported for steam-distillated Ashe Juniper biomass and an average liquid yield of 47.3% is reported Ashe Juniper biomass that has not undergone the steam distillation process. This work demonstrates that the energy content of steam distillated Ashe Juniper can be extracted and the conversion to bio-oil is another potential use for Ashe Juniper woodchip waste. An economic model of Ashe Juniper biomass developed previously by Jua´rez and Daugaard was used to examine the economic impact of steam-distilled Ashe Juniper by simulating a 4,046-hectare (10,000 acre) Ashe Juniper energy plantation. It was found that bio-oil could be produced for as little as $5.20/GJ on a lower heating value basis if re-investment of profits made from the sale of essential oils extracted during the steam distillation process was assumed. Bio-oil from un-distillated Ashe Juniper could be produced for $13.21/GJ.
Deterioration Mechanisms in Recent Air Cooled Turbine Generators
Authors: Moudy W. Howard
Published: October 2008

Several designs of recently installed air cooled turbine generators have developed serious deterioration and failures within the first few years of service. This paper discusses case histories of generator stator and rotor problems that have resulted in service interruption and major repairs.
The Air Cooled Condenser for Dry Countries
Authors: Adibfar Akbar , Refan Maryam
Published: October 2008

A reliable and economic power production in thermal power plants depends highly upon the optimum selection of site equipment and their best possible arrangement. One of the most significant systems which play a crucial role in power production is the Cooling System. Playing the most pivotal role in back pressure of steam turbine, this system directly affects the power plant efficiency. This study analyzes the techno-economic aspect of Cooling System — with the special focus on ACC (Air Cooled Condenser) — due to the following advantages: Since ACC does not need water as the cooling medium, (not requiring medium fluid), it is been preferred over other cooling systems in dry regions. In addition to resolving the problem of water shortage in power plants, where there are environmental or geographical limitations, ACC is the best solution. The studies show that in the peak demand times, ACC has a much greater potential in higher power production in comparison to other dry cooling systems and thus can encourage the financer to consider ACC as an optimum alternative.
Performance Test Methods to Determine the Benefits of Various Gas Turbine Modernizations and Upgrades
Authors: Carlson Charles A. , Friedman Jeffrey R.
Published: October 2008

As gas turbine fleets age and newer technologies become available, there are opportunities to improve gas-turbine based power plant performance by physical modifications to both hardware and software. Mechanical modifications can include, but are not limited to, upgrades to turbine and/or compressor blades and vanes, replacement of seals, and the cleaning, repair, or refurbishment of existing engine components. Controls modifications can include upgrades to the engine logic designed to improve operation and reliability as well as gas turbine and plant performance. It is a challenge to determine the effects of the modernizations and upgrades by test, usually known as “comparative testing”. This is particularly true when another maintenance activity that affects performance takes place during the outage in which the modification occurs. Other difficulties arise when part load testing of gas turbine or plant performance is desired. This paper details some of the difficulties met in such testing, and the proposed optimized test protocols and agreements to meet these challenges.
Application of Neural Network Combined With CFD Modeling and Combustion Tuning in Large Coal-Fired Boilers
Authors: Schweitzer Y. , Cartina G. , Chudnovsky B. , Bar-Ziv E. , Talanker A.
Published: October 2008

The objective of the present work was to develop an optimization method for the prediction of the behavior of coals or coal blends in utility boilers, in order to specify the performance and pollutant emissions during the firing. Two methods have been used to study the performance of single coals or coal blends in power station boilers (1) experimental tests, where the coal/blend was fired in either a power station or in a test rig, and (2) use of coal combustion computational fluid dynamic (CFD). Here we will discuss both methods. We present experimental results, for 575 MWe tangentially-fired Combustion Engineering boilers of Israel Electric Corporation and 50 kWth test rig of Ben-Gurion University, that show the control of NOx and carbon content in fly ash (LOI). In addition to the experimental measurements we also established a large data base using a CFD code for a large spectrum of operational conditions. Validation of CFD results was made by comparison with both test rig and full-scale boilers measurements. Only after ensuring that good fit was obtained between experimental measurements and CFD results, was CFD used to establish the data base for coals/blends at a large spectrum of operational conditions. In some cases CFD was run for coals/blends never burned in the boiler, but burned in the test rig. The data obtained, experimental, showed that with tuning and modified nozzles NOx was considerably reduced: from 1200 to 570 mg/dNm3 @ 6% O2 for South African coal at full load. At partial loads NOx emission dropped from 1400 to about 800 mg/dNm3 @ 6% O2. High volatile coals, such as Colombian and Indonesian, firing led to additional NOx reduction to around 400 mg/dNm3 @ 6% O2 at full load. A very large data base was obtained in this effort and brought us to the idea of extending it by using a neural network algorithm [1]. We used these data as a base for the development of a code based on neural network and a mathematical optimization algorithm. The code was primarily intended for use by the plant personnel for better tuning coal-fired boilers to reduce NOx and minimize heat rate. The neural network develops non-linear mapping functions between the outputs of NOx, heat rate, LOI, etc. and the controllable boiler input parameters. The mapping functions are then analyzed by the mathematical optimization algorithm and optimal boiler operating condition are identified. Further, based on networks and a mathematical optimization algorithm we found a proper Adaro and KPC (Indonesian coals) blend and operation condition that led to NOx emission reduction less than 400 mg/dnm3 in a 575 MWe tangentially firing unit with a conventional firing system. This result was verified in experimentally in the boiler. The results presented in this work clearly show that the developed method for reduction emission and performance optimization is available and capable to achieve operational or environmental goals.
Calibration Uncertainty of PTC-6 Flow Sections
Authors: Nystrom James B. , Stacy Philip S.
Published: October 2008

PTC 6-2004 Performance Test Code on Steam Turbines [1] delineates fabrication and calibration requirements for throat tap flow nozzles with the purpose of obtaining the best feasible accuracy of flow measurement, a primary measurement to determine turbine performance. The Code requires nozzle discharge coefficient calibration results meet tight specifications for average value and rate of change with throat Reynolds number. Performance specifications were developed from large historical, empirical bases and an extensive theoretical analysis. Calibration uncertainty for PTC-6 Flow Meters using gravimetric flow measurement method in accordance with ASME/ANSI MFC 9M Measurement of Liquid Flow in Closed Conduits by Weighing Method [2] using a 100,000 lb capacity weigh tank is estimated. Calibration results are compared to Code requirements for about 330 meters with 1320 individual tap sets.
Comparison of Primary Flow Measurement Techniques Used During Combined Cycle Tests
Authors: Campbell W. Cary , Hopson Warren H. , Smith Mark A.
Published: October 2008

One of the most significant contributors to the overall uncertainty of a performance test of a combined cycle steam turbine is the uncertainty of the primary flow measurement. ASME performance test codes provide many alternative methods for determining flow. In two actual combined cycle tests performed in 2005, the following three alternate methods were used to determine the HP steam flow into the combined cycle steam turbines: 1) Derivation from measured HP feedwater flow using calibrated PTC 6 throat tap nozzles, 2) Derivation from LP condensate using calibrated PTC 6 throat tap nozzles, and 3) Derivation from LP condensate using calibrated orifice metering sections. This paper describes the design, calibration, and installation of each flow meter involved, the methods used to calculate the HP steam flow, the estimated uncertainty of the HP steam flow derived using each method, and the actual test results using each method. A comparison of the methods showed that there are distinct advantages with one of the methods and that very low uncertainties in HP steam flow can be achieved if sufficient attention is applied to the design, calibration, and installation of all flow meters involved.
Micro-CHP (Cooling, Heating, and Power): Not Just Scaled Down CHP
Authors: Chamra Louay M. , Mago Pedro J. , Stone Nick , Oliver Jason
Published: October 2008

The paper will introduce the research community to the Mississippi Micro-CHP (Cooling, Heating, and Power) and Bio-fuel Center, a unique research, demonstration and education center combining the resources and expertise from Mississippi State University Engineering, Agriculture, and the Mississippi Agricultural and Forestry Experiment Station (MAFES). The center is a vertically integrated program to study and demonstrate the entire bio-fuel utilization cycle from “woodchips to micro-CHPs”: feedstock production, conversion to bio-fuel/biogas, conversion to onsite electrical power, and utilization of the resulting waste heat to provide the site’s cooling and heating needs. The “micro” designates a focus on residential, small commercial and rural applications. The coupling of micro-CHP with bio-fuels has to do with addressing regional and demographic consideration of successful micro-CHP implementation as opposed to a one-strategy-fits-all approach. The paper will contrast characteristics of residential and small commercial establishments versus commercial/industrial CHP systems and form a list of desirable characteristics for micro-CHP components and overall micro-CHP system design. Based on these evaluations, future research plans for the Center will be suggested. Another factor that will be stressed is that Micro-CHP will best be utilized if designed as part of a whole building system. The characteristics of the building are as important as the characteristics of the equipment, and both should be designed to work together synergistically.