bluuebunny/crossref_metadata_2025 huggingface dataset:
Tools for Minimizing Probabilistic Confidence Intervals
Authors: Beachkofski Brian K. , Grandhi Ramana V.
Published: November 2008

For probabilistic designs or assessments to be acceptable, they must have the statistically robust confidence intervals provided by sampling methods. However, sample-based analyses require the number of function evaluations to be so great as to be impractical for many complex engineering applications. Efficient sampling methods allow probabilistic analysis on more applications than basic methods, although they still require a significant computational budget. This paper reviews a series of tools that aim to reduce variance in individual failure rate estimates which would reduce the confidence interval for the same number of evaluations. Several methods share a common goal, lowering the sample discrepancy within the sample space, that will create near optimal low-discrepancy sample sets. The optimization approaches include evolutionary algorithms, piecewise optimization, and centroidal Voronoi tessellation. The results of the optimization procedures show a much lower discrepancy than previous methods.
Development of Directionally Solidified (PWA 1437) and Conventionally Cast (PWA 1432) Superalloys for Industrial Gas Turbine Engine Blade Applications
Authors: Cetel Alan D. , Seetharaman Venkat
Published: November 2008

Pratt & Whitney (P&W) has developed and deployed two new alloys derived from its highly successful and well-established single crystal IGT alloy, PWA 1483. These alloys include a directionally solidified (DS), columnar-grained alloy (PWA 1437) and a conventionally cast (CC) alloy (PWA 1432). This paper demonstrates that the newly developed alloys possess creep and oxidation resistance superior to currently available IGT alloys, while maintaining attractive levels of hot corrosion resistance. The development program included an optimization of the PWA 1483 composition, with particular regard to the grain boundary strengthening elements (B, C, Zr), to derive alloys which could be utilized in DS and conventionally cast forms. Appropriate heat treatment and hot isostatic pressing (HIP) cycles for the alloys were established. In order to generate a comprehensive engineering property database for blade design, a thorough characterization program covering a variety of service-critical mechanical properties, including creep, LCF, and HCF properties, was completed. Cyclic hot corrosion and burner rig oxidation tests were conducted at 1650°F and 2000°F, respectively, on overlay coated as well as uncoated specimens. Castability trials conducted within P&W, as well as at several commercial foundries demonstrated that the new alloys possessed excellent castability for large IGT applications. The paper presents a comparative evaluation of mechanical, and environmental properties of the newly developed alloys against current IGT alloys such as IN 738 and GTD 111™ [1,2]. The new alloys exhibit improvements greater than 1.4X in creep life and 2.5X in uncoated oxidation life over the most capable production IGT alloys. A large production experience base now exists on PWA 1437 and PWA 1432 alloys in a wide variety of frame engine blade applications.
Monitoring Diffusion Coating Aging With Multi-Frequency Eddy Current MWM Sensors
Authors: Zilberstein Vladimir , Lyons Robert , Washabaugh Andrew , Grundy Dave , Craven Chris , Goldfine Neil , Khandelwal Pramod , Brozan Tony , Brindley William J.
Published: November 2008

Diffusion coatings are widely used to protect hot gas path components in land-based gas turbines and jet engines. Effective nondestructive assessment of the aged coating and substrate condition is critical for support of refurbish/replace/run decisions. In this paper, we present results on aging characterization of nickel aluminide and platinum aluminide coatings. The measurements were performed using a Meandering Winding Magnetometer (MWM®) eddy current sensor over a wide range of frequencies. Single-channel MWM sensors and multichannel imaging MWM-Arrays permit tracking of features of interest for a population of components and provide new capabilities for inspecting gas turbine components. These conformable sensors allow convenient manual and automated inspection on complex surfaces. Results on coating aging assessment suggest that the multiple frequency MWM technique can be implemented for characterization of diffusion coatings and base metals before and after component refurbishment.
Neural Network and Fuzzy Logic Diagnostics of 1X Faults in Rotating Machinery
Authors: El-Shafei A. , Hassan T. A. F. , Soliman A. K. , Zeyada Y. , Rieger N.
Published: November 2008

In this paper, the application of Neural Networks and Fuzzy Logic to the diagnosis of Faults in Rotating Machinery is investigated. The Learning-Vector-Quantization (LVQ) Neural Network is applied in series and in parallel to a Fuzzy inference engine, to diagnose 1x faults. The faults investigated are unbalance, misalignment, and structural looseness. The method is applied to a test rig [1], and the effectiveness of the integrated Neural Network and Fuzzy Logic method is illustrated.
Characterization of Fuel Composition Effects in H2/CO/CH4 Mixtures Upon Lean Blowout
Authors: Zhang Qingguo , Noble David R. , Meyers Andrew , Xu Kunning , Lieuwen Tim
Published: November 2008

This paper describes measurements of the dependence of lean blowout limits upon fuel composition for H2/CO/CH4 mixtures. Blowout limits were obtained at fixed approach flow velocity, reactant temperature, and combustor pressure at several conditions up to 4.4 atm and 470 K inlet reactants temperature. Consistent with prior studies, these results indicate that the percentage of H2 in the fuel dominates the mixture blowoff characteristics. That is, flames can be stabilized at lower equivalence ratios, adiabatic flame temperatures, and laminar flame speeds with increasing H2 percentage. Various methods of correlating these data were evaluated, using combinations of Lewis number (Lemix), adiabatic flame temperature (Tad), flame speed (SL), and chemical time (τchem). These correlations clearly indicate the significance of the mixture diffusivity, heat content, and flame propagation speed upon blowout characteristics across a wide fuel spectrum. Two basic models of flame stabilization discussed in the literature were evaluated — a well-stirred reactor based approach that considers the ratio of chemical and flow times, and a propagative mechanism that considers the ratio of flame and flow speed. Both mechanisms were able to correlate some, but not all segments of the data set.
Sensitivity Analysis of Nonlinear Forced Response for Bladed Discs With Friction Contact Interfaces
Authors: Petrov E. P.
Published: November 2008

An effective method is proposed to calculate sensitivity of nonlinear forced response levels for bladed discs with friction contact interfaces to variation of parameters of these interfaces, including clearances and interferences. First and second order sensitivity coefficients together with ranges of high fidelity for forced response and the sensitivity coefficients prediction are determined. Numerical investigations of the sensitivity of the multiharmonic steady-state forced response of bladed discs with friction contacts and gaps have been performed showing the capabilities and efficiency of the method proposed.
Fuel Oil In-Line Sampling Analysis
Authors: Salvucci Lucio A. , Donnelly Timothy C. , White Michael A.
Published: November 2008

The U.S. Navy is pursuing endeavors in support of propulsion gas turbines in terms of in-line fuel oil quality. Using a prototype laser technology, developed under the sponsorship of the Small Business Innovative Research Program that monitors the concentration of sediment and free water in JP-5 in real-time, the U.S. Navy is proceeding to expand it’s capabilities to monitor sediment and free water in Naval Distillate, NATO Code F-76, under flow conditions. The maximum fuel quality limitations for the U.S. Navy propulsion gas turbines are 40 parts per million (PPM) free water and 2.64 milligrams per liter (mg/liter) sediment contamination. The current prototype unit, being tested in aviation fuel (JP-5) systems, is capable of monitoring fuel quality within these systems where the maximum fuel quality limitations are 5 PPM free water and 2.0 mg/liter per liter sediment contamination. Current naval shipboard policy for gas turbine propelled hulls requires fuel quality testing at the discharge of the fuel oil service system filter separator discharge, which is the last sampling point prior to admittance into the gas turbine module. Incorporating this technology in unison with monitoring capabilities will eliminate the subjective and laborious laboratory sample testing presently conducted, reducing workload and provide Ship’s Force with real-time quality assurance data. Future enhancement of this technology is being initiated to develop the capability to analyze other potential fuel properties, such as specific gravity, in addition to sediment contaminant size distribution measurement. This will provide Ship’s Force with real-time data that can be used to detect off-specification fuel properties or on-board filtration equipment problems sooner than present. This can aid in more effective shipboard fuel quality control and prove essential in the selection of filtration systems aboard U.S. Naval vessels.
Improving Operational Availability of Gas Turbine Generators Aboard U.S. Navy DDG-51 Class Ships by Combining the Capabilities of the Integrated Condition Assessment System (ICAS) and the Generator Set’s Full Authority Digital Controller (FADC)
Authors: Russom Dennis M. , Leinbach Russell A. , Kozuhowski Helen J. , Golden Dana D.
Published: November 2008

Operational availability of Gas Turbine Generator Sets (GTGs) aboard the U.S. Navy’s DDG 51 Class ships is being enhanced through the combined capabilities of the ship’s Integrated Condition Assessment System (ICAS) and the GTG’s Full Authority Digital Control (FADC). This paper describes the ICAS and FADC systems; their current capabilities and the vision of how those capabilities will evolve in order to improve equipment readiness and reduce life cycle costs.
U.S. Navy Qualification of a GE LM2500+ Gas Turbine Engine
Authors: Hatcher Shaun , Batory Tom , Neff Robert , Kane Pat
Published: November 2008

This report is a comprehensive document citing the events pertaining to the qualification of the GE LM2500+ gas turbine engine for US Navy Service. The purpose of this report is to serve as documentation of the entire Qualification process that includes the 500-hour Rating Qualification Test and subsequent teardown inspection, High Impact Shock Testing, and the subsequent 100-hour post shock endurance test and teardown inspection. This report includes an assessment of the overall performance of the engine, General Electric’s capacity to meet specified test requirements, any questions or concerns that may have arisen during testing, and a conclusive statement about the outcome of the tests.
Long Term Thermal Stability of Several Gas Turbine Alloys
Authors: Pike L. M. , Srivastava S. K.
Published: November 2008

Ever increasing demands for lower gas turbine operating costs have led to the need for longer lasting components. This in turn, requires the availability of alloys which are reliable to such long lifetimes. In the mill produced condition, most alloys have desirable microstructures and mechanical properties. However, after exposure to the harsh temperatures found in gas turbine engines, the microstructures of most alloys will begin to change. The effects on the mechanical properties of such microstructural changes can range from mild deterioration to significant degradation. In this paper, the effects of thermal exposures at temperatures from 1200 to 1600°F for durations up to one year on the mechanical properties of three wrought gas turbine alloys will be reported. The alloys will include HAYNES® 188 alloy (Co-Ni-Cr-W), HAYNES 230® alloy (Ni-Cr-W), and HAYNES HR-120® alloy (Fe-Ni-Cr-Nb-N).
Empirical Correlations for Predicting Key Performance Parameters Due to Inlet Fogging
Authors: Utamura Motoaki
Published: November 2008

Empirical correlations to predict (1) drain mass flow rate, (2) temperature depression of intake air and (3) power increase to a given ambient and operating condition are derived. The cooling efficiency and drain ratio are expressed using separation of variables, i.e. relative spray amount, ambient wet bulb depression and fogger configuration (droplet spectrum, geometry of fog rack etc.). The correlation for power increase obtained as function of net specific spray water flow can be applied to overspray mode of operation. It is confirmed that the power increase predicted matches field data within error less than 10% in the range of net specific water amount up to 0.4% overspray and ambient wet bulb depression from 3.35 to 13.8deg.
Gas Turbine Development: More Than 50 Years Ago
Authors: van der Linden Septimus , von Rappard Axel
Published: November 2008

With the celebration of the 50th Anniversary of Turbo Expo and 125 years of ASME, it would be appropriate to once again review a paper read at the meeting in London, UK, of The Institution of Mechanical Engineers (founded 1847) on the 24th of February, 1939. This Paper was titled, “The Combustion Gas Turbine, it’s History Development and Prospects” by Adolf Meyer [1]. At the time, the first Industrial Gas Turbine generating set of 4000kW was on order by the City of Neuchatel [2], and cycle improvements for future units were already being proposed, as well as new fields of applications, such as Locomotives, Ship Propulsion, Wind Tunnels, Blast Furnace Plants, as well as Combined Gas Turbine and Steam Plants. In the section “Glimpse into the Future,” the field in which much progress was expected was the improvement in compressor efficiency and increased turbine inlet temperatures. Raising the overall efficiency of compressor and turbine to 92% and the inlet temperature to 2200 F, thermal efficiencies of 50% at the shaft coupling were envisioned, with units capable of delivering 65MW. These were the topics for three generations of engineers in several disciplines. This promising technology success would not have been possible without the coordinated leadership of far sighted managers of different OEM’s, and the tremendous courage for the introduction by the end-users.
A Probabilistic Framework for Risk Prediction of Gas Turbine Engine Components With Inherent or Induced Material Anomalies
Authors: Enright Michael P. , McClung R. Craig , Huyse Luc
Published: November 2008

Rare anomalies may be introduced during the metallurgical or manufacturing processes that may lead to uncontained failures of aircraft gas turbine engines. The risk of fracture associated with these anomalies can be quantified using a probabilistic fracture mechanics approach. In this paper, a general probabilistic framework is presented for risk assessment of gas turbine engine components subjected to either inherent or induced material anomalies. A summary of efficient computational methods that are applicable to this problem is also provided.
A Probabilistic Micromechanical Code for Predicting Fatigue Life Variability: Model Development and Application
Authors: Chan K. S. , Enright M. P.
Published: November 2008

This paper summarizes the development of a probabilistic micromechanical code for treating fatigue life variability resulting from material variations. Dubbed MicroFaVa (Micromechanical Fatigue Variability), the code is based on a set of physics-based fatigue models that predict fatigue crack initiation life, fatigue crack growth life, fatigue limit, fatigue crack growth threshold, crack size at initiation, and fracture toughness. Using microstructure information as material input, the code is capable of predicting the average behavior and the confidence limits of the crack initiation and crack growth lives of structural alloys under LCF or HCF loading. This paper presents a summary of the development of the code and highlights applications of the model to predicting the effects of microstructure on the fatigue crack growth response and life variability of the α + β Ti-alloy Ti-6Al-4V.
Vibratory Parameters of Blades From Coordinate Measurement Machine (CMM) Data
Authors: Sinha Alok , Hall Benjamin , Cassenti Brice , Hilbert Gary
Published: November 2008

This paper deals with the development of a procedure to model geometric variations of blades. Specifically, vibratory parameters of blades are extracted from CMM data on an integrally bladed rotor (IBR). The method is based on proper orthogonal decomposition (POD) of CMM data, solid modeling and finite element techniques. In addition to obtaining natural frequencies and mode shapes of each blade on an IBR, statistics of these modal parameters are also computed and characterized. Numerical results are validated by comparison with experimental results.
Fuel Moisturization for Natural Gas Fired Combined Cycles
Authors: Smith Raub W. , Johansen Aarron D. , Ranasinghe Jatila
Published: November 2008

Natural gas fired combined cycles have enjoyed increasing success in power generation over the past several years, driven to a significant degree by their high efficiency. This paper discusses development of a fuel moisturization system targeted at new construction that improves plant efficiency (∼0.16% points.), increases plant output (∼1.3%), and reduces NOx emissions (10%–15%). Since the inception of combined cycles, improvements in efficiency and power density have been largely driven by ever higher gas turbine operating temperatures. The steam bottoming cycle has also been refined, first by the addition of multiple pressure levels, then reheat, and more recently fuel heating, to utilize the gas turbine exhaust energy ever more efficiently. Further improvement is most effectively realized by a structural refinement of the cycle that allows more of the low level waste heat to be recovered to the fuel, where each additional Btu or Kcal is one fewer that needs to be purchased as fuel. This goal has been achieved with development of a Fuel Moisturization System to moisturize and superheat the fuel gas entering the gas turbine combustion system.
Preliminary Multidisciplinary Design Optimization System: A Software Solution for Early Gas Turbine Conception
Authors: Prado Pascal , Panchenko Yulia , Tre´panier Jean-Yves , Tribes Christophe
Published: November 2008

Preliminary Multidisciplinary Design Optimization (PMDO) project addresses the development and implementation of the Multidisciplinary Design Optimization (MDO) methodology in the Concept/Preliminary stages of the gas turbine design process. These initial phases encompass a wide range of coupled engineering disciplines. The PMDO System is a software tool intended to integrate existing design and analysis tools, decompose coupled multidisciplinary problems and, therefore, allow optimizers to speed-up preliminary engine design process. The current paper is a brief presentation of the specifications for the PMDO System as well as a description of the prototype being developed and evaluated. The current assumed e xible architecture is based on three software components that can be installed on different computers: a Java/XML MultiServer, a Java Graphical User Interface and a commercial optimization software.
Probabilistic High Cycle Fatigue Assessment Process for Integrally Bladed Rotors
Authors: Brown Jeffrey M. , Grandhi Ramana V.
Published: November 2008

This paper defines a probabilistic High Cycle Fatigue (HCF) assessment process for a fan or compressor Integrally Bladed Rotor (IBR). It identifies key design variables, how they are statistically modeled, the probabilistic integration technique, and the physics-based modeling process. It defines how previous eigensensitivity based reduced order models cannot be used for IBR assessment and validates an alternate approach. An autoregressive model accounts for correlation between IBR blade-to-blade variabilities. An approach is also defined to combine sector tuned stress variation and mistuning amplifications. Predicted stress variations integrate with a probabilistic Goodman Diagram to allow an IBR risk assessment. The paper concludes by summarizing several remaining areas that are necessary for a practical assessment process. These areas are probabilistic fluid dynamic prediction, probabilistic mission analysis, propagating model error, and the need for an effective validation strategy.
Gas Turbine Fed by Gas Produced From Biomass Pyrolysis
Authors: Moriconi Andrea , Quirini Catia , Moriconi Daniele , Moniconi Erica
Published: November 2008

The first industrial IPCC plant fed by biomass using a slow pyrolysis process to produce gas and wood coal is operating in Terni- Italy from the beginning of 2004. The plant provides about 4 MWe, when it is fed by 4 t/h of natural biomass (i.e. all natural materials used as energy sources) with a maximum humidity content of 20%. The article refers to the problems faced to reach a stable operation of the pyrolyser and to obtain a gas able to burn in a commercial gas turbine, without any modification of the combustion chamber, In addition, the characterization of tar components are discussed and economical possibilities to recover tar compounds are compared. The process is able to produce energy from biomass and from different kinds of residues, at really high efficiency compared with other conventional technologies: an economical analysis is made.
Statistics of the Peak Maximum Amplitude of the Forced Response of a Mistuned Bladed Disk
Authors: Sinha Alok
Published: November 2008

This paper examines the nature of the statistical distribution of the peak maximum amplitude of the forced response of a mistuned bladed disk. A range of values of the structural coupling between blades and the standard deviation of mistuning have been used, and it is determined if it is correct to describe the distribution of the peak maximum amplitude as Weibull. Also, using a neural network, a functional relationship between the peak maximum amplitude distribution and input parameters (structural coupling between blades and standard deviation of mistuning) is sought via coefficients of Hermite polynomials and 99 percentile peak maximum amplitude.
Experimental Investigations on Isothermal Swirling Flows in a Reverse Flow Annular Gas Turbine Combustor
Authors: Reddy K. Sudhakar , Reddy D. N. , Vara Prasad C. M.
Published: November 2008

An experimental work was carried out on confined swirling flows under non-combusting conditions in a reverse flow annular gas turbine combustor. Flow measurements with a five hole pitot probe are carried out in a flow apparatus of a geometrical configuration similar to the model of a swirl combustor. Mean flow results are obtained for different flow conditions to determine the effect of swirl on the recirculation zone and the variation of the swirl strength along the axis of the gas turbine combustion chamber. The boundaries of the recirculation region are plotted to compare the size and length of the zone with various swirlers. Minimum flow Reynolds number is required for flow recirculation; the effect of Reynolds number on determining which flow class is present for flow of interest in combustion chamber was investigated. The inlet swirl number is optimized for higher swirl strength and the inlet swirl number for which recirculation completely vanishes is also estimated.
Evolution of Photostimulated Luminescence During Thermal Cycling of Electron Beam Physical Vapor Deposited Thermal Barrier Coatings
Authors: Jayaraj B. , Franke B. , Laxman S. , Miranda D. , Liu J. , Byeon J. W. , Sohn Y. H.
Published: November 2008

Thermal barrier coatings (TBCs) are widely used for thermal protection of hot section components in turbines for propulsion and power generation. Development of a robust non-destructive evaluation (NDE) technique for TBCs is essential for quality control, life assessment and health monitoring that will facilitate reliable application, efficient maintenance and prevention of catastrophic failure. In this study, degradation of TBCs was non-destructively evaluated by photostimulated luminsecence (PSLS) and microstructurally examined as a function of furnace thermal cycling carried out in air with 10-minute heat-up, 1-, and 10-hour dwell duration at 2050°F (1121°C), and 10-minute forced-air quench. TBCs examined in this study consisted of electron beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia (YSZ) on grit-blasted (Ni,Pt)Al or as-coated (Ni,Pt)Al or shot-peened NiCoCrAlY bond coats and various superalloy substrates. Characteristics of subcritical-subsurface damage near the thermally grown oxide (TGO) were documented by cross-sectional scanning electron microscopy. Mechanisms of damage varied as a function of TBC type and thermal cycling dwell time, and included preferential grain boundary oxidation after ridge-induced micro-cracking, racheting and undulation of TGO/bond coat interface, internal oxidation of bond coats, and formation of Ni/Co-rich oxides. These microstructural observations are correlated to the evolution in compressive residual stress in the TGO scale determined by photostimulated luminescence shift, including stress-relief associated with subcritical cracking in the TGO scale, and stress-relaxation associated with racheting of the TGO/bond coat interface. Correlations between the microstructural development and the photostimulated luminescence from the TGO scale are discussed as a function of TBC type and thermal cycling dwell time.
Turbo-Machinery Requirements for Practical SOFC – Gas Turbine Hybrid Systems
Authors: Schonewald Roger W.
Published: November 2008

The integration of a solid oxide fuel cell (SOFC) and a gas turbine is a marriage of two otherwise disparate power generation technologies with the potential for significant efficiency and emissions benefits. This requires consideration of the integrated system with unique impacts to the design of both components. Gas turbines for such systems will be different from today’s heavy-duty gas turbines and require a modified mind set in their design approach. This paper explores gas turbines that will be required for integrated SOFC gas turbine power generation systems, the resulting gas turbine cycle, technology flow-down from today’s gas turbines, and economic considerations.
Mercury™ 50 Product Durability, Operation and Maintenance Review
Authors: Teraji David , Hettick Jeanne , Robison Miller
Published: November 2008

The Mercury™ 50 gas turbine operates with a recuperated cycle to produce 4600 kW with a high thermal efficiency and very low emissions. Commercialized in 2003, the Mercury 50 gas turbine has completed an extensive design, development, and field evaluation program that insured a reliable and durable product that is easy to operate and maintain. This results in maximizing operation reliability and availability and lowering maintenance cost, critical factors in the distributed generation and cogeneration power generation markets. 6 Sigma, robust engineering and Kaizen methodologies were used during the design and pre-production phases to collect valuable input from users and prove out the durability, operability and maintainability of the product. This paper will review the Mercury 50 design for durability and ease of operation and maintenance.
Electro-Hydrodynamic Control of Premixed Turbulent Methane Flames at Pressures Above 1 ATM
Authors: Hammer T. , Lins G. , Branston D. W. , Dinkelacker F. , Sakhrieh A. , Leipertz A.
Published: November 2008

Electric field control of combustion offers the potential of stabilizing flames and reducing emissions with comparatively little effort. Previous investigations of the effects of electric fields on flames were restricted to atmospheric pressure and the question whether field effects persist at higher pressures remained open. In the present work effects of electric fields on flame behavior are established for pressures up to 10 bar without any indication that this should be an upper limit. Voltage-current measurements and optical emission spectroscopy gave clear evidence that at all experimental conditions under investigation electric field induced ionization and dissociation reactions were negligible with regard to the combustion process. Thus it is concluded that all observed effects are due to electro-hydrodynamic distortions of the gas flow caused by electrostatic forces acting on the ions generated in the reaction zones of the flames. The concentration of pollutants such as CO, NO and NO2 in the presence of an electric field depends on the ratio U/p of electrode voltage U and pressure p which implies that the electric field strength required to obtain a given effect increases linearly with pressure. In an electric field directed towards the burner CO emissions could be reduced by about 90%, irrespective of pressure. The decrease of CO was accompanied by an increase of NOx by about 20%. The electric power required for a CO reduction of 90% amounted to 0.1% of the thermal power. The improvement of the lean blow-off limit upon application of an electric field observed so far ranges from 1 to 3% and increases with pressure.
Gas Turbine Fogging Technology — A State-of-the-Art Review: Part III — Practical Considerations and Operational Experience
Authors: Bhargava R. K. , Meher-Homji C. B. , Chaker M. A. , Bianchi M. , Melino F. , Peretto A. , Ingistov S.
Published: November 2008

The strong influence of ambient temperature on the output and heat rate of a gas turbine has popularized the application of inlet fogging and overspray for power augmentation. This paper focuses on practical considerations, for implementation of fogging technology, such as water quality requirements, foreign object damage, gas turbine inlet icing, intake duct design, changes in compressor performance characteristics, and blade coating distress problems. It also provides a checklist for users and project developers to facilitate the design and implementation of fogging systems. In addition, this paper covers operational experience and reviews the work pursued by gas turbine OEMs in the field of fogging technology. A list of unresolved issues and ongoing research related to the fogging technology is also provided.
Modeling of carbon fiber couch attenuation properties with a commercial treatment planning system
Authors: Mihaylov I. B. , Corry P. , Yan Y. , Ratanatharathorn V. , Moros E. G.
Published: November 2008

The purpose of this work is to evaluate the modeling of carbon fiber couch attenuation properties with a commercial treatment planning system (TPS, Pinnacle3, v8.0d). A carbon fiber couch (BrainLab) was incorporated into the TPS by automatic contouring of all transverse CT slices. The couch shape and dimensions were set according to the vendor specifications. The couch composition was realized by assigning appropriate densities to the delineated contours. The couch modeling by the TPS was validated by absolute dosimetric measurements. A phantom consisting of several solid water slabs was CT scanned, the CT data set was imported into the TPS, and the carbon fiber couch was auto‐contoured. Open (unblocked) field plans for different gantry angles and field sizes were generated. The doses to a point at depth, placed at the linac isocenter, were computed. The phantom was irradiated according to the dose calculation setup and doses were measured with an ion chamber. In addition, percent depth dose (PDD) curves were computed as well as measured with radiographic film. The calculated and measured doses, transmissions, and PDDs were cross‐compared. Doses for several posterior fields (0°, 30°, 50°, 75°, 83°) were calculated for 6 and photon beams. For model validation a nominal field size of was chosen and were delivered for each portal. The largest difference between computed and measured doses for those posterior fields was within 1.7%. A comparison between computed and measured transmissions for the aforementioned fields was performed and the results were found to agree within 1.1%. The differences between computed and measured doses for different field sizes, ranging from in increments, were within 2%. Measured and computed PDD curves with and without the couch agree from the surface up to depth. The PDDs indicate a surface dose increase resulting from the carbon fiber couch field modification. The carbon fiber couch attenuation for individual posterior oblique fields (75°) can be in excess of 8% depending on the beam energy and field size. When the couch is contoured in Pinnacle3 its attenuation properties are modeled to within 1.7% with respect to measurements. These results demonstrate that appropriate contouring together with relevant density information for the contours is sufficient for adequate modeling of carbon fiber supporting devices by modern commercial treatment planning systems.
Comparison of dose calculation algorithms for colorectal cancer brachytherapy treatment with a shielded applicator
Authors: Yan Xiangsheng , Poon Emily , Reniers Brigitte , Vuong Te , Verhaegen Frank
Published: November 2008

Colorectal cancer patients are treated at our hospital with high dose rate (HDR) brachytherapy using an applicator that allows the introduction of a lead or tungsten shielding rod to reduce the dose to healthy tissue. The clinical dose planning calculations are, however, currently performed without taking the shielding into account. To study the dose distributions in shielded cases, three techniques were employed. The first technique was to adapt a shielding algorithm which is part of the Nucletron PLATO HDR treatment planning system. The isodose pattern exhibited unexpected features but was found to be a reasonable approximation. The second technique employed a ray tracing algorithm that assigns a constant dose ratio with/without shielding behind the shielding along a radial line originating from the source. The dose calculation results were similar to the results from the first technique but with improved accuracy. The third and most accurate technique used a dose‐matrix‐superposition algorithm, based on Monte Carlo calculations. The results from the latter technique showed quantitatively that the dose to healthy tissue is reduced significantly in the presence of shielding. However, it was also found that the dose to the tumor may be affected by the presence of shielding; for about a quarter of the patients treated the volume covered by the 100% isodose lines was reduced by more than 5%, leading to potential tumor cold spots. Use of any of the three shielding algorithms results in improved dose estimates to healthy tissue and the tumor.
Clinical characterization of a proton beam continuous uniform scanning system with dose layer stacking
Authors: Farr J. B. , Mascia A. E. , Hsi W.‐C. , Allgower C. E. , Jesseph F. , Schreuder A. N. , Wolanski M. , Nichiporov D. F. , Anferov V.
Published: November 2008

A proton beam delivery system on a gantry with continuous uniform scanning and dose layer stacking at the Midwest Proton Radiotherapy Institute has been commissioned and accepted for clinical use. This paper was motivated by a lack of guidance on the testing and characterization for clinical uniform scanning systems. As such, it describes how these tasks were performed with a uniform scanning beam delivery system. This paper reports the methods used and important dosimetric characteristics of radiation fields produced by the system. The commissioning data include the transverse and longitudinal dose distributions, penumbra, and absolute dose values. Using a cyclotron's proton beam, the system provides field sizes up to 20 and in diameter for proton ranges in water up to 27 and , respectively. The dose layer stacking method allows for the flexible construction of spread‐out Bragg peaks with uniform modulation of up to in water, at typical dose rates of . For measuring relative dose distributions, multielement ion chamber arrays, small‐volume ion chambers, and radiographic films were employed. Measurements during the clinical commissioning of the system have shown that the lateral and longitudinal dose uniformity of 2.5% or better can be achieved for all clinically important field sizes and ranges. The measured transverse penumbra widths offer a slight improvement in comparison to those achieved with a double scattering beam spreading technique at the facility. Absolute dose measurements were done using calibrated ion chambers, thermoluminescent and alanine detectors. Dose intercomparisons conducted using various types of detectors traceable to a national standards laboratory indicate that the measured dosimetry data agree with each other within 5%.
A maximum likelihood proton path formalism for application in proton computed tomography
Authors: Schulte R. W. , Penfold S. N. , Tafas J. T. , Schubert K. E.
Published: November 2008

The limited spatial resolution in proton computed tomography (pCT) in comparison to x‐ray CT is related to multiple Coulomb scattering (MCS) within the imaged object. The current generation pCT design utilizes silicon detectors that measure the position and direction of individual protons prior to and post‐traversing the patient to maximize the knowledge of the path of the proton within the imaged object. For efficient reconstruction with the proposed pCT system, one needs to develop compact and flexible mathematical formalisms that model the effects of MCS as the proton traverses the imaged object. In this article, a compact, matrix‐based most likely path (MLP) formalism is presented employing Bayesian statistics and a Gaussian approximation of MCS. Using GEANT4 simulations in a homogeneous water cube, the MLP expression was found to be able to predict the Monte Carlo tracks of protons to within on average when employing cuts on the relative exit angle and exit energy. These cuts were found to eliminate the majority of events not conforming to the Gaussian model of MCS used in the MLP derivation.
Radiation transmission data for radionuclides and materials relevant to brachytherapy facility shielding
Authors: Papagiannis P. , Baltas D. , Granero D. , Pérez‐Calatayud J. , Gimeno J. , Ballester F. , Venselaar J. L. M.
Published: November 2008

To address the limited availability of radiation shielding data for brachytherapy as well as some disparity in existing data, Monte Carlo simulation was used to generate radiation transmission data for , , , , , , , , and photons through concrete, stainless steel, lead, as well as lead glass and baryte concrete. Results accounting for the oblique incidence of radiation to the barrier, spectral variation with barrier thickness, and broad beam conditions in a realistic geometry are compared to corresponding data in the literature in terms of the half value layer (HVL) and tenth value layer (TVL) indices. It is also shown that radiation shielding calculations using HVL or TVL values could overestimate or underestimate the barrier thickness required to achieve a certain reduction in radiation transmission. This questions the use of HVL or TVL indices instead of the actual transmission data. Therefore, a three‐parameter model is fitted to results of this work to facilitate accurate and simple radiation shielding calculations.
Measurement of electron density in dual‐energy x‐ray CT with monochromatic x rays and evaluation of its accuracy
Authors: Tsunoo Takanori , Torikoshi Masami , Ohno Yumiko , Uesugi Kentaro , Yagi Naoto
Published: November 2008

Information on electron density is important for radiotherapy treatment planning in order to optimize the dose distribution in the target volume of a patient. At present, the electron density is derived from a computed tomography (CT) number measured in x‐ray CT scanning; however, there are uncertainties due to the beam hardening effect and the method by which the electron density is converted from the CT number. In order to measure the electron density with an accuracy of , the authors have developed dual‐energy x ray CT using monochromatic x rays. They experimentally proved that the measured linear attenuation coefficients were only a few percent lower than the theoretical ones, which led to an accuracy within 2% for the electron density. There were three factors causing inaccuracy in the linear attenuation coefficient and the electron density: the influence of scattered radiation, the nonlinearity in the detector response function, and a theoretical process to derive the electron density from the linear attenuation coefficients. The linear attenuation coefficients of water were experimentally proved to differ by 1%–2% from the theoretical one even when the scattering effect was negligible. The nonlinearity of the response function played an important role in correcting the difference in the linear attenuation coefficient. Furthermore, the theoretical process used for deriving the electron density from the linear attenuation coefficients introduces about 0.6% deviation from the theoretical value into the resultant electron density. This deviation occurs systematically so that it can be corrected. The authors measured the electron densities for seven samples equivalent to soft tissue in dual‐energy x‐ray CT, and finally obtained them with an accuracy of around .
Semi‐empirical procedures for correcting detector size effect on clinical MV x‐ray beam profilesa)
Authors: Sahoo Narayan , Kazi Abdul M. , Hoffman Mark
Published: November 2008

The measured radiation beam profiles need to be corrected for the detector size effect to derive the real profiles. This paper describes two new semi‐empirical procedures to determine the real profiles of high‐energy x‐ray beams by removing the detector size effect from the measured profiles. Measured profiles are corrected by shifting the position of each measurement point by a specific amount determined from available theoretical and experimental knowledge in the literature. The authors developed two procedures to determine the amount of shift. In the first procedure, which employs the published analytical deconvolution procedure of other investigators, the shift is determined from the comparison of the analytical fit of the measured profile and the corresponding analytical real profile derived from the deconvolution of the fitted measured profile and the Gaussian detector response function. In the second procedure, the amount of shift at any measurement point is considered to be proportional to the value of an analytical function related to the second derivative of the real profile at that point. The constant of proportionality and a parameter in the function are obtained from the values of the shifts at the 90%, 80%, 20%, and 10% dose levels, which are experimentally known from the published results of other investigators to be approximately equal to half of the radius of the detector. These procedures were tested by correcting the profiles of 6 and x‐ray beams measured by three different ionization chambers and a stereotactic field diode detector with 2.75, 2, 1, and radii of their respective active cylindrical volumes. The corrected profiles measured by different detectors are found to be in close agreement. The detector size corrected penumbra widths also agree with the expected values based on the results of an earlier investigation. Thus, the authors concluded that the proposed procedures are accurate and can be used to derive the real profiles of clinical high‐energy x‐ray beams.
The role of medical physicists and the AAPM in the development of treatment planning and optimization
Authors: Orton Colin G. , Bortfeld Thomas R. , Niemierko Andrzej , Unkelbach Jan
Published: November 2008

Developments in radiotherapy treatment planning and optimization by medical physicists and the American Association of Physicists in Medicine are reviewed, with emphasis on recent work in optimization. It is shown that medical physicists have played a vital role in the creation of innovative treatment planning techniques throughout the past century, most significantly since the advent of computerized tomography for three‐dimensional (3D) imaging and high‐powered computers capable of 3D planning and optimization. Some early advances in 3D planning made by physicists include development of novel planning algorithms, beam's‐eye‐view, virtual simulation, dose‐volume histogram analysis tools, and bioeffect modeling. Most of the recent developments have been driven by the need to develop treatment planning for conformal radiotherapy, especially intensity modulated radiation therapy. These advances include inverse planning, handling the effects of motion and uncertainty, biological planning, and multicriteria optimization.
Color Doppler quantitative measures to predict outcome of biopsies in prostate cancer
Authors: Strigari Lidia , Marsella Annelisa , Canitano Stefano , Gomellini Sara , Arcangeli Stefano , Genovese Elisabetta , Saracino Biancamaria , Petrongari Maria Grazia , Sentinelli Steno , Crecco Marcello , Benassi Marcello , Arcangeli Giorgio
Published: November 2008

Purpose: The aim was to correlate the color Doppler flow activity pre‐ and postradiotherapy, using transrectal color Doppler ultrasonography (CDUS) and the positive biopsy rate after radiotherapy in patients with prostate cancer. Methods and materials: Analysis was carried out in 69 out of 160 patients who had undergone treatment with 3D‐conformal radiotherapy (3D‐CRT) to prostate and seminal vesicles. Patients were randomized to receive in 40 fractions in (arm A) and in 20 fractions in , 4 fractions per week (arm B). Color Doppler flow activity (CDFA) was evaluated calculating the vascularization index (VI), defined as the ratio between the colored and total pixels in the whole and peripheral prostate, delineated by a radiation oncologist on CDUS images, using EcoVasc a home‐made software. The difference between the post‐ and pre‐3D‐CRT maximum VI , named , was calculated in the whole and peripheral prostate for each patient. Then, and the detected biopsy outcome were analyzed using the receiver operating characteristics (ROC) technique. Results: The increased or decreased in patients with positive or negative biopsies, respectively, compared to the value before RT in both arms. The area under the ROC curve for in the whole and peripheral prostate is equal to 0.790 and 0.884, respectively. Conclusion: The index, comparing CDFA at compared to that before RT, allows the postradiotherapy positive biopsy rate to be predicted.
A comparison of texture quantification techniques based on the Fourier and S transforms
Authors: Brown Robert A. , Frayne Richard
Published: November 2008

Detecting differences in texture has been found to be useful in a variety of medical image analysis applications. One class of methods for texture estimation is based upon analysis of local frequency spectra produced by the S transform. Clinical applications have included detection of multiple sclerosis lesions and identification of brain tumor genotype. This paper describes a software application designed to detect texture differences in medical images, demonstrates and validates the ability of the technique to analyze magnetic resonance images obtained of an in vitro phantom with known textural features, and compares the results to alternative methods. Finally, some examples of texture analysis in several promising biomedical applications are included.