bluuebunny/crossref_metadata_2025 huggingface dataset:
Concepts Developed for a Multi-Phased, Vertical Axis Wind Turbine System With an Adjustable Inlet Air Scoop and Exit Drag Curtain
Authors: Krippene Brett C. , Sorensen Ira
Published: January 2011

A conceptual design is presented of a roof-top type, MULTI-PHASED VERTICAL AXIS WIND TURBINE SYSTEM with an ADJUSTABLE INLET AIR SCOOP and EXIT DRAG CURTAIN at a 100 Watt to 50 kWe commercial scale. The MULTI-PHASED VERTICAL AXIS WIND TURBINE (MVAWT) SYSTEM is cost effective in an environmentally friendly manner. It is especially useful in areas where it can benefit from the wind velocity increasing and streamlining effects that may occur around small hills, roof tops and tall buildings. The MVAWT system concentrates, collects and utilizes the available energy in the wind by way of a naturally yawed, downwind seeking, vertical axis orientated flow tube and integrated air turbine assembly with adjustable inlet air scoop and outlet drag sections mounted on the flow tube. The MVAWT system’s air turbine is a combination radial or mixed out-flow and reaction cross-flow type centrifugal fan design as mounted on the discharge end of the flow tube. This air turbine, being more of a radial instead of an axial flow or propeller type design, can potentially exceed the Betz limit of 59.26% energy recovery or effectiveness from the maximum energy available from the wind flowing through the inlet flow tube. A low pressure drop screen can be provided at the inlet and outlet to protect flying birds and mammals from being drawn into the integrated flow tube and air turbine assembly. Additionally, access to the rotating components for inspection and maintenance purposes is much safer, easier and less costly than with conventional propeller type wind turbine systems mounted on tall towers. No multiple staged wind turbine system as described herein has as yet been researched as to its technical feasibility and developed to the point of a prototype demonstration at a commercial size. Such parameters as overall performance, energy conversion efficiency, costs (installed, operating and maintenance), system reliability, public acceptance and environmental impacts have not yet been truly assessed. A Phase I - technical feasibility assessment and Phase II - prototype demonstration program for a nominal 10 kWe sized Multi-Phased Vertical Axis Wind Turbine system with an average power output in a 16 mph wind of as much as 2 kWe (kW-hr / hr) and as much as 10 kWe (kW-hr / hr) at a 28 mph wind velocity is suggested to provide this essential information to both the authors and the public at large.
Converting Low-Grade Heat Into Power Using a Supercritical Rankine Cycle With Zeotropic Mixture Working Fluid
Authors: Chen Huijuan , Goswami D. Yogi , Rahman Muhammad M. , Stefanakos Elias K.
Published: January 2011

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power is proposed and analyzed in this paper. A supercritical Rankine cycle does not go through two-phase region during the heating process. By adopting zeotropic mixtures as the working fluids, the condensation process happens non-isothermally. Both of the features create a potential in reducing the irreversibility and improving the system efficiency. A comparative study between an organic Rankine cycle and the proposed supercritical Rankine cycle shows that the proposed cycle improves the cycle thermal efficiency, exergy efficiency of the heating and the condensation processes, and the system overall efficiency.
Test Results and Status of the TOP Alignment System for Parabolic Trough Solar Collectors
Authors: Diver Richard B. , Moss Timothy A.
Published: January 2011

Parabolic trough solar power plants produce the lowest cost solar electricity, yet unsubsidized electricity from parabolic trough power plants costs about twice that from conventional sources. To make parabolic trough electricity more competitive, we are developing an innovative approach for rapidly and effectively evaluating the alignment of mirrors in parabolic trough power plants and prescribing corrective actions as needed. The Theoretical Overlay Photographic Collector Alignment Technique (TOPCAT) system could be used during construction, to improve the performance of existing power plants, or for routine maintenance. It is also an enabling technology for higher concentration ratio and lower cost trough solar collector designs needed to make solar electricity more competitive with conventional sources. In this paper a truck-mounted TOPCAT field characterization system is described. Test results from mirror alignment of an LS-3 loop in a commercial parabolic trough power plant in southern California are also presented. The performance improvements were measured using a comparative calorimetric technique which inherently accounts for variations in insolation levels, sun incident angle, and mirror and heat collection element (HCE) glass envelope cleanliness. Measurements indicate a 3.5% increase in thermal performance of an LS-3 loop aligned with the TOPCAT system. Benchmarking results of labor hours and materials show that the TOPCAT system is an extremely cost effective tool for improving the performance of existing parabolic trough power plants.
Design of Farm Waste-Driven Supply Side Infrastructure for Data Centers
Authors: Sharma Ratnesh , Christian Tom , Arlitt Martin , Bash Cullen , Patel Chandrakant
Published: January 2011

In this paper, we design a supply-side infrastructure for data centers that runs primarily on energy from digested farm waste. Although the information technology and livestock industries may seem completely disjoint, they have complementary characteristics that we exploit for mutual benefit. In particular, the farm waste fuels a combined heat and power system. The data center consumes the power, and its waste heat feeds back into the combined system. We propose a resource management system to manage the resource flows and effluents, and evaluate the direct and indirect economic benefits. As an example, we explain how a hypothetical farm of 10,000 dairy cows could fulfill the power requirements of a 1MW data center.
Material and Energy Process-Step Models of Solar Thermal Hydrogen Production Techniques
Authors: Al-Akkad Basel , Almodaris Mohamed , Howard Elliot , Abraham Jocin , Khorasani Sara , Ozalp Nesrin
Published: January 2011

This paper presents a thermo-economic assessment of three different hydrogen production processes using fossil fuels as feedstock. First, the paper provides process-step level energy and cost analysis for the solar reforming of natural gas. The same analysis is given for the solar cracking of natural gas. The results are compared with the thermo-economic process-step analysis of the steam reforming process. Based on the benchmark results, the paper discusses these three processes with respect to their economic viability. The data for the analysis is collected from literature, various vendors, and personal communications with people from industry and universities. The results are presented for unit hydrogen production by each technique and compared with the market price for hydrogen. An energy balance around each process-step is made to reveal the energy intensity of each process. Although the results show that the steam reforming of methane is still the most economical pathway for hydrogen production, it is only valid when the sequestration, storage, and transportation of hazardous emissions are not taken into account. Finally, this paper provides some ideas for the improvement of the most environmentally friendly hydrogen production technique; the solar cracking of natural gas.
Toward Efficient Reduction of CO2 to CO for Renewable Fuels
Authors: Doty F. David , Doty Glenn N. , Staab John P. , Holte Laura L.
Published: January 2011

Three major challenges — grid stability, domestic oil limitations, and climate change — could all be addressed simultaneously by using off-peak electrical energy to recycle CO2 into liquid fuels (such as gasoline, jet fuel, and diesel). Simulations have shown that recent innovations should make it practical to reduce CO2 to CO at over 66% of theoretical efficiency limits. When combined with other process advances, it would then be possible to synthesize most hydrocarbons and alcohols from point-source CO2 and clean off-peak grid energy (wind or nuclear) at system efficiencies in the range of 51–61%. Energy storage density in renewable, carbon-neutral kerosene is 44 MJ/kg, compared to ∼0.4 MJ/kg for Li-ion batteries. This process begins by electrolyzing water using clean energy to get the hydrogen required by the Reverse Water Gas Shift (RWGS) reactor and by a novel Renewable Fischer Tropsch Synthesis (RFTS) process. Off-peak grid energy averaged only $13/MWhr in the Minnesota hub in 2009. At such prices, the synthesized liquid fuels (“WindFuels”) should compete even when petroleum is only $50/bbl. Considerable effort over the past decade has been put into exploring high-temperature (HT) paths toward the production of renewable syngas (H2 + CO) that could lead to sustainable synthesis of liquid fuels; but competitive fuel production from these HT thermo-chemical routes still appears to be decades away. An alternative path — the RWGS reaction — utilizes much less aggressive conditions and should be much more practical. With low-cost hydrogen becoming available from off-peak wind and nuclear, efficient reduction of CO2 to CO becomes viable at moderate temperatures (750–1000 K) via the RWGS reaction. Challenges arise because of equilibrium limits imposed by the reaction thermodynamics below 800 K and because of competing methanation and coking reactions above 800 K to 1000 K, depending on the catalysts. Several promising sets of conditions and catalysts are being evaluated. To drive the reaction to the right, a multi-stage process is required with efficient separation processes. This in turn depends on advances in cost-effective gas-to-gas recuperators for relatively low pressures to limit parasitic methanation reactions. Another challenge may be passivation of the recuperator surfaces to minimize hydrogenation of the CO during the heat recovery. Preliminary simulations indicate reduction of CO2 to CO with about 2.2 MJ/kg-CO should be practical at commercial scale.
Modelling, Simulation and Assessment of Solar Thermal Power Plants: A First Step Towards Definition of Best Practice Approaches
Authors: Hirsch Tobias , Eck Markus , Buck Reiner , Dersch Ju¨rgen , Feldhoff Jan Fabian , Giuliano Stefano , Hennecke Klaus , Lu¨pfert Eckhard , Schwarzbo¨zl Peter
Published: January 2011

With 620 MWel in operation [1] and more than 2.000 MWel under construction, concentrated solar power (CSP) experiences a renaissance mainly in Spain and the USA, but also in many other countries in the earth’s sunbelt. Due to their large capacity (50 MWel and more) and thus large investment, CSP projects are characterised by an extensive project development process. In several stages of this process, mathematical models of the system predicting its energy yield are required, among others to: • assess single CSP projects (e.g., feasibility or due diligence studies), • compare different CSP concepts (e.g., technology, site), • optimise a project (e.g., solar field size, storage capacity), • investigate the influence of component characteristics (e.g., receiver characteristics), • optimise the operation strategy (e.g., on-line surveillance) or to • assess system performance during commissioning. The models used for these different tasks differ in complexity and accuracy, e.g. the accuracy of a model used for project assessment during commissioning has to be higher than a model used for a pre-feasibility study. At the moment, numerous modelling approaches exist and every project developer uses his own system model and assessment methodology. This confusing situation hinders the acceptance of CSP technology by potential investors. This paper presents a methodology for structuring systems into sub-systems. This is the first step towards a standardized modelling approach for CSP systems. It is not the intention of the authors to present a final model and assessment methodology but to start a broader discussion on this important topic. In fact, it aims at initiating an international working group, devoted to the definition of guidelines for modelling, simulation and assessment of CSP systems, covering all CSP technologies such as solar towers, parabolic troughs, linear Fresnel collectors and solar dishes.
The Impact of Hybrid Wet/Dry Cooling on Concentrating Solar Power Plant Performance
Authors: Wagner Michael J. , Kutscher Charles
Published: January 2011

This paper examines the sensitivity of Rankine cycle plant performance to dry cooling and hybrid (parallel) wet/dry cooling combinations with the traditional wet-cooled model as a baseline. Plants with a lower temperature thermal resource are more sensitive to fluctuations in cooling conditions, and so the lower temperature parabolic trough plant is analyzed to assess the maximum impact of alternative cooling configurations. While low water-use heat rejection designs are applicable to any technology that utilizes a Rankine steam cycle for power generation, they are of special interest to concentrating solar power (CSP) technologies that are located in arid regions with limited water availability. System performance is evaluated using hourly simulations over the course of a year at Daggett, CA. The scope of the analysis in this paper is limited to the power block and the heat rejection system, excluding the solar field and thermal storage. As such, water used in mirror washing, maintenance, etc., is not included. Thermal energy produced by the solar field is modeled using NREL’s Solar Advisor Model (SAM).
Experimental Investigation of Thermal Performance of Vapor Chamber Heat Sinks
Authors: Li Hung-Yi , Chiang Ming-Hung , Lee Chih-I , Yang Wen-Jei
Published: January 2011

This work experimentally studies the thermal performance of plate-fin vapor chamber heat sinks using infrared thermography. The effects of the fin width, the fin height and the Reynolds number on the thermal performance are considered. The results show that generated heat is transferred more uniformly to the base plate by a vapor chamber heat sink than by a similar aluminum heat sink. Therefore, the maximum temperature is effectively reduced. The overall thermal resistance of the vapor chamber heat sink declines as the Reynolds number increases, but the strength of the effect falls. The effect of the fin dimensions on the thermal performance is stronger at a lower Reynolds number.
Enhancement Potential of the Thermal Conversion Efficiency of Ice Cycles by Using of a Real Atkinson Cycle Implementation and (Very) High Pressure Turbo Charging
Authors: Gheorghiu Victor
Published: January 2011

Most recent implementations of the Atkinson cycle are not optimal from the point of view of Thermal Conversion Efficiency (TCE). For example, Toyota has put in its Prius II a gasoline engine which should achieve high efficiency by using a modified Atkinson cycle based on variable intake valve timing management. Firstly, this implementation of the Atkinson cycle is not the optimal solution because some of the air is first sucked from the intake manifold into the cylinder and subsequently returned back there. As a consequence, the oscillating air stream considerably reduces the thermal conversion efficiency of this cycle. Secondly, this implementation of the Atkinson cycle reaches only low levels of Indicated Mean Pressure (IMEP) and, thirdly, it is not suitable for part load Engine Operating Points (EOP) because of the lower TCE. For these reasons, this implementation of the Atkinson cycle is suitable only for hybrid vehicles, where the engine — because it is not directly linked mechanically to the wheels — works only in its best EOP. In this paper the losses in TCE of Internal Combustion Engine (ICE), especially for the Atkinson cycles, are analyzed in detail and a proposal is made for their reduction for aspirated and especially for high pressure supercharged engines.
On Shear Correction Factor in Vibration of Annular Sector Plates
Authors: Hejripour F. , Saidi A. R. , Mirtalaie S. H.
Published: January 2011

In the present study, the shear correction factors are obtained for annular sector plates using Differential Quadrature (DQ) Method. Based on the three-dimensional elasticity theory, the governing equations of motion for an annular sector plate are obtained. These equations together with the boundary conditions are discretized by employing DQ method. Following DQ procedure an eigenvalue problem is obtained that represents the natural frequencies and mode shapes of the plate. This procedure is also investigated for the analysis of the annular sector plates based on FSDT. The frequency of the first asymmetric mode of thickness direction for various shear correction factors are compared with the results of the three-dimensional elasticity theory. Therefore, the appropriate shear correction factor can be found. Some shear correction factors are obtained for various boundary conditions. It is shown that the value of the shear correction factor depends on the plate geometry and the boundary conditions.
Exact Electroelastic Field of a Functionally Graded Piezoelectric Cantilever Beam Subjected to Pure Body Force Loading
Authors: Emami A. A. , Hashemi R. , Kargarnovin M. H. , Naghdabadi R.
Published: January 2011

The electroelastic response of functionally graded piezoelectric cantilever beams which includes the effect of body force is presented in this paper. The material properties such as elastic compliance, piezoelectric and dielectric impermeability are assumed to be graded with different indices in the thickness direction according to exponential distributions. Systems of fourth order inhomogeneous partial differential equations (PDEs) which are satisfied by the stress and induction functions and involve the body force terms are derived. Spectral forms for electrical and mechanical variables in the x-axis are employed to convert the partial differential governing equations and the associated boundary conditions into sets of ordinary differential equations, and the resulting equations are solved in a closed form manner. Subsequently, in numerical studies, the effects of the material property graded indices are examined upon the electroelastic response of FGP cantilever beams under pure body force loadings.
Trajectory Planning for Manufacturing Robots: Algorithm Definition and Experimental Results
Authors: Gasparetto Alessandro , Lanzutti Albano , Vidoni Renato , Zanotto Vanni
Published: January 2011

In this paper an analysis of the experimental results yielded by a minimum time-jerk trajectory planning algorithm is presented. The technique considers both the execution time and the integral of the squared jerk along the trajectory, and the kinematic constraints of the robot manipulator under test. The need for a fast execution and the need for a smooth trajectory are taken into account by adjusting the values of two weights, whose suitable values are set with an “automatic” choice algorithm. The outcomes of the tests are compared with both simulations and experimental results obtained by using a “classic” spline trajectory planning algorithm. The experimental tests are carried out by using an accelerometer mounted on a Cartesian robot.
Entropy Based Classification of Road-Profiles
Authors: Bas¸lamıs¸lı S. C¸ag˘lar , O¨nel Selis
Published: January 2011

In this study, the Shannon entropies of six different road-profiles ranging from “very good asphalt road” to “dirt road (terrain)” were calculated. Results indicate that each type of road has a well defined entropy value and that the entropies of roads ranging from “very good asphalt” to “dirt road (terrain)” lie on a nearly linear locus. A second approach presented in this paper consists in measuring the sprung mass vertical acceleration of a vehicle running over segments of roads of different qualities and calculating the entropies of the acceleration signals. This procedure has been applied to assess the influence of nonlinear damping and vehicle speed. It has been seen that it is possible to identify the type of the road surface through the calculation of entropy if the vehicle operating parameters are known. Finally, it is observed that the locus of entropy values is concave on the plot of acceleration entropy versus root mean square (RMS) acceleration.
Development and Comparison of Laplace Domain and State-Space Models of a Half-Car With Flexible Body
Authors: Van Auken R. Michael
Published: January 2011

Math models of wheeled ground vehicle dynamics, including flexible body effects, have been the subject of research and development for many years. These models are typically based on a finite system of simultaneous ordinary differential equations (e.g., state-space models). Higher order models that include flexible body effects offer improved accuracy over a wider frequency range than lower order rigid body models; however higher order models are typically more sensitive to uncertainties in the model parameters and have increased computational requirements. Lower order models with the desired accuracy may be achieved by model reduction of higher order models. A more general infinite dimension Laplace transfer function is derived for beam bending governed by a fourth order wave equation. The resulting infinite dimension transfer functions for beam bending are then used to develop a transfer function model of a “half-car” with a flexible body. The infinite dimensional transfer function of the half-car model is then used to assess the accuracy of the state-space models. Differences between the models due to model reduction are compared to theoretical upper bounds.
Sensitivity Analysis of the Rectangular Trenches Employed in Suppression of the High-Speed Train-Induced Ground Vibrations
Authors: Younesian Davood , Sadri Mehran
Published: January 2011

Ground vibrations generated by high-speed trains are studied in this paper. Open trenches are included in modeling and the problem is formulated using elasticity theory. The ground is modeled by a semi-infinite domain and the embankment with finite layers and the high-speed train is simulated by moving loads. The analytical solution is obtained in frequency domain and the peak particle velocity (PPT) is then achieved for different types of open trenches with different aspect ratios and distance from the track centerline. A parametric study is then carried out and effects of different parameters including the train speed and ground properties on vibration reduction factors are investigated.
Concentration of Stress Around the Cylindrical Hole in an Initial Stressed Rectangular Orthotropic Thick Plate
Authors: Yahnioglu Nazmiye , Babuscu Yesil Ulku
Published: January 2011

An orthotropic pre-stressed thick plate with a cylindrical hole under additional static loading on the upper face-plane of the plate have been studied within the framework of the Three-Dimensional Linearized Theory of Elasticity (TDLTE) in Initially Stressed Bodies. The corresponding problem formulation is presented and, in order to find the solution to this problem, the 3D finite element method is employed. The numerical results on the concentration of the stress around the cylindrical hole and the influence of the initial forces, geometrical and mechanical parameters on these concentrations are presented in graphical form and discussed. According to these results, in particular it is established that the stress distributions around the cylindrical hole changed significantly with the initial stretching or compressing forces.
Mechanical Assessment of Maglev Vehicle: A Proposal for Implementing Maglev Trains in Iran
Authors: Yaghoubi Hamid , Sadat Hoseini M.
Published: January 2011

Rapid development of transportation industries worldwide, including railways and the never ending demand to shorten travel time during trade, leisure, etc. have caused planning and implementation of high-speed railways in many countries. Variety of such systems including magnetic levitation (maglev) has been introduced to the industry. Contrary to traditional railway vehicles, there is no direct contact between maglev vehicle and its guideway. These vehicles travel along magnetic fields that are established between the vehicle and its guideway. Therefore, these vehicles can travel at very high speeds. The replacement of mechanical components by electronics components overcomes restrictions of conventional railway. Manned maglev vehicles have recorded speed of travel equal to 581km/hr. This has practically paved the way to manufacture super high-speed trains. Currently, there are ElectroMagnetic Suspension (EMS) and ElectroDynamic Suspension (EDS) systems available to the industry. There are also varieties of vehicles that are manufactured based on these two types of systems. Mechanical engineering plays vital roles in design and analysis of suspension systems and corresponding vehicles. In this research, different types of maglev suspension systems and vehicles are studies. It is the purpose of this research to design a model for magnetic suspension system and a model for maglev vehicle. Static and dynamic live loads due to the maglev vehicle are investigated and mathematical model of maglev loading is presented. The proposed model for maglev vehicle is thoroughly analyzed for its static and dynamic loading. This study is focused on the dynamics of maglev vehicle. Modeling vehicle/guideway interactions and then explain the response characteristics of the maglev system for a five-car vehicle traveling on a single-span guideway, with emphasis on vehicle/guideway coupling effects are accomplished. Design of maglev vehicle with finite element method is also considered. Results justify practicality of the proposed suspension system and vehicle for Tehran-Mashhad maglev project.
Acoustic Emission and Fracture Characteristics of AISI D2 Tool Steel Tempered at Different Temperatures
Authors: Ahmadi Najafabadi M. , Teymuri Shandi J.
Published: January 2011

Acoustic emission (AE) has been known as an excellent technique to monitor crack propagation and fracture mechanism. For more domination on AE behavior of materials, comprehensive knowledge on effective parameters is necessary. Heat treatment as one of the important factors on AE characteristics of a material must be considered. This investigation is primarily aimed at studying the effect of tempering heat treatment on characteristics of acoustic emission signals monitored during tension tests of a cold-work tool steel. Single edge notched samples of AISI D2 cold-work tool steel were prepared. Then, respectively annealing, austenitizing and tempering were performed. Tempering was carried out at 5 different temperatures from 0 to 575 C. Finally, samples were loaded at tension and AE signals recorded synergistically. Analyzing of the characteristics of AE signals showed that: (a) In all tempering conditions, the AECC increases slowly at the beginning and rapidly at the point of crack growth, although at higher tempering temperatures we have gradual rise in AECC plot; (b) Increasing tempering temperature, average value of AE count number, amplitude, energy and peak frequency decreases; (c) At 525 C, because of secondary hardening, average value of investigated AE parameters increase strongly and (d) analyzing the relation between fracture mode, AE characteristics and tempering temperature showed that special AE behavior of specimens tempered at 525 C is because of the transformation of retained austenite in ferritic matrix.
Evaluation of the Effect of Gas Leakage on Operation of an Optical Engine
Authors: Kapusuz E. , Ekici B.
Published: January 2011

An experimental and numerical study is carried out to evaluate the significance of gas leakage for a non-lube optically accessible internal combustion engine and to obtain estimation for the gas flow out of the combustion chamber at each engine cycle and its effect on the in-cylinder component states during optical engine’s operation. Attention is paid to blow-by and circumferential flow through the gaps between the piston rings and the liner. Optical engines are typically operated without lubrication to avoid window fouling and generation of fluorescence by oil particles that interfere with laser diagnostic signals, in view of this circumstance significant blow-by is expected in optical engines due to lack of “wet-seal” on the cylinder walls which permits circumferential flow of gases through the piston ring pack region resulting in increased blow-by. Semi analytical model estimating the mass loss rate is incorporated into zero dimensional thermodynamic IC engine model which simulates in-cylinder processes. Predicted results are compared for leaking and non-leaking engine simulations.
Analytical and Numerical Investigation on Eccentric Journal Bearing
Authors: Omran Shobi M. , Ghafoori Ahangar R. , Eskandari A.
Published: January 2011

In this paper, analytical and numerical analyses of radial and tangential velocities and pressure of lubricant film have been considered in an eccentric journal bearing. A 2D flow of shear-thinning viscous fluid is followed by Carreau-Yasuda mathematical model between two eccentric cylinders. The model is mathematically conserved from eccentric coordinate to concentric coordinate due largely to easy solution. Therefore, the PDE equations were converted to the ODE equations with a set of nonlinear algebraic first order equations with their boundary conditions. These kinds of equations are called boundary value problems (BVP) that can be solved with shooting method. The results are compared with 2D numerical simulation in the Fluent software. Lubricant tangential velocity and pressure distributions are examined in the dynamic journal bearing. The comparison of the results revealed that numerical analysis as same as analytical approach is a reliable method for determining lubricant motion in the gap.
Increasing Penetration Rate of Drill String by Optimum Positioning of Stabilizers
Authors: Kazemi Reza , Jafari Ali Asghar , Faraji Mahyari Mohammad
Published: January 2011

In this research, optimum arrangements of drill string’s stabilizers are investigated. The optimum arrangement leads to biggest WOB without buckling. So the penetration rate of the drill bit can be increases. To this goal, the potential energy of drill string for axial and lateral vibration is written in an integral equation. In this equation, the effect of geometrical shortening, which causes nonlinear coupling between axial and lateral vibration, is considered. The work done by WOB force and weight of drill string is calculated. The mode summation method is employed to convert the integral potential energy of the continuous system to a discrete one. The effects of stabilizers are modeled by linear springs with large stiffness constant. Dropping and considering third and fourth order tensor of potential energy lead to linear and nonlinear stability analysis, respectively. Taking first and second order derivatives of discrete potential energy, the stability of drill string can be analyzed. Repeating this procedure for different numbers and positions of stabilizers, the optimum arrangement of stabilizers can be found. This method is employed to find the best arrangement of one and two stabilizers, by linear and nonlinear method.
Experimental Investigation of Heat Transfer and Pressure Drop for Two-Phase R134A Flow in a 1.65 mm Glass Tube
Authors: Tekin Bilgehan , Yazıcıog˘lu Almıla G. , Kerpic¸c¸i Hu¨snu¨ , Kakac¸ Sadık
Published: January 2011

Heat transfer in small scale media is a phenomenon that has been increasingly scrutinized in the past few decades. Refrigerant flow in microscale tubes and channels is a promising solution to be used in future refrigeration technology. Experimental studies are significant for the rating of the heat transfer and pressure drop in a given channel, and are important tools for optimizing applicable designs. An overview of the previous studies in this area has shown that most of the research does not focus on the low mass flow rates encountered in household refrigeration systems. In the current study, heat transfer in a copper tube with 1.65 mm inner diameter with two-phase R134a flow is experimentally investigated under low mass flow rate conditions. In the set-up constructed, instead of constant wall heat flux, which is the boundary condition mainly used in the microscale heat transfer studies in literature, constant wall temperature approach is applied. The experimental procedure is designed to focus on the temperatures and the flow rates observed during evaporation in a typical household refrigeration cycle. Since the flow is in the two-phase region, experiments for different quality values of R134a are conducted by pre-heating the refrigerant at different saturation temperatures and pressures. In microscale flow, a major problem is the increase in pressure drop compared to conventionally-sized channels, and the two-phase flow regime contributes to this increase. Therefore, in addition to the heat transfer, the pressure drop of the refrigerant along the tube is also measured. Thus, for various quality values, the pressure drop and the heat transfer for the refrigerant flow are examined. The experimental data obtained will be useful information for the two-phase flow modeling and the model verification.
Spectral Element Model for the Vibration of a Bending-Shear-Torsion Coupled Composite Timoshenko Beam
Authors: Lee Usik , Jang Injoon
Published: January 2011

In this paper, a spectral element model is developed for axially loaded bending-shear-torsion coupled composite laminated beams. The composite laminated beams are represented by the Timoshenko beam model based on the first-order shear deformation theory. The spectral element model is formulated by using the variational method from frequency-dependent dynamic shape functions. The dynamic shape functions are derived from exact wave solutions to the governing differential equations of motion which are transformed into the frequency-domain by using the DFT theory. The numerical results show that the present spectral model provides extremely accurate natural frequencies for an example problem when compared to the results obtained by using the conventional finite element model which is also presented in this paper.
Analysis of the Experimental and CFD-Based Theoretical Methods for Studying Rotordynamic Characteristics of Labyrinth Gas Seals
Authors: Pugachev Alexander O. , Deckner Martin
Published: January 2011

This paper presents an analysis of the experimental and theoretical methods used to study rotordynamic characteristics of short staggered labyrinth gas seal. Two experimental identification procedures referred to as static and dynamic methods are presented. The static method allows determining direct and cross-coupled stiffness coefficients of the seal by integrating measured circumferential pressure distribution in cavities at various shaft eccentric positions. In the dynamic method, identification of stiffness and damping coefficients is based on the rotor excitation using a magnetic actuator and utilizes the effect of alternation of rotor vibrations due to aerodynamic forces acting in the seal. The experimental results obtained by the static and dynamic methods demonstrate an apparent discrepancy most of all in the direct stiffness coefficients. A CFD-based model of the seal is used to predict rotordynamic coefficients and to analyze the discrepancies between the static and dynamic measurements. The seal forces are calculated in two ways similar to the experimental procedures. The predictions are in good agreement with experimental results obtained by both measurement techniques. The effects of pressure differential, inlet swirl, shaft rotational speed, shaft eccentricity, and inflow cavity on seal stiffness and damping are presented. The discrepancies between different methods must be kept in mind while studying rotordynamic characteristics of seals.
Hybrid Neural System for Gas Turbine Diagnostics: An Optimization Strategy
Authors: Matuck Gustavo Ravanhani , Barbosa Joa˜o Roberto , Bringhenti Cleverson , Lima Isaias
Published: January 2011

New health monitoring strategies were developed in the last decade aiming at improvement of gas turbines safety and reliability. Real time methodologies have been considered of major concern for safe operation at least cost. This paper describes a hybrid system approach for turboshaft faults diagnosis, using data obtained from a tuned high fidelity gas turbine simulator program, including those for multiple faults deteriorated performance. Kohonen neural network was used to analyze similarity together with an optimization strategy to reduce the volume of data used in the diagnostics phase. A Multi-Layer Perceptron (MLP) was used for training and validation. The MLP and Kohonen networks were tested for several configurations, in order to improve diagnosis. The hybrid system was also tested with noise-contaminated data and it was verified the capability of the neural approach to detect and isolate multiple faults better than the MLP alone. The results showed that the optimization strategy reduced significantly the database patterns and improved the learning process, demonstrating high precision to diagnose gas turbine operation problems. The reliability of the proposed system is explained both qualitatively and quantitatively.
A Simple Parametric Model for the Analysis of Cooled Gas Turbines
Authors: Gu¨len S. Can
Published: January 2011

A natural gas fired gas turbine combined cycle power plant is the most efficient option for fossil fuel based electric power generation that is commercially available. Trade publications report that currently available technology is rated near 60% thermal efficiency. Research and development efforts are in place targeting even higher efficiencies in the next two decades. In the face of diminishing natural resources and increasing carbon dioxide emissions, leading to greenhouse gas effect and global warming, these efforts are even more critical today than in the last century. The main performance driver in a combined cycle power plant is the gas turbine. The basic thermodynamics of the gas turbine, described by the well-known Brayton cycle, dictates the key design parameters that determine the gas turbine performance are the cycle pressure ratio and maximum cycle temperature at the turbine inlet. While performance calculations for an ideal gas turbine are straightforward with compact mathematical formulations, detailed engineering analysis of real machines with turbine hot gas path cooling requires complex models. Such models, requisite for detailed engineering design work, involve highly empirical heat transfer formulations embedded in a complex system of equations that are amenable only to numerical solutions. A cooled turbine modeling system incorporating all pertinent physical phenomena into compact formulations is developed and presented in this paper. The model is fully physics-based and amenable to simple spreadsheet calculations while illustrating the basic principles with sufficient accuracy and extreme qualitative rigor. This model is valuable not only as a teaching and training tool it is also suitable to preliminary gas turbine combined cycle design calculations in narrowing down the field of feasible design options.
Thermodynamic and Economic Evaluation of an IGCC Plant Based on the Graz Cycle for CO2 Capture
Authors: Sanz W. , Mayr M. , Jericha H.
Published: January 2011

The IEA World Energy Outlook 2009 predicts a considerable growth of the world’s primary energy demand and states that fossil fuels will remain the dominant source of primary energy. Among them coal will increase its share because of its vast reserves, its relatively even global distribution and its low prices compared to oil and gas. On the other hand the burning of coal emits larger quantities of CO2 than oil and gas. As CO2 is the leading cause for global warming, the use of coal for power generation demands a clean coal technology with carbon capture and storage (CCS). Therefore in this work it is suggested to combine a coal gasification unit with a Graz Cycle power plant, an oxy-fuel technology of highest efficiency. The firing of the syngas from coal gasification with pure oxygen avoids the expensive pre-combustion CO2 sequestration and leads to a working fluid of CO2 and steam, where CO2 is captured by simple steam condensation. In contrast to this, the more conventional technology is to send the syngas to a water-shift reactor and a CO2 scrubber so that a fuel containing mainly hydrogen is obtained which can be fired in a conventional combined cycle plant. In order to evaluate these two competing technologies a thermodynamic simulation as well as an economic cost analysis of both power cycles is performed. It turns out that the achievable efficiency of the Graz Cycle plant is — despite of the increased oxygen demand — far higher than that of a plant of conventional capture technology due to the avoidance of shift reaction and scrubbing. The following economic analysis shows mitigation costs of 22.5 €/ton CO2 avoided for the Graz Cycle plant compared to 33 €/ton for an IGCC plant with CO2 capture.
Influence of Channel Orientation on Heat Transfer in a Two-Pass Smooth and Ribbed Rectangular Channel (AR=2:1) Under Large Rotation Numbers
Authors: Huh Michael , Lei Jiang , Han Je-Chin
Published: January 2011

Experiments were conducted in a rotating two-pass cooling channel with an aspect ratio of 2:1 (Dh = 16.9 mm). Results for two surface conditions are presented: smooth and one ribbed configuration. For the ribbed channel, the leading and trailing walls are roughened with ribs (P/e = 10, e/Dh = 0.094) and are placed at an angle (α = 45°) to the mainstream flow. For each surface condition, two angles of rotation (β = 90°, 135°) were studied. For each angle of rotation, five Reynolds numbers (Re = 10K–40K) were considered. At each Reynolds number, five rotational speeds (Ω = 0–400 rpm) were considered. The maximum rotation number and buoyancy parameter reached were 0.45 and 0.85, respectively. Results showed that rotation effects are minimal in ribbed channels, at both angles of rotation, due to the strong interaction of rib and Coriolis induced vortices. In the smooth case, the channel orientation proved to be important and a beneficial heat transfer increase on the leading surface in the first pass (radially outward flow) was observed at high rotation numbers. The correlations developed in this study for predicting heat transfer enhancement due to rotation using the buoyancy parameter showed markedly good agreement with experimental data (+/-10%). Finally, heat transfer under rotating conditions on the tip cap showed to be quite dependent on channel orientation. The maximum tip cap Nu/Nus ratio observed was 2.8.
1D Tool for Stator-Rotor Cavities Integrated Into a Fluid Network Solver of Heavy-Duty Gas Turbine Secondary Air System
Authors: Bonzani F. , Bozzi L. , Mantero M. , Vinci A. , Innocenti L. , Micio M.
Published: January 2011

In order to improve performance of heavy-duty gas turbines, in terms of efficiency and reliability, accurate calculation tools are required to simulate the SAS (Secondary Air System) and estimate the minimum amount of cooling and sealing air to ensure the integrity of hot gas path components. A critical component of this system is the cavity formed between coaxial rotating and stationary discs, that needs a sealing flow to prevent the hot gas ingestion. This paper gives a general overview of a 1D tool for the analysis of stator-rotor cavities and its integration into an “in-house” developed fluid network solver to analyse the behaviour of the secondary air system over different operating conditions. The 1D cavity solver calculates swirl, pressure and temperature profiles along the cavity radius. Thanks to its integration into the SAS code, the cavity solver allows estimation of sealing air flows, taking into account directly of the interaction between inner and outer extraction lines of blades and vanes. This procedure has been applied to the AE94.3A secondary air system and the results are presented in terms of sealing flows variation for the cavities of second and third vane on gas turbine load and ambient conditions. In some different load conditions, calculated secondary air flows are compared to experimental data coming from the AE94.3A Ansaldo fleet.
Improved Blade Fault Diagnosis Using Discrete Blade Passing Energy Packet and Rotor Dynamics Wavelet Analysis
Authors: Lim Meng Hee , Leong M. Salman
Published: January 2011

Blade fault represents one of the most frequent causes of gas turbine failures. Although various measurement methods (i.e. pressure, strain gauges, and blade tip measurements) have been found to be effective in diagnosing blade faults, it is often difficult to deploy these methods under field conditions due to the requirement of mounting sensors in the interior of a running gas turbine. Vibration spectra analysis is inevitably still represents the most widely used method for blade fault diagnosis under field conditions. However, this method is known to be only effective in detecting severe blade fault conditions (i.e. terminal rubbing); whilst, minor and transient blade faults (i.e. geometry alterations, reduction in blade tip clearance, and Foreign Object Damage (FOD) event) are often left undetected. This makes vibration spectra analysis an unreliable tool for total blade fault diagnosis in the field. This study was thus conducted to investigate methods that can improve the sensitivity and reliability of vibration analysis for blade faults diagnosis. Two novel vibration analysis methods were formulated, namely the Rotor Dynamic Wavelet Map (RDWM) and Blade Passing Energy Packet (BPEP). Experimental results showed that the time-frequency display of RDWM could provide a clearer picture of the rotor dynamic characteristics of a rotor system compared to vibration spectra. RDWM also provides a better visualization of the blade condition in the rotor and enables discrimination of various blade fault conditions (i.e. creep rub and eccentricity rub). Meanwhile, the BPEP method which breaks the overall Blade Passing Frequency (BPF) component into instantaneous and discrete energy packets of running blades in the rotor system, enables a more sensitive detection of rotor eccentricity conditions and provides early warning for impending blade rubbing which is often undetectable in the vibration spectra.
A Study on the Flowfield of an Innovative Z-Flowpath Gas Turbine Combustor
Authors: Yu Zongming , Huang Yong , Wang Fang
Published: January 2011

Reverse flow combustors were widely used in small and micro gas turbine engines. The wall area of this type of combustors was quite large. And there were two flow turning points in their flow-path. Thus the wall cooling and main flow dilution were two intrinsic problems for them. Apart from that, their high pressure losses and heavy weight were also two problems which seriously deteriorate the performance of the engines. Moreover, their primary hole jets on opposite walls were non-symmetrical, which would affect the stability and intensity of the recirculation flows. In order to improve the combustion performance, a new conceptual Z-flowpath combustor was proposed. The new combustor consisted of two 45 degree yawing instead of returning in the main flow-path. The flowfield of the new combustor was predicted by the commercial code FLUENT, after a validation for the flowfield in a model reverse flow combustor with previous experimental results. The prediction showed that the flowfield of the primary zone in the Z-flowpath combustor was highly symmetrical, the size and the intensity of the recirculation zone were about 10 and 2 times greater than the normal reverse flow combustor, respectively, while the pressure loss and the total area of the flame tube wall of the Z-flowpath combustor were decreased dramatically to be 69.4% and 51% of that in the reverse flow combustor, respectively.