bluuebunny/crossref_metadata_2025 huggingface dataset:
The Relative Motion Between the Ball Guide and Slipper Retainer Within an Axial-Piston Swash-Plate Type Hydrostatic Pump
Authors: Manring Noah D.
Published: February 2008

The objectives of this research are to develop the equations that describe the relative motion between the ball guide and the slipper retainer within an axial-piston swash-plate type hydrostatic pump. Using a relationship between spherical and Cartesian coordinates, a contact point between the ball guide and the retainer is identified and matched for an observer on the ball guide and an observer on the retainer. Once a generic contact point is established, the position of a fixed particle on the ball guide is subtracted from the position of a particle on the retainer. The trajectory of this particle relative to the fixed particle on the ball guide is then used to describe the teardrop wear patterns that are expected to appear on the ball guide. These wear patterns are confirmed by experiments. Next, the velocity of a particle on the ball guide is subtracted from the velocity of a particle on the retainer at the contact point. Based upon this result it is shown that a relative velocity between the ball guide and the retainer is always maintained for a nonzero swash-plate angle and that the minimum relative velocity between the retainer and the ball guide may be increased by increasing one or all of the following: the design value of the retainer cone-angle, the radius of the ball guide, the operating speed of the pump, or the pump swash-plate angle.
Adaptive Control of a Class of Uncertain Dynamic Delay Systems
Authors: Oucheriah Said
Published: February 2008

A robust adaptive controller is developed for a class of uncertain linear dynamic delay-systems where the bound of uncertainty is unknown but its functional form is known. It is shown that if a constraint on the norm of the matrix associated with the delayed state is met, then the adaptive controller designed guarantees that all possible responses of the uncertain system are uniformly ultimately bounded. Finally, an example is included to illustrate the results developed in this paper.
Stability Robustness of Discrete-Time Singular Systems With Structured Parameter Perturbations
Authors: Chou Jyh-Horng , Chen Shinn-Horng , Zheng Liang-An
Published: February 2008

In this paper, the stability robustness of linear discrete-time singular systems with structured parameter perturbations is investigated. A new sufficient criterion is presented for ensuring that the linear discrete-time singular system remains regular, impulse-free, and asymptotically stable under structured parameter perturbations. The presented criterion is proved to be less conservative than the existing one reported recently.
A Reduced Order Time-Delay Control for Highly Simplified Brushless DC Motor
Authors: Chang Pyung H. , Park Suk-Ho , Lee Jung-Hoon
Published: February 2008

A reduced order time-delay control is derived and applied to the position control of a brushless DC motor with a highly simplified hardware configuration: use of six-step commutation without current control unit. In addition, the closed-loop stability has been analyzed by using the singular perturbation method. Throughout experimental studies, it is observed that reduced order time delay control effectively compensates for parameter variations and non-linearities, which a conventional PID control cannot handle with adequate performances. This result shows that reduced order time-delay control enables an economical design without compromising performance. More importantly, the example establishes a case that: a good control method can compensate for the hardware deficiency in a given plant, and as a result it even enables a simpler design of plants at the design stage.
Neural Network Design by Using Taguchi Method
Authors: Yang S. M. , Lee G. S.
Published: February 2008

One of the major difficulties in neural network applications is the selection of the parameters in network configuration and the coefficients in learning rule for fast convergence. This paper develops a network design by combining the Taguchi method and the back-propagation network with an adaptive learning rate for minimum training time and effective vibration suppression. Analyses and experiments show that the optimal design parameters can be determined in a systematic way thereby avoiding the lengthy trial-and-error.
On the Efficiency of Electric Power Generation With Piezoelectric Ceramic
Authors: Goldfarb Michael , Jones Lowell D.
Published: February 2008

This paper analyzes the efficiency of piezoelectric ceramic for purposes of electric power generation. An analytical model is presented which suggests that the primary problem of using PZT for electric power generation is that most energy is stored in the ceramic and returned to the mechanical port. The efficiency as a function of force input frequency and resistive load are derived based upon a linearized model of a commercially available PZT stack. The analysis yields counterintuitive results in that maximum efficiency occurs in a low frequency region, several orders of magnitude below the structural resonance of the stack. The analytical results are followed by presentation of experimental data that substantiate the model. The model is then utilized to show that, due to hysteresis in the ceramic, the efficiency of energy transfer is dependent on the amplitude of force input, and that greatest efficiencies can be achieved with maximum input forces.
The Control and Containment Forces on the Swash Plate of an Axial-Piston Pump
Authors: Manring Noah D.
Published: February 2008

In this research, the control and containment forces and moments acting on the swash plate of an axial-piston pump are examined. From a practical standpoint, swash plate control and containment devices take on many different designs; however, they must all resist the same essential moments and forces that attempt to dislocate the swash plate from its proper position. By considering the basic machine design without its control and containment mechanisms, this work generally derives the needed forces and moments for insuring proper swash-plate motion and thereby gives the designer of these machines a useful tool for designing control and containment devices of any type. The success of the actual control and containment devices will be measured by how well they exert the proper forces and moments on the swash plate which are presented here.
Modeling of Mechanical Systems Using Rigid Bodies and Transmission Line Joints
Authors: Krus Petter
Published: February 2008

Dynamic simulation of systems, where the differential equations of the system are solved numerically, is a very important tool for analysis of the detailed behavior of a system. The main problem when dealing with large complex systems is that most simulation packages rely on centralized integration algorithms. For large scale systems, however, it is an advantage if the system can be partitioned in such a way that the parts can be evaluated with only a minimum of interaction. Using transmission line models, with distributed parameters, physically motivated pure time delays are introduced in the communication between components. These models can be used to represent both lines in a hydraulic system and springs in mechanical systems. As a result, components and subsystems can be simulated more independently of each other. In this paper it is shown how flexible joints based on transmission line modeling (TLM) with distributed parameters can be used to simplify modeling of large mechanical link systems interconnected with other physical domains. Furthermore, it provides a straightforward formulation for parallel processing.
Friction Identification Using Evolution Strategies and Robust Control of Positioning Tables
Authors: Lee Seon-Woo , Kim Jong-Hwan
Published: February 2008

This paper presents an identification technique using evolution strategies (ES) for an integrated friction model of a positioning table. The friction model is based on Karnopp’s friction-velocity model with the rising static friction and spring-like property. Using the (μ + λ)-ES, the system parameters are identified with the experimental input and output data. The proposed control law consists of a conventional linear feedback control input, a friction compensation term and a sliding control input. The proposed control scheme can guarantee the stability of the overall system, even in the presence of the external disturbances and the modeling error between the real friction and the identified model. Experiments on an positioning table, called X-Y table, demonstrate the effectiveness of the proposed identification and control schemes.
Adaptive Sinusoidal Disturbance Rejection in Linear Discrete-Time Systems—Part II: Experiments
Authors: Ben Amara Foued , Kabamba Pierre T. , Ulsoy A. Galip
Published: February 2008

The problem of adaptive noise cancellation in an acoustic duct is discussed. An adaptive controller design approach based on parametrizing the set of stabilizing controllers using the Youla parametrization and tuning the Youla parameter to achieve regulation was presented in a companion paper [3]. Three controller adaptation algorithms are implemented to solve the noise cancellation problem in an acoustic duct. The experimental results indicate a mixed performance for each of the adaptation algorithms, with good performances observed only in some frequency ranges. The discrepancy between the expected and the observed performances is attributed to unmodeled nonlinearities in the speakers.
A Periodic Multirate Adaptive Pole Placer for Possibly Nonminimum Phase Plants
Authors: Arvanitis K. G.
Published: February 2008

A new indirect adaptive algorithm is derived for pole placement control of linear continuous-time systems with unknown parameters. The control structure proposed relies on a periodic controller, which suitably modulates the sampled output and discrete reference signals by a multirate periodically time-varying function. Such a control strategy allows us to assign the poles of the sampled closed-loop system to desired prespecified values, and does not make assumptions on the plant other than controllability, observability, and known order. The proposed indirect adaptive control scheme estimates the unknown plant parameters (and consequently the controller parameters) on-line, from sequential data of the inputs and the outputs of the plant, which are recursively updated within the time limit imposed by a fundamental sampling period T0. On the basis of the proposed algorithm, the adaptive pole placement problem is reduced to a controller determination based on the well-known Ackermann’s formula. Known indirect adaptive pole placement schemes usually resort to the computation of dynamic controllers through the solution of a polynomial Diophantine equation, thus introducing high order exogenous dynamics in the control loop. Moreover, in many cases, the solution of the Diophantine equation for a desired set of closed-loop eigenvalues might yield an unstable controller, and the overall adaptive pole placement scheme is then unstable with unstable compensators because their outputs are unbounded. The proposed control strategy avoids these problems, since here gain controllers are needed to be designed. Moreover, persistency of excitation and, therefore, parameter convergence, of the continuous-time plant is provided without making any assumption either on the existence of specific convex sets in which the estimated parameters belong or on the coprimeness of the polynomials describing the ARMA model, or finally on the richness of the reference signals, as compared to known adaptive pole placement schemes.
Dynamic Modeling of a Flexible Manipulator With Prismatic Links
Authors: Torby B. J. , Kimura I.
Published: February 2008

In this paper the equations of motion for a flexible multi-link manipulator are derived. Each link of the manipulator, including those with prismatic motion, is represented by two finite elements in three-dimensional space. The prismatic links are treated as beams with moving boundary conditions, and the position of finite-element node points are not changed relative to the link. The equations are generated using Maple V, and the paper discusses a general approach for eliminating small terms. A sample calculation is performed for a RRP (Stanford arm) manipulator, and the shift of natural frequencies with time are plotted. Results are compared to those obtained by the assumed-mode method.
Tracking Control of a Software Cam Machining System
Authors: Tsai Mi-Ching , Lee Yaw-Hwei
Published: February 2008

This paper presents a software cam manufacturing system. It includes a position tracking control system, a programmable cam profile, and a programmable variable angular velocity profile. The position tracking system consists of a rotary direct drive (DD) servo motor and a linear servo-motor. The rotary DD servo-motor is controlled to track the variable angular velocity profile, while the linear servo-motor is controlled to synchronously track the desired cam profile. Such a tracking control system is proposed to achieve a constant removal rate for fine machining (i.e., the relative tangential velocity at the contact point should be constant). A numerical method for off-line derivation of the variable angular velocity profile with respect to the desired cam profile is developed to achieve constant relative tangential velocity at the contact point. An experimental tracking control system with two servo controllers is developed to study the feasibility of this approach.
An H∞ Formulation of Quantitative Feedback Theory
Authors: Zhao Yongdong , Jayasuriya Suhada
Published: February 2008

The QFT robust performance problem in its entirety may be reduced to an H∞ problem by casting each specification as a frequency domain constraint either on the nominal sensitivity function or the complementary sensitivity function. In order to alleviate the conservative nature of a standard H∞ solution that is obtainable for a plant with parametric uncertainty we develop a new stability criterion to replace the small gain condition. With this new stability criterion it is shown that the existence of a solution to the standard H∞ problem guarantees a solution to the QFT problem. Specifically, we provide an explicit characterization of necessary frequency weighting functions for an H∞ embedding of the QFT specifications. Due to the transparency in selecting the weighting functions, the robust performance constraints can be easily relaxed, if needed, for the purpose of assuring a solution to the H∞ problem. Since this formulation provides only a sufficient condition for the existence of a QFT controller one can then use the resulting H∞ compensator to initiate the QFT loop shaping step.
Vehicle Steering Intervention Through Differential Braking
Authors: Pilutti Tom , Ulsoy Galip , Hrovat Davor
Published: February 2008

This paper examines the usefulness of a brake steer system (BSS) which uses differential brake forces for steering intervention in the context of Intelligent Transportation Systems. The resulting moment on the vehicle affects yaw rate and lateral position, thereby providing a limited steering function. The steering function achieved through BSS can then be used to control lateral position in an unintended road departure system. Control design models for the vehicle and the brake system are presented. A state feedback regulator and PID controller are developed to explore BSS feasibility and capability. Computer simulation results, using a nonlinear seven degree-of-freedom vehicle model are included, and show the feasibility and limitations of BSS.
Position Control of Flexible Robot Arms Using Mechanical Waves
Authors: O’Connor William , Lang Donogh
Published: February 2008

A novel position control strategy for flexible robot arms based on wave propagation and absorption techniques is presented. The arm is modeled by a lumped-parameter mass-spring system with an actuator at one end and a load mass at the other. The actuator is required to position the remote load and, simultaneously, to provide active vibration damping. It does so by propagating mechanical waves through the system and absorbing reflected waves. Only the first two masses and springs need to be characterized and observed to determine the required actuator movement. The control algorithm is robust and compares very favorably with the time-optimal performance of bang-bang control. It is also inherently adaptive.
Algorithm for Approximate Model Matching for Loops With Non-Negligible Feedback Dynamics
Authors: Aguirre Luis Antonio
Published: February 2008

This paper develops a new algorithm to solve the model matching problem in cases where the feedback dynamics should be taken into account in the design of the closed-loop system. One of the main features of the new method is that the matching is carried out by moment matching and is therefore approximate. The new algorithm is computationally simple and it permits the designer to choose relatively simple structures for the reference model and the controller. Numerical examples are included to illustrate the new approach.
An Algorithm for Time-Optimal Control Problems
Authors: Fotouhi-C. Reza , Szyszkowski Walerian
Published: February 2008

A numerical procedure to compute nonsingular, time-optimal solutions for nonlinear systems, which have fixed initial and final states, and are linear and bounded in control, is presented. Using the Pontryagin’s Minimum Principle, the corresponding nonlinear two-point boundary-value problem is formulated and solved by combination of the forward-backward and the shooting methods. The forward-backward procedure generates a good guess of the initial costates, which is crucial for the convergence of the shooting method. Numerical example of a two-link manipulator illustrates the proposed approach and the convergence of the procedure.
A Suboptimal N-Step-Ahead Cautious Controller for Adaptive Control Applications
Authors: Shi Jianjun , Apley Daniel W.
Published: February 2008

If there is little a priori knowledge of the plant parameters, the performance of certainty equivalence based adaptive controllers during the transient period, before the parameter estimates have converged, is usually less than adequate. This paper introduces a new suboptimal loss function with an N-step-ahead prediction horizon, similar in principle to standard predictive control loss functions, for adaptive control applications. However, the new loss function is modified so that the resulting control law possesses caution in the sense that the uncertainty in the parameter estimates is taken into account automatically. As such, the cautious controller achieves more robust performance than the corresponding certainty equivalence controller during the transient period when there is large uncertainty in the parameter estimates. The new cautious controller has a closed-form solution that involves only slightly more computational expense than the corresponding certainty equivalence predictive controller.
State Observer for Linear Time-Invariant Systems With Quantized Output
Authors: Sur Joono , Paden Brad E.
Published: February 2008

In this paper we introduce a state observer for linear time-invariant systems with quantized outputs. The observer employs an orthogonal projection operation at quantizer output discontinuities to enhance its convergence rate for stable systems. The increasing rate of convergence and stability has been proven by using Lyapunov second method. Some sufficient and necessary conditions of stability for the unstable systems are derived. The sufficient condition of noise stability is given and the maximal bound of noise stability is presented. The proposed methodology has been applied to state estimation of a DC-motor with optical encoder.
Comparative Evaluation of Combined Cycles and Gas Turbine Systems With Water Injection, Steam Injection, and Recuperation
Authors: Bolland O. , Stadaas J. F.
Published: February 2008

Combined cycles have gained widespread acceptance as the most efficient utilization of the gas turbine for power generation, particularly for large plants. A variety of alternatives to the combined cycle that recover exhaust gas heat for re-use within the gas turbine engine have been proposed and some have been commercially successful in small to medium plants. Most notable have been the steam-injected, high-pressure aeroderivatives in sizes up to about 50 MW. Many permutations and combinations of water injection, steam injection, and recuperation, with or without intercooling, have been shown to offer the potential for efficiency improvements in certain ranges of gas turbine cycle design parameters. A detailed, general model that represents the gas turbine with turbine cooling has been developed. The model is intended for use in cycle analysis applications. Suitable choice of a few technology description parameters enables the model to represent accurately the performance of actual gas turbine engines of different technology classes. The model is applied to compute the performance of combined cycles as well as that of three alternatives. These include the simple cycle, the steam-injected cycle, and the dual-recuperated intercooled aftercooled steam-injected cycle (DRIASI cycle). The comparisons are based on state-of-the-art gas turbine technology and cycle parameters in four classes: large industrial (123–158 MW), medium industrial (38–60 MW), aeroderivatives (21–41 MW), and small industrial (4–6 MW). The combined cycle’s main design parameters for each size range are in the present work selected for computational purposes to conform with practical constraints. For the small systems, the proposed development of the gas turbine cycle, the DRIASI cycle, are found to provide efficiencies comparable or superior to combined cycles, and superior to steam-injected cycles. For the medium systems, combined cycles provide the highest efficiencies but can be challenged by the DRIASI cycle. For the largest systems, the combined cycle was found to be superior to all of the alternative gas turbine based cycles considered in this study.
High-Temperature Coatings for Protection Against Turbine Deterioration
Authors: Tabakoff W. , Metwally M. , Hamed A.
Published: February 2008

In this research, an investigation was conducted to study the fly ash particles associated with the erosion behavior of alloys and coatings that are widely used in gas and steam turbines. The erosion behavior of many alloys and protective coatings has been investigated experimentally at high temperatures using a specially designed wind erosion tunnel. The erosion results show the effect of velocity, temperature, and impact angle on the erosion rate.
Processing Methods for High Reliability Silicon Nitride Heat Engine Components
Authors: Pujari V. K. , Tracey D. M.
Published: February 2008

The paper discusses highlights of a silicon nitride processing methodology that has been developed in the course of a major four-year DoE funded program in processing for reliability. The program focused on the attainment of high strength and reliability through the identification and subsequent control of strength-degrading flaws introduced during processing unit operations. Process control and NDE methods applied to achieve an optimized process with the potential to produce high-reliability advanced heat engine components are discussed. Concluding remarks are directed to the extensive tensile strength database that has been generated through testing of over 300 tensile rods produced by the optimized process.
Exploring How Shroud Constraint Can Affect Vibratory Response in Turbomachinery
Authors: Yang M.-T. , Griffin J. H.
Published: February 2008

Unusual resonant responses were observed during spin pit tests of shrouded blades. The unusual behavior consisted of blades that exhibited strong response over a broad range of frequencies. The frequencies of peak resonance were considerably lower than predicted and were also lower than those observed in other tests of nominally identical wheels. In addition, the tracking plots of blade amplitudes versus frequency were truncated rather than displaying the usual sharp peaks seen in other tests. The unusual response is potentially dangerous since high vibratory response could be excited over a broad range of operating speeds. The blades were designed to be free standing with gaps of approximately 0.25 mm between neighboring shrouds. It is hypothesized that shroud contact at the blade tips could cause the unusual vibratory response. A simple model of a blade with shroud contact is developed in order to determine if shroud contact could cause blades to vibrate in the observed manner. The model is unusual in that it seeks to explore how contact could cause the blade to respond at lower (rather than higher) frequencies since contact typically increases the constraints on a structure and raises its natural frequencies.
Blade Erosion in Automotive Gas Turbine Engine
Authors: Metwally M. , Tabakoff W. , Hamed A.
Published: February 2008

In this work, a study has been conducted to predict blade erosion and surface deterioration of the free power turbine of an automotive gas turbine engine. The blade material erosion model is based on three-dimensional particle trajectory simulations in the three-dimensional turbine flow field. The particle rebound characteristics after surface impacts were determined from experimental measurements of restitution ratios for blade material samples in a particulate flow tunnel. The trajectories provide the spatial distribution of the particle impact parameters over the blade surfaces. A semi-empirical erosion model, derived from erosion tests of material samples at different particulate flow conditions, is used in the prediction of blade surface erosion based on the trajectory impact data. The results are presented for the three-dimensional particle trajectories through the turbine blade passages, the particle impact locations, blade surface erosion pattern, and the associated erosion parameters. These parameters include impact velocity, impact angle, and impact frequency. The data can be used for life prediction and performance deterioration of the automotive engine under investigation.
The Performance Optimization of a Gas Turbine Cogeneration/Heat Pump Facility With Thermal Storage
Authors: von Spakovsky M. R. , Curti V. , Batato M.
Published: February 2008

With the push for greater energy conservation, the need for heating and/or power production is being filled by cogeneration facilities. Thus, the search for the best performance at the least cost for such multipurpose plants is made much more difficult by the fact that such facilities must meet differing goals or demands. Such a facility exists at the E´cole Polytechnique Fe´de´rale de Lausanne (EPFL) and has been studied in order to find the optimum modes of operation as a function of time for variations in both the heating and electrical demands this facility must meet. The results of this study are presented here. The plant itself provides heat and electricity for both the EPFL and the University of Lausanne and is projected to supply electricity to the exterior utility grid provided it can be shown to be economically viable. The plant’s primary components include two gas turbines, a heat recovery system, two heat pumps, a set of heat storage tanks, and both medium and low-temperature district heating networks. In order to find the optimum mode of operation, a mixed-integer linear programming approach was used, which balances the competing costs of operation and minimizes these costs subject to the operational constraints placed on the system. The effects of both the cost of the fuel and the costs of electricity sold and bought on the best performance of the system are evaluated. In addition, the important features of the modeling process are discussed, in particular the heat storage tanks, which complicate the optimization of the series of steady-state models used to model the overall quasi-steady-state behavior of the system.
Simulating Indirect Thrust Measurement Methods for High-Bypass Turbofans
Authors: Stevenson J. D. , Saravanamuttoo H. I. H.
Published: February 2008

As yet, there is no known reliable method for directly measuring the thrust of a turbofan in flight. Manufacturers of civil turbofans use various indirect thrust measurements to indicate performance of an engine to the flight deck. Included among these are: Engine Pressure Ratio (EPR), Integrated Engine Pressure Ratio (IEPR), Fan mechanical speed (N1), and various Turbine Gas Temperatures such as ITT or EGT. Of key concern is whether these thrust indicators give an accurate account of the actual engine thrust. The accuracy of these methods, which is crucial at take-off, may be compromised by various types of common engine deterioration, to the point where a thrust indicator may give a false indication of the health and thrust of the engine. A study was done to determine the effect of advanced engine cycles on typical values of these parameters. A preliminary investigation of the effects of common kinds of turbofan deterioration was conducted to see how these faults can affect both actual engine performance and the indirect thrust indicators.
Multi-objective Optimization in Unit Sizing of a Gas Turbine Cogeneration Plant
Authors: Yokoyama R. , Ito K.
Published: February 2008

An optimal planning method for cogeneration plants proposed earlier is extended to the case with multiple optimization criteria. Equipment capacities and utility maximum demands are determined so as to minimize both the annual total cost and the annual primary energy consumption in consideration of plants’ operational strategies for energy demand requirements. This problem is considered as a multi-objective optimization one, and a discrete set of Pareto optimal solutions is derived numerically by the weighting method. Through a numerical study on a simple cycle gas turbine cogeneration plant used for district heating and cooling, a trade-off relationship between the economic and energy-saving properties is clarified.
Optimal Operation of Cogeneration Plants With Steam-Injected Gas Turbines
Authors: Ito K. , Yokoyama R. , Matsumoto Y.
Published: February 2008

The effect of introducing steam-injected gas turbines into cogeneration plants is investigated from economical and energy-saving aspects on the basis of a mathematical programming approach. An optimal planning method is first presented by which the operational strategy is assessed so as to minimize the hourly running cost. Then, a case study is carried out on a plant used for district heating and cooling. Through the study, it is ascertained that the proposed method is a useful tool for the operational planning of steam-injected gas turbine plants, and that these plants can be attractive from economical and energy-saving viewpoints as compared with both simple-cycle gas turbine plus waste heat boiler plants and conventional energy supply ones.
The Design, Selection, and Application of Reciprocating Compressors for Fuel Gas Service
Authors: Hough D.
Published: February 2008

This paper describes the design and application of reciprocating compressors for fuel gas service. In fuel gas services and particularly power generation it is important to minimize all parasitic losses. Efficiency over a range of operating conditions requires sophisticated control systems and the paper describes the merits of each system and their effect on operating cost. Some of the important operational considerations are described together with major design features. The use of staging and the advantages of a modular approach to compressor design are also covered, which demonstrates the suitability of the reciprocating compressor for fuel gas service particularly when variation of inlet conditions cannot be avoided.
Mathematical Modeling of an Annular Gas Turbine Combustor
Authors: Sokolov K. Y. , Tumanovskiy A. G. , Gutnik M. N. , Sudarev A. V. , Zakharov Y. I. , Winogradov E. D.
Published: February 2008

A mathematical model for the description of axisymmetric swirled flow with diffusion combustion is based on numerical solution of the Reynolds equation with a k–W model of turbulence. The results of numerical and experimental investigations of local and general characteristics of flow, heat and mass transfer, combustion, and NOx formation in an annular combustor with opposite swirled air jets are presented. Satisfactory agreement between calculations and experiments is obtained. The dependences of combustor characteristics versus geometric and operational parameters are generalized.
Thermodynamic Heating With Various Types of Cogeneration Plants and Heat Pumps
Authors: Stachel K. , Frutschi H. U. , Haselbacher H.
Published: February 2008

The thermodynamic heating method combines cogeneration power plants and heat pumps in order to maximize the heating energy that can be derived from a given amount of fuel. In doing this, unnecessary waste of primary energy and environmental damage can be prevented. In this paper, four cogeneration systems—combined cycle plants, steam and gas turbine power plants, and gas engines—and heat pump systems are investigated and compared with respect to fuel utilization for realistic site conditions. It is shown that the combined cycle cogeneration power plant is superior to the other three types of power plant.
Numerical Investigation of Enhanced Dilution Zone Mixing in a Reverse Flow Gas Turbine Combustor
Authors: Crocker D. S. , Smith C. E.
Published: February 2008

An advanced method for dilution zone mixing in a reverse flow gas turbine combustor was numerically investigated. For long mixing lengths associated with reverse flow combustors (X/H > 2.0), pattern factor was found to be mainly driven by nozzle-to-nozzle fuel flow and/or circumferential airflow variations; conventional radially injected dilution jets could not effectively mix out circumferential nonuniformities. To enhance circumferential mixing, dilution jets were angled to produce a high circumferential (swirl) velocity component. The jets on the outer liner were angled in one direction while the jets on the inner liner were angled in the opposite direction, thus enhancing turbulent shear at the expense of jet penetration. Three-dimensional CFD calculations were performed on a three-nozzle (90 deg) sector, with different fuel flow from each nozzle (90, 100, and 110 percent of design fuel flow). The computations showed that the optimum configuration of angled jets reduced the pattern factor by 60 percent compared to an existing conventional dilution hole configuration. The radial average temperature profile was adequately controlled by the inner-to-outer liner dilution flow split.
Influence of Hardware Design on the Flow Field Structures and the Patterns of Droplet Dispersion: Part I—Mean Quantities
Authors: Wang H. Y. , McDonell V. G. , Samuelsen S.
Published: February 2008

In a gas turbine engine combustor, performance is likely tied to the spatial distribution of the fuel injected into the dome. The GE/SNECMA CFM56 combustor swirl cup is one example of a design established to provide a uniform presentation of droplets to the dome. The present study is part of a series to detail the dispersion of droplets in practical hardware, and to assess the effect of isolated parameters on the continuous- and dispersed-phase distributions. In this study, the influence of the swirling air outlet geometry is evaluated relative to the effect on the flow field structures and the patterns of droplet dispersion. This is accomplished by comparing the continuous-phase (air in the presence of a spray) and dispersed-phase (droplets) behavior downstream of the swirl cup assembly outfitted with two different conical expansions (“flares”). One features a narrow expansion angle, the other possesses a wide expansion angle. Two-component phase-Doppler interferometry was employed to provide the information of droplet size and velocity components as well as continuous-phase velocity components. Photographs of light scattered by droplets from a laser sheet were used for the study of flow field structures. This study reveals that (1) the air stream issued from the narrow flare remains close to the centerline and expands gradually downstream while the air stream issued from the wide flare expands immediately downstream of the swirl cup, and (2) the narrow flare provides weaker droplet dispersion, slower decay of droplet velocities, and finer droplet sizes compared to the wide flare. The results demonstrate that a relatively modest change in flare geometry can create a significant change in the structure of both the continuous and dispersed phases.
Temperatures in a Gas Turbine Vaporizer at Near Idle Engine Conditions
Authors: Vaskopulos T. , Polymeropoulos C. E. , Sernas V.
Published: February 2008

The work is a laboratory investigation of the effect of different liquids and liquid flow rates on the metal temperature of a gas turbine T vaporizer. Most of the experimentation was carried out using JP5. A limited number of runs using Diesel Fuel Marine and calibration runs using water provided additional data for different fluids. Conditions that approach local liquid depletion inside the vaporizer were identified by monitoring local overheating of the vaporizer metal. Because of apparatus limitations, testing was carried out only at vaporizer pressure and liquid flow rates approaching idle engine operation. An experimental correlation was developed allowing estimation of the mean vaporizer temperature as a function of input conditions and fluid properties.
A New Approach to the Challenge of Machinery Prognostics
Authors: Hansen R. J. , Hall D. L. , Kurtz S. K.
Published: February 2008

Current generation mechanical diagnostic equipment is designed to identify individual events or trends in the output of sensors mounted on a mechanical component, subsystem, or system. Such equipment can provide a useful indication that a failure condition may be developing, but it cannot provide reliable predictions of the remaining safe or operational life. Typically, these diagnostic systems simply compare the output of individual sensors against a priori thresholds to establish a measure of the system’s health. Two problems result from this approach: (1) There is no advantage taken of possible synergy among the sensors, i.e., the determination of health is one dimensional; and (2) the diagnosis provides only a statement regarding the current equipment health, but does not provide a prediction of the time remaining to failure. This often leads to an operational environment in which diagnostic equipment outputs are either ignored because of frequent false alarms or frequent (and costly) time-based preventive maintenance is performed to avoid hazardous failures. This paper describes a new approach to the development of a more robust diagnosis and prognostic capability. It is based on the fusion of sensor-based and model-based information. Sensor-based information is the essence of current diagnostic systems. Model-based information combines dynamic models of individual mechanical components with micromechanical models of relevant failure mechanisms, such as fracture and crack propagation. These micromechanical models must account for initial flaw size distribution and other microstructural parameters describing initial components condition. A specific application of this approach is addressed, the diagnosis of mechanical failure in meshing gears. Four specific issues are considered: (a) how to couple a validated numerical simulation of gear transmission error (due to tooth spacing irregularity, contour irregularity, or material inhomogeneity) with physically and empirically based descriptions of fatigue crack growth to predict a failure precursor signature at the component level; (b) how to predict the manifestation of this signature at the subsystem or system level where sensors are located; (c) how to fuse this model-based information with the corresponding sensor-based information to predict remaining safe or operational life of a gear; and (d) issues associated with extending this methodology to bearings and other rotating machinery components.
Improved Method for Flame Detection in Combustion Turbines
Authors: Roby R. J. , Hamer A. J. , Johnson E. L. , Tilstra S. A. , Burt T. J.
Published: February 2008

A fast response chemiluminescent flame detection approach is presented along with field test results from a fiber optic based flame detector device. Chemiluminescence, the light given off by molecules formed in their excited states, has long been recognized as a diagnostics method for use in combustion. The recent advent of higher quality optical fibers with improved transmission properties in the UV, as well as UV optical detectors, has made the use of chemiluminescence for gas turbine diagnostics and monitoring practical. Advances in combustor designs on new low-emissions machines as well as reliability issues with some existing machines are creating the need for improved flame dynamics measurements as well as improvements in reliability for existing measurements such as combustor flame detection. This paper discusses the technology, principle of operation, and detectors that operate on the chemiluminescence principle.
A Scanning Radiation Thermometry Technique for Determining Temperature Distribution in Gas Turbines
Authors: De Lucia M. , Masotti G.
Published: February 2008

A scanning radiation thermometry technique for determining temperature distributions in gas turbines is presented. The system, an enhancement of an earlier work, can be used by operators even without special training, since the temperature distribution is measured and corrected in terms of the error due to the reflected radiation only on the basis of the turbine’s known geometry and the physical properties of the materials. In the proposed model, the surface-exitent radiances are directly acquired via 360-deg scans. Experimental testing was performed on a static turbine-blading model. Since the angle factors emerged as a notable influence on the accuracy of the model, two angle factor calculation methods, selected for suitability from a literature survey, are exhaustively investigated, and their selection criteria defined.
Load Control–Strain Control Isochronous Stress–Strain Curves for High Temperature Nonlinear Analysis
Authors: Bechtel G. S. , Cook T. S.
Published: February 2008

Aircraft gas turbine components are subjected to severe operating conditions. High temperatures, large thermal strains, and mechanical loads combine to cause the material to undergo significant nonlinear behavior. In order to assure safe, durable components, it is necessary that analysis methods be available to predict the nonlinear deformation. General purpose finite element codes are available to perform elastic and viscoplastic analyses, but the analyses are expensive. Both large plastic and creep strain analyses can require significant computer resources, but typically a plastic solution is more economical to run than a time-stepping creep or viscoplastic model solution. For those applications where the deformation is principally time dependent, it is advantageous to include time-dependent creep effects in a “constant time” or “isochronous” analysis. Although this approach has been used in the past to estimate rupture life, this paper will present several significant new techniques for doing an isochronous analysis to analyze time-dependent deformation.
Experimental Investigation of Thermoelastic Deformation in Turbojet-Engine Bearings Under Maintenance Inspection
Authors: Kochevar A. J. , Bert C. W.
Published: February 2008

The present investigation examined the vertical and horizontal thermoelastic changes in the outside diameter of a turbojet-engine roller bearing. Thermal loads were imparted to the bearing by the hands of a bearing technician during a rework operation. A worst-case analysis was examined by assuming a three-minute dwell time and diametrically symmetric thermal loading. Contact temperature was experimentally determined and used in conjunction with a numerical model to simulate thermal propagation throughout the bearing outer ring. Diametric deflection data, obtained using the contact temperature in conjunction with analytic and finite elements, have been shown for comparative purposes. Experimental diametric expansions of the bearing outer ring were determined and compared with the predicted results. Assuming a worst-case scenario, this investigation yielded vertical expansions in the bearing outer ring’s diameter, which would be problematic for some bearings during the rework operation; appropriate corrective action was discussed.
Numerical Analysis of Nozzle and Afterbody Flow of Hypersonic Transport Systems
Authors: Esch T. , Giehrl M.
Published: February 2008

Using an implicit Finite-Volume Navier–Stokes code, the flow field in a Single Expansion Ramp Nozzle (SERN) for a hypersonic aircraft is studied. Comparisons between experimental data and CFD calculations for certain components of the integrated exhaust system (cold two-dimensional nozzle flow, high temperature reacting three-dimensional combustion chamber flow, and two-dimensional nozzle flow with external flow) are presented. To show the sensitivity of the considered components to off-design operating conditions, comprehensive numerical studies have been carried out. For the determination of nozzle performance a detailed two-dimensional analysis from transonic to hypersonic flight Mach numbers has been performed. A direct optimization method has been used to investigate the influence of the lower nozzle flap shape on the thrust vector.
Thermal Stability and Heat Transfer Characteristics of Methane and Natural Gas Fuels
Authors: Chin D. , Hermanson J. C. , Spadaccini L. J.
Published: February 2008

The thermal decomposition and heat transfer characteristics of gaseous, high-purity methane, several methane–hydrocarbon mixtures, and a typical natural gas fuel were evaluated using an electrically heated, stainless-steel tube test apparatus. Of several candidate heat transfer correlations, the Dittus–Boelter heat transfer correlation provided the best fit of the methane heat transfer data over the range of Reynolds numbers 10,000 to 215,000. The thermal stability (i.e., deposit formation) characteristics of the methane–hydrocarbon mixtures and the natural gas fuel were established and compared with the deposition characteristics of high-purity methane. Testing was conducted at wall temperatures up to 900 K (fuel temperatures to 835 K) for durations of up to 60 hours. Measurements of deposit mass indicated that there was essentially no deposit buildup for wall temperatures below 650 K. Deposit began to form at wall temperatures between 650 K and 775 K. Above 775 K, there was a rapid monotonic increase in deposition. The data suggest that the use of high-purity methane instead of natural gas at temperatures above 775 K could reduce the deposit thickness under similar operating conditions by as much as a factor of three, or permit operation at correspondingly higher temperatures.