bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of Linear Parameter-Varying Systems Using Nonlinear Programming
Authors: Lee Lawton H. , Poolla Kameshwar
Published: February 2008

This paper deals with the identification of a linear parameter-varying (LPV) system whose parameter dependence can be written as a linear-fractional transformation (LFT). We formulate an output-error identification problem and present a parameter estimation scheme in which a prediction error-based cost function is minimized using nonlinear programming; its gradients and (approximate) Hessians can be computed using LPV filters and inner products, and identifiable model sets (i.e., local canonical forms) are obtained efficiently using a natural geometrical approach. Some computational issues and experiences are discussed, and a simple numerical example is provided for illustration.
On Transmission Zeros of Mass-Dashpot-Spring Systems
Authors: Lin Jong-Lick
Published: February 2008

For a noncollocated mass-dashpot-spring system with B=CTΓ, a novel approach is proposed to gain a better insight into the fact that none of its transmission zeros lie in the open right-half of the complex plane. In addition, the transmission zeros have physical meanings and will simply be the natural frequencies of a substructure constrained in the equivalently transformed system. Moreover, it is also shown that transmission zeros interlace with poles along the imaginary axis for a mass-spring system with B=CTΓ. They also interlace with poles along the negative real axis for a mass-dashpot system with B=CTΓ. Finally, two examples are used to illustrate the interlacing property.
A Worst-Case Evaluation Method for Dynamic Systems
Authors: Ma Wen-Hou , Peng Huei
Published: February 2008

A worst-case evaluation method is presented in this paper. The objective of this method is to identify worst-case disturbances so that the performance of dynamic systems under extreme conditions can be evaluated. Depending on the dynamics and information structure of the system, the worst-case evaluation problems are classified into four cases. Classical optimal control and game theories are used to construct algorithms to obtain linear solutions analytically. Numerical schemes to solve nonlinear worst-case problems are also presented. Two case study examples are then presented—a truck rollover problem and a vehicle stability controller evaluation problem. In both cases, a combined analytical-numerical method is used. The nonlinear plant is first linearized. The analytical solution of the linearized plant is then used as the initial guess for the numerical scheme. The final worst-case disturbance is then obtained iteratively from the numerical scheme. It was found that the proposed worst-case evaluation method is able to produce much larger unwanted plant motions (roll/side slip in the two case studies) compared with traditional evaluation maneuvers.
On-Off Control With Specified Fuel Usage
Authors: Singhose William , Singh Tarunraj , Seering Warren
Published: February 2008

A method for generating on-off command profiles for flexible systems is presented. The command profiles move a system without residual vibration while using a specified amount of actuator fuel. Robustness to modeling errors can be incorporated into the design of the command signals. Techniques are presented that facilitate implementation and indicate prudent choices for the amount of fuel to be used. The method is compared to other command generation techniques that balance fuel usage and slew time.
Minimum Time Trajectory Optimization and Learning
Authors: Sadegh N. , Driessen B.
Published: February 2008

This paper presents a numerical algorithm for finding the bang-bang control input associated with the time optimal solution of a class of nonlinear dynamic systems. The proposed algorithm directly searches for the optimal switching instants based on a projected gradient optimization method. It is shown that this algorithm can be made into a learning algorithm by using on-line measurements of the state trajectory. The learning is shown to have the potential for significant robustness to mismatch between the model and the system. It learns a nearly optimal input through repeated trials in which it utilizes the measured terminal state error of the actual system and gradients based on the theoretical state equation of the system but evaluated along the actual state trajectory. The success of the method is demonstrated on an underactuated double pendulum system called the acrobot.
An Approach to Control Input Shaping With Application to Coordinate Measuring Machines
Authors: Jones Steven D. , Ulsoy A. Galip
Published: February 2008

Dimensional measurements obtained with Coordinate Measuring Machines (CMMs) are negatively affected by self-induced structural vibrations. In this paper, a control strategy that reduces the structural vibrations in a CMM is outlined and experimentally demonstrated. The control strategy, designated the Feedforward Filter, is developed by establishing the relationship between contemporary controller input shaping techniques and traditional notch filtering methods. Issues on both robustness and multiple mode vibrations are addressed. Controller input development takes place in the discrete time domain. This method provides results identical to those for optimal command input preshaping obtained through non-linear programming methods and requires considerably less computational effort. Experimental results show a 50 percent reduction in the peak-to-peak magnitude of structural vibrations as compared to unshaped bang-bang trajectories.
A Study on Sliding Mode State Estimation
Authors: Choi Jin-Hee , Misawa Eduardo A. , Young Gary E.
Published: February 2008

The design of sliding observers is discussed in the paper. The sliding observer is shown to have a simple structure and to be robust with respect to bounded nonlinearities and uncertainties. The Lyapunov-like stability method is used to investigate the stability of sliding observers without assuming the matching condition and a computer-aided design methodology is suggested. A numerical example based on an inverted pendulum with moving support is used to illustrate the proposed design methodology.
Coulomb Friction Limit Cycles in Elastic Positioning Systems
Authors: Bonsignore A. , Ferretti G. , Magnani G.
Published: February 2008

The state space control of a positioning system affected by torsional elasticity at the gearbox is considered, using a motor position transducer only. An output feedback, pole placement controller is used, with an additional integral action on the tracking error to cancel it at steady state. Both experiments and simulations point out that large oscillations may appear for some sets of closed-loop poles which yields, in contrast to stick-slip cycles, instantaneous motor velocity reversals. It is shown that such oscillations are induced by “pure” Coulomb friction. The period of the oscillations is predicted precisely following the Tsypkin’s relay control theory and also by the approximate describing function method. The latter also allows understanding of how oscillations depend on observer and feedback control design and on plant parameters; thus we are able to derive guidelines for the design of an oscillation free closed-loop system.
Simultaneous Stabilization and Pole Assignment by Two Level Controllers Consisting of a Gain Feedback and a Multirate Input Controller
Authors: Araki Mituhiko , Fukumitsu Ken’ichi , Hagiwara Tomomichi
Published: February 2008

A method of simultaneous pole assignment of a finite number of plant models is studied. Extending the idea of multi-structured multirate sampled-data controllers proposed in our previous work, this paper proposes a new method where a continuous-time gain feedback controller instead of a multirate sampled-data controller is used as the “internal structure.” By the proposed method, the plants precompensated by the internal structure can generally be made to satisfy an existing sufficient condition for simultaneous pole-assignability, and hence the class of the plant models for which simultaneous pole assignment can be attained becomes wider than that by the previous results. In particular, simultaneous pole assignment becomes possible for any finite number of plant models, provided that each model is controllable and observable.
Robust Damage-Mitigating Control of Mechanical Systems: Experimental Validation on a Test Apparatus
Authors: Zhang Hui , Ray Asok
Published: February 2008

The goal of damage-mitigating control is to achieve high performance of operating machinery without overstraining the mechanical structures and the potential benefit is an increase in the component service life with no significant loss of performance. This paper presents the design of a test apparatus, the synthesis of a damage-mitigating control system, and the results of experimentation where the objective is to demonstrate the concept of fatigue damage reduction as an extension of multivariable robust feedback control. The test apparatus is built upon a three-degree-of-freedom, two-input three-output mechanical structure. The methodology of the damage-mitigating control synthesis is built upon the principles of: (i) frequency-domain identification of the plant dynamics and modeling of uncertainties in the state-space setting; and (ii) robust control based on the H∞ approach by taking both plant dynamic performance and material degradation of structural components into consideration. Case studies on the test apparatus indicate that fatigue life of specimens can be substantially extended with no appreciable degradation in the dynamic performance of the mechanical system.
The Use of Multibody System Modeling and Multivariable System Decoupling Techniques in Vehicle Ride Control
Authors: Cherry A. S. , Jones R. P. , Potter T. E. C.
Published: February 2008

This paper describes the use of realistic analytical techniques to address automotive ride control. Multibody system (MBS) modeling techniques were used to develop a full vehicle model with suspension system representation, which was subsequently validated against experimental data. The resultant multivariable ride control problem was then decoupled in the frequency domain by the application of equivalence transformation techniques. It is shown that diagonalization can be achieved for the range of primary ride frequencies, and that the decoupled system then consists of three single-input/single-output (SISO) systems, one for each of the sprung mass modes. Finally, feedback control design for each sprung mass mode loop is illustrated by the application of modal damping.
Combined Braking and Cornering Limits as Related to Automobile Tire Marks
Authors: Smith Gregory C. , Bready Jon E. , Smith Craig C.
Published: February 2008

A four-tire quasi-steady state vehicle model is set forth utilizing the well-known friction circle model for each tire, and incorporating vehicle and roadway geometry, weight shift, and brake force distribution. The model equations are nondimensionalized for general applicability. A normalized chart defining limits of braking and cornering for a particular automobile is presented.
Catastrophes in Optimal Control
Authors: Nwokah Osita D. I. , Borzova E. , Happawana Gemunu S. , Afolabi Dare´
Published: February 2008

System optimization over a parameter space produces optimal solutions which lie on the bifurcation set of the ambient space. As such, the optimality (quality) metric (as a function of the parameters) is highly sensitive to the parameters, to the point of inducing instability for differential parameter variations. Singularities in this function diffeomorphically induce corresponding degenerate singularities in the optimal closed-loop characteristic polynomials, which serves as a signature for potential catastrophic loss of quality that is most easily exhibited by the resulting dynamic instability. In this paper, we examine the loss of quality in H∞ and related optimal systems via these diffeomorphic degenerate closed-loop poles.
Pointwise Optimal Control of Dynamical Systems Described by Constrained Coordinates
Authors: Radisavljevic V. , Baruh H.
Published: February 2008

A feedback control law is developed for dynamical systems described by constrained generalized coordinates. For certain complex dynamical systems, it is more desirable to develop the mathematical model using more general coordinates then degrees of freedom which leads to differential-algebraic equations of motion. Research in the last few decades has led to several advances in the treatment and in obtaining the solution of differential-algebraic equations. We take advantage of these advances and introduce the differential-algebraic equations and dependent generalized coordinate formulation to control. A tracking feedback control law is designed based on a pointwise-optimal formulation. The stability of pointwise optimal control law is examined.
A New Compensator for Servo Systems With Position Dependent Friction
Authors: Yen Jia-Yush , Huang Shih-Jung , Lu Shu-Shong
Published: February 2008

In this study, we present a new compensator design for systems with position dependent friction. Position dependent friction occurs between revolving parts that are conventionally used in mechanical systems. Because the friction force changes with the position, the conventional servo controller can not maintain consistent performance. In this paper, a modified Karnopp function is proposed to more accurately describe the friction force’s position dependency. A control methodology then exploits this position dependent friction model in order to cancel out the friction force variation and achieve ultimate boundedness [18]. Experimental results demonstrate that the controller achieves consistently good performance. Based on these results, a compensator design procedure is provided.
Multivariable Bilinear Vehicle Control Using Steering and Individual Wheel Torques
Authors: Langson Wilbur , Alleyne Andrew
Published: February 2008

The focus of this paper is the stabilization of vehicle motion to a prescribed path while integrating an increased subset of vehicle inputs than was previously attempted. The integration of the steering inputs and the wheel torque inputs is achieved within the context of bilinear feedback control. The bilinear terms in the model formulation are used to describe the effect of wheel steer angles on the effective moment arm associated with brake or drive torques applied at the relevant wheels. The wheel torques may assume both positive or negative values. A nonlinear state feedback controller which attempts to minimize a quadratic performance index is developed and simulations are used to evaluate the performance of the vehicle in an AHS lane tracking scenario. The simulations are performed on a previously developed nonlinear vehicle model.
Optimal Control of Arrays of Microcantilevers
Authors: Napoli Mariateresa , Bamieh Bassam , Dahleh Mohammed
Published: February 2008

In this paper we will present a model for an array of microcantilevers that are used in Atomic Force Microscopy and nano-scale manufacturing. The microcantilevers are connected to each other through a common base, and are individually actuated. The sensors are also integrated on each microcantilever. We consider the problem of controlling a tightly packed array of identical microcantilevers that are dynamically coupled. This system is an example of a spatially-invariant system with a distributed array of sensors and actuators. We exploit the spatial invariance of the problem to design optimal ℋ2 controllers for this array. An analytic expression for the optimal controller is derived in the transformed domain, and estimates of the coupling range of the controller is obtained.
Robust Decoupled System Design of Uncertain Multivariable Feedback Systems
Authors: Lin Chih-Min , Ying Chen-Ling
Published: February 2008

This paper presents a design algorithm of involving robust decoupled control of uncertain multivariable feedback systems. Two-degree-of-freedom system structure is adopted to handle the quantitative robustness and decoupled performance requirements. Quantitative feedback theory is applied for loop compensator design to achieve quantitative robustness. A decoupled model matching approach is employed for prefilter design to achieve input-output decoupling performance. Thus, the design method of two-degree-of-freedom compensators is proposed to achieve decoupled system control with quantitative robust performance. Since internal stability is satisfied, this design method performs appropriately for any stable or unstable, minimum or non-minimum phase system. The AFTI/F-16 flight control system is considered as the design example to illustrate the design algorithm.
Structural Control of Distributed Parameter Systems by Output Feedback
Authors: Yang S. M. , Jeng C. A.
Published: February 2008

Most of the controller design in distributed parameter systems requires not only the measurement and/or estimation of distributed states, but also the feedback gain in a function of time and spatial coordinates. These requirements are difficult, if not impossible, to meet in engineering implementation. An output feedback algorithm for the structural control of distributed parameter systems is presented in this paper. The algorithm employs a solution technique to simplify the functional Riccati equation into a set of algebraic equations such that sensor and actuator can be applied at discrete, instead of distributed, locations in the structure systems. The control law does not require any model discretization thereby preventing the spillover associated with discrete parameter models. An example of a slewing beam system in distributed parameter model is employed to demonstrate that the bending vibration can be effectively suppressed by a control input at the hub together with a minimal set of output measurements. The performance of the controller is shown superior to that of discrete systems using modal truncation techniques.
Comparison of Viscoelastic Models in Simulating the Transient Response of a Slewing Polymer Arm
Authors: Potvin M.-J. , Piedboeuf J.-C. , Nemes J. A.
Published: February 2008

In this paper, we analyze the transient behavior of a polymethylmethacrylate (PMMA) slewing beam. Experimental data shows that the Young’s modulus of PMMA varies considerably between 0 and 50 Hz. For accurate simulation, this variation must be modeled. Traditional stress-strain models such as the Voigt-Kelvin and the standard linear solid models are examined and shown to have only limited abilities. Models involving fractional derivatives, which are derivatives of an order between 0 and 1, give better results. An integration algorithm based on the Newmark family is described to compute the dynamic equations with a fractional derivative.
Coordinated Position Control of Multi-Axis Mechanical Systems
Authors: Chiu George T.-C. , Tomizuka Masayoshi
Published: February 2008

Position coordination of multi-axis mechanical systems is studied. Under the assumption that the coordination objective can be represented by smooth functions of the positions of the multiple axes control systems, a necessary coupling effect can be introduced to each axis by the proper choice of a Lyapunov-like function. The resulting, control law requires the knowledge of the desired trajectories and their time derivatives as well as actual position and velocity information. Implementation of the proposed control algorithm on a CNC feed drive system shows significant improvement in dimensional accuracy during high speed contouring.
Effects of Oxygen and Additives on the Thermal Stability of Jet Fuels
Authors: Heneghan S. P. , Martel C. R. , Williams T. F. , Ballal D. R.
Published: February 2008

A previously developed flowing single-pass heat-exchanger test rig (Phoenix rig) has been used to evaluate the effectiveness of various additives and the kinetic mechanism of both deposit formation and oxygen consumption. The Phoenix rig has been modified to include not just a heated single tube, but also a cooling test section and both hot and cold filters. The effects of flow conditions, antioxidants, and metal deactivator additives on the location and amount of the deposit are discussed. In general, antioxidants were effective at reducing the deposits on the hot test section, but almost invariably caused increased plugging of cool downstream filters. Downstream plugging of cool filters also increased with decreased temperatures in the heated section or with increased flow. Tests with both oxygen-saturated and oxygen-depleted fuels have shown that the solubility of oxygen is linearly related to the fraction of oxygen in a sparge gas, and that the amount of deposit is linearly related to the total quantity of dissolved oxygen passed. Finally, in contrast to initial modeling efforts, the consumption of oxygen is shown to be significantly more complex than a simple bimolecular, pseudo-first-order in oxygen, process. It is found to be much closer to pseudo-zero-order in the early stages, decaying to pseudo-first-order when the oxygen nears depletion.
A Novel Method for Refurbishing Used Hot Section Gas Turbine Blades
Authors: Kempster A. , Czech N.
Published: February 2008

During the normal operation of a land-based gas turbine, attack will occur of the gas-washed surfaces of the rotating stationary blades in the turbine hot section. This attack and its intensity can be variable depending on the blade’s position in the turbine hot section. This attack will progressively degrade these gas-washed surfaces even if these surfaces have been previously coated with a protective layer. During the service period of the turbine, it will be necessary to refurbish the blades from the hotter section of the turbine. One of the refurbishment steps will be to provide the blades with a suitable replacement coating to afford protection until the next service period. Conventional refurbishment techniques used to clean the blade surface rely on abrasive cleaning and / or chemical pickling. These processes may be capable of removing superficial oxidation and any residual coating but are not able consistently to remove the substrate material that has suffered from corrosive attack. It is important that this attacked substrate layer be removed completely, otherwise any residual corrosion products, particularly the presence of deeply penetrated sulfides in grain boundaries, could significantly reduce the life of any subsequent coating. The technique described in this paper essentially activates the surface layer of the substrate that is corroded, thus rendering it more easily removed by chemical and physical means. It is possible by this method to remove up to 400 μm of the substrate material and provided that all the corrosion products are contained within this zone, it is demonstrated how this produces a clean unattacked surface that is necessary for any subsequent welding, brazing, or recoating operation.
A Methane-Steam Reformer for a Basic Chemically Recuperated Gas Turbine
Authors: Adelman S. T. , Hoffman M. A. , Baughn J. W.
Published: February 2008

Several illustrative designs are presented for a methane-steam reformer (MSR) that is used as a chemical recuperator in a Basic Chemically Recuperated Gas Turbine power cycle (a “Basic” CRGT is defined as one without intercooling or reheat). In this cycle, an MSR, heated by the turbine exhaust flow, converts a methane-steam mixture into a hydrogen-rich fuel that powers the gas turbine. A computer code was developed to calculate the size and performance characteristics of counterflow reformers. The code consists of a one-dimensional marching scheme that integrates the chemical, thermodynamic, and geometric variables along the heat exchanger/reformer tubes. The calculated designs were selected to give near-minimum catalyst volumes. These designs show that maintaining a high reformer gas temperature, using combustion-side heat transfer augmentation techniques, and using a catalyst of high reactivity are critical to obtaining a compact reformer design.
Digital Control System Development for an Intercooled Recuperated Gas Turbine
Authors: Carlson R. J. , West P. M. , Azouz D. E.
Published: February 2008

The on-going development of a full authority digital engine control (FADEC) system for the US Navy’s Intercooled Recuperated (ICR) gas turbine requires a high level of system coordination to achieve the primary benefits of reduced specific fuel consumption and improved specific output power relative to a simple cycle engine. This paper describes the system requirements analysis and the implementation of control algorithms leading to the preliminary ICR control system design. The ICR control system is required to coordinate the actions of over 30 actuators using data taken from over 150 sensors. Primary control of the engine output power is provided by regulation of the fuel metering valve. Thermal management of the intercooler, recuperator, and variable area power turbine nozzle results in maximum cycle efficiency within safe operating limits. The new electronic engine controller (EEC) is based on a new open architecture Futurebus + backplane and is fully redundant in all operationally critical control functions. The EEC also features an operating panel and video display for local operation and maintenance of the control system. The graphic display and function keys provide access to control functions as well as assisting maintenance activities with built-in test diagnostics to trouble shoot failed circuitry.
Reduction of Combustion Irreversibility in a Gas Turbine Power Plant Through Off-Gas Recycling
Authors: Harvey S. P. , Knoche K. F. , Richter H. J.
Published: February 2008

Combustion in conventional fossil-fueled power plants is highly irreversible, resulting in poor overall energy conversion efficiency values (less than 40 percent in many cases). The objective of this paper is to discuss means by which this combustion irreversibility might be reduced in gas turbine power cycles, and the conversion efficiency thus improved upon. One such means is thermochemical recuperation of exhaust heat. The proposed cycle recycles part of the exhaust gases, then mixes them with fuel prior to injection into a reformer. The heat required for the endothermic reforming reactions is provided by the hot turbine exhaust gases. Assuming state-of-the-art technology, and making a number of simplifying assumptions, an overall efficiency of 65.4 percent was attained for the cycle, based on the lower heating value (LHV) of the methane fuel. The proposed cycle is compared to a Humid Air Turbine (HAT) cycle with similar features that achieves an overall efficiency of 64.0 percent. The gain in cycle efficiency that can be attributed to the improved fuel oxidation process is 1.4 percentage points. Compared to current high-efficiency gas turbine cycles, the high efficiency of both cycles studied therefore results mainly from the use of staged compression and expansion with intermediate cooling and reheating, respectively.
Design Considerations of a Versatile Simulator for High-Bypass Turbofans
Authors: Balan C.
Published: February 2008

The continuing requirement for performance improvement of higher thrust turbofans is met by increased bypass ratios. The trend toward higher bypass ratios and relatively large-diameter low-pressure-ratio fans requires innovative design approaches, which include shorter inlets, slimmer nacelles, shorter fan ducts and exhaust systems, and possible elimination of thrust reverser. The success of this new generation of high-bypass ducted turbofans depends on understanding the acoustic impact from reduced treatment areas, inlet-fan coupling and operability, as well as overall system performance. To achieve these goals a versatile scale model propulsion simulator large enough to operate as a fan rig, yet small enough to be installed in a wind tunnel for evaluating overall acoustic, operability, and system performance, was developed. The criteria of designing such a simulator and its capabilities are discussed in this paper.
The Design, Selection, and Application of Oil-Free Screw Compressors for Fuel Gas Service
Authors: Lelgemann K. D.
Published: February 2008

Fuel gas compressors installed in cogeneration systems must be highly reliable and efficient machines. The screw compressor can usually be designed to meet most of the gas flow rates and pressure conditions generally required for such installations. To an ever-increasing degree, alternative sources are being found for the fuel gas supply, such as coke-oven gas, blast-furnace gas, flare gas, landfill gas, and synthesis gas from coal gasification or from pyrolysis. A feature of the oil-free screw compressor when such gases are being considered is the isolation of the gas compression space from the bearing and gear lubrication system by using positive shaft seals. This ensures that the process gas cannot be contaminated by the lubricating oil, and that there is no risk of loss of lubricant viscosity by gas solution in the oil. This feature enables the compressed gas to contain relatively high levels of particulate contamination without danger of “sludge” formation, and also permits the injection of water or liquid solvents into the compression space, to reduce the temperature rise due to the heat of compression, or to “wash” any particulate matter through the compressor.
The Design, Selection, and Application of Oil-Injected Screw Compressors for Fuel Gas Service
Authors: Tsutsumi S. , Boone J.
Published: February 2008

Fuel gas compressors installed in cogeneration systems must be highly reliable and efficient machines, like the other main components, such as gas turbines, gas engines, etc. In the range of gas flow rate and pressure conditions generally required for such systems, the oil-injected screw compressor is often the most suitable compressor type for these requirements. Advantages of oil injected screw compressors are: improved compression efficiency; low discharge gas temperature; high reliability; simple mechanical construction; which all result from injection of lubricant into the compressor. Injected lubricant is discharged together with compressed gas on the high-pressure side but the oil is separated by a fine oil separation system down to a level that causes no problems for the downstream combustion equipment. The oil-injected screw compressor is equipped with an integral stepless capacity control by means of a slide valve, which makes part-load operation possible with reduced power consumption and improves overall system efficiency. As cogeneration systems, which are energy efficient and environmentally sound, are now increasing in number, so oil-injected screw compressors are expected to be used more widely.
The Applicability of Electrically Driven Accessories for Turboshaft Engines
Authors: Jarvis M. S. , Ostergren W. J. , Smith B.
Published: February 2008

Improved electrical power generation and actuation systems offer new design approaches for performing the engine control and accessory functions in helicopter propulsion systems. Present helicopter technology utilizes turboshaft engines with mechanically driven accessories. These accessories perform the functions of starting, fuel and lube pumping, variable stator actuation, and inlet particle separation. This paper discusses the applicability of replacing the mechanically driven accessories with their electrically driven counterparts. An electric accessory system is defined, which includes a switched reluctance starter/generator and its associated control unit; an electric pumping and actuation system; and the engine mounting for the starter/generator. A comparison between the mechanically and electrically driven accessory systems is performed on the basis of cost, weight, and reliability. Experience to date with switched reluctance machines and electrically driven turbo shaft accessory systems is summarized. The benefits of electrically driven accessories are shown and recommendations for future activity for his important technology are discussed.
Fan Noise Reduction From a Supersonic Inlet During Simulated Aircraft Approach
Authors: Nuckolls W. E. , Ng W. F.
Published: February 2008

A series of experiments was conducted to investigate the radiation of fan noise from a supersonic inlet during a simulated aircraft approach. A scaled-down model of an axisymmetric, mixed-compression, supersonic inlet (P-inlet) was used in conjunction with a 10.4 cm (4.1 in) diameter turbofan engine simulator as the noise source. The tests were conducted at an outdoor facility under static conditions. The main goal of the experiment was to reduce the forward radiating fan noise by modifying the auxiliary inlet doors. The modified doors are designed to reduce the inlet distortion to the fan face. In addition, the new door design also uses a converging flow passage in order to take advantage of the noise attenuation due to the choking effect at the auxiliary door. The simulator was tested at 60 percent design speed in an attempt to match the simulator noise source to that of a real aircraft engine on approach. Both aerodynamic and acoustic measurements were taken in the experiments. The results show that when compared to the original design, the modified auxiliary inlet doors reduced the circumferential inlet distortion to the fan face by a factor of two. The key result is that the blade passing frequency tone has been decreased by an average of 6 dB in the forward sector for the modified door design. Results from the closed auxiliary inlet door case are also presented to provide additional comparisons.
Strength Design and Reliability Evaluation of a Hybrid Ceramic Stator Vane for Industrial Gas Turbines
Authors: Nakakado K. , Machida T. , Miyata H. , Hisamatsu T. , Mori N. , Yuri I.
Published: February 2008

Employing ceramic materials for the critical components of industrial gas turbines is anticipated to improve the thermal efficiency of power plants. We developed a first-stage stator vane for a 1300°C class, 20-MW industrial gas turbine. This stator vane has a hybrid ceramic/metal structure, to increase the strength reliability of brittle ceramic parts, and to reduce the amount of cooling air needed for metal parts as well. The strength design results of a ceramic main part are described. Strength reliability evaluation results are also provided based on a cascade test using combustion gas under actual gas turbine running conditions.
Sound Power and Pressure Level Measurements in the Inlet and Outlet of an HRSG Duct
Authors: Jungbauer D. E. , Unruh J. F. , Rose S. , Pantermuehl P. J.
Published: February 2008

The ever-increasing size of cogeneration facilities has mandated the need for noise abatement in the design stage. Many noise projection models are available to the industry for predicting noise levels in and adjacent to new installations. However, the models all require accurate source noise information if valid noise predictions are to be expected. As a consequence of designing one of the world’s largest cogeneration installations involving eight Model W-701 turbine units and their Heat Recovery Steam Generators (HRSGs), it became apparent that the attention between the exhaust of the turbine and the outlet of the HRSGs was not well known. Not having this information posed potentially expensive noise abatement modifications during the design and construction phases. In order to verify the adequacy of scaling studies from a W-501 turbine and HRSG to the W-701 system, a comprehensive field test of an existing W-501 installation was conducted. This paper describes the design of an acoustic intensity and sound pressure probe to operate inside the high-temperature ductwork, the access engineering required, data acquisition, and final results concerning noise attenuation across the HRSG.
A Semi-Analytical Emission Model for Diffusion Flame, Rich/Lean and Premixed Lean Combustors
Authors: Rizk N. K. , Mongia H. C.
Published: February 2008

To enhance gas turbine combustor performance and emissions characteristics, better design methods need to be developed. In the present investigation, an emission model that simulates a detailed chemical kinetic scheme has been developed to provide the rate of reactions of the parent fuel, an intermediate hydrocarbon compound, CO, and H2. The intermediate fuel has variable carbon and hydrogen contents depending on operating conditions, that were selected in the development effort to simulate actual operation of rich/lean, diffusion flame, and lean combustor concepts. The developed reaction rate expressions address also the limited reaction rates that may occur in the near-wall regions of the combustor due to the admittance of radial air jets and cooling air in these regions. The validation effort included the application of the developed model to a combustor simulated by a multiple-reactor arrangement. The results indicate the accurate duplication of the calculations obtained from the detailed kinetic scheme using the developed model. This illustrates the great potential of using such a unified approach to guide the design of various types of combustor to meet the more stringent approach to guide the design of various types of combustor to meet the more stringent emissions and performance requirements of next-generation gas turbine engines.
A Blade-by-Blade Tip Clearance Measurement System for Gas Turbine Applications
Authors: Sheard A. G. , Killeen B.
Published: February 2008

It is difficult to make a reliable measurement of running clearance in the hostile environment over the blading of a modern gas turbine. When engine manufacturers require the measurement to be made over every blade during live engine tests, system reliability, ruggedness, and ease of operation are of primary importance. This paper describes a tip clearance measurement system that can measure clearance over every blade around a rotor. The measurement system concept is presented, and the system design described in detail. Commissioning of the measurement system on a compressor test facility, and the results obtained are discussed. An analysis of system performance during the commissioning trials concludes the paper.
Experimental Studies on Methane-Fuel Laboratory Scale Ram Combustor
Authors: Kinoshita Y. , Kitajima J. , Seki Y. , Tatara A.
Published: February 2008

The laboratory scale ram combustor test program has been investigating fundamental combustion characteristics of a ram combustor, which operates from Mach 2.5 to 5 for the super/hypersonic transport propulsion system. In our previous study, combustion efficiency had been found poor, less than 70 percent, due to a low inlet air temperature and a high velocity at Mach 3 condition. To improve the low combustion efficiency, a fuel zoning combustion concept was investigated by using a subscale combustor model first. Combustion efficiency more than 90 percent was achieved and the concept was found very effective. Then a laboratory scale ram combustor was fabricated and combustion tests were carried out mainly at the simulated condition of Mach 5. A vitiation technique was used to simulate a high temperature of 1263 K. The test results indicate that ignition, flame stability, and combustion efficiency were not significant, but the NOx emissions are a critical problem for the ram combustor at Mach 5 condition.
Technology Demonstration Nozzle for Mach 7 Turboramjets
Authors: Pirker K. , Knott U.
Published: February 2008

Under the German Hypersonic Technology Program, future-oriented designs and technologies for reusable space vehicles, such as SA¨NGER, are being developed. Pioneering the way in a new field of technology, MTU constructed and tested, with success from the very beginning, an actively cooled, asymmetric rectangular nozzle (SERN—single expansion ramp nozzle) of advanced design, characterized by the following innovative features: • rectangular, flap-controlled variable flow cross section; • liquid-hydrogen-cooled structures; • high-temperature-resistant sealing system for variable nozzle flaps; and • uncooled expansion ramp in carbon/carbon composite with anti-oxidation coating. Development of the nozzle called for the mastery of new manufacturing techniques; proof of concept was provided in the successful performance of initial tests of 300 second duration.
Turbine Engine Icing Spray Bar Design Issues
Authors: Bartlett C. S.
Published: February 2008

Techniques have been developed at the Engine Test Facility (ETF) of the Arnold Engineering Development Center (AEDC) to simulate flight through atmospheric icing conditions of supercooled liquid water droplets. Ice formed on aircraft and propulsion system surfaces during flight through icing conditions can, even in small amounts, be extremely hazardous. The effects of ice are dependent on many variables and are still unpredictable. Often, experiments are conducted to determine the characteristics of the aircraft and its propulsion system in an icing environment. Facilities at the ETF provide the capability to conduct icing testing in either the direct-connect (connected pipe) or the free-jet mode. The requirements of a spray system for turbine engine icing testing are described, as are the techniques used at the AEDC ETF to simulate flight in icing conditions. Some of the key issues facing the designer of a spray system for use in an altitude facility are identified and discussed, and validation testing of the design of a new spray system for the AEDC ETF is detailed. This spray system enables testing of the newest generation of high-thrust turbofan engines in simulated icing conditions.
The Development of an Aviation Fuel Thermal Stability Test Unit
Authors: Daggett D. L. , Veninger A. , Lewis C. , Bullock S. , Kamin R.
Published: February 2008

A test unit has been developed by Rolls-Royce for the U.S. Navy to use in evaluating fuel thermal deposition typically found in various aircraft engine components. Although the current Jet Fuel Thermal Oxidation Tester (JFTOT) provides a qualitative thermal stability evaluation, it may not be able to predict in-service problems. Conditioning and testing of the fuel under realistic conditions is crucial if one is to predict deposit formations accurately. Engine fuel deposit evaluations and evidence from unpublished Rolls-Royce laboratory rig tests were used to help design a test unit that would address fuel stability problems in current or future aircraft. The Aviation Fuel Thermal Stability (AFTS) test unit embodies test modules that were selected with extensive fuel systems experience to enable the evaluation of thermal deposition in various fuel components using properly conditioned fuel. The test modules are controlled and results are recorded by a computer. This paper includes a review of the AFTS test unit design and preliminary test results thereof.
Part-Load Operation of Combined Cycle Plants With and Without Supplementary Firing
Authors: Dechamps P. J. , Pirard N. , Mathieu Ph.
Published: February 2008

The design point performance of combined cycle power plants has been steadily increasing, because of improvements both in the gas turbine technology and in the heat recovery technology, with multiple pressure heat recovery steam generators. The concern remains, however, that combined cycle power plants, like all installations based on gas turbines, have a rapid performance degradation when the load is reduced. In particular, it is well known that the efficiency degradation of a combined cycle is more rapid than that of a classical steam plant. This paper describes a methodology that can be used to evaluate the part-load performances of combined cycle units. Some examples are presented and discussed, covering multiple pressure arrangements, incorporating supplemental firing and possibly reheat. Some emphasis is put on the additional flexibility offered by the use of supplemental firing, in conjunction with schemes comprising more than one gas turbine per steam turbine. The influence of the gas turbine controls, like the use of variable inlet guide vanes in the compressor control, is also discussed.
Ash Deposition in a Wood-Fired Gas Turbine
Authors: Ragland K. W. , Misra M. K. , Aerts D. J. , Palmer C. A.
Published: February 2008

A small four-stage gas turbine was directly fired with woodchips using a novel downdraft, gravel-bed combustor for a total 250 hours of tests. The average turbine blockage due to deposits was 0.19 percent per hour. The composition of deposits was studied using plasma emission spectroscopy and x-ray diffraction. The main constituents of the deposits were CaO, MgO, and K2SO4. The deposits contained 5 to 15 percent potassium and 0.5 to 3 percent sulfur.
Gas Turbine Acoustic Enclosure Design by the Statistical Energy Analysis Method
Authors: Lu L. K. H. , Mitchell M.
Published: February 2008

Acoustic enclosure design is a complex problem that involves the interaction of multiple components. Yet the present conventional approach uses a two-dimensional closed-form solution to evaluate transmission loss of acoustic wall. In this paper, Statistical Energy Analysis (SEA) was first studied for simple cases of radiation efficiency, transmission loss, and flanking path calculations. The effectiveness of the SEA method for complex systems was then demonstrated through a practical design application to gas turbine enclosure. It was found that SEA was a useful tool for gas turbine acoustic enclosure design.
Optimal Design of Split Ring Dampers for Gas Turbine Engines
Authors: Niemotka M. A. , Ziegert J. C.
Published: February 2008

Vibration analysis techniques used for labyrinth air seals are presented, along with a derivation of the methods used to calculate the dissipation capability of split ring dampers. After defining the problem in classical optimization format, the methods used to automate the process are presented, along with the results for a particular test case. For the case considered, the optimal designs were found to lie at or near the design space boundaries.
Nonlinear Behavior of a Magnetic Bearing System
Authors: Virgin L. N. , Walsh T. F. , Knight J. D.
Published: February 2008

This paper describes the results of a study into the dynamic behavior of a magnetic bearing system. The research focuses attention on the influence of nonlinearities on the forced response of a two-degree-of-freedom rotating mass suspended by magnetic bearings and subject to rotating unbalance and feedback control. Geometric coupling between the degrees of freedom leads to a pair of nonlinear ordinary differential equations, which are then solved using both numerical simulation and approximate analytical techniques. The system exhibits a variety of interesting and somewhat unexpected phenomena including various amplitude driven bifurcational events, sensitivity to initial conditions, and the complete loss of stability associated with the escape from the potential well in which the system can be thought to be oscillating. An approximate criterion to avoid this last possibility is developed based on concepts of limiting the response of the system. The present paper may be considered as an extension to an earlier study by the same authors, which described the practical context of the work, free vibration, control aspects, and derivation of the mathematical model.