bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of a Dry Low-NOx Gas Turbine Combustor Designed With a New Fuel Supply Concept
Authors: Wakabayashi T. , Ito S. , Koga S. , Ippommatsu M. , Moriya K. , Shimodaira K. , Kurosawa Y. , Suzuki K.
Published: September 2002

This paper describes the performance of a dry low-NOx gas turbine combustor designed with a new fuel supply concept. This concept uses automatic fuel distribution achieved by an interaction between the fuel jet and the airflow. At high loads, most of the fuel is supplied to the lean premixed combustion region for low-NOx, while at low loads, it is supplied to the pilot combustion region for stable combustion. A numerical simulation was carried out to estimate the equivalence ratio in the fuel supply unit. Next, through the pressurized combustion experiments on the combustor with this fuel supply unit using natural gas as fuel, it was confirmed that NOx emissions were reduced and stable combustion was achieved over a wide equivalence ratio range.
Mass Spectrometric Detection of Ionic and Neutral Species During Highly Preheated Air Combustion by Alkali Element Ion Attachment
Authors: Ishiguro T. , Matsunami A. , Matsumoto K. , Kitagawa K. , Arai N. , Gupta A. K.
Published: September 2002

The use of high temperature and low oxygen concentration air as the oxidizer for regenerative combustion has become of increasing interest because this technology results in higher thermal efficiency, low energy consumption, and reduced emission of pollutants, such as NOx and CO2, and compact size of the equipment. In this study information is provided on the effect of preheating the low oxygen concentration air on the formation and detection of chemical ions and neutral species formed in flames. These ions and species were detected directly using mass spectrometry. Such information also assists in determining the combustion mechanism. The intact ionic species have been detected only at downstream position of the flames. By applying an alkali element Li+ ion attachment technique, neutral species, such as Li+-attached ions have been also detected successfully. Three specific flame cases have been examined. They include using normal air (flame I), preheated air (flame II), and preheated air with low (diluted) oxygen concentration in air (flame III). The results show significant change in the spectra of the intact ionic species and the Li+-adduct neutral species amongst the three flames. The results also show that preheating the combustion air increases the number of chemical species formed in the flames. However, these chemical species decrease with low oxygen concentration (diluted) combustion air.
A Hybrid System Based on a Personal Turbine (5 kW) and a Solid Oxide Fuel Cell Stack: A Flexible and High Efficiency Energy Concept for the Distributed Power Market
Authors: Magistri L. , Costamagna P. , Massardo A. F. , Rodgers C. , McDonald C. F.
Published: September 2002

In this paper a high efficiency and flexible hybrid system representing a new total energy concept for the distributed power market is presented. The hybrid system is composed of a very small size (5 kW) micro gas turbine (named personal turbine—PT) presented in a companion paper by the authors coupled to a small size solid oxide fuel cell (SOFC) stack. The power of the whole system is 36 kW depending on the design parameters assumed for the stack. The design and off-design performance of the hybrid system have been obtained through the use of an appropriate modular code named “HS-SOFC” developed at the University of Genoa and described in detail in this paper. The results of the simulation are presented and discussed with particular regards to: choice of the hybrid system (HS) design point data, HS design point performance, off-design performance of PT and SOFC stack, and off-design performance of the whole HS. Some preliminary economic results are also included based on different fuel and capital cost scenarios and using the cost of electricity as the parameter for comparison between PT and HS.
Droplet Entrainment From a Shear-Driven Liquid Wall Film in Inclined Ducts: Experimental Study and Correlation Comparison
Authors: Ebner J. , Gerenda´s M. , Scha¨fer O. , Wittig S.
Published: September 2002

The primary objective of the present study is to clarify the droplet disintegration mechanism and the film properties of liquid oil films driven by shear stress, which is induced by a co-current gas flow. This work focuses on the flow behavior within the starting length of the complex two-phase flow and the effect of inclination on the entrainment rate. Many investigations have been performed in the past to determine the droplet entrainment in the gas core for fully developed flow conditions with respect to their relevance in pipes of power plants and various chemical engineering systems. In more recent work the effect of inclination has been studied in detail. Nevertheless, a lack of knowledge can be realized for droplet entrainment within the starting length of this complex flow type. Thus, fundamental experiments have been carried out to provide a data base for droplet entrainment of liquid disintegrated from an oil film within its starting length at several inclination angles of the flow. The experimental results have been compared with correlations from literature. Additionally, the wall film thickness has been measured to allow a fully coupled modeling of entrainment and liquid film properties depending on global flow parameters. Based on film Reynolds number, Weber number, a dimensionless film flow length, and a modified Froude number, taking into account the angle of inclination, correlations have been developed, where those from literature are not applicable.
Delamination Cracking in Thermal Barrier Coating System
Authors: Zhou Y. C. , Hashida T.
Published: September 2002

Delamination cracking in thermal barrier coating (TBC) system is studied with the newly developed theoretical model. A semi-infinite long interface crack is pre-existing. The thermal stress and temperature gradient in TBC system are designated by a membrane stress P and a bending moment M. In this case, the effects of plastic deformation, creep of ceramic coating, as well as thermal growth oxidation and temperature gradient in TBC system are considered in the model due to the fact that these effects are considered in the calculation of thermal stress. The energy release rate, mode I and mode II stress intensity factors, as well as mode mixed measure ψ, are derived. The emphatic discussion about PSZ/Ni-alloy reveals that the TBC system may not fail in the form of coating delamination during the period of heat hold. However, the failure may be in the form of coating delamination during cooling or in the heating period during the second cycle or later cycles. The conclusion is consistent with the experimental observations. The delamination of ceramic coating is induced by the compressive load in the coating.
Series of Parallel Arrangement in a Two-Unit Compressor Station
Authors: Ohanian S. , Kurz R.
Published: September 2002

This paper discusses how to determine the arrangement of compressors in a two-unit gas pipeline station where there is no standby unit. The compressors are driven by variable speed drivers such as gas turbines or variable frequency electric motors. Both series and parallel arrangements are analyzed in a transient simulation mode to determine which operation mode is more advantageous. Among the assumptions in this paper are the performance characteristics of the compressor. It will be outlined how these performance characteristics influence the conclusions.
Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals—Part II: Smooth and Honeycomb Geometries
Authors: Dawson M. P. , Childs D. W.
Published: September 2002

Results are presented from tests conducted using an experimental test facility to measure the leakage and dynamic impedance of smooth and honeycomb straight-bore annular gas seals. The test seals had a 114.3 mm (4.500 in.) bore with a length-to-diameter ratio of 0.75 and a nominal radial clearance of 0.19 mm (0.0075 in.). The honeycomb cell depth for both seals was 3.10 mm (0.122 in.), and the cell width was 0.79 mm (0.031 in.). Dynamic impedance and leakage measurements are reported using air at three supply pressures out to 1.72 Mpa (250 psi), three speeds out to 20,200 rpm, and exit-to-inlet pressure ratios of 40% and 50%. Comparisons to the predictions from the two-control-volume model of Kleynhans and Childs [1] are of particular interest. This model predicts that honeycomb seals do not fit the conventional frequency independent model for smooth annular gas seals. The experimental results verify this new theory. Numerical predictions from a computer program incorporating the new two-control-volume model of Kleynhans and Childs [1] correlate well with both measured seal leakage and dynamic impedances for the honeycomb seals.
Using Guided Balls to Auto-Balance Rotors
Authors: Wettergren H. L.
Published: September 2002

By using balancing balls constrained to move in a circular groove filled with oil, the vibration of rotating machinery can, under certain circumstances, be reduced. This paper shows that the damping from the oil reduces the instability region, i.e., the conditions when the balancing balls don’t find their equilibrium positions. However, the instability region seems to increase with increasing number of balancing balls. The critical ball damping ratio is highest just above the natural frequency and then rapidly decreases. Consequently, since the region between instability and critical damping is quite small, the ball damping should be made as small as possible without getting too close to the instability threshold. Bearing damping has a large effect on the instability region. High bearing damping will suppress the instability. The time it takes to reach the asymptotically stable position seems to increase with increasing number of balls. Keeping this time low is one of the most important things when designing a balancing ring.
Transient Rotordynamic Modeling of Rolling Element Bearing Systems
Authors: Liew A. , Feng N. , Hahn E. J.
Published: September 2002

Nonlinearity effects in rolling element bearings arise from Hertzian contact force deformation relationships, clearance between rolling elements and races, and the bearing-to-housing clearance. Assuming zero bearing-to-housing clearance, a simplified earlier analysis showed that rotor bearing systems (RBSs) with deep groove ball bearings can give rise to chaotic motion and jump. This paper extends the bearing model to include rolling element centrifugal load, angular contacts and axial dynamics; and illustrates their effects in a rigidly supported rigid RBS and a flexibly supported flexible RBS, the latter modeling an existing test rig. Results are presented on the effect of bearing preload on the unbalance response up to a speed of 18,000 rpm.
Optimum Design of Squeeze Film Dampers Supporting Multiple-Mode Rotors
Authors: El-Shafei A. , Yakoub R. Y. K.
Published: September 2002

In this paper a study of the optimum design of squeeze film dampers for multimode rotors is presented. The optimum design program obtains the best possible damper parameters for a given rotor to satisfy the minimization requirements for the objective function. The objectives are to minimize the amplitude response of the rotor at the critical speed, minimize the force transmitted to the support at the operating speed, or maximize the power dissipated by the damper. A combination of these objectives can also be used, with weighting factors to weigh the importance of each of these objectives. These are the possible objectives for the design of squeeze film dampers for aircraft engine applications. The basis of the optimum design program is an extremely fast algorithm which is able to quickly calculate the unbalance response of a rotor, for circular centered orbits of the journal in the damper. A commercial routine is used for the optimization, and is based on a complex direct search technique. The variation of the optimum clearance, length, and retainer spring stiffness are plotted against various rotor parameters. Recommendations for the design of squeeze film dampers are made. Applications to an aircraft engine illustrate the power of the developed algorithm.
A Predictive Rolling Contact Fatigue Crack Growth Model: Onset of Branching, Direction, and Growth—Role of Dry and Lubricated Conditions on Crack Patterns
Authors: Dubourg M. C. , Lamacq V.
Published: September 2002

Complex crack networks are initiated in rails under Rolling Contact Fatigue. This paper attempts to model the RCF crack propagation with a particular emphasis on the branching conditions and the parameters that play a role on them. The numerical tool proposed rests on the combination of the author’s RCF model, Hourlier and Pineau’s criterion for the branch prediction and experimental data and the corresponding models for fatigue crack extension that are derived from a Joint European project. Parametric studies on the influence of (i) residual stresses, (ii) both interfacial crack and wheel/rail contact frictional effects, (iii) neighboring crack are conducted to reach a better understanding of the RC crack propagation behavior and more particularly the branch conditions, i.e., the length of the primary crack prior to branch formation and the branch direction.
Flying Height Modulation Due to Disk Waviness of Sub-5 nm Flying Height Air Bearing Sliders
Authors: Thornton Brian H. , Nayak A. , Bogy D. B.
Published: September 2002

Two new air bearing slider designs are presented for storage densities greater than 100 Gb/in2 in hard disk drive (HDD) applications. Their dynamic frequencies and mode shapes are characterized, and they are used to study the flying height modulation (FHM) over wavy disks due to geometric effects as opposed to dynamic effects. It is found that low pitch designs experience large FHM at wavelengths on the order of the length of the sliders to one-eighth the length of the sliders due to a complex phase shift in the sliders trailing edge response as compared to the disk waviness. FHM due to disk waviness wavelengths from 2 mm to 0.16 mm was found to be a function of the sliders’ attitude (pitch angle) and the air bearing surface (ABS) geometry (pressure distribution over the ABS). The results presented suggest that the pitch should be greater than 100 μrad for the ABS designs presented and attention needs to be focused on the ABS design and disk morphology to avoid unacceptable FHM. An ABS design was introduced to reiterate the findings on geometric FHM showing an 83 percent decrease in geometric FHM. The FHM due to geometric effects of the slider designs studied in this paper could possibly be predicted by the disk morphology alone.
Influence of a Hard Surface Layer on the Limit of Elastic Contact—Part II: Analysis Using a Modified GW Model
Authors: Nogi Takashi , Kato Takahisa
Published: September 2002

The Greenwood and Williamson microcontact model of rough surfaces is modified to include the presence of a surface layer which is stiffer and harder than the substrate. The axisymmetric contact between a rigid spherical asperity and an elastic layered halfspace is analyzed numerically and correction factors for the contact area, load and the maximum von Mises stress are approximated to a closed form by using curve fits of the numerical results. The correction factors for the contact area and load are applied to the GW model to reflect the effect of the finite layer thickness and the substrate material. The correction factor for the maximum von Mises stress is used to calculate the plasticity index for layered surfaces. Parametric calculation of the ratio of plastic contact area to real contact area is carried out for a TiN-coated steel surface. The modified GW model is compared with a more rigorous real surface model and the validity of the present model is discussed. When the layer thickness is sufficiently large, the influence of the soft substrate can be neglected. A simple criterion for realizing the contact free of the effect of the substrate is proposed.
The Impact of Linear Deformations on Stationary Hydrostatic Thrust Bearings
Authors: Manring Noah D. , Johnson Robert E. , Cherukuri Harish P.
Published: September 2002

In this work, the operating sensitivity of the hydrostatic thrust bearing with respect to pressure-induced deformations will be studied in a stationary setting. Using the classical lubrication equations for low Reynold’s number flow, closed-form expressions are generated for describing the pressure distribution, the flow rate, and the load carrying capacity of the bearing. These expressions are developed to consider deformations of the bearing that result in either concave or convex shapes relative to a flat thrust surface. The impact of both shapes is compared, and the sensitivity of the flow rate and the load carrying capacity of the bearing with respect to the magnitude of the deformation is discussed. In summary, it is shown that all deformations increase the flow rate of the bearing and that concave deformations increase the load carrying capacity while convex deformations decrease this same quantity relative to a non-deformed bearing condition.
Dynamic Characteristics of an In-Contact Head Slider Considering Meniscus Force: Part 3—Wear Durability and Optimization of Surface Energy of Liquid Lubricant Under Perfect Contact Condition
Authors: Matsuoka Hiroshige , Fukui Shigehisa , Kato Takahisa
Published: September 2002

The authors developed a computer simulator for in-contact head slider motion where a 3-DOF model of head-suspension assembly was introduced and effects of meniscus force between the slider and the disk were considered. The contact force between a contact pad and a disk surface was taken into account and the dynamic characteristics of an in-contact head slider were discussed from the viewpoints of both bouncing vibration and wear durability by not only 3-DOF head-suspension assembly model over a sinusoidal disk surface undulation but also 1-DOF head-suspension assembly model over a sinusoidal disk surface undulation. In addition to the critical frequency of bouncing, the critical frequency of pressure was introduced. As a result of 3-DOF simulation and 1-DOF analysis, it was found that there exists an optimum surface energy at which the stability of bouncing vibration and wear durability becomes highest under perfect contact condition. Furthermore, the behavior of the optimum point for several design parameters were made clear.
Fatigue Life and Traction Modeling of Continuously Variable Transmissions
Authors: Nikas George K.
Published: September 2002

A model was developed to study the elastohydrodynamics and contact mechanics of toroidal Continuously Variable Transmission (CVT) type contacts. The aim is to predict the fatigue life, traction and efficiency of such contacts with the intention of making optimizations based on design criteria and constraints. A generalized Reynolds equation was developed for isothermal, transient lubrication of elliptical rough contacts with mixed rolling, two-dimensional sliding, and spinning conditions, incorporating any non-Newtonian model, roughness asperity isothermal elastoplastic interactions, and a three-dimensional subsurface stress analysis. The output is in the form of film thickness and traction maps, including contact efficiency, three-dimensional stress fields, and, finally, the predicted fatigue lives of CVT contacts, based on the Ioannides-Harris life model. A parametric study reveals the effect of surface roughness, lubricant bulk temperature, contact ellipticity ratio, slide-roll ratio, and contact load on the fatigue life, traction and contact efficiency of CVTs, and allows for design optimizations based on a compromise between life, traction and efficiency.
Three-Dimensional Elastic-Plastic Stress Analysis of Rolling Contact
Authors: Jiang Yanyao , Xu Biqiang , Sehitoglu Huseyin
Published: September 2002

Three-dimensional elastic-plastic rolling contact stress analysis was conducted incorporating elastic and plastic shakedown concepts. The Hertzian distribution was assumed for the normal surface contact load over a circular contact area. The tangential forces in both the rolling and lateral directions were considered and were assumed to be proportional to the Hertzian pressure. The elastic and plastic shakedown limits obtained for the three-dimensional contact problem revealed the role of both longitudinal and lateral shear traction on the shakedown results. An advanced cyclic plasticity model was implemented into a finite element code via the material subroutine. Finite element simulations were conducted to study the influences of the tangential surface forces in the two shear directions on residual stresses and residual strains. For all the cases simulated, the p0/k ratio (p0 is the maximum Hertzian pressure and k is the yield stress in shear) was 6.0. The Qx/P ratio, where Qx is the total tangential force on the contact surface in the rolling direction and P is the total normal surface pressure, ranged from 0 to 0.6. The Qy/P ratio (Qy is the total tangential force in the lateral direction) was either zero or 0.25. Residual stresses increase with increasing rolling passes but tend to stabilize. Residual strains also increase but the increase in residual strain per rolling pass (ratchetting rate) decays with rolling cycles. Residual stress levels can be as high as 2k when the Qx/P ratio is 0.6. Local accumulated shear strains can exceed 20 times the yield strain in shear after six rolling passes under extreme conditions. Comparisons of the two-dimensional and three-dimensional rolling contact results were provided to elucidate the differences in residual stresses and ratchetting strain predictions.
Effects of Wheel-Shaft-Fluid Coupling and Local Wheel Deformations on the Global Behavior of Shaft Lines
Authors: Lornage D. , Chatelet E. , Jacquet-Richardet G.
Published: September 2002

Rotating parts of turbomachines are generally studied using different uncoupled approaches. For example, the dynamic behavior of shafts and wheels are considered independently and the influence of the surrounding fluid is often taken into account in an approximate way. These approaches, while often sufficiently accurate, are questionable when wheel-shaft coupling is observed or when fluid elements are strongly coupled with local structural deformations (leakage flow between wheel and casing, fluid bearings mounted on a thin-walled shaft, etc.). The approach proposed is a step toward a global model of shaft lines. The whole flexible wheel-shaft assembly and the influence of specific fluid film elements are considered in a fully three-dimensional model. In this paper, the proposed model is first presented and then applied to a simple disk-shaft assembly coupled with a fluid film clustered between the disk and a rigid casing. The finite element method is used together with a modal reduction for the structural analysis. As thin fluid films are considered, the Reynolds equation is solved using finite differences in order to obtain the pressure field. Data are transferred between structural and fluid meshes using a general method based on an interfacing grid concept. The equations governing the whole system are solved within a time-marching procedure. The results obtained show significant influence of specific three-dimensional features such as disk-shaft coupling and local disk deformations on global behavior.
A Framework for Flutter Clearance of Aeroengine Blades
Authors: Khalak A.
Published: September 2002

A framework for flutter operability assessment, based upon a new set of similarity parameters, has been developed. This set consists of four parameters which embrace both the performance characteristics in terms of corrected mass flow and corrected speed, and the flight condition in terms of inlet temperature and density (or, equivalently, inlet pressure). It is shown that a combined mass-damping parameter, g/ρ*, novel in the field of turbomachinery aeroelasticity, can summarize the individual effects of mechanical damping, g, and blade mass ratio, μ. A particular selection of four nondimensional parameters, including g/ρ* and a compressible reduced frequency parameter, K*, allows for a decoupling of corrected performance effects from purely aeroelastic effects, for a given machine and a specific modeshape. This view of flutter operability is applied to the analysis of full-scale engine data. The data exhibits the trend that increasing K* and increasing g/ρ* have stabilizing effects, which is consistent with previous work in flutter stability. We propose that these trends hold generally, and apply the trends towards constructing a flutter clearance methodology, a test procedure which satisfies the requirements for comprehensive flutter stability testing.
Eigensolutions of Grouped Turbo Blades Solved by the Generalized Differential Quadrature Method
Authors: Kuang J. H. , Hsu M. H.
Published: September 2002

The eigenvalue problems of grouped turbo blades were numerically formulated by using the generalized differential quadrature method (GDQM). Different boundary approaches accompanying the GDQM to transform the partial differential equations of grouped turbo blades into a discrete eigenvalue problem are discussed. Effects of the number of sample points and the different boundary approaches on the accuracy of the calculated natural frequencies are also studied. Numerical results demonstrated the validity and the efficiency of the GDQM in treating this type of problem.
Efficiency Upgrading of an Ambient Pressure Molten Carbonate Fuel Cell Plant Through the Introduction of an Indirect Heated Gas Turbine
Authors: Lunghi P. , Ubertini S.
Published: September 2002

The efficient end environmentally friendly production of electricity is undoubtedly one of the 21st century priorities. Since renewable sources will be able to guarantee only a share of the future demand, the present research activity must focus on innovative energy devices and improved conversion systems and cycles. Great expectations are reserved to fuel cell systems. The direct conversion from chemical to electrical energy eliminates environmental problems connected with combustion and bypass the stringent efficiency limit due to Carnot’s principle. Still in infancy, high-temperature fuel cells present the further advantage of feasible cycle integration with steam or gas turbines. In this paper, a molten carbonate fuel cell plant is simulated in a cycle for power generation. The introduction of an external combustion gas turbine is evaluated with the aim of efficiency and net power output increase. The results show that the proposed cycle can be conveniently used as a source of power generation. As compared to internal combustion gas turbine hybrid cycles found in the literature the plant is characterized by fuel cell greater simplicity, due to the absence of pressurization, and gas turbine increased complexity, due to the presence of the heat exchange system.
Time-Dependent Mild to Severe Wear Transition in Oscillating Motion of Cylindrical Sliding Pairs Under Boundary Lubrication
Authors: Hiraoka Naofumi
Published: September 2002

Copper cylinder-on-silver plated copper cylinder wear tests in oscillating motion were carried out in oil. Time-dependent mild to severe wear transition was observed for a certain large load. The surface analyses and wear simulations were conducted and they revealed that the wear transition was attributable not to the wear-out of the silver plating, but to the increase of the contact pressure with increase of the number of oscillations, which was caused by the increase of sliding pair shape inconformity due to wear.
Designing Hot Working Processes of Nickel-Based Superalloys Using Finite Element Simulation
Authors: Kopp R. , Tschirnich M. , Wolske M. , Klo¨wer J.
Published: September 2002

Knowledge of correct flow stress curves of Ni-based alloys at high temperatures is of essential importance for reliable plastomechanical simulations in materials processing and for an effective planning and designing of industrial hot forming schedules like hot rolling or forging. The experiments are performed on a computer controlled servohydraulic testing machine at IBF. To avoid an inhomogeneous deformation due to the influence of friction and initial microstructure, a suitable specimen geometry and lubricant is used and a thermal treatment before testing has to provide a microstructure, similar to the structure of the material in the real process. The compression tests are performed within a furnace, which keeps sample, tools, and surrounding atmosphere on the defined forming temperature. The uniaxial compressions were carried out in the range of strain rates between 0.001 and 50s−1 and temperatures between 950 and 1280°C. Furthermore, two-stage step tests are carried out to derive the work hardening and softening behavior as well as the recrystallization kinetics of the selected Ni-based alloys. At the end of this work a material model is adapted by the previously determined material data. This model is integrated into the Finite Element program LARSTRAN/SHAPE to calculate a forging process of the material Alloy 617.
Friction Damping of Interlocked Vane Segments: Experimental Results
Authors: Berruti T. , Filippi S. , Gola M. M. , Salvano S.
Published: September 2002

Experimental methods and results of the stator bladed segment of an aircraft engine are presented. Investigation concerns the energy dissipation due to friction between contact surfaces of adjacent segments. The influence of the force normal to the contact surface (due to interference between adjacent segments) on friction damping is shown. Moreover, the experiments show the nature of friction at contact surfaces. The parameters of a contact model to be used in a numerical analysis have been identified from the experiments.
Spatially Continuous Power Flow Using a Scanning Laser Doppler Vibrometer
Authors: Blotter Jonathan D. , West Robert L. , Sommerfeldt Scott D.
Published: September 2002

This paper presents the validation of an experimental technique that maps the transfer of energy in vibrating structures. The technique is known as Experimental Spatial Power Flow (ESPF) and is unique in that it provides a spatially continuous representation of the power flow based on measurements from a scanning laser Doppler vibrometer. In this paper, the ESPF technique is validated by showing that ESPF results compare to within 10 percent of the results obtained using single point impedance head measurements. A simply supported plate excited by two shakers phased to act as an energy source and sink is used as the test object.
Application of Dynamic Fractional Differentiation to the Study of Oscillating Viscoelastic Medium With Cylindrical Cavity
Authors: Ingman D. , Suzdalnitsky J.
Published: September 2002

Oscillations of a viscoelastic medium with a cylindrical cavity are studied. The viscosity is taken into account in the form of an additional term in the constitutive equation, proportional to a fractional derivative of variable order. In the considered examples the order function corresponds to dependences obtained for real materials. A damping effect is observed in the amplitude behavior. The field which determines the order function demonstrates the viscoelastic behavior of the material under load.
Closed-Form Solutions to the Exact Optimizations of Dynamic Vibration Absorbers (Minimizations of the Maximum Amplitude Magnification Factors)
Authors: Nishihara Osamu , Asami Toshihiko
Published: September 2002

A typical design problem for which the fixed-points method was originally developed is that of minimizing the maximum amplitude magnification factor of a primary system by using a dynamic vibration absorber. This is an example of usual cases for which their exact solutions are not obtained by the well-known heuristic approach. In this paper, more natural formulation of this problem is studied, and algebraic closed-form exact solutions to both the optimum tuning ratio and the optimum damping coefficient for this classic problem are derived under assumption of undamped primary system. It is also proven that the minimum amplitude magnification factor, resonance and anti-resonance frequencies are entirely algebraic.
A Comparative Study and Analysis of Semi-Active Vibration-Control Systems
Authors: Jalili Nader
Published: September 2002

Semi-active (SA) vibration-control systems are those which otherwise passively generated damping or spring forces are modulated according to a parameter tuning policy with only a small amount of control effort. SA units, as their name implies, fill the gap between purely passive and fully active vibration-control systems and offer the reliability of passive systems, yet maintain the versatility and adaptability of fully active devices. During recent years there has been considerable interest towards practical implementation of these systems for their low energy requirement and cost. This paper briefly reviews the basic theoretical concepts for SA vibration-control design and implementation, and surveys recent developments and control techniques for these systems. Some related practical applications in vehicle suspensions are also presented.
Constrained Layer Damping Treatments for Microstructures
Authors: Hsu Yi-Chu , Shen I. Y.
Published: September 2002

This paper presents a bulk micromachining process to fabricate micro-constrained layer treatments (MCLT) on a microstructure to increase its damping, and demonstrates the damping improvement through calibrated experiments. MCLT consists of a silicon base structure (e.g., beams or plates), a viscoelastic photoresist layer, and an aluminum constraining layer. Silicon base beams and plates are fabricated from {100} wafer through Ethylene-Diamine-Pyrocatechol etch and buffered oxide etch. A 4.5-μm thick photoresist AZ4620 is spun on the silicon base beam as the viscoelastic layer. Finally, an aluminum layer is deposited through low-pressure vapor deposition as the constraining layer. To evaluate damping performance of MCLT, silicon beams with and without MCLT are subjected to swept-sine excitations by PZT from 0 to 100 kHz. In addition, a laser Doppler vibrometer and a spectrum analyzer measured frequency response functions (FRF) of the specimen. A finite element analysis identifies the resonance modes measured in FRF. Experimental results confirm that MCLT can increase damping of silicon beams by at least 40%. Significantly better damping performance is expected, if the loss factor of the viscoelastic layer is increased.
Transmissibility as a Differential Indicator of Structural Damage
Authors: Johnson Timothy J. , Adams Douglas E.
Published: September 2002

This article discusses the use of frequency domain transmissibility functions for detecting, locating, and quantifying damage in linear and nonlinear structures. Structural damage affects both the system poles and zeros; however, zeros are much more sensitive than poles to localized damage. This is because zeros depend on the input and output locations whereas poles do not. It is demonstrated here that since transmissibility functions are determined solely by the system zeros, they are potentially better indicators of localized linear and nonlinear types of damage. Furthermore, excitation measurements are not required to compute transmissibility functions so damage indices can be calculated directly from response measurements. It is also demonstrated that sensor arrays can sometimes be used to yield mixed transmissibility functions that are differential in nature, that is, they are less sensitive to gross fluctuations in the dynamic loading or environmental variables.
Ritz Series Analysis of Rotating Shaft System: Validation, Convergence, Mode Functions, and Unbalance Response
Authors: Zirkelback Nicole L. , Ginsberg Jerry H.
Published: September 2002

A shaft with attached rigid disks is modeled as a rotating Timoshenko beam supported by nonconservative, flexible bearing supports. The continuous shaft-disk system is described with kinetic and potential energy functionals that fully account for transverse shear, translational and rotatory inertia, and gyroscopic coupling. Ritz series expansions are used to describe the flexural displacements and cross-sectional rotations about orthogonal fixed axes. The equations of motion are derived from Lagrange’s equations and placed in a state-space form that preserves the skew-symmetric gyroscopic matrix as well as the full effects of the bearings. Both the general and adjoint eigenproblems for the nonsymmetric equations are solved. Bi-orthogonality conditions lead to the ability to evaluate dynamic response via modal analysis. Whirl speeds and logarithmic decrements calculated with the present model are verified with a finite element analysis. The present work provides two ways of evaluating the convergence of results to demonstrate an advantage of the Ritz method over other discretization methods. Natural mode functions and unbalance response are calculated for an example system.
A New Finding on the Dynamic Stiffness Matrices of Asymmetric and Axisymmetric Shafts
Authors: Raffa Francesco A. , Vatta Furio
Published: September 2002

In this paper the dynamic stiffness method is developed to analyze a rotating asymmetric shaft, i.e., a shaft whose transverse section is characterized by dissimilar principal moments of inertia. The shaft is modelled according to the Rayleigh beam theory including the effects of both translational and rotational inertia, and gyroscopic moments. The mathematical description is carried out in a reference system rotating at the shaft speed and is based on the exact solution of the governing differential equations of motion. The exact expressions of the shaft displacements are utilized for deriving the 8×8 complex dynamic stiffness matrix of the shaft. A new relationship is obtained which links the dynamic stiffness matrix of the asymmetric shaft to the 4×4 real dynamic stiffness matrix of the axisymmetric shaft.
Exact Solutions for Vibration of Multi-Span Rectangular Mindlin Plates
Authors: Xiang Y. , Wei G. W.
Published: September 2002

This paper presents the first-known exact solutions for the vibration of multi-span rectangular Mindlin plates with two opposite edges simply supported. The Levy type solution method and the state-space technique are employed to develop an analytical approach to deal with the vibration of rectangular Mindlin plates of multiple spans. Exact vibration frequencies are obtained for two-span square Mindlin plates with varying span ratios and two-, three- and four-equal-span rectangular Mindlin plates. The influence of the span ratios, the number of spans and plate boundary conditions on the vibration behavior of square and rectangular Mindlin plates is examined. The presented exact vibration results may serve as benchmark solutions for such plates.
A Stochastic Averaging Approach for Feedback Control Design of Nonlinear Systems Under Random Excitations
Authors: Elbeyli O. , Sun J. Q.
Published: September 2002

This paper presents a method for designing and quantifying the performance of feedback stochastic controls for nonlinear systems. The design makes use of the method of stochastic averaging to reduce the dimension of the state space and to derive the Ito^ stochastic differential equation for the response amplitude process. The moment equation of the amplitude process closed by the Rayleigh approximation is used as a means to characterize the transient performance of the feedback control. The steady state and transient response of the amplitude process are used as the design criteria for choosing the feedback control gains. Numerical examples are studied to demonstrate the performance of the control.
Nonlinear Control of a Shape Memory Alloy Actuated Manipulator
Authors: Elahinia Mohammad H. , Ashrafiuon Hashem
Published: September 2002

This paper presents a nonlinear, robust control algorithm for accurate positioning of a single degree of freedom rotary manipulator actuated by Shape Memory Alloy (SMA). A model for an SMA actuated manipulator is presented. The model includes nonlinear dynamics of the manipulator, a constitutive model of Shape Memory Alloy, and electrical and heat transfer behavior of SMA wire. This model is used for open and closed loop motion simulations of the manipulator. Experiments are presented that show results similar to both closed and open loop simulation results. Due to modeling uncertainty and nonlinear behavior of the system, classic control methods such as Proportional-Integral-Derivative control are not able to present fast and accurate performance. Hence a nonlinear, robust control algorithm is presented based on Variable Structure Control. This algorithm is a control gain switching technique based on the weighted average of position and velocity feedbacks. This method has been designed through simulation and tested experimentally. Results show fast, accurate, and robust performance of the control system. Computer simulation and experimental results for different stabilization and tracking situations are also presented.
New Method for Solution of Response of Nonlinear Hysteretic System
Authors: Liu J. L.
Published: September 2002

Piecewise interpolation polynomials are employed to approximate an arbitrary dynamic load. By extending the Duhamel integral, we can offer a numerical solution technique of the differential equation of motion in various kinds of material and damping cases in every branch of force-displacement relationship.
Analysis of Piecewise Linear Systems With Boundaries in Displacement and Time
Authors: Nakai Mikio , Murata Shinji , Hagio Seiji
Published: September 2002

A generalized solution methodology based on piecewise linear vector fields is proposed for piecewise linear systems with singular regions or asymmetric restoring forces which vary spatially and temporally. In matrix representation for these systems, state variables in each region can be explicitly expressed as a function of the time the orbit spends between two boundaries or the time when the orbit hits the boundary. The time can be determined by the Brent method, and periodic solutions can then be obtained. Analytical solutions are validated on a system with 3-regions of displacement and 2-regions of time, a circumferential vibration of gear meshing system, by using the newly developed numerical method.
Nonlinear Stochastic Drill-String Vibrations
Authors: Spanos P. D. , Chevallier A. M. , Politis N. P.
Published: September 2002

Lateral vibrations of drill-strings used in oil well operations are considered. A finite elements based discretization procedure leads to a nonlinear dynamic system which is used to represent the drill-string inertia and stiffness characteristics, as well as the elasticity of the wall of the well. Due to the erratic pattern and the uncertainty of the forces at the drill-bit, a stochastic dynamics approach is adopted in investigating the problem. The method of statistical linearization is used, and expressions for determining an equivalent linear system to model the drill-string dynamics are derived. Further, a Monte Carlo simulation of the system dynamics is conducted by means of an Auto Regressive Moving Average (ARMA) digital filter, and by integrating the equations of motion using the Newmark scheme. Numerical results pertaining to data obtained by measurement while drilling (MWD) tools are presented. It is hoped that this study will enhance the interest in using stochastic dynamics techniques in drilling system analysis and design, as they can capture quite appropriately the inherent uncertainty of the bit forces and, potentially, of other sources.
Two-Frequency Oscillation With Combined Coulomb and Viscous Frictions
Authors: Cheng Gong , Zu Jean W.
Published: September 2002

In this paper, a mass-spring-friction oscillator subjected to two harmonic disturbing forces with different frequencies is studied for the first time. The friction in the system has combined Coulomb dry friction and viscous damping. Two kinds of steady-state vibrations of the system—non-stop and one-stop motions—are considered. The existence conditions for each steady-state motion are provided. Using analytical analysis, the steady-state responses are derived for the two-frequency oscillating system undergoing both the non-stop and one-stop motions. The focus of the paper is to study the influence of the Coulomb dry friction in combination with the two frequency excitations on the dynamic behavior of the system. From the numerical simulations, it is found that near the resonance, the dynamic response due to the two-frequency excitation demonstrates characteristics significantly different from those due to a single frequency excitation. Furthermore, the one-stop motion demonstrates peculiar characteristics, different from those in the non-stop motion.
Vibration Control of the Rotating Flexible-Shaft/Multi-Flexible-Disk System With the Eddy-Current Damper
Authors: Fung Rong-Fong , Sun Jung-Hung , Hsu Shih-Ming
Published: September 2002

In this paper, the rotating flexible-Timoshenko-shaft/flexible-disk coupling system is formulated by applying the assumed-mode method into the kinetic and strain energies, and the virtual work done by the eddy-current damper. From Lagrange’s equations, the resulting discretized equations of motion can be simplified as a bilinear system (BLS). Introducing the control laws, including the quadratic, nonlinear and optimal feedback control laws, into the BLS, it is found that the eddy-current damper can be used to suppress flexible and shear vibrations simultaneously, and the system is globally asymptotically stable. Numerical results are provided to validate the theoretical analysis.
Experimental Investigation into the Instability of an Over-Hung Rigid Centrifuge Rotor Partially Filled With Fluid
Authors: Changsheng Zhu
Published: September 2002

The objective of this paper is to experimentally investigate the instability of an over-hung rigid centrifuge rotor partially filled with fluid. Specific emphasis has been placed on the developing process of rotor instability, the dynamical behavior of the rotor system while the instability occurs, and the frequency and direction of rotor whirl within the unstable region of rotational speeds. The effects of fluid-fill ratio on the rotor whirl frequency, the extent of the unstable region of rotational speeds, and the rotor imbalance are also studied. The detailed results clarify some issues and show some new phenomena on the instability of a rotor partially filled with fluid. The phenomena include: sub-synchronous frequency that does not result in instability of the rotor system and disappears in the unstable region at the larger fluid-fill ratios; different whirl frequencies entering the unstable region for slowly increasing and decreasing rotational speed operations; variable whirl frequency within the unstable region; hysteresis at the upper bound of the unstable region; and a break-down of the fluid free-surface.
Physical Realization of Generic-Element Parameters in Model Updating
Authors: Ahmadian H. , Mottershead J. E. , Friswell M. I.
Published: September 2002

The selection of parameters is most important to successful updating of finite element models. When the parameters are chosen on the basis of engineering understanding the model predictions are brought into agreement with experimental observations, and the behavior of the structure, even when differently configured, can be determined with confidence. Physical phenomena may be misrepresented in the original model, or may be absent altogether. In any case the updated model should represent an improved physical understanding of the structure and not simply consist of unrepresentative numbers which happen to cause the results of the model to agree with particular test data. The present paper introduces a systematic approach for the selection and physical realization of updated terms. In the realization process, the discrete equilibrium equation formed by mass, and stiffness matrices is converted to a continuous form at each node. By comparing the resulting differential equation with governing equations known to represent physical phenomena, the updated terms and their physical effects can be recognized. The approach is demonstrated by an experimental example.