bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Fault Detection Based on the Wavelet De-Noising Technique
Authors: Lin Jing , Zuo Ming J. , Fyfe Ken R.
Published: February 2004

For gears and roller bearings, periodic impulses indicate that there are faults in the components. However, it is difficult to detect the impulses at the early stage of fault because they are rather weak and often immersed in heavy noise. Existing wavelet threshold de-noising methods do not work well because they use orthogonal wavelets, which do not match the impulse very well and do not utilize prior information on the impulse. A new method for wavelet threshold de-noising is proposed in this paper; it not only employs the Morlet wavelet as the basic wavelet for matching the impulse, but also uses the maximum likelihood estimation for thresholding by utilizing prior information on the probability density of the impulse. This method has performed excellently when used to de-noise mechanical vibration signals with a low signal-to-noise ratio.
Suppression of Parametric Resonance in Cantilever Beam With a Pendulum (Effect of Static Friction at the Supporting Point of the Pendulum)
Authors: Yabuno Hiroshi , Murakami Tomohiko , Kawazoe Jun , Aoshima Nobuharu
Published: February 2004

The dynamic response of a parametrically excited cantilever beam with a pendulum is theoretically and experimentally presented. The equation of motion and the associated boundary conditions are derived considering the static friction of the rotating motion at the supporting point (pivot) of the pendulum. It is theoretically shown that the static friction at the pivot of the pendulum plays a dominant role in the suppression of parametric resonance. The boundary conditions are different between two states in which the motion of the pendulum is either trapped by the static friction or it is not. Because of this variation of the boundary conditions depending on the pendulum motion, the natural frequencies of the system are automatically and passively changed and the bifurcation set for the parametric resonance is also shifted, so that parametric resonance does not occur. Experimental results also verify the effect of the pendulum on the suppression of parametric resonance in the cantilever beam.
Nonlinear Dynamics of a Micro-Electro-Mechanical System With Time-Varying Capacitors
Authors: Luo Albert C. J. , Wang Fei-Yue
Published: February 2004

The natural frequency and responses of a micro-electro-mechanical system (MEMS) with time-varying capacitors are determined under an equivalent direct current (DC) voltage. Under alternating current (AC) voltages, the resonant condition and the corresponding resonant motion possessing a wide energy band for such a system are investigated because the motion with the wide energy band is very easily sensed. For a given voltage strength, the AC frequency band is obtained for chaotic resonant motions in the specific resonant layer. The numerical and analytical predictions of such a motion are in a acceptable agreement, and the dynamic model provides the range prediction of the alternating current and voltage on the capacitor agreeing with experimental measurements. The lower-order resonant motion has a higher energy than the higher-order resonant motions, which indicates that the lower-order resonant motion can be easily sensed. Although this model is developed from a specified MEMS, the analysis and results can be applied to other dynamic systems.
Nonlinear Interaction of an Elastic Pulse With a Frictional Contact Interface Between Two Anisotropic Dissimilar Media
Authors: Wang Yue-Sheng , Dai Hui-Hui , Yu Gui-Lan
Published: February 2004

The paper analyses the interaction of an elastic pulse of arbitrary form with a frictional contact interface between two anisotropic solids which are pressed together and at the same time loaded by the in-plane and anti-plane shearing tractions. The incident pulse is assumed strong enough to break friction so that localized separation and slip take place. Coulomb friction, which causes the non-linear coupling between the in-plane and anti-plane motions, is supposed along the contact interface. The sub-critical angle incidence is first considered. By using Fourier analysis, the problem is reduced to a set of algebraic equations. A method to get the solution of the equations with determination of the slip/stick/separation zones is developed. As an example, the detailed computation for the case of an incident parabolic stress pulse is carried out. Numerical results of the interface tractions and the slip velocities are presented for two contacting half-spaces of the same materials in the same orientation. The super-critical angle incidence is discussed. In this case the problem is cast to a set of non-linear Cauchy singular integral equations whose solution is still an open question in mathematics.
Experimental Study on Ball Screw Type Magnetic Friction Damper: Semiactive Control Using Electromagnet
Authors: Watanabe Tetsuya , Suzuki Kohei , Iiyama Fumiya , Sodeyama Hiroshi
Published: February 2004

This report deals with the fundamental behavior of friction dampers for piping systems installed in industrial facilities. Energy dissipating effect depends on sliding displacement and friction force. If the sliding motion increases, the effect of energy dissipation is expected to rise. In this report, a ball screw-type magnetic friction damper is proposed to adapt on piping systems. In order to increase the frictional sliding, this damper converts an axial motion to a rotating motion by a ball screw. Frictional behavior occurs between a rotation disk and a fixed disk on the frame of damper. Friction force depends on the permanent magnets located on the fixed disk. The fundamental characteristics such as load-displacement curves, damping force at the ball bearing and inertia force of the rotation disk are obtained by experiments and a calculation model is made from the experimental data. The calculated responses are, then, compared with the results from the experiment. The calculation model is applied to a one-degree-of-freedom-system in order to investigate the response reduction effect of the system. An electromagnet is applied on the damper instead of the permanent magnet to control friction force and the controlled behavior is evaluated.
Development of Large Capacity Semi-Active Seismic Damper Using Magneto-Rheological Fluid
Authors: Sodeyama Hiroshi , Suzuki Kohei , Sunakoda Katsuaki
Published: February 2004

In recent years, there has been increasing research in several industrial fields for development of semi-active vibration control devices. In particular, devices using magneto-rheological (MR) fluid have been attracting great research interest because they can realize high performance as capacity-variable dampers. MR fluids are controllable fluids that respond to applied magnetic fields. Applied magnetic fields drastically change the viscosity of MR fluids from an oily state to a semi-solid state. This paper describes a study on a large capacity device using an MR fluid, i.e., an MR damper. This developed MR damper provides a maximum damping force of 300 kN. Various tests were carried out and the dynamic characteristics, force-displacement hysteresis loops and controllable forces were investigated. These tests verified that the MR damper provides a technology that enables effective semi-active control of large-scale structure systems, i.e., real buildings and civil engineering structures.
Vibration Characteristics and Seismic Responses of Mechanical Structures With Hysteresis Elements
Authors: Fujita Katsuhisa , Kimura Tetsuya , Ohe Yoshikazu
Published: February 2004

Hysteresis elements such as elasto-plastic dampers are important for mechanical structures. They have nonlinearities and thus the vibration characteristics of mechanical structures with hysteresis elements are not clarified yet and need further studies. In this paper, the investigation of the dynamical stability of mechanical structures with a hysteresis element is performed by means of describing function method, which is on the basis of linear approximation of the hysteresis element. The nonlinear vibration system is composed of a linear spring-mass-damper structure system of any order and a hysteresis damper. The describing function of a hysteresis damper is derived and it is shown that the function remains upper half plane in the complex plane. According to the passivity of the linear structure system, this fact leads to the vibration system that is stable for any harmonic excitation. Next, the responses for seismic excitation are examined in simulation by using two typical models of the hysteresis element, a bilinear model and a Ramberg-Osgood model. The effects of the second stiffness of the dampers and the amplitude of the excitation motion are investigated using an actually recorded earthquake motion. The simulation results imply that the determination of the second stiffness requires the trade-off between an oscillation and a drift for designing earthquake-proof mechanical structures with the hysteresis damper.
Seismic Response Analysis of Piping Systems With Nonlinear Supports Using Differential Algebraic Equations
Authors: Fujita Katsuhisa , Kimura Tetsuya , Ohe Yoshikazu
Published: February 2004

Hysteresis elements such as elasto-plastic dampers are important elements for mechanical structures, especially for earthquake-proof structures. When such nonlinear supports are utilized for piping systems, the nonlinearities of the hysteresis elements and the geometrical complexity of the piping systems lead to complicated seismic responses, and thus further studies are required in order to enhance the reliability of the earthquake-proof design. In the seismic response analysis, the method of time history response analysis is widely used. In this paper, a method of nonlinear seismic response analysis for a piping systems using a combination of the FEM and the Differential Algebraic Equations (DAE) is proposed. As it is well known, the DAE is suitable for numerical analysis of time history responses for mechanical structures and machinery elements. According to the advantage of the DAE, the numerical modeling and simulation of a complex piping systems supported by the hysteresis elements can be easily carried out by using the proposed method. In order to verify the usefulness of the method, the time history responses of piping systems supported by a elasto-plastic damper is examined for seismic excitation by using the proposed method. The damper is modeled as a bilinear model. The effects of the second stiffness and the stiffness associated with the plastic deformation of the damper on the seismic responses are investigated using an actually recorded earthquake motion.
Evaluation for Mechanical Properties of Laminated Rubber Bearings Using Finite Element Analysis
Authors: Matsuda Akihiro
Published: February 2004

In this paper, improvements of evaluation method for mechanical properties of rubber materials and isolated rubber bearings are shown. The displacement/pressure mixed method of hyperelastic material considering the viscoelastic effect, compressibility and the softening effect for high damping rubber is formulated in the first place. Also, simple numerical model of the high damping rubber is proposed from experimental results. Mechanical properties of both high damping and natural rubber are calculated by developed finite element code. Next, an evaluation methods for mechanical properties (horizontal, vertical and horizontal-vertical coupled properties) of the natural rubber bearings is shown.
Identification of Structural Parameters Using the Wavelet Transform of Acceleration Measurements
Authors: Sone Akira , Hata Hiroaki , Masuda Arata
Published: February 2004

In this paper, the characteristic parameters of structures are estimated by a newly developed identification method based on the wavelet transform of acceleration measurements. In the proposed method, by using the localized nature and the moment condition of the analyzing wavelet, the equation of motion of the structure is translated to an algebraic equation in terms of the acceleration responses, so that one can identify the structural parameters only using the acceleration measurements. The basic performance of the proposed method and the influence of the observation noise as well as the sampling density of the scale parameter are discussed in numerical examples. Laboratory-scale experiments demonstrate that the proposed method is capable to identify the structural parameters such as damping matrix and the stiffness matrix in sufficient accuracy.
Stabilization of a Plastic-Deformed Structure by Air Jet Pulse
Authors: Kawashima Takeshi
Published: February 2004

When a strong earthquake occurs, many buildings are destroyed. For the inhabitants of such buildings, having sufficient time to take refuge is critical. This study presents the basic concept of a control system for stabilizing a plastic-deformed building by jetting out compressed gas while the inhabitants escape. This system features easy installation. Constant pressure gas is employed, and is controlled to jet or to stop jetting. The plastic-deformed building is modeled as a two-link inverted pendulum, and the design of the stabilizing controller is based on the sliding mode control theory. The validity of the system is confirmed by numerical simulations and model experiments. The results indicate that (1) an unstable structure can be stabilized by air jet pulses, (2) a robust bang-bang type controller can be derived by designing the switching surface to have an equivalent control input equal to zero, and (3) chattering of the control input is suppressed by setting an insensitive zone.
Motion Analysis of Pendulum-Type Isolation Systems During Earthquakes: Dynamic Test and Response Analysis on a Three Story Steel Frame Model Supported by Four Friction Pendulum Bearings
Authors: Okamura Shigeki , Fujita Satoshi , Ikenaga Masayoshi
Published: February 2004

After the Hanshin-Awaji Earthquake Disaster, the number of earthquake isolated buildings is increasing. Most of the base isolated buildings or structures are built on laminated rubber bearings in order to give them certain natural periods. This situation, however, also encourages structural engineers to research and develop nonrubber-type isolation systems such as linear motion bearing isolators and friction pendulum systems. It is considered that the nonrubber-type isolation systems can be applied to important industrial facilities, such as LNG tanks, boiler facilities and so on to refine their seismic reliabilities. In the device of the nonrubber-type isolation systems, the device which applied the sliding is especially noticed. However, when using nonrubber-type isolation systems with sliding in the open air circumstances, long term durability of the systems must be taken into account and it may be very difficult to maintain the friction coefficient of the system. In this study, the dynamic motion analysis and the experimental tests on the isolated structure mounted on four Friction Pendulum Bearing (FPB) Systems were carried out to investigate the performance of isolation due to the rotational motion which might be induced by the friction force difference in FPB system.
Restoring Force Characteristics of Laminated Rubber Bearings Under Various Restraining Conditions
Authors: Masaki Nobuo , Suzuki Shigenobu
Published: February 2004

We conducted the measurement of restoring force characteristics of laminated rubber bearings under various restraining conditions. In the experiment, we provided three laminated rubber bearings with various second shape factors S2=3,4,4.94. The restoring force is obtained by using a newly designed combined loading test apparatus. By using this apparatus, the laminated rubber bearing could be subjected to shear, compressive and rotational deformations independently. In this experiment, we defined the degree of restraint as the ratio of the bending moment to the restricting bending moment which was measured when the rotation angle of the laminated rubber bearing was zero radian. This means that the flanges on both sides of the laminated rubber bearings were kept parallel during horizontal deformations. From the experiment, it was confirmed that restoring force characteristics were affected by the degree of restraint. Some reduction in restoring forces was observed when the degree of restraint was small. In particular the laminated rubber bearing with a small second shape factor, namely the rubber bearing, had a slender shape, easily buckling under small horizontal displacement. It was also confirmed that bending stiffness of the laminated rubber bearing had shear strain dependency and vertical load i.e., surface pressure dependency. The results of this experiment reveal that we should consider the reduction of the restoring force if the upper or lower structure of the laminated rubber bearing is not sufficiently rigid.
Research and Development of Measurement Method for Structural Fracturing Process in Shake Table Tests Using Image Processing Technique
Authors: Fujita Satoshi , Furuya Osamu , Mikoshiba Tadashi
Published: February 2004

The largest three-dimensional shake table is now being constructed in Hyogo prefecture, Japan for a solution of fracturing process of structures, buildings, and soils. However, it seems to be difficult to measure the fracturing processes of the structures during severe earthquake by using conventional methods and equipment, because the three-dimensional measurement of larger dynamic displacement in excess of elastic region of the structure will be the key to a solution and cannot be obtained by any of the vibration pick-ups such as displacement transducers and so on. In this study, R&D of the new measurement method to clarify the fracturing process of the structures by applying a so-called motion capture technique, which has been mainly studied for modeling of human actions and motions. This paper describes the concept of the system, the outline of the proto-type image processing system developed in the study and the results of the shake table test using five-story steel-structure model to investigate the measurable accuracy of the system.
Evaluation of Aseismic Reliability of Actual Boiler Structures and a Study on Design of Seismic Ties Based on Proof Tests Using a Large Scaled Shaking Table
Authors: Aida Kiyoshi , Owa Yasuyuki , Suzuki Kohei , Fujita Satoshi
Published: February 2004

This paper deals with the evaluation of aseismic reliability of actual boiler plant structures in conjunction with seismic ties, installed between the boiler and the support structures. Proof tests were conducted with a coupled model using a large-scale shake table which verified that the ties acted as energy-absorbing devices against severe earthquakes. Since recent boiler structures are designed based on dynamic response analysis considering the boiler-structure interaction and the effect of energy dissipation of the ties, it is necessary to verify the accuracy of simulation methods. In view of this, the numerical models of the ties are discussed in post analysis. As a result of the post analysis, it is confirmed that (1) seismic ties of existing boiler plants designed by dynamic analysis provide sufficient durability, and (2) the support structures designed by conventional methods have enough aseismic reliability.
Seismic Performance Evaluation of Seismically Isolated Buildings Introduced to the Building Code of Japan
Authors: Midorikawa Mitsumasa , Iiba Masanori , Koshika Norihide
Published: February 2004

The Building Code of Japan (the Building Standard Law of Japan) has been changed from the former prescriptive type into a performance-based type in June, 2000. This paper presents the evaluation procedures for seismic performance of seismically isolated buildings against major earthquake motions newly introduced to the Building Code of Japan in October, 2000. The evaluation procedures apply the equivalent single-degree-of-freedom (ESDOF) system, equivalent linearization and response spectrum analysis. The basic concept of seismic design spectra for major earthquake motions is (1) basic design spectra defined at the engineering bedrock, and (2) evaluation of site response from geotechnical data of surface soil layers. The principle of evaluation procedures is that the predicted response values should not exceed estimated limit values. The evaluation criteria of each portion of a building are (1) the isolation system shall be designed so that the maximum response displacement does not exceed the design limit displacement, and (2) the structure above the isolation system and the foundation and structural elements below the isolation system shall be designed so that the working stress does not exceed the allowable stress. The scope of application of the evaluation procedures is (1) buildings not exceeding 60 meters in height, and (2) base isolation buildings on the soil layers excluding very soft soils.
Development of Seismic Design Code for High Pressure Gas Facilities in Japan
Authors: Shibata Heki , Suzuki Kohei , Ikeda Masatoshi
Published: February 2004

The Seismic Design Code for High Pressure Gas Facilities was established in 1982 in advance of those in other industrial fields, the only exception being that for nuclear power plants. In 1995, Hyogoken Nanbu earthquake caused approximately 6000 deaths and more than $1 billion (US) loss of property in the Kobe area, Japan. This unexpected disaster underlined the idea that industrial facilities should pay special consideration to damages including ground failure due to the liquefaction. Strong ground motions caused serious damage to urban structures in the area. Thus, the Seismic Design Code of the High Pressure Gas Facilities were improved to include two-step design assessments, that is, for Level 1 earthquakes (operating basis earthquake: a probable strong earthquake during the service life of the facilities), and Level 2 earthquakes (safety shutdown earthquake: a possible strongest earthquake with extremely low probability of occurrence). For Level 2 earthquakes, ground failure by possible liquefaction will be taken into account. For a Level 1 earthquake, the required seismic performance is that the system must remain safe without critical damage after the earthquake, including no gas leakage. For a Level 2 earthquake, the required seismic performance is that the system must remain safe without gas leakage. This means a certain non-elastic deformation without gas leakage may be allowed. The High Pressure Gas Safety Institute of Japan set up the Seismic Safety Promotion Committee to modify their code, in advance of other industries, and has continued to investigate more effective seismic design practices for more than 5 years. The final version of the guidelines has established design practices for the both Level 1 and Level 2 earthquakes. In this paper, the activities of the committee, their new design concepts and scope of applications are explained.
New Seismic Design Criteria of Piping Systems in High-Pressure Gas Facilities
Authors: Inaba Makoto , Ikeda Masatoshi , Shimizu Nobuyuki
Published: February 2004

After the Great Hyogoken-nanbu Earthquake (1995), the Seismic Design Code for High-Pressure Gas Facilities of Japan was amended. This amended code requires two-step seismic assessments, that is, the evaluation of the Level 1 Required Seismic Performance for Level 1 earthquakes and that of the Level 2 Required Seismic Performance for Level 2 earthquakes. Seismic design of piping systems is newly included within the scope of the code. For Level 2 earthquakes, possible ground displacement due to liquefaction is taken into account. The evaluation method of the Level 1 Required Seismic Performance is specified in the amended code and that of the Level 2 Required Seismic Performance is proposed in the guideline. The evaluation of the former is based on elastic design and that of the latter on elastoplastic design. The propriety of the design criteria of piping systems with respect to ground displacement was confirmed by large deformation tests. In this paper, seismic design criteria of piping systems in the amended code and the evaluation method of the Level 2 Required Seismic Performance proposed in the guideline are introduced, and the results of the large deformation tests are reported.
Design and Simulation of Robust and Adaptive Controls for a Nonlinear String System1
Authors: Jin Weiwei , Qu Zhihua , Lin Kuo-Chi
Published: February 2004

In this paper, vibration control of a nonlinear string system is considered. The system consists of a nonlinear string, two boundary supporting mechanisms, and a moving transporter at the base. To suppress the vibration, boundary control designs are carried out. A new robust and adaptive boundary controller is designed using the Lyapunov direct method. The proposed control is implemented at the two ends supporting the string to compensate for vibration induced by the base motion. It is shown that the adaptive/robust boundary control can asymptotically stabilize the nonlinear string. Numerical simulation of the closed loop system demonstrates the effectiveness of the proposed control.
Identifying Coulomb and Viscous Friction in Forced Dual-Damped Oscillators
Authors: Liang Jin-Wei , Feeny Brian F.
Published: February 2004

This paper presents a method for estimating Coulomb and viscous friction coefficients from responses of a harmonically excited dual-damped oscillator with linear stiffness. The identification method is based on existing analytical solutions of non-sticking responses excited near resonance. The method is applicable if the damping ratio of viscous component can be considered small. The Coulomb and viscous friction parameters can be extracted from two or more input-output amplitude pairs at resonance. The method is tested numerically and experimentally. Experimental results are cross checked with estimations from free-vibration decrements and also from friction measurements.
Control of Nonlinear Electro/Elastic Beam and Plate Systems (Finite Element Formulation and Analysis)
Authors: Wang D. W. , Tzou H. S. , Lee H.-J.
Published: February 2004

Adaptive structures involving large imposed deformation often go beyond the boundary of linear theory and they should be treated as “nonlinear” structures. A generic nonlinear finite element formulation for vibration sensing and control analysis of laminated electro/elastic nonlinear shell structures is derived based on the virtual work principle. A generic curved triangular piezoelectric shell element is proposed based on the layerwise constant shear angle theory. The dynamic system equations, equations of electric potential output and feedback control force defined in a matrix form are derived. The modified Newton-Raphson method is adopted for nonlinear dynamic analysis of large and complex piezoelectric/elastic/control structures. A finite element code for vibration sensing and control analysis of nonlinear active piezoelectric structronic systems is developed. The developed piezoelectric shell element and finite element code are validated and then applied to control analysis of flexible electro-elastic (piezoelectric/elastic) structural systems. Vibration control of constant-curvature electro/elastic beam and plate systems are studied. Time-history responses of free and controlled nonlinear electro/elastic beam and plate systems are presented and nonlinear effects discussed.
Substructure Analysis of a Flexible System Contact-Impact Event
Authors: Guo Anping , Batzer Steve
Published: February 2004

In this paper, the application of the substructure methodology to contact-impact analysis of flexible multibody systems is validated. Various impact model parameters that affect the model’s accuracy are presented. A contact-impact system is used that consists of a flexible cantilever bar longitudinally struck at its free end by a rigid body moving at a finite velocity. First, a dynamic model using the substructure method is established. Second, the initial conditions of the system’s dynamic responses during contact-impact are derived. Finally, a numeric contact-impact simulation is performed. The excellent agreement between the numeric solutions to both the substructure model and the analytical solutions demonstrates that the substructure model can successfully describe stress wave propagation within flexible bodies during contact-impact. The method can also clearly display the contact force time history and deformation distribution along the bar during contact-impact time and correctly predict the displacement of the contact surface of the flexible bar and the contact duration of the two bodies. It is shown that a larger substructure number will improve the accuracy of the numerical solutions, but an excessive number will lower the model’s accuracy since increasingly fine substructures increase the number of modal coordinates and lead to more serious computational round off errors and longer computational time.
Distributed Modal Voltages of Nonlinear Paraboloidal Shells With Distributed Neurons
Authors: Tzou H. S. , Ding J. H.
Published: February 2004

Effective health monitoring and distributed control of advanced structures depends on accurate measurements of dynamic responses of elastic structures. Conventional sensors used for structural measurement are usually add-on “discrete” devices. Lightweight distributed thin-film piezoelectric neurons fully integrated (laminated or embedded) with structural components can serve as in-situ sensors monitoring structure’s dynamic state and health status. This study is to investigate modal voltages and detailed signal contributions of linear or nonlinear paraboloidal shells of revolution laminated with piezoelectric neurons. Signal generation of distributed neuron sensors laminated on paraboloidal shells is defined first, based on the open-voltage assumption and Maxwell’s principle. The neuron signal of a linear paraboloidal shell is composed of a linear membrane component and a linear bending component; the signal of a nonlinear paraboloidal shell is composed of nonlinear and linear membrane components and a linear bending component due to the von Karman geometric nonlinearity. Signal components and distributed modal voltages of linear and nonlinear paraboloidal shells with various curvatures and thickness are investigated.
Seismic Soil-Structure Interaction Responses of N-Reactor Facility
Authors: Chen J. C. , Maslenikov O. R.
Published: February 2004

This paper summarizes our seismic analysis of the soil structure interaction (SSI) responses of N-reactor facility. In the SSI analysis, CLASSI computer codes were used to calculate SSI responses of the structures and to generate the input motions for the nonlinear reactor core analysis. In addition, the responses were compared to the responses from the SASSI analysis under review. The impact of the foundation modeling techniques and the effect of soil stiffness variations on SSI response were also investigated.
An Investigation of Excitation Method for Torsional Testing of a Large-Scale Steam Turbine Generator
Authors: Chen Yong
Published: February 2004

Presently, the “negative sequence current method” is widely used in field-testing to determine torsional vibration characteristics of steam turbine generator rotor systems. The natural frequencies of lower modes of vibration can be determined effectively in this way, but higher modes cannot be readily excited. To understand this phenomenon, modal analysis was employed to digitally simulate the dynamic response obtained in torsional vibration testing of a 200MW steam turbine generator rotor system. The calculations were consistent with field experimental results, showing that higher modes are difficult to excite by this method. The research also indicated that higher modes could be excited by certain experimental procedures. The conclusions provide guidelines for future field-testing of large-scale systems.
Vibration of Rectangular Orthotropic Elliptic Plates of Quadratically Varying Thickness Resting on Elastic Foundation
Authors: Gupta A. P. , Bhardwaj N.
Published: February 2004

The title problem is analyzed when nodal lines are concentric ellipses by using boundary characteristic orthonormal polynomials in Rayleigh-Ritz method for Winkler foundation where quadratically varying thickness is controlled by two independent taper constants. Numerical results for frequencies, nodal ellipses and mode shapes for first four modes of vibration are presented for plates of free, simply-supported and clamped edge conditions for various values of aspect ratio, taper, orthotropy and foundation parameters.
Identification of Multi-Axle Vehicle Loads on Bridges
Authors: Yu Ling , Chan Tommy H. T.
Published: February 2004

Both the time domain method (TDM) and frequency-time domain method (FTDM) are introduced and modified for the indirect identification of multi-axle vehicle loads from the bending moment responses of bridges. Two solutions to the over-determined set of equation involved in the identification methods are adopted. One is direct calculation of the pseudo inverse and another calculation of the pseudo inverse via the singular value decomposition technique for the ill-conditioned problems encountered. A few multi-axle vehicles were designed and constructed in the laboratory for validation purposes based on the ASSHTO standard specifications of highway bridges. Two kinds of frames between the tractor and trailer of trucks and, three types of vehicle suspension systems were simulated. Different multi-axle vehicle loads were identified from the measured bending moment responses of bridges under different operation condition in the laboratory. The effects of various vehicle and bridges parameters were evaluated. Comparative studies show that both TDM and FTDM methods involved in the moving force identification system (MFIS) are good identification methods and could efficiently identify the multi-axle vehicle loads on bridges.
Comparison of pulsed and downstream deposition of fluorocarbon materials from C3F8 and c-C4F8 plasmas
Authors: Martin Ina T. , Malkov Galiya Sh. , Butoi Carmen I. , Fisher Ellen R.
Published: February 2004

Materials deposited in continuous wave (cw) and pulsed low-pressure octafluoropropane (C3F8) and octafluorocyclobutane (c-C4F8) plasmas were characterized using Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy, static contact angle measurements, spectroscopic ellipsometry, and scanning electron microscopy (SEM). Fluorocarbon (FC) materials deposited in pulsed plasmas were less crosslinked than those deposited in cw plasmas with equivalent input powers. Within each system, higher F/C ratio materials were deposited by lowering the plasma input power/duty cycle. Using downstream depositions had a similar effect on film composition, but also resulted in decreased deposition rates. SEM analysis showed that decreases in the flexibility of the fluorocarbon films were correlated with increases in the percent of crosslinking. Additionally, the smoothness of the film surfaces suggests that polymerization processes occur on the substrate surface. Overall, films deposited in C4F8 plasmas were more crosslinked and less flexible than those deposited in C3F8 plasmas under the same conditions. The composition of the deposited FC films is correlated to the nature and relative concentrations of nascent ions previously measured in these plasma systems using plasma ion mass spectrometry.
Study of C4F8/CO and C4F8/Ar/CO plasmas for highly selective etching of organosilicate glass over Si3N4 and SiC
Authors: Ling Li , Hua X. , Li X. , Oehrlein G. S. , Celii F. G. , Kirmse K. H. R. , Jiang P. , Wang Yicheng , Anderson H. M.
Published: February 2004

We have examined the effect of CO addition to C4F8 or C4F8/Ar plasmas for selective etching of organosilicate glass (OSG) over SiC etch stop layers. The variation of important gas phase species, thin film etching rates and surface chemistry with feedgas composition was determined. CO addition exhibits dramatically different consequences on OSG/SiC etching selectivity when added to C4F8 or C4F8/Ar plasmas containing a high proportion of Ar. An improvement of the OSG/SiC etching selectivity results from CO addition to C4F8. We observe little CO dissociation in this case, which is plausible considering the lower dissociation energy threshold of C4F8 relative to CO. X-ray photoelectron spectroscopy (XPS) analysis of OSG and SiC surfaces shows that the etching selectivity improvement for C4F8/CO may be explained not only by an increase of the thickness and a reduction of the F/C ratio of the steady-state fluorocarbon surface layer on the SiC surface during etching, but little incorporation of CO into deposited fluorocarbon films. Adding CO to C4F8/Ar discharges with a high proportion of Ar leads to a reduction of the OSG/SiC etching selectivity. Significant dissociation of CO in Ar-rich C4F8/Ar/CO discharges is observed, consistent with the fact that the dissociation energy threshold of CO is lower than the Ar ionization and metastable energies. Oxygen incorporation in deposited fluorocarbon films and a reduction of the steady-state fluorocarbon surface layer thickness on SiC are observed by XPS in this case, explaining the loss of OSG/SiC etching selectivity for C4F8/Ar/CO discharges.
Control of nitrogen depth profile in ultrathin oxynitride films formed by pulse-time-modulated nitrogen beams
Authors: Samukawa Seiji , Minemura Youichi , Fukuda Seiichi
Published: February 2004

Ultrathin Si oxynitride (SiOxNy) films have been identified as leading candidates to replace conventional SiO2 gate dielectrics in current and future ultralarge-scale integrated circuits. Remote plasma processes to nitridate the top surface of thermally grown oxides have been developed and employed in complementary metal–oxide–silicon device applications. However, it is very difficult to control the nitrogen depth profile in ultrathin Si oxynitride film using plasma processing and there are many serious problems, such as plasma radiation damage and increases in interface state density due to the N penetrating into the SiO2–Si interface. To overcome these problems, we propose the use of pulse-time-modulated N2 neutral beams. We first found that the nitrogen depth profile in ultrathin Si oxynitride film could be controlled by changing the pulse-on time and source power in the pulse-time-modulated N2 neutral beams. We speculated that injected N2 was diffused due to the surface activation with the energetic neutral beam at a time constant of a few tens of microseconds in the thermal SiO2 film. Additionally, by increasing the substrate temperature to 300 °C, SiO–N bonds were effectively formed and a shallower, sharper, and higher density N concentration profile in a thin 2 nm SiO2 film was produced using a pulsed N2 neutral beam.
Reactive physical vapor deposition of TixAlyN: Integrated plasma-surface modeling characterization
Authors: Zhang Da , Schaeffer J. K.
Published: February 2004

Reactive physical vapor deposition (RPVD) has been widely applied in the microelectronic industry for producing thin films. Fundamental understanding of RPVD mechanisms is needed for successful process development due to the high sensitivity of film properties on process conditions. An integrated plasma equipment-target nitridation modeling infrastructure for RPVD has therefore been developed to provide mechanistic insights and assist optimal process design. The target nitridation model computes target nitride coverage based on self-consistently derived plasma characteristics from the plasma equipment model; target sputter yields needed in the plasma equipment model are also self-consistently derived taking into account the yield-suppressing effect from nitridation. The integrated modeling infrastructure has been applied to investigating RPVD processing with a Ti0.8Al0.2 compound target and an Ar/N2 gas supply. It has been found that the process produces athermal metal neutrals as the primary deposition precursor. The metal stoichiometry in the deposited film is close to the target composition due to the predominance of athermal species in the flux that reaches the substrate. Correlations between process parameters (N2 flow, target power), plasma characteristics, surface conditions, and deposition kinetics have been studied with the model. The deposition process is characterized by two regimes when the N2 flow rate is varied. When N2 is dilute relative to argon, target nitride coverage increases rapidly with increasing N2 flow. The sputter yield and deposition rate consequently decrease. For less dilute N2 mixtures, the sputter yield and deposition rate are stable due to the saturation of target nitridation. With increasing target power, the electron density increases nearly linearly while the variation of N generation is much smaller. Target nitridation and its suppression of the sputter yield saturate at high N2 flow rendering these parameters insensitive to target power variation. The deposition rate, however, increases with target power as a result of the increased ion energy and flux at the target.
Some considerations on heater design for simultaneous deposition of large-area double-sided high-Tc superconducting thin films
Authors: Chen J. J. , Tao B. W. , Liu X. Z. , Li Y. R.
Published: February 2004

Some important factors on heater design, which is used for the deposition of high-Tc superconducting thin films, have been discussed in this article. Compared to radiation heat transfer directly from the heater to the substrate, the conduction and convection due to the inlet gas (oxygen or/and argon) are negligible. A theoretical model based on radiation heat transfer has been proposed by which some heater configurations have been discussed in detail. The temperature distribution in a simultaneous deposition system with two sputtering sources is improved by either proper off-axis displacement accompanied with in-plane substrate rotation or increasing the distance of the two heating sheets. For a biaxial rotating substrate, a cylindrical heater is proposed. The temperature distribution in the heater can be modulated by varying the input power ratio of the two heating parts. And, the total radiation power imposed on the substrate in every out-of-plane revolution is excellently homogeneous.
Effects of voltage distribution along an induction coil and discharge frequency in inductively coupled plasmas
Authors: Edamura Manabu , Benck Eric C.
Published: February 2004

Recent etching processes often use low to middle plasma density in order to increase etching controllability or to reduce charging damages. In inductively coupled plasmas (ICPs) in low to middle plasma density, effects of a capacitively coupled discharge (E discharge) on the total plasma characteristic cannot be neglected. It is thus more difficult to understand the ICPs in low to middle density than to understand high-density ICPs which can be regarded as being generated by an inductively coupled discharge (H discharge) only. In this research, we changed the voltage distribution of the induction coil of an ICP-modified gaseous electronics conference reference cell by inserting a termination capacitor between the coil and the ground. We also changed the discharge frequencies (6.28 MHz, 13.56 MHz, and 20 MHz), and investigated their effects on Ar plasmas. As a result, it was observed that the structure of the E discharge was changed by the voltage distribution of the coil and, therefore, E-to-H mode transitions were dramatically altered. Although no difference between the electron energy distribution functions (EEDFs) was observed in a pure H discharge with an electrostatic shield for the experimental conditions studied (1.33 Pa and 150 W), it was observed that EEDFs were affected by the discharge frequency without an electrostatic shield, probably due to a decrease of electron density by the effect of an E discharge and an increase of the ratio of the E to H discharge with increasing discharge frequency.
Electron cyclotron resonance plasma enhanced metalorganic chemical vapor deposition system with monitoring in situ for epitaxial growth of group-III nitrides
Authors: Xu Yin , Gu Biao , Qin Fu-Wen
Published: February 2004

An electron cyclotron resonance (ECR) plasma enhanced metalorganic chemical vapor deposition (PEMOCVD) system equipped with reflection high-energy electron diffraction (RHEED) has been developed and utilized for epitaxial growth of GaN and AlN on sapphire substrates by PEMOCVD. Since the multicusp cavity-coupling ECR plasma source was adopted to provide active precursors, the growth temperatures were decreased to 600–700 °C and the working pressures were decreased down to the region <1 Pa also, which make RHEED monitoring in situ possible for the growth surface. The nitrogen plasma densities Ne∼1.0–3.0×1010 cm−3 with a uniformity <±5% over a 10 cm diameter area, the electron temperatures kTe∼2–3 eV, the ion temperatures kTi⩽1 eV, and the plasma potentials Vs<18 V near the substrate holder for the typical film growth conditions: The pressure Po∼3×10−1–8×10−1 Pa and the microwave power Pw∼400–750 W. The experiment results demonstrated important roles of the plasma for sapphire substrate pretreatment, initial nucleation, and epitaxy growth of a large lattice mismatch heterojunction, GaN/(0001) Al2O3 at low temperature. The chemistry and mechanism of hydrogen (H)-plasma cleaning and nitrogen (N)-plasma nitriding, and the 30° rotation of a (0001) nitride plane produced by the nitriding with respect to the (0001) Al2O3 to reduce the lattice constant mismatch are discussed. The epilayers of GaN and AlN with better quality and relatively smooth surface were obtained. The full width of half maximum (FWHM) of a GaN (0002) diffraction peak of x-ray diffraction from a 0.3 μm thick GaN film was 15 arc min and the FWHM of AlN (0002) diffraction peak from a 0.3 μm thick AlN film was 12 arc min. Film surface morphology was observed by atomic force microscopy.
Miniaturized vacuum gauges
Authors: Wilfert St. , Edelmann Chr.
Published: February 2004

Due to the rapid advancement in microsystem and micromachining technology in the past several years, the most important common pressure measuring principles have been successfully applied in miniaturized vacuum sensors. In addition to MicroPiranis®, microstructured gas friction gauges and miniaturized capacitance manometers have been developed recently too, whose dimensions are already in the millimeter and partly in the micrometer range. Exceptions in this development are ionization gauges which, due to their basic measuring principle, cannot be arbitrarily miniaturized without substantial restrictions in their operating performance. The article gives a rough summary of the present level of development of selected types of miniaturized vacuum gauges and points out limits and causes for the restricted miniaturizability of certain total pressure vacuum gauges.
Phase transformation of tungsten films deposited by diode and inductively coupled plasma magnetron sputtering
Authors: Chen G. S. , Tian H. S. , Lin C. K. , Chen Gin-Shiang , Lee H. Y.
Published: February 2004

In this work we employ conventional (diode) and inductively coupled plasma (ICP) magnetron sputtering to deposit tungsten thin films of thickness 40 nm. The effect of varying the deposition parameters (background pressure, substrate bias and, particularly, the argon sputtering pressure) on transformation of the films’ phases and related physical properties was investigated using grazing incidence x-ray diffraction, scanning electron microscopy, and transmission electron microscopy, as well as electrical resistivity evaluation and bending-beam stress measurements. Tungsten films deposited by diode sputtering at any argon sputtering pressure from 5×10−1 Pa (5×10−3 mb) up to 2.0 Pa over a broad parameter window are dominated by β–W, thus yielding resistivity that could reach ∼190 μΩ cm. Conversely, over a broad range of sputtering pressures and substrate biases, the ICP sputtering is capable of depositing α-W thin films that exhibit markedly reduced resistivity of only ∼20 μΩ cm. The impact of varying the deposition parameters on the residual stress, phase distribution, microstructure, and crystallinity of the deposited films is discussed in terms of an energy-enhanced deposition mechanism and the well-known zone-structure model proposed earlier.