摘要:

The nonlinear dynamics of planar motions of cantilevered pipes conveying fluid is studied via a tow‐mode discretization of the governing partial differential equation, after first replacing inertial nonlinear terms by equivalent ones in the equations of motion through a perturbation procedure. For hanging cantilevers, as the flow velocityUis increased to a critical value, the undeformed vertical configuration of the pipe becomes unstable and bifurcates into stable periodic orbits through a Hopf bifurcation. For a “standing” cantilever, in which the flow discharges from the free, upper end, the pipe is statically unstable for smallUif the pipe is sufficiently long; it regains stability through a subcritical pitchfork bifurcation at higherU, and this is followed by a Hopf bifurcation and periodic motions at still higherU. For certain parameter values these two bifurcations occur simultaneously (double degeneracy). By using center manifold theory and normal forms, it is shown that heteroclinic cycles exist in the reduced subsystem, suggesting the possible existence of chaotic behavior. Melnikov computations give guidance as to the likely location of chaotic regions in the parameter space. The numerical results, in which the existence of chaos is demonstrated, are presented in the form of phase portraits, bifurcation diagrams, and Lyapunov exponents.

ISSN:0001-4966    

DOI:10.1121/1.2028871

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The response of a nonlinear oscillator excited by white noise is considered. A truncated series of Hermite polynomials is used as an approximation to the probability density function. This series and the associated Fokker‐Planck equation are used to generate two sets of coupled differential equations for time‐dependent moments. The first set is for moments of variables evaluated at the same time; the solution yields, for example, the nonstationary mean‐square value. The second set is for moments of variables evaluated at two different times. This second set uses the solution of the first set as initial conditions. A single‐sided Fourier transform of the second set yields coupled complex algebraic equations that can be solved numerically for the spectrum. Examples are shown of spectra for the Duffing oscillator showing an increase in effective resonance frequency and broadening of the peak as the excitation level is increased, and for the van der Pol oscillator showing an entrained limit cycle response at low excitation level that disappears as the excitation level is increased. [Work supported by NSERC.]

ISSN:0001-4966    

DOI:10.1121/1.2028877

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Berkeley Speech Technologies, Inc. has been developing commercial text to speech synthesis technology for over 10 yr. What started out as a quick “technology transfer” has grown to become a complex body of “intellectual property” that has been realized in such products as a 100 000‐word talking dictionary, a telephone response system with 16 T‐T‐S lines on one board, a satellite communication system for trucks, and a portable talking computer for blind users. Practical considerations caused modification of the initial theoretical assumptions. From the beginning, it was assumed that high intelligibility and high phoneme accuracy were essential, but it was soon learned that 700 words per minute with a 25‐ms start and stop are equally important for blind users. Similarly, academic research had assumed wide bandwidth and low noise, but telephone systems require that all of the speech information be packed into a 3.5‐kHz telephone bandwidth. Initially, the choice was made to use demi‐syllable synthesis because it seemed to be an “engineering shortcut” that might cover gaps in standard scientific descriptions. As the technology developed, however, the decision was made to convert to a more scientifically based synthesis model because it offered higher quality, greater flexibility, and faster development, especially of new languages. Our 10‐yr development could not have been justified on the basis of expected financial return. However, it was and is fun.

ISSN:0001-4966    

DOI:10.1121/1.2028880

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

ITT A/CD is one of a few companies that has taken on the challenge of transferring speech technology from an abstract algorithm to a working system. In the mid‐1980s IIT A/CD developed moderate vocabulary, speaker‐dependent, connected speech recognition, and produced a series of single‐board recognizer products compatible with various personal computers and workstations. To date, over 400 single‐board recognizers have been ordered by over 30 customers. From these efforts a number of issues and experiences have surfaced that are critical to their successful operation. Some of these include: (1) robust performance across channels and microphones (every change to the microphone, analog recording setup, and room environment, will affect, and, most likely, lower performance); (2) training sensitivity (every shortcut taken in training, i.e., using fewer tokens, cross‐channel recordings, out‐of‐vocabulary training phrases, etc., will lower performance); (3) man‐machine interface (use psychologists to design user interfaces rather than engineers; otherwise they end up being just too complicated); (4) application specification (select only those applications that receive an overwhelming and compelling advantage from the technology).

ISSN:0001-4966    

DOI:10.1121/1.2028881

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

An important area of speech recognition is automatic recognition of connected digit strings (i.e., strings composed of the digits 0 through 9—including “oh”). Applications of this technology include credit card authorization, catalog ordering, dialing of telephone numbers, and data entry, to name just a few. For the past 2 yr AT&T, in cooperation with American Express Travel Related Services, has experimented with a system for automatic recognition of 10‐digit merchant identification codes, and 15‐digit customer credit card numbers, for the purpose of authorizing purchases charged to an AMEX card. (The problem of recognizing the transaction amount has also been studied, but this is a much more difficult problem and will not be discussed.) Field trial experience with the recognizer using about 1000 customers who provided 2000 connected digit strings over 800‐based dialed up telephone connections was correct recognition of 97%–98% of the strings with no rejections using constraints on the validity of both merchant identifications and credit card numbers. Several schemes for applying the constraints in a practical implementation were studied and will be discussed in the talk.

ISSN:0001-4966    

DOI:10.1121/1.2028885

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Neural networks can be used to make nonlinear transversal filters for signal processing. In some cases, signal estimation in noise can be enhanced by nonlinear filtering. Examples will be presented. Applications of neural networks in nonlinear control systems will also be presented. Self‐learning neural control systems for continuous bang‐bang control (the “broom‐balancer”) and for transient analog control (The “truck backer‐upper”) will be explained and demonstrated.

ISSN:0001-4966    

DOI:10.1121/1.2028888

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

More than 2500 ambient noise samples were collected in Behm Canal, Alaska, between July 1989 and January 1990. The data were obtained using a system deployed from a MINIMET buoy, and consist of one‐third octave analyses covering the 50 Hz through 63 kHz bands. Signatures obtained on an hourly schedule, were transmitted via the ARGOS satellite and entered into a LOTUS 1‐2‐3 database. Attempts to categorize the data by conventional means, e.g., manual sorting of plots of the signatures, or on a purely statistical basis, were unsatisfactory: thus the application of artificial neural networks was investigated. This approach yielded reasonable classifications and allowed atypical signatures to be identified and deleted from the database prior to performing statistical analysis. The groupings assigned by the network parallel those which might have been made by an analyst in that obviously different signatures are assigned to different classes, but in some cases the network makes more subtle distinctions than an analyst might. One network separated the signatures into 22 major groups (those containing at least 26 signatures) that include 90% of the data.

ISSN:0001-4966    

DOI:10.1121/1.2028898

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP