摘要:

As a part of the overall Urban Rail Supporting Technology Program, the U.S. Department of Transportation (DOT) Urban Mass Transit Administration (UMTA) has sponsored a program of in‐service testing and evaluation of four noise control treatments applied to an existing rail transit facility. Rail grinding, wheel truing, resilient wheels, and damped wheels were applied to selected rail sections and vehicles of the Southeastern Pennsylvania Transit Authority (SEPTA) and the resulting noise reductions were evaluated initially, at an interim point, and after112 yearsof normal operation. Measurements included car interior noise, wayside noise and ground‐borne vibration. The final tests and analyses have now been completed. One result is the determination that design of such a testing program must include prior knowledge of the transit vehicle noise characteristics in order to devise appropriate tests for evaluation of the full effectiveness of the noise reduction procedures in reducing wheel/rail noise. Results of the complete testing program are presented.

ISSN:0001-4966    

DOI:10.1121/1.2003916

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Railway train squeal noise on a curve of small radius consists of specific frequencies which correspond to the natural frequencies of the axial vibration of a wheel. Those vibrational modes are nodal modes, such as (4,0) or (7,0), and the damping coefficients of a wheel are small in those particular kinds of modes. To investigate the specific frequencies of squeal noise, we made an experimental apparatus which has a thin steel disk and a steel rod. For the purpose of our experiment we will assume that the disk serves as a wheel and the rod serves as a rail. The circumferential face of the disk is rubbed in the axial direction with the rod. The frequencies of squeal noise generated by this fundamental experiment are coincident with those of the nodal modes. Frequencies with a small damping coefficient tend to occur in the squeal noise. Thus, the results of the numerical model concerning the main frequency of squeal noise generated by the coupled vibration of a disk and a rod almost agreed with the results of our experimental model.

ISSN:0001-4966    

DOI:10.1121/1.2003917

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Acoustic emission signals carry potentially useful information about the criticality of deformation source mechanisms in materials, but signal processing techniques such as threshold counting, RMS voltage recording, peak detection, and spectral analysis often failed to extract such information unambiguously. The difficulty lies in the determination of the transfer characteristics of the structure and the sensor. We report experimental results of a computer‐based test system consisting of a large plate and a capacitive transducer [N. N. Hsu, J. A. Simmons, and S. C. Hardy, Materials Evaluations35(10), 100–106 (1977)]. The transient wave propagation behavior of the plate and the transfer function of the capacitive transducer are known. Consequently, unknown sources can be characterized by solving the Töplitz matrix directly. Explicit force‐time functions of simulated signals such as breaking glass capillaries, breaking pencil leads, dropping steel balls, electrical arcs, and pulsed piezoelectric transducers have been determined. These force‐time functions are then used to determine experimentally the transfer characteristics (impulse‐response) of various propagation structures and various ultrasonic transducers.

ISSN:0001-4966    

DOI:10.1121/1.2003921

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Amplitude and frequency characteristics of acoustic emission signals are estimated by the initial and boundary conditions of the dynamic equilibrium equation for a linear elastic medium. Except in some special cases, frequency responses of signals is controlled only by the frequency response function of specimens, in addition to the characteristic of the transducer. In these cases, the source mechanism of acoustic emission can be attributed to the above initial condition. This initial condition is decided by inhomogeneous deformation with respect to time and space, which gives a local inelastic strain Δε during the time interval ΔT(relaxation time) in the material. From a metallurgical viewpoint, it can be recognized that this local inelastic strain is introduced by stress concentration τbaround various inhomogeneities, such as grain boundary, cell boundary, inclusion, and precipitate, and relaxation time ΔTis controlled by frictional stress τfin the matrix. According to this model, acoustic emission signals can be well understood from a viewpoint of inhomogeneous deformation, which is described by stress terms τband τf. In addition to a historical survey of source mechanisms of acoustic emission, in this report emission signals during various type of yielding are analyzed and discussed from a viewpoint of inhomogeneous deformation.

ISSN:0001-4966    

DOI:10.1121/1.2003924

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A method to estimate a collision point on a metal rod is presented, which is based on spectral analyses of the signal detected by a single accelerometer attached to the rod. First, the transfer function from a forcing point to the detector is derived, where space‐variant and dispersive characteristics of the rod are taken into consideration in connection with varying diameter, the change of surrounding condition along the axis, and various transmission and reflection loss characteristics. Then an algorithm to estimate collision point is derived by using the obtained transfer function. The fundamental experimental results obtained by using a 17S aluminum rod of 2003 mm length and 10 mm diameter show that the estimated positions agree with the actual collision positions with a precision of less than 1 cm [O. Ikeda, T. Sato, J. Yamamoto and A. Manabe, J. Acoust. Soc. Am (to be published)].

ISSN:0001-4966    

DOI:10.1121/1.2003930

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

In analyzing the problem of vibration response and sound transmission through periodically stiffened plates and cylinders, the stiffeners are very often represented by line supports or by springs with equivalent translational and torsional stiffnesses. Sometimes, the effects of the stiffeners are also smeared out. As a result, the vibrational response and the transmission loss at low frequencies are often predicted to be stiffness controlled. Recent studies at Boeing has shown that in the “stiffness controlled” region, the structural response and noise transmission may be governed by the resonances of the stiffeners, depending upon the relationship between the natural frequency of the plate between the stiffeners and that of the stiffener. Therefore, noise transmission in the “stiffness controlled” region may be effectively controlled by applying damping treatment on the stiffeners. This recent understanding has grown out of the “intrinsic structural tuning” concept presented earlier (G. SenGupta and E. F. Small, J. Acoust. Soc. Am.58, S (A)(1975). The problems under consideration are discussed in terms of (1) stringer‐stiffened plates and (2) frame‐stiffened cylinders. Analytical as well as experimental results are presented. [Work supported by NASA‐Langley Research Center.]

ISSN:0001-4966    

DOI:10.1121/1.2003934

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The line drive admittance and the transfer admittance have been evaluated in closed form for a plate or membrane. The evaluation takes into account the influence of fluid loading. Both admittances are necessary for the evaluation of the transmission of free waves across a rib. In this calculation the rib is characterized by an impedance, and the influence of fluid loading can thus be ascertained. Computations illustrating this effect in a number of cases of interest are presented and discussed. In the case of the membrane the phenomenon associated with the critical frequency is introduced by assuming the tension to be frequency dependent.

ISSN:0001-4966    

DOI:10.1121/1.2003939

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The Burg algorithm for computing reflection coefficients of speech (sometimes called the covariance lattice) is compared with the autocorrelation method of linear prediction. Certain problems for small window sizes for both methods are discussed. Three dimensional displays of spectral representations and audio tapes of synthesis are used to illustrate the practical result that there appears to be no advantage to either approach for speech processing, other than the computational efficiency of the autocorrelation method. [Work supported by the Department of Defense.]

ISSN:0001-4966    

DOI:10.1121/1.2003944

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

By using a log spectrum approximation filter modeling a true log spectral envelope, a low bit rate and high‐quality vocoder was realized. The true log spectral envelope is represented by the low‐quefrency portion of the cepstrum modified by the low‐quefrency components involved in the rectified fine structure of the log spectrum. It can be obtained through an iteration of DFT‐rectifying‐IDFT for the higher quefrency portion of the speech cepstrum. In this vocoder, the speech synthesis is not based on the homomorphic method. The synthesis filter can be obtained without transforming the cepstrum to an impulse response, and the computation for the filter coefficients is very simple. The spectral envelope information is transmitted in the form of a differential cepstrum corresponding to the difference of two adjacent log spectral envelopes, and the data rate is very low.

ISSN:0001-4966    

DOI:10.1121/1.2003949

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Our source model, reported at an earlier meeting, excites the LPO speech spectrum with a low‐frequency band of pulses mixed with a high‐frequency band of noise. Pulses are low‐pass filtered and noise is high‐pass filtered at the same frequency, to yield a flat source spectrum. The cutoff frequency of the filters, a continuous variable, replaces the usual binary voiced/voiceless decision. Thirty‐six phoneme‐specific test sentences were processed through a single high‐quality vocoder (5 kHz bandwidth, 11 poles, no quantization, 100 frames/s), which was excited in turn by both the usual pulse/noise source and by the new source. Subjects rated the resulting speech separately on eight‐point buzziness and breathiness scales. The results show that the new source model greatly reduces perceived buzziness, occasionally at a cost of slightly increased breathiness. Any remaining inadequacies can probably be ascribed to the algorithm that extracts the cutoff frequency during analysis, rather than to the model itself. [Work supported by ARPA‐IPTO.]

ISSN:0001-4966    

DOI:10.1121/1.2003955

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP