摘要:

Expressions for the standard deviation of the amplitude response of a multimode transmission medium to signals with nonzero bandwidth are derived. In the “statistical” case (normal modes overlapping frequency and negligible coherent transmission), the standard deviation is found to be approximately 5.57(1 + 3.3⋅τW)−12 dB, where τ is the decay‐time constant of the energy of the normal modes andWis the bandwidth of the excitation signal. For spatial averaging, the standard deviation of the response fluctuation in decibels is approximately5.57 (1 + 3.3X/λ)−12 dB, whereXis the length of the (linear) averaging interval and λ is the wavelength of the excitation signal. For excitation signals with finite bandwidthW, the response fluctuations are given by5.57[(1 + 3.3τW)(1 − 3.3X/λ)]−12 dB, where λ is the average wavelength. These results are applicable to fluctuation problems in multipath transmission, random vibrations, concert hall acoustics, and power measurements in reverberation chambers.

ISSN:0001-4966    

DOI:10.1121/1.1911685

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

This paper deals with the analysis of the dynamic stresses and displacements in a cable subjected to longitudinal excitation simulating ocean‐wave motion. The cable is considered to be made up of two segments of different materials and different physical dimensions. External damping due to fluid action and internal damping due to viscoelastic material properties are considered. The payload mass attached to the end of the cable is considered to be attached to a rigid foundation by an elastic spring and dashpot. This model covers a large number of possible oceanographic applications ranging from salvage recovery of objects immersed in the ocean sediments to suspension of instrumentation packages from buoy systems. Numerical results are presented for a hypothetical system consisting of the payload attached to a steel‐nylon elastic cable exposed to sinusoidal excitation at the upper end. Forcing frequencies approaching the second natural frequency are shown to cause forces in the steel portion which are significantly higher than those predicted by a single degree of freedom discrete system. It is further shown that external damping reduces the amplitude response of the payload; but can cause an increase in the cable stress in the steel segment when compared to the undamped case.

ISSN:0001-4966    

DOI:10.1121/1.1911686

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

This paper determines the effects of amplitude quantizing on the performance of conventional or optimum multichannel space, time signal‐processing systems, with emphasis on underwater acoustic applications. The system output signal‐to‐disturbance ratio is chosen as the performance criterion. The selection of proper analog‐to‐digital conversion parameters is influenced both by the characteristics of the system and the characteristics of external fields in which the system is operating. The external disturbance is assumed to consist of sonar self‐noise, which included ambient sea noise and noise generated by nearfield noise sources, plane‐wave interference, reverberation, or, in general, any combination of these. Through the use of representative assumptions on the statistical properties of external fields in space and time domain, some useful criteria for selecting the parameters of quantization are derived.

ISSN:0001-4966    

DOI:10.1121/1.1911687

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The intense, coherent light of lasers permits the formation of clear, bright diffraction patterns. These diffraction phenomena, formerly considered an optical limitation, have been transformed into a useful measuring tool by laser radiation.

ISSN:0001-4966    

DOI:10.1121/1.1911688

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1911689

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1911690

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1911693

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1911694

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP