Engineering topics

Nakich, R. B.

Publications and source records attributed to Nakich, R. B..

5 records

NASA NTRS1974

Digital servo control of random sound test excitation

A digital servocontrol system for random noise excitation of a test object in a reverberant acoustic chamber employs a plurality of sensors spaced in the sound field to produce signals in separate channels which are decorrelated and averaged. The average signal is divided into a plurality of adjacent frequency bands cyclically sampled by a time division multiplex system, converted into digital form, and compared to a predetermined spectrum value stored in digital form. The results of the comparisons are used to control a time-shared up-down counter to develop gain control signals for the respective frequency bands in the spectrum of random sound energy picked up by the microphones.

Nakich, R. B.↗

NASA NTRS1974

Laser-scanning techniques for rapid ballistics identification

Two different laser-scanning methods may be utilized. In each case scanned cylindrical bullet surface is displayed ""unwrapped'' on oscilloscope screen. Bullets are compared by photographing each display and superimposing negatives of two images. With some modifications bullets can be scanned and compared by superimposing images on screen of dual-beam oscilloscope.

Woodburgy, R. C.↗

NASA NTRS1974

Apparatus for scanning the surface of a cylindrical body

A laser scanning system for providing a two-dimensional display of a cylindrical surface, such as to display striae of a fired bullet is described. The cylinder is scanned along its axis by vibrating one mirror in the laser beam path, and is scanned in a direction normal to its axis by vibrating a second mirror in a direction normal to the first or by rotating the bullet. Scan control signals are adjusted in phase to produce a synchronized display of a video signal obtained from detection of scattered light from the surface thus scanned by a laser beam.

Nakich, R. B.↗

NASA NTRS1973

Digital servo control of random sound fields

It is necessary to place number of sensors at different positions in sound field to determine actual sound intensities to which test object is subjected. It is possible to determine whether specification is being met adequately or exceeded. Since excitation is of random nature, signals are essentially coherent and it is impossible to obtain true average.

Nakich, R. B.↗

NASA NTRS1971

Digital decorrelator saves time and expense in acoustic testing of structures

Instantaneous signals from coherent random sound field are summed and time delayed to avoid introducing vectorial addition errors. Resultant statistically independent signals are applied to spectrometer. Displayed sound pressure level is proportional to square root of sum of squares of sound pressure levels taken over frequency range of interest.

Nakich, R. B.↗