Current Issue : April - June Volume : 2016 Issue Number : 2 Articles : 5 Articles
Cavitation in pumps must be detected and prevented. The present work is an attempt to use the\nsimultaneous measurements of vibration and sound for variable speed pump to detect cavitation.\nIt is an attempt to declare the relationship between the vibration and sound for the same discharge\nof 780 L/h and NPSHA of 0.754 at variable speeds of 1476 rpm, 1644 rpm, 1932 rpm, 2190\nrpm, 2466 rpm, and 2682 rpm. Results showed that: the occurrence of cavitation depends on the\nrotational speed, and the sound signals in both no cavitation and cavitation conditions appear in\nrandom manner. While, surveying the vibration and sound spectrums at the second, third, and\nfourth blade passing frequencies reveals no indications or phenomenon associated with the cavitation\nat variable speeds. It is recommended to survey the vibration spectra at the rotational and\nblade passing frequencies simultaneously as a detection unique method of cavitation....
In both fixed and rotary wing aircraft, the move toward lighter structures has resulted in an increase\nin structural vibration and interior noise. Porous materials have been proposed as acoustic\nabsorbers to reduce this noise. This paper discusses the development of equipment at the NASA\nGlenn Research Center for characterizing the acoustic performance of porous materials: a flow resistance\napparatus to measure the pressure drop across a specimen of porous material, and a\nstanding wave tube that uses a pair of stationary microphones to measure the normal incidence\nacoustic impedance of a porous material specimen. Specific attention is paid to making this equipment\nas flexible as possible in terms of specimen sizes need for testing to accommodate the small\nor irregular sizes often produced during the development phase of a new material. In addition,\ndue to the unknown performance of newly developed material, safety features are included on the\nflow resistance apparatus to contain test specimens that shed particles or catastrophically fail\nduring testing. Results of measurements on aircraft fiberglass are presented to verify the correct\nperformance of the equipment....
The problem of diffraction of a plane acoustic wave by a finite soft (rigid) cone is investigated. This\none is formulated as a mixed boundary value problem for the three-dimensional Helmholtz equation\nwith Dirichlet (Neumann) boundary condition on the cone surface. The diffracted field is\nsought as expansion of unknown velocity potential in series of eigenfunctions for each region of\nthe existence of sound pressure. The solution of the problem then is reduced to the infinite set of\nlinear algebraic equations (ISLAE) of the first kind by means of mode matching technique and orthogonality\nproperties of the Legendre functions. The main part of asymptotic of ISLAE matrix\nelement determined for large indexes identifies the convolution type operator amenable to explicit\ninversion. This analytical treatment allows one to transform the initial diffraction problem into\nthe ISLAE of the second kind that can be readily solved by the reduction method with desired accuracy\ndepending on a number of truncation. All these determine the analytical regularization\nmethod for solution of wave diffraction problems for conical scatterers. The boundary transition\nto soft (rigid) disc is considered. The directivity factors, scattering cross sections, and far-field diffraction\npatterns are investigated in both soft and rigid cases whereas the main attention in the\nnear-field is focused on the rigid case. The numerically obtained results are compared with those\nknown for the disc....
The learning-based speech recovery approach using statistical spectral conversion has been used for some kind of distorted speech\nas alaryngeal speech and body-conducted speech (or bone-conducted speech). This approach attempts to recover clean speech\n(undistorted speech) from noisy speech (distorted speech) by converting the statistical models of noisy speech into that of clean\nspeech without the prior knowledge on characteristics and distributions of noise source. Presently, this approach has still not\nattractedmany researchers to apply in general noisy speech enhancement because of somemajor problems: those are the difficulties\nof noise adaptation and the lack of noise robust synthesizable features in different noisy environments. In this paper, we adopted\nthe methods of state-of-the-art voice conversions and speaker adaptation in speech recognition to the proposed speech recovery\napproach applied in different kinds of noisy environment, especially in adverse environments with joint compensation of additive\nand convolutive noises.We proposed to use the decorrelated wavelet packet coefficients as a low-dimensional robust synthesizable\nfeature under noisy environments. We also proposed a noise adaptation for speech recovery with the eigennoise similar to the\neigenvoice in voice conversion. The experimental results showed that the proposed approach highly outperformed traditional\nnonlearning-based approaches....
A sliding magnetic clamp is used to hold a thin aluminum panel during a milling operation. The design includes a permanent\nmagnet group follower (slave module) which slides laterally over the panel attracted by another permanent magnet group (master\nmodule) attached to the industrial robot end effector from the machined side of the panel.The lateral sliding motion of the slave\nmodule in response to the master module motion is studied using a transfer function based motion model established considering\nthe lateral magnetic stiffness. The model is validated experimentally....
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