Zbigniew Engel

Audible noise of transmission lines caused by the corona effect: Analysis, modelling, prediction

Abstract The paper presents the results of investigations of audible noise of high voltage transmission lines of alternating current (a.c. UHV) caused by the corona effect. The investigation results concern the 400 kV lines in two basic layouts existing in Poland: single horizontal and double vertical. Environmental investigations in real conditions were executed in a whole year cycle with the short-term method. Apart from the results of the environmental investigations the paper contains also the laboratory investigation results. The influence of constructional design and environmental parameters on the sound level distribution along a span was analysed. The influence of the conductor surface state and weather conditions on the level and shape of the emitted audible noise spectrum was particularly taken into account. The evaluation of the influence of the line audible noise on the acoustic climate of the environment was carried out. The analysis of possibilities of the application of well known computational procedures to the prediction of the line audible noise caused by the corona effect in Polish conditions was executed and an original form of a line acoustic model with the audible noise prediction possibility as a function of rainfall was presented.

A vibroacoustic model of selected human larynx diseases.

With the present development of digital registration and methods for processing speech it is possible to make effective objective acoustic diagnostics for medical purposes. These methods are useful as all pathologies and diseases of the human vocal tract influence the quality of a patient’s speech signal. Diagnostics of the voice organ can be defined as an unambiguous recognition of the current condition of a specific voice source. Such recognition is based on an evaluation of essential acoustic parameters of the speech signal. This requires creating a vibroacoustic model of selected deformations of Polish speech in relation to specific human larynx diseases. An analysis of speech and parameter mapping in 29-dimensional space is reviewed in this study. Speech parameters were extracted in time, frequency and cepstral (quefrency) domains resulting in diagrams that qualified symptoms and conditions of selected human larynx diseases. The paper presents graphically selected human larynx diseases.

The modal low frequency noise of an elastically supported circular plate.

The modal low frequency noise generated by a vibrating elastically supported circular plate embedded into a flat infinite baffle has been examined. The main aim of this study is the analysis of the radiation efficiency. Low frequency approximated formulas have been presented. They are valid for all the limiting boundary conditions of the plate with its edge clamped, guided, simply supported or free as well as for all the intermediate axisymmetric boundary configurations. The formulas are expressed in the elementary form, useful for numerical computations. They are a generalization of some earlier published results. First, they are valid for axisymmetric and asymmetric modes since both kinds of modes play an important role in the low frequency range. Second, a single formula for the radiation efficiency, valid for all the axisymmetric boundary configurations, has been proposed. A numerical example for the sound power radiation has been given for some hatchway covers mounted on a ship deck.

Proposal for an Indexical Method of Evaluating Risk of Hand Tool Operators' Exposure to Mechanical Vibrations

The article presents proposals for an indexical evaluation of exposure of hand tool operators to vibrations. The presented indices have been developed on the basis of the results of laboratory tests. The examinations studied the effect of pressure force and grip force exerted by an operator on a hand tool as well as the amplitudes and frequencies of an exciting signal on vibrations transmitted in the hand-tool handle system.