Miha Boltezar

A coupled electromagnetic-mechanical-acoustic model of a DC electric motor

In this article, we present an investigation into the sound radiation from a permanent‐magnet DC electric motor using the finite‐element (FE) and boundary‐element (BE) models. A three‐times‐coupled electromagnetic‐mechanical‐acoustic numerical model was set‐up to predict the acoustic field. The first stage was to calculate the magnetic forces that excite the structure of the motor by using the FEM. In the second stage, the exciting magnetic forces were applied to the structural model, where the harmonic analysis was carried out using the FEM. The last stage was to model the acoustics by using the BEM. In order to evaluate the numerical model, the computational results were compared with the vibration and acoustic measurements and a reasonable agreement was found.

The influence of cochlear implantation on vowel articulation

ZusammenfassungZIEL DER STUDIE: Die Sprache tauber Personen unterscheidet sich deutlich von der Sprache von Menschen mit normalem Gehör. Das Ziel der vorliegenden Studie war es, die akustischen Änderungen in der Artikulation der Eckvokale des Vokaldreiecks bei tauben Kindern und Erwachsenen nach Implantation eines Cochlear-Implantats zu untersuchen. METHODEN: 13 prälingual ertaubte Kinder und 12 postlingual ertaubte Erwachsene wurden in die Studie eingeschlossen. Stimmproben der Eckvokale des Vokaldreiecks (/a/, /i/, und /u) wurden vor und 6 bis 12 Monate nach der Implantation analysiert. Die Frequenz des 1. (F1) und 2. (F2) Formanten sowie der F1/F2 Quotient aller drei Eckvokale und die Fläche des Vokaldreiecks wurden zu allen Messzeitpunkten berechnet und miteinander verglichen. ERGEBNISSE: Bei den Erwachsenen konnten keine signifikanten Unterschiede zwischen der Frequenz der Formanten, dem Quotienten F1/F2 und den Vokal-Dreieckflächen erhoben werden. Bei den Kindern wurde eine signifikante Änderung der Frequenz der Formanten beobachtet. Nach der Implantation sank F1 von /u/ signifikant. Der günstige Abfall von F1 von /i/ und der F1/F2 Quotienten von /i/ und /u/ war nahe der statistischen Signifikanz. Alle Veränderungen bewirkten eine bessere phonologische Differenzierung der beiden Vokale. Die signifikante Änderung von F1 von /u/ und die Änderung von F1 von /i/ führten zu einer Ausweitung des Vokalraums, die sich in einer Zunahme der Fläche des Vokaldreiecks ausdrückte. SCHLUSSFOLGERUNGEN: Es wird angenommen, dass das erworbene Hörvermögen und die Weiterentwicklung der neuromuskulären Kontrolle der Artikulation bei Kindern der Grund für die signifikante Besserung ist. Die Ergebnisse der Studie lassen auch vermuten, dass die Fläche des Vokaldreiecks ein nützlicher und sensitiver Indikator der präziseren Artikulation nach Implantation eines Cochlear-Implantats ist. Für eine maximale und schnellere Besserung der Artikulation sollte eine regelmäßige Sprachtherapie in der Rehabilitation tauber Personen nach Implantation inkludiert sein.SummaryPURPOSE: Speech of deaf persons differs considerably from that of speakers with normal hearing. The purpose of this study was to investigate the acoustic changes in articulation of corner vowels in deaf children and adults after cochlear implantation. METHODS: Thirteen prelingually deaf children and 12 postlingually deaf adults were included in the study. Voice samples of the isolated corner vowels /a/, /i/ and /u/ were analyzed before and 6–12 months after the implantation. The frequencies of the first (F1) and second (F2) formants, the F1/F2 ratio of all three corner vowels, and the area of the vowel triangle were calculated and compared before and 6–12 months after the implantation. RESULT: In the adults, no significant differences were detected in the formant frequencies, the F1/F2 ratio or the area of the vowel triangle. However, significant change in formant frequencies was detected in the group of 13 prelingually deaf children. After the implantation the F1 of /u/ decreased significantly, and favorable decreases of the F1 of /i/ and the F1/F2 ratio in /i/ and /u/ were close to being statistically significant. All changes caused better phonological difference between the two vowels. The significant change in the F1 of /u/ and the change of F1 of /i/ resulted in the expansion of the vowel space, which was expressed as an increase in the area of the vowel triangle. CONCLUSIONS: We suggest that in children the acquired hearing ability and further development of neuromuscular control of articulation are the reasons for the significant improvement after cochlear implantation. The results also suggest that the area of the vowel triangle is a useful and sensitive indicator of the more precise articulation after implantation. In order to achieve better and faster improvement of articulation, regular speech therapy should be included in the rehabilitation of deaf persons after cochlear implantation.

Measurement of the bending vibration frequencies of a rotating turbo wheel using an optical fibre reflective sensor

An optical fibre reflective sensor was used to analyse the vibrations of a rotating turbo wheel up to 20 400 rpm. The measured signal required correction because of the natural unevenness of the turbo wheel and because of the variable deflection. Because the turbo wheel was rotating the signal became distorted and so we used a special method to extract the frequencies of the vibrations from the power spectra. The analysis showed increased intensity of the first three natural frequencies with an increased speed of rotation. The experimental results match very well with those obtained by numerical computation.

A Generalized Magnetostrictive-Forces Approach to the Computation of the Magnetostriction-Induced Vibration of Laminated Steel Structures

This research introduces a new, numerical and experimental approach to the analysis of the vibration of laminated structures resulting from magnetostriction. The focus is on the in-plane magnetostriction of electrical steel and its transmission into the out-of-plane direction, in which laminated structures (e.g., transformer cores, stators, and rotors) exhibit the greatest vibration. A finite-element magnetostriction model is developed on an experimental basis and enables a general, in-plane and out-of-plane assessment of the magnetostrictive response. The magnetostriction model is compatible with various finite-element structural models and is incorporated into a structural model, updated based on experimental data, representing a clamped laminated structure. An experiment employing the operating-deflection-shapes method is used to assess the presented approach under various operating conditions.

Frequency Characteristics of Magnetostriction in Electrical Steel Related to the Structural Vibrations

The ac magnetostriction in electrical steel is commonly characterized in the time domain (e.g., the peak-to-peak, zero-to-peak amplitude) and also in the frequency domain (e.g., a harmonic analysis). However, due to the dynamical coupling of the test sample with the experimental setup, the characterization of the magnetostriction (especially the one in the frequency domain) can give the wrong result. This research focuses on an experimental frequency characterization of magnetostriction and gives the theoretical background of the test samples dynamical coupling with the experimental setup. The discussed natural dynamics of the test sample from the point of view of the different boundary conditions that can be used at the experiment gives a clear picture of the dynamical coupling. Besides the theoretical background, a detailed experimental approach is presented. This paper theoretically and experimentally shows that the dynamical coupling of the sample can result in incorrect characterization of the magnetostriction. However, with the theoretical guidelines presented, the dynamical coupling can be completely avoided, which results in an accurate characterization of the magnetostriction.

Estimating Vibration-Fatigue-Life on Experimentally Acquired Data

It is a common practice in the automotive industry to expose products to accelerated vibration tests, that simulate the load, predicted to occur during the products service time. To avoid long testing times, higher amplitudes are used. Usually such tests come late in the development process, and can result in unexpected costs. A common tool for predicting time-to-failure or expected fatigue-life of the product is the time-domain method, using the rainflow counting algorithm and the Palmgren-Miner summation method. However, if one chooses to apply this method inside a FEM environment on a large amount of nodes with different time histories dependent on the structure excitation, the time-domain method becomes computationally complex. This has led to more effective methods, that estimate the time-to-failure in frequency-domain but are less accurate, compared to the time-domain approach. In this research, a group of such methods is presented and compared using real signals, namely: Tovo-Benasciutti, Wirsching-Light, Petrucci-Zuccarello, empirical α0.75, Dirlik and Gao-Moan method. Separately, only some of those methods were already compared side by side. Usually the comparison was made on simulated random signals, while this research compares them based on a real signal, collected by measuring different groups of spectra (e.g. typical vibration test profiles, different background noise levels, spectral width, number of modes etc.). In existing studies, Dirlik is usually identified as most accurate but in this research, conclusions show, that the Tovo-Benasciutti and Zhao-Baker methods can be more accurate than the Dirlik method and should therefore also be considered for vibration fatigue analysis.

The Development of a Surface Waviness Pattern During Brake-Like Applications

Dynamical systems with contacts are often exposed to wear even under small loads. The wear develops at the micro, macro or global level and changes the contact shape. This changed contact shape alters the dynamics of the system and can further increase the wear. This research presents a numerical investigation of the interaction between the wear at the contacts and the dynamics. The research involves a dynamical model normally used in the research of car-brake dynamics and simulates the run-in wear of the brake pad and the development of waviness on disc. Special attention is given to the real roughness of the contacting surfaces and to on exact numerical simulation; because concurrent contacts between rough asperities occur, a specifically developed multibody dynamics approach is presented. This research shows that after the run-in period a concave pad produces a waviness pattern on the disc. Using a spectral analysis of the disc’s surface it is possible to show the effect of the wear particle-size and the pad-width on the surface waviness.Copyright