Adaptive muffler upgrades the conventional muffler with a variable geometry to extend its working range. Adaptive muffler systems, described in the available literature, operate on the principle of controlling only single property of th e muffler to tune its working range. During the adaptation process of these systems the basic principle of operation is not changed. Based on the literature review, the question arises whether it would be possible to control the principle of operation. At one instant it would work as a Helmholtz resonator, in the other as an expansion chamber or side branch resonator. Analytical calculations provided a positive answer and a muffler with four active valves was designed and constructed to confirm the theoreti cal expectations. Properties of proposed muffler were simulated with Finite Element Method. Results of simulations were validated with measurements. Finally, simulations of proposed muffler, working at different operating conditions , were performed. Simula tio ns have shown that the proposed system allows tuning of the muffler to a wide working frequency range. Such approach to muffler design eliminates the need for additional mufflers used in IC exhaust systems . Therefore a smaller volume of the proposed muffler enables the same effect as multiple non - adaptive conventional mufflers.
COBISS.SI-ID: 14180635
The most important parameter for rooms designed for speech (classroom or lecture room) is speech intelligibility. Speech intelligibility depends on the reverberation time, speech-to-noise ratio and geom- etry of the room, among others. At the Faculty of Mechanical Engineering, University of Ljubljana, the reverberation times in lecture rooms observed exceed the optimal value from 0.31 to 0.87 s and in some of them, speech intelligibility is below the threshold of good or even satisfactory. For reducing rever- beration time and improving speech intelligibility, an alternative method was proposed, by hanging art paintings on the room walls. Experiments have shown that by doing so, reverberation time can be reduced by increasing the absorption coefficient by more than 30% in the most audible part of the frequency spectra (between 500 and 1500Hz). The absorption coefficient can be increased by using different dimensions of paintings, different air spaces behind the canvas, by appropriate thickness of the paint layers and by adding absorption material behind the canvas. Subjective tests have also shown that paintings with proper colour combinations (pastel colours with prevailing green, blue and grey colours) are appropriate for soothing the undesirable effect of background sound (noise) by changing perception in the brain.
COBISS.SI-ID: 13908763
An adaptive muffler with a flexible internal structure is con- sidered. Flexibility is achieved using controlled flow valves. The pro- posed adaptive muffler is able to adapt to changes in engine operating conditions. It consists of a Helmholtz resonator, expansion chamber, and quarter wavelength resonator. Different combinations of the control valvesʼ states at different operating conditions define the main working principle. To control the valveʼs position, an active noise control approach was used. With the proposed muffler, the transmission loss can be increased by more than 10dB in the selected frequency range.
COBISS.SI-ID: 14021147
A necessity for suitable recognition of different machinery and equipment based on sound they generate is constantly present and will increase in the future . The main motivation of discrimination between different types of machinery sounds is to develop algorithms which can be used not only for end quality inspection, but for whole production line monitoring. Objective of our study is to recognize operation of individual machine in a production hall, where background noise level is high and is constantly changing. An exp erimental plan was designed and performed in order to confirm the hypothesis proposing that Automatic Speech Recognition algorithms can be applied for Automatic Machine Recognition. Design of the automatic machine recognition procedure used in our study wa s divided into three stages; Feature extraction, Training and Recognition (Classification). Additionally, a traditional MFCC (Mel - Frequency Cepstral Coefficient ) procedure was adjusted for machinery noise by using different filter compositions. Finally, tw o classifiers were compared, the k - NN classifier and the multivariate Gaussian distribution. Results of experiment show that machinery noise features (F requency C epstral C oefficient s) should be extracted by using linear filter compositions and processed wi th recognition algorithm based on the multivariate Gaussian distribution.
COBISS.SI-ID: 14265627
Colophony is a resin, obtained from pine trees. It is used in industry and in products for everyday life as well, so the exposure to it is actually very hard to avoid. In this paper, we have focused us on occupational exposure, which is frequent in electronic workers, in furniture and paper industries, in the production of adhesives, plastics, printing ink and synthetic rubber as well. Exposure is also frequent by those who are daily in contact with products, which contain colophony or in contact with pinewood (e.g. carpenters and woodworkers). The main allergens are oxidation products of abiotic-type acids, but cross-reactivity with fragrances, wood resins, Balsam of Peru, wood tar and oil of turpentine is also possible. In allergic patients, exposure to colophony manifests itself on the skin, mainly as allergic contact dermatitis. The diagnosis is based on history of exposure, clinical presentation and epicutaneous testing. Although the only effective treatment is complete avoidance of exposure, it is difficult to avoid colophony. Consequently, prophylaxis based on safe working practices, personal hygiene and protection is essential.
COBISS.SI-ID: 279820800