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Experimental Investigations of Acoustic Characteristics of Two Counter-Rotating Rotors.
(Lodz University of Technology. Faculty of Mechanical Engineering. Department Division of Dynamics., 2016) Rydlewicz, Wojciech; Błaszczak, Jarosław R.
The presented investigations are continuation of earlier researches performed in the Institute of Turbomachinery (Lodz University of Technology, Poland). The main aim of this paper is to investigate the acoustics properties of the chosen configuration of a flow set–up consisting of two coaxial counter–rotating rotors. Description and analysis of measurements are presented. As a consequence, conclusions about possibility of noise reduction of such a system are presented. According to the EU Directives, the main areas of application are multi–purpose helicopters with two coaxial counter–rotating rotors, drones and future passenger–aircrafts with next–generation aeroengines.
Sound wave absorption properties of multi-layers of different woven fabric structures
(Wydawnictwo Politechniki Łódzkiej, 2022) Bethalihem, Samuel; Barburski, Marcin; Witczak, Ewa
Nowadays, acoustic health is a priority issue in homes and offices. To address the problem, a variety of sound-absorbing materials are used, one of which is woven and nonwoven fabrics. This paper focused on the sound absorption analysis of two different woven fabric structures as an increasing layer and with base material nonwoven fabric. The fabrics' sound absorption properties were determined using an impedance tube across 80–5000 (Hz) frequencies. The result demonstrated that the absorption of sound energy through plain fabric decreases as the number of layers was increased. On the other hand, in the case of a sateen fabric structure, the absorption of sound energy increases with the number of layers. The absorption capabilities of sateen fabrics are particularly impressive in the high-frequency ranges. The double and triple layers of plain fabric, on the other hand, demonstrate high sound absorption results at frequencies below 1000 Hz in comparison to sateen fabric.
Wpływ ukształtowania sufitu na akustykę sali kinowej
(Wydawnictwo Politechniki Częstochowskiej ; Częstochowa, 2004) Jabłoński, Marek; Szer, Jacek
Przedstawiono porównanie własności akustycznych sali kinowej poddanej modernizacji dla różnego rodzaju konstrukcji sufitu. Wykorzystano program komputerowy bazujący na zmodyfikowanej metodzie promieniowej w celu oceny poprawności rozwiązań architektonicznych pod kątem wymagań akustycznych.