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Abstract

problem of sound radiation from an unflanged duct with mean flow of the medium taking into account existence of all allowable wave modes and, in particular, occurrence of the so-called unstable wave, which results in decay of radiation on and in vicinity of the duct axis. The flow is assumed to be uniform with the source of flow located inside the duct, which is the case frequently occurring in industrial systems. Mathematical considerations, accounting for multimodal and multifrequency excitation and diffraction at the duct outlet, are based on the model of the semi-infinite unflanged hard duct with flow. In the experimental set-up a fan, mounted inside the duct served as the source of flow and noise at the same time modelled as an array of uncorrelated sources of broadband noise, what led to the axisymmetrical shape of the sound pressure directivity characteristics. The theoretical analysis was carried out for the root mean square acoustic pressure in the far-field conditions. Experimental results are presented in the form of the measured pressure directivity characteristics obtained for uniform flow directed inwards and outwards the duct compared to this observed for the zero-flow case. The directivity was measured in one-third octave bands throughout five octaves (500 Hz - 16 kHz) which, for a duct with radius of 0.08 m, corresponds to the range 0.74-23.65 in the reduced frequency ka (Helmholtz number) domain. The results obtained are consistent with theoretical solutions presented by Munt and Savkar, according to whom the weakening of the on-axis and close-to-axis radiation should take place in the presence of medium flow. Experimental results of the present paper indicate that this effect is observed even for the Mach number as low as 0.036.
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Abstract

Integration of transport subsystems in transfer nodes of public transport in Poznań based on city railway stations, Poznań, being one of the strongest urban centers in the country, has a significant zone of impact (functional area). A natural consequence of this development model are significant communication issues caused by dynamic development of the suburban area. The solution of those issues is assumed to be basing the public communication system on a railway junction and, on its basis, creating the Poznań Metropolitan Railway. However, to ensure efficient functioning of such a system the need arises to integrate it with other systems of transport using transfer nodes. The aim of this article is to illustrate the potential of creating a polycentric system of multi-modal transfer nodes, based on existing city railway stations (district stations). The study focuses on the perspective of the passenger and the primary research method is the in-depth interview. This enabled to learn the opinion and identify the needs of passengers who use the facilities which are the subject of this study. The study also concentrated on analyzing thee communication behaviors of passengers and analyzing thee functioning of city stations themselves. Additionally, information was also acquired regarding the approximate destination of the passengers’ travel, which further allowed to specify the hypothetical impact range of individual city stations. Results of the study allowed to develop a range of recommendations intended to optimize the functioning of selected city railway stations, from a technical, as well as organization and management perspective. They have the potential to become a basis for developing a concept of sustainable public transport with a metropolitan reach.
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