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    Detection of sound from AVAS in urban environments
    (2024) Demirci, Bircan; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Forssén, Jens; Bolin, Karl
    Functionality of AVAS (Acoustic Vehicle Alert System) faces challenges in urban environments, where background noises may mask AVAS sounds. From a safety perspective, designing AVAS sounds that effectively warn vulnerable road users (without causing extensive environmental noise) is even more crucial in heavy vehicles since they have longer braking distances, greater momentum, and more blind spots than light vehicles. This study aims to contribute to the safety aspects of battery electric trucks (BEV trucks) by exploring their detectability in urban areas and their classification rate, which shows whether they can be distinguishable from cars. In this regard, listening tests were conducted with 51 participants: eight distinct vehicle sounds, five of which belong to a BEV heavy truck, one to an ICE (Internal combustion engine) truck, one to a BEV passenger car, and one to an ICE passenger car. Each vehicle sound was presented both at 10 and 20 km/h. In the first session of the test, participants were tasked with classifying approaching vehicles as either trucks or cars, without additional urban background noise (the equivalent levels are about 45 dB(A)). During the second session, they were tasked with detecting approaching vehicles amidst continuous urban background noise (the equivalent levels are in the range between 57 and 62 dB(A)) and then classifying the detected ones. The results revealed that in the first session of the test, where there was no additional background noise, 50% of the vehicles were correctly classified within the safe zone. The vast majority of the vehicles approaching at 10 km/h were classified within the safe zone, while those approaching at 20 km/h were classified within the unsafe zone. In the second session, with continuous urban background noise, 30% of the vehicles were detected and then correctly classified within safe distances. Unlike the first session, a large portion of the vehicles approaching at 20 km/h were detected and then correctly classified within the safe zone, while those approaching at 10 km/h were detected and then classified within the unsafe zone. While the ICE truck outperformed at both speeds and in both sessions, the accuracy of the BEV truck results varied depending on the session and vehicle speed. Moreover, the accuracy rates of the tasks’ results were mainly affected by whether the AVAS sound was in active mode or not, the modulation of the AVAS sound, and whether the tonal components of the BEV truck were dominant or not. These findings may provide insights into the current and future needs of designing AVAS sounds for electrified trucks.
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    Optimization of sound absorber: Design of sound absorber for the study of sound incidence in long narrow spaces such as corridors
    (2024) Apadanda, Rushi Ganapathi; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Kropp, Wolfgang
    Noise mitigation is of importance in areas where health and well-being of individuals is needed and this is especially true in spaces such as schools were noise can hinder learning and cognitive development of children. While acoustical treatment is often focused on classrooms where children and teachers spend large amount of time, corridors remain neglected despite their role in amplifying noise. Corridors with their unique dimension, non-diffuse sound field and source for housing furniture pose a challenge in sound proofing and hence an approach to optimise absorbers is needed and to understand the impact of sound incident angle. This thesis explores the design and optimization of a sound absorber system tailored for such environments, with a focus on mitigating noise levels in school corridors. The study investigates the performance of a resonant sound absorber, combining a micro-perforated panel, air gap, and porous material, aimed at absorbing sound in the mid-to-high frequency range 850 Hz-4000 Hz in diffuse and non-diffuse sound field conditions. Using theoretical modeling via the Transfer Matrix Method (TMM) and empirical validation through free-field and diffuse-field measurements, the absorber’s performance was analyzed under various sound incidence angles. The results demonstrate that the designed system effectively absorbs sound, with a resonance peak at 2000 Hz. The study also evaluates the impact of parameters such as porous material thickness, perforation size, and air gap on the absorption coefficient for varied incident angle. While the absorber achieved good efficiency, especially at the targeted resonance frequency, edge effects were observed in finite-size samples, leading to overestimation of absorption coefficients in certain cases. This research highlights the importance of optimizing sound absorbers for nondiffuse sound field environments like corridors, particularly at high frequency range, and offers a practical solution for enhancing acoustic comfort in schools
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    Towards development beyond GDP; case studies of Egnahemsfabriken and Uddebo
    (2024) Rehnberg, Frida; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Adelfio, Marco
    Alternative approaches to sustainability, such as initiatives resonating with the degrowth paradigm have the potential of showing how societies can develop with a focus beyond GDP. Considering the current demographic pattern in Sweden, many people will live in rurban and rural areas in the future. How to live and operate sustainably in these areas is explored in this thesis. More precisely, the aim is to explore two rural locations in Sweden, Egnahemsfabriken on Tjörn, and the village Uddebo, where civil society has organised to solve local issues - initiatives that resonate to a great extent with the degrowth paradigm, and initiatives that has brought a lot of positive outcomes locally. Through semi-structured interviews, these places are explored by delving into how these initiatives started, how it has developed, what challenges there have been and what is important to consider for the future. The results show that diversity among people, a lot of drive and energy, as well as unpaid time spent, and empty premises for a low rent/price, has been important in both areas. While Egnahemsfabriken seems to focus on reaching out locally, regionally and even nationally, and to influence other places and institutional levels, Uddebo seems to be more of a place where people move to do their own thing, to work less, do things together, but with great diversity where not everyone is engaged in local initiatives. Some of Egnahemsfabriken’s focuses for the future could be to reach out more to the local society and the municipality through e.g. meetings and low-threshold events, increase the long-term financial stability and make projects last longer, as well as continuing facilitating administration and collaboration with their partners. For Uddebo, preventing gentrification, doing bigger projects, and exploring local solutions for sharing/gift economy as well as other local platforms (e.g. local radio and local social media platform) were suggested.
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    Railway ground vibration prediction using a controlled source; development of an empirical method predicting ground borne vibrations using a falling weight
    (2024) Hultén, Hugo; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Forssén, Jens; Torres, Jorge
    Rail transport today plays a major role in sustainable transportation. But ground vibrations from trains and trams create unsustainable environments that lead to irritation and affect people’s sleep. Several methods are currently used to predict ground vibrations. These methods are used at different stages of railway design. Some are more accurate but costly, while others are simpler but less accurate. In this thesis, a method for predicting ground vibrations from railways is developed. The method consists of exciting the ground with a controlled source. The controlled source used is a falling weight. The method is compared with measurements on maximum weighted vibration level for both trains and trams and for different ground conditions. To verify the measurements, a numerical analysis is also performed. Finally, a model is developed using the falling weight ground vibration measurements to model a point source or a line source of finite length. Comparisons between falling weight and rail vehicles show that the frequency spectrum differs and that the model has little resemblance with the mean value of the ground vibrations.The decay with distance of the maximum vibration level is shown to be similar to that of the rail ground vibrations when using the point source model rather than modelling a finite line source.
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    Creating active boundary conditions with Planar loudspeaker arrays to absorb and reflect sound
    (2024) Müller, Anthea; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Ahrens, Jens; Ahrens, Jens; Sarradj, Ennes
    It was shown in the 1970s that a combination of two secondary sources are able to absorb sound energy in one-dimensional sound propagation in a duct. The primary source can be interpreted as being surrounded by a double-layer of secondary sources. This is inconvenient in two- and three-dimensional scenarios as surfaces of secondary sources have to be used, which are difficult to implement in practice. This thesis demonstrates that the same type of active absorption is possible also in open space, i.e., when the secondary sources do not fully enclose the primary source. In contrast to active noise canceling, the aim here is not to achieve active reduction in the downstream area by increasing the sound level in the upstream area, but rather to actively remove energy from the sound field. The focus here is particularly set on canceling out low frequencies to facilite practical measurements. For this, two boundary conditions are set, one in the upstream and one in the downstream area. To achieve the objective at the boundary conditions a set of FIR filters must be determined. This is done here with the help of the LMS method, which is extended to a MIMO (Multiple Input Multiple Output) system. First the results of Swinbanks for the active reduction inside the one dimensional duct are recreated with simulations and confirmed with an experiment. Based on these findings the approach is first extended two dimensions to perform absorption of cylindrical waves with the help of two line sources and then further extended to three dimensions to perform the absorption of spherical waves by means of one-dimensional distributions of point sources. Two experiments are carried out to confirm or refute the concepts introduced. These are first planned in detail with the help of simulations. The first experiment (Setup 1) demonstrates the active absorption of cylindrical waves emitted by line arrays in an outdoor free field setting. The second experiment (Setup 2) demonstrates the active absorption of sound emitted by a point source that is actively absorbed by curved arrays within a semi-anechoic chamber. The simulation results were confirmed in both setups with the measurement results. They proof that the active control of the downstream area whilst not influencing the upstream area is possible with the proposed boundary conditions within the limitations of the method and their test environments. In both experiments active reduction is achieved throughout the downstream area, achieving an averaged active reduction of 11 dB (3 dB over background noise level) in Setup 1 and an active averaged reduction of -27 dB (1 dB over background noise level) in Setup 2 at the boundary condition. Throughout the upstream area the average deviation from the undisturbed sound-field for Setup 1 is 0.3 dB, for Setup 2 it is 0.08 dB