Impact sound insulation is one of the most important aspects when assessing sound insulation of floor constructions in buildings. For assessing the impact sound insulation of aconstruction, a standard tapping machine is used as a sound source. However, the use of the current standard tapping machine has been criticised, especially with regard to measurement of wooden joist floors since the noise spectrum generated by a tapping machine differs from the spectrum generated by actual footfall. There are insufficient low frequency components in the noise spectrum produced by the tapping machine and it does not, therefore, accurately reflect low frequency noise from the construction.Reduce impact sound level from wooden joist floors are the main object of our study. It is important to be able to predict the sound insulation properties of wooden joist constructions at the design stage. To reduce the noise level in the receiving room, the input power transmitted through the construction must be estimated where the appropriate sound- and vibration-insulation can be designed.This study has investigated the waveform and frequency spectra of human footfall (walking, rum- ingand jumping); of the dropping of sand balls, sand bags and tires; and of the standard tapping machine. The impact sound power radiation from a wooden joist construction while applying different impact sources, such as actual footfall and the standard tapping machine, have also been studied.Research was also carried out regarding the development of a practical impact sound insulation calculation method for wooden joist floor constructions. The characteristics with regard to mechanical properties of floor construction was calculated using the impedance method. The impact sound level inside the sound receiving room was determined. The method developed can predict the basic performance of the wooden floor structure when excited by impact sounds. / Godkänd; 1995; 20070108 (biem)

Godkänd; 1996; 20080328 (ysko)

The technology for solar cars participating in the Bridgestone World Solar Challenge is constantly evolving. Teams from other universities are implementing innovative solutions in order to be a top contender in the event. JU Solar Team, the representatives for Jönköping University, are looking into applying wheel enclosures inside the body of the solar car, to improve the aerodynamics even further. Thus, the study will investigate how to integrate this component by using methods of design, fluid simulations and concept generation. In this case we are evaluating the effects of using enclosed wheels with the model from the 2019 solar car by JU Solar Team. The purpose of this is to generate empirical value for upcoming generations that will compete in the challenge. The study is built around the 2019 solar car with its dimensions and modules, this include; the wheel suspension, the car body, steering angle, wheel and rim. Simulations are performed with and without enclosed wheels, and stationary wheels and rotating wheels. Wheel rotation and fluid speed are inherited from the driving speed of 72 km/h. Models were simplified during simulations to save computational time.  The results show that wheel enclosures improve the aerodynamics of a solar car. With this simulation configuration and the fourth developed concept, an improvement of 8.22% was achieved.  The study is limited to models being simplified and basic simulations. The research found facilitates possible further investigation for wheel enclosures: manufacturing method, materials and strength evaluation.

Elongated particles in fluid flows are a big part of the world we are living in. Gaining knowledge on how particles behave in different fluid flows can potentially increase the efficiency of industrial processes and decrease the world's energy consumption as well as improve the properties of future materials. In this thesis, the orientation of elongated particles in two different flows are studied. The first case is a dilute fibre suspension in a turbulent flow and the second case is a semi-dilute fibril dispersion in a laminar flow. The fibres (cellulose acetate) are at least three orders of magnitude larger than the fibrils (nano-fibrillated cellulose). The turbulent flow case is half of a full channel flow, characterised by the friction Reynolds number, and is experimentally examined. This experiment is closely related to the papermaking process. Laser Doppler velocimetry measurements are preformed without fibres in order to make sure that the flow is turbulent and fully developed. Images of the fibres in the flow are acquired using a CCD-camera, from which it is possible to detect the fibres in an image processing step and extract both the positions and orientations of the fibres. A large parameter study is carried out, where the aspect ratio of the fibres, concentration and Reynolds number are changed. Short fibres are observed to align perpendicular to the flow, while the longer fibres are found to align in the flow direction. The fibres are also seen to accumulate in streamwise streaks, believed to be caused by velocity structures in the turbulent flow. The second flow case studied focusses on a semi-dilute dispersion in a laminar flow. It includes both experiments and numerical calculations of the fibril orientation. The aim of this study is to demonstrate that it is possible to control the fibril orientation with a fluid. In a semi-dilute dispersion, fibrils are interacting. However, no flocs or networks are formed. A flow focusing apparatus is used in order to hydrodynamically accelerate the dispersion with an outer fluid (sheath) flow. The mean orientation in the flow direction is experimentally studied by detecting the birefringence of the flowing dispersion. The orientation distribution is calculated by solving the Smoluchowski equation. The fibrils are seen to align in the flow direction both in the experiments and the calculations. Moreover, the alignment is found to increase with increasing acceleration. / QC 20120607

The collision threshold pressure (CTP), i.e. the smallest amount of subglottal pressure needed for vocal fold collision, has been explored as a possible complement or alternative to the now commonly used phonation threshold pressure (PTP), i.e. the smallest amount of subglottal pressure needed to initiate and sustain vocal fold oscillation. In addition, the effects of vocal warm-up (Paper 1) and vocal loading (Paper 2) on the CTP and the PTP have been investigated. Results confirm previous findings that PTP increases with an increase in fundamental frequency (F0) of phonation and this is true also for CTP, which on average is about 4 cm H2O higher than the PTP. Statistically significant increases of the CTP and PTP after vocal loading were confirmed and after the vocal warm-up, the threshold pressures were generally lowered although these results were significant only for the females. The vocal loading effect was minor for the two singer subjects who participated in the experiment of Paper 2. In Paper 3, the now commonly used audio spectral tilt (AST) is measured on the vowels of a large database (5277 sentences) containing speech of one male Swedish actor. Moreover, the new measure electroglottographic spectral tilt (EST) is calculated from the derivatives of the electroglottographic signals (DEGG) of the same database. Both AST and EST were checked for vowel dependency and the results show that while AST is vowel dependent, EST is not. Paper 4 reports the findings from a perception experiment on Swedish accents performed on 47 Swedish native speakers from the three main parts of Sweden. Speech consisting of one sentence chosen for its prosodically interesting properties and spoken by 72 speakers was played in headphones. The subjects would then try to locate the origin of every speaker on a map of Sweden. Results showed for example that the accents of the capital of Sweden (Stockholm), Gotland and southern Sweden were the ones placed correctly to the highest degree. / QC 20100915

This thesis deals with noise from wind turbines and low-frequency traffic noise. The aim was to gain practical experience by using different measurement techniques, where the wind noise was measured by emission, immission, ambisonic and binaural recordings. Both examined wind turbines have tonal components at 500Hz and 2000Hz. From the traffic noise one could notice two strong peaks in the 1/3 octave band at 50Hz and 63Hz. The investigation of it showed that the lower peak at 50Hz came from automobiles while the one at 63Hz were from heavy trucks. The binaural recordings were used in a listening test. A listening test was conducted where 15 test subjects estimated how annoying the noise is in relation to pink noise. The result showed that the annoyance level were higher for sound containing tonal components.

The Reduction of engine noise, one of the primary noise sources in trucks and busses, is essential in order to fulfill various noise emission regulations such as ISO 362 [1]. At the same time, it is equally important to meet market demands in order to attract new customers while competing with other brands to lower overall noise levels. Sound power is a convenient descriptor of noise emissions when compared to sound pressure it is not dependent on the distance from the source and the surrounding environment. A number of standards for sound power measurement exist, requiring different methods, tools and environments. In engine development at Scania the sound power level is measured for different engine types for noise level determination and comparison purposes. Additionally, attempts to reduce noise through modifications of engine parts require many iterations in which sound pressures recorded at specific microphone positions are of primary interest. The necessity of running each engine at different speeds and load conditions with various modifications during development (combined with time restrictions) narrows down the choices to ISO 3745 which involves measuring sound power with stationary microphones. Despite ISO3745 apparent ease of use, prerequisites such as the number of microphones, the distance limitation of the microphones and free field conditions often pose a practical challenge. In Scania’s anechoic chamber it is impossible to meet these requirements due to limitations inherent to the room design such as size, poor absorption and limited space on the underside of the engine. This thesis comprises engine acoustic simulations in Nastran together with various measurements. Based on these, guidelines for power calculation have been developed taking into account the level of uncertainty and correction factors.

On account of LN Akustikmiljö AB, the sound energy absorption of various rooms was estimated using two methods; by measuring the steady-­‐state sound pressure levels in the rooms when excited by a reference sound source and by measuring the reverberation time. The reason for the comparison was that the reverberation time was not always a satisfactory measure of the acoustical performance of rooms, even though it was the only requirement in Swedish standard SS 25268:2007[1]. Thus, it was suggested to try alternative methods to measure the acoustical performance of the rooms. Measurements were performed in 18 rooms with varying volume and acoustical treatment. The equivalent absorption area of each room was calculated from both methods. Comparison between the two methods showed large differences in the equivalent absorption area; however which value was the best representation of the actual real situation is a complex problem, which varies with the dimensions and acoustical treatment of the room and the frequency band and will need further research.

New noise regulations for civil aviation restrict the sound level that engines can emit to a great extent. Acoustic liners are the most widespread solution in order to damp sound in aircraft engines. Usually the Linearised Euler equations (LEE) are used to calculate the sound propagation through the engine. In addition, the viscous effects close to the near wall region, where the acoustic liner is located, are considered by the Myers impedance boundary condition. However, this boundary condition has been proved to be ill-posed and to not fully capture the viscous acoustics. Hence, a different approach is taken by using the full Linearised Navier-Stokes equations. In order to assess the validity of this method a computational model is created to reproduce the experimental work done by Aurégan et.al. where the scattering matrix of a two source model is measured and time domain simulations are done using LEE and Myers boundary condition in order to compare them. An improvement, with respect to the inviscid time domain simulations, is achieved when the upstream educed impedance values are used. Therefore, the Myers impedance boundary condition can still be used in numerical impedance eduction codes and the obtained values render good results if a viscous solution is adopted. Also, considering a viscous solution implies that both the hydrodynamic and the acoustic boundary layer need to be resolved. Nonetheless, the latter is very small compared to the hydrodynamic one and its inclusion will result in a very fine mesh that might increase the computational time. Thus, a second study is done in order to assess the importance of the acoustic boundary layer in these calculations, and to determine if some assumption can be applied in order to reduce the computational effort. To that purpose, all the simulations are done in the frequency domain since it is a lighter computational method than the time domain. Results of this second test case show that the resolution of the acoustic boundary layer is not a crucial factor in order to achieve an accurate solution.

In a coastal area, an alluvial lowland river has a free connection with the open sea and its flow is bidirectional. The river basin is often highly urbanized since it hosts valuable ecosystems and natural resources. Along with the growing population, climate change and human activities (e.g., industrialization, agricultural expansion, and fishery industry) pose a significant threat to the health of the river, leading to an unbalance of the flow and the sedimentation and also a considerable degradation of water quality. With long-term alluvial processes, the river often displays patterns such as meandering, braided, straight, wandering and anastomosing. In addition to the irregular geometry and bathymetry, a tidal river is typically influenced by the freshwater-saltwater interplay, which makes the hydrodynamic processes and sediment transport patterns extremely complicated. For many tidal river systems, cohesive sediment transported with the tides plays an important role. This is not only because of its interaction with flow but also due to its link to bed deformation. In this thesis, field measurements and numerical simulations of flow and sedimentation in a system, including a confluence and a meandering reach are presented and discussed. The numerical simulations are performed with the Delft3D package, which allows a coupling between complex river geometry, the bathymetry, the flow and the sediment boundaries in one module. Two morpho-dynamic models, a 2D depth-averaged model for the confluence and a 3D model for the meandering reach, are set up to disclose the fluvial processes in respective area. The objective of this thesis is, by means of extensive field measurements and numerical simulations, investigate flow features and sediment movement patterns in a tidal river. A comparatively long-term river-bed change, including a scour-hole at the confluence and asymmetric cross-sections at the bends, are also examined. Based on the perturbation theory, an improved sediment carrying capacity formula is also derived being suitable for calculations in a tidal environment. This study explores the variability of sediment transport, and reveals the relationship between the flow velocity and suspended load influenced by both the run-off and the tides. Their interactions also generate a different morphological regime as compared to a non-tidal river reach. This research may support a decision‐making process when considering the integrated tidal river management and it also provides a reference for other similar situations. The calibrated and validated model may therefore be a powerful tool for managers or researchers.