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I denna studie har man fokuserat på hur omfattande ljudnivåerna kan vara på ett så kallat flytande golv. Det har fördjupats i konstruktioner med Platonmatta för att få en uppfattning om hur de akustiska faktorerna yttrar sig när någon beträder golvet. Studien jämför resultat av steg- och trumljudnivåer med Granabkonstruktioner, som är en annan typ av flytande golv, samt hur Platonkonstruktionen står sig i förhållande till de lagstadgade riktvärdena. I denna studie har det fokuserats på hur ljudet uppfattas både objektivt och subjektivt eftersom mätvärden i vissa fall inte stämmer överens med den faktiska upplevelsen. Golvtesterna som genomförts har gett oss mätvärden och en objektiv upplevelse. Detta har resulterat i en optimal golvkonstruktion teoretiskt. Sammantaget visar denna studie att golvens konstruktion i stor utsträckning kan minimera steg- och trumljud. Alla Platonkonstruktioner som testats i studien har generellt gett bra akustiska värden för att vara ett överliggande golv. Den kunskapen kan vara till stor nytta när man projekterar ett flytande golv eftersom höga ljudnivåer i de lägre frekvenserna har visat sig påverka bland annat inlärnings- och koncentrationsförmågan. / This study highlights the intensity and the extent of sound levels produced by a so called floating floor. The study has closely observed floor constructions made of Platon mat in order to detect the acoustic factors and how they are manifested when stepping on the floor. The study also compares the results of step- and drum sound levels with Granab constructions, another type of floating floor, as well as how the Platon construction stands in relation to the statutory guide values. This study has focused on how the sound from a Platon floor is perceived in an objective and a subjective perspective, because in some cases measured values do not correspond to the actual experience. Measurements that have been carried out give an idea of how to design floors and what type of material should be used to obtain the most favorable sound level possible. Overall, this study shows that the design of the floors can, to a large extent, minimize step- and drum sounds. This knowledge can be of great use when designing a floating floor since it has been shown that high sound levels in the lower frequencies affect, among other things, our abilities of learning and concentrating. / Akustik, platongolv.

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The experimental program presented in this paper explores a passive acoustic baseball bat swing speed measurement technique to aid in product development and certification and to gauge player performance. The collection of experimental information is performed in two facilities?a swing/hit facility and a wind tunnel facility. The data acquired are pressures and velocities in the vicinity of the bat. Potential flow theory is utilized to better understand the signals generated in the experimental collection of data and to determine the fundamental relations applicable to the subsequent flow field produced by a moving bat. The measured flow resembles potential flow but with a distortion due to bat acceleration. The theoretical and experimental results are compared, and a qualitative similarity in the results is established.

Experiments were conducted to measure the thrust generated from a commercial jet engine. This thrust estimation was done using a pneumatic horn as the sound source with two arrays of microphones directly across the exhaust stream. The two arrays were separated by an axial distance downstream. Exhaust centerline measurements were taken at varying engine conditions, specifically; 30%, 50%, 60%, 70%, 80% and 100% engine power. An acoustic thrust estimation showed good agreement with measured thrust during the test campaign. In addition, a full traverse of the acoustic rig through the exhaust stream was completed for the purpose of tomography reconstruction. This reconstruction technique was able to pick up key features of the flow field. / Master of Science / A non-intrusive acoustic approach was used to measure the thrust produced by a commercial jet engine at all engine power levels. This acoustic approach was comprised of a sound source and receiving microphones placed on either side of the jet exhaust stream, just behind the engine. The acoustic measurements were compared to measurements by a load cell on the engine and showed excellent agreement. After the concept was proven, another experiment was conducted in which the sound source and microphones were moved vertically alongside the engine exhaust stream. These line of sight measurements were used to reconstruct the velocity and temperature gradients generated by the jet engine. The reconstructions showed good agreement with the engine geometry and was able to detect key flow features.

With the continual challenges associated with reducing aircraft engine noise, there is need for acoustic liner configurations that target broadband performance. This thesis experimentally and analytically investigates passive noise control methods to improve broadband frequency attenuation through various acoustic liner designs. The inclusion of acoustic metamaterials within these liners is examined and optimized. The metamaterials studied consist of resonant and non-resonant materials which include porous foams, microperforated plates (MPP), and embedded aluminum masses. Through finite element analysis, the understanding of the physics behind acoustics as well as aeroacoustics inspire their design. Sensitivity studies on the overall liner shape, facesheet properties, poro-elastic material properties, MPP's, as well as size and placement of embedded masses assist in successfully achieving broadband attenuation. Within the finite element study, an optimization tool will provide additional assistance in quantifying critical system parameters within the designs by minimizing the sum of the transmitted sound intensity over the design frequency bandwidth and hence maximizing attenuation. Broadband frequency absorption and attenuation is successfully achieved within the frequency range of 400-2600 Hz through the design of a varying depth optimized acoustic liner as well as a metamaterial-inspired liner. / Master of Science

No / A numerical method for sound propagation of higher-order cross-sectional modes in a duct of arbitrary cross-section and boundary conditions with nonzero, complex acoustic admittance has been considered. This method assumes that the cross-section of the duct is uniform and that the duct is of a considerable length so that the longitudinal modes can be neglected. The problem is reduced to a two-dimensional (2D) finite element (FE) solution, from which a set of cross-sectional eigen-values and eigen-functions are determined. This result is used to obtain the modal frequencies, velocities and the attenuation coefficients. The 2D FE solution is then extended to three-dimensional via the normal mode decomposition technique. The numerical solution is validated against experimental data for sound propagation in a pipe with inner walls partially covered by coarse sand or granulated rubber. The values of the eigen-frequencies calculated from the proposed numerical model are validated against those predicted by the standard analytical solution for both a circular and rectangular pipe with rigid walls. It is shown that the considered numerical method is useful for predicting the sound pressure distribution, attenuation, and eigen-frequencies in a duct with acoustically nonrigid boundary conditions. The purpose of this work is to pave the way for the development of an efficient inverse problem solution for the remote characterization of the acoustic boundary conditions in natural and artificial waveguides.

No / New representations and efficient calculation methods are derived for the problem of propagation from an infinite regularly spaced array of coherent line sources above a homogeneous impedance plane, and for the Green's function for sound propagation in the canyon formed by two infinitely high, parallel rigid or sound soft walls and an impedance ground surface. The infinite sum of source contributions is replaced by a finite sum and the remainder is expressed as a Laplace-type integral. A pole subtraction technique is used to remove poles in the integrand which lie near the path of integration, obtaining a smooth integrand, more suitable for numerical integration, and a specific numerical integration method is proposed. Numerical experiments show highly accurate results across the frequency spectrum for a range of ground surface types. It is expected that the methods proposed will prove useful in boundary element modeling of noise propagation in canyon streets and in ducts, and for problems of scattering by periodic surfaces.