Downsizing in cars lead to higher noise emissions through the addition of turbo-/superchargers. These noise emissions must be counteracted and cancelled in order to contribute to the overall quality feel of a car. This project follows a product development method in order to research if a new type of silencers are applicable in air induction systems in order to dampen noise emissions. The project also cover how to manufacture the new type of silencers, traditionally used as acoustic insulation in offices. The project covered everything from literature review on silencers, noise regulations, downsizing and traditional plastic manufacturing methods. After the analysis of the results, it stood clear that the new silencers are more effective than conventional solutions. A manufacturing process was also determined, which needs further research in order to derive what the manufacturing cost would be. The project resulted in strong indicators that the new silencers are promising but also opened up to new research questions.

Arbitrary high order numerical methods for time-harmonic acoustic scattering problems originally defined on unbounded domains are constructed. This is done by coupling recently developed high order local absorbing boundary conditions (ABCs) with finite difference methods for the Helmholtz equation. These ABCs are based on exact representations of the outgoing waves by means of farfield expansions. The finite difference methods, which are constructed from a deferred-correction (DC) technique, approximate the Helmholtz equation and the ABCs to any desired order. As a result, high order numerical methods with an overall order of convergence equal to the order of the DC schemes are obtained. A detailed construction of these DC finite difference schemes is presented. Details and results from an extension to heterogeneous media are also included. Additionally, a rigorous proof of the consistency of the DC schemes with the Helmholtz equation and the ABCs in polar coordinates is also given. The results of several numerical experiments corroborate the high order convergence of the proposed method. A novel local high order ABC for elastic waves based on farfield expansions is constructed and preliminary results applying it to elastic scattering problems are presented.

No description available.

Attitude Determination and Control System (ADCS) is often a complex system on-board any  satellite  which  needs  validation  and  testing  to  prove  its  operability  and  verify  its software  compatibility  with  hardware  and  other  subsystems.    One  failure  in  orbit  is extremely expensive in terms of cost and time due to payload preparation and launch. The ideal test bench would be the one that perfectly simulates the space environment and all its main factors such as weightlessness, Earth’s Magnetic Field (EMF), vacuum, neutral particles, plasma and radiation, among others.  The target in this case was the Earth’s Magnetic Field (EMF), solved with a Helmholtz Cage in a Merritt Configuration, and weightlessness, not implemented but analysed in detail where different alternatives are proposed, similar to market solutions.As  derived  from  literature  and  simulations  executed  along  this  M.  Sc.    Thesis,  the Merritt Cage seems beneficial against any other configuration in terms of magnetic field uniformity and effective volume.  After the design and assembly of the test bench, both properties were verified and successfully achieved, despite the lack of calibration, not executed because of time limitation, and tiny issues encountered along the full evolutionof the project. / Attitude Determination and Control System (ADCS) är ofta ett komplicerat system ombord på alla satelliter som behöver validering och testning för att bevisa dess användbarhet och  verifiera dess  programvarukompatibilitet med  hårdvara och  andra delsystem.   Ett fel  i  omloppsbana  är  extremt  dyrt  med  avseende  på  kostnader  och  tid  på  grund  av förberedelse  och  lansering  av  nyttolast  Den  ideala  testbänken  skulle  vara  den  som perfekt  simulerar  rymdmiljön  och  alla  dess  huvudfaktorer  såsom  viktlöshet,  Earth’s Magnetic  Field  (EMF),  vakuum,  neutrala  partiklar,  plasma  och  strålning,  bland  andra. Målet  i  detta  fall  var  EMF,  löst  med  en  Helmholtz-bur  i  en  Merritt-konfiguration,  och viktlöshet,  inte  implementerad  men  analyserad  i  detalj  där  olika  alternativ  föreslås, liknande marknadslösningar.Som härstammar från litteratur och simuleringar utförda längs denna M. Sc. Avhandling verkar Merritt Cage vara gynnsam mot annan konfiguration när det gäller magnetfältens enhetlighet och effektiv volym.  Efter konstruktionen och montering av testbänken, var båda egenskaperna verifierade och framgångsrikt uppnådda, trots bristen på kalibrering, inte  genomförda  på  grund  av  tidsbegränsning,  och  små  problem  som  uppstod  underprojektets fulla utveckling.

In this thesis, we explore a novel approach to solving the Helmholtz equation,the WaveHolz iteration method. This method aims to overcome some ofthe difficulties with solving the Helmholtz equation by providing a highlyparallelizable iterative method based on solving the time-dependent Waveequation. If this method proves reliable and computationally feasible it wouldhave great value for future application. Therefore, it is of interest to evaluatethe performance and properties of this method. To fully evaluate this method,the method was implemented and conclusions were based on results fromsimulations of the method. The method was able to solve problems in threedimensions and it seems that the method is very well suited for parallelized computations. To replicate real-world scenarios simulations of problems ininfinite and curvilinear domains were conducted. Based on the result presentedhere it is possible to further refine the method, especially regarding the setupof the domain and the implementation of boundary conditions for infinitedomains. / I detta examensarbete presenteras en ny metod för att lösa Helmholtz ekvation, WaveHoltz iterativa metod. Målet med denna metod är att undkomma vissa problem som uppstår med andra metoder för att lösa Helmholtz ekvation genom att tillhandahålla iterativ metod som baseras på lösningar av den tidsberoende vågekvationen samt kan parallelliseras effektivt. Om denna metod visar sig vara stabil och effektiv beräkningsmässigt skulle detta medföra stor potential för framtida tillämpningar. Av denna anledning undersöks metoden och dess egenskaper. För att fullt ut kunna evaluera denna method implementerades den vartefter simuleringar genomfördes och slutsatser drogs. Med metoden var att det var möjligt att lösa problem i tre dimensioner och metoden visade sig vara lämplig för parallella beräkningar. För att återskapa verklighetstrogna scenarion beräknades problem i oändliga och kroklinjiga domäner. Baserat på resultaten som presenteras i denna rapport är det möjligt att förfina metoden, speciellt vid konstruktionen av komplicerade beräkningsnät och randvillkoren för de oändliga problemen.

At the turn of the 20th century two contemporaries in their respective fields teamed up to develop a solution to an acoustic problem with the hard-surfaced vaulted ceilings being installed in many large spanning rooms being built at the time. In the spirit of their ingenuity, this research explores a 21st century solution to a similar problem in contemporary buildings; the desire for a durable, hard surface wall or ceiling material treatment that is more sound absorbent than other common surface treatments. To find a material answer to this desire an impedance tube was used to analyze the mid-frequency octave band absorption coefficients of various re-purposed existing materials and tiles created utilizing 3D print technology and Helmholtz resonators. Additionally, an empirical study of Helmholtz resonator geometry was performed by analyzing the sound absorption of resonant cavity shape changes. Finally, plots of the absorption coefficients for each material tested were created to provide a visual comparison against two common surface treatment materials, tectum and gypsum wall board. / Master of Architecture

Mémoire numérisé par la Direction des bibliothèques de l’Université de Montréal / Les étoiles massives (M≥8M.) deviennent des supernovae de type II à la fin de leur vie. Ce phénomène explosif est caractérisé par l'effondrement du cœur de Fer (56Fe) qui, sous l'influence de sa propre gravité se détache des couches externes qui l'enveloppent. La théorie prédit que le cœur de l'étoile survit à cette explosion sous la forme d'une étoile à neutrons. Cette dernière pourrait subir une collision avec une autre étoiles à neutrons. Comme résultat d'une telle collision, il y aura une expulsion de la matière neutronique. Pour décrire ces deux processus d'effondrement et de décompression, on doit posséder une bonne équation d'état. Or, dans la plupart des études sur la matière nucléaire dans les étoiles massives en implosion, les intégrales se trouvant dans les quantités fondamentales telles que la pression, l'énérgie et l'entropie des électrons ont été représentés par des expressions approchées de Chandrasekhar. Cependant, ces approximations ne sont plus valables à certaines conditions (basse densité et haute température), et il nous est impossible de savoir ce qui se passe dans le milieu stellaire dans de telles conditions; et même dans le cas où ces approximations sont valables, plusieurs questions se posent toujours sur le degré d'erreur dû à ces approximations qui peuvent être, parfois, trompeuses. Dans notre étude on a pris en considération l'effet de création de paires qu'aura lieu dans le milieu stellaire à des basses densités et hautes températures; l'inclusion de ce détail constitue un élément nouveau de cette étude. Le but de ce mémoire consiste à mener un calcul exact pour toutes les quantités physiques de l'équation d'état en évaluant numériquement ces intégrales, et aussi à voir quelles contributions elles peuvent apporter lors de leurs insertion dans des programmes déjà développés au Département de Physique de l'Université de Montréal, mais qui utilisent seulement des approximations. La bonne précision de nos calculs d'intégrales et les différentes méthodes utilisées pour vérifier leurs valeurs numériques nous a permis de faire des corrections importantes à toutes les quantités physiques de l'équation et, surtout, à l'entropie et l'énergie libre de Helmholtz. Ce calcul nous a permis aussi de déterminer les domaines de validité des expressions approchés de Chandrasekhar, souvent utilisées par les astrophysiciens, et celles de la limite "bulle chaude".

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O autor não apresentou resumo.

This thesis describes research on acoustically excited bluff body flow-fields, motivated by the problem of combustion instabilities in devices utilizing these types of flame-holders. Vortices/convective-structures play a dominant role in perturbing the flame during these combustion instabilities. This thesis addresses a number of issues related to the origin, evolution and the interaction of these structures with the flame. The first part of this thesis reviews the fluid mechanics of non-reacting and reacting bluff body flows. The second part describes the spatio/temporal characteristics of bluff-body flames responding to excitation. The key processes controlling the flame response have been identified as 1) the anchoring of the flame at the bluff body, 2) the excitation of flame-front wrinkles by the oscillating velocity field and 3) flame propagation normal to itself at the local flame speed. The first two processes control the growth of the flame response and the last process controls the decay. The third part of this thesis describes the effect of acoustic excitation on the velocity field of reacting bluff body flows. Acoustic disturbances excite the Kelvin-Helmholtz (KH) instability of the reacting shear layer. This leads to a spatially decaying vorticity field downstream of the bluff body in the shear layers. The length over which the decay occurs was shown to scale with the length of the recirculation zone of the bluff body, i.e. the length over which the velocity profile transitions from shear layer to wake. The flame influences this decay process in two ways. Gas expansion across the flame reduces the extent of shear by reducing the magnitude of negative velocities within the recirculation zone. This combined with the higher product diffusivity reduces the length of the recirculation zone, thereby further augmenting the decay of the vorticity fluctuations. Lastly, these results also revealed phase jitter - a cycle-to-cycle variation in the position of the rolled-up vortices. Close to the bluff-body, phase jitter is very low but increases monotonically in the downstream direction. This leads to significant differences between instantaneous and ensemble averaged flow fields and, in particular, the decay rate of the vorticity in the downstream direction.

Excessive fluid-borne noise in hydraulic systems is a problem the fluid power industry has long struggled to address. Traditional noise control devices such as Helmholtz resonators, tuning coils, and Herschel-Quincke tubes are generally too large for fluid power systems unless the speed of sound in the device can be reduced. A compliant lining can achieve this effect, but compliance (and lossy compliance) has had little attention in noise control in general, and in fluid power in particular. One means to achieve compliance in these devices, especially at elevated pressures, is through a liner made of syntactic foam, which in this case is a urethane host matrix with embedded hollow, polymer microspheres. The material properties at elevated pressure are unknown by the liner manufacturer, but are known to be pressure- and temperature-dependent. Therefore, the effect of hydrostatic pressures from 2.1-21 MPa and temperatures from 20-45 C on the liner properties, thus the device performance, are studied. For a Helmholtz resonator, a theoretical model is fit to experimentally-measured transmission loss of the device using a least-squares routine, which solves the inverse problem for the complex bulk modulus of the liner. These material properties are used to compare a predictive model of a tuning coil to experimental data, and in a parameter study of a Herschel-Quincke tube. The compliance of the liner is found to lower the effective sound speed by an order of magnitude and decrease the volume of the cavity of a Helmholtz resonator by up to two orders of magnitude. This work is expected to result is more compact noise control devices for fluid power systems.