Dissertations / Theses on the topic 'Acoustics and noise control (except architectural acoustics)'

The scope of this research concerns the passive damping of structural vibrations by the use of viscoelastic layers. It is motivated by the need for efficient numerical tools to deal with the medium frequency behaviour of industrial viscoelastic sandwich products. The sandwich modelling technique is based on the use of an interface element: the two deformable plates are modelled by special plate elements while the intermediate dissipative layer is modelled with interface elements. This interface element is based on the first-order shear deformation theory and assume constant peel and shear stresses in the polymer thickness. This element couples the lower and upper layers without additional degrees of freedom. The partition of unity finite element method (PUFEM) is applied to the development of enriched Mindlin plate elements. The element shape functions are obtained as the product of

partition of unity functions with arbitrary chosen enrichment functions. Polynomial enrichment leads to the generation of high-order polynomial shape functions and is therefore similar to a p-FEM technique. Numerical examples illustrate the use of both PUFEM Mindlin plate elements and interface elements for the simulation of viscoelastic sandwich structures.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished

O objetivo deste trabalho é avaliar o desempenho acústico de um sistema construtivo modular e industrializado por meio do método simplificado de campo indicado pelas normas ABNT NBR 15575-4:2013 e ISO 10052:2004, analisando as vedações verticais internas e externas quanto ao isolamento ao ruído aéreo e as comparando com análises já realizadas em outras edificações de trabalhos conhecidos. A indústria de construção civil, em todo o mundo, encontra-se em um momento dedicado à busca e implementação de estratégias de modernização do setor, a fim de se reduzir os custos e minimizar os desperdícios, investido em construções sustentáveis. Há uma necessidade de estudos baseados nos parâmetros da norma NBR 15575-4:2013 para a devida caracterização das tecnologias construtivas que surgem e ainda são consideradas novidade para o setor. A norma implica em uma série de exigências e recomendações, como por exemplo, o conforto acústico, que será abordado nesse trabalho. A metodologia utilizada foi baseada no método simplificado orientado pela ISO 10052:2004. Foram analisadas duas edificações de 40,0m2 cada. Uma delas é um sobrado, e a outra uma casa térrea. Foram feitas as medições de níveis de pressão sonora nos cômodos e nas fachadas, e as medições do tempo de reverberação dos cômodos. Depois de realizadas as medições foram feitas as análises pelo teste “t” de student. Em comparação com os padrões de outros países, percebeu-se que a norma ABNT NBR 15.575-4:2013 possui valores brandos, e que mesmo assim, as atuais técnicas construtivas brasileiras, em sua maior parte, não conseguem atingi-los. Através dos resultados encontrados, percebeu-se uma eficiência quanto ao isolamento ao ruído aéreo nas edificações modulares e industrializadas quando comparados às edificações de outras técnicas construtivas. Conclui-se, então, que o sobrado e a edificação térrea estão de acordo com os níveis de desempenho estabelecidos pelo norma ABNT NBR 15.575-4:2013.
The objective of this study is evaluate the modular and industrialized building system’s acoustic performance through the simplified field method indicated by ABNT NBR 15575-4:2013 and ISO 10052: 2004, analyzing the internal and external vertical seals for air noise insulation and comparing with previous analyzes in other approaches. The world construction industry is in a dedicated time to the pursuit and implementation of sector modernization strategies in order to reduce costs and minimize waste, invested in sustainable buildings. It’s is necessary studies based on the parameters of NBR 15575-4: 2013 for the proper characterization of building technologies that emerge and are still new to the sector. The standard implies a series of requirements and recommendations, such as the acoustic comfort, which will be addressed in this work. The methodology used was based on the simplified method guided by ISO 10052: 2004. Two buildings were analyzed, with 40,0m2 each. One of them is a two-story house, and the other is a ground floor building. Measurements of sound pressure levels were made in the rooms and on the frontages, and measurements of the reverberation time of rooms. After the measurements were made analyzes with test "t" student. Compared to the standards of other countries, it was realized that the ABNT NBR 15575-4: 2013 has soft values, and that even so, the current Brazilian construction techniques, for the most part, can not reach them. Through these results, it was noticed an efficiency about the isolation airnoise in modular and industrialized buildings compared to buildings of other construction techniques. It follows, then, that the floor and the ground floor building comply with the performance levels established by ABNT NBR 15575-4: 2013.

The prediction of the noise generated by en-route aircraft is gradually gaining in importance as the number of aircraft increases over the last few decades. While the studies of outdoor sound propagation have been focused on near ground propagation, the case when the sound source is high above the ground has not attracted much attention. At the same time there has been a lack of high-quality aircraft acoustic validation data sets that contain detailed acoustic, meteorology, and source-receiver position data. The DISCOVER-AQ data set, which was collected by Volpe in support of the Federal Aviation Administration (FAA), has greatly helped with studying the directivity and the Doppler effect in the comparison between simulation results and measurements.

Outdoor heating, ventilating, and air-conditioning (HVAC) units emit a significant amount of noise, which may lead to poor sound quality and a perceived low product quality. It is the job of the noise control engineer to reduce the undesired noise and improve the sound quality of the outdoor HVAC unit to decrease consumer annoyance. There is great interest in developing a detailed and accurate acoustic model of the outdoor HVAC unit so that the sound of the outdoor HVAC unit can be listened to before the unit is constructed. Having an acoustic model which can synthesize sounds allows the noise control engineer to evaluate and improve the sound quality of the outdoor HVAC unit during the design process, without the need for extensive prototyping. Acoustical holography methods will be used to identify and localize noise due to the fan, and other significant noise sources, to visualize the sound field. In the current study, an acoustic model is described which can be used to model the noise due to structural radiation and vortex shedding of the outdoor HVAC unit’s rotating fan blades, one of the top contributors to the unit’s overall noise level. This moving source model simulates the Doppler effect which occurs when the blade moves towards and away from a receiver. The results from this moving source model is shown for different source signals, including sinusoidal, bandpass random, repeating random, and sinusoidal with time-varying frequency source signals. The parameters of this moving source model will be optimized to reproduce the experimental results, including the power spectral densities, tonal power component, and auralizations.

Near-field Acoustical Holography is a tool that is conventionally used to visualize sound fields through an inverse process in a three-dimensional space so that either sound field projections or sound source localization can be performed. The visualization is conducted by using sound pressure measurements taken in the near-field region close to the surface of the unknown sound source. Traditional Fourier-based Near-field Acoustical Holography requires a large number of measurement inputs to avoid spatial truncation effects. However, the use of a large number of measurements is usually not feasible since having a large number of microphones is costly, and usually the array is limited in size by the physical environment, thus limiting the practicality of this method. In the present work, because of the desire to reduce the number of microphones required to conduct acoustical holography, a method known as Statistically Optimized Near-field Acoustical Holography initially proposed by Steiner and Hald was analyzed. The main difference between the present work and the concept mentioned by Steiner and Hald is the cylindrical coordinate system employed here for the purpose of experimenting on a bladeless fan, which resembles a cylindrical structure and which could be assumed to be a cylindrical source. The algorithm was first verified via simulations and measurements, and was then applied to experimental data obtained via pressure measurements made with a cylindrical microphone array. Finally, suggestions for noise control strategies for the bladeless fan are described, based on the measurement results.

Hydraulic systems have many applications in the construction, transportation, and manufacturing sectors. Recent design trends involve systems with higher working pressures and more compact systems, which are advantageous because of power density increase. However, these trends imply higher forces and larger vibration amplitudes while having lesser mass and damping, leading to higher noise levels. Meanwhile, hydraulic machinery started prospecting new applications with tighter noise regulations, a trend which was also pushed by the electrification tendency in several fields of transportation and agriculture. One method to attain noise mitigation is passive-noise canceling techniques have the advantage of not introducing energy to the system. This approach arranges pressure ripple waves in a destructive pattern by projecting a hydraulic circuit's geometry, configuration, and features.

This dissertation aims to predict fluid-borne noise sources and investigate passive noise-canceling solutions for multiple operations conditions targeting to impact many hydraulic systems and a broad range of operating conditions. Primarily a coupled system model strategy that includes a one-dimensional line finite element model is developed. The line model predicts pressure wave generation and propagation. The model features versatility since parameters like line diameter and material can be discretized node by node. Simulations are compared to measured data in a realistic novel hydraulic hybrid transmission for validation.

Subsequently, an extensive numerical investigation is performed by setting fixed parameters along the hydraulic lines' length and comparing several isolated geometric properties in simulation. The developed line model is also used to study the influence of line features such as diameter and extent of the conduit. Cost-effective and simple passive solution solutions such as Quincke tubes (parallel lines), expansion chambers, and closed branches are selected and investigated on simulation. Four target pressure ripples are chosen as indicators for summarizing passive line elements behavior. The frequency-domain behavior of the pressure ripple peaks regarding the line's length is identified and isolated in simulation at the 50-5000Hz frequency spectrum. An experiment test rig is designed to implement these solutions and the experiments show three developed passive elements as practical and effective solutions for reducing fluid borne noise sources. The selected designs yielded noise source attenuation over most of the frequency spectrum measured with piezoelectric pressure variation sensors and accelerometers in different positions in the hydraulic circuit. Sound pressure measurements detected reductions over 3dB in the best cases.

Also, a passive interference approach based on the principle of secondary source flow ripple cancellation was conceptualized, modeled, and implemented in a tandem axial-piston unit. The strategy consists of setting the phase between the two synchronous units to accomplish destructive interference in targeted unit harmonics. Two indexing strategies are investigated first analytically and then on simulation. One of the indexing strategies was implemented in a pre-existent commercial axial-piston tandem unit. Experiment results confirmed effectiveness for the first and third unit’s harmonics, where reductions over 15dB on pressure ripple were measured.

Finally, a fluid-structure interaction based on the poison coupling principle is developed using the method of characteristics. Transfer functions of the pipeline accelerations versus the pressure ripples on lines calculated on simulation and later obtained experimentally to highlight ta critical vibration band from 2000Hz to 3000Hz with high acceleration response.

Generally, heavier noise control treatments are favored over lighter ones since heavier acoustical materials tend to insulate (block) noise sources more effectively than do lighter materials. In automotive applications, however, heavier materials cannot always be adopted because of concerns over the total weight of the vehicle. Thus, it would be useful to identify lightweight acoustical treatments that can mitigate vehicle interior noise. Automotive sound packages have both absorption and barrier characteristics, and there is inevitably a trade-off between these two. Therefore, it is important to study the exchange between the absorption and transmission of acoustical materials particularly as it pertains to weight. Here, a procedure based on plane wave analysis is described that can be used to identify weight reduction opportunities by adjusting the acoustical properties of a generic sound package, consisting of a fibrous layer and a flexible microperforated panel surface treatment, so that it meets a target sound pressure level in a downstream interior space. It has been found, for the configuration studied here, that there are lightweight sound package configurations that can maintain acoustical performance equivalent to that of heavier noise treatments, and further, it has been found that the lightest treatments tend to favor barrier performance rather than absorption. Further, the impact of acoustical leaks has been considered, and it has been found that even very small leaks can result in a very substantial weight penalty if a specified level of acoustical performance is to be ensured. Further, the impact of changing the underlying panel mass and altering the frequency weighting used in the optimization process has also been considered.

The optimizer used in the proposed procedure requires considerable calculation time; hence, the acoustic pressure calculation time needs to be minimized to enhance the efficiency of the solution process. Thus, the transfer matrix method (TMM) for a two-dimensional case was used to calculate the interior acoustic pressure for a simple geometry as a starting point in the process of identifying the minimum-weight sound packages. The TMM is a widely used analytical approach to predicting the sound pressure (and particle velocity) for a system that can be represented as a series of subsystems. Although the TMM can offer fast and simple calculations for the acoustic system, its application is limited to a plane-wave-based model. Thus, the TMM is not the best option for the acoustic pressure prediction in a complex geometry such as a vehicle interior, that involves non-planar wave propagation. Therefore, a hybrid TMM-FEA method is proposed in this research to evaluate the acoustical performance of the sound package in more complex geometries (here, a vehicle-like cavity). So, in this research, the TMM was introduced to obtain the initial solutions that can be used in conjunction with the FEA tool to calculate the sound pressure field in the complex geometry case. The correlation between the results of these two approaches was then analyzed to develop a space-averaged pressure prediction model for various absorptive cases in the interior space. Finally, this SAP prediction model was used to generate an acoustic map that can be used to graphically estimate the SAPs in the complex geometry case.

In order to validate the usage of the developed equation for different sets of boundary conditions, several case studies were performed to study the effects of the surface impedance arrangements, geometrical shapes, and, lastly, the presence of extra features in the interior space. Finally, the SAP difference between the area near the driver’s right ear and the total interior cavity was studied to show that the SAP of the total cavity can be adjusted to evaluate the acoustic performance of the sound packages along the lines of conventional industry practice.

Recent advances in sensor technologies and data acquisition platforms have led to the era of Big Data. The rapid growth of artificial intelligence (AI), computing power and machine learning (ML) algorithms allow Big Data to be processed within affordable time constraints. This opens abundant opportunities to develop novel and efficient approaches to enhance the sustainability and resilience of Smart Cities. This work, by starting with a review of the state-of-the-art data fusion and ML techniques, focuses on the development of advanced solutions to structural health monitoring (SHM) and metamaterial design and discovery strategies. A deep convolutional neural network (CNN) based approach that is more robust against noisy data is proposed to perform structural response estimation and system identification. To efficiently detect surface defects using mobile devices with limited training data, an approach that incorporates network pruning into transfer learning is introduced for crack and corrosion detection. For metamaterial design, a reinforcement learning (RL) and a neural network based approach are proposed to reduce the computation efforts for the design of periodic and non-periodic metamaterials, respectively. Lastly, a physics-constrained deep auto-encoder (DAE) based approach is proposed to design the geometry of wave scatterers that satisfy user-defined downstream acoustic 2D wave fields. The robustness of the proposed approaches as well as their limitations are demonstrated and discussed through experimental data or/and numerical simulations. A roadmap for future works that may benefit the SHM and material design research communities is presented at the end of this dissertation.