A vibration-based sound power (VBSP) measurement method is appealing because of its potential versatility in application compared to pressure- and intensity-based methods. The VBSP method is based on the well-known elementary radiators approach and is reliant on the acoustic radiation resistance matrix. Previous research has developed and validated the VBSP method for flat plates and cylinders. This thesis details work on extending the VBSP method to arbitrarily-curved structures. The approach of computing surface normal velocities from 3D velocity data measured by a scanning laser Doppler vibrometer (SLDV) is presented. This approach is validated with experimental sound power results of a cylindrical shell using the VBSP method with 3D velocity and geometry data. The sound power results are shown to have good agreement with ISO 3741 results. Experimental sound power results from three simple-curved plates using the VBSP and ISO 3741 methods are shown to have good agreement. These experimental results indicate that the VBSP method is less sensitive to background noise than the ISO 3741 method. An overview of exploring inherent symmetry in the radiation resistance matrix is presented for the purpose of increasing efficiency in applying the VBSP method. Sound power sensitivity to the formulation of the radiation resistance matrix is explored as another relevant option for increasing the efficiency of the VBSP method for many cases and for extending the method to more complex structures. The results of the radiation resistance matrix exploration enable the VBSP method to apply to arbitrarily-curved structures. Experimental sound power results using the VBSP method with the simple-curved plate radiation resistance matrix and the ISO 3741 method are compared for two arbitrarily-curved panels and are shown to have good agreement. The VBSP method based on the simple-curved plate form of the radiation resistance matrix is shown to have excellent agreement with numerical results from boundary element models, which inherently use the appropriate form of the radiation resistance matrix.

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Today Atlas Copco Rock Drills AB hasn’t got any method to determine how many warning alarms they need on their machines and how they should be mounted to use their full potential. At the moment a travel alarm is usually placed in the front of the machine and a reverse alarm in the back. Then a measurement of the sound pressure level around the machine is performed to see if it is enough to pass the limit according to different ISO-standards. Otherwise they have to mount some extra alarms and then do the measurements again until the standards are fulfilled. The aim of this thesis work is to develop a method for determine how many alarms Atlas Copco Rock Drills AB need on the machines, and also how they should be mounted to fulfil the different criteria according to ISO-standards in the early phase of construction. From the different divisions within Atlas Copco Rock Drills AB (LHD, SDE and TME) arrived four different alarms, which are used on their machines. Sound pressure level measurements were conducted on these, in the anechoic chamber at audiological research centre at the university hospital in Örebro. In the LMS Test.Lab software a measurement sphere was built around the horns and based on the data obtained at the anechoic chamber sound directivity plots were made. Together with earlier machine measurement data from Atlas Copco Rock Drills AB, an Excel program was made constituting an example of how the horns should be mounted. LHD = Loaders and trucks/underground rock excavation SDE = Surface drilling equipment TME = Tunnelling and mining equipment / Idag har Atlas Copco Rock Drills AB inte någon metod för att bestämma hur många varningsalarm som behövs på sina maskiner samt var de ska placeras så de utnyttjar sin fulla potential. I nuläget monteras ett signalhorn vid främre delen och ett backlarm i bakre delen av maskinen. Sedan utförs en ljudtrycksmätning runt maskinen för att kontrollera om man uppfyller kraven från olika ISO-standader. Annars monteras fler alarm och mätningen utförs på nytt tills standarderna uppfylls. Detta examensarbete har som mål att ta fram en metod som bestämmer hur många alarm Atlas Copco Rock Drills AB behöver på sina maskiner, samt hur de skall placeras för att uppfylla kriterierna från olika ISO-standarder redan i konstruktionsstadiet.  Från de olika avdelningarna inom Atlas Copco Rock Drills AB (LHD, SDE och TME) mottogs fyra olika alarm, som används på maskinerna. På dessa utfördes ljudtrycksmätningar i det ekofria rummet vid audiologiskt forskningscentrum på universitetssjukhuset i Örebro. I programmet LMS Test.Lab byggdes en sfär av mätpunkter runt alarmen och baserat på insamlade data från det ekofria rummet konstruerades direktivitetsdiagram. Tillsammans med data som Atlas Copco Rock Drills AB redan hade från tidigare mätningar på maskiner gjordes ett Excel-program, som ger ett exempel på hur alarmen bör monteras. LHD = Loaders and trucks/underground rock excavation SDE = Surface drilling equipment TME = Tunnelling and mining equipment

Vertical axis wind turbines (VAWTs) have with time been outrivaled by the today common and economically feasible horizontal axis wind turbines (HAWTs). However, VAWTs have several advantages such as the possibility to put the drive train at ground level, lower noise emissions and better scaling behavior which still make them interesting for research. The work within this thesis is made in collaboration between the Department of Construction and Energy Engineering at Halmstad University and the Division for Electricity at Uppsala University. A 200 kW VAWT owned by the latter and situated close to Falkenberg in the southwest of Sweden has been the main subject of the research even if most learnings has been generalized to fit a typical vertical turbine. This particular turbine has a wooden tower which is semi-guy-wired, i.e. the tower is both firmly attached to the ground and supported by guy-wires. This thesis has two main topics both regarding VAWTs: eigenfrequency of the tower and the noise generated from the turbine. The eigenfrequency of a semi-guy-wired tower is studied and an analytical expression describing this is produced and verified by experiments and simulations. The eigenfrequency of the wire itself and how it is affected by wind load are also studied.  The noise characteristics of VAWTs have been investigated, both theoretically and by noise measurement campaigns. Both noise emission and frequency distribution of VAWTs has been studied. The work has resulted in analytical expressions for tower and wire eigenfrequency of a semi-guy-wired tower as well as recommendations for designing future towers for VAWTs. The noise emission of VAWTs has been studied and proven low compared to HAWTs. The noise frequency distribution of the 200 kW VAWT differs significantly from that of a similar size HAWTs with for example lower levels for frequencies below 3000 Hz.

Orientador: Stelamaris Rolla Bertoli / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-07T09:10:16Z (GMT). No. of bitstreams: 1 Brito_LuizAntonioPerroneFerreirade_D.pdf: 3739352 bytes, checksum: ef3ea005bce1f1b45574b05f490d22cf (MD5) Previous issue date: 2006 / Resumo: Várias cidades brasileiras estão enfrentando problemas de poluição sonora. O ruído de tráfego é a principal causa de incômodo seguido pelo ruído gerado pelos equipamentos utilizados na construção civil. É imperativo que sejam criados parâmetros para controlar a emissão e propagação do ruído gerado pela construção civil para manter uma certa qualidade de vida nas grandes cidades. O nível de potência sonora é um importante parâmetro para análise da propagação sonora no meio ambiente. Pode-se determinar o nível de potência sonora através da medição de intensidade sonora, ín sítu, mesmo na presença de outras fontes de ruído. Assim não é necessária a remoção do equipamento analisado para câmaras anecóicas ou reverberantes. Este trabalho estuda as correções na determinação do nível de potência sonora obtido através da técnica da intensimetria. Deve-se destacar a compilação do estado da arte sobre o assunto. Foram selecionados uma norma e um sistema de medição que possam ser utilizados nos canteiros de obras e indústrias ligadas a construção civil. Os resultados das medições do nível de potência sonora de uma furadeira elétrica, com e sem ruído de fundo, obtidos através da norma ISO 9614-2 (1995) foram comparados aos obtidos em uma camara reverberante através da norma ISO 3741 (1999). Esta comparação permitiu o estudo de três novos indices de campo, Fator de Absorção, Fator de Superf1cie e Fator de Relação da Área da Fonte e da Superf1cie de Medição, que foram utilizados de base para análise dos erros no resultado final do nível de potência sonora, formando uma metodologia confiável, que pode ser utilizada no controle do ruído ambiental / Abstract: Many Brazilian cities are facing noise pollution problems. Traffic noise is the main cause of inconvenience followed by noise generated by equipments used in civil construction. In order to maintain a certain life quality level in large cities it is paramount to control noise emission and propagation generated by civil construction. Sound power level is an important parameter to analyze environmental sound propagation. The sound power level can be determined through ín sítu measurement of sound intensity even in the presence of other sound sources. Therefore, it is not necessary to remove the analyzed equipment to anechoic or reverberation chambers. This work studies the corrections in the determination of the sound power level obtained through intensity technique. The state of art compilation about the subject should be pointed out. Both a standard and a measurement system, which can be used at construction sites and industries related to civil construction, were selected. Results from the sound power level measurements of an electric drill, with and without background noise, acquired through the standard ISO 9614-2 (1995) were compared to those acquired in a reverberation chambers through the standard ISO 3741(1999). This comparison allowed to study three new field indicators, the Absorption Factor, the Surface Factor and the Relation of Source to Measured Surface Area Factor which were used as base in the error analysis of the final result on sound power level, providing a reliable methodology that can be used in the control of environmental noise / Doutorado / Edificações / Doutor em Engenharia Civil

Sound power measurements of acoustic sources are typically performed in anechoic or reverberation chambers using acoustic pressure according to international standards. The anechoic chamber creates a free-field environment where the sound power is estimated from the squared pressure integrated over some enveloping surface. The reverberation chamber produces diffuse-field conditions, where sound power is proportional to the spatially averaged squared pressure. In semi-reverberant environments, the direct and reverberant energies each contribute to the total measured field. If the kinetic and potential components of acoustic energy density are weighted appropriately, the spatial variation of the field can be significantly reduced compared to squared pressure. This generalized energy density allows an adaptation of the sound power formulation by Hopkins and Stryker to be used to make an efficient and accurate in situ sound power estimate of a noise source in a non-ideal acoustical environment. Since generalized energy density optimizes the spatial uniformity of the field, fewer measurement positions are needed compared to traditional standards. However, this method breaks down for sources that are large and extended in nature and considerably underestimates the sound power. This thesis explores the practical limits of this method related to the sound power underestimation. It also seeks to understand the special considerations necessary to achieve accurate, survey-grade sound power data of large, extended noise sources through a laboratory study of custom extended and compact sources. A modified method to accurately and efficiently measure the sound power of large, extended sources is proposed with results.

This Master´s thesis deals with principles of determination of the sound power level. At the very beginning there is an explanation of important concepts. Afterwards there is an overview of standards that deal with the sound power level determination, including the ČSN EN ISO 9614-1 standard which is used for the experiment. Last but not least, there is described the experiment, consisting of several measurements of the same object, but every time with different configuration of measuring and sound reflective surfaces.

Vertical axis wind turbines (VAWTs) have with time been outrivaled by the today common and economically feasible horizontal axis wind turbines (HAWTs). However, VAWTs have several advantages such as the possibility to put the drive train at ground level, lower noise emissions and better scaling behavior which still make them interesting for research. The work within this thesis is made in collaboration between the Department of Construction and Energy Engineering at Halmstad University and the Division for Electricity at Uppsala University. A 200 kW VAWT owned by the latter and situated close to Falkenberg in the southwest of Sweden has been the main subject of the research even if most learnings has been generalized to fit a typical vertical turbine. This particular turbine has a wooden tower which is semi-guy-wired, i.e. the tower is both firmly attached to the ground and supported by guy-wires. This thesis has two main topics both regarding VAWTs: eigenfrequency of the tower and the noise generated from the turbine. The eigenfrequency of a semi-guy-wired tower is studied and an analytical expression describing this is produced and verified by experiments and simulations. The eigenfrequency of the wire itself and how it is affected by wind load are also studied.  The noise characteristics of VAWTs have been investigated, both theoretically and by noise measurement campaigns. Both noise emission and frequency distribution of VAWTs has been studied. The work has resulted in analytical expressions for tower and wire eigenfrequency of a semi-guy-wired tower as well as recommendations for designing future towers for VAWTs. The noise emission of VAWTs has been studied and proven low compared to HAWTs. The noise frequency distribution of the 200 kW VAWT differs significantly from that of a similar size HAWTs with for example lower levels for frequencies below 3000 Hz.

The two-point in situ method is a technique for measuring the room constant of a semi-reverberant room and the sound power of a source in that room simultaneously using two measurement positions. Using a reference directivity source, where the directivity factor along any given axis of the source has been measured, one is able to use the Hopkins-Stryker equation to measure both the room constant and the sound power level of another source rather simply. Using both numerical and experimental data, it was found that by using generalized energy density (GED) as a measurement quantity, the results were more accurate than those using squared pressure. The results also improved when one measurement position was near the source and the other measurement position was far from the source. This resulted in strong contribution of both the direct and reverberant fields in each of the measurement positions. Another improvement to the two-point method was the use of a local, spatial average around the measurement position. The assumptions in the Hopkins-Stryker equation rely on this average and it was found that a small local spatial average improved the measurements. However, this improvement was greater for squared pressure than for GED. Several source sound power levels and room constants were measured to show that these measurements are improved by using the suggested techniques.

Noise from information technology (IT) equipment is a significant problem in today's modern society. Active Noise Control (ANC) has shown promise in reducing the effect of IT fan noise on users. Though ANC has been applied to axial fans (such as those found in desktop computers), it has not been applied to centrifugal fans, such as those found in laptop computers. This work applies an ANC method to a centrifugal fan mounted in a mock laptop enclosure. This method is applied in four steps. First, secondary sources are placed in the vicinity of the fan. Second, an accurate model of the radiation from the fan and secondary sources is constructed. Third, the total power radiated from this system is minimized. This creates nodal lines in the vicinity of the fan. Fourth, ANC error sensors are placed on the nodal lines predicted by the model. This creates these nodal lines experimentally, thus creating the minimum power condition. The noise from the exhaust and inlets of the fan will first be controlled individually. Then the method will be applied to the combined system. Global sound power radiation will be measured in all cases.