This thesis describes the phase and amplitude correction of 12.7 mm diameter, Type-1 microphones for three frequency bands, including within the infrasound regime, and its application to acoustic measurements. Previous data stem from acoustic intensity measurements using two-dimensional, four-microphone probes, which emphasized the requirement of having the acoustic phase and amplitude difference be much greater than the interchannel mismatch. Although correcting the amplitude/phase is well-known, obtaining the necessary transfer functions in the infrasound regime is challenging because (1) signal-to-noise ratios are often poor, (2) long measurement times are required for averaging, and (3) microphone responses vary significantly across these low frequencies. In this paper, a convenient infrasound source previously studied for infrasound adverse effects on humans is intended for performing a relative calibration. This work also seeks to elaborate recommendations for probe spacing, averages or length recordings, and instrument mismatch. The last two chapters show the PAGE method application in infrasonic sources. Those chapters have the intensity measurements using free-field microphones with larger separation distances than commercial intensity probes but compact compared to state of the art in infrasonic arrays.

<p>This survey tries to find out if and how we can be influenced of extreme low and strong frequencies in the area 0-40 Hz. A group of 52 teachers/musicstudents and non musicstudents was trying to assess what they thought, experiences and tried to describe why they thought as they did, when they listen on three different versions of same musical piece. Without low frequent bass, original and strengthened bass, randomly mixed. Several different musical pieces was used in same survey. The work also makes a commitment to theories about the people's hearing and the will of ‘selfmotion’. The result gives a hint that participators in the survey prefer to listen to music on “balance”, rather then music with reinforced low bassfrequencies.</p>

This survey tries to find out if and how we can be influenced of extreme low and strong frequencies in the area 0-40 Hz. A group of 52 teachers/musicstudents and non musicstudents was trying to assess what they thought, experiences and tried to describe why they thought as they did, when they listen on three different versions of same musical piece. Without low frequent bass, original and strengthened bass, randomly mixed. Several different musical pieces was used in same survey. The work also makes a commitment to theories about the people's hearing and the will of ‘selfmotion’. The result gives a hint that participators in the survey prefer to listen to music on “balance”, rather then music with reinforced low bassfrequencies.

This thesis details an in investigation of two problems arising during the testing of a jet engine in a test cell, namely the formation and ingestion of vortices and the generation and propagation of infrasound. Investigation involved the use of computational fluid dynamic as well as analytical tools. The author extended the work of previous researchers by investigating the effect when a suction inlet in surrounded by four walls, (as it is in a test cell). A previously suspected but not documented small region of unsteady vortex was discovered to lie between the steady vortex and no vortex regions. The preferential attachment of the vortex, when formed, to a particular surface was investigated and a low velocity region near that surface has been proven as a possible cause. A cell bypass ratio > 90% was found to be necessary to avoid the formation of vortices in typical situations. Parametric studies (conducted cetaris paribus) on four different geometries and flow parameters were also conducted to determine how they affected the vortex formation threshold. Boundary layer thickness on the vortex attachment surface, upstream vorticity, size of suction inlet was found to have a direct relationship with probability of vortex formation whereas Reynolds number of flow was found to have an inverse relationship. Three hypotheses regarding the generation and propagation of infrasound in test cells were analysed. The first hypothesis states that the fluctuating of flow within the test cell led to a periodic fluctuation of pressure. The second hypothesis predicts a change in flow conditions can leads to a change in the acoustic reflection characteristics of the blast basket perforates. The final hypothesis proposes that changing engine location and size of augmenter, can lead to a reduction in the slip velocity between the engine exhaust jet and the cell bypass flow thus reducing the engine jet noise. The first hypothesis has been disproved using CFD techniques, although the results are as yet inconclusive. The second and third hypotheses have been proven to be potentially feasible techniques to be employed in the future. The changes proposed in the final hypothesis are shown to reduce the engine jet noise by up to 5 dB.

Electrical activity at volcanoes has been recently recognized as a potential new remote sensing technique for plume-forming eruptions. Volcanic electrical activity takes place in the conduit and plume and therefore has the benefit of being a direct indicator of surface activity. This is unlike seismic signals, which indicate magma/gas movement underground, and infrasound signals, which indicate a surface explosion but not necessarily the formation of an ash plume. There are two distinct types of volcanic electrical discharges: volcanic lightning and continual radio frequency (CRF) impulses. This dissertation explores the relationships between these two electrical signals and other commonly monitored volcanic parameters. For volcanic electrical activity to be widely adopted into monitoring platforms it is important to understand how electrical discharges at volcanoes are related to other monitored signals. I present a case study of the electrical activity at Sakurajima Volcano, Japan. The lightning mapping array (LMA) is used to record both lightning and CRF. I relate CRF to ash properties and show that CRF corresponds to eruptions containing more juvenile magma that has undergone milling as it is transported out of the conduit. Seismic, infrasound, and video data are used in conjunction with multivariable statistical methods on a suite of electrical parameters to show that high levels of volcanic electrical activity are related to eruptions with large infrasound signals (> 107 J), high initial velocities (> 55 m/s), and relatively tall plume heights (> 1 km). Finally, an examination of globally detected lightning at Bogoslof Volcano, AK shows the potential for volcanic lightning in plume tracking (0-100 km), even after the end of the explosive phase of the eruption.

Aujourd'hui, il n'existe pas d'étalon de référence pour la grandeur physique des pressions dynamiques infrasonores. La demande d'étalonnage d'une telle grandeur est apparue récemment, en réponse à des problématiques du domaine de la géophysique, étudiant la propagation d'ondes acoustiques dans l'atmosphère entre 20 Hz et 0,001 Hz, soutenue par la surveillance du respect du Traité d'Interdiction Complète des Essais Nucléaires (TICE). Dans le but de répondre à cet enjeu, cette thèse a pour objectif la réalisation d'un étalon primaire pour cette grandeur. Le contexte métrologique et quelques bancs d'étalonnage existants, utilisant des générateurs de pression dynamique infrasonore, sont présentés. Afin de concevoir le banc d'étalonnage primaire, les réponses en amplitude et en phase du générateur d'infrasons du CEA sont caractérisées analytiquement et expérimentalement. Par ailleurs, le principe de l'étalon primaire basé sur le pistonphone calculable utilise les mêmes modèles d'admittance acoustique de transfert des cavités cylindriques que ceux préconisés pour l'étalonnage primaire des microphones étalons par la méthode de la réciprocité en pression. Les limites des formulations normalisées sont identifiées pour les fréquences inférieures à 100 Hz. Deux solutions alternatives sont proposées, permettant de généraliser la gamme de fréquences au domaine des infrasons. La validité de ces formulations est démontrée expérimentalement. Enfin, à partir de ces travaux, le développement du banc primaire est détaillé, avec son modèle analytique et les choix mécaniques associés. / Currently, there is no reference standard for the dynamic infrasonic pressures physical quantity. The request for calibration of such a quantity has recently appeared, in response to geophysical issues, studying the propagation of acoustic waves in the atmosphere between 20 Hz and 0.001 Hz, supported by the monitoring of the respect of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). In order to meet this challenge, the aim of this thesis is to realize a primary standard for this quantity. The metrological context and some existing calibration benches, using infrasonic dynamic pressure generators, are presented. To design the primary calibration bench, the amplitude and phase responses of the CEA infrasound generator are characterized analytically and experimentally. In addition, the definition of the standard model is based on the primary method models for pressure calibration of standard microphones in the acoustic pressure range, using cylindrical cavities. The limits of the acoustic transfer admittance standard formulations for these cavities are identified for frequencies below 100 Hz. Two alternative solutions are proposed, allowing the frequency range to be extended to the infrasound domain. The validity of these formulations is demonstrated experimentally. Finally, based on this work, the development of the primary bench is detailed, with its analytical model and the associated mechanical choices.

Wind energy is one of the fastest-growing renewable energy technologies, and horizontal axis wind turbines (HAWT) have been the most common device to convert wind kinetic energy into electrical energy. As the capacities of wind turbines and scales of wind farm constructions are rapidly increasing over time, environmental impacts of wind energy are becoming more relevant and raising more attention than ever before. One of the major environmental concerns is noise emission from wind energy facilities, especially low-frequency noise and infrasound that allegedly cause so-called wind turbine syndrome. Therefore, a numerical simulation program capable to predict low-frequency noise and infrasound emission from wind turbines is a useful tool to aid future wind energy development. In this study of this thesis, a computer program named TDRIP (Time Domain Rotor Infrasound Prediction) is developed based on acoustic analogy theories. Farassat’s formulation 1A, a solution to Ffowcs Williams-Hawkings (FW-H) equation, is implemented in the TDRIP program to compute aerodynamically generated sound. The advantage of this program is its capability to simultaneously compute infrasound emission of multiple wind turbines in time domain, which is a challenging task for other aerodynamic noise prediction methods. The developed program is validated against results obtained from computational fluid dynamics (CFD) simulations. The program is then used to compute aerodynamic noise emitted from wind turbine rotors. The effects of wind direction, wind turbine siting, and phase of wind turbine rotation on consequent aerodynamic noise are investigated. Results of aerodynamic noise computation imply that wind turbine siting configuration or wind turbine phase adjustment can help reducing noise level at certain locations, which make the program ideal to be integrated into wind farm siting or control tools.

Baigiamajame magistro darbe nagrinėjamas dviejų vėjo jėgainių parkų keliamas triukšmas. Analizuojami triukšmo susidarymo ypatumai vėjo jėgainių parkų viduje bei sklaida parko išorėje. Vertinamos infragarso bei žemo dažnio garso dažninės charakteristikos vėjo jėgainių parkų aplinkoje. Darbą sudaro 4 skyriai. Pirmajame skyriuje apžvelgiama garso fizikinė prasmė, triukšmo šaltiniai, problema bei keliamo triukšmo poveikis žmonėms. Antrajame skyriuje aprašomi tyrimo objektai bei eksperimentinė vėjo jėgainių keliamo triukšmo tyrimų metodika. Trečiajame skyriuje pateikiami dviejų vėjo jėgainių parkų keliamo triukšmo tyrimų rezultatai bei analizė. Dviejų vėjo jėgainių parko Anužių kaime bei šešių vėjo jėgainių parko „Liepynė“ Kretingos rajone. Ketvirtajame skyriuje pateikiamas vėjo jėgainių parkų keliamo triukšmo modeliavimo rezultatai taikant „CadnaA“ modeliavimo programą. Taip pat pateikiamos bendros išvados, rekomendacijos, literatūros sąrašas ir publikacijų sąrašas šio darbo tema. Darbo apimtis – 103 p. teksto be priedų, 72 iliustr., 5 lent., 84 bibliografiniai šaltiniai. / In this master analyzing of noise dispersion around two wind farms. Analyzing the noise generation and dissemination characteristics of wind farms within and outside the park. Assessed infrasound and low frequency sound frequency response in the places around of wind farms. The master consists of 4 chapters. The first chapter provides an overview of sound physical meaning, sources of noise, the problem and the noise impact to people. The second section describes the objects of research, experimental wind noise research methodology. The third section presents the research results and analysis of two wind parks. Wind farm of two wind turbines in Anužiai village and wind farm of six wind turbines in „Liepynė“ Kretingos district. The fourth section describes the modeling results of wind park using simulation program „CadnaA“ . Also provides an overall conclusion, recommendations, bibliography and list of publications of this master. The volume of master – 103 pages text without attachments, 72 pictures, 5 tables, 84 references.

Infrasound is undetectable by the human ear and excessive exposure may be a substantial health risk. Low frequency sound propagates through walls with minimal attenuation, making it difficult to avoid. This study interprets the results from both analytical calculations and simulations of pressure waves propagating through a wall in one dimension. The wall is thin compared to the wavelength; the model implements properties of three materials commonly used in walls. The results indicate that the geometry of the wall, most importantly the small ratio between wall width and wavelength, is the prime reason for the low levels of attenuation observed in transmitted amplitudes of low frequency sounds, and that damping is negligible for infrasound. Furthermore, a one-dimensional homogeneous wall model gives rise to periodicity in the transmitted amplitude, which is not observed in experiments. Future studies should prioritize the introduction of at least one more dimension to the model, to allow for variable angles of incidence.

This Master thesis examines a phenomenon that occurs in the upper polar atmosphere, namely, Polar Mesospheric Winter Echoes, or PMWEs. PMWEs are radar echoes observed by Very High Frequency Mesosphere Stratosphere Troposphere (VHF MST) radar, from altitudes of 60 to 76 km at 7 to 15 UT, in the winter months from the middle of September to the beginning of May. The aforementioned specifications are the partial results of this thesis.PMWEs are generally understood to be caused by turbulence; however, radar data indicate some rare cases where PMWEs can be created with velocities exceeding the speed of sound, which is not possible with current turbulence theory. Kirkwood et al., 2006 and Belova, Kirkwood, and Sergienko, 2013 hypothesised that infrasound could generate the necessary conditions for PMWEs with velocities equal to or exceeding the speed of sound. Observations of PMWEs presented in this thesis have been carried out by the MST radar ESRAD, located at Esrange (67 56’N, 21 04’E) near Kiruna in northern Sweden. The radar operates at 52 MHz and has been performing continuous radar observations since Dec 1996. Observations of the infrasounds presented in this thesis were carried out by a microbarometer located close to Rymdcampus in Kiruna. Access to the data is restricted, but through university administration, this master’s thesis has been granted permission to use the data for the study of PMWEs. The instrument performed continuous infrasound measurements from the 24th of May 2016 and forward. This thesis will perform a full analysis of all radar data from the 17th of Dec 1996 until the 31st of Jan 2021 to assess the altitude interval, diurnal interval and yearly interval. The data given in the first section are a result of this work. Additionally, space weather parameters relation with the occurrence of PMWEs is analysed. Space weather parameters are very important for the chemistry and conditions present in the mesosphere. It is shown thatt here is a strong relation between solar wind and PMWE occurrence, decent relation with Kp index and no to weak relation with solar particle event (SPE). Correlating space weather and PMWEs in greater detail could be the subject of other studies. Last but most interesting, microbarometer data will be analysed for days where high-speed PMWEs are detected. Because of the rarity of these high-speed PMWEs, only seven total cases were found from 24 May 2016 onward, making the analysis of the infrasound measurements very limited, and no connection was found. However, it was found that days with high-speed PMWEs had an abnormally low amount of infrasound detections, further making analysis difficult but raising questions of why. This could mean that infrasound signals might be hindered from reaching the ground on days where we have high-speed PMWEs. No further conclusions can be made, as this indicates relation but not causation. Airborne infrasound instruments could be used to detect weaker infrasound signals due to being unaffected by wind disturbance at the ground.