To see the other types of publications on this topic, follow the link: Radiated noise.
Dissertations / Theses on the topic 'Radiated noise'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 45 dissertations / theses for your research on the topic 'Radiated noise.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Chiasson, Leo E. "Radiated noise from a three dimensional truss." Thesis, Monterey, California. Naval Postgraduate School, 1995. http://hdl.handle.net/10945/26192.
Full text
2
Chiasson, Leo E. Jr. "Radiated noise from a three dimensional truss." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36058.
Full textAbstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1995, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995.Includes bibliographical references (leaves 83-84).
by Leo E. Chiasson, Jr.
M.S.
3
Charpentier, Arnaud. "Active Control Of Noise Radiated From Personal Computers." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/35711.
Full textAbstract:
As an indirect consequence of increased heat cooling requirements, personal computers (PC) have become noisier due to the increased use of fans. Hard disk drives also contribute to the annoying noise radiated by personal computers, creating a need for the control of computer noise.
Due to size constraints, the implementation of passive noise control techniques in PC is difficult. Alternatively, active noise control (ANC) may provide a compact solution to the noise problems discussed above, which is the subject of this work.
First, the computer noise sources were characterized. The structure-borne path was altered passively through the decoupling of the vibrating sources from the chassis. Global noise control strategy was then investigated with a hybrid passive/active noise control technique based on folded lined ducts, integrating microphones and speakers, that were added to the PC air inlet and outlet. While the ducts were effective above 1000Hz, the use of a MIMO adaptive feedforward digital controller lead to significant noise reduction at the ducts outlets below 1000Hz. However, global performance was limited due to important airborne flanking paths. Finally, the same type of controller was used to create a zone of quiet around the PC user head location. It was implemented using multimedia speakers and microphones, while the computer was placed in a semi-reverberant environment. A large zone of quiet surrounding the head was created at low frequencies (250Hz), and its size would reduce with increasing frequency (up to 1000Hz).Master of Science
4
Awasthi, Manuj. "Sound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuities." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64158.
Full textAbstract:
Measurements have been performed to understand the sound source mechanism in turbulent boundary layer flow over two and three-dimensional surface discontinuities whose height is smaller than the incoming boundary layer thickness. The work was performed in two different types of boundary layers: a wall-jet flow and a conventional high Reynolds boundary layer. In the wall-jet flow, measurements of far field sound from two-dimensional forward facing steps, gaps with rounded corners and swept forward facing steps with rounded corners were made. The sound from a forward facing step is shown to exhibit effects of non-compactness. Rounding the step corner results in consistent drop in sound levels but the directivity of the sound field remains unchanged. The sound from gaps is dominated by the forward step component and remains unaffected by rounding of the backward step portion. The sound from swept forward facing steps was found to approximately obey an acoustic sweep independence principle up to a sweep angle of 30 deg when the spanwise inhomogeneity in the flow is accounted for using a simple source distribution model. Sweep independence is also observed for steps with corner rounding radii up to 25% of the step height.
The work performed in the high Reynolds number boundary layer included measurements on forward facing steps with rounded corners and a three-dimensional circular embossment with the same height as the forward step. The highest Reynolds number based on discontinuity height achieved in this work was approximately 93,000. The results show that rounding the forward step corner has the same qualitative effect on far field sound as in the wall-jet boundary layer. Quantitatively, for similar boundary layer edge velocity the sound is higher than in the wall-jet flow. The near field measurements show that the separation bubble downstream of the step shrinks as the step corner is rounded while the bubble upstream remains unaffected by it. The unsteady surface force in the lower half of the vertical face of the step was found to be independent of corner rounding. The force on the downstream surface shows similar character within the separation bubble for each rounding but decays faster with increasing downstream distance due to reduced bubble size. The unsteady force measurements were applied to the theory of Glegg et al. (2014) and the resultant of the unsteady forces on the vertical face and downstream surface placed at the top corner of the step is shown to qualitatively describe the far field sound. The acoustic sweep independence principle was applied to the far field sound from the circular embossment and it has been shown that the sound from the three-dimensional geometry can be predicted with reasonable accuracy using sound from a two-dimensional forward step with the same span.Ph. D.
5
Haikonen, Kalle. "Underwater radiated noise from Point Absorbing Wave Energy Converters : Noise Characteristics and Possible Environmental Effects." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-235016.
Full textAbstract:
The conversion of wave energy into electrical energy has the potential to become a clean and sustainable form of renewable energy conversion. However, like all forms of energy conversion it will inevitably have an impact on the marine environment, although not in the form of emissions of hazardous substances (gases, oils or chemicals associated with anticorrosion). Possible environmental issues associated with wave energy conversion include electromagnetic fields, alteration of sedimentation and hydrologic regimes and underwater radiated noise. Underwater noise has the potential to propagate over long distances and thus have the potential to disturb marine organisms far away from the noise source. There is great variation in the ability to perceive sound between marine organisms, one sound that is clearly audible to one species can be completely inaudible to another. Thus, to be able to determine potential environmental impact from WECs associated with underwater noise, the noise radiated from the WECs must be known. This thesis presents results from studies on the underwater radiated noise from four different full-scale WECs in the Lysekil Wave Power Project. Hydrophones were used to measure the underwater radiated noise from operating point absorbing linear WECs. The main purpose was to study the radiated noise from the operating WECs with emphasis on characteristics such as spectrum levels, Sound Pressure Level (SPL), noise duration and repetition rate. This to be able to determine the origin of the noise and if possible, implement design changes to minimize radiated noise. The results identified two main operational noises (transients with the bulk of the energy in frequencies <1 kHz). The SPL of the radiated noise fluctuated significantly, depending on wave height. Broadband SPLrms of the measurements ranged between ~110 dB and ~140 dB re 1 µPa and SPLpeak of specific noises ranges between ~140 and ~180 dB re µPa. Audibility was estimated range from 1km to 15 km depending critically on species and on assumptions of propagation loss. The noise is not expected to have any negative effects on behaviour or mask any signals, unless in the vicinity (<150m) of the WECs in significant wave heights. No physical damage, even in close vicinity are expected on either fish or marine mammals. Having the aim to have as little impact on the environment a possible, these studies are important. This way precautions can be implemented early in the technical development of this kind of renewable energy converters. The benefits from the WECs the Lysekil wave power project are believed to outweigh possible environmental impacts due to underwater radiated noise.Vid avhandlingens tryckläggning upptäcktes inte att tidpunkt för disputation var fel.
6
Burgemeister, Kym A. "Novel methods of transduction for active control of harmonic sound radiated by vibrating surfaces." Title page, contents and abstract only, 1996. http://hdl.handle.net/2440/37932.
Full textAbstract:
Large electric transformers such as those used in high voltage substations radiate an annoying low frequency hum into nearby communities. Attempts have been made to actively control the noise by placing a large number of loudspeakers as control sources around noisy transformers to cancel the hum. These cancellation systems require a large number of loudspeakers to be successful due to the imposing size of the transformer structures. Thus such systems are very expensive if global noise reduction is to be achieved. The aim of this thesis is to investigate theoretically and experimentally the use of thin perforated panels closely placed to a heavy structure to reduce the radiation of unwanted harmonic noise. These panels can themselves be vibrated to form a control source radiating over a large surface surrounding the primary source. The problem of the equipment overheating inside the enclosure is alleviated because the holes in the panels still allow natural cooling. An initial study is carried out to determine the resonance frequencies of perforated panels. The use of previously determined effective elastic properties of the panels and Finite Element Analysis to theoretically calculate their resonance frequencies is examined. Secondly the attenuation provided by active noise control using perforated panels as control sources is explored by use of a coupled analysis, where the primary source is assumed to influence the radiation of the perforated control panel. This analysis was found to predict poorly the amount of attenuation that could be achieved, so an uncoupled analysis is undertaken, where both the primary and control sources are assumed to radiate independently of each other. Not only does this greatly simplify the theoretical analysis but it also enables prediction of attenuation levels which are comparable to those determined experimentally. The theoretical model is reformulated to enable comparison of the sound power attenuation provided by perforated panel control sources with that of traditional acoustic and structural control sources. Finally, the use of modal filtering of traditional acoustic error sensor signals to give transformed mode (or power mode) sensors is examined. The independently radiating acoustic transformed modes of the panel are determined by an eigenanalysis and a theoretical analysis is presented for a farfield acoustic power sensor system to provide a direct measurement of the total radiated acoustic power. The frequency dependence of the sensor system, and the amount of global sound power attenuation that can be achieved is examined. Experimental measurements are made to verify the theoretical model and show that a sound power sensor implemented with acoustic sensors can be used in a practical active noise control system to increase the amount of attenuation that can be achieved. Alternatively the sound power sensor can be used to reduce the number of error channels required by a control system to obtain a given level of attenuation when compared to traditional error criteria. The power mode sensor analysis is then applied to the perforated panel control system, with similar results.Thesis (Ph.D.)--Engineering (Department of Mechanical Engineering), 1996.
7
Shen, Anne Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Optimised reduction of the radiated noise from the casing of a constant speed gearbox." Publisher:University of New South Wales. Mechanical & Manufacturing Engineering, 2008. http://handle.unsw.edu.au/1959.4/43020.
Full textAbstract:
This thesis presents a comprehensive methodology for predicting and minimising the noise radiated from a constant speed gearbox assembly by means of attaching optimally placed stiffening ribs on the casing. The procedure involves building an FE model of the gearbox, which is updated using modal parameters extracted from a modal test. This is followed by synthesis of the required FRFs with respect to the forcing degrees-of-freedom. The forces, which are assumed to act only at the bearings are identified from these FRFs and the measured operational velocities of the casing. The identified forces are then used to excite the updated FE model to re-calculate the vibration velocities. A boundary element method is used to calculate the final radiated sound power to be compared with that measured. The same forces are used later to excite the modified gearbox casing to determine the improvement given by optimised modification. The optimisation study minimises the vibration energy of the casing in 10% bands around critical frequencies, in this case the first two harmonics of the gearmesh frequency. To allow for errors in the model, the excitation is by white noise, so as to produce wide stop bands, rather than minimising the response at particular frequencies. The vibration energy is weighted for radiation efficiency, A-weighting, and relative source strength in the bands. The final optimal stiffener layout is validated through a final vibration and acoustic calculation on the updated gearbox model using the forces identified in the earlier steps. The study of one particular gearbox concludes that i) the proposed hybrid optimisation scheme produces a theoretical effective noise reduction of 3 dBA for the total sound power. ii) Because the gearmesh harmonics were targeted, a further 5 dB improvement was effectively gained by eliminating the tonal penalty which otherwise applied. iii) From plate studies it was demonstrated that the stiffening ribs could be attached using epoxy cement (to avoid welding) and that the properties of the cemented joint could be determined by model updating after attaching one rib, so as to obtain a better prediction of the final optimised result.
8
Risi, John D. "Analytical investigation of active control of radiated inlet noise from turbofan engines." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-08222009-040623/.
Full text
9
Song, Kyungyeol 1972. "Active control of radiated noise from a cylindrical shell using external piezoelectric panels." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29244.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002.Includes bibliographical references (p. 285-290).
Control architectures and methodologies are developed for the reduction of radiated noise from a thick-walled cylindrical shell using external piezoelectric panels. The proposed approach is to cover the shell's outer surface with curved active composite panels, and to reduce the radiated noise by controlling the motion of each panel's outer surface (i.e., the radiating surface), instead of the shell's outer surface. The use of external piezoelectric panels proposed in this thesis has significant advantages over the conventional approach of directly controlling the structure in reducing radiated noise from stiff structures. The reason is that the proposed approach needs much less control authority, and allows the control system to be significantly less dependent on the dynamic characteristics of the structure, than the conventional approach. The control architecture is composed of local controllers, which are implemented for each panel to reduce its vibration level, and a global controller, which makes the shell a weak radiator by coordinating all of the panels simultaneously. For each local control, two different feedback controllers are implemented simultaneously. The first feedback controller takes the acceleration of the outer surface of each panel and uses high gain to minimize its motion. The other feedback loop, which is denoted as the feedforward controller in this thesis, takes acceleration on the inside surface of the panel and aims at canceling the motion of radiating surface. Several controller configurations were designed, implemented and compared, in order to find the one that is the simplest to implement, while achieving the required closed-loop performance and stability margins.
(cont.) After covering the surface of the cylindrical shell with active composite panels, the panel-level tonal controllers were designed and implemented on the shell vibrating in water. The controllers yielded more than 20 dB of attenuation at the target frequency in the acceleration over the radiating surface, although the actual noise level was increased under closed-loop control due to the flaws in the internal accelerometers in the panels. For global control, a new wavenumber domain sensing method has been developed and applied to feedback controller design for active structural acoustic control. The approach is to minimize the total acoustic power radiated from vibrating structures in the wavenumber domain. We found that the method greatly simplifies the design of MIMO LQG controllers for active structural acoustic control, by reducing the effort to model the acoustic radiation from the structure, and by reducing significantly the number of transfer functions that should be identified to get a plant model. The new sensing method was numerically validated on a beam structure and a cylindrical shell with active composite panels mounted.
by Kyungyeol Song.
Ph.D.
10
Laws, Nathan. "A Parabolic Equation Analysis of the Underwater Noise Radiated by Impact Pile Driving." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/1083.
Full textAbstract:
Impact pile driving can produce extremely high underwater sound levels, which are of increasing environmental concern due to their deleterious effects on marine wildlife. Prediction of underwater sound levels is important to the assessment and mitigation of the environmental impacts caused by pile driving. Current prediction methods are limited and do not account for the dynamic pile driving source, inhomogeneities in bathymetry and sediment, or physics-based sound wave propagation.
In this thesis, a computational model is presented that analyzes and predicts the underwater noise radiated by pile driving and is suitable for shallow, inhomogeneous environments and long propagation ranges. The computational model uses dynamic source models from recent developments in the technical literature. Pile source models are coupled to a broadband application of the range-dependent acoustic model (RAMPE), a standard parabolic equation (PE) propagation code capable of modeling wave propagation through complex, range dependent environments. Simulation results are shown to be in good agreement with several observations of pile driving operations in the Columbia River between Portland, Oregon and Vancouver, Washington. The model is further applied to extend sound level predictions over the entire river and study the effects of sediment and bathymetry on the underwater sound levels present in the environment.
11
Kastner, Jeffrey F. "Far-field radiated noise mechanisms in high reynolds number and high-speed jets." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1181753004.
Full text
12
Boone, Andrew Johnson. "Active minimization of acoustic energy density to attenuate radiated noise from a diesel generator /." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1595.pdf.
Full text
13
Boone, Andrew J. "Active Minimization of Acoustic Energy Density to Attenuate Radiated Noise from a Diesel Generator." BYU ScholarsArchive, 2006. https://scholarsarchive.byu.edu/etd/1037.
Full textAbstract:
The focus of this thesis was to use active noise control (ANC) to globally minimize the tonal and broadband noise radiating from a diesel generator enclosure. The major goal of this research was to show that minimizing the noise within the enclosure can lead to an overall sound pressure level (SPL) reduction of radiated noise. The target levels for overall SPL reduction were at least 2 dBA. The control algorithms used in this research were based on a filtered-x LMS adaptive algorithm, which minimizes energy density (ED). Both feedforward and feedback control approaches were investigated. The noise spectrum produced by the diesel generator enclosure includes tonal and broadband components. The target range for control was from 0 to 300 Hz. Tonal frequencies at exterior locations were often reduced by 20 to 30 dB using feedforward control. With feedback control, tones were reduced 5 to 10 dB. Broadband control results were obtained at an exterior location using a feedforward control configuration. This control was achieved for frequencies between 100 and 600 Hz and levels were reduced by up to 5 dB. Some broadband control was achieved using feedback control, but this was limited to regions at the error sensor. An overall SPL reduction of 1.9 dBA outside the enclosure was achieved near the power terminal side of the enclosure. This was accomplished using tonal and broadband feedforward control. Experimental results show that control source placement, as well as error and reference sensor location, is key to global noise reduction.
14
Jaouani, Nassim. "Modelling of installation effects on the tonal noise radiated by counter-rotating open rotors." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC002.
Full textAbstract:
The Counter-Rotating Open Rotors (CROR) are identified as a possible alternative to turbofan engines for middle-range aircrafts. Providing significant fuel savings and reducing the green-house gas emissions, they may lead however to an increased noise radiation due to the absence of nacelle shielding. To properly predict the acoustic radiation of such systems is then mandatory both to reduce the source mechanisms of the isolated engine and to offer an optimal noise installation solution. Such an objective is tackled in the present thesis in two steps. In a first part, the research aims at predicting the tonal noise radiated from the first propeller of CROR mounted on the rear fuselage by means of a pylon (pusher configuration), considering both the pylon-wake and the uniform ow effects. From the Ffowcs Williams & Hawkings' formalism, three noise sources are identified. First the unsteady loading is computed using a similar procedure to the one used for the rotor-rotor wake interaction noise prediction. The velocity deficit in the pylon wake is locally expanded in two-dimensional Fourier gusts in a reference frame attached to the front rotor. The unsteady lift induced by each gust on a blade segment is calculated using a linearized analytical response function that accounts for a realistic geometry. The steady loading is the second source contribution and is evaluated using both a software based on the lifting-line theory and some numerical simulations for different reference source surfaces. Finally the thickness noise due to the blade volume displacement is included in the analysis using Isom's formulation. From the linear acoustic assumptions, all these sources modelled as equivalent acoustic dipoles rotating in a uniformly moving atmosphere are then summed to calculate the far-field noise. The whole methodology is assessed against wind-tunnel test data and reference software predictions. A parametric study considering several pylon positionings and pylon-wake configurations with blowing is performed in order to emphasize the relative contribution of the three noise sources. Secondly, the rotor- rotor wake interaction noise being recognized as the most significant contribution in isolated configuration, its modelling is completed by introducing the dynamics of the vortex occurring near the rear-rotor leading edge. A semi-analytical methodology is developed to determine a vortex attached over a at plate embedded in a uniform ow with incidence. Applied to the case of a rear blade going through a front-rotor wake, it provides a first estimate of the noise contribution of the vortexLes hélices contrarotatives constituent une alternative possible aux turboréacteurs pour les avions moyens- courriers. Réduisant significativement la consommation de carburant et les émissions de gaz à effet de serre, ils peuvent néanmoins conduire à un rayonnement sonore accru de par l'absence de carénage. Prédire correctement le rayonnement sonore de telles motorisations est donc indispensable pour réduire les mécanismes sources propres au moteur isolé ou assurer une solution d'installation acoustique optimale. Un tel objectif est abordé dans cette thèse en deux temps. Dans un premier temps, l’étude vise à prédire le bruit tonal rayonné par la première hélice d'un moteur monté à l'arrière du fuselage (configuration dite en pousseur), en considérant les effets du sillage du pylône supportant le moteur et de l'écoulement moyen. Partant du formalisme de Ffowcs Williams & Hawkings, trois sources sonores sont identifiées à cet effet. La charge instationnaire, tout d'abord, est calculée en s'appuyant sur une méthodologie similaire à celle utilisée pour la prédiction du bruit d'interaction de sillages entre les deux rotors. Le déficit de vitesse dans le sillage du mât est décomposé localement en rafales bidimensionnelles dans un repère attaché au rotor amont. La portance instationnaire induite par chaque rafale sur un segment de pale est calculée en utilisant une fonction de réponse analytique linéarisée considérant une géométrie réaliste. Deuxième contribution, la charge stationnaire est évaluée au moyen d'un logiciel s'appuyant sur la théorie de la ligne portante mais également via des simulations numériques pour différentes surfaces sources de référence. Enfin, le bruit d'épaisseur associé au déplacement du volume de la pale est inclus dans l'analyse à partir de la formulation d'Isom. D'après les hypothèses de l'acoustique linéaire, toutes ces sources modélisées comme des dipôles acoustiques tournant dans une atmosphère uniforme en mouvement sont ensuite sommées pour calculer le bruit en champ lointain. L'ensemble de la méthodologie est comparé à des données d'essai et des prédictions d'un logiciel de référence. Une étude paramétrique considérant plusieurs positionnements du pylône et des configurations avec soufflage est effectuée afin de bien mettre en évidence les contributions relatives des trois sources sonores. Dans un deuxième temps, le bruit d'interaction de sillages étant reconnu comme la contribution majoritaire en configuration isolée, sa modélisation est complétée en introduisant la dynamique du tourbillon se développant au voisinage du bord d'attaque du rotor aval. Une méthodologie semi-analytique est développée pour déterminer un tourbillon attaché au-dessus d'une plaque plane plongée dans un écoulement uniforme avec incidence. Appliquée au cas d'une pale aval traversant le sillage du rotor amont, elle fournit une première estimation de la contribution sonore du tourbillon
15
Ross, Bradley W. "Attenuation of Low Frequency Structurally Radiated Noise With an Array of Weak Radiating Cells." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36555.
Full textAbstract:
The concept of a weak sound radiating cell is proposed to reduce the low frequency radiated noise from structures. The cell consists of two coupled surfaces such that, when placed on a vibrating structure, the responses of the two surfaces are nearly out-of-phase and of equal strength over a wide frequency range. This structure response leads the cell to behave as an acoustic dipole and thus as a poor sound radiating source. The control of low frequency structurally radiated noise is then achieved by covering the structure with an array of these weak radiating cells, i.e. surface treatment. Thus, the surface treatment essentially transforms the response of the structure to that of a distributed array of dipoles yielding a low sound radiating structure. Theoretical models are developed to predict the performance of the cell. Experimental verification is performed for a single cell applied to a piston-like structure to demonstrate the concept on a simple radiating structure. The results demonstrated an overall sound power level reduction of 5.2 dB between 400-1600 Hz with maximum reductions over 30 dB at discrete frequencies. Finally, an array of weak radiating cells is experimentally applied to a more complex structure, a rectangular plate. The results of the plate experiments reveal an overall sound power level reduction of 10.2 dB between 100-1600 Hz with maximum reductions of 25 dB at discrete frequencies. These results demonstrate the potential of the weak radiating cell concept to reduce low frequency structurally radiated noise.Master of Science
16
Lidtke, Artur K. "Predicting radiated noise of marine propellers using acoustic analogies and hybrid Eulerian-Lagrangian cavitation models." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/413579/.
Full textAbstract:
Anthropogenic noise from a variety of merchant ships has been reported to be a major factor adversely aecting marine organisms. Consequently, scientists and regulators have become more vocal about encouraging, and possibly enforcing, quieter ships in the future. For this to be feasible from an engineering standpoint, a range of numerical methods must be made available to allow acoustic performance of vessels to be evaluated at the design stage. Cavitation is a major contributor to the hydroacoustic signature of a merchant vessel. The reason for this is the relatively high drop of pressure induced by the propeller, which in turn promotes the growth of vapour bubbles and cavities, oscillation and collapse of which act as strong acoustic sources. The entire process is made more dynamic by the non-uniform wake of the ship, propeller rotation, as well as the fact that vessels travel in a seaway. Because of its complexity, the problem of marine propeller noise is thus not widely studied numerically, which translates to the lack of tools readily available to designers willing to reduce the noise generated by ships. A set of numerical utilities are proposed which could be employed at the late design stage of a merchant ship in order to allow the designer to estimate the radiated noise and make informed decisions on how to improve the design. The methodology involves solving the turbulent flow over the propeller using Detached Eddy Simulation (DES) and modelling cavitation using a mass-transfer model. The porous Ffowcs Williams-Hawkings acoustic analogy is used to infer far-eld radiated noise caused by the blade rotation, pulsating cavitation, as well as non-linear noise sources in the propeller slip-stream. The cavitation model is also extended to incorporate Lagrangian bubbles dispersed downstream of the large cavities modelled using the baseline Schnerr-Sauer model via the volume fraction equation approach. This allows the broadband nature of cavitation noise to be captured. The methods are applied to a NACA 66 and the Delft Twist 11 hydrofoil test cases. Although there are limited validation data allowing all of the methods to be validated simultaneously, relatively good agreement is seen at intermediate validation stages. These include comparing the non-cavitating noise of the Insean E779a propeller to reference data, conducting acoustic predictions for idealised acoustic sources, as well as comparing cavitation patterns, cavity cloud shedding frequencies, and induced pressures to experimental data for hydrofoils and propellers. It is concluded that the presented methodology may be used to predict low-frequency noise due to cavitation in a relatively robust manner, although the method is yet to be tested and validated on more complex geometries. The hybrid Eulerian-Lagrangian model is still at an early stage and a range of areas for improvement have been identified, such as implementation of more realistic cavity break-up models as well as better coupling between the fluid and bubble solvers. Nonetheless, the method is demonstrated to be a promising tool at tackling the broadband cavitation noise components as it can capture the contribution of the mass of small, oscillating bubbles on the radiated pressure which would otherwise be unaccounted for in the baseline Eulerian framework.
17
Duncan, Alexander John. "The measurement of underwater acoustic noise radiated by a vessel using the vessel's own towed array." Curtin University of Technology, Department of Applied Physics, 2003. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=16340.
Full textAbstract:
The work described in this thesis tested the feasibility of using a towed array of hydrophones to: 1. localise sources of underwater acoustic noise radiated by the towvessel, 2. determine the absolute amplitudes of these sources, and 3. determine the resulting far-field acoustic signature of the tow-vessel. The concept was for the towvessel to carry out a U-turn manoeuvre so as to bring the acoustic section of the array into a location suitable for beamforming along the length of the tow-vessel. All three of the above were shown to be feasible using both simulated and field data, although no independent field measurements were available to fully evaluate the accuracy of the far-field acoustic signature determinations. A computer program was written to simulate the acoustic signals received by moving hydrophones. This program had the ability to model a variety of acoustic sources and to deal with realistic acoustic propagation conditions, including shallow water propagation with significant bottom interactions. The latter was accomplished using both ray and wave methods and it was found that, for simple fluid half-space seabeds, a modified ray method gave results that were virtually identical to those obtained with a full wave method, even at very low frequencies, and with a substantial saving in execution time. A field experiment was carried out during which a tug towing a 60-hydrophone array carried out a series of U-turn manoeuvres. The signals received by the array included noise radiated by the tow-vessel, signals from acoustic tracking beacons mounted on the tow-vessel, and transient signals generated by imploding sources deployed from a second vessel.Algorithms were developed to obtain snapshots of the vertical plane and horizontal plane shapes of the array from the transient data and to use range data derived from the tracking beacon signals to track the hydrophones in the horizontal plane. The latter was complicated by a high proportion of dropouts and outliers in the range data caused by the directionality of the hydrophones at the high frequencies emitted by the beacons. Despite this, excellent tracking performance was obtained. Matched field inversion was used to determine the vertical plane array shapes at times when no transient signals were available, and to provide information about the geoacoustic properties of the seabed. There was very good agreement between the inversion results and array shapes determined using transient signals. During trial manoeuvres the array was moving rapidly relative to the vessel and changing shape. A number of different array-processing algorithms were developed to provide source localisation and amplitude estimates in this situation: a timedomain beamformer; two frequency-domain, data independent beamformers; an adaptive frequency-domain beamformer; and an array processor based on a regularised least-squares inversion. The relative performance of each of these algorithms was assessed using simulated and field data. Data from three different manoeuvres were processed and in each case a calibrated source was localised to within 1 m of its known position at the source's fundamental frequency of 112 Hz.
Localisation was also successful in most instances at 336 Hz, 560 Hz and 784 Hz, although with somewhat reduced accuracy due to lower signal to noise ratios. Localisation results for vessel noise sources were also consistent with the positions of the corresponding items of machinery. The estimated levels of the calibrated source obtained during the three manoeuvres were all within 4.1 dB of the calibrated value, and varied by only 1.3 dB between manoeuvres. Results at the higher frequencies had larger errors, with a maximum variation of 3.8 dB between serials, and a maximum deviation from the calibrated value of 6.8 dB. An algorithm was also developed to predict the far-field signature of the tow-vessel from the measured data and results were produced. This algorithm performed well with simulated data but no independent measurements were available to compare with the field results.
18
GEORGE, JOHN K. "ANALYTICAL, NUMERICAL AND EXPERIMENTAL CALCULATION OF SOUND TRANSMISSION LOSS CHARACTERISTICS OF SINGLE WALLED MUFFLER SHELLS." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1181226367.
Full text
19
Kunovský, Martin. "Snižování hluku počítačů obkládáním stěn zvukoizolačními materiály a regulací otáček ventilátorů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229655.
Full textAbstract:
This thesis deals with the distribution of noise in the computer case and radiation into the neighborhood. Influence of geometrical shape and size of the computer case on radiated noise from the computer was investigated as well as effect of placement of the fan. Reducing noise by using sound absorbing material into computer case and result of the suitable position of the computer in the working environment were also tested. Simulation of the noise diffusion and effectivity of anti-noise equipment was executed in Ansys FEM program.
20
Ghangale, Dhananjay. "An efficient methodology based on two-and-a-half-dimensional finite element and boundary element methods for ground-borne vibration radiated by underground railway tunnels and the re-radiated noise emitted inside them." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667304.
Full textAbstract:
This thesis presents a methodology for assessing induced ground-borne vibration due to Underground railway infrastructures in the context of an urban environment. The methodology is based on a comprehensive numerical approach for modelling track/tunnel/soil systems considering a full-space model of the ground. This approach is formulated in the wavenumber-frequency domain and it is based on coupled finite element-boundary element method. An axisymmetric formulation to deal with circular underground railway tunnels is included in the approach in order to improve the computational speed of the methodology. This formulation can also be used for other types of railway tunnels if a circular boundary of the boundary element mesh is considered. The developed approach also includes asymptotic solutions of the Green's functions for large wavenumbers which results in an improvement of the accuracy of the overall methodology. A hybrid methodology which uses semi-analytical solutions of a cavity in a full-space in conjunction with the previously described approach has been developed with the aim of computing the energy flow radiated upwards by underground railway tunnels. Since this methodology uses finite elements to model the tunnel structure, its modelling detail is higher than the previously developed methodologies based on semi-analytical modelling of the tunnel structure. This hybrid methodology has been specifically designed for the study the vibration radiation of railway tunnels, the comparison between them and for the study of the insertion loss of mitigation measures at the sources, as soft rail-pads, under-ballast or under-slab mats, dynamics vibration absorbers, etc. In this thesis, this hybrid methodology is used to perform a comparison of the energy flow radiated upwards by various types of underground railway tunnels. Finally, a modelling approach for the re-radiated noise induced by a train passage inside railway tunnels is presented. This approach is based on the weak coupling between the comprehensive numerical approach for modelling track/tunnel/soil previously described and a two-and-a-half-dimensional boundary element method model for interior acoustics. Using this modelling approach, the influence of the fastener stiffness on the noise and vibration levels inside a simple tunnel as well as the relation between the noise emitted by the rails or the tunnel structure is investigated and discussed.Esta tesis presenta una metodología para evaluar la vibración inducida a través del terreno debido a infraestructuras ferroviarias soterradas en el contexto de un entorno urbano. La metodología se basa en un enfoque numérico integral para modelar sistemas de vía/túnel/terreno considerando un modelo de espacio completo del terreno. Este enfoque está formulado en el dominio de la frecuencia del número de onda y se basa en el método de los elementos finitos y el método de los elementos de contorno acoplados. Para mejorar la velocidad de cálculo de la metodología, se incluye una formulación axisimétrica para tratar túneles ferroviarios circulares. Esta formulación también se puede utilizar para otros tipos de túneles ferroviarios si se considera un contorno circular para la malla de elementos finitos. El enfoque desarrollado también incluye soluciones asimptóticas de las funciones de Green para grandes números de onda que resultan en una mejora de la exactitud de la metodología general. Se ha desarrollado una metodología híbrida que utiliza soluciones semi-analíticas de una cavidad en un espacio completo junto con el enfoque descrito anteriormente con el objetivo de calcular el flujo de energía de vibración radiado hacia arriba por túneles ferroviarias. Dado que esta metodología utiliza elementos finitos para modelar la estructura del túnel, su detalle de modelado es más alto que las metodologías desarrolladas anteriormente basadas en el modelado semi-analítico de la estructura del túnel. Esta metodología híbrida ha sido diseñada específicamente para el estudio de la radiación de vibración de túneles ferroviarios, la comparación entre ellos y para el estudio de la pérdida de inserción de medidas de mitigación, como suelas de baja rigidez, mantas bajo balasto o bajo losa, absorbentes de vibraciones dinámicos, etc. En esta tesis, esta metodología híbrida se utiliza para realizar una comparación del flujo de energía irradiado hacia arriba por varios tipos de túneles de ferrocarril subterráneo. Finalmente, se presenta un enfoque de modelado para el ruido re-irradiado inducido por un paso de tren dentro de los túneles ferroviarios. Este enfoque se basa en un acoplamiento débil entre el enfoque numérico integral para modelar el sistem vía/túnel/terreno descrito anteriormente y un modelo basado en método de los elementos de contorno 2.5D para la acústica interior del túnel. Usando este enfoque de modelado, se investiga y se discute la influencia de la rigidez de las fijaciones de carril en los niveles de ruido y vibración dentro de un túnel simple, así como la relación entre el ruido emitido por los carriles y la estructura del túnel.
21
Astfalck, Allen Electrical Engineering Australian Defence Force Academy UNSW. "Analysis of electromagnetic force and noise in inverter driven induction motors." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Electrical Engineering, 2002. http://handle.unsw.edu.au/1959.4/38671.
Full textAbstract:
This thesis is part of a major research project to analyse vibro-acoustic characteristics from variable speed inverter driven induction motors (VSIDIM). The overall projects??? aimed at providing a better understanding of the mechanisms of sound generation from electromagnetic origins and developing a numerical model to predict the sound power emitted from a VSIDIM. The scope of this thesis is to assess experimentally the effect of various controller strategies on the radiated sound power and to develop a finite element method for calculating the electromagnetic force distribution over the stator. Various sources of noise in induction motors and their behaviour with speed and load have been reviewed. Models of the electromagnetic field and vibro-acoustic character have been discussed. An outline of various techniques of reducing noise in induction motors through design of inverters and modifications to the motor structure has been given. Experiments were conducted to assess the effect of controller strategies on the radiated sound power. Three different supplies were tested: a dynamotor which produces an almost sinusoidal supply with very low harmonic content, an inverter with a low switching frequency (less than 1kHz) and an inverter with a high switching frequency (8kHz) and various levels of random modulation. Results indicate that the sound power level of the MSC drive is a lot higher than that of the VSC 2000 drive and the dynamotor drive. The sound power level of the VSC 2000 drive and the dynamotor drive increases almost linearly with motor speed, that for the MSC drive is almost independent of speed. The sound power level of the MSC drive is almost 28dB higher than that of the dynamotor drive at 450rpm and the difference is reduced to 14dB at 1500rpm where the aerodynamic noise becomes more dominant. It has been found that at the rated speed (1500rpm), the sound power level varies by less than 3dB from no load to full load for all three sources. Although increasing the switching frequency increases the cost of the inverters and switching losses, results from the MSC and VSC 2000 drives clearly show that it reduces the radiated sound power by shifting the harmonics into higher and inaudible frequency range. The tonal nature around the switching frequency has been reduced by increasing the levels of random modulation to spread the energy over a wider range of frequencies, although the sound power level has not varied by more than 0.2dB. A finite element model has been developed to calculate the electromagnetic force distribution. The quasi-static solution method has been implemented by stepping the rotor through the time domain using a fine regular mesh in the air gap. The stator currents were experimentally obtained while the rotor currents were obtained using a 4 parameter state space model of the motor. Results of the simulation indicate the influence of stator and rotor slots, saturation and time harmonics in the current. The calculated electromagnetic force distribution has been used in a FEM/BEM acoustic model and SEA acoustic model to predict the radiated sound power which agrees reasonably well with the measured sound, thus validating indirectly the electromagnetic force simulations.
22
Yagci, Tayfun. "Target Classification And Recognition Using Underwater Acoustic Signals." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/3/12606373/index.pdf.
Full textAbstract:
Nowadays, fulfillment of the tactical operations in secrecy has great importance for especially subsurface and surface warfare platforms as a result of improvements in weapon technologies. Spreading out of the tactical operations to the larger areas has made discrimination of targets unavoidable. Due to enlargement of the weapon ranges and increasing subtle hostile threats as a result of improving technology, &ldquovisual&rdquo
target detection methods left the stage to the computerized acoustic signature detection and evaluation methods. Despite this, the research projects have not sufficiently addressed in the field of acoustic signature evaluation. This thesis work mainly investigates classification and recognition techniques with TRN / LOFAR signals, which are emitted from surface and subsurface platforms and proposes possible adaptations of existing methods that may give better results if they are used with these signals. Also a detailed comparison has been made about the experimental results with underwater acoustic signals.
23
Guezgouz, Djamel. "Contribution à la modélisation du réseau électrique domestique en vue de la caractérisation du canal de propagation CPL." Phd thesis, Université François Rabelais - Tours, 2010. http://tel.archives-ouvertes.fr/tel-00922801.
Full textAbstract:
Le réseau électrique s'utilise aujourd'hui comme support de transmission des signaux Ethernet. C'est le concept des courants porteurs en ligne. Cette technique de transmission permet d'obtenir des débits supérieurs au Wifi. Cependant, la complexité des réseaux électriques et l'environnement électromagnétique domestique peuvent dégrader les performances de cette technologie. L'environnement électrique de l'habitat avec ses appareils électroménagers divers en font un milieu difficilement maitrisable. L'objectif est d'appréhender et de modéliser cet environnement et le comportement des équipements qui y sont déployés. Pour cela, ce mémoire présente plusieurs méthodes pour modéliser les lignes électriques dans l'habitat. Les modélisations existantes sont difficilement généralisables à un réseau électrique quelconque. Nous proposons une modélisation de type circuit électrique. Son intérêt réside dans la simplicité de l'outil de simulation d'un réseau électrique, réalisé par la mise en cascade de plusieurs blocs intégrés à la librairie SPICE. Les blocs SPICE proposés prennent en compte la dépendance fréquentielle des paramètres des quadripôles. Une étape de caractérisation expérimentale est développée pour implémenter ces blocs. Un réseau expérimental de test, constitué de différentes technologies de câble, a été caractérisé en termes de bruit, d'impédance et de pertes d'insertion. Le rayonnement émis lors d'une transmission CPL a aussi été mesuré.
24
Anderson, Monty J. "Active Control of the Human Voice from a Sphere." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5295.
Full textAbstract:
This work investigates the application of active noise control (ANC) to speech. ANC has had success reducing tonal noise. In this work, that success was extended to noise that is not completely tonal but has some tonal elements such as speech. Limitations such as causality were established on the active control of human speech. An optimal configuration for control actuators was developed for a sphere using a genetic algorithm. The optimal error sensor location was found from exploring the nulls associated with the magnitude of the radiated pressure with reference to the primary pressure field. Both numerically predicted and experimentally validated results for the attenuation of single frequency tones were shown. The differences between the numerically predicted results for attenuation with a sphere present in the pressure field and monopoles in the free-field are also discussed.The attenuation from ANC of both monotone and natural speech is shown and a discussion about the effect of causality on the results is given. The sentence “Joe took father’s shoe bench out” was used for both monotone and natural speech. Over this entire monotone speech sentence, the average attenuation was 8.6 dB with a peak attenuation of 10.6 dB for the syllable “Joe”. Natural speech attenuation was 1.1 dB for the sentence average with a peak attenuation on the syllable “bench” of 2.4 dB. In addition to the lower attenuation values for natural speech, the pressure level for the word “took” was increased by 2.3 dB. Also, the harmonic at 420 Hz in the word “father’s” of monotone speech was reduced globally up to 20 dB. Based on the results of the attenuation of monotone and natural speech, it was concluded that a reasonable amount of attenuation could be achieved on natural speech if its correlation could approach that of monotone speech.
25
Turcotte, Audrey. "Analyse intra-annuelle des fluctuations radiales des tiges et des racines adventives de l'épinette noire (Picea mariana (Mill. B.S.P.) /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2007. http://theses.uqac.ca.
Full textAbstract:
Thèse (M.Ress.Renouv.) -- Université du Québec à Chicoutimi, 2007.La p. de t. porte en outre: Mémoire présenté à l'Université du Québec à Chicoutimi comme exigence partielle de la maîtrise en ressources renouvelables. CaQCU Bibliogr.: f. [77]-82. Document électronique également accessible en format PDF.
26
Sulis, Sophia. "Méthodes statistiques utilisant des simulations hydrodynamiques d'atmosphères stellaires pour détecter des exoplanètes en vitesse radiale." Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4073/document.
Full textAbstract:
Considérant une série temporelle affectée par un bruit coloré dont les propriétés statistiques sont inconnues, la difficulté pour la détection de signaux périodiques est de contrôler le degré de confiance avec lequel les tests de détection rejettent l'hypothèse nulle en faveur de l'hypothèse alternative. L'objectif de cette thèse est de développer une nouvelle méthode utilisant des séries temporelles simulées du bruit pour améliorer ce contrôle. Dans le cas d'un échantillonnage régulier, nous avons analysé les performances de différents tests de détection appliqués à un périodogramme standardisé par le spectre simulé du bruit. La standardisation proposée entraîne, dans la majorité des cas, des tests de détection puissants dont les taux de fausses alarmes sont constants. Grâce au développement des distributions asymptotiques de ce périodogramme, nous avons déterminé des expressions analytiques pour les probabilités de fausses alarmes (PFA) et de détections de différents tests. Dans le cas d'un échantillonnage irrégulier, nous montrons qu'il est possible de combiner la standardisation proposée du périodogramme avec des techniques de bootstrap pour contrôler la PFA de manière fiable. La procédure peut être optimisée en utilisant les valeurs extrêmes généralisées. Cette étude a été appliquée au cas de la détection de planètes extrasolaires par la méthode des vitesses radiales dont l'une des principales barrières pour détecter des planètes de masse terrestre vient de l'activité de l'étoile hôte, notamment la convection de surface. Le travail effectué dans cette thèse a porté sur la contribution de simulations hydrodynamiques du bruit convectif dans le processus de détectionConsidering a time series affected by a colored noise of unknown statistics, a difficulty for periodic signal detection is to control the true significance level at which the detection tests are conducted. The objective of this thesis is to develop a new method using training datasets of the noise to improve this control. For the case of regularly sampled observations, we analyze the performances of various detectors applied to periodograms standardized using the noise training datasets. The proposed standardization leads, in some cases, to powerful constant false alarm rate tests. Thanks to the development of the asymptotical distribution of the standardized periodogram, we derive analytical expressions for the false alarm and detection rates of several tests. In the case of irregular sampling, we show that it is possible to combine the proposed periodogram standardization and bootstrap techniques to consistently estimate the false alarm rate. We also show that the procedure can be improved by using generalized extreme value distributions. This study has been applied to the case of extrasolar planet detection in radial velocity (RV) data. The main barrier to detect Earth-mass planets comes from the host star activity, as the convection at the stellar surface. This work investigates the possibility of using hydrodynamic simulations of the stellar convection in the detection process to control exoplanet detection claims
27
Vansteenkiste, Nathalie. "Réalisation d'un laser LNA monomode et asservi sur la transition 23S1-23P de l'hélium 4 (1083nm): utilisation pour quelques expériences de refroidissement radiatif d'atomes d'hélium 4 métastable." Phd thesis, Université Paris Sud - Paris XI, 1989. http://tel.archives-ouvertes.fr/tel-00011867.
Full textAbstract:
Ce mémoire présente quelques expériences de refroidissement radiatif transverse d'un jet d'hélium 4 métastable sur la transition 23S → 2 3P . Une première partie est consacrée à la description du laser à solide (LNA), en anneau, monomode et asservi sur la raie atomique à 1.083 micron de l'hélium, qui a été construit pour ces expériences. La seconde partie décrit quelques expériences de refroidissement radiatif transverse d'un jet d'hélium métastable qui ont été réalisées avec ce laser ; on y présente en particulier une expérience utilisant un piégeage cohérent de population ("résonance noire") sélectif en vitesse, qui a permis d'atteindre une température à une dimension de 2 microKelvins, inférieure à l'énergie de recul d'un seul photon.
28
Vansteenkiste, Nathalie. "Réalisation d'un laser LNA monomode et asservi sur la transition 2³S₁→ 2³P de l'hélium 4 (1083 nm) : utilisation pour quelques expériences de refroidissemnt radiatif d'atomes d'helium 4 métastable." Paris 11, 1989. http://www.theses.fr/1989PA112336.
Full textAbstract:
Ce mémoire présente quelques expériences de refroidissement radiatif transverse d'un jet d'hélium 4 métastable sur la transition 23 S 2 3P. Une première partie est consacrée à la description du laser à solide (LNA), en anneau, monomode et asservi sur la raie atomique à 1. 083 micron de l'hélium, qui a été construit pour ces expériences. La seconde partie décrit quelques expériences de refroidissement radiatif transverse d'un jet d'hélium métastable qui ont été réalisées avec ce laser ; on y présente en particulier une expérience utilisant un piégeage cohérent de population ("résonance noire") sélectif en vitesse, qui a. Permis d'atteindre une température à une dimension de 2 microKelvins, inférieure à l'énergie de recul d'un seul photon.
29
Wang, Lily. "La croissance radiale de l'épinette noire comme indicateur de changements climatiques à la limite des arbres au nord du Québec, Tree-ring growth of black spruce at arctic treeline in northern Québec : implication for climate change." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0022/NQ52266.pdf.
Full text
30
Assice, Antoine. "Detection en ondes millimetriques de defauts dielectriques ou semi-conducteurs dans un materiau a pertes." Toulouse 3, 1987. http://www.theses.fr/1987TOU30182.
Full textAbstract:
Utilisation de la radiometrie en ondes millimetriques dans la recherche de discontinuites dielectriques dans les materiaux composites. Simulation en ondes millimetriques des variations de puissance qui existent entre la zone homogene et la zone contenant le defaut
31
Pasquet, Guillaume. "Conception, réalisation et mise en oeuvre d'un microsystème pour la micro spectroscopie par résonance magnétique nucléaire." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00611547.
Full textAbstract:
Ce travail de thèse porte sur la conception, la réalisation et l'évaluation expérimentale d' un microsystème d'analyse dont l'originalité repose sur l'intégration d'une micro antenne planaire de spectroscopie par résonance magnétique nucléaire (SRMN) sur un système micro fluidique à base d'un polymère, le Cyclique Oléfine Copolymère (COC). La détermination des caractéristiques géométriques optimales du microsystème afin d'optimiser le couplage électromagnétique entre la micro antenne de détection et l'échantillon est effectuée à l'aide d'un modèle de calcul numérique, ce qui permet l'optimisation du rapport signal sur bruit (RSB). La réalisation du microsystème avec des procédés de micro fabrication développés au laboratoire ont permis de valides son fonctionnement dans un spectromètre dont le champ magnétique statique atteint 11.74 Tesla (fréquence de Larmor du proton égale à 500MHz). Travailler dans un champ aussi intense permet d'améliorer la sensibilité de détection mais nécessite de porter une attention particulière à l'homogénéité du champ magnétique qui, dans notre cas, peut être dégradée en raison de l'introduction du microsystème dans le spectromètre. En effet, les distorsions du champ magnétique, dues aux différentes susceptibilités magnétiques des matériaux constituant la microsonde, ont un impact direct sur la résolution spectrale. C'est pourquoi, une modélisation 3D par éléments finis est proposée afin de prévoir l'influence du microsystème sur la forme des raies spectrales et donc d'en déduire la résolution spectrale pouvant être espérée. La comparaison des résultats expérimentaux et ceux issus des simulations permet de valider le modèle de calcul numérique. Il apparait cependant nécessaire d'inclure le phénomène d'amortissement radiatif afin de pouvoir rendre compte des résultats expérimentaux relatifs à la résolution spectrale effectivement observée.
32
La, Delfa Patricio. "Contribution à la conception silencieuse par démarches directe et inverse de machines synchrones à aimants permanents et bobinage dentaire." Thesis, Ecole centrale de Lille, 2017. http://www.theses.fr/2017ECLI0036/document.
Full textAbstract:
Cette thèse porte sur la conception silencieuse par démarches inverses de machines synchrones à aimants permanents dotées de bobinages dentaires. Notre travail se focalise sur l’analyse des raies de forces radiales à l’origine du bruit magnétique. En premier lieu, un modèle direct électromagnétique, nous a permis de déterminer le spectre spatio-temporel de la force radiale dans l’entrefer. Ce dernier nous offre la possibilité d’obtenir pas à pas et de manière analytique l’induction radiale dans l’entrefer, résultat du produit de la force magnétomotrice totale et de la perméance d’entrefer globale. Plusieurs machines dotées d’un bobinage dentaire et distribué ont été évaluées, comparées à des simulations par éléments finis et corroborés par une analyse modale opérationnelle sur un prototype existant au laboratoire. Puis la démarche inverse de conception est abordée par le biais de deux outils « analytiques prédictifs » donnant les origines des ordres faibles spatio-temporels de la force radiale dans l’entrefer. Enfin, la résolution du problème inverse est conduite au moyen d’une boucle itérative d’optimisation donnant parmi un échantillon de solutions, une fonction de bobinage, visant à atténuer ou supprimer une raie potentiellement risquée en termes de nuisances acoustiquesThis thesis deals the quiet design by inverses approaches of synchronous machines with permanent magnets concentrated windings. Our work focuses on the analysis of magnetic noise origin of air gap radial force orders. Firstly a direct electromagnetic model allowed us to determine the spatio-temporal spectrum of air gap radial pressure. The latter offers us the possibility of obtaining step by step and in an analytical way the radial induction in the gap, result of the product of the total magnetomotive force and global air gap permeance. Several machines equipped with a concentrated winding and distributed were evaluated, compared to simulations by finite elements and corroborated by an operational deflection shape on an existing prototype in the laboratory. In the second time two inverse approaches named predictive methodology identified the radial pressure low order origin. Finally, the resolution of the inverse problem is carried out by means of an iterative optimization loop giving among a sample of solutions, a winding function, aimed at attenuating or eliminating a potential risky line in terms of acoustic nuisances
33
Výravská, Zdeňka. "Vliv stavební konstrukce na tepelnou zátěž prostoru." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226871.
Full textAbstract:
This master’s thesis focuses on effect of outer building construction on thermal load of space. The effect of translucent and non-translucent construction is discussed. The project of air-conditioning system is prepared for the two alternatives of the translucent construction, including the purchase price of the airconditioning system and glazing and the savings on summer cooling. Afterwards the period of the recovery of investment is calculated. The plan of the airconditioning system is connected to my bachelor’s thesis “Airconditioning in the car showroom”, the subject of which was the plan of the airconditioning system of the car showroom.
34
Wei, David, and 魏宏源. "Ship Hull Vibration And Its Underwater Radiated Noise." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/95307575782451055935.
Full textAbstract:
碩士國立臺灣大學
造船工程學系
81
The main goal of this paper is to determine the dominant source of the underwater noise radiated from a surface vessel at mid-frequency range. We find that it is not the "MACHINE-NOISE" but the "FLUID -NOISE" resulted from thep propeller. This could be demonstrated by the following arguement according to the experimental data : (1) The amplitude of the plate vibration of the side wall in the machine room of the ship and the water , did not increase with the increasing of rotating speed of the main engine ,that is, the underwater radiational noise induced by the main engine is NOT significant in the ship''s underwater ship noise. (2) When the hull plate of the A.P. part of the ship is forced by the "FLUID-NOISE" ,there is a wide-band noise observed in the far- field pressure field . The near-field pressure at the wet side of the hull plate of A.P part is predicted by "GALERKIN METHOD " and " MIN. ERROR METHOD ".the resonat mode of plate vibration is not in the far-field measured data while it exits in the near-field theoretical predication.
35
Chiu, Ching-Chun, and 邱清俊. "Prediction Model of Noise Radiated from a Power Machine Room." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/81783107418732089863.
Full text
36
Petitjean, Benoit P. "On the nonlinearities in the noise radiated from high-speed model jets." 2006. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-1668/index.html.
Full text
37
Yang, Ling-Fu, and 楊令甫. "Analysis and Inprovement of the Cable-induced Vibration and Radiated Noise for Cable Car System." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/75662857788703213319.
Full textAbstract:
碩士國立臺灣海洋大學
系統工程暨造船學系
98
Cable car system noise impact on the environment. Low-frequency noise caused by local residents would not feel comfortable. So need analysis and improvement of Vibration and Radiated Noise for Cable Car System. The purpose of this study contact for the cable and pulley drive vibration excitation point of the cable and the relationship between speed. The vibration transmitted from the truss to the cylindrical pillar, and cylindrical pillar made noise. Measurement of acceleration of the dynamic characteristics of cylindrical pillar and cable car system running. Using Frequency Response Function estimate of the force. And then substituted into SYSNOISE ,calculate the surface vibration of pillar resulting sound pressure level. Last substituted into SoundPLAN to simulation and compared with scene measurement data. Finally the results obtained by the simulation, before the improvement on the natural frequency of the pillar overall understanding. To know what is the best improvement for the noise on the environment to replacement of cables. On this study, the best solution for the cable is the cable car runs to 3m / s constant speed operation and replacement of the cable tie into the eight-legged, that can be optimized to improve.
38
Chang, Chieh-Shih, and 張婕詩. "A comparison of different approaches on the aeroacoustic noise radiated from airfoils for wind turbine blades." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/88173275815678367901.
Full textAbstract:
碩士國立臺灣大學
工程科學及海洋工程學研究所
97
The purpose of the research is to investigate the noises induced by flow over the wind blades. The noise analysis is conducted by the Broadband Noise Source Model and FW-H (Ffowcs Williams and Hawkings) Formula which are based on theory of Lighthill’s acoustic analogy. How the wind velocity, angle of attack as well as the inflow turbulent intensity influence the induced aerodynamic noise is discussed. First of all, the dynamic coefficients and flow field of three airfoils NACA64(3)-618、S809 and S822 were verified, and then the accurate information of turbulence was provided as the source to evaluate the sound energy distribution. Three types of noise models that provided different characteristics of the noise distribution were adopted in this wrok. Firstly Reynolds-averaged Navier-Stokes Equation with the k-e turbulent model was used to predict the turbulent flow field. When the inflow turbulent intensity was increased to 5% and 10%, it causes great changes to the flow field and obviously it is also one of the major facts to the flow induced noise. For aerodynamic noise analysis, Proundman’s BNS model was performed to get the acoustic energy density distribution over the entire calculating domain. Further, Curle’s Formula was adopted to predict the surface acoustic power along the solid boundary. In order to understand the details of flow induced noise one step further, the Large Eddy Simulation approach for the unsteady flow combined with the FW-H equation was used to predict the unsteady sound pressure signal. Then by Fourier Transformation the spectrum of the noise can be calculated and consequently the frequency distribution and the power output are achieved. It might be useful in reducing the flow induced aerodynamic noise. However, LES requires a very fine grid resolution to capture the large scale eddy. At this stage, our current computer resources are extremely difficult to satisfy the computational efforts. Therefore, only the small wind blades were taken as the analysis object in this study. This experience may be useful in large wind blade analysis in the near future.
39
McIntyre, Duncan. "Predicting cavitation-induced noise from marine propellers." Thesis, 2021. http://hdl.handle.net/1828/12552.
Full textAbstract:
Noise pollution threatens marine ecosystems, where animals rely heavily on sound for navigation and communication. The largest source of underwater noise from human activity is shipping, and propeller-induced cavitation is the dominant source of noise from ships. Mitigation strategies require accurate methods for predicting cavitation-induced noise, which remains challenging. The present thesis explores prediction and modelling strategies for cavitation-induced noise from marine propellers, and provides insight into models that can be used both during propeller design and to generate intelligent vessel control strategies. I examined three distinct approaches to predicting cavitation-induced noise, each of which is discussed in one of the three main chapters of this thesis: a high-fidelity computational fluid dynamics scheme, a parametric mapping procedure, and the use of field measurements. Each of these three chapters presents different insight into the acoustic behaviour of cavitating marine propellers, as well both real and potential strategies for mitigating this critical environmental emission.
A combined experimental and numerical study of noise from a cavitating propeller, focused on both the fundamental importance of experimental findings and the effectiveness of the numerical modelling strategy used, is detailed in the first main chapter of this thesis. The experimental results highlighted that loud cavitation noise is not necessarily associated with high-power or high-speed propeller operation, affirming the need for intelligent vessel operation strategies to mitigate underwater noise pollution. Comparison of the experimental measurements and simulations revealed that the simulation strategy resulted in an over-prediction of sound levels from cavitation. Analysis of the numerical results and experiments strongly suggested that the cavitation model implemented in the simulations, a model commonly used for marine propeller simulations, was responsible for the over-prediction of sound levels.
Ships are powered primarily by combustion engines, for which it is possible to generate "maps" relating the emission of pollutants to the engine’s speed and torque; the second main chapter of this thesis presents the methodology I developed for generating similar "maps" relating the level of cavitation-induced noise to the speed and torque of a ship's propeller. A proof-of-concept of the method that used the model propeller from the first main chapter is presented. To generate the maps, I used a low-order simulation technique to predict the cavitation induced by the propeller at a range of different speed and torque combinations. A pair of semi-empirical models found in the literature were combined to provide the framework for predicting noise based on cavitation patterns. The proof-of-concept map shows a clear optimal operating regime for the propeller.
The final main chapter of this thesis presents an analysis of field noise measurements of coastal ferries in commercial operation, the data for which were provided by an industrial partner. The key finding was the identification of cavitation regime changes with variation in vessel speed by their acoustic signatures. The results provide a basis for remotely determining which vessels produce less noise pollution when subject to speed limits, which have been implement in critical marine habitats, and which vessels produce less noise at a specific optimum speed.Graduate
40
Tsai, Chien-Chiu, and 蔡建秋. "The study of relevant parameters for traffic-induced vibration and low frequency noise radiated from box-girder bridges." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/92908303974721712655.
Full textAbstract:
碩士國立臺灣海洋大學
系統工程暨造船學系
100
To investigate vehicle trigger the box-bridge girder vibration and low frequency noise problem. This paper is divided into two parts to study, the first part is collecting the exciting force for large vehicle ,the second part is an elevated bridge finite element analysis. By field measurement, this paper discusses the measured whether the trend coincide with the simulation results. In this paper, measuring for large vehicle excitation force at No. 62 highway and comparison with other vehicles exciting force literature , The result show that the vehicle exciting force is depend on the vehicle weight, large vehicles caused by exciting force significant vibration frequency is about 10~12.5 Hz, small vehicles is about 16~31.5 Hz .It is the unique spectrum of the force for the vehicle. The summarized results verify that let the vehicle excitation force spectrum trend changed is caused by the gross vehicle weight mainly . Through the noise of the elevated bridge structure of the simulation of the railway system ,and summarized the results can be found in the elevated bridge structure-born noise is depend on the total weight of bridge. when the bridge is more heavier ; the structure-born noise is more smaller ;it also depend on the bridge of cross section . The correlation between the structure-born noise and the form of bridge columns (RC pier columns, steel columns)is not obvious. Keypoint: box-bridge girder、excitation force、structure-born noise.
41
Krishna, Kumar G. V. "Characterization of Flow Induced Noise Received by an Array Placed at Stagnation Point of an Underwater Axisymmetric Body." Thesis, 2017. http://etd.iisc.ernet.in/2005/3799.
Full textAbstract:
Given the interest on underwater axisymmetric cylindrical bodies for the development of high-speed underwater weapons, characterization of the boundary layer flow-induced noise received by a Sound NAvigation and Ranging (SONAR) is very important to improve sonar detection ranges. The debate on generating mechanisms of the flow induced noise received at the stagnation point is still on as there is no experimental evidence conclusively suggesting whether it is a near-field or far-field phenomenon, thereby introducing an element of uncertainty in the prediction models. Further, the models developed thus far were based on low Reynolds numbers involving flows in water tunnels and buoyant vehicles. Therefore, the main focus of the thesis is to measure the flow induced noise using a sonar fitted at the most forward stagnation point of an underwater axisymmetric body as realistically as possible and predict the same theoretically for identifying a suitable flow noise model for future use by designers. In order to meet the stated goal, two exclusive experiments were conducted at sea using an underwater autonomous high-speed axisymmetric vehicle fitted with a planar hydrophone array (8X8) in its nose cone which measured the flow noise signature. Two different sets of existing models are used in characterizing the flow noise received by the array, while the first set comprises of models developed based on the Turbulent Boundary Layer induced noise and other is based on the transition zone radiated noise model. Through this study, it was found that the transition zone radiated noise model is in close agreement with the measured data.
42
Kao, Jui-Hsiang, and 高瑞祥. "Theoretical Prediction of The Marine Propeller Radiated Blade Rate Noises – Including The Scattering Effect Due to Ship Hull." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/59078857508754789988.
Full textAbstract:
博士國立臺灣海洋大學
系統工程暨造船學系
92
Abstract The main objective of this thesis is to develop a new and efficient numerical method for predicting the far-field and near-field blade-rate noises of marine propellers operating in a non-uniform ship wake by linear acoustic theory. In addition, both the scattering effect from the ship hull and the reflecting effect from the free surface are included. In the present method, an exact analytic solution satisfying the linear wave equation for predicting acoustic pressure caused by unsteady sheet cavitations, unsteady thrusts and torques can be derived directly in time domain. The free surface effect is simulated by imaged method. The deriving process has no approximation about the distance between the noise source and field points. Thus, this method can be used to predict the acoustic pressure at both far and near fields, and the Doppler effect can be demonstrate in the near field evidently. The variation of the distance between the noise source and the field points will cause obvious in the near field. It is found that for computing far-field acoustic pressure induced by the unsteady sheet cavitation and thrust, noise sources on a blade can be replaced by an effective point noise source. However, in doing so, errors appear on the computation of the acoustic pressure induced by the unsteady torque force. In the near field, any kind of noise sources should be distributed on the entire propeller blades in order to avoid the errors, especially for unsteady thrust and torque. An iterative method in time domain for computing multi-frequency waves scattered from underwater obstacles is also developed. These equations derived in the present method are expressed in some forms relative to the retarded time, and the Fourier series is used to minimize the numerical error due to time interpolations. This iterative method is an alternative to the frequency-domain boundary element method (BEM); however, this method is more efficient than the BEM, and is found very robust. Computational results of the present method and BEM show good agreements for both low frequency and high frequency cases. To investigate the acoustic fields radiated by the propeller and scattered from the ship hull with free surface effect, a case of container ship is calculated in this thesis. Meanwhile, the pressure fluctuations induced by the propeller on the ship hull predicted by the present method is similar to the results by a higher-order panel method satisfying the Laplace equation in this case.
43
Μαραζιώτη, Παναγιώτα. "Ανάπτυξη πειραματικής και υπολογιστικής μεθόδου για την μελέτη αεροθερμοδυναμικού πεδίου και του εκπεμπόμενου θορύβου και ρυπών από συρρέουσες και ανακυκλοφορούσες τυρβώδεις φλόγες προπανίου." Thesis, 2006. http://nemertes.lis.upatras.gr/jspui/handle/10889/1439.
Full textAbstract:
Η παρούσα διατριβή μελετά τις δυνατότητες υπολογισμού του πεδίου ροής δύο λειτουργικών παραμέτρων συμπεριλαμβανομένων του εκπεμπόμενου θορύβου και των εκπεμπόμενων ρύπων. Εξετάζεται η αλληλεπίδραση της καύσης με το ρευστο-θερμοδυναμικό πεδίο και τις χημικές αντιδράσεις. Περιγράφονται συνοπτικά οι διέπουσες εξισώσεις, οι μέθοδοι και τα μοντέλα της τυρβώδους καύσης και επισημαίνονται τα πλεονεκτήματα του μοντέλου των μεγάλων δινών (LES) το οποίο επιλέχθηκε εδώ.
Αναπτύσσεται ένας εύχρηστος, από την ρευστοδυναμική υπολογιστική μεθοδολογία, πολυβηματικός μηχανισμός για δύο καύσιμα άμεσου ενδιαφέροντος το μεθάνιο και το προπάνιο. Προτείνεται, δηλαδή, ένα απλοποιημένο χημικό σχήμα για την οξείδωση των βασικών καυσίμων το οποίο περιέχει τον σχηματισμό του NΟx και της παραγωγής καπναιθάλης.
Μετά από ανάλυση του ρόλου της καύσης στην ακουστική διακρίνονται οι δύο χαρακτηριστικοί τύποι: του θορύβου τυρβώδους καύσης (βόμβος – roar) και του θορύβου από τις ταλαντώσεις της καύσης (combustion oscillation). Παρουσιάζεται η κυματική εξίσωση και εισάγεται η έννοια του θερμο-ακουστικού όρου ο οποίος είναι συνάρτηση της απελευθερωμένης θερμότητας (q) στην φλόγα και εμφανίζεται ως όρος πηγής στην βασική εξίσωση. Στη συνέχεια η φλόγα εξετάζεται ως αυτόνομος πηγή αλλά και ως ενισχυτής θορύβου.
Με την προσέγγιση της Προσομοίωσης των Μεγάλων Δινών (Large Eddy Simulation, LES) αναπτύχθηκε μια μεθοδολογία υπολογισμού του θορύβου που εκπέμπεται από το μέτωπο τυρβωδών φλογών διάχυσης. Στο πλαίσιο της προτεινομένης μεθοδολογίας το αποτέλεσμα ήταν η ανάπτυξη ενός τρισδιάστατου προγνωστικού υπολογιστικού κώδικα. Στην συνέχεια υπολογίζεται το αεροθερμοδυναμικό τυρβώδες πεδίο ροής μέσω τελειοποίησης κωδίκων του Εργαστηρίου Τεχνικής Θερμοδυναμικής, των κωδίκων που αναπτύχθηκαν στο πλαίσιο της παρούσης εργασίας αλλά και του εμπορικού κώδικα Fluent.
Η μεθοδολογία, που αναπτύχθηκε με την παρούσα ερευνητική εργασία, πιστοποιήθηκε μέσω μιας σειράς πρωτότυπων μετρήσεων, του εκπεμπόμενου θορύβου στις συρρέουσες, εφαπτόμενες και ανυψωμένες και ανακυκλοφορούσες (χαμηλού και υψηλού λόγου καυσίμου/αέρα) φλόγες, σε πρωτότυπες πειραματικές διατάξεις του Εργαστηρίου.
Συγκεκριμένα διαμορφώθηκε ένας καινοτόμος αεροδυναμικός φλογοσυγκρατητής πολλαπλών εγχύσεων που διατηρεί μια πλούσια γκάμα φλογών με ιδιαίτερα χαμηλό λόγο καυσίμου/αέρα. Επιτεύχθηκαν πειραματικές μετρήσεις, του ορμικού και θερμοκρασιακού πεδίου διαφόρων μορφών τυρβωδών φλογών, συντάχθηκαν σχετικά διαγράμματα και υπολογίσθηκαν οι αρχικές και οριακές συνθήκες των πειραμάτων.In the present work the calculation of two parameters, the radiated noise and pollutants are studied. The interaction between combustion, the aerothermodynamical field and the chemical reactions is studied. The equations, the methods and the models of turbulent combustion are described here and the advantages of the large eddy simulation model (LES) which has been chosen for this case, are marked. A multi-step chemistry mechanism is developed for two fuels of great interest: methane and propane. A simple chemical scheme for the oxidation of basic fuels which includes the formation of NOx and soot is suggested in the present work. After analyzing the role of combustion in the acoustics two types of noise are distinguished the turbulent combustion noise and the noise from combustion oscillation. The wave equation is presented and the definition of thermo acoustic term which is a function of the heat release q in flame and it appears as a source term in the basic equation. The flame is examined as an autonomous source as well as a noise amplifier. With the approach of large eddy simulation (LES) a methodology for the noise calculation is developed which noise is from the turbulent diffusion flame front. In the place of the suggested methodology the result was the development of a 3-D computational code. The turbulent aerothermodynamical flow field is computed by codes has been developed in the laboratory of technical thermodynamic and by the commercial code (fluent). The methodology, which has been developed in the present work, has been certificated through a series of original measurements of the emitted noise in coaxial, tangential and lifted flames in original experimentallayouts.
44
Turcotte, Audrey. "Analyse intra-annuelle des fluctuations radiales des tiges et des racines adventives de l'épinette noire (Picea mariana (Mill. B.S.P.)." Thèse, 2007. http://constellation.uqac.ca/413/1/25024861.pdf.
Full textAbstract:
Les fluctuations radiales des tissus des tiges et des racines d'épinette noire ont été enregistrées entre août 2004 et octobre 2005 en utilisant des dendromètres à pointe automatiques pour déterminer si le retour des fonctions hydriques normales limite le début de la croissance cambiale secondaire. En divisant les fluctuations radiales des tissus en phases de contraction, d'expansion et d'accroissement, des cycles de déshydratation et réhydratation des tissus furent définis. L'amplitude et la durée de chaque phase et des cycles complets ont été mesurées. Les cycles furent classifies selon quatre critères : leur durée, le moment d'apparition de chacune de leurs phases dans la journée, leur origine théorique en fonction de la température et leur phase d'accroissement positive (augmentation du rayon) ou négative (diminution du rayon). Cette classification a permis de séparer les variations radiales annuelles des arbres en cinq périodes : 1) période de stabilité du rayon après la saison de croissance, 2) période de contraction hivernale des tissus sous l'influence des températures froides, 3) période de réhydratation où le rayon augmentait rapidement jusqu'à atteindre celui de l'automne précédent, 4) période de stabilité du rayon avant la croissance et 5) période de croissance. Les périodes 1 et 4 présentaient les mêmes types de cycles, en proportions semblables. Durant la période de réhydratation et la période de croissance, l'épaisseur radiale des tissus augmentait de façon distincte. Les conditions environnementales moyennes ont été calculées pour chaque phase de chaque cycle afin d'approfondir l'analyse de la période printanière précédant l'éveil cambial (périodes 3, 4 et 5). Les corrélations entre l'amplitude des trois phases du cycle et les variables environnementales ont été étudiées. L'humidité relative, la température de l'air et la radiation solaire, trois variables impliquées dans la transpiration des arbres, influençaient l'amplitude des fluctuations de façon croissante, de la période de réhydratation (période 3) à la période de croissance (période 5). L'effet des précipitations sur l'amplitude des phases de contraction et d'accroissement augmentait aussi de la période 3 à la période 5, à mesure que l'eau de la fonte des neiges était utilisée. La réhydratation printanière a duré 50 jours. Le retour des fluctuations radiales estivales normales précédait le moment de l'éveil cambial de plus de trois semaines. Sur le site, l'éveil cambial de l'épinette noire n'était pas limité par la réhydratation complète des tissus ni par le retour des fonctions hydriques normales, mais vraisemblablement par les températures de l'air comme en témoigne la présence des cycles inversés durant la période précédant la croissance (période 4).
45
Laplante, Sandy. "Effet de l'éclaircie précommerciale et de l'éclaircie commerciale radiale et la qualité du bois de l'épinette noire de la sapinière à bouleau blanc du Saguenay-Lac-Saint-Jean." Thèse, 2009. http://constellation.uqac.ca/153/1/030113946.pdf.
Full textAbstract:
Les éclaircies précommerciales (EPC) et commerciales (EC) ont été appliquées récemment dans la forêt boréale du Québec dans le but d'accroître la croissance radiale d'une forêt afin de la garder stable et productive jusqu'à sa maturité. Le but principal de l'étude était d'établir une relation entre la croissance radiale des arbres et la qualité du bois dans les peuplements d'épinette noire (Picea mariana (Mill.) B.S.P.) traités par l'éclaircie. Un effectif de 35 arbres par site totalisant 10 sites EPC, 10 sites EC et 4 sites témoins a été mesuré, échantillonné puis analysé selon trois volets d'analyse; la croissance radiale, les propriétés mécaniques et les propriétés anatomiques du bois. La majorité des arbres a démontré une augmentation positive de la croissance radiale, allant jusqu'à 120% après l'EPC et jusqu'à 80% pour Î'EC (P< 0,0001, Tableau 3). Toutefois, cette augmentation est variable entre les sites et les individus. Des changements dans les propriétés du bois ont été mesurés suite au cerne de Fécîaïrcie. Pour les EC, la largeur du bois initial et le nombre de cellules formées dans le bois initial augmentent signifîcativement après le ceme de Fécîaircie (P = 0,0385 et P = 0,0188, Tableau 5). Pour les EPC, la largeur du bois initial augmente signifîcativement après le cerne de l'éclaircie (P = 0,0163, Tableau 4) mais pas le nombre de cellules formées dans le bois initial (P = 0,0841, Tableau 4). L'épaisseur tangentielle de la paroi cellulaire dans le bois mitial et le bois final ne présentent pas de variations significatives pour les deux traitements (Tableau 4 et 5). Pour ce qui est des forces mécaniques de rupture, elles diminuent signifîcativement après le cerne de Féclaircie mais de façon variable entre les sites et les individus. Les résultats de cette étude permettent de démontrer que les EPC et les EC ne modifient pas profondément les propriétés du bois et les changements rapportés chez ce dernier sont inférieurs aux changements rapportés dans la croissance radiale.