Relevant bibliographies by topics / Directivity effects

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  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers

Academic literature on the topic 'Directivity effects'

Author: Grafiati
Published: 4 June 2021
Last updated: 18 February 2022

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Journal articles on the topic "Directivity effects"

1

Xie, Junju. "Strong‐Motion Directionality and Evidence of Rupture Directivity Effects during the Chi‐Chi Mw 7.6 Earthquake." Bulletin of the Seismological Society of America 109, no. 6 (October 29, 2019): 2367–83. http://dx.doi.org/10.1785/0120190087.

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Abstract This article investigates the spatial distribution, predominant direction, and variations in the intensity measures (IMs) with orientation for classified pulse‐like and nonpulse motions during Chi‐Chi Mw 7.6 earthquake. The results show evidence of high polarization for long‐period spectral accelerations at relatively large source‐to‐site distances (50–100 km) north of the Chelungpu fault. The polarization of long‐period motions shows a clear correlation with the directivity parameters’ isochrone directivity predictor and ξ, indicating a connection between directionality and rupture directivity. The variation in strong‐motion directionality with the period is also studied. The discrepancy in directionality caused by strong directivity increases with the period from 1 to 10 s, which confirms a clear correlation of period‐dependent directionality with directivity effects. This study finds stronger directionality of pulse‐like motions than nonpulse motions for long periods over 3 s with higher maximum‐to‐median and maximum‐to‐minimum IM ratios. For periods over 3 s, the maximum‐to‐median ratios of pulse‐like motions are higher than the mean prediction of the Shahi and Baker (2014a) model, whereas those of nonpulse motions are lower than the prediction. However, this study does not find simple and clear results for the directions of the maximum component at different periods for pulse‐like and nonpulse motions. Despite clear differences between the unidirectional fling‐step and bidirectional forward directivity pulses, the effects of fling‐step and forward directivity are actually coupled in the waveforms.
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Nakazawa, Toshiyasu, and Naoaki Shinohara. "Study on aircraft noise directivity of behind the start of takeoff roll." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 3 (August 1, 2021): 3202–8. http://dx.doi.org/10.3397/in-2021-2330.

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This paper discusses aircraft noise directivity behind the start of takeoff roll. Aircraft noise has the radiation directivity because of aircraft engine mount position and the engine noise directivity. Thus, lateral noise directivity correction is recommended in airport noise calculation guidelines such as ECAC Doc.29 and ICAO Doc9911. In these guidelines, the directivity of flyover noise and the directivity at the start of takeoff roll on ground are prepared separately. A 90-degree dipole model is used for the directivity of the flyover noise, and another similar directivity is used for the directivity behind the start of takeoff roll. It is necessary to properly evaluate the directivity behind the takeoff roll because it has a large contribution to noise calculation of the vicinity of the airport. Therefore, we measured aircraft noise behind the start of takeoff roll with sound level meters placed half-concentrically around Narita Airport in Japan. From these measurement results, various types of aircraft noise directivity behind the takeoff roll are examined and considered the effects of weather conditions such as wind direction. Finally the differences from existing models are compared.
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Sheets, Nathan W., and Lily M. Wang. "Effects of sound source directivity on auralizations." Journal of the Acoustical Society of America 111, no. 5 (2002): 2331. http://dx.doi.org/10.1121/1.4777773.

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Tarbali, Karim, Brendon A. Bradley, and Jack W. Baker. "Ground Motion Selection in the Near-Fault Region considering Directivity-Induced Pulse Effects." Earthquake Spectra 35, no. 2 (May 2019): 759–86. http://dx.doi.org/10.1193/102517eqs223m.

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This paper focuses on the selection of ground motions for seismic response analysis in the near-fault region, where directivity effects are significant. An approach is presented to consider forward directivity velocity pulse effects in seismic hazard analysis without separate hazard calculations for ‘pulse-like’ and ‘non-pulse-like’ ground motions, resulting in a single target hazard (at the site of interest) for ground motion selection. The ability of ground motion selection methods to appropriately select records that exhibit pulse-like ground motions in the near-fault region is then examined. Applications for scenario and probabilistic seismic hazard analysis cases are examined through the computation of conditional seismic demand distributions and the seismic demand hazard. It is shown that ground motion selection based on an appropriate set of intensity measures (IMs) will lead to ground motion ensembles with an appropriate representation of the directivity-included target hazard in terms of IMs, which are themselves affected by directivity pulse effects. This alleviates the need to specify the proportion of pulse-like motions and their pulse periods a priori as strict criteria for ground motion selection.
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Spudich, Paul, Badie Rowshandel, Shrey K. Shahi, Jack W. Baker, and Brian S. J. Chiou. "Comparison of NGA-West2 Directivity Models." Earthquake Spectra 30, no. 3 (August 2014): 1199–221. http://dx.doi.org/10.1193/080313eqs222m.

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Five directivity models have been developed based on data from the NGA-West2 database and based on numerical simulations of large strike-slip and reverse-slip earthquakes. All models avoid the use of normalized rupture dimension, enabling them to scale up to the largest earthquakes in a physically reasonable way. Four of the five models are explicitly “narrow-band” (in which the effect of directivity is maximum at a specific period that is a function of earthquake magnitude). Several strategies for determining the zero-level for directivity have been developed. We show comparisons of maps of the directivity amplification. This comparison suggests that the predicted geographic distributions of directivity amplification are dominated by effects of the models’ assumptions, and more than one model should be used for ruptures dipping less than about 65 degrees.
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Hidayah Muhamad Adnan, Noor, Islam Md. Rafiqul, and AHM Zahirul Alam. "Effects of Inter-Element Spacing and Number of Elements on Planar Array Antenna Characteristics." Indonesian Journal of Electrical Engineering and Computer Science 10, no. 1 (April 1, 2018): 230. http://dx.doi.org/10.11591/ijeecs.v10.i1.pp230-240.

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<p>Planar array antenna is seen as one of the innovative solutions of massive MIMO and 5G networks since they provide directive beams. In this paper, planar array antenna with square and rectangular arrangements based on 2 x 2 antenna elements as one subarray was proposed. Then, array factor for the the planar array antenna with up to 64 antenna elements was calculated to analyze the effects of inter-element spacing and number of elements on the antenna characteristics. Higher values of inter-element spacing contributed to higher number of side lobes, narrower main lobe, higher directivity and lower half power beamwidth (HPBW). Inter-element spacing equals to 0.5λ was found to be the most suitable value for planar array antenna design based on the analysis. Meanwhile, higher number of antenna elements increased the value of directivity of the planar array with narrower HPBW. Therefore, there is a tradeoff between directivity and HPBW in designing planar array antenna for massive MIMO application. </p><p> </p>
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Ricketts, Todd. "Directivity Quantification in Hearing Aids: Fitting and Measurement Effects." Ear and Hearing 21, no. 1 (February 2000): 45–58. http://dx.doi.org/10.1097/00003446-200002000-00008.

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Shahbazi, Shahrokh, Iman Mansouri, Jong Wan Hu, Noura Sam Daliri, and Armin Karami. "Seismic Response of Steel SMFs Subjected to Vertical Components of Far- and Near-Field Earthquakes with Forward Directivity Effects." Advances in Civil Engineering 2019 (April 3, 2019): 1–15. http://dx.doi.org/10.1155/2019/2647387.

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In the near-field earthquake, forward directivity effects cause long-period pulse with a short effective time and a large domain in the velocity time history. This issue increases the ductility needs of structures, and in recent decades, the destructive effects of these kinds of records have been evaluated in comparison with far-field earthquakes. This brings about the necessity to compare a structure’s behavior subjected to vertical components of near-field (NF) earthquakes, including forward directivity effects vs. the effects of vertical components of far-field (FF) earthquakes. The present study investigated 3-, 5-, 8-, and 20-story steel moment frames with special ductility (SMF) through which modeling effects of panel zone have been applied, subjected to vertical component of near-field (NF) earthquakes with forward directivity and the vertical component of far-field earthquakes. By investigating the results, it can be clearly seen that the average values of the maximum displacement, shear force of the stories, and the velocity of each story under the impact of the near-field earthquake are greater than the amount of that under the effect of a far-field earthquake. However, this comparison is not valid for the amount of acceleration, axial force, and moments in the columns of the structures accurately.
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Sugar, Mitchell, and Paul Slaboch. "Directivity of sound propagation from an commercial supersonic engine inlet." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 2 (August 1, 2021): 4211–18. http://dx.doi.org/10.3397/in-2021-2633.

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The effects of mean flow variations on sound propagation from an axisymmetric commercial supersonic engine inlet were studied using numerical methods. A finite element model of the inlet was constructed in Ansys Fluent and used to solve for flow fields given by different initial conditions. Results from this model were fed into the aeroacoustic solver, Actran, and used to calculate far field radiated noise as well as the directivity of that noise. The acoustic source of this noise was a plane wave of a known strength placed at the fan face. In addition to assessing the effects of mean flow on the radiated noise transfer functions, the duct modes of the model were compared across different flow regimes. Relationships between mean flow parameters and the directivity of duct modes are developed. The results of this study will be used in further studies to gain a deeper understanding of how the underlying physics which govern the system create favorable or unfavorable directivity patterns.
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Ertuncay, Deniz, Petra Malisan, Giovanni Costa, and Stefano Grimaz. "Impulsive Signals Produced by Earthquakes in Italy and Their Potential Relation with Site Effects and Structural Damage." Geosciences 11, no. 6 (June 21, 2021): 261. http://dx.doi.org/10.3390/geosciences11060261.

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Near fault seismic records may contain impulsive motions in velocity-time history. The seismic records can be identified as impulsive and non-impulsive depending on the features that their waveforms have. These motions can be an indicator of directivity or fling step effect, and they may cause dangerous effects on structures; for this reason, there is increasing attention on this subject in the last years. In this study, we collect the major earthquakes in Italy, with a magnitude large or equal to Mw 5.0, and identify the impulsive motions recorded by seismic stations. We correlate impulsive motions with directivity and fling step effects. We find that most earthquakes produced impulsive signals due to the directivity effect, though those at close stations to the 30 October 2016 Amatrice earthquake might be generated by the fling step effect. Starting from the analyzed impulses, we discuss on the potential influence of site effects on impulsive signals and suggest a characterization based on the main displacement directions of the impulsive horizontal displacements. Finally, we discuss on the damage of three churches in Emilia, which were subject to impulsive ground motion, underlying in a qualitative way, how the characteristics of the pulses may have had influences the structural response of the façades.
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Dissertations / Theses on the topic "Directivity effects"

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Joshi, Varun Anil. "Near-Fault Forward-Directivity Aspects of Strong Ground Motions in the 2010-11 Canterbury Earthquakes." Thesis, University of Canterbury. Department of Civil and Natural Resources Engineering, 2013. http://hdl.handle.net/10092/8987.

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The purpose of this thesis is to conduct a detailed examination of the forward-directivity characteristics of near-fault ground motions produced in the 2010-11 Canterbury earthquakes, including evaluating the efficacy of several existing empirical models which form the basis of frameworks for considering directivity in seismic hazard assessment. A wavelet-based pulse classification algorithm developed by Baker (2007) is firstly used to identify and characterise ground motions which demonstrate evidence of forward-directivity effects from significant events in the Canterbury earthquake sequence. The algorithm fails to classify a large number of ground motions which clearly exhibit an early-arriving directivity pulse due to: (i) incorrect pulse extraction resulting from the presence of pulse-like features caused by other physical phenomena; and (ii) inadequacy of the pulse indicator score used to carry out binary pulse-like/non-pulse-like classification. An alternative ‘manual’ approach is proposed to ensure 'correct' pulse extraction and the classification process is also guided by examination of the horizontal velocity trajectory plots and source-to-site geometry. Based on the above analysis, 59 pulse-like ground motions are identified from the Canterbury earthquakes , which in the author's opinion, are caused by forward-directivity effects. The pulses are also characterised in terms of their period and amplitude. A revised version of the B07 algorithm developed by Shahi (2013) is also subsequently utilised but without observing any notable improvement in the pulse classification results. A series of three chapters are dedicated to assess the predictive capabilities of empirical models to predict the: (i) probability of pulse occurrence; (ii) response spectrum amplification caused by the directivity pulse; (iii) period and amplitude (peak ground velocity, PGV) of the directivity pulse using observations from four significant events in the Canterbury earthquakes. Based on the results of logistic regression analysis, it is found that the pulse probability model of Shahi (2013) provides the most improved predictions in comparison to its predecessors. Pulse probability contour maps are developed to scrutinise observations of pulses/non-pulses with predicted probabilities. A direct comparison of the observed and predicted directivity amplification of acceleration response spectra reveals the inadequacy of broadband directivity models, which form the basis of the near-fault factor in the New Zealand loadings standard, NZS1170.5:2004. In contrast, a recently developed narrowband model by Shahi & Baker (2011) provides significantly improved predictions by amplifying the response spectra within a small range of periods. The significant positive bias demonstrated by the residuals associated with all models at longer vibration periods (in the Mw7.1 Darfield and Mw6.2 Christchurch earthquakes) is likely due to the influence of basin-induced surface waves and non-linear soil response. Empirical models for the pulse period notably under-predict observations from the Darfield and Christchurch earthquakes, inferred as being a result of both the effect of nonlinear site response and influence of the Canterbury basin. In contrast, observed pulse periods from the smaller magnitude June (Mw6.0) and December (Mw5.9) 2011 earthquakes are in good agreement with predictions. Models for the pulse amplitude generally provide accurate estimates of the observations at source-to-site distances between 1 km and 10 km. At longer distances, observed PGVs are significantly under-predicted due to their slower apparent attenuation. Mixed-effects regression is employed to develop revised models for both parameters using the latest NGA-West2 pulse-like ground motion database. A pulse period relationship which accounts for the effect of faulting mechanism using rake angle as a continuous predictor variable is developed. The use of a larger database in model development, however does not result in improved predictions of pulse period for the Darfield and Christchurch earthquakes. In contrast, the revised model for PGV provides a more appropriate attenuation of the pulse amplitude with distance, and does not exhibit the bias associated with previous models. Finally, the effects of near-fault directivity are explicitly included in NZ-specific probabilistic seismic hazard analysis (PSHA) using the narrowband directivity model of Shahi & Baker (2011). Seismic hazard analyses are conducted with and without considering directivity for typical sites in Christchurch and Otira. The inadequacy of the near-fault factor in the NZS1170.5: 2004 is apparent based on a comparison with the directivity amplification obtained from PSHA.
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Sharma, R. "Simulation studies on effects of dual polarisation and directivity of antennas on the performance of MANETs." Thesis, Coventry University, 2014. http://curve.coventry.ac.uk/open/items/4cc65581-8030-45bc-8136-82fdf902052e/1.

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In the purview of efficient communication in MANETs for enhanced data rates and reliable routing of information, this thesis deals with dual polarised directional antenna based communication. This thesis proposes a dual polarised directional communication based cross-layer solution to mitigate the problems of interference, exposed nodes, directional exposed nodes, and deafness, and to achieve efficient routing of information. At the physical layer of network protocol stack, this thesis proposes the use of dual polarised directional antenna for the mitigation of interference. Use of dual polarised directional communication at the physical layer calls for appropriate modifications in the functionality of MAC and network layers. At the MAC layer, the DPDA-MAC protocol proposed in this thesis achieves mitigation of the problems of exposed nodes, directional exposed nodes and deafness, by using dual polarised directional antenna at physical layer. At network layer, the DPDA-MRP protocol presented in this thesis facilitates the discovery of multiple routes between the source and destination nodes to route information in accordance with the desired dual polarised directional communication. To achieve efficient dual polarised directional communication and routing of information, it is essential to maintain well populated Neighbour Table (NT) and Routing Table (RT). This thesis proposes a novel Corruption Detection Pulse (CDP) based technique to handle corruption of broadcast packets such as Link ID and RREQ arising due to hidden node problem. Since the nodes participating in the formation of MANETs have limited battery energy, the protocols proposed in this thesis are featured with a provision for dynamic power control to achieve energy efficient communication. Nodes maintain Received Signal Strength Indicator (RSSI) information in the NT, which along with the information of node location is used in the formulation of decision logic of dynamic power control. Through numerous simulation studies, this thesis demonstrates the benefits of dual polarised directional communication to enhance the performance of MANET. The design principles, benefits and conceptual constraints of proposed DPDA-MAC protocol are analysed with SPDA-MAC and CSMA/CA, while those for DPDA-MRP are analysed with SPDA-MRP and DSR through performance metrics of throughput, Packet Delivery Ratio (PDR) and per hop delay. The thesis also analyses the impact of variations of channel capacity, node density, rate of packet transmission and mobility of nodes on the performance of the proposed and conventional protocols invoked in MANETs.
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Ugurhan, Beliz. "Stochastic Strong Ground Motion Simulations On North Anatolian Fault Zone And Central Italy: Validation, Limitation And Sensitivity Analyses." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612413/index.pdf.

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Assessment of potential ground motions in seismically active regions is essential for purposes of seismic design and analysis. Peak ground motion intensity values and frequency content of seismic excitations are required for reliable seismic design, analysis and retrofitting of structures. In regions of sparse or no strong ground motion records, ground motion simulations provide physics-based synthetic records. These simulations provide not only the earthquake engineering parameters but also give insight into the mechanisms of the earthquakes. This thesis presents strong ground motion simulations in three regions of intense seismic activity. Stochastic finite-fault simulation methodology with a dynamic corner frequency approach is applied to three case studies performed in Dü
zce, L&rsquo
Aquila and Erzincan regions. In Dü
zce study, regional seismic source, propagation and site parameters are determined through validation of the simulations against the records. In L&rsquo
Aquila case study, in addition to study of the regional parameters, the limitations of the method in terms of simulating the directivity effects are also investigated. In Erzincan case study, where there are very few records, the optimum model parameters are determined using a large set of simulations with an error-minimization scheme. Later, a parametric sensitivity study is performed to observe the variations in simulation results to small perturbations in input parameters. Results of this study confirm that stochastic finite-fault simulation method is an effective technique for generating realistic physics-based synthetic records of large earthquakes in near field regions.
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Honoré-Foundotos, Laëtitia. "Génération d'accélérogrammes synthétiques large-bande : contribution à l’estimation de l’aléa sismique par validation d’approches en aveugle." Thesis, Nice, 2013. http://www.theses.fr/2013NICE4054/document.

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L’une des problématique scientifique majeure en sismologie est de pouvoir estimer les mouvements du sol attendus en un site pour un futur séisme. L’objectif de cette thèse est de tester et de valider deux méthodes de simulation des mouvements du sol basées sur l’approche des fonctions de Green empiriques et d’apporter des éléments pouvant aider au développement d’une méthodologie de simulation en aveugle. Dans une première partie, une méthode de simulation basée sur une approche stochastique en point-source est validée sur les données réelles de séismes récents bien instrumentés : le séisme des Saintes Mw6.4 et le séisme de L’Aquila Mw6.3. Nous avons développé une approche de simulation en aveugle en prenant en compte une incertitude sur le paramètre de rapport des chutes de contrainte C. Cette approche permet de générer un ensemble d’accélérogrammes synthétiques d’un séisme cible suffisamment variés pour être représentatifs d’un grand nombre de scénarios de sources possibles et prenant en compte dans un sens statistique de potentiels effets de directivité. Cette approche a également été appliquée à la simulation d’un séisme historique pyrénéen Mw6.1. Dans une seconde partie, nous nous appuyons sur un modèle de source étendue plus complexe, combinant des modèles cinématiques de sources composites fractales avec l’approche des FGEs. Le potentiel de la méthode est testé sur une application au séisme de L’Aquila. Cela a permis de produire des résultats très satisfaisants sur l’ensemble des paramètres des mouvements du sol analysés. Cette méthode de simulation apparaît comme étant très prometteuse pour la mise en œuvre d’une méthodologie de simulation en aveugle, même si la principale difficulté réside dans la nécessité de définir la variabilité de nombreux paramètres d’entrée mal connus dans le cadre de la simulation d’un futur séisme
One of the major scientific problems in seismology is to estimate the ground motions expected at a given site from a future earthquake. The aim of this thesis is to test and validate two different methods of ground motions simulation based on the empirical Green’s function approach and to provide elements that can help to develop a blind simulation methodology. In a first part, a simulation method based on a stochastic point source approach is validated on the real data of recent earthquakes well instrumented : the Les Saintes earthquake Mw6.4 and the L’Aquila earthquake Mw6.3. We have developed a blind simulation approach by taking into account an uncertainty on the parameter of stress drop ratio C. This approach allows to generate a set of synthetic accelerograms of a target earthquake varied enough to be representative of a large number of possible source scenario and taking into account in a statistical sense potential directivity effects. This approach is also applied to the simulation of an historical Pyrenean earthquake Mw6.1. In a second part, we use a more complex extended source model, combining kinematic models of fractal composite sources with EGF approach. The potential of the method is tested on an application to L’Aquila earthquake. This has produced very satisfying results on all ground motion parameters analyzed. This simulation method appears to be very promising for the implementation of a blind simulation methodology, even if the main difficulty lies in the need to define the variability of many poorly known input parameters in the simulation of a future earthquake
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Métais, Samuel. "Façonnage des ondes : de la superdirectivité à la superrésolution." Thesis, Sorbonne Paris Cité, 2019. http://www.theses.fr/2019USPCC008.

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Durant cette thèse nous nous sommes intéressés à la physique des ondes globale. En repartant de l’équation de d’Alembert, il émerge trois leviers principaux qui permettent le contrôle des ondes : contrôle sur les sources, contrôle sur les conditions aux limites, et contrôle sur le milieu de propagation lui-même. Dans un premier lieu, nous avons utilisé les propriétés d’une métasurface binaire électroniquement reconfigurable en cavité micro-ondes. Cet objet permet de contrôler le champ au sein de la cavité. Celle-ci a ensuite été ouverte, et nous avons montré que le contrôle s’étendait à l’émission en champ lointain. Ce système réalise donc une antenne compacte directive et reconfigurable. Dans un second temps, nous avons considéré l’approche métamatériaux pour réaliser une antenne dite superdirective. En effet, les antennes sont soumises à des limitations de directivité liées à leur taille, dont la prédiction date des années 40. En utilisant un milieu de fils, nous avons montré que ce métamatériau qui permet le contrôle du champ proche à une échelle sub-longueur d’onde, peut influencer le rayonnement d’une source unique au point de réaliser une antenne superdirective avec seulement quatre diffuseurs résonants passifs. Enfin, nous avons réalisé en acoustique une preuve de concept d’une nouvelle technique d’imagerie non-linéaire. Depuis l’illumination structurée, c’est l’imagerie d’agents de contraste, souvent fluorescent, qui permet de battre la limite de diffraction. Ici, nous proposons une idée basée sur l’effet Doppler. Nous montrons dans un premier temps qu’imager avec des sources et des récepteurs en rotation permet d’égaler au moins l’illumination structurée. Dans un second temps, nous montrons que cette rotation génère une information spectrale supplémentaire qui permet d’atteindre la super-résolution
During this PhD, we have taken interest in general wave physics. From d’Alembert’s wave equation, one can find three ways of controlling the waves : tuning the source distribution, for one part, altering the boundary conditions, for another part, and finally, modeling the propagation medium itself. Those three tools have been demonstrated during three different projects. Firstly, we have used an electronically reconfigurable binary métasurface to control the wave field inside a micro-wave cavity. Extending this concept to an open cavity, we have demonstrated that we can actually control the farfield emission of this system. This has allowed us to design a compact reconfigurable directive antenna from an open micro-wave cavity. Secondly, we have used the metamaterial approach to overcome the directivity limit of antenna that has been considered by the community since its prediction in the 40s. Using a wire medium, which is known for its sub-wavelength control of the nearfield, we have extended this to the farfield emission of a singular source inside. Using only four passive resonant scatterers, we have been able to make a single source superdirective. Lastly, we have designed and performed an acoustic experiment to create a new non-linear imaging technique. Ever since the contributions of structured illumination and non-linear fluorescent imaging, breaking the diffraction limit has been shown to be possible. We design here a new method, based on the Doppler effect, to get rid of contrast agents. Using rotating sources and receivers, we have shown that this system performs, in homodyne detection, as well as a structured illumination microscope. However, the spectral richness of the signal allows us to further hence the resolving power of our system, and hence, achieve true super-resolution
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Ruiz, Paredes Javier Antonio. "Génération d'accélérogrammes synthétiques large-bande par modélisation cinématique de la rupture sismique." Paris, Institut de physique du globe, 2007. http://www.theses.fr/2007GLOB0009.

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Afin de rendre les modélisations cinématiques de la rupture sismique plus réalistes au regard des modèles dynamiques, des contraintes physiques ont été introduites. Pour améliorer la modélisation de la vitesse de glissement sur le plan de faille, une évolution du modèle k-2 estproposée qui consiste à décomposer le glissement en sous-événements au travers d'une analyse par bandes de k. Ce modèle permet d'obtenir des vitesses de glissement proches d'une fonctionde type Kostrov, en préservant un spectre rayonné en w2 avec des amplitudes proportionnelles au coefficient de directivité Cd à hautes fréquences. Pour mieux contrôler les effets de directivité, un modèle cinématique basé sur une description de sources composites et sur une loi d'échellerégissant l'extension de la zone de nucléation des sous-événements est proposé. Ce modèle permet de réduire le coefficient de directivité apparent à une fraction de Cd, et de reproduirel'écart-type des relations d'atténuation. Afin de rendre les modèles de sources sismiques plus réalistes, une vitesse de rupture variable compatible avec la physique de la rupture doit être introduite. L'approche suivie qui relie analytiquement l'énergie de fracturation, le glissement et la vitesse de rupture, se traduit par une augmentation des pics d'accélérations modélisés à distance proche. Enfin, pour mieux rendre compte de la complexité de l'interaction du champ d'ondes avec le milieu géologique, une approche semi-empirique combinant le modèle de sources composites et des fonctions de Green Empiriques est proposée. Les simulations obtenues pour le séisme de Yamaguchi (Mw 5,9) reproduisent les principales caractéristiques du mouvement du sol
In order to make the broadband kinematic rupture modeling more realistic with respect to dynamic modeling, physical constraints are added to the rupture parameters. To improve the slip velocity function (SVF) modeling, an evolution of the k-2 source model is proposed, which consists to decompose the slip as a sum of sub-events by band of k. This model yields to SVFclose to the solution proposed by Kostrov for a crack, while preserving the spectral characteristics of the radiated wavefield, i. E. A w2 model with spectral amplitudes at high frequency scaled to the coefficient of directivity Cd. To better control the directivity effects, acomposite source description is combined with a scaling law defining the extent of the nucleation area for each sub-event. The resulting model allows to reduce the apparent coefficient of directivity to a fraction of Cd, as well as to reproduce the standard deviation of the new empirical attenuation relationships proposed for Japan. To make source models more realistic, avariable rupture velocity in agreement with the physics of the rupture must be considered. The followed approach that is based on an analytical relation between the fracture energy, the slip and the rupture velocity, leads to higher values of the peak ground acceleration in the vicinity ofthe fault. Finally, to better account for the interaction of the wavefield with the geological medium, a semi-empirical methodology is developed combining a composite source model with empirical Green functions, and is applied to the Yamaguchi, Mw 5. 9 earthquake. The modeled synthetics reproduce satisfactorily well the observed main characteristics of ground motions
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Honoré-Foundotos, Laëtitia. "Génération d'accélérogrammes synthétiques large-bande : contribution à l'estimation de l'aléa sismique par validation d'approches en aveugle." Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00920208.

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L'une des problématique scientifique majeure en sismologie est de pouvoir estimer les mouvements du sol attendus en un site pour un futur séisme. L'objectif de cette thèse est de tester et de valider deux méthodes de simulation des mouvements du sol basées sur l'approche des fonctions de Green empiriques et d'apporter des éléments pouvant aider au développement d'une méthodologie de simulation en aveugle. Dans une première partie, une méthode de simulation basée sur une approche stochastique en point-source est validée sur les données réelles de séismes récents bien instrumentés : le séisme des Saintes Mw6.4 et le séisme de L'Aquila Mw6.3. Nous avons développé une approche de simulation en aveugle en prenant en compte une incertitude sur le paramètre de rapport des chutes de contrainte C. Cette approche permet de générer un ensemble d'accélérogrammes synthétiques d'un séisme cible suffisamment variés pour être représentatifs d'un grand nombre de scénarios de sources possibles et prenant en compte dans un sens statistique de potentiels effets de directivité. Cette approche a également été appliquée à la simulation d'un séisme historique pyrénéen Mw6.1. Dans une seconde partie, nous nous appuyons sur un modèle de source étendue plus complexe, combinant des modèles cinématiques de sources composites fractales avec l'approche des FGEs. Le potentiel de la méthode est testé sur une application au séisme de L'Aquila. Cela a permis de produire des résultats très satisfaisants sur l'ensemble des paramètres des mouvements du sol analysés. Cette méthode de simulation apparaît comme étant très prometteuse pour la mise en œuvre d'une méthodologie de simulation en aveugle, même si la principale difficulté réside dans la nécessité de définir la variabilité de nombreux paramètres d'entrée mal connus dans le cadre de la simulation d'un futur séisme.
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Foundotos, Laetitia. "Génération d'accélérogrammes synthétiques large-bande. Contribution à l'estimation de l'aléa sismique par validation d'approches en aveugle." Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00918349.

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L'une des problématique scientifique majeure en sismologie est de pouvoir estimer les mouvements du sol attendus en un site pour un futur séisme. L'objectif de cette thèse est de tester et de valider deux méthodes de simulation des mouvements du sol basées sur l'approche des fonctions de Green empiriques (FGEs) et d'apporter des éléments pouvant aider au développement d'une méthodologie de simulation en aveugle. Dans une première partie, une méthode de simulation basée sur une approche stochastique en point-source est validée sur les données réelles de séismes récents bien instrumentés. Profitant de la disponibilité d'enregistrements de petits séismes de bonne qualité pouvant être utilisés comme FGEs, deux applications sont réalisées : une application au séisme des Saintes Mw = 6.4 et une application au séisme de L'Aquila Mw = 6.3. Nous avons développé une approche de simulation en aveugle en prenant en compte une incertitude sur le paramètre de rapport des chutes de contrainte C. Cette approche permet de générer un ensemble d'accélérogrammes synthétiques d'un séisme cible suffisamment variés pour être représentatifs d'un grand nombre de scénarios de sources possibles et prenant en compte dans un sens statistique de potentiels effets de directivité. De plus, la variabilité des mouvements du sol produite par notre approche de simulation en aveugle est cohérente avec la variabilité des prédictions des mouvements du sol purement empiriques. En se plaçant dans un vrai contexte de simulation en aveugle, cette approche a également été appliquée à la simulation d'un séisme historique pyrénéen Mw = 6.1. Dans une seconde partie, afin de se rapprocher des connaissances actuelles sur la complexité de la cinématique d'une source sismique, nous nous appuyons sur un modèle de source étendue plus complexe, combinant des modèles cinématiques de sources composites à distribution fractale avec l'approche des FGEs pour produire des accélérogrammes synthétiques large-bande. Le potentiel de la méthode est testé sur une application au séisme de L'Aquila en fixant les paramètres d'entrée donnant la meilleure opportunité de reproduire les enregistrements du séisme cible. Cela a permis de produire des résultats très satisfaisants sur l'ensemble des paramètres des mouvements du sol analysés. Cette méthode de simulation apparaît comme étant très prometteuse pour la mise en oeuvre d'une méthodologie de simulation en aveugle, même si la principale difficulté réside dans la nécessité de définir la variabilité de nombreux paramètres d'entrée mal connus dans le cadre de la simulation d'un futur séisme.
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JOW-YEH, LEE, and 李宙燁. "The Effects of the Directivity of Sound Source for Chamber Music Acoustics." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/22768559571656751653.

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碩士
國立臺灣科技大學
建築系
91
Effects of directional source on room acoustics of rectangular chamber music halls were evaluated based on acoustical simulations using Odeon 5.0 software and field measurements. For computer simulation, all surfaces were plane and relatively large. Controlling variables included size, proportion, stage layout, side-wall layouts, seating layouts, directivity of the source, and aiming direction of the sound sources. Acoustical measure clarity (C80) and early strength (G80) was used. In a 365-seat hall and an 831-seat hall, the field study examined the effects of room width, detached side reflectors, and aiming directions. A dodecahedron speaker source was compared to a speaker having the directivity similar to a trumpet, which was aiming to the front, the left, the right, and the top (30° tilting towards the front). Based on computer simulation, it has been found that the effects of source directivity significantly increased with increasing room width and slightly increased with the increasing overall size. Inside a 5000-m3 hall with nearly 1:2 width-to-length ratio, turning a trumpet sound source between +45° and -45° making 2.5dB~3dB difference on both C80 and G80. The effect became significantly large when the room width was increased from 17 m to 21 m. Lateral reflectors were useful for enhancing high frequency G80 for seats that located opposite to the aiming direction but splayed front side-walls were useless because the reflections were directed towards the end of the hall instead of crossing to the other side of the hall. Subdividing the hall with a lower centerpiece and higher perimeters was effective in reducing the difference due to turning aiming directions. The field measurement agreed with the computer modeling regarding the importance of room width. The larger and wider hall (27-m wide) caused a much higher directional difference than the smaller and narrower hall (17-m wide). Detached side reflectors (6 m apart from each other) were effective in enhancing G80 measured in right side audience when the source was aiming to the left of the hall. The top-aiming source caused very little difference from the front-aiming source. This can be attributed to the low ceiling in the smaller hall and the low proscenium arch as well as suspended ceiling in the larger hall.
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Dabin, Jason Anthony. "A statistical ultra wideband indoor channel model and the effects of antenna directivity on multipath delay spread and path loss in ultra wideband indoor channels." Thesis, 2004. http://library1.njit.edu/etd/fromwebvoyage.cfm?id=njit-etd2004-047.

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Books on the topic "Directivity effects"

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Martin, R. M. Wake geometry effects on rotor blade-vortex interaction noise directivity. Hampton, Va: Langley Research Center, 1990.

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Knott, J. M. Beam size effects on the directivity patterns of laser generated ultrasound at a water/solid interface. Manchester: UMIST, 1996.

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Wake geometry effects on rotor blade-vortex interaction noise directivity. [Washington, DC]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Division, 1990.

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Book chapters on the topic "Directivity effects"

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Akkar, Sinan, and Saed Moghimi. "Implementation of Near-Fault Forward Directivity Effects in Seismic Design Codes." In Recent Advances in Earthquake Engineering in Europe, 183–201. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-75741-4_7.

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Wang, Linwei, Changjun Yu, and Yi Huang. "The Effect of Ground Screen System on High-Frequency Surface Wave Radar Antenna Directivity." In Lecture Notes in Electrical Engineering, 805–13. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-6504-1_97.

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Mimoglou, Petros, Ioannis N. Psycharis, and Ioannis M. Taflampas. "Determination of the Parameters of the Directivity Pulse Embedded in Near-Fault Ground Motions and Its Effect on Structural Response." In Computational Methods in Applied Sciences, 27–48. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-47798-5_2.

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Xie, Yuedong, Wuliang Yin, and Lijun Xu. "Investigation of Beam Features of Unidirectional Rayleigh Waves Electromagnetic Acoustic Transducers (EMATs) by a Wholly Analytical Solution." In Studies in Applied Electromagnetics and Mechanics. IOS Press, 2020. http://dx.doi.org/10.3233/saem200021.

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Electromagnetic acoustic transducers (EMATs) are widely used in industries due to its non-contact nature. This paper investigates the beam features of unidirectional Rayleigh waves EMATs, especially the effect of the wire length on beam directivity. A wholly analytical model is developed to calculate the Lorentz force distribution and ultrasound displacement distribution. The modelling results indicate that, compared to the coil consists of shorter wires, the coil consists of longer wires results in a narrower bandwidth of main lobe of unidirectional Rayleigh waves, which means the ultrasound are more concentrated. This study can be used for unidirectional Rayleigh waves EMATs design and optimization.
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Zhang, Yimin, Xin Li, and Moeness G. Amin. "Mobile Ad Hoc Networks Exploiting Multi-Beam Antennas." In Handbook on Advancements in Smart Antenna Technologies for Wireless Networks, 398–424. IGI Global, 2009. http://dx.doi.org/10.4018/978-1-59904-988-5.ch019.

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This chapter introduces the concept of multi-beam antenna (MBA) in mobile ad hoc networks and the recent advances in the research relevant to this topic. MBAs have been proposed to achieve concurrent communications with multiple neighboring nodes while they inherit the advantages of directional antennas, such as the high directivity and antenna gain. MBAs can be implemented in the forms of multiple fixed-beam directional antennas (MFBAs) and multi-channel smart antennas (MCSAs). The former either uses multiple predefined beams or selects multiple directional antennas and thus is relatively simple; the latter uses smart antenna techniques to dynamically form multiple adaptive beams and thereby provides more robust communication links to the neighboring nodes. The emphases of this chapter lie in the offerings and implementation techniques of MBAs, random-access scheduling for the contention resolution, effect of multipath propagation, and node throughput evaluation.
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Conference papers on the topic "Directivity effects"

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Cika, Arta, Justin P. Coon, and Sunwoo Kim. "Effects of directivity on wireless network complexity." In 2017 15th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt). IEEE, 2017. http://dx.doi.org/10.23919/wiopt.2017.7959937.

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Chase, James, Andres Garzon, and Dimitri Papamoschou. "Directivity Effects of Shaped Plumes from Plug Nozzles." In 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2013. http://dx.doi.org/10.2514/6.2013-8.

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Ahmadi-Shokouh, J., S. H. Jamali, S. Safavi-Naeini, and G. Z. Rafi. "Switch loss and antenna directivity effects on MIMO antenna selection." In 2008 Canadian Conference on Electrical and Computer Engineering - CCECE. IEEE, 2008. http://dx.doi.org/10.1109/ccece.2008.4564614.

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Xiang Zhou, Jian-ping Peng, Lin Luo, Ze-yong Wang, and Xiao-rong Gao. "Effects of directivity function on total focusing method imaging performance." In 2014 IEEE Far East Forum on Nondestructive Evaluation/Testing (FENDT). IEEE, 2014. http://dx.doi.org/10.1109/fendt.2014.6928232.

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Wang, Jianwu, Guoqi Ni, Bin Huang, and Zhi Yang. "Effects of random errors on directivity of amplitude-weighted line arrays." In 2010 International Conference on Microwave and Millimeter Wave Technology (ICMMT). IEEE, 2010. http://dx.doi.org/10.1109/icmmt.2010.5524987.

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Sarpotdar, Shekhar, Ganesh Raman, and Alan Cain. "Actuation Signal Directivity and Supply Pressure Effects in Powered Resonance Tubes." In 42nd AIAA Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2004. http://dx.doi.org/10.2514/6.2004-678.

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Huang, Jie, Yu Liu, Jian Sun, Wensheng Zhang, and Cheng-Xiang Wang. "Effects of antenna height and directivity on 60 GHz indoor channels." In 2017 IEEE/CIC International Conference on Communications in China (ICCC). IEEE, 2017. http://dx.doi.org/10.1109/iccchina.2017.8330423.

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Buyanov, Yury, Evgeny Balzovsky, Eduard Nekrasov, and Vladimir Koshelev. "Directivity Characteristics of an Ultrawideband Hybrid Offset Antenna in the 1–4 GHz Frequency Range." In 2020 7th International Congress on Energy Fluxes and Radiation Effects (EFRE). IEEE, 2020. http://dx.doi.org/10.1109/efre47760.2020.9242150.

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Hustedt, B., R. Clark, and M. Scherwath. "Source/Receiver Directivity Effects on Q Measurements from Surface Seismic Reflection Data." In 60th EAGE Conference and Exhibition. European Association of Geoscientists & Engineers, 1998. http://dx.doi.org/10.3997/2214-4609.201408282.

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Cheong, Cheolung, and Soogab Lee. "Effects of discontinuous boundary conditions on the directivity of sound from a piston." In 6th Aeroacoustics Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2000. http://dx.doi.org/10.2514/6.2000-2072.

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