Acoustic noise reduction methods for the launch pad

[ES] Los niveles de presión acústica experimentados por las naves espaciales y las lanzaderas durante las fases iniciales del lanzamiento (ignición de motores y despegue) pueden ser muy significativos para estructuras ligeras y cargas externas y apéndices, como paneles solares y antenas. En este contexto, el fondo del canal de evacuación de gases actúa como un espejo desde el punto de vista acústico, y devuelve la energía liberada directamente al cohete y a las estructuras que transporta. Esta gran cantidad de energía puede poner en riesgo algunas misiones de lanzamiento, con las consecuencias económicas y de seguridad que ello conlleva. A pesar de esto, existe todavía poco conocimiento sobre las características de las fuentes y el comportamiento de las instalaciones de suelo en referencia a la dispersión, difusión y absorción del sonido. En este contexto se desarrollará el objetivo principal de esta Tesis, cuyo propósito es el diseño y optimización de un prototipo de sistema basado en un array de resonadores de Helmholtz para maximizar la absorción y dispersión del sonido y, por tanto, mitigar los niveles de presión sonora generados en estos eventos en el contexto aeroespacial. Los trabajos de esta Tesis se llevan a cabo en el marco del contrato Networking/Partnership Initiative de la Agencia Espacial Europea.[CA] Els nivells de pressió acústica experimentats pels vehicles espacials durant les fases inicials del llançament (ignició de motors i enlairament) són extremadament elevats i poden afectar significativament a estructures lleugeres transportades, com panells solars i antenes. L'intens soroll generat per les fonts primàries, el motor i el raig, es veu reforçat per la reflexió en el fons del canal d'evacuació de gasos, que actua com un mirall des del punt de vista acústic, i retorna l'energia alliberada directament al coet i a les estructures que transporta. Aquesta gran quantitat d'energia pot posar en risc algunes missions de llançament, amb les conseqüències econòmiques i de seguretat que això comporta. Tot i la rellevància d'aquest problema, el coneixement sobre les característiques de les fonts, el comportament de les instal·lacions de sòl en referència a la dispersió, difusió i absorció del so, i les possibles mesures per mitigar l'impacte és encara escàs. En aquest context es desenvoluparà l'objectiu principal d'aquesta Tesi, el propòsit de la qual és el disseny i optimització d'un prototip de sistema basat en una matriu de ressonadors de Helmholtz per maximitzar l'absorció i dispersió del so a nivell de terra i, d'aquesta manera, mitigar els nivells de pressió sonora generats en aquests esdeveniments en el context aeroespacial. Els treballs d'aquesta Tesi s'han dut a terme en el marc del contracte Networking/Partnership Initiative 441-2015 de l'Agència Espacial Europea.[EN] The sound pressure levels experienced by space vehicles during the initial stages of launch (engine ignition and lift-off) are extremely high and can significantly affect light transported structures, such as solar panels and antennas. The intense sound generated by the primary sources, the engine and the jet, is reinforced by the reflection at the bottom of the gas evacuation channel, which acts as a mirror from the acoustic point of view, and returns the energy released directly to the rocket and the structures it carries. This large amount of energy can put some launch missions at risk, with the economic and security consequences that this entails. Despite the relevance of this problem, knowledge about the characteristics of the sources, the behavior of ground facilities in reference to the dispersion, diffusion and absorption of sound, and the possible measures to mitigate the impact is still scarce. In this context, the main objective of this thesis will be developed. The purpose of this work is the design and optimization of a prototype system based on an array of Helmholtz resonators to maximize the absorption and dispersion of sound at ground level and, in this way, mitigate the sound pressure levels generated in these events in the aerospace context. The work of this thesis has been carried out within the framework of the Networking/Partnership Initiative contract 441-2015 of the European Space Agency.None of the work presented here could have been possible without the funding provided by the European Space Agency. In this institution, I want to specially thank Julián Santiago (who sadly passed away in December 2018) and Ivan Ngan, both from the Structures, Mechanisms and Materials Division, for their help to make this project possible.Herrero Durá, I. (2020). Acoustic noise reduction methods for the launch pad [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/146650TESI

Vibroacoustic effects of resonant sonic crystals in sound absorption

[EN] A resonant sonic crystal made of solid elastic clamped beams is experimentally analysed in this work. The sonic crystal studied in this work has three characteristics: (i) a low filling fraction, (ii) a high frequency Band Gap and (iii) resonant scatterers. Due to the properties (i) and (ii), the sonic crystal behaves as an equivalent fluid with acoustic properties very closed to ones of the air. This means that the crystal is almost impedance matched, being the crystal transparent to the incident waves. However, the resonant elements have a resonance frequency in the range analysed in this work, introducing an absorption peak due to the resonances produced by the vibroacoustic coupling. The two microphone transfer function method is used to measure the (complex) impedance and then to evaluate experimentally the absorption coefficient of the 2D SC made of a set of parallel solid beams in the low frequency regime.Authors ackowledge the support of the European Space Agency under the 441-2015 Co-Sponsored PhD "Acoustic Noise Reduction Methods for the Launch Pad"Herrero-Durá, I.; Picó Vila, R.; Sánchez Morcillo, VJ.; García-Raffi, LM.; Romero García, V. (2016). Vibroacoustic effects of resonant sonic crystals in sound absorption. Universidade do Porto. 1-7. http://hdl.handle.net/10251/181082S1

Acoustic behavior of the VEGA launch pad environment

[EN] The acoustic pressure levels experienced by the spacecraft and launchers during the lift-off is due among other factor by the reflection of the sound waves on the launch pad. The acoustic load distribution in the area of the launcher depends on the geometric, mechanical and acoustic characteristics of the ground facilities. This work is intended to study the acoustic environment of the launch pad. A numerical and experimental investigation is developed in order to study in the linear regime the acoustic behaviour of a subscale model of the VEGA's launch pad. The acoustic measurements are performed in an anechoic chamber using an electroacoustic source that emits incoherent noise, mimicking the real acoustic source. The acoustic pressure field is measured at different positions in front of the launch pad mock-up, in the area where the acoustic waves are reflected. Among the future perspectives of this work is to study and develop new methods for the mitigation of the sound pressure levels.Authors acknowledge the support of the European Space Agency under contract ¿Sonic Crystals For Noise Reduction At The Launch Pad¿ ESA ITT 1-7094 (ITI) and the 441-2015 Co-Sponsered PhD ¿Acoustic Reduction Methods for the Launch Pad¿. The work was supported by Spanish Ministry of Economy and Innovation (MINECO) and European Union FEDER through project FIS2015-65998-C2-2. Authors aknowledge Dhéric Mutel, Cyril Bernard and Clément Jost for their contribution to this workPicó Vila, R.; Herrero-Durá, I.; Sánchez Morcillo, VJ.; Salmerón-Contreras, LJ.; García-Raffi, LM. (2016). Acoustic behavior of the VEGA launch pad environment. Universidade do Porto. 1-6. http://hdl.handle.net/10251/181097S1

Sound absorption and diffusion by 2D arrays of Helmholtz resonators

[EN] We report a theoretical and experimental study of an array of Helmholtz resonators optimized to achieve both efficient sound absorption and diffusion. The analysis starts with a simplified 1D model where the plane wave approximation is used to design an array of resonators showing perfect absorption for a targeted range of frequencies. The absorption is optimized by tuning the geometry of the resonators, i.e., by tuning the viscothermal losses of each element. Experiments with the 1D array were performed in an impedance tube. The designed system is extended to 2D by periodically replicating the 1D array. The 2D system has been numerically modeled and experimentally tested in an anechoic chamber. It preserves the absorption properties of the 1D system and introduces efficient diffusion at higher frequencies due to the joint effect of resonances and multiple scattering inside the discrete 2D structure. The combined effect of sound absorption at low frequencies and sound diffusion at higher frequencies, may play a relevant role in the design of noise reduction systems for different applications.This research was funded by the European Space Agency under the Networking/Partnering Initiative (NPI) contract number 441-2015. In memoriam to Julián Santiago-Prowald, Senior Advisor for the Structures, Mechanisms and Materials Division of ESA, a great man that always gave us his tireless support. AC acknowledges financial support from Generalitat Valenciana through the grant APOSTD/2018/229. VRG acknowledges the financial support from RFI Le Mans Acoustique (Région Pays de la Loire) in the framework of the project HYPERMETA funded under the program Étoiles Montantes of the Région Pays de la Loire. Authors acknowledge the support of the European Space Agency under contract 441-2015 Co- Sponsored PhD ¿Acoustic Reduction Methods for the Launch Pad¿ and project TRP ESA AO/1-9479/18/NL/LvH ¿Launch Sound Level Reduction¿. This article is based upon work from COST Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology).Herrero-Durá, I.; Cebrecos, A.; Picó Vila, R.; Romero-García, V.; García-Raffi, LM.; Sánchez Morcillo, VJ. (2020). Sound absorption and diffusion by 2D arrays of Helmholtz resonators. Applied Sciences. 10(5):1-15. https://doi.org/10.3390/app10051690S115105Sigalas, M. M., & Economou, E. N. (1992). Elastic and acoustic wave band structure. Journal of Sound and Vibration, 158(2), 377-382. doi:10.1016/0022-460x(92)90059-7Matlack, K. H., Bauhofer, A., Krödel, S., Palermo, A., & Daraio, C. (2016). Composite 3D-printed metastructures for low-frequency and broadband vibration absorption. 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The finite-element time-domain method for elastic band-structure calculations. Computer Physics Communications, 238, 77-87. doi:10.1016/j.cpc.2018.12.016Cebrecos, A., Romero-García, V., & Groby, J. (2019). Complex Dispersion Relation Recovery from 2D Periodic Resonant Systems of Finite Size. Applied Sciences, 9(3), 478. doi:10.3390/app9030478Hussein, M. I., Leamy, M. J., & Ruzzene, M. (2014). Dynamics of Phononic Materials and Structures: Historical Origins, Recent Progress, and Future Outlook. Applied Mechanics Reviews, 66(4). doi:10.1115/1.4026911Sanchez-Perez, J. V., Rubio, C., Martinez-Sala, R., Sanchez-Grandia, R., & Gomez, V. (2002). Acoustic barriers based on periodic arrays of scatterers. Applied Physics Letters, 81(27), 5240-5242. doi:10.1063/1.1533112Martínez-Sala, R., Rubio, C., García-Raffi, L. M., Sánchez-Pérez, J. V., Sánchez-Pérez, E. A., & Llinares, J. (2006). Control of noise by trees arranged like sonic crystals. Journal of Sound and Vibration, 291(1-2), 100-106. doi:10.1016/j.jsv.2005.05.030Garcia-Raffi, L. M., Salmerón-Contreras, L. J., Herrero-Durá, I., Picó, R., Redondo, J., Sánchez-Morcillo, V. J., … Romero-García, V. (2018). Broadband reduction of the specular reflections by using sonic crystals: A proof of concept for noise mitigation in aerospace applications. Aerospace Science and Technology, 73, 300-308. doi:10.1016/j.ast.2017.11.048Sanchez-Perez, J. V., Castineira-Ibanez, S., Romero-Garcia, V., & Garcia-Raffi, L. M. (2015). PERIODIC SYSTEMS AS ROAD TRAFFIC NOISE REDUCING DEVICES: PROTOTYPE AND STANDARDIZATION. Environmental Engineering and Management Journal, 14(12), 2759-2769. doi:10.30638/eemj.2015.293Kandula, M. (2009). Broadband shock noise reduction in turbulent jets by water injection. Applied Acoustics, 70(7), 1009-1014. doi:10.1016/j.apacoust.2008.12.001Liu, Z., Zhang, X., Mao, Y., Zhu, Y. Y., Yang, Z., Chan, C. T., & Sheng, P. (2000). Locally Resonant Sonic Materials. Science, 289(5485), 1734-1736. doi:10.1126/science.289.5485.1734Fang, N., Xi, D., Xu, J., Ambati, M., Srituravanich, W., Sun, C., & Zhang, X. (2006). Ultrasonic metamaterials with negative modulus. Nature Materials, 5(6), 452-456. doi:10.1038/nmat1644Sugimoto, N., & Horioka, T. (1995). Dispersion characteristics of sound waves in a tunnel with an array of Helmholtz resonators. The Journal of the Acoustical Society of America, 97(3), 1446-1459. doi:10.1121/1.412085Theocharis, G., Richoux, O., García, V. R., Merkel, A., & Tournat, V. (2014). Limits of slow sound propagation and transparency in lossy, locally resonant periodic structures. New Journal of Physics, 16(9), 093017. doi:10.1088/1367-2630/16/9/093017Jiménez, N., Cox, T. J., Romero-García, V., & Groby, J.-P. (2017). Metadiffusers: Deep-subwavelength sound diffusers. Scientific Reports, 7(1). doi:10.1038/s41598-017-05710-5Ballestero, E., Jiménez, N., Groby, J.-P., Dance, S., Aygun, H., & Romero-García, V. (2019). Experimental validation of deep-subwavelength diffusion by acoustic metadiffusers. Applied Physics Letters, 115(8), 081901. doi:10.1063/1.5114877Romero-García, V., Sánchez-Pérez, J. V., & Garcia-Raffi, L. M. (2011). Tunable wideband bandstop acoustic filter based on two-dimensional multiphysical phenomena periodic systems. Journal of Applied Physics, 110(1), 014904. doi:10.1063/1.3599886Lagarrigue, C., Groby, J. P., & Tournat, V. (2013). Sustainable sonic crystal made of resonating bamboo rods. The Journal of the Acoustical Society of America, 133(1), 247-254. doi:10.1121/1.4769783Krynkin, A., Umnova, O., Yung Boon Chong, A., Taherzadeh, S., & Attenborough, K. (2010). Predictions and measurements of sound transmission through a periodic array of elastic shells in air. The Journal of the Acoustical Society of America, 128(6), 3496-3506. doi:10.1121/1.3506342Koussa, F., Defrance, J., Jean, P., & Blanc-Benon, P. (2013). Acoustical Efficiency of a Sonic Crystal Assisted Noise Barrier. Acta Acustica united with Acustica, 99(3), 399-409. doi:10.3813/aaa.918621Castiñeira-Ibáñez, S., Romero-García, V., Sánchez-Pérez, J. V., & Garcia-Raffi, L. M. (2010). Overlapping of acoustic bandgaps using fractal geometries. EPL (Europhysics Letters), 92(2), 24007. doi:10.1209/0295-5075/92/24007García-Chocano, V. M., Cabrera, S., & Sánchez-Dehesa, J. (2012). Broadband sound absorption by lattices of microperforated cylindrical shells. Applied Physics Letters, 101(18), 184101. doi:10.1063/1.4764560Lardeau, A., Groby, J.-P., & Romero-García, V. (2016). Broadband Transmission Loss Using the Overlap of Resonances in 3D Sonic Crystals. Crystals, 6(5), 51. doi:10.3390/cryst6050051Cavalieri, T., Cebrecos, A., Groby, J.-P., Chaufour, C., & Romero-García, V. (2019). Three-dimensional multiresonant lossy sonic crystal for broadband acoustic attenuation: Application to train noise reduction. Applied Acoustics, 146, 1-8. doi:10.1016/j.apacoust.2018.10.020Dimitrijević, S. M., García-Chocano, V. M., Cervera, F., Roth, E., & Sánchez-Dehesa, J. (2019). Sound Insulation and Reflection Properties of Sonic Crystal Barrier Based on Micro-Perforated Cylinders. Materials, 12(17), 2806. doi:10.3390/ma12172806Stinson, M. R. (1991). The propagation of plane sound waves in narrow and wide circular tubes, and generalization to uniform tubes of arbitrary cross‐sectional shape. The Journal of the Acoustical Society of America, 89(2), 550-558. doi:10.1121/1.400379Duclos, A., Lafarge, D., & Pagneux, V. (2009). Transmission of acoustic waves through 2D phononic crystal: visco-thermal and multiple scattering effects. The European Physical Journal Applied Physics, 45(1), 11302. doi:10.1051/epjap:2008203Romero-García, V., Theocharis, G., Richoux, O., & Pagneux, V. (2016). Use of complex frequency plane to design broadband and sub-wavelength absorbers. The Journal of the Acoustical Society of America, 139(6), 3395-3403. doi:10.1121/1.4950708Romero-García, V., Theocharis, G., Richoux, O., Merkel, A., Tournat, V., & Pagneux, V. (2016). Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators. Scientific Reports, 6(1). doi:10.1038/srep19519Jiménez, N., Huang, W., Romero-García, V., Pagneux, V., & Groby, J.-P. (2016). Ultra-thin metamaterial for perfect and quasi-omnidirectional sound absorption. Applied Physics Letters, 109(12), 121902. doi:10.1063/1.4962328Jiménez, N., Romero-García, V., Pagneux, V., & Groby, J.-P. (2017). Quasiperfect absorption by subwavelength acoustic panels in transmission using accumulation of resonances due to slow sound. Physical Review B, 95(1). doi:10.1103/physrevb.95.014205Jiménez, N., Romero-García, V., Pagneux, V., & Groby, J.-P. (2017). Rainbow-trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems. Scientific Reports, 7(1). doi:10.1038/s41598-017-13706-4Merkel, A., Theocharis, G., Richoux, O., Romero-García, V., & Pagneux, V. (2015). Control of acoustic absorption in one-dimensional scattering by resonant scatterers. Applied Physics Letters, 107(24), 244102. doi:10.1063/1.4938121Kergomard, J., & Garcia, A. (1987). Simple discontinuities in acoustic waveguides at low frequencies: Critical analysis and formulae. Journal of Sound and Vibration, 114(3), 465-479. doi:10.1016/s0022-460x(87)80017-2Sánchez-Dehesa, J., Garcia-Chocano, V. M., Torrent, D., Cervera, F., Cabrera, S., & Simon, F. (2011). Noise control by sonic crystal barriers made of recycled materials. The Journal of the Acoustical Society of America, 129(3), 1173-1183. doi:10.1121/1.3531815Christensen, J., Romero-García, V., Picó, R., Cebrecos, A., de Abajo, F. J. G., Mortensen, N. A., … Sánchez-Morcillo, V. J. (2014). Extraordinary absorption of sound in porous lamella-crystals. 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Advances in the Monitoring of Algal Blooms by Remote Sensing: A Bibliometric Analysis

[EN] Since remote sensing of ocean colour began in 1978, several ocean-colour sensors have been launched to measure ocean properties. These measures have been applied to study water quality, and they specifically can be used to study algal blooms. Blooms are a natural phenomenon that, due to anthropogenic activities, appear to have increased in frequency, intensity, and geographic distribution. This paper aims to provide a systematic analysis of research on remote sensing of algal blooms during 1999-2019 via bibliometric technique. This study aims to reveal the limitations of current studies to analyse climatic variability effect. A total of 1292 peer-reviewed articles published between January 1999 and December 2019 were collected. We read all the literature individually to build a database. The number of publications increased since 2004 and reached the maximum value of 128 in 2014. The publications originated from 47 countries, but the number of papers published from the top 10 countries accounted for 77% of the total publications. To be able to distinguish between climate variability and changes of anthropogenic origin for a specific variable is necessary to define the baseline. However, long-term monitoring programs of phytoplankton are very scarce; only 1% of the articles included in this study analysed at least three decades and most of the existing algal blooms studies are based on sporadic sampling and short-term research programs.Sebastiá-Frasquet, M.; Aguilar-Maldonado, JA.; Herrero-Durá, I.; Santamaría-Del-Ángel, E.; Morell-Monzó, S.; Estornell Cremades, J. (2020). Advances in the Monitoring of Algal Blooms by Remote Sensing: A Bibliometric Analysis. Applied Sciences. 10(21). https://doi.org/10.3390/app10217877102

Absorción sonora en cristales de sonido: aplicación en el lanzamiento de cohetes espaciales

[EN] The high acoustic pressure levels experienced by spacecrafts and launchers during the lift-off are due, among other factors, to the reflection of the sound waves in the launch pad. We propose in this work the use of sonic crystals in the launch pad, with the aim of reducing the effect of vibrations induced by the shock wave generated during the lift-off of the space vehicle. The effect of viscothermal losses in sonic crystals in sound absorption during the first stages of the rocket launch is studied. For this purpose, this kind of losses are modelled considering the sonic crystal as a rigid perforated panel and proposing an specific configuration for its placement in the launch pad.[ES] Los elevados niveles de presión acústica experimentados por cohetes espaciales y lanzaderas durante el despegue son debidos, entre otros factores, a la reflexión de las ondas de sonido en la plataforma de lanzamiento. Se propone el uso de cristales de sonido en la base de lanzamiento para reducir el efecto de las vibraciones inducidas por la onda de choque generada en el despegue del vehículo espacial. En este trabajo se estudia el efecto de las pérdidas viscotérmicas en cristales de sonido en la absorción del sonido durante las primeras fases del lanzamiento de cohetes espaciales. Para ello, se modelan este tipo de pérdidas considerando el cristal de sonido como un panel rígido perforado y proponiendo una configuración específica para su ubicación en la base de lanzamiento.Los autores agradecen el apoyo de European Space Agency (ESA) a través del doctorando cofinanciado 441- 2015 «Acoustic Noise Reduction Methods for the Launch Pad», el Ministerio de Economía y Competitividad a través del Proyecto Coordinado «Ondas de luz y sonido en cristales, medios estructurados y metamateriales», y la Conselleria de Educación, Investigación, Cultura y Deporte a través del Proyecto AICO/2016/060.Herrero Durá, I.; Picó Vila, R.; Sánchez Morcillo, VJ.; García Raffi, LM.; Romero García, V. (2017). Absorción sonora en cristales de sonido: aplicación en el lanzamiento de cohetes espaciales. REVISTA DE ACÚSTICA. 48(1):12-16. http://hdl.handle.net/10251/89684S121648

Atenuación del sonido mediante una distribución periódica de capas de agua pulverizada

[EN] In this experimental study the attenuation properties of the sound transmitted through a multilayer structure is analyzed. The layers consist of a saturated gas-vapordroplet suspension with a known size distribution. For this purpose, a water injection system has been designed to study the sound propagation through the system. To understand this phenomenon, the dependence of the sound propagation with the most significant parameters such as the droplet size, the spacing between nozzles and the pressure and flow of water in the system, is discussed.[ES] En este trabajo se presenta un estudio experimental en el que se analizan las propiedades de atenuación del sonido transmitido a través de una estructura multicapa, en la que cada uno de los elementos consiste en una lámina formada por gotas de agua con una distribución de tamaños alrededor de un valor medio. Para ello, se ha diseñado un sistema de inyección de agua que permite estudiar la propagación del sonido a través de tres capas de suspensión saturada de gas y gotas. Para comprender este fenómeno se analizará la dependencia del mismo con los parámetros más significativos del problema como son el tamaño de gota, la separación entre dispersores, la presión y el caudal de agua en el sistema de inyección.Herrero Durá, I.; Zaragozá Dolz, JJ.; Picó Vila, R.; Sánchez Morcillo, VJ.; García-Raffi, LM. (2015). Atenuación del sonido mediante una distribución periódica de capas de agua pulverizada. Revista de Acústica. 46(1-2):5-11. http://hdl.handle.net/10251/63635S511461-

Reflection of sound by Sonic Crystals: an application to the aerospace engineering

[EN] From the acoustical point of view one of the most extreme events is the lift-off of a rocket. In such events, an enormous amount of energy is liberated in the form of acoustic waves that are reflected in the launch pad, coming back over the rocket and affecting both the rocket and the load contained in the fairing. Here we propose a possible solution to reduce the sound pressure level in the area of the spacecraft-launcher: placing structures based on Sonic Crystals (SCs) at the launch pad to control waves reflecting on it. In this work preliminary reults, in linear regime and without considering dissipation, about the use of SCs to control the reflected waves in a broadband range of frequencies are presented. This proof of concept is experimentally tested in a sub-scale system, that works at ultrasonic frequencies in water. Different types of SCs and different geometries of the reflecting backing are tested. In particular, geometries that mimic that of the VEGA's launch pad of the European Space Agency (ESA).Authors acknowledge the support of the European Space Agency under contract "Sonic Crystals For Noise Reduction At The Launch Pad" ESA ITT 1-7094 (ITI) and the 441-2015 Co-Sponsored PhD "Acoustic Reduction Methods for the Launch Pad". The work was supported by Spanish Ministry of Economy and Innovation (MINECO) and European Union FEDER through project FIS2015-65998-C2-2García-Raffi, LM.; Salmerón-Contreras, LJ.; Herrero-Durá, I.; Picó Vila, R.; Redondo, J.; Sánchez Morcillo, VJ.; Cebrecos, A.... (2016). Reflection of sound by Sonic Crystals: an application to the aerospace engineering. Universidade do Porto. 1-10. http://hdl.handle.net/10251/181078S11

Broadband reduction of the specular reflections by using sonic crystals: A proof of concept for noise mitigation in aerospace applications

[EN] The broadband reduction of the specular reflections by sonic crystals (SCs) is theoretically and experimentally reported in this work. The analysed system consists of a sound source radiating a SC made of acoustically rigid scatterers embedded in water partially covering an open cavity. By comparison with a reference flat reflector, we observe that reflected waves spread in space as a consequence of the spatially modulated properties of the SC. Moreover, due to the different working frequency ranges of the SC a significant noise reduction is produced in a broadband region. Therefore, due to the spreading of the reflected waves, the system produces a broadband noise reduction in the area of the source. In particular, the noise reduction is close to 2 dB for the two octaves emitted by our source, which represents a decrease of 37% of the acoustic energy. The results shown in this work constitute a proof of concept for the use of SCs as broadband-noise reduction systems at the launch pad. An approach to the geometry of the Vega launch vehicle the European Space Agency is proposed and the limitations of the study are discussed. (C) 2017 Elsevier Masson SAS. All rights reserved.Authors acknowledge the support of the European Space Agency under contract "Sonic Crystals For Noise Reduction At The Launch Pad", ESA ITT 1-7094 (ITI) and the 441-2015 Co-Sponsored PhD "Acoustic Reduction Methods for the Launch Pad". The work was supported by Spanish Ministry of Economy and Innovation (MINECO) and European Union FEDER through project FIS2015-65998-C2-1 and FIS2015-65998-C2-2.García-Raffi, LM.; Salmerón-Contreras, L.; Herrero-Durá, I.; Picó Vila, R.; Redondo, J.; Sánchez Morcillo, VJ.; Staliunas, K.... (2018). Broadband reduction of the specular reflections by using sonic crystals: A proof of concept for noise mitigation in aerospace applications. Aerospace Science and Technology. 73:300-308. https://doi.org/10.1016/j.ast.2017.11.048S3003087

Aplicación de imágenes QuickBird al estudio de praderas submarinas de Posidonia oceanica en Denia

Herrero Durá, I. (2012). Aplicación de imágenes QuickBird al estudio de praderas submarinas de Posidonia oceanica en Denia. Universitat Politècnica de València. http://hdl.handle.net/10251/15276Archivo delegad