Proyectos

La experiencia internacional (Israel, Holanda, España) muestra que la recarga artificial de acuíferos es una herramienta eficaz para lograr gestionar la cantidad y calidad del recurso hídrico considerando integralmente las fuentes superficiales, subterráneas y su interacción. La presente iniciativa tiene como propósito diseñar un piloto de Recarga artificial para el acuífero de Pan de Azúcar y Elqui Bajo. Esto significa seleccionar la localización óptima con criterios hidrogeológicos (capacidad de almacenamiento, niveles piezométricos, velocidad de recarga, transmisibilidad, modelo hidrogeológico de recarga, etc), hidrogeoquímicos (calidad del agua, interacción suelo-agua, factores antrópicos, etc), socio-económicos (salud de la población, productividad, empleo, etc) y ambientales (aspectos ambientales, impactos ambientales). Una vez seleccionada la localización, está será caracterizada. Para ello se utilizará información bibliográfica general y específica disponible. Parte importante de esta información ha sido generada por el equipo UCN que en los últimos años ha ejecutado proyectos estudiando los acuíferos costeros en la región. También se generará información complementaria, con campañas de caracterización y monitoreo, necesaria para la aplicación de los criterios establecidos. Con la información de caracterización se determinará la técnica de infiltración más adecuada a partir de criterios técnicos-científicos. Para esto se modelará hidrogeológicamente la efectividad en el corto, mediano y largo plazo de la infiltración definida. Finalmente, se realizará el diseño ingenieril a nivel de detalle de la planta piloto que permita la inyección artificial el acuífero.

Work on the open problem of proving existence of minimizers in nonlinear elasticity in the paradigmatic neoHookean model. Finite element simulations, modelling, and experiments for swelling of polymer gels bonded to rigid substrates. Finite element simulations, modelling, and asymptotic analysis for Schallamach waves in the detachment of thin hydrogels. Proof that the transition, in elastomers and ductile materials, from multiple independent spherical cavitation to the coalescence stage occurs when the size, in the deformed configuration, of the opened cavities is comparable to the distance, in the reference configuration, between the cavitation singularities.

Overview: We have recently observed that shear shock waves are generated and subsequently propagate in the brain under impact conditions that are quite general. For example, a 35g impact, which is in the concussive range, propagates nonlinearly in the brain and develops into a thin, destructive 300g shock front. This highly localized increase in acceleration suggests that shear shock waves are a fundamental mechanism for traumatic injuries in the brain and in soft tissue. These observations were made with ultrasonic methods that we have developed based on clutter reducing high frame-rate (10,000 images/second) imaging sequences and high sensitivity (better than 1 micrometer) motion tracking algorithms. This imaging method offers a unique combination of imaging speed, accuracy, and penetration that interrogates a spatiotemporal regime not accessible to other imaging modalities. On the other hand, the physics of nonlinear elastic waves in soft solids has been practically unexplored. In particular, just a few theoretical papers have addressed the generation of nonlinear surfaces waves in soft solids. None experimental research has reached to the complete observation of nonlinear surface wave in soft solids. Therefore, the physics of the propagation of nonlinear surfaces waves and its consequences on soft solid, presents many experimental, theoretical, and numerical opportunities for investigation. With applications in the biomechanics of injuries as well as in geophysics due to that most of the damage produced by an earthquake is due to surface waves because they spread energy more efficiently. Goals: The general objective of this proposal is to reveal the physics governing the propagation of nonlinear surface waves in soft solids. The origin of the nonlinearity in these waves is unclear. Few authors suggest that it comes only from a geometrical effect due to the definition of the nonlinear strain tensor. However, at increased amplitudes, we hypothesize that the material nonlinearity also should play a role. The effect of these two nonlinear components is unknown. It has been predicted that the nonlinearity might distort the wave profile producing discontinuities in the particle displacement velocity or acceleration. Until now, no experimental clues about the conditions and parameters that generate these discontinuities have been found. Another open question in this topic is related to the penetration depth. Surface wave typically penetrates few wavelengths within the surface of propagation. However, in soft solids, typical wavelength are in the order of centimeters, making the penetrating wave an important subject of study. The effect of the nonlinear distortion with depth is unknown and an aim of this proposal. Thus, here we propose to develop models, theory and experiments that elucidate this questions and give us a clear picture of the behavior of these waves in soft materials like gelatin. Methodology: Unlike compressional shocks in fluids, elastic waves, such as surface waves, are practically unexplored due to the experimental challenges associated with observing waves at depth in solids. Current observations of surface waves are confined only at the free surface and restricted only to Rayleigh waves. Surface waves in other interfaces such as solid-fluid or solid-solid have not been experimentally explored in soft solids yet. Advanced ultrasound imaging techniques implemented on a highly customized imaging platform designed for high frame-rate imaging will be used to characterize fundamental surface wave physics in homogeneous soft solids. These observations and characterizations of nonlinear surface waves will be achieved with a number of steps that integrate advancements in ultrasound imaging, advancement in algorithms that measure the deformation and advancements in modeling. The advancement on the visualization of displacements will be validated using a fringe projection profilometry system, based on a high frame rate camera. We will perform experiments in the linear regime to characterize attenuation and dispersion, which interact with the nonlinearity and therefore, have a significant impact on the resulting kinematic of the medium, due to their frequency dependent nature. Custom two-dimensional imaging sequences, designed for shock wave tracking, will be implemented for a dedicated Linear array transducer that has 128 elements and can reach a spatial resolution of 200 microns at very high frame-rate in the order of 10000 frames per second. This ultrasound technology does not exist until now in Chile. Expected results: The results of this proposal will elucidate the origin of the nonlinear response of soft materials for the surface waves. We expect that at sufficiently high amplitude the material nonlinearity will be expressed. Additionally, due to the distortions of the wave profile generated by the nonlinearity, we expect to observe discontinuous particle displacement, velocity and/or acceleration. These discontinuities will be classified as a new type of shock wave. We hope to see that this new type of shock wave propagates over a longer distance than the compressional shock or shear shock, principally due to that surface waves spread reducing its amplitude proportionally to the square root of the propagation distance instead of typical reduction proportional to the propagation distance observed in bulk waves. We also expect the shock waves associated with surface waves are more likely to produce fracture or catastrophic event in soft solids. In the context of linear wave propagation, we expect to measure the power laws that govern the frequency dependent attenuation and dispersion for surface waves. If successful, this research would suggest the nonlinear surface waves as a new mechanism for injury. In addition, this research could become a platform to test shock wave ideas that are very difficult to prove in compressional waves. Thus, it would serve as an analogous physical system to study shock waves in general.

Dislocations are at the source of plastic behavior of metals and alloys, yet it is very difficult to quantitatively study their behavior. In order to improve this situation, it is proposed to use their interaction with elastic waves as a nonintrusive probe. The long-term aim of the research presented in this proposal is to enable the development of ultrasound technology as a practical non-intrusive tool for the characterization of plastic behavior of materials. In recent years, proposers have shown, using Resonant Ultrasound Spectroscopy (RUS), that an increase of dislocation density in aluminum by a factor of 6 leads to a change for the speed of shear waves on the order of 1%, a quantity that can be measured with an accuracy on the order of 0.1%. They have also shown that local measurements of the speed of shear waves in aluminum under standard testing conditions in tension provide a quantitative, accurate, nonintrusive and continuous relation between dislocation density and externally applied stress, and that an increase in dislocation density by a factor of ten in copper and aluminum leads to an increase in the value of the (nonlinear) parameter that characterizes second harmonic generation by 20 to 60%. This proposal seeks to go one more step towards a practical implementation of the proposed ultrasonic testing tool for pieces in service. Materials of wide use in industry, 304L steel and TWIP steel, will be used. And in addition to bulk ultrasonic and shear waves, surface Rayleigh waves will be tested, in order to develop techniques that are useful when pieces in service have a geometry that does not lend itself to bulk wave measurement. Both linear (wave propagation velocity and attenuation) and nonlinear (second harmonic generation) acoustics measurements will be performed, using bulk and surface waves, ex situ after mechanical treatment, and in situ under standard testing conditions. In addition, dislocation density will be measured using X-ray diffraction (XRD) , using both the modified Warren-Averbach and Rietveld methods. Additional characterization will be performed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The expected result of the proposed research is a set of measurements that relate acoustics parameters to dislocation density in 304L and TWIP steels. The specific goal is that these measurements will provide a framework for the development of devices to nondestructively measure the dislocation density of pieces in service.

Overview: We have recently observed that shear shock waves are generated and subsequently propagate in the brain under impact conditions that are quite general. For example, a 35g impact, which is in the concussive range, propagates nonlinearly in the brain and develops into a thin, destructive 300g shock front. This highly localized increase in acceleration suggests that shear shock waves are a fundamental mechanism for traumatic injuries in the brain and in soft tissue. These observations were made with ultrasonic methods that we have developed based on clutter reducing high frame-rate (10,000 images/second) imaging sequences and high sensitivity (better than 1 micrometer) motion tracking algorithms. This imaging method offers a unique combination of imaging speed, accuracy, and penetration that interrogates a spatiotemporal regime not accessible to other imaging modalities. On the other hand, the physics of nonlinear elastic waves in soft solids has been practically unexplored. In particular, just a few theoretical papers have addressed the generation of nonlinear surfaces waves in soft solids. None experimental research has reached to the complete observation of nonlinear surface wave in soft solids. Therefore, the physics of the propagation of nonlinear surfaces waves and its consequences on soft solid, presents many experimental, theoretical, and numerical opportunities for investigation. With applications in the biomechanics of injuries as well as in geophysics due to that most of the damage produced by an earthquake is due to surface waves because they spread energy more efficiently. Goals: The general objective of this proposal is to reveal the physics governing the propagation of nonlinear surface waves in soft solids. The origin of the nonlinearity in these waves is unclear. Few authors suggest that it comes only from a geometrical effect due to the definition of the nonlinear strain tensor. However, at increased amplitudes, we hypothesize that the material nonlinearity also should play a role. The effect of these two nonlinear components is unknown. It has been predicted that the nonlinearity might distort the wave profile producing discontinuities in the particle displacement velocity or acceleration. Until now, no experimental clues about the conditions and parameters that generate these discontinuities have been found. Another open question in this topic is related to the penetration depth. Surface wave typically penetrates few wavelengths within the surface of propagation. However, in soft solids, typical wavelength are in the order of centimeters, making the penetrating wave an important subject of study. The effect of the nonlinear distortion with depth is unknown and an aim of this proposal. Thus, here we propose to develop models, theory and experiments that elucidate this questions and give us a clear picture of the behavior of these waves in soft materials like gelatin. Methodology: Unlike compressional shocks in fluids, elastic waves, such as surface waves, are practically unexplored due to the experimental challenges associated with observing waves at depth in solids. Current observations of surface waves are confined only at the free surface and restricted only to Rayleigh waves. Surface waves in other interfaces such as solid-fluid or solid-solid have not been experimentally explored in soft solids yet. Advanced ultrasound imaging techniques implemented on a highly customized imaging platform designed for high frame-rate imaging will be used to characterize fundamental surface wave physics in homogeneous soft solids. These observations and characterizations of nonlinear surface waves will be achieved with a number of steps that integrate advancements in ultrasound imaging, advancement in algorithms that measure the deformation and advancements in modeling. The advancement on the visualization of displacements will be validated using a fringe projection profilometry system, based on a high frame rate camera. We will perform experiments in the linear regime to characterize attenuation and dispersion, which interact with the nonlinearity and therefore, have a significant impact on the resulting kinematic of the medium, due to their frequency dependent nature. Custom two-dimensional imaging sequences, designed for shock wave tracking, will be implemented for a dedicated Linear array transducer that has 128 elements and can reach a spatial resolution of 200 microns at very high frame-rate in the order of 10000 frames per second. This ultrasound technology does not exist until now in Chile. Expected results: The results of this proposal will elucidate the origin of the nonlinear response of soft materials for the surface waves. We expect that at sufficiently high amplitude the material nonlinearity will be expressed. Additionally, due to the distortions of the wave profile generated by the nonlinearity, we expect to observe discontinuous particle displacement, velocity and/or acceleration. These discontinuities will be classified as a new type of shock wave. We hope to see that this new type of shock wave propagates over a longer distance than the compressional shock or shear shock, principally due to that surface waves spread reducing its amplitude proportionally to the square root of the propagation distance instead of typical reduction proportional to the propagation distance observed in bulk waves. We also expect the shock waves associated with surface waves are more likely to produce fracture or catastrophic event in soft solids. In the context of linear wave propagation, we expect to measure the power laws that govern the frequency dependent attenuation and dispersion for surface waves. If successful, this research would suggest the nonlinear surface waves as a new mechanism for injury. In addition, this research could become a platform to test shock wave ideas that are very difficult to prove in compressional waves. Thus, it would serve as an analogous physical system to study shock waves in general.