Ultrasonic transmission through periodically perforated plates

Las estructuras periódicas macroscópicas han sido objeto de una intensa investigación durante las dos últimas décadas debido a su capacidad de imitar fenómenos ondulatorios que son inherentes a la escala atómica. Aunque las placas perforadas son estructuras muy comunes en acústica, éstas parecen guardar propiedades de transmisión de sonido inexploradas, cuyo estudio ha sido impulsado por el descubrimiento de la Transmisión Óptica Extraordinaria en láminas de metal perforadas con agujeros distribuidos periódicamente cuando interactúan con la luz. En el presente trabajo se muestra que las placas perforadas no sólo presentan máximos de transmisión total resonante y mínimos de la anomalía de Wood cuando los agujeros están distribuidos de forma periódica, sino también apantallamiento acústico extraordinario debido al cortocircuito hidrodinámico producido por el acoplamiento entre la placa y el fluido. También se detalla el rol de los parámetros geométricos de las placas perforadas en las características de transmisión, ilustrando diferentes estrategias para moldear el espectro de transmisión. La transmisión acústica a través de placas de aluminio con perforaciones regulares sumergidas en agua presenta una alta complejidad tanto a incidencia normal como cuando se varía el ángulo de incidencia del sonido. Aparecen ondas de superficie radiantes provenientes de la vibración de la placa, lo cual es demostrado usando un nuevo modelo teórico que incluye el acoplamiento elastoacústico completo. Gracias al estudio complementario de la transmisión y la propagación en placa de una placa fonónica sólido-sólido se retrata una perspectiva completa del efecto del acoplamiento. Como consecuencia directa, se observan fenómenos de plegamiento y bandas de propagación prohibida en modos tipo Scholte-Stoneley sin necesidad de corrugaciones o de agujeros. Finalmente, se comparan las propiedades de transmisión de agujeros individuales y redes de agujeros para luz, electrones y sonido analizando y comentando sus diferencias. Se ha encontrado que, aunque para la luz la red de agujeros en sí misma lleva a transmisiones del 100% y modos atrapados a la superficie, esto no se produce ni para electrones ni para sonido. En consecuencia, las resonancias del agujero constituyen el mecanismo clave que posibilita la existencia de fenómenos exóticos en sonido. Los resultados principales aquí mencionados son explicados de manera detallada y comentados sobre la base de datos teóricos y experimentales. El objetivo general de esta tesis es dilucidar por medios teóricos y experimentales los fenómenos físicos que se hayan involucrados en la transmisión acústica a través de placas perforadas. En este estudio se usa esencialmente el método de transmisión de ultrasonidos bajo el agua. Los modelos teóricos desarrollados tienen en cuenta la configuración experimental para poder establecer comparaciones precisas entre las medidas y los cálculos. Se toman en cuenta diversos factores que pueden modificar la transmisión de sonido a través de placas perforadas tales como: - La orientación de la onda incidente con respecto a la placa. .- Los parámetros geométricos que definen la placa, es decir, la distancia entre agujeros, el diámetro de los mismos y el espesor de la placa. .- Los parámetros elásticos relacionados con el contraste de impedancia entre el sólido y el fluido. .- El material contenido en los agujeros, de modo que se estudian no sólo placas fonónicas constituidas por un fluido y un sólido sino también aquellas formadas por dos sólidos distintos. Para el caso particular de una placa fonónica constituida por dos sólidos se emplea además una técnica para medir las vibraciones de la placa directamente en su superficie con el fin de complementar las medidas de transmisión de ultrasonidos. Desde una perspectiva teórica, el problema ha sido abordado para estructuras infinitas partiendo de diversas hipótesis.Estrada Beltrán, HA. (2011). Ultrasonic transmission through periodically perforated plates [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14119Palanci

CLOTH3D: Clothed 3D Humans

This work presents CLOTH3D, the first big scale synthetic dataset of 3D clothed human sequences. CLOTH3D contains a large variability on garment type, topology, shape, size, tightness and fabric. Clothes are simulated on top of thousands of different pose sequences and body shapes, generating realistic cloth dynamics. We provide the dataset with a generative model for cloth generation. We propose a Conditional Variational Auto-Encoder (CVAE) based on graph convolutions (GCVAE) to learn garment latent spaces. This allows for realistic generation of 3D garments on top of SMPL model for any pose and shape

Transient phenomena of polymer solutions

With the aid of a rotational viscometer, several transient phenomena were studied with different polymer solutions. In order to be acquainted with the operations of the rotational viscometer, viscosity measurements were made on polystyrene solution of a 7.14 wt. % NBS-2-35967 in a 35 - 65 mixture of aroclor and TCP, polyisobutylene (16.5% in mineral spirits), Indopol H-1900 (polyisobutylene) and 4.5% polyisobutylene in Primol 355. All these were done at a temperature of 77°F, except for Indopol H-1900 which was done at different temperatures. The results are listed in the section of tables and graphs. Viscosity was measured with a rotational viscometer. Its operational mechanism will be described in the chapter dealing with experimental equipment. Next the properties of a 4.5% polyisobutylene in Primol 355 was exclusively investigated in terms of shear stress versus rate of shear, recoverable shear at infinite time versus shear stress, displacement or flow history versus time and recoverable shear versus time as a function of shear stress. Having obtained the curves of displacement versus time and recoverable shear versus time of a 4.5% PIB solution and the 3% PIB solution available from previous experiments at Esso Research Center, the shear velocity profiles of displacement versus time and irreversible shear versus time was investigated. Recoverable shear (recoil measurements) was measured by a stop-load mechanism described in detail in later sections. Also investigated were a series of unpublished flow histories of a 3% PIB in Primol 355, beginning at time zero with the aid of a hi-speed camera. Having transformed the flow curves into shear curves, the phenomena in question being investigated is the existance of zero shear that occurs during the interval between .1 to .2 seconds for loads ranging between 5 and 500 grams. With the aid of a mathematical model and working in the area of complete elasticity, it was found that the zero shear is the result of two phenomena. These phenomena are the vibrations due to the string holding the weight and also due to the elasticity of the polymer solution. It was also found that the vibration due to the elastic property of the polymer solution had a very significant effect on the zero shear. The extent of that effect was also found to be a function of the load. The mathematical model used resulted in the following conclusion; the calculated inertial effects of the viscometer are much higher than the initially measured value, it predicts the zero shear phenomena, the spring constant for the polymer solution is a function of weight and it also gives an indication of the nature of the flow curves free of vibrational phenomena. The final results are graphs and tables describing viscosity measurements and transient phenomena occurring in the polymer solution

Integrated application of active controls (IAAC) technology to an advanced subsonic transport project. Conventional baseline configuration study

Characteristics of the U.S. domestic fleet were evaluated to determine the mission characteristics that would have the most impact on U. S. transport fuel use in the future. This resulted in selection of a 197-passenger (plus cargo), about 3710-km (2000 nmi) mission. The existing data base was reviewed and additional analysis was conducted as necessary to complete the technical descriptions. The resulting baseline configuration utilizes a double-lobe, but nearly circular, body with seven-abreast seating. External characteristics feature an 8.71 aspect ratio, 31.5-degree sweep wing, a T-tail empennage, and a dual CF6-6D2, wing-mounted engine arrangement. It provides for 22 LD-2 or 11 LD-3 containers plus bulk cargo in the lower lobe. Passenger/cargo loading, servicing provisions, taxi/takeoff speeds, and field length characteristics are all compatible with accepted airline operations and regulatory provisions. The baseline configuration construction uses conventional aluminum structure except for advanced aluminum alloys and a limited amount of graphite epoxy secondary structure. Modern systems are used, including advanced guidance, navigation, and controls which emphasize application of digital electronics and advanced displays

Surface nanostructuration and engineering by coarsening mechanisms

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 12-06-201

Advanced modelling of sports footwear

A need to reduce the number of design iterations, coupled with a requirement to reduce the weight of the new generation of TPU running shoes has lead to the use of finite element analysis (FE) within the athletic shoe industry. The collaborators in this research, adidas, were already using the technology, but only on individual parts, and on a reverse engineered basis. This thesis presents a thorough review into the materials used in athletic footwear, their application within running shoes and the methods of testing non-linear, highly deformable polymers and polymer foams. The fundamentals of the FE process are examined, along with a discussion of the current testing methods for shoes. The novelty in this work comes mainly from the comprehensive, logical progression through the modelling process as applied to this new area. Sample materials were tested, revealing new test methods. These were then analysed and converted for use in ABAQUS v6.5 which was the FE software used. The modelling of the sample materials, their tests, then shoe parts and midsole assemblies are discussed at length. At each stage the required complexities were added to the model, and these are detailed. This includes the import, conversion and repair of highly complex geometry, meshing techniques for this geometry, methods of building models of shoe assemblies and all relevant issues that arose from these processes. In addition, a shoe with an internal mechanism was modelled to assist in the design process. The effect of damage to shoe materials was also studied. Physical tests were carried out to verify all the FE models, and the results are presented. In addition, shoes taken from the end of the production line with the uppers attached were tested in order to compare the change in performance between the component parts and a finished product. The results of the modelling showed that was possible to construct and run full shoe assembliesw ithin a reasonablet ime. Fair prediction of the physical responseo f the assemblies was seen using material data taken directly from the sample data, but a method of correcting the initial error in the material test is presented which gives very good force/deflection results in TPU parts. A method of adjusting the entire assembly's material models is then presented, which improves the initial verification. In addition to force/deflection readings, digital image processing was used to monitor the structural response of the shoe during loading, and a set of structural metrics is put forward. The results of these indicated that while the shoe models were representing the cushioning response well, the shape of the shoe was not replicated, suggesting that the model in its present state would be unsuitable for use in some forms of test. Suggestions for improvement are made. Comparison of the structural metrics between shoe assemblies and production shoes suggests the possibility of a quantifiable metric for what would be considered a 'good' shoe. The repercussions of this are discussed in the conclusions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Broadband Dielectric Response in Hard and Soft PZT:Understanding Softening and Hardening Mechanisms

Lead zirconate titanate (Pb(Zr1-xTix)O3 or PZT) ferroelectric ceramics have been widely used in transducers, actuators, and sensors, since they posses high dielectric and piezoelectric properties with a relatively high temperature of operation. Commercially used PZT ceramics are always modified by different dopants and are divided into the "soft" (donor doped) and "hard" (acceptor doped) groups. Compared with the undoped composition, hard PZT often shows lower but more stable properties after ageing. In contrast, soft PZT shows higher properties and insensitivity to ageing. The difference in properties between the soft and hard PZT ceramics is rather large, even though the doping level is limited to a very low value (on the order of 1 mole %). The large difference of the physical properties between them mainly originates from the contributions from domain wall motion rather than properties of the crystal lattice. However, the mechanisms of hardening and softening are not well understood. In order to understand better the hardening and softening mechanisms, in this thesis the different contributions to the dielectric properties of soft and hard PZT ceramics are studied by means of a broadband dielectric spectroscopy from 10 mHz to 20 GHz. Properties at THz and infrared frequencies where only crystalline lattice contributes to the dielectric response were also investigated in collaboration with another group. In the frequency range below 20 GHz, the different contributions to the permittivity by domain wall motion were revealed in hard and soft materials. In order to correlate the properties to the microscopic structure of hard and soft PZT ceramics, the domain structures were also investigated by transmission electron microscopy. Piezoelectric spectroscopy was employed to help separating different contributions at frequencies below 100 Hz. The main results of this work are: The microwave dielectric dispersion of all PZT ceramics (including undoped, soft and hard PZT ceramics), which is characterized by a rapid decrease of the permittivity and a loss peak in the GHz frequency range, is contributed by both domain wall motion and piezoelectric grain resonances. These two mechanisms are separated by gradual poling of samples. The dispersion related to the domain wall motion appears at a higher frequency than the one related to grain resonance and constitutes the main contribution to the microwave dielectric properties of unpoled samples. Above the GHz frequency range, the dielectric properties of hard and soft PZT ceramics are rather close and approach the upper limit value of their intrinsic properties, which are identified by dielectric properties determined by THz dielectric spectrum. The contributions by domain wall motion make up more than 50% of the quasistatic dielectric properties (measured at 100 kHz) in all studied samples. Below GHz frequency range, another dielectric dispersion due to the domain wall creep, which manifests itself by a logarithmic decrease of permittivity with increasing frequency, is indentified in both soft and hard PZT ceramics in a relatively broad frequency region over at least eight decades. The difference of the dielectric properties between the hard and soft PZT mainly results from this logarithmic dispersion, since soft PZTs exhibit stronger logarithmic dispersion than hard PZTs. By controlling the doping kind and crystalline symmetry, the slope of the logarithmic function can be adjusted. Large values are observed in the system with disordered distribution of defect dipoles (soft, donor doped materials) while nearly zero slope could be observed in hard, acceptor doped materials with tetragonal structure with defect dipoles well aligned with polarization within domains. Rapid increase of both permittivity and loss below 1 Hz, which cannot be described by the logarithmic function, is observed in hard PZT ceramics. To interpret this behavior, results of dielectric spectroscopy were complemented by piezoelectric measurements in the frequency range from 10 mHz to 100 Hz. The absence of the strong dispersion in the piezoelectric properties and presence in the dielectric response strongly indicates that its origin is in charge transport (such as hopping conductivity) rather than in motion of domain walls. Nanodomains, observed in Fe3+-doped hard PZT with composition at morphotropic phase boundary do not lead to the high dielectric and piezoelectric properties, as would be expected from some theoretical models. Acceptor doping rapidly decreases the domain size in PZT ceramics with compositions in rhombohedral, tetragonal and MPB regions. This effect could not be interpreted by the decrease of the grain size according to the commonly assumed parabolic relationship between the domain size and grain size. The small domain size is rather related to the presence of oxygen vacancies which break continuity of polarization

Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015

This volume contains the full papers accepted for presentation at the ECCOMAS Thematic Conference on Multibody Dynamics 2015 held in the Barcelona School of Industrial Engineering, Universitat Politècnica de Catalunya, on June 29 - July 2, 2015. The ECCOMAS Thematic Conference on Multibody Dynamics is an international meeting held once every two years in a European country. Continuing the very successful series of past conferences that have been organized in Lisbon (2003), Madrid (2005), Milan (2007), Warsaw (2009), Brussels (2011) and Zagreb (2013); this edition will once again serve as a meeting point for the international researchers, scientists and experts from academia, research laboratories and industry working in the area of multibody dynamics. Applications are related to many fields of contemporary engineering, such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, mechatronic and autonomous systems, smart structures, biomechanical systems and nanotechnologies. The topics of the conference include, but are not restricted to: ● Formulations and Numerical Methods ● Efficient Methods and Real-Time Applications ● Flexible Multibody Dynamics ● Contact Dynamics and Constraints ● Multiphysics and Coupled Problems ● Control and Optimization ● Software Development and Computer Technology ● Aerospace and Maritime Applications ● Biomechanics ● Railroad Vehicle Dynamics ● Road Vehicle Dynamics ● Robotics ● Benchmark ProblemsPostprint (published version