205 research outputs found
Three-dimensional formulation of a strain-based geometrically nonlinear piezoelectric beam for energy harvesting
No full textIn this paper, the authors introduce a model of a strain-based geometrically nonlinear piezoelectric beam for modeling energy harvesters. A nonlinear shear-underfomable 3-D Rayleigh’s beam theory is used to model the displacement fields and can be considered as an interesting alternative to linear and highly nonlinear models commonly presented in the literature. The nonlinearities are introduced to reproduce the behavior of the flexible structure, since moderate to large displacements can occur in response of external loading conditions. The finite element method is used to model the piezolaminated bimorph configuration. Each finite element consists of two piezoelectric energy harvesters embedded or perfectly bonded to an elastic substrate. The electromechanical coupling includes axial and flexural effects as well as additional term that comes from the nonlinearity incorporated into the strain tensor. Additionally, the authors explore briefly two topics for linear harvesters: the influence of the electric domain on the structural properties and, the performance of the harvester near resonance in term of electric power output of a purely resistive network. As a validation case, a cantilevered piezoelectric energy harvester under base excitation is modeled. Alongside, the response to gust of a harvester embedded in a wing structure is analyzed.Fil: Beltramo, Emmanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Balachandran, Balakumar. University of Maryland; Estados UnidosFil: Preidikman, Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin
Computational dynamics of flapping wings in hover flight: A co-simulation strategy
No full textA co-simulation strategy for modeling the unsteady dynamics of flying insects and small birds as well as biologically inspired flapping-wing micro-air-vehicles is developed in this work. In particular, the dynamic system under study is partitioned in two subsystems (the structural model and the aerodynamic model) that exchange information in a strong way. The vehicle or insect system is modeled as a collection of rigid bodies and lifting surfaces that can undergo deformations such as spanwise twisting, in-plane bending, out-of-plane bending, and an arbitrary combination of these deformation mechanisms. To account for the loads associated with the airflow, an aerodynamic model based on an extended version of the unsteady vortex-lattice method is used. The motion equations are integrated by using a fourth-order predictor-corrector method along with a procedure to stabilize the solution of the resulting differential-algebraic equations. The numerical results obtained for the unsteady lift and dynamics of a fruit fly in free hover flight are found to be in close agreement with prior experimental results reported in the literature. Furthermore, the inclusion of an adequate wing deformation pattern results in an increase of the lift force compared with that of a rigid wing surface, pointing to the importance of wing flexibility on aerodynamic performance. From the findings reported in this paper, it is believed that the numerical simulation framework presented here could serve as a computational tool for further studies of flying insects and micro-air-vehicles.Fil: Roccia, Bruno Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; ArgentinaFil: Preidikman, Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; ArgentinaFil: Balachandran, Balakumar. University of Maryland; Estados Unido
Comparison of aerodynamic models for estimating loads on flapping wings
No full textEn este trabajo, distintos modelos aerodinámicos derivados del Método de Red de Vórtices Inestacionario (UVLM) se comparan en términos de la estimación de las cargas aerodinámicas produci- das por una sección de un ala batiente. El UVLM permite describir la evolución de las estelas vorticosas generadas por los cuerpos y en consecuencia, determinar la influencia de las mismas sobre las cargas aerodinámicas. Para tener en cuenta la influencia del vórtice de borde de ataque observado experimen- talmente, se introduce una modificación ad hoc de la fuerza resultante aerodinámica. Esta modificación es una generalización de la analogía de la succión de borde de ataque que elude la necesidad de mo- delar explícitamente la separación de flujo desde el borde de ataque. Las predicciones de los modelos son comparadas con valores experimentales y con resultados de simulaciones de dinámica de fluidos computacional (CFD) disponibles en la literatura. Se observa que, en general, la modificación de la carga aerodinámica mejora la correlación entre las predicciones de los modelos y los resultados experimentales.In this effort, different aerodynamic models derived from the Unsteady Vortex Lattice Method (UVLM) are compared in terms of the estimated aerodynamic loads produced by a flapping wing section. The UVLM can describe the evolution of the vortical wakes left behind by immersed bodies; therefore, it allows to determine their influence on the aerodynamic loads. To account for the influence of the experimentally observed leading edge vortex (delayed stall mechanism), an ad hoc modification of the aerodynamic force is introduced. This modification is a generalization of the leading edge suction analogy, which avoids the need to explicitly model the flow separation from the leading edge. The predictions of the models are compared with experimental data and with CFD simulation results available in the literature. It is observed that, in general, the modification of the aerodynamic load improves the correlation between the predictions of the models and the experimental results.Fil: Valdez, Marcelo Federico. Universidad Nacional de Salta. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; ArgentinaFil: Balachandran, Balakumar. University of Maryland College Park; Estados UnidosFil: Preidikman, Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin
Fast multipole accelerated unsteady vortex lattice method based computations
No full textThe authors present an accelerated aerodynamic computational model derived from the integration of the fast multipole method (FMM) with the unsteady vortex lattice method (UVLM) based aerodynamic model. It is determined that the performance of this computational model depends on the tuning of some FMM parameters and that there is a tradeoff between the computational speed and the accuracy of the computed loads. This tradeoff is examined by varying the truncation number, the order of the Gauss-Legendre quadrature, and the clustering parameter for the wake velocity calculations. Results of the computational cost reduction study achieved through the accelerated aerodynamic simulator are reported for a planar, rectangular lifting surface with a high aspect ratio. The computational approach presented in this paper is the first in the literature wherein the FMM has been implemented for an UVLM-based nonlinear, unsteady aerodynamic simulator. The approach has broad applicability for the study of aerodynamic and aeroelastic responses of aircraft systems and related decision support systems in dynamic data-driven application systems.Fil: Kebbie-Anthony, Abu. University of Maryland; Estados UnidosFil: Gumerov, Nail A.. University of Maryland; Estados UnidosFil: Preidikman, Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Balachandran, Balakumar. University of Maryland; Estados UnidosFil: Azarm, Shapour. University of Maryland; Estados Unido
Active Control of Sound Transmission Into Three-Dimensional Enclosures
No full textThe aim of this dissertation work is to understand active control of sound fields inside a three-dimensional rectangular enclosure into which noise is transmitted through a flexible boundary. To this end, analytical and numerical studies have been conducted. In the modeling efforts, a spherical wave excitation, which is generated by a noise source located in the near field of the flexible panel, is considered. Piezoelectric patches, which are bonded symmetrically to the top and bottom surfaces of the panel, are used as actuators. Microphones located inside and outside the enclosure serve as pressure sensors. The efforts account for panel interactions with both the external sound field and the enclosed sound field, and this feature makes it appealing for model-based active control schemes.
The feasibility of implementing two zero spillover schemes for active structural-acoustic control systems has been studied through analysis and experiments. These schemes have been developed to ensure that spillover does not occur outside the control bandwidth. The numerical results are found to be in good agreement with the corresponding experimental observations; attenuations ranging up to 18.1 dB are experimentally obtained for narrowband disturbances and an attenuation of 8.3 dB is obtained for broadband excitation in the frequency range of 40 Hz £ f £ 230 Hz.
The following contributions have resulted from this work: i) an analytical model capable of predicting the external pressure fields due to both the noise source and structural?acoustic interactions and that accounts for the general case of spherical wave propagation, ii) development of zero spillover, active structural-acoustic control schemes for controlling three?dimensional sound fields, and iii) a new relaxed zero spillover control scheme to ensure that the controlled response is bounded over the entire frequency range
Classification of a family of Lorenz knots with reducible symbolic sequences
No full textBased on symbolic dynamics of Lorenz maps, we prove that,
provided one conjecture due to Morton is true, then a countable family
of Lorenz knots associated to orbits of points in the renormalization
intervals of Lorenz maps are hyperbolic. This countable family contains
some of the hyperbolic Lorenz knots listed by J. Birman and I. Kofman
Nonlinear Oscillations of a Bistable Composite Shell: Experimental Studies
No full textThe dynamics of a cantilever bistable composite shell is investigated in the paper. The shell shape is derived from a region of a cone surface and is composed of eight composite layers. The proposed shell’s geometry and the asymmetric configurations of the layers give rise to the structure with bistability. A prototype of the shell is tested experimentally to detect nonlinear dynamic phenomena in the vicinity of each equilibrium point (in-well dynamics) and to study global (cross-well) oscillations. The experimental campaign shows strong softening resonance characteristics around I-shape and almost linear resonance curves for C-shape. Upon increasing the amplitude of excitation reversible snap-through and nonlinear chaotic oscillations are observed
DISTRIBUTED SENSING FOR FLEXIBLE STRUCTURES USING A FIBER OPTIC SENSOR SYSTEM
No full textIn this dissertation, a framework is developed and demonstrated for the use of a new shape measurement system consisting of fiber Bragg grating (FBG) based strain sensors, a shape determination algorithm based on Frenet frames, and a signal processing algorithm based on modal analysis techniques. The system is experimentally validated by using a long slender, aluminum cantilever structure (65.625"x2.0"x0.125") with eight serially multiplexed FBG sensors. The multiplexed FBG sensors measure the bending strain distribution along the cantilever structure, and this distribution is used to calculate the dynamic shape of the structure forced by a base excitation. The structural shape data is processed by using modal analysis techniques to determine the modal coefficients and the associated spatial modes that best represent the structure's vibration. The results obtained for the modal coefficients are found to compare well with results of Fourier transform analysis of signals recorded over time. Analysis by using the shape algorithm developed herein demonstrates the effectiveness of using a Frenet frame-based technique to determine the shape of the structure from recorded strain data. Sources of error due to factors such as the number of sensors and Taylor series approximation in the shape algorithm are examined.
The methodology discussed in this dissertation allows both static and dynamic monitoring of structural shape characteristics. This type of real-time analysis may be useful for applications in structural health monitoring where changes in the modal coefficients may lead to indications of damage to the structure and in applications such as sonar arrays and aircraft wings where knowledge of a structure's shape can yield improved results
Computational study on aerodynamically coupled piezoelectric harvesters
No full textIn this work, the authors present a two-dimensional computational model for predicting the aeroelastic response as well as the output power of vertically arranged harvesters by taking into account all aerodynamic interactions. The piezo-aeroelastic framework consists of the following: (1) an aerodynamic model based on the unsteady vortex-lattice method to compute the aerodynamic forces; (2) a discrete parameter model for each harvester with 3 degrees of freedom (plunge motion, pitch motion, and the voltage generated by the piezoelectric effect); (3) an inter-model connection to exchange information between models at each time step; and (4) a numerical scheme based on the Hamming’s fourth-order predictor–corrector method to integrate all the governing equations in the time domain. The results obtained allow us to infer new insights into the flutter onset as well as the post-critical behavior of harvester arrangements. An interesting finding is that the flutter speed is significantly decreased as the distance between the harvesters is reduced. The results suggest the strong possibility of effective energy extraction at low flow speeds using properly distributed harvester arrangements. However, in post-critical conditions, the output power is significantly enhanced as the free-stream speed is increased.Fil: Roccia, Bruno Antonio. Universidad Nacional de Río Cuarto. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Verstraete, Marcos Leonardo. Universidad Nacional de Río Cuarto. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Ceballos, Luis Ramon. Universidad Nacional de Río Cuarto. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Balachandran, Balakumar. University of Maryland; Estados UnidosFil: Preidikman, Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin
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