Browsing by Author "Tovar, Andrés"

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    Concurrent topology optimization of structures and materials
    (2013-12-11) Liu, Kai; Tovar, Andrés; Nematollahi, Khosrow; Koskie, Sarah; Anwar, Sohel
    Topology optimization allows designers to obtain lightweight structures considering the binary distribution of a solid material. The introduction of cellular material models in topology optimization allows designers to achieve significant weight reductions in structural applications. However, the traditional topology optimization method is challenged by the use of cellular materials. Furthermore, increased material savings and performance can be achieved if the material and the structure topologies are concurrently designed. Hence, multi-scale topology optimization methodologies are introduced to fulfill this goal. The objective of this investigation is to discuss and compare the design methodologies to obtaining optimal macro-scale structures and the corresponding optimal meso-scale material designs in continuum design domains. These approaches make use of homogenization theory to establish communication bridges between both material and structural scales. The periodicity constraint makes such cellular materials manufacturable while relaxing the periodicity constraint to achieve major improvements of structural performance. Penalization methods are used to obtain binary solutions in both scales. The proposed methodologies are demonstrated in the design of stiff structure and compliant mechanism synthesis. The multiscale results are compared with the traditional structural-level designs in the context of Pareto solutions, demonstrating benefits of ultra-lightweight configurations. Errors involved in the mult-scale topology optimization procedure are also discussed. Errors are mainly classified as mesh refinement errors and homogenization errors. Comparisons between the multi-level designs and uni-level designs of solid structures, structures using periodic cellular materials and non-periodic cellular materials are provided. Error quantifications also indicate the superiority of using non-periodic cellular materials rather than periodic cellular materials.
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    Design optimization of heterogeneous microstructured materials
    (2014) Emami, Anahita; Tovar, Andrés; Zhu, Likun; Wasfy, Tamer; Chen, Jie
    Our ability to engineer materials is limited by our capacity to tailor the material’s microstructure morphology and predict resulting properties. The insufficient knowledge on microstructure-property relationship is due to complexity and randomness in all materials at different scales. The objective of this research is to establish a design optimization methodology for microstructured materials. The material design problem is stated as finding the optimum microstructure to maximize the desired performance satisfying material processing constrains. This problem has been solved in this thesis by means of numerical techniques through four main steps: microstructure characterization, model reconstruction, property evaluation, and optimization. Two methods of microstructure characterizations have been investigated along with the advantages and disadvantages of each method. The first microstructure characterization method is a statistical method which utilizes correlation functions to extract the microstructural information. Algorithms for calculating these correlations functions have been developed and optimized based on their computational cost using MATLAB software. The second microstructure characterization method is physical characterization which works based on evaluation of physical features in microstructured domain. These features have been measured by means of MATLAB codes. Three model reconstruction techniques are proposed based on these characterization methods and employed to generate material models for further evaluation. The first reconstructing algorithm uses statistical functions to reconstruct the statistical equivalent model through simulating annealing optimization method. The second algorithm uses cellular automaton concepts to simulate the grain growth utilizing physical descriptors, and the third one generates elliptical inclusions in a material matrix using physical characteristic of microstructure. The finite element method is used to analysis the mechanical behavior of material models. Several material samples with different microstructural characteristics have been generated to model the micro-scale design domain of AZ31 magnesium alloy and magnesium matrix composite with silicon carbide fibers. Then, surrogate models have been created based on these samples to approximate the entire design domain and demonstrate the sensitivity of the desired mechanical property to two independent microstructural features. Finally, the optimum microstructure characteristics of material samples for fracture strength maximization have been obtained.
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    The Development of a Wireless Control System for Integration on Drones
    (Office of the Vice Chancellor for Research, 2015-04-17) Allen, Tim; Tovar, Andrés
    The use of remotely controlled drones has proven to assists humans in day to day life. Whether it be by keeping our military personnel safe, defusing bombs, or exploring parts of space humans have not yet reached. The purpose of this project was to develop a control system that can be used on a drone. The control system allows a user to control a radio controlled vehicle up to 300 yards away. It contains a wireless video feedback system so that the user can still control the vehicle even when it is out of the user’s line of sight. The user controls the vehicle with a custom made software package that includes a graphical user interface. The software takes commands from the user and transmits them through the serial port to an xBee module. The xBee module on the vehicle receives the information and transmits it to the microcontroller on the vehicle. The microcontroller then executes necessary commands and sends any feedback required. The software package includes controls for the steering, throttle, and camera control. The outcome of this project is a control system that can be incorporated in to future drone projects. The software is fully documented to make customizing it to individual projects simple. The circuitry on the receiving end of the control system contains serial ports to make it possible to integrate any other peripheral technology in to the existing control system. The end result of this project is a working prototype that will allow future students to build off of. This will expedite further research of drones at IUPUI. Mentor: Andres Tovar, Department of Mechanical Engineering, Purdue School of Engineering and Technology