Browsing by Subject "Finite element modeling"

Now showing 1 - 3 of 3
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    Bioengineered tissue mechanics: experimental characterization and a multi-component model
    (2013-08) Lai, Victor
    In the last few decades, tissue engineering has emerged as an interdisciplinary field of research which holds much promise as a complement to clinical medicine towards the overall improvement of personal health. Despite significant advances in this field, much work in TE continues to rely on an Edisonian approach of employing ad hoc methods to engineer tissues with desired properties without fundamental knowledge of the problem at hand. This thesis presents the development of a comprehensive model that predicts the mechanical properties of bioengineered tissue equivalents (TEs) based on its structure and composition, to enhance the understanding of the contribution of various biological components (e.g. biopolymeric fibers, cells, etc) to macroscopic mechanical properties of a tissue at different stages of tissue growth. The project framework considered bioengineered tissues as being composed of three components: fibrous networks, an interstitial matrix, and cells. The following interactions between different components were investigated: (a) multiple fiber networks, (b), fiber network + interstitial matrix, and (c) fiber network + cells. Experimentally, mechanical tests such as stress relaxation and tensile stretch to failure were coupled with electron microscopy, confocal microscopy, and biochemical analyses to probe tissue microstructure and composition. Constructs were formulated with varying compositions of the different components in a TE. These experimental results guided the development of the theoretical model. Modeling work built upon an existing single-component microstructural model by incorporating other components and morphological features as observed from experiment. Improvements to the model combined two approaches: (1) a microstructural approach via incorporation of morphological features observed from micrographs, and (2) a phenomenological approach using constitutive relations commonly employed for various biological structures. Model validation was done by comparing model predictions of mechanical behavior with experimental results; agreements and discrepancies alike shed insight into the complex interactions between different components the comprise a TE. Overall, the work presented in this thesis represented significant improvements to the predictive capabilities of our computational model, and established the foundation for further modifications to capture better the microstructure and mechanics of different components within a TE.
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    Instrumentation, Monitoring, and Modeling of the I-35W Bridge
    (Minnesota Department of Transportation, 2012-08) French, Catherine E.W.; Shield, Carol K.; Stolarski, Henryk K; Hedegaard, Brock D.; Jilk, Ben J.
    The new I-35W Bridge was instrumented incorporating "smart bridge technology" by Figg Engineering Group in conjunction with Flatiron-Manson. The purpose of the instrumentation was to monitor the structure during service, and to use this information to investigate the design and performance of the bridge. Instrumentation included static sensors (vibrating wire strain gages, resistive strain gages and thermistors in the foundation, bridge piers, and superstructure, as well as fiber optic sensors and string potentiometers in the superstructure) and dynamic sensors (accelerometers in the superstructure). Finite element models were constructed, taking into account measured material properties, to further explore the behavior of the bridge. The bridge was tested using static and dynamic truck load tests, which were used, along with continually collected ambient data under changing environmental conditions, to validate the finite element models. These models were applied to gain a better understanding of the structural behavior, and to evaluate the design assumptions presented in the Load Rating Manual for the structure. This report documents the bridge instrumentation scheme, the material testing, finite element model construction methodology, the methodology and results of the truck tests, validation of the models with respect to gravity loads and thermal effects, measured and modeled dynamic modal characteristics of the structure, and documentation of the investigated assumptions from the Load Rating Manual. It was found that the models accurately recreated the response from the instrumented bridge, and that the bridge had behaved as expected during the monitoring period.
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    Multiport DC-DC conversion incorporating integrated magnetics for renewables
    (2014-03) Biswas, Suvankar
    Multi-port converter design and analysis presents one of the most intriguing challenges in the incorporation of renewables in the power grid. Choice of topology is of paramount importance to improve the power conditioning. To this effect, the integrated Cuk topology achieves multiple objectives : low EMI, low component count, simplified MPPT tracking and power management, reduction of filter capacitor requirement, high efficiency. This is achieved by integrating all the magnetic components on a single core, and addition of soft-switching capability thereof. This thesis revisits the concept of integrated magnetics and formulates an elegant solution procedure to the problem of zero-ripple. It investigates the idea of utilizing the concept of a coupled-inductor filter on a three-port converter and removes the need for an external filter, thereby almost introducing an effective DC-DC transformer. The pre-FEM(finite element modelling) selection and design of the core and circuit aspects have been explained in this thesis. The simulation results are presented using PLECS. Additionally, some FEM results are added for the reduced three-winding structure. The validation of some design parameters are also discussed.A soft-switching scheme has also been demonstrated for a two-port converter with integrated magnetics. This has an active-clamp ZVS turn-on circuit with the addition of a ZCS turn-off. The design of the external components and simulation results for the same are presented as well.