Dynamic response analysis of a 900 kW wind turbine subject to ground excitation

This thesis exhibits the results of a study focused on the seismic behavior of a 900 kW wind turbine. As of the time of this writing, special engineering provisions for such loading events are not adequately defined. In order to accomplish the research objective, the author relies on available experimental data taken in 2009 from accelerometers attached to a wind turbine base and tower along with an eccentric mass shaker placed on the turbine foundation. On this basis, the dynamic properties of the wind turbine, including tower bending modes and natural frequencies were extracted. An attempt was made to quantify the damping ratios found in these bending modes by applying input shaking simulating the experimental excitation using the finite element program OpenSees. In this undertaking, possible sources of error are discussed. The author then describes a numerical study performed on a calibrated wind turbine like structure involving the application of a large range of actual recorded input motions. Adjustments are made to the original fixed-base model, placing the structure on a linearly elastic soil domain by using BridgePBEE, a graphical interface tool that eases simulation and functions as a pre and post processor. Using this code, the numerical study is further extended by varying the supporting ground stiffness. The study then compares the tower maximal shear and moment values for the studied rigid and flexible ground scenarios and explores trends in the lateral force lever-arm of the syste

Evaluation and Validation of Thorax Model Responses: A Hierarchical Approach to Achieve High Biofidelity for Thoracic Musculoskeletal System

As one of the most frequently occurring injuries, thoracic trauma is a significant public health burden occurring in road traffic crashes, sports accidents, and military events. The biomechanics of the human thorax under impact loading can be investigated by computational finite element (FE) models, which are capable of predicting complex thoracic responses and injury outcomes quantitatively. One of the key challenges for developing a biofidelic FE model involves model evaluation and validation. In this work, the biofidelity of a mid-sized male thorax model has been evaluated and enhanced by a multi-level, hierarchical strategy of validation, focusing on injury characteristics, and model improvement of the thoracic musculoskeletal system. At the component level, the biomechanical responses of several major thoracic load-bearing structures were validated against different relevant experimental cases in the literature, including the thoracic intervertebral joints, costovertebral joints, clavicle, sternum, and costal cartilages. As an example, the thoracic spine was improved by accurate representation of the components, material properties, and ligament failure features at tissue level then validated based on the quasi-static response at the segment level, flexion bending response at the functional spinal unit level, and extension angle of the whole thoracic spine. At ribcage and full thorax levels, the thorax model with validated bony components was evaluated by a series of experimental testing cases. The validation responses were rated above 0.76, as assessed by the CORA evaluation system, indicating the model exhibited overall good biofidelity. At both component and full thorax levels, the model showed good computational stability, and reasonable agreement with the experimental data both qualitatively and quantitatively. It is expected that our validated thorax model can predict thorax behavior with high biofidelity to assess injury risk and investigate injury mechanisms of the thoracic musculoskeletal system in various impact scenarios. The relevant validation cases established in this study shall be directly used for future evaluation of other thorax models, and the validation approach and process presented here may provide an insightful framework toward multi-level validating of human body models.</jats:p