Matching Items (2)
Description
Evacuated tube solar thermal collector arrays have a wide range of applications. While most of these applications are limited in performance due to relatively low maximum operating temperatures, these collectors can still be useful in low grade thermal systems. An array of fifteen Apricus AP-30 evacuated tube collectors was designed, assembled, and tested on the Arizona State University campus in Tempe, AZ. An existing system model was reprogrammed and updated for increased flexibility and ease of use. The model predicts the outlet temperature of the collector array based on the specified environmental conditions. The model was verified through a comparative analysis to the data collected during a three-month test period. The accuracy of this model was then compared against data calculated from the Solar Rating and Certification Corporation (SRCC) efficiency curve to determine the relative performance. It was found that both the original and updated models were able to generate reasonable predictions of the performance of the collector array with overall average percentage errors of 1.0% and 1.8%, respectively.
ContributorsStonebraker, Matthew (Author) / Phelan, Patrick (Thesis advisor) / Reddy, Agami (Committee member) / Bryan, Harvey (Committee member) / Arizona State University (Publisher)
Created2011
Description
Finite element models (FEMs) of spine segments validated in their intact states are often used to make predictions following structural modifications simulating surgical procedures, including posterior fusion with pedicle screws and rods (PSR) and laminectomy (removal of posterior column bone to decompress the spinal cord). The gold standard for spine FEM validation compares predicted vs. experimental intervertebral ranges of motion (ROM). Given that muscle co-contraction compresses the spine, validation that considers compression may produce a more robust FEM. One research goal was to evaluate an experimental method of compressing a lumbar spine segment through its sagittal plane balance (pivot) point (BP) using a 6DOF robotic test system. Experimental data supported the hypothesis that structural modifications, such as PSR and laminectomy alter the segment’s BP location and its compressive stiffness. However, evaluation showed that the experimental BP method is sensitive to specimen posture in the robotic test frame; slight flexion or extension produced shear loads during compression that affect BP location and should be included in specimen-specific FEMs to ensure similar load conditions. Another goal was to develop a uniquely calibrated specimen-specific FEM of an intact L4-5 motion segment using the experimental BP data. A specimen-specific FEM was created and calibrated using experimental BP compressive stiffness data, however matching experimental BP location data was unsuccessful. The BP-compression calibrated FEM was evaluated by comparing predicted responses to loads following simulated PSR and laminectomy to specimen-specific experimental data. Predictions using the BP-calibrated and ROM-calibrated FEMs were compared. The BP-calibration process helped identify an unrealistic FEM disc geometry (nucleus pulposus size and location). Both BP-compression and ROM-calibrated FEMs predicted effects of PSR on stiffness (compressive and flexural) that were greater than experimental, which helped identify a problem with simplified representations of bone in the posterior column and at the anterior column interface. The BP-compression calibrated FEMs predicted relative shifts in BP locations and bone surface strains during compression that were closer to experimental data than similarly modified ROM-calibrated FEMs. Collectively, these results support the use of BP measures in experimental and model-based investigations of surgical modifications of the spine.
ContributorsSawa, Anna Genowefa Ulrika (Author) / Abbas, James (Thesis advisor) / Crawford, Neil R (Thesis advisor) / Kelly, Brian P (Committee member) / Helms-Tillery, Stephen (Committee member) / Sadleir, Rosalind (Committee member) / Arizona State University (Publisher)
Created2023