A recently emerging engineering design approach entails studying the brilliant design solutions found in nature with an aim to develop design strategies that mimic the remarkable efficiency found in biological systems. This novel engineering approach is referred to as bio-inspired design. In this context, the present study quantifies the structure-property relations in bighorn sheep (Ovis canadensis) horn keratin, qualitatively characterizes the effects of a tapered spiral geometry (the same form as in a ram’s horn) on pressure wave and impulse mitigation, describes the stress attenuation capabilities and features of a ram’s head, and compares the structures and mechanical properties of some energy absorbent natural materials. The results and ideas presented herein can be used in the development of lightweight, energy absorbent, bio-inspired material designs. Among the most notable conclusions garnered from this research include: Horn keratin behaves in an anisotropic manner similar to a long fiber composite. Moisture content dominates the material behavior of horn keratin more than anisotropy, age, and stress-state. This makes moisture content the most influential parameter on the mechanical behavior of horn keratin. Tapered geometries mitigate the impulse generated by a stress wave due to the convergent boundary and a continually decreasing cross sectional area such that greater uniaxial stresses and subsequent axial deformation arises. Furthermore, the tapered geometry introduces small shear stresses that further decrease the impulse. Spiral geometries attenuate the impulse generated by a stress wave by the introduction of shear stresses along the length of the spiral. These shear stresses introduce transverse displacements that function to lessen the impulse. When both a taper and spiral geometry are used in a design, their synergistic effects multiplicatively reduce the impulse Tough natural materials have a high porosity, which makes them light-weight, while increasing their compressive energy absorption ability. Biomaterials whose functions include protection and energy absorption feature a multiscale, hierarchical, composite structure. The constituent materials are arranged in such ways to achieve a synergistic effect, where the properties of the composite exceed the properties of its constituents. Biological materials are therefore not confined to the law of mixtures.

<p dir="ltr">Tip leakage flows in unshrouded turbines lead to significant pressure losses and heat loads, both on the rotating blades and the adjacent casing surface. These penalties are influenced by the tip clearance size, highly pertinent to the new generation of small-core high-speed turbines. Tailored to decrease tip leakage effects, small-core turbines feature running clearances below 0.3mm, making small blade-to-blade clearance variations extremely relevant for the machine's performance. Therefore, tip clearance monitoring and assessment of the leakage flow structures are paramount to design strategies for this class of turbines. Due to the limitations of commercially available CFD tools to accurately resolve highly detached unsteady flows, in-situ empirical observations are required. Furthermore, the documentation of flow field relationships with the tip clearance is highly valuable for in-service engine applications, such as tip clearance estimations from more accessible measurements to provide feedback for clearance control systems.</p><p dir="ltr">The dissertation developed hereafter performs aerothermal measurements in the casing end wall of a small-core high-speed turbine at engine-representative conditions and a wide range of clearance values. A novel in-situ calibration procedure for capacitance probes is tailored to reduce the required clearance measurements and the experimental time. Its uncertainty analysis demonstrates improved prediction bands, supporting this method for tight clearance measurements. A thorough evaluation of the casing static pressure is performed with high-frequency miniature pressure transducers. Specific trends are identified with independent variations of operating pressure ratio, rotational speed, and tip clearance. The results revealed the existence of a clearance-dependent threshold rotational blade tip Reynolds, where the circumferential directionality of tip leakage flows reverses. The analysis of the convective heat flux field with varying operating parameters was achieved with Atomic Layer Thermopile sensors. The computed adiabatic parameters and unsteady contributors reveal high influence of the temperature field on the convective heat flux mechanisms. Lastly, the evaluation of the unsteady terms with tip clearance unveil the shift of thermal loads from the pressure to the suction side of the blade tip.</p><p dir="ltr">The achieved results have provided valuable insight into the underlying aerothermal mechanisms governing the tip clearance region, as well as connections with tip clearance size that could potentially be implemented on engine application systems.</p>

Indiana University-Purdue University Indianapolis (IUPUI) / Peripheral arterial disease is caused by plaque buildup in the peripheral arteries. Standard treatments are available when the blockage is proximal and focal, however when distal and diffuse the same type of the treatment options are not beneficial due to the diseased locations. Restoration of blood flow and further salvaging of the limb in these patients can occur in a retrograde manner through the venous system, called retroperfusion or arteriovenous reversal. Retroperfusion has been explored over the last century, where early side to side artery to venous connections had issues with valve competency prohibiting distal flows, edema buildup, and heart failure. However, more recent clinical studies create a bypass to a foot vein to ensure distal flows, and though the results have been promising, it requires a lengthy invasive procedure. It is our belief that the concerns of both retroperfusion approaches can be overcome in a minimally invasive/catheter based approach in which the catheter is engineered to a specific resistance that avoids edema and the perfusion location allows for valves to be passable and flow to reach distally. In this approach, the pressure flow relations were characterized in the retroperfused venous system in ex-vivo canine legs to locate the optimal perfusion location followed by in-vivo validation of canines. Six canines were acutely injured for 1-3 hours by surgical ligation of the terminal aorta and both external iliac arteries. Retroperfusion was successfully performed on five of the dogs at the venous popliteal bifurcation for approximately one hour, where flow rates at peak pressures reached near half of forward flow (37±3 vs. 84±27ml/min) and from which the slope of the P/F curves displayed a retro venous vasculature resistance that was used to calculate the optimal catheter resistance. To assess differences in regional perfusion, microspheres were passed during retroperfusion and compared to baseline microspheres passed arterially prior to occlusion in which the ratio of retroperfusion and forward perfusion levels were near the ratio of reversed and forward venous flow (0.44) throughout the limb. Decreases in critical metabolites during injury trended towards normal levels post-retroperfusion. By identifying the popliteal bifurication as a perfusion site to restore blood flow in the entirety of the distal ischemic limb, showing reversal of injury, and knowing what catheter resistances to target for further chronic studies, steps towards controlled retroperfusion and thus more efficient treatment options can be made for severe PAD patients.