Passive Cavity Deflation after Water Entry Facilitated by a Vented Tube

When an object enters water, a crater, or air cavity, can form around the object and remain attached as the object travels underwater. Cavities can be beneficial and reduce drag force but there may be times when the cavity needs to be removed. This research proposes a method to remove air cavities by letting air leave the cavity, deflating the cavity similar to how a balloon is deflated. To provide air a path to leave the cavity, a tube with vent holes is attached to the object. The vent holes are located near the object, where the air cavity forms, and allow the air to move from the cavity out through the tube. Cavities for objects with and without the vented tube are compared using images from a high-speed cameras. Different vented tube lengths, vented tube diameters, vent hole areas, and impact velocities are compared. If the vented tube is long enough that it is outside of the cavity then the air will leave and the cavity deflates. As the vented tube length and vented tube diameter increase, the amount of air that leaves the cavity increases. Similarly as vent hole area increases, the amount of air that leaves the cavity increases until the holes get too large and the cavity fills with water before all the air can leave, trapping the remaining air in the cavity. How impact velocity effects the amount of air that leaves the cavity depends on the vented tube length. The critical vented tube length required for deflation to occur depends on the sphere radius, impact velocity, and vented tube diameter. The noise the cavity makes and the acceleration of the object as it travels underwater are compared for deflating cavities and non-deflating cavities and the results show that cavity deflation reduces both noise and acceleration

Design, Manufacturing, and Integration of Fins for 2017-2018 OSU ESRA 30k Rocket

The Oregon State University (OSU) Experimental Sounding Rocket Association (ESRA) 30k Rocket Team is a student run rocket team that competes in the Intercollegiate Rocket Engineering Competition at Spaceport America. The goal of the competition is to launch a student designed, manufactured, and tested experimental sounding rocket to 30,000 ft carrying a 10 lb. scientific payload. One component of the rocket is the fins which provide stability for the rocket. The 2017-2018 OSU ESRA 30k rocket fins are composite fins with a clipped delta planform and a double diamond cross-section. The purpose of this thesis to present the design, manufacturing, integration, and testing processes for the 2017-2018 OSU ESRA 30k rocket fins. The goal is that this thesis will be a reference and a guide for future OSU rocket teams. Background research on fins and optimal fin design is presented and the manufacturing and integration processes are described in detail. Test results are also presented. Additionally, the many lesson learned throughout the process of designing, manufacturing, integrating, and testing the fins are presented to help future teams build better fins and avoid common mistakes. Key Words: ESRA, Rocket, Fins, Design, Manufacturing, Integration, Composite

Origin and significance of lamination in Lower Cretaceous stromatolites and proposal for a quantitative approach

Stromatolite lamination is typically defined as alternation of dark and light laminae. Study of Lower Cretaceous stromatolites fromthe Leza Fm(N Spain) supports this statement, but recognises additional complexities in lamination that have implications for interpreting accretion processes. These stromatolites are partial analogues of present-day coarse-grained carbonate stromatolites in the Bahamas and Shark Bay (Australia) that mainly form by trapping and binding carbonate sand. The Leza examples contain both grain-rich and micrite-rich laminae with scarce particles, suggesting that they accreted both by trapping and not trapping grains. Lamination in modern and ancient coarse-grained stromatolites is commonly defined by thinmicritic crusts that formed during interruptions in accretion and separate contiguous grainy laminae (repetitive lamination). Leza examples also contain these thin hiatal crusts and locally showrepetitive lamination, but their conspicuous macroscopic lamination is defined by thicker alternating grain-rich and micrite-rich laminae (alternating lamination). This indicates that, although hiatuses in accretion occurred, change in accretion process was the main cause of macroscopic lamination. These differences in accretion processes and lamination styles between Leza examples and modern coarse-grained stromatolites may reflect differences in their environmental settings. Modern examples occur in shallow marine tidal environments, whereas Leza Fm coarse-grained stromatolites developed in ideinfluencedwater-bodies in coastal-wetlands that experienced fluctuations inwater salinity and hydrochemistry. Analysis of lamina-thickness in these Cretaceous stromatolites and similar published examples provides a quantitative approach to the processes that underlie stromatolite lamination