Browsing by Author "Slagle, Adam Christopher"

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    Low Frequency Noise Reduction Using Novel Poro-Elastic Acoustic Metamaterials
    Slagle, Adam Christopher (Virginia Tech, 2014-06-04)
    Low frequency noise is a common problem in aircraft and launch vehicles. New technologies must be investigated to reduce this noise while contributing minimal weight to the structure. This thesis investigates passive and active control methods to improve low frequency sound absorption and transmission loss using acoustic metamaterials. The acoustic metamaterials investigated consist of poro-elastic acoustic heterogeneous (HG) metamaterials and microperforated (MPP) acoustic metamaterials. HG metamaterials consist of poro-elastic material with a periodic arrangement of embedded masses acting as an array of mass-spring- damper systems. MPP acoustic metamaterials consist of periodic layers of micro-porous panels embedded in poro-elastic material. This thesis examines analytically, experimentally, and numerically the behavior of acoustic metamaterials compared to a baseline poro-elastic sample. The development of numerical techniques using finite element analysis will aid in understanding the physics behind their functionality and will influence their design. Design studies are performed to understand the effects of varying the density, size, shape, and placement of the embedded masses as well as the location and distribution of microperforated panels in poro- elastic material. An active HG metamaterial is investigated, consisting of an array of active masses embedded within poro-elastic material. Successful tonal and broadband noise control is achieved using a feedforward, filtered-x LMS control algorithm to minimize the downstream sound pressure level. Low-frequency absorption and transmission loss is successfully increased in the critical frequency range below 500 Hz. Acoustic metamaterials are compact compared to conventional materials and find applications in controlling low-frequency sound radiation in aircraft and launch vehicles.
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    Morphing Hypersonic Inflatable Aerodynamic Decelerator (HIAD) Mechanisms and Controls
    Slagle, Adam Christopher (Virginia Tech, 2018-06-29)
    To enable a crewed mission to Mars, precision landing capabilities of Entry, Descent, and Landing (EDL) systems must be improved. The need for larger payloads, higher landing sites, and controllability has motivated the National Aeronautics and Space Administration (NASA) to invest in new technologies to replace traditional rigid aeroshell systems, which are limited in size by the payload envelope of existing launch vehicles. A Hypersonic Inflatable Aerodynamic Decelerator (HIAD) is an emerging technology that provides an increased drag area by inflating the aeroshell to diameters not possible with rigid aeroshells, allowing the vehicle to decelerate higher in the atmosphere, offering access to higher landing sites with more timeline margin. To enable a crewed mission to Mars, future entry vehicles will require precision landing capabilities that go beyond heritage EDL guidance strategies that utilize fuel-intensive and error-prone bank reversals. A novel Direct Force Control (DFC) approach of independently controlling the lift and side force of a vehicle that utilizes a HIAD with an aerodynamic shape morphing capability is proposed. To date, the mechanisms and controls required to morph an inflatable structure to generate lift have not been explored. In this dissertation, novel morphing HIAD concepts are investigated and designed to satisfy mission requirements, aerodynamic tools are built to assess the aerodynamic performance of morphed blunt body shapes, and a structural feasibility study is performed using models correlated to test data to determine the forces required to generate the desired shape change based on a crewed mission to Mars. A novel control methodology is introduced by applying a unique DFC strategy to a morphing HIAD to enhance precision landing capabilities of EDL systems, and the ability of a morphing HIAD to safely land a vehicle on Mars is assessed by performing a closed-loop feedback simulation for a Mars entry trajectory. Finally, a control mechanism is demonstrated on a small-scale inflatable structure. Conclusions and contributions of this research are presented along with a discussion of future research opportunities of morphing HIADs.