An Acoustic Analysis of Valveless Pulsejet Engines

Valveless pulsejets are extremely simple aircraft engines; essentially cleverly designed tubes with no moving parts. These engines utilize pressure waves, instead of machinery, for thrust generation, and have demonstrated thrust-to-weight ratios over 8 and thrust specific fuel consumption levels below 1 lbm/lbf-hr – performance levels that can rival many gas turbines. Despite their simplicity and competitive performance, they have not seen widespread application due to extremely high noise and vibration levels, which have persisted as an unresolved challenge primarily due to a lack of fundamental insight into the operation of these engines. This thesis develops two theories for pulsejet operation (both based on electro-acoustic analogies) that predict measurements better than any previous theory reported in the literature, and then uses them to devise and experimentally validate effective noise reduction strategies. The first theory analyzes valveless pulsejets as acoustic ducts with axially varying area and temperature. An electro-acoustic analogy is used to calculate longitudinal mode frequencies and shapes for prescribed area and temperature distributions inside an engine. Predicted operating frequencies match experimental values to within 6% with the use of appropriate end corrections. Mode shapes are predicted and used to develop strategies for suppressing higher modes that are responsible for much of the perceived noise. These strategies are verified experimentally and via comparison to existing models/data for valveless pulsejets in the literature. The second theory analyzes valveless pulsejets as acoustic systems/circuits in which each engine component is represented by an acoustic impedance. These are assembled to form an equivalent circuit for the engine that is solved to find the frequency response. The theory is used to predict the behavior of two interacting pulsejet engines. It is validated via comparison to experiment and data in the literature. The technique is then used to develop and experimentally verify a method for operating two engines in anti-phase without interfering with thrust production. Finally, Helmholtz resonators are used to suppress higher order modes that inhibit noise suppression via anti-phasing. Experiments show that the acoustic output of two resonator-equipped pulsejets operating in anti-phase is 9 dBA less than the acoustic output of a single pulsejet.

Cooperative Design, Cooperative Science: Investigating Collaborative Research through Design with Floracaching

This dissertation presents a case study of collaborative research through design with Floracaching, a gamified mobile application for citizen science biodiversity data collection. One contribution of this study is the articulation of collaborative research through design (CRtD), an approach that blends cooperative design approaches with the research through design methodology (RtD). Collaborative research through design is thus defined as an iterative process of cooperative design, where the collaborative vision of an ideal state is embedded in a design. Applying collaborative research through design with Floracaching illustrates how a number of cooperative techniques—especially contextual inquiry, prototyping, and focus groups—may be applied in a research through design setting. Four suggestions for collaborative research through design (recruit from a range of relevant backgrounds; take flexibility as a goal; enable independence and agency; and, choose techniques that support agreement or consensus) are offered to help others who wish to experiment with this new approach. Applying collaborative research through design to Floracaching yielded a new prototype of the application, accompanied by design annotations in the form of framing constructs for designing to support mobile, place-based citizen science activities. The prototype and framing constructs, which may inform other designers of similar citizen science technologies, are a second contribution of this research.

RACHMANINOFF AND MEDTNER: SELECTED WORKS FROM THE SOLO AND COLLABORATIVE PIANO REPERTOIRE

Sergei Rachmaninoff and Nikolai Medtner occupy a special place in the history of Russian music. Both composers were exceptional pianists and left us some of the greatest works in the piano repertoire. Although these composers shared many similarities, and were often compared, their musical languages and views on composition were very different. Unfortunately, Medtner’s music, which Rachmaninoff admired greatly, has remained neglected for several generations of performers and listeners. In my dissertation I will explore the similarities and contrasts in Rachmaninoff’s and Medtner’s music. Through these performances, I hope to encourage other musicians to discover the imaginative power of Medtner’s music. Of course, no such encouragement is needed for Rachmaninoff’s extremely popular music; however, the technical and musical challenges of performing that repertoire are an invaluable part of every pianist’s education. This dissertation project was presented in three recitals which were performed in Gildenhorn Recital Hall at the Clarice Smith Performing Arts Center of the University of Maryland on May 8, 2014, December 5, 2014 and March 21, 2016. The following pieces comprised the survey of Rachmaninoff music: Vocalise Op. 34, Variations on a Theme of Corelli Op. 42, Piano Concerto No 2 Op. 18, Selected Songs Opp. 4 and 8, and two Moments Musicaux Op. 16 - Nos 3 and 4. The following pieces were included to represent Medtner: Sonata for Violin and Piano Op. 57 in E minor “Epica”, Fairy Tales for solo piano Op. 20 No 1, Op. 26 No 3 and Op. 51 No 1, and Selected Songs Op. 6 and 15. My partners in this project were Lilly Ahn, soprano, Jennifer Lee, violin and Nadezhda Christova, piano. All three recitals can be found in the Digital Repository at the University of Maryland (DRUM).

Large-Scale Controlled-Condition Experiment to Evaluate Light Weight Deflectometers for Modulus Determination and Compaction Quality Assurance of Unbound Pavement Materials

Compaction control using lightweight deflectometers (LWD) is currently being evaluated in several states and countries and fully implemented for pavement construction quality assurance (QA) by a few. Broader implementation has been hampered by the lack of a widely recognized standard for interpreting the load and deflection data obtained during construction QA testing. More specifically, reliable and practical procedures are required for relating these measurements to the fundamental material property—modulus—used in pavement design. This study presents a unique set of data and analyses for three different LWDs on a large-scale controlled-condition experiment. Three 4.5x4.5 m2 test pits were designed and constructed at target moisture and density conditions simulating acceptable and unacceptable construction quality. LWD testing was performed on the constructed layers along with static plate loading testing, conventional nuclear gauge moisture-density testing, and non-nuclear gravimetric and volumetric water content measurements. Additional material was collected for routine and exploratory tests in the laboratory. These included grain size distributions, soil classification, moisture-density relations, resilient modulus testing at optimum and field conditions, and an advanced experiment of LWD testing on top of the Proctor compaction mold. This unique large-scale controlled-condition experiment provides an excellent high quality resource of data that can be used by future researchers to find a rigorous, theoretically sound, and straightforward technique for standardizing LWD determination of modulus and construction QA for unbound pavement materials.