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Time-frequency analysis techniques are proposed as a necessary tool for the analysis of acoustics generated by helicopter transient maneuvering flight. Such techniques are necessary as the acoustic signals related to transient maneuvers are inherently unsteady. The wavelet transform is proposed as an appropriate tool, and it is compared to the more standard short-time Fourier transform technique through an investigation using several appropriately sized interrogation windows. It is shown that the wavelet transform provides a consistent spectral representation, regardless of employed window size. The short-time Fourier transform, however, provides spectral amplitudes that are highly dependent on the size of the interrogation window, and so is not an appropriate tool for this situation. An extraction method is also proposed to investigate blade-vortex interaction noise emitted during helicopter transient maneuvering flight. The extraction method allows for the investigation of blade-vortex interactions independent of other sound sources. The method is based on filtering the spectral data calculated through the wavelet transform technique. The filter identifies blade-vortex interactions through their high amplitude, high frequency impulsive content. The filtered wavelet coefficients are then inverse transformed to create a pressure signature solely related to blade-vortex interactions. This extraction technique, along with a prescribed wake model, is applied to experimental data extracted from three separate flight maneuvers performed by a Bell 430 helicopter. The maneuvers investigated include a steady level flight, fast- and medium-speed advancing side roll maneuvers. A sensitivity analysis is performed in order to determine the optimal tuning parameters employed by the filtering technique. For the cases studied, the optimized tuning parameters were shown to be frequencies above 7 main rotor harmonics, and amplitudes stronger than 25% (−6 dB) of the energy in the main rotor harmonic. Further, it is shown that blade-vortex interactions can be accurately extracted so long as the blade-vortex interaction peak energy signal is greater or equal to the energy in the main rotor harmonic. An in-depth investigation of the changes in the blade-vortex interaction signal during transient advancing side roll maneuvers is then conducted. It is shown that the sound pressure level related to blade-vortex interactions, shifts from the advancing side, to the retreating side of the vehicle during roll entry. This shift is predicted adequately by the prescribed wake model. However, the prescribed wake model is shown to be inadequate for the prediction of blade-vortex interaction miss distance, as it does not respond to the roll rate of the vehicle. It is further shown that the sound pressure levels are positively linked to the roll rate of the vehicle. Similar sound pressure level directivities and amplitudes can be seen when vehicle roll rates are comparable. The extraction method is shown to perform admirably throughout each maneuver. One limitation with the technique is identified, and a proposal to mitigate its effects is made. The limitation occurs when the main rotor harmonic energy drops below an arbitrary threshold. When this happens, a decreased spectral amplitude is required for filtering; which leads to the extraction of high frequency noise unrelated to blade-vortex interactions. It is shown, however, that this occurs only when there are no blade-vortex interactions present. Further, the resulting sound pressure level is identifiable as it is significantly less than the peak blade-vortex interaction sound pressure level. Thus the effects of this limitation are shown to be negligible. / text

Yes / Purpose: Two binocular sources of information serve motion-in-depth (MID) perception: changes in disparity over time (CD), and interocular velocity differences (IOVD). While CD requires the computation of small spatial disparities, IOVD could be computed from a much lower-resolution signal. IOVD signals therefore might still be available under conditions of binocular vision impairment (BVI) with limited or no stereopsis, e.g. amblyopia. Methods: Sensitivity to CD and IOVD was measured in adults who had undergone therapy to correct optical misalignment or amblyopia in childhood (n=16), as well as normal vision controls with good stereoacuity (n=8). Observers discriminated the interval containing a smoothly-oscillating MID “test” stimulus from a “control” stimulus in a two-interval forced choice (2IFC) paradigm. Results: Of the BVI observers with no static stereoacuity (n=9), one displayed evidence for sensitivity to IOVD only, while there was otherwise no sensitivity for either CD or IOVD in the group. Generally, BVI observers with measurable stereoacuity (n=7) displayed a pattern resembling the control group: showing a similar sensitivity for both cues. A neutral-density (ND) filter placed in front of the fixing eye in a subset of BVI observers did not improve performance. Conclusions: In one BVI observer there was preserved sensitivity to IOVD but not CD, though overall only those BVI observers with at least gross stereopsis were able to detect disparity-based or velocity-based cues to MID. The results imply that these logically distinct information sources are somehow coupled, and in some cases BVI observers with no stereopsis may still retain sensitivity to IOVD. / UK Biotechnology and Biological 498 Sciences Research Council (BBSRC): BB/M002543/1 (Alex R. Wade) BB/M001660/1 (Julie 499 M. Harris) and BB/M001210/1 (Marina Bloj)

Helicopters are versatile vehicles that can vertically take off and land, hover, and perform maneuver at very low forward speeds. These characteristics make them unique for a number of civilian and military applications. However, the radial and azimuthal variation of dynamic pressure causes rotors to experience adverse phenomena such as transonic shocks and 3-D dynamic stall. Adverse interactions such as blade vortex interaction and rotor-airframe interaction may also occur. These phenomena contribute to noise and vibrations. Finally, in the event of an engine failure, rotorcraft tends to descend at high vertical velocities causing structural damage and loss of lives. A variety of techniques have been proposed for reducing the noise and vibrations. These techniques include on-board control (OBC) devices, individual blade control (IBC), and higher harmonic control (HHC). Addition of these devices adds to the weight, cost, and complexity of the rotor system, and reduces the reliability of operations. Simpler OBC concepts will greatly alleviate these drawbacks and enhance the operating envelope of vehicles. In this study, the use of Gurney flaps is explored as an OBC concept using a physics based approach. A three dimensional Navier-Stokes solver developed by the present investigator is coupled to an existing free wake model of the wake structure. The method is further enhanced for modeling of Blade-Vortex-Interactions (BVI). Loose coupling with an existing comprehensive structural dynamics analysis solver (DYMORE) is implemented for the purpose of rotor trim and modeling of aeroelastic effects. Results are presented for Gurney flaps as an OBC concept for improvements in autorotation, rotor vibration reduction, and BVI characteristics. As a representative rotor, the HART-II model rotor is used. It is found that the Gurney flap increases propulsive force in the driving region while the drag force is increased in the driven region. It is concluded that the deployable Gurney flap may improve autorotation characteristics if deployed only over the driving region. Although the net effect of the increased propulsive and drag force results in a faster descent rate when the trim state is maintained for identical thrust, it is found that permanently deployed Gurney flaps with fixed control settings may be useful in flare operations before landing by increasing thrust and lowering the descent rate. The potential of deployable Gurney flap is demonstrated for rotor vibration reduction. The 4P harmonic of the vertical vibratory load is reduced by 80% or more, while maintaining the trim state. The 4P and 8P harmonic loads are successfully suppressed simultaneously using individually controlled multi-segmented flaps. Finally, simulations aimed at BVI avoidance using deployable Gurney flaps are also presented.

Orientador: Jose Antenor Pomilio / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-09T17:17:10Z (GMT). No. of bitstreams: 1 Silva_LeonardodeAraujo_D.pdf: 14156071 bytes, checksum: f544bd5c73e51000deee838abcc80fa7 (MD5) Previous issue date: 2007 / Resumo: Nesta tese é introduzida uma nova estratégia de controle que permite a síntese de indutâncias negativas para realização da compensação série de linhas de transmissão. O método, que é baseado na estratégia SDR (Síntese Direta de Reatâncias), opera com realimentação de estados e requer a medição de variáveis locais. Em relação aos métodos tradicionais, usando capacitores, a compensação através de indutância negativa pode ter desempenho superior, pois é possível conseguir sistemas mais estáveis, sem risco de ressonâncias, e com desempenho dinâmico superior, o que permite a realização de outras funções desejáveis, tais como o amortecimento de oscilações eletromecânicas e a compensação de cintilação luminosa. Dada a elevada potência requerida pela aplicação, sugere-se a utilização do Conversor Multinível em Cascata Assimétrico, que apresenta alto rendimento e é capaz de produzir uma tensão de saída de baixo conteúdo harmônico. Para este conversor, foi introduzida uma estratégia de controle que permite uma implementação sem que sejam necessárias fontes CC. Sugere-se também um procedimento para escolha do capacitor de filtragem que permite uma redução da corrente no conversor para uma dada condição de operação. São apresentados alguns estudos sobre a estabilidade da compensação série com indutância negativa. Para a técnica de controle proposta, são realizados estudos de autovalores, que permitem verificar a robustez com variação de parâmetros. Através de simulações, verificasse a estabilidade com a presença de elementos não modelados na planta, como capacitâncias parasitas. Também são apresentados estudos sobre a estabilidade para um modelo de simulação da ressonância subsíncrona, que considera o modelo do gerador e características mecânicas do eixo da turbina. Os resultados obtidos com estes estudos de estabilidade, bem com os resultados experimentais, indicam que a técnica proposta é viável para a aplicação / Abstract: This thesis introduces a new control strategy of realizing negative inductances with static converters for series compensation of transmission lines. The proposed method, which is basedon DRS (Direct Reactance Synthesis) technique, requires state feedback of variables that can be measured locally. The use of negative inductances instead of capacitors may yield performance improvement because there is no risk of resonance and it is possible to obtain higher stability margins and better dynamic performance. Consequently, it is possible to realize some useful functions that are not possible with conventional strategies, just as flicker ompensation and smoothing of electromechanical oscillations. Series compensation requires high power static converters and, due to this, the use of the Asymmetrical Cascaded Multilevel Converters (ACMC) is suggested. This high efficiency power converter is capable of producing a low THD output voltage using less power switches than other topologies. This thesis also introduces a DC control strategy for ACMC, which may allow negative inductance implementation with no DC sources. It is also suggested a design procedure for choosing the filter capacitance that reduces the required current capability of the power converter. Some studies regarding the stability of series compensation with negative inductances were carried on. For the new control strategy, it was possible to perform the eigenvalues analysis, that proved therobustness under some parameters variations. The stability considering elements that were not modeled, just as stray capacitances or generator and turbine shaft, were tested through simulations. The simulations and experimental results corroborate to prove that the control strategy is suitable for this application / Doutorado / Energia Eletrica / Doutor em Engenharia Elétrica

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