Pitch Transition Research Articles

Extreme wind speed ramp events: A measurement-based approach for improving the modelling of ultimate loads for wind turbine design

Ramp events, i.e., significant changes in wind speed in a short time period, have become critically important to end-users. However, only a few studies address their impact on wind turbine loads. To the best of the authors’ knowledge, these results have not yet been validated with measurements. Therefore, this paper aims to investigate the impact of extreme wind speed ramps on ultimate wind turbine loads using eight months of offshore measurements. We also compare the measured loads with simulations following the International Electrotechnical Commission (IEC) extreme turbulence model, in order to improve the modelling of ultimate loads. This is because events with a 10-min horizontal wind speed standard deviation higher than the prescribed IEC turbulence class, in line with other research, are primarily associated with ramp events. They are found to be design driving for the blade root flap-wise moments below and beyond rated wind speed, but not in the transition region. The high-frequency analysis of these moments showed a sudden pitch transition from the inactive to the active region. In general, the loads associated with ramp events did not exceed the simulations. In addition, non-ramp related extreme loads around rated wind speed, which exceeded the simulations, were associated with standard deviations slightly above the normal turbulence model (NTM) of IEC for a waked turbine, indicating the impact of wake added turbulence. In conclusion, for the ultimate load analysis, the wind speed time series should include a sudden pitch transition from the inactive to the active region in addition to wake added turbulence.

Melody Extraction From Polyphonic Music Using Particle Filter and Dynamic Programming

Melody extraction from polyphonic music is one important but challenging task in the music information retrieval community. In this paper, a new melody extraction method based on the particle filter and dynamic programming is proposed. The constant-Q transform is first introduced for multiresolution spectral analysis of polyphonic music. Then, the melody extraction is modeled in the Bayesian filtering framework, and the particle filter is used to get a rough melody contour. Specially, the pitch transition probability of adjacent frames is approximated according to the statistical analysis based on one publicly available dataset, and the likelihood of frame-wise pitches is defined by considering pitch salience, spectral smoothness, and timbre similarity. After that, the preliminary melodic contour obtained by particle filter is smoothed to achieve the frame-wise pitch range limitation. Finally, the dynamic programming is used to accurately track the final melodic contour. The proposed method requires no prior information, and is suitable for both instrumental and vocal melodies. The experimental results show that the performances of the proposed method is robust among four publicly available datasets comparing with the state-of-the-art methods, and it achieves the highest averaged raw pitch accuracy and raw chroma accuracy performances with lower octave errors.

The role of variable pitch in motion blades and variable rotational speed in an industrial fan stall

Stall-induced vibration places fundamental limitations on industrial fan performance and remains a persistent problem in the development of industrial fans and compressors. In this paper, we present an experimental programme that utilised two strategies to study rotating stall recovery patterns in an industrial fan. The experimental facility incorporated a fan with both variable pitch in motion blades and a variable speed drive. The facility enabled us first, to study the evolution of unsteady pressure signals on the fan casing whilst varying fan blade pitch and then to examine varying fan rotational speed. Consequently, we were able to recover a fan from stall either by varying blade pitch at constant speed, or by varying speed at constant blade pitch. We also studied the physical flow phenomena associated with stall recovery by cross-correlating signals from circumferentially offset high frequency response pressure transducers and then analysed the cross-spectra. This enabled us to gain insight into the transient fluid flow behaviour associated with stall recovery in the studied industrial fan class. The transient fluid flow behaviour associated with stall recovery by varying blade pitch was indicative of both a mild and progressive transition. In contrast, stall recovery by varying fan speed occurred more suddenly. In comparison with the variable pitch transition, the variable speed transition was more indicative of recovery from mild surge. From this we may conclude that stall recovery via variable speed resulted in significantly higher unsteady mechanical stress induced in fan rotating components than recovery via variable pitch. Higher bending stresses in the fan blades are more likely to result in mechanical failure, and therefore we may conclude that the studied fan is more ‘stall tolerant’ when one operates it as a variable pitch fan rather than as a variable speed fan.

Effects of musical training on the early auditory cortical representation of pitch transitions as indexed by change‐N1

The effects of musical training on the early auditory cortical response to pitch transitions in music were investigated by use of the change-N1 component of auditory event-related potentials. Musicians and non-musicians were presented with music stimuli comprising a melody and a harmony under various listening conditions. First, when the subjects played a video game and were instructed to ignore the auditory stimuli, the onset of stimuli elicited a typical, fronto-central onset-N1, whereas melodic and harmonic pitch transitions within the stimuli elicited so-called change-N1s that were more posterior in scalp distribution. The pitch transition change-N1s, but not onset-N1, were enhanced in musicians. Second, when the listeners attended to the same stimuli as above to detect infrequently occurring target stimuli, the change-N1 elicited by pitch changes (in non-target stimuli) was augmented, in non-musicians only when the target was easily detectable, and in both musicians and non-musicians when it was difficult to detect. Thus, the early, obligatory cortical response to pitch transitions during passive listening was chronically enhanced by training in musicians, and, reflecting this training-induced enhancement, the task-related modulation of this response was also different between musicians and non-musicians. These results are the first to demonstrate the long-term effects of training, short-term effects of task and the effects of their interaction on the early (~100-ms) cortical processing of pitch transitions in music. The scalp distributions of these enhancement effects were generally right dominant at temporal electrode sites, suggesting contributions from the radially oriented subcomponent of change-N1, namely, the Tb (N1c) wave of the T-complex.

Vocal perfection in yodelling—pitch stabilities and transition times

Background. Yodelling is a special kind of vocal performance in traditional music which consists of rapid and repeated changes in pitch. It is assumed that these pitch changes are accompanied by register changes. Material and methods. We analysed, using the laryngograph, yodelling on different vowels by four professional yodelling teachers (two male, two female), four professional classically trained singers, and four untrained voices. Results. Results reveal that pitch changes in yodelling are associated with decrease of electroglottograpgic (EGG) contact quotient for the upper pitch, indicating a register shift. Furthermore, in contrast to untrained voices, for the yodellers lower and upper pitches were more stable with respect to fundamental frequency and perturbation values, and the pitch transitions were faster.

Microstructure and Mechanical Properties of C/C Composites with a Mesophase Pitch Transition Layer

Carbon/carbon (C/C) composites,with a mesophase pitch transition layer between carbon fiber and pyrocarbon,were prepared by two step technique of liquid impregnation-carbonization and chemical vapor infiltration (CVI).The microstructure and mechanical properties of the as-obtained composites were studied by polarized light microscope (PLM),scanning electron microscope (SEM), conventional and high resolution transmission electron microscope (TEM,HRTEM) and mechanical properties tests,respectively.Results show that the mesophase pitch carbon exhibits lamellar structure, while the pyrocarbon exhibits like-crinkle lamellar structure under SEM and the granular structure under TEM.Under HRTEM,the degree of alignment of lattice fringes decreases gradually for mesophase pitch carbon,pyrocarbon and carbon fiber.The non-brittle fracture behavior of the composites is related to multiple crack deflections caused by the multi-interface and micro-cracks within the matrix carbon layer.The flexural strength and the fracture toughness (K_(IC)) of C/C composites are 244MPa and 9.7MPa·m~(1/2),respectively.

Speech pitch coding system

A plurality of pitch period transition paths are extracted by a pitch tracking over a frame, and a path of a minimum average prediction gain over the frame is selected from the extracted paths. A subsequent preliminary pitch selection may be executed in a sub-frame processing to select a plurality of candidates from the neighborhood of the pitch of the transition path selected for each sub-frame by using the inner product of the input speech signal and each codevector. Finally, a pitch period having a minimum waveform distortion is selected for each sub-frame.

The discrimination of tonality in Japanese popular songs : Feature vector and the entropy of pitch transition

The discrimination of tonality in Japanese popular songs : Feature vector and the entropy of pitch transition

The perception of sine‐wave analogs of speech

Subjects identified various sets of tone stimuli which consisted of one, two, or three sine‐wave components. The stimuli varied in their degree of similarity to the syllables /ba/, /ab/, /ds/, and /ad/. Half of the subjects performed an auditory labeling task in which they identified the direction and location of the pitch transition. The other half of the subjects performed a phonetic labeling task in which they identified the tones as the CV syllables upon which they were based. The results showed a strong interaction between stimulus components and labeling performance. When a low‐frequency component (similar to an F1) was present, the phonetic‐label subjects performed best while the auditory‐label subjects performed worst. Also, various masking effects were present for the auditory‐label subjects which were not present for the phonetic‐label subjects. The results indicate that phonetic processing is not necessarily invoked by stimulus structure alone. However, when phonetic processing is engaged, the output of auditory analysis becomes unavailable for further processing. These results suggest that auditory and phonetic modes of processing may be mutually exclusive. Furthermore, the findings provide another demonstration of the reality of a distinct speech mode of perception. [Work supported by NIMH.]