Pitch Frequency Research Articles

A novel concept of floating absorber for motion mitigation in floating offshore wind turbines

This paper proposes the innovative concept of floating absorber for motion mitigation in floating wind turbines on spar supports. The floating absorber consists in a spar floater coupled with the floating wind turbine by an elastic spring and a viscous damper in parallel. It is conceived to act as a resonant mass tuned to the pitch frequency of the floating wind turbine and, for this purpose, its parameters are calibrated based on the well-established fixed point tuning procedure typically applied for tuned mass dampers. For validation, extensive time-domain numerical simulations are performed on a multi-degree-of-freedom computational model of the coupled system, considering thirty-six different configurations of the floating absorber and fifteen different combinations of wind-wave conditions. The results demonstrate a considerable effectiveness of the floating absorber in reducing the pitch motion of the floating wind turbine. A main advantage over conventional tuned mass devices is that the absorber is not housed in the nacelle of the wind turbine but floats close to the floating wind turbine. This not only ensures reduced costs of installation and maintenance of the floating absorber but allows, also, to increase its mass without causing extra weight on the floating wind turbine, exploiting hydrodynamic added mass as well, with consequent benefits in terms of motion mitigation in the floating wind turbine. Another relevant result is that, for a given mass of the floating absorber and a given attachment point of the parallel spring-dashpot, the performances of the floating absorber do not vary significantly with its geometry. This is important to facilitate design and manufacturing of the floating absorber, confirming the robustness of the proposed concept and its great potential for motion mitigation in floating wind turbines.

Injection and Escape: A new model on the thrust generated by a thin pitching plate

We have proposed a physical model to describe the underlying physics behind the drag or thrust produced by a pitching panel in a uniform stream. Over the clockwise and counterclockwise pitching motions, the model categorizes Injection and Escape kinematic phases. The former estimates the total fluid volume gathered at the trailing edge, and the latter amount to the fluid volume fenced by the plate reaching the trailing edge. To verify our proposed model, we have performed three-dimensional simulations using an immersed boundary-based numerical code for the flow past a thin pitching plate at a Reynolds number of Re = 1000 for the aspect range of 0.54≤AR≤16 at maximum pitching angle of θmax=5°,15° with pitching frequency St=0.5,1. Our model reveals that the plate generates a net thrust in a pitching cycle when Injection dominates Escape and conversely for the drag cases.

Microbubbles drag reduction characteristics of underwater vehicle during pitching movement

In this study, we investigate the effects of ventilation parameters and motion characteristics on the drag reduction characteristics of microbubbles during the pitching motion of underwater vehicle. Based on the Population Balance Model (PBM), a numerical method is established that takes into account the phenomenon of microbubbles aggregation and breakage. The effects of the pitching frequency and ventilation volume coefficient on drag and lift are conducted in this study. The results show that the numerical method can accurately predict the distribution and force characteristics of microbubbles for the vehicle in pitching motion. Added mass force of the water phase is weakened when the vehicle is surrounded by microbubbles during the pitching motion. This causes a gradual decrease in the phase difference between the drag and lift coefficients under different pitching frequencies. Moreover, the drag rate of the microbubble is inversely related to the pitch angle. Namely, the drag reduction rate of microbubbles decreases with an increase in pitch angle. The drag coefficient decreases significantly when the vehicle is covered by the microbubbles. This leads to the phase of the drag coefficient slightly lagging behind the pitch angle. Furthermore, the lift coefficients of vehicle are similar for different ventilation flow rates.

An Experimental and Numerical Evaluation of the Aerodynamic Performance of a UAV Propeller Considering Pitch Motion

Considering the vibration generated by a propeller-driven UAV or encountering gust, the propeller will perform a very complex follower motion. A pitch and rotating coupled motion is proposed in the present work that can take more complex unsteady performance of follower force than a regular fixed-point rotating motion. In order to evaluate the unsteady follower force and conduct parametric study, an extensive ground test bench was designed for this purpose where the whole test system was driven by a linear servo actuator and the follower force was measured by a 6-component balance. For CFD simulation, coupled motion in particular needs detailed unsteady aerodynamic model; therefore, a high-fidelity CFD-based study integrated with the overset mesh method was complemented to solve the unsteady fluid of varying conditions. The results suggest that a significant influence on unsteady follower force is observed, and the mean value of in-plane force does not equal to zero during the coupled motion process. Compared with the regular fixed-point rotation of propeller, the fluctuation frequency of follower force in present work couples the rotation and pitch motion frequencies. In addition, the oscillation amplitude of out-plane force and torque is positively related with the pitch frequency, pitch amplitude, and relative length from leading edge of wing to the rotation center. For example, the oscillation amplitude of 1-blade’s out-plane force and torque increases by 57.122% and 66.542% for the 5 Hz-5 deg case compared with the 5 Hz-3 deg case, respectively. However, the torque is not sensitive to frequency of pitch motion. The generally excellent agreement evident between the ground test and numerical simulation results is important as guidance for our future investigation on “dynamic” aerodynamic performance of a propeller-driven UAV.

Suboptimal Algorithm for Measuring Pitch Frequency Using Discrete Fourier Transform of a Speech Signal

Suboptimal Algorithm for Measuring Pitch Frequency Using Discrete Fourier Transform of a Speech Signal

Detecting emotion change instant in speech signal using spectral patterns in pitch coherent single frequency filtering spectrogram

Emotional intelligence means an ability to understand how others are feeling so that one can adjust according to others' emotional needs. Machines with emotional intelligence must understand human emotions as well also be informative about their emotional changes. Several researchers have tried to detect emotions from speech but little work is done in the area where machines could predict emotional changes. In the proposed work we have tried to analyze the spectrum of the glottal source to predict emotional changes. The glottal source spectrum is represented as a single-frequency filtering spectrogram. Single frequency spectrogram has high resolution in the time and frequency domain simultaneously. A single-frequency filtering spectrogram is fed to EfficientNetB7 to predict time-instant emotional changes. The performance of the proposed method is evaluated on two datasets IEMOCAP and RAVDESS. The proposed method shows high accuracy in comparison to other state-of-the-art techniques used for emotion prediction.

A new collective anomaly detection approach using pitch frequency and dissimilarity: Pitchy anomaly detection (PAD)

Anomaly detection in time series is an important process that can aid in both preprocessing and postprocessing, particularly in biomedical data modalities where anomalies often signify the presence of disorders that require identification. However, quasi-periodic data behavior frequently poses a challenge in detecting collective anomalies, especially when they fall within the normal data range. This difficulty makes detecting collective anomalies particularly challenging. This paper proposes a new method for detecting collective anomalies using pitch frequency information from the frequency domain and dissimilarity metric scores in a sliding window approach. The proposed method called pitchy anomaly detection (PAD) is expected to be effective in the analysis of quasi-periodic time series data. To evaluate the effectiveness of the PAD approach, it is compared to three other benchmark time series anomaly detection methods. Due to the particular interest in quasi-periodic data modalities, the comparative analysis is conducted under five different anomalous conditions on anomaly-added benchmark electrocardiography (ECG) datasets. The results show that the PAD approach yields promising classification performance results for detecting collective anomalies.

Analysis of dynamic stall control on a pitching airfoil using dynamic mode decomposition

Dynamic mode decomposition (DMD) technology is used to analyze the control of dynamic stall on a pitching S809 airfoil using an off-surface rod. The unsteady flows around the original and the controlled airfoil are simulated by using the SST k-ω turbulence model. With the introduction of the off-surface rod, the hysteresis effect of the dynamic stall process of the original airfoil is considerably reduced, and the clockwise sub-loop of the pitching moment coefficient is eliminated. The improvement of the dynamic stall process is beneficial to the safe and high-efficiency operations of wind turbine. The coherent structure of the unsteady flow fields are decoupled by the DMD method compiled by an in-house code in MATLAB. Results reveal that the hysteresis effect is dominated by mode 2 with a pitching frequency and mode 3 with twice the pitching frequency. The global energy of the two modes is reduced by the off-surface rod, which alleviates the hysteresis effect for the original airfoil.

A Novel Approach for Improving Guitarists’ Performance Using Motion Capture and Note Frequency Recognition

New guitarists face multiple problems when first starting out, and these mainly stem from a flood of information that they are presented with. Students also typically struggle with proper pitch frequency recognition and accurate left-hand motion. A variety of relevant solutions have been suggested in the existing literature; however, the majority have ultimately settled on two approaches. The first is finger motion capture, wherein researchers focus on extracting finger positions through analyzing images and videos. The second is note frequency recognition, wherein researchers focus on analyzing notes and frequencies from audio recordings. This paper proposes a novel hybrid solution that includes both finger motion capture and note frequency recognition in order to conduct a full assessment and give feedback on a guitarist’s performance. To classify hand positions, several classification algorithms are tested. The random forest algorithm obtained superior results, with an accuracy of 99% for overall hand movement and an average of 97.5% for the classification of each finger. Meanwhile, two algorithms were tested for note recognition, where the harmonic product spectrum (HPS) approach obtained the highest accuracy of 95%.

Competition between audiovisual correspondences aids understanding of interactions between auditory and visual perception

An audiovisual correspondence (AVC) refers to an observer's seemingly arbitrary yet consistent matching of sensory features across the two modalities; for example, between auditory pitch height and visual height or visual size. Research on AVCs frequently uses a speeded classification procedure in which participants are asked to rapidly classify the pitch of a sound accompanied either by a congruent or an incongruent visual object (e.g., high pitches are congruent with higher/smaller visual objects and incongruent with lower/larger visual objects). To investigate the strength of these pitch AVCs (height, size, spatial frequency, brightness, sharpness), trials where the height AVC competed with each other AVC in terms of pitch congruency were created. For example, when classifying pitch height, participants were presented with trials where both visual height and size were congruent or incongruent with pitch; additionally, there were trials where height was congruent but size was incongruent (i.e., high pitch matched with large object at high height) and trials where size was congruent but height was incongruent (i.e., high pitch matched with small object at low height). Based on previous work, congruency between pitch and height was expected to be more important than congruency between pitch and spatial frequency, brightness, sharpness, or size. As predicted, in all four studies, RTs when only height was congruent were just as fast as when both dimensions were congruent. In contrast, RTs when only spatial frequency, brightness, sharpness, or size was congruent (and height was incongruent) were just as slow as when both dimensions were incongruent. These results reinforce the superiority of the pitch-height AVC and can be interpreted based on the metaphor used for pitch in English, showing the importance of semantic/linguistic effects to understanding AVCs.

Predicting Intoxication Using Motorcycle and Head Movements of Riders Wearing Alcohol Intoxication Goggles

The movement of a motorcycle is one of the critical factors that influences the stability of the ride. It has been established that the gait patterns of drunk and sober people are distinct. However, drunk motorcycle (MC) drivers’ balance has not been investigated as a predictor of intoxication. This paper characterized and used MC and head movements, such as pitch and roll, to predict intoxication while riding. Two separate experiments were conducted to monitor MC and head movement. Male participants were recruited between the ages of 23 and 50 to participate in the study. Participants used alcohol intoxication goggles (AIG) to simulate blood alcohol content (BAC) while driving on a straight path. Placebo goggles were used for control. Results showed that pitch and roll amplitudes of the MC could distinguish drivers wearing placebo and AIGs, as well as the pitch and roll frequency of the head. Deep learning can be used to predict the intoxication of MC riders. The predictive accuracy of the algorithm shows a viable opportunity for the use of movement to monitor drunk riders on the road.

Revisiting Reentry Roll Resonance

This paper revisits the subject of reentry roll resonance, which occurs when the roll rate and pitch frequency become equal in a spinning reentry vehicle. A first-principles model is developed and analyzed numerically and by using a reduced-order pendulum model for the relative phase of the roll and pitch/yaw axes. The results show good qualitative agreement with recent flight data and provide a natural physical interpretation. Based on the model it is suggested that sustained roll resonance depends primarily on the initial phase relationship between the pitch and roll axes, in addition to the vehicle moments of inertia and the vehicle symmetry. Finally the model is used to propose a mechanism for sustained resonance in vehicles spinning about a major axis, a condition previously thought to be forbidden.

Cortical representation of musical pitch in event-related potentials

Neural coding of auditory stimulus frequency is well-documented; however, the cortical signals and perceptual correlates of pitch have not yet been comprehensively investigated. This study examined the temporal patterns of event-related potentials (ERP) in response to single tones of pitch chroma, with an assumption that these patterns would be more prominent in musically-trained individuals than in non-musically-trained individuals. Participants with and without musical training (N = 20) were presented with seven notes on the C major scale (C4, D4, E4, F4, G4, A4, and B4), and whole-brain activities were recorded. A linear regression analysis between the ERP amplitude and the seven notes showed that the ERP amplitude increased or decreased as the frequency of the pitch increased. Remarkably, these linear correlations were anti-symmetric between the hemispheres. Specifically, we found that ERP amplitudes of the left and right frontotemporal areas decreased and increased, respectively, as the pitch frequency increased. Although linear slopes were significant in both groups, the musically-trained group exhibited marginally steeper slope, and their ERP amplitudes were most discriminant for frequency of tone of pitch at earlier latency than in the non-musically-trained group (~ 460 ms vs ~ 630 ms after stimulus onset). Thus, the ERP amplitudes in frontotemporal areas varied according to the pitch frequency, with the musically-trained participants demonstrating a wider range of amplitudes and inter-hemispheric anti-symmetric patterns. Our findings may provide new insights on cortical processing of musical pitch, revealing anti-symmetric processing of musical pitch between hemispheres, which appears to be more pronounced in musically-trained people.

Neural coding of dichotic pitches in auditory midbrain.

Dichotic pitches such as the Huggins pitch (HP) and the binaural edge pitch (BEP) are perceptual illusions whereby binaural noise that exhibits abrupt changes in interaural phase differences (IPDs) across frequency creates a tonelike pitch percept when presented to both ears, even though it does not produce a pitch when presented monaurally. At the perceptual and cortical levels, dichotic pitches behave as if an actual tone had been presented to the ears, yet investigations of neural correlates of dichotic pitch in single-unit responses at subcortical levels are lacking. We tested for cues to HP and BEP in the responses of binaural neurons in the auditory midbrain of anesthetized cats by varying the expected pitch frequency around each neuron's best frequency (BF). Neuronal firing rates showed specific features (peaks, troughs, or edges) when the pitch frequency crossed the BF, and the type of feature was consistent with a well-established model of binaural processing comprising frequency tuning, internal delays, and firing rates sensitive to interaural correlation. A Jeffress-like neural population model in which the behavior of individual neurons was governed by the cross-correlation model and the neurons were independently distributed along BF and best IPD predicted trends in human psychophysical HP detection but only when the model incorporated physiological BF and best IPD distributions. These results demonstrate the existence of a rate-place code for HP and BEP in the auditory midbrain and provide a firm physiological basis for models of dichotic pitches.NEW & NOTEWORTHY Dichotic pitches are perceptual illusions created centrally through binaural interactions that offer an opportunity to test theories of pitch and binaural hearing. Here we show that binaural neurons in auditory midbrain encode the frequency of two salient types of dichotic pitches via specific features in the pattern of firing rates along the tonotopic axis. This is the first combined single-unit and modeling study of responses of auditory neurons to stimuli evoking a dichotic pitch.

Tracking the emergence of a pitch hierarchy using an artificial grammar requires extended exposure

IntroductionThe tonal hierarchy is a perceived musical structure implicitly learned through exposure. Previous studies have demonstrated that new grammars, for example based on the Bohlen-Pierce scale, can be learned in as little as 20 minutes.MethodsIn this study, we created two grammars derived from the Bohlen-Pierce scale similar in complexity to the western tonal hierarchy. Participants rated the goodness-of-fit of all Bohlen-Pierce scale notes in a probe tone paradigm before and after 30 minutes of exposure to one of the two grammars. Participants were then asked about their experience in a short interview.ResultsResults do not support the learning of the artificial grammar: correlations between goodness-of-fit ratings and pitch frequency distribution of a grammar were no different before and after exposure to a grammar. Interviews suggest that participants are bad at identifying the strategy they used to complete the task. Testing the strategies reported on the data revealed that ratings decreased with increasing distance of the probe tone from the tonic.DiscussionThis is consistent with early brain responses to chromatic pitches of the tonal hierarchy. We suggest that longer exposure time is necessary to learn more complex grammars.

Experimental assessment of Theodorsen's function for uncoupled pitch–plunge motion

The accuracy of Theodorsen's lift model for pure-pitch, pure-plunge and combined pitch–plunge oscillations of a two-dimensional model is compared with wind tunnel results. The reduced frequency of the oscillation was in the range of 0.01<k<0.15, and the freestream Reynolds number was in the range of 130 000<Re<400 000. The lift response to an uncoupled combined pitch–plunge motion (for which the frequency of pitch and plunge motions were not the same) is discussed using experimental results. The Theodorsen’s lift model is rewritten for the general uncoupled pitch–plunge motions by a linear superposition of all components of the airfoil bound circulation. Both amplitude and phase from the Theodorsen's function are compared with those of the wind tunnel data, and the results are discussed. The Theodorsen’s function is found to be a good estimator for both pure-pitch and pure-plunge motions. It further appropriately estimates the lift amplitude for the case of coupled pitch–plunge motion; however, the prediction is not accurate for the uncoupled pitch–plunge motion. A motion amplitude ratio is defined, which shows the level of aperiodicity of the motion. Discrepancy between experimental and analytical results increase with the reduction of the lift amplitude ratio and with the deviation of frequency ratio from unity.

Detection of the Bedload Movement with an Acoustic Sensor in the Yangtze River, China

The acoustic method, which enables continuous monitoring with great temporal resolution, is an alternative technique for detecting bedload movement. In order to record the sound signals produced by the impacts between gravel particles and detect the bedload motion, in this study, a hydrophone is placed close to the riverbed at the upper Yangtze River. Three categories of raw audio signals—moving gravel particles, ship engines, and flow turbulence—are collected and investigated. Signal preprocessing is performed using spectral subtraction to reduce the noise of the background sound, and the sound signal characteristic parameters are then calculated. In this paper, we propose a novel method for detecting and extracting bedload motion parameters, including peak frequency, pitch frequency, and energy eigenvector. When a segment of a speech signal meets the indicators for all three feature parameters simultaneously, the segment signal is classified as a bedload motion sound signal. Further work will be conducted to investigate bedload transport using the extracted audio signal.

Contribution of the ventral pouch in the production of mouse ultrasonic vocalizations.

Mouse ultrasonic vocalizations (USVs) are of communicative significance and can serve as one of the major tools for behavioral phenotyping in mouse models of neurological disorders with social communication deficits. Understanding and identifying the mechanisms and role of laryngeal structures in generating USVs is crucial to understanding neural control of its production, which is likely dysfunctional in communication disorders. Although mouse USV production is accepted to be a whistle-based phenomenon, the class of whistle is debatable. Contradictory accounts exist on the role of a specific rodent intralaryngeal structure-the ventral pouch (VP), an air-sac-like cavity, and its cartilaginous edge. Also, inconsistencies in the spectral content of fictive USVs and real USVs in models without the VP points us to re-examine the role of the VP. We use an idealized structure, based on previous studies, to simulate a two-dimensional model of the mouse vocalization apparatus with the VP and without the VP. Our simulations were performed using comsol Multiphysics to examine characteristics of vocalizations beyond the peak frequency (f_{p}), like pitch jumps, harmonics, and frequency modulations, important in context-specific USVs. We successfully reproduced some of the crucial aspects of mouse USVs mentioned above, as observed through the spectrograms of simulated fictive USVs. Conclusions about the lack of a role of the mouse VP were previously made in studies primarily examining f_{p}. We investigated the impact of the intralaryngeal cavity and the alar edge on the simulated USV features beyond f_{p}. For the same combinations of parameters, removing the ventral pouch resulted in an alteration of the call characteristics, dramatically removing the variety of calls observed otherwise. Our results thus provide evidence supporting the hole-edge mechanism and the possible role of the VP in mouse USV production.

Study on aerodynamic performance and wake characteristics of a floating offshore wind turbine under pitch motion

The unsteady aerodynamic characteristics and interference effects of floating offshore wind turbine (FOWT) are mainly affected by the pitch motion of the ocean platform. Based on computational fluid dynamics (CFD) and advanced overset grid technology, the aerodynamic performance and wake characteristics of a fully configured wind turbine with rotating blades, nacelle , and tower are studied in this paper. The effects of the amplitude and frequency of pitch motion on the wind turbine aerodynamic loads and flow field are investigated herein in detail. The power and thrust between numerical simulation and experiment are compared. The results show that the grid and simulation parameters used in this study can accurately capture the aerodynamic characteristics and the flow field around wind turbines. The influence of the pitch amplitude and frequency on the performance of wind turbines is discussed. The complex flow interaction between the tip vortex, tower shedding vortex, and the turbulent wake was observed. The present results indicate that the pitch motion amplitude and frequency have a great influence on the power, thrust, and wake characteristics.

Hydrodynamic characteristics of a pitching hydrofoil in unsteady uniform inflow with special emphasis on the hysteresis effect

Numerical flow simulations on a Clark-Y pitching hydrofoil are carried out to study the effect of an unsteady uniform inflow on the dynamic characteristics and the corresponding flow structure. The representative hysteresis phenomenon of pitching hydrofoil is observed and analyzed emphatically. In this study, the pitching motion trajectory is a triangular wave with mean incidence of α0 = 10° and amplitude of Δα0 = 5° at a pitching frequency f* of 2 Hz. The amplitude of unsteady uniform velocity ΔU is set 0, 0.75, 1.50, 3.0 respectively, and the frequency of unsteady uniform velocity f of 1, 2, 4 were chosen. The numerical method is validated through the experimental results at ΔU = 0. Results revealed that pitching motion and unsteady uniform inflow both lead to the occurrence of hysteresis effect, and two hysteresis effect quantization parameters (the hysteresis parameter εCL and hysteresis area SCL) were defined. Results showed that the relationship between ΔU, f and the two parameters is respectively linear and nonlinear. Meanwhile, the values of ΔU, f directly determine the contribution of unsteady uniform inflow to hydrodynamic hysteresis effect. In addition, ΔU and f have a significant impact on the flow structures and the development of vortices. However, ΔU and f don't change vortex structure directly, but affect the formation and dwell time of vortex structure significantly, thus leading to the different hydrodynamic characteristics.