Pitch Period Research Articles

Characterization of wake interference between two tandem offshore floating vertical-axis wind turbines: Effect of platform pitch motion

The wake interference within the offshore wind farms, especially with the tandem arrangement scenario, affects the designed total power output. Also, the six degrees of freedom motions of the platforms not only can change the aerodynamics of the offshore floating wind turbines, but also may influence the wake interference between them. In the present study, the effect of the platform pitch motion on the wake interference between two tandem offshore floating vertical-axis wind turbines (VAWTs) is characterized using the improved delayed detached-eddy simulation (IDDES). First, the power performance of the downstream turbine (VAWT Ⅱ) at different separation distances, 2D ≤ LS ≤ 10D, and tip speed ratios, 0.4 ≤ TSRⅡ ≤ 1.5, are analyzed, assuming that the upstream turbine (VAWT Ⅰ) is bottom-fixed and operates at an optimal TSRⅠ of 1.2. Then, the effects of the pitch amplitude, 5° ≤ APⅠ ≤ 15°, and pitch period, 2TⅠ ≤ TPⅠ ≤ 8TⅠ, on the wake interference are characterized by assuming that the platform pitch motion of VAWT Ⅰ follows a prescribed simple harmonic law. The results show that locating VAWT Ⅱ in the medium wake region of VAWT Ⅰ, e.g., LS = 6D, can appropriately balance the power performance and space cost of the bottom-fixed turbine array. Also, the platform pitch motion can reduce the mean velocity deficit in the core wake region of VAWT Ⅰ. The mean wake deficit reduction increases the averaged power coefficient of VAWT Ⅱ, e.g., up to 22.67% when LS = 6D, TSRⅡ = 1.2, APⅠ = 15°, and TPⅠ = 4TⅠ. In addition, relatively larger pitch amplitudes and smaller pitch periods will further alleviate the negative effect of the wake interference. This study may serve as a reference for designing offshore floating wind farms.

Influence of pitching motion on the hydrodynamic performance of a horizontal axis tidal turbine considering the surface wave

A CFD numerical method is established under the wave-current condition, used to analyze the hydrodynamic performance of a horizontal-axis tidal turbine based on floating platform with rotation and pitching motion. The inflow direction load, pitch moment and power coefficients with different depths of the blade tip-immersion, the periods and amplitudes of the pitch, wave heights are obtained. The three coefficients have obvious periodically fluctuated with the pitching and wave frequencies, while the time mean of those have changed little with increasing of the depth of blade tip-immersion, wave height, pitch (wave) period and pitching amplitude. So considering damping and additional mass forces, a load fitting model is established, and the damping and additional mass coefficients are calculated by the least square method. The influence of damping coefficient on the hydrodynamic loads is obvious, while the influence of additional mass coefficient on that can be neglected, and the damping coefficient of inflow direction load coefficient is basically stable. The damping coefficients of the pitching moment and power coefficients fluctuate periodically, but the mean value of damping coefficients keep stable. The research results in this paper are important for studying the coupling motion of the turbine and the floating platform.

Control Considerations for Very Large Floating Wind Turbines

Increasingly large floating wind turbines (FWTs) are being introduced to access the offshore wind resource over deep water at lower cost. In connection with designing a 25 MW semi-submersible wind turbine, we examine the scaling trends associated with the dynamic performance of the generator torque and blade pitch controllers and highlight the challenges that may be encountered for such devices. The increased rotor inertia, reduced blade pitch rates, longer platform pitch and surge natural periods, and flexible modes of the tower, platform, and rotor all affect the ability of the controller to track the desired rotor speed. The effects of control design and tuning choices on the FWT behavior in representative wind and wave conditions are shown.

Model tests and numerical simulations on the parametric resonance of the deep draft semi-submersible under regular waves

Parametric resonance of the deep draft semi-submersible (DDS) under regular waves are investigated experimentally and numerically. Special focus is put on the occurrence of parametric resonance under weak or failure mooring condition. Firstly, model tests with and without mooring chains are conducted in wave flume. From results of model without mooring chains, it is observed that parametric resonance occurs when wave period is about the natural period of heave and half of the natural period of pitch or roll. The steady amplitude of parametric resonance is larger under higher wave. In heading waves, parametric resonance occurs in roll direction, while parametric resonance occurs in both roll and pitch direction for beam wave. For the model with 12 mooring chains, parametric resonance does not occur under strong mooring restriction. Whereas for the model with four mooring chains representing a failure mooring condition, parametric resonance occurs in pitch direction. Then, numerical simulations under cases same as experiments are conducted using a potential-theory based weakly nonlinear model. Parametric resonance is successfully reproduced numerically. Furthermore, through comparison with experiments, it is found that the numerical model accurately predicts steady amplitudes and occurring wave periods of parametric resonance except for cases with four mooring chains.

Numerical analysis of the porpoising motion of a blended wing body aircraft during ditching

The ditching performance of a BWB aircraft is studied using the numerical method. The unsteady Reynolds-Averaged Navier-Stokes equations and the Realizable k−ε turbulence model are solved by the finite volume method, the implicit volume-of-fluid model is adopted to capture the water-air interface, the six-degree-of-freedom model is employed to couple fluid dynamics and aircraft rigid-body kinematics, and the global moving mesh is used to deal with the relative motion between the aircraft and the water. The accuracy of the present numerical method is validated by the high-speed ditching experiment of a 3D flat plate. The porpoising motion of the BWB aircraft during ditching is discovered for the first time, and this motion is independent of the initial pitch angle, i.e., the amplitude and period of the motion and load curves are coincident for different initial angles. The porpoising motion is determined by a couple of hydrodynamic and aerodynamic loads, and the total load peak is mainly caused by the former. The hydrodynamic load is mainly from the staggered positive-negative pressure stripe on the aircraft belly. The variation in aerodynamic load is mainly induced by the compression work in the dynamic ground effect.

Numerical Study on the Tank Heel Determination Using Smoothed Particle Hydrodynamics

Tank heel minimization is a significant issue in the design of LNG fuel tanks because it is associated with stable suction pump operation and thermal shock requirements during LNG bunkering. This study examined how the LNG tank heel is minimized, maintaining a suction pump fully submerged in LNG during dynamic vessel motion. The study assumed two LNG fuel tanks mounted on the forward deck of a 50,000 deadweight class oil product carrier. Information on the dimensions and shape of the LNG fuel tank was determined from Wartsila’s brochure, and the specifications of Vanzetti’s suction pump were referred to. The LNG fuel tank and LNG heel were modeled as rigid elements and hydrodynamically smoothed-particles, respectively. The number of particles could be determined by performing even keel analyzes by adding or subtracting particles until the target head was satisfied under the gravity load. To simulate the motion of the LNG fuel tank, the pitch and roll periods and amplitudes of the ship were calculated using the DNV classification rules. Visual observations of the dynamic flow during the pitch and roll motions with respect to the ship’s center of mass showed that the roll motion was more critical from the viewpoint of the LNG heel than the pitch motion. After performing the simulations for three cycles of roll and pitch motions, the suction pump submergence was reviewed in the last cycle. Under the conditions assumed in this study, a filling ratio of 15% was determined as the minimum LNG tank heel. Although the LNG heel has customarily been determined, the LNG heel needs to be determined through hydrodynamic analyses of each vessel because it depends on the shape of the fuel tank and the vessel motion characteristics.

Design and Analysis of Horizontal Axis Wind Turbine (HAWT) Blades Using CFD

Abstract: Within the current years wind power is extensively taken into consideration and applied as one of the most promising renewable electricity assets. In the recent studies have a look at, aerodynamic analysis of horizontal axis turbine is achieved with the aid of using cfd. Blades which can be often possible for industrial grade wind turbines embody a directly span-wise profile in conjunction with airfoil fashioned go sections. Wind tunnel test is applied in order to check aerodynamic efficiency wind turbine blade. The goal of this study is to design a wind turbine. The layout manner includes the choice of the sun machine for max efficiency and wind turbine kind and the determination of the blade airfoil, pitch attitude distribution along the radius, and chord duration distribution along the radius. The pitch angle and chord period distributions are optimized primarily based on conservation of angular momentum and principle of aerodynamic forces on an airfoil. Blade element momentum (BEM) principle is first derived then used to conduct a parametric observe to be able to determine if the optimized values of blade pitch and chord period create the maximum green blade geometry. This work includes a discussion of the most important parameters in wind turbine blade layout to maximize efficiency. Keywords: Wind Turbine, HAWT, BEM Theory, Parametric Study, Maximization of efficiency etc.

RETRACTED ARTICLE: Powerful basic frequency extraction from monophonic signs utilizing versatile sub-band separating

Basic frequency (f0) extraction assumes a significant function in the handling of monophonic signals, for example, discourse and tune. It is fundamental in different ongoing applications like feeling acknowledgment, discourse/performing voice segregation, etc. A few f0 extraction techniques have been proposed throughout the long term, yet nobody calculation functions admirably for both discourse and tune. Previously an efficient method for extracting pitch from speech signals for HMM-based speech synthesis system, voicing detection and pitch estimation is performed using the mean signal obtained from Continuous Wavelet Transform (CWT) coefficients. Both objective and subjective evaluation results show that the quality of speech synthesized with the proposed pitch estimation method is much better compared with HMM-based speech synthesis systems developed using the state-of-the-art pitch extraction methods, namely, Robust Algorithm for Pitch Tracking (RAPT) and Speech Transformation and Representation using Adaptive Interpolation of weighted spectrum (STRAIGHT) employed in HTS. Zero-frequency filter (ZFF) is used to derive the locations of impulse excitation. An algorithm is presented for the estimation of the fundamental frequency (F0) of speech or musical sounds, the well-known autocorrelation method with a number of modifications that combine to prevent errors. The algorithm has several desirable features. Error rates are about three times lower than the best competing methods, as evaluated over a database of speech recorded together with a laryngograph signal. In this paper, we propose a novel methodology that can precisely appraise f0 from discourse just as tunes. To begin with, voiced/unvoiced recognition is performed utilizing a novel RNN-LSTM based methodology. At that point, each voiced edge is disintegrated into a few sub-groups. From each sub-band of a voiced casing, the applicant pitch periods are distinguished utilizing autocorrelation and non-straight activities. At last, Viterbi interpreting is utilized to shape the last pitch forms. The presentation of the proposed technique is assessed utilizing mainstream discourse (Keele, CMU-Cold), and melody (MIR-1K, Verses) information bases. The assessment results show that the proposed strategy performs similarly well for discourse and monophonic melodies and is superior to the best in class techniques. Further, the viability of proposed f0 extraction strategy is exhibited by building up an intelligent SARGAM learning apparatus. The most generally utilized f0 extraction strategies are Praat and Riveted. The proposed method increases the performance nearly 81.8% and 35.2% compared to existing methods.

Usage of Prosody Modification and Acoustic Adaptation for Robust Automatic Speech Recognition (ASR) System

Most of the automatic speech recognition (ASR) systems are trained using adult speech due to the less availability of the children's speech dataset. The speech recognition rate of such systems is very less when tested using the children's speech, due to the presence of the inter-speaker acoustic variabilities between the adults and children's speech. These inter-speaker acoustic variabilities are mainly because of the higher pitch and lower speaking rate of the children. Thus, the main objective of the research work is to increase the speech recognition rate of the Punjabi-ASR system by reducing these inter-speaker acoustic variabilities with the help of prosody modification and speaker adaptive training. The pitch period and duration (speaking rate) of the speech signal can be altered with prosody modification without influencing the naturalness, message of the signal and helps to overcome the acoustic variations present in the adult's and children's speech. The developed Punjabi-ASR system is trained with the help of adult speech and prosody-modified adult speech. This prosody modified speech overcomes the massive need for children's speech for training the ASR system and improves the recognition rate. Results show that prosody modification and speaker adaptive training helps to minimize the word error rate (WER) of the Punjabi-ASR system to 8.79% when tested using children's speech.

Research on hydrodynamic characteristics of horizontal axis tidal turbine with rotation and pitching motion under free surface condition

To obtain the hydrodynamic loads of a floating horizontal-axis tidal turbine with rotation and pitching motion under the free surface condition, a numerical simulation method based on CFD is established. The inflow direction load, power and pitching moment coefficients at different pitch periods, pitch amplitudes and blade tip-immersion depths were analyzed. The results show that the instantaneous values of the inflow direction load, power and pitching moment coefficients have obvious periodic fluctuations, and the fluctuation amplitude increases with the increase of the pitch frequency and amplitude. On this basis, the damping and additional mass coefficients are obtained based on the least square method. The damping coefficient of inflow direction load and power coefficients fluctuates periodically, and the fluctuation period is equal to the pitch period. The damping coefficient of pitching moment coefficient also fluctuates periodically, and the fluctuation period is not only related to pitch period, but also related to the rotation period of the turbine. The research findings can provide relevant data for studying the coupling motion of floating tidal current energy device and control design of the output electricity.

Aerodynamic performance assessment of φ-type vertical axis wind turbine under pitch motion

The floating vertical axis wind turbine (VAWT) is considered as a competitive device in the utilization of offshore wind energy. However, the platform pitch motion would affect its aerodynamic behavior. In this paper, the aerodynamic performance of a floating φ-type VAWT under pitch motion is investigated by using the Improved Delayed Detached Eddy Simulation SST k−ω turbulence model. After verifying the feasibility of the numerical model, the effects of pitch motion amplitude and period on the aerodynamic characteristics were evaluated, and the impacts of these observations were elucidated. The results showed that the averaged net power coefficient increment of about 1.5%–15% could be obtained under platform pitch motions, and the fluctuation of aerodynamic loads was found to increase. Besides, the pitch motion pattern could be regarded as the combination of surge and heave motions, which explained the similarity of their effects on the wind turbine aerodynamics. Furthermore, it was found that the frequency of the peak torque coefficient would change under different periods of pitch motion, which should be noticed in the design of floating wind turbine. Finally, it was concluded that the current study provided additional information about the effect of pitch motion on wind turbine aerodynamics.

Acoustic cues to coda stop voicing contrasts in Australian English-speaking children.

While voicing contrasts in word-onset position are acquired relatively early, much less is known about how and when they are acquired in word-coda position, where accurate production of these contrasts is also critical for distinguishing words (e.g., dog vs. dock). This study examined how the acoustic cues to coda voicing contrasts are realized in the speech of 4-year-old Australian English-speaking children. The results showed that children used similar acoustic cues to those of adults, including longer vowel duration and more frequent voice bar for voiced stops, and longer closure and burst durations for voiceless stops along with more frequent irregular pitch periods. This suggests that 4-year-olds have acquired productive use of the acoustic cues to coda voicing contrasts, though implementations are not yet fully adult-like. The findings have implications for understanding the development of phonological contrasts in populations for whom these may be challenging, such as children with hearing loss.

Effects of vocal nodules on acoustic characteristics of voice in children : an acoustic analysis of voice.

Objective : In the present study, an attempt was made to evaluate the acoustic characteristics of voice in pediatric patients with vocal nodules using acoustic analysis of voice. Methods : Thirty-five pediatric patients with vocal nodules and 32 control children without dysphonia were enrolled in this study. Their voice samples were analyzed using the Multi-Dimensional Voice Program. Acoustic parameters of voice, such as pitch period perturbation quotient (PPQ), amplitude perturbation quotient (APQ), and noise-to-harmonic ratio (NHR), were measured. Results : In phonation at a loudness of over 80 dBA, the PPQ, APQ, and NHR values of the voice significantly increased in children with vocal nodules than in the control children without dysphonia. The sensitivities and specificities of PPQ, APQ, and NHR for prediction of vocal nodules in children were 62.86% and 84.38%, 74.29% and 75.00%, and 31.43% and 93.75%, respectively. Discussion : The present findings suggest that vocal nodules affect vocal fold vibration, resulting in impaired control of pitch and loudness leading to increased noise components. NHR could be used to evaluate the efficacy of treatment, such as voice rehabilitation, in pediatric patients with vocal nodules because of its high specificity for prediction of vocal nodules in children. J. Med. Invest. 68 : 276-279, August, 2021.

Sensitivity Study on Influencing Factors of Coupled Motion Characteristics for Truss Spar

In the absence of mooring condition, the heave and pitch coupled equations are established considering the effect of static stability and wave surface elevation for a truss spar platform. The influence of the change of the pitch period and the external excitation force (combined wave loads and wind loads together) on the stability of the heave-pitch coupling motion is studied by means of numerical iteration method. The results show that when the wave frequency is close to the natural heave frequency besides the heave-pitch frequency ratio is close to 2: 1, both of the amplitude of heave and pitch motion are increased considering the wind loads. It is about 12 percent increase for heave motion, while 8 percent for pitch motion. Meanwhile, there is a penetration phenomenon between heave and pitch. And the wind load play a more important role in pitch motion, the characteristic frequency of pitch motion will have an obvious change between 1/2 times sub harmonic motion frequency component and 1 time forced motion frequency component considering the wind load.

Experimental investigation on a dual chamber floating oscillating water column moored by flexible mooring systems

A series of 1:50 model tests are conducted to study the motion responses and energy harvesting performance of a novel dual chamber floating oscillating water column device moored by three flexible mooring systems in regular and irregular waves. This novel energy conversion device consists of one traditional oscillating water column chamber and one Backward Bend Duct Buoy chamber. The mooring systems, include one modified Catenary Anchor Leg Mooring concept and two compact mooring systems, designed for station keeping of this specific floating device. Strong nonlinearities of mooring tension are found, especially in the low wave period sea conditions. It is also found that the surge and yaw motion has significant differences when the device moored by the different mooring systems. The pitch and heave natural periods are derived from their Responses Amplitude Operator curves. The performance of spectral methods in mooring fatigue damage estimation depends on mooring configuration and material. It is seen that the attached clump weights affect the fatigue damage of the compact mooring rope. It has been found that the novel device shows good performance in energy harvesting within broad range of wave periods, and the influence of mooring configuration on energy conversion performance depends on the wave height.

Surgical effects of type-I thyroplasty and fat injection laryngoplasty on voice recovery

ObjectiveType-I thryroplasty, also known as medialization thyroplasty (MT) and autologous fat injection laryngoplasty (FIL) are one of the main surgical treatments for unilateral vocal fold paralysis (UVFP). Both procedures have the same concept of completing the glottal closure by medializing the vocal fold, although the surgical approaches are quite different. In order to assess these surgical effects, we examined the treatment outcomes and benefits of the two surgeries. MethodsWe collected data from the 135 phonosurgeries that we performed out of 375 patients with UVFP at Osaka Voice Center, Osaka Kaisei Hospital from January 2009 to February 2013. After excluding cases with glottal level differences on phonation, either MT or FIL were performed on 80 cases. The inclusion criteria for the present study were: (1) patients had no history of previous phonosurgery, and (2) functional evaluations were available before/after surgery. Consequently, 43 participants (12 for MT and 31 for FIL) were enrolled in this study. Surgical effects were evaluated by means of the maximum phonation time (MPT), pitch period perturbation quotient (PPQ), amplitude perturbation quotient (APQ), and harmonic to noise ratio (HNR) just before, one month, and 6 months after surgery. ResultsBoth MT and FIL showed significant improvement in MPT (MT, p = 0.005; FIL, p < 0.001) and PPQ (MT, p = 0.047; FIL, p = 0.041) at 1 month postoperation. We also compared the variation of each variable between the two procedures, but there were no significant differences in these parameters. However, MPT, APQ, and HNR at the post-MT after 6 months worsened compared to those at 1 month posttreatment, whereas MPT showed only a slight decrease from the 1st month to the 6th month in those with FIL. ConclusionBoth MT and FIL were effective for the voice recovery in patients with UVFP. Our findings suggest that surgical results in FIL might be better than those in MT 6 months after surgery, although there were no significant differences between these two procedures 1 month postoperation.

Speech Signal Analysis in Phase Domain

Speech signal analysis based on the Phase Spectrum (PS) in the recent years becomes more popular to the researchers due to its attractive properties. Though some problem arises during its processing but appropriate modification gives the useful result. In this study, we proposed a new method of speech signal analysis based on its phase spectral representation. After analyzing the PS we modified it vocal tract dominated spectrum by utilizing the minimum-phase stable component of the speech spectrum. The modified signal holding only the phase spectral component is used for the parametric modeling of the speech signal to estimate the characteristics of vocal tract perfectly. This extracted feature was found to provide complementary evidence from the magnitude spectrum of speech but with better resolution. According to perceptual analysis, the PS takes precedence over the magnitude spectrum. This research utilizes the Group Delay (GD) spectrum as a representative of the PS because of its meaningful characteristic. All pole modeling is performed on the signal evaluated from the GD spectrum to find the resonances of the vocal tract system accurately. The effectiveness of the method is tested by synthesizing some vowels over a range of pitch periods from low to high pitched speech. The validity of the proposed method is also verified by plotting the formant contour on the spectrogram of a sentence from the TIMIT database and standard F2-F1 plot of natural speech spoken by male and female speakers. The proposed method performs better than the state-of-the-art methods.

Periodicity Pitch Perception.

This study presents a computational model to reproduce the biological dynamics of “listening to music.” A biologically plausible model of periodicity pitch detection is proposed and simulated. Periodicity pitch is computed across a range of the auditory spectrum. Periodicity pitch is detected from subsets of activated auditory nerve fibers (ANFs). These activate connected model octopus cells, which trigger model neurons detecting onsets and offsets; thence model interval-tuned neurons are innervated at the right interval times; and finally, a set of common interval-detecting neurons indicate pitch. Octopus cells rhythmically spike with the pitch periodicity of the sound. Batteries of interval-tuned neurons stopwatch-like measure the inter-spike intervals of the octopus cells by coding interval durations as first spike latencies (FSLs). The FSL-triggered spikes synchronously coincide through a monolayer spiking neural network at the corresponding receiver pitch neurons.

Implementation of xgboost for classification of parkinson’s disease

Parkinson’s Disease (PD) is an advanced neurodegenerative illness. It is about 90% of PD sufferer shows speech disorders in the initial stages. Hence, in this research, speech features were applied to classify this illness. The most famous speech features used in PD research are jitter, shimmer, fundamental frequency parameters, harmonicity parameters, Recurrence Period Density Entropy (RPDE), Detrended Fluctuation Analysis (DFA), and Pitch Period Entropy (PPE).Those features were then called as baseline features used in this research. In this research, the XGBoost algorithm was used for the classification of PD. Initially, the whole baseline features were used in the XGBoost algorithm and obtained an accuracy score of the model 84.80%. For improving the model, feature selection was performed by plotting feature importance, which causes features of locShimmer (Fscore = 3) was excluded from the model. After feature selection was performed, the accuracy score of the model has increased to 85.60 %. We tried to improve the model using for second features selection, by excluding features with F-score values less than 20. However, after performed this feature selection, the accuracy of the model was decreased to 84.40 %. Thus, the model used is the model with an accuracy of 85.60%.

Determination of glottal closure instants from clean and telephone quality speech signals using single frequency filtering

A new approach for determining the glottal activity from speech signals is presented in this paper. The approach is based on the use of single frequency filtering (SFF), proposed recently for voice activity detection. The variance (across frequency) of the spectral envelopes at each sampling instant is derived using the SFF of speech signal. The variance plot shows discontinuities corresponding to the impulse-like excitation within each glottal cycle. The proposed method uses filtering, thus avoiding the window effects of block processing, but the temporal resolution of the frequencies is still determined by the filtering process. The method also does not assume any knowledge of the average pitch period to derive the glottal activity features, such as the locations of the glottal closure instants (GCIs). The proposed GCI detection method is evaluated on five databases and compared with four existing methods on clean speech and telephone quality speech. From the experiments, it is observed that the performance of the proposed method is comparable to the existing methods on clean speech and significantly better on telephone quality speech.