Dynamic Pitch Research Articles

A robust adaptive error state Kalman filter for MEMS IMU attitude estimation under dynamic acceleration

Accurate estimation of attitude (pitch, roll) is a prerequisite for ensuring safe navigation during vehicle control execution. In dynamic environments, the presence of acceleration often degrades the accuracy and robustness of attitude estimation using traditional algorithms with Micro-Electro-Mechanical Systems (MEMS) Inertial Measurement Unit (IMU). This paper proposes a robust adaptive error state Kalman filter (RAESKF) algorithm for attitude estimation of MEMS IMU under dynamic acceleration conditions. The RAESKF algorithm decomposes the true attitude Direction Cosine Matrix (DCM) into nominal and error components. An error state Kalman filter is utilized to fuse real-time measurements from MEMS gyroscope and accelerometer, estimating the error component, which is then used to correct the nominal attitude DCM. Furthermore, within the error state Kalman filtering framework, a dynamic acceleration robust adaptive adjustment strategy is implemented. This strategy relies on real-time data monitoring, threshold-based decision-making, and switching mechanisms. It adaptively selects between dynamic acceleration model compensation and online adjustment of the measurement noise covariance matrix. The primary objective of this strategy is to mitigate the impact of disturbance induced by dynamic acceleration on attitude estimation, thereby enhancing the accuracy and robustness. Laboratory rotation experiments have demonstrated that the algorithm improved pitch and roll measurement accuracy by at least 8.81% and 11.69%, respectively, under rotational conditions. In dynamic acceleration conditions, pitch and roll measurement accuracy improved by at least 42.76% and 67.21%, respectively.

Aerodynamic Characterization of a Hypersonic Projectile Using Acceleration-Based Measurements and Numerical Methods

Armor-piercing fin-stabilized projectiles stand out by their exceptionally high slenderness ratios and ground-level flight at super- and hypersonic speeds. As space constraints limit the integration of measurement equipment into such slender test models, nonintrusive measurement techniques become favorable. The present analysis demonstrates a renewed approach to the free-flight technique, which sets models into unconstrained flight through the test section. It enabled the evaluation of the quasi-steady drag, lift, and pitching moment characteristics, and, to some extent, also the dynamic pitch damping characteristics. An alternative to the free-flight technique is the free-oscillation technique, which limits the motion to a rotation around the center of gravity. The free-oscillation technique allowed a higher-fidelity analysis of the static and dynamic pitching moments. Both methods were based on the analysis of the accelerations derived from trajectory tracking. This acceleration-based approach enabled the evaluation of the highly nonlinear characteristics. The high slenderness of the investigated projectile leads to a significant contribution of the viscous forces to the overall drag. These viscous forces are sensitive to the laminar-turbulent boundary-layer state, as well as the thermal boundary conditions. The application of a high-resolution schlieren system enabled the assessment of the local laminar-turbulent boundary-layer state, while the use of low- and high-enthalpy testing facilities enabled the assessment of the aerothermal influence. Steady-state Reynolds-averaged Navier–Stokes simulations, which included laminar-turbulent transition modeling, were employed to replicate the results of the experimental efforts.

On the unsteady aerodynamics of flapping wings under dynamic hovering kinematics

Hummingbirds and insects achieve outstanding flight performance by adapting their flapping motion to the flight requirements. Their wing kinematics can change from smooth flapping to highly dynamic waveforms, generating unsteady aerodynamic phenomena such as leading-edge vortices (LEV), rotational circulation, wing wake capture, and added mass. This article uncovers the interactions of these mechanisms in the case of a rigid semi-elliptical wing undergoing aggressive kinematics in the hovering regime at Re∼O(103). The flapping kinematics were parametrized using smoothed steps and triangular functions and the flow dynamics were simulated by combining the overset method with large eddy simulations. The analysis of the results identifies an initial acceleration phase and a cruising phase. During the former, the flow is mostly irrotational and governed by the added mass effect. The added mass was shown to be responsible for a lift first peak due to the strong flapping acceleration. The dynamic pitching and the wing wake interaction generate a second lift peak due to a downwash flow and a vortex system on the proximal and distal parts of the wing's pressure side. Conversely, aerodynamic forces in the cruising phase are mainly governed by the growth and the establishment of the LEV. Finally, the leading flow structures in each phase and their impact on the aerodynamic forces were isolated using the extended proper orthogonal decomposition.

A CFD Analysis of Oscillating Airfoil with Leading Edge Roughness: Comparing Correlations for Equivalent Sand Grain Roughness

Numerical simulations express surface roughness as equivalent sand grain roughness values, so the correlation is required to convert realistic roughness into equivalent sand grain roughness values. The correlations were designed to match the wall velocity distributions for static cases with roughness, and they accurately predicted roughness effects when applied to URANS simulations. Several studies have examined the roughness effect on dynamic pitching airfoils. Still, they have only considered the presence of roughness, neglecting the process of converting the actual roughness to equivalent sand-grain roughness. Thus, in the present study, we apply a static case-based equivalent sand-grain roughness correlation to dynamic pitching analysis to validate the suitability of each correlation and verify the significance of correlation parameters. It was observed from a comparison study between numerical aerodynamic coefficients and experimental data from Ohio State University that physical parameters such as skewness and roughness height were important parameters to predict the dynamic stall behaviour more accurately. It was also observed that dynamic stall prediction accuracy is affected by the frequency and type of airfoil, and through this, it was confirmed that there are additional factors to consider when using an equivalent sand grain roughness correlation on pitching airfoils.

Dynamic individual pitch control for wake mitigation: Why does the helix handedness in the wake matter?

Wind farm flow control aims at mitigating wake effects in order to maximize power production in wind farms. This work mostly focuses on the Helix strategy, which relies on individual pitch control to radially offset the application point of the thrust force from the rotor center and to dynamically change its azimuthal position. Previous studies have shown that power gains for a downstream turbine are higher for a counter-clockwise (CCW) rotation of the application point than for a clockwise (CW) one. In the CCW case, the wake develops as a right-handed helix, while in the CW case, a left-handed helix is observed. Using Large Eddy Simulations, this paper shows that the helix handedness in the wake matters due to its interaction with the wake swirl. Results of the CCW and CW helix first highlight the formation of streamwise vorticity in the near wake, which is transformed into strong coherent vortices in the far wake. Those vortex structures, to some extent similar to the counter-rotating vortex pair in the wake of yawed wind turbines, are responsible for (i) displacing the wake thanks to their induced velocities and (ii) deforming the shape of the wake.

Experimental comparison of induction control methods for wind farm power maximization on a scaled two-turbine setup

Induction control methods offer a potential solution to minimizing wake effects that occur in large wind farms. This paper presents an experimental study on multiple induction control methods for wind farm power maximization. Wind tunnel experiments were conducted on two aligned scaled wind turbines. The upstream turbine was operated with static induction control, periodic dynamic induction control with collective pitch actuation, and dynamic individual pitch control (the helix approach). All wind farm control implementations were compared to a baseline case, which optimized the individual power extraction of both turbines. Tomographic particle image velocimetry was used to measure the wake of the upstream turbine. Based on turbine measurements, grid searches were employed to discover the optimal frequency and amplitude of the pitch actuation in the dynamic induction control cases. While static induction control showed increased wake velocities in the near wake, it did not provide an overall increase in power production of the two-turbine array. Dynamic induction control methods, especially the helix approach in the counterclockwise direction, were seen to significantly increase the total power output compared to the baseline control case. However, this improvement came with a larger amount of pitch actuation and increased fatigue loading of structural components in the fore-aft direction.

Novel Fuzzy Logic Controls to Enhance Dynamic Frequency Control and Pitch Angle Regulation in Variable-Speed Wind Turbines

This study introduced a novel control approach based on fuzzy logic control (FLC) to enhance the frequency regulation capacity of variable-speed wind turbines (VSWTs). The proposed method integrates FLC within droop and inertia control loops. Real-time measurements of the system frequency and the rate of change of frequency (ROCOF) serve as inputs to the FLC, enabling the method to improve the frequency response by VSWTs. In addition, the method employs FLC for pitch angle frequency control, optimizing reserve power for frequency regulation under varying wind speed levels. The innovative aspect of this study lies in the simultaneous application of FLC to pitch angle frequency control and droop/inertia control, leading to the enhanced frequency regulation capability of VSWTs and smoother operation across a range of wind speeds. Compared with traditional methods, the proposed approach provides a comprehensive and effective solution to the challenges associated with frequency regulation in VSWTs. Through simulations across different wind speed scenarios, the proposed control method demonstrated the best performance among various mature methods, highlighting the efficacy of the proposed method on the frequency regulation of VSWTs under different wind speeds. This study’s findings highlight the potential of the proposed FLC-based method to optimize frequency regulation and contribute to more reliable and efficient wind energy systems.

The influence of dynamic pitching on the aerodynamic performance of large horizontal axis wind turbines

To delve into the aerodynamic changes of wind turbines during pitching, this study employs the user-defined function (UDF) and dynamic mesh technique. The dynamic aerodynamic performance of a 3.3 MW turbine blade during variable pitch is investigated via numerical simulation. The results show that the optimal pitch angle increases with increasing incoming wind speed. At the initial and final stages of pitch change, the wind turbine experiences the influence of impact loads, leading to minor fluctuations in torque and thrust coefficients. Within the dynamic pitch change process, the pitch angle notably affects the aerodynamic performance of airfoils at blade x/ c = 0~0.6 c cross sections. The primary stress area of the airfoil contracts, with the blade root experiencing comparatively less impact. In the constant-wind-speed pitching scenario, the low-speed region in the immediate wake of the wind turbine diminishes, resulting in a 10.7% enhancement in the average wind speed at 2.5D wake.

The auditory P2 is influenced by pitch changes but not pitch strength and consists of two separate subcomponents

Abstract The P2 component of the auditory evoked potential has previously been shown to depend on the acoustic stimulus properties and prior exposure to the materials. Here, we show that it is also affected by acoustic changes, as P2 amplitudes were strongly enhanced in response to voice pitch changes with a stepwise pattern compared to dynamic pitch changes typical for natural speech, and also reflected the magnitude of these pitch changes. Furthermore, it is demonstrated that neither the P2 nor any other component is affected by the harmonicity of the materials. Despite no prior exposure and a weaker pitch, artificially created inharmonic versions of the materials elicited similar activity throughout the auditory cortex. This suggests that so-called harmonic template neurons observed in animal studies are either absent or do not exist in sufficient number in the human auditory cortex to detect their activity extracranially. Crucially, morphology as well as scalp maps and source reconstructions of the EEG data showed that the P2 appears to consist of two separate subcomponents. While the “P2a” was localised to the auditory cortex, the subsequent “P2b” included generators spread across the auditory cortex and association areas. The two subcomponents thus likely reflect processing at different stages of the auditory pathway.

Experimental and Numerical Investigations of Mini-Tab Device for Active Flow Control

The next generation of aircraft is likely to exhibit a breadth of aeromechanic and aeroelastic behaviors that will be exacerbated by the turbulent flows generated in urban environments. Exploitation of novel flow control technologies will be critical in offering greater control authority to enable this new generation of aerial vehicles for faster, safer, and more efficient flight. This study experimentally investigates the efficacy of a mini-tab active flow control device using a novel dynamic test rig. Under steady conditions, the mini-tab response exhibited nonlinearity with deployment height. Under dynamic conditions, the lift and pitching moments displayed hysteresis around their quasi-steady counterparts at low reduced frequencies (k=0.05) but displayed significant deviations at middle to high reduced frequencies (k=0.15 to 0.31) due to the formation of a tab vortex that propagates downstream. It was demonstrated, for the first time experimentally, that mini-tab dynamic performance is insensitive to unsteady airfoil motions in pitch and plunge—representative of flutter onset. Finally, an existing mini-tab model was extended to capture vortex formation on the upper and lower airfoil surfaces and modified to incorporate mini-tab rate-dependence on vortex initiation. The model showed good agreement with experimental data in both periodic and transient scenarios.

Aging affects auditory contributions to focus perception in Jianghuai Mandarina).

Speakers can place their prosodic prominence on any locations within a sentence, generating focus prosody for listeners to perceive new information. This study aimed to investigate age-related changes in the bottom-up processing of focus perception in Jianghuai Mandarin by clarifying the perceptual cues and the auditory processing abilities involved in the identification of focus locations. Young, middle-aged, and older speakers of Jianghuai Mandarin completed a focus identification task and an auditory perception task. The results showed that increasing age led to a decrease in listeners' accuracy rate in identifying focus locations, with all participants performing the worst when dynamic pitch cues were inaccessible. Auditory processing abilities did not predict focus perception performance in young and middle-aged listeners but accounted significantly for the variance in older adults' performance. These findings suggest that age-related deteriorations in focus perception can be largely attributed to declined auditory processing of perceptual cues. Poor ability to extract frequency modulation cues may be the most important underlying psychoacoustic factor for older adults' difficulties in perceiving focus prosody in Jianghuai Mandarin. The results contribute to our understanding of the bottom-up mechanisms involved in linguistic prosody processing in aging adults, particularly in tonal languages.

Perception of dynamic pitch and prominence in speech

The perception of dynamic – constantly changing – pitch in speech has been extensively studied in psychoacoustics and linguistics. In psychoacoustic studies, listeners are usually presented with short stimuli such as vowels or syllables, and their ability to discriminate a pair of stimuli is assessed. On the other hand, linguistic studies concern intonation over an utterance. Intonation entails not only acoustic prominence realised by pitch, duration, and loudness, but also listeners’ knowledge about the relative prominence between syllables or between words in their language. This paper discusses a series of speech perception experiments using both psychoacoustic and linguistic tasks. Participants judged either relative pitch height or prominence between two pitch peaks or valleys in an utterance. Native English speakers in different age and dialectal groups were tested. The results showed that, first, listeners’ pitch height discrimination in the utterance context seems to be more accurate than previously reported. Second, there is a robust perceptual asymmetry between pitch peaks and valleys, the valleys posing significant challenges in perception. Third, listeners’ perception of pitch height and prominence is disassociated. The findings taken together suggest an intricate interaction between the physical properties of the stimuli and listeners’ top-down knowledge in the perception of speech intonation.

Perceptual training facilitates Mandarin tone production for preschoolers with cochlear implants: Evidence from acoustic analysis

This study primarily aimed to investigate the benefits of an established perceptual training in the production of lexical tones for Mandarin-speaking preschoolers with cochlear implants (CIs). Thirty-two pediatric CI recipients were tested in this study. Half of the child participants received five sessions of high variability phonetic training (HVPT) within a period of three weeks, whereas the other half served as control who did not receive the formal training. Production of Mandarin tones was recorded before the provision (pretest) and after (posttest) the completion of the training protocol, which was coded and analyzed acoustically with automatic pitch tracking implemented in the software of Praat. Results showed significantly enhanced concave characteristic of dynamic pitch contours for the trained children’s Mandarin tones produced in posttest relative to pretest using growth curve analysis. Moreover, a tonal ellipse analysis indicated significantly improved tone differentiability and tone hit rate from pretest to posttest following training. By contrast, no significant changes were observed in the control children between the two test sessions. The findings represent initial acoustic evidence of HVPT-induced benefits in lexical tone production for CI users, which supports the application of this perceptual training protocol to aural rehabilitation practice.

A Bipedal Walking Model Considering Trunk Pitch Angle for Estimating the Influence of Suspension Load on Human Biomechanics.

Suspended loads have been shown to improve loaded-walking economy. Establishing a biped walking model with dynamic trunk pitch angles can provide more comprehensive estimates of the human biomechanical response under suspended loads. We developed the trunk-load- hip dynamics, modified the spring-loaded-inverted-pendulum (SLIP) model, and optimized the loaded-walking pattern for minimal energetic cost. 9 subjects participated in experiments using a powered backpack to validate the model's performance, conducting two trials: Load-Suspended (LS) and Load-Locked (LL). The averaged correlation coefficient of simulated and experimental hip trajectory, vertical and horizontal GRFs, and individual leg mechanical (ILM) powers are 0.96, 0.97, 0.93, and 0.81, respectively. The RMS error between simulated and experimental peaks of vertical GRFs, braking peaks of horizontal GRFs, and energetic costs was under 10%. Simulation also provides observation on the effect of suspended load on dynamic trunk pitch angles and torques, and leg stiffness. Both the simulation and experiment demonstrated the advantages of LS in reducing GRFs and energetic cost. Additionally, the simulation shows the peaks of trunk flexion and extension torque are reduced by 34.77% (p<0.05) and 37.88% (p<0.05) in LS. The model effectively estimates hip trajectory, vertical and horizontal GRFs, ILM powers, and energetic cost, and provides observations on trunk behavior under different load conditions. The model also supports the advantages of suspension load. Appropriate models could comprehensively reveal the mechanism between the mechanical systems and human biomechanics responses, guide the design of carrying load devices, and provide rapid evaluation of its effects.

The effects of dynamic stalls on the aerodynamics and performance of a Darrieus rotor during self-start

Darrieus turbines face difficulty to self-start, especially in environments with fluctuating inflows that cause them to deviate repeatedly from their designed operating parameters. To elucidate the self-starting process in this study, a three-bladed Darrieus rotor was simulated numerically with vector diagrams to facilitate visualizations on the rotor behaviors. Based on segments of the average rotor torque coefficients (Cτ), the self-starting process consisted of linear and accelerated phases, with the first two segments in the linear phase and the next two segments in the accelerated phase. The simulation showed that the self-starting process was largely influenced by dynamic stalls. The rotor experienced difficulty to self-start in the first segment as it encountered a region of “dead band” with a negative mean cyclical caused by a reverse dynamic stall. This dynamic stall and its corresponding dead band disappeared in the second segment, which initiated the transition into the accelerated phase. In the third segment, forward dynamic stalls that formed boosted the generation and accelerated the angular speed of the rotor toward its peak. Finally, without any dynamic stalls formed in the fourth segment due to reduced values of the inflow angles on the blades, they reduced drastically until the rotor reached its steady phase. Outcomes from this work demonstrate that understanding the effects of unsteady aerodynamics is vital to improving the self-starting process. Potential design improvements on the rotor that address this aspect include static and dynamic pitching, blade flaps, intracyclical control, and flow controls using blowing and suction mechanisms.

Effect of a rotational damper on a moored and articulated multibody offshore system in waves

Motions and loads of an articulated and moored floating platform consisting of multiple bodies in waves are investigated through numerical analysis. The wave–structure interaction (WSI) problem is solved using a high-fidelity viscous–flow solver that couples nonlinear rigid body motions, multibody interactions with an internal connection, and mooring dynamics. The study focuses on two modular floating structures (MFSs) connected by a flexible joint, with and without a rotational damper, and positioned using four symmetrical mooring lines. Multibody responses and the corresponding loads acting on the mooring lines and hinged joints are analyzed. Our results reveal that the influence of the damper on heave motions is less significant. Notably, the presence of the rotational damper has a noticeable impact on pitch motions between the two hinged MFSs. Introducing a rotational damper on the flexible joint effectively dampens the highly dynamic pitch motions while not imposing additional loads on the flexible joints.

Recognition of Speech With Dynamic Pitch Manipulation in Noise: Effects of Manipulation Methods.

Dynamic pitch, which is defined as the variation in fundamental frequency in speech, is one of the acoustic cues that affect speech recognition in noise. Built on the evidence that a symmetrical manipulation of dynamic pitch led to poorer speech recognition, the present study examined the effect of an asymmetrical manipulation method on speech recognition in noise by younger and older adults. Speech recognition accuracy in noise was measured from younger adults with normal hearing in Experiment 1, and speech reception threshold (in dB SNR) from older adults with normal hearing to mild-moderate hearing loss in Experiment 2. The dynamic pitch contours of the speech stimuli were manipulated using both symmetrical and asymmetrical methods. Younger adults recognized speech better in noise with asymmetrical than symmetrical manipulation, and with weakened than strengthened dynamic pitch. A substantial amount of variability was observed in a group of older listeners. This variability was predominately predicted by the listeners' age but not hearing thresholds or their ability to perceive dynamic pitch in fluctuating noise. The asymmetrical manipulation of dynamic pitch had a less negative effect than the symmetrical manipulation. This effect also interacted with pitch-change direction. These findings suggest the influence of perceptual naturalness on speech recognition with signal modification. Directions for future research are also discussed.

Effect of gurney flaps on a nonslender delta wing during large-amplitude and high-frequency dynamic pitching

The flow control effect of Gurney flaps on 50° swept delta wings during large-amplitude and high-frequency pitching were investigated both experimentally and numerically. Both force and velocity measurements were conducted and compared with the numerical simulation results. The lift hysteresis was found to be significantly affected by the Gurney flaps. It was found that the leading-edge Gurney flap (LG) acts to redistribute the vorticity over the suction surface of the wing during the upstroke process. The formation and development of the leading-edge vortex (LEV) on the suction surface was delayed by the LG, which was accompanied by enhancement of the lift at high angles of attack. The lower surface pressure can be altered with the flow velocity being slowed down by the trailing-edge Gurney flap (TG), which improves overall lift performance of the pitching wing at small to moderate angles of attack.

Aerodynamic analysis of a novel pitch control strategy and parameter combination for vertical axis wind turbines

The performance of a vertical axis wind turbine (VAWT) deteriorates at low tip speed ratios (TSR) and it is mainly characterized by flow separation and dynamic stall. Several mitigating techniques have been developed recently based on flow separation and dynamic stall research activities. One of such techniques is the use of blade pitch angle control, which shows very promising optimal performance in VAWTs. However, its adaptation for periodic variation of the angle of attack remains an important issue that needs to be addressed urgently. Therefore, this paper proposes a novel pitch control strategy based on the VAWT-shape pitch motion to achieve blade dynamic pitch with the rotational parameters (TSR and azimuth angle). The pitch scale factor (μ) is introduced to proportionally vary the angle of attack. High accuracy computational fluid dynamics (CFD) methods are used to simulate dynamic changes in pitch angle, flow field and vortex shedding vorticity, with the turbulence modelled using the SST k-ω model. The results show that a 146% increase in power coefficient can be achieved using a μ of 0.3 at TSR of 1.25. Additionally, the use of dual pitch scale factors (dpsf) in the windward and leeward regions causes intense transient torque fluctuations at 0° (360°) and 180° azimuths due to a breaking distance in pitch angular velocity at these azimuths. Adding a weight function into the fitting process of the dpsf pitch curve effectively minimize these fluctuations.

Numerical Simulations of the NREL Phase VI Wind Turbine with Low-Amplitude Sinusoidal Pitch

Currently, most wind turbine performance analyses and simulations are performed assuming constant pitch and yaw angles during each rotation. Nevertheless, induced vibration or rotor imbalance can affect the pitch or yaw angle within each rotation. In this study, the effects of low-amplitude sinusoidal pitch angle oscillations of the blade on the performance of a wind turbine was investigated numerically by comparing it against the baseline (without pitch variations). Large eddy simulations were performed in which the motion of blades was handled by the curvilinear immersed boundary (CURVIB) method. The grid resolution was increased near the moving immersed boundaries using dynamic overset grids to resolve rotating blades. It was found that low-amplitude (up to 3 degrees) sinusoidal oscillations in the pitch angle negligibly affected the mean torque but increased its fluctuations and created distinct features in the wake of the turbine. In fact, the turbine’s mean torque at wind speed of 15 m/s decreases from 1245 N.m to 1223 N.m, while its fluctuation (standard deviation) increases from 2.85 N.m to 7.94 N.m, with a dynamic pitch of 0.5 degrees and frequency of 3.6 Hz.