Pitch Dynamics Research Articles

Deep reinforcement learning-based antilock braking algorithm

Tires play an important role in the performance of vehicular safety systems. Antilock braking system is one of the most important active safety systems that interacts with the tires. Unlike a variety of existing algorithms which are tuned to a specific tire, this research proposes a model-free reinforcement learning-based control algorithm which can adapt to changing tire characteristics and there by effectively utilising the available grip at tire–road interface. The simulation model, consisting of brake actuator dynamics, transportation delays, tire relaxation behaviour, vehicular longitudinal and pitch dynamics, is trained using more than 350,000 random tires. To reduce training time, a parallelisation architecture has been proposed which distributes learning and simulation tasks to different CPU cores. Finally, a conditional variance-based sensitivity analysis with over twelve thousand tires indicate improved grip utilisation at tire–road interface and decreased sensitivity of stopping distance on tire nonlinearity compared to literature version of Bosch algorithm.

Structure and Dynamics of Supramolecular Polymers: Wait and See.

The introduction of stereogenic centers in supramolecular building blocks is used to unveil subtle changes in supramolecular structure and dynamics over time. Three stereogenic centers based on deuterium atoms were introduced in the side chains of a benzene-1,3,5-tricarboxamide (BTA) resulting in a supramolecular polymer in water that at first glance has a structure and dynamics identical to its achiral counterpart. Using three different techniques, the properties of the double helical polymers are compared after 1 day and 4 weeks. An increase in helical preference is observed over time as well as a decrease in the helical pitch and monomer exchange dynamics. It is proposed that the polymer of the chiral monomer needs time to arrive at its maximal preference in helical bias. These results indicate that the order and tight packing increase over time, while the dynamics of this supramolecular polymer decrease over time, an effect that is typically overlooked but unveiled by the isotopic chirality.

Single channel digital controller design for a high spinning rate rolling airframe missile

AbstractSpinning/Rolling Airframe Missiles (RAM) mostly use an analog (ON-OFF type) control approach that deflects control surfaces (fins) at minimum and maximum positions continuously, and control is achieved by applying phase shift between the minimum and maximum deflections during a complete roll cycle. Therefore, the control signal shape changes continuously during the roll cycle. In this study, a novel single channel digital controller is designed and tested for a high spinning rate (10–20 Hz) RAM. The digital controller adjusts the amplitude of fin deflections instead of applying a phase shift. In this way, control signal shapes are predetermined in design to completely decouple yaw and pitch dynamics. At the beginning of each roll cycle, the algorithm decides on the control signal shape and amplitude to apply throughout the cycle. Delays on the actuator system and sensor measurements which might lead to instability at high spinning rates are handled effectively thanks to the predetermined control signal shapes that are changing with 90-degree intervals. Detailed geometry of a surface-to-air spinning missile is used to obtain aerodynamic coefficients for the entire flight regime (i.e. from launch to terminal phase) via Missile DATCOM. The 6-DOF flight dynamics model and the controller algorithms are built in MATLAB/Simulink environment. The proposed digital controller is tested systematically for various scenarios and the performance is compared with the conventional analog control approach. The digital controller gives better performance compared to the analog approach under the influence of servo delays and sensor noise.

Cascaded adaptive integral backstepping sliding mode and super-twisting controller for twin rotor system using bond graph model

This work presents a bond graph (BG) model and a robust cascaded controller for a twin-rotor system (TRS). The BG model accounts for all the energetic and dynamical couplings. An adaptive integral backstepping sliding mode (AIBSM) controller is used in the outer loop to control the slow yaw and pitch dynamics of the mechanical sub-system whereas a higher-order sliding mode (HOSM) observer-based super-twisting algorithm (STA) controller is used in the inner loop to control the fast electromechanical actuator dynamics. The gain of the discontinuous control term of the integral backstepping sliding mode (IBSM) controller is adjusted by using an adaptive switching gain law, where the adaptive gain decreases or increases as the system state variables move closer to or away from a sliding surface; thereby reducing chatter and discontinuities near the sliding manifold, and ensuring a nearly smooth reference signal to the inner-loop controller. The unavailable states are estimated by using an unscented Kalman filter. All the used controllers are shown to be Lyapunov stable. The performance of the developed controller is validated through simulation and experiment, and it is further compared with other existing robust controllers. The proposed controller is robust against un-modeled dynamics and external disturbances, and it performs better, in terms of trajectory tracking error and disturbance rejection, than presently existing controllers for the TRS.

Attitude estimation for artillery shells using magnetometers and frequency detection of accelerometers

The article proposes a method to estimate the attitude of an artillery shell in free flight. It uses strapdown accelerometers and magnetometers, and circumvents the intrinsic inability of accelerometers to provide direction information during free flight by employing them not to measure the gravity but to estimate the velocity w.r.t. the air. This is achieved in an innovative way, through frequency detection applied to the pitch and yaw rotational dynamics generated by aerodynamic moments, directly visible on the accelerometers’ signals. The determination of the shell’s velocity without any ground-based position radar is a first contribution. The velocity variation gives information regarding the shell’s orientation that complements the direction given by the 3-axis magnetometer. The two sources of information are combined into an attitude estimate by a specific nonlinear observer. Experimental results obtained with a gyrostabilized supersonic 155mm shell are presented.

Quasi-LPV Modeling of Guided Projectile Pitch Dynamics through State Transformation Technique

In this paper, we develop a reliable Linear Parameter-Varying (LPV) model of the pitch channel dynamics of a fin-stabilized projectile. Among the available LPV design approaches, the State Transformation is analyzed, being particularly suitable for a class of systems defined as output nonlinear, and compatible with the projectile dynamics formulation. The State Transformation provides a quasi-LPV representation, which corresponds to an exact transformation of the original nonlinear model, preserving relevant couplings that are usually lost through the classical approximation methods. Some important considerations regarding the limitations of this approach are also discussed and verified in the missile dynamics. The accuracy of the obtained quasi-LPV model is assessed by means of open-loop simulations, comparing the performance to the original nonlinear model at selected flight conditions.

Resonant passive energy balancing of morphing helicopter blades with bend\u2013twist coupling

With increasing demand for rotor blades in engineering applications, improving the performance of such structures using morphing blades has received considerable attention. Resonant passive energy balancing (RPEB) is a relatively new concept introduced to minimize the required actuation energy. This study investigates RPEB in morphing helicopter blades with lag–twist coupling. The structure of a rotating blade with a moving mass at the tip is considered under aerodynamic loading. To this end, a three-degree-of-freedom (3DOF) reduced-order model is used to analyse and understand the complicated nonlinear aeroelastic behaviour of the structure. This model includes the pitch angle and lagging of the blade, along with the motion of the moving mass. First, the 3DOF model is simplified to a single-degree-of-freedom model for the pitch angle dynamics of the blade to examine the effect of important parameters on the pitch response. The results demonstrate that the coefficient of lag–twist coupling and the direction of aerodynamic moment on the blade are two parameters that play important roles in controlling the pitch angle, particularly the phase. Then, neglecting the aerodynamic forces, the 3DOF system is studied to investigate the sensitivity of its dynamics to changes in the parameters of the system. The results of the structural analysis can be used to tune the parameters of the blade in order to use the resonant energy of the structure and to reduce the required actuation force. A sensitivity analysis is then performed on the dynamics of the 3DOF model in the presence of aerodynamic forces to investigate the controllability of the amplitude and phase of the pitch angle. The results show that the bend–twist coupling and the distance between the aerodynamic centre and the rotation centre (representing the direction and magnitude of aerodynamic moments) play significant roles in determining the pitch dynamics.

Chaotic Assessment of the Heave and Pitch Dynamics Motions of Air Cushion Vehicles

In this study, three degrees of freedom nonlinear air cushion vehicle (ACV) model is introduced to examine the dynamic behavior of the heave and pitch responses in addition to the cushion pressure of the ACV in both time and frequency domains. The model is based on the compressible flow Bernoulli's equation and the thermodynamics nonlinear isentropic relations along with the Newton’s second law of translation and rotation. In this study, the dynamical investigation was based on numerical simulation using the stiff ODE solvers of the Matlab software. The chaotic investigations of the proposed model is provided using the Fast Fourier Transform (FFT), the Poincaré maps, and the regression analysis. Three control design parameters are investigated for the chaotic studies. These parameters are: ACV mass (M), the mass flowrate entering the cushion volume (m ̇_in), and the ACV base radius (r). Chaos behavior was observed for heave, and pitch responses as well as the cushion pressure.

Chaotic Assessment of the Heave and Pitch Dynamics Motions of Air Cushion Vehicles

In this study, three degrees of freedom nonlinear air cushion vehicle (ACV) model is introduced to examine the dynamic behavior of the heave and pitch responses in addition to the cushion pressure of the ACV in both time and frequency domains. The model is based on the compressible flow Bernoulli's equation and the thermodynamics nonlinear isentropic relations along with the Newton’s second law of translation and rotation. In this study, the dynamical investigation was based on numerical simulation using the stiff ODE solvers of the Matlab software. The chaotic investigations of the proposed model is provided using the Fast Fourier Transform (FFT), the Poincaré maps, and the regression analysis. Three control design parameters are investigated for the chaotic studies. These parameters are: ACV mass (M), the mass flowrate entering the cushion volume (m ̇_in), and the ACV base radius (r). Chaos behavior was observed for heave, and pitch responses as well as the cushion pressure.

A Control Allocation approach to induce the center of pressure position and shape the aircraft transient response

This paper presents a Control Allocation formulation aimed at altering the dynamic transient response of an aircraft by exclusive means of the aerodynamic effectiveness of its control effectors. This is done, for a given Flight Control System architecture and, optionally, closed-loop performance, by exploiting the concept of Control Center of Pressure, i.e. the center of pressure due to only aerodynamic control forces. Two formulations are proposed, and their advantages and disadvantages presented. The first is based on the straightforward augmentation of the control effectiveness matrix, the second on a weighting matrix to prioritize control effectors. The latter is implemented in three application studies on a box-wing aircraft configuration with redundant control surfaces: a simple pull-up maneuver, a trajectory tracking task, and an altitude holding task in turbulent atmosphere. Results show that the proposed formulation can significantly impact performance metrics that are closely related to the aircraft transient response. In the best case scenario, the aircraft is able to completely cancel the non-minimum phase behavior typical of pitch dynamics, hence achieving a sharp initial response to longitudinal commands. If compared to a standard Control Allocation algorithm, the proposed formulation results in improved tracking precision, better disturbance rejection, and a measurably improved feeling of comfort on board.

Finite-Time Approximation-Free Attitude Control of Quadrotors: Theory and Experiments

In this article, a novel finite-time approximation-free control scheme is proposed for the attitude tracking of quadrotor unmanned aerial vehicles. Prescribed performance functions are employed to transform the original attitude tracking problem into an alternative system stabilization problem. By incorporating a finite-time error compensation mechanism into the recursive control design, the finite-time error convergence, and singularity-free property can be guaranteed simultaneously. Compared with the existing approximation-based control schemes, the presented controller has a simple cascade proportional-like structure and less computational burden, and the coupling among the roll, pitch, and yaw dynamics can be successfully handled without requiring any model information or function approximations. With the proposed control scheme, the attitude tracking error can be retained within a prescribed boundary and converge into a sufficiently small region around origin in finite time. Extensive comparative experiments on a three degree-of-freedom (3-DOF) quadrotor platform are performed to validate the effectiveness of the proposed control scheme.

Chaotic Assessment of the Heave and Pitch Dynamics Motions of Air Cushion Vehicles

In this study, a three degrees of freedom nonlinear air cushion vehicle (ACV) model is introduced to examine the dynamic behavior of the heave and pitch responses in addition to the cushion pressure of the ACV in both time and frequency domains. The model is based on the compressible flow Bernoulli’s equation and the thermodynamics nonlinear isentropic relations along with the Newton second law of translation and rotation. In this study, the dynamical investigation was based on a numerical simulation using the stiff ODE solvers of the Matlab software. The chaotic investigations of the proposed model are provided using the Fast Fourier Transform (FFT), the Poincaré maps, and the regression analysis. Three control design parameters are investigated for the chaotic studies. These parameters are: ACV mass (<i>M</i>), the mass flow rate entering the cushion volume (<i>ṁin</i>), and the ACV base radius (r). Chaos behavior was observed for heave, and pitch responses as well as the cushion pressure.

Estimation on IMU yaw misalignment by fusing information of automotive onboard sensors

In the development of automotive electronics, nearly every automobile is equipped with an inertial measurement unit (IMU). However, the yaw misalignment of the IMU is inevitable when mounted to a vehicle's body. It is difficult to measure directly, so its estimation is required to acquire accurate data from the IMU. This study proposes a method for the IMU and automotive onboard sensors to estimate the yaw misalignment autonomously. In order to estimate the IMU yaw misalignment, first, the attitude and velocity integration method in the vehicle level frame is presented. In addition, the attitude error dynamics consisting of yaw misalignment, pitch, and roll, and velocity error dynamics consisting of longitudinal and lateral velocities, are derived. Then, on the basis of the error dynamics and observation equations, the degree of the observability of the yaw misalignment is analyzed through the piece-wise constant system (PWCS) and singular value decomposition (SVD) theory. Next, a Kalman filter is implemented to estimate the yaw misalignment and the velocity error. Finally, an experimental test in straight line acceleration and deceleration maneuvers is conducted to verify the yaw misalignment estimation method. When the longitudinal or lateral acceleration varies, the yaw misalignment is observable and can be estimated without aids from external information. After compensating for the yaw misalignment, the accuracy of the state estimation result, such as lateral velocity, can be improved significantly when the IMU is integrated with other sensors.

Development of sprung mass non-linear mathematical model of pitch dynamics with trailing arm suspension

Military vehicles are required to negotiate drastic ride environments. Therefore, the vibration magnitudes which are transmitted to the vehicle chassis through the suspension system due to dynamic vehicle-terrain interactions, are usually large. Hence, it is necessary to study the vibrations that are transmitted to the sprung mass as it negotiates different types of terrain at different speeds. The present study is focused on the development of sprung mass non-linear pitch dynamics mathematical model of a military vehicle with a trailing arm torsion bar suspension system. The trailing arm kinematics and dynamics are incorporated into the non-linear governing equations of motion of the sprung and unsprung masses which consider the effects of sprung mass large pitch angular motions. The model is solved by coding in Matlab. The sprung mass non-linear pitch dynamics mathematical model is validated with an equivalent multi-body dynamics model which is developed by using MSC.ADAMS. This mathematical model would play a key role to fine-tune the vehicle and suspension parameters as well as comparatively evaluate the performance of the hydro-gas suspension system. The model can further be extended to include the military vehicle weapon recoil effects which can cause considerable magnitudes of vehicle pitch. Apart from simulating ride dynamics of the entire vehicle, the influence of movement with crane payload on the military recovery vehicle pitch dynamics can also be brought out as a useful extension of this mathematical model.

Generalized composite noncertainty-equivalence adaptive control of a prototypical wing section with torsional nonlinearity

The paper presents a generalized composite noncertainty-equivalence adaptive control system for the control of a prototypical aeroelastic wing section using a single trailing-edge control surface. The plunge–pitch (two-degree-of-freedom) dynamics of this aeroelastic system include torsional pitch-axis nonlinearity. The open-loop system exhibits limit cycle oscillations beyond a critical free-stream velocity. It is assumed that parameters of the model are not known. The objective is to suppress the oscillatory responses of the system. Based on the immersion and invariance approach, a generalized composite noncertainty-equivalence adaptive (NCEA) control system for regulation of the pitch angle is designed. The control system consists of a control module and a composite parameter identifier—designed independently. The composite integral parameter estimation law is based on (1) the immersion and invariance (I&I) theory, (2) gradient-based adaptation algorithm, and (3) classical certainty-equivalence adaptive (CEA) update rule. Besides the composite integral component, the full parameter estimate also includes a judiciously chosen nonlinear algebraic function. This composite identifier inherits stronger stability properties. Using the Lyapunov analysis, asymptotic suppression of the limit cycle oscillations and the boundedness of system trajectories are established. Interestingly, in the closed-loop system including the composite update rule, there exist two attractive manifolds to which the system’s trajectories converge. Simulation results are presented which show the suppression of the oscillatory plunge displacement and pitch angle responses despite uncertainties in the model parameters. Furthermore, the performance and stability properties of this composite NCEA control system—including the gradient-based adaptation and the update rule of the CEA system—are better than the simple NCEA system.

What Makes Online Review Videos Helpful? Evidence from Product Review Videos on Youtube

With the rapid growth and popularity of YouTube, an increasing number of consumers rely on online product review videos to obtain product-related information. Review videos, with visual and sound cues, can convey product experiences in rich and immersive ways and have a powerful impact on consumer’s perceptions and intentions to purchase the product. As the provision of online review videos grows and consumers increasingly rely on them for their purchase decisions, understanding factors that contribute to the perceived helpfulness of video reviews becomes critical for video review management. This paper examines how various video content characteristics—information accessibility, positivity, and subjectivity—and voice characteristics of reviewers—speech rate, pitch, and speech dynamics—are associated with the perceived helpfulness. We collect detailed data on 14,486 electronic product review videos posted on YouTube and employ speech recognition and natural language processing techniques to extract sentimental and speech characteristics. We find that video viewers perceive online product review videos that are more information-accessible, more positive, and less subjective as more helpful. In addition, review videos created by reviewers with faster speech rates, lower voice pitch, and more vocal dynamicity are perceived as more helpful. We additionally find that reviewers’ popularity can moderate the effect of information accessibility, positivity, and reviewers’ voice characteristics on perceived review helpfulness.

Comparison of wave–structure interaction dynamics of a submerged cylindrical point absorber with three degrees of freedom using potential flow and computational fluid dynamics models

In this paper, we compare the heave, surge, and pitch dynamics of a submerged cylindrical point absorber, simulated using potential flow and fully resolved computational fluid dynamics (CFD) models. The potential flow model is based on the time-domain Cummins equation, whereas the CFD model uses the fictitious domain Brinkman penalization technique. The submerged cylinder is tethered to the seabed using a power take-off (PTO) unit, which restrains the heave, surge, and pitch motions of the converter and absorbs energy from all three modes. It is demonstrated that the potential theory overpredicts the amplitudes of heave and surge motions, whereas it results in an insignificant pitch for a fully submerged axisymmetric converter. It also underestimates the slow drift of the buoy, which the CFD model is able to capture reliably. Furthermore, we use fully resolved CFD simulations to study the performance of a three degrees of freedom cylindrical buoy under varying PTO coefficients, mass density of the buoy, and incoming wave heights. It is demonstrated that the PTO coefficients predicted by the linear potential theory are sub-optimal for waves of moderate and high steepness. The wave absorption efficiency improves significantly when a value higher than the predicted value of the PTO damping is selected. Simulations with different mass densities of the buoy show that converters with low mass densities have an increased tension in their PTO and mooring lines. Moreover, the mass density also influences the range of resonance periods of the device. Finally, simulations with different wave heights show that at higher heights, the wave absorption efficiency of the converter decreases and a large portion of available wave power remains unabsorbed.

Robust Adaptive Control Barrier Functions: An Adaptive and Data-Driven Approach to Safety

A new framework is developed for control of constrained nonlinear systems with structured parametric uncertainty. Forward invariance of a safe set is achieved through online parameter adaptation and data-driven model estimation. The new adaptive data-driven safety paradigm is merged with a recent adaptive controller for systems nominally contracting in closed-loop. This unification is more general than other safety controllers as contraction does not require the system be invertible or in a particular form. The method is tested on the pitch dynamics of an aircraft with uncertain nonlinear aerodynamics.

The moment-to-moment pitch dynamics of child-directed speech shape toddlers' attention and learning.

Young children have an overall preference for child-directed speech (CDS) over adult-directed speech (ADS), and its structural features are thought to facilitate language learning. Many studies have supported these findings, but less is known about processing of CDS at short, sub-second timescales. How do the moment-to-moment dynamics of CDS influence young children's attention and learning? In Study 1, we used hierarchical clustering to characterize patterns of pitch variability in a natural CDS corpus, which uncovered four main word-level contour shapes: 'fall', 'rise', 'hill', and 'valley'. In Study 2, we adapted a measure from adult attention research-pupil size synchrony-to quantify real-time attention to speech across participants, and found that toddlers showed higher synchrony to the dynamics of CDS than to ADS. Importantly, there were consistent differences in toddlers' attention when listening to the four word-level contour types. In Study 3, we found that pupil size synchrony during exposure to novel words predicted toddlers' learning at test. This suggests that the dynamics of pitch in CDS not only shape toddlers' attention but guide their learning of new words. By revealing a physiological response to the real-time dynamics of CDS, this investigation yields a new sub-second framework for understanding young children's engagement with one of the most important signals in their environment.

LMI-Based Robust Stabilization of a Class of Input-Constrained Uncertain Nonlinear Systems with Application to a Helicopter Model

This paper is concerned with the robust stabilization of a class of continuous-time nonlinear systems, with an application to the pitch dynamics of a simple helicopter model, via an affine state-feedback control law using the linear matrix inequality (LMI) approach. The nonlinear dynamics is subject to norm-bounded parametric uncertainties and disturbances. In addition, the problem of actuator nonlinearity is addressed by considering the saturation effect of the control law. We demonstrate first that the synthesis problem of the saturated controller is expressed in terms of bilinear matrix inequalities (BMIs). Thanks to the Schur complement lemma and the matrix inversion lemma, we convert these BMIs into LMIs allowing the simultaneous computation of the two gains of the affine controller. Furthermore, we address in this work the estimation problem of the domain of attraction using the invariant set concept. This is solved by computing the largest attractive invariant ellipsoid. Compared with previous works, the research procedure of such ellipsoidal set is achieved in a single step with a reduced number of LMI constraints and then with less conservative conditions. A portfolio of numerical results is presented. The effectiveness and robustness of the proposed saturated controller in the stabilization of the adopted helicopter pitch model toward parametric uncertainties and disturbances are illustrated through simulation results.