Pitch Angle Rate Research Articles

Angular rate enhanced Overload Controller Design for Low-speed UAVs

This paper investigates the overload controller for low-speed UAV maneuvering flight. Compared with high-speed and supersonic vehicles, low-speed UAVs are more sensitive to atmospheric disturbances during maneuvering and their signals are more sensitive. This paper combines UAV overload control theory and L1 adaptive theory to propose a longitudinal attitude control method based on overload control for low-speed UAVs. The method uses overload as the outer loop and pitch angle rate as the inner loop, and provides a reliable control scheme for maneuvering low-speed UAVs. Through simulation experiments, the controller proposed in this paper is compared with the conventional classical three-loop overload controller. The results show that the controller of this paper has faster angular rate response and stronger anti-interference capability under the same overload corresponding conditions.

Adaptive Performance-Constrained Synchronization Control for Hypersonic Flight Vehicle Swarms: A Novel Finite-Time Convergence Protocol Methodology

This paper proposes a novel neural adaptive performance-constrained synchronization tracking control algorithm for multiple hypersonic flight vehicles (HFVs), which are subject to actuator faults and full-state constraints. The proposed method is based on advanced Lyapunov finite-time stability theory and a sophisticated backstepping design scheme. The longitudinal model of HFV is converted into velocity and altitude subsystems through functional decomposition. Our method presents three significant contributions over the existing state-of-the-art approaches: (a) ensuring finite-time convergence of HFVs systems by guaranteeing that the setting time is lower bounded by a positive constant that is related to the initial states; (b) utilizing a tan-type Barrier Lyapunov function (BLF) to ensure that the synchronization tracking errors of velocity, altitude, flight path angle, angle of attack, and pitch angle rate are maintained within certain performance bounds; and (c) designing a neural adaptive control algorithm and adaptive parameter laws by combining the backstepping design technique and radial basis function neural networks (RBFNNs) to handle unknown actuator faults and modeling uncertainties. Finally, comparative simulations are conducted to validate the efficacy of the proposed scheme.

Constraints on the IBEX Ribbon’s Origin from Its Evolution over a Solar Cycle

In 2009, the Interstellar Boundary Explorer (IBEX) discovered a narrow “ribbon” of energetic neutral atom emissions across the sky with properties correlated with the solar wind latitudinal structure and the interstellar magnetic field draped around the heliosphere. It is widely believed that the ribbon is formed from the escape of heliospheric ENAs into the local interstellar medium and their eventual return as secondary ENAs. However, there is no consensus on the rate of pitch angle scattering of these PUIs before they become secondary ENAs. We test two opposing limits of scattering rates (“weak” versus “strong”) by solving a time-dependent model of the ribbon that evolves with the solar cycle, and we compare them to IBEX observations over 2009–2019. First, we find that both models qualitatively reproduce the evolution of IBEX fluxes for most of the data set, with a few exceptions, although the strong (or “spatial retention”) scattering model greatly underestimates the observed fluxes. Regardless, time dependence of fluxes cannot distinguish these models. Second, the ribbon’s geometric properties, i.e., its center and radius, are significantly different between the models. The spatial retention model reproduces the observed ribbon centers as a function of energy and time slightly better than the weak scattering model, and the spatial retention model reproduces the observed ribbon radius over energy and time almost perfectly, whereas the weak scattering model compares poorly. Our analysis favors the spatial retention mechanism as the source of the IBEX ribbon, but it requires modification to increase the flux of ENAs observed at 1 au.

Pitch angle scattering of fast particles by low frequency magnetic fluctuations

The adiabatic invariance of the magnetic moment during particle motion is of fundamental importance to the dynamics of magnetized plasma. The related rate of pitch angle scattering is investigated here for fast particles that thermally stream through static magnetic perturbations. For a uniform magnetic field with a localized perturbation, it is found that the curvature parameter κ2=min(Rc/ρL) does not predict the level of pitch angle scattering. Instead, based on numerical integration of particle orbits in prescribed magnetic fields, we derive predictions for the particle scattering rates, which can be characterized by the relative perturbation amplitude A≃δB/B, and the particle Larmor radius normalized by the field-aligned wavelength of the perturbations, ρL/λ||. Particles with ρL/λ||≃1 are subject to strong pitch angle scattering, while the level of scattering vanishes for both the limits of ρL/λ||≪1 and ρL/λ||≫1. The results are summarized in terms of a scattering operator, suitable for including the described scattering in basic kinetic models.

Conditions of Loss Cone Filling by Scattering on the Curved Field Lines for 30 keV Protons During Geomagnetic Storm as Inferred From Numerical Trajectory Tracing

AbstractThe rate of pitch angle scattering on the curved magnetic field lines is well parameterized by the ratio of the minimum field line curvature radius to the maximum effective particle gyroradius (K = RC/rg). The critical value of this ratio (Kcr) corresponding to the loss cone filling is of special interest since it corresponds to the low altitude isotropic boundaries (IBs). The early theoretical estimates gave Kcr = 8, whereas recent estimations of the K parameter on the field lines corresponding to the observed IBs during the geomagnetic storms revealed KIB values in the range of 3–30. We numerically trace the trajectories of the 30 keV protons in the magnetic field of the global magnetohydrodynamic simulation of the intense storm in order to infer statistical distribution of Kcr. The electric field and effects of nonstationarity are neglected in this study. It is found that although the Kcr values do show some variations during the course of the storm, its range is rather narrow 4 < Kcr < 8. The result suggests that higher KIB values found in the observational studies, if not caused by the magnetosphere‐ionosphere mapping error, should be attributed to some other mechanism of pitch angle scattering. The Kcr values tend to be lower (4–6) during the main phase because the region of low K values approaches the Earth and the equatorial loss cone size becomes larger due to a larger equatorial magnetic field in the near‐earth region. The remaining variation of Kcr is explained by the presence of the guide component of the magnetic field.

Adaptive fault tolerant control for hypersonic vehicle with input saturation and state constraints

This paper proposes an adaptive control scheme for hypersonic vehicle with external disturbances, parametric uncertainties, actuator failures, input saturation and state constraints. Firstly, the longitudinal model of generic hypersonic vehicle is divided into velocity subsystem and altitude subsystem. Secondly, based on the tangent barrier Lyapunov function and auxiliary system, two adaptive fault tolerant controllers are designed for velocity subsystem and altitude subsystem, respectively, which can solve the problem of input saturation. By using the controllers, the flight states containing the angle of attack, flight path angle, pitch angle and pitch angle rate can be guaranteed in prospective ranges. Finally, the Lyapunov stability theory and numerical simulations are adopted to verify the effectiveness of the presented controllers.

Adaptive control for hypersonic vehicle with input saturation and state constraints

The tracing control problem of hypersonic vehicle subject to external disturbances, parametric uncertainties, input saturation and state constraints. Firstly, the longitudinal model of the hypersonic vehicle is converted to the velocity subsystem and altitude subsystem based on the functional decomposition. Secondly, two adaptive anti-saturation controllers are proposed for the velocity subsystem and altitude subsystem with the unknown upper bound of external disturbances. By using the asymmetric barrier Lyapunov function, the two controllers can make flight path angle, angle of attack and pitch angle rate keep within the certain ranges. Meanwhile, the auxiliary system is introduced to deal with the problem of input saturation and a low-pass filter is designed to avoid the “explosion of terms” in traditional backstepping control caused by the complicated differentiations of the virtual control signals. Finally, the effectiveness of the presented control strategy is verified by the Lyapunov stability theory and numerical simulations results.

Power extraction performance of three types of flapping hydrofoils at a Reynolds number of 1.7E6

Abstract This work focuses on the hydrodynamic performance analyses of three different types of flapping hydrofoils, in this case the pitch-heave (PH), left-swing (LS), and right-swing (RS) types, in their power extraction regimes via two dimensional CFD simulations. The power extraction performance is presented in an isocontour parametric map and is investigated from a comparison of the kinematics parameters and the development of unsteady vortices among the three types. It is found from the parametric analysis and comparison that the LS-type of flapping hydrofoil outperforms the PH and RS-types due to relatively high forces as well as the good synchronization of the forces and moment with the translational velocity and pitch angular rate, respectively upon the different aspects of the vortex development. Consequently, the power extraction performance improves from the LS to the PH and then to the RS-types. It is also recognized from another isocontour parametric map that the maximum power-extraction efficiency is achieved at a similar maximum effective angle of attack, at the maximum effective angle of attack rate, and at the maximum pitch angle rate for the LS and RS types, while the range of the maximum effective angle of attack rate is lower in the PH-type hydrofoil.

Effects of sudden change in pitch angle on oscillating wind turbine airfoil performances

In this paper, the aerodynamic performances of a wind turbine airfoil in sinusoidal pitching motion was numerically predicted and analyzed using the two-dimensional singularity method. A parametric study based on the sudden pitch angle rate variation, the reduced frequency and the pitching amplitudes have been investigated.The results highlight the sudden change effect in pitch angle on the aerodynamic performances of the airfoil and the shedding wake. The aspect of lift and drag coefficient loops and hysteresis were customized regarding to the pure sinusoidal motion case. The dynamic stall phenomenon, which occurs during the rapid change in pitch angle, produces more drag forces influencing the wind turbines performance.

Barrier Lyapunov function-based adaptive control for hypersonic flight vehicles

This paper presents an adaptive control strategy for hypersonic flight vehicles (HFVs) subject to parametric uncertainties, external disturbances and faulty actuators. Besides the guaranteed tracking performance, the main novelty of this study is to strictly constrain the flight states, which are crucial to hypersonic flights, such as the bounded angle of attack required by the scramjet. To achieve this, the disturbed control-oriented model of HFVs with uncertain parameters and faulty actuators is first rewritten into a parameterized form, based on which novel adaptive controllers are then designed for velocity and altitude subsystems. By introducing barrier Lyapunov functions to design procedures, specific tracking performances of velocity and altitude are guaranteed, while the other flight states of angle of attack, flight path angle, pitch angle and pitch angle rate can be kept within the prescribed ranges. Command filters are employed in the back-stepping design for altitude subsystem to limit the magnitudes of virtual controls and to avoid the complicated analytical calculations. In addition, an adaptive inverse is integrated into the adaptive control scheme to sufficiently compensate for the unknown dead-zone nonlinearity in elevator. It is shown that the developed control system regulates the tracking errors within some neighborhoods of zero, which become sufficiently small by proper adjustments on design parameters. Finally, the numerical simulation is provided for comparison and verification purposes.

Analysis of Lower-Limb Motion during Walking on Various Types of Terrain in Daily Life

Objective:This research analyzed the lower-limb motion in kinetic and kinematic way while walking on various terrains to develop Foot-Ground Contact Detection (FGCD) algorithm using the Inertial Measurement Unit (IMU). Background: To estimate the location of human in GPS-denied environments, it is well known that the lower-limb kinematics based on IMU sensors, and pressure insoles are very useful. IMU is mainly used to solve the lower-limb kinematics, and pressure insole are mainly used to detect the foot-ground contacts in stance phase. However, the use of multiple sensors are not desirable in most cases. Therefore, only IMU based FGCD can be an efficient method. Method: Orientation and acceleration of lower-limb of 10 participants were measured using IMU while walking on flat ground, ascending and descending slope and stairs. And the inertial information showing significant changes at the Heel strike (HS), Full contact (FC), Heel off (HO) and Toe off (TO) was analyzed. Results: The results confirm that pitch angle, rate of pitch angle of foot and shank, and acceleration in x, z directions of the foot are useful in detecting the four different contacts in five different walking terrain. Conclusion: IMU based FGCD Algorithm considering all walking terrain possible in daily life was successfully developed based on all IMU output signals showing significant changes at the four steps of stance phase. Application: The information of the contact between foot and ground can be used for solving lower-limb kinematics to estimating an individuals location and walking speed.

Identifying pitching mode of aerial planting projectile by the use of image processing

Aerial planting is a new and affordable method, which is used for purposes of reforestation and restoring pastures. In this study, flight dynamics of an aerial planting projectile has been simulated using data of the wind tunnel test. By creating the projectile graphical model and using the results of dynamic equations for this model, pitching angle has been simulated graphically by recording the pitch attitude of the graphical model and, by applying spectral filtration the rate of pitch angle at any point of the trajectory is calculated. Primary dynamic model parameters including the coefficients of regression equation of motion are estimated by applying the least squares estimator. Comparison of the estimated coefficients from image processing and coefficients given to the simulation program reveals high accuracy of the model resulting from the image processing data used in this method and approves wind tunnel test data by graphical model and calibration of camera measurement. Also, an experimental test setup has been created and the images of projectile falling down in the presence of fan flow have been captured with high-speed digital camera. By decreasing the ambient light intensity, the images and measurement noise of theta angle increases. By applying recursive least square algorithm, sensitivity of coefficients and robustness of this algorithm has been analyzed. The analysis results indicate that the estimation of coefficients using image processing data has great accuracy.

입사각제어를 위한 통합유도조종법칙

통합유도조종(IGC, Integrated Guidance and Control)은 기존의 분리형 유도조종루프의 성능한계를 극복하기 위해 제안된 개념이다. 본 논문에서는 입사각제어가 가능한 새로운 형태의 IGC 기법을 제안하였다. 제안된 IGC는 자동조종성능과 유도성능을 동시에 얻기 위해 받음각, 피치각속도, 피치각, 시선각을 상태변수로 고려한다. 제안된 IGC의 제어특성을 고찰하기 위하여 비선형 상태방정식에 대한 가제어성 해석 및 평형점 해석을 수행 하였다. IGC 모델에 대한 제어기법으로는 LQR(Linear Quadratic Regulator)을 사용하였으며 LQR을 IGC에 적용하기 위한 방법을 상세하게 설명하였다. 수치 시뮬레이션을 통해 분리형 유도조종루프와 IGC의 성능을 비교하였다. 성능 비교 결과 IGC는 급격한 기동이 필요한 유도기하에 대하여 분리형 유도조종루프에 비해 우수한 유도성능을 보임을 확인하였다. The concept of the IGC(Integrated Guidance and Control) has been introduced to overcome the performance limit of the SGC(Separated Guidance and Control) loop. A new type of IGC with impact angle constraint has been proposed in this paper. Angle of attack, pitch angle rate, pitch angle and line of sight angle are considered as state variables. A controllability analysis and equilibrium point analysis have been carried out to investigate the control characteristic of the prposed IGC. The LQR(Linear Quadratic Regulator) has been adopted for the control law and detailed explanations about the adoption has been provided. The performance comparison between the IGC and the SGC has been carried out. The result of numerical simulations shows that the IGC guarantees better guidance performance than the SGC when the agile maneuver is needed for a specific guidance geometry.

Resonant scattering of plasma sheet electrons by whistler‐mode chorus: Contribution to diffuse auroral precipitation

A quantitative analysis is presented of the resonant scattering of plasma sheet electrons (∼100 eV–20 keV) at L = 6 due to resonant interactions with whistler‐mode chorus. Using wave parameters modeled from observations under geomagnetically disturbed conditions, it is demonstrated that the rate of pitch angle scattering can exceed the level of strong diffusion over a broad energy range (200 eV–10 keV) containing the bulk of the injected plasma sheet population. Scattering by chorus appears to be more effective than previous analyses of resonant interaction with electrostatic electron cyclotron waves. Chorus scattering is therefore a major contributor to the origin of the diffuse aurora and should also control the MLT distribution of injected plasma sheet electrons. The rates of scattering are sensitive to the distributions of wave power with respect to wave normal direction and wave frequency spectrum. Upper‐band chorus (ω/Ωe > 0.5) is the dominant scattering process for electrons below ≈5 keV while lower‐band chorus (0.1 ≤ ω/Ωe ≤ 0.5) is more effective at higher energies especially near the loss cone.

Numerical simulation of asymmetric particle precipitation by pitch angle diffusion

A numerical simulation code is developed to evaluate the loss rate of particles trapped in a mirror magnetic field geometry with asymmetric loss cones. The one‐dimensional model can accommodate particle diffusion at any prescribed rate and loss cones of any prescribed sizes, and it incorporates the important effect of atmospheric backscattering. Numerical solutions for the loss cone particle distribution function calculated for the case of equal loss cones provide an acceptable simulation of the well‐known modified Bessel function solution. The code provides the first quantitative solutions for any specified rate of pitch angle scattering for the general case of arbitrary asymmetry in loss cone size. In the case of weak or moderate diffusion the ratio of particle precipitation fluxes into the two loss cones can provide a sensitive measurement of the rate of particle scattering, but to utilize this important diagnostic property, one must also have information on the fraction of particles that are backscattered from the atmosphere.