Aerodynamic Disturbances Research Articles

Attitude Stabilization of Spacecraft in Very Low Earth Orbit by Center-Of-Mass Shifting

At very low orbital altitudes (≲450 km) the aerodynamic forces can become major attitude disturbances. Certain missions that would benefit from a very low operational altitude require stable attitudes. The use of internal shifting masses, actively shifting the location of the spacecraft center-of-mass, thus modulating, in direction and magnitude, the aerodynamic torques, is here proposed as a method to reject these aerodynamic disturbances. A reduced one degree-of-freedom model is first used to evaluate the disturbance rejection capabilities of the method with respect to multiple system parameters (shifting mass, shifting range, vehicle size, and altitude). This analysis shows that small shifting masses and limited shifting ranges suffice if the nominal center-of-mass is relatively close to the estimated center-of-pressure. These results are confirmed when the analysis is extended to a full three rotational degrees-of-freedom model. The use of a quaternion feedback controller to detumble a spacecraft operating at very low altitudes is also explored. The analysis and numerical simulations are conducted using a nonlinear dynamic model that includes the full effects of the shifting masses, a realistic atmospheric model, and uncertain spacecraft aerodynamic properties. Finally, a practical implementation on a 3U CubeSat using commercial-off-the-shelf components is briefly presented, demonstrating the implementation feasibility of the proposed method.

Theoretical and practical aspects of the development of devices for suppressing dust streams such as "electrostatic gate" for industrial ventilation systems

The main objective of this work is to study the behavior of fine dust fractions (aerosols) of different nature in a non-uniform electric field (corona discharge) under electric, gravitational, aerodynamic and other disturbances. Determination of fundamental principles, and development of methods for controlling fine-fraction particles with predetermined physical characteristics. This article also presents the results of practical application of the developed methods.

Novel Non-Model-Based Fault Detection and Isolation of Satellite Reaction Wheels Based on a Mixed-Learning Fusion Framework

Abstract This paper suggests a model-free framework for Fault Detection and Isolation (FDI) of satellite reaction wheels for the first time. The proposed FDI method is based on multi-classifier fusion with diverse learning algorithms and configured in a parallel form where a unique module simultaneously performs both detection and isolation tasks. In other words, a multi-classifier-based arrangement is presented on the basis of Mixed Learning strategy where four classic and well-practised classification schemes including Random Forest, Support Vector Machine, Partial Least Square, and Naive Bayes are incorporated into FDI module in order to make a decision on the occurrence of a fault and its location. Extensive simulation results with a high-fidelity nonlinear spacecraft simulator considering gyroscopic effects, measurement noise, and exogenous aerodynamic disturbance signals show that the proposed FDI scheme can cope with faults affecting reaction wheel torques and obtain promising FDI performances in most of the designed scenarios.

Measuring System of Air Parameters of the Helicopter with a Stationary Receiver a Flow, Ion-Label and Aerometric Measurement Channels

It is shown that the known limitations on the measurement of air parameters on board the helicopter due to significant aerodynamic disturbances introduced by inductive flows of vortex column of main rotor. This determines the need to create the means of measurement, taking into account the aerodynamics and dynamics of the helicopter flight. The known direction of overcoming these limitations is the use for measuring the information of aerodynamic field of vortex column of main rotor and its perception by means of the stationary multi-functional aerometric receiver. However, the need to protect a large number of full-pressure tubes installed in the flow channel of the multifunctional aerometric receiver, strict requirements for the identity and stability of the characteristics of the large number aerometric channels, complicate the design, reduce reliability, increase cost, inhibit the use of the air parameters measurement system on helicopters of various classes and purposes. Principles of construction, functional scheme, features of perception of primary information of measuring system of air parameters of the helicopter with the stationary receiver of a stream, ion-label and aerometric measuring channels are showed. Algorithms for processing primary information at various stages and flight modes, including: in the parking lot before the launch of the power plant and when rotating the rotor, when taxiing and maneuvering on the earth’s surface, on takeoff and landing modes and when flying at low speeds, at flight speeds, when the stationary receiver of primary information leaves the zone of the vortex column of the rotor using ion-label and aerometric measuring channels, are presented. It is shown that the proposed approaches to the construction, models and algorithms for processing the primary information of the measuring system air parameters of helicopter with ion-label and aerometric measurement channels allow to determine the speed and direction of the wind vector, altitude-velocity parameters of motion relative to the environment and atmospheric parameters in a wide range of helicopter operation, which determines its competitive advantages in solving problems of piloting and provide the flight safety of helicopters of different classes and purposes.

Fractional-Order Control for Robust Position/Yaw Tracking of Quadrotors With Experiments

Quadrotors are highly maneuverable lightweight drones, which are prone to aerodynamic disturbances, vibrations, and uncertainties. These factors stand for a problem that demands robust control laws. For position tracking, the control problem is exacerbated, because the plant is underactuated in the coordinates of interest, requiring a high-performance attitude tracking to resolve underactuation. In this brief, a novel fractional-order controller is proposed by considering a well-posed map that relates the position/yaw control to the desired attitude references. The attitude control is continuous and enforces and sustains a sliding motion in finite time for exponential convergence of the tracking errors to fulfill a “virtual” position controller. The resulting closed-loop system is robust against the continuous disturbances that are not necessarily differentiable in the conventional sense. A numerical study based on the simulations is presented to analyze the advantages of the fractional actions to design a physically realizable controller, and the experiments are discussed to expose the reliability of the proposed fractional scheme implemented in an “X” configuration quadrotor.

Iterative learning control and initial value estimation for probe–drogue autonomous aerial refueling of UAVs

In a probe–drogue aerial refueling system, the drogue is affected not only by wind disturbances but also by strong disturbances from the tanker vortex and receiver forebody bow wave. Along with the aerodynamic disturbances acting on the receiver aircraft, it is difficult for the probe to capture the moving drogue in the docking stage. This paper studies the model of the probe–drogue aerial refueling system under aerodynamic disturbances, and proposes docking control method based on iterative learning control to compensate for the docking errors caused by aerodynamic disturbances. For receiver aircraft with different maneuverability, three control strategies are proposed to achieve a trade-off between safety and control precision. Furthermore, a practical method is proposed to predict the initial value of the learning controllers, which can significantly improve the iterative learning speed of the proposed methods. Finally, simulations demonstrate that the proposed control methods are simple and efficient for the docking control of autonomous probe–drogue aerial refueling.

Reduction of power consumption on quadrotor vehicles via trajectory design and a controller-gains tuning stage

This work presents a methodology for reducing power consumption on quadrotor vehicles. The proposed methodology combines both, a trajectory design procedure and a controller-gains tuning stage. The quadrotor is operated in closed-loop by means of a terminal sliding modes controller, whose stability analysis is provided by using a strict Lyapunov function. The trajectory design stage allows designing an optimal trajectory with smooth transitions by minimizing a criterion function using dynamic optimization theory. Furthermore, in order to reduce power consumption, a performance index depending on the tracking error and the quadrotor inputs is used on a control-gains tuning stage based on a nature inspired evolutionary meta-heuristic algorithm, namely the cuckoo search algorithm. The quadrotor terminal sliding modes controller is compared to another sliding mode control algorithm, and the performance of each controller is assessed by considering aero-dynamical disturbances and parametric uncertainties. Numerical simulations show that the tracking error and power consumption are reduced when the trajectory tracking and controller-gains tuning stages are used. Besides, it is shown that the proposed terminal sliding modes controller outperforms a conventional sliding mode control scheme.

Fault diagnosis for satellite sensors and actuators using nonlinear geometric approach and adaptive observers

SummaryThis paper presents a novel scheme for diagnosis of faults affecting sensors that measure the satellite attitude, body angular velocity, flywheel spin rates, and defects in control torques from reaction wheel motors. The proposed methodology uses adaptive observers to provide fault estimates that aid detection, isolation, and estimation of possible actuator and sensor faults. The adaptive observers do not need a priori information about fault internal models. A nonlinear geometric approach is used to avoid that aerodynamic disturbance torques have unwanted influence on the fault estimates. An augmented high‐fidelity spacecraft model is exploited during design and validation to replicate faults. This simulation model includes disturbance torques as experienced in low Earth orbits. This paper includes an analysis to assess robustness properties of the method with respect to parameter uncertainties and disturbances. The results document the efficacy of the suggested methodology.

The wind field in a cattle feedlot: measurements and simulations

Cup and sonic anemometers were operated in and about an empty pen (60 m × 68 m) on the outer (south) edge of a large cattle feedlot in southern Alberta. Mean wind speed, measured at constant height above ground, varied by more than a factor of four across the pen, the spatial transects being distinct for different wind directions—implying (for instance) that efforts to quantify feedlot gas emissions by micrometeorological methods will be prone to error, unless the drastic lateral inhomogeneity of wind statistics is accounted for. A subset of the observations, selected for southerly winds and weak thermal stratification, were aggregated and compared with steady-state, three-dimensional numerical simulations using “ASL3D”, a Reynolds-averaged Navier–Stokes model with eddy viscosity closure that represents the influences both of feedlot windbreak fences and of topography (Wilson, 2018). Simulations confirm that wind drag on the tall (H ≈ 3 m), low porosity (25%) slatted wooden fences was by far the dominant aerodynamic disturbance at this site. Various options were tested for the placement of computational domain boundaries, and it was found that the influence of fences at the faraway edges of neighbouring pens is practically negligible in comparison with that of the fences lying immediately upwind—that is, the transect of relative mean wind speed within the instrumented pen was largely determined by the nearest upwind fence(s). It is also concluded that when the mean wind is obliquely incident on low porosity fences of this type, simulations are improved if the horizontal wind component tangential to the fence is forced to vanish (at the fence).

On the mechanics of composite structure and electromagnetics of microstrip antenna

Composite structures with desire mechanical properties can be tailored to embed microstrip antenna in aerospace systems for reducing aerodynamic disturbance. The performance of a rectangular microstrip antenna in composite structures is analyzed in spectral domain in this work. Analysis shows that the electromagnetics of antenna in spectral domain is similar to the mechanics of composite structure in space domain. The electrical field, the immittance (impedance or admittance), and the current density are equivalent to the stress, strain, and stiffness in mechanics of composite structures. The governing equations, though may be of different dimensions, are also similar. It shall be expected that the performance of a microstrip antenna on composite structures is different from that on isotropic structures; just as the mechanics of the former is so different from that of the latter. Analysis confirms that antenna performance depends on the structure’s electromagnetic properties; similar to the mechanics of c...

Bees with attitude: the effects of directed gusts on flight trajectories.

ABSTRACTFlight is a complicated task at the centimetre scale particularly due to unsteady air fluctuations which are ubiquitous in outdoor flight environments. Flying organisms deal with these difficulties using active and passive control mechanisms to steer their body motion. Body attitudes of flapping organisms are linked with their resultant flight trajectories and performance, yet little is understood about how isolated unsteady aerodynamic phenomena affect the interlaced dynamics of such systems. In this study, we examined freely flying bumblebees subject to a single isolated gust to emulate aerodynamic disturbances encountered in nature. Bumblebees are expert commanders of the aerial domain as they persistently forage within complex terrain elements. By tracking the three-dimensional dynamics of bees flying through gusts, we determined the sequences of motion that permit flight in three disturbance conditions: sideward, upward and downward gusts. Bees executed a series of passive impulsive maneuvers followed by active recovery maneuvers. Impulsive motion was unique in each gust direction, maintaining control by passive manipulation of the body. Bees pitched up and slowed down at the beginning of recovery in every disturbance, followed by corrective maneuvers which brought body attitudes back to their original state. Bees were displaced the most by the sideward gust, displaying large lateral translations and roll deviations. Upward gusts were easier for bees to fly through, causing only minor flight changes and minimal recovery times. Downward gusts severely impaired the control response of bees, inflicting strong adverse forces which sharply upset trajectories. Bees used a variety of control strategies when flying in each disturbance, offering new insights into insect-scale flapping flight and bio-inspired robotic systems.This article has an associated First Person interview with the first author of the paper.

Platoon Control Under a Novel Leader and Predecessor Following Scheme With the Use of an Advanced Aerodynamic Model

The longitudinal platoon control problem is considered under a leader and predecessor following scheme with a novel velocity-dependent spacing policy. With this spacing policy, the steady-state intervehicle distances increase with increasing cruise velocity and more so for vehicles that are closer to the leader. Since significant changes might be encountered in intervehicle distances during the travel due to the variations in the velocity of the leader, the problem is studied together with a more accurate modeling of aerodynamic effects within a platoon formation. Based on a standard feedback linearization approach, a dynamic output feedback synthesis problem is formulated with two H∞ performance objectives. One of the performance objectives is linked to the string stability of the platoon formation, while the other can be shaped in a way to maintain small spacing errors without aggressive vehicle maneuvers. A synthesis procedure is then outlined based on linear matrix inequality optimization (LMI). The new control scheme is investigated for a three-vehicle platoon by using an advanced aerodynamic model developed based on extensive fluid dynamic simulations. It is observed in this investigation that a desirable platoon operation can be achieved even with a simple aerodynamic model, provided that the controller is designed in a way to ensure good disturbance attenuation. Nevertheless, an accurate modeling of aerodynamic disturbances might be needed especially for the first vehicle after the leader when the cruising velocity varies over a wide range.

Robust control of post-stall pitching maneuver based on finite-time observer

This article presents a robust finite-time maneuver control scheme for the longitudinal attitude dynamic of the aircraft with unsteady aerodynamic disturbances and input saturation. To efficiently eliminate the influence of unsteady aerodynamic disturbances, nonlinear finite-time observers are developed. Despite the existence of the nonlinearity and the coupling between aircraft states and unsteady aerodynamic disturbances, the proposed observers can still precisely estimate the unmeasurable unsteady aerodynamic disturbances in finite time. To attenuate the effect caused by input saturation, a finite-time auxiliary system is constructed. With the error between the desired control input and saturation input as the input of the auxiliary system, the additional signals are generated to compensate for the effect of input saturation. Combined with the finite-time observers and the finite-time auxiliary system, a robust finite-time backstepping attitude control design is developed. The finite-time convergence of all closed-loop system signals is rigorously proved via Lyapunov analysis method under the developed robust attitude control schemes. Finally, simulation results are presented to illustrate the effectiveness of the proposed attitude control approaches.

Tracking Control Design for Quadrotor Unmanned Aerial Vehicle

The model of a quadrotor unmanned aerial vehicle (UAV) is nonlinear and dynamically unstable. A flight controller design is proposed on the basis of Lyapunov stability theory which guarantees that all the states remain and reach on the sliding surfaces. The control strategy uses sliding mode with a backstepping control to perform the position and attitude tracking control. This proposed controller is simple and effectively enhance the performance of quadrotor UAV. In order to demonstrate the robustness of the proposed control method, White Gaussian Noise and aerodynamic moment disturbances are taken into account. The performance of the nonlinear control method is evaluated by comparing the performance with developed linear quadratic regulator and existing backstepping control technique and proportional-integral-derivative from the literature. The comparative performance results demonstrate the superiority and effectiveness of the proposed control strategy for the quadrotor UAV.

Robust Backstepping Control of Wing Rock Using Disturbance Observer

Wing rock is a highly nonlinear phenomenon when the aircraft suffers undesired roll-dominated oscillatory at high angle of attack (AOA). Considering the strong nonlinear and unsteady aerodynamic characteristics, an uncertain multi-input and multi-output (MIMO) nonlinear wing rock model is studied, and system uncertainties, unsteady aerodynamic disturbances and externaldisturbancesareconsideredinthedesignofwingrockcontrollaw. Tohandletheproblemof multipledisturbances,arobustcontrolschemeisproposedbasedontheextendedstateobserver(ESO) and the radial basis function neural network (RBFNN) technique. Considering that the effectiveness of actuators are greatly decreased at high AOA, the input saturation problem is also handled by constructing a corresponding auxiliary system. Based on the improved ESO and the auxiliary system, a robust backstepping control law is proposed for the wing rock control. In addition, the dynamic surface control (DSC) technique is introduced to avoid the tedious computations of time derivatives for the virtual control laws in the backstepping method. The stability of the closed-loop system is guaranteed via rigorously Lyapunov analysis. Finally, simulation results are presented to illustrate the effectiveness of the ESO and the proposed wing rock control approach.

Определение возмущений, действующих на макеты малых спутников на аэродинамическом столе

Определение возмущений, действующих на макеты малых спутников на аэродинамическом столе

Efficiency of terminal control in the trans-atmospheric first stage of an aerospace system under atmospheric and aerodynamic disturbances

Multi-step terminal control of the subhypersonic first stage of an aerospace system in trans-atmospheric climb is considered. Passive motion of spacecraft in conditions of joint influence of atmospheric and aerodynamic disturbance is analyzed. Achieving the prescribed value of the trajectory inclination angle is the terminal motion condition. Terminal height is a controlled value. An algorithm of terminal control for the formation of the command value of aerodynamic lift coefficient is proposed. The Newton method with one or more iterations at a control step is used in determining command control. The serviceability and efficiency of the algorithm compensating the influence of atmospheric and aerodynamic disturbances on the preset terminal altitude condition of spacecraft motion are analyzed. The results of simulating spacecraft motion with terminal control for maximally rarefied atmosphere and for different levels of deviation of the drag coefficient are discussed.

Aerodynamic Drag Analysis of 3-DOF Flex-Gimbal GyroWheel System in the Sense of Ground Test.

GyroWheel is an innovative device that combines the actuating capabilities of a control moment gyro with the rate sensing capabilities of a tuned rotor gyro by using a spinning flex-gimbal system. However, in the process of the ground test, the existence of aerodynamic disturbance is inevitable, which hinders the improvement of the specification performance and control accuracy. A vacuum tank test is a possible candidate but is sometimes unrealistic due to the substantial increase in costs and complexity involved. In this paper, the aerodynamic drag problem with respect to the 3-DOF flex-gimbal GyroWheel system is investigated by simulation analysis and experimental verification. Concretely, the angular momentum envelope property of the spinning rotor system is studied and its integral dynamical model is deduced based on the physical configuration of the GyroWheel system with an appropriately defined coordinate system. In the sequel, the fluid numerical model is established and the model geometries are checked with FLUENT software. According to the diversity and time-varying properties of the rotor motions in three-dimensions, the airflow field around the GyroWheel rotor is analyzed by simulation with respect to its varying angular velocity and tilt angle. The IPC-based experimental platform is introduced, and the properties of aerodynamic drag in the ground test condition are obtained through comparing the simulation with experimental results.

Functional Validation of K-Type (NiCr-NiMn) Thin Film Thermocouple on Low Pressure Turbine Nozzle Guide Vane (LPT NGV) of Gas Turbine Engine

This study presents a concerted approach developed for experimental measurement of surface temperature of critical aeroengine components using a non non-intrusive sensor that is compatible with structural integrity and endurance requirements of high temperature environments. Contrary to wire type thermocouples that cause structural degradation and aerodynamic disturbance in the flow path, the present study proposes a thin film thermocouple (TFTC) that is deposited using electron beam (E-beam) evaporation process. The basic experimentation and proof-of-concept studies are carried out to suit the deposition of K-Type TFTC on a turbine nozzle guide vane that is made of nickel based super alloy. The performance of TFTC is compared to that of wire type thermocouples. The Seebeck co-efficient of the developed K-Type TFTC is found to be 42 μV/°C, with a time constant and drift of 1.11784 ms and 0.4 °C/hour respectively. Based on the feasibility studies and characterization results of prototype TFTC, the deposition of similar TFTC was carried out on low pressure turbine nozzle guide vane (LPT NGV) of an aeroengine using same optimized parameters and procedures. The results presented vindicate the application of the proposed methodology for a developmental aero gas turbine engine.

Robust sliding mode control with ESO for dual-control missile

This paper proposes a novel composite dual-control by combing the integral sliding mode control (ISMC) method based on the finite time convergence theory with extended state observer (ESO) for a tracking problem of a missile with tail fins and reaction-jet control system (RCS). First, the ISMC method based on finite time convergence is utilized to design the control law of tail fins and the pulse control of RCS for the dual-control system, ensuring the system with rapid response and high accuracy of tracking. Then, ESO is employed for the estimation of aerodynamic disturbances influenced by the airflow of thruster jets. With the characteristic of high accuracy estimation of ESO, the chattering free tracking performance of the attack angle command and the robustness of the control law are achieved. Meanwhile, the stability of the dual-control system is analyzed based on finite time convergence stability theorem and Lyapunov's theorem. Finally, numerical simulations demonstrate the effectiveness of the proposed design.