Envelope Protection System Research Articles

Limit protection systems for safety operational envelope of submarine

To enhance the operational stability of submarines, this study conducts a comparative analysis of three pitch limit protection systems based on the reference model, potential function, and dynamic trim algorithm. The proposed depth limit protection system adjusts the depth command by comparing the desired depth, calculated by the outer-loop controller, against a predefined depth limit. Similarly, the pitch limit protection systems modify the command pitch calculated by the inner-loop controller to ensure it does not exceed the pitch limit. Submarine maneuvering simulations were conducted to verify the performance of the envelope protection system, which comprises depth and pitch limit protection systems. Simulation results confirmed the effectiveness of these methods, with the dynamic trim algorithm demonstrating superior control efficiency. This study advances submarine safety and stability by developing and validating advanced pitch limit protection systems.

Investigation of the Efficacy of a New Envelope Protection System on Different Wind Turbines

Bu çalışmada, rüzgar elektrik santrallerinde yaygın olarak bulunan yatay eksenli rüzgar türbinlerini aşırı yüklenmelerden korumak için geliştirilen yenilikçi uyarlanabilir bir zarf koruma sistemi kısaca açıklanmıştır. Sistem tasarımı, rüzgar türbinlerini aşırı itki kuvvetinden koruyacak şekilde gerçekleştirilmiş olup, farklı kanat sayıları ve rotor çaplarındaki Türbin A, Türbin B ve Türbin C olarak adlandırılan rüzgar türbinleri üzerindeki etkinliği simülasyonlar ile gösterilmiştir. Simülasyon sonuçları, yeni zarf koruma sisteminin değişik rüzgar türbinlerine uyarlanabildiği ve türbinleri önceden belirlenen itki kuvveti sınır değerleri içinde çalıştırarak koruyabileceğini göstermiştir.

Adaptive envelope protection control of wind turbines under varying operational conditions

This study introduces a new Envelope Protection System (EPS) algorithm for wind turbines. The algorithm is adaptive to turbine-changing operational conditions and can effectively reduce turbine excessive/ultimate loads. Through an adaptive neural network, the proposed algorithm continuously monitors instantaneous wind and turbine states. Simultaneously, it predicts the near future response of the turbine load and detects its future crossing with a predefined safe envelope limit by comparing the actual wind speed to a theoretically estimated wind speed. When required, a protection action is applied based on the comparison to keep the turbine load response within the safe limit. In this paper, the thrust force is used as the critical load and is chosen as the limit parameter. Simulations are carried out using the MS (Mustafa Sahin) Bladed Wind Turbine Simulation Model for the National Renewable Energy Laboratory (NREL) 5 MW turbine under normal turbulent winds with different mean values. Simulations show that the EPS algorithm adapts to varying operational conditions such as changes in turbine operating point in the below rated, transition, and above rated regions, as well as rotor blade icing and successfully reduces the excessive thrust forces. Performance analyses indicate that, for keeping the thrust force within the limit, the proposed EPS algorithm reduces the thrust force by 98.89%, 98.43%, 99.26% relative to standard baseline controls in the aforementioned regions, respectively and by 99.61% under blade icing. Also, the mean value and the fluctuations of thrust force are reduced up to 5.52% and 68.7%, respectively. Depending on the operating region, the mean power decreases up to 2.07% or increases up to 1.21%, while power fluctuations decrease up to 30.97%.

Conceptual design and preliminary experiment of icing risk management and protection system

Icing is one of the main external environmental factors that causes aircraft to lose control. The flight safety assurance system under icing condition is particularly important. However, most of the systems do not consider the coupling characteristics of aerodynamics and flight dynamics of icing aircraft. This will affect the accuracy of the calculation results. Besides, the icing risk management system helps the pilot to realize the possible dangers in advance and perform correct maneuvers, based on quantitative assessment and visualization methods of flight risk. The envelope protection system realizes flight safety guarantee based on the real-time boundary protection method of key flight parameters. Finally, based on distributed simulation technology, a flight simulator was used as a platform to integrate the icing risk management system and envelope protection system to realize man-in-the-loop simulation. Two fictional but historically motivated icing scenarios are designed to test the system, and the results demonstrate that the icing risk management and protection system would be useful for aviation safety and can also be used for pilot training and reproducing flight accidents to find the causes.

Flying by Feeling: Communicating Flight Envelope Protection through Haptic Feedback

ABSTRACT Modern aircraft can be equipped with a flight envelope protection system: automation which modifies pilot control inputs to ensure that the aircraft remains within the allowable limits. Overruling the pilot inputs may lead to mode confusion, even when visual or auditory feedback is provided to alert pilots. We advocate using active control devices to make the flight envelope protection system tangible to the pilot. This paper presents the main findings of an evaluation of three haptic feedback designs for flight envelope protection. The first concept used both force feedback and vibro-tactile alerts, producing promising, yet inconclusive, results. The second concept used asymmetric vibrations to give directional alerting cues, which did not result in improved performance on initial use, but which did yield improved learning rate for the task. The third system employed force feedback to physically guide the pilot away from flight envelope limits, which yielded safety improvements from the first use, but created dependence: pilot performance degraded immediately after the force feedback was removed. From this, we advise to use asymmetric vibrations during training for flight envelope excursions, to leverage active control interfaces for providing force feedback during operation, and reevaluate a combination of both to combine their advantages for single-pilot operations.

Database-Driven Safe Flight-Envelope Protection for Impaired Aircraft

In this paper, an online flight envelope protection system is developed and implemented on impaired aircraft with structural damage. The whole protection system is designed to be a closed loop of several subsystems, including system identification, damage classification, flight-envelope prediction, and fault-tolerant control. Based on the information given by damage classification, the flight envelopes are explicitly retrieved, processed online from the database, and fed into the fault-tolerant controller, which makes the protection system adaptive to a wide range of abnormal conditions. Simulation results show that with envelope protection, loss-of-control accidents are more likely to be prevented, since excessive commands to the controller are restricted based on the updated information of the changed flight envelopes. In this way, the fault tolerance of the impaired aircraft can be effectively enhanced.

Online Safe Flight Envelope Protection for Icing Aircraft Based on Reachability Analysis

Icing encountered by an aircraft in flight can pose a great threat to flight safety, which is the foremost concern in aviation. Ice accretion has nonlinear and coupling properties, and therefore, a conventional envelope protection system cannot successfully deal with the condition. A safe flight envelope based on reachability analysis is proposed in this paper as a basis for designing an online envelope protection system for aircraft under icing conditions. This system uses a neural network method to identify changes in the aerodynamic coefficients and to classify the degrees of icing and uses a database-driven approach to solve the onboard safe flight envelope computation problem. The database of icing safe flight envelopes is created offline and can be retrieved in real time. The Research Civil Aircraft Model (RCAM) encountering icing conditions in the climbing phase was taken as an example to verify the feasibility of the online safe flight envelope protection system. The simulation results showed that the system can classify the degrees of icing efficiently, prevent the aircraft from deviating from the safe flight envelope, guide it back to the envelope along the fastest path, and reduce the risk of loss of control under icing conditions.

Design of a Haptic Feedback System for Flight Envelope Protection

Several modern aircraft use a passive control manipulator: a spring–damper system that generates command signals to the flight control computers in combination with a flight envelope protection system that limits pilot inputs when approaching the aircraft limits. This research project aims to increase pilot awareness of this protection system through the use of force feedback on the control device, that is, haptics. This paper describes in detail how the haptic feedback works and when it triggers; another paper will discuss the results of an experimental evaluation. With the current haptic design, pilots can get five cues: first, a discrete force cue when approaching the limits; second, an increased spring coefficient for control deflections that bring the aircraft closer to its limits; third, a stick shaker for low velocities; fourth, if a low-velocity condition requires an input, the stick is moved forward to the desired control input; and finally, the stick follows the automatic Airbus “pitch-up” command during an overspeed condition. This novel system is expected to help pilots correctly assess the situation and decide upon the right control action. It will be evaluated in two scenarios close to the flight envelope limits: a windshear and an icing event.

Adaptive Neural Networks-Based Dynamic Inversion Applied to Reconfigurable Flight Control and Envelope Protection Under Icing Conditions

Aircraft icing can result in degradation of the aerodynamic characteristics and reduction of the control effectiveness, which would pose serious threats to flight safety. Reconfigurable flight control and envelope protection of iced aircraft have become an effective solution to ensure flight safety in icing encounters. In this study, the dynamic model of the iced aircraft was established, and high precision numerical simulation method and wind tunnel virtual flight experiment were applied to obtain the icing aerodynamic database. Furthermore, the reconfigurable flight control law was designed by using the adaptive neural networks based dynamic inversion (ANN-DI) control method. Simulation results demonstrate that the control method behaves well tracking performance and strong robustness in the presence of modeling errors and control surface damage. After that, an icing envelope protection system was designed based on control limiting strategy and the ANN-DI control was applied to calculate the control surface deflection limits based on the limit values of the key flight safety parameters. Finally, the designed icing envelope protection system has been verified through simulation in two autopilot modes under icing conditions. The simulation results obtained here show that the system could keep the key flight safety parameters such as the flight speed, the angle of attack (AOA), the side slip angle, and bank angle within the flight safe region under icing conditions. The method proposed in this study is expected to provide flight safety measures for in-flight icing.

Probabilistic Flight Envelope Estimation with Application to Unstable Overactuated Aircraft

This paper proposes a novel and practical framework for safe flight envelope estimation and protection, in order to prevent loss-of-control-related accidents. Conventional analytical envelope estimation methods fail to function efficiently for systems with high dimensionality and complex dynamics, which is often the case for high-fidelity aircraft models. In this way, this paper develops a probabilistic envelope estimation method based on Monte Carlo simulation. This method generates a probabilistic estimation of the flight envelope by simulating flight trajectories with extreme control effectiveness. It is shown that this method can significantly reduce the computational load compared with previous optimization-based methods and guarantee feasible and conservative envelope estimation of no less than seven dimensions. This method was applied to the Innovative Control Effectors aircraft, an overactuated tailless fighter aircraft with complex aerodynamic coupling between control effectors. The estimated probabilistic flight envelope is used for online envelope protection by a database approach. Both conventional state-constraint-based and novel predictive probabilistic flight envelope protection systems were implemented on a multiloop nonlinear dynamic inversion controller. Real-time simulation results demonstrate that the proposed framework can protect the aircraft within the estimated envelope and save the aircraft from maneuvers that otherwise would result in loss of control.

Safety Analysis for Icing Aircraft during Landing Phase Based on Reachability Analysis

Icing is one of the leading causes of fatal aircraft accidents worldwide. Encountering icing conditions, dynamic characteristics of the aircraft will be damaged, thereby greatly affecting flight safety. Research on real-time estimations of the safety envelope under icing conditions is critical to improve flight safety. In order to determine the safety envelope, the reachability analysis based on the level set method is presented. The reachable set is obtained via computing the Hamilton-Jacobi partial differential equation (HJPDE), which is based on optimal control and is used in the landing phase of an aircraft. The results show that icing will shrink the safety envelope. Particularly under severe icing conditions, the stall speed of the aircraft will increase, and dynamic behavior will be more sensitive. A slight change of command by the pilot may contribute to the flight state moving outside the safety envelope. Furthermore, the effect of flap deflection was considered, which positively impacts the expanding safety envelope during the landing phase. Finally, a maneuvering coping strategy based on safety envelope is proposed. Examples are provided using the NASA’s generic transport model (GTM), and the results can be applied to flight safety risk assessment, providing theoretical guidance for the design of envelope protection systems.

Planing Avoidance Control for a Supercavitating Underwater Vehicle Based on Potential Functions

In this paper, we focus on planing avoidance control for a supercavitating underwater vehicle based on the potential function method. The planing margin can be calculated using the relative position between the cavity center and vehicle center at the end of the vehicle. The planing margin was transformed into a limit variable such as the pitch angle and yaw angle limit. To prevent the vehicle attitude from exceeding the limit variable, a potential function based planing envelope protection method was proposed. The planing envelope protection system overrides commands from the tracking controller, and the vehicle attitude converges to a desired angle, in which the potential function is minimized. Numerical simulations were performed to analyze the physical feasibility and performance of the proposed method. The results showed that the proposed methods eliminated the planing, allowing the vehicle to follow tracking commands.

Design of a safety operational envelope protection system for a submarine

A safety operational envelope (SOE) is an area that guarantees the safety of a submarine from accidents, such as jamming and flooding. In this study, a submarine envelope protection system (EPS) was designed to prevent submarine excursion from the SOE. Modeling of the hull force, propeller force, and main ballast tank blowing was performed. The SOE was established based on a crash stop and emergency rising maneuver simulation. In the estimation model, a linear compensator and neural network are employed to estimate the submarine dynamics. The command limit is calculated using the estimation model and the dynamic trim algorithm, and it is restricted by the limit avoidance. The EPS was applied to a submarine maneuvering simulation program and its performance was verified by a depth change simulation. The designed EPS prevents the submarine from exceeding the limit boundary and the control system can thereby enhance the operational stability.

Automation Situation Awareness Display for a Flight Envelope Protection System

This paper presents an interface system display that is conceived to improve pilot situation awareness with respect to a flight envelope protection system, developed for a midsized transport aircraft. The new display is designed to complement existing cockpit displays by augmenting them with information related to both aircraft state and control automation. In particular, the proposed display provides cues about the state of automation directly in terms of pilot control actions, in addition to flight parameters. The paper also presents results of a piloted simulation-based evaluation, which was designed to validate the developed interface by assessing the relevance of the displayed information, as well as the adequacy of the display layout.

Adaptive Control Within a Flight Envelope Protection System

An adaptive control augmentation is presented for desired systems containing a feedforward term and is applied to a controller within a flight envelope protection system for a transport-class aircraft. By recovering the baseline controller’s nominal performance in the presence of failures and disturbances, the proposed controller is able to improve aircraft performance, reducing pilot workload and allowing pilots to focus their attention on determining a course of action to prevent the offnominal condition from propagating into a loss-of-control sequence. Combined with the flight envelope protection system and other technologies, the proposed algorithm can form an integrated system for preventing aircraft loss of control. Nonlinear simulation results show the efficacy of the proposed control law.

Design of a Flight Envelope Protection System for NASA’s Transport Class Model

This paper presents a flight envelope protection system for NASA’s Transport Class Model. The developed protection scheme is based on a command-limiting architecture that accounts for aircraft adverse aerodynamics, unusual attitude, and structural integrity and is designed to augment a standard gain-scheduled flight control law. The scheme also includes an energy protection system, which relies on an automatic throttle control loop that implements a total energy control law. In the setup adopted, the limits of the protected envelopes are actively adjusted to ensure, on the one hand, that the aircraft always stays in a safe flight condition and, on the other hand, that the pilot has enough control authority to perform aggressive maneuvers, if needed. Batch simulations demonstrate the efficacy of the protection system in maintaining the aircraft within desired safe conditions.

잠수함의 종동요각 한계예측 알고리즘 설계

An envelope protection system is a control system that allows a submarine to operate freely using its own operational envelope without exceeding the structural limit, dynamic limit, and control input limit. In this paper, an envelope protection system for the pitch angle of a submarine is designed using a dynamic trim algorithm. A linear quadratic regulator and artificial neural network are used for the true dynamics approximation. A submarine maneuvering simulation program developed using experimental data is used to validate the designed envelope protection system. Simulation results show the effectiveness of the designed envelope protection system.

Design of a safety operational envelope protection system for the pitch angle of a submarine

Submarines have a safety operating envelope, the boundary of which is closely related to structural limits and the safety of crew. An envelope protection system guarantees that the submarine does not exceed the boundary, which reduces the frequency of operational accidents and mission time. In this article, an envelope protection system for the pitch angle is designed for a submarine. The envelope protection system consists of limit detection and limit avoidance. Limit detection is designed using a dynamic trim algorithm, and command limiting is used for the limit avoidance. An artificial neural network is adopted for on-line learning and modeling uncertainty compensation, and a linear quadratic regulator is employed to stabilize the error dynamics. A submarine maneuvering simulation program developed from the experimental data is used to validate the designed envelope protection system. The simulation results show the effectiveness of the envelope protection system.

Design and evaluation of a Flight Envelope Protection haptic feedback system

Abstract: This paper describes the design and evaluation of a shared control, haptic feedback system to communicate Flight Envelope Protection System intent. The concept uses a combination of stiffness feedback and vibration to communicate proximity of the aircraft state to flight envelope boundaries. In addition, a stick center shift can be applied by the envelope protection system to cooperatively perform corrective actions in case of severe excursions of the envelope margins. Results from the evaluation experiment show improved performance with haptic feedback in both scenarios. Workload ratings were unaffected. Pilot opinion was unanimously positive, especially with regard to the combination of stiffness feedback and vibration cues.

A predictive envelope protection system using linear, parameter-varying models

A parameter-varying, model-predictive envelope protection system is developed simplifying the controller structures required to keep the aircraft within a safe angle-of-attack and normal load factor envelope. The idea of a quasi-steady flight condition is used to map the flight envelope limits onto the setpoint values of a single flight control law. Since no mode switching is required, the selected level of automation, i.e., autopilot and flight management functionalities, is independent from the proximity to any angle-of-attack and normal load factor limit. In contrast to previous approaches, the proposed algorithm makes use of a quasi-linear, parameter-varying control loop model to adapt to the true nonlinear aircraft behavior. A variance-based sensitivity analysis highlights the most significant scheduling variables within this control loop model and, therefore, indicates the option of model reduction and improvement in efficiency, respectively. The proposed envelope protection system is evaluated throughout virtual flight tests with the unmanned flight test platform ULTRA-Dimona showing promising overall performance also in the presence of wind and turbulence.