Adaptive Inversion Research Articles

On the Method of Adaptive Waveform Inversion with Zero‐Offset VSP Data

AbstractIn this paper, we develop a waveform inversion method to estimate the interval velocity and quality factor Q with zero‐offset VSP data. The inversion is done in the time domain and the objective function is constructed using the undisturbed segment of the direct downgoing wave. According to the signal‐to‐noise ratio and the interference of upgoing wave, our method can adaptively choose the undisturbed segment of the direct downgoing wave as long as possible, so it can make use of the most of the data. A new data weighting scheme is proposed to make the objective function more sensitive to Q. To deal with the ill‐posed nature of waveform inversion, the recently developed multiplicative regularization approach is adopted, which can adaptively determine the regularization parameter as the iterations proceed. In addition, a nonlinear transform is applied to the unknown model parameters to constrain them within their upper and lower bounds. For reducing computational cost, the analytic expressions of the elements of the Jacobian matrix are given. The application of this method on the synthetic VSP data and real data demonstrates the effectiveness of this method, and indicates this method is less sensitive to random noise and upgoing waves.

Piloted Simulator Evaluation Results of New Fault-Tolerant Flight Control Algorithm

A high fidelity aircraft simulation model, reconstructed using the Digital Flight Data Recorder (DFDR) of the 1992 Amsterdam Bijlmermeer aircraft accident (Flight 1862), has been used to evaluate a new Fault-Tolerant Flight Control Algorithm in an online piloted evaluation. This paper focuses on the piloted simulator evaluation results. Reconfiguring control is implemented by making use of Adaptive Nonlinear Dynamic Inversion (ANDI) for manual fly by wire control. After discussing the modular adaptive controller setup, the experiment is described for a piloted simulator evaluation of this innovative reconfigurable control algorithm applied to a damaged civil transport aircraft. The evaluation scenario, measurements and experimental design, as well as the real-time implementation are described. Finally, reconfiguration test results are shown for damaged aircraft models including component as well as structural failures. The evaluation shows that the FTFC algorithm is able to restore conventional control strategies after the aircraft configuration has changed dramatically due to these severe failures. The algorithm supports the pilot after a failure by lowering workload and allowing a safe return to the airport. For most failures, the handling qualities are shown to degrade less with a failure than the baseline classical control system does.

Nonminimum phase adaptive inverse control for settle performance applications

Single-track hard disk drive (HDD) seek performance is measured by settle time, t s , defined as the time from the arrival of a seek command until the measured position reaches and stays within an acceptable distance from the target track. Our previous work has shown feedforward dynamic inversion, coupled with an aggressive desired trajectory y d , is capable of achieving high performance settle times when the closed-loop dynamics are time-invariant and accurately modeled. In contrast, we describe an adaptive inversion procedure in this paper which removes the requirement for accurate initial models and tracks the position-variant dynamics present in our Servo Track Writer (STW) experimental apparatus. The proposed indirect adaptive inversion algorithm relies on a recursive least squares (RLS) estimate of the closed-loop dynamics. Pre-filtering of the RLS input signals, covariance resetting, and relative NMP system partitioning are necessary additions to the baseline adaptive algorithm in order to achieve fast settle times. Compared to the nonadaptive solution with accurate system identification, we show the adaptive algorithm achieves a 22% reduction in average settle time and a 53% reduction in settle time standard deviation.

Adaptive inverse dynamics control of robots with uncertain kinematics and dynamics

It has been about two decades since the first globally convergent adaptive tracking controller was derived for robots with dynamic uncertainties. However, not until recently has the problem of concurrent adaptation to both the kinematic and dynamic uncertainties found its solution. This adaptive controller belongs to passivity-based control. Though passivity-based controllers have many attractive properties, in general, they are not able to guarantee the uniform performance of the robot over the entire workspace. Even in the ideal case of perfect knowledge of the manipulator parameters, the closed-loop system remains nonlinear and coupled. Thus the closed-loop tracking performance is difficult to quantify, while the inverse dynamics controllers can overcome these deficiencies. Therefore, in this work, we will develop a new adaptive Jacobian tracking controller based on the inverse manipulator dynamics. Using the Lyapunov approach, we have proved that the end-effector motion tracking errors converge asymptotically to zero. Simulation results are presented to show the performance of the proposed controller.

Nonlinear Reconfiguring Flight Control Based on Online Physical Model Identification

This paper presents a study on fault tolerant flight control of a benchmark aircraft model. Reconfiguring control is implemented by making use of adaptive nonlinear dynamic inversion for manual and autopilot control. The weakness of classical nonlinear dynamic inversion, its sensitivity to modeling errors, is circumvented here by making use of a real-time identified physical model of the damaged aircraft. With help of the Boeing 747 benchmark simulation model, including the realistic component as well as the structural failure modes, it is possible to analyze the damage accommodation capabilities of the considered approach. In failure conditions, the damaged aircraft model is identified by the so-called two-step method in real time and this model is applied subsequently to the model-based adaptive nonlinear dynamic inversion routine in a modular structure, which allows flight control reconfigurations online. After discussing the modular adaptive controller setup, reconfiguration test results are shown for damaged aircraft models using a desktop computer as well as the moving base Simulation, Motion, and Navigation Research Flight Simulator of Delft University. These results indicate satisfactory failure handling capabilities of this fault tolerant control setup, for component as well as structural failures.

Nonlinear Robust Adaptive Control of Flexible Air-Breathing Hypersonic Vehicles

This paper describes the design of a nonlinear robust adaptive controller for a flexible air-breathing hypersonic vehicle model. Because of the complexity of a first-principle model of the vehicle dynamics, a control-oriented model is adopted for design and stability analysis. This simplified model retains the dominant features of the higher-fidelity model, including the nonminimum phase behavior of the flight-path angle dynamics, the flexibility effects, and the strong coupling between the engine and flight dynamics. A combination of nonlinear sequential loop closure and adaptive dynamic inversion is adopted for the design of a dynamic state-feedback controller that provides stable tracking of the velocity and altitude reference trajectories and imposes a desired set point for the angle of attack. A complete characterization of the internal dynamics of the model is derived for a Lyapunov-based stability analysis of the closed-loop system, which includes the structural dynamics. The proposed methodology addresses the issue of stability robustness with respect to both parametric model uncertainty, which naturally arises when adopting reduced-complexity models for control design, and dynamic perturbations due to the flexible dynamics. Simulation results from the full nonlinear model show the effectiveness of the controller.

Flight Control Reconfiguration based on a Modular Approac

This paper describes a reconfiguring flight control algorithm for damaged aircraft based upon a modular approach. This approach combines real time physical model identification with adaptive nonlinear dynamic inversion. The sensitivity of NDI to modeling errors is eliminated here by making use of a real time identified model of the aircraft. In failure situations, the damaged aircraft model is identified by the two step method and this updated model is supplied to the model-based adaptive NDI routine, which reconfigures for the failure in real time. Reconfiguration test results for damaged aircraft models indicate good failure handling capabilities of this fault tolerant control setup, for component as well as structural failures.

무추력 비행체를 대상으로 한 적응 통합 유도제어기 설계

The guidance controller of the conventional aircraft consists of inner-loop (autopilot) and outer-loop (guidance). If the guidance controller can be designed as an integrated guidance and control (IGC), the various advantages exist. The integrated guidance and control formulation can compensate for the effect of autopilot lag. An integrated approach also helps avoid the iterative procedure involved in tuning the guidance and autopilot subsystems, if designed separately. Integrated design is also less susceptible to saturation and stability problems. This paper presents an approach to IGC design for the unpowered air vehicle with the only flaperon using a combination of adaptive output feedback inversion and backstepping techniques. Adaptive neural networks are trained online with available measurements to compensate for unmodeled nonlinearities in the design process.

Design and Implement of Wire Tension Control System for Multi-wire Saw

Based on the analysis of the mechanical structure principle of multi-wire saw, the wire-supplying system model is studied from a point of view of kinematics and factors that influence wire tension is investigated to overcome the deficiency in traditional multi-wire saw tension control system. A mechanical and electrical wire tension control scheme is proposed, in which torque motor is used to produce tension on wire instead of hammer, and intelligent controller is designed by using adaptive inverse algorithm to reduce the speed synchronization trace error of multi-motor system; The scheme reduces the wire vibration intensity greatly. The hardware platform of tension control system based on field bus is designed and realized. The test results of XQ300A multi-wire saw prove the feasibility and reliability of the system. The control scheme features high precision and easy realization of tension control,low wire-broken fault rate and convenient tensioning.

Perception of Emotional Valences and Activity Levels from Vowel Segments of Continuous Speech

This study aimed to investigate the role of voice source and formant frequencies in the perception of emotional valence and psychophysiological activity level from short vowel samples (approximately 150 milliseconds). Nine professional actors (five males and four females) read a prose passage simulating joy, tenderness, sadness, anger, and a neutral emotional state. The stress carrying vowel [a:] was extracted from continuous speech during the Finnish word [ta:k:ahan] and analyzed for duration, fundamental frequency (F0), equivalent sound level (L(eq)), alpha ratio, and formant frequencies F1-F4. Alpha ratio was calculated by subtracting the L(eq) (dB) in the range 50 Hz-1 kHz from the L(eq) in the range 1-5 kHz. The samples were inverse filtered by Iterative Adaptive Inverse Filtering and the estimates of the glottal flow obtained were parameterized with the normalized amplitude quotient (NAQ = f(AC)/(d(peak)T)). Fifty listeners (mean age 28.5 years) identified the emotional valences from the randomized samples. Multinomial Logistic Regression Analysis was used to study the interrelations of the parameters for perception. It appeared to be possible to identify valences from vowel samples of short duration ( approximately 150 milliseconds). NAQ tended to differentiate between the valences and activity levels perceived in both genders. Voice source may not only reflect variations of F0 and L(eq), but may also have an independent role in expression, reflecting phonation types. To some extent, formant frequencies appeared to be related to valence perception but no clear patterns could be identified. Coding of valence tends to be a complicated multiparameter phenomenon with wide individual variation.

English

A method to determine the moving tank and missile impact forces on a bridge is developed. The presentmethod is an online adaptive recursive inverse algorithm, which is composed of the Kalman filter and therecursive least square estimator (RLSE), to estimate the force inputs on the bridge structure. The state equationsof the bridge structure were constructed by using the model superposition and orthogonal technique. Byadopting this inverse method, the moving tank and missile impact force inputs acting on the bridge structuresystem can be estimated from the measured dynamic responses. Besides, this work presents an efficientweighting factor applied in the RLSE, which is capable of providing a reasonable estimation results. The resultsobtained from the simulations show that the method is effective in determining the moving tank and missileimpact forces, so that the acceptable results can be obtained.Defence Science Journal, 2008, 58(6), pp.752-761, DOI:http://dx.doi.org/10.14429/dsj.58.1703

Adaptive Dynamic Inversion via Time-Scale Separation

This paper presents a full state feedback adaptive dynamic inversion method for uncertain systems that depend nonlinearly upon the control input. Using a specialized set of basis functions that respect the monotonic property of the system nonlinearities with respect to control input, a state predictor is defined for derivation of the adaptive laws. The adaptive dynamic inversion controller is defined as a solution of a fast dynamical equation, which achieves time-scale separation between the state predictor and the controller dynamics. Lyapunov-based adaptive laws ensure that the predictor tracks the state of the nonlinear system with bounded errors. As a result, the system state tracks the desired reference model with bounded errors. Benefits of the proposed design method are demonstrated using Van der Pol dynamics with nonlinear control input.

Improved Adaptive–Reinforcement Learning Control for Morphing Unmanned Air Vehicles

This paper presents an improved Adaptive-Reinforcement Learning Control methodology for the problem of unmanned air vehicle morphing control. The reinforcement learning morphing control function that learns the optimal shape change policy is integrated with an adaptive dynamic inversion control trajectory tracking function. An episodic unsupervised learning simulation using the Q-learning method is developed to replace an earlier and less accurate Actor-Critic algorithm. Sequential Function Approximation, a Galerkin-based scattered data approximation scheme, replaces a K-Nearest Neighbors (KNN) method and is used to generalize the learning from previously experienced quantized states and actions to the continuous state-action space, all of which may not have been experienced before. The improved method showed smaller errors and improved learning of the optimal shape compared to the KNN.

Structured Adaptive Model Inversion Controller for Mars Atmospheric Flight

The new vision for manned Mars exploration presents challenges that are critically different from past experiences with robotic missions. Safe precision landing requirements for manned missions make it necessary to fly a controlled entry trajectory, rather than the more robust ballistic entry trajectory traditionally used for robotic missions. Large variations and uncertainties in Mars atmospheric properties also pose a significant challenge. Model reference adaptive control has not been previously used for Mars entry control, but is an attractive candidate. It has an adaptation mechanism that reduces tracking errors in the presence of uncertain parameters such as atmospheric density, and vehicle properties such as aerodynamic coecients and inertias. This paper develops and implements two dierent adaptive control systems for the Mars ellipsled vehicle, and evaluates them with non real-time simulation for Mars atmospheric flight from entry interface to parachute deployment. Results presented in the paper demonstrate that learning rates and other parameters can be tuned to obtain acceptable tracking performance during an entire entry trajectory. A Structured Adaptive Model Inversion controller that specifically adapts for atmospheric density variations, vehicle aerodynamic coecients, and vehicle inertias is judged to be a promising candidate for a Mars entry vehicle controller.

A Peak Power Reduction Method with Adaptive Inversion of Clustered Parity-Carriers in BCH-Coded OFDM Systems

In this paper, we propose a simple peak power reduction (PPR) method based on adaptive inversion of parity-check block of codeword in BCH-coded OFDM system. In the proposed method, the entire parity-check block of the codeword is adaptively inversed by multiplying weighting factors (WFs) so as to minimize PAPR of the OFDM signal, symbol-by-symbol. At the receiver, these WFs are estimated based on the property of BCH decoding. When the primitive BCH code with single error correction such as (31,26) code is used, to estimate the WFs, the proposed method employs a significant bit protection method which assigns a significant bit to the best subcarrier selected among all possible subcarriers. With computer simulation, when (31,26), (31,21) and (32,21) BCH codes are employed, PAPR of the OFDM signal at the CCDF (Complementary Cumulative Distribution Function) of 10-4 is reduced by about 1.9, 2.5 and 2.5dB by applying the PPR method, while achieving the BER performance comparable to the case with the perfect WF estimation in exponentially decaying 12-path Rayleigh fading condition.

Adaptive Multiscale Streamline Simulation and Inversion for High-Resolution Geomodels

Summary A particularly efficient reservoir simulator can be obtained by combining a recent multiscale mixed finite-element flow solver with a streamline method for computing fluid transport. This multiscale-streamline method has shown to be a promising approach for fast flow simulations on high-resolution geologic models with multimillion grid cells. The multiscale method solves the pressure equation on a coarse grid while preserving important fine-scale details in the velocity field. Fine-scale heterogeneity is accounted for through a set of generalized, heterogeneous basis functions that are computed numerically by solving local flow problems. When included in the coarse-grid equations, the basis functions ensure that the global equations are consistent with the local properties of the underlying differential operators. The multiscale method offers a substantial gain in computation speed, without significant loss of accuracy, when basis functions are updated infrequently throughout a dynamic simulation. In this paper, we propose to combine the multiscale-streamline method with a recent "generalized travel-time inversion" method to derive a fast and robust method for history matching high-resolution geocellular models. A key point in the new method is the use of sensitivities that are calculated analytically along streamlines with little computational overhead. The sensitivities are used in the travel-time inversion formulation to give a robust quasilinear method that typically converges in a few iterations and generally avoids much of the time-consuming trial-and-error seen in manual history matching. Moreover, the sensitivities are used to enforce basis functions to be adaptively updated only in areas with relatively large sensitivity to the production response. The sensitivity-based adaptive approach allows us to selectively update only a fraction of the total number of basis functions, which gives substantial savings in computation time for the forward flow simulations. We demonstrate the power and utility of our approach using a simple 2D model and a highly detailed 3D geomodel. The 3D simulation model consists of more than 1,000,000 cells with 69 producing wells. Using our proposed approach, history matching over a period of 7 years is accomplished in less than 20 minutes on an ordinary workstation PC.

Adaptive Dynamic Inversion for Nonaffine-in-Control Uncertain Systems via Time-Scale Separation. Part II

This paper presents an adaptive dynamic inversion method for uncertain nonaffine-in-control dynamical systems. Online approximation of the adaptive dynamic inversion controller is performed using time-scale separation. The resulting control signal is sought as a solution of a "fast" dynamical equation, which inverts a series-parallel model, whose state is shown to track the state of the original nonaffine-in-control system. The design methodology is constructive, and numerically verifiable sufficient conditions on the system parameters are given. A simulation example, motivated by aerospace applications, illustrates the theoretical results.

Novel Control Scheme for Helicopter Flight: Fuzzy Immune Adaptive Model Inversion Control

A novel control scheme, fuzzy immune adaptive model inversion control, was put forward, aiming at the large flight envelope curve control problem of helicopter. The proposed scheme was designed based on model inversion theory, biology immune response mechanism and fuzzy control method. It could achieve effective control throughout large flight envelope curve via the design of fuzzy immune online-compensation element, only needing a static inverse model on the basis of a single flight condition. Simulation results comparing with the neural network adaptive control method show the system based on the proposed scheme has better real-time performance. It can offer adaptive compensation in time for model inverse errors caused by the changes of flight conditions and achieve accurate commands tracking. Stronger robustness has been demonstrated in the case of control surface damage and sensor output noise. Good three-axis uncoupled performance has also been shown.

NEW TECHNIQUES TO CONQUER THE IMAGE RESOLUTION ENHANCEMENT PROBLEM

This paper presents some new techniques for high resolution (HR) image processing and compares between them. The paper focuses on two main topics, image interpolation and image super- resolution. By image interpolation, we mean extracting an HR image from a single Degraded low resolution (LR) image. Polynomial based image interpolation is reviewed. Some new techniques for adaptive image interpolation and inverse image interpolation are presented. The other topic treated in this paper is image super-resolution. By image super resolution, we mean extracting a single HR image either from multiple observations or multiple frames. The paper focuses on the problem of image super resolution using wavelet fusion and presents several super resolution reconstruction algorithms based on the idea of wavelet fusion.

適応的画像方向反転を利用したＨ．２６４／ＡＶＣ拡張符号化方式

We have developed a new video coding method called adaptive picture direction inversion coding (APDIC) that improves coding efficiency by utilizing the dependency of the spatial direction of images in intra/inter coding. This method involves inverting the direction of input pictures horizontally and/or vertically, and then selecting the best pattern by using a rate-distortion optimization method. Decoders can identify the selected inverting pattern by using an invert flag in the bitstream so that they can decode the sequence in the right position. We implemented APDIC into a H.264/AVC based video encoder. The experimental results show that the bitrate obtained using this method is reduced by up to 4.3% for natural image sequences and 7.6% for the most typical artificial images.