0

IN THIS ISSUE

Research Papers

J. Dyn. Sys., Meas., Control. 2013;136(2):021001-021001-12. doi:10.1115/1.4025672.

An in-line axial-piston swash-plate pump with pressure compensator is widely used for its fast speed of response and power economy. Although several simulation based design approaches exist to minimize issues like fluid-born noises, ample scope exists for more exhaustive design analysis. The most popular pressure compensator for a variable displacement pump with a spool valve actuating the control and bias cylinders has been taken up here. With an existing comprehensive flow dynamics model, an updated model for swiveling dynamics has been coupled. The dynamics also includes the force containment and friction effects on the swash plate. A design optimization has been accomplished for the pressure compensator. The target of the optimal design has been set as minimizing the transient oscillations of the swash plate, the compensator spool, pressures in the bias and control cylinders along with avoidance of both over-pressurization and cavitation in the bias cylinder. It has been found that the orifice diameters in the spring-side and at the metering port of the spool valve and in the backside of the bias cylinder have critical role in arriving at an optimum design. The study has led to a useful design procedure for a pressure compensated variable displacement pump.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021002-021002-10. doi:10.1115/1.4025607.

Pendulum models have been studied as benchmark problems for development of nonlinear control schemes, as well as reduced-order models for the dynamics analysis of gait, balance and fall for humanoid robots. We have earlier introduced the reaction mass pendulum (RMP), an extension of the traditional inverted pendulum models, which explicitly captures the variable rotational inertia and angular momentum of a human or humanoid. The RMP consists of an extensible “leg”, and a “body” with moving proof masses that gives rise to the variable rotational inertia. In this paper, we present a thorough analysis of the RMP, which is treated as a three-dimensional (3D) multibody system in its own right. We derive the complete kinematics and dynamics equations of the RMP system and obtain its equilibrium conditions. We show that the equilibria of this system consist of an unstable equilibrium manifold and a stable equilibrium manifold. Next, we present a nonlinear control scheme for the RMP, which is an underactuated system with three unactuated degrees of freedom (DOFs). This scheme asymptotically stabilizes this underactuated system at its unstable equilibrium manifold, with a vertically upright configuration for the “leg” of the RMP. The domain of convergence of this stabilization scheme is shown to be almost global in the state space of the RMP. Numerical simulation results verify this stability property of the control scheme and demonstrate its effectiveness in stabilizing the unstable equilibrium manifold.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021003-021003-14. doi:10.1115/1.4025596.

This paper develops a simple continuation method for the approximate solution of optimal control problems. The class of optimal control problems considered include (i) problems with bounded controls, (ii) problems with state variable inequality constraints (SVIC), and (iii) singular control problems. The method used here is based on transforming the state variable inequality constraints into equality constraints using nonnegative slack variables. The resultant equality constraints are satisfied approximately using a quadratic loss penalty function. Similarly, singular control problems are made nonsingular using a quadratic loss penalty function based on the control. The solution of the original problem is obtained by solving the transformed problem with a sequence of penalty weights that tends to zero. The penalty weight is treated as the continuation parameter. The paper shows that the transformed problem yields necessary conditions for a minimum that can be written as a boundary value problem involving index-1 differential–algebraic equations (BVP-DAE). The BVP-DAE includes the complementarity conditions associated with the inequality constraints. It is also shown that the necessary conditions for optimality of the original problem and the transformed problem differ by a term that depends linearly on the algebraic variables in the DAE. Numerical examples are presented to illustrate the efficacy of the proposed technique.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021004-021004-9. doi:10.1115/1.4025711.

An innovative approach is proposed for generating discrete-time models of a class of continuous-time, nonautonomous, and nonlinear systems. By continualizing a given discrete-time system, sufficient conditions are presented for it to be an exact model of a continuous-time system for any sampling periods. This condition can be solved exactly for linear and certain nonlinear systems, in which case exact discrete-time models can be found. A new model is proposed by approximately solving this condition, which can always be found as long as a Jacobian matrix of the nonlinear system exists. As an example of the proposed method, a van der Pol oscillator driven by a forcing sinusoidal function is discretized and simulated under various conditions, which show that the proposed model tends to retain such key features as limit cycles and space-filling oscillations even for large sampling periods, and out-performs the forward difference model, which is a well-known, widely-used, and on-line computable model.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021005-021005-11. doi:10.1115/1.4025796.

Traditionally, multimode input shaping controllers are tuned to systems' frequencies. This work suggests an alternative approach. A frequency-modulation (FM) input shaping technique is developed to tune the resonant frequencies of a system to a set of frequencies that can be eliminated by a single-mode primary input shaper. Most of the current input shaping techniques can be used as primary input shapers for the FM input shaping technique. Virtual feedback is used to modulate the closed-loop frequencies of a simulated double-pendulum model of an overhead crane to the point where the closed-loop second mode frequency becomes an odd-multiple of the closed-loop first mode frequency, which is the necessary condition for a satisfactory performance of most single-mode input shapers. The primary input shaper is based on the first mode frequency of the closed-loop system model. The input commands to the plant of the virtual feedback system are then used to drive the physical double-pendulum. Simulations results, using primary zero-vibration (ZV) and zero-vibration-derivative (ZVD) input shapers, are presented. The performance is validated experimentally on a scaled model of a double-pendulum overhead crane.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021006-021006-7. doi:10.1115/1.4025797.

This paper deals with the problem of joint state and parameter estimation based on a set adaptive observer design. The problem is formulated and solved for an LPV (linear parameter-varying) system. The resolution methodology avoids the exponential complexity obstruction usually encountered in the set-membership parameter estimation. A simulation example is presented to illustrate the efficiency of the proposed approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021007-021007-7. doi:10.1115/1.4025694.

Chatter is an undesirable dynamic phenomenon in machining processes, which causes cutting disturbance, overcut, quick tool wear, etc., and thus seriously impairs workpiece quality. To mitigate chatter, traditional methods called passive control focus on optimizing working spindle speeds and depths of cut. But they have inherent disadvantages in gaining highly efficient machining. On the contrary, the research in this paper is along the line of active control. Specifically, an adaptive algorithm is developed based on Fourier series analysis to deal with the so-called regenerative cutting force which causes chatter. As a result, chatter is remarkably mitigated. The performance improvement is illustrated by numerical simulation in terms of both stability lobes diagram (SLD) and surface location error (SLE).

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021008-021008-11. doi:10.1115/1.4025858.

Modern spark ignited (SI) internal combustion engines maintain their air-to-fuel ratio (AFR) at a desired level to maximize the three-way catalyst conversion efficiency and durability. However, maintaining the engine AFR during its transient operation is quite challenging due to rapid changes of driver demand or engine throttle. Conventional transient AFR control is based upon the inverse dynamics of the engine fueling dynamics and the measured mass air flow (MAF) rate to obtain the desired AFR of the gas mixture trapped in the cylinder. This paper develops a linear quadratic (LQ) tracking controller to regulate the transient AFR based upon a control-oriented model of the engine port fuel injection (PFI) wall wetting dynamics and the air intake dynamics from the measured airflow to the manifold pressure. The LQ tracking controller is designed to optimally track the desired AFR by minimizing the error between the trapped in-cylinder air mass and the product of the desired AFR and fuel mass over a given time interval. The performance of the optimal LQ tracking controller was compared with the conventional transient fueling control based on the inverse fueling dynamics through simulations and showed improvement over the baseline conventional inverse fueling dynamics controller. To validate the control strategy on an actual engine, a 0.4 l single cylinder direct-injection (DI) engine was used. The PFI wall wetting dynamics were simulated in the engine controller after the DI injector control signal. Engine load transition tests for the simulated PFI case were conducted on an engine dynamometer, and the results showed improvement over the baseline transient fueling controller based on the inverse fueling dynamics.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021009-021009-10. doi:10.1115/1.4025753.

This paper proposes a new adaptive filter structure containing two subfilters, a fault detection and isolation (FDI) filter, and a main-filter for redundant inertial measurement unit (RIMU)/global positioning system (GPS) integrated navigation system tolerant toward faults of inertial sensors. The purpose of subfilters is compensation of sensor level bias (SLB) of the RIMU during in-flight alignment for successful FDI processing. Also, that of the main-filter is providing of error compensated navigation solution based on the good FDI result. To achieve these purposes, two coordinate frames, sub-body frame (SBF) and master-body frame (MBF), are defined first. Then, two different error models for the RIMU are formulated in the SBF for sensor level compensation and in the MBF for module level compensation, respectively. Based on the formulated error models, an adaptive filter structure is designed. Some numerical simulations are performed to validate the performance of the proposed adaptive filter structure.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021010-021010-10. doi:10.1115/1.4025798.

A new automatic method to tune the parameters of high order linear controllers is presented. The autotuning is achieved by minimizing, without constraints, a cost function that is related to the open loop shaping problem. The effort demanded from the designer is similar to that required to tune a low order controller, such as proportional integral (PI) or proportional integral differential (PID). The capabilities of the new method are demonstrated on two examples.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021011-021011-10. doi:10.1115/1.4025801.

The goal of this paper is to clarify the robustness and performance constraints in the design of control systems based on disturbance observer (DOB). Although the bandwidth constraints of a DOB have long been very well-known by experiences and observations, they have not been formulated and clearly reported yet. In this regard, the Bode and Poisson integral formulas are utilized in the robustness analysis so that the bandwidth constraints of a DOB are derived analytically. In this paper, it is shown that the bandwidth of a DOB has upper and lower bounds to obtain a good robustness if the plant has nonminimum phase zero(s) and pole(s), respectively. Besides that the performance of a system can be improved by using a higher order disturbance observer (HODOB); however, the robustness may deteriorate, and the bandwidth constraints become more severe. New analysis and design methods, which provide good robustness and predefined performance criteria, are proposed for the DOB based robust control systems. The validity of the proposals is verified by simulation results.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021012-021012-12. doi:10.1115/1.4025693.

This paper develops feedback controllers for walking in 3D, on level ground, with energy efficiency as the performance objective. Assume The Robot Is A Sphere (ATRIAS) 2.1 is a new robot that has been designed for the study of 3D bipedal locomotion, with the aim of combining energy efficiency, speed, and robustness with respect to natural terrain variations in a single platform. The robot is highly underactuated, having 6 actuators and, in single support, 13 degrees of freedom. Its sagittal plane dynamics are designed to embody the spring loaded inverted pendulum (SLIP), which has been shown to provide a dynamic model of the body center of mass during steady running gaits of a wide diversity of terrestrial animals. A detailed dynamic model is used to optimize walking gaits with respect to the cost of mechanical transport (CMT), a dimensionless measure of energetic efficiency, for walking speeds ranging from 0.5 $(m/s)$ to 1.4 $(m/s)$. A feedback controller is designed that stabilizes the 3D walking gaits, despite the high degree of underactuation of the robot. The 3D results are illustrated in simulation. In experiments on a planarized (2D) version of the robot, the controller yielded stable walking.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021013-021013-9. doi:10.1115/1.4026013.

This paper is concerned with the asymptotic stability issue for a class of stochastic Takagi–Sugeno (TS) fuzzy systems with time-varying delays. Then, by utilizing a delay-fractioning method, the stochastic analysis theory combined with the matrix inequality technique, a new set of sufficient condition in terms of linear matrix inequalities is presented which ensures the asymptotic stability of the stochastic TS fuzzy systems with time-delays. The results obtained in this paper are delay-dependent in the sense that they depend on not only the lower bound but also the upper bound of the time-varying delay. Numerical examples are given to illustrate the effectiveness and less conservativeness of the obtained results.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021014-021014-7. doi:10.1115/1.4025751.

Management of a very large number of distributed energy resources, energy loads, and generators, is a hot research topic. Such energy demand management techniques enable appliances to control and defer their electricity consumption when price soars and can be used to cope with the unpredictability of the energy market or provide response when supply is strained by demand. We consider a multi-agent system comprising multiple energy loads, each with a dedicated controller. This paper introduces our latest research in self-organization of coordinated behavior of multiple agents. Energy resource agents (RAs) coordinate with each other to achieve a balance between the overall consumption by the multi-agent collective and the stress on the community. In order to reduce the overall communication load while permitting efficient coordinated responses, information exchange is through indirect communications between RAs and a broker agent (BA). This gives a decentralized coordination approach that does not rely on intensive computation by a central processor. The algorithm presented here can coordinate different types of loads by controlling their set-points. The coordination strategy is optimized by a genetic algorithm (GA) and a fast coordination convergence has been achieved.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021015-021015-11. doi:10.1115/1.4025914.

This paper presents a model of an electric variable valve timing (EVVT) system and its closed-loop control design with experimental validation. The studied EVVT uses a planetary gear system to control the engine cam timing. The main motivation of utilizing the EVVT system is its fast response time and the accurate timing control capability. This is critical for the combustion mode transition control between the spark ignition (SI) and homogeneous charge compression ignition (HCCI) combustion, where the engine cam timing needs to follow a desired trajectory to accurately control the engine charge and recompression process. A physics-based model was developed to study the characteristics of the EVVT system, and a control oriented EVVT model, with the same structure as the physics-based one, was obtained using closed-loop system identification. The closed-loop control strategies were developed to control the EVVT to follow a desired trajectory. Both simulation and bench test results are included.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021016-021016-14. doi:10.1115/1.4025815.

A high-speed path-following controller for long combination vehicles (LCVs) was designed and implemented on a test vehicle consisting of a rigid truck towing a dolly and a semitrailer. The vehicle was driven through a 3.5 m wide lane change maneuver at 80 km/h. The axles of the dolly and trailer were steered actively by electrically-controlled hydraulic actuators. Substantial performance benefits were recorded compared with the unsteered vehicle. For the best controller weightings, performance improvements relative to unsteered case were: lateral tracking error 75% reduction, rearward amplification (RA) of lateral acceleration 18% reduction, and RA of yaw rate 37% reduction. This represents a substantial improvement in stability margins. The system was found to work well in conjunction with the braking-based stability control system of the towing vehicle with no negative interaction effects being observed. In all cases, the stability control system and the steering system improved the yaw stability of the combination.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021017-021017-13. doi:10.1115/1.4025755.

In this paper, a new position domain synchronization control (PDSC) law is proposed for contour control of multi-DOF nonlinear robotic manipulators with the main goal of improving contour tracking performance. The robotic manipulator is treated as a master-slave motion system, where the position of the master motion is used as an independent reference via equidistant sampling, and the slave motions are described as functions of the master motion. To build this relationship, the dynamics of the original system is transformed from time domain to position domain. The new control introduces synchronization and coupled errors in the control law to further coordinate the master and slave motions. Stability analysis is performed based on the Lyapunov method for the proposed PDSC, and simulations are conducted to verify the effectiveness of the developed control system.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021018-021018-9. doi:10.1115/1.4025802.

In this paper, we present an adaptive estimation framework predicated on multiagent network identifiers with undirected and directed graph topologies. Specifically, the system state and plant parameters are identified online using N agents implementing adaptive observers with an interagent communication architecture. The adaptive observer architecture includes an additive term which involves a penalty on the mismatch between the state and parameter estimates. The proposed architecture is shown to guarantee state and parameter estimate consensus. Furthermore, the proposed adaptive identifier architecture provides a measure of agreement of the state and parameter estimates that is independent of the network topology and guarantees that the deviation from the mean estimate for both the state and parameter estimates converge to zero. Finally, an illustrative numerical example is provided to demonstrate the efficacy of the proposed approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):021019-021019-6. doi:10.1115/1.4025803.

This paper proposes a systematic procedure to address the limit cycle prediction of a Nonlinear Takagi–Sugeno–Kang (NTSK) fuzzy control system with adjustable parameters. NTSK fuzzy can be linearized by describing function method. The stability of the equivalent linearized system is then analyzed using the stability equations and the parameter plane method. After that the gain–phase margin (PM) tester has been added, then gain margin (GM) and phase margin for limit cycle are analyzed. Using NTSK fuzzy control system can help to have fewer rules. In order to analyze the stability with the same technique of stability analysis, the results of NTSK fuzzy control system will be compared with Dynamic fuzzy control system [1]. Computer simulations show differences between both systems.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(2):021020-021020-10. doi:10.1115/1.4025998.

This article describes a general framework to generate linearized models of satellites with large flexible appendages. The obtained model is parameterized according to the tilt of flexible appendages and can be used to validate an attitude control system over a complete revolution of the appendage. Uncertainties on the characteristic parameters of each substructure can be easily considered by the proposed generic and systematic multibody modeling technique, leading to a minimal linear fractional transformation (LFT) model. The uncertainty block has a direct link with the physical parameters avoiding nonphysical parametric configurations. This approach is illustrated to analyze the attitude control system of a spacecraft fitted with a tiltable flexible solar panel. A very simple root locus allows the stability of the closed-loop system to be characterized for a complete revolution of the solar panel.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(2):021021-021021-11. doi:10.1115/1.4025987.

This paper is concerned with the problem of robust reliable H control for a class of uncertain Takagi-Sugeno (TS) fuzzy systems with actuator failures and time-varying delay. The main objective is to design a state feedback reliable H controller such that, for all admissible uncertainties as well as actuator failure cases, the resulting closed-loop system is robustly asymptotically stable with a prescribed H performance level. Based on the Lyapunov-Krasovskii functional (LKF) method together with linear matrix inequality (LMI) technique, a delay dependent sufficient condition is established in terms of LMIs for the existence of robust reliable H controller. When these LMIs are feasible, a robust reliable H controller can be obtained. Finally, two numerical examples with simulation result are utilized to illustrate the applicability and effectiveness of our obtained result.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(2):021022-021022-12. doi:10.1115/1.4025813.

A novel pneumatic valve was constructed to improve the response of air-actuated brakes for heavy vehicles to demand pressures generated during electronically controlled braking by an order of magnitude. Investigations were made into the interactions between the magnetic, mechanical, and electrical subsystems of the valve with a view toward informing design optimization. The valve was modeled using a magnetic circuit approach. The quasi-static model included the influences of the permanent magnet, field-line fringing, saturation, and the coil. Mechanical forces outputted by the model matched physical measurements with an error smaller than 10%, and magnetic fluxes throughout the circuit were generally within 20% of those found from experiments based on Faraday's law of induction, Gaussmeter measurements, and FEA simulations. A magneto-mechanical simulation of the valve switching states was created using mechanical and electrical equations, and curve-fits to the outputs of the magnetic circuit model. The simulation produced time histories of the valve's armature position that matched experimental measurements and adequately predicted working pressures. The final model required an approximation to the influence of the coil based on experimental results. Consequently, further research is recommended into the influence of solenoid coils on fringing in magnetic circuits.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(2):021023-021023-11. doi:10.1115/1.4025985.

This article examines the observability of a modified loosely coupled global positioning system/inertial navigation system (GPS/INS) filter and analyzes the sideslip and attitude estimation capability of the filter. The modified filter is a loosely coupled integration which does not include a pitch rate gyro and which uses GPS course information as a measurement of heading when the vehicle is driving straight. Experimental tests are conducted which show that the modified filter has the same observability characteristics as a standard loosely coupled filter during turning events. The observability of a loosely coupled integration using only a four degree of freedom (DOF) inertial measurement unit (IMU) is also discussed and examined by experiment, as well as the sideslip and roll angle estimation performance. Finally, the error characteristics of the modified loosely coupled integration with the five DOF IMU when the filter is unobservable are studied. Monte Carlo simulations of long periods of straight driving with various sensor qualities are presented to show the worst case attitude errors when the filter is unobservable.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Dyn. Sys., Meas., Control. 2013;136(2):024501-024501-5. doi:10.1115/1.4025671.

A dynamic mirror actuator utilizing antagonistic piezoelectric stack actuators is presented for use in laser printers. Exhibiting hysteresis and other nonlinearities in open-loop operation, the dynamic mirror actuator (DMA) requires a control structure to achieve accurate mirror positioning. A linear DMA model is developed for extending operational bandwidth under closed-loop control, employing explicit piezoelectric stack actuator (PESA) charging dynamics and incorporating two modes for single input control of opposing PESA drives. Compared to constitutive models from literature, the proposed model displays a comparable fit with experimental frequency response data while retaining a lower model order. As further validation, simulated step response data are shown to agree with experimental data.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):024502-024502-5. doi:10.1115/1.4025861.

This brief paper investigates the control of a robotic bulldozing operation. Optimal blade position control laws were designed based on a hybrid dynamic model to maximize the predicted material removal rate of the bulldozing process. Experiments were conducted with a scaled-down robotic bulldozing system. The control laws were implemented with various tuning values. As a comparison, a rule-based blade control algorithm was also designed and implemented. The experimental results with the best optimal controller demonstrated a 33% increase in the average material removal rate compared to the rule-based controller.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):024503-024503-5. doi:10.1115/1.4025814.

The air content in hydraulic transmission fluids significantly reduces bulk modulus of the fluid and causes a drop in the stiffness and response of the hydraulic system. It is consequently very important to monitor the air content in hydraulic fluid for ensuring the hydraulic works in good condition. In this paper, a novel method is presented in which the sampled fluid flows slowly into a vacuum chamber and the pressure of separated air is measured. A model of pressure-time characteristics is established, with moisture content taken into account as well, since moisture is volatile in vacuum and its content in tributyl phosphate (TBP) based fluid is usually too high to be neglected. The model can be simplified, which turned out to be a nonlinear least square problem. Comparison between the measured and calculated value shows that the model matches well with the experimental data.

Topics: Pressure , Fluids , Vacuum , Water
Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2013;136(2):024504-024504-7. doi:10.1115/1.4025862.

An efficient nonprobabilistic robust reliability method for H robust controller design of parametric uncertain systems is presented by describing the uncertain parameters as interval variables. Design optimization of H robust controller is carried out by solving a robust reliability based optimization problem, by which the disturbance attenuation, control cost, and robust reliability can be taken into account simultaneously. By the method, a robust reliability measure of an uncertain control system satisfying required H robust performance can be obtained, and the robustness bounds of uncertain parameters such that the control cost of the system is guaranteed can be provided. The presented formulations are in the framework of linear matrix inequality and thus can be carried out conveniently. The presented method provides an essential basis for reasonable tradeoff between reliability and control cost in controller design of uncertain systems. Active control design of vehicle suspension is employed for illustrating the effectiveness and feasibility of the presented method.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(2):024505-024505-6. doi:10.1115/1.4025988.

This brief paper proposes a dynamic data-driven method for stability monitoring of rotorcraft systems, where the underlying concept is built upon the principles of symbolic dynamics. The stability monitoring algorithm involves wavelet-packet-based preprocessing to remove spurious disturbances and to improve the signal-to-noise ratio (SNR) of the sensor time series. A quantified measure, called Instability Measure, is constructed from the processed time series data to obtain an estimate of the relative instability of the dynamic modes of interest on the rotorcraft system. The efficacy of the proposed method has been established with numerical simulations where correlations between the instability measure and the damping parameter(s) of selected dynamic mode(s) of the rotor blade are established.

Commentary by Dr. Valentin Fuster