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## Design of Fuzzy Supervisor-Based Adaptive Process Control Systems

### New Approaches in Intelligent Control (2016-01-01) 107: 1-42 , January 01, 2016

The modern industrial processes are difficult to model and control by classical means for their nonlinearity, inertia, model uncertainty and varying parameters. The adaptive fuzzy logic controllers (AFLCs) improve the system performance but are computationally hard to design and embed in programmable logic controllers (PLCs) for wider industrial applications. In this chapter a design approach for simple AFLCs is suggested, based on main controllers—linear, FLC or parallel distributed compensation (PDC), and fuzzy logic supervisors (FLSs) for on-line auto-tuning of their gains or scaling factors. The effect is a continuous adaptation of the control surface in response to plant changes. Approximation of the designed AFLC to a PDC equivalent on the basis of neuro-fuzzy and optimization techniques enables the stability analysis of the AFLC system using the indirect Lyapunov method and also its PLC implementation. The AFLC is applied for the real time control of the processes in a chemical reactor, a dryer, a two-tank and an air-conditioning systems, decreasing overshoot, settling time, control effort and coupling compared to classical FLC and linear control systems.

## Effects of tip injection on the performance of a multi-stage high-pressure compressor

### CEAS Aeronautical Journal (2011-12-01) 2: 99-110 , December 01, 2011

Within the European research project NEWAC (New Aero Engine Core Concepts), a multi-stage high-pressure compressor equipped with a tip injection system upstream of the first rotor was tested in three different configurations at MTU Aero Engines. One aim of the test campaign was to investigate the effects of tip injection on the compressor performance. This paper gives an overview of the influences of tip injection on the characteristics of the first three stages. Following an outline of the motivation for tip injection, it is assessed to what extent the surge behavior of the tested compressor is affected by tip injection. The assessment is made by evaluating the surge line extension due to tip injection. If the injection system is applied in an engine, re-matching of its turbo components will occur. Due to this fact, the focus is placed on evaluating the benefits afforded by the use of the injection system in an aircraft engine. The test results are integrated in an existing engine model for a next generation geared turbofan engine and off-design simulations are performed. In this way, changes in surge margin due to tip injection are evaluated. In addition to mere tip injection tests, measurement data of test cases is analyzed, in which mass flow recirculation was simulated. The evaluation of these tests is discussed analogously to the test cases of tip injection. It is found that tip injection prevents the generation of stall cells almost completely. The analyses also show that the stage matching of the multi-stage compressor is changed by tip injection at the front stage. According to the synthesis calculations carried out, recirculation increased the surge margin at part speed by up to about 35% relative to the reference compressor without tip injection.

## Simulation of Flight Dynamics for Helicopter Icing

### Proceedings of the 14th International Conference on Man-Machine-Environment System Engineering (2015-01-01) 318: 341-348 , January 01, 2015

This allows unregistered users to read the abstract as a teaser for the complete chapter. The formulas for calculating the variation of aerodynamic coefficient of iced blade airfoil were introduced according to rotor icing test data from NASA and the formulas for aerodynamic force and moment of rotor icing were deduced. Further, the model of flight dynamics for helicopter icing was built. Icing effect on trim characteristics and stability of certain single-rotor helicopter in hover and forward speed was studied. The results show that whether in hover or forward flight, when the helicopter iced, the amount of the collective control, the longitudinal control, and the lateral control of the rotor, the tail rotor collective control as well as the roll angle increases, while the pitch angle decreases; the longitudinal long-period and short-period mode goes more stable, and the same as the lateral helical mode, while the roll mode and Dutch roll mode go more unstable.

## Periodic solution and bifurcation of a suspension vibration system by incremental harmonic balance and continuation method

### Nonlinear Dynamics (2016-01-01) 83: 941-950 , January 01, 2016

A compressed air generator hang under vehicle is simplified as a suspension mass connected to a vertical spring and two horizontal springs. It is configured generally as a geometrical negative stiffness to reduce dynamic stiffness. The periodic motion, chaotic motion and bifurcation of the compressed air generator model are investigated using the incremental harmonic balance method in combination with arc length continuation technique. The stability and bifurcation route are also distinguished with Floquet theory. The system exhibits a period doubling bifurcation route to chaos in different regions of excitation frequency. The stiffness ratio of the vertical spring and the horizontal spring has a significant influence on the dynamic response. When the vertical stiffness is close to the stiffness at horizontal direction, resonance occurs with the emergence of the chaotic motion. The dynamic response of the vibration system can be improved by reducing the stiffness in the horizontal direction to increase the stiffness ratio.

## Soft Computing Approach for Model Order Reduction of Linear Time Invariant Systems

### Circuits, Systems, and Signal Processing (2015-11-01) 34: 3471-3487 , November 01, 2015

Most of the physical systems can be represented by mathematical models. The mathematical procedure of system modeling often leads to a comprehensive description of a process in the form of higher-order differential equations which are difficult to use either for analysis or for controller synthesis. It is, therefore, useful and sometimes necessary to find the possibility of some equations of the same type but of lower order that may be considered to adequately reflect almost all essential characteristics of the system under consideration. This paper proposes a new method for order reduction of higher-order linear time invariant systems based on stability equation method and particle swarm optimization algorithm. Reduced-order model will definitely be stable if the original model is stable. The superiority of the proposed method is illustrated by numerical examples of single-input, single-output systems and multiple-input and multiple-output systems. The results are compared with well-known methods available in the literature.

## Dynamic characteristic and stability analysis of a beam mounted on a moving rigid body

### Archive of Applied Mechanics (2005-03-01) 74: 415-426 , March 01, 2005

### Summary

The phenomenon of dynamic stiffening has drawn general interest in flexible multi-body systems. In fact, approximately analytical, numerical and experimental research have proved that both dynamic stiffening and dynamic softening can occur in flexible multi-body systems. In this paper, the nonlinear dynamic model of a beam mounted on both the exterior and the interior of a rigid ring is established by adopting the general Hamilton's variational principle. The dynamic characteristics of the system are studied using a theoretical method when the rigid ring translates with constant acceleration or rotates steadily. The research proves theoretically that both dynamic stiffening and dynamic softening can occur in both the translation as well as the rotation state of multi-body systems. Furthermore, the approximate vibration frequency, critical value and post-buckling equilibria of the translational beam with constant acceleration are obtained by employing the assumed modes method, which validates the theoretical results. The*L*^{2} norm stability of the trivial equilibrium of the system with the external beam and the*L*^{∞} norm stability of the bending of the external beam are proved by employing the energy-momentum method.

## Stability and bifurcation dynamics for a nonlinear controlled system subjected to parametric excitation

### Archive of Applied Mechanics (2017-03-01) 87: 479-487 , March 01, 2017

Through both analytical and numerical approaches, stability and bifurcation dynamics are studied for a nonlinear controlled system subjected to parametric excitation. The controlled system is a typical case of a two-degree-of-freedom system composed of a parametrically excited pendulum and its driving device. Three types of critical points for the modulation equations are considered near the principle resonance and internal resonance, which are characterized by a double zero and two negative eigenvalues, a double zero and a pair of purely imaginary eigenvalues, and two pairs of purely imaginary eigenvalues, respectively. With the aid of normal form theory, the stability regions for the initial equilibrium solutions and the critical bifurcation curves are obtained analytically, which exhibit some new dynamical behaviors. A time integration scheme is used to find the numerical solutions for these bifurcations cases, which confirm these analytical predictions.

## Existence, number, and stability of limit cycles in weakly dissipative, strongly nonlinear oscillators

### Nonlinear Dynamics (2010-10-01) 62: 321-332 , October 01, 2010

Oscillators control many functions of electronic devices, but are subject to uncontrollable perturbations induced by the environment. As a consequence, the influence of perturbations on oscillators is a question of both theoretical and practical importance. In this paper, a method based on Abelian integrals is applied to determine the emergence of limit cycles from centers, in strongly nonlinear oscillators subject to weak dissipative perturbations. It is shown how Abelian integrals can be used to determine which terms of the perturbation are influent. An upper bound to the number of limit cycles is given as a function of the degree of a polynomial perturbation, and the stability of the emerging limit cycles is discussed. Formulas to determine numerically the exact number of limit cycles, their stability, shape and position are given.

## Analysis of the effects of nonlinear viscous damping on vibration isolator

### Nonlinear Dynamics (2015-03-01) 79: 2325-2332 , March 01, 2015

In this paper, vibration isolator of single degree of freedom systems having a nonlinear viscous damping is studied under force excitation. Stability of the steady state periodic response has been discussed. The influence of damping coefficients on the force transmissibility and displacement transmissibility is investigated. The relationship between amplitude and frequency is derived by using the averaging method. Results reveal that the performance of the nonlinear isolator has some beneficial effects compared with linear isolator in a certain range. Numerical simulations are presented to illustrate the results.

## Partially unstable attractors in networks of forced integrate-and-fire oscillators

### Nonlinear Dynamics (2017-04-03): 1-14 , April 03, 2017

The asymptotic attractors of a nonlinear dynamical system play a key role in the long-term physically observable behaviors of the system. The study of attractors and the search for distinct types of attractor have been a central task in nonlinear dynamics. In smooth dynamical systems, an attractor is often enclosed completely in its basin of attraction with a finite distance from the basin boundary. Recent works have uncovered that, in neuronal networks, unstable attractors with a remote basin can arise, where almost every point on the attractor is locally transversely repelling. Herewith we report our discovery of a class of attractors: partially unstable attractors, in pulse-coupled integrate-and-fire networks subject to a periodic forcing. The defining feature of such an attractor is that it can simultaneously possess locally stable and unstable sets, both of positive measure. Exploiting the structure of the key dynamical events in the network, we develop a symbolic analysis that can fully explain the emergence of the partially unstable attractors. To our knowledge, such exotic attractors have not been reported previously, and we expect them to arise commonly in biological networks whose dynamics are governed by pulse (or spike) generation.