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Yordanova, Snejana T.
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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 online autotuning 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 neurofuzzy 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 twotank and an airconditioning systems, decreasing overshoot, settling time, control effort and coupling compared to classical FLC and linear control systems.
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By
Kern, M.; Horn, W.; Hiller, S.J.; Staudacher, S.
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2 Citations
Within the European research project NEWAC (New Aero Engine Core Concepts), a multistage highpressure 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, rematching 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 offdesign 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 multistage 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.
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By
Shabgard, Mohammadreza; Seyedzavvar, Mirsadegh; Abbasi, Hossein
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2 Citations
Electro discharge process has been introduced as an innovative method in production of nanosized particles in recent years. This research aimed to produce graphite nanofluid by submerged electro discharge process and evaluate the features of synthesized nanofluid, including particle size, thermal conductivity, and stability of suspension. The effects of pulse current, pulse ontime, base fluid composition, and temperature of base fluid during discharge process on the size and agglomeration of synthesized nanoparticles have been investigated. For the thermal conductivity measurement of nanofluids, a modified device based on transient hot wire technique was developed. According to metallurgical observations, the original structure of synthesized graphite nanoparticles was hexagonal and the shape of suspended particles was globular with uniform size distribution below 50 nm. Nevertheless, a low pulse ontime is strongly recommended for production of nanofluids with smaller size of particles and aggregations, along with higher stability of suspensions. The results revealed considerable enhancement in the thermal conductivity of nanofluids up to 73 % at medium temperature of 40 °C. Furthermore, the application of 1 vol% of gum acacia as surfactant provided significant stability of suspension over a long period of time even without being subjected to the ultrasonic homogenization process.
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By
Zhang, Ruimin; Zhao, Junbo; Dong, Jingang
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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 singlerotor 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 longperiod and shortperiod mode goes more stable, and the same as the lateral helical mode, while the roll mode and Dutch roll mode go more unstable.
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By
Yuanping, Li; Siyu, Chen
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3 Citations
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.
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By
Bunimovich, Leonid; Webb, Benjamin
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The dynamics of most real networks are time delayed. These time delays are important as they can often have a destabilizing effect on the network’s dynamics. Here we introduce the notion of intrinsic stability, which is stronger than the standard notion of stability used in the study of network dynamics or more generally in the study of multidimensional systems. The difference between a stable and an intrinsically stable network is that an intrinsically stable network maintains its (intrinsic) stability as nondistributed timedelays are incorporated into or removed from the network. Importantly, determining whether a network is intrinsic stability is fairly easy for concrete systems. Therefore, one can analyze the stability of a timedelayed network by analyzing the stability of the much simpler undelayed version of the network. One can simplify this analysis even further by removing the network’s implicit timedelays, which further reduces the network to a lowerdimensional system which can be used to gain improved stability estimates of the original unreduced network. A network can also be expanded in ways that preserves its intrinsic stability, which suggests how a network with an evolving structure can maintain its stability as it grows. Thus, intrinsic stability is the property that ensures the stability not only of a network but also of its reductions, expansions, and its timedelayed variants. We illustrate these results and techniques on various examples of Cohen–Grossberg neural networks.
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By
Sikander, Afzal; Prasad, Rajendra
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21 Citations
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 higherorder 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 higherorder linear time invariant systems based on stability equation method and particle swarm optimization algorithm. Reducedorder model will definitely be stable if the original model is stable. The superiority of the proposed method is illustrated by numerical examples of singleinput, singleoutput systems and multipleinput and multipleoutput systems. The results are compared with wellknown methods available in the literature.
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By
Xiao, S. F.; Chen, B.
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Summary
The phenomenon of dynamic stiffening has drawn general interest in flexible multibody systems. In fact, approximately analytical, numerical and experimental research have proved that both dynamic stiffening and dynamic softening can occur in flexible multibody 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 multibody systems. Furthermore, the approximate vibration frequency, critical value and postbuckling equilibria of the translational beam with constant acceleration are obtained by employing the assumed modes method, which validates the theoretical results. TheL^{2} norm stability of the trivial equilibrium of the system with the external beam and theL^{∞} norm stability of the bending of the external beam are proved by employing the energymomentum method.
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By
Yu, Weiqin; Chen, Fangqi; Li, Na; Wang, Tianbo; Zhao, Shouwei
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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 twodegreeoffreedom 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.
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By
Bonnin, Michele
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2 Citations
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.
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