Search results for "nonlinear"
showing 10 items of 3684 documents
Observation and identification tools for non-linear systems: application to a fluid catalytic cracker
2005
In this paper we recall general methodologies we developed for observation and identification in non-linear systems theory, and we show how they can be applied to real practical problems. In a previous paper, we introduced a filter which is intermediate between the extended Kalman filter in its standard version and its high-gain version, and we applied it to certain observation problems. But we were missing some important cases. Here, we show how to treat these cases. We also apply the same technique in the context of our identifiability theory. As non-academic illustrations, we treat a problem of observation and a problem of identification, for a fluid catalytic cracker (FCC). This FCC uni…
Fiber laser mode locked through an evolutionary algorithm
2015
Mode locking of fiber lasers generally involves adjusting several control parameters, in connection with a wide range of accessible short-pulse dynamics. In this Letter, we experimentally demonstrate the ability of an evolutionary algorithm to prescribe a set of cavity parameters entailing specific self-starting mode locking. The prescribed parameters are applied to electrically driven polarization controllers, thus shaping the effective nonlinear transfer function at play within the fiber cavity. According to the specifications of the objective function used for the optimization procedure, various short-pulse regimes are obtained. Our versatile method represents an effective novel avenue f…
Finite-Difference Time-Domain Simulation of Towers Cascade Under Lightning Surge Conditions
2015
In this paper, the simulation of towers cascade under lightning surge conditions is presented. Finite-difference time-domain method is used to solve both the Maxwell's and telegraph equations. Maxwell's equations and the time-domain resistivity model of Darveniza are used to simulate the nonlinear behavior of the grounding system. Telegraph equations are used to describe the propagation in the overhead lines. Multiple ionizations, on different grounding electrodes belonging to various towers, can be implemented simultaneously, without making assumptions on the shape of the ionized areas.
A nonlinear dynamical approach to the path correction of multi-steering articulated vehicles
2020
When designing articulated tractor-trailer systems, engineers should take care to contrast some undesired phenomena associated with the lateral dynamics: the path off-tracking, namely the trajector...
Development and validation of a nonlinear dynamic impact model for a notch impact
2015
Finite element simulations are being more and more applied when studying the crash-worthiness of vehicles during impact. This paper deals with setting up such a simulation and discusses several ways to simplify and verify a simulated crash. For this purpose, a notch impact-testing machine will be released from a certain angle and crash into a model constructed with three different wall thicknesses. The plastic and elastic deformation is measured in the front of the model and is then used for validation of the simulation. In the end, the simulation was found to be in good agreement with the real crash data.
Simultaneous zonation and calibration of pipe network parameters
2003
A procedure for simultaneously zoning and calibrating pipe network parameters is proposed and applied to the determination of pipe resistance coefficients. The methodology is aimed at grouping the parameters of all the pipes into a small number of zone parameters, constrained to keep the difference between the computed and the measured water heads below a given tolerance. It is shown that, in the case of nonlooped networks, the methodology leads to a linear minimization problem where the objective function is a measure of the heterogeneity of the estimated parameters. In the case of looped networks an iterative procedure, where the linear problem is coupled with a nonlinear problem having a…
Stability analysis of rotor whirl under nonlinear internal friction by a general averaging approach
2016
The two main sources of internal friction in a rotor-shaft system are the shaft structural hysteresis and the possible shrink-fit release of the assembly. The internal friction tends to destabilize the over-critical rotor running, but a remedy against this effect may be provided by a proper combination of some external damping in the supports and an anisotropic arrangement of the support stiffness, or at most by the support damping alone, depending on the system geometry. The present analysis reported here considers a general asymmetric rotor-shaft system, where the rotor is perfectly rigid and is constrained by viscous–flexible supports having different stiffnesses on two orthogonal plane…
EEMD based analysis of vehicle crash responses
2015
The vehicle crash is a complex process with nonlinear large deformation of structures. The analysis of the crash process is one of the challenges for all vehicle safety researchers. In this paper, the Ensemble Empirical Mode Decomposition (EEMD) method is applied in the analysis of crash responses in order to achieve some meaningful results. With the help of EEMD, the crash responses are decomposed into a trend signal and some high frequency fluctuations. By studying the load path of vehicle design, each component is corresponding to the structure of vehicle body. Consequently, some parameters of vehicle crash model can be identified. A frontal crash of Toyota Yaris is employed for demonstr…
A Novel Approach to the Characterization and Modelig of Microwave Transistor Packages
1994
A novel approach to the characterization and modeling of microwave transistor packages through dedicated VNA measurements is presented. By combining a multi-step partitioning method with the use of purposely realized - but technologically simple - "package style" test devices, the proposed technique permits to derive in a systematic manner an equivalent circuit for both the transistor package and the test-fixture mount employed for the characterization. Since it does not rely on the indirect, optimization-based, conventional extraction methods of the literature, nor on a simplified circuit structure for the overall parasitic fourport embedding the active device, it is able to provide a high…
Semiactive vibration control of nonlinear structures through adaptive backstepping techniques withH∞performance
2011
This article presents a new approach to the vibration mitigation problem in structures subject to seismic motions. These kinds of structures are characterised by the uncertainties of the parameters that describe their dynamics, such as stiffness and damping coefficients. Moreover, the dampers used to mitigate the vibrations caused by earthquakes are usually nonlinear devices with frictional or hysteretic dynamics. We propose an adaptive backstepping controller to account for the uncertainties and the nonlinearities. The controller is formulated in such a way that it satisfies an H∞ performance. It is designed for a 10-storey building whose base is isolated with a frictional damper (passive …