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Transient Behaviour (transient + behaviour)
Selected AbstractsInfluence of inertia, topography and gravity on transient axisymmetric thin-film flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2004Roger E. Khayat Abstract This study examines theoretically the development of early transients for axisymmetric flow of a thin film over a stationary cylindrical substrate of arbitrary shape. The fluid is assumed to emerge from an annular tube as it is driven by a pressure gradient maintained inside the annulus, and/or by gravity in the axial direction. The interplay between inertia, annulus aspect ratio, substrate topography and gravity is particularly emphasized. Initial conditions are found to have a drastic effect on the ensuing flow. The flow is governed by the thin-film equations of the ,boundary-layer' type, which are solved by expanding the flow field in terms of orthonormal modes in the radial direction. The formulation is validated upon comparison with the similarity solution of Watson (J. Fluid Mech 1964; 20:481) leading to an excellent agreement when only 2,3 modes are included. The wave and flow structure are examined for high and low inertia. It is found that low-inertia fluids tend to accumulate near the annulus exit, exhibiting a standing wave that grows with time. This behaviour clearly illustrates the difficulty faced with coating high-viscosity fluids. The annulus aspect is found to be influential only when inertia is significant; there is less flow resistance for a film over a cylinder of smaller diameter. For high inertia, the free surface evolves similarly to two-dimensional flow. The substrate topography is found to have a significant effect on transient behaviour, but this effect depends strongly on inertia. It is observed that the flow of a high-inertia fluid over a step-down exhibits the formation of a secondary wave that moves upstream of the primary wave. Gravity is found to help the film (coating) flow by halting or prohibiting the wave growth. The initial film profile and velocity distribution dictate whether the fluid will flow downstream or accumulate near the annulus exit. Copyright © 2004 John Wiley & Sons, Ltd. [source] A smooth switching adaptive controller for linearizable systems with improved transient performanceINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 9 2006Jeng Tze Huang Abstract The certainty equivalent control has achieved asymptotic tracking stability of linearizable systems in the presence of parametric uncertainty. However, two major drawbacks remain to be tackled, namely, the risk of running into singularity for the calculated control input and the poor transient behaviour arising frequently in a general adaptive system. For the first problem, a high gain control is activated in place of the certainty equivalent control until the risk is bypassed. Among others, it requires less control effort by taking advantages of the bounds for the input vector field. Moreover, the switching mechanism is smooth and hence avoids possible chattering behaviour. Next, to solve the second problem, a new type of update algorithm guaranteeing the exponential stability of the overall closed-loop system, on a weaker persistent excitation (PE) condition, is proposed. In particular, it requires no filtering of the regressor and hence is easier to implement. Simulation results demonstrating the validity of the proposed design are given in the final. Copyright © 2006 John Wiley & Sons, Ltd. [source] Composite adaptive and input observer-based approaches to the cylinder flow estimation in spark ignition automotive enginesINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 2 2004A. Stotsky Abstract The performance of air charge estimation algorithms in spark ignition automotive engines can be enhanced using advanced estimation techniques available in the controls literature. This paper illustrates two approaches of this kind that can improve the cylinder flow estimation for gasoline engines without external exhaust gas recirculation (EGR). The first approach is based on an input observer, while the second approach relies on an adaptive estimator. Assuming that the cylinder flow is nominally estimated via a speed-density calculation, and that the uncertainty is additive to the volumetric efficiency, the straightforward application of an input observer provides an easy to implement algorithm that corrects the nominal air flow estimate. The experimental results that we report in the paper point to a sufficiently good transient behaviour of the estimator. The signal quality may deteriorate, however, for extremely fast transients. This motivates the development of an adaptive estimator that relies mostly on the feedforward speed-density calculation during transients, while during engine operation close to steady-state conditions, it relies mostly on the adaptation. In our derivation of the adaptive estimator, the uncertainty is modelled as an unknown parameter multiplying the intake manifold temperature. We use the tracking error between the measured and modelled intake manifold pressure together with an appropriately defined prediction error estimate to develop an adaptation algorithm with improved identifiability and convergence rate. A robustness enhancement, via a ,-modification with the ,-factor depending on the prediction error estimate, ensures that in transients the parameter estimate converges to a pre-determined a priori value. In close to steady-state conditions, the ,-modification is rendered inactive and the evolution of the parameter estimate is determined by both tracking error and prediction error estimate. Further enhancements are made by incorporating a functional dependence of the a priori value on the engine operating conditions such as the intake manifold pressure. The coefficients of this function can be learned during engine operation from the values to which the parameter estimate converges in close to steady-state conditions. This feedforward learning functionality improves transient estimation accuracy and reduces the convergence time of the parameter estimate. Copyright © 2004 John Wiley & Sons, Ltd. [source] Hyperreal transients in transfinite RLC networksINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 6 2001A. H. Zemanian Abstract Up to the present time, there have been no transient analyses of RLC transfinite networks. Standard analyses of transfinite networks have been restricted to purely resistive ones. In this paper, it is shown how non-standard analysis can be used to examine the transient behaviour of transfinite networks having lumped resistors, inductors, and capacitors. To do so, the time line is expanded into the hyperreal time line, and the transients obtained take on hyperreal values. It is also shown how the diffusion of signals on artificial RC cables and the propagation of waves on artificial RLC transmission lines can ,pass through infinity' and penetrate transfinite extensions of those cables and lines. Less precisely but more suggestively, we can say that diffusions and waves can reach,with appreciable values,nodes that are transfinitely far away from their starting points, but that it will take infinitely long times in order to get there. Copyright © 2001 John Wiley & Sons, Ltd. [source] The effects of correlated arrivals at a server with credit-based traffic policingINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2001K. Mitchell Abstract In this paper we observe the steady state and transient behaviour of correlated cell arrivals into a server with credit-based traffic policing. We derive expressions for the lag- k correlations of the departure process from the traffic policing mechanism, and observe how dependencies in the departure stream affect cell loss at the server. The results illustrate the impact of the second-order statistics and the higher moments of the cell arrival processes on the traffic policing mechanism performance. Copyright © 2001 John Wiley & Sons, Ltd. [source] The evaluation of small cogeneration for residential heatingINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2002Kris R. Voorspools Abstract The decision whether or not to install small cogeneration for residential purposes mainly depends on individual economic considerations, combined with ecological awareness. Since in most cases, the economic balance is still unfavourable, government grants are considered in order to bridge this economic barrier. It is however still unclear how these grants are best spent to obtain an optimal environmental benefit. In the case of cogeneration, mainly static and simplified methods are used, completely neglecting the dynamic interaction between the cogeneration systems and the central power system and the dynamic response of the cogeneration units themselves. In this paper, these issues are discussed in two parts. The first part clarifies how an actual cogeneration unit, if necessary in combination with a back-up boiler and heat storage, will respond to a certain demand. For this purpose, experiments were performed to establish the transient and stationary behaviour of the system. It is shown that the transient heating of the cogeneration engine is rather slow (e.g. half an hour after cold start, the engine only produced 65% of the heat it would have in stationary regime) where the electric transient behaviour is negligible. In the second part of the paper, dynamic simulations are performed to quantify the impact (primary energy saving and reduction in greenhouse-gas emissions) of the massive installation of cogeneration for residential heating. Two important parameters are isolated. First, the interaction with the expansion of the central power system is very important. If the installation of cogeneration prevents the commissioning of new power plants, the potential energy saving and (especially) emission reduction are reduced. The second parameter is the annual use of the cogeneration units. Here, the potential energy saving and emission reduction increase with increasing annual use. Copyright © 2002 John Wiley & Sons, Ltd. [source] A novel approach to extract accurate design parameters of PiN diodeINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 6 2007Tarek Ben Salah Abstract Accurate modelling of PiN diode transient behaviour is necessary to extract design parameters which are not documented in datasheets. To meet this requirement, this paper introduces a novel approach giving the possibility to identify accurate parameters of a given device. The used technique is based only on two stages. First, the design parameters are initialized and optimized. Second, they are refined by minimizing the cost function which depends on the transient switching parameters (IRM, VRM and trr). With a simple and CPU time-saving approach this technique leads to extract design parameters without necessarily knowing the exact technological architecture of the PiN diode. Moreover, in order to validate the proposed approach and the parameter extraction procedure three commercial diodes are tested. A good agreement between experimental and simulation data is obtained. Copyright © 2007 John Wiley & Sons, Ltd. [source] Development and simulation studies of an unsteady state biofilter model for the treatment of cyclic air emissions of an ,-pinene gas streamJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2005Christina Dirk-Faitakis Abstract This paper describes the development and simulation of an unsteady state biofilter model used to predict dynamic behaviour of cyclically-operated biofilters and compares it with experimental results obtained from three, parallel, bench-scale biofilters treating both periodically fluctuating concentrations and constant concentrations of an ,-pinene-laden gas stream. The dynamic model, using kinetic parameters estimated from the constant concentration biofilter, was able to predict the performance of cyclic biofilters operating at short cycle periods (ie, in the order of minutes and hours). Steady state kinetic data from a constant concentration biofilter can be used to predict unsteady state biofilter operation. At a 24 h cycle period, the dynamic model compared well with experimental results. For long cycle periods (ie, hours and days), removal efficiency decreased after periods of non-loading: the longer the period of non-loading, the poorer the biofilter's performance at the re-commencement of pollutant loading. At longer time scales the model did not effectively predict transient behaviour, as adsorption and changes in kinetic parameters were not accounted for. Modelling results showed that similar biofiltration performance for the cyclic and constant concentration biofiltration of ,-pinene is expected for biofilters operating solely in the first order kinetics regime. Poorer performance for cyclic biofilters following Monod kinetics spanning the entire kinetics range is expected as the cycle amplitude increases. The most important parameters affecting the performance of a cyclically-operated biofilter with short cycle periods are: amplitude of cyclic fluctuations, Cg, max/Cg, relative value of the half-saturation constant in the Monod expression, Ks, and effective diffusivity of ,-pinene in the biofilm, De. Copyright © 2005 Society of Chemical Industry [source] Stable high-order finite-difference methods based on non-uniform grid point distributionsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2008Miguel Hermanns Abstract It is well known that high-order finite-difference methods may become unstable due to the presence of boundaries and the imposition of boundary conditions. For uniform grids, Gustafsson, Kreiss, and Sundström theory and the summation-by-parts method provide sufficient conditions for stability. For non-uniform grids, clustering of nodes close to the boundaries improves the stability of the resulting finite-difference operator. Several heuristic explanations exist for the goodness of the clustering, and attempts have been made to link it to the Runge phenomenon present in polynomial interpolations of high degree. By following the philosophy behind the Chebyshev polynomials, a non-uniform grid for piecewise polynomial interpolations of degree q,N is introduced in this paper, where N + 1 is the total number of grid nodes. It is shown that when q=N, this polynomial interpolation coincides with the Chebyshev interpolation, and the resulting finite-difference schemes are equivalent to Chebyshev collocation methods. Finally, test cases are run showing how stability and correct transient behaviours are achieved for any degree q
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