1,450 research outputs found
Self-Evaluation Applied Mathematics 2003-2008 University of Twente
This report contains the self-study for the research assessment of the Department of Applied Mathematics (AM) of the Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) at the University of Twente (UT). The report provides the information for the Research Assessment Committee for Applied Mathematics, dealing with mathematical sciences at the three universities of technology in the Netherlands. It describes the state of affairs pertaining to the period 1 January 2003 to 31 December 2008
Influence of stochastic estimation on the control of subsonic cavity flow – A preliminary study
This work aims at understanding how the different elements involved in the feedback
loop influence the overall control performance of a subsonic cavity flow based on reducedorder
modeling. To this aim we compare preliminary and limited sets of experimental
results obtained by modifying some relevant characteristics of the loop. Our results support
the findings in the literature that use of quadratic stochastic estimation is preferable to the
linear one for real-time update of the model parameters. They also seem to indicate the
merit of using more than one time sample of the pressure for performing the real-time
update of the model through stochastic estimation. The effect of using two different sets of
pressure signals for the stochastic estimation also corroborates previous findings indicating
the need for optimizing the number and the placement of the sensors used in the feedback
control loop. Finally we observed that the characteristics of the actuator can alter
significantly the overall control effect by introducing in the feedback loop additional,
undesirable frequency components that are not modeled and hence controlled. A
compensator for the actuator is currently being designed that will alleviate this problem thus
enabling a clearer understanding of the overall control technique
Predictive Encoder and Buffer Control for Statistical Multiplexing of Multimedia Contents
International audienceStatistical multiplexing of video contents aims at transmitting several variable bit rate (VBR) encoded video streams over a band-limited channel. Rate-distortion (RD) models for the encoded streams are often used to control the video encoders. Buffering at the output of encoders is one of the several techniques used to smooth out the fluctuating bit rate of compressed video due to variations in the activity of video contents. In this paper, a statistical multiplexer is proposed where a closed-loop control of both video encoders and buffers is performed jointly. First, a predictive joint video encoder controller accounting for minimum quality, fairness, and smoothness constraints is considered. Second, all buffers are controlled simultaneously to regulate the buffering delays. This delay is adjusted according to a reference delay constraint. The main idea is to update the encoding rate for each video unit according to the average level of the buffers, to maximize the quality of each program and effectively use the available channel rate. Simulation results show that the proposed scheme yields a smooth and fair video quality among programs thanks to the predictive control. A similar buffering delay for all programs and an efficient use of the available channel rate are ensured thanks to the buffer management and to the predictive closed-loop control
Further development of feedback control of cavity flow using experimental based reduced order model
In our recent work we presented preliminary results for subsonic cavity flow control using a reduced-order model based feedback control derived from experimental measurements. The model was developed using the Proper Orthogonal Decomposition of PIV images in conjunction with the Galerkin projection of the Navier-Stokes equations onto the resulting spatial eigenfunctions. A linear-quadratic optimal controller was designed to reduce cavity flow resonance by controlling the time coefficient and tested in the experiments. The stochastic estimation method was used for real-time estimation of the corresponding time coefficients from 4 dynamic surface pressure measurements. The results obtained showed that the controller was capable of reducing the cavity flow resonance at the design Mach 0.3 flow, as well as at other flows with slightly different Mach number. In the present work we present several improvements made to the method. The reduced order model was derived from a larger set of PIV measurements and we used 6 sensors for the stochastic estimation of the instantaneous time coefficients. The reduced order model so obtained shows a better convergence of the time coefficients. This combined with the 6-sensor estimation improves the control performance while using a scaling factor closer to the theoretically expected value. The controller also performed better in off design flow conditions
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