Simultaneous measurements of velocity fields in thermal turbulence by USV and PIV

To test the validity of the ultrasonic velocimetry (USV) in thermal turbulence, we performed an experiment in water thermal turbulence. In this experiment, the velocity field was simultaneously measured by USV and particle image velocimetry (PIV), and then the measured velocity profiles, $w_{\mathrm{USV}}(t,z)$ and $w_{\mathrm{PIV}}(t,z)$, were compared. Due to equipment limitations, the measured velocity range was narrow $(\left|w\right|\lesssim 8\mathrm{mm}/s)$ compared to the measurable range of USV (±91.3 mm/s), which made the test a severe one. Nevertheless, it was found that the correlation coefficient $C_{\mathrm{corr}}$ between $w_{\mathrm{USV}}(t,z)$ and $w_{\mathrm{PIV}}(t,z)$ exceeds 0.9 and that $C_{\mathrm{corr}}$ increases as $w$ increases. The results of this test show that USV method outputs data agreeing with PIV data except when the fluid velocity is so small that the digitization unit of USV ($\Delta u=0.72\mathrm{mm}/s$ in this test) is elicited explicitly. This encourages us to believe that in thermal turbulence the USV is as reliable a technique as the PIV method.     

Finite-time H∞ control of uncertain networked control systems with randomly varying communication delays

This paper is concerned with the problem of finite-time $H_{\mathrm{\infty }}$ stability analysis of uncertain discrete-time Networked Control Systems (NCSs) with varying communication delays in a random fashion. Both measurement and actuation delays are modeled by two independent Bernoulli distributed white sequences. A dynamic output feedback controller is designed to realize finite time control for this class of NCSs with prescribed $H_{\mathrm{\infty }}$ performance level. An iterative algorithm is developed to compute the controller's parameters by means of the Cone Complementarity Linearization Method (CCLM). The validity and feasibility of the proposed stability criterion are confirmed via numerical simulation examples.     

Robust state estimation for a class of uncertain nonlinear systems: Comparison of two approaches

In this paper, two approaches for robust state estimation of a class of Lipschitz nonlinear systems are proposed. First, a novel Unknown Input Observer (UIO) is designed without observer matching condition satisfaction. Then, an $H_{\infty }$ observer for approximate disturbance decoupling is proposed. Sufficient conditions for the existence of both proposed observers are derived based on a Lyapunov function. The achieved conditions are formulated in terms of a set of linear matrix inequalities (LMIs) and optimal gain matrices are obtained. The minimum values of the disturbance attenuation levels for both methods are obtained through solving optimization problems. Finally, the proposed approaches are compared by simulation studies of an automated highway system.