A Model-Based Predictive Controller of the Level of Steel in the Mold with Disturbances Using a Repetitive Structure

Keeping the level of steel in the mold of the continuous casting process constant is fundamental for the quality of the steel produced and, consequently, its commercial value. It is challenging, considering the several disturbances that cause undesired variations in the mold level. The aim of this paper is to apply a repetitive structure composed of two controllers, a generalized predictive controller (GPC) and a repetitive GPC (R-GPC) with constraints to mitigate the bulging and clogging/unclogging disturbances and the casting speed variation in the mold level of the process. The R-GPC controller has the same characteristics as the GPC, such as performance, robustness to disturbances, and insertion of constraints, and its advantage is the elimination of periodic disturbances. The repetitive structure will be implemented with a robustness filter and tuned by a genetic algorithm (GA). The controller tests are performed by simulations of a nonlinear mathematical model of the mold level, validated using real data from the steel industry. The proposed controller reduces the bulging disturbance amplitude by 98.5% and at 25% of the frequency of reversions in the valve. Consequently, the proposed controller allows an increase in the valve life span, a reduction in maintenance costs, and quality improvement in the steel slab.

Binary Repetitive Model Predictive Active Flow Control Applied to an Annular Compressor Stator Cascade with Periodic Disturbances

Novel pressure gain combustion concepts invoke periodic flow disturbances in a gas turbine's last compressor stator row. This contribution presents studies of mitigation efforts on the effects of periodic disturbances on an annular compressor stator rig. The passages were equipped with pneumatic active flow control influencing the stator blade's suction side, and a rotating throttling disc downstream of the passages inducing periodic disturbances. For steady blowing, it is shown that with increasing actuation amplitudes $c_\mu$, a hub corner vortex's extension deteriorating the suction side flow can be reduced, resulting in an increased static pressure rise coefficient~$C_p$ of a passage. The effects of the induced periodic disturbances could not be addressed, by using steady blowing actuation. Considering a corrected total pressure loss coefficient $\zeta^*$, which includes the actuation effort, the stator row's efficiency decreases with higher $c_\mu$. Therefore, a closed-loop approach is presented to address the effects of the disturbances more specifically, thus lowering the actuation effort. For this, a Repetitive Model Predictive Control (RMPC) was applied, taking advantage of the disturbance's periodic nature. The presented RMPC formulation is restricted to a binary control domain to account for the used solenoid valves' switching character. An efficient implementation of the optimization within the RMPC is presented, which ensures real-time capability. As a result, $C_p$ increases in a similar magnitude but with a lower actuation mass flow of up to 66\,\%, resulting in a much lower~$\zeta^*$ for similar values of $c_\mu$.

NUMERICAL INVESTIGATION OF UNSTEADY COMBUSTOR TURBINE INTERACTION FOR FLEXIBLE POWER GENERATION

In the present study low-frequency disturbances introduced by a periodic load variation have been simulated and superimposed to the inhomogeneous, unsteady flow entering a 3-stage, high-pressure industrial gas turbine fed by a can-type combustion chamber comprising 6 silo-burners. The effects of the unsteadiness realized at the combustor exit have been investigated by means of Detached Eddy Simulations, whereby a density-based solution approach with detailed thermodynamics has been employed. The periodic disturbances at the turbine inlet have been obtained by means of an artificially generated, unsteady field, resulting from a two-dimensional snapshot of the flow field at the combustor exit. Also, a combustor failure has been mimicked by reducing (respectively increasing) the mean temperature in some of the turbine inlet regions corresponding to the outlet of two burners. The propagation and amplitude changes of temperature fluctuations have been analyzed in the frequency domain. Tracking of the temperature fluctuations' maxima at the lowest frequencies revealed characteristic migration patterns indicating that the corresponding fluctuations persist with a non-negligible amplitude up to the last rows. A distinct footprint could also be observed at the same locations when a combustor failure was simulated, showing that, in principle, the early detection of combustor failures is indeed possible.

Separation Control of NACA0015 Airfoil using Plasma Actuators

Separation control of NACA0015 airfoil using plasma actuators was investigated. Plasma actuators in spanwise array, which consists of 21 electrodes, were located at the leading edge of the airfoil to give temporal periodic disturbances with phase variations into its boundary layer. The cord length of the airfoil was c = 100mm and corresponding Reynolds number was fixed at Re = 63,000. Non-dimensional frequency of the disturbance was chosen at F+ = 0.5 or 6. The gap between adjacent electrode was set as 1mm, and phase difference of the temporal periodic disturbances between adjacent electrode was set at φ = 0 or π. Velocity field was measured by conventional two-component PIV using a CCD camera (Imperx, B1922, 1920 x 1460pixels) and Nd-YAG laser (Quantel, Evergreen, 140mJ/pulse). Both large field of view (FOV) images capturing whole wing with surrounding flow and smaller FOV images focused on the separation bubble near leading edge were evaluated. Surface pressure was monitored by pressure transducers through pressure taps on the upper surface of airfoil. Lift and drag against the airfoil were measured using a two-component force balance.

Voltage Balancing of Multiphase FCML Converters with Coupled Inductors

<div>Flying capacitor voltage balancing is critical for the performance of flying capacitor multilevel (FCML) converters. This paper investigates the intrinsic capacitor voltage balancing of multiphase FCML converters with coupled inductors. It is shown that the coupled inductor provides flying capacitor voltage balancing that minimizes steady-state imbalances due to periodic disturbances compared to converters with uncoupled inductors. A dynamic model of natural balancing of the converter is derived and used to estimate the time required for the flying capacitors to settle from an initial imbalance. The theoretical predictions are verified with analytical derivations, SPICE simulations, and experimental results.</div>

Voltage Balancing of Multiphase FCML Converters with Coupled Inductors

<div>Flying capacitor voltage balancing is critical for the performance of flying capacitor multilevel (FCML) converters. This paper investigates the intrinsic capacitor voltage balancing of multiphase FCML converters with coupled inductors. It is shown that the coupled inductor provides flying capacitor voltage balancing that minimizes steady-state imbalances due to periodic disturbances compared to converters with uncoupled inductors. A dynamic model of natural balancing of the converter is derived and used to estimate the time required for the flying capacitors to settle from an initial imbalance. The theoretical predictions are verified with analytical derivations, SPICE simulations, and experimental results.</div>

The effect of periodic disturbances and carrying capacity on the significance of selection and drift in complex bacterial communities

Understanding how periodical disturbances affect the community assembly processes is vital for predicting temporal dynamics in microbial communities. The effect of dilutions as disturbances are poorly understood. We used a marine bacterial community to investigate the effect of disturbance (+/-) and carrying capacity (high/low) over 50 days in a dispersal-limited 2x2 factorial crossover study in triplicates. The community's disturbance regime was crossed halfway. We modelled the rate of change in community composition between replicates and used this rate to quantify selection and ecological drift. The disturbed communities increased in Bray-Curtis similarity with 0.011+/-0.0045 (Period 1) and 0.0092+/-0.0080 day-1 (Period 2), indicating that selection dominated community assembly. The undisturbed communities decreased in similarity at a rate of -0.015+/-0.0038 day-1 in Period 1 and were stable in Period 2 at 0.00050+/-0.0040 day-1, suggesting drift structured community assembly. Interestingly, carrying capacity had minor effects on community dynamics. This study is the first to show that stochastic effects are suppressed by periodical disturbances resulting in exponential growth periods due to density-independent biomass loss and resource input. The increased contribution of selection as a response to disturbances implies that ecosystem prediction is achievable.