Terminal Sliding Mode Control with Unidirectional Auxiliary Surfaces for Hypersonic Vehicles Based on Adaptive Disturbance Observer

A novel flight control scheme is proposed using the terminal sliding mode technique, unidirectional auxiliary surfaces and the disturbance observer model. These proposed dynamic attitude control systems can improve control performance of hypersonic vehicles despite uncertainties and external disturbances. The terminal attractor is employed to improve the convergence rate associated with the critical damping characteristics problem noted in short-period motions of hypersonic vehicles. The proposed robust attitude control scheme uses a dynamic terminal sliding mode with unidirectional auxiliary surfaces. The nonlinear disturbance observer is designed to estimate system uncertainties and external disturbances. The output of the disturbance observer aids the robust adaptive control scheme and improves robust attitude control performance. Finally, simulation results are presented to illustrate the effectiveness of the proposed terminal sliding mode with unidirectional auxiliary surfaces

Three-dimensional CFD modeling of transport phenomena in multi-channel anode-supported planar SOFCs

In this study, a three-dimensional computational fluid dynamics (CFD) model is developed and applied for anode-supported planar SOFC involving multi-channels. The developed model is first validated in agreement with the experimental data obtained at same conditions. Three different flow arrangements (co-, counter- and cross-flow) are simulated and compared in terms of cell overall performance and various transport phenomena occurred inside the SOFC single cell functional components. Local distribution of temperature, mass flow rate, current density, gas concentrations of reactants and products in both fuel and air sides under different flow arrangements is predicted and presented. It is found that the co-flow and counter-flow arrangements have a better performance than that of the cross-flow arrangement at the same operating conditions. It is also found that the temperature for the three flow arrangements is unevenly distributed and the significant temperature gradients exist along the length of the cell. The mass flow rate of fuel at the inlet of each channel is uniform, however its difference between the side channel and the channel at the center is increasing along the fuel flow direction, which reaches a maximum value at the outlet region. It is also predicted that the maximum current density is located at the interfaces between the channels, ribs and the electrodes resulting in a large over-potential and a heat source in the electrodes, which is harmful to the cell overall performance and working life time. (C) 2015 Elsevier Ltd. All rights reserved

Three-Dimensional CFD Modeling of Transport Phenomena in a Cross-Flow Anode-Supported Planar SOFC

In this study, a three-dimensional computational fluid dynamics (CFD) model is developed for an anode-supported planar SOFC from the Chinese Academy of Science Ningbo Institute of Material Technology and Engineering (NIMTE). The simulation results of the developed model are in good agreement with the experimental data obtained under the same conditions. With the simulation results, the distribution of temperature, flow velocity and the gas concentrations through the cell components and gas channels is presented and discussed. Potential and current density distributions in the cell and overall fuel utilization are also presented. It is also found that the temperature gradients exist along the length of the cell, and the maximum value of the temperature for the cross-flow is at the outlet region of the cell. The distribution of the current density is uneven, and the maximum current density is located at the interfaces between the channels, ribs and the electrodes, the maximum current density result in a large over-potential and heat source in the electrodes, which is harmful to the overall performance and working lifespan of the fuel cells. A new type of flow structure should be developed to make the current flow be more evenly distributed and promote most of the TPB areas to take part in the electrochemical reactions