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Aircraft System Identification
No full textIn a fairly complex system like aircraft, modeling and parameter estimation plays a crucial role in determining its stability and control characteristics
Frequency Domain Based Robust Flutter Analysis of Swept Back Wing Using μ Method
No full textThe present work deals with the robust flutter analysis of a sweptback wing in frequency domain in the presence of various parametric uncertainties. The methodology adopted for the studies is based on the structured singular value () method. method requires valid description of various uncertainties associated with the aeroelastic system and then introducing these uncertainties to the nominal aeroelastic system in the form of a feedback loop. This feedback representation of uncertainties results in the Linear Fractional Transformation (LFT) model of the uncertain aeroelastic system which is then used for robust stability studies using method. This method is implemented in MATLAB and validation studies are carried out for 3DOF airfoil system in the presence of various structural and aerodynamic uncertainties. Further, the present method is extended to study the robust flutter of AGARD 445.6 sweptback wing in the presence of structural and aerodynamic uncertainties at various Mach numbers
Neural Modeling and Parameter Estimation
No full textThe neural modeling of a dynamic system is presented in this chapter. The former literature reported that ordinary differential equations can be solved by an neural-network-based approach (Lagaris et al. 1998
Improved stability performance of a feedback active noise control using a Steiglitz-McBride adaptive notch filter and robust secondary path identification based on variable step size Griffiths LMS algorithm
No full textA stable feedback active noise control (FBANC) system with an improved performance in a broadband disturbance environment is proposed in this article. This is achieved by using a Steiglitz-McBride adaptive notch filter (SM-ANF) and robust secondary path identification (SPI) both based on variable step size Griffiths least mean square (LMS) algorithm. The broadband disturbance severely affects not only FBANC input synthesized but also the SPI.TheSM-ANFestimated signal has narrowband component that is utilized for the FBANC input synthesis. Further, the SM-ANF error has broadband component utilized to get the desired signal for SPI. The use of variable step size Griffiths gradient LMS algorithm for SPI enables the removal of broadband disturbance and non-stationary disturbance from the available desired signal for better SPI. For a narrowband noise field, the proposed FBANC improves the convergence rate significantly (20 times) and the noise reduction from 10 dB to 15 dB (50%improvement) over the conventional FBANC (without SM-ANF and variable step size Griffiths LMS adaptation for SPI)
Hot corrosion properties of plasma sprayed La2Ce2O7/YSZ vis-à-vis La2Ce2O7/cluster paired zirconia thermal barrier coatings
No full textBilayered thermal barrier topcoats have lead to a remarkable breakthrough in overcoming the disadvantages of the conventional yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). The present work is devoted to studying the hot corrosion properties of two different bilayered ceramic topcoats, viz., (i) lanthanum cerium oxide with the formula La2Ce2O7 (LCO)/YSZ and LCO/cluster paired zirconia (gadolinia, dysprosia and yttria stabilized zirconia -(Gd,Dy,Y)SZ) plasma sprayed TBCs. Plasma spray grade YSZ and (Gd,Dy,Y)SZ are prepared by co-precipitation and solution combustion techniques as reported in the literature. The effect of thickness of the plasma sprayed top LCO layer in bilayered LCO/YSZ and LCO/(Gd,Dy,Y)SZ TBC systems under Type I hot corrosion condition is examined. The LCO/(Gd,Dy,Y)SZ bilayered coating with 100 μm LCO thickness exhibits better hot corrosion resistance than the LCO/YSZ system. The phase transformation of t′-ZrO2 to m-ZrO2 in LCO/(Gd,Dy,Y)SZ (100/150 μm) TBC is reduced markedly (60%) compared to LCO/YSZ (100/150 μm) TBC
Characterization of Digital Power Amplifier-Based Active Magnetic Bearings
No full textActive magnetic bearings (AMB’s) are used to support rotors using magnetic forces, without any solid to solid contact. The AMB system has four main components: power amplifier, electromagnetic actuator, sensor and controller. In this work, the characterization of power amplifier for the AMB system is undertaken. The gain and phase lag of the power amplifiers over the operating frequency is obtained experimentally. Equivalent circuit models are made for the power amplifier. These characteristics of the amplifiers are used in developing the control algorithm for the AMB. The experimental results of these characterizations will help in understanding the gain of the power amplifier and also the lag between the signal input and the output signal over the desired frequency range
Nd2Ti2O7 (NTO) with high curie temperature (TC) for high temperature sensor applications
No full textPerovskite-like layered structured (PLS) materials with A2B2O7 structure are promising materials for high temperature applications because of their high curie temperatures. These materials show linearity in resistivity vs. temperature, therefore, are preferred for high temperature sensor applications. Neodymium titanate (Nd2Ti2O7) is one of the prominent PLS materials with high curie temperature (TC ≥ 1500 °C). Nd2Ti2O7 (NTO) was synthesized by mixed oxide route and the powder was calcined at 1250 °C for 2 h. NTO samples were sintered in the temperature range of 1325–1400 °C for 2 h. The sintered samples were characterized for dielectric constant (K), P-E hysteresis loop and DC electrical resistivity (ρ) from 100 to 900 °C. The sintered density was highest at 1375 °C for NTO samples (>94.85% Th.). DC resistivity was found to decrease linearly from 1014 to 106 Ω cm with the rise in temperature from 100 to 900 °C, therefore, confirming as a prospective high temperature sensor material
Thermal oxidation of stainless steel substrate with tunable spectral selectivity: Transition from a reflecting to a highly absorbing Cr–Fe spinel surface.
No full textThe conventional methods of obtaining solar selective surfaces for high temperature solar thermal applications involve coating of the substrate by various methods such as physical vapor deposition, plasma spraying, anodization, etc. The present work is an attempt to enhance the optical properties of metals by heat treatment. The oxide layers formed by annealing of stainless steel 304 (SS 304) enhance the absorptance in the solar spectrum region. Influences of oxidation temperature and oxidation time span on the values of solar absorptance and thermal emittance have been studied. The annealing of SS 304 substrate was carried out in air at 600–900 °C. The time period of annealing plays a crucial role in the amount of oxides formed and thus is a variable parameter. The absorptance values obtained with isothermal oxidation at shorter and longer durations have been compared at a temperature of 900 °C. A cyclic loading approach is also employed to arrive at the optimal absorptance of the samples. It is further used to study the dependency of solar absorptance on the reaction kinetics with respect to varying oxidation time. Under the optimized annealing conditions, heat-treated SS 304 sample exhibited an absorptance of 0.920 and an emittance of 0.37. A plausible model for the high optical absorption in these oxidized surfaces with relatively low thermal emittance is rationalized. High temperature materials such as Inconel and Nimonic have also been subjected to isothermal annealing and the absorptance values were found to be 0.887 and 0.880, respectively
Passive ranging for infrared search and track system mounted on an aircraft
No full textThis paper presents two passive ranging algorithms viz. i. Extended Kalman Filter (EKF) in Modified Spherical Coordinates (MSC), ii. Pseudo Linear Estimator (PLE) for an Infrared Search and Track (IRST) system mounted on an aircraft. Detailed mathematical formulations for both algorithms are presented. Target-Aircraft relative simulation scenarios are generated, and the performance of algorithms has been presented. The robustness of the algorithms for sensor noise levels and aircraft maneuvers has been clearly brought out
Experimental and finite element numerical studies on the post-buckling behavior of composite stiffened panels
No full textAircraft composites structures are typically made using stiffened skin construction as it provides a minimum weight solution to many design problems. However, designers are reluctant to allow composite stiffened structures to operate in the post-buckled load regimes due to their poor inter-laminar properties. The post-buckling response of cocured composite stiffened panels is explored by experiments and numerical simulations. An integrated progressive damage finite element model is presented which captures inter and intra-laminar failures in panels. Detailed analysis of measured experimental structural responses in terms of strain, deformations, the failure mode is carried out and validated from the numerical analysis