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Fatigue crack growth analysis using surrogate modelling techniques for structural problems
No full textThis paper addresses the polynomial-based response surface models for fatigue crack growth problems. The fatigue crack growth behaviour of critical pin-loaded lug with through-the-thickness crack at a hole was analysed using finite-element (FE) tools. The stress intensity factor (SIF) and fatigue crack growth life for the incremental crack length of the attachment lug was predicted using Virtual Crack Closure Technique (VCCT) approach and crack growth laws, respectively. The polynomial-based surrogate model was built using the FE characterisation of the relationship between various crack parameters such as crack size, load applied, thickness, stress intensity factor and fatigue crack growth life. Then, using the developed model, stress intensity factors and fatigue crack growth life for various parameters were obtained without the help of FE tools. Hence, the computation cost of using finite-element tools was reduced
Identification of a Flexible Aircraft Derivatives
No full textThis chapter discusses the neural modeling of the flexible aircraft and how to extract the aerodynamic derivatives and structural mode shape parameters of flexible modes using the neural partial differentiation (NPD) method. The effects of flexibility on the flight dynamics of an aircraft have been shown to be quite significant, especially as the frequencies of its elastic modes become lower and approach those of the rigid body modes (Zerweckh et al. 1990; Meirovitch and Tuzcu 2001). The chapter discusses the neural modeling of the flexible aircraft and how to extract the aerodynamic derivatives and structural mode shape parameters of flexible modes using the NPD method. The effects of flexibility on the flight dynamics of an aircraft have been shown to be quite significant, especially as the frequencies of its elastic modes become lower and approach those of the rigid body modes (Colin et al. 2008; Majeed 2014). The characteristics of such flexible aircraft are altered significantly from those of a rigid aircraft, and the design of the flight control system may become drastically more complex (Bucharles and Vacher 2002). Therefore, mathematical modeling of a flexible aircraft for dynamic analysis and control system design is a major issue in flexible aircraft dynamics. The characteristics of such flexible aircraft are altered significantly from those of a rigid aircraft, and the design of the flight control system may become drastically more complex. Therefore, mathematical modeling of a flexible aircraft for dynamic analysis and control system design is a major issue in flexible aircraft dynamics
Nonlinear filter and neural modeling for calibration of aircraft airdata system
No full textCalibration of aircraft airdata system deals with the reconstruction of flight path trajectories from the noisy flight data using six-degree-of-freedom equations of aircraft. Aircraft system dynamics are highly nonlinear in rapid variations of the aircraft motion and require the use of a nonlinear filtering algorithm. In this paper, a methodology based on data-driven decision making is introduced to obtain the accurate values of aircraft flow angles (angle of attack and angle of sideslip) and static pressure from its noisy measurements. For this, the integration of fault detection and isolation approach to the adaptive nonlinear filter is applied to dynamic maneuvers, and a neural model of calibration function is established over a flight envelope using the filter estimates. A deterministic airdata calibration function is derived by estimating its coefficients from the established neural model using the neural partial differentiation method. The cascading impact of adaptive estimation and neural modeling of airdata calibration function reduces the development cost of an aircraft. The investigations are initially made on simulated flight data under various conditions of wind and turbulence and later extended to the flight data of aircraft to identify the calibration function valid over a flight envelope. The complementary flight data are used to validate the calibration function and are compared with online estimation results of the robust filter. The experimental results show that the proposed algorithm can isolate and rectify the fault and exhibits more accurate estimates directly with neural modeling than the nonadaptive version of the filter
Screen printed copper and tantalum modified potassium sodium niobate thick films on platinized alumina substrates
No full textWe show how sintering in different atmospheres affects the structural, microstructural, and functional properties of ~30 μm thick films of K0.5Na0.5NbO3 (KNN) modified with 0.38 mol% K5.4Cu1.3Ta10O29 and 1 mol% CuO. The films were screen printed on platinized alumina substrates and sintered at 1100 °C in oxygen or in air with or without the packing powder (PP). The films have a preferential crystallographic orientation of the monoclinic perovskite phase in the [100] and [−101] directions. Sintering in the presence of PP contributes to obtaining phase-pure films, which is not the case for the films sintered without any PP notwithstanding the sintering atmosphere. The latter group is characterized by a slightly finer grain size, from 0.1 μm to ~2 μm, and lower porosity, ~6% compared with ~13%. Using piezoresponse force microscopy (PFM) and electron backscatter diffraction (EBSD) analysis of oxygen-sintered films, we found that the perovskite grains are composed of multiple domains which are preferentially oriented. Thick films sintered in oxygen exhibit a piezoelectric d33 coefficient of 64 pm/V and an effective thickness coupling coefficient kt of 43%, as well as very low mechanical losses of less than 0.5%, making them promising candidates for lead-free piezoelectric energy harvesting applications
Rotordynamic Analysis and Redesign of High-Pressure Turbine Test Rig
No full textThe high-speed test rigs pose several operational problems originating from rotordynamics, bearings, lubrication and thermal gradients. When the critical speeds exist within the design speed, it is possible to accelerate the rotor through resonant speed zones in many applications. However, in very few cases, the resonance crossovers pose serious problems resulting from operational schedules and demand major modifications to rotor-bearing system. The design modifications, driven by rotordynamic considerations, carried out for an existing high-speed test rig with serious operability issues are presented in this paper. During operation, one of the bearings supporting the rotor has failed twice causing significant damages. On both occasions, the bearing failure took place when the rotor was approaching the first critical speed. Considering the difficulty experienced to pass the first critical speed quickly, the rotor-bearing system of the rig is completely redesigned with safe separation margin away from the design speed. Designer’s challenges arising from overall layout, manufacturing, imported hardware, assembly and operation are highlighted while addressing the problem. The turbine stage could be tested successfully up to its design speed after implementing all design modifications
Facile synthesis of CuCr2O4/CeO2 nanocomposite: A new Fenton like catalyst with domestic LED light assisted improved photocatalytic activity for the degradation of RhB, MB and MO dyes
No full textHere, we report the findings on CuCr2O4/CeO2 (CCO/CeO2) nanocomposite as a new heterogeneous Fenton like catalyst for the degradation of rhodamine B (RhB), methylene blue (MB) and methyl orange (MO) under domestic LED light irradiation. An extensive characterization of the samples were performed using several physicochemical techniques. A careful monitoring of photo-activities reveals the best performance of 10%CCO/CeO2 showing complete degradation of 10 ppm RhB, MB and MO dyes within 15, 20 and 30 min, respectively, in presence of 4 mM of H2O2. The visible light absorption of CeO2 is enhanced by CCO. The radical trapping and coumarin fluorescence probe methods suggest the generation of radical dotOH in the catalytic pathways. A comprehensive analysis of radical dotOH generation in presence and in absence of LED irradiation is presented to underscore both the Fenton like reactions of the nanocomposite system. Importantly, the nanocomposite catalyst shows encouraging recycling behavior through an intermediate heat treatment. The Fenton like catalytic behavior of marginally active CeO2 is dramatically enhanced in presence of CCO in the nanocomposite due to larger creation of oxygen vacancy. Finally, a plausible explanation of this novel catalytic behavior based on band bending across the junction of the two semiconducting oxides has been presented
Dual-Site Cooperation for High Benzyl Alcohol Oxidation Activity of MnO2in Biphasic MnOx-CeO2Catalyst Using Aerial O2in the Vapor Phase
No full textSelective oxidation of benzyl alcohol to benzaldehyde in the vapor phase has drawn growing interest recently. In this work, MnOx–CeO2 mixed oxide compositions have been prepared by a coprecipitation method and tested for their oxidation activities of benzyl alcohol to benzaldehyde in the vapor phase. Detailed structural analyses have indicated that MnOx–CeO2 catalysts contain two phases, namely, α-MnO2 and fluorite CeO2 phases. The benzyl alcohol oxidation activity of pure MnO2 is more than 7 times higher compared to that of CeO2, indicating a much higher intrinsic oxidation ability of the MnO2 phase. Further, enhancement of the benzyl alcohol oxidation rate over MnO2 in 10%MnOx–CeO2 catalyst by 13 times is observed in relation to pure MnO2. The role of CeO2 in the MnOx–CeO2 catalyst has also been investigated, which indicates that the oxidation activity is almost independent of CeO2. However, stronger adsorption of benzyl alcohol over the MnOx–CeO2 catalysts compared to that of MnO2 points to the role of CeO2 in adsorption. Thus, both the CeO2 and the MnO2 components have different roles in the catalytic process—adsorption of benzyl alcohol on the CeO2 surface and its oxidation on MnO2 at the interface. The cooperation between the two sites toward oxidation could happen due to jumping of adsorbed benzyl alcohol from the surface of the CeO2 phase to the closest Mn4+ site in the MnO2 phase at the contact surface with MnO2 by thermal motion
Measurement accuracy enhancement with multi-event detection using the deep learning approach in Raman distributed temperature sensors
No full textIn this work, we present a novel deep learning framework for multi-event detection with enhanced measurement accuracy from the measured data of a Raman Optical Time Domain
Reflectometer (Raman-OTDR). We demonstrate the utility of a deep learning-based approach by comparing the results from three popular neural networks, i.e. vanilla recurrent neural network (RNN), long short-term memory (LSTM), and gated recurrent unit (GRU). Before feeding the experimentally obtained data to the neural network, we sanitize our data through a correlation filtering operation to suppress outlier noise spikes. Based on experiments with Raman-OTDR
traces consisting of single temperature event, we show that the GRU is able to provide better performance compared to RNN and LSTM models. Specifically, a bidirectional-GRU (bi-GRU) architecture is found to outperform other architectures owing to its use of data from both previous as well as later time steps. Although this feature is similar to that used recently in one dimension convolutional neural network (1D-CNN), the bi-GRU is found to be more effective in providing enhanced measurement accuracy while maintaining good spatial resolution. We also propose and demonstrate a threshold-based algorithm for accurate and fast estimation of multiple events. We demonstrate a 4x improvement in the spatial resolution compared to post-processing using conventional total variational denoising (TVD) filters, while the temperature accuracy is maintained within ± 0.5 oC of the set temperature
Kinked silicon nanowires prepared by two-step MACE process: Synthesis strategies and luminescent properties.
No full textWe report the controlled fabrication of kinked silicon nanowires (SiNWs) using ethanol mixed facile two-step metal-assisted chemical etching (MACE) method. Accordingly, the kink angle, straight path, and the number of kinks in kinked SiNWs are controlled by varying the volume of ethanol and etching time in high concentrated plating and etching solutions. The silver nanoparticles (AgNPs) during the etching need to travel a critical length (≥1.5 μm) in a vertical direction before the kink formation. The presence of ethanol in etching solution affects the availability of H2O2 and HF at Si/Ag interface and has a major effect on the etching process. The room temperature photoluminescence (PL) emission of kinked SiNWs is tuned from the red region to the blue region by controlling the amount of ethanol in the etching solution. The temporal behaviour of the PL data of the kinked SiNWs has been provided to understand in depth the optical transition processes
Polymer-derived silicon carbide micro powders through selective solvent precipitation of high molecular weight polycarbosilane.
No full textSynthetic route to β-SiC micro powders through selective solvent precipitation (SSP) of high-molecular-weight (HMF) polycarbosilane. (PCS) was developed. PCS (>3000 Da) was obtained through pyrolysis polycondensation of Polydimethylsilane. Spectral data confirmed that PCS could be fractionated and precipitated during the process without disturbing its molecular structure. Fractionated fine PCS powders were converted into crystalline β-SiC particles through ceramization at 1200–1450 °C under argon. XRD patterns revealed a strong and sharp peak at a diffraction angle of 35.8°, thereby confirm the β-SiC structure and purity. SEM analysis confirmed the particle morphology and aggregation of β-SiC particles. Particle size analysis results show that the SiC particles' size is in the range of 10–100 μm. Thermal data prove the high thermal stability of PCS-HMF. β-SiC particles were thermally inert up to 1000 °C and became reactive beyond 1000 °C