Fluid-Structure Interaction Modeling of A F/A-18 Twin-Tail Buffet Using Non-linear Eddy Viscosity Models

When turbulent flow generates unsteady differential pressure over an aircraft\u27s structure, this may generate buffeting, a random oscillation of the structure. The buffet phenomenon is observed on a wide range of fighter aircraft, especially fighters with twin-tail. More research is needed to better understand the physics behind the vortical flow over a delta wing and the subsequent tail buffet. This dissertation reports the modeling and simulation of a steady-state one-way fluid-structure interaction for the tail buffet problem observed on a F/A-18 fighter. The time-averaged computational results are compared to available experimental data. Next, computations are extended to simulate an unsteady two-way fluid-structure interaction problem of the tail buffet of a F/A-18 fighter. For the modeling herein, a commercial software ANSYS version 14.0, is employed. For the fluid domain, the unsteady Reynolds-averaged Navier Stokes (URANS) equations with different turbulent models are utilized. The first turbulence model selected is the modified Spalart-Allmaras model (SARRC) with a strain-vorticity based production and curvature treatment. The second turbulence model selected is the Non-linear Eddy Viscosity Model (NLEVM) based on the Wilcox k–ω model. This model uses the formulation of an explicit algebraic Reynolds stress model. The structural simulation is conducted by a finite element analysis model with shell elements. Both SARRC and NLEVM turbulence models are in ANSYS software. The experimental data used for validation were conducted on a simplified geometry: a 0.3 Mach number flow past a 76-deg delta wing pitched to 30-deg. Two vertical tails were placed downstream of the delta wing. The present work is the first ever study of the tail buffet problem of the F/A-18 fighter with two-way fluid-structure interaction using the two advanced turbulence models. The steady-state, time-averaged, one-way fluid-structure interaction case of the present investigation indicates that simulations employing the NLEVM and SARRC turbulence models do not match the experimental data. These results are somewhat expected for the steady-state, one-way simulation, because it involves no force and displacement transfer between the fluid and structural domains. For the unsteady two-way fluid-structure interaction case, both models result in more favorable agreement with the experimental data by optimizing the available computational resources particularly when compared to prior simulations by other researchers. Results from the NLEVM model produce improved pressure predictions on the tail as compared to the results from the SARRC model. Based on the simulation results, it is concluded that the buffet problem should be simulated as a two-way fluid-structure interaction. The NLEVM turbulence model is recommended in predicting vortical flow characteristics over a delta wing. The NLEVM turbulence model is necessary to predict the pressure distribution not only over the aircraft surface but also the tails since they experience the wake of vortices

Bifunctional supported catalysts for fine chemical synthesis

The objective was to prepare and optimise solid acid and solid base catalysts for liquid phase reactions. The approach has been to functionalize porous silica support materials with acid and base catalytic groups. Solid acid, solid base and bifunctional solid acid/base catalysts were studied. Evidence for acid-base cooperative catalytic mechanisms was found, suggesting that these bifunctional catalysts could show significant advantages over singly functionalized materials of mixtures thereof. Silicas functionalized with tethered aminopropyl groups were prepared by both a grafting method and a sol–gel method. The solids were fully characterized and were tested in the nitroaldol condensation between nitromethane and benzaldehyde to afford nitrostyrene and the aldol reaction between 4-nitrobenzaldehyde and acetone to afford 4-(4-nitrophenyl)-4-hydroxy-2-butanone. The catalytic activities of these materials were found to be dependent on the dispersion and accessibilities of the active sites which, in turn, depend on the methods utilized for the catalyst preparation. Solid acid catalysts were prepared by grafting silica with mercaptopropyl-trimethoxysilane (MPTS) followed by oxidation. The influence of the oxidation procedure on the acidity of the catalyst is described. The use of concentrated HNO3 optimizes the oxidation process and increases the concentration of active sites in comparison to H2O2. The activities of these catalysts were tested in the deacetalization of benzaldehyde dimethyl acetal to benzaldehyde. The use of solid acid and solid base catalysts in the same system was examined, in a two-stage acid-catalyzed deacetalization and base-catalyzed Henry reaction. Solid bifunctional acid-base catalysts were prepared by grafting on amorphous silica in two ways: 1) by grafting propylsulfonic acid and aminopropyl groups to the silica surface (NH2-SiO2-SO3H) and 2) by grafting aminopropyl groups and then partially neutralizing with phosphotungstic acid, relying on the H2PW12O40- ion for surface acidity (NH2-SiO2-NH3+[H2PW12O40-]. These two bifunctional catalysts were compared with each other and with the singly functionalised catalysts described above. Surface acidities and basicities were characterized by adsorption calorimetry, using SO2 as a probe for surface basicity and NH3 for surface acidity. Catalytic activities were measured in the tandem deacetalization/Henry reaction described above, and in an aldol reaction in which a cooperative acid-base catalytic mechanism is thought to be effective. Overall NH2-SiO2-SO3H catalysts showed higher concentrations and strengths of both acid and base sites, and higher activities. Both catalysts showed evidence of cooperative acid-base catalytic sites. Even in the deacetalization/Henry reaction, the bifunctional catalysts exhibited a catalytic advantage over physical mixtures of singly functionalized catalysts. A further bifunctional acid-base catalyst was prepared and studied by tethering proline to silica. In this case, the catalyst was chiral and was tested in the asymmetric aldol reaction between acetone and 4-nitrobenzaldehyde. Grafting methods with and without protecting groups for the active sites on proline were investigated. Remarkably the optimised supported proline catalysts showed higher activities and higher enantioselectivities than proline in homogeneous solution, and showed minimal loss in activity with time. Both activity and enantioselectivity depended strongly on the nature of the reaction solvent

Biodegradation of the Alkaline Cellulose Degradation Products Generated during Radioactive Waste Disposal.

The anoxic, alkaline hydrolysis of cellulosic materials generates a range of cellulose degradation products (CDP) including α and β forms of isosaccharinic acid (ISA) and is expected to occur in radioactive waste disposal sites receiving intermediate level radioactive wastes. The generation of ISA's is of particular relevance to the disposal of these wastes since they are able to form complexes with radioelements such as Pu enhancing their migration. This study demonstrates that microbial communities present in near-surface anoxic sediments are able to degrade CDP including both forms of ISA via iron reduction, sulphate reduction and methanogenesis, without any prior exposure to these substrates. No significant difference (n = 6, p = 0.118) in α and β ISA degradation rates were seen under either iron reducing, sulphate reducing or methanogenic conditions, giving an overall mean degradation rate of 4.7×10−2 hr−1 (SE±2.9×10−3). These results suggest that a radioactive waste disposal site is likely to be colonised by organisms able to degrade CDP and associated ISA's during the construction and operational phase of the facility

Microbial fuel cells: From fundamentals to applications. A review

© 2017 The Author(s) In the past 10–15 years, the microbial fuel cell (MFC) technology has captured the attention of the scientific community for the possibility of transforming organic waste directly into electricity through microbially catalyzed anodic, and microbial/enzymatic/abiotic cathodic electrochemical reactions. In this review, several aspects of the technology are considered. Firstly, a brief history of abiotic to biological fuel cells and subsequently, microbial fuel cells is presented. Secondly, the development of the concept of microbial fuel cell into a wider range of derivative technologies, called bioelectrochemical systems, is described introducing briefly microbial electrolysis cells, microbial desalination cells and microbial electrosynthesis cells. The focus is then shifted to electroactive biofilms and electron transfer mechanisms involved with solid electrodes. Carbonaceous and metallic anode materials are then introduced, followed by an explanation of the electro catalysis of the oxygen reduction reaction and its behavior in neutral media, from recent studies. Cathode catalysts based on carbonaceous, platinum-group metal and platinum-group-metal-free materials are presented, along with membrane materials with a view to future directions. Finally, microbial fuel cell practical implementation, through the utilization of energy output for practical applications, is described

Synthesis of a novel multifunctional organic–inorganic nanocomposite for metal ions and organic dye removals

Abstract In this study, we used solvent assisted mechano-synthesis strategies to form multifunctional organic–inorganic nanocomposites capable of removing both organic and inorganic contaminants. A zeolite X (Ze) and activated carbon (AC) composite was synthesized via state-of-the-art mechanical mixing in the presence of few drops of water to form Ze/AC. The second composite (Ze/L/AC) was synthesized in a similar fashion, however this composite had the addition of disodium terephthalate as a linker. Both materials, Ze/AC and Ze/L/AC, were characterized using scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Powdered X-ray diffraction (P-XRD), Fourier-transform infrared spectrometry (FTIR), Accelerated Surface Area and Porosimetry System (ASAP), and thermal gravimetric analysis (TGA). The SEM–EDS displayed the surface structure and composition of each material. The sodium, oxygen and carbon contents increased after linker connected Ze and AC. The P-XRD confirmed the crystallinity of each material as well as the composites, while FTIR indicated the function groups (C=C, O–H) in Ze/L/AC. The contaminant adsorption experiments investigated the effects of pH, temperature, and ionic strength on the adsorption of methylene blue (MB) and Co(II) for each material. In MB adsorption, the first-order reaction rate of Ze/L/AC (0.02 h−1) was double that of Ze/AC (0.01 h−1). The reaction rate of Ze/L/AC (4.8 h−1) was also extraordinarily higher than that of Ze/AC (0.6 h−1) in the adsorption of Co(II). Ze/L/AC composite achieved a maximum adsorption capacity of 44.8 mg/g for MB and 66.6 mg/g for Co(II) ions. The MB adsorption of Ze/AC and Ze/L/AC was best fit in Freundlich model with R2 of 0.96 and 0.97, respectively, which indicated the multilayer adsorption. In the Co(II) adsorption, the data was highly fit in Langmuir model with R2 of 0.94 and 0.92 which indicated the monolayer adsorption. These results indicated both materials exhibited chemisorption. The activation energy of Ze/L/AC in MB adsorption (34.9 kJ mol−1) was higher than that of Ze/L/AC in Co (II) adsorption (26 kJ mol−1)

Aerodynamic low fidelity shape optimization of helicopter rotor blades in hover using genetic algorithms and the adjoint method

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. The Aerodynamic shape design of a helicopter rotor is a challenging problem that is required for designing a rotor disk with high efficiency. This work proposes a CFD validated process to find the optimal blade configuration of a helicopter blade in hover. The adjoint method is used to find the optimal shape of the blade sectional airfoil. Multi-objective optimization is carried out on the Caradonna-Tung rotor with figure of merit and coefficient of thrust as objective functions. Coefficient of Thrust is included in this study to limit the reduction of total thrust due to figure of merit enhancements. The multi-objective genetic algorithms (MOGA) optimization technique is applied with the thrust solidity ratio as a physical constraint, and blade root chord, tip chord, point of taper initiation, twist distribution as design parameters. The aerodynamic performance calculations are performed using the corrected blade element momentum theory (BEMT) that showed an excellent agreement with the wind-tunnel experimental data of the baseline rotor. A CFD-Based simulation is used to evaluate both the baseline Caradonna-Tung and the optimal blade Aerodynamic characteristics with an ideal gas k-ω SST turbulence model using FLUENT’s solver. Results show a great enhancement in the inflow ratio and blade tip vortices of the optimal blade. A CFD sensitivity study of each design variable is performed and showed the validity of the low fidelity optimization, Corrected BEMT, for this problem. This optimization method can be used to achieve satisfactory results with less computational power comparing to CFD based optimization approaches

Catalytic performance of nano-hybrid graphene and titanium dioxide modified cathodes fabricated with facile and green technique in microbial fuel cell

Finite resources of the world's fossil fuel give rise to the irresistible urge to explore alternative renewable energy routes such as microbial fuel cells (MFCs). The limited productivity is one of the main obstacles for MFC scalability. In this study, a dual-chamber MFC was assembled and equipped with fabricated modified cathodes with titanium dioxide (TiO2) or hybrid graphene (HG) which mainly improved the catalytic activity of the cathode. The graphite paste (GP) bare electrode was modified by both nanomaterials using a green and facile technique. The results showed that the modified cathodes resulted in a considerable improvement for the MFC performance, i.e., the power density reaching levels of 80 mW/m2 for GP-TiO2 and 220 mW/m2 for GP-HG compared to 30 mW/m2 for GP electrode. Additionally, the modified electrodes exhibited lower charge transfer resistance (Rct) compared to the bare electrode. Therefore, these modified electrodes, fabricated by an eco-friendly method, could be used as alternatives to the precious expensive metals like Pt