Effects of advance ratio on elytra-hindwing interaction in forward flying Coleopteran beetle

In the present study, numerical simulations are performed to explore the significance of elytron-hindwing interaction in the forward flying Coleopteran beetle. The study investigates the effects of hindwing stroke amplitude (A/c) and advance ratio (J), (which is defined as the ratio of the incoming air velocity to the wing flapping velocity), on the aerodynamic forces. The wing kinematics of a Coleopteran beetle is constructed by using a combination of translation and rotation motion. The elytron is modeled by using a cambered airfoil that mimics the real geometry of the beetle wing, and the hindwing is modeled by using an elliptical profile. The results indicate that the beetle cruises with a constant velocity at approximately J = 0.3 in the tandem wing arrangement. It is observed that the angle of the net force vector relative to the stroke plane tilts systematically according to the flying speed. The influence of vortex structures on the beetle aerodynamic forces is analyzed. The elytron-hindwing interaction is found to be beneficial to the vertical force generation of hindwing as well as for the elytron when J > 0.0. The vortices interaction is observed during the downstroke period, and the leading edge vortex (LEV) of the elytron is captured by LEV of the hindwing that enhances the total vertical force. During the upstroke translation phase, the combined trailing edge vortex of elytron interacts/merges with the LEV of the hindwing and increases the horizontal force.     

A study on the combustion characteristies of coaxial jet furnaces with swirl flow

This study is an analysis of the turbulent diffusion flame with swirl flow and the calculated results are compared with experimental data in cases of various swirl numbers and air-fuel ratios. The mathematical model is restricted to single-phase, diffusion controlled combustion with swirl flow. Values of local flow properties are obtained by solving appropriate differential equation for continuity, momentum, stagnation enthalpy, concentration, turbulence energy, dissipation rate of turbulence energy, and the mean square of concentration fluctuation. The method is proposed for calculating the local probability of chemical reaction on the use of the probability density function for the mixture fraction.     

Interdiffusion analysis for NiAl versus superalloys diffusion couples

Solid-to-solid diffusion couples, β-NiAl (B2) versus various commercial superalloys (i.e., CM247, GTD-111, IN-939, IN-718, and Waspalloy) were examined to quantify the rate of Al interdiffusion as a function of initial superalloy composition. The diffusion couples were assembled with Invar steel jig encapsulated in Ar by sealing in quartz capsules and annealed at 1050 °C for 96 h. Concentration profiles measured by electron probe microanalysis in the single-phase β-NiAl region were used to determine interdiffusion fluxes and effective interdiffusion coefficients of individual components in the single-phase β-NiAl side of the couple. The values determined using experimental concentration profiles of the single-phase β-NiAl side of the couple were used to predict effective interdiffusion coefficients in multiphase superalloy side of the couple based on mass balance and local continuity of interdiffusion fluxes. Microstructural and compositional stability of protective coatings (e.g., NiCoCrAlY and NiAl) as a function of superalloys composition are discussed based on effective interdiffusion coefficients predicted from diffusion couple studies. This article was presented at the Multicomponent-Multiphase Diffusion Symposium in Honor of Mysore A. Dayananda, which was held during TMS 2006, 135th Annual Meeting and Exhibition, March 12–16, 2006, in San Antonio, TX. The symposium was organized by Yongho Sohn of University of Central Florida, Carelyn E. Campbell of National Institute of Standards and Technology, Richard D. Sisson, Jr., of Worcester Polytechnic Institute, and John E. Morral of Ohio State University.     

Oxygen diffusion through Al-doped amorphous SiO2

Oxygen (O) diffusion through pure and aluminum (Al)-doped amorphous silica is investigated by using secondary ion mass spectrometry to profile the diffusion of an¹⁸O tracer. The oxides are formed by the thermal oxidation of polymer-derived SiCN and SiAlCN ceramics. The authors demonstrate that a small amount of Al dopant can significantly inhibit both the interstitial and network diffusion of O. The activation energy of O network diffusion for Al-doped silica is two times higher than that for pure silica. The results are discussed in terms of the modification of Al doping on the network structure of the otherwise pure silica. This article was presented at the Multicomponent-Multiphase Diffusion Symposium in Honor of Mysore A. Dayananda, which was held during TMS 2006, the 135th Annual Meeting and Exhibition, March 12–16, 2006, in San Antonio, TX. The symposium was organized by Yongho Sohn of University of Central Florida, Carelyn E. Campbell of National Institute of Standards and Technology, Richard D. Sisson, Jr., of Worcester Polytechnic Institute, and John E. Morral of Ohio State University.     

Electromagnetic wave absorption properties of nanocrystalline Fe-based P/M sheets incorporating multi-walled carbon nanotubes

Nanocrystalline soft magnetic Fe₇₃Si₁₆B₇Nb₃Cu₁ (at.%) powders were mixed with fine multi-walled carbon nanotube (MWNT) powders and polyurethane based binders. The mixtures were tape-cast, dried and then cold-rolled to form EM wave absorption sheets. The MWNT powders were added to the Fe-based powders up to 1 wt.% to improve the EM wave absorption properties. The processed sheets with 0.5 mm in thickness were cut into toroidal shape to measure the S-parameter, permeability, permittivity, and power loss at the high frequency of 10 MHz to 10 GHz. As a result, improved absorption properties were obtained from the sheets incorporating MWNT. The results were caused by the increase of dielectric loss of the absorption sheets, which was due to the addition of MWNT powder inducing a notable increase in complex permittivity.     

Influence of corner radius on the near wake structure of a transversely oscillating square cylinder

The near wake flow field features of transversely oscillating square section cylinders with different corner radii were studied in an attempt to assess the influence of corner radius. The investigation was performed by using particle image velocimetry (PIV) technique in a water channel with a turbulence intensity of 6.5%. Five models were studied with r/B=0, 0.1, 0.2, 0.3 and 0.5 (r is the corner radius and B is the characteristic dimension of the body), and the body oscillation was limited to lock-in condition (at fe/fo=1.0; fe is the excitation frequency and fo is the vortex shedding frequency from a stationary cylinder at the same Re). The corner radius was found to significantly influence the flow features around the bodies. Except for r/B=0.5, for all the other cases of r/B ratios, cycle-to cycle variation in the mode of vortex shedding was observed in the case of oscillating cylinders inducing highly non-linear wake characteristics. Apart from variation in the shedding mode, changes in shedding cycle timing were also observed for sharp and rounded square cylinders. The hgher the r/B ratio, shedding in the near wake was found to be more uniform (lesser variation in shedding cycle timings). Another admissible shedding mechanism is newly identified to operate in the near wake of oscillating cylinders now being called as the ‘passive shedding’ mechanism. Results indicate that increasing the corner radius suppresses the possible instabilities of the cylinder.     

GPU-based collision analysis between a multi-body system and numerous particles

The use of a graphics processing unit (GPU) is an ideal solution for problems on data-parallel computations. The serial CPU-based program for collision analysis between a multi-body system and numerous particles is rebuilt as a parallel program that uses the advantages of a GPU. In this study, a GPU is used to effectively perform multi-body dynamic simulation with particle dynamics. The multibody system has 20 circular objects, 19 spring-damper force elements, and 2 revolute joints. The motion equations are formulated using the Cartesian coordinate system, and the implicit Hilber-Hughes-Taylor integration algorithm is used for the integral equation. To detect collisions between a multi-body system and particles or between particles, a spatial subdivision algorithm and a discrete element modeling are used. The developed program is verified by comparing the results with ADAMS. The numerical efficiencies of the serial program using CPU and the parallel program using GPU are compared according to the number of particles. The results show that the greater the number of particles, the more computing time can be saved. For example, when the number of particles is 900, the computing speed of the parallel analysis program is about five times faster than that of the serial analysis program.