Vaughn College of Aeronautics and Technology

About: Vaughn College of Aeronautics and Technology is a education organization based out in New York, New York, United States. It is known for research contribution in the topics: Gravitational microlensing & Planetary system. The organization has 727 authors who have published 708 publications receiving 14082 citations. The organization is also known as: College of Aeronautics.

Interpretation of harmonic response diagrams

Abstract: This chapter discusses the interpretation of harmonic response diagrams. The emphasis is on the measurement of the harmonic response of linear lumped parameter systems. When this frequency response data has been obtained, it is usual to present it in one of several graphical forms. The precision with which this can be done depends a great deal on a prior theoretical knowledge of the system whose behavior is represented by the graph in question. In the case of harmonic response measurements, it is the response curve that is known and the transfer function that is the unknown. It is often possible to fit asymptotes, by trial and error, and to establish break frequencies and slopes that enable the system time constants, and the order of the transfer function to be estimated with some fair degree of success. A great deal depends upon whether the form of the transfer function is known in advance, and whether or not the assumption of linearity is valid for the measurements that were taken.

Effects of aeronautical conditions on passivation cracking of micro-structures of IC packages

Abstract: Passivation cracking is one of the main failures of ICs and thermo-mechanical failures are the root cause. A major cause for these failures is due to the different Coefficients of Thermal Expansion (CTE), different Young's modulus, Poisson's ratios of package materials under different temperatures and some mechanical loadinds. Therefore the working conditions of compound materials used here is expected to have a pronounced influence on the local stress distribution in the passivation layer. The aeronautical conditions mainly include different temperatures and overloads as well as the vibration conditions. Here the finite element simulations and the maximum principal stress theory are applied here to investigate the effects of aeronautical conditions on passivation cracking of microstructures of IC packages, and the result will pave the way for compound materials selection in IC packages and usage under aeronautical conditions.

Microstructure Evolution Mechanism of Single and Multi-pass in Laser Cladding Based on Heat Accumulation Effect for Invar Alloy

Abstract: This work explores how the process parameters in laser cladding affect the evolution of the microstructure of the single-pass and multi-pass cladding layers of Invar alloys. The research examined the cladding layers from three aspects: (1) the transformation of grain size, heat-affected zone (HAZ) width, ratio of the columnar crystal to the equiaxed crystal, and change of Fe content of the cladding layer; (2) the effects of heat accumulation on grain size, HAZ width, and remelting zone; and (3) the hardness distribution of single-pass and multi-pass cladding layers. The investigation has the following four findings: (1) the cladding layer is composed of equiaxed crystals at the top and columnar crystals at the bottom of the cladding layer; (2) the processing parameters have significant effects on the width of the HAZ, proportion between the columnar and equiaxed crystals, and the change of Fe content of the cladding layer; (3) the gradual accumulation of heat causes the increase in HAZ width, the grain size, and the area of the remelting zone; and (4) the hardness progressively reduces from the top to the bottom along the direction of the centerline of the cladding layer.

Numerical Investigation of Heat Transfer Enhancement in a Slot Channel Induced by a Piezoelectric Fan

Abstract: Heat transfer enhancement in an isothermal slot channel due to vortices shedding from a vibrating piezoelectric fan is numerically investigated at $\pmb{Re}=\mathbf{500}$. The numerical simulations are performed for the dimensionless frequency $\pmb{Sr}$ and dimensionless amplitude $\pmb{A}$ in the ranges of 0 ~ 1 and 0 ~ 0.25, respectively. Effects of Prandtl number $(\mathbf{0.1}\leq\pmb{Pr}\leq\mathbf{10})$ on the heat transfer enhancement for different fluids are also discussed. The results show that vibration of the piezoelectric fan can significantly enhance the heat transfer performance of the downstream walls of the fan. A critical dimensionless amplitude value of 0.1 is found for the heat transfer enhancement of the fan. Moreover, the benefits of fan vibration in enhancement of wall heat transfer are found to be very sensitive to $\pmb{Pr}$. The maximum heat transfer enhancement ratio of 41.6% is obtained when $\pmb{Pr}$ is approximately equal to 1.