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Articles 1 - 20 of 20
Full-Text Articles in Mechanical Engineering
A Comparative Verification Of Forecasts From Two Operational Solar Wind Models, Donald C. Norquist, Warner C. Meeks
A Comparative Verification Of Forecasts From Two Operational Solar Wind Models, Donald C. Norquist, Warner C. Meeks
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The solar wind (SW) and interplanetary magnetic field (IMF) have a significant influence on the near‐Earth space environment. In this study we evaluate and compare forecasts from two models that predict SW and IMF conditions: the Hakamada‐Akasofu‐Fry (HAF) version 2, operational at the Air Force Weather Agency, and Wang‐Sheeley‐Arge (WSA) version 1.6, executed routinely at the Space Weather Prediction Center. SW speed (Vsw) and IMF polarity (Bpol) forecasts at L1 were compared with Wind and Advanced Composition Explorer satellite observations. Verification statistics were computed by study year and forecast day. Results revealed that both models’ mean Vsw are …
Bi-Material Attachment Through A Soft Tissue Interfacial System, Y. X. Liu, S. Thomopoulos, Victor Birman, J. S. Li, G. M. Genin
Bi-Material Attachment Through A Soft Tissue Interfacial System, Y. X. Liu, S. Thomopoulos, Victor Birman, J. S. Li, G. M. Genin
Mechanical and Aerospace Engineering Faculty Research & Creative Works
No abstract provided.
Uncertainty Quantification Integrated To Cfd Modeling Of Synthetic Jet Actuators, Srikanth Adya, Daoru Frank Han, Serhat Hosder
Uncertainty Quantification Integrated To Cfd Modeling Of Synthetic Jet Actuators, Srikanth Adya, Daoru Frank Han, Serhat Hosder
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The Point-Collocation Non-intrusive Polynomial Chaos (NIPC) method has been applied to a stochastic synthetic jet actuator problem used as one of the test cases in the CFDVAL2004 workshop to demonstrate the integration of computationally efficient uncertainty quantification to the high-fidelity CFD modeling of synthetic jet actuators. The test case included the simulation of an actuator generating a synthetic jet issued into quiescent air. The Point-Collocation NIPC method is used to quantify the uncertainty in the long-time averaged u and v-velocities at several locations in the flow field due to the uniformly distributed uncertainty introduced in the amplitude and frequency of …
"Pull-In" Of A Pre-Stressed Thin Film By An Electrostatic Potential: A 1-D Rectangular Bridge And A 2-D Circular Diaphragm, Gang Duan, Kai Tak Wan
"Pull-In" Of A Pre-Stressed Thin Film By An Electrostatic Potential: A 1-D Rectangular Bridge And A 2-D Circular Diaphragm, Gang Duan, Kai Tak Wan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
A one-dimensional (1-D) rectangular pre-stressed thin film clamped at two opposite ends is actuated by an electrostatic voltage applied to a pad directly underneath. the pre-stress is allowed to be either tensile or compressive in nature. at a critical applied voltage, the film becomes unstable and makes direct contact with the pad, leading to "pull-in". an elastic model is constructed to account for the phenomenon over ranges of film pad gap and residual stress. the results compare favorably with finite element analysis (FEA) in literature and experimental data and possess distinct advantages over other available closed-form solutions. the model is …
Investigations Of Femtosecond-Nanosecond Dual-Beam Laser Ablation Of Dielectrics, Cheng Hsiang Lin, Zheng Hua Rao, Lan Jiang, Wu Jung Tsai, Ping Han Wu, Chih Wei Chien, Shean Jen Chen, Hai Lung Tsai
Investigations Of Femtosecond-Nanosecond Dual-Beam Laser Ablation Of Dielectrics, Cheng Hsiang Lin, Zheng Hua Rao, Lan Jiang, Wu Jung Tsai, Ping Han Wu, Chih Wei Chien, Shean Jen Chen, Hai Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
We have conducted experimental investigations for the micromachining of dielectrics (fused silica) using an integrated femtosecond (is) and nanosecond (ns) dual-beam laser system at different time delays between the fs and ns pulses. We found that the maximum ablation enhancement occurs when the fs pulse is shot near the peak of the ns pulse envelope. Enhancements up to 13.4 times in ablation depth and 50.7 times in the amount of material removal were obtained, as compared to fs laser ablation alone. the fs pulse increases the free electron density and changes the optical properties of fused silica to have metallic …
Prediction Of The Transport Properties Of A Polyatomic Gas, Zhi Liang, Hai-Lung Tsai
Prediction Of The Transport Properties Of A Polyatomic Gas, Zhi Liang, Hai-Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
An Ab Initio Molecular Potential Model is Employed in This Paper to Show its Excellent Predictability for the Transport Properties of a Polyatomic Gas from Molecular Dynamics Simulations. a Quantum Mechanical Treatment of Molecular Vibrational Energies is Included in the Green and Kubo Integral Formulas for the Calculation of the Thermal Conductivity by the Metropolis Monte Carlo Method. using CO2 Gas as an Example, the Fluid Transport Properties in the Temperature Range of 300-1000 K Are Calculated Without using Any Experimental Data. the Accuracy of the Calculated Transport Properties is Significantly Improved by the Present Model, Especially for the Thermal …
Functioncad: A Functional Modeling Application Based On The Function Design Framework, Robert L. Nagel, Kenneth L. Perry, Robert B. Stone, Daniel A. Mcadams
Functioncad: A Functional Modeling Application Based On The Function Design Framework, Robert L. Nagel, Kenneth L. Perry, Robert B. Stone, Daniel A. Mcadams
Mechanical and Aerospace Engineering Faculty Research & Creative Works
This paper presents a functional modeling application, Function CAD, based on integrated functional and process modeling within the Function Design Framework. Function CAD provides for mixed, hierarchical models of environment, process and function with relationships represented via flows of material, energy and signal. This paper discusses the technical details of the Function CAD software including its two major components: (1) the library, libFCAD, for handling the internal representation of the model and (2) the GUI for user-Based model manipulation and visualization. the application of Function CAD within a computational, function- based conceptual design process is discussed along with the plugin …
A Natural Language To Component Term Methodology: Towards A Form Based Concept Generation Tool, Matt Robert Bohm, Robert B. Stone
A Natural Language To Component Term Methodology: Towards A Form Based Concept Generation Tool, Matt Robert Bohm, Robert B. Stone
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Over the last few decades design researchers have put forward theories and proposed methodologies that increase the chance that a design team will reliably arrive at the optimal solution to a given design problem. Studies, however, bear out that theories and methodologies alone will not guarantee an optimal or even good design solution. Instead, a breadth of knowledge across multiple engineering domains and the time and tools to thoroughly evaluate the design space are as important as any prescriptive design method. This work presents one of the underlying engineering technologies needed to leverage artificial intelligence approaches to thoroughly search the …
Validating Module Heuristics On Large Scale Products, Rachel Day, Robert B. Stone, Katie Grantham Lough
Validating Module Heuristics On Large Scale Products, Rachel Day, Robert B. Stone, Katie Grantham Lough
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Decreasing time and costs is a major objective in many businesses today. Including modularity in the early design phases can effectively decrease time spent on and costs associated with a project. the task of identifying modules within a product early in the design process (when decisions are less expensive) is made less daunting by using the techniques of functional modeling and module heuristics. This paper discusses the results of the initial efforts to verify the module heuristics on large products (products with functional models consisting of more than 30 sub-functions) since the module heuristics were originally developed on small products. …
Measurement Of Refractive Index Change Of Optical Fiber Core Induced By Femtosecond Laser Scanning, Y. Han, T. Wei, Hai-Lung Tsai, Hai Xiao
Measurement Of Refractive Index Change Of Optical Fiber Core Induced By Femtosecond Laser Scanning, Y. Han, T. Wei, Hai-Lung Tsai, Hai Xiao
Mechanical and Aerospace Engineering Faculty Research & Creative Works
We report a new method to measure the refractive index change in optical fiber core induced by femtosecond (fs) laser exposure. An in-line Fabry-Perot interferometer, serving as the measurement platform, is constructed on a commercial single-mode optical fiber by onestep femtosecond (fs) laser fabrication. A positive refractive index change is observed and measured accurately as the laser pulse energy surpasses the ablation threshold.
Observations Of Temporal Group Delays In Slow-Light Multiple Coupled Photonic Crystal Cavities, S. Kocaman, Xiaodong Yang, J. F. Mcmillan, M. B. Yu, D. L. Kwong, C. W. Wong
Observations Of Temporal Group Delays In Slow-Light Multiple Coupled Photonic Crystal Cavities, S. Kocaman, Xiaodong Yang, J. F. Mcmillan, M. B. Yu, D. L. Kwong, C. W. Wong
Mechanical and Aerospace Engineering Faculty Research & Creative Works
We demonstrate temporal group delays in coherently coupled high- Q multicavity photonic crystals, in an all-optical analog to electromagnetically induced transparency. We report deterministic control of the group delay up to 4x the single cavity lifetime in our room-temperature chip. Supported by three-dimensional numerical simulations and theoretical analyses, our multipump beam approach enables control of the multicavity resonances and intercavity phase, in both single and double transparency peaks. The standing-wave wavelength-scale photon localization allows direct scalability for chip-scale optical pulse trapping and coupled-cavity quantum electrodynamics.
Combined H∞-Feedback Control And Iterative Learning Control Design With Application To Nanopositioning Systems, Brian E. Helfrich, Chibum Lee, Douglas A. Bristow, Jingyan Dong, Srinivasa M. Salapaka, Placid M. Ferreira, X. H. Xiao, Andrew G. Alleyne
Combined H∞-Feedback Control And Iterative Learning Control Design With Application To Nanopositioning Systems, Brian E. Helfrich, Chibum Lee, Douglas A. Bristow, Jingyan Dong, Srinivasa M. Salapaka, Placid M. Ferreira, X. H. Xiao, Andrew G. Alleyne
Mechanical and Aerospace Engineering Faculty Research & Creative Works
This paper examines a coordinated feedback and feedforward control design strategy for precision motion control (PMC) systems. It is assumed that the primary exogenous signals are repeated; including disturbances and references. Therefore, an iterative learning control (ILC) feedforward strategy can be used. The introduction of additional non-repeating exogenous signals, including disturbances, noise, and reset errors, necessitates the proper coordination between feedback and feedforward controllers to achieve high performance. A novel ratio of repeated versus non-repeated signal power in the frequency domain is introduced and defined as the repetitive-to-non-repetitive (RNR) ratio. This frequency specific ratio allows for a new approach to …
Three-Dimensional Modeling Of Transport Phenomena And Their Effect On The Formation Of Ripples In Gas Metal Arc Welding, Z. H. Rao, J. Zhou, S. M. Liao, Hai-Lung Tsai
Three-Dimensional Modeling Of Transport Phenomena And Their Effect On The Formation Of Ripples In Gas Metal Arc Welding, Z. H. Rao, J. Zhou, S. M. Liao, Hai-Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Distinct, periodic arc-shaped ripples are observed on the surface of the weld bead in almost any welded components which have a significant effect on weld quality. This article presents the complex transport phenomena and their effect on the formation of ripples in three-dimensional moving gas metal arc welding. The transient distributions of the melt flow velocity and temperature in the weld pool, weld pool shape and dynamics, and solidified weld bead are calculated. It is found that the surface ripples are formed by the interplay between the up-and-down weld pool dynamics, caused mainly by the periodic droplet impingements, and the …
Effects Of Shielding Gas Compositions On Arc Plasma And Metal Transfer In Gas Metal Arc Welding, Z. H. Rao, S. M. Liao, Hai-Lung Tsai
Effects Of Shielding Gas Compositions On Arc Plasma And Metal Transfer In Gas Metal Arc Welding, Z. H. Rao, S. M. Liao, Hai-Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
This article presents the effects of shielding gas compositions on the transient transport phenomena, including the distributions of temperature, flow velocity, current density, and electromagnetic force in the arc and the metal, and arc pressure in gas metal arc welding of mild steel at a constant current input. The shielding gas considered includes pure argon, 75% Ar, 50% Ar, and 25% Ar with the balance of helium. It is found that the shielding gas composition has significant influences on the arc characteristics; droplet formation, detachment, transfer, and impingement onto the workpiece; and weld pool dynamics and weld bead profile. As …
Direct Numerical Simulation Of Hypersonic Turbulent Boundary Layers With Varying Freestream Mach Number, L. (Lian) Duan, I. Beekman, M. P. Mart́In
Direct Numerical Simulation Of Hypersonic Turbulent Boundary Layers With Varying Freestream Mach Number, L. (Lian) Duan, I. Beekman, M. P. Mart́In
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In this paper, the effects of freestream Mach number on the statistics and large-scale structures in compressible turbulent boundary layers are investigated using direct numerical simulations (DNS). DNS of turbulent boundary layers with nominal freestream Mach number ranging from 3 to 8 are performed. The validity of Morkovin's scaling, strong Reynolds analogy, and Walz's equation are assessed. We find that many of the scaling relations used to express compressible boundary layer statistics in terms of incompressible boundary layers still hold for the range of freestream Mach number considered. Compressibility effects are enhanced with increasing freestream Mach number but remain insignificant, …
Influence Of Interactions Between Turbulence And Radiation On Transmissivities In Hypersonic Turbulent Boundary Layers, A. M. Feldick, L. (Lian) Duan, M. F. Modest, M. P. Martín, D. A. Levin
Influence Of Interactions Between Turbulence And Radiation On Transmissivities In Hypersonic Turbulent Boundary Layers, A. M. Feldick, L. (Lian) Duan, M. F. Modest, M. P. Martín, D. A. Levin
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In the current paper, a high-fidelity large eddy simulation solver is coupled to our modified line-by-line radiative transport equation solver to study the effects of absorption turbulence-radiation interations in a hypersonic turbulent boundary layer, representative of the Orion CEV entering Earth's atmosphere, at peak heating condition. The turbulent and radiation fields represent extreme conditions typical of Orion, as the simulated boundary layer represents the region of high turbulence coupled to region of highest incident radiation. A simplification in the calculation of molecular spectra with a single temperature property database in allows for tractable calculation of spectral properties. A comparison of …
Direct Detection Of No Produced By High-Temperature Surface-Catalyzed Atom Recombination, Dušan A. Pejaković, Jochen Marschall, Lian Duan, Maria P. Martin
Direct Detection Of No Produced By High-Temperature Surface-Catalyzed Atom Recombination, Dušan A. Pejaković, Jochen Marschall, Lian Duan, Maria P. Martin
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The surface-catalytic recombination of oxygen and nitrogen atoms to form nitric oxide was confirmed by the direct detection of product NO molecules, using single-photon laser-induced fluorescence spectroscopy. Experiments were performed from room temperature to 1200 K in a quartz diffusion-tube sidearm reactor enclosed in a high temperature tube furnace. Atomic nitrogen was generated using a microwave discharge, and atomic oxygen was produced via the rapid gas-phase titration reaction N + NO → O + N2. The use of isotopically labeled titration gases 15N16O and 15N18O allowed for the unambiguous identification of nitric oxide produced by the O + N surface …
Guidance And Control For Chase Uav Via Sliding Mode Approach, Takeshi Yamasaki, S. N. Balakrishnan
Guidance And Control For Chase Uav Via Sliding Mode Approach, Takeshi Yamasaki, S. N. Balakrishnan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
This study focuses on integrated guidance and control for a chasing UAV against a maneuvering target. a sliding mode approach is selected to develop the integrated guidance and control using a full model of nonlinear, rigid body, 6 Degree-Of-Freedom equations of motion including nonlinear aerodynamics for the target-following capability and maneuverability enhancement against uncertain target maneuvers. Intermediate control variables for the integrated guidance and control system are carefully selected and approximated time derivatives of a sliding surface are applied such that a sliding surface structure is simple and sufficient to propagate the actuator input to the sliding surface in order …
Direct Numerical Simulation Of Hypersonic Turbulent Boundary Layers. Part 2. Effect Of Wall Temperature, L. (Lian) Duan, I. Beekman, M. P. Martín
Direct Numerical Simulation Of Hypersonic Turbulent Boundary Layers. Part 2. Effect Of Wall Temperature, L. (Lian) Duan, I. Beekman, M. P. Martín
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In this paper, we perform direct numerical simulation (DNS) of turbulent boundary layers at Mach 5 with the ratio of wall-to-edge temperature T w/T ℘ from 1.0 to 5.4 (Cases M5T1 to M5T5). The influence of wall cooling on Morkovin's scaling, Walz's equation, the standard and modified strong Reynolds analogies, turbulent kinetic energy budgets, compressibility effects and near-wall coherent structures is assessed. We find that many of the scaling relations used to express adiabatic compressible boundary-layer statistics in terms of incompressible boundary layers also hold for non-adiabatic cases. Compressibility effects are enhanced by wall cooling but remain insignificant, and the …
Measurement Sensitivity In Tapping-Mode Atomic Force Microscopy Using A Bi-Harmonic Drive Signal, Santosh R. Kodandarama, Douglas A. Bristow
Measurement Sensitivity In Tapping-Mode Atomic Force Microscopy Using A Bi-Harmonic Drive Signal, Santosh R. Kodandarama, Douglas A. Bristow
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In tapping mode atomic force microscopy, surface features are measured indirectly via the amplitude of the tapping cantilever. a change in surface profile is detectable only if it results in an amplitude change that is significant enough to be measured by the optics. Previous works have focused on improving sensitivity through the system's Q-factor, either by changing physical cantilever properties or using feedback control, but those approaches undesirably slow down the dynamic response. in this work we take a novel approach to sensitivity amplification by reshaping the tapping trajectory. by shaping the trajectory so that the probe spends a greater …