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Full-Text Articles in Mechanical Engineering

Implementing A Linear Quadratic Spacecraft Attitude Control System, Daniel Kolosa Dec 2015

Implementing A Linear Quadratic Spacecraft Attitude Control System, Daniel Kolosa

Master's Theses

This thesis implements a linear quadratic attitude control system for a low-thrust spacecraft. The goal is to maintain spacecraft alignment with a time-varying thrust vector needed for trajectory change maneuvers. A linear quadratic attitude control approach is used to maintain spacecraft pointing throughout flight. This attitude control strategy uses the thrust-acceleration input obtained from a linear quadratic optimal trajectory control model that simulates the trajectory of a spacecraft in orbit maneuvers. This attitude model simulates a CubeSat, a small satellite that is equipped with a low-thrust propulsion and attitude control system. An orbit raising and a plane change scenario is ...


The Effect Of Sensor Mass, Sensor Location, And Delamination Location Of Different Composite Structures Under Dynamic Loading, Albert Darien Liu Jan 2013

The Effect Of Sensor Mass, Sensor Location, And Delamination Location Of Different Composite Structures Under Dynamic Loading, Albert Darien Liu

Master's Theses and Project Reports

This study investigated the effect of sensor mass, sensor location, and delamination location of different composite structures under dynamic loading. The study pertains to research of the use of accelerometers and dynamic response as a cost-effective and reliable method of structural health monitoring in composite structures. The composite structures in this research included carbon fiber plates, carbon fiber-foam sandwich panels, and carbon-fiber honeycomb sandwich panels. The composite structures were manufactured with the use of a Tetrahedron MTP-8 heat press. All work was conducted in the Cal Poly Aerospace Structures/Composites Laboratory. Initial delaminations were placed at several locations along the ...


Improving The Aerospace Capstone Design Experience Through Simulation Based Learning, Wm. Michael Butler, Janis P. Terpenny, Richard M. Goff, Rajkumar S. Pant, Heidi M. Steinhauer Jan 2012

Improving The Aerospace Capstone Design Experience Through Simulation Based Learning, Wm. Michael Butler, Janis P. Terpenny, Richard M. Goff, Rajkumar S. Pant, Heidi M. Steinhauer

Center for e-Design Publications

A key role of universities is to prepare students to work in their chosen profession upon completion of their degree program. Engineering capstone design courses are often the only required courses that challenge students to draw on nearly all of the students’ previous collegiate learning experiences and to synthesize and apply these to creating a new solution to an engineering problem. Aside from internship and co-op experiences, these are often the first courses that expose engineering students to some of the technical and political issues that they will often face in their professional engineering careers. Industry often looks at these ...


Nondestructive Detection And Characterization Of Damages In Honeycomb Composite Structures, Cory Foreman Jan 2008

Nondestructive Detection And Characterization Of Damages In Honeycomb Composite Structures, Cory Foreman

Retrospective Theses and Dissertations

This thesis discusses many existing methods of nondestructive evaluation used on honeycomb structures ranging from ultrasonic transduction to various low frequency techniques. The focus, however, is given to a newly developed technique based on hysteresis effects in force-displacement curves. The area enclosed by the hysteresis loop represents the amount of energy absorbed by the sample during the loading and unloading phases. It is believed that the cause of the energy absorption is due to increased internal frictional loses which occur when the sample is damaged. The loop area was found to correlate well with the level of damage sustained by ...


Numerical Investigation Of Effect Of Buoyancy On The Wake Of A Heated Cylinder In Contra Flow, Khyati B. Varma Jan 2007

Numerical Investigation Of Effect Of Buoyancy On The Wake Of A Heated Cylinder In Contra Flow, Khyati B. Varma

Retrospective Theses and Dissertations

Flow over a cylinder is a classically and practically interesting problem. A number of studies focus on the vortex shedding and wake instability of an unheated cylinder. Inspite of its applications flow over a heated cylinder operating in a mixed convection region has received very little attention. The present study aims at the numerical investigation of unsteady heat transfer for a laminar flow past a circular cylinder with small aspect ratio (L/d=7) or finite spanwise length with no-slip wall conditions. A circular cylinder is exposed to approaching flow stream in the direction of gravity or opposing the direction ...


A Technique For Shape Optimization Of Ducted Fans, David Firel Schaller Jan 2007

A Technique For Shape Optimization Of Ducted Fans, David Firel Schaller

Retrospective Theses and Dissertations

Ducted fans have found renewed interest particularly in the field of micro aerial vehicles. The complex flow interactions between the rotor, shroud and nacelle hinder the design of optimal lifting duct shapes. Further, the optimum duct shape changes with freestream velocity and rotor configuration. Analytic equations are insufficient to model and predict the performance of ducted fans, yet general CFD solvers are too slow to be used for optimization. For this research, a genetic algorithm is coupled with a simplified CFD solver based on a momentum source rotor model, creating an efficient shape optimization technique for ducted fan systems. The ...


Experimental Observations Of Shear Band Nucleation And Propagation In A Bulk Metallic Glass Using Wedge-Like Cylindrical Indentation , Antonia Maki Antoniou Jan 2006

Experimental Observations Of Shear Band Nucleation And Propagation In A Bulk Metallic Glass Using Wedge-Like Cylindrical Indentation , Antonia Maki Antoniou

Retrospective Theses and Dissertations

Bulk metallic glasses (BMGs), or amorphous metal alloys, have a unique combination of properties such as high strength, large elastic strain limit (up to 2%), corrosion resistance and formability. These unique properties make them candidates for precision mechanical elements, hinge supports, contact surfaces as well as miniaturized systems (MEMS). However, their limited ductility hinders further realizations of their industrial potential. Under uniaxial tension tests, metallic glass fails in a brittle manner with unstable propagation of a single shear band. There is a need to understand the conditions for shear band nucleation and propagation in order to achieve a superior material ...


Ultrasonic System Models And Measurements , Ana Lilia Lopez-Sanchez Jan 2005

Ultrasonic System Models And Measurements , Ana Lilia Lopez-Sanchez

Retrospective Theses and Dissertations

In this work ultrasonic models and measurements are used to characterize a number of the important elements of an ultrasonic measurement system as well as the entire system. Ultrasonic measurement models for predicting the response from reference reflectors are described, including a new ultrasonic measurement model recently developed to simulate the ultrasonic response of an infinitely long cylindrical cavity. The reference reflectors considered include spherical pores, flat-bottom holes and side-drilled holes, which are commonly used in nondestructive evaluation studies. These reflectors are employed in a series of modeling/experimental studies to assess where approximate and more exact scattering models are ...


A Numerical Approach To Model And Predict The Energy Absorption And Crush Mechanics Within A Long-Fiber Composite Crush Tube , Leon Pickett Jr. Jan 2005

A Numerical Approach To Model And Predict The Energy Absorption And Crush Mechanics Within A Long-Fiber Composite Crush Tube , Leon Pickett Jr.

Retrospective Theses and Dissertations

Past research has conclusively shown that long fiber structural composites possess superior specific energy absorption characteristics as compared to steel and aluminum structures. However, destructive physical testing of composites is very costly and time consuming. As a result, numerical solutions are desirable as an alternative to experimental testing. Up until this point, very little numerical work has been successful in predicting the energy absorption of composite crush structures. This research investigates the ability to use commercially available numerical modeling tools to approximate the energy absorption capability of long-fiber composite crush tubes. This study is significant because it provides a preliminary ...


Ultrasonic Guided Waves In Composite Plates: A Study Of Interface Bond Condition And Material Properties Determination With Broadband Focused Air-Coupled Ultrasounds , Sorin Vasile Teles Jan 2004

Ultrasonic Guided Waves In Composite Plates: A Study Of Interface Bond Condition And Material Properties Determination With Broadband Focused Air-Coupled Ultrasounds , Sorin Vasile Teles

Retrospective Theses and Dissertations

This work is focused on two important aspects of the study of the composite materials: characterization of interface bonding in layered composites and evaluation of elastic material properties in air-coupled experiments.;The characterization of interface condition in a layered composite is critical to understand the behavior of the material under various stress situations. A closed disbond, alternatively known as zero-volume disbond or " kissing-disbond" (KSD) is difficult to detection by conventional normal-incidence ultrasonic nondestructive evaluation (NDE) methods. Such undetected defect may be dangerous because it can produce a significant decrease in structural integrity or lead to a catastrophic failure under certain ...


Stochastic Models For Material Removal Rate (Mrr) In Chemical Mechanical Planarization (Cmp) Process , Changxue Wang Jan 2004

Stochastic Models For Material Removal Rate (Mrr) In Chemical Mechanical Planarization (Cmp) Process , Changxue Wang

Retrospective Theses and Dissertations

Most of the previous work related to the prediction of the material removal rate (MRR) in CMP process to date has been concerned with the ideal case, wherein there is no randomness associated with either the pad or the slurry. In the work of this dissertation, we investigated the material removal rate (MRR) by taking some of the randomness into account, including randomly varying pad asperity heights and/or randomly varying slurry particle sizes.;The MRR decay phenomenon as well as the MRR variation on the slurry particle size distribution has gained more and more attention in CMP industry. However ...


An Adaptively-Refined Quadtree Grid Method For Incompressible Flows , Stuart Scott Ochs Jan 1998

An Adaptively-Refined Quadtree Grid Method For Incompressible Flows , Stuart Scott Ochs

Retrospective Theses and Dissertations

A quadtree grid method used in conjunction with a pressure-based flow solution algorithm for the incompressible Navier-Stokes equations is presented. Two different flow solution methods are studied, each a cell-centered, primitive variable, finite volume procedure based on the SIMPLE algorithm. Solution adaptive grid refinement is used to resolve high-gradient flow regions;The quadtree grid, which is composed of quadrilateral cells that can be subdivided into four quadrants, is examined, and the quadtree data structure, and its advantages when used in the numerical solution of the Navier-Stokes equations, is discussed;Two flow solution methods, including their theoretical formulations, solution procedures, and ...


Aerodynamics Study Of The Flowfield At A Shelterbelt , Chien-Jung Yu Jan 1997

Aerodynamics Study Of The Flowfield At A Shelterbelt , Chien-Jung Yu

Retrospective Theses and Dissertations

Shelterbelts are used world-wide for such purposes as reduction of soil errosion, control of snow drift, and provision of an effective agrometeorological method of field microclimate management and yield enhancement. Whether performing a wind tunnel test, conducting a field observation, or implementing a numerical simulation to investigate shelterbelt effects, researchers are more interested in an optimum reduction in a thin air lasier near the ground on the leeside of the shelterbelt rather than total wind-speed reduction in the whole flowfield. The purpose of this study is to formulate a Navier-Stokes based scheme to simulate the turbulent aerodynamic characteristics of a ...


Flexible Composite Propeller Design Using Constrained Optimization Techniques , Abdul Monuem Khan Jan 1997

Flexible Composite Propeller Design Using Constrained Optimization Techniques , Abdul Monuem Khan

Retrospective Theses and Dissertations

An investigation of a conventional propeller, made from composite materials, was conducted in which its characteristics were studied under quasi-static aerodynamic loading. Also, optimized designing of a composite propeller was performed for various constrained and unconstrained design objectives. Only symmetric ply stacking sequences were considered to eliminate the effect of centrifugal force on the propeller. Results show that the ply stacking sequence has an effect on the propeller characteristics of a conventional propeller. Proper stacking sequence of the composite propeller improves its performance as compared to its metallic counterpart. An improvement of about 47% in the propeller thrust coefficient was ...


Effects Of Ballistic Impact Damage On Thin And Thick Composites , Zahid Iqbal Baig Jan 1997

Effects Of Ballistic Impact Damage On Thin And Thick Composites , Zahid Iqbal Baig

Retrospective Theses and Dissertations

Use of composite materials is growing rapidly because they offer weight reduction, durability and better fatigue life as compared to metals. Despite of their advantages, there are some problems associated with the use of composites, and impact resistance is one of the weak areas in composites. Low speed impact damage has been the focus of attention of researchers for quite some time but studies of high speed impact damage is still in its preliminary stages. In this study, effects of ballistic impact on thin and thick composite panels were investigated. Damage due to high speed impact in composites is a ...


Magnetostrictive Vibration Generation System, Alison B. Flatau, David Hall Apr 1996

Magnetostrictive Vibration Generation System, Alison B. Flatau, David Hall

Iowa State University Patents

A shaker with a Terfenol-D rod actuator includes a mass coupled to both ends of the rod through a spring seat, a spring seat/adjuster and a spring washer. The actuator is mounted inside a cylindrical coil, which in turn is mounted inside a cylindrical permanent magnet, which in turn is mounted inside a cylindrical housing. An electrical drive system provides a predetermined excitation signal to the coil to cause the rod to vibrate under the influence of the magnetic field generated by the coil. One embodiment features a vibrating mass on one end of the rod. An implantable shaker ...


A Methodology To Investigate Automobile Handling And Stability , John Samsundar Jan 1996

A Methodology To Investigate Automobile Handling And Stability , John Samsundar

Retrospective Theses and Dissertations

The problems investigated in this study are (1) the design and analysis of strategies to control the rear wheel steering on four wheel steering automobiles; and (2) the estimation of lateral stability regions for a nonlinear 2 DOF vehicle;Rear Wheel Controllers are developed using linear optimal control theory under the assumption that all states are available, however, this assumption is rarely true. A methodology is then developed to use a minimum number of measurable states to obtain suboptimal rear wheel steering controllers which are less expensive and could be practically implemented. The methodology is based on achieving zero phase ...


Unsteady Incompressible Viscous Flow Past Stationary, Pitching Or Oscillating Airfoil Leading Edges , Rajesh Bhaskaran Jan 1996

Unsteady Incompressible Viscous Flow Past Stationary, Pitching Or Oscillating Airfoil Leading Edges , Rajesh Bhaskaran

Retrospective Theses and Dissertations

The objective of this study is to obtain a better understanding of the fundamental mechanisms governing the unsteady flow past airfoil leading edges. The approach taken is to study the leading edge in isolation and to use the semi-infinite parabola as a model for the leading-edges of conventional airfoils. Numerical solution methods were developed and implemented for the two-dimensional, unsteady, incompressible Navier-Stokes and boundary-layer equations for arbitrary motion of the parabola. Navier-Stokes solutions of the impulsively-started flow past a stationary parabola and of the flow past a pitching parabola compare well with the corresponding computational results for the NACA0012 airfoil ...


Toward All Speeds Euler/Navier-Stokes Flow Solutions On Unstructured Meshes , Laith Abdul Jabbar Zori Jan 1996

Toward All Speeds Euler/Navier-Stokes Flow Solutions On Unstructured Meshes , Laith Abdul Jabbar Zori

Retrospective Theses and Dissertations

This study presents a time-marching, density-based flow solution method at all speeds for Euler and Navier-Stokes equations on unstructured meshes. For two-dimensional flow problems, an explicit Runge-Kutta multi-stepping scheme and an implicit Gauss-Seidel time-iterative scheme are developed. Both methods solve the flow equations on cell-vertex, median-dual, triangular meshes. For three-dimensional flow problems, an explicit Runge-Kutta time-stepping scheme is developed. A cell-vertex, median-dual, tetrahedral discretization is utilized in tessellating the three-dimensional computational domain;Flow discontinuities, such as shocks, are accurately captured using a higher-order reconstruction scheme based on Roe's upwind flux-difference-splitting. The viscous flux terms are computed efficiently by using ...


An Interacting Boundary Layer Method For Unsteady Compressible Flows , Robert Edwin Bartels Jan 1994

An Interacting Boundary Layer Method For Unsteady Compressible Flows , Robert Edwin Bartels

Retrospective Theses and Dissertations

A time accurate compressible interactive boundary layer procedure for airfoils using the quasi-simultaneous method of Veldman is developed. It couples the high frequency transonic small disturbance equation with the complete set of unsteady compressible boundary equations in Levy-Lees variable form, using a pseudo-time derivative of displacement thickness for enhanced stability. Included is a simple procedure for time accurately updating the viscous wake location. The basis of the interaction is an extension of the asymptotic matching condition of Davis for unsteady compressible interaction. This analysis identifies several possible unsteady transonic separation structures and highlights the importance of the pseudo-time derivative in ...


Design Of A Wing Section In Ground Effect: Application To High Speed Ground Transportation , Christoph Hiemcke Jan 1994

Design Of A Wing Section In Ground Effect: Application To High Speed Ground Transportation , Christoph Hiemcke

Retrospective Theses and Dissertations

This dissertation attempts to fully explain the aerodynamic ground effect phenomenon, which occurs when a wing flies over a nearby plane. The long-term motivation is to determine the feasibility of a train that achieves aerodynamic levitation above a flat guideway. Such a train would rely exclusively on lifting surfaces, rather than on steel wheels, lifting fans, or magnetic fields.;As a first step in the study of an aerodynamically suspended train, a wing section must be designed. This dissertation focuses on the preliminary design and the experimental investigation of a two-dimensional airfoil in ground effect. For application to high-speed ground ...


Computation Of The Integrated Aerodynamic And Propulsive Flowfields Of A Generic Hypersonic Space Plane , Ganesh Wadawadigi Jan 1993

Computation Of The Integrated Aerodynamic And Propulsive Flowfields Of A Generic Hypersonic Space Plane , Ganesh Wadawadigi

Retrospective Theses and Dissertations

A new upwind, parabolized Navier-Stokes (PNS) code has been developed to compute two- and three-dimensional (3-D) chemically reacting, turbulent flows with hydrogen-air chemistry. The code is a modification of the 3-D upwind PNS (UPS) airflow code. The code solves the PNS equations using a finite-volume, upwind, TVD (Total Variation Diminishing) method based on Roe's approximate Riemann solver that has been modified to account for nonequilibrium effects. The fluid medium is assumed to be a chemically reacting mixture of thermally perfect (but calorically imperfect) gases in thermal equilibrium. Two turbulence models have been incorporated into the code including an algebraic ...


A Numerical Investigation Of Laminar Airfoil Stall , Daniel Wayne Black Jan 1993

A Numerical Investigation Of Laminar Airfoil Stall , Daniel Wayne Black

Retrospective Theses and Dissertations

The details of an interacting boundary layer algorithm capable of calculating large scale laminar separation past airfoils at low speeds is given. Rationale behind various convergence acceleration methods is given. It is shown that linear based acceleration methods are limited to 50% savings in convergence rate. A nonlinear extrapolation method is proposed and tested on two simple model problems. Savings exceed the 50% limitation of the previous methods. Boundary layer results for laminar flow past symmetric airfoils at zero incidence are presented as a test of the methods. Leading edge marginal separation results at finite Reynolds numbers are presented. Richardson ...


A Dynamically Adaptive Mesh Method For Internal Flows , John William Slater Jan 1992

A Dynamically Adaptive Mesh Method For Internal Flows , John William Slater

Retrospective Theses and Dissertations

A dynamic solution adaptive mesh method was implemented into a finite-volume numerical method for solving unsteady flowfields described by the two-dimensional, unsteady, Navier-Stokes and Euler equations. The objective was to improve the resolution and accuracy of solutions which contained flow gradients which varied in strength and position with time. Variational principles were used to formulate the mesh equations with which meshes were generated to have the desired smoothness, orthogonality, and volume adaption qualities. The adaption of the mesh to the flow solution was driven by the presence of flow gradients. The dynamics of the mesh was accounted for in the ...


Propagation Of Elastic Waves Through Inhomogeneous, Anisotropic Materials , Ali Minachi Jan 1992

Propagation Of Elastic Waves Through Inhomogeneous, Anisotropic Materials , Ali Minachi

Retrospective Theses and Dissertations

The recent advances in the field of ultrasonic nondestructive inspection have demanded a more precise knowledge of the propagation of sound beams within materials. Quantitative models for propagation of ultrasonic fields from a transducer can be used as tools to both analyze the inspection data and to predict inspection results. An approximate Gauss-Hermite model was developed a few years ago to predict the ultrasonic fields radiated into isotropic and anisotropic materials, through planar or simply curved interfaces by focused or unfocused transducers. The paraxial approximation used in the development of that model has allowed many functions to be evaluated analytically ...


Use Of The Conventional And Tangent Derivative Boundary Integral Equations For The Solution Of Problems In Linear Elasticity , Karim Heinz Muci Küchler Jan 1992

Use Of The Conventional And Tangent Derivative Boundary Integral Equations For The Solution Of Problems In Linear Elasticity , Karim Heinz Muci Küchler

Retrospective Theses and Dissertations

Regularized forms of the traction and tangent derivative boundary integral equations of elasticity are derived for the case of closed regions. The hypersingular and strongly singular integrals of the displacement gradient representation are regularized independently, through identities of the fundamental solution and its various derivatives, before the boundary integral equations are formed. Besides the displacements and the tractions, only the tangential derivatives of the displacements evaluated at the singular point appear in the regularized equations making them well suited for numerical treatment. The regularization of the hypersingular integrals demands that the displacement components have Holder continuous first derivatives at the ...


The Influence Of Turbulence On Combustion In Open Pre-Mixed Flames , Eldon Stanley Powell Jan 1980

The Influence Of Turbulence On Combustion In Open Pre-Mixed Flames , Eldon Stanley Powell

Retrospective Theses and Dissertations

No abstract provided.