Engineering Commons^™

Retention Forces For Drops On Microstructured Superhydrophobic Surfaces, Shaur Humayun, R. Daniel Maynes, Julie Crockett, Brian D. Iverson

Faculty Publications

Accurate models of retention forces between drops and superhydrophobic (SH) surfaces are required to predict drop dynamics on the surface. This retention force is, in turn, useful in modeling heat transfer rates for dropwise condensation on a SH surface. Drop contact angle distribution and base area on SH surfaces are essential factors for predicting retention forces. The present work measures the contact angle distribution and base area shapes of various drop sizes over a wide range of solid fraction for inclined microstructured SH surfaces at the point of drop departure. Base area shape was found to be well approximated using …

Fatigue Damage Characterization By Surface Roughness And Instrumented Micro – Hardness Measurements, Suraj Sanjay Nikam

Masters Theses

Fatigue is an essential consideration in the design of high performance, safety-critical structures, and components, as fatigue failure constitutes more than 70% of failures in dynamically loaded components. This research aims to shed light on the effect of surface roughness on the micro-hardness in metals through experimental techniques (Part 1), the correlation between the traditional fatigue testing and instrumented cyclic micro-hardness testing to determine the material properties modeled by Ramberg - Osgood relationship(Part 2), and the effect of the fatigue damage on micro-hardness and surface roughness (Part 3).

For this research, Al 7075 - T651 and Al 6061 - T651 …

Mesoscale Modeling Of Shape Memory Alloys By Kinetic Monte Carlo–Finite Element Analysis Methods, Adam David Herron

Theses and Dissertations

A coupled kinetic Monte Carlo – Finite Element Analysis (kMC–FEA) method is developed with a numerical implementation in the Scalable Implementation of Finite Elements at NASA (ScIFEN). This method is presented as a mesoscale model for Shape Memory Alloy (SMA) material systems. The model is based on Transition State Theory and predicts the nonlinear mechanical behavior of the 1st order solid–solid phase transformation between Austenite and Martensite in SMAs. The kMC–FEA modeling method presented in this work builds upon the work of Chen and Schuh [1, 2]. It represents a “bottom-up” approach to materials modeling and could serve as a …

Design And Testing Of A Linear Compliant Mechanism With Adjustable Force Output, William Niemeier

USF Tampa Graduate Theses and Dissertations

This thesis presents a novel compliant mechanism with adjustable force output. The force comes from the bending of a rectangular cross section beam within the mechanism. By rotating this beam with a stepper motor, the force output of the mechanism changes. A model was made to simulate this mechanism, and a prototype was made based off of this data. A test apparatus was constructed around this mechanism, and a series of tests were performed. These tests adjusted parameters such as beam rotation speed and weight in order to characterize the system. Adjustments were made based on this information and the …

Simulation Of Hemiparetic Function Using A Knee Orthosis With Variable Impedance And A Proprioception Interference Apparatus, Christina-Anne Kathleen Lahiff

USF Tampa Graduate Theses and Dissertations

Individuals with stroke have neuromuscular weakness or paralysis on one side of the body caused by some muscles disengaging and overexciting other muscles. Hyperextension of the knee joint and complete lack of plantar flexion of the ankle joint are common symptoms of stroke. This thesis encompasses the simulation of hemiparetic function using both a knee orthosis with variable impedance, specifically in terms of stiffness and damping, and the Proprioception Interference Apparatus.

The section regarding the knee orthosis with variable impedance focuses on the creation and implementation of a small, lightweight, and adjustable orthotic device to be positioned around the knee …

Nonlinear Phenomena In A Column Of Liquid In A Rotating Manometer, S. Kelly

Dr. S. Graham Kelly

No abstract provided.

Energy Losses In Tires, Joseph Walter, F. Conant

Dr. Joseph D. Walter

Tire rotation is impeded by a drag force of 10 to 20 lb per 1000‐lb load in normal vehicle operation. The principal cause is hysteresis, which is a function of the viscoelastic properties of the rubber and cord components, the way these materials are used in the tire, and the way the tire is operated. The influence of material properties has been well documented, and many laboratory tests have been developed for their measurement. Of even greater importance to energy losses, however, is tire construction. This subject is developed by consideration of the forces and moments involved in tire operation …

Continuous Dynamic Modelling Of Bimorph Piezoelectric Cantilevered Actuators Considering Hysteresis Effect And Dynamic Behaviour Analysis

Faculty of Engineering University of Malaya

Bimorph Piezoelectric Cantilevered (BPC) actuators have been of increasing interest in micro-manipulation processes during recent years. Due to properties such as transverse vibration, the performance and manoeuvrability have considerably improved, compared with conventional longitudinal piezoelectric actuators. Therefore, dynamic modelling of such actuators has been the centre of attraction. For this purpose, a target point on the actuator, e.g. the cantilever end tip, is usually considered as the actuator output. One degree of freedom lumped and continuous type dynamic models have been considered in prior research works. These types of modelling lead to two significant issues. First, the effect of higher …

Modified Robust External Force Control With Disturbance Rejection With Application To Piezoelectric Actuators

Faculty of Engineering University of Malaya

In micromanipulation applications, controlling the force exerted on the object is of great importance. In such cases, any uncontrolled forces may damage the object or cause system failure. However, the presence of disturbances such as impedance uncertainties and hysteresis can strongly degrade force control performance and even lead to instability. Therefore, accurate force control when internal and external disturbances occur is a significant challenge. Conventional control methods usually have a number of restrictive conditions especially on the disturbance bounds. To rectify those issues, a modified robust disturbance rejection-based force control approach is proposed in this paper. For this purpose, an …

Material Characterization Of Nitinol Wires For The Design Of Actuation Systems, Sean P. Kennedy

Master's Theses

A series of tests were performed on nickel-titanium alloy wire, also known as nitinol, to determine the plausibility of designing an actuator using this wire as the method of actuation. These tests have been designed to fully characterize how the wire behaves under steady state and transient conditions allowing for a specific wire selection to be made given known actuator specifications which will result in an efficient design. The wire transient data can be used to design a controller which reduces the actuation time. The research done for the overall project covers a wide scope including wire hysteresis, nitinol transition …

Universal Scaling And Intrinsic Classification Of Electro-Mechanical Actuators, Sambit Palit, Ankit Jain, Muhammad A. Alam

Birck and NCN Publications

Actuation characteristics of electromechanical (EM) actuators have traditionally been studied for a few specific regular electrode geometries and support (anchor) configurations. The ability to predict actuation characteristics of electrodes of arbitrary geometries and complex support configurations relevant for broad range of applications in switching, displays, and varactors, however, remains an open problem. In this article, we provide four universal scaling relationships for EM actuation characteristics that depend only on the mechanical support configuration and the corresponding electrode geometries, but are independent of the specific geometrical dimensions and material properties of these actuators. These scaling relationships offer an intrinsic classification for …

Three-Phase Contact Line Phenomena In Droplets On Solid And Liquid Surfaces: Electrocapillary, Pinning, Wetting Line Velocity Effect, And Free Liquid Surface Deformation, Roxana Shabani

Electronic Theses and Dissertations

In this dissertation physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wetting line) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL) phenomena which encompass the wetting line energy (WLE) or pinning, the wetting line velocity (WLV), and the contact angle hysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the interfacial phenomena such as the air film lubrication effect and the liquid free surface deformation were taken into account to explain the dual equilibrium …

Static And Dynamic Components Of Droplet Friction, Peter Robert Griffiths

USF Tampa Graduate Theses and Dissertations

As digital microfluidics has continued to mature since its advent in the early 1980's, an increase in new and novel applications of this technology have been developed. However, even as this technology has become more common place, a consensus on the physics and force models of the motion of the contact line between the fluid, substrate, and ambient has not been reached. This uncertainty along with the dependence of the droplet geometry on the force to cause its motion has directed much of the research at specific geometries and droplet actuation methods.

The goal of this thesis is to help …

Characterization And Biomechanical Analysis Of The Human Lumbar Spine With In Vitro Testing Conditions, Dean K. Stolworthy

Theses and Dissertations

Biomechanical testing of cadaveric spinal segments forms the basis for our current understanding of healthy, pathological, and surgically treated spinal function. Over the past 40 years there has been a substantial amount of data published based on a spinal biomechanical testing regimen known as the flexibility method. This data has provided valuable clinical insights that have shaped our understanding of low back pain and its treatments. Virtually all previous lumbar spinal flexibility testing has been performed at room temperature, under very low motion rates, without the presence of a compressive follower-load to simulate upper body weight and the action of …

Dual-Stage Thermally Actuated Surface-Micromachined Nanopositioners, Neal B. Hubbard

Theses and Dissertations

Nanopositioners have been developed with electrostatic, piezoelectric, magnetic, thermal, and electrochemical actuators. They move with as many as six degrees of freedom; some are composed of multiple stages that stack together. Both macro-scale and micro-scale nanopositioners have been fabricated. A summary of recent research in micropositioning and nanopositioning is presented to set the background for this work. This research project demonstrates that a dual-stage nanopositioner can be created with microelectromechanical systems technology such that the two stages are integrated on a single silicon chip. A nanopositioner is presented that has two stages, one for coarse motion and one for fine …

Bistable Operation Of A Two-Section 1.3-Mm Inas Quantum Dot Laser—Absorption Saturation And The Quantum Confined Stark Effect, Xiaodong Huang, A. Stintz, Hua Li, Audra Rice, G. T. Liu, L.F. Lester, Julian Cheng, K.J. Malloy

Faculty Publications

Room temperature, continuous-wave bistability was observed in oxide-confined, two-section, 1.3- m quantum-dot (QD) lasers with an integrated intracavity quantum-dot saturable absorber. The origin of the hysteresis and bistability were shown to be due to the nonlinear saturation of the QD absorption and the electroabsorption induced by the quantum confined Stark effect.

An Investigation Of A Computer Technique For Determining The Characteristic Parameters Of A Viscoelastic Model With Hysteresis Effects From Transient Experimental Data, Stephen Jack Clark

Theses and Dissertations

The object of this work was to develop a computer technique for determining the characteristic parameters of spring-mass system with hysteresis effects from transient experimental data. The technique was intended to be utilized to determine the parameters of models of systems where complex geometry and rate dependent properties would make a determination of the model parameters most difficult, and where the parameters typically obtained from static test would not characterize the rate dependent properties accurately.

Investigation Of Aerodynamic Hysteresis, Gerald Heber Peterson

Theses and Dissertations

The word hysteresis is derived from a Greek word meaning "to lag 'behind". As specifically applied to fluid flow around bodies with transient angles of attack in and near the stall region, "aerodynamic hysteresis" is used to describe the effect of delay in boundary layer separation and reattachment upon the lift, drag and pitching moment. Experimental work done on airfoils by H. Studer showed that for increasing angles of attack flow "separation is delayed to an angle of attack appreciably greater than that for a stationary airfoil. On the return movement, re-establishment of a smooth flow is also delayed." [1]* …