Browsing by Author "Dick, Andrew J"

Now showing 1 - 7 of 7
  • Thumbnail Image
    Item
    Analytical investigation of vibration attenuation with a nonlinear tuned mass damper
    (2015-04-24) Atzil, Aaron M; Dick, Andrew J; Ghorbel, Fathi H; O'Malley, Marcia K; Nagarajaiah, Satish
    Vibration attenuation devices are used to reduce the vibrations of various mechanical systems and structures. In this work, an analytical method is proposed to provide the means to investigate the influence of system parameters on the dynamic response of a system. The method of multiple scales is used to calculate an approximate broadband solution for a two degree-of-freedom system consisting of a linear primary structure and a nonlinear tuned mass damper. The model is decoupled, approximate analytical solutions are calculated, and then they are combined to produce the desired frequency-response information. The approach is initially applied to a linear two degree-of-freedom system in order to verify its performance. The approach is then applied to the nonlinear system in order to study how varying the values of parameters associated with the nonlinear absorber affect its ability to attenuate the response of the primary structure. Finally, the analytical solution is compared to a numerical solution in order to determine how well it approximates the nonlinear system frequency-response.
  • Thumbnail Image
    Item
    Clinical Evaluation of an Upper Limb Exoskeleton for Rehabilitation After Incomplete Spinal Cord Injury
    (2015-04-21) Fitle, Kyle D; O'Malley, Marcia K.; Dick, Andrew J; Kortum, Philip T
    In recent years robotic rehabilitation has emerged as an effective rehabilitation tool for motor impairment caused by multiple types of injuries and ailments. Incomplete spinal cord injury (SCI) is one of the injury types which is a prime candidate for robotic rehabilitation, but this field is relatively young and unexplored. The MAHI Exo II is a five degree-of-freedom (DOF) robotic exoskeleton which was designed for rehabilitation of the upper-limb following SCI or stroke. Upper-limb impairment is one of the factors which SCI patients rate as most significant in their post-injury decrease in quality of life. Therefore, the MAHI Exo II has the potential to make strides in improving the quality of life of patients in novel ways. This thesis presents research which has been done towards this aim. The first section presents a study on incomplete SCI rehabilitation with the MAHI Exo II. This study used the robotic system to provide resistance therapy for elbow flexion/extensioin, forearm pronation/supination, wrist flexion/extension, and wrist radial/ulnar deviation. The robot was also used to record position data in a backdriving-evaluation mode in order to analyze the change in subject movement quality over the course of therapy using several robotic quality of movement metrics. Subject improvement was also measured by standard clinical impairment measures used for SCI. Ten subjects enrolled in the study and eight finished the entire protocol. The results of this study spurred further research into more effective control and treatment strategies for the MAHI Exo II. In the second portion of this thesis, I present details on the Assist-as-Needed rehabilitation study. This experiment sought to apply assistive therapy with the MAHI Exo II using a novel adaptive control strategy and compare it to a non-adaptive controller in a parallel controlled study. This type of comparison has not been done before for robotic rehabilitation. The assistive nature of the controller allowed a wider inclusion criteria for incomplete SCI. The same joints were trained in this study and most of the same clinical and robotic measures were used to evaluate motor ability improvement. One of the secondary features of the study design is the sequential group assignment with co-variates minimization. The study is currently in progress at the time of this writing, but some preliminary results are presented in this section.
  • Thumbnail Image
    Item
    Hardware- versus Human-centric Assessment of Rehabilitation Robots
    (2015-04-20) Rose, Chad Gregory; O'Malley, Marcia K.; Ghorbel, Fathi H; Dick, Andrew J
    Individuals with disabilities arising from neurological injury require rehabilitation of the distal joints of the upper extremities to regain the ability to independently perform activities of daily living (ADL). Robotic rehabilitation has been shown to effectively conduct high intensity, long duration therapy and quantitatively assess the effects of therapy. This thesis presents methods and results for validating rehabilitation devices for training and assessment. Traditionally, methods for validating rehabilitation robots relied on robotic characterizations, which enables comparison of different designs' performance independent of a human user. An example of this method is presented here, in particular quantifying the torque output, range of motion, closed loop position performance, and high spatial resolution of two rehabilitation devices. However, these traditional validation methods do not assess the effect wearing the robot has on the user, and a new assessment method has been developed to address this shortcoming of traditional methods. A novel hand and wrist device was assessed through kinematic analysis of synergistic movements, as quantified by velocity- and position-dependent metrics. This experimental approach is promising for the characterization of multi-articular wearable robots as measurement tools in robotic rehabilitation. Together, the two methods presented can be used to validate rehabilitation robotic devices.
  • Thumbnail Image
    Item
    High fidelity numerical study of nonlinear impact wave propagation: methods, analysis, and applications
    (2014-11-06) Liu, Yu; Dick, Andrew J; Akin, John E; Stanciulescu, Ilinca
    Various systems and structures are subjected to impact loading in industrial and military applications. Many of these impact loads have very high magnitudes and very short durations, resulting in high frequency content. Under some conditions, the response to these loading conditions can be significantly influenced by nonlinearities. The goal of this thesis is to develop new tools for studying the nonlinear wave propagation which can result from this extreme impact loading and provide an in-depth understanding of the underlying physical process. It consists of analytical, numerical, and experimental studies. Two new numerical methods are developed for high fidelity simulation of nonlinear wave propagations: the alternating frequency-time finite element method (AFT-FEM) and the alternating wavelet-time finite element method (AWT-FEM). A perturbation based approach is developed to derive analytical formula of the wavenumber for one-dimensional rod model. By employing these numerical and analytical methods, numerical simulations of wave propagations in both infinite and finite domains for one-dimensional and two-dimensional structures are conducted to explore nonlinear behaviors in the responses. Experimental efforts are also made to verify numerical results of impact wave propagation. Through comparison with other existing numerical approaches, the advantages of AWT-FEM in computational efficiency and high fidelity are demonstrated and the method is employed for applications of nonlinear force identification and drill-string stability monitoring.
  • Thumbnail Image
    Item
    Magnetic Flux Leakage Sensing: Modeling & Experiments
    (2015-07-20) Trevino Garcia, David A; Ghorbel, Fathi Hassan; Dick, Andrew J; Clark, John W; O'Malley, Marcia; Dutta, Sushant
    Nondestructive evaluation (NDE) is the inspection of samples for physical defects without altering the sample in question in any aspect. Magnetic Flux Leakage (MFL) has become one of the most widely used NDE techniques in robotic inspection of energy pipelines to prevent catastrophic failures. The MFL technique uses a magnetic field to magnetize ferromagnetic materials and correlates anomalies in the uniform field level to defects in the structure. Defect detection using the MFL technique is a mature area of work. However, defect characterization is an open research problem that can be decomposed into the Forward and Inverse Problems. The first problem deals with the characterization of the MFL signal for known defect shapes and dimensions, while the second one deals with the characterization of the defect shape from a known MFL signal. Several aspects of the MFL technique are not well understood yet, like the interplay of the MFL field for 3-dimensional defects. Another aspect that is not clear yet is the spatial properties of the MFL field components produced by complex 3-dimensional defect shapes. This dissertation addresses three issues identified with the MFL Forward Problem. An analytical 3-dimensional MFL model based on the Magnetic Dipole Model (MDM) and derived from Maxwell’s equations is presented. Under specific conditions, the magnetic field generated by a surface-breaking defect can be mathematically described as if it is caused by magnetic charges on the surface of the defect; such phenomenon can be described through Maxwell’s equations. The improved MDM characterizes the magnetic charges on the surface of the defect by using two parameters instead of one. Consequently, the MFL Forward Problem of complex defect shapes can be solved through the application of the improved model. Likewise, this thesis also studies the nature of the MFL signals in order to have a deep understanding of the Forward Problem. Therefore, a study of the correlation between the MFL signals (axial, radial, and tangential) through the improved MDM is addressed. The analysis exhibits the existence of a correlation between the three components of the MFL signal under some conditions. These results open more avenues in the field to better understand the physics of the MFL phenomenon. Hence, a methodology for the approximation of the behaviors of two MFL signal components from one extracted component is addressed. Additionally, another important approach to the MFL Forward Problem is conducted through experimentation. This dissertation explores a revolutionary 2-D type of sensing technology for application to MFL inspection known as Magneto Optical (MO) film. The feasibility of using the MO sensing in the MFL technique is presented through the development of an analytical model. Experimental and simulation validations are presented for the three approaches related to the MFL Forward Problem. Finally, this dissertation discusses the impact that these different contributions make toward solving the Inverse Problem.
  • Thumbnail Image
    Item
    Modeling and Analysis of an In-line Pump Jet Thruster for Swimming Robots
    (2015-04-24) Kirmizi, Mehmet; Ghorbel, Fathi Hassan; Akin, John E.; Dick, Andrew J
    Nowadays, underwater robots play a significant role in many aspects of industry such as mine hunting, sea floor mapping, sub-sea pipeline construction and pipe surveys. Ever increasing demand on better control systems of underwater robots ignites engineers on modeling the systems for perfection. Since they are the lowest chain of the control problem, yet the most important ones. Thrusters are the most crucial parts of the underwater robot actuation. The need for maneuvering precision, for small and fast dynamic positioning, for precise motion and position control and for station keeping made developments of thruster modeling inevitable. The fundamental difficulty in modeling of a thruster is that axial flow velocity is an unmeasurable state, yet the model depends on that variable. This work addresses this difficulty. It explores the dynamics of in-line pump jet thrusters which are used for underwater robotic actuation. This work uses impeller geometry characterization, fluid flow analysis through impeller blades and through pump jet, thrust modeling and DC motor modeling. The main contribution of this work is incorporation of axial flow velocity into thruster modeling in order to resolve the unmeasurable state problem, thanks to the dynamical properties of impeller geometry and flow conditions through impeller blades.
  • Thumbnail Image
    Item
    Nanomechanical Characterization of 1D Nanomaterials for Structure and Energy Applications
    (2014-11-18) Loya, Phillip Edward; Lou, Jun; Vajtai, Robert; Dick, Andrew J
    Classical fracture mechanics and conventional dislocation based understanding of metal yield and failure was well researched and understood until the recent advancement of electron microscopy techniques and the ability to produce small-scale metal samples. Once a critical dimension with respect to grain or geometrical size for a metal was reached, the deformation and fracture behaviors began to deviate from traditional theories and predictions. Recent research has focused on one-dimensional (1D) nanomaterials produced from their bulk counterparts to probe corresponding mechanical behaviors. However, this could alter the intrinsic material properties due to modifications caused by the milling/machining process. In this thesis, metal nanowires/fibers produced by an alternative process, and samples with controlled defect density, were used to gain a fundamental understanding of the critical dimension effects and small-scale mechanical behavior of metals. Another important aspect of this thesis is the development of a state-of-the-art nanomechanical characterization technique in the transmission electron microscope, where a detailed structure-property relationship could be reliably established with unprecedented resolutions. In the first part, single crystalline silver fibers were grown with dimensions varying from 2μm down to 400 nm and investigated using an advanced in-situ method. A critical dimension was observed near 1μm, below which the yield stress began to increase and the number of deformation slip bands began to decrease. Secondly, single crystal Mo-alloy fibers produced by a similar technique were pre-strained to introduce pre-existing dislocations and simulate bulk characteristics. In-situ tensile test showed the pre-straining effect on the yield stress, and the existence of a negative strain rate sensitivity. Next, pristine Mo-alloy fibers were irradiated with He and Ar ions to test the effects of irradiation induced defects on their mechanical behaviors at this length scale. A clear size effect was observed depending on the damage produced by the irradiation. Finally, a detailed description of an in-situ quantitative TEM stage based on a MEMS device and its successful applications are presented. This set-up was designed and built to compliment the in-situ SEM test by offering high resolution observations of the microstructural evolution under testing conditions and providing additional insights to the important structure-property relationship.