Analysis of crack geometry and location by means of a multi probe potential drop technique

openIl metodo del Direct Current Potential Drop è una tecnica spesso utilizzata nell'ambito della meccanica della frattura per la stima della posizione e della geometria di una cricca di fatica. Tramite questo studio vengono esaminate le applicazioni di questo metodo utilizzando sonde multiple di potenziale in provini a barra con differenti configurazioni. I risultati ottenuti sono poi analizzati sia con metodi matematici che con analisi agli elementi finiti.The Direct Current Potential Drop (DCPD) method is a commonly employed technique for crack detection and measurement of crack length in fatigue experiments. The current study specifically examines the applications of this technique using multiple potential probes on round bar specimens with varying set-ups. The obtained results are analyzed using both mathematical models and Finite Element Analysis (FEA)

Analysis of electromagnetic interference from power system processing and transmission components for Space Station Freedom

The goal is to analyze the potential effects of electromagnetic interference (EMI) originating from power system processing and transmission components for Space Station Freedom.The approach consists of four steps: (1) develop analytical tools (models and computer programs); (2) conduct parameterization studies; (3) predict the global space station EMI environment; and (4) provide a basis for modification of EMI standards

Application of state-of-the-art FEM techniques to magnetostatic NDE

A typical example of the complexities involved in the numerical modeling of electromagnetic phenomena is that of modeling the magnetic flux leakage inspection of gas transmission pipelines. The problem calls for three-dimensional modeling of motionally induced currents (using transient analysis), modeling nonlinearity of the ferromagnetic parts, and accurate modeling of the permanent magnet used in the magnetizer. Researchers, have thus far simplified the problem using several assumptions, including that of axisymmetry, and modeling velocity effects using steady-state analysis. However, there has been no attempt to quantify the errors introduced by these assumptions. Also, due to the unavailability of commercial codes to solve three-dimensional motion-related problems using transient analysis, a detailed study of the true nature of velocity effects has not been possible;This dissertation implements and evaluates state-of-the-art finite element modeling techniques applied to the specific problem of modeling magnetic flux leakage inspection of gas pipelines. This provides the basis from which conclusions can be drawn on the general problem of modeling magnetostatic phenomena. Axisymmetric and three-dimensional models are developed capable of modeling velocity effects. A detailed analysis of the differences between axisymmetric and three-dimensional geometries, based on a study of permeability variations in the vicinity of defects is presented. Also, the need for transient analysis is argued based on results generated. As part of this study, serious problems (including spurious solutions and corner singularities) associated with the traditional node-based finite-element techniques, when applied to the three-dimensional modeling, are discussed. In this work, new and efficient numerical modeling concepts, using the edge-based finite-element technique are employed to overcome these problems;This study demonstrates the need for accurate modeling of the full three-dimensional geometry, incorporating velocity effects and nonlinear permeability, for realistic predictions of flux leakage inspection tools. Major contributions of this work include: (1) detailed analysis of the physical processes associated with the magnetic flux leakage tool, (2) design ideas to improve the performance of the tool, and (3) development of an edge-based finite element code for modeling magnetostatic nondestructive testing applications in three-dimensions incorporating velocity effects. This is the first study of this nature, applied to pipeline inspection, and, many of the conclusions presented can be applied to nondestructive testing techniques in general

Holographic Vitrification

We establish the existence of stable and metastable stationary black hole bound states at finite temperature and chemical potentials in global and planar four-dimensional asymptotically anti-de Sitter space. We determine a number of features of their holographic duals and argue they represent structural glasses. We map out their thermodynamic landscape in the probe approximation, and show their relaxation dynamics exhibits logarithmic aging, with aging rates determined by the distribution of barriers.Comment: 100 pages, 25 figure

Numerical Simulation

Nowadays mathematical modeling and numerical simulations play an important role in life and natural science. Numerous researchers are working in developing different methods and techniques to help understand the behavior of very complex systems, from the brain activity with real importance in medicine to the turbulent flows with important applications in physics and engineering. This book presents an overview of some models, methods, and numerical computations that are useful for the applied research scientists and mathematicians, fluid tech engineers, and postgraduate students

Fifth NASA Intercenter and Contractors Conference on Plasma Physics. Part 2 - Plasma physics research at NASA Langley Research Center

Annotated bibliography of plasma physics research papers including plasma spectroscopy, crossed field plasma accelerators and electric forces on satellites, and collisionless plasma - conferenc

Observing the Functional Maturation of the Female Prefrontal Cortex Using Ventral Hippocampal Stimulation

Adolescence is a time when the brain continues to mature. Specifically the prefrontal cortex (PFC) goes through a process of disinhibition to inhibition as we age. Inputs to this region have a frequency dependent maturation pattern in male rats, but this has not been studied in females. We focused on frequency dependent responses in the medial PFC that are evoked by stimulation to the ventral hippocampus. This was conducted by measuring Local Field Potential responses in the medial PFC via in vivo electrophysiology. We found that stimulating with a 10 Hz train response showed no difference across age groups. In contrast, a 20 Hz train of stimulation revealed an age-dependent shift through increasing suppression of the signal. Finally, a 40 Hz train stimulation evoked suppression in all three age groups, but in different magnitudes. With these established patterns we can compare a normal PFC maturation with factors such as chronic drug use and stress