Research reports: 1990 NASA/ASEE Summer Faculty Fellowship Program

Reports on the research projects performed under the NASA/ASEE Summer Faculty Fellowship Program are presented. The program was conducted by The University of Alabama and MSFC during the period from June 4, 1990 through August 10, 1990. Some of the topics covered include: (1) Space Shuttles; (2) Space Station Freedom; (3) information systems; (4) materials and processes; (4) Space Shuttle main engine; (5) aerospace sciences; (6) mathematical models; (7) mission operations; (8) systems analysis and integration; (9) systems control; (10) structures and dynamics; (11) aerospace safety; and (12) remote sensin

Fluid Mud Underflows in Coastal Dredge Disposal

This manuscript presents the results of a thorough theoretical and experimental investigation on fluid mud underflows generated in a typical coastal dredge disposal operation. The main goal of this investigation is to understand the propagation dynamics of fluid mud underflows that depends upon a number of factors, including: concentrations, rheological properties and released configurations of fluid mud. Laboratory experiments were conducted with different initial fluid mud concentrations in three different experimental set-ups: rectangular flume for constant volume release, rectangular flume for constant flux release, and a square pool for radial constant flux release of fluid mud. The experiments in the rectangular flume generated two-dimensional underflows. The experiments in the pool simulated typical open water pipeline disposal operations with submerged vertical discharge configuration in the field and radially axisymmetric three-dimensional fluid mud underflows were generated in these experiments. As expected, constant volume release experiments generated gravity currents that exhibit slumping, inertial and viscous propagation phases while constant flux release experiments generated initial horizontal buoyant jets which then transform into gravity currents that exhibit inertial and viscous propagation phases. The experiments showed that the propagations of underflows were significantly influenced by the non-Newtonian rheology of released fluid mud. Underflows formed by initial low concentration of fluid mud release did not experience the viscous propagation phase in the limited experimental set-ups that were used in the experimental investigation. However, high concentration fluid mud releases rapidly transitioned into viscous propagation phase, sometimes even bypassing the expected inviscid phase. The inter-transitions of propagation phases were determined from experimental data and they were related to the initial source parameters by deriving order-of-magnitude expressions for transitions. The theoretical part of this investigation also includes experimental evaluation of three mathematical modeling approaches to model the inertial and viscous propagation of fluid mud gravity currents. These three mathematical modeling approaches are, from simplest to the most complex: force-balance, box model and shallow water/lubrication theory approximation. The force-balance and box model solutions for viscous propagation of non-Newtonian gravity currents were non-existent and hence, derived in this investigation. For the inertial propagation of fluid mud gravity currents, it was concluded that box model would be the most efficient analytical model due to its closed-form solution for all of the release configurations, and its predictive accuracy (based upon its experimental evaluation and inter-comparison of the models). For the viscous propagation, self-similar solution based on the lubrication theory approximation would be the better choice. However, only box model solution can provide analytical solution for all possible release configurations which make it a good alternative, especially for quick predictions. The results of this study are expected to be useful for predicting the temporal fate of fluid mud underflows in coastal dredge disposal operations

NON-CARTESIAN MAGNETIC RESONANCE IMAGING STRATEGIES: IMPROVEMENTS IN ACCELERATED CARDIAC MAGNETIC RESONANCE IMAGING AND TECHNICAL CONSIDERATIONS

Magnetic Resonance Imaging (MRI) is a medical imaging modality that is essential for the imaging of heart because of its unparalleled soft tissue contrast and lack of ionizing radiation. However, the dynamic nature of the heart, together with the motion introduced by respiration, make it a challenging task to generate MRI images without motion-induced artifacts. Traditional approaches deal with physiological motion by acquiring the necessary information to create an image in segments over many heartbeats via electrocardiogram (ECG) gating. Nevertheless, advancements in MRI scanner hardware and image reconstruction techniques, over the past decade, have led to the emergence of real-time MRI acquisitions of cardiac scans where the MRI signal used in reconstructing one image is collected in a single shot. The temporal window during which data is collected from the MRI scanner is extremely short (<50ms) for adequately imaging the heart, and such “real-time” accelerated imaging entails the recovery of image information from severely undersampled data. Existing techniques that address the problem of reconstructing images from highly undersampled MRI data come with costs, either in the form of additional MRI scans a priori or aggressive assumptions on the underlying spatiotemporal properties of the object being imaged. In this work, a thorough investigation of one such method that requires a lengthy calibration pre-scan is performed, and novel techniques, which leverages the insights gained from this investigation and incorporates other unprecedented ways of tackling the problem, that facilitate the real-time monitoring of cardiac function, without the inconvenience of a separate calibration scan and assumptions on the statistical properties of the heart’s motion, were developed and evaluated in animal and human subject studies, producing images with comparable quality to existing cardiac MRI techniques. The developed techniques have significant potential of improving the patient’s experience in the clinic, while preserving diagnostic power. They also have the potential to enhance other real-time MRI scenarios such as MRI-guided procedures where a priori calibration scans are infeasible. Advisor and First Reader: Daniel A. Herzka, PhD Assistant Professor, Biomedical Engineering Johns Hopkins University School of Medicine Second Reader: Aravindan Kolandaivelu, MD Assistant Professor, Cardiology Johns Hopkins University School of Medicin

Quantum-Mechanical Approach to Collision-Induced Radiative Emissions

Charge exchange is a process that occurs in an atomic collision where an electron from one of the colliding particles is transferred to the other; typically from a neutral atom or molecule to an ion. Electrons transferred into an excited energy state then decay into a lower-energy state and emit photons during this process. This phenomenon of collision-induced radiative emissions is of great interest in astrophysics and experimental x-ray spectroscopy research since it helps understand the production of x-rays in astrophysical settings. On the theoretical side, obtaining a description of these radiative emissions involves numerical work since a closed-form solution is not possible. Using standard numerical approaches, one needs to rely on models and approximations, especially in collision problems involving many-electron systems. Consequently, results obtained in this way can be at odds with experimental observations and/or results from different theoretical methods. In this dissertation, the main method is the two-centre basis generator method performed within the independent electron model. It is a dynamical approach to solving atomic collision problems and has shown to be reliable in describing charge exchange and other electronic processes. This work gives an extensive view on the applicability of this approach in the context of collision-induced radiative emissions where present results from a variety of ion-atom and ion-molecule collisions are benchmarked with results from previous studies

Advanced modeling in Lorentz force eddy current testing

Nowadays, there is an increasing demand on reliable and efficient methods to evaluate materials and components in a nondestructive way. Particularly in the field of aerospace engineering, the components are subject to fulfill high quality and safety standards, which necessitate methods with a high accuracy, repeatability and inspection speed. This work deals with the nondestructive testing method Lorentz force eddy current testing. Unlike traditional eddy current methods, the induction process is based on relative motion between a permanent magnet and the object under test. An integral part of this thesis is the development of a new magnet system with improved characteristics. The proposed design is based on the Halbach principle and is made of Neodymium-Iron-Boron alloys. Besides that, it contains a piece made of highly saturating iron-cobalt. In this sense, it was possible to increase and focus the magnetic flux density in the vicinity of the specimen. The development of a decent optimization strategy allows to determine problem specific magnet designs in dependence on the measurement requirements. In the further course of this thesis, numerical simulations are performed addressing the uncertainty and sensitivity analysis of the system. Therefore, the model parameters are investigated in terms of their statistical properties. The resulting stochastic electromagnetic field problem is solved by means of the generalized polynomial chaos technique in combination with the finite element method. This enabled the identification of most influencing parameters in the system. In the context of the uncertainty analysis, it is observed that the velocity obeys characteristic oscillations. In order to deepen the understanding of this phenomenon, an analytical approach is presented to evaluate the electromagnetic fields and forces while taking into account the resistive and inductive character of the moving conductor. Finally, an alternative Lorentz force eddy current testing system is proposed where the object under test is encompassed by a ring magnet. The working principle is exemplified by theoretical considerations. This work contributes to increase the knowledge and understanding about Lorentz force eddy current testing and intends to advance the current state of the art with new and innovative approaches.In der heutigen Zeit steigt der Bedarf an effizienten und leistungsfähigen Verfahren zur zerstörungsfreien Prüfung von Werkstoffen und Bauteilen rasant an. Besonders in den Bereichen Luft- und Raumfahrttechnik unterliegen die Bauteile hohen Qualitätsstandards im Sinne der Sicherheit. Dies setzt Verfahren mit hoher Genauigkeit, Wiederholbarkeit und Schnelligkeit voraus. Diese Arbeit befasst sich mit der Methode der Lorentzkraft-Wirbelstromprüfung. Im Gegensatz zu klassischen Induktionsverfahren werden die Wirbelströme aufgrund einer Relativbewegung zwischen einem Permanentmagneten und dem Prüfobjekt hervorgerufen. Ein zentraler Gegenstand dieser Arbeit stellt die Entwicklung eines neuen Magnetsystems dar. Dieses basiert auf dem Halbach-Prinzip und besteht neben den bekannten Neodym-Eisen-Bor Legierungen aus einer Eisen-Kobalt-Verbindung mit hoher Sättigungsmagnetisierung. In diesem Sinn war es möglich die magnetische Flussdichte in der Nähe des Prüfkörpers zu fokussieren und zu verstärken. Die Entwicklung einer geeigneten Optimierungsroutine erlaubt die flexible Identifikation der Magnetgeometrie in Abhängigkeit der gestellten Anforderungen. Im weiteren Verlauf wurden numerische Simulationen zur Unsicherheits- und Sensitivitätsanalyse durchgeführt. Im Zuge dessen wurden die Modellparameter hinsichtlich ihrer statistischen Eigenschaften untersucht. Das zugrunde liegende stochastische Feldproblem wurde mit Hilfe der Methode des "Generalized Polynomial Chaos" gelöst. Dies ermöglichte die Identifikation der wichtigsten Einflussgrößen im System. Im Zusammenhang mit der Unsicherheitsanalyse wurden charakteristische Oszillationen der Relativgeschwindigkeit zwischen Permanentmagnet und Prüfkörper beobachtet. Um diese Phänomene besser verstehen zu können, wurde ein analytischer Zugang entwickelt, der die Bestimmung der elektromagnetischen Felder und Lorentzkräfte ermöglicht. Zu guter Letzt wird ein alternatives System zur Lorentzkraft-Wirbelstromprüfung vorgestellt, indem der Prüfkörper von einem Ringmagneten umschlossen ist. Die prinzipielle Funktionsweise des neuen Systems wird mit theoretischen Vorbetrachtungen in Form von analytischen Lösungen aufgezeigt. Die Arbeit vertieft die Kenntnisse über die Lorentzkraft-Wirbelstromprüfung und enthält neue sowie innovative Ansätze, die den Stand der Technik vorantreiben

Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015

This volume contains the full papers accepted for presentation at the ECCOMAS Thematic Conference on Multibody Dynamics 2015 held in the Barcelona School of Industrial Engineering, Universitat Politècnica de Catalunya, on June 29 - July 2, 2015. The ECCOMAS Thematic Conference on Multibody Dynamics is an international meeting held once every two years in a European country. Continuing the very successful series of past conferences that have been organized in Lisbon (2003), Madrid (2005), Milan (2007), Warsaw (2009), Brussels (2011) and Zagreb (2013); this edition will once again serve as a meeting point for the international researchers, scientists and experts from academia, research laboratories and industry working in the area of multibody dynamics. Applications are related to many fields of contemporary engineering, such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, mechatronic and autonomous systems, smart structures, biomechanical systems and nanotechnologies. The topics of the conference include, but are not restricted to: ● Formulations and Numerical Methods ● Efficient Methods and Real-Time Applications ● Flexible Multibody Dynamics ● Contact Dynamics and Constraints ● Multiphysics and Coupled Problems ● Control and Optimization ● Software Development and Computer Technology ● Aerospace and Maritime Applications ● Biomechanics ● Railroad Vehicle Dynamics ● Road Vehicle Dynamics ● Robotics ● Benchmark ProblemsPostprint (published version

Aerial Vehicles

This book contains 35 chapters written by experts in developing techniques for making aerial vehicles more intelligent, more reliable, more flexible in use, and safer in operation.It will also serve as an inspiration for further improvement of the design and application of aeral vehicles. The advanced techniques and research described here may also be applicable to other high-tech areas such as robotics, avionics, vetronics, and space