Temperature Effects on Adhesive Bond Strengths and Modules for Commonly Used Spacecraft Strucutral Adhesives
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Lapshear Testing↗
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Dynamic Analysis and Control of Lightweight Manipulators with Flexible Parallel Link Mechanisms
The objective is the theoretical analysis and the experimental verification of dynamics and control of a two link flexible manipulator with a flexible parallel link mechanism. Nonlinear equations of motion of the lightweight manipulator are derived by the Lagrangian method in symbolic form to better understand the structure of the dynamic model. The resulting equation of motion have a structure which is useful to reduce the number of terms calculated, to check correctness, or to extend the model to higher order. A manipulator with a flexible parallel link mechanism is a constrained dynamic system whose equations are sensitive to numerical integration error. This constrained system is solved using singular value decomposition of the constraint Jacobian matrix. Elastic motion is expressed by the assumed mode method. Mode shape functions of each link are chosen using the load interfaced component mode synthesis. The discrepancies between the analytical model and the experiment are explained using a simplified and a detailed finite element model.
Lee, Jeh Won↗
Computational Methods for Structural Mechanics and Dynamics
Topics addressed include: transient dynamics; transient finite element method; transient analysis in impact and crash dynamic studies; multibody computer codes; dynamic analysis of space structures; multibody mechanics and manipulators; spatial and coplanar linkage systems; flexible body simulation; multibody dynamics; dynamical systems; and nonlinear characteristics of joints.
Stroud, W. Jefferson↗
Dynamic analysis and control of lightweight manipulators with flexible parallel link mechanisms
The flexible parallel link mechanism is designed for increased rigidity to sustain the buckling when it carries a heavy payload. Compared to a one link flexible manipulator, a two link flexible manipulator, especially the flexible parallel mechanism, has more complicated characteristics in dynamics and control. The objective of this research is the theoretical analysis and the experimental verification of dynamics and control of a two link flexible manipulator with a flexible parallel link mechanism. Nonlinear equations of motion of the lightweight manipulator are derived by the Lagrangian method in symbolic form to better understand the structure of the dynamic model. A manipulator with a flexible parallel link mechanism is a constrained dynamic system whose equations are sensitive to numerical integration error. This constrained system is solved using singular value decomposition of the constraint Jacobian matrix. The discrepancies between the analytical model and the experiment are explained using a simplified and a detailed finite element model. The step response of the analytical model and the TREETOPS model match each other well. The nonlinear dynamics is studied using a sinusoidal excitation. The actuator dynamic effect on a flexible robot was investigated. The effects are explained by the root loci and the Bode plot theoretically and experimentally. For the base performance for the advanced control scheme, a simple decoupled feedback scheme is applied.
Lee, Jeh Won↗
Inelastic and Dynamic Fracture and Stress Analyses
Large deformation inelastic stress analysis and inelastic and dynamic crack propagation research work is summarized. The salient topics of interest in engine structure analysis that are discussed herein include: (1) a path-independent integral (T) in inelastic fracture mechanics, (2) analysis of dynamic crack propagation, (3) generalization of constitutive relations of inelasticity for finite deformations , (4) complementary energy approaches in inelastic analyses, and (5) objectivity of time integration schemes in inelastic stress analysis.
Atluri, S. N.↗
Application and use of Multi Body Dynamic Simulations for In Space Mechanisms
The Thermal and Mechanical Analysis Branch of the Space System Department (ES22) is actively growing and expanding a new mechanical analysis capability. In recent years, there has been an increase in the demand for Multi Body Dynamics (MBD) analysis to support small ESPA ring size spacecraft, cubesats, lunar surface operations and large spacecraft with complex operations or deployables. Requirements can be balanced for both needs to ensure mechanism is verified for launch. Multi-body dynamics is the study of multiple rigid or flexible bodies that are linked together or are in contact and the associated kinematics and dynamics of the system. The typical outputs include performance information, loads, and deflections of mechanical systems. They routinely support the development of robotic mechanisms, deployment mechanisms, landing simulations, control systems, and conops planning.
Multi Body Dynamics Analysis↗
Design study of an air pump and integral lift engine ALF-504 using the Lycoming 502 core
Design studies were conducted for an integral lift fan engine utilizing the Lycoming 502 fan core with the final MQT power turbine. The fan is designed for a 12.5 bypass ratio and 1.25:1 pressure ratio, and provides supercharging for the core. Maximum sea level static thrust is 8370 pounds with a specific fuel consumption of 0.302 lb/hr-lb. The dry engine weight without starter is 1419 pounds including full-length duct and sound-attenuating rings. The engine envelope including duct treatment but not localized accessory protrusion is 53.25 inches in diameter and 59.2 inches long from exhaust nozzle exit to fan inlet flange. Detailed analyses include fan aerodynamics, fan and reduction gear mechanical design, fan dynamic analysis, engine noise analysis, engine performance, and weight analysis.
Rauch, D.↗
Gravity gradient determination with tethered systems
A detailed investigation of the Earth's gravity field is needed for application to modern solid earth and oceanic investigations. The use of gravity gradiometers presents a technique to measure the intermediate wavelength components of the gravity field. One configuration of a gradiometer involves a tethered pair of masses orbiting the Earth and stabilized by vertical gravity gradient of the earth. A mesurement of the tension in such a system, called the DUMBBELL system is described. It allows the determination of the vertical gradient of the anomalous component of the Earth's gravtiy field. Preliminary analysis of the dynamics, mechanization, expected signal levels and noise environment indicates that the Dumbbell system is feasible.
Kalaghan, P. M.↗
Theoretical and software considerations for nonlinear dynamic analysis
In the finite element method for structural analysis, it is generally necessary to discretize the structural model into a very large number of elements to accurately evaluate displacements, strains, and stresses. As the complexity of the model increases, the number of degrees of freedom can easily exceed the capacity of present-day software system. Improvements of structural analysis software including more efficient use of existing hardware and improved structural modeling techniques are discussed. One modeling technique that is used successfully in static linear and nonlinear analysis is multilevel substructuring. This research extends the use of multilevel substructure modeling to include dynamic analysis and defines the requirements for a general purpose software system capable of efficient nonlinear dynamic analysis. The multilevel substructuring technique is presented, the analytical formulations and computational procedures for dynamic analysis and nonlinear mechanics are reviewed, and an approach to the design and implementation of a general purpose structural software system is presented.
Schmidt, R. J.↗
NASA LeRC/Akron University Graduate Cooperative Fellowship Program and Graduate Student Researchers Program
On June 1, 1980, the University of Akron and the NASA Lewis Research Center (LERC) established a Graduate Cooperative Fellowship Program in the specialized areas of Engine Structural Analysis and Dynamics, Computational Mechanics, Mechanics of Composite Materials, and Structural Optimization, in order to promote and develop requisite technologies in these areas of engine technology. The objectives of this program are consistent with those of the NASA Engine Structure Program in which graduate students of the University of Akron participate by conducting research at Lewis. This report is the second on this grant and summarizes the second and third year research effort, which includes the participation of five graduate students where each student selects one of the above areas as his special field of interest. Each student is required to spend 30 percent of his educational training time at the NASA Lewis Research Center and the balance at the University of Akron. His course work is judiciously selected and tailored to prepare him for research work in his field of interest. A research topic is selected for each student while in residence at the NASA Lewis Research Center, which is also approved by the faculty of the University of Akron as his thesis topic for a Master's and/or a Ph.D. degree.
Fertis, D. G.↗
Structure property behavior of polyimide siloxane segmented copolymers
Procedures were developed for preparing soluble fully imidized polyimide-polydimethyl siloxane segmented copolymers of wide ranging compositions. At low siloxane levels, the materails behave as modified polyimides. At higher concentrations, the materials are analogous to thermoplastic elastomers. Characterization by dynamic mechanical and thermal analysis methods will be reported along with an assesment of the bulk mechanical properties and the surface behavior. The surface behavior is particularly interesting since the materials can be tailored to have siloxane surfaces even at rather low siloxane contents. This influences a number of properties such as the coefficient of friction and, importanly, the degradation of these materials under aggressive oxygen environments (e.g., atomic oxygen, oxygen plasma).
Arnold, C. A.↗
Life cycles of persistent anomalies. II - The development of persistent negative height anomalies over the North Pacific Ocean
Consideration is given to the potential sources for the development of cases defined by strong and persistent negative height anomalies over the central North Pacific. The analyses of Dole (1986) are extended by providing a more complete synoptic description of the developments and additional diagnostic analysis to identify dynamical mechanisms responsible for the developments. The synoptic characteristics of the developments are reviewed and the barotropic and baroclinic processes of the developments are analyzed. The reproducibility and representativeness of the results are examined. The observed characteristics suggest that the large-scale flow anomalies develop as a result of an instability of three-dimensional wintertime mean flow.
Dole, Randall M.↗
Analysis of propellant slosh dynamics and generation of an equivalent mechanical model for use in preliminary voyager autopilot design studies
Linearized dynamic equations and mechanical model for propellant sloshing in Lunar Excursion Module Descent Propulsion System /LEMDPS/
Lance, T. A.↗
Phobos and deimos: Analysis of surface features, ejecta dynamics and a volatile loss mechanism
The question of whether the crater population on Phobos represents a production population or an equilibrium population is considered. The absolute ages of cratered surfaces are interpreted and analyzed. A computer program was developed to study the dynamics of material ejected from Martian satellites and to investigate the hypothesis that at least some of the extensive set of linear features discovered on the surface of Phobos could be the result of secondary cratering from the Stickney impact. The possibility that Deimos was catastrophically disrupted by a large impact but subsequently reaccreted is considered as well as the probability the Phobos had an impact nearly large enough to disrupt it are also discussed.
Davis, D. R.↗
Computational Methods for Structural Mechanics and Dynamics, part 1
The structural analysis methods research has several goals. One goal is to develop analysis methods that are general. This goal of generality leads naturally to finite-element methods, but the research will also include other structural analysis methods. Another goal is that the methods be amenable to error analysis; that is, given a physical problem and a mathematical model of that problem, an analyst would like to know the probable error in predicting a given response quantity. The ultimate objective is to specify the error tolerances and to use automated logic to adjust the mathematical model or solution strategy to obtain that accuracy. A third goal is to develop structural analysis methods that can exploit parallel processing computers. The structural analysis methods research will focus initially on three types of problems: local/global nonlinear stress analysis, nonlinear transient dynamics, and tire modeling.
Stroud, W. Jefferson↗
Comparisons of Kinematics and Dynamics Simulation Software Tools
Kinematic and dynamic analyses for moving bodies are essential to system engineers and designers in the process of design and validations. 3D visualization and motion simulation plus finite element analysis (FEA) give engineers a better way to present ideas and results. Marshall Space Flight Center (MSFC) system engineering researchers are currently using IGRIP from DELMIA Inc. as a kinematic simulation tool for discrete bodies motion simulations. Although IGRIP is an excellent tool for kinematic simulation with some dynamic analysis capabilities in robotic control, explorations of other alternatives with more powerful dynamic analysis and FEA capabilities are necessary. Kinematics analysis will only examine the displacement, velocity, and acceleration of the mechanism without considering effects from masses of components. With dynamic analysis and FEA, effects such as the forces or torques at the joint due to mass and inertia of components can be identified. With keen market competition, ALGOR Mechanical Event Simulation (MES), MSC visualNastran 4D, Unigraphics Motion+, and Pro/MECHANICA were chosen for explorations. In this study, comparisons between software tools were presented in terms of following categories: graphical user interface (GUI), import capability, tutorial availability, ease of use, kinematic simulation capability, dynamic simulation capability, FEA capability, graphical output, technical support, and cost. Propulsion Test Article (PTA) with Fastrac engine model exported from IGRIP and an office chair mechanism were used as examples for simulations.
Yeu-Sheng Paul Shiue↗
Executive summary: Mod-1 wind turbine generator analysis and design report
Activities leading to the detail design of a wind turbine generator having a nominal rating of 1.8 megawatts are reported. Topics covered include (1) system description; (2) structural dynamics; (3) stability analysis; (4) mechanical subassemblies design; (5) power generation subsystem; and (6) control and instrumentation subsystem.
Source record↗
Current research activities: Applied and numerical mathematics, fluid mechanics, experiments in transition and turbulence and aerodynamics, and computer science
Research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics, numerical analysis, fluid mechanics including fluid dynamics, acoustics, and combustion, aerodynamics, and computer science during the period 1 Apr. 1992 - 30 Sep. 1992 is summarized.
Source record↗