Structural dynamics branch research and accomplishments to FY 1992

This publication contains a collection of fiscal year 1992 research highlights from the Structural Dynamics Branch at NASA LeRC. Highlights from the branch's major work areas--Aeroelasticity, Vibration Control, Dynamic Systems, and Computational Structural Methods are included in the report as well as a listing of the fiscal year 1992 branch publications

Residual vibration reduction of high-speed pick-and-place parallel robot using input shaping

Because of their elastic links and joints, high-speed parallel robots for pick-and-place operations inevitably suffer from residual vibrations that significantly degrade their positioning accuracy. An effective approach based on the input shaping technique is presented in this paper for suppressing the residual vibration in these parallel robots. After addressing the design principle of an input shaper for a parallel robot with flexible actuated joints, a robust optimal input shaper is developed by considering the configuration-dependent flexible modes and minimizing the maximum percentage of residual vibration at the end-effector. The input shaper allows a good overall performance to be achieved throughout the entire workspace. Experimental results on a 4-DOF SCARA-type parallel robot show that the residual vibration of the end-effector is dramatically reduced and the dynamic positioning accuracy of the robot significantly improved

Soil-structure interaction modelling for an offshore wind turbine with monopile foundation

The last decade, there has been an increased use of offshore sites for harvesting wind energy. With a more complex environment than onshore, leading to higher energy prices, cost reductions becomes important for the industry. With this in mind, the REDWIN research project has been initiated, supported by the Norwegian Reseach Counsil ENERGIX program. The goal of the program is to reduce cost in offshore wind by integrated structural and geothecnical design. This thesis contributes to this project by investigating the influence on fatigue damage and maximum moments on an OWT, for different soil-structure interaction models. The models has been applied on the NREL 5MW monopile wind turbine. To investigate the effect of soil damping, three different soil-structure interaction models has been investigated. The reference model has a stiffness matrix at the mudline, according to that developed by Passon (2006) for the Offshore Code Comparison Collaboration 3 (Jonkman and Musial, 2010). The second model uses the same stiffness matrix, with a rotational dashpot damper, to account for soil damping. The third model has been developed by NGI (Norwegian Geotechnical Institute) for the REDWIND project, and is a kinematic hardening soil model. The accumulated fatigue damage on the OWT structure is reduced by 11% at the mudline, when applying a rotational dashpot damper to account for soil damping. At the tower root, the reduction of fatigue damage is 16%. With the kinematic hardening model, the reduction of fatigue damage is 3% at the mudline, and 7% at the tower root. Both models are seen relative to the reference model, with no soil damping. The results show that damping has a significant effect on fatigue damage for a bottom fixed offshore wind turbine. The difference between the models, are due to different damping characteristics, and implies that a dashpot damper tend to over-estimate soil damping.M-MP

Rotorcraft aeroelastic stability

Theoretical and experimental developments in the aeroelastic and aeromechanical stability of helicopters and tilt-rotor aircraft are addressed. Included are the underlying nonlinear structural mechanics of slender rotating beams, necessary for accurate modeling of elastic cantilever rotor blades, and the development of dynamic inflow, an unsteady aerodynamic theory for low-frequency aeroelastic stability applications. Analytical treatment of isolated rotor stability in hover and forward flight, coupled rotor-fuselage stability in hover and forward flight, and analysis of tilt-rotor dynamic stability are considered. Results of parametric investigations of system behavior are presented, and correlation between theoretical results and experimental data from small and large scale wind tunnel and flight testing are discussed

NASA Tech Briefs, April 1991

Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Lewis Structures Technology, 1988. Volume 1: Structural Dynamics

The specific purpose of the symposium was to familiarize the engineering structures community with the depth and range of research performed by the Structures Division of the Lewis Research Center and its academic and industrial partners. Sessions covered vibration control, fracture mechanics, ceramic component reliability, parallel computing, nondestructive testing, dynamical systems, fatigue and damage, wind turbines, hot section technology, structural mechanics codes, computational methods for dynamics, structural optimization, and applications of structural dynamics

Space station systems: A bibliography with indexes (supplement 6)

This bibliography lists 1,133 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1987 and December 31, 1987. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems. The coverage includes documents that define major systems and subsystems, servicing and support requirements, procedures and operations, and missions for the current and future Space Station