Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Structural dynamics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Identification of the dynamics of a two-dimensional grid structure using least square lattice filters

The basic theory of least square lattice filters and their use in identification of structural dynamics systems is summarized. Thereafter, this theory is applied to a two-dimensional grid structure made of overlapping bars. Previously, this theory has been applied to an integral beam. System identification results are presented for both simulated and experimental tests and they are compared with those predicted using finite element modelling. The lattice filtering approach works well for simulated data based on finite element modelling. However, considerable discrepancy exists between estimates obtained from experimental data and the finite element analysis. It is believed that this discrepancy is the result of inadequacies in the finite element modelling to represent the damped motion of the laboratory apparatus.

Montgomery, R. C.↗
NASA NTRS2000

Characterization of Microgravity Environment on Mir

This paper presents the microgravity analysis results using dynamic response data collected during the first phase of the Mir Structural Dynamics Experiment (MiSDE). Although MiSDE was designed and performed to verify structural dynamic models, it also provided information for determining microgravity characteristics of the structure. This study analyzed ambient responses acquired during orbital day-to-night and night-to-day transitions, crew treadmill and ergometer exercises, and intentional crew activities. Acceleration levels for one-third octave bands were calculated to characterize the microgravity environment of the station. Spectrograms were also used to analyze the time transient nature of the responses. Detailed theoretical background and analysis results will also be included in the final draft.

Kim, Hyoung↗
NASA NTRS1981

Elastic body dynamics

Most of the structural dynamics resources allocated to the Space Shuttle are concentrated on the flight events which result in critical structural loads and/or minimum control stability margins. Since these events are primarily sub-orbital, the data base of interest to those involved in orbital experimentation is somewhat limited. A brief discussion of available data is given. Although estimates of peak acceleration levels and the associated frequency spectrum in the payload bay due to thrusting of the various control system thrusters were made, the actual levels and time histories must be based on updated structural math models and a detailed knowledge of the input forcing functions.

Holder, B. W.↗
NASA NTRS1973

Seismic analysis of nuclear power plant structures

Primary structures for nuclear power plants are designed to resist expected earthquakes of the site. Two intensities are referred to as Operating Basis Earthquake and Design Basis Earthquake. These structures are required to accommodate these seismic loadings without loss of their functional integrity. Thus, no plastic yield is allowed. The application of NASTRAN in analyzing some of these seismic induced structural dynamic problems is described. NASTRAN, with some modifications, can be used to analyze most structures that are subjected to seismic loads. A brief review of the formulation of seismic-induced structural dynamics is also presented. Two typical structural problems were selected to illustrate the application of the various methods of seismic structural analysis by the NASTRAN system.

Go, J. C.↗
NASA NTRS1987

The climatic wind regime in the lower thermosphere from meteor radar observations

The determination of climatic norms of wind regime parameters in the lower thermosphere requires some questions of a methodical and scientific character to be settled. Among those of methodical character is: how to properly construct climatic circulation models using limited experimental data obtained by various methods during different time periods and in different geographical regions. The most important questions of a scientific character are: what main dynamic structures characterize the wind regime and how are these structures related to various atmospheric parameters and to the dynamic structures in the overlying and underlying atmospheric layers. These questions are considered and discussed.

Portnyagin, Yu. I.↗
NASA NTRS1981

The structure and dynamics of the heliospheric current sheet

It has been suggested that the sector structure observed in the interplanetary magnetic field may be interpreted in terms of a warped equatorial current sheet in the heliosphere. The reported study seeks to investigate this suggestion and to provide a clear picture of the topology of the current sheet. An analysis is presented of the magnetic field data obtained by the Pioneer 10 and 11 spacecraft during the time from 1972 to 1976, taking into account a range of heliocentric distances from 1 to 8.5 AU. The single most convincing observation in support of the warped current sheet hypothesis is the almost complete disappearance of the sector structure in the Pioneer 11 data when the spacecraft reaches a heliographic latitude of 16 deg in 1976. The observation suggests that the spacecraft was consistently above the current sheet for a period of several months.

Thomas, B. T.↗
NASA NTRS1982

Dynamics and control of a large space antenna

It is pointed out that large space antennae and other large space structures will play an important role in the coming decades as commercial applications of space become feasible. A investigation is conducted of the structural dynamics and the control properties for a 64-meter diameter center fed antenna. Attention is given to antenna configuration and structural dynamic porperties, the attitude and structural control system, disturbance assessment, hardware sizing, the construction of weighting matrices, and numerical results. It is found that structural uncertainties and model error can cause serious performance deterioration and can even destabilize the controllers. Flight test and in-orbit system identification of critical structural modes will insure performance and reduce risk for large space antenna missions.

Wang, S. J.↗
NASA NTRS2018

International Space Station Model Correlation Analysis

This paper summarizes the on-orbit structural dynamic data and the related modal analysis, model validation and correlation performed for the International Space Station (ISS) configuration ISS Stage ULF7, 2015 Dedicated Thruster Firing (DTF). The objective of this analysis is to validate and correlate the analytical models used to calculate the ISS internal dynamic loads and compare the 2015 DTF with previous tests. During the ISS configurations under consideration, on-orbit dynamic measurements were collected using the three main ISS instrumentation systems; Internal Wireless Instrumentation System (IWIS), External Wireless Instrumentation System (EWIS) and the Structural Dynamic Measurement System (SDMS). The measurements were recorded during several nominal on-orbit DTF tests on August 18, 2015. Experimental modal analyses were performed on the measured data to extract modal parameters including frequency, damping, and mode shape information. Correlation and comparisons between test and analytical frequencies and mode shapes were performed to assess the accuracy of the analytical models for the configurations under consideration. These mode shapes were also compared to earlier tests. Based on the frequency comparisons, the accuracy of the mathematical models is assessed and model refinement recommendations are given. In particular, results of the first fundamental mode will be discussed, nonlinear results will be shown, and accelerometer placement will be assessed.

Modal Analysis↗
NASA NTRS2000

Modal Analysis and Model Correlation of the Mir Space Station

This paper will discuss on-orbit dynamic tests, modal analysis, and model refinement studies performed as part of the Mir Structural Dynamics Experiment (MiSDE). Mir is the Russian permanently manned Space Station whose construction first started in 1986. The MiSDE was sponsored by the NASA International Space Station (ISS) Phase 1 Office and was part of the Shuttle-Mir Risk Mitigation Experiment (RME). One of the main objectives for MiSDE is to demonstrate the feasibility of performing on-orbit modal testing on large space structures to extract modal parameters that will be used to correlate mathematical models. The experiment was performed over a one-year span on the Mir-alone and Mir with a Shuttle docked. A total of 45 test sessions were performed including: Shuttle and Mir thruster firings, Shuttle-Mir and Progress-Mir dockings, crew exercise and pushoffs, and ambient noise during night-to-day and day-to-night orbital transitions. Test data were recorded with a variety of existing and new instrumentation systems that included: the MiSDE Mir Auxiliary Sensor Unit (MASU), the Space Acceleration Measurement System (SAMS), the Russian Mir Structural Dynamic Measurement System (SDMS), the Mir and Shuttle Inertial Measurement Units (IMUs), and the Shuttle payload bay video cameras. Modal analysis was performed on the collected test data to extract modal parameters, i.e. frequencies, damping factors, and mode shapes. A special time-domain modal identification procedure was used on free-decay structural responses. The results from this study show that modal testing and analysis of large space structures is feasible within operational constraints. Model refinements were performed on both the Mir alone and the Shuttle-Mir mated configurations. The design sensitivity approach was used for refinement, which adjusts structural properties in order to match analytical and test modal parameters. To verify the refinement results, the analytical responses calculated using original and refined math models were compared with the measured responses. The results from this study show that the refined models predict more accurately the dynamics of the actual structure. The MiSDE test and analysis results provided the information and experience on test design, flight testing, and data analysis for the ISS and other future spacecraft, which are critical to the verification of analytical models and structural loads.

Kim, Hyoung M.↗
NASA NTRS2002

Power Law Versus Exponential Form of Slow Crack Growth of Advanced Structural Ceramics: Dynamic Fatigue

The life prediction analysis based on an exponential crack velocity formulation was examined using a variety of experimental data on glass and advanced structural ceramics in constant stress-rate ("dynamic fatigue") and preload testing at ambient and elevated temperatures. The data fit to the strength versus In (stress rate) relation was found to be very reasonable for most of the materials. It was also found that preloading technique was equally applicable for the case of slow crack growth (SCG) parameter n > 30. The major limitation in the exponential crack velocity formulation, however, was that an inert strength of a material must be known priori to evaluate the important SCG parameter n, a significant drawback as compared to the conventional power-law crack velocity formulation.

Choi, Sung R.↗
NASA NTRS2001

Dynamic Testing of a Subscale Sunshield for the Next Generation Space Telescope (NGST)

The NGST sunshield is a lightweight, flexible structure consisting of multiple layers of pretensioned, thin-film membranes supported by deployable booms. The structural dynamic behavior of the sunshield must be well understood in order to predict its influence on observatory performance. Ground tests were carried out in a vacuum environment to characterize the structural dynamic behavior of a one-tenth scale model of the sunshield. Results from the tests will be used to validate analytical modeling techniques that can be used in conjunction with scaling laws to predict the performance of the full-sized structure. This paper summarizes the ground tests and presents representative results for the dynamic behavior of the sunshield.

Lienard, Sebastien↗
NASA NTRS1973

Thermal-dynamic modeling study

Study provides basic information for designing models and conducting thermal-dynamic structural tests. Factors considered are development and interpretation of thermal-dynamic structural scaling laws; identification of major problem areas; and presentation of model fabrication, instrumentation, and test procedures.

Ojalvo, I. U.↗
NASA NTRS2002

Impact Testing of a Stirling Converter's Linear Alternator

The U.S. Department of Energy (DOE), in conjunction with the NASA John H. Glenn Research Center and Stirling Technology Company, are currently developing a Stirling convertor for a Stirling Radioisotope Generator (SRG). NASA Headquarters and DOE have identified the SRG for potential use as an advanced spacecraft power system for future NASA deep-space and Mars surface missions. Low-level dynamic impact tests were conducted at NASA Glenn Research Center's Structural Dynamics Laboratory as part of the development of this technology. The purpose of this test was to identify dynamic structural characteristics of the Stirling Technology Demonstration Convertor (TDC). This paper addresses the test setup, procedure, and results of the impact testing conducted on the Stirling TDC in May 2001.

Suarez, Vicente J.↗
NASA NTRS2024

The Role of Magnetic Reconnection in the Structure and Dynamics of Fast Coronal Mass Ejections

Both observations and models of flare-associated coronal mass ejections (CMEs) suggest that magnetic reconnection in an ejection's wake substantially increases the net, outward Lorentz force acceler­ating the CME. A stronger outward force can cause a feedback loop, driving further magnetic reconnection in a "reconnective instability." The flux accretion model captures this by relating reconnected flux, ∆ rec , and magnetic field strength, B CME , to increased outward Lorentz force, ∆F r . To better understand recon­nection's role in CME dynamics, we analyze two snapshots from a 2.5D, MHD simulation of a breakout eruption. Outward Lorentz forces increase substantially as reconnection proceeds, caused primarily by "flank currents," which flow just inside the boundary of the rising ejection's wake and parallel to its axis. This model's reconnection jet also alters the ejection's internal structure, an effect that could be sought in observations. Analyzing reconnection-induced Lorentz forces in 3D simulations could provide additional insights into CME dynamics.

Magnetic Reconnection↗
NASA NTRS1986

Solar array flight dynamic experiment

The purpose of the Solar Array Flight Dynamic Experiment (SAFDE) is to demonstrate the feasibility of on-orbit measurement and ground processing of large space structures dynamic characteristics. Test definition or verification provides the dynamic characteristic accuracy required for control systems use. An illumination/measurement system was developed to fly on space shuttle flight STS-31D. The system was designed to dynamically evaluate a large solar array called the Solar Array Flight Experiment (SAFE) that had been scheduled for this flight. The SAFDE system consisted of a set of laser diode illuminators, retroreflective targets, an intelligent star tracker receiver and the associated equipment to power, condition, and record the results. In six tests on STS-41D, data was successfully acquired from 18 retroreflector targets and ground processed, post flight, to define the solar array's dynamic characteristic. The flight experiment proved the viability of on-orbit test definition of large space structures dynamic characteristics. Future large space structures controllability should be greatly enhanced by this capability.

Schock, R. W.↗
NASA NTRS1987

Solar array flight dynamic experiment

The purpose of the Solar Array Flight Dynamic Experiment (SAFDE) is to demonstrate the feasibility of on-orbit measurement and ground processing of large space structures' dynamic characteristics. Test definition or verification provides the dynamic characteristic accuracy required for control systems use. An illumination/measurement system was developed to fly on space shuttle flight STS-41D. The system was designed to dynamically evaluate a large solar array called the Solar Array Flight Experiment (SAFE) that had been scheduled for this flight. The SAFDE system consisted of a set of laser diode illuminators, retroreflective targets, an intelligent star tracker receiver and the associated equipment to power, condition, and record the results. In six tests on STS-41D, data was successfully acquired from 18 retroreflector targets and ground processed, post flight, to define the solar array's dynamic characteristic. The flight experiment proved the viability of on-orbit test definition of large space structures dynamic characteristics. Future large space structures controllability should be greatly enhanced by this capability.

Schock, Richard W.↗