Engineering topics

Hunt, David L.

Publications and source records attributed to Hunt, David L..

4 records

NASA NTRS1992

Application of an enhanced Coordinate Modal Assurance Criterion

This paper presents an extension of the Coordinate Modal Assurance Criterion (COMAC) for spatial comparison of mode shapes. As is the case for the original COMAC, this enhanced COMAC helps identify degrees of freedom differences between test and analysis modes, but also overcomes some of the limitations of the original COMAC. The original COMAC cannot identify errors caused by scaling or polarity mistakes in the test data. Such mistakes are easily made during modal tests and not always easily detected since they do not affect the subjective quality of a frequency response function.

Hunt, David L.↗

NASA NTRS1990

Development and implementation of a shuttle modal inspection system

One of the major tasks between Space Shuttle flights is inspection of the orbiter subsystems such as control surfaces, vertical tail, and wings. To date, inspection techniques have consisted primarily of visual and X-ray methods, which are not only time consuming but not as comprehensive as desired. Previous shuttle component and orbiter ground modal testing revealed that orbiter component damage could be identified using standard modal test methods. As a result, NASA has procured a dedicated shuttle modal inspection system (SMIS) that will be used for subsystem inspection. This paper presents a background on the use of modal testing to detect shuttle component damage, details on this new implementation, and an early use of the SMIS capability to investigate a potential orbiter vibration problem.

Hunt, David L.↗

NASA NTRS1990

Simulation of on-orbit modal tests of large space structures

This paper describes a procedure to analytically simulate a modal test of an on-orbit large space structure (LSS), extract the modal properties, and evaluate the success of the modal test. This procedure addresses some of the major challenges to performing an on-orbit modal test of an LSS including high modal density, low frequency modes, and limitations in excitation capabilities. A finite element model of the orbiting structure is used to predict acceleration responses due to thruster excitations, time-domain modal extraction methods are used to estimate the modal properties, and comparison of frequencies and cross-orthogonality values is used to evaluate the success of the modal test. Several alternative excitation patterns and sensor arrangements were evaluated using a space station model as an example. Results of the simulations indicate that the choice of excitation functions is critical to the success of the test.

Blelloch, Paul↗

NASA NTRS1987

Modal survey of the space shuttle solid rocket motor using multiple input methods

The ability to accurately characterize propellant in a finite element model is a concern of engineers tasked with studying the dynamic response of the Space Shuttle Solid Rocket Motor (SRM). THe uncertainties arising from propellant characterization through specimem testing led to the decision to perform a model survey and model correlation of a single segment of the Shuttle SRM. Multiple input methods were used to excite and define case/propellant modes of both an inert segment and, later, a live propellant segment. These tests were successful at defining highly damped, flexible modes, several pairs of which occured with frequency spacing of less than two percent.

Brillhart, Ralph↗