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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.

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At least 127 records · Page 7
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NASA NTRS2012

International Space Station Modal Correction Analysis

This paper summarizes the on-orbit modal test and the related modal analysis, model validation and correlation performed for the ISS Stage ULF4, DTF S4-1A, October 11,2010, GMT 284/06:13:00.00. The objective of this analysis is to validate and correlate analytical models with the intent to verify the ISS critical interface dynamic loads and improve fatigue life prediction. For the ISS configurations under consideration, on-orbit dynamic responses were collected with Russian vehicles attached and without the Orbiter attached to the ISS. ISS instrumentation systems that were used to collect the dynamic responses during the DTF S4-1A included the Internal Wireless Instrumentation System (IWIS), External Wireless Instrumentation System (EWIS), Structural Dynamic Measurement System (SDMS), Space Acceleration Measurement System (SAMS), Inertial Measurement Unit (IMU) and ISS External Cameras. 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 modal parameters were performed to assess the accuracy of models for the ISS configuration under consideration. Based on the frequency comparisons, the accuracy of the mathematical models is assessed and model refinement recommendations are given. Section 2.0 of this report presents the math model used in the analysis. This section also describes the ISS configuration under consideration and summarizes the associated primary modes of interest along with the fundamental appendage modes. Section 3.0 discusses the details of the ISS Stage ULF4 DTF S4-1A test. Section 4.0 discusses the on-orbit instrumentation systems that were used in the collection of the data analyzed in this paper. The modal analysis approach and results used in the analysis of the collected data are summarized in Section 5.0. The model correlation and validation effort is reported in Section 6.0. Conclusions and recommendations drawn from this analysis are included in Section 7.0.

Fotz[atrocl. Lrostom↗
NASA NTRS2019

Modern Modal Testing: A Cautionary Tale IMAC XXVII

Over the past 50 years, great advances have been achieved in both analytical modal analysis (i.e. finite element models and analysis) and experimental modal analysis (i.e. modal testing) in aerospace and other fields. With the advent of more powerful computers, higher performance instrumentation and data acquisition systems, and powerful linear modal extraction tools, analysts and test engineers have a breadth and depth of technical resources only dreamed of by our predecessors. However, some observed recent trends indicate that hard lessons learned are being forgotten or ignored, and possibly fundamental concepts are not being understood. These trends have the potential of leading to the degradation of the quality of and confidence in both analytical and test results. These trends are a making of our own doing, and directly related to having ever more powerful computers, programmatic budgetary pressures to limit analysis and testing, and technical capital loss due to the retirement of the senior component of a bimodal workforce. This paper endeavors to highlight some of the most important lessons learned, common pitfalls to hopefully avoid, and potential steps that may be taken to help reverse this trend.

bimodal workforce↗
NASA NTRS1983

Modal test and analysis correlation

Modal testing plays a significant role in experimentally measuring the modal parameters used directly for response analysis of spacecraft or indirectly to update a mathematical model for use in response analysis. Developments in modal testing and correlation of results to analytical models are discussed. Several procedures to semi-automate correlation of resonant frequency and mode shape test data to the model have been shown to be valid for hypothetical problems but have not been successful in practice. Improving the correlation of frequencies and mode shapes does not necessarily improve the correlation of modal force coefficients. The paper discusses other parameters, such as kinetic energy and strain energy, which may be more significant in the correlation process. Because the most demanding requirement of a modal test is in determining dynamic loads, the authors asssume that objective, minimally discussing theoretical developments, summarizing their results, and giving sample data.

Wada, B. K.↗
NASA NTRS1991

A modal aeroelastic analysis scheme for turbomachinery blading

An aeroelastic analysis is developed which has general application to all types of axial-flow turbomachinery blades. The approach is based on linear modal analysis, where the blade's dynamic response is represented as a linear combination of contributions from each of its in-vacuum free vibrational modes. A compressible linearized unsteady potential theory is used to model the flow over the oscillating blades. The two-dimensional unsteady flow is evaluated along several stacked axisymmetric strips along the span of the airfoil. The unsteady pressures at the blade surface are integrated to result in the generalized force acting on the blade due to simple harmonic motions. The unsteady aerodynamic forces are coupled to the blade normal modes in the frequency domain using modal analysis. An iterative eigenvalue problem is solved to determine the stability of the blade when the unsteady aerodynamic forces are included in the analysis. The approach is demonstrated by applying it to a high-energy subsonic turbine blade from a rocket engine turbopump power turbine. The results indicate that this turbine could undergo flutter in an edgewise mode of vibration.

Smith, Todd E.↗
NASA NTRS1976

Modal seismic analysis of a nuclear power plant control panel and comparison with SAP 4

The application of NASTRAN to seismic analysis by considering the example of a nuclear power plant control panel was considered. A modal analysis of a three-dimensional model of the panel, consisting of beam and quadri-lateral membrane elements, is performed. Using the results of this analysis and a typical response spectrum of an earthquake, the seismic response of the structure is obtained. ALTERs required to the program in order to compute the maximum modal responses as well as the resultant response are given. The results are compared with those obtained by using the SAP IV computer program.

Pamidi, M. R.↗
NASA NTRS2009

Modal Vibration Analysis of Large Castings

The art of experimental modal vibration analysis (MVA) has been extended to apply to large castings. This extension was made to enable the use of experimental MVA as a relatively inexpensive, simple means of assessing the internal structural integrity of tread shoes of crawler transporters used to move spacecraft to the launch pad at Kennedy Space Center. Each tread shoe is made from cast iron and weighs about a ton (has a mass .907 kg). The present extended version of experimental MVA could also be applied to other large castings. It could be especially useful to manufacturers as a means of rapidly discriminating against large castings that contain unacceptably large concentrations of internal defects. The use of experimental MVA to assess structural integrity is not new. What are new here are those aspects of the extension of experimental MVA that pertain to the application of MVA to objects so massive that it may not be practical or cost effective to mount them in special test fixtures that impose special test boundary conditions to test them in place under normal conditions of use.

Werlink, Rudolph J.↗
NASA NTRS1998

Potential and Limitations of the Modal Characterization of a Spacecraft Bus Structure by Means of Active Structure Elements

Theoretical and experimental studies have been performed to investigate the potential and limitations of the modal characterization of a typical spacecraft bus structure by means of active structure elements. The aim of these studies has been test and advance tools for performing an accurate on-orbit modal identification which may be characterized by the availability of a generally very limited test instrumentation, autonomous excitation capabilities by active structure elements and a zero-g environment. The NASA LARC CSI Evolutionary Testbed provided an excellent object for the experimental part of this study program. The main subjects of investigation were: (1) the selection of optimum excitation and measurement to unambiguously identify modes of interest; (2) the applicability of different types of excitation means with focus on active structure elements; and (3) the assessment of the modal identification potential of different types of excitation functions and modal analysis tools. Conventional as well as dedicated modal analysis tools were applied to determine modal parameters and mode shapes. The results will be presented and discussed based on orthogonality checks as well as on suitable indicators for the quality of the acquired modes with respect to modal purity. In particular, the suitability for modal analysis of the acquired frequency response functions as obtained by excitation with active structure elements will be demonstrated with the help of reciprocity checks. Finally, the results will be summarized in a procedure to perform an on-orbit modal identification, including an indication of limitation to be observed.

Grillenbeck, Anton M.↗
NASA NTRS1983

Nonlinear effect on modal data analysis method

How the presence of nonlinearities in structural test data can be detected when using modern linear modal data analysis methods is discussed. The extent to which linear algorithms can provide useful information on nonlinear systems was discussed. The modal data analysis method successfully identified the frequency components (but not damping) of the true solution of a nonlinear systems. It was found that the approximate modal parameters of the linear system can be identified by the modal method when low levels of nonlinearities are present. The modal method successfully identified the modal parameters of a linear mode in the presence of a nonlinear response.

Horta, L. G.↗
NASA NTRS1988

Modal cost analysis for simple continua

The most popular finite element codes are based upon appealing theories of convergence of modal frequencies. For example, the popularity of cubic elements for beam-like structures is due to the rapid convergence of modal frequencies and stiffness properties. However, for those problems in which the primary consideration is the accuracy of response of the structure at specified locations, it is more important to obtain accuracy in the modal costs than in the modal frequencies. The modal cost represents the contribution of a mode in the norm of the response vector. This paper provides a complete modal cost analysis for simple continua such as beam-like structures. Upper bounds are developed for mode truncation errors in the model reduction process and modal cost analysis dictates which modes to retain in order to reduce the model for control design purposes.

Hu, A.↗
NASA NTRS2020

Space Launch System Mobile Launcher Modal Pretest Analysis

NASA is developing an expendable heavy lift launch vehicle capability, the Space Launch System, to support lunar and deep space exploration. To support this capability, an updated ground infrastructure is required including modifying an existing Mobile Launcher system. The Mobile Launcher is a very large heavy beam/truss steel structure designed to support the Space Launch System during its buildup and integration in the Vehicle Assembly Building, transportation from the Vehicle Assembly Building out to the launch pad, and provides the launch platform at the launch pad. The previous Saturn/Apollo and Space Shuttle programs had integrated vehicle ground vibration tests of their integrated launch vehicles performed with simulated free-free boundary conditions to experimentally anchor and validate structural and flight controls analysis models. For the Space Launch System program, the Mobile Launcher will be used as the modal test fixture for the ground vibration test of the first Space Launch System flight vehicle, Artemis 1, programmatically referred to as the integrated vehicle modal test. The integrated vehicle modal test of the Artemis 1 integrated launch vehicle will have its core and second stages unfueled while mounted to the Mobile Launcher while inside the Vehicle Assembly Building, which is currently scheduled for the summer of 2020. The Space Launch System program has implemented a building block approach for dynamic model validation. The modal test of the Mobile Launcher is an important part of this building block approach in supporting the integrated vehicle modal test since the Mobile Launcher will serve as a structurally dynamic test fixture whose modes will couple with the modes of the Artemis 1 integrated vehicle. The Mobile Launcher modal test will further support understanding the structural dynamics of the Mobile Launcher and Space Launch System during rollout to the launch pad, which will play a key role in better understanding and prediction of the rollout forces acting on the launch vehicle. The Mobile Launcher modal test is currently scheduled for the summer of 2019. Due to a very tight modal testing schedule, this independent Mobile Launcher modal pretest analysis has been performed to ensure there is a high likelihood of successfully completing the modal test (i.e. identify the primary target modes) using the planned instrumentation, shakers, and excitation types. This paper will discuss this Mobile Launcher modal pretest analysis for its three test configurations and the unique challenges faced due to the Mobile Launcher’s size and weight, which are typically not faced when modal testing aerospace structures.

Akers, James C.↗
NASA NTRS2020

Space Launch System Mobile Launcher Modal Pretest Analysis

NASA is developing an expendable heavy lift launch vehicle capability, the Space Launch System, to support lunar and deep space exploration. To support this capability, an updated ground infrastructure is required including modifying an existing Mobile Launcher system. The Mobile Launcher is a very large heavy beam/truss steel structure designed to support the Space Launch System during its buildup and integration in the Vehicle Assembly Building, transportation from the Vehicle Assembly Building out to the launch pad, and provides the launch platform at the launch pad. The previous Saturn/Apollo and Space Shuttle programs had integrated vehicle ground vibration tests of their integrated launch vehicles performed with simulated free-free boundary conditions to experimentally anchor and validate structural and flight controls analysis models. For the Space Launch System program, the Mobile Launcher will be used as the modal test fixture for the ground vibration test of the first Space Launch System flight vehicle, Exploration Mission ? 1( now referred to as Artemis 1), programmatically referred to as the Integrated vehicle modal test. The Integrated vehicle modal test of the Exploration Mission - 1 integrated launch vehicle will have its core and second stages unfueled while mounted to the ML while inside the Vehicle Assembly Building, which is currently scheduled for the late spring or early summer of 2020. The Space Launch System program has implemented a building block approach for dynamic model validation. The modal test of the Mobile Launcher is an important part of this building block approach in supporting the integrated vehicle modal test since the Mobile Launcher will serve as a structurally dynamic test fixture whose modes will couple with the modes of the Exploration Mission ? 1 test vehicle. The Mobile Launcher modal test will further support understanding the structural dynamics of the Mobile Launcher and SLS during rollout to the launch pad, which will play a key role in better understanding and prediction of the rollout forces acting on the launch vehicle. The Mobile Launcher modal test is currently scheduled for the summer of 2019. Due to a very tight modal testing schedule, this Mobile Launcher modal pretest analysis has been performed to ensure there is a high likelihood of being able to successfully complete the modal test (i.e. identify the primary target modes) using the planned instrumentation, shakers, and excitation types. This paper will discuss this Mobile Launcher modal pretest analysis and the unique challenges faced due to the Mobile Launcher's size and weight, which are typically not faced when modal testing aerospace structures.

Akers, James C.↗
NASA NTRS1973

Stress, stability, and vibration of complex, branched shells of revolution.

A comprehensive computer program, designated BOSOR4, for analysis of the stress, stability, and vibration of segmented, ring-stiffened, branched shells of revolution and prismatic shells and panels is described. The program performs large-deflection axisymmetric stress analysis, small-deflection nonsymmetric stress analysis, modal vibration analysis with axisymmetric nonlinear prestress included, and buckling analysis with axisymmetric or nonsymmetric prestress. One of the main advantages of the code is the provision for realistic engineering details such as eccentric load paths, internal supports, arbitrary branching conditions, and a library of wall constructions. The program is based on the finite-difference energy method, which is very rapidly convergent with increasing numbers of mesh points.

Bushnell, D.↗
NASA NTRS1974

Stress, stability and vibration of complex, branched shells of revolution

A comprehensive computer program, designated BOSOR4, for analysis of the stress, stability, and vibration of segmented, ring-stiffened, branched shells of revolution and prismatic shells and panels is described. The program performs large-deflection axisymmetric stress analysis, small-deflection nonsymmetric stress analysis, modal vibration analysis with axisymmetric nonlinear prestress included, and buckling analysis with axisymmetric or nonsymmetric prestress. One of the main advantages of the code is the provision for realistic engineering details such as eccentric load paths, internal supports, arbitrary branching conditions, and a 'library' of wall constructions. The program is based on the finite-difference energy method, which is very rapidly convergent with increasing numbers of mesh points. The organization of the program is briefly described with the flow of calculations charted for each of the types of analysis. Overlay charts and core storage requirements are given for the CDC 6600, IBM 370/165, and UNIVAC 1108 versions of BOSOR4.

Bushnell, D.↗
NASA NTRS1989

Computing Stress, Stability, And Vibration Of Shells

BOSOR4 computer program developed as comprehensive program for analysis of stress, stability, and vibration of complex, branched shells of revolution made of elastic materials. Used to analyze prismatic shells and panels. Performs large-deflection axisymmetric stress analysis, small-deflection nonsymmetric stress analysis, modal vibration analysis with axisymmetric nonlinear prestress included, and buckling analysis with axisymmetric or nonsymmetric prestress. One main advantage, provisions for such realistic engineering details as eccentric load paths, internal supports, arbitrary branching conditions, and "library" of wall constructions. Based on finite-difference energy method and offers very rapid convergence with increasing numbers of mesh points. Written in FORTRAN 77.

Bushnell, David↗
NASA NTRS1993

High Temperature Composite Analyzer (HITCAN) demonstration manual, version 1.0

This manual comprises a variety of demonstration cases for the HITCAN (HIgh Temperature Composite ANalyzer) code. HITCAN is a general purpose computer program for predicting nonlinear global structural and local stress-strain response of arbitrarily oriented, multilayered high temperature metal matrix composite structures. HITCAN is written in FORTRAN 77 computer language and has been configured and executed on the NASA Lewis Research Center CRAY XMP and YMP computers. Detailed description of all program variables and terms used in this manual may be found in the User's Manual. The demonstration includes various cases to illustrate the features and analysis capabilities of the HITCAN computer code. These cases include: (1) static analysis, (2) nonlinear quasi-static (incremental) analysis, (3) modal analysis, (4) buckling analysis, (5) fiber degradation effects, (6) fabrication-induced stresses for a variety of structures; namely, beam, plate, ring, shell, and built-up structures. A brief discussion of each demonstration case with the associated input data file is provided. Sample results taken from the actual computer output are also included.

Singhal, S. N↗
NASA NTRS2005

Damage Prediction Models for Advanced Materials and Composites

In the present study, the assessment and evaluation of various acoustic tile designs were conducted using three-dimensional finite element analysis, which included static analysis, thermal analysis and modal analysis of integral and non-integral tile design options. Various benchmark specimens for acoustic tile designs, including CMC integral T-joint and notched CMC plate, were tested in both room and elevated temperature environment. Various candidate ceramic matrix composite materials were used in the numerical modeling and experimental study. The research effort in this program evolved from numerical modeling and concept design to a combined numerical analysis and experimental study. Many subjects associated with the design and performance of the acoustic tile in jet engine exhaust nozzle have been investigated.

Xie, Ming↗
NASA NTRS1996

Active Control of Fan Noise: Feasibility Study: Theoretical Analysis for Coupling of Active Noise Control Actuator Ring Sources to an Annular Duct with Flow - Volume 6

The objective of this effort is to develop an analytical model for the coupling of active noise control (ANC) piston-type actuators that are mounted flush to the inner and outer walls of an annular duct to the modes in the duct generated by the actuator motion. The analysis will be used to couple the ANC actuators to the modal analysis propagation computer program for the annular duct, to predict the effects of active suppression of fan-generated engine noise sources. This combined program will then be available to assist in the design or evaluation of ANC systems in fan engine annular exhaust ducts. An analysis has been developed to predict the modes generated in an annular duct due to the coupling of flush-mounted ring actuators on the inner and outer walls of the duct. The analysis has been combined with a previous analysis for the coupling of modes to a cylindrical duct in a FORTRAN computer program to perform the computations. The method includes the effects of uniform mean flow in the duct. The program can be used for design or evaluation purposes for active noise control hardware for turbofan engines. Predictions for some sample cases modeled after the geometry of the NASA Lewis ANC Fan indicate very efficient coupling in both the inlet and exhaust ducts for the m = 6 spinning mode at frequencies where only a single radial mode is cut-on. Radial mode content in higher order cut-off modes at the source plane and the required actuator displacement amplitude to achieve 110 dB SPL levels in the desired mode were predicted. Equivalent cases with and without flow were examined for the cylindrical and annular geometry, and little difference was found for a duct flow Mach number of 0.1. The actuator ring coupling program will be adapted as a subroutine to the cylindrical duct modal analysis and the exhaust duct modal analysis. This will allow the fan source to be defined in terms of characteristic modes at the fan source plane and predict the propagation to the arbitrarily-located ANC source plane. The actuator velocities can then be determined to generate the anti-phase mode. The resulting combined fan source/ANC pressure can then be calculated at any desired wall sensor position. The actuator velocities can be determined manually or using a simulation of a control system feedback loop. This will provide a very useful ANC system design and evaluation tool.

Kraft, R. E.↗
NASA NTRSDate not supplied

Modal Test and Analysis Correlation of Wind Tunnel Blades for the National Transonic Facility

NASA has a significant maintenance challenge with the aging wind tunnel infrastructure across the agency . Wind tunnel blades, such as the ones in the National Transonic Facility at NASA Langley Research Center, have been subjected to damage from impacts and fatigue. Accurate analytical models of these blades are necessary to either recertify replacement blades to be built or for redesign of these blades. In this paper an upgraded finite element model of these wind tunnel blades with the capability of representing damage is presented. An eigenvalue analysis of the structural model is performed, and the boundary conditions are adjusted to simulate the natural frequencies obtained by experimental testing of a set of twenty five blades in 1992. Additional numerical studies of the effect of delamination damage on the natural frequencies of the blade are conducted using the tuned finite element model.

wind tunnel↗