SEARCH · Engineering Papers

Results for “transient dynamic analysis”

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.

SourceResearch connectionFrom yearThrough year

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

At least 163 records · Page 9

All sources NASA NTRS DOE OSTI

NASA NTRS1989

Analysis of the transient compressible vapor flow in heat pipes

The transient compressible one-dimensional vapor flow dynamics in a heat pipe is modeled. The numerical results are obtained by using the implicit non-iterative Beam-Warming finite difference method. The model is tested for simulated heat pipe vapor flow and actual vapor flow in cylindrical heat pipes. A good comparison of the present transient results for the simulated heat pipe vapor flow with the previous results of a two-dimensional numerical model is achieved and the steady state results are in agreement with the existing experimental data. The transient behavior of the vapor flow under subsonic, sonic, and supersonic speeds and high mass flow rates are successfully predicted. The one-dimensional model also describes the vapor flow dynamics in cylindrical heat pipes at high temperatures.

Jang, J. H.↗

NASA NTRS1992

Finite element approach for transient analysis of multibody systems

A three-dimensional, finite element based formulation for the transient dynamics of constrained multibody systems with trusslike configurations is presented. A convected coordinate system is used to define the rigid-body motion of individual elements in the system. Deformation of each element is defined relative to its convected coordinate system. The formulation is oriented toward joint-dominated structures. Through a series of sequential transformations, the joint degree of freedom is built into the equations of motion of the element to reduce geometric constraints. Based on the derivation, a general-purpose code has been developed. Two examples are presented to illustrate the application of the code.

Wu, Shih-Chin↗

NASA NTRS1973

Transient analysis using conical shell elements

The use of the NASTRAN conical shell element in static, eigenvalue, and direct transient analyses is demonstrated. The results of a NASTRAN static solution of an externally pressurized ring-stiffened cylinder agree well with a theoretical discontinuity analysis. Good agreement is also obtained between the NASTRAN direct transient response of a uniform cylinder to a dynamic end load and one-dimensional solutions obtained using a method of characteristics stress wave code and a standing wave solution. Finally, a NASTRAN eigenvalue analysis is performed on a hydroballistic model idealized with conical shell elements.

Yang, J. C. S.↗

NASA NTRS1973

Dynamic analysis of an open-cycle gas-core nuclear rocket

Reactivity and flow disturbances were used to investigate the transient response of a conceptual open cycle gas core nuclear rocket engine. The disturbances were made with the system initially operating at its steady state design point. Results of the study show that the feedbacks associated with the propellant density and propellant temperature have a dominant effect on the response of the system. Furthermore, there appears to be a rather limited range of values of these propellant feedback coefficients for which the gas core nuclear rocket has a stable response. The system was rather insensitive to a fuel flow rate disturbance, whereas a similar disturbance in the propellant flow rate caused large changes in reactor power. For a similar disturbance in the propellant flow rate caused large changes in reactor power. For most reactivity and flow rate disturbances, the response showed oscillations of various intensity.

Turney, G. E.↗

NASA NTRS1980

Nonlinear transient analysis by energy minimization: A theoretical basis for the ACTION computer code

The formulation basis for establishing the static or dynamic equilibrium configurations of finite element models of structures which may behave in the nonlinear range are provided. With both geometric and time independent material nonlinearities included, the development is restricted to simple one and two dimensional finite elements which are regarded as being the basic elements for modeling full aircraft-like structures under crash conditions. Representations of a rigid link and an impenetrable contact plane are added to the deformation model so that any number of nodes of the finite element model may be connected by a rigid link or may contact the plane. Equilibrium configurations are derived as the stationary conditions of a potential function of the generalized nodal variables of the model. Minimization of the nonlinear potential function is achieved by using the best current variable metric update formula for use in unconstrained minimization. Powell's conjugate gradient algorithm, which offers very low storage requirements at some slight increase in the total number of calculations, is the other alternative algorithm to be used for extremely large scale problems.

Kamat, M. P.↗

NASA NTRS1980

Rotordynamics analysis for the HPFTP (High Pressure Fuel Turbopump) of the SSME (Space Shuttle Main Engine). SSME turbopump technology improvements via transient rotordynamics analysis

The results of both linear (stability and synchronous response) and transient nonlinear analyses are reported. Dynamic coefficients were developed for the HPFTP interstage seals, and introduced into the rotordynamic model. The influence on HPFTP rotordynamics of a change in interstage seals from the smooth stepped design to a smooth straight configuration was examined. The sensitivity of the stability and synchronous results to changes in bearing stiffnesses and damping was determined. The influence on rotordynamic stability of a change from the stiff symmetric bearing carrier design to an asymmetric bearing carrier configuration was also studied.

Childs, D. W.↗

NASA NTRS1984

STARS: A general-purpose finite element computer program for analysis of engineering structures

STARS (Structural Analysis Routines) is primarily an interactive, graphics-oriented, finite-element computer program for analyzing the static, stability, free vibration, and dynamic responses of damped and undamped structures, including rotating systems. The element library consists of one-dimensional (1-D) line elements, two-dimensional (2-D) triangular and quadrilateral shell elements, and three-dimensional (3-D) tetrahedral and hexahedral solid elements. These elements enable the solution of structural problems that include truss, beam, space frame, plane, plate, shell, and solid structures, or any combination thereof. Zero, finite, and interdependent deflection boundary conditions can be implemented by the program. The associated dynamic response analysis capability provides for initial deformation and velocity inputs, whereas the transient excitation may be either forces or accelerations. An effective in-core or out-of-core solution strategy is automatically employed by the program, depending on the size of the problem. Data input may be at random within a data set, and the program offers certain automatic data-generation features. Input data are formatted as an optimal combination of free and fixed formats. Interactive graphics capabilities enable convenient display of nodal deformations, mode shapes, and element stresses.

Gupta, K. K.↗

NASA NTRS1985

Preliminary analysis of selected gas dynamic problems

The VAST computer code was used to analyze SSME main combustion chamber start-up transients and the IUS flow field for a damaged nozzle was investigated to better understand the gas dynamic considerations involved in vehicle problems, the effect of start transients on the nozzle flow field for the SSME, and the possibility that a damaged nozzle could account for the acceleration anomaly noted on IUS burn. The results obtained were compared with a method of characteristics prediction. Pressure solutions from both codes were in very good agreement and the Mach number solution on the nozzle centerline deviates substantially for the high expansions for the SSME. Since this deviation was unexpected, the phenomenon is being further examined.

Prozan, R. J.↗

NASA NTRS1997

Implementation of Free-Formulation-Based Flat Shell Elements into NASA Comet Code and Development of Nonlinear Shallow Shell Element

This study presents a transient nonlinear finite element analysis within the realm of a multi-body dynamics formulation for determining the dynamic response of a moderately thick laminated shell undergoing a rapid and large rotational motion and nonlinear elastic deformations. Nonlinear strain measure and rotation, as well as 'the transverse shear deformation, are explicitly included in the formulation in order to capture the proper motion-induced stiffness of the laminate. The equations of motion are derived from the virtual work principle. The analysis utilizes a shear deformable shallow shell element along with the co-rotational form of the updated Lagrangian formulation. The shallow shell element formulation is based on the Reissner-Mindlin and Marguerre theory.

Barut, A.↗

NASA NTRS1975

A discussion of dynamic stability measurement techniques

Techniques for the measurement of the dynamic stability of linear systems are discussed. Particular attention is given to an analysis of the errors in the procedures, and to methods for calculating the system damping from the data. The techniques discussed include: transient decay, moving block analysis, spectral analysis, random decrement signatures, transfer function analysis, and parameter identification methods. The special problems of rotorcraft dynamic stability testing are discussed.

Johnson, W.↗

NASA NTRS1992

Thermoviscoplastic response of thin plates subjected to intense local heating

A finite element method is employed to investigate the thermoviscoplastic response of a half-cylinder to intense localized transient heating. Thermoviscoplastic material behavior is characterized by the Bodner-Partom constitutive model. Structure geometry is modeled with a three-dimensional assembly of CST-DKT plate elements incorporating the large deflection von Karman assumptions. The paper compares the results of a dynamic analysis with a quasi-static analysis for the half-cylinder structure with a step-function transient temperature loading similar to that which may be encountered with shock wave interference on a hypersonic leading edge.

Byrom, Ted G.↗

NASA NTRS2011

Time-Frequency Analysis of Rocket Nozzle Wall Pressures During Start-up Transients

Surveys of the fluctuating wall pressure were conducted on a sub-scale, thrust- optimized parabolic nozzle in order to develop a physical intuition for its Fourier-azimuthal mode behavior during fixed and transient start-up conditions. These unsteady signatures are driven by shock wave turbulent boundary layer interactions which depend on the nozzle pressure ratio and nozzle geometry. The focus however, is on the degree of similarity between the spectral footprints of these modes obtained from transient start-ups as opposed to a sequence of fixed nozzle pressure ratio conditions. For the latter, statistically converged spectra are computed using conventional Fourier analyses techniques, whereas the former are investigated by way of time-frequency analysis. The findings suggest that at low nozzle pressure ratios -- where the flow resides in a Free Shock Separation state -- strong spectral similarities occur between fixed and transient conditions. Conversely, at higher nozzle pressure ratios -- where the flow resides in Restricted Shock Separation -- stark differences are observed between the fixed and transient conditions and depends greatly on the ramping rate of the transient period. And so, it appears that an understanding of the dynamics during transient start-up conditions cannot be furnished by a way of fixed flow analysis.

Baars, Woutijn J.↗

NASA NTRS2010

Analysis of the STS-126 Flow Control Valve Structural-Acoustic Coupling Failure

During the Space Transportation System mission STS-126, one of the main engine's flow control valves incurred an unexpected failure. A section of the valve broke off during liftoff. It is theorized that an acoustic mode of the flowing fuel, coupled with a structural mode of the valve, causing a high cycle fatigue failure. This report documents the analysis efforts conducted in an attempt to verify this theory. Hand calculations, computational fluid dynamics, and finite element methods are all implemented and analyses are performed using steady-state methods in addition to transient analysis methods. The conclusion of the analyses is that there is a critical acoustic mode that aligns with a structural mode of the valve

Jones, Trevor M.↗

NASA NTRS1983

On the dynamic response and collapse of slender guyed booms for space application

A procedure is developed for the analysis of the nonlinear transient response of an initially imperfect slender guyed boom having a concentrated mass at the tip. The analysis is compared with laboratory experiments, and the validated procedure is employed to study the transient response of a boom to suddenly applied step loads and prescribed initial velocities. Both cases approximate the transient conditions associated with commencing and terminating a slewing maneuver in space. Two nonlinear effects are examined, namely cable slackening and beam column behavior. It is shown that dynamic buckling of the boom may occur with excitations which result in slackening of a cable. It is also shown that transverse boom tip deflections are sensitive only to initial eccentricities when certain threshold values are exceeded. Design guidelines are established for combinations of pulse level and duration which meet performance requirements for allowable deflections.

Housner, J. M.↗

NASA NTRS1953

Dynamics of mechanical feedback-type hydraulic servomotors under inertia loads

An analysis of the dynamics of mechanical feedback-type hydraulic servomotors under inertia loads is developed and experimental verification is presented. The analysis, which is developed in terms of two physical parameters, yields direct expressions for the following dynamic responses: (1) the transient response to a step input and the maximum cylinder pressure during the transient and (2) the variation of amplitude attenuation and phase shift with the frequency of a sinusoidally varying input. The validity of the analysis is demonstrated by means of recorded transient and frequency responses obtained on two servomotors. The calculated responses are in close agreement with the measured responses. The relations presented are readily applicable to the design as well as to the analysis of hydraulic servomotors.

Gold, Harold↗

NASA NTRS1989

Concurrent algorithms for transient FE analysis

Information on concurrent algorithms for transient finite element analysis is given in viewgraph form. Information is given on concurrent dynamic algorithms, interprocessor communication, the performance of the BAR problem on the 32 Processor Hypercube, computational efficiency and accuracy analysis.

Ortiz, M.↗

NASA NTRS1991

Analysis of the one-dimensional transient compressible vapor flow in heat pipes

The transient compressible one-dimensional vapor flow dynamics in a heat pipe is modeled. The numerical results are obtained by using the implicit non-iterative Beam-Warming finite difference method. The model is tested for simulated heat pipe vapor flow and actual vapor flow in cylindrical heat pipes. A good comparison of the present transient results for the simulated heat pipe vapor flow with the previous results of a two-dimensional numerical model is achieved and the steady state results are in agreement with the existing experimental data. The transient behavior of the vapor flow under subsonic, sonic, and supersonic speeds as well as high mass flow rates are successfully predicted.

Jang, Jong H.↗

NASA NTRS1978

CODSTRAN - Composite durability structural analysis

CODSTRAN (COmposite Durability STRucture ANalysis) a NASA Lewis Center computer program for the prediction of defect growth and fracture of composite structures when subjected to service loads is presented. Organization, capabilities and present status are discussed. Organizational aspects include executive, input, output, analysis and composite mechanics modules. Capabilities include: durability assessment of large structures and complex structural parts from composites, structural response due to static, cyclic, transient impact and thermal loads, and criteria for static, cyclic, and dynamic fracture. At the present state of development some of CODSTRAN's analysis capabilities include composite mechanics, static failures, and lamination residual stresses. An application in which CODSTRAN is used to predict the defect growth in a flat specimen, with a center through-slit under tension is studied. When completed, CODSTRAN will account for geometry and material nonlinearities, environmental effects as well as static, cyclic and dynamic fracture.

Chamis, C. C.↗