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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 415 records · Page 23

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NASA NTRS1981

On the motion of a flexible shallow spherical shell in orbit

A mathematical model for the motion of a large, flexible shallow spherical shell in a circular orbit is presented. For small elastic displacements and attitude angles the linearized equations for the roll and yaw (out-of-plane) motions completely separate from the pitch (in-plane) and elastic motions. However, the pitch and only the axisymmetric elastic modes are seen to be coupled in the linear range. With the shell's symmetry axis following the local vertical, the structure undergoes a static deformation under the influence of gravity and inertia. Further, the pitch and roll motions are unstable due to the unfavorable moment of inertia distribution. A rigid lightweight dumbbell with heavy tip masses and connected to the shell at its apex by a spring loaded double gimbal joint is proposed to gravitationally stabilize the structure. It is noted that the dumbbell motion can excite only those elastic modes having one nodal diameter. A sensitivity study of the system response characteristics to the key system parameters is carried out.

Kumar, V. K.↗

DOE OSTI2025

Fingerprints of Triaxiality in the Charge Radii of Neutron-Rich Ruthenium

We present the first measurements with a new collinear laser spectroscopy setup at the Argonne Tandem Linac Accelerator System, utilizing its unique capability to deliver neutron-rich refractory metal isotopes produced by the spontaneous fission of 252 Cf. We measured isotope shifts from optical spectra for nine radioactive ruthenium isotopes 106–114 Ru, reaching deep into the mid-shell region. The extracted charge radii are in excellent agreement with predictions from the Brussels-Skyrme-on-a-Grid models that account for the triaxial deformation of nuclear ground states. We show that triaxial deformation impacts charge radii in models that feature shell effects, in contrast to what could be concluded from a liquid drop analysis. This indicates that this exotic type of deformation should not be neglected in regions where it is known to occur, even if its presence cannot be unambiguously inferred through laser spectroscopy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS2011

Dynamic Shape Reconstruction of Three-Dimensional Frame Structures Using the Inverse Finite Element Method

A robust and efficient computational method for reconstructing the three-dimensional displacement field of truss, beam, and frame structures, using measured surface-strain data, is presented. Known as shape sensing , this inverse problem has important implications for real-time actuation and control of smart structures, and for monitoring of structural integrity. The present formulation, based on the inverse Finite Element Method (iFEM), uses a least-squares variational principle involving strain measures of Timoshenko theory for stretching, torsion, bending, and transverse shear. Two inverse-frame finite elements are derived using interdependent interpolations whose interior degrees-of-freedom are condensed out at the element level. In addition, relationships between the order of kinematic-element interpolations and the number of required strain gauges are established. As an example problem, a thin-walled, circular cross-section cantilevered beam subjected to harmonic excitations in the presence of structural damping is modeled using iFEM; where, to simulate strain-gauge values and to provide reference displacements, a high-fidelity MSC/NASTRAN shell finite element model is used. Examples of low and high-frequency dynamic motion are analyzed and the solution accuracy examined with respect to various levels of discretization and the number of strain gauges.

Gherlone, Marco↗

NASA NTRS1978

On sound transmission into a heavily-damped cylinder

A mathematical model for the transmission of sound into a thin monocoque cylindrical shell is discussed. The model is used to evaluate an oblique plane wave incident upon a flexible thin cylindrical shell. The solution is applicable to the transmission of sound under actual flight conditions. The model is then used to determine curves of cylinder-transmission loss for heavily damped cylinders. Numerical results are found for several plane-wave incidence angles for a narrow-bodied jet fuselage made of aluminum. It is noted that damping (i.e., the loss factor) increases, dips because of reduced cylinder resonances, and eventually disappears when the loss factor of the shell is large enough.

Koval, L. R.↗

NASA NTRS1991

Knowledge-based Autonomous Test Engineer (KATE)

Mathematical models of system components have long been used to allow simulators to predict system behavior to various stimuli. Recent efforts to monitor, diagnose, and control real-time systems using component models have experienced similar success. NASA Kennedy is continuing the development of a tool for implementing real-time knowledge-based diagnostic and control systems called KATE (Knowledge based Autonomous Test Engineer). KATE is a model-based reasoning shell designed to provide autonomous control, monitoring, fault detection, and diagnostics for complex engineering systems by applying its reasoning techniques to an exchangeable quantitative model describing the structure and function of the various system components and their systemic behavior.

Parrish, Carrie L.↗

NASA NTRS2014

A Coupled Fluid-Structure Interaction Analysis of Solid Rocket Motor with Flexible Inhibitors

A capability to couple NASA production CFD code, Loci/CHEM, with CFDRC's structural finite element code, CoBi, has been developed. This paper summarizes the efforts in applying the installed coupling software to demonstrate/investigate fluid-structure interaction (FSI) between pressure wave and flexible inhibitor inside reusable solid rocket motor (RSRM). First a unified governing equation for both fluid and structure is presented, then an Eulerian-Lagrangian framework is described to satisfy the interfacial continuity requirements. The features of fluid solver, Loci/CHEM and structural solver, CoBi, are discussed before the coupling methodology of the solvers is described. The simulation uses production level CFD LES turbulence model with a grid resolution of 80 million cells. The flexible inhibitor is modeled with full 3D shell elements. Verifications against analytical solutions of structural model under steady uniform pressure condition and under dynamic condition of modal analysis show excellent agreements in terms of displacement distribution and eigen modal frequencies. The preliminary coupled result shows that due to acoustic coupling, the dynamics of one of the more flexible inhibitors shift from its first modal frequency to the first acoustic frequency of the solid rocket motor.

Yang, H. Q.↗

NASA NTRS2013

A Census of X-ray Gas in NGC 1068: Results From 450 ks of CHANDRA High Energy Transmisson Grating Observations

We present models for the X-ray spectrum of the Seyfert 2 galaxy NGC 1068. These are fitted to data obtained using the High Energy Transmission Grating on Chandra. The data show line and radiative recombination continuum emission from a broad range of ions and elements. The models explore the importance of excitation processes for these lines including photoionization followed by recombination, radiative excitation by absorption of continuum radiation, and inner shell fluorescence. The models show that the relative importance of these processes depends on the conditions in the emitting gas and that no single emitting component can fit the entire spectrum. In particular, the relative importance of radiative excitation and photoionization/recombination differs according to the element and ion stage emitting the line. This in turn implies a diversity of values for the ionization parameter of the various components of gas responsible for the emission, ranging from log(E ) = 1 to 3. Using this, we obtain an estimate for the total amount of gas responsible for the observed emission. The mass flux through the region included in the HETG extraction region is approximately 0.3M/yr, assuming ordered flow at the speed characterizing the line widths. This can be compared with what is known about this object from other techniques.

galaxies: Seyfert↗

NASA NTRS1988

A preliminary investigation of finite-element modeling for composite rotor blades

The results from an initial phase of an in-house study aimed at improving the dynamic and aerodynamic characteristics of composite rotor blades through the use of elastic couplings are presented. Large degree of freedom shell finite element models of an extension twist coupled composite tube were developed and analyzed using MSC/NASTRAN. An analysis employing a simplified beam finite element representation of the specimen with the equivalent engineering stiffness was additionally performed. Results from the shell finite element normal modes and frequency analysis were compared to those obtained experimentally, showing an agreement within 13 percent. There was appreciable degradation in the frequency prediction for the torsional mode, which is elastically coupled. This was due to the absence of off-diagonal coupling terms in the formulation of the equivalent engineering stiffness. Parametric studies of frequency variation due to small changes in ply orientation angle and ply thickness were also performed. Results showed linear frequency variations less than 2 percent per 1 degree variation in the ply orientation angle, and 1 percent per 0.0001 inch variation in the ply thickness.

Lake, Renee C.↗

NASA NTRS1988

A preliminary investigation of finite-element modeling for composite rotor blades

Lake, Renee C.↗

NASA NTRS1987

Nonisothermal elasto-visco-plastic response of shell-type structures

A mathematical model and solution methodologies for analyzing structural response of thin, metallic shell-type structures under large transient, cyclic or static thermomechanical loads is disussed. Among the system responses, which are associated with these load conditions, are thermal buckling and creep buckling. Thus, geometric as well as material-type nonlinearities (of high order) can be anticipated and have been considered in the development of the mathematical model. Furthermore, this was accommodated in the solution procedures. A complete true ab-inito rate theory of kinematics and kinetics for continuum and curved thin structures, without any restriction on the magnitude of the strains or the deformation, was formulated. The time dependence and large strain behavior are incorporated through the introduction of the time rates of the metric and curvature in two coordinate systems, a fixed (spatial) one and a convected (material) coordinate system. The relations between the time derivative and the covariant derivatives (gradients) have been developed for curved space and motion, so that the velocity components supply the connection between the equations of motion and the time rate of change of the metric and curvature tensors.

Simitses, G. J.↗

NASA NTRSDate not supplied

Progress on Electric Motor Noise Modeling

Progress toward the development of a motor noise model for system type studies is presented. The presentation focuses on efforts to model the motor shell vibrations and the resulting acoustic radiation. Finite element and experimental modal analysis results for a 4 kW motor are presented and compared. An analytical model for the acoustic radiation is presented.

Urban Air Mobility↗

NASA NTRS1992

Mechanics of anisotropic plates and shells - A new look at an old subject

A number of aspects of the mechanics of anisotropic plates and shells are discussed. The topics covered include computational models of anisotropic plates and shells, consequences of anisotropy on deformation couplings, symmetry types, stress concentrations and edge effects, and importance of transverse shear deformation; recent applications and recent advances in the modeling and analysis of anisotropic plates and shells; and new research directions.

Noor, A. K.↗

DOE OSTI2025

Convective shells in the interior of Cepheid variable stars: Overshooting models based on hydrodynamic simulations

Context. Because Cepheid variable stars have long been used as a cosmic benchmark for scaling distances in our Galaxy and beyond, the accuracy of stellar evolution models for Cepheids have wide-reaching effects. However, our understanding of the dynamics in the interiors of these physically complex stars is limited. Aims. Our goal is to provide a detailed multi-dimensional picture of hydrodynamic convection and convective boundary mixing in the interior of Cepheids. Methods. Using the Modules for Experiments in Stellar Astrophysics (MESA), we studied the structure of intermediate-mass stars that cross the instability strip. Then, we performed two-dimensional hydrodynamic simulations of six stars with the fully compressible Multidimensional Stellar Implicit Code (MUSIC). Our simulations did not model the radial pulsations but focused on the interior structure of this family of stars. We developed and applied a new statistical analysis to examine convection and convective boundary mixing in the interior of these stellar simulations. Results. Based on a grid of MESA models, we demonstrated that a common structure for intermediate mass Cepheids includes an interior convective shell as well as a thin outer convective envelope. Using the extreme value theory approach to analyze our MUSIC simulation data, we found that overshooting above the convective shell fills the space between these convectively unstable layers. We developed a new statistical analysis that provides a clearer picture of how overshooting fills this layer; it also allowed us to formulate a detailed comparison between overshooting above and below the convective shell. Our analysis effectively decomposes the overshooting layer into two layers: a weak overshooting layer and a strong overshooting layer. Statistically, this is accomplished by decomposing the strongly non-Gaussian probability density function into a mixture of gamma distributions. Using our mixture model, we showed that the ratio of overshooting lengths above and below the convective shell depends directly on the radial extent of the convective shell as well as its depth in the star. We proposed a new form for the diffusion coefficient that addresses the need for overlapping overshooting layers between convective shells. We introduced the idea of a “super-mixing layer” where overshooting from both the convective shell and the convective envelope results in efficient mixing and could be viewed as merging the two adjacent convective zones.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2010

Effect of Microscopic Damage Events on Static and Ballistic Impact Strength of Triaxial Braid Composites

The reliability of impact simulations for aircraft components made with triaxial-braided carbon-fiber composites is currently limited by inadequate material property data and lack of validated material models for analysis. Methods to characterize the material properties used in the analytical models from a systematically obtained set of test data are also lacking. A macroscopic finite element based analytical model to analyze the impact response of these materials has been developed. The stiffness and strength properties utilized in the material model are obtained from a set of quasi-static in-plane tension, compression and shear coupon level tests. Full-field optical strain measurement techniques are applied in the testing, and the results are used to help in characterizing the model. The unit cell of the braided composite is modeled as a series of shell elements, where each element is modeled as a laminated composite. The braided architecture can thus be approximated within the analytical model. The transient dynamic finite element code LS-DYNA is utilized to conduct the finite element simulations, and an internal LS-DYNA constitutive model is utilized in the analysis. Methods to obtain the stiffness and strength properties required by the constitutive model from the available test data are developed. Simulations of quasi-static coupon tests and impact tests of a represented braided composite are conducted. Overall, the developed method shows promise, but improvements that are needed in test and analysis methods for better predictive capability are examined.

Littell, Justin D.↗

NASA NTRS1990

Error detection and control for nonlinear shell analysis

A problem-adaptive solution procedure for improving the reliability of finite element solutions to geometrically nonlinear shell-type problem is presented. The strategy incorporates automatic error detection and control and includes an iterative procedure which utilizes the solution at the same load step on a more refined model. Representative nonlinear shell problem are solved.

Mccleary, Susan L.↗

NASA NTRS1975

On sound transmission into a thin cylindrical shell under 'flight conditions'

A mathematical model for sound transmission into a thin cylindrical shell is used to study sound transmission under flight conditions, i.e., under conditions of external air flow past a pressurized cylinder at flight altitude. Numerical results for different incidence angles are presented for a typical narrow-bodied jet in cruising flight at 10,660 m with interior pressure at 2440 m. A comparison is made between no-flow sound transmission at standard conditions on the ground to sound transmission under flight conditions. It is shown that at M = 0, the cylinder transmission loss (TL) has dips at the cylinder ring frequency (fR) and the critical frequency (fc) for a flat panel of same material and thickness as shell. Between fR and fc, cylinder TL follows a mass-law behavior. Flow provides a modest increase in TL in the mass-law region, and strongly interacts with the cylinder resonances below fR.

Koval, L. R.↗

NASA NTRS1992

Modelling a single phase voltage controlled rectifier using Laplace transforms

The development of a 20 kHz, AC power system by NASA for large space projects has spurred a need to develop models for the equipment which will be used on these single phase systems. To date, models for the AC source (i.e., inverters) have been developed. It is the intent of this paper to develop a method to model the single phase voltage controlled rectifiers which will be attached to the AC power grid as an interface for connected loads. A modified version of EPRI's HARMFLO program is used as the shell for these models. The results obtained from the model developed in this paper are quite adequate for the analysis of problems such as voltage resonance. The unique technique presented in this paper uses the Laplace transforms to determine the harmonic content of the load current of the rectifier rather than a curve fitting technique. Laplace transforms yield the coefficient of the differential equations which model the line current to the rectifier directly.

Kraft, L. Alan↗

NASA NTRSDate not supplied

Classical Flutter Analysis of X-57 Aircraft Mod II, III, and IV Configurations

To support airworthiness assessment of the X-57 electric propulsion demonstrator aircraft, the National Aeronautics and Space Administration (NASA) completed classical flutter analysis of the Mod II, Mod III, and Mod IV aircraft configurations. Aeroelastic analysis was primarily performed using the ZAERO analysis code developed by Zona Technology. Supplemental computational fluid dynamics (CFD) flutter analysis for the Mod III and Mod IV configurations was performed using NASA’s FUN3D software to verify the aeroelastic behavior at deployed flaps conditions. The NASTRAN finite element models (FEMs) used for aeroelastic analysis were developed by NASA. The final Mod II FEM utilized shell elements for the wing and fuselage, and beam elements for the tail and wing control surfaces. For Mod III and Mod IV aircraft models, shell element wing FEMs developed throughout the Mod III/IV wing design cycle were utilized. The fuselage and empennage FEM components were shared between the Mod II, III, and IV aircraft models. ZAERO analyses predicted flutter boundaries were >60% beyond the X-57 flight-test envelope never exceed airspeed (V NE ) for all configurations. Aeroelastic Reynolds-averaged Navier–Stokes (RANS) CFD simulations using FUN3D of the Mod III/IV configurations predicted flap mode instability did not occur until at least speeds of 60% higher than the Mod III/IV maximum flap deployment airspeed (V FE ).

Keerti K. Bhamidipati↗