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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Computation of Effective Mechanical Properties and Mechanical Erosion Modeling of TPS Materials

The goal of this presentation is to provide a general overview of the multi-scale modeling formulation to determine if there is additional surface recession in Thermal Protection Systems (TPS) materials as a result of mechanical erosion due to high shear conditions during atmospheric entry. This modeling process is performed at different scales by leveraging two computational frameworks developed at NASA: the Porous Microstructure Analysis (PuMA) software, and the Porous material Analysis Toolbox based on OpenFOAM (PATO). PuMA specializes in computing effective macro-scale material properties by performing material response simulations on 3D digital micro-scale representations of porous micro-structures. The modeling of TPS materials at the micro-scale is essential to understand how they behave as part of a heat shield assembly. The first part of the presentation will detail the implementation of PuMA’s cell-centered finite volume elasticity solver, which allows the computation of macro-scale effective mechanical properties of heterogeneous and anisotropic materials such as fibrous and woven TPS composites. These homogenized mechanical properties are used by PATO’s mechanical erosion model to predict the TPS material’s recession at a larger scale. This work will also provide some examples of multi-scale analysis from the fiber level up to the unit cell. The second part of the presentation will focus on the macro-scale approach to determine if erosion at the heat shield’s surface occurs due to mechanical and thermal loads experienced during atmospheric entry. To accomplish this, a solid mechanics module was integrated within PATO enabling it to model the potential mechanical erosion in three steps: first, after obtaining the effective mechanical properties with PuMA, the implemented stress analysis solver computes the stress and the displacement fields for the TPS material using the wall shear stress tensor, computed using a CFD solver, as boundary conditions; then, regions on the surface where the stress meets the failure criteria are identified; finally, the failed material is removed and the mesh is redistributed accordingly. The outcome is a model capable of predicting the total recession in the material due to surface chemistry and mechanical erosion.

Mechanical Properties↗
NASA NTRS1976

Application of a novel finite difference method to dynamic crack problems

A versatile finite difference method (HEMP and HEMP 3D computer programs) was developed originally for solving dynamic problems in continuum mechanics. It was extended to analyze the stress field around cracks in a solid with finite geometry subjected to dynamic loads and to simulate numerically the dynamic fracture phenomena with success. This method is an explicit finite difference method applied to the Lagrangian formulation of the equations of continuum mechanics in two and three space dimensions and time. The calculational grid moves with the material and in this way it gives a more detailed description of the physics of the problem than the Eulerian formulation.

Chen, Y. M.↗
NASA NTRS2003

Shuttle Systems 3-D Applications: Application of 3-D Graphics in Engineering Training for Shuttle Ground Processing

This project illustrates an animation of the orbiter mate to the external tank, an animation of the OMS POD installation to the orbiter, and a simulation of the landing gear mechanism at the Kennedy Space Center. A detailed storyboard was created to reflect each animation or simulation. Solid models were collected and translated into Pro/Engineer's prt and asm formats. These solid models included computer files of the: orbiter, external tank, solid rocket booster, mobile launch platform, transporter, vehicle assembly building, OMS POD fixture, and landing gear. A depository of the above solid models was established. These solid models were translated into several formats. This depository contained the following files: stl for sterolithography, stp for neutral file work, shrinkwrap for compression, tiff for photoshop work, jpeg for Internet use, and prt and asm for Pro/Engineer use. Solid models were created of the material handling sling, bay 3 platforms, and orbiter contact points. Animations were developed using mechanisms to reflect each storyboard. Every effort was made to build all models technically correct for engineering use. The result was an animated routine that could be used by NASA for training material handlers and uncovering engineering safety issues.

Godfrey, Gary S.↗
NASA NTRS1987

Stochastic and hybrid-stress plate/shell finite elements for hot-section components

The research effort in the Center for the Advancement of Computational Mechanics at Georgia Tech has two main thrusts. The first of these is the development of special approaches for the numerical stress analysis of solids and structures whose material and geometric properties are uncertain. The second seeks to develop and implement high-efficiency plate and shell elements. The stochastic element method, currently being implemented, will be able to more accurately portray the probabilistic nature of stress, strain, and displacement in actual structures. Current research has provided a hybrid-stress shell element whose behavior is acceptable for aspect ratios as high as 30 to 1. Thus, substantially more complex analyses will be practicable as soon as this element is fully implemented. An additional advantage of the hybrid approach is that it permits more accurate stress-recovery at the upper and lower surfaces of the shell, an important consideration in high thickness-gradient applications. The software associated with the above research is being implemented in the form of extensions to the Nessus code. The hybrid shell element has been successfully tested in several small-deformation elastic analyses. The theoretical formulation of the stochastic elements is essentially complete; its implementation is just beginning.

Atluri, S. N.↗
NASA NTRS1992

Numerical procedures for three-dimensional computational surface thermochemistry

Models and equations for surface thermochemistry and near-surface thermophysics of aerodynamically-heated thermal protection materials are reviewed, with particular emphasis on computational boundary conditions for surface mass and energy transfer. The surface energy and mass balances, coupled with an appropriate ablation or surface catalysis model, provide complete thermochemical boundary conditions for a true multidisciplinary solution of the fully coupled fluid-dynamics/solid mechanics problem. Practical approximate solutions can be obtained by using a detailed model with full thermophysics for either the solid or fluid phase amd a semianalytic method for the other half of the problem. A significant increase in the state-of-the-art in aerothermal computational fluid dynamics is possible by uniting CFD methodology with surface thermochemistry boundary conditions and the heat-balance-integral method.

Milos, Frank S.↗
NASA NTRS1993

Unified Ultrasonic/Eddy-Current Data Acquisition

Imaging station for detecting cracks and flaws in solid materials developed combining both ultrasonic C-scan and eddy-current imaging. Incorporation of both techniques into one system eliminates duplication of computers and of mechanical scanners; unifies acquisition, processing, and storage of data; reduces setup time for repetitious ultrasonic and eddy-current scans; and increases efficiency of system. Same mechanical scanner used to maneuver either ultrasonic or eddy-current probe over specimen and acquire point-by-point data. For ultrasonic scanning, probe linked to ultrasonic pulser/receiver circuit card, while, for eddy-current imaging, probe linked to impedance-analyzer circuit card. Both ultrasonic and eddy-current imaging subsystems share same desktop-computer controller, containing dedicated plug-in circuit boards for each.

Chern, E. James↗
NASA NTRS1993

Comment on tangential wave motion in unstable combustors

An attempt is made to gain insight into the injection boundary instability mechanism as captured by a simple computational tool developed for liquid rocket engines. Considerable evidence is generated supporting a hypothesis that destructive tangential-mode instabilities in liquid-fuel combustors are driven by combustion processes occurring at the propellant-wetted injector face. The driving action is found to be directly analogous to a burning solid propellant surface mechanism, responsible for solid rocket motor instabilities. Since the proposed instability mechanism has not been fundamentally confirmed, experimental research is strongly recommended.

Litchford, Ron J.↗
NASA NTRS1992

Thermal mechanical analysis of sprag clutches

Work done at Case Western Reserve University on the Thermal Mechanical analysis of sprag helicopter clutches is reported. The report is presented in two parts. The first part is a description of a test rig for the measurement of the heat generated by high speed sprag clutch assemblies during cyclic torsional loading. The second part describes a finite element modeling procedure for sliding contact. The test rig provides a cyclic torsional load of 756 inch-pounds at 5000 rpm using a four-square arrangement. The sprag clutch test unit was placed between the high speed pinions of the circulating power loop. The test unit was designed to have replaceable inner ad outer races, which contain the instrumentation to monitor the sprag clutch. The torque loading device was chosen to be a water cooled magnetic clutch, which is controlled either manually or through a computer. In the second part, a Generalized Eulerian-Lagrangian formulation for non-linear dynamic problems is developed for solid materials. This formulation is derived from the basic laws and axioms of continuum mechanics. The novel aspect of this method is that we are able to investigate the physics in the spatial region of interest as material flows through it without having to follow material points. A finite element approximation to the governing equations is developed. Iterative Methods for the solution of the discrete finite element equations are explored. A FORTRAN program to implement this formulation is developed and a number of solutions to problems of sliding contact are presented.

Mullen, Robert L.↗
NASA NTRS1988

Development of automation and robotics for space via computer graphic simulation methods

A robot simulation system, has been developed to perform automation and robotics system design studies. The system uses a procedure-oriented solid modeling language to produce a model of the robotic mechanism. The simulator generates the kinematics, inverse kinematics, dynamics, control, and real-time graphic simulations needed to evaluate the performance of the model. Simulation examples are presented, including simulation of the Space Station and the design of telerobotics for the Orbital Maneuvering Vehicle.

Fernandez, Ken↗
NASA NTRS2016

Scalable Implementation of Finite Elements by NASA _ Implicit (ScIFEi)

Scalable Implementation of Finite Elements by NASA (ScIFEN) is a parallel finite element analysis code written in C++. ScIFEN is designed to provide scalable solutions to computational mechanics problems. It supports a variety of finite element types, nonlinear material models, and boundary conditions. This report provides an overview of ScIFEi (\Sci-Fi"), the implicit solid mechanics driver within ScIFEN. A description of ScIFEi's capabilities is provided, including an overview of the tools and features that accompany the software as well as a description of the input and output le formats. Results from several problems are included, demonstrating the efficiency and scalability of ScIFEi by comparing to finite element analysis using a commercial code.

Warner, James E.↗
NASA NTRS1998

Advanced Exploration Technologies: Micro and Nano Technologies Enabling Space Missions in the 21st Century

Some of the many new and advanced exploration technologies which will enable space missions in the 21st century and specifically the Manned Mars Mission are explored in this presentation. Some of these are the system on a chip, the Computed-Tomography imaging Spectrometer, the digital camera on a chip, and other Micro Electro Mechanical Systems (MEMS) technology for space. Some of these MEMS are the silicon micromachined microgyroscope, a subliming solid micro-thruster, a micro-ion thruster, a silicon seismometer, a dewpoint microhygrometer, a micro laser doppler anemometer, and tunable diode laser (TDL) sensors. The advanced technology insertion is critical for NASA to decrease mass, volume, power and mission costs, and increase functionality, science potential and robustness.

Krabach, Timothy↗
NASA NTRS1976

Singularity computations

An approach is described for singularity computations based on a numerical method for elastoplastic flow to delineate radial and angular distribution of field quantities and measure the intensity of the singularity. The method is applicable to problems in solid mechanics and lends itself to certain types of heat flow and fluid motion studies. Its use is not limited to linear, elastic, small strain, or two-dimensional situations.

Swedlow, J. L.↗
NASA NTRS1977

Cooling considerations for design of a radial inflow turbine

A numerical study to determine the temperature distribution in the rotor of a radial inflow turbine is presented. Internal cooling passages are modeled in the present formulation in order to carry out solid and coolant temperature computations simultaneously resulting in a considerable computer time savings. The stresses due to centrifugal and thermal loadings are determined in an actual rotor and the effect of cooling design on its mechanical integrity is discussed.

Hamed, A.↗
NASA NTRS1979

Space environment and lunar surface processes

The development of a general rock/soil model capable of simulating in a self consistent manner the mechanical and exposure history of an assemblage of solid and loose material from submicron to planetary size scales, applicable to lunar and other space exposed planetary surfaces is discussed. The model was incorporated into a computer code called MESS.2 (model for the evolution of space exposed surfaces). MESS.2, which represents a considerable increase in sophistication and scope over previous soil and rock surface models, is described. The capabilities of previous models for near surface soil and rock surfaces are compared with the rock/soil model, MESS.2.

Comstock, G. M.↗
NASA NTRSDate not supplied

Mechanical Erosion Modeling of TPS Materials

The goal of this work is to predict the mechanical response of TPS materials, and specifically, to determine if there is additional surface recession in the heat shield’s surface as a result of mechanical erosion due to the mechanical and thermal loads experienced during atmospheric entry. To accomplish this, a solid mechanics module was integrated within the PATO material response code, enabling it to model the potential mechanical erosion in three steps: first, having the effective mechanical properties as function of temperature, the implemented stress analysis solver computes the stress and the displacement fields for the TPS material using the wall shear stress tensor, computed with the DPLR hypersonic CFD code, as boundary conditions; then, regions on the surface where the stress meets the failure criteria are identified; finally, the failed material is removed and the mesh is redistributed accordingly. The outcome is a model capable of predicting the total recession in the TPS material due to surface chemistry and mechanical erosion.

Stress Analysis↗
NASA NTRS1991

Simplified computational methods for elastic and elastic-plastic fracture problems

This paper presents an overview of some of the recent (1984-1991) developments in computational/analytical methods in the mechanics of fracture: (i) analytical solutions for elliptical or circular cracks embedded in isotropic or transversely isotropic solids (the crack-plane being at an arbitrary angle to the axis of transverse isotropy), with crack-faces being subjected to arbitrary tractions; (ii) finite-element or boundary-element alternating methods for two- and three-dimensional crack problems; (iii) a "direct-stiffness" method for stiffened panels with flexible fasteners and with multiple cracks, using the alternating method; (iv) multiplesite-damage near a row of fastener holes; (v) analysis of cracks with bonded repair patches; (vi) methods for generation of weight-functions for 2- and 3-D crack problems, and (vii) domain-integral methods for elastic-plastic or inelastic crack mechanics.

Aging Aircraft↗
NASA NTRS1996

Solid Surface Combustion Experiment Completes a Series of Eight Successful Flights

The Solid Surface Combustion Experiment (SSCE) was the first combustion experiment to fly in the space shuttle and the first such experiment in the NASA spaceflight program since Skylab. SSCE was actually a series of experiments designed to begin to characterize flame spreading over solid fuels in microgravity and the differences of this flame spreading from normal gravity behavior. These experiments should lead to a better understanding of the physical processes involved--increasing our understanding of fire behavior, both in space and on Earth. SSCE results will help researchers evaluate spacecraft fire hazards. These experiments were conceived by the principal investigator, Professor Robert A. Altenkirch, Dean of Engineering at Washington State University. In the first five flights, the fuel sample--ashless filter paper instrumented with three thermocouples--was mounted in a sealed chamber filled with a 50-percent or 35-percent mixture of oxygen in nitrogen at pressures of 1.0, 1.5, and 2.0 atm. In the next three flights, a polymethyl methacrylate (plexiglass) fuel was instrumented with three thermocouples and tested in a 70-percent or 50-percent mixture of oxygen and nitrogen at pressures of 1.0 and 2.0 atm. SSCE is a self-contained, battery-operated experiment that can be flown either in the shuttle middeck or in the Spacelab module. More information about the hardware configuration have been published. This past year, the final two of eight flights were completed on STS-64 and STS-63. The NASA Lewis Research Center designed and built the SSCE payload and performed engineering, testing, scientific, and flight operations support. The SSCE project was supported in some way by nearly every major sector of Lewis' organization. Professor Altenkirch developed a numerical simulation of the flame-spreading process from first principles (of fluid mechanics, heat transfer, and reaction kinetics). The spread rates, flame shape, and thermodynamic data from the SSCE flights are being compared directly with the results of the computational model. Results from the eight flights will be used to formulate an improved solid-phase pyrolysis model. In addition, some results of the flights have been published and presented at international combustion symposiums. Additional solid fuel combustion experiments are being investigated for future tests with the existing hardware.

Source record↗