Results for “Finite element model updating” — Page 8

NASA NTRS2017

Near Earth Asteroid Scout Solar Sail Thrust and Torque Model

The Near Earth Asteroid (NEA) Scout is a solar sail mission whose objective is to scout at least one Near Earth Asteroid to help prepare for human missions to Near Earth Asteroids. NEA Scout will launch as a secondary payload on the first SLS-Orion mission. NEA Scout will perform a small trim maneuver shortly after deploy from the spent SLS upper stage using a cold gas propulsion system, but from that point on will depend entirely on the solar sail for thrust. As such, it is important to accurately characterize the thrust of the sail in order to achieve mission success. Additionally, the solar sail creates a relatively large solar disturbance torque that must be mitigated. For early mission design studies a flat plate model of the solar sail with a fixed center of pressure was adequate, but as mission concepts and the sail design matured, greater fidelity was required. Here we discuss the progress to a three-dimensional sail model that includes the effects of tension and thermal deformation that has been derived from a large structural Finite Element Model (FEM) developed by the Langley Research Center. We have found that the deformed sail membrane affects torque relatively much more than thrust; a flat plate model could potentially model thrust well enough to close mission design studies, but a three-dimensional solar sail is essential to control system design. The three-dimensional solar sail model revealed that thermal deformations of unshielded booms would create unacceptably large solar disturbance torques. The original large FEM model was used in control and mission simulations, but was resulted in simulations with prohibitive run times. This led us to adapt the Generalized Sail Model (GSM) of Rios-Reyes. A design reference sail model has been baselined for NEA Scout and has been used to design the mission and control system for the sailcraft. Additionally, since NEA Scout uses reaction wheels for attitude pointing and control, the solar torque model is essentially to successfully design the NEA Scout momentum management control system. We have also updated the estimate of diffusivity used for the aluminized sail material based on optical testing of wrinkled sail material. The model presented here represents the current state of the art of NASA's ability to model solar sail thrust and torque.

Heaton, Andy↗

NASA NTRS1987

DYCAST: A finite element program for the crash analysis of structures

DYCAST is a nonlinear structural dynamic finite element computer code developed for crash simulation. The element library contains stringers, beams, membrane skin triangles, plate bending triangles and spring elements. Changing stiffnesses in the structure are accounted for by plasticity and very large deflections. Material nonlinearities are accommodated by one of three options: elastic-perfectly plastic, elastic-linear hardening plastic, or elastic-nonlinear hardening plastic of the Ramberg-Osgood type. Geometric nonlinearities are handled in an updated Lagrangian formulation by reforming the structure into its deformed shape after small time increments while accumulating deformations, strains, and forces. The nonlinearities due to combined loadings are maintained, and stiffness variation due to structural failures are computed. Numerical time integrators available are fixed-step central difference, modified Adams, Newmark-beta, and Wilson-theta. The last three have a variable time step capability, which is controlled internally by a solution convergence error measure. Other features include: multiple time-load history tables to subject the structure to time dependent loading; gravity loading; initial pitch, roll, yaw, and translation of the structural model with respect to the global system; a bandwidth optimizer as a pre-processor; and deformed plots and graphics as post-processors.

Pifko, A. B.↗

NASA NTRS2001

A High-Order Finite Spectral Volume Method for Conservation Laws on Unstructured Grids

A time accurate, high-order, conservative, yet efficient method named Finite Spectral Volume (FSV) is developed for conservation laws on unstructured grids. The concept of a 'spectral volume' is introduced to achieve high-order accuracy in an efficient manner similar to spectral element and multi-domain spectral methods. In addition, each spectral volume is further sub-divided into control volumes (CVs), and cell-averaged data from these control volumes is used to reconstruct a high-order approximation in the spectral volume. Riemann solvers are used to compute the fluxes at spectral volume boundaries. Then cell-averaged state variables in the control volumes are updated independently. Furthermore, TVD (Total Variation Diminishing) and TVB (Total Variation Bounded) limiters are introduced in the FSV method to remove/reduce spurious oscillations near discontinuities. A very desirable feature of the FSV method is that the reconstruction is carried out only once, and analytically, and is the same for all cells of the same type, and that the reconstruction stencil is always non-singular, in contrast to the memory and CPU-intensive reconstruction in a high-order finite volume (FV) method. Discussions are made concerning why the FSV method is significantly more efficient than high-order finite volume and the Discontinuous Galerkin (DG) methods. Fundamental properties of the FSV method are studied and high-order accuracy is demonstrated for several model problems with and without discontinuities.

Wang, Z. J.↗

NASA NTRS2021

Computational Inference of Vibratory System with Incomplete Modal Information Using Parallel, Interactive and Adaptive Markov Chains

Inverse analysis of vibratory system is an important subject in fault identification, model updating, and robust design and control. It is challenging subject because 1) the problem is oftentimes underdetermined while the measurements are limited and/or incomplete; 2) many combinations of parameters may yield results that are similar with respect to actual response measurements; and 3) uncertainties inevitably exist. The aim of this research is to leverage upon computational intelligence through statistical inference to facilitate an enhanced, probabilistic framework using incomplete modal response measurement. This new framework is built upon efficient inverse identification through optimization, whereas Bayesian inference is employed to account for the effect of uncertainties. To overcome the computational cost barrier, we adopt Markov chain Monte Carlo (MCMC) to characterize the target function/distribution. Instead of using single Markov chain in conventional Bayesian approach, we develop a new sampling theory with multiple parallel, interactive and adaptive Markov chains and incorporate it into Bayesian inference. This can harness the collective power of these Markov chains to realize the concurrent search of multiple local optima. The number of required Markov chains and their respective initial model parameters are automatically determined via Monte Carlo simulation-based sample pre-screening followed by K-means clustering analysis. These enhancements can effectively address the aforementioned challenges in finite element inverse analysis. The validity of this framework is systematically demonstrated through case studies.

K Zhou↗

NASA NTRS1998

WARP3D-Release 10.8: Dynamic Nonlinear Analysis of Solids using a Preconditioned Conjugate Gradient Software Architecture

This report describes theoretical background material and commands necessary to use the WARP3D finite element code. WARP3D is under continuing development as a research code for the solution of very large-scale, 3-D solid models subjected to static and dynamic loads. Specific features in the code oriented toward the investigation of ductile fracture in metals include a robust finite strain formulation, a general J-integral computation facility (with inertia, face loading), an element extinction facility to model crack growth, nonlinear material models including viscoplastic effects, and the Gurson-Tver-gaard dilatant plasticity model for void growth. The nonlinear, dynamic equilibrium equations are solved using an incremental-iterative, implicit formulation with full Newton iterations to eliminate residual nodal forces. The history integration of the nonlinear equations of motion is accomplished with Newmarks Beta method. A central feature of WARP3D involves the use of a linear-preconditioned conjugate gradient (LPCG) solver implemented in an element-by-element format to replace a conventional direct linear equation solver. This software architecture dramatically reduces both the memory requirements and CPU time for very large, nonlinear solid models since formation of the assembled (dynamic) stiffness matrix is avoided. Analyses thus exhibit the numerical stability for large time (load) steps provided by the implicit formulation coupled with the low memory requirements characteristic of an explicit code. In addition to the much lower memory requirements of the LPCG solver, the CPU time required for solution of the linear equations during each Newton iteration is generally one-half or less of the CPU time required for a traditional direct solver. All other computational aspects of the code (element stiffnesses, element strains, stress updating, element internal forces) are implemented in the element-by- element, blocked architecture. This greatly improves vectorization of the code on uni-processor hardware and enables straightforward parallel-vector processing of element blocks on multi-processor hardware.

Koppenhoefer, Kyle C.↗

NASA NTRS2024

Risk of Bone Fracture due to Spaceflight-induced Changes to Bone

The Human Research Program (HRP) is taking a biomechanical approach to assessing subsequent fracture risk in active astronauts as a consequence of spaceflight exposure. Triennial testing of active and retired astronauts continues as Space Medicine monitors for a premature diagnosis of primary osteoporosis, which is associated with age-related bone loss and skeletal fragility. This updated 2023 Fracture Evidence Report has expanded the description of skeletal changes to capture the full effects of spaceflight on bone: • Recent analysis of fractures from health records of the full astronaut cohort, suggests an increased incidence rate of hip and spine fractures in astronauts following longer spaceflight duration flights compared to incident rates found in shorter duration flights. • Routine preflight-to-postflight surveillance by DXA (dual-energy x-ray absorptiometry) does not provide the full detection of loss and recovery in the long-duration (LD) astronaut nor the full recovery of hip trabecular bone. • The inclusion of hip quantitative computed tomography (QCT) in flight studies delineates effects of spaceflight, of countermeasures, and of post-flight recovery on cortical and trabecular bone parameters—some of which are verified predictors of hip fracture in the aged. • QCT detects and compares the distinct countermeasure effects of the pharmaceutical alendronate and of resistive exercise (on the Advanced Resistive Exercise Device, ARED) in specific cortical and trabecular bone sub-regions during spaceflight. • A published comparison of QCT-determined loss rates of hip trabecular bone in LD astronauts compared to terrestrial cohorts suggest that accelerated loss rates in trabecular volumetric BMD (vBMD) during spaceflight might be analogous to skeletal effects of accelerated loss rates in females due to menopause, potentially leading to disruptions in trabecular microarchitecture. • A dataset of finite element (FE) estimates of hip bone strength in aging terrestrial cohorts (spanning astronaut age-range) provides comparative context for changes in the FE of hip bone strength in LD astronauts, including comparison (force unit of newton) to percentiles (50th, 75th, and 100th) of sex-matched aged humans with hip fractures. • Risk of fracture, due to the mechanical overloading of bones, is being updated with IMPACT, the next-generation tool suite for probabilistic risk assessment (PRA) for exploration missions being created by the Exploration and Medical Capability Element (ExMC) at NASA. IMPACT is currently in development and will not be included in this 2024 update. The risk for fracture necessitates understanding the relationship between applied loads to bone and the biomechanical competence of bone. The Risk for Early Onset Osteoporosis focuses on the weakened condition of bone (including development of new technologies, measurements of novel skeletal attributes, translation of multiple measures to an index of bone fragility, and interpretations of data used to reflect a weakened bone), while the Risk for Fracture assesses factors that influence the probability an astronaut would encounter applied loads exceeding the biomechanical competence of bones, resulting in fracture. This Evidence Report combines the research gaps and tasks associated with both risks.

Fracture↗

NASA NTRSDate not supplied

Component Characterization of an eVTOL Reference Model for Crashworthiness Studies

Researchers at the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) have conducted a series of structural component and seat level tests to improve finite element model (FEM) characterization of a representative vertical take-off and landing (eVTOL) test article developed by NASA. A full-scale dynamic test was conducted on the representative eVTOL test article in November of 2022. The test article represented a high wing, six passenger eVTOL design concept and is referred to as the lift plus cruise (LPC) test article. The full-scale test identified limitations in the analytical models used to predict aircraft structural response, in particular the composite material models did not effectively capture brittle failure of the structure which were measured during dynamic loading. To better understand the mechanism behind the composite material failure mechanisms observed and to improve the FEM, intact sample specimens of the composite airframe structure were recovered from the test article post-test and used in material characterization testing. In addition, the seat configurations used in the LPC test article were further studied using isolated seat and anthropomorphic test device (ATD) drop tower testing. Dynamic compression tests and three-point bend tests, conducted at varied impact speeds, were performed on the recovered frame section specimens. Additional testing was conducted to characterize the material properties of the forming foam, which remained in the frames after fabrication. These tests were used to improve characterization of the damage and failure parameters of the composite material model used in the FE model of the LPC test article. Seat level tests were conducted on the seats used in the LPC test article using acceleration pulses inclusive of current general aviation and rotorcraft certification load levels as well as conditions representative of those measured at the seat base during the LPC test. The structural material models and seat environment models of the LPC test article FEM were calibrated using the generated component test data. The updates made to these models were then integrated into the LPC FEM and simulated in the full-scale test condition. Results demonstrated the effectiveness of component testing to improve predictive capability of composite aerospace structural models within the crash and dynamic loading environments. Demonstration of the LPC FEM response across an accumulation of coupon, component, seat environment, and full-scale test levels provides confidence in the predictive capability of this model for future use in the study of occupant safety within eVTOL relevant crash environments.

Craswhorthiness↗

NASA NTRSDate not supplied

Component Characterization of an eVTOL Reference Model for Crashworthiness Studies

Researchers at the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) have conducted a series of structural component and seat level tests to improve finite element model (FEM) characterization of a representative vertical take-off and landing (eVTOL) test article developed by NASA. A full-scale dynamic test was conducted on the representative eVTOL test article in November of 2022. The test article represented a high wing, six passenger eVTOL design concept and is referred to as the lift plus cruise (LPC) test article. The full-scale test identified limitations in the analytical models used to predict aircraft structural response, in particular the composite material models did not effectively capture brittle failure of the structure which were measured during dynamic loading. To better understand the mechanism behind the composite material failure mechanisms observed and to improve the FEM, intact sample specimens of the composite airframe structure were recovered from the test article post-test and used in material characterization testing. In addition, the seat configurations used in the LPC test article were further studied using isolated seat and anthropomorphic test device (ATD) drop tower testing. Dynamic compression tests and three-point bend tests, conducted at varied impact speeds, were performed on the recovered frame section specimens. Additional testing was conducted to characterize the material properties of the forming foam, which remained in the frames after fabrication. These tests were used to improve characterization of the damage and failure parameters of the composite material model used in the FE model of the LPC test article. Seat level tests were conducted on the seats used in the LPC test article using acceleration pulses inclusive of current general aviation and rotorcraft certification load levels as well as conditions representative of those measured at the seat base during the LPC test. The structural material models and seat environment models of the LPC test article FEM were calibrated using the generated component test data. The updates made to these models were then integrated into the LPC FEM and simulated in the full-scale test condition. Results demonstrated the effectiveness of component testing to improve predictive capability of composite aerospace structural models within the crash and dynamic loading environments. Demonstration of the LPC FEM response across an accumulation of coupon, component, seat environment, and full-scale test levels provides confidence in the predictive capability of this model for future use in the study of occupant safety within eVTOL relevant crash environments.

Craswhorthiness↗

NASA NTRSDate not supplied

Operational Modal Analysis of the Space Launch System Mobile Launcher on the Crawler Transporter ISVV-010 Rollout

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 between the Vehicle Assembly Building and launch pad 39B by the Crawler Transporter, and provides the launch platform at the launch pad. As part of the Verification and Validation of the Mobile Launcher and Crawler Transporter, two rollouts of the Mobile Launcher transported by the Crawler Transporter, Integrated System Verification and Validation (ISVV) 005 and 010, have been performed to demonstrate the Crawler Transporter’s ability to transport the Mobile Launcher. ISVV-005 occurred in September 2018 and ISVV-010 occurred in late June 2019. ISVV-005 and ISVV-010 also provided the opportunity to gather data that can be used identify the Mobile Launcher on the Crawler Transporter rollout modal characteristics and refine the estimates of the Artemis I integrated launch vehicle rollout forcing functions. While the rollout environment has historically produced relatively small launch vehicle structural loads for the Saturn/Apollo and Space Shuttle programs in comparison to launch and ascent loads, these relatively small structural loads are inputs to structural fatigue analyses. The same holds true for the Space Launch System. Because the rollout forces acting on the Mobile Launcher and the Crawler Transporter are not directly measurable, Operational Modal Analysis techniques, instead of traditional Experimental Modal Analysis techniques, provide an empirical means to identify the Mobile Launcher on the Crawler Transporter rollout modal characteristics. The ISVV-010 rollout modal characteristics provide important supplemental modal information, which along with the Mobile Launcher modal test that was performed in June 2019 immediately prior to ISVV-010 rollout, combine to reduce uncertainty in the test correlated Mobile Launcher on the Crawler Transporter finite element model. A well test correlated finite element model will play a key role in the Building Block approach the Space Launch System program has implemented as part of its certification process for the Artemis I flight and in refining the Artemis I rollout forcing functions. At the time of the ISVV-005 rollout in September 2018, the Mobile Launcher was still undergoing construction, and therefore its modal characteristics are not directly comparable to those of the Mobile Launcher during the June 2019 Mobile Launcher modal test and subsequent ISVV-010 rollout. Hence the ISVV-005 rollout modal characteristics will not be looked at in this paper. This paper will briefly describe the Mobile Launcher and Crawler Transporter physical characteristics, ISVV-010 rollout data collection, the challenges in implementing Operational Modal Analysis techniques due in part to the Crawler Transporter harmonics, and how these challenges were overcome to obtain the ISVV-010 Mobile Launcher on the Crawler Transporter rollout modal characteristics.

Apollo↗

NASA NTRS2021

Operational Modal Analysis of the Space Launch System Mobile Launcher on the Crawler Transporter ISVV-010 Rollout

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 between the Vehicle Assembly Building and launch pad 39B by the Crawler Transporter, and provides the launch platform at the launch pad. As part of the Verification and Validation of the Mobile Launcher and Crawler Transporter, two rollouts of the Mobile Launcher transported by the Crawler Transporter, Integrated System Verification and Validation (ISVV) 005 and 010, have been performed to demonstrate the Crawler Transporter’s ability to transport the Mobile Launcher. ISVV-005 occurred in September 2018 and ISVV-010 occurred in late June 2019. ISVV-005 and ISVV-010 also provided the opportunity to gather data that can be used identify the Mobile Launcher on the Crawler Transporter rollout modal characteristics and refine the estimates of the Artemis I integrated launch vehicle rollout forcing functions. While the rollout environment has historically produced relatively small launch vehicle structural loads for the Saturn/Apollo and Space Shuttle programs in comparison to launch and ascent loads, these relatively small structural loads are inputs to structural fatigue analyses. The same holds true for the Space Launch System. Because the rollout forces acting on the Mobile Launcher and the Crawler Transporter are not directly measurable, Operational Modal Analysis techniques, instead of traditional Experimental Modal Analysis techniques, provide an empirical means to identify the Mobile Launcher on the Crawler Transporter rollout modal characteristics. The ISVV-010 rollout modal characteristics provide important supplemental modal information, which along with the Mobile Launcher modal test that was performed in June 2019 immediately prior to ISVV-010 rollout, combine to reduce uncertainty in the test correlated Mobile Launcher on the Crawler Transporter finite element model. A well test correlated finite element model will play a key role in the Building Block approach the Space Launch System program has implemented as part of its certification process for the Artemis I flight and in refining the Artemis I rollout forcing functions. At the time of the ISVV-005 rollout in September 2018, the Mobile Launcher was still undergoing construction, and therefore its modal characteristics are not directly comparable to those of the Mobile Launcher during the June 2019 Mobile Launcher modal test and subsequent ISVV-010 rollout. Hence the ISVV-005 rollout modal characteristics will not be looked at in this paper. This paper will briefly describe the Mobile Launcher and Crawler Transporter physical characteristics, ISVV-010 rollout data collection, the challenges in implementing Operational Modal Analysis techniques due in part to the Crawler Transporter harmonics, and how these challenges were overcome to obtain the ISVV-010 Mobile Launcher on the Crawler Transporter rollout modal characteristics.

Apollo↗

NASA NTRS2002

Program Instrumentation and Trace Analysis

Several attempts have been made recently to apply techniques such as model checking and theorem proving to the analysis of programs. This shall be seen as a current trend to analyze real software systems instead of just their designs. This includes our own effort to develop a model checker for Java, the Java PathFinder 1, one of the very first of its kind in 1998. However, model checking cannot handle very large programs without some kind of abstraction of the program. This paper describes a complementary scalable technique to handle such large programs. Our interest is turned on the observation part of the equation: How much information can be extracted about a program from observing a single execution trace? It is our intention to develop a technology that can be applied automatically and to large full-size applications, with minimal modification to the code. We present a tool, Java PathExplorer (JPaX), for exploring execution traces of Java programs. The tool prioritizes scalability for completeness, and is directed towards detecting errors in programs, not to prove correctness. One core element in JPaX is an instrumentation package that allows to instrument Java byte code files to log various events when executed. The instrumentation is driven by a user provided script that specifies what information to log. Examples of instructions that such a script can contain are: 'report name and arguments of all called methods defined in class C, together with a timestamp'; 'report all updates to all variables'; and 'report all acquisitions and releases of locks'. In more complex instructions one can specify that certain expressions should be evaluated and even that certain code should be executed under various conditions. The instrumentation package can hence be seen as implementing Aspect Oriented Programming for Java in the sense that one can add functionality to a Java program without explicitly changing the code of the original program, but one rather writes an aspect and compiles it into the original program using the instrumentation. Another core element of JPaX is an observation package that supports the analysis of the generated event stream. Two kinds of analysis are currently supported. In temporal analysis the execution trace is evaluated against formulae written in temporal logic. We have implemented a temporal logic evaluator on finite traces using the Maude rewriting system from SRI International, USA. Temporal logic is defined in Maude by giving its syntax as a signature and its semantics as rewrite equations. The resulting semantics is extremely efficient and can handle event streams of hundreds of millions events in few minutes. Furthermore, the implementation is very succinct. The second form of even stream analysis supported is error pattern analysis where an execution trace is analyzed using various error detection algorithms that can identify error-prone programming practices that may potentially lead to errors in some different executions. Two such algorithms focusing on concurrency errors have been implemented in JPaX, one for deadlocks and the other for data races. It is important to note, that a deadlock or data race potential does not need to occur in order for its potential to be detected with these algorithms. This is what makes them very scalable in practice. The data race algorithm implemented is the Eraser algorithm from Compaq, however adopted to Java. The tool is currently being applied to a code base for controlling a spacecraft by the developers of that software in order to evaluate its applicability.

Havelund, Klaus↗

NASA NTRS1993

Computational mechanics needs study

In order to assess the needs in computational mechanics over the next decade, we formulated a questionnaire and contacted computational mechanics researchers and users in industry, government, and academia. As expected, we found a wide variety of computational mechanics usage and research. This report outlines the activity discussed with those contacts, as well as that in our own organizations. It should be noted that most of the contacts were made before the recent decline of the defense industry. Therefore, areas which are strongly defense-oriented may decrease in relative importance. In order to facilitate updating of this study, names of a few key researchers in each area are included as starting points for future literature surveys. These lists of names are not intended to represent those persons doing the best research in that area, nor are they intended to be comprehensive. They are, as previously stated, offered as starting points for future literature searches. Overall, there is currently a broad activity in computational mechanics in this country, with the breadth and depth increasing as more sophisticated software and faster computers become more available. The needs and desires of the workers in this field are as diverse as their background and organizational products. There seems to be some degree of software development in any organization (although the level of activity is highly variable from one organization to another) which has any research component in its mission. It seems, however, that there is considerable use of commercial software in almost all organizations. In most industrial research organizations, it appears that very little actual software development is contracted out, but that most is done in-house, using a mixture of funding sources. Government agencies vary widely in the ratio of in-house to out-house ratio. There is a considerable amount of experimental verification in most, but not all, organizations. Generally, the amount of experimental verification is more than we expected. Of all the survey contacts, one or two believe that the resources they are allocated are sufficient, but most do not. Some believe they have only half the resources they need. Some see their resource deficits as short-term, while others see it as a trend which will continue or perhaps worsen. The pessimism is stronger in the defense and aerospace industry. When considering only the nonlinear development efforts, there appears to be an even mix of geometric and material nonlinearity. There is not much particular emphasis in linear analysis unless it is in extension of current analysis capabilities to larger problems. The primary exception is concern about modeling of composites, where proven methodologies have trailed element and computer hardware development. Most of the people we spoke to use finite element techniques, but there is some finite difference and boundary element work ongoing. There is also some interest in multiple methods. Coupling of finite elements and boundary elements appears to be of high interest, since the two analysis types are complementary.

Griffin, O. Hayden, Jr.↗