Lee Peterson

Improved Damage Location Accuracy Using Strain Energy-Based Mode Selection Criteria

A method is presented for selecting the subset of identified structural vibration modes to be used in finite element model correlation for structural damage detection. The method is hased on a ranking of the modes using measured modal strain energy and is a function of only the measured modal parameters. It is shown that a mode selection strategy based on maximum modal strain energy produces more accurate update results than a strategy based on minimum frequency. Strategies that use the strain energy stored by modes in both the undamaged and damaged structural configuration are considered. It is demonstrated that more accurate results are obtained when the modes are selected using the maximum strain energy stored in the damaged structural configuration. The mode selection techniques are applied to the results of a damage detection experiment on a suspended truss structure that has a large amount of localized modal behavior.

Selection of experimental modal data sets for damage detection via model update

When using a finite element model update algorithm for detecting damage in structures, it is important that the experimental modal data sets used in the update be selected in a coherent manner. In the case of a structure with extremely localized modal behavior, it is necessary to use both low and high frequency modes, but many of the modes in between may be excluded. In this paper, we examine two different mode selection strategies based on modal strain energy, and compare their success to the choice of an equal number of modes based merely on lowest frequency. Additionally, some parameters are introduced to enable a quantitative assessment of the success of our damage detection algorithm when using the various set selection criteria.

M3tk: A Robot Mobility and Manipulation Modeling Toolkit

In this brief paper, we present an overview of the M3tk software for modeling robotic systems. M3tk contains basic kinematics, inverse kinematics, dynamics and inverse dynamics capabilities for articulated multi-rigid body systems. Written in C++, the software features a core kinematics and dynamics library, a linear algebra library specialized for use with the algorithms in M3tk, and a Graphical User Interface with full 3D visualization. It contains implementations of multiple contact mechanics models and the ability to model terrain through heightfields. M3tk also features an ability to model terrains with spatially distributed properties. There is also an ability to manipulate objects using a joystick. This paper summarizes M3tk without delving into the details of the code.Copyright

An Evaluation of Structural Analysis Methodologies for Space Deployable Structures

Benchmarks are introduced for evaluating the performance of numerical simulations of space deployable structures. These benchmarks embody the key challenges of interest to future large space deployable structures, including large angle motion, contact between flexible bodies, and the presence of both soft and stiff mechanical components. The benchmarks were used in companion studies to evaluate the ADAMS multibody dynamics code, the LS-Dyna nonlinear finite element code, and the Sierra large-scale parallel nonlinear finite element code. In the past, only multibody codes would have been considered for this application. This study found that all three codes could be used for these benchmarks, a finding that may lead to larger scale, higher fidelity simulations in the future.

Development of Multi-Physics Dynamics Models for High-Frequency Large-Amplitude Structural Response Simulation

An analytic approach is demonstrated to reveal potential pyroshock-driven dynamic effects causing temporary power losses in the Thermo-Electric (TE) module bars of the Mars Science Laboratory (MSL) Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). This study utilizes high-fidelity finite element analysis with SIERRA/PRESTO codes to estimate wave propagation effects due to large-amplitude suddenly-applied pyroshock loads in the MMRTG. A high fidelity model of the TE module bar was created with ∼30 million degrees-of-freedom (DOF). First, a quasi-static preload was applied on top of the TE module bar, then transient tri-axial displacement inputs were simultaneously applied on the preloaded module. The applied displacement inputs were derived from measured acceleration signals during MMRTG shock qualification tests performed at the Jet Propulsion Laboratory. An explicit finite element solver in the SIERRA/PRESTO computational environment, along with a 3000 processor parallel super-computing framework at NASA-AMES, was used for the simulation. The simulation results were investigated both qualitatively and quantitatively. The predicted shock wave propagation results provide detailed structural responses throughout the TE module bar, and key insights into the dynamic response (i.e., loads, displacements, accelerations) of critical internal spring/piston compression systems, TE materials, and internal component interfaces in the MMRTG TE module bar. They also provide confidence on the viability of this high-fidelity modeling scheme to accurately predict shock wave propagation patterns within complex structures. This analytic approach is envisioned for modeling shock sensitive hardware susceptible to intense shock environments positioned near shock separation devices in modern space vehicles and systems.

Simulation of the continuous parametric identification of an accelerating aeroelastic system

The influence of longitudinal acceleration on the characteristics of an aeroelastic system are investigated in this paper. Using numerical simulation for a typical wing section, we show that for longitudinal accelerations that are typically achieved by aircraft, the aeroelastic characteristics in accelerated flight are comparable to those in stabilized flight conditions. This suggests that flutter testing could be performed in accelerated flight, thereby reducing the cost and risk involved in determining the aeroelastic behavior of aircraft.