501 research outputs found
Spatiotemporal video-domain high-fidelity simulation and realistic visualization of fullâfield dynamic responses of structures by a combination of high-spatial-resolution modal model and video motion manipulations
Structures with complex geometries, material properties, and boundary conditions exhibit spatially local dynamic behaviors. A highâspatialâresolution model of the structure is thus required for highâfidelity analysis, assessment, and prediction of the dynamic phenomena of the structure. The traditional approach is to build a highly refined finite element computer model for simulating and analyzing the structural dynamic phenomena based on detailed knowledge and explicit modeling of the structural physics such as geometries, materials properties, and boundary conditions. These physics information of the structure may not be available or accurately modeled in many cases, however. In addition, the simulation on the highâspatialâresolution structural model, with a massive number of degrees of freedom and system parameters, is computationally demanding. This study, on a proofâofâprinciple basis, proposes a novel alternative approach for spatiotemporal videoâdomain highâfidelity simulation and realistic visualization of fullâfield structural dynamics by an innovative combination of the fundamentals of structural dynamic modeling and the advanced video motion manipulation techniques. Specifically, a lowâmodalâdimensional yet highâspatial (pixel)âresolution (as many spatial points as the pixel number on the structure in the video frame) modal model is established in the spatiotemporal video domain with fullâfield modal parameters first estimated from lineâofâsight video measurements of the operating structure. Then in order to simulate new dynamic response of the structure subject to a new force, the force is projected onto each modal domain, and the modal response is computed by solving each individual singleâdegreeâofâfreedom system in the modal domain. The simulated modal responses are then synthesized by the fullâfield mode shapes using modal superposition to obtain the simulated fullâfield structural dynamic response. Finally, the simulated structural dynamic response is embedded into the original video, replacing the original motion of the video, thus generating a new photoârealistic, physically accurate video that enables a realistic, highâfidelity visualization/animation of the simulated fullâfield vibration of the structure. Laboratory experiments are conducted to validate the proposed method, and the error sources and limitations in practical implementations are also discussed. Compared with highâfidelity finite element computer model simulations of structural dynamics, the videoâbased simulation method removes the need to explicitly model the structure's physics. In addition, the photoârealistic, physically accurate simulated video provides a realistic visualization/animation of the fullâfield structural dynamic response, which was not traditionally available. These features of the proposed method should enable a new alternative to the traditional computerâaided finite element model simulation for highâfidelity simulating and realistically visualizing fullâfield structural dynamics in a relatively efficient and userâfriendly manner
Optical response of the bulk stabilized mosaic phase in Se doped TaSSe
The layered van der Waals material, TaS features a meta-stable mosaic
phase on the verge of a nearly commensurate to commensurate charge density wave
transition. This meta-stable or 'hidden' phase can be reached by laser pumping
the low temperature, commensurate charge density wave phase. Here we report the
stabilization of a bulk, equilibrium mosaic phase in 1T-TaSSe
single crystals observed with transport and optical spectroscopy experiments.
We identify a bulk pseudogap in the mosaic phase of approximately 200 meV at
the lowest temperatures, while the CCDW phase can be obtained by heating and
instead has a full optical gap of about 100 meV. Surprisingly, a spectral
weight analysis shows that Se doping gives rise to an increased charge density
despite the fact that this is formally an isovalent substitution. This finding
is consistent with the recent observation that the mosaic phase is stabilized
as equilibrium phase through the appearance of charged defects.Comment: 7 pages, 3 figure
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Condition/damage monitoring methodologies.
COSMOS, in cooperation with the Advanced National Seismic System (ANSS), is sponsoring an invited workshop entitled Strong-Motion Instrumentation of Buildings. The workshop is motivated by the need to obtain broad input from earthquake engineering professionals for the purpose of developing guidelines for strong motion instrumentation of buildings as part of the ANSS instrument installation effort. The ANSS has been authorized capital finding for 6,000 strong-motion instruments. It is expected that funding for purchase and installation of instruments will be appropriated over a period of several years. The instrument installations must meet multiple monitoring objectives including instrumentation of buildings of various types, urban reference stations, and emergency response and recovery actions. An important opportunity therefore, exists to comprehensively define strong-motion monitoring needs as an underpinning basis for developing guidelines for installation of this important monitoring system. This workshop will specifically address instrumentation of buildings
Spatiotemporal video-domain high-fidelity simulation and realistic visualization of fullâfield dynamic responses of structures by a combination of high-spatial-resolution modal model and video motion manipulations
Structures with complex geometries, material properties, and boundary conditions exhibit spatially local dynamic behaviors. A highâspatialâresolution model of the structure is thus required for highâfidelity analysis, assessment, and prediction of the dynamic phenomena of the structure. The traditional approach is to build a highly refined finite element computer model for simulating and analyzing the structural dynamic phenomena based on detailed knowledge and explicit modeling of the structural physics such as geometries, materials properties, and boundary conditions. These physics information of the structure may not be available or accurately modeled in many cases, however. In addition, the simulation on the highâspatialâresolution structural model, with a massive number of degrees of freedom and system parameters, is computationally demanding. This study, on a proofâofâprinciple basis, proposes a novel alternative approach for spatiotemporal videoâdomain highâfidelity simulation and realistic visualization of fullâfield structural dynamics by an innovative combination of the fundamentals of structural dynamic modeling and the advanced video motion manipulation techniques. Specifically, a lowâmodalâdimensional yet highâspatial (pixel)âresolution (as many spatial points as the pixel number on the structure in the video frame) modal model is established in the spatiotemporal video domain with fullâfield modal parameters first estimated from lineâofâsight video measurements of the operating structure. Then in order to simulate new dynamic response of the structure subject to a new force, the force is projected onto each modal domain, and the modal response is computed by solving each individual singleâdegreeâofâfreedom system in the modal domain. The simulated modal responses are then synthesized by the fullâfield mode shapes using modal superposition to obtain the simulated fullâfield structural dynamic response. Finally, the simulated structural dynamic response is embedded into the original video, replacing the original motion of the video, thus generating a new photoârealistic, physically accurate video that enables a realistic, highâfidelity visualization/animation of the simulated fullâfield vibration of the structure. Laboratory experiments are conducted to validate the proposed method, and the error sources and limitations in practical implementations are also discussed. Compared with highâfidelity finite element computer model simulations of structural dynamics, the videoâbased simulation method removes the need to explicitly model the structure's physics. In addition, the photoârealistic, physically accurate simulated video provides a realistic visualization/animation of the fullâfield structural dynamic response, which was not traditionally available. These features of the proposed method should enable a new alternative to the traditional computerâaided finite element model simulation for highâfidelity simulating and realistically visualizing fullâfield structural dynamics in a relatively efficient and userâfriendly manner
Modeling and diagnosis of structural systems through sparse dynamic graphical models
a b s t r a c t Since their introduction into the structural health monitoring field, time-domain statistical models have been applied with considerable success. Current approaches still have several flaws, however, as they typically ignore the structure of the system, using individual sensor data for modeling and diagnosis. This paper introduces a Bayesian framework containing much of the previous work with autoregressive models as a special case. In addition, the framework allows for natural inclusion of structural knowledge through the form of prior distributions on the model parameters. Acknowledging the need for computational efficiency, we extend the framework through the use of decomposable graphical models, exploiting sparsity in the system to give models that are simple to fit and understand. This sparsity can be specified from knowledge of the system, from the data itself, or through a combination of the two. Using both simulated and real data, we demonstrate the capability of the model to capture the dynamics of the system and to provide clear indications of structural change and damage. We also demonstrate how learning the sparsity in the system gives insight into the structure's physical properties
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Structural health monitoring algorithm comparisons using standard data sets
The real-world structures are subjected to operational and environmental condition changes that impose difficulties in detecting and identifying structural damage. The aim of this report is to detect damage with the presence of such operational and environmental condition changes through the application of the Los Alamos National Laboratoryâs statistical pattern recognition paradigm for structural health monitoring (SHM). The test structure is a laboratory three-story building, and the damage is simulated through nonlinear effects introduced by a bumper mechanism that simulates a repetitive impact-type nonlinearity. The report reviews and illustrates various statistical principles that have had wide application in many engineering fields. The intent is to provide the reader with an introduction to feature extraction and statistical modelling for feature classification in the context of SHM. In this process, the strengths and limitations of some actual statistical techniques used to detect damage in the structures are discussed. In the hierarchical structure of damage detection, this report is only concerned with the first step of the damage detection strategy, which is the evaluation of the existence of damage in the structure. The data from this study and a detailed description of the test structure are available for download at: http://institute.lanl.gov/ei/software-and-data/
Acceleration of Ultra-High Energy Cosmic Rays in the Colliding Shells of Blazars and GRBs: Constraints from the Fermi Gamma ray Space Telescope
Fermi Gamma ray Space Telescope measurements of spectra, variability time
scale, and maximum photon energy give lower limits to the apparent jet powers
and, through gammagamma opacity arguments, the bulk Lorentz factors of
relativistic jets. The maximum cosmic-ray particle energy is limited by these
two quantities in Fermi acceleration scenarios. Recent data are used to
constrain the maximum energies of cosmic-ray protons and Fe nuclei accelerated
in colliding shells of GRBs and blazars. The Fermi results indicate that Fe
rather than protons are more likely to be accelerated to ultra-high energies in
AGNs, whereas powerful GRBs can accelerate both protons and Fe to >~ 10^{20}
eV. Emissivity of nonthermal radiation from radio galaxies and blazars is
estimated from the First Fermi AGN Catalog, and shown to favor BL Lac objects
and FR1 radio galaxies over flat spectrum radio quasars, FR2 radio galaxies,
and long-duration GRBs as the sources of UHECRs.Comment: 8 pages, 3 figures, ApJ, in pres
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Vibration modeling and supression in tennis racquets.
The size of the 'sweet spot' is one measure of tennis racquet performance. In terms of vibration, the sweet spot is determined by the placement of nodal lines across the racquet head. In this studx the vibrational characteristics of a tennis racquet are explorod to discover the size and location of the sweet spot. A numerical model of the racquet is developed using finite element analysis and the model is verified using the results from an experimental modal analysis. The affects of string tension on the racquet's sweet spot and mode shapes are then quantified. An investigation is also carried out to determine how add-on vibrational datnpers affect the sweet spot
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