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1دورية أكاديمية
المؤلفون: Bilgunde, Prathamesh N., Bond, Leonard J.
المصدر: Aerospace Engineering Conference Papers, Presentations and Posters
مصطلحات موضوعية: Ultrasonics, Solid media, Wave propagation, Finite-element analysis, Dynamics and Dynamical Systems, Mechanics of Materials
الوصف: The aim of this work is to improve modelling capabilities and reliability of wave propagation models using a commercial finite element package (COMSOL). The current model focusses on investigating the error and accuracy with the change in spatial and temporal discretization. To increase the reliability and inclusiveness of the finite element method, wave propagation has been modelled in solid medium with a cylindrical defect (side drilled hole), in a fluid medium and in a fluid-solid immersion model. The numerical predictions are validated through comparisons with available analytical solutions and experimental data. The model is being developed to incorporate additional complexity and ranges of properties, including operation at elevated temperature.
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/aere_conf/67Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1072&context=aere_confTest
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2دورية أكاديمية
المؤلفون: Lin, Shibin, Ashlock, Jeramy C.
المصدر: Civil, Construction and Environmental Engineering Publications
مصطلحات موضوعية: Fourier analysis, Downhole methods, Controlled source seismology, Surface waves and free oscillations, Site effects, Wave propagation, Geotechnical Engineering
الوصف: To improve the accuracy of shallow seismic shear wave velocity profiling, we propose a minimally invasive hybrid surface-and-borehole method that enhances the detection of higher modes of Rayleigh wave dispersion data. The new method combines techniques from the multichannel analysis of surface waves and multichannel simulation with one receiver (MSOR) methods to record components of Rayleigh wave motion at the surface as well as at shallow depths within the soil mass. The performance of the proposed method is demonstrated through computational and experimental studies. We show that individual modes of Rayleigh waves can exhibit different dominant depths at which their motion is most significant. This is demonstrated through a numerical study of eigenvectors of layered soil profiles via the stiffness matrix method, and confirmed by a finite element simulation of the apparent dispersion trends recorded at shallow depths using MSOR. Upon superimposing dispersion data recorded via the receivers at various depths, the resulting multimode dispersion data is used in a multi-objective inverse analysis, for which the difference between experimental and theoretical dispersive phase-velocity spectra are minimized for multiple modes simultaneously. In the numerical study, we demonstrate that the resulting inverted profiles and theoretical dispersion data have improved accuracy relative to single-mode inversion. Preliminary field tests are performed using the new hybrid method, and the results are shown to support the conclusions of the numerical study and confirm the feasibility of the proposed technique. Although the use of multiple modes in surface wave testing is not new, the proposed hybrid method can provide more accurate and complete multimodal dispersion data than achieved with surface-only Rayleigh wave methods. As a result, errors because of misidentification or partial measurement of higher modes may be minimized, thus reducing statistical uncertainty in the inverted profiles.
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/ccee_pubs/68Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1067&context=ccee_pubsTest
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3دورية أكاديمية
المصدر: Center for Nondestructive Evaluation Conference Papers, Posters and Presentations
مصطلحات موضوعية: blades, finite element analysis, plates (structures), Rayleigh waves, wave propagation, wind turbines, nondestructive evaluation, Aerospace Engineering, Materials Science and Engineering, Structures and Materials
الوصف: This paper presents the investigation of discrete, out-of-plane waviness in thick composite plates with applications to wind turbine blades. The investigation was carried out with the help of air coupled ultrasonics and a two-step procedure was framed to assist production line implementation. The first step involved detection of marcels, and the second step involved the characterization of these marcels with the help of an index called aspect ratio. A set of standardized samples with known aspect ratios were fabricated and used for this study. Finite element models were created to understand the wave propagation in wavy composite plates. All the experimental data was correlated with numerical B-Scans and conclusions concerning the method were made.
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/cnde_conf/39Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1022&context=cnde_confTest
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4دورية أكاديمية
المؤلفون: Garton, M., Gray, Timothy A., Thompson, R. Bruce, Gray, I.
المصدر: Center for Nondestructive Evaluation Conference Papers, Posters and Presentations
مصطلحات موضوعية: ultrasonic wave propagation, nondestructive testing, ray tracing, acoustic transducers, nondestructive evaluation, QNDE, Materials Science and Engineering, Structures and Materials
الوصف: UTSim is a software package developed to help plan and refine ultrasonic inspections for complex shaped components. The software reads 3D solid‐model CAD representations of the components. Virtually any shape or complexity of object can be loaded and examined using the ultrasonic ray tracing tools in UTSim. For many applications, the software can also be used to model ultrasonic beam propagation as well as the response from flaws within a component. This presentation will give an overview of UTSim and its features and will demonstrate examples of its ultrasonic simulation capabilities.
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/cnde_conf/69Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1065&context=cnde_confTest
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5دورية أكاديمية
المصدر: Geological and Atmospheric Sciences Publications
مصطلحات موضوعية: air, economics, storms, surges (fluid), anticyclones, weather forecasting, atmospheric circulation, cold front, synoptic meteorology, wave propagation, Asia, Atmospheric Sciences, Geology
الوصف: Since a cold surge is a hazardous weather phenomenon in east Asia, the rapid population increase and economic growth over the past two decades require improvement in forecasting cold surges and their related weather events over this region. However, without a better understanding of these events, this task cannot be accomplished. A cold surge with a well-defined cold front passing through Taiwan was selected to illustrate its impact on the east Asian weather system. This case is typical of a large portion of surges occuring in the region. Major findings of this study are as follows. Coupling with the upper ridge-trough structures of the wave train straddling the eastern seaboard of northeast Asia, cold surges occur sequentially. A cold front with a prefront high pressure zone is formed by the new surge outflow interacting with the anticyclone of the aging surge. The warm moist air advected northeastward along the cold front assists the development of the new surge's low center, while the prefront high pressure zone facilitates the formation of a double-cell structure in the local Hadley circulation. The southeastward propagation of the cold front is driven by the eastward-propagating short-wave trough through the couplets of both new and aging cold surges. The surface weather conditions in the low-elevation zones of Taiwan are modulated by the cold surge flow, but the high-elevation areas may be affected instead by the tropical southeast Asian high. Despite the success of the prior and post-WMONEX (Winter Monsoon Experiment) research in exploring the tropical-midlatitude interaction, the close interaction of cold surges with local weather systems and the planetary-scale circulation in east Asia, illustrated by the case study presented, provides another dimension of cold surge research.
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/ge_at_pubs/19Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1030&context=ge_at_pubsTest
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6دورية أكاديمية
المؤلفون: Gallus, William A., Jr., Segal, Moti
المصدر: Geological and Atmospheric Sciences Publications
مصطلحات موضوعية: Agronomy, atmospheric temperature, atmospheric turbulence, computer simulation, gravity waves, moisture, soils, vegetation, wave propagation, weather forecasting, convective system, forecast rainfall, soil moisture, rain, numerical model, sensitivity analysis, United States, Agronomy and Crop Sciences, Atmospheric Sciences, Geology
الوصف: The impact of soil moisture on the forecast of a small-scale convective system, and sensitivity of results to the convective parameterization used, are investigated through Eta Model simulations (run in an operational-like setting) of a convective system occurring on 27 May 1997 in Texas. The event was influenced by a southwestward-propagating gravity wave from early morning convection in Arkansas that intersected a slow-moving cold front, releasing extreme conditional static instability. Isolated heavy rainfall, over 100 mm, occurred in some regions. A control simulation with 22-km horizontal resolution reasonably simulated the event, even though mesoscale influences such as the gravity wave important to this event are often poorly captured by numerical models. A series of sensitivity tests were performed to examine the impact of soil moisture on the simulations. Two different convective parameterizations were used for the tests. Although domain average precipitation is found to generally vary in a straightforward way with soil moisture, peak precipitation in the regions of intense convection shows more complex behavior. Sensitivity of precipitation amounts to soil moisture differs significantly among runs having different convective parameterizations. For instance, with the Kain-Fritsch convective scheme, relatively dry soil is found to result in stronger convective outflows that converge with stronger ambient flow to greatly enhance the precipitation in the region where heaviest rainfall occurs. With the Betts-Miller-Janjic scheme, drier soil generally results in less precipitation than in the control run, although some enhancement in peak amount does occur within a narrow range of drying. The differences between the peak quantitative precipitation forecasts in the runs is primarily due to the inclusion of a convective downdraft in the Kain-Fritsch parameterization, and its impact on secondary convective development. Additional sensitivity tests find limited impact from prescribed vegetation coverage. A final ...
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/ge_at_pubs/26Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1023&context=ge_at_pubsTest
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7دورية أكاديمية
المؤلفون: Tammaro, Michael Joseph, Evans, James W.
المصدر: Mathematics Publications
مصطلحات موضوعية: carbon monoxide, chemical reactions, computer simulation, equations of motion, mathematical models, oxidation, phase transitions, reaction kinetics, surfaces, chemical diffusivity, chemical wave propagation, lattice gas model, diffusion in gases, Biological and Chemical Physics, Mathematics, Physics
الوصف: We analyze the spatiotemporal behavior in a lattice-gas model for the monomer-dimer reaction on surfaces. This model, which mimics catalytic CO-oxidation, includes a mobilemonomer adspecies (representing CO), an immobile dissociatively adsorbed dimer species (representing O), and afinitereaction rate (for CO2 production). We characterize in detail the propagation of the chemical wave or reaction front produced when the stable reactive steady-state of the model displaces the metastable CO-poisoned state. In the regime of high CO-mobility, such propagation can be described directly within a “hydrodynamic” reaction-diffusion equation formalism. However, we show that the chemical diffusivity of CO is dependent on the O coverage, reflecting the percolative nature of CO-transport through a background of immobile O. We also emphasize that gradients in the coverage of immobile O induce a diffusive flux in the highly mobile CO. These features significantly influence wave propagation and reaction front structure. In addition, our analysis accounts for the feature that in this hydrodynamic regime, correlations persist in the distribution of adsorbed immobile O, and that these influence the reaction kinetics, the steady states, and the percolation and diffusion properties. To this end, we utilize a “hybrid” approach which incorporates a mean-field reaction-diffusion treatment of adsorbed CO, coupled with a lattice-gas treatment of adsorbed O [Tammaro et al., J. Chem. Phys. 103, 10277 (1995)].
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/math_pubs/28Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1027&context=math_pubsTest
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8دورية أكاديمية
المؤلفون: Ahmed, Salahuddin, Thompson, R. Bruce
المصدر: Center for Nondestructive Evaluation Publications
مصطلحات موضوعية: elastic waves, plane waves, acoustic testing, anisotropy, attenuation, calculation methods, cubic lattices, phase velocity, polycrystals, stainless steels, ultrasonic waves, wave propagation, Aerospace Engineering, Materials Science and Engineering, Structures and Materials
الوصف: The unified theory for elastic wave propagation in polycrystalline materials, developed by Stanke and Kino [J. Acoust. Soc. Am. 75, 665–681 (1984)], has been applied to compute the propagation constants in materials consisting of cubic crystallites with texture. The particular texture considered here is one in which one of the cube axes of each crystallite is aligned in a preferred direction with the other two being randomly oriented, leading to a material with macroscopic transverse isotropy. The calculations are done for plane waves under the assumption that the single crystal anisotropy is not large. Numerical results for the variations of attenuation and phase velocity with direction of propagation and frequency are presented for L, SH, and SVwaves.
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/cnde_pubs/11Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1004&context=cnde_pubsTest
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9دورية أكاديمية
المؤلفون: Li, Yan, Thompson, R. Bruce
المصدر: Ames Laboratory Publications
مصطلحات موضوعية: metals, plates, wave propagation, anisotropy, ultrasonic testing, texture, refraction, Engineering Mechanics, Engineering Science and Materials, Materials Science and Engineering, Structures and Materials
الوصف: Ultrasonic S0 waves (fundamental symmetric Lamb modes) are being considered in several laboratories for the nondestructive characterization of the texture (preferred grain orientation) and formability of metal sheets and plates. In a typical experimental setup, the velocities of the S0 waves are measured as a function of wave propagation angle with respect to the rolling direction of the plate. However, the S0 waves are known to be dispersive, and that dispersion must be considered in order to isolate the small, texture‐induced shifts in the S0 wave velocity. Currently, there are two approximate dispersion correction methods, one proposed by Thompson et al.9 and the other introduced by Hirao and Fukuoka.20 In this paper, these two methods will be evaluated using an exact theory for wave propagation in orthotropic plates. Through the evaluation, the limits of the current texture measurement techniques are established. It is found that when plate thickness to wavelength ratio is less than 0.15, both Thompson’s and Hirao’s methods work satisfactorily. When the thickness to wavelength ratio exceeds 0.3, neither Thompson’s nor Hirao’s dispersion correction method provides adequate corrections for the current texture measurement techniques. Within the range of 0.15–0.3, Thompson’s method is recommended for weakly anisotropic sheets and plates and Hirao’s method may be more appropriate for some strongly anisotropic cases.
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/ameslab_pubs/11Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1010&context=ameslab_pubsTest
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10دورية أكاديمية
المؤلفون: Li, Yan, Thompson, R. Bruce
المصدر: Ames Laboratory Publications
مصطلحات موضوعية: anisotropy, plates, sound waves, dispersion relations, wave propagation, analytical solution, Engineering Science and Mechanics, Engineering Mechanics, Engineering Science and Materials, Materials Science and Engineering, Structures and Materials
الوصف: Dispersion curves are developed for elastic wave propagation in an anisotropic plate of monoclinic or higher symmetry. Emphasis is placed on analytic expressions for various features. Generalization of the isotropic Rayleigh–Lamb dispersion relations are derived for the cases of (a) propagation along a material symmetry axis and (b) propagation in a general direction. Examination of the high‐frequency limit of the lowest symmetric and antisymmetric mode dispersion curves yields expressions for the half‐space surface or Rayleigh wave velocity. It is shown that the dispersion curves for these modes can exhibit multiple crossings in approaching this limit, and an analytic solution is presented for the constant crossing interval that occurs for propagation along symmetry directions. The analytic results are illustrated by extensive numerical calculations for a variety of degrees of anisotropy with emphasis placed on the relationship between the slowness curves governing partial wave propagation and various features of the dispersion curves.
وصف الملف: application/pdf
العلاقة: https://lib.dr.iastate.edu/ameslab_pubs/3Test; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1003&context=ameslab_pubsTest
