Numerically quantifying energy loss caused by squirt flow     

Beatriz Quintal  Eva Caspari  Klaus Holliger  Holger Steeb 《Geophysical Prospecting》2019,67(8):2196-2212

In interconnected microcracks, or in microcracks connected to spherical pores, the deformation associated with the passage of mechanical waves can induce fluid flow parallel to the crack walls, which is known as squirt flow. This phenomenon can also occur at larger scales in hydraulically interconnected mesoscopic cracks or fractures. The associated viscous friction causes the waves to experience attenuation and velocity dispersion. We present a simple hydromechanical numerical scheme, based on the interface-coupled Lamé–Navier and Navier–Stokes equations, to simulate squirt flow in the frequency domain. The linearized, quasi-static Navier–Stokes equations describe the laminar flow of a compressible viscous fluid in conduits embedded in a linear elastic solid background described by the quasi-static Lamé–Navier equations. Assuming that the heterogeneous model behaves effectively like a homogeneous viscoelastic medium at a larger spatial scale, the resulting attenuation and stiffness modulus dispersion are computed from spatial averages of the complex-valued, frequency-dependent stress and strain fields. An energy-based approach is implemented to calculate the local contributions to attenuation that, when integrated over the entire model, yield results that are identical to those based on the viscoelastic assumption. In addition to thus validating this assumption, the energy-based approach allows for analyses of the spatial dissipation patterns in squirt flow models. We perform simulations for a series of numerical models to illustrate the viability and versatility of the proposed method. For a 3D model consisting of a spherical crack embedded in a solid background, the characteristic frequency of the resulting P-wave attenuation agrees with that of a corresponding analytical solution, indicating that the dissipative viscous flow problem is appropriately handled in our numerical solution of the linearized, quasi-static Navier–Stokes equations. For 2D models containing either interconnected cracks or cracks connected to a circular pore, the results are compared with those based on Biot's poroelastic equations of consolidation, which are solved through an equivalent approach. Overall, our numerical simulations and the associated analyses demonstrate the suitability of the coupled Lamé–Navier and Navier–Stokes equations and of Biot's equations for quantifying attenuation and dispersion for a range of squirt flow scenarios. These analyses also allow for delineating numerical and physical limitations associated with each set of equations.  相似文献   

Evaluation of Terrestrial Laser Scanner and Structure from Motion photogrammetry techniques for quantifying soil surface roughness parameters over agricultural soils     

Alex Martinez-Agirre  Jesús Álvarez-Mozos  Milutin Milenković  Norbert Pfeifer  Rafael Giménez  José Manuel Valle  Álvaro Rodríguez 《地球表面变化过程与地形》2020,45(3):605-621

The surface roughness of agricultural soils is mainly related to the type of tillage performed, typically consisting of oriented and random components. Traditionally, soil surface roughness (SSR) characterization has been difficult due to its high spatial variability and the sensitivity of roughness parameters to the characteristics of the instruments, including its measurement scale. Recent advances in surveying have greatly improved the spatial resolution, extent, and availability of surface elevation datasets. However, it is still unknown how new roughness measurements relates with the conventional roughness measurements such as 2D profiles acquired by laser profilometers. The objective of this study was to evaluate the suitability of Terrestrial Laser Scanner (TLS) and Structure from Motion (SfM) photogrammetry techniques for quantifying SSR over different agricultural soils. With this aim, an experiment was carried out in three plots (5 × 5 m) representing different roughness conditions, where TLS and SfM photogrammetry measurements were co-registered with 2D profiles obtained using a laser profilometer. Differences between new and conventional roughness measurement techniques were evaluated visually and quantitatively using regression analysis and comparing the values of six different roughness parameters. TLS and SfM photogrammetry measurements were further compared by evaluating multi-directional roughness parameters and analyzing corresponding Digital Elevation Models. The results obtained demonstrate the ability of both TLS and SfM photogrammetry techniques to measure 3D SSR over agricultural soils. However, profiles obtained with both techniques (especially SfM photogrammetry) showed a loss of high-frequency elevation information that affected the values of some parameters (e.g. initial slope of the autocorrelation function, peak frequency and tortuosity). Nevertheless, both TLS and SfM photogrammetry provide a massive amount of 3D information that enables a detailed analysis of surface roughness, which is relevant for multiple applications, such as those focused in hydrological and soil erosion processes and microwave scattering. © 2019 John Wiley & Sons, Ltd.  相似文献   

An updated and unified earthquake catalogue for the Western Balkan Region   总被引：1，自引：0，他引：1  

Snježana Markušić  Zeynep Gülerce  Neki Kuka  Llambro Duni  Ines Ivančić  Slavica Radovanović  Branislav Glavatović  Zoran Milutinović  Sinan Akkar  Svetlana Kovačević  Jadranka Mihaljević  Radmila Šalić 《Bulletin of Earthquake Engineering》2016,14(2):321-343

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Seasonal and diurnal variability of pressure fluctuation in the infrasound frequency range observed in the Czech microbarograph network     

Tereza Šindelárová  Michal Kozubek  Jaroslav Chum  Kateřina Potužníková 《Studia Geophysica et Geodaetica》2016,60(4):747-762

Infrasound environments in the Czech microbarograph network were studied. Reference Fourier amplitude spectra were calculated from data measured at three microbarograph sites of the network in May 2011-April 2012; directional analysis of infrasound arrivals in the frequency band 0.15-0.4 Hz was performed for the microbarograph array at Panská Ves in May 2014-April 2015. Diurnal, seasonal and site-to-site variability of the reference spectra was evaluated. Site-to-site variability is influenced by the location of the respective sensors in the open air and inside the observatory buildings and by local noise phenomena like wind turbines. Diurnal variability is well developed in summer with maximum ambient noise levels during the daytime and minima at night. Seasonal variability is observed at night with maxima in winter and minima in summer. Wind and wind eddies seem to be an important source of ambient noise in measurements in the Czech microbarograph network. A distinct spectral peak occurs near 0.2 Hz with amplitudes by about one order of magnitude higher in winter than in summer. Its seasonal variability is related to seasonal propagation of microbaroms from the source region in the Northern Atlantic.  相似文献   

Sinkhole‐Native Oil‐Degrading Microbial Consortium for Hydrocarbon‐Polluted Seawater Remediation          下载免费PDF全文

Manuel Alejandro Lizardi‐Jiménez  Eva Yahaira López Sánches  Adrián Gómez‐de‐Jesús  Norberto Ulises García‐Cruz  Cesar Ignacio Hernández‐Flores 《洁净——土壤、空气、水》2016,44(8):1046-1050

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Tree‐age control on reconstructed debris‐flow frequencies: examples from a regional dendrogeomorphic reconstruction in the Crimean Mountains          下载免费PDF全文

Karel Šilhán  Tomáš Pánek  Jan Hradecký  Markus Stoffel 《地球表面变化过程与地形》2015,40(2):243-251

The Crimean Mountains (Ukraine) are renowned for the highest occurrence of debris flows along the northern coast of the Black Sea, but information on their origin, frequency and triggers is widely lacking. This study reconstructs a regional time series of debris flows in eight catchments located on the slopes above Yalta. Dendrogeomorphic analyses were performed on 1122 increment cores selected from 566 black pines (Pinus nigra ssp. pallasiana) with clear signs of external damage induced by past debris‐flow activity. The trees sampled were divided into old and young trees. The sample contains 361 young trees with post‐1930 innermost rings and 205 old trees with pre‐1930 germination dates. The two groups of trees were analyzed separately to identify possible age effects in the reconstructed debris‐flow series and to assess the ability of P. nigra to record geomorphic disturbances over time. We date a total of 215 debris flows back to ad 1701 and observe a mean decadal frequency of 6.9 events, with a peak in activity during the 1940s (20 events). The young trees record an increase in debris‐flow activity over the last 70 years, whereas the frequency of events remained fairly constant in the old trees for the same period. By contrast, the formation of reaction wood became increasingly scarce with increasing tree age whereas the occurrence of abrupt growth suppression increased. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Advanced frame element for seismic analysis of masonry structures: model formulation and validation          下载免费PDF全文

Eva Raka  Enrico Spacone  Vincenzo Sepe  Guido Camata 《地震工程与结构动力学》2015,44(14):2489-2506

This paper presents a masonry panel model for the nonlinear static and dynamic analysis of masonry buildings suitable for the seismic assessment of new and existing structures. The model is based on an equivalent frame idealization of the structure and stems from previous research on force‐based frame elements. The element formulation considers axial, bending, and shear deformations within the framework of the Timoshenko beam theory. A phenomenological cyclic section law that accounts for the shear panel response is coupled, through equilibrium between shear and bending forces along the element, with a fiber‐section model that accounts for the axial and bending responses. The proposed panel model traces with a low computational burden and numerical stability the main aspects of the structural behavior of masonry panels and is suitable for analyses of multi‐floor buildings with a relatively regular distribution of openings and with walls and floors organized to grant a box‐like behavior under seismic loads. The model capabilities are validated though analyses of simple unreinforced masonry panels and comparisons with published experimental results. The model accuracy is strongly dependent on the fiber and shear constitutive laws used. However, the formulation is general, and laws different from those employed in this study are easily introduced without affecting the model formulation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Responses of large-scale coronal structures to chromospheric activity     

Františsek Fárník  Paul Hick  Zdeněk Švestka 《Solar physics》1993,146(2):313-330

We have followed the transit of two active regions across the western solar limb during June 29 through July 2, 1980, as imaged in 3.5–16 keV X-rays by HXIS aboard the SMM. During frequent brightenings of large-scale coronal structures, hard X-ray emission in the 11–16 keV energy band was recorded up to altitudes of 76 000 km. Soft X-rays could be seen in excess of 250 000 km altitude above the photospheric active region. Many X-ray brightenings low in the corona in the active regions were followed by enhancements high in the corona in the large-scale coronal structures. Although subsequent enhancements rarely appeared in the same position, similar portions of the corona brightened intermittently, indicating that the general configuration of the coronal structures above the active regions did not change much, in spite of the frequent energy inputs. These inputs were of two kinds: nonthermal, with very fast response at high coronal altitudes within seconds or tens of seconds, and thermal, with a delay of several minutes. The nonthermal response is short-lived, reflecting the time profile of the primary source; the thermal response is more gradual and longer lasting than the primary source. In some enhancements of large-scale coronal structures both these kinds of response occur and can be clearly recognized. There are also active-region hrightenings without any response in the high corona and,vice versa, high-corona brightenings without any obvious primary source; in the latter case, it is likely that the source was hidden behind the limb.  相似文献   

Variogram-Based Descriptors for Comparison and Classification of Rock Texture Images     

Díaz  Gonzalo F.  Ortiz  Julián M.  Silva  Jorge F.  Lobos  Rodrigo A.  Egaña  Álvaro F. 《Mathematical Geosciences》2020,52(4):451-476

Mathematical Geosciences - Rock characterization is typically performed by geologists in mining companies and involves the analysis of several meters of drill-hole samples to describe distinctive...  相似文献   

Fractal characteristics of pore structure of compacted bentonite studied by ESEM and MIP methods     

Sun  Haiquan  Mašín  David  Najser  Jan  Neděla  Vilém  Navrátilová  Eva 《Acta Geotechnica》2020,15(6):1655-1671

Acta Geotechnica - In this paper, we aim to clarify microstructure of bentonite from Cerny vrch deposit in the Czech Republic. We adopt results of ESEM and MIP experiments performed at various...  相似文献