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971.
972.
973.
We propose a mathematical representation to qualitatively describe the spatio-temporal slip evolution during earthquake rupture
in an efficient and easy-to-use manner for numerical simulations of strong ground motion. It is based on three basis functions
and associated expansion coefficients. It is an extension of the approach of Ide and Takeo, (J Geophys Res, 102:27379–27391, 1997). We compare our approach and theirs using simple kinematic source models to illustrate differences
between the two approaches, and show that our approach more accurately represents the spatio-temporal slip evolution. We also
propose a technique based on our representation for extracting a spatio-temporal slip velocity function from a kinematic source
model obtained by the conventional source inversion. We then demonstrate the feasibility of our procedure with application
to an inverted source model of the 26 March 1997 Northwestern Kagoshima, Japan, earthquake (M
W6.1). In the simulations for actual earthquakes, source models obtained from kinematic source inversions are commonly employed.
Our scheme could be used as an interpolation method of slip time functions from relatively coarse finite-source models obtained
by conventional kinematic source inversions. 相似文献
974.
Quantitative microbial risk assessment: uncertainty and measures of central tendency for skewed distributions 总被引:1,自引:1,他引:0
K. K. Benke A. J. Hamilton 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):533-539
In the past, arithmetic and geometric means have both been used to characterise pathogen densities in samples used for microbial
risk assessment models. The calculation of total (annual) risk is based on cumulative independent (daily) exposures and the
use of an exponential dose–response model, such as that used for exposure to Giardia or Cryptosporidium. Mathematical analysis suggests that the arithmetic mean is the appropriate measure of central tendency for microbial concentration
with respect to repeated samples of daily exposure in risk assessment. This is despite frequent characterisation of microbial
density by the geometric mean, since the microbial distributions may be Log normal or skewed in nature. Mathematical derivation
supporting the use of the arithmetic mean has been based on deterministic analysis, prior assumptions and definitions, the
use of point-estimates of probability, and has not included from the outset the influence of an actual distribution for microbial
densities. We address these issues by experiments using two real-world pathogen datasets, together with Monte Carlo simulation,
and it is revealed that the arithmetic mean also holds in the case of a daily dose with a finite distribution in microbial
density, even when the distribution is very highly-skewed, as often occurs in environmental samples. Further, for simplicity,
in many risk assessment models, the daily infection risk is assumed to be the same for each day of the year and is represented
by a single value,
which is then used in the calculation of p
Σ, which is a numerical estimate of annual risk, P
Σ, and we highlight the fact that is simply a function of the geometric mean of the daily complementary risk probabilities (although it is sometimes approximated
by the arithmetic mean of daily risk in the low dose case). Finally, the risk estimate is an imprecise probability with no
indication of error and we investigate and clarify the distinction between risk and uncertainty assessment with respect to
the predictive model used for total risk assessment. 相似文献
975.
深层软基加固处理方案试验研究 总被引:1,自引:0,他引:1
在软土地区既有铁路线旁修建复线时,为控制施工期沉降与工后沉降,保证既有线路与新建线路的稳定性,对新建复线的深层软基加固区,通过现场试验采用6种方法分7个观察项目进行了对比研究。试验结果表明:无论是沉降分析、稳定分析或是对既有线的影响分析,用粉喷桩加固地基比用砂井、插塑板及土工布加固地基均有着显而易见的优越性,相对来说短而密的粉喷桩较长而疏的粉喷桩加固效果更好。 相似文献
976.
977.
Vesiculation and crystallization in ascending magmas are key processes that control the eruption behavior, and they interplay each other through the water exsolution process. We conducted a numerical study in order to quantitatively understand the water exsolution and crystallization processes in natural eruptions (decompression history is unknown) and in laboratory experiments (the amount of decompression is constant with time). The numerical results, which take into account homogeneous or heterogeneous nucleation and growth of bubbles with varying diffusivity of water, viscosity, and the amount of decompression, provide a quantitative understanding of their control on bubble formation and water exsolution in the constant amount of decompression. The bubble nucleation in the homogeneous nucleation can be divided into two regimes – the diffusion control regime and viscosity control regime – depending on the modified Peclet number and the effective supersaturation. In the cases of both homogeneous and heterogeneous nucleations, the bubble growth is controlled by diffusion or viscosity, depending on the modified Peclet number and bubble number density. The water exsolution rate, which is controlled by the modified Peclet number in the viscosity control regime and by the bubble number density and diffusive driving force in the diffusion control regime, acts as an effective cooling rate in a decompression-induced crystallization process. A comparison of the numerical results with the results of laboratory experiments suggests that water exsolution proceeds by the diffusion-limited growth of bubbles under disequilibrium vesiculation through the heterogeneous nucleation of bubbles, and this in turn controls the crystallization kinetics of microlite with the homogeneous nucleation of microlite and the diffusion-limited growth of crystal. The several orders of variation of microlite number density with the amount of decompression in laboratory experiments can be interpreted as the effect of the amount of decompression on the driving force for the diffusive bubble growth that controls the water exsolution rate. 相似文献
978.
This paper deals with the evaluation of seismic site effects due to the local topographical and geotechnical characteristics. The amplification of surface motions is calculated by a numerical method combining finite elements in the near field and boundary elements in the far field (FEM/BEM). The numerical technique is improved by time truncation. In the first part of this article, the accuracy and the relevance of this optimized method are presented. Moreover, parametric studies are done on slopes, ridges and canyons to characterize topographical site effects. The second part deals with sedimentary valleys. The complexity of the combination of geometrical and sedimentary effects is underlined. Extensive parametrical studies are done to discriminate the topographical and geotechnical effects on seismic ground movement amplifications in two-dimensional irregular configurations. Characteristic coefficients are defined to predict the amplifications of horizontal displacements. The accuracy of this quantitative evaluation technique is tested and discussed. 相似文献
979.
B. Cochepin L. Trotignon O. Bildstein C.I. Steefel V. Lagneau J. Van der lee 《Advances in water resources》2008,31(12):1540-1551
Porosity evolution at reactive interfaces is a key process that governs the evolution and performances of many engineered systems that have important applications in earth and environmental sciences. This is the case, for example, at the interface between cement structures and clays in deep geological nuclear waste disposals. Although in a different transport regime, similar questions arise for permeable reactive barriers used for biogeochemical remediation in surface environments.The COMEDIE project aims at investigating the coupling between transport, hydrodynamics and chemistry when significant variations of porosity occur. The present work focuses on a numerical benchmark used as a design exercise for the future COMEDIE-2D experiment. The use of reactive transport simulation tools like Hytec and Crunch provides predictions of the physico-chemical evolutions that are expected during the future experiments in laboratory. Focus is given in this paper on the evolution during the simulated experiment of precipitate, permeability and porosity fields.A first case is considered in which the porosity is constant. Results obtained with Crunch and Hytec are in relatively good agreement. Differences are attributable to the models of reactive surface area taken into account for dissolution/precipitation processes. Crunch and Hytec simulations taking into account porosity variations are then presented and compared. Results given by the two codes are in qualitative agreement, with differences attributable in part to the models of reactive surface area for dissolution/precipitation processes. As a consequence, the localization of secondary precipitates predicted by Crunch leads to lower local porosities than for predictions obtained by Hytec and thus to a stronger coupling between flow and chemistry. This benchmark highlights the importance of the surface area model employed to describe systems in which strong porosity variations occur as a result of dissolution/precipitation. The simulation of highly non-linear reactive transport systems is also shown to be partly dependent on specific numerical approaches. 相似文献
980.
In this work we study mixed finite element approximations of Richards’ equation for simulating variably saturated subsurface flow and simultaneous reactive solute transport. Whereas higher order schemes have proved their ability to approximate reliably reactive solute transport (cf., e.g. [Bause M, Knabner P. Numerical simulation of contaminant biodegradation by higher order methods and adaptive time stepping. Comput Visual Sci 7;2004:61–78]), the Raviart–Thomas mixed finite element method (RT0) with a first order accurate flux approximation is popular for computing the underlying water flow field (cf. [Bause M, Knabner P. Computation of variably saturated subsurface flow by adaptive mixed hybrid finite element methods. Adv Water Resour 27;2004:565–581, Farthing MW, Kees CE, Miller CT. Mixed finite element methods and higher order temporal approximations for variably saturated groundwater flow. Adv Water Resour 26;2003:373–394, Starke G. Least-squares mixed finite element solution of variably saturated subsurface flow problems. SIAM J Sci Comput 21;2000:1869–1885, Younes A, Mosé R, Ackerer P, Chavent G. A new formulation of the mixed finite element method for solving elliptic and parabolic PDE with triangular elements. J Comp Phys 149;1999:148–167, Woodward CS, Dawson CN. Analysis of expanded mixed finite element methods for a nonlinear parabolic equation modeling flow into variably saturated porous media. SIAM J Numer Anal 37;2000:701–724]). This combination might be non-optimal. Higher order techniques could increase the accuracy of the flow field calculation and thereby improve the prediction of the solute transport. Here, we analyse the application of the Brezzi-Douglas-Marini element (BDM1) with a second order accurate flux approximation to elliptic, parabolic and degenerate problems whose solutions lack the regularity that is assumed in optimal order error analyses. For the flow field calculation a superiority of the BDM1 approach to the RT0 one is observed, which however is less significant for the accompanying solute transport. 相似文献