199,652 research outputs found
Type curve interpretation of late-time pumping test data in randomly heterogeneous aquifers
No full textThe properties of heterogeneous media vary spatially in a manner that can seldom be described with certainty. It may, however, be possible to describe the spatial variability of these properties in terms of geostatistical parameters such as mean, integral (spatial correlation) scale, and variance. Neuman et al. (2004) proposed a graphical method to estimate the geostatistical parameters of (natural) log transmissivity on the basis of quasi–steady state head data when a randomly heterogeneous confined aquifer is pumped at a constant rate from a fully penetrating well. They conjectured that a quasi–steady state, during which heads vary in space-time while gradients vary only in space, develops in a statistically homogeneous and horizontally isotropic aquifer as it does in a uniform aquifer. We confirm their conjecture numerically for Gaussian log transmissivities, show that time-drawdown data from randomly heterogeneous aquifers are difficult to interpret graphically, and demonstrate that quasi–steady state distance-drawdown data are amenable to such interpretation by the type curve method of Neuman et al. The method yields acceptable estimates of statistical log transmissivity parameters for fields having either an exponential or a Gaussian spatial correlation function. These estimates are more robust than those obtained using the graphical time-drawdown method of Copty and Findikakis (2003, 2004a). We apply the method of Neuman et al. (2004) simultaneously to data from a sequence of pumping tests conducted in four wells in an aquifer near Tuebingen, Germany, and compare our transmissivity estimate with estimates obtained from 312 flowmeter measurements of hydraulic conductivity in these and eight additional wells at the site. We find that (1) four wells are enough to provide reasonable estimates of lead log transmissivity statistics for the Tu ̈bingen site using this method, and (2) the time-drawdown method of Cooper and Jacob (1946) underestimates the geometric mean transmissivity at the site by 30–40%
Effetti di troncamento su campi random multiscala in domini finiti
No full textÈ stato dimostrato da Neuman (1990), Di Federico e Neuman (1997) e Di Federico et al. (1999) che il variogramma di potenza di un campo frattale isotropo o anisotropo può essere costruito sovrapponendo variogrammi esponenziali o Gaussiani di campi (modi) statisticamente omogenei con incrementi mutuamente non correlati e varianza proporzionale a una potenza 2H della scala di correlazione spaziale, do-ve H è il coefficiente di Hurst. Nella sovrapposizione vengono introdotte soglie di troncamento inferiore e superiore, rispettivamente proporzionali alle dimensioni di dominio (finestra campionaria) e scala di suppor-to (volume campionato). Il presente lavoro si propone di valutare numericamente la fondatezza di tale ipote-si. In particolare si esaminano soglie di troncamento di larga scala, attraverso la generazione su dominio fini-to di numerose realizzazioni di campi multivariati Gaussiani bidimensionali con variogrammi di potenza isotropi (che descrivono “fractional Brownian motion”, o fBm). I variogrammi presentano valori di H pari a 0.25 e 0.75, corrispondenti rispettivamente a fBm anti-persistenti e persistenti. Sebbene i variogrammi cam-pionari spaziali omnidirezionali di realizzazioni singole non rispettino il modello di potenza imposto se non in casi isolati, lo riproducono invece fedelmente se considerati e mediati sull’insieme delle realizzazioni ge-nerate. I risultati ottenuti mostrano che il variogramma di potenza si conserva pressoché inalterato in finestre di dimensioni inferiori estratte dal dominio iniziale. Nel presente lavoro si dimostra come i suddetti vario-grammi di potenza, ottenuti da realizzazioni multiple su finestre finite, possano essere rappresentati con suc-cesso per mezzo di variogrammi di potenza troncati con una soglia di larga scala. I risultati hanno notevoli implicazioni nell’interpretazione degli effetti di scala delle variabili idrogeologiche (Neuman e Di Federico, 2003), fondamentali per la comprensione dei fenomeni di flusso e trasporto in formazioni porose naturali
D. M. Neuman, The Life of Music in North India. The Organization of an Artistic Tradition
No full textHelffer Mireille. D. M. Neuman, The Life of Music in North India. The Organization of an Artistic Tradition. In: L'Homme, 1994, tome 34 n°131. pp. 206-209
Anisotropy, lacunarity, and upscaled conductivity and its autocovariance in multiscale random fields with truncated power variograms
No full textIt has been shown by Di Federico and Neuman [1997, 1998a, b] that observed multiscale behaviors of subsurface fluid flow and transport variables can be explained within the context of a unified stochastic framework, which views hydraulic conductivity as a random fractal characterized by a power variogram. Such a random field is statistically nonhomogeneous but possesses homogeneous spatial increments. Di Federico and Neuman [1997] have demonstrated that the power variogram and associated spectra of a statistically isotropic fractal field can be constructed as a weighted integral from zero to infinity (an infinite hierarchy) of exponential or Gaussian variograms and spectra of mutually uncorrelated fields (modes) that are homogeneous and isotropic. We show in this paper that the same holds true when the field and its constituent modes are statistically anisotropic, provided the ratios between principal integral (spatial correlation) scales are the same for all modes. We then analyze the effect of filtering out (truncating) modes of low, high, and intermediate spatial frequency from this infinite hierarchy in the real and spectral domains. A low-frequency cutoff renders the truncated hierarchy homogeneous. The integral scales of the lowest- and highest-frequency cutoff modes are related to length scales of the sampling window (domain) and data support (sample volume), respectively. Taking the former to be proportional to the latter renders expressions for the integral scale and variance of the truncated field dependent on window and support scale (in a manner previously shown to be consistent with observations in the isotropic case). It also allows (in principle) bridging across scales at a specific locale, as well as among locales, by adopting either site-specific or generalized variogram parameters. The introduction of intermediate cutoffs allows us to account, in a straightforward manner, for lacunarity due to gaps in the multiscale hierarchy created by the absence of modes associated with discrete ranges of scales (for example, where textural and structural features are associated with distinct ranges of scale, such as fractures having discrete ranges of trace length and density, which dissect the rock into matrix blocks having corresponding ranges of sizes). We explore mathematically and graphically the effects that anisotropy and lacunarity have on the integral scale, variance, covariance, and spectra of a truncated fractal field. We then develop an expression for the equivalent hydraulic conductivity of a box-shaped porous block, embedded within a multiscale log hydraulic conductivity field, under mean-uniform flow. The block is larger than the support scale of the field but is smaller than a surrounding sampling window. Consequently, its equivalent hydraulic conductivity is a random variable whose variance and spatial autocorrelation function, conditioned on a known mean value of support-scale conductivity across the window, are given explicitly by our multiscale theory
Harold M. Frost T J Musculoskel Neuron Interact 2001; 2(2):117-119 William F. Neuman Awardee 2001
No full textTribute to Harold M. Frost, honorary president of ISMNI, who received the William F. Neuman Award from the American Society of Bone and Mineral
Research October 2001
Harold M. Frost T J Musculoskel Neuron Interact 2001; 2(2):117-119 William F. Neuman Awardee 2001
No full textTribute to Harold M. Frost, honorary president of ISMNI, who received the William F. Neuman Award from the American Society of Bone and Mineral
Research October 2001
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