Micromechanical approach to effective viscoelastic properties of micro‐fractured geomaterials          下载免费PDF全文

Cássio B. Aguiar  Samir Maghous 《国际地质力学数值与分析法杂志》2018,42(16):2018-2046

The aim of this paper is to formulate a micromechanics‐based approach to non‐aging viscoelastic behavior of materials with randomly distributed micro‐fractures. Unlike cracks, fractures are discontinuities that are able to transfer stresses and can therefore be regarded from a mechanical viewpoint as interfaces endowed with a specific behavior under normal and shear loading. Making use of the elastic‐viscoelastic correspondence principle together with a Mori‐Tanka homogenization scheme, the effective viscoelastic behavior is assessed from properties of the material constituents and damage parameters related to density and size of fractures. It is notably shown that the homogenized behavior thus formulated can be described in most cases by means of a generalized Maxwell rheological model. For practical implementation in structural analyses, an approximate model for the isotropic homogenized fractured medium is formulated within the class of Burger models. Although the approximation is basically developed for short‐term and long‐term behaviors, numerical applications indicate that the approximate Burger model accurately reproduce the homogenized viscoelastic behavior also in the transient conditions.  相似文献   

RETRACTED ARTICLE: Horizontal global solar radiation estimation using hybrid SVM-firefly and SVM-wavelet algorithms: a case study     

Mohammadi  Kasra  Shamshirband  Shahaboddin  Danesh  Amir Seyed  Zamani  Mazdak  Sudheer  Ch. 《Natural Hazards》2020,102(3):1613-1614

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Analytical solutions to the transient,unsaturated transport of water and contaminants through horizontal porous media     

《Advances in water resources》2005,28(10):1102-1111

We present a range of analytical solutions to the combined transient water and solute transport for horizontal flow. We adopt the concept of a scale and time dependent dispersivity used for contaminant transport in aquifers and apply it to transient, unsaturated horizontal flow to develop similarity solutions for both constant solute concentration and solute flux boundary conditions. Through the use of a specific form of the water profile as used by Brutsaert [Water Resour Res 1968:4;785], the solute profiles can be reduced to a simple quadrature. We also derive a solution for the instantaneous injection of water and solute into a horizontal media for an arbitrary dispersivity. It is found that the solute concentration remains constant in both space and time as the water redistributes, suggesting that the solute does not disperse relative to the water.  相似文献   

IAGC Membership Form     

《Applied Geochemistry》2005,20(11):II

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Multiple longshore sand bars in the upper Chesapeake Bay     

Thomas J. Dolan  Robert G. Dean 《Estuarine, Coastal and Shelf Science》1985,21(5):727-743

In the upper Chesapeake Bay (Maryland, U.S.A.) field surveys were conducted at 18 multiple longshore sand bar sites. The multiple bar systems were found in water depths less than approximately 2 m (mean sea level), and exhibited mild bottom slopes of 0·0052 or less. The number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction, ranging from 12 to 70 m. Bar height also typically increased with distance offshore and ranged from 0·03 to 0·61 m. A grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as ‘fine sand’. A review of the literature data indicated that the Chesapeake Bay multiple bars possessed similar characteristics to those found in Gelding Bay (Baltic Sea); similarities in fetch, wave height and tidal range between the two bays may account for this finding. The surf-scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy, and wave height appeared to be an important factor in controlling bar spacing and bar height. A multiple wave break point hypothesis was discussed as a possible mechanism for the formation of Chesapeake Bay multiple longshore bars, and limited observational evidence appeared to support such a mechanism.  相似文献   

A critical state model for sands dependent on stress and density     

Y.P. Yao  D.A. Sun  T. Luo 《国际地质力学数值与分析法杂志》2004,28(4):323-337

An elastoplastic model for sands is presented in this paper, which can describe stress–strain behaviour dependent on mean effective stress level and void ratio. The main features of the proposed model are: (a) a new state parameter, which is dependent on the initial void ratio and initial mean stress, is proposed and applied to the yield function in order to predict the plastic deformation for very loose sands; and (b) another new state parameter, which is used to determine the peak strength and describe the critical state behaviour of sands during shearing, is proposed in order to predict simply negative/positive dilatancy and the hardening/softening behaviour of medium or dense sands. In addition, the proposed model can also predict the stress–strain behaviour of sands under three-dimensional stress conditions by using a transformed stress tensor instead of ordinary stress tensor. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Shoreline response to multi-functional artificial surfing reefs: A numerical and physical modelling study     

《Coastal Engineering》2006,53(7):589-611

The results of a series of 2DH numerical and 3D scaled physical modelling tests indicate that processes governing shoreline response to submerged structures, such as artificial surfing reefs, are different from those associated with emergent offshore breakwaters. Unlike the case of emergent offshore breakwaters, where shoreline accretion (salient development) is expected under all structural/environmental conditions, the principal mode of shoreline response to submerged structures can vary between erosive and accretive, depending on the offshore distance to the structure. The predominant wave incidence angle and structure crest level also have important implications on the magnitude of shoreline response, but not on the mode of shoreline response (i.e. erosion vs. accretion). Based on the results obtained here, a predictive empirical relationship is proposed as a preliminary engineering tool to assess shoreline response to submerged structures.  相似文献   

Influence of soft clays on the response spectra for structures in eastern Canada     

Ren  Tinawi  Marc Sarrazin  Andr  Filiatrault 《Soil Dynamics and Earthquake Engineering》1993,12(8):469-477

The 1990 edition of the National Building Code of Canada (Associate Committee of the National Building Code, National Research Council, Ottawa, 1990) makes a clear distinction between eastern and western Canada in terms of seismic acceleration and velocity zones. While it is well established that ground motions can be amplified significantly through loose clay deposits, no results are available that take into consideration the typical high frequency content of ground motions in eastern Canada. This paper develops ground amplification curves for clays having depths between 10 and 70 m excited by typical eastern Canadian ground motions scaled to two different values of peak horizontal accelerations. Simplified free-field spectral design curves, which could be used by structural designers, are proposed. The curves show that maximum spectral accelerations occur for structural periods between 0.2 and 0.5 s. In addition, soil depth does not appear to be an important parameter controlling the response of typical clay deposits in eastern Canada.  相似文献   

Estimates of winter currents on the Israeli continental shelf     

《Coastal Engineering》2005,52(1):93-102

A simplified analytical model for continental shelf wind-driven currents is adopted. The calculated results compare favorably with extensive field measurements from two separate sources. The model is used to hindcast the current climatology on the Israeli continental shelf. The maximum northward/southward alongshore currents at 10-m water depth, with a return period of 100 years, are found to be 1.28 and 0.53 m/s, respectively.  相似文献   

A Chinese Perspective     

《Marine Policy》2005,29(2):139-146

Regarding the regime of military and intelligence gathering activities in the EEZ, China argues that the freedoms of navigation and overflight in the EEZ have certain restrictions including that the activity must be peaceful and not threaten to use force against the coastal State. This includes military surveys, military maneuvers, and military reconnaissance which are a form of battlefield preparation. These activities are also subject to due regard for the rights of the coastal State. China also argues that there are serious shortcomings regarding the regime of marine scientific research (MSR) in the EEZ and that marine surveys or military surveys carried out by MSR platforms require the consent of the coastal State.  相似文献