Non‐local damage modelling of concrete: a procedure for the determination of model parameters     

Giang D. Nguyen  Guy T. Houlsby 《国际地质力学数值与分析法杂志》2007,31(7):867-891

This paper presents a procedure for the determination of parameters of non‐local damage models. This is to assure a consistent response of a non‐local damage model, as choice of the internal length and other parameters of the model are varied. Correlations between the internal length and other parameters governing the local constitutive behaviour of the model are addressed and exploited. Focus is put on the relationship between the internal length of the non‐local model and the width of the fracture process zone. Numerical examples are used to demonstrate the rigour of the proposed method. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Bald kelp: natural and harvesting-induced frond loss in the South African kelp Ecklonia maxima     

C Elston  LM Price 《African Journal of Marine Science》2015,37(3):373-381

Ecklonia maxima dominates kelp beds on the west coast of southern Africa, and is commercially and ecologically valuable. Some plants lose all their secondary blades (fronds), leaving only the gas-filled bulb and short primary blade at the top of the stipe. These ‘bald’ kelps may persist for months or longer, occupying substratum space but contributing little to productivity. We investigated natural causes of balding in five kelp beds in False Bay, South Africa, and the effect of simulated commercial frond-harvesting on loss of fronds. Densities of sporophytes with and without fronds were measured at the water surface during low tides. Generalised linear modelling analysis showed a significant relationship between balding and site (whether sheltered from or exposed to swell/wind), position in the kelp bed (shoreward or seaward) and total E. maxima density. We conclude that balding is caused mainly by drying of meristematic basal regions of fronds during emersion of kelp heads at low tide. After partial harvesting of fronds, kelp heads floated higher out of the water, but after 95 days frond loss was significantly higher only when fronds were cut too close to the primary blade, possibly because of damage to meristematic tissue. Nevertheless, increased emersion that results from frond-harvesting may increase desiccation and blade loss and we suggest caution in setting harvest limits for this kelp.  相似文献   

桐柏碰撞造山带及其邻区变形特征与构造格局   总被引：3，自引：2，他引：1  

刘鑫  李三忠  索艳慧  刘晓春  刘恩山  戴黎明 《岩石学报》2010,26(4):1289-1302

桐柏碰撞造山带及其邻区可以划分为九个大地构造单元,自北向南分别是:华北克拉通南缘岩石构造单元——宽坪岩群、具弧后盆地性质的二郎坪岩石构造单元、具岛弧性质的秦岭杂岩单元、龟山岩组和南湾岩组构成的俯冲前缘楔构造带、构造混杂岩带、桐柏北部高压岩片单元、桐柏核部杂岩单元、桐柏南部高压岩片单元以及随州构造变形带。根据详细的构造解析以及新的地质年代学资料,本文将中生代以来的构造变形划分为五幕,前两幕变形主要发育在构造混杂岩带以南的各个岩石构造单元中,之后的三幕变形则波及整个研究区。第一幕变形的时间约为255～238Ma,以发育区域上透入性的片理及北西西向的拉伸线理为主,并导致了高压岩片早期自西向东的挤出。第二幕变形的时间约为230～215Ma,以自北向南的逆冲推覆构造为主,使得高压岩片进一步垂向抬升。第三幕变形应早于下侏罗统,以近北西西向的宽缓褶皱为主要特征,该幕变形期间桐柏核部杂岩及其两侧高压岩片单元发生同步的抬升。第四幕变形大致发生在140～130Ma之间,主要表现为桐柏核部杂岩两侧走滑型韧性剪切带的活动,桐柏核部杂岩表现出向东的挤出。第五幕变形发生在120～80Ma,表现为北西向及北东向的脆性断裂活动,并切割以上所有构造形迹。桐柏高压岩片的抬升剥露受多幕变形控制,呈阶段性的抬升。  相似文献   

New Methodology to Characterize Shear Behavior of Joints by Combination of Direct Shear Box Testing and Numerical Simulations     

Van-Manh Nguyen  Heinz Konietzky  Thomas Frühwirt 《Geotechnical and Geological Engineering》2014,32(4):829-846

A new procedure is presented, which combines big shear box tests on rocks and corresponding numerical simulations with explicit consideration of joint roughness to get deeper insight into the shear behavior of rock joints. The procedure consists of three parts: (1) constant normal load- or CNS-shear box tests with registration of shear- and normal-components of stress and displacements and deduction of basis rock mechanical parameters; (2) high resolution 3D-scanning of joint surface to deduce joint topography; and (3) set-up, run and evaluation of 3-dimensional numerical model with explicit duplication of joint roughness as back-analysis of shear box tests. The numerical back-analysis provides deeper insight into the joint behavior at the micro-scale. Several parameters can be deduced, like micro-slope angle distribution, aperture size distribution, local normal stress distribution and detailed analysis of dilation in relation to shear direction. The potential of the new procedure is illustrated exemplary by shear box tests on slate.  相似文献   

Statistical data fusion of multi-sensor AOD over the Continental United States     

Sweta Jinnagara Puttaswamy  Hai M. Nguyen  Amy Braverman  Xuefei Hu 《国际地球制图》2014,29(1):48-64

This article illustrates two techniques for merging daily aerosol optical depth (AOD) measurements from satellite and ground-based data sources to achieve optimal data quality and spatial coverage. The first technique is a traditional Universal Kriging (UK) approach employed to predict AOD from multi-sensor aerosol products that are aggregated on a reference grid with AERONET as ground truth. The second technique is spatial statistical data fusion (SSDF); a method designed for massive satellite data interpolation. Traditional kriging has computational complexity O(N³), making it impractical for large datasets. Our version of UK accommodates massive data inputs by performing kriging locally, while SSDF accommodates massive data inputs by modelling their covariance structure with a low-rank linear model. In this study, we use aerosol data products from two satellite instruments: the moderate resolution imaging spectrometer and the geostationary operational environmental satellite, covering the Continental United States.  相似文献   

Floodplain hydrology of the Mekong Delta,Vietnam     

Nguyen Nghia Hung  José Miguel Delgado  Vo Khac Tri  Le Manh Hung  Bruno Merz  András Bárdossy  Heiko Apel 《水文研究》2012,26(5):674-686

The Mekong Delta is one of the largest and most intensively used estuaries in the world. Each year it witnesses widespread flooding which is both the basis of the livelihood for more than 17 million people but also the major hazard. Therefore, a thorough understanding of the hydrologic and hydraulic features is urgently required for various planning purposes. While the general causes and characteristics of the annual floods are understood, the inundation dynamics in the floodplains in Vietnam which are highly controlled by dikes and other control structures have not been investigated in depth. Especially, quantitative analyses are lacking, mainly due to scarce data about the inundation processes in the floodplains. Therefore, a comprehensive monitoring scheme for channel and floodplain inundation was established in a study area in the Plain of Reeds in the northeastern part of the Vietnamese Delta. This in situ data collection was complemented by a series of high‐resolution inundation maps derived from the TerraSAR‐X satellite for the flood seasons 2008 and 2009. Hence, the inundation dynamics in the channels and floodplains, and the interaction between channels and floodplains, could be quantified for the first time. The study identifies the strong human interference which is governed by flood protection levels, cropping patterns and communal water management. In addition, we examine the tidal influence on the inundation in various parts of the Delta, since it is expected that climate change‐induced sea level rise will increase the tidal contribution to floodplain inundation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Ensemble rainfall forecasting with numerical weather prediction and radar‐based nowcasting models     

Shan He  Srivatsan V. Raghavan  Ngoc Son Nguyen  Shie‐Yui Liong 《水文研究》2013,27(11):1560-1571

The overall objective of this study is to improve the forecasting accuracy of the precipitation in the Singapore region by means of both rainfall forecasting and nowcasting. Numerical Weather Predication (NWP) and radar‐based rainfall nowcasting are two important sources for quantitative precipitation forecast. In this paper, an attempt to combine rainfall prediction from a high‐resolution mesoscale weather model and a radar‐based rainfall model was performed. Two rainfall forecasting methods were selected and examined: (i) the weather research and forecasting model (WRF); and (ii) a translation model (TM). The WRF model, at a high spatial resolution, was run over the domain of interest using the Global Forecast System data as initializing fields. Some heavy rainfall events were selected from data record and used to test the forecast capability of WRF and TM. Results obtained from TM and WRF were then combined together to form an ensemble rainfall forecasting model, by assigning weights of 0.7 and 0.3 weights to TM and WRF, respectively. This paper presented results from WRF and TM, and the resulting ensemble rainfall forecasting; comparisons with station data were conducted as well. It was shown that results from WRF are very useful as advisory of anticipated heavy rainfall events, whereas those from TM, which used information of rain cells already appearing on the radar screen, were more accurate for rainfall nowcasting as expected. The ensemble rainfall forecasting compares reasonably well with the station observation data. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Detection of mines in acoustic images using higher order spectral features     

Chandran  V. Elgar  S. Nguyen  A. 《Oceanic Engineering, IEEE Journal of》2002,27(3):610-618

A new pattern-recognition algorithm detects approximately 90% of the mines hidden in the Coastal Systems Station Sonar0, 1, and 3 databases of cluttered acoustic images, with about 10% false alarms. Similar to other approaches, the algorithm presented here includes processing the images with an adaptive Wiener filter (the degree of smoothing depends on the signal strength in a local neighborhood) to remove noise without destroying the structural information in the mine shapes, followed by a two-dimensional FIR filter designed to suppress noise and clutter, while enhancing the target signature. A double peak pattern is produced as the FIR filter passes over mine highlight and shadow regions. Although the location, size, and orientation of this pattern within a region of the image can vary, features derived from higher order spectra (HOS) are invariant to translation, rotation, and scaling, while capturing the spatial correlations of mine-like objects. Classification accuracy is improved by combining features based on geometrical properties of the filter output with features based on HOS. The highest accuracy is obtained by fusing classification based on bispectral features with classification based on trispectral features.  相似文献   

Direct parameter identification of fractured porous medium     

V.V. Nguyen 《Advances in water resources》1983,6(1):11-14

A direct method of parameter identification for a fracture porous medium can be formulated. The coefficient of piezo-conductivity and the virtual fracture transmissivity can be determined using a combination of graphical methods and approximate formulae. Field calculation provides a practical demonstration of the proposed approach.  相似文献   

Long-term variations in leaf area index and light extinction in a Fagus sylvatica stand as estimated from global radiation profiles     

Q. Wang  J. Tenhunen  A. Granier  M. Reichstein  O. Bouriaud  D. Nguyen  N. Breda 《Theoretical and Applied Climatology》2004,79(3-4):225-238

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