共查询到20条相似文献，搜索用时 31 毫秒
1.
B. Sheikhbeigi M.Sc. M. B. Ghofrani Ph.D. 《International Journal of Environmental Science and Technology》2007,4(2):253-262
The role of gas turbine power plants in electrical energy production has been considerably increased in the last two to three decades. Various methods have been proposed to improve the performance of gas turbine cycles. In this research, two methods, a reheat cycle and a cycle with a reheat and a recuperator, were investigated and compared with a simple cycle. The main objective of this paper is to study the performance of an simple cycle and reheat cycle under actual conditions. In this regard, all processes are treated as actual, and in particular a relatively simple and reliable approach is used to predict the amount of cooling air. The results obtained on the basis of a model developed for this research show that reheating in the context of a realistic study may lead to an improvement both in efficiency and in specific net work using recuperator cause to decrease NOx emission. 相似文献
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《Geodinamica Acta》2000,13(1):19-27
Thermal profiles in Morocco present a negative gradient in the first 60 to 150 m depth. The importance of this subsurface disturbance seems to represent a change of soil surface temperature rather than a lithological contrast or a circulation of fluid. This world-wide phenomenon is expressed in Morocco by a warming of approximately 1.5 to 3 °C over last 100 to 300 years. Particularly intensive deforestation in northeastern Morocco adds to climatic variations to give a more marked surface temperature anomaly. 相似文献
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A simple model for compaction of a sand, that may be useful in various geotechnical applications is presented. The model has been formulated in terms of the cyclic stress and strain amplitudes. The compaction properties of a dry sand are characterized by a common compaction curve described by two coefficients. The second aim of this paper is to show some applications of the theory proposed. The attention has been restricted to the two extreme cases of practical importance, namely to the behaviour of a dry sand (or a saturated sand but in free draining conditions), and to the behaviour of saturated sand in undrained conditions. Some numerical algorithms showing how to deal with those problems are presented and illustrated on the following examples: settlement and pore pressure generation in a soil stratum subjected to an earthquake, settlement of a foundation, pore pressure generation and liquefaction in a sea-bed. The results obtained suggest that the model proposed, as well as a method of dealing with boundary value problems can serve as a useful tool for the analysis of a sandy subsoil subjected to cyclic loadings. 相似文献
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A.G. Brown L.S. Basell R.C. Scrivener 《Proceedings of the Geologists' Association. Geologists' Association》2009,120(4):275-281
This paper presents a first approach to using a sediment budget methodology for paired terrace staircase sediments in SW England. Although a budget approach has become firmly established in Holocene fluvial studies, it has not been used in Pleistocene sequences due to the problems of temporal resolution, catchment changes and downstream loss from the system. However, this paper uses a budget approach in a paired non-glaciated basin, primarily as a method of interrogating the terrace record concerning the degree of reworking and new sediment input required to produce the reconstructed terrace sequences. In order to apply a budget approach a number of assumptions have to be made and these are justified in the paper. The results suggest that the Exe system can most parsimoniously be explained principally by the reworking of a Middle Pleistocene floodplain system with relatively little input of new resistant clasts required and a cascade-type model in geomorphological terms. Whilst this maybe partially a result of the specific geology of the catchment, it is likely to be representative of many Pleistocene terrace systems in NW Europe due to their litho-tectonic similarities. This cascade-type model of terrace formation has archaeological implications and sets the context for the Palaeolithic terrace record in the UK. Future work will involve the testing of this and similar budget models using a combination of landscape modelling and chronometric dating. 相似文献
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Summary As part of an effort to understand the mechanics of fine fragment formation in coal, which is important in studies of respirable dust due to mining, fracture toughness measurements and the strain energy density (SED) theory were applied to calculate the crush zone size under a cutting tool in coal. This zone is the major source of fine fragments in the 1 to 10 µm size range. The model used in these calculations is a boundary element program containing a failure criterion based on the SED theory. The boundary element program calculates linear elastic stresses at numerous points in the coal material ahead of a cutting bit. These stresses are then input to a subroutine called critical flaw length and orientation (CFLO) which uses the SED theory to determine the CFLO for a small crack at the boundary element stress computation point. The extent of crushing is based on earlier postulates about the role of inherent flaws in a fragmentation process. To form 1 to 10 µm fragments requires firstly a local stress strong enough to activate flaws with a characteristic length less than 1 to 10 µm and secondly, a flaw density sufficient to provide an average spacing between flaws also on the order of 1 to 10 µm. The locus of active 10 µm flaws represents the maximum possible extent of fine fragmentation in the 10 µm or less size range assuming that a sufficient inherent flaw density exists. The approach offers a first order approximation to the extent of crushing under a tool tip. The size and shape of the crush zone volume is affected by the attack angle and geometry of the tool. 相似文献
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Relation Between Level Set and Truncated Pluri-Gaussian Methodologies for Facies Representation 总被引：1，自引：1，他引：0
Trond Mannseth 《Mathematical Geosciences》2014,46(6):711-731
Truncated Gaussian/pluri-Gaussian representations and level set representations are two methodologies for implicit representation that can be applied to large-scale subsurface structures. Identification of facies in a petroleum reservoir from dynamic well data is a common field of application for these representation methodologies. No comparison of the methodologies has appeared in the literature to date. The paper seeks to improve on this situation by comparing selected level set and truncated Gaussian/pluri-Gaussian representations in detail. Strong similarities are found, in the sense that every truncated Gaussian/pluri-Gaussian representation considered has a level set counterpart. Furthermore, the transition from a truncated Gaussian/pluri-Gaussian representation to the corresponding level set representation is easily accessible. In addition to the comparison aspect, this paper also introduces a novel level set representation—the hierarchical level set representation—that removes a difficulty present in existing level set representations in a shape estimation setting. It is shown that the hierarchical level set representation corresponds to a well-known truncated pluri-Gaussian representation. 相似文献
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A feasible methodology for landslide susceptibility assessment in developing countries: A case-study of NW Nicaragua after Hurricane Mitch 总被引：1，自引：0，他引：1
Marta Guinau Raimon Palls Joan Manuel Vilaplana RISKNAT Research Group 《Engineering Geology》2005,80(3-4):316-327
In October 1998, Hurricane Mitch triggered a large number of landslides (mainly debris flows) in Honduras and Nicaragua, resulting in a high death toll and in considerable damage to property. In recent years, a number of risk assessment methodologies have been devised to mitigate natural disasters. However, due to scarcity of funds and lack of specialised personnel few of these methodologies are accessible to developing countries. To explore the potential application of relatively simple and affordable landslide susceptibility methodologies in such countries, we focused on a region in NW Nicaragua which was among the most severely hit during the Mitch event. Our study included (1) detailed field work to produce a high-resolution inventory landslide map at 1 : 10,000 scale, and (2) a selection of the relevant instability factors from a Terrain Units Map which had previously been generated in a project for rural development. Based on the combination of these two datasets and using GIS tools we developed a comparative analysis of failure-zones and terrain factors in an attempt to classify the land into zones according to the propensity to landslides triggered by heavy rainfalls. The resulting susceptibility map was validated by using a training and a test zone, providing results comparable to those reached in studies based in more sophisticated methodologies. Thus, we provide an example of a methodology which is simple enough to be fully comprehended by non-specialised technicians and which could be of help in landslide risk mitigation through implementation of non-structural measures, such as land planning or emergency measures. 相似文献
11.
S. G. Mozharovskii 《Astronomy Reports》2017,61(1):70-73
Numerical simulations are used to establish a number of dependencies between small perturbations in physical quantities in the photosphere and small variations in the Stokes profiles of spectral lines. A perturbation of any physical quantity in the model photosphere shifts every point in a line profile in the direction perpendicular to the tangent to the profile at that point. The actions on the wing of a spectral line of perturbations in the magnetic field and radial velocity are equivalent for a particular ratio of these perturbations (if the line is fully split in the magnetic field). If the response of part of a line wing is considered as a shift in wavelength, the area under the curve representing the response to perturbations in the magnetic field and radial velocity has a simple physical meaning. 相似文献
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N.O. Kozhevnikov 《Russian Geology and Geophysics》2012,53(11):1243-1251
Testing TEM systems has to include field experiments with physical models commensurate to the real transmitter–receiver configurations and to the target subsurface features. A large horizontal loop closed across a known resistance is a convenient model in this respect. It is convenient to lay in the field, it has manageable parameters, and its natural response is easy to calculate.A field-size experiment and numerical modeling were applied to investigate the model wire loop response to eddy current in a uniform conductive ground, both at early and late times. The higher the resistivity of the ground the larger the time range in which the measured response matches the predicted one, other things being equal.The experiments show that (i) closed loops laid near a transmitter–receiver system are applicable to test the quality of the latter as a tool for TEM or other similar resistivity surveys; (ii) current induced in the model loop can be used to infer the resistivity of the ground; (iii) a closed loop slows down the growth and reduces the amplitude of voltage induced at early times in a receiver loop or in a multiturn coil. 相似文献
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Eric Robinson 《Geology Today》2020,36(4):134-139
Visiting a stately home open to the public can be a geological excursion in addition to a journey into social history. This is an experience akin to Darwin speculating whether his next landfall would present him with ‘igneous or metamorphic’ rocks to test his early geological knowledge, even before he had received Lyell's Principles when the Beagle reached Buenos Aires. In Britain the prospects are good when the house is Victorian or Edwardian, and we are facing the rich industrialists investing his wealth in opulent interiors within a High Gothic external architecture. In the West of England, this can be tested by a visit to Tyntesfield, a mansion acquired by the National Trust to the south of Bristol in South West England in 2002. Reputed to be little changed from being a family home, it has become a place where booking a timed visit is advised, such is public interest. It also has an added interest in that the Trust is in receipt of a grant from the Heritage Lottery Fund in order to carry out repairs and refurbishment of the many ancillary buildings of the landscaped estate. The work is proceeding alongside public visits, so offering insight into building conservation. 相似文献
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自适应滤波器 总被引：3，自引：3，他引：0
熊光楚 《物探化探计算技术》2000,22(2):147-153
自适应滤波器是一个空间域的数字滤波器。它对不应作滤波处理的点不作滤波,使滤波过程对区域成分的畸变降到最小。它采用一元三点内插法作插值,使滤波公司简单,计算速度快而又能保证精度。判别局部成分的标志及滤波计算都只用局部成分前二个点及后三个点,因而边缘损失小。 相似文献
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基于标准化降水指数的内蒙古地区干旱时空变化特征 总被引：1，自引：0，他引：1
利用内蒙古及周边地区70个气象站1951~2014年降水数据,采用标准化降水指数等方法,对内蒙古近64年气候干旱时空变化进行分析。结果表明:研究区近64年来除西部年际、春、秋、冬季,中部春、秋季及东部春、冬季气候趋于湿润外,其他均趋于干旱。中、东部年际、植(作)物生长期SPI在2001年和1990年左右发生突变,东部突变后趋于干旱并在2006年左右又发生明显转折后趋于湿润。西部在1960s干旱严重,中、东部在1990s至2000s干旱严重。西部年际SPI由西北向东南、东部由南向北干旱趋势速率呈阶梯状下降,中部干旱趋势速率较西、东部快;植(作)物生长期SPI空间变化与年际一致,但西、中部干旱趋势明显的区域有所扩大。 相似文献
16.
Continental erosion is known to be strongly controlled by climate but the way by which geomorphological systems respond to climate change still remains poorly understood. Recent numerical modelling suggests that drainage networks are subjected to strong spatial fluctuations but few studies of natural systems have addressed this phenomenon because of the difficulty of documenting the evolution of erosional landscapes. A detailed field analysis has allowed reconstruction of the past topography of a drainage basin located in southern France where remnants of a past landscape are well preserved. A change from a smooth to a present-day dissected landscape is observed and related to a change in the dominant processes of erosion. This evolution is interpreted in terms of fluctuations in drainage network extent in response to a Holocene increase in precipitation. 相似文献
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The representation of the surface of a rock fracture and a numerical method to simulate fluid flow in single fractures are the keys to understanding the hydraulic behaviour of rock fractures. In this paper, a cellular automaton (CA) approach is used to generate the single fracture structure, which is assumed to be composed of contacts and voids. We develop a CA evolution rule to produce a contact area, and randomly model a single rock fracture with different contact ratios to reflect natural fracture properties such as dead voids, islands and tortuous flow path. Then, based on the localisation theory of a CA, a numerical method to simulate fluid flow in single fractures with contacts is developed. In this method, the fracture is discretised into a system composed of cell elements. Different apertures, i.e., zero for contacts and non-zero for voids, are assigned to each cell element. Therefore, the contribution of the cell elements in a contact on a cell’s transmissivity can be ignored completely. The local transmissivity is assumed to conform to the cubic law. The fluid flow in a fracture with different contact situations is then modelled using the method established in this paper. The fluid flow path, flow velocity and fluid head distributions as well as the channel flow in the fracture are well-modelled. The flow behaviour of the fracture strongly depends on the effective fluid flow path. 相似文献
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We present an algorithm to simulate curvilinear hydraulic fractures in plane strain and axisymmetry. We restrict our attention to sharp fractures propagating in an isotropic, linear elastic medium and driven by the injection of a laminar, Newtonian fluid governed by lubrication theory, and we require the existence of a finite lag region between the fluid front and the crack tip. The key novelty of our approach is in how we discretize the evolving crack and fluid domains: we utilize universal meshes (UMs), a technique to create conforming triangulations of a problem domain by only perturbing nodes of a universal background mesh in the vicinity of the boundary. In this way, we construct meshes, which conform to the crack and to the fluid front. This allows us to build standard piecewise linear finite element spaces and to monolithically solve the quasistatic hydraulic fracture problem for the displacement field in the rock and the pressure in the fluid. We demonstrate the performance of our algorithms through three examples: a convergence study in plane strain, a comparison with experiments in axisymmetry, and a novel case of a fracture in a narrow pay zone. 相似文献
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Helen J. Boon 《Natural Hazards》2014,71(1):683-701
This paper reports exploratory research conducted in a flood-impacted rural Australian town to identify the factors which residents perceived as supporting community resilience to disaster. There is a gap in this research area centred in the Australian disaster context. Since Australia is predicted to be highly impacted by the effects of climate change in the form of an increased incidence of flooding, an urgent need exists to examine the factors that confer resilience to disaster-impacted localities to inform suitable disaster mitigation and adaptation policies for the future. Because of the complexity of community resilience and its interrelationship with individual resilience, a multi-method approach was used: a demographic study to assess community stability and functioning before and after the flood disaster, focus group interviews to obtain from community members their views on what supported them and their community resilience and a survey to generalise the interview findings. Our operating hypothesis was that individuals remaining in the town post-flood were likely to be resilient to the flood disaster. The demographic study results pointed to a resilient community after the floods as they reflected stability in population numbers and socio-economic indicators. The interviews and survey showed that individual resilience was promoted by social connectedness and a sense of place, a factor that was also negatively linked to the desire to relocate from the community. The use of structural equation modelling of our results provided verification of prior research findings about the role of sense of place in supporting individuals’ resilience. Results are discussed in the context of future climate change adaptation policy. 相似文献