共查询到20条相似文献，搜索用时 62 毫秒
1.
Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment designin frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of materialproperties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer (i.e., mass equation) and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety (FOS), which is definitely useful forembankment design in frozen ground regions. 相似文献
2.
A coupled water and heat transport mode is established based on the Richards equation to study water flow and heat
transport in soil during freezing process. Both the finite difference and finite element method are used in the discretization,
respectively. Two different computer programs are written and used to simulate an indoor unidirectional frozen test. The
freezing depth, freezing rate and temperature variation are compared among lab tests, finite difference calculation simulation
and finite element calculation simulation. Result shows that: the finite difference method has a better performance in
freezing depth simulation while the finite element method has a better performance in numerical stability in
one-dimensional freezing simulation. 相似文献
3.
David Gubbins 《Geophysical Journal International》1983,73(3):641-652
Summary. Most of the Earth's magnetic field and its secular change originate in the core. Provided the mantle can be treated as an electrical insulator, stochastic inversion enables surface observations to be analysed for the core field. A priori information about the variation of the field at the core boundary leads to very stringent conditions at the Earth's surface. The field models are identical with those derived from the method of harmonic splines (Shure, Parker & Backus) provided the a priori information is specified appropriately.
The method is applied to secular variation data from 106 magnetic observatories. Model predictions for fields at the Earth's surface have error estimates associated with them that appear realistic. For plausible choices of a priori information the error of the field at the core is unbounded, but integrals over patches of the core surface can have finite errors. The hypothesis that magnetic fields are frozen to the core fluid implies that certain integrals of the secular variation vanish. This idea is tested by computing the integrals and their standard and maximum errors. Most of the integrals are within one standard deviation of zero, but those over the large patches to the north and south of the magnetic equator are many times their standard error, because of the dominating influence of the decaying dipole. All integrals are well within their maximum error, indicating that it will be possible to construct core fields, consistent with frozen flux, that satisfy the observations. 相似文献
The method is applied to secular variation data from 106 magnetic observatories. Model predictions for fields at the Earth's surface have error estimates associated with them that appear realistic. For plausible choices of a priori information the error of the field at the core is unbounded, but integrals over patches of the core surface can have finite errors. The hypothesis that magnetic fields are frozen to the core fluid implies that certain integrals of the secular variation vanish. This idea is tested by computing the integrals and their standard and maximum errors. Most of the integrals are within one standard deviation of zero, but those over the large patches to the north and south of the magnetic equator are many times their standard error, because of the dominating influence of the decaying dipole. All integrals are well within their maximum error, indicating that it will be possible to construct core fields, consistent with frozen flux, that satisfy the observations. 相似文献
4.
A stochastic model to quantify the steady-state crustal geotherms subject to uncertainties in thermal conductivity 总被引：1，自引：0，他引：1
In this communication the 1-D steady-state heat conduction problem is solved in a stochastic framework incorporating uncertainties in the depth-dependent thermal conductivity. For this purpose, a new approach to the perturbation method, an expansion series method, which allows for the incorporation of a large variance in the controlling parameters, has been used. This method helps in avoiding assumptions on the probability distribution of the parameter and instead uses information pertaining to the mean and spatial correlation structure. This information is easily available in most geological situations and hence the thermal conductivity is assumed to have a Gaussian coloured noise correlation structure. With this information the stochastic heat conduction equation in equilibrium is solved and analytical expressions for the first two moments, that is, the mean and variance of the temperature field, are obtained. The expression for variance shows that it is highly dependent on the coefficient of variability of thermal conductivity, on the correlation length scale and on the depth. The methodology developed has been applied to quantify the steady-state geotherms, along with their associated error bounds, on a standard crustal model. 相似文献
5.
6.
YE Shu GUO Chuying HAN Jiayin ZHANG Leiming DAI Guanhua WEN Xuefa YU Guirui 《资源与生态学报(英文版)》2019,10(2):127-136
Fluctuations in soil greenhouse gas (GHG) are an important part of the terrestrial ecosystem carbon-nitrogen cycle, but uncertainties remain about the dynamic change and budget assessment of soil GHG flux. Using high frequency and consecutive soil GHG fluxes measured with an automatic dynamic chamber system, we tested the applicability of the current Forest-DNDC model in simulating soil CH4, CO2 and N2O fluxes in a temperate broad-leaved Korean pine forest at Changbai Mountain. The results showed that the Forest-DNDC model reproduced general patterns of environmental variables, however, simulated seasonal variation in soil temperature, snow melt processes and soil moisture partly deviated from measured variables, especially during the non-growing season. The modeled CH4 flux was close to the field measurement and co-varied mainly with soil temperature and snowpack. The modeled soil CO2 flux had the same seasonal trend to that of the observation along with variation in temperature, however, simulated CO2 flux in the growing season was underestimated. The modeled N2O flux attained a peak in summer due to the influence of temperature, which was apparently different from the observed peak of N2O flux in the freeze-thaw period. Meanwhile, both modeled CO2 flux and N2O flux were dampened by rainfall events. Apart from consistent estimation of annual soil CH4 flux, the annual accumulation of CO2 and N2O was underestimated. It is still necessary to further optimize model parameters and processes using long-term high-frequency observation data, especially transference of heat and water in soil and GHG producing mechanism. Continues work will improve modeling, ecosystem carbon-nitrogen budget assessment and estimation of soil GHGs flux from the site to the region. 相似文献
7.
青藏高原北部五道梁地表热量平衡方程中各分量特征 总被引：4，自引：0，他引：4
利用青藏高原北部五道梁地区实测的太阳辐射及气象资料,计算分析了高原北部地面热量平衡方程中各分量特征,定义了一个无量纲参量土壤热平衡系数k。结果显示:五道梁地区地表净辐射及地面加热场强度表现为夏季大,冬季小,地表净辐射累年平均通量为65.5 W/m2;土壤热通量自1997年来有增大的趋势;土壤热平衡系数有增大的趋势,平均值为1.17;感热及潜热是地面热平衡方程中的大项,其中感热居首位,潜热居其次;暖季感热、潜热以相反的趋势变化,Bowen比β值有下降的趋势。 相似文献
8.
9.
The effect of temperature rising for frozen soil because of dynamic load was investigated by indoor tests.Roadway and railway embankments are always loaded by dynamic loads such as earthquakes and vehicles.Because the Qinghai-Tibetan Plateau is a re-gion where earthquakes occur frequently,it is essential to consider the temperature-rising effect of earthquakes or vehicles on railway and road embankment.In this paper and according to the theories of heat transfer and dynamic equilibrium equations,as-suming frozen soil as thermal elastic-viscoplastic material,taking the combination of thermal and mechanical stresses into account,we present the numerical formulae of this dynamic problem,and the computer program of the two-dimensional finite element is written.Using the program,the dynamic response analyses for embankments loaded by earthquake are worked out.Analysis in-dicated that the temperature-rising effect result from earthquakes for embankment in nonuniform distribution in some small areas,the maximum rising temperature is 0.16 ?C for consideration in this paper. 相似文献
10.
活动层土壤热状况是寒区陆面物理过程研究的重要内容之一。利用五道梁能量收支观测站1993年9月～2000年12月份实测辐射及土壤热通量资料结合五道梁气象站1961-2010时段的气象资料分析了近50 a来该地区活动层土壤的热状况。结果表明：五道梁地区土壤热通量有显著的年际、年代际变化;20世纪60～80年代,土壤热通量小于0.0 W/m2,活动层土壤以放热为主,自90年代以来,土壤热通量大于0.0 W/m2,活动层土壤以吸热为主。过去50 a中该地土壤热通量呈现增大趋势,平均每10 a土壤热通量增大0.31 W/m2。土壤热通量随净辐射的增大而增大。土壤热平衡系数的变化特点与土壤热通量的变化特点一致。60～80年代,活动层土壤热平衡系数<1,该地区冻土相对比较稳定,而自90年代以来此间土壤热平衡系数<1,表明该地多年冻土呈现出退化迹象。活动层土壤热平衡系数可表示为气温、地表温度及水汽压的函数。 相似文献
11.
Numerical simulation is known as an effective method for mechanical properties during frozen soil excavation. In order to reveal the development of cutting force, effective stress and cutting fragments in frozen silt during the cutting process, we introduce an explicit finite element program LS-DYNA to establish a two-dimensional numerical model of the frozen soil cut. We also use the Holmquist-Johnson-Cook(HJC) damage constitutive model for simulating the variation of soil mechanical properties according to the strong dependence between the cutting tool and frozen silt during the process with different cutting depths, angles and velocities. Meanwhile, a series of experimental results are acquired of frozen silt cutting to prove the application of the HJC model during simulation of cutting force variations. The result shows that the cutting force and fragment size are strongly influenced by cutting depths and cutting velocities increased, and the maximum effective stress at points where the tool contacts frozen soil during the cutting process. In addition, when the cutting angle is 52°, the cutting force is the smallest, and the cutting angle is optimum. Thus, the prediction of frozen soil mechanical properties on the cutting process by this model is conducive to selecting machinery equipment in the field. 相似文献
12.
Vibration due to moving traffic loads is an important factor which induces frozen soil damage; this paper analyzed these vibration characteristics of frozen soil foundation under track loads. Firstly, seismic observation array(SOA) technology was applied to monitor the three dimensional dynamic characteristics of frozen soil under movable track load in a permafrost region and seasonal frozen soil area. Secondly, a numerical simulation for the response of frozen soil under movable track load was performed based on finite element analysis(FEA). The results show that dynamic characteristics of frozen soil in perpendicular and parallel direction of the track are obviously different. In the direction perpendicular to the track, the vertical acceleration amplitude had an abrupt increase in the 9–10 m from the track line. In the direction parallel to the track, the acceleration in vertical and horizontal direction had a quick attenuation compared to the other direction. Lastly, various parameters were analyzed for the purpose of controlling the dynamic response of frozen soil and the vibration attenuation in frozen soil layer. 相似文献
13.
Ricardo A. Olea 《Natural Resources Research》2011,20(4):377-388
The triangular distribution is a popular choice when it comes to modeling bounded continuous random variables. Its wide acceptance
derives mostly from its simple analytic properties and the ease with which modelers can specify its three parameters through
the extremes and the mode. On the negative side, hardly any real process follows a triangular distribution, which from the
outset puts at a disadvantage any model employing triangular distributions. At a time when numerical techniques such as the
Monte Carlo method are displacing analytic approaches in stochastic resource assessments, easy specification remains the most
attractive characteristic of the triangular distribution. The beta distribution is another continuous distribution defined
within a finite interval offering wider flexibility in style of variation, thus allowing consideration of models in which
the random variables closely follow the observed or expected styles of variation. Despite its more complex definition, generation
of values following a beta distribution is as straightforward as generating values following a triangular distribution, leaving
the selection of parameters as the main impediment to practically considering beta distributions. This contribution intends
to promote the acceptance of the beta distribution by explaining its properties and offering several suggestions to facilitate
the specification of its two shape parameters. In general, given the same distributional parameters, use of the beta distributions
in stochastic modeling may yield significantly different results, yet better estimates, than the triangular distribution. 相似文献
14.
Soil temperature records obtained from the active layer above permafrost at a site in northern Alaska during autumn and winter have variance spectra inconsistent with a purely conductive heat-transfer system. Although conductive heat-transfer theory predicts that temperature fluctuations are attenuated with depth, sub-diurnal thermal variance at the 50-cm level, near the base of the active layer, exceeded that at the 10-cm level. Short segments of the temperature record were drawn from three distinct periods of soil-frost conditions: (1) at the maximum vertical development of the active layer in early autumn; (2) during frost penetration and the formation of a zero curtain in early winter; and (3) after freezeback of the active layer. The variance spectra of these time series show systematic seasonal transitions that reflect changing mechanisms of heat transfer. During the first and second periods, heat transfer by internal evaporation and condensation dominates at wavelengths in the diurnal range. The spectral traces are not strongly self-similar and the fractal dimensions indicate extreme space-filling, especially at deeper levels. Once the active layer is frozen, conductive heat transfer dominates, producing a trend toward self-similarity. Both the thermal variance and the fractal dimension decrease with depth in the frozen regime. [Key words: Alaska, active layer, coupled flow, fractal dimension, frozen ground, heat transfer, permafrost, soil freezing, spectral analysis, zero curtain.] 相似文献
15.
16.
Soil freeze-thaw process is closely related to surface energy budget,hydrological activity,and terrestrial ecosystems.In this study,two numerical experiments(including and excluding soil freeze-thaw process)were designed to examine the effect of soil freeze-thaw process on surface hydrologic and thermal fluxes in frozen ground region in the Northern Hemisphere based on the state-of-the-art Community Earth System Model version 1.0.5.Results show that in response to soil freeze-thaw process,the area averaged soil temperature in the shallow layer(0.0175?0.0451 m)decreases by 0.35℃in the TP(Tibetan Plateau),0.69℃in CES(Central and Eastern Siberia),and 0.6℃in NA(North America)during summer,and increases by 1.93℃in the TP,2.28℃in CES and 1.61℃in NA during winter,respectively.Meanwhile,in response to soil freeze-thaw process,the area averaged soil liquid water content increases in summer and decrease in winter.For surface heat flux components,the ground heat flux is most significantly affected by the freeze-thaw process in both summer and winter,followed by sensible heat flux and latent heat flux in summer.In the TP area,the ground heat flux increases by 2.82 W/m2(28.5%)in summer and decreases by 3.63 W/m2(40%)in winter.Meanwhile,in CES,the ground heat flux increases by 1.89 W/m2(11.3%)in summer and decreases by 1.41 W/m2(18.6%)in winter.The heat fluxes in the Tibetan Plateau are more susceptible to the freeze-thaw process compared with the high-latitude frozen soil regions.Soil freeze-thaw process can induce significant warming in the Tibetan Plateau in winter.Also,this process induces significant cooling in high-latitude regions in summer.The frozen ground can prevent soil liquid water from infiltrating to deep soil layers at the beginning of thawing;however,as the frozen ground thaws continuously,the infiltration of the liquid water increases and the deep soil can store water like a sponge,accompanied by decreasing surface runoff.The influence of the soil freeze-thaw process on surface hydrologic and thermal fluxes varies seasonally and spatially. 相似文献
17.
Coupling numerical simulation with remotely sensed information for the study of frozen soil dynamics
The acquisition of spatial-temporal information of frozen soil is fundamental for the study of frozen soil dynamics and its feedback to climate change in cold regions. With advancement of remote sensing and better understanding of frozen soil dynamics, discrimination of freeze and thaw status of surface soil based on passive microwave remote sensing and numerical simulation of frozen soil processes under water and heat transfer principles provides valuable means for regional and global frozen soil dynamic monitoring and systematic spatial-temporal responses to global change. However, as an important data source of frozen soil processes, remotely sensed information has not yet been fully utilized in the numerical simulation of frozen soil processes. Although great progress has been made in remote sensing and frozen soil physics, yet few frozen soil research has been done on the application of remotely sensed information in association with the numerical model for frozen soil process studies. In the present study, a distributed numerical model for frozen soil dynamic studies based on coupled water-heat transferring theory in association with remotely sensed frozen soil datasets was developed. In order to reduce the uncertainty of the simulation, the remotely sensed frozen soil information was used to monitor and modify relevant parameters in the process of model simulation. The remotely sensed information and numerically simulated spatial-temporal frozen soil processes were validated by in-situ field observations in cold regions near the town of Naqu on the East-Central Tibetan Plateau. The results suggest that the overall accuracy of the algorithm for discriminating freeze and thaw status of surface soil based on passive microwave remote sensing was more than 95%. These results provided an accurate initial freeze and thaw status of surface soil for coupling and calibrating the numerical model of this study. The numerically simulated frozen soil processes demonstrated good performance of the distributed numerical model based on the coupled water-heat transferring theory. The relatively larger uncertainties of the numerical model were found in alternating periods between freezing and thawing of surface soil. The average accuracy increased by about 5% after integrating remotely sensed information on the surface soil. The simulation accuracy was significantly improved, especially in transition periods between freezing and thawing of the surface soil. 相似文献
18.
Recent years have seen a large number of high-speed railways built and will be built in seasonal frozen soil regions of China. Although high-speed railways are characterized by being fast, comfortable and safe, higher standards for deformation of the railways' frozen subgrade are required. Meanwhile, changes in subgrade soil temperatures are the main factors affecting the deformation of frozen subgrade. Therefore, this paper selected typical test subgrade sections of the Harbin–Qiqihar Line, a special line for passenger transport built in the deep seasonal frozen soil regions of China, to monitor field temperatures. Also, the temperature changing laws of railways' subgrade in this region was analyzed by using testing data, the aim of which is to provide a technical support for future design and construction of buildings and structures in a deep seasonal frozen soil region. 相似文献
19.
遥感反演土壤蒸发/植被蒸腾二层模型在华北地区的应用 总被引：5，自引：2，他引：3
利用一种可操作的地表蒸散遥感反演二层模型,以我国华北平原为研究区,选择2004年的3月至6月华北地区主要农作物冬小麦的生长季节作为研究时段,利用MODIS遥感卫星数据,结合地面130多个气象台站的空气温湿度实测数据,实现了土壤蒸发和植被蒸腾的反演。采用国家生态网络禹城综合试验站利用涡度相关系统观测的地表总蒸散半小时平均的数据进行了模型验证,结果表明模型估算的地表可利用能量与地面实测数据的相关系数可以达到0.92,均方差为30.4w.m-2;模型估算的地表总蒸散值与地面实测数据的相关系数为0.85,均方差为21.3 w.m-2,由此证明了模型的可用性。 相似文献
20.
河流水质风险评价的灰色-随机风险率方法 总被引：3，自引：2，他引：3
提出了量化影响河流水质的随机不确定性与灰色不确定性的水质超标灰色－随机风险率概念，建立了水质超标灰色－随机风险率评价模型。在水质单项参数评价模型中，将河流污染物浓度变量的分布处理成灰色概率分布，将污染物浓度超过水质类别标准值的风险率处理成灰色概率，即水质超标灰色－随机风险率。在水质综合评价模型中，河流水环境系统被考虑为担任某一使用可能的可靠性系统，而任意一种水质参数超标意味着河流水体使用功能不能得到应有的保证，也即表明水体综合评价超标，最后借鉴系统可靠性分析的理论和方法计算水质综合超标率。该方法应用于黄河花园口断面重金属污染风险评价。 相似文献