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41.
在三维地质建模中,由于地质剖面与医学CT有本质上的相似性,因此,轮廓线的三维表面重建技术有广泛的应用。目前,较为成熟的算法并没有考虑地质数据的特殊性,由于地质体形态复杂多变,地质剖面稀疏、数据来源多样等特点,将普适的算法应用到地质建模中,只是解决了重建曲面的合理性,并没有关注曲面的几何质量,导致曲面无法达到地质建模对于模型质量的要求。本文针对地质数据的特点,提出了一种新的轮廓线表面重构方法。在不改变轮廓线连接的合理性与正确性的情况下,通过生成过渡剖面轮廓线,克服传统方法生成曲面过于粗糙的缺点,以提高建模质量。在Creatar三维地质基础平台上,对多种情况的剖面数据实验结果表明,在数据稀疏的情况下达到了良好的建模效果。该方法的扩展模型满足了地质剖面轮廓线建模中复杂地质情况,以及交叉剖面数据的曲面重建,且算法复杂度低,实现简单,有较强的实用性。 相似文献
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A key factor for computing environmental contours is the appropriate modeling of the dependence structure among the environmental variables. It is known that all the information on the dependence structure of a set of random variables is contained in the copulas that define their multivariate probability distribution. Provided that copula parameters are estimated by means of statistical inference using observations, recordings, numerical or historical data, uncertainty is unavoidably introduced in their estimates. Parametric uncertainty in the copulas parameters then introduces uncertainty in the environmental contours. This study deals with the assessment of uncertainty in environmental contours due to parametric uncertainty in the copula models that define the dependence structure of the environmental variables. A point estimation approach is adopted to estimate the statistics of the uncertain coordinates of the environmental contours considering they are given in terms of inverse functions of conditional copulas. A case study is reported using copulas models estimated from storm hindcast data for the Gulf of Mexico. Uncertainty in environmental contours of significant wave height, peak period and wind speed is assessed. The accuracy of the point estimation of the mean and variance of the contour coordinates is validated based on Monte Carlo simulations. A parametric study shows the manner in which greater parametric uncertainty induces larger variability in the environmental contours. The influence of parametric uncertainty for different degrees of association is also analyzed. The results indicate that variability between contours considering parametric uncertainty can be meaningful. 相似文献
44.
Environmental contours are often used in design of marine structures to identify extreme environmental conditions that may give rise to extreme loads and responses. Recently, attention has been given to the fact that different methods exist for establishing such contours, and that in some cases significant differences may be obtained from the various methods.In this study, another aspect of the uncertainty related to the calculation of environmental contours is addressed, namely the uncertainty due to sampling variability when environmental contours are constructed based on metocean data of finite sample size. The uncertainty of environmental contours for the joint distribution of significant wave height and wave period for different sample sizes (10, 25 and 100 years of data) are investigated considering different underlying datasets and for different estimation methods for the joint distribution. Both cases where samples are drawn from a known joint distribution of wave height and periods and cases where samples are drawn from a real hindcast dataset and fitted to the joint distribution are considered. The uncertainty of the estimated contours is quantified and discussed in light of differences that can be anticipated from the different methods used to calculate the contours. Moreover, the potential bias from assuming different estimation methods is illustrated. 相似文献
45.
This study presented a quantitative comparison of cockpit and doline karst by examining the numbers and characteristics of typical types of landform entities that are developed in Guilin（Guangxi, China）, La Alianza（PR, USA）, Avalton（KY, USA）, and Oolitic（IN, USA）. Five types of landform entities were defined： isolated hill（IH）, clustered hills（CHs）, isolated sinkhole（IS）, clustered sinkholes（CSs）, and clustered hills with sinkholes（CHSs）. An algorithm was developed to automatically identify these types of landform entities by examining the contour lines on topographic maps of two cockpit karst areas（Guilin and La Alianza） and two doline karst areas（Oolitic and Avalton）. Within each specific study area, the CHSs is the least developed type yet with a larger size and higher relief. The IH and IS entities are smaller in size, lower in relief, and outnumber their clustered counterparts. The total numbers of these types of entities are quite different in cockpit and doline karst areas. Doline karst is characterized by more negative（IS and CSs） than positive（IH and IHs） landforms and vice versa for cockpit karst. For example, the Guilin study area has 1192 positive landform entities in total, which occupy 9.81% of the total study area. It has only 622 negative landform entities occupying only 3.91% of the total study area. By contrast, the doline karst in Oolitic has 130 negative while only 10 positive landform entities. The positive and negative landforms in Oolitic occupy 12.68% and 2.61% of the total study area, respectively. Furthermore, average relief and slope of the landform entities are much higher and steeper in the cockpit karst than the doline karst areas. For instance, the average slope of CHs in Alvaton is 3.90 degrees while it is 19.78 degrees in La Alianza. The average relief of CSs is 4.07 m and 34.29 m in Oolitic and Guilin respectively. Such a difference within a specific area or between the cockpit and doline karst may reveal different controls on 相似文献
46.
Changes expected in Mexico City's seismic response due to land subsidence caused by groundwater extraction are examined. Settlements of the land surface observed in the recent past are compiled and processed to predict regional subsidence in the near future. This information is used in combination with the iso-depth and iso-period maps stipulated by the building code to estimate the compaction of surface sediments and the shortening of soil periods. The time-progressive evolution of the official seismic zoning maps and the associated site-specific response spectra is predicted. The same is done with spectral response contours expressed in terms of the site and structure periods. The subsidence effects are considered through an impact factor, which represents the increase or decrease in the spectral ordinates with respect to the current values specified for design purposes. The detrimental or beneficial effects depend on the relative values of the structure and site periods. 相似文献
47.
Preliminary numerical simulation of potential earthquake-induced tsunami in East China Sea 总被引：1，自引：0，他引：1
In this paper,we present a numerical simulation of the propagation of a tsunami in the East China Sea,which might be induced by a hypothetical M8.5 earthquake in Okinawa Trough. Our results show that the initial maxi-mum wave height of tsunami could reach as high as 4.3 m for the hypothetical earthquake. It would take 3.5～4 hours for the tsunami to propagate to the coast of Zhejiang Province,and 7～8 hours to the near-shore of Shanghai. The peak tsunami height could be up to about 2 m in the coast of Zhejiang Province. Based on the numerical ex-periments,we plot the arrival time contours of tsunami in East China Sea and time history curves on the three ob-servational stations,and discussed the significance of the pre-analysis. 相似文献
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等高线须以相似的光滑曲线逼近实际地貌形态,并综合地形在一定限度内的地势起伏,其智能化控制对地貌表达具有重要的实用价值。绘图员绘制曲线时能凭经验捕捉到数据点所包含的几何形状信息,而张力样条函数和三次B样条曲线在节点插值时,严格要求二阶参数连续,不符合人的经验直觉,是节点对参数曲线连接光滑度的过分限制。根据人工绘制等高线的规则,提出将三次Beta样条曲线作为基于人工绘制约束的等高线插值的数学模型,通过引入形状控制参数放松对曲线的光滑性的要求,增加了控制等高线形状的自由度,把C2连续的三次B样条松弛成为G2连续的Beta样条,实验结果表明插值的等高线符合地形综合度要求。 相似文献
50.
The algorithm we present here is useful for measuring the planimetric discrepancy between two models which can be represented by contours. In cartography the paradigm of such models is represented by digital terrain models (DTMs). The measure we propose is based on an area enclosed between homologous contours (two level contours, each belonging to two different models). Our measure is similar to another used previously, although, in the previous studies, the area enclosed between homologous contours was computed manually or it was restricted to particular conditions. The innovation of our approach consists of the automation of the entire process and in the constraint elimination. The main problem to solve before computing the horizontal shift measure is how to determine the area enclosed between homologous contours. This is a problem because there is no bijective correspondence between homologous contours, and therefore the identification of the homologous contours is not a trivial task. Our approach overcomes this difficulty by closing following the limit of the DTM the open contours (the contours which cut the limit of the DTM) and classifying them by the external level. We achieve the automation assisted by the Boolean polygon operations, specifically using the symmetric difference operation. Our algorithm facilitates the computation of accuracy of a DTM by comparison with another and it is applicable in such fields as hydrology (precision estimation of the hydrological features), cartographic generalization, and civil engineering. Finally we use our measure for estimating the planimetric discrepancy between the same streams derived from different DEMs (different sources and precisions). 相似文献