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排序方式: 共有428条查询结果,搜索用时 31 毫秒
361.
提高现代舰艇磁隐身能力的前提是准确地了解和掌握舰艇空间磁场分布,和舰艇所处地区的地磁场分布情况.针对目前磁场插值或拟合中存在的精度不够高,需要网格化等问题,本文提出了一种基于正交多项式的平面磁场拟合方法.不同于一维正交多项式的拟合方法,此方法首先从一般的完备二维多项式族出发,然后用Gram-Schmidt正交化过程将此完备二维多项式族正交化,得到数值正交基底,然后以此正交基进行平面磁场拟合.为了解决分块拟合问题,又提出了紧支的概念,通过与拉格朗日二维插值的船模试验及仿真比较,发现此方法拟合精度比较高,能够较准确的反映平面磁场的分布,有一定的工程实用价值. 相似文献
362.
Genetic algorithms for determining the parameters of cellular automata in urban simulation 总被引:1,自引:0,他引:1
This paper demonstrates that cellular automata(CA) can be a useful tool for analyzing the process of many geographical phenomena.There are many studies on using CA to simulate the evolution of cites.Urban dynamics is determined by many spatial variables.The contribution of each spatial variable to the simulation is quantified by its parameter or weight.Calibration procedures are usually required for obtaining a suitable set of parameters so that the realistic urban forms can be simulated.Each pa-rameter has a unique role in controlling urban morphology in the simulation.In this paper,these pa-rameters for urban simulation are determined by using empirical data.Genetic algorithms are used to search for the optimal combination of these parameters.There are spatial variations for urban dynam-ics in a large region.Distinct sets of parameters can be used to represent the unique features of urban dynamics for various subregions.A further experiment is to evaluate each set of parameters based on the theories of compact cities.It is considered that the better set of parameters can be identified ac-cording to the utility function in terms of compact development.This set of parameters can be cloned to other regions to improve overall urban morphology.The original parameters can be also modified to produce more compact urban forms for planning purposes.This approach can provide a useful ex-ploratory tool for testing various planning scenarios for urban development. 相似文献
363.
林友勤 《地震工程与工程振动》2007,27(3):64-69
为了能够利用振动法测量316国道洪塘大桥预应力体外索的索力,本文根据理想弦的振动方程以及梁的横向振动方程,建立起有灌浆预应力体外索索力的计算模型,该计算模型中含有两个权重系数λ1、λ2。利用该桥体外预应力索的模型实验数据,通过最小二乘法拟合出系数λ1、λ2并得到体外索索力的计算公式。误差分析表明该体外索索力计算公式误差小,可以用于洪塘大桥体外索索力计算以及该桥体外索长期健康监测。 相似文献
364.
365.
Taken fractal dimension, compact ratio, urban centroid and urban principal axis as the urban spatial characteristic indices, Tianjin city’s urban area is investigated in the last 26 years in a quantitative perspective, and its traits and changes during different periods are also analyzed. It is clear that these indices can not only scientifically and explicitly assess the urban morphology, urban direction and its changes and trends, but also uncover long-term effects of economy and urban planning on urban morphology. 相似文献
366.
367.
Seong-Seung Kang Jun-Mo Kim Katsuhiko Kaneko Katsuhiko Sugawara Yuzo Obara 《Island Arc》2003,12(3):247-255
Abstract Stress measurement is performed to estimate the states of in situ rock stress at the Torigata open‐pit limestone mine in Japan using the compact conical‐ended borehole overcoring (CCBO) technique. A set of back and forward analyses are then carried out to evaluate the states of regional and local in situ rock stresses and the mine‐induced rock slope stability using a 3‐D finite element model. The maximum horizontal local in situ rock stress measured by the CCBO technique acts in the northeast–southwest direction. The horizontal regional tectonic stresses obtained by the back analysis are in good agreement with those of the horizontal local in situ rock stress measured by the CCBO technique. However, the horizontal regional tectonic stress is more compressive than the horizontal local in situ rock stress. This is because the horizontal regional stress due to gravity is not considered in the back‐analyzed horizontal regional tectonic stress, but it is included in the local in situ rock stress measured by the CCBO technique. The local stress obtained by the forward analysis, especially its horizontal components, is in good agreement with the horizontal local in situ rock stress measured by the CCBO technique, and the magnitude of the vertical normal stress increases more rapidly than those of the horizontal normal stresses with depth. As a result, the ratio of the horizontal normal stress to the vertical normal stress is largest at the nearest excavation level and decreases with depth. This means that the stress field within the mine‐induced rock slope is affected by the horizontal components of the local in situ rock stress. 相似文献
368.
在坝基施工过程中,利用声波测井方法确定坝基卸荷回弹张裂面应进行相对异常和地质物探趋势面分析研究,才能保证物探资料的可靠性及直接指导设计变更和施工组织.地质物探趋势面分析是作者的一种新提法. 相似文献
369.
A technique has been developed to control the strength of moistened sand in a quantifiable, accurate and reproducible way, while other mechanical properties were maintained. Strength of dry sand was increased through adding a small amount of liquid. In order to control the additional cohesion of moist sand, the influence of the surface tension of the liquid was investigated. Direct shear experiments were performed on four granular materials at confining stress levels below 1 kPa. It has been found that the surface tension of the added liquid controlled the additional apparent cohesion of sand with high accuracy. The mechanical properties of moist sand show dynamic similarity towards natural brittle rock, which enables analogue modelling of fault formation, fault reactivation and tension fracture formation in the brittle regime with a controlled strength profile. Furthermore, experimental results fit well to shear strength models. From this followed the direct proportionality of the unsaturated shear strength parameter φb relative to the matrix suction, measured at low stress levels. Moreover, shear strength turned out to be also a function of grain size and the grain shape. 相似文献
370.