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A three-dimensional general mathematical hydroelastic model dealing with the problem of wave interaction with a floating and a submerged flexible structure is developed based on small amplitude wave theory and linear structural response. The horizontal floating and submerged flexible structures are modelled with a thin plate theory. The linearized long wave equations based on shallow water approximations are derived and results are compared. Three-dimensional Green’s functions are derived using fundamental source potentials in water of finite and infinite depths. The expansion formulae associated with orthogonal mode-coupling relations are derived based on the application of Fourier transform in finite and infinite depths in case of finite width in three-dimensions. The usefulness of the expansion formula is demonstrated by analysing a physical problem of surface gravity wave interaction with a moored finite floating elastic plate in the presence of a finite submerged flexible membrane in three-dimensions. The numerical accuracy of the method is demonstrated by computing the complex values of reflected wave amplitudes for different modes of oscillation and mooring stiffness. Further, the effect of compressive force and modes of oscillations on a free oscillation hydroelastic waves in a closed channel of finite width and length for floating and submerged elastic plate system is analysed. 相似文献
213.
从两个方面模拟研究了低低卫-卫跟踪观测技术恢复地球重力场的空间分辨率. 利用重力位系数作为扰动量,积分30天的轨道,研究重力位系数变化引起低低卫-卫跟踪星间距离和速率变化,结果表明,对于地球重力场模型EGM96的前120阶,998%和97%的位系数扰动引起星间距离和速率变化的均方差大于1×10-5m和1×10-7m/s,并且星间距离观测值对地球重力场的反应更为敏感. 不考虑非保守力误差的影响,用随机误差为1×10-5m和1×10-6m/s的星间距离和速率变化作模拟观测量,恢复了78阶地球重力场位系数,结果表明,采用随机误差为1×10-5m的星间距离恢复地球重力场的精度明显高于1×10-6m/s的星间速率结果,但是如果考虑非保守力误差影响,则星间测速的优越性大大增强. 相似文献
214.
西陇海兰新经济带节点城市的发展方向与产业分工 总被引:18,自引:3,他引:15
西陇海兰新经济带是我国西部大开发战略重点区域“两带一区”的重要组成部分。本文分析了西陇海兰新经济带节点城市发展与布局的总体特征,采用多层次多目标综合测度模型定量评价经济带上全部城市的综合竞争力,并把西安、兰州、乌鲁木齐确定为经济带上的一级节点城市,把咸阳、嘉峪关、宝鸡、酒泉、克拉玛依、哈密、石河子、库尔勒、天水、奎屯共10个城市确定为经济带上的二级节点城市。进而以此为依据,对西陇海兰新经济带各级节点城市进行发展方向定位和产业分工。 相似文献
215.
水文响应单元法在盐渍化风险评价中的应用 总被引:3,自引:1,他引:2
运用水文响应单元(HRUs)法评价洮儿河流域地下水环境空间变化对盐渍化风险等级的影响过程,利用反映地下水环境空间变化的3个重要参数:水文区权重(HZ)、水位埋深(DTW)和水位上升速率(RR),由其3个等级网格值算术相乘HRU = DTW*RR*HZ在GIS 平台上生成2001年水文响应单元图。结果表明:(1)洮儿河流域整体上盐渍化风险非常小,低风险区主要分布在水文区A、水文区B和水文区D中的安广镇、烧锅镇一带,主要原因是由于区域地下水位下降、水文区A水文及水文地质条件较好;(2)高风险区主要分布在莫莫格湿地、镇赉县境内和来福-叉干镇一带,主要是由于嫩江排泄通道受阻、地表水体的补给以及水田不合理的灌溉造成的。 相似文献
216.
Lukáš Gábor Vojtěch Barták Vincent Lecours 《International journal of geographical information science》2020,34(8):1567-1584
ABSTRACT Species distribution models (SDMs) are widely used in ecology and conservation. However, their performance is known to be affected by a variety of factors related to species occurrence characteristics. In this study, we used a virtual species approach to overcome the difficulties associated with testing of combined effects of those factors on performance of presence-only SDMs when using real data. We focused on the individual and combined roles of factors related to response variable (i.e. sample size, sampling bias, environmental filtering, species prevalence, and species response to environmental gradients). Results suggest that environmental filtering is not necessarily helpful and should not be performed blindly, without evidence of bias in species occurrences. The more gradual the species response to environmental gradients is, the greater is the model sensitivity to an inappropriate use of environmental filtering, although this sensitivity decreases with higher species prevalence. Results show that SDMs are affected to the greatest degree by the species response to environmental gradients, species prevalence, and sample size. Models’ accuracy decreased with sample size below 300 presences. Furthermore, a high level of interactions among individual factors was observed. Ignoring the combined effects of factors may lead to misleading outcomes and conclusions. 相似文献
217.
基于地理国情信息编制自然资源资产负债表,以广安市为研究区开展了编制自然资源资产负债表技术方法研究,从数量、质量和价值3个方面,运用数值统计与空间分布格局相结合的方法探究编制广安市自然资源资产负债表。研究结果表明:(1)地理国情矢量数据作为制作自然资源资产数据集的基础数据,在统计自然资源资产面积和空间分布上有极大的优势,可以直观地反映上述两项指标。(2)多光谱遥感影像数据,可用于部分质量和价值指标核算。(3)自然资源资产负债表的编制,需要多部门专业数据支持。 相似文献
218.
The use of Local Environmental Knowledge has been considered as an important strategy for adaptive management in the face of Global Environmental Change. However, the unprecedented rates at which global change occurs may pose a challenge to the adaptive capacity of local knowledge systems. In this paper, we use the concept of the shifting baseline syndrome to examine the limits in the adaptive capacity of the local knowledge of an indigenous society facing rapid ecosystem change. We conducted semi-structured interviews regarding perceptions of change in wildlife populations and in intergenerational transmission of knowledge amongst the Tsimane’, a group of hunter-gatherers of Bolivian Amazonia (n = 300 adults in 13 villages). We found that the natural baseline against which the Tsimane’ measure ecosystem changes might be shifting with every generation as a result of (a) age-related differences in the perception of change and (b) a decrease in the intergenerational sharing of environmental knowledge. Such findings suggest that local knowledge systems might not change at a rate quick enough to adapt to conditions of rapid ecosystem change, hence potentially compromising the adaptive success of the entire social-ecological system. With the current pace of Global Environmental Change, widening the gap between the temporal rates of on-going ecosystem change and the timescale needed for local knowledge systems to adjust to change, efforts to tackle the shifting baseline syndrome are urgent and critical for those who aim to use Local Environmental Knowledge as a tool for adaptive management. 相似文献
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220.