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Difference between Responses of Potato Plant Height to Corrected FAO-56-recommended Crop Coefficient and Measured Crop Coefficient 被引量:4
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作者 陈秋帆 代兴梅 +2 位作者 陈劲松 颜雄 彭尔瑞 《Agricultural Science & Technology》 CAS 2016年第3期551-554,共4页
This study was conducted to establish a simple convenient method for calculating crop coefficient, and provide a certain basis for the research of the empirical formula for calculating crop coefficient with plant heig... This study was conducted to establish a simple convenient method for calculating crop coefficient, and provide a certain basis for the research of the empirical formula for calculating crop coefficient with plant height which could be measured conveniently with regional differences, especially for the establishment of accurate irrigation schedule of potato in Yunnan. By the field experiment on potato under the condition of drip irrigation, it was found that the models of plant height with corrected FAO-56-recommended K and measured K were a quartic polynomial and a cubic polynomial, respectively, and the polynomial of potato plant height with measured crop coefficient was simpler with higher degree of fitting; and the differences between the period with the highest change rate of potato plant height and the periods with the greatest FAO-56-recommended K and measured K exhibited a differences of 3 d. In conclusion: In the future study of simple or empirical formula calculation of crop coefficient, plant height should be considered as a main dependent variable in that the calculation result would be closer to the measured crop coefficient with the problem of regional difference existing in the FAO method solved and the formula might be simpler; and the irrigation time of potato should be 3 d earlier than the irrigation time determined according to the corrected FAO-56-recommended crop coefficient, especially in the key water requirement stages of potato. 展开更多
关键词 POTATO Plant height Crop coefficient Field planting
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Terrain Rendering LOD Algorithm Based on Improved Restrictive Quadtree Segmentation and Variation Coefficient of Elevation 被引量:3
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作者 Zhenwu Wang Xiaohua Lu 《Journal of Beijing Institute of Technology》 EI CAS 2018年第4期617-622,共6页
Aiming to deal with the difficult issues of terrain data model simplification and crack disposal,the paper proposed an improved level of detail(LOD)terrain rendering algorithm,in which a variation coefficient of eleva... Aiming to deal with the difficult issues of terrain data model simplification and crack disposal,the paper proposed an improved level of detail(LOD)terrain rendering algorithm,in which a variation coefficient of elevation is introduced to express the undulation of topography.Then the coefficient is used to construct a node evaluation function in the terrain data model simplification step.Furthermore,an edge reduction strategy is combined with the improved restrictive quadtree segmentation to handle the crack problem.The experiment results demonstrated that the proposed method can reduce the amount of rendering triangles and enhance the rendering speed on the premise of ensuring the rendering effect compared with a traditional LOD algorithm. 展开更多
关键词 terrain data model simplification crack disposal level of detail(LOD)terrain rendering algorithm variation coefficient of elevation node evaluation function restrictive quadtree segmentation
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Characteristics of ventilation coefficient and its impact on urban air pollution 被引量:1
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作者 路婵 邓启红 +2 位作者 刘蔚巍 黄柏良 石灵芝 《Journal of Central South University》 SCIE EI CAS 2012年第3期615-622,共8页
The temporal variation of ventilation coefficient was estimated and a simple model for the prediction of urban ventilation coefficient in Changsha was developed. Firstly, Pearson correlation analysis was used to inves... The temporal variation of ventilation coefficient was estimated and a simple model for the prediction of urban ventilation coefficient in Changsha was developed. Firstly, Pearson correlation analysis was used to investigate the relationship between meteorological parameters and mixing layer height during 2005-2009 in Changsha, China. Secondly, the multi-linear regression model between daytime and nighttime was adopted to predict the temporal ventilation coefficient. Thirdly, the validation of the model between the predicted and observed ventilation coefficient in 2010 was conducted. The results showed that ventilation coefficient significantly varied and remained high during daytime, while it stayed relatively constant and low during nighttime. In addition, the diurnal ventilation coefficient was distinctly negatively correlated with PM10 (particle with the diameter less than 10 μm) concentration in Changsha, China. The predicted ventilation coefficient agreed well with the observed values based on the multi-linear regression models during daytime and nighttime. The urban temporal ventilation coefficient could be accurately predicted by some simple meteorological parameters during daytime and nighttime. The ventilation coefficient played an important role in the PM10 concentration level. 展开更多
关键词 ventilation coefficient mixing layer height particulate matter multi-linear regression
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Reconstruction of understory terrain based on machine learning combined with GEDI and AW3D30 data
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作者 XU Weifeng LI Jun +1 位作者 PENG Dailiang WEN Di 《Journal of Mountain Science》 2025年第6期2159-2176,共18页
Accurate reconstruction of understory terrain is essential for environmental monitoring and resource management.This study integrates 1:10,000 Digital Elevation Model,Global Ecosystem Dynamics Investigation(GEDI),and ... Accurate reconstruction of understory terrain is essential for environmental monitoring and resource management.This study integrates 1:10,000 Digital Elevation Model,Global Ecosystem Dynamics Investigation(GEDI),and AW3D30 Digital Surface Model data,combined with three machine learning algorithms—Random Forest(RF),Back Propagation Neural Network(BPNN),and Extreme Gradient Boosting(XGBoost)—to evaluate the performance of canopy height inversion and understory terrain reconstruction.The analysis emphasizes the impact of topographic and vegetation-related factors on model accuracy.Results reveal that slope is the most influential variable,contributing three to five times more to model performance than other features.In low-slope areas,understory terrain tends to be underestimated,whereas high-slope areas often result in overestimation.Moreover,the Normalized Difference Vegetation Index(NDVI)and land cover types,particularly forests and grasslands,significantly affect prediction accuracy,with model performance showing heightened sensitivity to vegetation characteristics in these regions.Among the models tested,XGBoost demonstrated superior performance,achieving a canopy height bias of-0.06 m,a root mean square error(RMSE)of 4.69 m for canopy height,and an RMSE of 9.82 m for understory terrain.Its ability to capture complex nonlinear relationships and handle high-dimensional data underlines its robustness.While the RF model exhibited strong stability and resistance to noise,its accuracy lagged slightly behind XGBoost.The BPNN model,by contrast,struggled in areas with complex terrain.This study offers valuable insights into feature selection and optimization in remote sensing applications,providing a reference framework for enhancing the accuracy and efficiency of environmental monitoring practices. 展开更多
关键词 Canopy height Understory terrain Machine learning Digital Elevation Model Global Ecosystem Dynamics Investigation
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山地光伏阵列风荷载地形效应风洞试验研究 被引量:2
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作者 徐亚洲 田锐 +2 位作者 李冰 蒋福林 郝彬 《土木工程学报》 北大核心 2026年第2期35-46,共12页
为研究山地光伏阵列风荷载的地形效应,进行山地光伏阵列的刚性测压风洞试验和CFD(Computational Fluid Dynamics)数值模拟。通过改变地形坡度、风向角和光伏组件倾角,研究了山地光伏阵列风荷载的地形效应以及组件间的干扰效应。结果表明... 为研究山地光伏阵列风荷载的地形效应,进行山地光伏阵列的刚性测压风洞试验和CFD(Computational Fluid Dynamics)数值模拟。通过改变地形坡度、风向角和光伏组件倾角,研究了山地光伏阵列风荷载的地形效应以及组件间的干扰效应。结果表明,0°风向角为结构整体最不利的工况,45°风向角时,光伏阵列的局部风压系数会出现极大值;随着光伏组件倾角的增大,第一排光伏组件的风压系数会变大,且遮蔽效应会变强;地形会减弱遮蔽效应,地形坡度越大遮蔽效应越不明显;地形效应改变了气流方向且对气流有加速作用,大坡度地形时,下游光伏组件风压系数可能转为负数;光伏组件倾角小于地形坡度时,光伏组件背面风压转为向上的推力,较大倾角的光伏组件对山地光伏支架结构的抗风更有利。 展开更多
关键词 光伏支架结构 风洞试验 风压系数 地形效应
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基于CNN-Transformer架构的电磁传播损耗预测算法
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作者 万勇 李骏杰 +1 位作者 孙伟峰 戴永寿 《现代电子技术》 北大核心 2026年第6期43-48,共6页
为了解决传统经验传播损耗模型预测精度不足的问题,提出一种基于CNN-Transformer架构的电磁传播损耗预测算法,通过构建回归模型进行精准的传播损耗预测。通过斯皮尔曼系数法提取有效特征,利用CNN提取与传播损耗预测高度相关的浅层特征,... 为了解决传统经验传播损耗模型预测精度不足的问题,提出一种基于CNN-Transformer架构的电磁传播损耗预测算法,通过构建回归模型进行精准的传播损耗预测。通过斯皮尔曼系数法提取有效特征,利用CNN提取与传播损耗预测高度相关的浅层特征,将从卫星图像中获取的传播路径上地物特征序列进行位置编码,增强对传播路径中不同地物特征顺序对传播损耗影响的理解。最后将CNN提取的浅层特征与位置编码后的地物特征输入到Transformer模型,通过多头自注意力机制捕捉特征间的全局关联性,从而有效校正传播损耗的预测结果。实验结果表明,所提出的CNN-Transformer方法显著降低了传播损耗预测的均方根误差(RMSE),达到了3.3745 dB,同时保持了0.8956的较高确定性系数(R^(2))。所提的电磁传播损耗预测算法为无线通信传播特性研究领域提供了参考,具有一定的应用价值。 展开更多
关键词 电磁传播 损耗预测 TRANSFORMER CNN 斯皮尔曼系数法 地物类型 位置编码
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蜂窝梁腹板的局部屈曲及高厚比限值研究
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作者 毕然 贾连光 +1 位作者 王庆贺 耿凯 《工程力学》 北大核心 2026年第2期234-247,共14页
为避免蜂窝梁腹板局部屈曲对结构产生不利影响,应明确孔参数对腹板局部屈曲的影响并确定腹板的高厚比限值。采用试验和有限元分析方法,研究在静载和往复荷载作用下,楼板、腹板开孔率、横向加劲肋和腹板高厚比对蜂窝梁破坏模式、承载能... 为避免蜂窝梁腹板局部屈曲对结构产生不利影响,应明确孔参数对腹板局部屈曲的影响并确定腹板的高厚比限值。采用试验和有限元分析方法,研究在静载和往复荷载作用下,楼板、腹板开孔率、横向加劲肋和腹板高厚比对蜂窝梁破坏模式、承载能力、延性和耗能性能的影响;给出考虑径高比、孔型和边界条件的开孔板剪切屈曲系数计算公式和蜂窝梁不发生弹塑性屈曲的腹板高厚比限值。研究结果表明,楼板组合作用使腹板的屈曲滞后,设置横向加劲肋能够避免腹板的屈曲,增大腹板开孔率使孔角更易进入塑性而形成塑性铰破坏模式。随腹板高厚比的增加(48.0~85.3),承载力和极限位移降低43%和33%,延性和耗能降低15%和36%。径高比在0.2~0.8变化时,圆孔板和六边形孔板蜂窝钢梁的腹板高厚比限值为79.7倍~48.4倍和76.7倍~47.0倍的钢号修正系数。 展开更多
关键词 蜂窝梁 腹板高厚比 剪切屈曲系数 静载 往复荷载
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换热器高度排布方式对汽车冷却模块进风特征的影响
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作者 鲍国 赵兰萍 +1 位作者 王建新 杨志刚 《热科学与技术》 北大核心 2026年第1期42-49,共8页
冷却模块进风特征包括冷却风量及进风不均匀性,与车辆冷却性能及风阻密切相关。本文在整车CFD仿真结果与风洞实验结果的对比基础上,分析了冷却模块中不同换热器高度排布下,各换热器的来流平均速度和速度分布不均匀系数,以及车辆冷却阻... 冷却模块进风特征包括冷却风量及进风不均匀性,与车辆冷却性能及风阻密切相关。本文在整车CFD仿真结果与风洞实验结果的对比基础上,分析了冷却模块中不同换热器高度排布下,各换热器的来流平均速度和速度分布不均匀系数,以及车辆冷却阻力系数的变化规律。发现冷凝器的高度及三个换热器的高度排布方式会对前端气流的流动特征产生显著影响。增加换热器高度能够有效提升该换热器的进风速度和进风量。低速工况下增加换热器高度能够显著提升来流均匀性,冷凝器尤为明显。在所研究的11种排列方式中,“中-中-高”和“中-低-高”排列方式具有较好的冷却模块来流均匀性和较小的冷却阻力系数,且在低速工况下各换热器均具有较高的进风速度。 展开更多
关键词 冷却模块 换热器高度排布 进风速度及不均匀性 冷却阻力系数 计算流体力学
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考虑有效应力系数影响下地应力变化对页岩裂缝扩展影响研究
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作者 张晨曦 唐慧莹 +2 位作者 唐裕鑫 陈月 邓文斌 《地质力学学报》 北大核心 2026年第1期197-212,共16页
页岩气水平井多段压裂裂缝形态受地层三向应力分布影响,单井应力剖面是预测压裂缝高的重要依据,有效应力系数(Biot系数)及纵向网格分辨率均会影响应力剖面解释结果,进而影响缝高预测的准确性。文章采用不同Biot系数(常值及随测井变化函... 页岩气水平井多段压裂裂缝形态受地层三向应力分布影响,单井应力剖面是预测压裂缝高的重要依据,有效应力系数(Biot系数)及纵向网格分辨率均会影响应力剖面解释结果,进而影响缝高预测的准确性。文章采用不同Biot系数(常值及随测井变化函数)与不同纵向网格分辨率计算应力剖面,模拟分析不同应力剖面下平面三维裂缝形态差异,系统总结Biot系数对应力剖面及裂缝形态的影响规律,并进行纵向网格分辨率及Biot解释方法优选。结果显示:随着Biot系数降低,地层应力纵剖面变化幅度增大,水力裂缝纵向扩展能力受到抑制;提高压裂模型纵向网格分辨率有助于减小应力极值影响范围,1 m纵向网格分辨率下模拟效率与精度达到较好平衡;采用经验公式及孔弹性模型计算Biot系数所得结果相近,与室内实验结果误差为3.68%~3.93%,能更好匹配不同层位应力试验结果,且模拟缝高相较于Biot常值更接近实际井缝高监测结果,与同井位直改平井微地震监测缝高误差为8.64%~9.94%。由初始地应力拟合效果及后续模拟缝高与监测结果匹配程度可以看出,选取合理的Biot系数能更真实预测地应力分布及裂缝扩展形态。通过深入讨论Biot系数及纵向网格分辨率对应力剖面及裂缝形态影响,可为后续页岩气井应力分布计算及压裂缝高预测提供参考。 展开更多
关键词 页岩气 水力压裂 地应力剖面 Biot系数 压裂缝高
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第五代PSU/NCAR中尺度模式系统(MM5)介绍I:地形及地表分类参数处理(TERRAIN模块) 被引量:1
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作者 王劲松 张华 李耀辉 《甘肃气象》 2000年第2期4-9,共6页
利用TERRAIN模块的主要功能、结构和原理对模块的安装和操作使用给予了说明。同时 ,为了加深读者对该模块的认识 ,对不同分辨率的地形、地表分类参数的处理进行比较 ,分析结果表明 ,高分辨率地形及地表分类资料的选取能更真实地反映出... 利用TERRAIN模块的主要功能、结构和原理对模块的安装和操作使用给予了说明。同时 ,为了加深读者对该模块的认识 ,对不同分辨率的地形、地表分类参数的处理进行比较 ,分析结果表明 ,高分辨率地形及地表分类资料的选取能更真实地反映出下垫面的实际特征 ,是今后进行中尺度天气预报和数值模拟的基础之一。 展开更多
关键词 地形 地表分类参数 MM5 天气预报 数值预报
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顾及剩余地形模型的区域似大地水准面精化
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作者 丁永哲 王建强 《江西科学》 2026年第1期10-18,共9页
为构建区域高精度似大地水准面,针对重力场模型空间分辨率不足的问题,采用剩余地形模型(RTM)补偿重力场模型截断误差。基于2个不同测区的GNSS水准数据,评估EGM2008等超高阶重力场模型在不同区域内的适用性,并通过多项式曲面、多面函数... 为构建区域高精度似大地水准面,针对重力场模型空间分辨率不足的问题,采用剩余地形模型(RTM)补偿重力场模型截断误差。基于2个不同测区的GNSS水准数据,评估EGM2008等超高阶重力场模型在不同区域内的适用性,并通过多项式曲面、多面函数和BP神经网络构建残余高程异常拟合模型。结果表明,EGM2008模型在平原区域适用性较好,而SGG-UGM-2模型在山地区域表现较好;经过RTM改正后,两区域的高程异常拟合精度平均提升11.85%和8.12%;通过多面函数法构建的残余高程异常拟合模型精度最优,两区域计算精度分别为1.67、3.67 cm。 展开更多
关键词 似大地水准面 重力场模型 剩余地形模型 高程异常 拟合模型
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弹性环厚度及凸台高度对阻尼系数的实验研究
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作者 母博伟 贾学辉 +3 位作者 谢子强 徐科繁 梁恩波 张广辉 《节能技术》 2026年第1期8-12,共5页
为探究弹性环式挤压油膜阻尼器(ERSFD)中弹性环厚度与凸台高度对其阻尼性能的影响规律,本文搭建了包含基座、激振器及动态测试系统的实验台,采用正交简谐激励并利用电涡流位移传感器测量结构振动响应,结合无油与供油状态下的动力学特性... 为探究弹性环式挤压油膜阻尼器(ERSFD)中弹性环厚度与凸台高度对其阻尼性能的影响规律,本文搭建了包含基座、激振器及动态测试系统的实验台,采用正交简谐激励并利用电涡流位移传感器测量结构振动响应,结合无油与供油状态下的动力学特性系数识别方法计算油膜阻尼系数。实验测试了弹性环厚度(0.8 mm、1.0 mm)和凸台高度(0.1~0.7 mm)共10组参数组合的阻尼特性。结果表明,凸台高度对阻尼系数影响显著,凸台高度越低,阻尼系数越大;而弹性环厚度变化(在0.8 mm至1.0 mm范围内)对阻尼系数的影响相对较小。该研究为ERSFD的优化设计,特别是关键几何参数凸台高度的选择,提供了重要的实验依据。 展开更多
关键词 挤压油膜阻尼器 弹性环厚度 凸台高度 阻尼系数 油膜阻尼
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煤矿深部大断面硐室围岩稳定性模拟研究
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作者 樊磊 芮旭升 《煤》 2026年第1期13-16,共4页
近年来,伴随我国浅部煤炭资源的枯竭,深部矿井中出现了不同断面尺寸的巷道。由于深部大断面硐室具有地应力复杂、断面尺寸大等特点,其控制难度大幅增加。文章采用FLAC 3D软件对某深部大断面巷道进行开挖模拟,通过硐室断面尺寸高度(6 m、... 近年来,伴随我国浅部煤炭资源的枯竭,深部矿井中出现了不同断面尺寸的巷道。由于深部大断面硐室具有地应力复杂、断面尺寸大等特点,其控制难度大幅增加。文章采用FLAC 3D软件对某深部大断面巷道进行开挖模拟,通过硐室断面尺寸高度(6 m、8 m、10 m、12 m、14 m),对巷道围岩应力、塑性区的数值变化和分布规律进行了研究。研究结果表明:断面高度对硐室两帮影响较大。随着巷道断面高度的增加,在围岩深度0~12 m范围内,两帮垂直应力逐渐减小;在12~20 m范围内,两帮垂直应力趋于16 MPa.而在围岩深度0~20 m范围内,顶底板垂直应力基本保持不变。并且,随着巷道断面高度的增加,顶板和两帮围岩塑性区的破坏深度和范围增长明显。研究结果一定程度上揭示了深部大断面硐室围岩的变形破坏规律,为深部大断面硐室围岩控制设计提供了参考依据。 展开更多
关键词 大断面硐室 应力比系数 断面尺寸高度 数值模拟分析
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Analysis of Wave Height in Front of a Wave Absorbing Structure with Rubble Foundation 被引量:2
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作者 Li Rongqing Xie Shileng Engineer, The First Design Institute of Navigation Engineering, The Ministry of Communications, Tianjin Professor and Senior Engineer, Deputy Chief Engineer, The First Design Institute of Navigation Engineering, The Ministry of Communications, Tianjin 《China Ocean Engineering》 SCIE EI 1992年第3期251-264,共14页
Wave absorbing structures have been widely applied in many countries. In the present paper, the wave heights in front of a vertical wave absorbing structure with rubble foundation as well as in the wave chamber of the... Wave absorbing structures have been widely applied in many countries. In the present paper, the wave heights in front of a vertical wave absorbing structure with rubble foundation as well as in the wave chamber of the structure are analysed using an approximative calculation method, and the dissipating effect of the structure is verified. On the basis of the results of regular waves, the relative wave heights of irregular waves in front of the wave absorbing structure as well as in the chamber have also been analysed. 展开更多
关键词 wave absorbing structure reflection coefficient wave height analysis irregular waves
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The Preliminary Discussion of the Potential of GNSS-IR Technology for Terrain Retrievals 被引量:7
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作者 Xiaolei WANG Xiufeng HE +1 位作者 Qin ZHANG Zijin NIU 《Journal of Geodesy and Geoinformation Science》 2021年第2期79-88,共10页
The expansion of research and applications of Global Navigation Satellite Systems(GNSS)has revealed the information of reflecting surface in inherent multipath errors.GNSS signals,usually used to measure position,have... The expansion of research and applications of Global Navigation Satellite Systems(GNSS)has revealed the information of reflecting surface in inherent multipath errors.GNSS signals,usually used to measure position,have been demonstrated that they can be used to retrieve water properties including water level,soil moisture,snow depth,and vegetation water content,which are important for climate analysis and water resources monitoring.Reflected GNSS signals with different azimuths can carry information of the corresponding reflecting zone,which means every reflected signal has distinct"signal-tonoise ratio(SNR)characteristics"influenced by specific reflecting zones—and the parameter named"Reflector Height(RH)"deduced from SNR frequency is focused on in this study.Thus,after interpolation of a series of reflector height by coordinates of the footprint,products describing highly detailed terrain over a reflecting footprint can be produced.Data of three GNSS sites in Earth Scope Plate Boundary Observatory,named P025,P351 and P101,was used to evaluate the terrain after calculating the terrain slopes and correcting the footprint following the slopes.A comparison of the results with a digital elevation model(DEM)showed that it is possible to retrieve terrain by GNSS-Interferometric Reflectometry(GNSS-IR);and the comparison with terrain slopes from DEMs in previous research also validated its potential. 展开更多
关键词 GNSS-IR terrain retrieval signal-to-noise ratio reflector height
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Hydrodynamic Performance of A Floating Breakwater System Under the Terrain of Islands and Reefs: A 3D Experimental Study 被引量:1
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作者 GUO Jian-ting JI Chun-yan ZHANG Yong-bin 《China Ocean Engineering》 CSCD 2024年第6期1047-1056,共10页
With the acceleration of marine construction in China,the exploitation and utilization of resources from islands and reefs are necessary.To prevent and dissipate waves in the process of resource exploitation and utili... With the acceleration of marine construction in China,the exploitation and utilization of resources from islands and reefs are necessary.To prevent and dissipate waves in the process of resource exploitation and utilization,a more effective method is to install floating breakwaters near the terrain of islands and reefs.The terrain around islands and reefs is complex,and waves undergo a series of changes due to the impact of the complex terrain in transmission.It is important to find a suitable location for floating breakwater systems on islands and reefs and investigate how the terrain affects the system’s hydrodynamic performance.This paper introduces a three-cylinder floating breakwater design.The breakwater system consists of 8 units connected by elastic structures and secured by a slack mooring system.To evaluate its effectiveness,a 3D model experiment was conducted in a wave basin.During the experiment,a model resembling the islands and reefs terrain was created on the basis of the water depth map of a specific region in the East China Sea.The transmission coefficients and motion responses of the three-cylinder floating breakwater system were then measured.This was done both in the middle of and behind the islands and reefs terrain.According to the experimental results,the three-cylinder floating breakwater system performs better in terms of hydrodynamics when it is placed behind the terrain of islands and reefs than in the middle of the same terrain. 展开更多
关键词 3D model experiment terrain of islands and reefs floating breakwater(FB) hydrodynamic performance wave transmission coefficients motion responses
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Incorporating shape constraints in generalized additive modelling of the height-diameter relationship for Norway spruce 被引量:4
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作者 Natalya Pya Matthias Schmidt 《Forest Ecosystems》 SCIE CSCD 2016年第2期112-125,共14页
Background: Measurements of tree heights and diameters are essential in forest assessment and modelling. Tree heights are used for estimating timber volume, site index and other important variables related to forest ... Background: Measurements of tree heights and diameters are essential in forest assessment and modelling. Tree heights are used for estimating timber volume, site index and other important variables related to forest growth and yield, succession and carbon budget models. However, the diameter at breast height (dbh) can be more accurately obtained and at lower cost, than total tree height. Hence, generalized height-diameter (h-d) models that predict tree height from dbh, age and other covariates are needed. For a more flexible but biologically plausible estimation of covariate effects we use shape constrained generalized additive models as an extension of existing h-d model approaches. We use causal site parameters such as index of aridity to enhance the generality and causality of the models and to enable predictions under projected changeable climatic conditions. Methods: We develop unconstrained generalized additive models (GAM) and shape constrained generalized additive models (SCAM) for investigating the possible effects of tree-specific parameters such as tree age, relative diameter at breast height, and site-specific parameters such as index of aridity and sum of daily mean temperature during vegetation period, on the h-d relationship of forests in Lower Saxony, Germany. Results: Some of the derived effects, e.g. effects of age, index of aridity and sum of daily mean temperature have significantly non-linear pattern. The need for using SCAM results from the fact that some of the model effects show partially implausible patterns especially at the boundaries of data ranges. The derived model predicts monotonically increasing levels of tree height with increasing age and temperature sum and decreasing aridity and social rank of a tree within a stand, The definition of constraints leads only to marginal or minor decline in the model statistics like AIC An observed structured spatial trend in tree height is modelled via 2-dimensional surface fitting. Conclusions: We demonstrate that the SCAM approach allows optimal regression modelling flexibility similar to the standard GAM but with the additional possibility of defining specific constraints for the model effects. The longitudinal character of the model allows for tree height imputation for the current status of forests but also for future tree height prediction. 展开更多
关键词 height-diameter curve Norway spruce Shape constrained additive models Impact of climate change Varying coefficient models
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Modelling Orthometric Heights from a Combination of Ellipsoidal Heights and Gravimetric Geoid Model in Rivers State, Nigeria
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作者 Kurotamuno P. Jackson Elochukwu C. Moka 《International Journal of Geosciences》 2020年第4期184-196,共13页
Many applications in geodesy, hydrography and engineering require geoid-related heights. Spirit leveling which is the traditional means of obtaining geoid- or mean sea level-related heights is slow, time-consuming and... Many applications in geodesy, hydrography and engineering require geoid-related heights. Spirit leveling which is the traditional means of obtaining geoid- or mean sea level-related heights is slow, time-consuming and costly. Global Navigation Satellite Systems (GNSS) offer faster and relatively cheaper way of obtaining geoid-related heights when geoidal undulation is applied to ellipsoidal heights. However, difficulties involved in determining acceptable geoid height have seriously hampered the application of GNSS for leveling in Rivers State, thus necessitating the need to develop an acceptable geoid model which will serve as a means of conversion of GNSS-delivered ellipsoidal heights to their orthometric heights equivalent. In pursuance of this objective, a detailed gravimetric geoid has been evaluated for Rivers State, Nigeria. The computation of the geoid was carried out by the traditional remove-restore procedure. The Earth Geopotential Model 2008 (EGM08) was applied as the reference field for both the remove and restore parts of the procedures;spherical Fast Fourier Transform (FFT) was employed for the evaluation of the Molodenskii’s integral formula for the height anomaly, (ζ) to yield the quasi-geoid;while the Residual Terrain Modelling (RTM) was done by prism integration. The classical gravimetric geoid over Rivers State was obtained from the rigorously evaluated quasi-geoid by adding the quasi-geoid to geoid (N?- ζ) correction it. The minimum and maximum geoid height values are 18.599 m and 20.114 m respectively with standard deviation of 0.345 m across the study area. Comparison of the gravimetric geoidal heights with the GPS/Leveling-derived geoidal heights of 13 stations across Rivers State, Nigeria showed that the absolute agreement with respect to the GPS/leveling datum is generally better than 7 cm root mean squares (r.m.s) error. Results also showed that combining both GPS heights and the computed Rivers State geoid model can give orthometric heights accurate to 3 cm post-fit using a 4-parameter empirical model. The geoid model can thus serve as a good alternative to traditional leveling when used with GPS leveling, particularly for third order leveling in the study area. 展开更多
关键词 GEOID MODELLING Remove-Compute-Restore Fast Fourier Transform Residual terrain Model Ellipsoidal heightS Orthometric heightS
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Strategies for Advancing Road Construction Slope Stability: Unveiling Innovative Techniques for Managing Unstable Terrain
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作者 Guy Oyéniran Adeoti Judicaël Koffi Agbelele +2 位作者 Crespin Prudence Yabi Rufin Nongnidé Kinhoun Éric Adéchina Alamou 《Open Journal of Civil Engineering》 2023年第4期572-616,共45页
This comprehensive review paper explores various aspects of geotechnical engineering, with a focus on the management of unstable terrains, numerical methods for solving complex soil and consolidation problems, rheolog... This comprehensive review paper explores various aspects of geotechnical engineering, with a focus on the management of unstable terrains, numerical methods for solving complex soil and consolidation problems, rheological analysis of suspensions and muddy soils, and stability analysis of slopes. It begins by examining the unique physicochemical properties of cohesive sediments, including cohesion and specific surface area. The temporal evolution of deposit concentration and average bed concentration in unstable terrains is discussed, along with settling behavior of isolated particles and hindered settling using empirical equations. Key sedimentation theories, such as Kynch’s theory, and geotechnical consolidation theories, including Terzaghi’s consolidation equation and Gibson’s theory, are presented. The investigation interrelates these theories and principles to offer a holistic view of managing unstable terrains. It also addresses the challenges associated with experimental determination of constitutive relationships and presents alternative simplification methods proposed by researchers. Additionally, it delves into numerical methods for solving nonlinear partial differential equations governing soil behavior, emphasizing the need for numerical frameworks and discussing various techniques and associated challenges. The rheological analysis section covers material flow behavior, rheological behavior models, and the rheological properties of water and cohesive sediment mixtures. Fundamental geotechnical calculations, constitutive laws, and failure criteria are explained, highlighting their relevance in geotechnical engineering applications. This paper provides a multidimensional perspective on geotechnical engineering, offering valuable insights into soil properties, consolidation processes, numerical methods, rheological analysis, and slope stability assessment for professionals in the field. 展开更多
关键词 Consolidation Processes Managing Unstable terrain Numerical Methods Safety coefficient Slope Stability Assessment Soil Cohesion
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