大气折光系数测定及在悬索桥基准索股线形测量中的应用     

王欢  刘成龙  杨雪峰  王永 《测绘通报》2019,(5):129-133

大跨度悬索桥基准索股跨中位置处于百米高空，如何测得精确的垂度值，对主缆线形进行控制至关重要。本文分析了影响悬索桥基准索股垂度测量精度的主要因素，提出了基于实时大气折光系数改正的单向三角高程的跨中垂度测量新方法。在桥址区建立高精度的高差基准，通过对桥址区的大气折光系数的测定及改正试验，证明该测量方法切实可行。基准索股跨中垂度采用双测站进行测量，当双测站所测同一点绝对垂度互差小于10 mm时，取双测站所测垂度均值作为该点的垂度值。该方法的测量结果达到设计精度要求，对同类工程测量项目有借鉴意义。  相似文献   

基于内模原理的汽车主动悬挂系统的减振控制     

窦同水  唐功友 《中国海洋大学学报(自然科学版)》2011,(Z1):165-168,174

研究路面粗糙度扰动作用下的汽车主动悬挂系统的减振控制问题。首先简化单自由度四分之一悬挂系统模型,建立路面粗糙度扰动模型。然后基于内模原理设计汽车主动悬挂系统的减振控制结构,并利用线性系统的极点配置方法设计系统的减振控制律。最后利用数字仿真验证了减振控制律的有效性。  相似文献   

地震作用下大跨度悬索桥几何非线性影响分析     

聂利英  李硕娇  殷玉梅 《地震学刊》2011,(6):682-687

大跨度悬索桥几何非线性主要来自3个方面：缆索垂度效应、梁柱效应、大位移引起的几何形状变化。鉴于地震波高频成分振幅大,低频成分振幅小的特点,很难对地震作用下大跨度悬索桥几何非线性的影响做出定性判断。目前大跨度桥梁的几何非线性研究主要集中在斜拉桥,且不同的学者得出了不同的结论。本文以逐级加大振幅的Ⅳ类场地多条地震波为激励,通过对称与非对称的2座典型大跨度悬索桥的几何非线性影响对比分析,探讨了几何非线性对大跨度悬索桥重要地震响应量的影响程度及其原因,并提出了相应的抗震设计参考建议。  相似文献   

Fuzzy Optimization Neural Network Approach for Ice Forecast in the Inner Mongolia Reach of the Yellow River/Approche d'Optimisation Floue de Réseau de Neurones pour la Prévision de la Glace Dans le Tronçon de Mongolie Intérieure du Fleuve Jaune     

《水文科学杂志》2013,58(2)

Abstract

In ice forecasting, a key problem is the forecast of freeze-up and break-up dates. Ice-water mechanics and the principle of heat-exchange were mainly adopted in previous research. However, the mathematical models in these studies are complex and many parameters are required in relation to upstream and/or downstream gauging stations. Moreover, too many assumptions or simplifications for these parameters and constraints directly lead to low accuracy of the models and limitations as to their practical applications. This paper develops a fuzzy optimization neural network approach for the forecast of freeze-up date and break-up date. The Inner Mongolia reach lies in the top north of the Yellow River, China. Almost every year ice floods occur because of its special geographical location, hydrometeorological conditions and river course characteristics. Therefore, it is of particular importance for ice flood prevention to forecast freeze-up date and break-up date accurately. A case study in this region shows that the proposed methodology may allow obtaining useful results.  相似文献   

Influences of coupled wind–water processes on suspended sediment grain size: an example from tributaries of the Yellow River / Influences de processus couplés éoliens-hydriques sur la granulométrie des matières en suspension: exemple d'affluents du Fleuve Jaune     

《水文科学杂志》2013,58(5)

Abstract

Some unique coupled wind–water erosion processes exist in the desert-loess transitional zone in the middle Yellow River basin. Based on data from 40 stations on 29 rivers, a study was made on the influence of such processes on suspended sediment grain-size characteristics of the tributaries of the Yellow River. Results show that the percentage of >0.05-mm grain size decreases with the increased annual mean precipitation, but increases with the increase in the annual mean number of sand-dust storm days. The percentage of <0.01-mm grain size increases with the increase in the annual mean precipitation, but decreases with the increase in the annual number of sand-dust storm days. Based on annual mean data from 40 stations, multiple regression equations were established between the percentages of >0.05-mm grain size (r _>0.05) and <0.01-mm grain size (r _<0.01), annual mean precipitation (P _m) and annual mean number of sand-dust storm days (D _ss). On this basis, the relative contributions of the variations in D _ss and P _m to the variation in r _>0.05 and r _<0.01 were estimated. The results indicate that the variation in sand-dust storm frequency exerts greater influences on the variation in grain-size characteristics of suspended load than does the variation in annual mean precipitation. With the increase in the coupled wind–water processes index, expressed by P _m/D _ss, the percentage of >0.05-mm grain size in suspended sediment decreases and the percentage of <0.01-mm grain size increases. With the variation in P _m/D _ss, different combinations of r _>0.05 with r _<0.01 appear, which have some influence on the formation of hyperconcentrated flows. There exist some optimal ratios of coarse to fine fractions in suspended sediment that make sediment concentrations of hyperconcentrated flows the highest. The optimal r _>0.05/r _<0.01 value is related to some range of the index P _m/D _ss. When the P _m/D _ss index falls in this range, the optimum combination of relative coarse with fine sediments in the suspended load appears, and thus results in the peak values of sediment concentration.  相似文献   

Fuzzy logic model approaches to daily pan evaporation estimation in western Turkey / Estimation de l’évaporation journalière du bac dans l’Ouest de la Turquie par des modèles à base de logique floue     

《水文科学杂志》2013,58(6)

Abstract

Abstract Evaporation is one of the fundamental elements in the hydrological cycle, which affects the yield of river basins, the capacity of reservoirs, the consumptive use of water by crops and the yield of underground supplies. In general, there are two approaches in the evaporation estimation, namely, direct and indirect. The indirect methods such as the Penman and Priestley-Taylor methods are based on meteorological variables, whereas the direct methods include the class A pan evaporation measurement as well as others such as class GGI-3000 pan and class U pan. The major difficulty in using a class A pan for the direct measurements arises because of the subsequent application of coefficients based on the measurements from a small tank to large bodies of open water. Such difficulties can be accommodated by fuzzy logic reasoning and models as alternative approaches to classical evaporation estimation formulations were applied to Lake Egirdir in the western part of Turkey. This study has three objectives: to develop fuzzy models for daily pan evaporation estimation from measured meteorological data, to compare the fuzzy models with the widely-used Penman method, and finally to evaluate the potential of fuzzy models in such applications. Among the measured meteorological variables used to implement the models of daily pan evaporation prediction are the daily observations of air and water temperatures, sunshine hours, solar radiation, air pressure, relative humidity and wind speed. Comparison of the classical and fuzzy logic models shows a better agreement between the fuzzy model estimations and measurements of daily pan evaporation than the Penman method.  相似文献   

Statistical and geostatistical investigations into the effects of the Gabcikovo hydropower plant on the groundwater resources of northwest Hungary / Analyses statistiques et géostatistiques des effets de la centrale hydroélectrique de Gabcikovo sur les ressources en eaux souterraines du Nord-Ouest de la Hongrie     

《水文科学杂志》2013,58(4)

Abstract

Abstract The construction of the Gabcikovo hydropower plant and the diversion of the Danube River over 25 km into an artificial channel in 1992 influenced the groundwater regime of the region considerably. Statistical and geostatistical methods are used to quantify changes of different groundwater characteristics on the Hungarian side of the river based on observations in the time period 1960–2000. External drift kriging was used to interpolate groundwater levels and the other related variables. While mean groundwater levels did not change appreciably, there are significant changes in the variability. Standard deviations of the groundwater levels and the amplitude of the annual cycle decreased near the old river bed of the Danube. The water-level fluctuations of the Danube have a decreased influence on the groundwater dynamics. Interrelationships between water levels in wells have also changed.  相似文献   

Fossilisation of a silica diagenesis reaction front on the mid-Norwegian margin     

Raluca Cristina Neagu  Joe Cartwright  Richard Davies  Lars Jensen 《Marine and Petroleum Geology》2010

The diagenetic transformation of biogenic silica from opal-A to opal-CT was recognised on seismic reflection data over an area of 78 × 10³ km² on the mid-Norwegian margin. The opal-A/CT diagenetic boundary appears as a positive, high amplitude reflection that generally cross-cuts the hosting stratigraphy. We demonstrate that it is not a sea bottom simulating reflection (BSR) and also that is not in thermal equilibrium with the present day isotherms. We present arguments that three styles of deformation associated with the opal-A/CT reflection – polygonal faulting, regional anticlines and synclines and differential compaction folding – indicate that the silica diagenesis reaction front is fossilised at a regional scale. Isochore maps demonstrate the degree of conformity between the opal-A/CT reflection and three seismic horizons of Late Miocene to Early Pliocene age that potentially represent the paleo-seabed when ‘fossilisation’ of the reaction front took place. The seismic interpretational criteria for recognition of a fossilised diagenetic front are evaluated and the results of our study are integrated with previous studies from other basins of the NE Atlantic in order to determine if the arrest of silica diagenesis was diachronous along this continental margin.  相似文献   

利用Adobe Photoshop对悬沙颗粒图像预处理     

于翔  宋家驹  刘连君 《海洋技术学报》2007,26(4):23-26

利用光学悬浮沙粒径谱仪现场拍摄的悬沙颗粒图像具有两个特点:1、边缘亮度不均匀:2、边缘不清晰。为了测量颗粒粒径,需要做边缘提取。由于悬沙颗粒的上述两个特点,二值化后的颗粒图像容易产生边缘失真和边缘不闭合现象,为了解决这个问题,文中介绍利用Adobe Photoshop对悬沙颗粒的预处理。  相似文献   

Møre Margin: Crustal structure from analysis of Expanded Spread Profiles     

Ingi Olafsson  Eirik Sundvor  Olav Eldholm  Kjersti Grue 《Marine Geophysical Researches》1992,14(2):137-162

Analysis in both the x—t and —p domains of high-quality Expanded Spread Profiles across the Møre Margin show that many arrivals may be enhanced be selective ray tracing and velocity filtering combined with conventional data reduction techniques. In terms of crustal structure the margin can be divided into four main areas: 1) a thicker than normal oceanic crust in the eastern Norway Basin; 2) expanded crust with a Moho depth of 22 km beneath the huge extrusive complex constructed during early Tertiary breakup; 3) the Møre Basin where up to 13–14 km of sediments overlie a strongly extended outer part with a Moho depth at 20 km west of the Ona High; and 4) a region with a 25–27 km Moho depth between the high and the Norwegian coast. The velocity data restricts the continent-ocean boundary to a 15–30 km wide zone beneath the seaward dipping reflector wedges. The crust west of the landward edge of the inner flow is classified as transitional. This region as well as the adjacent oceanic crust is soled by a 7.2–7.4 km s^–1 lower crustal body which may extend beneath the entire region that experienced early Tertiary crustal extension. At the landward end of the transect a 8.5 km s^–1 layer near the base of the crust is recognized. A possible relationship with large positive gravity anomalies and early Tertiary alkaline intrusions is noted.  相似文献