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用极少投影对受腐蚀的管道进行CT成象,采用了GP法,ART法以及新提出的快速几何迭代算法,取得了较好的重建结果。对实验投影数据进行了射束硬化校准和高通滤波预处理,用预处理后的数据反演得到了满意的图象。此法也可适用于由1—2种材料构成的工件无损检测。 相似文献
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地震作用下储罐与管道连接波纹管的动力响应 总被引:2,自引:2,他引:2
针对储罐与管道连接这个抗震薄弱环节进行研究,考虑了储罐与地基、管道与地基的相互弹性作用及流固耦合作用,使计算模型比较符合工程实际情况。将储罐罐壁看作为刚体,将波纹管部分和管道部分分别用旋转锥壳单元和空间梁单元离散化,通过分析得到波纹管与储罐连接接合面、波纹管与管道连接接合面不同单元之间的位移协调约束方程,并用罚函数法进行处理。根据流体力学速度势理论和有限元法的基本理论,利用哈密尔顿变分原理推导出储罐与管道连接波纹管系统动力分析方程,编制了系统动力分析有限元程序,计算了垂直地震激励不同场地土地基条件下储罐与管道连接波纹管位移响应。 相似文献
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涡激振动下管桥段的模糊动力可靠性研究 总被引:3,自引:0,他引:3
本文首先给出了管道在流体作用下的力学模型,并对风力作用下管道产生涡激振动的机理进行了分析,从而建立了管桥在风力作用下的力学模型和相应的振动微分方程,同时给出了管桥的固有特性和动力响应分析结果,然后,在此基础上,提出了首超模糊失效、模糊疲劳失效和混合失效等三类模糊失效准则,并依据这些准则分析给出了动力可靠性的计算公式,最后,给出了具体的算例。 相似文献
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基于土体的等效粘弹性模型,结合场地典型剖面的土体特性以及室内实验确定的各力学参数,采用时域积分和迭代的方法研究了沁河倒虹吸管道在地震作用下的反应,分析了管道截面中间底部点绝对地震位移、顶部点相对于底部点的地震动位移及管道动静综合主应力的变化规律;并根据有限元时程法的分析结果,按照混凝土承载能力极限状态设计式,对管身混凝土的抗拉、抗压安全度进行校核。结果表明,在人工地震波、调整后的E1 Centro和Pulgas地震波分别输入的情况下沁河渠道倒虹吸管道均满足抗震要求。 相似文献
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受沉陷作用埋地管道破坏判别方法 总被引:2,自引:0,他引:2
大地地震震害经验表明,场地的不均匀沉陷是导致埋地管线破坏地重要原因之一。提出一个适用的管道破坏判别方法十分重要本文提出了一个新的方法,用以分析受沉的埋地管道的反应,该方法发迹了沉陷区和非沉陷区都用弹性地基梁的分析途径,在沉陷区考虑了管道几何大变形,克服了现有方法公适用于无限远处发生最大沉陷的缺陷,适用于任何沉陷参数的情况。 相似文献
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It is possible and common to obtain equivalent natural frequency and damping for a soil-foundation system from results of experimental or numerical analysis assuming the system has a single degree of freedom. Three approaches to extract natural frequency and damping were applied to the vertically vibrated soil-foundation system. The sensitivity of the computed natural frequency and damping to the soil properties was evaluated through parametric studies. About 10–20% of discrepancy in values of natural frequency was observed due to different approaches. The results help to assess the reliability of equivalent soil properties determined from the reported natural frequency of the system. Finally the results obtained using theoretical predictions with linear soil properties measured in situ were compared to those calculated from experimental data. The prediction and experimental results showed good agreements if the embedment of the foundation is neglected with stepped sine test but considered with impulse test. 相似文献
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Previous experimental studies of capillary barriers have identified highly hysteretic soil moisture retention characteristics in the materials used. In this study, numerical modelling is used to analyse the role of soil moisture hysteresis in capillary barrier functioning. Comparisons between published experimental results and model simulations indicate that soil moisture hysteresis was a necessary inclusion in the modelling approach to adequately reproduce pore water pressure distributions and the timing of breakthrough occurrences. Under hypothetical intermittent infiltration and evaporation conditions, the predicted volumetric water content in the moisture retention layer was significantly different for hysteretic and non‐hysteretic models. The hysteresis effect was found to be dependent on the nature of infiltration–evaporation cycling, although the predicted volume of flow through the hysteretic barrier was lower than that of the non‐hysteretic case, regardless of the nature of the cyclic upper boundary conditions. For practical engineering designs, where the water leakage through the barrier is the primary concern, the inclusion of soil moisture hysteresis in numerical modelling is needed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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A one‐dimensional, two‐layer solute transport model is developed to simulate chemical transport process in an initially unsaturated soil with ponding water on the soil surface before surface runoff starts. The developed mathematical model is tested against a laboratory experiment. The infiltration and diffusion processes are mathematically lumped together and described by incomplete mixing parameters. Based on mass conservation and water balance equations, the model is developed to describe solute transport in a two‐zone layer, a ponding runoff zone and a soil mixing zone. The two‐zone layer is treated as one system to avoid describing the complicated chemical transport processes near the soil surface in the mixing zone. The proposed model was analytically solved, and the solutions agreed well with the experimental data. The developed experimental method and mathematical model were used to study the effect of the soil initial moisture saturation on chemical concentration in surface runoff. The study results indicated that, when the soil was initially saturated, chemical concentration in surface runoff was significantly (two orders of magnitude) higher than that with initially unsaturated soil, while the initial chemical concentrations at the two cases were of the same magnitude. The soil mixing depth for the initially unsaturated soil was much larger than that for the initially saturated soil, and the incomplete runoff mixing parameter was larger for the initially unsaturated soil. The higher the infiltration rate of the soil, the greater the infiltration‐related incomplete mixing parameter. According to the quantitative analysis, the soil mixing depth was found to be sensitive for both initially unsaturated and saturated soils, and the incomplete runoff mixing parameter was sensitive for initially saturated soil but not for the initially unsaturated soil; the incomplete infiltration mixing parameter behaved just the opposite. Some suggestions are made for reducing chemical loss from runoff. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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In ecosystem research great effort is made in measuring soil water tension, because this is a critical calibration variable for modelling soil water fluxes. In this paper the spatial heterogeneity and temporal dynamics of soil tensions and their consequences for the determination of water fluxes are investigated. Studies were carried out at a Norway spruce stand in the Fichtelgebirge (NE Bavaria). Standard tensiometers were installed at three soil depths (20 each) on the whole experimental plot, as well as 45 microtensiometers as a dense grid in a small soil pit. Microtensiometry at the centimetre scale showed that, depending on rain intensity and initial soil water tension, even a soil without discernible macrostructure may show preferential water infiltration. At the stand scale the variability of soil hydraulic properties and tree root distribution causes substantial heterogeneity of soil water tension, as observed by standard tensiometers. A functional relationship between increasing spatial heterogeneity of tensiometer readings and increasing soil water tension was found, which was particularly pronounced after longer dry periods. Also at low soil water tension, where spatial heterogeneity was low, the calculation of water fluxes from tensiometer values was critical, owing to the fact that small differences in measuring soil water tension resulted in big differences in calculated water fluxes. At high soil water tension in summer the spatial heterogeneity of tensiometer readings was extremely high. At our experimental site, since 30% of the total rain in summer falls in events having a precipitation rate greater than 5 mm h−1, preferential water and solute flow was an important phenomenon. We conclude that the validation of calculated water fluxes using measured soil water tension at the stand scale is not an appropriate tool, because of measurement difficulties, considerable spatial heterogeneity, especially in dry periods, and the great variability of soil hydraulic properties. © 1998 John Wiley & Sons, Ltd. 相似文献
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Use of soil moisture data and curve number method for estimating runoff in the Loess Plateau of China 总被引:2,自引:0,他引:2
The Soil Conservation Service curve number (CN) method commonly uses three discrete levels of soil antecedent moisture condition (AMC), defined by the 5‐day antecedent rainfall depth, to describe soil moisture prior to a runoff event. However, this way may not adequately represent soil water conditions of fields and watersheds in the Loess Plateau of China. The objectives of this study were: (1) to determine the effective soil moisture depth to which the CN is most related; (2) to evaluate a discrete and a linear relationship between AMC and soil moisture; and (3) to develop an equation between CN and soil moisture to predict runoff better for the climatic and soil conditions of the Loess Plateau of China. The dataset consisted of 10 years of rainfall, runoff and soil moisture measurements from four experimental plots cropped with millet, pasture and potatoes. Results indicate that the standard CN method underestimated runoff depths for 85 of the 98 observed plot‐runoff events, with a model efficiency E of only 0·243. For our experimental conditions, the discrete and linear approaches improved runoff estimation, but still underestimated most runoff events, with E values of 0·428 and 0·445 respectively. Based on the measured CN values and soil moisture values in the top 15 cm of the soil, a non‐linear equation was developed that predicted runoff better with an E value of 0·779. This modified CN equation was the most appropriate for runoff prediction in the study area, but may need adjustments for local conditions in the Loess Plateau of China. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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An identification procedure of soil profile characteristics from two free field acclerometer records 总被引:2,自引:0,他引:2
In this paper, an analytical, numerical and experimental approach for identifying soil profile characteristics by using system identification and free field records, is presented. First, a theoretical soil amplification function for two sites is defined and expressed in terms of the different parameters of the layers constituting the soil profiles (thickness, damping ratio, shear wave velocity and unit weight). Then, this function is smoothed with an analogous function obtained from experimental data by using the least squares minimization technique. The identification of the parameters is performed by solving, numerically, a non-linear optimisation problem. To demonstrate the numerical efficiency and the validity of this approach, two examples are treated. The first one consists in the identification of characteristics of a given uniform soil layer. The second example consists in the experimental validation of this approach with the data recorded within the Garner Valley Down Hole Array (GVDA). Finally, this approach is applied to identify, simultaneously, soil profile characteristics of sites from only a single soil acceleration record at free surface of each site. This procedure is utilised to identify soil profile characteristics of sites by using strong ground motions data recorded during the recent Boumerdes earthquake of May 21, 2003. 相似文献
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《中国科学:地球科学(英文版)》2016,(12)
BeiDou Navigation Satellite System reflectometry(BDS-R) is an emerging area of BD(BeiDou) applications that uses multipath reflected signals in microwave remote sensing.Soil moisture estimation is one of the potential important applications of BDS-R.This study aims to investigate the feasibility of soil moisture estimation based on BD B1 band interference signals,which are composed of direct and reflected BD signals and can be readily captured using low-cost commercial BDS receivers.In this paper,a theoretical background for soil estimation from interference signals was introduced,and an analysis of field experimental data was conducted.First,a cosine model for the interference signal power was built,and a non-uniform power spectrum analysis was performed on the received interference signals to determine its main frequency.Then,a least squares curve fitting was applied on the interference signal power to extract its phase.The relationship between the soil moisture and the phase was then determined.Two months of experimental data were collected at BaoXie,Wuhan and analyzed for further inversion.Experimental results show that the phase of the interference signals increases with the increase of soil moisture.The correlation coefficient between the phase and the in-situ soil moisture value is approximately 0.8.Finally,the relationship between the phase and soil moisture is employed to estimate soil moisture.Results show that using BDS-R to measure soil moisture is feasible,which demonstrates a great potential of new application of the BD system. 相似文献
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BeiDou Navigation Satellite System reflectometry (BDS-R) is an emerging area of BD (BeiDou) applications that uses multipath reflected signals in microwave remote sensing. Soil moisture estimation is one of the potential important applications of BDS-R. This study aims to investigate the feasibility of soil moisture estimation based on BD B1 band interference signals, which are composed of direct and reflected BD signals and can be readily captured using low-cost commercial BDS receivers. In this paper, a theoretical background for soil estimation from interference signals was introduced, and an analysis of field experimental data was conducted. First, a cosine model for the interference signal power was built, and a non-uniform power spectrum analysis was performed on the received interference signals to determine its main frequency. Then, a least squares curve fitting was applied on the interference signal power to extract its phase. The relationship between the soil moisture and the phase was then determined. Two months of experimental data were collected at BaoXie, Wuhan and analyzed for further inversion. Experimental results show that the phase of the interference signals increases with the increase of soil moisture. The correlation coefficient between the phase and the in-situ soil moisture value is approximately 0.8. Finally, the relationship between the phase and soil moisture is employed to estimate soil moisture. Results show that using BDS-R to measure soil moisture is feasible, which demonstrates a great potential of new application of the BD system. 相似文献
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Soil characterization for seismic damage scenarios purposes: application to Angra do Heroísmo (Azores) 总被引:1,自引:1,他引:0
Angra do Heroismo, the main town of Terceira Island in the Azores Archipelago, was hit in 1980 by a 7.2 magnitude earthquake that caused great destruction in the central part of the town. Taking into consideration the high seismic hazard of the region and the cultural and social importance of Angra do Heroísmo, the elaboration of damage scenarios is of particular importance to implement measures for preserve and protect the town against future earthquakes. The first step is to perform microzonation studies in order to characterize the soil seismic behaviour. Taking into consideration the available geologic, geotechnical and geophysical information, a detailed soil characterization was performed based on the results from numerical modelling and the analysis of microtremor experimental measurements. Nine different soil profiles were identified, characterized and classified. Discussion on the detailed soil classification and the Eurocode 8 soil classification is presented. This study shows that even with an available code, microzonation studies must be developed in order to identify differences on soil behaviour inside the interested area. It shows also that the use of experimental measurements presents a great help on soil characterization. The obtained detailed classification will be used on the estimation of damage scenarios for Angra do Heroísmo. 相似文献