共查询到19条相似文献，搜索用时 281 毫秒
1.
According to the structural characteristics of hazardous waste landfill,a new model based on the finite element method(FEM)is developed.The detection layer is considered as a sealed space and it is assumed that total current flows through the leak for the high resistivity of geomembrane liner.The leak current is regarded as a positive point current I and the other current source is-I.Electrical potential of an arbitrary point in detection layer satisfies Poisson equation. Experiments for detecting leaks in liner were carried out.Excellent agreement between experimental data and simulated model data validates the new model.Parametric curves for a single leak show that with optimum selection of field survey parameters leaks can be detected effectively.For multiple leaks,the simulated results indicate that they are detectable when leak separation is larger than measurement spacing. 相似文献
2.
Omnidirectional imaging sensors have been used in more and more applications when a very large field of view is required. In this paper, we investigate the unwrapping, epipolar geometry and stereo rectification issues for omnidirectional vision when the particular mirror model and the camera parameters are unknown in priori. First, the omnidirectional camera is calibrated under the Taylor model, and the parameters related to this model are obtained. In order to make the classical computer vision algorithms of conventional perspective cameras applicable, the ring omnidirectional image is unwrapped into two kinds of panoramas： cylinder and cuboid. Then the epipolar geometry of arbitrary camera configuration is analyzed and the essential matrix is deduced with its properties being indicated for ring images. After that, a simple stereo rectification method based on the essential matrix and the conformal mapping is proposed. Simulations and real data experimental results illustrate that our methods are effective for the omnidirectional camera under the constraint of a single view point. 相似文献
3.
The strain monitoring and stress analysis of a new type of post-prestressed tunnel liner were carried out. The instrumentation block of the tunnel liner, with the dimensions of 12.06 m in length, 6 500 mm in diameter, and 650 mm in thickness, was post-prestressed with the unbonded tendons, each of which consists of 8 pieces of double-looped strands and the axial spacing of the tendons is 500 mm. Concrete strain meters, rebar meters, load cell and zero-stress meters were installed for the strain monitoring. The tensioning loads were applied incrementally in three cycles (50%, 77% and 100%) at the concrete age of 28 d and the tensioning work lasted for 187.1 h. Strain readings were taken before and after each cycle during tensioning period and at the specified time interval after tensioning period. It is found that concrete creep developed over tensioning period is 30% of total strain and 41.5% of elastic strain respectively. Prestress force in the unbonded tendon and concrete stress in the liner were evaluated according to the observed strain variations. Both of them are time-dependent, and about 5.3%, 8.3% and 9.0% of the prestress losses are observed at the age of 1 d, 30 d and 60 d respectively after stressing. The distribution of prestress in the liner is relatively uniform and meets the design requirement. 相似文献
4.
A model for incipient movement of sediment in rolling pattern was established. In this model, the starting of sediment particles under low transport rate, the exposure degree of sediment, the lateral slope of water surface and the effect of transverse circulating current induced by the hydraulic structure of bend flow were fully considered. A theoretical formula for the incipient velocity of non-cohesive and non-uniform sediment in sloping river bends was developed. The results from the theoretical formula compared well with the experimental data. 相似文献
5.
Aiming at piezoresistive pressure sensors,this paper studies simulation of standard pressure by using benchmark current source and self-calibration of the sampling data characteristics.A data fusion algorithm for sample set is presented which transforms a surface problem into a curve fitting and interpolation problem.The simulation result shows that benchmark current source simulating pressure is successful and data fusion algorithm is effective.The maximum measurement error is only 0.098 kPa and maximum relative error is 0.92% at 0-45 kPa and -10-45℃. 相似文献
6.
《天津大学学报(英文版)》2020,(5)
Supercapacitors,or electric double-layer capacitors(EDLCs),are the new generation of energy storage devices to store electrical charges and provide high power densities and long cyclic life compared to other storage devices.EDLC mainly consists of activated carbon electrodes and an electrolyte,and the performance of EDLC depends on the activated carbon electrodes.In this work,the structural changes of activated carbon electrodes are analyzed using commercial 2.7 V/9500 F EDLCs in its manufacturing process.It is found that there is no significant change in morphology and crystal structure of the activated carbon,but its specific surface area(SSA) reduced greatly.The SSA of activated carbon was decreased by 23% after they were manufactured or converted into electrodes and finally retained only 40% of SSA after the capacitance test.Besides,the SSA of the positive electrodes was found to decrease critically than that of the negative electrodes.The SSA of the external positive electrodes is only 14.3% after floating test at 65℃. 相似文献
7.
A good mechanical model of magnetorheological damper (MRD) is essential to predict the shock isolation performance of MRD in numerical simulation. But at present, the mechanical models of MRD were all derived from the experiment subjected to harmonic vibration loads. In this paper, a commercial MRD (type RD-1005-3) manufactured by Lord Corporation was studied ex-perimentally in order to investigate its isolation performance under the impact loads. A new me-chanical model of MRD was proposed according to the data obtained by impact test. A good agreement between the numerical results and test data was observed, which showed that the model was good to simulate the dynamic properties of MRD under impact loads. It is also demon-strated that MRD can improve the acceleration and displacement response of the structure obvi-ously under impact loads. 相似文献
8.
The clock generator and OOK modulator for RFID (Radio Frequency Identification) presented in this paper consist of a current source and delay elements. The simple constant-gm structure is adopted in the current source design and the current consumption of the current source is only about 2 μA. The delay elements, the clock generator and OOK modulator are introduced in detail in the paper. The designed circuits are fabricated by 0.6 μm CMOS process. The area of the core circuit is only about 400 μmμ0 μm. The delay time of all three samples is in the range of 9 μs to 21 μs when the supply voltage varies from 2 V to 4 V. As the measured results satisfy the system requirements, these circuit structures are suitable for RFID application. 相似文献
9.
In early research, capture and manipulation of particles were mainly achieved by means of light, electricity and plasma in micro-fabficaton and micro-assembly. A new method is proposed using micro-water jet to form water tweezers to capture solid particles and implement position control of micro-particles. This paper analyzes the basic prin- ciple of water tweezers, and the discrete element method and smoothed particle hydrodynamics method are employed to establish a solid-liquid coupling model used in analyzing the trapping mechanism. A flow field model is set up to simulate dynamic characteristic of water tweezers based on computa- tional fluid dynamics （CFD）. Selection of boundary conditions, initial guess, solver control and convergence strategies of the model are discussed. Velocity and pressure of streamline are predicted and discussed under certain input conditions. Simu- lation results demonstrate that it is an efficiently theoretical method to eventually trap solid particles by water tweezers. 相似文献
10.
Ren-peng CHEN Yun-min CHEN Wei XU Zhi-gang LIANG Wei FENG 《浙江大学学报(A卷英文版)》2008,9(3):293-302
Based on polarization mechanisms, such as electronic, ionic and orientational polarizations, a new equation for dielectric permittivity of soil is proposed to interpret the dielectric behavior of a mixture like soil, in terms of polarization process of its components and the interactions between its components. The dielectric permittivity is expressed in terms of a fre- quency-dependent part and a frequency-independent part. These two parts correspond to polarizations occurred at different fre- quency range. It is a new volumetric mixing model with theoretical background. Based on time domain reflectometry （TDR） measurements of saturated soil samples and test data from literature, comparisons of this model with some well established mixing models show that the curves for saturated sand soils and slurries resulted from the new equation, which agree well with TDR measurements, are close to those calculated from Birchak＇s model. 相似文献
11.
杨惠山 《泉州师范学院学报》2003,21(2):23-27
应用有限时间热力学理论，建立一类较普遍的不可逆斯特林热机模型，研究存在热阻、热漏、回热损失斯特林热机的优化性能，导出了热漏损失服从一般传热规律时热机的功率与效率间的优化关系，讨论了不同情况下热漏和回热损失对热机性能的影响，从而可为二热源热机的研制和优化设计提供新的理论指导。 相似文献
12.
Design of ERT system 总被引：2，自引：0，他引：2
INTRODUCTION Electrical resistance tomography (ERT) is a technique producing images based upon variations in conductivity, and has great potential in process ap- plications (Tapp et al., 2003). In an ERT system, current is injected to a pair of drive electrodes and voltage measurements are taken between sense elec- trode pairs, yielding resistance information for image reconstruction (Cilliers et al., 2001). Traditional ERT systems usually use high fre- quency sinusoidal waveforms as … 相似文献
13.
建立一类较普遍的不可逆斯特林热机模型，研究存在热阻、热漏、回热损失时斯特林热机的优化性能，导出了热漏损失服从一般传热规律时热机的功率与效率间的优化关系，从而可为二热源热机的研制和优化设计提供新的理论指导． 相似文献
14.
胎儿心电(Fetal Electrocardiogram,FECG)是通过安置在母体腹部表面电极间接检测到的微弱信号,其中含有各种形式的干扰信号,如何将胎儿心电从强背景干扰中分离出来,具有重要的临床应用价值。独立成分分析(Independent Component Analysis,ICA)是近年发展起来的一种新的盲源分离技术(Blind source separation,BSS)。本文将ICA方法应用于胎儿心电信号的提取,并对胎儿心电的在线提取进行了研究,取得了较好的胎儿心电分离效果。 相似文献
15.
开发的电流场实验装置采用水做为媒质,由于水的电阻率比铁板大得多,不再需要可输出大电流的稳压源,使用实验室里常见的电压源就行.另外,新实验装置还可以完成一些静电场模拟实验,如同轴电缆和偏心圆柱导体模型等.利用新实验装置进行了实验测试,将实验测量值与有限元分析软件ANSYS的计算值进行对比.结果表明,新实验装置在当前实验室环境下是可行的.与传统实验装置相比,新实验装置更加灵活、方便,能提供多种测量模型,适合学生进行开发性实验. 相似文献
16.
In operational equating situations, frequency estimation equipercentile equating is considered only when the old and new groups have similar abilities. The frequency estimation assumptions are investigated in this study under various situations from both the levels of theoretical interest and practical use. It shows that frequency estimation equating can be used under circumstances when it is not normally used. To link theoretical results with practice, statistical methods are proposed for checking frequency estimation assumptions based on available data: observed‐score distributions and item difficulty distributions of the forms. In addition to the conventional use of frequency estimation equating when the group abilities are similar, three situations are identified when the group abilities are dissimilar: (a) when the two forms and the observed conditional score distributions are similar the two forms and the observed conditional score distributions are similar (in this situation, the frequency estimation equating assumptions are likely to hold, and frequency estimation equating is appropriate); (b) when forms are similar but the observed conditional score distributions are not (in this situation, frequency estimation equating is not appropriate); and (c) when forms are not similar but the observed conditional score distributions are (frequency estimation equating is not appropriate). Statistical analysis procedures for comparing distributions are provided. Data from a large‐scale test are used to illustrate the use of frequency estimation equating when the group difference in ability is large. 相似文献
17.
William Demuth Blum 《Journal of Experimental Education》2013,81(4):219-267
Wilcox (16) proposed a latent structure model for answer-until-correct tests that can solve various measurement problems including correcting for guessing without assuming guessing is at random. This paper proposes a closed sequential procedure for estimating true score that can be used in conjunction with an answer-until-correct test. For criterion-referenced tests where the goal is to determine whether an examinee’s true score is above or below a known constant, the accuracy of the new procedure is exactly the same as a more conventional sequential solution. The advantage of the new procedure is that it eliminates the possibility of using an inordinately large number of items when in fact a large number of items is not needed; typical sequential procedures always allow this possibility. In addition, the new procedure appears to compare favorably to traditional tests where the number of items to be administered is fixed in advance. 相似文献
18.
以HI76303电导电极为例,从电学基本理论出发,研究了电导仪产生边界效应的原因,分析得出电极外部回路是产生边界效应的根本原因。电导仪测定的电导率结果为探头外部和探头内部溶液并联形成的电导率值;通过计算发现,电极敏感区域为直径约8 cm的椭球体。切断电极外部回路是消除边界效应的根本方法。以HI76303电导电极为基础,设计了一种改进型电极,计算表明,改进型电极工作时电势在激励电极之间均匀下降,电极外部溶液电势处处相等且为零,电极内部电流密度处处一致,电极外部电流密度为零。实验数据显示其有效地消除了边界效应。 相似文献
19.
为了提高对汽车缸套的无心外圆磨外径加工的加工精度和加工效率,设计了一套针对汽缸套外径的在线监测和上下料机构,采用了电涡流传感器来进行在线监测缸套外径尺寸,在达到尺寸要求时,自动报警,上下料机构自动地将已加工好的汽缸套从工位移开。详述了外径测量方案与系统程序,并分析了可能导致检测误差的相关因素。 相似文献