| In recent years, a large scale of highway construction is booming in whole country. The inspection and evaluation of highway will face increasingly onerous tasks. Therefore, the old inspection methods of thickness quality, such as bore and sampling, can't satisfy the developing requirement, not only for their low efficiency, bad representation, poor accuracy, but also for their destruction to the built highway. So, the Non Destructive Testing with simple operation, high accuracy and efficiency, need rapid developments. Ground Penetrate Radar is such a NDT, which has a twenty-years' history.The principle of GPR is similar to the ordinary radar. It works near the surface of the road and transmits electromagnetic (EM) wave to the pavement layers. When the electromagnetic wave propagates in the pavement layers, it will be reflected at the interface of two different kinds of medium. As we know, different medium have different dielectric constant. The reflected wave will be received by the receive antenna and transferred to digital data. We can analyze the data that saved by the computer of GPR to deduce the medium's property, situation, location and so on. Being a kind of nondestructive, untouched method, it has many advantages such as high precision, low cost, abundant content, non-destruction and rapidness. It can collect data at the speed of 80 km/h. the data can be processed by special software and the GPR can offer color images and information of road service level. We can take some measure to rehabilitate road according to the data that GPR provides;By now, GPR data interpretation can't be automated eventually due to many artificial respects. The result is subjective and incorrect. Therefore, we need make automated-analysis software quickly. Making software is based on algorithm, namely, the mathematic model of EM wave propagation. Then echo wave simulation is usedto examine the model, because echo wave simulation is one of the effective ways toevaluate the propagation theory. Therefore, we can model the echo wave of the pavement structure that we have already known and compare it to the actual wave. If they do not match very well, we can adjust some parameters to improve it. In the past, many scholars had working on it, but they didn't agree to each other. The difference among them is so big that we don't know which to choose to analyze the roads in our country. To find out the propagation theory that suits to roads in our country, a method of EM finite elements is discussed in this dissertation.The application of finite elements method (FEM) in electromagnetics has a history of 30 years. The prosperous future of this method stems from presses in the applications and developments of projects, such as equipment enlargements, equipment integration, and diversity of products. All above need quantitative calculation of high precision and optimize design on the electric equipment or its components.Inverse calculation about layer parameters via radar signals is still in the phase of exploration, because the course of EM propagation in the pavement is so complicated. At present, there are more than 30 enterprises overseas that specialize exploitation and distribution of FEM software, such as America, Canada, Britain, etc. The products include MSC/EMAS, ELECTRO, ANSYS, and so on. But they have some limits and lack flexibility in analysis of concrete problems. Henan engineering research center for road NDT technology made an attempt by FFT in the year of 2002, but the results were not very good. In this dissertation, the principle of FEM in EM was discussed, then the Pulse Radar and three-layered pavements were analyzed with 20-noded and 4-noded isoparametric elements respectively. Then, corresponding FEM programs are compiled in Fortran90. So a forward model was built up to describe the transmitting of electromagnetic in the radar and pavements, according to the system identification method. Compared with the methods of finite difference or FFT, the results are more precise and effective, which ar... |
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