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1、毕业设计（论文）外文翻译题目学院专业学生学号指导教师名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 1 页，共 13 页 - - - - - - - - - 毕业论文外文翻译1 An integrated GPS accelerometer data processing technique for structural deformation monitoring W. S. Chan Y. L. Xu X. L. Ding W. J. Dai Received: 9 Novemb
2、er 2005 / Accepted: 11 August 2006 / Published online: 7 September 2006? Springer-Verlag 2006 Abstract Global Positioning System (GPS) is being actively applied tomeasure static and dynamic displacement responses of large civil engineering structures under winds. However, multipath effects and low s
3、ampling frequencies affect the accuracy of GPS for displacement measurement.On the other hand, accelerometers cannot reliably measure static and low-frequency structural responses, but can accurately measure high frequency structural responses. Therefore, this paper explores the possibility of integ
4、rating GPS-measured signals with accelerometer-measured signals to enhance the measurement accuracy of total (static plus dynamic) displacement response of a structure. Integrated data processing techniques using both empirical mode decomposition (EMD) and an adaptive filter are presented. A series
5、of motion simulation table tests are then performed at a site using three GPS receivers, one accelerometer, and one motion simulation table that can simulate various types of motion defined by input wave time histories around a pre-defined static position.The proposed data processing techniques are
6、applied to the recorded GPS and accelerometer data to find both static and dynamic displacements. These results are compared with the actual displacement motions generated by the motion simulation table. The comparative results demonstrate that the proposed technique can significantly enhance the me
7、asurement accuracy of the total displacement of a structure. Keywords ： GPS structural deformation monitoring ? Accelerometer ?Integrated data processing ? Static and dynamic displacements ? Empirical mode decomposition (EMD) ? Adaptive filter 1 Introduction Structural displacement is a key paramete
8、r to assess the integrity and safety of a large civil engineering structure,such as a tall building or a long cable-supported bridge, under winds. Wind-induced responses of such a large structure are mainly monitored by accelerometers,and dynamic displacement responses are then obtained 名师资料总结 - - -
9、精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 2 页，共 13 页 - - - - - - - - - 毕业论文外文翻译2 often through a double integration of the measured acceleration responses. An accelerometer is able to extract acceleration responses of a structure with natural frequency up to 1,000 Hz becaus
10、e of the high sampling frequency (Roberts et al. 2004). However, an accelerometer is insensitive to acceleration changes. The velocity and displacement integrated from the uncompensated acceleration signals will drift over time due to unknown integration constants, and a high-pass filter should be u
11、sed to cope with low-frequency drift introduced during the integration process. It is therefore recognized that an accelerometer is incapable of measuring static and low-frequency dynamic displacement responses of a structure. After the Soviet union launched the first man-made satellite, the United
12、States John Hobbes Jin Daxue applied physics laboratory researchers put forward now that can be known to the location of the observatory know satellite position, so when the satellite position is known, should also can measure the location of the receiver. This is the basic idea of navigation satell
13、ite.The basic principle of GPS navigation system is to measure the known position of satellite to the distance between the user receiver, and then integrated satellite data can know the location of the receiver. To achieve this purpose, the position of the satellite can be recorded by spaceborne clo
14、ck time to find out in the satellite ephemeris. While the user is the distance to the satellite by record time experienced by the satellite signal transmission to the user, then its multiplied by the speed of light is (because of the atmosphere, the ionosphere disturbance, the distance is not the re
15、al distance between the user and satellite, but the pseudorange (PR) : when the normal work of the GPS satellites, will continue to use the binary 1 s and 0 s element consisting of pseudo-random code (pn code) launch navigation message.GPS system using the pseudo code of A total of two kinds, respec
16、tively is civil C/A code and military P (Y) code. C/A code frequency 1.023 MHz, repeat cycle A millisecond, code spacing 1 millisecond, equivalent to 300 m; P code frequency 10.23 MHz, 266.4 days, repeat cycle code spacing 0.1 microseconds, equivalent to 30 m. And Y code is on the basis of P code, s
17、ecrecy performance is better. Navigation message includes satellite ephemeris, working conditions, and clock correction, ionospheric delay correction, correction of atmospheric 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 3 页，共 13 页 - - - - - - - - - 毕业论文外文翻译3 refr
18、action, etc. It from the satellite signal - | A useful - cn: demodulation; Useful - tw: demodulation -, 50 b/s - | A useful - cn: modulation; Useful - tw: modulation - launched on the carrier frequency. Navigation message contains five child frame each main frame of the long frame 6 s.The first thre
19、e frames each 10 word; Repeat every 30 seconds, updated every hour. Two frames after 15000 b. The contents of the navigation message includes telemetry code, transform code, 1, 2, 3 data blocks, one of the most important is the ephemeris data. When users receive the navigation message, extract the s
20、atellite time and compare with their own clock can be learned that the distance between the satellite and the user, using the navigation message of satellite ephemeris data show the location at the time of the satellite launch cables, users in the WGS - 84 - | A useful - cn: geodetic coordinate syst
21、em; Useful - tw: geodetic coordinate system - the location information such as speed can be learned.Visible GPS satellite navigation system part of the role of the navigation message is continuously launch. However, due to the user receiver using the clock with satellite spaceborne clock cant always
22、 be synchronized, so in addition to the users 3 d - | A useful - cn: coordinates; Useful - tw: coordinates - x, y, z, will also introduce a t is the time difference between the satellite and receiver as unknowns, and then use four equations to solve the four unknown number. So if you want to know th
23、e receivers position, can receive at least four of the satellite signal. In order to promote the accuracy of the civilian, the scientific development of another technology, called Differential global positioning system (Differential GPS), hereinafter referred to as DGPS. I.e. using near known refere
24、nce coordinate point (measured by other methods), to correct the error of GPS. Then add the instant (real time) error value to itself coordinate operation consideration, can obtain more accurate values. GPS navigation with 2 d and 3 d navigation points, when the satellite signal is not enough to pro
25、vide 3 d navigation services, and the elevation accuracy obviously not enough, sometimes up to 10 times the error 7. But the improvement in terms of latitude and longitude error is very small. Satellite positioning receiver in high-rise buildings is taking longer to catch the satellite signal. Globa
26、l Positioning System (GPS) is now actively applied to measure static and dynamic displacement responses of a large civil engineering structure under winds 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 4 页，共 13 页 - - - - - - - - - 毕业论文外文翻译4 due to its global coverage
27、 and continuous operation under all meteorological conditions. However, the accuracy of GPS for displacement measurement depends on many factors such as satellite coverage,atmospheric effects, multipath, and the GPS data processing method. The Nyquist frequency of a modern dual-frequency GPS receive
28、r of 20 Hz sampling rate is 10 Hz, which is good enough to detect natural frequencies of a civil engineering structure. However, when concerning structural dynamic displacement monitoring, the accuracy of quantization of the structural dynamic displacement is important. This requires the sampling ra
29、te to be much higher than the frequency components of interest in the continuous signal of structural deformation. For instance, when considering a 10 cycles per second sinusoidal wave being sampled at 20 samples per second, only 2 samples can be obtained for each sine wave cycle, which is definitel
30、y not enough to reconstruct this sine wave. In order to assess the best performance of GPS (Leica GX1230 GPS receiver) in dynamic displacement measurements, calibration tests using a motion simulation table were carried out in an open area in Hong Kong (Chan et al. 2005). The results showed that the
31、 GPS could measure dynamic displacements properly if the motion frequency was 1Hz. This result may change slightly if the measurement site is changed. Clearly, the measurement performance of GPS is complementary to that of an accelerometer. This paper thus explores the possibility of integrating GPS
32、-measured signals with accelerometer-measured signals to enhance the measurement accuracy of total (static plus dynamic) displacement response of large civil engineering structures. The concept of integrating signals from GPS and accelerometer for structural deformation monitoring was presented by R
33、oberts et al. (2004). and Liet al. (2005). In the integration algorithms proposed by Roberts et al. (2004), the measurement signals from an accelerometer were filtered by a conventional filter to remove high-frequency noise, and the measurement signals from a GPS were filtered using an adaptive filt
34、er to reduce multipath. The single integration of acceleration signals from the accelerometer was then performed to find velocity signals. The velocity signals from the accelerometer were reset using the velocity constant calculated from the GPS 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - -
35、 - 名师精心整理 - - - - - - - 第 5 页，共 13 页 - - - - - - - - - 毕业论文外文翻译5 data. These calibrated velocity signals were integrated to obtain displacement signals, and the displacement signals were finally reset with the GPS coordinates to obtain the actual displacement of a structure. Their results revealed t
36、hat, with the proposed integration scheme, millimeter-accurate positioning could be maintained within several tens of seconds. The displacement obtained by the earlier method was actually dynamic displacement only. Li et al. (2005) further isolated the static and quasi-static displacement components
37、 from the GPS data and added them to the dynamic displacement to obtain the total displacement of a structure under winds. Large civil engineering structures are typically very slender and accordingly their low-frequency responses to winds are very difficult to accurately measure with accelerometers
38、. Furthermore, besides wind-induced dynamic displacement, wind-induced static displacement of a structure measured by GPS is likely to be contaminated by multipath. Hence, it is difficult to apply the existing integration scheme to the total displacement response of large civil engineering structure
39、s. In this regard, this paper presents different integrated GPS/accelerometer data processing techniques, based on the empirical mode decomposition (EMD) and an adaptive filter, to enhance the measurement accuracy of total (static plus dynamic) displacement response of a large civil engineering stru
40、cture under winds. The EMD developed by Huang et al. (1998) is a data-processing tool that can decompose any complicated data set into a small number of intrinsic mode functions (IMF) and a final residual. The EMD method has been successfully used to extract time-varying mean wind speed from typhoon
41、 induced non-stationary wind records for long cable supported bridges (Xu and Chen 2004) and tall buildings (Chen and Xu 2004). The adaptive filter is a signal decomposer that extracts information of interest from the contaminated signal using the cross-correlation between reference and primary time
42、 series (Ge et al. 2000, Roberts et al. 2002). In recognition that the multipath is repeatable on every sidereal day, Ge et al. (2000) successfully applied adaptive filtering to GPS data to reduce the multipath. To assess the effectiveness of the proposed integrated data processing techniques, 名师资料总
43、结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 6 页，共 13 页 - - - - - - - - - 毕业论文外文翻译6 a series of motion simulation table tests are performed at a site using three GPS receivers, one accelerometer, and one motion simulation table. Static tests, with the GPS antenna instal
44、led on the motion simulation table that is in stationary condition, are first performed at the test site to estimate the amount of multipath. The motion simulation table is then used to generate various types of dynamic displacement response around a pre-defined static position.The GPS and accelerom
45、eter measurement data are recorded within the same time period as the static tests but on the next sidereal day. The proposed data processing techniques are then applied to the recorded GPS and accelerometer data to find both static and dynamic displacements. The effectiveness of the integrated meth
46、ods is finally assessed through the comparison of the integrated results with the original motions generated by the motion simulation table. 2 Empirical Mode Decomposition and Adaptive FilterThe EMD used in this study is to decompose GPS measured structural displacement response time history x(t) in
47、to a number of IMF components and a final residual through a sifting process (Huang et al. 1998): x(t) =cj(t) + r(t)NeWhere Ne is the number of IMF components; and r(t)Ne is the final residual. This final residual of the structural displacement response time history, measured by GPS, is a monotonic
48、function that can be defined as the mean displacement of the structure. As the concept of this decomposition is based on the direct extraction of the energy associated with various intrinsic time scales of the time history itself, mode mixing during the sifting process would be possible. A criterion
49、, termed the intermittency check, was thus suggested by Huang et al. (1999) to separate the waves of different periods into different modes based on the period length. In this study, the EMD with an intermittency check and a cutoff frequency _c are used to process acceleration time history measured
50、by an accelerometer so as to obtain a high-frequency dynamic response of frequency components greater than the cutoff frequency. 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 7 页，共 13 页 - - - - - - - - - 毕业论文外文翻译7 An adaptive filter, used as a signal decomposer, ope