Optimal GPS/accelerometer integration algorithm for monitoring the vertical structural dynamics

The vertical structural dynamics is a crucial factor for structural health monitoring (SHM) of civil structures such as high-rise buildings, suspension bridges and towers. This paper presents an optimal GPS/accelerometer integration algorithm for an automated multi-sensor monitoring system. The closed loop feedback algorithm for integrating the vertical GPS and accelerometer measurements is proposed based on a 5 state extended KALMAN filter (EKF) and then the narrow moving window Fast Fourier Transform (FFT) analysis is applied to extract structural dynamics. A civil structural vibration is simulated and the analysed result shows the proposed algorithm can effectively integrate the online vertical measurements produced by GPS and accelerometer. Furthermore, the accelerometer bias and scale factor can also be estimated which is impossible with traditional integration algorithms. Further analysis shows the vibration frequencies detected in GPS or accelerometer are all included in the integrated vertical defection time series and the accelerometer can effectively compensate the short-term GPS outages with high quality. Finally, the data set collected with a time synchronised and integrated GPS/accelerometer monitoring system installed on the Nottingham Wilford Bridge when excited by 15 people jumping together at its mid-span are utilised to verify the effectiveness of this proposed algorithm. Its implementations are satisfactory and the detected vibration frequencies are 1.720 Hz, 1.870 Hz, 2.104 Hz, 2.905 Hz and also 10.050 Hz, which is not found in GPS or accelerometer only measurements

A survey on cyber security of CAV

With the ever fast developments of technologies in science and engineering, it is believed that CAV (connected and autonomous vehicles) will come into our daily life soon. CAV could be used in many different aspects in our lives such as public transportation and agriculture, and so on. Although CAV will bring huge benefits to our lives and society, issues such as cyber security threats, which may reveal drivers’ private information or even pose threat to driver’s life, present significant challenges before CAV can be utilised in our society. In computer science, there is a clear category of cyber security attacks while there is no specific survey on cyber security of CAV. This paper overviews different passive and active cyber security attacks which may be faced by CAV. We also present solutions of each of these attacks based on the current state-of-the-art, and discuss future improvements in research on CAV cyber security

The Outlier Knowledge of Products Based On Grey Privacy Information

Product attributes are closely related to consumers\u27 willingness to buy on e-commerce. Some products are considered that few people would buy them online, but in fact they have large sales volume, such as underwear products. This study analyzed from the perspective of the product grey private information of why consumers buy and who is buying these products, what kind of relationship between the purchasing comments and product attributes of these products. Firstly, we select the companies with certain influence to the exploratory research to study the company\u27s comments, and do the data mining of the top 10 products of the best sales and the last 10 products of the poor sales. Secondly, we analyzed the product attributes of the 14 enterprises again by the iterative method and compared with the first exploration result. Thirdly, we studied on the value of common knowledge and outlier knowledge for these products. The study found that common knowledge has the sensitive interval for the price of grey private products, the product price, the discount of the product and the sales volume of the product have significant relationship. The discovery of outlier knowledge is open and the comfort is very different. There is a significant positive correlation between the time of marketing and the sales volume: simple, natural, health products and sales are related; the extreme situations are not universal, but have good room for growth

Towards a Severity Assessment Method for Potential Cyber Attacks to Connected and Autonomous Vehicles

CAV (connected and autonomous vehicle) is a crucial part of intelligent transportation systems. CAVs utilize both sensors and communication components to make driving decisions. A large number of companies, research organizations, and governments have researched extensively on the development of CAVs. The increasing number of autonomous and connected functions however means that CAVs are exposed to more cyber security vulnerabilities. Unlike computer cyber security attacks, cyber attacks to CAVs could lead to not only information leakage but also physical damage. According to the UK CAV Cyber Security Principles, preventing CAVs from cyber security attacks need to be considered at the beginning of CAV development. In this paper, a large set of potential cyber attacks are collected and investigated from the aspects of target assets, risks, and consequences. Severity of each type of attacks is then analysed based on clearly defined new set of criteria. The levels of severity for the attacks can be categorized as critical, important, moderate, and minor. Mitigation methods including prevention, reduction, transference, acceptance, and contingency are then suggested. It is found that remote control, fake vision on cameras, hidden objects to LiDAR and Radar, spoofing attack to GNSS, and fake identity in cloud authority are the most dangerous and of the highest vulnerabilities in CAV cyber security

Deflection Monitoring of the Forth Road Bridge by GPS

Researchers at the IESSG at the University of Nottingham, in conjunction with colleagues from Brunel University, have carried out deflection monitoring work on structures, notably bridges, for a decade. Initial work was carried out on the Humber Bridge, London\u27s Millennium Bridge and the Wilford Footbridge in Nottingham. These trials were carried out over a number of years, using a whole succession of GPS receivers. The initial trials showed that the use of carrier phase GPS could indeed allow sub centimetre movements to be detected, in addition to which, the frequencies of the movements could be calculated. Today, the authors are carrying out such work using state of the art dual frequency surveying grade code and carrier phase GPS receivers. The Forth Road Bridge has an overall length of 2.5 km, a main span length of 1,005m, and was opened in 1964. Traffic has steadily increased over this bridge, from 4 million vehicles in 1964 to over 23 million in 2002. In addition, the heaviest commercial vehicles weighed 24 tonnes; the current limit is 44 tonnes. When the bridge opened, it brought to an end an 800 year history of ferryboat service across the river at Queensferry. Such bridges experience traffic loading greater than that initially anticipated. The following paper details how GPS can be used to evaluate the performance of such a structure. On the 8 and 9 February 2005, a series of tests was conducted upon the Forth Road Bridge in Scotland. During the trials, 7 Survey grade GPS receivers were located upon the bridge, and a further two located as reference stations adjacent to the structure. In addition, a high accuracy Applanix INS, POS-RS, was also located upon the bridge; this is the subject of another paper. Of the 7 receivers on the bridge, four were located at the 1/8, 1/4, 1/2 and 3/4 span on the East side of the deck, whilst a fifth was located at the 1/2 span on the west side of the bridge. A further two receivers were located on top of the two towers at the south end of the bridge. All the receivers gathered data, almost non-stop, for a 48 hour period, at a rate of 10Hz or 20 Hz. Leica 530, 510 and GPS1200 receivers were used during the trials. During the trials, a weather station was used to gather the wind speed and direction, as well as the temperature. This could then be used to evaluate the total force i.e. wind and traffic, experienced by the bridge. During previous trials upon structures, the 10Hz GPS data has been densified with accelerometers capable of gathering data at up to 1,000 Hz. However, as this structure is so large, such high speed movements were not expected, and hence no accelerometers were used, and only the INS. The Ordnance Survey of Great Britain has 74 active station GPS receivers located around the UK. These stations gather data at 1Hz, but then the data is made available at a 15s epoch rate to the public via their web site. In addition to this, the OS are currently establishing their own Network RTK system in the UK. During the trials, the GPS data from a number of OS stations located adjacent to Edinburgh were gathered for the IESSG in order to use these as a comparison with the bridge data processed relative to the reference stations next to the bridge. During the trials, gusts of up to 60 mph were experienced, and the traffic loading was very heavy, especially at rush hour times. In addition, during the trials, a 100 tonne lorry passed over the bridge, and a series of trials were carried out with two 40 tonne lorries, equipped with DGPS to ascertain their locations, and having the bridge closed to other traffic. This is the most controlled of all the trials, as the wind loading is known from the weather station and the only traffic present on the bridge are the two 40 tonne lorries. The expected movements were calculated from the FEM, and the true results compared very well to these. Further to this, during the trials, IESSG staff took shifts to occupy the points, sitting in cars whilst the GPS receivers gathered the data to post-process in an On The Fly manner. During the data gathering exercise, it was evident that the bridge did move, and it was also possible to see a rippling effect on the bridge deck. On processing the data, movements of almost a metre were seen and the rippling effect was evident in the data as well. The results are compared to finite element models (FEM) that exist of the bridge. The 3D coordinates available from the GPS results were transformed into frequencies of the structure\u27s movements. These frequencies and magnitudes of the movements compared very well with the FEM. The following paper details the trials, as well as the post processing techniques carried out on the single and dual frequency carrier phase data. The results are given for all the locations upon the bridge, showing how the bridge moves over a 46 hour period with a variety of loading. Further to this, detail is given on how the GPS results were compared to the FEM, and how such results can indeed be used for structural health monitoring. Reprinted with permission from The Institute of Navigation (http://ion.org/) and The Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation, (pp. 1016-1021). Fairfax, VA: The Institute of Navigation

Vibration frequencies extraction of the Forth Road Bridge using high sampling GPS data

This paper proposes a scheme for vibration frequencies extraction of the Forth Road Bridge in Scotland from high sampling GPS data. The interaction between the dynamic response and the ambient loadings is carefully analysed. A bilinear Chebyshev high-pass filter is designed to isolate the quasistatic movements, the FFT algorithm and peak-picking approach are applied to extract the vibration frequencies, and a GPS data accumulation counter is suggested for real-time monitoring applications. To understand the change in the structural characteristics under different loadings, the deformation results from three different loading conditions are presented, that is, the ambient circulation loading, the strong wind under abrupt wind speed change, and the specific trial with two 40 t lorries passing the bridge. The results show that GPS not only can capture absolute 3D deflections reliably, but also can be used to extract the frequency response accurately. It is evident that the frequencies detected using the filtered deflection time series in different direction show quite different characteristics, and more stable results can be obtained from the height displacement time series. The frequency responses of 0.105 and 0.269Hz extracted from the lateral displacement time series correlate well with the data using height displacement time series

Analysis of the dynamic response of a long span bridge using GPS/accelerometer/anemometer under typhoon loading

Large flexible engineering structures, such as long span bridges or tall buildings, are susceptible to quasistatic and dynamic deformations caused by different loadings, thus accurate displacement measurements are desirable to assess the integrity and reliability of the structure. In this study, an integrated system that includes Global Positioning System (GPS), accelerometer and anemometer was developed to obtain the responses of a long span bridge to the extreme wind loadings. Spectral analysis based on the Fast Fourier Transform (FFT) algorithm was first carried out to detect the dominant frequencies of the middle pylon. Then the noisy GPS displacement measurements and accelerometer data are de-noised using the Vondrak filter, and the low frequency disturbance was separated from GPS displacement time series. A least-squares based displacement reconstruction scheme using noise-mitigated accelerations was employed, and the Tikhonov regularization scheme with optimal selected regularization factor was used to alleviate the ill-posedness. At last, an adaptive recursive least squares (RLS) filter was adopted to separate the slow-varying movements, and the total displacement with enhanced measurement accuracy was obtained from the combined quasi-static and high-frequency dynamic displacements. A field monitoring data set collected on the Erqi Yangtze River Bridge, a three-tower cable-stayed bridge located in Wuhan, China, was used to validate the effectiveness of the proposed integration processing scheme. The GPS/accelerometer/anemometer installed on the center supporting tower was used to characterize the interaction between the responses and the ambient wind loadings. The results demonstrate the proposed technique can significantly improve the measurement accuracy of pylon displacement under strong winds. The deformation accuracy with the amplitude of several millimeters can be successfully detected,and the spectrum of the pylon response obtained from both GPS data and accelerometer data reveals the identified first dominant frequency of the middle pylon is 0.172 Hz

Detection of high-speed railway subsidence and geometry irregularity using terrestrial laser scanning

Subsidence and geometry deformation monitoring are essential for safe transportation on a high-speed railway. Terrestrial laser scanning (TLS) is able to collect dense three-dimensional point data from the survey scene and achieve highly accurate measurements; therefore, it is considered to be one of the most promising surveying techniques for railway track geometry deformation monitoring. This paper proposes a new approach that uses TLS to detect subsidence and irregularities in a track by fitting boundaries of the cross section of the track. In addition, for a section of local railway, an outdoor experiment was performed to ascertain the feasibility and accuracy of this method. The deformations detected with TLS were compared with the field measurements gathered with other methods such as those from a track inspection car. The results indicate that the subsidence difference between TLS and precise leveling is 2–3 mm, and the difference in the geometric parameters of the tracks is 1–2 mm. Finally, the possible causes of error involved with TLS are discussed

Real-time deformation monitoring of bridges using GPS/Accelerometers

The need for conducting real-time bridge deformation monitoring is addressed in the context of the development of bridge management system (BMS) and land transportation safety in this thesis. Current instruments used for bridge dynamic deformation monitoring are compared in terms of system productivity and reliability. An integrated sensor system of Global Positioning System (GPS) receiver and triaxial accelerometer is then proposed with the capabilities to accurately monitor long-term deformation and short-term dynamics of a bridge. Since the investigation of the bridge dynamic responses is of great importance in research and practice, the emphasis of this thesis is on the monitoring of dynamic bridge deformation. Zero baseline (ZBL) and short baseline (SBL) tests are conducted to evaluate the performance of three types of Leica GPS receivers at 10 Hz sampling rate. Statistic characteristics of positioning solutions and the achievable accuracy of each receiver type are analysed, which are employed to design optimal filters for various GPS error suppressions. By using a moving average (MA) technique, millimetre baseline accuracy can be achieved even with a single frequency receiver. It demonstrates the possibilities to conduct millimetre bridge deformation monitoring if appropriate filtering techniques are applied to the positioning solutions and integer ambiguity has been fixed. A simple but accurate triaxial accelerometer calibration technique is proposed in the thesis with a solid mathematical derivative to evaluate the precisions of estimated parameter offsets. A specially designed cage is used to house a GPS antenna with a triaxial accelerometer to avoid complex sensor alignment and simplify the coordinate transformations between different reference frames. The determination of instantaneous attitude of an accelerometer body frame is realised by three GPS stations on the deck of a bridge at a rate of 10 Hz and the sensed 3D accelerations are then transformed into a bridge coordinate system (BCS) simultaneously. BCS is the computation frame of a hybrid bridge deformation monitoring system (BDMS). Important issues in sensor integration such as local gravity determination, synchronisation of time series from different sensors are addressed. Bridge trials are briefed with the emphasis on the instrument configuration for effective error mitigation and sensor integration. A group of reference stations consisting of two reference stations closely setup near a bridge and the permanent continuous GPS stations are recommended for reducing relative tropospheric delay, multipath, and receiver noise both at reference stations and monitoring sites. GPS satellite sky distribution and its impact on propagating ranging errors in mid latitude areas such as in the UK and high latitude areas are analysed both with analytical and simulation approaches. The error propagation formulae are derived to analyse the defects of current satellite constellation on the GPS positioning solutions in each direction of a BCS. This is further exploited to improve the component accuracy of particular interest through changing the dilution of precision (DOP) values. The degree of positioning improvement is illustrated with GPS/GLONASS positioning. A simulator according to ranging error propagation is used to simulate the achievable accuracy from the best and the worst GPS constellations. Modified precise satellite ephemeris by inserting the positions of pseudolites is employed to investigate the changes of DOP values in each direction of a BCS. The summaries of this simulation have universe significance in guiding the selection of the best locations of pseudolites. Adaptive Finite Impulse Response (FIR) filtering or adaptive filtering (AF) for short and important application issues are addressed in the thesis. Autocorrelation lags of ZBL and SBL tests of each type of receiver are used to determine the filter lengths according to the fundamentals of low pass and high pass filter designs. A real-time AF algorithm is introduced and widely employed as an analytical tool in the error mitigation and real bridge deformation signal extraction. The application defects of MA technique in bridge deformation monitoring are compared with AF approach according to the component analysis of GPS positioning solutions. A recursive AF algorithm is proposed to gradually isolate actual bridge deflection signals from multipath and receiver noise both at reference stations and monitoring sites. Spectral analysis is applied to the input and output signals to investigate the efficiency of the designed filter. In order to effectively isolate actual bridge deformation, misalignment and its consequence are demonstrated with day-to-day shifted time series of bridge deflection. Cross-correlation is also used to analyse the feasibility and efficiency of the proposed AF algorithm. Acceleration aided AF approach is detailed in the thesis. A simple algorithm, based on the principles of digital signal filtering and optimal filter design, is proposed to estimate relative displacements of bridge sensed by a triaxial accelerometer in three dimensions. With the relative displacements, GPS receiver noise has been filtered out and the cleaned displacements are obtained. AS another data fusion approach, a software package based on discrete Fourier transform (DFT) to integrate GPS and accelerometer data with a position output rate up to that of a triaxial accelerometer is introduced. Relative tropospheric delay is another major error source identified in GPS-based bridge deformation monitoring. Methods applied to distinguish the impacts of multipath and tropospheric delay are presented. The cause for relative tropospheric delay is analysed and microclimate effect is recognised as the major impact factor in this particular environment. Numerical calculations also confirm the assumption. The way to effectively remove relative tropospheric delay is recommended. The research emphasis in this thesis is to develop a prototype of a hybrid BDMS to achieve centimetre level positioning accuracy at each epoch in three dimension of a BCS. The findings from this research are summarised and the future work is predicted