Description:
Vibration testing is an essential component in Structural Health Monitoring (SHM). It can provide vital information regarding the integrity of critical structure; for instance, it can provide information on progressive failure monitoring of composites structure in the aerospace industry. Over the past decade, there have been many successful researches showing extraordinary ability of Fiber Bragg grating (FBG) sensors as a dynamic sensor. Ability of acquiring both static and dynamic strain measurements, make FBG sensor as a good alternative to replace the conventional vibration sensors. In addition the physical size of FBG sensor provides greater access to embed them in composite structures without affecting to any properties of the composite. However, in most applications to date, people have used only the FBG with wavelength 1550 nm. Moreover, FBG sensors with this wavelength are commonly use in industries such as telecommunications and medical industries. However, there is an option of using near infra-red (NIR) FBG range which comparably cheap in term of total system design. This paper details the use of near infra-red (NIR) FBGs as dynamic sensors; a part of SHM system for the monitoring of the damages in a thin glass fiber composite plates. Results reveal that the NIR FBG range gives good response to an impact and; also to applied high frequency vibrations.
Description:
This paper presents a comparative study conducted on the performance of the commonly used object tracking and location prediction algorithms for mobile robot navigation in a dynamically cluttered and GPS-denied mining environment. The study was done to test the different algorithms for the same set criteria (such as accuracy and computational time) under the same conditions.The identified commonly used algorithms for object tracking and location prediction of moving objects used in this investigation are Kalman filter (KF), extended Kalman filter (EKF) and particle filter (PF). The study results of those algorithms are analyzed and discussed in this paper. A trade-off was apparent. However, in overall performance KF has shown its competitiveness.The result from the study has found that the KF based algorithm provides better performance in terms of accuracy in tracking dynamic objects under commonly used benchmarks. This finding can be used in development of an efficient robot navigation algorithm.
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Proceedings of the IEEE International Conference on Industrial Technology
Description:
Distorted spectra of Fibre Bragg Gratings (FBG) sensors have been using in most of research on identifying delaminations in composites which is the most common cause of failures of laminated composite structures. However, it has been shown that there are multiple causes which can produce a similar response spectrum of an FBG sensor. As a consequence an integrated additional monitoring system would enhance the prediction power of FBG based monitoring system. In this research paper we introduce a "FBG-AE hybrid system" concept for the detection of delaminations in composite structures which uses same FBG sensor network for monitor damage using two independent responses from the sensors. The proposed system use spectral responses from FBG sensors and extract strain and acoustic emission data for monitoring purpose. The proposed concept has experimentally investigated with convincing results.
Description:
Image sensors are generating limitless digital images every day. Image forgery like splicing and copy-move are very common type of attacks that are easy to execute using sophisticated photo editing tools. As a result, digital forensics has attracted much attention to identify such tampering on digital images. In this paper, a passive (blind) image tampering identification method based on Discrete Cosine Transformation (DCT) and Local Binary Pattern (LBP) has been proposed. First, the chroma components of an image is divided into fixed sized non-overlapping blocks and 2D block DCT is applied to identify the changes due to forgery in local frequency distribution of the image. Then a texture descriptor, LBP is applied on the magnitude component of the 2D-DCT array to enhance the artifacts introduced by the tampering operation. The resulting LBP image is again divided into non-overlapping blocks. Finally, summations of corresponding inter-cell values of all the LBP blocks are computed and arranged as a feature vector. These features are fed into a Support Vector Machine (SVM) with Radial Basis Function (RBF) as kernel to distinguish forged images from authentic ones. The proposed method has been experimented extensively on three publicly available well-known image splicing and copy-move detection benchmark datasets of color images. Results demonstrate the superiority of the proposed method over recently proposed state-of-the-art approaches in terms of well accepted performance metrics such as accuracy, area under ROC curve and others.
Description:
2018 International Conference on Digital Image Computing: Techniques and Applications, DICTA 2018
Description:
Image sensors are generating limitless digital images every day. Image forgery like splicing and copy-move are very common type of attacks that are easy to execute using sophisticated photo editing tools. As a result, digital forensics has attracted much attention to identify such tampering on digital images. In this paper, a passive (blind) image tampering identification method based on Discrete Cosine Transformation (DCT) and Local Binary Pattern (LBP) has been proposed. First, the chroma components of an image is divided into fixed sized non-overlapping blocks and 2D block DCT is applied to identify the changes due to forgery in local frequency distribution of the image. Then a texture descriptor, LBP is applied on the magnitude component of the 2D-DCT array to enhance the artifacts introduced by the tampering operation. The resulting LBP image is again divided into non-overlapping blocks. Finally, summations of corresponding inter-cell values of all the LBP blocks are computed and arranged as a feature vector. These features are fed into a Support Vector Machine (SVM) with Radial Basis Function (RBF) as kernel to distinguish forged images from authentic ones. The proposed method has been experimented extensively on three publicly available well-known image splicing and copy-move detection benchmark datasets of color images. Results demonstrate the superiority of the proposed method over recently proposed state-of-the-art approaches in terms of well accepted performance metrics such as accuracy, area under ROC curve and others.
Description:
2018 International Conference on Digital Image Computing: Techniques and Applications, DICTA 2018
Description:
This paper presents a summary of research which was conducted in developing a new human-like navigation methodology based on the Agoraphilic algorithm. This new methodology is capable of maneuvering robots in both static and dynamically clutter unknown environments. The Agoraphilic algorithm is an "optimistic" navigation algorithm. The algorithm is based on free space attraction rather than repulsion of obstacles for navigation. Therefore, this algorithm directs robots to follow the free space leading to the goal instead of avoiding obstacles. This approach has eliminated many draw backs of the traditional APF algorithm. However, the major limitation of the previously developed Agoraphilic algorithm could only deal with static environment. The new proposed algorithm has successfully extended the capacity of Agoraphilic algorithm to deal with environment cluttered with dynamic obstacles. The new Agoraphilic algorithm uses a tracking and prediction methodology to estimate the path of unknown moving objects. The estimated locations of the moving objects are combined with static object locations in the robot's visible region to generate time-varying free space attractive forces. These time varying forces maneuver the robot to the goal in dynamically cluttered unknown environment without collusions. To demonstrate the algorithm's ability, several simulations were performed. Furthermore, the new algorithm was tested and bench-marked against other APF published work under similar environment and conditions. The comparative results are discussed and showed the effectiveness of the new Algoraphilic navigation algorithm.
Description:
Structural Health Monitoring Systems based on embedded FBG sensors, to identify damage conditions, are largely dependent on the spectral distortion of the sensors. The uneven stress gradient occurring along the grating of FBG sensors, due to damage inside composite structures can be estimated by analyzing significant changes that appear in the FBG response spectra. However, the stochastic nature of the distorted shape of the FBG spectra makes it difficult to interpret and quantify the existing damage at the location of the FBG sensors. This research works on a novel concept of the "Distortion I ndex (DI)" which is defined using distorted spectra of FBG sensors. I t was observed that the DI increases with t he i ncrease in damage size.
Description:
Fibre Bragg Grating (FBG) sensors are extremely sensitive to changes of strain, and are therefore an extremely useful candidate for Structural Health Monitoring (SHM) systems of composite structures. Sensitivity of FBGs to strain gradients originating from damage was observed as an indicator of initiation and propagation of damage in composite structures. To date there have been numerous research works done on distorted FBG spectra due to damage accumulation under controlled environments. Unfortunately, a number of related unresolved problems remain in FBG-based SHM systems development, making the present SHM systems unsuitable for real life applications. This paper reveals a novel configuration of FBG sensors to acquire strain reading and an integrated statistical approach to analyse data in real time. The proposed configuration has proven its capability to overcome practical constraints and the engineering challenges associated with FBG-based SHM systems. A fixed filter decoding system and an integrated artificial neural network algorithm for extracting strain from embedded FBG sensor were proposed and experimentally proved. Furthermore, the laboratory level experimental data was used to verify the accuracy of the system and it was found that the error levels were less than 0.3% in strain predictions.
Description:
Recent advances in fibre optic sensor technologies have provided great opportunities to develop more sophisticated in-situ SHM systems. There have been a large number of research reports on health monitoring of composite structures using Fibre Bragg Grating (FBG) sensors. Distortion of FBG sensors has been successfully used by many researchers to identify damage and to locate damage in composite structures. Observations of the distorted sensor spectrums due to stress concentrations caused by delaminations and cracks, have been using to estimate the damage conditions. The majority of the research works were focused on the investigation of the spectra of a FBG sensor embedded in the vicinity of a damage, in order to detect and identify the damage by relating to the distortion of the FBG sensor spectra. However the cause of the distortion of FBG spectra not only depends on the consequences of accumulated damage but also loading types and the fibre orientation. Embedding FBG's in-between non parallel fibre layers and the application of torque have caused substantial distortions to the FBG spectra. A reference FBG spectra needs to be incorporated to FBG measurements to identify the variations to the FBG spectrum and to distinguish the other effects causing distortions. For this purpose, a fixed FBG based system was developed to measure the reflected FBG spectra in time domain. The fixed FBG method was used to estimate the peak using non distorted FBG spectra previously. Unfortunately there was no work done on the identification of distortions of FBG spectra using fixed FBG sensors. This paper details the research work performed to identify distortions of reflected spectra of an embedded FBG sensors inside a composite laminate. The developed method will provide the flexibility of input FBG time domain data directly to post processing algorithms for decoding and damage identification.
Description:
Structural Health Monitoring Systems based on embedded FBG sensors, to identify damage conditions, are largely dependent on the spectral distortion of the sensors. The uneven stress gradient occurring along the grating of FBG sensors, due to damage inside composite structures can be estimated by analysing significant changes that appear in the FBG response spectra. However, the stochastic nature of the distorted shape of the FBG spectra makes it difficult to interpret and quantify the existing damage at the location of the FBG sensors. There are several indexing methods proposed by researchers. We have previously presented a novel concept of the “Distortion Index (DI)” which is defined using distorted spectra of FBG sensors. It was observed that the DI increases with the increase in damage size. The Distortion Index (DI) is introduced to create a correlation between the damage and the distortion of the response spectra of a FBG sensor. This index provides the ability to generalise the distortion of FBG spectra for a particular structure. The index can be used to quantify the damage in the structure relative to its original condition, which can be the condition of structure during a regulated time, i.e. a month uninterrupted operation or first hours in operation, of a structure can be used as no damage condition. In this paper we discuss the application of distortion index and comparison with available several other indexes.
Description:
Timber bridges are significant asset in bridge inventory. However, managing aging timber bridges stock is a major challenge. Most of the timber bridges has already reached its design service life, and needs to be replaced. The limited financial resources to maintain these bridges and the depleting supply of quality hardwood timber have created a need for a cost effective alternative for the replacement of these timber bridges. Fibre composite girders are a viable solution, but manufacturing cost needs to be reduced to make it commercially viable. A major research and development project on fibre composite alternative girders to replace existing hard-wood timber girders was carried out by the Centre of Excellence in Engineered Fibre Composites (CEEFC). This project was in collaboration with the Queensland Department of Transport and Main Roads (DTMR) and two industry partners. This project aims to develop commercially viable fibre composite bridge girders for the Australian market through the use of advanced manufacturing processes. These full-scale girders have undergone rigours testing including proof load testing, fatigue testing and ultimate strength testing to prove its viability as a suitable replacement girder. This paper presents the performance of these girders and discusses important issues encountered in the production of these fibre composite replacement girders. It is concluded that both fibre composite bridge girder concepts developed by the industry partners meet the set design criteria.
Description:
During the past decade, many successful studies have evidently shown remarkable capability of Fiber Bragg Gratings (FBG) sensor for dynamic sensing. Most of the research works utilized the 1550 nm wavelength range of FBG sensors. However near infra-red (NIR) FBG sensors can offer the lower cost of Structural health Monitoring (SHM) systems which uses cheaper silicon sources and detectors. Unfortunately, the excessive noise levels that experienced in NIR wavelengths have caused the rejection of sensor that operating in this range of wavelengths for SHM systems. However, with the appropriate use of signal processing tools, these noisy signals can be easily ‘cleaned’. Wavelet analysis is one of the powerful signal processing tools nowadays, not only for time-frequency analysis but also for signal denoising. This present study revealed that the NIR FBG range gave good response to impact signals. Furthermore, these ‘noisy’ signals’ response were successfully filtered using one dimensional wavelet analysis.