Resilient Packet Ring (RPR), defined by the IEEE 802.17 working group, is a new solution to metropolitan area network. RPR adopts the packet-based dual ring structure so that it can provide the protection capability similar to the SDH as well as dynamic bandwidth allocation. The design of fairness control mechanism to allocate the
bandwidth is a key problem for RPR. Currently, two different modes of fairness algorithm have been proposed in the RPR standard, the aggressive mode (AM) and the conservative mode (CM). However, there are several limitations for these modes, such as the amount of the bandwidth allocated oscillates permanently under unbalanced traffic scenarios. In this paper, we propose a novel fairness control mode. The simulation experiment shows the range of traffic oscillation controlled by our mode is significantly damped compared to current RPR algorithm.
This paper reports our work on the applications of fiber Bragg grating-based strain sensors for the vibration tests and mode analysis on concrete structures. The arrayed fiber grating strain sensors, which were wavelength-division-multiplexed along the fibers, were attached onto the reinforced bars (rebars) before concrete was poured in to form a 5.5m long, 0.3m wide, 0.15m deep reinforced concrete beam. The embedded sensors will provide quasi-distributed real-time dynamic strain information along the length of the beam. For verification with the FBG strain sensors, some electrical accelerometers were also placed on the top surface of the concrete beam. All the data from FBG sensors and electrical accelerometers were recorded and analyzed by a computer. In the experiments, a hammer and an electrical shaker were used to excite the structure. The experimental results obtained with the FBG sensors show good consistency with the theoretical analysis.
Development in sensing technologies and data acquisition systems is making it possible for engineers to acquire the actual state of strains and stresses in structures at construction stage and during their service life. The knowledge of actual internal forces in a structure is key to identification of parameters such as stiffness and support conditions enabling the structural performance to be accurately estimated. This paper reports on the theoretical and experimental work carried out using fibre Bragg gating (FBG) strain sensors, embedded into and attached onto the concrete beam, to obtain the strain distribution of the concrete beam, therefore deduce the information of the applied load.
Fiber Bragg grating (FBG)-based strain and temperature sensor array were embedded into the concrete structure in order to provide real-time information on its strain and temperature distribution. The sensors were wavelength- multiplexed along a single fiber. The temperature and strain sensors were specially designed and optimized for their measurands. The calibration experiments of those FBG sensors, and parameter monitoring during the structural curing processes were also presented in this paper. These fiber optic strain and temperature sensor show many advantages over the traditional electrical strain gauges and thermocouples.
Initially developed for applications in the aerospace industry, fiber-optic Bragg grating sensors (FBG) have attracted attention in the civil engineering community. The interest in FBG sensors has been motivated by the potential advantages they can offer over existing sensing technologies. They are, immune to electromagnetic interference, small in size and can be easier to install than traditional electrical resistance strain gauges. They can also be multiplexed, that is, a single fiber may have more than one change. Although field test of FBG sensors have been reported in literature, there is a dearth of information on their installation procedures, their precision in quantifying strains of concrete structures, and robustness requirements for embedment in concrete structures. In particular the harsh environment during the construction of concrete structures is a great challenge in the installation of these fragile sensors. The paper reports on our experiences with FBG sensors in concrete structures. FBG sensor have been sued to quantify strain, temperature and to capture vibration signals. Th result of these studies indicate that, if properly installed, FBG sensors can survive the sever conditions associated with the embedment process and yield accurate measurements of strains and vibration response, so it is possible to benefit from their potential advantages.
It is known that certain design consideration must be given to the concrete structures to cater for possible ambient temperature variations. The thermal stress that results from these changes can cause damage in concrete structures ifthey are restrained or ignored in the design stage. The thermal effects in concrete structures are mainly due to the surrounding environmental conditions and some other special effects, such as the heat of hydration during construction and casting of the bitumen. In this paper, we present our preliminary results on monitoring the non-linear temperature profiles of simulated bridge decks due to various environmental contributing factors using fiber Bragg grating (FBG) sensors and thermocouples. We will also present the data on the variations of the temperature profiles in the concrete due to different thickness of the bitumen topping.
KEYWORDS: Sensors, Fiber Bragg gratings, Telecommunications, Control systems, Signal attenuation, Signal detection, Fiber optics sensors, Multiplexing, Data acquisition, Metals
We report on the use of fiber Bragg grating (FBG) foot sensors to study the reaction of human being subjected to floor vibration. The entire testing system comprises the multiplexed FBG foot sensors, the communication link between the sensors and the vibrating slab, the control and synchronization software, the graphical user interface, and the data acquisition and analysis system. The pressure distributions over different parts of the foot are obtained at different floor vibrating frequencies and with different distances from the vibrating source. These results show great potential in the application of the FBG foot sensors to study the biomechanics of balancing on a vibrating floor. It has also been demonstrated that the system is robust and able to work under harsh conditions. Further development towards practical implementation of the system is proposed.
In concrete curing process, the temperature and the volume of the structure, and the inner pressure/stress exerted on the rebars will change in a fashion that depends on the composition of the concrete mixture. The temperature, strain and pressure changes at various points of a 3m long concrete structure with a mixture of cement, water and aggregate were monitored over a period of several days. Fiber Bragg grating based sensors were used to monitor these parameters in vivo. These sensors were designed and optimized to measure the temperature, strain and pressure respectively.
In this paper, we report the development of an Er3-doped dual-wavelength fiber laser constructed from a
quasi-ring structure incorporated with two cascaded fiber Bragg gratings (FBGs). A total output power of
8.5 dBm and a mode suppression ratio of more than 50 dB have been obtained in the cw operation case.
The mode competition phenomenon for dual wavelengths lasing has been investigated by reducing the
wavelength spacing of the two FBGs. With mode locking, switching from one wavelength to the other, and
between single- and dual- wavelength lasing has been demonstrated by adjusting the rf frequency of an
intensity modulator in the laser cavity.
In this paper, we present our work on the fiber Bragg grating (FBG) sensors for structural health monitoring in 5m long concrete structures. Two sets of sensors were securely fastened onto the surfaces of the top and bottom reinforced bars respectively before concrete was poured in. Another set of the sensors was mounted onto the slab surface. These sensors were then monitored to observe the strain experienced at different locations within concrete slab. Loading and unloading cycle tests and failure test were performed on the completed structure. From the results obtained using the FBG sensors, we were able to correlate t he load-strain behavior of the slabs to the failure state as observed on the slab surface. These data are useful in determining the maximum allowable load before failure sets in. At the same time, we made comparisons of the data obtained using our FBG sensors with those obtained with electrical strain gauges. The two sets of data show a similar trend during the loading and unloading tests as well as during the failure tests.
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