203 research outputs found
Development of wireless sensor network using Bluetooth Low Energy (BLE) for construction noise monitoring
In this paper the development of a Wireless Sensor Network (WSN) for construction noise identification and sound locating is investigated using the novel application of Bluetooth Low Energy (BLE). Three WSNs using different system-on-chip (SoC) devices and networking protocols have been prototyped using a Raspberry Pi as the gateway in the network. The functionality of the system has been demonstrated with data logging experiments and comparisons has been made between the different WSN systems developed to identify the relative advantages of BLE. Experiments using the WSN for vehicle noise identification and sound location have further demonstrated the potential of the system. This paper demonstrates the versatility of a BLE WSNs and the low power consumption that is achievable with BLE devices for noise detection applications
Modeling the performance of distributed fiber optical sensor based on spontaneous Brillouin scattering
An optical model to simulate the distributed fiber optical sensor based on spontaneous Brillouin spectrum is derived. The reliability of this model is validated with experimental measurements. Using this analytical expression, parametric studies are conducted to investigate impacts of key factors including fiber loss, signal to noise ratio, bandwidth and
scanning step on the optical fiber sensor measurement error. The simulation results exhibit good agreement with previous published calculation results. Applying this novel model into the data interpretation, measurement error of distributed fiber optical sensor based on spontaneous Brillouin scattering can be better controlled
Modelling tertiary creep in geomaterials using a continuum damage mechanics approach.
Tertiary creep is often observed in soft rocks and it represents a problem in a mining environment.
Tertiary creep behaviour appears due to progressive micro cracking of the material and would result in a
loss of strength and stiffness, which may eventually lead to failure and a complete loss of load carrying capability
of the material. In this paper, the authors combined the continuum damage mechanics within the framework
of hyperplasticity, thus encompassing viscoplasticity and damage within a single theory. The authors
present a family of models which obeys the laws of thermodynamics. The entire constitutive behaviour is derived
from two scalar potentials; a free energy potential which provides the elasticity law, and a dissipation
potential which provides the yield function, the direction of plastic flow and the evolution of a damage variable.
No additional assumptions are required. These new models require only few parameters which have physical
meanings and are capable of capturing tertiary creep observed in soft rocks
Distributed Fiber Optics Strain Measurements for Monitoring Geotechnical Structures
Recent advances in strain measurement using optical fibers provide new opportunities for monitoring the performance of geotechnical structures during and after construction. Brillouin optical time-domain reflectometry (BOTDR) is an innovative technique that allows measurement of full strain profiles using standard optical fibers. In this paper, two case studies illustrating the application of the distributed optical fiber strain sensors are presented. One is monitoring of an old masonry tunnel when a new tunnel was constructed nearby and the other is monitoring the behavior of secant piled walls for basement construction. Both sites are located in London. The advantages and limitations of this new sensor technology for monitoring geotechnical structures are discussed
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Simulation of BOTDA and Rayleigh COTDR systems to study the impact of noise on dynamic sensing
This is the author acepted manuscript. It is currently under an indefinite embargo pending publication of the final version.Dynamic distributed sensing of strain and temperature is the key for real-time structural health monitoring (SHM) across a wide range of geo-engineering challenges, for which Brillouin Optical Time Domain Analysis (BOTDA) and Rayleigh Coherent Optical Time Domain Reflectometry (COTDR) are promising candidates. A noise model with specific parametric simulation of the two systems has been developed. Noise in both laser(s) and detector is independently simulated to identify the key noise sources. In this simulation, although averaging can significantly enhance the signal-to-noise ratio (SNR) in the two systems, it is a barrier to dynamic sensing due to its time-consuming accumulation procedure. The sequence of averaging in the signal processing workflow can vary the SNR for the two systems. The system components should be optimized to reduce the averaging times to achieve the required system specifications, especially the dynamic sensing performance.This project was carried out under the UCL-Cambridge Centre
for Doctoral Training in Photonic Systems Development, with funding
from EPSRC (EP/G037256/1) gratefully acknowledged. The funding
from Cambridge Centre for Smart Infrastructure and Construction is
acknowledged
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Micro-scale visualization of Microbial-Induced Calcium Carbonate Precipitation (MICP) processes
Microbial-Induced Calcium Carbonate (CaCOā ) Precipitation (MICP) has been explored for its potential engineering applications such as soil stabilization, but our understanding of the fundamental MICP processes at the microscale is limited. In this study, real-time in situ micro-scale experiments were conducted using glass slides and microfluidic chips (synthetic porous media which simulate soil matrices to model the conditions similar to actual MICP treatments) to visualize the CaCOā precipitation process. The results of this study show that irregularly-shaped CaCOā precipitates initially emerged on bacterial aggregates and subsequently dissolved with time as regularly-shaped CaCOā crystals started growing; less stable and smaller CaCOā crystals may dissolve at the expense of growth of more stable and larger CaCOā crystals. The time-dependent phase transformation of CaCOā precipitates makes the size of the crystals formed during MICP highly dependent on the time interval between cementation solution injections during a staged injection procedure. When the injection interval was 3-5 hours, a larger number of crystals (200-1000 per 10ā¶ Ī¼mĀ³) with smaller sizes (5-10 Ī¼m) was produced. When the injection interval was longer (23-25 hours), the crystals were larger (10-80 Ī¼m) and fewer in number (5-20 per 10ā¶ Ī¼mĀ³). The direct observation of MICP processes in this study improves the understanding of MICP fundamentals and the effect of MICP processes on the properties of CaCOā crystals formed after MICP treatment. These observations will therefore be useful for designing future MICP treatment protocols which improve the properties and sustainability of MICP-treated samples
The use of distributed fibre-optic strain data to develop finite element models for foundation piles
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