In this paper, the most recent progress as well as challenges of distributed optical fiber sensing (DOFS) in industrial applications is discussed. Compared to the vast market of sensors used to measure strain or temperature, the success of distributed optical fiber sensing (DOFS) at the industrial level is very limited, at best. One of the reasons for this lack of the wider acceptance is the mismatch between the commercially available systems and actual industrial requirements, especially for the spatial resolution and precision. These requirements are organized and clarified in the paper. It also describes the hybrid Brillouin-Rayleigh system, which exhibits capabilities surpassing those of strain gauges. The principles of the system are illustrated considering the fiber calibration methodology. Formulas required for determining strain, temperature, and hydro-pressure are derived and discussed. Finally, the examples of applications are presented.
This paper discusses an implementation of Hybrid Boundary Node Method (Hybrid BNM) to the heat conduction analysis within bodies containing thin-walled structures. As an application, the thermal analysis in carbon nanotubes (CNT) based composites is presented. CNTs are predicted to possess superior heat conductivity and may, even with a small amount embedded, substantially improve heat conducting behavior of polymers. In this paper the equivalent heat conductivities of CNT-based nanocomposites are evaluated using a 3-D nanoscale representative volume element (RVE) model and the hybrid boundary node method (Hybrid BNM). The temperature distribution and heat flux concentration are studied. The equivalent heat conductivity of the RVE as a function of the nanotube length is calculated and discussed, and, moreover, an approximate formula for its evaluation for an RVE containing single nanotube is proposed. Computations indicate that addition of about 7.2% to 17% (volume fraction) of CNT to the polymer matrix may result in the increase of heat conductivity of the composite varying from 49% to 334% both for short and long CNT.
We propose a novel method to improve the spatial resolution of Brillouin optical time-domain reflectometry (BOTDR), referred to as synthetic BOTDR (S-BOTDR), and experimentally verify the resolution improvements. Due to the uncertainty relation between position and frequency, the spatial resolution of a conventional BOTDR system has been limited to about one meter. In S-BOTDR, a synthetic spectrum is obtained by combining four Brillouin spectrums measured with different composite pump lights and different composite low-pass filters. We mathematically show that the resolution limit, in principle, for conventional BOTDR can be surpassed by S-BOTDR and experimentally prove that S-BOTDR attained a 10-cm spatial resolution. To the best of our knowledge, this has never been achieved or reported.
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