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資料番号: SA1004501000

Dielectric barrier discharge plasma actuators (DBD-PA) and fiber Bragg grating (FBG) sensors have been investigated for active control of flow separation around a NACA0024 airfoil. Tangential jets were produced in the vicinity of the DBD-PA slightly aft of the leading edge of the airfoil. The flow separation control ability was evaluated at low Reynolds number in an open-circuit wind tunnel. Phase- and time-averaged velocity distributions around the airfoil were measured using Particle Image Velocimetry, and the flow separation control ability of the DBD-PA was assessed at 8°, 12° and 16° angle of attack. An FBG sensor was attached to a chord-wise cantilever near the trailing edge of the airfoil on the pressure surface. This was used to measure strain fluctuations in the cantilever root due to flow-induced oscillations. The feasibility of this system to detect flow separation was studied, where the standard deviations of strain fluctuations significantly increased when the flow was separated. This was utilized in an open-loop control system to detect flow separation by FBG then apply active control with the DBD-PA to reattach the flow.

Optical fiber sensors are used in order to monitor strain distribution of a structure, because they have many advantages for structural health monitoring. By using Fiber Bragg Grating (FBG) sensors with a general interrogation system e.g. Wavelength Division Multiplexing (WDM) makes it possible to measure only average strain within the gauge length. In addition, it is necessary to allocate enough numbers of FBG sensors for monitoring stress concentration overall. Therefore, it is expected to apply a distributed strain sensor with the higher spatial resolution and the longer sensing length to accurate and effective monitoring of stress concentration. We present a new strain measurement system with a long gauge FBG sensor based on Optical Frequency Domain Reflectometry (OFDR), which enables us to measure fully distributed strain at special high spatial resolution. In this paper, we describe the principle and optical simulation model of the proposed measurement system and show results of numerical calculations.

This study develops a new inverse analysis technique for estimating damage patterns in notched composite laminates using an embedded fiber Bragg grating (FBG) sensor. The damage pattern near the notch was investigated by using a layer-wise finite-element model with cohesive elements for cracks and delamination. The reflection spectrum of the FBG sensor was simulated from the strain distribution obtained along the gage length. We approximated the typical damage pattern (splits, transverse cracks, and delamination) near the notch using some variables; these were then estimated through mathematical programming by minimizing the differences of spectrum shapes between the inputs (e.g. experiments) and the estimations. This damage identification procedure was applied to numerical examples, i.e. simulation results, for a notched CFRP cross-ply laminate. The damage patterns estimated from the calculated reflection spectra were almost identical to those obtained by the simulation. Finally, we estimated the damage pattern of a notched laminate from a measured reflection spectrum of an embedded FBG sensor and demonstrated the capability of the developed identification procedure for practical applications.

This paper proposes a new approach to estimate the damage pattern of a notched cross-ply laminate using an embedded Fiber Bragg Grating (FBG) sensor. The damage pattern near the notch was investigated by finite element analysis with cohesive elements for the onset and the extension of various cracks. Then, the reflection spectrum of the FBG sensor was analyzed from the strain distribution obtained in the damage analysis. Based on the above analysis, the damage pattern is optimized as an inverse problem in the damage analysis, while the spectrum shape is adopted as the objective function. In the estimation scheme, the strain distribution of the FBG sensor is calculated by the damage analysis using the damage pattern expressed by the residual strength distribution of the cohesive elements. We estimated the damage patterns of the notched cross-ply laminate from the reflection spectra obtained in the analysis and those measured in the experiment. The estimated damage patterns agreed well with those corresponding to the input spectra.