• International Journal of Naval Architecture and Ocean Engineering
• /
• v.13 no.1
• /
• pp.223-235
• /
• 2021

The Vortex-Induced Vibration (VIV) test system on deepwater riser based on Bare Fiber Bragg Grating (BFBG) sensor technology was designed. Meanwhile, a riser VIV response numerical model was established based on the work-energy principle. The results show that the first-order vibration frequency dominates the vibration of the riser, and as the velocity increases, the dominant frequency of the riser gradually increases under the effect of different top tensions. At the same velocity, as the top tension increases step by step, the dominant frequency and fatigue damage at the same position along the axial length of the riser both gradually decreases. The model test and numerical simulation show a relatively consistent change, maintaining a high degree of agreement. The process control system based on BFBG of model test has excellent performance, and FBG sensors have great advantages in VIV test of a vertical riser in water.

• International Journal of Concrete Structures and Materials
• /
• v.3 no.1
• /
• pp.33-37
• /
• 2009

Fiber Bragg grating (FBG) sensors already have been the focus for structural health monitoring (SHM) due to their distinguishing advantages. However, as bare optical fiber is very fragile, bare FBG strain sensor without encapsulation can not properly be applied in practical infrastructures. Therefore encapsulation techniques for making encapsulated FBG strain sensor show very important in pushing forward the application of FBG strain sensors in SHM. In this paper, a simplified approximate method to analyze the stress transferring rules for embedded FBG strain sensors in concrete monitoring is put forward according to mechanics of composite materials. Shear lag theory is applied to analyze the stress transferring rule of embedded FBG strain sensor in measured host material at the first time. The measured host objects (concrete) and the encapsulated FBG strain sensor are regarded as a composite, and then the stress transfer formula and stress transfer coefficient of encapsulated FBG strain sensor are obtained.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.36D no.10
• /
• pp.45-50
• /
• 1999

We report a solder-clad fiber Bragg grating(FBG) temperature sensor in order to obtain better Bragg wavelength sensitivity to temperature than a bare FBG sensor. The solder-clad FBG sensor shows a wavelength sensitivity improvement by a factor of four compared to the case of a bare FBG sensor at temperatures below $110^{\circ}C$. However, it has a sensitivity of 0.01 $nm/^{\circ}C$ at temperatures over $110^{\circ}C$, which is identical to that of a bare FBG sensor. Bragg wavelength of the sensor shows a blue-shift below $110^{\circ}C$ because the sensor is fabricated above melting temperature of solder. The thermal stress at the FBG-solder interface has been relieved by annealing, which results in a stable operation.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.8 no.6
• /
• pp.1-5
• /
• 2008

As bare Fiber Bragg Grating (FBG) sensors are very fragile, bare FBG without encapsulation is not properly applied in practical infrastructures directly due to the harsh environment in practical engineering. Steel sleeve packaged FBG strain sensor is widely used in civil engineering. Since FBG senses both strain and temperature simultaneously, for accurate measurement of strain, temperature compensation for FBG strain sensors is indispensable. In this paper, based on the FBG's strain and temperature sensing principles, the temperature compensation techniques for steel sleeve packaged FBG sensors are brought forward. And the experiment of concrete early-age shrinkage monitoring by dual FBG sensors is carried out to test the feasibility of the temperature compensation technique.