Application of fiber Bragg grating based strain sensor in pipeline vortex-induced vibration measurement

The vortex-induced vibrations(VIV)is an important topic of study in many different scientific and engineering fields.While VIV can be of benefit in some cases,oftentimes,it is an undesirable phenomenon that can be quite dangerous.In particular for offshore pipelines,VIV can lead to fatiguing of the pipe structure and can cause disastrous consequences if left unchecked.A number of different methods have been applied to the measurement of VIV,especially for the elongated,thin cylindrical structures.The use of fiber optic fiber Bragg gratings(FBGs)in particular has gained popularity over the recent years due to their distinct properties.However,FBGs are also very fragile and are susceptible to failure when placed in harsh environments without protection.In this paper,56 FBGs encapsulated in stainless steel tubes were applied to the measurement of VIV in a28-m model pipeline under controlled and uncontrolled conditions.Tests show that the encapsulated sensors possessed good sensitivity as well as fatigue life(>80000 cycles).The measurements from FBGs were also high enough to allow frequency domain analysis of the pipeline VIV under the two conditions.The authors conclude that the encapsulated FBGs are a viable tool for the study of VIV in pipeline structures.