A parameter identification technique for detection of spacer locations in an assembly of two coaxial flexible tubes

Assemblies of two horizontal coaxial flexible tubes with loosely held space rs to maintain the annular gap between the coaxial tubes, are generally use d in nuclear reactor for carrying hot fluid inside the inner tube with an i nsulating gas filled annulus between the outer and inner tubes to reduce he at losses. The appropriate location of these spacers is important for maint aining coaxiality and preventing contact between inner and outer tubes due to bending creep of inner tube. Determination of spacer locations is theref ore an important task. The conventional method of inspection may be costly and time consuming. This paper presents a non-intrusive technique based on vibration measurement, developed for the detection of such spacer spring lo cations in the assembly of the two coaxial tubes. The technique is based on a parameter identification approach. It involves the identification of spa cer locations by updating the position parameters of the spacer in a Finite Element (FE) structural model through the optimization of an error criteri on based on the difference between measured and computed natural frequencie s of the assembly of the two coaxial tubes. A gradient-based method is used for optimization in the FE model updating problem. The proposed technique has been validated by numerical simulation as well as on a laboratory scale experimental setup. (C) 2000 Elsevier Science S.A. All rights reserved.