12 Model Updating of Fluid-Structure Interaction Effects on Piping System 135 Fig. 12.3 Data acquisition 'ω 2 Ms 0 ρ0RT Mf +jw Cs 0 0 Cf + Ks 0 0 Kf ("u p #=0 (12.1) where Mf, Cf and Kf are the acoustic fluid mass, fluid damping and fluid stiffness matrices, respectively, Ris the acoustic fluid boundary matrix, ff is the acoustic fluid load vector, pis the acoustic pressure vector, uis the fluid element displacement vector and ρo is the mean fluid density, ωis the angular frequency of the pressure oscillation, and MS, CS and KS are the structure solid mass, damping and stiffness matrices, respectively. 12.3.2.2 Model ANSYS ® v. 18 was used to create the model comprising of structure domain for pipe, cap and supports and acoustic fluid domain for the inner liquid filling the pie as shown in Fig. 12.4. The model was built so as to incorporate the additional length and mass due to cap fittings. Effective length and cap mass along with other dimensions are included in Table 12.1. Table 12.2 includes the material properties of Steel, Water and Stainless Steel used for the simulation. Higher order solid elements exhibiting quadratic pressure behavior were used for acoustic domain whereas higher order solid elements exhibiting quadratic displacement were used to model structure domain. Full model analyses were performed with unsymmetric method with acoustic elements and direct method without acoustic elements to extract a mode shapes in the range of 10–2500 Hz;
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