Dynamic analysis of offshore pipelines affected irregular waves

Regular wave records are generally used in stabilization of offshore pipelines, however it?s known that, while evaluating wave statistics, surface profiles resemble irregular wave profiles more than regular wave profiles in marine environment. Irregular wave records can be transformed into regular wave records by Fast Fourier Transform (FFT) Method or Zero-Up Crossing Or Zero Down Crossing Method. In this study, based on Fast Fourier Transform Method, a limited irregular wave records are examined and transformed into regular wave records. The convenience of real wave profiles and its spectrum with those of employed waves that are obtained from FFT is compared by Chi-square test. The outputs from Fast Fourier Transform is basically utilized in determining the design wave parameters.After testing its convenience between regular and irregular waves, regular waves? records are utilized to calculate the hydrodynamic forces based on waves that affect to offshore pipeline connected to shore. Eventhough there are several wave theories (Stokes, Cnoidal, Solitary), Lineer (Airy) wave theory is used in calculating wave velocities and accelerations. Vertical and horizontal forces on pipeline for each sinüsoidal wave, obtained from FFT, are calculated in accordance with various time intervals and cross-sections on pipeline. Total forces on pipeline can be calculated by combining whole sinusoidal waves, having different phase angles and amplitudes, corresponding to pipeline?s coordinates.Artifical weighted supports, designed with certain distances, are sized cosidering balance of vertical and horizontal wave forces.Stabilizated pipeline is dynamically analysed under wave forces. İnfluence lines and time history methods are used in dynamic analysis to find displacements and interval stresses-reactions of pipeline. İnfluence lines method is analyzed in two ways, analitic and computational (SAP2000). Outputs of these two ways convenience is observed. Displacements are calculated with computer supported method by using SAP2000 software. İnstant displacements from Time History Method are compared with those of influence lines methods. According to maximum values of interval stresses-reactions obtained from both methods is employed in sizing the crosssections of pipeline.