Eliminating the irregular frequencies in wave-body interaction: An investigation for accuracy assessment with higher-order elements

The presence and elimination of irregular frequencies in wave-body interaction are reviewed by referring to the fundamental properties of the integral equations and a predictive measure that can be beneficial for wave-induced response assessment is proposed through numerical applications. By adopting higher-order elements and considering the hydroelastic response of the floating body, this study explores three interrelated questions: (i) how widely adopted irregular frequency suppression techniques perform, (ii) how, if possible, can these techniques be effectively applied, and (iii) how can the estimations be accepted as accurate for a given discretization, that is, finding a quantitative measure to relate the employed discretization to the frequency range for which the specified error threshold is not exceeded. The investigation involves three hull forms, a barge model along with the DTMB 5415 and KCS ships, and two techniques that extend the solution domain for suppression, namely the extended boundary integral equation method (EBIEM) and combined boundary integral equation method (CBIEM). The barge model is used for preliminary analyses to identify the existing patterns. DTMB 5415 and KCS allow the transfer of findings to practical applications and assess their validity. Three assessment measures in terms of frequency are employed by considering the hydrodynamic coefficients. In the present setting, it is observed that EBIEM is far more effective, and CBIEM cannot provide adequate suppression. The frequency envelope obtained by taking two quadratic elements per wave length is found to be a proper measure for estimating the frequency range that can be confidently studied.