Research on load design for large containership based on nonlinear springing analysis in frequency domain

• New frequency-domain nonlinear load prediction, faster and more convenient. • Nonlinear wave-induced vibration characteristics of containership in regular wave. • Influence of generalized second-order hydrodynamic forces on vibration response. This study presents a novel load design methodology for large containerships, addressing limitations in conventional nonlinear wave-induced vibration analysis. Compared with irregular waves, regular waves exhibit fewer frequency components for testing nonlinear wave-induced vibrations, primarily limited to the fundamental wave frequency and its harmonics. While traditional three-dimensional linear hydroelastic methods based on potential flow theory are restricted to calculating linear springing, this research introduces significant innovations: (1) a superposition approach of multiple regular waves to simulate irregular wave conditions, and (2) the unique incorporation of second-order hydrodynamic force effects in nonlinear hydroelastic response analysis. These advancements represent a substantial improvement in fluid-structure interaction modeling accuracy. The study employs nonlinear hydroelastic theory and computational methods to solve frequency-multiplied wave-induced vibration responses of container ships under regular wave conditions. Through spectral analysis and time-history bandpass filtering techniques, the research successfully decomposes the response into low-frequency and high-frequency components. The three-dimensional (3D) frequency-domain hydroelastic nonlinear analysis enables comprehensive calculation of motion responses and structural loads, including vertical bending moments, horizontal bending moments, and torsional moments. Numerical simulations demonstrate strong agreement with experimental results, particularly for hull motions and loads in oblique wave conditions. The validation confirms that the proposed frequency-domain nonlinear hydroelastic method provides an effective tool for evaluating nonlinear wave-induced vibration response characteristics of large container ships during preliminary structural design stages. This methodology offers valuable insights for ship designers to assess critical structural responses early in the design process.