# Inspection of stability of a general roll-damping of a ship via non-perturbative approach

## TL;DR

This paper examines the stability of ship roll-damping using a non-perturbative approach to improve maritime safety under real-world conditions.

## Contribution

The study introduces a non-perturbative method to analyze nonlinear ship dynamics without Taylor expansion, offering a novel approach to stability analysis.

## Key findings

- A generalized model of ship dynamics is developed, incorporating inertia, damping, restoring, and external forces.
- The non-perturbative approach produces results strongly agreeing with original numerical solutions.
- Bifurcation analysis reveals how physical properties influence stability and motion patterns in the system.

## Abstract

The current study explores nonlinear stability in vessels with roll-damping to ensure safety in realistic maritime conditions, thereby expanding stability. It develops a generalized model that considers operating situations, nonlinearities, and hydrodynamic factors. One degree of freedom (1DOF) of nonlinear ship dynamics is included in the exiting model. The prototypical incorporates inertia, damping, restoring forces, and external forces. The objective is to examine the responsible non-perturbative method (NPA) in determining periodic response of a damped and conservative coupled system. In contrast to all other traditional perturbation techniques, NPA’s goal is to convert a weakly oscillator of nonlinear of ordinary differential equation (ODE) into a linear one without consuming Taylor expansion. A strong agreement with original numerical solution (NS) is validated. Using Galerkin technique, the inquiry produces an advanced, comparable linear ODE. Quantitative comparisons verify that final solution agrees with advanced solution. The resonance area, situated within stability zone and exhibiting complex relationships between forces in the system, is influenced by all physical properties. An approximate solution up to the second order is found by applying the multiple-time scales method (MTSM), which evaluates the system’s stability configuration and highlights both the stable and unstable features. Changes in bifurcation parameters have an impact on curvature of the bifurcation curve. Additionally, phase portraits, Poincaré maps, and bifurcation diagrams are used to perform a bifurcation analysis of the designated models and identify the different motions of the system.

The online version contains supplementary material available at 10.1038/s41598-026-38505-8.