Damage stability evaluation of polar navigation vessels under ice accumulation

With the gradual reduction in Arctic sea ice extent and the continuous expansion of polar shipping routes, navigation activities in high-latitude areas have increased significantly. However, polar vessels are exposed to extremely harsh environmental conditions, with marine icing and accidental hull damage being two of the most critical threats to navigation safety. Ice accretion on ship superstructures and decks not only increases displacement but also results in non-uniform mass distribution, shifting the center of gravity upward and forward, thus significantly impairing stability. When hull damage and subsequent flooding occur under icing conditions, the combined effects can significantly increase the risk of capsizing. Existing studies have primarily focused on either marine icing or damaged stability in isolation, while systematic investigations into their coupled influence remain limited. To address this gap, this study conducts a comprehensive stability assessment of a polar vessel under combined ice accumulation and asymmetric damage conditions.

An ice accretion prediction model based on spray icing theory is first established. This model considers both wave-generated spray and wind-driven spray, which are the dominant sources of marine icing during polar navigation. The model integrates the principles of mass conservation and energy balance, considering sensible heat flux, latent heat flux, evaporative heat flux, and radiative heat flux during the entire icing process. A freezing coefficient is introduced to quantify the proportion of impinging spray droplets that freeze upon impact. The DTMB 5415 ship is selected as the reference vessel. Model validation is conducted by comparing the predicted freezing coefficient with published results, showing good agreement. Parametric analyses are subsequently conducted to investigate the effects of wind speed and ambient temperature on ice accretion over different icing durations (6 h, 12 h, and 18 h), which correspond to continuous severe weather conditions encountered by polar research vessels. Based on the predicted ice mass distribution, the variations in ship displacement, center of gravity, trim, and draft are calculated. Static stability analyses are performed for both intact and damaged conditions. The ship is subdivided into 16 watertight compartments, and an asymmetric midship damage scenario, involving Compartments No.9–No.10 on the starboard side, is considered. Righting arm (GZ) curves are calculated to assess the impacts of icing duration and hull damage on static stability, with reference to the requirements specified in the IMO International Code on Intact Stability. Furthermore, dynamic stability is assessed using the ultimate dynamic inclination angle, which represents the maximum heel angle the ship can withstand under combined wind and wave excitation. The corresponding maximum allowable wind speed is determined by analyzing the dynamic stability curve at a resonance angle of 20°, in accordance with relevant stability assessment criteria.

The results show that wind speed and ambient temperature are the primary factors influencing ice accretion. Ice accumulation increases almost linearly with wind speed due to enhanced spray production and rises rapidly as the ambient temperature decreases, with the freezing coefficient approaching unity. After 6 h, 12 h, and 18 h of icing, the total ice mass reaches 700.056 t, 1 526.124 t, and 2 213.192 t, respectively, causing a significant forward and upward shift in the ship’s center of gravity. For intact ships, increasing icing duration results in a continuous reduction in the maximum righting arm, the angle of vanishing stability, and the area under the GZ curve. The intact ship fails to satisfy the IMO static stability requirements after 18 h of icing. For damaged ships, stability deterioration is more pronounced: after 12 h of icing, the maximum righting arm decreases to 0.071 m, far below the IMO criterion of 0.2 m at a heel angle of 30°. Dynamic stability analysis further reveals the severe impact of combined icing and damage. For the intact ship without icing, the ultimate dynamic inclination angle is 64.8°, corresponding to a maximum allowable wind speed of 33.1 m/s. In contrast, for the damaged ship under 6 h of icing, the ultimate dynamic inclination angle decreases to 62.1°, and the maximum allowable wind speed drops sharply to 16.0 m/s, representing a reduction of more than 50% in wind resistance capability. These results demonstrate that the synergistic effect of ice accumulation and hull damage severely impairs both static and dynamic stability, thereby posing significant risks to polar navigation safety.

This study provides a systematic assessment framework for evaluating the stability of polar vessels under combined icing and hull damage conditions. The findings offer valuable insights for polar ship design, operational risk assessment, and the development or revision of stability criteria for vessels operating in ice-prone regions. Future work should focus on incorporating time-domain flooding processes and transient damage scenarios to further enhance the accuracy and applicability of stability evaluations for polar vessels.