Study on ice load characteristics of polar ships during oblique sailing based on discrete element method

As global warming accelerates the melting of sea ice, the Arctic region witnesses an increase in ship navigation. The brash ice area, composed of brash ice of various sizes and shapes, is a common operational scenario for polar ships. Understanding the ice load characteristics of polar ships during oblique navigation in brash ice regions is crucial. This can enhance ship navigation safety in the complex polar marine environment, provide a reference for polar navigation route planning, and fill the gap in the current research that mainly focuses on straight-sailing conditions.

This study selects a specific type of polar ship as the research object and utilizes the discrete element method (DEM) to predict the ice loads on the ship during oblique navigation through brash ice regions. First, a numerical model of the target ship is established. The model parameters include a ship model with a scale ratio of 60, a total length of 2.04 m, a beam of 0.37 m, and a design draft of 0.13 m. The ice particles have a density of 917.0 kg/m³, a Poisson's ratio of 0.3, and other specific properties. The accuracy of the model is verified by comparing it with the experimental results from the literature under the straight-sailing condition. Then, different oblique-sailing angles (0° −15°), speeds (0.6, 0.7 m/s), and ice thicknesses (0.011 67, 0.014 97 m) are set. The ice-load calculation is carried out based on the momentum conservation equation, angular momentum conservation equation, and the linear spring contact force model in the DEM.

The results show that as the drift angle increases, the ice-breaking resistance and lateral force on the ship increase non-linearly. For example, at a speed of 0.6 m/s, an ice concentration of 70%, and an ice thickness of 0.014 97 m, when the drift angle is 15°, the ice-breaking resistance and lateral force increase by 4.25 times and 6.04 times respectively, compared to the straight-sailing condition. In terms of speed, when the drift angle is between 0° and 10°, the ice-breaking resistance increases slowly, but when it exceeds 10°, it increases significantly. The lateral force also increases non-linearly, and the influence of speed on the lateral force is more significant than whether the ship is on the ice-facing side. Regarding the influence of ice thickness, when the drift angle is greater than 10°, the ice-breaking resistance and lateral force increase significantly as the ice thickness increases.

In conclusion, this research provides reliable data support for the safety assessment of ships during oblique navigation in polar brash ice regions. It offers a valuable reference for predicting and studying ice loads on polar ships under such conditions. Ship operators should be cautious when increasing speed or entering thicker ice areas, especially when the drift angle is greater than 10°. This is to avoid potential risks caused by sudden changes in ice-breaking resistance and lateral force, ensuring the safe and stable navigation of polar ships in complex ice-covered waters.