Objective As the ship unsinkability calculation method based on two-dimensional slicing has such problems as limited modeling ability and insufficient applicability to complex ship types, this study proposes a surface element method-based ship unsinkability calculation method based on a three-dimensional fully attached ship model.

Method s Adopting a discrete three-dimensional triangular panel model, the normal directions of the ship panels and damaged compartment are set opposite each other so that their buoyancy cancels each other out and causes buoyancy loss. A waterline surface segmentation algorithm is used to achieve the matching of wet surface elements in any floating state. Based on the Gaussian formula, the integration of drainage volume is transformed into the integration of wet surface area, and the drainage volume and waterline surface elements are further solved through the panel projection integration method. Newton's iterative method is then used to calculate the floating state of the damaged ship and conduct an unsinkability evaluation. Taking the Wigley numerical ship model and ONRT standard inner capsized ship model as examples, the accuracy of the algorithm is verified and an unsinkability evaluation is conducted for the ONRT fully attached ship model.

Results The results show that the form-complex structure can be introduced into computational domain, and the errors is the geometric ones that induced from the three-dimensional model when it discretized as facet model. Conclusion The calculation example shows that the proposed method has reliable calculation accuracy, strong applicability to complex ship types and practical engineering value.