Ship Collision Internal Mechanics: Safeguarding Critical Ship Compartments

Licentiatavhandling, 2026

The adoption of new energy systems onboard vessels, including small modular reactors (SMRs), LNG fuel tanks, and large-scale battery installations, has increased the need for protective structural systems capable of mitigating collision damage. This is particularly important for vessels containing critical compartments, such as SMR compartments, where failure of the side-shell structural could have severe safety and environmental consequences. The objective of this thesis is to investigate the crashworthiness of existing and novel protective ship-side structures and assess their ability to protect critical ship compartments during collision events.

To achieve this objective, a set of functional criteria is proposed to assess the capability of crashworthy side structures to protect critical ship compartments. Following the strength-design philosophy, which aims to limit structural intrusion during collision events, the criteria require preservation of the innermost barrier, striking-vessel intrusion of no more than 20% of the ship breadth, and acceleration levels within the protected compartment below 1.0g. The collision response of protective side structures was investigated using nonlinear finite element (FE) analyses in Abaqus/Explicit at three scales to examine the internal mechanics of collision, including damage progression and energy dissipation mechanisms. At the component scale, a steel-concrete tube subjected to compression was analysed to validate the concrete material model used in the study. At the small scale, representative conventional side-shell (reference), X-core, Y-core, and concrete-filled structures subjected to bulb impact loading were investigated to assess their energy absorption and deformation mechanisms. Finally, ship-scale collision simulations involving the chemical and oil tanker were performed to evaluate structural performance against the proposed functional criteria.

The small-scale analyses demonstrate that structural arrangement strongly influences collision performance by governing damage distribution and the activation of multiple deformation barriers. The reference, X-core, Y-core, and concrete-filled structures exhibited different balances between energy absorption and structural weight. Building on these findings, a novel three-barrier (TB) structural concept was developed in this thesis. The TB arrangement introduces an additional protective barrier within the side structure, distributing collision loads across multiple structural layers. Hence, the TB concept achieved the highest overall structural efficiency of the investigated structures, while the concrete-filled configuration provided high initial impact resistance at the expense of a significant increase in structural weight. The ship-scale simulations further showed that the reference and X-core configurations experienced penetration of the innermost barrier at relatively low collision speeds. By comparison, the TB structure satisfied all proposed functional criteria across the investigated collision scenarios.

Overall, the results demonstrate that collision crashworthiness depends on structural strength, the sequence of deformation and the distribution of damage during impact. The findings contribute to the understanding of collision-resilient structural design and indicate that the proposed TB concept could enhance the protection of critical compartments in future vessels carrying novel energy systems. Future work should extend the pre-sent internal mechanics perspective to the study of external collision dynamics and ultimate limit state (ULS) design assessment.