Ocean Engineering, Vol. 357(2026) 125418, 2026. 6.

Title: Simplified analytical method for dropped object assessment in offshore and new fueled ship

Author(s): Jung Kim, JongWon Kim, Hoki Lee, Jung-Kwan Seo, Jong-Hun Woo

Abstract:

In offshore projects such as FLNG and FPSO, safety studies against accidental scenarios including collision, dropped objects, and explosions are mandatorily per formed to ensure operational safety. Among these, dropped object accidents are of particular concern since a wide range of cargo containers required for offshore operation and maintenance are frequently transported and lifted, exposing the crane lifting zone to constant risk. Accordingly, structural strength assessment against dropped object accident has been a compulsory requirement for offshore platforms. Recently, the needs of such safety studies has been extended beyond offshore facilities to merchant vessels, as the adoption of new fuels such as LNG and ammonia has raised awareness of potential leakage and accident hazards. In particular, ship owners increasingly demand dropped object strength assessments for hazardous zones in the vicinity of fuel tanks and bunkering areas of alternative-fuel container ships. Conventionally, safety studies derive design loads for various accidental scenarios based on probabilistic approaches and evaluate structural integrity through nonlinear transient finite element (FE) analyses. While FE-based approaches provide reliable results, they require significant computational resources and long simulation times, which limit their applicability during early design stages and significantly increase the engineering workload in detailed design phases. Although some simplified theoretical approaches enabling strength assessment without FE analysis have been proposed, they often yield overly conservative results compared to actual FE simulations and experiments, leading to unnecessary structural reinforcement for dropped object risk zones. In this study, a generalized analytical approach for dropped object assessment applicable to both offshore structures and new-fueled ships is proposed. In general, the design criterion for dropped object accident typically aims to prevent severe damage to critical equipment and human located underneath the dropped-object impact area. Therefore, in conventional offshore construction projects, the allowable criterion has been established such that penetration of the impacted deck must not occur in the event of a dropped-object incident. Accordingly, this study suggests an analytical formulation to evaluate whether perforation occurs when a dropped object impacts a stiffened deck plate. The validity of the proposed formulation is investigated through comparison with nonlinear FE simulations and experimental data. The comparison results confirm that the method can reliably capture the energy absorption capacity without the need for detailed FE modeling and analysis. Consequently, the proposed approach is expected to be useful not only for preliminary dropped object strength design but also as a complementary tool for detailed safety assessments in both offshore facilities and emerging alternative-fuel ships.