# Dropped Object Impact Analysis Considering Frequency and Consequence for LNG-FPSO Topside Module
## 2 Literature Review  
Recently, the application of QRA technology is required. In particular, the application of CFD and nonlinear finite element analysis (FEA) is required to quantify accident risks by quantitatively analyzing the effects of an accident. The reliability of these methods is improved using empirical data, such as results and accident cases. Steel construction institute (SCI) [8] published a procedure for the probabilistic assessment of fire load and structural response. This procedure includes the application of CFD-assisted three-dimensional (3D) fire simulation to capture the essence of an actual fire accident. It also evaluates design accidental loads (DALs) by adopting a conventional exceedance curve of heat dose. Although DALs are probabilistically determined, their use in a complete structural consequence analysis and probabilistic safety assessment is not straightforward. [PERSON] et al. [9] and [PERSON] and [PERSON] [10] proposed another quantitative procedure, the joint industry project on the explosion and fire engineering of floating, production, storage and off-loading units, which randomly generates fire scenarios based on an input of several random variables associated with individual probability density functions. This procedure follows the same exceedance curve-based approach as DAL determination, resulting in the same limitations [11]. Accidents on offshore structures occur frequently. Accident statistics for floating offshore units state that falling objects are the most common type of marine accidents, as illustrated in Figure 1[12]. The collision of a falling object with the deck structure or equipment during the operational scope of a topside crane can cause structural damage or interrupt operations. It may even lead to pipeline gas leakage or a fire disaster, endangering lives and health, and damaging the marine environment [12; 13]. Although international rules and regulations strongly recommend the evaluation of probabilistic impact risk from dropped objects in the offshore industry, most engineers find it difficult to estimate a reliable failure probability because there are no tangible guidelines on probabilistic impact analysis for dropped objects [14]. Therefore, an effective impact analysis method for dropped objects on a topside platform is crucial for marine engineering. Several relevant analytical methods have been proposed for offshore risk assessment. Numerical simulation techniques have been used to address structural integrity in the case of impact scenarios. The selection of relevant design accidental loads is dependent on a safety philosophy to provide a satisfactory level of safety. The loads defined by the present study represent the level of safety considered acceptable by DNVGL-OS-A101 [15] and are generally based on accidental loads affecting safety functions with an individual frequency of occurrence in the order of \(1\times 10^{-4}\) per year. This will normally correspond to an overall frequency of 5 \(\times\)\(10^{-4}\) per year as the impairment frequency limit. [PERSON] et al. [16] simulated the response of stiffened plates to dropping objects using nonlinear finite element software, where various boundary conditions, horizontal speed of dropped items, and geometry of dropped items were considered. The effective contact area, speed of dropping items, and impact location served as important factors influencing the safety of offshore platforms. [PERSON] [17] focused on the Accidental Limit State (ALS) basis used for the offshore platforms in Norway and other geographical locations, and dealt with the development of an operational design standard for ALS to establish damage tolerance and robustness [18]. [PERSON] [19] illustrated a true strain and stress relation for mild steel that was suitable for implementation in finite element models. The true strain and stress relation was utilized to simulate a plate punching experiment until fracture using the finite element model (FEM).