In this study, a method for analyzing the collision and interaction between ice bergy bits and a Mark III type liquid natural gas (LNG) carrier was considered, and the structural safety of a ship's hull and cargo containment system (CCS) was evaluated. In the analysis, a constitutive model implementing the strain rate dependant mechanical property was used to consider the typical material characteristics of ice rationally. A relatively simple and easy ice structure interaction analysis procedure, compared with the accurate but complicated FSI analysis scheme, was suggested. When the ice bergy bits collided with ship's side hull under the four assumed scenarios, the structural behaviors of the ship structure and LNG CCS were simulated by applying the suggested ice collision analysis procedure using the commercial hydro-code LS-DYNA. In addition, the effects of the shapes and colliding speed of the ice bergy bits on the ice-structure interaction and safety of the CCS were examined in detail.
The sloshing pressure acting on a membrane-type LNG CCS is a typical irregular impact load, and the structural response of a tank system induced by sloshing also shows very complex behavior, including fluid structure interaction. Therefore, it is not easy to accurately estimate the sloshing impact pressures and resulting structural response. Moreover, a huge time consuming process to deal with the enormous pressure data obtained during a model tank test and the following structural analysis would be inevitable. To reduce the computation time for structural analysis, in this study, a rational structural modeling strategy was considered, and a simplified scheme to analyze the dynamic structural responses of an LNG CCS was introduced, which was based on the concept of the linear combination of the triangular response functions obtained by a transient response analysis of structures under unit triangular impact pressure. A structural analysis of a real Mark III membrane type insulation system under the sloshing impact pressure time histories obtained by model tests was performed using the various proposed structural models and simplified analysis scheme. The results were investigated in detail, including the elastic support effects of the hull structure.
This study evaluates the computational efficiency based on the parallel processing mode and domain decomposition method of the FDS model to enhance the computational performance of fire simulation. A single compartment of dimensions 12.0 m × 3.8 m × 3.0 m is considered along with a rectangular fire source (0.4 m × 0.4 m) fueled by n-Heptane. The computational domain was divided into 136,000 cells forming a grid size of 0.1 m, and the computational efficiency for each calculation was evaluated by the wall clock time for a simulation time of 300 s using a computational framework with 24 cores of a single CPU and a 256 GB shared memory system. The MPI and hybrid mode in FDS parallel offers a greater speed-up capability than the OpenMP mode, and the domain decomposition method used greatly affects the computational efficiency. The maximum speed-up with the OpenMP mode was less than 1.5 for a single computational domain, which indicates that there is an optimal condition for thread assignment and domain decomposition in the OpenMP mode. The present study is expected to contribute toward obtaining effective fire simulation results with limited computing power and time in fire protection engineering.
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