Due to environmental pollution, regulations on existing petroleum-based fuels are increasing day by day. LNG is in the spotlight as an eco-friendly fuel that does not emit NOx or SOx, but its boiling point is -163°C, so it needs to be handled with care. Materials that can be used at the above temperature are defined by IMO through the IGC Code. Among them, 9% nickel steel has great advantages in yield strength and tensile strength under cryogenic conditions, but it is difficult to use in arc welding such as FCAW for various reasons. This study is a study to apply fiber laser welding to solve this problem. As a previous study, this study conducted a study to find a welding heat source. After performing bead on plate welding, the optimal heat source was derived by analyzing the shape of the bead and adjusting the parameters of the heat source model. In this case, by applying the multi-island genetic algorithm, which is a global optimization algorithm, not the intuition of the researcher, accurate results could be derived in a wide range.

PURPOSES : This study aims to determine the type (e.g., melting point, freezing point, latent heat fusion) and optimal content of phase change material (PCM) based on the numerical and experimental analyses evaluating the effects of heat transfer in PCM-modified asphalt pavement systems. METHODS : The effect of PCM on the thermophysical properties of PCM-modified asphalt concrete can be taken as an effective volumetric heat capacity. The volumetric fraction of PCM was calculated using an iterative method. The numerical model was established and computed using the MATLAB 2020 software. The optimum PCM design tool was developed to select the type and contents of the PCM. The PCM was chosen based on the following criteria: black-ice-formation delay time, minimize temperature increase, and increase temperature area. To validate the numerical model, asphalt mixtures were modified with varying PCM contents, and the temperature response of the PCMmodified asphalt samples was examined via temperature test. RESULTS : The numerical results showed that incorporating PCM into the asphalt mixture can slow the cooling rate of the pavement system. The predicted results from the optimum PCM design tool were highly consistent with the measured values from the laboratory temperature test. CONCLUSIONS : The temperature of PCM-modified asphalt pavement can be predicted via numerical method. The effect of PCM on the thermophysical properties can be considered as effective volumetric heat capacity; while the volume fraction of PCM can be calculated via an iterative method. The accuracy of the numerical model was confirmed by a high agreement between the measured and predicted values.