## 1 Introduction  
Hazardous and noxious substances (HNSs) are widely known as liquid and mixed-liquid substances that can have harmful effects on the marine environment [1]. Large quantities of HNSs are transported by sea. If an HNS-related accident occurs in a port or on a ship, harmful substances are diffused in the vicinity of the ships in different ways depending on the type of spill material (e.g., sinking, floating, evaporating, dissolving) [2]. Indeed, it is difficult to cope with HNS accidents because of the high risk associated with various HNSs with bioaccumulative, biodegradable, toxic, and explosive characteristics [3; 4; 5; 6; 7; 8]. To date, many government authorities and environmental organizations have concentrated their effort on establishing emergency planning against HNS disasters. There is still a lack of information on HNS characteristics under HNS accident scenarios. Indeed, it is difficult to perform experiments directly on HNS propagation in real circumstances because of the toxicity of HNSs with various chemical properties. Nevertheless, [PERSON] et al. [2]dissolved a small amount of styrene, an HNS, in the sea and monitored the residual concentration over time. They reported that the spilled styrene was above 50% of the total HNS amount only for 1 h in the early stage of the accident. This report can be useful in making subtle plans for accident response. Because they conducted the experiment for directly releasing HNS in the actual sea, however, they could cause severe safety problems and destroy the marine ecosystem in the experiment. Considering the safety and environmental issues, direct experiments need to be strongly restricted. This is why the available experimental data related to HNS propagation is hardly available. The computational fluid dynamics (CFD) approach has been a promising way to investigate the diffusion characteristics of HNSs near ships in the sea ([PERSON], 2009; [PERSON], 2010; [PERSON], 2011). [PERSON] et al. (2018) developed a three-dimensional prediction model involving the hydrodynamic model and the oil-spill model. They compared the real photos taken for oil-spill propagation in the Arabian Gulf region with the oil-spill model. Their model also made an accurate prediction for a credible analysis of oil spills. [PERSON] et al. (2018) developed the OILTRANS model that consists of two inter-linked models, namely, the particle-transport model, based on the Lagrangian equation, and the oil-fates model. This model was applied to a spill accident that had occurred during a ship-to-ship fuel transfer in the Celtic Sea in 2009. The model was compared with aerial observations of the movement of the oil layer and showed good agreement in estimating the oil trajectory within ten days. [PERSON] et al. (2018) focused mainly on the validation of their own three-dimensional and high-resolution oil-spill model. They constructed a high-resolution grid with a size ranging from 440 m \(\times\) 440 m to 500 m \(\times\) 500 m. They simulated the trajectory of the spilled oil and compared the results with the historical information from the motor vessel (M/V) Marathassa oil spill. [PERSON] et al. (2018) also suggested a prediction model of oil-spill trajectory, which was coupled with hydrodynamics, oil transport, and a weathering model. They focused mainly on the validation of the developed model by comparison with the observed data from oil spills in the Tuscany Archipelago region. Most of the previous works mentioned above mainly reported oil-spill accidents, not general HNS accidents (2018). Their simulation results were obtained in domains with tens to hundreds of kilometers. This approach is called the far-field analysis, by which the local propagation of a substance spilled from the ship cannot be predicted. The main purpose of this far-field analysis is to show the bulk motion of a spilled substance based on acquired data of winds and sea currents.