## 1 Introduction
For an exposure standard, three forms, namely peak limitation, short-term exposure limit (STEL), and eight-hour time-weighted average, have been suggested. Peak limitation refers to the maximum or peak airborne concentration of a substance determined over the shortest analytically practical period, which does not exceed 15 min. The STEL is the time-weighted average maximum airborne concentration of a substance calculated over a 15 min period. Eight-hour time-weighted average (TWA) is the maximum average airborne concentration of a substance when calculated over an eight-hour working day for a five-day working week. For NO\({}_{2}\), 5 ppm STEL and 3 ppm TWA were suggested. Model tests and computational fluid dynamics (CFD) analyses are primarily performed to observe the flow phenomenon around exhaust pipes. The model test has been widely performed in the past and offers excellent accuracy; however, it requires a significant amount of time and money to obtain all the information regarding the flow field. CFD has been used extensively recently; however, the amount of data accumulated, such as those from model tests, are insufficient. Hence, a review of various design conditions can be provided rapidly and economically. [PERSON] and [PERSON] [5] summarized the law of similarity for exhaust smoke and suggested a method for an accurate simulation. [PERSON] et al. [6] summarized studies pertaining to ship exhaust smoke flow by performing tests and CFD simulations after 1930. Additionally, [PERSON] et al. [7] conducted an exhaust smoke flow experiment using a simple vessel and superstructure. [PERSON] and [PERSON] [8] simulated the temperature and concentration of exhaust smoke around ships via large eddy simulations. [PERSON] et al. [1] computed the exhaust smoke temperature around a container ship and verified the CFD results via a ship trial. [PERSON] et al. [2] conducted a parametric study pertaining to the design parameters affecting exhaust smoke. [PERSON] et al. [9] simulatedthe weakening effect of the exhaust smoke of a ship traveling at various wind speeds, ship speeds, exhaust smoke velocities, and temperatures. Regarding exhaust smoke flow, numerous numerical studies have been conducted to investigate the turbulent boundary layer and wake around ships ([PERSON] et al. [10]; [PERSON] [11]). [PERSON] et al. [12] observed the flow around a ship during helicopter take-off and landing via CFD simulations and real-line measurements. [PERSON] and [PERSON] [13] predicted the wake of a ship via detached eddy simulations and compared the results with the measurement results from an actual ship. The different plume behaviors of the exhaust from different numbers of container ship stacks were quantitatively analyzed based on mass fraction via CFD simulation [14]. The effects of the efflux velocity, operational conditions, stack geometry, and buoyancy on the exhaust dispersion of generic frigates have been investigated numerically [15]. Most studies relevant to exhaust smoke flow from a ship have been conducted for the navigating status, i.e., under the condition that a high relative wind speed and the wind direction affect the flow fields. This is appropriate for general merchant ships but not for special-purpose vessels, such as drill ships, offshore plants, and operation support vessels. For the latter, the exhaust smoke flow is primarily affected by wind because they operate in a stationary state at sea. Therefore, in this study, the exhaust smoke flow around an anchor-handling tug supply vessel in a stationary state is analyzed via CFD simulation. By changing the wind speed and direction, we assess whether the environment is suitable for the crew members. The commercial CFD software ([[https://www.ansys.com/products/fluids](https://www.ansys.com/products/fluids)]([https://www.ansys.com/products/fluids](https://www.ansys.com/products/fluids)), accessed on 4 June 2023), ANSYS Fluent, is used for the grid system and numerical simulations.