## 1 Introduction  
Global economic growth has led to high demand for worldwide shipping. However, since the increase in maritime traffic requires many ships, the noise caused by the ships is rising in coastal areas and underwater ecosystems. [PERSON] and [PERSON] [1] reported and assessed the extent of noise exposure for residents within the vicinity of Dublin Port by long-term measurements for 45 days. [PERSON] et al. [2] also focused on the noise level in the Mediterranean port city and suggested the Strategic Noise Map and Action Plans to reduce the noise levels and exposure of the population to the noise by performing 24-h noise measurements. [PERSON] et al. [3] and [PERSON] et al. [4] assessed an acoustical characterization by using short- and long-term measurements for five different small vessels that move around at various speeds in every type of port and produced noise map in Livorno's canals. As part of the INTERREG Marititimo-Maritime projects, [PERSON] et al. [5] reported the complaints by the citizens living near the ports by investigating the port noise in the North Tyrrhenian Sea. Underwater-radiated noise from ships has also adversely affected marine ecosystems by disturbing natural acoustic signals, such as that of whales, in the ocean. [PERSON] et al. [6] reported that artificial underwater noise could harm fish hearing and their body. [PERSON] et al. [7] reported the adverse impact of underwater noise on marine mammals like dolphins and proposed the underwater noise management system. In this regard, developed countries, including the European Union and the United States, have already adopted specific guidelines for regulating underwater noise from ships. Underwater-radiated sound is also crucial from a military aspect, and specialized weapon systems, such as submarines, should be able to simultaneously operate at high speed and secure stealth via low noise design. Underwater-radiated noise generated by surface and underwater vehicles, such as ships and submarines, can be subdivided into two parts based on its generation mechanism. The first part involves mechanical noises due to the structural vibration, and the second part involves flow noise generated via the flow dynamic mechanism without structural vibrations. Engines and generators are primary sources of structural vibration in vehicles, and underwater propellers are dominant sources of flow noise. At low speeds, mechanical noise typically contributes more to underwater-radiated sound than the flow noise. However, as the vehicle speed increases, the flow noise becomes more dominant. Specifically, when the speed reaches the so-called cavitation inception speed (CIS), the cavitation noise provides the highest contribution to the overall underwater noise. Thus, propeller cavitation noise is one of the most critical issues, which is considered in developing high-speed and low-noise surface or underwater vehicles [8]. Cavitation in an underwater propeller can be classified into sheet cavitation and tip-vortex cavitation, based on the structure of cavitation formation. The volumetric acceleration of cavitation produces cavitation noise as per the acoustic analogy. Given that the sheet cavitation forms and collapses periodically in association with propeller rotation, peak acoustic pressure signal due to sheet cavitation is observed at the blade passing frequency of the propeller, and thus it shows tonal characteristics [9; 10]. Conversely, tip-vortex cavitation develops along the tip-vortex line, which forms helical curves that start from the propeller blade tip and extend towards the downstream direction. The underwater-radiated noise due to tip-vortex cavitation exhibits the characteristic of broadband noise due to the random behavior of the cavitation bubble [11; 12]. Given that the noise levels are broadly increased in the high-frequency range when cavitation occurs, the high-speed operation of the ship and submarine is restricted.