The dynamic and the whipping phenomena through an underwater explosion (UNDEX) experiments and simulations were verified. Furthermore, the comparison of the simulation and experimental results were conducted. The experiment was conducted at a reservoir and the MegaMEX was used as an explosive. The simulation was performed by combining the DAA-based USA code with the LS-Dyna which is a finite element analysis code, and for the gas bubble, the second-generation Geers–Hunter model was used. For the experiment, the natural frequency analysis of the structure was carried out to establish the explosion condition and four underwater explosion tests were carried out. Acceleration, velocity, strain and underwater pressures were measured by underwater explosion experiments, and acceleration, velocity and strain were compared. In this research, the whipping phenomenon by underwater explosion was confirmed through experiments and simulation. The results of this study are expected to contribute to the improvement of UNDEX simulation technique.

A review of the 2nd generation of intact stability by the International Maritime Organization is performed. The main issues with the new stability criteria are reviewed. In particular, the physical background and related mathematical formulations of the pure loss of stability and parametric roll are summarized. Based on a literature review, benchmark calculation results for 17 different types of ships are discussed, and the final results are in excellent agreement with our physical expectations. Some relatively serious design problems are found in the application of the new stability criteria to sample ships built in Korea, and possible technical solutions are proposed, which have to be improved in the coming years.

This paper presented theoretical and experimental models for the investigation of the amplitude of the vertical motion of a cylinder by a two-dimensional linear wave, passing through a circular horizontal cylinder close to the free surface in water. To consider the effect of the free surface, the Gap ratio = d/a was introduced by dividing the distance d between the centre of the cylinder and the water surface by the radius a of the cylinder. In this study, the smaller the Gap ratio, the greater the effect of the free surface, and it was theoretically calculated that it caused severe fluctuations in the hydrodynamic coefficients. In particular, by expanding previous studies for the calculation of hydrodynamic coefficients, the oscillating amplitude of the cylinder close to the free surface was proved by experiment.

The Ministry of Land, Infrastructure, and Transport conducted a demonstration project targeting pilot areas to commercialize drone delivery services in urban areas and to present a standard model. In this study, flight data on drone delivery routes in Ulju and drone hovering in Yeosu were collected and analyzed for flight safety. Since there are no domestic or international regulations on the stability of drone flight, we were given the task of analyzing whether drone path flight should be maintained within a 10 m error range from the planned path line by the Korea Transportation Safety Authority and whether hovering works while satisfying the left and right radius errors and altitude errors within 3 m. Accordingly, the drone flight path data analyzed in Ulju met the criteria of up to 1.07%, and the hovering data analyzed in Yeosu met the criteria of less than 3% for the entire section data. Therefore, the drone flight stability evaluation analyzed in this paper is considered to have been passed. Based on the results of this study, is the data are expected to serve as a cornerstone for establishing guidelines for drone delivery flight data analysis regulations.