## 1 Introduction  
Around the world, the magnitude and the frequency of seismic activity are increasing, and so too are the effects on property and human lives. The 1999 Taiwan earthquake resulted in over 2000 casualties and some 10 billion dollars of damage to property, and the earthquake of magnitude 7 in Haiti in 2010 caused tens of thousands of casualties, with the collapse of social infrastructure resulting in massive economic losses. The earthquake and tsunami that occurred in Japan in 2011 resulted in more than 10,000 lost lives as well as the explosion at and subsequent leakage of hazardous radioactive isotopes from the Daiichi nuclear power plant. When a structure is damaged due to an earthquake, general structures incur only primary damage such as collapse, but fluid storage structures can cause secondary damage such as environmental pollution or personal injury from the escape of internal fluid. To prevent such disasters, it is important for a fluid storage structure to accurately contain the flow characteristics of the fluid inside the structure and for the fluid dynamic pressure acting on the structure to be accurately calculated [1]. To calculate the hydraulic pressure of a fluid, [PERSON] [2] developed a theoretical equation for the hydraulic pressure acting on a structure when an earthquake occurs in a vertical dam, ands proposed an approximate solution. Based on the approximate solution, some of the water stored in the reservoir is loaded on to the dam body as an additional mass, and the concept of generating a load equal to the hydraulic pressure on the dam body by the seismic force applied to the added mass during an earthquake was additionally proposed. [PERSON] [3,4] proposed a mechanics-based method of modeling the dynamic effects of fluid inside a fluid storage structure by seismic loads as convective mass and impact mass, assuming that the structure wall is a rigid body, and [PERSON] [5; 6; 7; 8] found a theoretical solution to the hydraulic pressure generated during earthquakes in a vertical dam in a lake composed of compressible fluid. [PERSON] [9] conducted a study on a brief seismic response analysis method for flexible tanks based on the boundary solution induced by the analysis, and [PERSON] [10] proposed a method of modeling a structure as an axisymmetric finite element (FE) for the detailed seismic response analysis of a cylindrical fluid storage tank and analyzed the fluid region using a fluid-added mass matrix based on the boundary analysis method. Due to the recent development of numerical analysis techniques, various analysis techniques that can directly model fluid inside a fluid storage structure have been proposed. Through such analysis methods, studies have begun to analyze flow characteristics inside a fluid storage structure under seismic loads and to compare and analyze similarities with experiments. However, most of these studies only estimate the fluctuation characteristics of internal fluid by repeatedly loading the same load or using a sine wave, so it is difficult to estimate the fluid flow characteristics and hydraulic pressure generated by a real earthquake [11]. Several other dynamic hydraulic pressure studies have analyzed the flow characteristics of fluid inside a fluid storage structure when a real earthquake occurs as well as the hydraulic pressure acting on the wall of a fluid storage structure [12; 13]. However, each real earthquake has its own characteristics, so any analyzed fluid flow characteristics and hydraulic pressure cannot necessarily be considered representative results for all earthquakes. [PERSON] and [PERSON] proposed well-known equations for calculating hydraulic pressure that have been applied in actual designs. However, [PERSON]'s equation is suited to dams, not to other types of structures, because [PERSON]'s equation does not take into account the width of a structure (or the width of the fluid), only the height. Therefore, even if a structure's width changes, the hydraulic pressure of the fluid always remains constant.