Poseokjeong is a place for enjoying poetry and arts while drinking from floating wine cups. About the year of construction, as I mentioned before using Samguk Yusa, it's often argued that it already existed in the time of the 49th King Heongang, so therefore was constructed during the reign of the 48th King Gyeongmyeong. However, though it is not official, the records in the Hwarang Segi manuscript suggest that it was constructed in the early years of Unified Silla. I'll briefly explain its shape. As you see here, there's an inlet. And then, the main part through which the water flows. Then, there's an outlet. In fact, in old times, there was an installment in the shape of a turtle spouting water in front of the inlet. But that has long been gone. As we have seen in the pictures from 1916, Poseokjeong was quite damaged. But afterwards, based on historical research, it was reconstructed in the form we see now. The stone used in rebuilding Poseokjeong constitutes 63 granite blocks. The overall shape resembles an abalone which is why it is called Poseokjeong. The overall length, this length here is 10.3 meters. The overall circumference is 22 meters. And the average depth, the depth varies from place to place, but the average is 22 centimeters. The width also varies from 24 to 40 centimeters. It's not consistent either. And the elevation difference between the inlet and the outlet is 40 centimeters. Now, we will look at some interesting phenomena from the perspective of fluid mechanics. This part of the lecture will be delivered by Professor Lee, Sang-Joon of POSTCH Mechanical Engineering. Professor Lee is an expert in experimental fluid mechanics, is highly regarded in Korea, and produced many research results. Now then, Professor Lee, Sang-Joon. I'm Lee, Sang-Joon of POSTECH Mechanical Engineering as introduced by Professor Youm, Young Il. Now I'll talk about the fluid mechanical characteristics and principles of Poseokjeong. Poseokjeong has an inlet, a channel that water flows through, and an outlet. The inlet and the outlet have a difference of about 40 centimeters in elevation. This difference in elevation causes fluid to flow down the channel and exit through the outlet. Another characteristic is that the width of the channel, varies widely from 24 centimeters to as wide as 40 centimeters. By varying the channel width, the speed in which fluid flows can be slowed down. In addition, due to such variance in the width, eddies are created in parts of the channel that get wider. And to confirm such phenomena, Professor Jang, Keun Shik of KAIST did an experiment a while ago with a 1/6 scale model of Poseokjeong. For this experiment, he used floating matters such as styrofoam to float along on the fluid. At places like these where the width of the channel changes, the flow slows down at a wider section, speeds up at a narrower section, and again slows down at a wider section. This causes flow separation in fluid. At sections where the width is significantly wider, bigger eddy current appears. So, the differences in the width of the channel and the changes in the speed of the flow are the fluid mechanical characteristics of Poseokjeong. Poseokjeong is actually built with many granite stones. As I have mentioned earlier, they used granite stones in varying the channel like this or making a sharp turn in the direction of the flow to achieve the characteristics that allowed various forms of vortex flow. Actually, when we look at the results from such model experiments, the flow of the fluid is accelerated right after the inlet. And when it reaches this part where the channel changes, it continues to flow down by its inertia. Therefore, a vortex forms here, and at a place like this where the channel becomes wider a vortex forms as well. Starting from the inlet and along the flow through the entire channel, there are many places where the width of the channel changes and the direction of the flow sharply changes. Due to these changes many vertices form. To confirm these characteristics, an on-site experimental investigation was conducted at Poseokjeong. To time the flow, they filled up a cup with water and floated it down the channel. For a big cup, it took about 8 minutes for a complete turn, and for a smaller cup, it took over 10 minutes. When they were experimenting on the site, they filled the channel only up to two thirds of the depth. What we could learn from the investigation was that at places where relatively large vortices or eddies formed, the cup stopped and rotated along the current for a certain amount of time. While the cup stopped and rotated like this, one would pick up the cup and drink from it. The time it takes to make one complete turn is influenced by factors such as the size of the cup, the amount of liquor inside, and the starting location.
