A paper entitled “Hybrid Numerical Scheme of Preissmann Slot Model for Transient Mixed Flows” by the Korean research team attracted attention from academia. Dr. Seungsoo Lee from the APEC Climate Center joined this Korean reseach team and greatly contributed to the completion of the paper. This paper was published in Water, an online public journal (Water, http://www.mdpi.com/2073-4441/10/7/899).

Water is one of the prestigious online public journals in the water-related science technology field including ecology and water resource management.

Numerical modeling of water flows in sewer pipe that can be easy to use for a specific purpose plays an important role in solving water issues in the city such as the design of sewer systems, sewer pipe damage detection, and floods.

General water flow in the sewer pipe is free surface flow due to gravity in a free surface condition caused by contact between the atmosphere and the water surface.

But during extreme flood events, it often becomes a partly free surface, partly pressurized flow (mixed flow), or fully pressurized flow. The numerical modeling of transient mixed flows is associated with infrastructure damage or operational problems. Pressurized flow occurs due to the pressure difference between both ends of the pipe when the pipe was completely full of water.

The numerical modeling of transient mixed flows is associated with infrastructure damage or operational problems. However, it is difficult to find a straightforward way because two different flow regimes should be considered in the same domain.

When using two governing equations, it is difficult to tract the mixed flows interfaces and switch smoothly between the two systems. If each mathematical equation is applied on free surface flow and pressurized flow in sewer pipe where the transient mixed flow appears, it is difficult to track interfaces between the two mixed flows.

And also it is difficult to explain the phenomenon of switching completely into one of these flows in the sewer pipe.

Accordingly, the research team including Dr Seungsoo Lee from the APEC Climate Center presented a new technique in 'Water' to explain and predict the flow of water in the sewer systems during sudden heavy rainfall events.

The preissman slot model is one of the most used models to conceptualize water flow in urban sewer systems.

However, previous studies utilizing the numerical solutions from Preissman slot model found that it could be distorted by unnecessary error values when the water flow condition is switched from free surface flow to pressurized flow.

For this reason, Dr. Seungsoo Lee’s research team suggested a hybrid numerical method of Preissman slot model to transient mixed flow.

This scheme proved that it is better to explain the transited mixed flow in the sewer system under various conditions compared to the conventional water flow numerical modeling scheme.

Dr. Seungsoo Lee said that “the research results released in this paper could provide a base scheme for establishing the real time flood warning system by predicting better water flows in sewer pipe in the city area.”

And he also said “They can contribute to reducing the damage to human life and property. By using them, we can reliably predict the flow of water in urban sewer pipes and exactly identify flooding areas that are caused by severe rain storms.”