Multi-Objective Optimal Control for Wastewater Trea...

Jo Mar 3, 2025

Wastewater treatment process (WWTP) is difficult to control because its biological, physical and chemical phenomena are complex and they are interrelated and highly nonlinear.

Recently, model predictive control (MPC), which employs a prediction model of the plant to optimize future plant behavior, has been a popular approach for WWTP. Since WWTPs are multivariable, multi-objective optimization of MPC is required.

Kim Kyong Jin, a researcher at the Faculty of Automation Engineering, has proposed a nonlinear multi-objective MPC (NMMPC) to realize a multivariable control for WWTPs.

The proposed multi-objective optimal control comprises a self-organizing radial basis function neural network (SORBFNN) identifier, a model predictive controller and a multi-objective optimization method. He developed the SORBFNN as a model identifier for approximating the online states of dynamic systems. The solution of the multi-objective optimization is obtained by a gradient method which can shorten the solving time of optimal control problems.

The experiments have revealed that the proposed control technique gives satisfactory tracking and disturbance rejection performance for WWTPs.

Design Method of Multi-Layer Film in Optical Filter...

Jo Mar 2, 2025

Analysis of CO₂ is very important in several fields including chemical industry as well as estimation of environment, monitoring of disasters, etc.

Laser spectrum technology is effective for minimal gas analysis in the fields of environment and industrial measurement. Coherent light source which can be adjusted to the narrow width of spectrum can detect an absorption line of the matter and avoid interference of signals caused by other kinds of matter.

Narrowband filter is a major element for separating fine spectrum including gas analysis. Narrowband filter for breaking broadband has a complex structure of over 60 layers. The most widely-used narrowband filter is Fabry-Perot interferometer. This filter, which has a spacer between two reflective layers, forms interference maximum for the beam that satisfies the resonance condition according to the thickness of the spacer, thus ensuring sharp spectrum transmission.

In order to analyze CO₂ in a gaseous mixture, Kye Song Chol, a researcher at the Faculty of Mechanical Science and Technology, has designed a multi-layer system of the filter for selectively filtering the absorption line of CO₂ gas and cutting absorption lines of other air components.

As common Fabry-Perot narrow band filters have high spectral selectivity, he designed a double Fabry-Perot filter, which has low spectral selectivity and high transmittance at reference wavelength. For broadband cutoff, he combined a double Fabry-Perot filter and a broadband filter of symmetrical period structure, thus ensuring the necessary spectral characteristics and improving manufacturability. To increase the transmittance of band on which CO₂ absorption line is located, he applied the equivalent theorem of a symmetrical period coating system and the index distribution of antireflection.

This filter consists of a double Fabry-Perot narrowband filter and a wideband filter placed on both sides of the Ge substrate, which can provide the required spectral characteristics while avoiding the complex structure of more than 60 layers of the conventional one.

Seasonal Divisions and Folk Customs in March

Jo Mar 1, 2025

In our country, March is the time when spring sets in.

Seasonal divisions in March are kyongchip and chunbun.

Kyongchip, which literally means the time when hibernating worms start to wriggle, awakened by the melting ice and the rain with thunder, falls around March 5 by the solar calendar.

Chunbun, which means the period in the middle of spring, falls around March 21 by the solar calendar. In this period, there is almost no difference in the length of the day and the night, and although it often blows hard, the weather gets mild and the ground thaws out.

Around kyongchip and chunbun, the Korean people used to mend the fences and spring-clean houses and surroundings to clear away the traces of winter before starting farming. In addition, they liked making delicious food with edible herbs coming out green and fresh in the fields to enjoy the flavor of spring.

The typical herbs are shepherd’s purse and wild garlic.

They also used to pick various kinds of medicinal herbs for storage and do peasants’ dancing and singing to add a zest to farming, hoping for a good harvest.