Ocean wave energy has great potential to cope with increasing energy demand since it is renewable, sustainable and green energy and its overall resource is estimated to be around 2TW.

Some wave energy devices can be modeled as submerged oscillating bodies, which requires a deep understanding of hydrodynamic interaction between ocean waves and submerged bodies.

Many numerical methods have been proposed for bodies in irregular or arbitrary shapes, but it is important to specify boundary conditions on a virtual cylindrical surface between mean free surface and seabed.

Rim Un Ryong, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has investigated three-dimensional linear interaction between a submerged oscillating body in arbitrary shape and the regular water wave with finite depth.

First, he derived an exact Dirichlet-to-Neumann (DtN) boundary condition on a virtual cylindrical surface, where the virtual surface was chosen to enclose the body and extract an interior subdomain with finite volume from the horizontally unbounded water domain.

Then, he applied the DtN boundary condition to solve the interaction between the body and the linear wave in the interior subdomain with the boundary integral equation.

He has validated the proposed method via a submerged vertical cylinder. The result shows a good agreement with the analytical results of precedent papers.

For more information, please refer to his paper “Free surface wave interaction with a submerged body using a DtN boundary condition” in “Theoretical and Computational Fluid Dynamics” (SCI).

A single-tuned harmonic filter is a passive harmonic filter widely used to eliminate harmonics in power systems.

Minimizing the impedance of the filter at the corresponding harmonic frequency makes the harmonic voltage produced by the harmonic current generated by the non-linear load a minimum. This is the principle of filtering in a single-tuned harmonic filter.

While eliminating the corresponding harmonic, the single-tuned harmonic filter affects the fundamental power factor. That is because the single-tuned harmonic filter itself is capacitive at the fundamental frequency. In the past, most power systems were inductive at the fundamental frequency, so in general, their capacitive characteristics played a positive role in raising the power factor of power systems. But nowadays, with the widespread use of power electronic devices, there have been more and more loads that are non-inductive at the fundamental frequency in the power systems. In this case, using conventional single-tuned harmonic filters results in the decrement of the fundamental power factor and the increment of transmission loss. In order to overcome these disadvantages, it is necessary to develop a new type of filter that eliminates harmonics but does not influence the fundamental power factor.

Ji Kuk Ryol, an institute head at the Faculty of Electrical Engineering, has proposed a novel single-tuned harmonic filter, which can remove harmonics with the fundamental power factor unchanged.

The proposed filter can be applied to filtering the harmonics made by a load whose fundamental power factor is 1 or capacitive.

You can find more information in his paper “Novel Single Tuned Harmonic Filter not Affecting Fundamental Power Factor” in “Journal of Electrical Power & Energy Systems” (EI).

Sensing nitrogen oxide gas is important for measuring pollution gas and detecting pollution sources from vehicles and chemical processes in the atmosphere and for diagnosing the diseases of human body by measuring NO₂ gas from breathing. Therefore, it is necessary to measure the range of dilute concentration and to develop a less power-consuming electrochemical method.

Kim Yong Hyok, a researcher at the Faculty of Electronics, has designed the structure of a new NO₂ gas sensor and conducted a qualitative analysis of its performance. In addition, he has established its manufacturing process and experimentally analyzed the bias voltage properties.

The new sensor can linearly sense NO₂ gas of up to 100ppm.