Simulation of Acoustical Field of Ballistic Shock T...

Jo May 26, 2023

Shock wave therapy (SWT) is a physical treatment that uses focused or unfocused shock wave to treat a variety of diseases including plantar fascitis, chronic pain, erectile dysfunction, bone ache, heart disease, and osteoarthritis. Most SWT devices use electrohydraulic or electromagnetic source that results in focused shock waves by a reflector or an acoustic lens. The ballistic SWT device, scaled down in size, consists of a hand piece within which compressed air is used to fire a projectile that strikes a metal applicator placed on the skin.

More reliable measurements and modeling on the pressure field of the device should be conducted in order to clarify the beneficial effect of shock wave.

Many new data on the pressure field of ballistic shock wave were presented by their successful studies although the experimental results were not identical with each other. The origin for different results in those literatures is likely related to the settings on the devices and measurement conditions, which might arouse ambiguity on clarifying physical and biological mechanism.

Pae Kyong Nam, a researcher at the Faculty of Physics, has developed a Lattice Boltzmann model based on mass and momentum conservation equations and Tait equation of state to elucidate propagation behavior of the ballistic shock wave. He has modeled the weak compressible flow with the mass and momentum conservation equations to obtain the macroscopic variables such as density, velocity and pressure. In order to solve the equations mentioned above, he has closed the system with a relation between the pressure and conserved variables by using the Tait equation of state (EOS).

The applicator used in the simulation was a convex shaped applicator with a 15mm diameter, referred to as unfocused, whose effective radius of curvature was 41mm, and the center was extended approximately 0.7mm from the edge.

A simulated pressure waveform is generally in good agreement with the previous experimental results, which has a leading positive phase and a subsequent negative phase.

You can find more information in his paper “Simulation of Acoustical Field of Ballistic Shock Therapy Device by the Lattice Boltzmann Method” in “Physics of Wave Phenomena” (SCI).

Research on Analysis of Internal Flow of Reactor wi...

Jo May 24, 2023

A research team led by Choe Hyon Chol, a researcher at the Faculty of Mechanical Science and Technology, has proposed a reactor of a new type which ensures smooth ignition of pulverized anthracite coal and determined the most reasonable parameters.

More precise analysis of flow in a non-oil ignition reactor considering the effect of plasma is very important for several purposes such as raising the efficiency of a reactor, lengthening its service life, etc.

First, he proposed a conical air plasma reactor based on the cyclone principle as the most reasonable reactor for the ignition of anthracite coal.

Next, he created a geometrical model of the conical air plasma reactor and meshing and performed a CFD simulation by ANSYS Fluent using an RNG κ-ε turbulence model.

Through the numerical simulation of the joule heating process inside the reactor on an MHD model, he verified that the average temperature on the central axis increases with the cone angle and decreases with the increase in the inlet velocity, and it decreases as the inside diameter of the electrode increases.

The simulation on the electrochemical reaction and combustion process of plasma arc and pulverized coal-air mixture showed that as the cone angle increases, CO quantity increases and then decreases, and as the inlet velocity and the inside diameter of the electrode increase, CO quantity increases.

The reactor is regarded as essential for all kinds of furnaces for high temperature as well as boilers as it uses no heavy oil but pulverized anthracite coal, natural solid fuel.

It is simple in structure, easy to build and environmentally-friendly.

A New Method to Determine Cluster Number based on R...

Jo May 22, 2023

Clustering analysis is being applied to many fields of engineering and social science. One of the most important problems in clustering is to determine the number of clusters properly. The K-means clustering algorithm is widely used due to its simplicity. However, application of this algorithm is restricted by the fact that K must be chosen at the start. Thus, correct selection of K is essential, especially in this algorithm.

Many approaches to infer K and estimate the significance of the clustering result have been proposed. In those approaches, the first thing to be done beforehand is determination of the range of K. And, clustering is performed for every possible value of K, and then the value of the cluster number is determined. This is at a disadvantage of high complexity in the case of a great number of data points or high dimension. This would seem to become more serious when clustering big datasets is required and when it comes to density functions.

Ri Yong Ae, a lecturer at the Faculty of Applied Mathematics, has proposed a new method to determine the cluster number without clustering for every K in K-means.

First, introducing a new statistics RVR (ratio of variance to range), she proposed an algorithm to determine the cluster number K and perform clustering.

Then, to evaluate the effectiveness, she performed a simulation test with different types of datasets.

She has concluded that the proposed method has observed a significant improvement in speed and quality of determination of the cluster number and clustering, and the proposed algorithm would be used efficiently and widely for clustering of multi-dimensional data.

If further information is needed, please refer to her paper “A New Method to Determine Cluster Number without Clustering for Every K based on Ratio of Variance to Range (RVR) in K-Means” in “Mathematical Problems in Engineering” (SCI).