Study on Parameter Decision Method for Modeling of ...

Jo May 30, 2023

A research team led by Jong Ji Song, a researcher at the Faculty of Mechanical Science and Technology, has suggested a method of modeling the output boundary conditions of a cardiovascular system, which is very important to properly simulate blood flow in a cardiovascular system.

Modeling of output boundary conditions of a cardiovascular system is, in essence, that of one of the several parts not reflected in a three-dimensional modeling for simulation analysis, that is, reflecting the change in the characteristic quantities in several parts omitted in the three-dimensional model as boundary conditions.

Blood vessels not reflected in the three dimensional model of a cardiovascular system are modeled by parameters such as resistance (R), elasticity (E) and compliance (C) to form an electrical circuit analogous model. From this model, output pressure waveforms are formed.

They modeled the output of the artery in a series connection of proximal resistance R_p to the parallel connection of compliance C and distal resistance R_d to reflect the transient of blood flow and the elasticity of a blood vessel. They modeled the coronary output in the combination of resistance of coronary artery R_a, coronary compliance C_a, microcirculation resistance R_am, myocardial compliance C_im, coronary vein resistance R_v and ventricular pressure P_im(t).

Then, from the model mentioned above, he obtained blood pressure waveforms at the artery output and coronary output of the model whose heart rate is 80 beats/min, cardiac output 120mL, diastolic and systolic pressures 80mmHg and 130mmHg respectively, split ratio of coronary and system circulation 0.04 and that of left and right coronary artery 7/3.

Setting these blood pressure waveforms as output boundary conditions, they performed analysis by ANSYS Fluent 19.2 during two heart rate cycles.

They applied the boundary conditions to five persons who were to have heart operations and compared them with the clinical data.

The comparison showed the error of systolic pressure, diastolic pressure and one cycle cardiac output were -1.07~0.86%, -1.1~0.88% and -0.89~1.87% respectively, which means this method of modeling output boundary conditions is very effective.

The suggested method can be applied to a cardiac operation simulating system for the simulation and analysis of the preoperative and postoperative state of blood flow in the cardiovascular system. In addition, it can predict the effectiveness of planned operations and relapse after operations, and provide clinical simulation results for postoperative healing programs.

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.