• Journal of the Korean Geotechnical Society
• /
• v.36 no.8
• /
• pp.49-60
• /
• 2020

A fully coupled thermo-hydro-mechanical model is established to evaluate frost heave behaviour of saturated frost-susceptible soils. The method is based on mass conservation, energy conservation, and force equilibrium equations, which are fully coupled with each other. These equations consider various physical phenomena during one-dimensional soil freezing such as latent heat of phase change, thermal conductivity changes, pore water migration, and the accompanying mechanical deformation. Using the thermo-hydro-mechanical model, a sensitivity analysis study is conducted to examine the effects of the geotechnical parameters and external conditions on the amount of frost heave and frost heaving rate. According to the results of the sensitivity analysis, initial void ratio significantly affects each objective as an individual parameter, whereas soil particle thermal conductivity and temperature gradient affect frost heave behaviour to a greater degree when applied simultaneously. The factors considered in this study are the main factors affecting the frost heaving amount and rate, which may be used to determine the frostbite sensitivity of a new sample.

• Proceedings of the SAREK Conference
• /
• 2007.11a
• /
• pp.364-369
• /
• 2007

A system heat pump provides the benefits of comfort, energy conservation and easy maintenance. Recently, the system heat pump has been employed in small and medium-sized buildings. However, the performance data and control algorithm for system heat pump are limited in literature due to complicated system parameters and operating conditions. In the present study, the performance of a system heat pump with two indoor unit is measured by varying indoor loads, EEV opening, and compressor speed. In addition, the integral optimum regulator which includes MIMO control algorithm is proposed. The capacity modulation and optimum capacity for each indoor unit can be adjusted by utilizing the EEVs opening and compressor speed. The proposed scheme shows appropriate control performance at test conditions.

• Transactions of the Korean hydrogen and new energy society
• /
• v.33 no.1
• /
• pp.47-54
• /
• 2022

In this study, we performed numerical analysis for 1 kWe SOFC stack of internal manifold types according to the different manifold sizes to verify the influence of the flow uniformity into each cell. To simulate the flow phenomena in the stack, the continuity and momentum conservation equations including the standard k-𝜺 turbulent model for the steady-state conditions were applied. From the calculation results, we verified that the pressure drop from inlet pipes to outlet pipes decreased to a log scale as the manifold size increased in the internal manifold types. Also, we found that the flow uniformity increased on an exponential scale as the manifold size increased. In addition, the calculation results showed that the flow uniformity gradually improved as the fuel and oxygen utilization increased.

• 한국신재생에너지학회:학술대회논문집
• /
• 2009.11a
• /
• pp.600-605
• /
• 2009

A general purpose viscous flow solver Ansys CFX is used to study a Savonius type wave energy converter in a 3D numerical viscous wave tank. This paper presents the results of a computational fluid dynamics (CFD) analysis of the effect of blade configuration on the performance of 3 bladed Savonius rotors for wave energy extraction. A piston-type wave generator was incorporated in the computational domain to generate the desired incident waves. A complete OWC system with a 3-bladed Savonius rotor was modeled in a three dimensional numerical wave tank and the hydrodynamic conversion efficiency was estimated. The flow over the rotors is assumed to be two-dimensional (2D), viscous, turbulent and unsteady. The CFX code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme and with the adoption of the hexahedral mesh and the moving mesh techniques in areas of moving surfaces. Turbulence is modeled with the k.e model. Simulations were carried out simultaneously for the rotor angle and the helical twist. The results indicate that the developed models are suitable to analyze the water flows both in the chamber and in the turbine. For the turbine, the numerical results of torque were compared for all the cases.

• Transactions of the Korean hydrogen and new energy society
• /
• v.22 no.3
• /
• pp.363-371
• /
• 2011

In this paper, a three-dimensional hydrogen desorption model is developed to precisely study the hydrogen desorption kinetics and resultant heat and mass transport phenomena in metal hydride hydrogen storage vessels. The metal hydride hydrogen desorption model, i.e. governed by the conservation of mass, momentum, and thermal energy is first experimentally validated against the temperature evolution data measured on a cylindrical $LaNi_5$ metal hydride vessel. The equilibrium pressure used for hydrogen desorption simulations is derived as a function of H/M atomic ratio and temperature based on the experimental data in the literature. The numerical simulation results agree well with experimental data and the 3D desorption model successfully captures key experimental trends during hydrogen desorption process. Both the simulation and experiment display an initial sharp decrease in the temperature mainly caused by relatively slow heat supply rate from the vessel external wall. On the other hand, the effect of heat supply becomes influential at the latter stages, leading to smooth increase in the vessel temperature in both simulation and experiment. This numerical study provides the fundamental understanding of detailed heat and mass transfer phenomena during hydrogen desorption process and further indicates that efficient design of storage vessel and heating system is critical to achieve fast hydrogen discharging performance.

• Journal of the Korean Solar Energy Society
• /
• v.36 no.4
• /
• pp.21-29
• /
• 2016

Commercial wind farm design tools and the national wind map are used to determine the implementation potential of offshore wind power in Korea in this study. For this, the territorial waters of Korea were divided into nine analysis regions and a commercial CFD code was used to obtain wind resource maps at 100m A.S.L. which is the hub height of a 5MW wind turbine used in this study. With the wind resource obtained, factors including water depth, distance from substations, minimum and maximum capacity of a wind farm, distance between turbines and wind farms were considered to determine wind power potential. Also, the conservation areas, military zones, ports, fishing grounds, etc. were considered and excluded. As the result, a total capacity of 6,720 MW was found to be the implementation potential and this corresponds to $3.38MW/km^2$ in API. Also if the distance from the substation is not considered, the potential increased to be 10,040 MW. This offshore wind farm potential is considered enough to satisfy the target of wind farm capacities in the 7th national plan for electricity demand and supply.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.1
• /
• pp.189-205
• /
• 1996

The twin-roll type strip continuous casting process(or direct rolling process) of steel materials is characterized by two rotating water cooled rolls receiving a steady supply of molten metal which solidifies onto the rolls. A solidification analysis of molten metal considering phase transformation and thermofluid is performed using finite diffefence method with curvilinear coordinate to reduce computing time and molten region analysis with arbitrary shape. An enthalpy-specific heat method is used to determine the temperatures inthe roll and the steel. The temperature distribution of cooling roll is calculated using two dimensional finite element method, because of complex roll shape due to cooling hole in rolls and improvemnt accuracy of calculation result. The energy equaiton of cooling roll is solved simultanuously with the conservation equaiton of molten metal in order to consider heat transfer through the cooling roll. The calculated roll temperature is compared to experimental results and the heat transfer coefficient between cooling roll surface and rolling material(steel) is also determined from comparison of measured roll temperature and calculated temperature.

• Steel and Composite Structures
• /
• v.46 no.6
• /
• pp.759-772
• /
• 2023

This manuscript presents a comprehensive mathematical model to investigate buckling stability and postbuckling response of bio-inspired composite beams with helicoidal orientations. The higher order shear deformation theory as well as the Timoshenko beam theories are exploited to include the shear influence. The equilibrium nonlinear integro-differential equations of helicoidal composite beams are derived in detail using the energy conservation principle. Differential integral quadrature method (DIQM) is employed to discretize the nonlinear system of differential equations and solve them via the Newton iterative method then obtain the response of helicoidal composite beam. Numerical calculations are carried out to check the validity of the present solution methodology and to quantify the effects of helicoidal rotation angle, elastic foundation constants, beam theories, geometric and material properties on buckling, postbuckling of bio-inspired helicoidal composite beams. The developed model can be employed in design and analysis of curved helicoidal composite beam used in aerospace and naval structures.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.1 no.4
• /
• pp.171-181
• /
• 1977

This paper is aiming at calculating NOx concentration, which is one of the harmhul components of emission from the gasoline engine, formed in the combustor through the presess of combustion. Instantaneous temperature and concentration of each components for each division can be determined by the solution of simulatneous equation of reaction equation and equation of energy conservation, inputting the estimated temperature with a considerably wide rage of temperature. After determining instantaneous temperature and instantanous concentration of each components, the nonequilibrium calculation is performed based on the reaction kinetics in order to determine NOx concentration. To summarize the result abtained from the above method ;through the passage of NO concentration, NO concentration is the highest in the first division and it is gradually decreasing through the following divisions In the final division, NO concentation is the lowest.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.2
• /
• pp.475-483
• /
• 1993

A computer simulation model of a hermetic reciprocating type of refrigeration compressor has been developed. The compressor simulation model constitutes 6 control volumes, to each of which conservation laws of mass and energy are applied to yield full description of the refrigerant state along its passage. Instead of ideal gas assumption. real gas equation is employed. Some of valve-related input data required for the simulation are acquired from test bench experiments. The refrigerant states such as pressure and temperature, etc., mass flow rates, and valve motions can be predicted by the simulation. The calculated P-V diagram shows a good agreement with experimental result.