• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.12
• /
• pp.3317-3328
• /
• 1995

The objective of the present study is to predict the characteristics of heat and mass transfer around an evaporative condenser. Numerical calculations have been performed using multi-zone method to investigate heat transfer rate and evaporation rate with the variation of inlet condition(velocity, relative humidity and temperature) of the moist air, the flow rate of the cooling water and the shape of the condenser tube. From the results it is found that the profile of heat flux is the same as that of evaporation rate since heat transfer along the gas-liquid interface is dominated by the transport of latent heat in association with the vaporization(evaporation) of the liquid film. The evaporation rate and heat transfer rate is increased as mass flow rate increases or relative humidity and temperature decrease respectively. But the flow rate of the cooling water hardly affect the evaporation rate and heat flux along the gas-liquid interface. The elliptic tube which the ratio of semi-minor axis to semi-major axis is 0.8 is more effective than the circular tube because the pressure drop is decreased. But the evaporation rate and heat flux shown independency on the tube shape.

• Computers and Concrete
• /
• v.15 no.5
• /
• pp.735-758
• /
• 2015

This work deals with unilateral effect of quasi-brittle materials, such as concrete. For this propose, a two-dimensional meso-scale model is presented. The material is considered as a three-phase material consisting of interface zone, matrix and inclusions - each constituent modeled by an appropriate constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes randomly placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements developed here in order to capture the effects of phase debonding and interface crack closure/opening. As an initial approximation, the inclusion is modeled as linear elastic as well as the matrix. Our main goal here is to show a computational homogenization-based approach as an alternative to complex macroscopic constitutive models for the mechanical behavior of the quasi-brittle materials using a finite element procedure within a purely kinematical multi-scale framework. A set of numerical examples, involving the microcracking processes, is provided. It illustrates the performance of the proposed model. In summary, the proposed homogenization-based model is found to be a suitable tool for the identification of macroscopic mechanical behavior of quasi-brittle materials dealing with unilateral effect.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.3
• /
• pp.19-25
• /
• 2010

The purpose of this study is to gain a better understanding of the effects of fuel stratification on reducing the pressure-rise rate at high load in HCCI combustion. It was found that fuel stratification offers good potential to achieve a staged combustion event and reduced pressure-rise rates. The engine is fueled with Di-Methyl Ether (DME) which has unique 2-stage heat release. Numerical analysis is conducted with single and multi-zones model and detailed chemical reaction scheme is done by chemkin and senkin. Calculation result shows that proper fuel stratification prolongs combustion duration and reduce pressure rise rate. Besides IMEP, combustion efficiency and indicated thermal efficiency keep constant. However, too wide fuel stratification increases pressure rise rate and CO and NOx emissions in exhaust gas.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.42 no.11
• /
• pp.911-918
• /
• 2014

In this paper, a selective activation strategy of cohesive elements using user subroutine UMPC was studied as an efficient solution for the added compliance problem in cohesive zone model crack propagation analyses. The cohesive elements were inserted between every bulk elements in region where cracks were expected to initiate and propagate, but initially not activated by tying the cohesive nodes using multi-point constraints. During analyses, the cohesive elements for which specified criterion was met were selectively activated by releasing the constraints. The effect of initial cohesive stiffness and the release criterion on the crack propagation behavior was carefully investigated.

• Ocean Systems Engineering
• /
• v.4 no.2
• /
• pp.83-97
• /
• 2014

Wave propagation in a three-dimensional (3D) fully nonlinear numerical wave tank (NWT) is studied based on velocity potential theory. The governing Laplace equation with fully nonlinear boundary conditions on the moving free surface is solved using the indirect desingularized boundary integral equation method (DBIEM). The fourth-order predictor-corrector Adams-Bashforth-Moulton scheme (ABM4) and mixed Eulerian-Lagrangian (MEL) method are used for the time-stepping integration of the free surface boundary conditions. A smoothing algorithm, B-spline, is applied to eliminate the possible saw-tooth instabilities. The artificial wave speed employed in MTF (multi-transmitting formula) approach is investigated for fully nonlinear wave problem. The numerical results from incorporating the damping zone (DZ), MTF and MTF coupled DZ (MTF+DZ) methods as radiation condition are compared with analytical solution. An effective MTF+DZ method is finally adopted to simulate the 3D linear wave, second-order wave and irregular wave propagation. It is shown that the MTF+DZ method can be used for simulating fully nonlinear wave propagation very efficiently.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.57 no.6
• /
• pp.1-7
• /
• 2015

Most of chloride diffusion models based on finite difference method (FDM) could not express the diffusion in horizontal direction at each elevation. To overcome these weakness, two dimensional chloride ion penetration model based on finite element method (FEM) to be able to combine various multi-physics simultaneously was suggested by introducing moving mesh technique. To avoid the generation of mesh being able to be distorted depending on the relative movement of water level to static concrete, a rectangular type of mesh was intentionally adopted and the total number of meshes was empirically selected. The simulated results showed that the contents of surface chloride decreased following to the increase of elevation in the top part of low sea level, whereas there were no changes in the bottom part of low level. In the DuraCrete model, the diffusion coefficient of splashed zone is generally smaller than submerged zone, whereas the trend of Life365 model is reverse. Therefore, it could be understood that the developed model using moving mesh technique effectively reflects $DuraCrete^{TM}$ model rather than $Life365^{TM}$ model. In the future, the model will be easily expanded to be combined with various multi-physics models considering water evaporation, heat of hydration, irradiation effect of sun and so on because it is based on FEM.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.2
• /
• pp.174-182
• /
• 2012

In previous research, most occupant said that they have not operated ventilation system installed in the house, because of increasing of energy consumption and unconcern of ventilation. Therefore, it is necessary to applied the sensor based demand controlled ventilation for the IAQ(Indoor Air Quality) and improvement of energy efficiency in ventilation strategy. The propose of this study is to present a application method of IR(Infrared) sensor for multi-zone DCV(Demand Controlled Ventilation) in the apartment house. It is possible that IR sensor could be used for DCV, because that could detect the occupant and action. IR sensor based DCV strategies are established to evaluate characteristic of application in the apartment house and simulated by Contam program. As a result, they have some week points though, if they would be applied DCV with optimum strategy, it would be useful to improve IAQ, to reduce energy consumption.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.18 no.10
• /
• pp.93-98
• /
• 2019

Recently, with the development of the aerospace and automotive industries, the demand for high-melting-point materials has increased. However, high-melting-point materials are difficult to cut through conventional machining methods. Thermally assisted machining (TAM) is a method for improving the machinability by preheating the materials. A laser, the most commonly used device for TAM, has high efficiency through local preheating but is not sufficient for maintaining a high preheating temperature due to rapid cooling. However, the use of multi-heat sources can supplement the disadvantage of a single heat source. The high preheating temperature can be maintained with a wide and deep heat-affected zone (HAZ) by multi-heat sources. The purpose of this study is to analyze the preheating effects of multi-heat sources using laser plasma. Thermal analysis and preheating experiments were carried out. As a result, the high preheating effect of multi-heat sources compared with a single heat source was verified.

• Journal of Soil and Groundwater Environment
• /
• v.25 no.4
• /
• pp.58-66
• /
• 2020

Since the typical horn-type ultrasonic equipment induces a reaction at the probe tip, the sonochemical reaction has a limitation that it occurs only in a specific area. As one of the ways to overcome this limitation, an ultrasonic device with multi-stepped horn equipped with several oscillators has been developed. The objective of this study was to investigate the sonochemical effects induced by acoustic cavitation system in 20 kHz multi-stepped ultrasonic horn using calorimetry, KI dosimetry and the luminol test. The sonochemical effects of multi-stepped ultrasonic horn were compared with that of the typical horn-type 20 kHz ultrasonic device. The effect of immersion depth and power on the sonochemical reaction was investigated in the ultrasonic system with multi-stepped ultrasonic horn. Higher calorimetric energy was obtained at higher immersion depth and power conditions. Sonochemical effects increased significantly when using the high immersion depth and input power. However, as the input power increased, the cavitation reaction zone concentrated around the ultrasonic horn. Additionally, the experiments to examine the effect of liquid temperature was conducted. The smaller sonochemical reaction was obtained for the higher liquid temperature. The effect on temperature seems to be closely related to liquid conditions such as viscosity and vapor pressure of water.

• The Journal of Fisheries Business Administration
• /
• v.40 no.2
• /
• pp.71-103
• /
• 2009

This study is designed to propose the ways of the multilateral cooperation system for effective management of fisheries resources in the various overlapping zones established by bilateral fisheries agreements between Korea, China and Japan in North East Asia as semi-enclosed sea. It is necessary to build multilateral fisheries cooperation between Korea, China and Japan in North East Asia because conservation & management of transboundary fish stocks could not be guaranted effectively by the management of fisheries resources in the area where piled up the current-fishing-pattern zone, as white zone and the various grey zone as middle zone, and the interim measures zone of bilateral fisheries agreements between Korea, China and Japan are piled up. Fisheries management in Korea, China and Japan by the bilateral fisheries agreements in North East Asia is faced with difficulties manage fisheries resources. International relationship on fisheries is maintained by bilateral fisheries agreements based on UNCLOS. However fisheries resources are over-exploited and the recovery of the fisheries resources is very slow because proper conservation and management of transboundary fish stocks which article 63(1) of UNCLOS defines have not prepared yet. Thus close cooperation among the coastal States for a proper conservation and management of transboundary fish stocks is necessary. Since the transboundary fish migrate within the EEZs of two or more coastal States, there is a need to manage the fish stocks in the region between Korea, China and Japan through a multi-lateral mechanism at ccircumference area of the current-fishing-pattern zone as white zone. Coastal States must guarantee sustainable maintenance of transboundary fish stocks through the regional cooperation for a proper conservation & management because one coastal State alone could not guarantee conservation and management of fish stocks. Thus there is a need to build multilateral fisheries cooperation between Korea, China and Japan in North East Asia. There are many successful instances including the Barents' sea for a proper conservation & management of transboundary fish stocks. The Barents' sea is one of the best research object to study the regional cooperation for a conservation & management of transboundary fish stocks in North East Asia. In conclusion, it is necessary to build a multilateral fisheries cooperation system between Korea, China and Japan in North East Asia to conserve and manage transboundary fish stocks effectively. It seems desirable that the range of the area to conserve and manage fish stocks should may be any partial area in the current-fishing-pattern zone and interim measures zone between Korea and China, Jeju middle zone between Korea and Japan, interim measures zone of bilateral fisheries agreements between China and Japan.