• Journal of Advanced Marine Engineering and Technology
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• v.28 no.4
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• pp.648-656
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• 2004

In this study, a highly efficient shell-and-tube heat exchanger with plate fins is considered to improve thermal performance of the conventional shell-and-tube heat exchanger. This type of shell-and-tube heat exchanger with plate fins of various shape is simulated three-dimensionally using a commercial thermal-fluid analysis code. CFX4.4. The effect of the shape of the plate fin on heat transfer characteristics is also investigated by the simulation. Plate fins of four different shapes. plane, plane-slit. wave. and wave-slit fins, are considered. The flow fields, pressure drop and heat transfer characteristics in the heat exchanger are calculated. It is proved that the shell-and-tube heat exchanger with plate fins is superior to the conventional shell-and-tube heat exchanger without plate fins in terms of heat transfer. The shape of the plate fin is important in the performance of a heat exchanger such as heat transfer and pressure drop.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.3
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• pp.229-238
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• 2016

In this paper, we have studied isolation enhancement using a suppression of surface wave to improve performance of array antenna. To reduce isolation between elements of array antenna, perfect magnetic conductor(PMC) and SOFT-surface is designed and located at center of ground plane, isolation and gain is simulated by commercial full wave simulator(HFSS). As a result, isolation of more than 40 dB and gain improvement of 2.2 dBi are obtained at E-plane array in case of both PMC and SOFT-surface. At H-plane array, air coupling is dominant compared to coupling by surface wave. It is conclude that this study is useful for design of compact array antenna and performance improvement of array antenna.

• Journal of Aerospace System Engineering
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• v.10 no.1
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• pp.86-94
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• 2016

In this paper, position control of focal plane compensation device using piezoelectric actuator is conducted. The forcal plane compensation device installed on earth observation satellite camera compensates micro-vibration from reaction wheels. In this study, four experimental models of the open-loop compensation device are derived using MATLAB system identification toolbox in the input range of 0~50Hz. Subsequently, the PID controller for each model is designed and the performance test of each controller is conducted through MATLAB/Simulink. According to frequency response analysis of the closed-loop compensation device system, the PID controller designed for 38~50Hz input range has enough tracking performance for the whole 0~50Hz input range. The maximum output error is about $1{\mu}m$ for the input range. The simulation results has been verified by the experimental method.

• The Journal of the Acoustical Society of Korea
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• v.18 no.6
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• pp.17-30
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• 1999

This paper proposes a new stereophonic acoustic echo canceller to prevent impairments on the voice quality and to remove acoustic echo effectively appearing in stereo environment at the instant of abrupt change of the transmission room environment in teleconferencing system. In stereophonic acoustic echo canceller, the major defective problems are the large computational complexity of estimating echo path systems due to the long impulse response of the true echo paths and the performance degradation of echo canceller due to large correlation between dual stereo signals. Moreover, the change of the suboptimal solution for the echo canceller was considered as a critical deficient factor on to the performance of stereophonic echo canceller. To overcome these problems, this paper proposes pseudo stereophonic acoustic echo canceller using Hyper-plane projection algorithm, which shows the robustness to the environment change of the transmission room and the efficiency of computational complexity.

• Earthquakes and Structures
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• v.19 no.6
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• pp.459-469
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• 2020

An external prestressed steel-bar truss unit was developed as a new strengthening technology to enhance the seismic performance of an in-plane masonry wall structure while taking advantage of the benefits of a prestressed system. The presented method consists of six steel bars: two prestressed vertical bars to introduce a prestressing force on the masonry wall, two diagonal bars to resist shear deformation, and two horizontal bars to maintain the configuration. To evaluate the effects of this new technique, four full-scale specimens, including a control specimen, were tested under combined loadings that included constant-gravity axial loads and cyclic lateral loads. The experimental results were analyzed in terms of the shear strength, initial stiffness, dissipated energy, and strain history. The efficiency of the external prestressed steel-bar truss unit was validated. In particular, a retrofitted specimen with an axial load level of 0.024 exhibited a more stable post behavior and higher energy dissipation than a control specimen with an observed complete sliding failure. The four vertical bars of the adjacent retrofitting units created a virtual column, and their strain values did not change until they reached the peak shear strength. The shear capacity of the masonry wall structure with external prestressed steel-bar truss units could be predicted using the model suggested by Yang et al.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.16-24
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• 2021

This experimental study was conducted to evaluate the in-plane and out-of-plane seismic performances of an unreinforced masonry walls (URMs) strengthened with prestressed steel-bar truss systems developed in the present investigation. The truss systems were installed on both faces of the walls. All the wall specimens were subjected to lateral in-plane or out-of-plane cyclic loads at the fixed gravity stress of 0.25 MPa. The seismic performance of the strengthened specimens was compared to that measured in the counterpart URM. When compared with the lateral load-displacement curve of the URM, the strengthened walls exhibited the following improvements: 190% for initial stiffness, 180% for peak strength, 610% for accumulated energy dissipation capacity, and 510% for equivalent damping ratio under the in-plane state; the corresponding improvements under the out-of-plane state were 230% for initial stiffness, 190% for peak strength, 240% for accumulated energy dissipation capacity, and 120% for equivalent damping ratio, respectively. These results indicate that the developed technique is very promising in enhancing the overall seismic performance of URM.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.15-23
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• 1998

A three dimensional simulation of the fluid flow in an automotive torque converter was conducted adopting the mixing plane model implemented in the computational fluid dynamics program CFD-ACE. The present numerical results for performance characteristics showed a good agreement with the experimental results. In the flow of the torque converter, recirculating flow regimes were found mostly at the suction side of each element, which caused the performance decrease. The recirculating flow can be minimized by the optimization of the blade geometries.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.40-45
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• 2001

Recently, the use of numerical simulation has been increased rapidly because of the development of high performance computer systems. The present study is aimed to investigate flow characteristics of a two-dimensional sharp plane. Unsteady calculation by FDM(Finite Difference Method) based upon SOLA scheme which was performed at $Re=2{\times}10^4$in viscous incompressible flow within a finite domain on the irregular grid formation. Total numbers of irregular grids are $8{\times}10^4$. The minimum grid size is 1/100 of the plane length L which is the representative length. The inclined angles of every objects are $15^{\circ}, \;30^{\circ}\;and\; 45^{\circ}.$ And, the edge angle of the plane is $30^{\circ}.$ This study discussed the flow characteristics in term of the turbulent intensity, vorticity and frequency analysis. Developed flows show that the periodic Karman vortices occur at the back of the plane.

• Tribology and Lubricants
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• v.19 no.6
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• pp.311-320
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• 2003

In this study a general Galerkin FE formulation of the incompressible Reynolds equation is derived for lubrication analyses of noncontacting mechanical face seals. Then, the formulation is applied to analyze the flexibly mounted stator­type reactor coolant pump seals of local nuclear power plants, which have deep straight grooves or plane coning on their primary seal ring faces. Their various lubrication performances have been predicted. Results show that the analyzed deep straight groove seal should have a net coning of less than 0.6 to satisfy the leakage limit. And for the same amount of equilibrium opening force the plane coning seal requires to have a 3 times higher dimensionless coning than the deep straight groove seal.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2003.11a
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• pp.193-200
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• 2003

In this study a general Galerkin FE formulation of the incompressible Reynolds equation is derived for lubrication analyses of noncontacting mechanical face seals. Then, the formulation is applied to analyze the flexibly mounted stator-type reactor coolant pump seals of local nuclear power plants, which have deep straight grooves or plane coning on their primary seal ring faces. Their various lubrication performances have been predicted. Results show that the analyzed deep straight groove seal should have a net coning of less than $0.6\;{\mu}m$ to satisfy the leakage limit. And for the same amount of equilibrium opening force the plane coning seal requires to have a 3 times higher dimensionless coning than the deep straight groove seal.