• Journal of the Korean Institute of Gas
• /
• v.16 no.2
• /
• pp.31-37
• /
• 2012

This paper describes to analyze the ventilation performance of a room air conditioner for indoor comfort control. An experimental apparatus consists of a test room, the room air conditioner, a tracer gas measurement system, a supply fan and a controller. Ventilation performance as a function of human occupancy is evaluated with supply ventilation air using a tracer gas technique of CO2 gas in the test room. The ventilation performance is evaluated in a step-down method based on ASTM Standard E741-83 and is found to increase with increasing supply ventilation rate. The CO2 gas concentration is decayed rapidly without human occupancy. The ventilation performance without human occupancy increases up to 55% and the ventilation performance with one person increases up to 25% at the supply air of 570 lpm comparing with a natural reduction after one hour. A modeling for ventilation performance of a room air conditioner in a test room is presented using experimental datum.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.29 no.4
• /
• pp.309-315
• /
• 2016

Recently, finite element analysis technique has been widely used for structural and mechanical understandings of human body in the dentistry field. This research proposed an effective finite element modeling method based on CT images, and parametric studies were performed for the occlusal simulation. The analyses were performed considering linear material behaviors and nonlinear geometrical effect, and validated with the experimental results. In addition, the skull models with two different molar relations such as Class I and full-CUSP Class II were generated and the analyses were performed using the proposed analytical method. As results, the relationships between the mandibular movement and occlusal force of both two models showed similar tendency in human occlusal force. However, stress was evenly distributed from teeth to facial bone in the skull model with Class I, while stress concentration was appeared in the model with full-CUSP Class II due to the changes of occlusal surfaces of the model.

• Steel and Composite Structures
• /
• v.37 no.2
• /
• pp.117-136
• /
• 2020

Curved steel-concrete composite box girder has been widely adopted in urban overpasses and ramp bridges. In order to investigate its mechanical behavior under complicated and combined bending, shear and torsion load, two large-curvature composite box girders with interior angles of 25° and 45° were tested under static hogging moment. Based on the strain and deflection measurement on critical cross-sections during the static loading test, the failure mode, cracking behavior, load-displacement relationship, and strain distribution in the steel plate and rebar were investigated in detail. The test result showed the large-curvature composite box girders exhibited notable shear lag in the concrete slab and steel girder. Also, the constraint torsion and distortion effect caused the stress measured at the inner side of the composite beam to be notably higher than that of the outer side. The strain distribution in the steel web was approximately linear; therefore, the assumption that the plane section remains plane was approximately validated based on strain measurement at steel web. Furthermore, the full-process non-linear elaborate finite element (FE) models of the two specimens were developed based on commercial FE software MSC.MARC. The modeling scheme and constitutive model were illustrated in detail. Based on the comparison between the FE model and test results, the FE model effectively simulated the failure mode, the load-displacement curve, and the strain development of longitudinal rebar and steel girder with sufficient accuracy. The comparison between the FE model and the test result validated the accuracy of the developed FE model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.3
• /
• pp.245-252
• /
• 2007

The important problems from the point of view of preventing global warming are to save the power consumption of automotive air-conditioning systems and reduce the refrigerant amount filled. To achieve such requirements, integral receiver/dryer (R/D) condensers were developed recently. Typical integral R/D condensers have extra headers that play the role of R/D. Except an extra header and somewhat complex tube array resulting from the extra header, the most integral R/D condensers have almost the same specification that tube has multi channels, fin has louvers, flow in tube is parallel, etc. When integral condensers are applied, it is known that the refrigerating effect increases, resulting from the increase of subcooling degree in condenser, and the refrigerant amount used saves. In spite of several merits, integral condensers have not been applied a lot. That is why there is an uncertainty in performance, using integral condensers. The objective of this study is to theoretically optimize the tube array in an integral R/D condenser that is really being applied to some vehicles. The tube array has a great effect on the performance of the integral condenser as well as common ones. Through computer simulation, we could see that the tube array, 14-6-3-5-3-4, in the same condenser was the best, comparing heat release rate, pressure drop, etc. to the real array, 17-5-3-3-2-5. It should be noted that the optimization is based on the condenser performance only.

• Journal of Institute of Control, Robotics and Systems
• /
• v.22 no.4
• /
• pp.293-300
• /
• 2016

The Voice recognition is one of convenient methods to communicate between human and robots. This study proposes a speech recognition method using speech recognizers based on Hidden Markov Model (HMM) with a combination of techniques to enhance a biped robot control. In the past, Artificial Neural Networks (ANN) and Dynamic Time Wrapping (DTW) were used, however, currently they are less commonly applied to speech recognition systems. This Research confirms that the HMM, an accepted high-performance technique, can be successfully employed to model speech signals. High recognition accuracy can be obtained by using HMMs. Apart from speech modeling techniques, multiple feature extraction methods have been studied to find speech stresses caused by emotions and the environment to improve speech recognition rates. The procedure consisted of 2 parts: one is recognizing robot commands using multiple HMM recognizers, and the other is sending recognized commands to control a robot. In this paper, a practical voice recognition system which can recognize a lot of task commands is proposed. The proposed system consists of a general purpose microprocessor and a useful voice recognition processor which can recognize a limited number of voice patterns. By simulation and experiment, it was illustrated the reliability of voice recognition rates for application of the manufacturing process.

• Journal of IKEEE
• /
• v.21 no.4
• /
• pp.338-347
• /
• 2017

This paper describes the design and fabrication of a high power amplifier which is a component of TDL(Tactical Data Link) aircraft terminal. We applied high-speed frequency hopping technology, cognitive radio technology, and receive filter bank technology to efficiently use limited frequency resources with radar and other communication equipment using the same frequency band. The high-power amplifier is physically composed of a transmitter, a receiver, a mechanical part, and a cable assembly, and is designed to meet temperature characteristics and electrical characteristics such as maximum transmission distance and reception sensitivity. Modeling and simulator were used to satisfy the requirement of high power amplifier. The transmit power and the noise figure were measured at 50.02dBm and 2.682dB, respectively. It was confirmed that all the required specifications were satisfied in the electrical characteristics test and the environmental characteristic test.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.536-542
• /
• 2017

A great deal of difficulty is encountered in the thermo-mechanical analyses of nozzle assembly for solid propellant rocket motors. The main issue in this paper is the modeling of the boundary conditions and the connections between the various components-gaps, relative movements of the components, contacts, friction, etc. This paper evaluated the complex phenomena of nozzle assembly during burning time with co-simulation which include fluid, thermal surface reaction/ablation and structural analysis. The validity of this approach was verified by comparison of analysis results with measured strains.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.939-941
• /
• 2017

The use of composites is increasing for lightweight aerospace structures. Among these structures, the ring frame and the parts of the projectile body are mainly made of a fiber reinforced composite material which is less susceptible such as delamination to structural damage. As the use of fiber reinforced composites increases, interest in modeling efficient methods of stiffness and strength is increasing. This paper predict the mechanical strength according to the repeating unit cell(RUC) of the 2-D triaxial braided composites of fiber reinforced composites. Yarn slice definition, incremental approach and stiffness reduction model were used as strength prediction. Finally, the results of strength prediction are verified by comparing with experimental data of 2-D triaxial braided composites specimens.

• Steel and Composite Structures
• /
• v.20 no.3
• /
• pp.651-669
• /
• 2016

The behavior of shear connectors plays a significant role in maintaining the required strength of a composite beam in normal and hazardous conditions. Various types of shear connectors are available and being utilized in the construction industry according to their use. Channel connectors are a suitable replacement for conventional shear connectors. These connectors have been tested under different types of loading at ambient temperature; however, the behavior of these connectors at elevated temperatures has not been studied. This investigation proposes a numerical analysis approach to estimate the behavior of channel connectors under fire and compare it with the numerical analysis performed in headed stud and Perfobond shear connectors subjected to fire. This paper first reviews the mechanism of various types of shear connectors and then proposes a non-linear thermo-mechanical finite element (FE) model of channel shear connectors embedded in high-strength concrete (HSC) subjected to fire. Initially, an accurate nonlinear FE model of the specimens tested at ambient temperature was developed to investigate the strength of the channel-type connectors embedded in an HSC slab. The outcomes were verified with the experimental study performed on the testing of channel connectors at ambient temperature by Shariati et al. (2012). The FE model at ambient temperature was extended to identify the behavior of channel connectors subjected to fire. A comparative study is performed to evaluate the performance of channel connectors against headed stud and Perfobond shear connectors. The channel connectors were found to be a more economical and easy-to-apply alternative to conventional shear connectors.

• 한국태양에너지학회:학술대회논문집
• /
• 2009.11a
• /
• pp.80-85
• /
• 2009

Mathematical modeling and performance simulation results were shown for the solar thermal storage system which used heat pipe. The thermal storage system was composed of thermal storage tank and charging/discharging heat exchanger with one by the heat pipes. Heat pipe heat exchanger was attached to system, and could carry out charging and discharging to thermal storage tank at the same time. Height of the thermal storage tank was 600 mm, and that of the charging/discharging heat exchanger was 400 mm. Length of the heat pipe was the same as the total height of thermal storage system, and outer and inner diameter were 25.4 mm(O.D.) and 21.4 mm(I.D.) respectively. Diameter of the circular was 43 mm(O.D.), and fin geometries were considered as the design parameters. High temperature phase change material(PCM), $KNO_3$ and low temperature PCM, $LINO_3$ were charged to storage tank to adjust working temperature. Total size of thermal storage system able to get heat capacity more than 500 kW was calculated and the results were shown in this study. Number of heat pipe was required more than maximum 500, and total length of thermal storage system was calculated to the more than maximum 3 m at various condition.