• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.419-423
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• 2011

Unlike other non-destructive inspection method, AE Structural defects that are likely to grow in the operation status can be detected, and the advantage of being due to the continuous monitoring of large structures has been widely used to evaluate the stability. AE sensor used to detect sound wave that occurs between 20kHz to 20MHz. and Sound wave result may vary depending on sensor's sensitivity. In this paper, Tensile test conducted on STS 304 and SS400, and tries to detect the crack signal. In tensile test, specimens were conducted using different sensor sensitivity to the same tensile test condition. The crack signal parameters divided into 4 types of communities by conducting cluster analysis. It was demonstrated that crack signal of two sensor is not different by statistical analysis of null hypotheses. Based on the results, waveform of this tension test is crack signal.

• Journal of the Korean Society for Railway
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• v.19 no.5
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• pp.565-575
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• 2016

Wheel reprofiling is frequently conducted to remove faults such as flange wear, flat areas, and cracks that occur in railway vehicle operation. We analyzed the dynamic performances of a vehicle before and after wheel reprofiling to grasp the influence of reprofiling on the dynamic behavior of the vehicle. We measured the wheel profile of the test vehicle and conducted a running test to analyze the vibration and comfort characteristics of the test vehicle. The result of the test indicated that vibration of the test vehicle after wheel reprofiling was reduced compared to that before wheel reprofiling. And, comfort level of the test vehicle after wheel reprofiling was improved by about 3dB laterally and vertically. Consequently, the positive effect of wheel reprofiling on the dynamic performance of vehicle was verified.

• Journal of IKEEE
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• v.24 no.1
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• pp.216-224
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• 2020

This paper proposes an impedance design method of the test device for evaluating Low Voltage Ride Through(LVRT) and High Voltage Ride Through(HVRT) functions. The LVRT/HVRT test device should have ability to generate the fault voltage specified in the grid code for a certain period and to limit the magnitude of the fault current with the design specification. In this paper, the impedance design method for auto transformer is proposed based on a equivalent model of a tap-change auto-transformer during LVRT/HVRT operation. In addition, to generate various fault voltages required the LVRT/HVRT test, tap impedance design in the auto transformer is considered. To verify the validity of the proposed design method, the design process of the 10MVA LVRT/HVRT test device was conducted and the design results was verified through simulation models.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.12
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• pp.1093-1098
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• 2007

Tilting trains are currently in operation in 13 countries around the world. With the advances in tilting technology, verification of economic efficiency, and changes in economic situations, the introduction of tilting trains will rapidly spread across the globe. The measurement system is composed of the industrial computers installed in the console and the measurement racks mounted on each car. It is utilized to accumulate the data by the communication card and the optical cable. The optical cable and power cable are coupled at the connector located in joint of train to make easy to disconnect car each other. The signal conditioner is designed to choose and to extend the channel for each sensor readily. The sensor measurement rack has adopted as decentralization method. It is installed in each car to minimize the cable length. In also, it is manufactured based on 19"rack and covered to protect the cable. In this study, the programs for measurement and analysis were also developed to understand the traction system characteristics of TTX. Using this measurement system, we studied that acceleration test, re-powering test, and gradually powering test. The acceleration performance of TTX is 1.735 km/h/s, and it is inner standard value. The notch test result from 1 to 7 steps, DC link voltage is under standard value, and the output electric current of inverter is controlled normally. From the test results, we saw the performances of the traction systems are normal.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.625-638
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• 2016

This paper presents field study and numerical modeling results for a single-cell low-fill concrete box culvert under a flexible pavement subjected to traffic loading. The culvert in the field test was instrumented with displacement transducers to capture the deformations resulting from different combinations of static and traffic loads. A low-boy truck with a known axle configuration and loads was used to apply seven static load combinations and traffic loads at different speeds. Deflections under the culvert roof were measured during loading. Soil and pavement samples were obtained by drilling operation on the test site. The properties of the soil and pavement layers were determined in the laboratory. A 3-D numerical model of the culvert was developed using a finite difference program FLAC3D. Linear elastic models were used for the pavement layers and soil. The numerical results with the material properties determined in the laboratory were compared with the field test results. The observed deflections in the field test were generally smaller under moving loads than static loads. The maximum deflections measured during the static and traffic loads were 0.6 mm and 0.41 mm respectively. The deflections computed by the numerical method were in good agreement with those observed in the field test. The deflection profiles obtained from the field test and the numerical simulation suggest that the traffic load acted more like a concentrated load distributed over a limited area on the culvert. Elastic models for culverts, pavement layers, and surrounding soil are appropriate for numerical modeling of box culverts under loading for load rating purposes.

• English Language & Literature Teaching
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• v.8 no.1
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• pp.165-198
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• 2002

The purpose of this research is to improve the writing ability of students by an ideal test model of English writing based on strategies of procedural learning stages enhancing the level of students' writing ability. Assessment of writing in the field of English education has been limited so far to very restricted areas with no appropriate scientific scrutiny. Assessment is really meaningful only when it exactly estimates the ability of students. Since English writing competence has become indispensable in this era of global village, writing instruction should be most emphasized. The most forceful method of busting writing instruction is to utilize the so-called washback effect of testing. So, to develop a good test model of writing, the first thing that is required is to inspect writing strategy in steps and, then, testing itself. First of all, analyzed with a special reference to the 6th high school English curriculum were the goals and contents of the syllabus reflected in one kind of junior high textbook and eight different kinds of senior high textbooks. Then questionnaires on the whole area of writing and tendencies of English writing classes were given to 100 English teachers, 300 students. The results of questionnaires were statistically analyzed. Then, some suggestions and opinions about the questioning method were made: the procedural strategy in steps, English writing instruction and test model of assessment were applied to the syllabus referring to teaching plans. On the bases of the results of the questionnaires, three pretests and a final test of English writing were administered to verify the effect of enhanced English writing competence which had been gradually promoted and, through the promotion, produced the test criteria of English writing. In conclusion, guidance and evaluation of English writing through in steps are really indispensable to increase student's practical ability and, accordingly, we are in need of the development of a testing method of useful writing practiced in school class above anything else. So, it is necessary to further the study on methods to assess writing ability on the bases of participation and fluency of students with their keen interest in English. Also, to intensify the effect of the test model, more accommodating reorganization of syllabus is required in our education. For instance, we need a flexible operation in organizing time units from the current 50 minutes to 100-130 minutes.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.290-293
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• 2017

A direct-connected, continuous type combustion test facility was developed to test a supersonic combustor model used in scramjet engines. The facility requirements were determined by assuming the flight speed of Mach 5, yielding the combustor inlet flow speed of Mach 2. Also the cross-section of the supersonic combustor under test was assumed as $32mm{\times}70mm$. As a result, the facility was designed to have the flow total pressure of 548 kPaA, total temperature of 1,320 K, and flow rate of 0.776 kg/s. The facility consists of a turbo type air compressor, electric air heater, vitiation air heater and a two dimensional facility nozzle to accelerate the flow to Mach 2. Also, an oxygen supply system was added to compensate the vitiation. The exhaust de-pressurization system is not added. Designed pressure, temperature, and flow rate were verified through the test operation of the facility.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.53 no.3
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• pp.276-285
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• 2017

The research vessel NARA equipped with an azimuth thruster system was built in 2015. There are few vessels with this propulsion system in Korea. This vessel has two modes such as the normal for maneuvering and the power for investigation, and the other two modes as one axis and two axes on the operating. This type of vessels does not seem to have a clear grasp of the maneuvering character in comparison with the vessel with a conventional propulsion system. So the authors carried out the sea test for the turning, the zigzag and the inclination, and the results are as follows. In turning test, the case of using the two axes mode is much better than the case of using the one axis mode for the elements of turning, such as advance, transfer, tactical diameter and final diameter, but turning hard over the rudder in full speed is very vulnerable to capsize in both modes. In zigzag test, the yaw quicking responsibility index, T is very large excessively, which means a bad counter maneuvering ability, so an operator has to keep in mind that in turning operation. If necessary to avoid collision at head on situation, it may be a more effective method to use the crash astern stop than the turning according to the conditions and circumstances for the shortest stopping distance is very short.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.109-114
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• 2008

This paper presents the development status of a subscale precooled turbojet engine "S-engine" for the hypersonic cruiser and space place. S-engine employs the precooled-cycle using liquid hydrogen as fuel and coolant. It has $23cm{\times}23cm$ of rectangular cross section, 2.6 m of the overall length and about 100 kg of the target weight employing composite materials for a variable-geometry rectangular air-intake and nozzle. The design thrust and specific impulse at sea-level-static(SLS) are 1.2 kN and 2,000 sec respectively. After the system design and component tests, a prototype engine made of metal was manufactured and provided for the system firing test using gaseous hydrogen in March 2007. The core engine performance could be verified in this test. The second firing test using liquid hydrogen was conducted in October 2007. The engine, fuel supplying system and control system for the next flight test were used in this test. We verified the engine start-up sequence, compressor-turbine matching and performance of system and components. A flight test of S-engine is to be conducted by the Balloon-based Operation Vehicle(BOV) at Taiki town in Hokkaido in October 2008. The vehicle is about 5 m in length, 0.55 m in diameter and 500 kg in weight. The vehicle is dropped from an altitude of 40 km by a high-altitude observation balloon. After 40 second free-fall, the vehicle pulls up and S-engine operates for 60 seconds up to Mach 2. High altitude tests of the engine components corresponding to the BOV flight condition are also conducted.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.144-152
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• 2011

In order to investigate the operation performance behaviors of the UAV's propulsion system to be operated long time in high altitude, the engine performance tests, which are simulated in the altitude engine test facility should be needed. If the test is performed in a existing altitude engine test facility, additional test apparatuses are required. Among them a proper design of the inlet and exhaust ducts that may directly affect the engine performance is very important. If the design is not adequate, the engine performance loss due to the flow behavior change and the pressure loss may be not similar to the real engine performance. In this work, firstly the engine inlet and exhaust ducts to be mounted to the existing altitude facility are modelled in 3D and its flow behaviors and pressure losses are analyzed using a commercial CFD tool, ANSYS's CFX, and the engine performance with the duct losses is calculated using the performance analysis program developed by C. Kong et al. Finally, the optimized inlet and exhaust ducts' configurations are proposed through the repeated analyses of various duct configurations.