• 한국농공학회논문집
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• 제52권3호
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• pp.73-79
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• 2010

In the present study, the loading frequency dependencies of cyclic shear strength and elastic shear modulus of reconstituted clay were examined by performing undrained cyclic triaxial tests and undrained cyclic triaxial tests to determine deformation properties. The result of undrained cyclic triaxial test of reconstituted and saturated clay shows that a faster frequency leads to higher stress amplitude ratio, but when the frequency becomes fast up to a certain point, the stress amplitude ratio will reach its maximum limit and the frequency dependence becomes insignificant. And also, the result of undrained cyclic triaxial deformation test shows a fact that a faster loading frequency leads to higher equivalent shear modules and smaller hysteresis damping ratio, and confirms the frequency dependence of cohesive soil. Meanwhile, the result of the creep test shows that continuing creep is created in the undrained cyclic triaxial test with slow loading frequency rate, and since loading rate becomes slower at the vicinity of the maximum and the minimum deviator stress due to sine wave loading, the vicinity of the maximum and the minimum deviator stress shall be more influenced by creep.

• 대한조선학회논문집
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• 제54권2호
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• pp.125-131
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• 2017

In order to develop test and performance analysis techniques for a CRP propulsion, a CRP dynamometer which can be installed inside the model ship was designed and manufactured. The object ship was the 16000TEU container carrier, which has test results for the single propeller. The design concept of the present CRP is that forward & after propellers have the same power ratio and their RPM ratio is 0.75:1. To begin with, we checked the performance of the CRP dynamometer through the calibration and then installed it inside the model ship. After the model ship setup including the design CRP and the rudder in the Large Cavitation Tunnel(LCT), a series of model tests composed of power ratio check, propeller behind wake(PBW) test, cavitation observation and pressure fluctuation tests was conducted. Through the model test and data analysis for CRP, the experimental technique was established and the improved method for CRP design was suggested.

• 시스템엔지니어링학술지
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• 제14권2호
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• pp.41-48
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• 2018

This paper describes the systems engineering development process for the Departure from Nucleate Boiling Ratio (DNBR) algorithm using FPGA. Current Core Protection Calculator System (CPCS) requirement and DNBR logic are analyzed in the reverse engineering phase and the new FPGA based DNBR algorithm is designed in the re-engineering phase. FPGA based DNBR algorithm is developed by VHSIC Hardware Description Language (VHDL) in the implementation phase and VHDL DNBR software is verified in the software Verification & Validation phase. Test cases are developed to perform the software module test for VHDL software modules. The APR 1400 simulator is used to collect the inputs data in 100%, 75%, and 50% reactor power condition. Test input signals are injected to the software modules following test case tables and output signals are compared with the expected test value. Minimum DNBR value from developed DNBR algorithm is validated by KEPCO E&C CPCS development facility. This paper summarizes the process to develop the FPGA-based DNBR calculation algorithm using systems engineering approach.

• 한국추진공학회지
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• 제25권6호
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• pp.20-28
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• 2021

극초음속 유동 시험에 활용되고 있는 충격파 터널 등은 원하는 시험 조건을 얻기 위해 격막의 파열 압력비를 맞추어 운용한다. 주로 금속 재질로 이루어진 격막은 정확한 압력비를 맞추기 위해 특정 형태로 가공하거나 강제 파열 장치를 사용하여 개방한다. 격막의 개방 과정은 수백 microsecond 동안 파열과 변형을 통해 이루어지는데, 동일한 압력비에서도 개방 정도와 개방 소요 시간에 따라 시험 조건이 달라질 수 있을 것으로 예상된다. 본 연구에서는 격막의 두께 및 재질 차이를 반영할 수 있는 파열모델을 적용하여 수치 해석을 수행하고 충격파의 형성과 정체 조건의 특성에 대해 살펴보았다. 격막 파열로 인해 생성된 충격파의 속도는 격막 개방 속도에 비례하였으며, 격막의 최종 개폐율 및 소요 시간에 따라 저압관 끝단에 형성되는 정체 압력과 시험 시간에 차이가 나타나는 것을 확인할 수 있었다.

• Structural Engineering and Mechanics
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• 제74권5호
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• pp.657-670
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• 2020

Due to the high compressive and tensile strength of ultra-high performance concrete (UHPC), UHPC used in steel concrete composite structures provided thinner concrete layer compared to ordinary concrete. This leaded to the headed stud shear connectors embedded in UHPC had a low aspect ratio. In order to systematic investigate the effect of headed stud with low aspect ratio on the structural behaviors of steel UHPC composite structure s this paper firstly carried out a test program consisted of twelve push out specimens. The effects of stud height, aspect ratio and reinforcement bars in UHPC on the structural behaviors of headed studs were investigated. The push out test results shows that the increasing of stud height did not obviously influence the structural behaviors of headed studs and the aspect ratio of 2.16 was proved enough to take full advantage of the headed stud strength. Based on the test results, the equation considering the contribution of weld collar was modified to predict the shear strength of headed stud embedded in UHPC. The modified equation could accurately predict the shear strength of headed stud by comparing with the experimental results. On the basis of push out test results, bending tests consisted of three steel UHPC composite slabs were conducted to investigate the effect of shear connection degree on the structural behaviors of composite slabs. The bending test results revealed that the shear connection degree had a significantly influence on the failure modes and ultimate resistance of composite slabs and composite slab with connection degree of 96% in s hear span exhibited a ductile failure accompanied by the tensile yield of steel plate and crushing of UHPC. Finally, analytical model based on the failure mode of composite slabs was proposed to predict the ultimate resistance of steel UHPC composite slabs with different shear connection degrees at the interface.

• 한국소음진동공학회논문집
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• 제16권2호
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• pp.163-168
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• 2006

The PWR Nuclear Fuel assembly consists of more than 250 fuel rods that are supported by leaf springs in the cells of more than 10 Spacer Grids (SG) along the rod length. Since it is not easy to conduct mechanical tests on a full-scale model basis, the small-scaled rod bundle $(5\times5)$ which is called partial fuel assembly is generally used for various performance tests during the development stage. As one of the small-scaled tests, a flow test should be carried out in order to verify the performance of the spacer grid to obtain the Flow-Induced Vibration (FIV) characteristics of the scaled fuel assembly over the specified flow range. A vibration test should be also performed to obtain the modal parameters of the assembly prior to the flow test. In this study, we want to develop the estimation procedure of the damping ratio for the scaled test assembly. For the damping factor of the partial fuel assembly and the grid cage at the first vibration mode, as one of the vibration tests, a so-called pluck testing has been performed in air as a preliminary test prior to in-flow damping measurement test. Logarithmic decrement method is used for calculation of the damping ratio. Estimated damping ratio of the partial fuel assembly is about $0.7\%$ with reasonable error of $2\%$ for the previous results. Nonlinear behavior of the partial fuel assembly might be stem mainly from the rod-grid support configuration.

• 한국전자파학회논문지
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• 제17권3호
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• pp.272-279
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• 2006

본 논문에서는 W-CDMA(Wide band Code Division Multiple Access) 시스템에서 채널 측정 및 프레임 동기 확인에 사용되는 파일럿 비트 패턴의 프레임 동기 단어(frame synchronization words) 성능을 분석한다. 또한 W-CDMA 시스템에서는 두 개의 수신 단말기를 갖지 않고도, 다른 주파수의 측정을 하기 위해 압축 모드(compressed mode)를 사용한다. 제안된 프레임 동기용 이원 부호의 우선 쌍 간의 보완 매핑(complementary mapping) 관계를 이용하면, 압축 모드에서도 프레임 동기 특성을 유지함을 컴퓨터 시뮬레이션을 통하여 확인한다. 검출 확률과 오 경보 확률을 갖는 수신기 동작 특성(ROC: Reciever Operating Characteristic) 곡선은 LLRT(Log Likely-hood Ratio Test), GLRT(Generalied Likeiyhood Ratio Test), 연판정(soft correlation test), 경 판정(hard correlarion test)과 같은 다양한 검출법(detection metrics)을 이용하여 레일레이 페이딩 채널에서 제안된 프레임 동기 단어의 성능 분석에 사용된다. 이 논문의 파일럿 비트 패턴의 성능에 대한 연구 결과는 3세대 W-CDMA 시스템에서 프레임 동기의 설계 및 구현에 유용한 참고 자료가 될 수 있을 것이다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.503-506
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• 2005

The PWR Nuclear Fuel assembly consists of more than 250 fuel rods that are supported by leaf springs in the cells of more than 10 Spacer Grids (SG) along the rod length. Since it is not easy to conduct mechanical tests on a full-scale model basis, the small-scaled rod bundle (5$\times$5) is generally used for various performance tests during the development stage. As one of the small-scaled tests, a flow test should be carried out in order to verify the performance of the spacer grid like the coolant mixing performance and to obtain the Flow-Induced Vibration (FIV) characteristics of the rod bundle over the specified flow range. A vibration test should be also performed to obtain the modal parameters of the bundle prior to the flow test. In this study, we want to develop the estimation procedure of the damping ratio for the small scaled test bundle. For the damping factor of the rod bundle and the grid case at the first vibration mode, as one of the vibration tests, a so-called pluck testing has been performed in air as a preliminary test prior to in-flow damping measurement test. Logarithmic decrement method is used for calculation of the damping ratio. Estimated damping ratio of the rod bundle is about 0.7% with reasonable error of 2% for the previous results. Nonlinear behavior of the rod bundle might be stem mainly Iron the rod-grid support configuration.

• 한국과학교육학회지
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• 제16권3호
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• pp.314-328
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• 1996

This study investigated the literature about science process skills' evaluation to analyse transition of evaluation objectives before and after a Scholastic Ability Test for College Entrance. In the literature survey the researcher established a 3 dimensional science assessment framework with X axis as science concept, Y axis as science process skills and Z axis as problem context. In order to analysis and compare each items the researcher selected 210 items from the 1st to the 7th trials and 138 items from the 1st to 4th Scholastic Ability Test for College Entrance and sampled 2873 science achievement test items from 10 high schools. In accordance with this taxonomy the researcher analysed and compared science process skills item forms. The following results were drawn : The items were evenly distributed in all the four areas(Earth Science, Biology, Physics and Chemistry) of the science concept domain, but they were heavily concentrated on data analysis and drawing a conclusion in science process domain. In the domain of problem context school context was the majority. In spite of distribution like this the ratio on science process skills measurement items and science achievement test items was increased after the Scholastic Ability Test for College Entrance was given. Also the ratio on item expression type was increased. Item form was almost 5 options selection type in the national level test. Although there were 4 options selection type, 5 options selection type, short answer type, essay type in school level test, rising from 33.1% to 65.5% on 5 options selection type is exhibited. This study showed that the school level item form was better various than the nation level. This point like this is the evidence for the improvement toward the science process skills test and influenced by Scholastic Ability Test for College Entrance. The ratio on the item which joined with the 3 axes had a mean of 99.3% in nation level test and mean 44.9% in school achievement test level. But the ratio in the school achievement test level increased after the Scholastic Ability Test for College Entrance was given. In view of this study we must furthermore study the item types which can evaluate valjdately science process skill's five stage each and evaluation method by the high school students' problem solving patterns and features in scientific inquiry on all science process skills elements.

• 한국지반환경공학회 논문집
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• 제25권6호
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• pp.5-12
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• 2024

현재 저수지 제체의 차수성 및 안전성 확보를 위해 약액을 저압으로 주입하여 제체 손상을 최소화하는 그라우팅 공법이 보편적으로 사용되고 있으나, 내구성 확보와 체계적인 고화재의 배합비 결정방법이 정립되어 있지 않은 문제들이 있다. 본 연구에서는 원지반과 고화재를 다양한 중량비율로 교반·혼합하였을 경우 혼합체의 투수계수와 강도를 실내시험을 통해 확인하였으며, 시험결과들의 분석을 통해 최적 배합비를 제안하였다. 실내실험을 위한 공시체는 고화재의 배합량을 고려하여 제작하였다. 투수시험용 공시체는 사질토와 점성토 별 고화재 배합량 1.5kN/m³에 대해 제작하였으며, 투수시험 결과 차수 성능이 확보되어 각종 설계기준을 만족하는 것을 확인하였다. 강도시험을 위한 공시체는 점성토의 경우 5가지, 사질토는 3가지 배합비로 각각 3개 총 24개의 시편을 제작하였으며, 시험 결과 사질토와 점성토 모두 배합량 2.0kN/m³ 이하에서는 일축압축강도가 재령일이 증가함에 따라 선형적으로 증가하는 경향을 나타냈다. 따라서 현장에 적용되는 최적의 배합비는 고화재 배합량을 1.5kN/m³ 및 2.0kN/m³으로 결정하였다. 또한 현재 운영 중인 노후 저수지 개보수사업 설계사례를 대상으로 실험성과를 반영한 수치해석을 실시한 결과 저수지 제체의 차수 및 안전성 증대 효과를 확인하였다.