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대학 신입생들의 수학 기초학력 평가자료들 간의 상관관계 및 오류 유형 분석
장민우,표용수,Jang, Min Woo,Pyo, Yong-Soo 영남수학회 2016 East Asian mathematical journal Vol.32 No.4
In this paper, we analyzed the correlation among scores of the mathematics B-type grade of College Scholastic Ability Test(CSAT), scores of Mathematics Level Assessment(MLA) and written test scores of Basic Mathematics Subject(BMS) made by students. Especially, we examined the relationship between CSAT grade with results of MLA and results of BMS through survey of students who changed their grades and learned about reasons. In addition, we analyzed error types for the descriptive problem solving in BMS written tests..
Running Safety and Behavior Tests for a Scaled-Down Railway Vehicle Crossing a Floating Bridge
장민우,서성일,문형석 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.6
This paper proposes a test method to evaluate the operability of railway vehicles crossing floating bridges. To inspect the dynamic response of the floating bridge to the railway vehicle, the test setup was separated into wave tank and shake table tests. A scaled-down model representing a unit length of the floating bridge span was manufactured for the wave tank test. Several harmonic waves were artificially created and the displacement at the center above the top surface was measured using an optical position sensor. The response of the floating structure was analyzed to extract the relative amplitude versus the input wave for sway, heave, and roll. The harmonic motions using these responses were simultaneously used as input signals for a six-degree-of-freedom shake table. The scaled-down bogie model ran back and forth repeatedly on the railway placed on the shake table. The acceleration measured from the railway vehicle was analyzed to evaluate the running safety and behavior. All tests were performed without allowing derailment and showed sufficient margin to satisfy the running safety and behavior standards. The proposed test method was successfully conducted and showed a remarkable potential to evaluate the operation of railway vehicles on floating bridges under various wave conditions.
Pseudo-Dynamic Test for Soil-Structure Interaction Analysis using Shake Tables
장민우,김재관 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.5
This paper presents an effective pseudo-dynamic (PSD) test method for analyzing the response of a multi degree of freedom structural system. In addition to the physical and numerical substructuring of the structure, the effect of the soil-structure interaction (SSI) is numerically modeled without a large soil box. The governing equation is separated into those for the superstructure and the base. These are coupled equations that can be solved recursively with the prediction of the superstructure acceleration, for which polynomial extrapolation is employed. The input for the structure is then obtained by solving the coupled equilibrium equations for experimental and analytically modeled systems. The restoring force applied underneath the superstructure is measured and used to update the superstructure acceleration. The stability condition for the proposed method is investigated, revealing a longer range of the convergence criterion than the Newmark explicit method. The implicit feature of the proposed method enables PSD tests irrespective of the modal properties, if the sampling frequency condition is satisfied. Additionally, the amplitude decay and period elongation are investigated for accuracy comparison in the structural responses. A series of PSD tests are performed using a two degree of freedom shear-building model to validate the proposed method. The experiment is performed on one part of the physical structure, while a numerical simulation is performed on the other part of the structure and on the SSI. The test results confirm that the proposed PSD algorithm is reliable for simulating the substructure and SSI effect.
SMIT를 활용한 지진하중을 받는 전단 구조물의 응답모드 특성에 관한 연구
장민우 한국지진공학회 2018 한국지진공학회논문집 Vol.22 No.3
The improvement in computing systems and sensor technologies devotes to conduct data-driven structural health monitoring algorithms for existing civil infrastructures. Despite of the development of techniques, the uncertainty oriented from the measurement results in the discrepancy to the actual structural parameters and let engineers or decision makers hesitate to adopt such techniques. Many studies have shown that the modal identification results can be affected by the uncertainties due to the applied methods and the types of loading. This paper aims to compare the performance of modal identification methods using Structural Modal Identification Toolsuite (SMIT) which has been developed to facilitate multiple identification methods with a user-friendly designed platform. The data fed into SMIT processes three stages for the comprehensive identification including preprocessing, eigenvalue estimation, and post-processing. The seismic and white noise response for shear frame model was obtained from numerical simulation. The identified modal parameters is compared to the actual modal parameters. In order to improve the quality of coherence in identified modal parameters, several hurdles including modal phase collinearity and extended modal amplitude coherence were introduced. Numerical simulation conducted on the 5 dof shear frame model were used to validate the effectiveness of using these parameters.
Hierarchical neural network for damage detection using modal parameters
장민우,김재관,Joonhyeok Lee 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.70 No.4
This study develops a damage detection method based on neural networks. The performance of the method is numerically and experimentally verified using a three-story shear building model. The framework is mainly composed of two hierarchical stages to identify damage location and extent using artificial neural network (ANN). The normalized damage signature index, that is a normalized ratio of the changes in the natural frequency and mode shape caused by the damage, is used to identify the damage location. The modal parameters extracted from the numerically developed structure for multiple damage scenarios are used to train the ANN. The positive alarm from the first stage of damage detection activates the second stage of ANN to assess the damage extent. The difference in mode shape vectors between the intact and damaged structures is used to determine the extent of the related damage. The entire procedure is verified using laboratory experiments. The damage is artificially modeled by replacing the column element with a narrow section, and a stochastic subspace identification method is used to identify the modal parameters. The results verify that the proposed method can accurately detect the damage location and extent.
추출용매에 따른 브로콜리의 항산화와 항염증에 대한 효과
장민우,하배진 한국식품위생안전성학회 2012 한국식품위생안전성학회지 Vol.27 No.4
Broccoli has a functional substance, sulforaphane that has effects of anticancer, antioxidant, antimicrobial and anti-inflammatory. Sulforaphane, one of the hydrolysis products of glucoraphanin in broccoli, cabbage and kale, was contributed to the role of antioxidant. Broccoli contains a number of bioactive compounds including glucosinolates, S-methyl cysteine sulfoxide and many antioxidants. The ethanol extract (BE), hexane extract (BH),propylene glycol extract (BP) and butylenesglycol extract (BB) of broccoli were used to investigate the antioxidation and anti-inflammatory effects of sulforaphane extracts from broccoli. The high scavenging abilities of DPPH, O2−were observed. Also sulforaphane extracts from broccoli showed the inhibition effect on NO rate. These results demonstrated that sulforaphane extracts from broccoli could be useful as an antioxidation and anti-inflammatory functional ingredient.