• ETRI Journal
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• v.45 no.3
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• pp.404-417
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• 2023

This paper proposed a novel method for constructing quasi-cyclic low-density parity-check (QC-LDPC) codes of medium to high code rates that can be applied in cloud data storage systems, requiring better error correction capabilities. The novelty of this method lies in the construction of sparse base matrices, using a girth greater than 4 that can then be expanded with a lift factor to produce high code rate QC-LDPC codes. Investigations revealed that the proposed large-sized QC-LDPC codes with high code rates displayed low encoding complexities and provided a low bit error rate (BER) of 10^-10 at 3.5 dB E_b/N₀ than conventional LDPC codes, which showed a BER of 10^-7 at 3 dB E_b/N₀. Subsequently, implementation of the proposed QC-LDPC code in a softwaredefined radio, using the NI USRP 2920 hardware platform, was conducted. As a result, a BER of 10^-6 at 4.2 dB E_b/N₀ was achieved. Then, the performance of the proposed codes based on their encoding-decoding speeds and storage overhead was investigated when applied to a cloud data storage (GCP). Our results revealed that the proposed codes required much less time for encoding and decoding (of data files having a 10 MB size) and produced less storage overhead than the conventional LDPC and Reed-Solomon codes.

• Wind and Structures
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• v.31 no.1
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• pp.31-41
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• 2020

A new type of bridge deck section consisting of four-box decks, two side decks for vehicular traffic lanes and two middle decks for railway traffic, has been experimentally investigated for determining its aerodynamic properties. The eight flutter derivatives were determined by the Iterative Least Squares (ILS) method for this new type of four-box deck model, with two windshields of 30 mm and 50 mm height respectively. Wind tunnel experiments were performed for angles of attack α = ±6°, ±4°, ±2° and 0° and Re numbers of 4.85×105 to 6.06×105 and it was found that the four-box deck with the 50 mm windshields had a better aerodynamic performance. Also, the results showed that the installation of the windshields reduced the values of the lift coefficient CL for the negative angles attack in the range of -6° to 0°, but the drag coefficient CD increased in the positive angle of attack range. However, galloping instability was not encountered for the tested reduced wind speeds, of up to 9.8. The aerodynamic force coefficients and the flutter derivatives for the four-box deck model were consistent with the results reported for the Messina triple-box bridge deck, but were different from those reported for the twin-box bridge decks.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.5
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• pp.445-450
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• 2011

In order to estimate a yacht sail performance, measuring system of aerodynamic forces acting on the yacht sail is constructed and experiments of flexible model sail are carried out at the medium-size subsonic wind tunnel of Chungnam National University. Experimental results for a flexible sail are compared with experimental and numerical results of fixed shape sail. In case of a fixed shape sail, lift and drag coefficients are rarely changed at all velocity conditions. However, those of the flexible sail are decreased as the incoming velocity is increased. These are understandably resulted from shape variations due to the flexible material. Therefore aero-elastic similarity should be more carefully considered in the model test rather than other similarities.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.48-51
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• 2011

사장교에서 케이블은 하중을 지지하는 주요 부재로, 케이블 장력은 사장교의 건전성과 안전도 평가에 있어서 매우 중요한 변수이다. 케이블 장력을 추정하기 위한 대표적인 방법으로는 로드셀을 이용한 직접법과 진동 계측 자료를 이용한 간접법 등이 있으며, 최근에는 자기장-응력 관계를 이용한 EM(Elasto-Magnetic) 센서 측정법이 개발되어 케이블 장력 추정에 적용되었다. 본 논문에서는 세 가지 장력 추정 기법을 실제 시공중인 사장교에 적용하여, 그 성능을 상호 비교하였다. 본 연구는 한국의 KAIST와 미국 Northeastern 대학교의 공동연구로 수행되었다. 대상 교량은 부산 화명동과 김해 초정리를 연결하기 위해 현재 건설중인 화명대교이다. 화명대교의 교량 형식은 2주탑 콘크리트 사장교 (주탑 경간장 270m, 총 사장교 구간장 500m)이며, 사장재로는 MS (Multi-Strand) 형 케이블이 사용되었다. 실험 당시 화명대교는 중앙경간의 폐합 후 선형관리를 위한 장력조정작업을 수행하였으며, 케이블 재긴장시의 정확한 장력관리를 위하여 로드셀을 이용한 Lift-off test방법으로 케이블의 장력을 측정하였다. 이와 동시에 두 개의 케이블을 대상으로 진동 가속도 센서와 EM 센서를 설치하고 장력 계측을 수행하였으며, 재긴장 단계별 장력 변화치를 지속적으로 계측하였다. 계측된 결과를 바탕으로 케이블 장력 추정 기법의 정확성 및 실교량에서의 활용성을 비교하였다.

• Transactions of The Korea Fluid Power Systems Society
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• v.2 no.2
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• pp.1-7
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• 2005

For the reliability evaluation of the track drive unit(TDU), firstly, we analyzed the major failure modes through FMEA(failure mode & effects analysis), FTA(failure tree analysis), and 2-stage QFD(quality function deployment), and then quantitatively determined the priority order of test items. The Minitab analysis was also performed for prediction of life distribution and parameters of TDU by use of field failure data collected from 430 excavators for two years. In addition, we converted the fluctuation load in field conditions into the equivalent load, and for evaluation of the accelerated lift by the cumulative fatigues, the equivalent load is again divided into the fluctuation load by reference of test time. And then, by use of the test method in this paper, the acceleration factor(AF) of needle bearing inside planetary gear which is the most weakly designed part of TDU is achieved as 5.3. This paper presents the quantitative selection method of test items for reliability evaluation, the determination method of the accelerated life test time, and the method of non-failure test time based on a few of samples. And, we proved the propriety of the proposed methods by experiments using a TDU for a 30 ton excavator.

• Journal of Korean Association for Spatial Structures
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• v.14 no.2
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• pp.69-78
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• 2014

The purpose of this study is to increase applicability of high strength steel, HSA800 to the structure. Selected study of structure is to consider high strength steel, and following parts, 1) Tensile member with no consider of buckling, 2) Truss existing both tension and compression members with small slenderness ratio. This studied structure is included tension column hang on to the upper bridge truss. The structure element quantity with apply HSA800 instead of SM570 is reduced about 38.9% of tension column and 29.7% of bridge truss. In addition, the number of element's division is reduced about two sections due to reduction of self weight that the crane is able to lift up. This improves to reduce erection sequence and construction period which can save about a month. All connections are reviewed as welding and bolt. Also, the cost of welding is reduced about 41.3% due to apply HSA800. In conclusion, applying HSA800 to the hanging structure aggressively can secure economic and constructability.

• Korean Journal of Community Nutrition
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• v.5 no.4
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• pp.697-708
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• 2000

The purpose of this study is to analyze the contents of the questionnaires used in dietary surveys and to evaluate each item in relation to the item construction strategy. Articles of which the contents were related to food, nutrition, diet, dietary behavior, and related areas. Published from 1997 to 1999 were searched fir and a total of 121 questionnaires were collected and analyzed. The questions in the questionnaires were classified into related areas and sub-areas. Among the keywords in the title of the articles, the term 'nutritional status'(or 'dietary intake status') was most frequently used. The terms such as dietary status, obesity, health, food habit, and dietary behavior were also frequency used. Major topics of the items in the questionnaires varied according to the life cycle of the subjects of the study. The topics most frequently asked in each lift cycle were as follows : overeating, snack, and food preference for preschool- and school-aged children ; anthropometry, weight control, and snack for middle and highschool students : meal skipping, smoking, and drinking for college students : disease, smoking, drinking, and exercise for adults : and smoking, drinking, disease and perceived health for the elderly. Inappropriate questions with complicated language, typographic and grammatic errors, unnecessary words, and negative questions were found. Therefore, care should be taken to construct each question so as to avoid possible misinterpretation. Also, a standardized questionnaire be developed for survey researchers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.308-315
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• 2007

This study is performed to find out the climb performance of light airplane, Chang Gong-91, as a part of flight test to acquire the certification. Chang Gong-91 is a 5-passenger light aircraft of normal category with single reciprocating engine, and the first officially certified by Korean Ministry of Construction and Transportation in 1993. These flight test procedure and data for climb performance are used to get type certification. We have got maximum climb rate for operating altitude, best angle of climb speed, best rate of climb speed, and absolute ceiling of Chang Gong-91 using drag polar data reduction method from sawtooth climb flight data. Also we compare the form drag coefficient from the results of climb performance and Oswald's effectiveness coefficient to design values using lift-drag curve of light airplane.

• Journal of Drive and Control
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• v.15 no.4
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• pp.17-22
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• 2018

Mobile hydraulics require higher energy efficiency, and a simpler as well as robust design, than general industrial hydraulics. The 6/3-way directional control valve is widely used as a mobile hydraulic control valve. However, since the 6/3-way directional control valve is a spool type valve, it is difficult to maintain the load. A counterbalance valve is typically used, to maintain the load, and lift down. However, in an industrial field using a mobile hydraulics device, a pilot controlled check valve may be used to implement holding and lifting operation of the self-weight load, and a relief valve may be used simply to exert back pressure. But no comparative analysis of advantages and disadvantages of each method was revealed. In this study, various methods of holding and unloading load with self-weight in mobile hydraulics are investigated, and compared through simulation using AMESim software. This is experimentally verified by using Festo's mobile hydraulic test rig TP800.

• Journal of Drive and Control
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• v.18 no.2
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• pp.46-55
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• 2021

A forklift is a powered industrial vehicle used to lift and move materials over short distances. Nowadays, almost all forklifts are equipped with an automatic transmission due to its improved operator comfort and increased productivity. Thanks to marked improvement of transmission control unit equipped with highly-advanced microcontrollers, recently developed automatic transmission for forklift have various auxiliary functions such as creep, auto retardation, and automatic shift with excellent shift quality. This paper deals with the creep function which enables one to maneuver a forklift at the designated low speed by slip control of clutches. The design of creep function was based on four modes of creep operation depending on the status of the operator's shift lever and accelerator pedal. Control algorithms and control parameters for each mode were designed to achieve the desired static and dynamic performance. Vehicle test for the designed creep function was carried out with an independently developed embedded controller. Test results confirmed good creep speed control without speed error at a steady state with a mild shift shock during mode changes by stepping or releasing the accelerator.