• 사물인터넷융복합논문지
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• 제7권4호
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• pp.9-14
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• 2021

고신뢰성을 요구하는 컴퓨팅 시스템에서 저장장치의 수명예측방법은 데이터 보호뿐만 아니라 활용성을 극대화 할 수 있기 때문에 시스템 관리하기 위한 중요한 요소 중 한 가지이다. 최근 여러 저장시스템에서 저장장치로 사용되고 있는 SSD(Solid State Drive)의 수명은 이를 구성하고 있는 낸드 플래시 메모리의 수명이 실질적인 수명과 연결된다. 따라서 SSD를 이용하여 구성한 저장시스템에서는 낸드 플래시 메모리의 수명을 정확하고 효율적으로 예측하는 방법이 필요하다. 본 논문에서는 낸드 플래시 메모리 불량 발생빈도를 이용하여 플래시 메모리 기반 저장장치의 수명 예측을 최적화할수 있는 방법을 제안한다. 이를 위해 DWPD(Drive Writes Per Day) 단위로 데이터를 처리할 때 발생하는 불량 발생빈도를 수집하기 위한 비용 매트릭스(Cost Metrix)를 설계한다. 그리고 경사하강법(Gradient Descent)을 이용하여 수명의 마감이 발생하는 경사도까지 남은 비용을 예측하는 방법을 제안한다. 마지막으로 시뮬레이션을 통해 임의의 불량이 발생했을 때 제안하는 방법을 통한 수명예측의 우수성을 증명했다.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2022년도 춘계학술대회
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• pp.542-545
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• 2022

최근 중대재해의 처벌관련법이 건설 환경에 대한 관심을 끌고 있다. 공사현장의 안전관리를 점검하는 일반적인 방법은 근무자가 직접 그들의 눈으로 현장을 확인하는 것이다. 하지만 이 방식은 근무자의 능력의 한계에 영향을 받을 수밖에 없고, 그 결과 피로와 작업 능률 저하를 일으키게 된다. 이런 이유로, 이는 효율적인 방법이 될 수 없다. 이에 우리는 본 연구를 통해 상기 방법을 보완할 수 있는 효율적인 ICT 안전관리 시스템을 제안하여, 작업환경 및 공사 현장 안전에 도움 주고자 한다. 본 논문은 RFID를 활용한 출입 관리 시스템 설계와 소음 센서 및 미세 먼지 센서를 통한 현장 정보 모니터링 방식을 설명한다. 또한, PIR 센서로 중장비와 사람 간의 사고를 예방하고, 자이로 센서를 통해 작업 중인 건물의 기울기를 파악하여 안전사고를 예방할 수 있는 시스템을 제안한다.

• Wind and Structures
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• 제35권4호
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• pp.255-268
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• 2022

Light-weight or low-damped structures may encounter the unsteady galloping instability that occurs at low reduced wind speeds, where the classical quasi-steady assumption is invalid. Although this unsteady phenomenon has been widely studied for rectangular cross sections with one side perpendicular to the incidence flow, the effect of the mean wind angle of attack has not been paid enough attention yet. With four sectional models of different side ratios and geometric shapes, the presented research focuses on the effect of the wind angle of attack on unsteady galloping instability. In static tests, comparatively strong vortex shedding force was noticed in the middle of the range of flow incidence where the lift coefficient shows a negative slope. In aeroelastic tests with a low Scruton number, the typical unsteady galloping, which is due to an interaction with vortex-induced vibration and results in unrestricted oscillation initiating at the Kármán vortex resonance wind speed, was observed for the wind angles of attack that characterize relatively strong vortex shedding force. In contrast, for the wind angles of attack with relatively weak shedding force, an "atypical" unsteady galloping was found to occur at a reduced wind speed clearly higher than the Kármán-vortex resonance one. These observations are valid for all four wind tunnel models. One of the wind tunnel models (with a bridge deck cross section) was also tested in a turbulent flow with an intensity about 9%, showing only the atypical unsteady galloping. However, the wind angle of attack with the comparatively strong vortex shedding force remains the most unfavorable one with respect to the instability threshold in low Scruton number conditions.

• 한국지반환경공학회 논문집
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• 제24권1호
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• pp.45-50
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• 2023

강우에 의한 비탈면 재해를 방지하기 위해서는 신속히 강우를 배제하는 것이 매우 중요하다. 국내에서는 지하수위를 낮추기 위한 방법으로 경제성과 시공성이 뛰어나고, 배수 성능이 좋은 수평배수공을 보편적으로 적용하고 있다. 그러나 현장에서 시공되는 수평배수공의 경우 다른 용수의 유무나 지반의 조건과 관계없이 획일적으로 시공되는 경우가 많으며, 유지관리가 원활하게 이루어지지 않고 있어 수평배수공의 배수 성능을 기대하기 힘든 경우가 많다. 이에 본 연구에서는 모형토조를 이용해 인공지반을 조성하여 수평배수공 실험을 수행하였다. 수평배수공 배수 면적을 일정량 통제해 통제면적 0%, 25%, 50%, 75% 상태의 수평배수공 유출량을 측정하였으며, 측정값과 설계 도서 등을 바탕으로 수평배수공을 정량적으로 평가할 수 있는 평가표(안)를 제안하여 현장적용이 가능한 기초자료로서 제안하고자 한다.

• Design & Manufacturing
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• 제17권2호
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• pp.9-14
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• 2023

In this study, an experiment was conducted to confirm the applicability of the external shape control of the ultrasonic knife to the CFRTP material, which is the base material of thermoplastic. TC910 based on polyamide6 (PA6) was used as the material. The slope 와 and tool transfer speed of the material and tool were selected as process factors for processing, and the following results were obtained. Under all cutting conditions using an ultrasonic knife, friction heat caused by high-frequency vibration was issued at 150℃ at the contact part between the material and the knife during cutting. As a result of the cutting force analysis, the faster the transfer speed, the higher the cutting force as the angle of entry of the blade increased, and the size of the cutting force changed during cutting. As for the size of the burr in accordance with the transfer speed condition, the smallest burr occurred at 150mm/min in the side part, and the smallest burr occurred at 150mm/min and 200mm/min in the case of the outlet burr. The size of the burr according to the entry angle tended to decrease as the tool entry angle increased, and the side part tended to increase as the tool entry angle increased. As a result of the cutting surface analysis, it was confirmed that the base material was eluted under all conditions, and the faster the transfer speed, the lower the elution phenomenon of the base material. Based on the above results, cutting the CFRTP material with an ultrasonic knife is possible, but the effect on heat generation caused by friction needs to be minimized, and further research needs to be conducted on this.

• Steel and Composite Structures
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• 제45권2호
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• pp.205-218
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• 2022

Proper calculation of splitting tensile strength (STS) of concrete has been a crucial task, due to the wide use of concrete in the construction sector. Following many recent studies that have proposed various predictive models for this aim, this study suggests and tests the functionality of three hybrid models in predicting the STS from the characteristics of the mixture components including cement compressive strength, cement tensile strength, curing age, the maximum size of the crushed stone, stone powder content, sand fine modulus, water to binder ratio, and the ratio of sand. A multi-layer perceptron (MLP) neural network incorporates invasive weed optimization (IWO), cuttlefish optimization algorithm (CFOA), and electrostatic discharge algorithm (ESDA) which are among the newest optimization techniques. A dataset from the earlier literature is used for exploring and extrapolating the STS behavior. The results acquired from several accuracy criteria demonstrated a nice learning capability for all three hybrid models viz. IWO-MLP, CFOA-MLP, and ESDA-MLP. Also in the prediction phase, the prediction products were in a promising agreement (above 88%) with experimental results. However, a comparative look revealed the ESDA-MLP as the most accurate predictor. Considering mean absolute percentage error (MAPE) index, the error of ESDA-MLP was 9.05%, while the corresponding value for IWO-MLP and CFOA-MLP was 9.17 and 13.97%, respectively. Since the combination of MLP and ESDA can be an effective tool for optimizing the concrete mixture toward a desirable STS, the last part of this study is dedicated to extracting a predictive formula from this model.

• Geomechanics and Engineering
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• 제35권5호
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• pp.511-523
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• 2023

Canal-side roads frequently collapse due to an unexpectedly greater soft-clay thickness with a rapid drawdown situation. This causes annually increased repair and reconstruction costs. This paper aims to explore the effect of soft-clay thickness on the failure in the canal-side road in the case study of Phra Nakhon Si Ayutthaya rural road no. 1043 (AY. 1043). Before the actual construction, a field vane shear test was performed to determine the undrained shear strength and identify the thickness of the soft clay at the AY. 1043 area. After establishing the usability of AY. 1043, the resistivity survey method was used to evaluate the thickness of the soft clay layer at the failure zone. The screw driving sounding test was used to evaluate the undrained shear strength for the road structure with a medium-stiff clay layer at the failure zone for applying to the numerical model. This model was simulated to confirm the effect of soft-clay thickness on the failure of the canal-side road. The monitoring and testing results showed the tendency of rapid drawdown failure when the canal-side road was located on > 9 m thick of soft clay with a sensitivity > 4.5. The result indicates that the combination of resistivity survey and field vane shear test can be successfully used to inspect the soft-clay thickness and sensitivity before construction. The preliminary design for preventing failure or improving the stability of the canal-side road should be considered before construction under the critical thickness and sensitivity values of the soft clay.

• 아태비즈니스연구
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• 제14권3호
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• pp.67-88
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• 2023

Purpose - This study examined the effect of empowering leadership on adaptive performance and verified the mediating effect of job challenge in the relationship between empowering leadership and adaptive performance. Additionally, this study investigated the moderating effect of agentic and communal traits in the relationship between supervisor's empowering leadership and adaptive performance of subordinates. Design/methodology/approach - This study used data collected from 279 participants via an online platform. Multiple regression analysis, bootstrapping, hierarchical regression analysis, and simple slope test were used to analyze the data. Findings - First, supervisor's empowering leadership had a positive effect on adaptive performance. Second, job challenge was found to mediate the relationship between supervisor's empowering leadership and adaptive performance. Third, the agentic trait showed a moderating effect on strengthening the relationship between supervisor's empowering leadership and adaptive performance. However, communal trait did not show a moderating effect. Research implications or Originality - This study examined the moderating effect of agentic traits in the relationship between empowering leadership and adaptive performance, which has not been investigated before.

• 한국재료학회지
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• 제33권10호
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• pp.377-384
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• 2023

Exploring earth-abundant, highly effective and stable electrocatalysts for electrochemical water splitting is urgent and essential to the development of hydrogen (H₂) energy technology. Iron-cobalt layered double hydroxide (FeCo-LDH) has been widely used as an electrocatalystfor OER due to its facile synthesis, tunable components, and low cost. However, LDH synthesized by the traditional hydrothermal method tends to easily agglomerate, resulting in an unstable structure that can change or dissolve in an alkaline solution. Therefore, studying the real active phase is highly significant in the design of electrochemical electrode materials. Here, metal-organic frameworks (MOFs) are used as template precursors to derive FeCo-LDH from different iron sources. Iron salts with different anions have a significant impact on the morphology and charge transfer properties of the resulting materials. FeCo-LDH synthesized from iron sulfate solution (FeCo-LDH-SO₄) exhibits a hybrid structure of nanosheets and nanowires, quite different from other electrocatalysts that were synthesized from iron chloride and iron nitrate solutions. The final FeCo-LDH-SO₄ had an overpotential of 247 mV with a low Tafel-slope of 60.6 mV dec^-1 at a current density of 10 mA cm^-2 and delivered a long-term stability of 40 h for the OER. This work provides an innovative and feasible strategy to construct efficient electrocatalysts.

• Advances in concrete construction
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• 제16권4호
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• pp.177-188
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• 2023

In the context of the shortage of river sand, two types of manufactured sand (MS) were used to partially replace river sand (RS) to design manufactured sand concrete (MSC). A total of 81 specimens were designed for uniaxial compression test and beam flexure test. Two parameters were considered in the tests, including the types of MS (i.e. limestone manufactured sand (LMS), pebble manufactured sand (PMS)) and the MS replacement percentage (i.e., 0%, 25%, 50%, 75%, 100%). The stress-strain curves of MSC were obtained. The effects of these parameters on the compressive strength, elastic modulus, peak strain, toughness and flexural strength were discussed. Additionally, the sensitivity of particle size distributions to the performance of MSC was evaluated based on the grey correlation analysis. The results showed that compared with river sand concrete (RSC), the rising slope of the stress-strain curves of limestone manufactured sand concrete (LMSC) and pebble manufactured sand concrete (PMSC) were higher, the descending phrase of LMSC were gentle but that of PMSC showed an opposite trend. The physical and mechanical properties of MSC were affected by the MS replacement percentage except the compressive strength of PMSC. When the replacement percentage of LMS and PMS were 50% and 25% respectively, the corresponding performances of LMSC and PMSC were better. In generally, when the replacement percentage of LMS and PMS were same, the comprehensive performance of LMSC were better than that of PMSC. The constitutive model and the equations for mechanical properties were proposed. The influence of particle ranging from 0.15 mm to 0 mm on the performance of MSC was lower than particle ranging from 4.75 mm to 0.15 mm but this influence should not be ignored.