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Characteristics of Hysteretic Behavior of Circular Steel Column using SM490 for Loading Rate (재하속도에 따른 SM490강재 원형강기둥의 이력거동 특성)

  • Jang, Gab Chul;Chang, Kyong Ho
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.6A
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    • pp.935-941
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    • 2006
  • The hysteretic behavior of steel structure under cyclic and dynami loading such as earthquake is different to that under static loading. Because structural steels on dynamic deformation is different to static deformation with respect with mechanical characteristics and stress-strain relationship. Therefore, to accurately predict the hysteretic behavior of steel structures such as circular steel columns under cyclic and dynamic loading, the difference of loading carrying capacity and deformation according to loading rate, assumed static and dynamic deformation state, must be investigated. In this study, numerical analyses of circular steel column using SM490 for change of loading rate and diameter-thickness ratio(D/t) were carried out by using three-dimensional elastic-plastic finite element analysis and dynamic cyclic plasticity model of SM490 developed by the authors. Characteristics of hysteretic behavior of circular steel column using SM490, load carrying capacity and energy dissipation ratio, were clarified by analysis results.

Development of a smart rain gauge system for continuous and accurate observations of light and heavy rainfall

  • Han, Byungjoo;Oh, Yeontaek;Nguyen, Hoang Hai;Jung, Woosung;Shin, Daeyun
    • Proceedings of the Korea Water Resources Association Conference
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    • 2022.05a
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    • pp.334-334
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    • 2022
  • Improvement of old-fashioned rain gauge systems for automatic, timely, continuous, and accurate precipitation observation is highly essential for weather/climate prediction and natural hazards early warning, since the occurrence frequency and intensity of heavy and extreme precipitation events (especially floods) are recently getting more increase and severe worldwide due to climate change. Although rain gauge accuracy of 0.1 mm is recommended by the World Meteorological Organization (WMO), the traditional rain gauges in both weighting and tipping bucket types are often unable to meet that demand due to several existing technical limitations together with higher production and maintenance costs. Therefore, we aim to introduce a newly developed and cost-effective hybrid rain gauge system at 0.1 mm accuracy that combines advantages of weighting and tipping bucket types for continuous, automatic, and accurate precipitation observation, where the errors from long-term load cells and external environmental sources (e.g., winds) can be removed via an automatic drainage system and artificial intelligence-based data quality control procedure. Our rain gauge system consists of an instrument unit for measuring precipitation, a communication unit for transmitting and receiving measured precipitation signals, and a database unit for storing, processing, and analyzing precipitation data. This newly developed rain gauge was designed according to the weather instrument criteria, where precipitation amounts filled into the tipping bucket are measured considering the receiver's diameter, the maximum measurement of precipitation, drainage time, and the conductivity marking. Moreover, it is also designed to transmit the measured precipitation data stored in the PCB through RS232, RS485, and TCP/IP, together with connecting to the data logger to enable data collection and analysis based on user needs. Preliminary results from a comparison with an existing 1.0-mm tipping bucket rain gauge indicated that our developed rain gauge has an excellent performance in continuous precipitation observation with higher measurement accuracy, more correct precipitation days observed (120 days), and a lower error of roughly 27 mm occurred during the measurement period.

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Damage characterization of hard-brittle rocks under cyclic loading based on energy dissipation and acoustic emission characteristics

  • Li, Cheng J.;Lou, Pei J.;Xu, Ying
    • Geomechanics and Engineering
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    • v.31 no.4
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    • pp.365-373
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    • 2022
  • In order to investigate the damage evolution law of rock specimens under cyclic loading, cyclic loading tests under constant loads with different amplitudes were carried out on limestone specimens with high strength and brittleness values using acoustic emission (AE) technology and the energy evolution and AE characteristics were evaluated. Based on dissipated energy density and AE counts, the damage variable of specimen was characterized and two damage evolution processes were analyzed and compared. The obtained results showed that the change of AE counts was closely related to radial deformation. Higher cyclic loading values result in more significant radial strain of limestone specimen and larger accumulative AE counts of cyclic loading segment, which indicated Felicity effect. Regarding dissipated energy density, the damage of limestone specimen was defined without considering the influence of radial deformation, which made the damage value of cyclic loading segment higher at lower amplitude loads. The damage of cyclic loading segment was increased with the magnitude of load. When dissipated energy density was applied to define damage, the damage value at unloading segment was smaller than that of AE counts. Under higher cyclic loading values, rocks show obvious damage during both loading and unloading processes. Therefore, during deep rock excavation, the damages caused by the deformation recovery of unloading rocks could not be ignored when considering the damage caused by abutment pressure.

A Study on Efficient Design of Surveillance RADAR Interface Control Unit in Naval Combat System

  • Dong-Kwan Kim;Dong-Han Jung;Won-Seok Jang;Young-San Kim;Hyo-Jo Lee
    • Journal of the Korea Society of Computer and Information
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    • v.28 no.11
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    • pp.125-134
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    • 2023
  • In this paper, we propose an efficient surveillance RADAR(RAdio Detection And Ranging) interface control unit(ICU) design in the naval combat system. The proposed design applied a standardized architecture for modules that can be shared in ship combat system software. An error detection function for each link was implemented to increase the recognition speed of disconnection. Messages that used to be sent periodically for human-computer interaction(HCI) are now only transmitted when there is a change in the datagram. This can reduce the processing load of the console. The proposed design supplements the radar with the waterfall scope and time-limited splash recognition in relation to the hit check and zeroing of the shot when the radar processing ability is low due to the adoption of a low-cost commercial radar in the ship. Therefore, it is easy for the operator to determine whether the shot is hit or not, the probability of wrong recognition can be reduced, and the radar's resources can be obtained more effectively.

Influence of loading and unloading of hydraulic support on the caving property of top coal

  • Huayong Lv;Fei Liu;Xu Gao;Tao Zhou;Xiang Yuan
    • Steel and Composite Structures
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    • v.48 no.1
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    • pp.103-111
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    • 2023
  • The caving property of top coal is a key factor to the success of top coal caving mining. The influence law of cyclic loading and unloading of hydraulic support on top coal caving is of great significance to improve the recovery rate of top coal. The similar simulation methods were used to study the dynamic evolution of the top coal cracks under the multi-cycle action of the support, and the parameters of top coal cracks were analyzed quantitatively in this paper. The results show that the top coal cracks can be divided into horizontal cracks and vertical cracks under the cyclic loading and unloading of the support. With the increase of the times of the support cycles loading and unloading, the load on the support decreases, the fractal dimension of the cracks increases, the number and total length of the top coal cracks increases, and the top coal caving is getting better. With the increase of the times of multi-cycle loading and unloading, the fractal dimension, total crack length and crack rate of top coal show a trend of rapid increase first and then increase slowly. Both the total length of the top coal cracks and the crack rate basically show linear growth with the change of the fractal dimension. The top coal caving can be well improved and the coal resource recovery rate increased through the multi-cycle loading and unloading.

A Study on the Relationship between Response Spectrum and Seismic Fragility Using Single Degree of Freedom System (단자유도 해석모델을 활용한 응답스펙트럼과 지진취약도 곡선과의 관계에 대한 연구)

  • Park, Sangki;Cho, Jeong-rae;Cho, Chang-beck;Lee, JinHyuk;Kim, Dong-Chan
    • Journal of the Earthquake Engineering Society of Korea
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    • v.27 no.6
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    • pp.245-252
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    • 2023
  • In general, the design response spectrum in seismic design codes is based on the mean-plus-one-standard deviation response spectrum to secure high safety. In this study, response spectrum analysis was performed using seismic wave records adopted in domestic horizontal design spectrum development studies, while three response spectra were calculated by combining the mean and standard deviation of the spectra. Seismic wave spectral matching generated seismic wave sets matching each response spectrum. Then, seismic fragility was performed by setting three damage levels using a single-degree-of-freedom system. A correlation analysis was performed using a comparative analysis of the change in the response spectrum and the seismic fragility concerning the three response spectra. Finally, in the case of the response spectrum considering the mean and standard deviation, like the design response spectrum, the earthquake load was relatively high, indicating that conservative design or high safety can be secured.

Effect of Adding Graphene/Carbon Nanotubes (FCN) on the Mechanical Properties of Polyamide-Nylon 6 (그래핀/탄소나노튜브(FCN) 첨가에 따른 Polyamide-Nylon 6의 기계적 특성에 미치는 영향)

  • Seung-Jun Yeo;Hae-Reum Shin;Woo-Seung Noh;Man-Tae Kim
    • Journal of the Korean Society of Industry Convergence
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    • v.26 no.6_3
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    • pp.1297-1303
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    • 2023
  • Research on enhancing the mechanical strength, lightweight properties, electrical conductivity, and thermal conductivity of composite materials by incorporating nano-materials is actively underway. Thermoplastic resins can change their form under heat, making them highly processable and recyclable. In this study, Polyamide-Nylon 6 (PA6), a thermoplastic resin, was utilized, and as reinforcing agents, fused carbon nano-materials (FCN) formed by structurally combining Carbon Nanotube(CNT) and Graphene were employed. Nano-materials often face challenges related to cohesion and dispersion. To address this issue, Silane functional groups were introduced to enhance the dispersion of FCN in PA6. The manufacturing conditions for the composite materials involved determining the use of a dispersant and varying FCN content at 0.05 wt%, 0.1 wt%, and 0.2 wt%. Tensile strength measurements were conducted, and FE-SEM analysis was performed on fracture surfaces. As a result of the tensile strength test, it was confirmed that compared to pure PA6, the strength of the polymer composite with a content of 0.05 wt% was improved by about 60%, for 0.1 wt%, about 65%, and for 0.2 wt%, the strength was improved by 50%. Also, when compared according to the content of FCN, the best strength value was shown when 0.1 wt% was added. The elastic modulus also showed an improvement of about 15% in the case of surface treatment compared to the case without surface treatment, and an improvement of about 70% compared to pure PA6. Through FE-SEM, it was confirmed that the matrix material and silane-modified nanomaterial improved the dispersibility and bonding strength of the interface, helping to support the load evenly and enabling effective stress transfer.

Voice Activity Detection Method Using Psycho-Acoustic Model Based on Speech Energy Maximization in Noisy Environments (잡음 환경에서 심리음향모델 기반 음성 에너지 최대화를 이용한 음성 검출 방법)

  • Choi, Gab-Keun;Kim, Soon-Hyob
    • The Journal of the Acoustical Society of Korea
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    • v.28 no.5
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    • pp.447-453
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    • 2009
  • This paper introduces the method for detect voices and exact end point at low SNR by maximizing voice energy. Conventional VAD (Voice Activity Detection) algorithm estimates noise level so it tends to detect the end point inaccurately. Moreover, because it uses relatively long analysis range for reflecting temporal change of noise, computing load too high for application. In this paper, the SEM-VAD (Speech Energy Maximization-Voice Activity Detection) method which uses psycho-acoustical bark scale filter banks to maximize voice energy within frames is introduced. Stable threshold values are obtained at various noise environments (SNR 15 dB, 10 dB, 5 dB, 0 dB). At the test for voice detection in car noisy environment, PHR (Pause Hit Rate) was 100%accurate at every noise environment, and FAR (False Alarm Rate) shows 0% at SNR15 dB and 10 dB, 5.6% at SNR5 dB and 9.5% at SNR0 dB.

A study on failure probability characteristic based on the reliability analysis according to the variation of boundary conditions (신뢰성 기반 쉴드터널의 경계조건 변화에 따른 파괴확률 특성에 관한 연구)

  • Gyu-Phil Lee;Young-Bin Park
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.25 no.6
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    • pp.447-458
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    • 2023
  • In this study, a comparison model considering the stochastic characteristics of the load and member resistance of the shield tunnel segment lining as well as the variability of the boundary condition was selected and reliability analysis was performed, and the adequacy of the limit state design was analyzed by calculating the probability of failure and reviewing the structural safety. For the analysis considering the probability characteristics of these ground constants, the ground spring coefficient was considered as the mean value by calculating the quantitative value by applying the Muirwood formula, and the coefficient of variation was selected based on the existing research data to review the models according to the change of ground boundary conditions. Through the structural analysis of these models and the reliability analysis using MCS technique, the failure probability and reliability index were calculated to examine the changes in the failure probability due to changes in ground boundary conditions.

The effect of in-situ stress parameters and metamorphism on the geomechanical and mineralogical behavior of tunnel rocks

  • Kadir Karaman
    • Geomechanics and Engineering
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    • v.37 no.3
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    • pp.213-222
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    • 2024
  • Determination of jointed rock mass properties plays a significant role in the design and construction of underground structures such as tunneling and mining. Rock mass classification systems such as Rock Mass Rating (RMR), Rock Mass Index (RMi), Rock Mass Quality (Q), and deformation modulus (Em) are determined from the jointed rock masses. However, parameters of jointed rock masses can be affected by the tunnel depth below the surface due to the effect of the in situ stresses. In addition, the geomechanical properties of rocks change due to the effect of metamorphism. Therefore, the main objective of this study is to apply correlation analysis to investigate the relationships between rock mass properties and some parameters related to the depth of the tunnel studied. For this purpose, the field work consisted of determining rock mass parameters in a tunnel alignment (~7.1 km) at varying depths from 21 m to 431 m below ground surface. At the same excavation depths, thirty-seven rock types were also sampled and tested in the laboratory. Correlations were made between vertical stress and depth, horizontal/vertical stress ratio (k) and depth, k and Em, k and RMi, k and point load index (PLI), k and Brazilian tensile strength (BTS), Em and uniaxial compressive strength (UCS), UCS and PLI, UCS and BTS. Relationships were significant (significance level=0.000) at the confidence interval of 95% (r = 0.77-0.88) between the data pairs for the rocks taken from depths greater than 166 m where the ratio of horizontal to vertical stress is between 0.6 and 1.2. The in-situ stress parameters affected rock mass properties as well as metamorphism which affected the geomechanical properties of rock materials by affecting the behavior of minerals and textures within rocks. This study revealed that in-situ stress parameters and metamorphism should be reviewed when tunnel studies are carried out.