Effect of Loading Rate on the Fracture Behavior of Nuclear Piping Materials Under Cyclic Loading Conditions

김진원,최명락,김윤재 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.6

This study investigated the loading rate effect on the fracture resistance under cyclic loading conditions to understand clearly the fracture behavior of piping materials under seismic conditions. J–R fracture toughness tests were conducted under monotonic and cyclic loading conditions at various displacement rates at room temperature and the operating temperature of nuclear power plants (i.e., 316°C). SA508 Gr.1a low-alloy steel and SA312 TP316 stainless steel piping materials were used for the tests. The fracture resistance under a reversible cyclic load was considerably lower than that under monotonic load regardless of test temperature, material, and loading rate. Under both cyclic and monotonic loading conditions, the fracture behavior of SA312 TP316 stainless steel was independent of the loading rate at both room temperature and 316°C. For SA508 Gr.1a low-alloy steel, the loading rate effect on the fracture behavior was appreciable at 316°C under cyclic and monotonic loading conditions. However, the loading rate effect diminished when the cyclic load ratio of the load (R) was −1. Thus, it was recognized that the fracture behavior of piping materials, including seismic loading characteristics, can be evaluated when tested under a cyclic load of R = −1 at a quasistatic loading rate.

간헐적이고 불규칙적인 부하 조건에서 바이오필터의 Xylene 제거 성능 및 세균 활성

이은희,최선아,조경숙 한국입자에어로졸학회 2011 Particle and Aerosol Research Vol.7 No.1

The effects of different transient loading conditions on xylene removability and bacterial activity were evaluated in the polyurethane (PU) biofilter inoculated with Rhodococcus sp. EH831: BF1 (the control) was operated under continuous and constant loading (200±50 ppm); BF2 under continuous and constant loading after a 2-week long-term shutdown;BF3 under discontinuous (8 h on/16 h off on weekdays and a 2 day-shutdown at weekends) and constant loading BF4under discontinuous and high loading (700 ± 300 ppm); and BF5 under continuous and fluctuating loading (high loading for 8 h and low loading (75±25 ppm) for 16 h on weekdays and low loading at weekends). Xylene removal efficiencies in the BF1, BF2,BF3 and BF5 were ranged 83 –89%, indicating that 2-week long-term shutdown,intermittent or fluctuant loading condition did not significantly influence the biofilter performance. However,discontinuous and high load condition (BF4) caused to deteriorate xylene removability to 52%. Rhodococcus sp. EH831 could be maintained at 109~1010 CFU/g-dry PU under 5 kinds of loading conditions. The result of polymerase chain reaction-terminal-restriction fragment length polymorphismshowed that there was no significant change in bacterial community structures by different loading conditions.

An Experimental Study on Hydrodynamic Forces of Korea Autonomous Surface Ship in Various Loading Conditions

Thi Thanh Diep Nguyen,Van Thuan Mai,이산,윤현규 한국항해항만학회 2022 한국항해항만학회지 Vol.46 No.2

Currently, shipping by sea is becoming common because of the low price and the safety of goods. The ship is designed as a larger vessel to meet the need of this development. In the design stage, the investigation of hydrodynamic forces acting on the ship hull is very important in predicting the ship's maneuverability. Given that the ship docks at various ports for loading or discharging goods, the ship usually operates in various loading conditions, depending on the site condition and other various factors. Hence, it is necessary to investigate the effect of the loading condition on the hydrodynamic forces acting on the ship, to most accurately determine the maneuverability of the ship. In this study, an experiment of Korea Autonomous Surface Ship (KASS) was conducted at the towing tank of Changwon National University to measure the hydrodynamic forces acting on the KASS. The loading condition considered in this experiment is determined based on the draft, which was decreased by 5% for each loading condition. The smallest draft is 85% of the design draft. The static test as Oblique Towing Test (OTT), Circular Motion Test (CMT), Circular Motion Test with Drift (CMTD) is performed in the various loading conditions. First, the hydrodynamic forces in the Oblique Towing test (OTT) are compared with the result of other institutes. Second, the hydrodynamic forces in various drift angle, yaw rate and loading conditions are measured. Finally, the influence of the loading conditions on the hydrodynamic coefficient is discussed.

침수-하중조건에서의 암석물성 변화가 암반의 구조적 안정성에 미치는 영향 평가

박승훈,허진,이준희,박정찬,권상기 한국자원공학회 2015 한국자원공학회지 Vol.52 No.3

This research was carried out to evaluate the influence of rock property change under saturated-loading condition on the stability of an underground opening. Rock samples were divided into saturated-loading and unsaturated-loading conditions in order to observe the variation of mechanical properties of the rock after loading using a creep test machine. Measured thermal conductivity and porosity from various laboratory tests showed the variation of rock properties. Tensile strength was found to be more significantly decreased in saturated condition. It was also found that uniaxial compressive strength in saturated condition decreased more significantly compared to that in unsaturated condition. A numerical modeling using FLAC3D was carried out to evaluate the stability of a pillar with a consideration of the rock property change expected in saturated-loading condition. It was recommended to use the changed properties instead of the initial rock properties to analyze the stability of the unused underground mines or openings. 본 연구에서는 폐광산 주변 암반의 안정성 평가를 위한 침수 환경과 가압조건에 따른 암석물성 변화가지하공간의 안정성에 미치는 영향을 평가하기 위해 수행하였다. 암석물성 변화를 관찰하기 위하여 시료의 절반을 포화시킨 상태(침수조건)와 나머지 절반을 포화시키지 않은 상태(비침수조건)로 구분하였다. 본 실험은 크립시험기를 이용하여 하중을 주어 침수 및 가압환경을 조성하여 실시하였다. 암석 실험 결과에서는 침수조건에서열전도도와 공극률의 물성 변화가 나타났다. 간접인장강도는 하중 증가에 따른 암석강도 저하가 확인되었고, 일축압축강도에서도 침수조건에서 암석강도가 낮게 나타났다. 또한, FLAC3D를 이용한 수치모델링에서는 광주의 안전율이 침수조건에서 저하되는 것을 확인하였다. 폐광산 및 지하공간의 용도변경과 재활용 시에는 광산이운영되었던 초기 암석물성을 사용하지 않고 침수환경에 따른 암석물성 변화를 고려한 암반의 안정성 평가가필요하다.

Effects of cold joint and loading conditions on chloride diffusion in concrete containing GGBFS

Yoo, S.W.,Kwon, S.J. Butterworth Scientific ; Elsevier Science Ltd 2016 Construction & building materials Vol.115 No.-

RC (Reinforced Concrete) structures undergo deterioration and the initiated corrosion in the steel is considered as one of the most critical problems. For efficient construction of structures, construction joint should be installed, however cold joint occurs reluctantly due to delayed concrete placing and poor condition of the old concrete surface. The chloride ingress in cold joint concrete is more rapid than that in sound concrete, and it is also affected by loading conditions. This paper presents a quantitative evaluation on chloride diffusion coefficient considering the effects of cold joint and loading conditions. For the work, concrete samples with 0.6 of w/b (water to binder) ratio are prepared. Compressive and tensile stresses are induced with 30% and 60% of ultimate strength, respectively. The chloride diffusion coefficients in accelerated condition are measured under loading, and the effects of cold joint and loading levels are evaluated. In order to investigate an effect of GGBFS (Ground Granulated Blast Furnace Slag) on chloride diffusion, 40% of GGBFS replacement ratio is considered for OPC (Ordinary Portland Cement) and the GGBFS effect is evaluated considering cold joint and loading levels. The effects of stress level, pore structure improvement through GGBFS, and cold joint on chloride diffusion coefficient are quantitatively investigated.

CPT-Based p-y Analysis for Piles Embedded in Clays under Cyclic Loading Conditions

김가람,경두현,박동규,김인철,이준환 대한토목학회 2016 KSCE Journal of Civil Engineering Vol.20 No.5

The design of offshore mono-piles is subjected to various uncertainties more than inland cases, due to experimental difficulties in characterizing required soil parameters under offshore environment. In this study, a CPT-based p-y method is proposed for monopiles embedded in clay under cyclic loading conditions. As offshore mono-piles are particularly targeted in this study, the cyclic loading condition was introduced as an important design consideration. Based on the effective cone factor, the ultimate lateral soil resistance and p-y function were formulated as a function of CPT cone resistance and cyclic loading effect factor with consideration of the number of loading cycle. As the CPT-based p-y function utilizes the continuous CPT profile directly, detailed depth profile of soil characteristics can also be directly taken into account for the analysis without additional sampling and testing procedure. The load transfer analysis using the proposed CPT-based p-y analysis for cyclic loading condition was programmed using the discretized implementation algorithm for the beam-on-elastic foundation model. To validate the CPT-based p-y analysis method, the calculated lateral load responses were compared with the results obtained from the finite element analysis and case examples for static and cyclic loading conditions.

머신러닝 기법을 활용한 유황별 LOADEST 모형의 적정 회귀식 선정 연구: 낙동강 수계를 중심으로

김종건 ( Jonggun Kim ),박윤식 ( Youn Shik Park ),이서로 ( Seoro Lee ),신용철 ( Yongchul Shin ),임경재 ( Kyoung Jae Lim ),김기성 ( Ki-sung Kim ) 한국농공학회 2017 한국농공학회 학술대회초록집 Vol.2017 No.-

This study is to determine the coefficients of regression equations and to select the optimal regression equation in the LOADEST model after classifying the whole study period into 5 flow conditions for 16 watersheds located in the Nakdonggang waterbody. The optimized coefficients of regression equations were derived using the gradient descent method as a learning method in Tensorflow which is the engine of machine-learning method. In South Korea, the variability of streamflow is relatively high, and rainfall is concentrated in summer that can significantly affect the characteristic analysis of pollutant loads. Thus, unlike the previous application of the LOADEST model(adjusting whole study period), the study period was classified into 5 flow conditions to estimate the optimized coefficients and regression equations in the LOADEST model. As shown in the results, the equation #9 which has 7 coefficients related to flow and seasonal characteristics was selected for each flow condition in the study watersheds. When compared the simulated load(SS) to observed load, the simulation showed a similar pattern to the observation for the high flow condition due to the flow parameters related to precipitation directly. On the other hand, although the simulated load showed a similar pattern to observation in several watersheds, most of study watersheds showed large differences for the low flow conditions. This is because the pollutant load during low flow conditions might be significantly affected by baseflow or point-source pollutant load. Thus, based on the results of this study, it can be found that to estimate the continuous pollutant load properly the regression equations need to be determined with proper coefficients based on various flow conditions in watersheds. Furthermore, the machine-learning method can be useful to estimate the coefficients of regression equations in the LOADEST model.

머신러닝 기법을 활용한 유황별 LOADEST 모형의 적정 회귀식 선정 연구: 낙동강 수계를 중심으로

김종건,박윤식,이서로,신용철,임경재,김기성,Kim, Jonggun,Park, Youn Shik,Lee, Seoro,Shin, Yongchul,Lim, Kyoung Jae,Kim, Ki-sung 한국농공학회 2017 한국농공학회논문집 Vol.59 No.4

This study is to determine the coefficients of regression equations and to select the optimal regression equation in the LOADEST model after classifying the whole study period into 5 flow conditions for 16 watersheds located in the Nakdonggang waterbody. The optimized coefficients of regression equations were derived using the gradient descent method as a learning method in Tensorflow which is the engine of machine-learning method. In South Korea, the variability of streamflow is relatively high, and rainfall is concentrated in summer that can significantly affect the characteristic analysis of pollutant loads. Thus, unlike the previous application of the LOADEST model (adjusting whole study period), the study period was classified into 5 flow conditions to estimate the optimized coefficients and regression equations in the LOADEST model. As shown in the results, the equation #9 which has 7 coefficients related to flow and seasonal characteristics was selected for each flow condition in the study watersheds. When compared the simulated load (SS) to observed load, the simulation showed a similar pattern to the observation for the high flow condition due to the flow parameters related to precipitation directly. On the other hand, although the simulated load showed a similar pattern to observation in several watersheds, most of study watersheds showed large differences for the low flow conditions. This is because the pollutant load during low flow conditions might be significantly affected by baseflow or point-source pollutant load. Thus, based on the results of this study, it can be found that to estimate the continuous pollutant load properly the regression equations need to be determined with proper coefficients based on various flow conditions in watersheds. Furthermore, the machine-learning method can be useful to estimate the coefficients of regression equations in the LOADEST model.

침수-하중 조건에서의 결정질 화강암의 열적, 역학적 물성 변화

허진(Jin Heo),이재철(Jae Chul Lee),서정범(Jung Bum Seo),박승훈(Seung Hun Park),박정찬(Jung Chan Park),권상기(Sang Ki Kwon) 한국암반공학회 2014 터널과지하공간 Vol.24 No.3

지하 하중 조건에서 암석물성이 변한다는 것은 잘 알려져 있다. 따라서 침수상태에 놓인 폐광산이나 폐공동에서의 하중에 따른 암석 물성변화와 일반적인 건조상태의 하중에 따른 물성 변화와의 관계에 대하여는 연구가 필요하다. 침수-하중 조건에서의 암석 물성 변화를 파악하기 위해 다양한 실험실 실험이 실시되었다. 암석에 가해지는 하중은 단축압축강도의 20~80%로 조절하였다. 침수 및 건조 조건에서 동일한 하중을 가할 경우 발생하는 암석의 열적, 역학적, 물리적 물성 변화를 비교함으로써 건조조건에 비해 침수조건에서의 물성변화가 더 크게 일어남을 알 수 있었다. It is well known that rock properties can be affected by loading in underground condition. In the case of flooded underground mine or tunnels, rock properties variation due to loading might be different from the loading in dry condition. In order to verify the influence of saturated loading condition on rock properties, various laboratory tests had been carried out. Loading on the rock specimen was controlled to be ranged in between 20 ~ 80% of UCS. By comparing the variation of thermal, mechanical, and physical properties of rock specimens under the same load in saturated and dry condition, it was possible to find that the rock properties can be more significantly disturbed in the saturated loading condition than in dry loading condition.

Effect of Load Condition on Turning Performance of a VLCC in Adverse Weather Conditions

Zaky, Mochammad,Yasukawa, Hironori Korean Society of Ocean Engineers 2018 Journal of advanced research in ocean engineering Vol.4 No.2

The load condition significantly influences ship maneuverability in calm water. In this research, the effect of the load condition on turning performance of a very large crude oil carrier (VLCC) sailing in adverse weather conditions is investigated by an MMG-based maneuvering simulation method. The relative drift direction of the ship in turning to the wave direction is $20^{\circ}-30^{\circ}$ in ballast load condition (NB) and full load condition (DF) with a rudder angle $35^{\circ}$ and almost constant for any wind (wave) directions. The drifting displacement in turning under NB becomes larger than that under DF at the same environmental condition. Advance $A_d$ and tactical diameter $D_t$ become significantly small with an increasing Beaufort scale in head wind and waves when approaching, although $A_d$ and $D_t$ are almost constant in following wind and waves. In beam wind and waves, the tendency depends on the plus and minus of the rudder angle.