• 제어로봇시스템학회논문지
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• 제11권2호
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• pp.103-108
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• 2005

Loading/Unloading task in the real industry is performed by crane, but most of the loading/unloading task with the weight of 5kg∼30kg is done by human workers and this kind of work causes industrial disaster of workers. Therefore it is necessary to develop low cost loading/unloading manipulator system to prevent this kind of industrial accidents. This paper is concerned with the design and fabrication of 2 axis pneumatic manipulators using on/off solenoid valves and accurate position control without respect to the external load and low damping in the pneumatic rotary actuator. To overcome the change of external load, switching of control parameter using LVQNN (Learning Vector Quantization Neural Network) is newly applied, which estimates the external loads in the pneumatic cylinder. As an underlying controller, a state feedback controller using position, velocity and acceleration is applied to the switching control system. The effectiveness of the proposed control algorithms are demonstrated through experiments of pneumatic cylinder with various loads.

• 한국안전학회지
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• 제15권4호
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• pp.35-40
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• 2000

The influence of cyclic loading history on the creep behavior of the 30 vol% hot-pressed $SiC_f/Si_3N_4copmposite was experimentally investigated at $1200^{\circ}C$. The duration of loading/unloading had great effects on the creep behaviors. The short term duration cyclic loading history test results showed significant reduction in the primary and steady-state creep rates. For example, 300sec loading/300sec unloading history resulted in 70% lower steady-state creep rate than that of the continuous loading. However the long term duration cyclic loading history test results showed little change in creep rates compared to those of the continuous one. The reason for the significant change in the short term duration cycles was estimated due to the change in the stress redistribution between the fiber and matrix during the creep recovery in the primary stage.

• 한국안전학회지
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• 제13권4호
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• pp.96-101
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• 1998

J-R curve tests were performed on 1T compact specimens of SA516 Gr. 70 carbon steels under reverse cyclic loading. A Direct-Current Potential Drop (DCPD) method, one of the nondestructive techniques to detect flaw of structure, is being increasingly used for monitoring crack initiation and stable crack growth in typical fracture mechanics specimens for J-R testing. In many aspects this method is simpler than the unloading compliance method. The objective of this paper is to evaluate the J-R Curve according to the crack length measurement techniques under reverse cyclic loading. In order to prove the reliability and repeatability of the DCPD method, the crack length measured by using DCPD method was compared to one determined from unloading compliance. Consequently, this DCPD method correlated well with J-R curves and crack extension measurements determined from unloading compliance method.

• Structural Engineering and Mechanics
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• 제77권2호
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• pp.179-196
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• 2021

Experimental investigations on the seismic behaviors of the PVC-FRP Confined Reinforced Concrete (PFCRC) columns under low cyclic loading are carried out and two variable parameters including CFRP strips spacing and axial compression ratio are considered. The PFCRC column finally fails by bending and is characterized by the crushing of concrete and yielding of the longitudinal reinforcement, and the column with a high axial compression ratio is also accompanied by the cracking of the PVC tube and the fracture of CFRP strips. The hysteretic curves and skeleton curves of the columns are obtained from the experimental data. With the increase of axial compression ratio, the stiffness degradation rate accelerates and the ductility decreases. With the decrease of CFRP strips spacing, the unloading sections of the skeleton curves become steep and the ductility reduces significantly. On the basis of fiber model method, a numerical analysis approach for predicting the skeleton curves of the PFCRC columns is developed. Additionally, a simplified skeleton curve including the elastic stage, strengthening stage and unloading stage is suggested depending on the geometric drawing method. Moreover, the loading and unloading rules of the PFCRC columns are revealed by analyzing the features of the skeleton curves. The quantitative expressions that are used to predict the unloading stiffness of the specimens in each stage are proposed. Eventually, an analytical model for the PFCRC columns under low cyclic loading is established and it agrees well with test data.

• 수산해양기술연구
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• 제59권2호
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• pp.181-187
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• 2023

Laver aquaculture, which occupies a large proportion in the aquaculture industry in Korea, is still highly dependent on human labor. Therefore, it is necessary to study the development of an automatic system to improve the working environment and increase the efficiency of aquaculture production systems. The purpose of this study is to evaluate the economic feasibility of an improved system in a study for the loading-unloading and automatic weighing systems in laver aquaculture industry. Economic analysis of the developed unloading and automatic weighing system were implemented under various conditions to calculate more accurate benefits and costs. As a result of this study, the economic feasibility was found to be very high in the three models: net present value (NPV), benefit-cost ratio (B/C), internal rate of return (IRR). Moreover, the results of sensitivity analysis showed that the economical efficiency of the automatic loading, unloading, and weighing system in laver aquaculture was very high.

• 한국시뮬레이션학회논문지
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• 제10권2호
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• pp.33-46
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• 2001

Recently, the usage of containers in marine transportation is rapidly increasing. The problem of ship stability is important because of its direct influence to the loss of the human-life, ship, and merchandise. However, the assessment for ship stability during container loading/unloading in port is dependent on human experience only. On the other hand, the emerging information and communication technologies of shipbuilding industrial environments are rapidly changing. To respond to the situation, a new paradigm has been matured with new concepts such as the concrete method. Especially, all the efforts are shown to be concentrated to realize the concept of Simulation Based Design(SBD) based on three dimensional Computer Aided Design(CAD) model. In this paper, ship model-based simulation methodology for design and operation of ship is suggested, and for the verification of suggested methodology, the system for stability assessment of ship during container loading/unloading was developed using ENVISION, a general-purpose simulation system. The developed system consists of geometric modeling subsystem, basic calculation subsystem, and Computer Aided Engineering(CAE) subsystem. In addition, interface to CAE/CAD /simulation system such as SIKOB and ENVISION is provided.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.378-381
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• 2009

In this study, the repetitive loading-unloading tensile tests with AZ31B magnesium sheet metal have been conducted under various elevated temperatures to check out how the Young's moduli of the sheets evolve during the plastic deformation. The loading-unloading tests have been carried out at every 1% of strain increment. With the tested results, some damage parameters of magnesium sheets based on the Lemaitre's continuum damage theory could be calculated at room temperature, $100^{\circ}C$, $150^{\circ}C$, $200^{\circ}C$ and $250^{\circ}C$. It has been shown that the critical damage parameters obtained in all temperature conditions are within the range of 0.12 to 0.18.

• Geomechanics and Engineering
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• 제31권4호
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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.

• 지질공학
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• 제31권2호
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• pp.149-163
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• 2021

특성이 서로 다른 화강암, 대리암 그리고 사암에 대하여 일축압축시험과 반복재하시험을 실시하여 암석의 손상특성을 분석하였다. 일축압축시험으로 암석들의 강도, 탄성상수 그리고 손상기준응력을 결정하였고 이를 반복재하시험의 결과와 비교하였다. 반복재하시험으로 측정된 암석들의 평균 강도는 일축압축시험으로 측정된 값보다 약간 작거나 유사였다. 특히 강도가 높고 공극률이 낮은 암석들이 공극률이 매우 큰 연약한 암석들에 비해 반복하중에 의한 피로현상에 더 민감하였다. 반복 재하-제하 과정에서 발생되는 암석의 영구변형률은 암종에 따라 약간의 차이는 있으나 암석의 손상상태를 파악할 수 있는 유용한 도구로 활용할 수 있다는 것을 확인하였다. 특히 응력-누적영구변형률 곡선은 화강암과 대리암에 대하여 균열손상응력을 추정할 수 있는 가능성을 보여주었다. 시험과정에 미소파괴음을 측정하여 암석의 손상상태를 판단할 수 있는 펠리시티 비를 계산하였다. 공극이 매우 많고 연약한 사암은 미소파괴음의 방출이 매우 미약하여서 펠리시티 비의 계산에 어려움이 있었다. 반면 공극이 적고 취성의 특성을 보이는 화강암과 대리임의 경우 반복재하단계에서 계산된 펠리시티 비를 통하여 암석의 균열손상응력을 추정할 수 있는 가능성을 보여주었다. 향후 더 많은 시료와 다양한 종류의 암석을 대상으로 추가적인 시험을 진행하여 공통적인 결과를 도출한다면 유사한 조건을 갖는 암반의 손상과 변형 거동을 파악하는 데 도움이 될 수 있을 것으로 판단된다.

• 한국산학기술학회논문지
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• 제16권5호
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• pp.3426-3433
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• 2015

본 논문은 제한된 철도 수송능력 환경에서 여객과 화물을 동시에 수송하기 위한 복합화물열차의 화물 배치를 위한 방법 중, 라운드 컨베이어 시스템과 세로형 순환식 시스템. 가로형 순환식 시스템을 각각 P 택배사의 지역간 운송 화물량을 기준으로 부산에서 대구, 대전, 오송을 거쳐 서울에 도착함을 가정하여 각각 도착역별로 상하차 시간을 계산하였다. 그 결과 가로형 순환식 시스템은 화물 적재 가능량도 적었으며 상하차 시간도 434초로 가장 많이 소요되었고 세로형 순환식 시스템이 상차 시간이 다소 많이 소요되었지만, 총 소요시간에서는 408초로 가장 우수한 특성을 보였다. 각각 시스템별로 상하차 시간을 비교함으로 향후 복합화물열차 제작시에 유용한 방법을 제시하고 복합화물열차의 화물 운송 효율을 증진하고자 한다.