• Structural Engineering and Mechanics
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• 제4권1호
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• pp.49-59
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• 1996

This paper considers large deflection problem of a simply supported beam with variable are length subjected to a point load. The beam has one of its ends hinged and at a fixed distance from this end propped by a frictionless support over which the beam can slide freely. This highly nonlinear flexural problem is solved by elliptic-integral method and shooting-optimization technique, thereby providing independent checks on the new solutions. Because the beam can slide freely over the frictionless support, there is a maximum or critical load which the beam can carry and it is dependent on the position of the load. Interestingly, two possible equilibrium configurations can be obtained for a given load magnitude which is less than the critical value. The maximum arc-length was found to be equal to about 2.19 times the fixed distance between the supports and this value is independent of the load position.

• KIEAE Journal
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• 제7권5호
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• pp.135-142
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• 2007

This is an experimental study on the structural characteristics of reinforced concrete beams using of the oyster shells as a substitute fine aggregate of concrete. In this study, the main factors consist of the grain sizes and the percentage of substitution of oyster shells to fine aggregate in the equal water cement ratio. The results of the study showed as followed. The initial load value of them represented similar constant within 10% of the maximum load value in each test beam. But the maximum load value and the ultimate load value decreased with increased grain size and the rate of substitution. As the grain size of oyster shells became smaller, the load values of them were somewhat higher. The deflection among deformation properties of reinforced concrete beams with oyster shells represented typical curves like that of normal reinforced concrete. In the deformation of steel and concrete, the deformation was proportionated to the load till yield point and from yield point until approaching the ultimate load point. One type was typical curve of the load and the deformation and the other type irregularly was changed to very small deformation for the load increase centering around load axis. After the analyzing structural behaviors and the properties of reinforced concrete test beams with oyster shells, the most excellent grain size of oyster shells represented 1.0mm and less or 5.0mm and less with taking uniformly, and the percentage of practicable substitution of them to fine aggregate was about 30%.

• Structural Engineering and Mechanics
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• 제66권4호
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• pp.445-452
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• 2018

In this paper the effects of particle size and model scale of concrete have been investigated on point load index, tensile strength, and the failure processes using a PFC2D numerical modeling study. Circular and semi-circular specimens of concrete were numerically modeled using the same particle size, 0.27 mm, but with different model diameters of 75 mm, 54 mm, 25 mm, and 12.5 mm. In addition, circular and semi-circular models with the diameter of 27 mm and particle sizes of 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, and 1.27 mm were simulated to determine whether they can match the experimental observations from point load and Brazilian tests. The numerical modeling results show that the failure patterns are influenced by the model scale and particle size, as expected. Both Is(50) and Brazilian tensile strength values increased as the model diameter and particle sizes increased. The ratio of Brazilian tensile strength to Is(50) showed a reduction as the particle size increased but did not change with the increase in the model scale.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.153-156
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• 2001

Maximum Power Point Tracking(MPPT) is used in wind power generation systems to maximize wind power turbin output power, irrespective of wind speed conditions and of the load electrical characteristics. In this paper we do the equivalent modeling the mechanical energy of wind power turbine according to wind speed into the synchronous generator. We analyse the equivalent modeling output part of rectifier into DC/DC converter input part theoretically. We design a control algorithm for variable voltage according to wind speed intensity and density so that load voltage of chopper is controlled steadily using the maximum power point tracking (MPPT) control method. We analyse a battery charging characteristics and a charging circuit for power storage enabling the supply of stable power to the load. We design a system and do the modeling of it analytically so that it supplies a stable power to the load by constructing a DC-AC inverter point. Also we design a charging circuit usable in actual wind power generation system of 30kW and confirm its validity.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.153-156
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• 2001

Maximum Power Point Tracking(MPPT) Is used in wind power generation systems to maximize wind power turbin output power, irrespective of wind speed conditions and of the load electrical characteristics. In this paper we do the equivalent modeling the mechanical energy of wind power turbine according to wind speed into the synchronous generator. We analyse the equivalent modeling output part of rectifier into DC/DC converter input part theoretically. We design a control algorithm for variable voltage according to wind speed intensity and density so that load voltage of chopper is controlled steadily using the maximum power point tracking(MPPT) control method. We analyse a battery charging characteristics and a charging circuit for power storage enabling the supply of stable power to the load. We design a system and do the modeling of it analytically so that it supplies a stable power to the load by constructing a DC-AC inverter point. Also we design a charging circuit usable in actual wind power generation system of 30kW and confirm its validity.

• Journal of Biosystems Engineering
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• 제31권1호
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• pp.16-23
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• 2006

Depth and working load control is one of the most important technique in control system for tractor rotary implement automation. Keeping the depth consistent is critical to bring along crops and to improve the efficiency and quality of the following operations. Keeping the load of engine consistent is an essential factor for the efficiency of operation and engine protection of tractor. In this study we investigated the possibility of application of depth and working load control system for tractor using a proportional valve through field tests. Depth control was implemented by the ascent and descent of 3 point linkage for the change of setting depth. There were 4 mm and 5.2 mm control deviations for setting depths of 50mm and 100mm, respectively. Load control was operated appropriately by the ascent and of descent of 3 point link for the change of setting working load. The standard deviations between setting load and engine load were 171 rpm at 1.3 km/h and 164 rpm at 2.3 km/h tractor travel velocity. The results of experiment showed that the characteristics of response was sufficient to be used as the implement depth and working load control system for tractor using proportional valve.

• Structural Engineering and Mechanics
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• 제91권4호
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• pp.335-347
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• 2024

This paper presents the behavior of geopolymer concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars. In the study, ordinary Portland cement concrete and geopolymer concrete beams having GFRP bars were prepared and tested under four-point loading. The load-deflection diagrams and load capacities of the tested beams were obtained. It was observed that the tested beams exhibited good ductility and significant deflection capacity. The results showed that increasing the tension GFRP reinforcement ratio caused enhancement in the strength capacity of geopolymer concrete beams. In addition, the tested beams were analyzed to obtain the load capacity and the load-deflection responses. The theoretical load-deflection curves and load bearing capacities have been predicted well with the test results. Parametric study has been performed to determine the influences of concrete strength, shear span to depth ratio (a/d) and reinforcement ratio on the behavior of geopolymer concrete beams longitudinally reinforced with GFRP bars. It was concluded that increasing concrete strength led to an increase in load capacity. Besides, the ultimate load increased as the reinforcement ratio increased. On the other hand, increasing a/d ratio reduced the ultimate load value of GFRP reinforced geopolymer concrete beams.

• 한국지반환경공학회 논문집
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• 제8권1호
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• pp.21-26
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• 2007

터널이나 지하굴착의 설계와 시공에서 암석의 강도평가는 매우 중요한 요소이다. 하지만, 실무에서는 암석의 일축압축강도시험(UCST)를 실시하기에는 시간과 노력이 많이 소요되며 시험개수에도 제한을 받는다. 이 방법을 보완하기 위한 시험법으로 제시된 것이 점하중강도 시험(PLST)이다. 그러나 실무에서는 지역과 암종에 따른 구분없이 점하중강도 지수를 통합하여 사용하는 경우가 많아 정확한 강도를 유추하는데 문제점이 있다. 이 연구의 목적은 경기 편마암복합체내 일축압축강도와 점하중강도의 상관관계를 분석함으로써 시공현장에서 사용하는 식에 대한 값을 제시하고자 한다.

• 오토저널
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• 제13권5호
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• pp.51-64
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• 1991

In this paper, an attempt is made to analyze the impulsive stress directly underneath the concentrated impact point for a supported square plate by using the three-dimensional dynamic theory of elasticity and the potential theory of displacement (stress function) on the supposition that the load, F$_{*}$0 sin .omega.t, acted on the central part of it. The results obtained from this study are as follows: 1. The impulsive stress cannot be analyzed directly underneath the acting point of concenrated impact load in privious theories, but can be analyzed by using the three-dimensional dynamic theory of elasticity and the potential theory of displacement. 2. Theorically, with increasing the pulse width of applied load, it was possible to clarify that the amount of stress in the point of concentrated impact load was increased and that of stress per unit impulse was decreased. 3. The numerical inversion of laplace transformation by the use of the F.F.T algorithm contributes the reduction of C.P.U time and the improvement of the accuracy or results. 4. In this paper recommended, it is found that the approximate equation of impact load function P (.tau.) = A.tau. exp (-B.tau.), and P (.tau.) =0.85A exp (-B.tau.) sinC.tau. could actually apply to all impact problem. In compared with the experimental results, the propriety of the analytical method is reasonable.

• Structural Engineering and Mechanics
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• 제67권2호
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• pp.185-206
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• 2018

This paper studies the non-axisymmetric 3D problem on the dynamics of the moving load acting in the interior of the hollow cylinder surrounded with elastic medium and this study is made by utilizing the exact equations of elastodynamics. It is assumed that in the interior of the cylinder the point located with respect to the cylinder axis moving forces act and the distribution of these forces is non-axisymmetric and is located within a certain central angle. The solution to the problem is based on employing the moving coordinate method, on the Fourier transform with respect to the spatial coordinate indicated by the distance of the point on the cylinder axis from the point at which the moving load acts, and on the Fourier series presentation of the Fourier transforms of the sought values. Numerical results on the critical moving velocity and on the distribution of the interface normal and shear stresses are presented and discussed. In particular, it is established that the non-axisymmetricity of the moving load can decrease significantly the values of the critical velocity.