• 한국철도학회논문집
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• 제13권4호
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• pp.431-439
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• 2010

강섬유콘크리트는 터널의 숏크리트와 산업슬래브포장과 같은 적용 분야에서는 벌써 주목할 정도로 성공적인 반면에 일반적인 건설실무에서는 적용가능성이 주로 경제적인 이유로 해서 지금 까지는 부분적으로 제한되었다. 동적하중을 받는 특수한 분야 예를 들면 충격하중, 지진하중 및 철도의 피로하중등과 같은 동적하중이 작용하는 구조물에 대해서는 흥미로운 가능성을 열어 놓고 있다. 따라서 연구에서는 저자 연구소에서 수행한 다양한 동하중을 받는 구조물에 강섬유콘크리트를 적용할 수 있도록 강섬유콘크리트의 에너지 감쇠, 충격특성 및 피로거동 등을 실험적으로 수행한 연구결과로 보여준다.

• 정보보호학회논문지
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• 제17권4호
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• pp.47-52
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• 2007

본 논문에서는 파이프 해쉬 함수를 가진 동적 파이프 해쉬 함수를 제안한다. 안전도를 높이기 위하여, 압축함수를 추가하여 파이프 기반 동적 해쉬 함수를 제안하였다. 제안한 동적 파이프 해쉬 함수는 다중충돌공격에 안전하고 압축 사이즈를 가변할 수 있기 때문에 많은 장점을 가지고 있다. 예를 들어, 디지털 서명 프로토콜에서 사용자가 보다 큰 키 사이즈를 선택하여 높은 안전도를 요구한다면, 동적 해쉬 함수를 사용하여 압축사이즈를 증가시켜 쉽게 실현할 수 있다.

• 한국응용과학기술학회지
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• 제37권6호
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• pp.1669-1677
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• 2020

이 연구의 목적은 14주 고유수용성 저항운동이 사회복지시설 이용 여성 노인의 근지구력, 동적 평형성 및 보행능력에 미치는 영향이었다. 이 연구에 참여한 대상자는 평균연령이 70세 전후의 30의 여성 노인을 운동집단 15명과 통제집단 15명으로 구성하였다. 대상자들은 운동프로그램 전과 후에 근지구력(30초 의자 앉았다 일어서기), 동적 평형성(3m 왕복 걷기)과 보행능력(10m 걷기, 400m 걷기)을 검사하였다. 운동집단은 주 3회 60분간 스위스 볼을 이용한 고유수용성 저항운동을 하였다. 연구 결과 하체 근지구력에서는 유의한 개선이 있었고, 동적 평형성을 평가하는 3m 왕복 걷기에서도 유의한 개선이 있었다. 보행능력인 10m 걷기와 400m 걷기에서도 유의한 개선이 있었다. 결론적으로 고유수용성 저항운동에 의한 동적평형성과 보행능력의 개선은 여성 노인의 낙상 관련 가능성을 감소시킬 것이다.

• Wind and Structures
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• 제14권5호
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• pp.383-411
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• 2011

Roof is an integral part of building envelope. It protects occupants from environmental forces such as wind, rain, snow and others. Among those environmental forces, wind is a major factor that can cause structural roof damages. Roof due to wind actions can exhibit either flexible or rigid system responses. At present, a dynamic test procedure available is CSA A123.21-04 for the wind uplift resistance evaluation of flexible membrane-roofing systems and there is no dynamic test procedure available in North America for wind uplift resistance evaluation of rigid membrane-roofing system. In order to incorporate rigid membrane-roofing systems into the CSA A123.21-04 testing procedure, this paper presents the development of a load cycle. For this process, the present study compared the wind performance of rigid systems with the flexible systems. Analysis of the pressure time histories data using probability distribution function and power spectral density verified that these two roofs types exhibit different system responses under wind forces. Rain flow counting method was applied on the wind tunnel time histories data. Calculated wind load cycles were compared with the existing load cycle of CSA A123.21-04. With the input from the roof manufacturers and roofing associations, the developed load cycles had been generalized and extended to evaluate the ultimate wind uplift resistance capacity of rigid roofs. This new knowledge is integrated into the new edition of CSA A123.21-10 so that the standard can be used to evaluate wind uplift resistance capacity of membrane roofing systems.

• 대한조선학회논문집
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• 제54권2호
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• pp.96-101
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• 2017

Amphibious assault vehicles have been used in the Marine Corps. In recent years, their ability to move faster is becoming one of the most important considerations. At high speeds, the vehicle tends to sink at the stern and sometimes the opposite occurs. Such dynamic trim plays a significant role in determining the vehicle's hydrodynamic performance. Furthermore, an excessive trim by stern upsets the viewing angle. We have thus considered a stern hydrofoil to reduce the dynamic trim of the amphibious assault vehicle. Laboratory-scale resistance tests were conducted in a towing tank at the Seoul National University (SNU). This study aims to make a preliminary assessment of the hydrodynamic performance of the vehicle with the stern hydrofoil and to investigate permissible speed range of the vehicle. The experimental results show that the stern hydrofoil can successfully achieve a reduction of both the dynamic trim and the hydrodynamic resistance at running speeds above 20 km/h.

• Structural Engineering and Mechanics
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• 제62권3호
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• pp.373-380
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• 2017

Concrete structures are often subjected to long-term static and short-term dynamic loads. Due to a relatively low tensile strength and energy dissipating characteristics, the impact resistance of concrete is considered poor. This study investigates the feasibility of using polypropylene fibers to improve the impact resistance of reinforced concrete slabs. Fourteen polypropylene fiber reinforced concrete slabs were fabricated and tested using a drop weight test. The effects of slab thickness, fiber volume fractions, and impact energy on the dynamic behaviors were evaluated mainly in terms of impact resistant, crack patterns, and failure modes. The post impact induced strains versus time responses were obtained for all slabs. The results showed that adding the polypropylene fiber at a dosage of 0.90% by volume of concrete leads to significant improvement in the overall structural behavior of the slabs and their resistance to impact loading. Interestingly, the enhancement in the behavior of the slabs using a higher fiber dosage of 1.2% was not as good as achieved with 0.90%.

• 콘크리트학회지
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• 제9권3호
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• pp.189-197
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• 1997

본 연구에서는 보통의 일반콘크리트와 플라이애쉬를 혼입한 강섬유보강 콘크리트의 해수에 대한 저항성을 고찰하기 위하여 수행되었다. 콘크리트 배합 인자를 물.시멘트비, 강섬유혼입률, 플라이애쉬 혼입률별로 각각 제조하였으며, 표준수(수도물)와 인공으로 제조한 해수에 장기간 침지한 경우와 건조와 습윤의 반복작용에 의한 촉진시험으로 시험을 수행하여 콘크리트의 성능저하에 미치는 영향을 비교.고찰하였다. 시험방법은 소정의 재령에 각각의 배합조건별로 압축강도와 재령 1일을 기준으로 길이변화와 동탄성계수를 측정하여 성능저하정도를 비교분석하였다. 그 결과 강섬유와 플라이애쉬의 적정량의 혼입은 콘크리트의 내해수성을 현저히 개선시키는 효과를 나타내었다.

• Journal of Magnetics
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• 제21권2호
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• pp.239-243
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• 2016

High temperature superconductor (HTS) magnet systems usually employ metal current leads which bridge between the cryogenic environment and room temperature. Such current leads are the dominant heat load for these magnet systems due to a combination of electrical resistance and heat conduction. HTS flux pumps enable large currents to be injected into a HTS magnet circuit without this heat load. We present results from an axial-type HTS mechanically rotating flux pump which employs a ferromagnetic circuit and a Cu-stabilized coated conductor (CC) HTS stator. We show the device can be described by a simple circuit model which was previously used to describe barrel-type flux pumps, where the model comprises an internal resistance due to dynamic resistance and a DC voltage source. Unlike previously reported devices, we show the internal resistance and DC voltage in the flux pump are not exactly proportional to frequency, and we ascribe this to the presence of eddy currents. We also show that this axial-type flux pump has superior current injection capability over barrel-type flux pumps which do not incorporate a magnetic circuit.

• Advances in concrete construction
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• 제17권1호
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• pp.45-52
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• 2024

In this study, the fresh properties of paraffin-mixed concrete, compressive strength, resistance to frost damage, and resistance to composite deterioration under freeze-thaw and salt environment were investigated. The compressive strength of paraffin-mixed concrete was almost the same as that of unmixed concrete, and no decrease in strength was observed, unlike the concrete with entrained air in consideration of freeze-thaw resistance. Concerning the freeze-thaw resistance of paraffin-mixed concrete, the relative dynamic modulus of elasticity (RDME) did not decrease even without entrained air. In addition, no decrease in the RDME was observed in the combined deterioration with salt damage, and it was confirmed that the mass reduction was suppressed compared to the concrete without paraffin. The freeze-thaw resistance of concrete when paraffin is mixed may be improved due to the reduction in the amount of frozen water and the mixed paraffin particles exist in the concrete as pore fillers with a size of 200 ㎛ or less, which act as substitutes for air voids. This resulted in reduction of the apparent air void spacing and thereby relieving the pore pressure.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 전력전자학술대회 논문집
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• pp.239-244
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• 1998

We propose a nonlinear feedback controller that can control the induction motors with high dynamic performance by means of decoupling of motor speed and rotor flux. A new recursive adaptation algorithm for rotor resistance which can be applied to our nonlinear feedback controller is also presented in this paper. Some simulation results show that the adaptation algorithm for rotor resistance is robust against the variation of stator resistance and mutual inductance. In addition, it is computationally simple and has small estimation errors.