• 한국안전학회지
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• 제18권4호
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• pp.143-147
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• 2003

The present investigation examined hammering performance, physiological response, preceived exertion, and user preference with regard to hammering in vertical (wall) and horizontal (bench) orientations, and with regard to using two different hammers. Ten male subjects participated in the experiment. The results support previous findings that horizontally oriented hammering is faster than vertically oriented hammering. In addition, the results suggest that hammer differences can affect hammering performance and perceived exertion; although, the exact contributions of specific design characteristics could not be quantitatively determined. However, participants subjectively identified handle design, weight, and mass distribution as critical factors.

• 한국산업융합학회 논문집
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• 제26권2_2호
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• pp.285-291
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• 2023

In this paper, in order to secure the safety and productivity of pine cone harvest, modeling and structural analysis of the hammering system for pine cone harvest drone that can easily access pine cone of Pinus koraiensis and collide with them to harvest them was performed. It calculate the equivalent stress for the structure of the hammering system and the yield strength of the applied material by applying the shear force of the stalk at which the pine cone is separated from the branch, and it is to verify the safety of the structure and propose an optimal design through appropriate factor of safety and design change. The shear force of the stalk at which the pine cone was separated from the branch was 468 N, and was applied to both ends of the hammering system. The yield strength of SS400 steel used in the hammering system is 245 ㎫, and the design change and structural analysis were performed so that the Von Mises stress could be less than 122.5 ㎫ by applying the factor of safety of 2.0 or more. As a result of the structural analysis of the frist modeling, the Von Mises stress was 220.3 ㎫, the factor of safety was 1.12, and the stress was concentrated in the screw fastening holes. As a result of the design change of the screw fastening holes, the Von Mises stress was 169.4 ㎫, the factor of safety was 1.45, and the stress was concentrated on the side part. As a result of the design change by changing screw fastening holes and adding ribs, the Von Mises stress was 121.6 ㎫, and the factor of safety was 2.02. The safety of the hammering system was secured with an optimal design with little change in mass. There was no deformation or damage as a result of experimenting on pine cone harvest by manufacturing the hammering system with an optimal design.

• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.221-232
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• 2012

We analyzed the manufacturing procedure, specifications, repair history, and details of celestial movements of the water-hammering type $Honsang$ (celestial globe). Results from our study on the remaining $Honsangs$ in China and Japan and on the reconstruction models in Korea were applied to our conceptual design of the water-hammering type $Honsang$. A $Honui$ (armillary sphere) and $Honsang$ using the water-hammering method were manufactured in $Joseon$ in 1435 (the 17th year of King $Sejong$). $Jang$ $Yeong-Sil$ developed the $Honsang$ system based on the water-operation method of $Shui$ $y{\ddot{u}}n$ $i$ $hsiang$ $t'ai$ in China. Water-operation means driving water wheels using a water flow. The most important factor in this type of operation is the precision of the water clock and the control of the water wheel movement. The water-hammering type $Honsang$ in $Joseon$ probably adopted the $Cheonhyeong$ (天衡; oriental escapement device) system of $Shui$ $y{\ddot{u}}n$ $i$ $hsiang$ $t'ai$ in China and the overflow mechanism of $Jagyeongnu$ (striking clepsydra) in $Joseon$, etc. In addition to the $Cheonryun$ system, more gear instruments were needed to stage the rotation of the $Honsang$ globe and the sun's movement. In this study, the water-hammering mechanism is analyzed in the structure of a water clock, a water wheel, the $Cheonhyeong$ system, and the $Giryun$ system, as an organically working operation mechanism. We expect that this study will serve as an essential basis for studies on $Heumgyeonggaknu$, the water-operating astronomical clock, and other astronomical clocks in the middle and latter parts of the $Joseon$ dynasty.

• Tribology and Lubricants
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• 제37권4호
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• pp.129-135
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• 2021

An air-bearing stage uses externally pressurized air as the lubricant between the stage and the rail. The supporting force generated by the supplied air makes the stage rise and move smoothly with extremely low friction. Mechanical contacts rarely happen, the bearing surfaces do not produce wear particles, and dust is not generated. It also has the advantage of having low energy loss and high precision. Because of its advantages, an air-bearing stage is used in several types of machines that require high precision. In this article, the effect of the pocket depth on the hammering phenomena of the air bearing is studied. An analysis program is developed to calculate the dynamic behavior of the stage by solving the Reynolds equation between the stage and the guideway and the equations of motion on the stage. The acceleration, constant movement, and deceleration are applied to the stage. The stage is modeled as a five-degree-of-freedom system. In the course of the dynamic behavior, the hammering phenomena occur under some special conditions. The deeper the pocket, the more unstable the behavior of the stage, and air hammering occurs when it exceeds a certain depth. In addition, the higher the supply pressure, the more unstable the behavior of the stage. However, hammering occurs even with a shallow pocket depth. Other conditions that affect the hammering phenomena are calculated and discussed.

• Journal of Astronomy and Space Sciences
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• 제30권3호
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• pp.187-192
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• 2013

Honsangui (celestial globe) which is a water-hammering method astronomical clock is recorded in "Juhaesuyong" which is Volume VI of supplement from "Damheonseo", written by Hong Dae-Yong (1731~1783). We made out the conceptual design of Hong Dae-Yong's Honsangui through the study on its structure and working mechanism. Honsangui consist of three rings and two layers, the structure of rings which correspond to outer layer is similar to his own Tongcheonui (armillary sphere) which is a kind of armillary sphere. Honsang sphere which correspond to inner layer depicts constellations and milky way and two beads hang on it as Sun and Moon respectively for realize the celestial motion. Tongcheonui is operated by the pendulum power but Honsangui is operated by water-hammering method mechanism. This Honsangui's working mechanism is the traditional way of Joseon and it was simplified the working mechanism of Shui y$\ddot{u}$n i hsiang t'ai which is a representative astronomical clock of China. This record of Honsangui is the only historical record about the water-hammering method working mechanism of Joseon Era and it provide the study of water-hammering method mechanism with a vital clue.

• 전기전자학회논문지
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• 제27권3호
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• pp.220-224
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• 2023

로우 해머는 특정 행(row)에 연속적으로 액세스할 때 인접한 행에서 비트 플립이 발생하는 현상으로 데이터 손상과 보안 문제, 컴퓨팅 성능 저하를 야기한다. 본 논문은 2ynm DRAM에서 TCAD 시뮬레이션을 통해 로우 해머의 원인과 대응 방법을 분석한다. 실험에서는 트랩의 파라미터와 소자의 구조를 변화시키면서 로우 해머 현상을 재현하고, 트랩 밀도, 온도. 액티브 위스 등과의 관계를 분석한다. 실험 결과, 트랩 파라미터와 소자 구조의 변화는 ΔV_cap/pulse에 직접적인 영향을 미치는 것을 확인하였다. 이를 통해 로우 해머에 대한 근본적인 이해와 대응 방안 모색이 가능하고 DRAM의 안정성과 보안을 향상시키는데 기여할 수 있다.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권1호
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• pp.19-30
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• 2002

This paper addresses characteristics of compressible flow dynamics inside a pipe with an accumulator and an inlet orifice. It also presents a simple but stable numerical method associated with the accumulator-orifice calculation. In particular, a focus is given to developing a method of finding an optimum design of the accumulator-orifice system (i.e., the accumulator size and the throttle resistance) that gives the most effective dissipation of the water-hammering problem. It is found that there exists indeed an optimum set of parameter values for the most effective dissipation of the wave energy.

• 한국안전학회지
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• 제26권1호
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• pp.1-7
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• 2011

When the pumps stopped in the operation by the power failure, the hydraulic transients take place in the sudden change of a velocity of pipe line. Each and every water hammer problem shows the critical stage to be greatly affected the facts of safety and reliability in case of power failure. The field tests of the water hammer executed at Cheong-Yang booster pump station having an air chamber. The effects were studied by both the practical experiments and the CFD(Computational Fluid Dynamics : Surge 2008). The result states that the system with water hammering protection equipment was much safer when power failure happens. The following data by a computational fluid dynamic analysis are to be shown below, securing the system stability and integrity. (1) With water hammering protection equipment. (1) Change of pressure : Up to $15.5\;kg/cm^2$ in contrary to estimating $16.88\;kg/cm^2$. (2) Change rate of water level : 52~33% in contrary to estimating 55~27%. (3) Note that the operational pressure of pump runs approx. 145 m, lowering 155 m of the regularity head of pump. (4) Note that the cycle of water hammering delays from 80 second to 100 second, together with easing the function of air value at the pneumatic lines. (2) Change of pressure without water hammering protection equipment : Approximate $22.86\;kg/cm^2$. The comprehensive result says that the computational fluid dynamics analysis would match well with the practical field-test. It was able to predict Max. or Min. water hammering time in a piping system. This study aims effectively to alleviate water hammering in a pipe line to be installed with air chamber at the pumping station and results in making the stability of pump system in the end.

• 대한기계학회논문집A
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• 제36권9호
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• pp.1103-1108
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• 2012

주증기관은 보일러와 터빈을 연결하는 주요계통이다. 운전조건으로 인한 배관시스템에 손상을 제한 할 수 있기 때문에 수격현상 해석은 중요하다. 배관시스템의 불안정한 유동에 의해 생성되는 수격현상은 압력의 과도한 변화, 진동 및 소음을 일으킬 수 있다. 주증기관 구조는 운전환경아래 압력맥동 및 여러 진동 등을 안전하게 견딜 수 있도록 설계되어야 한다. 본 논문에서는 정지 및 정상 운전기간 동안 배관에 유입되는 수격현상을 과도조건에 적용하여 ASME 피로수명 방법론과 유한요소해석에 따라 주증기관의 구조건전성을 평가하였다. 계산된 교번응력 및 피로응력 평가 결과, ASME 피로수명의 허용요건을 만족하였다.

• 설비공학논문집
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• 제4권1호
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• pp.57-64
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• 1992

A computer program was developed for the prediction of transient flow in a water supply system. where an air chamber is installed to reduce the water hammering. The governing equations based on a characteristic method are solved using a finite difference method. A design process of an air chamber is shown in the present paper considering the effects of the initial air volume and the discharge coefficients of the orifice on the total volume and over-all performance of the chamber.