• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1994년도 가을 학술발표회 논문집
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• pp.182-190
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• 1994

Mattress foundations using geogrids are often used on soil foundations to increase the supporting capability of a mattress-soil foundation system, in which the mattress foundation trasmits a point load applied above to a wider area of the soil foundation underneath. To examine this load dispersion capability of the mattress foundation, model experiments were carried out on lab-floor. Expecially, the effect of the thickness of the mattress and the subgrade modulus of the soil foundation on load dispersion are considered. The load distribution and the tensile force generated on geogrid of the upper part of the mattress are examined in the paper.

• Steel and Composite Structures
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• 제22권6호
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• pp.1391-1415
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• 2016

Limit load of pressure bearing structures was reviewed in this article. By means of the finite element analysis, limit load of pressurized cylinder with nozzle was taken as an example. Stress classification method and Elastic-plastic finite element analysis combining with limit load determination methods were used to determine limit load of cylinder with nozzle. Comparison of limit load determined by different methods, the results indicated that limit load determined by linearization method was the smallest. Limit load determined by twice elastic slope criterion was the nearest than experimental results. Elastic-plastic finite element analysis had comparably computational precision, but required time consuming. And then the requirements of computer processing and storage capacity by power system became higher and higher. Most of criteria for limit load estimation included any human factors based on a certain substantive characteristics of experimental results. The reasonable criterion should be objective and operational.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.1166-1175
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• 1993

The objective of this study is to measure contra-retractive adhesion and lift resistance acting on the rim section of a circular wheel for analyses of their effects on the dynamic load. A circular iron wheel was used for experiments. A part of the wheel rim was cut off, and transducers which can measure normal and tangential forces were installed in this section. Experiments were conducted on a laboratory soil bin which was filled with clayey soil under wet and dry conditions. The mechanism of generating contra -retractive adhesion on a circular wheel were analyzed by the experiments and motion analyses of the wheel. Effects of lift resistance on dynamic load were analyzed by measured forces under wet soil conditions in comparison in comparison with those under dry conditions. The showed that a part of the lift resistance were transferred to the dynamic load. These results may become basic data and ideas for analyses of tractor dynamic under wet soil conditions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.141-146
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• 2000

Crack closure and growth behavior of physically short fatigue cracks under random loading are investigated by performing narrow- and wide-band random loading tests for various stress ratios. The importance of the crack closure phenomenon is examined by predicting the growth lives of short cracks using obtained crack opening behavior. Artificially prepared two-dimensional, short through-thickness cracks are used. The crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks. Most of the life prediction ratios are within the factor of 2 scatter band except several data at very short crack sizes, indicating that crack growth predictions based on the measured crack opening data are excellent. From the results obtained in this study, it can be concluded that crack closure is the primary factor governing fatigue crack growth of short cracks under random loading as well as under constant-amplitude loading.

• 한국전산구조공학회논문집
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• 제20권4호
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• pp.485-492
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• 2007

본 논문에서는 1편에서 얻어진 온도분포와 박리시간이력을 이용하여 지하박스구조물의 열응력을 산정하고 이에 기반한 열모멘트를 산청하였다. 또한 이때의 온도분포를 바탕으로 구조물의 열적비선형성을 고려한 극한모멘트를 산정하여 구조물의 내하력을 산정하였다. 그 결과 상부슬래브의 부모멘트 구간은 단면의 온도경사에 의해서 발생하는 열모멘트에 의해 지배받는 것으로 나타났다. 반면 정모멘트 구간은 박리에 의해 화염에 노출된 철근의 항복응력에 의해 지배받는 것으로 나타났다.

• 대한조선학회 특별논문집
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• 대한조선학회 2011년도 특별논문집
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• pp.36-38
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• 2011

As the increase of the fuel oil price, the demand for saving of the ship running cost is growing. To meet the needs of the shipowners, the method for low load operation has been developed by engine licenser. As one of low load operation, the turbocharger cut-out system can be utilized flexibly both full and part load operation. It can be possible to optimize fuel consumption at both full and part load operation. Tests by engine licenser with 12K98MC engine have proven that the fuel oil consumption can be reduced approximately 5%. In this paper we will study the application of main engine turbocharger cut-out system onboard a vessel. One of four turbochargers with MAN Diesel & Turbo 12K98MC-C and 12K98ME-C engine is cut out with swing gate valve. The fuel oil consumption is measured during sea trial and engine shop test.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권1호
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• pp.87-97
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• 2014

In this study, the model tests were conducted on the short piles installed in sands under a horizontal pullout load to investigate their behavior characteristics. From the horizontal loading tests where dimensions of the pile diameter and length, and loading point were varied, the horizontal pullout resistance and the rotational and translational movement pattern of the pile were investigated. As a result, the horizontal pullout resistance of the pile embedded in sands was dependent on the pile length, diameter, loading point, etc. The ultimate horizontal pullout load tended to increase as the loading point (h/L) moved to the bottom from the top of the pile, regardless of the ratio between the pile length and diameter (L/D), reached the maximum value at the point of h/L = 0.75, and decreased afterwards. When the horizontal pullout load acted on the upper part above the middle of the pile, the pile rotated clockwise and moved to the pullout direction, and the pivot point of the pile was located at 150-360mm depth below the ground surface. On the other hand, when the horizontal pullout load acted on the lower part of the pile, the pile rotated counterclockwise and travelled horizontally, and the rotational angle was very small.

• International Journal of Fluid Machinery and Systems
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• 제9권2호
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• pp.182-193
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• 2016

Introduction of intermittent electricity production systems like wind and solar power to electricity market together with the deregulation of electricity markets resulted in numerous start/stops, load variations and off-design operation of water turbines. Hydraulic turbines suffer from the varying loads exerted on their stationary and rotating parts during load variations since they are not designed for such operating conditions. Investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of a rotating vortex rope (RVR) in the draft tube. The RVR induces pressure pulsations in the axial and rotating directions called plunging and rotating modes, respectively. This results in oscillating forces with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. This study investigates the effect of transient operations on the pressure fluctuations exerted on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors for this purpose. The model was run in off-cam mode during different load variations. The results showed that the transients between the best efficiency point and the high load occurs in a smooth way. However, during transitions to the part load a RVR forms in the draft tube which induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode. Formation of the RVR during the load rejections coincides with sudden pressure change on the runner while its mitigation occurs in a smooth way.

• 대한기계학회논문집A
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• 제33권10호
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• pp.1054-1064
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• 2009

본 연구에서는 인장시험 및 유한요소해석으로 재료의 파단 진변형률을 구하고, 궁극적으로 재료의 진응력-진변형률을 얻는 방법을 제안했다. 먼저 인장시험으로 얻은 응력-변형률 선도를 네킹점에서 선형 외삽해, 초기 진응력-진변형률 곡선을 설정하고, 이를 유한요소해석에 채택했다. 유한요소해석 후 Bridgman 계수 및 평판 수정계수들을 사용해, 단축 상태의 하중-진변형률 선도를 얻어 파단진변형률을 실험-해석적으로 구했다. 이 예측 파단진변형률의 실험치 대비 오차는 3% 미만이다. 이렇게 구한 파단 진변형률과 이에 상응하는 파단진응력을 구해 파단점을 결정한다. 이어 네킹점과 결정한 파단점을 연결하는 네킹 후 진응력-진변형률 선형선도를 확보하고, 이를 네킹 전의 실험선도와 결합해 최종적으로 재료의 진응력-진변형률 선도를 완성했다. 본 연구에서 제시한 실험-해석적 진응력-진변형률 곡선 획득 방법은 SS400 평판시편과 같이 파단면적 측정이 어려운 경우, 그 유용함이 배가된다.

• 한국자동차공학회논문집
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• 제22권2호
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• pp.156-165
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• 2014

This paper is the first investigation on the effect of flow control methods on the part load performance in a spark ignition engine. For comparison of the methods, two control devices, port throttling and masking, were applied to a conventional engine without any design change of the intake port. Steady flow evaluation shows that steady flow rates per unit opening area and swirl ratio are very low compared with the port throttling and saturated from mid-stage valve lift, however, swirl increases slightly as the lift is higher in case of 1/4 masking control. In the part load performance, the effect of simple port throttling on lean misfire limit expansion is limited and insufficient; on the other hand a masking improves the limit considerably without any port modification for increasing swirl. Also the results show that the intake flow control improves the combustion with following two mechanisms: stratification induced by the combination of the flow pattern and the fuel injection timing attribute to ignition ability and the intensified flow ensure fast burn. In addition fuel consumption reduces under the flow controls and the reduction rate is different according to the operation conditions and control methods. At the Stoichiometric and/or low speed and low load the throttling method is more advantageous; however vice versa at lean and high load condition. Finally, the throttling is more efficient for HC reduction than masking, on the other side the NOx emissions increase under the masking and decrease under the port throttling compared with conventional port scheme.