• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.380-391
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• 2014

In this study, the scale effect on the performance of the podded propeller of tractor type is investigated. Turbulent flow computations are carried out for Reynolds numbers increasing progressively from model scale to full scale using the CFD analysis. The result of the flow calculation for model scale Reynolds numbers agrees well with that of the experiment of a large cavitation tunnel. The existing numerical analysis indicates that the performance of the podded propeller blades is mainly influenced by the advance coefficient and relatively little by the Reynolds number. However, the drag of pod housing with propeller in operation is different from that of pod housing without propeller due to the acceleration and swirl of propeller slipstream which is altered by propeller loading as well as the pressure recovery and friction according to Reynolds number, which suggests that the pod housing drag under the condition of propeller in operation is the key factor of the scale effect on the performance between model and full scale podded propellers. The so called 'drag ratio', which is the ratio of pod housing drag to total thrust of podded propeller, increases as the advance coefficient increases due to accelerated flow in the slipstream of the podded propeller. However, the increasing rate of the drag ratio reduces continuously as the Reynolds number increases from model to full scale progressively. The contribution of hydrodynamic forces, which acts on the parts composed of the pod housing with propeller operating in various loading conditions, to the thrust and the torque of the total propeller unit are presented for a range of Reynolds numbers from model to full scales.

• 대한기계학회논문집A
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• 제30권11호
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• pp.1425-1432
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• 2006

Coating layers on a coated sheet steel frequently affect distributions of strain rate of sheets and deteriorate the frictional characteristics between sheets and tools in sheet metal forming. Thus, it is important to identify the deformation behavior of these coatings to ensure the success of the sheet forming operation. In this study, the technique using nano-indentation test, FE-simulation and Artificial Neural Network(ANN) were proposed to determine the power law stress-strain behavior of coating layer and the power law behavior of extracted coating layers was examined using FE-simulation of drawing and nano-indentation process. Also, deep drawing test was performed to estimate the formability and frictional characteristic of coated sheet, which was calculated using the linear relationship between drawing force and blank holding force obtained from the deep drawing test. FE-simulations of the drawing process were respectively carried out for single-behavior FE-model having one stress-strain behavior and for layer-behavior FE-model which consist of coating and substrate separately. The results of simulations showed that layer-behavior model can predict drawing forces with more accuracy in comparison with single-behavior model. Also, mean friction coefficients used in FE-simulation signify the value that can occur maximum drawing force in a drawing test.

• 대한기계학회논문집
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• 제15권1호
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• pp.145-153
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• 1991

본 연구에서는 Toh가 개발하여 stretchforming에 응용한 강소성 대변형 이론 을 압연문제에 적용하여 강소성 대변형 유한요소 프로그램을 개발하는데 있다.

• 대한치과교정학회지
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• 제46권2호
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• pp.73-80
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• 2016

Objective: The purpose of this study was to investigate the static (SFF) and kinetic frictional forces (KFF) in sliding mechanics of hybrid bracket systems that involve placing a conventional bracket (CB) or active self-ligating bracket (ASLB) on the maxillary anterior teeth (MXAT) and a passive SLB (PSLB) on the maxillary posterior teeth (MXPT). Methods: The samples consisted of two thoroughbred types (group 1, anterior-CB + posterior-CB; group 2, anterior-ASLB + posterior-ASLB) and four hybrid types (group 3, anterior-CB + posterior-PSLB-type 1; group 4, anterior-CB + posterior-PSLB-type 2; group 5, anterior-ASLB + posterior-PSLB-type 1; group 6, anterior-ASLB + posterior-PSLB-type 2) (n = 13 per group). After maxillary dentition alignment and maxillary first premolars removal in the stereolithographically-made typodont system, a $0.019{\times}0.025$-inch stainless steel wire was drawn through the right quadrant of the maxillary arch at 0.5 mm/min for 5 min. The SFF and KFF were measured with a mechanical testing machine and statistical analyses were performed. Results: Four different categories of SFF and KFF were observed among all groups (all p < 0.001). Group 1 demonstrated the highest SFF and KFF; groups 4 and 3 were second and third highest, respectively. The fourth category included groups 2, 5, and 6. Placing PSLBs on the MXPT resulted in significant SFF and KFF reductions in cases with CBs on the MXAT, but not in cases with ASLBs on the MXAT. Conclusions: These data might aid in the development of a hybrid bracket system that enables low-friction sliding of an archwire through the MXPT.

• 대한토목학회논문집
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• 제3권4호
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• pp.1-10
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• 1983

평면내력(平面內力)을 받는 철근(鐵筋)콘크리트슬래브, 판(板) 및 쉘 등(等)의 벽부재(壁部材)의 정확한 변형해석(變形解析)을 위하여 균열의 마찰일팽창거동(摩擦一膨脹擧動), 인장증강효과(引張增剛効果) 및 철근의 연결작용(連結作用)을 고려한 실제적인 해석모델을 수립하였다. 본 연구의 이론(理論)에 입각한 전산(電算)프로그램을 작성(作成)하여 포괄적인 변형해석이 수행되었으며, 새로운 개념의 마찰평형설계(摩擦平衡設計)와 종래(從來)의 무마찰평형설계(無摩擦平衡設計)에 입각한 철근설계에 대하여 각각 균열폭을 계산하여 비교하였다. 마찰설계개념에 의해 철근을 설계했을 경우 종래의 무마찰설계보다 변형량이 상당히 감소됨을 발견하였다. 또한, 철근직경과 균열간격이 균열폭에 미치는 영향을 연구(硏究)하였다. 본(本) 연구(硏究)에서 개발된 해석모델로 철근콘크리트부재(部材)의 좀 더 실제적이고 정확한 변형해석(變形解析)을 할 수 있게 되었다.

• 한국산학기술학회논문지
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• 제11권9호
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• pp.3599-3609
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• 2010

연안개발과 해안매립을 사용하여 개발된 새로운 도시 건설의 수요가 증가하면서 해안구조물과 고층구조물의 시공이 증가하는 추세이다. 이러한 구조물에서 수평력과 인발력을 받는 구조물의 기초의 적용이 증가하고 있으며, 특히 구조물에서 인발력에 효과적으로 저항하기 위한 기초형식으로 선단확장형말뚝의 사용이 증가하고 있는 실정이다. 압축력을 받는 기초에 관한 많은 연구들이 이루어지고 있으나, 선단확장형말뚝의 인발저항에 관한 연구는 미비한 상태이다. 따라서 본 논문에서는 국외 4개 현장을 대상으로 선단확장형말뚝을 시공하고 정재하시험을 실시하여 말뚝의 지지력 및 하중-변위특성과 주면마찰력을 고려한 하중분담을 고찰하였다. 또한 3차원 유한요소해석 및 이론에 의해 산정된 극한인발력과 현장시험의 극한인발력을 비교 평가하였다.

• 한국항공우주학회지
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• 제41권8호
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• pp.625-631
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• 2013

핀풀러의 신뢰도를 몬테카를로 시뮬레이션을 통해서 예측하였다. 예측방법은 응력-강도 간섭 모델에 근거한다. 이 모델은 강도가 응력보다 작을 경우를 고장으로 간주한다. 본 연구에서 강도는 핀을 예정된 거리까지 후퇴시키는데 필요한 에너지로, 응력은 이 핀의 운동을 방해하는데 소요되는 에너지로 간주하였다. 전자는 주로 화약량에 의해 결정되고 후자는 여러 가지 마찰력과 반발방지장치에서 소모되는 에너지에 의존한다. 응력과 강도 변수들은 해석적 성능 모델로부터 계산하였다. 본 연구에서 제시된 방법은 많은 시료가 필요하지 않기 때문에 유사한 종류의 파이로 장치 신뢰도 계산에도 적용될 수 있다.

• 한국강구조학회 논문집
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• 제12권3호통권46호
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• pp.259-268
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• 2000

마찰접합에 있어서 작용외력은 고력볼트로 체결된 접합부재간의 마찰면에 작용하는 마찰력에 의해 전달된다. 이 마찰력은 마찰면의 미끄럼계수와 고력볼트 조임력의 곱에 비례한다. 그러나 너트회전법에 의한 조임시 고력볼트 조임력은 많은 인자에 의해 영향을 받는다. 여유나사길이와 길이-직경비는 고력볼트 조임력을 지배하는 중요한 인자 중에 하나이다. 따라서 본 논문은 여유나사길이와 길이-직경비에 따른 고력볼트 세트(F10T, M16, M20, M22, M24)의 기계적 특성에 관한 실험을 통하여 고력볼트의 정확한 체결 방법을 제공하고자 한다.

• Structural Engineering and Mechanics
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• 제23권3호
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• pp.293-308
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• 2006

This paper presents a complete and consistent formulation to study the seismic response of a free-standing ship supported by an arrangement of n keel blocks which are all located in a dry dock. It is considered that the foundation of the system is subjected to both horizontal and vertical in plane excitation. The motion of the system is classified in eight different modes which are Rest (relative), Sliding of keel blocks, Rocking of keel blocks, Sliding of the ship, Sliding of both keel blocks and the ship, Sliding and rocking of keel blocks, Rocking of keel blocks with sliding of the ship, and finally Sliding and rocking of keel blocks accompanied with sliding of the ship. For each mode of motion the governing equations are derived, and transition conditions between different modes are also defined. This formulation is based on a number of fundamental assumptions which are 2D idealization for motion of the system, considering keel blocks as the rigid ones and the ship as a massive rigid block too, allowing the similar motion for all keel blocks, and supposing frictional nature for transmitted forces between contacted parts. Also, the rocking of the ship is not likely to take place, and the complete ship separation from keel blocks or separation of keel blocks from the base is considered as one of the failure mode in the system. The formulation presented in this paper can be used in its entirety or in part, and they are suitable for investigation of generalized response using suitable analytical, or conducting a time-history sensitivity analysis.

• Wind and Structures
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• 제30권2호
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• pp.165-180
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• 2020

To determine tornadic wind loads, the wind pressure, forces and moments induced by tornadoes on civil structures have been studied. However, in most previous studies, only the individual building of interest was included in the wind field, which may be suitable to simulate the case where a tornado strikes rural areas. The statistical data has indicated that tornadoes induce more significant fatalities and property loss when they attack densely populated areas. To simulate this case, all buildings in the community of interest should be included in the wind field. However, this has been rarely studied. To bridge this research gap, this study will systematically investigate the influence of a community of buildings on tornadic wind fields by modeling all buildings in the community into the wind field (designated as "the Community case under tornadic winds"). For comparison, the case in which only a single building is included in the tornadic wind field (designated as "the Single-building case under tornadic winds") and the case where a community of buildings are included in the equivalent straight-line wind field (designated as "the Community case under straight-line winds") are also simulated. The results demonstrate that the presence of a number of buildings completely destroys the pattern of regular circular strips in the distribution of tangential velocity and pressure on horizontal planes. Above the roof height, the maximum tangential velocity is lower in the Community case under tornadic winds than that in the Single-building case under tornadic winds because of the higher surface friction in the Community case; below the roof height, greater tangential velocity and pressure are observed in the Community case under tornadic wind fields, and more unfavorable conditions are observed in the Community case under tornadic winds than under the equivalent straight-line winds.