• Geomechanics and Engineering
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• 제33권1호
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• pp.91-99
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• 2023

To test the effect of various pile tip shape series of model scale loading tests were carried out on test piles with special pile tips. Special pile tips were made using the 3D printer and were attached to the bottom end of the test pile for loading tests. The pile tips were made to have 30°, 45°, 60° inclined tips, as well as a rounded tip. The main objective of the test was to observe the effect of various pile tip shapes on settlement and penetrability of the pile. Moreover, a numerical model simulating the pile loading test carried out in this study was established and verified based on the loading test results. From this, the stress concentration around the pile tip was investigated. This will allow us to analyze the decrease of stress concentration around the pile tip which is the main cause of the pile tip damage during pile installation. However, modifying the pile tip shape will eventually increase the settlement of the pile. By estimating the degree of increase in pile settlement, the viability and the efficiency of the pile shape modification was judged. In addition, case studies on the effect of different pile tip shape and ground conditions on pile settlement and stress dispersion was conducted.

• 소성∙가공
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• 제11권4호
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• pp.312-322
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• 2002

In this study, an innovative semi-solid die casting technology to replace heavier cast iron compressor parts with lightweight aluminum castings was proposed, and the application possibility for home-appliance component was investigated. The most important factors regarding the semi-solid die casting process are the reheating process of the raw materials to the semi-solid state, specifications of the forming machine, the optimal injection conditions and die design. Materials used in this study were A3S7 and hSn alloys fabricated by the electromagnetic stirring process. The optimal injection conditions for semi-solid die casting process were Presented with the reheating conditions of the semi-solid materials. To investigate the effect of plunger tip shape on the formability and mechanical properties in semi-solid die casting process for complicated shape part, two kinds of plunger tip shape with long and short plunger tip taper are proposed.

• Computers and Concrete
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• 제17권1호
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• pp.107-127
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• 2016

Concrete is a heterogeneous material containing many weaknesses such as micro-cracks, pores and grain boundaries. The crack growth mechanism and failure behavior of concrete structures depend on the plastic deformation created by these weaknesses. In this article the non-linear finite element method is used to analyze the effect of presence of micro pore near a crack tip on both of the characteristics of crack tip plastic zone (its shape and size) and crack growth properties (such as crack growth length and crack initiation angle) under pure shear loading. The FE Code Franc2D/L is used to carry out these objectives. The effects of the crack-pore configurations and the spacing between micro pore and pre-excising crack tip on the characteristics of crack tip plastic zone and crack growth properties is highlighted. Based on the obtained results, the relative distance between the crack tip and the micro pore affects in very significant way the shape and the size of the crack tip plastic zone. Furthermore, crack growth length and crack initiation angle are mostly influenced by size and shape of plastic zone ahead of crack tip. Also the effects of pore decrease on the crack tip by variation of pore situation from linear to perpendicular configuration. The critical position for a micro pore is in front of the crack tip.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.243-248
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• 2011

The 3-dimensional flow field has been investigated by numerical analysis in a 2.5MW wind turbine blade. Complicated and separated flaw phenomena in the wind turbine blade were captured by the Reynolds-averaged Navier-Stokes(RANS) steady flaw simulation using general-purpose code, CFX and the mechanism of vortex structure behavior is elucidated. The vortical flow field in a wind turbine rotor is dominated by the tip vortex and hub separation vortex. The tip vortex starts to be formed near the blade tip leading edge. As the tip vortex develops in the tangential direction, interacting with boundary layer from the blade tip trailing edge. The hub separation vortex is generated near the blade hub leading edge and develops nearly in the span-wise direction. Furthermore, 3-dimensional blade tip shape has been designed for increasing shrift power and reducing thrust force on the wind turbine blade. It is expected that the behavior of the tip vortex and hub separation vortex plays a major role in aerodynamic and aeroacoustic characteristics.

• 한국항공우주학회지
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• 제38권10호
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• pp.985-991
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• 2010

노즐 목 근처에 설치된 핀틀 형상이 노즐 내부 유동과 추력에 미치는 영향을 공압 실험으로 고찰하여 제시하였다. 핀틀 이동으로 노즐 목 면적이 감소하면 연소실 압력은 부드럽게 상승하나 추력은 핀틀 형상에 따라 증가 패턴이 다르게 나타났다. 동일한 노즐 목과 연소실 압력 조건에서 추력은 전체적으로 핀틀 형상이 오목한 것 보다는 볼록한 것이 컸다. 노즐 벽면 압력과 핀틀에 작용하는 하중은 핀틀 형상은 물론 핀틀 위치 및 노즐 목면적에 따라 큰 차이를 보였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권1호
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• pp.59-63
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• 2000

For the Mo-tip field emitter array, the method by which the geometrical structure of the gate insulator wall could be modified in order to improve field emission properties(turn-on voltage and gate leakage current). The device having a gate insulator of complex shape, which means the combined geometrical structure with round shape made by wet etching and vertical shape made by dry etching processes, was fabricated and the field emission properties of the three kinds of devices were compared. As a result, the electric field applied to tip apex could be increased and gate leakage current could be decreased by employing the gate insulator having geometrical wall structure of mixed shape. Finally, the obtained empirical results were analyzed by simulation of electric field distribution at/near the tip apex and gate insulator using SNU-FEAT simulator.

• 한국지반공학회논문집
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• 제39권1호
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• pp.27-38
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• 2023

본 연구에서는 3D 프린팅 기술을 활용하여 타입말뚝 선단의 모양에 따른 관입성 분석을 현장 축소모형시험을 통해 관찰하고, 대변형 수치해석을 통해 타입 중 말뚝 선단에 집중되는 최대응력의 변화를 확인하였다. 3D 프린터를 통하여 다양한 직경, 각도 그리고 모양의 말뚝 선단 모형을 제작하였고, 이를 현장 축소모형시험에 활용하였다. 이를 통해, 말뚝 선단 조건에 따른 말뚝의 침하량의 변화를 관찰하였다. 더 나아가, 대변형 수치해석 기법을 적용하여 다양한 말뚝 선단 조건에 따른 타입 중 말뚝 선단부의 최대응력의 변화와 최대응력 작용 위치 또한 확인하였다. 현장 축소모형시험과 대변형 수치해석의 결과 분석을 토대로 말뚝 선단 조건의 변화를 통해 타입말뚝의 관입성을 향상 시킬 수 있으며 선단부에 집중되는 최대응력 또한 완화 시켜 말뚝 시공 중 말뚝 손상을 방지할 수 있을 것으로 결론지을 수 있었다.

• 한국유체기계학회 논문집
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• 제12권2호
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• pp.39-45
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• 2009

Leakage flow through turbine blade tip gap causes strong leakage vortex near the blade suction side and induces large aerodynamic losses. In this study, the conventional plane tip and various squealer tip blades were tested in a linear cascade in order to measure the effect of the tip shape on the total pressure loss. Three tip gap clearances of 0.6%, 1.3%, and 2.0% of blade span were tested. Flow measurement was conducted at one chord downstream from the trailing edge with a five-hole probe. Results showed that the leakage vortex was stronger than passage vortex and the mass averaged overall total pressure loss through the cascade was the lowest for suction side blade tip case. For all tested cases, the area averaged overall total pressure loss was increased as the tip clearance increased.

• 대한치과기공학회지
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• 제23권2호
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• pp.171-177
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• 2002

The purpose of this study is to evaluate force per unit displacements according to the shape of a clasp arm and flexibility of the material. Effect of four shape parameters of a clasp, base width and thickness and tip width and thickness, on tip displacement and force per unit displacement was investigated to get the fact that displacement and force per unit displacement at the tip increase as thickness and width of clasp arm increase just as expected. But force per unit displacement is much more affected by the change in thickness than by change in width. So it is effective to increase the thickness rather than width in order to increase the force at the tip using the same amount of the material.

• 한국정밀공학회지
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• 제15권7호
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• pp.78-84
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• 1998

The problem of autobody corrosion has been addressed over the past decade by the increasing use of zinc and zinc alloy coated steels in automotive application. This paper describes the evaluation of formability, weldability and painted corrosion performance of galvalume steel sheet. This paper presents an overview of the program and some initial test results on the weldability, lifetime of the electrode tip shape of the spot welding and corrosion protection. Galvalume steel sheet improved corrosion performance and spot weldability of galvalume steel sheet was not changed under the influence of the variation of welding current. And tip shape has influenced on the lifetime of tip for galvalume steel sheet.