• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.875-885
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• 1989

This work is concerned with the chatter suppression by inserting viscoelastic materials into tool clamping area. Chatter was observed with and without the viscoelastic materials during cutting tests, where the overhang of the tool was made long so that the tool may be a major cause for the chatter. Two viscoelastic materials were used and the effects of thickness and prestrain were investigated. impact tests were performed on the tool in cases where the tool post was set on the cross slide and was free from any boundary conditions. Material properties of the viscoelastic materials were also obtained from resonance test results. The effects on the chatter suppression by the type of the viscoelastic material and prestrain are discussed in relation with the measured material properties.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.4
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• pp.481-486
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• 2010

Recently, carbon fiber reinforced plastic (CFRP) have been used in various fields because of its high specific modulus, and chemical properties. Most products in which CFRP composites are used are manufactured by joining the product components by bolts or pins. Holes for bolts and pins decrease the strength of the components because these holes act as notches in the structures. In this study, the fracture strength of CFRP plain-weave composite plates containing holes is experimentally investigated to examine the effects of hole-size and specimen width on notched tensile strength. The results show that the characteristic length considered in the point stress criterion depends on the hole size and specimen width. There exists a certain relation between notched tensile strength and characteristic length. Fracture criterion is redefined on basis of this relation.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.3
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• pp.18-25
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• 2006

In order to perform system requirements quickly and accurately, an automatic design program of solid rocket motors(SRM) structure designated as the 'ProDes software' has been developed and verified. from given system design criteria and constraints, it has the capabilities to design, analysis, simulation and drawing process to greatly reduce the over 'design cycle time' and manpower of a project. The conception of the program is modular, and calculations are performed step by step allowing parametric design studies and providing final selected design goal. Each configurations of SRM components and joint types composed of various master models is obtained from the data base module of the library. Between the design results of the ProDes software and those of the previous detail design of the established motor showed good agreements.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1183-1189
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• 2015

This study focuses on the design of the tapered joints of a wind power turbine. The main variables of the tapered joint are the transmitted torque, shaft diameter, contact area of the tapered ring, and tightening torque of the bolts, which applies a compressive pressure from the hub to the shaft. The stress distribution of the taper fit was calculated under axisymmetric plane strain conditions because of the small taper angle. The axial displacement of the clamp can be calculated from the radial elastic deformation and the taper angle. The stress field of each ring is obtained from the cylinder stress equation. To verify the accuracy of the calculation, finite element (FE) analysis was performed, and the results of the calculation and FE analysis were compared. The hoop stress of the tapered surface showed a discrepancy of approximately 10, but the trends of the stress distributions of each component and the relative movement obtained by FE analysis were in good agreement with the analytical calculation results.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.250-250
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• 2022

호안은 유수로부터 제방과 하안을 보호하는 구조물로 태풍 또는 집중호우로 인한 홍수로부터의 안정성이 확보되어야 한다. 일반적으로 호안공법은 강성호안과 연성호안으로 구분되는데 호안재료로써의 기준과 설치 및 유지상태 기준에 따라 다르게 해석되고 있는 것이 현실이다. 최근에는 호안공법의 재료의 연결성에 따라 강성호안과 연성호안을 구분짓는다고 언급되기도 한다. 본 연구에서는 친환경 석재를 사용하고 재료와 기반재의 체결을 통해 연결성을 확보하고 굴요성을 갖게 하는 연성호안공법에 대해 실규모 실험을 계획하였다. 수리 안정성 검토를 위한 실규모 실험은 안동 하천실험센터에서 수행하였다. 실험에 사용된 수로는 8°의 경사를 갖는 급경사수로에서 수행하였으며, 수로의 제원은 폭 3m, 길이 30m 의 직사각형 형태의 직선수로로 이루어져 있다. 시험체는 실규모로 제작되며 실험수로 내 2m × 10m 의 제원을 갖는 공간에 제작된 호안공을 크레인을 이용하여 실험수로에 설치하였다. 수리 안정성 실험은 실험대상유량을 단계별로 나누어 점차적으로 증가시키고, 시험체의 이탈, 파괴 등의 큰 변화가 발생(미국 재료시험학회 연결형 콘크리트 블록 시험방법, ASTM D 7277)하였을 경우 실험을 종료하도록 계획하였다. 수리량 측정항목은 유속, 수위 등이 있으며, 호안공 의 물리적 변화는 3D스캐너를 이용하여 설치 전·후 변위를 검토하였다. 총 3회에 걸쳐 실험을 수행하였으며 실험조건에 따라 일부 시험체에서 돌출 또는 침하현상이 발생하기도 하였으나 호안의 손상이나 이탈, 연성기반재의 찢어짐 등 안정정을 저해하는 호안공 시험체의 변화는 발생하지 않는 것으로 확인되었다. 실험결과 실험수로에서 발생가능한 최대유량인 4.6cms 조건에서 본 호안공법은 약 337.7N/m² 의 소류력을 확보하는 것으로 확인되었다.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.80-80
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• 2017

국내에서 대부분 생산되는 사료(사일리지) 수확 작업은 베일 생산 및 비닐 래핑 작업이 독립적으로 수행되고 있어서 비효율적이다. 본 연구에서 개발한 조사료 수확기는 수집, 롤링, 베일 네트 생성, 래핑, 래핑 종료 및 베일 방출작업을 통합적으로 수행하도록 설계-제작하였다. 통합형 다목적 조사료수확기의 설계는 3D 디자인 툴 (CATIA V5R18)을 이용하여 실시하였으며, 기구부 23 파트 어셈블리, 전기제어 어셈블리, 유압요소기술을 통합하여 통합시작기를 제작하였다. 기초 프레임, 오거장치파트, 픽업장치파트, 하부롤러파트, 상부롤러파트, 하부 프레임 및 주행부 파트, 래핑회전파트, 롤러부 구동 동력부, 유압파트, 전기제어파트, 드로우바파트, 체결 및 컨트롤러 파트 등 25개 파트로 구성되어 있다. 본 연구에서 개발한 시작기의 견인력 및 소요동력 분석은 선행 연구에서 사용한 Brixius (1987) 제안 모델을 체택하여 분석하였다. 이 Brixius 제안 모델은 견인력 예측에서 토양변수 및 토양강도 특성을 나타내는 원추지수 (Cone Index, CI)를 이용하여 트랙터의 견인력 예측에 사용하였다. 또한 트랙터-조사료수확기 시스템의 소요 견인력을 예측하는데 있어, 트랙터-조사료수확기 시스템이 운용되는 토양조건과 트랙터의 마력에 따른 소요 견인력 특성을 분석하기 위해 대표적으로 3수준의 토양조건 (CI: 356 kPa, 543 kPa, 1,429 kPa)을 적용하였으며, 베일의 개당 최대무게는 최고 수준인 옥수수 기준으로 800 kgf를 적용하였다. 본 연구에서 적용된 3수준의 CI 조건은 연구팀에서 선행연구과정 (토양특성에 따른 최적 경운작업 시스템 개발, 2006)에서 분석한 전국 10개 지역의 33개 지점의 경반층 CI지수의 측정범위인 1,050-3,170 kPa에 대해 견인력이 많이 소요되는 열악한 조건 수준을 적용하였다. 각 작업에 사용된 소요동력은 베일 작업시 (ASABE D497.7, 2011) 그리고 래핑작업시 (Zhortuylov et al., 2013)를 사용하였으며 두 소요마력을 트랙터-조사료 수확기 시스템의 필요 소요마력의 합계로 계산하였다. 트랙터-조사료수확기 시스템의 최소 소요 동력, 차축 소요 동력과 PTO 소요 동력을 Zoz and Grisso (2003)을 이용하여 계산하였다. 연구에서는 기본적으로 ASAE의 작업속도 및 작업효율을 적용하였는데, 적용된 조사료수확기의 현장 작업효율은 60-86%의 범위이고 일반적으로 70%를 적용하고 이때 작업속도는 2.5-8.0 km/h이며 전형적으로 5.0 km/h를 기준하고 있다. 자주식 (SP; sief-propelled machine) 조사료수확기의 경우 작업속도가 2.5-10.0 km/h의 범위에서 작업효율은 60-85% 범위이다. 적용되는 조사료 수확기의 작업효율인 60-85% 범위에서 일반적으로 적용되는 작업효율인 70%를 적용하면 트랙터의 소요동력은 95hp를 적정 작업환경으로 하였다.

• Journal of Intelligence and Information Systems
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• v.8 no.1
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• pp.103-117
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• 2002

Recently, many researchers have developed applications for automated contract and negotiation using agent technologies on electronic commerce. Especially, they have tried to study negotiation mechanism applying agent instead of buyers and sellers. Traditional researches, however, often had limitations. In the researches of automated negotiation, the agents had to negotiate with the other agents for a simple negotiation issue because the mechanisms were naive. In the researches of negotiation by user interaction, the agents did not have supported the procedures and methodologies for making the automated negotiation but only supported the users by providing communication environment during the negotiation process by users. In this paper, we propose efficient negotiation model using the modified negotiation model of the game theory. In the proposed model, the agents negotiate automatically with the partner agent and make good benefits by the strategic method during the negotiation process. Each agent makes negotiation issues with user's requirements and exchanges its suggestion alternatively in each step of the negotiation process. The agent evaluates degree of satisfaction for the opposite's suggestion and uses it in the next step of suggestion. To find out the negotiation strategies of opposite side, the agent uses teaming by weights of issues. As a result, the agent improves each own benefits for the contract and reduces the unbalance of its benefits through the proposed negotiation mechanism. We implement the negotiating agents according to the proposed mechanism and prove the efficiency of the proposed model by various experimentation.

• Composites Research
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• v.31 no.4
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• pp.139-144
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• 2018

Long Fiber-reinforced composites have advantages of excellent production efficiency and formability of complex shapes compared to conventional continuous fiber reinforced composite materials. However, if we need to make complicated composite shapes or to assemble parts made of different materials, a variety of joining methods are needed. In general, long fiber prepreg sheet (LFPS) contains mold release agent to facilitate demolding after thermoforming. Therefore, mechanical fastening is required in addition to the adhesive bonding to get proper joining strength. In this study, we proposed a stainless steel insert for co-cure bonding which cures LFPS and bonds the stainless steel insert through thermoforming process. The wing of the insert which is spread during the thermoforming process induces adhesion and mechanical wedging effect and serves as a hook to resist the pulling force. The burn-out method was used to confirm the unfolded state of the stainless steel insert wings inserted into the composite material. The static pull-out test was performed to quantitatively evaluate the joining strength. From these experimental results, the condition which guarantees the most appropriate joining strength was derived.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.466-472
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• 2013

The use of a concrete track is gradually growing in urban and high-speed railways in many part of the world. The resilient pad, which is essentially when concrete tracks are used, plays the important role of relieving the impact caused by train loads. The simple fatigue test[1] to estimate the variable stiffness of resilient pads is usually performed, but it differs depending on the practical conditions of different railways. In this study, the static stiffness levels of used resilient pads according to passing tonnages levels were measured in laboratory tests. Also, the simple fatigue test and the multi-stress accelerated degradation test for new resilient pads were performed in a laboratory. The static stiffness of the used pad was compared with the results of tests of usage times and cycles. The results of the comparison showed that the variable static stiffness levels of the used pad were similar to results of the multi-stress accelerated degradation test considering the fatigue and heat load. With a T-NT equation related to the degree of the multi-stress accelerated degradation, a model of multi-stress accelerated degradation for a resilient pad was devised. It was found through this effort that the total acceleration factor was approximately 2.62. Finally, this study proposes an equation for a multi-stress accelerated degradation model for polyurethane resilient pads.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1063-1069
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• 2012

In present paper, we used magnesium alloy having a lower density and higher electrical conductivity for bipolar plate to reduce the weight of PEM fuel cell. The silver was coated to prevent corrosion and form passivation film on the metal surface with sputtering. In acid proof evaluation for setting optimal coating conditions, the homogeneity of coating thickness was improved by coating with the thickness of 3 ${\mu}m$ which not indicated any micro cracks and the temperature $180^{\circ}C$. The performance test and evaluation based on the clamping pressure and channel depth to determine the configuration of bipolar plate for assembling single cell was implemented. And then we assembled single cell with this bipolar plate and implemented the performance test to ensure and compare the current-voltage performance followed as several factors such as coating or non-coating, the change of clamping pressure, the change of channel depth, etc. As these results, the maximum power density of single cell with the coated bipolar plate was 192 $mW/cm^2$ and it was confirmed that the power density per unit mass was better than existing metal bipolar plate.