• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2008년 영문 학술대회
• /
• pp.871-876
• /
• 2008

The blade vibration problem of bladed disk is the most critical subject to consider since it directly affects the stable performance of the engine as well as life of the engine. Especially, due to complicated vibration pattern of the bladed disk, more effort was required for vibration analysis and test. The research of measuring the vibration of the bladed disk, using NSMS(Non-intrusive stress measurement) instead of Aeromechanics testing method requiring slip ring or telemetry system with strain gauge, was successful. These testing can report the actual stresses seen on the blades; detect synchronous resonances that are the source of high cycle fatigue(HCF) in blades; measure individual blade mis-tuning and coupled resonances in bladed disks. In order to minimize the error being created due to heat expansion, the tip timing sensor is installed parallel to the blade trailing edge, yielding optimal result. Also, when working on finite element analysis, the whole bladed disk has gone through three-dimensional analysis, evaluating the family mode. The result of the analysis matched well with the test result.

• 설비공학논문집
• /
• 제15권11호
• /
• pp.943-956
• /
• 2003

A numerical program has been developed for the simulation of automotive engine cooling system. The program determines the mass flow rate of engine coolant circulating the engine cooling system and radiator cooling air when the engine speed is adopted by appropriate empirical correlation. The program used the method of thermal balance at individual element through the model for radiator component in radiator analysis. This study has developed the program that predicts the coolant mass flow rate, inlet and outlet temperatures of each component in the engine cooling system (engine, transmission, radiator and oil cooler) in its state of thermal equilibrium. This study also combined the individual programs and united into the total performance analysis program of the engine cooling system operating at a constant vehicle speed. An air conditioner system is also included in this engine cooling system so that the condenser of the air conditioner faces the radiator. The effect of air conditioner to the cooling performance, e.g., radiator inlet temperature, of the radiator and engine system was examined. This study could make standards of design of radiator capacity using heat rejection with respect to the mass flow rate of cooling air. This study is intended to predict the performance of each component at design step or to simulate the system when specification of the component is modified, and to analyze the performance of the total vehicle engine cooling system.

• 한국의류학회지
• /
• 제45권4호
• /
• pp.674-684
• /
• 2021

Recent advances in electronic technology have engendered a need for research on the use of smart materials in clothing. Electro-conductive fibers are expected to be a crucial element of wearable devices. Therefore, in this study, we have attempted to develop electro-conductive threads and cables using silver nanowires. Based on the characteristics of silver nanowire, in which electro-conductivity can be imparted via heat treatment, we prepared conductive threads by coating nylon yarn with silver nanowires and curing at temperatures of 140℃, 150℃, and 160℃. Conductive threads cured at 140℃ had the highest conductivity, followed by threads cured at 160℃ and 150℃ respectively. The order of the electrical conductivity of the threads after tensile testing was consistent with the original order of the conductivity of the threads. When we evaluated the sensing performance of electro-conductive cables fabricated from these threads, the cables manufactured from threads cured at 140℃ and 160℃ were found to function normally within temperature and humidity sensors. All the cables operated normally in illuminance and electrocardiogram sensors. Thus, we believe that threads made of silver nanowire have sufficient electrical conductivity to be utilized as wearable sensors.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• 제25권4호
• /
• pp.196-220
• /
• 2021

This study formulates a new geometric parameterization scheme to effectively address numerical analysis subject to the variation of the fiber radius of a square unit cell. In particular, the proposed mesh-morphing approach may lead to a parameterized weak form whose bilinear and linear forms are affine in the geometric parameter of interest, i.e. the fiber radius. As a result, we may certify the reduced basis analysis of a square unit cell model for any parameters in a predetermined parameter domain with a rigorous a posteriori error bound. To demonstrate the utility of the proposed geometric parameterization, we consider a two-dimensional, steady-state heat conduction analysis dependent on two parameters: a fiber radius and a thermal conductivity. For rapid yet rigorous a posteriori error evaluation, we estimate a lower bound of a coercivity constant via the min-θ method as well as the successive constraint method. Compared to the corresponding finite element analysis, the constructed reduced basis analysis may yield nearly the same solution at a computational speed about 29 times faster on average. In conclusion, the proposed geometric parameterization scheme is conducive for accurate yet efficient reduced basis analysis.

• 한국응용과학기술학회지
• /
• 제38권6호
• /
• pp.1561-1567
• /
• 2021

지르코니아 복합체는 지르코니아 전구체, 알루미나 전구체, 그리고 유기 실란의 혼합물을 플라스틱 기판 위에 코팅하여 졸 겔 공정과 저온의 광경화 과정, 그리고 열처리 공정 등 세 단계를 거쳐 합성하였고, FT-IR과 XPS 분석을 통하여 지르코니아 전구체와 알루미나 전구체의 비율에 따라 합성된 복합체내 Zr 원소와 Al 원소 비율이 일치함을 확인하였다. 코팅된 복합체는 파장이 420 nm 이상인 가시광선 영역에서 96 % 이상의 투과도를 보였고, 기계적 강도는 연필 강도 9H 이상을 나타내었다. 특히 지르코니아와 알루미나의 몰 비가 1:4의 비율의 복합 코팅제의 나노 압입 경도가 1.212 GPa로 가장 높은 것으로 확인되었다.

• Tribology and Lubricants
• /
• 제35권1호
• /
• pp.24-29
• /
• 2019

In this work we investigated the friction and wear characteristics of a magnesium alloy, which has been receiving much attention as a light metal in industrial applications such as automobiles and aerospace. Magnesium is one of the lightest structural material that has high specific strength, lightweight, low density and good formability. However, current issue of using magnesium alloy is that magnesium has weakness against temperature. As the temperature increases, magnesium undergoes poor creep resistance and ease of softening, and therefore, its mechanical strength decreases sharply. To solve this issue, a new type of magnesium alloy that retains high strength at high temperature has been proposed. The tribological behavior of this alloy was investigated using a tribotester with reciprocating motion and heating plate. A stainless steel ball was used as a counter surface. Results showed that extrusion process has similar wear behavior to the commonly used casting process but retains good mechanical strength and durability. The presence of an alloying element enhanced the wear properties especially in high temperature. This study is expected to be utilized as fundamental data for the replacement of high density materials currently used in mechanical industries to a much lighter and durable heat-resistant materials.

• Nuclear Engineering and Technology
• /
• 제51권7호
• /
• pp.1805-1815
• /
• 2019

While nickel-based alloys have been widely used for power plants due to corrosion resistance and good mechanical properties, during the last couple of decades, failures of nuclear components increased gradually. One of main degradation mechanisms was primary water stress corrosion cracking at dissimilar metal welds of piping and reactor head penetrations. In this context, precise estimation of welding effects became an important issue for ensuring reliability of them. The present study deals with a series of finite element analyses and crack growth rate evaluation of Alloys 690/152. Firstly, variation of residual stresses and equivalent plastic strains was simulated taking into account welding of a cylindrical block. Subsequently, extraction and pre-cracking of compact tension (CT) specimens were considered from different locations of the block. Finally, crack growth curves of the alloys and heat affected zone were developed based on analyses results combined with experimental data in references. Characteristics of crack growth behaviors were also discussed in relation to mechanical and fracture parameters.

• 한국기계가공학회지
• /
• 제18권7호
• /
• pp.48-55
• /
• 2019

Soldiers have been exposed to the risk of chilblains in cold winters. Recent studies have described sensors and IOT devices that use independent power sources based on piezoelectric energy harvesting. Therefore, the heated shoes with an independent power source have been developed. For the application of energy harvesting to shoes, it is necessary to develop a unique harvester by considering human gait characteristics. Energy harvesters and ceramics were designed and fabricated in this study. The performances of these harvesters and ceramics were evaluated experimentally. Then, the harvesters and ceramics with superior performance were selected and applied to the system. Thereafter, the heating and charging performance of the system was tested under real walking conditions. The results show that the developed system can generate adequate energy to charge the battery and heat the shoes.

• 한국해양공학회지
• /
• 제35권3호
• /
• pp.203-215
• /
• 2021

Current industrial practices and approaches are simplified and do not describe the actual behavior of plated elements of offshore topside structures for safety design due to fires. Therefore, it is better to make up for the defective methods with integrated fire safety design methods based on fire resistance characteristics such as residual strength capacity. This study numerically investigates the residual strength of steel stiffened panels exposed to hydrocarbon jet fire. A series of nonlinear finite element analyses (FEAs) were carried out with varying probabilistic selected exposures in terms of the jet fire location, side, area, and duration. These were used to assess the effects of exposed fire on the residual strength of a steel stiffened panel on a ship-shaped offshore structure. A probabilistic approach with a feasible fire location was used to determine credible fire scenarios in association with thermal structural responses. Heat transfer analysis was performed to obtain the steel temperature, and then the residual strength was obtained for the credible fire scenarios under compressive axial loading using nonlinear FEA code. The results were used to derive closed-form expressions to predict the residual strength of steel stiffened panels with various exposure to jet fire characteristics. The results could be used to assess the sustainability of structures at risk of exposure to fire accidents in offshore installations.

• Geomechanics and Engineering
• /
• 제24권6호
• /
• pp.531-543
• /
• 2021

Freezing and thawing of pore water within backfill can affect the stability of retaining wall as the phase change of pore water causes changes in the mechanical characteristics of backfill material. In this study, the effects of freezing and thawing on the mechanical performance of retaining wall with granular backfill were investigated for various temperature and groundwater level (GWL) conditions. The thermal and mechanical finite element analyses were performed by assigning the coefficient of lateral earth pressure according to phase change of soil for at-rest, active and passive stress states. For the at-rest condition, the mobilized lateral stress and overturning moment changed markedly during freezing and thawing. Active-state displacements for the thawed condition were larger than for the unfrozen condition whereas the effect of freezing and thawing was small for the passive condition. GWL affected significantly the lateral force and overturning moment (Mo) acting on the wall during freezing and thawing, indicating that the reduction of safety margin and wall collapse due to freezing and thawing can occur in sudden, unexpected patterns. The beneficial effect of an insulation layer between the retaining wall and the backfill in reducing the heat conduction from the wall face was also investigated and presented.