• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 추계학술대회 논문집
• /
• pp.1019-1022
• /
• 2002

Pipe-cutting machines have been used in many fields. Recently, an automatic pipe-cutting machine that uses magnet has born developed. In this paper, a magnetic-type automatic pipe-cutting machine that attaches itself and performs unmanned cutting process is proposed. It is designed that there is a room at the bottom of its body to contain a magnet. And it uses magnetic force between the magnet and the pipe surface to prevent slip and to attach the machine to the pipe against gravity. Also the magnetic force is adjustable by changing the gap between the magnet and the pipe. This machine is, however, necessary to control cutting velocity for the elevation of work efficiency and the adjustable faculties. During pipe cutting process, the gravity acting on the pipe-cutting machine widely varies. That is, the cutting machine gets fast when moving from the top to the bottom of the pipe and slow when moving from the bottom to the top. Actually the system is kind of a non-linear system where the gravity is function of climbing angle of the cutting machine along the pipe. Especially jerking motion is critical. Therefore, authors design the non-linear controller that estimates the current position of the machine along the pipe and compensates the effect of gravity in this paper. It receives the feed back signal from the encoder.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2014년도 추계학술대회 논문집
• /
• pp.402-403
• /
• 2014

Damping of multi-span tube with loose supports according to the finite support clearances is investigated through the experimental modal analysis. Loose intermediate support leads to strong nonlinearity in tube dynamics, provides statistical nature, and increases tube damping through impacting and friction at the supports. Fraction of critical damping was estimated by the modal curve fitting to parameter estimation from the measured frequency response functions. Magnitude of random excitation force, which can reproduce the in-situ excitation in operating environment, was maintained as constant value with a fine tolerance during vibration testing. Range of input force was carefully selected to cover from the low magnitude excitation for linearly behaved tube motion to high magnitude of force for nonlinearly-behaved tube motion. Estimated critical damping ratio shows scatters in data and tends to increase as the magnitude of rising force and decrease with upward frequency variation. Larger size of support gap increases multi-span tube damping for high magnitude of excitation.

• Transactions on Electrical and Electronic Materials
• /
• 제16권4호
• /
• pp.190-193
• /
• 2015

Insulation breakdown characteristics of an inverter surge resistant enameled wire were investigated in a twisted pair prepared with organic/inorganic hybrid nanocomposite. Organic polymer was polyesterimide-polyamideimide (EI/AI) and inorganic material was a nano-sized silica. The enamel thickness was 50 μm and the diameters of enameled copper wires were 0.75, 1.024, and 1.09 mm, respectively. There were many air gaps in a twisted pair. Therefore, when the voltage was applied to the twisted pair, enamel erosion took place in the air gap area because of partial discharge according to Paschen’s law. The insulation lifetime of the hybrid wire (HW) was 41,750 sec, which was 515.4 times more than the 81 sec of EI/AIW. In addition, the shape parameter of HW was 2.58, which was 3.4 times higher than 0.75 of EI/AIW.

• 한국유체기계학회 논문집
• /
• 제7권4호
• /
• pp.7-15
• /
• 2004

The design point of the cross-flow fan is generally based on the region within low static pressure and high flow rate. It relatively makes high dynamic pressure at low speed because a working fluid passes through an impeller blade twice. However, it has low static pressure efficiency between $30\%$ and $40\%$ because of relative high impact loss. The purpose of this study is to research the reciprocal relation among each parameter. Experiments and numerical analyses are conducted on effects of a stabilizer and a rearguider on performance analysis of a cross-flow fan. Two-dimensional, unsteady governing equations are solved using FVM, PISO algorithm, sliding grid system and standard $k-{\epsilon}$ turbulence model. Experiments are also carried out to estimate the performance of the modeled cross-flow fan. It is clarified that the rearguider of Archimedes type has excellent results for the most part.

• 대한기계학회논문집
• /
• 제12권1호
• /
• pp.81-94
• /
• 1988

본 연구에서는 표면상태가 다양한 고온면을 충돌온류에 의하여 냉각하는 방식이 광범위하게 응용되고 있는 점에 유의하여 표면조도, 노즐직경 및 분류속도를 변화시키고 노즐끝에 전열면의 직경과 동일한 원형판을 부착하여 비철액체를 막고 문극내에 온류액체를 강제유동시킴으로써 열전달에 미치는 모든 영향을 실험에 의해 고찰하고 고찰하고 포화수온류에 의한 열류속의 무차원관계식을 도출하는 것을 본 연구의 목적으로 하였다.

• 설비공학논문집
• /
• 제29권12호
• /
• pp.645-653
• /
• 2017

Thermal and flow modeling and fin structure optimization were performed to reduce the weight of an electrical device with a staggered fin. First, a numerical model for thermal and flow characteristics was suggested, and then, the model was verified experimentally. Using the verified model, improvement in cooling performance of the cooling system through the staggered fins was predicted. As a result, 87.5% of total heat generated was dissipated through the cooling fins, and a thermal island was observed in the rotor because of low velocity of the internal air flow through the air gap. In addition, it was confirmed that the staggered fin improves the cooling performance but it also increases the total pressure drop within the cooling system, by maximizing the leading edge effect. Based on this analysis result, the effect of each design parameter on the thermal and flow characteristics was analyzed to select the main optimal design parameters, and multi-objective optimization was performed by considering the cooling performance and the fin weight. In conclusion, the optimized fin structure improved the cooling performance by 7% and reduced the fin weight by 28% without any compromise of the pressure drop.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
• /
• pp.353-353
• /
• 2008

트랜지스터 속도는 현저하게 향상되어지는 반면에 RFICs(RF integrated circuits)는 대용량화, 고속화, 고집적화, 소형화, 고 효율화 온칩(on-chip) 수동소자의 부재에 의해 발전을 이루지 못하였다. 즉, 최근 전자기기의 집적화, 초소형화 됨에 따라 실장 밀도를 높이기 위해 부품의 소형화가 강하게 요구되는 동시에 Radio Frequency(RF)에서 이용가능한 수동소자인 capacitor를 개발하고자 본 논문에서는 손가락 모양(interdigital configuration)을 갖는 RF capacitor를 Ansoft사의 HFSS를 이용하여 이상적인 S-parameter, 정전용랑(capacitance), 손실계수(loss tangent)를 도출하고자 한다. 680um의 $Al_2O_3$ 기판에 BST doped MgO을 30um, Chromium과 gold를 각각 5um로 증착시켰다. 핑거 개수 (n, number), 핑거 길이(1, length), 핑거 간격(g, gap), 핑거 너비(w, width)를 변화 시켜가면서 이상적인 결과 값에 가까운 모양 (interdigital configuration)을 얻을 수 있었다. 핑거 수 3 개 일 때 입력 값에 대하여 손실 없는 출력 값(투과값)을 갖는 $S_{21}$이 1.5GHz에서 6dB이하로 떨어졌으며 핑거 간격이 줄고 핑거 너비가 커지고 핑거길이가 커질수록 높은 캐패시턴스 값을 갖는 것을 확인 할 수 있었다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
• /
• pp.395-398
• /
• 1999

In ac PDP(plasma Display Panel), the discharge characteristics is very important to display clear images. In this paper, we have studied the measurement of voltage transfer curves which show the discharge characteristics in AC PDP. The change of the effective wall capacitance during a discharge is also studied. These depend on lateral spreading of charge distribution and the strength of the discharge. As a parameter of the frequency, we observed the effects of the frequency in voltage transfer curves and in effective wall capacitance changes. As frequency increases, minimum sustain voltage and firing voltage decrease. In upper region of gap voltage the chance of the effective wall capacitance is independent of frequency.

• 한국초전도ㆍ저온공학회논문지
• /
• 제13권2호
• /
• pp.9-12
• /
• 2011

Superconducting motor has a lot of benefits from high power density for ship propulsions, so a number of research project are in progress worldwide. Despite of all the benefits, there is always a difficulty of cryo-moving part for conventional air-core superconducting synchronous motors. In order to get rid of this moving cryogenic part, we propose a homopolar superconducting synchronous motor, which has high temperature superconducting armature and field coils. The rotor is supposed to be made of iron only and excited by the stationary HTS field coils. The stationary field coils make the cooling system simple and easy to realize because there is no cryo-moving part. A design result of a 10 hp homopolar synchronous motor is presented in this paper. The self and mutual inductance of the motor having the size of air gap as variable parameter are calculated by a 3-dimemsional finite element method. The value of design variables such as the dimension of a motor and the number of turns, etc. is decided by performing the coordinate transformation of the calculated inductance. The operating frequency is supposed to be below 5 Hz for low rotating speed which is needed for a purpose of ship propulsion. Low frequency also has the benefit of low AC losses.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1154-1159
• /
• 2004

Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. Experiments are performed for Inconel 600 plates changing several process parameter such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between plate and plate, etc. The follow conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/ aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power . Welding characteristics of austienite Inconel 600 using a continuous wave Nd:YAG laser are experimentally investigated. This paper describes the weld ability of inconel 600 for machine structural use by Nd:YAG laser.