• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 금형가공 심포지엄
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• pp.53-60
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• 2002

Recently, the development of aerospace and automobile industries brought new technological challenges, related to the growing complexity of products and new geometry models. High speed machining using 5-Axis milling machine is widely used for 3D sculptured surface parts. 5-axis milling of turbine blade generates the vibration, deflection and twisting caused from thin and cantilever shape. So, the surface roughness and the waviness of workpiece are not good. In this paper, The effects of cutter orientation and lead/tilt angle in 5-Axis high speed ball end-milling of turbine blade were investigated to improve the geometric accuracy and surface integrity. The experiments were performed at lead/tilt angle $15^{\circ}$ of workpiece with four cutter directions such as horizontal outward, horizontal inward, vertical outward, and vertical inward. Workpiece deflection, surface roughness and machined surface were measured with various cutter orientations such as cutting direction, and lead/tilt angle. The results show that when 5-axis machining of turbine blade, the best cutting strategy is horizontal inward direction with tilt angle. The results show that when 5-axis machining of turbine blade, the best cutting strategy is horizontal inward direction with tilt angle.

• 대한기계학회논문집A
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• 제39권4호
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• pp.415-421
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• 2015

본 연구는 햅틱 진동자의 개발과정에 있어 성능인자의 단계별 설정절차와 성능 및 소형화를 위한 자석의 착자방법에 대한 연구를 수행하였다. 착자방법에 대한 연구는 수평착자와 수직착자의 구성방법에 따른 전자기력을 비교분석하여 수행하였으며, 수행결과 수평착자가 우수한 것으로 나타났다. 시스템적 설계 절차로는 제품의 특성으로부터 설계 인자를 설정하는 단계적 절차를 구성하여 시작품을 제작하고 시험을 통하여 검증하였다. 해석적 방법에서는 진동응답 특성 해석과 전기장의 해석을 독립적으로 수행하였으며, 시험결과와의 검증을 통해 잘 일치하는 결과를 도출하였다. 제품신뢰성 확보를 위한 신뢰성 기반 설계인자는 스프링 높이, 용접 위치, 코일의 위치로 선정하였다. 그리고 설계 인자에 따른 전자기장 민감도 및 성능 변화를 분석하였고 이를 바탕으로 신뢰성 기반의 고성능 햅틱 진동자를 구현할 수 있도록 설계방법을 제시하였다.

• Structural Engineering and Mechanics
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• 제30권3호
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• pp.369-382
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• 2008

An oscillator of two lumped masses linked through a vertical spring moves forward in the horizontal direction, initially at a certain height, over a horizontal Euler beam and descends on it due to its own weight. Vibration of the beam and the oscillator is excited at the onset of the ensuing impact. The impact produced by the descending oscillator is assumed to be either perfectly elastic or perfectly plastic. If the impact is perfectly elastic, the oscillator bounces off and hits the beam a number of times as it moves forward in the longitudinal direction of the beam, exchanging its dynamics with that of the beam. If the impact is perfectly plastic, the oscillator (initially) sticks to the beam after its first impact and then may separate and reattach to the beam as it moves along the beam. Further events of separation and reattachment may follow. This interesting and seemingly simple dynamic problem actually displays rather complicated dynamic behaviour and has never been studied in the past. It is found through simulated numerical examples that multiple events of separation and impact can take place for both perfectly elastic impact and perfectly plastic impact (though more of these in the case of perfectly elastic impact) and the dynamic response of the oscillator and the beam looks noisy when there is an event of impact because impact excites higher-frequency components. For the perfectly plastic impact, the oscillator can experience multiple events of consecutive separation from the beam and subsequent reattachment to it.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.103-107
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• 2009

Because individual HRTFs (Head-Related Transfer Functions) vary from a person to a person, a HRTF database has been measured by researchers to investigate the inter-subject variation, and to generate high fidelity virtual sound image. Individual HRTFs not only vary between subjects but also vary due to wearing clothes and glasses in daily life. However, influence of different dressing condition on the measured HRTF was not sufficiently investigated. To quantify the effect of wearing clothes and glasses, dummy's HRTF is measured in an anechoic chamber with various dressing condition, and is evaluated in the sense of spectral distortion. HRTFs are measured both in the median plane and in the horizontal plane. In the median plane, under 6kHz, effect of different wearing clothes and glasses is negligible. Over 6kHz, however, effect of clothing distorts HRTF about 6dB in the sense of spectral distortion. Moreover, at high frequencies, effect of glasses is no longer negligible. In the horizontal plane, at some azimuths, even additional light cloth over the dummy can change the spectrum of HRTF (6dB spectral distortion) especially when sound source is at contralateral positions. Therefore, HRTF measurement with different wearing conditions can broaden the capability of HRTF customization whose technique utilizes a HRTF database.

• 한국소음진동공학회논문집
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• 제19권6호
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• pp.620-627
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• 2009

Shaking table test was carried out to obtain dynamic characteristics of TLCDs with uniform and non-uniform sections for both horizontal and vertical tubes. The input to the table is harmonic acceleration with constant magnitude. The output is horizontal dynamic force which is measured by load cell installed below the TLCD. Transfer functions are experimentally obtained using the ratio of input and output. Natural frequency, the most important design factor, is compared to that by theoretical equation for TLCDs with five different water levels. System identification process is performed for experimentally obtained transfer functions to find the dynamic characteristics of head loss coefficient and effective mass of TLCDs. It is found that their magnitudes are larger for a TLCD with non-uniform section than with uniform section and natural frequencies are close to theoretical ones.

• 대한조선학회논문집
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• 제36권2호
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• pp.105-113
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• 1999

본 논문에서는 선체 단면의 St'Venant 비틂강성은 물론 굽힘-비틂 강성과 전단-비틂 강성 및 선체 개단면과 폐단면 연결부에서의 변위와 단면력의 연속조건을 고려한 보유추이론을 적용하여 수평 비틂 거동의 연성도가 크고, 비틂에 대해 유연한 선체 거더의 수평 비틂 연성 고유진동 감도해석방법을 제시하였다. 제시된 방법을 토대로 대형 컨테이너 운반선의 적화상태 변경시의 고유진동수를 감도해석 결과를 이용하여 추정한 결과는 통상적 재해석 결과와 비교하여 오차 1%이내의 매우 양호한 부합성을 나타내었다. 아울러, 수평거동과 비틂거동의 연성도가 큰 선박의 경우 선체 중량 중심이 형 깊이의 10%까지 변화할 경우에 고유진동수가 최대 8%까지 변화함을 확인하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.977-981
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• 2002

The ordinary differential equations governing free vibrations of elastic horizontally curved beams are derived, in which the effect of shear deformation as well as the effects of vertical, rotatory and torsional inertias are included. Frequencies and mode shapes are computed numerically for parabolic curved beams with the hinged-hinged, hinged-clamped and clamped-clamped ends. Comparisons of natural frequencies between this study and ADINA are made to validate the theories and numerical methods developed herein. The lowest three natural frequency parameters are reported, with and without the effect of shear deformation, as functions of the three non-dimensional system parameters: the horizontal rise to span length ratio, the slenderness ratio and the stiffness parameter.

• Smart Structures and Systems
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• 제14권3호
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• pp.367-376
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• 2014

Ambient vibration techniques are nowadays a very popular tool to assess dynamic properties of buildings. Due to its non destructive character, this method is particularly valuable, especially for health monitoring of historical monuments. The present ambient vibration experiment consists on the evaluation of vibration modes of a Medieval tower. Situated in Soncino (close to Cremona, in the Northern Italian region named Lombardia), the tower of 41.5 meters height has been monitored by seismometers located at different points inside the structure. Spectral ratios of the recorded ambient vibrations clearly identify a fundamental mode at about 1 Hz, with a slight difference in the two horizontal components. A second mode is also evidenced at approx 4-5 Hz, with a moderate degree of uncertainty. The records of a ML 4.4 earthquake, occurred during the monitoring period, confirm the information obtained by microtremor analysis. Daily variations of both 1st and 2nd mode were detected: these variations, of an amount up to 2%, seem to be well related with the temperature.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 춘계학술대회 논문집
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• pp.136-143
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• 2001

In this study, a numerical analysis for soil-pile interaction systems in multi-layered half planes under a forced vibration is presented. The soil-pile interaction system is divided into two parts, so called near field and far field. The near field soil using finite elements and piles using beam elements are modeled. The far field soil media is implemented using boundary elements those can automatically satisfy the condition of wave radiation. These two fields are numerically coupled by imposing displacement compatibility condition at the interface between the near field and the far field. For the verification, the forced vibration test was simulated and the response under horizontal and vertical harmonic loads at the pile cap in the layered half plane was determined. The results are compared to the theoretical and experimental results of the literatures to verify the proposed soil-pile interaction analysis formulation.

• Wind and Structures
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• 제7권3호
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• pp.203-214
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• 2004

This paper describes a method for developing a multi-degree-of freedom aero-elasto-plastic model of a base-isolated mid-rise building. The horizontal stiffness of isolators is modeled by several tension springs and the vertical support is performed by air pressure from a compressor. A lead damper and a steel damper are modeled by a U-shaped lead line and an aluminum line. With this model, the frequency ratio of torsional vibration to sway vibration, and plastic displacements of isolation materials can be changed easily when needed. The results of isolation material tests and free vibration tests show that this model provides the object performance. The peak displacement factors are about 4.5 regardless of wind speed in wind tunnel tests, but their gust response factor decreases with increment of wind speed.