• Wind and Structures
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• 제16권4호
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• pp.341-354
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• 2013

This paper presents an experimental investigation concerning the peak amplitudes of oscillation of a square prism due to Vortex-Induced-Vibrations (VIV) as a function of the mass damping parameter $m^*{\zeta}$ (the so called Griffin--plot); $m^*$ and ${\zeta}$ being, respectively, the non-dimensional mass and the mechanical (structural) damping ratio. With this purpose in mind, an electromagnetic actuator has been employed to provide controlled damping. During the experiments the mass--damping parameter was in the range 0.15 < $m^*{\zeta}$ < 2.4. Experiments show that there is a value of $m^*{\zeta}$ below which VIV appears combined with galloping and the prism oscillation increases monotonically with the incoming flow velocity. For $m^*{\zeta}$ >0.3 the present experiments show a well-defined VIV phenomenon and, consequently, a Griffin-plot can be defined.

• 한국정밀공학회지
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• 제26권2호
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• pp.54-62
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• 2009

The purpose of this study is to develop a piezo injector driver for common-rail direct injection diesel engines. In this research, we analyzed the electrical and mechanical characteristics of the piezo actuator through experiments. Current flow and charging voltage of the piezo injector are controlled by the PWM signal of variable duty ratio in order to realize both fast response and low peak current. The optimal switching duty ratio was designed by modeling and analyzing of the piezo driver circuit. In order to avoid resonance and unacceptably long settling time, appropriate frequency range of the PWM signal was derived based on the driver circuit model. The developed injector driver was validated by experiments under various fuel rail pressure, injection duration, and charging voltage.

• The Journal of Korean Physical Therapy
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• 제25권5호
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• pp.311-315
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• 2013

Purpose: Forward head posture is a typical symptom in people who use computers for long periods of time. Respiration is a complex function involving co-operation of muscular, skeletal, and nervous systems. Abnormal posture can have a negative effect on respiratory function. The purpose of this study was to investigate the relationship between forward head posture and respiratory function in young adults. Methods: Forty-six healthy subjects participated in this study. Craniovertebral angle was measured for assessment of the forward head posture. The respiratory function of all subjects was evaluated by measuring forced vital capacity (FVC), forced expiratory volume at one second (FEV1), forced expiratory volume at one second/forced vital capacity (FEV1/FVC) ratio, and peak expiratory flow (PEF). The baseline of forward head posture was less than 49 degrees. Results: : Significant differences for predicted FVC and FEV1 were observed between the two groups, however, no statistically significant differences in FEV1/FVC ratio and PEF were observed between the two groups. Conclusion: Results of this study demonstrate that forward head posture has a negative effect on respiratory function in young adults.

• 대한기계학회논문집B
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• 제22권3호
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• pp.386-398
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• 1998

The present experiment is conducted to investigate heat transfer characteristics on the impinging surface with secondary flows around circular nozzle jets. The changed vortex pattern around jet affects significantly the flow characteristics and heat transfer coefficients on the impinging surface. The effects of the jet vortex control are also considered with jet nozzle-to-plate distances and main jet velocities. The vortex pattern around a jet is changed from a convective instability to an absolute instability with a velocity suction ratio of the main jet and the secondary counterflow. With the absolute instability condition, the jet potential core length increases and the heat transfer on the impinging surface is increased by small scale eddies. The region of high heat transfer coefficients is enlarged with the high Reynolds number due to increasing secondary peak values. The effect of suction flows is influenced largely with collars attached the exit of the jet nozzle because the attached collar guides well the counterflow around the main jet.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.465-471
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• 2000

The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angel of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder according to the direction of the angle of attack.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권8호
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• pp.319-324
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• 2003

AIN thin films are deposited on Si (100) and $SiO_2$/Si substrates by using an RF magnetron sputtering method and by changing the conditions of deposition variables, such as RF power, $N_2$/Ar flow ratio, and substrate temperature ($T_sub$). For all the deposited AIN films, XRD Peak patterns are monitored to examine the effect of deposition condition on the crystal orientation. Highly (002)-oriented AIN films are obtained at following nominal deposition conditions; RF Power : 350W, $N_2$/Ar ratio = 10/20, T$_{sub}$ : $250^{\circ}C$, and working pressure = 5mTorr, respectively. AIN-based SAW devices are fabricated using a lift-off method by varying the thickness of AIN layer. Insertion losses and side-lobe rejection levels of fabricated SAW devices are extracted from their frequency response characteristics, which are also compared in terms of AIN thickness and substrate. Relationships between the film properties of AIN films and the frequency responses of SAW devices are discussed. It is concluded from the experimental results that the (002)-preferred orientation as well as the surface roughness of AIN film may play a crucial role of determining the device performances of AIN-SAW devices.s.

• 대한기계학회논문집B
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• 제24권7호
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• pp.976-983
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• 2000

The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angle of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder due to the presence of a ground plate nearby.

• Computers and Concrete
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• 제29권 5호
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• pp.323-334
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• 2022

In order to study the axial compression performance of basalt-fiber reinforced recycled concrete (BFRRC) filled circular steel tubular short columns, the axial compression performance tests of seven short column specimens were conducted to observe the mechanical whole-process and failure mode of the specimens, the load-displacement curves and the load-strain curves of the specimens were obtained, the influence of design parameters on the axial compression performance of BFRRC filled circular steel tubular short columns was analyzed, and a practical mathematical model of stiffness degradation and a feasible stress-strain curve equation for the whole process were suggested. The results show that under the axial compression, the steel tube buckled and the core BFRRC was crushed. The load-axial deformation curves of all specimens show a longer deformation flow amplitude. Compared with the recycled coarse aggregate (RCA) replacement ratio and the basalt fiber dosage, the BFRRC strength has a great influence on the peak bearing capacity of the specimen. The RCA replacement ratio and the BFRRC strength are detrimental to ductility, whereas the basalt fiber dosage is beneficial to ductility.

• Clinical and Experimental Pediatrics
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• 제49권4호
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• pp.417-423
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• 2006

목 적 : 항암제와 방사선 치료의 개발, 골수나 조혈모세포 이식 기회의 증가로 소아 백혈병과 고형 종양을 가진 환아들이 장기 생존하게 되면서 치료에 따른 장기 부작용, 특히 심장 독성에 크게 관심을 가지게 되었다. 항암제에 의한 심장 독성을 파악하는데 가장 적절한 방법은 비침습적이면서 정량적으로 측정할 수 있는 심초음파라고 할 수 있다. 본 연구에서는 이미 소아암으로 진단을 받고 치료를 받는 중이거나 치료를 종료한 환아들을 대상으로 조직 도플러 영상을 사용하여 심실 기능을 평가하고, 향후 동질환의 환아에서 조기 및 후기 심독성을 조기에 발견하기 위한 방법으로 반복적인 조직 도플러 영상을 적용하는데 기여하고자 하였다. 방 법 : 2005년 4월 1일부터 7월 1일까지 계명대학교 동산의료원 소아 종양 크리닉을 방문한 항암치료 중이거나 항암치료 종료된 환아 23명을 대상으로 하였다. 전체 대상 환아군(1군)은 단축 분획 29% 이상(2군), 28% 이하의 군(3군)으로 나누고, anthracyclin 사용군(4군)과 미사용군(5군)으로 다시 나누었다. M-mode와 간헐파 도플러를 이용하여 단축 분획, 구혈률, 승모판막으로 유입되는 혈류의 E, A 속도, DT, IVRT를 측정하였고, 조직 도플러 영상을 이용하여 심첨 4, 2 방도에서 중격, 전벽, 하벽, 측벽의 기저부, 중간, 심첨 부위의 Sm, Em, Am 속도를 측정하였다. 측정한 값을 이용하여 modified Tei index, E/A, E/Em ratio를 구하였다. 결 과 : 환아의 평균 나이는 8년 4개월이었고 남아 12명, 여아 11명이었다. 항암제 중 anthracyclin을 사용한 환아(4군)는 13명이었고, 방사선 치료를 받은 환아는 4명이었으며 단축 분획이 28% 이하인 환아(3군)는 6명이었다. 대조군의 평균 나이는 6년 6개월이었고 남아 6명, 여아 3명이었다. 환아군과 대조군간에 성별, 나이에 있어서 유의한 차이는 없었다. 대조군과 1군의 E/Em ratio는 $7.06{\pm}1.64$, $6.46{\pm}1.85$로 두 군간에 P<0.05로 의미있는 차이가 있었으나 다른 측정값들은 유의한 차이가 없었다. 대조군과 2, 3, 4, 5군간에도 E/Em ratio는 P<0.05로 의미있는 차이가 있었다. 2, 3군과 4, 5군간에는 측정값들의 군간의 유의한 차이가 없었다. 결 론 : 좌심실 평균 이완기압을 반영한다고 알려져 있는 E/Em ratio에서 대조군과 항암 치료 군간에 차이가 확인됨으로써 항암 치료 이후의 심장 기능 부전은 수축기 기능 변화가 아닌 이완기 기능 변화가 먼저 오는 것을 알 수 있었다. 심장 이완기 기능을 평가하는 간헐파 도플러 측정값들에서는 두 군간에 차이가 없음으로 이완기 기능을 평가하는데는 조직 도플러 영상을 이용하는 것이 더 민감한 방법이었다. 따라서 항암 치료 이후에도 장기적으로 관심을 가지고 심장 기능에 대한 잦은 추적 관찰이 필요하겠고, 추적 관찰하는 방법으로는 조직 도플러 영상을 이용한 심초음파 검사가 비침습적이고 간편하며 유용한 방법일 수 있다.

• 대한기계학회논문집B
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• 제26권4호
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• pp.578-586
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• 2002

Flow structures around a rectangular prism have been investigated by using a PIV(Particle Image Velocimetry) technique. A thick turbulent boundary layer was generated by using spires arid roughness elements. The boundary layer thickness, displacement thickness and momentum thickness were 650mm, 117.4mm and 78mm, respectively. The ratio between the model height(40mm) and the boundary layer thickness H/$\delta$, was 0.06. The Reynolds number based on the free stream velocity and the height of the model was 7.9$\times$10$^3$. The PIV measurements were performed at three different wall normal planes. Three recirculation regions at forward facing step, top of the roof and backward facing step are clearly seen and show three dimensional features. Dramatic changes of flow patterns are observed in the wake regions in the different spanwise wall normal planes. Instead of reattachment and recirculation zone, rising streamlines are depicted at the normal planes near the side wall due to the interaction with a rising horse shoe vortex. The peak of turbulent kinetic energy occurs at the separation bubble on top of the roof and the magnitude is 2.5 times higher compared with that of the wake region.