• 한국소음진동공학회논문집
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• 제21권5호
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• pp.447-454
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• 2011

This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated. The effects of the design parameters(cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function(OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased. The control performance is finally estimated for the clamped beam. More than 10 dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

• 한국가시화정보학회지
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• 제14권2호
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• pp.12-17
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• 2016

In this work, we investigate the flow velocity controllability of a diffuser-type multiple hydrofoil duct by experimental and numerical flow visualization approaches. The flow velocity controllability is analyzed by changing the angle of the hydrofoil near the outlet, which is the diffuser, while the incoming flow velocity is 0.6 m/s in the experiment. When the diffuser angle is changed from 0 to 7.5 degree, the maximum velocity inside the duct is varied from 1.35 m/s to 1.52 m/s. Also, it is shown from the numerical analysis that the maximum velocity is varied from 1.09 m/s to 1.17 m/s in the same condition. Thus, the aspect of the acceleration in the duct due to the increase of the diffuser angle is similar between the both approaches. Therefore, the multiple hydrofoil duct can be used to control the flow speed inside the duct for continuously extracting power close to a rated capacity.

• 대한물리의학회지
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• 제9권3호
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• pp.271-278
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• 2014

PURPOSE: This study researched the effects of different types of high heels on the muscles surrounding the cervical spine, the thoracic spine, and the lumbar spine by analyzing muscle activation of the paraspinal muscles during walking while wearing high heels. The high heels were all of the same height: 8cm. METHODS: The 28 subjects in this experiment were females in their 20s with a foot size of 225-230mm. To measure the muscle activation of the paraspinal muscles, EMG electrodes were attached on the paraspinal muscles around C6, T7, and L5. The muscle activation during walking while wearing 8cm high wedge heels, setback heels, and french heels was measured. The measurements were performed 3 times each and the mean value of the result was used for analysis. Two kinds of velocity were used in this study. One of the velocity was 2.5 m/s. The other was 3.5 m/s. RESULTS: The muscle activation of paraspinal muscles increased significantly according to increase of walking velocity. But there was no significant difference according to the heel types. CONCLUSION: In view of the results, the height of heels and the velocity of walking are more convincing variables than the width of the heels on the muscle activation of paraspinal muscles. So wearing high heels is not recommended for those who have pain or functional problem of cervical and lumbar vertebrae.

• 한국운동역학회지
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• 제23권4호
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• pp.327-333
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• 2013

The purpose of this study was to investigate the effects of different types of attentional focus(internal focus vs. external focus) on the dart throwing mechanics. Seven expert dart throwing athletes were assigned to an internal focus group and other seven athletes were assigned to an external focus group. Each group was asked to throw dart either under verbal instruction or without instruction. During dart throwing, accuracy(radial error), consistency(bivariate variable error), dart velocity, acceleration, elbow joint ROM, elbow joint angular velocity, EMD(electromechanical delay), iEMG of biceps brachii and triceps brachii, and CI(coactivation index) were collected and analyzed. Nither instruction type nor instruction itself affected in accuracy and consistency. However, in dart velocity and acceleration, there was an interaction between instruction and attentional focus types. Velocity and acceleration increased in the internal condition, where as they decreased in the external condition. The ROM of elbow joint did not affected by instruction and attention type. However, similar to dart velocity and acceleration, angular velocity increased in internal focus group, while it decreased in external focus group. EMG showed no difference with any condition. In conclusion, internal focus is better than external focus for dart throwing.

• 천문학회지
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• 제37권1호
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• pp.15-39
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• 2004

We analyse the results of mass models derived from the HI rotation! curves of spiral galaxies and find that the slope of the luminous mass-circular velocity relation is close to 4. The luminous mass-circular velocity relation with a slope of about 4 can be explained by an anti-correlation between the mass surface density of luminous matter and the mass ratio of the dark and luminous components. We also argue that the conspiracy between luminous and dark matter exists in a local sense (producing a flat or smooth rotation curve) and in a global sense (affecting the mass ratio of the dark and luminous matter), maintaining the luminous mass-circular velocity relation with a slope of about 4. We therefore propose that the physical basis of the Tully-Fisher relation lies in the luminous mass-circular velocity relation. While the slope of the luminous mass-circular velocity relation is fairly well defined regardless of the dark matter contribution, the zero-point of the relation is still to be determined. The determination of the slope of the Tully-Fisher relation needs one more step: the mean trend of the luminosity-luminous mass relation determines the overall shape (slope) of the Tully-Fisher relation. The key parameter needed to determine the zero-point of the luminous mass-circular velocity relation and the slope of the Tully-Fisher relation obviously is the luminous mass-to-light ratio.

• 제어로봇시스템학회논문지
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• 제19권6호
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• pp.555-562
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• 2013

This paper presents the optimal array of optical mice for the accurate velocity estimation of a mobile robot. It is assumed that there can be some restriction on the installation of two or more optical mice at the bottom of a mobile robot. First, the velocity kinematics of a mobile robot with an array of optical mice is derived, which maps the velocity of a mobile robot to the velocities of optical mice. Second, taking into account the consistency in physical units, the uncertainty ellipsoid is obtained to represent the error characteristics of the mobile robot velocity estimation owing to noisy optical mouse measurements. Third, a simple but effective performance index is defined as the inverse of the volume of the uncertainty ellipsoid, which can be used for the optimization of the optimal optical mouse placement. Fourth, simulation results for the optimal placement of three optical mice within a given elliptical region are given.

• 전자공학회논문지
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• 제50권9호
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• pp.55-59
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• 2013

Sub-$0.1{\mu}m$로 스케일이 감소함에 따라 기생 저항 효과가 크게 발생되는 dc Ids 측정 데이터 없이 측정 S-파라미터로부터 얻어진 RF Ids를 사용하여 벌크 MOSFET의 포화영역에서 게이트 전압 종속 유효 캐리어 속도를 추출하는 새로운 방법이 개발되었다. 이 방법은 바이어스 종속 기생 게이트-소스 캐패시턴스와 유효 채널 길이의 복잡한 추출 없이 포화영역의 유효 캐리어 속도를 추출할 수 있게 한다. 이러한 RF 기술을 사용하여 벌크 포화 속도를 초과하는 전자 속도 overshoot 현상이 $0.065{\mu}m$ 게이트 길이의 벌크 N-MOSFET에서 관찰되었다.

• 대한기계학회논문집B
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• 제25권11호
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• pp.1535-1542
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• 2001

A high resolution digital cinematic Particle Image Velocimetry(PIV) has been developed. The system consists of a high speed CCD camera, a continuous Ar-ion laser and a computer with camera controller. To improve the spatial resolution, we adopt a Recursive Technique for velocity interrogation. At first, we obtain a velocity vector fur a larger interrogation window size based on the conventional two-frame cross-correlation PIV analysis using the FFT algorithm. Based on the knowing velocity information, more spatially resolved velocity vectors are obtained in the next iteration step with smaller interrogation windows. When the correct velocity vector at the first step is found to be critical, a Multiple Correlation Validation(MCV) technique is applied to decrease the spurious vectors. The MCV technique turns out to improve SNR(Signal to Noise Ratio) of the correlation table. The developed cinematic PIV method has been applied to the measurement of the unsteady flow characteristics of a Rushton turbine mixer. A total of 3,245 instantaneous velocity vectors were successfully obtained with 4 ms time resolution. The acquired spatial resolution corresponds to the conventional high resolution digital PIV system using a 1K ${\times}$ 1K CCD camera.

• 대한기계학회논문집B
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• 제22권7호
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• pp.1013-1021
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• 1998

Various vortical structures are investigated by using three kinds of flow visualization methods in branch pipe flows. There are two typical flow patterns when a jet from the branch pipe with various angles is injected to the main pipe cross flow. The velocity range of cross flow of the main pipe is 0.2 m/s ~ 1.2 m/s and the corresponding Reynolds number, R$_{p}$ is of the range 1.5 * 10$^{3}$ ~ 9.02 * 10$^{3}$. The velocity ratio(R), jet velocity/cross flow velocity, is chosen from 1.3 to 4. The subsequent behavior and development of the ring vortices which are created at the jet boundary mainly depend on the velocity ratio. An empirical relation for the shedding frequency of the ring vortices is derived. It is also found that there are two different vortex shedding mechanism in the mixing of two fluid streams.s.

• 대한기계학회논문집B
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• 제21권4호
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• pp.509-517
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• 1997

Results of flat plate compressible boundary layer calculation, based on discrete formulation of DSMC method, are presented in low Mach number and low Knudsen number range. The free stream is a uniform flow of pure nitrogen at various Mach numbers in low pressures (i.e. rarefied gas). Complete thermal accommodation and diffuse molecular reflections are used as the wall boundary condition, replacing unreal no-slip condition used in continuum calculations. In the discrete formulation of DSMC method, there is no need to use ad hoc assumptions on transport properties like viscosity and thermal conductivity, instead viscosity is calculated from values of other field variables (velocity and shear stress). Also the results are compared with existing self-similar continuum solutions. In all Mach number cases computed, velocity slip is most pronounced in regions near the leading edge where continuum formulation renders the solution singular. As the boundary layer develops further downstream, velocity slips asymptote to values that are between 10 to 20% of the magnitude of free stream velocity. When the free stream number density is reduced, so the gas more rarefied, the velocity slip increases as expected.