• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.759-764
• /
• 2003

Numerical simulations are conducted to investigate the mechanism of hovering flight by single flapping wing, and to examine the effect of the phase difference between the fore- and hindwings in hovering flight by two flapping wings. The numerical method used is based on an immersed boundary method in Cartesian coordinates. The Reynolds number considered is Re=150 based on the maximum translational velocity and chord length of the wing. For single flapping wing, the stroke plane angles are $0^{\circ}$, $30^{\circ}$, $60^{\circ}$, $75^{\circ}$ and $90^{\circ}$ and the downstroke angles of attack are varied for each stroke angle. Results show that for each stroke plane angle, there is an optimal angle of attack to maximize the vertical force. Below the stroke angle of $60^{\circ}$, wake capturing reduces the negative vertical force during the upstroke. For two flapping wings, The phase lags of the hindwing are $0^{\circ}$, $90^{\circ}$, $180^{\circ}$ and $270^{\circ}$. The amplitudes of the stroke are 2.5 and 4.0 times the chord length at each phase lag. The results show that maximum vertical force is generated when the phase lag is zero, and the amplitude of the vertical force is minimum at the phase lag of $180^{\circ}$.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집E
• /
• pp.367-372
• /
• 2001

The paper presents an improved way of aerodynamic quality in Korean Very High Speed Railway, The pantograph model being under development dissatisfies the required grade of aerodynamic lift force. So the present work proposes modified configurations of panheads to maintain consistent aerodynamic characteristics. Analysis has been performed using commercial CFD program. Simulation based analysis has been conducted with two different models. One is to attach the thin plate on the crossbar and the other is the use of trapezoidal cross section in contact strip. Various length of thin plate is simulated for flow velocity and acceptable value of plate length is selected which satisfy the necessary average lift force. Aerodynamic variation on the panheads strip is studied.

• 전기학회논문지
• /
• 제57권1호
• /
• pp.40-45
• /
• 2008

This paper presents an optimal design of a permanent magnet actuator(PMA) using a parallel genetic algorithm. Dynamic characteristics of permanent magnet actuator model are analyzed by coupled electromagnetic-mechanical finite element method. Dynamic characteristics of PMA such as holding force, operating time, and peak current are obtained by no load test and compared with the analyzed results by coupled finite element method. The permanent magnet actuator model is optimized using a parallel genetic algorithm. Some design parameters of vertical length of permanent magnet, horizontal length of plunger, and depth of permanent magnet actuator are predefined for an optimal design of permanent magnet actuator model. Furthermore dynamic characteristics of the optimized permanent magnet actuator model are analyzed by coupled finite element method. A displacement of plunger, flowing current of the coil, force of plunger, and velocity of plunger of the optimized permanent magnet actuator model are compared with the results of a primary permanent magnet actuator model.

• 한국기계가공학회지
• /
• 제9권1호
• /
• pp.1-7
• /
• 2010

A new flow mode of ER fluid available for controlling the damping force by using DME(Discrete Multi-Electrode) is presented in this study. Various characteristics about the flow of ER fluid through the experiment of ER cluster behavior visualization can be assumed. The pressure in electrode length and voltage division mode is measured. An actuator with a damping effect through DME ER damper will be developed. This damper controls the damping force by using the displacement and velocity of the plant which consists of the various electrode length and voltage modes without a controller in the real system.

• 한국소음진동공학회논문집
• /
• 제12권9호
• /
• pp.717-724
• /
• 2002

In this study, a numerical analysis for the piston secondary dynamics of small refrigeration reciprocating compressors is performed. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the change in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the hydrodynamic force and moment as functions of crank angle under compressor running conditions. The results explored the effects of the radial clearance, lubricant viscosity, length of the cylinder wall, and pin location on the stability of the piston.

• 한국재료학회지
• /
• 제17권7호
• /
• pp.371-375
• /
• 2007

In-situ observation of electromigration behavior of eutectic SnPb solder was performed as a function of line length at $100^{\circ}C$, $6{\times}10^4A/cm$ condition in a scanning electron microscope chamber. The incubation time for edge drift and the edge drift velocity increase as line length increases, which are discussed with the void nucleation stage of solder bump and the electromigration back flux force, respectively. Finally, the existence of electromigration product (jL) and its line length dependency are also discussed.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.389-394
• /
• 2007

Numerical simulations are conducted to investigate the mechanism for force generation of an insect with tandem wing configuration. Various stroke amplitudes, stroke plane angles and phase difference between the fore- and hind-wings are considered. The Reynolds number is 150 based on the chord length and maximum translation velocity of the wing. When an insect requires high lift such as takeoff, it flaps its wings in parallel at a lower stroke plane angle and a bigger stroke amplitude than those in the hovering. With wings in counter-stroke, the lift fluctuations decrease, and moreover mean lift force decreases. Interactions among the fore-wing, hind-wing and vortices are examined to explain the force variations

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1998년도 하계학술대회 논문집 B
• /
• pp.611-613
• /
• 1998

A structure of musculotendon model with a fatigue profile is investigated. The Hill-type musculotendon model can predicts the decline in muscle force for a given fatigue profile. It consists of nonlinear activation and contraction dynamics based on the physiological concepts. It is normalized for generalization to deal with the various muscles. Muscle force generated by continuous tetanic electrical monophasic pulsewidth modulation stimulation is decreased in time. A fatigue profile is expressed by a function of intramuscular acidification and applied to the relationship between muscle force and shortening velocity in contraction dynamics. The results of computer simulation are well matched with data in a literature which are isometrically performed for knee extension muscles. Also change in optimal fiber length has an effect only on muscle time, constant not on the steady-state tetanic force.

• 한국산학기술학회논문지
• /
• 제16권4호
• /
• pp.2883-2890
• /
• 2015

준설토 이송의 효율을 증가시키기 위한 연구로써 전자기력을 배관에 인가하여 유동저항을 줄이고, 윤활 층에서의 유속을 침강 임계속도이상으로 증가시키어 침강으로 인한 폐색을 방지하는 기술을 개발하였으며, 이를 대규모 장거리 송토현장에 적용하기 위하여 송토 거리 500m 규모의 현장에서 그 영향을 검토하는 실험을 진행하였으며, 실험결과 유동효율 증대로 인한 송토 유량이 30% 이상 증가함을 실험을 통해 보였다. 이를 검증하기 위하여 전자기장 인가장치와 계측장비로 초음파 유속 프로파일러를 사용하여 배관 내 유속프로파일을 모니터링 하여 그 데이터를 비교분석하여 효과를 검증하였다.

• The Journal of Korean Physical Therapy
• /
• 제25권3호
• /
• pp.136-142
• /
• 2013

Purpose: The application of transcutaneous electrical nerve stimulation (TENS) is beneficial for joint movements, inhibition of spasticity, and the improvement of walking ability in patients with chronic hemiplegia. This study aimed to identify the effect of the application of TENS to the knee extensor on the affected side with respect to postural-sway distance and velocity during the sit-to stand movement. Methods: We included 19 patients with post-stroke hemiplegia in this study. They underwent measurements during the sit-to stand movement on a force plate with 5 different stimulation dosages applied over 7 s:No TENS, high-frequency and high intensity TENS, high-frequency and low intensity TENS, low-frequency and high intensity TENS, and low-frequency and low intensity TENS The 5 different condition were administered in random order. Results: The group that received TENS application exhibited a significant decrease in path length and average velocity of center of pressure (COP) displacement compared with the group that did not receive TENS application. TENS dosage at low frequency (3Hz) and high intensity yielded a significant decrease in path length, average velocity, mediolateral distance and anteroposterior distance of COP displacement (p<0.05). Conclusion: Our results demonstrated the effectiveness of the application of low-frequency TENS on STS performance. These findings provide useful information on the application of TENS for the reduction of postural sway during the sit-to-stand movement after stroke.