• Title/Summary/Keyword: stability limit velocity

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The Effects of Injector and Swirler on the Flame Stability in a Model Combustor (모델연소기에서의 분사기와 선회기의 영향)

  • Park, Seung-Hun;Lee, Dong-Hun;Bae, Chung-Sik
    • 한국연소학회:학술대회논문집
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    • 1998.10a
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    • pp.9-21
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    • 1998
  • The optimization of frontal device including fuel nozzle and swirler is required to secure the mixing of fuel and air, and the combustion stability in the gas turbine combustor design for the reduction of pollutant emissions and the increase of combustion efficiency. The effects of injection nozzle and swirler on the flow field, spray characteristics and consequently the combustion stability, were experimentally investigated by measuring the velocity field, droplet sizes of fuel spray, lean combustion limit and the temperature field in the main combustion region. The effect of fuel injection nozzle was tested by adopting three different nozzles; a dual orifice fuel nozzle, a hollow cone nozzle and a solid cone nozzle. These tests were combined with the three different swirler geometries; a dual-stage swirler with 40$^{\circ}$ /-4 5$^{\circ}$ vanes and two single-stage swirlers with 40$^{\circ}$ vane angle having 12 and 16vanes, respectively. Flow fields and spray characteristics were measured with APV(Adaptive Phase Doppler Velocimetry) under atmospheric condition using kerosine fuel. Temperatures were measured by Pt-PtI3%Rh, R-type thermocouple which was 0.2mm thick. It was found that the dual swirler resulted in the biggest recirculation zone with the highest reverse flow velocity at the central region, which lead the most stable combustion. The various combustion characteristics were observed as a function of the combination between the injector and swirler, that gave a tip for the better design of gas turbine combustor.

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Effects of Microwave Induction on the Liftoff and NOx Emission in Methane Micro Jet Flames (메탄 마이크로 제트화염의 부상과 NOx 배출에 대한 마이크로파 효과)

  • Jeon, Young Hoon;Lee, Eui Ju
    • Journal of the Korean Society of Combustion
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    • v.21 no.2
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    • pp.22-28
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    • 2016
  • High efficient and environment friendly combustion technologies are used to be operated an extreme condition, which results in unintended flame instability such as extinction and oscillation. The use of electromagnetic energy is one of methods to enhance the combustion stability and a microwave as electromagnetic wave is receiving increased attention recently because of its high performance and low-cost system. In this study, an experiment was performed with jet diffusion flames induced by microwave. Micro jet was introduced to simulate the high velocity of industrial combustor. The results show that micro jet flames had three different modes with increasing oxidizer velocity; attached yellow flame, lifted flame, and lifted partially premixed flame. As a microwave was induced to flames, the overall flame stability and blowout limit were extended with the higher microwave power. Especially the interaction between a flame and a microwave was shown clearly in the partially premixed flame, in which the lift-off height decreased and NOx emission measured in post flame region increased with increasing microwave power. It might be attributed to increase of reactivity due to the abundance of radical pool and the enhanced absorption to thermal energy.

Active Structural Acoustical Control of a Smart Panel Using Direct Velocity Feedback (직접속도 피드백을 이용한 지능판의 능동구조음향제어)

  • Stephen J, Elliott;Paolo, Gardonio;Young-Sup, Lee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.14 no.10
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    • pp.1007-1014
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    • 2004
  • This paper presents a study of low frequencies volume velocity vibration control of a smart panel in order to reduce sound transmission. A distributed piezoelectric quadratically shaped polyvinylidene fluoride (PVDF) polymer film is used as a uniform force actuator and an array of $4\;{\times}\;4$ accelerometer is used as a volume velocity sensor for the implementation of a single-input single-output control system. The theoretical and experimental study of sensor-.actuator frequency response function shows that this sensor-actuator arrangement provides a required strictly positive real frequency response function below about 900 Hz. Direct velocity feedback could therefore be implemented with a limited gain which gives reductions of about 15 dB in vibration level and about 8 dB in acoustic power level at the (1,1) mode of the smart panel. It has been also shown that the shaping error of PVDF actuator could limit the stability and performance of the control system.

An Experimental Study on Velocity Profile in a Vegetated Channel (식생수로의 유속분포에 관한 실험적 연구)

  • Kwon, Do Hyun;Park, Sung Sik;Baek, Kyung Won;Song, Jai Woo
    • Proceedings of the Korea Water Resources Association Conference
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    • 2004.05b
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    • pp.957-960
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    • 2004
  • From a water-environmental point of view, with a change of understanding and concern about vegetation, it changes that vegetation acts as stability of channel and bed, providing habitats and feed for fauna, and means improving those with appreciation of the beautiful but resistant factor to the flow So, it becomes important concern and study subjects that turbulent structure by vegetation, shear stress and transport as well as roughness and average velocity by vegetation. But from a hydraulic point of view, vegetation causes resistance to the flow and can increase the risk of flooding, Therefore, this thesis concern the flow characteristics in vegetated open channels. According to the experimental results, $z_0$ was on an average $0.4h_p$ in a vegetated open channel. So, the elevation corresponding to zero velocity in a vegetated channel was the middle of roughness element. The limit for logarithmically distributed profile over the roughness element was from $z_0$ to $0.80h_{over}$ for a vegetated channel. Among the existing theory, the method of Kouwen et al.(1969), Haber(1982), and El-Hakim and Salama(1992) except Stephan(2001) gave a very good value compared to the measured velocity profile.

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Analysis of the Effect of Contact Stiffness on the Out-of-plane Motion of a Disc Brake System using 2-DOE Model (2자유도 모텔을 이용한 디스크 브레이크의 면외 운동에 미치는 접촉강성의 영향 분석)

  • 신기홍;조용구;차병규;오재응
    • Transactions of the Korean Society of Automotive Engineers
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    • v.12 no.2
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    • pp.160-167
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    • 2004
  • A two degree-of-freedom mathematical model is presented to investigate the friction mechanism of a disc brake system. A contact parameter is introduced to describe the coupling between the in-plane and the out-of-plane motions. The model with the contact parameter is considered under the assumption that the out-of-plane motion depends on the friction force along the in-plane motion. In order to describe the relationship between the friction force and the out-of plane motion, the dynamic friction coefficient is considered as a function of both relative velocity and normal farce. Using this friction law, a contact stiffness matrix along the normal direction can be obtained. The out-of-plane motion is then investigated by both the stability analysis and the numerical analysis for various parametric conditions. The results show that the stiffness parameters of the pad and the disc must be controlled at the same time. Also, the numerical analysis shows the existence of limit cycle caused by the effect of intermittent contact stiffness.

The Effects of Home Based Exercise Program on Balance Recovery in a Post-Stroke Population (뇌졸중 환자의 균형능력 회복을 위한 가정운동프로그램 효과)

  • Jang, Sang-Hun;Bang, Hyun-Soo;Jung, Byeong-Ok
    • Journal of Digital Convergence
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    • v.12 no.7
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    • pp.297-304
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    • 2014
  • The present study was designed to investigate the effect of home based exercise program on balance recovery of stroke patients. In total, 20 participants were assigned to a control group(n=10) or exercise group(n=10) between September 2013 and December 2013. In addition to existing physiotherapy, the exercise group received home based exercise program consisting of weight transfer, training endurance, mobility, sensory retraining, lower limb exercise for 30 minutes, 2 times a week, for 8 weeks, every time for 30 minutes. Balance ability was assessed by measuring foot pressure(FP), limit of stability(LOS) and velocity sway(VS) by using Biorescue and by using the functional reaching test(FRT). To compare the improvement level of each group's balance ability, examination of independent sample T was done. Significant differences between control group and exercise group in LOS, VS of affect side and FRT were observed. This study showed that home based exercise program application was effective strategy on balance recovery in a post stroke population.

Optimum Design of Journal Bearings considering the Wear Rate (마멸율에 관한 저널베어링의 최적설계)

  • 임오강;이왕진
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.15 no.1
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    • pp.155-164
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    • 2002
  • The journal bearings use in machine parts which move relative to each other and those reduce friction and wear of journals. The journal bearings are designed to operate in the hydyodynamic lubrication regime, but elastohydrodynamic lubrication nay occur if the pressures are too high or the running speeds are too low at machine elements. It is the phenomenon that the lubricant film is broken and some parts of surfaces are in rolling contact, so that wear will increase in mixed lubrication regime. The purpose of this study is to minimize the wear rate of journal bearings for extending machine life. The wear mate in mixed lubricated regime is selected as objective function because most of wear of the journal bearings develops in elastohydrodynamic lubrication. The journal bearings we represented by a bearing radius, shaft radius, and bearing width, but the bearing radius only is selected as design variables due to a bearing radius has an influence on friction loss, stability limit velocity, and film parameter, which are used as constraints. For numerical calculation, PLBA, that is a class of the RQP algorithm, is used.

Active Structural Acoustical Control of a Smart Structure using Uniform Force Actuator and Array of Accelerometers (균일힘 액추에이터와 가속도계 배열을 이용한 지능구조물의 능동구조 음향제어)

  • ;Stephen J Elliott;Paolo Gardonio
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.05a
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    • pp.368-373
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    • 2003
  • This paper presents a study of low frequencies volume velocity vibration control of a smart panel in order to reduce sound transmission. A distributed piezoelectric quadratically shaped polyvinylidene fluoride (PVDF) polymer film is used as a uniform force actuator and an array of 4$\times$4 accelerometer is used as a volume velocity sensor for the implementation of a single-input single-output con rot system. The theoretical and experimental study of sensor-actuator frequency response function sho vs that this sensor-actuator arrangement provides a required strictly positive real frequency response function below about 900Hz. Direct velocity feedback could therefore be implemented with a limited gain which gives reductions of about 15㏈ in vibration level and about 8 ㏈ in acoustic power level at the (1, 1) mode of the smart Panel. It has been also shown that the shaping error of PVDF actuator could limit he stability and performance of the control system.

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Iris Recognition using Multi-Resolution Frequency Analysis and Levenberg-Marquardt Back-Propagation

  • Jeong Yu-Jeong;Choi Gwang-Mi
    • Journal of information and communication convergence engineering
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    • v.2 no.3
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    • pp.177-181
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    • 2004
  • In this paper, we suggest an Iris recognition system with an excellent recognition rate and confidence as an alternative biometric recognition technique that solves the limit in an existing individual discrimination. For its implementation, we extracted coefficients feature values with the wavelet transformation mainly used in the signal processing, and we used neural network to see a recognition rate. However, Scale Conjugate Gradient of nonlinear optimum method mainly used in neural network is not suitable to solve the optimum problem for its slow velocity of convergence. So we intended to enhance the recognition rate by using Levenberg-Marquardt Back-propagation which supplements existing Scale Conjugate Gradient for an implementation of the iris recognition system. We improved convergence velocity, efficiency, and stability by changing properly the size according to both convergence rate of solution and variation rate of variable vector with the implementation of an applied algorithm.

Optimal Gas-Flow Conditions for Stabilization of Lean-Burn Combustion (희박연소 안정화를 위한 가스유동장 조건에 관한 연구)

  • 이기형;이창식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.3
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    • pp.763-770
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    • 1995
  • Gas flow characteristics within the cylinder is important factors in impoving lean combustion stability. This paper shows the effects of various flow fields generated by a swirl control valve(SCV) on combustion process in a 4-valve spark ignition engine. An impulse swirl/tumble meter was used to elucidation the steady-state flow characteristics, and a rotating grating type LDV was developed to measure the mean velocity and tunbulence intensity in relation to the crank angle. These methodologies were applied to clarify the correlation between gas flow characteristics and combustion stability at a lean air fuel ratio. An analysis of the correlation revealed the gas flow conditions required to optimize a lean-burn system.