• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.195-203
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• 2003

Spray and Mixing characteristics of the unlike impinging triplet injectors (F-O-F, O-F-O) were investigated with the variation of the momentum ratio of oxidizer to fuel. The spray pattern was measured using a backlit stroboscopic photography technique, and mixing efficiency was measured using a mechanical patternator. Kerosene/water were used as a propellant simulant. From the experimental results, it is found that a O-F-O type injector has a good atomization. And as the momentum ratio increases, the mixing efficiency decreases rapidly.

• Journal of ILASS-Korea
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• v.20 no.3
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• pp.168-174
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• 2015

Combustion instability is critical problem in developing liquid rocket engine. There have been many efforts to solve this problem. In this study, the method was sought through the injector as part of these efforts to suppress combustion instability. If the injector can suppress the disturbance coming from the supply line as a kind of buffer it will serve to reduce combustion instability. Especially we target at gas propellant oscillation in gas-centered swirl coaxial injector. The phenomenon is simulated with acoustic excitation of speaker. The film thickness response at injector exit was measured by using a liquid film electrode. Also the response of spray to the disturbance was observed by high-speed photography. Gas-liquid momentum flux ratio and the frequency of feeding gas oscillation were changed to investigate the effect of these experimental parameters. The trend of response by varying these parameters and the cause of weak points was studied to suggest the better design of injector for suppressing combustion instability.

• Journal of ILASS-Korea
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• v.13 no.2
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• pp.79-84
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• 2008

The correlations for cross-flow have not been well established, because of the complexity of breakup and atomization mechanism. A study was performed to investigate the characteristics of spray behaviour of liquid jet in the bag breakup regime injected into low-speed cross-flow with the pressure single-hole nozzle. The shadow-graphy method was used for the cross-flow jet visualization. The experimental variables of liquid jet were nozzle diameter $(0.3mm{\sim}1.0mm)$, injection pressure $(50kPa{\sim}150kPa)$, and the velocity of cross-flow $(27m/s{\sim}42m/s)$. The highest penetration trajectories of liquid jet are governed by the momentum ratio $({\rho}_{\iota}U_{\iota}^2/{\rho}_aU_{cross}^2)$ rather than the Weber number and the new empirical equations of the highest penetration trajectory and breakup point at low-speed corss-flow are established.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.438-444
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• 2010

The spray characteristics of jet in crossflow (JICF) to improve the atomization and mixing characteristics of liquid Jet, while minimizing the impact on crossflow, were studied experimentally. By varying the temperature, velocity, pressure of crossflow and the speed, pressure of liquid Jet, the spray boundary (outer boundary, inner boundary) with the change of crossflow and liquid jet momentum ratio (q) were measured and led the experimental formula, compared with the results of previous work. Specifically, when the jet penetration with the shape of injector were measured, in the case of dual orifice Injector, under the influence of front orifice, the jet penetration of back orifice was improved approximately 18% ($L_h$ = 4 mm), compared with single orifice injector.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.2
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• pp.15-22
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• 2003

Computational study using the 2-dimensional, compressible, Navier-Stokes equations is performed to predict the discharge coefficient of air flow through a film-cooling hole. In order to investigate the effect of internal/external flows on discharge coefficient, the present computational results which are obtained for three flow cases, only external flow, only internal flow, and no flow, are compared with experimental ones. It is found that the computational results predict the discharge coefficient of the film-cooling hole in a reasonable accuracy and the external crossflow reduces the discharge coefficient, while the internal crossflow increases the discharge coefficient in a range of momentum flux ratio $I_{c-jet}$ > 1 due to the total pressure loss and boundary layer effect.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.57-60
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• 2011

The spray characteristics according to the recess length of the GCSC injector and the change of momentum flux ratio(MFR) of the gas and the liquid have been examined through high pressure cold flow test using a high pressure chamber. The liquid in this experiment was water, and the gas was nitrogen. The spray images were taken by a back-lit strobe imaging technique. Results showed that the spray was a wide hollow cone at the lower MFR(liquid velocity was fixed) and the spray became a narrow solid cone as the MFR was increased. And the injector with short recess length produced a narrow solid cone at the higher MFR.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.16-19
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• 2011

An experimental study on the spray characteristics of Gas-centered swirl coaxial injectors(GCSCI) for high-performance staged combustion rocket engines has been carried out using cold flow tests. In this study, water and gaseous nitrogen are used as working fluids and a back-lit photography technique with image processing for the measurements of spray characteristics. Our study is focused on the effect of injector geometries like as gap thickness of liquid nozzle and gas nozzle and momentum flux ratio for fundamental understanding of the injectors.

• Smart Structures and Systems
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• v.31 no.5
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• pp.455-467
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• 2023

Impact damper is a passive damping system that controls undesirable vibration with mass block impacting with stops fixed to the excited structure, introducing momentum exchange and energy dissipation. However, harmful momentum exchange may occur in the random excitation increasing structural response. Based on the mechanism of impact damping system, a semi-active impact damper (SAID) with controllable impact timing as well as a semi-active control strategy is proposed to enhance the seismic performance of engineering structures in this paper. Comparative experimental studies were conducted to investigate the damping performances of the passive impact damper and SAID. The extreme working conditions for SAID were also discussed and approaches to enhance the damping effect under high-intensity excitations were proposed. A numerical simulation model of SAID attached to a frame structure was established to further explore the damping mechanism. The experimental and numerical results show that the SAID has better control effect than the traditional passive impact damper and can effectively broaden the damping frequency band. The parametric studies illustrate the mass ratio and impact damping ratio of SAID can significantly influence the vibration control effect by affecting the impact force.

• Korean Journal of Applied Biomechanics
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• v.17 no.4
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• pp.27-36
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• 2007

The purpose of this study was to investigate the effect of the upper body in order to increase a propulsive force in the old's walking. The subjects were each 10 males, the latter term of the aged and former term of the aged. There were three walking speeds of slow(about 5km/h), medium(about 6km/h), and maximum speed(about 7km/h). The subjects walking 11m were filmed the 5m section (from 3m to 8m) by 2-video cameras using three dimensional cinematography. And we computed different mechanical quantities and especially computed the relative momentum in order to achieve this study's aim. In this study, we was able to acquire some knowledge. The step length and step frequency increased in proportion to the walking speed, and the faster walking speed, the shorter ratio of supporting time( both legs supporting time/one step length time). When it was one leg support phase, the torso was indicated to generate the momentum in order to produce the propulsive force of walking. The upper and lower body had a cooperative relation for walking such as keeping step rate with the arms to legs and maintaining the body balance. The opposition phase for upward-and-downward direction of the torso and arms in walking was functioned to prevent the increase rapidly toward vertical direction of the center of gravity. The arms had contributed to coordinate the tempo of legs and the posture maintenance of the upper body. And by absorbing the relative momentum from the upper torso with arms to the lower torso, it had the rhythmical movement on upward-and-downward direction reducing the vertical reaction force. On account of the relations of absorption and generation of the propulsive force and the production of vertical impulse in the lower torso when walking by maximum speed, it was showed that the function of lower torso was come up as important problem for the mechanical posture stability and propulsive force coordination.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.1
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• pp.1-12
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• 1996

The fully developed tubulent momentum and heat transfer induced by the square- ribbed roughness elements on both the inner and outer wall surfaces in the concentric annuli are studied analytically based on a modified turbulence model. Heat transfer coefficients for two conditions, i.e, a) inner wall heated as constant heat flux and outer wall insulated b) inner wall insulated and outer wall heated as constant heat flux, are investigated. The analytical results of the fluid flow are verified by experiment. The experiment is done with a pitot tube and a X-type hot wire anemometer to measure the time mean velocity profiles, zero shear stress positions, maximum velocity profiles and friction factors, and etc. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, Nusselt number and Prandtl number.