• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.46-55
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• 2005

For the sea-level performance test of rocket motor designed to operate in the upper atmosphere, ejectors with no induced secondary flow are generally used, which serves dual purposes of evacuating the test cell and performing as a supersonic exhaust diffuser (SED). The main concern of this research is to simulate starting transients in order to visualize evolution of internal shock structures in SED with different initial cell (vacuum chamber) pressures. RANS code with low Reynolds $k-\varepsilon$ turbulence model was employed for these computations. Numerical results were compared with the pressure measurements previously performed [Proceedings of 2004 Annual Conference, KIMST], and showed good agreements with pressure-time history of measured data. In the case of low vacuum chamber pressure, abrupt impingement of the under-expanded supersonic jet from the nozzle onto the diffuser wall was observed, whereas initial impingement point was located downstream and moved slowly upstream in the case of non-vacuum chamber pressure. In spite of initially dissimilar evolution of shock structures, iso-mach contour revealed that the steady shock structures had little difference except the location of flow separation and normal shock.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.313-316
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• 2011

This paper investigates CFD investigation on single phase supersonic nozzle flow and 2-phase subson ic flow prior to rocket nozzle supersonic 2-phase flow with water injection within the flame deflector. Numerical results of supersonic nozzle single phase flow showed no notable unrealistic behavior as it captures the usual shock cell structures. Three-dimensional 2-phase flow analysis has also been performed to verify whether the approach can grab the droplet behavior during cooling by water injection. It is expected these basic studies will enhance the cooling problem analysis of supersonic 2-phase rocket plume in the future.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.7
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• pp.1210-1218
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• 2001

In this paper, A X-band voltage-controlled hair-pin resonator oscillator(VCHRO) is able to a local oscillator or a signal source in transmitter/receiver of a microwave communication system for mobile radar, is designed and fabricated In order to apply mobile radar system is used the hair-pin resonator stronger on shock or vibration than the dielectric resonator, and also, in order to improvement the phase noise and output power is used a system of serial feedback format A hair-pin resonator was simulated by momentum method of HP ADS and then a oscillator circuit was designed that operates at 10.525 GHz by nonlinear method in harmonic balance simulation. The HRO generated output power of 6.93 dBm at 10.525 GHz, phase noise of -57.74 dBc at 100 kHz offset from carrier and the 2'nd harmonic was suppressed -23.90 dBc.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.664-669
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• 2001

The characteristics of dual coaxial jet which composed of inner supersonic nozzle of 26500 in constant expansion rate with 1.91 design Mach number and outer converging one with $40^{\circ}$ converging angle with the variation of outer nozzle stagnation pressures are experimentally investigated in this paper. In which the stagnation pressure for the inner supersonic nozzle is 750kPa thus, the inner jet leaving the nozzle is slightly underexpanded. The plenum pressures of outer nozzle are varied from 200 to 600kPa. Flow visualizations by shadowgraph method, impact pressure and centerline static pressure measurements of dual coaxial jet are presented. The results show that the presence of outer jet affects significantly the structures and pressure distributions of inner jet. And outer jet causes Mach disk which does not appear for the case of single jet stream. As the stagnation pressure of outer jet increases, impact pressure undulation is severe, but the average impact pressure keeps high far downstream.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.9 s.114
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• pp.937-948
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• 2006

In this study, a fluid/structure coupled analysis system for simulating complex flow-induced vibration (FIV) phenomenon of cascades has been developed. The flow is modeled using Euler and Wavier-Stokes equations with different turbulent models. The fluid domains are modeled using the unstructured grid system with dynamic deformations due to the motion of structural boundary. The Spalart-Allmaras (S-A) and the SST ${\kappa}-{\omega}$ turbulent models are used to predict the transonic turbulent flows. A fully implicit time marching scheme based on the Newmark direct integration method is used in order to solve the coupled governing equations for viscous flow-induced vibration phenomena. For the purpose of validation for the developed FIV analysis system, comparison results for computational analyses of steady and unsteady aerodynamics and flutter analyses are presented in the transonic flow region. In addition, flow-induced vibration analyses for the isolated cascade and multi-blades cascade models have been conducted to show the physical fluid-structure interaction effects in the time domain.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.648-654
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• 2011

The feed-water piping system constitutes a complex flow impedance network incorporating dynamic transfer characteristics which will amplify some pulsation frequencies. Understanding pressure pulsation waves for the feed-water recirculation piping system with cavitation problem of flow control valve is very important to prevent acoustic resonance. Feed water recirculation piping system is excited by potential sources of the shock pulse waves by cavitation of flow control valve. The pulsation becomes the source of structural vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation affects the reliability of the plant piping system. This paper discusses the piping vibration due to the effect of shock pulsation by the cavitation of the flow control valves for the recirculation piping of feed-water pump system in combined cycle power plants.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.107-115
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• 2003

Nondestructive testing was carried out in order to evaluate the structural integrity and construction quality of the slurry wall of the underground LNG storage tank. 9 test points were selected, and the wall thickness, rebar spacing, and compressive strength of the slurry wall were evaluated by stress wave impact-resonance method, GPR, sonic velocity, and rebound testing, respectively. As results, the wall thickness, rebar sparing and estimated compressive strength satisfy the design criteria.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.793-802
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• 2006

In this study, a fluid/structure coupled analysis system for simulating complex flow-induced vibration (FIV) phenomenon of cascades has been developed. The flow is modeled using Euler and Wavier-Stokes equations with different turbulent models. The fluid domains are modeled using the unstructured grid system with dynamic deformations due to the motion of structural boundary. The Spalart-Allmaras (S-A) and the SST ${\kappa}-{\omega}$ turbulent models are used to predict the transonic turbulent flows. A fully implicit time marching scheme based on the Newmark direct integration method is used in order to solve the coupled governing equations for viscous flow-induced vibration phenomena. For the purpose of validation for the developed FIV analysis system, comparison results for computational analyses of steady and unsteady aerodynamics and flutter analyses are presented in the transonic flow region. In addition, flow-induced vibration analyses for the isolated cascade and multi-blades cascade models have been conducted to show the physical fluid-structure interaction effects in the time domain.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.198-206
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• 2020

In this study, the dynamic structural behavior of pressure vessels due to pressure pulse initiated by implosion of neighbouring airbacked equipments including Unmanned Underwater Vehicles (UUV), sensor system, and so on were dealt with for the structural design and safety assessment of pressure hulls of submarine. The dynamic buckling and collapse responses of pressure vessel in deep sea were investigated considering the effects of initial hydrostatic pressure and fluid-structure interactions. The governing equations for circular cylindrical shells were formulated theoretically assuming a relatively simple displacement fields and the derived nonlinear simultaneous ordinary differential equations were analysed by developed numerical solution algorithm. Finally, the introduced safety assessment procedures for the dynamic buckling behaviors of pressure hulls due to implosion pressure pulse were validated by comparing the theoretical analysis results with those of experiments for examples of simple cylinders.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.10
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• pp.947-954
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• 2009

Starting from the Eu's GH(Generalized Hydrodynamic) theory, the multi-species GH numerical solver is developed in this research and its computatyional behaviors are examined for the hypersonic rarefied flow over an axisymmetric body. To improve the accuracy of the developed multi-species GH solver, various slip-wall boundary conditions are tested and the computed results are compared. Additionally, in order to validate the entropy characteristics of the GH equation, the entropy production and entropy generation rates of the GH equation are investigated in the 1-dimensional normal shock structure test at a high Knudsen number.