• 유체기계공업학회:학술대회논문집
• /
• 2003.12a
• /
• pp.639-645
• /
• 2003

Design optimization of a transonic compressor rotor (NASA rotor 37) using response surface method and three-dimensional Navier-Stokes analysis has been carried out in this work. Baldwin-Lomax turbulence model was used in the flow analysis. Two design variables were selected to optimize the stacking line of the blade, and mass flow was used as a design variable, as well, to obtain new design point at peak efficiency. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, adiabatic efficiency was successfully improved, and new design mass flow that is appropriate to an improved blade was obtained. Also, it is found that the design process provides reliable design of a turbomachinery blade with reasonable computing time.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.03a
• /
• pp.1409-1416
• /
• 2010

It is essential to predict a blasting-induced excavation damage zone (EDZ) beyond the proposed excavation line of a tunnel because the unwanted damage area requires extra support system for tunnel safety. Complicated blasting process which may hinder a proper characterization of the damage zone can be effectively represented by two loading mechanisms. The one is a dynamic impulsive load generating stress waves outwards immediately after detonation. The other is a gas pressure that remains for a relatively long time. Since the gas pressure reopens up the arrested cracks and continues to extend some cracks, it contributes to the final formation of EDZ induced by blasting. This paper presents the simple method to evaluate EDZ induced by gas pressure during blasting in rock. The EDZ is characterized by analyzing crack propagation from the blasthole. To do this, a model of the blasthole with a number of radial cracks of equal length in an infinite elastic plane is considered. In this model, the crack propagation is simulated by using three conditions, the crack propagation criterion, the mass conservation of the gas, and the adiabatic condition. As a result, the stress intensity factor of the crack generally decreases as crack propagates from the blasthole so that the length of the crack is determined. In addition, the effect of rock properties, initial number of cracks, and the adiabatic exponent are investigated.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.2
• /
• pp.155-162
• /
• 2003

Design optimization of a transonic compressor rotor (NASA rotor 37) using response surface method and three-dimensional Navier-Stokes analysis has been carried out in this work. Baldwin-Lomax turbulence model was used in the flow analysis. Three design variables were selected to optimize the stacking line of the blade. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, adiabatic efficiency was successfully improved. It is also found that the design process provides reliable design of a turbomachinery blade with reasonable computing time.

• 유체기계공업학회:학술대회논문집
• /
• 2001.11a
• /
• pp.135-142
• /
• 2001

Design optimization of a transonic compressor rotor (NASA rotor 37) using response surface method and three-dimensional Navier-Stokes analysis has been carried out in this work. Baldwin-Lomax turbulence model was used in the flow analysis. Three design variables were selected to optimize the stacking line of the blade. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, adiabatic efficiency was successfully improved. Ana, it is found that the design process provides reliable design of a turbomachinery blade with reasonable computing time.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.1
• /
• pp.72.2-72.2
• /
• 2010

We use three-dimensional hydrodynamic simulations to investigate nonlinear gravitational responses of gas to, and the resulting drag force on, a massive perturber moving on a circular orbit through a uniform gaseous medium. We assume that the background medium is non-rotating and adiabatic with index 5/3, and represent the perturber using a Plummer potential with softening radius a. This work extends our previous study where we showed that the drag force on a straight-line trajectory is proportional to a0.45 if the perturber is massive enough. This indicates that the orbital decay of supermassive black holes (SMBHs) near galaxy centers may take much longer than the prediction of the linear force formula applicable for low-mass perturbers. For the circular orbits are considered, however, we find that the nonlinear drag force becomes independent of a, but dependent instead on the orbital radius R as $\varpropto$ R0.5. This suggests not only that the choices of large values of a, for resolution issues, in recent numerical experiments for mergers of SMBH, are marginally acceptable, but also that the gaseous drag indeed provides an efficient mean for the orbtial decay of SMBHs.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.21 no.2
• /
• pp.1-6
• /
• 2013

In high-speed vehicle, selection of fuel, configuration of components and cooling system are required to solve the heating issue by aerodynamic heating and inner combustion process. This subsystem consists of fuel tank, supply pump, various control valve, heat exchanger, including reactor, connecting line, adiabatic structures and insulations. In this paper, applicable fuel property is considered at flight characteristic of hypersonic vehicles. In this regard, current state of fuel/cooling system technology is identified.

• Korean Journal of Optics and Photonics
• /
• v.3 no.4
• /
• pp.266-272
• /
• 1992

A coherent anti-Stokes Raman spectroscopy (CARS) technique is applied to measure temperature profile in a flame. The CARS signal is obtained with BOXCARS phase matching to get better spatial resolution. A program routine for calculating temperature of the flame from the measured CARS spectra is studied. The routine includes the line broadening mechnism of the molecules described with a modified energy gap (MEG) law by using the perturbation theory. We have found that the temperature profile obtained with the MEG law is properly fit with the results measured with a thermocoulpe and calculated with the adiabatic theory.

• Journal of Korean Society for Atmospheric Environment
• /
• v.22 no.3
• /
• pp.271-285
• /
• 2006

A two-dimensional photochemical transport model (2D PTM) is simulated to describe the transport and chemical reaction of ozone related to aerosols in the troposphere and stratosphere. The vertical profiles and total amounts of ozone, which are advected by both residual Eulerian circulation and the adiabatic circulation under certain circumstance, have been compared with the observation data such as ozonesondes, Brewer spectrometer, the Upper Atmosphere Research Satellite (UARS), and the Total Ozone Mapping Spectrophotometer (TOMS). As a result, we find that the observed distribution of ozone Is adequately reproduced in the model at middle and high latitude in the Northern Hemisphere as well as at Phang ($36^{\circ}\;02'N,\;129^{\circ}\;23'E$) in South Korea. In particular, the 2D PTM is well simulated in the ozone decrease due to the Pinatubo volcanic eruption in 1991. However, ozone mixing ratio are more underestimated than those of UARS and ozonesondes, because are very sensitive to the latitude of transport across the tropopause associated with both Rummukainen errors and off-line model. Relative mean bias errors and relative root mean square errors of ozone calculations using the 2D PTM are shown within${\pm}10%$, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.9
• /
• pp.989-996
• /
• 2009

RF and microwave power is a basic quantity in electromagnetic metrology which linked directly to major electro-magnetic quantities such as attenuation, RF voltage, antenna characteristics and field strength. This paper deals with a power meter and power sensor with associated theory for RF and microwave power measurement. We study the theory and the key aspects in design of a 3.5 mm coaxial microcalorimeter which works from 50 MHz to 26.5 GHz as a primary microwave power standard.

• Journal of Astronomy and Space Sciences
• /
• v.19 no.3
• /
• pp.207-214
• /
• 2002

One of the way to derive design parameters of the fuel feeding system in satellite propulsion system is to analyze unsteady flow of liquid propellant (hydrazine). During steady thruster firing the flow rate is constant: if a thruster valve is abruptly shut down among a set of thrusters, pressure spikes much higher than the initial tank pressure occur. This renders the fuel flow unsteady, and the fluid pressure and flow rate to oscillate. If the pressure spikes are high enough, there are possibilities that propellant explosively decomposes, thruster valves we damaged, and adiabatic detonation of the hydrazine propellant is potentially incurred. Reflected shockwaves could also affect the calibration and operation of the pressure transducers. These necessitate the analysis of unsteady flow in the propulsion system design, and pressure behavior inside the propellant line obtained through some governing parameter variation is presented in this work.