• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.55-63
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• 2012

The turbulent flow characteristics in a coaxial injector were investigated by the nonlinear $k-{\varepsilon}-f_{\mu}$ model of Park et al.[1] and large eddy simulation (LES). In order to analyze the geometric effects on the scalar mixing for nonreacting variable-density flows, several recessed lengths and momentum flux ratios are selected at a constant Reynolds number. The nonlinear $k-{\varepsilon}-f_{\mu}$�� model proposed the meaningful characteristics for various momentum flux ratios and recess lengths. The LES results showed the changes of small-scale structures by the recess. When the inner jet was recessed, the development of turbulent kinetic energy became faster than that of non-recessed case. Also, the mixing characteristics were mainly influenced by the variation of shear rates, but the local mixing was changed by the adoption of recess.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.1
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• pp.10-19
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• 1993

As a method to measure the absorbing characteristics of microwave absorber, the various microwave measuring method can be used fundamentally. There is, however, a big problem in measuring errors, since the wavelength of microwave such as used for radar is very short. Therefore, this research aimed to design and fabricate a converting adaptor of 20mm .PHI. coaxial tube from a Type - N connector to $20mm\phi$ coaxial tube and to use it for evaluating absorption characteristics of microwave absorber. Furthermore, the measurements of absorbing characteristics and material constants have been performed and reviewed, which were carried out by using the coaxial tube and by using rectangular waveguide, res- pectively. As a result, the validity of the proposed measuring method has been confirmed.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.3
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• pp.9-17
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• 2006

The influences of recess length of a liquid/liquid swirl coaxial injector on spray characteristics were investigated. It was revealed that the internal impinging phenomenon played an important role in the spray characteristics, such as spray angle and breakup length. Also, as the recess length increased, the mean drop size increased due to the increase of effective film thickness and mixing efficiency increased, but in the case of very deep recess length, the mixing efficiency decreased.

• Smart Structures and Systems
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• v.1 no.4
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• pp.385-404
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• 2005

The paper presents a model to calculate reinforcement strain using measured crack width in members under applied tension, flexure, and/or shear stress. Crack mapping using a new type of distributed coaxial cable sensors for health monitoring of large-scale civil engineering infrastructure was recently proposed and developed by the authors. This paper shows the results and performance of such sensors mounted on near surface of two flexural beams and a large scale reinforced concrete box girder that was subjected to cyclic combined shear and torsion. The main objectives of this health monitoring study was to correlate the sensor's response to strain in the member, and show that magnitude of the signal's reflection coefficient is related to increases in applied load, repeated cycles, cracking, and reinforcement yielding. The effect of multiple adjacent cracks, and signal loss was also investigated. The results shown in this paper are an important step in using the sensors for crack mapping and determining reinforcement strain for in-situ structures.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.2
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• pp.93-99
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• 2016

In this paper, higher order coupler using small size waveguide which applicable for mobile Ku-band multimode monopulse satellite tracking antenna system, has been designed, implemented and tested. Proposed higher order mode coupler adopts a coaxial structure for low profile characteristic considering installation property to mobile satellite terminal system. In addition, by using proposed coupler, extracted tracking error signal pattern has measured and confirmed that required tracking accuracy is satisfied in desired frequency band. In the future, proposed coupler could utilize for multimode monopulse satellite tracking system for high tracking accuracy.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.577-580
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• 2010

Coaxial injectors using GCH4/LOx as propellants was designed with shear(gas)/shear(liquid) type and shear(gas)/swirl(liquid) type. Spray characteristics were investigated by cold flow test. Spray patterns of the shear/shear and the shear/swirl type injectors were like a spout of water and hollow cone, respectively. Atomization efficiency of the shear/swirl type injector was better than atomization efficiency of the shear/shear type injector.

• Journal of Magnetics
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• v.20 no.2
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• pp.186-192
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• 2015

This paper describes the electromagnetic and mechanical characteristics of coaxial magnetic gear (CMG) with a low gear ratio. The analysis models are restricted to a CMG with a gear ratio of less than 2. The electromagnetic characteristics including transmitted torque and iron losses are presented according to the variation of the gear ratio. The pole pairs of high speed rotor are chosen as 6, 8 and 10 by considering the torque capability. As the gear ratio approaches 1, both iron losses on the ferromagnetic materials and eddy current losses on the rotor permanent magnets are increased. The radial and tangential forces on the modulating pieces are calculated using the Maxwell stress tensor. When the maximum force is exerted on the modulating pieces, the mechanical characteristics including stress and deformation are derived by structural analysis. In CMG models with a low gear ratio, the maximum radial force acting on modulating pieces is larger than that in CMG models with a high gear ratio, and the normal stress and normal deformation are increased in a CMG with a low gear ratio. Therefore, modulating pieces should be designed to withstand larger radial forces in CMG with a low gear ratio compared to CMG with a high gear ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.699-703
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• 2017

Numerical simulations of closed-type and open-type single injectors were conducted to investigate the flow characteristics of a swirl-coaxial injector used in a liquid rocket engine. Numerical analysis was conducted using a commercial program ANSYS FLUENT. The injectors has three models with different recess length. Numerical analysis was conducted to investigate the variation of the flow characteristics of the injector when the flow condition were changed. It was also compare and analyzed with experimental results. The results obtained from the numerical simulation show that the difference between the inlet pressure and the discharge coefficient is not significant.

• Journal of the Korean Solar Energy Society
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• v.24 no.3
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• pp.27-38
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• 2004

A numerical investigation has been carried out for a solar system, which consists of all glass solar vacuum tubes Water is heated as it flows through the coaxial fluid conduit inserted in each tube. The space between the exterior of the fluid conduit and the glass tube is filled with antifreeze solution. This is to facilitate heat transfer from the solar heated absorber surface to water and to prevent the functional problems due to freezing in frigid weather conditions. A one-dimensional steady state model is fully described which will be used to develop three-dimensional model using STAR-CD. These models could be used efficiently in designing all-glass solar collector tubes with different geometrical parameters other than those considered in the present analysis. Results show good agreement when compared with other experimental data demonstrating the reliability of the present model.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.7
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• pp.1385-1390
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• 2011

A coaxial-conical-radial transmission line conversion circuits have been investigated to realize a low loss high performance microwave power divider/combiner. In order to optimize the characteristics of the device, the power divider/combiner was designed separately with two parts-the inner part and the outer part. Utilizing the rectangular approximation of the outer part, we can design the low loss device which is not affected by the partition number N of the outer part. The small return loss which is lower than 20dB was obtained on the frequency range of 5.15GHz(7.45~12.60GHz). A conical connector was employed for smooth connection between the central coaxial line and the outer radial line. Making use of the $47^{\circ}$ and $90^{\circ}$ 2-stage conical connector, the return loss lower than 30dB was obtained on the operating frequency range of 5GHz. The total return loss of the designed divider/combiner was lower than 20dB on the frequency range of 5GHz for the partition number N=11, N=12 and N=16.