• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.315-319
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• 2009

Investigation of the lateral force fluctuations in an axisymmetric overexpanded compressed truncated perfect (CTP) nozzle for the shutdown transient is presented. These nozzles experience side-loads during start-up and shut-down operations, because of the flow separation at nozzle walls. Two types of flow separations such as free shock separation (FSS) and restricted shock separation (RSS) shock structure occur. A two-dimensional unsteady numerical simulation has been carried out over an axisymmetric CTP nozzle to simulate the lateral force fluctuations in nozzle during shutdown process. Reynolds Averaged Navier-Stokes equations are numerically solved using a fully implicit finite volume scheme. Governing equations are solved by coupled implicit scheme. Two equation k-$\omega$ SST turbulence model is selected. Unsteady pressure is measured at four locations along the nozzle wall. Present pressure variation compared well with the experimental data. During shutdown transient, separation pattern varies from FSS to RSS and finally returns to FSS. Several pressure peaks are observed during the RSS separation pattern. These pressure peaks generate lateral force or side loads in rocket nozzle.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.47-52
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• 2002

The supersonic flow around multi-stage rocket system is analyzed using 3-D compressible unsteady flow solver. A Chimera overset grid technique is used for the calculation of present configuration and grid around the core rocket is composed of 3 zones to represent fins in the core rocket. Flow solver is parallelized to reduce the computation time, and an efficient parallelization algorithm for Chimera grid technique is proposed. AUSMPW+ scheme is used for the spatial discretization and LU-SGS for the time integration. The flow field around multi-stage rocket was analyzed using this developed solver, and the results were compared with that of a sequential solver The speed-up ratio and the efficiency were measured in several processors. As a result, the computing speed with 12 processors was about 10 times faster than that of a sequential solver. Developed flow solver is used to predict the trajectory of booster in separation stage. From the analyses, booster collides against core rocket in free separation case. So, additional jettisoning forces and moments needed for a safe separation are examined.

• Journal of computational fluids engineering
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• v.13 no.4
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• pp.80-85
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• 2008

The prediction of the separation trajectories of external stores released from a military aircraft is an important task in the aircraft design area having the objective to define the operational and release envelopes. This paper presents the results obtained for store separation by employing commercial softwares, FLUENT and CFD-FASTRAN. FLUENT treats the rigid body motion by employing a remeshing scheme. CFD-FASTRAN uses Chimera(overset) grid and interpolations. It was found that, for the prediction of the trajectories and behavior of the stores separated from the wing, both codes show the good agreement with the experimental results.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.374-377
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• 2008

The prediction of the separation trajectories of the external stores released from a military aircraft is an important task in the aircraft design area having the objective to define the operational and release envelopes. This paper presents the results obtained for store separation by employing commercial sorftwares, FLUENT and CFD-FASTRAN. FLUENT treats the rigid body motion by employing the remeshing scheme. CFD-FASTRAN uses the chimera(overset) grid and interpolations. It was found that, for the prediction of the trajectories and behavior of the stores separated from the wing, both codes shows the good agreement with the experimental results.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.374-377
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• 2008

The prediction of the separation trajectories of the external stores released from a military aircraft is an important task in the aircraft design area having the objective to define the operational and release envelopes. This paper presents the results obtained for store separation by employing commercial sorftwares, FLUENT and CFD-FASTRAN. FLUENT treats the rigid body motion by employing the remeshing scheme. CFD-FASTRAN uses the chimera(overset) grid and interpolations. It was found that, for the prediction of the trajectories and behavior of the stores separated from the wing, both codes shows the good agreement with the experimental results.

• ETRI Journal
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• v.37 no.4
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• pp.780-786
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• 2015

This paper describes an audio source separation that is based on nonnegative matrix factorization (NMF) and expectation maximization (EM). For stable and highperformance separation, an effective auxiliary source separation that extracts source residuals and reprojects them onto proper sources is proposed by taking into account an ambiguous region among sources and a source's refinement. Specifically, an additional NMF (model) is designed for the ambiguous region - whose elements are not easily represented by any existing or predefined NMFs of the sources. The residual signal can be extracted by inserting the aforementioned model into the NMF-EM-based audio separation. Then, it is refined by the weighted parameters of the separation and reprojected onto the separated sources. Experimental results demonstrate that the proposed scheme (outlined above) is more stable and outperforms existing algorithms by, on average, 4.4 dB in terms of the source distortion ratio.

• Journal of the Korean Data and Information Science Society
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• v.13 no.2
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• pp.129-138
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• 2002

This paper deals with logistic regression models for analysing separation rates from majors. The model building procedure shows how to incoporate the effects of some factors causing from three-way nested sampling scheme and discusses what type of characteristics as independent variables directly affecting the rates should be considered.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.474-477
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• 2005

In tactical theater, it is crucial to detect ground moving targets and to locate them precisely. This problem can be resolved by using SAR (Synthetic Aperture Radar) sensors providing GMTI (Ground Moving Target Indication) capability. In general, to implement a robust GMTI sensor is not simple because of the strong competitions between target signals and clutter signals on the ground, and low speed of moving targets. Contrary to the case that a delay canceller is mostly suitable for ground surveillance radars, DPCA (Displaced Phase Centered Antenna) or STAP (Space Time Adaptive Processing) techniques have been adapted for GMT! function of modem airborne radars. In this paper, anew scheme of DPCA using two passive antennas with vertical separation is proposed, which also provides good clutter cancellation performance. The proposed scheme enables us to scan straight ahead of the carrying platform that is impossible with typical DPCA configuration. Simulations using various conditions have been performed to validate the proposed scheme, and the results are acceptable.

• Korean Journal of Remote Sensing
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• v.22 no.3
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• pp.229-234
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• 2006

In tactical theater, it is crucial to detect ground moving targets and to locate them precisely. This problem can be resolved by using SAR (Synthetic Aperture Radar) sensors providing GMTI (Ground Moving Target Indication) capability. In general, to implement a robust GMTI sensor is not simple because of the strong competitions between target signals and clutter signals from the ground, and low speed of moving targets. Contrary to the case that a delay canceller is mostly suitable for ground surveillance radars, DPCA (Displaced Phase Centered Antenna) or STAP (Space Time Adaptive Processing) techniques have been widely adapted for GMTI function of modern airborne radars. In this paper, a new scheme of DPCA using two passive antennas with vertical separation is proposed, which also provides good clutter cancellation performance. The proposed scheme realizes full azimuth coverage for DPCA operation on an airborne platform, which is impossible with classical DPCA configuration. Simulations using various conditions have been performed to validate the proposed scheme, and the results are acceptable.

• Journal of Power Electronics
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• v.16 no.2
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• pp.480-489
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• 2016

A novel hybrid carrier-based pulse width modulation (CBPWM) scheme that combines unipolar and dipolar modulations is proposed for single-phase three-level rectifiers, which are widely applied in railway traction drive systems. The proposed CBPWM method can satisfy the volt-second balancing principle in the complete modulation index region through overmodulation compensation. The modulation scheme features two modulation modes: unipolar and dipolar. The operation range limits of these modulation modes can be modified by changing the separation coefficient. In comparison with the traditional unipolar CBPWM, the proposed hybrid CBPWM scheme can provide advantageous features, such as lower high-order harmonic distortion of the line current and better utilization of switching frequency. The separation coefficient value is optimized to achieve the maximum utilization of these advantages. The experimental results verify the feasibility and effectiveness of the proposed hybrid CBPWM scheme.