• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.573-577
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• 2009

Dynamic behavior simulation of supersonic engine was performed and PI control algorithm was studied for the buzz control in the inlet and the thrust control. Firstly, required thrust was tracked according to the fuel flow control and then inlet pressure was regulated through the nozzle throat area control so that the buzz margin has the positive all the time. The control was performed according to the change of flight Mach number, altitude and angle of attack. The proportional gain and the integral gain for regulating the buzz margin was induced and simulated. In the results, it was confirmed and satisfied that control target in the operating area was changed the angle of attack from $0^{\circ}$ to $10^{\circ}$ at the flight Mach number of 2.1~3.0.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.4
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• pp.13-21
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• 2011

Seismic structure pounding between adjacent superstructures may induce the destruction of pier and bridge superstructures and cause local damage that leads to the collapse of the whole bridge system. The pounding problem is related to the expansion of joints, gap distance and seismic response of the abutments. In this research, methods of the contact element approach, the linear spring model, the Kelvin-Voigt model and the Hertz model were studied to analyse the pounding characteristics. The shaking table test for a model specimen such as a bridge superstructure with elastomeric bearings was performed to evaluate the contact element approach methods. Relationships between the time history response from the numerical analysis results and the measured response from the shaking table test are compared. The experimental results were not well matched with the numerical analysis results using the existing pounding stiffness models. Therefore, in this study, coefficients are proposed to calculate the appropriate pounding stiffness ratio.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.5-13
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• 2016

In this study, Coupled Eulerian-Lagrangian (CEL) analysis, which is one of the large deformation analyses, was incorporated to investigate excavation damage zone (EDZ) under TBM advancement. Considering the quasi-static condition, the dynamic analysis was performed to simulate the real TBM advancement and subsequently a case study on mesh and TBM excavation rate was carried out for satisfying a balance of accuracy and economic computational time. Based on this, a series of parametric studies were performed for different rock types and tunnel diameters. From the numerical analysis results, it is found that EDZ was taken to range within 0.4D(D=tunnel diameter) for most rocks. It is also found that the EDZ tends to increase as the tunnel diameter increases.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.5
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• pp.390-396
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• 2007

In the present study, we have developed a flapping wing using a smart material to mimic the nature's flyers, birds. The wing consists of composite frames, a flexible PVC film and a surface actuator, and the main wing motions are flapping, twisting and camber motions. To change the camber, a Macro-Fiber Composite(MFC) is used as the surface actuator, and it's structural response is analyzed by the use of piezoelectric-thermal analogy. To measure the lift and thrust simultaneously, a test stand consisting of two load cells is manufactured. Some aerodynamic tests are performed for the wing in a subsonic wind tunnel to evaluate the dynamic characteristics. Experimental results show that the main lift is mostly affected by the forward velocity and the pitch angle, but the thrust is mostly affected by the flapping frequency. The effect of the camber generated by the MFC actuator can produce the sufficient lift increment of up to 24.4% in static condition and 20.8% in dynamic condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.2
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• pp.187-196
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• 2013

A numerical model was developed to predict the density wave oscillation (DWO) in the furnace wall tubes of a fossil-fired once-through boiler. The transient flow fields in the tubes were obtained using a 1D finite volume method in the time domain. A header model was also implemented to simulate the parallel tube connection of the wall tubes. The inlet and outlet mass flow variation in one of the parallel tubes was examined after a heat perturbation to find the DWO. After successful verification with experimental results reported in literature, the developed model was applied to the wall tubes of a 700-MW boiler furnace. In contrast to the simulation of Takitani's experiment, in which the unstable power thresholds tended to rise in the reduced bypass channel flow, no remarkable changes were observed in the power thresholds in the parallel channel modeling of the wall tubes of the boiler furnace.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.5
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• pp.437-445
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• 2016

Recently, polyurethane foam has been used in various industry fields to preserve temperature environment of structures, and a wide range of loads from the static to the dynamic are imposed on the material during a life period. The biggest characteristic of polyurethane foam is porosity as being polymeric material, and it is generally known that insulation performance of the material strongly depends on internal void size. In addition, polyurethane foam's mechanical behavior has high dependence on strain rate and temperature as well as being highly non-linear ductile for compression. In the non-linear compressive behavior, volume fraction of voids and elastic modulus decrease as strain increases. Therefore, in this study, temperature-dependent viscoplastic-damage constitutive model was developed to describe the non-linear compressive behavior with the aforementioned features of polyurethane foam.

• Journal of Korea Water Resources Association
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• v.34 no.5
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• pp.449-458
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• 2001

In order to verify the numerical model, which was developed to simulate the behavior of the two-phase fluid flow in a single fracture, the characteristic equation of relative permeability was incorporated into the developed numerical model, and the computed results were compared with the experimental results of the model test. As results of the sensitivity analysis on the roughness and the aperture size of fracture, the gas velocity was inversely proportional to the fracture roughness, and not proportional to the square of aperture size which is usually observed in single phase flow in a single fracture. The numerical model was applied to the underground LPG storage terminal in order to check the field applicability. The simultaneous flow of water and gas in accordance with the operation pressures in a single fracture near cavern was simulated by the model. It was shown that the leaked gas was able to be controlled in a single fracture neither by the pressure of operation nor by that of groundwater in case the fracture became smoother in roughness and smaller in aperture size.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.895-906
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• 2014

A fundamental study of the dynamically penetrating anchor (DPA - colloquially known as torpedo anchor) embedded into deep seabed was conducted using measurement data and numerical approaches. Numerical simulation of such a structure penetration was often suffered by severe mesh distortion arising from very large soil deformation, complex contact condition and nonlinear soil behavior. In recent years, a Coupled Eulerian-Lagrangian method (CEL) has been used to solve geomechanical boundary value problems involving large deformations. In this study, 3D finite element analyses using the CEL formulation are carried out to simulate the construction process of dynamic anchors. Through comparisons with results of field measurements, the CEL method in the present study is in good agreement with the general trend observed by in-situ measurements and thus, predicts a realistic large deformation movement for the dynamic anchors by free-fall dropping, which the conventional FE method cannot. Additionally, the appropriate parametric studies needed for verifying the characteristic of dynamic anchor are also discussed.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.48-52
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• 2003

A mathematical dynamic model of fuel cell was formulated in order to design the control system which will meet the control object. The control objective is set to regulate the airflow in the load change by utilization of airflow and the pressure difference between anode and cathode is maintained below a limit range. Simulation result of 10kW polymer electrolyte membrane fuel cell (PEMFC) clearly demonstrates that response time need to be less. than 1 seconds for the control requirements. Besides, pressure difference was allowed in pressure range less than 0.01 atm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.4
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• pp.385-391
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• 2014

A wheeled armored vehicle is a military vehicle that has been developed to enhance combat capabilities and mobility for the army. The wheeled armored vehicle has a high center of gravity, and it operates on unpaved and sloped roads. Therefore, this vehicle has a high risk of rollover crashes. To design the interior of the military vehicle, the crew's safety during rollover crashes is an important factor. However, actual vehicle tests for design are extremely expensive. In this paper, nonlinear dynamic analysis is performed to simulate the rollover crashes and the passenger injury is assessed for a wheeled armored vehicle. The scope of this research is the rollover condition, FE modeling of the wheeled armored vehicle and the dummy, arrangement of dummies, assessment of passenger injuries, and simulation model for rollover crashes.