• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.167-169
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• 2003

This paper presents a theoretical study concerning multibubble dynamics in a sound field and the numerical validation for it by employing our new CFD code MTS-DiCUP. In recent papers, the author has shown theoretically that an unknown characteristic frequency, named 'transition frequency,' exists in a multibubble system. For a N -bubble case, up to 2N -1 transition frequencies per bubble have been predicted, only N ones of them correspond to the natural frequencies of the system. The transition frequencies that do not correspond to the natural frequencies give rise to the phase reversal of bubbles' pulsation without resonant response. In this paper, it has been suggested theoretically that those transition frequencies may cause the sign reversal of the secondary Bjerknes force, which is an interaction force acting between acoustically coupled gas bubbles. This theoretical result has been validated by the direct numerical simulation, at least in a qualitative sense.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.157-161
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• 2007

The prediction of the safe separation of the external stores carried on military aircraft is an important task in the aerodynamic design area having the objective to define the operational, release envelopes. The major concern of this study is only safe jettison problem with ejections. This work consists of concept and some results for external store configurations. A Computational Fluid Dynamics technique is applied to calculate the aerodynamic forces. The FLUENT with an implicit Euler solver is used for the present simulations. The computational results are validated against the experimental data.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.137-139
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• 2004

The monopropellant hydrazine thrusters are widely used for the satellite on-board propulsion system fulfilling various missions in space. They have outstanding features caused by the nearly unlimited restart capability and the very high credibility. The sole monopropellant thruster used at precent in nation is MRE-1 that is a standard component of NASA. It can produce 4.45 N of nominal thrust. Due to the glowing complexity with a satellite mission, the needs for thrusters of the diverse performance are being increased. The numerical simulation could give useful information to develop a new type thruster instead of the experiments performed previously. Therefore it is critical to make a reliable computer code to prepare design change of a thruster. In this paper, the performance analysis and validation of the satellite monopropellant hydrazine thruster currently used is accomplished as the preliminary study to serve valuable data for future design change.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.215-220
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• 2004

A mathematical formulation based on two-phase, two-fluid hyperbolic conservation laws is developed to investigate propagation of shock waves in one- and two-dimensions. We used a high resolution upwind scheme called the split-coefficient matrix method. Two extreme cases are computed for validation of the computer code: the states of a pure gas and a pure liquid. Computed results agreed well with the previous experimental and numerical results. It is studied how the shock wave propagation pattern is affected by the void fraction in the two-phase flow. The shock structure in a two-phase flow turned out, in fact, much deviated from the shape well known in the gas only phase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.4
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• pp.695-702
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• 2001

In this paper, the drop/impact simulation for a mobile phone has been carried out with the explicit code LS-DYNA and its validation has been experimentally verified. The small size of this kind of electronics products makes it time-consuming, and difficult to conduct drop tests to detect the failure mechanism and identify their drop behaviors. Strict drop/impact performance criteria of such hand held electronic products as mobile phones play an important role in their design because these products must withstand both normal and unexpected shock. Usually, the product durability on drop impact depends on designers experience. The present reliable methodology of drop/impact simulation provides an efficient and powerful vehicle to improve the design quality and reduce the design period.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.512-519
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• 2009

Flow pulsation in the gap connecting with two parallel channels is investigated by RANS and URANS approaches. The two parallel channels are connected by a small channel called for a gap. The parallel channels are designed to have different cross section area with its ratio of 0.5. Computations are conducted using a CFX 11.0 code. The bulk Reynolds number is 60,000. Predicted results are compared with the previous experimental data. Mean velocity profile at the center of gap region are compared with experiments for its validation. Spectral analysis on the lateral velocity in the center of the gap was performed. Auto correlation for the axial-flow velocity pattern was presented. The unsteady structure of the flow pulsation was visualized in the region of the gap in the parallel channel.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.423-428
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• 1995

Simulation models have been developed to predict the overall behavior of the CANDU plant systems during normal operational transients. For real time simulation purpose, simplified thermal hydraulic models are applied with appropriate system control logics, which include primary heat transport system solver with its component models and secondary side system models. The secondary side models are mainly used to provide boundary conditions for primary system calculation and to accomodate plant power control logics. Also, for the effective use of simulation package, hardware oriented basic simulation network has been established with appropriate graphic display system. Through validation with typical plant power maneuvering cases using proven plant performance analysis computer code, the present simulation package shows reasonable capability in the prediction of the dynamic behavior of plant variables during operational transients of CANDU plant, which means that this simulation tool can be utilized as a basic framework for full scope simulation network through further improvements.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.84-90
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• 2000

Integrated tools are developed for the analysis of the aerodynamic performance and aeroacoustics of helicopter rotors. Heli-NK(Helicopter Navier-Stokes & Kirchhoff) code is for hovering and heli-PA(Helicopter Panel & Acoustic analogy) for forward flight. The former showed its ability to predict the hovering efficiency and high-speed impulsive noise level. Thrust calculation, noise levels, and noise directivity patterns are investigated to confirm the availability of the latter. With some proper validation and improvements. these codes will be more useful and practical.

• Journal of the Korean Society of Visualization
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• v.10 no.3
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• pp.42-47
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• 2012

Experimental data for the flows in a mixing tank with a bottom agitator are useful for the validation of CFD commercial code. A hybrid volume PIV measurement technique was constructed to measure the flows inside of the mixing tank. The measurement system consists of three cameras. An agitator was installed at the bottom of the tank and it rotates clockwise and counterclockwise. Using the constructed measurement system, instantaneous vector fields were obtained. A phase averaging technique was adopted for the measured instantaneous three-dimensional velocity vector fields. Turbulent properties were evaluated from the instantaneous vector fields.

• Steel and Composite Structures
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• v.8 no.1
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• pp.35-52
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• 2008

The paper investigates the seismic performance of a Partially-Restrained (PR) steel-concrete composite frame using the probabilistic approach. The analysed frame was tested at the ELSA laboratory of the Joint Research Centre of Ispra (Italy), while the representative beam-to-column composite connections were tested at the Universities of Pisa, Milan and Trento (Italy). The component modelling of both interior and exterior composite joints is described first, including the experimental-numerical validation. The Latin Hypercube method has been used to draw the probabilistic distribution curves of joints, and then the whole PR composite frame has been analysed. Pushover and incremental dynamic analyses have been carried out using the non-linear FE code SAP2000 version 9.1. The fragility and performance curves of the PR composite frame have been determined for four damage limit states.