• Journal of computational fluids engineering
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• v.3 no.1
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• pp.22-29
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• 1998

Parallel implementation is conducted for a SIMPLER finite volume model. The present parallelism is based on domain decomposition and explicit message passing using MPI and SHMEM. Two parallel solvers to tridiagonal matrix equation are employed. The implementation is verified on the Cray T3E system for a benchmark problem of natural convection in a sidewall-heated cavity. The test results illustrate good scalability of the present parallel models. Performance issues are elaborated in view of convergence as well as conventional parallel overheads and single processor performance. The effectiveness of a localized matrix solution algorithm is demonstrated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.1
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• pp.193-201
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• 1995

The role of thermal contact resistance between a casting and a metal mold as well as natural convection in the melt during solidification of a pure metal is numerically studied. Numerical simulation is performed for a rectangular cavity using the coordinate transformation by boundary-fitted coordinate and pure aluminum is used as the phase- change material. The influences of thermal contact resistance on the interface shape and position, solidified volume fraction, temperature field and local heat transfer are investigated.

• Journal of Mechanical Science and Technology
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• v.18 no.4
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• pp.699-708
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• 2004

Natural gas hydrate typically contains 85 wt.% water and 15 wt.% natural gas, and commonly belongs to cubic structure I and II. When referred to standard conditions, 1 ㎤ solid hydrate contains up to 200㎥ of natural gas depending on pressure and temperature. Such the large volume of natural gas hydrate can be utilized to store and transport a large quantity of natural gas in a stable condition. In the present investigation, experiments were carried out for the formation of natural gas hydrate governed by pressure, temperature, gas compositions, etc. The results show that the equilibrium pressure of structure II is approximately 65% lower and the solubility is approximately 3 times higher than structure I. It is also found that for the sub-cooling of structure I and II of more than 9 and 11 K respectively, the hydrates are rapidly being formed. It is noted that utilizing nozzles for spraying water in the form of droplets into the natural gas dramatically reduces the hydrate formation time and increases its solubility at the same time.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.213-221
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• 1998

The investigation regarding the ignition system of a plasma jet explored by using a constant volume vessel. The purpose of this study is to elucidate relation between the characteristics of the configuration and jet ejection of plasma jet plug, when the sub energy were supplied at plasma jet ignition system. From the results of a visualization by the schlieren system, the jut ejection for plasma jet ignition are depended on the jet plug configuration and sub energy, but the configuration of plasma jet plug is more influenced than the sub energy on the plasma jet ejection. And the plasma jet ignition strongly influences upon the combustion enhancement than the conventional spark ignition.

• Transactions of Materials Processing
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• v.15 no.9 s.90
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• pp.641-647
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• 2006

During the injection molding process an excessive packing can occur in the smaller volume cavity because of volumetric difference of the family-mold. It causes warpage by increased residual stress in the product and flesh by over packing. In this study, we used a variable-runner system for the filling balance of the cavities by changing the cross-sectional area of a runner, and confirmed the filling imbalance by temperature and pressure sensors. We carried out experiments to examine the influence of types of resins such as LDPE/ABS/PA6,6 on the filling balancing of the system, in order to help mold designers, who can easily adopt the variable-runner system to their design. We also examined filling imbalance in the system with CAE analysis.

• The KSFM Journal of Fluid Machinery
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• v.3 no.3 s.8
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• pp.12-18
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• 2000

In this study, experimental and numerical analyses are carried out to investigate the performance of centrifugal pump with various air admitting conditions. Experiments on the pump performance under air-water two-phase flow are accomplished using a centrifugal pump with semi-open type impeller having three, five and seven blades, respectively. Also, the numerical analysis of turbulent air-water two-phase flow using the finite volume method has been carried out to obtain the pressure, velocities and void fraction on the basis of a so-called bubbly flow model with the constant size and shape of cavity. The results obtained through this study show the reasonable agreements within the range of bubbly flow regime. There are promising developments concerning application of the present study for the flow in a centrifugal pump with two-phase flow conditions and efforts must be followed to improve the turbulence model and two-phase flow model for turbomachinery.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.28 no.1
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• pp.13-20
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• 2006

The articulation disorders associated with velopharyngeal insufficiency (VPI) in cleft palate patients are interested to clinicians particularly. The purpose of this study was to investigate mainly the oropharyngeal air pressure and overall air flow in cleft palate patients. The pressure-measuring catheter was positioned at the midportion of the oropharyngeal cavity with a facial mask. Test words were composed of 9 meaningless polysyllabic words and 17 meaningful words. Aerophone II and Nasometer II were used to measure peak air pressure, mean air pressure, maximum flow rate, volume, phonatory flow rate, nasalance. The data shows that airflow of the cleft palate patient group were higher than those of the control group. Intraoral air pressure of the cleft palate patient group was lower than those of the control group. The first vowel formant and first Bandwidths of the cleft palate patient group were higher than those of the control group.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.93-96
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• 2006

The heat transfer enhancement by pulsatile flow in the plate heat exchanger has been investigated numerically in the present study. The numerical study was performed in the range of the mass flux from 0.04 to 0.12 kg/s. The results showed that the pulsatile flow produces resonating vortex shedding at the groove sharp edges and a strong transient vortex rotation within the grooved channels. As a result, the mixing between the trapped volume in the grooved cavity and the main stream was enhanced. Good agreements between the predictions and measured data are obtained in steady flow. And the heat transfer of pulsatile flow is about 2.4 times than steady flow when frequency is 10 Hz and the mass flux of cold side is 0.04 kg/s.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.335-341
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• 2001

The bubble cavitation and cloud cavitation are the major sources of cavitation-induced sound and vibration. A numerical method which predicts the trajectory and volume change of a cavity is developed, to predict the cavitation noise of a body. It is shown, by using the numerical method, that the cavitation inception and events rate is strongly dependent on the screening effect caused by the pressure gradient around a body, which is confirmed experimentally. Additionally, the effectiveness of a cavitation control method utilizing air injection is investigated experimentally. It is demonstrated that the noise level of the cloud cavitation can be significantly reduced by the air-injection method.

• Journal of KSNVE
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• v.8 no.5
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• pp.849-855
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• 1998

An analysis of lateral hydrodynamic forces of compressor labyrinth seals is presented. Basic equations are derived using a two-control-volume model for compressible flow. Blasius' wall friction-factor formula and jet flow theory are used for the calculaton of wall shear stresses and recirculation velocity in the cavity. Linearized zeroth-order and first-order perturbation equations are developed for a small motion about the centered position by expansion in the eccentricity ratio. Integraton of the resultant first-order pressure distribution over the seal defines the rotordynamic coefficients. As an application a rotordynamic analysis of the balance drum labyrinth seal found in an ethylene regrigeration copmressor is carried out. The rotordynamic characteristic results of the labyrinth seal are presented and compared with other types of seals, honeycomb seal and smooth seal.