• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.676-685
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• 1993

A mathematical model was developed to quantify the separation process of threshed grain-straw mixtures. It was made to predict the separation loss from a separation unit consisted of stationary crimped sieve with rotating inner rotor. Experiments were performed to prove the mathematical model by changing various levels of pertinent variables for rice. Good Agreement between the simulated results and observed data under the various test conditions, such as inclination angle of the separator, vane pitch, rotor speed, MOG/G ratio, feed rate, and crop variety and moisture content, were confirmed.

• Journal of Advanced Navigation Technology
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• v.27 no.6
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• pp.710-715
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• 2023

Urbanization brings many challenges such as traffic, housing, and environment. To solve these problems, researchers are working on new transportation systems like urban air mobility (UAM). UAM aircraft should fly safely without burdening the existing air traffic system in the early stage of low-density operation. The airspace should also be managed and operated efficiently. Therefore it is important to make urban air traffic predictable by using corridors and collecting data on low-density operations in the early stage. For this purpose various simulations are needed before operation to create scenarios that estimate potential collisions between UAM aircraft and to evaluate the risks of aircraft spacing, loss of separation (LoS), and near mid air collision (NMAC). This paper focuses on identifying the requirements and considerations for setting separation standards for urban air traffic based on the results of studies.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.219-226
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• 2002

This paper is concerned with the effects of periodically approaching upstream wakes on cascade-flow and loss. The reduced frequency of the periodic wakes was varied in the narrow range from 0.5 to 0.7 Corresponding to a wake-passing through the cascade, two velocity deficits appeared near the boundary layer contour in the downstream from about 60% chord-length. The first velocity deficit was caused by a periodic wake and the second one appeared after some delayed time. The second velocity deficit was interpreted as the results of reattachment of flow-separation. The higher reduced frequency decreased the duration time of separation appearance and the lesser losses of blade were resulted.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1185-1197
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• 1997

Three-dimensional flow within a film-cooling hole, which is normally oriented to the main flow, has been measured by using a straight five-hole probe for the blowing ratios of 1.0 and 2.0. The length-to-diameter ratio of the injection hole is fixed to be 1.0 throughout the whole experiments. The result shows that the secondary flow within the hole is strongly affected by the main flow and flow separation at the hole inlet. The higher blowing ratio provides less influence of the main flow on the injectant flow. The three-dimensional flow at the hole exit is considerably altered due to the strong interaction between the injectant and main flow. The aerodynamic loss produced inside the injection hole is mainly attributed to the inlet flow separation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.1
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• pp.38-44
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• 2007

Using the mathematical model suggested by Bennet et al.(1992), the reflection and transmission coefficients by a circular pile breakwater has been investigated in the framework of potential theory. Flow separation due to sudden contraction and expansion is generated and is the main cause of significant energy loss. Therefore, evaluation of exact energy loss coefficient is critical to enhance the reliability of mathematical model. To obtain the energy loss coefficient, 2-dimensional turbulent flow is analyzed using the FLUENT commercial code. The energy loss coefficient can be obtained from the pressure difference between upstream and downstream. Energy loss coefficient is the function of porosity and the relation equation between them is suggested throughout the curve fitting processing. To validated the suggested relation, comparison between the analytical results and the experimental results is made for four different porosities with good agreement.

• Journal of Korean Medicine Rehabilitation
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• v.29 no.2
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• pp.91-99
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• 2019

Objectives The loss of maternal care during early postnatal period may increase development of mood-related disorders, such as depression, anxiety, and personality disorders. In this study, the effect of acupuncture on depression in relation with cell proliferation in the hippocampal gyrus dentatus was investigated using maternal-separated rat pups. Methods On the postnatal 14th day, rat pups from six dams were grouped into following groups: maternal care group, maternal separation group, maternal separation and non-acupoint-acupunctured group, maternal separation and Zusanli-acupunctured group, and maternal separation and fluoxetine-treated group. Acupuncture was performed from postnatal 28th day to postnatal 37th day. The rat pups that belong in the maternal separation and fluoxetine-treated group were injected subcutaneously with 5 mg/kg fluoxetine hydrochloride once a day for the same period of time. To evaluate activity of the rat pups, open field test was performed. Immunohistochemistry for serotonin (5-hydroxytryptamine, 5-HT) and tryptophan hydroxylase (TPH) in the dorsal raphe and for 5-bromo-2'-deoxyuridine (BrdU) in the hippocampal gyrus dentatus was conducted. Results The present results reveal that the activity was decreased by maternal separation. In contrast, acupuncture at Zusanli overcame maternal separation-induced hypoactivity. Maternal separation suppressed TPH expression and 5-HT synthesis in the dorsal raphe and decreased cell proliferation in the hippocampal gyrus dentatus of rat pups. In contrast, acupuncture at Zusanli alleviated maternal separation-induced decrease of 5-HT synthesisand TPH expression. Conclusions The present results demonstrate that acupuncture at Zusanli ameliorated depressive state through increasing cell proliferation and enhancing 5-HT synthesis.

• The KSFM Journal of Fluid Machinery
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• v.17 no.5
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• pp.27-36
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• 2014

This paper presents a numerical investigation of the effect of the rotation speed on the performance in a transonic axial compressor with the dihedral stator. Four stator geometries with different stacking line variables were tested in the flow simulations over the whole operating range. It was found that a large shroud loss at the rotor outlet and the subsequent shroud corner separation in the stator passage occurred at low mass flow rate with the 100 % design speed. The hub dihedral stator could suppress the shroud loss region and consequently improve the stall margin. In case of the 70 % design speed condition as the mass flow rate decreased, it was seen that the high loss region was placed at the midspan of the rotor passage. The dihedral stator slightly affected the local diffusion factor, but the performance of the compressor was not changed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.615-622
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• 2000

Numerical simulation is performed with Denton's code to get pressure loss coefficients in wide range of reverse flow incidence(from -90 degree to +85 degree) for an axial compressor cascade. As a results, it is found that the pressure loss coefficient is increased with incidence and there exist critical incidence which corresponds to the maximum pressure loss coefficient. Pressure loss coefficient with bigger incidence than its critical value is decreased. The effect of increasing incidence in a cascade extremely reduce the mass flow rate by the large flow separation region. Consequently this effect reduce the portion of dynamic pressure in the total pressure loss and beyond the critical incidence the pressure loss coefficient decrease.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.195-201
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• 2008

In the jet engines on the aircrafts cruising at high altitude over 20 km and subsonic speed, the Reynolds number in terms of the compressor blades becomes very low. In such an operating condition with low Reynolds number, it is widely reported that total pressure loss of the air flow through the compressor cascades increases dramatically due to separation of the boundary layer and the secondary-flow. But the detail of flow mechanisms causes the total pressure loss has not been fully understood yet. In the present study, two series of numerical investigations were conducted to study the effects of Reynolds number on the aerodynamic characteristics of compressor cascades. At first, the incompressible flow fields in the two-dimensional compressor cascade composed of C4 airfoils were numerically simulated with various values of Reynolds number. Compared with the corresponding experimental data, the numerically estimated trend of total pressure loss as a function of Reynolds number showed good agreement with that of experiment. From the visualized numerical results, the thickness of boundary layer and wake were found to increase with the decrease of Reynolds number. Especially at very low Reynolds number, the separation of boundary layer and vortex shedding were observed. The other series, as the preparatory investigation, the flow fields in the transonic compressor, NASA Rotor 37, were simulated under the several conditions, which corresponded to the operation at sea level static and at 10 km of altitude with low density and temperature. It was found that, in the case of operation at high altitude, the separation region on the blade surface became lager, and that the radial and reverse flow around the trailing edge become stronger than those under sea level static condition.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.2
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• pp.69-75
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• 2010

In this paper, we analyze an effect co-existence between digital television (DTV) and 802.22 wireless regional area network (WRAN) systems. We set DTV as an interfering system and 802.22 WRAN as a victim system. When they share the same spectrum, we calculate the minimum separation distance. In analysis, we compare a minimum coupling loss (MCL) with a transmission loss (TL) for determining whether there exists the potential interference or not. The minimum separation distance is determined when the TL is larger than the MCL. In this case, the DTV system does not affect any harmful effect to 802.22 WRAN.