• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.3
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• pp.132-139
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• 2003

The effects of casing shapes on the performance and the interaction between an impeller and a casing in a small-sized centrifugal compressor are investigated. Especially, numerical analyses are conducted for the centrifugal compressor with both a circular casing and a volute one. The optimum design for each element (i.e., impeller, diffuser and casing) is important to develop an efficient and compact compressor using alternative refrigerant as working fluids. Typical rotating speed of the compressor is in the range of 40,000∼45,000 rpm. The impeller has backswept blades due to tip clearance and a vane diffuser has wedge type. In order to predict the flow pattern inside an entire impeller, vaneless diffuser and casing, calculations with multiple frames of reference method between the rotating and stationery parts of the domain are carried out. For computations of compressible turbulent flow fields, the continuity and time-averaged Navier-Stokes equations are employed. To evaluate the performance of two types of casings, the static pressure recovery and loss coefficients are obtained for various flow rates. Also, static pressure distributions around casings are studied for different casing shapes, which are very important to predict the distribution of radial load. The static pressure around the casing and pressure difference between the inlet and outlet of the compressor are measured for the circular casing.

• Design & Manufacturing
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• v.13 no.3
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• pp.53-58
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• 2019

This paper presents Artificial Neural Network(ANN) method to predict maximum injection pressure of injection molding machine and weights of injection molding products. 5 hidden layers with 10 neurons is used in the ANN. The ANN was conducted with 5 Input parameters and 2 response data. The input parameters, i.e., melt temperature, mold temperature, fill time, packing pressure, and packing time were selected. The combination of the orthogonal array L27 data set and 23 randomly generated data set were applied in order to train and test for ANN. According to the experimental result, error of the ANN for weights was $0.49{\pm}0.23%$. In case of maximum injection pressure, error of the ANN was $1.40{\pm}1.19%$. This value showed that ANN can be successfully predict the injection pressure and the weights of injection molding products.

• Journal of Drive and Control
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• v.18 no.3
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• pp.8-15
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• 2021

A rear axle steering (RAS) system is attached to the rear of medium and large commercial vehicles that transport large cargo. The existing RAS systems are driven by electro-hydraulic actuator (EHA), and most commercialized EHAs consist of electric motors, hydraulic pumps, relief valves, prefill valves and cylinders. The prefill valve required for such EHAs is a type of check valve with extremely low cracking pressure that should not allow RAS to have noise or vibration, and the prefill valve prevents system negative pressure as well as unstable operation. Most papers on this topic rely on experiments to predict valve performance, and theoretically detailed modeling of valves or pipelines is performed, but it is very rare to evaluate hydraulic vibration characteristics by analysing everything from hydraulic pumps to valves comprehensively. In this study, we proposed an experimental circuit that can predict the performance of the prefill valve. The study also analysed the pressure-flow pulsation that is transmitted to the valve through the pipeline, and how the transmitted pressure-flow pulsation affects the valve vibration.

• Korea-Australia Rheology Journal
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• v.13 no.1
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• pp.47-54
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• 2001

Prediction of the maximum packing volume fraction with non-spherical particles has been one of the important problems in powder technology. The sphericity of fly ash particles depending on the particle diameter was measured by means of a CCD image processing instrument. An algorithm to predict the maximum packing volume fraction with non-spherical particles is proposed. The maximum packing volume fraction is used to predict the slurry viscosity under well dispersed conditions. For this purpose, Simha's cell model is applied for concentrated slurry with wide particle size distribution. Also, Usui's model developed for aggregative slurries is applied to predict the non-Newtonian viscosity of dense fly ash - water slurry. It is certified that the maximum packing volume fraction for non-spherical particles can be successfully used to predict slurry viscosity. The pressure drop in a pipe flow is predicted by using the non-Newtonian viscosity of dense fly ash-water slurry obtained by the present model. The predicted relationship between pressure drop and flow rate results in a good agreement with the experimented data obtained for a test rig with 50 mm inner diameter tube. Base on the design procedure proposed in this study, a feasibility study of fly ash hydraulic transportation system from a coal-fired power station to a controlled deposit site is carried out to give a future prospect of inexpensive fly ash transportation technology.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.4
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• pp.55-63
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• 2009

This paper reports on the theoretical and experimental study of the pressure ripples in a pressure unbalanced type vane pump which have widespread use in industry. Because they can infinitely vary the volume of the fluid pumped in the system by a control. Pressure ripples occur due to the flow ripples induced by geometry of side plate, leakage flow, reverse flow from the outlet volume produced by pressure difference between pumping chamber and outlet volume when the pumping chamber connected with the outlet volume. In this paper, we measured the pressure variation of a pumping chamber, reaction force on a cam ring, the mathematical model for analyzing the pressure ripples which included vane detachment and fluid inertia effects in notch area has been presented, and was applied to predict the level and the wave form of the pressure ripples according to operating conditions.

• The KSFM Journal of Fluid Machinery
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• v.5 no.4 s.17
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• pp.32-39
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• 2002

The purpose of this 3-D numerical simulation is to calculate and examine the complex 3-D stall phenomena on the rotor blade and wake distribution of the wind turbine. The flow characteristics of 500kW Horizontal Axis Wind Turbine (HAWT) are compared with the calculated 3-D stall phenomena and wake distribution. We used the CFX-TASCflow to predict flow and power characteristics of the wind turbine. The CFD results are somewhat consistent with the BEM (Blade Element Momentum) results. And, the rotational speed becomes faster, the 3-D stall region becomes smaller. Moreover, the pressure distribution on the pressure side that directly gets the incoming wind grows high as it goes toward the tip of the blade. The pressure distribution on the blade's suction side tells us that the pressure becomes low in the leading edge of the airfoil as it moves from the hub to the tip. However, we are not able to precisely predict on the power coefficient of the rotor blade at the position of generating complex 3-D stall region.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.900-907
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• 2000

The three-dimensional turbulent flow in curved pipes susceptible to flow-accelerated corrosion has been analyzed numerically to predict the pressure and shear stress distributions on the inner surface of the pipes. The analysis employs the body-fitted non-orthogonal curvilinear coordinate system and a standard $ {\kappa}-{\varepsilon}$ turbulence model with wall function method. The finite volume method is used to discretize the governing equations. The convection term is approximated by a high-resolution and bounded discretization scheme. The cell-centered, non-staggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of a modified version of momentum interpolation scheme. The SIMPLE algorithm is employed for the pressure and velocity coupling. The numerical calculations have been performed for two curved pipes with different bend angles and curvature radii, and discussions have been made on the distributions of the primary and secondary flow velocities, pressure and shear stress on the inner surface of the pipe to examine applicability of the present analysis method. As the result it is seen that the method is effective to predict the susceptible systems or their local areas where the fluid velocity or local turbulence is so high that the structural integrity can be threatened by wall thinning degradation due to flow-accelerated corrosion.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.485-492
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• 2001

Weathered soil is one of the most representative soils in Korea. In this study, a series of cyclic triaxial tests was carried out to predict the post-cyclic deformation behavior of weathered soils in case of non-liquefaction. Excess pore pressure response during cyclic loading and volumetric strain during the dissipation of excess pore pressure were measured varying the confining pressure, relative density and cyclic stress ratio. Based on the test results, it Is found that the modified excess pore pressure ratio, excess pore pressure ratio normalized by cyclic stress ratio, is uniquely correlated with the number of cycles irrespective of confining pressure and cyclic stress ratio. Using the newly proposed MEPPR(modified excess pore pressure ratio) concept, it is possible to easily evaluate the excess pore pressure and the settlement of weathered soils due to cyclic loading by greatly reduced number of tests. It is also verified that the reconsolidation volumetric strain is independent of the way how the excess pore pressure was generated.

• Journal of Korean Society of Water and Wastewater
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• v.34 no.5
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• pp.335-344
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• 2020

Due to global climate change, mega-droughts have occurred frequently. Since long-term droughts make it difficult to secure the water resources, water supply needs to be restricted in a reasonable manner. In the event of limited water supply, the waterworks need to develop a restricted water supply strategy. This study showed that analyzing daily water supply could be used to respond to the first stage of a drought. According to an analysis of Korea's major water authorities, there was about 7~21% of room for daily minimum water supply in case of a drought. Restricting the water supply by lowering pressure is a good strategy for local water authorities with high water leakage rate since leakage is inversely dependent with pressure. For this method, it is necessary to quantify water deficiency and pressure at each node using a simulation. Since DDA-based software is not possible to predict changes in demand at nodes with pressure reduction, WaterGEMS, a PDA software, was used to quantitatively predict water shortages and pressures at each node. Locations where water is deficient need to install booster pumps or to be dispatched with water tank truck and bottled water. Without these support, lowering pressure could not be an option for water works. This paper suggests a method for waterworks to plan a drought by lowering pressure to restrict water supply using daily water supply analysis and PDA based simulation.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.259-266
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• 2010

The heat flowrate and pressure dorp of $CO_2$ in a multi-tube-in-tube helical coil type gas cooler were predicted using LMTD method and compared with the experimental data. The mass flowrate of $CO_2$ and coolant were varied from 0.06 to 0.075 [kg/s], and the cooling pressure of gas cooler were from 8 to 10 [MPa], respectively. The LMTD method is used to predict the heat flowrate and pressure drop of supercritical $CO_2$ during in-tube cooling. The equations used by LMTD method were Gnielinski correlation for $CO_2$ and Dittus-Boelter correlation for coolant, respectively. The equation used to predict the pressure drop of $CO_2$ and coolant is Blasius correlation. In comparison of heat flowrate and pressure drop of $CO_2$ measured by experiment to that predicted by LMTD method, the experimental heat flowrate and pressure drop of $CO_2$ in the multi-tube-in-tube helical coil type gas cooler shows a relatively good agreement with that predicted by LMTD method.