• The KSFM Journal of Fluid Machinery
• /
• v.1 no.1 s.1
• /
• pp.64-71
• /
• 1998

The non-uniform pressure generated in the volute generally are propagating upstream. As a result, outlet conditions of rotaing impeller are changed and the performance degrades. The major object of this research is to develop the numerical method which can calculate the effects of impeller and volute flow field interactions. Under the assumption of steady three-dimensional incompressible turbulent flow, the time averaged N-S equations involving $k-{\epsilon}$ turbulent model was solved by the F.V.M. To verify the computational method, the calculations are compared with experimental results published in literature and show satisfactory agreement with them, The three-dimensional flow characteristics within the volute of a centrifugal fan at design and off-design operating points have also been studied.

• Journal of Energy Engineering
• /
• v.21 no.4
• /
• pp.411-418
• /
• 2012

The effect of built-in volume ratio of expander on the performance of a two-loop Rankine cycle system for engine waste heat recovery of vehicle has been investigated. In the case of positive displacement expander in the various operating condition of the vehicle, it can operate in both under-expansion and over-expansion conditions. Therefore, the analysis of off-design performance for the expander is very important. Furthermore, the volume and weight of the expander as well as the efficiency must be considered in the optimization of the expander. This study shows that the built-in volume ratio of expander causing under-expansion at a target condition is more desirable considering the off-design performance and size of the expander, based on the simple modeling of off-design operation of the expander.

• Journal of Mechanical Science and Technology
• /
• v.16 no.8
• /
• pp.1144-1153
• /
• 2002

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.

• Archives of design research
• /
• v.2 no.1
• /
• pp.107-115
• /
• 1989

In my previous research (1986), I considered a general characteristics of a visual image of products. There were really many difficulties in designing all kinds of needs in compliance with the all of their requests in order to satisfy consumers. In addition, under the characteristics of goods, the consumers seem to choose an opti$$\mu$ com\ulcornerbinations after considering the combinations of trade-off. Therefore, this study that selected a watch as an object on this study was analyzed a Design Assessment Structure under the trade-off. As a result of this research: First, an effect of a negative superiority appeared under the trade-off condition among ifems when consumers purchased products. Second, these four items were extracted from the eight items which were suggested in this study through an analysis of factors. Third, the three courses were conformed when a consumer purchased a watch. Fourth, in the all kinds of goods, the price which was considered as an important point was not important item ina relation to a purchasing behavior. According to the concomitant effects, we figured out these four items, that is, form, thickness, readability and wearing and its have to be considered a lot when designing a watch.

• Proceedings of the KIPE Conference
• /
• 2012.07a
• /
• pp.230-231
• /
• 2012

This paper describes a gate driver that operates numerous semiconductor switch in the solide-state pulsed power modulator. the proposed gate driver is designed to receive both the isolated drive-power and the on/off pulse signals through the transformer. Moreover, the IGBT-switch can be quickly turned off by adding protection circuit. Therefore it protects the IGBT-switch from the arc condition that frequently occurs in high-voltage pulse application. To comprehend operating characteristic of each IGBT-switch in pulse output condition, the device consisting of a high efficiency soft-switching capacitor charger and two series stacking IGBT-switch is developed. Finally, the relability of the proposed gate driver and the device for its test are proved through PSpice simulation and experiments.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.25 no.6
• /
• pp.451-458
• /
• 2020

In this study, a trade-off analysis of a power conversion system (PCS) is performed in accordance with a power semiconductor device to establish the suitable operating frequency range for the anyplace induction heating system. A resonant network is designed under each operating frequency condition to compare and analyze the PCS losses depending on the power semiconductor device. On the basis of the simulation results, the PCS losses and frequency condition are calculated. The calculated results are then used for a trade-off analysis between Si-MOSFET and GaN-HEMT based on PCS. The suitable operating frequency range is determined, and the validity of the analysis results is verified by the experiment results.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.26 no.4
• /
• pp.52-65
• /
• 1984

In general precise estimation of hourly of daily distribution of the long-term run-off should be very important in a design of source of irrigation. However, there have not been a satisfying method for forecasting of stationar'y long-term run-off in Korea. Solving this problem, this study introduces unit-hydrograph method frequently used in short-term run-off analysis into the long-term run-off analysis, of which model basin was selected to be Sumgin-river catchment area. In the estimation of effective rainfall, conventional method neglects the Soil moisture condition of catchment area, but in this study, the initial discharge (qb) occurred just before rising phase of the hydrograph was selected as the index of a basin soil moisture condition and then introduced as 3rd variable in the analysis of the reationship between cumulative rainfall and cumulative loss of rainfall, which built a new type of separation method of effective rainfall. In next step, in order to normalize significant potential error included in hydrological data, especially in vast catchment area, Snyder's correlation method was applied. A key to solution in this study is multiple correlation method or multiple regressional analysis, which is primarily based on the method of least squres and which is solved by the form of systems of linear equations. And for verification of the change of characteristics of unit hydrograph according to the variation of a various kind of hydrological charateristics (for example, precipitation, tree cover, soil condition, etc),seasonal unit hydrograph models of dry season(autumn, winter), semi-dry season (spring), rainy season (summer) were made respectively. The results obtained in this study were summarized as follows; 1.During the test period of 1966-1971, effective rainfall was estimated for the total 114 run-off hydrograph. From this estimation results, relative error of estimation to the ovservation value was 6%, -which is mush smaller than 12% of the error of conventional method. 2.During the test period, daily distribution of long-term run-off discharge was estimated by the unit hydrograph model. From this estimation results, relative error of estimation by the application of standard unit hydrograph model was 12%. When estimating by each seasonal unit bydrograph model, the relative error was 14% during dry season 10% during semi-dry season and 7% during rainy season, which is much smaller than 37% of conventional method. Summing up the analysis results obtained above, it is convinced that qb-index method of this study for the estimation of effective rainfall be preciser than any other method developed before. Because even recently no method has been developed for the estimation of daily distribution of long-term run-off dicharge, therefore estimation value by unit hydrograph model was only compared with that due to kaziyama method which estimates monthly run-off discharge. However this method due to this study turns out to have high accuracy. If specially mentioned from the results of this study, there is no need to use each seasonal unit hydrograph model separately except the case of semi-dry season. The author hopes to analyze the latter case in future sudies.

• 유체기계공업학회:학술대회논문집
• /
• 2001.11a
• /
• pp.185-190
• /
• 2001

The cavitation causes suction performance and efficiency of the high-speed pump to be reduced significantly To diminish these effects, the inducer has been used. Most of the inducer is designed at a maximum efficiency point of the pump, therefore suction performance drop due to effects of flow separation and inlet inverse flow is often observed at off-design point. The objective of this study is to find out the cavitation modes at various conditions by applying event detection technique and to design an inducer reducing cavitation. The pressure fluctuations at each cavitating condition were measured at inducer inlet and outlet locations using pressure transducers, which were located 90 degrees apart from each other to identify the cavitation modes. The time-frequency characteristics were analyzed by using Choi-williams distribution. In the second part of this paper, the inducer design method which uses nominal performance characteristic and onset condition of cavitation is introduced and applied to real situation.

• Journal of the Korean Geotechnical Society
• /
• v.33 no.11
• /
• pp.73-82
• /
• 2017

Recently, offshore bucket cut-off walls were developed to solve several problems in conventional offshore cut-off walls. In this study, a numerical analysis was carried out to investigate the seepage stability of offshore bucket cut-off walls. The ground was assumed as uniform homogeneous sand and steady state flow conditions were applied. The flow condition was compared among 2-dimensional flow (2-D), 2-dimensional concentrated flow (2-DC), and axisymmetric flow. The analysis results showed that the seepage velocities in axisymmetric flow were about 1.5 and 2 times larger than those of 2-DC and 2-D flow conditions, respectively. Thereafter, the axisymmetric flow condition was applied because the seepage flow was concentrated toward the center of the circular-shaped wall. A parametric study was performed varying bucket radius, penetration depth, total head difference between in and outside of the wall. The exit gradient, which used for the calculation of piping stability, decreased with increase of the penetration depth and bucket radius. Design charts were proposed to estimate the factor of safety and the exit gradient at various analysis conditions. Finally, the design equation was proposed to calculate the exit gradient for the preliminary design of the bucket cut-off wall.

• New & Renewable Energy
• /
• v.10 no.1
• /
• pp.6-19
• /
• 2014

Organic Rankine cycle (ORC) has been widely used to convert renewable energy such as solar energy, geothermal energy, or waste energy etc., to electric power. For a small scale output power less than 10 kW, turbo-expander is not widely used than positive displacement expander. However, the turbo-expander has merits that it can operate well at off-design points. Usually, the available thermal energy for a small scale ORC is not supplied continuously. So, the mass flowrate should be adjusted in the expander to maintain the cycle. In this study, nozzles was adopted as stator to control the mass flowrate, and radial-type turbine was used as expander. The turbine operated at partial admission. R245fa was adopted as working fluid, and supersonic nozzle was designed to get the supersonic flow at the nozzle exit. When the inlet operating condition of the working fluid was varied corresponding to the fluctuation of the available thermal energy, optimal operating condition was investigated at off-design due to the variation of mass flowrate.