• Journal of the Society of Naval Architects of Korea
• /
• v.45 no.3
• /
• pp.280-287
• /
• 2008

In this paper, a mathematical model for a ship manoeuvring with low forward speed in shallow water was suggested. Based on the cross flow model with low forward speed in deep sea, hull, propeller and rudder models were modified to consider the shallow water effects. Static drift and PMM tests were performed to obtain the cross flow drag coefficients and hydrodynamic coefficients. To validate suggested mathematical model, numerical simulation results were compared with those of sea-trials. Through comparisons, it was concluded that suggested mathematical model could give proper estimation on turning test results.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2019.05a
• /
• pp.154-155
• /
• 2019

에어보트(Air boat)는, 선체 상부에 대형 프로펠러를 장착하고 이의 추진력으로 고속 주행하는 특수형태의 선박이다. 선체 밑바닥은 판옥선처럼 평평하고 매끈하기 때문에 장애물에 걸리지 않아 얕은 수면, 개펄, 빙상, 늪지수풀 등 일반선박이 가기 어려운 지역에도 갈 수 있어, 특히 인명구조용으로 많이 이용되고 있다. 그러나 평평한 선저 때문에 파랑이 있거나 측면 바람이 강한 지역에서는, 에어보트는 직진성을 잃어버리고 풍하로 밀리게 되며, 개펄이나 얼음위에서는 정지거리가 길어지는 단점을 가지고 있다. 이 연구에서는 에어보트 선저에 스키드를 장착하여 횡류방지는 물론 직진성을 개선하였으며, 해상 시운전을 통해 성능을 검증하였다.

• The KSFM Journal of Fluid Machinery
• /
• v.17 no.5
• /
• pp.19-26
• /
• 2014

The cross flow turbine attracts more and more attention for its relatively wide operating range and simple structure. In this study, a novel type of micro cross flow turbine is developed for application to a step in an irrigational channel. The head of the turbine is only H=4.3m and the turbine inlet channel is open ducted type, which has barely been studied. The efficiency of the turbine with inlet open duct channel is relatively low. Therefore, a guide nozzle on the turbine inlet is attached to improve the performance of the turbine. The guide nozzle shapes are investigated to find the best shape for the turbine. The guide nozzle plays an important role on directing flow at the runner entry, and it also decreases the negative torque loss by reducing the pressure difference in Region 1. There is 12.5% of efficiency improvement by attaching a well shaped guide nozzle on the turbine inlet.

• The KSFM Journal of Fluid Machinery
• /
• v.17 no.5
• /
• pp.67-71
• /
• 2014

Recently, the cross flow turbine attracts more and more attention for its good performance over a large operating regime at off design point. This study adopts a very low head cross flow turbine that has barely been studied before, and investigates the effect of air layer on the performance of the cross flow turbine. As open duct is applied in this study and free surface model is used between the air layer and water, an engineering definition of efficiency, instead of traditional definition of efficiency, is used. As torque at the runner fluctuates up and down at a reasonable limit, statistical method is used. Pressure and water volume fraction contours are shown to present the characteristics of air-water flow. With constant air suction in the runner chamber, the water level gradually drops below the runner and efficiency of the turbine can be raised by 10 percent. All considered, the effect of air layer on the performance of turbine is considerable.

• The KSFM Journal of Fluid Machinery
• /
• v.16 no.1
• /
• pp.40-46
• /
• 2013

Recently, the duct system with a cross flow fan was used to improve the ventilation in various industrial fields. For the efficient ventilation, it is necessary to design the duct system based on the flow characteristics around the cross flow fan. In the present study, the flow characteristics around a cross flow fan in the ventilation duct were predicted by using the moving mesh and sliding interface techniques for the rotation of blades. To design the duct system with the high performance of ventilation, the CFD simulations were repeated with the revised duct model based on the DOE. With the numerical results of flow rate through the ventilation duct with various geometric parameters, the optimized geometry of ventilation duct to maximize the flow rate was obtained by using the Kriging approximation method. From the performance curves of cross flow fan in the original and optimized models of ventilation duct, it was observed that the flow rate through the optimized model is about 16 percent larger than that through the original model.

• Journal of Biosystems Engineering
• /
• v.22 no.3
• /
• pp.279-288
• /
• 1997

This study was worked out to obtain fundamental data needed for developing a continuous type dryer. The drying process in a cross-flow type continuous dryer was expressed as partial differential equations, and a drying simulation model for predicting rice moisture content, rice temperature, drying air absolute humidity, drying air temperature was developed by using the finite difference method. To validate the performance of the drying simulation model, a prototype continuous dryer was constructed in this study. The size of the test dryer was one-tenth to that of a commercial continuous dryer. The difference in the outlet rice moisture content between the predicted values and the measured values was within 0.5%, that of outlet rice temperature was below $3^{\circ}C$, that of drying air temperature in drying bed was within $8^{\circ}C$ and that of relative humidity of outlet drying air was big because of the different measuring point. In addition, a drying simulation model for a actual size continuous dryer with double flow was developed in this study. This drying simulation model included the rice mixing effect in the middle of drying length. The difference of outlet moisture content between the predicted and the measured values showed below 0.5% in this study.

• Journal of the Society of Naval Architects of Korea
• /
• v.42 no.1 s.139
• /
• pp.50-56
• /
• 2005

The performance of Traditional Korean Fishing Boat is surveyed based on Report on Investigation of Korean Fishing Boat. The characteristics of Traditional Korean fishing Boat of hull form, rudder, sail are studied from the view point of modern sailing boat design. As a result we find her hull form is an excellent candidate of mother ship for modern boat design and the great sized rudder of Traditional Korean Fishing Boat makes a role of the centerboard of modern sailing host. And also we find the sail of Traditional Korean fishing Boat is more useful for sailing against the wind direction than an ordinary Lug sail.

• Proceedings of the SAREK Conference
• /
• 2009.06a
• /
• pp.1244-1250
• /
• 2009

In this study it is intended to review the moving characteristics of smoke by performing visualization for the calculation of the optimal smoke exhaust air volume in case a fire occurs in tunnels where transverse ventilation is applied, and to obtain basic data necessary for the design of smoke exhaust systems by deriving optimal smoke exhaust operational conditions under various conditions. As a result of this study, when the critical velocity in the tunnel is 1.75 m/s and 2.5 m/s, the optimal smoke exhaust air volume has to be more than $173\;m^3/s$, $236\;m^3/s$ for the distance of the smoke moving which can limit the distance to 250m. In addition, in case of uniform exhaust the generated smoke is effectively taken away if the two exhaust holes near the fire region are opened at the same time.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.3
• /
• pp.286-293
• /
• 2003

The unsteady flow characteristics and associated blade tonal noise of a cross-flow fan are predicted by computational methods. The incompressible Navier-Stokes equations are time-accurately solved for obtaining the pressure fluctuations between the rotating blades and the stabilizer. and the sound pressure is predicted using Curie's equation. The discrete noise characteristics of three impellers with a uniform and two random pitch (type-A and -B) blades are compared by their SPL (Sound Pressure Level) spectra. and the frequency modulation characteristics of the BPF (Blade Passing Frequency) noise are discussed. Besides. a mathematical model is proposed for the prediction of discrete blade tonal noise and is validated with available experimental data. The fan performance is also compared with experimental data. indicating that the random pitch effect does not significantly alter the performance characteristics at ${\phi}$ 〉 0.4

• Journal of computational fluids engineering
• /
• v.16 no.3
• /
• pp.95-103
• /
• 2011

In the block type VHTR core, there are inevitable gaps among core blocks for the installation and refueling of the fuel blocks. These gaps are called bypass gap and the bypass flow is defined as a coolant flows through the bypass gap. Distribution of core bypass flow varies according to the reactor operation since the graphite core blocks are deformed by the fast neutron irradiation and thermal expansion. Furthermore, the cross-flow through an interfacial gap between the stacked blocks causes flow mixing between the coolant holes and bypass gap, so that complicated flow distribution occurs in the core. Since the bypass flow affects core thermal margin and reactor efficiency, accurate prediction and evaluation of the core bypass flow are very important. In this regard, experimental and computational studies were carried out to evaluate the core bypass flow distribution. A multi-block experimental apparatus was constructed to measure flow and pressure distribution. Multi-block effect such as cross flow phenomenon was investigated in the experiment. The experimental data were used to validate a CFD model foranalysis of bypass flow characteristics in detail.