• Ocean Science Journal
• /
• v.41 no.4
• /
• pp.195-199
• /
• 2006

Comparative study was carried out for an acoustic iterative inverse method to estimate bubble size distributions in water. Conventional bubble sizing methods consider only sound attenuation for sizing. Choi and Yoon [IEEE, 26(1), 125-130 (2001)] reported an acoustic iterative inverse method, which extracts the sound speed component from the measured sound attenuation. It can more accurately estimate the bubble size distributions in water than do the conventional methods. The estimation results of acoustic iterative inverse method were compared with other experimental data. The experimental data show good agreement with the estimation from the acoustic iterative inverse method. This iterative technique can be utilized for bubble sizing in the ocean.

• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.6
• /
• pp.184-191
• /
• 2002

This paper presents the thermal behavior of a synchronous linear motor with high speed and force. Such a linear motor can successfully replace ball lead screw in machine tools because it has a high velocity, acceleration and good positioning accuracy. On the other hand, low efficiency and high heating up during operation are disadvantage of linear motors. For the application of linear motors to machine tools a water-cooling system is often used. In this research, structure of the linear motor and water cooler is changed to improve the thermal behavior of the linear motor. Some important effects of an integrated cooler, an U-cooler and a thermally symmetrical cooler are presented.

• The KSFM Journal of Fluid Machinery
• /
• v.14 no.1
• /
• pp.61-65
• /
• 2011

A series of water tests of a fuel pump for liquid rocket engines are performed at a room temperature. According to the test results, the head coefficient of the pump follows the conventional similarity rule - unlike this, the pump shows better efficiency with higher rotational speed. Also, it is found that the pressure at the rear bearing outlet is higher than expected because the inlet of bypass pipe line is narrow. Furthermore, the cavitation performance of the fuel pump is found to be sufficient for the engine operation and is better at the lower flow ratio and higher rotational speed.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.1055-1060
• /
• 2005

In evaluating the stability of underground structures and designing prevention methods against the lateral flow, it is necessary to predict the amount and the distribution of the lateral earth pressure acting on these retaining structures. However, because the lateral deformation of real ground is a very complex phenomenon influenced by interaction between volumetric deformation bringing an increase of stability of ground and shear deformation causing failure of ground, any appropriate methods for estimating the lateral earth pressure in consideration of the geotechnical properties of ground and the construction conditions in embankment have not been developed as yet. Therefore, a prediction method, which considers effects of a construction speed of embankment, using the Boussinesq's solution based on the elasticity theory without using complex numerical analyses such as finite element analyses is proposed in this research.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.207-212
• /
• 2003

Recently there has been a remarkable increase in the number of high speed and large ships, and the high power involved for propulsion of above ships have brought high pitch ratio and high skew propeller. The recent tendency toward highly skewed propeller has increased the load on propeller blades and the fatigue strength of propeller blades has become the critical point in design of propellers for above ships. In this paper fatigue tests in sea water were carried out on propeller material of Ni-Al bronze. The stress and environmental conditions of the test were selected to be close to those of full size propellers in use. The effect of stress ratio, stress frequency, revolution number of propeller for above ships numbers and so on were discussed.

• Aerospace Engineering and Technology
• /
• v.10 no.1
• /
• pp.122-128
• /
• 2011

A series of water tests of a Lox pump for liquid rocket engines are performed at a room temperature. According to the hydraulic test results, the head coefficient is slightly decreased when the rotational speed of the pump is increased. However the efficiency is high at the high-speed test. Also, according to the cavitation test results, the cavitation performance of the pump is found to be decreased when the flow ratio is less than 92%. Furthermore, the vibration characteristic is analyzed using measured high frequency data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.9
• /
• pp.810-817
• /
• 2001

Performance of a water-to-water multi-type heat pump system using R22 which has tow indoor units has been investigated experimentally. The refrigerant flow rate of each indoor unit was regulated by an electronic expansion valve and the total refrigerant flow rate of the system was controlled by a variable speed compressor. In the system, evaporator outlet pressure of refrigerant and outlet temperatures of secondary fluid from indoor units were selected as control variables. Experiments were executed for both cooling and heating modes using PID control method with fuzzy logic, and results of the test are compared with a classical PID method. In the case of PID control with fuzzy logic, the fuzzy control rules corrects PID parameters each time. Results show that PID control with fuzzy logic has the merits of quick response and reduced overshoot.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.8 no.1
• /
• pp.65-75
• /
• 1996

A pilot plant, which is simplified the hot water heating control system of a large scale residential building, is used to investigate the effects of control methods and operating conditions on the system performance and to compare control characteristics. Digital variable structure controller(DVSC) and digital PI controller are implemented to control the speed of the circulating pump for the pilot plant using PC. For the DVSC, a control algorithm is suggested, which using a nonlinear sliding surface and a PID sliding surface outside and inside of output error boundary layer, respectively. Smith predictor algorithm is used for the compensation of long dead time. The suggested DVSC yields improved control performance compared with existing DVSC using linear sliding surface only. the system responses with the suggested DVSC shows good responses without overshoot for various operating conditions and robust under external disturbances compared with digital PI controller.

• The Journal of Korean Academy of Prosthodontics
• /
• v.15 no.1
• /
• pp.43-47
• /
• 1977

The purpose of this study was to determine human pulp reactions to temporary cements such as zinc oxide-eugenol cement, modified zinc oxide-eugenol cement (Cavitec) and calcium hydroxide cement (Dycal). Deep class V cavities were prepared in the human teeth with ultrahigh-speed handpiece operating at a free running speed of 300,000 r.p.m., using # 701 bur and water spray coolant. The cavities were flushed with water, dried with cotton pellets and filled with zinc oxide-eugenol cement, modified zinc oxide-eugenol cement and calcium hydroxide cement respectively. The teeth were divided into two groups, which one group was extracted after One day and the other was extracted after seven days. The samples were examined with microscope and the findings were as follows; 1. The pulp reactions to temporary cements were generally mild. Among them the reactions were moderate in zinc oxide-eugenol cement and, slight in calcium hydroxide cement. 2. Calcium hydroxide cement may be used properly as temporary cement for the purpose of pulp protection.

• Journal of Ocean Engineering and Technology
• /
• v.18 no.1
• /
• pp.80-84
• /
• 2004

The initial hull form of a 3 G/T and 30 knots class coastal leisure boat is newly developed. The performances measured, resistance, trim and sinkage, are investigated in a high-speed, circulating water channel (CWC). The effect of a fin attached on the hull side is studied together. Wave patterns are observed to clarify the relationship between the resistance performance and the wave characteristics. It can be found that the fin plays a role of increasing the resistance performance above a certain velocity.