• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.4
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• pp.64-71
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• 2022

For the development of an improved upper-stage engine, research on a staged combustion cycle liquid rocket engine is in progress. A cold flow test, ignition test, and combustion test plans were established and performed to develop reignition combustion technology. In order to solve the problem of purge gas flowing into the fuel line, which may cause cavitation in the turbo pump during reignition, the test results of each stage were analyzed. Based on the analysis results, the purge gas inflow problem was solved by reducing the overlapping time between the operation of the bubble removal valve and the opening of the purge valve and the engine fuel valve. Based on this, the reignition combustion test was successfully performed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.8
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• pp.23-28
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• 2019

The structural integrity of a surface metal coating was evaluated through numerical results to improve the efficiency and reduce the damage caused by cavitation in ships and marine plants. The goal was to ensure structural strength and performance, even if the thickness of the wing is reduced to reduce the weight of the material and surface coating. Analytical methods were used for four models: a non-coating model, one with the same thickness after coating, one with a thickness reduction of 3% after coating, and one with thickness reduction of 5% after coating. With a thickness reduction of 5% after coating, the stress was increased to 12%, and the safety factor was 0.99%, so the structural integrity was insufficient. However, a better material or a thicker coating could allow a sufficient safety factor to be secured. The structural integrity was improved by the coating, and even when the weight was reduced up to 5%, the structural integrity could be sufficiently secured due to the coating effect.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.27-34
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• 1989

A potential-based panel method is formulated for the analysis of a partially cavitating 2-dimensional hydrofoil. The method employs dipoles and sources distributed on the foil surface to represent the lifting and cavity problems, respectively. The kinematic boundry condition on the wetted portion of the foil surface is satisfied by requiring that the total potential vanish in the inner flow region of the foil. The dynamic boundary condition on the cavity surface is satisfied by requiring that the potential vary linearly, i.e., the velocity be constant. Green's theorem then results in a potential-based boundary value problem rather than a usual velocity-based formulation. With the singularities distributed on the exact hydrofoil surface, the pressure distributions are predicted with more improved accuracy than the zero-thickness hydrofoil theory, especially near the leading edge. The theory then predicts the cavity shape and cavitation number for an assumed cavity length. To improve the accuracy, the sources and dipoles on the cavity surface are moved to the newly computed cavity surface, where the boundary conditions are satisfied again. It was found that five iterations are necessary to obtain converged values, while only two iterations are sufficient for engineering purpose.

• Textile Coloration and Finishing
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• v.14 no.6
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• pp.305-312
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• 2002

In order to give a silk-like touch to PET fabrics, the PET fabrics were treated with NaOH alkaline solution in various conditions. In alkaline treatment, the liquor flow type pilot weight reduction apparatus with magnetostrictive ultrasonic transducer was used for the study. The effects of ultrasonic application, treatment time and temperature at NaOH 4% and 6"A solution on the decomposition rate of PET fabrics. From the results of the decomposition rate of PET fabrics, the qualitative and quantitative analysis of oligomer after decomposition of PET fabrics carried out by the HPLC. On the other hand, the surface pore characteristics of decomposition PET fabrics measured by porosimetery. The pore characteristics on the surface of treated PET fiber depended on the decomposition rate and did not depend on the ultrasonic cavitation. The pore diameter of alkaline untreated PET fiber were 15A and those of treated PET fibers were 5~6$\AA$ at the maximum pore volume. The average pore sizes of fiber before and after treatment were 141 h and 160h, respectively. Total amount of oligomer of the untreated PET fibers were 1.70wt% and 67.7% of total oligomer occupied with PET cyclic trimer and PET cyclic tetramer. Total amount of oligomer of fiber with 26.9% and 48.0% of weight loss without ultrasonic application were 1.78wt% and 1.79wt%, respectively. Also total amount oligomer of fibers which were reduced 27.7% and 48.2% of weight loss with ultrasonic application were 1.74wt%. This result showed that the removal rate of oligomer in the process of alkaline hydrolysis with ultrasonic higher than that of without ultrasonic application.tion.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.566-575
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• 2011

Since LPG (Liquefied petroleum gas) fuel supply system has an advantage of low emission characteristics, many studies have been conducted. In spite of the advantage of LPG supply system, a higher vapor pressure and lower viscosity than diesel or gasoline fuel may cause unstable running of fuel pump by the deterioration in lubrication performance and chemical reaction with rubber parts than that of diesel and gasoline fuel. Therefore its physical properties can cause the deterioration of durability. In this research, we developed an external type LPG pump which has the advantage of the price competitiveness and the convenient maintenance for LPLi system. The experiments were carried out in order to assess characteristics of the external type fuel pump at different fuel composition and temperature. As a result, there aren't any differences between internal and external type pump performance. It is observed that the same level of efficiency was maintained for both pumps as flow rate was increased with higher fuel temperature and more contents of propane in the fuel. And the pressure difference in LPLi system is maintained at constant with the various fuel compositions and temperatures due to their own characteristics of fuel supply system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.10
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• pp.865-871
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• 2014

This study was conducted with the aim of developing a venturi-type air supply system for a microbubble generator. In order to determine the influence of the varying geometry of the venturi tube on the flow characteristics, a computational fluid dynamics (CFD) simulation was performed using the commercial CFD software ANSYS CFX-15. Furthermore, in order to elucidate the effects of variation in major design dimensions such as the air supply hole size, position of holes, and number of holes on the air supply characteristics, two-phase multiflow CFD analysis was performed. The analysis results showed that the starting point of expansion on the venturi tube with 0.75 is the best hole position and that the air supply hole size and the number of holes are linearly proportional to the amount of air.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.520-527
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• 1988

Liquid ejectors are widely used as marine pumps, inducer stage for the boiler feed water pump, boiler recirculating pump, cooling water recirculating pump in boiling water type nuclear reactor and a deep well pump, because of their high working confidence and simplicity. Furthermore, it requires only a modest net positive suction head for cavitation-free operation and it can be installed in remote location from mechanical power source. It is not easy to presume the friction losses, because it is complicately affected by area ratio, flowrate ratio, nozzle spacing, throat length, shape of liquid ejector and so on. Therefore, the optimization of liquid ejector design is still dependent, to a large extent, on the experimental results and empirical procedures. On the design of the liquid ejector, the area ratio and the nondimensional throat length are the most important design factors among the mentioned above. In this experiment, the effects of the area ratio and the nondimensional throat length to ejector efficiency are carried out systematically by the combination of 4 kinds of motive nozzle and 2 kinds of throat length. In this paper, the present experimental results are compared with the calculated ones by the previous computer aided design program based on one dimensional flow equation. And also, an empirical equation for the working limit of liquid ejector is reported.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.1
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• pp.19-27
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• 2015

As the recent regulation of Internaional Maritime Organization (IMO) is enforced, the advanced technology of Ballast water treatment system (BWTS) is needed to meet its requirements. Until now, there are two kinds of the BWTS technologies such as physical methods (Membrane and UV) and chemical methods (Chlorin and Ozone). However, these conventional methods have some limitations of auxiliary power, low productivity, residual treatment and etc. In order to overcome these problems, this paper introduces the new kind of BWTS based on mechanical principle and investigates the effect of rotating disc shapes on flow characteristics between rotating and stationary discs by computational fluid dynamics (CFD). Planar and Step types can make the local cavitation generated along radius, and Circular type can increase the intensity of shear stress.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.392-399
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• 2009

The paper concerns the description of the step by step development process of the new fixed blade runner called "Mixer" suitable for the uprating of the Francis turbines units installed at the older low head hydropower plants. In the paper the details of hydraulic and mechanical design are presented. Since the rotational speed of the new runner is significantly higher then the rotational speed of the original Francis one, the direct coupling of the turbine to the generator can be applied. The maximum efficiency at prescribed operational point was reached by the geometry optimization of two most important components. In the first step the optimization of the draft tube geometry was carried out. The condition for the draft tube geometry optimization was to design the new geometry of the draft tube within the original bad draft tube shape without any extensive civil works. The runner blade geometry optimization was carried out on the runner coupled with the draft tube domain. The blade geometry of the runner was optimized using automatic direct search optimization procedure. The method used for the objective function minimum search is a kind of the Nelder-Mead simplex method. The objective function concerns efficiency, required net head and cavitation features. After successful hydraulic design the modal and stress analysis was carried out on the prototype scale runner. The static pressure distribution from flow simulation was used as a load condition. The modal analysis in air and in water was carried out and the results were compared. The final runner was manufactured in model scale and it is going to be tested in hydraulic laboratory. Since the turbine with the fixed blade runner does not allow double regulation like in case of full Kaplan turbine, it can be profitably used mainly at power plants with smaller changes of operational conditions or in case with more units installed. The advantages are simple manufacturing, installation and therefore lower expenses and short delivery time for turbine uprating.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.65-76
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• 1996

A screw propeller is usually accepted as a propulsor of many kinds of ships. However, for high speed vessels, screw propeller has large cavitation area on the blades so propeller efficiency is decreased and erosion can be happened. To avoid this problem, supercavitating propeller and waterjet are generally used for high speed vessels. In this paper, we introduced the self-propulsion test procedure which has been developed for high speed vessels in Hyundai Maritime Research Institute. The model ship used in experiment represents catamaran about 5.3 m in length. To minimize the experimental errors, two impellers were driven by a single motor. Thrust was calculated by converting the measured pressure to flow rates at the nozzle exit. The test procedure is composed of resistance test, self propulsion test and analysis. In order to measure the pressure, pressure tabs were installed around the nozzle exit and connected to the pressure sensor by vinyl tube.