• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.327-333
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• 2008

The cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has developed a base code for simulating cavitating flows past cylinders and hydrofoils. The governing equation is the Navier-Stokes equation based on homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved in liquid and vapor phase, separately. The solver employs an implicit preconditioning algorithm in curvilinear coordinates. The computations have been carried out for the cylinders with spherical, 1- and 0-caliber forebody and hydrofoil of ALE and NACA cross-section and, then, compared with experiments and other numerical results. Fairly good agreements with experiments and numerical results have been achieved. The present base code has shown the feasibility to solve the cavitating flow past supercavitating torpedo after the improvement for compressibility effects and interactions with hot exhaust gas of propulsive rocket.

• Corrosion Science and Technology
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• v.11 no.5
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• pp.205-212
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• 2012

With recent advances in engineering and technology, a damage on industrial machineries performing high-speed and high-power requirements has become a problem. There is an increasing possibility of cavitation damage, especially in pumps, propellers and high-speed vessels in a flowing liquid accordingly. There are several factors affecting cavitation damage on materials, including viscosity, pressure, temperature, amplitude applied. In this study, effects of cavity pressure in seawater on the damage for 5083-O aluminium alloy were evaluated by modulating amplitude. Trend of the damage with respect to time and amplitude was analyzed comparatively, and surface degradation of specimens was investigated by using Scanning Electron Microscope(SEM) and 3D microscope. The result reveals that the amount of the damage increased consistently with the increase in time and amplitude while the plastic deformation zone where no appreciable damage occurred was in less than 30 minutes.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.9
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• pp.53-61
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• 2000

The manufacture of a marine propeller typically requires long lead time to generate 5-axis tool path. Hence it may take several weeks to manufacture a satisfactory propeller with a general purpose CAD/CAM system. In this research a dedicated 5-axis CAD/CAM system for machining marine propellers has been developed, The system employs various methods to enhance the productivity : interference-free tool path generation employing check vectors and optimum cutter size determinants. In addition an iterative NURBS modeling technique is used to improve the accuracy of the modeled surface and effective cutting conditions are determined and recommended empirically to increase the productivity. The proposed CAD/CAM system has been implemented with C++ and OpenGL graphic library on the Windows system. The system validation and sample results are also given and discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.12
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• pp.1055-1062
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• 2008

Engineering materials have been studied and developed remarkably for a long time. But, few reports about marine propeller materials are presented. Recently, some researchers have studied the material strength of marine propellers. However, studies on parametric sensitivity and probabilistic distribution of fatigue life of propeller materials have not been made yet. In this study, a method to predict the probabilistic distributions of fatigue life of propeller materials is presented, and the influence of several parameters on the life distribution is discussed.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2012.06a
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• pp.184-184
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• 2012

Recently, as a result of the application of large and multi-blade propellers with high efficiency for large vessels, the vertical bending stiffness of propulsion shafting system tends to be declined. For some specific vessels, the shaft arrangement leads to the forward stern tube bearing to be omitted, decreasing vertical bending stiffness. In this respect, decreased vertical bending stiffness causes the problem which is the blade order resonance frequency to be placed within the operational range of propulsion shafting system. To verify whirling vibration, the measurement should be carried out covering the range of MCR, however, the range is un-measurable. To resolve the measurement issue, this study shows the measuring method and the estimating method of whiling vibration by using resonance frequency of sub harmonic.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.17 no.1
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• pp.29-38
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• 2009

This paper surveys the historical perspective and design considerations for developing the human powered aircraft(HPA). Especially the weight and materials, aerodynamics, flight controls, and power trains are focused. The average power a human can produce and sustain is approximately 200${\sim}$250 W which is a critical design constraint of HPA. The survey shows that the empty weight of HPA was in the 30${\sim}$40 kg range(90${\sim}$110 kg include pilot). Thus, in order to design a successful HPA, the value of power to weight ratio should be 2.0 W/kg or above. The HPA design technique could be applied directly to the development of an unmanned high altitude airplanes used for atmospheric research, where light structures, low Reynolds number aerodynamics and high efficiency propeller design are required as well.

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2171-2175
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• 2002

Helicopter dynamics are plenty of nonlinearity. A complete mathematical model including propeller dynamics and fortes generated by the propellers is very difficult to obtain. So the method used to design to design a controller is a parameter estimation. Design controller based on variable structure system. This paper deals with LQR control technique to control efficiently, its elevation angle and azimuth one. The purpose of the experiment is to design a controller allows to use a desired elevation angle and azimuth ones. The system model has a helicopter model with 2-degree-of freedom. The simulation results were verified usefulness of controller.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1012-1013
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• 2006

Marine technology must advance to meet the needs of a wealthier and more demanding public while at the same time provide greater environmental protection. Pollution noise and vibration is the specific issue being discussed in this paper Noise is of course due to vibration from high speed engines driving generators, entilators, winch and other gear, while underwater noise pollution results from the propellers and the resistance produced by the hull of the ship moving through the water. Vibration is also a factor in potential damage to sensitive electronic gear and metal fatigue. The issue of noise pollution does not cease when a vessel enters her berth and the main engines shut down. There is still the matter of ventilation and other mechanical factors at work to maintain a comfortable, efficient environment. We measured the noise level and vibration displacement in the training ship A-Ra at underway and Berth. The authors analyzed the frequency of noise and maximum vibration displacement in the position.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.3
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• pp.296-303
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• 2014

The Axiom propeller is a unique 3 bladed propeller and it enables to generate the same amount of thrust going ahead as it does going astern because of its 's' type skew-symmetric blade section. A earlier variant of the design (Axiom I propeller) performed a low propeller efficiency, maximum 35 % efficiency, and further blade outline design was carried out to achieve a higher efficiency. The optimized new blade outline (Axiom II propeller) has more conventional Kaplan geometry shape than Axiom I propeller. Model tests of open water performance and propeller cavitation for both propellers were conducted at Emerson Cavitation Tunnel in order to compare their performances. Experiment results revealed that Axiom II propeller provides a maximum 53 % efficiency and provides better efficiency and cavitation performance over the Axiom I propeller under similar conditions.

• Journal of Ship and Ocean Technology
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• v.4 no.2
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• pp.13-23
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• 2000

A low-order potential based boundary element method is applied to the prediction of the flow around the cavitating propeller in steady or in unsteady inflow. For given cavitation number, the cavity shape is determined in an iterative manner until the kinematic and the dynamic boundary conditions are both satisfied on the approximate cavity boundary. In order to improve the solution behavior near the tip region, a hyperboloidal panel geometry and a modified split panel method are applied. The method is then extended to include the analysis of time-varying cavitating flows around the propeller blades via a time-step algorithm in time domain. In the method, the steady state oscillatory solution is obtained by incremental stepping in the itme domain. Finally, the present method is validated through comparison with other numerical results and experimental data.