• Transactions of the Society of Information Storage Systems
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• v.5 no.1
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• pp.19-35
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• 2009

The present work is an experimental and analytical study on a flexible disk rotating close to a rigid rotating disk in open air. In the analytical study, the air flow in the gap between the flexible disk and the rigid disk is modeled using Navier-Stokes and continuity equations while the flexible disk is modeled using the linear plate theory. The flow equations are discretized using the cell centered finite volume method (FVM) and solved numerically with semi-implicit pressure-linked equations (SIMPLE algorithm). The spatial terms in the disk equation are discretized using the finite difference method (FDM) and the time integration is performed using fourth-order Runge-Kutta method. An experimental test-rig is designed to investigate the dynamics of the flexible disk when rotating close to a co-rotating, a counter-rotating and a fixed rigid disk, which works as a stabilizer. The effects of rotational speed, initial gap height and inlet-hole radius on the flexible disk displacement and its vibration amplitude are investigated experimentally for the different types of stabilizer. Finally, the analytical and experimental results are compared.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.2
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• pp.162-170
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• 2014

A CFD(Computational Fluid Dynamics) analysis is presented to predict hydrodynamic characteristics of a marine propeller. A commercial RANS(Reynolds Averaged Navier-Stokes equation) solver, namely FLUENT, is utilized in conjunction with fully unstructured meshes around rotating propeller. Mesh generation process is greatly accelerated by using fully unstructured meshes composed of both isotropic and anisotropic tetrahedral elements. The anisotropic tetrahedral elements were used in the flow domain near the blade and shaft, where the viscous effect is important, having complex shape yet resolving the thin boundary layers. For other regions, isotropic tetrahedral elements are utilized. Two different approaches simulating rotational effect of the propeller are employed, namely Moving reference frame technique for steady simulation, and Sliding mesh technique for unsteady simulation. Both approaches are applied to the propeller open water (POW) test simulation. The current results, which are thrust and torque coefficients, are compared with available experimental data.

• Journal of the Korean Graphic Arts Communication Society
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• v.23 no.2
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• pp.117-128
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• 2005

Printing inks are basically dispersions of solid pigment particles in a vehicle. Pigment flocculation and/or colloidal aggregates created by thixotrope additives form a three- dimensional network in the inks. This structure complicates the flow behaviour of inks. However, if the internal structure is formed under control, the printing process will benefit from it because the ink must satify rheological requirements over a very wide range of shear conditions. The presence of internal structure results in the following prominent non-Newtonian rheological properties: viscoelasticity, yield stress, shear thinning and thixotropy. If the components of printing inks were changed, the rheological characteristics such as viscosity, yield stress, viscoelasticity and tack value were considerably varied. Thus, in this paper, the effects of changing the content of rosin modified phenolic resin on rheological properties of the vehicle will be studied. For that, the rheological properties were found by flow, yield stress, creep and oscillation measurements using Bohlin C-VOR Rotational Rheometer. And Emulsion rheology and its microstructure will be investigated.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.4
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• pp.23-30
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• 1993

This rape deals with the experimental and theoretical investigations on the aerodynamic performance of the Wells turbine. The two-dimensional cascade theory is used to estimate the thrust and torque of turbine, and finally to yield an efficiency of turbine. The turbine is assumed to rotate with a constant rotational speed in a sinusoidally varying unsteady flow field. Experimental approach is made in a wave simulator, producing a sinusoidally reciprocating air flow corresponding to the wave motion in an Oscillating Water Column(OWC) chamber. Performance data of turbine measured at various operating conditions are analyzed and compared to numerical results in order to understand the overall features of a Wells turbine.

• International Journal of Fluid Machinery and Systems
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• v.5 no.4
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• pp.161-167
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• 2012

Small-sized axial fans are used as air coolers for electric equipment. There is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although, it causes the deterioration of the efficiency and the increase of noise. Then, the adoption of contra-rotating rotors for small-sized fans is proposed for the improvement of the performance. In the case of contra-rotating rotors, blade row distance between the front and the rear rotors influences on the performance and the noise. Therefore, it is important to clarify the optimum blade row distance between front and rear rotors. The performance curves of the contra-rotating small-sized axial fan under the condition of different blade row distances are shown and the blade row interaction between the front and the rear rotors are discussed by the numerical results. Furthermore, the optimum blade row distance of the contra-rotating small-sized axial fan is considered.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2434-2439
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• 2008

This paper was studied on the cavitation instability of a Solution Pump Inducer in an absorption chiller-heater. Inlet pressure of LiBr and rotational speed at nominal mode are 2,800 Pa and 3,500 rpm respectively. Due to the marginal operation of available NPSH, the cavitation performance of the inducer is critical for the stable operation without the deterioration of head performance. In the study, cavitation performance and its mode of instability was investigated experimentally. Water was used as the working fluid and the test inducer was scaled up as 1.75 times for detail measurements and flow visualization. Inlet pressure was controlled by a vacuum pump. This research focused on types of cavitation instability and phenomena to investigate the possibility of harmful damage due to cavitation instability. Casing wall pressure and instantaneous inlet pressure was measured to observe the unsteady flow characteristics. Through the visualization and spectrum analysis of pressure, the occurrence region and intensity of asymmetric cavitation and cavitation surge are analyzed in the test inducer.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.77-80
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• 2010

A series of hydraulic tests of a Lox pump are performed using water at a room temperature. According to the test results, the Lox pump satisfies its design requirement but both the head and the efficiency do not fully follow the conventional similarity rule. The deviation of the head from the rule is assumed to be due to the increased volute loss at high rotational speed. Furthermore, it is found that when the pump rotates with the flow ratio less then the design requirement the leakage flowrate seems to be increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.8
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• pp.409-417
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• 2015

A simplified rotary heat-exchanger model was developed with an assumption of a linear temperature distribution along the flow direction. Based on the model, the exact fluid solution and solid temperature variations were obtained and verified from a comparison with previous numerical studies. The heat transfer in the rotary heat exchanger was investigated using the theoretical solutions. The heat exchanger's effectiveness was shown to be saturated, with a rotational-speed increase that is higher than a critical value that is solely dependent on the thermal capacity of the solid matrix but independent of the fluid flow rate; the saturated value of the effectiveness was determined only by the NTU of the heat exchanger. Where the thermal diffusivity of the solid matrix is so slight that the thermal penetration depth becomes smaller than the matrix thickness, the effective thermal capacity of the solid matrix decreased according to the penetration depth.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.390-392
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• 2003

Video mosaicing techniques have been widely used in virtual reality environments. Especially in GIS field, video mosaics are becoming more and more common in representing urban environments. Such applications mainly use spherical or panoramic mosaics that are based on images taken from a rotating camera around its nodal point. The viewpoint, however, is limited to location within a small area. On the other hand, 2D-mosaics, which are based on images taken from a translating camera, can acquire data in wide area. The 2D-mosaics still have some problems : it can‘t be applied to images taken from a rotational camera in large angle. To compensate those problems , we proposed a novel method for creating video mosaics in 3D space. The proposed algorithm consists of 4 steps: feature -based optical flow detection, camera orientation, 2D-image projection, and image registration in 3D space. All of the processes are fully automatic and successfully implemented and tested with real images.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.84-88
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• 2008

The UAV propulsion system that will be operated for long time at more than 40,000ft altitude should have not only fuel flow minimization but also high reliability and durability. If this UAV propulsion system may have faults, it is not easy to recover the system from the abnormal, and hence an accurate diagnostic technology must be needed to keep the operational reliability. For this purpose, the development of the health monitoring system which can monitor remotely the engine condition should be required. In this study, a fuzzy trend monitoring method for detecting the engine faults including mechanical faults was proposed through analyzing performance trends of measurement data. The trend monitoring is an engine conditioning method which can find engine faults by monitoring important measuring parameters such as fuel flow, exhaust gas temperatures, rotational speeds, vibration and etc. Using engine condition database as an input to be generated by linear regression analysis of real engine instrument data, an application of the fuzzy logic in diagnostics estimated the cause of fault in each component. According to study results, it was confirmed that the proposed trend monitoring method can improve reliability and durability of the propulsion system for a long endurance UAV to be operated at medium altitude.