• Journal of the Society of Naval Architects of Korea
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• v.40 no.4
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• pp.30-36
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• 2003

Lately, the cavitation and erosion phenomena in the rudder have been increased for high-speed container ships. However, cavitation is not prone to occur in model experiments because of low Reynolds number. In order to predict the cavitation phenomena, the - analysis of the viscous flow in the rudder gap is positively necessary In this study, numerical calculation was applied to the two-dimensional flow around the rudder gap using FLUENT code. The velocity and pressure field were numerically acquired and cavitation phenomena could be predicted. And the case that the round bar was installed in the rudder gap was analyzed. For reducing the acceleration force when fluid flow through the gap, modified rudder shape is proposed, It is shown that modified rudder shape restrain the pressure drop at the entrance of the gap highly both in the computational results and in the model experiment, and reduce the cavitation bubbles.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.50-53
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• 2001

An experimental research work for the fracture and notch strength of thick laminates has been performed to develop high quality composite notches for structural use. Thus, the multi-directional laminates are designed and compared to the baseline aluminum. The difference of notch strength caused by manufacturing techniques is also discussed. The notches of selected materials are evaluated by the static test and low-velocity impact test. Failure modes are also observed and assessed. Material design is evaluated by the FEA(finite element analysis) and confirmed by experiments. The successful results are obtained for thick composite notches, which shows higher strength than aluminum notches.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.85-88
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• 2002

We have implemented a system of falling weight impact tester. Absorbed energy of orthotropic composites with using T300 fiber, which are composed of the same fiber and stacking number is higher than that of quasi-isotropic specimen over impact energy 7J, but in case of using T700 fiber, much difference does not show. Also, absorbed energy of orthotropic composites with using T300 fiber, which are composed of stacking number and orientation became more than that of T700 fiber specimen; however great change doesn't show in case of quasi-isotropic specimens. Delamination area of impacted specimens was measured with ultrasonic C-scanner to find correlation between impact energy and delamination area. Delamination area and frequency responses was evaluated between impacted and unimpacted specimens. There is a strong correlation between frequency responses and impact-induced delamination. The presence and scale of damages have been investigated based on the variations of frequency responses.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.381-388
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• 1998

Hot and humid weather in summer generally brings about discomfort. Experiments on which relative humidity makes effects on the comfort sensation were performed to the young and the aged using sensation vote. From July to October 1996, seven college students and eleven aged people were exposed for 2 hours under six different conditions in the Pukyong National University test chamber so as to determine the effects of relative humidity on thermal and comfort sensations. Subjects were wearing same clothes, and the mean clo value was 0.5. The mean radiant temperature was equal to the air temperature and air velocity in the occupied zone around 0.lm/s. In the experiments, it was found that discomfort could be largely reduced when the humidity is controlled to low values in the settled high temperature.

• Journal of Biomedical Engineering Research
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• v.16 no.2
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• pp.183-190
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• 1995

The use of ultrasound pulsed Doppler systems has become increasingly popular due to the advantages of easy measurements of blood velocity, volume blood blow, and irregularities of the circulatory system. However, the 2-D Doppler systems have several problems, such as range ambiguity, low signal to noise ratio, and slow frame rate. The mean frequency aliasing problem originating from the pulse repetition frequency is one of major limitations in pulsed Doppler systems. A conventional approach to resolve this problem is tracking the mean frequency close to and beyond the Nyquist frequency along the temporal axis. In this paper, a new concept of tracking the mean frequency along the spatial axis is proposed. The proposed technique is fault tolerant by nature and more suitable for multi gate and 2-D Doppler system than conventional methods.

• Journal of Biomedical Engineering Research
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• v.16 no.3
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• pp.279-288
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• 1995

Ultrasonic Doppler systems for the purpose of estimating blood flow velocity, blood flow volume, and flow imaging are commonly used due to advantages of non-invasive and real time observation. Specially, the technical developments of color flow mapping (2-D Doppler) systems have made a relatively rapid progress. However, the 2-D Doppler systems have several problems, such as the range ambiguity, low signal to noise ratio, and slow frame rate. The slow frame rate problem is resolved by using the spatial average which is a method to acquire more data samples for mean frequency estimation. In this paper, spatial average method using the 2nd order sampling instead of quadrature sampling is proposed. The experimental results show that the proposed methods have good performance and easy application to the color flow mapping system.

• International Journal of Ocean System Engineering
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• v.3 no.1
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• pp.44-48
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• 2013

This paper describes the design and implementation of a practical underwater positioning system, which is applicable for shallow water depth conditions. In this paper, two strategies are used to enhance the navigation performance. First, a low-cost acoustic-ranging-based precise navigation solution for shallow water is designed. Then, the outlier rejection algorithm is introduced by designing a velocity gate. The acoustic-ranging-based navigation is implemented by modifying the long base line solution. To enhance the tracking precision, the outlier rejection algorithm is introduced. The performance of the developed approach is evaluated using experiments. The results demonstrate that precise shallow water depth navigation can be implemented using the suggested approaches.

• The KSFM Journal of Fluid Machinery
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• v.6 no.1 s.18
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• pp.30-36
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• 2003

This paper presents the analysis of flows through three different types of radial compressor impeller by using quasi-three-dimensional analysis method. The method obtains two-dimensional solution for velocity distribution on meridional plane, and then calculates approximately the static pressure distributions on blade surfaces. Finite difference method is used for the solutions of governing equations. The compressors have low level compression-ratio and 12 straight radial blades with no backsweep. The results are compared with experimental data and the results of three-dimensional inviscid analysis with those by finite element method. It is found that the agreements with experimental data are good for the cases where viscous effects are not dominant.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.67-70
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• 2005

The carbon fiber reinforced/epoxy laminated composites were fabricated with initial fiber failures within the unidirectional fiber pre-pregnated ply. The fiber failures were made intentionally either parallel to and/or perpendicular to the unidirectional fibers within the ply. The pre-made clear-cut cracks were found to be healed partially after laminating process. The laminates were impacted with or without initial fiber failures within the laminates. The force versus deflection curves were compared. The partially healed laminates showed the reduced laminate stiffness as compared to those without any intentional fiber failures. The impact curves were compared with size and the location of the initial failures varied.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.7
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• pp.779-784
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• 2005

This paper presents the theory of similarity transformations applied to the momentum and energy equations for laminar, forced, external boundary layer flow over a horizontal flat plate which leads to a set of non-linear, ordinary differential equations of phase change material slurry(PCM Slurry). The momentum and energy equation set numerically to obtain the non-dimensional velocity and temperature profiles in a laminar boundary layer are solved. The heat transfer characteristics of PCM slurry was numerically investigated with similar method. It is clarified that the similar solution method of Newtonian fluid can be used reasonably this type of PCM slurry which has low concentration. The data of local wall heat flux and convective heat transfer coefficient of PCM slurry are higher than those of water more than 150$\~$200$\%$, approximately.