• Journal of Advanced Marine Engineering and Technology
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• v.39 no.2
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• pp.136-142
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• 2015

The shell and tube heat exchanger is an essential part of a power plant for recovering transfer heat between the feed water of a boiler and the wasted heat. The baffles are also an important element inside the heat exchanger. Internal materials influence the flow pattern in the bed. The influence of baffles in the velocity profiles was observed using a three-dimensional PIV (Particle Image Velocimetry) around baffles in a horizontal circular tube. The velocity of the particles was measured before the baffle and between them in the test tube. Results show that the velocity vectors near the front baffle flow along the vertical wall, and then concentrate on the upper opening of the front baffle. The velocity profiles circulate in the front and rear baffle. These profiles are related to the Reynolds number (Re) or the flow intensity. Velocity profiles at lower Re number showed complicated mixing to obtain the velocities and concentrate on the lower opening of the rear baffle as front wall. Numerical simulations were performed to investigate the effects of the baffle and obtain the velocity profiles between the two baffles. In this study, a commercial CFD package, Fluent 6.3.21 with the turbulent flow modeling, k-${\epsilon}$ are adopted. The path line and local axial velocities are calculated between two baffles using this program.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.10
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• pp.820-826
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• 2009

The anisotropic phonon conductions with varying Joule heating rate of the silicon film in Silicon-on-Insulator devices are examined using the electron-phonon interaction model. It is found that the phonon heat transfer rate at each boundary of Si-layer has a strong dependence on the heating power rate. And the phonon flow decreases when the temperature gradient has a sharp change within extremely short length scales such as phonon mean free path. Thus the heat generated in the hot spot region is removed primarily by heat conduction through Si-layer at the higher Joule heating level and the phonon nonlocality is mainly attributed to lower group velocity phonons as remarkably dissimilar to the case of electrons in laser heated plasmas. To validate these observations the modified phonon nonlocal model considering complete phonon dispersion relations is introduced as a correct form of the conventional theory. We also reveal that the relation between the phonon heat deposition time from the hot spot region and the relaxation time in Si-layer can be used to estimate the intrinsic thermal resistance in the parallel heat flow direction as Joule heating level varies.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.693-698
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• 2002

For the evaluation of the plasma display panel (PDP)'s noise, vibration and sound characteristics of fanless PDP are measured and investigated. PDP is a type of two-electrode vacuum tube which operates on the same principle as a household fluorescent light. An inert gas such as argon or neon is injected between two glass plates on which transparent electrodes have been formed, and the glass is illuminated by generating discharge. For this discharge, both high voltage and currents are needed and cause an acoustic noise. We investigated the noise characteristics connected with both a electromagnetic elements from SMPS to panel through X, Y and logic board, and a mechanical elements form panel to case through transfer path which related with vibration and heat. To reduce the noise of PDP, a discharge pulse memory design related with both higher brightness and lower power consumption is important and mechanical characteristics connected with dissipation process of both heat and vibration generated by panel discharge must be investigated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.11
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• pp.1074-1083
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• 2011

Noise of digital camera has been noticeable to its users. Particularly, noise of a barrel assembly module in zoom in/zoom out operation is recorded while taking a video. Reduction of barrel noise becomes crucial but there are not many studies on noise of digital camera due to its short history of use. In this study, experiment-based analyses are implemented to identify sources of noise and vibration because of complexity and compactness of the barrel system. Output noise is acquired in various operation conditions using synchronization for spectral analysis. Noise sources of a barrel assembly in zoom operating are first identified by the comparison with gear frequency analysis and then correlation analysis between noise and vibration is applied to confirm the generation path of noise. Analysis on noise transfer characteristic of zoom module is also carried out in order to identify the most contributing components. One of possible countermeasures of noise in zoom operating is investigated by an experimental approach.

• Journal of Internet Computing and Services
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• v.5 no.5
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• pp.129-138
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• 2004

In the telecommunications network, multicasting is widely used recently. Multicast tree problem is modeled as the NP-complete Steiner problem in the networks. In this paper, we study algorithms for finding efficient multicast trees with hop and node degree constraints. Multimedia service is an application of multicasting and it is required to transfer a large volume of multimedia data with QoS(Quality of Service). Though heuristics for solving the multicast tree problems with one constraint have been studied. however, there is no optimum algorithm that finds an optimum multicast tree with hop and node degree constraints up to now. In this paper, an approach for finding an efficient multicast tree that satisfies hop and node degree constraints is presented and the experimental results explain how the hop and node degree constraints affect to the total cost of a multicast tree.

• Earthquakes and Structures
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• v.12 no.6
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• pp.699-712
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• 2017

This study evaluates the effectiveness of a newly developed retrofitting scheme for masonry-infilled non-ductile RC frames experimentally and by numerical simulation. The technique focuses on modifying the load path and yield mechanism of the infilled frame to enhance the ductility. A vertical gap between the column and the infill panel was strategically introduced so that no shear force is directly transferred to the column. Steel brackets and small vertical steel members were then provided to transfer the interactive forces between the RC frame and the masonry panel. Wire meshes and high-strength mortar were provided in areas with high stress concentration and in the panel to further reduce damage. Cyclic load tests on a large-scale specimen of a single-bay, single-story, masonry-infilled RC frame were carried out. Based on those tests, the retrofitting scheme provided significant improvement, especially in terms of ductility enhancement. All retrofitted specimens clearly exhibited much better performances than those stipulated in building standards for masonry-infilled structures. A macro-scale computer model based on a diagonal-strut concept was also developed for predicting the global behavior of the retrofitted masonry-infilled frames. This proposed model was effectively used to evaluate the global responses of the test specimens with acceptable accuracy, especially in terms of strength, stiffness and damage condition.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.183-190
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• 2008

This paper deals with the characteristics of idle vibration due to the type of constant velocity joints. Based on the kinematics model of constant velocity joints, a offset between the tripod center and tullip center plays a important role in generating unwelcome forces. Moreover, it induced additional forces in lateral direction of a vehicle movement according to the angle of the spider in idle vibration. The difference of mass for each constant velocity joint types affect the natural frequency of the driveshaft and the powertrain. When the static torque is applied to the constant velocity joints, the natural frequencies of the driveshaft are reduced nearby 50Hz. There will be a big opportunity that the dirveshaft and constant velocity joints would be a transfer path of idle vibration at D or R gear range. Experiments indicate that TJ type is better than SFJ and DOJ in idle vibration.

• Geomechanics and Engineering
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• v.14 no.5
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• pp.439-451
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• 2018

The stress path characteristics of surrounding rock in the formation of gob were analysed and the unloading was solved. Taking Chengchao Iron Mine as the engineering background, the model for analysing the instability of deep gob was established based on the mechanism of stress relief in deep mining. The energy evolution law was investigated by introducing the local energy release rate index (LERR), and the energy criterion of instability of surrounding rock was established based on the cusp catastrophe theory. The results showed that the evolution equation of the local energy release energy of the surrounding rock was quartic function with one unknown and the release rate increased gradually during the mining. The calculation results showed that the gob was stable. The LERR per unit volume of the bottom structure was relatively smaller, which mean the stability was better. The LERR distribution showed that there was main energy release in the horizontal direction and energy concentration in the vertical direction which meet the characteristics of deep mining. In summary, this model could effectively calculate the stability of surrounding rock in the formation of gob. The LERR could reflect the dynamic process of energy release, transfer and dissipation which provided an important reference for the study of the stability of deep mined out area.

• Journal of Game and Entertainment
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• v.2 no.1
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• pp.8-16
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• 2006

The development of multicast communication services in the Internet is expected to lead a stable packet transfer even though On-Line Games generate heavy traffic. The Core Based Tree scheme among many multicast protocols is the most popular and suggested recently. However, CBT exhibits two major deficiencies traffic concentration or poor core placement problem. Thus, measuring the bottleneck link bandwidth along a path is important to understand the performance of multicast. We propose a method in which the core router's state is classified into SS(Steady State), NS(Normal State) and BS(Bottleneck State) according to the estimated link speed rate, and also the changeover of multicast routing scheme for traffic overload. In addition, we introduce Anycast routing tree, an efficient architecture for constructing shard multicast trees.

• Journal of Advanced Navigation Technology
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• v.16 no.3
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• pp.518-525
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• 2012

The modulation transfer function is generally used as a method to estimate the characteristics of this kind of optical system because it cannot reappear or implement image of the object perfect. By the way, it is difficult to assess the optical system with existing MTF method since the reaction between diffraction and aberration of aperture is very complicate if the aberration is very small. The MTF has to be calculated considering the numerical aperture, defocusing, OPD and phase difference. We validate its feasibility using bessel function as an estimating method, and then realize it through illustration in this paper.