• Journal of the Society of Naval Architects of Korea
• /
• v.50 no.6
• /
• pp.399-406
• /
• 2013

In the present study, the flat plate model test method is developed to evaluate the skin friction of the marine coating in the cavitation tunnel. Six-component force balance is used to measure the profile drag of the flat plate and strut. LDV(laser Doppler velocimetry) technique is also employed to evaluate the drag and to figure out the reason of the drag reduction. The flow velocities above the surface can be used to assess the skin friction, combined with direct force measurement. Since the vortical structure in the coherent turbulence structure influences on the skin friction in the high Reynolds number regime, the interaction between the turbulence structure and the surface wall is paying more attention. This sort of thing is important in the passive control of the turbulent boundary layer because the skin friction can't be determined only by wall condition. As complicated flow phenomena exist around a paint film, systematic measurement and analysis are necessary to evaluate the skin friction appropriately.

• Nuclear Engineering and Technology
• /
• v.2 no.3
• /
• pp.163-178
• /
• 1970

Deformation modes at room temperature and the interaction between slip lines and ${\gamma}$' precipitate particles in heat treated Rene 41 were studied by means of replica techniques in an electron microscope. The alloy had been deformed by compression after aging for times up to 9300 hr at 76$0^{\circ}C$ and 87$0^{\circ}C$. The slip structure observed was similar to that of o brass, i.e., consisting of single slip lines occurred on the｛111｝<110> system. The slip structure was also correlated with aging conditions. Slip lines appeared to pass through ${\gamma}$' particles, shearing them with the matrix even after a prolonged heat treatment. It was concluded on the basis of comparison with previously published data that ${\gamma}$' particles remain at least partially coherent with the matrix even in a greatly overaged condition.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.9 no.2
• /
• pp.131-140
• /
• 1998

MAI(Multi-Access Interference) and fast channel variation due to the fading environment are the major problems in the mobile CDMA communication systems. Recently, interest has been increasing in applying the Adaptive Linear MMSE Detector to MAI cancellation in the CDMA reverse link. In this paper, we propose a modified Adaptive Linear MMSE Detector structure which can be used in Long-duration code CDMA system in the presence of independent Rayleigh fading. We use independent multiple tap-weight vector structure to cope with the variation of spreading sequence pattern between neighbor symbols because of the Long-duration code. In this case, more exact channel parameter estimation is required. To solve this problem, we use coherent CDMA structure which can track the channel parameters like amplitude and phase by employing the low power pilot channel in the CDMA reverse link.

• Journal of the Korean Dietetic Association
• /
• v.11 no.3
• /
• pp.273-285
• /
• 2005

This study examined the structure and contents of the information provided by the web sites, in terms of clarity, business goal, authority, sustainment of operation and responsibility of customer care, as well as menus. The findings from the analysis of 217 web sites selected from 5 major portal sites, are 1) most of catering business over internet are located around Seoul area, 2) almost 80% of the selected sites are administered by professional agents or firms while the remnants by individuals, 3) except menu and price, any additional information is hardly shown, 4) about three quarter of the sites opened after 2001, that is coherent with the trend of the growth of internet users and eating-out, 5) it is strongly required to create healthful cyber space for the customers, 6) a small number of the sites(12.4%) try to manage access from customers, 7) many sites(73.7%) open the channels for feedback from the customers 8) among the types of catering services offered by the sites, home party is the most popular and the kinds of cuisine, Korean, Japanese, and Chinese, are divided into almost same proportion of the sites, 9) the average number of dishes is 33.5, 10) they offer 7 to 8 different dishes of grain, 4 to 6 of meat, 4 to 10 of fishes, 5 to 13 of vegetables, 1 of fruits, and 1 to 3 of dairy products, 11) The majority of price level is ₩15,001 - ₩20,000.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.13 no.10
• /
• pp.2039-2044
• /
• 2009

The PSK carrier signal recovery circuit using multi-layer coupled line was analyzed and designed. The fabricated carrier recovery 6 port element with multi-layer coupled line structure gets the simple architecture. It is possible to implement the carrier signal recovery circuit of the same structure with the multi-layer six port phase correlator of the direct receiver front-end. Based on the analysis of RML carrier recovery circuit using the multi-layer coupled line 6-port phase correlator, the multi-layer coupled line carrier signal recovery structure for multi-mode coherent demodulation was proposed. The fabricated multi-layer coupled line carrier signal recovery circuit for quadrature phase shift-keying shows a good carrier signal characteristic with a constant phase and phase error below ${\pm}3o$.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.13 no.6
• /
• pp.545-555
• /
• 2020

This paper presented efficient transceiver structure using sub-band processing for underwater communication in terms of covertness and performance improvement. In aspect of covertness, encrypted coded-bits are divided into groups, and center frequency and sub band are determined by coded-bits of each group. Therefore, as center frequencies are changed randomly, it maintain the covertness effectively. In aspect of performance improvement, the performance of underwater communication mainly depends on multi-path propagation characteristics, Doppler-spread, and frame synchronization. Accordingly, in order to overcome these effects, non-coherent energy detector and turbo equalization method are employed in receiver side. Furthermore, optimal frame synchronization was proposed. Through the simulation and lake experiment, performance analysis was conducted. Especially in the lake experiment, as a result of applying optimal frame synchronization method to receiver structure, errors are corrected in most frames.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.4
• /
• pp.167-173
• /
• 1999

In this paper the failure behavior of the reinforced earth retaining wall structures according to the deformed types of the face was studied by model test using carbon rods. In model test the behavior of the face for the model of the reinforced earth wall was divided into three cases : the displacement of the top part(case 1), the lateral displacement(case 2) and the displacement of the lower part (case 3). The photographic method was applied to examine the failure line of the deformed wall with the naked eye. The failure line shows a parabolic shape for case 1, a large circular arc for case 2 and a logarithmic spiral for case 3 in the experimental results. The design failure line for the coherent gravity structure hypothesis was most similar to the failure line for the case of the lower part displacement.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.7
• /
• pp.1036-1043
• /
• 1993

GaAs/AIGaAs resonant tunneling structures have been grown by atmospheric pressure MOCVD. Resonant tunneling diodes fabricated with the structure grown at 650t showed a high peak-to-valley (P/V) current ratio of 2.35 at room temperature. P/V current ratio increased to 15.3 at 77K. Numerically calculated peak current agrees well with the experimental result. Resonant tunneling diodes with AIGaAs as a barrier and InGaAs as a quantum well and a spacer layer yielded a high P/V current ratio of 4.0 and a peak current density of 8.6KA/c# at room temperature because of increased carrier supply.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.6
• /
• pp.2160-2170
• /
• 1991

Three-dimensional turbulent structures in the near field of elliptic jet were experimentally investigated by using a three-color, three-component Laser Doppler Velocimeter. The Reynolds number based on the nozzle exit velocity and nozzle equivalent diameter(De) was about 4*10$^{4}$. The turbulent characteristics of a sharp-edged elliptic nozzle with aspect ratio of 2 were analyzed along major and minor axis at X/De=2,3,5,7 and along the centerline up to X/De=14. Quantities measured at each point with the 3-D LDV system were three orthogonal velocity components, turbulent intensity, skewness, flatness, and Reynolds shear stress. The nondimensional mean velocities coincided well with the Schlichting's empirical curve with going downstream. Elliptic jet of AR=2 had two switching points at about X/De=2 and 16. The turbulent intensity along the minor axis was distributed widely than that along the major axis. In the near field, X/De<5, the Reynolds shear stresses of the inner part of the elliptic jet had negative value, which indicated the enhancement of entrainment toward the inner part.

• Advances in materials Research
• /
• v.8 no.4
• /
• pp.295-311
• /
• 2019

In this study, a three-dimensional Finite Element Model has been developed to estimate the size of the weakened zone in a bi-material a ceramic bonded to metal. The calculations results were compared to those obtained using Scanning Electron Microscope (SEM). In the case of elastic-plastic behaviour of the structure, it has been shown that the simulation results are coherent with the experimental findings. This indicates that Finite Element modeling allows an accurate prediction and estimation of the weakening effect of residual stresses on the bonding interface of Alumina. The obtained results show us that the three-dimensional numerical simulation used by the Finite Element Method, allows a good prediction of the weakened zone extent of a ceramic, which is bonded with a metal.