• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3962-3973
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• 2022

Several critical heat flux (CHF) correlations including the look-up table in the MARS code have been assessed for the prediction of CHF in a downward-flow narrow rectangular channel. For the assessment, we built an experiment database that covers pressures between 1.01 and 39.0 bar, gap sizes between 1.09 and 6.53 mm, mass fluxes up to 25,772 kg/m²s, and under one-sided and two-sided heating conditions. The results of the assessment showed that the Kaminaga correlation has the best overall prediction compared to others. However, because the correlation uses global variables, such as inlet and outlet subcooling and total heat transfer area, it is difficult to use in a system code. A new CHF correlation is then proposed by replacing the global variables in the Kaminaga correlation with local ones and adding correction factors to consider the effect of gap size, mass flux, and the number of heating walls. Additional correction factor is added to consider the effect of inlet subcooling. It is shown that the new one is better than the Kaminaga correlation and it is easy to implement to any system code.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.390-394
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• 2003

It is very important to simulate various mobile communication channels for the reliable system design and performance tests. Therefore, a new method is proposed in this paper to improve the conventional one for the purpose of the efficient channel simulation having various characteristics. A newly proposed method can simulate any narrow band channel very efficiently from the given Doppler power spectrum model. Also, it has many simulation advantages considering the variety of wireless channel conditions since parameters related with channel characteristics, such as a signal power, signal to noise ratio, direct signal power ratio, etc., can be easily changed according to various propagation environments to be tested.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.9
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• pp.638-643
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• 2003

Channel width dependence of hot-carrier effect in nMOSFET with shallow trench isolation is analyzed. $I_{sub}$- $V_{G}$ and $\Delta$ $I_{ㅇ}$ measurement data show that MOSFETs with narrow channel-width are more susceptible to the hot-carrier degradation than MOSFETs with wide channel-width. By analysing $I_{sub}$/ $I_{D}$, linear $I_{D}$- $V_{G}$ characteristics, thicker oxide-thickness at the STI edge is identified as the reason for the channel-width dependent hot-carrier degradation. Using the charge-pumping method, $N_{it}$ generation due to the drain avalanche hot-carrier (DAHC) and channel hot-electron (CHE) stress are compared. are compared.

• Journal of Advanced Navigation Technology
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• v.11 no.1
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• pp.9-16
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• 2007

In this paper, the Bit Error Ratio (BER) performances of the D8PSK modulation schemes for VDL Mode-2 are analyzed according to the matched and unmatched cases of the channel filters. The carrier frequency and phase offset effects are analyzed with unmatched case. Generally in digital transmission techniques, the Root Raised Cosine filters which are used as channel filters are applied to both sides at transmitter and receiver in order to achieve no ISI, but in VDL Mode-2, the Raised Cosine Filter is used only in transmission section and the receiver section uses general low pass filter, therefore we could not achieve ISI reduction effects but can have better spectrum quality. From the simulation results, the error probability is increased slightly (1~2dB) with use of un-matched channel filter, we got the conclusions that carrier phase offset do not effect to bit error ratio, but the frequency offset effect is so serious. Finally, narrow band D8PSK modulation signals are generated by the use of Digital Up-Converter and then its features are compared with analog modulator.

• Journal of the Korean Institute of Navigation
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• v.24 no.5
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• pp.423-433
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• 2000

Nowadays LNG has been beginning to take the place of petroleum as fuel all over the world and VLCC of LNG will take the same sea routes that had been used by VLCC tankers of petroleum in the last part of the 20th century. The transportation of LNG by a VLCC include more dangerous nature of sea peril than that of petroleum. We already know the dimensions of a disaster a LNG tanker could bring about in the case of the LNG tanker, Yuyo-Maru No. 10 in the Tokyo Bay of Japan in 1974. From the point of safety when we construct a LNG base or LNG pier in the base, the appropriate government authority and constructing company had better take sea pilots or some ships handling experts to participate in a prior consultation of the design of the project. A G/T 100,000 ton LNG base and pier were completed in November of 1996 in Inchon harbour in Korea and VLCC of LNG of G/T 100,000 ton class have been entering into the base ever since. This study was started and completed In comply with the requisition of the Sea Pilot Association of Inchon harbour in advance of the opening of the LNG base. As the entrance and exit channels leading to Inchon harbour were constructed in the years of 1930s, it was one of the most pressing works for Inchon sea pilots in 1996 to certify the method of safe passing maneuvering of a G/T 100,000 ton of LNG tanker through the Pudo narrow channel prior to commencing actual piloting of the VLCC of LNG. The authors made some mathematical models computing maneuvering of a vessel changing her course with her control surface through a narrow channel and computed maneuvering of a G/T 100,000 ton of LNG tanker and also made maneuvering simulations of the vessel by a desk-top simulator. The results of computations and simulations are well coincided with each other in qualitative aspects to assure safe passing of the VLCC of LNG.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2000.06a
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• pp.115-155
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• 2000

Nawadays LNG has been beginning to take the place of petroleum as fuel all over the world and VLCC tankers of LNG will take the same sea routes that had been used by VLCC tankers of petroleum in the last pat of he 20th century. The transportation of LNG by a VLCC include more dangerous nature of sea peril than that of petroleum. We already know the dimensions of a disaster a LNG tanker could bring about in the case of the LNG tanker, Yuyo-Maru No. 10 in the Tokyo Bay of Japan in 1974. From the point of safety when we construct a LNG base or LNG pier in the base, the appropriate government authority and constructing company had better take sea pilots or some ships handling experts to participate in a prior consultation of the design of the project. A G/T 100,000 ton LNG base and pier were completed in November of 1996 in Inchon harbour in Korea and LNG VLCC tankers of G/T 100,000 ton class have been entering into the base ever since. This study was started and completed to comply with the requisition of the Sea Pilot Association of Inchon harbour in advance of the opening of the LNG base. As the entrance and exit channels leading to Inchon harbour were constructed in the years of 1930s, it was one of the most pressing works for Inchon sear pilots in 1996 to certify the method of safe passing maneuvering of a G/T 100,000 ton LNG tanker through the Pudo narrow channel prior to commercing actual piloting of the LNG VLCC tanker. The author made some mathematical models computing maneuvering of a vessel changing her course with her control surface through a narrow channel and computed maneuvering of a G/T 100,000 ton LNG tanker and also made maneuvering simulations of the vessel by a desk-top simulator. The results of computations and simulations are well coincided with each other in qualitative aspects to assure safe passing of the LNG VLCC.

• Nuclear Engineering and Technology
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• v.51 no.8
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• pp.1886-1896
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• 2019

Modern small modular nuclear reactors can be built on a barge in ocean, therefore, their flow characteristics depend upon the ocean motions. In the present research, effect of rolling motion on flow and friction characteristics of laminar flow through vertical and horizontal narrow channels has been studied. A computer code has been developed using MPS method for two-dimensional Navier-Stokes equations with rolling motion force incorporated. Numerical results have been validated with the literature and have been found in good agreement. It has been found that the impact of rolling motions on flow characteristics weakens with increase in flow rate and fluid viscosity. For vertical narrow channels, the time averaged friction coefficient for vertical channels differed from steady friction coefficient. Furthermore, increasing the horizontal distance from rolling pivot enhanced the flow fluctuations but these stayed relatively unaffected by change in vertical distance of channel from the rolling axis. For horizontal narrow channels, the flow fluctuations were found to be sinusoidal in nature and their magnitude was found to be dependent mainly upon gravity fluctuations caused by rolling.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.74-84
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• 2008

UWB radio systems have drawn attention during the last few years. These systems are the core technique for ubiquitous home and enable to co-exist with other narrow band systems over the same frequency without interfering them. But UWB signals have a very low power per pulse, so they are affected by strong narrow band interferences. Specially, IEEE 802.11a systems which operate around 5GHz overlap the band of UWB signals and they will interfere with UWB systems significantly. In this paper, we propose a novel narrow band interference suppression method based on singular value decomposition(SVD) algorithm for DS-UWB in IEEE 802.15.4a channel model. The proposed method is very effective and robust for both a single user DS-UWB system and a multiuser DS-UWB system to reduce the narrow band interference.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.55 no.3
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• pp.252-263
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• 2019

In order to understand the tidal current and mean flow at the west channel of Yeoja Bay in the South Sea of Korea, numerical model experiments and vorticity analysis were carried out. The currents flow north at flood and south at ebb respectively and have the reversing form in the west channel. Topographical eddies are found in the surroundings of Dunbyong Island in the east of the channel. The flood currents flow from the waters near Naro Islands through the west channel and the coastal waters near Geumo Islands through the east channel. The ebb currents from the Yeoja Bay flow out along the west and the east channels separately. The south of Nang Island have weak flows because the island is located in the rear of main tidal stream. Currents are converged at ebb and diverged at flood in the northwest of Jeokgum Island. Tidal current ellipses show reversing form in the west channel but a kind of rotational form in the east channel. As the results of tide induced mean flows, cyclonic and anticyclonic topographical eddies at the northern tip but eddies with opposite spin at the southern tip are found in the west channel of Yeoja Bay. The topographical eddies around the islands and narrow channels are created from the vorticity formed at the land shore by the friction between tidal currents and the west channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.460-466
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• 2007

There are two coordination functions in IEEE 802.11 standard. One is PCF, polling based function, and the other is DCF, contention based function. DCF is simpler than PCF but the performance is similar with the latter. That's the reason why DCF is more popular than PCF. However, DCF has a risk of collision with other nodes in the network because the function is a distributed contention based one. CSMA/CA of DCF has collision avoidance algorithm in it, but the performance of avoidance algorithm has limitations. In this paper we proposed a new scheme called TAR(Tone-based Access scheme with Repetitive conention). In TAR, there is narrow contention-only channel other than original data transmitting channel, so that both a data transmission and the contention can be performed simultaneously. The TAR uses the same contention concept with the CSMA/CA, but it has the originality for the narrow contention channel and the repetitive contention scheme which greatly reduce the collision probability. We proved the performance of TAR by some simulations, and it showed good results.