• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.551-558
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• 2004

Recently, fuel prices have been continually raised in diesel engine. Such a change in the fuel price influences enormously the development trend of marine diesel engines for slow speed, In other words, the focus was shifted from large diameter and high speed to low fuel consumption. Accordingly, more efforts are being made for engine manufacturing and development to develop highly efficient engines. In this study. a single cylinder 4 stroke cycle DI slow speed diesel engine was designed and manufactured, a 4 stroke cycle was configured and basic performances were evaluated. The results are as follows. The optimal fuel injection timing had the lowest value when specific fuel consumption was in BTDC 8~$10^{\circ}$, a little more delayed compared to high speed diesel engines. Cycle variation of engines showed about 5% difference at full loads. This is a significantly small value compared to the cycle variation in which stable operation is possible, showing the high stability of engine operation is good. The torque and brake thermal efficiency of engine increased with an increase of engine 250-450 rpm. but fuel consumption ratio increased from the 450 rpm zone and thermal efficiency abruptly decreased. Mechanical efficiency was maximally 70% at a 400 rpm that was lower than normal engines according to the increase of mechanical frictional loss for cross head part. The purpose of this study was to get more practical engines by comparing the above results with those of slow speed 2 stroke cycle diesel engines.

• Korean Journal of Materials Research
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• v.19 no.9
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• pp.457-461
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• 2009

Recently, metal molding has become essential not only for automobile parts, but also mass production, and has greatly influenced production costs as well as the quality of products. Its surface has been treated by carburizing, nitriding and induction hardening, but these existing treatments cause considerable deformation and increase the expense of postprocessing after treatment; furthermore, these treatments cannot be easily applied to parts that requiring the hardening of only a certain section. This is because the treatment cannot heat the material homogeneously, nor can it heat all of it. Laser surface treatment was developed to overcome these disadvantages, and, when the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature.

• The Journal of the Korea Contents Association
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• v.2 no.1
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• pp.86-97
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• 2002

In this thesis, we propose a high-speed information network management mode based on layering and partitioning concepts of ITU-T G.805 We describe an information mood of the configuration of VP and VC networks and an information mode to manage faults in high-speed information networks. In order to efficient manage faults, us distinguish between an alarm with a fault that has negative effects on services and an alarm with an alert that barely affects services. Thus, we propose two types of computational models to treat all of these alarms, a fault alarm processing system and an alert alarm processing system. We also describe procedures of alarm processing and we describe the scope and processing course of NMS and SubNMS when rerouting a fault VP and VC fault connection. Lastly, we describe the implementation and analysis of the performance of the proposed fault alarm processing system. We compare the alarm processing tire of each priority according to the alarm occurrence ratio.

• Journal of Satellite, Information and Communications
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• v.3 no.1
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• pp.8-14
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• 2008

In this paper, we analyze throughput performance of MF-TDMA scheme and QS MC-DS/CDMA(quasi-synchronous MC-DS/CDMA) scheme based on scrambling on WH sequence and PPGC sequence in early frequency offset caused by high speed transfer terminal. QS MC-DS/CDMA scheme with scrambled WH sequence shows 5.7% higher throughput than MF-TDMA scheme and 8% higher throughput than QS MC-DS/CDMA with PPGC sequence in high speed transfer terminal environment such as maximum 1000Km/h speed with high frequency of Ka-band. Finally, we show that QS MC-DS/CDMA scheme with scrambled WH sequence is more efficient than traditional MF-TDMA scheme at the aspect of throughput in DVB-RCS system with Ka frequency band.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.6
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• pp.111-118
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• 2004

The work presented in this paper concerns the aerodynamic characteristics and compression wave generated in a tunnel when a high speed train enters it. A large number of solutions have been proposed to reduce the amplitude of the pressure gradient in tunnels and some of the most efficient solutions consist of (a) addition ofa blind hood, (b) addition of inclined part at the entrance, and (c) holes in the ceiling of the tunnel. These are numerically studied by using the three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, based on FEM method. Computational results showed that the smaller inclined angle leads to the lower pressure gradient of compression wave front. This study indicated that the most efficient slant angle is in the range from $30^{\circ}$ to $50^{\circ}$. The maximum pressure gradient is reduced by $26.81\%$ for the inclined angle of $30^{\circ}$ as compared to vertical entry. Results also showed that maximum pressure gradient can be reduced by $15.94\%$ in blind hood entry as compared to $30^{\circ}$ inclined tunnel entry. Furthermore, the present analysis showed that inclined slant angle has little effect on aerodynamic drag. Comparison of the pressure gradient between the inclined tunnel hood and the vertical entry with air vent holes indicated that the optimum inclined tunnel hood is much more effective way in reducing pressure gradient and increasing the pressure rise time.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.501-506
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• 2001

Computer modeling is essential to evaluate possible design of suspension for a railway vehicles. By creating a simulation, the engineers are able to assess the feasibility of a given design and change the design factors to get a better design. But if one wishes to perform complex analysis on the simulation, such as railway vehicle dynamic, the computational time can become overwhelming. Therefore, many researchers have turned to surrogate modeling. A surrogate model is essentially a regression performed on a data sampling of the simulation. In the most general sense, metamodels(surrogate model) take the form $y(x)=f(x)+{\varepsilon}$, where y(x) is the true simulation output, f(x) is the metamodel output, and $\varepsilon$ is the error between the two. In this paper, a second order polynomial equation is partially used as a metamodel to represent the forty-six dynamic performances for high speed train. The number of factors as design variables of the metamodel is twenty-nine, which are composed the dynamic characteristics of suspension. This metamodel is used to search the optimum values of suspension characteristics which minimize the dynamic responses for high speed train. This optimization is a multi-objective problem which have many design variables. This paper shows that the response surface model which is made through the design of analysis of computer experiments method is very efficient to solve this complex optimization problem.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10b
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• pp.647-649
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• 1998

본 논문에서는 초고속 인터넷 통신과 서비스를 효율적으로 구축, 개발하기 위해 현재 대두되는 여러 구축 방안들을 좀 더 구체적으로 정형화시킨 3단계 방안을 제시하고 일부 ISP 업체에 이 방안을 시험적으로 적용해 봄으로써 미래 초고속 인터넷 통신 구축의 확실한 해결책이 무엇인지를 검증해 볼 수 있는 방향을 제시했다.

• 전기의세계
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• v.29 no.12
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• pp.804-808
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• 1980

The specific objective of this paper is to develop an useful power flow program for real time applications. Great emphasis has been put to the combination of algorithms and programming techniques for high speed, low storage, reliability, versatility and simplicity. A practical application in several cases has produced satisfiable results.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.11a
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• pp.450-450
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• 2004

• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.8
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• pp.1085-1090
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• 1995

The Discrete Cosine Transform(DCT) is effective technique for image compression, which is widely used in the area of digital signal processing. In this paper, an efficient DCT processor is proposed and simulated by using Verilog HDL. This algorithm is improved 60% in processing speed, but it's somewhat complicate compared with Y. Arai's algorithm. This algorithm will be used efficiently for real time image processing.