• ETRI Journal
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• v.24 no.2
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• pp.153-160
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• 2002

High Altitude Platforms-craft maintaining stations in the stratosphere at altitudes of around 20 km-have been proposed as a means of supporting wireless telecommunications. They could exploit the best aspects of both terrestrial and satellite systems and support efficient frequency re-use plans. For solar powered platforms the power available for the downlink amplifiers may be minimal, particularly at night and/or higher latitudes. This paper discusses a novel type of link based on a modulated retro-directive transponder carried by the HAP. Relying chiefly on the ground station infrastructure, this would substantially reduce power consumption on the platform. We investigate the efficiency of the transponder aperture as a function of its area by developing general models for losses in the transmission lines which interconnect antenna pairs in the retro-directive array.

• Korean Journal of Computational Design and Engineering
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• v.10 no.6
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• pp.381-391
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• 2005

The design methodology of injection molding die has been changed from two-dimensional drafting to three-dimensional solid modeling, which is due to many advantages over the conventional methodology in terms of design modification and data associativity. In addition to the solid modeling capability, it is required for a mold designer to utilize a database management system that facilitates efficient mold design. In the paper presented is the implementation of a software program which automatically generates three-dimensional mold-bases including standard parts and slider parts, conforming to given geometric constraints. It is based on a commercial CAD system (Unigraphics NX) along with related API (application program interface) libraries. The research is expected to reduce design efforts and simplify construction of a complex three-dimensional mold-base model that is comprised of standard parts and slider parts, by use of the three-dimensional database and automatized geometric dimensioning.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.91-96
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• 2003

In this report, numerical investigations have demonstrated, that the displacement underneath a moving loa야ng reach a maximum value, if the speed of the load is equal to propagation velocity of the maximum wave. The load speed for which the maximum displacement occurs is called critical speed. The critical speed divides the velocities in a subcritical and a super-critical region. By means of calculations the dynamic behaviour of the slab track-soil is investigated. For concrete slab track dynamic wheel load are given in dependence of relevant excitation mechanism and speed of the train. These loads can be used for the dimensioning of the track as well as for the prognosis of the vibrations at the track and the surrounding soil.

• IE interfaces
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• v.13 no.4
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• pp.709-716
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• 2000

In this paper, We analyze a capacity dimensioning and performance of the access line to the X.25 packet network when the AO/DI internet service is connected via D-channel. We show the forecasting methodology of the traffic demand of the D-channel internet services when the TDX-1OA switching system accommodates the target number of subscriber. Based on the traffic demand forecast, the required capacity of the access line is suggested to prevent bottleneck problem in the access line to the X.25 packet network.

• Structural Engineering and Mechanics
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• v.78 no.1
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• pp.67-75
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• 2021

This work studies the behaviour of a steel portal frame selection under fire exposure, considering both span lengths and fire exposure times as variables. Such structures combine carbon steel (S275), fireproof micro-alloyed steel (FR), and coatings of intumescent paint with variable thicknesses, improving thereby the flame retardant behaviour of the steel structure. Thus, the main contribution of this study is the optimization of the portal frames by combining both steels, analysing the resulting costs influence on the final dimensions. Besides, the topological optimization of each steel component within the structure is also defined, in accordance with the following variables: weather conditions, span, paint thickness, and cost of steel. The results mainly confirmed that using both FR and S275 grades with intumescent painting is the Pareto optimum when considering performance, feasibility and costs of such portal frames widely used for industrial facilities.

• Steel and Composite Structures
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• v.18 no.1
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• pp.149-163
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• 2015

Orthotropic steel highway bridges exist almost everywhere in world, especially in Europe. The design of these bridges started very early in 20th century and ended with a conventional orthotropic steel bridge structure, which is today specified in DIN FB 103. These bridges were mostly built in 1960's and exhibit damages in steel structural parts. The primary reason of these damages is the high pressure that is induced by wheel- loads and therefore damages develop especially in heavy traffic lanes. Constructive rules are supplied by standards to avoid damages in orthotropic steel structural parts. These rules are first given in detail in the standard DIN 18809 (Steel highway- and pedestrian bridges- design, construction, fabrication) and then in DIN- FB 103 (Steel bridges). Bridges built in the past are today subject to heavier wheel loads and the frequency of loading is also increased. Because the vehicles produced today in 21st century are heavier than before and more people have vehicle in comparison with 20th century. Therefore dimensioning or strengthening of orthotropic steel bridges by using stiffer dimensions and shorter spans is an essence. In the scope of this study the complex geometry of conventional steel orthotropic bridge is generated by FE-Program and the effects of cross beam web thickness and cross beam span on steel bridge are assessed by means of a parameter study. Consequently, dimensional and constructional recommendations in association with cross beam thickness and span will be given by this study.

• Korean Journal of Computational Design and Engineering
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• v.13 no.3
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• pp.235-242
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• 2008

This paper proposes a method for improving the process plan quality by use of dimensional tolerances. Dimensioning and tolerancing plays a key role in manufacturing process plan because the final part must ensure conformance with the dimensions and tolerances in its drawing. As a first step for the improvement of process plan quality, two resultant tolerances in design and process plan should be compared each other, and so a tolerance chart is used for acquisition and comparison of the two tolerances. In addition to two kinds of design and manufacturing tolerances, operational sequences or paths for the resultant dimension and tolerance are additionally recognized for measuring the quality of process plan quantitatively. Rooted tree is applied to find the related paths for the manufacturing resultant tolerances. A quality coefficient is defined by the components of two tolerances and their relations, the paths related to manufacturing resultant tolerances and the difficulty of an operation. In order to improve the quality of manufacturing process plan, the paths that two kinds of tolerances are the same or different in the rooted tree are recognized respectively and a method for tolerance rearrangement is developed. A procedure for improving the quality is suggested by combining the coefficient and the tolerance rearrangement method. A case study is applied to illustrate the efficiency of improvement method.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.1
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• pp.139-144
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• 2010

In the automotive electronic industry, the development of vehicle's door wiring harness (W/H) system for new applications is driven continuously for the low-cost and the high strength performance for electronic components. The problem of the fatigue strength estimation for materials and components containing natural defects, inclusions, or inhomogeneities is of great importance both scientifically and industrially. This article gives some insight into the dimensioning process with special focus on the fatigue analysis of wiring harness (W/H) in vehicle's door structures. The results from endurance tests using slim test specimens were compared with the results from FEM for predicted fatigue life. The expectation for the life of components is affected by the microstructural features with complex stress state arising from the combined service loading and residual stresses.

• The Journal of the Korea Contents Association
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• v.5 no.3
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• pp.175-181
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• 2005

Recent measurements of local-area and wide-area traffic have shown that network traffic exhibits at a wide range of scales-Self-similarity. Self-similarity is expressed by long term dependency, this is contradictory concept with Poisson model that have relativity short term dependency. Therefore, first of all for design and dimensioning of next generation communication network, traffic model that are reflected burstness and self-similarity is required. Here self-similarity can be characterized by Hurst parameter. In this paper, when different many data traffic being integrated under various environments is arrived to communication network, Hurst Parameter's change is analyzed and compared with simulation results.

• Electronics and Telecommunications Trends
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• v.17 no.5 s.77
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• pp.37-46
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• 2002

이동통신에서는 무선자원의 효율적인 사용을 위하여 variable rate vocoder 및 VoX 기법을 이용한 음성 전송이 일반적 추세이며, 버스티 특성을 갖는 패킷 트래픽의 경우 statistical multiplexing을 이용하여 무선 채널의 사용을 극대화 시킨다. 트래픽 밀도를 나타내는 Erlang 용량은 일정속도의 회선교환 트래픽에 대하여 동시에 점유할 수 있는 dedicated circuit의 수에 기초하는 개념이므로 statistical multiplexing으로 처리되는 데이터 패킷의 트래픽 밀도는 queuing model에 근거한 데이터 스루풋이 현실적이다. 그러나 이동통신 시스템에서 트래픽 특성을 달리하는 circuit 및 패킷 타입의 혼합 서비스가 동시에 제공될 경우 네트워크 planning을 위한 구성 시스템의 용량산정을 위해 트래픽 밀도의 통합적인 표현을 요구한다. 따라서 Erlang 용량과 데이터 스루풋의 상호 변환을 통하여 네트워크 구성요소의 용량 산정에 적당한 용량표현을 선택할 수 있다. 본 고에서는 트래픽 처리기로서의 통신시스템을 기술하기 위하여 일반적인 텔레트래픽 시스템 모델과 파라미터를 정의한다. 또한 음성 및 비음성 서비스의 혼합 트래픽 환경에서 트래픽 밀도계산을 위한 Erlang 용량과 데이터 스루풋의 상호 변환 관계를 소개한다. 마지막으로 3G1x 무선접속환경에서 음성 및 HSPD 서비스가 공존할 경우 기지국 CE dimensioning에 필요한 혼합 트래픽 Erlang 용량 산출 방법을 기술한다.