• International Journal of Automotive Technology
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• 제8권4호
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• pp.403-411
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• 2007

This article describes a methodology based on experiments and 1D modeling work related to the exhaust system analysis of a small two-stroke engine. The primary goal of this work was to understand how the design criteria of a compact exhaust system influenced the exhaust port pressure, since its evolution controls not only engine performance but also exhaust emissions. On the experimental side, a fully instrumented 50cc two-stroke engine was used to check the behavior of three different exhaust systems. A problem related to instantaneous pressure measurements in unsteady, hot flow was detected and solved during the study. To build the 1D model of the three exhaust systems, experimental information on the steady flow and the impulse test rigs was obtained under controlled conditions in specific facilities. Accurate comparisons between measured and calculated exhaust port instantaneous pressures were obtained from the following different exhaust system configurations: a straight duct, a tapered pipe and the three compact exhaust systems. The last step in the method used this model to analyze the pressure waves inside the exhaust system and detect the influence of the geometric parameters. The results should lead to improvements in the design process of complex compact exhaust systems in two-stroke engines.

• 융합보안논문지
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• 제7권4호
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• pp.29-34
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• 2007

본 논문에서는 CB 트라이의 단점을 보완한 RCB 트라이를 제안한다. 먼저 CB 트라이의 경우 처음으로 축약된 구조를 시도하였으나 데이터의 양이 증가함에 따라 트리의 균형을 맞추기 위해 사용되는 더미노드들로 인해 삽입에 상당한 어려움을 가지고 있다. 반면 계층적으로 표현한 HCB 트라이는 map이 오른쪽으로 증가하는 것을 막기 위해 일정 깊이를 주어 깊이에 다다르면 새로운 트리를 만들어 연결시키는 방법을 이용하였다. 결과적으로 입력과 검색 속도를 상당히 빠르게 진전시킬 수 있었으나 CB 트라이와 마찬가지로 더미노드를 사용하고 여러 트리의 링크를 사용하기 때문에 저장공간이 커지는 단점을 안고 있다. 본 논문에서 제안한 RCB 트라이는 더미노드를 완전히 없애 성능이 60% 향상되었다.

• Advances in Energy Research
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• 제1권1호
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• pp.53-78
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• 2013

Methane carbon dioxide reforming (MCDR) is a promising way of utilizing greenhouse gas for hydrogen-rich fuel production. Compared with other types of reactors, Compact Reformers (CRs) are efficient for fuel processing. In a CR, a thin solid plate is placed between two porous catalyst layers to enable efficient heat transfer between the two catalyst layers. In this study, the physical and chemical processes of MCDR in a CR are studied numerically with a 2D numerical model. The model considers the multi-component gas transport and heat transfer in the fuel channel and the porous catalyst layer, and the MCDR reaction kinetics in the catalyst layer. The finite volume method (FVM) is used for discretizing the governing equations. The SIMPLEC algorithm is used to couple the pressure and the velocity. Parametrical simulations are conducted to analyze in detail the effects of various operating/structural parameters on the fuel processing behavior.

• 천문학회지
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• 제46권6호
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• pp.243-251
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• 2013

We present results on the intrinsic brightness temperature of a sample of compact radio sources observed at 86 GHz using the Global Millimeter VLBI Array. We use the observed brightness temperatures at 86 GHz and the observed superluminal motions at 15 GHz for the sample in order to constrain the characteristic intrinsic brightness temperature of the sample. With a statistical method for studying the intrinsic brightness temperatures of innermost jet cores of compact radio sources, assuming that all sources have the same intrinsic brightness temperature and the viewing angles of their jets are around the critical value for the maximal apparent speed, we find that sources in the sample have a characteristic intrinsic brightness temperature, $T_0=4.8^{+2.6}_{-1.5}{\times}10^9K$, which is lower than the equipartition temperature for the condition that the particle energy equals to the magnetic field energy. Our results suggest that the VLBI cores seen at 86 GHz may be representing a jet region where the magnetic field energy dominates the total energy in the jet.

• Journal of information and communication convergence engineering
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• 제14권4호
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• pp.222-226
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• 2016

A design method for a compact square loop antenna fed by a microstrip (MS) line for indoor digital television (DTV) applications is proposed. The proposed antenna consists of a square loop, circular sectors, and an MS line. The square loop combined with circular sectors is printed on one side of a substrate, and a $75-{\Omega}$ MS line is printed on the other side. The circular sectors are used as a wideband balun or transition to connect the MS line and the square loop. A prototype of the proposed square loop antenna operating in the DTV band (470-806 MHz) is designed and fabricated on an FR4 substrate. Experimental results show that the proposed antenna has the desired impedance characteristics in the frequency band of 464-1,220 MHz (89.8%) for a voltage standing wave ratio (VSWR) of <2 covering the DTV band, and a broadside gain of 0.8-3.3 dBi in the DTV band.

• 설비공학논문집
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• 제13권11호
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• pp.1114-1124
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• 2001

The application of carbon dioxide as an attractive natural working fluid in air cooling and heating system is increasingly important in view of the CFC substitution problem. The thermal performance of compact evaporator was analyzed using section-by-section method. The effects of the two-dimensional nonuniformity of air flow through the evaporator is presented. The detrimental effect of the aid flaw nonuniformity on the thermal performance of the evaporator is found to be significant for many typical applications. It is shown that total heat transfer rate of evaporator using $CO_2$ is higher than that using R134a at the simulation conditions.

• 한국세라믹학회지
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• 제31권4호
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• pp.347-358
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• 1994

Creep densification and grain growth of alumina powder compacts during high temperature processing were investigated. The creep densification and grain growth of alumina powder compacts during various sintering processes were analyzed by employing the consitutive model by Kwon and Kim. Theoretical results from the constitutive model were compared with various experimental data of alumina powder compacts in the literature including pressureless sintering, sinter forging and hot pressing. The proposed constitutive equations were implemented into finite element analysis program (ABAQUS) to simulate densification for more complicated geometry and loading conditions. The effects of friction between die and powder compact or punch and powder compact during sinter forging and hot pressing are investigated by using the finite element method. Also, high temperature forming processing of alumina compact with complicated shape was simulated.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.270-271
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• 2006

Nd-Fe-B type powder was sintered using spark plasma sintering method. Fabricated compact sintered at the temperature of $700\;^{\circ}C$, is found to be a composite magnet with Nd-Fe-Co-B and ${\alpha}-Fe$. The compact sintered at $700\;^{\circ}C$ shows slightly low coercivity and large remanent magnetization comparing to the compact sintered at $600^{\circ}C$ due to the formation of ${\alpha}-Fe$ phase, resulting in the large maximum energy product. Maximum energy product tends to decrease with decreasing thickness of sintered compacts below 0.5 mm in thickness.

• 열처리공학회지
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• 제34권2호
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• pp.60-65
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• 2021

In this study, the effect of pressure type and foaming agent on the microstructural change of Al foam produced by powder compact processing was investigated. Better foaming characteristic is easily obtained from extrusion process with strong plastic deformation and preheating than that by uniaxial pressing with preheating. In current powder compact foaming process using TiH2/MgH2 mixture as a foaming agent, a temperature of 670℃ and addition of 30% MgH2 in TiH2 foaming agent was chosen as the most suitable foaming condition. The aluminum (Al) foams with maximum porosity of around 70%, relatively regular pore size and distribution were successfully produced by means of the powder metallurgy method and extrusion process.

• 대한수학회논문집
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• 제38권1호
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• pp.243-256
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• 2023

We deal with a type of inverse pseudo-orbit tracing property with respect to the class of continuous methods, as suggested and studied by Pilyugin [54]. In this paper, we consider a continuous method induced through the diffeomorphism of a compact smooth manifold, and using the concept, we proved the following: (i) If a diffeomorphism f of a compact smooth manifold M has the robustly pointwise inverse pseudoorbit tracing property, f is structurally stable. (ii) For a C1 generic diffeomorphism f of a compact smooth manifold M, if f has the pointwise inverse pseudo-orbit tracing property, f is structurally stable. (iii) If a diffeomorphism f has the robustly pointwise inverse pseudo-orbit tracing property around a transitive set Λ, then Λ is hyperbolic for f. Finally, (iv) for C¹ generically, if a diffeomorphism f has the pointwise inverse pseudo-orbit tracing property around a locally maximal transitive set Λ, then Λ is hyperbolic for f. In addition, we investigate cases of volume preserving diffeomorphisms.