• Title/Summary/Keyword: boundary characteristics

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Efficient electromagnetic boundary conditions to accelerate optimization of RF devices

  • Cho, Yong-Heui
    • International Journal of Contents
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    • v.7 no.4
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    • pp.50-55
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    • 2011
  • To achieve efficient field formulations and fast numerical computations, the reciprocal relations and equivalence between tangential and normal boundary conditions for electromagnetic fields are discussed in terms of the Maxwell's differential equations. Using the equivalence of each boundary condition, we propose the six essential boundary conditions, which may be applicable to matching electromagnetic discontinuities to efficiently design RF devices. In order to verify our approach, the reflection characteristics of a rectangular waveguide step are compared with respect to six essential boundary conditions.

Characteristics of the major tribological parameters in boundary lubrication (경계윤활에서의 주요 Tribological 인자의 특성)

  • 류종관;김대은
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1998.10a
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    • pp.82-90
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    • 1998
  • Machines that normally operate under fluid film lubricated condition also experience surface damage. This is largely due to the failure of the lubricant film which leads to boundary lubrication. Thus, it is important to have a good understanding of boundary lubrication behavior. In this paper the major tribological parameters that influence the boundary lubrication properties are evaluated. It is shown that disk roughness, hardness and normal load affect the friction and wear of metals in boundary lubrication. Also, the mechanism of surface damage is attributed to abrasion and wear particle interaction.

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Design of a Sliding Mode Controller with Nonlinear Boundary Transfer Characteristics

  • Kim, Yoo K.;Gi J. Jeon
    • 제어로봇시스템학회:학술대회논문집
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    • 2001.10a
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    • pp.164.2-164
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    • 2001
  • Sliding mode control (SMC) with variable nonlinear boundary layer is proposed. Two Fuzzy logic controllers (FLCs) are used to decide both boundary layer thickness and nonlinear interpolation using sigmoid function in the boundary layer. The nonlinear interpolation in the boundary layer suing FLC reduces stead state error and chattering. Sigmoid function is used to nonlinear interpolation in the boundary layer sigmoid function parameter with FLC. To demonstrate its performance, the Proposed control algorithm is applied to a simple nonlinear system.

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Generation of inflow turbulent boundary layer for LES computation

  • Kondo, K.;Tsuchiya, M.;Mochida, A.;Murakami, S.
    • Wind and Structures
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    • v.5 no.2_3_4
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    • pp.209-226
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    • 2002
  • When predicting unsteady flow and pressure fields around a structure in a turbulent boundary layer by Large Eddy Simulation (LES), velocity fluctuations of turbulence (inflow turbulence), which reproduce statistical characteristics of the turbulent boundary layer, must be given at the inflow boundary. However, research has just started on development of a method for generating inflow turbulence that satisfies the prescribed turbulence statistics, and many issues still remain to be resolved. In our previous study, we proposed a method for generating inflow turbulence and confirmed its applicability by LES of an isotropic turbulence. In this study, the generation method was applied to a turbulent boundary layer developed over a flat plate, and the reproducibility of turbulence statistics predicted by LES computation was examined. Statistical characteristics of a turbulent boundary layer developed over a flat plate were investigated by a wind tunnel test for modeling the cross-spectral density matrix for use as targets of inflow turbulence generation for LES computation. Furthermore, we investigated how the degree of correspondence of the cross-spectral density matrix of the generated inflow turbulence with the target cross-spectral density matrix estimated by the wind tunnel test influenced the LES results for the turbulent boundary layer. The results of this study confirmed that the reproduction of cross-spectra of the normal components of the inflow turbulence generation is very important in reproducing power spectra, spatial correlation and turbulence statistics of wind velocity in LES.

A Study on the Buckling Characteristics of Double-Layer Latticed Domes whose Boundary Configuration are Elliptical (경계부 형상이 타원형인 복층 래티스 돔의 좌굴 특성에 관한 연구)

  • Seo, Young-Ill;Kwun, Ik-No;Kwun, Taek-Jin
    • Journal of Korean Association for Spatial Structures
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    • v.2 no.3 s.5
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    • pp.71-79
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    • 2002
  • The purpose of this paper is to study the buckling characteristics of elliptical latticed domes under conservative loading conditions. The latticed domes are usually designed in geometrically spherical shape. For this type of latticed domes, many researchers have researched and even the simplified estimation codes for the buckling load level have been available. However, geometrically elliptical latticed domes have been often constructed, and show different buckling characteristics following with geometrical parameters as rise-to-span ratio and so on. Therefore, it is necessary to investigate the general tendency of buckling characteristics of the elliptical latticed domes. In this paper, to find out some buckling characteristics of elliptical latticed domes, height, boundary configuration and gap are used as the shape coefficients. For each model with different parameters, the eigen values and the buckling loads are evaluated.

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A study on the boundary layer characteristics of TP620 hydrofoil in the steady state (정상상태인 박용 TP620 익형의 경계층 특성 연구)

  • 서봉록;김시영
    • Journal of Advanced Marine Engineering and Technology
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    • v.10 no.4
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    • pp.50-56
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    • 1986
  • This report deals with a study on the boundary layer characteristics of TP620 hydrofoil in the steady state by using two dimensional boundary layer theory. On the basis of complex velocity and laminar and turbulent boundary layer theory, the author attempts to know some tendency by evaluating the performance characteristic values of TP620 hydrofoil working in a uniform flow. In deriving characteristic values, he calculates numerically velocity, momentum thickness, skin friction coefficient, shape factor, and displacement thickness on the TP620 hydrofoil working at each attack angle in a uniform flow. Applying this present numerical calculation using Thwaites' and Head's method, the results of boundary layer on the hydrofoil are shown to be influenced by surface velocity and attack angle.

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A study on the Design Expression of the Boundary surfaces and Environment-friendly characteristics in contemporary Housing (현대 집합주택 내외부 경계 표현방식과 친환경적 특성에 관한 연구)

  • Lee, Dong-Ki
    • Proceeding of Spring/Autumn Annual Conference of KHA
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    • 2009.04a
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    • pp.253-257
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    • 2009
  • Along with emergence of recent issues such as 'minimization of energy consumption' and 'natural environment and human health' amid the flow of requirements for nature-friendly architecture, attempts for boundary, which has a variety of possibilities as the intermediate territory between interior and exterior space of the architecture, have been pursued actively. On the ground of close relationships between urban area and architecture in a modern society, the boundary between interior and exterior is being exhibited in a wide variety of way of expressions, not as a single plane any longer. In line with this, researcher analyzed interior and exterior boundary according to its type targeting modern housing complex in Europe, and also investigated characteristics thereof. And, having provided the results as basic materials in order to seek amenity of local apartment houses and diversification of housing plan as well, the researcher intends to be of a help to bring physical changes in both building and exterior design, and also to give a new meaning in an environment-friendly aspect.

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Extraction and Regularization of Various Building Boundaries with Complex Shapes Utilizing Distribution Characteristics of Airborne LIDAR Points

  • Lee, Jeong-Ho;Han, Soo-Hee;Byun, Young-Gi;Kim, Yong-Il
    • ETRI Journal
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    • v.33 no.4
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    • pp.547-557
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    • 2011
  • This study presents an approach for extracting boundaries of various buildings, which have concave boundaries, inner yards, non-right-angled corners, and nonlinear edges. The approach comprises four steps: building point segmentation, boundary tracing, boundary grouping, and regularization. In the second and third steps, conventional algorithms are improved for more accurate boundary extraction, and in the final step, a new algorithm is presented to extract nonlinear edges. The unique characteristics of airborne light detection and ranging (LIDAR) data are considered in some steps. The performance and practicality of the presented algorithm were evaluated for buildings of various shapes, and the average omission and commission error of building polygon areas were 0.038 and 0.033, respectively.

A Study on the Design Characteristics of Communal Spaces in Vertical Urban Multi-Family Housing Community -Focused on the Territories of a Unit Boundary, Building Interior and Exterior Boundary- (수직적 도시 공동주거 커뮤니티에 적용된 공유공간의 계획특성 연구 -단위세대 경계부와 주거동 내부 및 경계부 영역을 중심으로-)

  • Cho, Min-Jung
    • KIEAE Journal
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    • v.11 no.5
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    • pp.55-67
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    • 2011
  • The purpose of this research is to find applicable design characteristics and methods of communal spaces in vertical urban multi-family housing. With this goal, several overseas' multi-family housing projects are selected and their communal spaces are identified. The design characteristics of the communal spaces are analyzed with a special focus on the territories such as an individual unit boundary, building interior and exterior boundary. In terms of the framework for analysis, territoriality, openness, and unique characteristics are reviewed. As a result, the communal spaces are created using various spatial composition methods such as addition, subtraction, connection, extension, accumulation, and isolation. The communal space programs are integrated in plans and sections throughout the buildings. Visual openness and connection with surrounding urban environments are articulated by void spaces, transparent and translucent building materials, green spaces, and applications of graphical images. Communal identities and aesthetics are emphasized by unique building forms and space arrangements. The uses of finish materials, colors, objects, and images add strong characters to the communal spaces. For a further research, it is necessary to combine a design method study with residents' behaviors and community interactions.

The Effects of Team Network Characteristics and Boundary Spanning Activities on Knowledge Management Performances: The Mediating Role of Trust (팀 네트워크 특성과 경계관리 활동이 지식경영 성과에 미치는 영향: 팀 신뢰의 매개역할)

  • Goh, Yumi;Kim, Jee-Young;Chung, Myung-Ho
    • Knowledge Management Research
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    • v.14 no.5
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    • pp.101-120
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    • 2013
  • The effective management of knowledge has become one of the critical success factors in current organizations. In spite of the extensive use of Knowledge Management System (KMS), useful information and knowledge resources are still transmitted through personal networks among people in organizations. Thus, social network theory which focuses on social relationships in organization can be a fruitful theoretical resource for enhancing Knowledge Management (KM) performances. In this study, we investigate the effects of intra-team network characteristics (i.e., group density and degree of centralization) and external boundary spanning activities on knowledge management performances of a team. We also acknowledge that all group members do not necessarily agree on the team goal and actively disseminate useful information and knowledge. Drawing on the political perspective on KM which emphasizes the role of trust among group members, we examine the mediating effects of team trust between internal/external network characteristics and KM performances. From the data of 220 teams in financial companies in Korea, we found that: (1) group density had positive effects on KM performances (i.e., knowledge creation, sharing, and use). (2) However, centralization was not significantly associated with KM performances. (3) Team trust was found to be an important factor mediating the relationship between intra-team network characteristics, boundary spanning activities, and KM performances. Based on these results, we discuss and suggest possible implications of the findings when designing and implementing KM practices.

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