• Transactions on Control, Automation and Systems Engineering
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• 제3권3호
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• pp.181-189
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• 2001

The software components of embedded control systems get extremely complex as they are designed into distributed systems get extremely complex as they are designed into distributed systems consisting of a large number of inexpensive microcontrollers interconnected by low-bandwidth real-time networks such as the controller area network (CAN). While recently emerging middleware technologies such as CORBA and DCOM address the complexity of distributed programming, they cannot be directly applied to distributed control system design due to their excessive resource demand and inadequate communication models. In this paper, we propose a CORBA-based middleware design for CAN-based distributed embedded control systems. Our design goal is to minimize its resource need and make it support group communication without losing the IDL (interface definition language) level compliance to the OMG standards. To achieve this, we develop a transport protocol on the CAN and a group communication scheme based on the well-known publisher/subscriber model. The protocol effectively realizes subject-based addressing and supports anonymous publisher/subscriber communication. We also customize the method invocation and message passing protocol, referred to as the general inter-ORB protocol (GIOP), of CORBA so that CORBA method invocations are efficiently serviced on a low-bandwidth network such as the CAN. This customization includes packed data encoding and variable-length integer encoding for compact representation of IDL data types. We have implemented our CORBA-based middleware on the mArx real-time operating system we have developed at Seoul National University. Our experiments clearly demonstrate that it is feasible to use CORBA in developing distributed embedded control systems possessing severe resource limitations. Our design clearly demonstrates that it is feasible to use a CORBA-based middleware in developing distributed embedded systems on real-time networks possessing severe resource limitations.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1149-1164
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• 1997

In this study, the applicability of the RNG k-.epsilon. model to the analysis of the complex flows is studied. The governing equations based on a non-orthogonal coordinate formulation with Cartesian velocity components are used and discretized by the finite volume method with non-staggered variable arrangements. The predicted results using the RNG k-.epsilon. model of three complex flows, i.e., the flow over a backward-facing step and a blunt flat plate, the flow around a 2D model car are compared to these from the standard k-.epsilon. model and experimental data. That of the unsteady axisymmetric turbulent flow within a cylinder of reciprocating model engine including port/valve assembly and the spray characteristics within a chamber of direct injection model engine are compared to these from the standard k-.epsilon. model and experimental data. The results of reattachment length, separated eddy size, average surface pressure distribution using the RNG k-.epsilon. model show more reasonable trends comparing with the experimental data than those using the modified k-.epsilon. model. Although the predicted rms velocity using the modified k-.epsilon. model is lower considerably than the experimental data in incylinder flow with poppet valve, predicted axial and radial velocity distributions at the valve exit and in-cylinder region show good agreements with the experimental data. The spray tip penetration predicted using the RNG k-.epsilon. model is more close to the experimental data than that using the modified k-.epsilon. model. The application of the RNG k-.epsilon. model seems to have some potential for the simulations of the unsteady turbulent flow within a port/valve-cylinder assembly and the spray characteristics over the modified k-.epsilon. model.

• 산업경영시스템학회지
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• 제43권2호
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• pp.137-145
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• 2020

Various elements of Fabrication (FAB), mass production of existing products, new product development and process improvement evaluation might increase the complexity of production process when products are produced at the same time. As a result, complex production operation makes it difficult to predict production capacity of facilities. In this environment, production forecasting is the basic information used for production plan, preventive maintenance, yield management, and new product development. In this paper, we tried to develop a multiple linear regression analysis model in order to improve the existing production capacity forecasting method, which is to estimate production capacity by using a simple trend analysis during short time periods. Specifically, we defined overall equipment effectiveness of facility as a performance measure to represent production capacity. Then, we considered the production capacities of interrelated facilities in the FAB production process during past several weeks as independent regression variables in order to reflect the impact of facility maintenance cycles and production sequences. By applying variable selection methods and selecting only some significant variables, we developed a multiple linear regression forecasting model. Through a numerical experiment, we showed the superiority of the proposed method by obtaining the mean residual error of 3.98%, and improving the previous one by 7.9%.

• Structural Engineering and Mechanics
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• 제31권4호
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• pp.439-451
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• 2009

The paper deals with the problem related to the modelling of riveted assemblies for crashworthiness analysis of full-scale complete aircraft structures. Comparisons between experiments and standard FE computations on high-energy accidental situations onto aluminium riveted panels show that macroscopic plastic strains are not sufficiently localised in the FE shells connected to rivet elements. The main reason is related to the structural embrittlement caused by holes, which are currently not modelled. Consequently, standard displacement FE models do not succeed in initialising and propagating the rupture in sheet metal plates and along rivet rows as observed in the experiments. However, the literature survey show that it is possible to formulate super-elements featuring defects that both give accurate singular strain fields and are compatible with standard displacement finite elements. These super-elements can be related to the displacement model of the hybrid-Trefftz principle of the finite element method, which is a kind of domain decomposition method. A feature of hybrid-Trefftz finite elements is that they are mainly used for elastic computations. It is thus proposed to investigate the possibility of formulating a hybrid displacement finite element, including the effects of a hole, dedicated to crashworthiness analysis of full-scale aeronautic structures.

• Geomechanics and Engineering
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• 제6권2호
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• pp.99-115
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• 2014

Uncertainties in design variables and design equations have a significant impact on the safety of geotechnical structures like retaining walls and slopes. This paper presents a possible framework for obtaining the partial safety factors based on reliability approach for different random variables affecting the stability of a reinforced concrete cantilever retaining wall and a slope under static loading conditions. Reliability analysis is carried out by Mean First Order Second Moment Method, Point Estimate Method, Monte Carlo Simulation and Response Surface Methodology. A target reliability index ${\beta}$ = 3 is set and partial safety factors for each random variable are calculated based on different coefficient of variations of the random variables. The study shows that although deterministic analysis reveals a safety factor greater than 1.5 which is considered to be safe in conventional approach, reliability analysis indicates quite high failure probability due to variation of soil properties. The results also reveal that a higher factor of safety is required for internal friction angle ${\varphi}$, while almost negligible values of safety factors are required for soil unit weight ${\gamma}$ in case of cantilever retaining wall and soil unit weight ${\gamma}$ and cohesion c in case of slope. Importance of partial safety factors is shown by analyzing two simple geotechnical structures. However, it can be applied for any complex system to achieve economization.

• Structural Engineering and Mechanics
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• 제69권6호
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• pp.667-676
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• 2019

Minimizing the stress concentration around hypotrochoid hole in finite metallic plates under in-plane loading is an important consideration in engineering design. In the analysis of finite metallic plate, the effective factors on stress distribution around holes include curvature radius of the corner of the hole, hole orientation, plate's aspect ratio, and hole size. This paper aims to investigate the impact of these factors on stress analysis of finite metallic plate with central hypotrochoid hole. To obtain the lowest value of stress around a hypotrochoid hole, a swarm intelligence optimization method named ant lion optimizer is used. In this study, with the hypothesis of plane stress circumstances, analytical solution of Muskhelishvili's complex variable method and conformal mapping is employed. The plate is taken into account to be finite, isotropic and linearly elastic. By applying suitable boundary conditions and least square boundary collocation technique, undefined coefficients of stress function are found. The results revealed that by choosing the above-mentioned factor correctly, the lowest value of stress would be obtained around the hole allowing to an increment in load-bearing capacity of the structure.

• 대한건축학회논문집:계획계
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• 제34권11호
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• pp.113-123
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• 2018

First of all, the multi-story Housing applying resident's participation in europe was classified by the menu selection method, the two-step supply method and the cooperative method. And then I analyzed flexible unit plan of cases for deriving the planning methode and the characteristics of flexibility. First, I analyzed the area and form of the unit plan, structure and Installation, fixed and variable elements to derive the planning method. The area of units are distributed from a minimum of $35m^2$ to a maximum of $150m^2$, and many of the unit planes have a narrow front and a deep depth. The structure is a long-span wall-structure or a skeleton structure, and is designed without any columns and bearing walls in the interior space for flexibility in spatial composition. The vertical shafts are located in the center of the unit in a box-form or in the corner at the unit dividing wall for free placement of interior wall. Fixed elements are framework and facility systems. Most of the future residents in the two-steps supply method and the cooperative method were able to freely design the internal space within the zoning concept proposed by the architect and change the location of the facade element within module system proposed by the architect. Second, the characteristics of the flexibility applied to the unit plan were divided in integrated flexibility, functional flexibility, construction flexibility, and supply flexibility. The integrated flexibility enables residents to give the variable space combination based on the complex structure of the inner space for providing various living experiences. Regarding functional flexibility, the three-dimensional spatial structure with neutral space has multi-functionality according to the needs of residents and easily accepts mixing of hybrid programs such as work and residence. Constructive flexibility allows residents to create identity by freely planning interior space and changing the size or location of facade components in a determined system of architects. Finally, various types of size and space composition are proposed and realized in the whole building applying menu selection method, so that flexibility in the offer can accommodate and integrate various types of living.

• 한국추진공학회지
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• 제15권5호
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• pp.35-47
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• 2011

추력 및 혼합비 조절을 목적으로 제작된 유량조절밸브를 AMESim(4.3.0) 시뮬레이터를 통해 모델링 을 수행했다. BLDC 모터(Brushless D.C. motor)를 이용하는 유량밸브의 조절을 위하여 속도조절기법을 제안했으며, 실험을 통해 그 성능을 보였다. BLDC 모터의 속도제어 기법을 이용하는 조절밸브는 P제어 보다 시스템 활용 시 용이하고, 유량조절 실험결과를 통해 시스템에 적용 가능성을 시사했다. 플런 저 형상에 따라 유량 조절 특성을 평가했고, 두 개의 조절밸브를 이용하는 혼합비 조절의 경우 동일한 플런저 형상을 적용하는 것이 적절했다. 혼합비 조절 시 섭동 폭을 줄이기 위해 밸브 플런저의 형상을 수정한 결과 0.5%로 감소했다.

• 대한조선학회논문집
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• 제31권3호
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• pp.12-18
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• 1994

공학설계에 있어서 최적해를 얻기 위한 방법중의 하나로 최적화방법이 많이 사용되어 왔으나, 기존의 최적화방법에서는 설계점이 국부 최적점으로 빠져 들어갈 경우 그 영역을 벗어날 수 있는 방법이 없기 때문에, 최적화의 초기점을 달리하여 반복계산을 수행하여야 하는 불편한 점이 있었다. 유전적 알고리즘은 기존의 최적화방법에 비하여 다수의 설계점을 동시에 탐색하는 특성이 있어 국부 최적점에 빠질 가능성이 적은 반면, 계산시간이 많이 소요되고 전체 최적점 근처까지는 잘 수렴하나 정확한 최적점을 잘 찾지 못하는 한계가 있다. 본 연구에서는 유전적 알고리즘과 직접탐색법을 결합하여 이들의 단점을 보완한 즉, 전체 최적점을 보다 효율적으로 찾고 계산시간을 줄일 수 있는 방법을 제시하였다. 이 방법은 유전적 알고리즘을 이용하여 최적점이 존재하는 영역을 찾은 후에, 그 영역에서 직접탐색법을 이용하여 보다 정확한 최적점을 찾는 것으로, 예제를 통하여 제안된 방법의 유용성을 보였다.

• 지구물리와물리탐사
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• 제26권2호
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• pp.77-83
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• 2023

이 논문에서는 타원 기둥 형태의 이상체에 의한 자력 벡터와 자력 변화율 텐서 반응식을 유도하였다. 화성암 관입이나 킴벌라이트 구조 등은 축 대칭성을 가지면서 주향 방향과 수직한 방향의 반지름이 서로 다른 타원 기둥 형태를 가지는 경우가 많다. 이런 타원 기둥의 자력 반응은 이전 논문에서 유도한 중력 변화율 텐서에 자화 방향에 대한 정보를 포함시킨 포아송 관계식을 이용하여 유도하였다. 타원 기둥의 자력 변화율 텐서는 벡터 자력을 미분하여 유도하는데 삼중 적분으로 표현되는 타원 기둥의 인력 퍼텐셜을 각 축방향으로 3회 미분한 총 10개의 삼중 미분 함수를 구하는 것과 동일하다. 미분과 적분의 순서는 바꾸는 것이 가능하므로 결과적으로 자력 변화율 텐서는 타원 기둥의 인력 퍼텐셜을 3회 미분한 후, 깊이 방향으로 적분하고 나머지 이중 적분은 복소 평면에서 타원 기둥의 단면을 폐곡선으로 하는 경로를 따라 선적분으로 변환하여 유도된다. 이 논문에서 복소 평면에서 선적분으로 유도한 자력 및 자력 변화율 텐서 반응식은 립쉬츠-한켈 적분으로 유도한 원기둥의 자력 및 자력 변화율 텐서 반응식과 완벽하게 일치함을 보였다.