• 한국위성정보통신학회논문지
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• 제11권2호
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• pp.55-59
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• 2016

기존 무선에너지 하비스팅시스템에서 유저는 하나의 Hybirid-AP (H-AP)로부터 에너지와 정보를 동시에 받았다. 하지만 무선에너지 하비스팅은 거리가 멀수록 감쇄가 심하기 때문에 H-AP에서 거리가 먼 유저들은 낮은 하비스팅 효율 가진다 (이중 근거리/원거리 문제). 이러한 문제를 해결하기 위해서 본 논문은 Power beacon (PB)을 통해 유저에게 별도의 파워를 공급하는 비결합 무선에너지 하비스팅 네트워크를 시스템 모델로 사용하였다. 이 논문의 주된 목적은 다양한 제약 조건과 Quality of service (QoS), 그리고 Quality of harvested power (QoP)를 만족하면서 목적 함수인 Energy efficiency (EE)를 최대화 하는 것이다. 제안된 시스템은 라그랑지안 쌍대 분해법 이론을 기반으로 EE 최대화를 위한 최적의 시간 스케줄링 알고리즘을 제안한다. 이 알고리즘을 통해 프레임 분해 요소, H-AP의 송신파워, 그리고 PB의 송신파워의 최적 값과 EE의 최대값을 구할 수 있다. 모의 실험 결과는 제안된 알고리즘으로 파라미터가 최적 값으로 빠르게 수렴하고 제안된 모델의 성능이 기존의 시스템 모델보다 우수하다는 것을 증명한다.

• 한국소음진동공학회논문집
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• 제15권3호
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• pp.251-258
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• 2005

The free vibration of a spinning flexible disk-spindle system supported by hydro dynamic bearings (HDB) in an HDD is analyzed by FEM. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The flexible supporting structure with a complex shape which includes stator core, housing, base plate, sleeve and thrust pad is modeled by using a 4-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility. The dynamic coefficients of HDB are calculated from the HDB analysis program, which solves the perturbed Reynolds equation using FEM. Introducing the virtual nodes and the rigid link constraints defined in the center of HDB, beam elements of the shaft are connected to the solid elements of the sleeve and thrust pad through the spring and damper element. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigen value problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies with the experimental ones. Also the effect of supporting structures to the natural modes of the total HDD system is rigorously analyzed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.572-578
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• 2003

The free vibration of a spinning flexible disk-spindle system supported by hydro dynamic bearings in a HDD is analyzed by FEM. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The flexible supporting structure with a complex shape which includes stator core, housing, base plate, sleeve and thrust pad is modeled by using a 4-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility. The dynamic coefficients of HDB are calculated from the HDB analysis program, which solves the perturbed Raynolds equation using FEM. Introducing the virtual nodes and the rigid link constraints defined in the center of HDB, beam elements of the shaft are connected to the solid elements of the sleeve and thrust pad through the spring and damper element. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigenvalue problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies with the experimental ones. Also the effect of supporting structures to the natural modes of the total HDD system is rigorously analyzed.

• 대한기계학회논문집A
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• 제21권8호
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• pp.1195-1208
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• 1997

Bellows is a component in piping systems which absorbs mechanical deformation with flexibility. Its geometry is an axial symmetric shell which consists of two toroidal shells and one annular plate or conical shell. In order to analyze bellows, this study presents the finite element analysis using a conical frustum shell element. A finite element analysis is developed to analyze various bellows. The validity of the developed program is verified by the experimental results for axial and lateral stiffness. The formula for calculating the natural frequency of bellows is made by the simple beam theory. The formula for fatigue life is also derived by experiments. The shape optimal design problem is formulated using multiple objective optimization. The multiple objective functions are transformed to a scalar function by weighting factors. The stiffness, strength and specified stiffness are considered as the multiple objective function. The formulation has inequality constraints imposed on the fatigue limit, the natural frequencies, and the manufacturing conditions. Geometric parameters of bellows are the design variables. The recursive quadratic programming algorithm is selected to solve the problem. The results are compared to existing bellows, and the characteristics of bellows is investigated through optimal design process. The optimized shape of bellows is expected to give quite a good guideline to practical design.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.859-865
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• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered bearing and flexible supporting structures by using the finite element method and the mode superposition method. The appropriate finite element equations for polygon mirror are described by rotating annular sector element using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. The rotating components except for the polygon mirror are modeled by Timoshenko beam element including the gyroscopic effect. The flexible supporting structures are modeled by using a 4-node tetrahedron element and 4-node shell element with rotational degrees of freedom. Finite element equations of each component of the polygon mirror scanner motor and the flexible supporting structures are consistently derived by satisfying the geometric compatibility in the internal boundary between each component. The rigid link constraints are also imposed at the interface area between sleeve and sintered bearing to describe the physical motion at this interface. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem by using the restarted Arnoldi iteration method. Unbalance responses in time and frequency domain are performed by superposing the eigenvalues and eigenvectors from the free vibration analysis. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results. This research also shows that the flexibility of supporting structures plays an important role in determining the unbalance response of the polygon mirror scanner motor.

• 대한토목학회논문집
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• 제9권1호
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• pp.33-40
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• 1989

철근 콘크리트 뼈대구조는 설계변수가 많고, 목적함수의 제약조건이 복잡하여 주로 반복적인 재해석에 의하여 최적해에 접근하는 방법이 사용되고 있다. 본 연구에서는 다단계분할(multilevel decomposition)에 의하여 최적화 문제를 형성하여 재해석과정을 줄이고 효과적으로 설계변수를 취할 수 있도록 하였다. 최적화의 단계는 첫째 단계에서 비선형거동에 의한 재분배모멘트의 설계공간을 계산하여 설계모멘트에 대한 제약조건식을 형성하고, 둘째 단계에서는 재분배 모멘트를 최적화하였으며, 셋째 단계에서는 설계단면을 최적화하였다. 이때 재분배 모멘트의 최적화에 따른 첫째 단계의 모멘트의 설계공간의 변화는 부재력 변화량 추정(force approximation technique)에 의하여 수정하도록 하며, 변수를 단계별로 줄여 수렴을 가속화시킬 수 있도록 하였다. 최적화 문제의 목적함수로는 경비함수를 취하였으며 영국 CP110의 한계상태설계법을 이용하여 부재의 응력제약조건식을 유도하고, 설계예를 통하여 본 연구의 타당성과 효율성을 구명하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.145-150
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• 2007

The spacer grid set is a component in the nuclear fuel assembly. The set supports the fuel rods saftely. Therefore, the spacer gl1d set should have sufficient strength for the external impact forces. The fretting wear occurs between the spring of the fuel rod and the spacer grid due to tile flow-induced vibration. The conceptual design of the spacer grid set is performed based on the Independence Axiom of axiomatic design. Two functional requirements are defined and corresponding design parameters are selected. The overall flow of the design is defined according to the application of axiomatic design. The design for the impact load is carried out by using nonlinear dynamic analysis to determine the length of the dimple. Topology optimization is carried out to determine a new configuration of the spring. The fretting wear is reduced by shape optimization using the homology theory. In the design to reduce the fretting wear, the deformed shape of the spring should be the same as that of the fuel rod. This condition is transformed to a function and considered as a constraint in the shape optimization process. The fretting wear is expected to be reduced due to the homology constraint. The objective function is minimizing the maximum stress to allow a slight plastic deformation. Shape optimization results are confirmed through nonlinear static analysis because the contact area becomes wider.

• KIEAE Journal
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• 제10권1호
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• pp.73-83
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• 2010

In urban regeneration, resident participation and respect of residents' need have become a major important issue. The purpose of this study is to identify residential area improvement characteristics expected by local residents. Data used for this study were collected from survey which used questionnaire and village image map construction tool kit, developed for facilitating the residents' participation in an actual housing improvement area at Kwngjoo, Korea. The major contents surveyed through questionnaire were first, future images of the area second, directions of improvement third, preferred architectural types such as high or low rise buildings. and a total of 335 data was collected within 4 days during 12-14 December, 2008. The kit was used by parents of students at a local elementary school, and 205 image maps were collected. Content analysis was to analyse characteristics of villages shown in the constructed image maps. Lynch's five elements were utilized to select areas for analysis. As a result, types of buildings desired by residents at the selected four local areas were identified. In general, residents desired their village to be improved with low and mid rise buildings, respecting existing cultural assets. This study showed that there is certain characteristics in relation to the selected areas. Besides, the tool kit used this study showed the effectiveness in collecting opinions from young households in the improvement area within a short time. The tool is expected to be useful in attracting residents and in facilitating participation of wide range of local residents by improving the constraints stemming from time and space.

• Steel and Composite Structures
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• 제25권1호
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• pp.105-116
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• 2017

This paper presents the dynamic stability study of laminated composite plates with different force combinations and aspect ratios. Optimum non-diverging stacking is obtained for certain loading combination and aspect ratio. In addition, the stability force is maximized for a definite operating frequency. A dynamic version of the principle of virtual work for laminated composites is used to obtain force-frequency relation. Since dynamic stiffness governs the divergence or flutter, an efficient optimization method is necessary for the response functional and the relevant constraints. In this way, a model based on the ant colony optimization (ACO) algorithm is proposed to search for the proper stacking. The ACO algorithm is used since it treats with large number of dynamic stability parameters. Governing equations are formulated using classic laminate theory (CLT) and von-Karman plate technique. Load-frequency relations are explicitly obtained for fundamental and secondary flutter modes of simply supported composite plate with arbitrary aspect ratio, stacking and boundary load, which are used in optimization process. Obtained results are compared with the finite element method results for validity and accuracy convince. Results revealed that the optimum stacking with stable dynamic response and maximum critical load is in angle-ply mode with almost near-unidirectional fiber orientations for fundamental flutter mode. In addition, short plates behave better than long plates in combined axial-shear load case regarding stable oscillation. The interaction of uniaxial and shear forces intensifies the instability in long plates than short ones which needs low-angle layup orientations to provide required dynamic stiffness. However, a combination of angle-ply and cross-ply stacking with a near-square aspect ratio is appropriate for the composite plate regarding secondary flutter mode.

• 전기전자학회논문지
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• 제25권2호
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• pp.362-370
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• 2021

본 논문에서는 휠체어 사용자의 이동권 확보를 위한 계단 승강 로봇 개발에 있어 ToF센서 및 IMU의 데이터를 기반으로 자율 계단 승강 기법을 제시하였다. 자율 계단 계단 승강 기법은 랜딩기어 동작 시점을 위치로 구분하고 상태 머신을 활용하여 제어하였다. 본 연구에서 제시한 이론의 검증을 위해 표준 기준의 모형 계단을 제작하여 실험하였다. 진입각 확보 실험을 통해 랜딩기어의 동작 길이 평균 오차는 2.19%, Pitching 기준 진입각 평균 오차는 2.78%로 부드러운 진입을 확인하였고, 자율 계단 승강 기법의 단계 구분 및 상태 전이를 검증하였다. 제안된 기법의 실적용 시 교통약자들의 이동제약을 줄일 수 있을 것이고, 이동권 보장을 통한 자립심의 고취가 기대된다.