• 소성∙가공
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• 제28권4호
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• pp.212-218
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• 2019

In this study, the first drawing die for the production of coil wedge is redesigned in order to enhance properties such as dimensional accuracy, dimensional uniformity, non-magnetism, and residual stress. The equivalent strain distribution is observed to be asymmetric at certain corners of the product and un-filling of material is also observed at the same location, based on the results of FEM simulation for the current drawing process. Additionally, a relatively huge amount of deformation is concentrated on the surface of the reference product leading to an increase in magnetic component and surface residual stress. After re-designing the cross-section of the first drawing step process conformed to relatively higher amount of reduction ratio, reduction of both surface residual stress and the volume fraction of magnetic component could be achieved for the finally-drawn coil wedge product.

• Steel and Composite Structures
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• 제42권2호
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• pp.161-172
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• 2022

In this paper, four specimens of CFST column joints with endplates and long bolts are tested in the scenario of progressive collapse. Flush endplate and extended endplate are both adopted in this study. The experimental results show that increasing the thickness of the endplate could improve the behavior of the joint, but delay the mobilization of catenary action. The thickness of the endplate should not be relatively thick in comparison to the diameter of the bolts, otherwise catenary action would not be mobilized or work effectively. Effective bending deformation of the endplate could help the formation and development of catenary action in the joints. The performance of flexural action in the joint would affect the formation of catenary action in the joint. Extra middle-row bolts set at the endplates and structural components set below the bottom beam flange should be used to enhance the robustness of joints. A special weld access hole between beam and endplate should be adopted to mitigate the chain damage potential of welds. It is suggested that the structural components of joints should be independent of each other to enhance the robustness of joints. Based on the component method, a formula calculating the stiffness coefficient of preloaded long bolts was proposed whose results matched well with the experimental results.

• 한국지진공학회논문집
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• 제9권3호
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• pp.1-8
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• 2005

본 연구는 지진으로 인하여 발생한 건물의 피해액을 보다 객관적으로 예측 평가할 수 있는 ACM(Advanced Component Method) 개발 방법에 관한 것이다. ACM은 지금까지의 재래식 손실 평가방법에 사용된 구조 기술자들의 주관적인 관점과 전문가적 견해에서 탈피하여, 지진의 크기에 따른 구조형식이 각기 다른 건물들의 내진 성글 평가 기술에 바탕을 둔 지진 손실 평가 방법이다. 그 과정을 살펴보면 먼저 선별된 전형적인 건축 구조물에 대하여 비선형 정적 내진 해석인 pushover 해석을 실행하여 그들의 건물 능력도와 각 부재의 비선형 응답을 계산한다. 지진하중은 ADRS(Acceleration-Displacement Response Spectrum)의 응답 가속도와 응답 변위의 형태로 표현하여 이를 건물 능력도와 함께 능력 스펙트럼법(Capacity Spectrum Method) 기법을 이용하여 건물의 내진 성능점을 찾는다. 또한 전체 건물을 주요 구조체인 기둥, 보, 슬래브 등과 비구조체인 비내력 벽판, 외벽 장식용 요소 등을 각각 분리하여 건물 각 부재들의 지진 응답 변위에 따른 피해율을 산출한다. 이들 각 부재들의 피해는 그 부재들의 특성에 따른 적절한 보수보강기법과 그에 따른 비용산정 모델을 이용하여 각 부재의 금전적인 피해액으로 전환한다. 마지막으로 Monte Carlo기법을 이용하여 지금까지 얻은 건물의 응답과 각 부재들의 지진에 따른 피해율, 그리고 그 부재들의 비용산정 모델을 종합하여 전체 건물의 최종의 피해율을 얻는다. 특히, 현존하는 건물에 사용된 재료와 설계 가정 하중의 가변성에 따른 건물 거동에 대한 불확실성 등을 고려하기 위하여 Latin Hypercube 추출 기법을 사용하며, 마지막으로 본 연구의 사례평가를 위하여 과거 일어났던 지진 피해정보와 손실 자료들을 바탕으로 ACM방법과 재래식 방법을 이용한 건물 손실 평가 방법을 비교 분석하였다.

• 대한기계학회논문집A
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• 제31권10호
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• pp.999-1008
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• 2007

The spacer grid set is a component in the nuclear fuel assembly. The set supports the fuel rods safely. Therefore, the spacer grid set should have sufficient strength for the external impact forces such as earthquake. The fretting wear occurs between the spring of the fuel rod and the spacer grid due to flow-induced vibration. Conceptual design of the spacer grid set is performed based on the Independence Axiom of axiomatic design. Two functional requirements are defined for the impact load and the fretting wear, and corresponding design parameters are selected. The overall flow of design is defined according to the application of axiomatic design. 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. The deformation of a structure is called homologous if a given geometrical relationship holds before, during, and after the deformation. 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.

• Ocean Systems Engineering
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• 제6권2호
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• pp.191-201
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• 2016

Stern bearing is a key component of marine propulsion plant. Its environment is diverse, working condition changeable, and condition severe, so that stern bearing load is of strong time variability, which directly affects the safety and reliability of the system and the normal navigation of ships. In this paper, three affecting factors of the stern bearing load such as hull deformation, propeller hydrodynamic vertical force and bearing wear are calculated and characterized by random theory. The uncertainty mathematical model of stern bearing load is established to research the relationships between factors and uncertainty load of stern bearing. The validity of calculation mathematical model and results is verified by examples and experiment yet. Therefore, the research on the uncertainty load of stern bearing has important theoretical significance and engineering practical value.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.525-530
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• 2003

Recently an automobile industry is concerned about an automobile wiring harness system. It means that development of component modules is on the increase. An importance of the connector in one part of the modules will be enhanced. A connector is made of P.B.T. (Poly Butylene Terephthalate). PBT is resistant to the high temperature. This paper deals with thermal strain of connector. According as temperature increase, effects of the temperature and thermal strains give an analysis of the deformation using ABAQUS. This apparent thermal strain results actually from the variation of temperature. Being based on this analysis, axiomatic design applies to design parameters of the connector. As compared with CAE analysis, a performance improvement makes certain of the truth of the matter.

• 한국항만학회지
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• 제8권1호
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• pp.41-47
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• 1994

The present paper discusses the nonlinear wave deformation due to a submerged coastal structure. Theory is based on the frequency-domain method using the third order perturbation and boundary integral method. Theoretical development to the second order perturbation and boundary integral method. Theoretical development to the second order Stokes wave for a bottom-seated submerged breakwater to the sea floor is newly expanded to the third order for a submerged coastal structure shown in Figure 1. Validity is demonstrated by comparing numerical results with the experimental ones of a rectangular air chamber structure, which has the same dimensions as that of this study. Nonlinear waves become larger and larger with wave propagation above the crown of the structure, and are transmitted to the onshore side of the structure. These characteristics are shown greatly as the increment of Ursell number on the structure. The total water profile depends largely on the phase lag among the first, second and third order component waves.

• Structural Engineering and Mechanics
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• 제52권4호
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• pp.787-813
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• 2014

Starting with Hamilton's variational principle, the governing field equations for the steady state response of thin-walled beams under harmonic forces are derived. The formulation captures shear deformation effects due to bending and warping, translational and rotary inertia effects and as well as torsional flexural coupling effects due to the cross section mono-symmetry. The equations of motion consist of four coupled differential equations in the unknown displacement field variables. A general closed form solution is then developed for the coupled system of equations. The solution is subsequently used to develop a family of shape functions which exactly satisfy the homogeneous form of the governing field equations. A super-convergent finite element is then formulated based on the exact shape functions. Key features of the element developed include its ability to (a) isolate the steady state response component of the response to make the solution amenable to fatigue design, (b) capture coupling effects arising as a result of section mono-symmetry, (c) eliminate spatial discretization arising in commonly used finite elements, (d) avoiding shear locking phenomena, and (e) eliminate the need for time discretization. The results based on the present solution are found to be in excellent agreement with those based on finite element solutions at a small fraction of the computational and modelling cost involved.

• Geomechanics and Engineering
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• 제27권6호
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• pp.551-560
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• 2021

Due to the low strength and high compressibility characteristics, the loess deposits tunnels are prone to large deformations and collapse. An accurate stability evaluation for loess deposits is of considerable significance in deformation control and safety work during tunnel construction. 37 groups of representative data based on real loess deposits cases were adopted to establish the stability evaluation model for the tunnel project in Yan'an, China. Physical and mechanical indices, including water content, cohesion, internal friction angle, elastic modulus, and poisson ratio are selected as index system on the stability level of loess. The data set is randomly divided into 80% as the training set and 20% as the test set. Firstly, principal component analysis (PCA) is used to convert the five index system to three linearly independent principal components X1, X2 and X3. Then, the principal components were used as input vectors for probabilistic neural network (PNN) to map the nonlinear relationship between the index system and stability level of loess. Furthermore, Leave-One-Out cross validation was applied for the training set to find the suitable smoothing factor. At last, the established model with the target smoothing factor 0.04 was applied for the test set, and a 100% prediction accuracy rate was obtained. This intelligent classification method for loess deposits can be easily conducted, which has wide potential applications in evaluating loess deposits.

• 한국산업융합학회 논문집
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• 제25권3호
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• pp.357-363
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• 2022

In this study, in order to develop an non-slip metal grating, the stability of the grating according to the span of the grating and the gap and height of the bearing bar was evaluated. The optimal shape design of the grating was performed using the results of determining the stability of the grating. The purpose of this study is to determine the stability according to the spacing and height of the bearing bar by applying the design pressure at the design stage to develop the anti-skid grating, and to design the optimal shape for cost reduction. In the optimal design, the target variable was set as the mass, and the optimal design of the grating was performed based on about 20%. Regardless of the height of the bearing bar of the grating, the stress and deformation of the span and the grating showed a proportional tendency to each other, and it was found that the stress decreased as the height of the bearing bar increased. Based on the structural analysis results, an optimal design was performed using mass as the objective variable, and the existing 2mm thickness was changed to 1.6mm, reducing the mass by about 19%. The stress increased by about 4.4% compared to the maximum stress of the existing grating, but the minimum safety factor was 3.1, indicating that the optimally designed grating was stable.