• 한국강구조학회 논문집
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• 제24권5호
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• pp.511-520
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• 2012

상 하부 스플릿 T 접합부는 부분강접 접합부의 한 형태로 접합부에 사용된 T-stub의 두께 및 고력볼트 게이지 거리 변화에 따라서 충분한 휨강도를 갖는다. 뿐만 아니라 상 하부 스플릿 T 접합부는 강재의 종류, 보 및 기둥의 규격, 접합부 형상 등의 조합에 의하여 보통모멘트골조 혹은 특수모멘트골조에 적용 가능한 충분한 연성능력을 갖는 내진접합부로 설계 및 시공 된다. 그러나 이러한 상 하부 스플릿 T 접합부에 대한 국내의 연구는 아직 미흡한 상황이며 적합한 설계식의 제안도 이루어지고 있지 않다. 그러므로 상 하부 스플릿 T 접합부의 국내 적용을 위해서는 많은 실험 및 해석적 연구가 필요한 상황이다. 따라서 이 연구는 FEMA의 상 하부 스플릿 T 접합부에 대한 설계식을 검토하고 국내의 적용 가능성을 타진하고자 진행하였다.

• Korea-Australia Rheology Journal
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• 제19권4호
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• pp.191-199
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• 2007

Precision injection molding process is of great importance since precision optical products such as CD, DVD and various lens are manufactured by those process. In such products, birefringence affects the optical performance while residual stress that determines the geometric precision level. Therefore, it is needed to study residual stress and birefringence that affect deformation and optical quality, respectively in precision optical product. In the present study, we tried to predict residual stress, final shrinkage and birefringence in injection molded parts in a systematic way, and compared numerical results with the corresponding experimental data. Residual stress and birefringence can be divided into two parts, namely flow induced and thermally induced portions. Flow induced birefringence is dominant during the flow, whereas thermally induced stress is much higher than flow induced one when amorphous polymer undergoes rapid cooling across the glass transition region. A numerical system that is able to predict birefringence, residual stress and final shrinkage in injection molding process has been developed using hybrid finite element-difference method for a general three dimensional thin part geometry. The present modeling attempts to integrate the analysis of the entire process consistently by assuming polymeric materials as nonlinear viscoelastic fluids above a no-flow temperature and as linear viscoelastic solids below the no-flow temperature, while calculating residual stress, shrinkage and birefringence accordingly. Thus, for flow induced ones, the Leonov model and stress-optical law are adopted, while the linear viscoelastic model, photoviscoelastic model and free volume theory taking into account the density relaxation phenomena are employed to predict thermally induced ones. Special cares are taken of the modeling of the lateral boundary condition which can consider product geometry, histories of pressure and residual stress. Deformations at and after ejection have been considered using thin shell viscoelastic finite element method. There were good correspondences between numerical results and experimental data if final shrinkage, residual stress and birefringence were compared.

• Journal of Mechanical Science and Technology
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• 제17권12호
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• pp.1835-1843
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• 2003

This paper introduces the development of the caliper system for a geometry PIG (Pipeline Inspection Gauge). The objective of the caliper system is to detect and measure dents, wrinkles, and ovalities affect the pipe structural integrity. The developed caliper system consists of a finger arm, an anisotropic permanent magnet, a back yoke, pins, pinholes and a linear hall effect sensor. The angle displacement of the finger arm is measured by the change of the magnetic field in sensing module. Therefore the sensitivity of the caliper system mainly depends on the magnitude of the magnetic field inside the sensing module. In this research, the ring shaped anisotropic permanent magnet and linear hall effect sensors were used to produce and measure the magnetic field. The structure of the permanent magnet, the back yoke and pinhole positions were optimized that the magnitude of the magnetic field range between a high of 0.1020 Tesla and a low of zero by using three dimensional nonlinear finite element methods. A simulator was fabricated to prove the effectiveness of the developed caliper system and the computational scheme using the finite element method. The experimental results show that the developed caliper system is quite efficient for the geometry PIG with good performance.

• Structural Engineering and Mechanics
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• 제72권6호
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• pp.713-722
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• 2019

Micromechanics is a technique for the analysis of composites or heterogeneous materials which focuses on the components of the intended structure. Each one of the components can exhibit isotropic behavior, but the microstructure characteristics of the heterogeneous material result in the anisotropic behavior of the structure. In this research, the general mechanical properties of a 3D anisotropic and heterogeneous Representative Volume Element (RVE), have been determined by applying periodic boundary conditions (PBCs), using the Asymptotic Homogenization Theory (AHT) and strain energy. In order to use the homogenization theory and apply the periodic boundary conditions, the ABAQUS scripting interface (ASI) has been used along with the Python programming language. The results have been compared with those of the Homogeneous Boundary Conditions method, which leads to an overestimation of the effective mechanical properties. According to the results, applying homogenous boundary conditions results in a 33% and 13% increase in the shear moduli G₂₃ and G₁₂, respectively. In polymeric composites, the fibers have linear and brittle behavior, while the resin exhibits a non-linear behavior. Therefore, the nonlinear effects of resin on the mechanical properties of the composite material is studied using a user-defined subroutine in Fortran (USDFLD). The non-linear shear stress-strain behavior of unidirectional composite laminates has been obtained. Results indicate that at arbitrary constant stress as 80 MPa in-plane shear modulus, G₁₂, experienced a 47%, 41% and 31% reduction at the fiber volume fraction of 30%, 50% and 70%, compared to the linear assumption. The results of this study are in good agreement with the analytical and experimental results available in the literature.

• 한국생산제조학회지
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• 제22권3_1spc호
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• pp.573-579
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• 2013

Once-through helically coiled steam generator tubes subjected to external pressure are of interest because of their application to advanced small- and medium-sized integral reactors, in which a primary coolant with a relatively higher pressure flows outside the tubes, while secondary water with a relatively lower pressure flows inside the tubes. Another notable point is that the values of the mean radius to thickness ratio of these steam generator tubes are very small, which means that a thick-walled cylinder is employed for these steam generator tubes. In the present paper, the maximum allowable pressure of helically coiled and thick-walled steam generator tubes with through-wall cracks under external pressure is investigated based on a detailed nonlinear three-dimensional finite element analysis. In terms of the crack orientation, either circumferential or axial through-wall cracks are considered. In particular, in order to quantify the effect of the crack location on the maximum external pressure, these cracks are assumed to be located in the intrados, extrados, and flank of helically coiled cylinders. Moreover, an evaluation is also made of how the maximum external pressure is affected by the ovality, which might be inherently induced during the tube coiling process used to fabricate the helically coiled steam generator tubes.

• 한국전산구조공학회논문집
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• 제30권6호
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• pp.559-566
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• 2017

본 논문은 시공단계에서 가설지주 설치를 요구하지 않는 역삼각 트러스 거더로 보강된 새로운 합성 데크플레이트 시스템을 제안한다. 제안된 시스템은 기존 시스템 대비 증가된 강성과 강도를 보유할 뿐 아니라 절대 층고 변화를 최소 수준으로 낮출 수 있으며 기존의 H형강 및 U형 합성보와 같은 다양한 형태의 합성보 부재와 함께 사용될 수 있다. 제안된 시스템의 시공단계 하중에 대한 구조적 성능을 평가하기 위해 5.5m의 스팬을 갖는 5개의 시험체를 제작하여 현장 조건과 유사한 재하하중을 단계적으로 적용시켜 실험을 수행하였다. 실험결과로부터 각 시험체 별 하중-변위 그래프를 구해 비선형 3차원 유한요소해석결과와 비교하였다. 비교 결과 보강 트러스 거더와 데크플레이트 사이에 효율적인 하중 분배가 이루어져 두 구조요소가 잘 일체화되었을 뿐 아니라 시공단계 하중에서의 최대 처짐이 건축구조기준의 제한치를 하회하여 사용성 조건을 잘 만족시킴을 알 수 있다.

• 한국전산구조공학회논문집
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• 제33권2호
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• pp.137-144
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• 2020

본 논문에서는 시공단계에서 서포트가 필요 없는 UHPC 충전형 상현재를 활용한 트러스 데크플레이트 시스템을 제안하고자 한다. 제안된 시스템은 기존의 시스템과 동일한 절대 층고를 유지하면서 증대된 강성과 강도를 보유하며 효과적으로 처짐을 제어한다. 제안된 시스템 및 기존의 시스템의 구조 성능을 평가하기 위해 4.6m의 순 스팬을 갖는 5개의 실험체를 제작하였고 점진적으로 하중을 증가시키며 4점 휨 실험을 수행하였다. 실험을 토대로 실험체별 하중-처짐 그래프를 도출하였고 변수에 따른 비교 및 분석을 진행하였다. 그리고 실험을 기준으로 수행한 비선형 3차원 유한요소해석결과와의 비교를 진행하였다. 비교 및 분석 결과, 기존의 트러스 데크플레이트를 제외한 모든 실험체들이 시공단계 하중에서 건축구조설계기준 및 강구조설계기준에서 제한하는 처짐 기준을 만족하였으며, 실험과 유한요소해석의 결과가 서로 유사한 것을 확인하였다.

• 대한조선학회논문집
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• 제31권3호
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• pp.80-86
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• 1994

자유수면을 항주하는 선박에 의하여 발생되는 비선형 조파현상을 해석하기 위한 수치해석법을 개발하였다. 유동은 비점성, 비압축성으로 가정하고 선체 및 자유수면 형상과 일치하는 좌표계의 생성을 위하여 타원형 편미분방정식을 수치해석하여 물체적합 좌표계를 생성하였으며 변환된 정규격자 물체적합 좌표계에 대한 Euler방정식을 유한차분법(Finite Difference Method)을 이용하여 계산하였다. 수치해석을 위하여 시간에 대한 미분항은 전진차분, 공간에 대한 미분항은 중심차분법으로 이산화하였고 대류항에는 수치계산의 안정을 위해 인위적인 소산(dissipation)항을 첨가하였다. 자유수면의 형상은 매 시간 단계마다 자유수면 경계조건들을 만족하도록 다시 계산되었고 격자점들은 자유수면형상의 변화에 적합하게 다시 생성되도록 하였으며 압력에 대한 Poisson방정식은 반복연산법에 의하여 풀고 그 결과를 이용하여 속도를 외삽하였다. 개발된 수치해석법의 검증을 위해 수식선형인 Wigley 모형에 대한 계산을 Fn=0.250-0.408에 대하여 수행하고, 그 결과를 실험 결과와 비교하여 잘 일치함을 보였다.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.3059-3072
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• 2022

A Jacobian-Free Newton Krylov Two-Nodal Coarse Mesh Finite Difference algorithm based on Nodal Expansion Method (NEM_TNCMFD_JFNK) is successfully developed and proposed to solve the three-dimensional (3D) and multi-group reactor physics models. In the NEM_TNCMFD_JFNK method, the efficient JFNK method with the Modified Incomplete LU (MILU) preconditioner is integrated and applied into the discrete systems of the NEM-based two-node CMFD method by constructing the residual functions of only the nodal average fluxes and the eigenvalue. All the nonlinear corrective nodal coupling coefficients are updated on the basis of two-nodal NEM formulation including the discontinuity factor in every few newton steps. All the expansion coefficients and interface currents of the two-node NEM need not be chosen as the solution variables to evaluate the residual functions of the NEM_TNCMFD_JFNK method, therefore, the NEM_TNCMFD_JFNK method can greatly reduce the number of solution variables and the computational cost compared with the JFNK based on the conventional NEM. Finally the NEM_TNCMFD_JFNK code is developed and then analyzed by simulating the representative PWR MOX/UO₂ core benchmark, the popular NEACRP 3D core benchmark and the complicated full-core pin-by-pin homogenous core model. Numerical solutions show that the proposed NEM_TNCMFD_JFNK method with the MILU preconditioner has the good numerical accuracy and can obtain higher computational efficiency than the NEM-based two-node CMFD algorithm with the power method in the outer iteration and the Krylov method using the MILU preconditioner in the inner iteration, which indicates the NEM_TNCMFD_JFNK method can serve as a potential and efficient numerical tool for reactor neutron diffusion analysis module in the JFNK-based multiphysics coupling application.

• Steel and Composite Structures
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• 제41권5호
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• pp.761-773
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• 2021

This study presents a 3D non-linear finite element (FE) assessment of dynamic soil-structure interaction (SSI). The numerical investigation has been performed on the time domain through a Finite Element (FE) system, while considering the nonlinear behavior of soil and the multi-directional nature of genuine seismic events. Later, the FE outcomes are analyzed to the recorded in-situ free-field and structural movements, emphasizing the numerical model's great result in duplicating the observed response. In this work, the soil response is simulated using an isotropic hardening elastic-plastic hysteretic model utilizing HSsmall. It is feasible to define the non-linear cycle response from small to large strain amplitudes through this model as well as for the shift in beginning stiffness with depth that happens during cyclic loading. One of the most difficult and unexpected tasks in resolving soil-structure interaction concerns is picking an appropriate ground motion predicted across an earthquake or assessing the geometrical abnormalities in the soil waves. Furthermore, an artificial neural network (ANN) has been utilized to properly forecast the non-linear behavior of soil and its multi-directional character, which demonstrated the accuracy of the ANN based on the RMSE and R² values. The total result of this research demonstrates that complicated dynamic soil-structure interaction processes may be addressed directly by passing the significant simplifications of well-established substructure techniques.