• 대한기계학회논문집B
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• 제36권4호
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• pp.425-430
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• 2012

본 연구에서는 비상시 전기 공급용 MCFC 프리커버터의 천연가스(메탄)로부터 수소의 생산량을 증가시키는 경우를 수치적으로 해석하였다. 상용 코드를 사용하였으며 촉매는 다공성 매질로 시뮬레이션 하였다. 3가지 주요 화학반응인 수증기 개질반응(SR), 수성 가스 전환(WGS) 및 직접 수증기 개질 반응(DSR)은 사용자 부프로그램을 사용하여 해석하였다. 프리컨버터에서 10%의 연료전환율을 얻기 위해 요구되는 추가 열량을 벽면을 통해 공급하게 되면 프리컨버터의 벽면 부근에서만 매우 불균일한 온도 분포와 화학반응이 일어나는 것으로 분석되었다. 이와 같은 현상은 매우 작은 열전도율을 갖는 다공성 매질의 촉매와 흡열반응으로 설명되어질 수 있다. 해석결과 프리컨버터의 길이가 짧은 경우가 보다 균일한 연료전환율을 보여 주며, 촉매의 유지 보수 면에도 길이가 짧은 경우가 유리함을 보여 주었다.

• 한국지반공학회논문집
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• 제18권4호
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• pp.215-228
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• 2002

동반논문(오세붕, 2002)에서는 전체 변형도 영역의 거동을 모델할 수 있는 GUX( 구성모델을 ABAQUS 코드(Hibbit 등, 2001)에 구현하였다. 먼저 정확도 해석을 통하여 동반논문에서 구현한 내재적 응력적분 기법이 해의 정확도를 확보함을 알 수 있었다. GUX 모델은 전응력 개념에 의거한 비등방경화 탄소성 구성모델이므로 완전 배수 또는 비배수 삼축시힘시 응력-변형도 관계를 입력하여 대상문제를 배수 및 비배수조건에 따라 해석할 수 있다. 본 연구에서는 연약지반 및 풍화토 지반상 성토시 안정성 문제와 지반-말뚝계의 축하중 재하시 거동에 대한 예제 해석을 수행하였다. 그리고 대변형 해석을 통하여 기하학적 비선형성을 고려하였고 전체 변형도 거동을 합리적으로 모델하는 GUX 모델을 이용한 결과를 Mises 모델 결과와 비교하였다.

• 대한기계학회논문집A
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• 제26권3호
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• pp.479-486
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• 2002

In this study, the progressive inelastic deformation, so called, thermal ratchet phenomenon which can occur in high temperature structures of liquid metal reactor was simulated with thermal ratchet structural test facility and 316L stainless steel test cylinder. The thermal ratchet deformation at the reactor baffle cylinder of the liquid metal reactor can occur due to the moving temperature distribution along the axial direction as the sodium free surface moves up and down under the cyclic heat-up and cool-down transients. The ratchet deformation was measured with the laser displacement sensor and LVDTs after cooling the structural specimen which is heated up to 55$0^{\circ}C$ with steep temperature gradients along the axial direction. The temperature distribution of the test cylinder along the axial direction was measured with 28 channels of thermocouples and was used for the ratchet analysis. The thermal ratchet deformation was analyzed with the constitutive equation of nonlinear combined hardening model which was implemented as ABAQUS user subroutine and the analysis results were compared with those of the test. Thermal ratchet load was applied 9 times and the residual displacement after 9 cycles of thermal load was measured to be 1.79mm. The ratcheting deformation shapes obtained by the analysis with the combined hardening model were in reasonable agreement with those of the structural tests.

• Geomechanics and Engineering
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• 제5권5호
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• pp.463-483
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• 2013

Considering the influences of fluid penetration, casing, excavation processes of wellbore and perforation tunnels, the seepage-deformation finite element model of oil and gas well coupled with perforating technique is established using the tensile strength failure criterion, in which the user-defined subroutine is developed to investigate the dynamic evolvement of the reservoir porosity and permeability. The results show that the increases of perforation angle and decreases of perforation density lead to a higher fracture initiation pressure, while the changes of the perforation diameter and length have no evident influences on the fracture initiation pressure. As for initiation location for the fracture in wellbore, it is on the wellbore face while considering the presence of the casing. By contrast, the fractures firstly initiate on the root of the tunnels without considering casing. Besides, the initial fracture position is also related with the perforation angle. The fracture initiation position is located in the point far away from the wellbore face, when the perforation angle is around $30^{\circ}$; however, when the perforation angle is increased to $45^{\circ}$, a plane fracture is initiated from the wellbore face in the maximum horizontal stress direction; no fractures was found around perforation tunnels, when the angel is close to $90^{\circ}$. The results have been successfully applied in an oilfield, with the error of only 1.1% comparing the fracture initiation pressure simulated with the one from on-site experiment.

• Structural Engineering and Mechanics
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• 제67권6호
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• pp.643-658
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• 2018

In this paper, we introduce a new framework for running the finite element (FE) packages inside an online Loop together with MATLAB. Contrary to the Hardware-in-the-Loop techniques (HiL), in the proposed Software-in-the-Loop framework (SiL), the FE package represents a simulation platform replicating the real system which can be out of access due to several strategic reasons, e.g., costs and accessibility. Practically, SiL for sophisticated structural design and multi-physical simulations provides a platform for preliminary tests before prototyping and mass production. This feature may reduce the new product's costs significantly and may add several flexibilities in implementing different instruments with the goal of shortlisting the most cost-effective ones before moving to real-time experiments for the civil and mechanical systems. The proposed SiL interconnection is not limited to ABAQUS as long as the host FE package is capable of executing user-defined commands in FORTRAN language. The focal point of this research is on using the compiled FORTRAN subroutine as a messenger between ABAQUS/CAE kernel and MATLAB Engine. In order to show the generality of the proposed scheme, the limitations of the available SiL schemes in the literature are addressed in this paper. Additionally, all technical details for establishing the connection between FEM and MATLAB are provided for the interested reader. Finally, two numerical sub-problems are defined for offline and online post-processing, i.e., offline optimization and closed-loop system performance analysis in control theory.

• Structural Engineering and Mechanics
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• 제68권3호
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• pp.299-312
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• 2018

In this paper, an extended finite element method is proposed to analyze both geometric and material non-linear behavior of general Functionally Graded Material (FGM) plate-shell type structures. A user defined subroutine (UMAT) is developed and implemented in Abaqus/Standard to study the elastoplastic behavior of the ceramic particle-reinforced metal-matrix FGM plates-shells. The standard quadrilateral 4-nodes shell element with three rotational and three translational degrees of freedom per node, S4, is extended in the present study, to deal with elasto-plastic analysis of geometrically non-linear FGM plate-shell structures. The elastoplastic material properties are assumed to vary smoothly through the thickness of the plate-shell type structures. The nonlinear approach is based on Mori-Tanaka model to underline micromechanics and locally determine the effective FGM properties and self-consistent method of Suquet for the homogenization of the stress-field. The elasto-plastic behavior of the ceramic/metal FGM is assumed to follow Ludwik hardening law. An incremental formulation of the elasto-plastic constitutive relation is developed to predict the tangent operator. In order to to highlight the effectiveness and the accuracy of the present finite element procedure, numerical examples of geometrically non-linear elastoplastic functionally graded plates and shells are presented. The effects of the geometrical parameters and the volume fraction index on nonlinear responses are performed.

• Steel and Composite Structures
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• 제35권6호
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• pp.739-752
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• 2020

This paper aims to investigate cyclic plasticity of a new type of high-performance austenitic stainless steel with both high strength and high ductility. The new stainless steel termed as QN1803 has high nitrogen and low nickel, which leads to reduction of cost ranging from 15% to 20%. Another virtue of the new material is its high initial yield strength and tensile strength. Its initial yield strength can be 40% to 50% higher than conventional stainless steel S30408. Elongation of QN1803 can also achieve approximately 50%, which is equivalent to the conventional one. QN1803 also has a corrosion resistance as good as that of S30408. In this paper, both experimental and numerical studies on the new material were conducted. Full-range true stress-true strain relationships under both monotonic and cyclic loading were obtained. A cyclic plasticity model based on the Chaboche model was developed, where a memory surface was newly added and the isotropic hardening rule was modified. A user-defined material subroutine was written, and the proposed cyclic plasticity model can well evaluate full-range hysteretic properties of the material under various loading histories.

• Composites Research
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• 제25권5호
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• pp.136-140
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• 2012

본 논문에서는 복합재료 IM rod가 적용된 골절부의 세포 분화과정을 모사하기 위해 유한요소해석을 실시하였다. 세포의 골화과정을 해석하기 위해 편향 변형률을 이용한 메카노 규제 이론을 사용하였으며, 반복 계산을 위해 Python 코드를 이용하여 서브루틴을 구현하였다. 치료에 가장 적절한 복합재료 IM rod의 강성을 찾기 위해 직물 탄소섬유/에폭시 복합재료 (WSN3k)의 적층각도를 바꾸어 해석을 실시하였다. 골절부에 가해지는 기계적 자극에 따른 치료효율을 비교하기 위해 두 가지 초기 하중 조건을 적용하였다. 그 결과 치료효율은 강성의 차이보다 하중에 의해 큰 영향을 받았으며, 초기 하중이 몸무게의 10%이고, 적층순서가 $[{\pm}45]_{nT}$일 때 치료효율이 가장 높았다.

• 한국전산구조공학회논문집
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• 제29권5호
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• pp.437-445
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• 2016

현재 많은 산업에서 구조물의 온도환경 유지를 위한 단열재로 폴리우레탄 폼이 사용되며, 수명 동안 정적 및 동적의 다양한 하중이 이에 부과된다. 폴리우레탄 폼은 고분자재료로써 다공성이며, 단열성능은 내부기공의 크기에 크게 의존한다. 또한, 폴리우레탄 폼의 기계적 거동은 변형률 속도 및 온도에 대한 의존성이 큰 동시에 압축에 대하여 큰 비선형 연성거동을 보인다. 이러한 비선형 연성 압축거동 중에 폴리우레탄 폼은 변형률의 증가에 따라 기공율과 탄성계수의 감소를 보인다. 따라서 본 연구에서는 상기 특성들을 포함한 폴리우레탄 폼의 변형률 속도 및 온도 의존 비선형 압축거동을 모사하기 위하여 온도 의존 손상 점소성 구성방정식이 개발되었다.

• Composites Research
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• 제26권2호
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• pp.91-98
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• 2013

복합재 이중-겹침 볼트 체결부의 파손을 예측하기 위해 손상계수를 고려한 강성저하 방법과 Hashin의 3차원 파손판정식에 근거한 3차원 유한요소해석 방법을 제안하였다. 기지 혹은 면내(In-plane) 전단 손상을 고려하기 위해 손상변수를 이용하는 Ladeveze 이론을 섬유방향 강성저하와 연계하여 사용하였고, 수지 압축/전단, 수지 인장/전단, 섬유압축, 섬유 인장 등 4가지 파손모드를 고려하였다. 상업용 유한요소 프로그램인 ABAQUS를 이용하여 마찰력과 볼트 체결력을 고려하였고, 강성저하모델 처리를 위해 ABAQUS의 사용자 정의 부프로그램을 이용하였다. 제안된 유한요소해석 방법을 검증하기 위해 복합재 이중겹침 볼트 체결부 시험 결과와 파손강도를 비교한 결과 7~16% 오차를 보임을 확인하였다.