• Smart Structures and Systems
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• 제29권4호
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• pp.577-588
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• 2022

Oil refineries' Fluid Catalytic Cracking Units (FCCU) when in full operation may exhibit strong fluid dynamics caused by turbulent flow in the piping system that may induce vibrations in other mechanical and structural components of the Unity. This paper reports on the experimental-theoretical-computational program performed to get the vibration properties and the dynamic response amplitudes to find out alternative solutions to attenuate the excessive vibrations that were causing fatigue fractures in components of the bottle like reactor-regenerator of an FCC unit in operation in an existing oil refinery in Brazil. Solutions to the vibration problem were sought with the aid of a 3D finite element model calibrated with the results obtained from experimental measurements. A short description of the found solutions is given and their effectiveness are shown by means of numerical results. The solutions were guided by the concepts of structural stiffening and dynamic control performed by a nonlinear pendulum controller whose mechanical design was based on parameters determined by means of a parametric study carried out with 2D and 3D mathematical models of the coupled pendulum-structure system. The effectiveness of the proposed solutions is evaluated in terms of the fatigue life of critical welded connections.

• Geomechanics and Engineering
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• 제34권4호
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• pp.397-408
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• 2023

Pipe pile walls are commonly used as retaining structures for excavation projects, particularly in densely populated coastal cities such as Hong Kong. Pipe pile walls are preferred in reclaimed land due to their cost-effectiveness and convenience for installation. However, the pre-bored piling techniques used to install pipe piles can cause significant ground disturbance, posing risks to nearby sensitive structures. This study reports a well-documented case history in a reclamation site, and it was found that pipe piling could induce ground settlement of up to 100 mm. Statutory design submissions in Hong Kong typically specify a ground settlement alarm level of 10 mm, which is significantly lower than the actual settlement observed in this study. In addition, lateral soil movement of approximately 70 mm was detected in the marine deposit. The lateral soil displacement in the marine deposit was found to be up to 3.4 and 3.1 times that of sand fill and CDG, respectively, mainly due to the relatively low stiffness of the marine deposit. Based on the monitoring data and site-investigation data, a 3D numerical analysis was established to back-analyze soil movements due to the installation of the pipe pile wall. The comparison between measured and computed results indicates that the equivalent ground loss ratio is 20%, 40%, and 20% for the fill, marine deposit and CDG, respectively. The maximum ground settlement increases with an increase in the ground loss ratio of the marine deposit, whereas the associated influence radius remains stationary at 1.2 times the pipe pile wall depth (H). The maximum ground settlement increases rapidly when the thickness of marine deposit is less than 0.32H, particularly for the ground loss ratio of larger than 40%. This study provides new insights into the pipe piling construction in reclamation sites.

• 한국지반환경공학회 논문집
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• 제21권8호
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• pp.15-27
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• 2020

본 연구에서는 말뚝에 작용하는 부마찰과 관련된 원심모형실험 및 실규모 현장실험 등 기발표 자료에 대한 고등3차원 유한요소해석을 수행하였다. 이를 통해 기존연구에서는 충분히 고려되지 못했던 부마찰이 작용하는 말뚝의 거동 특성을 상세히 분석하였다. 즉 수치해석을 통해 기존연구에서는 고려하지 못했던 부마찰에 의한 말뚝의 침하와 군효과, 군말뚝에서 희생말뚝의 영향과 말뚝두부와 기초판 사이의 상호거동, 말뚝-인접지반의 경계면 요소(interface element)의 유무 및 시간 의존적인 부마찰의 발생특성 등 다양한 요소들을 분석할 수 있었다. 원심모형실험의 경우 중력가속도가 1g에서 특정한 값으로 증가하는 경우 흙의 자중 증가로 인해 말뚝에 비교적 큰 부마찰이 발생하는 것을 확인하였다. 군말뚝의 경우 희생말뚝 유무 및 말뚝두부와 기초판과의 연결여부에 따라 말뚝의 거동이 크게 영향을 받는 것으로 나타났다. 특히 부마찰은 압밀과 관련된 시간의존적 특성을 가지므로 압밀이 진행 중인 말뚝의 거동을 분석할 경우 압밀을 고려한 해석을 수행하는 것이 합리적인 것으로 분석되었다. 이러한 일련의 고찰을 통하여 기존연구의 한계를 적절하게 보완하면서 부마찰을 받는 말뚝의 거동을 명확히 분석할 수 있었다.

• Computers and Concrete
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• 제21권1호
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• pp.11-20
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• 2018

The possibilities of non-linear analysis of reinforced-concrete structures are under development. In particular, current research areas include structural analysis with the application of advanced computational and material models. The submitted article aims to evaluate the possibilities of the determination of material properties, involving the tensile strength of concrete, fracture energy and the modulus of elasticity. To evaluate the recommendations for concrete, volume computational models are employed on a comprehensive series of tests. The article particularly deals with the issue of the specific properties of fracture-plastic material models. This information is often unavailable. The determination of material properties is based on the recommendations of Model Code 1990, Model Code 2010 and specialized literature. For numerical modelling, the experiments with the so called "classic" concrete beams executed by Bresler and Scordelis were selected. It is also based on the series of experiments executed by Vecchio. The experiments involve a large number of reinforcement, cross-section and span variants, which subsequently enabled a wider verification and discussion of the usability of the non-linear analysis and constitutive concrete model selected.

• Steel and Composite Structures
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• 제30권3호
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• pp.217-230
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• 2019

One of the most important design criteria in underground structure is to design lightweight protective layers to resist significant blast loads. Sandwich blast resistant panels are commonly used to protect underground structures. The front face of the sandwich panel is designed to resist the blast load and the core is designed to mitigate the blast energy from reaching the back panel. The design is to allow the sandwich panel to be repaired efficiently. Hence, the underground structure can be used under repeated blast loads. In this study, a novel sandwich panel, named RC panel - Helical springs- RC panel (RHR) sandwich panel, which consists of normal strength reinforced concrete (RC) panels at the front and the back and steel compression helical springs in the middle, is proposed. In this study, a detailed 3D nonlinear numerical analysis is proposed using the nonlinear finite element software, AUTODYN. The accuracy of the blast load and RHR Sandwich panel modelling are validated using available experimental results. The results show that the proposed finite element model can be used efficiently and effectively to simulate the nonlinear dynamic behaviour of the newly proposed RHR sandwich panels under different ranges of free air blast loads. Detailed parameter study is then conducted using the validated finite element model. The results show that the newly proposed RHR sandwich panel can be used as a reliable and effective lightweight protective layer for underground structures.

• 한국수자원학회논문집
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• 제55권1호
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• pp.33-42
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• 2022

본 연구에서는 3차원 상용 수치모형 Flow-3D를 활용하여 상류 수위(유입유량) 변동, 격벽의 간격(pool의 길이) 변화, 잠공 유무 등에 따른 아이스 하버 어도 내 흐름 양상을 분석하였다. 수치모의 결과의 적합성을 입증하기 위해 경안천 대곡교 하류에 설치된 실제 어도에서 3차원 초음파 유속계를 사용하여 어도 출구부 단면 유속과 유량을 관측하였다. Flow-3D 모형에는 난류 모듈로 4가지를 선택할 수 있는데, 관측 자료로 검증 결과 RNG 모형이 아이스하버 어도 내 흐름 특성을 가장 잘 재현하였다. 하천의 유량 전량이 어도로만 유입되어 흐른다는 조건에서 수위 변화에 따른 어도 내 유속구조를 모의해 보았다. 그 결과 최저수위에서는 잠입류와 표면류가 혼재하여 발생하였는데, 최저수위에서 약 10 cm 이상만 수위가 상승하여도 모든 pool에서 잠입류가 사라지고 오직 표면류만 발생하였다. 예상과 달리 수위가 조금 상승해도 흐름이 꽤 단순하게 표면류 위주로 발생하였다. 격벽간 간격을 늘려주면 수위가 상승하더라도 잠입류와 표면류가 혼재되어 나타나는 현상이 지속되었다. 그리고 격벽 하단에 잠공이 있는 경우가 없는 경우에 비해 잠입류가 여러 pool에서 생성되는 경향을 보였다. 보다 적극적인 어도 사후 관리로 잠공 폐색을 막아 어도 내 다양한 흐름이 생성될 수 있도록 유도하는 것이 필요해 보인다.

• 한국지반공학회논문집
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• 제33권3호
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• pp.29-36
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• 2017

NATM 공법에서 터널을 확대하거나 피난갱과 같이 좁은 단면에 록볼트를 설치하는 경우에는 록볼트를 경사지게 설치하거나 또는 짧은 볼트를 연결하여 시공할 수밖에 없다. 국내외에서 실시된 경사 록볼트에 대한 연구는 아직 미흡한 실정이며 실제 현장에 적용하기 위해서는 경사 록볼트의 거동특성에 대한 연구가 필요하다고 사료된다. 본 연구에서는 3차원 유한요소해석을 사용하여 경사 록볼트 시공 시 록볼트의 설치각도와 설치길이에 따른 최대 중립점 발생위치의 변화를 확인하고 이에 따른 록볼트에 의한 원지반 아치형성영역의 두께 변화를 비교 분석하여 지반보강효과에 대해 확인하였다. 해석결과 표준지보패턴(설치길이 4m)에선 설치각도가 감소할수록 터널 주변지반의 변형범위는 증가하여 지반보강효과가 감소하는 것을 알 수 있었다. 또한, 설치길이가 증가함에 따라 설치각도에 의한 영향을 적게 받은 것으로 나타났으며 설치각도 $45^{\circ}$ 이하에서는 설치길이의 영향을 받지 않는 것으로 나타났다. 이러한 결과로부터 경사록볼트의 설치각도는 $45^{\circ}$이상으로 하여 아칭영역을 확보하도록 하여야 하며, 설치각도 $75^{\circ}$이상인 경우 직각으로 설치하는 경우와의 보강효과의 차이가 크지 않음을 확인하였다. 또한 추가적인 상세 검토를 통하여 NATM 터널에서의 경사록볼트 설계지침을 제시하고자 하였다.

• 한국자동차공학회논문집
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• 제3권3호
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• pp.19-28
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• 1995

The explicit scheme for finite element analysis of sheet metal forming problems has been widely used for providing practical solutions since it improves the convergency problem, memory size and computational time especially for the case of complicated geometry and large element number. The explicit schemes in general use are based on the elastic-plastic modelling of material requiring large computation time. In the present work, rigid-plastic explicit finite element method is introduced for analysis of sheet metal forming processes in which plane strain normal anisotropy condition can be assumed by dividing the whole piece into sections. The explicit scheme is in good agreement with the implicit scheme for numerical analysis and experimental results of auto-body panels. The proposed rigid-plastic explicit finite element method can be used as robust and efficient computational method for prediction of defects and forming severity.

• 한국농공학회논문집
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• 제56권3호
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• pp.1-9
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• 2014

The aim of this study is to develop a simulation model for analyzing 2D truss structure using Generic Agricultural System Simulator (GASS). Although the truss is simple structure, numerical methods based on matrix analysis are cumbersome and complicated. This study suggests simple and convenient methods to remove calculating steps for whole stiffness matrices. The simulation environment based on independency of object-oriented components on GASS consists of component development and component deploy stages. A component for a truss structure is implemented based on equilibrium equations at nodes. The simulator can analyze truss structures through deploying components with attributes and links. The examples using GASS show intuitive graphical results of the movements of truss nodes.

• International Journal of Automotive Technology
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• 제5권3호
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• pp.145-153
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• 2004

Potential fuel economy improvements and environmental legislation have renewed interest in Gasoline Direct Injection (GDI) engines. Computational models of fuel injection and mixing processes pre-ignition are being developed for engine optimisation. These highly transient thermofluid models require verification against temporally and spatially resolved data-sets. The authors have previously established the capability of PDA to provide suitable temporally and spatially resolved spray characteristics such as mean droplet size, velocity components and qualitative mass distribution. This paper utilises this data-set to assess the predictive capability of a numerical model for GDI spray prediction. After a brief description of the two-phase model and discretisation sensitivity, the influence of initial spray conditions is discussed. A minimum of 5 initial global spray characteristics are required to model the downstream spray characteristics adequately under isothermal, atmospheric conditions. Verification of predicted transient spray characteristics such as the hollow-cone, cone collapse, head vortex, stratification and penetration are discussed, and further improvements to modelling GDI sprays proposed.