• Wind and Structures
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• 제34권3호
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• pp.291-301
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• 2022

Although mostly used in wind turbine market, single rotor wind turbines have problems with transportation and installation costs due to their large size. In order to solve such problems, multi-rotor wind turbine is being proposed; however, light weight design of multi-rotor wind turbine is required considering the installation at offshore or deep sea. This study proposes the systematic design process of the multi-rotor wind turbine focused on its supporting structure with simultaneous consideration of static and dynamic behaviors in an ideal situation. 2D and successive 3D topology optimization process based on the density method were applied to minimize the compliance of supporting structure. To realize the conceptual design obtained by topology optimization for manufacturing feasibility, the derived 3D structure was modified to have shell structures and optimized again through parametric design using the design of experiments and the response surface method for detail design of their thicknesses and radii. The resultant structure was determined to satisfy the stress and the buckling load constraint as well as to minimize the weight and the resultant supporting structure were verified numerically.

• 한국공간구조학회논문집
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• 제9권1호
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• pp.61-68
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• 2009

본 연구는 와플구조의 구조적 거동에 파악하고자 한다. 와플슬래브의 두께, 주요 보의 깊이와 기둥의 크기를 변수로 하여 와플구조의 모드형상과 고유진동수를 파악하고자 하였다. 또한 쉘요소와 입체요소를 사용한 유한요소모델의 해석결과를 비교하였다. i)레벨2에서 주요 보의 깊이가 증가함에 따라, ii)레벨3에서 와플슬래브 두께가 감소함에 따라 모드진동수는 증가하였다. 3차원 모델과 2차원 모델의 모드형상은 유사한 형상을 보였다. 또한, 3차원 모델과 2차원 모델사이의 모드진동수는 25%에서 36%의 차이를 보였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권6호
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• pp.730-740
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• 2018

Hydrofoil is the direct component to generate thrust for underwater glider. It is significant to improve propulsion efficiency of hydrofoil. This study optimizes the shape of a hydrofoil using Free-Form Deformation (FFD) parametric approach and Surrogate-based Optimization (SBO) algorithm. FFD approach performs a volume outside the hydrofoil and the position changes of control points in the volume parameterize hydrofoil's geometric shape. SBO with adaptive parallel sampling method is regarded as a promising approach for CFD-based optimization. Combination of existing sampling methods is being widely used recently. This paper chooses several well-known methods for combination. Investigations are implemented to figure out how many and which methods should be included and the best combination strategy is provided. As the hydrofoil can be stretched from airfoil, the optimizations are carried out on a 2D airfoil and a 3D hydrofoil, respectively. The lift-drag ratios are compared among optimized and original hydrofoils. Results show that both lift-drag-ratios of optimized hydrofoils improve more than 90%. Besides, this paper preliminarily explores the optimization of hydrofoil with root-tip-ratio. Results show that optimizing 3D hydrofoil directly achieves slightly better results than 2D airfoil.

• 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.

• 한국지반공학회논문집
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• 제22권10호
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• pp.69-76
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• 2006

지하수흐름에 대한 신뢰성 해석을 실시하였으며, 흐름에 관여하는 매개변수들이 목표 값의 파괴확률을 초과하는데 미치는 영향을 알아보았다. 본 연구를 위하여 2차원 지하수흐름 프로그램을 3-D 프로그램 DGU-FLOW로 확장하여 제작하고, 이를 1계 및 2계 신뢰성 프로그램에 연계하였다. 3차원 흐름 프로그램의 검증은 지하굴착지반의 지하수 흐름 해석 문제를 풀고 이를 MODFLOW 프로그램과 비교하여 수행하였다. 신뢰성부분 또한 몬테칼로 해석을 수행하여 나타난 파괴확률을 비교함으로써 검증하였으며 지하수 흐름에 대한 1계 및 2계 신뢰성해석을 수행하여 산정된 파괴확률 값은 몬테칼로 해석을 통하여 나온 값과 매우 근접하였다. 토질층의 투수계수에 대한 매개변수 해석결과 투수계수의 평균과 분산의 증가는 목표 수량을 초과하는 파괴확률의 증가를 가져오는 것으로 나타났다. 또한 파괴확률의 민감도는 여러흐름 변수중에서 흐름영역 경계부의 일정 수두에 가장 민감한 것으로 나타났다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.64-71
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• 2009

The stresses acting on shotcrete lining of tunnel have been measured virtually by monitoring instruments installed during construction. However, the malfunction of instrument and the lack of consistency of signal have always been controversial, but re-installation of instrument after construction of tunnel lining is practically impossible. Therefore, authors have carried out the study to develop a new technique for estimating the stress acting on shotcrete lining during and after construction. In the technique, stresses of shotcrete lining can be estimate by the measurement of deformation of free face. Therefore, the relationships between the stresses of shotcrete lining and deformation of free surface are indispensable factor. In this paper, the parametric study using 2D FEM analysis was carried out to estimate the relationships between the stress level acting on the tunnel shotcrete lining and the deformation near the free face (e.g. artificial crack in this study). The distribution of stresses of shotcrete lining is also investigated in this study as the preliminary investigation for the large-scale tunnel lining test and detailed 3D FEM analysis.

• 한국추진공학회지
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• 제21권3호
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• pp.61-67
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• 2017

본 연구에서는 VOF 기법을 이용하여 3D 그레인 형상의 연소표면적을 계산하는 프로그램을 개발하고 연소표면적 결과를 이용하여 내탄도 성능해석을 수행하였다. 연소표면적 계산 수행 시 격자 크기, 난류화염속도, 단위 계산시간을 기초로 한 매개변수의 의존성을 확인하고, 상용 3D 모델링 소프트웨어를 이용하여 산출한 면적 결과와 비교하였다. 개발 프로그램으로 산출한 연소표면적 결과를 바탕으로 고체로켓모터의 내탄도 해석을 수행하였다. 임의의 추진제 조성으로 화학평형을 계산하고 시간에 따른 연소표면적 및 모터 내부 압력을 예측하였다. 웹(web) 연소 동안 평균 압력은 5.34 MPa 으로 기존 연구 결과와 약 20%의 차이를 보였다.

• Geomechanics and Engineering
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• 제12권3호
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• pp.505-522
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• 2017

A fundamental study of drilled shafts-soil systems subjected to lateral cyclic loading in weathered soil was conducted using numerical analyses. The emphasis was on quantifying the soil resistance of laterally cyclic loaded pile using 3D finite element analysis. The appropriate parametric studies needed for verifying the cyclic p-y characteristic are presented in this paper. A framework for determining the cyclic lateral load transfer curve (p-y curves) on the basis of numerical analyses is proposed. Through comparisons with results of field load tests, the three-dimensional numerical methodology in the present study is in good agreement with the general trend observed by in situ measurements and thus, represents a realistic soil-pile interaction for laterally loaded piles in soil than that of existing p-y method. It can be said that a rigorous present analysis can overcome the limitations of existing cyclic p-y methods to some extent by considering the effect of realistic three-dimensional combination of pile-soil forces. The proposed cyclic p-y curve is shown to be capable of predicting the behavior of the drilled shafts in weathered soil.

• 대한치과교정학회지
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• 제44권5호
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• pp.229-235
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• 2014

Objective: The aim of this study was to assess artifacts induced by metallic restorations in three-dimensional (3D) dental surface models derived by cone-beam computed tomography (CBCT). Methods: Fifteen specimens, each with four extracted human premolars and molars embedded in a plaster block, were scanned by CBCT before and after the cavitated second premolars were restored with dental amalgam. Five consecutive surface models of each specimen were created according to increasing restoration size: no restoration (control) and small occlusal, large occlusal, disto-occlusal, and mesio-occluso-distal restorations. After registering each restored model with the control model, maximum linear discrepancy, area, and intensity of the artifacts were measured and compared. Results: Artifacts developed mostly on the buccal and lingual surfaces. They occurred not only on the second premolar but also on the first premolar and first molar. The parametric values increased significantly with increasing restoration size. Conclusions: Metallic restorations induce considerable artifacts in 3D dental surface models. Artifact reduction should be taken into consideration for a proper diagnosis and treatment planning when using 3D surface model derived by CBCT in dentofacial deformity patients.

• Advances in nano research
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• 제9권4호
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• pp.295-307
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• 2020

The vibrational characteristics of Multi-Phase Nanocomposite (MPC) reinforced annular/circular plate under initially stresses are presented using the state-space formulation based on three-dimensional elasticity theory (3D-elasticity theory) and Differential Quadrature Method (DQM). The MPC reinforced annular/circular plate is under initial lateral stress and composed of multilayers with Carbon Nanotubes (CNTs) uniformly dispersed in each layer, but its properties change layer-by-layer along the thickness direction. The State-Space based Differential Quadrature Method (SS-DQM) is presented to examine the frequency behavior of the current structure. Halpin-Tsai equations and fiber micromechanics are used in the hierarchy to predict the bulk material properties of the multi-scale composite. A singular point is investigated for modeling the circular plate. The CNTs are supposed to be randomly oriented and uniformly distributed through the matrix of epoxy resin. Afterward, a parametric study is done to present the effects of various types of sandwich circular/annular plates on frequency characteristics of the MPC reinforced annular/circular plate using 3D-elasticity theory.