• Title/Summary/Keyword: Finite Element Analysis Method

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CFD analysis for effects of the crucible geometry on melt convection and growth behavior during sapphire single crystal growth by Kyropoulos process (사파이어 단결정의 Kyropoulos 성장시 도가니 형상에 따른 유동장 및 결정성장 거동의 CFD 해석)

  • Ryu, J.H.;Lee, W.J.;Lee, Y.C.;Jo, H.H.;Park, Y.H.
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.22 no.3
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    • pp.115-121
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    • 2012
  • Sapphire single crystals have been highlighted for epitaxial gallium nitride films in high-power laser and light emitting diode (LED) industries. Among the many crystal growth methods, the Kyropoulos process is an excellent commercial method for growing larger, high-optical-quality sapphire crystals with fewer defects. Because the properties and growth behavior of sapphire crystals are influenced largely by the temperature distribution and convection of molten sapphire during the manufacturing process, accurate predictions of the thermal fields and melt flow behavior are essential to design and optimize the Kyropoulos crystal growth process. In this study, computational fluid dynamic simulations were performed to examine the effects of the crucible geometry aspect ratio on melt convection during Kyropoulos sapphire crystal growth. The results through the evolution of various growth parameters on the temperature and velocity fields and convexity of the crystallization interface based on finite volume element simulations show that lower aspect ratio of the crucible geometry can be helpful for the quality of sapphire single crystal.

On the Use of Modal Derivatives for Reduced Order Modeling of a Geometrically Nonlinear Beam (모드 미분을 이용한 기하비선형 보의 축소 모델)

  • Jeong, Yong-Min;Kim, Jun-Sik
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.30 no.4
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    • pp.329-334
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    • 2017
  • The structures, which are made up with the huge number of degrees-of-freedom and the assembly of substructures, have a great complexity. In order to increase the computational efficiency, the analysis models have to be simplified. Many substructuring techniques have been developed to simplify large-scale engineering problems. The techniques are very powerful for solving nonlinear problems which require many iterative calculations. In this paper, a modal derivatives-based model order reduction method, which is able to capture the stretching-bending coupling behavior in geometrically nonlinear systems, is adopted and investigated for its performance evaluation. The quadratic terms in nonlinear beam theory, such as Green-Lagrange strains, can be explained by the modal derivatives. They can be obtained by taking the modal directional derivatives of eigenmodes and form the second order terms of modal reduction basis. The method proposed is then applied to a co-rotational finite element formulation that is well-suited for geometrically nonlinear problems. Numerical results reveal that the end-shortening effect is very important, in which a conventional modal reduction method does not work unless the full model is used. It is demonstrated that the modal derivative approach yields the best compromised result and is very promising for substructuring large-scale geometrically nonlinear problems.

Shape Design of Bends in District Heating Pipe System by Taguchi Method (다구찌 방법을 이용한 지역난방시스템의 벤드형상 설계)

  • Choi, Moon-Deok;Kim, Joo-Yong;Ko, Hyun-Il;Cho, Chong-Du
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.3
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    • pp.307-313
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    • 2010
  • In this study, alternative designs for the bends used in district heating pipes are investigated. The district heating pipes, which are subjected to temperatures of 10 to $120^{\circ}C$ and a water pressure of $16\;kgf/cm^2$, have to withstand thermomechanical cyclic loads when in use. These pipes comprise three concentric tubes: a steel pipe (internal), polyurethane (PUR) insulator (middle), and a high-density polyethylene (HDPE) case (external). In addition, the bends in the district heating pipe system are covered with foam pads that cause aging. In this study, an alternative bend design that does not involve the use of a foam pad is proposed to overcome the aging problem in the bends. In the proposed design, "shear rings" are added to the surface of a bend, and its dimensions are determined by a combination of the statistical (Taguchi) method and FEM. The geometrical parameters such as thickness, height, and number of the rings significantly affect the design optimization, and hence, they affect the results of the FEM.

Mechanical Bending Process and Application for a Large Curved Shell Plate by Multiple Point Press Machine (무금형 다점 펀치를 사용한 선체외판의 분할 성형 가공 정보 계산 시스템 개발)

  • Hwang, Se-Yun;Lee, Jang-Hyun;Ryu, Cheol-Ho;Han, Myung-Soo;Kim, Kwang-Ho;Kim, Kwang-Sik
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.6
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    • pp.528-538
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    • 2011
  • As a forming method for curved hull plates more efficient than the flame bending, mechanical bending using multi point press forming and die-less forming is discussed in this paper. the mechanical forming is a flexible manufacturing system for automatically forming of hull parts. It is especially suited to varied curved parts. This paper discusses a multiple point pressing machine composed of a pair of reconfigurable punches in order to achieve the rapid forming of curved hull plates using division forming and presents how forming information is obtained from the given design surface. Although the mechanical forming can be efficient in the metal forming, spring back after pressing is a phenomenon which must be carefully considered when quantifying the process variables. If the spring back is not accurately controlled, the fabricated shell plate cannot meet assembly tolerance. This paper describes the principles to calculate the proper stroke of each punch at the divided areas. the strokes are determined by an iterative process of sequential pressing and spring back compensation from an unfolded flat shape to its given design surface. FEA(finite element analysis) is used to simulate the spring back of the plate and the IDA(iterative displacement adjustment) method adjusts the offset of pressing punches from the deformation results and the design surface. The shape deviations of two surfaces due to spring back are compensated by integrated system using FEA and IDA method. For the practical application, It is aimed to develop an integrated system that can automatically perform the compensation process and calculate strokes of punches of the double sides' reconfigurable multiple-press machine and some experimental results obtained with mechanical bending are presented.

Thickness Design of Composite Pavement for Heavy-Duty Roads Considering Cumulative Fatigue Damage in Roller-Compacted Concrete Base (롤러전압콘크리트 기층의 누적피로손상을 고려한 중하중 도로의 복합포장 두께 설계)

  • Kim, Kyoung Su;Kim, Young Kyu;Chhay, Lyhour;Lee, Seung Woo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.42 no.4
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    • pp.537-548
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    • 2022
  • It is important to design the pavement thickness considering heavy-duty traffic loads, which can cause excessive stress and strain in the pavement. Port-rear roads and industrial roads have many problems due to early stress in pavement because these have a higher ratio of heavy loads than general roads such as national roads and expressways. Internationally, composite pavement has been widely applied in pavement designs in heavy-duty areas. Composite pavement is established as an economic pavement type that can increase the design life by nearly double compared to that of existing pavement while also decreasing maintenance and user costs. This study suggests a thickness design method for composite pavement using roller-compacted concrete as a base material to ensure long-term serviceability in heavy-duty areas such as port-rear roads and industrial roads. A three-dimensional finite element analysis was conducted to investigate the mechanical behavior and the long-term pavement performance ultimately to suggest a thickness design method that considers changes in the material properties of the roller-compacted concrete (RCC) base layer. In addition, this study presents a user-friendly catalog design method for RCC-base composite pavement considering the concept of linear damage accumulation for each container trailer depending on the season.

The Estimation of Buckling Load of Pressurized Unstiffened Cylindrical Shell Using the Hybrid Vibration Correlation Technique Based on the Experimental and Numerical Approach (실험적/수치적 방법이 혼합된 VCT를 활용한 내부 압력을 받는 원통형 쉘의 좌굴 하중 예측)

  • Lee, Mi-Yeon;Jeon, Min-Hyeok;Cho, Hyun-Jun;Kim, Yeon-Ju;Kim, In-Gul;Park, Jae-Sang
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.50 no.10
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    • pp.701-708
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    • 2022
  • Since the propellant tank structure of the projectile is mainly subjected to a compressive force, there is a high risk of damage due to buckling. Large and lightweight structures such as propellant tank have a complex manufacturing process. So it requires a non-destructive test method to predict buckling load to use the structure after testing. Many studies have been conducted on Vibration Correlation Technique(VCT), which predicts buckling load using the relationship between compressive load and natural frequency, but it requires a large compressive load to predict the buckling load accurately, and it tends to decrease prediction accuracy with increasing internal pressure in structure. In this paper, we analyzed the causes of the decrease in prediction accuracy when internal pressure increases and proposed a method increasing prediction accuracy under the low compressive load for being usable after testing, through VCT combined testing and FEA result. The prediction value by the proposed method was very consistent with the measured actual buckling load.

A Strategy of a Gap Block Design in the CFRP Double Roller to Minimize Defects during the Product Conveyance (제품 이송 시 결함 최소화를 위한 CFRP 이중 롤러의 Gap block 설계 전략)

  • Seung-Ji Yang;Young-june Park;Sung-Eun Kim;Jun-Geol Ahn;Hyun-Ik Yang
    • Composites Research
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    • v.37 no.1
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    • pp.7-14
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    • 2024
  • Due to the structural characteristic of a double roller, the double roller can have various deformation behaviors depending on a gap block design, even if dimensions and loading conditions for the double roller are the same. Based on this feature, we propose a strategy for designing the gap block of the carbon-fiber reinforced plastic (CFRP) double roller to minimize defects (e.g., sagging and wrinkling), which can be raised during the product conveying process, with the pursue of the lightweight design. In the suggested strategy, analysis cases are first selected by considering main design parameters and engineering tolerances of the gap block, and then deformation behaviors of these selected cases are extracted using the finite element method (FEM). Here, to obtain the optimal gap block parameters that satisfy the purpose of this study, deformation deviations in the contact area are calculated and compared using the extracted deformation behaviors. Note that the contact area in this work is located between the product and the roller. As a result, through the design method of the gap block proposed in this work, it is possible to construct the CFRP double roller that can significantly decrease the defects without changing the overall sizes of the roller. A detailed method is suggested herein, and the results are evaluated in a numerical way.

Effect of Tire Contact Stresses on Tensile Strains in the Surface of Thin Asphalt Pavement (접지압력이 앎은 아스팔트포장 표층 인장 변형률에 미치는 영향 분석)

  • Park, Dae-Wook;Park, Joon-Kyu
    • International Journal of Highway Engineering
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    • v.10 no.2
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    • pp.47-55
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    • 2008
  • In this paper, comparisons are presented on the predicted tensile strains which can affect the fatigue life of a thin asphalt concrete (AC) pavement near the surface of pavement from three-dimensional (3D) finite element (FE) using 3D measured tire contact stresses of a radial tire and a bias ply tire and a layered linear elastic program (BISAR). The objective was to analyze the stress distributions for a 11R22.5 radial tire and a $10{\times}20$ bias ply tire, and to compare the predicted tensile strains at the top and bottom of AC surface using different analysis methods. The results show that the stress distributions of two tires are similar but the 11R22.5 radial tire has much higher vertical contact stress than that of the $10{\times}20$ bias ply tire. The predicted tensile strains at the bottom of AC layer under the center of tire showed higher value by BM (BISAR with the measured contact area) method, which the measured tire contact area is used in a layered elastic program, while the tensile strain at the top of AC surface of 3.5cm offset distance from tire edge by 3D FE analysis showed the highest values among three analysis methods.

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Three-dimensional anisotropic inversion of resistivity tomography data in an abandoned mine area (폐광지역에서의 3차원 이방성 전기비저항 토모그래피 영상화)

  • Yi, Myeong-Jong;Kim, Jung-Ho;Son, Jeong-Sul
    • Geophysics and Geophysical Exploration
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    • v.14 no.1
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    • pp.7-17
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    • 2011
  • We have developed an inversion code for three-dimensional (3D) resistivity tomography including the anisotropy effect. The algorithm is based on the finite element approximations for the forward modelling and Active Constraint Balancing method is adopted to enhance the resolving power of the smoothness constraint least-squares inversion. Using numerical experiments, we have shown that anisotropic inversion is viable to get an accurate image of the subsurface when the subsurface shows strong electrical anisotropy. Moreover, anisotropy can be used as additional information in the interpretation of subsurface. This algorithm was also applied to the field dataset acquired in the abandoned old mine area, where a high-rise apartment block has been built up over a mining tunnel. The main purpose of the investigation was to evaluate the safety analysis of the building due to old mining activities. Strong electrical anisotropy has been observed and it was proven to be caused by geological setting of the site. To handle the anisotropy problem, field data were inverted by a 3D anisotropic tomography algorithm and we could obtain 3D subsurface images, which matches well with geology mapping observations. The inversion results have been used to provide the subsurface model for the safety analysis in rock engineering and we could assure the residents that the apartment has no problem in its safety after the completion of investigation works.

Numerical Analysis of Load Reduction for Underground Arch Structures with Soft Zone Using Expanded PolyStyrene Geofoam (EPS Geofoam을 이용한 Soft Zone 적용방법에 따른 지중아치구조물의 하중저감에 관한 해석 연구)

  • Kim, Soo-Ha;Park, Jong-Sup;Kang, Jun-Suk
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.19 no.10
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    • pp.24-30
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    • 2018
  • As the demand for underground space increases, many researchers have been studying the load reduction method using high compressible materials to solve for the stability problem of the overhead load and for the increase of the earth pressure which decreases the function of the underground structure. This paper determines the optimum soft zone and the effect of the using EPS Geofoam as a load reduction material to arch structures. A finite element analysis program, ABAQUS, is used to analyze the soil-structure interaction and the behavior of buried arch structures considering different four EPS Geofoam forms to confirm the most conservative shape. The optimum cross-sectional shape was determined by comparing the results of earth pressure reduction rate in accordance with the change of span-rise ratio and span length of the arch structure. It was confirmed that the earth pressure generated in the arch structure using the optimal soft zone selected by the numerical analysis was reduced by an average of 78%. In this study, the effect of EPS Geofoam on soil pressure reduction and its applicability to underground arch structures will provide an economical and conservative way to design underground structures and will help to increase the usability of deep underground space.