• Title/Summary/Keyword: non-continuum

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Evaluation of Crack-tip Cohesive Laws for the Mode I Fracture of the Graphene from Molecular Dynamics Simulations (그래핀의 모드 I 균열에 대한 분자동역학 해석으로부터 균열 선단 응집 법칙의 평가)

  • Kim, Hyun-Gyu
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.26 no.5
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    • pp.393-399
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    • 2013
  • In this paper, a novel approach to estimate cohesive laws for the mode I fracture of the graphene is presented by combining molecular dynamic simulations and an inverse algorithm based on field projection method and finite element method. The determination of crack-tip cohesive laws of the graphene based on continuum mechanics is a non-trivial inverse problem of finding unknown tractions and separations from atomic simulations. The displacements of molecular dynamic simulations in a region far away from the crack tip are transferred to finite element nodes by using moving least square approximation. Inverse analyses for extracting unknown cohesive tractions and separation behind the crack tip can be carried out by using conservation nature of the interaction J- and M-integrals with numerical auxiliary fields which are generated by systematically imposing uniform surface tractions element-by-element along the crack surfaces in finite element models. The preset method can be a very successful approach to extract crack-tip cohesive laws from molecular dynamic simulations as a scale bridging method.

Molecular Simulation Studies for Penetrable-Sphere Model : I. Equation of State (침투성 구형 모델에 관한 분자 전산 연구: I. 상태 방정식)

  • Kim, Chun-Ho;Suh, Soong-Hyuck
    • Polymer(Korea)
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    • v.35 no.4
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    • pp.325-331
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    • 2011
  • Molecular simulations via the molecular dynamics method have been carried out to an equation of state of penetrable-sphere model fluids over a wide range of packing fraction ${\phi}$ and finite repulsive energy ${\varepsilon}^*$. The resulting simulation data are compared to theoretical predictions from the two limiting cases of high- and low-penetrability approximations available in the literature. A good agreement between theoretical and simulation results is observed ill the case of ${\varepsilon}^*$ <3.0. However, for the highly repulsive energy systems of ${\varepsilon}^*{\geqq}3.0$, where the potential energy barrier is more than two times higher than the particle kinetic energy, a poor agreement is found due to the clustering formation and the non-continuum size effects in the dense systems of ${\phi}{\geqq}0.7$ and ${\varepsilon}^*$=6.0.

Synergistic Effects for Remediation of Salt-affected Soil using Dendranthema zawadskii var. latilobum and Soil Amendments under High-concentration Calcium Chloride (고농도 염화칼슘 농도처리에 따른 토양개량제와 구절초의 염분저감 상승효과)

  • Yoon, Yong-Han;Yang, Ji;Park, Je-Min;Ju, Jin-Hee
    • Journal of Environmental Science International
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    • v.30 no.10
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    • pp.803-809
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    • 2021
  • This study aimed to investigate the effects of soil amendment (heat-expanded clay and active carbon) and planting of Dendranthema zawadskii var. latilobum on the remediation of salt-affected soil and the plant growth under high calcium chloride (CaCl2) concentration. The experimental group comprised treatments including Non treatment (Cont.), heat-expanded clay (H), active carbon (AC), planting (P), heat-expanded clay+planting (H+P), active carbon+planting (AC+P). A 200 mL solution of CaCl2 at a concentration of 10 g·L-1 was applied as irrigation once every 2 weeks. Compared to the Cont., the incorporation of the 'heat-expanded clay' amendment decreased electrical conductivity of the soil leachate and cation exchange capacity, whereas the growth of Dendranthema zawadskii var. latilobum was relatively increased. These results suggest that the combination of 'heat-expanded clay' amendment and planting will mitigate negative effect of de-icing salts and improve plant growth in salt-contaminated roadside soils.

Reliability-based combined high and low cycle fatigue analysis of turbine blade using adaptive least squares support vector machines

  • Ma, Juan;Yue, Peng;Du, Wenyi;Dai, Changping;Wriggers, Peter
    • Structural Engineering and Mechanics
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    • v.83 no.3
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    • pp.293-304
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    • 2022
  • In this work, a novel reliability approach for combined high and low cycle fatigue (CCF) estimation is developed by combining active learning strategy with least squares support vector machines (LS-SVM) (named as ALS-SVM) surrogate model to address the multi-resources uncertainties, including working loads, material properties and model itself. Initially, a new active learner function combining LS-SVM approach with Monte Carlo simulation (MCS) is presented to improve computational efficiency with fewer calls to the performance function. To consider the uncertainty of surrogate model at candidate sample points, the learning function employs k-fold cross validation method and introduces the predicted variance to sequentially select sampling. Following that, low cycle fatigue (LCF) loads and high cycle fatigue (HCF) loads are firstly estimated based on the training samples extracted from finite element (FE) simulations, and their simulated responses together with the sample points of model parameters in Coffin-Manson formula are selected as the MC samples to establish ALS-SVM model. In this analysis, the MC samples are substituted to predict the CCF reliability of turbine blades by using the built ALS-SVM model. Through the comparison of the two approaches, it is indicated that the reliability model by linear cumulative damage rule provides a non-conservative result compared with that by the proposed one. In addition, the results demonstrate that ALS-SVM is an effective analysis method holding high computational efficiency with small training samples to gain accurate fatigue reliability.

An Experimental Study for the Strength Evaluation of Bolted Connection in Resin Transfer Molding Fiber Reinforced Polymeric Plastic (사출성형 섬유강화플라스틱 볼트 연결부의 강도 평가를 위한 실험적 연구)

  • Choi, Jinwoo;Kim, Sunhee
    • Journal of Urban Science
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    • v.11 no.2
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    • pp.25-30
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    • 2022
  • Resin Transfer Molding FRP (RTM FRP) is a fiber reinforced polymeric plastic which is manufactured by applying pressure to fibers, injecting resin into a mold, and then impregnating it. RTM FRP is a new construction material suitable for producing non-continuum structural elements such as sole plate because it has excellent strength and can produce many members in a short time. In this study, experiments were conducted to estimate the capacity of the bolted connection of RTM FRP. First, a tensile test was conducted to confirm the mechanical properties such as the tensile strength of the RTM FRP to be used for the bolted connection experiments. In addition, experiments were conducted on the bolted connection with the thickness of the RTM FRP and the edge distance of the bolt as variables. In the first experiment, F4.8 bolts were used, and shear failure of the bolt occurred before the RTM FRPs were failed. The F4.8 bolt is a general structural bolts used for the sole plate of a bridge bearing, and it was confirmed that the RTM FRP has a higher bold bearing strength than the shear strength of a F4.8 bolt. In the second experiment, G12.9 bolts were used, and shear failure of the bolt and bearing failure of the RTM FRP occurred simultaneously. In addition, as the thickness of the RTM FRP and the edge length of the bolt increased, the strength of the joint increased. When analogized with the bearing fracture equation of steel plate, the bolted connection of RTM FRP showed a bearing strength coefficient of 0.420 to 0.549 compared to the tensile strength, and it is considered that further research is needed.

Learning the Civilization of Modern Science and Technology through Animation Film: Focusing on Michel Ocelot's (애니메이션 감상을 통한 근대 과학기술 문명 탐구 - 미셸 오슬로의 <세 명의 발명가>를 중심으로)

  • Youn, Kyung Hee;Choi, Jeongyoon;Park, Yooshin
    • Cartoon and Animation Studies
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    • s.49
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    • pp.267-297
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    • 2017
  • This paper attempts a close-reading of Michel Ocelot's short animation film, (1979), and proposes it as an available text in art appreciation class for young students. stimulates the students' attention and intellectual curiosity thanks to the exotic and fantastic atmosphere, beautiful mise en scene, and intriguing plot. Ocelot's technique of decoupage used in this film rejuvenates both the traditional folk art and Lotte Reiniger's early experiments in the history of animation film. Ocelot subverts the ideal of modern male adult subject as unique possessor of scientific knowledge and technology, by adopting a female figure and a young child, who is also female, as main characters. The imaginative and subversive power of animation contributes to creating posthuman beings beyond the homocentric figure of Vitruvian Man. The posthuman condition supposes that human beings have the equal relationship of continuum with not only other humans but also non-human beings like all living things and inanimate matters. In order to teach and learn the posthuman condition, it is necessary to conceive an interdisciplinary and integrated curriculum including art, science, philosophy, history, and social sciences. Animation film serves excellently as educational text for the integrated curriculum of the posthuman.

Direct numerical simulations of viscoelastic turbulent channel flows at high drag reduction

  • Housiadas Kostas D.;Beris Antony N.
    • Korea-Australia Rheology Journal
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    • v.17 no.3
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    • pp.131-140
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    • 2005
  • In this work we show the results of our most recent Direct Numerical Simulations (DNS) of turbulent viscoelastic channel flow using spectral spatial approximations and a stabilizing artificial diffusion in the viscoelastic constitutive model. The Finite-Elasticity Non-Linear Elastic Dumbbell model with the Peterlin approximation (FENE-P) is used to represent the effect of polymer molecules in solution, The corresponding rheological parameters are chosen so that to get closer to the conditions corresponding to maximum drag reduction: A high extensibility parameter (60) and a moderate solvent viscosity ratio (0.8) are used with two different friction Weissenberg numbers (50 and 100). We then first find that the corresponding achieved drag reduction, in the range of friction Reynolds numbers used in this work (180-590), is insensitive to the Reynolds number (in accordance to previous work). The obtained drag reduction is at the level of $49\%\;and\;63\%$, for the friction Weissenberg numbers 50 and 100, respectively. The largest value is substantially higher than any of our previous simulations, performed at more moderate levels of viscoelasticity (i.e. higher viscosity ratio and smaller extensibility parameter values). Therefore, the maximum extensional viscosity exhibited by the modeled system and the friction Weissenberg number can still be considered as the dominant factors determining the levels of drag reduction. These can reach high values, even for of dilute polymer solution (the system modeled by the FENE-P model), provided the flow viscoelasticity is high, corresponding to a high polymer molecular weight (which translates to a high extensibility parameter) and a high friction Weissenberg number. Based on that and the changes observed in the turbulent structure and in the most prevalent statistics, as presented in this work, we can still rationalize for an increasing extensional resistance-based drag reduction mechanism as the most prevalent mechanism for drag reduction, the same one evidenced in our previous work: As the polymer elasticity increases, so does the resistance offered to extensional deformation. That, in turn, changes the structure of the most energy-containing turbulent eddies (they become wider, more well correlated, and weaker in intensity) so that they become less efficient in transferring momentum, thus leading to drag reduction. Such a continuum, rheology-based, mechanism has first been proposed in the early 70s independently by Metzner and Lamley and is to be contrasted against any molecularly based explanations.

A Study on the Development of Multiscale Bridging Method Considering the Particle Size and Concentration Effect of Nanocomposites (나노입자의 크기효과와 체적분율 효과를 동시 고려한 나노복합재의 멀티스케일 브리징 해석기법에 관한 연구)

  • Yang, Seung-Hwa;Yu, Su-Young;Cho, Maeng-Hyo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.22 no.4
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    • pp.343-348
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    • 2009
  • In this study, an efficient sequential bridging method to characterize both the particle size effect and concentration effect on the mechanical properties of nanocomposites at high volume fraction is suggested through a molecular dynamics(MD) simulations and micromechanics of composites materials. The Young's modulus and the shear modulus of the nanocomposites at various particle radius and at 12% volume fraction were obtained from MD simulations and multi-inclusion model was adopted to describe both modulus in continuum model. In order to describe the particle size effect, an additional phase, effective interface, was adopted as characteristic phase and the non-dilute concentration effect which appears at 12% volume fraction was describe via the variation of the elastic modulus of the infinite medium. Both the elastic modulus of the interface and infinite medium were fitted into functions of particle radius for the applicability of the present bridging method at various particle radii. Using the present bridging method the elastic modulus of the nanocomposites was efficiently obtained with accuracy. In addition, the effect of the interface thickness and modulus on the elastic modulus of the nanocomposite was investigated.

Dynamic Fracture Analysis of High-speed Impact on Granite with Peridynamic Plasticity (페리다이나믹 소성 모델을 통한 화강암의 고속 충돌 파괴 해석)

  • Ha, Youn Doh
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.32 no.1
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    • pp.37-44
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    • 2019
  • A bond-based peridynamic model has been reported dynamic fracture characteristic of brittle materials through a simple constitutive model. In the model, each bond is assumed to be a simple spring operating independently. As a result, this simple bond interaction modeling restricts the material behavior having a fixed Poisson's ratio of 1/4 and not being capable of expressing shear deformation. We consider a state-based peridynamics as a generalized peridynamic model. Constitutive models in the state-based peridynamics are corresponding to those in continuum theory. In state-based peridynamics, thus, the response of a material particle depends collectively on deformation of all bonds connected to other particles. So, a state-based peridynamic theory can represent the volume and shear changes of the material. In this paper, the perfect plasticity is considered to express plastic deformation of material by the state-based peridynamic constitutive model with perfect plastic flow rule. The elastic-plastic behavior of the material is verified through the stress-strain curves of the flat plate example. Furthermore, we simulate the high-speed impact on 3D granite model with a nonlocal contact modeling. It is observed that the damage patterns obtained by peridynamics are similar to experimental observations.

Analysis of Magnetic Flux Leakage based Local Damage Detection Sensitivity According to Thickness of Steel Plate (누설자속 기반 강판 두께별 국부 손상 진단 감도 분석)

  • Kim, Ju-Won;Yu, Byoungjoon;Park, Sehwan;Park, Seunghee
    • Journal of Korean Society of Disaster and Security
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    • v.11 no.2
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    • pp.53-60
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    • 2018
  • To diagnosis the local damages of the steel plates, magnetic flux leakage (MFL) method that is known as a adaptable non-destructive evaluation (NDE) method for continuum ferromagnetic members was applied in this study. To analysis the sensitivity according to thickness of steel plate in MFL method based damage diagnosis, several steel plate specimens that have different thickness were prepared and three depths of artificial damage were formed to the each specimens. To measured the MFL signals, a MFL sensor head that have a constant magnetization intensity were fabricated using a hall sensor and a magnetization yoke using permanent magnets. The magnetic flux signals obtained by using MFL sensor head were improved through a series of signal processing methods. The capability of local damage detection was verified from the measured MFL signals from each damage points. And, the peak to peak values (P-P value) extracted from the detected MFL signals from each thickness specimen were compared each other to analysis the MFL based local damage detection sensitivity according to the thickness of steel plate.