• Title/Summary/Keyword: Critical size effect

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Error Estimation and Adaptive Time Stepping Procedure for Structural Dynamics (구조동역학에서의 오차 추정과 시간간격 제어 알고리즘)

  • 장인식
    • Transactions of the Korean Society of Automotive Engineers
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    • v.4 no.4
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    • pp.190-200
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    • 1996
  • Step-by-step time integration methods are widely used for solving structural dynamics problem. One difficult yet critical choice an analyst must make is to decide an appropriate time step size. The choice of time step size has a significant effect on solution accuracy and computational expense. The objective of this research is to derive error estimate for newly developed time integration method and develop automatic time step size control algorithm for structural dynamics. A formula for computing error tolerance is derived based on desired period resolution. An automatic time step size control strategy is proposed based on a normalized local error estimate for the generalized-α method. Numerical examples demonstrate the developed strategy satisfies general design criteria for time step size control algorithm for dynamic problem.

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Droplet size prediction model based on the upper limit log-normal distribution function in venturi scrubber

  • Lee, Sang Won;No, Hee Cheon
    • Nuclear Engineering and Technology
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    • v.51 no.5
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    • pp.1261-1271
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    • 2019
  • Droplet size and distribution are important parameters determining venturi scrubber performance. In this paper, we proposed physical models for a maximum stable droplet size prediction and upper limit log-normal (ULLN) distribution parameters. For the proposed maximum stable droplet size prediction model, a Eulerian-Lagrangian framework and a Reitz-Diwakar breakup model are solved simultaneously using CFD calculations to reflect the effect of multistage breakup and droplet acceleration. Then, two ULLN distribution parameters are suggested through best fitting the previously published experimental data. Results show that the proposed approach provides better predictions of maximum stable droplet diameter and Sauter mean diameter compared to existing simple empirical correlations including Boll, Nukiyama and Tanasawa. For more practical purpose, we developed the simple, one dimensional (1-D) calculation of Sauter mean diameter.

A Study on the Effect of Change Management for the ERP Performance in Small and Medium Companies (변화관리요인이 중소기업의 ERP도입성과에 미치는 영향 연구)

  • Park, Chy-Gwan
    • Journal of Information Technology Applications and Management
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    • v.15 no.4
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    • pp.123-136
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    • 2008
  • This study tried to find out the effect of change management on the ERP performance in small and medium size companies. Communication, BPR management, education and training were selected as independent variables which might bring an effect on ERP performances which were classified as quality and quantity one. Structure equation model was built and analyzed with AMOS 5.0 version from data gathered through 127 companies which already implemented ERP systems. The result of this study shows that all the three independent variables give positive impacts on two dependent variables, which means change management is critical when small and medium size companies want to implement ERP systems.

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Size-dependent thermal behaviors of axially traveling nanobeams based on a strain gradient theory

  • Li, Cheng
    • Structural Engineering and Mechanics
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    • v.48 no.3
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    • pp.415-434
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    • 2013
  • This work is concerned with transverse vibrations of axially traveling nanobeams including strain gradient and thermal effects. The strain gradient elasticity theory and the temperature field are taken into consideration. A new higher-order differential equation of motion is derived from the variational principle and the corresponding higher-order non-classical boundary conditions including simple, clamped, cantilevered supports and their higher-order "offspring" are established. Effects of strain gradient nanoscale parameter, temperature change, shape parameter and axial traction on the natural frequencies are presented and discussed through some numerical examples. It is concluded that the factors mentioned above significantly influence the dynamic behaviors of an axially traveling nanobeam. In particular, the strain gradient effect tends to induce higher vibration frequencies as compared to an axially traveling macro beams based on the classical vibration theory without strain gradient effect.

A study on the prediction of the angular distortion in line heating with high frequency induction heating (고주파 유도가열을 이용한 선상가열 시 각 변형 예측에 관한 연구)

  • Park, Dong-Hwan;Jin, Hyung-Kook;Park, Soung-Sig;Shin, Sang-Beom
    • Journal of Welding and Joining
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    • v.33 no.1
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    • pp.80-86
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    • 2015
  • The purpose of this study is to establish the predictive method of the angular distortion caused by the line heating process with high frequency induction heating. In order to do it, the heat input model for the high frequency induction heating system was established through comparing the temperature evaluation results obtained by both FEA and experiment. The critical heating conditions to prevent the degradation of the work piece with various thicknesses were identified by FEA and microstructure test results. Under the critical heating conditions, the extensive line heating tests were performed. According to the test results, it was found that the angular distortion behavior of the heated plates could be defined as the function of heat intensity and the rigidity of heated plate. In addition, it was clarified that the angular distortion strongly depended on the size of test specimen such as the length and the width of the heated plate. Based on these results, the predictive equation for the angular distortion was established with the function of heat intensity, bending rigidity and size of heated plate.

Variables related to self-leadership of Korean nursing students: A systematic review and meta-analysis (국내 간호대학생의 셀프리더십 관련변인에 대한 체계적 문헌고찰 및 메타분석)

  • Cho, Myung Hee;Jung, In Ja;Park, Mi Kyung
    • The Journal of Korean Academic Society of Nursing Education
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    • v.26 no.3
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    • pp.213-224
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    • 2020
  • Purpose: This study considers the variables related to self-leadership of Korean nursing students and verifies the results of precedent studies through meta-analysis. Methods: This study selected a total of 48 precedent studies regarding the investigation of the correlation between variables related to self-leadership of nursing students conducted between 2009 and 2019 and carried out a meta-analysis. Results: For the effect size of variables related to self-leadership of nursing students, individual characteristics had a medium effect size (ESr=.49) and the effect size was larger for meta-cognition (ESr=.65), emotional intelligence (ESr=.58), and self-efficacy (ESr=.54). The characteristics of nursing competency (ESr=.45) also had a medium effect size and the effect size was larger for professional self-concept (ESr=.60), social support (ESr=.58), and critical thinking (ESr=.56). This result shows that individual characteristics were highly correlated with self-leadership compared to the characteristics of nursing competency. Conclusion: This study is significant in that it verified the effect of variables related to self-leadership and presented the direction and preliminary data for a follow-up study. It is necessary to include variables considering individual characteristics in the development of an educational program for improving self-leadership in the future.

Applicability of hiding-exposure effect to suspension simulation of fine sand bed (가는 모래의 부유 모의시 차폐효과 고려의 영향)

  • Byun, Jisun;Son, Minwoo
    • Journal of Korea Water Resources Association
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    • v.54 no.8
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    • pp.607-616
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    • 2021
  • The purpose of this study is to simulate the transport of nonuniform sediment considering the hiding-exposure effect numerically. In order to calculate the transport of multi-disperse suspended sediment mixtures, the set of advection-diffusion equations for each particle class is solved. The applicability of the numerical model is examined by comparing the simulation results with experimental data. In this study, we calculate the vertical distribution of total concentration of sediment particles using two approaches: (1) by considering the mixture as represented by a single size; and (2) by combining the concentration of the sediment corresponding to several particle size classes; From the simulation results, it is shown that both approaches calculate reasonable results due to the narrow range of size distribution. Under the condition of nonuniform sediment, the critical shear stress of the sediment particle is influenced by the size-selective entrainment, i.e., hiding-exposure effect. It is shown in this study that the effect of hiding-exposure effect on the erosion rates of fine sand is negligibly small.

Effect of Grain Size and Predeformation on Shape Memory Ability and Transformation Temperature in Iron Base Fe-Mn-Si System Shape Memory Alloy (다결정질 Fe-Mn-Si계 형상기억합금의 형상기억합금과 변태점에 미치는 결정입도와 이전가공의 영향)

  • Choi, Chong Sool;Kim, Hyun Woo;Jin, Won;Shon, In Jin;Baek, Seung Han
    • Journal of the Korean Society for Heat Treatment
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    • v.3 no.1
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    • pp.34-41
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    • 1990
  • Effects of grain size and cold rolling degree on shape memory ability and transformation temperature were studied in Fe-35% Mn-6% Si shape memory alloy. Md point of the alloy was determined by variation of yield stress with test temperature. The Md point measured in this way was linearly increased with increasing grain size. Shape memory ability of the alloy was decreased with increasing grain size, showing a minimum value at around $63{\mu}m$, and then increased with increasing grain size. From this result, it was concluded that the shape memory ability in the grain size smaller than a critical value is controlled by amount of retained ${\gamma}$ and prior ${\varepsilon}$ phase, but that the shape memory ability in the grain size greater than the critical value is mainly dominated by grain boundary area in unit volume of parent phase. The shape memory ability was decreased with increasing deformation degree. This was because the ${\gamma}$ content being available for the formation of ${\varepsilon}$ martensite during bending was decreased with increasing deformation degree.

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Kelvin Equation and Its Role in Nano Systems (켈빈 식과 이의 나노 계에서의 구실)

  • Lim, Kyung-Hee
    • Journal of the Korean Applied Science and Technology
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    • v.23 no.1
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    • pp.54-62
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    • 2006
  • Kelvin equation is revisited, which accounts for important phenomena observed frequently in nano-dispersion systems. They include vapor pressure increase for curved interfaces, nucleation, capillary condensation, Ostwald ripening and so on. The smaller the radius of curvature is, the more significant Kelvin equation becomes. Therefore, its meaning, curvature effect, and importance are examined and discussed.

The Effect of the Precursor Delivery Rate on low Pressure Flame Synthesis of $n-TiO_2$ Powder ($n-TiO_2$ 분말의 저압화염 합성에 미치는 전구체 전달속도의 영향)

  • 김태형
    • Journal of Powder Materials
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    • v.6 no.1
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    • pp.75-80
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    • 1999
  • The formation of $n-TiO_2$ powder by oxidation of Ti-ethoxied vapor in a flat flame burner reactor maintained under 20 torr has been studied. The produced powder were characterized in terms of crystal structure, chemical composition by XRD and TEM. The results showed that the powder consisted of loose agglomerated anatase and rutile particles and their size were about 10 nm and 20 nm, respectively. In the course of synthesis, changes of the flame color were happened to each condition during heating up the bubbler. The flame color transition phenomena reveled that a critical precursor delivery rate was needed for the powder formation (obtainable powder yield). The critical precursor delivery rate was estimated by a simple function of the bubbler temperature and the carrier gas flow rate. The critical precursor delivery rate was reviewed as an important variable of the nanopowder synthesis.

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