• Title/Summary/Keyword: Numerical and experimental results

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The variation of critical current by the formation of crack in a high-temperature superconducting tape (크랙에 의한 고온 초전도체 테이프의 임계전류 특성변화)

  • 박을주;설승윤
    • Progress in Superconductivity and Cryogenics
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    • v.4 no.1
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    • pp.73-77
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    • 2002
  • The variation of critical current by the formation of crack in a high temperature super-conducting tape was studied by experimental and numerical analyses. The current-voltage relation of HTS tape is measured by the four-point measurement method. Numerical analyses are used to solve two dimensional heat conduction equation, considering the temperature distribution. By comparing current-voltage relation of experimental and numerical results, the validity of numerical method is verified.

Numerical Analysis for Three-Dimensional Tsunami Force Acting on Multi-Onshore Structures (육상구조물군에 작용하는 지진해일파력의 3차원수치해석)

  • Lee, Kwang Ho;Ha, Sun Wook;Lee, Kui Seop;Kim, Do Sam
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.2B
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    • pp.175-185
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    • 2011
  • This study investigates tsunami force acting on a group of onshore structures numerically by using three-dimensional one-field model for immiscible multi-phase flows, which is based on Navier-Stokes solver. In particular, we studied on the characteristics of tsunami with respect to the arrangement of onshore structures and the distance from seawall trough numerical experiments. For validation of the numerical method used in this study to calculate tsunami force, numerical results for tsunami force on the structures in coastal area are compared with available experimental data. Furthermore, a detail study on the efficiency of the numerical method is performed for the estimation of tsunami force based on the hydrostatic and hydrodynamic methods in which the numerical results are used. The obtained results are compared to the previous experimental one and design criteria. Considering both experimental results and numerical analysis results, semi-empirical formula by regression analysis is proposed. As a result, it was confirmed that the numerical analysis is effective to estimate on tsunami force acting on onshore structures.

Experimental and numerical analysis of the punching behavior of RC isolated footings

  • Walid, Mansour;Sabry, Fayed;Ali, Basha
    • Steel and Composite Structures
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    • v.45 no.5
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    • pp.665-682
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    • 2022
  • In the current study, punching behavior of Reinforced concrete (RC) isolated footings was experimentally and numerically investigated. The experimental program consisted of four half-scale RC isolated footing specimens. The test matrix was proposed to show effect of footing area, reinforcement mesh ratio, adding internal longitudinal reinforcement bars and stirrups on the punching response of RC isolated footings. Footings area varied from 1200×1200 mm2 to 1500×1500 mm2 while the mesh reinforcement ratio was in the range from 0.36 to 0.45%. On the other hand, a 3D non-linear finite element model was constructed using ABAQUS/standard program and verified against the experimental program. The numerical results agreed well with the experimental records. The validated numerical model was used to study effect of concrete compressive strength; longitudinal reinforcement bars ratio and stirrups concentration along one or two directions on the ultimate load, deflection, stiffness and failure patterns of RC isolated footings. Results concluded that adding longitudinal reinforcement bars did not significantly affect the punching response of RC isolated footings even high steel ratios were used. On the contrary, as the stirrups ratio increased, the ultimate load of RC isolated footings increased. Footing with stirrups ratio of 1.5% had ultimate load equal to 1331 kN, 19.6% higher than the bare footing. Moreover, adding stirrups along two directions with lower ratio (0.5 and 0.7%) significantly enhanced the ultimate load of RC isolated footings compared to their counterparts with higher stirrups ratio (1.0 and 1.5%).

Optimum Design of Vaporizer Fin with Liquefied Natural Gas by Numerical Analysis

  • Jeong Hyo-Min;Chung Han-Shik;Lee Sang-Chul;Kong Tae-Woo;Yi Chung-Seub
    • Journal of Mechanical Science and Technology
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    • v.20 no.4
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    • pp.545-553
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    • 2006
  • Generally, the temperature drop under $0^{\circ}C$ on vaporizer surface creates frozen dews. This problem seems to increase as the time progress and humidity rises. In addition, the frozen dews create frost deposition. Consequently, heat transfer on vaporizer decreases because frost deposition causes adiabatic condition. Therefore, it is very important to solve this problem. This paper aims to study of the optimum design of used vaporizer at local LNG station. In this paper, experimental results were compared with numerical results. Geometries of numerical and experimental vaporizers were identical. Studied parameters of vaporizer are angle between two fins $(\Phi)$ and fin thickness $(TH_F)$. Numerical analysis results were presented through the correlations between the ice layer thickness $(TH_{ICE})$ on the vaporizer surface to the temperature distribution of inside vaporizer $(T_{IN})$, fin thickness $(TH_F)$, and angle between two fins $(\Phi)$. Numerical result shows good agreement with experimental outcome. Finally, the correlations for optimum design of vaporizer are proposed on this paper.

Theoretical and experimental investigation of piezoresistivity of brass fiber reinforced concrete

  • Mugisha, Aurore;Teomete, Egemen
    • Computers and Concrete
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    • v.23 no.6
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    • pp.399-408
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    • 2019
  • Structural health monitoring is important for the safety of lives and asset management. In this study, numerical models were developed for the piezoresistive behavior of smart concrete based on finite element (FE) method. Finite element models were calibrated with experimental data collected from compression test. The compression test was performed on smart concrete cube specimens with 75 mm dimensions. Smart concrete was made of cement CEM II 42.5 R, silica fume, fine and coarse crushed limestone aggregates, brass fibers and plasticizer. During the compression test, electrical resistance change and compressive strain measurements were conducted simultaneously. Smart concrete had a strong linear relationship between strain and electrical resistance change due to its piezoresistive function. The piezoresistivity of the smart concrete was modeled by FE method. Twenty-noded solid brick elements were used to model the smart concrete specimens in the finite element platform of Ansys. The numerical results were determined for strain induced resistivity change. The electrical resistivity of simulated smart concrete decreased with applied strain, as found in experimental investigation. The numerical findings are in good agreement with the experimental results.

Experimental and numerical investigations on the ratcheting characteristics of cylindrical shell under cyclic axial loading

  • Shariati, M.;Hatami, H.;Torabi, H.;Epakchi, H.R.
    • Structural Engineering and Mechanics
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    • v.44 no.6
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    • pp.753-762
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    • 2012
  • The ratcheting characteristics of cylindrical shell under cyclic axial loading are investigated. The specimens are subjected to stress-controlled cycling with non-zero mean stress, which causes the accumulation of plastic strain or ratcheting behavior in continuous cycles. Also, cylindrical shell shows softening behavior under symmetric axial strain-controlled loading and due to the localized buckling, which occurs in the compressive stress-strain curve of the shell; it has more residual plastic strain in comparison to the tensile stress-strain hysteresis curve. The numerical analysis was carried out by ABAQUS software using hardening models. The nonlinear isotropic/kinematic hardening model accurately simulates the ratcheting behavior of shell. Although hardening models are incapable of simulating the softening behavior of the shell, this model analyzes the softening behavior well. Moreover, the model calculates the residual plastic strain close to the experimental data. Experimental tests were performed using an INSTRON 8802 servo-hydraulic machine. Simulations show good agreement between numerical and experimental results. The results reveal that the rate of plastic strain accumulation increases for the first few cycles and then reduces in the subsequent cycles. This reduction is more rapid for numerical results in comparison to experiments.

Experimental and numerical analysis of fatigue behaviour for tubular K-joints

  • Shao, Yong-Bo;Cao, Zhen-Bin
    • Structural Engineering and Mechanics
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    • v.19 no.6
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    • pp.639-652
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    • 2005
  • In this paper, a full-scale K-joint specimen was tested to failure under cyclic combined axial and in-plane bending loads. In the fatigue test, the crack developments were monitored step by step using the alternating current potential drop (ACPD) technique. Using Paris' law, stress intensity factor, which is a fracture parameter to be frequently used by many designers to predict the integrity and residual life of tubular joints, can be obtained from experimental test results of the crack growth rate. Furthermore, a scheme of automatic mesh generation for a cracked K-joint is introduced, and numerical analysis of stress intensity factor for the K-joint specimen has then been carried out. In the finite element analysis, J-integral method is used to estimate the stress intensity factors along the crack front. The numerical stress intensity factor results have been validated through comparing them with the experimental results. The comparison shows that the proposed numerical model can produce reasonably accurate stress intensity factor values. The effects of different crack shapes on the stress intensity factors have also been investigated, and it has been found that semi-ellipse is suitable and accurate to be adopted in numerical analysis for the stress intensity factor. Therefore, the proposed model in this paper is reliable to be used for estimating the stress intensity factor values of cracked tubular K-joints for design purposes.

FE model updating and seismic performance evaluation of a historical masonry clock tower

  • Gunaydin, Murat;Erturk, Esin;Genc, Ali Fuat;Okur, Fatih Yesevi;Altunisik, Ahmet Can;Tavsan, Cengiz
    • Earthquakes and Structures
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    • v.22 no.1
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    • pp.65-82
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    • 2022
  • This paper presents a structural performance assessment of a historical masonry clock tower both using numerical and experimental process. The numerical assessment includes developing of finite element model with considering different types of soil-structure interaction systems, identifying the numerical dynamic characteristics, finite element model updating procedure, nonlinear time-history analysis and evaluation of seismic performance level. The experimental study involves determining experimental dynamic characteristics using operational modal analysis test method. Through the numerical and experimental processes, the current structural behavior of the masonry clock tower was evaluated. The first five experimental natural frequencies were obtained within 1.479-9.991 Hz. Maximum difference between numerical and experimental natural frequencies, obtained as 20.26%, was reduced to 4.90% by means of the use of updating procedure. According to the results of the nonlinear time-history analysis, maximum displacement was calculated as 0.213 m. The maximum and minimum principal stresses were calculated as 0.20 MPa and 1.40 MPa. In terms of displacement control, the clock tower showed only controlled damage level during the applied earthquake record.

A Numerical Study on the Smoke Control in Side-Platform Type Subway Station Fires (상대식 지하철 역사내 화재시 연기제어에 관한 수치해석적 연구)

  • Lee, Sung-Ryong;Ryou, Hong-Sun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.20 no.2
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    • pp.81-86
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    • 2008
  • In this study, numerical simulations were carried out to analyze the effect of the smoke extraction system and fire shutters in subway station fires using FDS 4.0. Subway station used in the experiment was 205 m long. Simulation results are validated by comparing with experimental results. Simulation results showed good agreement with experimental results within $20\;^{\circ}C$. 20 MW polystyrene was used as a fuel in the numerical prediction. Numerical predictions were performed in the side-platform type subway station in case of a train fire. Temperature and CO concentration were lowered by the operation of smoke extraction system.

Effects of Catalytic Reaction and Natural Convection on the Hot Surface Ignition of Methane-Air Mixtures (메탄-공기 예혼합기의 열면점화에 미치는 촉매반응 및 자연대류의 영향)

  • Kim, H.M.;Jurng, J.S.
    • Journal of the Korean Society of Combustion
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    • v.2 no.1
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    • pp.29-38
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    • 1997
  • In this study, the experimental and numerical investigations of the ignition of methane-air mixtures by a electrically heated wire have been carried out. In order to define the initial condition and make the analysis simple, the following control unit was developed; which heats the wire to the setting temperature in a very short time, and maintains the wire temperature constant until ignition. Experiments with the feedback control have been performed using nickel and platinum wires in normal gravity and microgravity. From experimental results, ignition temperatures in normal gravity are higher than those in microgravity, however, the dependences of ignition temperature on equivalence ratio are not affected by natural convection. Numerical calculations, including catalytic reaction for platinum, have been performed to analyze the experimental results in microgravity. Numerical results show that reactants near platinum wire are consumed by catalytic reaction, therefore, the higher temperature is needed to ignite the mixture with platinum wire.

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