• Steel and Composite Structures
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• v.36 no.5
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• pp.569-586
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• 2020

The behavior of composite steel-concrete beams depends on the transmission of forces between two parts: the concrete slab and the steel I-beam. The shear connector is responsible for the interaction between these two parts. Recently, an alternative shear connector, called Truss Type connector, has been developed; it aligns efficient structural behavior, fast construction and implementation, and low cost when compared to conventional connectors applied in composite structures. However, there is still a lack of full understanding of the mechanical behavior of the Truss Type connector, due to its novelty. Thus, this study aims to analyze the influence of variation of geometric and physical parameters on the shear resistance of the Truss Type connector. In order to investigate those parameters, a non-linear finite element model, able to simulate push-out tests of Truss Type connectors, was specifically developed and validated with experimental results. A thorough parametric study, varying the height, the angle between rods, the diameter, and the concrete strength, was conducted to evaluate the shear resistance of the Truss Type connector. In addition, an equation to predict the resistance of the original Truss Type shear connector was proposed.

• Journal of Navigation and Port Research
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• v.30 no.2
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• pp.125-130
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• 2006

Waves, which are the main source of ship motions in a seaway, considerably affect the performance of a ship. The study of waves and their impact on ship motions within harbors is an important aspect of the design and operation of harbors. The prediction of incoming groups of waves is particularly important for evaluating ship motion within a harbor. Such a prediction makes it possible to evaluate ship safety more accurately. The wave transformation model reported here is applied to actual ports based on Boussinesq wave equations both non-linear and dispersive wave processes be considered in order to capture physical effects such as wave shoaling, refractions, reflection and diffraction in variable depth environments. The prediction of incoming groups of waves is particularly important for evaluating ship motion within a harbor, Such a prediction makes it possible to evaluate ship safety more accurately and provide safe wave informations for navigation. Furthermore, a wave information support system is proposed for entering ships as one technique for improving the safety of ship operations. This system predicts the run of waves and reduces the danger by identifying the most dangerous point near the harbor entrance at the small wave groups.

• Tribology and Lubricants
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• v.30 no.2
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• pp.77-85
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• 2014

This study set out to predict the load capacity and rotordynamic coefficients of tilting-pad journal bearings, taking the pivot stiffness into account. The analysis uses rocker-back (cylindrical) and ball in socket (spherical) pivot models, both of which are based on Hertzian contact stress theory. The models ascertain the non-linear elastic deformation of the pivots according to the applied load, pivot geometry, and material properties. At present, the Reynolds equation for an isothermal, isoviscous, and incompressible fluid is used to calculate the film pressure by using the finite-element method, after which the Newton-Raphson method is used to simultaneously find the journal center location, pad angles, and pivot deflections. The bearing analysis, excluding the pivot models, is validated using predictions those are readily available in the literature. As the rotor speed increases, the predicted journal eccentricity and damping coefficients decrease, but the stiffness coefficients increase, as expected. Most importantly, the implementation of the pivot models increases the journal eccentricity but significantly decreases the stiffness and damping coefficients of the tilting-pad journal bearings.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.310-310
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• 2012

ZnO thin films were grown on porous silicon (PS) by plasma-assisted molecular beam epitaxy (PA-MBE). The optical properties of the ZnO thin films grown on PS were studied using room-temperature, low-temperature, and temperature-dependent photoluminescence (PL). The full width at half maximum (FWHM) of the near-band-edge emission (NBE) from the ZnO thin films was 98 meV, which was much smaller than that of ZnO thin films grown on a Si substrate. This value was even smaller than that of ZnO thin films grown on a sapphire substrate. The Huang-Rhys factor S associated with the free exciton (FX) emission from the ZnO thin films was found to be 0.124. The Eg(0) value obtained from the fitting was 3.37 eV, with ${\alpha}=3.3{\times}10^{-2}eV/K$ and ${\beta}=8.6{\times}10^3K$. The low- and high-temperature activation energies were 9 and 28 meV, respectively. The exciton radiative lifetime of the ZnO thin films showed a non-linear behavior, which was established using a quadratic equation.

• Journal of The Korean Astronomical Society
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• v.34 no.4
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• pp.285-287
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• 2001

We have studied the nonlinear evolution of a magnetized disk of isothermal gas, which is sustained by its self-gravity. Our objective is to investigate how the Jeans, Parker, and convective instabilities compete with each other in structuring/de-structuring large scale condensations in such disk. The Poisson equation for the self-gravity has been solved with a fourth-order accurate Fourier method along with the Green function, and the MHD part has been handled by an isothermal TVD code. When large wavelength perturbations are applied, the combined action of the Jeans and Parker instabilities suppresses the development of the convection and forms a dense core of prolate shape in the mid-plane. Peripheral structures around it are filamentary. The low density filaments connect the dense core to the diffuse upper region. On the other hand, when small wavelength perturbations are applied, the disk develops into an equilibrium state which is reminiscent of the Mouschovias's 2-D non-linear equilibrium of the classical Parker instability under an externally given gravity.

• Polymer(Korea)
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• v.24 no.5
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• pp.690-700
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• 2000

In this study, an elastomer-assistered compression molding process was investigated by experiments as well as modeling for the long-fiber reinforced thermoset composites. The consolidation pressure generated by fixed-volume and variable-volume conditions was thermodynamically derived for both elastomer and curing prepregs, and was compared with the pressure measured during curing of epoxy matrix. Exhibiting non-linear viscoelastic characteristics in the compressive stress-strain tests, the measured stress was well compared with a modifed KWW (Kohlrausch-Williame-Watts) equation, which is based on the Maxwell viscoelastic model. Using the developed model equations, the consolidation pressure generated by the elastomer was successfully predicted for the compression molding process of thermoset composite materials in tile closed mold system.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.188-195
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• 2010

Green water load is an important parameter to be considered in designing a modern ship or offshore structures like FPSO and FSRU. In this research, a numerical simulation method for green water phenomenon is introduced. The Navier-Stokes equations and the continuity equation are used as governing equations. The equations are calculated using Finite Difference Method(FDM) in rectangular staggered grid system. To increase the numerical accuracy near the body, the Cartesian cut cell method is employed. The nonlinear free-surface during green water incident is defined by Marker-density method. The green waters on a box in regular waves are simulated. The simulation results are compared with other experimental and computational results for verification. To check the applicability to moving ship, the green water of the ship which is towed by uniform force in regular wave, is simulated. The ship is set free to heave and to surge.

• Bulletin of the Korean Chemical Society
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• v.31 no.10
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• pp.2791-2796
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• 2010

In the present study, we constructed a membrane inlet assembly for selective permeation of volatile airborne organic compounds for subsequent analysis by time-of-flight mass spectrometry. The time-dependent diffusion of analytes through a $75\;{\mu}m$ thick polydimethylsiloxane membrane was measured by monitoring the ion signal after a step change in the sample concentration. The results fit well to a non-steady-state permeation equation. The diffusion coefficient, response time, and sensitivity were determined experimentally for a range of polar (halogenated) and nonpolar (aromatic) compounds. We found that the response times for several volatile organic compounds were greatly influenced by the alkyl chain length as well as the size of the substituted halogen atoms. The detection limits for benzene, ethylbenzene, and 2-propanol were 0.2 ppm, 0.1 ppm, and 3.0 ppm by volume, respectively, with a linear dynamic range greater than three orders of magnitude. These results indicate that the membrane inlet/time-of-flight mass spectrometry technique will be useful for a wide range of applications, particularly for in situ environmental monitoring.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.623-625
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• 2000

For the finite element analysis of highly saturated rotating machines involving rotation of a rotor such as dynamic analysis. cogging torque analysis and etc, so much time is needed because a new system matrix equation should be solved for each iteration and time step. It is proved in this paper that. in linear systems. the computational time can be greatly reduced by using the domain decomposition method (DDM). In nonlinear systems. however. this advantage vanishes because the stiffness matrix changes at each iteration especially when using the Newton-Raphson (NR) method. The transmission line modeling (TLM) method resolves this problem because in TLM method the stiffness matrix does not change throughout the entire analysis. In this paper, a new technique for FEA of rotating machines including rotation of rotor and non-linearity is proposed. This method is applied to a test problem. and compared with the conventional method.

• Journal of applied mathematics & informatics
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• v.11 no.1_2
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• pp.215-241
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• 2003

In this paper, solute transport in heterogeneous aquifers using a modified Fokker-Planck equation (MFPE) is investigated. This newly developed mathematical model is characterised with a time-, scale-dependent dispersivity. A two-dimensional finite volume quadrilateral mesh method (FVQMM) based on a quadrilateral background interpolation mesh is developed for analysing the model. The FVQMM transforms the coupled non-linear partial differential equations into a system of differential equations, which is solved using backward differentiation formulae of order one through five in order to advance the solution in time. Three examples are presented to demonstrate the model verification and utility. Henry's classic benchmark problem is used to show that the MFPE captures significant features of transport phenomena in heterogeneous porous media including enhanced transport of salt in the upper layer due to its parameters that represent the dependence of transport processes on scale and time. The time and scale effects are investigated. Numerical results are compared with published results on the some problems.