• Elastomers and Composites
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• v.50 no.2
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• pp.92-97
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• 2015

A study on reaction kinetics for a PTMG/TDI prepolymer with 2,2'-dichloro-4,4'-methylenedianiline (MOCA), of which formulations may be generally used for fabricating high performance polyurethane elastomers, was peformed using non-isothermal differential scanning calorimetry (DSC). A number of thermograms were obtained at several constant heating rates, and analysed using Flynn-Wall-Ozawa (FWO) isoconversional method for activation energy, $E_a$ and extended-Avrami equation for reaction order, n. Urea formation reaction of the present system was observed to occur through the simple exothermic reaction process in the temperature range of $100{\sim}130^{\circ}C$ for the heating rate of $3{\sim}7^{\circ}C/min$. and could be well-fitted with generalized sigmoid function. Though activation energy was nearly constant as $53.0{\pm}0.5kJ/mol$, it tended to increase a little at initial stage, but it decreases at later stage by the transformation into diffusion-controlled reaction due to the increased viscosity. Reaction order was evaluated as about 2.8, which was somewhat higher than the generally well-known $2^{nd}$ order values for the various urea reactions. Both the reaction order and reaction rate explicitly increased with temperature, which was considered as the indication of occurring the side reactions such as allophanate or biuret formation.

• Nuclear Engineering and Technology
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• v.50 no.3
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• pp.389-395
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• 2018

The present work aims to report the consequences of Darcy-Forchheimer medium in flow of Cross fluid model toward a stretched surface. Flow in porous space is categorized by Darcy-Forchheimer medium. Further heat transfer characteristics are examined via thermal radiation and heat generation/absorption. Transformation procedure is used. The arising system of nonlinear ordinary differential equations is solved numerically by means of shooting method. The effects of different flow variables on velocity, temperature, concentration, skin friction, and heat transfer rate are discussed. The obtained outcomes show that velocity was enhanced with the increase in the Weissenberg number but decays with increase in the porosity parameter and Hartman number. Temperature field is boosted by thermal radiation and heat generation; however, it decays with the increase in the Prandtl number.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.123-130
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• 2015

This paper presents a new formulation for transient simulations of microwave propagation in heterogeneous unbounded domains. In particular, perfectly-matched-layers(PMLs) are introduced to allow for wave absorption at artificial boundaries used to truncate the infinite extent of the physical domains. The development of the electromagnetic PML targets the application to engineering mechanics problems such as structural health monitoring and inverse medium problems. To formulate the PML for plane electromagnetic waves, a complex coordinate transformation is introduced to Maxwell's equations in the frequency-domain. Then the PML-endowed partial differential equations(PDEs) for transient electromagnetic waves are recovered by the application of the inverse Fourier transform to the frequency-domain equations. A mixed finite element method is employed to solve the time-domain PDEs for electric and magnetic fields in the PML-truncated domain. Numerical results are presented for plane microwaves propagating through concrete structures, and the accuracy of solutions is investigated by a series of error analyses.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.366-375
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• 1991

In this study, vibrational behavior of uniform pipe carrying a moving medium is studied by using a transfer matrix and the displacement function derived from the conventional beam theory. In various boundary conditions, flow velocity and mechanical property change of the variation of natural frequency are investigated. The Coriolis term in the original differential equation of motion has been ignored in the investigation. This method is used to study the variation of natural frequency with flow velocity for clamped-clamped, cantilevered, clamped-pinned, pinned-pinned, free-free straight pipe element. It is shown that clamped-clamped, free-free pipe have the highest natural frequency and critical velocity values while cantilevered pipe have the smallest natural frequency for the same mechanical properties. From the vibration effects of mechanical property variation, it is shown that bending stiffness and pipe length variation has large influence on natural frequency and critical velocity. Since the order of transfer matrix is not changed with boundary conditions of pipe element, this method proposed can be easily applied to personal-computer for vibration analysis of pipe element. Furthermore, this method can be extended to three-dimensional system by using a coordinate transformation for the analysis of piping systems.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.2
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• pp.121-131
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• 1986

The stiffness matrix of circularly curved frame elements including the warping effects is formulated by the solutions of vlasov's differential equations, and the procedure for the elastic static analysis of curved girder systems by the displacement method is presented. The validity of this method has been demonstrated by comparing the analysis results with other solutions. And if the tangential lines of the two frame element axes connected at any nodal point coincide, the transformation to the global coordinate system can be omitted when we analyze the structures consisting of circularly curved elements. The theory introduced in this thesis can be applied with sufficient accuracy to the structures built up with horizontally circular curved frame elements which have closed or open cross sections and are symmetric to the axis perpendicular to the plane of the curvature, such as prestressed concrete box girder bridges.

• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2077-2083
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• 2022

In the unlikely event of core disruptive accident in sodium cooled fast reactors, the reactor containment building would be bottled up with sodium and fission product aerosols. The behavior of these aerosols is crucial to estimate the in-containment source term as a part of nuclear reactor safety analysis. In this work, the evolution of sodium aerosol characteristics (mass concentration and size) is simulated using HAARM-S code. The code is based on the method of moments to solve the integro-differential equation. The code is updated to FORTRAN-77 and run in Microsoft FORTRAN PowerStation 4.0 (on Desktop). The sodium aerosol characteristics simulated by HAARM-S code are compared with the measured values at Aerosol Test Facility. The maximum deviation between measured and simulated mass concentrations is 30% at initial period (up to 60 min) and around 50% in the later period. In addition, the influence of humidity on aerosol size growth for two different aerosol mass concentrations is studied. The measured and simulated growth factors of aerosol size (ratio of saturated size to initial size) are found to be matched at reasonable extent. Since sodium is highly reactive with atmospheric constituents, the aerosol growth factor depends on the hygroscopic growth, chemical transformation and density variations besides coagulation. Further, there is a scope for the improvement of the code to estimate the aerosol dynamics in confined environment.

• Smart Structures and Systems
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• v.31 no.4
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• pp.421-436
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• 2023

This paper presents a vibration displacement measurement and damage identification method for a space truss structure from its vibration videos. Features from Accelerated Segment Test (FAST) algorithm is combined with adaptive threshold strategy to detect the feature points of high quality within the Region of Interest (ROI), around each node of the truss structure. Then these points are tracked by Kanade-Lucas-Tomasi (KLT) algorithm along the video frame sequences to obtain the vibration displacement time histories. For some cases with the image plane not parallel to the truss structural plane, the scale factors cannot be applied directly. Therefore, these videos are processed with homography transformation. After scale factor adaptation, tracking results are expressed in physical units and compared with ground truth data. The main operational frequencies and the corresponding mode shapes are identified by using Subspace Stochastic Identification (SSI) from the obtained vibration displacement responses and compared with ground truth data. Structural damages are quantified by elemental stiffness reductions. A Bayesian inference-based objective function is constructed based on natural frequencies to identify the damage by model updating. The Success-History based Adaptive Differential Evolution with Linear Population Size Reduction (L-SHADE) is applied to minimise the objective function by tuning the damage parameter of each element. The locations and severities of damage in each case are then identified. The accuracy and effectiveness are verified by comparison of the identified results with the ground truth data.

• Journal of Broadcast Engineering
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• v.12 no.2
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• pp.80-92
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• 2007

IPTV Services that is representative union service of broadcasting and telecommunication need guarantee of QoS, efficiency of multicasting, and hish bandwidth on the network. Because typical TDM based metro transport network was designed by transporting fixed voice traffic with stable and recovering method, it has a defect of bottleneck and a waste of bandwidth for acceptance of data traffic with burst feature and then all of data are treated equally at the transport network because it cannot classify between advanced high end service and best effort low end service. for completely resolving this kind of problem about increasing burst traffic and QoS issues, firstly we need to new design for transport network. This paper presents transformation method from TDM based metro transport network to packet based transport network and advantage and effectiveness of packet based transport network and also indicates technical factor and characters about method of packet transport system. As a result of research, the Packet Transport System, which is a transmission network for packet delivery, take in not only a specific character of legacy TDM but QoS, Multicast and high bandwidth, then, it is able to keep an effective bandwidth and a stabilized performance of packet transmissions. Additionally, if a fault be occurred on an optical link, the system is able to guarantee a differential QoS by an each service class using an algorithm to make certain of a traffic existence and contain a protective mechanism.

• The Journal of the Korea Contents Association
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• v.21 no.3
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• pp.616-625
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• 2021

Deep neural networks are an approximation method that approximates an arbitrary function to a linear model and then repeats additional approximation using a nonlinear active function. In this process, the method of evaluating the performance of approximation uses the loss function. Existing in-depth learning methods implement approximation that takes into account loss functions in the linear approximation process, but non-linear approximation phases that use active functions use non-linear transformation that is not related to reduction of loss functions of loss. This study proposes parametric activation functions that introduce scale parameters that can change the scale of activation functions and location parameters that can change the location of activation functions. By introducing parametric activation functions based on scale and location parameters, the performance of nonlinear approximation using activation functions can be improved. The scale and location parameters in each hidden layer can improve the performance of the deep neural network by determining parameters that minimize the loss function value through the learning process using the primary differential coefficient of the loss function for the parameters in the backpropagation. Through MNIST classification problems and XOR problems, parametric activation functions have been found to have superior performance over existing activation functions.

• Korean Journal of Veterinary Research
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• v.16 no.2
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• pp.151-158
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• 1976

The tuberculin test have been widely utilized to diagnose tuberculosis of the dairy cattle. It was reported that approximately 70% of the dairy cattle with positive tuberculin reaction in Korea had been non-pathogenic lesion. So the studies on the specific method to diagnose tuberculosis of them is really need in Korea. Therefore this study investigated upon the diagnostic method for cattle tuberculosis in the aspect of cellular-immunology. The results obtained in this investigation are summarized as follows: 1. All the tuberculin tests to the swine inoculated with BCG.(B group), Mycobacterium avium (A group) and Mycobacterium smegmatis (S group), respectively, were represented high positive reaction and were no differences in the species of inoculated bacteria. 2. In the migration inhibition test using Iymphocyte in circulating blood of the swine inoculated with three species of acid-fast bacteria respectively, the test to A group was represented slight positive for migration in the presence of $15{\mu}g/ml$-PPD and the other reaction were clear and total positive for migration inhibition in the presence of $25{\mu}g/ml$-PPD or more, and the test to B group was the same results as to A group approximately. The test to S group was represented slight positive for migration inhibition in the presence of $15{\mu}g/ml$-PPD, but the results were the same in the presence of $25{\mu}g/ml$-PPD and $35{\mu}g/ml$-PPD. These results showed that there were remarkable differences between group A, B and group S in the presence of $25{\mu}g/ml$-PPD and $35{\mu}g/ml$-PPD. 3. The transformation rates of lymphocyte in PPD treated tissue culture had no significance without any relation between PPD treatment and non-treatment but A group and B group showed significance. And A group and B group showed high significance in comparison with N group and S group in the LSD examination. 4. The infection rated in lymphocyte of BCG inoculated after 3 days tissue culturing were represented those of high infection but its cellular degeneration rates almost did not change. The infection rates in bacilli in N group and S group were low but after 3 days inoculation it shewed higher cellular degeneration.