• Journal of the Korean Institute of Gas
• /
• v.1 no.1
• /
• pp.120-126
• /
• 1997

The thermal decomposition of low density polyethylene(LDPE) and $25\%{\~}48\%$ chlorinated polyethylene(CPE) were studied using a dynamic thermogravimetry in the stream of nitrogen gas with 20ml/min. The mathematic method, differential (Friedman) and Integral (Ozawa) method were used to obtain value of activation energy of decomposition energy on the reaction. The activation energies evaluated by the above methods agree with each other very well. The maximum average activation energy calculated was 71.71kcal/mol. The thermal decomposition of LDPE and CPE were considered to be carried out by main chain scission and the thermogravimetric trace curve agree with the theoretical equation.

• 제어로봇시스템학회:학술대회논문집
• /
• 1996.10b
• /
• pp.612-615
• /
• 1996

In the continuous casting process, molten metal contacts the mold wall and the molten metal surface is subject to the mold oscillation. The mold oscillation results in the oscillation marks on the surface of solidified steel, which has undesirable effects on the quality of slabs. In order to reduce the oscillation marks by achieving soft contact of molten metal with the mold surface, alternating magnetic field is applied to the surface of molten metal. However, if the magnetic field strength becomes too strong, the melt flow induced by the magnetic field. causes the instability of the molten metal surface, which has also the bad influence on the slab quality. Therefore, it is very important to choose the optimal position of the inductor coil and the optimal level of electric power to minimize the surface defects. In the present work, as a first step toward the optimization problem of the process, numerical studies are performed to investigate the effects of coil position and the electric power level on the meniscus shape and the flow field. As numerical tools, the boundary integral equation method(BIEM) is used for the magnetic field analysis and the finite difference method (FDM) with orthogonal grid generation is used for the flow analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.1752-1761
• /
• 2000

This paper describes the far-field estimation using the near-field measurement data. Measurement in far-field region gives us the acoustical characteristics of the source but in general measurement is made in near-field such as acoustic water tank or anechoic chamber, so far-field acoustical characteristics of the source should be predicted from near-field data. In this case, the number of measurement points in the near field which relates to the accuracy of the predicted field and the amount of data processing, should be optimized. Existing papers say that measurement points is proportional to kL and depends on geometry and directivity of the source. But they do not give us any definite criterion for the required number of measurement points. Boundary Collocation Method which is one of the far-field prediction methods, is analyzed based on Helmholtz integral equation and Green function and it has been found that the number of measurement points is optimized as 0.54kL which is about one half of the existing results.

• Structural Engineering and Mechanics
• /
• v.64 no.4
• /
• pp.515-526
• /
• 2017

Dynamic response of functionally graded Carbon nanotubes (FG-CNT) reinforced pipes conveying viscous fluid under accelerated moving load is presented. The mixture rule is used for obtaining the material properties of nano-composite pipe. The radial force induced by viscous fluid is calculated by Navier-Stokes equation. The material properties of pipe are considered temperature-dependent. The structure is simulated by Reddy higher-order shear deformation shell theory and the corresponding motion equations are derived by Hamilton's principal. Differential quadrature (DQ) method and the Integral Quadrature (IQ) are applied for analogizing the motion equations and then the Newmark time integration scheme is used for obtaining the dynamic response of structure. The effects of different parameters such as boundary conditions, geometrical parameters, velocity and acceleration of moving load, CNT volume percent and distribution type are shown on the dynamic response of pipe. Results indicate that increasing CNTs leads to decrease in transient deflection of structure. In accelerated motion of the moving load, the maximum displacement is occurred later with respect to decelerated motion of moving load.

• Economic and Environmental Geology
• /
• v.16 no.4
• /
• pp.269-276
• /
• 1983

This paper describes three-dimensional (3-D) standard curves for single prismatic buried bodies in induced polarization (IP) method. Dipole-dipole IP responses for the bodies are calculated by the numerical modeling technique using an integral equation solution. The pattern of IP responses for conductive targets depends on the ratio of the width of body to the depth extent. The IP response of a body of six units in strike length approximates that of a two-dimensional body. In addition, if the strike length is long enough, a layered-earth interpretation is applicable for a body much longer than four units in width. Moving an IP line away from the center of a body alon gstrike produces an effect similar to that of increasing the depth. Moving the location of body along line has little effect to the pattern of IP responses.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.6 no.4
• /
• pp.983-999
• /
• 2014

The structural design of the ships includes two main issues which should be checked carefully, namely the extreme structural response (yielding & buckling) and the fatigue structural response. Even if the corresponding failure modes are fundamentally different, the overall methodologies for their evaluation have many common points. Both issues require application of two main steps: deterministic calculations of hydro-structure interactions for given operating conditions on one side and the statistical post-processing in order to take into account the lifetime operational profile, on the other side. In the case of ultra large ships such as the container ships and in addition to the classical quasi-static type of structural responses the hydroelastic structural response becomes important. This is due to several reasons among which the following are the most important: the increase of the flexibility due to their large dimensions (Lpp close to 400 m) which leads to the lower structural natural frequencies, very large operational speed (> 20 knots) and large bow flare (increased slamming loads). The correct modeling of the hydroelastic ship structural response, and its inclusion into the overall design procedure, is significantly more complex than the evaluation of the quasi static structural response. The present paper gives an overview of the different tools and methods which are used in nowadays practice.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.27 no.1
• /
• pp.63-72
• /
• 1990

The linear hydrodynamic forces, acting on a forced oscillating cylinder from its mean position on a free surface with a small amplitude, are calculated in the time domain. The integral equation method using a time dependent Green function is employed. The numerical results for the heaving and swaying circular cylinder are shown and give good agreements with others Furthermore it is shown that the use of the Green function, which is expressed by a series expansion or asymptotic expansion according to time range, reduces computing time greatly.

• Magazine of the Korea Concrete Institute
• /
• v.8 no.6
• /
• pp.205-212
• /
• 1996

This paper presents progressive fracture analysis of concrete using boundary element method and its stabilizing technique. To determine ultimate strength and to predict nonlinear behavior of concrete during progressive crack growth, the modelling of fracture process zone is done based on Dugdale-Barenblatt model with linear tension-softening curve. We regulate displacement and traction boundary integral equation of solids including crack boundary and analyze progressive fracture of concrete beam and compact tension specimen. Also a numerical technique which considers the growth of stress-free crack of concrete during the analysis and removes snapback of postpeak behavior is proposed.

• Journal of IKEEE
• /
• v.23 no.1
• /
• pp.318-321
• /
• 2019

The apparent soil resistivity is used for estimating multilayer soil parameters, such as, layer's depth and soil resistivity. The apparent soil resistivity can be measured, and also can be calculated if soil parameters are given, becacuse the apparent soil resistivity is a function of these parameters. Therefore, any optimization algorithms can be used to find these parameters which make the calculated apparent soil resistivity close to the measured one. The equation for calculating the apparent soil resistivity is complicated and time consumed, because it is composed of an infinite integral which includes a zero order Bessel's function of the first kind. In this paper, a fast algorithm for calculating the apparent soil resistivity of horizontal multilayer earth structure has been presented using complex image method.

• Journal of the Society of Naval Architects of Korea
• /
• v.30 no.1
• /
• pp.73-86
• /
• 1993

This paper describes a potential-based panel method for the prediction of steday performance of a marine propeller operating in a uniform oncoming flow. An integral equation with unknown dipole strengths is formulated by distributing the normal dipoles and/or sources on the blade and hub surfaces and the wake sheet, and is solved numerically upon discretization. A hyperboloidal panel has been adopted to compute the potential induced by a normal dipole on a non-planar quadrilateral panel. The Kutta condition is satisfied by iteratively annulling the pressure jumps at the trailing edge. Extensive convergence tests are carried out, and the influence of the wake model upon performance is studied. Predicted performance is shown to correlate well with the experiments.