• Journal of Plant Biology
• /
• v.28 no.1
• /
• pp.9-20
• /
• 1985

Dimensional variation of secondary xylem elements, such as vessel element and fiber, was investigated in root, stem and branch of Alnus hirsuta and A. firma. It is clear that vessel diameter in the root is the widest, next in the stem, and the least in the branch. Length of vessel element among them becomes, however, larger in following sequence; stem, root, and branch, whereas fiber diameter and length are the widest in the root, the second in the stem, and the least in the branch. The size of secondary xylem element at any one level in tree increases from the center (pith) of the organs through a number of annual rings to the outer.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.21 no.12
• /
• pp.1120-1131
• /
• 2011

Researches using time reversal acoustics(TRA) for impact localization have been paid attention to recently. Dispersion characteristics of Lamb waves, which restrict the utility of classical nondestructive evaluation based on time-of-flight information, can be compensated through the application of TRA to Lamb waves on a plate. This study investigates the spatial focusing performance of time reversal Lamb waves on a plate using finite element analysis. In particular, the virtual sensor effect caused by multiple wave reflections at the boundaries of a plate is shown to enable the spatial focusing of Lamb waves though a very small number of surface-bonded piezoelectric(PZT) sensors are available. The time window size of forward response signals, are normalized with respect to the number of virtual active sensors. Then their effects on the spatial focusing performance of Lamb waves are investigated.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.3
• /
• pp.170-177
• /
• 2009

In the present study, a finite element analysis of conjugate heat transfer problem inside a cavity with a heat-generating conducting body, where constant heat flux is generated, is conducted. A conduction heat transfer problem inside the solid body is automatically coupled with natural convection inside the cavity by using a finite element formulation. A finite element formulation based on SIMPLE type algorithm is adopted for the solution of the incompressible Navier-Stokes equations coupled with energy equation. The proposed algorithm is verified by solving the benchmark problem of conjugate heat transfer inside a cavity having a centered body. Then a conjugate natural heat transfer problem inside a cavity having a heat-generating conducting body with constant heat flux is solved and the effect of the Rayleigh number on the heat transfer characteristics inside a cavity is investigated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.319-322
• /
• 1999

In order to accurately measure the high voltage of 22.9[kV] power distribution lines, we investigated the temperature dependence of measuring voltage for single element and stack elements(22, 44, 66 layers, respectively). When one line voltage is 13, 20O[V], the error of measuring voltage with temperature(-25[$^{\circ}C$]~50[$^{\circ}C$]) was decreased with increasing of stack number and stack element with 66 layers was the least error of ${\pm}0.87%$.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.22 no.8
• /
• pp.756-762
• /
• 2012

A method of the low-frequency noise reduction in an enclosure by using an array of Helmholtz resonator is presented. An integral form of equation, which represents the acoustical coupling between the internal sound field and the resonator array, is formulated so that the boundary element method can be applied to solve the coupling problem. It is shown that the resonator array on the surface of the enclosure can be regarded as impedance patches on the boundary element. Experiments on a simple enclosure acoustically coupled with an array of resonators are conducted to verify the method. The predicted noise reduction by the boundary element method shows good agreement with the measured one. The effects of the resistance of resonators as well as the number of resonators on the noise reduction are demonstrated. As a practical example, the presented method is applied to the payload fairing of a space launcher with resonator arrays. It is demonstrated that the resistance of resonators affects significantly the required number of resonators to achieve a desired noise reduction.

• Korean Journal of Food Science and Technology
• /
• v.17 no.3
• /
• pp.208-212
• /
• 1985

The residence time distributions were measured experimentally to determine the effect of reverse screw elements at various screw configurations in twin screw extruder. A simple model was used to estimate the number of filled C-chamber on the forwarding screw. The inclusion of reverse-screw elements resulted in the increase of median residence time and the broadening of color distribution. True residence time was affected by using the reverse screw elements just before the die. The number of filled C-chamber was decreased with the increase of screw revolution speed at the same screw configuration.

• Journal of KSNVE
• /
• v.9 no.1
• /
• pp.103-112
• /
• 1999

A new modeling and analysis technique for one-dimensional distributed parameter systems is presented. First. discretized equations of motion in Laplace domain are derived by applying discretization methods for partial differential equations of a one-dimensional structure with respect to spatial coordinate. Secondly. the z and inverse z transformations are applied to the discretized equations of motion for obtaining a dynamic matrix for a uniform element. Four different discretization methods are tested with an example. Finally, taking infinite on the number of step for a uniform element leads to an exact dynamic matrix for the uniform element. A generalized modal analysis procedure for eigenvalue analysis and modal expansion is also presented. The resulting element dynamic matrix is tested with a numerical example. Another application example is provided to demonstrate the applicability of the proposed method.

• Korean Journal of Computational Design and Engineering
• /
• v.5 no.3
• /
• pp.207-214
• /
• 2000

For last 20 years, a number of researches and developments on finite element mesh generation has been carried out and most of them are comported of node generation part and node generation part. However these algorithms are inefficient in mesh veneration process and difficult to control the shape of elements when comparing with the generation of nodes and elements concurrently. In this study, therefore, an algorithm it proposed to generate nodes and elements concurrently for various two-dimensional objects having multiple holes. Inner node generation is performed by choosing three consecutive boundary nodes and comparing them with other close boundary nodes. As soon as inner nodes are determined, element generation is conducted based on the comparison of the distances among the generated inner nodes, three consecutive boundary nodes and other close boundary nodes. the generated element nodes become new boundary nodes for further repeated process. The processes are repeated through out each region until three consecutive boundary nodes finally form a tirangular element.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.22 no.2
• /
• pp.458-466
• /
• 1998

In this work, a frequency domain method is tested numerically and experimentally to improve nonlinear model parameters using the frequency response function at the nonlinear element connected point of structure. This method extends the force-state mapping technique, which fits the nonlinear element forces with time domain response data, into frequency domain manipulations. The force-state mapping method in the time domain has limitations when applying to complex real structures because it needd a time domain lumped parameter model. On the other hand, the frequency domain method is relatively easily applicable to a complex real structure having nonlinear elements since it uses the frequency response function of each substurcture. Since this mehtod is performed in frequency domain, the number of equations required to identify the unknown parameters can be easily increased as many as it needed, just by not only varying excitation amplitude bot also selecting excitation frequency domain method has some advantages over the classical force-state mapping technique in the number of data points needed in curve fit and the sensitivity to response noise.

• Kyungpook Mathematical Journal
• /
• v.47 no.3
• /
• pp.363-372
• /
• 2007

An element $a$ in a ring R is called left morphic if $$R/Ra{\simeq_-}1(a)$$. A ring is called left morphic if every element is left morphic. In this paper, an element $a$ in a ring R is called left ${\pi}$-morphic (resp. left G-morphic) if there exists a positive number $n$ such that $a^n$ (resp. $a^n{\neq}0$) is left morphic. A ring R is called left ${\pi}$-morphic (resp. left G-morphic) if every element is left ${\pi}$-morphic (resp. left G-morphic). The Morita invariance of left ${\pi}$-morphic (resp. left G-morphic) rings is discussed. Several relevant properties are proved. In particular, it is shown that a left Noetherian ring R with $M_4(R)$ left G-morphic or $M_2(R)$ left morphic is QF. Some known results of left morphic rings are extended to left G-morphic rings and left ${\pi}$-morphic rings.