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Lee, Usik,Min, Seunggyu,Kwon, Oh-Yang 한국비파괴검사학회 2003 한국비파괴검사학회지 Vol.23 No.6
A spectral element model-based structural damage identification method (SDIM) was derived in the previous study by using the damages-induced changes in frequency response functions. However the previous SDIM often provides poor damage identification results because the nonlinear effect of damage magnitude was not taken into account. Thus, this paper improves the previous SDIM by taking into account the nonlinear effect of damage magnitude. Accordingly an iterative solution method is used in this study to solve the nonlinear matrix equation for local damages distribution. The present SDIM is evaluated through the numerically simulated damage identification tests.
Dynamic Characteristics of a Damaged Plate
Lee, Usik The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.10
It is very important to well understand the dynamic characteristics of damaged structures to successfully develop or to choose a most appropriate structural damage identification method (SDIM) as the means of non-destructive testing. In this pope., the dynamic equation of motion for damaged plates is derived by introducing a damage distribution function, which may characterize the effective state of structural damages. It is found that structural damages may induce the coupling between modal coordinates. The effects of damages on the vibration characteristics of a plate depending on their locations, sizes, and magnitudes are numerically investigated in a systematic way. The numerical investigations are also given to the effects of damage-induced modal coupling on the changes in vibration characteristics and to the minimum number of natural modes required to predict sufficiently accurate vibration characteristics of damaged plates.
Lee Hansol,Gelija Devarajulu,Kim Usik,Lee Jinju,Chung Woon Jin 한국세라믹학회 2024 한국세라믹학회지 Vol.61 No.3
CsPbBr3 perovskite nanocrystal embedded glasses (PNEGs) based on the borosilicate system were synthesized with varying compositions to obtain a chemically stable PNEG compared with a PNEG based on the germanate system. Photo- luminescence (PL) and structural characteristics were examined to fi nd the proper heat-treatment conditions for high quantum effi ciency under a 450 nm blue light emitting diode (LED) excitation. The CsPbBr 3 within the glass matrix was observed by transmission electron microscope (TEM). Comparative studies on the thermal, photonic and water stabilities of the obtained borosilicate PNEG with those of a germanate PNEG were carried out. The borosilicate CsPbBr 3 PNEG was employed as a green phosphor along with K 2SiF6:Mn4+ as a red phosphor to compose a white LED with phosphor in silicone (PiS) and a remote PiS structure, whose color gamut was examined for display applications.
A Frequency Response Function-Based Damage Identification Method for Cylindrical Shell Structures
Usik Lee,Wonbee Jeong,Jooyong Cho 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.12
In this paper, a structural damage identification method (SDIM) is developed for cylindrical shells and the numerically simulated damage identification tests are conducted to study the feasibility of the proposed SDIM. The SDIM is derived from the frequency response function solved from the structural dynamic equations of damaged cylindrical shells. A damage distri-bution function is used to represent the distribution and magnitudes of the local damages within a cylindrical shell. In contrast with most existing modal parameters-based SDIMs which require the modal parameters measured in both intact and damaged states, the present SDIM requires only the FRF-data measured in the damaged state. By virtue of utilizing FRF-data, one is able to make the inverse problem of damage identification well-posed by choosing as many sets of excitation frequency and FRF measurement point as needed to obtain a sufficient number of equations.<br/>
Stability and dynamic analysis of oil pipelines by using spectral element method
Lee, Usik,Jang, Injoon,Go, Hansuk Elsevier 2009 Journal of loss prevention in the process industri Vol.22 No.6
<P><B>Abstract</B></P><P>In this paper, the wave characteristics, divergence stability and dynamics of the oil pipelines conveying internal flow are investigated by using the spectral element method which has been known as the exact solution method. The spectral element model is formulated from the governing differential equation of motion transformed into the frequency-domain by using the discrete Fourier transform theory. The internal flow velocity at which the divergence instability occurs is derived in an analytical form. Numerical studies are conducted to investigate the wave characteristics, divergence stability and dynamics of an oil pipeline depending on its viscoelasticity and internal flow velocity.</P>