비선형 최소제곱법을 이용한 점탄성 감쇠를 갖는 원통셸의 실험진동해석

민천홍(CHEON-HONG MIN),박한일(HAN-IL PARK),배수룡(SOO-RYONG BAE) 한국해양공학회 2008 韓國海洋工學會誌 Vol.22 No.3

It is a recent trend for advanced ships and submarines to incorporate composite structureswith viscoelastically damping material. Much research has been done on curve-fitting techniquesto identify vibration characteristic parameters such as natural frequencies, modal damping ratios, and mode shapes of the composite structure. In this study, an advanced technique for accurately determining vibration characteristic of a circular cylindrical shell-attached viscoelastically damping material is used, based on a multi-degree of freedom (MDOF) curve-fitting method. First, an initial value is obtained by using a linear least square method. Next,sung the initial value, the exact model parameters of the composite circular cylindrical shell are obtained by using a nonlinear least square method. Results show computation time is greatly decreased and accurate results are obtained by the MDOF curve-fitting method.

Model-based Methodology to Develop the Isochronous Stress-Strain Curves for Modified 9Cr Steels

Woo-Gon Kim,Song-Nan Yin,Ik-Hee Jung,Sung Ho Kim,Chan-Bock Lee 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Since high temperature materials are designed with a target life based on a specified amount of allowable strain and stress, their isochronous stress-strain curves (ISSC) are needed to avoid an excessive deformation during an intended service life. In this paper, a model-based methodology to develop the isochronous curves for a G91 steel is described. Creep strain-time curves were reviewed for typical high-temperature materials, and Garofalo's model which conforms well to the primary and secondary creep stages was proper for the G91 steel. Procedures to obtain an instantaneous elastic-plastic strain, e, were given in detail. Also, to accurately determine the Ph P2 and P3 parameters in the Garofalo's model, a nonlinear least square fitting (NLSF) method was adopted and useful. The long-term creep curves for the G91 steel can be modeled by the Garofalo's model, and the long-term ISSCs can be developed using the modeled creep curves.

PHEMT 비선형 모델을 이용한 IMT-2000 단말기용 전력증폭기 설계

김창우,박주상 慶熙大學校 레이저 工學硏究所 1999 레이저공학 Vol.10 No.-

The 2-stage Power Amplifiers with AlGaAs/InGaAs/GaAs PHEMT are designed for the new generation mobile communication IMT-2000 handsets. The parameters of Statz-Pucel's nonlinear model are extracted by a curve-fitting method. Comparing with measured S parameter, the validity of equivalent model parameters are proved. To achieve the high gain performance, the Drive(gain) amplifier was designed in the front stage of power amplifier. At 1.95 GHz, the 2-stage Power Amplifier designed in this paper was achieved with a ?? of 31 dB (1.26 W), power added efficiency of 39%, linear gain of 32 dB. The chip size is 1.35 X 2.27㎠.

초고온가스로 중간 열교환기용 Alloy 617의 장시간 크리프 변형률-시간 곡선 모델링

김우곤 ( Woo Gon Kim ),윤송남 ( Song Nan Yin ),김용완 ( Yong Wan Kim ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.10

The Kachanov-Rabotnov (K-R) creep model was proposed to accurately model the long-term creep curves above 10(5) hours of Alloy 617. To this end, a series of creep data was obtained from creep tests conducted under different stress levels at 950℃. Using these data, the creep constants used in the K-R model and the modified K-R model were determined by a nonlinear least square fitting (NLSF) method, respectively. The K-R model yielded poor correspondence with the experimental curves, but the modified K-R model provided good agreement with the curves. Log-log plots of ε*-stress and ε*-time to rupture showed good linear relationships. Constants in the modified K-R model were obtained as λ=2.78, and κ=1.24, and they showed behavior close to stress independency. Using these constants, long-term creep curves above 10(5) hours obtained from short-term creep data can be modeled by implementing the modified K-R model.

Generation of Isochronous Stress-Strain Curves with a Nonlinear Least Square Fitting Method for Modified 9Cr-1Mo Steel

김우곤,윤송남,구경회 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.5

This study deals with the generation of isochronous stress-strain curves for modified 9Cr-1Mo steel. Material property data (sy, D, and m) from tensile tests and strain-time curves from creep tests were obtained at 550 °C. On the basis of the experimental data, the creep curves were characterized by Garofalo’s creep model. The three parameters of P1, P2 and P3 in Garofalo’s model could be optimized properly by a nonlinear least square fitting analysis. The three parameters showed a good stress dependency with a linear relation. However, the P3 parameter, which represents the steady state creep rate, exhibited two-slope behavior with different stress exponents at a transient stress of about 250 MPa. The results verify that the long-term creep curves for G91 steel can be modeled by Garofalo’s model with only several short-term creep data. When the modeled creep curves are used, long-term isochronous curves of up to 105 h can be successfully constructed.

Lifetime prediction of NBR composite sheet in aviation kerosene by using nonlinear curve fitting of ATR-FTIR spectra

Ying Xiong,Shaoyun Guo,Guangshun Chen,Guangxian Li 한국공업화학회 2013 Journal of Industrial and Engineering Chemistry Vol.19 No.5

The accelerated thermal aging was performed for NBR composite sheet in aviation kerosene. It was observed by XPS and ATR-FTIR that some obvious changes related to silicon were caused by thermal aging. Based on careful analysis of ATR-FTIR spectra of various NBR samples, a probable aging mechanism for NBR composite sheet in aviation kerosene was proposed. With the help of nonlinear curve fitting of ATR-FTIR spectra and Arrhenius plot, the lifetime prediction equation of NBR composite sheet in aviation kerosene was obtained. The lifetime of NBR composite sheet in aviation kerosene at room temperature (25 8C) was 6467 days.

A novel method for extracting acoustic nonlinearity parameters with diffraction corrections

정현조,Shuzeng Zhang,Xiongbing Li 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.2

A new method for determining the acoustic nonlinearity parameter using a nonlinear data fitting method is proposed. Based on the quasilinear theory of Westervelt’s equation, the fundamental and second harmonic beam fields are expressed as a multi-Gaussian beam model that separates the attenuation and diffraction correction terms from the propagating plane waves. A nonlinear least squares curvefitting method is developed to extract the nonlinearity parameter without knowing the attenuation coefficients of the material being tested. The nonlinearity parameter of water is determined using the proposed method, and the result agrees well with the literature value. The attenuation coefficients of the fundamental and the second harmonic are also extracted and discussed.

Fixed -bed Adsorption of Food-Related Phenolic Acids on Charocal in Single Solute System

Lee, Won-Young,Park, Yong-Hee The Korean Society of Food Science and Nutrition 1998 Preventive Nutrition and Food Science Vol.3 No.2

Fixed-bed adsorption was adapted to separate phenolic acids from diluted phenolic solution. Break-through curve was obtained by nonlinear curve fitting method, and breakpoint, saturation time, and mass transfer coeffi-cient were calculated . Break point and saturation time were reached slower with $\rho$-coumaric acid than ferulic acid .The p-coumaric acid, having small molecular weight, is suposedly traveled longer pathway in characoal than ferulic acid. Fixed-bed adsorption iwht gallic acid having more hydroxyl functional group than other phenolic acids showed break point arrival and the largest saturation time. This fact means that there was bigger electrostatic affinity between gallic acid and charcoal than between other phenolic acids and charcoal.

Modified Equivalent Radius Approach in Evaluating Stress-Strain Relationship in Torsional Test

Bae. Yoon-Shin 한국방재학회 2008 한국방재학회논문집 Vol.8 No.2

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.

Modified Equivalent Radius Approach in Evaluating Stress-Strain Relationship in Torsional Test

배윤신 한국방재학회 2008 한국방재학회논문집 Vol.8 No.2

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship. Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.