• Title/Summary/Keyword: Initial Parameter

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Estimation of A New Initial Parameter for the Lloyd-Max Algorithm (로이드-맥스 알고리즘을 위한 새로운 초기 파라메타의 추정)

  • Eon Kyeong Joo
    • Journal of the Korean Institute of Telematics and Electronics B
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    • v.31B no.7
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    • pp.26-32
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    • 1994
  • The Lloyd-Max algorithm is an iterative scheme for design of the minimum mean square error quantizer. It is very simple in concept and easy to program into a computer. However its convergence and accuracy are primarily dependent upon the accuracy of the initial parameter. In this paper, a new initial parameter which converges to a specific value when the number of output levels becomes large is selected. And an estimator using curve fitting techique is suggested. In addition, performance of the proposed method is shown to be superior to that of the existing methods in accuracy and convergence.

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Edge wave propagation in an Electro-Magneto-Thermoelastic homogeneous plate subjected to stress

  • Kakar, Rajneesh;Kakar, Shikha
    • Structural Engineering and Mechanics
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    • v.53 no.6
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    • pp.1201-1214
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    • 2015
  • This paper introduces the combined effect of electric field, magnetic field and thermal field on edge wave propagating in a homogeneous isotropic prestressed plate of finite thickness and infinite length. The dispersion relation of edge wave has been obtained by using classical dynamical theory of thermoelasticity. The phase velocity has been computed and shown graphically for various initial stress parameter, electro-magneto parameter, electric parameter and thermoelastic coupling parameter.

Blank Design for Optimized Thickness Distribution for Axi-symmetric Superplastic Blow Forming (축대칭 초소성 블로성형의 두께분포 최적화를 위한 블랭크 설계)

  • 이정민;홍성석;김용환
    • Transactions of Materials Processing
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    • v.8 no.1
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    • pp.92-100
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    • 1999
  • A procedure is proposed for determining the initial thickness distribution in oder to produce a specified final thickness distribution for the axisymmetrical superplastic blow forming processes. Weighted parameter is introduced to improve the simple ad $d_traction method and the initial blank thickness distribution is obtained by optimizing the weighted parameter. This method is applied to superplastic free bulging process with the uniform thickness distribution of final shape to confirm its validity. The optimum initial blank thickness distributions is obtained from arbitrary axisymmetrical superplastic blow forming processes such as dome, cone and cylindrical cup forming with die contact. It is concluded that the ad $d_traction method with weighted parameter is an effective method for an optimum blank thickness distribution design.esign.

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Creep Life Prediction for Udimet 720 Material Using the Initial Strain Method (ISM)

  • Kong, Yu-Sik;Yoon, Han-Ki;Oh, Sae-Kyoo
    • Journal of Mechanical Science and Technology
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    • v.17 no.4
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    • pp.469-476
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    • 2003
  • Despite of considerable research results or uniaxial tension creep available for superalloys, few studies have been made on high temperature creep using the Initial Stram Method (ISM) In this paper, the real-time prediction of high temperature creep strength and creep lift for the nickel-based superalloy Udimet 720 (high-temperature and high-pressure gas turbine engine materials) was performed on round-bar type specimens under pure static load at the temperatures of 538$^{\circ}C$. 649$^{\circ}C$, and 704$^{\circ}C$. The predictive equation derived from the ISM in creep tests showed better reliability than those from LMP (Larson-Miller Parameter) and LMP-lSM (Larson Miller Parameter-Initial Strain Method) specially for long time creep prediction (10$^3$∼10$\^$5/h).

Effect of pre-magneto-electro-mechanical loads and initial curvature on the free vibration characteristics of size-dependent beam

  • Arefi, M.
    • Structural Engineering and Mechanics
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    • v.71 no.1
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    • pp.37-43
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    • 2019
  • This paper studies application of modified couple stress theory and first order shear deformation theory to magneto-electro-mechanical vibration analysis of three-layered size-dependent curved beam. The curved beam is resting on Pasternak's foundation and is subjected to mechanical, magnetic and electrical loads. Size dependency is accounted by employing a small scale parameter based on modified couple stress theory. The magneto-electro-mechanical preloads are accounted in governing equations to obtain natural frequencies in terms of initial magneto-electro-mechanical loads. The analytical approach is applied to investigate the effect of some important parameters such as opening angle, initial electric and magnetic potentials, small scale parameter, and some geometric dimensionless parameters and direct and shear parameters of elastic foundation on the magneto-electro-elastic vibration responses.

AN IMPROVED IMPLICIT EULER METHOD FOR SOLVING INITIAL VALUE PROBLEMS

  • YUN, BEONG IN
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.26 no.3
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    • pp.138-155
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    • 2022
  • To solve the initial value problem we present a new single-step implicit method based on the Euler method. We prove that the proposed method has convergence order 2. In practice, numerical results of the proposed method for some selected examples show an error tendency similar to the second-order Taylor method. It can also be found that this method is useful for stiff initial value problems, even when a small number of nodes are used. In addition, we extend the proposed method by using weighted averages with a parameter and show that its convergence order becomes 2 for the parameter near $\frac{1}{2}$. Moreover, it can be seen that the extended method with properly selected values of the parameter improves the approximation error more significantly.

Long Time Creep Strength and Life Prediction of Steam Turbine Rotor Steel by Initial Strain Method (화력발전용 로터강의 초기 변형률법에 의한 장시간 크리프 수명 및 강도 예측)

  • 오세규;정순억
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.6
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    • pp.1321-1329
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    • 1993
  • Long time creep strength and life prediction of 1% Cr-Mo-V and 12% Cr rotor steel were performed by using round-bar type specimens under static load at 500-600.deg. C TTP (time temperature parameter), MCM (minimum commitment method) and ISM (initial strain method newly devised) as life prediction methods were investigated, and the results could be summarized as follows. (1) The minimum parameter of SEE (standard error) by TTP was proved as LMP (larson-miller parameter), and the minimum parameter of RMS (root mean squares), by data less than 10$^{3}$hrs was MHP (manson-haferd parameter). (2) The parameters of the minimum and the maximum strength values predicted in $10^{5}$hrs creep life of 1% Cr-Mo-V steel by TTP were LMP and MSP, respectively. In case of 12% Cr steel above $550^{\circ}C$ OSDP (orr-sherby-dorn parameter) was minimum and MSP (manson-succop parameter) was maximum, but below $550^{\circ}C$, the inverse phenomena was observed. On the other hand the creep strengths before $10^{3}hrs$ life by MCM were similar to those by TTP, but the strengths after $10^{3}hrs$ life were 10-25% lower than those by TTP. (3) Creep strengths by ISM were maximum 5% lower than those by TTP. Because $10^{5}hrs$ strengths were similar to those of the lower band by TTP, the ISM was safer than the TTP.

The Initial Value Setting-Up Method for Extending the Range of the Optimal Step Parameter under LMS Algorithm (LMS 알고리즘에서 최적 매개변수의 선택 폭 확대를 위한 초기치의 설정방법)

  • Cho, Ki-Ryang;An, Hyuk;Choo, Byoung-Yoon;Lee, Chun-Jae
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.7 no.2
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    • pp.284-292
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    • 2003
  • In this paper, we carried out the numerical examination of the initial value setting-up method to extend the range of optimal step parameter in a adaptive system which is controlled by LMS algorithm. For initial value setting-up methods, the general method which select the initial value randomly and the other method which applies the approximate value obtained from the direct method to initial value, were used. And then, we compared to the ranges of step parameter setting, the convergence speeds of mean-square-error, and the stabilities during the convergence process when the initial values were applied to the optimal directivity synthesis problem. According to the numerical simulation results, the initial value setting-up method by means of the direct method provides wider range for the step parameter, more efficient capability for convergence and stability, and more error correction ability than the general method.

Evaluation of Analytical Parameters on Forming Limit Diagram based on Initial Geometrical Instability (초기 형상 불안정성 기반 성형한계선도의 이론적 변수에 따른 성형 한계영역 평가)

  • Noh, H.G.;Lee, B.E.;Kim, J.;Kang, B.S.;Song, W.J.
    • Transactions of Materials Processing
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    • v.23 no.4
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    • pp.199-205
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    • 2014
  • The current study examines the effect of the analytical parameter values on the theoretical forming limit diagram (FLD) based on the Marciniak-Kuczynski model (M-K model). Tensile tests were performed to obtain stress-strain curves and determine the anisotropic properties in the rolling, transverse and diagonal direction of SPCC sheet materials. The experimental forming limit curve for SPCC sheet material was obtained by limiting dome stretching tests. To predict the theoretical FLD based on the M-K model, the Hosford 79 yield function was employed. The effects of three analytical parameters - the exponent of the yield function, the initial imperfection parameter and the fracture criterion parameter - on the M-K model, were examined and the results of the theoretical FLD were compared to the experimentally measured FLD. It was found that the various analytical parameters should be carefully considered to reasonably predict the theoretical FLD. The comparison of the acceptable forming limit area between the theoretical and experimental FLD is used to compare the two diagrams.

Identification of the Most Conservative Condition for the Safety Analysis of a Nuclear Power Plant by Use of Random Sampling (무작위 추출 방법을 이용한 원자력발전소 보수적 안전해석 조건 결정)

  • Jeong, Hae-Yong
    • Journal of the Korean Society of Safety
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    • v.30 no.5
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    • pp.131-137
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    • 2015
  • For the evaluation of safety margin of a nuclear power plant using a conservative methodology, the influence of applied assumptions such as initial conditions and boundary conditions needs to be assessed deliberately. Usually, a combination of the most conservative initial conditions is determined, and the safety margin for the transient is evaluated through the analysis for this conservative conditions. In existing conservative methodologies, a most-conservative condition is searched through the analyses for the maximum, minimum, and nominal values of the major parameters. In the present study, we investigates a new approach which can be applied to choose a most-conservative initial condition effectively when a best-estimate computer code and a conservative evaluation methodology are utilized for the evaluation of safety margin of transients. By constituting the band of various initial conditions using the random sampling of input parameters, the sensitivity study for various parameters are performed systematically. A method of sampling the value of control or operation parameters for a certain range is adopted by use of MOSAIQUE program, which enables to minimize the efforts for achieving the steady-state for various different conditions. A representative control parameter is identified, which governs the reactor coolant flow rate, pressurizer pressure, pressurizer level, and steam generator level, respectively. It is shown that an appropriate distribution of input parameter is obtained by adjusting the range and distribution of the control parameter.