• Title/Summary/Keyword: large error

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Remeshing Criterion for Large Deformation Finite Element Analyses Based on the Error Calculation (오차계산에 기초한 대변형 유한요소 해석에서의 요소망 재구성 기준)

  • 김형종;김낙수
    • Transactions of Materials Processing
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    • v.4 no.1
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    • pp.92-104
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    • 1995
  • It often happens some elements are so largely distorted during a large-deformation finite element analysis that further calculation becomes impossible or the approximation error increases rapidly. This problem can be overcomed only by remeshing at several suitable stages. The present study aimed to establish the criterion based on the error estimators, and examined in the simulation and posterior error analysis of ring compression test to demonstrate the usefulness of them. The distribution of each error estimator and its variation during deformation were investigated. All the error estimators were increased monotonously with deformation and decreased rapidly at remeshing stage. It was shown that the error estimators suggested in this study are good measures as remeshing criterion for large deformation finite element analyses.

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On the Suitability of Centered and Upwind-Biased Compact Difference Schemes for Large Eddy Simulations (III) - Dynamic Error Analysis - (LES에서 중심 및 상류 컴팩트 차분기법의 적합성에 관하여 (III) -동적 오차 해석 -)

  • Park, No-Ma;Yoo, Jung-Yul;Choi, Hae-Cheon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.7
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    • pp.995-1006
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    • 2003
  • The suitability of high-order accurate, centered and upwind-biased compact difference schemes for large eddy simulation is evaluated by a dynamic analysis. Large eddy simulation of isotropic turbulence is performed with various dissipative and non-dissipative schemes to investigate the effect of numerical dissipation on the resolved solutions. It is shown by the present dynamic analysis that upwind schemes reduce the aliasing error and increase the finite differencing error. The existence of optimal upwind scheme that minimizes total numerical error is verified. It is also shown that the finite differencing error from numerical dissipation is the leading source of numerical errors by upwind schemes. Simulations of a turbulent channel flow are conducted to show the existence of the optimal upwind scheme.

In-Flight Alignment of SDINS without Initial Heading Information (초기 기수각 정보가 필요 없는 SDINS의 운항중 정렬)

  • 홍현수;이장규;박찬국
    • Journal of Institute of Control, Robotics and Systems
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    • v.8 no.6
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    • pp.524-532
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    • 2002
  • This paper presents a new in-flight alignment method for an SDINS under large initial heading error. To handle large heading error, a new attitude error model is introduced. The attitude errors are divided into heading error and leveling errors using a newly defined horizontal frame. Some navigation error dynamic models are derived from the attitude error model for indirect feedback filtering of the in-flight alignment system. A Kalman filter with Position measurement is designed to estimate navigation errors as the indirect feedback filter Simulation results show that the proposed in-flight alignment method reduces the heading error very quickly from more than 40deg to about 5deg so as to apply a refined navigation filter. The total alignment process including leveling mode and navigation mode in addition to the proposed one allows large initial values not only in heading error but also in leveling errors.

Waviness measurement of workpiece with a Large Surface Area (대면적 공작물의 기하학적 Waviness 측정)

  • Kang D.B.;Son S.M.;Ah J.H.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.10a
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    • pp.115-118
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    • 2005
  • A workpiece with a large surface area is likely to be uneven due to form error and waviness. These geometric disturbances can cause inaccurate micro shapes to be formed when micro features are micro-grooved into the surface and cause the resulting workpiece to fail to function as desired. Thus, real-time measurement and compensation is required to guarantee the form accuracy of micro features while machining a workpiece with a large surface area. In this study, a method is suggested for real-time measurement of geometric error for the micro grooving of a large flat surface using a laser displacement sensor. The measurements are demonstrated for the workpieces with large surface areas and the experimental results show that the waviness and form error are well detected.

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Nonlinear Filtering Approaches to In-flight Alignment of SDINS with Large Initial Attitude Error (큰 초기 자세 오차를 가진 관성항법장치의 운항중 정렬을 위한 비선형 필터 연구)

  • Yu, Haesung;Choi, Sang Wook;Lee, Sang Jeong
    • Journal of Institute of Control, Robotics and Systems
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    • v.20 no.4
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    • pp.468-473
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    • 2014
  • This paper describes the in-flight alignment of SDINS (Strapdown Inertial Navigation Systems) using an EKF (Extended Kalman Filter) and a UKF (Unscented Kalam Filter), which allow large initial attitude error uncertainty. Regardless of the inertial sensors, there are nonlinear error dynamics of SDINS in cases of large initial attitude errors. A UKF that is one of the nonlinear filtering approaches for IFA (In-Flight Alignment) are used to estimate the attitude errors. Even though the EKF linearized model makes velocity errors when predicting incorrectly in case of large attitude errors, a UKF can represent correctly the velocity errors variations of attitude errors with nonlinear attitude error components. Simulation results and analyses show that a UKF works well to handle large initial attitude errors of SDINS and the alignment error attitude estimation performance are quite improved.

On the Suitability of Centered and Upwind-Biased Compact Difference Schemes for Large Eddy Smulations (II) - Static Error Analysis - (LES에서 중심 및 상류 컴팩트 차분기법의 적합성에 관하여 (II) - 정적 오차 해석 -)

  • Park, No-Ma;Yoo, Jung-Yul;Choi, Hae-Cheon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.7
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    • pp.984-994
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    • 2003
  • The suitability of high-order accurate, centered and upwind-biased compact difference schemes for large eddy simulation is evaluated by a spectral, static error analysis. To investigate the effect of numerical dissipation on LES solutions, power spectra of discretization errors are evaluated for isotropic turbulence models in both continuous and discrete wavevector spaces. Contrary to the common belief, the aliasing errors from upwind-biased schemes are larger than those from comparable non-dissipative schemes. However, this result is the direct consequence of the definition of the power spectral density of the aliasing error, which poses the limitation of the static error analysis for upwind schemes.

The Effect of First Observation in Panel Regression Model with Serially Correlated Error Components

  • Song, Seuck-Heun
    • Communications for Statistical Applications and Methods
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    • v.6 no.3
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    • pp.667-676
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    • 1999
  • We investigate the effects of omission of initial observations in each individuals in the panel data regression model when the disturbances follow a serially correlated one way error components. We show that the first transformed observation can have a relative large hat matrix diagonal component and a large influence on parameter estimates when the correlation coefficient is large in absolute value.

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Development of large-scale 3D printer with position compensation system (구동부 변위의 보상이 가능한 지능형 대형 3D 프린터 개발)

  • Lee, Woo-Song;Park, Sung-Jin;Park, In-Soo
    • Journal of the Korean Society of Industry Convergence
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    • v.22 no.3
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    • pp.293-301
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    • 2019
  • Based on accurate image processing technology, a system for measuring displacement in ${\mu}m$ for drive error (position error, straightness error, flatness error) at a distance using parallel light and image sensor is developed, and a system for applying this technology development to a large 3D rapid prototyping machine and compensating in real time is developed to dramatically reduce the range of measurement error and enable intelligent 3D production of high quality products.

Multi-level Vector Error Diffusion for Smear Artifact Reduction in the Boundary Regions (경계 영역에서 색 번짐 감소를 위한 멀티레벨 벡터 오차 확산법)

  • 박태용;조양호;김윤태;하영호
    • Proceedings of the IEEK Conference
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    • 2003.11a
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    • pp.461-464
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    • 2003
  • This paper proposes the multi-level vector error diffusion for smear artifact reduction in the boundary regions. Smear artifact mainly results from a large accumulation of quantization error. Accordingly, to reduce these artifacts, the proposed method excludes the large quantization error in the error diffusion process by comparing the magnitude of the error vector with predetermined first threshold. In addition, if the vector norm of the difference between the error adjusted input vector and the primary co]or that has minimum vector norm for the error adjusted input vector is larger than second threshold, the error is excluded. As a result, the proposed method reduce smear artifact in the boundary region and produces visually pleasing halftone pattern.

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Machine Tool Error Compensation by using Measuring Plates (측정플레이트를 이용한 공작기계 오차보정)

  • 양종태;정성종
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1993.10a
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    • pp.187-192
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    • 1993
  • Thermal deformation causes large amount of machine tool errors. In order to compensate for thermal and geometric errors of the machine tool an off-line geometric adaptive control (GAC) scheme was developed. THe GAC method was realized by using a measuring plate made of precision spheres. Error vectors and volumetric errors were measured by the measuring plate. Error compensation models were obtained from error vectors and a kinematic chain of machine tools. Reliability of the GAC system of thermal and geometric errors were confrimed by large amount of experiments.

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