• Title/Summary/Keyword: numerical testing

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The Errors and Reducing Method in 1-dof Frequency Response Function from Impact Hammer Testing (충격햄머 실험에 의한 1자유도 주파수응답함수의 오차와 해결방법)

  • 안세진;정의봉
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.9
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    • pp.702-708
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    • 2002
  • The spectrum of impulse response signal from an impulse hammer testing is widely used to obtain frequency response function(FRF). However the FRFs obtained from impact hammer testing have not only leakage errors but also finite record length errors when the record length for the signal processing is not sufficiently long. The errors cannot be removed with the conventional signal analyzer which treats the signals as if they are always steady and periodic. Since the response signals generated by the impact hammer are transient and have damping, they are undoubtedly non-periodic. It is inevitable that the signals be acquired for limited recording time, which causes the errors. This paper makes clear the relation between the errors of FRF and the length of recording time. A new method is suggested to reduce the errors of FRF in this paper. Several numerical examples for 1-dof model are carried out to show the property of the errors and the validity of the proposed method.

The Durability Performance Evaluation of Automotive Components in the Virtual Testing Laboratory (차량 부품의 내구성 평가를 위한 가상시험실 구축)

  • Kim, Gi-Hoon;Kang, Woo-Jong;Kim, Dae-Sung;Ko, Woong-Hee;Lim, Jae-Yong
    • Transactions of the Korean Society of Automotive Engineers
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    • v.14 no.3
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    • pp.68-74
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    • 2006
  • The evaluation of durability performance in Virtual Testing Laboratory(VTL) is a new concept of vehicle design, which can reduce the automotive design period and cost. In this study, the multibody dynamics model of a car is built with a reverse engineering design. Hard points and masses of components are measured by a surface scanning device and imported into CAD system. In order to simulate the non-linear dynamic behavior of force elements such as dampers and bushes, components and materials are tested with specialized test equipments. An optimized numerical model for the damping behavior is used and the hysteresis of bush rubber is considered in the simulation. Loads of components are calculated in VTL and used in the evaluation of durability performance. In order to verify simulation results, loads of components in the vehicle are measured and durability tests are performed.

TD-CFIE Formulation for Transient Electromagnetic Scattering from 3-D Dielectric Objects

  • Lee, Young-Hwan;Jung, Baek-Ho;Sarkar, Tapan K.;Yuan, Mengtao;Ji, Zhong;Park, Seong-Ook
    • ETRI Journal
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    • v.29 no.1
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    • pp.8-17
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    • 2007
  • In this paper, we present a time domain combined field integral equation formulation (TD-CFIE) to analyze the transient electromagnetic response from dielectric objects. The solution method is based on the method of moments which involves separate spatial and temporal testing procedures. A set of the RWG functions is used for spatial expansion of the equivalent electric and magnetic current densities, and a combination of RWG and its orthogonal component is used for spatial testing. The time domain unknowns are approximated by a set of orthonormal basis functions derived from the Laguerre polynomials. These basis functions are also used for temporal testing. Use of this temporal expansion function characterizing the time variable makes it possible to handle the time derivative terms in the integral equation and decouples the space-time continuum in an analytic fashion. Numerical results computed by the proposed formulation are compared with the solutions of the frequency domain combined field integral equation.

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A Finite Element Analysis of Deformation-Induced Heating in Tensile Testing of Sheet Metals (박판 인장 시험에서 가공열의 영향에 관한 유한요소 해석)

  • ;Wagoner, R.H.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.4
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    • pp.680-688
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    • 1989
  • A numerical method for analyzing non-isothermal plastic deformation of sheet metals has been developed and sheet tensile tests have been analyzed using a two-dimensional finite element formulation. A modified Bishop`s method is used to solve the thermoplasticity problem in decoupled form at each time step. The accuracy of the analysis is confirmed by comparison with experimental data. The uniform elongation is found is drop by 0.1 to 2.7% at moderate strain rates, while total elongation decreases upto 6.0% during tensile testing in air compared to the isothermal case. The effect of deformation heating, becomes more pronounced as necking develops and at higher testing speed.

A Study on the Modeling of Electromagnetic Wave Propagation for the Detection of a Delamination in Concrete Specimens (콘크리트 내의 공동탐사를 위한 전자기파 모델링)

  • 조윤범;임홍철
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2000.04b
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    • pp.119-124
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    • 2000
  • The radar method is becoming one of the major nondestructive testing (NDT) techniques for concrete structures. Numerical modeling of electromagnetic wave is needed to analyze radar measurement results and to study the influence of measurement parameters on the radar measurements. Finite difference-time domain (FD-TD) method is used to simulate electromagnetic wave propagation through concrete specimens. Three concrete specimens with a 25 mm delamination embedded at 25 mm, 50 mm, and 75mm depth are modeled in 3-dimension. Also, thickness change of delamination and permittivity change are modeled.

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Comparison of Simulated PEC Probe Performance for Detecting Wall Thickness Reduction

  • Shin, Young-Kil;Choi, Dong-Myung;Jung, Hee-Sung
    • Journal of the Korean Society for Nondestructive Testing
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    • v.29 no.6
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    • pp.563-569
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    • 2009
  • In this paper, four different types of pulsed eddy current(PEC) probe are designed and their performance of detecting wall thickness reduction is compared. By using the backward difference method in time and the finite element method in space, PEC signals from various thickness and materials are numerically calculated and three features of the signal are selected. Since PEC signals and features are obtained by various types and sizes of probe, the comparison is made through the normalized features which reflect the sensitivity of the feature to thickness reduction. The normalized features indicate that the shielded reflection probe provides the best sensitivity to wall thickness reduction for all three signal features. Results show that the best sensitivity to thickness reduction can be achieved by the peak value, but also suggest that the time to peak can be a good candidate because of its linear relationship with the thickness variation.

Development of an Electromagnetic Nondestructive Testing Method for the Prevention of Defects in Steam Generator Tubes at Nuclear Power Plant (원자력발전소 증기발생기 전열관의 결함발생 예방을 위한 전자기 비파괴 검사방법 개발)

  • Shin, Young-Kil
    • Proceedings of the KIEE Conference
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    • 1996.07a
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    • pp.83-85
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    • 1996
  • Major cause of defects in steam generator tubes at nuclear power plant is the accumulation of magnetite and other byproducts of corrosion in the crevice gap between support plates and tubes. Since damaged tubes result in contamination of the secondary coolant by the radioactive primary coolant, they represent a safety hazard. Early detection of magnetite buildup is, therefore, imperative in order to take remedial measures such as chemical flushing. Although the eddy current testing is being used for the inspection of steam generator tubes, the interpretation of resulting signals is generally a difficult task. This paper uses the phase of sensor coil emf as the test signal to find a way of easier signal interpretation. Numerical study using FEM shows that the shape of resulting signal is good for identifying the relative position of the probe to the support plate, and for discreminating the different shapes and degrees of magnetite buildup in the crevice gap region.

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Optimal Release Policies of Software System with Scheduled Delivery Time (예정된 인도시기를 가진 Software시스템의 최적방출정책)

  • 정영배;신현재
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.9 no.13
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    • pp.29-32
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    • 1986
  • A decision procedure to determine when computer software should be released after testing is described. This paper extends optimum release policies minimizing the total expected software cost with a scheduled software delivery time under reliability requirement constraint. Such cost considerations enable us to make a release decision as to when transfer a software system from testing phase to operational phase. The underlying model is software reliability growth model described by a nonhomogeneous poisson process. It is assumed that the penalty cost function due to delay for a scheduled software delivery time is linearly proportional to time. Numerical examples are shown to illustrate the results.

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A Brief Overview of a Scale Independent Deformation Theory and Application to Diagnosis of Deformational Status of Solid-State Materials

  • Yoshida, Sanichiro
    • Journal of the Korean Society for Nondestructive Testing
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    • v.32 no.2
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    • pp.131-141
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    • 2012
  • A field theoretical approach to deformation and fracture of solid-state material is outlined, and its application to diagnosis of deformational status of metal specimens is discussed. Being based on a fundamental physical principle known as local symmetry, this approach is intrinsically scale independent, and capable of describing all stages of deformation on the same theoretical foundation. This capability enables us to derive criteria that can be used to diagnose transitions from the elastic to plastic regime, and the plastic to fracturing regime. For practical applications of these criteria, an optical interferometric technique known as electronic speckle-pattern interferometry is proved to be quite powerful; it is able to visualize the criteria as a whole image of the object on a real-time basis without numerical processing. It is demonstrated that this method is able to reveal loading hysteresis as well.

Optimal Release Policy for a Software System using Number of Software Test (소프트웨어의 테스트 회수(回數)를 이용한 최적방출정책(最適放出政策))

  • Go, Hyeon-U;Hwang, Ui-Cheol
    • Journal of Korean Society for Quality Management
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    • v.17 no.2
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    • pp.27-35
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    • 1989
  • Software developers often allocate a significant amount of effort to software testing. But for most business-related software system it is natural to expect the continued discovery of defects after the software system is released into field. Such defects are usually very expensive to fix and have the potential to cause great damages to the users. It is important to stop testing the software and release it to the users at the correct time. In this paper, we propose the determination of the optimal number of software test oy minimizing a total expected software cost. A numerical example is used when the criterion is the expected profit. The result indicates that the proposed software release policy based on the number of software test can be a good alternative to the existing policy.

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