Numerical Method to Estimate Uncertainties Associated With Positioning Error of Stain Measurement in Drop Test of Radioactive Waste Transport Casks

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Numerical Method to Estimate Uncertainties Associated With Positioning Error of

Stain Measurement in Drop Test of Radioactive Waste Transport Casks

Jongmin Lim* and Woo-seok Choi

Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon, Republic of Korea

*

[email protected]

1. Introduction

In this paper, a numerical analysis for the estimation of strain measurement uncertainties in a drop test of the radioactive waste transport casks is described. The numerical method is introduced to quantitatively estimate the uncertainty of the positioning error.

2. Sources of uncertainties in stain

measurements

2.1 Sources of Uncertainties

There are various types of uncertainties that can be induced in strain measurements. Typical sources of such uncertainties are as follows:

ˍ Sensitivity of stain gauge ˍ Temperature induced strain

ˍ Location and alignment of strain gauge ˍ Signal processing unit error

ˍ Data acquisition system error

In this paper, the uncertainty of location and alignment of strain gauge is considered

2.2 Uncertainties due to Location and Alignment of Strain Gauge

In attaching strain gauges on the surface of the specimen, errors can be introduced in the planar or angular directions from the intended position, thereby introducing uncertainty in the measured strain. Uncertainties due to this positioning error include manufacturing tolerances and errors of length measurement tool. These errors are statistically distributed around the intended nominal dimension

and can be expressed as Table 1 in consideration of the manufacturing tolerances of the ISO standard [1] and the uncertainties of the rulers used in attaching the gauge. The uncertainties considered assume a uniform distribution.

Table 1. Uncertainties due to positioning error of stain gage

Uncertainty Distribution Range

Location error (L1, L2) [mm] Uniform [-10,10]

Misalignment angle (ș) [ל] Uniform [-5,5]

Fig. 1. Mislocation and Misalignment of Strain Gauge.

3. Numerical method to estimate the

uncertainties due to mislocation and

misalignment of strain gauge

3.1 Numerical Method

It is very difficult to obtain the uncertainty of the positioning error of the strain gauge through experimental methods. Therefore, the Monte Carlo simulation is performed to obtain the statistical distribution of the strain using the displacement field obtained from computational analysis.

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In order to verify the effectiveness of the method, a drop analysis is performed on a virtual metal rectangular cask as shown in Fig. 2. The strain uncertainties are measured at 6 points. The results of the estimated strain uncertainty are shown in Fig. 3. From the results, it can be seen that the uncertainty is signigicantly affected by the strain gradient. Therefore, it is desirable to attach the strain gauge to a point with low uncertainty as well as high magnitude of strain that can represent physical phenomena.

4. Conclusion

In order to estimate the uncertainties of positioning error of strain gauge, the numerical method is

introduced. Using the drop analysis of the metal rectangular cask, the considered uncertainties can be quantitatively obtained.

ACKNOWLEDGMENTS

This work was supported by the KETEP and the MOTIE of the Republic of Korea (no. 2018710201770).

REFERENCES

[1] ISO 2768 ³*HQHUDO 7ROHUDQFHV IRU /LQHDU DQG $QJXODU'LPHQVLRQV´.

Fig. 2. Drop analysis of the metal rectangular cask.

Fig. 3. Quantitatively estimated strain uncertainties.

1 2 5 4 3 6

< Strain contour and measuring points >

1 2 3 4 5 6 Measuring Points 800 600 400 200 0 S tra in ( ȝ mm/ mm) CoV=12.8% CoV=1.8% CoV=3.1% _CoV=11.6% CoV=35.2% CoV=21.7%