• Journal of the Society of Naval Architects of Korea
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• v.41 no.4
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• pp.85-91
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• 2004

The objective of the present paper is to develop an analysis method for the correction of welding deformation of stiffened plate by line heating. In this paper, the equivalent loading method, based on the inherent strain theory, was used to analyze the heat-straightening of a stiffened plate. Equivalent loads were obtained by integrating the inherent strains which were determined from the highest temperature and the degree of restraint. Finally, the obtained equivalent loads were imposed, as applied loads, on the elastic analysis for the prediction of correction of welding deformation in stiffened plate. The proposed method is expected as a basic study in heat-straightening analysis of welding deformation in large scale block.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1151-1157
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• 2009

Nuclear power plants applying for the continued operation over design life are required to address the effects of reactor water environment in fatigue design requirement of the ASME Code. Reactor water environmental effects are generally evaluated by calculating fatigue correction factors on fatigue usage. This paper describes the application for pressurizer surge line of environmental fatigue correction factors and the strain rate impact in the application. From this paper, the environmental fatigue correction factors resulted from the assumption of a step change in temperature are especially compared with those calculated from the data measured during plant startup. As a conclusion of this paper, the design transient conditions applied to the fatigue design may be conservative in case of the environmental fatigue evaluation.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.815-818
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• 2002

The elliptic relaxation model(ERM) with the inhomogeneous correction intermediate between near wall with and far from the wall. The source of the ERM usually was appled quasi-homogeneous pressure-strain correlation in homogeneous situations. This formulation was easily applied to the linear model or non-linear pressure-strain model. It is observed that the boundary conditions of the relaxation operator dominate the homogeneous pressure-strain model in the near wall region. While looking at high-Reynolds number flows, it was found necessary to modify the effect of the relaxation operator throughout the log region by accounting for gradients of the flatness variable and turbulent length scales. These effects are kinematic blocking of the wall normal velocity fluctuation and pressure reflections from the surface. This model is wall distances and unit vectors which make the model applicable to flows boundary by a complex geometry. Inhomogeneous correction model is computed inertial and non-inertial channel flow These are compared DNS(Kim et at., Kristofffrsen & Andersson) for channel flow. The present model could be predicted well for rotating flows.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3764-3774
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• 2024

In accordance with Regulatory Guide 1.207, Rev.1, fatigue assessments must be conducted considering the influence of primary coolant environment in nuclear reactors. Environmental fatigue, resulting from corrosion in the primary coolant, is evaluated in air fatigue life assessments through the application of an environmental fatigue correction factor. This environmental fatigue correction factor depends on sulfur content, operating temperature, dissolved oxygen, and strain rate. It remains constant for sulfur content, operating temperature, and dissolved oxygen, while strain rate introduces potential errors based on the analysis method. The current fatigue evaluation procedure for air, following ASME B&PV Code Sec.III, NB-3200, employs elastic analysis with a simplified elastic-plastic correction factor(Ke). However, Ke factor is considered excessively conservative, prompting less conservative alternatives proposed by JSME, RCC-M, ASME Code Case N-779. This study applied both ASME Ke and JSME Ke for fatigue evaluations considering environmental effects. Additionally, fatigue assessments accounting for elastic-plastic effects were conducted using Neuber and Glinka methods, compared with actual experiments. The analysis systematically examined changes in fatigue life and the environmental fatigue correction factor due to plastic effects in environmental fatigue evaluations.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.3
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• pp.173-180
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• 2001

In the past few years, the nondestructive inspection technology has greatly developed due to the increased necessity to gain a complete understanding of the bridge behavior. Especially, the deformations of bridges contain a lot of informations about its health state. By measuring these deformations it is possible to analyze the loading and aging behavior of the structure. However, the current, methods (such as LVDT, dial gage, optical displacement transducer, etc) are often of changeable application on site and have the limitations of installation. In this paper, the classical beam theory was reviewed and the deflections of structure are estimated using measured strain which is easy to acquire. The applicability of this algorithm is verified by laboratory(simple reinforced concrete beam) and field test. By this test, we proposed correction factor to estimate deflection of reinforced concrete beam after cracking, and analyze about the generation of correction factor. Also fiber optic sensors as well as resistive strain gages were installed in the concrete beams to establish the applicability of fiber optic sensors in the field of civil engineering.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.129-133
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• 2000

It is reasonable to use the stereo vision and image processing technique to digitize 3D coordinates of grid points and to evaluate surface strains on a sheet metal parts. However this method has its intrinsic problems such as the difficulty in enhancement of bad images inevitable error due to digital image resolution of camera and frame grabber unreliability of strains and thickness evaluated from coarse grid on the corner area with large curvature and the limitation of the area that can be measured at a time. Therefore it is still hard to measure strain distribution over the entire surface of a medium,- or large-sized stamped part at a time even by using an automated strain measurement system. In this study the curvature correction algorithm based on the grid refinement and the geometry assembling algorithm based on the global error minimization (GEM) scheme are suggested. Several applications are presented to show the reliability and efficiency of these algorithms.

• Nuclear Engineering and Technology
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• v.43 no.1
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• pp.83-88
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• 2011

To define the effect of strain rate variation from 0.04% to 0.004%/s on environmental fatigue of CF8M cast stainless steel, which is used as a primary piping material in nuclear power plants, low-cycle fatigue tests were conducted at operating pressure and temperature condition of a pressurized water reactor, 15 MPa and $315^{\circ}C$, respectively. A high-pressure and high-temperature autoclave and cylindrical solid fatigue specimens were used for the strain-controlled low-cycle environmental fatigue tests. It was observed that the fatigue life of CF8M stainless steel is shortened as the strain rate decreases. Due to the effect of test temperature, the fatigue data of NUREG-6909 appears a slightly shorter than that obtained by KEPRI at the same stress amplitude of $1{\times}10^3$ MPa. The environmental fatigue correction factor $F_{en}$'s calculated with inputs of the test data increases with high strain amplitude, while the $F_{en}$'s of NUREG-6909 remain constant regardless of strain amplitude.

• Special Issue of the Society of Naval Architects of Korea
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• 2008.09a
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• pp.118-125
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• 2008

The deck plates of ship block is made of thin plates in their construction. A main reason of using thin plates is that deck plates don't need to support large structural loads. Therefore, out-of-plane deformations between stiffeners are frequent in deck blocks. Because these are got right by correction heating, they continuously causes quality problems in the final dock-building process. According to preceding research, the lifting process by cranes would offset the effect of correction heating. This study finds out the remained efficiency of correction heating when tensional loads are added by a lifting to corrected parts. We used inherent strains in calculating the efficiency, and established the methodology where the positions for callings are. For getting more accurate positions, besides the structural lifting analysis, welding deformation analysis with upper block and measured data from a serial ship are also referenced.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.2
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• pp.69-76
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• 2018

The paper presents preliminary investigation results for the effect of the baseline correction in the acceleration excitation method on finite element seismic analysis results (such as accumulated equivalent plastic strain, equivalent plastic strain considering cyclic plasticity, von Mises effective stress, etc) of nuclear safety Class I components. For investigation, finite element elastic-plastic time-history seismic analysis is performed for a surge line including a pressurizer lower head, a pressurizer surge nozzle, a surge piping, and a hot leg surge nozzle using the Chaboche hardening model. Analysis is performed for various seismic loading methods such as acceleration excitation methods with and without the baseline correction, and a displacement excitation method. Comparing finite element analysis results, the effect of the baseline correction is investigated. As a result of the investigation, it is identified that finite element analysis results using the three methods do not show significant difference.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1054-1064
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• 2009

In this work, we predict a true fracture strain using load-displacement curves from tensile test and finite element analysis (FEA), and suggest a method for acquiring true stress-strain (SS) curves by predicted fracture strain. We first derived the true SS curve up to necking point from load-displacement curve. As the beginning, the posterior necking part of true SS curve is linearly extrapolated with the slope at necking point. The whole SS curve is then adopted for FE simulation of tensile test. The Bridgman factor or suitable plate correction factors are applied to pre and post FEA. In the load-true strain curve from FEA, the true fracture strain is determined as the matching point to test fracture load. The determined true strain is validated by comparing with test fracture strain. Finally, we complete the true SS curve by combining the prior necking part and linear part, the latter of which connects necking and predicted fracture points.