• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.3
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• pp.305-311
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• 2014

In this paper, a new switching pattern is presented for multilevel inverters. With changing off-angel of each switch, the on time interval of all switches will approximately be equal and then the lifetime of inverter will increase, also using this method can reduce electrical stress on switches in higher levels of inverter. Switching angels as for desired modulation index are calculated using genetic algorithm whereas selective harmonics are controlled within the allowable range. The computed angels are simulated in Matlab/Simulink for respective circuits to validate the results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.5
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• pp.107-115
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• 2014

Highly functional mill turrets have been developed and continuously improved to shorten the manufacturing time and enable multiple uses. Among these, a mill turret with B-axis rotary table was developed. The B-axis rotary table should be evaluated for structural integrity. Moreover, its worm and worm gear for transmitting power should be able to endure fatigue damage. Therefore, this article presents a structural analysis of this type of B-axis rotary table and confirms its static stability by comparing the stress results to the allowable stress levels. Next, the dynamic stability of the rotary table was investigated via a mode analysis and a harmonic analysis in a range determined by the results of a modal analysis. Finally, a worm gear set, the main part that drives the rotary table, is analyzed for fatigue and to estimate its lifetime. The results of the fatigue analysis allowed a prediction of the life of the worm gear set. The analytical results show that the B-axis rotary table has good structural integrity.

• Journal of Korean Association for Spatial Structures
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• v.16 no.1
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• pp.35-42
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• 2016

Until recently, almost all ETFE film structures that have been erected is the cushion type because there are problems at lower allowable strength under elastic range and viscosity behaviour such as creep and relaxation of ETFE films under long-term stresses. But the number of tension type structures is currently increasing. This paper proposes the stretch fabrication of ETFE film to verify the applicability of ETFE films to tensile membrane structures. First of all, to investigate the possibility of application on tensile membrane structures, the stretch fabrication test is carried out, and it is verified that it is possible to increase the yield strength of the film membrane structures. After simulating the experiment also carries out an analytical investigation, and the effectiveness of the elasto-plastic analysis considering the viscous behavior of the film is investigated. Finally, post-aging tension measurement is conducted at the experimental facilities, and the viscosity behavior resulting from relaxation is investigated with respect to tensile membrane structures.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.1
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• pp.21-31
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• 2013

In this study, dynamic characteristics and seismic capacity of the nuclear power plant piping system are evaluated by model test results using multi-platform shake table. The model is 21.2 m long and consists of straight pipes, elbows, and reducers. The stainless steel pipe diameters are 60.3 mm (2 in.) and 88.9 mm (3 in.) and the system was assembled in accordance with ASME code criteria. The dynamic characteristics such as natural frequency, damping and acceleration responses of the piping system were estimated using the measured acceleration, displacement and strain data. The natural frequencies of the specimen were not changed significantly before and after the testing and the failure and leakage of the piping system was not observed until the final excitation. The damping ratio was estimated in the range of 3.13 ~ 4.98 % and it is found that the allowable stress(345 MPa) according to ASME criteria is 2.5 times larger than the measured maximum stress (138 MPa) of the piping system even under the maximum excitation level of this test.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.6
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• pp.192-199
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• 2002

Largely, there are three kinds of the design criteria of piping system in petrochemical plant. The first is on the pipe thickness in accordance with the design pressure of piping system. The second is on the static state evaluation by thermal growth and the other is on the dynamic evaluation by piping vibration. According to the ASME B31.3 code, the internal pressure design thickness fur straight pipe shall be calculated as a code formula. And the static design by thermal displacement is defined 7000 cycles of fatigue life in operating the piping system with a design condition. However, the dynamic design evaluation in comparative with small displacements of high frequencies to the static condition has not established clearly the method, yet. So, this study purposes to present the trial of a proposal of dynamic design criterion on the basis of static design method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.2
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• pp.79-86
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• 2014

This paper describes an integrity evaluation method for emergency diesel generator(EDG) and rotor part of EDG. EDG is a very important equipment in the nuclear power plant(NPP). EDG supplies electricity to the safety-related equipments for the safety shut down of NPP in an emergency situation of earthquake. The safety of the rotor part of EDG is also important during seismic impact from earthquake. The finite element modelling of the EDG including rotor part was constructed. The modal analysis of EDG was firstly performed. The first natural frequency was calculated and revealed higher than the cutoff frequency of seismic spectrum. Then the stress analysis was done to compare with the allowable stress. The safety of the rotor part was investigated by the finite element analysis of the rotor and journal bearing interaction to find film thickness and critical speed. The seismic load was applied to rotor part in a manner that the load was a weighted static load. Analysis results showed that the maximum stress was within the range of allowable stress and the film thickness is larger than the permissible minimum thickness, and the critical speed was out of the operating speed. Hence, the structural and dynamic integrity of EDG could be confirmed by the numerical analysis method used in this paper. However, dynamic analysis of a rotating rotor and supporting bearing with the seismic impact needs to be investigated in a more rigorous method since the seismic load to the rotating part complicates the behavior of rotating system.

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.79-85
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• 2009

Dowel-bar in the jointed concrete pavement has been designed and constructed by Foreign standard and experience in Korea. Timoshenko solution was evaluated for dowel bar design. However, various assumptions, Timoshenko solution evaluated only single dowel bar. Therefore, This study object is evaluated the guide line dowel size and arrangement that using the 3Dimensional Finite Element Method. Dowel bar behavior, Timoshenko solution and 3D FEM estimated used result. Dowel allowable stress and Friberg bearing stress estimated using result. The effects of Dowel Group Action were analyzed using Timoshenko range and Friberg range and 3D FEM.

• Nuclear Engineering and Technology
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• v.45 no.4
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• pp.513-522
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• 2013

The ODSCC detected in the TSP position of Ulchin 3&4 SGs are typical ODSCC of Alloy 600MA tubes. The causative chemical environment is formed by concentration of impurities inside the occluded region formed by the tube surface, egg crate strips, and sludge deposit there. Most cracks are detected at or near the line contacts between the tube surface and the egg crate strips. The region of dense crack population, as defined as between $4^{th}$ and $9^{th}$ TSPs, and near the center of hot leg hemisphere plane, coincided well with the region of preferential sludge deposition as defined by thermal hydraulics calculation using SGAP computer code. The cracks developed homogeneously in a wide range of SGs, so that the number of cracks detected each outage increased very rapidly since the first detection in the $8^{th}$ refueling outage. The root cause assessment focused on investigation of the difference in microstructure and manufacturing residual stress in order to reveal the cause of different susceptibilities to ODSCC among identical six units. The manufacturing residual stress as measured by XRD on OD surface and by split tube method indicated that the high residual stress of Alloy 600MA tube played a critical role in developing ODSCC. The level of residual stress showed substantial variations among the six units depending on details of straightening and OD grinding processes. Youngwang 3&4 tubes are less susceptible to ODSCC than U3 and U4 tubes because semi-continuous coarse chromium carbides are formed along the grain boundary of Y3&4 tubes, while there are finer less continuous chromium carbides in U3 and U4. The different carbide morphology is caused by the difference in cooling rate after mill anneal. There is a possibility that high chromium content in the Y3&4 tubes, still within the allowable range of Alloy 600, has made some contribution to the improved resistance to ODSCC. It is anticipated that ODSCC in Y5&6 SGs will be retarded more considerably than U3 SGs since the manufacturing residual stress in Y5&6 tubes is substantially lower than in U3 tubes, while the microstructure is similar with each other.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.1
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• pp.37-45
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• 2021

The construction of the tunnel portal should be careful because cover depth is shallow and it is difficult to exhibit the arching effect. Tunnel stability may be reduced with additional embankment above the portal of tunnel. In this study, in order to examine the stability of the tunnel according to additional embankment above the portal of tunnel, numerical analysis was performed while changing the ground conditions and height of embankment. As a result of the numerical analysis, it was found that the allowable flexural compressive stress of shotcrete and allowable axial force of rockbolts were exceeded when the height of additional embankment was 12 m in rock mass rating V. When considering the displacement, the range of the plastic region and the behavior of the support materials, the tunnel stability seems to be greatly reduced if the height of additional embankment above the portal of tunnel exceeds 10 m.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.2
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• pp.97-104
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• 2018

In this study, a structure satisfying the fatigue constraint is designed by applying the topology optimization based on the phase field design method. In order to predict life based on the stress value, high cycle fatigue failure theory in which stress acts within the range of elastic limit is discussed and three fatigue theories of modified-Goodman, Smith-Watson-Topper and Gerber theory are applied. To calculate the global maximum stress, a modified P-norm stress correction method is used. As a result, it is possible to obtain topology optimization results that minimize the volume while satisfying the fatigue constraints. By applying the phase field design method, a simple shape with a minimized gray scale was obtained, and the maximum stress value acting on the optimization result became very close to the allowable stress value due to the modified P-norm stress method. While previous studies does not consider the stress correction factor, this study proposes the determination method regarding the stress correction factor considering loading effects related to axial stress components.