• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.1
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• pp.240-250
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• 1995

A CPM (computational preston tube method) was developed to measure wall shear stress in a transitional boundary layer on a flat plate using Preston tubes. Correlation for the displacement factor of Preston tubes was improved for a CPM to be used in the transitional boundary layer. The distribution of skin-friction coefficient was reasonably predicted in the uniform free stream of 3.1% turbulence intensity. Reasonable and accurate estimation of displacement factor of Preston tubes was found to be of crucial importance for the CPM, especially in the laminar boundary layer. The mean velocity profiles of the boundary layer on the plate were also measured and presented.

• Advances in aircraft and spacecraft science
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• v.8 no.1
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• pp.31-51
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• 2021

Selective laser melting (SLM), one of the most widely used powder bed fusion (PBF) additive manufacturing (AM) technology, enables the fabrication of customized metallic parts with complex geometry by layer-by-layer fashion. However, SLM inherently poses several problems such as the discontinuities in the molten track and the steep temperature gradient resulting in a high degree of residual stress. To avoid such defects, thisstudy proposes a temperature thread multiscale model of SLM for the evaluation of the process at different scales. In microscale melt pool analysis, the laser beam parameters were evaluated based on the predicted melt pool morphology to check for lack-of-fusion or keyhole defects. The analysis results at microscale were then used to build an equivalent body heat flux model to obtain the residual stress distribution and the part distortions at the macroscale (part level). To identify the source of uneven heat dissipation, a liquid lifetime contour at macroscale was investigated. The predicted distortion was also experimentally validated showing a good agreement with the experimental measurement.

• Journal of Electrical Engineering and Technology
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• v.9 no.4
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• pp.1309-1314
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• 2014

The measurement of stator core loss for an induction motor at each manufacturing process is carried out in this paper. Iron loss in the stator core of induction motor changes after each manufacturing process due to the mechanical stress, which can cause the deterioration of the magnetic performances. This paper proposes a new iron loss measuring system of the stator core in an induction motor, which can be applied to the case when the distribution of magnetic flux density is not uniform along the magnetic flux path. In the system, the iron loss is calculated based on the induced voltage of the B-search coil and exciting current.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.219-222
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• 2001

The objective of the present study is to evaluate the effects of the stenting shapes on flow velocity and wall shear stress in angulated coronary stenosis by computer simulation. Coronary angiogram and Doppler ultrasound measurement in the patients with angulated coronary stenosis were obtained. Inlet wave velocity distribution obtained from in vivo intracoronary Doppler data was used for the numerical simulation. Spatial pattern of blood flow velocity and recirculation area were drawn through out the selected segment of coronary models. Wall shear stresses in the intracoronary stent models were calculated from three-dimensional computer simulation. A negative shear stress region, which is consistent with re-circulation area on flow pattern, was noted on the inner wall of post-stenotic area of pre-stenting model. The negative shear stress was disappeared after stenting. Shear stress in the post-stenting model was markedly reduced up to about two orders of magnitude compared to that of the pre-stenting model.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.108-113
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• 2001

Recently, the mechanical structures applied to many industrial products, especially in electronic products, appear to be miniaturized and complicated. This trend makes it difficult to analyze the stress distribution of those mechanical structures and generates new challenges for precise measurement of strain. Therefore, generally most of those cases largely depend on the finite element analysis. But the development of optical metrology which has the capability of non-contact, full-field and precise measurement makes it possible to solve these measuring problems. Among the optical measurement techniques, the electronic speckle pattern interferometry (ESPI) has been developed and considered as one of the most useful tools for measuring displacement and deformation. But the shortage of recognition and difficulties of measurement have limited its industrial applications in spite of its excellent capabilities. Therefore in this study, in order to enhance the industrial application of ESPI, the measurement of in-plane displacement of mechanical structure with ESPI, which is applied to washing machine and cannot be measured by strain gauges, was performed. And the verification of validity of FEA results was also done.

• Tunnel and Underground Space
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• v.23 no.6
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• pp.457-469
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• 2013

We have analyzed the regional in-situ stress pattern using 460 stress measurement data at about 100 test sites in Korea, and suggested correlation equations of stress-depth and stress ratio-depth. We made Korea Stress Map(KSM) as in-situ stress fields of the Korean peninsula, combining with a paleo-stress analysis according to the geological period and a stress estimation from focal mechanism. We confirmed the reliability and applicability of correlation equations derived in this study, comparing with worldwide stress-depth patterns, and also estimated the pattern of in-situ stress fields of north-eastern Asia including Korea, China and Japan, comparing with World Stress Map.

• Journal of Welding and Joining
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• v.31 no.4
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• pp.67-72
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• 2013

Overlay welding is carried out to improve the corrosion resistance, wear resistance and heat resistance on the surface of the chemical plant and steelmaking plant structures. In overlay welding, control of the bead size and the temperature distribution of weldment are particularly important because that is directly connected to the improvement of quality and productivity. The aim of this study is to model the welding heat source that is very useful to analyze the bead size and temperature distribution of weldment. To find the welding heat source model, numerical analyses are performed by using FE software MSC-marc.

• Journal of the Korean Society of Safety
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• v.8 no.4
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• pp.16-20
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• 1993

The combined effect of increased pressure/temperature and the reduced material thicknesses act to increase the stress on the radiator componets. The design life of the radiator is influenced by the cyclic stresses and corrosion, which act to weaken the materials, radiator mechanical failure occurs when a tube or solder Joint ruptures, causing coolant loss or insufficient heat rejection. Therefore, in this study, through strain measurement of the tubes in copper/brass radiator, the strain distribution of the tubes in radiator as function of temperature and pressure is obtained.

• Journal of the Korean Society of Safety
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• v.37 no.6
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• pp.102-107
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• 2022

South Korea will soon be a super-aged society, as more than 20.6% of its population will be 65 years and older by 2025. As of 2022, 17.5% of the total population in South Korea is 65 years and older, which exceeds the set threshold for an aged society, where more than 14% of the population is 65 years and older. The proportion of older subway construction workers has increased. Aging workers and their work stress negatively impact their workability. A previous study demonstrated that the stress index measured using the uBioMacpa measurement device (Macpa stress index) had a significant correlation with work stress in South Korea. The device tests vascular health and measures stress levels via Macpa signal analysis. In this study, the pulse waves of subway construction workers were measured using uBioMacpa to identify their stress levels. The stress levels were analyzed by age, years of service, job position, employment type, and work type. Herein, these statistics could not be easily represented by a normal distribution; therefore, the Kruskal-Wallis test, a nonparametric statistical method, was used for the analysis of data. The results showed that age, job position, employment type, and working type affected the Macpa stress index and the stress levels of workers increased with age. In terms of job position, technical engineers were more stressed than other workers because of their poor working environment. In terms of employment type, daily-wage workers were more stressed than other workers. In terms of working type, tunneling, waterproofing, and construction scored the highest Macpa stress indexes without any significant difference, whereas earthworks scored the lowest. Based on the analysis of Macpa stress index, safety and health management plans were proposed to reduce the stress levels of workers. Moreover, a manual for efficient stress management must be developed for subway construction workers.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1632-1642
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• 1992

When a blind hole of small diameter is drilled in the field of residual stress, strain relieved around the hole is function of magnitude of stress, patterns of stress distribution and hole geometry of diameter and depth. Relieved strain coefficients can be calculated from FEM analysis of relieved strain and actual stress. These relieved strain coefficients make it possible to measure residual stress which vary along the depth in the subsurface of stressed material. In this study, the calibration tests of residual stress measurement are carried out by drilling a hole incrementally on the cantilever or on the tensile test bar. Residual stresses can be determined from measured strains around a shallow hole by application of power series method. For the sake of reliable measurement of residual stress, much efforts should be done to measure relieved strains and hole depth more accurately comparing with conventional procedures of gage subject to the external load. Otherwise linear equations converting strains into stresses may yield erratic residual stresses because of ill-conditions of linear equations. With accurate measurements of relieved strains, residual stress even if varying along the depth can be measured. It is also possible to measure residual stress in the thin film of material by drilling a shallow hole.