• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.1
• /
• pp.81-90
• /
• 1985

For the prediction of the real vibration and stability behaviour of rotor-beaing systems, various additional effects were considered, which are simplified or neglected by conventional modeling of real rotors. These are specially coupled spring and damping coefficients of journal bearings, spring and damping coefficients of external supporting elements for bearings, static load exerting on gears or pulleys by power transmissions, excitation through the gear tolerance or failure, and positive or negative spring and damping characteristics of magnetic or sealing friction force. Considering these effects, a computer program for the calculation of free and forced vibration of rotating shafts supported by two or more bearings is developed, based on the transfer matrixed method. The reliability of the calculated resutls were ascertianed by comparing with the measured data on high speed rotors supported by two journal bearings.

• Proceedings of the KIEE Conference
• /
• 2006.07b
• /
• pp.705-706
• /
• 2006

Generally Short Circuit Test of transformers are tested according to IEEE std C57.12.00-2000, IEC 60076-5(2000-07), ES148(1998.6.26) or KS C4309(2003). But ES148(1998.6.26) is same as IEEE std C57. 12.00-2000 and KS C4309(2003) is revising coincidence with IEC 60076-5(2000-07). On this study condition of the transformers before short circuit test, calculation method for test current peak value, tolerance on the asymmetrical peak and r.m.s value, short circuit testing procedure, number of short circuit test, duration short circuit test, and detection of faults and evaluation of short circuit test result will be compared with ANSI and IEC.

• Nuclear Engineering and Technology
• /
• v.46 no.4
• /
• pp.481-488
• /
• 2014

An analysis of the uncertainty quantification related to LBLOCA using the Monte-Carlo calculation has been performed and compared with the tolerance level determined by the Wilks' formula. The uncertainty range and distribution of each input parameter associated with the LOCA phenomena were determined based on previous PIRT results and documentation during the BEMUSE project. Calulations were conducted on 3,500 cases within a 2-week CPU time on a 14-PC cluster system. The Monte-Carlo exercise shows that the 95% upper limit PCT value can be obtained well, with a 95% confidence level using the Wilks' formula, although we have to endure a 5% risk of PCT under-prediction. The results also show that the statistical fluctuation of the limit value using Wilks' first-order is as large as the uncertainty value itself. It is therefore desirable to increase the order of the Wilks' formula to be higher than the second-order to estimate the reliable safety margin of the design features. It is also shown that, with its ever increasing computational capability, the Monte-Carlo method is accessible for a nuclear power plant safety analysis within a realistic time frame.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.18 no.12
• /
• pp.947-954
• /
• 2006

Building energy consumption according to the ventilation has been considered to be an important subject. The purpose of this study is to investigate the cooling and heating loads in a test space with a forced ventilating system. In the test space, on/off controlled air-conditioning and forced ventilating facility were operated between 8 : 30 to 21 : 00 during 4 days and some important data like temperatures and energy consumption were measured to obtain actual thermal loads. The simulation was carried out in a mode of temperature level control using a TRNSYS 15.3 with a precisely measured air change amount and performance data of air-conditioner. Heating load and cooling load including sensible and latent were compared between by experiment and by simulation. Both of thermal loads associated with ventilation show a close agreement within an engineering tolerance.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.25 no.1
• /
• pp.1-5
• /
• 2020

Solar power generation systems require maximum power point tracking (MPPT) control to operate PV panels at their maximum power point (MPP). Most conventional MPPT algorithms are based on the slope-tracking concept. A typical slope-tracking method is the perturb and observe (P&O) algorithm. The P&O algorithm measures the current and voltage of a PV panel to find the operating point of the voltage at which the calculated power is maximized. However, the measurement error of the sensor causes irregularity in the calculation of the generated power and voltage control. This irregularity leads to the problem of not finding the correct MPP operating point. In this work, the power output of a PV panel based on the P&O algorithm is simulated by considering the insolation profiles from typical clear and cloudy weather conditions and the errors of current and voltage sensors. Simulation analysis suggests the optimal control period and perturbation voltage of MPPT to maximize its target efficiency under real weather conditions with sensor tolerance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.05a
• /
• pp.101-105
• /
• 2005

Hemming process, composed of flanging, pre-hemming and main hemming, is the last one of a series of forming processes conducted on the automotive panels, having a great influence on the outward appearance of them. The hem quality can be quantitatively defined by the hemming defects including turn-down, warp and roll-in. However, it is difficult to evaluate and predict the hem quality through the experimental measurement or the numerical calculation since the size of defects is very small. This study is focused on how to simulate in the finite element analysis (FEA) the same conditions as in the experiment. The FEA result on turn-down, that was obtained from a finite element model including the spring element linked to the flanging pad, had a good correlation with the experimental data. It was found that the radius of curvature of the flange deeply affects the final hem quality and therefore high rigidity of forming tools and tight assembling tolerance are highly recommended. An over-stroke of the main hemming punch is also proposed to reduce the turn-down.

• Proceedings of the KSR Conference
• /
• 2008.11b
• /
• pp.905-917
• /
• 2008

Road or Railway construction over soft ground is needed to be considered on secondary consolidation which will be caused differential settlement, lack of transport serviceability, higher maintenance cost. Especially for the railway construction in the second phase of Gyung-Bu or Ho-Nam high speed railway, concrete slab track has been adapted as a safe and cost effective geotechnical solution. In this case controlling the total settlement under the tolerance is essential. And pile supported geogrid reinforced construction method is suggested as a solution for the problem of the traditional method on soft soil treatments. Pile supported geogrid reinforced construction method consists of piles that are designed to transfer the load of the embankment through the compressible soil layer to a firm foundation. The load from the embankment must be effectively transferred to the piles to prevent punching of the piles through the embankment fill creating differential settlement at the surface of the embankment. The arrangement of the piles can create soil arching to carry the load of embankment to the piles. In order to minimize the number of piles geogrid reinforced pile supported construction method is being used on a regular basis. This method consists of one or more layers of geogrid reinforcement placed between the top of the piles and the bottom of the embankment. This paper presents several methods of pile supported geogrid reinforced construction and calculation results from the several methods and comparison of them.

• Progress in Medical Physics
• /
• v.25 no.1
• /
• pp.23-30
• /
• 2014

The purpose of this study is to evaluate the developed dose verification program for in vivo dosimetry based on transit dose in radiotherapy. Five intensity modulated radiotherapy (IMRT) plans of lung cancer patients were used in the irradiation of a homogeneous solid water phantom and anthropomorphic phantom. Transit dose distribution was measured using electronic portal imaging device (EPID) and used for the calculation of in vivo dose in patient. The average passing rate compared with treatment planning system based on a gamma index with a 3% dose and a 3 mm distance-to-dose agreement tolerance limit was 95% for the in vivo dose with the homogeneous phantom, but was reduced to 81.8% for the in vivo dose with the anthropomorphic phantom. This feasibility study suggested that transit dose-based in vivo dosimetry can provide information about the actual dose delivery to patients in the treatment room.

• Journal of the Korean Society of Radiology
• /
• v.12 no.1
• /
• pp.17-22
• /
• 2018

Multilayer mirrors are optical elements that can replace single crystal optical elements such as silicon or germanium, and they have artificial diffraction plane of a thickness of several nanometers. We examined the first Bragg angle and the reduction of reflectivity by variation of layer thickness in a W/Si multilayer mirror of small d-spacing. A W/Si multilayer mirror for an incidence angle of $0.55^{\circ}$ and an energy of 17.5 keV was designed and showed a maximum reflectivity of 72.67%. When the thickness of tungsten or silicon layer was simultaneously changed, the first Bragg angle was shifted and the reflectivity was reduced. When there was a change in thickness for one layer of W/Si multilayer, no change in the reflectivity was showed but the unevenness of the envelope was observed. Reduction of reflectivity was also observed at random Gaussian thickness variations. It is possible to predict the tolerance of multilayer mirror by examining the reflectivity degradation according to the thickness change in the W/Si multilayer mirror of small d-spacing.

• Korean Journal of Optics and Photonics
• /
• v.31 no.2
• /
• pp.96-104
• /
• 2020

A catadioptric omnidirectional zoom optical system using a hybrid lens (COZOSH) that performs simultaneously two functions of a lens and a mirror was designed at the visible wavelength range for daytime unmanned surveillance, and its performance was analyzed. The hybrid lens has lots of advantages in terms of fabrication and assembly of a COZOSH, because of the obviation of a lens boring process and reduction of the number of optical components. Additionally, we designed the COZOSH to expand the compressed inner-image region of a donut image at low spatial frequencies. As a result, the optimized design performance of the optical system that satisfies all initial design specifications was obtained from calculation of the modulation transfer function, spot diagram, and tolerance analysis. We confirmed that the COZOSH is a passively athermalized optical system under conditions of temperature variation from -30℃ to 50℃, by using athermalization analysis during zooming.