• KSTLE International Journal
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• v.5 no.1
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• pp.28-31
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• 2004

The object of the present work is the natural frequency analysis of subambient pressure tri-pad and pico sliders. Head/disk interaction during start/stop and constant speed were detected by using the acoustic emission (AE) test system. The frequency spectrum analysis is performed using the AE signal obtained during the head/disk interaction. The FFT (Fast Fourier Transform) analysis of the AE signals is used to understand the interaction between the AE signal and the state of contact. Natural frequency analysis was performed using the Ansys program. The results indicate acceptable accordance of finite element calculation results with the experimental results.

• International Journal of Fluid Machinery and Systems
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• v.2 no.1
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• pp.72-79
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• 2009

The effect of symmetric and asymmetric micro regenerative pump impellers on their pressure performance was studied. The shut off head of the pump with the symmetric impeller was about 2.5 times as that with the asymmetric impeller. The computation of the internal flow was performed to clarify the cause of the increase of the head. It was found that the contribution of the angular momentum supply was larger than that of shear stress for the head development in both cases. The larger head and momentum supply in the case of the symmetric impeller were caused by larger recirculated flow rate and larger angular momentum difference between the inlet and outlet to the impeller. The larger recirculated flow rate was caused by smaller pressure gradient in the direction of recirculated flow. The decrease of the circumferential velocity in the casing was attributed to the smaller local flow rate in the casing.

• Journal of Welding and Joining
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• v.16 no.2
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• pp.111-121
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• 1998

It is well recognized that a excessive temperature gradient from the junction of head to skirt in axial direction in a hot pressure vessel can cause unpredicted high thermal stress at the junction and/or in axial direction of a skirt. this thermal stress resulting from axial thermal gradient may be a major cause of unsoundness of structural integrity. In case of cyclic operation of hot pressure vessels, the thermal stress becomes one of the primary design consideration because of the possibility of fracture as a result of cyclic thermal fatigue and progressively incremental plastic deformation. To perform thermal stress analysis of the junction and cylindrical skirt of a vessel, or, at least, to inspect quantitatively the magnitude and effect of thermal stress, the temperature profile of the vessel and skirt must be known. This paper demonstrated the temperature distribution and thermal stress analysis for the junction of skirt to head using F.E. analysis. Effect of air pocket in crotch space was quantitatively investigated to minimize the temperature gradient causing the thermal stress in axial direction. Effect of the skirt height on thermal stresses was also studied. Analysis results were compared with theoretical formulas to verify th applicability to the strength calculation in design field.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.1
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• pp.92-99
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• 2006

The swirl ratio of a charge in the cylinder was estimated by calculating the ratio of the rotary speed of charge which could be simulated from the rotary speed of paddle in the swirl measurement apparatus, to the engine speed which could be calculated by measuring intake air flow rate. The automation of the swirl ratio measurement for cylinder head was achieved by controling both valve lift in cylinder head and a suction pressure of surge tank using two step-motors. The number of measurement position for calculating mean swirl ratio was varied by adjusting the interval of valve lift. The mean swirl ratio with varying the number of measurement position showed nearly constant value. Two measurement methods for measuring the swirl ratio were compared, one was to control the suction pressure of the surge tank with PID (proportional, integral, differential) mode with by-pass valve controlled by the step motor and the other did not control the surge tank pressure by fixing the by-pass valve. The difference of the mean swirl ratio between the two measurement methods showed nearly constant value with varying the number of measurement position. This means that the w/o PID control method could be preferred to the PID control method which has been used, due to the simpleness of the swirl measurement.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.60-68
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• 2010

In this study, the seepage flow monitoring method by hydaulic head loss rate graph was developed for the purpose of monitoring the seepage flow from the see side or from the lake on sea dike in which seepage force was varied periodically. The hydraulic head loss rate was defined in this method. The value of the rate is in the range from 0 to 1. the value of 0 means perfectly free flow of seepage. the value of 1 means perfect waterproofing. The value of coefficient of determination in the hydraulic head loss rate graph closer to 1 means that the seepage flow way is stable. The value of coefficient of determination in the hydraulic head loss rate graph closer to 0 means that the hole may exist or the piping may be in the progress. The pore water pressure data measured in Saemangeum sea dike was analyzed with the developed method The result showed that the variation of seepage flow state was detected sensitively by this method and the interception effect of sea dike could be estimated quantitatively.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.10 no.1
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• pp.44-50
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• 2014

There were many flaw issues of reactor vessel head penetration in USA fleets. USNRC issued 10CFR50.55a to implement reactor vessel head penetration ultrasonic examination performance demonstration(PD) in US for enhancement of inspection reliability. After September 2009, all US utilities inspected their RVHP with PD qualified system. Korea Hydro and Nuclear Power Company(KHNP) have developed reactor vessel head penetration performance demonstration system for ultrasonic test to apply for pressurized light-water reactor power plants in accordance with 10CFR50.55a since September 2011. RVHP configuration surveying and analysis, code requirement analysis, and performance demonstration specimen design were performed up to this day. Fingerprinting of manufactured specimen, development of test data management program, development of operation procedure, input of flawed data, and development of final report will be performed for the next step. This paper describes the development status of the performance demonstration system for reactor vessel head penetration ultrasonic examination in Korea.

• Korean Journal of Applied Biomechanics
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• v.30 no.3
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• pp.217-223
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• 2020

Objective: The purpose of this study was to analyze the effect of postural sway on the kinematic variables of the putter head during golf putting and to provide information to the importance of postural sway control in the putting stroke for novice golfers. Method: The center of pressure (CoP) and Kinematics variables of the putter head were calculated during 2 m flat golf putting using 8 motion capture cameras (250 Hz) and 2 force plate (1,000 Hz). SPSS 24.0 was used to perform Pearson's correlation coefficient and simple regression analysis, and the statistically significance level was set to .05. Results: As a result of analyzing the correlation between CoP variables and the putter head rotation angle, the CoP moving length, CoP moving range (ML direction), and CoP moving velocity (ML direction) showed a positive correlation with the putter head rotation angle (yaw axis) and were statistically significant. Conclusion: Therefore, In order to perform the accurate putting stroke maintaining the ball's directionality, it is determined that it is important to control posture sway in the ML directions by minimizing the movement and velocity of the CoP.

• Journal of Mechanical Science and Technology
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• v.19 no.5
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• pp.1182-1193
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• 2005

The capability of TRAC-M code to predict downcomer boiling effect during reflood phase in postulated PWR LOCA is evaluated using the results of downcomer effective water head and Cylindrical Core Test Facility (CCTF) experiments, which were performed at JAERI. With a full height downcomer simulator, effective water head experiment was carried out to investigate the applicability of the TRAC-M best estimate LOCA code to evaluate the effective water head with superheated wall temperature in downcomer. In order to clarify the effect of the initial superheat of the downcomer wall on the system and the core cooling behaviors during the reflood phase, two sets of analysis were also performed with a CCTF. Results show that TRAC­M code tends to under-predict downcomer effective water head and core differential pressure. However, the code results show a good agreement with the experimental results in downcomer temperature, heat flux and pressure. Finally, both experiment and calculation showed that the downcomer water head with the superheated downcomer wall is lower than that of the saturated wall temperature.

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.1
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• pp.1-9
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• 2015

In this study it was adopted on sea dike monitoring that the safety monitoring with statistical limits which was adapted usually on safety monitoring by measuring pressures, stresses or deformations. And also the hydraulic head loss rate change according to passage of time was calculated for the purpose of safety monitoring. Safety monitoring by setting the statistical limit on the measured pore water pressure graphs need to be supplemented with an additional method of monitoring because the difference between the rise and fall of the tide was irregular. Safety monitoring by the limits set from values predicted by linear regression and standard errors on the hydraulic head loss graph was not affected by irregularity of tide. But if the condition of an embankment is changed gradually and slowly, it will not be detected on the hydraulic head loss graph. The graph of hydraulic head loss rate for every 24 hours vs date showed clearly that the sea water blocking state was getting better or not even though it was changed gradually and slowly.

• The KSFM Journal of Fluid Machinery
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• v.4 no.3 s.12
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• pp.39-45
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• 2001

It is reported recently that the pump head deterioration near the best efficiency point, from single-phase flow to the choke due to air entrainment became less in a screw-type centrifugal pump than in a general centrifugal pump. Moreover, at a narrow tip clearance, the pump head became partially higher in two-phase flow than that in single-phase flow. However, the internal pressure fluctuations on this pump due to air entrainment have not been studied yet. For that reason, we have examined the influences of void fraction, flow coefficient and impeller tip clearance on pressure fluctuations in the casing. The void fraction became larger, the influence of tip clearance on pressure distribution became less.