• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.225-226
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• 2010

ISO 22266-1 issued in May 2009 provides guidelines for applying shaft torsional vibration criteria, under normal operating conditions, for the coupled shaft system and long blades of a turbine generator set. In case that a turbine generator vendor do not meet the separation margin of torsional natural frequencies in the technical specifications of the purchaser, this standard can present the reasonable and objective criteria about torsional vibration which both purchaser and supplier can agree on, while ensuring the integrity of turbine generator. This paper describes the application case of ISO 22266-1 for the establishment of torsinal vibration criteria under retrofitting the turbine generator of 'U' nuclear power plant.

• Journal of Korean Society on Water Environment
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• v.22 no.6
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• pp.977-981
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• 2006

In order to improve water quality in drinking water sources, Ministry of Environment (MOE) was implemented total water pollution load management (TWPLM) in all the major river basins. From the experience of the application of TWPLM, we could find some problems relating the target watershed, standard operating procedure (SOP) of establishment and implementation plan, water quality and flow rate, design flow, water quality model, margin of safety (MOS), and estimation of wasteload were found. The authors were reviewed ongoing TWPLM and presented the improvement schemes for a successful TWPLM. For the application of these suggestions, further detailed studies should be done to implement TWPLM in the future.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1123-1128
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• 2008

The necessity of online dynamic security assessment is getting apparent under Electricity Market environments, as operation of power system is exposed to more various operating conditions. For on-line dynamic security assessment, fast transient stability analysis tool is required for contingency selection. The TEF(Transient Energy Function) method is a good candidate for this purpose. The clustering of critical generators is crucial for the precise and fast calculation of energy margin. In this paper, we propose a new method for fast decision of mode of instability by using stability indices and energy margin. The method is a new version of our previous paper.[1] Case studies are showing very promising results.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.6
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• pp.145-152
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• 1998

This paper presents an optimum design of a rotor-bearing spindle system for a ultra centrifuge (80,000 RPM) supported by ball bearings with nonlinear stiffness characteristics. To obtain the nonlinear bearing stiffnesses, a ball bearing is modeled in five degrees of freedom and is analyzed quasi-statically. The dynamic behaviors of the nonlinear rotor-bearing system are analyzed by using a transfer-matrix method iteratively. For optimization. we use the cost function that simultaneously minimizes the weight of a rotor and maximizes the separation margins to yield the critical speeds as far from the operating speed as possible. Augmented Lagrange Multiplier (ALM) method is employed for the nonlinear optimization problem. The result shows that the rotor-bearing spindle system is optimized to obtain 9.5％ weight reduction and 21％ separation margin.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.11a
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• pp.15-18
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• 2001

In this paper, we investigate the rotordynamic characteristics of turbopump system for 9.5ton thrust liquid rocket engine. A finite element method is used to analyze the vibratior characteristics of a rotor-bearing system. The turbopump rotating system is modeled by shaft with sixty elements, nine rigid disks, four ball bearings and four floating ring seals. The calculation results show that the margin of 1st critical speed is increased from 12% to 68% by use of elastic damping ring. In addition, the margin of the 2nd critical speed near the operating speed is increased from 30% to 63% by the stiffness and damping of floating ring seals.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.508-513
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• 1997

One of the moot important constants to be Installed In COLSS, a monitoring system in CE typed reactors, is ROPM which would limit the operating space. This static ROPM was calculated from digital transient analysis assuming that every design basis transient was initiated from the most severe initial condition combination (LCO). Once It could be assured that core condition would not be located at none other than LCO, this static ROPM could be replaced with dynamic ROPM calculated at that condition and the dynamic ROPM would be definitely less than the static ROPM. In order to do, It must be required to calculate the transient discrete sensitivity parameters and parameters change distribution. The purpose of this report is just to propose the enlargement method for thermal margin.

• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.379-385
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• 2010

We developed a high-efficiency, wide-operating-range centrifugal blower stage to meet the demand for reduced total energy-consumption in sewage treatment plants. We improved the efficiency of the two-dimensional impeller using a shape optimization tool and one-dimensional performance prediction tool. A limit of the throat deceleration ratio was set to maintain the stall-margin of the impeller. The low solidity vaned diffuser and return channel were designed using a sensitivity analysis with orthogonal arrays and three-dimensional steady flow simulations. The low solidity diffuser was designed in order to improve the performance in the low-flow-rate region. The return channel was designed so that the total pressure loss in the return channel was minimized. Model tests of both the conventional and optimized blower stages were carried out, and the efficiency and operating range of both stages were compared. The optimized blower stage improved in stage efficiency by 3% and in operating range by 5% compared with the conventional blower stage.

• Korea Journal of Hospital Management
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• v.8 no.3
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• pp.118-142
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• 2003

This study is aimed at evaluating the financial structure of hospitals before and after the separation of prescription and drug dispensing policy started to be implemented in July 2000 and at making a suitable hospital managerial strategy through the verification of the factors which have effect on their profitability. This study investigated the hospitals which have passed the accredition review to be designated as a accredited training hospital each year for three years from 1999 to 2001. Those hospitals were selected from members of the Korea Hospital Association. 106 hospitals were targeted for analysis except for the hospitals whose financial statements and managerial performance were not reported faithfully. The financial indicators used in this study were stability indicators(liability to total assets, ratio of debt to fund balance, fixed ratio), liquidity indicators(current ratio, quick ratio), activity indicators(total assets turnover, fixed assets turnover), profitability indicators(net profit to total assets, net profit to net worth, operating margin), and operating expenses to patient revenues indicators(drug and supplies costs/payroll/overhead expenses). The result of this study are as follows: First, the analysis of the increase of loss-making hospitals before and after. The separation of prescription and drug dispensing policy shows that the number of loss-making hospitals increase after the separation(22.6% before the separation; 31.1% after the separation). However, there was no significant statistical difference. Second, the analysis of operating expenses to patient revenues indicators showed that the ratio of drug and supplies cost became lower in all hospitals but the ratio of payroll/overhead expenses became higher. Additionally, the factor which have the greatest effect on profitability was operating expenses to patient revenues indicators (drug and supplies costs/payroll/overhead expenses). Third, the analysis of managerial performance by four types of loss-loss, loss-profit, profit-loss and profit-profit compared the results before the separation with those after the separation revealed as follows : Reliance on liability to total assets became higher in the profit-loss type($56.2%{\rightarrow}66.4%$), lower in the loss-profit type($82.7%{\rightarrow}74.5%$). Total assets turnover became higher in the profit-profit type($1.3{\rightarrow}1.5$), but lower in the loss-profit type($0.8{\rightarrow}0.7$). Operating margin decreased to minus 5.9% from 4.3% in the profit-loss type, but increased to 7.2% from minus 7.8% in the loss-profit type. Forth, operating expenses to revenues indicators showed that the increase of payroll was the biggest in the profit-loss type($39.2%{\rightarrow}49.9%$) and that overhead cost decreased in the loss-profit type but that rather increased in other types.

• Journal of Preventive Medicine and Public Health
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• v.19 no.2 s.20
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• pp.213-223
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• 1986

Ratio analysis allows a hospital to evaluate its own performance over time and to compare its performance with that of other hospitals. For this study, three types of ratio analysis were conducted based on some data on hospitals in Massachusetts. First, Key ratios influencing financial performance were identified using discriminant analysis. Second, the financial structures of the teaching and the non-teaching hospitals were compared using ratios and multiple comparison method. Third, the effects of the prospective reimbursement law of the state on financial performance were examined using ratios and paired t-test. The purpose of the law is to reduce hospital costs by setting the revenue ceiling prior to the effective budget year. The findings of this study were as follows: 1) When hospitals were divided into three groups, according to their operating income, only profitability ratios showed a consistent difference among the groups. 2) In the discriminant analysis, five ratios were selected: current ratio, operating margin, return on assets, fixed assets turnover, and inventory turnover. They are the key ratios to be monitored periodically for the purpose of evaluating the financial performance of hospitals. 3) When teaching hospitals were compared with non-teaching hospitals, acid ratio, days of cash on hand, and inventory turnover were statistically significant before the law went into effect, whereas only fixed assets turnover and inventory turnover were significant afterward. Contrary to previous studies, profitability ratios of teaching hospitals were higher than those of non-teaching hospitals, although the differences were not statistically significant. 4) When the ratios between the two periods (before and after the law) were compared, three profitability ratios (operating margin, return on assets, and return on equity) were significant for teaching hospitals, whereas three activity ratios (total assets turnover, fixed assets turnover, current assets turnover) were significant for non-teaching hospitals. Furthermore, while both total operating revenue and expenses were decreased, net operating income was increased, due to a greater decrease in total operating expenses. This shows that the law can indeed, simultaneously, achieve both a reduction in costs as well as an improvement in the financial situation of hospitals.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.573-577
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• 2009

Dynamic behavior simulation of supersonic engine was performed and PI control algorithm was studied for the buzz control in the inlet and the thrust control. Firstly, required thrust was tracked according to the fuel flow control and then inlet pressure was regulated through the nozzle throat area control so that the buzz margin has the positive all the time. The control was performed according to the change of flight Mach number, altitude and angle of attack. The proportional gain and the integral gain for regulating the buzz margin was induced and simulated. In the results, it was confirmed and satisfied that control target in the operating area was changed the angle of attack from $0^{\circ}$ to $10^{\circ}$ at the flight Mach number of 2.1~3.0.