• Journal of the KSME
• /
• v.18 no.2
• /
• pp.118-121
• /
• 1978

지난번 강좌에서는 유압밸브의 스푸울에 작용하는 반경방향의 유동력(Iateral flow force)에 대해 서 그 원인과 대책을 소개하였다(대한기계학회지 vol.2, No.1).여기서는 스푸울에 작용하는 축방향 의 유동력(axial flow force)을 기술하는 방법과 이에 대한 보상방법(method of compensation)을 소개한다. 축방향의 유동력은 유체의 운동방정식을 적분형으로 고쳐 쓴, 소위 운동량 이론을 적용 함으로써 그 표현을 용이하게 얻을 수 있다. 그러므로 먼저 유동력의 보석에 적용될 수 있는 운 동량 이론을 소개하고, 스푸울의 형상이 비교적 간단한 경우에 대해서 유동력을 계산하고, 그 보상방법을 논의한다.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.745-749
• /
• 2002

This paper is on the study of flow force compensating method of spool type valve. A simple flow force compensating method using stepped spool is presented in this paper. It is easy to manufacture stepped spool in the presented method because the shape of it is simple. The method has the merit that the size of valve need not be increased. Actuating force required for driving means of spool can be decreased by the compensation of flow force. The effect of presented method is predicted through CFD analysis. The prototypes of flow force compensating Direct Drive Servo-Valve where the result of CFD analysis is reflected are manufactured, and the measurement of flow force is carried out. It is known from the measurement that the effect of flow force compensation is very similar to from CFD analysis.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.6
• /
• pp.145-150
• /
• 2003

This paper is on the study of flow force compensation for spool type valves. A simple method for flow force compensation using a stepped spool is presented in this paper. It is easy to manufacture the stepped spool of the presented method because the shape of it is simple. The method has another merit that the size of valve need not be increased. Actuating force required for driving the spool can be decreased through the compensation of flow force. The effect of presented method is predicted through CFD analysis. The results of the CFD analysis are also utilized for the optimization of step shape. The prototypes of flow force compensated Direct Drive Servo-Valve are manufactured, and the measurements of flow force are carried out. The measured effect of flow force compensation is very similar to that from the CFD analysis.

• Journal of Technology Innovation
• /
• v.18 no.2
• /
• pp.1-32
• /
• 2010

It is well known that compensation satisfaction of employees is closely related to work attitude, job commitment, and employees'intentions to stay on the job. These known facts can also be applied to the professionals engaged in science & technology as well. Many studies have concluded that the Korea's losing competitiveness in the area of science & technology was mainly attributed to the distorted compensation system. In this vein, this paper identifies the potential determinants that affect the compensation satisfaction of S&T professionals, and to empirically examines the determinants influences on job commitment and intention to stay. This was done by acquiring data from S&T professionals currently being employed in firms, universities, and institutions. Consequently, for professionals engaged in science & technology, the compensation satisfaction was demonstrated to be largely influenced by job accomplishment, monetary compensation, and social compensation in order. In conclusion, to improve compensation system for S&T professionals, firstly, it is recommended to enhance job accomplishment by endowing more discretionary authority to conduct research. Secondly, the relatively lower-valued labor forces in S&T area will necessitate more economic support and compensation. Finally, the social compensation should be strengthened by not only ameliorating social status, but also improving labor liquidity and job security.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.39 no.10
• /
• pp.1066-1074
• /
• 1990

In this paper, we attempt to control induction motors with high power efficiency as well as high dynamic performance by utilizing the recently developed theories : singular perturbation technique and noninteracting feedback control. Our controller consists of three subcontrollers` a saturation current controller, a decoupling controller, and a well-known flux simulator. The decoupling controller decouples rotor speed (or motor torque) and rotor flux linearly. Our controller does not need the rotor resistance that varies widely with the machine temperature. To illuminate the practical significance of our results, we present simulation and experimental results as well as mathematical performance analysis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.290-293
• /
• 2017

A direct-connected, continuous type combustion test facility was developed to test a supersonic combustor model used in scramjet engines. The facility requirements were determined by assuming the flight speed of Mach 5, yielding the combustor inlet flow speed of Mach 2. Also the cross-section of the supersonic combustor under test was assumed as $32mm{\times}70mm$. As a result, the facility was designed to have the flow total pressure of 548 kPaA, total temperature of 1,320 K, and flow rate of 0.776 kg/s. The facility consists of a turbo type air compressor, electric air heater, vitiation air heater and a two dimensional facility nozzle to accelerate the flow to Mach 2. Also, an oxygen supply system was added to compensate the vitiation. The exhaust de-pressurization system is not added. Designed pressure, temperature, and flow rate were verified through the test operation of the facility.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.10
• /
• pp.520-526
• /
• 2016

This study aims to develop a distress prediction model, in order to evaluate the distress prediction power for first-class hotels and to calculate the average financial ratio in the Seoul area by using the financial ratios of hotels in 2015. The sample data was collected from 19 first-class hotels in Seoul and the financial ratios extracted from 14 of these 19 hotels. The results show firstly that the seven financial ratios, viz. the current ratio, total borrowings and bonds payable to total assets, interest coverage ratio to operating income, operating income to sales, net income to stockholders' equity, ratio of cash flows from operating activities to sales and total assets turnover, enable the top-level corporations to be discriminated from the failed corporations and, secondly, by using these seven financial ratios, a discriminant function which classifies the corporations into top-level and failed ones is estimated by linear multiple discriminant analysis. The accuracy of prediction of this discriminant capability turned out to be 87.9%. The accuracy of the estimates obtained by discriminant analysis indicates that the distress prediction model's distress prediction power is 78.95%. According to the analysis results, hotel management groups which administrate low level corporations need to focus on the classification of these seven financial ratios. Furthermore, hotel corporations have very different financial structures and failure prediction indicators from other industries. In accordance with this finding, for the development of credit evaluation systems for such hotel corporations, there is a need for systems to be developed that reflect hotel corporations' financial features.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.11
• /
• pp.151-156
• /
• 2019

This study aims to develop a distress prediction model and to evaluate distress prediction power for the food services industry by using 2017 food service industry financial ratios. Samples were collected from 46 food service industries, and we extracted 14 financial ratios from them. The results show that, first, there are eight ratios (financial ratio, current ratio, operating income to sales, net income to assets, ratio of cash flows, income to stockholders' equity, rate of operating income, and total asset turnover) that can discriminate failures in food service industries and the top-level food service industries. Second, by using these eight financial ratios, the logit function classifies the top-level food service industries, and failures in the food service industry can be estimated by using logit analysis. The verification results as to accuracy in the estimated logit analysis indicate that the model's distress-prediction power is 89.1%.