• Structural Engineering and Mechanics
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• v.23 no.1
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• pp.1-13
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• 2006

Structural cracks may cause variations in structural stiffness and thus produce bilinear vibrations to structures. This study examines the dynamic behavior of structures with breathing cracks. A generalized algorithm based on the finite element method and bilinear theory was developed to study the influence of a breathing crack on the vibration characteristic. All the formulae derived in the time domain were applied to estimate the period of the overall bilinear motion cycle, and the contact effect was considered in the calculations by introducing the penetration of the crack surface. Changes in the dynamic characteristics of cracked structures are investigated by assessing the variation of natural frequencies under different crack status in either the open or closed modes. Results in estimation with vibrational behavior variation are significant compared with the experimental results available in the literature as well as other numerical calculations.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.6
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• pp.60-69
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• 2000

In order to obtain underwater or underground power sources, the closed cycle diesel engine is operated in the non air-breathing circuit system where the major species of the working fluid include oxygen, argon, and recycled exhaust gas. In the present study, the closed cycle diesel engine is designed to operate at the intake pressure between 2 and 3 bar. For operating in the open-cycle and closed-cycle situations, experimental apparatus using this diesel engine is made with ACAP as data acquisition system. In open, semi-open, and closed cycle modes, the predicted p-$\theta$ and P-V are compared with load bank power. Computation have been performed for wide range of major experimental parameters such as the specific fuel and oxygen concentrations, fuel conversion efficiency and polytropic exponent, IMEP and maximum cylinder pressure.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.4
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• pp.457-463
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• 2002

The closed cycle diesel engine is used in a closed circuit system which has no air breathing. The working fluid as intake mixture are consisted of oxygen, argon and recirculated exhaust gas in order to obtain underwater or underground power sources. In the present study, the high pressure diesel engine which can be operated by the closed cycle system with high intake pressure for increasing the net power rate is designed. It has been carried out to investigate the combustion characteristics of high pressure diesel engine according to the power rate. The maximum cylinder pressure and heat release rate were investigated. Also, major experimental data such as specific fuel consumption rate, oxygen concentrations, fuel conversion efficiency, polytropic exponent, and IMEP were compared with low pressure diesel engine experimental data.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.4
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• pp.446-453
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• 2000

The closed cycle diesel system is operated in closed circuit system where there is non air breathing with working fluid consisted of the combination of oxygen, argon and recycled exhaust gas for obtaining underwater or underground power sources. this study has been carried out to analysis the performance of closed cycle system by means of investigation on the combustion characteristics of diesel engine MTU8V183TE52 operating in open, semi-closed, and closed cycle modes. The combustion in closed mode starts a little bit earlier than in open cycle mode. The oxygen concentration and fuel consumption at 240kW closed cycle running are 21∼24% by volume and 77∼79kg/h, respectively. The maximum cylinder pressure and ignition delay time are investigated 110bar and 8.9degree. Also, The combustion simulation program has been studied to predict whether or not combustion. The results from numerical prediction for the basic, cylinder averaged quantities such as the cylinder pressure and the heat release showed excellent with the experimental data.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.3
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• pp.74-82
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• 2000

The concept and characteristics of the propulsion systems for the next generation flight vehicles are described in this paper, where Hey are grouped into air breathing engine, rocket engine and combined cycle engine according to the feeding system of oxidizer. Air breathing engine has its good reusability and superior performance at low altitude, but its usage is limited at high altitude due to the decreased air density. Rocket engine can be used over the wide range of altitude, but it has disadvantages in low specific impulse and high cost. The several types of combined cycle engine, which are being developed by the leading countries in the aerospace, are highlighted as a remarkable candidate for the next generation propulsion system.

• Progress in Medical Physics
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• v.23 no.1
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• pp.1-7
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• 2012

The purpose of this study was to develop the respiratory training system using individual characteristic guiding waveform to reduce the impact of respiratory motion that causes artifact in radiotherapy. In order to evaluate the improvement of respiratory regularity, 5 volunteers were included and their respiratory signals were acquired using the in-house developed belt-type sensor. Respiratory training system needs 10 free breathing cycles of each volunteer to make individual characteristic guiding waveform based on Fourier series and it guides patient's next breathing. For each volunteer, free breathing and guided breathing which uses individual characteristic guiding waveform were performed to acquire the respiratory cycles for 3 min. The root mean square error (RMSE) was computed to analyze improvement of respiratory regularity in period and displacement. It was found that respiratory regularity was improved by using respiratory training system. RMSE of guided breathing decreased up to 40% in displacement and 76% in period compared with free breathing. In conclusion, since the guiding waveform was easy to follow for the volunteers, the respiratory regularity was significantly improved by using in-house developed respiratory training system. So it would be helpful to improve accuracy and efficiency during 4D-RT, 4D-CT.

• Physical Therapy Korea
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• v.8 no.4
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• pp.71-80
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• 2001

근위축성 측색 경화증 (amyotrophic lateral sclerosis: ALS) 환자에게 있어 호흡기능장애는 죽음에 이르게 하는 주요 원인 중 하나이다. 본 연구는 근위축성 측색 경화증이 있으며 호흡기능이 약화되어 있는 51세의 여성 환자를 대상으로 호흡운동 치료를 시행한 후 폐기능(pulmonary function)이 증진되었는지를 알아보고자 실시하였다. 연구 대상자는 6주간의 호흡운동 치료 프로그램에 참여하였다. 호흡운동 치료 프로그램은 횡경막 호흡(diaphragmatic breathing), 복부근육강화(abdominal mu scles strengthening), 지갑입술 호흡(pursed lip breathing), 그리고 동기 유발성 흡기폐활량계(incentive spirometer)를 이용한 흡기운동 등으로 구성되었다. 폐기능 검사는 이동식 호흡측정기(spirometer: MICROSPIROHI-198)를 이용해서 시행하였다. 또한 하지 에르고미터(cycle- ergometer)를 이용해 운동 시간을 측정함으로써 폐기능의 증진 여부를 알아보았다. 연구 대상자는 6주간의 호흡운동 치료 기간 동안 노력성 폐활량(forced vital capacity: FVC)과 정상 예측치에 대한 노력성 폐활량의 비율(percentage of the predicted forced vital capacity: %FVC), 그리고 하지 에르고미터의 운동 시간에 있어 현저한 증가를 보였다. 그러나 노력성 폐활량에 대한 1초간 노력성 폐활량 비(FEV1/ FVC)에 있어서는 약간의 감소를 보였다. 근위축성 측색 경화증 환자에게 6주간의 호흡운동 치료를 실시한 결과, 폐기능의 증진에 효과적임을 알 수 있었으며, 앞으로 더 많은 연구 대상자에게 그 효과를 알아보는 연구가 필요할 것이다.

• Safety and Health at Work
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• v.9 no.4
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• pp.468-472
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• 2018

Background: Firefighters are required to use self-contained breathing apparatus (SCBA), which impairs ventilatory mechanics. We hypothesized that firefighters have elevated arterial $CO_2$ when using SCBA. Methods: Firefighters and controls performed a maximal exercise test on a cycle ergometer and two graded exercise tests (GXTs) at 25%, 50%, and 70% of their maximal aerobic power, once with a SCBA facemask and once with protective clothing and full SCBA. Results: Respiratory rate increased more in controls than firefighters. Heart rate increased as a function of oxygen consumption ($V_{O_2}$) more in controls than firefighters. End-tidal $CO_2$ ($ETCO_2$) during the GXTs was not affected by work rate in either group for either condition but was higher in firefighters at all work rates in both GXTs. SCBA increased $ETCO_2$ in controls but not firefighters. Conclusions: The present study showed that when compared to controls, firefighters' hypoventilate during a maximal test and GXT. The hypoventilation resulted in increased $ETCO_2$, and presumably increased arterial $CO_2$, during exertion. It is proposed that firefighters have altered $CO_2$ sensitivity due to voluntary hypoventilation during training and work. Confirmation of low $CO_2$ sensitivity and the consequence of this on performance and long-term health remain to be determined.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.1
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• pp.67-83
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• 2005

The evolution of hypersonic scramjet engines was reviewed from the 1960s to the present. Concepts of hypersonic air-breathing propulsion systems based on scramjet engine, such as combined-cycle engine, were described and compared with other high-speed propulsion systems. The development history of scramjet engines over the past 40 years odd was introduced with priority given to the efforts in the United States, and the current status of scramjet technology was reviewed through the recent development programs in several developed countries.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.6
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• pp.10-18
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• 2015

Performance requirement analysis and weight estimation of a reusable launch vehicle with a rocket-based air-breathing engine(RBCC : Rocket Based Combined Cycle) were performed. Performance model for an RBCC engine was developed and integrated with flight trajectory model. The integrated engine-trajectory model was validated by comparing the results with those from previous research reference. Based on the new engine-trajectory model and previous research results, engine performance requirements were derived for an reusable launching vehicle with gross take-off weight of 15 tones. Dependence of the propellant amount requirement on the mode transition Mach number of the engine was also analyzed.