• International Journal of Fluid Machinery and Systems
• /
• 제5권3호
• /
• pp.126-133
• /
• 2012

The transfer matrix and unsteady cavitation characteristics, cavitation compliance and mass flow gain factor, of cavitating inducer were evaluated by CFD using commercial software. Quasi-steady values of cavitation compliance and mass flow gain factor were obtained first by using steady calculations at various flow rate and inlet cavitation number. Then unsteady calculations were made to determine the transfer matrix and the cavitation characteristics. The results are compared with experiments to show the validity of calculations.

• International Journal of Fluid Machinery and Systems
• /
• 제9권2호
• /
• pp.160-168
• /
• 2016

In high speed turbopumps, cavitation occurs and often causes the flow instabilities such as cavitation surge and rotating cavitation. The occurrence of these cavitation instabilities is considered to relate to dynamic characteristics of the cavitation, which are modelled using a cavitation compliance and a mass flow gain factor. Various types of cavitation such as a blade surface cavitation, a tip leakage vortex cavitation, and a backflow vortex cavitation occur at the same time in the inducer and the dynamic characteristics of each cavitation have not been clarified yet in experiments. Focusing on the blade surface cavitation as one of fundamental cavitation, we investigated the dynamic characteristics of the blade surface cavitation on a flat plate hydrofoil in experiments in the present study.

• International Journal of Fluid Machinery and Systems
• /
• 제2권1호
• /
• pp.40-54
• /
• 2009

Cavitation instabilities in turbo-machinery such as cavitation surge and rotating cavitation are usually explained by the quasi-steady characteristics of cavitation, mass flow gain factor and cavitation compliance. However, there are certain cases when it is required to take account of unsteady characteristics. As an example of such cases, cavitation surge in industrial centrifugal pump caused by backflow vortex cavitation is presented and the importance of the phase delay of backflow vortex cavitation is clarified. First, fundamental characteristics of backflow vortex structure is shown followed by detailed discussions on the energy transfer under cavitation surge in the centrifugal pump. Then, the dynamics of backflow is discussed to explain a large phase lag observed in the experiments with the centrifugal pump.

• 대한의용생체공학회:의공학회지
• /
• 제23권4호
• /
• pp.309-315
• /
• 2002

1980년대에 동물과 인체에 이식한 기계식 인공 판막으로부터 핏트(pit)가 발견된 이래 그 원인으로 캐비테이션 현상이 주목받고 있다. 심실 압력 구배(dp/dt), 최대 폐쇄속도, 스퀴즈 유동 등과 같은 다양한 요소가 캐비테이션 발생의 임계값으로 연구되고 있다. 현재에는 기계식 판막의 표면 괴식의 원인으로서는 폐쇄직전에 발생하는 스퀴즈 유동과 수격현상 등이 주목받고 있다. 본 연구에서는 자연 심장에 비교적 가까운 압력 조건하에서 강체 홀더와 유연성을 부가한 홀더를 이용하여 모델 밸브의 디스크의 폐쇄 운동 및 밸브 표면 부위의 압력 변화를 측정하였다 실험 결과 모든 홀더에서 디스크 표면 근처에서 수증기 압력 이하의 압력 저하가 예상되었다. 또한 폐쇄 직전의 속도가 증가할수록 밸브의 표면 괴식도 증가하였다. 이들의 결과로부터 폐쇄 직전의 판막의 속도가 표면 괴식에 큰 영향을 미친다고 생각됐다.

• International Journal of Fluid Machinery and Systems
• /
• 제10권3호
• /
• pp.197-208
• /
• 2017

When Francis turbines operate at partial load, residual swirl in the draft tube causes low-frequency pulsation of pressure and power output. Scale effects and system response may bias the prediction of prototype behavior based on laboratory tests, but could be overcome by means of a 1D analytical model. This paper deals with the two most important features of such a model, the compliance and the source of excitation. In a distributed-parameter version, compliance should be represented as an exponential function of local pressure. Lack of similarity due to different Froude number can thus be compensated. The normally unknown gas content in the vortex cavity has significant influence on the pulsation, and should therefore be measured and considered as a test parameter.

• 대한의용생체공학회:의공학회지
• /
• 제19권3호
• /
• pp.285-290
• /
• 1998

최근 동물 또는 생체에 이식한 인공판막에 표면부식에 의한 파손 예가 보고되어 연구가 진행되고 있으나 가속내구시험에 대해서는 상세한 검토가 이루어지지 않았다. T. Yhuta 교수가 개발한 가속내구시험기를 이용하여 실험한 결과, 판막 주위의 컴플라이언스구조에 의한 부식이 진행되는 것을 관찰하였다. 본 연구에서는 컴플라이언스 구조의 위치와 크기가 다른 판막 고정용 홀더를 제작하여 컴플라이언스구조가 인공판막의 부식에 미치는 영향을 검토해따. 또한, 판막의 폐쇄속도가 표면부식에 영향을 미친다고 생각하여 고속도 비디오 카메라를 사용하여 폐쇄속도를 검토하였다. 그 결과, 컴플라이언스를 증가하면 판막의 속도도 증가하며 디스크표면 부식이 진행되는 것이 관찰됐다.

• 한국표면공학회지
• /
• 제49권1호
• /
• pp.26-31
• /
• 2016

In this paper, the characteristics of a cavitation-erosion damage behavior on the STS 304 and hot-dip aluminized STS 304 under cavitation environment in sea water solution was investigated. The electrochemical experiments were carried out by potential measurement, anodic/cathodic polarization test, Tafel analysis, and also galvanostatic experiment in current density variables for the samples. The apparatus of cavitation-electrochemical experiment was manufactured in compliance with modified ASTM G-32 standard, with the conditions of sea water temperature of $25^{\circ}C$ and the measurement, amplitude of $30{\mu}m$. The damage behavior was analyzed by an observation of surface mophologies and a measurement of damage depth by a scanning electron microscope(SEM) and a 3D microscope, respectively, after electrochemical test. After polarization experiment under cavitation environment, much higher damage depths for the hot-dip aluminized STS 304 were observed comparing to the untreated STS 304. In addition, higher corrosion current density in hot-dip aluminized STS 304 presented than that of untreated STS 304 as a result of Tafel analysis.

• Tuberculosis and Respiratory Diseases
• /
• 제77권4호
• /
• pp.161-166
• /
• 2014

Since tuberculosis (TB) remains a major global health concern and the incidence of multi-drug resistant (MDR)-TB is increasing globally, new modalities for the detection of TB and drug resistant TB are needed to improve TB control. The Xpert MTB/RIF test can be a valuable new tool for early detection of TB and rifampicin resistance, with a high sensitivity and specificity. Late-generation fluoroquinolones, levofloxacin, and moxifloxacin, which are the principal drugs for the treatment of MDR-TB, show equally high efficacy and safety. Systemic steroids may reduce the overall TB mortality attributable to all forms of TB across all organ systems, although inhaled corticosteroids can increase the risk of TB development. Although fixed dose combinations were expected to reduce the risk of drug resistance and increase drug compliance, a recent meta-analysis found that they might actually increase the risk of relapse and treatment failure. Regarding treatment duration, patients with cavitation and culture positivity at 2 months of TB treatment may require more than 6 months of standard treatment. New anti-TB drugs, such as linezolid, bedaquiline, and delamanid, could improve the outcomes in drug-resistant TB. Nontuberculous mycobacterial lung disease has typical clinical and immunological phenotypes. Mycobacterial genotyping may predict disease progression, and whole genome sequencing may reveal the transmission of Mycobacterium abscessus. In refractory Mycobacterium avium complex lung disease, a moxifloxacin-containing regimen was expected to improve the treatment outcome.

• The Journal of Korean Physical Therapy
• /
• 제13권3호
• /
• pp.719-726
• /
• 2001

Transdermal drug delivery offers various advantages over conventional drug delivery systems, such as avoidance gastrointestinal degradation and hepatic first-pass effect. encourages patient compliance. and possible sustained release of drugs. However, transdermal transport of drugs is low permeability of the stratum corneum, the superficial layer of the skin. Many physicochemical and biological factors influencing transdermal transport is described together with the corresponding experimental and clinical results. Phonophoresis is medical treatment with drugs introduced into the skin by ultrasound energy. Enhanced drug penetration is through to result from the biophysical alterations of skin structure by ultrasound waves. The frequency used for phonophoresis is usually from 20 kHz to 15MHz. Phonophoresis can be categorized in to three ranges: low-frequency range(below 1 MHz). therapeutic frequency range(1 to 3MHz), and high-frequency range(above 3 MHz). The depth of penetration of ultrasound into skin is inversely proportional to the frequency. Cavitation may cause mechanical stress. temperature elevation, or enhanced chemical reactivity causing drug transport. One theory is that ultrasound affects the permeation of the stratum corneum lipid structure as the limiting step in permeating through the skin. The range of indications for phonophoresis is wide. Aspecific classification of the range of indications is obtained by classification of pathological conditions. The continuous research is needed for many interesting issucs of phonophoretic transdermal delivory in new future.