• 한국시뮬레이션학회논문지
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• 제22권3호
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• pp.81-87
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• 2013

본 논문은 컴퓨터 해석프로그램인 SimulationX를 이용하여 굴삭기 주행모터의 내부에서 발생하는 서지압력의 저감 방법에 대하여 분석하는 연구이다. 설계민감도 해석을 통하여 설계상의 문제점을 파악하고 해결책에 접근하는 방법을 다룬다. 진행순서는 다음과 같다. 우선 현재 설계 된 주행모터에 장착된 밸브들의 동적거동을 분석하여 설계의 문제점을 찾아낸다. 그 후 많은 설계변수들 중 동적성능향상에 민감하다고 판단되는 변수를 도출하고 설계치수를 조정하여 동적성능 안정화의 경향을 살펴본다. 마지막으로 민감한 변수가 다수 일 경우 변수조합을 통해 효과적인 튜닝방법을 제안한다.

• Journal of Chest Surgery
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• 제53권6호
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• pp.332-338
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• 2020

Background: Attaining an adequate effective orifice area (EOA) is definitive goal in aortic valve replacement (AVR). The simple interrupted suture (SIS) technique could be a solution to achieve this goal, but limited data are available in the literature. This study aimed to compare hemodynamic differences between the SIS and non-everting mattress suture (NMS) techniques. Methods: From our database, 215 patients who underwent AVR for severe aortic stenosis were extracted to form the overall cohort. From March 2015 to November 2016, the SIS technique was used in 79 patients, while the NMS technique was used in 136 patients. Hemodynamic outcomes were evaluated, as detected by transthoracic echocardiography and computed tomography. Results: There were no significant differences in baseline characteristics between the 2 groups. On immediate postoperative echocardiography, the SIS group showed a significantly wider EOA (1.6±0.4 vs. 1.4±0.5 ㎠, p=0.007) and a lower mean pressure gradient (PG) (13.3±5.4 vs. 17.0±6.0 mm Hg, p<0.001) than the NMS group. On follow-up echocardiography, the SIS group continued to have a wider EOA (1.6±0.4 vs. 1.4±0.3 ㎠, p<0.001) and a lower mean PG (11.0±5.1 vs. 14.1±5.5 mm Hg, p<0.001). There was no significant difference in paravalvular leakage. Conclusion: The SIS technique for AVR was associated with a wider EOA and a lower mean PG. The SIS technique could be a reasonable option for AVR.

• Journal of Chest Surgery
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• 제53권5호
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• pp.285-290
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• 2020

Background: This study was conducted to evaluate the hemodynamic performance and the incidence of prosthesis-patient mismatch (PPM) after aortic valve replacement (AVR) using bovine pericardial valves (Carpentier-Edwards Perimount Magana and Magna Ease). Methods: In total, 216 patients (mean age, 70.0±10.5 years) who underwent AVR using stented bovine pericardial valves and had follow-up echocardiography between 3 months and 2 years (mean, 12.0±6.6 months) after surgery were enrolled. The implanted valve sizes were 19, 21, 23, and 25 mm in 32, 56, 99, and 29 patients, respectively. Results: On follow-up echocardiography, the mean transvalvular pressure gradients for the 19-mm, 21-mm, 23-mm, and 25-mm valves were 13.3±4.4, 12.6±4.2, 10.5±3.9, and 10.2±3.7 mm Hg, respectively. The effective orifice area (EOA) was 1.25±0.26, 1.54±0.31, 1.81±0.41, and 1.87±0.33 ㎠, respectively. These values were smaller than those suggested by the manufacturer for the corresponding sizes. No patients had PPM, when based on the reference EOA. However, moderate (EOA index ≤0.85 ㎠/㎡) and severe (EOA index ≤0.65 ㎠/㎡) PPM was present in 56 patients (11.8%) and 9 patients (1.9%), respectively, when using the measured values. Conclusion: Carpentier-Edwards Perimount Magna and Magna Ease bovine pericardial valves showed satisfactory hemodynamic performance with low rates of PPM, although the reference EOA could overestimate the true EOA for individual patients.

• 한국자동차공학회논문집
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• 제21권4호
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• pp.89-95
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• 2013

In this work, the evaluation of swirl nozzle injector performance was conducted by investigating effective area ($A_{eff}$), injection mass ($m_{inj}$), injection rate ($Q_{inj}$), and injection delay ($t_{delay}$) under various test conditions. To achieve these, fuel injection analysis system which was composed of fuel supply system, injection system, and control system was installed. At the same time, the swirl nozzle that had 12 orifice hole with $120^{\circ}$ injection angle was used in this work. It was revealed that the difference of injection mass ($m_{inj}$) between base and swirl nozzle injector increased as the injection pressure ($P_{inj}$) and energizing duration ($t_{eng}$) decreased under the same test conditions. The maximum injection rate ($Q_{inj}$) of swirl nozzle injector was higher than base nozzle injector about 2~5%. The injection performance of swirl nozzle was better than base nozzle at low injection pressure ($P_{inj}$) and short energizing duration ($t_{eng}$) conditions.

• Journal of Chest Surgery
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• 제40권3호
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• pp.200-208
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• 2007

배경: 대동맥판막 치환술 후 발생하는 환자-인공판막 부조화(patient-prosthesis mismatch, PPM)가 환자의 경과에 어떠한 영향을 주는가에 대해서는 아직 논란의 여지가 있다. 이 연구는 대동맥판막 치환술 후 PPM이 발생한 환자군과 PPM을 예방하기 위해 대동맥판륜 확장술을 시행한 환자군 간의 수술 결과와 경과를 비교해 보았다. 대상 및 방법: 1996년 1월부터 2006년 2월까지 stent가 있는 조직판막 혹은 기계판막을 이용하여 대동맥판막 치환술을 시행 받은 627명의 성인 환자를 연구대상으로 하였다. 치환된 대동맥판막의 indexed effective orifice area (iEOA)가 $0.85cm^2/m^2$ 이하인 경우를 PPM으로 정의 하였고 $0.65cm^2/m^2$ 이하는 심한 PPM으로 정의하였다 PPM은 103명(16.4%, PPM군)에서 발생하였고 심한 PPM은 11명(1.8%, SPPM군)에서 발생하였다. 동일한 연구 기간 동안 대동맥판륜 확장술을 시행 받은 환자(Annular Enlargement군, AE)는 모두 21명이었다. 결과: AE군의 평균 iEOA는 PPM군보다 더 컸다($0.95\;vs.\;0.76cm^2/m^2,\;p=0.00$). AE군은 PPM군보다 심폐바이패스 시간, 심장허혈 시간 및 수술 시간이 더 길었으며 수술 사망률이 더 높은 경향을 보였다(14.3% vs. 2.9%, p=0.06). 술 후 가장 최근에 시행한 심초음파 검사에서 SPPM군은 대동맥판막 판구 압력차(최고/평균)가 AE군보다 더 높게 나타났으며(72/45 mmHg vs. 38/25 mmHg, p=0.02/0.06), 대동맥판막 관련 문제(대동맥판막 재치환술 혹은 심한 대동맥판막 협착)가 더 많이 발생하였다(45.5% vs. 9.5%, p=0.03). 또한 대동맥판막 관련 문제가 발생한 환자들에서는 좌심실 심근량 감축(regression)을 관찰할 수 없었다. 결론: 협소한 대동맥판륜을 가진 환자에서 대동맥판륜 확장술의 시행여부는 대동맥판륜 확장술 자체의 위험도와 환자 상태 및 동반 질환 등을 함께 고려하여 신중히 결정하여야 한다. 하지만 대동맥판막 치환술 후 심한 PPM이 예상되는 환자에서는 대동맥판륜 확장술이 대안으로 이용될 수 있다.

• 대한의용생체공학회:의공학회지
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• 제27권6호
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• pp.418-426
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• 2006

In the artificial heart application, productivity and hemodynamic properties of artificial heart valves are crucial in successiful application to long term in vivo trials. This paper is about manufacture and assessment of trileaflet polymer heart valves using vacuum forming process(VFP). The VFP has many advantages such as reduced fabrication time, reproducibility due to relatively easy and simple process for manufacturing. Prior to VFP of trileaflet polymer heart valves, polyurethane(Pellethane 2363 80AE, Dow Chemical) sheet was prepared by extrusion. The sheets were heated and formed to mold shape by vacuum pressure. The vacuum formed trileaflet polymer heart valves fabrication is composed of two step method, first, leaflet forming and second, conduit forming. This two-step forming process made the leaflet-conduit bonding stable with any organic solvents. Hydrodynamic properties and hemocompatibility of the vacuum formed trileaflet polymer heart valves was compared with sorin bicarbon bileaflet heart valve. The percent effective orifice area of vacuum formed trileaflet polymer heart valves was inferior to bileaflet heart valve, but the increase of plasma free hemoglobin level which reflect blood damage was superior in vacuum formed trileaflet polymer heart valves Vacuum formed trileaflet polymer heart valves has high productivity, and superior hemodynamic property than bileaflet heart valves. Low manufacturing cost and blood compatible trileaflet polymer heart valves shows the advantages of vacuum forming process, and these results give feasibility in in vivo animal trials in near future, and the clinical artificial heart development program.