• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.76-80
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• 2012

산화제 과잉 삼중분사기에 대한 설계와 제작이 이루어졌으며, 이를 사용한 단일분사기 예연소기가 제작되어 연소시험을 수행하였다. 1100Hz의 1L 모드 고주파 불안정과 100 Hz 저주파 불안정이 관찰되었으며, 연소실 직경 수정과 터뷸런트 링 적용에 의해 고주파 불안정은 억제되었다. 현재는 저주파 압력섭동 억제에 주안을 두고 연구가 진행중에 있다.

• 한국소음진동공학회논문집
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• 제23권11호
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• pp.957-965
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• 2013

This paper deals with analytical methods for low frequency and high frequency brake squeal noise on brake-rear caliper. In order to improve low frequency and high frequency squeal noise, we take survey caliper bracket shape parameters and housing shape parameters. Besides, using the combination of bracket and housing parameter were surveyed. Thus, using the combination of bracket Alt_05 and housing Alt_45 specifications, instability analysis and brake dynamo test were carried out. Based upon the two models, low and high frequency squeal noise of base model were improved. But, for 6.0 kHz frequency noise, which is not improved, it needs to additionally study on instability analysis and combination of the other brake components.

• 반도체디스플레이기술학회지
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• 제19권4호
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• pp.88-93
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• 2020

Based on the capture-emission energy (CEE) maps of CMOS devices, a physics-informed machine learning model for the bias temperature instability (BTI)-induced threshold voltage shifts and low frequency noise is presented. In order to incorporate physics theories into the machine learning model, the integration of artificial neural network (IANN) is employed for the computation of the threshold voltage shifts and low frequency noise. The model combines the computational efficiency of IANN with the optimal estimation of Gaussian mixture model (GMM) with soft clustering. It enables full lifetime prediction of BTI under various stress and recovery conditions and provides accurate prediction of the dynamic behavior of the original measured data.

• 한국항공우주학회지
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• 제49권7호
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• pp.573-580
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• 2021

파라핀 왁스는 높은 후퇴율 때문에 하이브리드 로켓의 연료로 많은 각광을 받고 있다. 하지만 파라핀 연료의 연소에서도 비정상적인 저주파수 연소압력 진동이 관찰되고 있는데, 이는 연료 표면에 형성된 액체층과 액적의 유입과 관련이 있는 것으로 추론된다. 본 연구는 액적에 의한 추가적 연소와 저주파수 연소불안정 발생과의 관계를 분석하였다. 한편, 액적의 발생은 관성력과 액체의 표면장력의 비로 정의되는 We수(Weber Number)와 액체층의 Re수(Reynolds Number)에 따라 변화하는 것으로 알려져 있다. 따라서 일차적으로 실험실 규모의 로켓을 사용하여 We수에 따른 연소불안정의 발생여부를 관찰하였다. We수의 조절은 산화제 유량 변화를 통한 관성력의 변화와 LDPE(Low Density Polyethylene) 첨가에 의한 표면장력의 변화를 통해 시도하였다. 저주파수의 연소불안정의 발생은 특정한 We수 이상에서만 관찰되었고 임계 We수가 존재하는 것을 확인하였다.

• Asian Pacific Journal of Cancer Prevention
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• 제16권4호
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• pp.1545-1551
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• 2015

Purpose: Rectal cancers with high microsatellite-instable have clinical and pathological features that differentiate them from microsatellite-stable or low-frequency carcinomas, which was studied rarely in stage II rectal cancer, promoting the present investigation of the usefulness of microsatellite-instability status as a predictor of the benefit of adjuvant chemotherapy with fluorouracil in stage II rectal cancer. Patients and Methods: Data of 460 patients who underwent primary anterior resection with a double stapling technique for rectal carcinoma at a single institution from 2008 to 2012 were retrospectively collected. All patients experienced a total mesorectal excision (TME) operation. Survival analysis were analyzed using the Cox regression method. Results: Five-year rate of disease-free survival (DFS) was noted in 390 (84.8%) of 460 patients with stage II rectal cancer. Of 460 tissue specimens, 97 (21.1%) exhibited high-frequency microsatellite instability. Median age of the patients was 65 (50-71) and 185 (40.2%) were male. After univariate and multivariate analysis, microsatellite instability (p= 0.001), female sex (p<0.05) and fluorouracil-based adjuvant chemotherapy (p<0.001), the 3 factors were attributed to a favorable survival status independently. Among 201 patients who did not receive adjuvant chemotherapy, those cancers displaying high-frequency microsatellite instability had a better 5-year rate of DFS than tumors exhibiting microsatellite stability or low-frequency instability (HR, 13.61 [95% CI, 1.88 to 99.28]; p= 0.010), while in 259 patients who received adjuvant chemotherapy, there was no DFS difference between the two groups (p= 0.145). Furthermore, patients exhibiting microsatellite stability or low-frequency instability who received adjuvant chemotherapy had a better 5-year rate of DFS than patients did not (HR, 5.16 [95% CI, 2.90 to 9.18]; p<0.001), while patients exhibiting high-frequency microsatellite instability were not connected with increased DFS (p= 0.696). It was implied that female patients had better survival than male. Conclusion: Survival status after anterior resection of rectal carcinoma is related to the microsatellite instability status, adjuvant chemotherapy and gender. Fluorouracil-based adjuvant chemotherapy benefits patients of stage II rectal cancer with microsatellite-stable or low microsatellite-instable, but not those with high microsatellite-instable. Additionally, free of adjuvant chemotherapy, carcinomas with high microsatellite-instable have a better 5-year rate of DFS than those with microsatellite-stable or low microsatellite-instable, and female patients have a better survival as well.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.483-488
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• 2003

Frictional heating in brakes causes thermoelastic distortion of the contacting bodies and hence affects the contact pressure distribution. The resulting thermo-mechanical coupling can cause thermoelastic instability (TEI) if the sliding speed is sufficiently high, leading to non-uniform heating called hot spots and low frequency vibration known as hot judder. The vibration of brakes to the known phenomenon of frictionally-excited thermoelastic instability is estimated studying the interface temperature and pressure evolution with time. A simple model has been considered where a layer with half-thickness ${\alpha}$ slides with speed V between two half-planes which are rigid and non-conducting. The advantage of this properly simple model permits us to deduce analytically the critical conditions for the onset of instability, which is the relation between the critical speed and the growth rate of the interface temperature and pressure. Symmetrical component of pressure and temperature distribution at the layer interfaces can be more unstable than antisymmetrical component. As the thickness ${\alpha}$ reduces, the system becomes more apt to thermoelastic instability. Moreover, the evolution of the system beyond the critical conditions has shown that even if low frequency perturbations are associated with low critical speed, it might be less critical than high frequency perturbations if the working sliding speed is much larger than the actual critical speed of the system.

• 한국항공우주학회지
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• 제49권2호
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• pp.139-146
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• 2021

하이브리드 로켓 연소에서 산화제 스월 분사는 회전방향 속도성분이 경계층 유동에 영향을 미쳐 연소안정화에 기여한다. 그러나 스월 강도가 증가할수록 연소성능을 과도하게 변화시키는 문제점이 나타난다. 따라서 참고문헌[7]의 삽입연료와 함께 사용하여 연소성능 변화를 최소화 하면서 연소불안정 억제를 시도하였다. 이를 위해, 일련의 실험을 계획하여 스월 강도와 삽입연료 위치를 변화하며 연소불안정의 발생과 연소성능 변화를 관찰하였다. 실험결과, 스월 각 6°, 삽입연료 위치 310 mm 조합에서 연소불안정이 억제되었으며 연소압력, O/F 비 그리고 연료 후퇴율 등의 변화가 최소인 것으로 확인하였다. 또한 고주파수 대역의 압력진동(p')와 열방출진동(q')의 위상차가 π/2로 음의 결합을 형성하도록 연소조건을 유지하는 것이 저주파수 연소불안정 발생을 억제하는 필요충분조건임을 재확인하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.424-427
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• 2008

The longitudinal instability (POGO) of the rocket should not be occurred during the whole flight time for the large class liquid propulsion system to complete a mission successfully. The longitudinal instability is caused by the resonance between the propulsion system and rocket structure in the low frequency range below 50Hz, ordinarily. We can consider various types of propulsion system in the early stage of rocket development. So the longitudinal instability analysis tool is needed for corresponding to each propulsion system. This article deals the generalized method applied to the analysis on the low frequency dynamic characteristics of various types of liquid propulsion system.

• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1246-1257
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• 2004

The objective of this paper is to characterize dynamic pressure traces measured at self-excited combustion instabilities occurring in two combustion systems of different hardware. One system is a model lean premixed gas turbine combustor and the other a fullscale bipropellant liquid rocket thrust chamber. It is commonly observed in both systems that low frequency waves at around 300㎐ are first excited at the onset of combustion instabilities and after a short duration, the instability mode becomes coupled to the resonant acoustic modes of the combustion chamber, the first longitudinal mode for the lean premixed combustor and the first tangential mode for the rocket thrust chamber. Low frequency waves seem to get excited at first since flame shows the higher heat release response on the lower frequency perturbations with the smaller phase differences between heat release and pressure fluctuations. Nonlinear time series analysis of pressure traces reveals that even stable combustion might have chaotic behavior with the positive maximum Lyapunov exponent. Also, pressure fluctuations under combustion instabilities reach a limit cycle or quasi-periodic oscillations at the very similar run conditions, which manifest that a self-excited high frequency instability has strong nonlinear characteristics.

• 한국소음진동공학회논문집
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• 제14권1호
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• pp.50-55
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• 2004

In this study, slit-tones by plane impinging jet are investigated experimentally over the whole subsonic flow range, especially at low speeds, in order to obtain the instability behaviour of impinging plane jet. Slit-tones are generated at low speeds associated with laminar shear layer instability as well as at high speeds associated with turbulent instability. Most of low-speed slit-tones are induced by symmetric mode instability unless the slit is not so wide, in which case antisymmetric modes are induced like edge-tones. It is found that the frequencies at low speeds ate controled by the unstable condition of the vortex at the nozzle exit and its pairings by which the frequencies are decreased by half. In the case of symmetric modes related with low-speed slit-tones, frequencies lower than those associated with one-step pairings are not found.