• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.31-35
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• 2006

The delta-formulation of the Navier-Stokes equations has been popularly used in the aerodynamics area. Implicit algorithm can be easily implemented in that by using Taylor series expansion. This formulation is extended for an unsteady analysis by using a dual-time integration. In the meanwhile, the incompressible flows with heat transfers which occur in the area of thermo-hydraulics have been solved by a segregated algorithm such as the SIMPLE method, where each equation is discretised by using an under-relaxed deferred correction method and solved sequentially. In this study, the dual-time delta formulation is implemented in the segregated Navier-Stokes solver which is based on the collocated cell-centerd scheme with un unstructured mesh FVM. The pressure correction equation is derived by the SIMPLE method. From this study, it was found that the Euler dual-time method in the delta formulation can be combined with the SIMPLE method.

• Geomechanics and Engineering
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• 제28권2호
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• pp.171-180
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• 2022

Time-dependent stress-strain behaviour significantly influences the compressibility characteristics of the clayey soil. In this paper, a series of oedometer tests were conducted in two loading patterns and investigated the time-dependent compressibility characteristics of Indian Montmorillonite Clay, also known as black cotton soil (BC) soil, during loading-unloading stages. The experimental data are analyzed using a new non-linear function of the Elasto-Visco-Plastic Model considering Swelling behaviour (EVPS model). From the experimental result, it is found that BC soil exhibits significant time-dependent behaviour during creep compared to the swelling stage. Pore water entrance restriction due to consolidated overburden pressure and decrease in cation hydrations are responsible factors. Apart from it, particle sliding is also evident during creep. The time-dependent parameters like strain limit, creep coefficient and C_αe/C_c are observed to be significant during the loading stage than the swelling stage. The relationship between creep coefficients and applied stresses is found to be nonlinear. The creep coefficient increases significantly up to 630 kPa-760 kPa (during reloading), and beyond it, the creep coefficient decreases continuously. Several parameters like loading duration, the magnitude of applied stress, loading history, and loading path have also influenced secondary compressibility characteristics. The time-dependent compressibility characteristics of BC soil are presented and discussed in detail.

• Journal of Korean Neurosurgical Society
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• 제48권3호
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• pp.251-258
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• 2010

Objective : Despite rapid evolution of shunt devices, the complication rates remain high. The most common causes are turning from obstruction, infection, and overdrainage into mainly underdrainage. We investigated the incidence of complications in a consecutive series of hydrocephalic patients. Methods : From January 2002 to December 2009, 111 patients underwent ventriculoperitoneal (VP) shunting at our hospital. We documented shunt failures and complications according to valve type, primary disease, and number of revisions. Results : Overall shunt survival time was 268 weeks. Mean survival time of gravity-assisted valve (GAV) was 222 weeks versus 286 weeks for other shunts. Survival time of programmable valves (264 weeks) was longer than that of pressure-controlled valves (186 weeks). The most common cause for shunt revision was underdrainage (13 valves). The revision rate due to underdrainage in patients with GAV (7 of 10 patients) was higher than that for other valve types. Of 7 patients requiring revision for GAV underdrainage, 6 patients were bedridden. The overall infection rate was 3.6%, which was lower than reported series. Seven patients demonstrating overdrainage had cranial defects when operations were performed (41%), and overdrainage was improved in 5 patients after cranioplasty. Conclusion : Although none of the differences was statistically significant, some of the observations were especially notable. If a candidate for VP shunting is bedridden, GAV may not be indicated because it could lead to underdrainage. Careful procedure and perioperative management can reduce infection rate. Cranioplasty performed prior to VP shunting may be beneficial.

• 융합정보논문지
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• 제11권3호
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• pp.7-13
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• 2021

본 연구는 딥러닝(Deep Learning) 알고리즘 GAN 모델을 기반으로 초미세먼지(PM2.5) 인공지능 예측시스템을 개발한다. 실험 데이터는 시계열 축으로 생성된 온도, 습도, 풍속, 기압의 기상변화와 SO2, CO, O3, NO2, PM10와 같은 대기오염물질 농도와 밀접한 관련이 있다. 데이터 특성상, 현재시간 농도가 이전시간 농도에 영향을 받기 때문에 반복지도학습(Recursive Supervised Learning) 예측 모델을 적용하였다. 기존 모델인 CNN, LSTM의 정확도(Accuracy)를 비교분석을 위해 관측값(Observation Value)과 예측값(Prediction Value)간의 차이를 분석하고 시각화했다. 성능분석 결과 제안하는 GAN이 LSTM 대비 평가항목 RMSE, MAPE, IOA에서 각각 15.8%, 10.9%, 5.5%로 향상된 것을 확인하였다.

• Geomechanics and Engineering
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• 제7권3호
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• pp.279-295
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• 2014

A series of one-dimensional consolidation tests and triaxial creep tests were performed on Nansha clays, which are interactive marine and terrestrial deposits, to investigate their time-dependent behaviour. Based on experimental observations of oedometer tests, normally consolidated soils exhibit larger secondary compression than overconsolidated soils; the secondary consolidation coefficient ($C_{\alpha}$) generally gets the maximum value as load approaches the preconsolidation pressure. The postsurcharge secondary consolidation coefficient ($C_{\alpha}$') is significantly less than $C_{\alpha}$. The observed secondary compression behaviour is consistent with the $C_{\alpha}/C_c$ concept, regardless of surcharging. The $C_{\alpha}/C_c$ ratio is a constant that is applicable to the recompression and compression ranges. Compared with the stage-loading test, the single-loading oedometer test can evaluate the entire process of secondary compression; $C_{\alpha}$ varies significantly with time and is larger than the $C_{\alpha}$ obtained from the stage-loading test. Based on experimental observations of triaxial creep tests, the creep for the drained state differs from the creep for the undrained state. The behaviour can be predicted by a characteristic relationship among axial strain rate, deviator stress level and time.

• 대한기계학회논문집
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• 제19권2호
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• pp.322-329
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• 1995

Series of experimental work was performed to mold tensile specimens by using the injection molding machine Mold temperature, melt temperature and packing time were chosen as processing parameters for studying the effects of those conditions on the linear shrinkage of final product. Here, each processing variable was decided from the numerical simulation and resin manufacturer's suggested value. The effects of molding conditions on the linear shrinkage in flow direction of the resin were analyzed by measuring the parts 2, 10, 30 and 60 days after molding. As a result, the linear shrinkage increased with the higher mold and melt temperature, and the change of mold temperature has shown more influence. The linear shrinkage of polypropylene has been found to progress up to 30 day with the lapse of the time, and the amount of the linear shrinkage has shown to be between 2.14% and 2.75%. In addition, the effects of packing pressure on the weight has shown to be extremely significant up to freezing time, and proper packing time of the tensile specimen has been found to be 2.0 seconds.

• 한국정밀공학회지
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• 제25권6호
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• pp.40-46
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• 2008

Ultraprecision cutting of steels with geometrically defined single crystal diamond tools is handicapped by excessive tool wear. This paper presents a new approach to suppress the wear of single crystal diamond tool in cutting of steels. In general, it is said that the wear of diamond tool is caused by chemically reactive wear under high temperature and high pressure conditions. In order to suppress such chemical reactions, the time of contact between the diamond tool and the steel work in cutting was controlled by employing the intermittent cutting method such as fly-cutting. Series of intermittent cutting experiments have been carried out to control the tool-work contact time by changing one cycle of cutting length and cutting speed. The experimental results were shown that the tool wear was much dependent on the contact time regardless of the cutting speed, and that the wear was much suppressed by reducing the tool-work contact time. It is expected that the steels can be successfully cut with a single crystal diamond tool by controlling the contact time.

• 한국수자원학회논문집
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• 제45권5호
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• pp.455-464
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• 2012

이 논문에서는 관망시스템의 수격압 현상을 모의하기 위해서 합성 부정류 마찰 모형을 개발하였다. 부정류 마찰항을 고려하기 위한 방법으로 빈도 의존 마찰항과 순간 가속도 기반 마찰 모형을 합성하였으며, 특성선 방법을 모형 개발의 기반으로하였다. 관망에서의 부정류 모형으로 가장 널리 쓰이는 Zielke의 마찰항 모형과 Ramos의 마찰항 모형들과 종합적인 비교를 수행하였다. 모의 결과를 검증하기 위해서 고빈도로 수압을 측정할 수 있는 자료 획득체제를 구비한 관망시스템을 구축하였다. 정상상태에서 밸브 급폐로 야기된 수격압의 수압 시계열을 2가지 Reynolds수에서 확보하였다. 모의결과는 pilot 관망체제에서 확보한 실험 자료와 비교하였다. 부정류 마찰항 모형의 매개변수 보정을 위해서 시행착오 방법이 도입되었으며, 부정류 마찰항들을 비교한 결과는 수격압에서 수압이 감쇄되는 과정에 대한 전반적인 이해를 돕고자 하였다. 이와 같은 결과는 관망의 천이류를 적절히 예측하는데 부정류 마찰항의 적절한 고려가 필수적인 부분임을 알려 주고 있다.

• 한국방재안전학회논문집
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• 제6권2호
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• pp.49-56
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• 2013

본 논문에서는 재난변동풍하중을 받는 고층건물의 예비설계과정에서 필요로 하는 자료를 얻기 위하여 경계층풍동 실험을 실시했다. 먼저 본 실험에 앞서 경계층풍동내의 자연풍을 얻기 위하여 확산장치를 이용했고, 이로부터 평균풍속 수직분포, 난류강도, 파워스펙트럼으로 입증했으며, 이 후 변장비 1:2 강체모형을 이용 경계층풍동실험을 실시한 결과로부터 다음과 같은 결론을 얻을 수 있었다. 1. 경계층풍동에서의 평균풍속 및 난류강도의 수직분포가 자연풍과 같이 잘 실현되었다. 2. 변동풍속 스펙트럼은 Von Karman spectrum과 비교한 결과 잘 일치했다. 3. 변동압력 스펙트럼에서 풍상면의 피크분포는 0.01-0.1 Hz영역에서 발생했고, 풍후면은 0.1 Hz영역에서 발생했다. 4. 자기상관계수는 재난변동풍하중의 작용시간이 증가하면 정성확률과정으로 분포하는 사실을 알 수 있었다.

• 한국동물학회지
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• 제18권3호
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• pp.147-156
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• 1975

成熟한 Sprague-Dawley 系 雄性 흰쥐를 對照群(760 mmHg)과 低氣壓群인 500 mmHg 와 380 mmHg의 兩實驗群으로 나누어 15日間(1日當 1時間) 曝露시켜, 低氣壓이 血淸 glutamic oxaloacetic transaminase(GOT) 및 血淸 lactic dehydrogenase(LDH) 活性에 미치는 影響을 考察하였다. 血淸 GOT 및 LDH 含量은 兩群 共히 對照群에 比하여 顯著한 變化를 招來하였으며, 특히 GOT는 初期에 減少되고, 後期에 恒定持續性을 나타내어 對照群의 값에 近接하는 傾向이 나타났으며, 한편 LDH의 含量은 初期에 增加하고 後期에는 若干의 減少傾向이 나타났다. 一般的으로 이러한 變化는 흰쥐가 低氣壓의 曝露에 一時的인 恒定持續性을 나타내는 것을 보여주며 酵素의 含量의 變化는 低氣壓의 强度와 順化期間에 따라 다르며, 一般的으로 380 mmHg群은 500 mmHg群에 比하여 顯著한 變化相을 가져오는 것으로 思料된다.