• 대한토목학회논문집
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• 제31권5D호
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• pp.705-717
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• 2011

타워크레인은 건설현장의 전체 자재인양 중 약 50%의 물량을 인양하는 양중 장비로 그 수는 빠른 속도로 증가하고 있으나, 건설현장에서의 소홀한 안전관리로 타워크레인 관련 안전사고는 매년 지속적으로 발생되고 있는 실정이다. 특히, 텔레스코핑 작업은 타워크레인 설치단계에서 텔레스코핑 케이지를 유압으로 상승시킨 후 생긴 빈 공간에 새로운 마스트를 삽입하여 요구 높이까지 상승시키는 작업으로 고소에서 다수의 작업자가 동시에 작업을 실시하여 추락 및 낙하의 위험성이 존재하는 등 타 작업에 비해 재해사례 비중이 가장 높은 것으로 분석되었다. 본 연구의 목적은 타워크레인 작업 중 특히 위험성이 높은 것으로 조사 및 분석된 텔레스코핑 작업의 안전성 및 생산성을 향상시킬 수 있는 타워크레인 텔레스코핑 자동화기술의 개념모델을 제안하고 이에 대한 안전성 측면에서의 잠재적 성능을 분석함으로써 향후 타워크레인 텔레스코핑 자동화기술 실물 제작을 위한 원천자료를 제공하는 것이다.

• Journal of Mechanical Science and Technology
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• 제20권5호
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• pp.710-716
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• 2006

Micro-PIV system with a high speed CCD camera is used to measure the flow field near the advancing meniscus of a water slug in microchannels. Image shifting technique combined with meniscus detecting technique is proposed to measure the relative velocity of the liquid near the meniscus in a moving reference frame. The proposed method is applied to an advancing front of a slug in microchannels with rectangular cross section. In the case of hydrophilic channel, strong flow from the center to the side wall along the meniscus occurs, while in the case of the hydrophobic channel, the fluid flows in the opposite direction. Further, the velocity near the side wall is higher than the center region velocity, exhibiting the characteristics of a strong shear-driven flow. This phenomenon is explained to be due to the existence of small gaps between the slug and the channel wall at each capillary corner so that the gas flows through the gaps inducing high shear on the slug surface. Simulation of the shape of a static droplet inside a cubic cell obtained by using the Surface Evolver program is supportive of the existence of the gap at the rectangular capillary corners. The flow fields in the circular capillary, in which no such gap exists, are also measured. The results show that a similar flow pattern to that of the hydrophilic rectangular capillary (i.e., center-to-wall flow) is always exhibited regardless of the wettability of the channel wall, which is also indicative of the validity of the above-mentioned assertion.

• Geomechanics and Engineering
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• 제14권1호
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• pp.9-17
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• 2018

Brazilian splitting tests, uniaxial compression tests and triaxial compression tests are carried out on the coal samples cored from Shanxi group $II_1$ coal seam of Jiaozuo coal mine, Henan province, China, to obtain their property parameters. Considering the bedding has notable effect on the property parameter of coal, the samples with different bedding angles are prepared. The effects of bedding on the anisotropic characteristics of the coal seam are investigated. A geological geomechanical model is built based on the geology characteristics of the Jiaozuo coal mine target reservoir to study the effects of bedding on the fracture propagations during hydraulic fracturing. The effects of injection pressure, well completion method, in-situ stress difference coefficient, and fracturing fluid displacement on the fracture propagations are investigated. Results show bedding has notable effects on the property parameters of coal, which is the key factor affecting the anisotropy of coal. The hydraulic cracks trends to bifurcate and swerve at the bedding due to its low strength. Induced fractures are produced easily at the locations around the bedding. The bedding is beneficial to form a complicated fracture network. Experimental and numerical simulations can help to understand the effects of bedding on hydraulic fracturing in coalbed methane reservoirs.

• 드라이브 ㆍ 컨트롤
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• 제14권2호
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• pp.23-29
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• 2017

In this study, a flexible multi-body dynamic simulation model of a knuckle boom crane is developed to evaluate the stress of spindle and rack gears under dynamic working conditions. It is difficult to predict potential critical damage to a knuckle boom crane if only the static condition is considered during the development process. To solve this issue, a severe working scenario (high speed with heavy load) was simulated as a boundary condition for testing the integrity of the dynamic simulation model. The crane gear model is defined as a flexible body so contact analysis was performed. The functional motion of a knuckle boom crane is generated by applying forces at each end of the rack gear, which was converted from hydraulic pressure measured for the experiment. The bending and contact stress of gears are theoretically calculated to validate the simulation model. In the simulation, the maximum stress of spindle and rack gears are observed when the crane abruptly stops. Peak impact force is produced at the contact interface between pinion and rack gears due to the inertia force of the boom. However, the maximum stress (bending/contact) of spindle and rack are under the yield stress, which is safe from damage. By using the developed simulation model, the experiment process is expected to be minimized.

• 대한간호학회지
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• 제29권3호
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• pp.563-575
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• 1999

The purpose of this study was to examine the correlation between self-efficacy and self-care of hemodialysis patients. The subjects consisted of 140 hemodialysis patients who underwent hemodialysis at 2 university hospitals. The data were collected by questionnaires and chart review. The questinnaire used the self-efficacy tool developed by Kim Ju Hyune(1995) and the self-care tool developed by literature review and indepth open openended questions to 10 patients. Also, the questionnaire included physiologic data which collected through review of the patients' charts. The statistical analysis was used the SPSS program for frequency, mean, t-test, ANOVA and Pearson correlation. The results were as follows : 1. The mean score for general self-efficacy of hemodialysis patients was 3.103(1-4point) and there were significant differences according to percieved health. The mean score for specific self-efficacy of hemodialysis patients was 3.113 (1-4point) and there were significant differencies according to percieved health, side effects and complications which related hemodialysis. 2. The mean score for self-care of hemodialysis patients was 3.822(1-5point) and there were significant differencies according to marital status and economic level. 3. The relationship between general self-efficacy and self-care was a positive correlation(P＝.000). The relationship between specific self-efficacy and self-care was a positive correlation(P＝.000). In conclusion, this study revealed the level of self-efficacy and self-care, and the positive correlation between self-efficacy and self-care in hemodialysis patients. Therefore, intervention is needed to promote self-efficacy for self-care of hemodialysis patients. Considering the vulnerable self-care area same as checking blood pressure and weight, fluid restriction, social adjustment, exercise and rest, luther studies should develop self-efficacy promoting programs for self-care of hemodialysis patients.

• Journal of Korean Neurosurgical Society
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• 제56권1호
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• pp.28-33
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• 2014

Objective : Postoperative delirium is a common complication in the elderly after surgery but few papers have reported after spinal surgery. We analyzed various risk factors for postoperative delirium after spine surgery. Methods : Between May 2012 and September 2013, 70 patients over 60 years of age were examined. The patients were divided into two groups : Group A with delirium and Group B without delirium. Cognitive function was examined with the Mini-Mental State Examination-Korea (MMSE-K), Clinical Dementia Rating (CDR) and Global Deterioration Scale (GDS). Information was also obtained on the patients' education level, underlying diseases, duration of hospital stay and laboratory findings. Intraoperative assessment included Bispectral index (BIS), type of surgery or anesthesia, blood pressure, fluid balance, estimated blood loss and duration of surgery. Results : Postoperative delirium developed in 17 patients. The preoperative scores for the MMSE, CDR, and GDS in Group A were $19.1{\pm}5.4$, $0.9{\pm}0.6$, and $3.3{\pm}1.1$. These were significantly lower than those of Group B ($25.6{\pm}3.4$, $0.5{\pm}0.2$, and $2.1{\pm}0.7$) (p<0.05). BIS was lower in Group A ($30.2{\pm}6.8$ compared to $35.4{\pm}5.6$ in group B) (p<0.05). The number of BIS <40 were $5.1{\pm}3.1$ times in Group A, $2.5{\pm}2.2$ times in Group B (p<0.01). In addition, longer operation time and longer hospital stay were risk factors. Conclusion : Precise analysis of risk factors for postoperative delirium seems to be more important in spinal surgery because the surgery is not usually expected to have an effect on brain function. Although no risk factors specific to spinal surgery were identified, the BIS may represent a valuable new intraoperative predictor of the risk of delirium.

• 한국전산유체공학회지
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• 제18권4호
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• pp.1-8
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• 2013

The performance of small-size impellers with ruled surfaces was investigated for flank milling over a wide speed range, using computational fluid dynamics analyses and gas bench tests. An impeller with a ruled surface was designed, manufactured, and tested to evaluate the effects of blade loading, the backsweep angle, and the relative velocity distribution on the compressor performance. The simulations and tests were completed using the same compressor cover with identical inlet and outlet channels to accurately compare the performance of the abovementioned impeller with a commercial impeller containing sculptured blades. Both impellers have the same number of blades, number of splitters, and shroud meridional profiles. The backsweep angles of the blades on the ruled impeller were selected to work with the same pinched diffuser as for a sculptured impeller. The inlet-to-exit relative velocity diffusion ratio and the blade loading were provided to maximize the flow rate and to minimize the surge flow rate. The design flow rate, rpm, were selected same for both impellers. Test results showed that for the compressor stage with a ruled impeller, the efficiency was increased by 0.32% with an extended surge margin without a reduction in the pressure ratio as compared to the impeller with the sculptured design. It was concluded that an increased relative velocity diffusion coupled with a large backsweep angle was an effective way to improve the compressor stage efficiency. Additionally, an appropriate blade loading distribution was important for achieving a wide operating range and higher efficiency.

• Journal of Advanced Marine Engineering and Technology
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• 제39권10호
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• pp.1002-1010
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• 2015

Natural gas hydrates are newly emerging as an environment-friendly source of energy to substitute for fossil fuels in the 21stcentury.NGHs are reported to holds much amounts of natural gas (up to 182 standard volumes of gas per volume of hydrate); they are easy to store and safe to carry at about minus 20 degree Celsius under atmospheric pressure because of the self-preservation phenomenon of gas hydrates. The transporting method by gas-ice-hydrate ship carriers has been introduced and developed by a variety of industry and research institutions. Our team has been conducted to develop NGH total systems, including a breakthrough NGH carrier for sea transportation, since 2011. The NGH pellet carrier does not require a separate cooling system for cargo, and the initial temperature is maintained through insulation of the cargo tanks throughout the transport to the final destination. The heat conducted from the exterior and passing through the insulation material of the hull should be cut off as much as possible, but heat inflow inside the cargo tank from an external source is inevitable during transport. In this study, the heat transfer in a cargo tank of a 115K NGH carrier was analyzed through simulation with a commercial CFD code to estimate the boil-off gas/boil-off rate on the developed carrier and understand major hazards that could significantly impact the safety of the vessel.

• 대한기계학회논문집B
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• 제35권12호
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• pp.1343-1349
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• 2011

본 연구에서는 $100^{\circ}C$의 저온 열원을 이용하여 구동되는 랭킨 동력 사이클에 대하여, HFC-134a를 이용한 아임계 운전을 할 경우의 출력과 HFC-125 를 이용한 초월임계 운전을 할 경우의 출력을 서로 비교함으로써, 초월임계 운전에 의한 출력 향상 가능성을 연구하였다. 서로 다른 두 사이클들의 출력을 공정하게 비교하기 위하여, 각 사이클들을 3 개의 설계인자를 이용하여 최적화 하였다. 이 때, 보다 현실적인 결과를 위하여 기존의 연구와는 달리, 열교환 과정에서 작동유체의 열전달 및 압력강하 특성을 고려하였다. 시뮬레이션 결과, HFC-125 초월임계 사이클의 출력이 HFC-134a 아임계 사이클의 출력에 비해 본 연구의 시뮬레이션 조건 하에서 9.4% 향상 될 수 있음을 보였다.

• 한국산학기술학회논문지
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• 제14권4호
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• pp.1765-1773
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• 2013

본 연구에서는 단순천공배액술을 시행하고 호전된 환자들과 이차 수술로 단순천공배액술을 실시하거나 경막하복강단락술을 실시한 환자들의 임상적 경과 분석을 통해 뇌경막하수종 치료에 도움이 되고자 한다. 2006년 7월부터 2012년 6월까지 본원에서 뇌경막하수종으로 입원하여 단순천공배액술을 시행받은 16례 전체 환자를 대상으로 분석하였다. 연구결과 아스피린을 복용하고 있는 환자는 모두 이차 수술을 시행하였다(p<0.001). 경막하복강단락술을 시행한 환자 4명 중 2명이 아스피린을 복용하여 통계적으로 유의하였다(p=0.014). 경막하복강단락술을 시행한 그룹과 시행하지 않은 그룹 간의 비교 결과, 4명의 환자는 일차수술 후 GCS의 변화는 없었으나 추적 전산화단층촬영 상 정중선 편위가 심하였고 경막하수종은 증가하거나 변화가 없었으며 두통, 구토, 발열, 호흡곤란 등의 뇌압상승 증상을 보여 단락술을 결정하게 되었다(p=0.006). 아스피린을 복용했던 환자들의 수술적 치료는 주의를 요하며 개두술 과정에서 뇌척수액의 급격한 소실과 뇌압의 지나친 변화를 예방하는 것이 중요하다고 사료된다.