• 한국군사과학기술학회지
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• 제25권3호
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• pp.275-284
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• 2022

Linear Shaped Charge(LSC) is widely used as a separation system in the field of weapon system. However, there are some disadvantages that are charging lots of explosives due to lack of uniformity and having difficulties of the design of liner and explosives because of manufacturing process. In order to solve these problems, Precision Linear Shaped Charge(PLSC) that can design a liner independently and charge explosives uniformly has been developed. In this study, PLSC was designed to have a proper liner shape and amount of explosives, and the penetration test of PLSC with different stand-off distance from liner to target was conducted. On the basis of the penetration test results of PLSC, the numerical analysis method using AUTODYN was established and verified. The penetrative mechanism and characteristics of PLSC with targets of different materials was analyzed from experimental and numerical results.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.293-300
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• 2008

Efficient designing of SRM Grains in the field of Rocketry is still the main test for most of the nations of world for scientific studies, commercial and military applications. There is a strong need to enhance thrust, improve the effectiveness of SRM and reduce mass of motor and burning time so as to allow the general design to increase the weight of payload/on board electronics. Moreover burning time can be increased while keeping the weight of the propellant and thrust in desired range, so as to give the time to control / general design group in active phase for incorporating delayed cut off if required. A mathematical design, optimization & analysis technique for Slotted Tube Grain has been discussed in this paper. In order to avoid the uncertainties that whether the Slotted Tube grain configuration being designed is best suited for achieving the set design goals and optimal of all the available designs or not, an efficient technique for designing SRM Grain and then getting optimal solution is must. The research work proposed herein addresses and emphasizes a design methodology to design and optimize Slotted Tube Grain considering particular test cases for which the design objectives and constraints have been given. In depth study of the optimized solution have been conducted thereby affects of all the independent parametric design variables on optimal solution & design objectives have been examined and analyzed in detail. In doing so, the design objectives and constraints have been set, geometric parameters of slotted tube grain have been identified, performance prediction parameters have been calculated, thereafter preliminary designs completed and finally optimal design reached. A Software has been developed in MATLAB for designing and optimization of Slotted Tube grains.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 춘계 학술대회논문집
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• pp.203-208
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• 2001

Any circumferential variations of the impeller exit flow conditions influences on the volute inlet flow conditions. All these interactions are strongly coupled phd affect consequently the performance of centrifugal pumps. In this paper, a commercial CFD code, which solves three-dimensional quasi-steady Wavier-Stokes equations with an impeller/volute interaction, is used for the prediction of a centrifugal pump performance. The simplified model of an impeller/volute interaction requires affordable computing time and provides relevant results. As a result, detailed flow structures such as pressure rise, recovery and loss mechanism on the centrifugal pumps are obtained. Especially, hydraulic performances are compared between the case of impeller only and the case of impeller with volute configuration. In addition, pump performance at off-design operation are observed and discussed.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.105-109
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• 2003

가스터빈 시험장치의 실험 데이터로부터 얻어진 일부 성능 데이터를 이용하여 구성품 성능선도 (component characteristic)를 축척(scaling)하는 새로운 방법을 제안하였다. 성능해석의 오차를 최소화하기 위하여 실제 실험 데이터로부터 몇 개의 작동점들에 일치하는 일련의 구성품 성능선도들을 구하고 다항식(polynomial)을 이용하여 새롭게 성능선도를 구성하는 축척방법을 제안하였으며, 이때 얻어진 성능선도를 이용하여 탈설계점 성능해석을 수행하였다. 해석 결과 기존의 축척방법으로 얻어진 성능선도를 이용한 경우 설계점을 제외한 대부분의 탈설계점에서의 성능은 실제 엔진 성능과 잘 일치하지 않았다. 그러나 새로운 축척방법에 의해 얻어진 성능선도를 이용한 경우에는 최대 5％ 이내의 오차율을 보였다.

• 한국유체기계학회 논문집
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• 제5권2호
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• pp.15-21
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• 2002

The hydraulic performance analysis of an entire pump system composed of inducer, impeller, volute and seal for the application of turbopumps is numerically performed using three-dimensional Navier-Stokes equations. A quasi-steady mixing-plane method is used on the impeller/volute interface to simulate the unsteady interaction phenomena. From this work, the effects of each component on the pump performance are investigated at design and off-design conditions through the analysis of flow structures and loss mechanisms. The computational results are in a good agreement with experimental ones in terms of the headrise and efficiency even though very complex flow structures are present. It is found that the asymmetric pressure distribution along the volute wall constitutes the main reason of the difference between experimental and computational results, due to the limitation of the quasi-steady method. Since the volute was found to be over-designed by the pressure distribution of the volute wall, re-design of the volute has been performed, resulting in an improved performance characteristic.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.36-44
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• 2000

The flow at the impeller exit is important to validate engineering design and numerical analysis of pumps. We installed axisymmetric collector instead of the volute casing, so there is no interaction between the impeller and casing. A hot-film probe and a high response pressure transducer are used to investigate the flow at impeller exit and vaneless diffuser region for design and off design flow rate. For a single suction centrifugal pump of low specific speed, the flow field such as velocity, flow angle, and total pressure are measured by traversing the probe across the vaneless diffuser. These data can be used for performance prediction, design, and numerical analysis of pumps.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.371-379
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• 2000

A noise prediction method of axial flow fan is developed by incorporating through-flow method and vortex shedding noise model. Fan noise is assumed to be generated due to the pressure fluctuation induced by wake vortices of fan blades and radiate as diploe distribution. The wake vortices are analyzed by combining Karman vortex street model and through-flow analysis results, and the vortex-induced fluctuating pressure on blade surface is calculated by thin airfoil theory. The predicted sound pressure levels and directivity patterns of fan noise by the present method are favorably compared with fan noise test data. Furthermore, the present method is shown to be very useful for predicting the aero-acoustic performance map of the fan operated at off-design point.

• 한국추진공학회지
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• 제5권3호
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• pp.41-51
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• 2001

Split-triplet(F-O-O-F)형의 분사기 요소를 장착한 KSR-III 액체 로켓엔진의 성능과 연소장을 고찰하기 위해 수치해석을 수행하였다. 방사형 분사기 배열의 액체 로켓엔진의 수치해석 검증을 위해 2차원 축대칭과 3차원 계산을 수행하여 연소시험 결과와 비교하였다. 2차원 축대칭 계산과 3차원 해석을 통하여 성능 측면에서 오차가 약 3∼5% 정도의 정확도를 유지하며 예측하는 것을 볼 수 있었다. 3차원 해석에서는 연소장을 해석하여 분사기 면의 온도 분포가 연소 시험결과와 정성적으로 일치하는 것을 볼 수 있었다. 또한 충돌각의 감소와 분사기 배열의 직교-방사형으로 변경이 방사형 분사기배열의 국부적인 고온 영역을 감소시키며 성능에도 영향을 미치는 것을 볼 수 있었다. 이러한 해석을 통하여 분사기 배열과 충돌각 선정이 액체 로켓엔진의 성능과 연소장에 영향을 미치는 중요한 요인이 됨을 알 수 있었다.

• Physical Therapy Rehabilitation Science
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• 제6권4호
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• pp.176-181
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• 2017

Objective: The timed up and go (TUG) test is method used to determine the functional mobility of persons with stroke. Its reliability, validity, reaction rate, fall prediction, and psychological characteristics concerning ambulation ability have been validated. However, the relationship between TUG performance and community ambulation ability is unclear. The purpose of this study was to investigate whether the TUG performance time could indicate community ambulation levels (CAL) differentially in persons with chronic stroke. Design: Cross-sectional study. Methods: Eighty-seven stroke patients had participated in this study. Based on the self-reporting survey results on the difficulties experienced when walking outdoors, the subjects were divided into the independent community ambulation (ICA) group (n=35) and the dependent community ambulation group (n=52). Based on the area under the curve (AUC), the discrimination validity of the TUG performance time was calculated for classifying CAL. The Binomial Logistic Regression Model was utilized to produce the likelihood ratio of selected TUG cut-off values for the distinguishing of community ambulation ability. Results: The selected TUG cut-off values and the area under the curve were <14.87 seconds (AUC=0.871, 95% confidence interval=0.797-0.945), representing a mid-level accuracy. Concerning the likelihood ratio of the selected TUG cut-off value, it was found that the group with TUG performance times shorter than 14.87 seconds showed a 2.889 times higher probability of ICA than those with a TUG score of 14.87 seconds or longer (p<0.05). Conclusions: The TUG can be viewed as an assessment tool that is capable of classifying CAL.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.264-270
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• 2001

The hydraulic performance analysis of an entire pump system composed of an inducer, impeller, volute and seal for the application on turbopumps is performed using three-dimensional Wavier-Stokes equations. A quasi-steady mixing-plane method is used on the impeller/volute interface to simulate the unsteady interaction phenomena. From this wort the effects of each component on the pump performance are investigated at design and off-design conditions through the analysis of flow structures and loss mechanisms. The computational results are in a good agreement with experimental ones in terms of the headrise and efficiency even though very complex flow structures are present. It is found that the asymmetric pressure distribution along the volute wall constitutes the main reason of the difference between experimental and computational results due to the limitation of the applying the quasi-steady method. Since the volute was found to be over-designed according to the pressure distribution of the volute wall, redesign of the volute has been performed resulting in an improved performance characteristic.