• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.613-617
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• 2011

한국항공우주연구원은 비행시험용 스크램제트 엔진의 최적 형상을 도출을 목표로 추력 노즐 변화에 따른 스크램제트 엔진의 특성을 파악하고자 여러 가지 형상의 추력 노즐을 설계 및 제작하였다. 성능시험은 호주 University of Queensland의 T4 충격파 터널에서 수행되었으며, 총 8종의 노즐과 2 종의 측벽이 시험되었다. 본 논문에는 스크램제트 엔진의 추력 노즐과 측벽의 설계 및 사양을 정리하였다. 또한 스크램제트 엔진 Baseline의 정압력과 노즐 출구 피토 압력 분포를 계산한 결과 양의 비추력을 얻었음을 확인하였다.

• 대한전기학회논문지
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• 제40권8호
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• pp.782-791
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• 1991

In the fields of pattern recognition such as speech recognition, several new techniques using Artifical Neural network Models have been proposed and implemented. In particular, the Multilayer Perception Model has been shown to be effective in static speech pattern recognition. But speech has dynamic or temporal characteristics and the most important point in implementing speech recognition systems using Artificial Neural Network Models for continuous speech is the learning of dynamic characteristics and the distributed cues and contextual effects that result from temporal characteristics. But Recurrent Multilayer Perceptron Model is known to be able to learn sequence of pattern. In this paper, the results of applying the Recurrent Model which has possibilities of learning tedmporal characteristics of speech to phoneme recognition is presented. The test data consist of 144 Vowel+ Consonant + Vowel speech chains made up of 4 Korean monothongs and 9 Korean plosive consonants. The input parameters of Artificial Neural Network model used are the FFT coefficients, residual error and zero crossing rates. The Baseline model showed a recognition rate of 91% for volwels and 71% for plosive consonants of one male speaker. We obtained better recognition rates from various other experiments compared to the existing multilayer perceptron model, thus showed the recurrent model to be better suited to speech recognition. And the possibility of using Recurrent Models for speech recognition was experimented by changing the configuration of this baseline model.

• Journal of Positioning, Navigation, and Timing
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• 제7권1호
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• pp.43-52
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• 2018

In recent years, the need of high accuracy navigation for vehicles has increased due to the development of autonomous driving vehicles and increase in land transportation convenience. This study is performed for vehicle users to achieve a performance of centimeter-level positioning accuracy by utilizing Compact Network Real-time Kinematic (RTK) that is applicable as a national-level infrastructure. To this end, medium-baseline RTK was implemented in real time to estimate accurate integer ambiguities between reference stations for reliable generation of Network RTK correction using the linear combination of carrier-phase observations and L1/L2 pseudo-range measurements. The residual tropospheric error was estimated in real time to improve the accuracy of double-differenced integer ambiguity resolution between network configuration reference stations that have at least 30 km or longer baseline distance. In addition, C++ based software was developed to enable real-time generation and broadcasting of Compact Network RTK correction information by utilizing an accurately estimated double-differenced integer ambiguity values. As a result, the horizontal and vertical 95% accuracy was 2.5cm and 5.2cm, respectively, without performance degradation due to user's position change within the network.

• 한국측량학회지
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• 제25권3호
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• pp.207-213
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• 2007

다수의 고정수신기를 이용하여 이동수신기의 위치를 정확히 측정하고자 하는 필요성은 계속적으로 대두되고 있었으나, 현재 사용되고 있는 대부분의 상용 소프트웨어에서는 단일기선에 대한 GPS 결과만을 제공하고 있다. 따라서 본 논문에서는 다수의 단일기선 결과를 이용하여 네트워크를 구성함으로써 이동수신기의 위치측정 정확도를 향상시키기 위한 방안을 연구하였다. 이를 위해 기존의 측지 망 조정 이론을 도입하여 이동수신기의 위치결정 분야에 적용함으로써 위치정확도 향상 뿐만 아니라 전체적인 네트워크의 안정에도 기여할 수 있음을 알 수 있었다. 또한 측지망의 계수부족(Rank-deficiency)을 제거하기 위해서 하나의 고정수신기의 위치를 고정시키는 방법(RLESS), 이동수신기의 바이어스(Bias)를 최소화하는 방법(BLIMPBE), 그리고 고정수신기의 위치에 확률적 제약 조건을 주는 방법(SCLESS)에 대해서 비교 분석하였다. 네트워크 기반의 위치결정을 통해서 3차원 평균제곱근오차(RMSE)는 최대 3.5cm에서 2.1cm 수준으로 향상되었고, 기준점의 위치정확도에 따라 BLIMPBE 및 SCLESS 방법을 적절히 적용하는 것이 바람직할 것으로 판단된다.

• 시스템엔지니어링학술지
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• 제9권2호
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• pp.83-90
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• 2013

Integrated aircraft synthesis process for rapid analysis and design is described in this paper. Data flow between different analysis fields is described in details. All the data are divided into several groups according to importance and source of the data. Analysis of design requirements and certification regulations is carried out to determine baseline configuration of an aircraft. Overall design process can be divided into initial sizing, conceptual and preliminary design phases. Basic data for conceptual design are obtained from initial sizing, CAD and geometry analysis. Basic data are required input for weight, aerodynamics and propulsion analyses. Results of this analysis are used for stability and control, performance, mission, and load analysis. Feasibility of design is verified based on analysis results of each discipline. Design optimization that involves integrated process for aircraft analysis is performed to determine optimum configuration of an aircraft on a conceptual design stage. The process presented in this paper was verified to be used for light aircraft design.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.351-359
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• 2016

The Korean Prototype Gen-IV sodium-cooled fast reactor (PGSFR) is supposed to be loaded with a relatively-costly low-enriched U fuel, while its envisaged transuranic fuels are not available for transmutation. In this work, the U-enrichment reduction by improving the neutron economy is pursued to save the fuel cost. To improve the neutron economy of the core, a new reflector material, PbO, has been introduced to replace the conventional HT9 reflector in the current PGSFR core. Two types of PbO reflectors are considered: one is the conventional pin-type and the other one is an inverted configuration. The inverted PbO reflector design is intended to maximize the PbO volume fraction in the reflector assembly. In addition, the core radial configuration is also modified to maximize the performance of the PbO reflector. For the baseline PGSFR core with several reflector options, the U enrichment requirement has been analyzed and the fuel depletion analysis is performed to derive the equilibrium cycle parameters. The linear reactivity model is used to determine the equilibrium cycle performances of the core. Impacts of the new PbO reflectors are characterized in terms of the cycle length, neutron leakage, radial power distribution, and operational fuel cost.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.61-65
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• 2011

본 연구에서는 초음속 충동형 터빈의 노즐에서 나타나는 유동의 과소 과대팽창 문제를 최적화 기법을 이용하여 비대칭형상을 포함해 설계함으로써 개선시키고자 하였다. 노즐 형상 설계를 위해 8개의 설계변수를 설정하였으며 목적함수로는 후류 영역 출구까지의 정효율이 최대가 되도록 하였다. 최적화에는 iSIGHT-FD가 사용되었으며 근사최적화를 위한 방법으로는 Radial Basis Function을 이용하였다. 노즐유동의 계산에는 상용 코드인 FLUENT 6.3을 사용하였으며 개선된 노즐의 정효율은 기존 대비 1.35% 증가하였고 손실계수는 19.85% 감소하였다.

• Advances in aircraft and spacecraft science
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• 제10권4호
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• pp.317-334
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• 2023

This paper presents a basic methodology and a set of numerical tools for the preliminary design of solid-fueled ramjet missiles. An elementary code determines the baseline system configuration comprised of warhead, guidance-control, and propulsion masses and geometries from specific correlations found in the literature. Then, the system is refined with the help of external and internal ballistics codes. Equations of motion are solved for the flight's ascending, cruising, and descending stages and the internal ballistic set of equations designs the ramjet engine based on liquefying fuels. The combined tools sized the booster and the ramjet sustainer engines for a long-range missile, intended to transport 200 kg of payload for more than 300 km range flying near 14,000 m altitude at Mach 3.0. The refined system configuration had 600 mm in diameter and 8,500 mm in length with overall mass of 2,128 kg and 890 kg/m3 density. Ramjet engine propellant mass fraction was estimated as 74%. Increased missile range can be attained with paraffin-polyethylene blend burning at near constant regression rate through primary air mass flow rate control and lateral 2-D air intakes.

• 한국항공우주학회지
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• 제38권5호
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• pp.467-476
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• 2010

본 연구에서는 개념 설계 과정에서 항공 인증 규정 및 의사결정모델을 이용하여 최적화 문제 구성과 항공기 기준형상을 선정하는 프로세스를 정립하고, 이를 소형제트항공기에 적용하였다. 항공기 안전성을 보장하기 위한 최소안전 요구조건인 항공 인증 규정은 항공기 설계 초기단계에서부터 고려되어야 하는 사항으로 반드시 만족해야 한다. 인증 규정 및 사용자 요구도 분석 후, 산업공학기법인 Affinity Diagram, Nested Column Diagram, Quality Function Deployment (QFD), Pugh Concept Selection Matrix와 같은 의사결정모델을 사용하여 alternative 형상군에 대한 평가를 수행하였다. 그 후 Best alternative 형상에 대한 설계가능영역 분석을 통해 항공 인증 규정에 적합하고 객관적인 문제 구성 및 항공기 기준형상을 도출 할 수 있었다.

• Journal of Chest Surgery
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• 제57권3호
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• pp.231-239
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• 2024

Background: Although the modified Blalock-Taussig shunt remains the mainstay method of palliation for augmenting pulmonary blood flow in various congenital heart diseases, the shunt must be carefully designed to achieve the best outcomes. This study investigated the effect of shunt configuration on pulmonary artery growth and growth discrepancy. Methods: Twenty patients with successful modified Blalock-Taussig shunt takedown were analyzed. Pulmonary artery and shunt characteristics were obtained using computed tomography scans. Differences in the baseline and follow-up diameter ratios and growth in the ipsilateral and contralateral arteries were calculated. The angle between the shunt and pulmonary artery, as well as the distance from the main pulmonary artery bifurcation, were measured. Correlations between pulmonary arteries and shunt configurations were analyzed. Results: The median interval time between shunt placement and takedown was 154.5 days (interquartile range, 113.25-276.25 days). Follow-up values of the ipsilateral-to-contralateral pulmonary artery diameter ratio showed no significant correlation with the shunt angle (ρ=0.429, p=0.126) or distance (ρ=0.110, p=0.645). The shunt angle and distance from the main pulmonary bifurcation showed no significant correlation (ρ=-0.373, p=0.189). Pulmonary artery growth was negatively correlated with shunt angle (ipsilateral, ρ=-0.565 and p=0.035; contralateral, ρ=-0.578 and p=0.030), but not with distance (ipsilateral, ρ=-0.065 and p=0.786; contralateral, ρ=-0.130 and p=0.586). Conclusion: Shunt configuration had no significant effect on growth imbalance. The angle and distance of the shunt showed no significant correlation with each other. A more vertical shunt was associated with significant pulmonary artery growth. We suggest a more vertical graft design for improved pulmonary artery growth.