• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.277-284
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• 2017

This study is the results of the analytical research for a dual-model scramjet engine flowpath which is included inlet, isolator, combustor, and nozzle. To design a dual-mode scramjet engine and to investigate its performance, the performance analysis models and tools are required to develope for aerodynamic, thermodynamic characteristics, propulsion, and total system. Therefore, analysis models for air inlet, isolator, supersonic combustor, and nozzle of a dual-mode scramjet engine were accomplished, the performance characteristics of a dual-mode scramjet engine is investigated with using the developed analysis tools.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.19-27
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• 2018

In this study, a numerical study was conducted to characterize the E-D nozzle which changes according to the nozzle pressure ratios. Three different numerical analysis models were designed by changing the pintle inflection angles. When the nozzle pressure ratio is low, the outside air flows into the E-D nozzle to form an open flow field. As the nozzle pressure ratio increases, the flow transition occurs to become the closed flow field where the recirculation region is isolated inside the nozzle. Also, the highest thrust coefficient was obtained in the analytical model with high pintle inflection angle at all nozzle pressure ratios.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.29-29
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• 2011

국내에서 기존건축물의 내진성능평가 기법이 연구되기 시작한지 20여 년간 다양한 평가방법이 제안되었다. 그러나, 제안된 평가방법은 미국이나 일본의 평가 방법을 도입 및 수정하는 내용이 주가 되어 국내실정에 맞지 않는 부분도 많이 발견되었다. 따라서 국내에서 제안된 기존 건축물의 내진성능 평가기법, 지진피해예측에 근거한 보강건축물의 합리적인 선정방법 및 이들 건축물에 적합한 내진보강방법 등의 연구는 아직까지 초보적인 단계라고 할 수 있다. 이에 본 연구의 목적은 이러한 평가 기법을 적용한 국내 저층구조물의 내진성능을 평가하는 것이다. 저층구조물의 내진성능을 평가하기 위하여 1988년 내진설계가 도입되기 이전에 건립된 4층 규모의 학교구조물을 해석대상 구조물로 선정하였다. 대상 해석구조물의 내진성능평가는 일본의 내진성능 평가법을 참고하여 평가절차가 다소 복잡한 부분을 국내 실정에 맞게 개선시킨 내진화 우선도 평가방법과 정밀한 내진성능을 평하는 방법으로 세계적으로 널리 사용되고 있는 ATC-40 성능평가방법에서 등가단자유 모델로 변환 과정에서 등가유효감쇠 및 등가유효주기 산정 관계식의 문제점을 개선한 FEMA-440의 선형화 성능평가방법(Linearization Method)을 사용하여 구조물의 성능을 평가하였다. 내진 성능 평가를 위해 현재 전 세계적으로 널리 사용되고 있는 구조물 비선형 전용 해석 프로그램인 Perform-3D를 이용하여 해석을 수행하였다. 본 연구를 통해 기존 저층구조물로 선정한 학교구조물에 대한 내진성능을 평가한 결과, 내진화 우선도 평가법 및 FEMA-440의 내진성능 평가는 유사한 경향의 결과를 나타내었고, 두 평가결과를 요약하면 Y방향은 보와 기둥에 끼인 조적벽체의 영향으로 별도의 내진성능이 향상 보강이 필요없으나, X방향은 창문하부 허리 조적벽 등의 영향으로 다소 취성적인 내진성능을 보유하고 있어 충분한 내진성능 확보를 위한 추가적인 보강이 필요한 것으로 판단된다.

• Composites Research
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• v.27 no.6
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• pp.213-218
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• 2014

This paper predicted the strength of mechanical joint of composites under bending load by means of the characteristic curve method. The method has been employed only for tensile and compression load conditions, but in this study, this method was extended to the bending load condition. For the finite element analysis (FEA), the nonlinear analysis was conducted considering the contact and friction effects between composite material and pin. The failure strength and mode on characteristic curve were evaluate with Tsai-Wu failure theory. To validate the results of FEA, the experiments were conducted to find out the failure load by applying bending moment on the composite specimens. The results showed reasonable agreements with theoretical results. These results lead to a conclusion that the characteristic curve method can be applied to predict the bending strength of mechanical joint of composites.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.113-116
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• 2008

According to a domestic provision, test levels of the barrier are divided into seven categories(SB1 to SB7) and the corresponding crash conditions are specified. Meanwhile, standard types of concrete barriers with different dimensions have been constructed nation wide. Some studies aimed at finding a proper test level of each type of the concrete barrier have been carried out, but the reliable and consistent results have not been fully established yet. The purpose of this study is to find out the test level corresponding to the concrete barrier of type-2 through static test. AASHTO LRFD was referred to for the loading pattern and a magnitude of the load that simulate a vehicle crash assumed. The test results show that the ultimate strength of the type-2 satisfies the load level required for SB5. However, it seems that the type-2 does not comply with SB6, showing some differences in results from previous analytical studies. In order to take advantage of the static test in establishing the test level of the domestic barrier, more detailed provisions should be specified.

• Journal of Aerospace System Engineering
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• v.15 no.3
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• pp.30-44
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• 2021

Experimental investigation of counter-rotating propellers is subject to multiple time and cost constraint because of additional design parameters unlike single propeller. Also, a lot of computing time and resources are required for numerical analysis due to consideration of the interference between the upper and lower propellers. In the present study, numerical simulations were conducted to investigate the hover performance of counter-rotating propellers by using actuator method which is considered to be time-efficient. The accuracy of the present numerical methods was validated by comparing the ANSYS Fluent which is commercial CFD code. The axial spacing and rotational speed were selected as the analysis variables, and the aerodynamic performance was obtained under various conditions. Based on the obtained results, the Figure of Merit (FM) of single propeller and counter-rotating propellers and a prediction factor which enables prediction of counter-rotating propeller performance using a single propeller were derived to evaluate availability of the actuator method.

• Tunnel and Underground Space
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• v.32 no.6
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• pp.598-610
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• 2022

Avoiding a fault zone would be a best practice for safety in underground construction, which is only sometimes possible because of many restrictions and other field conditions. For instance, there is an ongoing conception of Korea-Japan subsea tunnels that inevitably cross a massive fault system in the Korea Strait. Therefore it was deemed necessary to find an efficient way of predicting the likely behaviour of underground structures under fault slip. This paper presents the findings from simple numerical analysis for investigating the stress induced at a normal fault with a dip of 45 degrees. We used a boundary element software that assumed constant displacement discontinuity, which allowed the displacement to be estimated separately at both the fault's hangingwall and footwall sides. The results suggested that a principal stress rotation of 45 degrees occurred at the edges of the fault during the slip, which was in agreement with the phenomenon for fault plane suggested in the body of literature. A simple numerical procedure presented in this paper could be adopted to investigate other fault-related issues associated with underground structure construction.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5C
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• pp.239-250
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• 2009

Tunnelling-induced settlements and lateral ground movements have been investigated by numerical parametric studies considering ground condition, excavation characteristics, and ground layers. Before the numerical study the existing methods of ground movement estimation have been collected and analysed to have some information of ground movements and to improve them providing a fundamental material for the numerical study. Numerical model simulation has been performed of a physical model test of tunnel excavation in which the ground movements were measured reliably and the results have been used to determine the numerical approach and the appropriate soil constitutive mode. With this procedure done, the results of numerical parametric studies have been put together to analyze and understand tunnelling-induced settlements and lateral ground movements.

• School Mathematics
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• v.11 no.1
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• pp.131-145
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• 2009

This research was designed to investigate the possibility to teach function concept and graph representation of functions in explicit manner toward at elementary level. Eight class-hours instruction was given to four Grade 5(age 11) students, and dynamic geometry software GSP was partially used in the class. Results indicate that the students could conceptualize the function relation, interpret linear function graphs, recognize the meaning of their slopes, and discuss the relationships among linear graphs and real life situation. Results also indicate that GSP helped students to recognize the relation between dots and the linear graph clearly and that GSP-line graph did decisive role for children to understand the meaning of graph representation of function.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.629-636
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• 2011

It has been suggested that buildings designed for strong ground motions will also have improved resistance to air blast loads. As an initial attempt to quantify this behavior, the responses of a ten story steel building, designed for the 1994 building code, with lateral resistance provided by perimeter moment frames, is considered. An analytical model of the building is developed and the magnitude and distribution of blast loads on the structure are estimated using available computer software that is based on empirical methods. To obtain the relationship between pressure, time duration, and standoff distance, these programs are used to obtain an accurate model of the air blast loading. A hemispherical surface burst for various explosive weights and standoff distances is considered for generating the air blast loading and determining the structural response. Linear and nonlinear analyses are conducted for these loadings. Air blast demands on the structure are compared to current seismic guidelines. These studies present the displacement responses, story drifts, demand/capacity ratio and inelastic demands for this structure.