• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.6
• /
• pp.126-136
• /
• 2018

A steel-plate concrete composite beam is composed of a steel plate, concrete and shear connector to combine inhomogeneous two materials. The steel plate is assembled by welding an existing composite beam. In this study, new steel-plate concrete composite beam, called a SPC Beam, was developed to reduce the shear connector and improve the workability. The SPC Beam was composed of folding steel plates and concrete, without a shear connector. The folding steel plate was assembled using high strength bolt instead of welding. To improve the workability in field construction, a hat-shaped Cap was attached to the junction with a slab. Monotonic load testing under two points was conducted under displacement control mode. The flexural strength of the specimen for positive moment and negative moment was calculated using the plastic stress distribution method. The test results showed that the flexural strength of the new SPC Beam had 80% of the strength of a complete composite beam. In addition, increasing the composite ratio was possible through clearance controls of the cap. In this study, the performance of the SPC Beam was verified through additional experiments and analyses with the cross-sectional shape and cap as variables, because the representative shape in the positive negative moment region is targeted.

• Journal of Navigation and Port Research
• /
• v.26 no.1
• /
• pp.137-145
• /
• 2002

Water flow simulations for environmental problems often require local detailed analyses for better understanding and accurate prediction of the fate of pollutant in water bodies. This study deals with the development and application of a two-dimensional flow an dispersion model to the coastal water area to find out possible changes due to the wide port development plan. As far as the spatial discretization is concerned, the finite element method is attractive because of its flexibility and ability to naturally treat complex coastal geometries. The model uses finite element theory and the Galerkin weighted-residual approach as its basis. Developed model is applied to the Busan New harbor Construction site. Results from the model were compared with the measured water level and flows in four stations. The flow pattern by the model shows to be similar to the observed data away from the construction site where the flow is not affected. From the simulation results, it is concluded that the model may be useful for numerous other studies for planning and management purposes, especially flow and pollution dispersion in the coastal water bodies where the flow is so complicated.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.5
• /
• pp.419-426
• /
• 2018

For an orbit transfer in a space exploration mission, a solid or liquid rocket booster is included at the last stage of the launch vehicle. During the orbit transfer, thrust misalignment can cause a severe orbit error. Three axis attitude control or spin stabilization can be implemented to minimize the error. Spin stabilization technique has advantages in structural simplicity and lightness. One of ways to apply the spin stabilization to the payload is to include a spin table system in the launch vehicle. In this paper, effect of the spin table system on separation dynamics of the payload is analyzed. Simple model of the spin table to mimic basic functions is designed and simulation environment is established with the model. Effect of the spin table is tested by evaluating separation dynamics of a payload with and without the spin table. Analysis on tolerance effect of separation spring constant on separation dynamics of a payload is conducted.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.3
• /
• pp.210-218
• /
• 2018

In order to generate meshes automatically for finite element analysis of complex structures such as aircraft, a large number of triangular elements are typically created. However, triangular elements are less accurate than rectangular elements, so it is difficult to obtain a reliable solution. This problem can be improved through the meshfree method using the back cell integration. However, this method also causes some problems such as over-use of the integration points and inefficiency of the integral domain. In order to improve these problems, a method of performing integration by setting the integral area based on a node basis has been proposed, but in the case of incompressible material problems, the numerical accuracy deteriorates due to the vibration phenomenon of the solution. Therefore, in this paper, the modified meshfree method is proposed which sets the integral domain as an element domain instead of the nodal domain, and the proposed method improves the numerical instability caused by the conventional meshfree method without decreasing the accuracy regardles of the shape of integral domain. The effectiveness of the modified meshfree method is verified by using 2-D examples.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.47 no.11
• /
• pp.753-760
• /
• 2019

Sparkjet actuator, also known as plasma synthetic jet actuator, which is a kind of active flow control actuator is considered as being high possibility for the supersonic flow control due to ejecting stronger jet compared to the other active flow control actuators. Sparkjet actuator generates high temperature and high pressure flow inside the cavity by using arc plasma and leads momentum by ejecting such flow through orifice or nozzle. In this research, numerical calculation of sparkjet actuator with respect to the location of electrodes which exists inside the cavity is conducted and the change of the performance of sparkjet actuator is suggested. As the location of electrodes goes closer to the bottom of the cavity, impulse is increased and the average pressure inside the cavity maintains higher. When the location of electrode is 25% and 75% of the entire cavity height, impulse is 2.515 μN·s and 2.057 μN·s, respectively. Each impulse is changed by about 9.92% and -10.09% compared to when the location of electrodes is 50% of the entire cavity height.

• Journal of Advanced Marine Engineering and Technology
• /
• v.41 no.3
• /
• pp.191-196
• /
• 2017

Owing to the harmful environmental effects of HCFC and CFC refrigerants discovered in the late 20th century, the need for environmentally friendly refrigerants such as $CO_2$ in cooling systems has increased. Air-source $CO_2$ heat pumps that utilize ambient heat in cold winter are less efficient because of a higher evaporation temperature, and it is difficult to manufacture the components of the heat pump owing to a super critical pressure of over 130 bar. This research aims to overcome these disadvantages and improve energy efficiency by introducing a new lower-pressure $CO_2$ auto-cascade heat pump system. $CO_2$-R32 zeotropic refrigerants were considered for two-stage expansion and effective cooling heat exchanging system configurations of the new auto-cascade heat pump. The results indicated that the efficiency of the two-stage expansion system was higher than that of the original one-stage expansion system. Furthermore, the two-stage expansion system showed significant performance improvements when the two-stage expansion stage from highest pressure of 70bar, intermediate expansion pressure of 25bar, and final low pressure of 10bar is applied. The COP of the new two-stage auto-cascade system (2.332) was 43.15% higher than that of the present simple auto-cascade system (1.629). Refrigerants having an evaporation temperature of $-10^{\circ}C$ or lower can be obtained that can be easily evaporated in an evaporator even at a low temperature.

• Journal of Korea Water Resources Association
• /
• v.41 no.9
• /
• pp.895-905
• /
• 2008

To analyze hydrologic processes in a watershed requires both various geographical data and hydrological time series data. Recently, not only geographical data such as DEM(Digital Elevation Model) and hydrologic thematic map but also hydrological time series from numerical weather prediction and rainfall radar have been provided as grid data, and there are studies on hydrologic analysis using these grid data. In this study, GRM(Grid based Rainfall-runoff Model) which is physically-based distributed rainfall-runoff model has been developed to simulate short term rainfall-runoff process effectively using these grid data. Kinematic wave equation is used to simulate overland flow and channel flow, and Green-Ampt model is used to simulate infiltration process. Governing equation is discretized by finite volume method. TDMA(TriDiagonal Matrix Algorithm) is applied to solve systems of linear equations, and Newton-Raphson iteration method is applied to solve non-linear term. Developed model was applied to simplified hypothetical watersheds to examine model reasonability with the results from $Vflo^{TM}$. It was applied to Wicheon watershed for verification, and the applicability to real site was examined, and simulation results showed good agreement with measured hydrographs.

• Journal of Korea Water Resources Association
• /
• v.41 no.9
• /
• pp.873-884
• /
• 2008

In this study, rainfall quantile was estimated using scale invariance property of rainfall data with different durations and the applicability of such property was evaluated for the rainfall data of South Korea. For this purpose, maximum annual rainfall at 22 recording sites of Korea Meteorological Administration (KMA) having relatively long records were used to compare rainfall quantiles between at-site frequency analysis and scale invariance property. As the results, the absolute relative errors of rainfall quantiles between two methods show at most 10 % for hourly rainfall data. The estimated quantiles by scale invariance property can be generally applied in the 8 of 14 return periods used in this study. As an example of down-scaling method, rainfall quantiles of $10{\sim}50$ minutes duration were estimated by scale invariance property based on index duration of 1 hour. These results show less than 10 % of absolute relative errors except 10 minutes duration. It is found that scale invariance property can be applied to estimate rainfall quantile for unmeasured rainfall durations.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.442-442
• /
• 2011

우리나라는 홍수조절이나 통제를 목적으로 10개의 다목적댐을 통한 홍수방재시스템을 운영하고 있다. 다목적댐 또한 방류능력과 저류능력에 한계가 있기 때문에 안정적인 홍수조절을 위해서는 유입량과 유출량을 미리 예측할 수 있어야 한다. 하지만, 강수량은 그 변동이 심하여 정확한 예측이 어렵기 때문에 합리적인 하천 구조물의 설계와 홍수예측기술의 발전을 위해서는 강우-유출 해석뿐만 아니라 과거의 수문자료를 사용한 통계적인 분석이 요구된다. 최근 기후변화로 인해 과거에 겪지 않았던 이상 기후현상이 빈번하게 나타나고 있다. 기상청발표에 따르면 최근 10년간(1996~2005) 15개 지점의 평균 연강수량은 1,458.7 m로 약 10 �時貂� 하였고, 특히 여름철은 18 %로 증가폭이 가장 크며 호우일수는 30년 평균이 2일인데 비하여 2.8일로 0.8일 증가하였다. 이러한 강수량 및 호우일수 증가는 여름철 심각한 수해를 초래할 수 있다. 본 연구는 기후변화로 인한 수해를 대비하여 홍수기중 저수지 제한수위운영의 안정성을 검토하였다. 연구 대상 지역은 광교저수지로 수원천 상류부인 경기도 수원시 장안구 연무동에 위치한다. 유역면적은 10.98 km, 유효저수량은 250.0 만$m3$이며, 현재 예비취수원으로 사용되고 있다. 기후변화에 따른 하류지역의 예상치 못한 홍수피해를 사전에 예방하기 위해 광교저수지 유역의 설계 강수량과 설계 홍수량을 산정하였다. 제한수위의 시나리오는 현재 시행중인 제한수위와 만수위를 포함하여 5개로 설정하였다. 설계 홍수량이 광교저수지로 유입될 때 시나리오에 따른 월류량은 웨어공식을 이용하여 산정하였으며 결론은 다음과 같다. 1. 39년간의 최다 일 강수량 자료를 사용하여 100년 빈도의 설계 강수량을 Gumbel 분포법으로 산정한 결과 344.4 mm임을 알 수 있었다. 2. 광교저수지 유역의 설계 홍수량을 SCS 방법을 이용하여 산정한 결과 $216.2\;m^3/s$/s로 나타났으며, 총 유입량은 $301.0\;m^3$/day로 파악되었다. 3. 광교저수지로 설계홍수량이 유입될 때 제한수위 시나리오에 따른 최대 방류량은 EL. 87 m의 경우 $23.1\;m^3/s$, EL. 89 m의 경우$27.5\;m^3/s$ EL. 91.36 m의 경우 $79.6\;m^3/s$, EL. 93 m의 경우 $121.1\;m^3/s$ EL. 95.2 m의 경우 $137.`\;m^3/s$이다. 광교저수지 하류부분의 하천정비기본계획상의 설계 홍수량은 $114\;m^3/s$로 홍수기중 저수지의 제한수위는 EL. 91.36 m이하로 설정하는 것이 바람직한 것으로 판단된다.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.12
• /
• pp.135-139
• /
• 2017

The main reason for heat accidents occurring at the after stern tube bearing (STB) is excessive local pressure caused by the deflection of the propulsion shaft due to propeller loads. The probability of a heat accident is increased by the low flexibility of the shaft system in very large crude oil carriers (VLCCs) as the engine power and shaft diameter increase and the distance decreases between the forward and after STBs. This study proposed shaft system with only an after STB and no forward STB for a flexibility acquisition method for a VLCC shaft system under hull deformation. A Hertzian contact condition was applied, which assumes a half-elliptical pressure distribution along the contact width for the calculation of the local squeeze pressure. The propeller loads, heat effect, and hull deflection under engine operating conditions are also considered. The results show that the required design criteria were satisfied by building a partial slope at the white metal, which is the material at the axial contact side in the after STB. This system could reduce building cost by simplification of the shaft system.