• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.3
• /
• pp.724-729
• /
• 2017

The crashworthiness of the fuel tank of a rotorcraft is verified through the crash impact test. The crash impact test has a high risk of failure due to the application of an excessive load, which can seriously affect the overall development schedule of the aircraft. Therefore, a lot of effort has been made to minimize the possibility of failure in the actual test by carrying out a numerical analysis of the crash impact test of the fuel tank in the initial design stage. Recently, an external auxiliary fuel tank was added to increase the cruising distance. In this study, the numerical analysis results of the crash impact test based on several different shapes of the external auxiliary fuel tank are presented, in order to evaluate its crashworthiness. For the numerical analysis, smoothed particle hydrodynamics (SPH), which is one of the fluid-structure coupled analysis methods, is applied and the test conditions prescribed by US military standards are reflected in the analysis conditions. In addition, the material property data previously obtained by the specimen test of the actual fuel tank is applied to the numerical analysis. As a result, the equivalent stress of the fuel tank material itself and the metal fitting is provided and the possibility of acquiring data for designing the crash-worthiness of the external auxiliary fuel tank is evaluated by examining the behavior and working load of the internal mounted components.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.29 no.1
• /
• pp.9-18
• /
• 2016

The slender structures such as high rise building or marine riser are highly susceptible to dynamic force exerted by fluid-structure interactions among which vortex-induced vibration(VIV) is the main cause of dynamic unstability of the structural system. If VIV occurs in natural frequency regime of the structure, fatigue failure likely happens by so-called lock-in phenomenon. This study presents the numerical analysis of dynamic behavior of both structure and fluid in the lock-in regimes and investigates the subjacent phenomena to hold the resonance frequency in spite of the change of flow condition. Unsteady and laminar flow was considered for a two-dimensional circular cylinder which was assumed to move freely in 1 degree of freedom in the direction orthogonal to the uniform inflow. Fluid-structure interaction was implemented by solving both unsteady flow and dynamic motion of the structure sequentially in each time step where the fluid domain was remeshed considering the movement of the body. The results show reasonable agreements with previous studies and reveal characteristic features of the lock-in phenomena. Not only the lift force but also drag force are drastically increasing during the lock-in regime, the vertical displacement of the cylinder reaches up to 20% of the diameter of the cylinder. The correlation analysis between lift and vertical displacement clearly show the dramatic change of the phase difference from in-phase to out-of-phase when the cylinder experiences lock-in. From the results, it can be postulated that the change of phase difference and flow condition is responsible for the resonating behavior of the structure during lock-in.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.26 no.5
• /
• pp.343-349
• /
• 2013

Crashworthy fuel cells have a great influence on improving the survivability of crews. Since 1960's, the US army has developed a detailed military specification, MIL-DTL-27422, defining the performance requirements for rotorcraft fuel cells. In the qualification tests required by MIL-DTL-27422, the crash impact test should be conducted to verify the crashworthiness of fuel cell. Success of the crash impact test means the improvement of survivability of crews by preventing post-crash fire. But, there is a big risk of failure due to huge external load in the crash impact test. Because the crash impact test itself takes a long-term preparation efforts together with costly fuel cell specimens, the failure of crash impact test can result in serious delay of a entire rotorcraft development. Thus, the numerical simulations of the crash impact test has been required at the early design stage to minimize the possibility of trial-and-error with full-scale fuel cells. Present study performs the numerical simulation using SPH(smoothed particle hydro-dynamic) method supported by a crash simulation software, LS-DYNA. Test condition of MIL-DTL-27422 is reflected on analysis and material data is acquired by specimen test of fuel cell material. As a result, the resulting equivalent stresses of fuel cell itself are calculated and vulnerable areas are also evaluated.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.9
• /
• pp.126-132
• /
• 2016

This study numerically investigates the characteristics of chemical reactions and thermal deformation in a steam reformer. These phenomena are significantly affected by the high-temperature burner gas and the process gas conditions. Because the high temperature of the burner gas ranges from 800 to 1000 K, the reformer tubes undergo substantial thermal deformation, eventually resulting in structural failure. Thus, it is necessary to understand the characteristics of the reaction and thermal deformation under the operating conditions to evaluate the reformer tubes for sustainable, stable operation. Extensive numerical simulations were carried out using commercial CFD code (ANSYS FLUENT/MECHANICA Ver. 13.0) while considering three-dimensional turbulent flows and combined heat transfer including conduction, convection, and radiation. Structural analysis considering conjugated heat transfer between solid tubes and fluid flows was conducted using the Fluid-Solid Interaction (FSI) method. The results show that when the injection temperature of the process gas and burner gas decreased, the hydrogen production rate decreased significantly, and thermal deformation decreased by at least 15 to 20%.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.5
• /
• pp.605-611
• /
• 2019

The fuel sloshing due to the rapid manoeuvre of the aircraft causes significant loads on internal components, which may break components or piping. In particular, a significant load is applied to the joint of the external fuel tank by sloshing movement, which may affect the safety of the aircraft when the joint of the external fuel tank is damaged. Therefore, in order to improve the survivability of aircraft and crew members, the design of external fuel tanks, and joints should be performed after evaluating the sloshing load through a numerical analysis of the fuel sloshing conditions. In this paper, a numerical analysis was performed on the sloshing test of the external fuel tank for rotorcraft. ALE (Arbitrary Lagrangian Eulerian) technique was used, and the test conditions specified in the U.S. Military Specification (MIL-DTL-27422D) was applied as the conditions for numerical analysis. As a result of the numerical analysis, the load on the joint of the external fuel tank was calculated. Moreover, the effects of sloshing movement on structural soundness were assessed through analysis of stress levels and margin of safety on metal fittings and composite containers.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.12
• /
• pp.918-923
• /
• 2018

The main function of a fuel tank is to store fuel. On the other hand, the structural soundness of the fuel tank is related directly to the survival of the crew in an emergency situation, such as an aircraft crash, and the relevant performance is demonstrated by a crash impact test. Because crash impact tests have a high risk of failure due to the high impact loads, various efforts have been made to minimize the possibility of trial and error in the actual test at the beginning of the design. Numerical analysis performed before the actual test is a part of such efforts. For the results of numerical analysis to be reflected in the design, however, the reliability of numerical analysis needs to be ensured. In this study, the results of numerical analysis and actual test data were compared to ensure the reliability of numerical analysis for the crash impact test of a rotorcraft fuel tank. For the numerical analysis of a crash impact test, LS-DYNA, crash analysis software, was used and the ALE (arbitrary Lagrangian Eulerian) technique was applied as the analysis method. To obtain actual test data, strain gages were installed on the metal fittings of the fuel tank and linked to the data acquisition equipment. The strain and stress of the fuel tank fitting were calculated by numerical analysis. The reliability of the numerical analysis was enhanced by assessing the error between the strain measurement of the upper fitting obtained from an actual fuel tank and the strain calculated from numerical analysis.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.2
• /
• pp.109-117
• /
• 2022

There has been an increasing number of studies on photovoltaic energy generation system in an offshore site with the largest energy generation efficiency, as increasing the researches and developments of renewable energies for use of offshore space and resources to replace existing fossil fuels and resolve environmental challenges. For installation and operation of floating photovoltaic systems in an offshore site with harsher environmental conditions, a stiffness of structural members comprising the total system must be reinforced to inland water spaces as dams, reservoirs etc., which have relatively weak condition. However, there are various limitations for the reinforcement of structural stiffness of the system, including producible size, total mass of the system, economic efficiency, etc. Thus, in this study, a floating breakwater is considered for reducing wave loads on the system and minimizing the reinforcement of the structural members. Wave reduction performances of floating breakwaters are evaluated, considering size and distance to the system. The wave loads on the system are evaluated using the higher-order boundary element method (HOBEM), considering the multi-body effect of buoys. Stresses on structural members are assessed by coupled analyses using the finite element method (FEM), considering the wave loads and hydrodynamic characteristics. As the maximum stresses on each of the cases are reviewed and compared, the effect of floating breakwater for floating photovoltaic system is checked, and it is confirmed that the size of breakwater has a significant effect on structural responses of the system.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.7
• /
• pp.1222-1230
• /
• 2022

The rotor blade is an important component of a tidal stream turbine and is affected by a large thrust force and load due to the high density of seawater. Therefore, the performance must be secured through the geometrical and structural design of the blade and the blade structural safety to which the composite material is applied. In this study, a 1 MW class large turbine blade was designed using the blade element momentum (BEM) theory. GFRP is a fiber-reinforced plastic used for turbine blade materials. A sandwich structure was applied with CFRP to lay-up the blade cross-section. In addition, to evaluate structural safety according to flow variations, static load analysis within the linear elasticity range was performed using the fluid-structure interactive (FSI) method. Structural safety was evaluated by analyzing tip deflection, strain, and failure index of the blade due to bending moment. As a result, Model-B was able to reduce blade tip deflection and weight. In addition, safety could be secured by indicating that the failure index, inverse reserve factor (IRF), was 1 or less in all load ranges excluding 3.0*Vr of Model-A. In the future, structural safety will be evaluated by applying various failure theories and redesigning the laminated pattern as well as the change of blade material.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.31 no.7
• /
• pp.53-64
• /
• 2002

$CO_2$ 20세기 초 천연 냉매 $CO_2$는 광범위하게 사용되었지만 프레온계 냉매의 출현으로 1940년경부터 $CO_2$냉매는 사용이 제한되었다. 그러나 반 세기 동안 사라졌던 $CO_2$냉매는 1980년 후반에 노르웨이 과학 기술대학 (NTNU)과 북구 최대 민간연구소 (SINTEF)의 Lorentzen 교수에 의해 $CO_2$천연 냉매 사용을 재고하게 되었다. 프레온계 냉매의 환경적 논쟁이 쟁점이 되면서 천연 냉매 사용을 재고하게 되었다. 특히 비가연성과 비유독성으로 인한 $CO_2$냉매가 주목을 받고 있다. 초월임계 사이클레서의 고압 제어에 대한 새로운 개념은 Lorentzen 교수와 동료 연구원에 의해서 특허로 제안되었다. 이에 대한 상업적 권리를 Norsk Hydro사는 1990년에 얻었고,1990년대 초반에 NTNU/SINTEF의 공동 연구개발 프로그램을 통해 기술 경쟁력과 실현 가능성이 검증되었다. 현재 연구소에서는 최초로 초월임계 $CO_2$사이클을 이용한 상업용 온수 열펌프 시스템, 2003년 시작할 연료전지 전기 자동차에 대한 연구를 수행하고 있다. NTNU/SINTEF에서 개발된 $CO_2$기술은 Hydro-SINTEF 공동 벤처 기업인 Shecco기술회사를 통해 제조업자에게 허가된다. 본 고에서는 NTNU/SINTEF에서 수행하였거나 수 중인 과제들을 중심으로 유럽의 $CO_2$시스템의 결과와 주요 개발 범위를 정리하였으며, 특히 작동유체로서의 $CO_2$냉매의 특징을 간단히 설명하고, 온 수 열 펌프, 자동차용 공조기 및 열 펌프, 상업 냉동기 등이 기술되었다. 그 외 압축기 위주의 요소기술 개발에 관한 내용도 기술되었고, 차세대 기술 경향과 전망에 대해서도 제시되었다. 제시되었다.성균 350$\times$$10^4$ CFU균, 방선균 434$\times$$10^4$ CFU균, 진균 676$\times$$10^4$ CFU균으로 진균의 개체수가 비교적 높게 나타났으며, 비산불지역에서는 호기성균 328$\times$$10^4$ CFU균, 방선균 319$\times$$10^4$ CFU균, 진균 461$\times$$10^4$ CFU균으로 진균의 개체수가 높게 나타났다. 토양미생물은 호기성균, 방선균, 진균 모두 비산불지역 보다 산불지역에서 많이 나타났다. 본 조사지역에서 호기성균은 활엽수림보다 침엽수림에서 많게 나타났으며, 방선균과 진균은 침엽수림보다 활엽수림에서 많이 나타났다.효과와 이를 이용한 자기냉동의 방법 그리고 최근에 이루어진 새로운 진전에 대해 소개하고 공기조화 및 냉동분야에의 적용 가능성을 전망해 보고자 한다.및 도입 등 선주들에게 다양한 선박건조자금을 제공하여 내수기반 확충에도 노력해야 할 것 이다.있었다., 인삼이 성장될 때 부분적인 영양상태의 불충분이나 기후 등에 따른 영향을 받을 수 있기 때문에 앞으로 이에 대한 많은 연구가 이루어져야할 것으로 판단된다.태에도 불구하고 [-wh]의미의 겹의문사는 병렬적 관계의 합성어가 아니라 내부구조를 지니지 않은 단순한 단어(minimal $X^{0}$ elements)로 가정한다. 즉, [+wh] 의미의 겹의문사는 동일한 구성요 소를 지닌 병렬적 합성어([$[W1]_{XO-}$ $[W1]_{XO}$ ]$_{XO}$)로 그리고 [-wh] 의미의 겹의문사는 중복된 발은을 지닌 한 단어로 ([W]$_{XO}$ )

• Journal of Bio-Environment Control
• /
• v.23 no.4
• /
• pp.293-302
• /
• 2014

This study was carried out to develop rain shelter which can make an appropriate size and environment for Chinese cabbage rainproof cultivation. Fifty three farms with chinese cabbage rainproof cultivation system have been investigated to set up width and height of rain shelter. Mostly the width of 6m was desired for rain shelter and the height of 1.6m for their eaves, so these values were chosen as the dimensions for rain shelter. After an analysis of their structural safety and installation costs by the specifications of the rafter pipe, Ø$25.4{\times}1.5t$ and 90cm have been set as the size of rafter that such size costs the least. This size is stable with $27m{\cdot}s^{-1}$ of wind velocity and 17cm of snow depth. Therefore it is difficult to apply this dimension to area with higher climate load. In order to sort out such problem, the rain shelter has been designed to avoid damage on frame by opening plastic film to the ridge. Once greenhouse band is loosen by turning the manual switch at the both sides of rain shelter and open button of controller is pushed then switch motor rises up along the guide pipe and plastic film is opened to the ridge. Chinese cabbage can be damaged by insects if rain shelter is opened completely as revealed a field. To prevent this, farmers can install an insect-proof net. Further, the greenhouse can be damaged by typhoon while growing Chinese cabbage therefore the effect of an insect-proof net on structural safety has been analyzed. And then structural safety has been analyzed through using flow-structure interaction method at the wind condition of $40m{\cdot}s^{-1}$. And it assumed that wind applied perpendicular to side of the rain shelter which was covered by insect-proof net. The results indicated that plastic film was directly affected by wind therefore high pressure occurred on the surface. But wind load on insect-proof net was smaller than on plastic film and pressure distribution was also uniform. The results of structural analysis by applying pressure data extracted from flow analysis indicated that the maximum stress occurred at the end of pipe which is the ground part and the value has been 54.6MPa. The allowable stress of pipe in the standard of structural safety must be 215 MPa or more therefore structural safety of this rain shelter is satisfied.