• Title/Summary/Keyword: critical angle method

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Study of numerical analysis and experiment for composite pressure hull on buckling pressure (외압을 받는 복합재 셸의 좌굴해석을 위한 실험 및 수치 해석 연구)

  • Jung H. Y.;Cho J. R.;Bae W. B.;Kwon J. H.;Choi J. H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.10a
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    • pp.410-413
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    • 2005
  • The results of an experimental and analytical study of composite pressure hull on buckling pressure are presented for LRN 300. Composite tensile test was done to know the composite material properties applied FE analysis for URN composite. We predicted the buckling and post buckling analysis of composite laminated cylindrical panels under external compression by using ABAQUS /Standard[Ver 6.4]. To obtain nonlinear static equilibrium solutions for unstable problems, where the load-displacement response can exhibit the type of nonlinear buckling behavior, during periods of the response, the load and/or the displacement may decrease as the solution evolves, used the modified Riks method. The modified Riks method is an algorithm that allows effective solution of such cases [7]. Experiments were conducted to verify the validation of present analysis for cross-ply laminated shells. The shells considered in the study have two different lamination patterns, $[{\pm}45/0/90]_{18s\;and}\;[/0/90]_{18s}$. Cylindrical panel of experiment and analysis have the radius of 200mm, length of 210mm and 60 degree of cutting angle. The critical load from experiment is $69\%$ of that of numerical analysis, because the fracture of matrix was generated before buckling. So URN 300 is not proper to use at the condition under high external pressue.

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Design of a Pendulum-type Anti-rolling System for USSV and Verification Based on Roll Damping Coefficient (무인반잠수정의 진자식 횡동요 저감 장치 설계 및 감쇠계수 기반 검증)

  • Jin, Woo-Seok;Kim, Yong-Ho;Jung, Jun-Ho;Lee, Kwangkook;Kim, Dong-Hun
    • Journal of the Society of Naval Architects of Korea
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    • v.56 no.6
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    • pp.550-558
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    • 2019
  • The roll motion of a general vessel, which is more influenced by resonance as compared to other motions, adversely affects the passenger and hull. Therefore, reducing the roll motion through an anti-rolling system is critical, and most ships use various devices such as anti-rolling tanks, bilge keels, and fin stabilizers to accomplish this. In this study, a simplified model is developed for the application of an anti-rolling device for unmanned semi-submersible vessels. The applied anti-rolling device is installed on the stern and stem of a ship using a pair of servo motors with added weight, and the motor is controlled through the Arduino. The moment of the motor is designed and implemented based on a mathematical model such that it is calculated through the restoring force according to the heel angle of the ship. The performance of the proposed system was verified by utilizing the roll damping coefficient calculated by the free-roll decay test and logarithmic decrement method and was validated by a towing tank test. The system is expected to be used for unmanned vessels to perform sustainable missions.

Preparation and Microwave Absorption Properties of the Fe/TiO2/Al2O3 Composites

  • Li, Yun;Cheng, Haifeng;Wang, Nannan;Zhou, Shen;Xie, Dongjin;Li, Tingting
    • Nano
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    • v.13 no.11
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    • pp.1850125.1-1850125.12
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    • 2018
  • To reduce the imbalance of impedance matching between the magnetic metal nanowires and free space, $Fe/TiO_2$ core/shell nanowire arrays with different diameters were fabricated in the templates of anodic aluminum oxide membranes by electrodeposition. The influences of the microstructure on the microwave absorption properties of the $Fe/TiO_2/Al_2O_3$ composites were studied by the transmission/reflection waveguide method. It was demonstrated experimentally that both the interfacial polarization and the diameter of the $Fe/TiO_2$ core/shell nanowires have critical effects on the microwave absorption properties. We also investigated the angle dependence of the microwave absorption properties. Due to the interfacial polarization and associated relaxation, the $Fe/TiO_2/Al_2O_3$ composites exhibited optimal microwave absorption properties when microwave propagation direction was accordant with the axis of the nanowires. Finally, we managed to obtain an optimal reflection loss of below -10 dB (90% absorption) over 10.2-14.8 GHz, with a thickness of 3.0 mm and the minimum value of -39.4 dB at 11.7 GHz.

An Acceleration Method for Processing LiDAR Data for Real-time Perimeter Facilities (실시간 경계를 위한 라이다 데이터 처리의 가속화 방법)

  • Lee, Yoon-Yim;Lee, Eun-Seok;Noh, Heejeon;Lee, Sung Hyun;Kim, Young-Chul
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2022.05a
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    • pp.101-103
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    • 2022
  • CCTV is mainly used as a real-time detection system for critical facilities. In the case of CCTV, although the accuracy is high, the viewing angle is narrow, so it is used in combination with a sensor such as a radar. LiDAR is a technology that acquires distance information by detecting the time it takes to reflect off an object using a high-power pulsed laser. In the case of lidar, there is a problem in that the utilization is not high in terms of cost and technology due to the limitation of the number of simultaneous processing sensors in the server due to the data throughput. The detection method by the optical mesh sensor is also vulnerable to strong winds and extreme cold, and there is a problem of maintenance due to damage to animals. In this paper, by using the 1550nm wavelength band instead of the 905nm wavelength band used in the existing lidar sensor, the effect on the weather environment is strong and we propose to develop a system that can integrate and control multiple sensors.

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Performance analyses of naval ships based on engineering level of simulation at the initial design stage

  • Jeong, Dong-Hoon;Roh, Myung-Il;Ham, Seung-Ho;Lee, Chan-Young
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.9 no.4
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    • pp.446-459
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    • 2017
  • Naval ships are assigned many and varied missions. Their performance is critical for mission success, and depends on the specifications of the components. This is why performance analyses of naval ships are required at the initial design stage. Since the design and construction of naval ships take a very long time and incurs a huge cost, Modeling and Simulation (M & S) is an effective method for performance analyses. Thus in this study, a simulation core is proposed to analyze the performance of naval ships considering their specifications. This simulation core can perform the engineering level of simulations, considering the mathematical models for naval ships, such as maneuvering equations and passive sonar equations. Also, the simulation models of the simulation core follow Discrete EVent system Specification (DEVS) and Discrete Time System Specification (DTSS) formalisms, so that simulations can progress over discrete events and discrete times. In addition, applying DEVS and DTSS formalisms makes the structure of simulation models flexible and reusable. To verify the applicability of this simulation core, such a simulation core was applied to simulations for the performance analyses of a submarine in an Anti-SUrface Warfare (ASUW) mission. These simulations were composed of two scenarios. The first scenario of submarine diving carried out maneuvering performance analysis by analyzing the pitch angle variation and depth variation of the submarine over time. The second scenario of submarine detection carried out detection performance analysis by analyzing how well the sonar of the submarine resolves adjacent targets. The results of these simulations ensure that the simulation core of this study could be applied to the performance analyses of naval ships considering their specifications.

Analysis of Shaping Parameters Influencing on Dimensional Accuracy in Single Point Incremental Sheet Metal Forming (음각 점진성형에서 치수정밀도에 영향을 미치는 형상 파라미터 분석)

  • Kang, Jae Gwan;Kang, Han Soo;Jung, Jong-Yun
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.39 no.4
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    • pp.90-96
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    • 2016
  • Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. Compared to conventional sheet forming processes, ISF is of a clear advantage in manufacturing small batch or customized parts. ISF needs die-less machine alone, while conventional sheet forming requires highly expensive facilities like dies, molds, and presses. This equipment takes long time to get preparation for manufacturing. However, ISF does not need the full facilities nor much cost and time. Because of the facts, ISF is continuously being used for small batch or prototyping manufacturing in current industries. However, spring-back induced in the process of incremental forming becomes a critical drawback on precision manufacturing. Since sheet metal, being a raw material for ISF, has property to resilience, spring-back would come in the case. It is the research objective to investigate how geometrical shaping parameters make effect on shape dimensional errors. In order to analyze the spring-back occurred in the process, this study experimented on Al 1015 material in the ISF. The statistical tool employed experimental design with factors. The table of orthogonal arrays of $L_8(2^7)$ are used to design the experiments and ANOVA method are employed to statistically analyze the collected data. The results of the analysis from this study shows that the type of shape and the slope of bottom are the significant, whereas the shape size, the shape height, and the side angle are not significant factors on dimensional errors. More error incurred on the pyramid than on the circular type in the experiments. The sloped bottom showed higher errors than the flat one.

Surface and size dependent effects on static, buckling, and vibration of micro composite beam under thermo-magnetic fields based on strain gradient theory

  • Mohammadimehr, Mehdi;Mehrabi, Mojtaba;Hadizadeh, Hasan;Hadizadeh, Hossein
    • Steel and Composite Structures
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    • v.26 no.4
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    • pp.513-531
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    • 2018
  • In this article, static, buckling and free vibration analyses of a sinusoidal micro composite beam reinforced by single-walled carbon nanotubes (SWCNTs) with considering temperature-dependent material properties embedded in an elastic medium in the presence of magnetic field under transverse uniform load are presented. This system is used at micro or sub micro scales to enhance the stiffness of micro composite structures such as bar, beam, plate and shell. In the present work, the size dependent effects based on surface stress effect and modified strain gradient theory (MSGT) are considered. The generalized rule of mixture is employed to predict temperature-dependent mechanical and thermal properties of micro composite beam. Then, the governing equations of motions are derived using Hamilton's principle and energy method. Numerical results are presented to investigate the influences of material length scale parameters, elastic foundation, composite fiber angle, magnetic intensity, temperature changes and carbon nanotubes volume fraction on the bending, buckling and free vibration behaviors of micro composite beam. There is a good agreement between the obtained results by this research and the literature results. The obtained results of this study demonstrate that the magnetic intensity, temperature changes, and two parameters elastic foundations have important effects on micro composite stiffness, while the magnetic field has greater effects on the bending, buckling and free vibration responses of micro composite beams. Moreover, it is shown that the effects of surface layers are important, and observed that the changes of carbon nanotubes volume fraction, beam length-to-thickness ratio and material length scale parameter have noticeable effects on the maximum deflection, critical buckling load and natural frequencies of micro composite beams.

Influence of Oxidation Inhibitor on Carbon-Carbon Composites : 7. Studies on Work of Adhesion and Fracture Toughness of Carbon-Carbon Composites (산화억제제를 첨가한 탄소/탄소 복합재료의 물성에 관한 연구 : 7. 탄소/탄소 복합재료외 부착력과 파괴인성)

  • 박수진;서민강;이재락
    • Polymer(Korea)
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    • v.25 no.3
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    • pp.435-440
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    • 2001
  • The objective of this study was to examine the effect of oxidation inhibitor contents on the work of adhesion, fracture toughness, and impact strength of the unidirectional carbon-carbon composites (C/C composites). The molybdenum disilicide ($MoSi_2$) used as an oxidation inhibitor was impregnated with phenolic resins to improve the anti-oxidation properties of the composites in different concentrations of 4, 12 and 20 wt%. Based on Wilhelmy equation, the work of adhesion of C/C composites was calculated by contact angle methods. Fracture toughness and impact strength were pressured by three-point bending test for the critical intensity factor ($K_IC$) and Izod test method, respectively. As a result, the composites made with $MoSi_2$ resulted in an increasing of both fracture toughness and impact strength. Especially, the composites made with 12 wt% $MoSi_2$ content showed the highest value of London dispersive component, $W_A\;^L$, in work of adhesion, resulting from improving the interfacial adhesion force among fibers, filler, and matrix in this system.

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A Study on the Adjustment of Eaves Curve and Roof Length of Three-Bay-Kan Buddhist Temples with the Hipped and Gable Roof (정면 3칸 팔작지붕 불전의 처마 곡선과 지붕 길이 조절에 관한 연구)

  • Wi, So-Yeon;Sung, Dae-Chul;Shin, Woong-Ju
    • Journal of architectural history
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    • v.26 no.3
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    • pp.39-49
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    • 2017
  • It is difficult to build a hipped and gable roof in slender rectangular type due to restraint in variation of lateral length caused by gongpo arranged on the side, purlin space and the form of gable part and aesthetical effect of chunyeo maru. Against this backdrop and with the assumption that this phenomenon is more apparent in roofs of three-bay-kan Buddhist temples with the hipped and gable roof among national treasure Buddhist temples, this study has aimed to prove that a roof can be built in a less slender rectangular type than that of flat form and to present the building methodology and found the following findings. First, The ratio of lateral to longitudinal length of the roof has been adjusted by protruding the chunyeo and the method of adjusting the ratio of lateral to longitudinal length of the roof is considered to be determined depending on the availability of woods to be used in chunyeo. Second, in order to symmetrically arrange the edge of the roof, which is critical from the perspective of construction morphology, the chunyeo angle has been intentionally adjusted to reduce the gap of length between the front roof and the lateral roof. To sum up, the characteristic of the hipped and gable roof, which is difficult to be built in slender rectangular type, is more clearly shown in the roof and it is identified that the length of the front roof and the lateral roof has been intentionally adjusted to achieve the symmetrical arrangement of roofline of the roof edge.

A Study on Aircraft Sensitivity Analysis for C.G Variation of Longitudinal Axis (항공기 세로축 무게중심의 변화에 따른 민감도 해석에 관한 연구)

  • 김종섭
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.6
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    • pp.83-91
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    • 2006
  • An advanced method of Relaxed Static Stability (RSS) is utilized for improving the aerodynamic performance of modern version supersonic jet fighter aircraft. The flight control system utilizes RSS criteria in longitudinal axis to achieve performance enhancements and improve stability. The flight control law of T-50 advanced trainer employs RSS concept in order to improve the aerodynamic performance and guarantee aircraft stability. The longitudinal center of gravity(X-c.g) varies as a function of external stores, fuel state and gear position. Shifts in X-c.g relate directly to longitudinal static margin in aircraft stability. This paper deals the maximum aft X-c.g for critical aircraft loadings and checks static margin limits using sensitivity such as damping, natural frequency, gain and phase margin. And nonlinear analysis was conducted for such as short period input. And also, this paper shows the T-50 aircraft stability based on the result of high angle of attack flight such as upright and inverted departure.