• 복합신소재구조학회 논문집
• /
• 제4권3호
• /
• pp.13-21
• /
• 2013

In this study, uniaxial compression tests were performed to investigates the stress-strain relations of Double Skinned Composite Tubular Columns reinforced with steel tube. The confined concrete has been known as the strength of concrete increases significantly. Specimens reinforced with outer and inner steel tube were tested by uniaxial compression test. To investigate the influence of concrete strength increase by confining conditions in steel tubes, 8 specimens with different thickness of tube, hollowness ratio and concrete strength were tested and compared with other researcher's concrete material model.

• 수산해양기술연구
• /
• 제51권3호
• /
• pp.405-413
• /
• 2015

Acoustic target strength (TS) measurement and theoretical acoustic scattering models were applied to estimate the TS for assessing the fish biomass. TS measurement was made of ex situ sailfin sandfish Arctoscopus japonicus at 70 and 120 kHz, and then compared to backscatter model prediction. The live sandfish was tethered in seawater using monofilament lines. Measurements were made versus incidence angle, $-50^{\circ}$ to $50^{\circ}$ relative to dorsal aspect directions. Distorted wave Born approximation (DWBA) model was used to calculated TS pattern. The TS values of sandfish (body length: 16.2 cm) at 70 and 120 kHz were -66.94 dB and -64.45 dB, respectively, and were about 20 dB lower than TS of other fishes in Korea waters. These TS levels were distributed within the range of the theoretical TS. Ex situ measurement and theoretical TS may be applied to improve acoustical detection and biomass estimation of the sandfish, and is necessary to measure with various lengths.

• 대한조선학회논문집
• /
• 제48권3호
• /
• pp.281-287
• /
• 2011

This paper explains the basic theory and a new development of for the residual strength prediction program of the asymmetrically damaged ships, being capable of searching moment-curvature relations considering neutral axis mobility. It is noted that moment plane and neutral axis plane should be separately defined for asymmetric sections. The validity of the new program is verified by comparing moment-curvature curves of 1/3 scaled frigate model where the results from new algorithm well coincide with experimental and nonlinear FEA results for intact condition and with nonlinear FEA results for damaged condition. Applicability of new algorithm is also verified by applying VLCC model to the newly developed program. It is proved that reduction of residual strengths is visually presented using the new algorithm when damage specifications of ABS, DNV and IMO are applied. It is concluded that the new algorithm shows very good performance to produce moment-curvature relations with neutral axis mobility on the asymmetrically damaged ships. It is expected that the new program based on the developed algorithm can largely reduce design period of FE modeling and increase user conveniences.

• International Journal of Ocean System Engineering
• /
• 제3권3호
• /
• pp.158-163
• /
• 2013

The acoustic target strength (TS) is one of the most important parameters for a submarine's stealth design. Because modem submarines are larger than their predecessors, TS must be managed at each design stage in order to reduce it. To predict the TS of a submarine, TASTRAN R1 was developed based on a Kirchhoff approximation in a high-frequency range. This program can present TS values that include multi-bounce effect in the exterior and interior of the structure by combining geometric optics (GO) and physical optics (PO) methods, anechoic coating effect by using the reflection coefficient, and response time pattern for a detected target. In this paper, TS calculations for a submarine model with the above effects are simulated by using this developed program, and the TS results are discussed.

• 콘크리트학회논문집
• /
• 제13권3호
• /
• pp.237-243
• /
• 2001

본 논문에서는 플라이애시 콘크리트의 재령에 따른 변화를 예측하기 위한 모델식을 제시하고 그 모델식의 유효성을 검토하였다. 기존에 행해졌던 실험결과를 모델식을 이용하여 회귀분석한 후에 그 결과를 플라이애시 대체량과 물-시멘트비에 따라 분석하였다. 해석결과에 의하면 예측 모델식은 실험결과를 일정오차내에서 잘 모델링하였다. 그러나 물-시멘트비가 매우 작은 경우에는 플라이애시 대체량이 증가하면 실험값과 예측값의 오차가 조금 증가하는 경향을 나타내었다. 플라이애시 대체량이 증가할수록 한계상대압축강도의 크기가 증가하였고 초기 겉보기 활성에너지도 한계상대압축강도와 같이 플라이애시 대체량이 증가할수록 증가하였다. 0.40이하의 물-시멘트비에서는 한계상대압축강도와 겉보기 활성에너지의 크기가 일정하고 물-시멘트비가 0.40을 초과하면 물-시멘트비의 증가에 따라 한계상대압축강도와 겉보기 활성에너지가 조금씩 증가하였다.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
• /
• pp.33.2-33.2
• /
• 2008

Korea Astronomy and Space Science Institute (KASI) is developing an empirical model for Korean Space Weather Prediction Center (KSWPC). This model predicts the geomagnetic storm strength (Dst minimum) by using only CME parameters, such as the source location (L), speed (V), earthward direction (D), and magnetic field orientation of an overlaying potential field at CME source region. To derive an empirical formula, we considered that (1) the direction parameter has best correlation with the storm strength (2) west $15^{\circ}$ offset from the central meridian gives best correlation between the source location and the storm strength (3) consideration of two groups of CMEs according to their magnetic field orientation (southward or northward) provide better forecast. In this talk, we introduce current status of the empirical storm prediction model development.

• Steel and Composite Structures
• /
• 제10권1호
• /
• pp.45-67
• /
• 2010

Composite steel-concrete structures are employed extensively in modern high rise buildings and bridges. This concept has achieved wide spread acceptance because it guarantees economic benefits attributable to reduced construction time and large improvements in stiffness. Even though the combination of steel and concrete enhances the strength and stiffness of composite beams, the time-dependent behaviour of concrete may weaken the strength of the shear connection. When the concrete loses its strength, it will transfer its stresses to the structural steel through the shear studs. This behaviour will reduce the strength of the composite member. This paper presents the development of an accurate finite element model using ABAQUS to study the behaviour of shear connectors in push tests incorporating the time-dependent behaviour of concrete. The structure is modelled using three-dimensional solid elements for the structural steel beam, shear connectors, concrete slab and profiled steel sheeting. Adequate care is taken in the modelling of the concrete behaviour when creep is taken into account owing to the change in the elastic modulus with respect to time. The finite element analyses indicated that the slip ductility, the strength and the stiffness of the composite member were all reduced with respect to time. The results of this paper will prove useful in the modelling of the overall composite beam behaviour. Further experiments to validate the models presented herein will be conducted and reported at a later stage.

• International Journal of Concrete Structures and Materials
• /
• 제10권3호
• /
• pp.257-269
• /
• 2016

Early-strength-concrete (ESC) made of Type I cement with a high Blaine value of $500m^2/kg$ reaches approximately 60 % of its compressive strength in 1 day at ambient temperature. Based on the 210 compressive test results, a generalized rateconstant material model was presented to predict the development of compressive strengths of ESC at different equivalent ages (9, 12, 18, 24, 36, 100 and 168 h) and maximum temperatures (20, 30, 40, 50 and $60^{\circ}C$) for design compressive strengths of 30, 40 and 50 MPa. The developed material model was used to find optimum curing regimes for precast prestressed members with ESC. The results indicated that depending on design compressive strength, conservatively 25-40 % savings could be realized for a total curing duration of 18 h with the maximum temperature of $60^{\circ}C$, compared with those observed in a typical curing regime for concrete with Type I cement.

• Structural Engineering and Mechanics
• /
• 제86권3호
• /
• pp.417-430
• /
• 2023

As the key part in the reinforced concrete column-steel beam (RCS) frame, the beam-column joints are usually subjected the axial force, shear force and bending moment under seismic actions. With the aim to study the seismic behavior of RCS joints with and without RC slab, the quasi-static cyclic tests results, including hysteretic curves, slab crack development, failure mode, strain distributions, etc. were discussed in detail. It is shown that the composite action between steel beam and RC slab can significantly enhance the initial stiffness and loading capacity, but lead to a changing of the failure mode from beam flexural failure to the joint shear failure. Based on the analysis of shear failure mechanism, the calculation formula accounting for the influence of RC slab was proposed to estimate shear strength of RCS joint. In addition, the finite element model (FEM) was developed by ABAQUS and a series of parametric analysis model with RC slab was conducted to investigate the influence of the face plates thickness, slab reinforcement diameter, beam web strength and inner concrete strength on the shear strength of joints. Finally, the proposed formula in this paper is verified by the experiment and FEM parametric analysis results.

• 한국전자파학회논문지
• /
• 제17권5호
• /
• pp.490-499
• /
• 2006

본 논문에서는 지상-항공기간 통신 시험을 통해 장거리 해상 통신 환경에서의 전파 손실을 측정하고 이를 구면 대지 반사 모델을 통한 예측값과 비교하였다. 전파 손실 측정을 위한 항공기 통신 시험은 서해상에서 실시되었으며, 비행 전 구간에 걸쳐 항공기에 장착된 수신기의 수신 신호 세기를 측정하였다. 이때 통신 시험이 수행된 비행 경로 중 반사파의 반사점 인근에 섬이 존재하여 이로 인한 반사파가 수신 신호 간섭을 줄 것으로 예상되었다. 따라서 섬에 의한 반사파까지 고려한 구면 대지 반사 모델에 반사 계수, 발산 계수 및 송수신기의 안테나 패턴을 적용하여 예측한 전파 경로 손실과 항공기 이용해 측정한 전파 손실을 비교하였다. 비교 결과, 섬에 의한 반사파를 고려한 구면 대지 반사 모델로 전파 손실을 정확하게 예측할 수 있음을 확인하였다.