• Advances in aircraft and spacecraft science
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• 제9권3호
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• pp.263-278
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• 2022

The time-varying structural reliability of an aeroelastic launch vehicle subjected to stochastic parameters is investigated. The launch vehicle structure is under the combined action of several stochastic loads that include aerodynamics, thrust as well as internal combustion pressure. The launch vehicle's main body structural flexibility is modeled via the normal mode shapes of a free-free Euler beam, where the aerodynamic loadings on the vehicle are due to force on each incremental section of the vehicle. The rigid and elastic coupled nonlinear equations of motion are derived following the Lagrangian approach that results in a complete aeroelastic simulation for the prediction of the instantaneous launch vehicle rigid-body motion as well as the body elastic deformations. Reliability analysis has been performed based on two distinct limit state functions, defined as the maximum launch vehicle tip elastic deformation and also the maximum allowable stress occurring along the launch vehicle total length. In this fashion, the time-dependent reliability problem can be converted into an equivalent time-invariant reliability problem. Subsequently, the first-order reliability method, as well as the Monte Carlo simulation schemes, are employed to determine and verify the aeroelastic launch vehicle dynamic failure probability for a given flight time.

• Wind and Structures
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• 제35권6호
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• pp.369-383
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• 2022

Wind tunnel experiment was carried out to study the cross-wind layer forces on a square cross-section building model using a synchronous multi-pressure sensing system. The stationarity of measured wind loadings are firstly examined, revealing the non-stationary feature of cross-wind forces. By converting the measured non-stationary wind forces into an energetically equivalent stationary process, the characteristics of local wind forces are studied, such as power spectrum density and spanwise coherence function. Mathematical models to describe properties of cross-wind forces at different layers are thus established. Then, a conditional simulation method, which is able to ex-tend pressure measurements starting from experimentally measured points, is proposed for the cross-wind loading. The method can reproduce the non-stationary cross-wind force by simulating a stationary process and the corresponding time varying amplitudes independently; in this way the non-stationary wind forces can finally be obtained by combining the two parts together. The feasibility and reliability of the proposed method is highlighted by an ex-ample of across wind loading simulation, based on the experimental results analyzed in the first part of the paper.

• Earthquakes and Structures
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• 제22권3호
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• pp.219-230
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• 2022

Knowing that the variability of soil properties is an important source of uncertainty in geotechnical analyses, we will study in this paper the effect of this variability on the seismic response of a structure within the framework of Soil Structure Interaction (SSI). We use the proposed and developed model (N2-ISS, Mekki et al., 2014). This approach is based on an extension of the N2 method by determining the capacity curve of the fixed base system oscillating mainly in the first mode, then modified to obtain the capacity curve of the system on a flexible basis using the concept of the equivalent nonlinear oscillator. The properties of the soil that we are interested in this paper will be the shear wave velocity and the soil damping. These parameters will be modeled at first, as independent random fields, then, the two parameters will be correlated. The results obtained showed the importance of the use of random field in the study of SSI systems. The variability of soil damping and shear wave velocity introduces significant uncertainty not only in the evaluation of the damping of the soil-structure system but also in the estimation of the displacement of the structure and the base-shear force.

• Advances in nano research
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• 제12권3호
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• pp.319-336
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• 2022

Evaluating the temporal and spatial changes in the ecosystem service value (ESV) of the Sanjiangyuan Nature Reserve is important for understanding the impact of human activities on natural ecosystem and guiding ecosystem restoration and environmental pollution control. In this study, remotely sensed land-cover data and the equivalent factor method were used to analyze the spatiotemporal evolution characteristics of the ESV in Sanjiangyuan Nature Reserve from 1992 to 2015, and regression analysis was employed to determine the factors driving changes in the ESV. The results show that grassland was the main type of ecosystem in the study area, and the transformation of grassland into bare areas was the primary change in land cover. Additionally, the ESV in the study area first decreased and then increased, with an annual growth rate of 0.69%. The ESV mainly increased in the north of the Yellow River's source area, and mainly decreased in the northwest of the Yangtze River's source area. Finally, the gross output value of agriculture, urbanization rate and proportion of secondary industry were found to be the main factors driving the ESV in the study area.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.517-530
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• 2022

In re-assessing the Jacket-type fixed steel structures, the current standards often allow the simplicity of corrosion sections using local buckling or equivalent section approach to applying empirical formulae of frame stress and resistance analyses. However, those approaches can lead to significant errors for non-uniform corroded frames in a specific area, including force distribution, stress, and allowable strength of the tubular section, compared to the actual cases. This paper investigates a suitable approach to determine the actual stress on non-uniform corroded tubular frames under compression through the non-linear ABAQUS model by considering the effect of large deformation on the frame axis and the frame section. There are 3 scenarios of interest. In the 1st and 2nd scenarios with simple corrosion cases, the stress ratios using the numerical model and theoretical formulae correspond to the calculation of allowable strength reduction ratios in standards. However, scenario 3, which describes non-uniform corroded sections based on survey data, provides considerable differences in results. Therefore, it proves the reliable and effective results when using this method to analyze the resistance of the actual corroded section in the Jacket platforms.

• Steel and Composite Structures
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• 제52권1호
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• pp.77-87
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• 2024

Analytical methods for assessment of the out-of-plane buckling of unbraced top chords of truss bridges may look obsolete while comparing them to finite element analysis. However they are, usually, superior when rapid assessment is necessary. Analytical methods consider the top chord as a bar on elastic supports provided by bracing (Holt, Timoshenko). Correct assessment of the support elasticity (stiffness) is crucial. In the case of truss bridge spans of traditional structural layout (cross-beams at the truss chord nodes only), the elasticity may be set based on the analysis of the, so called, U-frame stiffness. Here the analyses consider the U-frame itself (a pair of verticals and a cross-beam) or the U-frame with adjacent diagonals or the pair of diagonals (in the absence of verticals) and the members of the bottom chord in the adjacent panels. For all the cases, the stability analysis of the chord as a bar in compression is necessary. Unfortunately, the method cannot be applied to contemporary truss bridges without verticals, that usually have independent cross-beam decks (the cross-beams attached to truss chords at their nodes and between them). This is the motivation for the analysis resulting in the method of setting the stiffness of the equivalent U-frame for the aforementioned truss bridges. Truss girders of both, gussetless and gusseted, joints are taken into account.

• 상하수도학회지
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• 제34권3호
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• pp.211-220
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• 2020

When domestic sewage and rainwater runoff are discharged into a single sewer pipe, it is called a "combined sewer system." The sewage design standards in Korea specify the flow velocity based only on the volume of rainfall; therefore, sedimentation occurs on non-rainy days owing to the reduced flow rate and velocity. This sedimentation reduces the discharge capacity, causes unpleasant odors, and exacerbates the problem of combined sewer overflow concentration. To address this problem, the amount of sewage on non-rainy days, not just the volume of rainfall, should also be considered. There are various theories on sedimentation in sewer movement. This study introduces a self-cleansing velocity based on tractive force theory. By applying a self-cleansing velocity equivalent to the critical shear stress of a sand particle, sedimentation can be reduced on non-rainy days. The amount of sewage changes according to the water use pattern of citizens. The design hourly maximum wastewater flow was considered as a representative value, and the velocity of this flow should be more than the self-cleansing velocity. This design method requires a steeper gradient than existing design criteria. Therefore, the existing sewer pipelines need to be improved and repaired accordingly. In this study, five types of improvement and repair methods that can maximize the use of existing pipelines and minimize the depth of excavation are proposed. The key technologies utilized are trenchless sewer rehabilitation and complex cross-section pipes. Trenchless sewer rehabilitation is a popular sewage repair method. However, it is complex because the cross-section pipes do not have a universal design and require continuous research and development. In an old metropolis with a combined sewer system, it is difficult to carry out excavation work; hence, the methods presented in this study may be useful in the future.

• 구강회복응용과학지
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• 제35권3호
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• pp.132-142
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• 2019

목적: 본 유한요소해석적 연구는 새로운 Lock screw 시스템을 소개하고 그 역학적 특성을 분석하여 Lock screw가 지대주 나사 풀림을 방지할 수 있는지 알아보려고 한다. 연구 재료 및 방법: Lock screw는 임플란트 지대주 내부에 체결하여 지대주 나사 두부에 압축력을 가하는 장치이다. 그 효과를 알아보기 위해 CAD 프로그램을 이용하여 모델링을 하였고, 이를 다양한 하중조건 하에서 유한요소해석법을 이용해 분석하였다. 우선 지대주 나사의 조임회전력에 따른 전하중을 측정하고 이론 값과 비교하여 해석모델을 검증하였다. 검증된 해석 모델을 외부 하중이 없는 것과 178 N을 부여한 것으로 나누어 Lock screw의 조임회전력을 각각 10, 20, 30 Ncm으로 변화시켰고, 이때 임플란트 구성요소의 응력 분포가 어떠한 특성을 보이는지 살펴보았다. 결과: 여러 하중조건 하에서 Lock screw의 사용은 임플란트 구성요소의 항복강도를 넘어서는 등가응력을 발생시키지 않았다. 또한 지대주-지대주 나사 계면에서 축방향 하중의 증가를 보였다. 결론: Lock screw의 사용은 임플란트 구성요소에 과도한 응력을 가하지 않으며, 지대주-지대주 나사 계면의 마찰력을 증가시켜 지대주 나사 풀림을 방지할 수 있을 것으로 판단된다.

• 한국지반공학회논문집
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• 제38권11호
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• pp.119-135
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• 2022

본 논문에서는 대심도 가설 흙막이 벽체의 내진안전성을 검토하기 위해 평균재현주기 2,400년 수준(0.220g)을 목표로 Northridge(1994), Kobe(1995), 인공지진파 그리고 2.5Hz 정현파 총 네 가지 지진파를 가진하는 동적원심모형실험을 수행하였다. 원심모형실험은 대심도 굴착현장을 대상을 모사하였다. 모형지반은 상대밀도 55% 건조사질토지반으로 조성하였고, 모형벽체는 심도 24.8m의 지하연속벽 흙막이벽체와 중구경 강관 지보재로 보강된 공법을 모사하였다. 흙막이 시스템은 기반암 가속도가 배면지반, 벽체 상단과, 기반암 근처 하단부에서 증폭되었고, 중앙부에서는 상대적으로 감쇠되는 경향을 보였다. 벽체 전체최대휨모멘트와 지보재 전체최대축력이 유발되는 시점의 부재력을 정지상태 부재력과 비교하였다. 그 결과, 벽체 휨모멘트는 정모멘트와 부모멘트가 최대 10.1%, 36.2% 증가하였으며, 축력은 하단 지보재에서 최대 70% 증가하였다. 또한, Mononobe-Okabe(M-O) 동적토압이론과 Seed-Whitman(S-W) 동적토압이론을 활용한 등가정적해석을 수행하여 실험결과와 비교하였다. M-O 이론 등가정적해석이 휨모멘트 동적증가분을 과소평가하고, S-W 이론 등가정적해석은 과대평가하였다.

• Journal of Animal Science and Technology
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• 제46권3호
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• pp.405-414
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• 2004

본 연구는 한국 재래돼지의 도축전 절식과 숙성이 longissimus dorsi(LD), biceps femoris(BF) and triceps brachii(TB)의 육질에 미치는 영향을 조사하였다. 18 시간동안 절식은 LD에서 유의적으로(P < 0.05) 높은 최종 pH을 보였고, BF도 유사한 경향을 나타냈다. 근육 온도는 절식유무에 영향을 받지않아, 이 결과는 각 처리구의 돼지들은 각기 다른 온도와 pH의 영향을 받았다는 것을 의미한다. 이러한 영향은 LD의 경우 절식을 하지 않은 돼지에서 유의적으로 높은(P < 0.05) hunter $L^*$ 값과 가열감량에서 나타났다. 하지만 전단력은 차이가 없었다. 또한 BF와 TB의 육질은 도축전 절식유무에 의해 영향을 받지 않았다. LD에서 전단력은 숙성 7일까지 감소하였고, BF와 TB는 14일까지 유의적으로(P < 0.05) 감소했다. 숙성기간중 LD와 BF, 그리고 LD와 TB의 상관관계를 보았을 때, LD의 전단력 6kg은 BF와 TB에서 각각 6과 3.5 kg을 보였다. 본 연구의 결과에 따르면, 도축전 급여는 시각적인 육색은 개선하나, 가열감량을 증가시켜 맛은 감소시킬 것으로 판단되었다. 한편 LD의 숙성은 7일이 적절한 것으로 나타났고, TB와 같이 근본적으로 연한 고기는 숙성은 가열감량을 증가시키므로 숙성하지 않는 것이 바람직하다고 판단되었다. BF와 TB에서는 14일 숙성은 연도는 증가하나 다즙성은 감소할 것으로 판단되었다.