• 한국지반환경공학회 논문집
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• 제14권2호
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• pp.43-50
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• 2013

본 연구는 진동대 모형실험기를 이용하여 동하중 재하 시 네일 두부 구속방식에 따른 쏘일네일 보강사면의 거동에 관한 실험을 실시하였다. 진동대 모형실험은 네일 두부의 구속과 비구속조건 등을 변화시키면서 장주기 특성을 지닌 Hachinohe 지진파와 단주기 특성을 지닌 Ofunato 지진파를 적용하여 실험을 실시하였다. 실험으로부터 얻어진 결과를 바탕으로 사면의 파괴유형과 지반 가속도특성, 수직변위 및 수평변위를 비교 분석하였다. 진동대 모형실험을 수행한 결과 단주기파가 장주기파 보다 사면에 미치는 영향이 큰 것으로 나타났고, 네일 두부의 구속이 동하중에 대하여 전단저항력이 크게 발휘하는 것을 알 수 있었다. 또한 쏘일 네일 두부를 구속함으로써 지진하중 작용 시 사면의 안정성이 크게 향상됨을 확인할 수 있었다.

• Steel and Composite Structures
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• 제7권6호
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• pp.457-468
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• 2007

Analytical and experimental investigation on dynamic properties of extra lightweight concrete sandwich beams reinforced with various lay ups of carbon reinforced epoxy polymer composites (CFRP) are discussed. The lightweight concrete used in the core of the sandwich beams was made up of extra lightweight aggregate, Lica. The density of concrete was half of that of the ordinary concrete and its compressive strength was about $100Kg/cm^2$. Two extra lightweight unreinforced (control) beams and six extra lightweight sandwich beams with various lay ups of CFRP were clamped in one end and tested under an impact load. The dimension of the beams without considering any reinforcement was 20 cm ${\times}$ 10 cm ${\times}$ 1.4 m. These were selected to ensure that the effect of shear during the bending test would be minimized. Three other beams, made up of ordinary concrete reinforced with steel bars, were tested in the same conditions. For measuring the damping capacity of sandwich beams three methods, Logarithmic Decrement Analysis (LDA), Hilbert Transform Analysis (HTA) and Moving Block Analysis (MBA) were applied. The first two methods are in time domain and the last one is in frequency domain. A comparison between the damping capacity of the beams obtained from all three methods, shows that the damping capacity of the extra lightweight concrete decreases by adding the composite reinforced layers to the upper and lower sides of the beams, and becomes most similar to the damping of the ordinary beams. Also the results show that the stiffness of the extra lightweight concrete beams increases by adding the composite reinforced layer to their both sides and become similar to the ordinary beams.

• Earthquakes and Structures
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• 제14권3호
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• pp.273-283
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• 2018

Previous experimental researches indicate that reinforced concrete beam-column joints play an important role in the mechanical properties of moment resisting frame structures, so as to require proper design. In order to get better understanding of the beam-column joint performance, a rational model needs to be developed. Based on the former considerations, two typical models for calculating the shear carrying capacity of the beam-column joint including the inelastic reinforced concrete joint model and the softened strut-and-tie model are selected to be introduced and analyzed. After examining the applicability of two typical models mentioned earlier to interior beam-column joints, several adjustments are made to get better predicting of the test results. For the softened strut-and-tie model, four adjustments including modifications of the depth of the diagonal strut, the inclination angle of diagonal compression strut, the smeared stress of mild steel bars embedded in concrete, as well as the softening coefficient are made. While two adjustments for the inelastic reinforced concrete joint model including modifications of the confinement effect due to the column axial load and the correction coefficient for high concrete are made. It has been proved by test data that predicted results by the improved softened strut-and-tie model or the modified inelastic reinforced concrete joint model are consistent with the test data and conservative. Based on the test results, it is also not difficult to find that the improved beam-column joint model can be used to predict the joint carrying capacity and cracks development with sufficient accuracy.

• Asian-Australasian Journal of Animal Sciences
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• 제18권5호
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• pp.699-703
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• 2005

An experiment was conducted to investigate the effects of various dietary levels of Saccharomyces cerevisiae (SC) on the growth performance and meat quality (i.e., tenderness and oxidative stability) of Ross broiler chickens. Two hundred and forty dayold broiler chicks were fed four experimental diets with graded levels of SC at 0.0, 0.3, 1.0 and 3.0%. Each treatment consisted of six cages with 10 chicks per cage. Feed and water were provided ad libitum throughout the experiment that lasted for 5 wk. Birds were switched from starter to finisher diets at 3 wk of age. The average BW gains of broiler chickens increased (linear p<0.05) during either 0-3 or 0-5 wk of age as dietary SC levels increased. A linear effect (p<0.05) of SC on feed intake during either 4-5 wk or 0-5 wk of ages was also monitored. The addition of SC to the control diet significantly lowered shear forces in raw breast, raw thigh, and boiled drumstick meats (linear p<0.05). Upon incubation, 2-thio-barbituric acid-reactive substances (TBARS) values increased gradually in breast and thigh meats while more dramatic increase was noted in skin samples. The TBARS values of either breast or thigh meats were not significantly affected (p>0.05) by dietary treatments up to 10 d of incubation. At 15 d of incubation, TBARS values of breast and thigh meats from all SC-treated groups were significantly lower (p<0.05) than those of the control. It appears that dietary SC could enhance growth performance of broiler chickens, and improve tenderness and oxidative stability of broiler meats.

• Asian-Australasian Journal of Animal Sciences
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• 제26권12호
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• pp.1753-1761
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• 2013

The individual and interactive effects of Schisandra chinensis powder (SCP) and sodium nitrite additions on color, pH, water holding capacity, residual nitrite, 2-thiobarbituric acid reactive substances (TBARS), volatile basic nitrogen, texture properties, fatty acids, amino acids and sensory evaluation of cooked pork sausages were investigated after 20 d of storage at $4^{\circ}C$. The powders (0, 0.5 and 1.0%) were added to sausages either alone or in combination with nitrite (0 and 100 ppm). SCP added-sausages showed lower $L^*$ (lightness) and W (whiteness) values, and higher $b^*$ (yellowness) values than sausage containing no nitrite, and exhibited the highest $a^*$ values at a 0.5% addition (p<0.05). Residual nitrite and TBARS values were found to be significantly reduced as the addition levels of SCP increased (p<0.05). As the addition of SCP increased, the sausage showed gradually decreased brittleness, cohesiveness, springiness, gumminess and chewiness, while adhesiveness increased. Polyunsaturated fatty acid, n-6 and n-6/n-3 fatty acid ratio concentrations were significantly higher in sausages containing SCP (p<0.05). The addition of SCP to sausage significantly (p<0.05) increased the ammonia content (by 0.5% SCP) and aromatic amino acid concentrations (by 1.0% SCP) (p<0.05). Inclusion of SCP in sausage meat resulted in a significant deterioration in quality characteristics of flavor, springiness, juiciness and overall acceptability (p<0.05). As expected, the observed changes in $a^*$, W, pH, shear force, texture property, TBARS, fatty acid, amino acid and sensory score of sausages, depended on the rate of addition of nitrite (p<0.05). These results suggest that SCP addition is not an effective way of improving the sensory evaluation of sausages, but may beneficially affect TBARS, nitrite scavenging activity, fatty acid and amino acid content in pork sausages.

• Composites Research
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• 제23권3호
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• pp.13-18
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• 2010

나노 재료를 다룰 때 큰 문제 중의 하나는 반데르발스(van der Waals) 상호작용으로 응집되어 있는 나노 입자, 특히 CNT를 어떻게 효과적으로 분산시킬 수 있는가이다. 본 연구에서는 나노 입자를 효과적으로 분산시킬 수 있는 방법으로 코로나 방전(corona discharge) 현상과 정전식모(electrostatic flocking) 공정을 이용한 새로운 분산방법인 방전식모(dischare flocking) 장치를 고안하였으며 분산특성을 평가하기 위하여 방전식모 및 RFI 공정으로 복합재료 시편을 제작하여 전기적, 기계적 특성을 비교하였다. 더욱이, CNT와 에폭시의 기체 방전 효과를 평가하기 위하여 플라즈마 처리된 CNT를 사용하여 복합재료를 제작하였으며 전기적, 기계적 특성을 측정하였다. 방전식모 공정으로 제작 된 복합재료 시편의 특성은 RFI로 제작된 시편과 유사하였으며 방전식모 공정중의 기체방전 현상은 플라즈마 처리된 CNT에 영향을 주지 않았다.

• 대한토목학회논문집
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• 제33권3호
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• pp.855-864
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• 2013

지진격리장치로서 천연고무받침의 동적 특성은 주재료인 고무의 동적거동과 비선형 성질에 의존하고 있다. 역학적이나 환경적인 영향으로 인해 고무재료에 노화가 진행되고 결국에는 손상이 불가피하게 발생하게 된다. 고무재료의 노화에 주원인은 높은 온도에서 반응열로 인한 산화반응으로 알려져다. 이에 따라 천연고무받침에 대한 가속 열 노화실험을 수행하여 열 노화 전 후에 대해 받침의 특성값을 상호 비교하였다. 실험 결과 열 노화 현상은 전단강성과 에너지 감쇠 그리고 등가감소계수에 영향이 있음을 알 수 있었다. 또한 열 노화에 의한 동적특성의 저하를 실제 교량에 적용하여 천연고무받침의 열 노화가 교량의 내진성능에 미치는 영향을 수치해석을 통해 비교분석하였다. 그 결과 천연고무받침에 대하여 열 노화에 따른 기본 특성변화가 교량의 내진성능에 미치는 영향은 크지 않음을 알 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제39권1호
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• pp.19-27
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• 2015

최근에 국제해사기구(IMO)에서 선박 평형수 처리장치(Ballast water treatment system, BWTS)와 관련된 국제 규정을 강화함에 따라 이에 대응할 수 있는 BWTS 기술개발의 중요성이 대두되고 있다. 지금까지는 세계 각국에서 선박 평형수 처리기술을 처리방식에 따라 크게 물리적 방식(막분리, 원심분리, 자외선 등)과 화학적 처리방식(염소처리, 오존처리, 화확약품 등)으로 개발하여 왔으나, 기존의 기술 방식들은 추가적인 구동전력, 낮은 생산성, 잔류처리 문제 등으로 기술적인 보완이나 대안이 요구되고 있다. 본 연구에서는 기존과는 다른 새로운 방식의 기계식 방식 평형수 처리장치의 설계를 위한 유동해석 연구이다. 고속 회전하는 몇 가지 디스크 형상에 따라 유동에서 발생하는 여러 가지 유동특성을 전산유체해석(CFD)를 통하여 분석하였다. 평판형 및 계단형 형상에서는 반경을 따라서 국부적으로 공동현상이 발생가능하며, 원주형에서는 전단응력 강도를 높일 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제37권8호
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• pp.905-910
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• 2013

열교환기의 나선형 튜브에 난류모형을 적용하여 유동해석을 수행하였다. 난류모형은 Spalart-Allmaras과 k-${\varepsilon}$이고 시뮬레이션에는 정렬격자를 적용하였다. 레이놀즈 수 영향을 규명하기 위하여 Navier-Stokes 방정식을 풀어 속도벡터, 압력, 잔차, 마찰계수를 재연하였다. 나선형튜브는 원심력을 증가하여 튜브의 바깥부분에 벽전단 응력을 크게 하였다. 열전도율과 마찰저항의 증가는 곡률에 기인하며 튜브의 내부방향으로는 벽 전단응력이 감소했다. 원심력은 유체의 에너지를 증가시켜서 바깥쪽으로 열전도율을 증가시켰고 이는 내부유동의 압력강하 및 관마찰계수가 상호 밀접한 관계가 있음을 규명하여 주었다. 본 수치결과는 검증을 위하여 타 계산에서 얻어진 마찰계수 결과와 비교하였다.

• Steel and Composite Structures
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• 제35권3호
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• pp.439-447
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• 2020

This paper presents two sets of full three-dimensional thermoelastic finite element analyses of superimposed thermo-mechanically loaded Spar Wingskin Joints made with laminated Graphite Fiber Reinforced Plastic composites. The study emphasizes the influence of residual thermal stresses and material anisotropy on the inter-laminar delamination behavior of the joint structure. The delamination has been pre-embedded at the most likely location, i.e., in resin layer between the top and next ply of the fiber reinforced plastic laminated wingskin and near the spar overlap end. Multi-Point Constraint finite elements have been made use of at the vicinity of the delamination fronts. This helps in simulating the growth of the embedded delamination at both ends. The inter-laminar thermoelastic peel and shear stresses responsible for causing delamination damage due to a combined thermal and a static loading have been evaluated. Strain energy release rate components corresponding to the Mode I (opening), Mode II (sliding) and Mode III (tearing) of delamination are determined using the principle of Virtual Crack Closure Technique. These are seen to be different and non-self-similar at the two fronts of the embedded delamination. Residual stresses developed due to the thermoelastic anisotropy of the laminae are found to strongly influence the delamination onset and propagation characteristics, which have been reflected by the asymmetries in the nature of energy release rate plots and their significant variation along the delamination front.