• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.101-104
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• 2008

The sailfish is the fastest sea animal, reaching its maximum speed of 110km/h. On its skin, a number of V-shaped protrusions pointing downstream exist. Thus, in the present study, the possibility of reducing the skin friction using its shape is investigated in a turbulent boundary layer. We perform a parametric study by varying the height and width of the protrusion, the spanwise and streamwise spacings between adjacent ones, and their overall distribution pattern, respectively. Each protrusion induces a pair of streamwsie vortices, producing low and high shear stresses at its center and side locations, respectively. These vortices also interact with those induced from adjacent protrusions. As a result, the drag is either increased or unchanged for all the cases considered. In some cases, the skin friction itself is reduced but total drag including the form drag on the protrusions is larger than that of a smooth surface. Since the shape of present protrusions is similar to that used by Sirovich and Karlsson [Nature 388, 753 (1997)] where V-shaped protrusions pointing upstream were considered, we perform another set of experiments following their study. However, we do not obtain any drag reduction even with random distribution of those V-shaped protrusion.

• Structural Engineering and Mechanics
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• 제86권6호
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• pp.715-730
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• 2023

Broad studies have addressed the issue of structural element damage identification, however, rubber bearing, as a key component of load transmission between the superstructure and substructure, is essential to the operational safety of a bridge, which should be paid more attention to its health condition. However, regarding the limitations of the traditional bearing damage detection methods as well as few studies have been conducted on this topic, in this paper, inspired by the model updating-based structural damage identification, a two-stage bearing damage identification method has been proposed. In the first stage, we deduce a novel bearing damage localization indicator, called element relative MSE, to accurately determine the bearing damage location. In the second one, the prior knowledge of bearing damage localization is combined with sailfish optimization (SFO) to perform the bearing damage estimation. In order to validate the feasibility, a numerical example of a 5-span continuous beam is introduced, also the noise robustness has been investigated. Meanwhile, the effectiveness and engineering applicability are further verified based on an experimental simply supported beam and actual engineering of the I-40 Bridge. The obtained results are good, which indicate that the proposed method is not only suitable for simple structures but also can accurately locate the bearing damage site and identify its severity for complex structure. To summarize, the proposed method provides a good guideline for the issue of bridge bearing detection, which could be used to reduce the difficulty of the traditional bearing failure detection approach, further saving labor costs and economic expenses.

• EDISON SW 활용 경진대회 논문집
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• 제6회(2016년)
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• pp.44-48
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• 2016

물 속에서 고속으로 유영하는 상당수의 어류는 긴 부리 모양의 주둥이를 가진다. 대표적으로 지구상 가장 빠른 물고기인 돛새치가 있다. 이러한 사실은 이 독특한 형상과 고속운동의 상관관계에 대해 학구적 호기심을 자아냈고 그에 따라 본 연구를 수행하였다. 본 연구에서는 돛새치, 청새치들의 2차원 형상을 가지고 부리의 존재 유무가 항력에 미치는 영향을 분석하고 더 나아가 미사일의 spike가 항력에 미치는 영향을 분석하였다. 또한 부리가 방향전환 시 기동성 증진에도 기여하는지를 알아보았다. 해석을 위해 Kflow Edison_13와 2D_Comp_P 해석자를 활용하여 동일 유동조건에서 항력계수를 비교하였다. 그리고 돛새치가 방향 전환할 때 발생하는 모멘트계수를 얻기 위해 2D_Incomp_P 해석자를 활용하였다.