• Transactions of the Korean Society of Mechanical Engineers B
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• 제23권1호
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• pp.149-157
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• 1999

Heat transfer in a duct is augmented remarkably by rib turbulators. However, increasing friction loss is accompanied due to ribs disturbing flows. Hence, pressure drops and heat transfer are considered simultaneously to decide heat/mass transfer performance in a rib-roughened duct. In the present study, the effects of rib cross section shape on pressure drop through a duct are investigated as well as those on heat transfer characteristics. The results show that the characteristics of heat/mass transfer and friction loss in the duct roughened with triangular ribs are similar to those with square ribs, while significantly different from those with semicircular ribs. The best performance in the duct is obtained by using semicircular shaped ribs among three types of ribs for the large rib angles of ${\alpha}{\geq}63^{\circ}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제30권9호
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• pp.873-881
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• 2006

The present study investigates the pressure drop characteristics in rotating two-pass ducts. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter $(D_h)$ of 26.67mm. Rib turbulators are attached crossly in the four different arrangements on the leading and trailing surfaces of the test ducts. The ribs have a rectangular cross section of $2mm(e){\times}3mm(w)$ and an attack angle of $70^{\circ}C$. The pitch-to-rib height ratio (pie) is 7.5, and the rib height-to-hydraulic diameter ratio $(e/D_h)$ is 0.075. The results show that the highest pressure drop among each region appears in the turning region for the stationary case, but appears in the upstream region of the second pass for the rotating case. Effects of cross rib arrangements are almost the same in the first pass for the stationary and rotating cases. In the second pass, however, heat transfer and pressure drop are high for the cases with cross NN or PP type ribs in the stationary ducts. In the rotating ducts, they are high for the cases with cross NP or PP type ribs.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제25권11호
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• pp.1640-1649
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• 2001

The present study investigates the effects of various rib arrangements on heat/mass transfer in the cooling passage of gas turbine blades. A complex flow structure occurs in the cooling passage with rib turbulators which promote heat transfer on the wall. It is important to increase not only the heat transfer rates but also the uniformity of heat transfer in the cooling passage. A numerical computation is performed using a commercial code to calculate the flow structures and experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. A square channel (50 mm $\times$ 50 mm) with rectangular ribs (4 mm $\times$ 5 mm) is used fur the stationary duct test. The experiments focus on the effects of rib arrangements and gap positions in the discrete ribs on the heat/mass transfer on the duct wall. The rib angle of attack is 60°and the rib-to-rib pitch is 32 mm, that is 8 times of the rib height. With the inclined rib angle of attack (60°), the parallel rib arrangements make a pair of counter rotating secondary flows in the cross section, but the cross rib arrangements make a single large secondary flow including a small secondary vortex. These secondary flow patterns affect significantly the heat/mass transfer on the ribbed wall. The heat/mass transfer in the parallel arrangements is 1.5 ∼2 times higher than that in the cross arrangements. However, the shifted rib arrangements change little the heat/mass transfer from the inline rib arrangements. The gap position in the discrete rib affects significantly the heat/mass transfer because a strong flow acceleration occurs locally through the gap.

• Proceedings of the KSR Conference
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.1084-1089
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• 2004

Recently, Orthotropic steel deck bridges, which have long span decks, have been regarded as one of economical as well as durable bridge types. However, Orthotropic steel deck bridge is used by a lot of welding, which may cause welding defect and deformation of connections. This kind of system happens some damages by the fatigue cracks of welding. The cross-connection of longitudinal rib and transversal rib is one of the weakest point because of the fatigue. The secondary stresses which are from the out-plane deformation of transversal rib and the torsion of longitudinal rib make the topical stress concentration phenomenon. But, it is principle that a Bulkhead Plate is not established in the domestic design standard. Therefore, it is estimated that a study for the installing of Bulkhead Plate is needed. This study with considering these circumstances proves efficiency of Bulkhead Plate and will be presented optimal design details through finite element analysis according to change the geometrical system of Bulkhead Plate and the cross-connection area of longitudinal and transversal rib

• Journal of the Korean Ceramic Society
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• 제40권6호
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• pp.553-559
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• 2003

PDP rib is one of the important parts of manufacturing process and the sintering degree of rib plays an important role to prevent some problems such as cross talk. Nowadays, the screen-printing method, which is a low price and high production, is used to make a rib. However, it is hard to judge and value the sintering ratio of sintered body itself. In this study, we measured the sintering degree by the dielectric breakdown of pores with the potentiostat. We conformed that this has similar tendency to density of sintered samples and an error being expected by open and closed pores was inspected by change of the microstructure to scanning electron microscope. This result showed that the sintering degree of PDP rib could be analyzed into the electro-chemical method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.128-133
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• 2002

The heat transfer characteristics of a turbulent flow in a ribbed two-dimensional channel have been investigated numerically. The fully elliptic governing equations, coupled with a four-equation turbulence model, $\kappa-\omega-\bar{t^2}-\epsilon_t$, are solved by a finite volume method of SIMPLE type. Calculations have been carried out for three rib cross-sections : square, triangular, and semicircular, with various rib pitches and Reynolds numbers. The procedure appears to be satisfactory as the results for the square rib compare favorably with available experimental data and earlier calculation. The optimal rib pitch that yields the maximum heat transfer has been identified. It is also found that the square rib is most effective in enhancing the heat transfer. The semicircular rib, on the other hand, incurs the least amount of pressure drop but the improvement in heat transfer is substantially lower.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.177-184
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• 2004

Orthotropic steel deck bridge has much advantages such as the light deadweight, so the construction of orthotropic steel deck is profitable for the long-span bridges Although the system has a lot of merits, it happens some damages by the traffic density and the fatigue cracks of welding. The cross-connection of longitudinal rib and transversal rib is one of the weakest at the fatigue. The secondary stresses which are from the out-plane deformation of transversal rib and the torsion of longitudinal rib make the topical stress concentration phenomenon. The Bulkhead Plate for prevention of this stress concentration phenomenon was applied by changing the orthotropic steel deck of Williamsburg bridge in USA. But, it is principle that a Bulkhead Plate is not established in the domestic design standard. Therefore, it is estimated that the study for installation of Bulkhead Plate is needed. This study with considering these circumstances proves efficiency of Bulkhead Plate and will be presented optimal design details through finite element analysis according to change the geometrical of Bulkhead Plate and the cross-connection area of longitudinal and transversal rib

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.201-204
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• 2005

The bond characteristics of two types hybrid FRP (fiber reinforced polymer) reinforcing bars with different rib geometry were analyzed experimentally. Two types of hybrid FRP. reinforcing bars such as spiral and cross type with different relative rib area were considered in this test. All testing procedures including specimens preparation, set-up of test equipments and measuring devices were made according to the recommendations of CSA Standard S806-02. From the test results, it was found' that cross type hybrid FRP reinforcing bars showed the higher bond strength than that of spiral type's due to the higher relative rib area.

• Journal of computational fluids engineering
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• 제19권4호
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• pp.14-19
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• 2014

This study conducts shape optimization of rib turbulator on the internal cooling passage that has triangular cross-section of high pressure turbine nozzle. During optimization, various types of rib turbulator including angled, V-shaped, A-shaped and angled rib with intersecting rib are considered. Each type of rib turbulator is parameterized with attack angle(s), rib height, spacing ratio and bending/intersecting location. For optimization, Design of Experiment (DOE) and Kriging surrogate model are used to utilize computational resource more efficiently and Genetic Algorithm (GA) is used to search the optimum points. As a result, Pareto front of each type of rib turbulator with friction factor that relates to pressure drop in cooling passage and spatially averaged Nusselt number that relates to heat transfer on the wall is drawn and optimum points on the Pareto front are suggested.

• Wind and Structures
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• 제39권1호
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• pp.71-84
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• 2024

The wind-resistant performance of bridges is generally evaluated based on the strip assumption. For the arch rib of arch bridges, the situation is different due to the curve axis and the variable cross-sectional size. In the construction stage, the arch rib supported by a cable system exhibits flexible dynamic characteristics, and the wind-resistant performance attracts specially attention. To evaluate the wind-induced vibration of an arch rib with the maximum cantilever state, the finite element model was established to compute the structural dynamic characteristics. Then, a three-dimensional (3D) fluid-solid coupling analysis method was realized. After verifying the reliability of the method based on a square column, the wind-induced vibration of the arch rib was computed. The vortex-induced vibration (VIV) performance of the arch rib was focused and the flow field characteristics were discussed to explain the VIV phenomenon. The results show that the arch rib with the maximum cantilever state had the possibility of VIV at high wind speeds but the galloping was not observed. The lock-in wind speeds were larger than the results based on the strip assumption. Due to the vibration of arch rib, the frequency of shedding vortices along the arch axis trended to be uniform.