• Wind and Structures
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• v.34 no.1
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• pp.29-42
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• 2022

Following the BARC initiative, wind tunnel measurements have been performed on a 5:1 rectangular cylinder. Pressure distribution has been measured in several sections, checking the two-dimensionality of the flow around the model. Mean values compare well with previous data. These measurements have been processed using the standard Proper Orthogonal Decomposition (POD) and the snapshot POD to obtain phase-resolved cycles. This decomposition has been used to analyze the characteristics of the flow around the cylinder, in particular, the behavior of the recirculation bubble in the upper/lower surfaces. The effect of the angle of attack, the turbulence intensity and the Reynolds number has been studied. First and second modes extracted from POD have been found to be related to the reattachment of the flow in the upper surface. Increasing the angle of attack is related to a delay in the reattachment position, while an increase in turbulence intensity makes the reattachment point to move towards the windward face.

• Wind and Structures
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• v.21 no.1
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• pp.63-84
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• 2015

The shape of a tall building has significant impact on wind force generation and wind-induced dynamic response. To study the effect of recessed cavities, wind excitations on a wind-tunnel model of an H-section tall building were compared with those on a square-section building model. Characteristics of the fluctuating wind pressures on the side faces of the two tall buildings and their role in the generation of crosswind forces on the buildings were investigated with the space-time statistical tool of proper orthogonal decomposition (POD). This paper also compares the use of different pressure data sets for POD analysis in situations where pressures on two different surfaces are responsible for the generation of a wind force. The first POD mode is found to dominate the generation of crosswind excitation on the buildings.

• Journal of Industrial Technology
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• v.28 no.B
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• pp.135-141
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• 2008

In this paper, the Proper Orthogonal Decomposition (POD) method, which is a statistical analysis technique to find the modal characteristics of a structure, is adapted to identify the modal parameters of a tall chimney structure. A wind force time history, which is applied to the structure, is obtained by a wind tunnel test of a scale down model. The POD method is applied on the wind force induced responses of the structure, and the true normal modes of the structure can be obtained. The modal parameters including, natural frequency, mode shape, damping ratio and kinetic energy of the structure can be estimated accurately. With these results, it may be concluded that the POD method can be applied to obtain accurate modal parameters from the wind-induced building responses.

• International Journal of High-Rise Buildings
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• v.11 no.4
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• pp.277-286
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• 2022

In this study, The POD technique was applied to the fluctuating wind pressure of high aspect ratio circular cylinder to consider about its organizational structure, and considered about the characteristics of the fluctuating wind force obtained by synthesized the POD modes.

• Korean Journal of Organic Agriculture
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• v.16 no.4
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• pp.409-420
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• 2008

The highland area remained bare for the winter and spring seasons and this condition has resulted in soil erosion. In this areas, crop rotation by legume has not been commonly practiced. Thus, this study was carried out to evaluate the effects of the growth characteristics and nitrogen yield as a green manure crop according to sowing seasons of hairy vetch and woolly pod vetch. In this experiment, we was investigated the growth characteristics, winter tolerance, soil coverage and productivities of hairy vetch and woolly pod vetch. We cultivated two hairy vetch(Madison, H1) and two woolly pod vetch(Naomi, Haymaker) varieties in the highland area from 2006 to 2007. The result are summarized as follows; The plant height of hairy vetch increased with the progress of growth stage until flowering stage. The wintering rate of hairy vetch was $79{\sim}83%$ in highland area. But, the wintering rate of woolly pod vetch was $29.5{\sim}39.2%$. The 100% soil coverage of hairy vetch was reached between end of May and beginning of June under autumn sowing, and between end of June and beginning of July under spring sowing. The weeds density of hairy vetch field under autumn sowing was lower than that under spring sowing. Dry matter yield of hairy vetch was significantly higher than that of woolly pod vetch under autumn sowing. The dry matter yield of hairy vetch and woolly pod vetch were $5,255{\sim}5,405kg/ha$ and $3,520{\sim}3,640kg/ha$, respectively. But, hairy vetch in spring sowing was not significantly higher fresh matter yield than that of woolly pod vetch. The nitrogen content in hairy vetch and woolly pod vetch was $2.98{\sim}3.08$ and $2.74{\sim}3.21%$, respectively. There were no significant difference in nitrogen content of the hairy vetch and woolly pod vetch under the spring sowing. N-uptake of hairy vetch was significantly higher than that of woolly pod vetch in autumn sowing. The N uptake was $156{\sim}164\;kg/ha$ in hairy vetch and $96{\sim}101\;kg/ha$ in woolly pod vetch under autumn sowing. It was thought that hairy vetch was better than woolly pod vetch as a green manure crop in autumn sowing considering wintering rate and yield of dry matter in highland area. And woolly pod vetch could use as a green manure crop under spring sowing in highland area.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.6
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• pp.495-501
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• 2012

In this study, the natural frequencies and mode shape of an external mounting pod were verified using the modal analysis and modal testing technique for a pod mounted on an aircraft. The procedure associated with the FE model building of an external mounted pod to predict the dynamic behavior of aircraft structures is described. The simplified FE model reflecting the results of the modal testing of a pod is built through the optimization and will be applied to the structural dynamic model of an aircraft which is used to verified the stability of vibration and flutter of an aircraft.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.1-9
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• 2017

The cryogenic nitrogen spray of a swirl injector has been numerically investigated using three dimensional LES turbulence model to analyze the dynamic characteristics under supercritical condition. To predict the precise nitrogen properties under supercritical condition, SRK equation of state, Chung's method for viscosity and thermal conductivity and Takahashi's correlation based on Fuller's theory for diffusion coefficient are implemented. The complex flow structures due to interaction between flow field and acoustic field are observed inside and outside the injector under supercritical condition. FFT, POD, and DMD techniques are employed to understand the coherent structures. By implementing the FFT, the dominant frequencies are identified inside and outside the injector. The coherent flow structures related to the dominant frequencies are visualized using the POD and DMD techniques. In addition, the DMD provides the damping coefficient which is related with the instability prediction.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1073-1079
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• 2009

The proper orthogonal decomposition (POD) method can identify principal modes that optimally capture the energy content from large multi-dimensional data set. In this study unsteady pressure fields on the rotor blade surface of a helicopter in forward flight are expressed by a reduced order model based on the POD method. Special modes containing high energy are analyzed to investigate the aerodynamic characteristics in more efficient way. The CFD simulation of flowfields around helicopter rotor blade in hovering motion is also conducted to validate its prediction with experimental result. In the process 7 modes containing energy ratio 99% from 240 snapshots information are identified and utilized to construct a reduced order model.

• FLOWER RESEARCH JOURNAL
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• v.17 no.4
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• pp.285-290
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• 2009

This experiment was conducted to investigate the propagation system by seed to check growth, flowering, and making seed of three-year-old cactus of potted Mammillaria goldii. M. theresae, and M. pseudopeclinata. Plant height and width of them was 2.5~2.8 cm, and 2.8~3.1 cm, and seed formation of Mammillaria goldii and M. theresae had internal body taking130 to 135 days to ripening seeds, however, M. pseudopectinata had externals taking just 26 days to ripening seeds. The mean seeded pod from April to June of M. goldii was 50.0% and the number of seeds in a pod was 25.3. In M. theresae, the mean seeded pod from April to June was 57.3% and the number of seeds in a pod was 35.0. However, the highest rate of seeded pod on May of M. pseudopectinata was 75.0% and the number of seed in a pod was 66.0. The sib crossing was much more ripening seed fertilization than that of self cross ing in the Mammillaria. The self crossing was formed from 12.0% to 20.0% of seeded pod, from 12.0 to 16.0 number of seed in a pod. However, sib crossing obtained 58.0% of seeded pod, 30 seeds in a pod of M. goldii, 65.0% seeded pods and 40 seeds in a pod of M. theresae, and 75.0% seeded pod, 68 seeds in a pod of M. pseudopectinala as the highest of them.

• FLOWER RESEARCH JOURNAL
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• v.17 no.4
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• pp.291-296
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• 2009

This experiment was conducted to investigate the propagation system by seed to check growth, flowering, and making seed of four-year-old seedling cactus of potted Astrophytum asterias 'Nudum', A. asterias 'Super Kabuto', and A. myriostigma 'Nudum'. Plant height and width of Astrophytum asterias 'Nudum' and A. asterias 'Super Kabuto' was 5.3 to 5.5 cm, and 2.5 cm. However, plant height and width of A. myriostigma 'Nudum' was 7.6 cm and 5.6 cm as divided into 8 sections of body. In A. asterias 'Nudum', the mean seeded pod from April to September was 37.0% and the number of seeds in a pod was 43.0. In A. asterias 'Super Kabuto', the mean seeded pod from April to September was 22.5% and the number of seeds in a pod was 26.2. However, the mean seeded pod of A. myriostigma 'Nudum' from April to September was 32.3% and the number of seeds in a pod was 57.4. Especially, the seeded pod and the number of seeds in a pod of A. asterias 'Nudum' in July was the highest, 72.0% and 66.0. The sib crossing obtained much more seeded pods and the number of seeds per pod than that of selfing in the Astrophytum. The self crossing was formed from 9.0 to 20.0% of seeded pod, and 12.0 to 16.0 seeds in a pod. However, sib crossing was formed 60.0% seeded pod and 68.0 seeds in a pod on July of A. myriostigma 'Nudum'.