• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제32권9호
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• pp.122-129
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• 2004

An accurate thrust measurement is one of the critical paths to the successful test and evaluation program of small liquid propulsion engines. This study describes the design factors for the development of thrust measurement system (TMS) as well as manufacturing practice of TMS hardware. We investigate characteristics of the TMS and its performance through hot-firing test of small liquid engine in a vacuum test cell which is capable of simulating 100,000 ft of altitude or higher. For performance test of TMS, we measure thrusts by changing propellant injection pressure at steady state firing mode as well as at pulse firing mode. Measured eigen frequency of the TMS is 67 Hz. Linearity test of the TMS shows good performance with less than 0.5% of linearity error.

• Journal of Korean Association for Spatial Structures
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• 제15권1호
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• pp.65-73
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• 2015

This paper presents the structural model verification process of whole wind turbine blade including blade model which proposed in Part1 paper. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine which the wind tunnel and structural test data has publicly available is used for the study. In the Part1 of this paper, the processes of structural model development and verification process of blade only are introduced. The whole wind turbine composed by blade, rotor, nacelle and tower. Even though NREL has reported the measured values, the material properties of blade and machinery parts are not clear but should be tested. Compared with the other parts, the tower which made by steel pipe is rather simple. Since it does not need any considerations. By the help of simple eigen-value analysis, the accuracy of structural stiffness and mass value of whole wind turbine system was verified by comparing with NREL's reported value. NREL has reported the natural frequency of blade, whole turbine, turbine without blade and tower only models. According to the comparative studies, the proposed material and mass properties are within acceptable range, but need to be discussing in future studies, because our material properties of blade does not match with NREL's measured values.

• Journal of Korea Water Resources Association
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• 제31권6호
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• pp.757-768
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• 1998

rate of outflow is equated to the total rate of flow, both the state equation and its linearized equation yield almost identical oscillations of water levels. This shows that effects of pipe resistance on the surges are small, and justifies a free oscillation analysis. Free oscillation equation has six eigen modes of different periods, including a rigid mode which is existed when the pumped rate of outflow differs from the total rate of inflow. The six modes constitute a variety of surges dependent on different inflow and outflow conditions. Presence of the rigid mode needs sophisticated pump operations adjusted to real flood inflows.

• Journal of the Korean Society of Propulsion Engineers
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• 제20권6호
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• pp.46-53
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• 2016

It is required to predict a limit cycle amplitude controlled by system's nonlinear behavior as well as an eigen-frequency and initial growth rate of instabilities under the linear motions, in order to fully understand combustion instabilities in a lean premixed gas turbine combustor. Special focus of the current work is placed on the limit cycle amplitude prediction using flame describing function(FDF) where the ratio of a heat release fluctuation to a given flow perturbation is expressed as a function of frequency and amplitude. In this study, the CFD modeling work based on RANS is carried out to obtain FDF, which makes that the nonlinear thermo-acoustic model is successfully developed for predicting the limit cycle amplitude of the combustion instability.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제13권10호
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• pp.2180-2188
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• 2009

This paper is study on real-time hand gesture recognition system based on vision for intelligent robot control. We are proposed a recognition system using PCA and BP algorithm. Recognition of hand gestures consists of two steps which are preprocessing step using PCA algorithm and classification step using BP algorithm. The PCA algorithm is a technique used to reduce multidimensional data sets to lower dimensions for effective analysis. In our simulation, the PCA is applied to calculate feature projection vectors for the image of a given hand. The BP algorithm is capable of doing parallel distributed processing and expedite processing since it take parallel structure. The BP algorithm recognized in real time hand gestures by self learning of trained eigen hand gesture. The proposed PCA and BP algorithm show improvement on the recognition compared to PCA algorithm.

• International Journal of Ocean System Engineering
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• 제2권2호
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• pp.116-138
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• 2012

As in the other fields of mechanics, analytical methods represent an important analysis tool in marine hydrodynamics. The analytical approach is interesting for different reasons : it gives reference results for numerical codes verification, it gives physical insight into some complicated problems, it can be used as a simplified predesign tool, etc. This approach is of course limited to some simplified geometries (cylinders, spheres, ...), and only the case of one or more cylinders, truncated or not, will be considered here. Presented methods are basically eigenfunction expansions whose complexity depends on the boundary conditions. The hydrodynamic boundary value problem (BVP) is formulated within the usual assumptions of potential flow and is additionally simplified by the perturbation method. By using this approach, the highly nonlinear problem decomposes into its linear part and the higher order (second, third, ...) corrections. Also, periodicity is assumed so that the time dependence can be factorized i.e. the frequency domain formulation is adopted. As far as free surface flows are concerned, only cases without or with small forward speed are sufficiently simple to be solved semi-analytically. The problem of the floating body advancing in waves with arbitrary forward speed is far more complicated. These remarks are also valid for the general numerical methods where the case of arbitrary forward speed, even linearized, is still too difficult from numerical point of view, and "it is fair to say that there exists at present no general practical numerical method for the wave resistance problem" [9], and even less for the general seakeeping problem. We note also that, in the case of bluff bodies like cylinders, the assumptions of the potential flow are justified only if the forward speed is less than the product of wave amplitude with wave frequency.

• Korean Journal of Remote Sensing
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• 제23권2호
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• pp.89-101
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• 2007

This paper investigates the effects of the fusion of multifrequency (C and L bands) polarimetric SAR data in land-cover classification. NASA JPL AIRSAR C and L bands data were used to supervised classification in an agricultural area to simulate the integration of ALOS PALSAR and Radarsat-2 SAR data to be available. Several scattering features derived from target decomposition based on eigen value/vector analysis were used as input for a support vector machines classifier and then the posteriori probabilities for each frequency SAR data were integrated by applying a probabilistic ratio model as a decision level fusion methodology. From the case study results, L band data had the proper amount of penetration power and showed better classification accuracy improvement (about 22%) over C band data which did not have enough penetration. When all frequency data were fused for the classification, a significant improvement of about 10% in overall classification accuracy was achieved thanks to an increase of discrimination capability for each class, compared with the case of L band Shh data.

• Proceedings of the Plant Resources Society of Korea Conference
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• 한국자원식물학회 2019년도 춘계학술대회
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• pp.52-52
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• 2019

Buckwheat is well-known crop for containing a high contents of flavonoids that are effective in vascular disease. The current study was performed to estimate the influence of morphological characterization of Fagopyrum esculentum (ES) germplasm for seed's two major flavonoids contents: rutin and quercetin. We found that the red stem color, pale green leaf color, arrowhead leaf shape, white flower color, pale brown seed coat color, and egg-shaped seed were significantly associated with 77%, 56.7%, 83.7%, 98.7%, 70.8% and 74.5% germplasm, respectively. Overall, the rutin contents of ES germplasm ranged from 0.30 to 47.86 mg/100g dry weight (DW) and the quercetin contents ranged from 0 to 1.22 mg/100g DW. The rutin contents of germplasm possessing red stem color, pale green leaf color, arrowhead leaves, white flower color, pale brown seed coat color and egg-shaped seed ranged from 7.22 to 47.86 mg/100g DW. However, the quercetin contents of germplasm with red stem color and pale brown seed coat color ranged from 0 to 1.15 mg/100g DW, with pale green leaves ranged from 0 to 0.96 mg/100g, with arrowhead leaves and white flower ranged from 0 to 1.22 mg/100g and with egg-shaped seed ranged from 0.32 to 1.22 mg/100g DW. In PCA analysis, the first three principal components (PCs) showed Eigen value more than 1 and accounted for 51.70% of variation. For both higher contents of rutin and quercetin, the morphological evaluation in ES shows a tendency of red stem color, arrowhead leaves, pale green leaf color, white flower color, pale brown seed coat color and egg-shaped seed. From this information, we can assume the rutin and quercetin contents by the morphological characteristics of the germplasm. And It could be useful in improving the rutin and quercetin contents and selecting proper resources for cultivation in existing buckwheat cultivars.

• The Journal of the Acoustical Society of Korea
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• 제27권1호
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• pp.40-46
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• 2008

Weak target detection and localization in the presence of loud surface ship noise is a critical problem for matched field processing (MFP) in shallow water. For stationary sources, each signal component of received signal can be separated and interference can be suppressed using eigen space analysis schemes. However, source motion, in realistic cases, causes spreading of signal energies in their subspace. In this case, eigenvalues of target and interfere signal components are mixed and hard to be separated with usual phone space eigenvector decomposition (EVD) approaches. Our technique is based on mode space and utilizes the difference in their physical characteristics of surface and submerged sources. Performing EVD for modal cross spectral density matrix, interference components in the mode amplitude subspace can be classified and eliminated. This technique is demonstrated with synthetic data, and results are discussed.

• Steel and Composite Structures
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• 제52권3호
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• pp.343-356
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• 2024

This paper presents an analytical solution for correctly predicting the Lateral-Torsional Buckling critical moment of simply supported castellated beams, the solution covers uniformly distributed loads combined with compressive loads. For this purpose, the castellated beam section with hexagonal-type perforation is treated as an arrangement of double "T" sections, composed of an upper T section and a lower T section. The castellated beam with regular openings is considered as a periodic repeating structure of unit cells. According to the kinematic model, the energy principle is applied in the context of geometric nonlinearity and the linear elastic behavior of materials. The differential equilibrium equations are established using Galerkin's method and the tangential stiffness matrix is calculated to determine the critical lateral torsional buckling loads. A Finite Element simulation using ABAQUS software is performed to verify the accuracy of the suggested analytical solution, each castellated beam is modelled with appropriate sizes meshes by thin shell elements S8R, the chosen element has 8 nodes and six degrees of freedom per node, including five integration points through the thickness, the Lanczos eigen-solver of ABAQUS was used to conduct elastic buckling analysis. It has been demonstrated that the proposed analytical solution results are in good agreement with those of the finite element method. A parametric study involving geometric and mechanical parameters is carried out, the intensity of the compressive load is also included. In comparison with the linear solution, it has been found that the linear stability underestimates the lateral buckling resistance. It has been confirmed that when high axial loads are applied, an impressive reduction in critical loads has been observed. It can be concluded that the obtained analytical solution is efficient and simple, and offers a rapid and direct method for estimating the lateral torsional buckling critical moment of simply supported castellated beams.