• The KSFM Journal of Fluid Machinery
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• v.15 no.4
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• pp.55-60
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• 2012

The purpose of this study is to investigate the buckling load of filament-wound composite towers for large scale wind-turbine using finite element method(FEM). To define material properties, we used both the effective property method and the stacking properties method. The effective properties method is to assume that composite consists of one ply. The stacking properties method is to assume that composite consists of some stacked plies. First, linear buckling analysis of the tower, filament-wounded with angles of [${\pm}30$] was carried out by two methods for composite material properties, the stacking method and the effective method. and FE analysis was performed for the composite towers according to filament winding angles of [${\pm}30$], [${\pm}45$], [${\pm}60$]. FE analysis results using the stacking properties of the composite were in good agreement with the results by the effective properties. The difference between FEM results by material properties methods was approximately 0~2.3% in buckling Analysis and approximately 0~0.6% in modal analysis. And above the angle of [${\pm}60$], there was a little change of buckling load.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.73-78
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• 2011

The purpose of this study was to investigate the natural frequency of filament-wound composite towers for large scale wind-turbines using the finite element method (FEM). To define the material properties, we used both the effective property method and the stacking properties method. The effective properties method assumes that a composite consists of one ply. The stacking properties method assumes that a composite consists of several stacked plies. First, a modal analysis of the tower, filament-wound with angles of $[{\pm}30]$, was carried out using the two methods for composite material properties, the stacking method and effective method. Then, an FE analysis was performed for composite towers using filament winding angles of $[{\pm}30]$, $[{\pm}45]$, and $[{\pm}60]$. The FE analysis results using the stacking properties of the composite were in good agreement with the results from the effective properties method. The difference between the FEM and material properties methods was approximately 0~0.6%

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.79-84
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• 2011

The purpose of this study was to investigate the buckling load of filament-wound composite towers for large scale wind-turbines using the finite element method (FEM). To define the material properties, we used both the effective property method and stacking properties method. The effective properties method assumes that a composite consists of one ply. The stacking properties method assumes that a composite consists of several stacked plies. First, a linear buckling analysis of the tower, filament-wound with angles of $[{\pm}60]$, was carried out using the two methods for composite material properties: the stacking method and effective method. An FE analysis was also performed for the composite towers using the filament winding angles of $[{\pm}30]$, $[{\pm}45]$, and $[{\pm}60]$. The FE analysis results using the stacking properties of the composite were in good agreement with the results from the effective properties method. The difference between the FEM results and material properties method was approximately 0~2.3%. Above the angle of $[{\pm}60]$, there was little change in the buckling load.

• Explosives and Blasting
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• v.17 no.2
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• pp.45-51
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• 1999

To find out the characteristics and trend of dust fall in open cut limestone mine in-situ measurement and wind tunnel tests were carried out. In-siti measurement was done by two dust fall samplers at the Halls mine for 60 days. The laboratory test was done in the 100m long temporary wind tunnel installed at the yard of the institute. The most of dust falled within 25m form the dust source and only less than 0.5% defused up to over 100 meters. It was known that the dust fall at 100m away from souces were negligible.

• Wind and Structures
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• v.31 no.6
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• pp.561-573
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• 2020

Unsteady self-excited forces are commonly represented by parametric models such as rational functions. However, this requires complex multiparametric nonlinear fitting, which can be a challenging task that requires know-how. This paper explores the alternative nonparametric modeling of unsteady self-excited forces based on relations between flutter derivatives. By exploiting the properties of the transfer function of linear causal systems, we show that damping and stiffness aerodynamic derivatives are related by the Hilbert transform. This property is utilized to develop exact simplified expressions, where it is only necessary to consider the frequency dependency of either the aeroelastic damping or stiffness terms but not both simultaneously. This approach is useful if the experimental data on aerodynamic derivatives that are related to the damping are deemed more accurate than the data that are related to the stiffness or vice versa. The proposed numerical models are evaluated with numerical examples and with data from wind tunnel experiments. The presented method can evaluate any continuous fitted table of interpolation functions of various types, which are independently fitted to aeroelastic damping and stiffness terms. The results demonstrate that the proposed methodology performs well. The relations between the flutter derivatives can be used to enhance the understanding of experimental modeling of aerodynamic self-excited forces for bridge decks.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2010.05a
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• pp.13-16
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• 2010

This study is an Investigation on the Watertightness Properties of Rain-Block System on the Sliding-Roof Joint of Large-Span Membrane Structures. In this experimental, we test the watertightness performance of joint part of sliding door in roof of large span membrane structure(for pilot project) under environment of rain and wind. A shape of rain water blocking systems of joint part in sliding door verifies the defects and effects of water leakage prevention in precipitation with the wind conditions. For obtaining watertightness of large span membrane structures, it is necessary quality of joints and performance, and quality of membrane material of a retractable roof as well as a closed roof. Also, for obtaining quality in joints, it is essential to make a watertightness guideline for design of large-span membrane.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1861-1868
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• 2016

In this paper, a three-phase AC-DC high step-up converter is developed for application to microscale wind-power generation systems. Such an AC-DC boost converter prossessess the property of the single-switch high step-up DC-DC structure. For power factor correction, the advanced half-stage converter is operated under the discontinuous conduction mode (DCM). Simulatanously, to achieve a high step-up voltage gain, the back half-stage functions in the continuous conduction mode (CCM). A high voltage gain can be obtained by use of an output-capacitor mass and a coupled inductor. Compared to the output voltage, the voltage stress is decreased on the switch. To lessen the conducting losses, a low rated voltage and small conductive resistance MOSFETs are adopted. In addition, the coupled inductor retrieves the leakage-inductor energy. The operation principle and steady-state behavior are analyzed, and a prototype hardware circuit is realized to verify the performance of the proposed converter.

• International Journal of Ocean System Engineering
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• v.2 no.2
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• pp.97-105
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• 2012

A all floating structures operating within a limited area require, stationkeeping to maintain the motions of the floating structure within permissible limits. In this study, methods for selecting and optimizing the mooring system Caisson for floating wind turbines in shallow water are investigated. The design of the mooring system is checked against the governing rules and standards. Adequately verifying the design of floating structures requires both numerical simulations and model testing, the combination of which is referred to as the hybrid method of design verification. The challenge in directly scaling moorings for model tests is the depth and spatial limitations of wave basins. It is therefore important to design and build equivalent mooring systems to ensure accurate static properties (global restoring forces and global stiffness).

• Journal of Adhesion and Interface
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• v.21 no.1
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• pp.27-33
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• 2020

Adhesion property of epoxy adhesive was evaluated with different surface roughness of glass fiber reinforced composite (GFRC) and optimized condition of surface roughness was confirmed. Different sizes of alumina (Al2O3) particles were blasted to GFRC to control surface roughness of GFRC using sand blasting method. The surface roughness was measured and quantified via surface roughness tester. Contact angle was measured using four types of different solvents. Surface energies and work of adhesion between epoxy adhesive and GFRCs were calculated with different surface roughness of GFRC. Adhesion property between epoxy adhesive and GFRCs was evaluated using single lap shear test and adhesion property increased with surface roughness of GFRC. The fracture surface of GFRCs was observed to evaluate adhesion property. Finally, the optimized roughness condition of GFRCs was confirmed.

• 보존과학연구
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• s.19
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• pp.35-60
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• 1998

Cultural properties are valuable objects, which have exposed insevere environment and inherited for a long time but we don’t have correct information concerning materials, structure and skill of manufacture. Because the cultural properties have been destroyed by the deterioration elements as like wind, this must be carefully treated for investigation of exhibition and storage. Even if the observation is scientific research, we must not take actual sample from the object for obtaining information concerning the nature materials and skill of manufacture. so it is elementary principle to use non-destructive investigation method as analytical methods for cultural property. This contribution discusses the present condition and problem of X-ray fluorescence acting as a representative non-destructive investigation method and the difference of statistics to be connected with determination and finally explains the intend facts for analysis of data.