• Wind and Structures
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• v.30 no.2
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• pp.211-217
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• 2020

Vibrations of a wind turbine blade have a negative impact on its performance and result in failure of the blade, therefore an approach to effectively control vibration in turbine blades are sought by wind industry. The small domestic horizontal axis wind turbine blades induce flap wise (out-of-plane) vibration, due to varying wind speeds. These flap wise vibrations are transferred to the structure, which even causes catastrophic failure of the system. Shape memory alloys which possess physical property of variable stiffness across different phases are embedded into the composite blades for active vibration control. Previously Shape memory alloys have been used as actuators to change their angles and orientations in fighter jet blades but not used for active vibration control for wind turbine blades. In this work a GFRP blade embedded with Shape Memory Alloy (SMA) and tested for its vibrational and material damping characteristics, under martensitic and austenite conditions. The embedment portrays 47% reduction in displacement of blade, with respect to the conventional blade. An analytical model for the actuated smart blade is also proposed, which validates the harmonic response of the smart blade.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.3
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• pp.8-16
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• 2006

This paper discusses design sensitivity analysis and its application to a structural dynamics modification. Eigenvalue derivatives are determined with respect to the element parameters, which include intrinsic property parameters such as Young's modulus, density of the material, diameter of a beam element, thickness of a plate element, and shape parameters. Derivatives of stiffness and mass matrices are directly calculated by derivatives of element matrices. The first and the second order derivatives of the eigenvalues are then mathematically derived from a dynamic equation of motion of FEM model. The calculation of the second order eigenvalue derivative requires the sensitivity of its corresponding eigenvector, which are developed by Nelson's direct approach. The modified eigenvalue of the structure is then evaluated by the Taylor series expansion with the first and the second derivatives of eigenvalue. Numerical examples for simple beam and plate are presented. First, eigenvalues of the structural system are numerically calculated. Second, the sensitivities of eigenvalues are then evaluated with respect to the element intrinsic parameters. The most effective parameter is determined by comparing sensitivities. Finally, we predict the modified eigenvalue by Taylor series expansion with the derivatives of eigenvalue for single parameter or multi parameters. The examples illustrate the effectiveness of the eigenvalue sensitivity analysis for the optimization of the structures.

• Journal of Korea Foundry Society
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• v.37 no.2
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• pp.38-44
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• 2017

Given that the conventional extrusion of high-strength Al alloys such as 7075 aluminum alloys is difficult due to their very low extrudability as compared to that of 6061 aluminum alloys, thixo-extrusion can be used to obtain a high-strength material easily at a lower extrusion pressure as compared to conventional extrusion. In this study, hot- and thixo-extruded 7075 aluminum alloys are prepared by a vertical forward extrusion process and their microstructures, hardness levels, and compressive properties are investigated. Hot-extruded alloy bars are assessed to obtain a microstructure elongated in the extrusion direction, whereas with thixo-extruded alloy bars, it was possible to obtain a microstructure having fine and equiaxed grains by dynamic recrystallization. The resulting isotropy and improved formability at the hot deformation temperature of the thixo-extruded alloy were attributed to the fine and equiaxed grains formed by the thixo-extrusion process.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.5
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• pp.565-572
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• 2002

The design concept of diesel engines for sea-going ships has been directed to Low-speed/Long-Stroke type to improve the efficiencies of combustion and propelling. But time-delay inevitable at low speed gives much difficulties for governors to control the engine speed because they would be apt to go into unstable region especially when operating at low speed. The purpose of this paper is to study the problem of how the governor gain can be calculated dynamically in accordance with the valiance of engine speed to locate the engine still on the properly stable condition. In this study, the property of diesel engine was described as composed of combustion element including dead time and rotating element, and the ultimate gain for the speed control system to be located on the condition of stability limit was proposed based on the frequency characteristics. And the target gains with optimized stability also were proposed by giving proper margin to these ultimate conditions. The results were applied to a model system and the availability was confirmed to be satisfactory.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1801-1809
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• 2000

A study on the topology optimization of Hard-Disk-Driver(HDD) actuator arm in free vibration is presented. The purpose of this research is to increasse the natural frequency of the first lateral mode of the HDD actuator arm under the constraint of total moment of inertia, so as to facilitate the position control of high speed actuator am. The first lateral mode is an important factor in the position control process. Thus the topology optimization for 2-D model of the HDD actuator arm is considered. A new objective function corresponding to multieigenvalue optimization is suggested to improve the solution of the eigenvalue optimization problem. The material density of the structure is treated as the design variable and the intermediate density is penalized. The effects of different element types and material property functions on the final topology are studied. When the problem is discretized using 8-node element of a uniform density, the smoothly-varying density field is obtained without checker-board patterns incurred. As a result of the study an improved design of the HDD actuator arm is suggested. Dynamic characteristics of the suggested design are compared computationally with those of the old design. With the same amount of the moment of inertia, the natural frequency of the first lateral mode or the suggested design is subsequently increased over the existing one.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.419-422
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• 2002

We have studied dielectric properties in the smectic phases of 4-(6-ethoxy-1-trifluoromethyl-hexyloxycarbonyl)-phenyl-4-Nonyloxybiphenyl-4-carboxylat ( TFMEOHPNBC ) having fluorine attached to one of its benzene rings. Homogeneous and homeotropic 1.5 and 5${\mu}m$ thick test cells were prepared to analyze molecular dynamic property. We measured capacitance as a function of temperature in the frequency range between 20 Hz and 100 kHz by using HP4284A LCR meter. We observed that the homogeneous cell has high dielectric constant causing dipole moment in smectic $C^{\ast}$ phase, but we can see the dipole moments are canceled out in antiferroelectric phase. It is found that there are two kind of the relaxation director fluctuation below 100 kHz. The first is ionic or space charge contribution below 10 Hz, and the second is Goldstone mode near 1-2 kHz. We will discuss molecular dynamics in smectic phase from extra information such as x-ray and electrooptic data.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.456-459
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• 2003

Polychloroprene(CR) is well known as elastomer commonly utilized in the electrical. It is mainly used for cable jacket and insulator. The irradiation degradation property of polymer materials is very important to prevent unexpected accidents in the Nuclear Power Plant(NPP). The irradiation degradation is caused by the oxidation of polymer materials, and this oxidation is occurred by oxygen radical produced from air. In this study, we evaluate the oxidation properties of CR. CR is irradiated for 200, 400, 600, 1000 kGy radiation dose. The oxidation properties of irradiated CR are investigated by differential scanning calorimetry, dynamic mechanical properties and FT-IR/ATR. Glass transition temperature(Tg), decomposition onset temperature(DOT), loss modulus and mechanical tan $\delta$ values are compared together. The irradiation limit of CR in the NPP, is known for 500 kGy, and this is exactly matched with investigated results.

• Journal of KIISE:Databases
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• v.27 no.1
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• pp.79-89
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• 2000

For processing signature file in parallel, an effective signature file declustering method is needed. The Linear Code Decomposition Method(LCDM) used for the Hamming Filter may give a good performance in some cases, but due to its static property, it fails to evenly decluster signature file when signature are skewed. In addition, it has other problems such as limited scalability and non-determinism. In this paper we propose a new signature file declustering method, called Inner-product method, which overcomes those problems in the LCDM. The Inner-product method declusters signature file dynamically based on the signature difference which is computed by using signature inner product. we show through the simulation experiment that the Inner-product outperforms the LCDM under various data workloads.

• Fisheries and Aquatic Sciences
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• v.17 no.3
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• pp.299-304
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• 2014

The objective of this study was to elucidate the physicochemical characteristics of gelatin extracted from jellyfish Rhopilema hispidum. We investigated the proximate composition, amino acids, gel strength, gelling/melting points, dynamic viscoelastic properties, and viscosity of jellyfish gelatin. Jellyfish gelatin contained 12.2% moisture, 1.5% lipid, 2.1% ash, and 84.8% protein. Glycine, hydroxyproline, proline, and alanine were the predominant amino acids. The gelatin showed a gel strength of 31.2 kPa, a gelling point of $18.0^{\circ}C$, and melting point of $22.3^{\circ}C$. The gelatin was composed of ${\alpha}_1$-chain, ${\alpha}_2$-chain, ${\beta}$-chain, and ${\gamma}$-chain. During cooling and heating process, jellyfish gelatin showed lower elastic modulus (G') and loss modulus (G") values than mammalian gelatin. Jellyfish gelatin did not show superior rheological properties to mammalian gelatin, like other fish gelatin; however, it can be used in various food and cosmetic products not requiring high gel strength.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.171-176
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• 2011

The purposes of the research were to evaluate system performance and response of building structure under external load for full scale modal-testing-tower applied toggle bracing and lead rubber damper(LRD). The dynamic properties of the structure were measured before and after installing damper under harmonic excitation using the AMD and the results were compared. The harmonic excitation condition is to increase 0.01Hz sine sweep signal from 0.49Hz to 0.63Hz. As a result of measuring resonant frequency, before installing damper is 0.55Hz and after installing damper is 0.62Hz. The experimental results after installing damper were also distinguished from simulation results and the main cause of this results is temperature dependency property of rubber material.