• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.734-740
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• 2004

In this work, the effect of composite couplings and mass distributions on hub loads of a hingeless rotor in forward flight is investigated. The hingeless composite rotor is idealized as a laminated thin-walled box-beam. The nonclassical effects such as transverse shear and torsion warping are considered In the structural formulation. The nonlinear differential equations of motion are obtained by applying Hamilton’s principle. The blade responses and hub loads are calculated using a finite element formulation both in space and time. The aerodynamic forces acting on the blade are calculated using the quasi-steady strip theory. The theory includes the effects of reversed flow and compressibility. The magnitude of elastic couplings obtained by MSC/NASTRAN is compared with the classical pitch-flap($\delta$$_3$) coupling. It Is observed that the elastic couplings and mass distributions of the blade have a substantial effect on the behavior of $N_{b}$ /rev hub loads. About 40％ hub loads is reduced by tailoring or redistributing the structural properties of the blade.e.

• Wind and Structures
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• v.31 no.3
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• pp.217-227
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• 2020

Based on translation models, both Gaussian and non-Gaussian wind fields are generated using spectral representation method for investigating the influence of non-Gaussian characteristics and directivity effect of wind load on fatigue damage of wind turbine. Using the blade aerodynamic model and multi-body dynamics, dynamic responses are calculated. Using linear damage accumulation theory and linear crack propagation theory, crack initiation life and crack propagation life are discussed with consideration of the joint probability density distribution of the wind direction and mean wind speed in detail. The result shows that non-Gaussian characteristics of wind load have less influence on fatigue life of wind turbine in the area with smaller annual mean wind speeds. Whereas, the influence becomes significant with the increase of the annual mean wind speed. When the annual mean wind speeds are 7 m/s and 9 m/s at hub height of 90 m, the crack initiation lives under softening non-Gaussian wind decrease by 10% compared with Gaussian wind fields or at higher hub height. The study indicates that the consideration of the influence of softening non-Gaussian characteristics of wind inflows can significantly decrease the fatigue life, and, if neglected, it can result in non-conservative fatigue life estimates for the areas with higher annual mean wind speeds.

• Journal of Environmental Health Sciences
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• v.18 no.1
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• pp.6-11
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• 1992

This study was carried out to investigate exposure level, size distribution, and respirable mass fraction of airborne coal dust and heavy metal concentration of respirable coal dust at each work site in coal briquet factory from July 1991 to September 1991. Geometric mean of total dust concentration was 10.88mg/m$^{3}$ at storage shop, 8.22mg/m$^{3}$ at pulverize shop, and 3.79mg/m$^{3}$ at rotary press shop, respectively, but those at storage and pulverize shop were higher than TLV. Geometric mean of respirable coal dust concentration wat 1.03mg/m$^{3}$ at storage shop, 0.78mg/m$^{3}$ at pulverize shop, and 0.55mg/m$^{3}$ at rotary press shop, respectively, which were lower than TLV Aerodynamic 50% cutoff diameter of the suspended coal dust was 5$\mu$m at rotary press shop and 6.8$\mu$m at storage shop, ranged to thoracic particulate defined by ACGIH, and deposited in the region of repiratory system. The mass fraction rate of respirable dust to the total coal dust was 26.2% at rotary press shop, 18.8% at storage shop, and 13.8% at pulverize shop, respectively. Heavy metal concentrations of the respirable coal dust were 0.028mg/m$^{3}$ ib Fe, 0.0081mg/m$^{3}$ in Cu, and 0.0039mg/m$^{3}$ in Pb.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.1-6
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• 2004

This paper shows the study on the design and another applications of the spray-freeze dryer for the production of valuable material powders. Powder production and handling has been an integral part of material extracting processing and pharmaceutical processing because of the wide use of oral dosage forms. There are a few commonly used powder preparation methods including mechanical milling, precipitaion, spray drying, freeze drying, and so on. In general, methods available for preparing inhalation powders are limited due to certain inhalation powder's sensitive nature to the processing environments. This is particularly true for preparing dry powder aerosols where the aerodynamic particle size($<5{\mu}m$) and the size distribution are pivotal. Supercritical fluid antisolvent and spray freeze drying have recently emerged as promising techniques for producing powders for use in microcapsulation. However, the aerosol applications of these powders are yet to be explored. The purpose of this study is to test the feasibility of using spray freeze-dried valuable material powders for aerosolization.

• Wind and Structures
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• v.13 no.3
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• pp.235-256
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• 2010

The aeroelastic stability of bridge decks equipped with multiple tuned mass dampers is studied. The problem is attacked in the time domain, by representing self-excited loads with the aid of aerodynamic indicial functions approximated by truncated series of exponential filters. This approach allows to reduce the aeroelastic stability analysis in the form of a direct eigenvalue problem, by introducing an additional state variable for each exponential term adopted in the approximation of indicial functions. A general probabilistic framework for the optimal robust design of multiple tuned mass dampers is proposed, in which all possible sources of uncertainties can be accounted for. For the purposes of this study, the method is also simplified in a form which requires a lower computational effort and it is then applied to a general case study in order to analyze the control effectiveness of regular and irregular multiple tuned mass dampers. A special care is devoted to mistuning effects caused by random variations of the target frequency. Regular multiple tuned mass dampers are seen to improve both control effectiveness and robustness with respect to single tuned mass dampers. However, those devices exhibit an asymmetric behavior with respect to frequency mistuning, which may weaken their feasibility for technical applications. In order to overcome this drawback, an irregular multiple tuned mass damper is conceived which is based on unequal mass distribution. The optimal design of this device is finally pursued via a full domain search, which evidences a remarkable robustness against frequency mistuning, in the sense of the simplified design approach.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.474-484
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• 2017

This paper studies the applicability of an efficient numerical model based on artificial neural networks (ANNs) to predict the dynamic responses of the wing structure of an airplane due to atmospheric turbulence in the time domain. The turbulence velocity is given in the form of a stationary Gaussian random process with the von Karman power spectral density. The wing structure is modeled by a classical beam considering bending and torsional deformations. An unsteady vortex-lattice method is applied to estimate the aerodynamic pressure distribution on the wing surface. Initially, the trim condition is obtained, then structural dynamic responses are computed. The numerical solution of the wing structure's responses to a random turbulence profile is used as a training data for the ANN. The current ANN is a three-layer network with the output fed back to the input layer through delays. The results from this study have validated the proposed low-cost ANN model for the predictions of dynamic responses of wing structures due to atmospheric turbulence. The accuracy of the predicted results by the ANN was discussed. The paper indicated that predictions for the bending moments are more accurate than those for the torsional moments of the wing structure.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.2 s.140
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• pp.80-87
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• 2005

A set of experiments was carried out for obtaining the velocity field around the hydrofoil of finite span, using a wing of the NACA 0012 section in a circulating water channel. DPIV technique was used to measure the velocity field, and the velocity measurements along the span were done for 3 speeds, 3 submerged depths, and 4 angles of attack. Experimental data are compared with the theoretical assumptions, as well as the numerical findings by Lee and Lee(2004). Special care is given to the flow near the tips and in the region close to the leading edge. Though indirect, using the measured data of the velocity, it is now possible to compare the aerodynamic and the hydrodynamic strength of the circulation distribution of a wing in the framework of the lifting-line theory.

• 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.32 no.5
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• pp.439-452
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• 2021

The concept of Performance objective assessment is extended to wind engineering. This approach applies using the Database-Assisted Design technique, relying on the aerodynamic database provided by the National Institute of Standards and Technology (NIST). A structural model of a low-rise building is analyzed to obtain influence coefficients for internal forces and displacements. Combining these coefficients with time histories of pressure coefficients on the envelope produces time histories of load effects on the structure, for example knee and ridge bending moments, and eave lateral drift. The peak values of such effects are represented by an extreme-value Type I Distribution, which allows the estimation of the gust wind speed leading to the mean hourly extreme loading that cause specific performance objective compromises. Firstly a fully correlated wind field over large tributary areas is assumed and then relaxed to utilize the denser pressure tap data available but with considerably more computational effort. The performance objectives are determined in accordance with the limit state load combinations given in the ASCE 7-16 provisions, particularly the Load and Resistance Factor Design (LRFD) method. The procedure is then repeated for several wind directions and different dominant opening scenarios to determine the cases that produce performance objective criteria. Comparisons with two approaches in ASCE 7 are made.

• Journal of Environmental Science International
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• v.24 no.5
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• pp.679-687
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• 2015

Atmospheric aerosol particles were investigated at GNTECH university in Jinju city. Samples were collected using the Nanosampler period from January to December 2014. The Nanosampler is a 6 stage cascade impactor(1 stage : > $10{\mu}m$, 2 stage : $2.5{\sim}10{\mu}m$, 3 stage : $1.0{\sim}2.5{\mu}m$, 4 stage : $0.5{\sim}10{\mu}m$, 5 stage : $0.1{\sim}0.5{\mu}m$, back-up : < $0.1{\mu}m$) with the stages having 50% cut-off ranging from 0.1 to $10{\mu}m$ in aerodynamic diameter. The mass size distribution of Atmospheric aerosol particles was unimodal with peak at $1.0{\sim}2.5{\mu}m$ or $0.5{\sim}1.0{\mu}m$. The annual average concentrations of TSP, $PM_{10}$, $PM_{2.5}$, $PM_1$, $PM_{0.5}$ and $PM_{0.1}$ were $44.0{\mu}g/m^3$, $40.3{\mu}g/m^3$, $31.4{\mu}g/m^3$, $18.0{\mu}g/m^3$, $8.0{\mu}g/m^3$, $3.0{\mu}g/m^3$, respectively. On average $PM_{10}$, $PM_{2.5}$, $PM_1$, $PM_{0.5}$ and $PM_{0.1}$ make up 0.91, 0.70, 0.41, 0.19 and 0.07 of TSP, respectively. The annual average of $PM_{2.5}/PM_{10}$ ratio was 0.77.