• Structural Engineering and Mechanics
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• v.40 no.5
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• pp.665-688
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• 2011

This paper presents a theoretical analysis for the free vibration of rectangular tanks partially filled with an ideal liquid. Wet dynamic displacements of the tanks are approximated by combining the orthogonal polynomials satisfying the boundary conditions, since the rectangular tanks are composed of four rectangular plates. The classical boundary conditions of the tanks at the top and bottom ends are considered, such as clamped, simply supported, and clamped-free boundary conditions. As the facing rectangular plates are assumed to be geometrically and structurally identical, the vibration modes of the facing plates of the tanks can be divided into two categories: symmetric and antisymmetric modes with respect to the planes passing through the center of the tanks and perpendicular to the free liquid surface. The liquid displacement potentials satisfying the Laplace equation and liquid boundary conditions are derived, and the wet dynamic modal functions of a quarter of the tanks can be expanded by the finite Fourier transform for compatibility requirements along the contacting surfaces between the tanks and liquid. An eigenvalue problem is derived using the Rayleigh-Ritz method. Consequently, the wet natural frequencies of the rectangular tanks can be extracted. The proposed analytical method is verified by observing an excellent agreement with three-dimensional finite element analysis results. The effects of the liquid level and boundary condition at the top and bottom edges are investigated.

• Polymer(Korea)
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• v.37 no.1
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• pp.41-46
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• 2013

The glass transition temperature ($T_g$) and conversion (${\alpha}$) were measured for a diglycidyl ether of bisphenol A (DGEBA) epoxy/aromatic amine system incorporated with an organic-inorganic hybrid molecule, polyhedral oligomeric silsesquioxane (POSS). Samples isothermally cured at varying cure temperatures and times were analyzed by differential scanning calorimetry (DSC). $T_g$ vs. ln (time) data at an arbitrary reference were superposed by time-temperature shifts for the kinetically controlled reaction, and the shift factors were used to calculate an Arrhenius activation energy. Influence of POSS was investigated from $T_g$ vs. ${\alpha}$ data, which in turn were fitted with DiBenedetto equation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.3
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• pp.715-722
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• 2014

Three twisted rudders fit for large container ships have been developed; 1) the Z-twisted rudder that is an asymmetry type taking into consideration incoming flow angles of the propeller slipstream, 2) the ZB-twisted rudder with a rudder bulb added onto the Z-twisted rudder, and 3) the ZB-F twisted rudder with a rudder fin attached to the ZB-twisted rudder. The twisted rudders have been designed computationally with the hydrodynamic characteristics in a self-propulsion condition in mind. The governing equation is the Navier-Stokes equations in an unsteady turbulent flow. The turbulence model applied is the Reynolds stress. The calculation was carried out in towing and self-propulsion conditions. The sliding mesh technique was employed to simulate the flow around the propeller. The speed performances of the ship with the twisted rudders were verified through model tests in a towing tank. The twisted versions showed greater performance driven by increased hull efficiency from less thrust deduction fraction and more effective wake fraction and decreased propeller rotating speed.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.285-290
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• 2009

The main thrust of this paper is to investigate acceptable supply air conditions of a dedicated outdoor air system (DOAS) for highrise apartment buildings. As for a typical $132-m^2$ apartment unit, it was assumed that centralized DOAS-Ceiling Radiant Cooling Panel was installed. Transient behavior and control characteristics of each system were modeled numerically using a commercial equation solver program. The optimized dew point temperature of the DOAS was discussed on the basis of the ASHRAE standard 62.1-2007 and the current Korean ventilation standard for apartments. It was found that the optimized dew point temperature of the DOAS supply air accommodating total latent load of a space is $11-12^{\circ}C$ and the appropriate supply air temperature of the DOAS is $11-12^{\circ}C$ in cooling period and neutral temperature of $18-20^{\circ}C$ in intermediate period.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.624-630
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• 2006

This paper studies a modeling to demonstrate predicted reliability of the train control system components by performing an accelerated stress test. There are two tests for demonstrating predicted reliability; test run at the whole system level, and accelerated life test and accelerated stress test at the component level. In this paper, we imposed accelerated stress on the system and studied the train control system modeling for the accelerated stress test, which demonstrates predicted reliability according to whether or not the equipment is operating. Reliability of train control system consisting of electronic components varies drastically according to temperature so we considered the Arrhenius equation and the activation energy of electronic components. We also used reliability modeling with weighted average and calculated time necessary to complete the accelerated stress test on train control system.

• Proceedings of the Materials Research Society of Korea Conference
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• 1993.05a
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• pp.99-100
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• 1993

Calorimetric (D.S.C) studies were carried out on the nylon 4,6 single crystals grown from 1,4-butanediol solution at various crystallisation temperatures, based on the assessment of the lamellar thickness by small angle x-ray scattering. Samples were annealed mainly ot get rid of residual solvents inside the crystals. The effect of annealing on the crystal perfection is inferred from the measured thermal properties of the crystals. Accordig to the scanning rates less than 80 K/min., D. S C. melting peaks indicate that changes in the internal morphology of nylon 4,6 crystals preapred at different crystallisation temeratures yield a thermodynamic melting temperature. Tm, of 319 $^{\circ}C$, for the infinitely extended crystal thickness (1/ι). The obtained heat of fusion value for the inginite crystal thickness, Ho, was 270 J/g from the plot of measured feat of fusion ($\Delta$Hm) vs. reciprocal crystal thickness (1/ι). based on these values, the fold surface energy, $\delta$e. of 65.4 erg/$\textrm{cm}^2$ was obtained from Hoffman-Waeeks equation. The thermodynamic melting temperature and heat of fusion of the infinite crystal thickness for the solution grow nylon 4,6 single crystals are found to be higher than of the reported corresponding solution grown nylon 6,6 single crystals. pbtained crystallinity from D. S. C measurements ranges from 40 to 50 %, which is close to the reported yalue for the nylon 6,6 single ctystals but lower than we expected.

• Journal of Ocean Engineering and Technology
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• v.26 no.2
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• pp.14-19
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• 2012

There are insufficient data to consider the effect zone for the marine life of coastal fisheries, because no standard has been defined for the sound level of marine life. In this study, equations for distance attenuation were used to determine the effect zone for oceanic noises. A reference noise level was divided into 4 parts to consider the characteristics of the fishes, and the effect zone of each reference noise level was determined. To increase the reliability of the effect scope, approximately 100 repetitions of blasting work split into several parts by the boring depth, the sound level of the source caused by an increase in weight, and the effect zone were calculated using the prediction equation. According to the prediction, the maximum distance of the effect zone was 4.92 km.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.433-438
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• 2011

In this study, CdS combined activated carbon/$TiO_2$ (CdS-AC/$TiO_2$) composites were prepared by a sol-gel method to improve the photocatalytic performance of $TiO_2$. These composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and UV-vis analysis. The photocatalytic activities were examined by the degradation of methylene blue (MB) under visible light irradiation. The photodegradation rate of MB under visible light irradiation reached 90.1% in 120 min. The kinetics of MB degradation was plotted alongside the values calculated from the Langmuir-Hinshelwood equation. The 0.2 CAT sample showed the best photocatalytic activity, which might be due to an increase in the photo-absorption effect by activated carbon and the cooperative effect of CdS.

• Computers and Concrete
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• v.20 no.4
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• pp.429-437
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• 2017

In this study, the effect of the tensile strength and ratio of disc spacing to penetration depth on the efficiency of tunnel boring machine (TBM) is investigated using Particle flow code (PFC) in two dimensions. Models with dimensions of $150{\times}70mm$ made of rocks with four different tensile strength values of 5 MPa, 10 MPa, 15 MPa and 20 MPa were separately analyzed and two "U" shape cutters with width of 10 mm were penetrated into the rock model by velocity rate of 0.1 mm/s. The spacing between cutters was also varied in this study. Failure patterns for 5 different penetration depths of 3 mm, 4 mm, 5 mm, 6 mm, and 7 mm were registered. Totally 100 indentation test were performed to study the optimal tool-rock interaction. An equation relating mechanical rock properties with geometric characteristics for the optimal TBM performance is proposed. The results of numerical simulations show that the effective rock-cutting condition corresponding to the minimum specific energy can be estimated by an optimized disc spacing to penetration depth, which, in fact, is found to be proportional to the rock's tensile strength.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.3
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• pp.146-152
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• 2004

Cost effective simulation schemes for Wind Power Generation Systems (WPGS) considering wind turbine types, generators and load capacities have been strongly investigated by researchers. As an alternative, a true weather condition based simulation method using a real-time digital simulator (RTDS) is experimented in this paper for the online real-time simulation of the WPGS. A stand-alone WPGS is, especially, simulated using the Simulation method for WPGS using Real Weather conditions (SWRW) in this work. The characteristic equation of a wind turbine is implemented in the RTDS and a RTDS model component that can be used to represent any type of wind turbine in the simulations is also established. The actual data related to weather conditions are interfaced directly to the RTDS for the purpose of online real-time simulation of the stand-alone WPGS. The outcomes of the simulation demonstrate the effectiveness of the proposed simulation scheme. The results also signify that the cost effective verification of efficiency and stability for the WPGS is possible by the proposed real-time simulation method.