• Bulletin of the Korean Chemical Society
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• v.20 no.11
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• pp.1329-1334
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• 1999

The curing characteristics of diglycidyl ether of bisphenol A (DGEBA) with diaminodiphenylmethane (DDM) as a curing agent were studied using differential scanning calorimetry (DSC), rheometrics mechanical spectrometry (RMS), and dielectric analysis (DEA). The isothermal curing kinetics measured by DSC were well represented with the generalized auto-catalytic reaction model. With the temperature sweep, the inverse relationship between complex viscosity measured by RMS and ionic conductivity obtained from DEA was established indicating that the mobility of free ions represented by the ionic conductivity in DEA measurement and the chain segment motion as revealed by the complex viscosity measured from RMS are equivalent. From isothermal curing measurements at several different temperatures, the ionic conductivity contribution was shown to be dominant in the dielectric loss factor at the early stage of cure. The contribution of the dipole relaxation in dielectric loss factor became larger as the curing further proceeded. The critical degrees of cure, at which the dipolar contribution in the dielectric loss factor starts to appear, increases as isothermal curing temperature is increased. The dielectric relaxation time at the same degree of cure was shorter for a sample cured at higher curing temperature.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.1 s.145
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• pp.75-86
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• 2006

The scantling and structural design work is done during the initial stage in yacht design. This paper studies a procedure of the structural design for yacht with an illustrative design. Scantling of structural members and loads are defined based on the rules suggested by ISO(International Standard Organization) and ABS(American Bureau of Shipping). Also, FEA(Finite Element Analysis) model is presented for a practical guide for structural analysis. An equivalent structural element is used to simplify the composite material for the analysis.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.2
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• pp.86-90
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• 1994

This paper attempts to incorporate the initial crack damage effect into the existing idealized plate unit. For this purpose, a new concept which indicates the equivalent, reduced material properties due to initial cracks at the structural unit level, not at he microscopic aspect, is suggested, and a simplified mechanical plate model for the initially cracked plate in axial tension is formulated as a function of initial crack length, based on the finite-element solutions obtained by crack propagation analysis.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.389-397
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• 2010

Concrete has excellent mechanical properties, high durability, and economical advantages over other construction materials. Nevertheless, it is not an easy task to apply concrete to long span bridges. That's because concrete has a low strength to weight ratio. Ultra high performance concrete (UHPC) has a very high strength and hence it allows use of relatively small section for the same design load. Thus UHPC is a promising material to be utilized in the construction of long span bridges. However, there is a possibility of crack generation during the curing process due to the high binder ratio of UHPC and a consequent large amount of hydration heat. In this study, adiabatic temperature rise and mechanical properties were modeled for the stress analysis due to hydration heat. Adiabatic temperature rise curve of UHPC was modeled superposing 2-parameter model and S-shaped function, and the Arrhenius constant was determined using the concept of equivalent time. The results are verified by the mock-up test measuring the temperature development due to the hydration of UHPC. In addition, models for mechanical properties such as elastic modulus, tensile strength and compressive strength were developed based on the test results from conventional load test and ultrasonic pulse velocity measurement.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.459-465
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• 2015

There exist different kinds of aircrafts, such as conventional airplane, rotorcraft, fighter, and unmanned aerial vehicle. Their shape and feature are dependent upon their own assigned mission. One of the fundamental analyses performed during the aircraft design is the structural analysis. It becomes more complicated and requires severe computations because of the recent complex trends in aircraft structure. In order for efficiency in the structural analysis, a simplified approach, such as equivalent beam or plate model, is preferred. However, it is not clear which analysis will be appropriate to analyze the realistic configuration, such as an aircraft wing, i.e., between an equivalent beam and plate analysis. It is necessary to assess the limitation for both the one-dimensional beam analysis and the two-dimensional plate theory. Thus, in this paper, the static structural analysis results obtained by EDISON solvers were compared with the three-dimensional results obtained from MSC NASTRAN. Before that, EDISON program was verified by comparing the results with those from MSC NASTRAN program and other analytic solutions.

• Tunnel and Underground Space
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• v.31 no.4
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• pp.270-288
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• 2021

We proposed a numerical method to simulate the hydro-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) in the paper. As a part of DECOVALEX-2023 Task G, we verified the method via benchmarks with analytical solutions. DECOVALEX-2023 Task G aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as a group of tetrahedral grains and calculated the interaction of the grains and their interfaces using 3DEC. The micro-parameters of the grains and interfaces were determined by a new methodology based on an equivalent continuum approach. In benchmark modeling, a single fracture embedded in the rock was examined for the effects of fracture inclination and roughness, the boundary stress condition and the applied pressure. The simulation results showed that the developed numerical model reasonably reproduced the fracture slip induced by boundary stress condition, the fracture opening induced by fluid injection, the stress distribution variation with fracture inclination, and the fracture roughness effect. In addition, the fracture displacements associated with the opening and slip showed good agreement with the analytical solutions. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• Korean Journal of Acupuncture
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• v.21 no.2
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• pp.47-67
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• 2004

Objectives : In the present study, the effect of Scolopendrid Water-Alcohol Extract (SWAE) applied to acupuncture point BL23 (Shinsu) on the neuropathic pain was examined. A common source of persistent pain in humans is the neuropathic pain. Anti-convulsant drugs are used to treat the neuropathic pain. In the oriental medicine, Scolopendrid was used for long time to treat convulsant syndrome and back pain, etc. Methods : On the bases of the Scolopendrid clinical application, the effect of SWAE applied to the acupuncture point was tested in the rat model of neuropathic pain. Neuropathic pain was induced by tight ligation of L5 spinal nerve. When rats developed pain behaviors, One hundred microliter of SWAE was applied into the ipsilateral BL23 point at a dose of 10 mg/ml under enflurane anesthesia. The foot withdraw latency of the hind limb was measured for an indicator of pain level after each manipulation. Results : SWAE injection increased the mechanical threshold of the foot in the rat model of neuropathic pain significantly for the duration of 4h, suggesting a partial alleviation of pain. SWAE applied to BL23 point produced a significant improvement of mechanical sensitivity of the foot lasting for at least 4h. However, neither contralateral BL23 point, ST25 (Chonchu) point, nor LR3 (Taechung) point produce as much increase of mechanical sensitivity as ipsilateral BL23 point. And, this increase of mechanical sensitivity was dose-dependent. The improvement of mechanical threshold was interpreted as an analgesic effect. In addition, the analgesic effect of Scolopendrid 4 mg/kg injection is equivalent to that of gabapentin 50 mg/kg injection. The relations between SWAE-induced analgesia and endogenous nitric oxide(NO), inducible NO synthase (iNOS)/neuronal NO synthase (nNOS) were also examined. Results were turned out that both NO production and nNOS/iNOS protein expression which are increased by nerve injury were suppressed by SWAE injection applied to BL23 point. Conclusions : The data suggest 1) that SWAE produces a potent analgesic effect on the neuropathic pain model in the rat and 2) that SWAE-induced analgesia modulate endogenous NO through the suppression of nNOS/iNOS protein expression.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.9-19
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• 2020

An integrated finite element model composed of a boiler and its supporting steel structure for a 375-MW coal-fired power plant was developed. This study used the developed model for seismic analysis using SAP2000 software. For the complex superheaters, reheaters, economizers, and membrane walls of the boiler, which consisted of numerous tubes, a method of modeling them by the equivalent elements in the viewpoint of stiffness and/or inertia was proposed. In addition, a method of modeling for the connection between the boiler and steel structure was proposed. Many hangers that connect the boiler to the girders of a steel structure were transformed into equivalent hangers by decreasing the number. The displacements of the boiler stoppers on the buckstay and the posts of the steel structure were coupled by considering their interface condition. Static analysis under the self-loading condition for the developed integrated model was implemented, and the results of deformation indicated that the behavior of the steel members and the major components of the boiler were appropriate. In conclusion, the integrated model developed in this study can be used to evaluate the safety of the boiler and steel structure under seismic loads.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.5
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• pp.311-320
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• 2017

Suppression of sloshing is essential to achieve fast transportation and stable maneuvering of tanks partially filled with liquid. In this study, numerical simulations are performed to investigate the effects of the acceleration magnitude and the acceleration duration of triangular velocity profiles on sloshing when a rectangular tank moves horizontally. We previously reported, based on only the first natural mode, that sloshing is significantly suppressed when the acceleration duration equals the first natural period of sloshing. On the other hand, the present CFD simulations find the best acceleration duration for minimum sloshing and explains the results considering higher modes as well as the first mode. We also perform the analysis using an equivalent model based on masses and springs, and evaluate its accuracy by comparing it with the CFD simulation results.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.2000-2010
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• 2021

Mechanical moduli, such as Young's modulus (E), Bulks modulus (B), Shear modulus (S), longitudinal modulus (L), Poisson's ratio (σ) and micro Hardness (H) were theoretically calculated for (100-x)TeO₂+x MgO glasses, where x = 10, 20, 30, 40 and 45 mol%, based on the Makishima-Mackenzie model. The estimated results showed that the mechanical moduli and the microhardness of the glasses were improved with the increase of the MgO contents in the TM glasses, while Poisson's ratio decreased with the increase in MgO content. Moreover, the radiation shielding capacity was evaluated for the studied TM glasses. Thus, the linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), transmission factor (TF) and half-value thickness (𝚫_0.5) were simulated for gamma photon energies between 0.344 and 1.406 MeV. The simulated results showed that glass TM10 with 10 mol % MgO possess the highest LAC and varied in the range between 0.259 and 0.711 cm^-1, while TM45 glass with 45 mol % MgO possess the lowest LAC and vary in the range between 0.223 and 0.587 cm^-1 at gamma photon energies between 0.344 and 1.406 MeV. Furthermore, the BXCOM program was applied to calculate the effective atomic number (Z_eff), equivalent atomic number (Z_eq) and buildup factors (EBF and EABF) of the glasses. The effective removal cross-section for the fast neutrons (ERCSFN, ∑_R) was also calculated theoretically. The received data depicts that the lowest ∑_R was achieved for TM10 glasses, where ∑_R = 0.0193 cm² g^-1, while TM45 possesses the highest ERCSFN where ∑_R = 0.0215 cm² g^-1.