• Geomechanics and Engineering
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• v.30 no.6
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• pp.565-577
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• 2022

In this study, a series of three-dimensional numerical parametric study was conducted to investigate deformation mechanisms of an existing box culvert due to an adjacent multi-propped basement excavation in clays. Field measurements from an excavation case history are first used to calibrate a baseline Hardening Soil Small Strain (HS-small) model, which is subsequently adopted for parametric study. Results indicate that the basement-box culvert interaction along the basement centerline can be considered as a plane strain condition when the length of excavation (L) reaches 14 H_e (i.e., final excavation depth). If a plane strain condition (i.e., L/H_e=12.0) is assumed for analyzing the basement-box culvert interaction of a short excavation (i.e., L/H_e=2.0), the maximum settlement and horizontal movement of the box culvert are overestimated significantly by up to 15.7 and 5.1 times, respectively. It is also found that the deformation of box culvert can be greatly affected by the basement excavation if the distance between the box culvert and retaining wall is less than 1.5 H_e. The induced deformation in the box culvert can be dramatically reduced by improving the ground inside the excavation or implementing other precautionary measures. For example, by adding jet grouting columns within the basement and installing an isolation wall behind the retaining structures, the maximum settlements of box culvert are shown to reduce by 37.2% and 13.4%, respectively.

• Structural Engineering and Mechanics
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• v.86 no.2
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• pp.167-180
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• 2023

This work applies a four-known quasi-3D shear deformation theory to investigate the bending behavior of a functionally graded plate resting on a viscoelastic foundation and subjected to hygro-thermo-mechanical loading. The theory utilizes a hyperbolic shape function to predict the transverse shear stress, and the transverse stretching effect of the plate is considered. The principle of virtual displacement is applied to obtain the governing differential equations, and the Navier method, which comprises an exponential term, is used to obtain the solution. Novel to the current study, the impact of the viscoelastic foundation model, which includes a time-dependent viscosity parameter in addition to Winkler's and Pasternak parameters, is carefully investigated. Numerical examples are presented to validate the theory. A parametric study is conducted to study the effect of the damping coefficient, the linear and nonlinear loadings, the power-law index, and the plate width-tothickness ratio on the plate bending response. The results show that the presence of the viscoelastic foundation causes an 18% decrease in the plate deflection and about a 10% increase in transverse shear stresses under both linear and nonlinear loading conditions. Additionally, nonlinear loading causes a one-and-a-half times increase in horizontal stresses and a nearly two-times increase in normal transverse stresses compared to linear loading. Based on the article's findings, it can be concluded that the viscosity effect plays a significant role in the bending response of plates in hygrothermal environments. Hence it shall be considered in the design.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.151-158
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• 2006

Centrifuge tests have shown that a uniformly placed sand layer will first initiate liquefaction near the surface and that liquefaction will progress downward during shaking. This appears to be in conflict with the overburden stress effect on soil liquefaction (i.e., $K_0$ effect) observed in laboratory testing. This discrepancy can be explained by stress-induced densification at depth which overcomes the effect of confining stress on liquefaction resistance. Stress densification occurs in centrifuge model tests but its effect has generally not been considered when preparing or evaluating centrifuge models. A new centrifuge model preparation method is proposed by considering stress-induced densification upon spin-up. The proposed method can be used to explore $K_0$ effects. The method is supported in this study by numerical predictions.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.364-372
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• 2023

The space reactor is the primary energy supply for future space vehicles and space stations. The radiator is one of the essential parts of a space reactor. Therefore, the research on radiators can improve the heat dissipation power, reduce the quality of radiators, and make the space reactor smaller. Based on MOOSE multi-physics numerical calculation platform, a simulation program for the combination of heat pipe and fin at the end of heat pipe radiator is developed. It is verified that the calculation result of this program is accurate and the calculation speed is fast. Analyze the heat transfer characteristics of the combination with heat pipe and fin, and obtain its internal temperature field. Based on the calculation results, the influence of structural parameters on the heat dissipation power is analyzed. The results show that when the fin width is 0.25 m, fin thickness is 0.002 m, condensing section length is 0.5425 m and heat pipe radius is 0.014 m, the power-mass ratio is the highest. When the temperature is 700K-900K, the heat dissipation power increases 41.12% for every 100K increase in the operating temperature. Smaller fin width and thinner fin thickness can improve the power-mass ratio and reduce the radiator quality.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.287-294
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• 2009

Suction Drain Method is a relatively new technique to improve soft ground using vacuum pressure which can be directly applied to the soft ground through drains that the pore water pressure around them are decreased without changing total stress. This can accelerate volume changes and increase strength of the ground. This paper shows the results of field test of the suction drain method applied at dredged and reclaimed clay. To evaluate the improvement effects of soft ground by the suction drain method, this paper analyzed real-time field measurements to the results of the laboratory tests and numerical analysis. The comparisons of the settlement and shear strength between suction drain method and surcharge preloading method show possibilities for replacement of the preloading methods. The settlements by suction drain method were 2.3 times larger and undrained shear strength were 300%~400% higher than surcharge method. Moreover, the water content is decreased about 30% and the preconsolidation pressure is increased about $0.52kgf/cm^2$.

• Earthquakes and Structures
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• v.25 no.1
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• pp.27-41
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• 2023

This study focused on nonlinear effective stress site response analysis using two coupled constitutive models, that is, the DM model (Dafalias and Manzari 2004), which incorporated a simple plasticity sand model accounting for fabric change effects, and the PMDY03 model (Khosravifar et al. 2018), that is, a 3D model for earthquake-induced liquefaction triggering and postliquefaction response. A detailed parametric study was conducted to validate the effectiveness of nonlinear site response analysis and porewater pressure (PWP) generation through a true coupled formulation for assessing the initiation of liquefaction at ground level. The coupled models demonstrated accurate prediction of liquefaction triggering, which was in line with established empirical liquefaction triggering relations in published databases. Several limitations were identified in the evaluation of liquefaction using the cyclic stress method, despite its widespread implementation for calculating liquefaction triggering. Variations in shear stiffness, represented by changes in shear wave velocity (Vs1), exerted the most significant influence on site response. The study further indicated that substantial differences in response spectra between nonlinear total stress and nonlinear effective stress analyses primarily occurred when liquefaction was triggered or on the verge of being triggered, as shown by excess PWP ratios approaching unity. These differences diminished when liquefaction occurred towards the later stages of intense shaking. The soil response was predominantly influenced by the higher stiffness values present prior to liquefaction. A key contribution of this study was to validate the criteria used to assess the triggering of level-ground liquefaction using true coupled effective-stress constitutive models, while also confirming the reliability of numerical approximations including the PDMY03 and DM models. These models effectively captured the principal characteristics of liquefaction observed in field tests and laboratory experiments.

• Computers and Concrete
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• v.32 no.1
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• pp.75-85
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• 2023

This work utilizes simplified higher-order shear deformation beam theory (HSDBT) to investigate the vibration response for functionally graded carbon nanotube-reinforced composite (CNTRC) beam. Novel to this work, single-walled carbon nanotubes (SWCNTs) are distributed and aligned in a matrix of polymer throughout the beam, resting on a viscoelastic foundation. Four un-similar patterns of reinforcement distribution functions are investigated for the CNTRC beam. Porosity is another consideration taken into account due to its significant effect on functionally graded materials (FGMs) properties. Three types of uneven porosity distributions are studied in this study. The damping coefficient and Winkler's and Pasternak's parameters are considered in investigating the viscosity effect on the foundation. Moreover, the impact of different parameters on the vibration of the CNTRC beam supported by a viscoelastic foundation is discussed. A comparison to other works is made to validate numerical results in addition to analytical discussions. The findings indicate that incorporating a damping coefficient can improve the vibration performance, especially when the spring constant factors are raised. Additionally, it has been noted that the fundamental frequency of a beam increases as the porosity coefficient increases, indicating that porosity may have a significant impact on the vibrational characteristics of beams.

• Advances in concrete construction
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• v.14 no.3
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• pp.195-204
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• 2022

As a brittle failure mode, punching-shear failure can be widely found in traditional RC slab-column connections, which may lead to the entire collapse of a flat plate structure. In this paper, a novel RC slab-column connection with inner steel truss was proposed to enhance the punching strength. In the proposed connection, steel trusses, each of which was composed of four steel angles and a series of steel strips, were pre-assembled at the periphery of the column capital and behaved as transverse reinforcements. With the aim of exploring the punching behavior of this novel RC slab-column connection, a static punching test was conducted on two full-scaled RC slab specimens, and the crack patterns, failure modes, load-deflection and load-strain responses were thoroughly analyzed to explore the contribution of the applied inner steel trusses to the overall punching behavior. The test results indicated that all the test specimens suffered the typical punching-shear failure, and the higher punching strength and initial stiffness could be found in the specimen with inner steel trusses. The numerical models of tested specimens were analyzed in ABAQUS. These models were verified by comparing the results of the tests with the results of the analyzes, and subsequently the sensitivity of the punching capacity to different parameters was studied. Based on the test results, a modified critical shear crack theory, which could take the contribution of the steel trusses into account, was put forward to predict the punching strength of this novel RC slab-column connection, and the calculated results agreed well with the test results.

• Journal of Hydrogen and New Energy
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• v.34 no.5
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• pp.526-534
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• 2023

To evaluate the risk of leakage when using liquid hydrogen, a leakage test was conducted using liquid nitrogen in an outdoor environment rather than a laboratory environment. To assume a real-scale continuous leak, liquid nitrogen was allowed to leak for 5 minutes through a pipe with a diameter of 25.4 mm at a design spill rate of 60 L/min. The measurement system consisted of devices for climate conditions, LN2 spread and vapor clouds. The main experimental results are the liquid pool radius and the concentration of vapor cloud, and the radius of the liquid pool was compared with the numerical analysis results.

• The Journal of the Acoustical Society of Korea
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• v.27 no.4
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• pp.178-182
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• 2008

In measurements of the vibration of structures underwater with a laser Doppler vibrometer, the surface vibration is measured by means of detecting the phase change of the laser beam due to the structural vibration. The laser beam passes through the sound field radiated from the vibrating structures underwater. It experiences an additional phase change due to the change in refractive index in the radiated sound field. This phase change due to the sound field may cause the error in surface vibration measurements. In this paper, this phase change due to the radiated sound filed has been analyzed. The numerical simulation has been peformed to evaluate the phase change in sound field radiated from an infinite cylindrical structure vibrating underwater.