• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.39-43
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• 2008

Determination of strain associated with shear modulus and damping ratio during torsional test is complicated. This is due to nonuniform stress-strain variation occurring linearly with radius in a soil specimen in torsion. A conventional equivalent radius approach proposed by Chen and Stokoe appears to be adequate for evaluating strain associated with shear modulus at low to intermediate strain levels. This approach is less accurate for damping measurement, particularly at high strain. Modified equivalent radius approach was used to account for the nonuniform stress-strain effect more precisely. The modified equivalent radius approach was applied for hyperbolic, modified hyperbolic, and Ramberg-Osgood models. The results illustrate the usefulness of the modified equivalent radius approach and suggest that using a single value of equivalent radius ratio to calculate strains is not appropriate.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.97-103
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• 2008

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.1
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• pp.43-55
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• 2008

The complexity of determining strain associated with shear modulus and damping ratio in torsional tests has been resolved by means of several approaches. Particularly, the modified equivalent radius approach is adequate to when generating the plots of equivalent radius ratio versus strain more effectively over any range of strains in resonant column and torsional shear (RC/TS) tests. The modified equivalent radius approach was applied for hyperbolic, modified hyperbolic, and Ramberg-Osgood models in evaluating damping ratio. Results showed that using a single value of equivalent radius ratio based on conventional equivalent radius approach is not appropriate. A new model was developed to consider the soil damping behavior at small strains as well as hysteretic damping and it was attempted to determine adjustments are required in evaluating strain associated damping when combining the two damping components.

• Structural Engineering and Mechanics
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• v.90 no.1
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• pp.97-106
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• 2024

This paper presents a significant contribution to aided design by conducting an analytical examination of geometric links with the aim of establishing criteria for assessing an analogy measure of the extrinsic geometric and kinematic characteristics of the Variable Compression Ratio (VCR) engine with a Geared Mechanism (GBCM) in comparison to the existing Fixed Compression Ratio (FCR) engine with a Standard-Reciprocating Crankshaft configuration. Employing a mechanical approach grounded in projective computational methods, a parametric study has been conducted to analyze the kinematic behavior and geometric transformations of the moving links. The findings indicate that in order to ensure equivalent extrinsic behavior and maintain consistent input-output performance between both engine types, precise adjustments of intrinsic geometric parameters are necessary. Specifically, for a VCR configuration compared to an FCR configuration, regardless of compression ratio and gearwheel radius, for the same crankshaft ratios and stroke lengths, it is imperative to halve lengths of connecting rods, and crank radius. These insights underscore the importance of meticulous parameter adjustment in achieving comparable performance across different engine configurations, offering valuable implications for design optimization.

• Journal of the Optical Society of Korea
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• v.17 no.6
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• pp.538-542
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• 2013

We propose a simple model to elucidate the dispersion behavior of spiraling modes on silver nanowire by finding correspondence parameters and building a simple equivalent relationship with the planar insulator-metal-insulator geometry. The characteristics approximated for the proposed structure are compared with the results from an exact solution obtained by solving Maxwell's equation in cylindrical coordinates. The effective refractive index for our proposed equivalent model is in good agreement with that for the exact solution in the 400-2000 nm wavelength range. In particular, when the radius of the silver nanowire is 100 nm, the calculated index shows typical improvements; the average percentage error for the real part of the effective refractive index is reduced to only 5% for the $0^{th}$ order mode (11.9% in previous results) and 1.5% for the $1^{st}$ order mode (24.8% in previous results) in the 400-800 nm wavelength range. This equivalent model approach is expected to provide further insight into understanding the important behavior of nanowire waveguides.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.639-647
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• 2002

A simplified analytical procedure is presented to estimate the reduction of elastic lateral stiffness of steel moment frames arising from the radius-cut dogbone weakening. With the original radius-cut dogbone shape, it is almost impossible or too complicated to integrate analytically the mathematical expressions encountered when applying the conjugate beam method to compute the beam deflection component. In this study, the problem is circumvented by replacing the original radius-cut dogbone with an equivalent dogbone of constant width. The equivalence between the two is established by imposing an equal dogbone elongation criterion. This approach is justified by using a calibrated finite clement analysis. Then, the elastic lateral deflection components from the column, panel zone, and beam are derived for a typical beam-column subassembly. The derived results can be used to evaluate the reduction of the frame lateral stiffness. Case studies conducted within some practical ranges of frame configurations show that the reduction in frame lateral stiffness due to the presence of dogbone cut is on the order of 1 to 2 percent and is reasonably negligible in practical sense.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.9
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• pp.191-199
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• 1999

In the continuous cutting process such as turning operation, chip control is thought very important to achieve the unmanned manufacturing system. The prediction of chip breakage under the given conditions is a substantial element for chip control. In this paper, a systematic approach to know the chip breaking region is represented under the concept of equivalent parameters. to Verify the suggested model, cutting experiments are executed with a commercial type and two other type chip breakers which have modified chip breaker parameters such as land width, groove width and nose radius. predicted chip breaking regions using the 3D cutting model agrees with those obtained from the experiments.

• Computers and Concrete
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• v.21 no.6
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• pp.717-726
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• 2018

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that $SiO_2$ nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as $SiO_2$ nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of $SiO_2$ nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.

• Computers and Concrete
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• v.24 no.2
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• pp.125-135
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• 2019

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that SiO2 nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as SiO2 nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of SiO2 nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.93-107
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• 2013

Thermal conduction of the particulate composites or granular materials can be widely used in porous materials and geotechnical engineering. And it has continued to develop "effective thermal conductivity" of medium by modeling energy relationship among particles in medium. This study focuses on the development of the effective thermal conductivity at the unsaturated conditions of soils using the modified network model approach assisted by synthetic 3D random packed systems (DEM method, Discrete Element Method) at the particle scale. To verify the network model, three kinds of glass beads and the Jumunjin sand are used to obtain experimental values at various unsaturated conditions. The PPE (Pressure Plate Extractor) test is then performed to obtain SWCC (Soil-Water Characteristic Curve) of soil samples. In the modified network model, SWCC is used to adjust the equivalent radius of thermal cylinder at contact area between particles. And cutoff range parameter to define the effective zone is also adjusted according to the SWCC at given conditions. From a series of laboratory tests and the proposed network model, the modified network model which adopts a SWCC shows a good agreement in modeling thermal conductivity of granular soils at given conditions. And an empirical correlation between the fraction of the mean radius (${\chi}$) and thermal conductivity at given saturated condition is provided, which can be used to expect thermal conductivity of the granular soils, to estimate thermal conductivity of granular soils.