• Journal of Power System Engineering
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• v.12 no.2
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• pp.29-34
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• 2008

Bellows is widely used in many industrial fields as it provides a relatively simple means of absorbing mechanical shock, vibration and thermal deformation with flexibility. In this study, the inherent dynamic characteristics of curved bellows are numerically studied according to the variation of angle, curvature and crest density, etc. For these numerical studies, a parametric finite element modelling program of curved bellows is constructed using ANSYS APDL. The validity of numerical results obtained from ANSYS software is experimentally verified using the test model made by RP machine SLA 5000.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.765-774
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• 2004

This paper presents a damage assesment method for buried pipelines subjected to Deep Excavation-induced ground movements. Ground deformation characteristics resulting from 3D finite element analysis was represented mathematically by a hyperbolic tangential function. A parametric study was performed on excavation depth and burial position of pipeline. The result of the parametric study indicate that length of hyperbolic tangential function affects the results of damage assessment. Using numerical studies for buried pipeline response to ground movements by relative flexibility of the pipe-soil system. The result of numerical studies are presented in forms of design charts which can be readily used for various condition encountered in practices.

• Journal of computational fluids engineering
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• v.21 no.3
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• pp.77-88
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• 2016

A parametric study on a fluidic oscillator was performed numerically in this work. Three-dimensional unsteady Reynolds-averaged Navier-Stokes equations were solved to analyze the flow in the fluidic oscillator. As turbulence closure, $k-{\varepsilon}$ model was employed. Validation of the numerical results was performed by comparing numerical results with experimental data for frequency of the oscillation. The parametric study was performed using five geometric parameters. Performance of the fluidic oscillator was evaluated in terms of velocity ratio and pressure drop. The results show that the inlet channel width and the distance between splitters are important factors in determining the performance of the fludic oscillator.

• Journal of the Korean Society of Safety
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• v.35 no.3
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• pp.49-57
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• 2020

In comparison with the existing static reliability analysis methods, the dynamic reliability analysis(DyRA) method is more suitable for estimating the failure probability of a structure subjected to earthquake excitations because it can take into account the frequency characteristics and damping capacity of the structure. However, the DyRA is known to have an issue of numerical stability due to the uncertainty in random sampling of the earthquake excitations. In order to solve this numerical stability issue in the DyRA approach, this study proposed two earthquake-scale factors. The first factor is defined as the ratio of the first earthquake excitation over the maximum value of the remaining excitations, and the second factor is defined as the condition number of the matrix consisting of the earthquake excitations. Then, we have performed parametric studies of two factors on numerical stability of the DyRA method. In illustrative example, it was clearly confirmed that the two factors can be used to verify the numerical stability of the proposed DyRA method. However, there exists a difference between the two factors. The first factor showed some overlapping region between the stable results and the unstable results so that it requires some additional reliability analysis to guarantee the stability of the DyRA method. On the contrary, the second factor clearly distinguished the stable and unstable results of the DyRA method without any overlapping region. Therefore, the second factor can be said to be better than the first factor as the criterion to determine whether or not the proposed DyRA method guarantees its numerical stability. In addition, the accuracy of the numerical analysis results of the proposed DyRA has been verified in comparison with those of the existing first-order reliability method(FORM), Monte Carlo simulation(MCS) method and subset simulation method(SSM). The comparative results confirmed that the proposed DyRA method can provide accurate and reliable estimation of the structural failure probability while maintaining the superior numerical efficiency over the existing methods.

• Structural Engineering and Mechanics
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• v.13 no.6
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• pp.653-670
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• 2002

In order to ensure the structural dynamic stability of moving liquid-storage containers, the flow motion of interior liquid should be appropriately suppressed by means of mechanical devices such as the disc-type elastic baffle. In practice, the design of a suitable baffle requires a priori the parametric dynamic characteristics of storage containers, with respect to the design parameters of baffle, such as the installation location and inner-hole size, the baffle number, and so on. In this paper, we intend to investigate the parametric effect of the baffle parameters on the transient dynamic behavior of a cylindrical fuel-storage tank in an abrupt vertical acceleration motion. For this goal, we employ the ALE (arbitrary Lagrangian-Eulerian) kinematic description method incorporated with the finite element method.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.1
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• pp.110-116
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• 2015

This study investigates the whirling stability of a rotating shaft-disk system under parametric excitation using periodically varying torque. The equations of motion were derived using a lumped-mass model, and the Floquet method was employed to find the effects of torque fluctuation, internal and external damping, and rotational speed on whirling stability. Results indicated that the effect of torque fluctuation was considerable on the instability around resonance, but minimal on supercritical instability. Stability diagrams were sensitive to the parametric excitation frequency; critical torque decreased upon increasing excitation frequency, with faster response convergence or divergence. In addition, internal and external damping had a considerable effect on unstable regions, and reduced the effects of the parametric excitation frequency on critical torque and speed. Results obtained from the Floquet approach were in good agreement with those obtained by numerical integration, except for some cases with Floquet multipliers very close to unity.

• Journal of the Korean Data and Information Science Society
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• v.27 no.5
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• pp.1389-1397
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• 2016

Semi-parametric frailty model with nonparametric baseline hazards has been widely used for the analyses of clustered survival-time data. The frailty models can be fitted via an auxiliary Poisson hierarchical generalized linear model (HGLM). For the inferences of the frailty model marginal likelihood, which gives MLE, is often used. The marginal likelihood is usually obtained by integrating out random effects, but it often requires an intractable integration. In this paper, we propose to obtain the MLE via Laplace approximation using a Poisson HGLM approach for semi-parametric frailty model. The proposed HGLM approach uses hierarchical-likelihood (h-likelihood), which avoids integration itself. The proposed method is illustrated using a numerical study.

• Structural Engineering and Mechanics
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• v.40 no.5
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• pp.705-718
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• 2011

The aim of the investigation described in this paper is to study the nonlinear parametric vibrations and stability of a simply-supported viscoelastic beam with an intra-span spring. Taking into account a time-dependent tension inside the beam as the main source of parametric excitations, as well as employing a two-parameter rheological model, the equations of motion are derived using Newton's second law of motion. These equations are then solved via a perturbation technique which yields approximate analytical expressions for the frequency-response curves. Regarding the main parametric resonance case, the local stability of limit cycles is analyzed. Moreover, some numerical examples are provided in the last section.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.4
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• pp.259-264
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• 2023

In this study, we devised a parametric analysis workflow for efficiently analyzing the material properties of 3D woven materials. The parametric model uses wire spacing in the woven materials as a design parameter; we generated 2,500 numerical models with various combinations of these design parameters. Using MATLAB and ANSYS software, we obtained various material properties, such as bulk modulus, thermal conductivity, and fluid permeability of the woven materials, through a parametric batch analysis. We then used this large dataset of material properties to perform a regression analysis to validate the relationship between design variables and material properties, as well as the accuracy of numerical analysis. Furthermore, we constructed an artificial neural network capable of predicting the material properties of 3D woven materials on the basis of the obtained material database. The trained network can accurately estimate the material properties of the woven materials with arbitrary design parameters, without the need for numerical analyses.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.3
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• pp.250-258
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• 2018

Free Standing Hybrid Riser (FSHR) is comprised of vertical steel risers and Flexible Jumpers (FJ). They are jointly connected to a submerged Buoyancy Can (BC). There are several factors that have influence on the behavior of FSHR such as the span distance between an offshore platform and a foundation, BC up-lift force, BC submerged location and FJ length. An optimization method through a parametric study is presented. Firstly, descriptions for the overall arrangement and characteristics of FSHR are introduced. Secondly, a flowchart for optimization of FSHR is suggested. Following that, it is described how to select reasonable ranges for a parametric study and determine each of optimal configuration options. Lastly, numerical analysis based on this procedure is performed through a case study. In conclusion, the relation among those parameters is analyzed and non-dimensional parametric ranges on optimal arrangements are suggested. Additionally, strength analysis is performed with variation in the configuration.