• Wind and Structures
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• v.3 no.3
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• pp.193-207
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• 2000

The possible application of a spatially placed passive tuned liquid column damper system for suppressing coupled lateral-torsional responses of tall buildings is investigated in this paper. The wind loads acting on rectangular tall buildings are analytically expressed as 3-D stochastic model. Meanwhile, the 3-D responses of tall buildings may be coupled due to eccentricities between the stiffness and mass centers of the buildings. In these cases, torsional responses of the buildings are rather larger, and a TLCD system composed of several TLCD located near the sides of the buildings is more effective than the same TLCD placed at the building center in reducing both translational and torsional responses of the buildings. In this paper, extensive analytical and numerical work has been done to present the calculation method and optimize the parameters of such TLCD systems. The numerical examples show that the spatially placed TLCD system can reduce coupled along-wind, across-wind and torsional responses significantly with a fairly small mass ratio.

• Structural Engineering and Mechanics
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• v.55 no.2
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• pp.245-261
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• 2015

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies of eccentric hemi-spherical shells of revolution with variable thickness. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components $u_r$, $u_{\Theta}$, and $u_z$ in the radial, circumferential, and axial directions, respectively, are taken to be periodic in ${\theta}$ and in time, and algebraic polynomials in the r and z directions. Potential and kinetic energies of eccentric hemi-spherical shells with variable thickness are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to three or four-digit exactitude is demonstrated for the first five frequencies of the shells. Numerical results are presented for a variety of eccentric hemi-spherical shells with variable thickness.

• Structural Engineering and Mechanics
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• v.42 no.3
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• pp.353-362
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• 2012

In this paper decay and mapped elastodynamic infinite elements, based on modified Bessel shape functions and appropriate for Soil-Structure Interaction problems are described and discussed. These elements can be treated as a new form of the recently proposed Elastodynamic Infinite Elements with United Shape Functions (EIEUSF) infinite elements. The formulation of 2D horizontal type infinite elements (HIE) is demonstrated, but by similar techniques 2D vertical (VIE) and 2D corner (CIE) infinite elements can also be formulated. It is demonstrated that the application of the elastodynamical infinite elements is the easier and appropriate way to achieve an adequate simulation including basic aspects of Soil-Structure Interaction. Continuity along the artificial boundary (the line between finite and infinite elements) is discussed as well and the application of the proposed elastodynamical infinite elements in the Finite Element Method is explained in brief. Finally, a numerical example shows the computational efficiency of the proposed infinite elements.

• Structural Engineering and Mechanics
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• v.38 no.3
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• pp.283-300
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• 2011

A new conception of fundamental tasks in dynamics of the bridge-track-train systems (BTT), with the aim to evaluate moving load's models adequacy, has been developed. The 2D physical models of BTT systems, corresponding to the fundamental tasks, have been worked out taking into account one-way constraints between the moving unsprung masses and the track. A method for deriving the implicit equations of motion, governing vibrations of BTT systems' models, as well as algorithms for numerical integration of these equations, leading to the solutions of high accuracy and relatively short times of simulations, have been also developed. The derived equations and formulated algorithms constitute the basis for numerical simulation of vibrations of the considered systems.

• Tunnel and Underground Space
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• v.18 no.3
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• pp.202-213
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• 2008

In this study, theoretical approach of 3D seismic traveltime tomography was investigated. To guarantee the successful field application of 3D tomography, appropriate control of problem associated with blind zone is pre-requisite. To overcome the velocity distortion of the reconstructed tomogram due to insufficient source-receiver array coverage, the algorithm of 3D seismic traveltime tomography based on the Fresnel volume was developed as a technique of ray-path broadening. For the successful reconstruction of velocity cube, 3D traveltime algorithm was explored and employed on the basis of 2nd order Fast Marching Method(FMM), resulting in improvement of precision and accuracy. To prove the validity and field application of this algorithm, two numerical experiments were performed for globular and layered models. The algorithm was also found to be successfully applicable to field data.

• Geomechanics and Engineering
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• v.30 no.5
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• pp.423-435
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• 2022

Ground vibration generated repeatedly in blasting tunnel excavation sites is known to be one of the major hazards induced by blasting operations. Various studies have been conducted to minimize these hazards, both theoretical and empirical methods using electronic detonator, the deck charge method, the center-cut method among others Among these various existing methods for controlling the ground vibration, in this study, we investigated the cut method. In particular, we analyzed and compared the V-cut method, which is commonly used in tunnel blasting, to the double-drilled parallel method, which has recently been introduced in tunnel excavation site. To understand the rock fragmentation efficiency as well as the ground vibration controllability of the two methods, we performed in-situ field blasting tests with both cut methods at a tunnel excavation site. Additionally, numerical analysis by FLAC3D has been executed for a better understanding of fracture propagation pattern and ground vibration generation by each cut method. Ground vibration levels, by PPVs measured in field blasting tests and PPVs estimated in numerical simulations, showed a lower value in the double-drilled parallel compared with the V-cut method, although the exact values are quite different in field measurement and numerical estimation.

• Geomechanics and Engineering
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• v.29 no.4
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• pp.471-486
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• 2022

The effect of segmental joints is one of main importance for the segmental lining design when tunnels are excavated by a mechanized process. In this paper, segmental tunnel linings are analyzed by two numerical methods, namely the Beam-Spring Method (BSM) and the Solid-Interface Method (SIM). For this purpose, the Tehran Subway Line 6 Tunnel is considered to be the reference case. Comprehensive 2D numerical simulations are performed considering the soil's calibrated plastic hardening model (PH). Also, an advanced 3D numerical model was used to obtain the stress relaxation value. The SIM numerical model is conducted to calculate the average rotational stiffness of the longitudinal joints considering the joints bending moment distribution and joints openings. Then, based on the BSM, a sensitivity analysis was performed to investigate the influence of the ground rigidity, depth to diameter ratios, slippage between the segment and ground, segment thickness, number of segments and pattern of joints. The findings indicate that when the longitudinal joints are flexible, the soil-segment interaction effect is significant. The joint rotational stiffness effect becomes remarkable with increasing the segment thickness, segment number, and tunnel depth. The pattern of longitudinal joints, in addition to the joint stiffness ratio and number of segments, also depends on the placement of longitudinal joints of the key segment in the tunnel crown (similar to patterns B and B').

• Proceedings of the KIEE Conference
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• summer
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• pp.518-520
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• 2004

In these days, there is a demand to develop fault current limiters(FCLs) to reduce excessive fault current and protect electrical equipments which are installed in the transmission and distribution power systems. We considered the resistive superconducting FCLs among the various kinds of FCLs. In this study, in order to develop the resistive superconducting FCL of 6.6kV 200A $3\phi$, we designed the new mask pattern for etching YBCO films by means of numerical analysis method, current limiting experiments and visualization of bubbles in films and investigated dielectric performance of the designed mask by using elecrtostatic numerical analysis method and breakdown experiments. We etched YBCO films by using the newly designed mask, connected the etched films in series and in parallel, and designed the 6.6kV resistive SFCL and then we observed the current limiting characteristics of the SFCL.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.3
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• pp.29-36
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• 2002

A numerical analysis based on two-dimensional and three-dimensional incompressible Wavier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convective terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. Considering computation times, $\kappa$-$\varepsilon$ turbulence model with wall function is used.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.3
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• pp.110-117
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• 1998

A continuum-based configuration design sensitivity analysis method is developed for kinematically driven mechanical systems. The configuration design variable for mechanical systems is defined. The 3-1-3 Euler angle is employed as the orientation design variable. Kinematic admissibility conditions of configuration design change. Direct differentiation method is used to derive the governing equations of the design sensitivity. Numerical examples are presented to demonstrate the validity and effectiveness of the proposed method.