• Journal of the Korean Society for Railway
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• v.16 no.1
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• pp.20-25
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• 2013

The frame elements of modern high speed trains are typically fabricated with extruded aluminum panels. However, the sound transmission loss (STL) of extruded aluminum panels is less satisfactory than flat panels with the same surface density. This study proposes a method for prediction of the sound transmission loss of extruded aluminum panels using finite element analysis. The panel is modeled by finite element analysis, and the STL is calculated using a measure of Sommerfeld radiation at the specimen surface, boundary conditions, and the internal loss factor of the material. In order to verify the validity of the predicted value, intensity transmission loss was measured on the aluminum specimen according to ASTM E2249-02. The proposed method of analysis will be utilized to predict the sound insulation performance of extruded aluminum panels for railway vehicles in the design stage, and to establish measures for their improvement.

• Steel and Composite Structures
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• v.16 no.1
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• pp.21-44
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• 2014

The aim of this study is to determine the dynamic characteristics of long reinforced concrete highway bridges with post-tension tendons using analytical and experimental methods. It is known that the deck length and height of bridges are affected the dynamic characteristics considerably. For this purpose, Berta Bridge constructed in deep valley, in Artvin, Turkey, is selected as an application. The Bridge has two piers with height of 109.245 m and 85.193 m, and the total length of deck is 340.0 m. Analytical and experimental studies are carried out on Berta Bridge which was built in accordance with the balanced cantilever method. Finite Element Method (FEM) and Operational Modal Analysis (OMA) which considers ambient vibration data were used in analytical and experimental studies, respectively. Finite element model of the bridge is created by using SAP2000 program to obtain analytical dynamic characteristics such as the natural frequencies and mode shapes. The ambient vibration tests are performed using Operational Modal Analysis under wind and human loads. Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI) methods are used to obtain experimental dynamic characteristics like natural frequencies, mode shapes and damping ratios. At the end of the study, analytical and experimental dynamic characteristic are compared with each other and the finite element model of the bridge was updated considering the material properties and boundary conditions. It is emphasized that Operational Modal Analysis method based on the ambient vibrations can be used safely to determine the dynamic characteristics, to update the finite element models, and to monitor the structural health of long reinforced concrete highway bridges constructed with the balanced cantilever method.

• Steel and Composite Structures
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• v.35 no.1
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• pp.77-92
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• 2020

The present paper outlined a procedure for geometrically nonlinear dynamic analysis of functionally graded graphene platelets-reinforced (GPLR-FG) nanocomposite cylinder subjected to mechanical shock loading. The governing equation of motion for large deformation problems is derived using meshless local Petrov-Galerkin (MLPG) method based on total lagrangian approach. In the MLPG method, the radial point interpolation technique is employed to construct the shape functions. A micromechanical model based on the Halpin-Tsai model and rule of mixture is used for formulation the nonlinear functionally graded distribution of GPLs in polymer matrix of composites. Energy dissipation in analyses of the structure responding to dynamic loads is considered using the Rayleigh damping. The Newmark-Newton/Raphson method which is an incremental-iterative approach is implemented to solve the nonlinear dynamic equations. The results of the proposed method for homogenous material are compared with the finite element ones. A very good agreement is achieved between the MLPG and FEM with very fine meshing. In addition, the results have demonstrated that the MLPG method is more effective method compared with the FEM for very large deformation problems due to avoiding mesh distortion issues. Finally, the effect of GPLs distribution on strength, stiffness and dynamic characteristics of the cylinder are discussed in details. The obtained results show that the distribution of GPLs changed the mechanical properties, so a classification of different types and volume fraction exponent is established. Indeed by comparing the obtained results, the best compromise of nanocomposite cylinder is determined in terms of mechanical and dynamic properties for different load patterns. All these applications have shown that the present MLPG method is very effective for geometrically nonlinear analyses of GPLR-FG nanocomposite cylinder because of vanishing mesh distortion issue in large deformation problems. In addition, since in proposed method the distributed nodes are used for discretization the problem domain (rather than the meshing), modeling the functionally graded media yields to more accurate results.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.640-649
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• 2010

Coarse granular materials such as gravel and crushed stone have been used as an important fill materials to large soil structure of railway, road, dam and so on. Although much studies for general soil materials have been carried out domestically, the studies for coarse materials were insufficient. Particularly, it is the level in which the study for dynamic properties(Elastic modulus and damping ratio) of coarse materials, applies the foreign country literature. This is due to the lack of large equipment for element test. But large soil structures made of coarse granular materials are generally important infrastructures. Therefore, the reliable design parameters for coarse materials should be obtained for safe and economic design, construction and maintenance. Triaxial test is the laboratory test method that is capable of controlling a confining pressure and boundary condition. In this project, we made a multi-purpose large triaxial testing system. This testing system is able to test coarse granular materials with maximum particle diameter of 100mm and support both the load control and displacement control. The load cell is installed inside of triaxial cell and the axial displacement is measured locally in order to control and measure more accurately in the small strain level. The verification test of this testing system was carried out with urethane verification specimens. So, from now on the useful information for coarse granular materials are expected to suggested by performing many tests with various material and condition.

• Transactions on Electrical and Electronic Materials
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• v.18 no.5
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• pp.287-297
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• 2017

Novel power system stabilizers (PSSs) have been proposed to effectively dampen low frequency oscillations (LFOs) in multi-machine power systems and have attracted increasing research interest in recent years. Due to this attention, recently, fractional order controllers (FOCs) have found new applications in power system stability issues. Here, a tilt-integral-derivative power system stabilizer (TID-PSS) is proposed to enhance the dynamic stability of a multi-machine power system by providing additional damping to the LFOs. The TID is an extended version of the classical proportional-integral-derivative (PID) applying fractional calculus. The design of the proposed three-parameter tunable TID-PSS is systematized as a nonlinear time domain optimization problem in which the tunable parameters are adjusted concurrently using a modified group search optimization (MGSO) algorithm. An integral of the time multiplied squared error (ITSE) performance index is considered as the objective function. The proposed stabilizer is simulated in the MATLAB/SIMULINK environment using the FOMCON toolbox and the dynamic performance is evaluated on a 3-machine 6-bus power system. The TID-PSS is compared with both classical PID-PSS (PID-PSS) and conventional PSS (CPSS) using eigenvalue analysis and time domain simulations. Sensitivity analyses are performed to assess the robustness of the proposed controller against large changes in system loading conditions and parameters. The results indicate that the proposed TID-PSS provides the better dynamic performance and robustness compared with the PID-PSS and CPSS.

• Smart Structures and Systems
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• v.13 no.4
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• pp.615-636
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• 2014

Aluminium Foam Sandwich (AFS) panels are becoming always more attractive in transportation applications thanks to the excellent combination of mechanical properties, high strength and stiffness, with functional ones, thermo-acoustic isolation and vibration damping. These properties strongly depend on the density of the foam, the morphology of the pores, the type (open or closed cells) and the size of the gas bubbles enclosed in the solid material. In this paper, the vibrational performances of two classes of sandwich panels with an Alulight(R) foam core are studied. Experimental tests, in terms of frequency response function and modal analysis, are performed in order to investigate the effect of different percentage of porosity in the foam, as well as the effect of the random distribution of the gas bubbles. Experimental results are used as a reference for developing numerical models using finite element approach. Firstly, a sensitivity analysis is performed in order to obtain a limit-but-bounded dynamic response, modelling the foam core as a homogeneous one. The experimental-numerical correlation is evaluated in terms of natural frequencies and mode shapes. Afterwards, an update of the previous numerical model is presented, in which the core is not longer modelled as homogeneous. Mass and stiffness are randomly distributed in the core volume, exploring the space of the eigenvectors.

• Structural Engineering and Mechanics
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• v.47 no.6
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• pp.881-898
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• 2013

This paper describes analytical investigation into a new dual function system including a couple of shear links which are connected in series using chevron bracing capable to correlate its performance with magnitude of earthquakes. In this proposed system, called Chevron Knee-Vertical Link Beam braced system (CK-VLB), the inherent hysteretic damping of vertical link beam placed above chevron bracing is exclusively utilized to dissipate the energy of moderate earthquakes through web plastic shear distortion while the rest of the structural elements are in elastic range. Under strong earthquakes, plastic deformation of VLB will be halted via restraining it by Stopper Device (SD) and further imposed displacement subsequently causes yielding of the knee elements located at the bottom of chevron bracing to significantly increase the energy dissipation capacity level. In this paper first by studying the knee yielding mode, a suitable shape and angle for diagonal-knee bracing is proposed. Then finite elements models are developed. Monotonic and cyclic analyses have been conducted to compare dissipation capacities on three individual models of passive systems (CK-VLB, knee braced system and SPS system) by General-purpose finite element program ABAQUS in which a bilinear kinematic hardening model is incorporated to trace the material nonlinearity. Also quasi-static cyclic loading based on the guidelines presented in ATC-24 has been imposed to different models of CK-VLB with changing of vertical link beam section in order to find prime effectiveness on structural frames. Results show that CK-VLB system exhibits stable behavior and is capable of dissipating a significant amount of energy in two separate levels of lateral forces due to different probable earthquakes.

• Earthquakes and Structures
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• v.11 no.6
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• pp.1077-1099
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• 2016

One of the main shortcomings in the current passive base isolation system is lack of adaptability. The recent research and development of a novel adaptive seismic isolator based on magnetorheological elastomer (MRE) material has created an opportunity to add adaptability to base isolation systems for civil structures. The new MRE based base isolator is able to significantly alter its shear modulus or lateral stiffness with the applied magnetic field or electric current, which makes it a competitive candidate to develop an adaptive base isolation system. This paper aims at exploring suitable control algorithms for such adaptive base isolation system by developing a close-loop semi-active control system for a building structure equipped with MRE base isolators. The MRE base isolator is simulated by a numerical model derived from experimental characterization based on the Bouc-Wen Model, which is able to describe the force-displacement response of the device accurately. The parameters of Bouc-Wen Model such as the stiffness and the damping coefficients are described as functions of the applied current. The state-space model is built by analyzing the dynamic property of the structure embedded with MRE base isolators. A Lyapunov-based controller is designed to adaptively vary the current applied to MRE base isolator to suppress the quake-induced vibrations. The proposed control method is applied to a widely used benchmark base-isolated structure by numerical simulation. The performance of the adaptive base isolation system was evaluated through comparison with optimal passive base isolation system and a passive base isolation system with optimized base shear. It is concluded that the adaptive base isolation system with proposed Lyapunov-based semi-active control surpasses the performance of other two passive systems in protecting the civil structures under seismic events.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.146-153
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• 1996

A SCARA type direct drive robot which can be used in the assembly operation was designed and manufactured. Graphite fiber epoxy composite material was used in the fabrication of the robot arm structure in order to improve the speed of the robot arm with a high damping effect. For model-based control and sensitivity analysis of system parameters, the dynamic model of robot arm and drive servo amplifier parameters such as equivalent gains of PWM driver and velocity gains of servo system were estimated from frequency response tests. The complete dynamic model for overall robot system was used in the simulation of the open-loop control. The simulation results agreed reasonably well to the experimental results. The feedforward control using the dynamic models improved the trajectory tracking performance, decreasing the tracking error by factor of three compared with PID control. This study found that the inverse dynamic model of the robot arm including the drive servo system showed better performances than the case of arm dynamic model only.

• Korean Journal of Medicinal Crop Science
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• v.18 no.2
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• pp.74-78
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• 2010

This experiment was carried out to select suitable organic matter in To-jik nursery (self soil nursery) for complement To-jik nursery's defects that are deterioration of raw material by poor quality of seed ginseng and reduction of the quantity in seed ginseng production. Organic matter used were Yacto, rice bean, defatted rice bran, soybean cake and their mixture. As follows, bulk density in soil physical property by treating organic composts was the greatest in soybean cake and the next was followed by mix, Yacto, defatted rice bran, and rice bran treatment in order. Soil pore space ratio was totally the opposite; that was rice bran the first and followed by defatted rice bran, Yacto, mix and soybean cake treatment. The incidence rate of damping off by treating organic composts was 1.5% in both soybean cake and mix while the others was 1.0%. Emergence time was the same among treatment on April 16 and Emergence rate was the highest at 73% in Yacto. There was no significant differences among treatment in the growth of aboveground part but it was a little better in defatted rice bran treatment. In Yacto treatment, the growth of underground part, total root number per kan, rate of first grade ginseng seedling, and rate of usable ginseng seedling etc. were entirely higher but there was little differences. Using defatted rice bran was slightly lower in productivity compared to Yacto, but the possibility was high as a alternative for Yacto in a view of managing cost down.