• Wind and Structures
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• v.36 no.6
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• pp.423-434
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• 2023

Aerodynamic force coefficients are generally obtained from traditional wind tunnel tests or computational fluid dynamics (CFD). Unfortunately, the techniques mentioned above can sometimes be cumbersome because of the cost involved, such as the computational cost and the use of heavy equipment, to name only two examples. This study proposed to build a deep neural network model to predict the aerodynamic force coefficients based on data collected from CFD simulations to overcome these drawbacks. Therefore, a series of CFD simulations were conducted using different geometric parameters to obtain the aerodynamic force coefficients, validated with wind tunnel tests. The results obtained from CFD simulations were used to create a dataset to train a multilayer perceptron artificial neural network (ANN) model. The models were obtained using three optimization algorithms: scaled conjugate gradient (SCG), Bayesian regularization (BR), and Levenberg-Marquardt algorithms (LM). Furthermore, the performance of each neural network was verified using two performance metrics, including the mean square error and the R-squared coefficient of determination. Finally, the ANN model proved to be highly accurate in predicting the force coefficients of similar bridge sections, thus circumventing the computational burden associated with CFD simulation and the cost of traditional wind tunnel tests.

• Steel and Composite Structures
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• v.45 no.2
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• pp.249-261
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• 2022

This paper presents a numerical study to develop a guideline for estimating the plastic strength of elliptical steel slit damper with reasonable accuracy. The strut width increases from middle to end in elliptical steel slit damper and it is observed from the past studies that variation of the width is not considered for calculating the plastic strength of the damper. It is also noticed that the existing formulas for predicting plastic strength of this kind of damper may not be accurate and further refinement is warranted. Study is then carried on elliptical steel slit damper made of mild steel and having different geometry to find out equivalency of it with oblong steel slit damper having similar plastic strength. A few three-dimensional finite element models of seismic moment connection system with steel slit damper are developed and validated against past experiments for carrying the present study considering both the material nonlinearity as well as geometric nonlinearity. The results of the parametric studies have been compared with energy quantities and presented graphically to better understand the effects of different parameters on the system. Based on the pattern of parametric study results, closed-form semi-empirical algebraic expression of damper plastic strength is developed for elliptical steel slit damper which shows very good agreement with finite element analysis as well as experiments. This developed expression can now be used for elliptical steel slit damper in replacement with any type of damper in the design of moment connection.

• Earthquakes and Structures
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• v.23 no.3
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• pp.283-295
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• 2022

Seismic design codes permit the use of Equivalent Static Analysis of buildings considering torsional eccentricity e with dynamic amplification factors on structural eccentricity and some accidental eccentricity. Estimation of e in buildings is not addressed in codes. This paper presents a simple approximate method to estimate e in RC Moment Frame and RC Structural Wall buildings, which required no detailed structural analysis. The method is validated by 3D analysis (using commercial structural analysis software) of a spectrum of building. Results show that dynamic amplification factor should be applied on torsional eccentricity when performing Response Spectrum Analysis also. Also, irregular or mixed modes of oscillation arise in torsionally unsymmetrical buildings owing to poor geometric distribution of mass and stiffness in plan, which is captured by the mass participation ratio. These irregular modes can be avoided in buildings of any plan geometry by limiting the two critical parameters (normalised torsional eccentricity e/B and Natural Period Ratio 𝜏 =T_𝜃/T, where B is building lateral dimension, T_𝜃 uncoupled torsional natural period and T uncoupled translational natural period). Suggestions are made for new building code provisions.

• Advances in nano research
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• v.15 no.5
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• pp.423-439
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• 2023

The aim of this paper is to investigate the free vibration behavior of the micro sandwich beam composing of five layers such as functionally graded (FG) porous core, nanocomposite reinforced by carbon nanotubes (CNTs) and piezomagnetic/piezoelectric layers subjected to magneto electrical potential resting on silica aerogel foundation. The effect of foundation has been taken into account using Vlasov model in addition to rigid base assumption. For this purpose, an iterative technique is applied. The material properties of the FG porous core and FG nanocomposite layers are considered to vary throughout the thickness direction of the beams. Based on the Timoshenko beam theory and Hamilton's principle, the governing equations of motion for the micro sandwich beam are obtained. The Navier's type solution is utilized to obtain analytical solutions to simply supported micro sandwich beam. Results are verified with corresponding literatures. In the following, a study is carried out to find the effects of the porosity coefficient, porous distribution, volume fraction of CNT, the thickness of silica aerogel foundation, temperature and moisture, geometric parameters, electric and magnetic potentials on the vibration of the micro sandwich beam. The results are helpful for the design and applications of micro magneto electro mechanical systems.

• Journal of Radiation Protection and Research
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• v.28 no.4
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• pp.263-270
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• 2003

Monte Carlo simulation has been peformed to induce optimized parameters of the detector head of gamma camera for the diagnosis of breast cancer and to evaluate it under the diagnosis condition of the breast cancer. For the simulation, we used Tungsten collimator, having a lattice structured array with holes of $3mm{\times}3mm$ and septal thickness of 0.25 mm, which are corresponding to the pixellated photosensor. For driving optimum parameters we used Trade-Offs procedure between the geometric efficiency and the spatial resolution, varying the detector head components. In order to pre-evaluate the performance of the optimized detector head, we assumed diagnosis condition that the breast tumor is located in the middle of phantom with various sizes and its location is 25 mm from the collimator surface, considering background count caused by radiation sources from other organs. It was shown that the performance of the optimized detector head can be degraded according to the breast cancer size and the background count under real diagnosis conditions of breast cancer. Therefore, it is concluded that the spatial resolution, which is used as an indicator to distinguish the various sizes of breast cancer and is dependent on the characteristic of the detector head, appears to be meaningless in early diagnosis of the breast cancer.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3495-3501
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• 2013

The cross-sections of continuous multi-span beams are sometimes suddenly increased or stepped at the interior supports of continuous beams to resist high negative moments. This paper investigates inelastic lateral-torsional buckling of monosymmetric stepped I-beams subjected to pure bending. A three-dimensional finite-element program ABAQUS and a regression program were used to analytically develop new design equation. The flange thickness ratio, flange width ratio and stepped length ratio were considered as parameters of this study. The combined effects of residual stresses and geometric imperfection on inelastic lateral-torsional buckling of beams are considered. The proposed solution can be easily used to calculation for inelastic lateral torsional buckling strengths of monosymmetric beams with doubly stepped cross sections and to develop new design equations for inelastic lateral-torsional buckling resistances of stepped beams.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.1
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• pp.42-50
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• 2017

A study has been conducted to develop an aluminum EGR cooler for the LPL EGR system of a diesel engine. Aluminum has a much lower density and thermal conductivity that is about 12 times or more than that of stainless steel, so it is advantageous for use in an EGR cooler for weight reduction and cooling performance effects. A design process has been carried out to ensure heat dissipation performance in a restricted space to investigate the geometric parameters and satisfy the requirements for pressure drops at both fluid sides. The tubes of exhaust gas have been designed as extruded tubes. An aluminum EGR cooler consisting of extruded tubes entails a simpler manufacturing process compared to a stainless steel EGR cooler with conventional heat transfer fins. A prototype has been manufactured from the final model selected through the design process. The performance of the aluminum EGR cooler was evaluated and compared with that of the conventional one. The weight of the aluminum EGR cooler is reduced by 22.9%, while performance is significantly improved.

• Journal of Power System Engineering
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• v.18 no.4
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• pp.29-35
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• 2014

Plate heat exchanger are being applied in the field of OTEC (ocean thermal energy conversion) and SWAC (seawater air conditioning) system. This study is to analyze numerically the heat transfer and pressure drop characteristics by using solid works flow simulation in order to offer optimum design data of plate heat exchanger. Plater heat exchanger proposed in this study is four types. The geometric design parameters of plate heat exchanger are a channel space, a flow orientation, a plate array, the flowrate of working fluid and so on. The main results for numerical analysis of plate heat exchangers are summarized as follows. Heat transfer performance for the channel space of 2.4 mm shows the highest value compared to other spaces. And, the Type 4 plate heat exchanger in Table 2 is the highest performance. From the pressure drop characteristics of plate heat exchanger, the channel space of 3.2 mm shows the lowest value. And Type 1 plate heat exchanger in Table 2 is the lowest pressure drop.

• Steel and Composite Structures
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• v.21 no.6
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• pp.1227-1250
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• 2016

Most of the research work has been conducted on K-joints under static loading. Very limited information is available in consideration of fatigue strength of K-joints with concrete-filled chord. This paper aims to describe experimental and numerical investigations on stress concentration factors (SCFs) of concrete-filled circular chord and square braces K-joints under balanced axial loading. Experiment was conducted to study the hot spot stress distribution along the intersection of chord and braces in the two specimens with compacting concrete filled in the chord. The test results of stress distribution curves of two specimens were reported. SCFs of concrete-filled circular chord and square braces K-joints were lower than those of corresponding hollow circular chord and square brace K-joints. The corresponding finite element analysis was also conducted to simulate stress distribution along the brace and chord intersection region of joints. It was achieved that experimental and finite element analysis results had good agreement. Therefore, an extensive parametric study was carried out by using the calibrated finite element model to evaluate the effects of main geometric parameters and concrete strength on the behavior of concrete-filled circular chord and square braces K-joints under balanced axial loading. The SCFs at the hot spot locations obtained from ABAQUS were compared with those calculated by using design formula given in the CIDECT for hollow SHS-SHS K-joints. CIDECT Design Guide was generally quite conservative for predicting SCFs of braces and was dangerous for predicting SCFs of chord in concrete-filled circular chord and square braces K-joints. Finally SCF formulae were proposed for circular chord and square braces K-joints with concrete-filled in the chord under balanced axial loading. It is shown that the SCFs calculated from the proposed design equation are generally in agreement with the values derived from finite element analysis, which were proved to be reliable and accurate.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.792-800
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• 2021

This paper presents a new structure for a linear active magnetic bearing using a Halbach magnet array. The proposed magnetic bearing consisted of a Halbach magnet array, center magnet, and single coil. The proposed linear active magnetic bearing has a high dynamic force compared to the previous study. The high dynamic force could be obtained by varying the thickness of a horizontally magnetized magnet. The new structure of Halbach linear active magnetic bearing has a high dynamic force. Therefore, the proposed linear active magnetic bearing increased the bandwidth of the system. Magnetic modeling and optimal design of the new structure of the Halbach linear active magnetic bearing were performed. The optimal design was executed on the geometric parameters of the proposed linear active magnetic bearing using Sequential Quadratic Programming. The proposed linear active magnetic bearing had a static force of 45.06 N and a Lorentz force constant of 19.54 N/A, which is higher than previous research.