• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.444-449
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• 2005

In Seoul, several railway depots are located at the places where a public can easily access. Since a depot occupy a large amount of land itself, it is natural to use those sites for a public building construction such as an apartment complex or a transportation terminal, as an example. Most of the buildings on a depot, however, are exposed to vibration problems, because foundations are excited from the dynamic loading whenever heavy trains pass on the track. Severe vibration may cause a damage to building structures and a troublesome to a community. In this paper, some vibration practices have been examined in order to resolve the vibration problems. First, a critical speed of a train in a railway depot is evaluated. Then, a structural effect on the transmission of a vibration energy has been investigated. Finally, practical approaches to reduce the vibration level have been proposed. In this first half part of the paper, the focus has been on the critical speed and a structural transmission phenomena.

• IE interfaces
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• v.24 no.4
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• pp.281-294
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• 2011

This paper considers the rail crane scheduling problem which is defined as determining the sequence of loading/unloading container on/from a freight train. The objective is to minimize the weighted sum of the range of order completion time and makespan. The range of order completion time implies the difference between the maximum of completion time and minimum of start time of each customer order consisting of jobs. Makespan refers to the time when all the jobs are completed. In a rail freight terminal, logistics firms as a customer wish to reduce the range of their order completion time. To develop a methodology for the crane scheduling, we formulate the problem as a mixed integer program and develop three metaheuristics, namely, genetic algorithm, simulated annealing, and tabu search. To validate the effectiveness of heuristic algorithms, computational experiments are done based on a set of real life data. Results of the experiments show that heuristic algorithms give good solutions for small-size and large-size problems in terms of solution quality and computation time.

• Tunnel and Underground Space
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• v.16 no.4 s.63
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• pp.288-295
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• 2006

In this study, dynamic behavior of the vehicles is analyzed, while the track is subjected to lateral vibrations due to earthquake and blasting load. A computer program(WERIA, Wheel Rail Interaction Analysis) is used, which can simulate dynamic responses of vehicles subjected to lateral vibrations. The analysis considers two types of vehicles: I.e. power cars of KTX and Busan subway train. It can also consider the interaction with sub-structures such as tracks and soil. The creep force module is considered, and the running safety of railway vehicles subjected to earthquake and blasting loading is studied. Based on the results of this study, the running safety of the vehicles can be confirmed against lateral vibration.

• Steel and Composite Structures
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• v.27 no.5
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• pp.647-659
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• 2018

Through extensive research, there exist a new type of connection between railway bridge girders and steel-concrete composite panels. In addition to conventional shear connectors, newly developed blind bolts have been recently adopted for retrofitting. However, the body of knowledge on their influence and application to railway structures has not been thoroughly investigated. This study has thus placed a particular emphasis on the application of blind bolts on the Sydney Harbour Bridge as a feasible alternative constituent of railway track upgrading. Finite element modeling has been used to simulate the behaviours of the precast steel-concrete panels with common types of bolt connection using commercially available package, ABAQUS. The steel-concrete composite track slabs have been designed in accordance with Australian Standards AS5100. These precast steel-concrete panels are then numerically retrofitted by three types of most practical bold connections: head studded shear connector, Ajax blind bolt and Lindapter hollow bolt. The influences of bolt connections on load and stress transfers and structural behaviour of the composite track slabs are highlighted in this paper. The numerical results exhibit that all three bolts can distribute stresses effectively and can be installed on the bridge girder. However, it is also found that Lindapter hollow bolts are superior in minimising structural responses of the composite track slabs to train loading.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.388-395
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• 2009

An accelerated fatigue test is essentially required to maintain the reliability of the actual structures of KTX under operation conditions. However, actual fatigue life cannot be obtained because the conventional fatigue tests are not adequate to the real load conditions. Moreover foreign component makers have not provided data of the loading stresses (S) versus cycles at the failure (N). In this study, we suggested a deduction method of the S-N curve for establishing an accelerating test under various load levels. Load history was acquired from the field tests. A Rainflow method was used on the cycle counting of the field load data. After that, an S-N curve was obtained through the iteration process under the condition that the damage index satisfies to 1 in the Miner's rule. The deduced S-N curve was applied to the performance evaluation of Korean-made sealed knuckles compared with imports.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.3 s.108
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• pp.219-225
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• 2006

In Seoul, several railway depots are located at the places where a public can easily access. Since a depot occupy a large amount of land itself, it is natural to use those sites for a public building construction such as an apartment complex or a transportation terminal, as an example. Most of the buildings on a depot, however, are exposed to vibration problems, because foundations are excited from the dynamic loading whenever heavy trains pass on the track. Severe vibration may cause a damage to building structures and a troublesome to a community. In this paper, some vibration practices have been examined in order to resolve the vibration problems. First, a critical speed of a train in a railway depot is evaluated. Then, the structural effect has been investigated. Finally, practical approaches to reduce the vibration level have been proposed. In this first half part of the paper, the focus has been on the critical speed and a structural transmission phenomena.

• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.106-113
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• 2004

Recently, a new issue in designing spot welded structures such as automobile and train car bodies is to predict an economical fatigue design criterion. One of the most typical and traditional methods is to use a ΔP-N$\sub$f/ curve. However, since the fatigue data on the ΔP-N$\sub$f/ curve vary according to the welding conditions, materials, geometry of joint and fatigue loading conditions, it is necessary to perform the additional fatigue tests for determining a new fatigue design criterion of spot-welded lap joint having specific dimension and geometry. In this study, the stress distributions around spot welds of various spot welded lap joints such as in-plane bending type (IB type), tension shea. type (TS type) and cross tension type (CT type) were numerically analyzed. Using these results, the ΔP-N$\sub$f/ curves Previously obtained from the fatigue tests for each type were rearranged into the Δ$\sigma$-N$\sub$f/ relations with the maximum stresses at the nugget edge of the spot weld.

• Journal of the Korean Society of Safety
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• v.31 no.3
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• pp.82-88
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• 2016

Ballasted gravel will be damaged or worn by the repetitive train load. And these damages of ballast gravel could be increased by increasing vehicle speed. Therefore, various techniques for reducing the ballast pressure have been proposed, such as the attached pad type of sleeper bottom for ballasted track. In this study, spring stiffness test method were proposed to evaluate the performance of under sleeper pad for ballasted track. Standard ballast plate(SBP) was developed to simulate the ballast gravel and compared with the foreign test results. Experimental results showed a trend similar to the previous studies according to various loading plate type. specimen type(Type A, Type B) differences in spring stiffness according to hardness were not significant. Also, the FSP (Flat steel plate) - shaped jig is about 80% of the spring stiffness was greater than SBP. Therefore, to evaluate the actual spring stiffness of under sleeper pad for ballasted track, it was important to adopted the appropriate spring stiffness test method using the SBP to simulate actual field conditions.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2709-2716
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• 2020

Compositions of large nuclear cores (e.g. boiling water reactors) are highly heterogeneous in terms of fuel composition, control rod insertions and flow regimes. For this reason, they usually lack high order of symmetry (e.g. 1/4, 1/8) making it difficult to estimate their neutronic parameters for large spaces of possible loading patterns. A detailed hyperparameter optimization technique (a combination of manual and Gaussian process search) is used to train and optimize deep neural networks for the prediction of three neutronic parameters for the Ringhals-1 BWR unit: power peaking factors (PPF), control rod bank level, and cycle length. Simulation data is generated based on half-symmetry using PARCS core simulator by shuffling a total of 196 assemblies. The results demonstrate a promising performance by the deep networks as acceptable mean absolute error values are found for the global maximum PPF (~0.2) and for the radially and axially averaged PPF (~0.05). The mean difference between targets and predictions for the control rod level is about 5% insertion depth. Lastly, cycle length labels are predicted with 82% accuracy. The results also demonstrate that 10,000 samples are adequate to capture about 80% of the high-dimensional space, with minor improvements found for larger number of samples. The promising findings of this work prove the ability of deep neural networks to resolve high dimensionality issues of large cores in the nuclear area.

• Steel and Composite Structures
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• v.47 no.5
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• pp.601-613
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• 2023

Numerous methods have been proposed in predicting formability of sheet metals based on microstructural and macro-scale properties of sheets. However, there are limited number of papers on the optimization problem to increase formability of sheet metals. In the present study, we aim to use novel optimization algorithms in neural networks to maximize the formability of sheet metals based on tensile curve and texture of aluminum sheet metals. In this regard, experimental and numerical evaluations of effects of texture and tensile properties are conducted. The texture effects evaluation is performed using Taylor homogenization method. The data obtained from these evaluations are gathered and utilized to train and validate an artificial neural network (ANN) with different optimization methods. Several optimization method including grey wolf algorithm (GWA), chimp optimization algorithm (ChOA) and whale optimization algorithm (WOA) are engaged in the optimization problems. The results demonstrated that in aluminum alloys the most preferable texture is cube texture for the most formable sheets. On the other hand, slight differences in the tensile behavior of the aluminum sheets in other similar conditions impose no significant decreases in the forming limit diagram under stretch loading conditions.