• The Journal of the Convergence on Culture Technology
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• v.10 no.3
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• pp.833-838
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• 2024

The urban railway sleeper floating track(STEDEF) is a structure that structurally separates the sleepers and the concrete bed using sleeper boots and resilience pads to reduce vibration transmitted to the concrete bed. Recently, the resilience pads of sleeper floating tracks that have been in use for more than 20 years are deteriorating. Accordingly, in order to evaluate the performance of the resilience pad, a static spring stiffness test is being performed after extracting the resilience pad. This evaluation technique is performed after replacing the resilience pad in use. However, the track natural frequency can change depending on the resilience pad spring stiffness and the uplift and subsidence of the concrete bed. In this study, modal testing technique was used to evaluate the track natural frequency. For this purpose, the sleeper boots material, resilience pad spring stiffness, and track natural frequency according to concrete bed uplift and subsidence were measured using modal tests at a laboratory scale. It was analyzed that the natural frequency of the sleeper floating track was directly affected by changes in the spring stiffness of the resilience pad. In addition, the change in natural frequency due to the uplift and subsidence of the concrete bed was also found to be large. Therefore, it is believed that the modal test technique presented in this study can be used to evaluate the resilience pad deterioration and voided sleepers.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.6
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• pp.197-204
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• 2003

This paper develops a computer model for estimating the handling of a cabover type large-sized truck. The truck is composed of front and rear suspension systems, a frame, a cab, and ten tires. The computer model is developed using ADAMS. A shock absorber, a rubber bush, and a leaf spring aunt a lot on the dynamic characteristic of the vehicle. Their stiffness and damping coefficient are measured and used as input data of the computer model. Leaf springs in the front and rear suspension systems are modeled by dividing them three links and joining them with joints. To improve the reliability of the developed computer model, the frame is considered as a flexible body. Thus, the frame is modeled by finite elements using MSC/PATRAN. A mode analysis is performed with the frame model using MSC/NASTRAN in order to link the frame model to the computer model. To verify the reliability of the developed computer model, a double lane change test is performed with an actual vehicle. In the double lane change, lateral acceleration, yaw rate, and roll angle are measured. Those test results are compared with the simulation results.

• Wind and Structures
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• v.20 no.3
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• pp.423-448
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• 2015

In this paper the unsteady fluid-structure interaction (FSI) problems with large structural displacement are solved by partitioned solution approaches in the arbitrary Lagrangian-Eulerian finite element framework. The incompressible Navier-Stokes equations are solved by the characteristic-based split (CBS) scheme. Both a rigid body and a geometrically nonlinear solid are considered as the structural models. The latter is solved by Newton-Raphson procedure. The equation governing the structural motion is advanced by Newmark-${\beta}$ method in time. The dynamic mesh is updated by using moving submesh approach that cooperates with the ortho-semi-torsional spring analogy method. A mass source term (MST) is introduced into the CBS scheme to satisfy geometric conservation law. Three partitioned coupling strategies are developed to take FSI into account, involving the explicit, implicit and semi-implicit schemes. The semi-implicit scheme is a mixture of the explicit and implicit coupling schemes due to the fluid projection splitting. In this scheme MST is renewed for interfacial elements. Fixed-point algorithm with Aitken's ${\Delta}^2$ method is carried out to couple different solvers within the implicit and semi-implicit schemes. Flow-induced vibrations of a bridge deck and a flexible cantilever behind an obstacle are analyzed to test the performance of the proposed methods. The overall numerical results agree well with the existing data, demonstrating the validity and applicability of the present approaches.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.517-528
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• 2007

Domestic or international existing researches regarding rail damage factors are focused on laying, vehicle conditions, driving speed and driving habits and overlook characteristics of track structure (elasticity, maintenance etc). Also in ballast track, as there is no special lateral spring stiffness of track also called as ballast lateral resistance in concrete track, generally, existing study shows concrete track has 2 time shorter life cycle for rail replacement than ballast track due to abrasion. As a result of domestic concrete track design and operation performance review, concrete track elasticity is lower than track elasticity of ballast track resulting higher damage on rail and tracks. Generally, concrete track has advantage in track elasticity adjustment than ballast track and in case of Europe, in concrete track design, it is recommended to have same or higher performance range of vertical elastic stiffness of ballast track but domestically or internationally review on lateral spring stiffness of track is very minimal. Therefore, through analysis of service line track on site measurement and analysis on performance of maintenance, in this research, dynamic characteristic behaviors of commonly used ballast and concrete track are studied to infer elasticity of service line track and experimentally prove effects of track lateral spring stiffness that influence curved rail damage as well as correlation between track elasticity by track system and rail damage to propose importance of appropriate elastic stiffness level for concrete and ballast track.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.1
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• pp.37-44
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• 2019

A bond-based peridynamic model has been reported dynamic fracture characteristic of brittle materials through a simple constitutive model. In the model, each bond is assumed to be a simple spring operating independently. As a result, this simple bond interaction modeling restricts the material behavior having a fixed Poisson's ratio of 1/4 and not being capable of expressing shear deformation. We consider a state-based peridynamics as a generalized peridynamic model. Constitutive models in the state-based peridynamics are corresponding to those in continuum theory. In state-based peridynamics, thus, the response of a material particle depends collectively on deformation of all bonds connected to other particles. So, a state-based peridynamic theory can represent the volume and shear changes of the material. In this paper, the perfect plasticity is considered to express plastic deformation of material by the state-based peridynamic constitutive model with perfect plastic flow rule. The elastic-plastic behavior of the material is verified through the stress-strain curves of the flat plate example. Furthermore, we simulate the high-speed impact on 3D granite model with a nonlocal contact modeling. It is observed that the damage patterns obtained by peridynamics are similar to experimental observations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.11
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• pp.1231-1237
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• 2014

It is essential to perform driving performance tests of military vehicles on rough terrain. A full car test is limited by cost and time constraints, because of which a dynamic analysis via computer simulation is preferred. In this study, a vehicle model is developed using MSC.ADAMS, a commercial multibody analysis program, and compared via experiments. FTire is modeled using the results of a tire performance test to obtain the vertical stiffness. A nonlinear damper is modeled by a characteristic experiment. Leaf springs are modeled with beam force elements and consisted to a vehicle model. The vertical force and acceleration response of the wheel are identified when vehicle is passing over a simple bump as well as a sinusoidal road. The developed vehicle model is verified with the results of a full car test.

• Journal of Korean Society of Rural Planning
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• v.7 no.1 s.13
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• pp.61-76
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• 2001

During the performance of large scale tidal land reclamation project along the coast line, the construction of large scale structures such as sea-dikes, closing estuaries will induce big changes of near-shore hydraulic behavior. In this paper, its is aimed to verify the change of tide and currents after the construction of sea-dike of the Saemangeum project along the coast line. Numerical scale model "TRISULA" which development by Delft Hydraulics in the Netherlands was used. "TRISULA" is adopting the finite difference numerical scheme, and mostly using for hydro-dynamic solution along the sea and estuaries. Model boundary is covering $100{\times}170$ Km and constructed with $133{\times}337$ grids. Outer side boundary is divided 48 sections, and input 37 tidal components are gained from another big scale numerical "Yellow Sea" model. Model calibrations & verifications were performed th field tide & current datas which were measured along sea-dike alignment during Aug. $1997{\sim}Apr$. 1999. And then, numerical simulation with the tide condition dated 17 Apr. 1999 was performed with & without sea-dike construction condition for the comparison. Evaluated boundary is 20 km out-side from sea-dike alignment. Four cross lanes were set up, each of lane contains 3 points, for the comparison of sea-dike construction effects. Results showing the tidal amplitude is reducing approximately 20 cm after the construction of sea-dike during spring tide condition, amplitude 6.9m. Currents after construction of sea-dikes along the alignment, the northern part shows 50%(inner), 90%(outer) and the southern part shows 10%(inner) 50%(outer) of the currents before construction.

• Journal of Environmental Science International
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• v.12 no.7
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• pp.735-744
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• 2003

The field observations on a seasonal characteristic of organic matter and its origin in the surface sediment were carried out at 35 stations in Deukryang bay, southern coast of Korean Peninsula from May 1995 to February 1996. The analytical parameters were mud temperature, ignition loss(IL), chemical oxygen demand(COD), pheopigment, sulfide and water content. The origin and seasonal dynamics of organic matter in Deukryang Bay were analyzed by COD/IL, COD/sulfide ratio and principal component analysis(PCA). As a results of the mud temperature fluctuated between 2.1$^{\circ}C$ with the lowest mean 4.6$^{\circ}C$ in winter and 27.6$^{\circ}C$ with the highest mean 25.5$^{\circ}C$ in summer. The range of ignition loss(IL) was from 3.1% in autumn to 21.5% in winter. Chemical oxygen demand(COD) showed the highest mean value of 8.45 mg/g dry in spring within the range of 2.90∼18.21 mg/g dry, while it showed the lowest value of 4.33 mg/g dry in autumn within the range of 0.67∼10.37 mg/g dry. Pheopigments showed the highest mean value of 9.04 $\mu\textrm{g}$/g dry in autumn within the range of 1.36∼20.44 $\mu\textrm{g}$/g dry, while it did the lowest mean value of 2.20 $\mu\textrm{g}$/g dry in summer within the range of 0.33∼11.36 $\mu\textrm{g}$/g dry. The range of total sulfide (H$_2$S) was from no detect(ND) to 3.30 mg/g dry in spring. And water content showed the annual mean value of 43.6% within the range of 23.6∼54.9%. The source of organic matter by COD/IL and COD/sulfide ratio in Deukryang Bay had been producted by primary producer in sea water areas except the areas effected by small stream, domestic and animal wastes. And the analytical results of PCA was able to be divided into three different regions. The former was characterized by the shallow depth and authigenic organic matter from phytoplankton in northwest area and northeastern inner bay, the secondary was done by deeper depth and allochthonous one from lands in southeast area and eastern entrance of bay, and the latter was done by authigenic one from the farm of seaweeds such as, sea cabbage, sea mustard etc in western entrance of bay. But a study on the relationship between sulfide and COD concentration in the northeastern inner bay which was characterized by the water stagnation will to take much more studying including major constituents of organic matter in the future.