• Smart Structures and Systems
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• v.6 no.8
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• pp.905-920
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• 2010

Changes in temperature, loads and boundary conditions may have effects on the dynamic properties of large civil structures. Taking the Run Yang Suspension Bridge as an example, modal properties obtained from ambient vibration tests and from the structural health monitoring system of the bridge are used to identify and evaluate the modal parameter variability. Comparisons of these modal parameters reveal that several low-order modes experience a significant change in frequency from the completion of the bridge to its operation. However, the correlation analysis between measured modal parameters and the temperature shows that temperature has a slight influence on the low-order modal frequencies. Therefore, this paper focuses on the effects of the boundary conditions on the dynamic behaviors of the suspension bridge. An analytical model is proposed to perform a sensitivity analysis on modal parameters of the bridge concerning the stiffness of expansion joints located at two ends of bridge girders. It is concluded that the boundary conditions have a significant influence on the low-order modal parameters of the suspension bridge. In addition, the influence of vehicle load on modal parameters is also investigated based on the proposed model.

• Journal of the Korean Solar Energy Society
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• v.22 no.2
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• pp.61-69
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• 2002

Daylighting is a powerful vehicle of architectural expression and provides buildings a living quality due to constantly changing properties in intensity and color. As an environmental system, daylighting should be subjected to the same level of rigorous analysis and review that any environmental system receives. For example, increasing cooling loads and causing visual displeasure are easily occurred owing to the excessive sunlight through windows. Therefore, daylighting performance attributes and physical characteristics must be described qualitatively and quantitatively in early design process. In various architectural daylighting performance evaluation methods, the scale model experiment can be applied due to it's simplicity and usefulness. So, this study aims to evaluate the validation of scale model experiments in architectural daylighting performance. For the purpose, two scale model experiments under clear sky are conducted. And, the validation of the experiments are evaluated by computer simulations.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.04a
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• pp.433-440
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• 1998

For many decades, railroad technology was used to set up tracks with jointed rails and lengths in accordance with rolling and handling technology. The joints lead to drawbacks in the track and in controlling rising maintenance costs. So, railroad engineers became interested in eliminating joints to increase loads, speeds and improvements in rolling, welding, and fastening technology. Continuous welded rail(CWR) track has many advantages over the conventional jointed-rail track. In the case of the elimination of rail joints, it may cause the track to be suddenly and laterally buckled by thermal forces and vehicle load. Thermal forces are caused by an increase in the temperature of railway track. For many years, many analytical and experimental investigations have been conducted to improve the safety of CWR track by various research center in many country. In this paper, CWR track model and CWRB program is developed for buckling analysis using finite element method(FEM). The finite element discretization is used for a rail element with a total of 14 degrees of freedom. The stiffness of the fasteners, tie, and ballast bed is included by a set of spring elements. The investigation on the buckling modes and temperature of CWR track is presented in this paper

• Structural Engineering and Mechanics
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• v.55 no.1
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• pp.111-135
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• 2015

Bridge behavior under passing traffic loads has been studied for the past 50 years. This paper presents how to model congestion on bridges and how the maximum dynamic stress of bridges change during the passing of moving vehicles. Most current research is based on mid-span dynamic effects due to traffic load and most bridge codes define a factor called the dynamic load allowance (DLA), which is applied to the maximum static moment under static loading. This paper presents an algorithm to solve the governing equation of the bridge as well as the equations of motions of two real European trucks with different speeds, simultaneously. It will be shown, considering congestion in eight case studies, the maximum dynamic stress and how far from the mid-span it occurs during the passing of one or two trucks with different speeds. The congestion effect on the maximum dynamic stress of bridges can make a significant difference in the magnitude. By finite difference method, it will be shown that where vehicle speeds are considerably higher, for example in the case of railway bridges which have more than one railway line or in the case of multiple lane highway bridges where congestion is probable, current designing codes may predict dynamic stresses lower than actual stresses; therefore, the consequences of a full length analysis must be used to design safe bridges.

• Structural Engineering and Mechanics
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• v.56 no.5
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• pp.871-897
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• 2015

This paper presents a novel method based on sensitivity of structural response for identifying both the system parameters and input excitation force of a bridge. This method, referred to as "Adjoint Variable Method", is a sensitivity-based finite element model updating method. The computational cost of sensitivity analyses is the main concern associated with damage detection by these methods. The main advantage of proposed method is inclusion of an analytical method to augment the accuracy and speed of the solution. The reliable performance of the method to precisely indentify the location and intensity of all types of predetermined single, multiple and random damages over the whole domain of moving vehicle speed is shown. A comparison study is also carried out to demonstrate the relative effectiveness and upgraded performance of the proposed method in comparison to the similar ordinary sensitivity analysis methods. Moreover, various sources of error including the effects of noise and primary errors on the numerical stability of the proposed method are discussed.

• Journal of Aerospace System Engineering
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• v.14 no.4
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• pp.18-24
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• 2020

The counter-flow jet from a supersonic/hypersonic vehicle causes a structural change in the shock wave generated around the aircraft, which can lead to reduced drag and heat loads. Since the idea is to mount a counter-flow jet device for drag reduction in the aircraft, it is necessary to understand the effect of such a device on the entire aircraft. In this study, the effect of drag reduction due to counter-flow jet on a conventional rocket configuration was analyzed through CFD analysis. The results showed that the drag reduction effect was the largest in the blunt region and that the counter-flow jet also affected the downstream of the aircraft. The analysis indicated that the drag reduction effect by the counter-flow jet was about 10 to 25 % when targeting the entire rocket-shaped area, while the effect was as high as 50% when targeting only blunt objects.

• Proceedings of the KSR Conference
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• 2002.10a
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• pp.715-720
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• 2002

The dynamic load effects, generated by moving trains, are transferred to the railway bridges through tracks. The dynamic load effects may vary due to the dynamic characteristics of the applied vehicle loads and the railway bridges including the track system. However, the track models have been neglected or simplified by spring elements in the most studies since it is quite complicated to consider the track systems in the dynamic analysis models of railway bridges. In this study track system on railway bridges are modeled using a three-dimensional discrete-support model that can simulate the load carrying behavior of tracks. A 40m simply supported prestressed concrete box-girder system adopted for high-speed railway bridges are modeled for simulation works. The train models are composed of 20 cars for KTX. The dynamic response of railway bridges are found to be affected depending on whether the track model is considered for not. The influencing rate depends on the traveling speed and different wheel-axle distance. The dynamic bridge response decreases remarkably by the track systems around the resonant frequency. Therefore, the resonance effect can be reduced by modifying the track properties in the railway bridge, especially for KTX trains.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.219-226
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• 2003

The fatigue crack growth behavior of the SA516/60 steel used for pressure vessels was examined experimentally at room temperatures $25^{\circ}C$,$-30^{\circ}C$, $-60^{\circ}C$, $-80^{\circ}C$, $-100^{\circ}C$ and $-120^{\circ}C$ with stress ratio of R=0.05, 0.1 and 0.3. fatigue crack propagation rate da/dN related with stress intensity factor range $\Delta$K was influenced by stress ratio in stable than fatigue crack growth (Region II) with an increase in $\Delta$K. The resistance of fatigue crack growth at low temperature is higher compared with that at room temperature, which is attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and low temperatures are explained mainly by the crack closure and the strengthening due to the plasticity near the crack tip and roughness of the crack faces induced.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.2
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• pp.87-97
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• 2013

Recently the use of gas spring in the combat and commercial vehicle's suspension is increasing. Because of its nonlinear characteristics, the gas spring can support wide range of dynamic loads and gives good ride quality. In design of gas spring, isothermal and adiabatic processes are applied generally, but those processes could not produce heat transfer effect in the simulation. So in this study, heat transfer differential equation and BWR/Ideal state equation are used to calculate the pressure of gas spring which is changing with time. The numerical analysis showed that the pressure of gas spring forms a hysteresis loop in the both of the state equations. But the peak pressure value of BWR equation over 0.1Hz frequency are higher than that of adiabatic process. And the test results showed that the differences between test results and ideal gas equation are smaller than those of BWR equation, so the ideal equation is more accurate than BWR equation in this case.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.11
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• pp.1535-1542
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• 2015

An increasing number of electric vehicles (EVs) in power system affects its reliability in various aspects. Especially under high EV penetration level, new generating units are required to satisfy system's adequacy criterion. Wind power generation is expected to take the major portion of the new units due to environmental and economic issues. In this paper, the system reliability is analyzed using Loss of Load Expectation (LOLE) and Expected Energy Not Served (EENS) under each and both cases of increasing wind power generation and EVs. A probabilistic multi-state modeling method of wind turbine generator under various power output for adequate reliability evaluation is presented as well. EVs are modeled as loads under charging algorithm with Time-Of-Use (TOU) rates in order to incorporate EVs into hour-to-hour yearly load curve. With the expected load curve, the impact of EVs on the system adequacy is analyzed. Simulations show the reliability evaluation of increasing wind power capacity and number of EVs. With this method, system operator becomes capable of measuring appropriate wind power capacity to meet system reliability standard.