• 대한기계학회논문집A
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• 제28권10호
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• pp.1583-1589
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• 2004

In this paper, A new finite element method for the time domain analysis of the dynamic stress intensity factor of two-dimensional viscoelastic body with a stationary central crack under the transient dynamic load is presented, which is based on the intergrodifferential equations of motion in the isotropic linear viscoelasticity and the Galerkin's method. The vlscoelastic material is assumed to be elastic in dilatation and behaves like a standard linear solid in shear. As a numerical example, the Chen's problem in viscoelastodynamic version is solved for the parametric study about the effect of viscosity and relaxation time on the dynamic stress intensity factor.

• Journal of Biosystems Engineering
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• 제26권3호
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• pp.245-252
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• 2001

This study was carried out to investigate the effect of three factors(dynamic load, inflation pressure and multiple passes of the tire) on the contact pressure and the soil stresses under the tire. A series of soil bin experiment was conducted with a 6.00R14 radial-ply tire for sandy loam soil. Tire contact pressure at soil surface and soil stresses at 10cm and 20cm soil depth were measured for the three levels of dynamic load(1.17kN, 2.35kN and 3.53kN), for the three levels of tire inflation pressure(103.42kPa, 206.84kPa and 413.69kPa), and for five different number of passes(1, 2, 3, 4 and 5 pass). The following results were drawn from this study 1) As dynamic load, inflation pressure and number of passes of the tire increased, tire contact pressure at soil surface and soil stresses at 10cm and 20cm soil depth increased accordingly. Thus increased in dynamic load, inflation pressure and number of passes of the tire would increase soil compaction. 2) The effect of three different factors, or dynamic load, inflation pressure and number of passes of the tire, decreased as the soil depth increase. Consequently, it was found that the soil compaction at a shallow depth in soil is larger than that at deep place in soil. 3) The increase of dynamic load and number of passes increased soil stress exponentially, but the increase of inflation pressure increased soil stress linearly. The effect of tire inflation pressure on soil stress was relatively less than that of the dynamic load. Therefore, it was concluded that dynamic load is more important factor affecting soil compaction in comparison to the inflation pressure of tire.

• Structural Engineering and Mechanics
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• 제12권4호
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• pp.409-428
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• 2001

The characteristics of dynamic wheel loads of heavy vehicles running on bridge and rigid surface are investigated by using three-dimensional analytical model. The simulated dynamic wheel loads of vehicles are compared with the experimental results carried out by Road-Vehicles Research Institute of Netherlands Organization for Applied Scientific Research (TNO) to verify the validity of the analytical model. Also another comparison of the analytical result with the experimental one for Umeda Entrance Bridge of Hanshin Expressway in Osaka, Japan, is presented in this study. The agreement between the analytical and experimental results is satisfactory and encouraging the use of the analytical model in practice. Parametric study shows that the dynamic increment factor (DIF) of the bridge and RMS values of dynamic wheel loads are fluctuated according to vehicle speeds and vehicle types as well as roadway roughness conditions. Moreover, there exist strong dominant frequency resemblance between bounce motion of vehicle and bridge response as well as those relations between RMS values of dynamic wheel loads and dynamic increment factor (DIF) of bridges.

• Journal of Electrical Engineering and Technology
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• 제11권2호
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• pp.329-337
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• 2016

With the increasing deployment of distributed generators in the distribution system, a very large search space is required when dynamic programming (DP) is applied for the optimized dispatch schedules of voltage and reactive power controllers such as on-load tap changers, distributed generators, and shunt capacitors. This study proposes a new optimal voltage and reactive power scheduling method based on dynamic programming with a heuristic searching space reduction approach to reduce the computational burden. This algorithm is designed to determine optimum dispatch schedules based on power system day-ahead scheduling, with new control objectives that consider the reduction of active power losses and maintain the receiving power factor. In this work, to reduce the computational burden, an advanced voltage sensitivity index (AVSI) is adopted to reduce the number of load-flow calculations by estimating bus voltages. Moreover, the accumulated switching operation number up to the current stage is applied prior to the load-flow calculation module. The computational burden can be greatly reduced by using dynamic programming. Case studies were conducted using the IEEE 30-bus test systems and the simulation results indicate that the proposed method is more effective in terms of saving electric charges and improving the voltage profile than loss minimization.

• 한국강구조학회 논문집
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• 제10권2호통권35호
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• pp.187-199
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• 1998

고속철도는 고속으로 이동하는 일련의 이동질량효과를 일으켜 교량에 동적인 처짐을 일으킨다. 이러한 이동질량의 동적효과는 동일한 크기의 정적하중이 작용했을때에 비해 교량내부에 큰 응력을 발생시키고, 이때 발생하는 상반응력은 피로의 문제를 야기시켜 교량의 수명을 단축시킬수 있으며 과도한 응력은 교량의 안전에도 영향를 줄 수 있다. 그러나 지금까지 교량의 설계는 정적인 개념으로 되어왔는데, 예를 들면 동적인 영향을 고려하는데 단순히 정적하중에다 충격계수를 곱해준다. 그러나 충격계수의 고려는 단순하므로 동적인 거동에 영향을 미치는 모든 요소를 다 고려할 수는 없다. 따라서 이 연구에서는 고속철도의 이동질량 모형을 연구하여 이를 컴퓨터 모의 기법을 통해 해석하여 교량에 미치는 복잡한 동적 거 동특성을 제시하였다.

• Wind and Structures
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• 제8권4호
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• pp.251-268
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• 2005

This paper describes the work of the International Association for Wind Engineering Working Group E -Dynamic Response, one of the International Codification Working Groups set up at the Tenth International Conference on Wind Engineering in Copenhagen. Comparisons of gust loading factors and wind-induced responses of major codes and standards are first reviewed, and recent new proposals on 3-D gust loading factor techniques are introduced. Then, the combined effects of along-wind, crosswind and torsional wind load components are discussed, as well as the dynamic characteristics of buildings. Finally, the mathematical forms of along-wind velocity spectra for along-wind response calculation and codification of acceleration criteria are discussed.

• International Journal of Safety
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• 제9권2호
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• pp.16-21
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• 2010

In this study, the variations of transformed impact factors and load carrying capacity of highway bridges measured from the state of expansion joint are evaluated. the field loading tests were performed on the highway bridge with damaged expansion joint to investigate the variation of the load carrying capacity. From the field loading tests in case that damaged expansion joint exist or do not exist, the static displacements and dynamic displacements were measured, and TIF were calculated, respectively. dynamic test is performed in order to estimate dynamic displacement and TIF according to the level of damage of expansion joint. From the results of TIF, the load carrying capacity of highway bridges with damaged expansion joint were estimated.

• 한국산업융합학회 논문집
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• 제7권2호
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• pp.161-166
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• 2004

The impact factor of bridges is analyzed based on experimental data to examine the characteristics of the dynamic responses of bridges. The experimental impact factors are compared with the impact factor of Korean Highway Design Specification and Japan T-load in terms of the span length. According to the superstructural types of bridges, the variation of the impact factor is analyzed. When vehicles are passing on a bridge, the dynamic effect acts on the bridge impact factor more than at the time of design because of the velocity of vehicles, the surface roughness reduction due to the deterioration of the bridge deck pavement, and the disconnection of the bridge entrance and the expansion joint. Because the actual value is greater than the expected value at the time of design, the dynamic response of the bridge accelerates the deterioration of the bridge due to the accumulation of fatigue, and the bridge's life-time is shortened and can have an influence on the serviceability and safety of the bridge.

• Steel and Composite Structures
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• 제25권5호
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• pp.617-624
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• 2017

In this study, a new empirical method is presented to obtain Dynamic Increase Factor (DIF) in nonlinear static analysis of structures against sudden removal of a gravity load-bearing element. In this method, DIF is defined as a function of minimum ratio of difference between maximum moment capacity ($M_u$) and moment demand ($M_d$) to plastic moment capacity ($M_p$) under unamplified gravity loads of elements. This function determines the residual strength of a damaged building before amplified gravity loads. For each column removal location, a nonlinear dynamic analysis and a step-by-step nonlinear static analysis are carried out and the modified empirical DIF formulas are derived, which correspond to the ratio min $[(M_u-M_d)/M_p]$ of beams in the bays immediately adjacent to the removed column, and at all floors above it. Therefore, the new DIF can be used with nonlinear static analysis instead of nonlinear dynamic analysis to assess the progressive collapse potential of a moment frame structure. The proposed DIF formulas can estimate the real residual strength of a structure based on critical member.

• Journal of Biosystems Engineering
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• 제27권1호
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• pp.1-10
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• 2002

This study was carried out to investigate experimentally the effect of three factors(dynamic load, inflation pressure and number of passes of tire) on soil compaction under the tire. The experiment were conducted with a 6.00R14 radial-ply tire for sandy loam soil using soil bin system. To evaluate the effect of three factors on soil compaction under the tire, the sinkage. density and volume of soil under the tire were measured fur the three levels of dynamic load(1.17kN, 2.35kN and 3.53kN), for the three levels of tire inflation pressure(103.42kPa, 206.84kPa and 413.67kPa), and for three different number of passes(1, 3 and 5). The results of this study can be summarized as follows : 1. As dynamic load, inflation pressure and number of passes of the tire increased, soil sinkage and density increased. and volume of soil decreased. Thus increase in dynamic load, inflation pressure and number of passes of the tire would increase soil compaction. 2. The effect of tire inflation pressure on sinkage. density and volume of soil under the tire was relatively less than that of the dynamic load. Therefore, it was concluded that dynamic load was more important factor affecting soil compaction in comparison to the inflation pressure of tire. 3. The effect of three different factors on sinkage, density and volume of soil decreased as the soil depth increase. Consequently, it was fecund that soil compaction at a shallow depth in soil was larger than that at deep place in soil.