• Structural Engineering and Mechanics
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• 제77권5호
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• pp.627-635
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• 2021

The speed of rail vehicles become higher and higher over two decades, and China has unveiled a prototype high-speed train in October 2020 that has been able to reach 400 km/h. At such high speeds, wheel-rail force items that had previously been ignored in common computational model should be reevaluated and reconsidered. Aiming at this problem, a new model for investigating the vehicle-bridge interaction at high moving speed is proposed. Comparing with the common model, the new model was more accurate and applicable, because it additionally considers the second-order pseudo-inertia forces effect and its modeling equilibrium position was based on the initial deformed curve of bridge, which could include the influences of temperature, pre-camber, shrinkage and creep deformation, and pier uneven settlement, etc. Taking 5 km/h as the speed interval, the dynamic responses of the classical vehicle-bridge system in the speed range of 5 km/h to 400 km/h are studied. The results show that ignoring the second-order pseudo-inertia force will underestimate the dynamic response of vehicle-bridge system and make the high-speed railway bridge structure design unsafe.

• 한국자동차공학회논문집
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• 제11권5호
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• pp.156-162
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• 2003

The shock absorber is a part having a direct influence on the ride comfort, stability and dynamic load prediction of a vehicle. Thus, a rationally modeled shock absorber should be required in the dynamic analysis of vehicles. This thesis presents a modified model, based on Worden's hyperbolic tangent function, in order to fit experimental data on the velocity-damping force of a shock absorber. The hyperbolic tangent function correctly indicates the characteristics of a shock absorber, and has the advantage of containing physical causality. To evaluate the method, comparative evaluations of the linear model, the 5th polynomial model and Worden's model were carried out. The function presented in this paper is not only simple but also makes it possible to estimate the function coefficients easily and visually. In addition, it has the advantage of containing physical causality. Lastly, it effectively models the damping force of a shock absorber.

• 한국유체기계학회 논문집
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• 제14권5호
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• pp.48-54
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• 2011

Structural modifications of a ship may cause a fatal accident such as sinking and wrecking of ship. Especially, barge ship can be easily reconstructed to load more bulk cargo. In this study, for a real accident case, change of mooring force due to structural modification was analyzed to evaluate accident risk. A two dimensional dynamic model for the barge ship was constructed to compute mooring forces with related to floating motion. The equation of motion was established in Matlab code and buoyancy was calculated by using direct integration of submerged volume. The results showed that wind force, current force, and mooring force after rebuilding was approximately 4.3 kN, 14 kN, 1,561 kN respectively. The maximum force of mooring force according to the length of mooring cable were 1,614 kN at 30 m of mooring cable. Thus, an arbitrary modification of ship lead instability and unreliable result so that illegal rebuilding of ship should be avoided.

• 한국전기전자재료학회논문지
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• 제18권5호
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• pp.414-422
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• 2005

This paper shows the results of atomistic modeling for the Interaction between spherical nano abrasive and substrate In chemical mechanical polishing processes. Atomistic modeling was achieved from 2-dimensional molecular dynamics simulations using the Lennard-jones 12-6 potentials. We proposed and investigated three mechanical models: (1) Constant Force Model; (2) Constant Depth Model, (3) Variable Force Model, and three chemical models, such as (1) Chemically Reactive Surface Model, (2) Chemically Passivating Surface Model, and (3) Chemically Passivating-reactive Surface Model. From the results obtained from classical molecular dynamics simulations for these models, we concluded that atomistic chemical mechanical polishing model based on both Variable Force Model and Chemically Passivating-reactive Surface Model were the most suitable for realistic simulation of chemical mechanical polishing in the atomic scale. The proposed model can be extended to investigate the 3-dimensional chemical mechanical polishing processes in the atomic scale.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1479-1482
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• 2003

The shock absorber is a part having a direct influence on the ride comfort, stability and dynamic load prediction of a vehicle. Thus, a rationally modeled shock absorber should be required in the dynamic analysis of vehicles. This thesis presents a modified model, based on Worden's hyperbolic tangent function, in order to fit experimental data on the velocity-damping force of a shock absorber. The hyperbolic tangent function correctly indicates the characteristics of a shock absorber. and has the advantage of containing physical causality. To evaluate the method, comparative evaluations of the linear model. the 5th polynomial model and Worden's model were carried out. The function presented in this paper is not only simple but also makes it possible to estimate the function coefficients easily and visually. In addition, it has the advantage of containing physical causality. Lastly, it effectively models the damping force of a shock absorber.

• 한국해양공학회지
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• 제30권5호
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• pp.374-380
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• 2016

The large drift and angle of attack motion of an ROV (Remotely operated vehicle) cannot be modeled using the typical hydrodynamic coefficients of conventional straight running AUVs and specific slender bodies. In this paper, the ROV hull is divided into several simple-shaped components to model the hydrodynamic force and moment. The hydrodynamic force and moment acting on each component are modeled as the components of added mass force and drag using the known values for simple shapes such as a cylinder and flat plate. Since an ROV is operated under the water, the only environmental force considered is the current effect. The target ROV dealt with in this paper has six thrusters, and it is assumed that its maneuvering motion is determined using a thrust allocation algorithm. Tracking simulations are carried out on the ship’s surface near the stern, bow, and midship sections based on the modeling of the hydrodynamic force and current effect.

• Structural Engineering and Mechanics
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• 제28권5호
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• pp.515-524
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• 2008

In this paper the effect of prestressing force on the first flexural natural frequency of beams is studied. Finite element technique is used to model the beam-tendon system, and the prestressing force is applied in the form of initial tension in the tendon. It is shown that the effect of prestressing force on the first natural frequency depends on bonded and unbonded nature of the tendon, and also on the eccentricity of tendon. For the beams with bonded tendon, the prestressing force does not have any appreciable effect on the first flexural natural frequency. However, for the beams with unbonded tendon, the first natural frequency significantly changes with the prestressing force and eccentricity of the tendon. If the eccentricity of tendon is small, then the first natural frequency decreases with the prestressing force and if the eccentricity is large, then the first flexural natural frequency increases with the prestressing force. Results of the present study clearly indicate that the first natural frequency can not be used as an easy indicator for detecting the loss of prestressing force, as has been attempted in some of the past studies.

• 대한토목학회논문집
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• 제26권3C호
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• pp.171-180
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• 2006

앵커의 활동억지효과를 조사하기 위하여 일련의 모형실험을 수행하였다. 이를 위하여 앵커가 설치된 사면에 대한 모형실험 장치를 고안하였다. 그리고 모형실험시 각종 계측시스템을 이용하여 사면활동에 따른 앵커의 축력변화를 조사하였다. 모형실험결과 앵커의 면적비를 0.5%로 설치할 경우 네일의 사면활동에 대한 억지효과가 가장 크게 발휘된다. 앵커축력의 초기손실율은 초기인장력의 약 24%로 나타났다. 이는 기존의 현장실험결과(윤중만, 1997)에서 제안된 10%~25%의 범위와 일치함을 알 수 있다. 그리고 앵커의 유효인장력은 초기인장력의 70%에 해당하므로, 앵커의 초기인장력은 설계인장력보다 30%정도 증가하여 설계하여야 할 것이다. 한편, 앵커의 초기인장력이 증가하게 되면 사면지반의 상대밀도가 증가되어 사면은 취성파괴의 거동을 보임을 알 수 있다.

• 한국항해항만학회지
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• 제33권5호
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• pp.309-314
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• 2009

Manta형 무인잠수정(MUUTV)을 대상으로 회류수조에서의 모형실험을 통해 동일한 동체 모형에 대해 형상이 서로 다른 부가물을 부착했을 때의 동유체력 특성을 실험적으로 검토하였으며, 동유체력 측정 결과를 이론계산치와 비교하였다. 아울러 이를 바탕으로 운동안정성을 검토하여 최적의 부가물 형상 결정의 이론적 근거를 확립하였다.

• 한국자동차공학회논문집
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• 제7권5호
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• pp.154-161
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• 1999

An elastomeric bushing is a device used in automotive suspension systems to cushion the force transmitted from the wheel to the frame of the vehicle. A bushing is an elastomeric hollow cylinder which is bonded to a solid metal shaft at its inner surface and a metal sleeve at its outer suface. The relation between the force applied to the shaft or sleeve and their relative deformation is nolinear and exhibits features of viscoelasticity. Numerical solutions of the boundary value problem represent the exact bushing response for use in the method for determining the force relaxation function of the bushing. The new nonlinear viscoelastic bushing model, which is called Pipkin-Rogers model, is proposed and it is shown that the predictions of the proposed force-displacement relation are in very good agreement with the exact results. This new bushing model is thus very suitable for use in multi-body dynamics codes. The success of the present study for axial mode response suggests that the same approach be applied to other modes, such as torsional or radial modes.