• Structural Engineering and Mechanics
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• 제54권5호
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• pp.891-908
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• 2015

For a systematic study on wind-induced vibration characteristics of large hyperbolic cooling towers with different feature sizes, the pressure measurement tests are finished on the rigid body models of three representative cooling towers with the height of 155 m, 177 m and 215 m respectively. Combining the refined frequency-domain algorithm of wind-induced responses, the wind-induced average response, resonant response, background response, coupling response and wind vibration coefficients of large cooling towers with different feature sizes are obtained. Based on the calculating results, the parametric analysis on wind-induced vibration of cooling towers is carried out, e.g. the feature sizes, damping ratio and the interference effect of surrounding buildings. The discussion shows that the increase of feature sizes makes wind-induced average response and fluctuating response larger correspondingly, and the proportion of resonant response also gradually increased, but it has little effect on the wind vibration coefficient. The increase of damping ratio makes resonant response and the wind vibration coefficient decreases obviously, which brings about no effect on average response and background response. The interference effect of surrounding buildings makes the fluctuating response and wind vibration coefficient increased significantly, furthermore, the increase ranges of resonant response is greater than background response.

• Coupled systems mechanics
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• 제3권2호
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• pp.147-170
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• 2014

In the recent times, dimensions of heavy load carrying vehicle have changed significantly incorporating structural flexibility in vehicle body. The present paper outlines a procedure for the estimation of bridge response statistics considering structural bending modes of the vehicle. Bridge deck roughness has been considered to be non homogeneous random process in space. Influence of pre cambering of bridge surface and settlement of approach slab on the dynamic behavior of the bridge has been studied. A parametric study considering vehicle axle spacing, mass, speed, vehicle flexibility, deck unevenness and eccentricity of vehicle path have been conducted. Dynamic amplification factor (DAF) of the bridge response has been obtained for several of combination of bridge-vehicle parameters. The present study reveals that flexible modes of vehicle can reduce dynamic response of the bridge to the extent of 30-37% of that caused by rigid vehicle model. However, sudden change in the bridge surface profile leads to significant amount of increment in the bridge dynamic response even if flexible bending modes remain active. The eccentricity of vehicle path and flexural/torsional rigidity ratios plays a significant role in dynamic amplification of bridge response.

• Wind and Structures
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• 제16권5호
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• pp.411-431
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• 2013

A computational study of vortex-induced transverse vibrations of a cylinder with low mass-damping is presented. An Arbitrary Lagrangian-Eulerian (ALE) formulation of the Unsteady Reynolds-Averaged Navier-Stokes equations (URANS), along with the Spalart-Allmaras (SA) one-equation turbulence model, are coupled conservatively with rigid body motion equations of the cylinder mounted on elastic supports in order to study the amplitude and frequency response of a freely vibrating cylinder, its flow-induced motion, Vortex Street, near-wake flow structure, and unsteady loading in a moderate range of Reynolds numbers. The time accurate response of the cylinder from rest to its limit cycle is studied to explore the effects of Reynolds number on the start of large displacements, motion amplitude, and frequency. The computational results are compared with published physical experiments and numerical studies. The maximum amplitudes of displacements computed for various Reynolds numbers are smaller than the experimental values; however, the overall agreement of the results is quite satisfactory, and the upper branch of the limit-cycle displacement amplitude vs. reduced velocity response is captured, a feature that was missed by other studies. Vortex shedding modes, lock-in phenomena, frequency response, and phase angles are also in agreement with experiments.

• Structural Engineering and Mechanics
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• 제13권2호
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• pp.135-154
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• 2002

This paper presents the convected material frame approach to study the nonlinear behavior of inelastic frame structures. The convected material frame approach is a modification of the co-rotational approximation by incorporating an adaptive convected material frame in the basic definition of the displacement vector and strain tensor. In the formulation, each discrete element is associated with a local coordinate system that rotates and translates with the element. For each load increment, the corresponding strain-displacement and nodal force-stress relationships are defined in the updated local coordinates, and based on the updated element geometry. The rigid body motion and deformation displacements are decoupled for each increment. This modified approach incorporates the geometrical nonlinearities through the continuous updating of the material frame geometry. A generalized nonlinear function is used to derive the inelastic constitutive relation and the kinematic hardening is considered. The equation of motion is integrated by an explicit procedure and it involves only vector assemblage and vector storage in the analysis by assuming a lumped mass matrix of diagonal form. Several numerical examples are demonstrated in close agreement with the solutions obtained by the ANSYS code. Numerical studies show that the proposed approach is capable of investigating large deflection of inelastic planar structures and providing an excellent numerical performance.

• 한국항공우주학회지
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• 제49권1호
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• pp.31-40
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• 2021

현대의 항공기는 고성능이면서도 경량이다. 그래서 유연한 구조물의 특성이 나타나며 비행 성능에 영향을 미치거나 한계를 짓기도 한다. 이러한 유연 특성은 항공기 설계 초기 단계부터 분석이 필요한데, 이를 위해 유연 항공기의 동적·정적 거동을 분석할 수 있는 프로그램을 개발하였으며, 그 결과를 제시한다. 다물체 동역학 시뮬레이션 기법에 기반하여, 강체 비행 역학, 구조 진동 거동, 그리고 비정상 공기력 등을 세부 모듈로 개발하고 통합하였다. 마지막으로, 통합 시뮬레이션 프로그램을 이용하여 유연 특성 항공기의 등속 수평 비행과 선회비행을 분석하였다.

• Structural Engineering and Mechanics
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• 제89권4호
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• pp.421-436
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• 2024

This research addresses experimentally the relationship between the excitation frequency and both hoop and axial wall stresses in a water storage tank. A low-density polyethylene tank with six different aspect ratios (water level to tank radius) was tested using a shake table. A laminar box with sand represents a soil site to simulate Soil-Structure Interaction (SSI). Sine excitations with eight frequencies that cover the first free vibration frequency of the tank-water system were applied. Additionally, Ricker wavelet excitations of two different dominant frequencies were considered. The maximum stresses are compared with those using a nonlinear elastic spring-mass model. The results reveal that the coincidence between the excitation frequency and the free-vibration frequency of the soil-tank-water system increases the sloshing intensity and the rigid-like body motion of the system, amplifying the stress development considerably. The relationship between the excitation frequency and wall stresses is nonlinear and depends simultaneously on both sloshing and uplift. In most cases, the maximum stresses using the nonlinear elastic spring-mass model agree with those from the experiments.

• 대한치과교정학회지
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• 제49권6호
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• pp.393-403
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• 2019

Objective: Sliding mechanics using orthodontic miniscrews is widely used to stabilize the anchorage during extraction space closure. However, previous studies have reported that both posterior segment displacement and anterior segment displacement are possible, depending on the mechanical properties of the archwire. The present study aimed to investigate the effect of archwire stiffness and friction change on the displacement pattern of the maxillary posterior segment during anterior segment retraction with orthodontic miniscrews in sliding mechanics. Methods: A three-dimensional finite element model was constructed. The retraction point was set at the archwire level between the lateral incisor and canine, and the orthodontic miniscrew was located at a height of 8 mm from the archwire between the second premolar and first molar. Archwire stiffness was simulated with rectangular stainless steel wires and a rigid body was used as a control. Various friction levels were set for the surface contact model. Displacement patterns for the posterior and anterior segments were compared between the conditions. Results: Both the anterior and posterior segments exhibited backward rotation, regardless of archwire stiffness or friction. Among the conditions tested in this study, the least undesirable rotation was found with low archwire stiffness and low friction. Conclusions: Posterior segment displacement may be unavoidable but reducing the stiffness and friction of the main archwire may minimize unwanted rotations during extraction space closure.

• 대한기계학회논문집A
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• 제35권3호
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• pp.235-240
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• 2011

모함에 연결되어 통신 케이블의 가이드 역할을 하는 탄성 호스는 모함의 운동 조건을 결정하는 중요한 인자이다. 길이가 수 십 미터에 달하는 탄성 호스를 실제 상황에서 실험을 하기에는 어려움이 있으므로 해석을 통해 거동 특성을 분석하고자 한다. 탄성 호스는 곡률 반경에 대한 변형뿐만 아니라 축 방향에 대한 변형도 발생하므로, 축 방향에 대한 변형 구배가 좌표계에서 유도되는 절대 절점 좌표계로 모델링하였으며, 연속체 역학 개념을 도입함으로써 대변형 효과를 표현하도록 하였다. 탄성 호스의 끝 단에 연결된 모함은 강체 모델로 표현하였고, 조향각에 의해 운동이 결정되도록 하였다. 또한, 수중에서 호스가 거동할 때 발생하는 유체 저항력을 고려함으로써 수중에서의 탄성 호스 거동 특성을 분석 하였다.

• Ocean and Polar Research
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• 제32권4호
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• pp.361-367
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• 2010

The principal objective of this paper was to evaluate the steering characteristics of a tandem tracked vehicle, each side of which features two tandem tracks, when crawling on extremely cohesive soft soil. The tandem tracked vehicle is assumed to be a rigid-body with 6-dof. The dynamic analysis program of the tandem tracked vehicle was developed via Newmark's method and the incremental-iterative method. A terra-mechanics model of extremely cohesive soft soil was implemented according to the relationships of normal pressure to sinkage, of shear resistance to shear displacement, and of dynamic sinkage to shear displacement. In order to simplify the characteristics of contact interaction between track segments and cohesive soft soil, the characteristics of soil are equated to the properties of intact soil. In an effort to evaluate the steering characteristics of a tandem tracked vehicle crawling on extremely cohesive soft soil, a series of dynamic simulations were conducted for a tandem tracked vehicle model with respect to the front and rear steering angle, the steering ratio, and the initial velocity.

• 대한교통학회지
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• 제30권2호
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• pp.127-136
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• 2012

다중추돌사고의 형태는 연쇄 추돌이라고 불리우는 뒤로부터의 순차적인 추돌과 앞으로부터의 순차적인 추돌, 그리고 순서가 섞여 있는 추돌형태로 구분된다. 다중추돌사고에 대하여 몇가지 효과적인 재구성 해석 방안을 제시한다. 브레이크 다이브 등으로 인한 차량 파손과 승객 부상을 활용하는 전통적인 경험적 수법과 강체역학 범주내에서의 이론적인 해석 결과를 구하여 당장에의 실용적인 적용이 가능하도록 하였다. 국내에 보급이 확산되고 있는 영상사고기록장치를 활용하고 시뮬레이션 프로그램 등을 병행 활용하여 다중추돌사고를 효과적으로 해석하는 방안을 제시하였다. 저장 동영상에 대한 단순 직관적인 조사를 넘어설 수 있도록 동영상 분석 결과에 근거한 시뮬레이션 해석을 수행하여 다중추돌사고에 대한 구체적이고 다양한 정보의 획득을 가능하게 하여 원인 규명 및 책임 소재 등을 명확하게 구분할 수 있도록 하였다.