• Ocean Systems Engineering
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• 제8권1호
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• pp.57-77
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• 2018

The present paper deals with the finite element analysis of water tanks with rigid baffle. Fluid is discretized by two dimensional eight-node isoparametric elements and the governing equation is simulated by pressure based formulation to reduce the degrees of freedom in the domain. Both free vibration and force vibration analysis are carried out for different sizes and positions of block at tank bottom. The fundamental frequency depends on block height and it reduces with the increase of block height. The variation of hydrodynamic pressure on tank walls not only depends of the exciting frequency but also on the size and position of rigid block at tank bottom. The hydrodynamic pressure has higher value when the exciting frequency is equal and lower than the fundamental frequency of the water in the tank. Similarly, the hydrodynamic pressure increases with the increase of width of the block for all exciting frequencies when the block is at the centre of tank. The left and right walls of tank have experienced different hydrodynamic pressure when the block is placed at off-centre. However, the increase in hydrodynamic pressure on nearest tank wall becomes insignificant after a certain value of the distance between the wall and the rigid block.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 3차
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• pp.61-65
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• 2010

The performance of slopes during earthquake is often accessed in terms of permanent deformation. In the assessment of permanent deformation, Newmark-type rigid block analysis is widely used. Original Newmark-type block approach, however, assumes the potential sliding mass to be rigid, and has been criticized to be potentially unconservative. The paper reviews analytically the impact of this noncompliance assumption on computed permanent deformations. The results indicate that there is a simple criterion that can be used to determine the level of conservativeness of the rigid block approach in cases of gently-sloping slip surfaces and retaining walls.

• Coupled systems mechanics
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• 제8권4호
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• pp.351-375
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• 2019

The present work investigates the use of a rigid rocking block as a tool to reduce vibrations in a frame structure. The study is based on a simplified model composed by a 2-DOF linear system, meant to represent a general M-DOF frame structure, coupled with a rocking rigid block through a linear visco-elastic device, which connects only the lower part of the 2-DOF system. The possibility to restrain the block directly to the ground, by means of a second visco-elastic device, is investigated as well. The dynamic response of the model under an harmonic base excitation is then analysed in order to evaluate the effectiveness of the coupling in reducing the displacements and the drift of the 2-DOF system. The nonlinear equations of motion of the coupled assemblage 2-DOF-block are obtained by a Lagrangian approach and then numerically integrated considering some reference mechanical and geometrical quantities as variable parameters. It follows an extensive parametric analysis, whose results are summarized through behaviour maps, which portray the ratio between the maximum displacements and drifts of the system, with and without the coupling with the rigid block, for several combinations of system's parameters. When the ratio of the displacements is less than unity, the coupling is considered effective. Results show that the presence of the rocking rigid block improves the dynamics of the system in large ranges of the characterizing parameters.

• 한국지반공학회논문집
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• 제23권12호
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• pp.117-124
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• 2007

지진으로 인해 사면에 발생한 영구적 변형 계산시 고려된 공간평균과 유연도의 영향을 조사하였다. 현재 변위계산에는 Newmark이 제안한 강체블럭해석기법이 이 기법의 효율적인 계산능력으로 인해 광범하게 사용되고 있다. 그러나 이 해석기법은 지진응답해석과 변위해석을 별도로 수행하는 소위 분리해석법을 채택하고 있다. 당초의 Newmark 해석기법은 활동토사를 강성체로 가정했으며 이로 인하여 비보수적 결과가 도출될 수 있다는 비판을 받아왔다. 본 논문은 Newmark-형식의 해석에서 강성체 가정의 영향을 검토하였다. 활동토사에 작용하는 지진하중의 전체 효과를 공간평균기법을 사용하여 평가하였으며 그 결과를 주파수 영역에서 분석하였다. 해석결과로부터 활동토사의 유연도 수준을 결정하는 경우 사용할 수 있는 단순한 지표를 제시하였다.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1040-1053
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• 2002

This research deals with the influence of nonlinearities associated with impact and sliding upon the rocking behavior of a rigid block, which is subjected to two-dimensional horizontal and vertical excitation. Nonlinearities in the vibration were found to depend strongly on the effect of the impact between the block and the base, which involves an abrupt reduction in the system's kinetic energy. In particular, when sliding occurs, the rocking behavior is substantially changed. Response analysis using a non-dimensional rocking equation was carried out for a variety of excitation levels and excitation frequencies. The chaos responses were observed over a wide response region, particularly, in the cases of high vertical displacement and violent sliding motion, and the chaos characteristics appear in the time histories, Poincare maps, power spectra and Lyapunov exponents of the rocking responses. The complex behavior of chaotic response, in phase space, is illustrated by the Poincare map. The distribution of the rocking response is described by bifurcation diagrams and the effects of sliding motion are examined through the several rocking response examples.

• Journal of Mechanical Science and Technology
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• 제17권9호
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• pp.1249-1260
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• 2003

This present work focuses on the influence of nonlinearities associated with impact on the rocking behavior of a rigid body block subjected to a two-dimensional excitation in the horizontal and vertical directions. The nonlinearities in rocking system are found to be strongly dependent on the impact between the block and the base that abruptly reduces the kinetic energy. In this study, the rocking systems of the two types are considered : The first is an undamped rocking system model that disregards the energy dissipation during the impact and the second is a damped rocking system, which incorporates energy dissipation during the impact. The response analysis is carried out by a numerical method using a non-dimensional rocking equation in which the variations in the excitation levels are considered. Chaos responses are observed over a wide range of parameter values, and particularly in the case of large vertical displacements, the chaotic characteristics are observed in the time histories, Poincare sections, the power spectral density and the largest Lyapunov exponents of the rocking responses. Complex behavior characteristics of rocking responses are illustrated by the Poincare sections.

• 한국안전학회지
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• 제14권4호
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• pp.3-12
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• 1999

This research concentrates on the influence of non-linearities associated with impact for the nonlinear rocking behavior of rigid block subjected to one dimensional sinusoidal excitation of horizontal direction. The transition of two governing rocking equations, the abrupt reduction in the kinetic energy associated with impact, and sliding motion of block. In this study, two type of rocking vibration system are considered. One is the undamped rocking vibration system, disregarding energy dissipation at impact and the other is the damped rocking system, including energy dissipation and sliding motion. The response analysis using non-dimensional rocking equation is carried out for the change of excitation parameters and friction coefficient. The chaos responses were discovered in the wide response region, particularly, for the case of high excitation amplitude and their chaos characteristics were examined by the time history, Poincare map, power spectra and Lyapunov Exponent of rocking responses. The complex behavior of chaos response, in the phase space, were illustrated by Poincare map. The bifurcation diagram and Poincare map were shown to be effective in order to understand chaos of rocking system.

• Journal of Periodontal and Implant Science
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• 제44권5호
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• pp.251-258
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• 2014

Purpose: The preferred material for bone augmentation beyond the envelope of skeletal bone is the bone block graft, due to its dimensional stability. We evaluated the necessity of rigid fixation for the bone block graft, and compared the bone regeneration and volume maintenance associated with grafting using a synthetic hydroxyapatite block (HAB) and an autogenous bone block (ABB) without rigid fixation on rabbit calvaria over two different periods. Methods: Cylinder-shaped synthetic HAB and ABB were positioned without fixation on the rabbit calvarium (n=16). The animals were sacrificed at 4 or 8 weeks postoperatively, and the grafted materials were analyzed at each healing period using microcomputed tomography and histologic evaluation. Results: Integration of the graft and the recipient bed was observed in all specimens, although minor dislocation of the graft materials from the original position was evident in some specimens (six ABB and ten HAB samples). A tendency toward progressive bone resorption was observed in the grafted ABB but not in the grafted HAB, which maintained an intact appearance. In the HAB group, the area of new bone increased between 4 and 8 weeks postoperatively, but the difference was not statistically significant. Conclusions: The nonfixed HAB was successfully integrated into the recipient bed after both healing periods in the rabbit calvaria. In spite of limited bone formation activity in comparison to ABB, HAB may be a favorable substitute osteoconductive bone material.

• 한국지진공학회논문집
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• 제23권1호
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• pp.19-29
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• 2019

Recent earthquakes in Korea caused some damages to stone pagodas and thereby awakened the importance of earthquake preparedness. Korean stone pagodas which have been built with very creative style of material use and construction method are worthy of world heritage. Each stone pagoda consists of three parts: top; body; and base. However each tower is uniquely defined by its own features, which makes it more difficult to generalize the seismic assessment method for stone pagodas. This study has focused on qualitative preliminary evaluation of stone pagodas that enables us to compare the relative seismic performance across major aspects among many various Korean pagodas. Specifically an analytical model for multi-block stone pagodas is to be proposed upon the investigation of structural characteristics of stone pagoda and their dynamic behavior. A strategy for seismic evaluation of heritage stone pagodas is to be established and major evaluation factors appropriate for the qualitative evaluation are identified. The evaluation factors for overall seismic resisting behavior of stone pagodas are selected based on the dynamic motions of a rigid block and its limit state. Numerical simulation analysis using discrete element method is performed to analyze the sensitivity of each factor to earthquake and discuss some effects on seismic performance.

• 소성∙가공
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• 제4권3호
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• pp.267-281
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• 1995

Preform design is one of the critical fields in metal forming. The finite element method(FEM) has been effective in designing preforms and process sequence, for which the backward tracing scheme of the rigid-plastic FEM has been explored. In this work a program using the backward tracing scheme by the rigid-plastic FEM is developed for three-dimensional plastic deformation, which is an extension of the scheme from two-dimensional cases. The calculation of friction between workpiece and die, and handling of boundary conditions during backward tracing require sophisticated treatment. The developed program is applied to upsetting of a rectangular block and to side pressing of a cylindrical workpiece. The results of the two applications show feasibility of the program on three-dimensional plastic deformation.