• Title/Summary/Keyword: Laplace transformation

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A multiscale creep model as basis for simulation of early-age concrete behavior

  • Pichler, Ch.;Lackner, R.
    • Computers and Concrete
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    • v.5 no.4
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    • pp.295-328
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    • 2008
  • A previously published multiscale model for early-age cement-based materials [Pichler, et al.2007. "A multiscale micromechanics model for the autogenous-shrinkage deformation of early-age cement-based materials." Engineering Fracture Mechanics, 74, 34-58] is extended towards upscaling of viscoelastic properties. The obtained model links macroscopic behavior, i.e., creep compliance of concrete samples, to the composition of concrete at finer scales and the (supposedly) intrinsic material properties of distinct phases at these scales. Whereas finer-scale composition (and its history) is accessible through recently developed hydration models for the main clinker phases in ordinary Portland cement (OPC), viscous properties of the creep active constituent at finer scales, i.e., calcium-silicate-hydrates (CSH) are identified from macroscopic creep tests using the proposed multiscale model. The proposed multiscale model is assessed by different concrete creep tests reported in the open literature. Moreover, the model prediction is compared to a commonly used macroscopic creep model, the so-called B3 model.

A Study on Piano String Vibration (피아노현의 진동에 관한 연구)

  • Kang, T.-H.;Yoon, Y.-K.;Lee, S.-J.
    • The Journal of the Acoustical Society of Korea
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    • v.8 no.1
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    • pp.13-22
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    • 1989
  • This study made an analysis of the characteristics of vibration & tone color of the piano strings on which a concentrated mass was set to give variety of different variations to the gamut. Theoretical analyses in this study were based on discrete and continuous system, of which the former was transformed into a multi-degree of freedom system by dividing into a number of small parts, while the latter utilized mode summation and Laplace transformation methods. And experiments were carried out with setting concentrated masses on upright piano string.

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A simplified dynamic analysis for estimation of the effect of rotary inertia and diaphragmatic operation on the behaviour of towers with additional masses

  • Michaltsos, G.T.;Konstantakopoulos, T.G.
    • Structural Engineering and Mechanics
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    • v.10 no.3
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    • pp.277-288
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    • 2000
  • The present paper, deals with the dynamic analysis of a thin-walled tower with varying cross-section and additional masses. It, especially, deals with the effect of the rotary inertia of those masses, which have been neglected up to now. Using Galerkin's method, we can find the spectrum of the eigenfrequencies and, also, the shape functions. Finally, we can solve the equations of the problem of the forced vibrations, by using Carson-Laplace's transformation. Applying this method on a tall mast with 2 concentrated masses, we can examine the effect of the rotary inertia and the diaphragmatic operation of the above masses, on the 3 first eigenfrequencies.

Trajectory control of a flexible robot arm using inverse dynamics

  • Sasaki, Minoru;Yamagata, Eiji;Inooka, Hikaru
    • 제어로봇시스템학회:학술대회논문집
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    • 1988.10b
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    • pp.987-992
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    • 1988
  • In recent years there has been much interest in using light-weight, higher performance arms for both commercial and space-based applications, leading to the research of flexible robot manipulator. This paper is concerned with the trajectory control of a flexible arm using inverse dynamics. Inverse problems are important to robot control and programming, since they allow one to find the appropriate inputs necessary for producing the desired outputs. The input is obtained by the numerical inversion of Laplace transformation in the time domain. And we attempt the trajectory control experiment of a flexible arm using this calculated input. In this article we compare the numerical results with experimental results and can find good agreement. The results make clear that this technique has the good potential for the control of tip trajectory of flexible robot arms.

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The influence of different support movements and heights of piers on the dynamic behavior of bridges -Part I: Earthquake acting transversely to the deck

  • Michaltsos, George T.;Raftoyiannis, Ioannis G.
    • Interaction and multiscale mechanics
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    • v.2 no.4
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    • pp.431-454
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    • 2009
  • This paper presents a simple model for studying the dynamic response of multi-span bridges resting on piers with different heights and subjected to earthquake forces acting transversely to the bridge, but varying spatially along its length. The analysis is carried out using the modal superposition technique, while the solution of the resulting integral-differential equations is obtained via the Laplace transformation. It has been found that the piers' height and the quality of the foundation soil can affect significantly the dynamic behavior of such bridges. Typical examples showing the effectiveness of the method are presented with useful results listed.

Dynamic response for electromechanical integrated toroidal drive to electric excitation

  • Xu, Lizhong;Hao, Xiuhong
    • Structural Engineering and Mechanics
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    • v.26 no.6
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    • pp.635-650
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    • 2007
  • In this paper, the equivalent exciting force caused by electric excitation is derived. By dividing load and displacement vectors into mean values and time-varying ones, the dynamic equations of the system are transformed into linear ones for time-varying portion of the displacements. The analytical equations of the forced time responses of the drive system to electric excitations are obtained. Using the Laplace transformation, the transfer function of the drive system is obtained. These equations are used to analyze the time and frequency responses of the drive system to the electric excitation. It is known that electric excitation can cause forced responses of the drive system, the total dynamic responses are decided by three phase exciting voltages, exciting frequency and natural frequencies of the drive system, and the drive parameters have obvious influence on the time and frequency responses.

Study on Transient Temperature Distribution in Annular Fin of Uniform Thickness (均一두께 의 원통핀 에서 過渡溫度 分布 에 관한 硏究)

  • 손병진;박희용;이흥주
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.6 no.3
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    • pp.247-255
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    • 1982
  • The heat diffusion equation for an annular fin is analyzed by Laplace transformation. The fin has a uniform thickness, with its end insulated, and three different temperature profiles at the base such as step change, harmonic and exponential functions. The exact solutions for the temperature and heat flux of the fins are obtained with the infinite series. The series solutions converge rapidly for large values of dimensionless time, but slowly for small values. Therefore some approximate solutions are presented here to fine the temperature distribution and heat flux for small values of dimensionless time. Furthermore a simple approximate heat flux, .OMEGA.=1.13c.tau.$^{1}$2/ is found in the range of .tau. .leg. o.1/c for the exponential function at the base.

Two-Dimensional Modelling of the Cochlear Basilar Membrane (달팽이관 기저막의 이차원적 모델링)

  • 장순석
    • Journal of Biomedical Engineering Research
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    • v.15 no.4
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    • pp.439-446
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    • 1994
  • Two-Dimensional modelling of the Cochlear biomechanics is presented in this paper. The Laplace partial differential equation which represents the fluld mechanics of the Cochlea has been transformed into two-dimensional electrical transmission line. The procedure of this transformation is explained in detail. The comparison between one and two dimensional models is also presented. This electrical modelling of the basilar membrane (BM) is clearly useful for the next approach to the further development of active elements which are essenclal in the producing of the sharp tuning of the BM. This paper shows that two-dimension model is qualitatively better than one-dimensional model both in amplitude and phase responses of the BM displacement. The present model is only for frequency response. However because the model is electrical, the two-dimensional transmission line model can be extended to time response without any difficult.

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Dynamic behavior of a supporting structure subjected to a force of time dependent frequency (시간종속적 하중이 작용하는 구조물의 동특성)

  • 정태진;박영조
    • Journal of the korean Society of Automotive Engineers
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    • v.8 no.4
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    • pp.66-72
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    • 1986
  • Numerical analysis has been made on the dynamic behavior of a supporting structure subjected to a force of time dependent frequency. The effect of solid viscosity is studied when the frequency of external force passes through the first critical frequency of the simple beam for four times. Within the Euler-Bernoulli beam theory, the solutions are obtained by using finite Fourier and Laplace transformation methods with respect to space and time variables. The result shows that the maximum value of the dynamic deflection is considerably affected by the value of the solid viscosity as well as the frequency difference The maximum dynamic deflection is found to occur in the frequency lower limit C of 0.85-0.985 in the presence of the solid viscosity.

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Dynamic characteristics of an elastically supported beam (탄성적으로 지지된 보의 동특성)

  • 정태진;박영조;홍동표
    • Journal of the korean Society of Automotive Engineers
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    • v.8 no.2
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    • pp.43-50
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    • 1986
  • Numerical analysis has been made on the dynamic behavior of an elastically supported beam subjected to an axial force and solid viscosity when the frequency of external force passes through the first critical frequency of the beam. Within the Euler-Bernoulli beam theory the solutions are obtained by using finite Fourier sine transform and Laplace transformation methods with respect to space and time variables. Integrations involved in the theoretical results are carried out by Simpson's numerical integration rule. The result shows that the maximum value of the dynamic deflection are much affected by the value of a solid viscosity, an axial force, an elastic constant and ratio of .omega.$_{max}$/.omega.$_{1}$.

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