• Title/Summary/Keyword: RAMA

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Three-dimensional finite element modeling of a long-span cable-stayed bridge for local stress analysis

  • Lertsima, Chartree;Chaisomphob, Taweep;Yamaguchi, Eiki
    • Structural Engineering and Mechanics
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    • v.18 no.1
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    • pp.113-124
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    • 2004
  • The information on local stress acting in a bridge is required in many occasions such as fatigue assessment. The analysis by beam elements cannot yield this class of information adequately, while the finite element modeling of an entire long-span bridge by shell elements is impractical. In the present study, the hybrid modeling is tried out: only part of a bridge in which the point of interest is located is discretized by shell elements and the remaining part is modeled by beam elements. By solving a simple box girder problem, the effectiveness of this approach is discussed. This technique is then applied to the Rama IX Bridge for local stress evaluation. The numerical results compare very well with the results of a full-scale static loading test. The present research thus offers a practical yet accurate technique for the stress analysis of a long-span cable-stayed bridge.

Optimal sensor placement techniques for system identification and health monitoring of civil structures

  • Rao, A. Rama Mohan;Anandakumar, Ganesh
    • Smart Structures and Systems
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    • v.4 no.4
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    • pp.465-492
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    • 2008
  • Proper pretest planning is a vital component of any successful vibration test on engineering structures. The most important issue in dynamic testing of many engineering structures is arriving at the number and optimal placement of sensors. The sensors must be placed on the structure in such a way that all the important dynamic behaviour of a structural system is captured during the course of the test with sufficient accuracy so that the information can be effectively utilised for structural parameter identification or health monitoring. Several optimal sensor placement (OSP) techniques are proposed in the literature and each of these methods have been evaluated with respect to a specific problem encountered in various engineering disciplines like aerospace, civil, mechanical engineering, etc. In the present work, we propose to perform a detailed characteristic evaluation of some selective popular OSP techniques with respect to their application to practical civil engineering problems. Numerical experiments carried out in the paper on various practical civil engineering structures indicate that effective independence (EFI) method is more consistent when compared to all other sensor placement techniques.

Robust design of liquid column vibration absorber in seismic vibration mitigation considering random system parameter

  • Debbarma, Rama;Chakraborty, Subrata
    • Structural Engineering and Mechanics
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    • v.53 no.6
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    • pp.1127-1141
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    • 2015
  • The optimum design of liquid column dampers in seismic vibration control considering system parameter uncertainty is usually performed by minimizing the unconditional response of a structure without any consideration to the variation of damper performance due to uncertainty. However, the system so designed may be sensitive to the variations of input system parameters due to uncertainty. The present study is concerned with robust design optimization (RDO) of liquid column vibration absorber (LCVA) considering random system parameters characterizing the primary structure and ground motion model. The RDO is obtained by minimizing the weighted sum of the mean value of the root mean square displacement of the primary structure as well as its standard deviation. A numerical study elucidates the importance of the RDO procedure for design of LCVA system by comparing the RDO results with the results obtained by the conventional stochastic structural optimization procedure and the unconditional response based optimization.

Synthesis and Antibacterial Activity of Novel 5-(heteroaryl)isoxazole Derivatives (5-(Heteroaryl)isoxazole계 화합물의 합성 및 항균 활성)

  • RamaRao, R. Janaki;Rao, A.K.S. Bhujanga;Sreenivas, N.;Kumar, B. Suneel;Murthy, Y. L. N.
    • Journal of the Korean Chemical Society
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    • v.55 no.2
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    • pp.243-250
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    • 2011
  • The synthesis, characterization and antibacterial activity of novel isoxazole derivatives were reported. 3-Di (alkylamino)acryloalkanones were prepared and used as synthons to get the target isoxazole derivatives via reaction with hydroxylamine hydrochloride or hydroxylamine-O-sulphonic acid.

Linear shell elements for active piezoelectric laminates

  • Rama, Gil;Marinkovic, Dragan Z.;Zehn, Manfred W.
    • Smart Structures and Systems
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    • v.20 no.6
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    • pp.729-737
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    • 2017
  • Piezoelectric composite laminates are a powerful material system that offers vast options to improve structural behavior. Successful design of piezoelectric adaptive structures and testing of control laws call for highly accurate, reliable and numerically efficient numerical tools. This paper puts focus onto linear and geometrically nonlinear static and dynamic analysis of smart structures made of such a material system. For this purpose, highly efficient linear 3-node and 4-node finite shell elements are proposed. Both elements employ the Mindlin-Reissner kinematics. The shear locking effect is treated by the discrete shear gap (DSG) technique with the 3-node element and by the assumed natural strain (ANS) approach with the 4-node element. Geometrically nonlinear effects are considered using the co-rotational approach. Static and dynamic examples involving actuator and sensor function of piezoelectric layers are considered.

Sintering Behavior of Mechanically Alloyed Titanium - Titanium Nitride Nanocomposite Powders

  • Dabhade, Vikram V.;Panigrahi, B.B.;Godkhindi, M.M.;Rama Mohan, T. R.;Ramakrishnan, P.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.274-275
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    • 2006
  • The sintering behavior of titanium-titanium nitride nanocomposite powders has been studied by dilatometry. Titanium. titanium nitride nanocomposite powders were produced by the reactive milling of micron sized titanium powder $(12\;{\mu}m)$ in nitrogen atmosphere. The Ti-TiN nanocomposite powders milled for various durations along with the initial micron sized Ti powders were then sintered in the temperature range of $450-1000^{\circ}C$ by a constant rate of heating $(10^{\circ}C/min)$. The linear shrinkage, shrinkage rate, activation energy for sintering and microstructure has been studied and discussed as a function of milling time.

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Syntheses of Phenyl Styryl Ketone Resins and Their Applications to the Uptake of Lead(II) and Copper(II) Ions in Aqueous Solutions (페닐 스티릴 케톤 수지의 합성과 이들의 수용액상의 납(II)과 구리(II) 이온의 흡착에의 응용)

  • Akhtar Tashfeen;Paracha Rizwan N.;Hameed Shahid;Rama Nasim H.;Riaz Masud
    • Polymer(Korea)
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    • v.31 no.2
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    • pp.93-97
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    • 2007
  • Phenyl styryl ketone ligands 1-5 containing different functional groups were synthesized and attached to the aminated poly (styrene-divinvlbenzene) copolymer through diazotization. The coupling of the ligand with polymer was confirmed by FT-IR. The variation of the uptakes of Pb (II) or Cu (II) ions loaded in the prepared polymers (6-10) was examined at different pH values. An increase of metal uptake in the polymers was observed with the increase in pH value in aqueous solution.

Oscillation Results for Second Order Nonlinear Differential Equation with Delay and Advanced Arguments

  • Thandapani, Ethiraju;Selvarangam, Srinivasan;Vijaya, Murugesan;Rama, Renu
    • Kyungpook Mathematical Journal
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    • v.56 no.1
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    • pp.137-146
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    • 2016
  • In this paper we study the oscillation criteria for the second order nonlinear differential equation with delay and advanced arguments of the form $$([x(t)+a(t)x(t-{\sigma}_1)+b(t)x(t+{\sigma}_2)]^{\alpha})^{{\prime}{\prime}}+q(t)x^{\beta}(t-{\tau}_1)+q(t)x^{\gamma}(t+{\tau}_2)=0,\;t{\geq}t_0$$ where ${\sigma}_1$, ${\sigma}_2$, ${\tau}_1$ and ${\tau}_2$ are nonnegative constants and ${\alpha}$, ${\beta}$ and ${\gamma}$ are the ratios of odd positive integers. Examples are provided to illustrate the main results.