Articles written in Sadhana

    • Active control of non-stationary response of a two-degree of freedom vehicle model with nonlinear suspension

      G V Raju S Narayanan

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      Active control of non-stationary response of a two-degree of freedom vehicle model with nonlinear passive suspension elements is considered in this paper. The method of equivalent linearization is used to derive an equivalent linear model and optimal control laws are obtained by using stochastic optimal control theory based on full state information. Velocity squared quadratic damping and hysteretic type of stiffness nonlinearities are considered. The effect of the nonlinearities on the active system performance is studied. The performance of active suspensions with nonlinear passive elements is found to be superior to the corresponding passive suspension systems.

    • Chaos in mechanical systems — A review

      P Sekar S Narayanan

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      In this paper, a review of the various developments in the field of chaotic dynamics with specific emphasis on chaos in structural and mechanical systems is presented. The paper discusses some known chaotic systems such as the Lorenz, Rössler, Ueda and Henon attractors as well as chaos in Duffing and Van der Pol oscillators. The paper also covers chaos in piecewise linear systems, impacting oscillators and flow induced vibrating systems. Topics such as bifurcations and routes to chaos, different ways of characterising chaos, domains of attraction and control of chaos are also discussed.

    • High temperature effects on different grades of concrete


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      Concrete structures are liable to be exposed to fire during their lifetime. After exposure to high temperature, the strength of concrete is determined only by its residual properties. The method of cooling, after exposure, is one of the significant factors in determining the residual properties of concrete. The compressive strength, tensile strength, stress-strain response and elastic modulus of concrete are the important properties to be considered in the design of fire resistant structures. In this paper, the behaviour of high temperature exposure of three different grades of concrete M20, M45 and M60 are considered. The specimens were subjected to high temperature regime of 100°C–900°C and were cooled by different methods. The maximum degradation ofmechanical properties was observed between temperature regimes of 400°C to 600°C. High strength concrete was found to be more vulnerable compared to normal strength concrete. Mathematical models expressing the variation of different mechanical properties of concrete were developed and explained.

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