National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Thermally induced vibration control of composite plates and shells with piezoelectric active damping

Abstract: A coupled piezoelectric field is modelled with an expansion strain in the numerical formulation to analyse piezohygrothermoelastic laminated plates and shells. Finite element actuator and sensor equations are derived using a nine-noded field consistent shallow shell element. Thermally induced vibration control is attempted using piezoelectrically developed active damping. The influence of piezoelectric anisotropy on active damping is evaluated, adopting a simple modelling technique. With 40% reduced actuation capability in the lateral direction, the directionally active lamina is observed to be equally efficient in controlling the vibration. In general, the directionally active lamina is efficient if the primary actuation direction is oriented along the fibre direction or in the direction of bending. The directional actuation appeared to be more effective in the velocity feedback control for cantilevered plates and shells. However, in the simply supported case, a balanced actuation effort is required to provide better controllability, which can be achieved by tailoring the directional actuation. The importance of geometric curvature for the actuator performance is also highlighted.

Relative effect of slope and equilibrium line altitude on the retreat of Himalayan glaciers

Abstract: It has been observed that a majority of glaciers in the Himalayas have been retreating. In this paper, we show that there are two major factors which control the advance/retreat of the Himalayan glaciers. They are the slope of the glacier and changes in the equilibrium line altitude. While it is well known, that these factors are important, we propose a new way of combining them and use it to predict retreat. The functional form of this model has been derived from numerical simulations using an ice-flow code. The model has been successfully applied to the movement of eight Himalayan glaciers during the past 25 years. It explains why the Gangotri glacier is retreating while Zemu of nearly the same length is stationary, even if they are subject to similar environmental changes. The model has also been applied to a larger set of glaciers in the Parbati basin, for which retreat based on satellite data is available, though over a shorter time period.