Department of Mechanical Engineering

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In this paper we propose a model to relate Eulerian spatial and temporal velocity autocorrelations in homogeneous, isotropic and stationary turbulence. We model the decorrelation as the eddies of various scales becoming decorrelated. This enables us to connect the spatial and temporal separations required for a certain decorrelation through the 'eddy scale'. Given either the spatial or the temporal velocity correlation, we obtain the 'eddy scale' and the rate at which the decorrelation proceeds. This leads to a spatial separation from the temporal correlation and a temporal separation from the spatial correlation, at any given value of the correlation relating the two correlations. We test the model using experimental data from a stationary axisymmetric turbulent flow with homogeneity along the axis. © 2006 Cambridge University Press.

World University root node

Journal of Fluid Mechanics

A model relating Eulerian spatial and temporal velocity correlations

The paper deals with a mathematical model of a one degree of freedom robotic manipulator which has two rotary actuators located on the remote base to drive the manipulator via a pair of flexible tendons . With a recursive Newton-Euler approach dynamic equation of the manipulator is derived. Unlike earlier work in this field, the present work deals with tendons nonlinear stiffness and linear damping. Positions of the manipulator and torque requirement have been investigated for certain rotation of the actuators. Effects of various system parameters on the end-effactor position have also been investigated. A PD feedback controller is used for controlling the end-effactor positioning of manipulator.

Proceedings of the 12th National Conference on Machines and Mechanisms, NaCoMM 2005

Nonlinear dynamics of robotic manipulator with flexible tendons

Using laws of conservation, a general electrothermoelastic formulation has been developed for the analysis of smart structures. Based on this formulation a layer-by-layer finite element model has been developed using variational principle. It is shown that the layer-by-layer finite element modeling effectively captures the continuity of shear stress across the interface between piezolayers and the metallic host material. Several studies of actuation and sensing of single and multipatch smart beams have been carried out. The key difference between actuation and sensing has been brought out with regard to the variation of shear stress along the span at interfaces between piezopatch and the core. In addition, the influence of electric field along the span of a piezo cantilever beam has been studied, and it is shown that this electric field produces a large transverse shear stress resulting in a steplike deformation of the piezobeam. It is envisaged that this concept can be used to develop a switch in a microelectromechanical-system device. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

AIAA Journal

Electroelastic analysis and layer-by-layer modeling of a smart beam

The objective of this paper is to report new data for flow of gases, liquids, and liquid mixtures in 11 m long micro-channels. Three test sections of the following dimensions (a) 1.5 mm deep × 0.75 mm wide (MC1), (b) 0.5 mm deep × 0.95 mm wide (MC2), and (c) 0.3 mm. deep × 1.0 mm wide (MC3) were cut in a serpentine form on a stainless steel substrate. The gases studied were air, nitrogen, and oxygen. The liquids used were ethanol, methanol, and their mixtures. The measured flow rate and pressure drop were used to evaluate friction factors in the micro-channels. Analysis of friction factor versus Reynolds number relation shows a perceptible dependence on channel dimensions. Transitions to turbulent regime were identified by a change in slope of friction factor versus Reynolds number curve. Transitions were mild and occurred at lower Reynolds numbers than in normal channels. The results are interpreted in terms of a channel geometry parameter. © IMechE 2005.

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

Experimental investigation of fluid flow in long rectangular micro-channels

In the present study a family of plate models available for the analysis of laminated structures is compared under transverse loading for the point-wise data like maximum transverse deflection and local state of stress. Here, the plate models compared are Higher-order-Shear-Deformable (HSDI) model, Hierarchic model and Layerwise model. It is seen that all the models predict the deflections accurately. The local state of stress is computed using direct finite element data and equilibrium approach of post processing as well It is seen for HSDT and hierarchic models that the state of stress computed using direct finite element data is significantly different from exact one, whereas for the layerwise model it is accurately predicted. With equilibrium approach of post processing the local state of stress is accurately predicted by all the models. Further, the effect of the model on first-ply failure load obtained using the equilibrium approach of transverse stress extraction and Tsai-Wu failure criterion is studied. The effect of discretization error control by a one shot adaptive approach has been studied for the first-ply failure loads. It is seen that the control of discretization error together with equilibrium approach of post processing leads to significant reduction in the computed values of failure load. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference

Reliable computation of local quantities of interest in composite laminated plates

This paper presents the vibration control of a highly simplified two degree of freedom model of a helicopter. The vibration control study has been performed using both active and passive vibration control schemes. In the case of active vibration control, the feedback mechanism affects the stiffness of the system; whereas in passive vibration control, the absorber mass affects the inertia of the system. The active control is achieved using a combination of piezo stack sensor and actuator mechanism. A finite element model for the piezo stack mechanism has been developed to obtain a relation between deformation, applied/induced potential and externally applied mechanical load. The results of this study indicate that inclusion of sensor and actuator units increases the natural frequency of the system due to increase in stiffness of the system. It is observed that in the case of active vibration control, the frequency response of acceleration of the system is highly sensitive to small variations in the magnitude of gain around its optimum value and insensitive to changes in excitation frequency; whereas in passive vibration control, the frequency response does not exhibit any significant change in the characteristics with respect to the variation in the absorber mass, while it is highly sensitive to changes in operating frequency.

Vibration control of an idealized helicoptor model using piezo stack sensor-actuator

The flow field characteristics of an axisymmetric pulsed jet at operating conditions of Mj = 0.3, 0.65 and 0.8 are described using phase locked Particle Image Velocimetry (PIV) measurements. The pulsation in the jet flow is obtained by a rotating disk. Unlike piston generated incompressible pulse flows or shock wave generated supersonic pulse flows, a sinusoidal pulsation is added on a small amount of leaking base flow. The formation of vortex rings and the associated velocity, vorticity and entrainment fields are investigated changing pulsation frequency. In addition to the description of the flow properties by means of PIV, unsteady pressure measurements, near field acoustic measurements and thrust measurements are also made to explain the flow dynamics involved in pulsed jets. The results show that the initial region of the flow is dominated by the periodic turbulent stresses where a major increase in the mass flux and the entrainment has been measured. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

43rd AIAA Aerospace Sciences Meeting and Exhibit - Meeting Papers

The structure of a pulsed jet - A PIV study

The presence of a cutout in a laminated composite plate is of interest to the analysts. The main objective here is to study the interaction curves for a laminated composite plate with a centrally located cutout subjected to in-plane and shear loading, using a simple higher-order shear deformation theory based on four displacement functions (u0, v0, wb, ws) instead of the five that are commonly used in most higher-order theories. The finite element method is employed to study the buckling of laminated plates. © 2005 Elsevier Ltd.

3rd M.I.T. Conference on Computational Fluid and Solid Mechanics

Study of interaction curves for composite laminate with cutout

This article presents data on forced convective heat transfer for fluids in a 11-m long rectangular (0.75 mm. wide × 1.5 mm deep) serpentine-type mini-channel. The test section was fabricated by electro-discharge machining of a 2-mm thick stainless steel plate. The flow media experimented were air, ethanol, methanol, and their mixtures. Both laminar and turbulent flow regimes were covered in the case of liquids, but only turbulent regime was covered with air. The heat transfer coefficient is evaluated based on the heat carried away by the coolant and an average wall to mean fluid temperature difference. The Nusselt number is correlated through empirical correlations involving Reynolds number and Prandtl number, the hydraulic diameter being the length parameter. © IMechE 2005.

Experimental investigation of forced convective heat transfer to air, liquids, and liquid mixtures in a long narrow channel

The geometrically different planforms of near-wall plume structure in turbulent natural convection, visualized by driving the convection using concentration differences across a membrane, are shown to have a common multifractal spectrum of singularities for Rayleigh numbers in the range 1010-1011 at Schmidt number of 602. The scaling is seen for a length scale range of 25 and is independent of the Rayleigh number, the flux, the strength and nature of the large-scale flow, and the aspect ratio. Similar scaling is observed for the plume structures obtained in the presence of a weak flow across the membrane. This common non-trivial spatial scaling is proposed to be due to the same underlying generating process for the near-wall plume structures. © 2005 Cambridge University Press.