Department of Mechanical Engineering

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Kinematic modeling of a tree-type robotic system is presented in this chapter. In order to obtain kinematic constraints, a tree-type topology is first divided into a set of modules. The kinematic constraints are then obtained between these modules by introducing the concepts of module-twist, module-joint-rate, etc. This helps in obtaining the generic form of the Decoupled Natural Orthogonal Complement (DeNOC) matrices for a tree-type system with the help of module-to-module velocity transformations. Using the present derivation, link-to-link velocity transformation (Saha 1999a, b) turns out to be a special case of the module-to-module velocity transformation (Shah et al. 2012a) presented in this chapter. © 2013, Springer Science+Business Media Dordrecht.

World University root node

Intelligent Systems, Control and Automation: Science and Engineering

Kinematics of Tree-Type Robotic Systems

As reviewed in Chap. 2, Newton-Euler (NE) equations of motion are found to be popular in dynamic formulations. Several methods were also proposed by various researchers to obtain the Euler-Langrage’s form of NE equations of motion. One of these methods is based on velocity transformation of the kinematic constraints, e.g., the Natural Orthogonal Complement (NOC) or the Decoupled NOC (DeNOC), as obtained in Chap. 4. The DeNOC matrices of Eq. (4.28) are used in this chapter to obtain the minimal order dynamic equations of motion that have several benefits. © 2013, Springer Science+Business Media Dordrecht.

Dynamics of Tree-Type Robotic Systems

The study of flow physics in microshock tubes is of growing importance with the recent development of microscale technology. The flow characteristics in a microshock tube is considerably different from that of the conventional macroshock tube due to the boundary layer effects and high Knudsen number effects. In the present study an axisymmetric computational fluid dynamics (CFD) method was employed to simulate the microshock tube flow field with Maxwell's slip velocity and temperature jump boundary conditions, to accommodate the rarefaction effects. The effects of finite diaphragm rupture process and partial diaphragm rupture on the flow field and the wave propagations were investigated, in detail. The results show that the shock propagation distance attenuates rapidly for a microshock tube compared to a macroshock tube. For microshock tubes, the contact surface comes closer to the shock front compared to the analytical macroshock tube case. Due to the finite diaphragm rupture process the moving shock front will be generated after a certain distance ahead of the diaphragm and get attenuated rapidly as it propagates compared to the sudden rupture case. The shock-contact distance reduces considerably for the finite diaphragm rupture case compared to the sudden diaphragm rupture process. A partially burst diaphragm within a microshock tube initiates a supersonic flow in the vicinity of the diaphragm similar to that of a supersonic nozzle flow. The supersonic flow expansion leads to the formation of oblique shock cells ahead of the diaphragm and significantly attenuates the moving shock propagation speed. Copyright © 2013 by ASME.

Journal of Fluids Engineering, Transactions of the ASME

Effect of finite diaphragm rupture process on microshock tube flows

Boundary layers are subject to favorable and adverse pressure gradients because of both the temporal and spatial components of the pressure gradient. The adverse pressure gradient may cause the flow to separate. In a closed loop unsteady tunnel we have studied the initiation of separation in unsteady flow past a constriction (bluff body) in a channel. We have proposed two important scalings for the time when boundary layer separates. One is based on the local pressure gradient and the other is a convective time scale based on boundary layer parameters. The flow visualization using a dye injection technique shows the flow structure past the body. Nondimensional shedding frequency (Strouhal number) is calculated based on boundary layer and momentum thicknesses. Strouhal number based on the momentum thickness shows a close agreement with that for flat plate and circular cylinder. © 2013 Elsevier Ltd.

Journal of Fluids and Structures

Unsteady separation and vortex shedding from a laminar separation bubble over a bluff body

In this paper we propose a semi-active robot for climbing steep obstacles like steps, curbs, etc. The key novelty of the proposed robot lies in the use of a passive mechanism for climbing steps of smaller heights and motor only while climbing steps of bigger heights. Analysis of the robot's stability during its ascent phase is also investigated. Model based control is used to achieve step climbing. The other novelty of the robot, in contrast to existing active suspension step climbers, is that it does not need the knowledge of step height beforehand. Therefore, the mechanism has the advantage of height-independent climbing motion as in the case of passive mechanism along with the extra freedom of active joints for maintaining vehicle stability, only when required. Efficacy of the mechanism is exhibited through simulations on steps of various heights. © 2013 IEEE.

Proceedings of the IEEE International Conference on Control Applications

A semi-active robot for steep obstacle ascent

ZnO nano structure arrays on silicon substrate using chemical treatment have been developed. The morphology of nanostructures formulated thereafter was characterized using Field Emission Scanning Electron Microscope (FESEM), X-Ray Diffraction (XRD), Energy-Dispersive X ray Spectroscopy (EDAX). These structures are envisioned for Hydrogen sensing. High reconditionability with moderate sensitivity has been achieved with the developed nanostructures. © 2013 AIP Publishing LLC.

AIP Conference Proceedings

High aspect ZnO nanostructures based hydrogen sensing

This work is concerned with the removal of unwanted fluid through the source-sink pair. The source consists of fluid issuing out of a nozzle in the form of a jet and the sink is a pipe that is kept some distance from the source pipe. Of concern is the percentage of source fluid sucked through the sink. The experiments have been carried in a large glass water tank. The source nozzle diameter is 6 mm and the sink pipe diameter is either 10 or 20 mm. The horizontal and vertical separations and angles between these source and sink pipes are adjustable. The flow was visualized using KMnO4 dye, planer laser induced fluorescence and particle streak photographs. To obtain the effectiveness (that is percentage of source fluid entering the sink pipe), titration method is used. The velocity profiles with and without the sink were obtained using particle image velocimetry. The sink flow rate to obtain a certain effectiveness increase dramatically with lateral separation. The sink diameter and the angle between source and the sink axes don't influence effectiveness as much as the lateral separation. © 2012 Springer-Verlag.

Heat and Mass Transfer/Waerme- und Stoffuebertragung

Removal of unwanted fluid

This paper presents the results of an experimental study of the effects of porosity on the flow rate and Escherichia coli (E. coli) filtration characteristics of porous ceramic water filters (CWFs) prepared without a coating of silver. Clay-based CWFs were fabricated by sintering composites of redart clay and fine woodchips (sawdust) in three different proportions by volume, viz: 50:50, 65:35, and 75:25. Sintering the greenware below 1,000 C produced reddish colored pot of three different degrees of porosity and micro-and nanoscale pores, which are the key to efficient filtration. The porosities and pore size distribution frequencies of the sintered clay ceramics were characterized using mercury intrusion porosimetry (MIP). The porosity of the CWFs ranged from ∼36% to ∼47% and increased with increasing sawdust content in a linear fashion, and the pore size varied from ∼10 nm to ∼100 μm. The volume flow rates of water through the CWFs were investigated by measuring the cumulative amount of water flow as a function of time. The flow rate was found to increase with increasing porosity of the CWFs. The effective intrinsic permeabilities of the CWFs were then obtained from Darcy fits to the flow rate data. These were compared with values obtained using the Katz-Thompson method. Both approaches gave comparable results of permeability between ∼1 millidarcy to ∼50 millidarcy. The tortuosity of the CWFs was found from Hager's equation to range from ∼10 to ∼60. In general, while the permeability of the CWFs decreased with increasing clay content, tortuosity increased with increasing clay content. The CWFs removed E. coli from aqueous suspension very efficiently with average log reduction values between 5.7-6.4. The implications and limitations of the results are discussed for the effective filtration of water in the developing world. © 2013 American Society of Civil Engineers.

Journal of Environmental Engineering (United States)

Porosity, flow, and filtration characteristics of frustum-shaped ceramic water filters

Abstract We investigate the effect of a prescribed tangential velocity on the drag force on a circular cylinder in a spanwise uniform cross flow. Using a combination of theoretical and numerical techniques we make an attempt at determining the optimal tangential velocity profiles which will reduce the drag force acting on the cylindrical body while minimizing the net power consumption characterized through a non-dimensional power loss coefficient ( C PL). A striking conclusion of our analysis is that the tangential velocity associated with the potential flow, which completely suppresses the drag force, is not optimal for both small and large, but finite Reynolds number. When inertial effects are negligible (Re≪1), theoretical analysis based on two-dimensional Oseen equations gives us the optimal tangential velocity profile which leads to energetically efficient drag reduction. Furthermore, in the limit of zero Reynolds number (Re→0), minimum power loss is achieved for a tangential velocity profile corresponding to a shear-free perfect slip boundary. At finite Re, results from numerical simulations indicate that perfect slip is not optimum and a further reduction in drag can be achieved for reduced power consumption. A gradual increase in the strength of a tangential velocity which involves only the first reflectionally symmetric mode leads to a monotonic reduction in drag and eventual thrust production. Simulations reveal the existence of an optimal strength for which the power consumption attains a minima. At a Reynolds number of 100, minimum value of the power loss coefficient ( CPL = 0. 37) is obtained when the maximum in tangential surface velocity is about one and a half times the free stream uniform velocity corresponding to a percentage drag reduction of approximately 77 %; C PL = 0. 42 and 0. 50 for perfect slip and potential flow cases, respectively. Our results suggest that potential flow tangential velocity enables energetically efficient propulsion at all Reynolds numbers but optimal drag reduction only for Re→∞. The two-dimensional strategy of reducing drag while minimizing net power consumption is shown to be effective in three dimensions via numerical simulation of flow past an infinite circular cylinder at a Reynolds number of 300. Finally a strategy of reducing drag, suitable for practical implementation and amenable to experimental testing, through piecewise constant tangential velocities distributed along the cylinder periphery is proposed and analysed. © Cambridge University Press 2013.