Department of Mechanical Engineering

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This work addresses path planning for reactionless visual servoing of a redundant dual-arm space robot through exploration in the image space. The planner explores the image moment based feature space, impends acceleration to the image features and extends the feature tree. A reactionless visual servoing control law is integrated to extend the tree in the configuration space simultaneously. The proposed algorithm is able to incorporate the necessary coupling between the motions of the the dual arms and the base of the robot to ensure zero base reactions. Additionally, it also gives the flexibility to apply multiple constraints in both the image space and the configuration space. The effectiveness of the proposed framework is exhibited by implementing the algorithm on a numerical model of a 14-DoF dual arm space robot. © 2016 IEEE.

World University root node

IEEE International Conference on Intelligent Robots and Systems

Image space based path planning for reactionless manipulation of redundant space robot

An experimental investigation of evaporation of a pentane meniscus from a heated capillary slot is presented. A novel aspect of this study is that both the wicking height and steady state evaporation mass flow rate are measured simultaneously. Based on a macroscopic force balance, the apparent contact angle of the evaporating meniscus is experimentally estimated from the wicking height and mass flow rate. This is compared with the results obtained using evaporating thin-film theory. The experimentally estimated contact angle is slightly larger than that obtained from the thin-film model but both show similar trends. Further, it is found that the reduction in the meniscus height is primarily due to an increase in the apparent contact angle. The liquid and vapor pressure drops in the capillary are insignificant relative to the capillary pressure. © 2015 Elsevier Ltd All rights reserved.

International Journal of Heat and Mass Transfer

Experimental study on evaporation of pentane from a heated capillary slot

Biological systems are superior compared to robotic systems in their ability to adapt to new situations very quickly. Hence, it would be advantageous to take insights from the architecture of sensory-motor maps in designing controllers for robotic systems. Any movement can be represented either in task space or joint space of a given manipulator. Planning and control in task space essentially reduces the computational complexity compared to joint-space approaches due to fewer dimensions involved. Experimental evidences [1], point towards task space representation of motion in the brain. The transformation of these task space representations into joint space is however not trivial, as it forms an ill-posed problem. This constitutes the inverse kinematics (IK) problem for a given manipulator. We propose to use multiple paired forward and inverse models approach described in the following sections, to obtain multiple IK solutions. © 2016 IEEE.

Proceedings of the IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics

Learning inverse kinematic solutions of redundant manipulators using multiple internal models

Single image based camera calibration and pose estimation of the end-effector of a robot

The present study is concerned with the theoretical investigation of pull-in phenomena and their significance for assessing structural instability of a MEMS switch, modeled as electrostatically actuated micro-cantilever beam coupled with a rigid plate. The essential factors such as geometric and inertial nonlinearities, higher-order distribution of electrostatic pressure, and nonlinear squeeze film effect have been included in the dynamic model to accurately predict the pull-in voltages. The limit of structural stability due to pull-in behavior is numerically illustrated for both static and dynamic conditions of the device. The effects of varying the electrode length, structural nonlinearity, air-gap thickness, and plate length on pull-in instability are investigated. The pull-in voltage predicted numerically within the limit of operational voltage has been validated with the findings in 3D modeling software. It is perceived that a highly deformable micro-system loses its stability at high actuation voltage via static bifurcation due to pull-in instability. Furthermore, structural stability appears observed to be high by reducing the size of the device as the pull-in occurrence is at high applied voltage. The damping mechanism introduced into the device essentially stabilizes the device by switching the pull-in voltage to a high value. However, the obtained outcomes enable the satisfactory predictions of pull-in occurrence and subsequent understanding of structural instability and safe operating zones of the device. © 2016, Springer-Verlag Wien.

Acta Mechanica

Prediction of pull-in phenomena and structural stability analysis of an electrostatically actuated microswitch

The martensitic creep-resistant steel designated as ASTM A335 for plate and as P91 for pipe is primarily used for high-temperature and high-pressure applications in steam power plants due to its excellent high-temperature properties such as high creep strength, high thermal conductivity, low thermal expansion, and so on. However, in the case of welded joints of such steels, the presence of an inter-critical heat-affected zone (IC-HAZ) can cause the joint to have lower creep strength than the base metal. In the present study, the effect of post-welding heat treatment (PWHT) and weld groove designs on the overall microstructure and mechanical properties of P91 steel pipe welds produced by the gas tungsten arc welding process was studied. Various regions of welded joints were characterized in detail for hardness and metallographic and tensile properties. Sub-size tensile samples were also tested to evaluate the mechanical properties of the weld metal and heat-affected zone (HAZ) with respect to PWHT. After PWHT, a homogenous microstructure was observed in the HAZ and tensile test fracture samples revealed shifting of the fracture location from the IC-HAZ to the fine-grained heat-affected zone. Before PWHT, the conventional V-grooved welded joints exhibited higher tensile strength compared to the narrow-grooved joints. However, after PWHT, both narrow- and V-grooved joints exhibited similar strength. Fractography of the samples indicates the presence of carbide precipitates such as Cr23C6, VC, and NbC on the fracture surface. © 2016, ASM International.

Journal of Materials Engineering and Performance

Effect of Groove Design and Post-Weld Heat Treatment on Microstructure and Mechanical Properties of P91 Steel Weld

The present study describes how the effect of direction of welding is useful to minimize distortion in submerged arc welded double-sided fillet joints. In present work, angular distortion of 12 mm thick double-sided fillet welds was measured for same direction and reverse direction welding. It has been observed that the maximum magnitude of the angular distortion for reverse direction fillet welding is lower. Thermal history in horizontal and vertical plate of fillet welds was also measured for both same direction and reverse direction welding. After welding, the fillet welds were sectioned, polished and etched to measure the effect of direction of welding on weld bead geometry. To predict the temperature distribution and thermal history, a finite element (FE) elasto-plastic thermo-mechanical model has been developed for submerged arc welded double-sided fillet welds by using moving distributed heat source. The three-dimensional FE thermal model was verified by comparing peak temperature obtained with experimental values. The model results matched fairly well with experimental results with a variation of 6 percent for sample 1 and 7.5 percent for sample 2 for the maximum values of distortion, and a variation of 2-8 percent for peak temperatures in horizontal plate and 9 percent in web plate. © 2016, Korean Society of Steel Construction and Springer-Verlag Berlin Heidelberg.

International Journal of Steel Structures

On the prediction of effect of direction of welding on bead geometry and residual deformation of double-sided fillet welds

The objective of the present work is to investigate the heat transfer and pressure drop in flow boiling at low pressure with water as the working medium. The effect of pipe diameter, heat flux and mass flux on boiling pressure drop and local heat transfer coefficient is studied. In the present work, the available correlations are revisited for low pressure flow boiling. Comparison of local heat transfer coefficient with the existing correlation is carried out to identify an appropriate correlation which performs well in complete flow boiling range (subcooled regions and saturated regions) for water at low system pressure. Experiments are performed with eight test sections made of thin walled stainless steel (SS 304) tubes having inner diameters from 5.5 mm to 12 mm and length varying from 550 mm to 1000 mm. The system pressure is varying form 1 bar to 3 bar. No change in slope of heat transfer curve is found for subcooled regions. Heat transfer in all the three regions of subcooled boiling namely partial subcooled boiling, fully developed subcooled and net vapour generation are predicted by a single correlation. Tube diameter has no effect on boiling heat transfer distribution. However, tube diameter affects two phase pressure drop. Increase in mass flux increases the convective heat transfer coefficient. However, mass flux has no influence on subcooled and nucleate boiling heat transfer coefficient. Heat flux increases the boiling heat transfer coefficient. Increase in tube diameter and mass flux decreases the two-phase pressure drop. Most of all the correlations in the subcooled region predict heat transfer coefficient with reasonable accuracy. Kandlikar and Shah correlations perform well in the low pressure saturated boiling i.e. nucleate and convective. None of the available two-phase pressure drop correlations are able to predict the pressure drop in a low pressure system. A correlation is developed to predict two-phase pressure drop in low pressure flow boiling system with a reasonably good accuracy. © 2016 Elsevier Masson SAS

International Journal of Thermal Sciences

Boiling pressure drop and local heat transfer distribution of water in horizontal straight tubes at low pressure

The feasibility of running MPI-parallel, GPU-accelerated, multiphase flow simulations on Amazon's Elastic Compute Cloud (EC2) service is evaluated as an alternative computational resource. A cloud cluster on Amazon EC2 is compared to a conventional local high-performance computing cluster in terms of performance and cost. The steps necessary to set up a cloud cluster and acquire the appropriate hardware and software stacks are outlined. The incompressible multiphase flow solver is benchmarked on both cloud and local clusters by performing strong and weak scaling analyses. Amazon's EC2 service is competitive with the local cluster in a certain range of simulations, but there are some performance limitations, particularly in its GPU card performance and cluster network connection, which negatively impact the parallel simulations presented herein. Finally, Amazon's EC2 service is studied from an economic perspective and compared with a conventional local cluster. © 1999-2011 IEEE.

Computing in Science and Engineering

The feasibility of amazon's cloud computing platform for parallel, GPU-accelerated, multiphase-flow simulations

Instabilities arising in unsteady boundary layers with reverse flow have been investigated experimentally. Experiments are conducted in a piston driven unsteady water tunnel with a shallow angle diffuser placed in the test section. The ratio of temporal (Πt) to spatial (Πx) component of the pressure gradient can be varied by a controlled motion of the piston. In all the experiments, the piston velocity variation with time is trapezoidal consisting of three phases: constant acceleration from rest, constant velocity and constant deceleration to rest. The adverse pressure gradient (and reverse flow) are due to a combination of spatial deceleration of the free stream in the diffuser and temporal deceleration of the free stream caused by the piston deceleration. The instability is usually initiated with the formation of one or more vortices. The onset of reverse flow in the boundary layer, location and time of formation of the first vortex and the subsequent flow evolution are studied for various values of the ratio Πx/(Πx+Πt) for the bottom and the top walls. Instability is due to the inflectional velocity profiles of the unsteady boundary layer. The instability is localized and spreads to the other regions at later times. At higher Reynolds numbers growth rate of instability is higher and localized transition to turbulence is observed. Scalings have been proposed for initial vortex formation time and wavelength of the instability vortices. Initial vortex formation time scales with convective time, δ/ΔU, where δ is the boundary layer thickness and ΔU is the difference of maximum and minimum velocities in the boundary layer. Non-dimensional vortex formation time based on convective time scale for the bottom and the top walls are found to be 23 and 30 respectively. Wavelength of instability vortices scales with the time averaged boundary layer thickness. © 2015 Elsevier Masson SAS.