Department of Mechanical Engineering

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The condition number of the Generalized Inertia Matrix (GIM) of a serial chain can be used to measure its ill-conditioning. However, computation of the condition number is computationally very expensive. Therefore, this paper investigates alternative means to estimate the condition number, in particular, for a very long serial-chain. For this, the diagonal elements of the GIM are examined. It is found that the ratio of the largest and smallest diagonal elements of the GIM, when scaled using an initial estimate of the condition number, closely resembles the condition number. This significantly simplifies the process of detecting ill-conditioning of the GIM, which may help to decide on stability of the system at hand.

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Archive of Mechanical Engineering

Correlation between diagonal ratio and condition number of the generalized inertia matrix of a serial-chain

The field of robotics has grown a lot in last three to four decades. In this chapter, background and developments in the field of dynamics of robotic systems are presented. © 2013, Springer Science+Business Media Dordrecht.

Intelligent Systems, Control and Automation: Science and Engineering

Dynamics of Robotic Systems

Dynamics of Tree-Type Robotic Systems

Thermocells in box and flat cell configurations were demonstrated via simplified design and cost effective materials like activated charcoal and potassium ferri/ferrocyanide solution and MWCNTs respectively. Employing saturated concentrations of potassium ferri/ferrocyanide in aqueous solution as electrolyte in combination with the electrodes resulted in a highly feasible redox-mediated electron transfer. Effects of concentration of potassium ferri/ferrocyanide (0.1 mM, 1 M and 4 M in aqueous medium) on the performance of the devices were analyzed. The electrolyte trapped in agar-agar gel functions as a solid like medium. In the case of box configuration the maximum power density attained being 22.463 W/m2 yielding 20-30% of Carnot efficiency and 0.563 W/m2 for MWCNT based flat cells reaching 0.5-18% higher than the Carnot efficiency. The efficiency of the thermocells at different ΔT from 30 C to 130 C was reported. The power density increased by 14.92 times for activated charcoal thermocell operating in 1 M K 3[Fe(CN)6]/K4[Fe(CN)6] at ΔT = 60 C in comparison with MWCNT based thermocells at the same ΔT. Other low cost electrode materials like activated charcoal, acetylene black were employed to study the performance of thermocells. Cells were connected in series and parallel to study the feasibility of performance improvement at different ΔT. © 2013 Brazilian Metallurgical, Materials and Mining Association.

Journal of Materials Research and Technology

Thermocells of carbon material electrodes and its performance characteristics

The present work primarily deals with the study of the influence of internal moving pulsatile fluid on the dynamic stability of cantilever based single-walled carbon nanotubes considering the modified couple stress elasticity theory and the Timoshenko beam model. The axial fluid speed is characterized as simple harmonic variation about a constant mean speed. The second order method of multiple scales is employed in order to determine the closed-form expressions for the instability regions subjected to parametric resonance condition. The influences of the length scale parameter, Poisson's ratio, aspect ratio of SWCNTs, and the amplitude of static and dynamic components of the flow velocity, on the parametric instability regions are investigated. These results obtained from perturbation analysis are verified by solving the temporal equation using numerical technique.

20th International Congress on Sound and Vibration 2013, ICSV 2013

Parametric instability of carbon nanotubes conveying pulsatile flow considering modified couple stress theory

Accurate prediction of helicopter loads and response requires the development of a multi-disciplinary comprehensive analysis program. Helicopter loads and response is an aeroelastic problem as it involves interaction of the structural, inertia and aerodynamic operators. The objective of this paper is to describe the development of a comprehensive analysis code for helicopter aeroelastic analysis and present some of the validation studies. The helicopter modeled is a conventional one with a hingeless single main rotor and single tail rotor. The blade undergoes flap, lag, torsion and axial deformations and is modeled using beam finite elements. Tip sweep, pretwist, precone, predroop, torque offset and root offset are included in the model. Aerodynamic model includes Peters-He dynamic wake theory for inflow and the modified ONERA dynamic stall theory for airloads calculations. The complete 6-dof nonlinear equilibrium equations are solved for analyzing general flight conditions including steady maneuver. Validation studies presented in this paper include comparison of experimental data with the analysis results pertaining to (i) structural dynamics of swept-tip blades, (ii) whirl tower test and (iii) steady forward flight trim state of a helicopter. Results of a study showing the effects of the blade geometric parameters on the performance, response and loads of the rotor are also given.

IFASD 2013 - International Forum on Aeroelasticity and Structural Dynamics

Rotorcraft aeroelastic analysis using dynamic wake/dynamic stall models and its Validation

Rigid splitter plates in the wake of bluff bodies are known to suppress the primary vortex shedding. In the present work, we experimentally study the problem of a flexible splitter plate in the wake of a circular cylinder. In this case, the splitter plate is free to continuously deform along its length due to the fluid forces acting on it; the flexural rigidity (EI) of the plate being an important parameter. Direct visualizations of the splitter plate motions, for very low values of flexural rigidity (EI), indicate periodic traveling wave type deformations of the splitter plate with maximum tip amplitudes of the order of 1 cylinder diameter. As the Reynolds number based on cylinder diameter is varied, two regimes of periodic splitter plate motions are found that are referred to as mode I and mode II, with a regime of aperiodic motions between them. The frequency of plate motions in both periodic modes is found to be close to the plane cylinder Strouhal number of about 0.2, while the average frequencies in the non-periodic regime are substantially lower. The measured normalized phase speed of the traveling wave for both periodic modes is also close to the convection speed of vortices in the plane cylinder wake. As the flexural rigidity of the plate (EI) is increased, the response of the plate was found to shift to the right when plotted with flow speed or Re. To better capture the effect of varying EI, we define and use a non-dimensional bending stiffness, K*, similar to the ones used in the flag flutter problem, K*=EI/(0.5ρU2L3), where U is the free-stream velocity and L is the splitter plate length. Amplitude data for different EI cases when plotted against this parameter appear to collapse on to a single curve for a given splitter plate length. Measurements of the splitter plate motions for varying splitter plate lengths indicate that plates that are substantially larger than the formation length of the plane cylinder wake have similar responses, while shorter plates show significant differences. © 2013 Elsevier Ltd.

Journal of Fluids and Structures

Dynamics of a flexible splitter plate in the wake of a circular cylinder

The performance of a two-phase heat transport device such as the loop heat pipe is influenced by the evaporative heat transfer coefficient in the evaporator. From previous experiments with loop heat pipes, it has been observed that fluids with a high heat pipe figure of merit have a high heat transfer coefficient. Considering an evaporating extended thin film, this paper theoretically corroborates this experimental observation by deriving a direct link between the evaporative heat flux at the interface and the fluid figures of merit (namely interline heat flow parameter and heat pipe figure of merit) in the thin film. Numerical experiments with different working fluids clearly show that a fluid with high figure of merit also has a high cumulative heat transfer in the microregion encompassing the evaporating thin film. Thus, a loop heat pipe or heat pipe that uses a working fluid with a high interline heat flow parameter and heat pipe figure of merit will lead to a high evaporative heat transfer coefficient© 2013 by the American Institute of Aeronautics and Astronautics, Inc.

Journal of Thermophysics and Heat Transfer

Effect of heat pipe figure of merit on an evaporating thin film

Dynamic modelling of a multibody system plays very essential role in its analyses. As a result, several methods for dynamic modelling have evolved over the years that allow one to analyse multibody systems in a very efficient manner. One such method of dynamic modelling is based on the concept of the Decoupled Natural Orthogonal Complement (DeNOC) matrices. The DeNOC-based methodology for dynamics modelling, since its introduction in 1995, has been applied to a variety of multibody systems such as serial, parallel, general closed-loop, flexible, legged, cam-follower, and space robots. The methodology has also proven useful for modelling of proteins and hyper-degree-of-freedom systems like ropes, chains, etc. This paper captures the evolution of the DeNOC-based dynamic modelling applied to different type of systems, and its benefits over other existing methodologies. It is shown that the DeNOC-based modelling provides deeper understanding of the dynamics of a multibody system. The power of the DeNOC-based modelling has been illustrated using several numerical examples. © 2013 Author(s).

Mechanical Sciences

Evolution of the DeNOC-based dynamic modelling for multibody systems

A controller is an essential part of a robotic system in achieving desired motion. A Proportional Integral Derivative (PID) controller is the simplest form of controller used for this purpose. A PID controller is widely used in industries for the control of processes or machines. In a robotic system, e.g., an industrial robot, a PID controller independently controls motion of each joint ignoring the effects of the system’s dynamics. However, for accomplishing complex motion or task, a PID controller does not always result into best performance, as shown by Lewis et al. (2004), Kelly et al. (2005), and Craig (2006). The legged robots discussed in Chaps. 6 and 7 are meant to perform a variety of complex tasks. As a result, the use of a PID controller without taking into account dynamics of the legged robots would result into poor control performance. On the other hand, the use of model-based controllers (Lewis et al. 2004; Kelly et al. 2005) has become popular in order to improve the performance of the conventional PID controllers. The model-based controllers work based on the information of the dynamic model of a system. If the dynamic model of a robot is not very accurate, the model-based control approach will still be able to eliminate major nonlinearities due to the robot’s inertia. In this chapter, simulation of model-based control of several robotic systems will be carried out. © 2013, Springer Science+Business Media Dordrecht.