Mechanical Engineering
http://repository.iitgn.ac.in/handle/123456789/587
Thu, 23 Mar 2017 18:15:40 GMT2017-03-23T18:15:40ZComputational aeromechanics of annular wings unnamed aerial vehicle
http://repository.iitgn.ac.in/handle/123456789/2745
Computational aeromechanics of annular wings unnamed aerial vehicle
Goyal, Abheeti
Computational evaluation of the aerodynamic and propulsive characteristics of several annular wing-propeller configurations to assess the effect of propeller on the aerodynamic performance of the annular wing for application in UAVs is the focus of this work. This research work establishes the potential of annular wing-propeller configuration as a propulsive unit for unconventional UAVs. Higher propulsive efficiencies of ducted propellers make them suitable to propel UAVs whereas annular wings provide higher aerodynamic efficiencies than conventional wings. A cambered Clark-Y airfoil section for the annularwing and a 3-blade propeller with NACA 4412 airfoil section combine to form the annular wing-propeller system investigated in this work. Effect of parameters such as the tip clearance ratio and the position of the propeller within the annular wing for various advance ratios and angles of attack of the annular wing-propeller system are analyzed using RANS & LES models. Resulting velocity fields upstream and downstream, thrust and torque of the annular wing-propeller system are computed. Computed results are also validated against the experimental and computational results reported in the literature. The compressibility effects are also assessed for propeller advance ratios for which the propeller blade tips may exceed Mach 0.3. The relative performance of various annular wing-propeller configurations is studied in depth. LES captures the compressibility effects even with incompressible flow solver predicting realistic flow field in the vicinity of Mach 0.3. LES is found to resolve the flow field more intricately than RANS. Additionally, comparison of solo and contra-rotating propellers within the annular wing is also presented. Contra-rotating propeller-annular wing system is found to be superior to the solo propeller-annular wing configuration for UAV applications. The design of the annular wing-propeller configuration so developed is further investigated dynamically for an Annular Wing UAV in hover and forward flight. Longitudinal static stability analysis to compute the static margin and neutral point of the complete UAV with and without propeller effect assisted greatly in attaining the final annular wing UAV configuration. The mission statement of the annular wing UAV includes vertical take-off, hover, swivelling of the propulsive unit and forward flight. Propeller powered annular wing UAVs thus have a huge potential as a VTOL aircraft.
Thu, 01 Jan 2015 00:00:00 GMThttp://repository.iitgn.ac.in/handle/123456789/27452015-01-01T00:00:00ZTrackability analysis and tracking control of swirling pendulum -an underactuated mechanical system
http://repository.iitgn.ac.in/handle/123456789/2744
Trackability analysis and tracking control of swirling pendulum -an underactuated mechanical system
Shah, Ustav
Underactuated mechanical systems are essentially the systems which have lesser number of free control actuators than degrees of freedom. Due to their diverse applications and potential usage in multiple disciplines, tracking and control of this particular class of system has become an important research problem in the _eld of dynamics and control. There is a vast body of research on controlling this class of systems to enable such system to exploit its inherent dynamics in order to become agile, robust and e_cient. But, there is a limited literature available on solving a larger and important question on ability of a system to track any particular reference command. With this work, we have done preliminary analysis in the direction of answering this question by analyzing the 'trackability' of a system. The analysis is done by means of developing a new system which we refer to it as 'swirling pendulum' and an experimental setup of the same has been built from scratch as part of this work. Although many physical systems have been studied in control literature, this system possesses richer dynamics and deep coupling among its degrees of freedom. The Swirling pendulum has essentially two links, one of which swings in one plane and the other one swirls in di_erent planes. Due to its coupled dynamics, we see interesting behavior of this system about its static equilibria. Simpli_ed mathematical model of swirling pendulum is developed. This model is then improved by introducing non conservative forces like friction and motor dynamics whose parameters are identi_ed using standard system identi_cation techniques. We then quantify the ability to track the reference commands by analyzing the trackability index of di_erent reference commands using Markov parameter matrix of system. Also, projections of these reference commands on markov parameter reveal the closeness with which a particular trajectory can be partially tracked if not tracked perfectly. We validate these results with simulation on nonlinear plant model as well as experimentally comparing the tracking performance.
Fri, 01 Jan 2016 00:00:00 GMThttp://repository.iitgn.ac.in/handle/123456789/27442016-01-01T00:00:00ZA quasi-static approach to capture thermal fluctuations in micro-scale bio-filaments
http://repository.iitgn.ac.in/handle/123456789/2743
A quasi-static approach to capture thermal fluctuations in micro-scale bio-filaments
Garg, Mohit
The bending and twisting deformations of bio-ﬁlaments on intermediate length scales
of the order of 5-100 nm play a key role in many biological processes. For instance, the looping behavior of DNA molecules plays a pivotal role in gene expression. Therefore, modeling these bending and twisting deformations in bio-ﬁlaments is useful in many applications. While traditionally all-atom molecular dynamics approach, semiempirical approaches and continuum approach have been successfully applied to model such deformations, we focus on the continuum approach using Kirchhoff elastic rod model equations in this thesis. While continuum modeling has shown promise, one key ingredient that remains a challenge to accurately estimate is the respective constitutive law that describes the bending and twisting stiffnesses based on the atomic composition and arrangement. Further, these bio-ﬁlaments are typically present in viscous ﬂuid media and their deformations are signiﬁcantly affected by the forces resulting from interactions with randomly moving solvent particles. Since these thermal ﬂuctuations are arising from stochastic forces, if these forces can be modeled, qualitative observations and predictions about the bio-ﬁlament deformations could be made that are useful in characterizing various properties such as entropic stiffness. Thus the objective of this thesis is to develop a continuum model for bio-ﬁlaments that takes into account thermal ﬂuctuations. Such a model will serve two purposes; of helping make qualitative predictions and observations, and help estimate constitutive law for various bio-ﬁlaments from experimental data. Such a model can potentially be applied to model deformations of actin ﬁbers, microtubules, DNA, ﬂagella of bacteria, cilia of eukaryotic cells, etc.
There are two widely followed approaches in general to model thermal ﬂuctuations on particles, Langevin dynamics, in which viscous drag force and random forces due to motion of solvent particles are accounted for in Newton’s second law, and Brownian motion in which inertia forces are neglected. In this dissertation, we explore a simpler third alternative that is to model them using a quasi-static approach. In a quasi-static approach, we neglect both inertia forces and viscous forces and consider the stochastic
forces due to solvent medium. So, our model simulates deformation patterns (both planar and 3-dimensional) of ﬁlaments and therefore, can be used to infer the mechanical behavior and entropic properties. This approach will not however be able to capture dynamic changes in these deformation patterns with time. We also consider various options on how the stochastic forces can be discretized in relation to the continuum ﬁlament. In this approach, ﬁlament is treated as a continuous elastic ﬁlament with discrete stochastic forces acting on it. We show that the simulated ensemble of ﬁlaments generated through quasi-static dynamics signiﬁcantly resembles the experimental AFM image of DNA. At last, the generated model is validated by comparisons with published results from equilibrium rod theories and laboratory-scale experiments.
Fri, 01 Jan 2016 00:00:00 GMThttp://repository.iitgn.ac.in/handle/123456789/27432016-01-01T00:00:00Zlinear stability analysis of taylor couette MHD flow under the influence of steady axial magnetic field
http://repository.iitgn.ac.in/handle/123456789/2742
linear stability analysis of taylor couette MHD flow under the influence of steady axial magnetic field
Swapnil
Taylor Couette ﬂow is very common in engineering systems. It has been the basis for various ﬂuid ﬂow observations like viscometric viscosity measurements and observation of ﬁrst successful validation of Linear stability analysis. It becomes interesting to ﬁnd out what prompts the development of ﬂow from highly structured laminar ﬂow to totally chaotic turbulent ﬂow. So far, researchers and scientists have identiﬁed the interface between laminar and turbulent as ‘transition zone’, the dynamics of ﬂow within the transition zone comes within the framework of stability analysis. Stability analysis is a predictive tool for prediction of the onset of instabilities by identifying those set of parameters that cause this phenomena. The normal mode perturbations are introduced in the velocity ﬁeld to study the growth/decay rates of the perturbations as the ﬂow evolves in time. Reynolds number, axial wavenumber, aspect ratio of cylinders, velocity ratio of cylinders, Hartmann number, magnetic Reynolds number can be identiﬁed as input to the dynamic system and the output is the temporal frequency of perturbations. Finally neutral stability curves are plotted to ﬁgure out the ‘critical Reynolds number’ and the effect of applied magnetic ﬁeld on it. The work could be seen as an actualization of Linear stability theory to TC MHD ﬂows and characterize ﬂow system behavior.
Fri, 01 Jan 2016 00:00:00 GMThttp://repository.iitgn.ac.in/handle/123456789/27422016-01-01T00:00:00Z