Mechanical Engineering
http://repository.iitgn.ac.in/handle/123456789/587
2017-03-29T13:15:40ZTransient characterization of data center racks
http://repository.iitgn.ac.in/handle/123456789/2810
Transient characterization of data center racks
Fulpagare, Yogesh; Joshi, Yogendra; Bhargav, Atul
The increased computational and storage demand has increased the heat dissipation of servers in data centers. The flow inside the data center is highly dynamic due to various parameters such as server workload, server fan speed, tile porosity, Computer Room Air Conditioning (CRAC) air flowrates, CRAC supply & return air temperatures and data center cold & hot aisle arrangements. Data center facility level transient CFD analysis was reported in recent literature which needs weeks to accomplish the computation. Hence, such facility level simulations are difficult to achieve with good accuracy. The main contributions of this paper are transient experiments, transient CFD model & transient effects on thermal and flow field due to variation in server load of server rack inside the raised floor plenum data center.
In the current study we have developed a transient CFD model of three racks in a raised floor plenum data center room with cold and hot aisle containment based on experiments. The middle 42U (1U = 4.45 cm) rack houses four server simulators each having height of 10U. The flow tiles supply the cold air as inlet with average velocity of 1.53 m/s at 17°C. All the rack servers were modelled with 75% porosity and estimated thermal mass Each server simulator was assigned a total heat dissipation of 2500 W, with a total heat load of 10 kW per rack. The effect on rack inlet and outlet air temperatures were monitored by providing server heat loads as step & ramp inputs to the middle simulator rack. The results show that the rack level transient effects are significant and cannot be ignored.
2016-11-11T00:00:00ZComputational 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.
2015-01-01T00:00:00ZTrackability 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.
2016-01-01T00:00:00ZA 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.
2016-01-01T00:00:00Z