etd@IISc Community:
http://hdl.handle.net/2005/5
2015-11-10T17:04:17ZZr-based Bulk Metallic Glass A Study Of Processing, Welding And Subsurface Deformation Mechanism
http://hdl.handle.net/2005/1297
Title: Zr-based Bulk Metallic Glass A Study Of Processing, Welding And Subsurface Deformation Mechanism
Authors: Bhowmick, Ranadeep2011-07-17T18:30:00ZWorkspace Analysis Of The Stewart Platform Manipulator
http://hdl.handle.net/2005/2177
Title: Workspace Analysis Of The Stewart Platform Manipulator
Authors: Pradeep, R2013-07-31T18:30:00ZWood Fiber Filled Polyolefin Composites
http://hdl.handle.net/2005/508
Title: Wood Fiber Filled Polyolefin Composites
Authors: Karmarkar, Ajay
Abstract: The objective of the study is to improve the interfacial adhesion between the wood fibers and thermoplastic matrix. Efforts were also directed towards improving manufacturing processes so as to realize the full potential of wood fibers as reinforcing fillers. Chemical coupling plays an important role in improving interfacial bonding strength in wood-polymer composites. A novel compatibilizer with isocyanate functional group was synthesized by grafting m-Isopropenyl –α –α –dimethylbenzyl-isocyanate (m-TMI) onto isotactic polypropylene using reactive extrusion process. The compatibilizer was characterized with respect to its nature, concentration and location of functional group, and molecular weight.
There are two main process issues when blending polymers with incompatible filler: (1) creating and maintaining the target morphology, and (2) doing so with minimum degradation of fillers. A 28mm co-rotating intermeshing twin screw extrusion system was custom built and the design optimized for (1) blending biological fibers with thermoplastics, and (2) for melt phase fictionalization of thermoplastics by reactive extrusion.
To assess the effect of inclusion of wood fibers in polypropylene composites, a series of polypropylene wood fiber/wood flour filled composite materials having 10 to 50 wt % of wood content were prepared using the co-rotating twin screw extrusion system. m-TMI-g-PP and MAPP were used as coupling agents. Addition of wood fibers, at all levels, resulted in more rigid and tenacious composites. The continuous improvement in properties of the composites with the increasing wood filler is attributed to the effective reinforcement of low modulus polypropylene matrix with the high modulus wood filler. Studies on were also undertaken to understand effect of particle morphology, type and concentration of coupling agent, and effect of process additives on mechanical properties. Composites prepared with m-TMI-grafted-PP were much superior to the composites prepared with conventionally used maleated polypropylene in all the cases.
Non-destructive evaluation of dynamic modulus of elasticity (MoE) and shear modulus of wood filled polypropylene composite at various filler contents was carried out from the vibration frequencies of disc shaped specimens. The vibration damping behaviour of the composite material was evaluated. MoE and shear modulus were found to increase whereas damping coefficient decreased with the increasing filler content.
Knowledge of moisture uptake and transport properties is useful in estimating moisture related effects such as fungal attack and loss of mechanical strength. Hence, a study was undertaken to asses the moisture absorption by wood filled
polypropylene composites. Composites prepared with coupling agents absorbed at least 30% less moisture than composites without compatibilizer. Thermo-gravimetric
measurements were also carried out to evaluate the thermal stability and to evaluate kinetic parameters associated with thermal degradation of wood fiber and wood flour filled polypropylene composites. The moisture absorption and thermal behaviour are described based on analytical models.
High efficiency filler-anchored catalyst system was prepared by substituting of hydroxyl groups present on the cellulosic filler. The process involves immobilizing the cocatalyst onto the cellulosic filler surface followed by addition of metallocene catalyst and then polymerization of ethylene using this filler supported catalyst. The polymerization and composite formation takes place simultaneously. All the polymerization reactions were carried out in a high-pressure stirred autoclave. Effect of temperature, ethylene pressure, and cocatalyst to catalyst ratios (Al/TM ratios) were also studied. Studies on kinetics of polymerization showed that, higher Al/Zr ratio and higher temperature lead to higher polymerization rates but lower the molecular weight. A model incorporating effect of reaction parameter on polymerization rates has been developed.2009-05-19T12:15:49ZWeighted Least Squares Kinetic Upwind Method Using Eigendirections (WLSKUM-ED)
http://hdl.handle.net/2005/538
Title: Weighted Least Squares Kinetic Upwind Method Using Eigendirections (WLSKUM-ED)
Authors: Arora, Konark
Abstract: Least Squares Kinetic Upwind Method (LSKUM), a grid free method based on kinetic
schemes has been gaining popularity over the conventional CFD methods for computation
of inviscid and viscous compressible ﬂows past complex conﬁgurations. The main reason
for the growth of popularity of this method is its ability to work on any point distribution. The grid free methods do not require the grid for ﬂow simulation, which is an essential requirement for all other conventional CFD methods. However, they do require point distribution or a cloud of points.
Point generation is relatively simple and less time consuming to generate as compared
to grid generation. There are various methods for point generation like an advancing front method, a quadtree based point generation method, a structured grid generator, an unstructured grid generator or a combination of above, etc. One of the easiest ways of point generation around complex geometries is to overlap the simple point distributions generated around individual constituent parts of the complex geometry. The least squares grid free method has been successfully used to solve a large number of ﬂow problems over the years. However, it has been observed that some problems are still encountered while
using this method on point distributions around complex conﬁgurations. Close analysis
of the problems have revealed that bad connectivity of the nodes is the cause and this leads to bad connectivity related code divergence.
The least squares (LS) grid free method called LSKUM involves discretization of
the spatial derivatives using the least squares approach. The formulae for the spatial derivatives are obtained by minimizing the sum of the squares of the error, leading to a system of linear algebraic equations whose solution gives us the formulae for the spatial derivatives. The least squares matrix A for 1-D and 2-D cases respectively is given by
(Refer PDF File for equation)
The 1-D LS formula for the spatial derivatives is always well behaved in the sense that ∑∆xi2 can never become zero. In case of 2-D problems can arise. It is observed that the elements of the Ls matrix A are functions of the coordinate differentials of the nodes in the connectivity. The bad connectivity of a node thus can have an adverse effect on the nature of the LS matrices. There are various types of bad connectivities for a node like insufficient number of nodes in the connectivity, highly anisotropic distribution of nodes in the connectivity stencil, the nodes falling nearly on a line (or a plane in 3-D), etc. In case of multidimensions, the case of all nodes in a line will make the matrix A singular thereby making its inversion impossible. Also, an anisotropic distribution of nodes in
the connectivity can make the matrix A highly illconditioned thus leading to either loss in accuracy or code divergence. To overcome this problem, the approach followed so far is to modify the connectivity by including more neighbours in the connectivity of the node. In this thesis, we have followed a diﬀerent approach of using weights to alter the nature of the LS matrix A.
(Refer PDF File for equation)
The weighted LS formulae for the spatial derivatives in 1-D and 2-D respectively are
are all positive. So we ask a question : Can we reduce the multidimensional LS formula for the derivatives to the 1-D type formula and make use of the advantages of 1-D type
formula in multidimensions?
Taking a closer look at the LS matrices, we observe that these are real and symmetric
matrices with real eigenvalues and a real and distinct set of eigenvectors. The eigenvectors of these matrices are orthogonal. Along the eigendirections, the corresponding LS formulae reduce to the 1-D type formulae. But a problem now arises in combining the eigendirections along with upwinding. Upwinding, which in LS is done by stencil splitting, is essential to provide stability to the numerical scheme. It involves choosing a direction for enforcing upwinding. The stencil is split along the chosen direction. But it is not necessary that the chosen direction is along one of the eigendirections of the split stencil. Thus in general we will not be able to use the 1-D type formulae along the chosen direction. This diﬃculty has been overcome by the use of weights leading to WLSKUM-ED (Weighted Least Squares Kinetic Upwind Method using Eigendirections). In WLSKUM-ED weights are suitably chosen so that a chosen direction becomes an eigendirection of A(w). As a result, the multi-dimensional LS formulae reduce to 1-D type formulae along the eigendirections. All the advantages of the 1-D LS formuale can thus be made use of even in multi-dimensions.
A very simple and novel way to calculate the positive weights, utilizing the coordinate
diﬀerentials of the neighbouring nodes in the connectivity in 2-D and 3-D, has been
developed for the purpose. This method is based on the fact that the summations
of the coordinate differentials are of diﬀerent signs (+ or -) in different quadrants or octants of the split stencil. It is shown that choice of suitable weights is equivalent to a suitable decomposition of vector space. The weights chosen either fully diagonalize the least squares matrix ie. decomposing the 3D vector space R3 as R3 = e1 + e2 + e3, where e1, e2and e3are the eigenvectors of A (w) or the weights make the chosen direction the eigendirection ie. decomposing the 3D vector space R3 as R3 = e1 + ( 2-D vector space R2). The positive weights not only prevent the denominator of the 1-D type LS formulae from going to zero, but also preserve the LED property of the least squares method. The WLSKUM-ED has been successfully applied to a large number
of 2-D and 3-D test cases in various ﬂow regimes for a variety of point distributions
ranging from a simple cloud generated from a structured grid generator (shock reﬂection
problem in 2-D and the supersonic ﬂow past hemisphere in 3-D) to the multiple chimera
clouds generated from multiple overlapping meshes (BI-NACA test case in 2-D and
FAME cloud for M165 conﬁguration in 3-D) thus demonstrating the robustness of the
WLSKUM-ED solver. It must be noted that the second order acccurate computations
using this method have been performed without the use of the limiters in all the ﬂow regimes. No spurious oscillations and wiggles in the captured shocks have been observed, indicating the preservation of the LED property of the method even for 2ndorder accurate computations.
The convergence acceleration of the WLSKUM-ED code has been achieved by the use
of LUSGS method. The use of 1-D type formulae has simplified the application of LUSGS method in the grid-free framework. The advantage of the LUSGS method is that the
evaluation and storage of the jacobian matrices can be eliminated by approximating the split flux jacobians in the implicit operator itself. Numerical results reveal the attainment of a speed up of four by using the LUSGS method as compared to the explicit time marching method.
The 2-D WLSKUM-ED code has also been used to perform the internal ﬂow computations. The internal ﬂows are the ﬂows which are confined within the boundaries. The inflow and the outflow boundaries have a significant effect on these ﬂows. The
accurate treatment of these boundary conditions is essential particularly if the ﬂow condition at the outflow boundary is subsonic or transonic. The Kinetic Periodic Boundary Condition (KPBC) which has been developed to enable the single-passage (SP) ﬂow computations to be performed in place of the multi-passage (MP) ﬂow computations,
utilizes the moment method strategy. The state update formula for the points at the periodic boundaries is identical to the state update formula for the interior points and can be easily extended to second order accuracy like the interior points. Numerical results have shown the successful reproduction of the MP ﬂow computation results using the SP ﬂow computations by the use of KPBC. The inflow and the outflow boundary conditions at the respective boundaries have been enforced by the use of Kinetic Outer Boundary Condition (KOBC). These boundary conditions have been validated by performing the ﬂow computations for the 3rdtest case of the 4thstandard blade conﬁguration of the turbine blade. The numerical results show a good comparison with the experimental results.2009-06-24T07:07:29Z