etd@IISc Community:http://hdl.handle.net/2005/52018-02-20T01:09:29Z2018-02-20T01:09:29ZFeature-based Approach for Semantic Interoperability of Shape ModelsGupta, Ravi Kumarhttp://hdl.handle.net/2005/31402018-02-19T19:08:17Z2018-02-19T18:30:00ZTitle: Feature-based Approach for Semantic Interoperability of Shape Models
Authors: Gupta, Ravi Kumar
Abstract: Semantic interoperability (SI) of a product model refers to automatic exchange of meaning associated with the product data, among applications/domains throughout the product development cycle. In the product development cycle, several applications (engineering design, industrial design, manufacturing, supply chain, marketing, maintenance etc.) and different engineering domains (mechanical, electrical, electronic etc.) come into play making the ability to exchange product data with semantics very significant. With product development happening in multiple locations with multiple tools/systems, SI between these systems/domains becomes important. The thesis presents a feature-based framework for shape model to address these SI issues when exchanging shape models.
Problem of exchanging semantics associated with shape model to support the product lifecycle has been identified and explained. Different types of semantic interoperability issues pertaining to the shape model have been identified and classified. Features in a shape model can be associated with volume addition/subtraction to/from base-solid, deformation/modification of base-sheet/base surface, forming of material of constant thickness.
The DIFF model has been extended to represent, classify and extract Free-Form Surface Features (FFSFs) and deformation features in a part model. FFSFs refer to features that modify a free-form surface. Deformation features are created in constant thickness part models, for example, deformation of material (as in sheet-metal parts) or forming of material (as in injection molded parts with constant thickness), also referred to as constant thickness features. Volumetric features covered in the DIFF model have been extended to classify and represent volumetric features based on relative variations of cross-section and PathCurve.
Shape feature ontology is described based on unified feature taxonomy with definitions and labels of features as defined in the extended DIFF model. Features definitions are used as intermediate and unambiguous representation for shape features. The feature ontology is used to capture semantics of shape features. The proposed ontology enables reasoning to handle semantic equivalences between feature labels, and is used to map shape features from a source to target applications.
Reasoning framework for identification of semantically equivalent feature labels and representations for the feature being exchanged across multiple applications is presented and discussed. This reasoning framework is used to associate multiple construction paths for a feature and associate applicable meanings from the ontology. Interface is provided to select feature label for a target application from the list of labels which are semantically equivalent for the feature being exchanged/mapped. Parameters for the selected feature label can be mapped from the DIFF representation; the feature can then be represented/constructed in the target application using the feature label and mapped parameters. This work shows that product model with feature information (feature labels and representations), as understood by the target application, can be exchanged and maintained in such a way that multiple applications can use the product information as their understandable labels and representations. Finally, the thesis concludes by summarizing the main contributions and outlining the scope for future work.2018-02-19T18:30:00ZInverse Problems in Free Vibration Analysis of Rotating and Non-Rotating Beams and its Application to Random Eigenvalue CharacterizationSarkar, Korakhttp://hdl.handle.net/2005/31392018-02-19T07:42:07Z2018-02-18T18:30:00ZTitle: Inverse Problems in Free Vibration Analysis of Rotating and Non-Rotating Beams and its Application to Random Eigenvalue Characterization
Authors: Sarkar, Korak
Abstract: Rotating and non-rotating beams are widely used to model important engineering struc-tures. Hence, the vibration analyses of these beams are an important problem from a structural dynamics point of view. Depending on the beam dimensions, they are mod-eled using diﬀerent beam theories. In most cases, the governing diﬀerential equations of these types of beams do not yield any simple closed-form solutions; hence we look for the inverse problem approach in determining the beam property variations given certain solutions.
The long and slender beams are generally modeled using the Euler-Bernoulli beam theory. Under the premise of this theory, we study (i) the second mode tailoring of non-rotating beams having six diﬀerent boundary conditions, (ii) closed-form solutions for free vibration analysis of free-free beams, (iii) closed-form solutions for free vibration analysis for gravity-loaded cantilever beams, (iv) closed-form solutions for free vibration analysis of rotating cantilever and pinned-free beams and (v) beams with shared eigen-pair. Short and thick beams are generally modeled using the Timoshenko beam theory. Here, we provide analytical closed-form solutions for the free vibration analysis of ro-tating non-homogeneous Timoshenko beams. The Rayleigh beam provides a marginal improvement over the Euler-Bernoulli beam theory without venturing into the math-ematical complexities of the Timoshenko beam theory. Under this theory, we provide closed-form solutions for the free vibration analysis of cantilever Rayleigh beams under three diﬀerent axial loading conditions - uniform loading, gravity-loading and centrifu-gally loaded.
We assume simple polynomial mode shapes which satisfy the diﬀerent boundary conditions of a particular beam, and derive the corresponding beam property variations. In case of the shared eigenpair, we use the mode shape of a uniform beam which has a closed-form solution and use it to derive the stiﬀness distribution of a corresponding axially loaded beam having same length, mass variation and boundary condition. For the Timoshenko beam, we assume polynomial functions for the bending displacement and the rotation due to bending. The derived properties are demonstrated as benchmark analytical solutions for approximate and numerical methods used for the free vibration analysis of beams. They can also aid in designing actual beams for a pre-specified frequency or nodal locations in some cases. The eﬀect of diﬀerent parameters in the derived property variations and the bounds on the pre-specified frequencies and nodal locations are also studied for certain cases.
The derived analytical solutions can also serve as a benchmark solution for diﬀerent statistical simulation tools to find the probabilistic nature of the derived stiﬀness distri-bution for known probability distributions of the pre-specified frequencies. In presence of uncertainty, this flexural stiﬀness is treated as a spatial random field. For known probability distributions of the natural frequencies, the corresponding distribution of this field is determined analytically for the rotating cantilever Euler-Bernoulli beams. The derived analytical solutions are also used to derive the coeﬃcient of variation of the stiﬀness distribution, which is further used to optimize the beam profile to maximize the allowable tolerances during manufacturing.2018-02-18T18:30:00ZA Study of the Characteristics of Gas-On-Liquid Impinging InjectorsRakesh, Phttp://hdl.handle.net/2005/31262018-02-17T19:54:17Z2018-02-17T18:30:00ZTitle: A Study of the Characteristics of Gas-On-Liquid Impinging Injectors
Authors: Rakesh, P
Abstract: The work presented here pertains to investigations on gas-on-liquid type of impinging injectors with a generic approach with prospective applications in several areas, and at places with particular emphasis on cryogenic or semi-cryogenic liquid propellant rockets. In such
rockets, one of the components arrives at the injector in a gaseous phase after passing through the regenerative coolant passages or a preceding combustion stage. Most often, the injectors in such systems are of shear coaxial type. The shear coaxial injectors suffer from several disadvantages like complexity in design, manufacture and quality control. Adoption of impinging jet configuration can alleviate these problems in addition to providing further benefits in terms of cost, robustness in high temperature environment and manifolding.
However, there is very little literature on gas-on-liquid injectors either in this context or in any other Even for the simplest form of impinging injectors such as like-on-like doublets, literature provides no conclusive direction at describing a spray from the theoretical models of physical mechanisms. Empirical approach is still the prime mode of obtaining a proper understanding of the phenomena. Steady state spray characterization includes mainly of describing the spatial distribution of liquid mass and drop size distribution as a function of geometric and injection parameters. The parameters that are likely to have an impact on spray characteristics are orifice diameter, ratio of orifice length to diameter, pre-impingement length of individual jets, inter orifice distance, impingement angle, jet velocity and condition of the jet just before impingement. The gas-on- liquid configuration is likely to experience
some qualitative changes because of the expansion of the gas jet. The degree to
which each one of the above variables influences the drop size and mass distribution having implication to combustion performance forms the core theme of the thesis. A dedicated experimental facility has been built, calibrated and deployed exhaustively.
While spray drop size measurement is done largely by a laser diffraction instrument, some of the cases warranted an image processing technique. Two different image processing algorithms are developed in-house for this purpose. The granulometric image processing method developed earlier in the group for cryogenic sprays is modified and its applicability to gas-on-liquid impinging sprays are verified. Another technique based on the Hough transform which is feature extraction technique for extracting quantitative information has also been developed and used for gas-on-liquid impinging injectors. A comparative study of conventional liquid-on-liquid doublet with gas-on-liquid impinging injectors are first made to establish the importance of studying gas-on-liquid impinging injectors. The study identifies the similarities and differences between the two types and highlights the features that make such injectors attractive as replacements to coaxial configuration. Spray structure, drop-size mass distributions are quantified for the purpose
of comparison. This is followed by a parametric study of the gas-on-liquid impinging injectors carried out using identified control variables. Though momentum ratio appeared to be a suitable parameter to describe the spray at any given impingement angle, the variations due to impingement angle had to be factored in. It was found that normal gas momentum to liquid mass is an apt parameter to generalize the spray characteristics. It was also found that using identical nozzles for desired mass ratio could lead to rather large deflection of the spray which may not be acceptable in combustion chamber design. One way of overcoming this is to work with unequal orifice sizes for gas and liquid. It was found that using smaller gas orifice for a given liquid orifice resulted in lower SMD (Sauter Mean Diameter of the spray) for constant gas and liquid mass flow rates. This is attributable to the high dynamic
pressure of gas in the case of smaller gas orifices for the same mass flow rate. The impinging liquid jets with unequal momentum in the doublet configuration would
result in non-uniform mass and mixture ratio distribution within the combustion chamber
which may have to operate under varying conditions of mass flow rates and/or mixture
ratio. The symmetrical arrangement of triplet configuration can eliminate this problem at the same time generating finely atomized spray and a homogeneous mixture ratio. In view of the scanty literature available in this field, the atomization characteristics of the spray
generated by liquid centered triplet jets are examined in detail. It was found that as in the case of gas-on-liquid impinging doublets, normal gas momentum to liquid mass is an ideal parameter in describing the spray. Variants of this configuration are studied recently for many other applications too. As done in the case of doublets, efforts have also been made to compare gas centered triplet to liquid-liquid triplet. It was found that the trend of SMD of gas centered triplet is different from that of liquid-liquid triplets, thus pointing to a different mechanism in play. The SMD in the case of liquid-liquid triplets decreases monotonically with increasing specific normal momentum. It is to be noted that specific normal momentum is an ideal
parameter for describing the spray characteristics of liquid-liquid triplets and doublets. In the case of gas centered triplet the SMD first increases and then decreases with specific normal momentum, the inversion point depends on the gas mass flow rate for a constant specific normal momentum.
The thesis concludes with a summary of the major observations of spray structures for
all the above injector configurations and quantifies the parametric dependencies that would be of use to engineering design2018-02-17T18:30:00ZOn Three Dimensional High Lift Flow ComputationsGopalakrishna, Nhttp://hdl.handle.net/2005/31272018-02-17T20:11:49Z2018-02-17T18:30:00ZTitle: On Three Dimensional High Lift Flow Computations
Authors: Gopalakrishna, N
Abstract: Computing 3D high lift flows has been a challenge to the CFD community because of three important reasons: complex physics, complex geometries and large computational requirements. In the recent years, considerable progress has been made in understanding the suitability of various CFD solvers in computing 3D high lift flows, through the systematic studies carried out under High Lift Prediction workshops. The primary focus of these workshops is to assess the ability of the CFD solvers to predict CLmax and αmax associated with the high lift flows, apart from the predictability of lift and drag of such flows in the linear region. Now there is a reasonable consensus in the community about the ability of the CFD solvers to predict these quantities and fresh efforts to further understand the ability of the CFD solvers to predict more complex physics associated with these flows have already begun.
The goal of this thesis is to assess the capability of the computational methods in predicting such complex flow phenomena associated with the 3D High-Lift systems. For evaluation NASA three element Trapezoidal wing configuration which poses a challenging task in numerical modeling was selected. Unstructured data based 3D RANS solver HiFUN (HiFUN stands for High Resolution Flow Solver for UNstructured Meshes) is used in investigating the high lift flow. The computations were run fully turbulent, using the one equation Spalart-Allmaras turbulence model.
A summary of the results obtained using the flow solver HiFUN for the 3D High lift NASA Trapezoidal wing are presented. Hybrid unstructured grids have been used for the computations. Grid converged solution obtained for the clean wing and the wing with support brackets, are compared with experimental data. The ability of the solver to predict critical design parameters associated with the high lift flow, such as αmax and CLmax is demonstrated. The utility of the CFD tools, in predicting change in aerodynamic parameters in response to perturbational changes in the configuration is brought out. The solutions obtained for the high lift configuration from two variants of the Spalart-Allmaras turbulence model are compared. To check the unsteadiness in the flow, particularly near stall, unsteady simulations were performed on static grid. Lastly, hysteresis on lower leg of lift curve is discussed, the results obtained for quasi-steady and dynamic unsteady simulations are presented. Inferences from the study on useful design practices pertaining to the 3D high lift flow simulations are summarized.2018-02-17T18:30:00Z