Department of Mechanical Engineering

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IIT Jodhpur

Coalescence of secondary dendrite arms in terms of the evolution of specific surface area for a dendritic envelope with respect to the fraction solid during directional solidification is studied analytically in 2-D and 3-D frame of reference. For 2D case study, the dendritic growth has been captured by gradual penetration of a parabola with fixed tip radius (ρ) inside a square domain, while for 3D case study, we replace the parabola and square domain for 2-D case with a paraboloid of revolution and cubic domain, respectively. The dimensions of the enclosing volumes are characterized by the secondary dendrite arm-spacing. Coalescence obtained by the analytical solution is compared with existing dendrite growth simulation results obtained by phase-field method.

World University root node

Transactions of the Indian Institute of Metals

Evolution of specific surface area with solid volume fraction during coalescence with parabolic shape assumption for dendrite

Cutter deflections induce significant amount of surface error on machined components and it is one of the major obstacles towards achieving higher productivity in peripheral milling operation. These surface errors do not take one particular form and their shape and profile measured along axial direction, varies significantly with cutting conditions. The understanding and characterization of all possible surface error types is of immense value to process planners as it forms a basis for controlling and compensating them. This paper presents a methodology to classify surface error profiles and to relate the same with cutting conditions in terms of axial and radial engagement between cutter and workpiece. The proposed characterization scheme has been validated using computational studies and machining experiments. The importance of proposed characterization is further demonstrated in understanding peripheral milling of curved geometries where workpiece curvature influences radial engagement of the cutter that often changes surface error shape both qualitatively and quantitatively. Computational and experimental studies undertaken to study machining of curved geometries underline the importance of proposed characterization scheme in identifying correct cutting conditions for a given machining situation. © 2012 Elsevier B.V. All rights reserved.

Journal of Materials Processing Technology

On cutter deflection surface errors in peripheral milling

Reduction in specific and viscous dissipation rate in surface waters by flow control and contaminant removal are the goals of constructed wetlands. A two-dimensional simulation study on surface flow through a constructed wetland in Guilin, China is performed. The flow through the wetland is modeled and dynamically simulated by distinct case studies by varying both inlet width and inflow rate. Nonlinear increase in peak dynamic pressure and specific dissipation rates as a function of increasing inflow rate is reported for the different cases studied. The results of the numerical models confirm an increase in viscous dissipation, shear stress and dynamic pressure within the wetland with increase in inflow rate. These modeling results are used as inputs for performing a statistical data analysis. Further, a multivariate stochastic statistical framework has been proposed for the prediction of dissipation as a function of variables including inflow rate, inlet geometry and wall shear stress. Multivariate and variance analysis is performed to validate the appropriateness of the theoretical models proposed. Results provide simplified meaningful suggestions to constructed wetland design and related applications. © 2011 Springer-Verlag.

Stochastic Environmental Research and Risk Assessment

Numerical and multivariate stochastic approaches to characterize flow in a constructed wetland basin

Due to the trend of increasing power and reducing weight, the fan and compressor blades of turbo machinery might be more sensitive to flutter, which must strictly be avoided in the design process. In order to increase our understanding of the flutter phenomena for fan and compressor cascades, aero-elastic investigations are essential. In the present work experiments were performed in the specifically designed Oscillating Cascade Facility to investigate and quantify the unsteady aerodynamics forces and moments acting on a blade in a linear cascade of blades when the instrumented blade is stationary and the two adjacent blades on both sides of the instrumented blade are executing torsion-mode oscillations about their mid-chord. A 5-component strain gage balance was used to measure the unsteady aerodynamic forces on the model blade. The forces were measured for six inter-blade phase angles (i.e., the phase angle between the moving blade motions at a given frequency where the central blade is stationary) at low subsonic conditions, different reduced frequencies and different stagger. The time-variant forces were analyzed and variation of lift and drag coefficients for different inter-blade phase angles and reduced frequencies were plotted. The experimental results indicate that the inter-blade phase angle had a major effect on the variation of the unsteady forces and that reduced frequency had a somewhat less significant effect. Also in order to investigate the influence of the reduced frequency and interblade phase angles on the global stability of the cascade and its local contributions, experiments were performed for different reduced frequencies and phase angles. At the higher inter-blade phase angles (180°) the blade remains aerodynamically stable at 00 stagger, but the stability reduces at higher stagger angles. The blade is usually unstable when the interblade phase angle is 00. At different flow conditions, some of the inter-blade phase angles appear to be aerodynamically unstable. Copyright © 2012 by ASME.

Proceedings of the ASME Turbo Expo

Effect of adjacent blade motion on the aerodynamics of a linear cascade blade

Nonlinear dynamic analysis of a Cartesian manipulator carrying an end effector which is placed at different intermediate positions on the span is theoretically investigated with a single mode approach. The governing equation of motion of this system is formulated by using the D'Alembert principle in addition to profuse application of Dirac delta function to indicate the location of the intermediate end effector. Then the governing equation is further reduced to a second-order temporal differential equation of motion by using Galerkin's method. The method of multiple scales as one of the perturbation techniques is being used to determine the approximate solutions and the stability and bifurcations of the obtained approximate solutions are studied. Numerical results are demonstrated to study the effect of intermediate positions of the end effector placed at various locations on the link with other relevant system parameters for both the primary and secondary resonance conditions. It is worthy of note that the catastrophic failure of the system may take place due to the presence of jump phenomenon. The results are found to be in good agreement with the results determined by the method of multiple scales after solving the temporal equation of motion numerically. In order to determine physically realized solution by the system, basins of attraction are also plotted. The obtained results are very useful in the application of robotic manipulators where the end effector is placed at any arbitrary position on the robot arm. © 2011 Springer Science+Business Media B.V.

Nonlinear Dynamics

Nonlinear dynamic analysis of a Cartesian manipulator carrying an end effector placed at an intermediate position

In a typical commercial transport aircraft, Stiffened skin panels and frames contribute around 40% of the fuselage weight. In the current study a stiffened composite fuselage skin panel optimization engine is developed for optimization of the layups of composite panels and stringers using Genetic Algorithm (GA). The skin and stringers of the fuselage section are optimized for the strength and the stability requirements. The selection of the GA parameters considered for the optimization is arrived by performing case studies on selected problems. The optimization engine facilitates in carrying out trade studies for selection of the optimum ply layup and material combination for the configuration being analyzed. The optimization process is applied on a sample model and the results are presented.

European Space Agency, (Special Publication) ESA SP

Stiffened composite fuselage barrel optimization

We investigate the contact of a cylindrical punch with an adhesive elastic layer or film bonded to a rigid substrate. The classical assumption of Hertzian contact are coupled with tools of fracture mechanics to resolve the contact problem. The contact edge's singularity is resolved by introducing a Dugdale-Barenblatt model for the adhesive zone extending in front of the contact region. Exact governing equations so obtained are solved by a semi-analytical technique employing Chebyshev polynomials. We also extend the useful JKR approximation to the indentation of elastic layers as a particular case of our general solution. © 2012 Copyright Taylor and Francis Group, LLC.

Journal of Adhesion

Contact of a rigid cylindrical punch with an adhesive elastic layer

In this paper, a legged robot is modeled as a floating-base tree-type system where the foot-ground interactions are represented as external forces and moments. Dynamic formulation thus obtained is independent of the configuration or state of the legged robot. Framework for dynamic modeling is proposed with the concept of kinematic modules, where each module is a set of serially connected links. Legged robots are then considered to have several kinematic modules, and kinematic constraints among these modules are obtained in a similar way as those between the links. The latter approach turns out to be a special case of the former where each module has only one link. A velocity transformation based approach is used to obtain the minimal-order equations of motion, and module-level analytical expressions for the vectors and matrices appearing in them. Recursive algorithms for inverse and forward dynamics are proposed by using inter- and intra-modular recursions for the first time. Analyses of a planar biped and spatial quadruped are presented using the proposed methodology. Effectiveness of the proposed algorithms to model-based control schemes is also provided. © 2011 Elsevier Ltd All rights reserved.

Mechanism and Machine Theory

Modular framework for dynamic modeling and analyses of legged robots

This paper deals with the study of a submerged jet for the suction of unwanted fluid. This submerged jet is caused by the fluid coming out from a source. The presence of a sink in front of this source facilitates the suction of the fluid depending upon the source and sink flow rates, the axial and lateral separations of the source and sink, and the angle between the axes of the source and sink. The main purpose is the determination of the sink flow rate for 100 % removal of the source fluid as a function of these parameters. The experiments have been carried using a source nozzle 6 mm in diameter and two sizes for the sink pipe diameter: 10 mm and 20 mm. The main diagnostics used are flow visualization using dye and particle image velocimetry (PIV). The dependence of the required suction flow rate to obtain 100 % effectiveness on the suction tube diameter and angle is relatively weak compared to the lateral separation. © 2012 American Society of Mechanical Engineers.

Journal of Fluids Engineering, Transactions of the ASME

Study of submerged jet for suction of fluid

Safe operation of nuclear power plants is one of the major concerns and relies primarily on the integrity of the reactor pressure vessel. Neutron exposure induces temperature dependent embrittlement and can lead to loss of fracture toughness of reactor pressure vessel steel. Conventional fracture mechanics suffers from a serious limitation of non-transferability of fracture data from specimen level to component level as fracture resistance data obtained is largely geometry dependant. This difficulty is largely overcome by Gurson-Tvegaard-Needleman (GTN) model which models the drop in load carrying capacity of a material with the increase in plastic strain, considering nucleation, growth and coalescence of micro-voids in the material. However, determination of the model-parameters with experiments is extremely difficult and doubtful. Hence, a parametric study was undertaken to find out the effects of different parameters on material behaviour of reactor pressure vessel steel and to asses the parameter for best practical result with least metallographic study using a hybrid approach. The model parameters were finally verified by predicting ductile fracture in compact tension and three point bend specimen made from reactor pressure vessel steel. © 2011 Elsevier Ltd.