Department of Mechanical Engineering

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IIT Jodhpur

Present paper describes the microstructural and mechanical properties of creep strength enhanced Cr–Mo P91 steel subjected to a regime of tempering time 720–3000 h. Study on the effect of varying tempering time on microstructure revealed increase in size of precipitates, amount of precipitates and grain size. It was also observed that compared to particle size, effect of tempering time was more pronounced on the grain size. The various phases that formed in the tempered P91 steel were analyzed by X-ray diffraction. Yield strength and tensile strength were observed to be decreasing with increase in tempering time. Increase in duration of tempering time led to decrease in impact toughness of P91 specimens possibly due to cracking of secondary phase particles during straining and decohesion at precipitates and matrix interface. The tempering time also observed to be affecting the hardness of P91 steel but less pronounced compared to the yield strength and tensile strength. Tensile fracture and impact toughness fracture surfaces were studied by using scanning electron microscope. The fracture surface of tempered P91 tensile specimens indicated increased dimples and presence of fewer cleavage facets. The fracture surface of P91impact toughness specimens exhibited both inter lath-decohesion and ductile dimple tearing. © 2016, The Indian Institute of Metals - IIM.

World University root node

Transactions of the Indian Institute of Metals

Effect of Long-term Ageing on the Microstructure and Mechanical Properties of Creep Strength Enhanced Ferritic P91 Steel

Mechanical properties of creep enhanced ferritic (CSEF) steels is affected by various parameters, the solutionizing temperature is one of them. The present work demonstrates the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel. Optical metallography (OM) and Scanning electron microscopy (SEM) were carried out to study the microstructure of P91 steel in different heat treatment conditions. In order to determine the precipitates present in microstructure; X-ray analysis was performed. Moreover, the influence of solutionizing temperature on the mechanical properties (strength, hardness and impact toughness) has also been studied. © 2016 Elsevier B.V.

Materials Science and Engineering A

Effect of normalizing temperature on microstructural stability and mechanical properties of creep strength enhanced ferritic P91 steel

Non-conforming approximation methods are becoming increasingly popular because of the potential to apply to multi-material and multi-model analysis for both bounded and unbounded domains. In this paper, we present a least-square approximation based method to solve the one or two dimensional elliptic problems on an unbounded domain. The method gives exponential accuracy and shows superior performance when compared to other numerical methods. Differentiability estimates and the main stability estimate theorem, using a non-conforming spectral element method, are also discussed. The exponential convergence rate of the proposed method is also shown through rigorous error estimate and specific numerical examples. © 2016 Elsevier B.V.

Computer Methods in Applied Mechanics and Engineering

Exponentially accurate nonconforming least-squares spectral element method for elliptic problems on unbounded domain

In helicopters, the rotor blade structural dynamic characteristics play an important role in the overall performance of the vehicle, defined in terms loads, vibration and handling qualities. The placement of natural frequencies in flap and lag is a critical step in the design of a practical rotor blade. A systematic optimization procedure in the design of cross sectional variations of structural and inertial properties will greatly help in the design process. An optimization procedure developed for the placement of natural frequencies in a non-uniform rotor blade is presented in this paper. The first flap and the first lag natural frequencies are considered for the optimization. A single cell section is selected for the blade root cross section in this study. The wall thickness of the single cell section is selected as primary design variable. The secondary design variables, stiffness and structural mass properties are modelled as parametric equations of the primary design variable. In this work the constraints are imposed on minimum wall thickness to cater for axial stress due to centrifugal force. A gradient based method along with the interior penalty function is used for the optimization. To automate the complete optimization process, the optimization program is linked with the computational tools Cross Sectional Properties Evaluation (COPE ) and Structural Dynamics Analysis of Rotor Blade (SDAR). These codes are developed at Helicopter Lab of Aerospace Engineering department, IIT Kanpur and validated with experimental data. © 2016, American Helicopter Society International. All rights reserved.

5th Asian-Australian Rotorcraft Forum, ARF 2016

Optimum design of realistic helicopter rotor blade with variable properties

Rotor blades are constructed with composite materials. The root section of the rotor blade, which is made of thick composite layers, undergoes large dynamic loads. Due to this loading, thick composite section is amenable to various types of damages. This paper addresses a method for the analysis of damage prediction in root section of the rotor blade. Finite element model of root section of a composite main rotor blade is analysed in two stages. In the first step, rotor blade root is modeled with coarse mesh using continuum shell and solid elements. In this phase, damage initiation and evolution criteria for fibre and matrix are assessed using Hashin criteria. In the second stage, ply-by-ply FE sub-models are prepared and cohesive elements are introduced in the area of interest to study the tendency for delamination. Experimental study on rotor blade root section has been carried out for both static and fatigue loading cases. The results of FE analysis and experimentation are compared for the static case for stresses and displacements. The zone of damage initiation from FE static analysis is in agreement with the location of damage in experimentation under fatigue loading.

42nd European Rotorcraft Forum 2016

Damage assessment of composite main rotor blade by finite element simulation and experiment

We present a three-dimensional (3D) and fully Eulerian approach to capturing the interaction between two fluids and moving rigid structures by using the fictitious domain and volume-of-fluid (VOF) methods. The solid bodies can have arbitrarily complex geometry and can pierce the fluid-fluid interface, forming contact lines. The three-phase interfaces are resolved and reconstructed by using a VOF-based methodology. Then, a consistent scheme is employed for transporting mass and momentum, allowing for simulations of three-phase flows of large density ratios. The Eulerian approach significantly simplifies numerical resolution of the kinematics of rigid bodies of complex geometry and with six degrees of freedom. The fluid-structure interaction (FSI) is computed using the fictitious domain method. The methodology was developed in a message passing interface (MPI) parallel framework accelerated with graphics processing units (GPUs). The computationally intensive solution of the pressure Poisson equation is ported to GPUs, while the remaining calculations are performed on CPUs. The performance and accuracy of the methodology are assessed using an array of test cases, focusing individually on the flow solver and the FSI in surface-piercing configurations. Finally, an application of the proposed methodology in simulations of the ocean wave energy converters is presented. © 2016 Elsevier Inc.

Fulltext

Journal of Computational Physics

A 3D, fully Eulerian, VOF-based solver to study the interaction between two fluids and moving rigid bodies using the fictitious domain method

University of Melbourne

Understanding loss mechanisms in turbomachinery to increase efficiency

Due to high degrees of freedom of humanoids and induced redundancy, there are multiple ways of performing a given manipulation task. Finding optimal ways of performing tasks is one desirable property of any motion planning framework. This includes optimizing the path with respect to a certain objective function. Additionally, a variety of constraints need to be satisfied such as stability, self-collision and collision with objects in the environment and also kinematic closed-loop chains formed during the task. Time requirements of the planner is another important aspect that drives us to use sampling based methods. In this paper, we present an asymptotically optimal sampling based approach for generating statically stable motion plans. We use RRT∗-connect algorithm which we obtained by modifying RRT-Connect. Moreover, we use a gradient based inverse kinematics solver to generate goal configurations. We evaluate the efficacy of our approach in the results section in a simulation environment on Hubo+ robot model. The results show a significant improvement in path costs as well as overall optimality of the given task. Copyright © 2016 by ASME.

Proceedings of the ASME Design Engineering Technical Conference

Optimal task planning of humanoid in cluttered environment

Kinetic energy and scalar spectra from the measurements in high Rayleigh number axially homogeneous buoyancy driven turbulent flow are presented. Kinetic energy and concentration (scalar) spectra are obtained from the experiments wherein density difference is created using brine and fresh water and temperature spectra are obtained from the experiments in which heat is used. Scaling of the frequency spectra of lateral and longitudinal velocity near the tube axis is closer to the Kolmogorov-Obukhov scaling, while the scalar spectra show some evidence of dual scaling, Bolgiano-Obukhov scaling followed by Obukhov-Corrsin scaling. These scalings are also observed in the corresponding second order spatial structure functions of velocity and concentration fluctuations.

Physics of Fluids

Kinetic energy and scalar spectra in high Rayleigh number axially homogeneous buoyancy driven turbulence

The percentage of renewable energy sources such as solar, wind power and biomass in the energy mix of India is increasing every year. Solar power variability is an important issue for grid integration of solar photovoltaic power plants. The main objective of this paper is to forecast the power generated in a 5 MW solar PV plant owned by Gujarat Power Corporation Limited (GPCL) at Charanka solar park, Gujarat. Charanka is a location with an average of 320 sunny days in a year. Average solar insolation available here is 5.7-6.0 kWh/m2 per day. Data obtained from 1st March 2014-31st August 2014 is used for analysis purposes. In this paper a two stage procedure is used referred to as GNN (Generalized Neural Network) model. In the primary stage pre-processing is done on the raw data followed by neural network model for forecasting. © 2015 IEEE.