Department of Mechanical Engineering

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This paper discusses topology, shape and size optimization of fully compliant mechanisms for path generation applications using curved frame elements and genetic algorithm. The topology optimization problem is treated as a discrete '0-1' problem wherein the elastic modulus is chosen as 0 or some pre-specified value, and no intermediate value in between. As the Young's moduli are discrete topology design variables, function based genetic algorithm is employed for optimization. The size optimization variables are the lengths, in-plane widths and out-of-plane thicknesses of frame elements. Shape optimization is performed using the end slopes. Kirchhoff's shallow arch beam theory is employed along with corotational geometrically nonlinear formulation. Synthesis examples are presented to demonstrate the applicability of min-max criterion proposed to achieve a curved path specified using precision points. Copyright © 2006 by ASME.

World University root node

Proceedings of the ASME Design Engineering Technical Conference

On optimal design of compliant mechanisms for specified nonlinear path using curved frame elements and genetic algorithm

Flight test data of helicopters indicate that vibratory levels in the fuselage exhibit a wide spectrum of frequencies including a few below the rotor RPM. It is well known that helicopter blades operate in a complex aerodynamic environment, involving time varying heave, pitch and pulsating oncoming flow. During operation, some sections of the rotor blade undergo dynamic stall once in a revolution. This paper attempts to understand the reason for the existence of several frequencies in the response of the fuselage and the possible cause for this observed phenomenon by analysing the effects of dynamic stall and aeroelastic couplings on the response of 2-D airfoil. The ONERA dynamic stall model developed by Petot is modified by incorporating a higher order rational approximation of Theodorsen's lift deficiency function. This improved model is shown to provide a better correlation with experimental stall data. The response characteristics of a 2-D airfoil undergoing pitching and plunging motion in a pulsating oncoming flow, simulating the response of a cross-section of a helicopter rotor blade in forward flight are analysed. This study shows significant difference in the response characteristics of the airfoil for unsteady (dynamic stall model) and quasi-steady aerodynamic models. It is observed that the non-linear aerodynamics (dynamic stall effects) in association with aeroelastic couplings above a certain level lead to a bounded chaotic motion of the airfoil.

Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference

Rotor blade dynamic stall model and its influence on airfoil response

Since a majority of residential and industrial building hot water needs are around 50 °C, an integrated solar water heater could provide a bulk source that blends collection and storage into one unit. This paper describes the design, construction and performance test results of one such water-heating device. The test unit has an absorber area of 1.3 m2 and can hold 170 l of water, of which extractable volume per day is 100 l. Its performance was evaluated under various typical operating conditions. Every morning at about 7:00 a.m., 100 l of hot water were drawn from the sump and replaced with cold water from the mains. Although, during most of the days, the peak temperatures of water obtained are between 50 and 60 °C, the next morning temperatures were lower at 45-50 °C. Daytime collection efficiencies of about 60% and overall efficiencies of about 40% were obtained. Tests were conducted with and without stratification. Night radiation losses were reduced by use of a screen insulation.

Energy and Buildings

Performance evaluation of an integrated solar water heater as an option for building energy conservation

The bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system in itself is the critical part of a nuclear reactor. Any failure of this system can lead to grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. The present paper is an effort towards identifying and understanding the problems affecting the BMWs and is as well an attempt to highlight the current issues in the structural integrity assessment of structures having these welds. The basic aim of this work is to provide a clear understanding of the current structural safety issues and their importance in underpinning the use of BMWs in modern nuclear reactors. © IMechE 2006.

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

Use of bimetallic welds in nuclear reactors: Associated problems and structural integrity assessment issues

A generalized layer-wise stochastic finite element formulation is developed for the buckling analysis of both homogeneous and laminated plates with random material properties. The pre-buckled stresses are considered in the derivation of geometric stiffness matrix and the effect of variation in these stresses on the mean and coefficient of variation of buckling strength is studied. The mean buckling strength of plates under uniform stress assumption exactly matches with those reported in the literature. However, it is shown that the actual mean buckling strength of plates can be significantly different based on the pre-buckled stress analysis which depends on boundary constraints, principal material directions, aspect and thickness ratios of plates. The statistics of buckling strength is determined using a Taylor series expansion based mean centered first order perturbation technique. The stochastic finite element solutions obtained using layer-wise plate theory is also validated with analytical solutions presented in this paper. Parametric studies are conducted for different aspect ratios, ply orientations and boundary conditions. © 2006 Elsevier Ltd. All rights reserved.

International Journal of Mechanical Sciences

Generalized buckling analysis of laminated plates with random material properties using stochastic finite elements

Coupled electro-thermo-elastic equations applicable for the analysis of smart structures with piezoelectric patches/layers have been derived from the fundamental principles of mass, linear momentum, angular momentum, energy and charge conservation. The relevant constitutive equations have been obtained by using the second law of thermodynamics. The interaction of the electric field and polarization introduces distributed non-linear body force in the piezo material, and in addition renders the stress tensor non-symmetric due to distributed couple. Using the linear equations, and applying a layer-by-layer finite element model, the induced electric potential and mechanical deformations in the piezo and non-piezo core material have been obtained for various cases of actuation and sensing of a smart beam under external mechanical, electrical and thermal loadings. The mathematical formulation and the solution technique have been validated by comparing the results of the present study with those available in the literature. It is also shown that piezo patches can be effectively used for shape control. © 2006 IOP Publishing Ltd.

Smart Materials and Structures

Electro-thermo-elastic formulation for the analysis of smart structures

We propose an experimental method to study the instability of thin unsteady separation bubbles, i.e. of unsteady boundary layers with reverse flow. The unsteady boundary layer is created by controlled temporal and spatial variations of the velocity external to the boundary layer. We present results of the evolution of instability in different temporally varying flows in a shallow angle diffuser. Depending on the extent of reverse flow in the boundary we observe that instability can be spatially localised. © 2006 Springer.

Fluid Mechanics and its Applications

Localised instability in unsteady separation bubbles

A first-ply failure and buckling failure of laminated composite plates with and without centrally located cutout having random material properties are presented under uniaxial compressive loading. In both cases, an accurate pre-buckled stress analysis is needed. A layerwise plate model is used to solve both pre-buckling and buckling problems. The stochastic failure analysis is carried out using mean centered first order perturbation technique based stochastic finite element method. Micromechanics based approach is used to see the effect of variation in microlevel constituents, like fiber phase, matrix phase and volume fraction of each phase, on the effective macrolevel properties like the elastic moduli. Consequently the effect of uncertainty in these material properties on the first-ply failure load and buckling strength of the laminated plates is studied. The mean buckling strength of composite plates is validated with results available in literature. The validation of stochastic analysis is done with analytical result based on Kirchhoff-Love plate theory in conjunction with first-order perturbation technique. Parametric studies are also done to see the effect of lay-ups and boundary conditions on the mean and variance of buckling strength of plates. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Stochastic finite element failure analysis of laminated plates under uniaxial compressive loading

The design of laminated composite based components requires a detailed analysis of the response of the structure when subjected to external loads. For the analysis of laminated composite plates, several plate theories have been proposed in the literature. Generally, these plate theories are used to obtain certain global response quantities like the buckling load. However, the use of these theories to obtain local response quantities, i.e. point-wise stresses; interlaminar stresses and strains, can lead to significant errors. In this paper, a detailed study of the quality of the point-wise stresses obtained using higher-order shear deformable, hierarchic and layerwise theories is done for a plate under transverse loading. The effect of equilibrium based post-processing on the transverse stress quantities is also studied. From the detailed study it is observed that the layerwise theory is very accurate. However, for all the models proper mesh design is required to capture boundary layer effects, discretization error, etc. Using focussed adaptivity, and post-processed state of stress, accurate representation of the local state of stress can be obtained, even with the higher-order shear deformable theories. Using this approach, the first-ply failure load is obtained with the Tsai-Wu criterion. It is observed that use of an adaptive procedure leads to significantly lower failure loads as compared to those given in the literature. © 2005 Elsevier Ltd. All rights reserved.

Computers and Structures

Accurate computation of critical local quantities in composite laminated plates under transverse loading

This paper presents families of equivalent, intermediate and layerwise plate models. It is shown that the layerwise model approach, using high value of in-plane and transverse approximation orders is very accurate pointwise with respect to all the stress components and displacement components. However, using this model can be computationally expensive, especially when the number of layers is large. In this paper, a novel region-by-region modeling strategy is developed. By this strategy any of the above model can be put in any region of the domain. It is shown that by judiciously using layerwise models only in regions where solution is predominantly three-dimensional in nature, and lower order models elsewhere, the same accuracy (as the layerwise model) can be achieved at significantly lower computational cost. This strategy can be effectively used for analyzing laminated plates with complicated structural details (corners, cut-outs), material transitions and damaged regions in the form of delamination and ply damage. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.