Showing papers by "Ramin Sedaghati published in 2013"

Fused empirical mode decomposition and wavelets for locating combined damage in a truss-type structure through vibration analysis

Abstract: Structural health monitoring (SHM) is a relevant topic for civil systems and involves the monitoring, data processing and interpretation to evaluate the condition of a structure, in order to detect damage. In real structures, two or more sites or types of damage can be present at the same time. It has been shown that one kind of damaged condition can interfere with the detection of another kind of damage, leading to an incorrect assessment about the structure condition. Identifying combined damage on structures still represents a challenge for condition monitoring, because the reliable identification of a combined damaged condition is a difficult task. Thus, this work presents a fusion of methodologies, where a single wavelet-packet and the empirical mode decomposition (EMD) method are combined with artificial neural networks (ANNs) for the automated and online identification-location of single or multiple-combined damage in a scaled model of a five-bay truss-type structure. Results showed that the proposed methodology is very efficient and reliable for identifying and locating the three kinds of damage, as well as their combinations. Therefore, this methodology could be applied to detection-location of damage in real truss-type structures, which would help to improve the characteristics and life span of real structures.

Vibration analysis and design optimization of sandwich beams with constrained viscoelastic core layer

Abstract: Dynamic properties of sandwich beam-type structure are analyzed using finite element method based on a nonlinear model for displacement field in the viscoelastic core layer of the beam structure. R...

Design Optimization of Compound Cylinders Subjected to Autofrettage and Shrink-Fitting Processes

Abstract: The autofrettage and shrink-fit processes are used to increase the load bearing capacity and fatigue life of the pressure vessels under thermomechanical loads. In this paper, a design optimization methodology has been proposed to identify optimal configurations of a two-layer cylinder subjected to different combinations of shrink-fit and autofrettage processes. The objective is to find the optimal thickness of each layer, autofrettage pressure and radial interference for each shrink-fit, and autofrettage combination in order to increase the fatigue life of the compound cylinder by maximizing the beneficial and minimizing the detrimental residual stresses induced by these processes. A finite element model has been developed in ansys environment to accurately evaluate the tangential stress profile through the thickness of the cylinder. The finite element model is then utilized in combination with design of experiment (DOE) and the response surface method (RSM) to develop a smooth response function which can be effectively used in the design optimization formulation. Finally, genetic algorithm (GA) combined with sequential quadratic programming (SQP) has been used to find global optimum configuration for each combination of autofrettage and shrink-fit processes. The residual stress distributions and the mechanical fatigue life based on the ASME code for high pressure vessels have been calculated for the optimal configurations and then compared. It is found that the combination of shrink-fitting of two base layers then performing double autofrettage (exterior autofrettage prior to interior autofrettage) on the whole assembly can provide higher fatigue life time for both inner and outer layers of the cylinder.

Free Vibration Analysis of Electrorheological Fluid Sandwich Shell Structures Subjected to Large Deformation

Abstract: Due to the small linear region in electrorheological (ER) fluid, vibration analysis of the sandwich structure containing ER fluid should be investigated in nonlinear region where the material properties depend on frequency, amplitude and electric field. In present work, the nonlinear equations of motion have been obtained using finite element technique. The nonlinear amplitude dependent stiffness matrices in equations of motion have been previously expressed by B and N notations. In B-notation an asymmetric amplitude dependent stiffness matrix is achieved. On the other hand in N-notation a symmetric form of the nonlinear stiffness matrices is achieved. The main problem in nonlinear vibration analysis of structure using direct integration technique is the time-consuming integrations, which should be performed for several times throughout this method. Due to numerous degrees of freedom in sandwich shell/plate structures, the computational costs in finite element modeling of sandwich shell/plate structures becomes more expensive. In this study, by considering kinetic and potential energies attributed to the elastic and ER fluid layers and using Lagrange equations, nonlinear finite element formulation has been derived for the ER based sandwich shell structures. Also a new technique is developed to represent the equations of motion in a new notation referred to as H-notation which fundamentally reduces the computational costs in nonlinear vibration damping analysis of sandwich shell structure. Finally, parametric study is conducted to show the effect of small/ large displacement, electric field intensities and core thickness ratio on damping behavior of the ER based sandwich shell structures for different boundary conditions.Copyright © 2013 by ASME

Outer Surface Prior to Inner Surface Double Autofrettage Technique for a Compound Cylinder

Abstract: The autofrettage and shrink-fit processes are used to enhance the load carrying capacity and fatigue life of the pressure vessels Previous works were mainly concerned with increasing the compressive residual stress at the near bore area of the compound cylinders, ignoring the harmful high tensile residual stress developed at the outer part of the cylinder Also, the idea of multiple or re-autofrettage had been only used at the inner surface of the cylinder to increase the magnitude of compressive residual stress at the near bore area In this study, a new design approach is proposed by applying an autofrettage cycle on the external surface of the cylinder prior to an autofrettage cycle on the internal surface of the cylinder It is shown that this double autofrettage cycle not only increases the magnitude of compressive residual stress at the near bore area but also decreases the tensile residual stress at the near outer surface area Moreover, the proposed double autofrettage process has been combined with shrink-fit and standard inner surface autofrettage processes to produce new combinations of a two-layer compound cylinder The fatigue life for these new combinations has been evaluated to verify the improvement while using the double autofrettage processCopyright © 2013 by ASME