Prevention of Corrosion in Austenitic Stainless Steel through a Predictive Numerical Model Simulating Grain Boundary Chromium Depletion

In this chapter, a mathematical model for rate of formation of chromium carbides near the grain boundary, which is a pre-cursor to chromium depletion and corresponding sensitization behavior in stainless steels, is presented. This model along with the diffusion equation for chromium in the grain has been used to obtain chromium depletion profiles at various time and temperature conditions. Finite difference method has been used to solve the above equations in the spherical co-ordinate system and the results of time-temperature-sensitization diagrams of four different types of alloys have been compared with those of experiment from literature. For the problem of low temperature sensitization and corresponding inter-granular corrosion in austenitic stainless steel, it is very difficult to carry out experiment at higher temperatures and justify its validity at lower operating temperatures by extrapolation. The development of predictive models is highly useful in order to design the structures for prevention of corrosion of the material in aggressive environments.

Seismic Reliability Analysis in the Framework of Metamodelling Based Monte Carlo Simulation

A comparative study of various metamodelling approaches namely the least squares method (LSM), moving least squares method (MLSM) and artificial neural network (ANN) based response surface method (RSM) are presented to demonstrate the effectiveness to approximate the nonlinear dynamic response of structure required for efficient seismic reliability analysis (SRA) of structures. The seismic response approximation by the LSM, MLSM and ANN based RSMs are explained with a brief note on the important issue of ground motion bin generation. The procedure adopted herein for SRA is based on the dual response surface approach. In doing so, the repetition of seismic intensity for SRA at different intensity levels is avoided by including this as one of the predictors in the seismic response prediction model. A nonlinear SDOF system has been taken up to elucidate the effectiveness of various metamodels in SRA.

Agent Based Modelling of Smart Structures

Smart structures are complex systems situated in even more complex and large scale urban environments. This chapter opens the field of agent based modelling and simulation (ABMS) to civil engineers. ABMS offers a wide range of tools for implementing simulation models of systems with high degrees of interconnectivity and a large number of component subsystems. The ease of use for specialized engineers and the capabilities of integration with existent technologies and infrastructures, make agent based models a very attractive way to incorporate the social system in the design process of buildings. Moreover, ABMS allows for the testing and validation of structure wide control and automation systems. This chapter presents past and current efforts of using agent based modelling for smart structures, as well as the main challenges brought by this new interdisciplinary research domain.

Nonlinear System Identification of Smart Buildings

In this book chapter, a system identification method for modeling nonlinear behavior of smart buildings is discussed that has a significantly low computation time. To reduce the size of the training data used for the adaptive neuro-fuzzy inference system (ANFIS), principal component analysis (PCA) is used, i.e., PCA-based adaptive neuro-fuzzy inference system: PANFIS. The PANFIS model is evaluated on a seismically excited three-story building equipped with a magnetorheological (MR) damper. The PANFIS model is trained using an artificial earthquake that contains a variety of characteristics of earthquakes. The trained PANFIS model is tested using four different earthquakes. It was demonstrated that the proposed PANFIS model is effective in modeling nonlinear behavior of a smart building with significant reduction in computational loads.

FE Analysis and Experimental Investigation of Cracked and Un-Cracked Thin-Walled Tubular Components to Evaluate Mechanical and Fracture Properties

For investigation of fracture behavior and assessment of remaining life of critical thin-walled tubular components in industry, the transverse mechanical property and the axial fracture properties are essential. However, evaluation of these properties by machining suitable standard specimens from these components directly and subjecting them to standard tests is usually not feasible. In this chapter, the nonlocal version of the Rousselier's damage model has been used to predict the fracture resistance behavior of double-edged-notched-tensile specimens made from Zircaloy-4 material. Initially, the micro-mechanical parameters have been determined from the testing of ring-type specimens. Subsequently, these parameters were used in finite element analysis of the double-edged-notched-tensile specimen in order to predict the crack growth behavior and the crack path under applied displacement-controlled loading conditions. The fracture resistance behavior obtained in terms of J-R curve was also compared with the corresponding J-R curves of axially-cracked pin-loading-tension specimens.

Dynamic Analysis of Offshore Wind Turbine Structures

Wind turbines are slender flexible structures susceptible to strong wind fluctuations. The flexible wind turbine structure, when subjected to strong dynamic forces, it leads to an ideal condition for induced vibrations and resonance problems. Hence studying the dynamic response of these critical structures using the computational and experimental procedures becomes of utmost importance. This chapter reviews the theories used for the dynamic analysis of a modern day offshore wind turbine structure and applies these theories in analyzing realistic situations for offshore turbines under wave and wind action. The first half of the chapter gives a broad overview on the concepts of structural dynamics of wind turbine structures with illustrative examples that will enable the user to understand the methodology used to analyze these structures. The latter half of the chapter deals with the computational aspect of the analysis and focuses on the use of finite element software ANSYS 14 to model these critical structures.

Experiments on a Ring Tension Setup and FE Analysis to Evaluate Transverse Mechanical Properties of Tubular Components

Determination of transverse mechanical properties from ring specimens machined from tubular components is not straightforward due to presence of combined tension and bending stresses. Zircaloy tubes as used in nuclear reactors are manufactured through a complicated process of pilgering and heat-treatment and hence, the properties need to be determined in the as-manufactured condition. In this work, the authors perform ring-tensile tests on specimens of Zircaloy pressure tubes of Indian pressurized heavy water reactor in order to carry out integrity assessment of these tubes. As the loading condition in this test imposes both membrane and bending stresses in the cross-section of the ring, 3-D finite element analysis of the test setup was carried out in order to determine material stress-strain curve using an iterative technique. The effect of the design of the loading mandrel on the experimental stress-strain data has been investigated in detail. To validate the methodology, miniature tensile specimens have been tested and the data has been compared to those of ring specimens.

Acoustic Method for the Suppression of Acoustic and Aerodynamically Induced Vibration on Structures

The close relationship between noise and vibration is reviewed and analyzed for the suppression of noise and vibration in structures. The suppression of noise and vibration by acoustic means are addressed. For the first, an analysis is carried out by representing noise by monopoles and higher harmonics, and to devise a straight-forward method to counter their influence by selective secondary acoustic source. The second problem is analyzed using a methodology developed earlier for the computational scheme for the calculation of the acoustic disturbance to the aeroelasticity of structures. The generic approach of the latter consists of three parts. The first is the formulation of the acoustic wave propagation governed by the Helmholtz equation by using boundary element approach, to allow the calculation of the acoustic pressure on the acoustic-structure boundaries. The structural dynamic problem is formulated using finite elements. The third part involves the calculation of the unsteady aerodynamics loading on the structure using generic unsteady aerodynamics computational method.

Simulating Post-Earthquake Fire Loading in Conventional RC Structures

Post-earthquake fire (PEF) is one of the most complicated problems resulting from earthquake, presenting a serious risk to urban buildings. As most standards and codes ignore the possibility of PEF, buildings are too weak under PEF loads. This chapter is to investigate the effects of PEF loads on partially damaged RC buildings located in urban regions. To do that, a methodology named sequential analysis is introduced here via which the structural performance at various performance levels is evaluated under fire and PEF scenarios. Numerically, in order to simulate the earthquake loads, conventional pushover analysis is employed, with an explanation presented in the chapter to introduce the pushover analysis, its advantages and its limitations. To simulate the fire loads, standard fire curve (ISO 834) is used for simplicity.

Polynomial Correlated Function Expansion

Uncertainty quantification of civil engineering structures are often time consuming. Hence, one has to rely on equivalent models (EM) that represent the original functions with a specific level of accuracy. In this chapter, a fully equivalent operational model, referred as, Polynomial Correlated Function Expansion (PCFE) has been discussed. PCFE facilitates a systematic mapping between the input and output by expressing the output as a ranked order of component functions, with higher order component functions representing higher-order cooperative effect. The component functions are expressed in terms of extended bases and the unknown coefficients associated with the bases are determined by employing homotopy algorithm (HA). HA determines the unknown coefficients by minimizing the least-squared error and imposing an additional criteria defined as an objective function. Implementation of PCFE has been illustrated with two large scale problems. Results obtained have been compared with other popular techniques. For both the problems, PCFE outperforms popular EMs available in literature.