Advances in Structural Mechanics Modeled with FEM

It is well known that many structural and physical problems cannot be solved by analytical approaches. These problems require the development of numerical methods to get approximate but accurate solutions. The minite element method (FEM) represents one of the most typical methodologies that can be used to achieve this aim, due to its simple implementation, easy adaptability, and very good accuracy. For these reasons, the FEM is a widespread technique which is employed in many engineering fields, such as civil, mechanical, and aerospace engineering. The large-scale deployment of powerful computers and the consequent recent improvement of the computational resources have provided the tools to develop numerical approaches that are able to solve more complex structural systems characterized by peculiar mechanical configurations. Laminated or multi-phase composites, structures made of innovative materials, and nanostructures are just some examples of applications that are commonly and accurately solved by the FEM. Analogously, the same numerical approaches can be employed to validate the results of experimental tests. The main aim of this Special Issue is to collect numerical investigations focused on the use of the finite element metho

12th International Conference on Vibrations in Rotating Machinery

Since 1976, the Vibrations in Rotating Machinery conferences have successfully brought industry and academia together to advance state-of-the-art research in dynamics of rotating machinery. 12th International Conference on Vibrations in Rotating Machinery contains contributions presented at the 12th edition of the conference, from industrial and academic experts from different countries. The book discusses the challenges in rotor-dynamics, rub, whirl, instability and more. The topics addressed include: - Active, smart vibration control - Rotor balancing, dynamics, and smart rotors - Bearings and seals - Noise vibration and harshness - Active and passive damping - Applications: wind turbines, steam turbines, gas turbines, compressors - Joints and couplings - Challenging performance boundaries of rotating machines - High power density machines - Electrical machines for aerospace - Management of extreme events - Active machines - Electric supercharging - Blades and bladed assemblies (forced response, flutter, mistuning) - Fault detection and condition monitoring - Rub, whirl and instability - Torsional vibration Providing the latest research and useful guidance, 12th International Conference on Vibrations in Rotating Machinery aims at those from industry or academia that are involved in transport, power, process, medical engineering, manufacturing or construction

12th International Conference on Vibrations in Rotating Machinery

Since 1976, the Vibrations in Rotating Machinery conferences have successfully brought industry and academia together to advance state-of-the-art research in dynamics of rotating machinery. 12th International Conference on Vibrations in Rotating Machinery contains contributions presented at the 12th edition of the conference, from industrial and academic experts from different countries. The book discusses the challenges in rotor-dynamics, rub, whirl, instability and more. The topics addressed include: - Active, smart vibration control - Rotor balancing, dynamics, and smart rotors - Bearings and seals - Noise vibration and harshness - Active and passive damping - Applications: wind turbines, steam turbines, gas turbines, compressors - Joints and couplings - Challenging performance boundaries of rotating machines - High power density machines - Electrical machines for aerospace - Management of extreme events - Active machines - Electric supercharging - Blades and bladed assemblies (forced response, flutter, mistuning) - Fault detection and condition monitoring - Rub, whirl and instability - Torsional vibration Providing the latest research and useful guidance, 12th International Conference on Vibrations in Rotating Machinery aims at those from industry or academia that are involved in transport, power, process, medical engineering, manufacturing or construction

Intelligent Diagnosis and Smart Detection of Crack in a Structure from its Vibration Signatures

In recent years, there has been a growing interest in the development of structural health monitoring for vibrating structures, especially crack detection methodologies and on-line diagnostic techniques. In the current research, methodologies have been developed for damage detection of a cracked cantilever beam using analytical, fuzzy logic, neural network and fuzzy neuro techniques. The presence of a crack in a structural member introduces a local flexibility that affects its dynamic response. For finding out the deviation in the vibrating signatures of the cracked cantilever beam the local stiffness matrices are taken into account. Theoretical analyses have been carried out to calculate the natural frequencies and mode shapes of the cracked cantilever beam using local stiffness matrices. Strain energy release rate has been used for calculating the local stiffness of the beam. The fuzzy inference system has been designed using the first three relative natural frequencies and mode shapes as input parameters. The output from the fuzzy controller is relative crack location and relative crack depth. Several fuzzy rules have been developed using the vibration signatures of the cantilever beam. A Neural Network technique using multi layered back propagation algorithm has been developed for damage assessment using the first three relative natural frequencies and mode shapes as input parameters and relative crack location and relative crack depth as output parameters. Several training patterns are derived for designing the Neural Network. A hybrid fuzzy-neuro intelligent system has been formulated for fault identification. The fuzzy controller is designed with six input parameters and two output parameters. The input parameters to the fuzzy system are relative deviation of first three natural frequencies and first three mode shapes. The output parameters of the fuzzy system are initial relative crack depth and initial relative crack location. The input parameters to the neural controller are relative deviation of first three natural frequencies and first three mode shapes along with the interim outputs of fuzzy controller. The output parameters of the fuzzy-neuro system are final relative crack depth and final relative crack location. A series of fuzzy rules and training patterns are derived for the fuzzy and neural system respectively to predict the final crack location and final crack depth.To diagnose the crack in the vibrating structure multiple adaptive neuro-fuzzy inference system (MANFIS) methodology has been applied. The final outputs of the MANFIS are relative crack depth and relative crack location. Several hundred fuzzy rules and neural network training patterns are derived using natural frequencies, mode shapes, crack depths and crack locations. The proposed research work aims to broaden the development in the area of fault detection of dynamically vibrating structures. This research also addresses the accuracy for detection of crack location and depth with considerably low computational time. The objective of the research is related to design of an intelligent controller for prediction of damage location and severity in a uniform cracked cantilever beam using AI techniques (i.e. Fuzzy, neural, adaptive neuro-fuzzy and Manfis)

Seismic Risk Analysis for Nuclear Energy Facilities

Earthquakes are destructive natural disasters that can inflict various levels of damage on engineering structures and lead to other adverse consequences. Accurate seismic risk quantification of critical engineering structures such as nuclear power plants is of great importance, not only for answering public safety concern but also for facilitating risk-informed decision making. Seismic Probabilistic Risk Analysis (SPRA) has been widely used for seismic analysis and design of critical engineering structures. It combines the probabilistic model of the behavior of structural response given a ground-motion parameter (GMP) value (e.g., seismic fragility model) and the Probabilistic Seismic Hazard Analysis (PSHA) for the GMP in a mathematically rigorous manner. However, there are a number of issues on the engineering application of SPRA that need to be addressed before it can be readily implemented into current engineering practice. In current SPRA practice, both the fragility model and PSHA are based on a single GMP, which is adequate for the single-mode-dominant structures. For multiple-mode-dominant structures, whose response could be better predicted using multiple GMP,a vector-valued SPRA is conceptually more appropriate. However, vector-valued SPRA requires extensive computational efforts and extensive consultation of vector-valued PSHA from seismologists,which prevent it from being ready for engineering purposes. The objective of this study is to bridge the gaps between seismological analyses and engineering applications, i.e., to address the immediate issues in current vector-valued SPRA so that it can be readily applied into engineering practice. A new seismic hazard deaggregation procedure is developed for seismic risk analysis, which determines a set of controlling earthquakes that induce dominant hazard to the site of interest. A simplified approach to vector-valued SPRA is developed based on the controlling earthquakes. Integration over all possible earthquake occurrences in standard vector-valued SPRA is then avoided,which substantially improves the computational efficiency without losing accuracy. This overcomes the deficiencies and preserves the advantages of standard vector-valued SPRA. To facilitate performing the simplified approach, factors affecting the accuracy of the simplified approach are discussed and illustrated through the numerical examples. In addition, seismic capacity evaluation of nuclear facilities is an important task in a SPRA. However, following the current evaluation procedures, inconsistency in seismic capacity estimates are often obtained for the same facility in similar plants at different locations. The inconsistency also shows dependency on the GMP selected for defining seismic capacity. This inconsistency is conceptually undesirable for engineering purposes. To characterize the possible factors affecting the consistency in seismic capacity estimates, a comprehensive parametric study is performed in an analytical manner. Theoretical derivations and graphical illustrations are resorted to facilitate the analysis. Both general and case-by-case analyses are performed to show how each of these factors affects the consistency in seismic capacity estimates. This parametric study represents a wide coverage of seismic capacity evaluating problems for nuclear facilities, and hence can be used for interpreting results of similar kinds in current engineering practice

Vibration analysis of a plate with an arbitrarily orientated surface crack

This research presents a vibration analysis for a thin isotropic plate containing an arbitrarily orientated surface crack. The work has been motivated by the well known applicability of various vibrational techniques for structural damage detection in which the detection and localisation of damage to thin plate structures at the earliest stage of development can optimise subsystem performance and assure a safer life, and is intended to be an enhancement to previous work on cracked plates for which the orientation of the crack angle was not included. The novelty of this research activity has been in the assimilation of a significantly enhanced crack model within the analytical model of the plate, in modal space, and taking the form of a specialised Duffing equation. The governing equation of motion of the plate model with enhanced crack modelling is proposed to represent the vibrational response of the plate and is based on classical plate theory into which a developed crack model has been assimilated. The formulation of the angled crack is based on a simplified line-spring model, and the cracked plate is subjected to transverse harmonic excitation with arbitrarily chosen boundary conditions. In addition, the nonlinear behaviour of the cracked plate model is investigated analytically from the amplitude-frequency equation by use of the multiple scales perturbation method. For both cracked square and rectangular plate models, the influence of the boundary conditions, the crack orientation angle, crack length, and location of the point load is demonstrated. It is found that the vibration characteristics and nonlinear characteristics of the cracked plate structure can be greatly affected by the orientation of the crack in the plate. The dynamics and stability of the cracked plate model are also examined numerically using dynamical systems tools for representing the behaviour of this system for a range of parameters. Finally the validity of the developed model is shown through comparison of the results with experimental work and finite element analysis in order to corroborate the effect of crack length and crack orientation angle on the modal parameters, as predicted by the analysis. The results show excellent predictive agreement and it can be seen that the new analytical model could constitute a useful tool for subsequent investigation into the development of damage detection methodologies for generalised plate structures

MIT Space Engineering Research Center

The Space Engineering Research Center (SERC) at MIT, started in Jul. 1988, has completed two years of research. The Center is approaching the operational phase of its first testbed, is midway through the construction of a second testbed, and is in the design phase of a third. We presently have seven participating faculty, four participating staff members, ten graduate students, and numerous undergraduates. This report reviews the testbed programs, individual graduate research, other SERC activities not funded by the Center, interaction with non-MIT organizations, and SERC milestones. Published papers made possible by SERC funding are included at the end of the report

Assessing the behaviour of reinforced concrete columns under blast loads

This Thesis is concerned with the numerical investigation of the structural response of reinforced concrete columns under blast loads, by means of dynamic nonlinear finite element analysis. This study provides an in depth understanding of the mechanics underlying reinforced concrete structural response under blast loading and studying the effect of certain important design parameters on the exhibited behaviour. The numerical investigation was carried out through the use of a well-established commercial finite element package (Abaqus) and employed a numerical model capable of accounting for the brittle nature of concrete. The latter model forms an extension to the ‘brittle crack’ model (already available in Abaqus) and was developed in order to overcome the shortcomings of the existing concrete model in describing concrete material behaviour in compression. The verification of the validity of the numerical predictions is based on a comparative study with relevant experimental data. The validated models are then employed to investigate the effect of various parameters on the exhibited response and are used to identify the reasons that trigger the experimentally and numerically observed change in structural behaviour under high loading rates (compared to that established under static loading). On the basis of the predictions obtained from the FE analysis a new graphical method was developed, based on building complementary diagrams, for the effective derivation of Pressure-Impulse (P-I) diagrams. This method aims to overcome the problems associated with their inherent sensitivity to any change in the state of the analysed structural system. Through the combined use of the validated FE model and the proposed graphical method, P-I diagrams and the associated complementary diagrams are presented and the efficiency and applicability of the methodology is demonstrated

Novel Approaches for Structural Health Monitoring

The thirty-plus years of progress in the field of structural health monitoring (SHM) have left a paramount impact on our everyday lives. Be it for the monitoring of fixed- and rotary-wing aircrafts, for the preservation of the cultural and architectural heritage, or for the predictive maintenance of long-span bridges or wind farms, SHM has shaped the framework of many engineering fields. Given the current state of quantitative and principled methodologies, it is nowadays possible to rapidly and consistently evaluate the structural safety of industrial machines, modern concrete buildings, historical masonry complexes, etc., to test their capability and to serve their intended purpose. However, old unsolved problematics as well as new challenges exist. Furthermore, unprecedented conditions, such as stricter safety requirements and ageing civil infrastructure, pose new challenges for confrontation. Therefore, this Special Issue gathers the main contributions of academics and practitioners in civil, aerospace, and mechanical engineering to provide a common ground for structural health monitoring in dealing with old and new aspects of this ever-growing research field