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The Use of High-Performance Fatigue Mechanics and the Extended Kalman / Particle Filters, for Diagnostics and Prognostics of Aircraft Structures
Get PDFIn this paper, we propose an approach for diagnostics and prognostics of damaged aircraft structures, by combing high-performance fatigue mechanics with filtering theories. Fast & accurate deterministic analyses of fatigue crack propagations are carried out, by using the Finite Element Alternating Method (FEAM) for computing SIFs, and by using the newly developed Moving Least Squares (MLS) law for computing fatigue crack growth rates. Such algorithms for simulating fatigue crack propagations are embedded in the computer program Safe- Flaw, which is called upon as a subroutine within the probabilistic framework of filter theories. Both the extended Kalman as well as particle filters are applied in this study, to obtain the statistically optimal and semi-optimal estimates of crack lengths, from a series of noisy measurements of crack-lengths over time. For the specific problem, a simple modification to the particle filter, which can drastically reduce the computational burden, is also proposed. Based on the results of such diagnostic analyses, the prognostics of aerospace structures are thereafter achieved, to estimate the probabilistic distribution of the remaining useful life. By using a simple example of a single-crack near a fastener hole, we demonstrate the concept and effectiveness of the proposed framework. This paper thus forms the scientific foundation for the recently proposed concepts of VRAMS (Virtual Risk-Informed Agile Maneuver Sustainment) and Digital Twins of aerospace vehicles
Probability Density Transitions in the FitzHugh-Nagumo Model with Lévy Noise
Get PDFIn this paper, bifurcation analysis and numerical simulations are performed on the FitzHugh-Nagumo system in the presence of Lévy stable noise. The stationary probability density functions are obtained to examine the influences of noise intensity and stability index. Results show that under the influences of noise intensity and stability index, the dynamic of the FitzHugh-Nagumo model can be well characterized through the concept of stochastic bifurcation, consisting in qualitative changes of the stationary probability distribution. Then, the mean passage time between the resting and action state is investigated as functions of noise intensity and stability index of the external signal by means of numerical simulations. Dependences of the results on the parameters of Lévy noise are discussed to find the different mechanisms compared with Gaussian case
A Metamodel-Based Global Algorithm for Mixed-Integer Nonlinear Optimization and the Application in Fuel Cell Vehicle Design
Get PDFThis paper improves the adaptive metamodel-based global algorithm (AMGO), which is presented for unconstrained continuous problems, to solve mixed-integer nonlinear optimization involving black-box and expensive functions. The new proposed method is called as METADIR, which can be divided into two stages. In the first stage, the METADIR adopts extended DIRECT method to constantly subdivide the design space and identify the sub-region that may contain the optimal value. When iterative points gather into a sub-region to some extent, we terminate the search progress of DIRECT and turn to the next stage. In the second phase, a local metamodel is constructed in this potential optimal sub-region, and then an auxiliary optimization problem extended from AMGO is established based on the local metamodel to obtain the iterative points, which are then applied to update the metamodel adaptively. To show the performance of METADIR on both continuous and mixed-integer problems, numerical tests are presented on both kinds of problems. The METADIR method is compared with the original DIRECT on continuous problems, and compared with SO-MI and GA on mixed-integer problems. Test results show that the proposed method has better accuracy and needs less function evaluations. Finally, the new proposed method is applied into the component size optimization problem of fuel cell vehicle and achieves satisfied results
Population Exposure and Impacts from Earthquakes: Assessing Spatio-temporal Changes in the XX Century
Get PDFMedia and specialized scientific literature are often addressing the “increasing impact and ensuing damages due to natural hazards”. It is frequently argued that a rising frequency and intensity of hazards is responsible for the increase in losses. The role of increasing population exposure due to phenomenal population growth, or urbanization as a driver of risk is still insufficiently addressed. We investigate spatio-temporal changes in population exposure to seismic hazard and their role on impacts from earthquakes in the XX century. Spatial analysis is used to study historical population distributions in relation to seismic intensity, at the global and continental levels. Changes in number of victims were also analyzed, while considering the progress in frequency and magnitude of hazard events. There is also a focus on megacities and implications of fast urbanization for exposure and risk. We find that global population exposure in zones of severe seismic hazard has grown above overall population growth rates, with exposure growth rates being highest in the Americas, Asia, and Oceania. Results illustrate the relevance of population growth and exposure for risk assessment and disaster outcome, and underline the need for conducting detailed global mapping of settlements and population distribution
First Principles Molecular Dynamics Computation on Ionic Transport Properties in Molten Salt Materials
Get PDFBased on the Hellmann-Feynman theorem, which integrates the molecular dynamics simulation with computational quantum mechanics, this research simulates the ionic transport in the LiCl-KCl molten salt materials using so called “first principles molecular dynamics (FPMD)” technique without employing an empirical potential model. The main purpose of this computational FPMD focuses on the evaluation of important transport properties, such as diffusion coefficient, ionic conductivity, shear viscosity, and thermal conductivity, using the Green-Kubo relationship. All simulation results agree well with experimental data published in existing literatures within an acceptable range. FPMD calculations are proved to be a powerful tool for prediction of the molecular structure, transport properties, as well as ionic interactions from the microscopic aspect. It is expected to integrate further with a multi-scale simulation tool for future function expansion to macroscopic performance prediction
Simulation of Hot Shape Rolling of Steel in Continuous Rolling Mill by Local Radial Basis Function Collocation Method
Get PDFThe aim of this paper is to demonstrate the use of the novel Local Radial Basis Function Collocation Method (LRBFCM) [Šarler and Vertnik (2006)] in an industrial coupled thermo-mechanical problem of hot shape rolling of steel. The physical concept of such a large deformation problem is based on a two dimensional traveling slice model [Glowacki (2005)], which assumes deformation and heat flow only in the perpendicular direction to rolling. The solution is performed based on strong formulation. Elliptic Node Generation (ENG) is applied to reposition the nodes over a slice when necessary in order to sustain stability throughout the simulation. Coupled mechanical equilibrium steady Navier-Cauchy equations for a quasi-elastic material with temperature dependent material properties and the transient heat conduction equations are considered. The displacement and traction boundary conditions are assumed in the mechanical model and Dirichlet and Neumann boundary conditions in the thermal model, both specific for hot shape rolling. The solution procedure for mechanical model is based on local collocation on seven nodded influence domains with multiquadrics radial basis functions, augmented with the first order polynomials. Five nodded subdomains and explicit time-stepping are used in the thermal model. The elements of the thermomechanical LRBFCM model are tested on 3 different test cases: bending of a cantilever beam, compression and convective cooling. The results are compared with either FEM or analytical solution. The LRBFCM results of hot shape rolling of steel for a continuous 5 stand rolling mill are presented for the case of rolling of a rectangular billet from initial dimension 80 mm x 95 mm to a circular bar with a diameter of 60 mm. The advantage of the meshless method is in accuracy and straightforward node generation that does not require any polygonisation. The paper presents one of the increasingly emerging examples of the industrial use of LRBFCM
Buckley-Leverett Analysis for Transient Two-phase Flow in Fractal Porous Medium
Get PDFAnalysis of Buckley-Leverett solution in fractal porous medium does prediction of water saturation profile a favor. On the approximation that porous medium consists of a bundle of tortuous capillaries, a physical conceptual Buckley- Leverett model of transient two-phase flow in fractal porous medium is developed based on the fractal characteristics of pore size distribution. The relationship between water saturation and distance is presented according to Buckley-Leverett solution, and the proposed Buckley-Leverett expression is the function of fractal structural parameters (such as pore fractal dimension, tortuosity fractal dimension, maximum and minimum diameters of capillaries) and fluid properties (such as viscosity, contact angle and interfacial tension) in fractal porous medium The sensitive parameters that impact on Buckley-Leverett expression are formulated and their sensitivities on water saturation file are discussed
Flexoelectricity in Solid Dielectrics: From Theory to Applications
Get PDFFlexoelectricity phenomenologically describes the universal electromechanical coupling effect between electric polarization and strain gradient, and electric field gradient and elastic strain. In contrast to piezoelectricity which is invalid in materials with inversion symmetry, flexoelectricity exists, commonly, in all solid dielectrics. In this paper, a summary of the research on flexoelectricity is presented to illustrate the development of this topic. Flexoelectricity still have many open questions and unresolved issues in the developing field, although it has attracted a surge of attention recently. Here we review the theoretical investigations and experimental studies on flexoelectricity, and the aim of the current paper is to look into the potential applications of this electromechanical coupling effect
SPH and FEM Investigation of Hydrodynamic Impact Problems
Get PDFSimulation of hydrodynamic impact problems and its effect on surrounding structures, can be considered as a fluid structure coupling problem. The application is mainly used in automotive and aerospace engineering and also in civil engineering. Classical FEM and Finite Volume methods were the main formulations used by engineers to solve these problems. For the last decades, new formulations have been developed for fluid structure coupling applications using mesh free methods as SPH method, (Smooth Particle Hydrodynamic) and DEM (Discrete Element Method). Up to these days very little has been done to compare different methods and assess which one would be more suitable. In this paper the mathematical and numerical implementation of the FEM and SPH formulations for hydrodynamic problem are described. From different simulations, it has been observed that for the SPH method to provide similar results as FEM Lagrangian formulations, the SPH meshing, or SPH particle spacing needs to be finer than FEM mesh. To validate the statement, we perform a simulation of a hydrodynamic impact on an elasto-plastic plate structure. For this simple, the particle spacing of SPH method needs to be at least two times finer than FEM mesh. A contact algorithm is performed at the fluid structure interface for both SPH and FEM formulations. In the paper the efficiency and usefulness of two methods, often used in numerical simulations, are compared
Research and Improvement on the Accuracy of Discontinuous Smoothed Particle Hydrodynamics (DSPH) Method
Get PDFDiscontinuous smoothed particle hydrodynamics (DSPH) method based on traditional SPH method, which can be used to simulate discontinuous physics problems near interface or boundary. Previous works showed that DSPH method has a good application prospect [Xu et al, 2013], but further verification and improvement are demanded. In this paper, we investigate the accuracy of DSPH method by some numerical models. Moreover, to improve the accuracy of DSPH method, first order and second order multidimensional RDSPH methods are proposed by following the idea of restoring particle consistency in SPH (RSPH) method which has shown good results in the improvement of particle consistency and accuracy for non-uniform particles. This restoring particle consistency in DSPH (RDSPH) method has the advantages from both RSPH method and DSPH method. In addition, the accuracy of RDSPH methods near the interface, boundary and in non-uniform interior region are tested in one-dimensional and twodimensional spaces