A “Pseudo-excitation” approach for structural damage identification: From “Strong” to “Weak” modality

This paper presents a two-step approach for structural damage identification in beam structure using the influence line and bird mating optimizer (BMO). Local damage is simulated as the reduction of the elemental Young’s modulus and mass of beam element. The technique for damage localization based on influence line and its derivatives before and after damage for beam structure was outlined. An objective function comprised of dynamic acceleration is utilized for BMO algorithm. The dynamic response data under external force is calculated by Newmark integration method. Numerical examples of a simply supported beam was investigated. Effect of measurement noise is studied. Studies in the paper indicate that the proposed method is efficient and robust for identifying damages in beam structures.

This paper proposes a novel structural damage identification approach by modifying the original Tree Seeds Algorithm (TSA), termed as M-TSA. To enhance the performance of the standard TSA, a one-step K-means clustering mechanism is conducted before starting the seeds search, which turns out to be beneficial to improve the standard algorithm’s global search capacity. The objective function is formulated by using the frequency do-main data. The first several natural frequencies and the incomplete mode shape are employed to build up the objective function and the proposed M-TSA is adopted to obtain the optimal solution and reflect the structure’s health status. Numerical studies on a 26-bar truss are conducted to investigate the accuracy of using the proposed approach for structural damage identification. Two types of uncertainties including the finite element modelling errors and measurements noise, are considered simultaneously. The final identification results show that with the assistance of the K-means clustering, the proposed M-TSA is able to identify the damages accurately and the performance is better than the standard TSA.

The Cuckoo search (CS) algorithm is a simple and efficient global optimization algorithm and it has been applied to figure out large range of real-world optimization problem. In this paper, a new formula is introduced to the discovering probability process to improve the convergence rate and the Tournament Selection Strategy is adopted to enhance global search ability of the certain algorithm. Then an approach for structural damage identification based on modified Cuckoo search (MCS) is presented. Meanwhile, we take frequency residual error and the modal assurance criterion (MAC) as indexes of damage detection in view of the crack damage, and the MCS algorithm is utilized to identifying the structural damage. A simply supported beam and a 31-bar truss are studied as numerical example to illustrate the correctness and efficiency of the propose method. Besides, a laboratory work is also conducted to further verification. Studies show that, the proposed method can judge the damage location and degree of structures more accurately than its counterpart even under measurement noise, which demonstrates the MCS algorithm has a higher damage diagnosis precision.

An efficient methodology using static test data and changes in natural frequencies is proposed to identify the damages in structural systems. The methodology consists of two main stages. In the first stage, the Damage Signal Match (DSM) technique is employed to quickly identify the most potentially damaged elements so as to reduce the number of the solution space (solution parameters). In the second stage, a particle swarm optimization (PSO) approach is presented to accurately determine the actual damage extents using the first stage results. One numerical case study by using a planar truss and one experimental case study by using a full-scale steel truss structure are used to verify the proposed hybrid method. The identification results show that the proposed methodology can identify the location and severity of damage with a reasonable level of accuracy, even when practical considerations limit the number of measurements to only a few for a complex structure.

Numerical analysis of frictional contact between crack lips in the framework of Linear Elastic Fracture Mechanics by a mesh-free approach

The eddy-current problem for the time-harmonic Maxwell equations in domains and with conductors of general topology is considered. The existence of a unique magnetic field is proved for a suitable weak formulation. An equivalent strong formulation is then derived, where the conditions related to the specific geometry of the domain are made explicit. In particular, a new condition that must be satisfied by the magnetic field on the interface between a multiply-connected conductor and the non-conducting region is determined. Finally, the strong formulation of the problem for the electric field in the non-conducting region is derived, and the existence of a unique solution is proved. In conclusion, this leads to the determination of the complete set of equations describing the eddy-current problem in terms of the magnetic and the electric fields. Whether some commonly-used formulations satisfy the additional condition on the interface is also checked.

In this contribution, variational analysis of constrained optimization over a non-convex set is presented for the obstacle problem. The model describes Timoshenko’s plate with a crack indented by an obstacle given in the form of a curvilinear wedge and subjected to non-penetration constraints. The resulting variational inequality is studied in the weak and strong formulations on the union of convex sets with respect to the existence of a solution, which may be non-unique. The full system of boundary conditions hold at the crack surfaces is derived in the case study of admissible subsets.

RMVT-based meshless collocation and element-free Galerkin methods for the approximate 3D analysis of multilayered composite and FGM circular hollow cylinders

Daniel Dennett’s “intentional stance” theory is a leading specimen of the rationality theory, though Dennett vacillates in offering stronger and weaker variants. In the strong formulations, the theory is quite implausible; in its weak formulations, its content is too thin to have predictive implications. It also suffers from an inability to handle attributions over the entire range of mental states, including sensations like thirst, hunger, or itchiness. Finally, it offers no satisfactory story of how mental concepts are understood. An ostensibly related theory, the “teleological stance” theory, doesn’t really claim to explain mental state attribution.

This paper presents theoretical considerations on numerical modelling of magnetic fields in view of modeling a pulsatile magnetoactive pump based on the use of flexible magnetic material. To some extent, this publication fills a gap in the literature of numerical methods: the comparisons and analyses of some results obtained from the `old' FDS, the `popular' FEM. The authors, in previous publications, have presented numerical results that can be now considered as numerical facts. This contribution presents theoretical considerations from which the comparisons of the numerical results obtained from a strong formulation using finite difference schemes (FDS) and a weak formulation using finite element method (FEM) can be interpreted.

In this article, we propose to investigate numerically the steady bifurcation points and bifurcated branches in fluid mechanics by employing high‐order mesh‐free geometric progression algorithms. These algorithms are based on the use of the geometric progression (GP) in a high‐order mesh‐free approach. The first proposed algorithm is applied on a strong formulation using the moving least squares (MLS) approximation coupled with GP (HO‐MLS‐GPM). While the second proposed algorithm is applied on a weak formulation using the element‐free Galerkin (EFG) coupled also with GP (HO‐EFG‐GPM). The incompressibility condition is taken by introducing the penalty technique to transform the stationary Navier–Stokes equations verified by the pressure and velocity into ones verified by only the velocity. The high‐order mesh‐free algorithm permits to transform this nonlinear equations into a succession of linear ones. The GP allows to detect with precision the bifurcation points and the Lyapunov–Schmidt reduction is coupled with HO‐MLS‐GPM and HO‐EFG‐GPM as a continuation procedure to follow the many bifurcated branches. The aim of this resolution strategy concerns the treatment of the bifurcation phenomena for a fluid flow through an expansion in several geometries, where the steady flow becomes unstable after a critical Reynolds value. The obtained results are compared with those presented in literature and with those computed using the high‐order finite element algorithm coupled with GP.

The structural characteristic deflection shapes (CDS’s) such as mode shapes and operational deflection shapes are highly sensitive to structural damage in beam- or plate-type structures. Nevertheless, they are vulnerable to measurement noise and could result in unacceptable identification errors. In order to increase the accuracy and noise robustness of damage identification based on CDS’s using vibration responses of random excitation, joint approximate diagonalization (JAD) technique and gapped smoothing method (GSM) are combined to form a sensitive and robust damage index (DI), which can simultaneously detect the existence of damage and localize its position. In addition, it is possible to apply this approach to damage identification of structures under ambient excitation. First, JAD method which is an essential technique of blind source separation is investigated to simultaneously diagonalize a set of power spectral density matrices corresponding to frequencies near a certain natural frequency to estimate a joint unitary diagonalizer. The columns of this joint diagonalizer contain dominant CDS’s. With the identified dominant CDS’s around different natural frequencies, GSM is used to extract damage features and a robust damage identification index is then proposed. Numerical and experimental examples of beams with cracks are used to verify the validity and noise robustness of JAD based CDS estimation and the proposed DI. Furthermore, damage identification using dominant CDS’s estimated by JAD method is demonstrated to be more accurate and noise robust than by the commonly used singular value decomposition method.

Comparison of weak and strong formulations for 3D stress predictions of composite beam structures

The simulation of thermo-hydro-mechanical (THM) coupled processes, i.e., the prediction of interactions between temperature, fluids and mechanical properties within a repository system, is an essential prerequisite for performing and evaluating preliminary safety analysis in the site selection process.The presented open-source python software library Oscar is developed at the Federal Office for the Safety of Nuclear Waste Management (BASE) and has been released with its initial revision. The development of an own software library allows for the continuous development of expertise within BASE regarding numerical modelling and the diversification of the testing capabilities regarding the preliminary safety investigations. The choice for an open-source software strategy is motivated by the transparency requirement in the German site selection act and the potential to the provision of appropriately quality-assured and documented simulation tools to the public.The main goal of this in-house development is to provide a quality-assured, flexible and easy-to-use toolbox for the modelling of THM coupled processes using the finite element method with the following key features: Finite element analysis with the usual cell types for 1D, 2D and 3D modellings (edge, triangle, quadrilateral, tetrahedron, hexahedron). Generic shape function generator with predefined base-functions for linear, and quadratic elements. Script-based interface to the solution of the governing equations for the THM coupled processes in non-dimensional form in a symbolic manner with its strong or weak formulation. Predefined process solver classes for frequently used THM processes (e.g., heat conduction, fluid flow, mechanical deformation). Growing set of Jupyter notebooks of intensively documented tutorials to the finite element theory and to the usage of the presented software library. Growing set of Jupyter notebooks of documented examples and commonly known benchmarks for the modelling of THM coupled processes. The presented poster shows some key features of the software library and outlines potential applications.

This study presents a two-step FE model updating approach for health monitoring and damage identification of prestressed concrete girder bridges. To reduce the effects of modeling error in the model updating process, in the first step, modal-based model updating is used to estimate linear model parameters mainly related to the stiffness of boundary conditions and material properties. In the second step, a time-domain model updating is carried out using acceleration data to refine parameters accounting for the nonlinear response behavior of the bridge. In this step, boundary conditions are fixed at their final estimates using modal-based model updating. To prevent the convergence of updating algorithm to local solutions, the initial estimates for nonlinear material properties are selected based on the first-step model updating results. To validate the applicability of the two-step FE model updating approach, a series of forced-vibration experiments are designed and carried out on a pair of full-scale decommissioned and deteriorated prestressed bridge I-girders. In the first step, parameters related to boundary conditions, including stiffness of supports and coupling beams, as well as material properties, including initial stiffness of concrete material, are estimated. In the second step, concrete compressive strength and damping properties are updated. The final estimates of the concrete compressive strength are used to infer the extent of damage in the girders. The obtained results agree with the literature regarding the extent of reduction in concrete compressive strength in deteriorated concrete structures.