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Increasing computational power has led to the expansion of civil engineering research into using machine learning concepts for developing improved design strategies. These strategies are particularly useful for the design of extra-terrestrial habitats under uncertain environmental conditions. This paper focuses on building an unsupervised machine learning model (convolutional autoencoder) capable of detecting patterns in arch shapes and differentiating between their stress and displacement contours. Foremost, detailed discussions of the model's architecture and input data are presented. The variation of arch shapes and contours between cluster centroids in the latent space is determined, proving the capability of optimisation by moving towards clusters with optimal contours. Finally, a regression model is built to investigate the relationship between the input geometric variables and the latent space representation. We prove that the autoencoder and regression models produce arch shapes with logical structural contours given a set of input geometric variables. The results presented in this paper provide essential tools for the development of an automated design strategy capable of finding optimal arch shapes for extra-terrestrial habitats. [ABSTRACT FROM AUTHOR]

Dynamic reliability evaluation of large-scale reinforced concrete (RC) structures is one of the most challenging problems in engineering practices. Although extensive endeavors have been devoted to mechanical analysis of concrete structures in the past decades, it was recognized that the randomness from both structural parameters and excitations have significant effects on the dynamic behaviors of structures with complex nonlinearity, damage, energy dissipation, and plasticity. Thus, great difficulty exists in evaluating the nonlinear stochastic responses and dynamic reliability of the real-world complex structures of large degrees of freedom. In the present paper, a physically driven method for refined probabilistic response and seismic reliability evaluation of real-world RC structures is proposed via synthesis of the refined mechanical analysis and the physically-based uncertainty propagation. In this method, the material parameters can be treated as probabilistically dependent random variables characterized by vine copulas, and the ground motion is modeled by non-stationary Clough–Penzien spectrum. The uncertainty propagation of arbitrary response quantity(-ies) of interest is governed by the dimension-reduced probability density evolution equation (DR-PDEE). The intrinsic drift coefficients in the DR-PDEE are the physically driven force for the uncertainty propagation and can be identified via data from representative dynamic analyses of the structure. The time-variant reliability of the structures can be captured by solving the physically driven DR-PDEE, which cannot be achieved by the general Monte Carlo simulation (MCS) due to the prohabitively large computational cost. Finally, a practical engineering application is shown in this paper for the probabilistic response and seismic reliability evaluation of a 24-story RC shear wall structure with nearly 280,000 degrees of freedom (DOFs). [ABSTRACT FROM AUTHOR]

Pore defects are common defects in composites and can seriously affect the mechanical properties of composites. The present paper not only considers the pore defects, but also considers the influence of interface defects on the effective stiffness of 3D braided composites. A damage model is developed to predict the damage propagation of 3D braided composites considering pore defects. A multiscale simulation method using representative volume elements (RVE) combined with a micromechanical method and the finite element method is developed in this paper to meet the multiscale and periodic characteristics of 3D braided composites. The constituents at the microscale are composed of matrix, interface, fiber and pores, and the constituents at the mesoscale are composed of matrix, yarns and pores. The yarn at the microscale is homogenized by means of Mori–Tanaka model and extended double-inclusion model. The prediction and analysis methods of the existing models are compared with the experimental results to prove the effectiveness of the method. [ABSTRACT FROM AUTHOR]

This paper presents thermodynamic characteristics of functionally graded (FG) doubly-curved panels with varying circumferential size. The circumferential size considered in this paper means the circumferential rotating angle and varies according to certain rules in the longitudinal direction. The theoretical formulation is derived by using Hamilton's principle in conjunction with first-order shear deformation theory and the displacement and rotating components of the FG doubly-curved panels with varying circumferential size are described approximatively by employing meshfree Tchebychev point interpolation (TPIM) shape function. The thermal effects on the natural frequency of FG doubly-curved panels are studied by employing the thermo-elastic theory. For forced vibration analysis, rectangular and exponential pulse are considered. The convergence of the established theoretical modeling is verified by convergence studies, the validation of the established theoretical modeling is confirmed through comparison with the results of published literature and finite element method. In numerical example, the influences of geometry dimension, boundary conditions, thermal and external loads on the thermo-dynamic characteristics of FG doubly-curved panels with varying circumferential size are investigated systematically. The research results show that the established numerical model has converged basically when the number of node points is greater than Nx = 11 and the boundary spring stiffness increases by more than 1012; the maximum error of comparison results is less than 1%; the boundary conditions, power-law index p, starting angles φ0, temperature and starting circumference A have important influence on the thermodynamic response including free and forced vibration characteristics of FG doubly-curved panels with varying circumferential size. [ABSTRACT FROM AUTHOR]

In this paper, dynamic stability of a smart sandwich nanotube is investigated. The core of the nanostructure is made from a single-walled carbon nanotube (SWCNT), which is coated with two ZnO piezoelectric layers. The inner piezoelectric layer is taken as a sensor and the outer layer as an actuator. The sandwich nanotube is embedded in an elastic visco-Pasternak medium. The modified couple stress theory is utilized to consider the small-scale effect, and the Kelvin-Voigt model is used to model the carbon nanotube and the ZnO layers. The surface tension is taken into account using the Gurtin–Murdoch theory. The nonlinear governing equations, derived by the Hamilton principle, are solved using differential quadrature method (DQM), to investigate dynamic stability range, and to calculate natural frequencies. The results of this study are compared against existing similar data in the literature, presented for some simpler cases. Then, the effect of various parameters, including the small scale parameter, the ratio of piezoelectric layer thickness to nanotube thickness, surface stresses, the visco-elastic foundation effect, the magnetic field effect, and the electrical polarity are scrutinized on the system dynamic stability range. The results indicate that consideration of the small scale can reduce the transverse displacement and frequency while increasing the thickness of the piezoelectric layer leads to a higher frequency. Moreover, incorporating the surface stresses into the model can increase the stability. Using the modified couple stress theory can be considered the main novelty of this paper. [ABSTRACT FROM AUTHOR]

This article investigates the phenomenon of bifurcation induced by double grazing in a piecewise-smooth oscillator with a play, which is a common occurrence in many non-smooth dynamical systems namely gear systems with approval, flange contact in wheel-rail systems, and spacecraft docking. The study is carried out using a composite Poincaré mapping with bilateral constraint, which extends the local normal form mapping of one discontinuity boundary to two discontinuity boundaries. The paper first derives the local discontinuous mapping at the unilateral grazing point using the normal form of discontinuity mapping and determines the type of 3/2 singularity of the zero-time discontinuous mapping with a continuous vector field at the discontinuity boundary. The composite Poincaré mapping is then used to obtain non-classical local bifurcations caused by double grazing, including bifurcation from period-1 motion to period-2 motion, bifurcation from period-1 motion to period-3 motion, and bifurcation from period-1 motion to chaos. The results of the study are consistent with those obtained via direct numerical simulations, demonstrating the efficacy of the composite Poincaré mapping of double grazing. The paper sheds light on the behavior of non-smooth dynamical systems and provides insights into the mechanisms underlying bifurcation induced by double grazing. The findings have potential applications in various fields including engineering, physics, and biology. [ABSTRACT FROM AUTHOR]

In this paper a selected type of elasto-viscoplastic constitutive equations is considered. The viscoplastic model which was proposed by Marquis is generalized by allowing multiple terms describing the isotropic and the kinematic hardening. Furthermore, the presented model formulation enables one to use an arbitrary equivalent plastic strain function to describe the isotropic hardening behavior. What is more, the backstress evolution equation which was proposed by Marquis was modified so that any equivalent plastic strain function can be used in the recovery term now. The general form of the generalized constitutive model obtained this way was subsequently implemented into the finite element method (FEM). For that purpose, the radial-return mapping algorithm was utilized. The consistent tangent operator was derived for the considered class of models and is presented in the paper. A developed user material subroutine (UMAT) which allows one to use the viscoplastic models under consideration in the FEM program CalculiX is attached in the appendix section. A number of numerical simulations were conducted in order to verify the performance of the developed UMAT code. [ABSTRACT FROM AUTHOR]

Stresses are generated in plates under initial loads, which couple with the subsequent transverse deformation to affect the buckling and transverse vibration characteristics of plates. There exists no exact solution method for the stress field of a rectangular plate under arbitrary in-plane loads. In this paper, the stress field of a rectangular plate under arbitrary in-plane loads is solved based on the principle of minimum potential energy. The stress function is decomposed into homogeneous and special solutions. The homogeneous solution is represented by the Chebyshev polynomial while the special solution is expanded by the Fourier series. Then, the Ritz method is used to analyze the transverse vibration and buckling characteristics of the rectangular plate. The product of the boundary function and Chebyshev polynomial is used to build the vibration mode function. The present results are verified by comparing to existing studies and those obtained from finite element method (FEM). The effects of the magnitude and distribution of in-plane boundary stresses and boundary conditions on the dynamic characteristics and stability of the rectangular plate are analyzed. The method used in the paper has demonstrated improved convergence and accuracy with good universality. [ABSTRACT FROM AUTHOR]

In this paper, the forced vibration of a functionally porous sandwich beam with a viscoelastic core has been investigated. The upper and lower layers of the beam are made of functionally porous materials, and the porosity gradient in porous layers is distributed through their thickness. The core of the beam is made of viscoelastic materials. The Golla–Hughes–McTavish (GHM) model is employed to simulate the viscoelastic behavior of the core. Applying the Hamilton principle and Euler–Bernoulli theory, the governing equation of motion is obtained for a simply supported beam. The Newmark method is applied to solve the time-dependent differential equation of the beam. The results are compared with data from the literature review and a commercial finite element software. In the Results and Discussion section of the paper, a parametric study is performed to investigate the effects of porosity and viscoelastic parameters on the forced vibration of the beam. Finally, the results obtained by the GHM model are compared with the Kelvin–Voigt model for constant and variable input frequencies. According to the results, both models predict identical behavior for constant input frequency. However, the GHM model provides better results for the case of variable input frequency. [ABSTRACT FROM AUTHOR]

A matter of fact is that extremal principles have been introduced in mechanics in more (Euler, Lagrange) or less (Hamilton) than 200 years ago. One may also observe an impact of thermodynamic extremal principles based on maximum dissipation due to all the entropy production expressed in several disciplines. According fields are theory of communication, statistical mechanics and later physics of earth since already 70 years. The current paper offers some (historical) overview on several applications. "Ziegler's principle" is an implementation of the maximum entropy production going out to the dissipation and yielding a maximum dissipation. The goal of this paper is now the implementation of this extremal principle performed along an algebraic concept. Such a concept can be extended to a system with several internal variables as outlined by Coleman and Gurtin in context with the Gibbs (free) energy. [ABSTRACT FROM AUTHOR]

In this paper, the flexural wave propagation and its control of a novel piezoelectric composite pipe conveying fluid are investigated. Dual piezoelectric layers used as sensor and actuator are periodically arranged on the pipe, and a feedback amplifying circuit is applied from sensor to actuator, forming a self-powered phononic crystal (PC) control structure. The vibration reduction performance can be actively tuned by adjusting the feedback control gain instead of conventional changing the construction of pipe itself. The pipe is composed of functionally graded material (FGM), in which the material properties vary continuously along the radial direction, and a poroelastic medium is introduced. By using the Timoshenko beam theory and Hamilton's principle, a set of electromechanical coupling equations governing flexural vibration of the pipe is deduced. The band structure, band gap (BG) distribution and frequency response are presented by applying the spectral element technology. Comprehensive parametric studies are carried out. The results obtained validate the excellent vibration control effect of the proposed design, and further demonstrate the significant impacts of material, piezoelectric layers, feedback control and flowing fluid on the BG characteristics. This paper is expected to provide a technological reference for the vibration and elastic wave control of engineering composite pipe structures. [ABSTRACT FROM AUTHOR]

In structural dynamics, response modeling relies on parameters, which are to be identified by experiments. However, for satisfactory results, the design of such experiments is laborious and requires a comprehensive physical insight, which is limited. Furthermore, accurate models are high dimensional and can operate only with a large set of parameters, which increases the experimental effort even more. Efficient data sampling methods have been addressed in studies within areas of design of experiments and active learning. However, generating a data set for nonlinear dynamic systems poses an increased degree of difficulty, since the system needs to be guided through unknown dynamics to collect the desired data points. In this paper, we address this challenge by introducing a theoretical data generation framework for testing-integrated modeling. In the proposed framework, we use feedforward neural networks (FNNs) for inverse modeling of the nonlinear restoring force of the systems. By sequentially evaluating the accuracy of the trained model on a given test data set, the excitation signal applied on the system is adapted to generate optimal response data which allow the FNN model to learn the restoring force behavior. Hence, data generation is posed as an optimization problem and pattern search algorithm is used for sampling. The performance of the proposed framework is evaluated, and it is shown that it outperforms unsupervised sampling methods. [ABSTRACT FROM AUTHOR]

The indirect approaches based on the responses of specially designed moving vehicles on bridges to extract bridge dynamic properties have received great research attention. Wavelet transform (WT) is shown to be a useful tool for the analysis of vehicle responses and bridge damage detection in the vehicle-bridge interaction system. However, past studies have demonstrated that road surface roughness poses difficulty in applying wavelet analysis to successfully detect bridge damage. In this paper, a two-step method is proposed for bridge damage detection based on WT analysis of the residual contact response of the front and rear vehicle wheels of a four degrees of freedom (4-DOF) moving vehicle to reduce the influence of road surface roughness. In the first step, the generalized Kalman filter under unknown input (GKF-UI) developed by the authors is used to identify the unknown contact forces and the state vector of the vehicle. Due to the advantages of GKF-UI, acceleration and displacement sensors can be installed conveniently on the vehicle body instead of on the wheel axles in previous studies. Then, the contact-point bridge deflection responses of the front and rear vehicle wheels are estimated from the identified contact force and vehicle state. In the second step, the residual contact-point bridge deflection response is obtained by subtracting the front contact-point bridge deflection and rear contact-point bridge deflection with a time shift to reduce the influence of road surface roughness. Then, the locations of bridge damage can be identified based on WT of the singularities of residual contact-point bridge deflection response. Numerical examples of bridge damage detection demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a dynamic interaction model of the coupled system of railway bridge, foundation, subsoil, ballast, track, and high-speed train is presented, with special emphasis on the longitudinal interaction between the track and the bridge structure, taking into account the flexibility of the ballast. After a description of the model of this interaction system, the equations of motion are given separately for each subsystem. The discretization of the bedded rails is performed by two different approaches. In the first approach, the deflection of the rails is expanded into the eigenfunctions of a finitely long bedded beam representing the rails. In the second, simplified approach, the track response is represented by a superposition of the static deflection of the infinitely long bedded beam due to a concentrated load. The coupling of the bridge structure with the track is achieved by a component mode synthesis technique, which in the first approach leads to a representation of the equations of motion in state-space. A discrete substructure technique is used to couple this subsystem with the train model. The two presented strategies are verified by comparison with results of a finite element model of this interaction system. Several application examples reveal the influence of the horizontal track–bridge interaction and other modeling parameters on the dynamic bridge response. [ABSTRACT FROM AUTHOR]

The scope of this paper is to apply a model-correction-based strategy for efficient reliability analysis of uncertain dynamical systems based on a low-fidelity (LF) model whose outcomes are corrected in a probabilistic sense to represent the more realistic outcomes of a high-fidelity (HF) model. In the model-correction approach utilized, the LF model is calibrated to the HF model close to the so-called most probable point in standard normal space, which allows a more realistic assessment of the considered complex dynamical system. Since only few expensive limit state function evaluations of the HF model are required, an efficient reliability analysis is enabled. In an application example, the LF model describes an existing single-span railway bridge modelled as simply supported Euler–Bernoulli beam subjected to moving single forces representing the axle loads of a moving train. The HF modelling approach accounts for the bridge–train interaction by modelling the passing train as mass-spring-damper system, however increasing the computational effort of the limit state function evaluations. Failure probabilities evaluated with the model-correction approach are contrasted and discussed with failure probabilities of the sophisticated bridge–train interaction model evaluated with the first-order reliability method (FORM). It is demonstrated that the efficiency of the method depends on the correlation between the LF and the HF model. A comparison of the results of FORM and the model-correction-based approach shows that the latter provides reliable failure probability prediction of the HF model while leading to a significant reduction in computational effort. [ABSTRACT FROM AUTHOR]

The identification of frequency zones where waves propagate freely (i.e., propagation zones) and where they are attenuated (i.e., attenuation zones) in a railway track, plays an important role in a number of applications, such as nondestructive testing, structure-borne noise prediction, and vibration control. This paper presents a numerical model based on the wave finite element method to study wave propagation and attenuation in periodic supported rails. The model involves postprocessing of element matrices of a rail span (i.e., rail segment between two supports), which is modeled using three-dimensional finite elements meshed through the cross section. The model uses solid elements to capture the complex cross-sectional deformation of the waves and considers the dimensions of the periodic supports. In order to obtain accurate results, the stiffness and the damping coefficients of the supports are calibrated through a finite element model updating procedure that utilizes the modal parameters and the attenuation coefficients obtained from experiments. The results demonstrate that the proposed model is capable of (i) capturing the classic vibrational modes (i.e., vertical and lateral bending), (ii) describing the complex cross-sectional deformation and the mode conversions, and (iii) obtaining the wave propagation and attenuation regions of periodic supported rails. [ABSTRACT FROM AUTHOR]

In this paper, a modified time–frequency transform method is proposed by introducing a modified factor based on elastic wave theory and classical Fourier transform. The feasibility of the proposed method is verified by taking the front semi-cylindrical canyon and hill topography subject to horizontal anti-plane shear waves as the research object. Based on the analytical solution of wave field in frequency domain and modified time–frequency transform method, the modified wave field in time domain and the amplitude of surface displacement are obtained, and the wave effect of the front terrain is discussed. The results show that the wave effect of front canyon is stronger than that of the hill, and the range is wider that cannot be ignored under thousands of characteristic radii. The results and the proposed modified time–frequency transform method can provide theoretical reference and a new idea for earthquake engineering. [ABSTRACT FROM AUTHOR]