Large Structural Systems Research Articles

Frequency-band programmable piezoelectric energy harvesters with variable substrate material, tip mass and fractal architectures: Experimental and numerical investigations

To automate the approach of assessing the health and efficacy of large structural systems globally through structural health monitoring systems, a vast network of sensors that must be mounted throughout the entire structure and connected to a continuous power supply is necessary. Clusters of wires need to be placed throughout the structures to support the network, or batteries must be changed frequently, adding to the network’s high maintenance expenses. The present study investigates the scope of powering such low-energy devices with a localized renewable energy source based on smart piezoelectric components such as PZT-patched energy harvesting systems. This paper analyses the performance of the PZT patch mounted on different structures that are predominantly activated in d 31 mode. A vibration testing rig is manufactured to perform experiments for investigating the effect of material properties, natural frequencies, vibrating structural mass, and their interaction with the output power of a PZT transducer. Optimal mass, material, and structural configurations are attempted to be identified experimentally. The hypothesis, predictions, and results are evaluated further based on a converged finite element model. Subsequently, we introduce a novel concept of chiral fractal substrates in piezoelectric energy harvesters, wherein a significant improvement is noticed in the energy output along with increased frequency-band programmability. The power output of such architected and optimized energy harvesters holds the potential to serve as a reliable and sustainable alternative to conventional batteries, effectively providing a renewable source of power to energize and sustain low-power micro-electro-mechanical systems (MEMS) and devices.

Unconditionally Stable Central Difference Dissipative Algorithm for Multi-Directional Real-Time Hybrid Simulations of Large Nonlinear Structural Systems

ABSTRACT The central difference is a popular algorithm used to integrate the equations of motion, yet suffers from two drawbacks: (1) it is only conditionally stable and requires a small-time step to maintain numerical stability; (2) it is non-dissipative, and high-frequency spurious oscillations may appear and compromise the accuracy of the solution. These drawbacks are detrimental to applying the algorithm to the real-time hybrid simulation of large, complex nonlinear structural systems. In this paper, the conventional central difference algorithm is modified to overcome these drawbacks, and the modified algorithm is applied to the real-time hybrid simulation of complex structural systems.

Rotated block diagonal preconditioners for Navier-Stokes control problems

Fluid flow control problems play a crucial role in various industrial applications. The optimal control of the Navier-Stokes equations poses a significant challenge. By employing Oseen's approximation to linearize the problem, we encounter a series of large sparse structured linear systems. These coefficient matrices exhibit a two-by-two block structure with square blocks. Leveraging this block structure, we exploit matrix splitting preconditioners. Theoretical analysis indicates that the real parts of all eigenvalues of preconditioned matrix are equal to 1/2. A large number of eigenvalues are clustered in (1±i)/2. The imaginary part of the eigenvalues is bounded explicitly. The eigenvalue distribution predicts the fast convergence of Krylov subspace methods. To avoid solving the saddle point subsystems in the preconditioning procedure, we propose a practical variant of the preconditioner. The theoretical analysis demonstrates that if the approximation is sufficiently close to Schur complement, the eigenvalues of the modified preconditioned matrix will lie within a circle centered at the original eigenvalues with a radius less than 1. This implies that the modified preconditioner exhibits excellent performance in terms of preconditioning. The numerical experiments demonstrate that the generalized minimal residual method, when combined with the proposed preconditioners, proves to be an efficient and effective solution for Oseen's control optimization with a variable viscosity coefficient. The number of iterations required by the preconditioned methods remains unaffected by the mesh size used in finite element discretization and only marginally depends on the regularization parameter.

Closure to “Simultaneous Assessment of Damage and Unknown Input for Large Structural Systems by UKF-UI”

Closure to “Simultaneous Assessment of Damage and Unknown Input for Large Structural Systems by UKF-UI”

Discussion of “Simultaneous Assessment of Damage and Unknown Input for Large Structural Systems by UKF-UI”

Discussion of “Simultaneous Assessment of Damage and Unknown Input for Large Structural Systems by UKF-UI”

Buckling of Conventional and High-Strength Vanadium Steel Single- and Double-Angle Compression Members and Truss Subassemblies: Experimental and Computational Correlation Study

High-strength, low-alloy vanadium (HSLA-V) steel offers higher strength and toughness than conventional steel. The resulting lighter weight and more slender structural members are more susceptible to buckling in compression. This study establishes an understanding of buckling in this material and the ability to predict it analytically. A series of conventional ASTM A572 Grade 50 steel and HSLA-V (nominal Grade 80) steel angle compression members were tested at Lehigh University’s Advanced Technology for Large Structural Systems (ATLSS) laboratory. A general-purpose finite element (FE) software was used in this study to simulate the buckling and post-buckling behavior of the structural members. The objective of these simulations was to establish confidence in the ability to accurately predict buckling response. The influence of the following modeling parameters on the accuracy of the compression angle member simulation results was investigated: variation in material stress-strain relationship, residual stresses, and the shape and magnitude of geometric imperfections. For the truss subassembly simulations, the influence of the following parameters was also investigated: bracing and boundary element stiffness and design code assumptions of end conditions.

Simultaneous Assessment of Damage and Unknown Input for Large Structural Systems by UKF-UI

AbstractMuch progress has been made in the assessment of structural damage and unknown input (UI) using incomplete and noisy measurement signals. The unscented Kalman filter (UKF) has proved to be ...

On Bayesian active vibration control of structures subjected to moving inertial loads

This study introduces a novel Bayesian framework for online and real-time vibration control of beam type structures, which represent a comprehensive control system associated with input-state algorithms. Control design systems typically require knowledge of system states, which in structures are displacements and velocities at some degrees of freedom. Currently, full-field measurements of displacements and velocities in large structural systems are not feasible. Also, properties of the moving inertial loads as key parameters in control designs are assumed known; however, in practice, measuring their characteristics is a challenging issue. As a remedy, an observer is required to estimate quantities of interest needed in control algorithms via indirect measurement of structural response. To estimate the entire state of the system in the absence of input information, often the input needs to be estimated together with the unknown states. Three state of the art methods for estimation of input and states of a linear state-space system, namely augmented Kalman filter (AKF), dual Kalman filter (DKF), and joint input state estimation algorithm (JIS), were adopted to assess controller performance in the absence of direct displacement measurements in comparison to conventional Kalman filter (KF). The linear quadratic Gaussian (LQG) framework, in association with these three filters, presents a novel control algorithm. Various sensor networks featuring pure accelerations and a combination of strain gauges and accelerometers with different noise levels were considered. Extensive numerical examples and comparison with the passive control system proved the viability of input-state estimation as an integral part of active control algorithms in structural systems subjected to moving inertial loads with different speeds.

Deployable truss structure with flat-form storability using scissor-like elements

Deployable structures have received much attention in the building of large structural systems in space due to the limitations in the packaging capabilities of satellites and launch vehicles. Among various categories of deployable structures, deployable truss structures are most commonly used because of their high stiffness and strength. However, deployable truss structures typically have low packaging efficiency. To improve the packaging efficiency of deployable truss structures, this paper proposes a deployable truss structure that can be stored in a flat form. The proposed structure has a high packaging efficiency while preserving the major advantage of conventional deployable truss structures. The deployment motion is analyzed through a kinematic model, and the packaging efficiency is calculated and compared to a conventional deployable truss structure. The dynamic model of the proposed structure is derived and the deployment characteristics are investigated considering the driving force for deployment and gravity. Finally, the feasibility of the proposed structure is demonstrated with a deployment test of the prototype.

Sliding mode control design for the benchmark problem in real-time hybrid simulation

Real-time hybrid simulation (RTHS) is a novel cyber-physical testing technique for investigating especially large or complicated structural systems. Controllers are required to compensate for the dynamics of transfer systems that emulate the interactions between the physical and numerical substructures. Thus, both the stability and accuracy of RTHS testing highly depend on the effectiveness of the control strategy. This paper proposes a robust sliding mode controller (SMC) as a transfer system control strategy in RTHS. A design procedure of the SMC control strategy is presented. The benchmark problem on RTHS control is utilized for demonstration and validation of SMC for this class of problems. Virtual RTHS results show that the SMC strategy significantly improves the performance and robustness of RTHS testing.

Application of adaptive reliability importance sampling-based extended domain PSO on single mode failure in reliability engineering

The failures of mechanical structure featuring high nonlinearity, non-normal and non-independent are implicit function and small-probability events. This normally results in low computational efficient and accuracy for gradient algorithm scenario, which can hardly calculate models for large complex structure and flexible systems. To deal with the above constraints, an efficient and accurate reliability numerical method named adaptive reliability index importance sampling-based extended domain PSO (ARIIS-EDPSO) is proposed to combine the reliability numerical simulation and the particle swarm optimization (PSO) algorithm. The reliability index and limit state equation in ARIIS-EDPSO are regarded as the objective function and the constraint function. The Nataf transformation is adopted to complete the conversion process from an original variable space to an independent standard normal space, which only requires the marginal probability density function and the correlation coefficient among the random variables. To verify the effectiveness of the proposed ARIIS-EDPSO, experimental studies are conducted with five case studies. The results indicate that the constraint conflict function obtained via ARIIS-EDPSO is smaller than that is obtained via the other methods, and its convergence can be guaranteed. Also, the accuracy of the ARIIS-EDPSO is superior to the other methods for nonlinear reliability calculation. Furthermore, the ARIIS-EDPSO can accurately predict the failure probability. This approach exhibits advantageous global search ability, high efficiency and high accuracy in solving constrained reliability engineering problems.

Scaling effect on the moment and shear responses of three types of beam-to-column connectors used in mass timber buildings

To fully understand the structural behaviour of large structural systems under given loading scenarios, experimental testing of the entire system or of a representative part of it is often required. However, due to limited laboratory space and budget restrictions, tests are frequently performed on scaled down systems. The scaled tests allow investigating the influence of a large number of parameters, therefore providing in-depth understanding of the structural system response, an opportunity rarely achievable in full-scale testing due to cost related issues. As timber is known to be sensitive to size effects, it is unclear (i) how accurately tests performed on a scaled down timber structure would reproduce the full-scale system response and (ii) how scaled tests results must be interpreted to consider the scaling effect. This paper experimentally investigates the full-scale and quarter-scale moment and shear non-linear responses of three types of beam-to-column connectors currently used in post-and-beam mass timber buildings. Moreover, the paper discusses (i) how tests performed on scaled down timber buildings can be extrapolated to full-scale structures, and (ii) presents recommendations for the scaled down specimens to best replicate the response of the full-scale ones. A total of 12 full-scale and 18 quarter-scale tests were performed. Considering the scaling factor, results show that the overall non-linear responses of the quarter-scale connections closely match the full-scale responses. However, still taking into account the scale factor: (i) the average ratio of the quarter-scale to full-scale elastic stiffness is 0.74 and (ii) the tests performed on the scaled down connections typically result in a capacity 1.2 times higher than the capacity of the full-scale systems. Results also demonstrate the importance of using steel or aluminium connectors with similar material ductility in both the scaled down and full-scale connectors.

Implementation of real-time hybrid shake table testing using the UCSD large high-performance outdoor shake table

Large shake tables can provide extended capabilities to conduct large- and full-scale tests examining the seismic behaviour of structural systems that cannot be readily obtained from reduced scale or quasi-static testing conditions. Assessing the behaviour of large or complex structural systems introduces challenges such as high cost of full-scale specimens or capacity limitations of currently available shake tables. Some of these limitations may be overcome by employing the real-time hybrid shake table test method that requires only key subassemblies to be evaluated experimentally on the shake table while the remainder of the structure is modelled numerically. As a demonstration of the applicability of this testing method using a large shake table, a series of hybrid shake table tests were conducted on the University of California, UC San Diego large high-performance outdoor shake table (LHPOST) with capabilities to test full scale structural models. A physical specimen was coupled with a numerical model using hybrid simulation techniques and shown to reproduce reliable results with adequate mitigation of experimental errors.

Implementation of real-time hybrid shake table testing using the UCSD large high-performance outdoor shake table

Large shake tables can provide extended capabilities to conduct large- and full-scale tests examining the seismic behaviour of structural systems that cannot be readily obtained from reduced scale or quasi-static testing conditions. Assessing the behaviour of large or complex structural systems introduces challenges such as high cost of full-scale specimens or capacity limitations of currently available shake tables. Some of these limitations may be overcome by employing the real-time hybrid shake table test method that requires only key subassemblies to be evaluated experimentally on the shake table while the remainder of the structure is modelled numerically. As a demonstration of the applicability of this testing method using a large shake table, a series of hybrid shake table tests were conducted on the University of California, UC San Diego large high-performance outdoor shake table (LHPOST) with capabilities to test full scale structural models. A physical specimen was coupled with a numerical model using hybrid simulation techniques and shown to reproduce reliable results with adequate mitigation of experimental errors.

Assessing structural reliability using real-time hybrid sub-structuring

While numerical simulations can be used to predict the dynamic performance of structural systems, there are some instances where the dynamical behaviour and uncertainties of specific system components may be difficult to accurately model. In these instances, structural reliability assessments may be conducted by employing the cyber-physical real-time hybrid sub-structuring (RTHS) test method. In this approach, a numerical model of a larger structural system, incorporating uncertainty in specific parameters, is coupled with a physical test specimen of a system component to fully capture system-level dynamic interactions and facilitate uncertainty propagation. This paper specifically details a study performed to experimentally validate the previously proposed adaptive Kriging-Hybrid simulation (AK-HS) structural reliability method. The AK-HS method combines Kriging metamodeling, an adaptive learning algorithm, Monte Carlo simulation, and RTHS testing to iteratively estimate a structural system's probability of failure given random parameters in the numerical model. The method is validated with a series of bench-scale RTHS tests on a viscous damper connecting two adjacent 6-degree-of-freedom rigid body structures. The AK-HS method is shown to accurately predict probabilities of failure for systems with up to 24 random variables using a reasonable number of RTHS tests.

Investigation on Similarity between Dynamic Behavior of a Reduced-Scale One Span Historical Masonry Arch Bridge Model and Prototype Bridge

Experimental investigations of large and complex structural systems can be carried out by reduced-scale models in terms of convenience, time-saving and economical. This can be applied to different fields of study such as vibration, impact and explosion problems in structural engineering and allows reliable analysis to understand the static and dynamic behavior of real structures called a prototype. This study aims that a 1/3 reduced-scale model is created in the laboratory environment considering similitude requirements by selecting a single span historical masonry arch bridge as a prototype structure. For this purpose, the Operational Modal Analysis (OMA) Technique is utilized for experimental study to determine modal parameters of the prototype and model bridges. The similarity of the dynamic behavior of the reduced-scale bridge model and prototype are investigated. The analysis of the similarity in the dynamic behavior of the prototype and model bridge consists of comparing the natural frequencies and mode shapes by utilizing the modal assurance criterion (MAC) corresponding to the translational, bending and torsional modes. As a result of the study, it is concluded that the dynamic behavior of the reduced-scale bridge model is similar to the dynamic behavior of the prototype bridge.

Data mining-based damage identification of a slab-on-girder bridge using inverse analysis

Classical damage detection methods such as visual inspections have many limitations, i.e. time consuming procedure, costly process and ineffective for large and complex structural systems. To overcome these difficulties, a data mining-based damage identification approach is developed in this study. First four natural frequencies which obtained from the experimental modal analysis of a slab-on-girder bridge structure are used as an input database. The laboratory work is carried out through single-type and multiple-type damage scenarios. The applicability of machine learning, artificial intelligence and statistical data mining techniques are here examined using Support Vector Machine (SVM), Artificial Neural Network (ANN) and Classification and Regression Tree (CART) to predict the model behavior and damage severity. Then, a hybrid algorithm is proposed in the deployment step of Cross Industry Standard Process for Data Mining (CRISP-DM) model. According to the obtained results, the hybrid algorithm performs a better accuracy in compare to ANN technique itself.

Classical modal analysis and asymptotic modal analysis of structural and acoustic systems

The Classical Modal Analysis (CMA) method is commonly used to solve for the vibroacoustic response of large scale structural and acoustic systems. In this method, the modal equations of motion are developed and solved for the modal coefficients to form a modal series solution to predict the structural and acoustic responses. The CMA method generally works well in the low-to-medium frequency range. However, at high frequencies, the large number of modes required in the summation limits the usefulness of the CMA method and alternative methods, such as Statistical Energy Analysis (SEA) and Energy Finite Element Analysis (EFEA) have been developed. As an alternative to SEA and EFEA, the Asymptotic Modal Analysis (AMA) method has been developed in which the modal series summation in the CMA method is asymptotically approximated based on the overall frequency and band averaging of the modal series. The AMA method thereby predicts the band averaged frequency response in the high frequency range and also has the advantage of providing the spatial distribution of the response based on the summed modes in the frequency band. In this paper, an example of coupled cavity-plate system subject to external random white noise pressure load excitation is developed to illustrate the CMA and AMA methods and to address their accuracy.

A systematic wave-based method for analysis of large planar frame structures based on Timoshenko waveguide theory

This paper presents a new hybrid analytical/numerical systematic approach for continuous modeling of wave propagation in planar structural systems. To do so, a structure is considered as a number of waveguide elements that are connected to each other through different types of discontinuities. The wave propagation in waveguides is modeled using advanced Timoshenko beam theory to account for the rotary inertia, which provides accurate results for high-frequency excitations. The refraction matrices for different types of discontinuities such as change of material and cross section, various types of boundary conditions, and two- and three-member joints are presented using the existing literature, and the refraction matrices for a right-angled four-member joint is derived analytically for the first time. To provide a robust methodology for the analysis of large structural systems, a general new assembly procedure is introduced that is capable of assembling all of the propagation and refraction matrices in a single global system matrix. To insure the validity of the proposed methodology, detailed numerical examples are provided and their results are verified with finite element numerical method.

Application of model-based compensation methods to real-time hybrid simulation benchmark

Abstract Real-time hybrid simulation (RTHS) is an experimental testing technique widely used for performance evaluation of structural systems such as large buildings and bridges subjected to earthquake loading. While RTHS testing has demonstrated over the last 20 years to be an efficient and cost-effective alternative to shaking table tests, especially for large structural systems with rate-dependent behavior, accurate and stable results from this methodology are highly dependent on the test specimen, loading equipment, and controller design for dynamic compensation. This paper presents a study on the accuracy and stability of model-based compensation (MBC) approaches for the implementation of a real-time hybrid simulation benchmark problem. The controller architecture is based on feedforward compensator, designed for reference tracking, while a feedback regulator provides improved robustness for undesired disturbance and sensor noise. The results provide evidence of the improved performance of MBC controllers compared to benchmark results. Moreover, the MBC controllers surpass the benchmark controller in terms of robustness, when multiple partitioning cases and control plant uncertainty are considered in the numerical simulations.