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A novel approach is presented for the time-domain system identification of structural dynamic components exploiting the high spatial density of vision-based measurements. By using spatially dense measurements, the number of spatial measurement points is much larger than the dimensionality of the underlying dominant dynamics (i.e., the number of measurement points needed to meet observability of the targeted dynamics). This opens up the potential to develop new experimental identification methods that use this spatial overdetermination which were out of reach with conventional discrete sensors. The new approach presented in this paper directly extracts a relatively noise-free, low-order set of dynamic states by projecting the spatially dense time-domain measurements on a low-order dominant deformation motion basis. The basis is constructed by applying an over-complete singular value decomposition on the measurements. These dynamic states together with their numerically calculated first and second order time-derivatives are then used in a two-step identification of the structural dynamic parameters. Here, the structure of the model to identify is based on a-priori physical knowledge of the underlying set of partial differential equations, unlike a purely data-driven method. This approach has the benefits of providing a mathematical formulation that is straightforward to understand and implement and is time-efficient to solve. The presented approach is experimentally validated on a clamped plate as well as on a flexibly suspended plate which requires a correction of the rigid body motion. The identified models have shown to provide an accuracy up to 1 × 10-5 m with respect to the dominant measured motion components in both validation cases. ispartof: Mechanical Systems And Signal Processing vol:182 status: Published online

no ISBN/ISSN ispartof: Proceedings of TECNIACUSTICA 2022 ispartof: TECNIACÚSTICA 2022 location:Elche, Spain date:2 Nov - 4 Nov 2022 status: Published online

ispartof: pages:3577-3583 ispartof: ISMA-USD conference proceedings pages:3577-3583 ispartof: ISMA2022 - Noise and Vibration Engineering Conference location:Leuven status: published

At present, black-box and simulation-based optimization problems with multiple objective functions are becoming increasingly common in the engineering context. In many cases, the functional relationships that define the objective and constraints are only known as black-boxes, cannot be differentiated accurately, and may be subject to unexpected failures. Directional direct search techniques, in particular the direct multisearch (DMS) methodology, may be applied to identify Pareto fronts for such problems. In this work, we propose a mechanism for adaptively selecting search directions in the DMS framework, with the goal of reducing the number of black-box evaluations required during the optimization. Our method relies on the concept of simplex derivatives in order to define search directions that are optimal for a local, linear model of the objective function. We provide a detailed description of the resulting algorithm and offer several practical recommendations for efficiently solving the associated subproblems. The overall performance in an academic context is assessed via a standard benchmark. Through a realistic case study, involving the bi-objective design optimization of a mechatronic quarter-car suspension, the performance of the novel method in a multidisciplinary engineering setting is tested. The results show that our method is competitive with standard implementations of DMS and other state-of-the-art multi-objective direct search methods. ispartof: Optimization And Engineering vol:23 issue:3 pages:1411-1437 status: accepted

ispartof: Conference Proceedings of the Society for Experimental Mechanics Series ispartof: IMAC-XL Conference & Exposition on Structural Dynamics 2022 location:Orlando (Florida), USA status: Published online

The current interest in sustainable aviation is motivating the development of aircraft with better environmental performance. Within this context, advanced turboprops offer higher fuel efficiency compared to conventional turbofan engines. However, the cabin noise levels of propeller driven aircraft are significantly higher than those in common fanjets. The dominant noise sources in turboprop aircraft are the turbulent boundary layer noise, which is generated by the turbulent airflow exciting the fuselage, and the propeller induced noise caused by the periodic pressure fluctuations produced by the propeller blades passing near the fuselage. This paper presents the design of an innovative noise generation system that will be able to replicate, with a set of loudspeakers, the dynamic excitation given by both the turbulent boundary layer noise and the blade passing noise on a fuselage. The novelty of this system is the use of MIMO feedback controllers to simultaneously achieve desired sound pressure levels and spatial correlations at specific fuselage locations. The aim of the CONCERTO project (GA886836) is to develop cabin noise testing equipment that will be used to evaluate the interior noise of regional aircraft and to aid the development of noise reduction solutions. Firstly, a preliminary analysis of the noise generation system is carried out for a small-scale noise generation set-up. The system components are investigated and MIMO feedback control strategies are introduced. MIMO random control is used to replicate the random pressure field generated by the turbulent boundary layer excitation. The tonal components of the propeller induced excitation are then added to the broadband noise using a time waveform replication technique. The preliminary results for the small-scale set-up show that the power spectral densities of the measured microphone signals converge to those of the references within acceptable tolerance (±1.5 dB). Finally, the design of the modular mechanical structure for the full-scale innovative noise generation system is discussed. Proceedings can be found here: https://iiav.org/content/archives_icsv_last/2021_icsv27/indexbd58.html?va=viewpage&vaid=410 ispartof: pages:1-8 ispartof: "Advances in Acoustics, Noise and Vibration – 2021" Proceedings of the 27th International Congress on Sound and Vibration pages:1-8 ispartof: 27th International Congress on Sound and Vibration location:Virtual date:11 Jul - 16 Jul 2021 status: published

The optimization problems arising in modern engineering practice are increasingly simulation-based, characterized by extreme types of nonsmoothness, the inaccessibility of derivatives, and high computational expense. While generating set searches (GSS) generally offer a satisfying level of robustness and convergence to stationary points, the convergence rates may be slow. In order to accelerate the solution process without sacrificing robustness, we introduce (simplex) gradient-informed generating set search (GIGS) methods for solving bound-constrained minimization problems. These algorithms use simplex gradients, acquired over several iterations, as a guidance for adapting the search stencil to the local topography of the objective function. GIGS is shown to inherit first-order convergence properties of GSS and to possess a natural tendency for avoiding saddle points. Numerical experiments are performed on an academic set of smooth, nonsmooth and noisy test problems, as well as a realistic engineering case study. The results demonstrate that including simplex gradient information enables computational cost savings over non-adaptive GSS methods. ispartof: Computational Optimization And Applications vol:79 issue:1 pages:35-65 status: published

In the context of nonlinear model predictive control (NMPC) for robot manipulators, we address the problem of enabling the mixed and transparent use of algorithmic differentiation (AD) and efficient analytical derivatives of rigid-body dynamics (RBD) to decrease the solution time of the subjacent optimal control problem (OCP). Efficient functions for RBD and their analytical derivatives are made available to the numerical optimization framework CasADi by overloading the operators in the implementations made by the RBD library Pinocchio and adding a derivative-overloading feature to CasADi. A comparison between analytical derivatives and AD is made based on their influence on the solution time of the OCP, showing the benefits of using analytical derivatives for RBD in optimal control of robot manipulators. ispartof: pages:78-83 ispartof: Modeling, Estimation and Control Conference MECC 2021 vol:54 issue:20 pages:78-83 ispartof: Modeling, Estimation and Control Conference MECC 2021 location:Online and UT Austin, USA date:24 Oct - 27 Oct 2021 status: Published online

This article demonstrates a combined [Formula: see text] feedback control design for linear time-invariant and linear parameter-varying systems and optimal sensors and actuator selection. The combined design problem is systematically constructed as a mixed Boolean semidefinite programming optimization problem. We impose Big-M reformulations to the non-deterministic polynomial-time-hard coupled problem to be solved as a convex optimization problem using the branch and bound algorithm. The combined design of dynamic output feedback control along with optimal actuator selection for a linear time-invariant seismic rejection controller design serves as an application for validation by simulation. In addition, active vibration control of a smart composite plate along with optimal sensor and actuator selection validates the developed approach for linear parameter-varying controller synthesis. On comparing this approach with exhaustive search, it is observed that mixed Boolean semidefinite programming approaches have faster computation time, and comparing with the iterative reweighted ℓ1 norm algorithm and mixed Boolean semidefinite programming using outer approximations, mixed Boolean semidefinite programming yields a global solution.

Multi-material topology optimization has become a popular design optimization discipline since it allows to go a step further in topology optimization of the design of lightweight components and structures. However, it also presents additional challenges in terms of managing a higher complexity in the optimization problem, reliably estimating the manufacturing cost taking into account the cost of joining dissimilar materials, or assessing the manufacturability of the design. This paper proposes a set of methods that solve generic multi-material topology optimization problems, while including several novel aspects such as a comprehensive cost model, specific design rules for multi-material design, and model order reduction techniques to improve the computational efficiency. Two different examples, consisting of a sitting bench and a car cowling, have been solved in order to support the benefits of the approach.

In this paper, we propose a Feasible Sequential Linear Programming (FSLP) algorithm applied to time-optimal control problems (TOCP) obtained through direct multiple shooting discretization. This method is motivated by TOCP with nonlinear constraints which arise in motion planning of mechatronic systems. The algorithm applies a trust-region globalization strategy ensuring global convergence. For fully determined problems our algorithm provides locally quadratic convergence. Moreover, the algorithm keeps all iterates feasible enabling early termination at suboptimal, feasible solutions. This additional feasibility is achieved by an efficient iterative strategy using evaluations of constraints, i.e., zero-order information. Convergence of the feasibility iterations can be enforced by reduction of the trust-region radius. These feasibility iterations maintain feasibility for general Nonlinear Programs (NLP). Therefore, the algorithm is applicable to general NLPs. We demonstrate our algorithm's efficiency and the feasibility update strategy on a TOCP of an overhead crane motion planning simulation case., Accepted for publication at the IEEE Conference on Decision and Control 2022 (CDC 22)

In this work we present a novel approach for the time-domain system identification of structural dynamic components exploiting the high spatial density of vision-based measurements. By projecting the spatially dense, time-domain measurements on a low-order dominant deformation motion basis, relatively noise-free, low-order dynamic states could directly be extracted and used in an optimization procedure for the identification of the structural dynamic parameters. Here, a priori physical knowledge of the underlying set of partial differential equations is used to determine the structure of the model to identify. The presented approach is experimentally validated on a clamped plate as well as on a flexibly suspended plate which required a correction of the rigid body motion. The results of this work have shown to be highly accuracy up to 1e-5 meter with respect to the dominant measured motion components in both validation cases and encourage us to rethink other experimental testing techniques towards the use of vision-based measurements. ispartof: pages:2838-2851 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA2022) and the International Conference on Uncertainty in Structural Dynamics (USD2022) pages:2838-2851 ispartof: ISMA2022 International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:12 Sep - 14 Sep 2022 status: accepted

ispartof: Proceedings of ISMA2022 International Conference on Noise and Vibration Engineering ispartof: ISMA 2022 conference on Noise and Vibration Engineering location:Leuven, Belgium status: accepted

Finding a time-optimal trajectory through gates and tunnels is a difficult challenge in autonomous drone racing, especially in a fully autonomous context where the computations are all performed onboard. This paper presents an optimal control problem formulation to represent and solve the motion planning problem for a multirotor drone racing through a series of gates or tunnels, without a priori knowledge about the drone pose right in front of or behind the gates nor about the exact time instance when to pass through the gates. The formulation is shown to produce feasible trajectories for a set of handcrafted configurations, and has the potential to be fast enough for online replanning purposes. ispartof: pages:376-382 ispartof: 2022 IEEE 17th International Conference on Advanced Motion Control (AMC) pages:376-382 ispartof: 2022 IEEE 17th International Conference on Advanced Motion Control (AMC) location:Padova, Italy date:18 Feb - 20 Feb 2022 status: published

Identifying state-space models that are nonlinear in the parameters is still a challenge due to the non-convex nature of the objective function and possible regions of the parameter space where the model is non-contractive, even if the model structure is known in advance from physical knowledge. The optimization problem for estimating the model parameters can be formulated in different ways, including single shooting (unconstrained), hybrid shooting (partially constrained) or multiple shooting (fully constrained) formulations, and if the states can be measured or inferred, the estimation can also be formulated as an N-step-ahead prediction problem. In this paper, we compare these methods with respect to running time and robustness against initial parameters being in a non-contractive region and a contractive region, applied to an electromechanical positioning system. We show that for this system with states that can be partially measured and partially inferred, a two-step approach that involves the prediction error formulation and single shooting, is the most robust with respect to non-contractive initialization. The methods described in this paper are released as an open-source MATLAB toolbox that uses algorithmic differentiation and parallelization to speed up the computations. ispartof: pages:207-212 ispartof: Proceedings of IEEE 17th International Conference on Advanced Motion Control pages:207-212 ispartof: IEEE 17th International Conference on Advanced Motion Control location:Padova, Italy date:18 Feb - 20 Feb 2022 status: accepted

This paper presents a novel automotive state estimation approach aiming to provide reliable results for multi-objective estimation applications. Because single-objective estimators typically feature simple, dedicated models, they often lack accuracy for highly dynamically coupled systems such as vehicles. Therefore, this approach features a more complex, system-level, non-linear vehicle model containing more accurate physics. Based on the assumption that the estimator targets a specific number of quantities of interest, an extensive observability analysis is performed to ensure stable estimator operation. Firstly, a novel algorithm to detect unobservable estimator states is presented, followed by a methodology for detailed analysis on which estimator states are decoupled using the linearized Jacobians. It is shown that if the unobservable states are partially decoupled and have no dependency towards the quantities of interest, an observable transformation can be carried out which stabilizes the estimator during operation ensuring reliable and interpretable results for the quantities of interest. The methodology is validated using an experimental vehicle case for which sensor selection was performed and demonstrates the estimator performance as well as potential limitations for unobservable vehicle states. ispartof: pages:273-280 ispartof: Proceedings of the 8th International Conference on Vehicle Technology and Intelligent Transport Systems vol:1 pages:273-280 ispartof: 8th International Conference on Vehicle Technology and Intelligent Transport Systems location:Online date:27 Apr - 29 Apr 2022 status: Published online

ispartof: pages:1-9 ispartof: Proceedings of the 26th International Congress of Mechanical Engineering pages:1-9 ispartof: COBEM 2021 26th International Congress of Mechanical Engineering location:Virtual Conference (Brazil) status: Published online

To comply with the increasing complexity of new mechatronic systems and stricter safety regulations, advanced estimation algorithms are currently undergoing a transformation towards higher model complexity. However, more complex models often face issues regarding the observability and computational effort needed. Moreover, sensor selection is often still conducted pragmatically based on experience and convenience, whereas a more cost-effective approach would be to evaluate the sensor performance based on its effective estimation performance. In this work, a novel estimation and sensor selection approach is presented that is able to stabilise the estimator Riccati equation for unobservable and non-linear system models. This is possible when estimators only target some specific quantities of interest that do not necessarily depend on all system states. An Extended Kalman Filter based estimation framework is proposed where the Riccati equation is projected onto an observable subspace based on a Singular Value Decomposition (SVD) of the Kalman observability matrix. Furthermore, a sensor selection methodology is proposed, which ranks the possible sensors according to their estimation performance, as evaluated by the error covariance of the quantities of interest. This allows evaluating the performance of a sensor set without the need for costly test campaigns. Finally, the proposed methods are evaluated on a numerical example, as well as an automotive experimental validation case. ispartof: Sensors vol:21 issue:22 pages:1-20 ispartof: location:Switzerland status: Published online

In recent years reduced order modeling techniques for vibro-acoustic systems that are modeled with numerical techniques, such as the finite element method, have been established as a key technology in digital twin design. By reducing the order of the system, the complexity of the model can be alleviated to such a degree that the model can be run in a (near-)real time environment, allowing for integration of the model on an embedded system included with the physical asset, e.g. for state estimation. This paper demonstrates how to create a state space model of a vibro-acoustic finite element model including frequency dependent impedance boundary conditions. These systems are difficult to convert to a state space representation for two reasons: Firstly, the frequency dependency has to be preserved in the reduced order model. Secondly, the state space form only takes the previous time step into account, while the frequency dependent damping behavior would result in a convolution operation. This paper aims to solve both issues by approximating the frequency dependency using a digital filter bank approach, in which the individual filter banks use a frequency independent damping matrix. The filter bank is designed such that a near perfect reconstruction is achieved. Furthermore, it allows for banks with different frequency bandwidths to fine-tune the filter where the impedance changes rapidly as function of frequency. The frequency independent vibro-acoustic models in the filter banks are reduced using a Krylov subspace projection method. The resulting filter bank is converted to a state space form by converting the reduced order model to first order form and rewriting the finite impulse response filters in state space format. A second reduction is performed on these filters, due to the large number of filter coefficients, leading to a small and stable system level state space model. ispartof: Proceedings of the 27th International Congress on Sound and Vibration ispartof: The 27th International Congress on Sound and Vibration location:Online date:11 Jul - 16 Jul 2021 status: Published online

This paper presents the development of a cabin noise testing equipment that will be used to evaluate the interior noise of regional aircraft as well as to aid the development of noise reduction techniques. The innovative noise generation system consists of three loudspeaker arrays positioned around the fuselage circumference to synthesize a pressure field that is similar to the pressure field seen by the fuselage during a flight. The acoustic pressure field generated by the loudspeakers is measured by a number of microphones scattered on the fuselage surface. These microphone signals are then fed back to the controller with the purpose of minimising the error between the target pressure field and the measured one by means of an iterative learning approach. The number and location of the microphones used in the control loop are selected through a pre-test optimisation analysis, which aims to reduce the time and cost of the set-up. A small-scale electroacoustic demonstrator has been built to develop the feedback control approach. A frequency domain multi-input multi-output feedback controller is used to replicate the random pressure field generated by the turbulent boundary layer excitation. The multiharmonics of the propeller induced excitation are then added to the time histories of the broadband noise using a time waveform replication technique. Different arrangements of the driving signal distribution are investigated, and the results are then presented in terms of accuracy of the pressure field reproduction.

This paper presents an open toolchain tailored for deployment of nonlinear model predictive control for serial robots. The toolchain provides a direct workflow from problem definition to solution deployment on a serial robot based on open-source software. Thus, we provide an insightful selection of modules for rigid body dynamics, numerical optimization, and robot control, and a strategy to make them cooperate in a way that is efficient in terms of computation and engineering time. A detailed numerical study is presented for path-following MPC on a 7-degrees-of-freedom robot, showing the efficiency and ease of use of the presented toolchain while comparing its modules with other tools. ispartof: pages:9814-9819 ispartof: IFAC-PapersOnLine vol:53 issue:2 pages:9814-9819 ispartof: 21st IFAC World Congress on Automatic Control - Meeting Societal Challenges location:ELECTR NETWORK date:11 Jul - 17 Jul 2020 status: published

This paper investigates a metamaterial solution for efficient vibration attenuation and acoustic radiation reduction of an aluminum pipe. To this end, using unit cell predictions, locally resonant structures are designed to have a pronounced flexural resonance frequency at the vicinity of a dominant vibration mode of the pipe. A direct approach of the Bloch-Floquet theorem is adopted to provide the dispersion relation representing wave motion in an infinite metamaterial pipe. Using these wave dispersion relations, the frequency range of the stopband zone created by the metamaterial solution is predicted. The dynamic behavior of the finite counterpart is predicted using the Finite Element Method (FEM). The resonant structures are produced from polymethyl methacrylate (PMMA) panels and are added to the host structure. In order to properly characterize both the vibrational behavior of the metamaterial pipe and the acoustic radiation from its wall, impact tests using roving hammer technique is performed on the pipe and both accelerations and acoustic pressures are measured at different locations. The experimental results show a pronounced stopband zone created by the addition of a few rows of resonant structures. Moreover, comparisons between the measurements and numerical predictions show a good agreement. ispartof: Journal of Sound and Vibration vol:455 pages:96-117 status: published

Locally resonant metamaterials have recently emerged and gained attention in the field of noise control engineering. The addition of resonant structures to a flexible partition on a sub-wavelength scale enables a targeted frequency range of strongly reduced vibration and sound transmission. These structures have been widely studied and are typically analyzed using infinite periodic structure theory. The implications of nonsub-wavelength resonator spacing on the sound transmission loss of metamaterial partitions as well as on the representativeness of the infinite periodic structure modeling are, however, less well known. In this technical brief, it is shown that, although a shifted sound transmission loss peak can be predicted for partitions with nonsub-wavelength resonator spacing when using infinite periodic structure modeling, the sound transmission loss enhancement is not guaranteed for their finite structure counterparts.

Model-based force estimation is an emerging methodology in the mechatronic community given the possibility to exploit physically inspired high-fidelity models in tandem with ready-to-use cheap sensors. In this work, an inverse input load identification methodology is presented combining high-fidelity multibody models with a Kalman filter-based estimator and providing the means for an accurate and computationally efficient state-input estimation strategy. A particular challenge addressed in this work is the handling of the redundant state-description encountered in common multibody model descriptions. A novel linearization framework is proposed on the time-discretized equations in order to extract the required system model matrices for the Kalman filter. The presented framework is experimentally validated on a slider-crank mechanism. The nonlinear kinematics and dynamics are well represented through a rigid multibody model with lumped flexibilities to account for localized interaction phenomena among bodies. The proposed methodology is validated estimating the input torque delivered by a driver electro-motor together with the system states and comparing the experimental data with the estimated quantities. The results show the stability and accuracy of the estimation framework by only employing the angular motor velocity, measured by the motor encoder sensor and available in most of the commercial electro-motors. ispartof: Sensors vol:21 issue:13 ispartof: location:Switzerland status: Published online

A common requirement in optimal control problems arising in autonomous navigation is that the decision variables are constrained to be outside certain sets. Such set exclusion constraints represent obstacles that must be avoided by the motion system. This paper presents a simple and efficient method for solving optimization problems with general set exclusion and implicit constraints. The method embeds the set exclusion constraints in a quadratic penalty framework and solves the inner optimization problems using a proximal algorithm that deals directly with the implicit constraints.We derive convergence results for this method by transforming the generated iterates to points of are formulated problem with complementarity constraints. Furthermore, the practical application of the solution method is validated in numerical simulations of a model predictive control approach to path planning for a mobile robot. Finally, a runtime comparison with state-of-the-art solvers applied to the problem with complementarity constraints illustrates the efficiency of the proposed method. ispartof: Automatica vol:127 status: Published online

Metamaterials have recently emerged and shown potential as lightweight and compact noise and vibration solutions. By adding or embedding resonant structures to or in a flexible host structure on a sub-wavelength scale, stop bands can be created, which enable frequency ranges of strong vibration and noise attenuation. These often periodic structures are typically analyzed using infinite periodic structure theory, based on a representative unit cell model. The stop bands in metamaterials are generally analyzed by means of dispersion curves. For complex unit cell models, however, this rapidly becomes computationally expensive. Therefore, in this work, model order reduction is applied to finite element unit cell models for stop band predictions. In view of designing metamaterials for a targeted frequency range, the reduced order modeling approach is next introduced in a design optimization routine. The results show that the reduced order models for stop band predictions enable substantial gains in metamaterial analysis and fast metamaterial design optimization. ispartof: pages:2487-2501 ispartof: Proceedings of ISMA 2020 pages:2487-2501 ispartof: International Conference on Noise and Vibration Engineering - ISMA 2020 location:Leuven, Belgium date:7 Sep - 9 Sep 2020 status: published

Resonant metamaterials are a lightweight noise insulation solution due to their tunable stop band effect. In previous works, the authors have shown how resonant metamaterials can be manufactured and fully integrated into a thermoformed twin sheet panel. This work shows an design optimisation procedure for the resonant structure of the metamaterial panel, based on its modal effective mass. Additionally, foam is added in the core of the panel, to achieve high noise insulation performance at the high-frequency range, which is deteriorated by the slits introduced to create the resonant structures. Two panels are designed, targeting single and double stop bands. Their insertion loss is experimentally evaluated, showing a pronounced noise insulation performance at the stop band targeted frequency, and no loss of noise insulation in the high-frequency range thanks to the foam addition. Therefore, this work shows that resonant metamaterials can be designed through optimisation and work in synergy with classical solutions while keeping a lightweight design. ispartof: pages:2513-2524 ispartof: Proceedings of ISMA 2020 pages:2513-2524 ispartof: International Conference on Noise and Vibration Engineering - ISMA 2020 location:Leuven - Belgium date:7 Sep - 9 Sep 2020 status: accepted

ispartof: Proceedings of ISMA2020 including USD2020 ispartof: International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:7 Sep - 9 Sep 2020 status: published

© 2018 Elsevier Ltd In this work, the framework of isogeometric shell analysis is applied to the simulation of the dynamic behaviour of thin components measured by a 3D laser scanner. To this end, a B-spline surface is reconstructed to describe the mid-surface of the components and is used for the analysis. The exact thickness distribution is also described through the B-spline basis functions and is considered in the numerical integration. Two components manufactured through deep drawing are studied and the surface fitting procedure is adapted to their particular geometry. The results are finally validated through experimental testing of these components. ispartof: Computers & Structures vol:201 pages:15-25 status: published

In this work, we explore new parametric models of a sphere with rational Bézier patches. The geometry is represented as a spherical tessellation with various topologies. The tiles are degeneracy-free rational Bézier surfaces, obtained using a general composite mapping method. Five novel, topologically distinct tilings are described, four of which have conforming parameterizations. The mesh of the fifth tiling is nonconforming despite having equal interface knot vectors (intrinsic nonconformity). We apply these novel geometries in three case studies that are proposed as benchmark problems for C0- and C1-multipatch IGA methods. ispartof: Computer Methods in Applied Mechanics and Engineering vol:332 pages:255-279 status: published

Pantographic sheets are metamaterials constituted by two interconnected layers of straight fibers. One of the great features of these structures is that they are extremely elastically compliant toward large nonlinear deformations. To model pantographic lattices, Kirchhoff rods based on Euler–Bernoulli assumptions can be used. Otherwise, if the fibers are sufficiently dense, homogenization of the microstructure results in a two-dimensional second-order gradient continuum model. The discrete and continuum models have in common the fact that their energy terms depend on the second-order derivatives of the displacement field, such that the classical finite element method cannot be directly employed. We propose instead the use of the isogeometric analysis where the basis functions are endowed with a higher inter-element continuity, allowing the rotation-free discretization of these problems. The discrete and continuum models are compared to existing benchmarks and are found in excellent agreement, validating the proposed approach. ispartof: Continuum Mechanics and Thermodynamics vol:31 issue:4 pages:1-14 status: published

© 1982-2012 IEEE. An important bottleneck in the design, operation, and exploitation of mechatronic powertrains is the lack of accurate knowledge of broadband external loading. This is caused by the intrusive nature of regular torque measurements. This paper proposes a novel nonintrusive approach to obtain torsional load information on mechatronic powertrains. Online coupled state/input estimation is performed through an augmented nonlinear Kalman filter. This estimation approach exploits general lumped-parameter physics-based models in order to create a widely applicable framework. This paper considers both extended (EKF) and unscented Kalman filtering approaches. Contrary to previous works, no considerable difference in accuracy is obtained from experiments, with a considerably lower computational load for the EKF. This paper reveals the benefits of including rotational acceleration measurements from a theoretical perspective, which is demonstrated through the experimental validation. This drastically increases the broadband accuracy. The result of this paper is an accurate and noninvasive virtual torque sensor with a sufficiently broad bandwidth for use in condition monitoring, control, and future design optimization. ispartof: IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS vol:65 issue:3 pages:2378-2387 status: published

Wave propagation in complex periodic systems is often addressed with the Bloch theorem, and consists in applying periodic boundary conditions to a discretized unit cell. While this method has been developed for structures periodic by translation, in a recent work, for quasi-one-dimensional wave propagation, it has been shown that screw (translation plus rotation) and glide (translation plus reflection) periodicities can be accounted for as well, keeping the Cartesian coordinate system but revisiting the periodic boundary conditions. The goal of the present paper is to generalize this concept to quasi-two-dimensional wave propagation (two dimensional waves propagating in three dimensional structures). Dispersion relations for a set of reduced problems are then compared to results from the classical method, when available. By considering a smaller periodicity, the computational cost is decreased and the number of folding curves and non-interacting intersecting curves is reduced, improving their interpretability. While the size of a unit cell is divided by a factor two when glide symmetries are considered, this ratio is significantly increased for screw or rotational symmetries. Moreover, the proposed revisited Bloch method is applicable to screw symmetric structures that do not possess purely translational symmetries, and for which the classical method cannot be used (e.g. chiral nanotubes, longitudinally wrinkled helicoids). publisher: Elsevier articletitle: Bloch theorem with revised boundary conditions applied to glide, screw and rotational symmetric structures journaltitle: Computer Methods in Applied Mechanics and Engineering articlelink: http://dx.doi.org/10.1016/j.cma.2017.01.034 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved. ispartof: Computer Methods in Applied Mechanics and Engineering vol:318 pages:497-513 status: published

This paper presents a simple yet flexible method for coupling non-conforming NURBS patches in isogeometric frameworks. It consists of virtually refining bordering patches to derive coupling constraints in a master-slave formulation. These constraints are then enforced via a substitution method for condensation of the slave variables, thereby reducing the model size. In the special case of hierarchical meshes, the method results in an exact connection. For an arbitrary non-conforming configuration, the master-slave formulation takes the interface constraints into account in a least-squares sense. This yields an accurate weak coupling without overconstraining the interface. The coupling relationships only depend on the mesh itself and not on any problem-dependent parameters, allowing them to be generated in a pre-processing step with very limited numerical efforts. Besides this low computational cost, the main merit of the proposed method lies in its simplicity and robustness, yielding good results for arbitrarily strongly non-conforming patch configurations. Several numerical examples are studied for different problem types requiring C0- or C1-continuity, in particular time-harmonic acoustics and (dynamic) thin plate bending. Benchmarking of the proposed approach against existing similar techniques illustrates its superior accuracy and robustness. publisher: Elsevier articletitle: A robust patch coupling method for NURBS-based isogeometric analysis of non-conforming multipatch surfaces journaltitle: Computer Methods in Applied Mechanics and Engineering articlelink: http://dx.doi.org/10.1016/j.cma.2016.06.022 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved. ispartof: Computer Methods in Applied Mechanics and Engineering vol:316 pages:235-260 status: published

This paper investigates the influence of the boundary conditions on the stop band effect in finite locally resonant metamaterial beams. In a first step, a Timoshenko beam with tuned vibration absorbers is used to describe a metamaterial beam. The influence of different boundary conditions for beams with different lengths as well as of tuned vibration absorbers with different amounts of added mass or different tuned frequencies is assessed numerically. It is found that edge modes are present inside the stop band frequency region predicted by the unit cell analysis and these edge modes reduce the level of vibration attenuation achieved. Three solutions are analysed to reduce the effect of the edge modes: (i) varying the tuned frequency, (ii) the number or (iii) the positions of the individual tuned vibration absorbers added to the host structure. In a second step, the results of the numerical investigation are experimentally validated: the experimental results are in good agreement with the numerical results.

The loads to which a wind turbine gearbox is subjected during its lifetime can be a valuable source of information to decrease maintenance cost and downtime through enhanced monitoring, control and design. However, this load information is difficult to acquire since suitable direct load sensors are intrusive and expensive. Therefore, this paper focuses on indirect load measurement through a virtual sensing algorithm. The resulting virtual load sensor estimates the incoming load on the low speed planetary stage of the gearbox by combining strain measurements on the external surface of the ring gear with a physics-based model. The algorithm is deployed for real-time execution on low-cost embedded hardware to make a cost-effective load sensor. The effect of the configuration parameters of the virtual load sensor on the execution time and memory usage is examined in order to verify which configurations can be deployed. Since these configuration parameters also affect the estimation accuracy, the design of the virtual load sensor is tackled as a co-design problem. The resulting virtual load sensor, which is deployable for real-time execution, achieves an RMS estimation error of 0.6% in a numerical validation, using 4 strain gauges on the ring gear. ispartof: Journal of Physics : Conference Series vol:1618 ispartof: The Science of Making Torque from Wind (TORQUE 2020) location:Delft date:28 Sep - 2 Oct 2020 status: Published online

Most companies do not take assembly aspects of a product into account during the early design process. This often results in designs that are optimal from a performance point of view, but are hard or impossible to assemble. This leads to numerous design changes late in the product development process, causing significant extra costs. To solve this issue, a co-optimization framework is developed that takes into account the assemblability as a constraint during the performance optimization. The presented framework is applied to minimize the mass of a gearbox with constraints on the axle stiffness and the first resonance frequency of the housing, while also respecting a set of assembly rules. The assembly rules take into account the complexity of the assembly, for instance the number of unique standard parts used and geometric properties like weight and dimensions.In each iteration, the performance of the design is evaluated with a parametrized finite element model, while a numerical assemblability score of the current design is estimated based on the assembly STP file. The obtained performance and assemblability metrics and their combination serves as a constraints and objective function for the design optimization. ispartof: pages:2753-2762 ispartof: Proceeding of ISMA2020 including USD2020 pages:2753-2762 ispartof: ISMA-USD Noise and Vibration Engineering Conference 2020 location:Leuven, Belgium (Virtual event) date:7 Sep - 9 Sep 2020 status: published

This paper discusses the design and validation of a thermoformed locally resonant metamaterial panel tuned to attenuate the excitation of the first acoustic mode of a cavity. Moreover, it brings resonant metamaterials closer to industrial realisations by exploiting a cheap and widely used production process. The concept is explained, and it is shown how the stop band can be tuned to a targeted frequency. Additionally, multiple stop bands are achieved by combining two differently tuned locally resonant parts in the same metamaterial panel. The proposed thermoformed metamaterial panels have similar weight as the original panel and superior experimentally evaluated insertion loss performance in the frequency range of the stop band. ispartof: APPLIED ACOUSTICS vol:156 pages:78-82 status: published

Vibro-acoustic locally resonant metamaterials with structural stop band behaviour can lead to a strongly increased sound transmission loss in a targeted frequency range. This work assesses the impact of damping in the constituents of metamaterial plates on their acoustic insulation performance by means of infinite periodic and finite structure modelling. Besides applying the hybrid Wave Based - Finite Element unit cell method for infinite plates and the Finite Element Method for finite plates, qualitative dispersion curve based predictions are extended to quantitative sound transmission loss approximations by introducing a dispersion curve based equivalent plate method. Both an idealised and a realisable locally resonant metamaterial plate are analysed. Damping in the resonators in particular is found to have an important impact in and around the stop band, reducing the sound transmission loss peak, but improving the subsequent dip and reducing resonant transmission in a broadening frequency range around the stop band. The damping influenced sound transmission loss predictions for the realisable locally resonant metamaterial plate are experimentally validated by means of insertion loss measurements. It is shown that, by including damping in the infinite periodic structure modelling, acoustic insulation performance predictions with improved accuracy are obtained. ispartof: JOURNAL OF SOUND AND VIBRATION vol:461 status: Published online

Stringent regulations for CO2 emissions and noise pollution reduction demand lighter and improved Noise, Vibration Harshness (NVH) solutions in automotive industries. Designing light, compact and, at the same time, improved NVH solutions is often a challenge, as low noise and vibration levels often require heavy and bulky additions, especially to be effective in the low frequency regime. Recently, locally resonant metamaterials have emerged among the novel NVH solutions because of their performant NVH properties combined with lightweight and compact design. Due to the characteristic of stop band behavior, frequency ranges where free wave propagation is inhibited, metamaterials can beat the mass law, be it at least in some tunable frequency ranges. Previously the authors demonstrated how metamaterials can reduce the vibrations in a simplified shock tower upon shaker excitation. In this work, the authors apply the metamaterial concept on the real rear shock towers of a vehicle. In order to be able to benchmark the solution, a test vehicle is chosen, which is equipped in its commercial version with a 1.46 kg tuned vibration absorber (TVA) on each of the rear shock towers as NVH solution. It is shown that the metamaterial solution allows to achieve similar interior NVH performance, while reducing the added mass by 48%. The metamaterial additions are realized through additive manufacturing and they are designed to be effective around 190 Hz, as was the case for the original solution. Both experimental results and numerical validation of a road test are presented. ispartof: SAE Technical Papers ispartof: location:Grand Rapids (MI), USA status: published

The compressive sensing-moving horizon estimator (CS-MHE) is an approach for joint state/input estimation. It integrates compressive sensing principles into a moving horizon estimator, enabling to exploit shape functions to model an input, resulting in better observability and wider input bandwidth in comparison to other input models. With the final aim of using the CS-MHE for the estimation of forces and torques in rotating machinery which exhibit some form of periodicity, the authors have recently investigated Fourier shape functions. A first experimental validation showed very accurate estimation under the hypothesis of no spectral leakage, i.e., the MHE window, the sampling rate and the Fourier dictionary match a known input periodicity, with the input consisting of few sinusoidal components. This paper discusses the problem of spectral leakage that can result if the MHE window does not match the signal periodicity. In particular, we show how to remove the link between the MHE window and a Fourier dictionary, we discuss how the autocorrelation can be employed to detect the periodicity and we list further possible alternatives to enhance a sparse solution. The discussion is supported by numerical and experimental investigations.

A Wind Turbine (WT) is a complex system in which many sub-systems interact and influence one another. To properly predict its behavior through simulation, a system-level modelling approach is necessary. A system-level model can capture the complex multiphysical interactions between sub-systems. Port-based modelling tools (e.g. AMESim, Simscape) offer an appealing solution to build such system-level models, as the assembly of a model is simplified to selecting and connecting a number of blocks. The mechanical models available in these port-based tools are often limited. Rotary shafts are often represented using a lumped rotational inertia with a single Degree of Freedom (DOF). This paper presents an approach that allows embedding more detailed flexible multibody models into a port-based model. The multibody model contains geometrical details in 3D, where the port-based framework is inherently 1D; therefore this technique is called 1D-3D Nesting. This allows achieving higher modelling accuracy for critical components while retaining the advantages of the port-based approach for system-level modelling, and a reasonable computation cost for dynamic simulations. The technique is applied on a case of industrial complexity, the NREL WT drivetrain. Nested 3D models of two shafts are incorporated into a system-level model of the drivetrain which also includes the rotor aerodynamics, gearbox, generator and controller. Using this model, the response of the WT during a Low Voltage Ride Through (LVRT) is simulated. The effect of including the nested 3D models on the torsional dynamics of the turbine and the resulting bearing forces is assessed by comparing the simulation to a baseline model. ispartof: pages:523-537 ispartof: Conference for Wind Power Drives pages:523-537 ispartof: Conference for Wind Power Drives location:Aachen date:12 Mar - 13 Mar 2019 status: published

To enhance the sound insulation performance of double panel partitions at their mass-air-mass resonance frequency, novel compact and low-mass solutions are sought. This paper investigates the use of the locally resonant vibro-acoustic metamaterial concept as a possible solution. The metamaterial solution is applied to one panel of a double panel partition in order to enhance the sound transmission loss at the mass-air-mass resonance. To design the metamaterial solution and predict its sound transmission loss performance, an extension of the multiple reflection theory is proposed, incorporating the dynamic mass of a metamaterial panel. The latter is obtained from the metamaterial plate dispersion curves, calculated using finite element based unit cell modeling. The designed metamaterial solution is manufactured and its insertion loss is measured. The novel design outperforms the original double panel and an equivalent total mass double panel configuration in the targeted mass-air-mass resonance frequency region. The predictions obtained with the proposed method are in good agreement with the experimentally obtained results. This demonstrates the potential of the metamaterial solution to enhance the acoustic insulation at the mass-air-mass resonance and indicates that the proposed method allows a fast, simple and representative indication of their acoustic insulation performance. ispartof: Journal of Sound and Vibration vol:442 pages:28-44 status: published

With the emergence of isogeometric analysis (IGA), numerical rotation-free solutions to high-order partial differential equations (PDEs) are facilitated. Indeed, IGA allows the use of high-order-continuous basis functions through the domain. For periodic systems, the Bloch theorem is useful for analyzing wave propagation, restricting the analysis to a single unit cell and applying periodic boundary conditions. However, in the literature, boundary conditions are only accounting for C0-continuity, and we propose in the present paper to enforce the G1-continuity as well or to maintain the angle in case of unit cells meeting at kinks. While G1-continuity is enforced by maintaining the collinearity between adjacent control points, in the presence of kinks, variations of the field derived with respect to opposite in-plane edge normals are linked by the Rodrigues rotation matrix. This method applied at collocation points belonging to the unit cell edges can be viewed as a novel approach of coupling multi-patch geometries with kinks, avoiding the use of nonlinear multipliers or additional bending strip elements. Both transfer-matrix and indirect methods of the Bloch theorem are investigated, for respectively quasi-one and quasi-two-dimensional wave propagation in periodic structures discretized by NURBS-based IGA. Dispersion curves of a set of numerical problems treating isogeometric rotation-free extensible elastica (beams) and Kirchhoff-Love shells are then analyzed. publisher: Elsevier articletitle: Bloch theorem for isogeometric analysis of periodic problems governed by high-order partial differential equations journaltitle: Computer Methods in Applied Mechanics and Engineering articlelink: http://dx.doi.org/10.1016/j.cma.2016.09.015 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved. ispartof: Computer Methods in Applied Mechanics and Engineering vol:311 pages:743-763 status: published

This paper presents a second order optimization method based on the WFEM framework that enables the optimization of finite 1D periodic structures and 2D infinite ones. While optimization at the unit cell level has been done in previous studies, it did not account for the boundary conditions and excitation on the system, which might have an important influence on its dynamics. The proposed methodology exploits semi-analytical derivatives in an optimization algorithm that combines line search and trust region methods. It is tested and validated in a parameter identification procedure and subsequently used to minimize the mean square velocity of metabeams with clamped free boundary conditions. Finally, it is applied to the optimization of the sound transmission loss of a metapanel in the structural-acoustic coincidence region. The proposed scheme is versatile and can be used in a wide range of applications including, model updating, homogenization, design optimization and possibly damage detection. ispartof: Mechanical Systems And Signal Processing vol:139 status: Published online

ispartof: pages:3761-3776 ispartof: COMPDYN 2019 Proceedings vol:2 pages:3761-3776 ispartof: 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2019) location:Crete status: Published online

This paper disseminates the use of a coupled 1D simulation-estimation framework employed for multi-actuated ground vehicle tyre force virtual sensing. The forces generated in the tyre contact patches govern the vehicle motion and behaviour on the road. Therefore, they are highly relevant for Advanced Driver Assistance Systems (ADAS) and Automated Driving (AD) technologies, especially when it comes to ensuring vehicle stability and driving safety in extreme manoeuvres. However, some ADAS and AD features require accurate and robust estimation of additional vehicle dynamics related quantities. Thus, this paper proposes a framework for the consistent use of 1D vehicle models of different complexity together with state-of-the-art estimation techniques to enable joint state, disturbance, parameter (SDP) estimation. ispartof: 2019 IEEE International Conference on Connected Vehicles and Expo (ICCVE) proceedings ispartof: 2019 IEEE International Conference on Connected Vehicles and Expo (ICCVE) location:Graz, Austria date:4 Nov - 8 Nov 2019 status: Published online

The bending wave stop band behavior of locally resonant metamaterial and phononic crystal plates can strongly improve the vibration performance of flexible plates in targeted frequency ranges. Their acoustic insulation performance, however, is found to strongly depend on the stop band mechanism, also influencing the frequency range of improvement. While sound transmission loss improvements are predicted for both infinite periodic plates, the finite phononic crystal plate performance can differ significantly.

Double panel partitions with a foam core suffer from a poor sound transmission loss at the mass-spring-mass resonance frequency. This paper investigates the use of vibro-acoustic resonant metamaterials as a solution to improve the acoustic insulation performance for this vibro-acoustic problem while adding only 8% of mass to the complete double panel. To design the metamaterial, unit cell analysis is applied to calculate dispersion curves and predict the stop band behaviour, while the sound transmission loss is predicted with Heckl’s model extended with the equivalent dynamic mass of the metamaterial. The dynamic mass is obtained from the dispersion curves analysis, which allows to take into account complex and realizable resonator geometries. The designed metamaterial double panel is realized and its experimentally measured insertion loss shows a strong improvement around the mass-spring-mass resonance of the original double panel. The predicted insulation performance agrees well with the measured performance, validating the proposed method. ispartof: pages:3111-3123 ispartof: Proceedings of ISMA 2018 pages:3111-3123 ispartof: International Conference on Noise and Vibration Engineering - ISMA 2018 location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: published

In many mechanical applications, a design optimization is performed on the frequency response functions of the mechanical system. In this work, a novel model reduction technique is explored for the parametric analysis of the frequency response functions of dynamical mechanical systems. This approach entails two novel aspects. First, a super-local reduced order basis is introduced which allows models of much lower order compared to models obtained with single, frequency independent reduced order basis approaches. Secondly, a novel hyper-reduction scheme is introduced which selects a subset of the considered, discrete frequency domain and computes the corresponding interpolation matrix. During the online phase, the full frequency domain response is reconstructed by interpolating between these sampled frequency lines. The proposed approach is validated numerically on an academic mass-spring-damper system and shows promising results. ispartof: pages:2461-2468 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA2018) and the International Conference on Uncertainty in Structural Dynamics (USD2018) pages:2461-2468 ispartof: ISMA 2018 International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: published