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See detailNitsche’s method method for mixed dimensional analysis: conforming and non-conforming continuum-beam and continuum-plate coupling
Nguyen, VP; Kerfriden, Pierre; Claus, SPA et al

in Computer Methods in Applied Mechanics & Engineering (2014)

A Nitche’s method is presented to couple different mechanical models. They include coupling of a solid and a beam and of a solid and a plate. Both conforming and non-conforming formulations are presented ... [more ▼]

A Nitche’s method is presented to couple different mechanical models. They include coupling of a solid and a beam and of a solid and a plate. Both conforming and non-conforming formulations are presented. In a non-conforming formulation, the structure domain is overlapped by a refined solid model which is needed to either get more accuracy or to capture highly nonlinear events. Applications can be found in multi-dimensional analyses in which parts of a structure are modeled with solid elements and others are modeled using a coarser model with beam and/or plate elements. Discretisations are performed using both standard Lagrange elements and high order NURBS (Non Uniform Rational Bsplines) based isogeometric elements. We present various examples to demonstrate the performance of the method. [less ▲]

Detailed reference viewed: 260 (17 UL)
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See detailA node-based smoothed extended finite element method (NS-XFEM) for fracture analysis
Vu-Bac, N.; Nguyen-Xuan, H.; Chen, L. et al

in Computer Modeling in Engineering & Sciences (2011), 73(4), 331-355

This paper aims to incorporate the node-based smoothed finite element method (NS-FEM) into the extended finite element method (XFEM) to form a novel numerical method (NS-XFEM) for analyzing fracture ... [more ▼]

This paper aims to incorporate the node-based smoothed finite element method (NS-FEM) into the extended finite element method (XFEM) to form a novel numerical method (NS-XFEM) for analyzing fracture problems of 2D elasticity. NS-FEM uses the strain smoothing technique over the smoothing domains associated with nodes to compute the system stiffness matrix, which leads to the line integrations using directly the shape function values along the boundaries of the smoothing domains. As a result, we avoid integration of the stress singularity at the crack tip. It is not necessary to divide elements cut by cracks when we replace interior integration by boundary integration, simplifying integration of the discontinuous approximation. The key advantage of the NS-XFEM is that it provides more accurate solutions compared to the XFEM-T3 element. We will show for two numerical examples that the NS-XFEM significantly improves the results in the energy norm and the stress intensity factors. For the examples studied, we obtain super-convergent results. [less ▲]

Detailed reference viewed: 31 (1 UL)
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See detailA node-based smoothed finite element method with stabilized discrete shear gap technique for analysis of Reissner-Mindlin plates
Nguyen-Xuan, H.; Rabczuk, T.; Nguyen-Thanh, N. et al

in Computational Mechanics (2010), 46(5), 679-701

In this paper, a node-based smoothed finite element method (NS-FEM) using 3-node triangular elements is formulated for static, free vibration and buckling analyses of Reissner-Mindlin plates. The discrete ... [more ▼]

In this paper, a node-based smoothed finite element method (NS-FEM) using 3-node triangular elements is formulated for static, free vibration and buckling analyses of Reissner-Mindlin plates. The discrete weak form of the NS-FEM is obtained based on the strain smoothing technique over smoothing domains associated with the nodes of the elements. The discrete shear gap (DSG) method together with a stabilization technique is incorporated into the NS-FEM to eliminate transverse shear locking and to maintain stability of the present formulation.Aso-called node-based smoothed stabilized discrete shear gap method (NS-DSG) is then proposed. Several numerical examples are used to illustrate the accuracy and effectiveness of the present method. [less ▲]

Detailed reference viewed: 67 (0 UL)
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See detailNonlinear Model Predictive Control for Ecological Driver Assistance Systems in Electric Vehicles
Sajadi Alamdari, Seyed Amin UL; Voos, Holger UL; Darouach, Mohamed

in Robotics and Autonomous Systems (2018)

Detailed reference viewed: 92 (12 UL)
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See detailNonlinear Observation and Control of a Lightweight Robotic Manipulator Actuated by Shape Memory Alloy (SMA) Wires
Quintanar Guzman, Serket UL

Doctoral thesis (2019)

In the last decade, the industry of Unmanned Aerial Vehicles (UAV) has gone through immense growth and diversification. Nowadays, we find drone based applications in a wide range of industries, such as ... [more ▼]

In the last decade, the industry of Unmanned Aerial Vehicles (UAV) has gone through immense growth and diversification. Nowadays, we find drone based applications in a wide range of industries, such as infrastructure, agriculture, transport, among others. This phenomenon has generated an increasing interest in the field of aerial manipulation. The implementation of aerial manipulators in the UAV industry could generate a significant increase in possible applications. However, the restriction on the available payload is one of the main setbacks of this approach. The impossibility to equip UAVs with heavy dexterous industrial robotic arms has driven the interest in the development of lightweight manipulators suitable for these applications. In the pursuit of providing an alternative lightweight solution for the aerial manipulators, this thesis proposes a lightweight robotic arm actuated by Shape Memory Alloy (SMA) wires. Although SMA wires represent a great alternative to conventional actuators for lightweight applications, they also imply highly nonlinear dynamics, which makes them difficult to control. Seeking to present a solution for the challenging task of controlling SMA wires, this work investigates the implications and advantages of the implementation of state feedback control techniques. The final aim of this study is the experimental implementation of a state feedback control for position regulation of the proposed lightweight robotic arm. Firstly, a mathematical model based on a constitutive model of the SMA wire is developed and experimentally validated. This model describes the dynamics of the proposed lightweight robotic arm from a mechatronics perspective. The proposed robotic arm is tested with three output feedback controllers for angular position control, namely a PID, a Sliding Mode and an Adaptive Controller. The controllers are tested in a MATLAB simulation and finally implemented and experimentally tested in various different scenarios. Following, in order to perform the experimental implementation of a state feedback control technique, a state and unknown input observer is developed. First, a non-switching observable model with unknown input of the proposed robotic arm is derived from the model previously presented. This model takes the martensite fraction rate of the original model as an unknown input, making it possible to eliminate the switching terms in the model. Then, a state and unknown input observer is proposed. This observer is based on the Extended Kalman Filter (EKF) for state estimation and sliding mode approach for unknown input estimation. Sufficient conditions for stability and convergence are established. The observer is tested in a MATLAB simulation and experimentally validated in various different scenarios. Finally, a state feedback control technique is tested in simulation and experimentally implemented for angular position control of the proposed lightweight robotic arm. Specifically, continuous and discrete-time State-Dependent Riccati Equation (SDRE) control laws are derived and implemented. To conclude, a quantitative and qualitative comparative analysis between an output feedback control approach and the implemented state feedback control is carried out under multiple scenarios, including position regulation, position tracking and tracking with changing payloads. [less ▲]

Detailed reference viewed: 81 (7 UL)
See detailNormative Multiagent Systems: Guest Editors' Introduction
Boella, Guido; Pigozzi, Gabriella UL; Singh, Munindar P. et al

in Logic Journal of the IGPL (2010), 18(1), 13

Detailed reference viewed: 96 (0 UL)
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See detailNovel C-ITS support for Electric Buses with Opportunity Charging
Seredynski, Marcin; Viti, Francesco UL

in Proceedings of IEEE-ITS Conference (2017)

Detailed reference viewed: 71 (5 UL)
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See detailA novel numerical integration technique over arbitrary polygons
Natarajan, Sundararajan; Mahapatra, D Roy; Bordas, Stéphane UL et al

Scientific Conference (2009, April)

In this paper, a new numerical integration technique [1] on arbitrary polygons is presented. The polygonal do- main is mapped conformally to the unit disk using Schwarz-Christoffel mapping [2] and a ... [more ▼]

In this paper, a new numerical integration technique [1] on arbitrary polygons is presented. The polygonal do- main is mapped conformally to the unit disk using Schwarz-Christoffel mapping [2] and a midpoint quadrature rule defined on the unit circle is used. This method eliminates the need for a two level isoparametric mapping usuall required [3]. Moreover the positivity of the Jacobian is guaranteed. We present numerical results for a few benchmark problems in the context of polygonal finite elements that show the effectiveness of the method. [less ▲]

Detailed reference viewed: 94 (0 UL)
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See detailA Null-Space metric for the analysis of partial network observability in sensor location problems
Rinaldi, Marco; Viti, Francesco UL; Corman, Francesco

Scientific Conference (2013)

Detailed reference viewed: 86 (0 UL)
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See detailNumerical analysis of free-surface flow through rotating machines
Schippke, Henning; Zilian, Andreas UL

Presentation (2013)

In the context of the transformation process currently taking place in the energy production sector, energy gained from renewable power sources shall replace the present mixture, which mostly relies on ... [more ▼]

In the context of the transformation process currently taking place in the energy production sector, energy gained from renewable power sources shall replace the present mixture, which mostly relies on fossil burnings. Therefore, in the future most of the energy shall be gained by harvesting power from sun, wind or water, geothermal heat or biomass. In case of converting energy from wind into electrical power wind turbines are used in general, while hydropower turbines are the state-of-the-art machinery to derive energy from running water. In order to convert the potential energy from running water as well water wheels pose the method of choice. Turbines in air or water represent mechanically a two-field system, in which the structure of the turbine is surrounded by a streaming fluid. Due to the elasticity of the rotor blades the stresses of the fluid onto the structure deform the blades, which in return yield a time-dependent flow domain. Therefore turbines in a streaming fluid represent a typical example of fluid-structure interaction. Furthermore, in case of water wheels the surrounding air as third field and additional fluid phase comes into play introducing a free surface. In this contribution the governing equations of incompressible fluid flow are presented using primal variables and discretised via the space-time finite element method [3]. The discretised model equations of the fluid are stabilised using an SUPG/PSPG approach. Shape and test functions are continuous within the space-time slabs, while across the space- time slabs the shape and test functions are continuous only in space, but discontinuous in time yielding a time-discontinuous Galerkin approach. Due to the moving rotor blades a mesh moving technique needs to be incorporated into the computational set-up. Considering the occurring large but regular displacements of the flow boundary arising from the rotating rotor blades the shear-slip mesh update method (SSMUM) [1] as discontinuous mesh moving technique is applied. In case of water wheels the free surface is described implicitly via a Level-Set function [2] yielding a single fluid phase with almost discontinuous density and viscosity. The verification and validation of the developed numerical scheme is carried out with the help of computing classical benchmark problems as well as via a comparison to existing experimental data. [less ▲]

Detailed reference viewed: 77 (3 UL)
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See detailNumerical analysis of the inclusion-crack interaction by the extended finite element method
Natarajan, S; Kerfriden, P; Mahapatra, D Roy et al

in International Journal for Computational Methods in Engineering Science and Mechanics (2014)

One of the partition of unity methods, the extended finite ele- ment method (XFEM), is applied to study the inclusion-crack in- teractions in an elastic medium. Both the inclusions and the crack are ... [more ▼]

One of the partition of unity methods, the extended finite ele- ment method (XFEM), is applied to study the inclusion-crack in- teractions in an elastic medium. Both the inclusions and the crack are modelled within the XFEM framework. A structured quadri- lateral mesh is used and the influence of crack length, the number of inclusions, and the geometry of the inclusions on the crack tip stress field are numerically studied. The interaction integral for non-homogeneous materials is used to compute the stress intensity factors ahead of the crack tip. The accuracy and flexibility of the XFEM is demonstrated by various numerical examples. [less ▲]

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See detailNumerical evaluation of buckling behaviour induced by compression on patch-repaired composites
Deng, Jian; Zhou, Guangming; Bordas, Stéphane UL et al

in Composite Structures (2017), 168

A progressive damage model is proposed to predict buckling strengths and failure mechanisms for both symmetric and asymmetric patch repaired carbon-fibre reinforced laminates subjected to compression ... [more ▼]

A progressive damage model is proposed to predict buckling strengths and failure mechanisms for both symmetric and asymmetric patch repaired carbon-fibre reinforced laminates subjected to compression without lateral restrains. Solid and cohesive elements are employed to discretize composite and adhesive layers, respectively. Coupling with three dimensional strain failure criteria, an energy-based crack band model is applied to address the softening behaviour in composites with mesh dependency elimination. Both laminar and laminate scaled failure are addressed. Patch debonding is simulated by the cohesive zone model with a trapezoidal traction–separation law applied for the ductile adhesive. Geometric imperfection is introduced into the nonlinear analysis by the first order linear buckling configuration. Regarding strengths and failure patterns, the simulation demonstrates an accurate and consistent prediction compared with experimental observations. Though shearing is the main contributor to damage initiation in adhesive, stress analysis shows that lateral deformation subsequently reverses the distribution of normal stresses which stimulates patch debonding at one of the repair sides. The influence of patch dimensions on strengths and failure mechanisms can be explained by stress distributions in adhesive and lateral deformation of repairs. Comparison between symmetric and asymmetric regarding strength and failure modes shows that structural asymmetry can intensify lateral flexibility. This resulted in earlier patch debonding and negative effects on strengths. [less ▲]

Detailed reference viewed: 63 (2 UL)
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See detailNumerical integration over arbitrary polygonal domains based on Schwarz-Christoffel conformal mapping
Natarajan, S.; Bordas, Stéphane UL; Roy mahapatra, D.

in International Journal for Numerical Methods in Engineering (2009), 80(1), 103-134

This paper presents a new numerical integration technique on arbitrary polygonal domains. The polygonal domain is mapped conformally to the unit disk using Schwarz-Christoffel mapping and a midpoint ... [more ▼]

This paper presents a new numerical integration technique on arbitrary polygonal domains. The polygonal domain is mapped conformally to the unit disk using Schwarz-Christoffel mapping and a midpoint quadrature rule defined on this unit disk is used. This method eliminates the need for a two-level isoparametric mapping usually required. Moreover, the positivity of the Jacobian is guaranteed. Numerical results presented for a few benchmark problems in the context of polygonal finite elements show that the proposed method yields accurate results. © 2009 John Wiley & Sons, Ltd. [less ▲]

Detailed reference viewed: 199 (0 UL)
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See detailNumerical integration over arbitrary surfaces in partition of unity finite elements
Natarajan, Sundararajan; dal Pont, Stefano; Hung, Nguyen-Xuan et al

Scientific Conference (2009, September)

Detailed reference viewed: 112 (0 UL)
See detailNumerical Investigation into the Primary Breakup of Liquid Jets and Sheets
Kannan, Kumar UL

Doctoral thesis (2012)

Detailed reference viewed: 123 (3 UL)
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See detailNumerical methods for fracture/cutting of heterogeneous materials
Sutula, Danas UL; Agathos, Konstantinos UL; Ziaei Rad, Vahid UL et al

Presentation (2016, December)

Detailed reference viewed: 174 (15 UL)
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See detailNumerical Modeling of Flow-Driven Piezoelectric Energy Harvesters
Ravi, Srivathsan UL; Zilian, Andreas UL

Scientific Conference (2016, June 09)

A specific class of energy harvester devices for renewable energy resources is investigated, that allow conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations of a piezo ... [more ▼]

A specific class of energy harvester devices for renewable energy resources is investigated, that allow conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations of a piezo-ceramic composite structure positioned in the flow field [3,4]. In this way, potentially harmful flow fluctuations are harnessed to provide independent power supply to small electrical devices. In order to harvest energy from fluid flows by means of piezoelectric materials the kinetic energy of the fluid first has to be transformed to cyclic straining energy of the piezoelectric material which is then transformed to electrical energy under the presence of an attached electrical circuit representing the powered electrical device or charged battery. This energy converter technology simultaneously involves the interaction of a composite structure and a surrounding fluid, the electric charge accumulated in the piezo-ceramic material and a controlling electrical circuit. In order to predict the efficiency and operational properties of such future devices and to increase their robustness and performance, a mathematical and numerical model of the complex physical system is required to allow systematic computational investigation of the involved phenomena and coupling characteristics. The research is devoted to introducing a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by the space-time finite element method based on a mixed velocity-stress/rate form of the potential-dielectric displacement framework. The space-time finite element [2,3] model incorporates a novel method to enforce equipotentiality on the electrodes covering the piezoelectric patches, making the charge unknowns naturally appear in the formulation. This enables to adapt any type of electrical circuit added to the electromechanical problem. To validate the formulation, the case of piezoelectric triple layer EHD driven by base excitations, as described in [1] is chosen. The closed-form solution from [1] is compared to numerical solution proposed in this work. The variation of the electric potential through the thickness of the piezoelectric patch, assumed to be linear in many closed-form solutions, is shown to be quadratic in nature. The research contributes to the mathematical modeling and numerical discretization of complex multi- physics system in an efficient way which facilitates an ideal basis for precise and transient coupling. This may lead to improved convergence and numerical efficiency in comparison with portioned approaches. This methodology also provides new insights and in-depth understanding on design requirements on such energy harvesting devices in terms of their robustness and efficiency. [less ▲]

Detailed reference viewed: 122 (18 UL)
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See detailNumerical Modelling of Piezoelectric Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

Scientific Conference (2013)

This paper introduces a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled ... [more ▼]

This paper introduces a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by the space-time finite element method based on a mixed velocity-stress/rate form of the potential-dielectric displacement framework. The results will be compared to the simple cases with closed-form solution available from literature. [less ▲]

Detailed reference viewed: 117 (16 UL)
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See detailNumerical Modelling of Piezoelectric Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

in 2nd ECCOMAS Young Investigators Conference (YIC 2013) (2013)

This paper introduces a monolithic approach that provides simultaneous solution to the coupled system which involves volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for ... [more ▼]

This paper introduces a monolithic approach that provides simultaneous solution to the coupled system which involves volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by space-time nite element method based on mixed velocity-stress/ rate of potential-dielectric displacement setting. The results will be compared to the simple cases with closed-form solution available from literature. [less ▲]

Detailed reference viewed: 96 (17 UL)