Toward fluid-structure-piezoelectric simulations applied to flow-induced energy harvesters

Poster (2019, November 15)

The subject deals with the simulation of flow-induced energy harvesters. We focus in particular on the modelling of autonomous piezo-ceramic power generators to convert ambient fluid-flow energy into ... [more ▼]

The subject deals with the simulation of flow-induced energy harvesters. We focus in particular on the modelling of autonomous piezo-ceramic power generators to convert ambient fluid-flow energy into electrical energy. The vibrations of an immersed electromechanical structure with large amplitude have to be taken into account in that case. One challenge consists in modelling and predicting the nonlinear coupled dynamic behaviour for the improved design of such devices. The set of governing equations is expressed in integral form, using the method of weighted residuals, and discretized with finite elements using the open source package FEniCS. Preliminary results of separated problems using FEniCS will be detailed and discussed (e.g. Navier-Stokes with or without moving meshes, nonlinear elasticity, aeroelasticity and electromechanical coupling). The objective is to validate each problem independently before coupling all the phenomena in a monolithic framework. Those simulations involve nonlinearities at many levels of modeling. The perspective of using reduced order models to limit the computational cost (in time and memory) will be discussed in an outlook to this work. [less ▲]

Poroelastic material characterisation by means of Artificial Neural Network

Presentation (2019, November 13)

Poroelastic problems require multiscale and multiphysics techniques that are expensive and time-consuming, which result in either several simplifications or costly experimental tests. The latter motivates ... [more ▼]

Poroelastic problems require multiscale and multiphysics techniques that are expensive and time-consuming, which result in either several simplifications or costly experimental tests. The latter motivates us to develop a more efficient approach to address more complex problems with an acceptable computational cost. In this manuscript, first, the necessary equations derived from Asymptotic homogenisation for poroelastic media are mentioned. Then, the variational formulation of the cell problems is carried out and solved by the open-source FE package FEniCS. This is followed by presenting the advantages and downsides of macroscale properties identification via asymptotic homogenisation and the application of Artificial Neural Network (ANN) to solve the issues stated as its downsides by means of bypassing the process of solving the cell problems. Finally, we study a practical example, namely, spatial dependent porosity (in macroscale) to demonstrate the feasibility of using the provided framework to include more details. Further applications, including growth and remodelling, are subjects of future articles. [less ▲]

Optimum Design for Sparse FDA-MIMO Automotive Radar

in Sedighi, Saeid; Shankar, Bhavani; Mishra, Kumar Vijay (Eds.) et al Optimum Design for Sparse FDA-MIMO Automotive Radar (2019, November 03)

Automotive radars usually employ multiple-input multiple-output (MIMO) antenna arrays to achieve high azimuthal resolution with fewer elements than a phased array. Despite this advantage, hardware costs ... [more ▼]

Automotive radars usually employ multiple-input multiple-output (MIMO) antenna arrays to achieve high azimuthal resolution with fewer elements than a phased array. Despite this advantage, hardware costs and desired radar size limits the usage of more antennas in the array. Similar trade-off is encountered while attempting to achieve high range resolution which is limited by the signal bandwidth. However, nowadays given the demand for spectrum from communications services, wide bandwidth is not readily available. To address these issues, we propose a sparse variant of Frequency Diverse Array MIMO (FDA-MIMO) radar which enjoys the benefits of both FDA and MIMO techniques, including fewer elements, decoupling, and efficient joint estimation of target parameters. We then employ the Cram\'{e}r-Rao bound for angle and range estimation as a performance metric to design the optimal antenna placement and carrier frequency offsets for the transmit waveforms. Numerical experiments suggest that the performance of sparse FDA-MIMO radar is very close to the conventional FDA-MIMO despite 50\% reduction in the bandwidth and antenna elements. [less ▲]

Inbetriebnahme und Monitoring einer Feldtestfläche zur außenliegenden Lufttemperierung

in Völker, Conrad; Kornadt, Oliver; Jentsch, Mark (Eds.) et al Schriftenreihe der Professur Bauphysik, Bauphysiktage 2019 in Weimar - Bauphysik in Forschung und Praxis (2019, September 25)

Der Beitrag ist inhaltlich dem Forschungsprojekt „Low Exergy Utilisation - Einsatz von außen-liegender Wandtemperierung bei der Gebäudesanierung - Feldtest, CO2- Wärmepumpe mit Eisspeicher“ (kurz LEXU II ... [more ▼]

Der Beitrag ist inhaltlich dem Forschungsprojekt „Low Exergy Utilisation - Einsatz von außen-liegender Wandtemperierung bei der Gebäudesanierung - Feldtest, CO2- Wärmepumpe mit Eisspeicher“ (kurz LEXU II, Förderkennzeichen 0327370Y) zugeordnet. Im Rahmen des Pro-jektes wurde ein Großdemonstrator mit außenliegender Wand- und Lufttemperierung (kurz aWT & aLT) zusammen mit einem niederexergetischen Versorgungssystem, bestehend aus Eisspeicher, Wärmepumpe und PVT-Hybridkollektoren realisiert. Zur Heizperiode 2018/19 wurde die „Feldtestanlage“ in Betrieb genommen, sodass derzeit Messdaten generiert wer-den. In dem Forschungsprojekt wird der Demonstrator über eine Heizperiode und eine Kühl-periode messtechnisch begleitet und ausgewertet. Dabei wird der Großdemonstrator und alle Komponenten umfassend messtechnisch ausgewertet (~300 Messwerte). Ziel des Beitrags ist eine Darstellung der Grundlagen der außenliegenden Lufttemperierung, als niederexergetische und schnell regelbare Ergänzung zur außenliegenden Wandtemperie-rung. Bei der außenliegenden Lufttemperierung wird zwischen thermisch aktivierter Be-standswand und neuem Wärmedämm-Verbundsystem ein Luftspalt geschaffen, durch den Außenluft geführt und temperiert werden kann. Diese temperierte Außenluft wird dem dahin-terliegenden Raum (im Feldtest ein Büroraum mit rund 20 m² Grundfläche und zwei Arbeits-plätzen) als Frischluft zur Verfügung gestellt. Aufbauend auf den Grundlagen wird die Inbe-triebnahme der bereits umgesetzten Feldtestfläche mit möglichen Regelstrategien geschildert. Abschließend sollen erste Messergebnisse der Feldtestfläche dargestellt und diskutiert wer-den. Interessant sind hier vor allem (im Vergleich zur außenliegenden Wandtemperierung) die möglichen Zeitkonstanten und die erreichbaren Wärmeströme nach Innen (z.B. mögliche Wärmeübertragung als Kombination aus Konvektion im Luftspalt und Wärmeleitung durch die Bestandswand). Themengebiet: Energieeffiziente Gebäude & Bauphysik und Sanierung & Behaglichkeit und Raumklima [less ▲]

Interview with Prof. Dr Jane Winters (School of Advanced Study, University of London)

Diverse speeches and writings (2019)

In this interview, Professor Jane Winters gives an overview of her career, starting as a medieval historian to becoming a professor in digital history. She talks about her main work with born digital ... [more ▼]

In this interview, Professor Jane Winters gives an overview of her career, starting as a medieval historian to becoming a professor in digital history. She talks about her main work with born digital archives and reflects on how web archive changes historical research. ‘History from below’ with a big interest in genealogy and local history being very popular in the UK, she describes the character of digital history in her country and the response of both amateur and professional historians to digitisation. She pleads for more digital pedagogy at an earlier stage of the curriculum and underlines the importance of the relationship between digital humanities and other stakeholders like librarians and archivists. In her view, the next big challenge in digital humanities will be the non-text media analysis. [less ▲]

Fracture mechanism simulation of inhomogeneous anisotropic rocks by extended finite element method

in Theoretical and Applied Fracture Mechanics (2019), 104

The vast majority of rock masses is anisotropic due to factors such as layering, unequal in-situ stresses, joint sets, and discontinuities. Meanwhile, given the frequently asymmetric distribution of pores ... [more ▼]

The vast majority of rock masses is anisotropic due to factors such as layering, unequal in-situ stresses, joint sets, and discontinuities. Meanwhile, given the frequently asymmetric distribution of pores, grain sizes or different mineralogical compounds in different locations, they are often classified as inhomogeneous materials. In such materials, stress intensity factors (SIFs) at the crack tip, which control the initiation of failure, strongly depend on mechanical properties of the material near that area. On the other hand, crack propagation trajectories highly depend on the orthotropic properties of the rock mass. In this study, the SIFs are calculated by means of anisotropic crack tip enrichments and an interaction integral are developed for inhomogeneous materials with the help of the extended finite element method (XFEM). We also use the T-stress within the crack tip fields to develop a new criterion to estimate the crack initiation angles and propagation in rock masses. To verify and validate the proposed approach, the results are compared with experimental test results and those reported in the literature. It is found that the ratio of elastic moduli, shear stiffnesses, and material orientation angles have a significant impact on the SIFs. However, the rate of change in material properties is found to have a moderate effect on these factors and a more pronounced effect on the failure force. The results highlight the potential of the proposed formulation in the estimation of SIFs and crack propagation paths in inhomogeneous anisotropic materials. [less ▲]

Interview with Prof. Dr David Bodenhamer (Indiana University-Purdue University Indianapolis)

Diverse speeches and writings (2019)

In this interview, Professor David Bodenhamer gives an overview of his career, from his beginnings as a constitutional legal historian to becoming a new digital historian. He illustrates how GIS changed ... [more ▼]

In this interview, Professor David Bodenhamer gives an overview of his career, from his beginnings as a constitutional legal historian to becoming a new digital historian. He illustrates how GIS changed the nature of his work and explains the notion of ‘deep mapping’, emphasizing the importance of our human experience with places. He concludes by outlining the most exciting developments going on in digital history in his view. [less ▲]

Structural shape optimization of three dimensional acoustic problems with isogeometric boundary element methods

in Computer Methods in Applied Mechanics and Engineering (2019), 355

The boundary element method (BEM) is a powerful tool in computational acoustics, because the analysis is conducted only on structural surfaces, compared to the finite element method (FEM) which resorts to ... [more ▼]

The boundary element method (BEM) is a powerful tool in computational acoustics, because the analysis is conducted only on structural surfaces, compared to the finite element method (FEM) which resorts to special techniques to truncate infinite domains. The isogeometric boundary element method (IGABEM) is a recent progress in the category of boundary element approaches, which is inspired by the concept of isogeometric analysis (IGA) and employs the spline functions of CAD as basis functions to discretize unknown physical fields. As a boundary representation approach, IGABEM is naturally compatible with CAD and thus can directly perform numerical analysis on CAD models, avoiding the cumbersome meshing procedure in conventional FEM/BEM and eliminating the difficulty of volume parameterization in isogeometric finite element methods. The advantage of tight integration of CAD and numerical analysis in IGABEM renders it particularly attractive in the application of structural shape optimization because (1) the geometry and the analysis can be interacted, (2) remeshing with shape morphing can be avoided, and (3) an optimized solution returns a CAD geometry directly without postprocessing steps. In the present paper, we apply the IGABEM to structural shape optimization of three dimensional exterior acoustic problems, fully exploiting the strength of IGABEM in addressing infinite domain problems and integrating CAD and numerical analysis. We employ the Burton–Miller formulation to overcome fictitious frequency problems, in which hyper-singular integrals are evaluated explicitly. The gradient-based optimizer is adopted and shape sensitivity analysis is conducted with implicit differentiation methods. The design variables are set to be the positions of control points which directly determine the shape of structures. Finally, numerical examples are provided to verify the algorithm. [less ▲]

Weak and strong from meshless methods for linear elastic problem under fretting contact conditions

in Tribology International (2019), 138

We present numerical computation of stresses under fretting fatigue conditions derived from closed form expressions. The Navier-Cauchy equations, that govern the problem, are solved with strong and weak ... [more ▼]

We present numerical computation of stresses under fretting fatigue conditions derived from closed form expressions. The Navier-Cauchy equations, that govern the problem, are solved with strong and weak form meshless numerical methods. The results are compared to the solution obtained from well-established commercial package ABAQUS, which is based on finite element method (FEM). The results show that the weak form meshless solution exhibits similar behavior as the FEM solution, while, in this particular case, strong form meshless solution performs better in capturing the peak in the surface stress. This is of particular interest in fretting fatigue, since it directly influences crack initiation. The results are presented in terms of von Mises stress contour plots, surface stress profiles, and the convergence plots for all three methods involved in the study. [less ▲]

A gradient weighted extended finite element method (GW-XFEM) for fracture mechanics

in Acta Mechanica (2019), 230

In this study, a gradient weighted extended finite element method (GW-XFEM) is presented for the analysis of fracture problems. For this method, the domain discretization is the same as the standard XFEM ... [more ▼]

In this study, a gradient weighted extended finite element method (GW-XFEM) is presented for the analysis of fracture problems. For this method, the domain discretization is the same as the standard XFEM. However, the gradient field is constructed by considering the influences of the element itself and its adjacent elements. Based on the Shepard interpolation, the weighted strain filed can be obtained, which will be utilized to construct the discretized system equations. The validity of the presented method is fully investigated through several numerical examples. From these results, it is shown that compared with standard XFEM, the presented method can achieve much better accuracy, efficiency and higher convergence, when dealing with fracture analysis. [less ▲]