Implicit Description Research Articles

Explicit and implicit description of the factors impact on the NO 2 concentration in the traffic corridor

Explicit and implicit description of the factors impact on the NO 2 concentration in the traffic corridor

Robust Stability Analysis of a Simple Data-Driven Model Predictive Control Approach

In this paper, we provide a theoretical analysis of closed-loop properties of a simple data-driven model predictive control (MPC) scheme. The formulation does not involve any terminal ingredients, thus allowing for a simple implementation without (potential) feasibility issues. The proposed approach relies on an implicit description of linear time-invariant systems based on behavioral systems theory, which only requires one input-output trajectory of an unknown system. For the nominal case with noise-free data, we prove that the data-driven MPC scheme ensures exponential stability for the closed loop if the prediction horizon is sufficiently long. Moreover, we analyze the robust data-driven MPC scheme for noisy output measurements for which we prove closed-loop practical exponential stability. The advantages of the presented approach are illustrated with a numerical example.

UNILIPID, a Methodology for Energetically Accurate Prediction of Protein Insertion into Implicit Membranes of Arbitrary Shape.

The insertion of proteins into membranes is crucial for understanding their function in many biological processes. In this work, we present UNILIPID, a universal implicit lipid-protein description as a methodology for dealing with implicit membranes. UNILIPID is independent of the scale of representation and can be applied at the level of all atoms, coarse-grained particles down to the level of a single bead per amino acid. We provide example implementations for these scales and demonstrate the versatility of our approach by accurately reflecting the free energy of transfer for each amino acid. In addition to single membranes, we describe the analytical implementation of double membranes and show that UNILIPID is well suited for modeling at multiple scales. We generalize to membranes of arbitrary shape. With UNILIPID, we provide a methodological framework for a simple and general parameterization tuned to reproduce a selected reference hydrophobicity scale. The software we provide along with the methodological description is optimized for specific user features such as real-time response, live visual analysis, and virtual reality experiences.

How and why we should move beyond natural selection in museums to tackle teleology

BackgroundMuseum displays commonly use a “VIST” approach (Variation, Inheritance, Selection, and Time) to explain evolution to visitors. I contend that this framework, by focusing narrowly on natural selection, unintentionally reinforces intuitive teleological thinking and a “survival of the fittest” mentality. Exhibits that incorporate all the forces (or mechanisms) of evolution will instead challenge visitors’ preconceptions and enable them to develop a deeper understanding of evolution. In particular, visitors will appreciate that evolution is not progressive, with modern humans as the “most evolved” species.ResultsExplicit and implicit description of the forces of evolution is surveyed in 12 museums: 4 in Texas, 7 elsewhere in the U.S., and the Natural History Museum in London. Museum exhibits focus primarily on natural selection (explicit in 10 of 12) and often mention mutation (explicit in 7). Only the American Museum of Natural History in New York, in my sample, provides an explicit explanation of genetic drift.ConclusionsHeavy emphasis on natural selection and limited explanation of stochastic forces contributes to an impoverished view of evolution. Exhibits should more effectively convey the complexity of microevolution. Computer simulations showing the interactions of evolutionary forces can accomplish this goal.

Modeling of Growth using an Immersed Finite Element Method

AbstractTo prevent remeshing, we explore the use of a non‐boundary‐fitted finite element method for the computational modeling of growth including contact mechanics. Accordingly, we utilize a mesh‐related mapping procedure for the use of implicit geometry description by a level set function within the framework of immersed methods. Hence, our framework provides a setting to include patient‐specific geometries based on imaging data as we use a level set function for the implicit geometry description. In this contribution, we show that the proposed approach is a viable alternative for problems with mesh‐related obstacles, in particular when large growth simulations on complex patient‐specific geometries are of primary interest.

Level‐set‐based method for designing novel brushed synchronous machines

AbstractNowadays, research on electromagnetic devices increasingly focuses on multiphysics three‐dimensional complex systems. However, this kind of simulations require huge computational resources and consequently very high CPU time. Ristagno et al. proposed a level‐set based method allowing meshing step savings in any iterative processes (as movement modeling or optimization processes). The level‐set method lies in implicit description of moving fronts as described in the study by Osher et al. (1988). Inspired by Räisänen et al., all physical parameters (material properties, supply or armature movement) are implemented by projection of mathematical functions. In this paper, the authors proposes to study and design a new kind of mechanical commutator for DC machines thanks to this coupled method. Indeed, there is a renewed interest in DC machines because they can be suitable for small mobilities. To be noted, small mobility concerns all kind of vehicles (2 wheels–4 wheels–autonomous vehicles such as drones) that have speeds below 50 km/h. However, specifications for traction applications are difficult to achieve for such a rustic machine and requires some modifications. That is why, inspired by usual synchronous machine, the commutator has been redesigned to obtain expected theoretically signal waveform. Furthermore, numerical coupled simulations have been used to design both machine and supply simultaneously. This work has led to the manufacture of a proof of concept and preliminary results are very promising.

Buckling and post-buckling of variable stiffness plates with cutouts by a single-domain Ritz method

Structural components with variable stiffness can provide better performances with respect to classical ones and offer an enlarged design space for their optimization. They are attractive candidates for advanced lightweight structural applications whose functionalities often impose the presence of cutouts that requires accurate and effective analysis for their design. In the present work, a single-domain Ritz formulation is proposed, implemented and validated for the analysis of buckling and post-buckling behaviour of variable stiffness plates with cutouts. The plate model is based on the first-order shear deformation theory with nonlinear von Karman strain–displacement relationships. The plate generalized displacements are approximated with trial functions built as products of one-dimensional Legendre orthogonal polynomials. The non linear governing equations system is then deduced from the stationarity of the energy functional; the involved matrices are numerically computed by a special integration algorithm based on the implicit description of the cutout via suitable level-set functions. The formulation has been implemented in a computer code which has been used to validate the method through comparison with literature solutions for variable angle tow laminates with circular cutouts. Several investigations on buckling and post-buckling behaviour of variable angle tow composite plates with cutouts having different shapes and dimensions are then presented to illustrate the approach capabilities, provide benchmark results and point out features and design opportunities of the variable stiffness concept for the buckling and post-buckling design of advanced lightweight structures.

A level set-based procedure for the cohesive modeling of yarn–yarn contacts in woven composite RVEs

Decohesion processes involved in debonding between yarns and matrix or sliding between contacting yarns constitute important failure mechanisms in woven composites. The geometry of the yarn architecture however makes it difficult to avoid interpenetrations between neighboring yarns in their geometrical description. This motivated recent works using a level set-based methodology to generate smooth geometries without interpenetration for generated Representative Volume Elements (RVEs) and experimental image-based samples. Such tools require introducing gaps between contacting yarns, which may be debatable when taken too large or may be computationally costly for thin gap, locally dictating the mesh size. To avoid this, the yarns contacting surfaces can be discretized using interface elements. Yet, identifying such contacting surfaces is complex. An implicit geometry description based on distance fields is used here to extract a geometry that supports cohesive zones, identifying the interface of yarn–yarn contacts and eliminating the gaps using manipulations on distance fields of the individual yarns. This allows generating conforming tetrahedral meshes with inserted cohesive elements in the contact areas. The methodology is shown to reduce the size of finite element models of woven composite RVEs by over two orders of magnitude, thereby paving the way towards affordable damage simulations on such RVEs.

Conceptual integration of ecosystem services and natural capital within Irish national policy: An analysis over time and between policy sectors

Ecosystem service (ES) and natural capital (NC) concepts have been promoted as influential tools for environmental management within national public policy. To achieve this potential, these concepts must transition across the science-policy interface and become integrated within governance systems. This study examines 25-years of ES and NC concepts within national public policy at two levels: explicit use of terminology, and implicit description of services. Using the case-study of Ireland as a country with significant bio-based industry and dependence on its NC, we ask when, where, and what conceptual integration has occurred within the national policy landscape. Data were collected using mixed-methods content analysis applied to 50 Irish policy and reporting documents spanning 1996-2020. Results showed i) conceptual integration began in 2008; ii) explicit use of ES was more common than NC (442 compared to 92 uses); iii) explicit use disproportionately occurred within biodiversity policy and environmental reports; iv) use of explicit terminology contained interdisciplinary themes; v) implicit descriptions of ESs differed between policy types; vi) cultural service descriptions were identified throughout the sample whereas regulating services were more visible in more recent documents. Overall conceptual integration was found to be present but fragmented, which may create a barrier to achieving a policy landscape that is responsive to emerging ES science. Conceptual integration is dependent on the broader environmental and governance context and further research is required to understand how this impacts downstream implementation and operation. We conclude by commenting on the implications for future conceptual integration and environmental policy development.

Truss Parametrization of Topology Optimization Results with Curve Skeletons and Meta Balls

AbstractTruss-like shapes can occur in topology optimization described by an assembly of finite elements or its boundary represented as a polygon mesh. Such shape description does not cover a common engineering parametrization like the lines of a frame structure and its corresponding cross-section. This article addresses the truss-parametrization of such optimization using curve skeletons and Meta Balls. While the curve skeleton is common in the truss-parametrization, including Meta Balls can lead to an overall implicit and smooth shape description.

Toward Simplified Physics-Based Memristor Modeling of Valence Change Mechanism Devices

Memristors are promising nanoelectronic devices for the implementation of future AI-driven sensor-processor electronic systems, which are essential for the ongoing digitalization of our world. Accurate and computationally cost-effective models for the manufactured memristors are essential for the design of such systems, especially for the simulation of large circuits. In this brief we address the simplification of the JART memristor model, a generic physics-based model of Valence Change Mechanism (VCM) memristors which accurately describes the dynamic behavior of fabricated memristor devices. Furthermore, the proposed model and simplification methodology have the potential to capture the dynamics of a wide range of memristor devices. Importantly, the implicit description of the current through the memristor is replaced by an explicit mathematical relationship. The proper reproduction of memristor dynamics, verified by applying the system-theoretic Dynamic Route Map (DRM) graphical analysis tool, applicable to first-order systems, can be observed through the proposed simplified model and enables the time-efficient simulation of large arrays of VCM devices.

Heat transfer augmentation in microchannel heat sink based on isogeometric topology optimization framework

This paper focuses on a design problem of branching microchannel heat sink based on solving the thermal-fluid problem in isogeometric analysis approach. A brand new topology optimization framework is proposed to determine the distribution of the microchannels, which comprises two coupled computational layers: the upper layer for channel geometry representation and the lower layer for cooling analysis. In the upper layer, several flexible components fitting two Bézier curves as the central line describe the geometry explicitly, which is quite different from the implicit and conventional level-set description ways of topology optimization, fully releasing the deformation ability of the components. By moving, rotating, deforming, bending, overlapping and merging the level-set-based components, the channel geometry gene-rates and is ready to be projected onto the lower layer for the physical field analysis purpose. The lower layer is discretized using a NURBS patch, and NURBS-based isogeometric analysis is adopted to solve the coupled thermal-fluid problem in the structure and calculate the structural sensitivity so as to drive the upper layer to iterate. Comparing with the conventional topology optimization methods, the proposed method has obvious advantages in terms of computational effectiveness and geometry description. A design of multi-layer cold plate is constructed under this framework, aiming at obtaining the best heat dissipation effect under the constraints of volume dissipation and pressure drop. In the final, simulations and experiments are performed to demonstrate these advantages of this framework.

A new finite element approach to model microscale strain localization within olivine aggregates

Abstract. This paper presents a new mesoscopic full field approach for the modeling of microstructural evolutions and mechanical behavior of olivine aggregates. The mechanical framework is based on a reduced crystal plasticity (CP) formulation which is adapted to account for non-dislocation glide strain-accommodating mechanisms in olivine polycrystals. This mechanical description is coupled with a mixed velocity–pressure finite element (FE) formulation through a classical crystal plasticity finite element method (CPFEM) approach. The microstructural evolutions, such as grain boundary migration and dynamic recrystallization, are also computed within a FE framework using an implicit description of the polycrystal through the level-set approach. This numerical framework is used to study the strain localization, at the polycrystal scale, on different types of pre-existing shear zones for thermomechanical conditions relevant to laboratory experiments. We show that both fine-grained and crystallographic textured pre-existing bands favor strain localization at the sample scale. The combination of both processes has a large effect on strain localization, which emphasizes the importance of these two microstructural characteristics (texture and grain size) on the mechanical behavior of the aggregate. Table 1 summarizes the list of the acronyms used in the following.

Modelling of faults in LoopStructural 1.0

Abstract. Without properly accounting for both fault kinematics and observations of a faulted surface, it is challenging to create 3D geological models of faulted geological units. Geometries where multiple faults interact, where the faulted surface geometry significantly deviate from a flat plane and where the geological interfaces are poorly characterised by sparse datasets are particular challenges. There are two existing approaches for incorporating faults into geological surface modelling. One approach incorporates the fault displacement into the surface description but does not incorporate fault kinematics and in most cases will produce geologically unexpected results such as shrinking intrusions, fold hinges without offset and layer thickness growth in flat oblique faults. The second approach builds a continuous surface without faulting and then applies a kinematic fault operator to the continuous surface to create the displacement. Both approaches have their strengths; however, neither approach can capture the interaction of faults within complicated fault networks, e.g. fault duplexes, flower structures and listric faults because they either (1) impose an incorrect (not defined by data) fault slip direction or (2) require an over-sampled dataset that describes the faulted surface location. In this study, we integrate the fault kinematics into the implicit surface, by using the fault kinematics to restore observations, and the model domain prior to interpolating the faulted surface. This new approach can build models that are consistent with observations of the faulted surface and fault kinematics. Integrating fault kinematics directly into the implicit surface description allows for complexly faulted stratigraphy and fault–fault interactions to be modelled. Our approach shows significant improvement in capturing faulted surface geometries, especially where the intersection angle between the faulted surface and the fault surface varies (e.g. intrusions, fold series) and when modelling interacting faults (fault duplex).

Development of a random particle generator for the distinct lattice spring model

Particles in a regular arrangement will always be simplistically used in the discrete numerical analysis to represent materials ranging from steels to geomaterials (e.g., rock and concrete). As for those heterogeneous materials, this simplification violates reality more or less. In this work, a random particle model generator is developed to provide a computational model for the Distinct Lattice Spring Model (DLSM). The generator covers the determination of particles within polygons and the linkage formation between particles. Firstly, the computational domain represented by an implicit description is initially discretized into polygons based on the Centroidal Voronoi diagrams and then optimized by the topology optimization algorithm. Subsequently, the random particles are located within the polygons by using the minimal inner tangent circle, in which the centroid of the polygons are regarded as the particle centre and determined by the simplex method. Based on the Delaunay triangulation algorithm, the particles will be initially linked together. To avoid the long-range interaction between particles that could fail to predict the elastic response, the initial linkage will be re-detected by a second contact detection law. Compared with the particle model in a regular arrangement, the irregularity along the model boundary in an arbitrary computational domain can be eliminated by the random particle model. Prior to fracture problems, the elastic response of the random particle model under the framework of the DLSM is numerically verified by the beam bending problem. In the following, the crack propagation of the quasi-brittle materials is investigated by using a modified cohesive damage-plasticity model (m-CDPM), in which the linear elastic, nonlinear and softening stages are included. As for the crack path preference occurring in the regular particle model, it can be alleviated by the random particle model. Besides, the applicability of the random particle model associated with the m-CDPM on fracture problems is investigated by two numerical examples including the semi-circular bending and tension-shear tests.

An Extended Three-Dimensional Finite Strain Constitutive Model for Shape Memory Alloys

AbstractA 3D finite-strain constitutive model for shape memory alloys (SMAs) is proposed. The model can efficiently describe reversible phase transformation from austenite to self-accommodated and/or oriented martensite, (re)orientation of martensite variants, minor loops, latent heat effects, and tension–compression asymmetry based on the Eulerian logarithmic strain and the corotational logarithmic objective rate. It further accounts for smooth thermomechanical response; temperature dependence of the critical force required for (re)orientation, temperature, and load dependence of the hysteresis width; and asymmetry between forward and reverse phase transformation, and it is flexible enough to address the deformation response in the concurrent presence of several phases, i.e., when austenite, self-accommodated, and oriented martensite co-exist in the microstructure. The ability of the proposed model to describe the aforementioned deformation response characteristics of SMAs under multiaxial, thermomechanical, and nonproportional loading relies on the set of three independent internal variables, i.e., the average volume fraction of martensite variants, their preferred direction, and the magnitude of the induced inelastic strain, which further allow for an implicit description of a fourth internal variable, the volume fraction of oriented as opposed to self-accommodated martensite. The calibration of the model and its numerical implementation in an efficient scheme are presented. The model is validated against experimental results associated with complex thermomechanical paths, including tension/compression/torsion experiments, and the efficiency of its numerical implementation is verified with simulations of the response of a biomedical superelastic SMA stent and an SMA spring actuator.

Two-Scale Optimization and Generation of Anisotropic Cellular Designs in the Context of Additive Manufacturing

Within the context of gradient-based optimization of cellular structures, we aim to optimize designs in a two-scale setting and generate respective geometric descriptions that are additively manufacturable in powder-bed systems. We analyze representative unit cells for their suitability and present a workflow to generate cellular designs by means of a parameterized unit cell, for which an implicit surface description is described. After performing homogenization-based optimization, we compare the predicted performance of the homogenized model to a full-resolution finite element (FE) analysis. Throughout the whole process, special attention is paid to the consistent integration of manufacturing limitations in terms of horizontal overhang and feature size.We discuss the performance of cellular components with maximized stiffness. Our numerical experiment for a single-load scenario demonstrates that using isotropic micro-structures is not beneficial, even when graded. We further observe that using anisotropic micro-structures leads to improvements only in very specific cases, e.g. with a uniformly distributed load. However, the conclusion may be different for anisotropic cells with non-uniform parameterization and other loading scenarios. Instead of conducting further tedious investigations for stiffness maximization, we finally demonstrate the benefit of cellular designs for a thermo-mechanical example.

Localization of Fučík curves for the second order discrete Dirichlet operator

In this paper, we deal with the second order difference equation with asymmetric nonlinearities on the integer lattice and we investigate the distribution of zeros for continuous extensions of positive semi-waves. The distance between two consecutive zeros of two different positive semi-waves depends not only on the parameters of the problem but also on the position of one of these zeros with respect to the integer lattice. We provide an explicit formula for this distance, which allows us to obtain a new simple implicit description of all non-trivial Fučík curves for the discrete Dirichlet operator. Moreover, for fixed parameters of the problem, we show that this distance is bounded and attains its global extrema that are explicitly described in terms of Chebyshev polynomials of the second kind. Finally, for each non-trivial Fučík curve, we provide suitable bounds by two curves with a simple description similar to the description of the first non-trivial Fučík curve.

Characteristic Model-Based Control Approach for Complex Network Systems

In this paper, characteristic model-based modeling and control approaches for complex dynamical networks based on sampled data are studied. It shows that the characteristic model, in which underline network topological structures are simplified, can provide a straightforward and implicit description for network dynamics. The induced parameter estimation method can further make the model adaptive and purely data-driven. Moreover, a control law based on this model is also proposed to govern the network dynamics. Finally, the theoretical results are verified through numerical simulations of modeling and stabilizing a dynamical network.

Implicit water model within the Zimm-Bragg approach to analyze experimental data for heat and cold denaturation of proteins

Studies of biopolymer conformations essentially rely on theoretical models that are routinely used to process and analyze experimental data. While modern experiments allow study of single molecules in vivo, corresponding theories date back to the early 1950s and require an essential update to include the recent significant progress in the description of water. The Hamiltonian formulation of the Zimm-Bragg model we propose includes a simplified, yet explicit model of water-polypeptide interactions that transforms into the equivalent implicit description after performing the summation of solvent degrees of freedom in the partition function. Here we show that our model fits very well to the circular dichroism experimental data for both heat and cold denaturation and provides the energies of inter- and intra-molecular H-bonds, unavailable with other processing methods. The revealed delicate balance between these energies determines the conditions for the existence of cold denaturation and thus clarifies its absence in some proteins.