bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of deep learning models with simple method to assess the problem of antimicrobial peptides prediction
Authors: Lobanov M. Y. , Slizen M. V. , Dovidchenko N. V. , Panfilov A. V. , Surin A. A. , Likhachev I. V. , Galzitskaya O. V.
Published: March 2023

Antibiotic‐resistant strains are an emerging threat to public health. The usage of antimicrobial peptides (AMPs) is one of the promising approaches to solve this problem. For the development of new AMPs, it is necessary to have reliable prediction methods. Recently, deep learning approaches have been used to predict AMP. In this paper, we want to compare simple and complex methods for these purposes. We used the BERT transformer to create sequence embeddings and the multilayer perceptron (MLP) and light attention (LA) approaches for classification. One of them reached about 80 % accuracy and specificity in benchmark testing, which is on par with the best available methods. For comparison, we proposed a simple method using only the amino acid composition of proteins or peptides. This method has shown good results, at the level of the best methods. We have prepared a special server for predicting the ability of AMPs by amino acid composition: http://bioproteom.protres.ru/antimicrob/.
One‐bit wideband reconfigurable reflectarray with stable beam‐scanning gain for X‐band application
Authors: Zheng Kailang , Xu Kuiwen , Chen Shichang , Zhou Tao , Pan Xiao‐Min , Zhang Changming , Yu Xianbin
Published: March 2023

A wideband and electrically reconfigurable reflectarray (RRA) is presented for X‐band application. The unit cell is composed of two heterogeneous resonators, that is, a split resonator ring and a metallic patch, and two positive‐intrinsic‐negative (PIN) diodes integrated between these two resonators. A bias circuit on the bottom layer is designed to achieve the switching of the two states via properly placing the PIN diodes on the resonators with minimal electric field. One‐bit phase quantization is obtained by switching two different resonant mode via controlling the ON or OFF state of two PIN diodes. The simulated results show that the proposed unit cell can achieve one‐bit phase quantization with 180° ± 20° and reflection coefficients of ‐1 dB from 9.5 to 10.8 GHz, corresponding relative bandwidth of 12.81%. In addition, a fully functional 12 × 12 RRA fed by a linearly polarized horn is theoretically designed, simulated, and fabricated. The measured results show that the main beam can be steered from −50° to +50° at operating frequency, for example, 10.1 GHz with 1.5 dB gain loss within the scanning range and 20.34% aperture efficiency. In addition, the measured average gain is about 17.5 dBi and 3 dB gain bandwidth is about 15.68% from 9.4 to 11 GHz. In virtue of wide bandwidth, stable radiation gain, and good beam scanning capability, the proposed RRA is promising for future wireless communication and radar.
Signal preprocessing routines for the detection and classification of human micro‐Doppler radar signatures
Authors: Tekir Onur , Yılmaz Betül , Özdemir Caner
Published: March 2023

In this study, we introduce a radar sensor that we have developed for the micro‐Doppler signature measurements together with three consecutive signal preprocessing routines that are to be used for primary detection and classification of human gait and movements. The developed C‐band radar sensor has been used in a series of human walking and running experiments that were conducted at Mersin University facilities. First, the raw data collected in time domain are transformed to two‐dimensional (2D) time‐frequency plane to investigate the Doppler characteristics of human movements. To detect and extract the main body signature of the human, a Kalman filter‐based torso signature detection methodology is introduced as the first preprocessing tool. Then, to be able to better detect the other body parts’ signatures, the torso's response is thoroughly extracted from the 2D time‐Doppler image as the second preprocessing routine by applying a circular shift procedure along each time‐bin. As the last procedure, envelopes of the micro‐Doppler signatures on the 2D time‐Doppler image plane are determined by another routine based on human Doppler threshold method. To assess the success and the validity of the proposed pre‐signal processing tools, they are applied to the measured data collected via different experiments of human movements. After applying all these steps, the torso signature and envelopes of all other body parts’ signatures are marked and determined with good fidelity.
A low‐profile low‐sidelobe beam steering metasurface lens based on amplitude‐phase control
Authors: Yuan Yi , Huang Chao , Ding Jun , Guo Chenjiang
Published: March 2023

In this letter, a low‐profile low‐sidelobe beam steering metasurface lens (metalens) is presented. The proposed metalens achieves asymmetric polarization conversion using only a single layer with a low profile. Aiming at the metalens, a modified Taylor synthesis method for amplitude modulation is proposed, which reduces the sidelobe level (SLL) while the beam is tilted. Compared with the previous beam steering metasurface, it has a low profile and SLL. The experimental results are in good agreement with the simulated ones.
A new amide from the fruiting bodies of Tricholoma bakamatsutake
Authors: Zhang Feng‐Ming , Lu Bin , Wang Yue‐Hu , Yu Fu‐Qiang
Published: March 2023

A new amide tricholomine C was isolated from the dried fruiting bodies of Tricholoma bakamatsutake. Its structure was identified by a combination of nuclear magnetic resonance spectroscopic analysis and electronic circular dichroism (ECD) calculations. The ethyl alcohol crude extract and tricholomines A–C from T. bakamatsutake were evaluated for neuroprotective activities. Of these substances, the crude extract showed weak neurite outgrowth‐promoting activity in rat pheochromocytoma (PC12) cells, as well as weak inhibitory activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE).
Deforestation alters species interactions
Authors: Howes Benjamin , González‐Suárez Manuela , Jensen Henrik Jeldtoft , Anjos Luiz dos , Develey Pedro F. , Hatfield Jack H. , Morante‐Filho José Carlos , Uezu Alexandre , Banks‐Leite Cristina
Published: March 2023

Interspecific interactions are a major determinant of stability in ecological communities and are known to vary with biotic and abiotic conditions. Deforestation is the primary driver of the ongoing sixth mass extinction, yet its effect on species interactions remains largely unexplored. We investigate how deforestation affects species interactions using a complex systems model and a co‐occurrence dataset of 363 bird species, observed across 134 sites, from 5 regions across the Brazilian Atlantic Forest totalling 27,226 interactions. Both theoretical and empirical results show that interspecific interactions vary non‐monotonically with forest cover and are more positive than average in areas with higher forest cover, and to a lesser extent in highly deforested areas. Observed differences in interactions reflect both species turnover and changes in pairwise interactions. Our results point to changes in stability across the gradient of deforestation that may lead to varying community resilience to environmental perturbations.

Key Interdisciplinary Aspects

Species interactions are expected to vary due to the biological, chemical and physical changes caused by deforestation on their local environment.

We use a mathematical complex systems approach, as well as ecological data, to show that species interactions are more positive in highly forested areas.

We propose that the alteration of species interactions caused by deforestation will affect the stability of communities and their resilience to future perturbations (e.g. climate change).
Finite‐time fault detection for nonlinear delayed system with dynamic quantization and multiple packet dropouts
Authors: Wu Zhihui , Zhao Xue , Chen Cai , Zhao Yue
Published: March 2023

The attention of this article is mainly paid to the finite‐time fault detection (FD) problem for nonlinear delayed system with dynamic quantization and multiple packet dropouts. The probabilistic interval time‐varying delay is addressed, which might fall into two intervals with known probability. The measurement signals are quantized by a dynamic quantizer and then transmitted over communication network, where the multiple packet dropouts might occur. The main objective of the considered problem is to design a finite‐time FD filter such that the FD system is stochastically finite‐time stable (SFTS) with guaranteed performance in the presence of probabilistic interval time‐varying delay, dynamic quantization and multiple packet dropouts. Based on Lyapunov stability theory, sufficient criteria for the presence of the desired finite‐time FD filter are presented. Afterwards, the desired filter gain matrices are given via solving certain linear matrix inequalities (LMIs). Finally, a simulation example is used to show the applicability of the obtained finite‐time FD algorithm.
Measure concentration and the Schrödinger equation
Authors: Yserentant Harry
Published: March 2023

This talk pursued the aim to represent the solutions of the electronic Schrödinger equation as traces of higher‐dimensional functions. This allows to decouple the electron‐electron interaction potential but comes at the price of a degenerate elliptic operator replacing the Laplace operator on the higher‐dimensional space. The surprising observation is that this operator can without much loss again be substituted by the Laplace operator, the more successful the larger the system under consideration is. This is due to a nontrivial concentration of measure phenomenon that has much to do with the random projection theorem known from probability theory and can, for example, serve as a building block for the construction of iterative methods that map sums of products of orbitals and geminals onto functions of the same type.
External problems of steady vibrations in the theory of elastic materials with a triple porosity structure
Authors: Svanadze Merab
Published: March 2023

In this paper, the linear theory of elasticity for materials with a triple porosity (macro, meso and micro levels of porosities) structure based on the volume fraction concept is considered. The external boundary value problems (BVPs) of steady vibrations of this theory are investigated. Namely, the uniqueness theorem for classical solutions of these BVPs is established. Then, the basic properties of the surface (single‐layer and double‐layer) potentials are given. Finally, on the basis of the properties of potentials, the existence theorems for classical solutions of the above mentioned BVPs of steady vibrations are proved by means of the potential method (boundary integral equation method) and the theory of singular integral equations.
A novel anisotropic stress‐driven model for bioengineered tissues accounting for remodeling and reorientation based on homeostatic surfaces
Authors: Holthusen Hagen , Rothkranz Christiane , Lamm Lukas , Brepols Tim , Reese Stefanie
Published: March 2023

A co‐rotated formulation of the intermediate configuration is derived in a thermodynamically consistent manner. As a result of this formulation, algorithmic differentiation (AD) and the equations of the material model can be combined directly, i.e., the equations can be implemented into the AD tool and the corresponding derivatives can be calculated using AD. This is not possible when the equations are given in terms of the intermediate configuration, since the multiplicative decomposition suffers from an inherent rotational non‐uniqueness. Moreover, a novel stress‐driven kinematic growth model is presented that takes homeostasis and fiber reorientation into account and is based on the co‐rotated formulation. A numerical example reveals the promising potential of both the co‐rotated formulation and the stress‐driven growth model.
Core thickness optimization of buckling‐endangered sandwich columns under compressive loads
Authors: Nuño Miguel , Schröder Kai-Uwe
Published: March 2023

Optimizing the core thickness of a sandwich structure can be a computationally expensive task. In this work, an optimization approach for slender columns is presented. The approach iteratively determines the optimal thickness distribution using the second derivative of the eigenmodes as an input for the shape function. To demonstrate its capabilities, it is applied to simple columns constrained according to Euler's buckling cases. The optimization results are validated with detailed finite element models and compared to those from a nonlinear least squares‐based optimization.
Two‐dimensional meso‐structural simulation of concrete fracture by the implementation of zero‐thickness cohesive interface elements
Authors: Najafi Koopas Rasoul , Rauter Natalie , Lammering Rolf
Published: March 2023

Concrete is considered as a non‐homogeneous material and from a mesoscopic point of view is constituted of three main phases, namely aggregates, mortar matrix and interfacial transition zone (ITZ). To investigate the damage process of concrete materials at the mesoscale due to mechanical loading, an explicit numerical model with full representation of the three mesoscopic phases is required. To this end, in this work, a Python code is developed to generate zero‐thickness cohesive interface elements in two‐dimensions (2D). The generated code is capable of generating two‐dimensional quadratic cohesive interface elements (i) within the mortar elements, (ii) within the aggregates elements and (iii) at interfaces between mortar and aggregates. To simulate the crack propagation, the generated zero thickness‐cohesive elements are preinserted at the interface of solid elements and different traction‐separation laws are assigned to them to simulate all potential crack paths. The implemented algorithms to generate the cohesive elements are discussed in detail and numerical examples of crack propagation in concrete is presented using Abaqus/CAE. The numerical results are compared with those in the literature qualitatively to validate the performance of the model. The developed method provides the possibility to investigate the damage processes in meso‐and micro‐scales underlying the macroscopic behavior of the semi‐brittle materials.
Modeling the size‐effect of metamaterial beams under bending via the relaxed micromorphic continuum
Authors: Sarhil Mohammad , Scheunemann Lisa , Schröder Jörg , Neff Patrizio
Published: March 2023

Mechanical metamaterials are media with periodic unit cells comprised of tailored geometry in order to accomplish extraordinary bulk mechanical properties which can not be found in conventional materials. However, metamaterials exhibit size‐effect phenomena which can be captured by enriched continua. In this work, the relaxed micromorphic model will be used to reproduce the mechanical response of an assumed metamaterial. The solution of the fully discretized metamaterial is used as a reference that the homogeneous relaxed micromorphic model should meet. We discuss the parameters identification and boundary conditions. Our analysis indicates that the relaxed micromorphic model faithfully reproduces the size‐effect.
Approaches for optimizing surrogate models considering uncertain parameters
Authors: Oberleiter Thomas , Willner Kai
Published: March 2023

Surrogate models are a common tool to perform expensive optimization or uncertainty analysis in a cost‐effective way. The structure and the application of surrogate models is well known, but there is still potential for improvement. The structure of the surrogate model can be divided into three parts, which can be considered separately. The sampling plan, the black box and the selection of the model itself. The optimization of the surrogate models in the sampling plan and the black box is presented on the basis of two case studies. In the sampling plans, the example of the FOSS method is used to show how sampling points are found for an optimized uncertainty analysis with a low number of sampling points. It is taken into account that the result space is not uniformly relevant for the uncertainty consideration with fuzzy parameters. If the black box is a problem from mechanics, known information can be used for an optimized surrogate modeling. For a Finite‐Element‐Method (FEM) black box, it makes sense to consider the maximum possible number of sampling points and maximum accuracy of the FEM‐black box with regard to the surrogate modeling. As the case study shows, a reduction of the accuracy in the FEM calculation, by using a lower mesh density, can lead to an increasing accuracy of the surrogate model.
Curved, linear Kirchhoff beams formulated using tangential differential calculus and Lagrange multipliers
Authors: Kaiser Michael Wolfgang , Fries Thomas-Peter
Published: March 2023

Linear Kirchhoff beams, also known as curved Euler‐Bernoulli beams, are reformulated using tangential differential calculus (TDC). The model is formulated in a two dimensional Cartesian coordinate system. Isogeometric analysis (IGA) is employed, hence, NURBS are used for the geometry definition and generation of sufficiently smooth shape functions. Dirichlet boundary conditions are enforced weakly using Lagrange multipliers. As a post‐processing step, the obtained FE solution is inserted into the strong form of the governing equations and this residual error is integrated over the domain in an L2‐sense. For sufficiently smooth physical fields, higher‐order convergence rates are achieved in the residual errors. For classical benchmark test cases with known analytical solutions, we also confirm optimal convergence rates in the displacements.
An Inverse Neural Particle Method for Flow Field Reconstruction
Authors: Wessels Henning
Published: March 2023

Physics‐Informed Neural Networks (PINNs) are a novel discretization scheme for the solution of partial differential equations (PDEs), where a neural network is chosen as global ansatz function. The problem of solving the PDE is then cast as an optimization problem and addressed by training the neural network. PINNs have been promoted to perform particularly well in inverse problems. This contribution presents recent advances of the Neural Particle Method, an updated Lagrangian Physics‐Informed Neural Network, in the inverse problem of reconstructing flow fields from sparse data.
Numerical comparison of biofilm growth models using prominent modeling approaches
Authors: Klempt Felix , Soleimani Meisam , Junker Philipp
Published: March 2023

To make implants, especially oral implants, safer and more durable in patients bodies, in silico models proof to be a useful tool to investigate the growth behavior of harmful biofilms causing implant loss. In literature, most growth models fall into one of two categories: either the growth is calculated volumetricly or by adjusting the density of the growing biological body. The volumetric models perform a kinematic split F = FeFg in which the growth part of the deformation tensor is a direct function of the nutrient concentration Fg = Fg(c). The density based models, on the other hand, develop the density variable φ via an evolution equation. To make existing models more accurate and increase the predictability of those models, a combination of the existing growth models is presented. The model combines the volumetric growth model implemented by a kinematic split of the deformation tensor as a function of a growth parameter Fg(α). The numerical example presented here shows sensible growing behaviour. The combined model thus makes a very promising approach in simulating growth more accurately.
A detailed surface reaction mechanism to investigate oxidation of methane over nickel catalyst
Authors: Rakhi  , Günther Vivien , Mauss Fabian
Published: March 2023

We have developed a kinetically consistent detailed surface reaction mechanism for modeling the oxidation of methane over a nickel‐based catalyst. A one‐dimensional model, LOGEcat based on the single‐channel 1D catalyst model, is used to perform the simulations. The original multi‐step reaction mechanism is thermodynamically consistent and consists of 52 reactions. By thermodynamic consistency, we mean that the equilibrium is achieved with the support of the Arrhenius parameters and does not depend on the thermochemistry of the species involved in the considered reactions. The detailed mechanism developed in this investigation contains 26 reversible reactions. These reactions are obtained with the use of the thermochemistry of the species. The study focuses on ensuring kinetic consistency and this is done with the help of thermodynamic analysis by bringing the thermochemistry of the species in play in order to develop a surface reaction mechanism. The new mechanism can be used to understand the other processes, for example, steam‐ and dry‐reforming of methane over nickel, however, the main focus of the paper is to check the performance of the detailed mechanism for catalytic partial oxidation of methane. The applicability of the mechanism is checked for various reactor conditions in terms of parameters such as temperature and pressure by comparing the results with the available reference data. The detailed mechanism developed in this study is able to accurately express oxidation of methane over the nickel catalyst for the considered reactor conditions.
A Continuous Model for Demand‐Side Management in an Aggregator Model in Electricity Markets
Authors: Thünen Anna , Ulke Alena
Published: March 2023

We develop a novel time continuous Stackelberg game to model the interaction of costumers and aggregators in electricity markets. It features time dependent pricing policies that aim to align electricity consumption with its availability. Furthermore the model has the special potential of scalability with respect to the amount of costumers. We illustrate that in fact the aggregator can create an incentive to the costumer that is then changing its consumption behavior.
Adaptive methods for MOR in non‐linear FE simulations of unit cells
Authors: Özmen Yasemin , Scheunemann Lisa , Nigro Paulo S. B. , Schröder Jörg
Published: March 2023

In this contribution, an adaptive method for Model Order Reduction (MOR) is presented for simulating physically non‐linear material behavior of micro‐heterogeneous structures. The method is purely online and includes a Galerkin projection, which is performed using a projection operator initially gained by a Proper Orthogonal Decomposition (POD). By this projection, the number of degrees of freedom to solve for is decreased drastically and can be projected back to the vector space of the high fidelity problem after the solution process. The composition of the projection operator follows an adaptive algorithm, which evaluates an update of the operator if convergence is not ensured during the Newton Raphson scheme. Later on, during the simulation, the number of degrees of freedom to solve is controlled using a POD‐based control criterion for sorting out non‐relevant basis vectors from previous updates. This results in an efficient method and leads to a satisfying speedup of the simulation process. The performance and efficiency of the presented adaptive MOR scheme is investigated in numerical simulations of a hexagon‐shaped unit cell.
Growth of green wood based on a phase field model
Authors: Wulf Jan Bernd , Muench Ingo
Published: March 2023

Tree engineering is a young discipline utilizing trees as structural elements, where the determination of limit loads in tree trunks is of great importance. Simple numerical models underestimate the load‐bearing capacity of green wood in contrast to experimental bending tests. A well‐known reason for this is the residual stress state of the living tree lowering compressive stress towards the trunks surface. This results in an overall stress state, which increases the load capacity, since the tensile strength of wood is commonly higher than its compressive strength. By determining the residual growth stress, a more accurate evaluation of the load‐bearing capacity of a living tree is possible. The residual stress state is a non‐linear and time dependent function in thickness direction of the trunk. In order to simulate growth and growth stress, a phase field model is employed.

The morphology of a tree is the result of innumerable and often temporary environmental stimuli, which also change and interact with the genetically predisposed growth tropisms. Therefore, we use image processing to capture the individual tree morphology of an existing tree, which is based within the phase field model as predefined growth direction. This is the basis for primary growth in the model. Additionally the model simulates the secondary growth, which corresponds to the thickness of the trunk. Except in tropical areas, this growth is associated with growth rings, which we assign as an attribute to the modelled material. While in the branch structure several tropisms (e.g. gravitropism) are responsible for the off‐centre accumulation of woody material, in the stem region we only follow the stress‐induced growth. This mechanism can respond to either the principal tensile stress or the principal compressive stress in our model, as this difference is observed in hardwoods and softwoods.

Since the wood matrix represents an anisotropic material with a distinct fiber direction, we approach it in our model by a transversely isotropic constitutive law, whose principal direction coincides with the growth direction.
Factors influencing the dynamic stiffness in short‐fiber reinforced polymers
Authors: Magino Nicola , Köbler Jonathan , Andrä Heiko , Welschinger Fabian , Müller Ralf , Schneider Matti
Published: March 2023

In short‐fiber reinforced polymers, fatigue damage is typically characterized by measuring the dynamic stiffness and its degradation under cyclic loading. Computational homogenization methods may be used to characterize the fatigue behavior of the composite via numerical predictions. Such an approach may reduce the experimental effort significantly. In the previous works, the authors proposed an elastic fatigue damage model for predicting the relative stiffness degradation of short‐fiber reinforced materials. However, the absolute value of the dynamic stiffness within the first cycle showed deviations from the expected elastic material behavior. Thus, the effect of viscoelastic polymer behavior as well as different microstructure descriptors on the dynamic stiffness is studied in the work at hand.
Data‐based prediction of the viscoelastic behavior of short fiber reinforced composites
Authors: Marr Julian , Zartmann Lukas , Reinel-Bitzer Doris , Andrä Heiko , Müller Ralf
Published: March 2023

The viscoelastic behavior of short fiber reinforced polymers (SFRPs) partly depends on different microstructural parameters such as the local fiber orientation distribution. To account for this by simulation on component level, two‐scale methods couple simulations on the micro‐ and macroscale, which involve considerable computational costs. To circumvent this problem, the generation of a viscoelastic surrogate model is presented here. For that purpose, an adaptive sampling technique is investigated and data are obtained by creep simulations of representative volume elements (RVEs) using a fast Fourier transform (FFT) based homogenization method. Numerical tests confirm the high accuracy of the surrogate model. The possibility of using that model for efficient material optimization is shown.
Artefact Indicator for Flow‐based Temporal Interpolation of Power Doppler Ultrasound
Authors: Biberger Simon , Mercier Gwenael , Wallinger Christian , Buckton Daniel , Scherzer Otmar
Published: March 2023

Power Doppler ultrasound is a sonography technique to detect and visualise blood circulation. Its acquired image sequences suffer from poor temporal resolution and artefacts caused by aliasing, noise, large displacements, shearings or out‐of‐plane movements. These pitfalls distort flow fields and have unforeseen consequences on flow‐based temporal interpolations. We propose a method to detect artefacts caused by such distorted flow fields and to improve the visual quality by replacing regions with detected artefacts by locally better results. This is demonstrated on real data.
Model‐free data‐driven inelasticity in Haigh‐Westergaard space ‐ a study how to obtain data points from measurements
Authors: Ciftci Kerem , Hackl Klaus
Published: March 2023

Model‐free data‐driven computational mechanics replace phenomenological models with numerical simulations in strain‐stress space based on sample data sets. The approach has recently been extended to inelasticity problems employing structured data sets, tangent space information, and transition rules. Coverage of qualified data states and calculation of the related tangent space is critical from the standpoint of actual application. This study applies the data‐driven paradigm to elasto‐plasticity with isotropic hardening. We develop our method using Haigh‐Westergaard coordinates, which provide information on the underlying material yield surface. Based on this, we employ a combined tension‐torsion test to cover the yield surface knowledge and a single tensile test to determine the tangent space. Under compatibility and equilibrium requirements, the resulting data‐driven technique minimizes the distance over the Haigh‐Westergaard space augmented by directions in the tangent space.
Solving phase‐field fracture problems in the tensor train format
Authors: Risthaus Lennart , Schneider Matti
Published: March 2023

Phase‐field models for the quasi‐static simulation of brittle fracture where the crack is approximated by a damage phase‐field are limited by the necessary memory and computation time. In this contribution, we study the applicability of low‐rank methods to phase‐field fracture models, specifically the tensor train (TT) format. To this end, we investigate the low‐rank structure of the crack phase‐field. Additionally, we present an implementation of an alternating minimization scheme to solve the coupled displacement and damage problem in the TT format. We show the evolution of the TT ranks of the displacement and damage fields for a specific example.
Weak solutions to gradient flows in metric measure spaces
Authors: Górny Wojciech , Mazón José M.
Published: March 2023

Due to the fact that in a metric space there is (in general) no notion of directional derivatives, the definition of solutions to gradient flows in metric measure spaces necessarily avoid their direct use. The most classical example is the heat flow, or more generally the p‐Laplacian evolution equation, which has been studied as the gradient flow in L2 of the p‐Cheeger energy. Typically, solutions are defined using the semigroup theory through a subdifferential of the energy. Other popular approaches include variational solutions and the weighted energy‐dissipation formalism. In this paper, using the first‐order differential structure on a metric measure space introduced by Gigli, we characterize the subdifferential in L2 of the p‐Cheeger energy. This gives rise to a new notion of solutions to the p‐Laplacian evolution equation in metric measure spaces. In the case p = 1, we introduce a metric analogue of the Anzellotti pairing and obtain a Green‐Gauss formula, which is then used in place of Gigli's structure to characterise the 1‐Laplacian operator and study the total variation flow.
Investigation of a Realistic Flap Modeling Using a Combination of Chimera Method and Grid Deformation on a Wing Fuselage Configuration
Authors: Hillebrand Marco , Müller Jens , Ullah Junaid , Lutz Thorsten
Published: March 2023

Flap deflections of an aircraft wing for active load alleviation within CFD simulations are realized using pure grid deformation due to time saving and low modeling complexity. In this case, spanwise gaps are neglected, which are present in reality during a flap deflection. Another possibility to realize the deflections is the combination of pure grid deformation and Chimera method, which allows the modeling of the gap between flap and wing or consecutive flaps. The overall aim of this work is the analysis of the aerodynamic effects caused by the different modeling approaches realizing leading and trailing edge flap deflections. The comparison of the modeling methods is investigated on the DLR LEISA configuration, which is a generic wing‐fuselage configuration. For active gust load alleviation, the leading edge flaps are deflected downward and the trailing edge flaps are deflected upward. Due to the downward deflection of the leading edge flaps, vortices are formed using the combined Chimera method as a result of the gap consideration. These vortices lead to a local drag increase resulting in a difference between both modeling methods in the spanwise as well as global drag coefficient. With the pure grid deformation these vortices do not occur. Due to the upward trailing edge deflection, the combined Chimera method leads to a pressure compensation via the effective gap enlargement, which is not present in the pure grid deformation. Overall, the combined Chimera method offers a good possibility to model the induced drag as well as the pressure compensation at a large flap deflection.
A comparison of a level set method and the method of moving asymptotes for the topology optimization of flexible components in multibody systems
Authors: Azari Nejat Ali , Held Alexander , Seifried Robert
Published: March 2023

The gradient‐based topology optimization of flexible multibody systems is considered, where the floating frame of reference method is utilized to model the flexible components with an appropriate efficiency. Thereby, the quality of the optimization results depends, among others, on the chosen gradient calculation strategy and the applied optimization algorithm. Here, both a fully‐coupled time‐continuous adjoint sensitivity analysis and a weakly‐coupled equivalent static load method are tested for gradient calculation. Moreover, both the method of moving asymptotes and a level set method are taken to solve the optimization problem. Different combinations of the mentioned gradient strategies and optimization algorithms are applied for the topology optimization of a flexible piston rod in a slider‐crank mechanism. The corresponding results and comparisons shall be used as quality benchmarks for further studies.
Scaled boundary isogeometric analysis with C1 coupling for Kirchhoff‐Love theory
Authors: Arf Jeremias , Reichle Mathias , Klinkel Sven , Simeon Bernd
Published: March 2023

Scaled boundary isogeometric analysis (SB‐IGA) describes the computational domain by proper boundary NURBS together with a well‐defined scaling center; see [5]. More precisely, we consider star convex domains whose domain boundaries correspond to a sequence of NURBS curves and the interior is determined by a scaling of the boundary segments with respect to a chosen scaling center. However, providing a decomposition into star shaped blocks one can utilize SB‐IGA also for more general shapes. Even though several geometries can be described by a single patch, in applications frequently there appear multipatch structures. Whereas a C0 continuous patch coupling can be achieved relatively easily, the situation becomes more complicated if higher regularity is required. Consequently, a suitable coupling method is inevitably needed for analyses that require global C1 continuity.

In this contribution we apply the concept of analysis‐suitable G1 parametrizations [2] to the framework of SB‐IGA for the C1 coupling of planar domains with a special consideration of the scaling center. We obtain globally C1 regular basis functions and this enables us to handle problems such as the Kirchhoff‐Love plate and shell, where smooth coupling is an issue. Furthermore, the boundary representation within SB‐IGA makes the method suitable for the concept of trimming. In particular, we see the possibility to extend the coupling procedure to study trimmed plates and shells.

The approach was implemented using the GeoPDEs package [1] and its performance was tested on several numerical examples. Finally, we discuss the advantages and disadvantages of the proposed method and outline future perspectives.
Closed‐form buckling analysis of unsymmetrically laminated plates
Authors: Schreiber Philip , Mittelstedt Christian
Published: March 2023

The local stability of thin‐walled fibre‐reinforced plastic composite beams can be reduced to individual laminates using discrete plate theory. These individual plates receive a supporting effect from their surrounding structure, which is modelled with rotational restraints. In the present investigation, this buckling problem is described by a closed‐form solution. The energy‐based method works with the Rayleigh quotient and the principle of the stationary value of the elastic potential energy. For the analysis of unsymmetrically laminated plates, the classical laminated plate theory (CLPT) considers both the plate deflection and the in‐plane displacements. The first‐order shear deformation theory (FSDT) and third‐order shear deformation theory (TSDT) additionally describe the cross‐sectional rotations and thus take transverse shear deformations into account. In addition to the direct consideration of the bending‐extension couplings, these have also been investigated using the reduced bending stiffness (RBS) method. The investigation shows the influence of bending‐extension coupling on the stability of compressively loaded unsymmetrically laminated plates. Moreover, it is found that the transverse shear stiffness reduces the critical load at relatively high plate thicknesses. The closed‐form analytical solution and the RBS method show good agreement with finite element analyses. The presented closed‐form analytical methods provide explicit solutions for the critical compressive load of unsymmetric laminates under different boundary conditions. Due to the explicit solution, this method is significantly more computationally efficient than numerical, semi‐analytical or exact methods. The present methods are characterised by a simple applicability as well as a very high computational efficiency and are very suitable for preliminary design as well as optimisation of laminated structures.
Dynamic Crack Propagation in a Lattice Boltzmann Method for Solid Mechanics
Authors: Müller Henning , Schlüter Alexander , Müller Ralf
Published: March 2023

In recent years, Lattice Boltzmann methods (LBMs) have been adapted and developed to simulate the behavior of solids. They have already been applied to fractures as well. However, until now, our previous work has been restricted to stationary cracks.

In this work, we regard the reduced 2D case of anti‐plane shear deformation with mode III crack opening. The wave equation is the governing equation for this problem, which is solved via an LBM.

The main contribution of this work is the introduction of an algorithm to handle crack growth in an LBM for solids. The underlying scheme is based on geometric assumptions, which is well suited for the regular lattice used by the LBM. A fracture criterion based on the stress intensity factor is implemented and illustrated by a numerical example.
A new shape optimization approach for fracture propagation
Authors: Suchan Tim , Welker Kathrin , Wollner Winnifried
Published: March 2023

Within this work, we present a novel approach to fracture simulations based on shape optimization techniques. Contrary to widely‐used phase‐field approaches in literature the proposed method does not require a specified ‘length‐scale’ parameter defining the diffused interface region of the phase‐field. We provide the formulation and discuss the used solution approach. We conclude with some numerical comparisons with well‐established single‐edge notch tension and shear tests.
Homogenisation for macroscopic shell structures with application to textile‐reinforced mesostructures
Authors: Mester Leonie , Klarmann Simon , Klinkel Sven
Published: March 2023

In the analysis of textile‐reinforced shell structures full‐scale models are often impractical due to the complex nature of the meso‐structure. The structure is assumed to be globally periodic which allows the definition of a representative volume element (RVE). In this contribution, the RVE is embedded within a first‐order homogenisation framework, where the meso‐to‐macro transition is governed by the Hill‐Mandel condition. In a coupled multiscale approach the macroscopic scale is analysed using shell elements. Each macroscopic integration point is linked to an RVE which accounts for the total thickness of the shell. The macroscopic shell strains are applied on the RVE by means of suitable boundary conditions. On the mesoscopic scale, a boundary value problem is solved in order to obtain equivalent material parameters which are returned to the macroscopic scale. Here, a discrete model of the textile‐reinforcement on the mesostructure is obtained by adapting the approach from the scaled boundary finite element method (SBFEM) in which solids are described by means of their boundary surfaces. These are scaled into one central point, the so‐called scaling center. The required star‐shaped domains are obtained by subdivision. Combination with the isogeometric analysis (IGA) allows to directly facilitate the NURBS (Non‐Uniform Rational B‐Splines) functions describing the boundaries in commonly used CAD software. A key point is the choice of suitable boundary conditions for the RVE. In this contribution a set of periodic boundary conditions will be presented. The proposed method for the analysis of textile‐reinforced shell structures is validated by means of numerical examples.
Linear and nonlinear thermoviscoelastic behavior of polyamide 6
Authors: Keursten Johannes , Kehrer Loredana , Böhlke Thomas
Published: March 2023

Thermoplastic polyamides are used in many industrial areas due to their potential in lightweight applications. Polyamides serve as matrix material in fiber reinforced thermoplastics, for instance. The mechanical behavior of polyamides is characterized by pronounced viscoelastic effects that are strongly affected by environmental conditions like temperature or humidity. In this work, linear thermoviscoelastic behavior of polyamide 6 is considered. Viscoelastic behavior is modeled by the generalized Maxwell model while extended time‐temperature superposition is used to model temperature dependency. A temperature‐frequency sweep conducted by dynamic mechanical analysis serves as input for the model. By horizontal and vertical shifting, master curves of the loss factor, storage modulus, and loss modulus are obtained. Based on this, limitations of time‐temperature superposition and linear thermoviscoelastic modeling are discussed. Furthermore, it is shown that the horizontal shifts can be well approximated by the Williams‐Landel‐Ferry equation for temperatures above and below the glass transition temperature.
Hybrid Digital Twins: A Proof of Concept for Reinforced Concrete Beams
Authors: von Danwitz Max , Kochmann Thank Thank , Sahin Tarik , Wimmer Johannes , Braml Thomas , Popp Alexander
Published: March 2023

Digital twins map physical objects, processes, and further entities from the real (physical) world into digital space. Going one step further, hybrid digital twins combine physics‐based modeling with data‐based techniques to form a simulation tool with predictive power. In the light of an increasing digitalization of our built world, such digital twins have great potential to contribute to the protection of critical technical infrastructures. In case of bridges, digital twins can have a key role in structural health monitoring. This contribution outlines a path to approach these goals and provides a proof of concept of a hybrid digital twin for steel‐reinforced concrete beams as a representative component in civil engineering structures.

Four model components are combined to form the hybrid digital twin, namely, a physics‐based full‐order model, a fast‐to‐evaluate reduced‐order model, a purely data‐driven model, and a baseline model. Applied to the concrete beam, the full‐order model is based on a novel finite element formulation allowing for efficient modeling of slender structures embedded into solid bodies. We use this method to capture the interaction between reinforcement components and concrete matrix of the beam. As reduced‐order model, a physics‐informed neural network is trained with parts of the available measurement data and with the governing equations of a simplified physical model. The data‐driven model localizes cracks in the concrete in a statistical outlier analysis of fiber‐optical strain measurement data. In completion, the baseline model estimates the system behavior based on a closed‐from expression from civil engineering literature.

The proposed hierarchy of four models with decreasing model complexity allows to select an appropriate model according to an application specific trade‐off between model accuracy and cost. We demonstrate the combination of physics‐based modeling with data‐driven techniques based on sensor data measured in a physical four‐point bending test of the reinforced concrete beam.
Electrostatic Body Forces and their Implications for Cracks
Authors: Schlosser Alexander , Ricoeur Andreas
Published: March 2023

A Griffith‐type crack in a dielectric solid under electromechanical loading is investigated by numerically solving the combined boundary value problem. The focus is on the contribution of electrostatically induced body forces, coming along with the still controversially discussed Maxwell stress tensor, to the crack tip loading. A 1/r‐singularity of compressive stress is found to evolve at the crack tip, however, just being dominant over the mechanically induced 1/√r‐behavior within a very small region.
Approximate computational model for the local postbuckling of omega‐stringer‐stiffened composite panels
Authors: Schilling Jakob C. , Mittelstedt Christian
Published: March 2023

Typical thin‐walled structures are found in applications like aircraft, spacecraft and marine vessels. For this type of structure, stability behaviour is crucial. The better this behaviour is understood, the better the full lightweight potential can be exploited. For composite structures especially, new fast analysis tools for preliminary design are required to address this issue. Therefore, the local postbuckling of omega‐stringer‐stiffened composite panels is the subject of a new computational model. The analysis method is computationally highly efficient because it is based on a closed‐form analytical approach. The explicit solution is derived based on the principle of the minimum of the total elastic potential. Furthermore, the solution assumes that the initial eigenform does not substantially change in the early postbuckling regime. In this way, the plates of the skin and stringer can be included explicitly in the analysis. Compared to finite element analysis and a closed‐form computational model found in the literature, the new analysis tool is assessed. The results indicate excellent agreement for panels, where the bay plate is the most critical element of the panel. The new computational model promises to be a highly efficient tool in the preliminary design framework.
Phase‐field modeling of chemically reactive multi‐component and multi‐phase systems
Authors: Seupel Andreas , Roth Stephan , Kiefer Bjoern
Published: March 2023

The present phase‐field approach is based on a mixture theory for multiple components and phases within the framework of non‐equilibrium thermodynamics of internal state variables. More specifically, diffuse interfaces are included in the state potential by terms depending on spatial gradients of the component mass fractions as well as order parameters representing different phases. Coupled field equations of generalized Cahn‐Hilliard and Allen‐Cahn type are derived directly from a local entropy balance, under the assumption of a localized Gibbs fundamental equation. Additionally, thermodynamically consistent kinetics for equilibrium reactions are formulated. The field equations are recast into a mixed variational formulation, which allows a discretization by finite elements with low‐order ansatz functions. The numerical implementation is discussed by means of a benchmark problem for reactive binary systems, of which the thermodynamic equilibrium solution is known.