A monolithic approach toward coupled electrodynamic–thermomechanical problems with regard to weak formulations

Weak formulations of boundary value problems are the basis of various numerical discretization schemes. They are classically derived applying the method of weighted residuals or a variational principle. For electrodynamical and caloric problems, variational approaches are not straightforwardly obtained from physical principles like in mechanics. Weak formulations of Maxwell’s equations and of energy or charge balances thus are frequently derived from the method of weighted residuals or tailored variational approaches. Related formulations of multiphysical problems, combining mechanical balance equations and the axioms of electrodynamics with those of heat conduction, however, raise the additional issue of lacking consistency of physical units, since fluxes of charge and heat intrinsically involve time rates and temperature is only included in the heat balance. In this paper, an energy-based approach toward combined electrodynamic–thermomechanical problems is presented within a classical framework, merging Hamilton’s and Jourdain’s variational principles, originally established in analytical mechanics, to obtain an appropriate basis for a multiphysical formulation. Complementing the Lagrange function by additional potentials of heat flux and electric current and appropriately defining generalized virtual powers of external fields including dissipative processes, a consistent formulation is obtained for the four-field problem and compared to a weighted residuals approach.

Octree Optimized Micrometric Fibrous Microstructure Generation for Domain Reconstruction and Flow Simulation

Over recent decades, tremendous advances in the field of scalable numerical tools and mesh immersion techniques have been achieved to improve numerical efficiency while preserving a good quality of the obtained results. In this context, an octree-optimized microstructure generation and domain reconstruction with adaptative meshing is presented and illustrated through a flow simulation example applied to permeability computation of micrometric fibrous materials. Thanks to the octree implementation, the numerous distance calculations in these processes are decreased, thus the computational complexity is reduced. Using the parallel environment of the ICI-tech library as a mesher and a solver, a large scale case study is performed. The study is applied to the computation of the full permeability tensor of a three-dimensional microstructure containing 10,000 fibers. The considered flow is a Stokes flow and it is solved with a stabilized finite element formulation and a monolithic approach.

Artificial Compressibility Methods for the Incompressible Navier–Stokes Equations Using Lowest-Order Face-Based Schemes on Polytopal Meshes

We investigate artificial compressibility (AC) techniques for the time discretization of the incompressible Navier–Stokes equations. The space discretization is based on a lowest-order face-based scheme supporting polytopal meshes, namely discrete velocities are attached to the mesh faces and cells, whereas discrete pressures are attached to the mesh cells. This face-based scheme can be embedded into the framework of hybrid mixed mimetic schemes and gradient schemes, and has close links to the lowest-order version of hybrid high-order methods devised for the steady incompressible Navier–Stokes equations. The AC time-stepping uncouples at each time step the velocity update from the pressure update. The performances of this approach are compared against those of the more traditional monolithic approach which maintains the velocity-pressure coupling at each time step. We consider both first-order and second-order time schemes and either an implicit or an explicit treatment of the nonlinear convection term. We investigate numerically the CFL stability restriction resulting from an explicit treatment, both on Cartesian and polytopal meshes. Finally, numerical tests on large 3D polytopal meshes highlight the efficiency of the AC approach and the benefits of using second-order schemes whenever accurate discrete solutions are to be attained.

Does a Staggered Scheme Pay Off on Large-scale Hydraulic-mechanical Simulations?

<p>From previous studies it is evident that decoupled simulations lack the ability to capture certain coupled effects, such as the Noordbergum effect or the Mandel-Cryer effect in a hydraulic-mechanical context. Thus, for detailed simulations of geotechnical or geological system, coupled simulations are usually chosen. For example, thermal-hydraulic-mechanical (THM) coupled systems, and even chemical and biological couplings (THMCB), are considered in simulations used to assess barrier integrity over long time spans in the context of geological waste disposal.</p><p>This paper is restricted to coupled hydraulic-mechanical (HM) systems. A monolithic approach is both stable and accurate for strongly coupled systems. However, as site-scale models of geological disposal facilities are also large in spatial dimensions, it is worth to investigate how staggered methods may cut down the computational costs. The fixed-stress split appears to be a promising approach for staggered schemes in terms of stability, consistency, accuracy, and efficiency.</p><p>While adding another iteration level in comparison to monolithic schemes, staggered schemes allow for lower-order approximation spaces, whereas monolithic schemes require Taylor-Hood elements resulting in a larger number of degrees of freedom per element. Both coupling schemes are implemented in the the open-source finite-element (FE) software OpenGeoSys and used to simulate a large-scale model, which is oriented towards a real site in planning in Russia. Simulation results are compared in terms of accuracy, coupling effects and performance.</p>

Comparing double-step and penalty-based semirecursive formulations for hydraulically actuated multibody systems in a monolithic approach

The simulation of mechanical systems often requires modeling of systems of other physical nature, such as hydraulics. In such systems, the numerical stiffness introduced by the hydraulics can become a significant aspect to consider in the modeling, as it can negatively effect to the computational efficiency. The hydraulic system can be described by using the lumped fluid theory. In this approach, a pressure can be integrated from a differential equation in which effective bulk modulus is divided by a volume size. This representation can lead to numerical stiffness as a consequence of which time integration of a hydraulically driven system becomes cumbersome. In this regard, the used multibody formulation plays an important role, as there are many different procedures for the constraint enforcement and different sets of coordinates to choose from. This paper introduces the double-step semirecursive approach and compares it with a penalty-based semirecursive approach in case of coupled multibody and hydraulic dynamics within the monolithic framework. To this end, hydraulically actuated four-bar and quick-return mechanisms are analyzed as case studies. The two approaches are compared in terms of the work cycle, energy balance, constraint violation, and numerical efficiency of the mechanisms. It is concluded that the penalty-based semirecursive approach has a number of advantages compared with the double-step semirecursive approach, which is in accordance with the literature.

A Queer Approach to Understanding LGBT Vulnerability during the COVID-19 Pandemic

Throughout the COVID-19 pandemic, advocates have argued for the inclusion of lesbian, gay, bisexual, and trans (LGBT) people in humanitarian response efforts. Yet the application of this differential focus has been mixed among international policy guidelines and national programs. This research note details a queer theoretical approach to humanitarian crises that considers the intersectional factors that produce specific vulnerabilities within LGBT communities. We take two examples from distinct LGBT communities during the COVID-19 pandemic to demonstrate the analytical risk of treating the umbrella acronym LGBT, indicating distinct identity groups, as monolithic and not differentiating within identity groups based on other factors. We contend that this monolithic approach risks obviating the way different structural forces further compound precarity during crisis. Thus, we make the case for rooting intersectional approaches in any queer analyses of crisis.

Politics of Religion in Tehmina Durrani’s Blasphemy

Generally regarded as one of the most influential factors in the human history, religion has frequently been used as a strong political force by the ruling pundits. In the hands of retrogressive elites, religion has often been operated as an aggressive tool to subdue the voices of the common. In the recent political history of the subcontinent, the aforementioned political role of religion can hardly been overemphasized. Made on the rhetoric of Islam, Pakistan has frequently identified herself as Islam ka Qilla (fortress of Islam) since the very inception till date. Such a monolithic approach of religion has substantially shaped the individual and collective socio-political consciousness of people in Pakistan. Driving the country’s contemporary sensitivities, the politics of religion pivots Pakistani society. The contemporary English fiction in Pakistan largely represents the cultural issues, deeply rooted in religion. Tehmina Durrani, one of the most acclaimed Pakistani novelists, frequently writes about the religiosity and the status of women in Pakistan. Setting against this socio-political preference of religion in Pakistani society, it is proposed that Tehmina Durrani’s Blasphemy can be read as a critique of the retrogressive roles of clergy and aristocracy in Pakistan. Highlighting Pakistan’s patriarchal and religious society, it is contended that Blasphemy is a realistic representation of the wretched conditions of women. Investigating the politics of religion in Pakistan’s rural setting, the paper foregrounds Tehmina’s bold stance on issues of women in the harsh social conditions caused by the nexus of retrogressive clergy and oppressive feudal aristocracy.

Disentangling genetic feature selection and aggregation in transcriptome-wide association studies

ABSTRACTThe success of transcriptome-wide association studies (TWAS) has led to substantial research towards improving its core component of genetically regulated expression (GReX). GReX links expression information with phenotype by serving as both the outcome of genotype-based expression models and the predictor for downstream association testing. In this work, we demonstrate that current linear models of GReX inadvertently combine two separable steps of machine learning - feature selection and aggregation - which can be independently replaced to improve overall power. We show that the monolithic approach of GReX limits the adaptability of TWAS methodology and practice, especially given low expression heritability.

Indigenous childhood in Argentina: Parenting, care and formative experiences of Qom and Mbyá children

Recent investigations in South American anthropology have focused on children in a range of contexts. In ethnographic research with children from indigenous communities in Argentina, we have considered social categories that result in different ways of being a child. In this way, this article presents a model that departs from a traditional, monolithic approach to childhood. The aim is to examine the first stage of life, guided by nominal references, childrearing and the formative experiences of children, with a focus on the network of social relations during this stage of live, particularly, linguistic development, religion and play.