Integration Scheme Research Articles

Challenges and Lessons Learned From Pseudo‐Dynamic Hybrid Simulations on Ductile Steel Braced Frame Systems

ABSTRACTPerformance‐based seismic design, which emerged more than two decades ago, requires accurate numerical models to capture the response of structural elements that undergo inelastic deformations under random loading histories. High‐fidelity benchmark test results under real natural hazards are therefore required to assist researchers and practitioners with this effort. Substructuring pseudo‐dynamic hybrid simulation (PsDHS) is an efficient, yet effective testing method for evaluating the system‐level response of structures under extreme loading scenarios, and for forming a database of high‐fidelity benchmark test results. In PsDHS, the response of the critical structural components is captured in a laboratory through physical testing and is integrated with the numerical response of the remainder of the structure in a numerical model, by establishing a communication framework between the two. The former is referred to as a physical substructure and the latter is often referred to as the integration module. Despite its efficiency and effectiveness, large‐scale hybrid simulation introduces researchers to a range of non‐trivial challenges, especially in laboratories that are new to the methodology. This paper presents challenges and lessons learned from 21 large‐scale pseudo‐dynamic hybrid simulations on different ductile steel braced frame systems including a buckling‐restrained braced frame (BRBF), a special concentrically braced frame (SCBF), a yielding brace system (YBS) equipped with cast steel yielding connectors (YCs), and eccentrically braced frames (EBFs) designed with cast steel replaceable modular yielding links (CMLs). Details for each hybrid simulation including the experimental setups, reference buildings, earthquake records, etc. along with selected results are presented. Challenges that were faced in each hybrid simulation related to hardware, the control system, integration schemes, etc., and attempted solutions are discussed. The findings from each set of hybrid simulations on each braced frame system are summarized. The experimental results are organized as a dataset in an online data repository, which is available for download. The organization of the dataset is presented to facilitate access to the experimental results. In the end, concluding remarks and visions for future research are presented.

Perceptions of community healthcare workers on the use of teledentistry for seniors in Singapore: A qualitative study

Objective This study aimed to identify barriers and facilitators surrounding the implementation of TDOCS from Community Health Workers (CHW)'s perspective before TDOCS implementation. Methods A descriptive qualitative study was conducted through semistructured interviews with a purposive sampling of CHWs from partner nursing homes and home care teams. A French framework outlining barriers to asynchronous oral teleconsultation adoption was used to develop the topic guide for this study. Then, the Consolidated Framework for Implementation research (CFIR 1.0) was used to guide coding and analysis. Results A total of 43 CHWs from participating institutions were interviewed prior to receiving teledentistry training. Perceived barriers included low awareness about the importance of dental care, limiting conditions to T-DOCS participation among beneficiaries, limited understanding of T-DOCS, perceived low self-efficacy among CHWs, manpower shortages, perceived low priority of dental care, competition with other nursing duties and restricted access due to COVID-19. Facilitators included existing relationships between CHWs and beneficiaries, receptivity towards participation, CHWs’ motivation to upskill and improve dental care for seniors, prior experience with other telemedicine technology, perceived need for change, supportive management, colleagues and existing impediments to access dental care. Conclusion This study identified barriers and facilitators to implementing T-DOCS from the CHWs’ perspectives. We recommend for targeted CHW training, programme champions, workflow integration and incentivisation schemes. Addressing challenges like manpower strain and resource limitations through efficient scheduling and capacity building is vital for sustainability. Policy-level support, including legal frameworks, funding and regulatory structures, is essential for integrating teledentistry into mainstream healthcare.

Versatile static synchronous machine based offshore wind farm integration scheme

Versatile static synchronous machine based offshore wind farm integration scheme

An explicit peridynamics model for hydraulic fracturing in porous media

PurposeThe purpose of this paper is to systematically investigate the hydraulic fracture branching phenomena in porous media under different loading conditions and the stepwise phenomenon. The effect of the pore pressure in hydraulic fracturing branching is studied, and more evidence for the stepwise phenomenon with the peridynamics approach is provided.Design/methodology/approachA fully coupled fluid-filled explicit peridynamics model is developed to simulate the complex evolution of crack branching and stepwise phenomena in saturated porous media. Based on the peridynamics theory, an explicit time integration scheme is used to solve the coupled equation system including rock deformation, fluid flow and fracture propagation. Using the proposed model, a series of peridynamic computational tests are performed to examine two common kinds of phenomena observed in hydraulic fracturing: the crack branching phenomenon and the stepwise phenomenon.FindingsFor crack branching phenomenon, the results obtained indicate that sufficient loading is required in order to initiate the crack branching process. Compared with the stress applied on crack surfaces condition, crack branching is more easily induced with the stress applied on boundaries. In addition, for the fluid-driven crack (stress applied on crack surfaces), the existence of pore pressure will depress the growth and branching of the crack. For stepwise phenomena, the results obtained indicate that the peridynamics is a promising tool to study the stepwise phenomenon. The stepwise phenomenon is more distinct under mechanical loading conditions due to the solid behaviour. A sudden jump or crack extension will happen when enough energy is accumulated in the hydraulic fracturing system.Research limitations/implicationsIn this study, the explicit method is used, which means it is conditionally stable, and the critical time step needs to be decided. The reason to use the explicit method is for the study purpose; the explicit method is faster and has no need for matrix inversions.Originality/valueThis study helps to understand the effect of the pore pressure in hydraulic fracturing branching and provides more evidence for the stepwise phenomenon with peridynamics.

Dynamics characteristics of variable stiffness curvilinear fiber-reinforced layered composite beam under moving load by sinusoidal shear flexible beam model including nonlinear and thermal effects

In this study, the dynamic response behavior of curvilinear fibers based layered-composite beam under transversely moving load is investigated considering linear and nonlinear analyses. The formulation is developed applying sinusoidal shear flexible beam theory, geometrical nonlinearity based on von Kármán’s assumption, and the constitutive equation fulfilling the plane stress situation through the width of arbitrarily lay-up composite beam. The load on the beam is treated as moving with uniform velocity, acceleration and also oscillatory motion with time. The governing nonlinear dynamic equations are framed employing Hamilton’s principle and by adopting finite element approach. The response of beam in time domain is obtained solving the governing equations through direct time integration method by Newmark integration scheme. and the results are viewed through the frequency-amplitude relationship. A detailed parametric study involving curvilinear fiber path angles, lay-up ply angles, thickness ratio, moving load velocity, and acceleration, and forcing frequency is made on the dynamic behavior of variable stiffness beam with curvilinear fiber beam. The effect of thermal environment and boundary conditions on the vibrational response behavior of beam is also predicted.

Discontinuous Galerkin discretization of coupled poroelasticity–elasticity problems

Abstract This work is concerned with the analysis of a space–time finite element discontinuous Galerkin method on polytopal meshes (XT-PolydG) for the numerical discretization of wave propagation in coupled poroelastic–elastic media. The mathematical model consists of the low-frequency Biot’s equations in the poroelastic medium and the elastodynamics equation for the elastic one. To realize the coupling suitable transmission conditions on the interface between the two domains are (weakly) embedded in the formulation. The proposed PolydG discretization in space is coupled with a dG time integration scheme, resulting in a full space–time dG discretization. We present the stability analysis for both semidiscrete and fully discrete formulations, and derive error estimates in suitable energy norms. The method is applied to various numerical test cases to verify the theoretical bounds. Examples of physical interest are also presented to investigate the capability of the proposed method in relevant geophysical scenarios.

Time‐Domain Spectral BFS Plate Element With Lobatto Basis for Wave Propagation Analysis

ABSTRACTA computationally efficient spectral Kirchhoff plate element is presented for time‐domain analysis of wave propagation at high frequencies in thin isotropic plates. It employs a ‐continuous spectral interpolation based on the modified bi‐Hermite polynomials using the Gauss–Lobatto–Legendre (GLL) points as a basis with selective collocation of rotational and twisting degrees of freedom (DOFs) at element edge and corner nodes. The lowest order version of the proposed element reduces to the classical Bogner–Fox–Schmit (BFS) element for Kirchhoff plates. The GLL basis allows diagonalisation of the mass matrix using the nodal quadrature technique, which enhances the computational efficiency. The numerical properties of the proposed element are comprehensively evaluated, including the conditioning of the system matrices. Moreover, the effect of employing different numerical integration schemes and nodal sets is examined in both static and free vibration analyses. The effectiveness of the proposed element in wave propagation problems is evaluated by comparing its performance to the converged solutions achieved using the BFS element with a very fine mesh. Results demonstrate that the current element, without and even with mass matrix diagonalisation delivers exceptional accuracy while also exhibiting faster convergence and enhanced computational efficiency than the existing Kirchhoff plate elements.

Development of an Extended State Observer for Monitoring of a PWR Based on a Two-Point Kinetic Model

Accurate estimation of unmeasured system states and disturbances in a pressurized water reactor (PWR) is essential for effective control, operation optimization, and safety monitoring. To this end, this paper investigates the estimation of unmeasured system states and disturbances of the PWR system during load-following operation. First, a mathematical model for the PWR system is established based on the two-point kinetics equations with one equivalent delayed neutron precursor group. Subsequently, an extended state observer (ESO) integration scheme, incorporating two coupled ESOs, is constructed to estimate unmeasured system states, including relative density of delayed neutron precursor, average fuel temperature, total reactivity, xenon concentration, and iodine concentration, along with time-varying disturbances, with the use of measurements of the PWR system only. According to the Lyapunov stability theorem, it is proved that the estimation error dynamic of the proposed ESO integration scheme is uniformly ultimately bounded stable. Finally, simulation results confirm that the proposed ESO integration scheme provides higher estimation accuracy and stronger robustness against measurement noises, model uncertainties, and external disturbances compared to both a high-gain observer and a high-order sliding mode observer.

Mathematical Logic Integration Scheme in Ushul Fiqh

This research is aimed to arrange an integration scheme between mathematical logic and ushul fiqh which focuses on the discussion of mafhum mukholafah. This study is designed by using a qualitative design, which conducted by using library research/literature study. It was carried out by collecting materials related to research from books, scientific journals, literature and other publications that were worthy of being used as sources for research studies by describing the data through several expert opinions. The results of this study indicate that there is an integration between mathematical logic and the science of mantiq, especially in the discussion of the inverse of a statement with mafhum mukholafah. However, there is also a gap between them, there are still objects of study in ushul fiqh that cannot be accommodated in mathematical logic.

Growth-based monolithic 3D integration of single-crystal 2D semiconductors.

The demand for the three-dimensional (3D) integration of electronic components is steadily increasing. Despite substantial processing challenges, the through-silicon-via (TSV) technique emerges as the only viable method for integrating single-crystalline device components in a 3D format1,2. Although monolithic 3D (M3D) integration schemes show promise3, the seamless connection of single-crystalline semiconductors without intervening wafers has yet to be demonstrated. This challenge arises from the inherent difficulty of growing single crystals on amorphous or polycrystalline surfaces after the back-end-of-the-line process at low temperatures to preserve the underlying circuitry. Consequently, a practical growth-based solution for M3D of single crystals remains unknown. Here we present a method for growing single-crystalline channel materials, specifically composed of transition metal dichalcogenides, on amorphous and polycrystalline surfaces at temperatures low enough to preserve the underlying electronic components. Building on this developed technique, we demonstrate the seamless monolithic integration of vertical single-crystalline logic transistor arrays. This accomplishment leads to the development of unprecedented vertical complementary metal oxide semiconductor (CMOS) arrays composed of grown single-crystalline channels. Ultimately, this achievement provides opportunities for M3D integration of various electronic hardware in the form of single crystals.

Efficient simulation of hydrodynamic bearings using the SBFEM with eigenvalue problem derivatives

AbstractThis work presents a semi-analytical solution of the Reynolds equation under Gümbel conditions for hydrodynamic bearings in rotordynamic simulations. The algorithm is based on the SBFEM (scaled boundary finite element method) in combination with eigenvalue problem derivatives. The pressure field is discretized by standard finite elements along the circumferential coordinate, while an exact analytical formulation is used in the axial direction. This transforms the partial differential equation into a system of ordinary differential equations and leads to an eigenvalue problem. The computation of the continuously changing eigenvalues and eigenvectors is achieved by accurate Taylor approximations so that the repeated call of a numerically expensive eigensolver can be avoided. The algorithm is incorporated into a time integration scheme for the dynamic analysis of a simple system, consisting of a rotor with two degrees of freedom in a hydrodynamic bearing. Thereby, the method is verified, and its numerical efficiency is demonstrated. For a bearing with a slenderness ratio (length-to-diameter ratio) of 1, the computational time is reduced to $$8.8\%$$ 8.8 % compared to a standard FVM (finite volume method) solution.

Switchable Pancharatnam-Berry Phases in Heterogeneously Integrated THz Metasurfaces.

The Pancharatnam-Berry (PB) phase has revolutionized the design of metasurfaces, offering a straightforward and robust method for controlling wavefronts of electromagnetic waves. However, traditional metasurfaces have fixed PB phases determined by the orientation of their individual elements. In this study, an innovative structural design and integration scheme is proposed that utilizes vanadium dioxide, a phase-change material, to achieve thermally controlled dynamic PB phase control within the metasurface. By leveraging the material's properties, this can dynamically alter the optical orientation of individual elements of the metasurface and achieve temperature-dependent local phase modulation based on the geometric phase principle. This approach, combined with advanced fabrication processing technology, paves the way for next-generation dynamic devices with customizable functions.

VARIATIONAL-DIFFERENCE SOLUTION OF DEFORMATION AND BUCKLING PROBLEMS OF ELASTOPLASTIC SHELLS OF REVOLUTION WITH ELASTIC FILLER UNDER COMBINED QUASI-STATIC AND DYNAMIC AXISYMMETRIC LOADINGS

The paper suggests a formulation and method for a numerical solution of deformation and buckling of elastoplastic shells of revolution with elastic filler under quasi-static and dynamic loadings. The problem is solved in a two-dimensional plane or generalized axisymmetric formulation with torsion. The governing system of equations is written in a Cartesian or cylindrical coordinate system. Modeling of deformation of an elastic-plastic shell is carried out based on the hypotheses of the theory of shells of the Timoshenko type, taking into account geometric nonlinearities. Kinematic relations are written in velocities and formulated in the metric of the current state. The elastoplastic properties of the shell are described by the flow theory with nonlinear isotropic hardening. Filler modeling is based on continuum mechanics hypotheses. The filler material is assumed to be linearly elastic. The variational equations of motion of structural elements (both shells and filler) are reduced from the three-dimensional equation of the balance of virtual powers of the work of continuum mechanics taking into account the accepted hypotheses of the theory of shells or a flat deformed state or generalized axisymmetric deformation with torsion. The modeling of the contact interaction between the shell and the filler is based on the condition of nonpenetration along the normal and slippage along the tangential. The finite-difference method and an explicit time integration scheme of the cross type are used to solve the defining system of equations. Approbation of the technique was carried out on the problem of buckling of a steel cylindrical shell with an elastic filler under quasi-static and dynamic compression by an external pressure that linearly increases with time. The results of the numerical study are compared with calculations performed using two other approaches developed earlier by the authors. The first approach is based on full-scale modeling of the process of deformation of the shell and filler within the framework of continuum mechanics. In the second approach, a simplified formulation is used, in which the deformation of the shell is modeled according to the hypotheses of the theory of non-sloping shells of the Timoshenko type taking into account geometric nonlinearities, and the filler is modeled according to the Winkler foundation hypothesis. The developed approaches make it possible to model the nonlinear subcritical deformation of shells of revolution with an elastic filler, to determine the ultimate (critical) loads in a wide range of loading rates taking into account geometric shape imperfections, to study buckling in axisymmetric and non-axisymmetric shapes under dynamic and quasi-static combined loadings in plane and axisymmetric deformations.

The Mechanical Properties and Energy Absorption of AuxHex Structures.

Based on a combination of hexagonal honeycomb and re-entrant honeycomb cells, the concept of novel hybrid cell structures was developed. Experimental studies and numerical analyses of the behaviour of the analysed structures under in-plane compression in two compression directions were carried out. Explicit finite element analyses with an explicit integration scheme, incorporating plastic deformation and ductile damage evolution models, were employed to analyse the entire deformation process, including plastic and damage stages. Good agreement was obtained between the results of the numerical analyses and the experimental studies.

Exploratory Study of a Green Function Based Solver for Nonlinear Partial Differential Equations

This work explores the numerical translation of the weak or integral solution of nonlinear partial differential equations into a numerically efficient, time-evolving scheme. Specifically, we focus on partial differential equations separable into a quasilinear term and a nonlinear one, with the former defining the Green function of the problem. Utilizing the Green function under a short-time approximation, it becomes possible to derive the integral solution of the problem by breaking it into three integral terms: the propagation of initial conditions and the contributions of the nonlinear and boundary terms. Accordingly, we follow this division to describe and separately analyze the resulting algorithm. To ensure low interpolation error and accurate numerical Green functions, we adapt a piecewise interpolation collocation method to the integral scheme, optimizing the positioning of grid points near the boundary region. At the same time, we employ a second-order quadrature method in time to efficiently implement the nonlinear terms. Validation of both adapted methodologies is conducted by applying them to problems with known analytical solution, as well as to more challenging, norm-preserving problems such as the Burgers equation and the soliton solution of the nonlinear Schrödinger equation. Finally, the boundary term is derived and validated using a series of test cases that cover the range of possible scenarios for boundary problems within the introduced methodology.

Serial dependencies in motor targeting as a function of target appearance.

In order to bring stimuli of interest into our central field of vision, we perform saccadic eye movements. After every saccade, the error between the predicted and actual landing position is monitored. In the laboratory, artificial post-saccadic errors are created by displacing the target during saccade execution. Previous research found that even a single post-saccadic error induces immediate amplitude changes to minimize that error. The saccadic amplitude adjustment could result from a recalibration of the saccade target representation. We asked if recalibration follows an integration scheme in which the impact magnitude of the previous post-saccadic target location depends on the certainty of the current target. We asked subjects to perform saccades to Gaussian blobs as targets, the visuospatial certainty of which we manipulated by changing its spatial constant. In separate sessions, either the pre-saccadic or post-saccadic target was uncertain. Additionally, we manipulated the contrast to further decrease certainty, changing the spatial constant mid-saccade. We found saccade-by-saccade amplitude reductions only with a currently uncertain target, a previously certain one, and a constant target contrast. We conclude that the features of the pre-saccadic target (i.e., size and contrast) determine the extent to which post-saccadic error shapes upcoming saccade amplitudes.

A NURBS-based isogeometric formulation for geometrically nonlinear analysis of shells

Due to their high slenderness, shell structures are vulnerable to collapse caused by loss of stability, hence nonlinear analysis is crucial to ensure a safe design. The advantage of isogeometric analysis (IGA) to exactly describe the geometry of the problem independently of the degree of discretization and allow easy refinements has led to its increasing application in shell analysis. However, IGA does not remove the shear and membrane locking presented by fully integrated shell elements based on Reissner-Mindlin's theory. Thus, several alternatives have been proposed in the literature to solve the locking problem, such as mixed formulation and reduced integration. This work aims to study the effectiveness of different reduced integration schemes to eliminate or alleviate locking in the context of stability and geometrically nonlinear analysis of Reissner-Mindlin shells based on the degenerated solid approach. The proposed formulation is applied to the stability analysis of plates and shells, where critical loads and nonlinear equilibrium paths are evaluated and compared to solutions available in the literature or obtained by the Finite Element Method. Excellent results were obtained, demonstrating that a very accurate and efficient approach for nonlinear analysis of plates and shells can be achieved by using high regularity basis functions obtained by k-refinement and an appropriate reduced integration scheme. This approach not only avoids locking but also reduces the computational cost of nonlinear analysis of shells.

Nonlinear dynamic analysis of prestressed cable structure under random aerodynamic loading

Abstract. This paper includes the development and dynamic analysis of a mathematical model of an elastic prestressed cable structure such as those used in light roof structures known as “tensile structures” in which the external loads are balanced by tensile forces in the cables. Due to the light weight of this structural model the aerodynamic loads are critical and determine the design.The model consists of four same length and section cables arranged in an X-shape in a planar view, fixed at one end, with an equivalent mass of the system in the center node, their other extremity. The cables are not in a plane: two opposite cables have their supports in the same positive vertical height, and the other two opposite cables have their support in the same negative vertical height.There are forces acting on the central node in the x, y and z directions modeling random aerodynamic loading simulated by a Monte Carlo-type procedure inspired by Prof. Franco’s Synthetic Wind Method. This technique involves creating several loading series combining different harmonic components with amplitudes and frequencies obtained from an adopted PSD (Power Spectrum Density Function) with randomly chosen phases. This results a large number of response displacements and tensions to be statistically treated to render sound engineering design decisions. The model admits large displacements so that a nonlinear dynamic approach is adopted. A numerical step-by-step finite differences time integration scheme is also implemented.

The Matrix‐Free Macro‐Element Hybridized Discontinuous Galerkin Method for Steady and Unsteady Compressible Flows

ABSTRACTThe macro‐element variant of the hybridized discontinuous Galerkin (HDG) method combines advantages of continuous and discontinuous finite element discretization. In this paper, we investigate the performance of the macro‐element HDG method for the analysis of compressible flow problems at moderate Reynolds numbers. To efficiently handle the corresponding large systems of equations, we explore several strategies at the solver level. On the one hand, we utilize a second‐layer static condensation approach that reduces the size of the local system matrix in each macro‐element and hence the factorization time of the local solver. On the other hand, we employ a multi‐level preconditioner based on the FGMRES solver for the global system that integrates well within a matrix‐free implementation. In addition, we integrate a standard diagonally implicit Runge–Kutta scheme for time integration. We test the matrix‐free macro‐element HDG method for compressible flow benchmarks, including Couette flow, flow past a sphere, and the Taylor–Green vortex. Our results show that unlike standard HDG, the macro‐element HDG method can operate efficiently for moderate polynomial degrees, as the local computational load can be flexibly increased via mesh refinement within a macro‐element. Our results also show that due to the balance of local and global operations, the reduction in degrees of freedom, and the reduction of the global problem size and the number of iterations for its solution, the macro‐element HDG method can be a competitive option for the analysis of compressible flow problems.

Physics‐Based Spiking Neural Network as a Surrogate Model for Viscoplastic Material Law in Impulsively Loaded Beams

ABSTRACTIn the present study, the nonlinear material law of an in‐house FEM solver is substituted by physics‐informed neural networks (PINNs) and by physics‐based spiking neural networks (SNNs) for predicting the dynamic response of beams under impact loading. In the first part of this study concerning PINNs, the physics are included in the loss function of a deep neural network, also called a second‐generation neural network. The main advantage of using PINNs compared to classical ANNs is that they are considered data‐efficient function approximators. In the second part of this study, leaky integrate and fire (LIF) layers are deployed instead of dense layers in the PINN architecture, leading to a physics‐based third‐generation SNN, which enhances the PINN architecture in terms of energy efficiency. Third‐generation SNNs are inspired by the human brain function, where the information is processed via spikes. The spikes introduce sparse behavior, leading to a more energy‐efficient and sustainable deep learning method when implemented in neuromorphic hardware. The PINNs and physics‐based SNNs are employed in the implicit integration scheme of the material law of the in‐house FEM solver at the Gaussian level, and results are compared with the in‐house FEM solution in two different initial boundary value (IBV) problems. This study aims to show that PINNs can predict nonlinear material behavior and that the use of a physics‐based loss function enables the utility of less data in the training of the neural networks. Moreover, we show that we can enhance PINNs regarding energy consumption by adding a LIF layer. Therefore, the energy consumption is compared when the physics‐based SNN is deployed on the Loihi neuromorphic chip and on the CPU.