Iterative Coupling Research Articles

Iterative coupling of a fundamental electricity market model and an agent-based simulation model to reduce the efficiency gap

Fundamental optimization models can determine normative cost-optimal systems following theoretical assumptions of markets with perfect competition and perfect foresight. However, in real markets, deviations from ideal assumptions need to be considered for designing efficient policies: they may lead to higher costs than theoretically expected and contribute to the so-called “efficiency gap”. Agent-based simulation models can consider market inefficiencies but are not ideally suited for determining normative systems. This work aims to reduce the efficiency gap between theoretically cost-optimal system configurations and their implementations in non-perfect markets by coupling a fundamental electricity market model and an agent-based model. A fully automated iterative coupling is demonstrated, and its convergence behavior is investigated for two coupling parameters. Fast convergence is observed when integrating peak capacity usage from the previous agent-based simulation into the fundamental model. However, the efficiency gap is reduced only to limited extent as no information on hourly dispatch is transferred between the models. Conversely, when using hourly storage dispatch as coupling parameter, it takes longer to achieve convergence. In return, the efficiency gap is reduced to larger extent. The proposed iterative coupling thus allows the identification of realizable cost-optimal systems, which means that they are achievable under non-perfect market conditions.

An Innovative and Efficient Implementation of Matrix-Free Newton Krylov Method for Neutronics/Thermal-hydraulics Coupling Simulation

The core physical behavior of reactors is essentially the result of multi-physical fields coupling feedback. High-fidelity neutronics/thermal-hydraulics (N/TH) analysis can simulate and predict nuclear reactor core phenomena realistically, providing advanced and reliable technical means during the design and safety analysis of nuclear reactor. In this work, an efficient and robustness coupling method using power density as the coupling parameter, Matrix-Free Newton Krylov (MFNK) method, is successfully developed and innovatively implemented in HNET for high-fidelity N/TH coupling simulation. To enhance the efficiency and stability, the multi-level generalized equivalence theory-based CMFD (ML-gCMFD) iterative acceleration method and ML-gCMFD coupling acceleration method are proposed. In addition, the nonlinear preconditioning and hybrid perturbation size formula are implemented to further improve the convergence. Finally, to evaluate the numerical accuracy, convergence, efficiency and stability of MFNK method, a series of representative problems, including a three-dimensional (3D) single fuel pin problem, VERA Benchmark Problem 6, and VERA Benchmark Problem 7, are analyzed by comparing with the current N/TH coupling methods. Numerical results indicate that MFNK method can obtain strong stability, high convergence performance, and relatively high computational efficiency while ensuring high accuracy. It demonstrates that MFNK method has significant performance advantages and potential for high-fidelity N/TH coupling simulation.

Alternating iterative coupling of hydrological and hydrodynamic models applied to Lingjiang river basin, China

Alternating iterative coupling of hydrological and hydrodynamic models applied to Lingjiang river basin, China

On the implementation in Abaqus of the global–local iterative coupling and acceleration techniques

This paper presents results and convergence study of the Global–Local Iterative Coupling through the implementation in the commercial software Abaqus making use of the co-simulation engine. A hierarchical modeling and simulation approach is often required to alleviate modeling burdens. Particular focus has been devoted here on convergence acceleration and performance optimization. Two applications in statics with nonlinear material behavior and geometrically nonlinear formulation are considered here: first a holed curved plate under traction with elastic–plastic material, then a pre-stressed bolted joint connecting two plates between each other and subjected to traction load. Three different convergence acceleration techniques are compared in terms of convergence performance and accuracy. An inexact solver strategy is proposed to improve computing time performance. The results show promising results for the coupling technology and constitute a step forward in the availability of non-intrusive multi-scale modeling capabilities for complex structures and assemblies.

Phase-field modeling and effective simulation of non-isothermal reactive transport

We consider single-phase flow with solute transport where ions in the fluid can precipitate and form a mineral, and where the mineral can dissolve and release solute into the fluid. Such a setting includes an evolving interface between fluid and mineral. We approximate the evolving interface with a diffuse interface, which is modeled with an Allen–Cahn equation. We also include effects from temperature such that the reaction rate can depend on temperature, and allow heat conduction through fluid and mineral. As Allen–Cahn is generally not conservative due to curvature-driven motion, we include a reformulation that is conservative. This reformulation includes a non-local term that makes the use of standard Newton iterations for solving the resulting non-linear system of equations very slow. We instead apply L-scheme iterations, which can be proven to converge for any starting guess, although giving only linear convergence. The three coupled equations for diffuse interface, solute transport and heat transport are solved via an iterative coupling scheme. This allows the three equations to be solved more efficiently compared to a monolithic scheme, and only few iterations are needed for high accuracy. Through numerical experiments we highlight the usefulness and efficiency of the suggested numerical scheme and the applicability of the resulting model.

A time-domain FEM-BEM iterative coupling algorithm with dual-independent discretizations in both time and space domains

A time-domain (TD) FEM-BEM iterative coupling algorithm with dual-independent discretizations in both time and space domains for dynamics is presented, allowing the independent temporal and spatial discretizations and solutions for each sub-domain in the coupled model. According to the continuity and equilibrium equations between the sub-domains of TD-FEM and TD-BEM, as well as the continuity condition along time, the displacement and force converting matrices and the time inter/extra-polation scheme in time domain are derived to exchange data between TD-FEM and TD-BEM nodes on the interface, which are not required to be positionally matched. The proposed iterative coupling algorithm with dual-independent discretizations in time and space domains is verified by two examples to be of the advantages of the independence for one's own formulation, high computational accuracy, good flexibility and versatility.

Transition-metal-free iterative two-fold reductive coupling and 1,3-borotropic shift to form 1,4-skipped dienes.

We report herein a transition-metal-free two-fold reductive coupling between prenal (allyl) tosylhydrazone and boronic acids/1,3-borotropic shift cascade to furnish 1,4-skipped dienes. In this work, a single batch operation produces (E,E)-1,4-skipped dienes by undergoing a second reductive coupling of the transient boronic acid, which developed in situ following the first reductive allylation and a cascade 1,3-boron migration. Remarkably, the protocol is compatible with various aryl- and alkyl-substituted boronic acids, is scalable and has demonstrated on 61 substrates with yields up to 98%.

Stereodivergent synthesis of 2-oxo-oligopyrrolidines by an iterative coupling strategy.

Natural linear polyamines play diverse roles in physiological processes by interacting with receptors at the cellular level. Herein, we describe the stereodivergent synthesis of oligopyrrolidines, which are conformationally constrained polyamines. We synthesized dimeric and trimeric 2-oxo-oligopyrrolidines using an iterative coupling strategy. The key to our success is an iridium-catalyzed trans/cis-selective nucleophilic addition and subsequent threo/erythro-stereoselective reduction. The synthesized pyrrolidines show varying cytotoxicities against a human cancer cell line depending on the number of rings and their stereochemistry.

Reactivity of 1,3-enyne MIDA boronates: exploration of novel 1,2-alkyne shift via gem-difluorination.

The discovery of a new class of heteroatom-rich boron-containing molecules (BCMs) and iterative cross-coupling (ICC) partners created a toolbox for future drug developments using organoboron compounds. Herein, we report the potential utility of 1,3-enyne MIDA boronates to access diverse gem-difluoro MIDA boronates via novel 1,2-alkyne shift. This unique reactivity of 1,3-enyne MIDA boronates offers facile access to previously challenging β-difluorinated alkyl borons. Furthermore, we demonstrated the synthesis of various novel furan-based BCMs via 5-endo-dig cyclization and iterative coupling partners via copper-catalyzed hydroboration and platinum-catalyzed diboration reaction.

Practical N-to-C peptide synthesis with minimal protecting groups

Accessible drug modalities have continued to increase in number in recent years. Peptides play a central role as pharmaceuticals and biomaterials in these new drug modalities. Although traditional peptide synthesis using chain-elongation from C- to N-terminus is reliable, it produces large quantities of chemical waste derived from protecting groups and condensation reagents, which place a heavy burden on the environment. Here we report an alternative N-to-C elongation strategy utilizing catalytic peptide thioacid formation and oxidative peptide bond formation with main chain-unprotected amino acids under aerobic conditions. This method is applicable to both iterative peptide couplings and convergent fragment couplings without requiring elaborate condensation reagents and protecting group manipulations. A recyclable N-hydroxy pyridone additive effectively suppresses epimerization at the elongating chain. We demonstrate the practicality of this method by showcasing a straightforward synthesis of the nonapeptide DSIP. This method further opens the door to clean and atom-efficient peptide synthesis.

Validation and analysis of a coupled fluid-ablation framework for modeling low-temperature ablator

Ablation of certain highly volatile materials, such as camphor, naphthalene, and dry ice, can be achieved at relatively mild hypersonic conditions in unheated wind tunnels. This provides a convenient way to test fundamental aspects of the ablation process, develop measurement techniques, and validate numerical simulations. In this study, we develop a coupled framework between hypersonic flow and material response solvers and validate the numerical approach against recent experiments conducted by the von Karman Institute of Fluid Dynamics. The flow environment is modeled with an overset near body - Cartesian solver developed within CHAMPS. The solver is equipped with capabilities for automatic mesh generation, adaptive mesh refinement (AMR), and an interpolation algorithm for exchanging boundary conditions with external solvers. The material domain is modeled with a network of one-dimensional rays, incorporating a heat conduction solver, several types of surface ablation models, and a coupled system of surface balance equations required for coupling with the flow solver. The material environment in the simulation aims to closely match the experimental design of the ablating sample, which included a thin layer of camphor applied on top of a copper holder. By taking into account the cooling effect introduced by the back structure, we were able to achieve close agreement with the experimental data for the stagnation point recession and the overall shape change of the geometry. The obtained results are also compared to uncoupled equilibrium-based and steady-state (coupled) solutions, highlighting the importance of the coupled approach for modeling ablation problems. In addition, we explore the effects of different transport properties on the ablation rate of the material, highlighting a strong dependence on the diffusivity of the ablating species. Finally, using the flexibility of the developed algorithm, we explore the effect of the iterative scheme and coupling frequency between the solvers on the accuracy of the solution and the overall duration of the simulation.

An iterative decomposition coupling algorithm between TD-FEM and TD-BEM with independent spatial discretization on the interface

An iterative decomposition coupling algorithm between TD-FEM and TD-BEM with independent spatial discretization on the interface

Modelling the post‐buckling behaviour of steel sheets under induction heating

AbstractInduction heating has many engineering applications. To accurately describe the induction heating process of thin steel sheets one needs to account for their mechanical deformation. This might strongly affect the magnetic configuration since thin sheets are prone to thermal buckling, leading to large supercritical deformations. We suggest a modelling strategy combining a computationally highly efficient structural mechanical shell description for the thin sheet with a standard continuum model for eddy current and thermal problems through an iterative coupling algorithm. All benchmark problems are solved numerically using the finite element method.

Modular Framework for the Solution of Boundary-coupled Multiphysics Problems

This paper presents a modular multiphysics framework developed for OpenFOAM. The framework is built around an iterative implicit coupling scheme based on a multi-region partitioned approach. This scheme allows the implementation of formal implicit time-marching schemes, which improves the stability of strongly interacting coupled problems. This methodology allows physical interactions to be handled through specifically designed interface boundary conditions. It also allows region-specific solvers to be implemented as modular class solvers. The coupling methodology is handled with a main program that manages solver-specific actions. The aim of this framework is to facilitate the implementation and testing of new multiphysics coupling problems in an integrated code structure. To show the capabilities of the framework to integrate new physics, solvers and boundary conditions requirements are discussed. Also, three validated examples involving fluid-structure interactions, conjugate heat transfer, and fluid-structure-thermal interactions are presented. Although all these problems are boundary-coupled multiphysics problems, the framework is conceptually not limited to this kind of problems. The benefit of this work to the OpenFOAM community is a general and modular framework that facilitates the setup and solution of diversified multiphysics problems, and that illustrates the implementation of modular interface boundary conditions between physics regions.

Synthesis of lysiformine, a marine-derived 3-hydroxypyridine alkaloid

A synthesis of the bisindole alkaloid lysiformine is reported. The heterocyclic skeleton of the natural product was assembled from a kojic acid-derived pyridine using iterative Suzuki coupling and reductive alkylation reactions. The NMR spectroscopic data of the synthetic sample was in excellent agreement to the natural product, confirming that lysiformine is a rare example of a marine natural product harbouring a 3-hydroxypyridine.

A suggested dynamic soil – structure interaction analysis

In this paper, a new methodology for time domain analysis of buildings on raft foundations considering soil – structure interaction is proposed. Sub-structuring technique is used to separate the building as super-structure and the underneath soil as sub-structure. The super-structure can be modeled using any numerical method. However, in this paper the super-structure is modeled via the BEM to consider the real interaction area between column and slabs. The dynamic load is considered as an earthquake acceleration record that can be transformed to equivalent dynamic loads acting on the super-structure floors. The sub-structure is analyzed using the dual reciprocity boundary element method as closed domain. New iterative coupling technique is proposed between the super and sub-structures to reduce the computational effort and required storage. An example is presented to demonstrate the strength and the practicality of the proposed methodology.

Comparison of different CFD-FEM coupling methods in advanced structural fire analysis

The research approach of multi-physical field coupling can be used to analyze the structural fire resistance problem. In the process of numerical simulation, multiple coupling interfaces are involved. Regarding fluid-thermal-solid coupling, most of the previous numerical studies on structural fire resistance have used the adiabatic surface temperature (AST) parameters in order to accurately describe complex boundary conditions in fire analysis. This approach belongs to the iterative coupling form, and the other type of direct coupling form is rarely used. In this paper, the specific scenario of a steel column surrounded by fire source is selected as a typical case to explore the thermodynamic phenomena of the steel column. Based on the computational fluid dynamics (CFD) method, the fire model analysis in the fluid domain was first implemented to investigate the distribution laws of the spatial velocity and temperature fields. Then the fluid-thermal-solid coupling was realized via iterative coupling (Adiabatic Surface Temperature method, AST method) and direct coupling (Full Conjugate Heat Transfer method, FCHT method) respectively to obtain the steel column temperatures. The accuracy of these two coupling methodologies was verified by comparing their results with the experimental data, and the accuracy of AST method depends on the reasonable sampling of fire analysis results. Following this, structural model analysis was completed using the solid temperature as the boundary condition to achieve the solid thermal-mechanical coupling. The yield strength degradation of the steel column after heating was explored. Finally, the non-necessity of fluid-mechanical-solid coupling in structural fire resistance was discussed.

Coupled KIPP-EDGE2D modeling of parallel transport in the SOL and divertor plasma for the ITER baseline scenario

The KInetic code for Plasma Periphery (KIPP) models the parallel (along magnetic field lines) propagation of charged particles in the scrape-off layer (SOL) and divertor of tokamaks. An iterative coupling between KIPP and a 2D edge fluid code, EDGE2D, which in turn is coupled to the Monte Carlo solver for neutrals, EIRENE, was used to achieve a converged KIPP-EDGE2D-EIRENE solution. In the iterative coupling algorithm, KIPP transfers kinetic parallel electron and ion heat conductivities to EDGE2D, whereas EDGE2D returns to KIPP 2D distributions of macroscopic plasma parameters across the computations grid. The initial EDGE2D-EIRENE solution simulated the SOL and divertor plasma of the ITER inter-edge localized mode (ELM) baseline scenario. This work employs the same methodology as an earlier study based on the analysis of JET high radiative H-mode conditions, with strong nitrogen injection leading to partial detachment at divertor targets (Chankin et al 2022 Plasma Phys. Control. Fusion 64 095007). The results are qualitatively similar to those of the JET study in demonstrating the strong heat flux limiting effect, together with the rise in electron and ion temperatures in the main SOL. At the same time, the kinetic effects of the parallel propagation of charged particles are not expected to drastically change the target power deposition at divertor targets calculated by EDGE2D-EIRENE alone.

Inverse Polyamidoamine (i‐PAMAM) Dendrimer Antimicrobials

AbstractHere we redesigned the branches of polyamidoamine (PAMAM) dendrimers by moving the amide carbonyl group on the other side of the amide nitrogen atom, transforming the β‐alaninyl‐amidoethylamine branch, which easily undergoes retro‐Michael reactions and renders PAMAMs intrinsically unstable, into a more stable glycyl‐amidopropylamine branch. The resulting inverse PAMAM (i‐PAMAM) dendrimers have the same carbon framework as PAMAMs and only differ by the position of the carbonyl group. In contrast to PAMAMs which are prepared in solution and are difficult to purify, we synthesize i‐PAMAMs using high‐temperature solid‐phase peptide synthesis by iterative coupling and deprotection of the commercially available N,N‐bis(N′‐Fmoc‐3‐aminopropyl)glycine and purify them preparative reverse phase HPLC. Our i‐PAMAM dendrimers show no detectable degradation over time. We demonstrate this new class of dendrimers with the synthesis of antimicrobial dendrimers with potent yet non‐membrane disruptive activities against both Gram‐negative and Gram‐positive bacteria.

Research on the friction and wear mechanism of a polymer interface at low temperature based on molecular dynamics simulation

Two polymers and five metal pairs were tested at six low temperature points and three constant load speeds. The tribological properties were determined by joint iterative coupling of the temperature, load and friction velocity value. Molecular dynamics simulation was used to study the micro-tribological properties of friction pairs at the atomic scale. The macro-tribological performance test results were similar to the results of the molecular dynamics simulation and exhibited the same trend. Two profound hypothermia points were predicted. The evolution of the tribological mechanism and properties of the polymer interface under different working conditions at low temperature were revealed on the macroscopic and atomic scales.