Hybrid Simulation Research Articles

The multi-scale polarizable pseudo-particle solvent coarse-grained approach: From NaCl salt solutions to polyelectrolyte hydration.

We discuss key parameters that affect the reliability of hybrid simulations in the aqueous phase based on an efficient multi-scale coarse-grained polarizable pseudo-particle approach, denoted as pppl, to model the solvent water, whereas solutes are modeled using an all atom polarizable force field. Among those parameters, the extension of the solvent domain (SD) at the solute vicinity (domain in which each solvent particle corresponds to a single water molecule) and the magnitude of solute/solvent short range polarization damping effects are shown to be pivotal to model NaCl salty aqueous solutions and the hydration of charged systems, such as the hydrophobic polyelectrolyte polymer that we have recently investigated [Masella et al., J. Chem. Phys. 155, 114903 (2021)]. Strong short range damping is pivotal to simulate aqueous salt NaCl solutions at moderate concentration (up to 1.0M). The SDextension (as well as short range damping) has a weak effect on the polymer conformation; however, it plays a pivotal role in computing accurate polymer/solvent interaction energies. As the pppl approach is up to two orders of magnitude computationally more efficient than all atom polarizable force field methods, our results show it to be an efficient alternative route to investigate the equilibrium properties of complex charged molecular systems in extended chemical environments.

Design of Hybrid Bandpass Filter Chips with High Selectivity and Wideband Using IPD and FBAR Technology

A novel hybrid bandpass filter (BPF) with wideband and high selectivity is proposed in this paper. The hybrid BPF is composed of two film bulk acoustic resonator (FBAR) cells and three lumped component resonators realized by the integrated passive device (IPD) technology. The ABCD matrix to S-parameters matrix method is used to calculate the frequency response of the BPF. Moreover, the expressions of transmission zeros (TZs) have been extracted. In the design process, an iterative design approach is proposed to improve the circuit and layout of the hybrid filter based on the packaged acoustic-electric hybrid simulation effect. Finally, two parts of the filter are packaged based on the flip-chip method, and two prototypes for the BPF are measured. The measured results of two chips with 3 dB fractional bandwidth of 13.7% and 15.8% are designed and fabricated, which verifies the validity of the proposed design principle.

Nonlinear excitation of energetic particle driven geodesic acoustic mode by Alfvén instability in ASDEX-Upgrade Tokamak

Recently, the coexistence of multiple energetic particle driven instabilities was observed in experiments on the ASDEX-Upgrade tokamak (Lauber et al 2018 27th IAEA Fusion Energy Conf.). A hybrid simulation using the MEGA code was performed to investigate the properties of those instabilities. The basic mode properties obtained in the simulations, such as mode frequencies, mode numbers, and inward energetic particle (EP) redistribution, are in good agreement with the experiments. It is found that the energetic particle driven geodesic acoustic mode (EGAM) is initially stable, then zonal flow gradually occurs with the growth of the Alfvén instability, and finally, the EGAM is nonlinearly excited and the amplitude exceeds the Alfvén instability. The dependence of EGAM properties on EP pressure and pitch angle distribution is analyzed. The EGAM amplitude increases with EP pressure. The nonlinearly excited EGAM is a high-frequency branch that appears even under the condition of a slowing-down EP distribution. The resonant particles are also analyzed, but the dominant resonant particles of the EGAM in the linear growth phase are not found because the EGAM does not grow in the linear regime. In the phase space of pitch angle variable Λ and energy E, it is found that initially the Alfvén instability is excited by EPs with poloidal frequency 70 kHz, then, after the saturation of the Alfvén instability, the resonance region moves towards lower energy and touches the EGAM resonance line, and finally, EGAM is excited by the particles with poloidal frequency 50 kHz . This process is a kind of resonance overlap.

Selective online model updating in hybrid simulation of a full‐scale steel moment frame

AbstractThis study presents the implementation of an online model updating algorithm within a full‐scale hybrid simulation (HS) of a six story, four bay steel moment frame. The experimental substructure consists of a cruciform subassembly generating critical data on the nonlinear behavior of the first story column and two beams with reduced beam sections (RBSs) on each side. The updating algorithm focuses on the modeling parameters of plastic hinge elements representing the RBSs in the numerical model. A smooth plasticity model is utilized for beam plastic hinges with updating parameters identified from on‐line experimental data through a modified version of the unscented Kalman filter. The HS shows that the numerical beam hinges based on simple hysteretic model with updated parameters are able to capture the characteristic behavior observed in experiments. Due to fracture of beam flanges is observed in the experiments, a selective updating concept is proposed to allow for updating multiple numerical components accounting for asymmetric behavior and variability in the response. The selective updating method is validated through virtual HSs that are better able to identify and isolate the effects of fracture and other behavioral characteristics. The combination of results from physical and virtual tests highlights the benefits of model updating on the local and overall system‐level response.

Comparing hybrid method simulations to hydrogen dispersion and explosion tests

With an increase in the production and storage of hydrogen, it is likely that an increased number of explosions in which hydrogen plays a central role will occur unless a step change increase in safety is seen. Modelling releases of hydrogen and explosions arising from the delayed ignition of premixed gas clouds of hydrogen is carried out today using analytical and numerical approaches and most recently, using a hybrid methodology with the commercially available software exploCFD. Hybrid simulation methodology relies on the calculation of an analytically derived source term which is then used as an input for a 2D numerical simulation. In this paper we further our earlier validation work and test the ability of the hybrid methodology to predict flammable gas dispersion and subsequent explosions arising from hydrogen releases. Hydrogen has some particularly unique properties; it is the lightest of fuels – meaning masses involved are very small, and it has the highest laminar burning velocity – an order of magnitude greater than most hydrocarbons. The hybrid methodology is compared against previously documented 3D corner tests and dispersion tests. Excellent agreement between overpressure prediction and the reported experimental data for explosion against equivalence ratio is observed. The data from the hydrogen jet release simulations also compare extremely well to the previously reported experimental data. The results show that it is difficult to justify the use of far more laborious, time and cost-intensive purely numerical methods, or the use of largely uncertain more crude methods still widely used today.

Kinetic-magnetohydrodynamic hybrid simulation of infernal modes in circular tokamak plasmas with effects of kinetic thermal ions

Abstract Effects of the kinetic thermal ions on ideal infernal modes and resistive infernal modes have been investigated by using magnetohydrodynamic (MHD) simulation without kinetic thermal ions and kinetic-MHD hybrid simulation with kinetic thermal ions. For the ideal infernal modes, the pressure profile is significantly flattened at the saturated state for both the models with and without the kinetic thermal ions. As the beta value decreases, the ideal infernal modes are stabilized while the resistive infernal modes are still unstable. For the resistive infernal modes, while the saturated pressure profile is significantly flattened in the MHD simulation without kinetic thermal ions, the pressure profile is not flattened at the saturated state in the kinetic-MHD hybrid simulation with kinetic thermal ions. The suppression of the saturation level by the effects of the kinetic thermal ions results from the phase mismatch between the radial velocity and perturbed pressure mode structures. This indicates that kinetic thermal ions play an essential role for the suppression of pressure profile flattening due to slowly growing resistive MHD instabilities.

Conditional adaptive time series compensation and control design for multi-axial real-time hybrid simulation

The structural performance of critical infrastructure during extreme events requires testing to understand the complex dynamics. Shake table testing of buildings to evaluate structural integrity is expensive and requires special facilities that can allow for the construction of large-scale test specimens. An attractive alternative is a cyber-physical testing technique known as Real-Time Hybrid Simulation (RTHS), where a large-scale structure is decomposed into physical and numerical substructures. A transfer system creates the interface between physical and numerical substructures. The challenge occurs when using multiple actuators connected with a coupler (i.e., transfer system) to create translation and rotation at the interface. Tracking control strategies aim to reduce time delay errors to create the desired displacements that account for the complex dynamics. This paper proposes two adaptive control methodologies for multi-axial real-time hybrid simulations that improve capabilities for a higher degree of coupling, boundary, complexity, and noise reduction. One control method integrates the feedback proportional derivative integrator (PID) control with a conditional adaptive time series (CATS) compensation and inverse decoupler. The second proposed control method is based on a coupled Model Predictive Control (MPC) with the CATS compensation. The performance of the proposed methods is evaluated using the virtual multi-axial benchmark control problem consisting of a steel frame as the experimental substructure. The transfer system consists of a coupler that connects two hydraulic actuators generating the translation and rotation acting at the joint. Through sensitivity analysis, parameters were tuned for the decoupler components, CATS compensation, and the control design for PID, LQG, and MPC. Comparative results among different control methods are evaluated based on performance criteria, including critical factors such as reduction in the time delay of bothactuators. The research findings in this paper improve the tracking control systems for the multi-axial RTHS of building structures subjected to earthquake loading. It provides insight into the robustness of the proposed tracking control methods in addressing uncertainty and improves the understanding of multiple output controllers that could be used in future cyber-physical testing of civil infrastructure subjected to natural hazards.

Numerical Simulation Analysis of the Correlation between Hydrodynamic Noise of Hydraulic Turbines and Defects in Runner Blades

To investigate the hydrodynamic noise characterization of hydraulic turbines with runner blade defects, this article establishes the intact machine model and three kinds of models with runner blade defects. Using the Computational Fluid Dynamic (CFD) and Computational Acoustic (CA) hybrid simulation computational methods, the hydrodynamic noise field of the hydraulic turbine is numerically simulated, and the results of the acoustic near field and acoustic far field are shown. 1. The double-row leaf grille and the runner are the primary sound source areas of the hydraulic turbine, and the intensity of sound radiation from these areas is positively correlated with the degree of runner blade defects. 2. As the runner blade defects develop, the sound power level (SWL) increases more significantly in the guide vanes near the nose of the spiral case in the double-row leaf grille. The most pronounced increase in the SWL is observed at the defective craters on the runner blades. 3. The frequency of the defective noise signal is primarily concentrated in the low-frequency band. The dominant frequency amplitude associated with runner blade defects increases and rises after the occurrence of defects. Secondary frequency changes are also observed, and the location of these changes varies at different receiving points.

Unveiling the transition of tumbling and tank-treading dynamics of star-shaped polyelectrolytes in shear flow by modulating the solution's dielectric properties.

The effects of the solution's dielectric properties on the conformation and dynamics of star-shaped polyelectrolytes in shear flow are investigated using a hybrid simulation method coupling multi-particle collision dynamics and molecular dynamics. The simulation results showed that by modulating the dielectric properties of the solution, star-shaped polyelectrolytes showed a three-step dynamic behavior transition from tumbling to tank-treading to tumbling dynamics under shear flow. The analysis indicated that this distinct transition in dynamics could be attributed to the uneven distribution of counterions induced by shear on the chain, resulting in a change in the polyelectrolyte conformation and degree of segmental alignment in arms. These findings contribute to a comprehensive understanding of the non-equilibrium dynamics of star-shaped polyelectrolytes in shear flow and offer a viable approach for controlling the dynamic behavior of star-shaped polyelectrolytes by adjusting the dielectric properties of the solution.

Simulation modelling and analysis of linkage-controlled traffic scheme in Waterway Transport Key Nodes

As global shipping undergoes rapid expansion, pivotal waterway transport systems—including significant nodes like the Panama Canal, the Suez Canal, and the Three Gorges-Gezhouba dams—are increasingly emerging as system-wide bottlenecks that limit transportation capabilities. Recognizing the pressing need for efficient traffic organization at these critical junctures, we designed a hybrid simulation model, which integrates Cellular Automaton and Multi-Agent methods, to analyse traffic efficiency and evaluate different ship organization schemes at these key waterway nodes. The Three Gorges-Gezhouba dams serve as a case study, where we crafted and executed four simulation scenarios that accommodate a range of variables such as different traffic organization schemes, traffic flow volumes, and anchorage capacities. Key operational indicators such as the maximum average waiting time of ships at the anchorage, and the period when the anchorage along the waterway reaches saturation, provide insights into the system's operational condition. The simulation outcomes highlight the proposed model's capability to accurately quantify the impact of implementing a linkage-control scheme and underscore the utility of dynamic adjustment of water area ranges under linkage-control for managing various traffic scenarios. Consequently, our research not only enriches high-precision simulation methodologies but also bolsters decision-making processes concerning ship traffic organization at Waterway Transport Key Nodes.

Simulation of hybrid boiling nano fluid flow with convective boundary conditions through a porous stretching sheet through Levenberg Marquardt artificial neural networks approach

In the domain of artificial neural networks, the Levenberg-Marquardt technique stands out for its innovative approach and convergent stability. It generates a numerical approach for the progression of a hybrid Cu–Al2CO3/water nanofluid on a porous stretched sheet (HNF-PSS), employing regression plots, state transition measures, histogram representations, and mean squared errors. This work explores the analysis of the fluid flow problem associated with HNF-PSS, introducing a novel application of an intelligent computing system that utilizes the effectiveness of neural networks trained by the Levenberg-Marquardt algorithm (NN-TLMA). The initial mathematical expression, expressed in terms of partial differential equations (PDEs) for HNF-PSS, undergoes transformation into dimensionless nonlinear ordinary differential equations (ODEs). The collection of data for the envisioned NN-TLMA involves parameters influencing the velocity of the HNF-PSS system model, generated using the Lobatto IIIa formula. The efficacy of the suggested NN-TLMA for solving the HNF-PSS is robustly verified by examinations of state transition dynamics, regression analyses, mean square error, and error histogram studies. The consistent alignment of the obtained results with corresponding solutions attests to the legitimacy of the structure, achieving a high level of accuracy within the range of 10–6 to 10–8. Insightful findings demonstrate that the thermal Biot number contributes significantly to an upsurge in fluid temperature. Furthermore, an augmentation in nanofluid concentration and thermal profile is found to increase the porosity strength of the medium. Nevertheless, an attenuation in the velocity profile is noted under these conditions. The application of this simulation work can be found in optimizing the designs of heat exchanger, in biomedical application and in renewable energy processes.

Improved implementation of concentrated plasticity models in real-time hybrid simulation

Real-time hybrid simulation (RTHS) is a cost-effective experimental testing technique for evaluating the dynamic response of structural systems. In RTHS, a portion of the structure is modeled numerically (i.e., numerical substructure), while the remaining part is tested physically (i.e., experimental substructure). These substructures are coupled in real time. A significant challenge in RTHS is accurately computing the dynamic response of the numerical substructure in real time during testing. Constrained by this challenge, numerical substructures in RTHS are often oversimplified (e.g., spring-mass-dashpot models), failing to capture more complex dynamic behaviors and limiting the applicability of RTHS. However, with the increasing use of innovative structural systems, new materials, and advanced design guidelines to ensure resilient and sustainable civil infrastructure against natural hazards, the demand for real-time executable higher-fidelity numerical substructures in RTHS is growing. Consequently, concentrated plasticity model (CPM) has gained attention as the numerical substructure in RTHS for its good balance between numerical accuracy and computational efficiency, as well as its popularity in structural engineering applications. Currently, static condensation is utilized to prevent an increase in computational degrees of freedom (DOFs) induced by the hinges in CPM, aiming to save computational cost. However, this method proves counterproductive for nonlinear analyses. While reducing the number of computational DOFs, it complicates the stiffness representation, thereby necessitating more demanding arithmetic operations for stiffness updating. In this study, multi-point constraints are applied to enhance the computational efficiency, specifically for nonlinear analyses involving stiffness updating, and the versatility of CPM. Moreover, direct stiffness updating method and sparse matrix-vector multiplication are introduced for further enhancement in computation. An open-source MATLAB/Simulink-based computational tool, namely the Hybrid2D, is developed to promote the use of the improved CPMs in RTHS as numerical substructures. Numerical simulations are first conducted to verify the accuracy and the computational efficiency of the improved CPMs in Hybrid2D. Subsequently, two RTHS examples are experimentally conducted to demonstrate the effectiveness of the Hybrid2D in enabling RTHS with a higher-fidelity numerical substructure for more complex structural systems.

Modeling the Saturation of the Bell Instability Using Hybrid Simulations

The nonresonant streaming instability (Bell instability) plays a pivotal role in the acceleration and confinement of cosmic rays (CRs), yet the exact mechanism responsible for its saturation and the magnitude of the final amplified magnetic field have not been assessed from first principles. Using a survey of hybrid simulations (with kinetic ions and fluid electrons), we study the evolution of the Bell instability as a function of the parameters of the CR population. We find that at saturation, the magnetic pressure in the amplified field is comparable with the initial CR anisotropic pressure, rather than with the CR energy flux, as previously argued. These results provide a predictive prescription for the total magnetic field amplification expected in the many astrophysical environments where the Bell instability is important.

Chemical stability of anion exchange membranes for alkaline fuel cells and water electrolysers: Experiment, multi-dimensional modeling and hybrid simulations

The unstable nature of anion exchange membranes (AEMs) has hindered the progress of alkaline fuel cells and water electrolyzers. Density functional theory (DFT) can explore the correlation between the structure and properties of model compounds. However, theoretical explorations of AEMs remain immensely insufficient owing to the complexity of modeling the realistic solution system which caused by multi-dimensional parameters such as polymer chain entanglement, steric hindrance, and migration of ions. In this study, molecular dynamic simulation was utilized to obtain the multi-dimensional parameters of polyelectrolytes, which were considered when calculating the degradation energy barrier by DFT, thus leading to more accurate results and optimizing the conventional DFT calculations. Combined with the computational works, pyridinium functionalized polyolefin and polyether sulfone were synthesized to verify the feasibility of the simulation scheme. This optimized scheme fills the gap in the DFT calculations scale and is easy to extend to other types of AEMs, which help design the chemically stable AEMs and promote the development of alkaline fuel cells and water electrolysers.

The hybrid (physical-computational) cardiovascular simulator to study valvular diseases

To better understand the impact of valvular heart disease (VHD) on the hemodynamics of the circulatory system, investigations can be carried out using a model of the cardiovascular system. In this study, a previously developed hybrid (hydro-numerical) simulator of the cardiovascular system (HCS) was adapted and used. In our HCS Björk-Shiley mechanical heart valves were used, playing the role of mitral and aortic ones. In order to simulate aortic stenosis (AS) and mitral regurgitation (MR), special mechanical devices have been developed and integrated with the HCS. The simulation results proved that the system works correctly. Namely, in the case of AS − the mean pulmonary arterial pressure was increased due to increased preload of the left ventricle and the decrease in right ventricular preload was caused by a decrease in systemic arterial pressure. The severity of AS was performed based on the transaortic pressure gradient as well as using the Gorlin and Aaslid equations. In the case of severe AS, when the mean gradient was above 40 mmHg, the aortic valve orifice area was 0.5 cm2, which is in line with ACC/AHA guidelines. For the case of MR − with increasing severity of MR, there was a decrease in the left ventricular pressure and an increase in left atrial pressure. Using mechanical heart valves to simulate VHD by the HCS can be a valuable tool for biomedical research, providing a safe and controlled environment to study and understand the pathophysiology of VHD.

2.5‐D Local Hybrid Simulations of Discontinuity‐Driven Compressional Boundaries Under Various Magnetic Field Geometries

AbstractIn the ion foreshock, there are many foreshock transients driven by back streaming foreshock ions. When the foreshock ions interact with tangential discontinuities (TDs), hot flow anomalies form if the foreshock ion‐driven current decreases field strength at TDs, but the opposite situation has been paid little attention. Using 2.5‐D local hybrid simulations, we show that a compressional boundary with enhanced field strength and density can form. We examine how the foreshock ions interact with TDs under various magnetic field geometries to drive currents that lead to compressional boundaries. The current driven by the foreshock ions should peak on its initial side of a TD so that the enhanced field strength at the TD in turn increases this current by keeping more foreshock ions on their initial side. Which side the current peaks can be determined by whether the foreshock ions initially cross the TD and/or how their velocity is projected into the local perpendicular direction. Additionally, the foreshock ion‐driven currents from two sides could compete, and whether a compressional boundary forms is determined by the net current profile. Because such compressive structures in the foreshock can drive magneto sheath jets and cause many geoeffects, it is necessary to fully understand their formation.

2.5‐D Local Hybrid Simulations of Hot Flow Anomalies Under Various Magnetic Field Geometries

AbstractHot flow anomalies are ion kinetic phenomena that play an important role in geoeffects and particle acceleration. They form due to the currents driven by demagnetized foreshock ions around a tangential discontinuity (TD). To understand the profile of such currents around a TD with foreshock ions on both sides, we use 2.5‐D local hybrid simulations of TDs, interacting with a planar shock with various shock geometries. We find that the electric field direction relative to the TD plane provides information about how the foreshock ion‐driven currents affect the magnetic field around the TD. For TDs embedded in the quasi‐parallel shock on both sides, the foreshock ions from one side of TD can cross it determining the current profile on the other side. In contrast, for TDs embedded in the quasi‐perpendicular shock, sheath‐leaked ions enter the TD and determine the current profile. We find that the foreshock ultra‐low frequency waves can periodically modulate how foreshock ions interact with the TD and thus the current profile. Studying the effects of various magnetic field configurations allows us to build a more comprehensive model of hot flow anomalie formation.

Effects of axial compression ratio on seismic behavior of shallow‐buried rectangular stations: Hybrid simulation and quasi‐static test

AbstractIn the absence of experimental investigations on column members of underground structures, full‐scale column specimens were tested to explore the seismic behavior of shallow‐buried subway stations at various depths. The axial compression ratios of internal column specimens were set as 0.16, 0.33, and 0.40. Both hybrid simulations and quasi‐static tests were performed on the station columns. The hybrid simulations illustrated the drift demands of internal columns, while the load‐carrying capacity and deformation capacity were obtained from the quasi‐static tests. Hybrid simulations at low, moderate, and high‐intensity levels were conducted to study the seismic responses of shallow‐buried rectangular stations. The hybrid simulations suggest that the most severe damage occurred in the station when the axial compression ratio of the tested column reached 0.40. Central columns suffered severe stiffness deterioration under high‐level earthquake excitation, especially in stations at greater depths. Meanwhile, the quasi‐static test results indicate that the ultimate load of the central columns increases with increasing axial compression, but this leads to a significant decrease in the ductility of columns. Besides, the sectional analysis results show that the central columns are prone to tension‐controlled failure, and the safety margin for flexural response deteriorates with an increasing axial compression ratio. The test results indicate that shallow‐buried rectangular stations are susceptible to flexure‐controlled structural failure when their central columns possess a relatively low axial compression ratio and a high shear span‐to‐depth ratio. The failure mechanism of station columns is revealed by both the hybrid simulations and quasi‐static tests, and the findings from the full‐scale tests are beneficial for the practical design of shallow‐buried rectangular stations.

Hybrid simulation of a steel frame with Dissipative Replaceable Link Frames

AbstractIn the last decades, high priority has been given to enhancing the seismic resilience of structures by reducing the damage of structural and non-structural elements after a disaster. In this context, the European Research Fund for Coal and Steel (RFCS) project DISSIPABLE was funded to perform large demonstration tests of steel frames equipped with easily repairable seismic dissipative devices. The paper extensively describes the experimental campaign carried out at the University of Trento on a steel frame equipped with innovative Dissipative Replaceable Link Frame (DRLF) systems, composed of two rigid columns connected by weakened beams at their ends. Hybrid Simulation was employed, enabling to physically test the first floor of the building yet allowing for considering the response of the remaining five floors, which were numerically simulated. A bidimensional frame was tested under increasing seismic intensity levels: Damage Limitation, Significant Damage and Near Collapse limit states. The experimental results proved that the DRLF system was able to dissipate energy and protect the primary elements of the structure from plasticisation. Moreover, the structure's re-centring capability was verified to ensure the components' replaceability. Finally, the calibration of the nonlinear model was performed following the tests, which allowed to develop a high-fidelity model suitable for further numerical investigation.

Unconditionally Stable Central Difference Dissipative Algorithm for Multi-Directional Real-Time Hybrid Simulations of Large Nonlinear Structural Systems

ABSTRACT The central difference is a popular algorithm used to integrate the equations of motion, yet suffers from two drawbacks: (1) it is only conditionally stable and requires a small-time step to maintain numerical stability; (2) it is non-dissipative, and high-frequency spurious oscillations may appear and compromise the accuracy of the solution. These drawbacks are detrimental to applying the algorithm to the real-time hybrid simulation of large, complex nonlinear structural systems. In this paper, the conventional central difference algorithm is modified to overcome these drawbacks, and the modified algorithm is applied to the real-time hybrid simulation of complex structural systems.