Hybrid Simulation Strategy Research Articles

Optimization design of TEM cell based on multi-stage curved edge transition structure and magnetic loss method

This article describes how to raise the TEM cells' operating bandwidth and lower their VSWR. A multi-stage curved-edge transition structure for minimizing VSWR and a magnetic loss mechanism for extending the operating bandwidth are proposed by evaluating the workings and constraints of TEM cells. A hybrid simulation strategy based on the particle swarm algorithm and 3D electromagnetic simulation (EM) software is suggested in order to identify the optimal quickly. In the 3D EM simulation software, the TEM cell's 3D model is created, the VSWR and return loss were solved for. It is possible to raise the operational bandwidth from 0–2 GHz to 0–5 GHz. At 0-3 GHz, measurement and simulation results are practically equal. At 3-4.5 GHz, measurement results differ somewhat from simulation results. At 4.5-5 GHz, measurement results greatly diverge from simulation results, and the parameters no longer fulfill standard criteria.

A Numerical Simulation of PFPE Lubricant Kinetics in HAMR Air Bearing

This report investigates the kinetics of lubricant molecules in the HAMR air bearing to understand the initiation and growth of PFPE contamination on the head surface. The collisions with the air bearing induce three forces—drag, thermophoresis, and lift. Of these, we find that lift forces are negligible. Then, a sensitivity analysis of the remaining two forces reveals the conditions where they dominate. Further, a hybrid simulation strategy is utilized to track their movements. The results show that the contaminations (smear) highly depend on the interplay between the thermophoresis and drag forces. We then explain the mechanism of the formation of the various observed patterns. Finally, we offer some recommendations to exploit the air bearing to contain smear on the head.

A Hybrid Simulation Model to Predict the Cooling Energy Consumption for Residential Housing in Hong Kong

In Hong Kong, buildings consume 90% of the electricity generated and over 60% of the city’s carbon emissions are attributable to generating power for buildings. In 2018, Hong Kong residential sector consumed 41,965 TJ (26%) of total electricity generated, with private housing accounting for 52% and public housing taking in 26%, making them the two major contributors of greenhouse gas emissions. Furthermore, air conditioning was the major source consuming 38% of the electricity generated for the residential building segment. Strategizing building energy efficiency measures to reduce the cooling energy consumption of the residential building sector can thus have far-reaching benefits. This study proposes a hybrid simulation strategy that integrates artificial intelligence techniques with a building energy simulation tool (EnergyPlus™) to predict the annual cooling energy consumption of residential buildings in Hong Kong. The proposed method predicts long-term thermal energy demand (annual cooling energy consumption) based on short-term (hourly) simulated data. The hybrid simulation model can analyze the impacts of building materials, construction solutions, and indoor–outdoor temperature variations on the cooling energy consumed in apartments. The results indicate that using low thermal conductivity building materials for windows and external walls can reduce the annual cooling energy consumption by 8.19%, and decreasing the window-to-wall ratio from 80% to 40% can give annual cooling energy savings of up to 18%. Moreover, significant net annual cooling energy savings of 13.65% can be achieved by changing the indoor set-point temperature from 24 °C to 26 °C. The proposed model will serve as a reference for building energy efficiency practitioners to identify key relationships between building physical characteristics and operational strategies to minimize cooling energy demand at a minimal time in comparison to traditional energy estimation methods.

A Transient 3-D Thermal Modeling Method for IGBT Modules Considering Uneven Power Losses and Cooling Conditions

Junction temperature is a key parameter for the safe operation of power semiconductor devices in power electronic systems. However, it is difficult to forecast the accurate thermal stress of the device in field use. Consequently, engineers tend to use higher rated devices to maintain excessive margin, resulting in a higher cost. In this article, a transient 3-D thermal modeling method for insulated gate bipolar transistor (IGBT) modules is proposed to obtain accurate temperature distribution considering uneven power losses and cooling conditions. The analytical model of uneven switching energy losses among the parallel IGBT chips in modules is built according to the analysis of device simulation results. The effect of uneven cooling conditions on temperature distribution in IGBT modules is considered by thermal-fluid cosimulation. Furthermore, a hybrid simulation strategy is proposed to obtain the transient thermal behavior in three dimensions. Through appropriate interface design, the power loss model is connected with the finite element model to achieve field-circuit cosimulation with multiple time steps, which takes full consideration of the multiphysical coupling effects among power loss, temperature, and flow fields. Finally, the thermal stresses of IGBT modules under different operating conditions are forecast by the proposed method.

Dynamic response of structures to thunderstorm outflows: Response spectrum technique vs time-domain analysis

Thunderstorms are transient events. Design wind velocity and wind-induced damage are often related to them. Despite this, research on thunderstorm loading of structures is still fragmentary and uncertain due to their complexity, short duration and small size. These issues make it difficult to set physically realistic and simple models as well as to gather real data. This favoured the implementation of refined methods based on limited measurements. The European Projects “Wind and Ports” and “Wind, Ports and Sea” realised an extensive monitoring network from which many thunderstorm outflow records were extracted. They were analysed to inspect their characteristics and to formulate methods coherent with measurements. Firstly, the response spectrum technique conceived for earthquakes was extended to thunderstorms. Then, a hybrid simulation strategy was proposed and time-domain integrations of the structural response were applied. This paper provides a joint calibration and advancement of these two methods, leading to results that substantially agree, especially faced with their conceptual and operative diversities. This confirms the potential of the response spectrum technique to become a suitable tool for calculating the thunderstorm loading of structures and the efficiency of hybrid simulations and time-domain analyses to investigate, with a limited computational burden, advanced structural issues.

Multiscale Simulations of Lamellar PS–PEO Block Copolymers Doped with LiPF6 Ions

We report the results of atomistic simulations of the structural equilibrium properties of PS–PEO block copolymer (BCP) melt in the ordered lamellar phase doped with LiPF6 salt. A hybrid simulation strategy, consisting of steps of coarse-graining and inverse coarse-graining, was employed to equilibrate the melt at an atomistic resolution in the ordered phase. We characterize the structural distributions between different atoms/ions and compare the features arising in BCPs against the corresponding behavior in PEO homopolymers for different salt concentrations. In addition, the local structural distributions are characterized in the lamellar phase as a function of distance from the interface. The cation–anion radial distribution functions (RDF) display stronger coordination in the block copolymer melts at high salt concentrations, whereas the trends are reversed for low salt concentrations. Radial distribution functions isolated in the PEO and PS domains demonstrate that the stronger coordination seen in B...

A hybrid simulation technique for electrothermal studies of two-dimensional GaN-on-SiC high electron mobility transistors

In this work, a hybrid simulation technique is introduced for the electrothermal study of a two-dimensional GaN-on-SiC high electron mobility transistor. Detailed electron and phonon transport is considered by coupled electron and phonon Monte Carlo simulations in the transistor region. For regions away from the transistor, the conventional Fourier's law is used for thermal analysis to minimize the computational load. This hybrid simulation strategy can incorporate the physical phenomena over multiple length scales, including phonon generation by hot electrons in the conduction channel, frequency-dependent phonon transport in the transistor region, and heat transfer across the whole macroscale device.

Hybrid Reynolds-Averaged/Large-Eddy Simulation of a Cavity Flameholder: Modeling Sensitivities

Steady-state and scale-resolving simulations have been performed for flow in and around a model scramjet combustor flameholder. The cases simulated corresponded to those used to examine this flowfield experimentally using particle image velocimetry. A variety of turbulence models were used for the steady-state Reynolds-averaged simulations, which included both linear and nonlinear eddy viscosity models. The scale-resolving simulations used a hybrid Reynolds-averaged/large-eddy simulation strategy that is designed to be a large-eddy simulation everywhere except in the inner portion (log layer and below) of the boundary layer. Hence, this formulation can be regarded as a wall-modeled large-eddy simulation. This effort was undertaken to formally assess the performance of the hybrid Reynolds-averaged/large-eddy simulation modeling approach in a flowfield of interest to the scramjet research community. The numerical errors were quantified for both the steady-state and scale-resolving simulations before making any claims of predictive accuracy relative to the measurements. The hybrid Reynolds-averaged/large-eddy simulation results were also carefully scrutinized to ensure that even the coarsest grid had an acceptable level of resolution to meet accepted guidelines for large-eddy simulation and that the time-averaged statistics were acceptably accurate. The autocorrelation and its Fourier transform were the primary tools used for this assessment. Both simulation strategies accurately predicted the mean streamwise velocity distribution within the cavity, although the Reynolds-averaged simulations that used a linear eddy viscosity model tended to overpredict the strength of the primary cavity recirculation zone. Second-order moments of the velocity field were found to be highly sensitive to the turbulence model chosen for the Reynolds-averaged simulations, with all models overpredicting the intensity of the velocity fluctuations within the cavity flameholder. The hybrid Reynolds-averaged/large-eddy simulation results also overpredicted the velocity variances and covariances, unless a filtering operation was applied using a filter size that matched the control volume used to process the particle image velocimetry measurements. This observation suggests that a significant fraction of the turbulence energy was not resolved by the measurements. Taking this uncertainty into account, the second-order statistics extracted from the hybrid simulation strategy could not be shown to be any more accurate than the “best” Reynolds-averaged result.

Initial conditions and modeling for simulations of shock driven turbulent material mixing

Abstract We focus on the simulation of shock-driven material mixing driven by flow instabilities and initial conditions (IC). Beyond complex multi-scale resolution issues of shocks and variable density turbulence, me must address the equally difficult problem of predicting flow transition promoted by energy deposited at the material interfacial layer during the shock interface interactions. Transition involves unsteady large-scale coherent-structure dynamics capturable by a large eddy simulation (LES) strategy, but not by an unsteady Reynolds-Averaged Navier–Stokes (URANS) approach based on developed equilibrium turbulence assumptions and single-point-closure modeling. On the engineering end of computations, such URANS with reduced 1D/2D dimensionality and coarser grids, tend to be preferred for faster turnaround in full-scale configurations. With suitable initialization around each transition – e.g., reshock, URANS can be used to simulate the subsequent near-equilibrium weakly turbulent flow. We demonstrate 3D state-of-the-art URANS performance in one such flow regime, in the context of a sequential LES/URANS hybrid simulation strategy. We first simulate canonical shock-tube (AWE and CEA) experiments with an implicit LES (ILES) strategy. We report new validation studies benchmarking ILES with the available turbulence velocity and mixing data from the CEA laboratory studies. In turn, the ILES generated flow data is then used to initialize and as reference to assess the 3D URANS. We find that by prescribing (ILES generated) physics-based 3D IC and allowing for 3D convection with just enough resolution, the computed dissipation in 3D URANS blends effectively with the modeled dissipation to yield significantly improved statistical predictions.

Hybrid simulation strategy for multiple planar collisions with changing topologies and local deformation

The development of a hybrid strategy for the simulation of multiple plastic-elastic collisions is presented. The strategy attempts to bridge the gap between finite element methods (FEM), which typically require excessively long computation times for multiple impact simulations, and lumped parameter approaches that cannot provide accurate local deformation information. The proposed strategy employs a finite element routine solely to simulate the impact phase, thereby obtaining detailed local deformation information. The simulation of the flight phase between impacts, however, proceeds under rigid body dynamics, resulting in significant reduction in computation time. The transfer of control between FEM and rigid body dynamics is automatic and the points of contact need not be known a priori. The progressive object internal plastic strain, determined from FEM, is retained from one impact to the next, thereby ensuring a certain degree of continuity of the physical properties of the body. An example is presented to demonstrate the efficacy of this approach.