Multiphysics Modeling Approach Research Articles

An inventive multi-scale, multiphysics modelling approach and comparative analysis of distinctive features of planar ionization waves in air: II. Positive streamers

A robust numerical framework for positive streamer modelling based on electro-hydrodynamic equations coupled with Poisson and Helmholtz differential equations for the photoionization process is presented. The proposed multi-layer meshing scheme in a 2D non-axisymmetric finite-element model along with a hybrid meshing technique presented in part I of this series paper for negative streamers provide high accuracy, spatial resolution, and capability to present the major features of both positive and negative streamers. In addition, the presented model is utilized to simulate multi positive and negative streamers propagation in a non-uniform electric field in the air. The main characteristics of the positive and negative streamers including the morphology, distribution pattern of space charges, local electric field, diameter, length, and velocity are presented, discussed, and compared with the experiment. Moreover, the impacts of initial seed density and voltage on the propagation of streamers are presented and explained. The branching mechanism arising from Laplacian instability and its impact on the streamer parameters such as tip electric field and dominant charge density is explained.

Contribution of the dipole–dipole interaction to targeting efficiency of magnetite nanoparticles inside the blood vessel: A computational modeling analysis with different magnet geometries

The widespread use of magnetite nanoparticles inside the bloodstream for diagnostic and therapeutic purposes has made the influence of the interaction forces between these nanoparticles an important issue for predicting their behavior for improving the effectiveness of the protocols. Magnets with various geometries have been used in different biomedical applications, such as targeted drug delivery, to guide drugs carrying magnetite nanoparticles to specific areas. In this regard, using computational modeling, we have employed a multiphysics modeling approach using the particle tracing module in the COMSOL software environment to investigate the behavior of magnetite nanoparticles considering not only the magnetophoretic force, but also the dipole–dipole interaction forces between the nanoparticles. The effects of different geometries of magnets on the induced magnetic flux density and the laminar flow velocity inside the bloodstream were studied as well. The results of our study show that each geometry of the magnet induces different magnetic flux density profile and laminar velocity inside the blood flow. The behavior of ferrofluid flow is dependent on the geometry of the magnet and its remanent flux density. By increasing the size of magnetic nanoparticles, the magnetophoretic force enhances the particle velocity in the direction perpendicular to the vessel's walls, which could result in pull out. The results also reveal that the magnetic dipole–dipole interactions between nanoparticles could lead to the induction of higher dipole–dipole interaction forces in regions close to the magnet, especially on the upper wall of the blood vessel.

Fluid-Structure Interaction in Coronary Stents: A Discrete Multiphysics Approach

Stenting is a common method for treating atherosclerosis. A metal or polymer stent is deployed to open the stenosed artery or vein. After the stent is deployed, the blood flow dynamics influence the mechanics by compressing and expanding the structure. If the stent does not respond properly to the resulting stress, vascular wall injury or re-stenosis can occur. In this work, a Discrete Multiphysics modelling approach is used to study the mechanical deformation of the coronary stent and its relationship with the blood flow dynamics. The major parameters responsible for deforming the stent are sorted in terms of dimensionless numbers and a relationship between the elastic forces in the stent and pressure forces in the fluid is established. The blood flow and the stiffness of the stent material contribute significantly to the stent deformation and affect its rate of deformation. The stress distribution in the stent is not uniform with the higher stresses occurring at the nodes of the structure. From the relationship (correlation) between the elastic force and the pressure force, depending on the type of material used for the stent, the model can be used to predict whether the stent is at risk of fracture or not after deployment.

Multiphysics modelling of photon, mass and heat transfer in coral microenvironments.

Coral reefs are constructed by calcifying coral animals that engage in a symbiosis with dinoflagellate microalgae harboured in their tissue. The symbiosis takes place in the presence of steep and dynamic gradients of light, temperature and chemical species that are affected by the structural and optical properties of the coral and their interaction with incident irradiance and water flow. Microenvironmental analyses have enabled quantification of such gradients and bulk coral tissue and skeleton optical properties, but the multi-layered nature of corals and its implications for the optical, thermal and chemical microenvironment remains to be studied in more detail. Here, we present a multiphysics modelling approach, where three-dimensional Monte Carlo simulations of the light field in a simple coral slab morphology with multiple tissue layers were used as input for modelling the heat dissipation and photosynthetic oxygen production driven by photon absorption. By coupling photon, heat and mass transfer, the model predicts light, temperature and O2 gradients in the coral tissue and skeleton, under environmental conditions simulating, for example, tissue contraction/expansion, symbiont loss via coral bleaching or different distributions of coral host pigments. The model reveals basic structure–function mechanisms that shape the microenvironment and ecophysiology of the coral symbiosis in response to environmental change.

Numerical investigation and comparative analysis of nanofluid cooling enhancement for TEG and TEC systems

To enhance the energy conversion of thermoelectric devices, graphene nanoplatelets (GNPs) nanofluids are generally utilized into heat exchangers to boost the cooling capability for thermoelectric generators (TEGs) and thermoelectric coolers (TECs). In this study, a fluid-thermal-electric multiphysics coupled model is developed to uncover the performance enhancements of both TEG and TEC systems using nanofluids, by which the thermodynamic and thermoelectric performances associated with the nanofluid flow behaviors can be taken into account simultaneously. The enhancement effects of nanofluid weight concentration on heat transfer, TEG's electricity generation, and TEC's cooling capability are comprehensively investigated for varying Reynolds numbers (Re). The numerical analysis demonstrates the validity of performance improvements by using nanofluids in TEG/TEC systems, which also shows that the enhancement effect increases with the nanoparticle concentration but reduces with Re. Specifically, with a 0.1 wt% nanofluid used instead of water cooling for Re = 100, the output power and the conversion efficiency are enhanced by 11.38% and 5.7% for the TEG system, while the cooling power and the coefficient of performance (COP) of the TEC system are improved by 12.13% and 9.1%, respectively. The enhancement ratios, however, decrease rapidly to be less than 5% with the increasing Re, and gradually reach a steady level when Re exceeds 1200. Of particular interest is that the performance enhancement of the TEC system proves much stronger than that of the TEG system with nanofluids used as coolants in various Re cases, suggesting that the application of nanofluids seems more promising for a TEC system. This work provides a multiphysics coupling modeling approach to reveal the enhancement effect of nanofluids on thermoelectric performances, which may bring new implications for the optimization design of thermoelectric systems.

Start-Up of a Solid Oxide Fuel Cell System with a View to Materials Science-Related Aspects, Control and Thermo-Mechanical Stresses

The start-up of a solid oxide fuel cell (SOFC) is investigated by means of numerical simulation with a view to material and operational constraints on a component and system level, as well as thermo-mechanical stresses. The applied multi-physics modeling approach couples thermal-, electrochemical, chemical-, and thermo-mechanical phenomena. In addition to constraints, emphasis is given to degrees of freedom with respect to manipulated and controlled variables of the system. Proper ramping during the start-up procedure keeps critical parameter values within a safe regime. Of particular interest are gradient in terms of temperature and chemical concentrations. Nevertheless, simulations show that thermo-mechanical stresses are relatively high during the initial start-up phase, the system is, thus, more susceptible to failure. The combination of multi-physics modeling in conjunction with practical control aspects for start-up of an SOFC, which is presented in this paper, is important for applications.

Data Driven Approach for Predicting Thermal Runaway in Li Ion Battery

Safety problems of high energy density and high-power Li-ion batteries (LIBs) associated with thermal runaway (TRA) have become a serious problem resulting in massive recalls by manufacturers, and at times even endangering the lives of the consumers. In general, the TRA consists of a battery’s rapid self-heating sourced from exothermic (electro-)chemical reactions and/or mechanical abuse. It is impossible to directly monitor the occurring events during the TRA in practical operating conditions (e.g., in cell phones or electric vehicles). However, the change in electrical parameters (pattern) during the TRA-like events could potentially indicate the existence of a failure, thus allowing to foresee the LIBs malfunction.In this contribution, we employ multi-physics modeling and machine learning (ML) to address this important TRA problem in LIBs. Specifically, we use ML techniques to learn and predict the likelihood of the TRA, using the data acquired from the multi-physics modeling of LIBs. The multi-physics modeling approach is comprised of a coupled thermal, electrochemical (P2D model) and degradation sub-models. In this work, a degradation phenomenon leading to the TRA is the solid electrolyte interface (SEI) formation/decomposition in the negative electrode. Subsequently, due to the time-varying characteristic of the variables affecting TRA (i.e, voltage, C-rate, state-of-charge, temperature, etc.), we propose three ML techniques, namely, Support Vector Machine, Deep Neural Network, and Recurrent Neural Network to be customized and applied for determining the TRA likelihood. For deep learning methods, we propose a new activation function, TK-MARS, based upon a partitioning based multivariate adaptive regression spline (MARS). Finally, to mitigate the uncertainty of the prediction results under different degradation conditions, we built an ensemble framework (i.e., a committee of single prediction models) incorporating the trained individual models, in order to maximize the robustness and generalization power of the prediction for a new unseen observation without prior knowledge on the degradation. Thus, the developed combined multi-physics and ML modeling approach establish a basis for accelerated or ‘on-the-fly’ prediction of the TRA as well as a framework for extending machine learning methodologies to broad applications in electrochemistry.

Transient system-level performance and thermo-mechanical stress analysis of a solid oxide fuel cell-based power generation plant with a multi-physics approach

A solid oxide fuel cell-based (SOFC) power generation plant is analyzed with a view to performance as well as thermo-mechanical stresses. Emphasis is given to design and operation constraints of individual components as well as control-relevant aspects. We use a multi-physics modeling approach for simulations in design and off-design (part-load) under steady-state and transient conditions. Simulations confirm that the temperature distribution plays a pivotal role. For the SOFC the electrolyte is exposed to higher stresses compared to those in the electrodes. Disturbances in operation, e.g. in terms of current extraction, should be avoided because of resulting temperature excursions. This systems engineering perspective in which performance, durability issues and control aspects are combined, provides additional insights on a system level of practical relevance.

Modeling of Degradation of Solid Oxide Fuel Cell (SOFC) at Stack-Scale

Solid Oxide Fuel Cells (SOFC) converts chemical energy of a fuel (hydrogen or reformed hydrocarbons) to electricity directly with high efficiency. High-temperature operation of the SOFC makes it a fuel-flexible device; however, the high temperatures induce some degradation mechanisms. Degradation of the SOFC is a barrier against its widespread use and commercialization. Therefore, a thorough analysis is necessary to investigate mitigation strategies for reducing the degradation rate and so improving performance.Degradation experiments are time consuming and costly. Modeling of the SOFC stack is therefore a good alternative for studying degradation mechanisms and mitigation techniques. However, computational cost of numerical simulations of an SOFC is high because of the multiphysics modeling approach that is needed to take care of the interactions of physics such as flow distribution, mass transport, charge and energy transfer. The high computational cost of the numerical models hinders 3D modeling of the SOFC even at a single-cell scale. Therefore, 1D and 2D models with all physics included have been developed, or 3D models with simplifying assumptions, such as isothermal approach, have been developed. To the best of the authors’ knowledge, all the degradation models of the SOFC are developed at a single-cell scale, even most of them concentrate on a part of the electrodes and electrolyte.Here, a homogenized model of a full stack in 3D is used to investigate the degradation with a reasonable computational time. The homogenized model considers flow in manifolds, and in the active domain it considers all relevant physics, i.e. currents, gas flows, heat transport, mass balances and mechanical stresses. It does so by use of a homogenized description of all physics, such that it correctly represent the physics without describing the geometrical detail but rather represent the response of all layers effectively. It was shown that the model predicts the overall responses of the stack in a realistic manner, while it is about two orders of magnitude faster than conventional stack models where the geometry inside the stack is explicitly represented.The model includes transport equations of mass, momentum, species, charges, and energy. In this study, the following degradation mechanisms are added to the model: nickel particles coarsening (agglomeration) which decreases triple-phase boundary (TPB) length and electric conductivity of anode electrode, chromium poisoning at the cathode side which reduces TPB length of cathode electrode, and corrosion of interconnect which increases ASR (area specific resistance) through the resistance of oxide scale against electric charge transfer.The transient model takes less than a day to simulate tens of thousands of hours of degradation on a workstation with Intel Xeon 3.7 GHz 6-core processor. The peak RAM (random access memory) is about 10 GB for the simulations. The volume averages of the aforementioned degradation in the active domain over time are qualitatively consistent with common trends reported in the literature. Moreover, the model resolves distributions of the degradation mechanisms over the active domain. Therefore, it can be used to modify the stack design to minimize degradation rates. Moreover, cells that experience high degradation rates could be exchanged with the ones at safe regions of the stack to improve its lifetime. Figure 1

Multi-physics continuum modelling approaches for metal powder additive manufacturing: a review

PurposeThis paper aims to present a systematic approach in the literature survey related to metal additive manufacturing (AM) processes and its multi-physics continuum modelling approach for its better understanding.Design/methodology/approachA systematic review of the literature available in the area of continuum modelling practices adopted for the powder bed fusion (PBF) AM processes for the deposition of powder layer over the substrate along with quantification of residual stress and distortion. Discrete element method (DEM) and finite element method (FEM) approaches have been reviewed for the deposition of powder layer and thermo-mechanical modelling, respectively. Further, thermo-mechanical modelling adopted for the PBF AM process have been discussed in detail with its constituents. Finally, on the basis of prediction through thermo-mechanical models and experimental validation, distortion mitigation/minimisation techniques applied in PBF AM processes have been reviewed to provide a future direction in the field.FindingsThe findings of this paper are the future directions for the implementation and modification of the continuum modelling approaches applied to PBF AM processes. On the basis of the extensive review in the domain, gaps are recommended for future work for the betterment of modelling approach.Research limitations/implicationsThis paper is limited to review only the modelling approach adopted by the PBF AM processes, i.e. modelling techniques (DEM approach) used for the deposition of powder layer and macro-models at process scale for the prediction of residual stress and distortion in the component. Modelling of microstructure and grain growth has not been included in this paper.Originality/valueThis paper presents an extensive review of the FEM approach adopted for the prediction of residual stress and distortion in the PBF AM processes which sets the platform for the development of distortion mitigation techniques. An extensive review of distortion mitigation techniques has been presented in the last section of the paper, which has not been reviewed yet.

Computational modeling of drug transport and mixing in the chemofilter device: enhancing the removal of chemotherapeutics from circulation.

Intra-arterial chemotherapy (IAC) is the preferred treatment for non-resectable hepatocellular carcinoma. A large fraction of IAC drugs, e.g., Doxorubicin, pass into systemic circulation, causing cardiac toxicity and reducing effectiveness of the procedure. These excessive drugs can be captured by the Chemofilter-a 3D-printable, catheter-based device deployed in a vein downstream of the liver during IAC. In this study, alternative configurations of the Chemofilter device were compared by evaluating their hemodynamic and filtration performance through multiphysics computational fluid dynamics simulations. Two designs were evaluated, a honeycomb-like structure of parallel hexagonal channels (honeycomb Chemofilter) and a cubic lattice of struts (strutted Chemofilter). The computationally optimized Chemofilter design contains three honeycomb stages, each perforated and twisted, which improved Doxorubicin adsorption by 44.6% compared to a straight channel design. The multiphysics simulations predicted an overall 66.8% decrease in concentration with a 2.9mm-Hg pressure drop across the optimized device compared to a 50% concentration decrease observed during in-vivo experiments conducted with the strutted Chemofilter. The Doxorubicin transport simulations demonstrated the effectiveness of the Chemofilter in removing excessive drugs from circulation while minimizing pressure drop and eliminating flow stagnation regions prone to thrombosis. These results demonstrate the value of the multiphysics modeling approach in device optimization and experimental burden reduction.

Transient temperature effects on the optical power wavelength shift of a high-power laser system

The effect of junction temperature change on the wavelength shift and optical power output of high-power laser systems utilizing a fiber laser design is investigated using a mathematical model. Several laser diode array configurations, along with two different cooling fluids, are used to analyze the laser performance by numerically calculating the optical power out of the fiber laser for each case. The modeling approach presented here captures the dependence of optical power output on laser diode junction temperature by way of the optical power interactions between the laser diodes and fiber gain media components. Through the presented research, the beginning of a Multiphysics modeling approach has been created for better understanding the thermal requirements for a robust and practical high-power laser system. Future research will build off this and focus on the temperature dependent aspects of individual components (laser diodes, fiber gain media, and combining optics) in high power laser systems. In conjunction, high fidelity modeling of the listed components will provide a clear picture of the aggregate system-level thermal requirements. Gains in system-level thermal knowledge are instrumental for progress in high power laser technology and application.

3D multiphysics modeling aided APU development for vehicle applications: A thermo-structural investigation

Solid oxide fuel cells (SOFC) are suitable for on-board electricity generation as Auxiliary Power Unit (APU) to support the electric power supply in heavy-duty vehicles. In order to satisfy the requirements of a lightweight fuel cell stack for mobile applications, thin-walled components must be used for the stack structure. This necessity is associated with material, process and design difficulties that must be solved in order to achieve a successful utilization. In this work a novel lightweight SOFC stack design with metal-supported cell was studied both numerically and experimentally. The metallic components are made from the Intermediate Temperature Metal (ITM), a high performance, high chromium ferritic stainless steels alloy. The multiphysics modeling approach (fluid dynamics, heat transfer, structural mechanics) was utilized in this work to predict the temperature distribution and the thermo-structural behavior of the new developed design. Geometric details of the fuel cell stack components as well as appropriate nonlinear, temperature and time-dependent constitutive models were developed to describe the material behavior. Experimental data were used to determine the material model parameters and validated the simulation results. The three-dimensional stress and deformation distributions in the individual stack components were evaluated and their maximum values for elements at risk were identified. Thus, the developed model enables the investigation of sustainability and serviceability of the structural elements to ensure a reliable operation of the stack. The developed computational model can be used as a design tool for parametric studies and optimization analysis to investigate the effects of process boundary conditions, material properties as well as geometrical design parameters and their variation on the induced thermal stresses.

Evolutionary topology optimization for acoustic-structure interaction problems using a mixed u/p formulation

In this work, we present a topology optimization method for acoustic-structure interaction problems, which combines bi-directional evolutionary structural optimization (BESO) with a mixed displacement-pressure (u/p) formulation as an effective and straightforward design method for a multi-physics system involving acoustic-structure interactions. Due to the binary characteristics of the BESO and the multi-physics modeling approach of the mixed formulation, the proposed optimization procedure could benefit from high computational efficiency and high-quality design in acoustic-structure interaction problems. Several topology optimization problems for vibro-acoustic systems are carried out, in order to demonstrate the effectiveness of the presented method.

Radio frequency response of flexible microstrip patch antennas under compressive and bending loads using multiphysics modeling approach

This research article studies the effect of compression and bending loads on resonant frequency of microstrip patch antennas using COMSOL Multiphysics software (will be called COMSOL hereafter). In this study, copper microstrip patch antenna of dimension 30 mm × 25 mm on polydimethylsiloxane (PDMS) substrate of dimension 50 mm × 50 mm is considered. The interface bonding is assumed to be ideal between the patch and substrate. Both Ansoft HFSS and COMSOL are used to model and analyze the original geometry of the microstrip patch antenna without applying physical load to make sure that the design and the impedance match is satisfactory. Then, COMSOL is used to find deformed shape of the microstrip patch antenna under different values of compression and bending loads. The deformed geometries are reanalyzed using COMSOL radio frequency (RF) simulation. The resonant frequencies at different load levels are obtained and the effect of loading and boundary conditions on the resonant frequency shift is discussed.

Multiscale Modeling of Structure, Transport and Reactivity in Alkaline Fuel Cell Membranes: Combined Coarse-Grained, Atomistic and Reactive Molecular Dynamics Simulations.

In this study, molecular dynamics (MD) simulations of hydrated anion-exchange membranes (AEMs), comprised of poly(p-phenylene oxide) (PPO) polymers functionalized with quaternary ammonium cationic groups, were conducted using multiscale coupling between three different models: a high-resolution coarse-grained (CG) model; Atomistic Polarizable Potential for Liquids, Electrolytes and Polymers (APPLE&P); and ReaxFF. The advantages and disadvantages of each model are summarized and compared. The proposed multiscale coupling utilizes the strength of each model and allows sampling of a broad spectrum of properties, which is not possible to sample using any of the single modeling techniques. Within the proposed combined approach, the equilibrium morphology of hydrated AEM was prepared using the CG model. Then, the morphology was mapped to the APPLE&P model from equilibrated CG configuration of the AEM. Simulations using atomistic non-reactive force field allowed sampling of local hydration structure of ionic groups, vehicular transport mechanism of anion and water, and structure equilibration of water channels in the membrane. Subsequently, atomistic AEM configuration was mapped to ReaxFF reactive model to investigate the Grotthuss mechanism in the hydroxide transport, as well as the AEM chemical stability and degradation mechanisms. The proposed multiscale and multiphysics modeling approach provides valuable input for the materials-by-design of novel polymeric structures for AEMs.

Numerical Modelling for the Thermal Performance Assessment of a Semi-Opaque Façade with a Multilayer of Nano-Structured and Phase Change Materials

The aim of our present study was to assess and compare the thermo-physical and energy behaviour of different integrated building façades, using a multi-physics simulation approach. Advanced integrated façades composed of opaque modules, one of them with a phase change materials (PCM) layer, the others with multilayer panels, combined with transparent ones, consisting of nano-structured materials and new-generation photovoltaic systems, were investigated. A multi-physics approach was used for the design optimization of the studied components and evaluation of their thermo-physical and heat transfer performance. In particular, computational fluid dynamics (CFD) multi-physics transient simulations were performed to assess air temperature and velocity fields inside the ventilated cavities. Analysis of heat and mass exchange through all the components was assessed during heating and cooling mode of a reference building. The typical Mediterranean climate was considered. Results comparison allowed the dynamic heat transfer evaluation of the multilayer façades as a function of variable climatic conditions, and their flexibility and adaptability exploitation, when different energy strategies are pursued. The multi-physics modelling approach used, proved to be a strong tool for the energy design optimization and energy sustainability evaluation of different advance materials and building components.

(Invited) Requirements for Highly Accurate Multiphysics Modeling of SiC Power MOSFETs and Power Modules

With the current needs towards achieving significantly higher power density and energy efficiency of power conversion, the industry is highly interested in replacing mature Silicon devices with the emerging Silicon Carbide (SiC)-based technology in the new generation of power electronics systems. Multi-physics modelling represents a very important design step used to evaluate and confirm the potential of SiC devices in a wide-range of power electronics applications before any prototypes are constructed. It enables a detailed assessment of SiC technology with respect to different performance aspects including dynamics, thermal capabilities, and robustness against abnormal operating conditions. As a prototypical example, this paper presents a highly accurate modelling procedure for analyzing short-circuit (SC) capabilities of a commercial SiC power MOSFET (80mΩ, 1.2kV). First, the actual MOSFET structure is modeled in Synopsys Sentaurus TCAD tool suite and calibrated to match the I-V and C-V MOSFET characteristics, taking into account the mobility degrading effects and interface states at the SiC/SiO2 interface. In the next step, TCAD mix-mode simulations are performed using the developed physical model to gain a better understanding of the design parameters like cell pitch, channel length and p-base doping concentration and their impact on the MOSFET SC and dynamic characteristics considering temperature dependencies and design constraints. Accordingly, a trade-off analysis between improved SC capabilities and a good MOSFET dynamic performance will be discussed, which can be further used as a guideline for developing an optimized MOSFET structure. Moreover, a detailed three-dimensional electromagnetic model of the SC measurement setup will be presented in order to identify the influence of the circuit parameters on the current profile of the Device-Under-Test (DUT) during the SC events and to optimize the measurement setup. For a comparison between the measured and simulated MOSFET waveforms, coupling of electrical and electromagnetic domains will be performed in LTSpice, Saber and TCAD mix-mode tool. As a result, this paper will demonstrate the accuracy of three device models side-by-side: the compact device model implemented in LTSpice, the behavioral model of Saber, and the TCAD numerical model. Finally, the paper emphasizes the requirements for a very accurate and efficient multi-domain modelling procedure that can be integrated in the overall development process of SiC power MOSFETs. Fig. 1 A comprehensive analysis of short-circuit (SC) capabilities of a commercial SiC power MOSFET (80mΩ, 1.2kV) based on a multi-physics modelling approach. Figure 1

Effect of Ultrafast Imaging on Shear Wave Visualization and Characterization: An Experimental and Computational Study in a Pediatric Ventricular Model

Plane wave imaging in Shear Wave Elastography (SWE) captures shear wave propagation in real-time at ultrafast frame rates. To assess the capability of this technique in accurately visualizing the underlying shear wave mechanics, this work presents a multiphysics modeling approach providing access to the true biomechanical wave propagation behind the virtual image. This methodology was applied to a pediatric ventricular model, a setting shown to induce complex shear wave propagation due to geometry. Phantom experiments are conducted in support of the simulations. The model revealed that plane wave imaging altered the visualization of the shear wave pattern in the time (broadened front and negatively biased velocity estimates) and frequency domain (shifted and/or decreased signal frequency content). Furthermore, coherent plane wave compounding (effective frame rate of 2.3 kHz) altered the visual appearance of shear wave dispersion in both the experiment and model. This mainly affected stiffness characterization based on group speed, whereas phase velocity analysis provided a more accurate and robust stiffness estimate independent of the use of the compounding technique. This paper thus presents a versatile and flexible simulation environment to identify potential pitfalls in accurately capturing shear wave propagation in dispersive settings.

Experimental validation of electric bus powertrain model under city driving cycles

Battery electric city bus model has been created and validated with measurement results from a full-scale city bus prototype. The model utilises multi-physics modelling approach with multiple-domains from friction-tyre and transmission model to electrical drive and a simplified battery model. For the electrical drive model, four approaches to model the losses were studied. The modelled and measured motor torque, speed, current in the battery and inverter, and the bus speed were compared under two bus line driving cycles using three payloads. The simulated results were in good agreement with the experimental results; the error between the simulated and measured energy consumptions was 1.5% with the most accurate model.