Real-time Simulation Applications Research Articles

Real-time soft body dissection simulation with parallelized graph-based shape matching on GPU

Background and ObjectiveInteractive soft tissue dissection has been a fundamental procedure in virtual surgery systems. Existing cutting algorithms involve complex topology changes of simulation meshes, which can increase simulation overhead and produce visual artifacts. In this paper, we proposed a novel graph-based shape-matching method that allows for real-time, flexible, progressive, and discontinuous cuts on soft tissue. MethodsWe employed shape-matching constraints within the position-based dynamics (PBD) framework, a widely adopted approach for real-time simulation applications. The soft tissue was effectively modeled using overlapping clusters, each governed by shape-matching constraints. The dissection process was bifurcated into two distinct stages. In the first stage, the surgical scalpel presses the surface of the soft tissue. The soft tissue is cut apart when the surface pressure exceeds a threshold, entering the second stage. To address the discrepancy between the visual mesh and the simulation model during cluster separation, we developed an Aggregate Finding Connected Components (AFCC) algorithm, optimized for GPU computation and integrated with a background grid. This approach also avoids ghost forces and fragmentation artifacts. To control the increase in the number of clusters, we also propose a merging strategy that can run in parallel. ResultsOur simulation outcomes demonstrated that the AFCC dissection algorithm effectively manages cluster separation and expansion with robustness. There were no ghost forces between the cutting surface and unrealistic fragments. Our simulation capability extended to supporting intricate and discontinuous cutting routes. Our dissection simulation maintained real-time performance even with over 100,000 particles constituting the soft tissue. ConclusionsOur real-time and robust surgical dissection simulation technique enables the performance of complex cuts in various surgical scenarios, demonstrating its potential in virtual surgery applications.

A Variational Autoencoder Cascade Generative Adversarial Network for Scalable 3D Object Generation and Reconstruction

Generative Adversarial Networks (GANs) for 3D volume generation and reconstruction, such as shape generation, visualization, automated design, real-time simulation, and research applications, are receiving increased amounts of attention in various fields. However, challenges such as limited training data, high computational costs, and mode collapse issues persist. We propose combining a Variational Autoencoder (VAE) and a GAN to uncover enhanced 3D structures and introduce a stable and scalable progressive growth approach for generating and reconstructing intricate voxel-based 3D shapes. The cascade-structured network involves a generator and discriminator, starting with small voxel sizes and incrementally adding layers, while subsequently supervising the discriminator with ground-truth labels in each newly added layer to model a broader voxel space. Our method enhances the convergence speed and improves the quality of the generated 3D models through stable growth, thereby facilitating an accurate representation of intricate voxel-level details. Through comparative experiments with existing methods, we demonstrate the effectiveness of our approach in evaluating voxel quality, variations, and diversity. The generated models exhibit improved accuracy in 3D evaluation metrics and visual quality, making them valuable across various fields, including virtual reality, the metaverse, and gaming.

Kirchhoff rod-based three-dimensional dynamical model and real-time simulation for medical-magnetic guidewires

Background and Objective: Magnetic guidewire, fabricated from hard-magnetic soft composites, has recently emerged as an appropriate candidate for magnetic actuation systems to perform intravascular surgical navigation, owing to its elastic, magnetically steerable properties and good interphase with biological tissues. A suitable and efficient mathematical model for the magnetic guidewire is essential in the system to execute remote manipulation and active control. Methods: This paper presents a real-time Kirchhoff rod-based dynamical modeling approach, the magneto-elastic rod model, to simulate magnetic guidewire, which provides accurate simulations for two- and three-dimensional dynamic deflections induced by external magnetic fields and obtains deformed guidewire shapes in quasi-static status. Results: The proposed model is capable of describing the intrinsic principles of elastic body actuation by torques generated from the hard-magnetic soft matrix. The effectiveness of the developed model is validated, and the real-time simulation application is conducted via the semi-implicit numerical integration method. Conclusions: It has been shown that the presented dynamical model captures large nonlinear deformations and transient responses of the magnetic guidewire in an imitated human blood environment, which could offer robust support for the construction of a simulated magnetically driven surgical system.

Increasing situation awareness in healthcare through real-time simulation

Research into real-time simulation applications outside of manufacturing environments has extended to sociotechnical systems such as healthcare over the past decade, where a number of published studies have demonstrated proof-of-concept models for near-future resource planning. Using real-time decision-support systems, people take decisions supported by the output of simulations. However real-time simulation frameworks abstract human intervention to an “external decision-maker,” with little regard to the complexities of underlying decision-making constructs, and how design and development decisions can impact the quality of decision-support. One such construct is situation awareness (SA), which is a precursor to decision-making. It is a dynamic state of knowledge about how a situation is unfolding; one approach to enhancing situation awareness is the provision of appropriate real-time information. We argue that design, development and implementation decisions should be focused at the interface between decision-making and decision-support. This integrative literature review proposes a SA framework integrating models of SA with a technical perspective for real-time simulation, to support an understanding of the cognitive needs of users alongside technical details during the development process. The implications for the usefulness and usability of real-time decision-support tools are discussed with application to Emergency Departments.

실시간 시뮬레이터를 활용한 철도차량 PMSM 제어시스템의 시계열 기반 안정도 추정

This paper deals with numerical analysis method for system stability, which is applied to the mathematical model of permanent magnet synchronous motor for railway vehicle as one of the application of real-time digital simulation. Specifically, this study deals with bifurcation numerical analysis, one of analytic method to study nonlinear dynamics of a system, for system design or its inspection technique of the system model. XPPAUT is used to analyze the electrical motion of this complex system, so it can introduce theoretical approach to design real-time computing environment based on OPAL-RT for electrification system parts of railroad vehicle model. Within the real-time simulation framework, the paper also provides time-series based system stability estimation by performing statistical processes for auto-regressive model construction. The proposed approach can reduplicate verification process by screen studying of the model for improvement during real-time simulation or further hardware-in-the-loop test system.

A Comparison of Time-Domain Implementation Methods for Fractional-Order Battery Impedance Models

This paper is a comparative study of the multiple RC, Oustaloup and Grünwald–Letnikov approaches for time domain implementations of fractional-order battery models. The comparisons are made in terms of accuracy, computational burden and suitability for the identification of impedance parameters from time-domain measurements. The study was performed in a simulation framework and focused on a set of ZARC elements, representing the middle frequency range of Li-ion batteries’ impedance. It was found that the multiple RC approach offers the best accuracy–complexity compromise, making it the most interesting approach for real-time battery simulation applications. As for applications requiring the identification of impedance parameters, the Oustaloup approach offers the best compromise between the goodness of the obtained frequency response and the accuracy–complexity requirements.

Real-Time Simulation of a Cerebellar Scaffold Model on Graphics Processing Units.

Large-scale simulation of detailed computational models of neuronal microcircuits plays a prominent role in reproducing and predicting the dynamics of the microcircuits. To reconstruct a microcircuit, one must choose neuron and synapse models, placements, connectivity, and numerical simulation methods according to anatomical and physiological constraints. For reconstruction and refinement, it is useful to be able to replace one module easily while leaving the others as they are. One way to achieve this is via a scaffolding approach, in which a simulation code is built on independent modules for placements, connections, and network simulations. Owing to the modularity of functions, this approach enables researchers to improve the performance of the entire simulation by simply replacing a problematic module with an improved one. Casali et al. (2019) developed a spiking network model of the cerebellar microcircuit using this approach, and while it reproduces electrophysiological properties of cerebellar neurons, it takes too much computational time. Here, we followed this scaffolding approach and replaced the simulation module with an accelerated version on graphics processing units (GPUs). Our cerebellar scaffold model ran roughly 100 times faster than the original version. In fact, our model is able to run faster than real time, with good weak and strong scaling properties. To demonstrate an application of real-time simulation, we implemented synaptic plasticity mechanisms at parallel fiber–Purkinje cell synapses, and carried out simulation of behavioral experiments known as gain adaptation of optokinetic response. We confirmed that the computer simulation reproduced experimental findings while being completed in real time. Actually, a computer simulation for 2 s of the biological time completed within 750 ms. These results suggest that the scaffolding approach is a promising concept for gradual development and refactoring of simulation codes for large-scale elaborate microcircuits. Moreover, a real-time version of the cerebellar scaffold model, which is enabled by parallel computing technology owing to GPUs, may be useful for large-scale simulations and engineering applications that require real-time signal processing and motor control.

Robust Model Predictive Control for Dynamics Compensation in Real-Time Hybrid Simulation

Hybrid simulation is an efficient method to obtain the response of an emulated system subjected to dynamic excitation by combining loading-rate-sensitive numerical and physical substructures. In such simulations, the interfaces between physical and numerical substructures are usually implemented using transfer systems, i.e., an arrangement of actuators. To guarantee high fidelity of the simulation outcome, conducting hybrid simulation in hard real-time is required. Albeit attractive, real-time hybrid simulation comes with numerous challenges, such as the inherent dynamics of the transfer system used, along with communication interrupts between numerical and physical substructures, that introduce time delays to the overall hybrid model altering the dynamic response of the system under consideration. Hence, implementation of adequate control techniques to compensate for such delays is necessary. In this study, a novel control strategy is proposed for time delay compensation of actuator dynamics in hard real-time hybrid simulation applications. The method is based on designing a transfer system controller consisting of a robust model predictive controller along with a polynomial extrapolation algorithm and a Kalman filter. This paper presents a proposed tracking controller first, followed by two virtual real-time hybrid simulation parametric case studies, which serve to validate the performance and robustness of the novel control strategy. Real-time hybrid simulation using the proposed control scheme is demonstrated to be effective for structural performance assessment.

High performance computing engines for the FPGA-based simulation of the ULM

This paper presents a design methodology for the FPGA-based simulation of the Universal Line Model (ULM). The proposed approach yields a higher computational performance compared to alternative implementations reported in the literature. Such performance allows the use of the FPGA model in real-time simulation applications or for the acceleration of offline EMT programs. A state-space approach is used to perform the time-domain simulation of the pole-residue form of the rational fitting of the characteristic admittance and propagation functions. The paper also discusses the appropriate scheduling of the ULM computations and proper management of the history terms that lead to an optimized hardware utilization, low latency response times, and higher computational performances using floating-point arithmetic.

Numerical transient and steady state analytical modeling of the wellbore temperature during drilling fluid circulation

In this paper, a transient model that describes the heat transfer processes in the wellbore during circulation is presented. A simulation of the transient effect on these heat transfer processes was achieved by using a numerical approach to solve the thermal balance equations that describe the heat flow in that system. The present model can be applied for both laminar and turbulent flow regimes through the convective heat transfer coefficient (CHTC). The run time of the present model is relatively short, hence it can be applied for real-time simulation applications. This was achieved by simplifying the model and reducing the calculation complexity. Moreover, the present model has gone through different validation processes. First, the present model is reduced to a steady state condition and solved analytically. This solution was used as a reference to verify the results of the numerical model. Additionally, a grid sensitivity analysis was performed. Second, the analytical solution was validated through a comparison with the known literature. Finally, the assumptions that were made to simplify the model were verified by comparing the results with the comprehensive version of the model. The effect of the flow rate and the flow regime on the wellbore temperature profile are examined. The results showed a reverse effect of the flow rate on the bottom hole temperature within each flow regime. However, a significant increase in the bottom hole temperature is observed as the flow regime changed from laminar flow to turbulent flow. Changing the flow regime from laminar to turbulent will affect the value of the CHTC leading to a significant increase in wellbore fluid temperature. It is also shown that the maximum temperature at the annulus is located where the rate of heat exchange between the annulus and the pipe and the heat from the formation to the annulus is equal.

A fast and stable first-order method for simulation of flexible beams and cables

Gradient deficient beam elements (commonly known as cable elements in the literature) based on the absolute nodal coordinate formulation (ANCF) have great potential for large-scale and real-time simulation applications. In this report, a novel and stable first-order integration method for the gradient deficient ANCF element is developed in a simple linear form. The extension of the integration method to the fully parameterized cable element is also discussed. The method involves splitting the elastic potential using the quadrature points involved in the numerical integration of the continuous body and treating the forces developed by the potential at each quadrature point as though it has arisen from a relaxed constraint in the compliant constraints formalism. The integration method exhibits excellent stability properties, scales well, and can be solved efficiently, with only a single linear solve. Efficient methods for computing the required Jacobians and deformation functions and solving the resulting linear equation are discussed. The integration method is tested in three dimensions, on a cable segment formed from multiple elements and compared to other first-order integration methods in terms of the speed and accuracy. The method is demonstrated via simulating various systems, including a pendulum, a cantilever bar, and a flexible beam dropped onto cylindrical supports. Lastly, the utility and use cases of the proposed integrator are discussed.

Dynamic average modelling of renewable generation sources for real time simulation

The increase in microgrids and smart grid research comprising renewable generation sources with advanced grid control functionalities is driving the need for sophisticated simulation and hardware in the loop (HIL) test facilities using digital real time simulators (DRTS). Unlike traditional off line simulation tools, DRTS provides fast, continuous real time operation as well as hardware interfaces to test the operation of physical control, protection and power devices before they are installed in the smart/micro grid application. The available computation resources of the DRTS to achieve fast, continuous real time operation impose a limitation on the size and level of detail of the power system model for the simulation and HIL application. Reduced dynamic models that represent the power system and control dynamics with sufficient accuracy provide an acceptable trade-off between the required computation resources and size of the power system model for large simulation applications. This paper discusses the dynamic average modelling of renewable energy generation sources for real time simulation applications.

A Diesel Engine Modelling Approach for Ship Propulsion Real-Time Simulators

A turbocharged diesel engine numerical model, suitable for real-time ship manoeuvre simulation, is presented in this paper. While some engine components (mainly the turbocharger, intercooler and manifolds) are modelled by a filling and emptying approach, the cylinder simulation is based on a set of five-dimensional numerical matrices (each matrix is generated by means of a more traditional thermodynamic model based on in-cylinder actual cycle). The new cylinder calculation approach strongly reduces the engine transient computation time, making it possible to transform the simulation model into a real-time executable application. As a case study, the simulation methodology is applied to a high speed four stroke turbocharged marine diesel engine, whose design and off design running data are available from the technical sheet. In order to verify the suitability of the proposed model in real-time simulation applications, a yacht propulsion plant simulator is developed. Numerical results in ship acceleration and deceleration manoeuvres are shown, reducing the simulation running time of 99% in comparison with the corresponding in-cylinder actual cycle engine model.

FPGA-Based Real-Time Simulation of High-Power Electronic System With Nonlinear IGBT Characteristics

The hardware-in-the-loop simulation plays a vital role in the test of high-power electronic system. Although the application of field-programmable gate array (FPGA) embedded system has enabled the real-time system simulating below 500 ns, the transient characteristic of high-voltage insulated-gate bipolar transistor (HVIGBT) is largely compromised. In this paper, a new piecewise HVIGBT model, considering its driver circuit effect and parasite parameter, is proposed for FPGA-based real-time simulation applications. With the attempt to reduce the simulation latency, we propose an FPGA solver with a parallel structural to divide the system into several layers. The model could not only provide accurate system-level performance of the power electronic converter but also give an insight into the transient behavior effect of high-power electronic system. Finally, a case study about emulation of traction system of high-speed train is also presented. Implementations are made on an FPGA Kintex-7 embedded in National Instruments FlexRIO PXIe-7975. The obtained results show that the proposed modeling algorithm can achieve both accuracy and efficiency within a fixed real-time simulation time step of 25 ns.

Design and implementation of a real-time hardware-in-the-loop testing platform for a dual-rotor tail-sitter unmanned aerial vehicle

Tail-sitter vertical take-off and landing (VTOL) vehicle is a promising airframe among all the unmanned aerial vehicles (UAV), although challenges regarding the control strategies remain for civil applications, such as high susceptibility to wind disturbance while hovering. A real-time hardware-in-the-loop (HIL) simulation method for a tail-sitter UAV, an efficient tool for developing the control system, is presented in this paper. A nonlinear six-degrees-of-freedom dynamic model that covers the full angle-of-attack range is derived using the component breakdown approach. The environmental model is further introduced in the real-time simulation application to provide prevailing and gust wind conditions. A commonly used open-source flight controller was embedded in the proposed HIL framework. This HIL testbed can help researchers minimise the time spent debugging the controller program and moving from the simulation control system to the practical control one. The HIL simulation system was validated with the typical complete flight scenarios of a tail-sitter, including hovering, forward transition, cruise, and back transition. The results demonstrate that the HIL system can be an efficient tool for verifying the performance of hardware and software designs of the control system at the development stage for tail-sitter UAVs.

Hybrid modeling of power electronic system for hardware-in-the-loop application

In real-time simulation applications, hardware-in-the-loop (HIL) within nanosecond time step of large size power electronic systems involving high-frequency control strategy is still a big challenge today. In this paper, we propose a new hybrid modeling approach based on a novel nodal analysis and solving method in order to achieve both fast and accurate real-time simulation. The decoupling method allows dealing with circuit element separately regardless the size of power electronic system. After system matrix is obtained, an innovative approach using Cholesky decomposition is proposed. At last, a comparative case study of traction system in the electrical locomotive train is also presented. For this case study, implementations are made on a Field Programmable Gate Arrays (FPGA) Kintex-7 embedded in National Instruments FlexRIO PXIe-7975. Results obtained show that the proposed modeling algorithm can achieve both accuracy and efficiency within a 50ns fixed real-time simulation time step. Besides, the comparison with results obtained from Simpower system in Matlab allows evaluating the accuracy of our proposed modeling approach.

Numerical stiffness study of multi-physical solid oxide fuel cell model for real-time simulation applications

Real-time fuel cell model and simulations can help to develop the fuel cell system, especially for the effective implementation of the advanced online diagnostic tool by the multi-dimensional multi-physical approach. However, the strong numeric stiffness observed in the physical equations of the high dimensional real-time model can lead to an overrun error for real-time simulation, which could be critical for online diagnosis accuracy, or even cause control failure. In this paper, the real-time simulation of a two-dimensional tubular solid oxide fuel cell model is developed. Moreover, the stiff issues of the control-oriented real-time fuel cell model are analyzed thoroughly through the calculations and comparisons of the time constants and eigenvalues for the dynamic ordinary differential equations of the nonlinear fuel cell model. An appropriate solving approach with second-order accuracy is then proposed to reduce the influence of the specific stiffness issue during the real-time simulation. The proposed solving algorithm is proofed to be L-stable and thus can make the stiff fuel cell model executed with a reduced computation time. The experimental results show that the developed multi-physical tubular fuel cell model can be effectively executed in real-time within milliseconds range with over hundreds of control volumes.

Methods for building ATRU real‐time model based on different application scenarios

This study introduces three methods for building an auto-transformer rectifier units (ATRU) real-time model based on different application scenarios. Real-time models run on an advanced real-time simulator that has the capability to leverage central processing units and field programming gate arrays. In the first section, the disadvantages of the off-line simulation are explained and the solution is offered through real-time simulation. In the second section, applications of real-time simulation in a more electric aircraft (MEA) electric power system will be presented. In the third section, methods to build the ATRU real-time model are illustrated based on requirements and different scenarios. Simulations are conducted to demonstrate the agreement between the results and analysis.

FLIGHTLABTMmodeling for real-time simulation applications

Modeling and simulation are used to support a wide range of applications including design, analysis, operations research, test and evaluation, training, etc. Each application has different fidelity requirements and computational limitations. Consequently, a variety of models are required to support a single aircraft type throughout its life cycle. Validation and configuration management of this array of models is costly. FLIGHTLAB[Formula: see text]is a software tool that supports selective fidelity modeling and simulation to insure trace-ability and commonality between models, ranging from the comprehensive models required for design to the real time models required for training and hardware-in-the-loop testing. Providing a single tool with this range of modeling options greatly enhances the configuration management capability. Also once the highest fidelity, comprehensive, model is validated, it can be used to provide reference data for validation of simpler models, thereby expediting the validation process for all levels of modeling. This paper describes the real-time simulation capability of FLIGHTLAB[Formula: see text]models and their trace-ability to higher level FLIGHTLAB[Formula: see text]models.

Modeling of synchronous electric machines for real-time simulation and automotive applications

Recent research in the field of vehicle electrification has indicated that synchronous machines, which include the permanent magnet synchronous machine (PMSM) and the externally excited synchronous machine (EESM), represent a viable solution for electric propulsion. A challenging problem for synchronous machines drives employed in automotive applications is to obtain accurate mathematical models which can deal with parametric variation and which are suitable for real-time simulations and synthesis of control laws. The goal of this paper is to provide a mathematical modeling framework for synchronous machines that can answer to this challenging problem. To this end, using the rotor reference frame, the mathematical models of PMSMs and EESMs are constructed taking into account also the parametric variation due to magnetic saturation and temperature variation. Then, a complex state-space bilinear model for both EESM and PMSM with parametric variation due to magnetic saturation and temperature are developed. Considering the parametric variation as a polytopic bounded disturbance, it is then shown how to split the bilinear complex model in two PWA variable parameter state-space models suitable for a cascade control structure. Based on the developed models, a dynamic unified simulator was constructed in Matlab®/Simulink®. Measurement data obtained in a real test-bench system were used to verify the accuracy of the simulator. The discrete-time simulator was then integrated in an industrial hardware-in-the-loop test bench for real-time evaluation of a current control scheme in EESM drives.