Full-scale Simulation Research Articles

Optimized machine learning approaches for identifying vertical temperature gradient on ballastless track in natural environments

Due to the exposure of ballastless track to various geographical and meteorological conditions, the effects of temperature evolution on the performance of ballastless track should be considered. However, accurately predicting the vertical temperature gradient (VTG) on ballastless track in thermal environments has been challenging. This study develops four machine learning (ML) approaches, i.e., support vector regression (SVR), random forest (RF), extreme gradient boosting (XGBOOST), and artificial neural network (ANN), to identify the ballastless track’s VTG evolution in natural environments. The above ML approaches with hyperparameters optimized are trained and tested by 2000 samples from full-scale finite element simulation. The temperature field monitoring on ballastless track is performed to validate its temperature distribution simulation. The results show the XGBOOST-based method has the best accuracy for identifying the ballastless track’s VTG among the four selected ML approaches. Furthermore, the stacking-based hybrid framework is proposed to further improve the four selected ML approaches. For the stacking strategy, the improvement percentage of MAE of performance and transferability to the four selected ML approaches are 11.51%-55.43%, and 42.27%-77.79%, respectively. The proposed ML approaches are proven capable and efficient for predicting the temperature evolution of track engineering.

On the importance of using region-dependent material parameters for full-scale human brain simulations

An accurate finite element (FE) model of the human brain reliably predicting its response to loading offers great possibilities for brain injury prevention, disease prediction, and surgical guidance. However, the brain is a very complex organ. One important aspect is the structural heterogeneity, both on a macroscopic and microscopic level. This also results in heterogeneous mechanical properties, which highly depend on the brain regions. The extent to which this heterogeneity affects the mechanical response of an FE simulated full brain remains largely unexplored. In this work, we investigate the importance of using region-specific material parameters when modelling the full human brain. Additionally, we assess how a prefixed Poisson’s ratio used for the determination of regional parameters affects the response of the full brain under loading. Finally, we compare the simulation results when using parameter sets that have been determined from the unconditioned and preconditioned behaviour of human brain tissue. Our results show that accounting for region-dependent properties leads to significant differences in the predicted strain state compared to simulations assuming homogeneous material properties. Also the Poisson’s ratio and using unconditioned or preconditioned data sets significantly affects the results of full-scale brain simulations, highlighting the importance of carefully selecting the material parameters used. The presented analyses have important implications for choosing appropriate region-dependent material parameters for full-scale FE human brain simulations in the future to ensure reliable predictions.

Digital Twin for Complex Logistics Systems: The Case Study of a Large-Scale Automated Order Picking and Fulfillment System

Digital twins for complex logistics systems and their practical implementation from a simulation modeling point of view as well as operational performance improvement are presented in this paper. The case study is a large-scale fully automated order picking and fulfillment system in a major fresh-food retail warehouse with a high degree of complexity of interactions as well as operational logic. The paper outlines the development of a full-scale discrete event simulation model as a basis for digital twins with a high level of data integration and modeling detail. The paper demonstrates the significant role that digital twins play in analyzing and improving the operational performance of such systems that owing to their complexity and dynamism, the consequences of managerial decisions are impossible to estimate.

High Fidelity Physics-Based Simulation of a 512-Channel 4D-Radar Sensor for Automotive Applications

Radar has emerged as a core sensing technology for many active-safety and comfort related advanced driver assistance systems (ADAS) being deployed in today’s vehicles. Using radar technology, the ego vehicle can simultaneously detect the range and velocity of multiple targets. With multiple-input, multiple-output (MIMO) arrays, it is also possible to detect the angle of arrival of targets in azimuth and elevation. 4D automotive radar sensors can determine the range, velocity, azimuth and elevation angles-of-arrival (AoA) of targets in a traffic scene. Currently, radar-returns from traffic scenes have been mainly obtained through measurement. While measurement is valuable, it can be costly, time consuming, restrictive due to practicality issues and also unsafe in some corner-case traffic scenarios. Simulation has emerged as a potential alternative source of synthetic radar-returns that can be used to develop, test and refine signal processing techniques and detection algorithms. A key challenge in simulation has been to retain an accurate representation of actors in full-scale traffic scenes while still being able to solve electrically large problems efficiently. The introduction of MIMO arrays further increases the complexity and computational load demands of such simulations. In this paper, we present a computationally efficient, high fidelity, physics-based simulation workflow for a 77 GHz frequency-modulated continuous-waveform (FMCW)-based, 512-channel MIMO radar sensor. We demonstrate how the synthetic radar returns obtained from full-scale traffic scene simulations can be used to create 4D-radar point clouds. The accuracy of the synthetic radar returns is then evaluated by overlaying the resulting 4D-radar point clouds on 4 corresponding full-scale traffic scenes with varying levels of complexity. Results from this study demonstrate how accurate radar returns obtained from simulation can be used to develop next-generation radar sensors for autonomous vehicles.

Development of an MUM-T Integrated Simulation Platform

In this paper, we present a platform that can simulate Manned-UnManned Teaming (MUM-T) situations using various hardware and software being integrated. MUM-T, which combines unmanned aerial vehicles (UAVs) with an existing manned vehicle (MV), is growing into an indispensable strategy thanks to enormous advantages it provides. In order to test this indispensable strategy which involves flight control algorithms being applied for various MUM-T situations, it is certainly needed to run and evaluate three-dimensional (3D) MV-UAVs combined simulations in realistic environments. However, there is no such simulator that enables such 3D MUM-T simulations as well as the Human Interface (HI) for both MV pilot and the mission manager at a ground station. In this paper, we propose an MUM-T integrated simulation platform (MUM-T ISP) that combines a single full-scale helicopter simulator (for MV simulation) and multiple Iris/PX4-Autopilot (for UAVs simulation), along with specially developed HI devices (TM and TV). Tactical Monitor (TM), one of the HI devices, is a touchable tablet which allows the MV pilot to interact with UAVs by simple actions (e.g. touching a button), and the other HI device called Tactical Viewer (TV) allows the mission manager at a ground station to closely monitor the MUM-T situation via realistic 3D displays of MV and UAVs. The proposed MUM-T ISP is tested on several mission scenarios and then evaluated by actual pilots and the mission manager based on sensible criteria. It is expected that the proposed simulation platform may serve well as a training tool for prospective MV pilots working with UAVs, and also as a research tool for flight engineers developing control algorithms that make MV and UAVs work together.

A numerical study on THM coupled behavior in the high-level radioactive waste disposal system

It is essential to securely isolate high-level radioactive waste from the biosphere, and geologic disposal of it at a deep underground repository is considered the most effective method. Therefore, it is crucial to research the complex thermo-hydro-mechanical-chemical (THMC) coupled behavior in geological disposal systems parallel with numerical simulation. DECOVALEX is an international cooperating project to efficiently develop numerical methods and models and validate through test results for predicting the THMC interactions in the disposal systems. In Task C of DECOVALEX-2023, the modeling teams focus on understanding pore pressure development and THM interactions in the host rock and buffer material during the FE experiment, a 1:1 scale in-situ heater test based on Nagra’s Reference repository design. We used OGS-FLAC3D for the numerical simulation, combining OpenGeoSys for TH simulation and FLAC3D for M simulation. At the first phase of the task, a simple two-dimensional benchmark problem was defined to set up the numerical model. THM coupled processes in the bentonite were simulated with a two-phase flow system, and we investigated the temperature and pressure variations on the given monitoring position. Vaporization induced by a temperature increase in the bentonite was observed at the heater’s vicinity, and flow occurred by capillarity, and pressure difference was well simulated. Additionally, the flow process was dominant in the near field of engineering barrier, while we observed thermal pressurization in the far-field area. We plan to apply the developed model to a full-scale three-dimensional numerical simulation for the next phase.

Failure Analysis of Tubing Collapse in a Gas Well

The tubing used in a gas well rarely collapses and fails during applying annulus pressure. In this study, the failure causes of tubing collapse were analyzed by means of data verification, macroscopic observation, magnetic particle inspection, physical and chemical inspection, optical microscopy, and tubing collapse test. Mechanical analysis of the string and full‐scale physical simulation test simulating downhole working conditions. Finally, the verification analysis of the collapse test is carried out by the finite element analysis (FEA). The results showed that (1) the physical dimension, physical and chemical properties, and collapse resistance of this batch of tubing met the requirements of the tubing ordering technical standard. (2) Assuming that the well packer slip was unsealed and could slide freely, the mechanical theoretical analysis of collapsed tubing string and collapse test under simulated working condition load was carried out, which reproduced the load when the tubing collapsed. It can be seen from this that the packer did fail. (3) The FEA calculation results showed that when the external pressure was greater than 30.75 MPa, it would inevitably lead to collapse failure in case of packer unsealed. In conclusion, the root cause for the collapse failure of the 105th underground tubing string was that the packer lost its sealing function, resulting in an abnormal axial load. While under the action of external pressure, the tubing was overloaded and collapsed. It is recommended to carry out verification tests on the material performance of packer slip, the dimensional changes of packer tool outer diameter and inner diameter under actual well conditions, the creep behavior of packer seal, and the performance of shear pin under actual working conditions, especially in the well containing H2S, so as to prevent the pressure leakage of gas well annulus caused by packer unsealing and the reoccurrence of such downhole string collapse accidents. The first collapse test under simulated working condition load is conducted in this paper. Analyzing the collapse failure work and putting forward suggestions to effectively prevent similar failures from happening again are of great significance to the oilfield.

COUPLED EFFECT OF VARIABLE WETTABILITY AND BODY FORCE ON FLUID FLOW THROUGH NANOCHANNELS: A MULTISCALE APPROACH

Fluid flow through sub-micron domains has been an area of active research in recent years with immense scientific and technological interests. Such flows can show deviation in behavior from the theories of classical hydrodynamics, thus opening up a new paradigm to exploit these unique effects in applications related to transport and detection. By performing extensive molecular-dynamics (MD) simulations of fluid flow through a parallel plate nanochannel of non-uniform wetting characteristics, we bring out the coupled effect of surface wettability and applied body force on interfacial slip. Our results reveal distinctive slip-stick alteration which can be useful in designing channels with engineered effective slip. Moreover, in this study, we revisit a hybrid molecular-continuum multiscale model which can significantly reduce the computational cost of full-scale MD simulations and further provide a framework to discern the flow behavior for a wide spectrum of length scales. The results obtained from this study may provide useful insights, thus carrying immense implications towards designing of multifaceted nanoscale devices and futuristic smart surfaces.

УДОСКОНАЛЕННЯ МЕТОДУ ВИЯВЛЕННЯ ТА ЛОКАЛІЗАЦІЇ НЕЛЕГАЛЬНИХ ТОЧОК ДОСТУПУ ДО БЕЗДРОТОВОЇ МЕРЕЖІ ОБ'ЄКТІВ ІНФОРМАЦІЙНОЇ ДІЯЛЬНОСТІ

Extensive use of mobile devices has led to increased Internet connections and the deployment of new wireless LANs. According to the latest Cisco research, by 2023, 66% of the world's population will be Internet users worldwide. More than 28 billion devices will be connected to the global network. In the last two decades, we have witnessed the birth and development of a technology that has significantly changed our work and life - IEEE 802.11, also known as Wi-Fi. Wi-Fi is a favorite way to connect to the Internet because of its ease of use and flexibility. To connect to a wireless network, you only need to be within range. That is, consumers and businesses will increasingly rely on mobile networks. However, it should be noted that each new opportunity of digitalization also gives new opportunities to cybercriminals and therefore, the problem of security of wireless networks today is one of the main problems of IT technologies. The inevitable proliferation of wireless networks and the growing traffic in these networks can lead to many information security incidents. The main threats are aimed at interception, breach of confidentiality and integrity of transmitted data, attacks on the availability of transmission channel nodes and their substitution. The article analyzes the existing methods of detecting unauthorized access points to information. The method of detection and localization of unauthorized access points to information circulating in the wireless network at the objects of information activities has been improved. Natural modeling of detection of unauthorized interference in the information wireless network of the enterprise was carried out. Full-scale simulation confirmed the accuracy of localization of an unauthorized point of access to information in the Wi-Fi network – up to 2 m. This will allow timely detection and localization of unauthorized access points to information in the wireless network of enterprises and institutions.

Информационно-измерительная система для натурного моделирования пожароопасной ситуации

Introduction. Sensors that respond to an increase in temperature, an increase in the concentration of carbon monoxide and smoke are currently used to register a fire hazardous situation. However, at the initial stage of overheating of materials, they release fine aerosol particles, invisible to ordinary vision. Sensors that register the excess concentration of fine particles can be used in information systems for fire early warnings. Goals and objectives. Development and implementation of an information-measuring system for full-scale experimental modeling of a fire hazardous situation. Analysis of aerosol particles released from various materials when they are heated. Methods. A new methodology and technique for conducting experimental studies based on the information-measuring system was developed. Heating of various materials to a temperature at which the release of aerosol particles began took place in a special chamber. The mass and number concentrations of aerosol particles were measured in a wide range of their sizes (from 3 nm to 100 μm) while heating the materials. All selected measuring instruments used in the information-measuring system were of the approved type. Results and discussion. The change in the concentration of aerosol particles during prolonged heating of the materials described by the optimal polynomials found to analyze the results in this study. Determined the minimum temperatures at which the studied materials begin to release aerosol particles in an amount exceeding the background level. Described the characteristic sizes of aerosol particles for various materials.Conclusion. The results of the work are the basis for the implementation of a new type of security systems designed for the early fire warning at its very early stage. We recommend the use of sensors that measure the concentration of fine aerosol particles as the basis for fire prevention information systems. Keywords: information-measuring system; full-scale simulation of a fire hazardous situation; aerosol particles; number concentration; mass concentration.

Studying occupant’s heat exposure and thermal comfort in the kitchen through full-scale experiments and CFD simulations

This study investigated kitchen heat exposure and thermal comfort through full-scale experiments and computational fluid dynamics (CFD) simulations. Experiments were conducted in a kitchen-style climate chamber with three stove conditions, three exhaust flowrates of range hood, three external conditions and three makeup air sources. CFD simulations were conducted accordingly to explore more nuances aspects of kitchen thermal environment. The experimental results showed that as the existence of a high-temperature stove, the air temperatures around the cooking staff, the net thermal radiations and local skin temperatures at exposed body parts increased significantly during the cooking period. External conditions and the makeup air source can significantly affect thermal distributions across the kitchen space and the heat exposures around the cooking staff. By adding partitions, using induction cooktops, and turning on the kitchen air conditioner can help to reduce cooking staff’s heat exposure from the gas-burning stove. The CFD simulations were consistent with the measured experimental results. The heat exposure in the cooking zone is shown to be dominated by horizontal thermal asymmetry. The occupants’ thermal comfort in the kitchen can be improved if the makeup air source came from the cooler side with a higher flowrate of range hood.

Development of a Complex Mathematical and Hardware-in-the-Loop Simulation of the System for Controlling the Skew of Sections of Mechanization of the Wing

In this paper, an innovative approach to the development of a skew control system is discussed to increase the speed and quality of the development of this system. To achieve this goal, we chose the Hardware-in-the-Loop simulation method, which involved creating a mathematical model to test a real control unit. This method reduced time and material costs at both the development and testing stages by enabling quick reconfiguration of the system and the changing parameters of the control model. As a result of this work, we developed a complex of mathematical and full-scale simulations, which included the SCS simulation scheme with distortion detection algorithms and SCS semi-random simulation stand.

Interwell simulation model for the advection dispersion equation

We propose an interwell simulation model for the advection dispersion equation (ISADE) to predict the concentration of contaminant observed at the pumping well. This method comprises of two main steps. Initially, the model divides the aquifer or reservoir into a series of 1D injector-producer pairs and uses the historical contaminant observation data to estimate five major unknowns in each of these control volumes: the interwell connectivity, the pore volume, the volumetric flowrate at the grid face, the dispersion coefficient, and the number of grid cells in each control volume. Finally, once the history matching process is complete, the estimated variables are used to predict the concentration of contaminant observed at the wells. One main advantage of modeling contaminant production using the ISADE model is that it is computationally cheaper than the full physics model as it uses a series of one-dimensional connections between each producer-injector pair with all pairs connected to each other by interconnectivity factors. The advection diffusion equations is then solved for each of these pairs independently. Three examples were presented to test the effectiveness of the ISADE model. Each of the three examples involves flow of fluid in a synthetic heterogeneous aquifer with different well configurations and varying concentrations of the contaminant released into the aquifers at some injection locations. In Examples 1 and 3, non-reactive contaminants were introduced into the respective aquifers through injection wells, while in Example 2, nonreactive contaminant was introduced into the aquifer from a from a node on one of its boundary. All the examples studied show that the results obtained from ISADE closely match those from the full-scale simulation model. Furthermore, the model can easily handle changes in input parameters such as the concentration of contaminants released in the aquifer, and the injection and production rates.

Suspended water nanodroplets evaporation and its deviation from continuum estimations

Although droplets evaporation is fundamental to many applications and phenomena, accurate prediction of their evaporation trajectory is still a technological gap today. This is even more so for nanodroplets when compared to the macro-sized droplets. Since it is technically challenging to observe real nanodroplets evaporation today, this contribution uses full atomistic molecular dynamics simulations to observe and quantify suspended water nanodroplets evaporation. There are two main findings to this contribution. First, it is shown in detail that continuum analysis significantly over predicts the evaporation rate of nanodroplets. This makes continuum analysis unsuitable to predict water nanodroplets’ behavior. Secondly, this contribution illustrates the use of data-driven approach that can be used for nanodroplets evaporation behavior prediction, instead of running full atomistic molecular dynamics simulations for every different condition, which can be prohibitively expensive. The paper hopes to encourage scientists working in similar field to share their MD results for nanodroplets evaporation to build a data-driven model that could be used to predict nanodroplets evaporation trajectory at a fraction of the cost of full-scale MD simulations.

Large-scale three-dimensional simulation of proton exchange membrane fuel cell considering detailed water transition mechanism

It is of great significance to gain deeper and clearer understanding of the transport mechanism inside proton exchange membrane (PEM) fuel cell under on-board conditions to propel its commercialization process. This study investigates detailed water transition mechanism in PEM fuel cell catalyst layer from the perspective of macroscale performance model. Full layout of single cell structure and variable operating conditions are considered. Six combinations of water transition mechanism are analyzed and a self-adaptive mechanism related with local vapor saturation state is proposed, which is determined and validated by comparing the simulation results with experimental data from commercial-level laboratory. The influence of simulation scale is also investigated by comparing calculation results of typical single-channel domain with practical single-cell domain. Results show that appropriate water transition mechanism equips the model with decent adaptability to multi-condition prediction. Single-channel simulation domain tends to gain misjudgment on water removal capability and could be used for preliminary evaluation. Full-scale single-cell simulation domain should be the first choice for structure designing work, especially under practical working condition. The proposed method serves as a potential solution to multi-condition simulation with good adaptability and fidelity, which is one of the urgent requirements for PEM fuel cell R&D.

A Cost-Effective and DC-Fault Tolerant Alternate Arm Converter With Wide Range Voltage Adaptability

In this article, an enhanced three-arm alternate arm multilevel converter (AAMC), called T-type AAMC (T-AAMC), is proposed for achieving dc fault ride-through capability with reduced semiconductor power devices compared to the hybrid modular multilevel converter (MMC). The upper and lower dc arms of T-AAMC are formed by half-bridge submodules (SMs) and series devices for lower construction costs, while the ac arm uses full-bridge SMs to realize dc fault tolerance. First, the arm phase-shift conducting modulation is applied for energy balance of converter stacks under wide-range operation by adjusting the arm phase-shift angle to match ac grid voltage and power factor. Then, the SM number, power device number, and SM capacitance are evaluated for T-AAMC under optimized modulation design. Analyses illustrate that 43% SMs, 17% power devices, and 44% energy storage requirement are reduced with the proposed topology than that with hybrid MMC. Furthermore, the closed-loop control system is designed to dynamically regulate the energy sharing between dc and ac stacks. Finally, full-scale simulations and down-scaled experiments are performed to verify the feasibility of the proposed converter and the theoretical analysis of its modulation and implementation.

Modeling and simulation of the start-up process of a 660MW ultra-supercritical circulating fluidized bed boiler

This study involved the development of a full-scale dynamic simulation model for a 660MW ultra-supercritical circulating fluidized bed (CFB) boiler–with the largest scale and maximum capacity. The boiler is presently under construction in China and includes a water-steam system, an air-flue gas system, a material supply system, and an ash circulation system. The gas–solid flow in the furnace was modeled based on the “core-annulus” flow structure, and the six-equation solution for the water–steam flow was used to simulate the dynamic behaviors of the water-steam system. Based on a design condition of 50% turbine heat acceptance (THA), a steady-state simulation model was established and calibrated. Consequently, cold and hot start-up processes at 0-50% THA were simulated to investigate the dynamic behaviors of the CFB boiler. Compared with the design conditions, the steady-state and transient simulation models demonstrated high accuracy.

Data Generation for Modeling Attacks on UAVs for the Purpose of Testing Intrusion Detection Systems

Today, issues related to ensuring the safety of UAVs are very relevant. Researchers need to develop new protection methods to detect attacks in a timely manner and implement mitigation measures. The authors propose a new concept of attack detection "from inside" the UAV. The idea is to analyze the cyber-physical parameters of the UAV, which may indicate an attack, and its possible consequences. It was determined that to detect an attack and determine the consequences to which it can lead, it is necessary to control not only the initial parameters, but also the internal cyber-physical parameters of the UAV. This will allow predicting the possible consequences of an attack and taking emergency measures. A scheme of the impact of an attack on UAVs and the relationship with security incidents, built using an ontological approach, has been worked out. Two main essences of the UAV are considered - the physical and digital aspects of the UAV. Examples of chains of attacks leading to various consequences are also shown. In the review part, the analysis of methods and algorithms for detecting spoofing attacks using data generators is carried out, based on which conclusions are drawn about their advantages and disadvantages. Further, based on the experiments performed, the authors propose a method for assessing the quality of data and a method for generating anomalous data sets similar to real attack data, which can be used to develop and test methods for detecting and blocking attacks. The architecture of the experimental stand, which was used in the framework of full-scale simulation, is described. At this stand, designed to parse GPS spoofing attacks (GPS spoofing), several scenarios of a normal flight, and then several attack scenarios, were tested. Based on the results of the experiments, a method has been proposed that allows simulating the data corresponding to the attack with the required accuracy. A method for assessing the quality of fake data has also been proposed.

Estimation of torsional and global loads for a wave-piercing high-speed catamaran at full-scale in irregular bow quartering seas using CFD simulation

Catamarans experience more types of global load than monohulls, these include pitch connecting moment, transverse bending moment, and split force. High-speed catamarans are widely used for passenger transportation but as the speed and size increase the severity of loads rises due to slam induced effects. In this study, full-scale CFD simulations are undertaken to investigate the loads acting on a 98m Incat wave-piercer catamaran (Hull 061) HSV2 Swift. Simulations are performed for conditions of a selected sea trial run in bow quartering seas at 20 knots forward speed undertaken by the Naval Surface Warfare Center, Carderock Division (NSWCCD), enabling comparisons and validation. In order to estimate internal global loads at different sections of the vessel, rigid body dynamics is applied based on the hydrodynamic and inertia forces. Those internal loads include longitudinal bending moment (LBM), pitch connecting moment (PCM), torsional moment (TorM), transverse bending moment (TBM), split force and prying moment. The estimated and measured global loads are also compared with design loads limits provided by DNV GL rules, and peak values of pitch and roll accelerations corresponding to each slam load are determined at the same wave height and wave period as the sea trial. The application of CFD to simulate sea trials runs in oblique seas is shown to provide a reliable estimation of slam induced loads for application in early design stages.

Real Full-Scale Experiment and Numerical Simulation оf a Fire in a Compartment of a Passenger Railway Car. A Comparative Analysis

Real Full-Scale Experiment and Numerical Simulation оf a Fire in a Compartment of a Passenger Railway Car. A Comparative Analysis