Kind Of Simulation Research Articles

Modeling multi-legged robot locomotion with slipping and its experimental validation

Multi-legged robots with six or more legs are not in common use, despite designs with superior stability, maneuverability, and a low number of actuators being available for over 20 years. This may be in part due to the difficulty in modeling multi-legged motion with slipping and producing reliable predictions of body velocity. Here, we present a detailed measurement of the foot contact forces in a hexapedal robot with multiple sliding contacts, and provide an algorithm for predicting these contact forces and the body velocity. The algorithm relies on the recently published observation that even while slipping, multi-legged robots are principally kinematic, and employ a friction law ansatz that allows us to compute the shape-change to body-velocity connection and the foot contact forces. This results in the ability to simulate motion plans for a large number of contacts, each potentially with slipping. Furthermore, in homogeneous environments, this kind of simulation can run in (parallel) logarithmic time of the planning horizon.

On the effect of background seismicity in physics-based earthquake simulations

Physics-based simulations have been extensively employed to generate synthetic earthquake catalogs over the past decade. In this kind of simulation, primary known faults are typically modeled, while smaller and intermediate faults are often neglected. As a result, the location of earthquakes in the simulation is confined to the modeled faults. Furthermore, due to the elimination of off-fault seismicity, a complete match of the frequency-magnitude distribution of the synthetic catalog with observed data is not achieved. This paper presents an approach to include off-fault seismicity (or background seismicity) within the simulation. First, background earthquakes are separated from the primary faults’ earthquakes, and a fault section is assigned to each event. By employing a scaling relationship, the dimensions of these fault sections are determined according to the magnitude of the corresponding event. The fault section’s slip rates are estimated based on the observed frequency-magnitude distribution. Combining the background fault model with the primary fault model results in a comprehensive model that accounts for all stress interactions between fault elements within the simulator in actual locations. As a result, a broader range of frequency-magnitude distribution in the synthetic catalog can be matched to the observations. A case study using one of the available simulators, Virtual Quake, on a sample area is presented. The results demonstrate that eliminating off-fault seismicity could lead to an underestimated assessment of the earthquake probabilities for the whole region and a biased estimation of earthquake rates in individual faults.

Simulation of long-term storage dynamics of headwater reservoirs across the globe using public cloud computing infrastructure

Reservoirs play an important role in relation to water security, flood risk, hydropower and natural flow regime. This study derives a novel dataset with a long-term daily water-balance (reservoir volume, inflow, outflow, evaporation and precipitation) of headwater reservoirs and storage dynamics across the globe. The data is generated using cloud computing infrastructure and a high resolution distributed hydrological model wflow_sbm. Model results are validated against earth observed surface water area and in-situ measured reservoir volume and show an overall good model performance. Simulated headwater reservoir storage indicate that 19.4–24.4 % of the reservoirs had a significant decrease in storage. This change is mainly driven by a decrease in reservoir inflow and increase in evaporation. Deployment on a kubernetes cloud environment and using reproducible workflows shows that these kind of simulations and analyses can be conducted in less than a day.

Comparative study on the molecular evolution of changqing petroleum coke during air and pure oxygen combustion: A ReaxFF method analysis

Based on reactive force field (ReaxFF) simulation, the molecular evolution mechanism of air combustion simulation and pure oxygen combustion simulation of Changqing petroleum coke was studied. On the basis of the original petroleum coke molecular model, N2 and O2 molecules were added to construct the air combustion simulation model and the pure oxygen combustion simulation model respectively. The number of molecules, main products, and typical hydrocarbon gases in the two simulation results were analyzed by setting up the LAMMPS in. file. Finally, the molecular changes of pyrrole and pyridine were described. The results show that the main reaction interval of pure oxygen combustion is earlier than that of air combustion. In the main reaction temperature range, the reaction rate of pure oxygen combustion is higher than that of simulated air combustion. At 170 ps, the two simulations reaction speed is the fastest time point; Pyridine is more stable than pyrrole. The research on the distinction and comparison of two kinds of simulation has certain guiding significance for the clean utilization of petroleum coke combustion process in industry.

Fractional Extended Diffusion Theory to capture anomalous relaxation from biased/accelerated molecular simulations.

Biased and accelerated molecular simulations (BAMS) are widely used tools to observe relevant molecular phenomena occurring on time scales inaccessible to standard molecular dynamics, but evaluation of the physical time scales involved in the processes is not directly possible from them. For this reason, the problem of recovering dynamics from such kinds of simulations is the object of very active research due to the relevant theoretical and practical implications of dynamics on the properties of both natural and synthetic molecular systems. In a recent paper [A. Rapallo et al., J. Comput. Chem. 42, 586-599 (2021)], it has been shown how the coupling of BAMS (which destroys the dynamics but allows to calculate average properties) with Extended Diffusion Theory (EDT) (which requires input appropriate equilibrium averages calculated over the BAMS trajectories) allows to effectively use the Smoluchowski equation to calculate the orientational time correlation function of the head-tail unit vector defined over a peptide in water solution. Orientational relaxation of this vector is the result of the coupling of internal molecular motions with overall molecular rotation, and it was very well described by correlation functions expressed in terms of weighted sums of suitable time-exponentially decaying functions, in agreement with a Brownian diffusive regime. However, situations occur where exponentially decaying functions are no longer appropriate to capture the actual dynamical behavior, which exhibits persistent long time correlations, compatible with the so called subdiffusive regimes. In this paper, a generalization of EDT will be given, exploiting a fractional Smoluchowski equation (FEDT) to capture the non-exponential character observed in the relaxation of intramolecular distances and molecular radius of gyration, whose dynamics depend on internal molecular motions only. The calculation methods, proper to EDT, are adapted to implement the generalization of the theory, and the resulting algorithm confirms FEDT as a tool of practical value in recovering dynamics from BAMS, to be used in general situations, involving both regular and anomalous diffusion regimes.

Mancha3D Code: Multipurpose Advanced Nonideal MHD Code for High-Resolution Simulations in Astrophysics

The Mancha3D code is a versatile tool for numerical simulations of magnetohydrodynamic (MHD) processes in solar/stellar atmospheres. The code includes nonideal physics derived from plasma partial ionization, a realistic equation of state and radiative transfer, which allows performing high-quality realistic simulations of magnetoconvection, as well as idealized simulations of particular processes, such as wave propagation, instabilities or energetic events. The paper summarizes the equations and methods used in the Mancha3D (Multifluid (-purpose -physics -dimensional) Advanced Non-ideal MHD Code for High resolution simulations in Astrophysics 3D) code. It also describes its numerical stability and parallel performance and efficiency. The code is based on a finite difference discretization and a memory-saving Runge–Kutta (RK) scheme. It handles nonideal effects through super-time-stepping and Hall diffusion schemes, and takes into account thermal conduction by solving an additional hyperbolic equation for the heat flux. The code is easily configurable to perform different kinds of simulations. Several examples of the code usage are given. It is demonstrated that splitting variables into equilibrium and perturbation parts is essential for simulations of wave propagation in a static background. A perfectly matched layer (PML) boundary condition built into the code greatly facilitates a nonreflective open boundary implementation. Spatial filtering is an important numerical remedy to eliminate grid-size perturbations enhancing the code stability. Parallel performance analysis reveals that the code is strongly memory bound, which is a natural consequence of the numerical techniques used, such as split variables and PML boundary conditions. Both strong and weak scalings show adequate performance up to several thousands of processors (CPUs).

A Novel Framework for Spatiotemporal Analysis of Temperature Profiles Applied to Europe

Abstract Vertical temperature profiles influence the wind power generation of large offshore wind farms through stability-dependent effects such as blockage and gravity waves. However, numerical tools that are used to model these effects are often computationally too expensive to cover the large variety of atmospheric states occurring over time. Generally, an informed decision about which representative nonidealized situations to simulate is missing because of the lack of easily available information on representative vertical profiles, taking into account their spatiotemporal variability. Therefore, we present a novel framework that allows a smart selection of vertical temperature profiles. The framework consists of an improved analytical temperature model for the atmospheric boundary layer and lower troposphere, a subsequent clustering of these profiles to identify representatives, and last, a determination of areas with similar spatiotemporal characteristics of vertical profiles. When applying this framework on European ERA5 data, physically realistic representatives were identified for Europe, excluding the Mediterranean. Two or three profiles were found to be dominant for the open ocean, whereas more profiles prevail for land. Over the open ocean, weak temperature gradients in the boundary layer and a clear capping inversions are widespread, and stable profiles are absent except in the region of the East Icelandic Current. Interestingly, according to the ERA5 data, at its resolution, coastal areas and seas surrounded by land behave more similar to the land areas than to the open ocean, implying that a larger set of model integrations are needed for these areas to obtain representative results for offshore wind power assessments in comparison with the open ocean. Significance Statement Numerical tools used to simulate the effect of large, offshore wind farms on neighboring farms and the atmosphere are very expensive. Therefore, they can only be computed for a limited number of cases. As temperature is one of the most important parameters in these kinds of simulations, this work provides a new vertical temperature model and an analysis framework that allows for a smart selection of these cases such that they ideally represent the full variation of the atmosphere’s temperature profiles.

Effect of initial phase on the ablative Rayleigh–Taylor instability

The effect of initial perturbation phase on the ablative Rayleigh–Taylor instability is investigated by numerical simulations. We aim at the growth of harmonic amplitudes and the formation of spikes and bubbles in single- and two-mode coupling cases, respectively. In the two-mode coupling case, two kinds of simulations are performed: two modes with relatively small linear growth rate difference and two modes with relatively large linear growth rate difference. The initial relative phase between the original two modes has a significant effect on the growth of harmonic amplitudes, and in different initial relative phases, the structures of spikes and bubbles begin to show great differences in the nonlinear stage. Fortunately, the harmonic amplitudes are weakened at a specific initial relative phase. This has a certain enlightening significance for the stabilization of ablative Rayleigh–Taylor instability.

A statistical modeling approach based on the small-scale field trial and meteorological data for preliminary prediction of the impact of low temperature on Eucalyptus globulus trees

Eucalyptus trees are important for industrial forestry plantations because of their high potential for biomass production, but their susceptibility to damage at low temperatures restricts their plantation areas. In this study, a 6-year field trial of Eucalyptus globulus was conducted in Tsukuba, Japan, which is the northernmost reach of Eucalyptus plantations, and leaf damage was quantitatively monitored over four of six winters. Leaf photosynthetic quantum yield (QY) levels, an indicator of cold stress-induced damage, fluctuated synchronously with temperature in the winters. We performed a maximum likelihood estimation of the regression model explaining leaf QY using training data subsets for the first 3 years. The resulting model explained QY by the number of days when the daily maximum temperature was below 9.5 °C over approximately the last 7 weeks as an explanatory variable. The correlation coefficient and coefficient of determination of prediction by the model between the predicted and observed values were 0.84 and 0.70, respectively. The model was then used to perform two kinds of simulations. Geographical simulations of potential Eucalyptus plantation areas using global meteorological data from more than 5,000 locations around the world successfully predicted an area that generally agreed with the global Eucalyptus plantation distribution reported previously. Another simulation based on meteorological data of the past 70 years suggested that global warming will increase the potential E. globulus plantation area in Japan approximately 1.5-fold over the next 70 years. These results suggest that the model developed herein would be applicable to preliminary predictions of E. globulus cold damage in the field.

Different kinds of simulation during literary reading: Insights from a combined fMRI and eye-tracking study

Mental simulation is an important aspect of narrative reading. In a previous study, we found that gaze durations are differentially impacted by different kinds of mental simulation. Motor simulation, perceptual simulation, and mentalizing as elicited by literary short stories influenced eye movements in distinguishable ways (Mak & Willems, 2019). In the current study, we investigated the existence of a common neural locus for these different kinds of simulation. We additionally investigated whether individual differences during reading, as indexed by the eye movements, are reflected in domain-specific activations in the brain. We found a variety of brain areas activated by simulation-eliciting content, both modality-specific brain areas and a general simulation area. Individual variation in percent signal change in activated areas was related to measures of story appreciation as well as personal characteristics (i.e., transportability, perspective taking). Taken together, these findings suggest that mental simulation is supported by both domain-specific processes grounded in previous experiences, and by the neural mechanisms that underlie higher-order language processing (e.g., situation model building, event indexing, integration).

Hardware in loop network simulators — An insight overview

Network simulation is a method of using software or a tool which can be used to mimic the network conditions that exist in pre-defined places. This kind of simulation allows the developers, designers, researchers and the network planners to intelligently plan, design, develop and test their applications or research work in changing network conditions. With varying network conditions either because of wireless nature or because of user mobility, it is very difficult to simulate the exact network conditions with the existing network simulators. These network simulators are flexible, re-usable and reliable. But they have a limitation of not being able to replicate the actual network conditions in the laboratories. This calls for a system in the loop or hardware in the loop concept to be extended to the network simulators. The idea of system in the loop is not new. In this paper, an overview with the fundamental understanding of the hardware-in-loop concept for network simulators, their applications and a review of the existing hardware-in-loop network simulators with their advantages and disadvantages is presented.

Computational study of MHD mixed convective flow of Cu/Al2O3-water nanofluid in a porous rectangular cavity with slits, viscous heating, Joule dissipation and heat source/sink effects

ABSTRACT A mathematical model is presented to analyze the mixed convective magnetohydrodynamic (MHD) flow of two different nanofluids within a cavity saturated with porous media. The Tiwari–Das model, along with Maxwell and Brinkman formulations, is adopted to feature the characteristics of the considered nanofluids. The two different working fluids of this investigation are considered aluminum oxide -water and copper -water nanofluids. The impacts of viscous dissipation, internal heat generation/absorption, magnetic field, and Joule heating are examined in this model. The robust, well-tested Marker And Cell (MAC) algorithm is utilized to numerically solve the transformed, dimensionless, nonlinear coupled two-dimensional momentum and energy conservation equations with the prescribed wall boundary conditions. The comparative study finds an upright accordance with the literature. The effect of various pertinent parameters on the rate of heat transfer, isotherms and streamlines contour distributions in the enclosure is graphically displayed. With an increment in nanoparticles volume fraction, the velocity and heat transfer inside the rectangular enclosure are increased. The -water nanofluid and -water nanofluid in order have and higher average heat transfer rate when nanoparticles are suspended into water. This kind of simulation may be useful in electromagnetic nanomaterials processing and hybrid fuel cells.

Energy Aware Job Scheduling and Simulation in a Cloud Datacenter

Virtualization technology is used by cloud systems for the users to utilize cloud resources through Virtual Machines.These VM’s process the task requests made by users. Ever since inefficient hardware utilization is the concernfor the future and the environment, efficient work load balancing and allocation of VMs helps to bring down thehardware usage and results to efficient working. That being said, this paper proposes task scheduling frameworkwhere the task will be assigned to a VMs running on the active hosts(servers) through preemption as required andclassification of the cloudlets. The algorithm that we have taken into consideration will categorize the cloudletsinto three distinct types and allocate them a VM based on first come, first served resource time in regards to thatparticular host. This in turn will reduce the energy consumption by having lesser machines running in the activestate meanwhile preserving efficient utilization of the active servers. Such kind of simulations are fairly achievedusing the CloudSim framework

A time-varying SIRD model for dynamic vaccination strategies against COVID-19

Abstract Introduction The COVID-19 pandemic has demonstrated how the optimal allocation of the limited doses of vaccine available represents one of the main useful measures to mitigate the transmission of the infection and reduce the mortality associated with it, especially at an early stage of the pandemic. The use of a compartmental model allows us to understand which population groups to vaccinate and to what extent to act depending on the type of health or social objective to be achieved. Methods A time-varying susceptible-infected-recovered-deceased (SIRD) compartmental model, stratified into ten age groups, was developed on Italian data. Simulations were performed every 15 days from December 2020 to April 2021. An optimal vaccination strategy was achieved by minimizing deaths or infected, considering the total vaccine doses available. Results We showed how the effects of a vaccination campaign can be planned in a way that maximizes lives saved and/or minimizes infections. Regarding the minimization of deaths, the model prioritizes the elderly (>80 years) and then those between 60 and 80 years, in all simulations. Regarding the cost function of new infections, the first simulation assigns all available doses to those over 90 years of age. In the later simulations, the doses are assigned mainly to the 20-29-year-old and the 89+ year old. Conclusions Optimal allocation of available vaccine doses is useful in mitigating transmission of infection and reducing mortality. Application of the mathematical model can be useful at the beginning of an epidemic caused by a new pathogen, when data are scarce, and it is therefore necessary to introduce a standardized approach. This kind of simulation is useful to understand whether the implemented vaccination strategy needs to be recalibrated, too. Key messages • Time-varying compartmentalised models can be used both to continuously inform decision-makers about changes in epidemic traits and to simulate the effects of targeted pandemic containment strategies. • The application of compartmental models can be very useful at the onset of an epidemic to more successfully contain it and structure the health, political, and economic plan.

Numerical approach for a strongly coupled thermomechanical process with multi-phase transition and applications in additive manufacturing

<p indent="0mm">We propose a monolithic incremental Lagrangian framework based on the hot optimal transportation meshfree (HOTM) method for a strongly coupled thermomechanical process with multiphase transition. The HOTM method combines the optimal transportation meshfree method and the variational thermomechanical constitutive updates. This numerical approach is applied to conduct meshfree direct numerical simulations (DNS) for metal additive manufacturing. We present two kinds of simulations, the powder bed selective laser melting (SLM) and the laser material deposition technology referred to as extreme high-speed laser material deposition (EHLA) at the powder scale. In the simulations, the powder particles are modeled explicitly using the size distribution measured in experiments and discretized using nodes and material points. The governing equations, including the linear momentum conservation and energy conservation equations, are solved simultaneously in the meshfree framework to predict the deformation, temperature, and local state of the powder particles. A full-field constitutive model is developed to simulate multiphase flow with melting and solidification. The Lagrangian feature of the HOTM method overcomes various challenges in the DNS of melt pool thermodynamics in additive manufacturing. The proposed approach is used to quantify the influence of the main processing parameters, such as the powder size distribution, laser power, laser radius, deposition speed, powder mass flow, and axial feed on the layer thickness, surface roughness, and porosity of the bonding zone. It further enables an in-depth understanding of quality control in additive manufacturing.

Modeling of gaseous emissions and soot in 3D-CFD in-cylinder simulations of spark-ignition engines: A methodology to correlate numerical results and experimental data

In order to reduce development costs and time-to market, 1D and 3D CFD tools can support engine design providing reliable estimations of the tailpipe emissions. In particular, 3D-CFD in-cylinder simulations can evaluate formation of both soot and gaseous pollutants inside the combustion chamber. The main issue in such kind of simulations is the validation against experimental findings. In fact, the complexity of the emission measurements does not allow a straightforward one-to-one comparison between numerical and experimental results. Therefore the present paper aims at providing, on the one hand, a robust numerical framework for both gaseous and solid emissions, on the other hand a dedicated post-processing for a fair comparison between simulations and experiments. From a numerical standpoint, a simplified approach is dedicated to gaseous emissions, while a more detailed one is reserved to soot modeling. The latter is based on the Sectional Method, whose reaction rates are tabulated following 0D chemical kinetic simulations of a purposely designed surrogate in a constant pressure reactor. Simulations and experiments proposed in the present analysis are referred to a high-performance turbocharged direct-injection spark-ignition engine operated at part-load and low rpms. On equal performance, revving speed and mean mixture quality, different injection timings are investigated. The developed numerical approach and post-processing ensure a good agreement between simulations and experiments.

Wind loads prediction using LES: Inflow generation, accuracy and cost assessment for the case of Torre Gioia 22

In this paper, Large Eddy Simulations, LES, are used in order to evaluate wind loads on a recently designed high-rise building located in Milan, Italy. The selected case study is taken as an example of a typical wind loading assessment, characterized by a complex geometry due to both the shape of the tower and the presence of surroundings. Firstly, the sensitivity of the results to the adopted mesh is analysed. Then, results are compared to wind tunnel measurements and the economical viability of such kind of simulations is discussed. The paper aims at providing an overview of the main factors which can contribute to the success of such analyses and evaluate their accuracy. Not specialized readers will hopefully gain a better insight into the critical aspects which characterize such simulations, while the interested readers will find numerous practical considerations useful for their setup.

Modeling and Simulation of TiO2/Se Sensor for Detection of CO Gas Using Comsol Multiphysics

Metal oxide sensors are being used from past three decades. They still suffer from some disadvantages, such as high operating temperature, high power consumption, sensor stability, and cross sensitivity. Since the cost of development of these sensors is high, it is important to develop a mathematical model to economically predict the behavior of these sensors. In this context, research work focused on evaluating the performance of these sensors using numerical analysis software. In this work, modeling and simulating the gas sensing properties of Titanium dioxide/Selenium (MOS) sensor material to detect carbon monoxide (CO) gas using Comsol Multiphysics software has been proposed. The gas sensing simulation was performed using ‘Reaction engineering,’ ‘Transport of diluted species,’ ‘Surface reactions,’ and ‘Laminar flow’ interfaces of Comsol Multiphysics software on Titanium dioxide/Selenium material. Two kinds of simulations, space independent and space dependent simulation, was performed on this material in a constant volume gas chamber. The geometry was created in space dependent node, Comsol. The carbon monoxide gas was injected through gaussian pulse feed inlet at different concentrations (1 ppm, 5 ppm, 10 ppm, and 15 ppm) into the gas chamber and MOS sensor layer was allowed to reach steady state. The adsorption simulation on sensor layer exposed to carbon monoxide (CO) gas shows the change in surface concentration of the adsorbed CO molecules on the sensor layer.

Simulation of crack propagation through voxel-based, heterogeneous structures based on eigenerosion and finite cells

This paper presents an algorithm for the efficient simulation of ductile crack propagation through heterogeneous structures, as e.g. metallic microstructures, which are given as voxel data. These kinds of simulations are required for e.g., the numerical investigation of wear mechanisms at small length scales, which is still a challenging task in engineering. The basic idea of the proposed algorithm is to combine the advantages of the Finite Cell Method allowing for a convenient integration of heterogeneous finite element problems with the eigenerosion approach to still enable the mesh-independent simulation of crack propagation. The major component is to switch from finite subcells to finite elements wherever the crack progresses, thereby automatically adaptively refining at the crack tip by managing the newly appearing nodes as hanging nodes. Technically relevant problems of crack propagation at the microscale are mostly linked with sub-critical crack growth where the crack moves fast and stepwise with subsequent load cycles. Therefore, inertia may become important which is why dynamics are taken into account by spreading the mass of the eroded elements to the nodes to avoid a loss in mass resulting from the erosion procedure. Furthermore, a certain treatment for the finite cell decomposition is considered in order to ensure efficiency and accuracy. The numerical framework as well as the voxel decomposition techniques are analyzed in detail in different three-dimensional numerical examples to show the performance of the proposed approach.

Impact of multiple reflections on urban acoustics

Understanding how the urban form contributes to noise is important for the successful acoustic design of cities. The amplification of sound is mainly due to the multiple reflections that occur between the high and parallel walls of urban canyons. This study explores the use of ray tracing at the urban scale through the measurement and simulation of three configurations. These are referred to as “1D”, “2D” and “3D”. Impulse response measurements performed at points located on the top of the façades show an increase of 6 dB for the “2D” case and 11 dB for the “3D” case. These results are consistent with ray tracing simulations. This kind of simulation is useful to determine the influence of the street aspect ratio on the sound level. Since specular reflections are related to geometry, a spatialized representation is proposed and discussed.