Small-scale Simulation Research Articles

Intrusive and non-intrusive uncertainty quantification methodologies for pyrolysis modeling

In this work we discuss and compare multiple uncertainty analysis methodologies for pyrolysis modeling. Using Arrhenius equation as the pyrolysis model and kinetic parameters for PMMA material as uncertain variables, different approaches for stochastic uncertainty quantification and their computational effort are analyzed. First non-intrusive (NI) methods are compared through convergence analysis where the deterministic model can be used as is to ascertain the statistical moments, followed by an intrusive polynomial chaos (IPC) approach which requires reformulation of the deterministic model, but solution of the model only once. The applied NI methods include Monte Carlo based simulations, regression and projection based non-intrusive polynomial chaos (NIPC) methods. The uncertainty analysis and convergence comparison is performed for three materials including the effects of overlapping reactions and dependent parameters. In general for different uncertain parameters and materials, IPC gave accurate statistical information in a single model run compared to NIPC projection requiring runs ranging from tens to hundreds and NIPC regression requiring runs in range of thousands to generate converged statistics. However, in case of only a few uncertain parameters, presence of non-polynomial functions in the model and small-scale simulations, projection based NIPC outshines IPC in terms of simplicity and applicability.

Study on reasonable loading mode of small-scale roadway model and its application in mining engineering

The small-scale roadway model is often used in the fine simulation of mining engineering. The determination of the structure and load conditions of the model has an important influence on the accuracy of the simulation. In this paper, a large-scale stratum model and a small-scale roadway model are established by using finite element method. The optimal loading mode of the roadway model and its applicability under different roof-sidewall stiffness ratios are studied. The simulation accuracy of the roadway model is quantitatively evaluated by comparing the distribution laws of stress field and strain field with those of the stratum models. Under the same roof-sidewall stiffness ratio, the similarity between the simulation results of the roadway model and the stratum model under displacement load is much higher than that under stress load. Under the same load mode, the stress and strain similarity between the stratum model and roadway model increases with the increase of the roof-sidewall stiffness ratio. Furtherly, the simulation application of the roadway drilling pressure relief is carried out. Compared with the large-scale stratum model with small-size elements, the small-scale roadway model under displacement load also shows obvious stress transfer after drilling pressure relief, while it has faster computational efficiency. Finally, a small-scale roadway model simulation method suitable for surrounding rock disaster occurrence mechanism and control is proposed.

Hysteresis behavior of Auxetic Perforated Steel Plate Shear Walls with elliptical and peanut-shaped cutouts

Although auxetic (negative Poisson’s ratio) materials and structures have unique mechanical properties, their application in earthquake-resistant structures is rarely reported. This paper proposed a novel Auxetic Perforated Steel Plate Shear Wall (AP-SPSW) for seismic mitigation in building structures. The AP-SPSW incorporates the unique mechanical properties of auxetic materials and structures to reduce out-of-plane buckling and improve seismic performance of SPSWs. Both elliptical and peanut-shaped perforation configurations were proposed for the AP-SPSW. Through small-scale numerical simulations of the auxetic unit cells, the deformation mode of the auxetic perforated material was discussed and a preliminary design was presented to ensure the materials with negative Poisson’s ratio. In addition, ten AP-SPSW specimens were prepared for cyclic loading tests, which demonstrated that the AP-SPSW possesses stable hysteresis behavior and excellent energy dissipation capacity. Key parameters affecting the hysteresis performance of the AP-SPSW were identified as porosity of the perforated panel and thickness of the ligament between neighboring perforations. This study also focused on the global shear buckling behavior of the auxetic perforated panel plates. It was found that the auxetic deformation mechanism benefits shear buckling resistance in the SPSW panel. Finally, an analytical model was proposed for the shear strength of the auxetic panel. The limitations of this study were also discussed, along with the work required for further exploration. The results of this study provide valuable insights for the development of innovative seismic-resistant structures that incorporate auxetic materials and structures.

Constraining Circumgalactic Turbulence with QSO Absorption Line Measurements

Our knowledge of the circumgalactic medium (CGM) is mostly based on quasar absorption line measurements. These have uncovered a multiphase medium that is likely highly turbulent, but constraints of this turbulence are limited to measurements of the nonthermal width of absorption line components (b turb) and the line-of-sight velocity dispersion between components (σ LOS). Here we analyze a suite of CGM simulations to determine how well these indirect measures are related to the underlying CGM. Our simulations track the nonequilibrium evolution of all commonly observed ions and consist of two main types: small-scale simulations of regions of homogenous CGM turbulence and global simulations of inhomogenous turbulence throughout a galactic halo. From each simulation, we generate mock spectra of Si ii, Si iv, C iv, and O vi, which allow us to directly compare b turb and σ LOS to the true line-of-sight turbulence (σ 1D). In the small-scale simulations, b turb is only weakly correlated with σ 1D, likely because it measures random motions within individual warm CGM clouds, which do not sample the overall random motions. Meanwhile, σ LOS and σ 1D are strongly correlated with σ 1D ≈ σ LOS + 10 km s−1 in the densest regions we simulated, although the strength of this correlation depended weakly on the gas phase being probed. Our large-scale simulations also indicate that b turb and σ 1D are largely uncorrelated and that σ 1D ≈ σ LOS + 10 km s−1 on average, although it varies along individual sight lines. Moreover, the σ LOS distributions from our global simulations are similar to recent observations, suggesting that this quantity may provide useful constraints on circumgalactic turbulence regardless of the axis probed.

The intrinsic alignment of red galaxies in DES Y1 redMaPPer galaxy clusters

ABSTRACT Clusters of galaxies trace the most non-linear peaks in the cosmic density field. The weak gravitational lensing of background galaxies by clusters can allow us to infer their masses. However, galaxies associated with the local environment of the cluster can also be intrinsically aligned due to the local tidal gradient, contaminating any cosmology derived from the lensing signal. We measure this intrinsic alignment in Dark Energy Survey (DES) Year 1 redMaPPer clusters. We find evidence of a non-zero mean radial alignment of galaxies within clusters between redshifts 0.1–0.7. We find a significant systematic in the measured ellipticities of cluster satellite galaxies that we attribute to the central galaxy flux and other intracluster light. We attempt to correct this signal, and fit a simple model for intrinsic alignment amplitude (AIA) to the measurement, finding AIA = 0.15 ± 0.04, when excluding data near the edge of the cluster. We find a significantly stronger alignment of the central galaxy with the cluster dark matter halo at low redshift and with higher richness and central galaxy absolute magnitude (proxies for cluster mass). This is an important demonstration of the ability of large photometric data sets like DES to provide direct constraints on the intrinsic alignment of galaxies within clusters. These measurements can inform improvements to small-scale modelling and simulation of the intrinsic alignment of galaxies to help improve the separation of the intrinsic alignment signal in weak lensing studies.

DEVELOPMENT OF PREDICTING MOTION OF FLOATING CAISSON UNDER REGULAR AND IRREGULAR WAVES

Breakwaters for outer harbor facilities are considerably affected by wave conditions, rendering the control of caisson motion difficult. Its motion during breakwater installation is important to improve its operational efficiency and safety. In recent years, caisson motion has been studied using 3D solid-gas-liquid three-phase simulations. Nakamura et al. (2021) investigated the dynamic characteristics of floating caissons under regular and irregular waves. Takagi et al. (2021) studied its sway and contact with mounds when the bottom clearance was changed and demonstrated the validity of their numerical method. However, due to inevitable scale effects of the small-scale experiments and simulations, these studies require examination at a large scale. In this study, the numerical simulation developed by Arikawa et al. (2009) was used to investigate the motion characteristics of life-sized floating caissons under regular and irregular waves for case studies conducted at the Port of Kochi (Ishimi et al. 1996).

Design, construction and modeling of a small-scale high temperature field rotor test rig

In-field validation of radiation thermometer performance is time consuming and expensive, especially when prototype experiments are performed. This study focuses on the development of a novel small-scale high temperature field simulation test rig for measuring turbine blade surface temperatures under changing environmental conditions. When developing and testing a radiation thermometer, the testing is typically performed directly on a test rig that can simultaneously provide a standardized environment and compare temperature data. This apparatus allows for static and dynamic temperature testing in a hostile environment by combining temperature, particle, and atmospheric effects. In the present study, a test rig will be utilized to analyze and validate the radiation thermometer, which will be subjected to harsh combined environmental variables with a temperature range of up to 2000K. Notably, the rotating head structure of the two materials allows for the application of a vast range of temperature measurements (700–2000 K), which is a distinctive characteristic of the design. The requirements of the test rig are defined based on the specimens to be tested. The necessity for the combined complete test setup, as well as its design and functionality, are discussed in this paper. Finally, validation experiments are conducted to demonstrate the test rig's accuracy in measuring turbine blade surface temperature, which is 0.25%.

Experimental Simulation of Deformation Effect Propagation Due to Explosion on the Surface of a Small-Scale Model

The use of small-scale models is an important area of research today. An investigation is conducted on the response of a small-scale model’s vibrating surface. For this model, a small-scale surface explosion is used for loading. According to the article, the methodology includes procedures, model development, the explosive materials used, measurement and evaluation methods, software, and the technique used. Signal processing and response evaluation rely on a scientific method—the backward Fourier-transform principle—for frequency filtering. In this study, the simulation results are used to confirm the basic physical properties of the viscoelastic system. It is primarily investigated whether wave processes are confirmed on the new material. In terms of single wave propagation, the results summarize the characteristics of these waves (attenuation, velocity of propagation, etc.). Conclusions are targeted at the possibility of correlating three types of results: small-scale simulations, numerical simulations, and a real full-scale experiment.

Hydraulic fracturing process in rocks – small-scale simulations with a novel fully coupled DEM/CFD-based thermo-hydro-mechanical approach

In the paper, a two-dimensional (2D) numerical simulation of a small-scale hydraulic fracturing process in rock specimens possessing a single injection slot was conducted. A unique DEM/CFD-based pore-scale thermal-hydro-mechanical (THM) model was used to simulate two-phase laminar fluid flow (water and gas) with heat transfer in non-saturated porous materials with low porosity. Using a DEM fully coupled with CFD (based on a fluid flow network composed of channels in a continuous domain between discrete elements) and heat transfer at the mesoscale, a series of numerical calculations for small cohesive granular specimens of simplified spherical mesostructure with one injection slot were carried out. Plane strain compression conditions were assumed. Both the fluid (diffusion and advection) and bonded particles (conduction) were involved in heat transfer. The impacts of the fluid's dynamic viscosity, gas phase content, and temperature difference between the rock matrix and the fluid injection on the process of hydraulic fracture initiation and propagation were all examined in-depth. It was discovered that those effects were all of great significance to the behaviour of a single hydraulic fracture.

Three-dimensional experimental-scale phase-field modeling of dendrite formation in rechargeable lithium-metal batteries

This paper presents a phase-field based numerical study on the 3D formation of dendrites due to electrodeposition in an experimental-scale lithium metal battery. Small-scale 3D simulations were firstly conducted to elucidate the characteristics and resolution requirements of the numerical framework. Using a four-fold anisotropy model to simulate the growth of lithium deposition, the dependency of dendrite morphology on charging conditions (ϕb=−0.7V and ϕb=−1.4V) on a (larger) experimental-scale metal anode was demonstrated. The dendrite shape was found to shift from a smoother, tree-like formation at the lower applied voltage, to a more spike-like, highly branched structure at the higher voltage. The resulting morphological parameters, such as dendrite propagation rates, volume-specific area, and side branching rates, were compared against published experimental data and found to be comparable to the reported ranges for the electrodeposition of spike- or tree-like metal dendrites. This finding supports our previous observation that dendrite formation is connected to the competition between the lithium cation diffusion and electric migration, generating an uneven distribution of Li+ on the electrode surface. This observation also gives insight into dendrite inhibition strategies focusing on enhancing the diffusion of lithium ions to achieve a more uniform concentration field on the anode surface.

Crystal plasticity finite element modelling on the influence of grain size and shape parameters on the tensile stiffness and yield strength

A highly parallelised three-dimensional finite element crystal plasticity framework is used to investigate the influence of grain sphericity, number of cross-sectional grains and grain size distribution on the tensile stiffness and yield strength in austenitic stainless steel. Open-source software packages Neper and FEpX were adopted to generate a wide range of synthetic 3D microstructures and to perform crystal plasticity simulations, respectively. Aspects of small-scale simulations with reasonable accuracy and caution in modelling the mechanical properties of thin and/or large grain size specimens are also discussed. This study aims to provide guidelines for estimating mechanical properties in single-phase polycrystalline materials exhibiting wide grain size distributions.

Physics-statistics-based hybrid simulation scheme of coupled nonstationary hurricane wind and wave fields for long-span floating bridges

Abstract Long-span bridges with floating towers have recently drawn great attention from the engineering community. Due to their sensitivity to the aerodynamic and hydrodynamic loads during extreme storms, accurate and efficient simulation tools for hurricane winds and waves are needed for improved understanding of the complex dynamics of the fully coupled wind–wave–structure interaction system. Conventional simulation schemes usually generate winds and waves separately, and hence cannot capture the intense wind–wave interactions under hurricanes. In this study, a physics-statistics-based hybrid simulation scheme of nonstationary hurricane wind and wave fields is presented, where the winds and waves are coupled in both large and small scales. To simulate the large-scale winds and waves, a height-resolving hurricane wind model is coupled with a parametric hurricane wave model through a dependence between sea surface roughness and surface wind speed. In the small-scale simulations, the nonstationary wind fluctuations are statistically obtained by a Hilbert-wavelet-based scheme in which the target parameters (e.g. fluctuation intensity) are estimated based on the local sea state, while the nonstationary sea surface elevations are physically acquired by solving the governing equation of the nonlinear wave evolution under the action of winds. The simulation fidelity of the proposed physics-statistics-based hybrid scheme is demonstrated by generating the coupled nonstationary wind and wave fields approaching to a hypothetical long-span bridge with floating towers under a hurricane event.

Diffuse modelling of pearlite growth in Calphad-coupled multicomponent multi-phase-field simulations

During cooling of steels and cast irons, austenite can decompose by a eutectoid transformation into pearlite, a two-phased mixture of ferrite and cementite. Since the internal lamellar structure is commonly too fine to be distinguished on the scale of the austenite grain structure, pearlite is often modelled as an effective, pseudo-single phase. Such a pragmatic treatment would also be desirable to reduce the computational effort of large-scale multi-phase-field simulations, but a fundamental hindrance is that no consistent thermodynamic description exists for effective pearlite in multicomponent databases. Alternatively, we here propose to model pearlite as diffuse mixture of two phases with individual local fractions and concentrations, such that solute partitioning and thermodynamic driving forces can be consistently derived from standard Calphad databases. The essential computational advantage is that only the outer interfaces of the pearlite nodules have to be numerically resolved, which allows for increased grid spacing and time-steps. The impact of the unresolved lamellar structure on the curvature undercooling is modelled analytically based on a characteristic spacing, which may be calibrated either experimentally or by small-scale simulations. The potential and the limitations of the new approach, implemented in the frame of the Micress® software, shall be discussed.

An improved Eulerian scheme for calculating proppant transport in a field-scale fracture for slickwater treatment

Field-scale proppant transport simulation is vital to the development of unconventional resources. Previous research on proppant transport and distribution has mainly focused on small-scale and experimental-scale proppant simulations, and few studies are related to field-scale proppant deployment. In this paper, through coupling of the slickwater flow, proppant flow, and dynamic crack propagation, an improved Eulerian scheme for calculating proppant transport in a field-scale fracture for slickwater treatment is presented. In the improved Eulerian scheme, the effect of the fracture width on the proppant settling rate and the effect of the increase in the settling bed height on the proppant bed build-up rate are taken into consideration. In addition, a new retardation coefficient is introduced to account for the effect of proppant retardation on the proppant flow. The Eulerian scheme is verified through comparison with published works, including experimental results and simulation results, and sensitivity analysis is conducted. Based on the results of this research, we conclude that the lower viscosity slickwater causes the proppant distribution to become more even, and thus, the proppant bed becomes longer and higher. As the proppant diameter increases, the proppant distribution in the fracture becomes more even, and the fracture area supported by the proppant becomes larger. The optimal initial proppant concentration for obtaining the largest propped fracture area is 0.15–0.25. The greater the density of the slickwater is, the more even the proppant distribution is, and the larger the propped fracture area is.

Connecting small-scale to large-scale structures of fast neutrino-flavor conversion

We present a systematic study of fast neutrino-flavor conversion (FFC) with both small-scale and large-scale numerical simulations in spherical symmetry. We find that FFCs can, in general, reach a quasisteady state, and these features in the nonlinear phase are not characterized by the growth rate of FFC instability but rather angular structures of the electron neutrino lepton number (ELN) and the heavy one. Our result suggests that neutrinos can almost reach a flavor equipartition even in cases with low growth rate of instability (e.g., shallow ELN crossing) and narrow angular regions (in momentum space) where flavor conversions occur vigorously. This shows that ELN and heavy-neutrino lepton number angular distributions cannot provide a sufficient information to determine total amount of flavor conversion in neutrinos and antineutrinos of all flavors. Based on the results of our numerical simulations, we provide a new approximate scheme of FFC that is designed so that one can easily incorporate effects of FFCs in existing classical neutrino transport codes for the study of core-collapse supernova and binary neutron star merger. The scheme has an ability to capture key features of quasisteady state of FFCs without solving quantum kinetic neutrino transport, which will serve to facilitate access to FFCs for core-collapse supernova and binary neutron star merger theorists.

An inter-scale simulation method for TSV 3D IC based on linear superposition algorithm and TSV model sharing strategy

TSV Three-Dimensional Integrated Chips (TSV 3D ICs) contains extremely large number of irregularly distributed TSVs. As the decreases of size and pitch, the interaction among TSVs and substrate becomes significant. However, the existing fine mesh simulations for small number of TSVs rarely consider the global influence, the current multiscale simulations for package or wafer cannot assess all TSVs' structural state quickly. Therefore, the inter-scale simulation method considering the interactions between small-scale and large-scale simulations is proposed. The model sharing strategy decomposes the finite element analysis (FEA) simulation into a series of linear superposition algorithm (LSA) simulations, making it possible to obtain the detailed structural response of all TSVs concerning the global influence quickly. In addition, the equivalent properties of large yield TSVs are recalculated and fed back to the global simulation to reconstruct a more accurate global model for iterative simulation. The single TSV fine mesh simulations validate the reliability of the established LSA simulator. The TSV chip simulation under single point bending load shows that the relative error of stress is less than 0.0125 % of the global simulation, and it is 1.63 % of the fine mesh simulations, Meanwhile, the solution time is reduced to 2.2 % of the FEA method, and the memory consumption is only 0.088 %.

Demonstrating the Test Procedure for Preventive Maintenance of Aging Concrete Bridges

Deteriorated facility maintenance is a critical social issue in advanced countries. Its cost increases when considering the social consequences in terms of asset value and direct maintenance costs. Data from Korea’s Ministry of Land, Infrastructure, and Transport shows that there were 3454 bridges aged 30 years or over in Korea in 2017; this number will increase to 10,961 by 2027. In thirty years, maintenance costs will be incurred for more than 32,000 old bridges in Korea. These trends are also observed in the US, Japan, and Korea. Diverse studies have been conducted to predict the residual life of old bridges via bridge performance evaluation and load-carrying capacity assessments. However, criteria for evaluating bridge performance and verifying the effect of bridge maintenance are yet to be established due to two reasons. First, most studies on performance evaluation, maintenance, and rehabilitation techniques have been performed on limited specimens from building elements or through small-scale simulations that do not reflect the deterioration factors of complex materials in diverse environments. Second, the performance evaluation of bridges is difficult compared to quantitative state evaluations. As a method of predicting the future performance of aged concrete bridges, it is effective to understand the actual aged bridges through experiments, and this study intends to propose the method.

Modelling the accretion and feedback of supermassive black hole binaries in gas-rich galaxy mergers

ABSTRACTWe introduce a new model for the accretion and feedback of supermassive black hole (SMBH) binaries to the ketju code, which enables us to resolve the evolution of SMBH binaries down to separations of tens of Schwarzschild radii in gas-rich galaxy mergers. Our subgrid binary accretion model extends the widely used Bondi–Hoyle–Lyttleton accretion into the binary phase and incorporates preferential mass accretion on to the secondary SMBH, which is motivated by results from small-scale hydrodynamical circumbinary disc simulations. We perform idealized gas-rich disc galaxy merger simulations using pure thermal or pure kinetic active galactic nuclei (AGNs) feedback. Our binary accretion model provides more physically motivated SMBH mass ratios, which are one of the key parameters for computing gravitational wave (GW) induced recoil velocities. The merger time-scales of our simulated SMBH binaries are in the range tmerge ∼ 10–400 Myr. Prograde in-plane equal-mass galaxy mergers lead to the shortest merger time-scales, as they experience the strongest starbursts, with the ensuing high stellar density resulting in a rapid SMBH coalescence. Compared to the thermal AGN feedback, the kinetic AGN feedback predicts longer merger time-scales and results in more core-like stellar profiles, as it is more effective in removing gas from the galaxy centre and quenching star formation. This suggests that the AGN feedback implementation plays a critical role in modelling SMBH coalescences. Our model will be useful for improving the modelling of SMBH mergers in gas-rich galaxies, the prime targets for the upcoming LISA GW observatory.

Early Warning of the Carbon-Neutral Pressure Caused by Urban Agglomeration Growth: Evidence from an Urban Network-Based Cellular Automata Model in the Greater Bay Area

Carbon neutrality is becoming an important development goal for regions and countries around the world. Land-use cover/change (LUCC), especially urban growth, as a major source of carbon emissions, has been extensively studied to support carbon-neutral planning. However, studies have typically used methods of small-scale urban growth simulation to model urban agglomeration growth to assist in carbon-neutral planning, ignoring the significant characteristics of the process to achieve carbon neutrality: large-scale and long-term. This paper proposes a framework to model large-scale and long-term urban growth, which couples a quantity module and a spatial module to model the quantity and spatial allocation of urban land, respectively. This framework integrates the inertia of historical land-use change, the driving effects of the urbanization law (S-curve), and the traction of the urban agglomeration network to model the long-term quantity change of urban land. Moreover, it couples a partitioned modeling framework, spatially heterogeneous rules derived by geographically weighted regression (GWR), and quantified land-use planning orientations to build a cellular automata (CA) model to accurately allocate the urbanized cells in a large-scale spatial domain. Taking the Guangdong–Hong Kong–Macao Greater Bay Area (GHMGBA) as an example, the proposed framework is calibrated by the urban growth from 2000 to 2010 and validated by that from 2010 to 2020. The figure of merit (FoM) of the results simulated by the framework is 0.2926, and the simulated results are also assessed by some evidence, which both confirm the good performance of the framework to model large-scale and long-term urban growth. Coupling with the coefficients proposed by the Intergovernmental Panel on Climate Change (IPCC), this framework is used to project the carbon emissions caused by urban growth in the GHMGBA from 2020 to 2050. The results indicate that Guangzhou, Foshan, Huizhou, and Jiangmen are under great pressure to achieve the carbon-neutral targets in the future, while Hong Kong, Macao, Shenzhen, and Zhuhai are relatively easy to bring up to the standard. This research contributes to the ability of land-use models to simulate large-scale and long-term urban growth to predict carbon emissions and to support the carbon-neutral planning of the GHMGBA.

Small-scale dynamo in cool stars

Context. All cool main sequence stars including our Sun are thought to have magnetic fields. Observations of the Sun revealed that small-scale turbulent magnetic fields are present even in quiet regions. Simulations further showed that such magnetic fields affect the subsurface and photospheric structure, and thus the radiative transfer and emergent flux. Since small-scale turbulent magnetic fields on other stars cannot be directly observed, it is imperative to numerically study their effects on the near surface layers. Aims. Until recently comprehensive three-dimensional simulations capturing the effect of small-scale turbulent magnetic fields only exist for the solar case. A series of investigations extending small-scale dynamo simulations for other stars has been started. Here we aim to examine small-scale turbulent magnetic fields in stars of solar effective temperature but different metallicity. Methods. We investigate the properties of three-dimensional simulations of the magneto-convection in boxes covering the upper convection zone and photosphere carried out with the MURaM code for metallicity values of M/H = {–1.0,0.0,0.5} with and without a small-scale dynamo. Results. We find that small-scale turbulent magnetic fields enhanced by a small-scale turbulent dynamo noticeably affect the subsurface dynamics and significantly change the flow velocities in the photosphere. Moreover, significantly stronger magnetic field strengths are present in the convection zone for low metallicity. Instead, at the optical surface the averaged vertical magnetic field ranges from 64G for M/H = 0.5 to 85G for M/H = –1.0.