Parameters Of Numerical Model Research Articles

Design and AC Modeling of a Bipolar GNR-h-BN RTD With Enhanced Tunneling Properties and High Robustness to Edge Defects

This paper proposes a robust to defects and short length device (RDSLD), a newly in-plane resonant tunneling diode (RTD), and its ac-modeling with the minimum length of 3 nm. The proposed structure has robust performance in the presence of defects. It also has a high degree of flexibility in tuning electronic specifications. By using bipolar doping and a special h-boron nitride barrier pattern, these unique features are obtained. The simulation results verify that the proposed structure has the potential for replacing conventional RTD diodes. Such that the peak-to-valley ratio (PVR) and the maximum current of 4500, 450 nA for perfect bowtie and 3.45, 1256 nA for rhombic barrier shape structure are obtained, respectively. Also, negative differential resistance (NDR) is observed in all of the structures with vacancy and impurity defects. The effect of the geometrical parameters on the charge transmission of the device is another issue that is addressed in this paper. Furthermore, the analytical and numerical capacitance model parameters are presented.

Sensitivity to Physical and Numerical Aspects of Large-Eddy Simulation of Stratocumulus

Abstract A series of numerical experiments where both physical and numerical model parameters are varied with respect to a reference setup is used to investigate the physics of a stratocumulus cloud and the performance of a large-eddy simulation (LES) model. The simulations show a delicate balance of physical processes with some sensitivities amplified by numerical model features. A strong feedback between cloud liquid, cloud-top radiative cooling, and turbulence leads to slow grid convergence of the turbulent fluxes. For a methodology that diagnoses cloud liquid from conserved variables, small errors in the total water amount result in large liquid water errors, which are amplified by the cloud-top radiative cooling leading to large variations of buoyancy forcing. In contrast, when the liquid–radiation–buoyancy feedback is not present in simulations without radiation, the turbulence structure of the boundary layer remains essentially identical for grid resolutions between 20 and 1.25 m. The present runs suggest that the buoyancy reversal instability significantly enhances the entrainment rate. Even though cloud-top radiative cooling is regarded as a key attribute of stratocumulus, the present simulations suggest that surface fluxes and surface shear significantly contribute to the total turbulent kinetic energy. Turbulence spectra exhibit inertial range scaling away from the confinement effects of the surface and inversion. Fine grid resolution LESs agree with observations, especially with respect to cloud liquid and vertical velocity variance, and exhibit grid convergence without any model tuning or ad hoc model choices.

Multidimensional Geodynamic Modeling in the Southeast Carpathians: Upper Mantle Flow‐Induced Surface Topography Anomalies

AbstractSpectral variations of gravity and topography data show nonisostatic compensation of elevation in the Southeast Carpathians that is consistent with our new residual topography calculations. Multidimensional thermomechanical models are created to consider a possible mantle flow component of the surface topography with varying temperature models and crustal configurations. The temperature anomalies derived from large‐scale P wave velocity anomalies and combined temperature model are estimated as input for the parametric numerical modeling experiments. Model results show that a surface uplift (up to ~1 km) develops in the southeastern Carpathians due to the rising hot upper mantle beneath the region. The upwelling flow is also in concordance with observations such as volcanism and enhanced surface heat flow in the region. Subsidence in the eastern part (0.5–1 km over the Vrancea zone and the Focsani Basin) forms in relation to the downgoing Vrancea slab. The findings indicate the significant role of upper mantle structures on the present‐day anomalous topography related to proposed postcollisional tectonics in the Southeast Carpathians.

Possible roles of fall speed parameters of different graupel densities on microphysics and electrification in an idealized thunderstorm

AbstractGraupel is often parametrized as “medium‐density” ice particles with a bulk density of 400 kg m−3 and corresponding fixed fall speed parameters in numerical models. In natural clouds, however, graupel has an extensive range of densities, and its fall speed is closely related to its density ρg. In this study, the possible responses of the microphysical and electrical structures of a simulated thunderstorm to varying ρg and its corresponding fall speed parameters were examined using the Advanced Research Weather and Forecasting Model (ARW‐WRF) with an explicit charging and discharge lightning scheme. Six sensitivity tests were performed with different ρg and corresponding fall speed parameters. ρg ranges from 350–850 kg m−3, to represent relatively low‐ (350, 450 kg m−3), medium‐ (550, 650 kg m−3), and high‐ (750, 850 kg m−3) density assumptions. In low‐density cases, the ice water path (IWP) could be comparable with the liquid water path (LWP), while the LWP exceeds the contribution of the IWP to the total water path (TWP) in high‐density cases. The results show that melting rates and precipitation were enhanced when ρg was increased from low to high values, resulting in a smaller size and lighter mean mass due to a shorter residence time and faster fall speed.Different assumptions about graupel density also resulted in different electrical structures in the simulated clouds. The clouds produced in the low‐ and medium‐density cases are mainly charged with conventional tripole or positive dipole structures, while the ones formed in the high‐density cases present “bottom‐heavy” tripole structures. The upper positive regions become weaker, with reduced negative noninductive charging rates, as graupel falls faster and less graupel is negatively charged at higher altitude. It is also found that a faster fall speed of graupel does not necessarily mean stronger flash density, although lightning activities are correlated with higher fall speed.

Sensitivity determined simultaneous estimation of multiple parameters in coupled models: part I—based on single model component sensitivities

While various data assimilation algorithms based on Bayes’ theorem have been developed for state estimation, some of these algorithms have also been applied to model parameter estimation. Coupled model parameter estimation (CPE) adjusts model parameters using available observations; then, the observation-adjusted parameters can greatly mitigate the model bias, which has great potential to reduce climate drift and enhance forecast skill in coupled climate models. However, given numerous model parameters that are associated with multiple time scales, how to conduct CPE with the simultaneous estimation of multiple parameters (SEMP) is still a popular research topic. With the aid of 3 coupled models, ranging from the conceptual coupled model to the intermediate coupled circulation model, this study has developed a systematic method to implement the SEMP–CPE. Linking coupled model sensitivities with the signal-to-noise ratio of the CPE, the SEMP–CPE method uses a timescale structure with coupled model sensitivities to determine which and how many parameters are estimated simultaneously in each CPE cycle to minimize the error of the coupled model simulation. Given that in a coupled model, the timescales by which different model components sensitively respond to a parameter perturbation can be quite different due to their different variabilities in their characteristic timescales, the first part of our study series focuses on the SEMP–CPE associated with single model component sensitivities. The results show that the quality of the model state analysis (in terms of assimilation) improves with the number of parameters being estimated by the order of sensitivities until the signal-to-noise ratio reaches a low threshold. Only when the most impactful physical parameters are estimated is the error of the state estimation consistently decreasing; as well as the signal-to-noise ratio in state-parameter covariance in SEMP scheme is enhanced. While only the signal extracted from the SEMP–CPE reaches saturated, the signal-to-noise ratio in the SEMP–CPE is maximized, and the state estimation error is minimized. Otherwise, if the parameters with low sensitivities are included in the CPE, the error of the state estimation increases instead. These results provide some insight into simultaneously estimating multiple parameters in a biased coupled general circulation model that assimilates real observations, which further improves climate analysis and prediction initialization.

Numerical FEA parametric analysis of CAI behaviour of CFRP stiffened panels

This paper examined the effect of numerical modelling parameters on the accuracy and computational efficiency of Carbon Fibre Reinforced Polymer (CFRP) stiffened panels under Compression After Impact (CAI). Pristine and damaged CFRP stiffened panels were subjected to compression in Abaqus® software using Cohesive Zone Model (CZM) method. Various case studies were examined and the effect of the stiffness parameters of the cohesive elements was critically assessed. Moreover, the required number of cohesive zones to fully capture the damage mechanisms of the impacted and pristine panels under compressive loading was examined. The results showed that a wrong set of parameters can even lead to neglecting the induced damage and can cause severe convergence problems in the numerical model. The importance of the Overall Meshing Factor (OMF) was highlighted and a user-defined subroutine (USDFLD) was applied to capture the decrease in the load bearing capability of an impacted panel prior to the compressive loading, since CZM was found insufficient for this scope. The above-mentioned remarks illustrated the process of investigating the optimum numerical parameters set to achieve an accurate and efficient finite element modelling of the stiffened panels structural performance and maximum load-carrying capability, when subjected to CAI loading.

Experimental and numerical study on the seismic performance of a self-centering bracing system using closed-loop dynamic (CLD) testing

This study investigates the seismic performance of a newly developed self-centering bracing system using a novel experimental technique named as closed-loop dynamic (CLD) testing. The bracing, named piston-based self-centering (PBSC) apparatus, employs Ni-Ti superelastic shape memory alloy (SMA) bars inside a sleeve-piston assembly for its self-centering mechanism. During cyclic tension-compression loading, the SMA bars are only subjected to tension avoiding buckling and leading to flag-shaped symmetric force-deformation hysteresis. Initially, a braced frame building fitted with PBSC is seismically designed and the preliminary sizing of the brace is determined. For testing, considering the lab capability, the brace is fabricated at a reduced scale. The process of “Closed-loop dynamic testing” starts with the brace test (step 1) under strain-rate loading to characterize the numerical model parameters (step 2), which are then scaled-up as per similitude law and implemented in a finite element software, S-FRAME’s PBSC brace model (step 3). Then the braced frame building is analyzed under an earthquake (step 4) and the axial force-deformation response of the brace under consideration is captured (step 5). In order to further understand and validate the actual response of the brace under earthquake type loading, the axial deformation obtained from S-FRAME is scaled-down (step 6) and used as input parameters for testing the reduced scale brace (step 7). The obtained response (step 8) is further scaled-up and used to match the S-FRAME’s PBSC model for validation (step 9). Iterations from step 3 to step 9 will be required until the experimental and numerical results converge. Convergence criteria used for this validation include both the energy dissipation capacity and initial stiffness within 10% accuracy. Reasonable agreement between the numerical and experimental results is achieved in the closed-loop dynamic testing. The PBSC brace shows excellent self-centering capability under various earthquake loadings.

Numerical analyses of a hydraulic hybrid powertrain system for a transit bus

A dynamic programming optimization algorithm has been applied on a transit bus model in MATLAB in order to assess the fuel economy improvement potential by implementing a hydraulic hybrid powertrain system. The numerical model parameters have been calibrated using experimental data obtained on a Belgrade?s public transport bus. This experiment also provided the representative driving cycle on which to conduct simulation analyses. Various functional parameters of a hydraulic hybrid system have been evaluated for obtaining the best possible fuel economy. Dynamic programming optimization runs have been completed for various hydraulic accumulator sizes, preload values and accumulator foam quantities. It has been shown that a fuel economy improvement of 28% can be achieved by implementing such a system.

Numerical study of the effect of confining pressure on the rock breakage efficiency and fragment size distribution of a TBM cutter using a coupled FEM-DEM method

Confining pressure is an important factor that affects the rock breakage efficiency of Tunnel Boring Machines (TBMs). This study analyses the influence of the confining pressure on the rock breakage process, rock breakage efficiency and fragmentation distribution after crushing using a coupled FEM-DEM method. First, the parameters of the rock numerical model are calibrated using numerical uniaxial compression tests and Brazilian tests. Second, the rock breakage by the cutter is simulated under different confining pressures, and the influence of the confining pressure on the rock breakage process is determined. Third, using a post-processing program developed for extracting the induced fragments, the distribution of fragments after rock fragmentation is obtained, which accurately provides the fractured area of the rock to determine the variation of the specific energy (SE) with confining pressure. Finally, the equivalent length distributions of the fragments are analysed using the fractal method. The results show that the confining pressure has a significant inhibitory effect on the propagation of median cracks. The angle of the lateral crack increases with increasing confining pressure, and the length of the crack first increases and then decreases. The maximum normal force and the maximum indentation distance also increase first and then decrease with increasing confining pressure. The SE first increases with increasing confining pressure; however, when the confining pressure reaches the first critical value, the SE begins to decrease with increasing confining pressure and then continues to increase after the confining pressure reaches the second critical value. The variation of the fractal dimension with the confining pressure is similar to the variation of the SE with the confining pressure.

Numerical investigation of the combined effect of forced and free thermal convection in synthetic groundwater basins

The theoretical examination of the combined effect of water table configuration and heat transfer is relevant to improve understanding of deep groundwater systems, not only in siliciclastic sedimentary basins, but also in fractured rocks or karstified carbonates. Numerical model calculations have been carried out to investigate the interaction of topography-driven forced and buoyancy-driven free thermal convection in a synthetic, two-dimensional model. Effects of numerous model parameters were systematically studied in order to examine their influence on the Darcy flux, the temperature and the hydraulic head field. It was established that higher geothermal gradients and greater model depths facilitate the evolution of time-dependent free thermal convection in agreement with changes of the thermal Rayleigh number and the modified Péclet number. However, increasing water table slope and anisotropy coefficient favor the formation of stationary forced thermal convection. Free thermal convection mainly affects the deeper part of the midline and the discharge zone of the synthetic model. In the examined model basins, the position of the maximum hydraulic head is located within the bottom thermal boundary layer near the recharge zone. This divergent stagnation point underlies a local downwelling zone characterized by underpressure. These simulations draw attention to the importance of understanding the combined effect of forced and free thermal convection in sedimentary basins regarding regional groundwater flow patterns, and temperature distributions.

Adaptive cycle jump and limits of degradation in micromechanical fatigue simulations of fibre-reinforced plastics

This research investigates the influence of numerical parameters of micromechanical fatigue damage models on the obtained progressive damage behaviour of fibre-reinforced plastics at transverse tensile fatigue loads. The simulated damage behaviour is evaluated using experimentally observed crack patters published in the literature. The investigated numerical model parameters are (1) whether or not the model considers static failure within a simulated load cycle, (2) the degree of material property degradation after sudden failure and (3) the size of the cycle jump. The results reveal a significant influence of the degree of material degradation and of the cycle jump on the simulated matrix crack formation at both higher and lower fatigue loads. Static failure within a simulated load cycle primarily affects the damage behaviour at higher fatigue loads. The paper gives recommendations of the parameter choice for plausible progressive fatigue damage simulation results. Regarding the cycle jump, an adaptive algorithm is proposed and implemented. This approach leads to plausible fatigue damage results paired with a significant reduction of computation time comparing to a cycle-by-cycle analysis.

A 3D fluid-solid interaction model of the air puff test in the human cornea

We present a numerical model of a contactless test commonly used to assess the biomechanics of the human cornea. The test, consisting in a rapid air jet applied to the anterior surface of the cornea, is controversial. Although the numerous studies documented in the literature have not been able yet to clarify its relevance as a diagnostic tool, the test has the potential to be combined with inverse analysis procedures to characterize the parameters of numerical models of the cornea. With the final goal of employing the air puff test in advanced material identification algorithms, here we propose to model the cornea with standard finite elements and the fluids filling the anterior chamber of the eye with a meshfree discretization. The interaction between moving fluids and deforming cornea is accounted for by modifying the interface boundary conditions of both fluid and solid. The proposed model represents the first fully 3D example of an aqueous-cornea fluid-solid interaction analysis which uses a robust meshfree approach for the fluid. Although we restrict our scope to isotropic nonlinear materials, numerical results confirm the undeniable importance of including internal fluids in the simulation of the air puff test. Thus the proposed approach stands as a procedural paradigm for the identification of the mechanical parameters of the human cornea.

Bayesim: A tool for adaptive grid model fitting with Bayesian inference

Bayesian inference is a widely used and powerful analytical technique in fields such as astronomy and particle physics but has historically been underutilized in some other disciplines including semiconductor devices. In this work, we introduce bayesim, a Python package that utilizes adaptive grid sampling to efficiently generate a probability distribution over multiple input parameters to a forward model using a collection of experimental measurements. We discuss the implementation choices made in the code, showcase two examples in photovoltaics, and discuss general prerequisites for the approach to apply to other systems. Program summaryProgram Title: BayesimProgram Files doi:http://dx.doi.org/10.17632/fch5m6p3nn.1Licensing provisions: GNU General Public License 2Programming language: Python 3Supplementary material: uncertainty_figure.pngNature of problem: Many parameters in forward numerical models, e.g. for photovoltaic (PV) device behavior, are difficult to measure via direct experiment. In addition, in early-stage PV materials (and many other systems of interest), there are many unknown parameters and a desire to know their values in a small amount of time to enable high-throughput materials screening, making the time investment for direct measurement prohibitive. However, measurement of electrical properties of devices is comparatively easy, cheap, and automatable.Solution method: We employ Bayesian inference to “invert” the device models using the high-throughput experimental data, running the model forward with many combinations of parameters and generating a probability distribution over the inputs. This enables fitting of a number of parameters limited only by the quantity of experimental data and computational power available. The code is available open-source as a Python package and includes features such as adaptive grid fitting, model uncertainty calculation, and a variety of visualization options.Additional comments: The code is freely available on Github (https://github.com/pv-lab/bayesim) and thoroughly documented online ( https://pv-lab.github.io/bayesim/_build/html/index.html).

Discrete Element Method Model Optimization of Cylindrical Pellet Size

The DEM (Discrete Element Method) is one option for studying the kinematic behaviour of cylindrical pellets. The DEM experiments attempted to optimize the numerical model parameters that affected time and velocity as a cylindrical vessel emptied. This vessel was filled with cylindrical pellets. Optimization was accomplished by changing the coefficient of friction between particles and selecting the length accuracy grade of the sample cylindrical pellets. The initial state was a series of ten vessel-discharge experiments evaluated using PIV (Particle Image Velocimetry). The cylindrical pellet test samples were described according to their length in three accuracy grades. These cylindrical pellet length accuracy grades were subsequently used in the DEM simulations. The article discusses a comparison of the influence of the length accuracy grade of cylindrical pellets on optimal calibration of time and velocity when the cylindrical vessel is emptied. The accuracy grade of cylindrical pellet length in the DEM sample plays a significant role in relation to the complexity of a created simulation.

Unconventional hydrocarbon prospects in Ordovician and Silurian mudrocks of the East European Craton (Poland): Insight from three-dimensional modelling of total organic carbon and thermal maturity

Three-dimensional, structural and parametric numerical modelling was applied to unravel the unconventional hydrocarbon potential of a W-dipping, Lower Palaeozoic mudrock succession, which subcrops for some 700 km in the Baltic, Podlasie and Lublin basins across the SW margin of East European Craton in Poland. Input data comprised structural and thickness maps of Ordovician and Silurian strata and the results of thermal maturity (mean vitrinite-equivalent reflectance, % Ro) and total organic carbon (TOC, % wt.) modelling. A new, spatial interpretation of vitrinite-reflectance variability indicates that the regional, W-increasing thermal maturity pattern breaks into a series of domains, bounded by abrupt maturity variations. In total, 14 tectono-thermal domains were recognised and their boundaries traced to known and inferred faults, mostly of NW‒SE and NE‒SW orientations. On the basis of a combination of thermal maturity and total organic carbon levels (0.6% > Ro<2.4%, and TOC >1.5% wt.), good-quality, unconventional reservoirs can be expected in the Sasino Formation (Caradoc) and Jantar Formation (early Llandovery) in the central and western Baltic Basin. The Jantar Formation also is likely to be prospective in the western Podlasie Basin. Marginal-quality reservoirs may occur in the Sasino and Jantar formations within the Podlasie and Lublin basins and in the Pasłęk Formation (late Llandovery) across all basins. Poorto moderate-quality, unconventional reservoirs could be present in the Pelplin Formation (Wenlock) in the Lublin and southern Podlasie basins. In spite of a considerable hydrocarbon loss during multiphase basin inversion, the Ordovician and Silurian mudrocks still contain huge quantities of dispersed gas. Successful exploitation of it would require the adoption of advanced fracking methods.

Comparison of the value of passive safety coefficients for car crash with lighting column made of aluminum or composite material based on numerical simulation

Numerical simulations have become more and more important in recent years for the design of supporting road equipment structures. These structures are important for ensuring the proper level of passive safety for drivers and passengers. These structures also allow the reduction of costs of entry for new products on the market and reduction of the total cost of production. In this paper was shown comparison of passive safety coefficient ASI and THIV for lighting column made of composite material and aluminum based on experimentally verified numerical simulation. FEM was used to carry out the simulation which was implemented in LS Dyna to determine passive safety coefficients, whose algorithm was written in MATLAB. Authors presented parameters of numerical model of the car and lighting column with the ground. The accepted boundary and initial conditions were chosen in order to show the behaviour of the lighting column during a collision with a car.

The statistical impact of experimental result scatter of asphalt mixtures on their numerical modelling

The paper presents selected test results of asphalt mixture conducted in low temperatures. The obtained parameters are highly diverse. It concerns ultimate breaking loads, stiffness parameters related to Young's modulus but also the fracture course. Statistical analysis upon the results makes it possible to relevantly estimate the material-defining parameter values. Such a random approach leads to the mean values of breaking and fracture-triggering loads, dealing with their dispersion too. The estimated parameters allow to form appropriate numerical models of asphalt mixture specimens. This type of analysis supports the laboratory tests. The paper presents the authors' simplified model considering non-uniform material features. The results reflect the scatter of real laboratory test outcomes. In order to do so an algorithm to calibrate the numerical model parameters was created.

Numerical study on responses of an existing metro line to staged deep excavations

Responses of a substructure adjacent to deep excavations are complex, especially when the substructure is connected to the supporting systems of the excavations. In this study, a three-dimensional (3D) numerical model is developed by finite difference (FD) software, FLAC3D v5.0, to examine the responses of a metro line to deep excavations through a case history in Shanghai, China. The developed numerical model includes four deep excavations, which were located at two sides of the metro line and were connected to the structures of the metro station. These deep excavations were constructed in stages and the construction processes are simulated in accordance with the practical execution. Responses of the rails to the deep excavations are illustrated and the numerical results are compared to the measured data to validate the developed numerical model and input parameters. Moreover, 3D structural responses of the metro station and shield tunnels to the deep excavations are presented and analyzed. Numerical results indicate that (i) the walls of the station move upward during the excavations and the slabs are uplifted by the walls; (ii) The station heaves significantly whereas the shield tunnels settle slightly. (iii) The station will be distorted if the unloading is asymmetric.

Solar and Shading Potential of Different Configurations of Building Integrated Photovoltaics Used as Shading Devices Considering Hot Climatic Conditions

This study investigates the use of building-integrated photovoltaics (BIPVs) as shading devices in hot climates, with reference to the conditions of Saudi Arabia. It used parametric numerical modelling to critically appraise the potential of eight design configurations in this regard, including vertical and horizontal shading devices with different inclination angles. The study assumed that the examined shading devices could be entirely horizontal or vertical on the three exposed facades, which is common practice in architecture. The study found that the examined configurations offered different solar and shading potentials. However, the case of horizontal BIPV shading devices with a 45° tilt angle received the highest amount of annual total insolation (104 kWh/m2) and offered effective window shading of 96% of the total window area on average in summer. The study concluded that, unlike the common recommendation of avoiding horizontal shading devices on eastern and western facades, it is possible in countries characterised with high solar altitudes such as Saudi Arabia to use them effectively to generate electricity and provide the required window shading.

Specialized finite elements for numerical simulation of the flexibly-reconfigurable roll forming process

Flexibly-reconfigurable roll forming (FRRF) process is suggested in recent years as a response to the needs of modern manufacturing industries for small-lot or even single-lot production of doubly-curved sheet metal surfaces with reduced costs. In FRRF, a sheet metal is deformed by the use of two bent rollers with non-constant roll gap where the rolling and roll-bending mechanisms are imposed together. Thanks to FRRF process, the costs due to the manufacturing of dies are reduced; however, the computational cost for process design becomes significant as each design may be used for a few or even a single production. Hence, the net production rate is controlled by computational time that can be several times longer than the forming time. Considering the deformation mechanism in FRRF, this study tries to specialize an analysis method to FRRF that is accurate and efficient. This is accomplished by an in-house Matlab implementation of an efficient finite element approach and testing various combinations of elements and variational formulations (mixed and irreducible) to find the best combination of them for numerical simulation of FRRF. For this purpose, first a set of preliminary comparisons are made to select: (1) the best integration method for the elements with irreducible formulation, (2) the best stress components to be included in the nodal parameters for the elements with mixed formulation, and (3) the best elemental class (Serendipity or Lagrangian) for the elements with nonlinear interpolation in at least two directions. Then, the best variational formulation is decided for each elemental family by comparing the simulation results in a range of numerical model parameters. Finally, the FE model parameters are optimized for each candidate by a surrogate-based Pareto optimization method, and the best element/formulation couple is selected among all the candidates by the technique for order of preference by similarity to ideal solution (TOPSIS). Moreover, in order to identify the most decisive parameters in the analysis and design of FRRF process, the response of FRRF to variation of several process parameters including thickness, width, rollers' curvature radius, roll gap distribution, and material properties is investigated and the results are compared with those reported by the other studies.