scholarly journals An FFT-based spectral solver for interface decohesion modelling using a gradient damage approach

2019 ◽  
Vol 65 (4) ◽  
pp. 925-939 ◽  
Author(s):  
L. Sharma ◽  
R. H. J. Peerlings ◽  
P. Shanthraj ◽  
F. Roters ◽  
M. G. D. Geers
Keyword(s):  
Deformation Gradient ◽  
Scaling Relations ◽  
Model Parameters ◽  
Constitutive Behaviour ◽  
Phase Boundaries ◽  
Model Predictions ◽  
Damage Field ◽  
Numerical Performance ◽  
Sharp Interfaces ◽  
Cohesive Zones

AbstractThis work presents a fast Fourier transform (FFT) based method that can be used to model interface decohesion. The inability of an FFT solver to deal with sharp interfaces discards the use of conventional cohesive zones to model the interfacial mechanical behaviour within this framework. This limitation is overcome by approximating sharp interfaces (e.g. grain/phase boundaries) with an interphase. Within the interphase, the background plastic constitutive behaviour is inherited from the respective adjacent grains. The anisotropic kinematics of the decohesion process is modelled using a damage deformation gradient that is constructed by mapping the opening strains (in normal and tangential modes) to the associated projection tensors. The degradation (damage) of the interfacial opening resistances is modelled via a dimensionless nonlocal damage variable that prevents localisation of damage within the interphase. This nonlocal variable results from the solution of a gradient damage based regularisation equation within the interphase subdomain. The damage field is constrained to the interphase region by applying a relatively large penalisation on the damage gradients inside the interphase. The extent of nonlocality ensures that the damage is largely uniform in the direction perpendicular to the interphase, thus making its thickness the theoretical lengthscale for dissipation. To achieve model predictions that are objective with respect to the interphase thickness, scaling relations of the model parameters are proposed. The numerical performance is shown for a uniform opening case and then for a propagating crack. Finally, an application to an artificial polycrystal is shown.

Impact of random soil properties on stress–strain response

2004 ◽  
Vol 41 (2) ◽  
pp. 351-355 ◽  
Author(s):  
Dieter Stolle ◽  
Peijun Guo ◽  
Gabriel Sedran
Keyword(s):  
Soil Properties ◽  
Constitutive Modelling ◽  
Soil Parameters ◽  
Strain Response ◽  
Constitutive Behaviour ◽  
Stress Strain ◽  
Deterministic Analysis ◽  
Model Predictions ◽  
Random Variability ◽  
The Impact

This paper analyzes the impact of natural random variation of soil properties on the constitutive modelling of geomaterial behaviour. A theoretical framework for accommodating variation in soil properties is presented. The framework is then used to examine the consequence of parameter variability on stress–strain relations. An important observation is that average soil parameters from a series of tests on small specimens, in which density of the specimens varies randomly, do not necessarily reflect the average constitutive behaviour of soil. Model predictions are shown to be consistent with the experimental data.Key words: random variability, deterministic analysis, soil parameters, constitutive model.

Experiences with computer simulation at two large wastewater treatment plants in northern Poland

2002 ◽  
Vol 45 (6) ◽  
pp. 209-218 ◽  
Author(s):  
J. Makinia ◽  
M. Swinarski ◽  
E. Dobiegala
Keyword(s):  
Computer Simulation ◽  
Wastewater Treatment ◽  
Nutrient Removal ◽  
Wastewater Treatment Plants ◽  
Biological Nutrient Removal ◽  
Model Parameters ◽  
Total N ◽  
Northern Poland ◽  
Model Predictions ◽  
Steady State Simulation

Mathematical modelling and computer simulation have became a useful tool in evaluating the operation of wastewater treatment plants (WWTPs) in terms of nutrient removal capability. In this study, steady-state simulation results for two large biological nutrient removal WWTPs are presented. The plants are located in two neighbouring cities Gdansk and Gdynia in northern Poland. Simulations were performed using a pre-compiled model and layouts (MUCT and Johannesburg processes) implemented in the GPS-X simulation package. The monthly average values of conventional parameters, such as COD, Total Suspended Solids, total N, N-NH4+, P-PO4− were used as input data. The measured effluent concentrations of COD, N-NH4+, N-NO3− and P-PO4− as well as reactor MLSS were compared with model predictions. During calibration, performed from the process engineering perspective, default values of only five model parameters were changed. The opportunities for further applications of such models in municipal WWTPs are discussed.

scholarly journals The Magnetized Disk-Halo Transition Region of M51

2018 ◽  
Vol 14 (A30) ◽  
pp. 319-322 ◽  
Author(s):  
M. Kierdorf ◽  
S. A. Mao ◽  
A. Fletcher ◽  
R. Beck ◽  
M. Haverkorn ◽  
...  
Keyword(s):  
Transition Region ◽  
Large Scale ◽  
Model Parameters ◽  
Very Large Array ◽  
X Band ◽  
Model Predictions ◽  
The Galaxy ◽  
Linearly Polarized ◽  
Grand Design ◽  
Different Depths

AbstractAn excellent laboratory for studying large scale magnetic fields is the grand design face-on spiral galaxy M51. Due to wavelength-dependent Faraday depolarization, linearly polarized synchrotron emission at different radio frequencies gives a picture of the galaxy at different depths: Observations at L-band (1 – 2 GHz) probe the halo region while at C- and X-band (4 – 8 GHz) the linearly polarized emission probe the disk region of M51. We present new observations of M51 using the Karl G. Jansky Very Large Array (VLA) at S-band (2 – 4 GHz), where previously no polarization observations existed, to shed new light on the transition region between the disk and the halo. We discuss a model of the depolarization of synchrotron radiation in a multilayer magneto-ionic medium and compare the model predictions to the multi-frequency polarization data of M51 between 1 – 8 GHz. The new S-band data are essential to distinguish between different models. Our study shows that the initial model parameters, i.e. the total regular and turbulent magnetic field strengths in the disk and halo of M51, need to be adjusted to successfully fit the models to the data.

Viscoelastic behavior of an epoxy resin during cure below the glass transition temperature: Characterization and modeling

2018 ◽  
Vol 53 (2) ◽  
pp. 155-171 ◽  
Author(s):  
Alice Courtois ◽  
Martin Hirsekorn ◽  
Maria Benavente ◽  
Agathe Jaillon ◽  
Lionel Marcin ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Epoxy Resin ◽  
Viscoelastic Behavior ◽  
Mechanical Analysis ◽  
Strain History ◽  
Model Parameters ◽  
Degree Of Cure ◽  
Model Predictions

This paper presents a viscoelastic temperature- and degree-of-cure-dependent constitutive model for an epoxy resin. Multi-temperature relaxation tests on fully and partially cured rectangular epoxy specimens were conducted in a dynamic mechanical analysis apparatus with a three-point bending clamp. Master curves were constructed from the relaxation test results based on the time–temperature superposition hypothesis. The influence of the degree of cure was included through the cure-dependent glass transition temperature which was used as reference temperature for the shift factors. The model parameters were optimized by minimization of the differences between the model predictions and the experimental data. The model predictions were successfully validated against an independent creep-like strain history over which the temperature varied.

scholarly journals On acceleration of <1 MeV/n He ions in the corotating compression regions near 1 AU: STEREO observations

2009 ◽  
Vol 27 (9) ◽  
pp. 3677-3690 ◽  
Author(s):  
R. Bučík ◽  
U. Mall ◽  
A. Korth ◽  
G. M. Mason
Keyword(s):  
Solar Wind ◽  
Total Pressure ◽  
Solar Wind Speed ◽  
Shock Acceleration ◽  
Model Parameters ◽  
Corotating Interaction Region ◽  
Reverse Shock ◽  
Compression Region ◽  
Model Predictions

Abstract. Observations of multi-MeV corotating interaction region (CIR) ions are in general consistent with models of CIR shock acceleration and transport. The presence of suprathermal particles near 1 AU in unshocked compression regions is not adequately explained. Nonetheless, more recent works demonstrate that unshocked compression regions associated with CIRs near 1 AU could energize particles. In the energy range from ~0.1 to ~1 MeV/n we investigate CIR events observed in 2007–2008 by the STEREO A and B spacecraft. We treat the predictions of compression acceleration by comparing the observed ion intensities with the model parameters. These observations show that the ion intensity in CIR events with in-situ reverse shock is well organized by the parameters which characterize the compression region itself, like compression width, solar wind speed gradients and the total pressure. In turn, for CIR events with the absence of the shocks the model predictions are not fulfilled.

scholarly journals Semi-analytic forecasts for JWST – II. Physical properties and scaling relations for galaxies at z = 4–10

2019 ◽  
Vol 490 (2) ◽  
pp. 2855-2879 ◽  
Author(s):  
L Y Aaron Yung ◽  
Rachel S Somerville ◽  
Gergö Popping ◽  
Steven L Finkelstein ◽  
Harry C Ferguson ◽  
...  
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
High Redshift ◽  
Formation Rate ◽  
Distribution Functions ◽  
Scaling Relations ◽  
Physical Parameters ◽  
Model Parameters ◽  
Galaxy Populations ◽  
The Impact

ABSTRACT The long anticipated James Webb Space Telescope (JWST) will be able to directly detect large samples of galaxies at very high redshift. Using the well-established, computationally efficient Santa Cruz semi-analytic model, with recently implemented multiphase gas partitioning, and H2-based star formation recipes, we make predictions for a wide variety of galaxy properties for galaxy populations at z = 4–10. In this work, we provide forecasts for the physical properties of high-redshift galaxies and links to their photometric properties. With physical parameters calibrated only to z ∼ 0 observations, our model predictions are in good agreement with current observational constraints on stellar mass and star formation rate distribution functions up to z ∼ 8. We also provide predictions representing wide, deep, and lensed JWST survey configurations. We study the redshift evolution of key galaxy properties and the scaling relations among them. Taking advantage of our models’ high computational efficiency, we study the impact of systematically varying the model parameters. All distribution functions and scaling relations presented in this work are available at https://www.simonsfoundation.org/semi-analytic-forecasts-for-jwst/.

Modification of a Predictive Model To Include the Influence of Fat Content on Salmonella Inactivation in Low-Water-Activity Foods

2020 ◽  
Vol 83 (5) ◽  
pp. 801-815
Author(s):  
LISA M. TRIMBLE ◽  
JOSEPH F. FRANK ◽  
DONALD W. SCHAFFNER
Keyword(s):  
Water Activity ◽  
Survival Data ◽  
Peanut Butter ◽  
Weibull Model ◽  
Fat Content ◽  
Mitigation Strategies ◽  
Model Parameters ◽  
Least Squares Regression ◽  
Salmonella Spp ◽  
Model Predictions

ABSTRACT Low-water-activity (aw) foods (including those containing fat) are often implicated in outbreaks of Salmonella spp. The influence of fat content on survival in foods such as peanut butter remains unclear. Certain Salmonella serovars can survive for long periods in harsh temperatures and low moisture conditions. The objective of this study was to determine the influence of fat content on the survival of Salmonella in low-aw foods and expand an existing secondary inactivation model previously validated for lower-fat foods. Whey protein powder supplemented with peanut oil was equilibrated to five target aw values (aw &lt; 0.60), inoculated with a dried four-strain cocktail of Salmonella, vacuum sealed, and stored at 22, 37, 50, 60, 70, and 80°C for 48 h, 28 days, or 168 days. Survival data were fitted to Weibull, Biphasic-linear, Double Weibull, and Geeraerd-tail models. The Weibull model was chosen for secondary modeling due to its ability to satisfactorily describe the data over most of the conditions under study. The influence of temperature, fat content, and aw on the Weibull model parameters was evaluated using nonlinear least squares regression, and a revised secondary model was developed based on parameter significance. Peanut butter, chia seed powder, toasted oat cereal, and animal crackers within the aw range of the model were used to validate the modified model within its temperature range. Fat content influenced survival in samples held at temperatures ≥50°C, whereas aw influenced survival at 37 and 70°C. The model predictions demonstrated improved % bias and % discrepancy compared with the previous model. Weibull model predictions were accurate and fail-safe in 38 and 58%, respectively, of the food and environmental conditions under study. Predictions were less reliable for peanut butter held at 80°C. This study provides data and a model that can aid in the development of risk mitigation strategies for low-aw foods containing fat. HIGHLIGHTS

scholarly journals Simulating tubulin-associated unit transport in an axon: using bootstrapping for estimating confidence intervals of best-fit parameter values obtained from indirect experimental data

2017 ◽  
Vol 473 (2201) ◽  
pp. 20170045 ◽  
Author(s):  
I. A. Kuznetsov ◽  
A. V. Kuznetsov
Keyword(s):  
Experimental Data ◽  
Confidence Intervals ◽  
Surrogate Data ◽  
Model Parameters ◽  
Model Predictions ◽  
Estimate Parameter ◽  
Minimum Number ◽  
Percentile Bootstrap ◽  
Parameter Values ◽  
Best Fit

In this paper, we first develop a model of axonal transport of tubulin-associated unit (tau) protein. We determine the minimum number of parameters necessary to reproduce published experimental results, reducing the number of parameters from 18 in the full model to eight in the simplified model. We then address the following questions: Is it possible to estimate parameter values for this model using the very limited amount of published experimental data? Furthermore, is it possible to estimate confidence intervals for the determined parameters? The idea that is explored in this paper is based on using bootstrapping. Model parameters were estimated by minimizing the objective function that simulates the discrepancy between the model predictions and experimental data. Residuals were then identified by calculating the differences between the experimental data and model predictions. New, surrogate ‘experimental’ data were generated by randomly resampling residuals. By finding sets of best-fit parameters for a large number of surrogate data the histograms for the model parameters were produced. These histograms were then used to estimate confidence intervals for the model parameters, by using the percentile bootstrap. Once the model was calibrated, we applied it to analysing some features of tau transport that are not accessible to current experimental techniques.

The Dynamics of Vortex Amplifiers. Part 1: Analytical Model

1985 ◽  
Vol 107 (3) ◽  
pp. 176-181 ◽  
Author(s):  
E. E. Kitsios ◽  
R. F. Boucher
Keyword(s):  
Time Delay ◽  
Dynamic Response ◽  
Dynamic Modeling ◽  
Rotational Inertia ◽  
Model Parameters ◽  
Static Characteristics ◽  
Time Constants ◽  
Admittance Matrix ◽  
Model Predictions ◽  
Semi Empirical

A semi-empirical technique for the dynamic modeling of vortex amplifiers is demonstrated with reference to one particular vortex amplifier geometry. The model parameters are determined explicitly from the amplifier static characteristics and geometry except for two which are estimated from measurements of the amplifier’s dynamic response. The two are time constants associated with the chamber time delay and the vortex rotational inertia. The model is linearized about a working point and is presented in terms of an admittance matrix. The paper is continued in Part 2 where two of the amplifier’s transfer admittances are measured experimentally and compared with the model predictions.

scholarly journals On the Possible Existence of Non-Fisher Universality Classes

2012 ◽  
Vol 57 (9) ◽  
pp. 964
Author(s):  
A.I. Ivanitskyi ◽  
K.A. Bugaev
Keyword(s):  
Phase Diagram ◽  
Critical Exponents ◽  
Additional Condition ◽  
Scaling Laws ◽  
Scaling Relations ◽  
Model Parameters ◽  
Scaling Relation ◽  
Traditional Form ◽  
Universality Classes ◽  
Definition Of

The critical exponents α, α', β, γ', and δ of the model of quark-gluon bags with surface tension are found as functions of the most general model parameters. Two versions of the model that generate the phase diagram of the strongly interacting matter with critical or tricritical endpoint, respectively, are considered. The analysis of the relations between the critical exponents (scaling laws) shows that the scaling can be violated in a general case. The question whether it is possible to restore the scaling laws with the help of the Fisher definition of the α's exponent and its generalizations α'c and α'm is studied. It is shown that the Fisher scaling relation can be recovered with the help of the generalizations α'c and α'm, whereas no definition of the α' index is able to recover the Griffiths scaling relation in its traditional form. It is explicitly demonstrated that the additional condition α = α' is not sufficient to restore the Griffiths scaling relation in the traditional form. A generalization of this scaling relation which is valid for all known models is suggested. The obtained results allow us to conclude on the possible existence of the non-Fisher universality classes, for which the traditional scaling relations can be violated, whereas the generalized scaling laws can be established.

Sign in / Sign up

Export Citation Format

Share Document