scholarly journals Strain dependent vorticity in sheared granular media

2021 ◽  
Vol 249 ◽  
pp. 02010
Author(s):  
Dong Wang ◽  
Joshua A. Dijksman ◽  
Jonathan Barés ◽  
Hu Zheng
Keyword(s):  
Flow Field ◽  
Granular Media ◽  
Total Surface Area ◽  
Packing Fraction ◽  
Differential Method ◽  
Displacement Fields ◽  
Data Set ◽  
Quantitative Metrics ◽  
Particle Packings ◽  
Strain Dependent

Displacement fields in sheared particle packings often display vortex-like structures that reveal essential features about the mechanical state of the collection of particles. There are several metrics to quantify these flow field features, yet extracting such quantitative metrics from flow field or particle tracking data involves making numerous choices on the time and length scales over which to average. Here we employ a much used experimental data set on sheared disk packings to explore how such arbitrary data mining choices affect the obtained results. We focus on calculating the strain dependent vorticity, as this metric is a differential method hence potentially sensitive to the way it is computed. We find that the total surface area with an absolute vorticity above a certain threshold approaches a plateau value as shear progresses. This plateau value exhibits a non-monotonic dependence on packing fraction. We also show which range of choices yields results that can support an analysis method independent, physical interpretation of the flow field data.

Small Horizontal Axis Wind Turbine: Analytical Blade Design and Comparison With RANS-Prediction and First Experimental Data

2013 ◽  
Author(s):  
Tom Gerhard ◽  
Michael Sturm ◽  
Thomas H. Carolus
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Wind Turbine ◽  
Horizontal Axis ◽  
Analytical Models ◽  
Power Coefficient ◽  
Analysis Tool ◽  
Computational Domain ◽  
Horizontal Axis Wind Turbine ◽  
Data Set

State-of-the-art wind turbine performance prediction is mainly based on semi-analytical models, incorporating blade element momentum (BEM) analysis and empirical models. Full numerical simulation methods can yield the performance of a wind turbine without empirical assumptions. Inherent difficulties are the large computational domain required to capture all effects of the unbounded ambient flow field and the fact that the boundary layer on the blade may be transitional. A modified turbine design method in terms of the velocity triangles, Euler’s turbine equation and BEM is developed. Lift and drag coefficients are obtained from XFOIL, an open source 2D design and analysis tool for subcritical airfoils. A 3 m diameter horizontal axis wind turbine rotor was designed and manufactured. The flow field is predicted by means of a Reynolds-averaged Navier-Stokes simulation. Two turbulence models were utilized: (i) a standard k-ω-SST model, (ii) a laminar/turbulent transition model. The manufactured turbine is placed on the rooftop of the University of Siegen. Three wind anemometers and wind direction sensors are arranged around the turbine. The torque is derived from electric power and the rotational speed via a calibrated grid-connected generator. The agreement between the analytically and CFD-predicted kinematic quantities up- and downstream of the rotor disc is quite satisfactory. However, the blade section drag to lift ratio and hence the power coefficient vary with the turbulence model chosen. Moreover, the experimentally determined power coefficient is considerably lower as predicted by all methods. However, this conclusion is somewhat preliminary since the existing experimental data set needs to be extended.

scholarly journals Trends of tropical tropospheric ozone from 20 years of European satellite measurements and perspectives for the Sentinel-5 Precursor

2016 ◽  
Vol 9 (10) ◽  
pp. 5037-5051 ◽  
Author(s):  
Klaus-Peter Heue ◽  
Melanie Coldewey-Egbers ◽  
Andy Delcloo ◽  
Christophe Lerot ◽  
Diego Loyola ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Total Ozone ◽  
Atlantic Coast ◽  
Convective Cloud ◽  
Differential Method ◽  
Retrieval Algorithm ◽  
Data Set ◽  
Cloud Data ◽  
The Individual ◽  
Column Ozone

Abstract. In preparation of the TROPOMI/S5P launch in early 2017, a tropospheric ozone retrieval based on the convective cloud differential method was developed. For intensive tests we applied the algorithm to the total ozone columns and cloud data of the satellite instruments GOME, SCIAMACHY, OMI, GOME-2A and GOME-2B. Thereby a time series of 20 years (1995–2015) of tropospheric column ozone was generated. To have a consistent total ozone data set for all sensors, one common retrieval algorithm, namely GODFITv3, was applied and the L1 reflectances were also soft calibrated. The total ozone columns and the cloud data were input into the tropospheric ozone retrieval. However, the tropical tropospheric column ozone (TCO) for the individual instruments still showed small differences and, therefore, we harmonised the data set. For this purpose, a multilinear function was fitted to the averaged difference between SCIAMACHY's TCO and those from the other sensors. The original TCO was corrected by the fitted offset. GOME-2B data were corrected relative to the harmonised data from OMI and GOME-2A. The harmonisation leads to a better agreement between the different instruments. Also, a direct comparison of the TCO in the overlapping periods proves that GOME-2A agrees much better with SCIAMACHY after the harmonisation. The improvements for OMI were small. Based on the harmonised observations, we created a merged data product, containing the TCO from July 1995 to December 2015. A first application of this 20-year record is a trend analysis. The tropical trend is 0.7 ± 0.12 DU decade−1. Regionally the trends reach up to 1.8 DU decade−1 like on the African Atlantic coast, while over the western Pacific the tropospheric ozone declined over the last 20 years with up to 0.8 DU decade−1. The tropical tropospheric data record will be extended in the future with the TROPOMI/S5P data, where the TCO is part of the operational products.

Discrete Models for Particle Packings

1992 ◽  
Vol 278 ◽  
Author(s):  
A. Jagota ◽  
E.I. Dupont
Keyword(s):  
Particle Motion ◽  
Computational Models ◽  
Effective Conductivity ◽  
Packing Fraction ◽  
Random Packing ◽  
Simultaneous Equations ◽  
Discrete Models ◽  
Particle Center ◽  
Net Flux ◽  
Particle Packings

AbstractDiscrete computational models for the viscosities, sintering rates, and transport properties of sintering particle packings are presented. The packing is represented by a set of nodes (the particle centroids) connected by links (inter-particle contacts). The models for the mechanical behavior enforce equilibrium for each particle which leads to a set of simultaneous equations for the particle motion. Electrical or thermal transport through inter-particle contacts is modelled by imposing zero net flux at a node which also leads to a set of simultaneous equations for the value of potential at each particle center. The model is used to simulate the compaction of spheres to generate a threedimensional random packing. Statistical properties of the computed packing such as packing fraction, percolation threshold, and coordination number are compared with those of an experimental random packing. Results are also presented for the effective conductivity of mixtures of particles with very different conductivities.

Midspan Flow-Field Measurements for Two Transonic Linear Turbine Cascades at Off-Design Conditions

2001 ◽  
Author(s):  
D. B. M. Jouini ◽  
S. A. Sjolander ◽  
S. H. Moustapha
Keyword(s):  
Flow Field ◽  
Turbine Blade ◽  
Density Ratio ◽  
Leading Edge ◽  
Field Measurements ◽  
Reynolds Numbers ◽  
Experimental Results ◽  
Tabular Form ◽  
Data Set ◽  
Turbine Cascades

The paper presents detailed mid-span experimental results from two transonic linear turbine cascades. The blades for the two cascades were designed for the same service and differ mainly in their leading-edge geometries. One of the goals of the study was investigate the influence of the leading-edge metal angle on the sensitivity of the blade to positive off-design incidence. Measurements were made for incidence values of −10.0°, 0.0°, +4.5°, +10.0°, and +14.5° relative to design incidence. The exit Mach numbers varied roughly from 0.5 to 1.2 and the Reynolds numbers from about 4×105 to 106. The measurements include the midspan losses, blade loadings and base pressures. In addition, the axial-velocity-density ratio (AVDR) was extracted for each operating point The AVDR was found to vary from about 0.98 at −10.0° of incidence to about 1.27 at +14.5°. Thus, the data set also provides some evidence of the influence AVDR on axial turbine blade performance. Detailed experimental results for turbine blade performance at off-design incidence are very scarce in the open literature, particularly for transonic conditions. Among other things, the present results are intended to expand the database available in the open literature. To this end, the key aerodynamic results are presented in tabular form, along with the detailed geometry of the cascades. The results could be used in the development of new or improved correlations for use in the early stages of design. They could also be used to evaluate the ability of current CFD codes to capture reliably the variation in losses and other aerodynamic quantities with variations in blade incidence.

Effect of Rotating Speed on Performance of Electrical Submersible Pump

2019 ◽  
Author(s):  
Yang Yang ◽  
Ling Zhou ◽  
Weidong Shi ◽  
Chuan Wang ◽  
Wei Li ◽  
...  
Keyword(s):  
Flow Field ◽  
Current Trend ◽  
Performance Testing ◽  
Flow Fields ◽  
Computational Domain ◽  
Submersible Pump ◽  
Data Set ◽  
Rotating Speed ◽  
Compact Size ◽  
Electrical Submersible Pump

Abstract High speed rotating pump is the current trend in pump’s development and application, which has the advantages of compact size and energy-saving features. The electrical submersible pump, typically called an ESP, is an efficient and reliable artificial-lift method for lifting moderate to high volumes of fluids from wellbores, which have been wildly used for oil or groundwater extraction. To verify the similarity of pump performance under different rotating speeds, a typical ESP is selected as the model pump. By employing the numerical simulation and performance testing methods, the external performance characteristics and internal flow fields under different rotating speeds of the pump are studied. The entire computational domain is established by two stages ESP, and then meshed with the high-quality structured grid based on the Q-type and Y-type block topology. Grid sensitivity analysis is carried out to determine the appropriate mesh density for mesh independent solution. SST k-ω turbulence model with standard wall function in conjunction with Reynolds-Averaged Navier-Stokes (RANS) equations is used to solve the steady flow field. The results show that the increase in the rotating speed could increase the ESP’s head significantly. ESP’s external characteristics under different speeds meet the similar conversion rule quite well. In addition, the flow field distributions in the main flow components of the pump have great similarity at different rotating speeds. The experimental test results for a prototype show good agreement with the simulation results, including the pump’s head, efficiency and axial force. This paper provides a data set for further understanding of the effects of rotating speeds on ESP’s performance and inner flow fields.

Deformation Mechanisms of Auxetic Microstructures for Energy Absorption Applications

2016 ◽  
Vol 821 ◽  
pp. 428-434
Author(s):  
Petr Koudelka ◽  
Michaela Neuhauserova ◽  
Tomáš Fíla ◽  
Daniel Kytýř
Keyword(s):  
True Strain ◽  
Deformation Energy ◽  
Image Correlation ◽  
Parametric Modelling ◽  
Two Dimensional ◽  
Displacement Fields ◽  
Static Compression ◽  
Full Field ◽  
Strain Dependent ◽  
Quasi Static Compression

In this work parametric modelling was utilized to design and produce two types of porous microarchitectures with auxetic compressive properties suitable for deformation energy mitigation applications such as blast and bullet protection. The samples were directly produced from acrylic material using a high resolution 3D printer and their compressive mechanical characteristics were tested. Two different structures exhibiting in-plane negative strain dependent Poisson’s ratio were selected for the analysis: i) two-dimensional inverted (re-entrant) honeycomb and ii) two-dimensional cut missing-rib. Stress-strain relationships were established from a set of quasi-static compression experiments where the strain fields were evaluated using digital image correlation applied to measure the full-field displacements on the samples' surface. From the displacement fields true strain – true stress curves were derived for each sample and relative elastic moduli were evaluated.

scholarly journals Is Synthetic The New Real? Performance Analysis of Time Series Generation Techniques with Focus on Network Load Forecasting

2021 ◽  
Author(s):  
Muhammad Haris Naveed ◽  
Umair Hashmi ◽  
Nayab Tajved ◽  
Neha Sultan ◽  
Ali Imran
Keyword(s):  
Synthetic Data ◽  
Real Data ◽  
Generative Adversarial Networks ◽  
Data Set ◽  
Qualitative And Quantitative ◽  
Adversarial Networks ◽  
Network Load ◽  
Quantitative Metrics ◽  
Real Performance ◽  
Analysis Of Time Series

This paper explores whether Generative Adversarial Networks (GANs) can produce realistic network load data that can be utilized to train machine learning models in lieu of real data. In this regard, we evaluate the performance of three recent GAN architectures on the Telecom Italia data set across a set of qualitative and quantitative metrics. Our results show that GAN generated synthetic data is indeed similar to real data and forecasting models trained on this data achieve similar performance to those trained on real data.

scholarly journals Effect of the coefficient of restitution and friction in the granular Leidenfrost effect in the absence of gravity. A numerical study

2021 ◽  
Vol 249 ◽  
pp. 14016
Author(s):  
Daniel Schiochet Nasato ◽  
Heiko Briesen
Keyword(s):  
Coefficient Of Friction ◽  
Parametric Study ◽  
Granular Media ◽  
Numerical Study ◽  
Packing Fraction ◽  
Coefficient Of Restitution ◽  
Granular System ◽  
The Coefficient Of Friction ◽  
Leidenfrost Effect ◽  
Microgravity Conditions

In this study the granular Leidenfrost effect in the absence of gravity is investigated numerically by means of the discrete element method. Apart from identifying the phenomena, a parametric study to quantify the influence of the coefficient of restitution and friction in the packing fraction of the granular media is carried on numerically. Surprisingly, both the coefficient of restitution and the coefficient of friction exhibit an influence of the same magnitude in the packing fraction of the granular system, which has not been reported in experiments and simulation of granular Leidenfrost regime under gravity or microgravity conditions.

scholarly journals Trends of tropical tropospheric ozone from twenty years of European satellite measurements and perspectives for Sentinel-5 Precursor

2016 ◽  
Author(s):  
Klaus-Peter Heue ◽  
Melanie Coldewey-Egbers ◽  
Andy Delcloo ◽  
Christophe Lerot ◽  
Diego Loyola ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Total Ozone ◽  
Atlantic Coast ◽  
Convective Cloud ◽  
Differential Method ◽  
Retrieval Algorithm ◽  
Data Set ◽  
Cloud Data ◽  
One Year ◽  
The Individual

Abstract. In preparation of the TROPOMI/S5P launch in autumn 2016 a tropospheric ozone retrieval based on the convective cloud differential method was developed. For intensive tests we applied the algorithm to the total ozone columns and cloud data of the satellites GOME, SCIAMACHY, OMI, GOME-2A and GOME-2B. Thereby a time series of 20 years (1995–2015) of tropospheric ozone columns was retrieved. To have a consistent total ozone data set for all sensors one common retrieval algorithm, namely GODFITv3, has been applied to all sensors and the L1 reflectances have also been soft calibrated. These data were input into the tropospheric ozone retrieval. However, the Tropical Tropospheric Ozone Columns (TTOC) for the individual instruments still showed small differences and therefore we harmonised the data set. For this purpose a multi-variant function was fitted to the averaged difference between SCIAMACHY's TTOC and those from the other sensors. The original TTOC was corrected by the fitted offset. GOME-2B data were corrected relative to the harmonised data from OMI and GOME-2A. The harmonisation leads to a better agreement between the different instruments. Also a direct comparison of the TTOCs in the overlapping periods proves that GOME-2A agrees much better with SCIAMACHY after the harmonisation. The improvements for OMI were small. The GOME and SCIAMACHY data overlap for one year for the complete tropics, this turned out to be insufficient to extrapolate back until 1995. Based on the harmonised observations, we created a merged data product, containing the TTOC from July 1995 to Dec. 2015. A first application of this 20 years record is a trend analysis. The global tropical trend is 0.75 ± 0.12 DU decade−1. Regionally the trends reaches up to 1.8 DU decade−1 like on the African Atlantic coast, over the Western Pacific the tropospheric ozone declined over the last 20 years with up to 0.8 DU decade−1. The tropical tropospheric data record will be extended in the future with the TROPOMI/S5P data, where the TTOC is part of the operational products.

Effects of Outlier Flow Field on the Characteristics of In-Cylinder Coherent Structures Identified by POD-Based Conditional Averaging and Quadruple POD

2018 ◽  
Author(s):  
Rui Gao ◽  
Li Shen ◽  
Kwee-Yan Teh ◽  
Penghui Ge ◽  
Fengnian Zhao ◽  
...  
Keyword(s):  
Flow Field ◽  
Coherent Structures ◽  
Large Scale ◽  
Flow Fields ◽  
High Energy ◽  
Data Set ◽  
Engine Cylinder ◽  
Conditional Averaging ◽  
Engine Cycle ◽  
Low Order

Proper Orthogonal Decomposition (POD) offers an approach to quantify cycle-to-cycle variation (CCV) of the flow field inside the internal combustion engine cylinder. POD decomposes instantaneous flow fields (also called snapshots) into a series of orthonormal flow patterns (called POD modes) and the corresponding mode coefficients. The POD modes are rank-ordered by decreasing kinetic energy content, and the low-order, high-energy modes are interpreted as constituting the large-scale coherent flow structure that varies from engine cycle to engine cycle. Various POD-based analysis techniques have thus been proposed to characterize engine flow field CCV using these low-order modes. The validity of such POD-based analyses rests, as a matter of course, on the reliability of the underlying POD results (modes and coefficients). Yet a POD mode can be disproportionately skewed by a single outlier snapshot within a large data set, and an algorithm exists to define and identify such outliers. In this paper, the effects of a candidate outlier snapshot on the results of POD-based conditional averaging and quadruple POD analyses are examined for two sets of crank angle-resolved flow fields on the mid-tumble plane of an optical engine cylinder recorded by high-speed particle image velocimetry. The results with and without the candidate outlier are compared and contrasted. In the case of POD-based conditional averaging, the presence of the outlier scrambles the composition of snapshot subsets that define large-scale flow pattern variations, and thus substantially alters the coherent flow structures that are identified; for quadruple POD, the shape of coherent structures as well as the number of modes to define them are not significantly affected by the outlier.

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