scholarly journals Modelling multiple-simultaneous impact problems with a nonlinear smooth approach: pool/billiard application

2021 ◽  
Author(s):  
Raúl Gismeros Moreno ◽  
Eduardo Corral Abad ◽  
Jesús Meneses Alonso ◽  
María Jesús Gómez García ◽  
Cristina Castejón Sisamón
Keyword(s):  
Computational Cost ◽  
Nonlinear Behaviour ◽  
Friction Forces ◽  
Distinctive Features ◽  
Simultaneous Impact ◽  
Smooth Contact ◽  
Impact Problems ◽  
Multiple Impact ◽  
Impact Events

AbstractSmooth approaches are able to model reasonably well contact/impact events between two bodies, showing some peculiarities when dealing with certain geometries and arising certain issues with the detection of the initial instant of contact. The characterization of multiple-simultaneous interaction systems, considering (or not) energy dissipation phenomena (mainly friction), is always an interesting research topic, addressed from different perspectives. In the present work, the process of design, optimization and verification of a multiple-impact, day-to-day multibody novel model is shown. Specifically, we have decided to focus on a pool/billiard game due to its geometry simplicity. The model involves several balls moving freely and rolling, suffering different kinds of contacts/impacts among them and against the cushions and the cloth. In this system, the proper modelling of both contact and friction forces in the multiple, simultaneous contacts and impacts events is critical to obtain consistent results. In addition, these forces are complicated to model because of its nonlinear behaviour. The different existing approaches when dealing with multiple-contact events are briefly described, along with their most distinctive features. Then, the interactions identified on the model are implemented using several nonlinear contact-force models, following a smooth-based approach and considering friction phenomena, aiming at determining the most suitable set of both contact and friction force models for each of these implemented interactions, which take place simultaneously, thus resulting in a complex system with multiple impacts. Subsequently, the solving method that provides the most accurate results at the minimum computational cost is determined by testing a simple shot. Finally, the different interactions on the model are verified using experimental results and previous works. One of the main goals of this work is to show the some of the issues that arise when dealing with multiple-simultaneous impact multibody systems from a smooth-contact approach, and how researchers can deal with them.

Gender Diversity in the Senior Management of Large Technology Companies

2022 ◽  
pp. 1945-1962
Author(s):  
Yakira Fernández-Torres ◽  
Ricardo Javier Palomo-Zurdo ◽  
Milagros Gutiérrez-Fernández
Keyword(s):  
Corporate Governance ◽  
Boards Of Directors ◽  
Business Performance ◽  
Industrial Revolution ◽  
Gender Diversity ◽  
Female Representation ◽  
Distinctive Features ◽  
Representation Of Women ◽  
The Relationship

As a key part of the fourth industrial revolution, technology companies have become the most valuable companies in the world in terms of market capitalization. Surprisingly, however, these companies have been overlooked by studies of gender diversity in corporate governance even though their highly distinctive features may cause major differences in gender diversity with respect to companies in other sectors. The goal of this chapter is therefore to provide the first characterization of gender diversity in the corporate governance of large technology companies—specifically those with the highest market value—and explore the relationship between gender diversity and business performance. To achieve this goal, descriptive statistical analysis is used. Data correspond to the period 2005 to 2017. The findings confirm the under-representation of women on the boards of directors of 162 publicly listed companies. The findings also show that the most profitable companies are those that have the greatest female representation on their boards of directors.

Flutter Amplitude Saturation by Nonlinear Friction Forces: Reduced Model Verification

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
Carlos Martel ◽  
Roque Corral ◽  
Rahul Ivaturi
Keyword(s):  
Oscillation Amplitude ◽  
Computational Cost ◽  
Model Verification ◽  
Reduced Model ◽  
Limit Cycle Oscillation ◽  
Nonlinear Friction ◽  
Disk Model ◽  
Friction Forces ◽  
Elastic Oscillation ◽  
Bladed Disk

The computation of the final, friction saturated limit cycle oscillation amplitude of an aerodynamically unstable bladed-disk in a realistic configuration is a formidable numerical task. In spite of the large numerical cost and complexity of the simulations, the output of the system is not that complex: it typically consists of an aeroelastically unstable traveling wave (TW), which oscillates at the elastic modal frequency and exhibits a modulation in a much longer time scale. This slow time modulation over the purely elastic oscillation is due to both the small aerodynamic effects and the small nonlinear friction forces. The correct computation of these two small effects is crucial to determine the final amplitude of the flutter vibration, which basically results from its balance. In this work, we apply asymptotic techniques to consistently derive, from a bladed-disk model, a reduced order model that gives only the time evolution on the slow modulation, filtering out the fast elastic oscillation. This reduced model is numerically integrated with very low computational cost, and we quantitatively compare its results with those from the bladed-disk model. The analysis of the friction saturation of the flutter instability also allows us to conclude that: (i) the final states are always nonlinearly saturated TW; (ii) depending on the initial conditions, there are several different nonlinear TWs that can end up being a final state; and (iii) the possible final TWs are only the more flutter prone ones.

scholarly journals Identification and Characterization of a nodH Ortholog from the Alfalfa-Nodulating Or191-Like Rhizobia

2007 ◽  
Vol 20 (2) ◽  
pp. 138-145 ◽  
Author(s):  
M. F. Del Papa ◽  
M. Pistorio ◽  
W. O. Draghi ◽  
M. J. Lozano ◽  
M. A. Giusti ◽  
...  
Keyword(s):  
Sinorhizobium Meliloti ◽  
Single Copy ◽  
Nod Factors ◽  
Distinctive Features ◽  
Genetic Mosaic ◽  
Strict Requirement ◽  
Identification And Characterization ◽  
Local Synteny ◽  
Marked Specificity

Nodulation of Medicago sativa (alfalfa) is known to be restricted to Sinorhizobium meliloti and a few other rhizobia that include the poorly characterized isolates related to Rhizobium sp. strain Or191. Distinctive features of the symbiosis between alfalfa and S. meliloti are the marked specificity from the plant to the bacteria and the strict requirement for the presence of sulfated lipochitooligosac-charides (Nod factors [NFs]) at its reducing end. Here, we present evidence of the presence of a functional nodH-encoded NF sulfotransferase in the Or191-like rhizobia. The nodH gene, present in single copy, maps to a high molecular weight megaplasmid. As in S. meliloti, a nodF homolog was identified immediately upstream of nodH that was transcribed in the opposite direction (local synteny). This novel nodH ortholog was cloned and shown to restore both NF sulfation and the Nif+Fix+ phenotypes when introduced into an S. meliloti nodH mutant. Unexpectedly, however, nodH disruption in the Or191-like bacteria did not abolish their ability to nodulate alfalfa, resulting instead in a severely delayed nodulation. In agreement with evidence from other authors, the nodH sequence analysis strongly supports the idea that the Or191-like rhizobia most likely represent a genetic mosaic resulting from the horizontal transfer of symbiotic genes from a sinorhizobial megaplas-mid to a not yet clearly identified ancestor.

Multiscale mechanical characterization of biomimetic physically associating gels

2006 ◽  
Vol 21 (8) ◽  
pp. 2084-2092 ◽  
Author(s):  
Thomas F. Juliano ◽  
Aaron M. Forster ◽  
Peter L. Drzal ◽  
Tusit Weerasooriya ◽  
Paul Moy ◽  
...  
Keyword(s):  
Triblock Copolymer ◽  
Injury Risk ◽  
Mechanical Response ◽  
Measurement Techniques ◽  
Synthetic Materials ◽  
Copolymer Gels ◽  
Ballistic Gelatin ◽  
Stress States ◽  
Impact Events

The mechanical response of living tissue is important to understanding the injury-risk associated with impact events. Often, ballistic gelatin or synthetic materials are developed to serve as tissue surrogates in mechanical testing. Unfortunately, current materials are not optimal and present several experimental challenges. Bulk measurement techniques, such as compression and shear testing geometries, do not fully represent the stress states and rate of loading experienced in an actual impact event. Indentation testing induces deviatoric stress states as well as strain rates not typically available to bulk measurement equipment. In this work, a ballistic gelatin and two styrene-isoprene triblock copolymer gels are tested and compared using both macroscale and microscale measurements. A methodology is presented to conduct instrumented indentation experiments on materials with a modulus far below 1 MPa. The synthetic triblock copolymer gels were much easier to test than the ballistic gelatin. Compared to ballistic gelatin, both copolymer gels were found to have a greater degree of thermal stability. All of the materials exhibit strain-rate dependence, although the magnitude of dependence was a function of the loading rate and testing method.

scholarly journals Characterization of Hydraulic Power in Free-Stream Installations

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Olivier Cleynen ◽  
Stefan Hoerner ◽  
Dominique Thévenin
Keyword(s):  
Open Channel ◽  
Flow Model ◽  
Computational Cost ◽  
Characteristic Parameter ◽  
Operating Speed ◽  
Improve Performance ◽  
Hydraulic Power ◽  
One Dimensional ◽  
Low Computational Cost

The performance of open-channel hydropower devices can be optimized by maximizing the product of their load, hydraulic, and generator efficiencies. The maximum hydraulic power theoretically available must be defined according to the operational scenario retained for the device of interest. In the case of a device operating within a wide, unobstructed channel, the existence of a maximum hydraulic power and the operating speed required to reach it are first predicted using a one-dimensional flow model. This model is then extended to account for the effect of device ducting. As a result, given the available surface level drop and a single duct characteristic parameter, the model predicts the optimum device operating speed, whether the duct can improve performance, and the relative duct size which maximizes the installation’s power density, all at a very low computational cost.

scholarly journals Speeding Up Discovery of Auxetic Zeolite Frameworks by Machine Learning

2020 ◽  
Author(s):  
Romain Gaillac ◽  
Siwar Chibani ◽  
François-Xavier Coudert
Keyword(s):  
Machine Learning ◽  
Mechanical Properties ◽  
Dft Calculations ◽  
Force Field ◽  
Computational Cost ◽  
Training Data ◽  
Elastic Response ◽  
Data Set ◽  
Classical Level

<div> <div> <div> <p>The characterization of the mechanical properties of crystalline materials is nowadays considered a routine computational task in DFT calculations. However, its high computational cost still prevents it from being used in high-throughput screening methodologies, where a cheaper estimate of the elastic properties of a material is required. In this work, we have investigated the accuracy of force field calculations for the prediction of mechanical properties, and in particular for the characterization of the directional Poisson’s ratio. We analyze the behavior of about 600,000 hypothetical zeolitic structures at the classical level (a scale three orders of magnitude larger than previous studies), to highlight generic trends between mechanical properties and energetic stability. By comparing these results with DFT calculations on 991 zeolitic frameworks, we highlight the limitations of force field predictions, in particular for predicting auxeticity. We then used this reference DFT data as a training set for a machine learning algorithm, showing that it offers a way to build fast and reliable predictive models for anisotropic properties. The accuracies obtained are, in particular, much better than the current “cheap” approach for screening, which is the use of force fields. These results are a significant improvement over the previous work, due to the more difficult nature of the properties studied, namely the anisotropic elastic response. It is also the first time such a large training data set is used for zeolitic materials. </p></div></div></div><div><div><div> </div> </div> </div>

scholarly journals Speeding Up Discovery of Auxetic Zeolite Frameworks by Machine Learning

2020 ◽  
Author(s):  
Romain Gaillac ◽  
Siwar Chibani ◽  
François-Xavier Coudert
Keyword(s):  
Machine Learning ◽  
Mechanical Properties ◽  
Dft Calculations ◽  
Force Field ◽  
Computational Cost ◽  
Training Data ◽  
Elastic Response ◽  
Data Set ◽  
Classical Level

<div> <div> <div> <p>The characterization of the mechanical properties of crystalline materials is nowadays considered a routine computational task in DFT calculations. However, its high computational cost still prevents it from being used in high-throughput screening methodologies, where a cheaper estimate of the elastic properties of a material is required. In this work, we have investigated the accuracy of force field calculations for the prediction of mechanical properties, and in particular for the characterization of the directional Poisson’s ratio. We analyze the behavior of about 600,000 hypothetical zeolitic structures at the classical level (a scale three orders of magnitude larger than previous studies), to highlight generic trends between mechanical properties and energetic stability. By comparing these results with DFT calculations on 991 zeolitic frameworks, we highlight the limitations of force field predictions, in particular for predicting auxeticity. We then used this reference DFT data as a training set for a machine learning algorithm, showing that it offers a way to build fast and reliable predictive models for anisotropic properties. The accuracies obtained are, in particular, much better than the current “cheap” approach for screening, which is the use of force fields. These results are a significant improvement over the previous work, due to the more difficult nature of the properties studied, namely the anisotropic elastic response. It is also the first time such a large training data set is used for zeolitic materials. </p></div></div></div><div><div><div> </div> </div> </div>

Floor Reliability With Respect to “Slip and Fall”

2005 ◽  
Author(s):  
Ralph Lipsey Barnett ◽  
Peter Joseph Poczynok
Keyword(s):  
Force Plate ◽  
Frictional Resistance ◽  
Reliability Theory ◽  
Extreme Value Statistics ◽  
Horizontal Resistance ◽  
Friction Forces ◽  
Statistical Characterization ◽  
Friction Resistance ◽  
First Time

For a given community of walkers and a specific type of ambulation, force-plate studies have established the required level of horizontal resistance for stable locomotion. This stochastic floor loading is resisted by friction forces which must be great enough to prevent slipping. A statistical characterization of frictional resistance has recently been developed using extreme value statistics. Reliability theory provides a method for combining the floor loading and friction resistance which, for the first time, enables one to determine in a rational manner the probability of slipping. This paper presents a formula describing the “slip and fall” reliability of a floor/footwear couple.

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