scholarly journals Comparative Analysis of Different Tube Models for Linear Rheology of Monodisperse Linear Entangled Polymers

Polymers ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 754 ◽  
Author(s):  
Volha Shchetnikava ◽  
Johan Slot ◽  
Evelyne van Ruymbeke
Keyword(s):  
Experimental Data ◽  
Comparative Analysis ◽  
Hierarchical Model ◽  
Linear Viscoelasticity ◽  
Star Polymers ◽  
Contour Length ◽  
Large Set ◽  
Linear Polymers ◽  
Entangled Polymers ◽  
Constraint Release

The aim of the present paper is to analyse the differences between tube-based models which are widely used for predicting the linear viscoelasticity of monodisperse linear polymers, in comparison to a large set of experimental data. The following models are examined: Milner–McLeish, Likhtman–McLeish, the Hierarchical model proposed by the group of Larson, the BoB model of Das and Read, and the TMA model proposed by the group of van Ruymbeke. This comparison allows us to highlight and discuss important questions related to the relaxation of entangled polymers, such as the importance of the contour-length fluctuations (CLF) process and how it affects the reptation mechanism, or the contribution of the constraint release (CR) process on the motion of the chains. In particular, it allows us to point out important approximations, inherent in some models, which result in an overestimation of the effect of CLF on the reptation time. On the contrary, by validating the TMA model against experimental data, we show that this effect is underestimated in TMA. Therefore, in order to obtain accurate predictions, a novel modification to the TMA model is proposed. Our current work is a continuation of earlier research (Shchetnikava et al., 2014), where a similar analysis is performed on well-defined star polymers.

Modeling the Rheology of Commercial Long Chain Branched Polymer Melts

2003 ◽  
Vol 804 ◽  
Author(s):  
Seung Joon Park ◽  
Ronald G. Larson
Keyword(s):  
Experimental Data ◽  
Hierarchical Model ◽  
Polymer Melts ◽  
Quantitative Agreement ◽  
Branched Polymers ◽  
Linear Polymers ◽  
Branched Polymer ◽  
Long Chain Branching ◽  
Wide Range ◽  
Long Chain

ABSTRACTThe predictions of a general “hierarchical model” for the rheology of general mixtures of linear and branched polymers are compared to experimental data for well-defined long-chain branched polymers. For a wide range of branched polymer melts, which include star-linear blends, H-polymers, and comb polymers, the predictions of the model agree well with experimental data. We apply the hierarchical model to metallocene-catalyzed polyethylenes (mPEs), in which the branched structures are generated by a Monte Carlo method based on the known reaction kinetics. The hierarchical model captures the shape of the curves of viscoelastic moduli vs. frequency of mPEs well and predicts accurately the effect of long chain branching on the linear viscoelastic properties. The quantitative agreement of the hierarchical model prediction with experimental data of well-defined long-chain branched polymers and mPEs shows that information on branching structure could be inferred from rheological measurements on combinatorial sets of mixtures of an unknown branched with different combinations of linear polymers.

Comparative analysis and verification of engineering methods of shallow cracks effect for fracture toughness prediction for reactor pressure vessels

2020 ◽  
pp. 140-165
Author(s):  
V. I. Kostylev ◽  
B. Z. Margolin
Keyword(s):  
Experimental Data ◽  
Fracture Toughness ◽  
Comparative Analysis ◽  
Nuclear Reactor ◽  
Probabilistic Approach ◽  
Pressure Vessels ◽  
Local Methods ◽  
European Method ◽  
Shallow Crack ◽  
Reactor Pressure

The main features of shallow cracks fracture are considered, and a brief analysis of methods allowing to predict the temperature dependence of the fracture toughness KJC (T) for specimens with shallow cracks is given. These methods include DA-method, (JQ)-method, (J-T)-method, “local methods” with its multiparameter probabilistic approach, GP method uses power approach, and also two engineering methods – RMSC (Russian Method for Shallow Crack) and EMSC (European Method for Shallow Crack). On the basis of 13 sets of experimental data for national and foreign steels, a detailed verification and comparative analysis of these two engineering methods were carried out on the materials of the VVER and PWR nuclear reactor vessels considering the effect of shallow cracks.

Control and measuring modernization systems of the “Soil Channel” stand and the development of a wheel motion mathematical model in stand conditions

Trudy NAMI ◽  
2021 ◽  
pp. 25-34
Author(s):  
B. B. Kositsyn ◽  
Kh. Chzhen ◽  
R. L. Gazizullin
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Thrust Force ◽  
Bench Test ◽  
Large Set ◽  
Virtual Experiments ◽  
Automatic Mode ◽  
Wheel Rolling ◽  
Adaptive Laws ◽  
Stand Conditions

Introduction (problem statement and relevance). A promising direction for reducing a vehicle moving energy is the application of adaptive laws for controlling the power supplied to the propeller based on neural networks. To create a training array of the latter, a large set of experimental data is required, the collection of which, as a rule, is carried out by using research stands, such as the “Soil Channel”. But the fi eld studies require a lot of resources.The purpose of the study was to create a wheel rolling mathematical model in the conditions of the stand, with the help of which it would be possible to organize the collection of needed statistical data on the wheel rolling modes by calculation them in an automatic mode.Methodology and research methods. The paper describes the “Soil Channel” bench test, held by the Department of “Multipurpose tracked vehicles and mobile robots” of Bauman Moscow State Technical University. A list of the control and measuring systems components used in the process of its modernization in order to automate the collection of experimental data was considered. The “Soil Channel” stand mathematical model was presented which was based on the use of experimentally obtained dependences of the specifi c longitudinal thrust force on sliding and the specifi c longitudinal thrust force on the specifi c circumferential force.Scientifi c novelty and results. The developed mathematical model has been verifi ed on the basis of the data obtained in the course of fi eld studies. Conclusions were made about the suitability of the developed mathematical model of wheel motion under the stand conditions for conducting virtual experiments.Practical signifi cance. The data obtained by applying the developed mathematical model can be used to create a training array of a neural network to provide the implementation of adaptive laws for controlling the power supplied to the propeller.

scholarly journals Comparative analysis of methods to determine deflection in steel beams: theoretical analysis, finite element and experimental

2020 ◽  
pp. 32-37
Author(s):  
Gabriela Alor-Saavedra ◽  
Francisco Alejandro Alaffita-Hernández ◽  
Beatris Adriana Escobedo-Trujillo ◽  
Oscar Fernando Silva-Aguilar
Keyword(s):  
Differential Equation ◽  
Experimental Data ◽  
Finite Element ◽  
Comparative Analysis ◽  
Theoretical Analysis ◽  
Comparative Study ◽  
Steel Beams ◽  
Physical Systems ◽  
Theoretical Part ◽  
Made In

This work makes a comparative study of two methods to determine deflection in steel beams: (a) Theoretical and (b) Finite element. For method (a) the solution of the differential equation associated with the modeling of the deflection of a beam is found, while for method (b) a simulation is made in Solidworks. Both methods are compared with experimental data in order to analyze which of the methods presents less uncertainty and show the usefulness of the theoretical part in the modeling of physical systems.

scholarly journals Approximate Analytical Models of Shock-Wave Structure at Steady Mach Reflection

Fluids ◽  
2021 ◽  
Vol 6 (9) ◽  
pp. 305
Author(s):  
Mikhail V. Chernyshov ◽  
Karina E. Savelova ◽  
Anna S. Kapralova
Keyword(s):  
Experimental Data ◽  
Shock Wave ◽  
Comparative Analysis ◽  
Analytical Model ◽  
Mach Reflection ◽  
Supersonic Jet ◽  
Wave Structure ◽  
Analytical Models ◽  
Analytical Prediction ◽  
Shock Wave Structure

In this study, we obtain the comparative analysis of methods of quick approximate analytical prediction of Mach shock height in planar steady supersonic flows (for example, in supersonic jet flow and in narrowing channel between two wedges), that are developed since the 1980s and being actively modernized now. A new analytical model based on flow averaging downstream curved Mach shock is proposed, which seems more accurate than preceding models, comparing with numerical and experimental data.

scholarly journals Differential and integral cross sections for electron elastic scattering by ammonia for incident energies ranging from 10 eV to 20 keV

2018 ◽  
Vol 64 (5) ◽  
pp. 498
Author(s):  
Hocine Aouchiche
Keyword(s):  
Experimental Data ◽  
Elastic Scattering ◽  
Cross Sections ◽  
Optical Potential ◽  
Large Set ◽  
Quantum Calculation ◽  
Hartree Fock ◽  
Spherical Complex ◽  
Static Part ◽  
Model Point

Differential and integral cross sections for elastic scattering of electron by NH3 molecule are investigated for the energy ranging from 10 eV to 20 keV.  The calculations are carried out in the framework of partial wave formalism describing the target molecule by means of one center molecular Hartree-Fock functions.  A spherical complex optical potential used includes a static part – obtained here numerically from quantum calculation – and fine effects like correlation, polarization and exchange potentials. The results obtained in this model point out clearly the role played by the exchange and the correlation-polarization contributions in particular at lower scattering angles and lower incident energies. Both differential and integral cross sections obtained are compared with a large set of experimental data available in the literature and well agreement is found throughout the scattering angles and whole energy range investigated here.

scholarly journals Static stability predicts the continuum of interleg coordination patterns in Drosophila

2018 ◽  
Author(s):  
Nicholas S. Szczecinski ◽  
Till Bockemühl ◽  
Alexander S. Chockley ◽  
Ansgar Büschges
Keyword(s):  
Experimental Data ◽  
Static Stability ◽  
Fruit Flies ◽  
Coordination Pattern ◽  
Large Set ◽  
Summary Statement ◽  
Walking Speeds ◽  
Coordination Patterns ◽  
Phase Relationships ◽  
The Continuum

AbstractDuring walking, insects must coordinate the movements of their six legs for efficient locomotion. This interleg coordination is speed-dependent; fast walking in insects is associated with tripod coordination patterns, while slow walking is associated with more variable, tetrapod-like patterns. To date, however, there has been no comprehensive explanation as to why these speed-dependent shifts in interleg coordination should occur in insects. Tripod coordination would be sufficient at low walking speeds. The fact that insects use a different interleg coordination pattern at lower speeds suggests that it is more optimal or advantageous at these speeds. Furthermore, previous studies focused on discrete tripod and tetrapod coordination patterns. Experimental data, however, suggest that changes observed in interleg coordination are part of a speed-dependent spectrum. Here, we explore these issues in relation to static stability as an important aspect of interleg coordination in Drosophila. We created a model that uses basic experimentally measured parameters in fruit flies to find the interleg phase relationships that maximize stability for a given walking speed. Based on this measure, the model predicted a continuum of interleg coordination patterns spanning the complete range of walking speeds. Furthermore, for low walking speeds the model predicted tetrapod-like patterns to be most stable, while at high walking speeds tripod coordination emerged as most optimal. Finally, we validated the basic assumption of a continuum of interleg coordination patterns in a large set of experimental data from walking fruit flies and compared these data with the model-based predictions.Summary statementA simple stability-based modelling approach can explain why walking insects use different leg coordination patterns in a speed-dependent way.

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