Numerical Simulations
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Milan Moravčík

The paper presents an analysis of an actual problem related to dynamic effects to road bridges due to travelling a heavy vehicle over the bridge. Numerical simulations of the dynamic response are applied on a fictitious simple beam of the length Lb = 52 m with an artificial irregularity at midspan, corresponding to a characteristic span L (b5) = 52 m of the ten-span continuous box girder bridge. A heavy four-axle truck m v = 32 t is used for dynamic excitation, travelling over the bridge at passing speed of 70km / h. The obtained results are compared to results of the experimentally tested ten-span continuous pre-stressed reinforced concrete girder bridge at the same speed.

2021 ◽  
Yang Liu ◽  
Ningsong Qu ◽  
Zhi Qiu

Abstract Electrolyte jet electrochemical turning is an effective method to realize high-quality machining of titanium alloy rotating components; however, minimal research has been carried out in this field. This is because it is difficult to control the machining flow field, which leads to poor machining surface quality. In this work, numerical simulations were used to optimize the machining flow field and reduce the proportion of gas that mixed into the machining area. This can promote participation of the tool electrode tip in the electrochemical reaction and improve the machining efficiency. The effectiveness of the optimized machining flow field for jet electrochemical turning was verified experimentally. The results showed that all three kinds of revolving TB6 titanium alloy samples with different structures could maintain the original contour shape, with a contour error <1% and a machined surface roughness reaching Ra 2.414 μm. The results demonstrate the application potential of the jet electrochemical turning process.

Solid Earth ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 2407-2424
Steffen Abe ◽  
Hagen Deckert

Abstract. We investigate the influence of stress conditions during fracture formation on the geometry and roughness of fracture surfaces. Rough fracture surfaces have been generated in numerical simulations of triaxial deformation experiments using the discrete element method and in a small number of laboratory experiments on limestone and sandstone samples. Digital surface models of the rock samples fractured in the laboratory experiments were produced using high-resolution photogrammetry. The roughness of the surfaces was analyzed in terms of absolute roughness measures such as an estimated joint roughness coefficient (JRC) and in terms of its scaling properties. The results show that all analyzed surfaces are self-affine but with different Hurst exponents between the numerical models and the real rock samples. Results from numerical simulations using a wide range of stress conditions to generate the fracture surfaces show a weak decrease of the Hurst exponents with increasing confining stress and a larger absolute roughness for transversely isotropic stress conditions compared to true triaxial conditions. Other than that, our results suggest that stress conditions have little influence on the surface roughness of newly formed fractures.

Marta Maria Rasteiro dos Santos ◽  
Yannick Bury ◽  
Stephane Jamme

Abstract The flow resulting from the rotation of a series of thin plates that initially separate two gases of different densities is analysed using Direct Numerical Simulations. The ninety degrees plates' rotation forms a vorticity shear layer and a density interface in between the tips of two neighbouring plates. Results of this study show that the shape of these layers strongly depends on the plate tip-based Reynolds number that can be varied thanks to a parametrisation of the plates' opening law. Different regimes are identified corresponding to single- or multi-mode initial interfaces, with or without the occurrence of starting vortices during the formation of the shear layer. The density interfaces resulting from this procedure are particularly well-suited to serve as initial conditions for the study of the Richtmyer-Meshkov instability-induced mixing. Results of this study also provide a description of vortex formation in stratified flows.

2021 ◽  
Vol 2021 (1) ◽  
Kaushik Dehingia ◽  
Hemanta Kumar Sarmah ◽  
Yamen Alharbi ◽  
Kamyar Hosseini

AbstractIn this study, we discuss a cancer model considering discrete time-delay in tumor-immune interaction and stimulation processes. This study aims to analyze and observe the dynamics of the model along with variation of vital parameters and the delay effect on anti-tumor immune responses. We obtain sufficient conditions for the existence of equilibrium points and their stability. Existence of Hopf bifurcation at co-axial equilibrium is investigated. The stability of bifurcating periodic solutions is discussed, and the time length for which the solutions preserve the stability is estimated. Furthermore, we have derived the conditions for the direction of bifurcating periodic solutions. Theoretically, it was observed that the system undergoes different states if we vary the system’s parameters. Some numerical simulations are presented to verify the obtained mathematical results.

2021 ◽  
Jummy Funke David ◽  
Sarafa A. Iyaniwura

Abstract We extended a class of coupled PDE-ODE models for studying the spatial spread of airborne diseases by incorporating human mobility. Human populations are modeled with patches, and a Lagrangian perspective is used to keep track of individuals’ places of residence. The movement of pathogens in the air is modeled with linear diffusion and coupled to the SIR dynamics of each human population through an integral of the density of pathogen around the population patch. In the limit of fast diffusion pathogens, the method of matched asymptotic analysis is used to reduce the coupled PDE-ODE model to a nonlinear system of ODEs for the average density of pathogens in the air. The reduced system of ODEs is used to derive the basic reproduction number and the final size relation for the model. Numerical simulations of the full PDE-ODE model and the reduced system of ODEs are used to assess the impact of human mobility, together with the diffusion of pathogens on the dynamics of the disease. Results from the two models are consistent and show that human mobility significantly affects disease dynamics. In addition, we show that an increase in the diffusion rate of pathogen leads to a smaller epidemic.

2021 ◽  
Melani Barrios ◽  
Gabriela Reyero ◽  
Mabel Tidball

In this article, we study a fractional control problem that models the maximization of the profit obtained by exploiting a certain resource whose dynamics are governed by the fractional logistic equation. Due to the singularity of this problem, we develop different resolution techniques, both for the classical case and for the fractional case. We perform several numerical simulations to make a comparison between both cases.

Geophysics ◽  
2021 ◽  
pp. 1-17
Roman Pevzner ◽  
Stanislav Glubokovskikh ◽  
Roman Isaenkov ◽  
Pavel Shashkin ◽  
Konstantin Tertyshnikov ◽  

Instrumenting wells with distributed acoustic sensors (DAS) and illuminating them with passive or active seismic sources allows precise tracking of temporal variations of direct-wave traveltimes and amplitudes, which can be used to monitor variations in formation stiffness and density. This approach has been tested by tracking direct-wave amplitudes and traveltimes as part of a CCS project where a 15 kt supercritical CO2 injection was monitored with continuous offset VSPs using nine permanently mounted surface orbital vibrators (SOVs) acting as seismic sources and several wells instrumented with DAS cables cemented behind the casing. The results show a significant (from 15 to 30%) increase of strain amplitudes within the CO2 injection interval, and travetime shifts of 0.3 to 0.4 ms below this interval, consistent with full-wave 1.5D numerical simulations and theoretical predictions. The results give independent estimates of the CO2 plume thickness and P-wave velocity reduction within it.

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