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Improvement of an unbaffled stirred tank mixing characteristics using variable speed impeller
Gebouský, Ondřej; Haidl, Jan; Bodnár, J.; Pivokonský, Martin
2024 - English
Unbaffled mixing tanks with magnetically driven impellers are increasingly used in biotechnological and pharmaceutical industries, combining the benefits of a closed, sterile environment with easy equipment cleanability. On the other hand, missing internals, such as baffles or cooling coils, have an adverse effect on the equipment mixing characteristics, namely the batch\nhomogenization time. In our previous research, we uncovered that the eccentricity and inclination of the impeller – both employed routinely to enhance the mixing characteristics of unbaffled vessels – are not fully effective in the suppression of central vortex formation resulting in the increase in the homogenization time. In this work, we propose a simple solution to counteract the central vortex formation – a periodical variation of impeller rotational speed. This approach destabilizes the central vortex, significantly reducing homogenization time while maintaining the benefits of the original unbaffled setup. This innovation can seamlessly integrate into existing industrial setups, promising efficiency gains for biotech and pharmaceutical production.
Keywords:
unbaffled mixing tanks; variable rotational speed; vortex destabilization; mixing time improvement
Available in digital repository of the ASCR
Improvement of an unbaffled stirred tank mixing characteristics using variable speed impeller
Unbaffled mixing tanks with magnetically driven impellers are increasingly used in biotechnological and pharmaceutical industries, combining the benefits of a closed, sterile environment with easy ...
Applying a two degree of freedom model for drive-by identification
Bayer, Jan
2024 - English
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving spring-mass the second DOF. The response of the moving spring-mass is simulated on a bridge model using different road profiles and compared to parameters of the corresponding two DOF system. The focus is the spectral shift that can be observed on the moving spring-mass during its passage along the bridge and could possibly be applied for drive-by identification. The accuracy mainly depends on the relation of the moving spring-mass to the bridge mass and the relation between the natural frequency of the spring-mass and those of the bridge. The simulations showed that road profile can significantly reduce the accuracy of identified results, which imposes limits on practical applications.
Keywords:
drive-by identification; structural health monitoring; finite element analysis; road roughness; two DOF system
Available in digital repository of the ASCR
Applying a two degree of freedom model for drive-by identification
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving ...
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Fischer, Cyril; Náprstek, Jiří
2024 - English
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type nonlinear model. Determining the response probability density function involves solving the Fokker-Planck equation, which is generally a challenging task. Hence, semi-analytical and numerical methods come into play. This contribution reviews several possible techniques and spotlights the exponential-polynomial-closure method. The shown results are limited, as the paper reflects an early stage of the relevant research direction.
Keywords:
Fokker-Planck equation; stochastic averaging; numerical solution; Galerkin approximation; van der Pol-type oscillator; partial amplitudes; exponential-polynomial-closure method
Available in digital repository of the ASCR
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type ...
Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav; Macháček, Michael
2024 - English
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by polyethylene, and used for low-voltage power lines. The susceptibility to loss of stability is analyzed for cable without and with simulated icing observed on similar real conductors. In the first case, the proneness to galloping was excluded based on the results of CFD simulation and the Den Hartog criterion. In latter case, the possible occurrence of galloping was confirmed. The critical wind velocity for the ice-covered cable was calculated utilizing quasi-steady theory. Finally, the amplitudes of limit cycle oscillation for supercritical wind speeds were estimated based on simplified numerical analysis.
Keywords:
aerial bundled cable; wind effects; galloping; limit cycle oscillation
Available in digital repository of the ASCR
Galloping of insulated bundled overhead line simplified analysis
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by ...
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2024 - English
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The rectangle object was exposed to the airflow having a given velocity at different angles of the wind attack in the wind tunnel with the aim to obtain the curves of the aerodynamic coefficients and Strouhal number depending on the impact angle. The comparative numerical 3D simulations of the wind tunnel testing were performed using COMSOL Multiphysics and OpenFoam both incorporating the Large Eddy Simulation (LES) method.
Keywords:
rectangle 2:1; wind tunnel; LES simulation; aerodynamic characteristics
Available in digital repository of the ASCR
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The ...
Finite element approximation of fluid structure interaction using Taylor-Hood and Scott-Vogelius elements
Vacek, Karel; Sváček, P.
2024 - English
This paper addresses the problem of fluid flow interacting a vibrating solid cylinder described by one degree of freedom system and with fixed airfoil. The problem is described by the incompressible Navier-Stokes equations written in the arbitrary Eulerian-Lagrangian (ALE) formulation. The ALE mapping is constructed with the use of a pseudo-elastic approach. The flow problem is numerically approximated by the finite element method (FEM). For discretization of the fluid flow, the results obtained by both the Taylor-Hood (TH) element and the Scott-Vogelius (SV) finite element are compared. The TH element satisfies the Babuška-Brezzi inf-sup condition, which guarantees the stability of the scheme. In the case of the SV element the mesh, that is created as a barycentric refinement of regular triangulation, is used to satisfy the Babuška-Brezzi condition. The numerical results for two benchmark problems are shown.
Keywords:
finite element method; arbitrary Lagrangian-Eulerian method; Scott-Vogelius element; Taylor-Hood element
Available in digital repository of the ASCR
Finite element approximation of fluid structure interaction using Taylor-Hood and Scott-Vogelius elements
This paper addresses the problem of fluid flow interacting a vibrating solid cylinder described by one degree of freedom system and with fixed airfoil. The problem is described by the incompressible ...
The American origin of the French Revolution
Ottinger, Sebastian; Rosenberger, L.
2024 - English
We show that the French combatants’ exposure to the United States increased support for the French Revolution a decade later. French regions from which more American combatants originated had more revolts against feudal institutions, revolutionary societies, volunteers for the revolutionary army, and emigrants from the Old Regime’s elite. To establish causality, we exploit two historical coincidences: i) originally, a French army of seven and a half thousand was ready to sail, but one-third did not, ii) among those deployed, only some regiments were stationed in New England. Only combatants exposed to New England affected the French Revolution after their return.
Keywords:
institutional change; French Revolution; American War of Independence
Fulltext is available at external website.
The American origin of the French Revolution
We show that the French combatants’ exposure to the United States increased support for the French Revolution a decade later. French regions from which more American combatants originated had more ...
Survey expectations, adaptive learning and inflation dynamics
Rychalovska, Y.; Slobodyan, Sergey; Wouters, R.
2024 - English
The use of survey information on inflation expectations as an observable in a DSGE model can substantially refine identification of the shocks that drive inflation. Optimal integration of the survey information improves the model forecast for inflation and for other macroeconomic variables. Models with expectations based on an Adaptive Learning setup can exploit survey information more efficiently than their Rational Expectations counterparts. The resulting time-variation in the perceived inflation target, in inflation persistence, and in the sensitivity of inflation to various shocks provide a rich and consistent description of the joint dynamics of realized and expected inflation. Our framework produces a reasonable interpretation of the post-Covid inflation dynamics. Our learning model successfully identifies the more persistent nature of the recent inflation surge.
Keywords:
inflation; expectations; survey data
Fulltext is available at external website.
Survey expectations, adaptive learning and inflation dynamics
The use of survey information on inflation expectations as an observable in a DSGE model can substantially refine identification of the shocks that drive inflation. Optimal integration of the survey ...
COVID-19 and political preferences through stages of the pandemic: the case of the Czech Republic
Bičáková, Alena; Jurajda, Štěpán
2024 - English
We track the effects of the COVID-19 pandemic on political preferences through ‘high’ and ‘low’ phases of the pandemic. We ask about the effects of the health and the economic costs of the pandemic measured at both personal and municipality levels. Consistent with the literature, we estimate effects suggestive of political accountability of leaders during ‘high’ pandemic phases. However, we also find that the pandemic political accountability effects are mostly short-lived, and do not extend to the first post-pandemic elections.
Keywords:
COVID-19; political preferences; election outcomes
Fulltext is available at external website.
COVID-19 and political preferences through stages of the pandemic: the case of the Czech Republic
We track the effects of the COVID-19 pandemic on political preferences through ‘high’ and ‘low’ phases of the pandemic. We ask about the effects of the health and the economic costs of the pandemic ...
Flow simulations approach for flocculation tanks
Idžakovičová, Kristýna; Bílek, Vojtěch; Haidl, Jan; Isoz, M.; Pivokonský, Martin
2024 - English
Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and savings of operational costs. However, it is currently based on trial-and-error experimental approaches. In this contribution, we focus on flow modeling in stirred flocculation tanks that would, after coupling with a calibrated model of particle aggregation, enable simulationbased flocculation optimization. Despite the abundance of literature on stirred tank modeling, there is no universal agreement on the methodology used to describe turbulence nor on the approach to the computational mesh creation. Consequently, there is no unified methodology for simulations and their validation. To address this, we present a best-practice methodology for economical, yet reliable flow simulations in the said device. This methodology includes the choice of the turbulence model, the approach to the design of a high quality mesh suitable for arbitrary geometries, and results evaluation. It is developed based on an extensive literature review, a multitude of flow simulations using several meshes of progressively higher quality and resolution, and various strategies to converge to steady-state flow conditions. The simulation quality indicators used here involve comparison with the experimental data on fluid velocity, stirrer power output, and flow rate through the impeller zone. Additionally, the resulting flow simulation models are compared using tracer transport simulations, hinting at their potential for coupling with particle aggregation models.
Keywords:
flocculation tank; stirring; MRF; CFD; OpenFOAM
Available in digital repository of the ASCR
Flow simulations approach for flocculation tanks
Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and ...
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