The influence of rotating domain size in a rotating frame of reference approach for simulation of rotating impeller in a mixing vessel

This paper presents simulation of rotating impeller in a mixing vessel by means of Computational Fluid Dynamics (CFD). A special emphasis is devoted to the study of influence of the choice of numerical model for simulation of rotation of impeller when mixing a Newtonian fluid in a vessel equipped with Rushton impeller, and operating under turbulent flow conditions. In order to determine the best simulation approach experimental validation of the selected problem is done by means of Particle Image Velocimetry (PIV) system. When using the rotating frame of reference approach, the stirring vessel geometry has to be split into a stationary and rotating part, and the questionarises where to position the interface between both regions in order to avoid numerical errors, originating in numerical approximations at the interface. To answer this question, a comparison between the CFD based numerical results and experimental results, was made

The Existence of Shared Muscle Synergies Underlying Perturbed and Unperturbed Gait Depends on Walking Speed

Muscle synergy theory assumes that the central nervous system generates a wide range of complex motor outputs by recruiting muscle synergies with different strengths and timings. The current understanding is that a common set of muscle synergies underlies unperturbed as well as perturbed walking at self-selected speeds. However, it is not known whether this is the case for substantially slower walking. The aim of this study was to investigate whether a shared set of muscle synergies underlies balance recovery responses following inward-and outward-directed perturbations in the mediolateral direction at various perturbation onsets and walking speeds. Twelve healthy subjects walked at three walking speeds (0.4, 0.6, and 0.8 m/s) on a treadmill while perturbations were applied to the pelvis using the balance assessment robot. A set of sixteen EMG signals, i.e., eight muscles per leg, was measured and decomposed into muscle synergies and weighting curves using non-negative matrix factorization. The muscles included were left and right tibialis anterior, soleus, gastrocnemius medialis, gastrocnemius lateralis, rectus femoris, hamstring, gluteus medius, and gluteus maximus. In general, four muscle synergies were needed to adequately reconstruct the data. Muscle synergies were similar for unperturbed and perturbed walking at a high walking speed (0.8 m/s). However, the number of similar muscle synergies between perturbed and unperturbed walking was significantly lower for low walking speeds (0.4 and 0.6 m/s). These results indicate that shared muscle synergies underlying perturbed and unperturbed walking are less present during slow walking compared to fast walking

Cooling analysis of a light emitting diode automotive fog lamp

Efficiency of cooling fins inside of a light emitting diode fog lamp is studied using computational fluid dynamics. Diffusion in heat sink, natural convection and radiation are the main principles of the simulated heat transfer. The Navier-Stokes equations were solved by the computational fluid dynamics code, including Monte Carlo radiation model and no additional turbulence model was needed. The numerical simulation is tested using the existing lamp geometry and temperature measurements. The agreement is excellent inside of few degrees at all measured points. The main objective of the article is to determine the cooling effect of various heat sink parts. Based on performed simulations, some heat sink parts are found to be very ineffective. The geometry and heat sink modifications are proposed. While radiation influence is significant, compressible effects are found to be minor

Numerical modeling of mixing in a vessel with a Rushton impeller

Prispevek obravnava numerično modeliranje mešanja newtonske tekočine v mešalni posodi, v kateri je nameščeno turbinsko Rushtonovo mešalo. Obravnavan je ustaljeni turbulentni tokovni rezim, opisan s časovno povprečnim Navier-Stokesovim sistemom enačb. Numerično reševanje temelji na uporabi dvoenačbnega modela turbulence in metode končnih prostornin. Posebna pozornostje namenjena modeliranju vrtenja mešala ter izračunu mehanske moči za mešanje, kakor tudi nekaterim poenostavitvam, ki omogočajo hitrejši izračun zahtevnih diskretnih modelov.This paper presents numerical modeling of mixing a Newtonian fluid in a stirring vessel with a Rushton impeller. The stationary turbulent flow is governed by the time-averaged Navier-Stokes equations. For the numerical approach, a two-equation turbulence model with the finite-volume method was used. The focus is on impeller rotation, a determination of the stirrer power and a simplification that can lead to faster solving of complicated discreet models

Numerical modelling of mixed convection of micropolar fluid flow in cavity

V prispevku je predstavljen sklopljenega primera naravne in prisilne konvekcije v toku mikropolarnih tekočin preko kotanje. Glede na tok klasinih tekoćčin, kjer je zajeto le translatorno gibanje delov tekočine, se v primeru mikropolarnih tekočin k translatornemu gibanju prišteva tudi gibanje tekočine zaradi rotacije togih nedeformabilnih delcev okrog srediišča določenega majhnega volumna, kar je opisano s pomočjo vektorja mikrorotacije. Numerično modeliranje dodatnih mikro vplivov se izvede z modificiranjem klasičnega sistema Navier-Stokesovih enačb, ki predstavljajo osnovo orodja za numerično simulacijo toka tekočine. Prispevek poda rezultate tokovnega, temperaturnega in mikrorotacijskega polja izračunanega z računskim algoritmom za reševanje modificiranih Navier-Stokesovih enačb s pomočjo metode robnih elementov (MRE), natančneje z Robno-območno integralsko metodo.The contribution deals with numerical simulation of mixed convection of micropolar fluid flow in cavity. In contrast to simple fluids, where only translational movement of material particles is accounted for, in micropolar fluids additional to the translational movement is also movement due to the rotation of rigid particles about the center of a small volume element, which is described by the micro-rotation vector. Thus the classical Navier-Stokes system of equations, which forms the basis for derivation of modern flow simulation tools, needs to be modified, to incorporate additional micro effects into the computational method. The submitted work presents results of flow, thermal and micrortation fields solved with a computational algorithm, based on the application of the Boundary Element Method (BEM) or Boundary Domain Integral Method to the modified Navier-Stokes equations

Comparison of CFD simulation of Darrieus water turbine using the rigid body solver and the MFR method

Med tehnologijami za izkoriščanje vodne energije se vse pogosteje uporabljajo tudi prilagojene tehnologije za izkoriščanje energije vetra. K njihovemu razvoju pripomorejo sodobne računalniške simulacije. Predstavljena je primerjava dveh metod numerične simulacije Darrieusove turbine s poudarkom na ustreznosti delovanja nove metode z uporabo modela gibanja togega telesa (modul 6DOF). Ta omogoča simulacijo turbine, pri kateri je le-ta gnana s tokom tekočine, se pravi, da bolje opiše realne obratovalne razmere kot uveljavljen postopek MFR.Among technologies for stream energy extraction there are new emerging technologies using adapted wind energy extraction technologies. Their development is enhanced by using modern computer simulations. This document presents a comparison between two methods for numerical simulation of Darrieus turbine with emphasis on the suitability of the new rigid body solver. It enables the simulation of a turbine that is flowdriven, which better describes the real operating conditions than the MFR method

Influence of Treadmill Speed and Perturbation Intensity on Selection of Balancing Strategies during Slow Walking Perturbed in the Frontal Plane

Background. Common understanding is that adequate foot placement (stepping strategy) is crucial in maintaining stability during walking at normal speed. The aim of this study was to investigate strategies that humans use to cope with lateral perturbations during very slow walking. Methods. Ten healthy individuals underwent an experimental protocol whereby a set of perturbations directed inward (medially to a stance leg) and outward (laterally to a stance leg) of three intensities (F1=5%, F2=10%, and F3=15% of body weight), applied at three instances of a stance phase, were delivered in random order to the pelvis using a balance assessment robot while walking on a treadmill at three walking speeds (S1=0.4, S2=0.6, and S3=0.8 m/s). We analyzed the peak center of mass displacements; step length, step width, and step times; and the lateral component of ground reaction force for perturbations that were delivered at the beginning of the gait cycle. Results. Responses after inward perturbations were similar at all tested speeds and consistently employed stepping strategy that was further facilitated by a shortened stance. Wider and shorter steps were applied with increased perturbation intensity. Responses following outward perturbations were more complex. At S1, hip strategy (impulse-like increase of mediolateral ground reaction force) augmented with ankle strategy (mediolateral shift of the center of pressure) mainly contributed to responses already during the stance phase. The stance duration was significantly longer for all perturbation intensities. At S2, the relative share of hip strategy was reduced while with increased perturbation intensity, stepping strategy was gradually added. The stance duration was significantly longer for F1 and F2. At S3, stepping strategy was mainly used while the duration of stance was similar to the one in unperturbed walking. Responses following both inward and outward perturbations at all speeds were characterized by temporary slowing down movement in a sagittal plane that was more pronounced with increased perturbation intensity. Conclusions. This study provides novel insights into balancing strategies used at slower walking speeds which may be more relevant to understand the challenges of gait stability following perturbations in the frontal plane in clinical populations

Comparison of dynamic balancing responses following outward lateral perturbations during walking of healthy and post-stroke subjects

Efficient dynamic balancing and movement coordination during walking are essential for stability. The objective of this preliminary study was to assess dynamic balancing responses in a selected post-stroke subject and to compare them with those assessed in neurologically intact individual. Balance Assessment Robot, a haptic robot that interfaces to a pelvis of a subject walking on an instrumented treadmill, was used to deliver perturbing pushes to the pelvis. We have assessed centre-of-pressure (CoP) and horizontal components of ground reaction forces (GRF) following outward pushes. The results have shown that depending on the amplitude of a perturbing push neurologically intact individual responded predominantly by “ankle” and “hip” strategies at lower amplitude of perturbation and “ankle” and “stepping” strategies at higher amplitude of perturbation. Post-stroke subject responded mainly by “ankle” and “hip” strategies when perturbed on the sound leg while the response when perturbed on the impaired leg was similar to the one observed in healthy subject. These preliminary results indicate that post-stroke subjects might be reluctant or not able to perform “cross step” with their impaired leg which is needed when counteracting outward perturbation