The hard life of air bubbles crossing a fluid/fluid interface

We investigate the dynamics of isolated air bubbles crossing the horizontal interface separating two Newtonian immiscible liquids initially at rest by means of experiments and DNS. High-speed video imaging is used to obtain a detailed evolution of the various interfaces involved in the system. The size of the bubbles and the viscosity contrast between the two liquids are varied by more than one and four orders of magnitude, respectively, making it possible to obtain bubble shapes ranging from spherical to toroidal. A variety of flow regimes is observed, including that of small bubbles remaining trapped at the fluid–fluid interface in a film-drainage configuration. In most cases, the bubble succeeds in crossing the interface without being stopped near its undisturbed position and, during a certain period of time, tows a significant column of lower fluid which sometimes exhibits a complex dynamics as it lengthens in the upper fluid. Direct numerical simulations of several selected experimental situations are performed with a code employing a volume-of-fluid type formulation of the incompressible Navier–Stokes equations. Comparisons between experimental and numerical results confirm the reliability of the computational approach in most situations but also points out the need for improvements to capture some subtle but important physical processes, most notably those related to film drainage. Influence of the physical parameters highlighted by experiments and computations, especially that of the density and viscosity contrasts between the two fluids and of the various interfacial tensions, is discussed and analysed in the light of simple models

Practical Implementation of Second Generation Wavelet Transformation on 2D Images by Transformation Matrixes

To perform second generation wavelet transformation in digital signal processing is a common operation. Most obvious way to carry out this task is by program cycle management. Computational software usually executes direct matrix algebraic operations much faster, compared to cycles. Avoiding organizing cycles, can increase the processing speed by magnitudes. This paper introduces transformation matrixes to execute the key steps of wavelet transformation: filtering and downsampling. By the employment of the described transformational matrixes, wavelet transformation and filtering of two dimensional images or discrete datasets could be easier and faster

Practical Implementation of Second Generation Wavelet Transformation on 2D Images by Transformation Matrixes

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Park Vector Based Sliding Mode Control of UPS With Unbalanced and Nonlinear Load

In this paper an inverter is taken as a member of Variable Structure System (VSS). A new Park vector based variable structure control (VSC) method is proposed. A modified definition of the Park vector is introduced to handle the effect of zero phase-sequence component caused by an asymmetrical load. The design of a sliding mode controller consists of two main steps. Firstly, the design of the sliding surface, secondly, the design of the control which holds the system trajectory on the sliding surface. A complex sliding surface is proposed. The inverter is switched in such a way that the system trajectory gets as close to the sliding surface as possible. This paper focuses on the switching rule. Experimental results of a 100 KVA inverter are presented

Identifikacija modela trenja s histerezom korištenjem tenzorskog produkta

Engineers encounter the problem of friction in any mechanical system. Friction force is strongly nonlinear and varies considerably while the system is working. In the case of high-precision applications friction makes the situation even more complex, as the stick-slip effect occurs near the target position. This paper introduces a pneumatic servo-system for investigation of the behavior of friction near the target position. A new model is proposed which takes the hysteresis loop of the friction also into consideration emphasizing the importance of hysteresis.This paper presents the tensorproduct (TP) based modeling of friction which is suitable for control design. The main advantage of the TP model transformation is that due to its polytopic model form Linear Matrix Inequality (LMI) can be immediately applied to the resulting model to yield controllers with guaranteed performance. The main contribution of this paper is the application of TP model transformation making the identification of friction parameters unnecessary by utilizing directly the measured data itself.Inženjeri se susreću s pojavom trenja u svakom mehaničkom sustavu. Sila trenja ima izraženu nelinearnost i promjenjiva je ovisno o radnim uvjetima procesa. U slučaju pozicioniranja s visokom preciznošću trenje dodatno komplicira situaciju, što rezultira pojavom oscilatornog ponašanja u okolini referentne pozicije sustava upravljanja. U ovom radu je predstavljen pneumatski servosustav koji se koristi za analizu ponašanja sile trenja u blizini referentne pozicije. Predložen je novi model sile trenja koji uzima u obzir histereznu karakteristiku trenja. U radu je predstavljeno modeliranje trenja na principu tenzorskog produkta koji je prikladan za sintezu sustava upravljanja. Glavna prednost transformacije modela korištenjem tenzorskog produkta je što politopski oblik modela u obliku linearnih matričnih nejednadžbi omogućava njegovu direktnu primjenu za sintezu regulatora s garantiranim performansama. Glavni znanstveni doprinos ovog rada je primjena transformacije modela trenja korištenjem tenzorskog produkta, pri čemu identifikacija parametara trenja postaje suvišna direktnim korištenjem izmjerenih podataka

Cognitive Model for Image Sensor Motion Control

This paper presents a neurobiology and cognitive psychology inspired model, implemented using a neural-network-like parallel computational strategy. The goal of the model is to show how a visual cortex inspired system can control camera alignment using a given camera hardware setup, in a similar way to the brain´s controlling eye movements. The system (computational model and camera hardware) are integrated into an experimental environment, the Intelligent Space, a room of ubiquitous computing. The intelligent space is based on several Distributed Intelligent Network Devices (DIND). A DIND has a sensor input, integrated intelligence and a communication interface. The model presented in this paper serves as the integrated intelligence component of a particular DIND. The proposed model implemented in a parallel hardware performs real time operation

How to Use NI Elvis/Labview in Mechatronics Engineering Education?

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Magnetic Angular Rate and Gravity Sensor Based Supervised Learning for Positioning Tasks

This paper deals with sensor fusion of magnetic, angular rate and gravity sensor (MARG). The main contribution of this paper is the sensor fusion performed by supervised learning, which means parallel processing of the different kinds of measured data and estimating the position in periodic and non-periodic cases. During the learning phase, the position estimated by sensor fusion is compared with position data of a motion capture system. The main challenge is avoiding the error caused by the implicit integral calculation of MARG. There are several filter based signal processing methods for disturbance and noise estimation, which are calculated for each sensor separately. These classical methods can be used for disturbance and noise reduction and extracting hidden information from it as well. This paper examines the different types of noises and proposes a machine learning-based method for calculation of position and orientation directly from nine separate sensors. This method includes the disturbance and noise reduction in addition to sensor fusion. The proposed method was validated by experiments which provided promising results on periodic and translational motion as well